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Sample records for functional cross linking

  1. Biocatalytic cross-linking of pectic polysaccharides for designed food functionality

    DEFF Research Database (Denmark)

    Zaidel, Dayang Norulfairuz Abang; Meyer, Anne S.

    2012-01-01

    Recent research has demonstrated how cross-linking of pectic polysaccharides to obtain gel formation can be promoted by enzymatic catalysis reactions, and provide opportunities for functional upgrading of pectic polysaccharides present in agro-industrial sidestreams. This review highlights...... the mechanisms of formation of functional pectic polysaccharide cross-links, including covalent cross-links (notably phenolic esters and uronyl ester linkages) and non-covalent, ionic cross-links (which involve calcium and borate ester links). The treatise examines how such cross-links can be designed via...

  2. Assessment of protein function following cross-linking by alpha-dicarbonyls.

    Science.gov (United States)

    Miller, Antonia G; Gerrard, Juliet A

    2005-06-01

    Protein cross-linking via the Maillard reaction with alpha-dicarbonyl compounds has been the subject of intense scrutiny in the literature. We report here a study of the impact of this cross-linking on enzyme function. Protein function following glycation was examined by treating ribonuclease A with methylglyoxal, glyoxal, and diacetyl, which cross-linked the enzyme and impaired its activity. The effects of two reported Maillard reaction inhibitors, aminoguanidine and 3,5-dimethylpyrazole-1-carboxamidine, on the cross-linking reaction were assessed, with a parallel measurement of the effect on enzyme activity. The results demonstrate that preventing protein cross-linking does not necessarily preserve enzyme activity. These results cast doubt on the likely efficacy of some purported antiaging compounds in vivo.

  3. Removal of anionic azo dyes from aqueous solution by functional ionic liquid cross-linked polymer

    Energy Technology Data Exchange (ETDEWEB)

    Gao, Hejun [Key Laboratory of Colloid and Interface Chemistry, Shandong University, Ministry of Education, Jinan 250100 (China); Chemical Synthesis and Pollution Control Key Laboratory of Sichuan Province, China West Normal University, Nanchong 637000 (China); Kan, Taotao [CNOOC Energy Technology and Services-oilfield Technology Services Co., Tanggu, Tianjin 300452 (China); Zhao, Siyuan; Qian, Yixia; Cheng, Xiyuan; Wu, Wenli [School of Chemistry and Chemical Engineering, Shandong University, Jinan 250100 (China); Wang, Xiaodong [Shandong Provincial Analysis and Test Center, Jinan 250100 (China); Zheng, Liqiang, E-mail: lqzheng@sdu.edu.cn [Key Laboratory of Colloid and Interface Chemistry, Shandong University, Ministry of Education, Jinan 250100 (China)

    2013-10-15

    Highlights: • Equilibrium, kinetic and thermodynamic of adsorption of dyes onto PDVB-IL was investigated. • PDVB-IL has a high adsorption capacity to treat dyes solution. • Higher adsorption capacity is due to the functional groups of PDVB-IL. • Molecular structure of dyes influences the adsorption capacity. -- Abstract: A novel functional ionic liquid based cross-linked polymer (PDVB-IL) was synthesized from 1-aminoethyl-3-vinylimidazolium chloride and divinylbenzene for use as an adsorbent. The physicochemical properties of PDVB-IL were investigated by Fourier transform infrared spectroscopy, scanning electron microscopy and thermogravimetric analysis. The adsorptive capacity was investigated using anionic azo dyes of orange II, sunset yellow FCF, and amaranth as adsorbates. The maximum adsorption capacity could reach 925.09, 734.62, and 547.17 mg/g for orange II, sunset yellow FCF and amaranth at 25 °C, respectively, which are much better than most of the other adsorbents reported earlier. The effect of pH value was investigated in the range of 1–8. The result shows that a low pH value is found to favor the adsorption of those anionic azo dyes. The adsorption kinetics and isotherms are well fitted by a pseudo second-order model and Langmuir model, respectively. The adsorption process is found to be dominated by physisorption. The introduction of functional ionic liquid moieties into cross-linked poly(divinylbenzene) polymer constitutes a new and efficient kind of adsorbent.

  4. Exogenous collagen cross-linking recovers tendon functional integrity in an experimental model of partial tear.

    Science.gov (United States)

    Fessel, Gion; Wernli, Jeremy; Li, Yufei; Gerber, Christian; Snedeker, Jess G

    2012-06-01

    We investigated the hypothesis that exogenous collagen cross-linking can augment intact regions of tendon to mitigate mechanical propagation of partial tears. We first screened the low toxicity collagen cross-linkers genipin, methylglyoxal and ultra-violet (UV) light for their ability to augment tendon stiffness and failure load in rat tail tendon fascicles (RTTF). We then investigated cross-linking effects in load bearing equine superficial digital flexor tendons (SDFT). Data indicated that all three cross-linking agents augmented RTTF mechanical properties but reduced native viscoelasticity. In contrast to effects observed in fascicles, methylglyoxal treatment of SDFT detrimentally affected tendon mechanical integrity, and in the case of UV did not alter tendon mechanics. As in the RTTF experiments, genipin cross-linking of SDFT resulted in increased stiffness, higher failure loads and reduced viscoelasticity. Based on this result we assessed the efficacy of genipin in arresting tendon tear propagation in cyclic loading to failure. Genipin cross-linking secondary to a mid-substance biopsy-punch significantly reduced tissue strains, increased elastic modulus and increased resistance to fatigue failure. We conclude that genipin cross-linking of injured tendons holds potential for arresting tendon tear progression, and that implications of the treatment on matrix remodeling in living tendons should now be investigated.

  5. Age-Related Long-Term Functional Results after Riboflavin UV A Corneal Cross-Linking.

    Science.gov (United States)

    Caporossi, Aldo; Mazzotta, Cosimo; Baiocchi, Stefano; Caporossi, Tomaso; Denaro, Rosario

    2011-01-01

    Purpose. To report a comparative prospective long-term functional analysis after Riboflavin UV A corneal cross-linking (CXL) in three different age groups of patients affected by progressive keratoconus (KC). Methods. Functional analysis comprised paediatric patients (≤18 years) included 152 eyes (29.5%); intermediate group (19-26 years) 286 eyes (55.4%), and adults (≥27 years) 78 eyes (15.1%). CXL was performed according to the Siena protocol by using the Vega CBM (Caporossi-Baiocchi-Mazzotta) X linker (CSO, Florence, Italy) at Siena University by the same authors. Pre- and post-op examinations included UCVA, BSCVA, corneal topography, and surface aberrometry (CSO Eye Top, Florence, Italy), at 48 months followup. Results. At 48 months followup paediatrics, intermediate, and adult patients showed a mean gain in UCVA of +0.2, +0.14 and +0.12 Snellen lines. BSCVA gained by a mean of +0.21, +0.2, and +0.1 Snellen lines. K(max) was reduced by a mean value of -0.9 D, -0.6 D, and -0.5 D, respectively. Coma values improved by a mean of -0.45 μm, -0.91 μm, and -0.19 μm, respectively. Treatment ensured a long-term keratoconus stabilization in over 90% of treated patients. Conclusion. According to our long-term comparative results, epithelium-off Riboflavin UV A cross-linking should be the first choice therapy of progressive KC, particularly in paediatric age and patients under 26 years.

  6. Age-Related Long-Term Functional Results after Riboflavin UV A Corneal Cross-Linking

    Directory of Open Access Journals (Sweden)

    Aldo Caporossi

    2011-01-01

    Full Text Available Purpose. To report a comparative prospective long-term functional analysis after Riboflavin UV A corneal cross-linking (CXL in three different age groups of patients affected by progressive keratoconus (KC. Methods. Functional analysis comprised paediatric patients (≤18 years included 152 eyes (29.5%; intermediate group (19–26 years 286 eyes (55.4%, and adults (≥27 years 78 eyes (15.1%. CXL was performed according to the Siena protocol by using the Vega CBM (Caporossi-Baiocchi-Mazzotta X linker (CSO, Florence, Italy at Siena University by the same authors. Pre- and post-op examinations included UCVA, BSCVA, corneal topography, and surface aberrometry (CSO Eye Top, Florence, Italy, at 48 months followup. Results. At 48 months followup paediatrics, intermediate, and adult patients showed a mean gain in UCVA of +0.2, +0.14 and +0.12 Snellen lines. BSCVA gained by a mean of +0.21, +0.2, and +0.1 Snellen lines. Kmax was reduced by a mean value of −0.9 D, −0.6 D, and −0.5 D, respectively. Coma values improved by a mean of −0.45 μm, −0.91 μm, and −0.19 μm, respectively. Treatment ensured a long-term keratoconus stabilization in over 90% of treated patients. Conclusion. According to our long-term comparative results, epithelium-off Riboflavin UV A cross-linking should be the first choice therapy of progressive KC, particularly in paediatric age and patients under 26 years.

  7. Morphological and functional correlations in riboflavin UV A corneal collagen cross-linking for keratoconus.

    Science.gov (United States)

    Mazzotta, Cosimo; Caporossi, Tomaso; Denaro, Rosario; Bovone, Cristina; Sparano, Caterina; Paradiso, Anna; Baiocchi, Stefano; Caporossi, Aldo

    2012-05-01

    To investigate the correlations between corneal structural modifications assessed by in vivo corneal confocal microscopy with visual function [uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA)] and morphological data (corneal topography, pachymetry, elevation analysis) after riboflavin UV A corneal collagen cross-linking (CXL) for the stabilization of progressive keratoconus. Forty-four eyes with progressive keratoconus were enrolled in the Siena Eye Cross Study (prospective nonrandomized phase II open trial). All eyes underwent Riboflavin UV A CXL. Preoperative and postoperative evaluation comprised: UCVA, BSCVA, optical pachymetry (Visante OCT, Zeiss, Germany), corneal topography (CSO, Florence, Italy) and tomography (Orbscan IIz; B&L, Rochester, NY, USA) and in vivo confocal microscopy (Heidelberg Retina Tomograph II; Rostock, Heidelberg Gmbh, Germany). Examinations were performed preoperatively 6 months and one day before treatment and at 1, 3, 6 and 12 months of follow-up. In vivo corneal confocal microscopy showed time-dependent postoperative epithelial and stromal modifications after cross-linking. Epithelial thinning associated with stromal oedema and keratocytes apoptosis explained initial tendency towards slightly reduced VA and more glare one month postoperatively in 70% of eyes. Furthermore, a statistically not significant early worsening of topographic mean K values was observed. Orbscan II analysis significantly underestimated pachymetric values after treatment. Pachymetric underestimation was rectified by high-resolution optical pachymetry provided by the Visante OCT system. After the third post-CXL month, epithelial thickening, disappearance of oedema and new collagen compaction recorded by in vivo corneal confocal microscopy explained the improvements in visual performance during the follow-up. Changes in stromal reflectivity and collagen compaction observed by in vivo confocal microscopy were associated with corneal

  8. Microtubule-Actin Cross-Linking Factor 1: Domains, Interaction Partners, and Tissue-Specific Functions.

    Science.gov (United States)

    Goryunov, Dmitry; Liem, Ronald K H

    2016-01-01

    The cytoskeleton of most eukaryotic cells is composed of three principal filamentous components: actin filaments, microtubules (MTs), and intermediate filaments. It is a highly dynamic system that plays crucial roles in a wide range of cellular processes, including migration, adhesion, cytokinesis, morphogenesis, intracellular traffic and signaling, and structural flexibility. Among the large number of cytoskeleton-associated proteins characterized to date, microtubule-actin cross-linking factor 1 (MACF1) is arguably the most versatile integrator and modulator of cytoskeleton-related processes. MACF1 belongs to the plakin family of proteins, and within it, to the spectraplakin subfamily. These proteins are characterized by the ability to bridge MT and actin cytoskeletal networks in a dynamic fashion, which underlies their involvement in the regulation of cell migration, axonal extension, and vesicular traffic. Studying MACF1 functions has provided insights not only into the regulation of the cytoskeleton but also into molecular mechanisms of both normal cellular physiology and cellular pathology. Multiple MACF1 isoforms exist, composed of a large variety of alternatively spliced domains. Each of these domains mediates a specific set of interactions and functions. These functions are manifested in tissue and cell-specific phenotypes observed in conditional MACF1 knockout mice. The conditional models described to date reveal critical roles of MACF1 in mammalian skin, nervous system, heart muscle, and intestinal epithelia. Complete elimination of MACF1 is early embryonic lethal, indicating an essential role for MACF1 in early development. Further studies of MACF1 domains and their interactions will likely reveal multiple new roles of this protein in various tissues.

  9. Keratoconus, cross-link-induction, comparison between fitting exponential function and a fitting equation obtained by a mathematical model.

    Science.gov (United States)

    Albanese, A; Urso, R; Bianciardi, L; Rigato, M; Battisti, E

    2009-11-01

    With reference to experimental data in the literature, we present a model consisting of two elastic elements, conceived to simulate resistance to stretching, at constant velocity of elongation, of corneal tissue affected by keratoconus, treated with riboflavin and ultraviolet irradiation to induce cross-linking. The function describing model behaviour adapted to stress and strain values. It was found that the Young's moduli of the two elastic elements increased in cross-linked tissues and that cross-linking treatment therefore increased corneal rigidity. It is recognized that this observation is substantially in line with the conclusion reported in the literature, obtained using an exponential fitting function. It is observed, however, that the latter function implies a condition of non-zero stresses without strain, and does not provide interpretative insights for lack of any biomechanical basis. Above all, the function fits a singular trend, inexplicably claimed to be viscoelastic, with surprising perfection. In any case, using the reported data, the study demonstrates that a fitting equation obtained by a modelling approach not only shows the evident efficacy of the treatment, but also provides orientations for studying modifications induced in cross-linked fibres.

  10. Polysiloxane Functionalized Carbon Dots and Their Cross-Linked Flexible Silicone Rubbers for Color Conversion and Encapsulation of White LEDs.

    Science.gov (United States)

    Wang, Yunfeng; Yin, Zhengmao; Xie, Zheng; Zhao, Xinxin; Zhou, Chuanjian; Zhou, Shuyun; Chen, Ping

    2016-04-20

    In this work, aminopropylmethylpolysiloxane (AMS) functionalized luminescent carbon dots (AMS-CDs) were prepared via a one-step solvothermal method. AMS-CDs could be self- or co-cross-linking with AMS to form 3D flexible transparent silicone rubbers (SRs) where CDs acted as cross-linking points, so the loading fraction of AMS-CDs could be adjusted from 10 to 100 wt %, thus modulating fluorescence properties and flexibility of silicone rubbers. Because of the self-curing property and high thermal stability, AMS-CDs were also studied in white LEDs (WLEDs), serving as a color conversion and encapsulation layer of GaN based blue LEDs simultaneously that would avoid the traditional problem of poor compatibility between emitting and packaging materials. And the color coordinate of AMS-CDs based WLEDs (0.33, 0.28) was very close to the pure white light. In addition, the obtained CDs cross-linked SRs had good transparency (T > 80%) at 510-1400 nm and high refractive indexes (1.33-1.54) that could meet the need of commercial packaging materials and optical application. AMS-CDs were also promising to be used in the UV LEDs based WLEDs according to their wide wavelength emission and flexible optoelectronic device.

  11. Highly stable pyridinium-functionalized cross-linked anion exchange membranes for all vanadium redox flow batteries

    Science.gov (United States)

    Zeng, L.; Zhao, T. S.; Wei, L.; Zeng, Y. K.; Zhang, Z. H.

    2016-11-01

    It has recently been demonstrated that the use of anion exchange membranes (AEMs) in vanadium redox flow batteries (VRFBs) can reduce the migration of vanadium ions through the membrane due to the Donnan exclusion effect among the positively charged functional groups and vanadium ions. However, AEMs are plagued by low chemical stability in harsh chemical environments. Here we propose and fabricate a pyridinium-functionalized cross-linked AEM for VRFBs. The pyridinium-functionalized bromomethylated poly (2,6-dimethyl-1,4-phenylene oxide) exhibits a superior chemical stability as a result of the strengthened internal cross-linking networks and the chemical inertness of the polymer backbone. Therefore, the membrane exhibits littler decay in a harsh environment for 20 days during the course of an ex situ immersion test. A cycling test also demonstrates that the VRFB assembled with the membrane enable to retain 80% of the initial discharge capacity over 537 cycles with a capacity decay rate of 0.037% cycle-1. Meanwhile, the membrane also shows a low vanadium permeability and a reasonably high conductivity in supporting electrolytes. Hence, all the measurements and performance tests reported in this work suggest that the membrane is a promising AEM for redox flow batteries to achieve excellent cycling stability and superior cell performance.

  12. Aliphatic polycarbonates based on carbon dioxide, furfuryl glycidyl ether, and glycidyl methyl ether: reversible functionalization and cross-linking.

    Science.gov (United States)

    Hilf, Jeannette; Scharfenberg, Markus; Poon, Jeffrey; Moers, Christian; Frey, Holger

    2015-01-01

    Well-defined poly((furfuryl glycidyl ether)-co-(glycidyl methyl ether) carbonate) (P((FGE-co-GME)C)) copolymers with varying furfuryl glycidyl ether (FGE) content in the range of 26% to 100% are prepared directly from CO2 and the respective epoxides in a solvent-free synthesis. All materials are characterized by size-exclusion chromatography (SEC), (1)H NMR spectroscopy, and differential scanning calorimetry (DSC). The furfuryl-functional samples exhibit monomodal molecular weight distributions with Mw/Mn in the range of 1.16 to 1.43 and molecular weights (Mn) between 2300 and 4300 g mol(-1). Thermal properties reflect the amorphous structure of the polymers. Both post-functionalization and cross-linking are performed via Diels-Alder chemistry using maleimide derivatives, leading to reversible network formation. This transformation is shown to be thermally reversible at 110 °C.

  13. Corneal collagen cross-linking

    Directory of Open Access Journals (Sweden)

    Jankov II Mirko

    2010-01-01

    Full Text Available Corneal collagen cross-linking (CXL with riboflavin and ultraviolet-A (UVA is a new technique of corneal tissue strengthening by using riboflavin as a photosensitizer and UVA to increase the formation of intra- and interfibrillar covalent bonds by photosensitized oxidation. Keratocyte apoptosis in the anterior segment of the corneal stroma all the way down to a depth of about 300 microns has been described and a demarcation line between the treated and untreated cornea has been clearly shown. It is important to ensure that the cytotoxic threshold for the endothelium has not been exceeded by strictly respecting the minimal corneal thickness. Confocal microscopy studies show that repopulation of keratocytes is already visible 1 month after the treatment, reaching its pre-operative quantity and quality in terms of functional morphology within 6 months after the treatment. The major indication for the use of CXL is to inhibit the progression of corneal ectasias, such as keratoconus and pellucid marginal degeneration. CXL may also be effective in the treatment and prophylaxis of iatrogenic keratectasia, resulting from excessively aggressive photoablation. This treatment has also been used to treat infectious corneal ulcers with apparent favorable results. Combination with other treatments, such as intracorneal ring segment implantation, limited topography-guided photoablation and conductive keratoplasty have been used with different levels of success.

  14. Collagen cross linking: Current perspectives

    Directory of Open Access Journals (Sweden)

    Srinivas K Rao

    2013-01-01

    Full Text Available Keratoconus is a common ectatic disorder occurring in more than 1 in 1,000 individuals. The condition typically starts in adolescence and early adulthood. It is a disease with an uncertain cause and its progression is unpredictable, but in extreme cases, vision deteriorates and can require corneal transplant surgery. Corneal collagen cross-linking (CCL with riboflavin (C3R is a recent treatment option that can enhance the rigidity of the cornea and prevent disease progression. Since its inception, the procedure has evolved with newer instrumentation, surgical techniques, and is also now performed for expanded indications other than keratoconus. With increasing experience, newer guidelines regarding optimization of patient selection, the spectrum of complications and their management, and combination procedures are being described. This article in conjunction with the others in this issue, will try and explore the uses of collagen cross-linking (CXL in its current form.

  15. Functional hydrophilic polystyrene beads with uniformly size and high cross-linking degree facilitated rapid separation of exenatide.

    Science.gov (United States)

    Li, Qiang; Zhao, Lan; Zhang, Rongyue; Huang, Yongdong; Zhang, Yan; Zhang, Kun; Wu, Xuexing; Zhang, Zhigang; Gong, Fangling; Su, Zhiguo; Ma, Guanghui

    2016-04-01

    A high cross-linking polystyrene(PSt)-based anion-exchange material with uniformly size, high ion exchange capacity, and high hydrophilicity was synthesized by a novel surface functionalization approach in this study. Uniformly sized PSt microspheres were prepared by the membrane emulsion polymerization strategy, and then modified by (1) conversing resid ual surface vinyl groups to epoxy groups followed by quaternization, and (2) decorating aromatic ring matrix including nitration, reduction and attachment of glycidyltrimethylammonium chloride. The 3-D morphology and porous features of microspheres were observed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The surface of the modified PSt became roughness but the particle size remained same. Meanwhile, FT-IR spectra and laser scanning confocal microscope (LCSM) indicated that the modification groups had been successfully covalently coated onto the PSt microspheres. Modified PSt microspheres showed greatly improved hydrophilicity and biocompatibility with 0.387mmol/mL ion exchange capacity (IEC). In the application evaluation procedure, exenatide can be purified from 42.9% (peptide crudes) to 88.6% by modified PSt column with 97.1% recovery yield. This modified PSt microspheres had a large potential in application for efficient separation of peptides.

  16. Theoretical studies of the functional role of the cross-linked histidine-tyrosine copper-B ligand of cytochrome c oxidase

    Science.gov (United States)

    McDonald, William J.

    In the present work density functional theory calculations were performed to explore the vibrational and electronic spectral changes associated with proton and electron transfer from the CuB center at the active site of cytochrome c oxidase that lead to the formation of either the PR or PM intermediates in the catalytic reduction of dioxygen to water. Furthermore, the thermodynamics of proton and electron transfer from the cross-linked histidine-tyrosine Cu B ligand were explored to assess the possible role of this ligand as a proton and/or electron donor during enzymatic turnover. Characteristic calculated cross-linked imidazole-phenolate and imidazole-phenoxyl radical vibrational frequencies and isotope shifts are in good agreement with the vibrational spectra of the PR and PM intermediates of the bo3 quinol oxidase from E. coli and R. sphaeroides and P. denitrificans suggesting that the Y244 (bovine numbering) is deprotonated in the PR intermediate, and is a tyrosyl radical in P M. Furthermore, using isodesmic reactions, the cross-linked phenol is found to be a significantly stronger acid than an unmodified phenol in the gas-phase, and likely in the inhomogeneous low-dielectric environment of the membrane bound enzyme, supporting the conclusion that the cross-linked tyrosine is a proton donor during enzymatic turnover. Time-dependent density functional theory calculations qualitatively reproduce the red-shift in the UV/visible absorption spectrum of a cross-linked imidazole-phenolate anion compared to the imidazole-phenol. Furthermore, the unique ˜500 nm absorption of a cross-linked imidazole-phenoxyl radical is correctly predicted using TDDFT and may be assigned as an imidazole-phenoxyl radical pi-to-pi* transition. Furthermore, this absorption is predicted in the spectrum of a Cu2+-imidazole-phenoxyl biradical model.

  17. Electrospinning formaldehyde cross-linked zein solutions

    Science.gov (United States)

    In order to develop zein fibers with improved physical properties and solvent resistance, formaldehyde was used as the cross-linking reagent before spinning. The cross-linking reaction was carried out in either acetic acid or ethanolic-HCl where the amount of cross-linking reagent was between 1 and...

  18. High-density functionalization and cross-linking of DNA: "click" and "bis-click" cycloadditions performed on alkynylated oligonucleotides with fluorogenic anthracene azides.

    Science.gov (United States)

    Pujari, Suresh S; Ingale, Sachin A; Seela, Frank

    2014-10-15

    High density functionalization of DNA with ethynyl and octadiynyl side chains followed by CuAAC "click labeling" with 9-azidomethylanthracene was performed. Alkynyl DNA was also cross-linked with fluorogenic 9,10-bis-azidomethylanthracene employing the "bis-click" reaction. By this means the fluorescence of the anthracene moiety was imparted to the virtually nonfluorescent DNA. Phosphoramidites of 8-aza-7-deaza-2'-deoxyadenosine with short and long linker arms in a steric nondemanding 7-position were utilized in solid phase oligodeoxynucleotide synthesis. High density alkynylated DNA-without anthracene residues-was found to be of comparable stability with both long and short linker arms. High density anthracene functionalized DNA became less stable with the short linker compared to that with the long linker connectivity. Interstrand cross-linked homodimers constructed from alkynylated oligonucleotides with fluorogenic 9,10-bis-azidomethylanthracene were hybridized with complementary strands to form double helices. They are more stable when the linker was located at a terminus than in a central position. Short linker anthracene adducts were destabilizing compared to long linker adducts. The fluorogenic anthracene residues not only have a significant effect on the duplex stability, but also impart fluorescence to the species. Fluorescence of cross-linked double helices with long linker connectivity was quenched when the cross-link was in a terminal position and was dequenched when the linker was connecting the two double helices at the center of the molecule. The fluorescence of the anthracene cross-linked double helices was strongly increased (dequenched) when the correct base pair was formed, while no change occurred upon mismatch formation.

  19. Cross-linked Composite Gel Polymer Electrolyte using Mesoporous Methacrylate-Functionalized SiO2 Nanoparticles for Lithium-Ion Polymer Batteries

    Science.gov (United States)

    Shin, Won-Kyung; Cho, Jinhyun; Kannan, Aravindaraj G.; Lee, Yoon-Sung; Kim, Dong-Won

    2016-05-01

    Liquid electrolytes composed of lithium salt in a mixture of organic solvents have been widely used for lithium-ion batteries. However, the high flammability of the organic solvents can lead to thermal runaway and explosions if the system is accidentally subjected to a short circuit or experiences local overheating. In this work, a cross-linked composite gel polymer electrolyte was prepared and applied to lithium-ion polymer cells as a safer and more reliable electrolyte. Mesoporous SiO2 nanoparticles containing reactive methacrylate groups as cross-linking sites were synthesized and dispersed into the fibrous polyacrylonitrile membrane. They directly reacted with gel electrolyte precursors containing tri(ethylene glycol) diacrylate, resulting in the formation of a cross-linked composite gel polymer electrolyte with high ionic conductivity and favorable interfacial characteristics. The mesoporous SiO2 particles also served as HF scavengers to reduce the HF content in the electrolyte at high temperature. As a result, the cycling performance of the lithium-ion polymer cells with cross-linked composite gel polymer electrolytes employing methacrylate-functionalized mesoporous SiO2 nanoparticles was remarkably improved at elevated temperatures.

  20. Cross-linked Composite Gel Polymer Electrolyte using Mesoporous Methacrylate-Functionalized SiO2 Nanoparticles for Lithium-Ion Polymer Batteries.

    Science.gov (United States)

    Shin, Won-Kyung; Cho, Jinhyun; Kannan, Aravindaraj G; Lee, Yoon-Sung; Kim, Dong-Won

    2016-05-18

    Liquid electrolytes composed of lithium salt in a mixture of organic solvents have been widely used for lithium-ion batteries. However, the high flammability of the organic solvents can lead to thermal runaway and explosions if the system is accidentally subjected to a short circuit or experiences local overheating. In this work, a cross-linked composite gel polymer electrolyte was prepared and applied to lithium-ion polymer cells as a safer and more reliable electrolyte. Mesoporous SiO2 nanoparticles containing reactive methacrylate groups as cross-linking sites were synthesized and dispersed into the fibrous polyacrylonitrile membrane. They directly reacted with gel electrolyte precursors containing tri(ethylene glycol) diacrylate, resulting in the formation of a cross-linked composite gel polymer electrolyte with high ionic conductivity and favorable interfacial characteristics. The mesoporous SiO2 particles also served as HF scavengers to reduce the HF content in the electrolyte at high temperature. As a result, the cycling performance of the lithium-ion polymer cells with cross-linked composite gel polymer electrolytes employing methacrylate-functionalized mesoporous SiO2 nanoparticles was remarkably improved at elevated temperatures.

  1. Cross-linked Composite Gel Polymer Electrolyte using Mesoporous Methacrylate-Functionalized SiO2 Nanoparticles for Lithium-Ion Polymer Batteries

    Science.gov (United States)

    Shin, Won-Kyung; Cho, Jinhyun; Kannan, Aravindaraj G.; Lee, Yoon-Sung; Kim, Dong-Won

    2016-01-01

    Liquid electrolytes composed of lithium salt in a mixture of organic solvents have been widely used for lithium-ion batteries. However, the high flammability of the organic solvents can lead to thermal runaway and explosions if the system is accidentally subjected to a short circuit or experiences local overheating. In this work, a cross-linked composite gel polymer electrolyte was prepared and applied to lithium-ion polymer cells as a safer and more reliable electrolyte. Mesoporous SiO2 nanoparticles containing reactive methacrylate groups as cross-linking sites were synthesized and dispersed into the fibrous polyacrylonitrile membrane. They directly reacted with gel electrolyte precursors containing tri(ethylene glycol) diacrylate, resulting in the formation of a cross-linked composite gel polymer electrolyte with high ionic conductivity and favorable interfacial characteristics. The mesoporous SiO2 particles also served as HF scavengers to reduce the HF content in the electrolyte at high temperature. As a result, the cycling performance of the lithium-ion polymer cells with cross-linked composite gel polymer electrolytes employing methacrylate-functionalized mesoporous SiO2 nanoparticles was remarkably improved at elevated temperatures. PMID:27189842

  2. Solvent-free covalent functionalization of multi-walled carbon nanotubes and nanodiamond with diamines: Looking for cross-linking effects

    Energy Technology Data Exchange (ETDEWEB)

    Basiuk, Elena V., E-mail: elenagd@unam.mx [Centro de Ciencias Aplicadas y Desarrollo Tecnologico, Universidad Nacional Autonoma de Mexico, Circuito Exterior, Ciudad Universitaria, 04510 Mexico, D.F. (Mexico); Nanophysics Department, Italian Institute of Technology, via Morego 30, 16163 Genova, Liguria (Italy); Basiuk, Vladimir A. [Nanophysics Department, Italian Institute of Technology, via Morego 30, 16163 Genova, Liguria (Italy); Instituto de Ciencias Nucleares, Universidad Nacional Autonoma de Mexico, Circuito Exterior, Ciudad Universitaria, 04510 Mexico, D.F. (Mexico); Facultad de Ciencias, Universidad Autonoma del Estado de Morelos, Av. Universidad 1001, Col. Chamilpa, 62209 Cuernavaca, Morelos (Mexico); Meza-Laguna, Victor; Contreras-Torres, Flavio F.; Martinez, Melchor [Centro de Ciencias Aplicadas y Desarrollo Tecnologico, Universidad Nacional Autonoma de Mexico, Circuito Exterior, Ciudad Universitaria, 04510 Mexico, D.F. (Mexico); Rojas-Aguilar, Aaron [Centro de Investigacion y de Estudios Avanzados, Instituto Politecnico Nacional, Av. Instituto Politecnico Nacional 2508, Col. San Pedro Zacatenco, 07360 Mexico, D.F. (Mexico); Salerno, Marco [Nanophysics Department, Italian Institute of Technology, via Morego 30, 16163 Genova, Liguria (Italy); and others

    2012-10-15

    Highlights: Black-Right-Pointing-Pointer Diamines were used for one-step functionalization of nanotubes and nanodiamond. Black-Right-Pointing-Pointer We found experimental evidences of cross-linking effects in these nanomaterials. Black-Right-Pointing-Pointer We found a strong orientation effect in the functionalized carbon nanotubes. - Abstract: The covalent functionalization of carbon nanomaterials with diamines is a way to enhance the mechanical strength of nanocomposites due to cross-linking effects, to form complex networks for nanotube-based electronic circuits, as well as is important for a number of biomedical applications. The main goal of the present work was to covalently functionalize pristine multi-walled carbon nanotubes and nanodiamond with three aliphatic diamines (1,8-diaminooctane, 1,10-diaminodecane and 1,12-diaminododecane) and one aromatic diamine (1,5-diaminonaphthalene), by employing a simple one-step solvent-free methodology, which is based on thermal instead of chemical activation. We looked for experimental evidences of cross-linking effects in the carbon nanomaterials synthesized by using solubility/dispersibility tests, atomic force microscopy, scanning and transmission electron microscopy, as well as Fourier-transform infrared spectroscopy and thermogravimetric analysis for additional characterization.

  3. The Architecture of Cross-Hemispheric Communication in the Aging Brain: Linking Behavior to Functional and Structural Connectivity

    Science.gov (United States)

    Kragel, James E.; Madden, David J.; Cabeza, Roberto

    2012-01-01

    Contralateral recruitment remains a controversial phenomenon in both the clinical and normative populations. To investigate the neural correlates of this phenomenon, we explored the tendency for older adults to recruit prefrontal cortex (PFC) regions contralateral to those most active in younger adults. Participants were scanned with diffusion tensor imaging and functional magnetic rresonance imaging during a lateralized word matching task (unilateral vs. bilateral). Cross-hemispheric communication was measured behaviorally as greater accuracy for bilateral than unilateral trials (bilateral processing advantage [BPA]) and at the neural level by functional and structural connectivity between contralateral PFC. Compared with the young, older adults exhibited 1) greater BPAs in the behavioral task, 2) greater compensatory activity in contralateral PFC during the bilateral condition, 3) greater functional connectivity between contralateral PFC during bilateral trials, and 4) a positive correlation between fractional anisotropy in the corpus callosum and both the BPA and the functional connectivity between contralateral PFC, indicating that older adults' ability to distribute processing across hemispheres is constrained by white matter integrity. These results clarify how older adults’ ability to recruit extra regions in response to the demands of aging is mediated by existing structural architecture, and how this architecture engenders corresponding functional changes that allow subjects to meet those task demands. PMID:21653286

  4. Chemical cross-linking of Chlamydia trachomatis

    DEFF Research Database (Denmark)

    Birkelund, Svend; Lundemose, AG; Christiansen, Gunna

    1988-01-01

    Purified elementary bodies (EBs) of Chlamydia trachomatis serovar L2 were analyzed by chemical cross-linking with disuccinimidyl selenodipropionate. The effect of the cross-linking was analyzed by immunoblotting sodium dodecyl sulfate-polyacrylamide gel electrophoresis-separated components which...

  5. Spontaneous stacking of purple membranes during immobilization with physical cross-linked poly(vinyl alcohol) hydrogel with retaining native-like functionality of bacteriorhodopsin

    Science.gov (United States)

    Yokoyama, Yasunori; Tanaka, Hikaru; Yano, Shunsuke; Takahashi, Hiroshi; Kikukawa, Takashi; Sonoyama, Masashi; Takenaka, Koshi

    2017-05-01

    We previously discovered the correlation between light-induced chromophore color change of a photo-receptor membrane protein bacteriorhodopsin (bR) and its two-dimensional crystalline state in the membrane. To apply this phenomenon to a novel optical memory device, it is necessary that bR molecules are immobilized as maintaining their structure and functional properties. In this work, a poly(vinyl alcohol) (PVA) hydrogel with physical cross-linkages (hydrogen bonds between PVA chains) that resulted from repeated freezing-and-thawing (FT) cycles was used as an immobilization medium. To investigate the effects of physically cross-linked PVA gelation on the structure and function of bR in purple membranes (PMs), spectroscopic techniques were employed against PM/PVA immobilized samples prepared with different FT cycle numbers. Visible circular dichroism spectroscopy strongly suggested PM stacking during gelation. X-ray diffraction data also indicated the PM stacking as well as its native-like crystalline lattice even after gelation. Time-resolved absorption spectroscopy showed that bR photocycle behaviors in PM/PVA immobilized samples were almost identical to that in suspension. These results suggested that a physically cross-linked PVA hydrogel is appropriate for immobilizing membrane proteins in terms of maintaining their structure and functionality.

  6. The effect of cross-link distributions in axially-ordered, cross-linked networks

    Science.gov (United States)

    Bennett, C. Brad; Kruczek, James; Rabson, D. A.; Matthews, W. Garrett; Pandit, Sagar A.

    2013-07-01

    Cross-linking between the constituent chains of biopolymers has a marked effect on their materials’ properties. In certain of these materials, such as fibrillar collagen, increases in cross-linking lead to an increase in the melting temperature. Fibrillar collagen is an axially-ordered network of cross-linked polymer chains exhibiting a broadened denaturation transition, which has been explained in terms of the successive denaturation with temperature of multiple species. We model axially-ordered, cross-linked materials as stiff chains with distinct arrangements of cross-link-forming sites. Simulations suggest that systems composed of chains with identical arrangements of cross-link-forming sites exhibit critical behavior. In contrast, systems composed of non-identical chains undergo a crossover. This model suggests that the arrangement of cross-link-forming sites may contribute to the broadening of the denaturation transition in fibrillar collagen.

  7. Jacket-free stir bar sorptive extraction with bio-inspired polydopamine-functionalized immobilization of cross-linked polymer on stainless steel wire.

    Science.gov (United States)

    Zhang, Zixin; Zhang, Wenpeng; Bao, Tao; Chen, Zilin

    2015-08-14

    Stainless steel wire (SSW) is a good substrate for stir bar sorptive extraction (SBSE). However, it is still a challenge to immobilize commonly used cross-linked polymers onto SSW. In this work, we present a new approach for immobilization of the cross-linked organic polymer onto SSW for jacket-free SBSE. A dopamine derivative was firstly synthesized; by introducing a mussel-inspired polydopamine process, a stable coating layer was finally generated on the surface of SSW. Secondly, the cross-linked polymer was synthesized on the polydopamine-modified SSW by using acetonitrile as the porogen, acrylamide (AA) as the functional monomer, ethylene glycol dimethacrylate (EGDMA) as the cross-linker and 2,2'-azobis (2-methylpropionitrile) as the initiator. A diluted pre-polymerization solution was carefully prepared to generate a thin layer of the polymer. The prepared poly(EGDMA-AA)-modified stir bar showed high stability and good tolerance toward stirring, ultrasonication, organic solvents, and strong acidic and basic conditions. Morphology and structure characterization of coatings were performed by scanning electron microscopy and Fourier transform infrared spectra, respectively. The prepared poly(EGDMA-AA)-modified stir bar showed great extraction efficiency toward protoberberines, with enrichment factors of 19-42. An SBSE-HPLC method was also developed for quantitative analysis of protoberberines. The method showed low limits of detection (0.06-0.15 ng mL(-1)), wide linear range (0.5-400 ng mL(-1)), good linearity (R≥0.9980) and good reproducibility (RSD≤3.60% for intra-day, RSD≤4.73% for inter-day). The developed method has been successfully applied to determine protoberberines in herb and rat plasma samples, with recoveries of 88.53-114.61%. Copyright © 2015 Elsevier B.V. All rights reserved.

  8. Cross-linking chemistry of squid beak.

    Science.gov (United States)

    Miserez, Ali; Rubin, Daniel; Waite, J Herbert

    2010-12-03

    In stark contrast to most aggressive predators, Dosidicus gigas (jumbo squids) do not use minerals in their powerful mouthparts known as beaks. Their beaks instead consist of a highly sclerotized chitinous composite with incremental hydration from the tip to the base. We previously reported l-3,4-dihydroxyphenylalanine (dopa)-histidine (dopa-His) as an important covalent cross-link providing mechanical strengthening to the beak material. Here, we present a more complete characterization of the sclerotization chemistry and describe additional cross-links from D. gigas beak. All cross-links presented in this report share common building blocks, a family of di-, tri-, and tetra-histidine-catecholic adducts, that were separated by affinity chromatography and high performance liquid chromatography (HPLC) and identified by tandem mass spectroscopy and proton nuclear magnetic resonance ((1)H NMR). The data provide additional insights into the unusually high cross-link density found in mature beaks. Furthermore, we propose both a low molecular weight catechol, and peptidyl-dopa, to be sclerotization agents of squid beak. This appears to represent a new strategy for forming hard tissue in animals. The interplay between covalent cross-linking and dehydration on the graded properties of the beaks is discussed.

  9. Molecular Structures of Isolevuglandin-Protein Cross-Links.

    Science.gov (United States)

    Bi, Wenzhao; Jang, Geeng-Fu; Zhang, Lei; Crabb, John W; Laird, James; Linetsky, Mikhail; Salomon, Robert G

    2016-10-17

    Isolevuglandins (isoLGs) are stereo and structurally isomeric γ-ketoaldehydes produced through free radical-induced oxidation of arachidonates. Some isoLG isomers are also generated through enzymatic cyclooxygenation. Post-translational modification of proteins by isoLGs is associated with loss-of-function, cross-linking and aggregation. We now report that a low level of modification by one or two molecules of isoLG has a profound effect on the activity of a multi subunit protease, calpain-1. Modification of one or two key lysyl residues apparently suffices to abolish catalytic activity. Covalent modification of calpain-1 led to intersubunit cross-linking. Hetero- and homo-oligomers of the catalytic and regulatory subunits of calpain-1 were detected by SDS-PAGE with Western blotting. N-Acetyl-glycyl-lysine methyl ester and β-amyloid(11-17) peptide EVHHQKL were used as models for characterizing the cross-linking of protein lysyl residues resulting from adduction of iso[4]LGE2. Aminal, bispyrrole, and trispyrrole cross-links of these two peptides were identified and fully characterized by mass spectrometry. Aminal and bispyrrole dimers were both detected. Furthermore, a complex mixture of derivatives of the bispyrrole cross-link containing one or more additional atoms of oxygen was found. Interesting differences are evident in the predominant cross-link type generated in the reaction of iso[4]LGE2 with these peptides. More aminal cross-links versus bispyrrole are formed during the reaction of the dipeptide with iso[4]LGE2. In contrast, more bispyrrole versus aminal cross-links are formed during the reaction of EVHHQKL with iso[4]LGE2. It is tempting to speculate that the EVHHQKL peptide-pyrrole modification forms noncovalent aggregates that favor the production of covalent bispyrrole cross-links because β-amyloid(11-17) tends to spontaneously oligomerize.

  10. Characterization of Cross-Linked Lipase Aggregates

    DEFF Research Database (Denmark)

    Prabhavathi Devi, Bethala Lakshmi Anu; Guo, Zheng; Xu, Xuebing

    2009-01-01

    Commercially available microbial lipases from different sources were immobilized as cross-linked enzyme aggregates (CLEAs) using different precipitants and glutaraldehyde as cross-linkers. These CLEAs were assayed based on esterification between lauric acid and n-propanol in solvent-free systems...... change upon CLEA formation. This work presents a characterization of CLEAs based on an esterification activity assay, which is useful for exploring the synthetic application potential of CLEA technology with favorable perspectives....

  11. Cross-linked structure of network evolution

    Science.gov (United States)

    Bassett, Danielle S.; Wymbs, Nicholas F.; Porter, Mason A.; Mucha, Peter J.; Grafton, Scott T.

    2014-03-01

    We study the temporal co-variation of network co-evolution via the cross-link structure of networks, for which we take advantage of the formalism of hypergraphs to map cross-link structures back to network nodes. We investigate two sets of temporal network data in detail. In a network of coupled nonlinear oscillators, hyperedges that consist of network edges with temporally co-varying weights uncover the driving co-evolution patterns of edge weight dynamics both within and between oscillator communities. In the human brain, networks that represent temporal changes in brain activity during learning exhibit early co-evolution that then settles down with practice. Subsequent decreases in hyperedge size are consistent with emergence of an autonomous subgraph whose dynamics no longer depends on other parts of the network. Our results on real and synthetic networks give a poignant demonstration of the ability of cross-link structure to uncover unexpected co-evolution attributes in both real and synthetic dynamical systems. This, in turn, illustrates the utility of analyzing cross-links for investigating the structure of temporal networks.

  12. Cross-linked structure of network evolution

    Energy Technology Data Exchange (ETDEWEB)

    Bassett, Danielle S., E-mail: dsb@seas.upenn.edu [Department of Bioengineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104 (United States); Department of Physics, University of California, Santa Barbara, California 93106 (United States); Sage Center for the Study of the Mind, University of California, Santa Barbara, California 93106 (United States); Wymbs, Nicholas F.; Grafton, Scott T. [Department of Psychology and UCSB Brain Imaging Center, University of California, Santa Barbara, California 93106 (United States); Porter, Mason A. [Oxford Centre for Industrial and Applied Mathematics, Mathematical Institute, University of Oxford, Oxford OX2 6GG (United Kingdom); CABDyN Complexity Centre, University of Oxford, Oxford, OX1 1HP (United Kingdom); Mucha, Peter J. [Carolina Center for Interdisciplinary Applied Mathematics, Department of Mathematics, University of North Carolina, Chapel Hill, North Carolina 27599 (United States); Department of Applied Physical Sciences, University of North Carolina, Chapel Hill, North Carolina 27599 (United States)

    2014-03-15

    We study the temporal co-variation of network co-evolution via the cross-link structure of networks, for which we take advantage of the formalism of hypergraphs to map cross-link structures back to network nodes. We investigate two sets of temporal network data in detail. In a network of coupled nonlinear oscillators, hyperedges that consist of network edges with temporally co-varying weights uncover the driving co-evolution patterns of edge weight dynamics both within and between oscillator communities. In the human brain, networks that represent temporal changes in brain activity during learning exhibit early co-evolution that then settles down with practice. Subsequent decreases in hyperedge size are consistent with emergence of an autonomous subgraph whose dynamics no longer depends on other parts of the network. Our results on real and synthetic networks give a poignant demonstration of the ability of cross-link structure to uncover unexpected co-evolution attributes in both real and synthetic dynamical systems. This, in turn, illustrates the utility of analyzing cross-links for investigating the structure of temporal networks.

  13. Method of preparing cross-linked enzyme particles

    NARCIS (Netherlands)

    Mateo, C.; Van Langen, L.M.; Van Rantwijk, F.

    2004-01-01

    The invention relates to a method of preparing cross-linked enzyme particles using a cross-linking agent. According to the invention, the enzyme particles are formed and subsequently cross-linked using a cross-linking agent having at least n reactive groups where N>=3 and a molecular weight of

  14. Method of preparing cross-linked enzyme particles

    NARCIS (Netherlands)

    Mateo, C.; Van Langen, L.M.; Van Rantwijk, F.

    2004-01-01

    The invention relates to a method of preparing cross-linked enzyme particles using a cross-linking agent. According to the invention, the enzyme particles are formed and subsequently cross-linked using a cross-linking agent having at least n reactive groups where N>=3 and a molecular weight of >2,00

  15. The cross linking of EPDM and NBR rubber

    Directory of Open Access Journals (Sweden)

    Samardžija-Jovanović Suzana

    2005-01-01

    Full Text Available In the process of macromolecule cross linking, the choice of type and quantity of the components and the experimental conditions are important to obtain the new cross linked materials with better mechanical and chemical characteristics. The cross linking method depends on the rubber type and structure. Intermolecular cross linking results in the formation elastomer network. The basis of the cross linking process, between ethylene propylene diene rubber (EPDM and acrylonitrile butadiene rubber (NBR, is a chemical reaction. Fillers and other additives are present in different mass ratios in the material. The exploitation properties of the cross linked materials depend on the quantity of additive in the cross linked systems.

  16. Elevated carboxy terminal cross linked telopeptide of type I collagen in alcoholic cirrhosis: relation to liver and kidney function and bone metabolism

    DEFF Research Database (Denmark)

    Møller, S; Hansen, M; Hillingso, J

    1999-01-01

    BACKGROUND: The carboxy terminal cross linked telopeptide of type I collagen (ICTP) has been put forward as a marker of bone resorption. Patients with alcoholic liver disease may have osteodystrophy. AIMS: To assess circulating and regional concentrations of ICTP in relation to liver dysfunction...

  17. [Corneal collagen cross-linking for keratoconus].

    Science.gov (United States)

    Zotov, V V; Pashtaev, N P; Pozdeeva, N A

    2015-01-01

    Over the last decade, corneal collagen cross-linking (CXL) has become a conventional treatment method for progressive keratoconus. Laboratory studies have shown that CXL increases the diameter of collagen fibers and also the number of intra- and interfibrillar cross-links, thus, increasing biomechanical strength of the irradiated cornea. As confirmed by a series of clinical and randomized controlled trials, CXL is able to slow down and, perhaps, to stop the progression of keratoconus. In most post-CXL patients visual acuity improves, while keratometric readings, spherical equivalent, and higher order aberrations reduce. Although published results prove CXL effective in the treatment of progressive keratoconus, its late consequences are yet unknown. This article reviews the stages of CXL development and results of published experimental and clinical studies. Prospects for CXL modifications that do not require epithelial debridement are discussed.

  18. Thermal Analyse sof Cross-Linked Polyethylene

    Directory of Open Access Journals (Sweden)

    Radek Polansky

    2007-01-01

    Full Text Available The paper summarizes results obtained during the structural analyses measurements (Differential Scanning Calorimetry DSC, Thermogravimetry TG, Thermomechanical analysis TMA and Fourier transform infrared spectroscopy FT-IR. The samples of cross-linked polyethylene cable insulation were tested via these analyses. The DSC and TG were carried out using simultaneous thermal analyzer TA Instruments SDT Q600 with connection of Fourier transform infrared spectrometer Nicolet 380. Thermomechanical analysis was carried out by TMA Q400EM TA Instruments apparatus.

  19. Collagen cross-linking in thin corneas

    Directory of Open Access Journals (Sweden)

    Prema Padmanabhan

    2013-01-01

    Full Text Available Collagen cross-linking (CXL has become the standard of care for progressive keratoconus, after numerous clinical studies have established its efficacy and safety in suitably selected eyes. The standard protocol is applicable in eyes which have a minimum corneal thickness of 400 μm after epithelial debridement. This prerequisite was stipulated to protect the corneal endothelium and intraocular tissues from the deleterious effect of ultraviolet-A (UVA radiation. However, patients with keratoconus often present with corneal thickness of less than 400 μm and could have otherwise benefited from this procedure. A few modifications of the standard procedure have been suggested to benefit these patients without a compromise in safety. Transepithelial cross-linking, pachymetry-guided epithelial debridement before cross-linking, and the use of hypoosmolar riboflavin are some of the techniques that have been attempted. Although clinical data is limited at the present time, these techniques are worth considering in patients with thin corneas. Further studies are needed to scientifically establish their efficacy and safety.

  20. Cross-linking for microbial keratitis

    Directory of Open Access Journals (Sweden)

    Jayesh Vazirani

    2013-01-01

    Full Text Available The success of collagen cross-linking as a clinical modality to modify the clinical course in keratoconus seems to have fueled the search for alternative applications for this treatment. Current clinical data on its efficacy is limited and laboratory data seems to indicate that it performs poorly against resistant strains of bacteria and against slow growing organisms. However, the biological plausibility of crosslinking and the lack of effective strategies in managing infections with these organisms continue to focus attention on this potential treatment. Well-conducted experimental and clinical studies with controls are required to answer the questions of its efficacy in future.

  1. Anisotropic Thermal Conductivity Measurements on Cross-Linked Polybutadienes in Uniaxial Elongation

    Science.gov (United States)

    Venerus, David C.; Kolev, Dimitre

    2008-07-01

    Cross-linked elastomers have numerous applications including automobiles, sporting goods, and biomedical devices. During both their processing and application, these materials experience large mechanical stresses and thermal gradients. In this study, we investigate the mechanical and thermal transport behavior of cross-linked polybutadienes. These materials have been prepared by cross linking well-entangled polybutadienes using an organic peroxide cross-linking agent at low concentration. Samples obtained after nearly complete conversion of the cross-linking agent, which can be characterized as lightly cross-linked (i.e., more than 10 entanglements per cross-link), were subjected to a series of large strain, uniaxial deformations. Measurements of the tensile stress and two components of the thermal conductivity tensor will be reported as a function of elongation. These data are also used to examine the stress-thermal rule in which the stress and thermal conductivity tensors are linearly related.

  2. The Cross - linking reaction of HEC

    Institute of Scientific and Technical Information of China (English)

    XIONG Jian; YE Jun; XUAN Zhiyong; XIE Guohui

    2001-01-01

    @@ Cellulose ethers are important components for light industries such as food and papermaking industries. Its modification research is a frontline science to widen their uses and realize their industrialization. The target of modification is to make high production value, low input and meet the needs better in industries. O-(2-hydroxyethl) cellulose (HEC) is one of the best-known cellulose ether derivatives. It is mainly used as thickeners, dispersants, adhesives, extenders, and films because of its water solubility and gel-forming properties. The present research,by means of cross-linking, we study the influence on HEC about rheological behavior.This will provide a feasible scheme for cellulose ethers modification.

  3. The Cross - linking reaction of HEC

    Institute of Scientific and Technical Information of China (English)

    XIONG; Jian

    2001-01-01

    Cellulose ethers are important components for light industries such as food and papermaking industries. Its modification research is a frontline science to widen their uses and realize their industrialization. The target of modification is to make high production value, low input and meet the needs better in industries.  O-(2-hydroxyethl) cellulose (HEC) is one of the best-known cellulose ether derivatives. It is mainly used as thickeners, dispersants, adhesives, extenders, and films because of its water solubility and gel-forming properties. The present research,by means of cross-linking, we study the influence on HEC about rheological behavior.This will provide a feasible scheme for cellulose ethers modification.……

  4. Formation and cleaning function of physically cross-linked dual strengthened water-soluble chitosan-based core-shell particles.

    Science.gov (United States)

    Dong, Yanrui; Xiao, Congming

    2017-09-01

    Facile and mild ionic cross-linking and freezing/thawing technologies were applied to prepare double strengthened core-shell particles by using water-soluble chitosan (WSC), sodium alginate (SA) and poly(vinyl alcohol) (PVA) as starting materials. The aqueous solution contained WSC and PVA was dropped in ethanol to form beads. The beads were converted into WSC/PVA hydrogel particles by being subjected to three freeze/thaw cycles. Subsequently, ionic cross-linked hydrogel layer was formed around each WSC/PVA particle to generate core-shell particulates. Fourier transform infrared spectra confirmed the combination among various components. Dynamic mechanical thermal analysis indicated that the storage modulus of the core-shell hydrogel was improved obviously. Thermogravimetric analysis exhibited the thermal stability of the particles was also enhanced by incorporation of PVA. It was found that the particles were able to adsorb carbon dioxide, lead ion and copper ion. The adsorption capacities of dry particles toward carbon dioxide, Pb(II) and Cu(II) could reach 199.62, 39.28 and 26.03mg/g, respectively. The rates of the particles for binding Pb(II) and Cu(II) at initial stage were 26.57 and 4.30%/min, respectively. These experimental results suggested that the particles were an efficient sorbent for removing hazardous substances such as carbon dioxide and heavy-metal ions. Copyright © 2017 Elsevier B.V. All rights reserved.

  5. Cytokines and growth factors cross-link heparan sulfate

    Science.gov (United States)

    Migliorini, Elisa; Thakar, Dhruv; Kühnle, Jens; Sadir, Rabia; Dyer, Douglas P.; Li, Yong; Sun, Changye; Volkman, Brian F.; Handel, Tracy M.; Coche-Guerente, Liliane; Fernig, David G.; Lortat-Jacob, Hugues; Richter, Ralf P.

    2015-01-01

    The glycosaminoglycan heparan sulfate (HS), present at the surface of most cells and ubiquitous in extracellular matrix, binds many soluble extracellular signalling molecules such as chemokines and growth factors, and regulates their transport and effector functions. It is, however, unknown whether upon binding HS these proteins can affect the long-range structure of HS. To test this idea, we interrogated a supramolecular model system, in which HS chains grafted to streptavidin-functionalized oligoethylene glycol monolayers or supported lipid bilayers mimic the HS-rich pericellular or extracellular matrix, with the biophysical techniques quartz crystal microbalance (QCM-D) and fluorescence recovery after photobleaching (FRAP). We were able to control and characterize the supramolecular presentation of HS chains—their local density, orientation, conformation and lateral mobility—and their interaction with proteins. The chemokine CXCL12α (or SDF-1α) rigidified the HS film, and this effect was due to protein-mediated cross-linking of HS chains. Complementary measurements with CXCL12α mutants and the CXCL12γ isoform provided insight into the molecular mechanism underlying cross-linking. Fibroblast growth factor 2 (FGF-2), which has three HS binding sites, was also found to cross-link HS, but FGF-9, which has just one binding site, did not. Based on these data, we propose that the ability to cross-link HS is a generic feature of many cytokines and growth factors, which depends on the architecture of their HS binding sites. The ability to change matrix organization and physico-chemical properties (e.g. permeability and rigidification) implies that the functions of cytokines and growth factors may not simply be confined to the activation of cognate cellular receptors. PMID:26269427

  6. Cross-link guided molecular modeling with ROSETTA.

    Directory of Open Access Journals (Sweden)

    Abdullah Kahraman

    Full Text Available Chemical cross-links identified by mass spectrometry generate distance restraints that reveal low-resolution structural information on proteins and protein complexes. The technology to reliably generate such data has become mature and robust enough to shift the focus to the question of how these distance restraints can be best integrated into molecular modeling calculations. Here, we introduce three workflows for incorporating distance restraints generated by chemical cross-linking and mass spectrometry into ROSETTA protocols for comparative and de novo modeling and protein-protein docking. We demonstrate that the cross-link validation and visualization software Xwalk facilitates successful cross-link data integration. Besides the protocols we introduce XLdb, a database of chemical cross-links from 14 different publications with 506 intra-protein and 62 inter-protein cross-links, where each cross-link can be mapped on an experimental structure from the Protein Data Bank. Finally, we demonstrate on a protein-protein docking reference data set the impact of virtual cross-links on protein docking calculations and show that an inter-protein cross-link can reduce on average the RMSD of a docking prediction by 5.0 Å. The methods and results presented here provide guidelines for the effective integration of chemical cross-link data in molecular modeling calculations and should advance the structural analysis of particularly large and transient protein complexes via hybrid structural biology methods.

  7. Adsorption characteristics of rebaudioside A and stevioside on cross-linked poly(styrene-co-divinylbenzene) macroporous resins functionalized with chloromethyl, amino and phenylboronic acid groups.

    Science.gov (United States)

    Ye, Fayin; Yang, Ruijin; Hua, Xiao; Zhao, Guohua

    2014-09-15

    The adsorptive separation of each steviol glycoside from aqueous solutions by polymeric adsorbents has attracted a lot of interest in recent years. The adsorption properties of chloromethylated cross-linked poly(styrene-co-divinylbenzene) macroporous resins, functionalised with chloromethyl, amino and phenylboronic acid groups, towards rebaudioside A and stevioside were studied. The results revealed that the resins with amino and phenylboronic acid groups preferred to adsorb stevioside rather than rebaudioside A, and their adsorption kinetics fitted a pseudo-second-order model. Isothermal equilibrium curves of rebaudioside A and stevioside showed a good fitness with the Langmuir and Freundlich models. The adsorption of rebaudioside A and stevioside onto resins was a spontaneous and exothermic process as indicated by the negative values in free energy and enthalpy. Results from the resin-packed column demonstrated that an effluent rich in rebaudioside A (purity 98%) was obtained prior to the breakthrough point of stevioside.

  8. Cross Linked Metal Particles for Low Noise Bolometer Materials

    Science.gov (United States)

    2016-12-12

    SECURITY CLASSIFICATION OF: This final report summarizes WSU’s progress from 4/2/2015 to 09/30/2016 on the project, "Cross-linked Metal Particles ...2016 Final Report: Cross-linked Metal Particles for Low-noise Bolometer Materials The views, opinions and/or findings contained in this report are...peer-reviewed journals: Number of Papers published in non peer-reviewed journals: Final Report: Cross-linked Metal Particles for Low-noise Bolometer

  9. An Open Data Format for Visualization and Analysis of Cross-Linked Mass Spectrometry Results.

    Science.gov (United States)

    Hoopmann, Michael R; Mendoza, Luis; Deutsch, Eric W; Shteynberg, David; Moritz, Robert L

    2016-11-01

    Protein-protein interactions are an important element in the understanding of protein function, and chemical cross-linking shotgun mass spectrometry is rapidly becoming a routine approach to identify these specific interfaces and topographical interactions. Protein cross-link data analysis is aided by dozens of algorithm choices, but hindered by a lack of a common format for representing results. Consequently, interoperability between algorithms and pipelines utilizing chemical cross-linking remains a challenge. pepXML is an open, widely-used format for representing spectral search algorithm results that has facilitated information exchange and pipeline development for typical shotgun mass spectrometry analyses. We describe an extension of this format to incorporate cross-linking spectral search results. We demonstrate application of the extension by representing results of multiple cross-linking search algorithms. In addition, we demonstrate adapting existing pepXML-supporting software pipelines to analyze protein cross-linking results formatted in pepXML. Graphical Abstract ᅟ.

  10. Characterization of Interstrand DNA-DNA Cross-Links Using the α-Hemolysin Protein Nanopore.

    Science.gov (United States)

    Zhang, Xinyue; Price, Nathan E; Fang, Xi; Yang, Zhiyu; Gu, Li-Qun; Gates, Kent S

    2015-12-22

    Nanopore-based sensors have been studied extensively as potential tools for DNA sequencing, characterization of epigenetic modifications such as 5-methylcytosine, and detection of microRNA biomarkers. In the studies described here, the α-hemolysin protein nanopore embedded in a lipid bilayer was used for the detection and characterization of interstrand cross-links in duplex DNA. Interstrand cross-links are important lesions in medicinal chemistry and toxicology because they prevent the strand separation that is required for read-out of genetic information from DNA in cells. In addition, interstrand cross-links are used for the stabilization of duplex DNA in structural biology and materials science. Cross-linked DNA fragments produced unmistakable current signatures in the nanopore experiment. Some cross-linked substrates gave irreversible current blocks of >10 min, while others produced long current blocks (10-100 s) before the double-stranded DNA cross-link translocated through the α-hemolysin channel in a voltage-driven manner. The duration of the current block for the different cross-linked substrates examined here may be dictated by the stability of the duplex region left in the vestibule of the nanopore following partial unzipping of the cross-linked DNA. Construction of calibration curves measuring the frequency of cross-link blocking events (1/τon) as a function of cross-link concentration enabled quantitative determination of the amounts of cross-linked DNA present in samples. The unique current signatures generated by cross-linked DNA in the α-HL nanopore may enable the detection and characterization of DNA cross-links that are important in toxicology, medicine, and materials science.

  11. Effect of Cross-Linking and Enzymatic Hydrolysis Composite Modification on the Properties of Rice Starches

    Directory of Open Access Journals (Sweden)

    Gao-Qiang Liu

    2012-07-01

    Full Text Available Native rice starch lacks the versatility necessary to function adequately under rigorous industrial processing, so modified starches are needed to meet the functional properties required in food products. This work investigated the impact of enzymatic hydrolysis and cross-linking composite modification on the properties of rice starches. Rice starch was cross-linked with epichlorohydrin (EPI with different concentrations (0.5%, 0.7%, 0.9% w/w, on a dry starch basis, affording cross-linked rice starches with the three different levels of cross-linking that were named R1, R2, and R3, respectively. The cross-linked rice starches were hydrolyzed by α-amylase and native, hydrolyzed, and hydrolyzed cross-linked rice starches were comparatively studied. It was found that hydrolyzed cross-linked rice starches showed a lower the degree of amylase hydrolysis compared with hydrolyzed rice starch. The higher the degree of cross-linking, the higher the capacity to resist enzyme hydrolysis. Hydrolyzed cross-linked rice starches further increased the adsorptive capacities of starches for liquids and decreased the trend of retrogradation, and it also strengthened the capacity to resist shear compared to native and hydrolyzed rice starches.

  12. Self-assembly made durable: water-repellent materials formed by cross-linking fullerene derivatives.

    Science.gov (United States)

    Wang, Jiaobing; Shen, Yanfei; Kessel, Stefanie; Fernandes, Paulo; Yoshida, Kaname; Yagai, Shiki; Kurth, Dirk G; Möhwald, Helmuth; Nakanishi, Takashi

    2009-01-01

    Fullerene flakes: A diacetylene-functionalized fullerene derivative self-organizes into flakelike microparticles (see picture). Both the diacetylene and C(60) moieties can be effectively cross-linked, which leads to supramolecular materials with remarkable resistivity to solvent, heat, and mechanical stress. Moreover, the surface of the cross-linked flakelike objects is highly durable and water-repellent.

  13. Cross-linked Polyelectrolyte and Its Function in Adsorption of Fluid and Excess Nitrogen Waste Products: an Experimental Study on Dialysate Effluent Fluid.

    Science.gov (United States)

    Tayebi Khosroshahi, Hamid; Abedi, Behzad; Daneshvar, Sabalan; Alizadeh, Effat; Khalilzadeh, Mohammadreza; Abedi, Yaghoub

    2017-07-01

    One of the most important issues in patients with chronic kidney disease is fluid retention and volume overload accompanied by retention of nitrogenous waste products and some electrolytes. Bowel fluid contains high levels of urea, creatinine, uric acid, and electrolytes, which make it a potential candidate for intestinal excretion of nitrogen wastes and electrolytes. Cross-linked polyelectrolyte (CLP) is a polymer that, given orally, absorbs excess fluid, electrolyte, and nitrogenous waste products. In an experimental study on 30 hemodialysis patients, the effect of CLP on adsorption of fluid, urea, creatinine, uric acid, sodium, and potassium were evaluated. For this purpose, 500 mL of effluent fluid of each patient were collected at the 1st hour of dialysis. The concentrations of the abovementioned products were measured by standard methods. Then the dialysate effluent samples were treated with 6 g of CLP and incubated for 4 hours at 37°C. Up to 80% of effluent fluid water was adsorbed by CLP. There were significant reductions in urea, creatinine, uric acid, and sodium levels in the remaining effluent fluid (P substitute for conventional dialysis methods, especially hemodialysis.

  14. Radiation cross-linked polyolefin-insulated wire

    Science.gov (United States)

    Sano, K.; Ishitani, H.

    Because radiation cross-linked polyolefin has excellent mechanical heat resistance, its application limit can be expanded extremely by improving the resistance against heat oxidation and flame. This paper is concerning a halogen free radiation cross-linked polyolefin-insulated wire having excellent heat resistance and flameretardant property, which is used for appliances.

  15. Tailoring the properties of cholecyst-derived extracellular matrix using carbodiimide cross-linking.

    LENUS (Irish Health Repository)

    Burugapalli, Krishna

    2009-01-01

    Modulation of properties of extracellular matrix (ECM) based scaffolds is key for their application in the clinical setting. In the present study, cross-linking was used as a tool for tailoring the properties of cholecyst-derived extracellular matrix (CEM). CEM was cross-linked with varying cross-linking concentrations of N,N-(3-dimethyl aminopropyl)-N\\'-ethyl carbodiimide (EDC) in the presence of N-hydroxysuccinimide (NHS). Shrink temperature measurements and ATR-FT-IR spectra were used to determine the degree of cross-linking. The effect of cross-linking on degradation was tested using the collagenase assay. Uniaxial tensile properties and the ability to support fibroblasts were also evaluated as a function of cross-linking. Shrink temperature increased from 59 degrees C for non-cross-linked CEM to 78 degrees C for the highest EDC cross-linking concentration, while IR peak area ratios for the free -NH(2) group at 3290 cm(-1) to that of the amide I band at 1635 cm(-1) decreased with increasing EDC cross-linking concentration. Collagenase assay demonstrated that degradation rates for CEM can be tailored. EDC concentrations 0 to 0.0033 mmol\\/mg CEM were the cross-linking concentration range in which CEM showed varied susceptibility to collagenase degradation. Furthermore, cross-linking concentrations up to 0.1 mmol EDC\\/mg CEM did not have statistically significant effect on the uniaxial tensile strength, as well as morphology, viability and proliferation of fibroblasts on CEM. In conclusion, the degradation rates of CEM can be tailored using EDC-cross-linking, while maintaining the mechanical properties and the ability of CEM to support cells.

  16. In vitro cross-linking of elastin peptides and molecular characterization of the resultant biomaterials.

    Science.gov (United States)

    Heinz, Andrea; Ruttkies, Christoph K H; Jahreis, Günther; Schräder, Christoph U; Wichapong, Kanin; Sippl, Wolfgang; Keeley, Fred W; Neubert, Reinhard H H; Schmelzer, Christian E H

    2013-04-01

    Elastin is a vital protein and the major component of elastic fibers which provides resilience to many vertebrate tissues. Elastin's structure and function are influenced by extensive cross-linking, however, the cross-linking pattern is still unknown. Small peptides containing reactive allysine residues based on sequences of cross-linking domains of human elastin were incubated in vitro to form cross-links characteristic of mature elastin. The resultant insoluble polymeric biomaterials were studied by scanning electron microscopy. Both, the supernatants of the samples and the insoluble polymers, after digestion with pancreatic elastase or trypsin, were furthermore comprehensively characterized on the molecular level using MALDI-TOF/TOF mass spectrometry. MS(2) data was used to develop the software PolyLinX, which is able to sequence not only linear and bifunctionally cross-linked peptides, but for the first time also tri- and tetrafunctionally cross-linked species. Thus, it was possible to identify intra- and intermolecular cross-links including allysine aldols, dehydrolysinonorleucines and dehydromerodesmosines. The formation of the tetrafunctional cross-link desmosine or isodesmosine was unexpected, however, could be confirmed by tandem mass spectrometry and molecular dynamics simulations. The study demonstrated that it is possible to produce biopolymers containing polyfunctional cross-links characteristic of mature elastin from small elastin peptides. MALDI-TOF/TOF mass spectrometry and the newly developed software PolyLinX proved suitable for sequencing of native cross-links in proteolytic digests of elastin-like biomaterials. The study provides important insight into the formation of native elastin cross-links and represents a considerable step towards the characterization of the complex cross-linking pattern of mature elastin. Copyright © 2013 Elsevier B.V. All rights reserved.

  17. Research Progress in Corneal Cross-linking Agents

    Institute of Scientific and Technical Information of China (English)

    Na Li; Xiujun Peng; Zhengjun Fan

    2014-01-01

    Corneal collagen cross-linking with UVA-riboflavin is cur-rently the only method for preventing the progression of kera-toconus from the pathological perspective. Topical application of a direct cross-linking agent is now attracting widespread at-tention in clinical settings..This article reviews the research progress in the application of indirect or direct cross-linking agents (e.g., riboflavin, glucose, ribose, glutaraldehyde, formaldehyde,.glyceraldehyde,.short chain aliphatic β-nitro alcohol, and genipin) in the treatment of corneal diseases and analyzes the cross-linking efficacy,.toxicity,.and merits and disadvantages of each cross-linking agent,.providing clinical information for further studies.

  18. ROLE OF CORNEAL COLLAGEN CROSS LINKING IN KERATOCONUS

    OpenAIRE

    Atul; Superna; Bhimasankar; Vijayleela

    2015-01-01

    To evaluate the outcome of collagen cross linkage using riboflavin 0.1% and ultraviolet A radiation of a wavelength 370nm . PURPOSE : To determine the effect of collagen cross linking for keratoconus on pachymetry , corneal topography, uncorrected visual acuity, specular count, IOP at 1, 3, 6 months . METHODS : The current study was designed as a prospective interventional trial of corneal collagen cross - linking in subjects w...

  19. Linking Gestures: Cross-Cultural Variation during Instructional Analogies

    Science.gov (United States)

    Richland, Lindsey Engle

    2015-01-01

    Deictic linking gestures, hand and arm motions that physically embody links being communicated between two or more objects in the shared communicative environment, are explored in a cross-cultural sample of mathematics instruction. Linking gestures are specifically examined here when they occur in the context of communicative analogies designed to…

  20. Covalently Cross-Linked Arabinoxylans Films for Debaryomyces hansenii Entrapment

    Directory of Open Access Journals (Sweden)

    Ramsés González-Estrada

    2015-06-01

    Full Text Available In the present study, wheat water extractable arabinoxylans (WEAX were isolated and characterized, and their capability to form covalently cross-linked films in presence of Debaryomyces hansenii was evaluated. WEAX presented an arabinose to xylose ratio of 0.60, a ferulic acid and diferulic acid content of 2.1 and 0.04 µg∙mg−1 WEAX, respectively and a Fourier Transform Infra-Red (FT-IR spectrum typical of WEAX. The intrinsic viscosity and viscosimetric molecular weight values for WEAX were 3.6 dL∙g−1 and 440 kDa, respectively. The gelation of WEAX (1% w/v with and without D. hansenii (1 × 107 CFU∙cm−2 was rheologically investigated by small amplitude oscillatory shear. The entrapment of D. hansenii decreased gel elasticity from 1.4 to 0.3 Pa, probably by affecting the physical interactions between WEAX chains. Covalently cross-linked WEAX films containing D. hansenii were prepared by casting. Scanning electron microscopy images show that WEAX films containing D. hansenii were porous and consisted of granular-like and fibre microstructures. Average tensile strength, elongation at break and Young’s modulus values dropped when D. hansenii was present in the film. Covalently cross-lined WEAX containing D. hansenii could be a suitable as a functional entrapping film.

  1. Elasticity of cross-linked semiflexible biopolymers under tension.

    Science.gov (United States)

    von der Heydt, Alice; Wilkin, Daniel; Benetatos, Panayotis; Zippelius, Annette

    2013-09-01

    Aiming at the mechanical properties of cross-linked biopolymers, we set up and analyze a model of two weakly bending wormlike chains subjected to a tensile force, with regularly spaced inter-chain bonds (cross-links) represented by harmonic springs. Within this model, we compute the force-extension curve and the differential stiffness exactly and discuss several limiting cases. Cross-links effectively stiffen the chain pair by reducing thermal fluctuations transverse to the force and alignment direction. The extra alignment due to cross-links increases both with growing number and with growing strength of the cross-links, and is most prominent for small force f. For large f, the additional, cross-link-induced extension is subdominant except for the case of linking the chains rigidly and continuously along their contour. In this combined limit, we recover asymptotically the elasticity of a weakly bending wormlike chain without constraints, stiffened by a factor of 4. The increase in differential stiffness can be as large as 100% for small f or large numbers of cross-links.

  2. Hydrogen peroxide and ferulic acid-mediated oxidative cross-linking ...

    African Journals Online (AJOL)

    STORAGESEVER

    2009-12-15

    Dec 15, 2009 ... Oxidative cross-linked casein mediated by hydrogen peroxide and ferulic acid was prepared at ... functional properties of food proteins treated (Motoki and. Seguro, 1998 ..... Team of Northeast Agricultural University (No.

  3. Cross-linking of the delta subunit to one of the three alpha subunits has no effect on functioning, as expected if delta is a part of the stator that links the F1 and F0 parts of the Escherichia coli ATP synthase.

    Science.gov (United States)

    Ogilvie, I; Aggeler, R; Capaldi, R A

    1997-06-27

    A mutant of the Escherichia coli F1F0-ATPase has been generated (alphaQ2C) in which the glutamine at position 2 of the alpha subunit has been replaced with a cysteine residue. Cu2+ treatment of ECF1 from this mutant cross-linked an alpha subunit to the delta subunit in high yield. Two different sites of disulfide bond formation were involved, i.e. between Cys90 (or the closely spaced Cys47) of alpha with Cys140 of delta, and between Cys2 of alpha and Cys140 of delta. Small amounts of other cross-linked products, including alpha-alpha, delta internal, and alpha-alpha-delta were obtained. In ECF1F0, there was no cross-linking between the intrinsic Cys of alpha and Cys140. Instead, the product generated between Cys2 of alpha and Cys140 of delta was obtained at near 90% yield. Small amounts of alpha-alpha and delta internal were present, and under high Cu2+ concentrations, alpha-alpha-delta was also formed. The ATPase activity of ECF1 and ECF1F0 was not significantly affected by the presence of these cross-links. When Cys140 of delta was first modified with N-ethylmaleimide in ECF1F0, an alpha-delta cross-link was still produced, although in lower yield, between Cys64 of delta and Cys2 of alpha. ATP hydrolysis-linked proton pumping of inner membranes from the mutant alpha2QC was only marginally affected by cross-linking of the alpha to the delta subunit. These results indicate that Cys140 and Cys64 of the delta subunit and Cys2 of the alpha subunit are in close proximity. This places the delta subunit near the top of the alpha-beta hexagon and not in the stalk region. As fixing the delta to the alpha by cross-linking does not greatly impair either the ATPase function of the enzyme, or coupled proton translocation, we argue that the delta subunit forms a portion of the stator linking F1 to F0.

  4. CrossWork: Software-assisted identification of cross-linked peptides

    DEFF Research Database (Denmark)

    Rasmussen, Morten; Refsgaard, Jan; Peng, Li;

    2011-01-01

    The increased interest in chemical cross-linking for probing protein structure and interaction has led to a large increase in literature describing new cross-linkers and search programs. However, this has not led to a corresponding increase in the analysis of large and complex proteins. A major...... obstacle is that the new cross-linkers are either not readily available and/or have a low reactivity. In combination with aging search programs that are slow and have low sensitivity, or new search programs that are described but not released, these efforts do little to advance the field of cross......-linking. Here we present a method pipeline for chemical cross-linking, using two standard cross-linkers, BS3 and BS2G, combined with our freely available CrossWork search program. By this approach we generate cross-link data sufficient to derive structural information for large and complex proteins. Cross...

  5. Analytical characterisation of glutardialdehyde cross-linking products in gelatine-gum arabic complex coacervates

    Energy Technology Data Exchange (ETDEWEB)

    Fuguet, Elisabet [Advanced Measurement and Imaging, Unilever Food and Health Research Institute, Olivier van Noortlaan 120, 3133 AT Vlaardingen (Netherlands)], E-mail: eli.fuguet@gmail.com; Platerink, Chris van [Advanced Measurement and Imaging, Unilever Food and Health Research Institute, Olivier van Noortlaan 120, 3133 AT Vlaardingen (Netherlands); Department of Biomolecular Mass Spectrometry, Bijvoet Center for Biomolecular Research, Utrecht University, Sorbonnelaan 16, 3584 CA Utrecht (Netherlands); Janssen, Hans-Gerd [Advanced Measurement and Imaging, Unilever Food and Health Research Institute, Olivier van Noortlaan 120, 3133 AT Vlaardingen (Netherlands); van' t Hoff Institute for Molecular Sciences, University of Amsterdam, Nieuwe Achtergracht 166, 1018 WV Amsterdam (Netherlands)

    2007-11-26

    Encapsulates having shells of cross-linked mixtures of proteins and polysaccharides are widely used in the food and pharmaceutical industry for controlled release of actives and flavour compounds. In order to be able to predict the behaviour and the release characteristics of the microcapsules, a better understanding of the nature and extent of the cross-linking reaction is needed. Several analytical techniques were applied for the characterisation of glutardialdehyde (GDA) cross-linked encapsulates made of gelatine and gum arabic. To allow the use of sensitive, high-resolution methods such as chromatography and mass spectrometry, the sample first had to be hydrolysed. In this way, a mixture of amino acids, small peptides and the cross-link moieties was obtained. High-resolution liquid chromatography coupled to high-resolution mass spectrometry (HPLC-MS) was applied to detect possible cross-link markers through a comparison of HPLC-MS mass-chromatograms obtained for cross-linked and non-cross-linked coacervates. HPLC-MS/MS was used to identify the species responsible for the differences. Cross-linking occurred between GDA molecules and lysine and hydroxylysine {epsilon}-amino groups, and up to eight cross-link products of different nature could be identified. They included pyridinium ions and Schiff bases, and also unreacted GDA condensation products. Next, based on the insight gained in the possible chemical structures present in the cross-link markers, methods for selective labelling of these functionalities were employed to allow easier detection of related reaction products. Both liquid chromatography (LC) and gas chromatography (GC) were used in these experiments. Unfortunately, these approaches failed to detect new cross-link markers, most likely as a result of the low levels at which these are present.

  6. Current status of accelerated corneal cross-linking

    Directory of Open Access Journals (Sweden)

    Michael Mrochen

    2013-01-01

    Full Text Available Corneal cross-linking with riboflavin is a technique to stabilize or reduce corneal ectasia, in diseases such as keratoconus and post-laser-assisted in situ keratomileusis (LASIK ectasia. There is an interest by patient as well as clinicians to reduce the overall treatment time. Especially, the introduction of corneal cross-linking in combination with corneal laser surgery demands a shorter treatment time to assure a sufficient patient flow. The principles and techniques of accelerated corneal cross-linking is discussed.

  7. Inverted bulk-heterojunction solar cell with cross-linked hole-blocking layer

    Science.gov (United States)

    Udum, Yasemin; Denk, Patrick; Adam, Getachew; Apaydin, Dogukan H.; Nevosad, Andreas; Teichert, Christian; S. White, Matthew.; S. Sariciftci, Niyazi.; Scharber, Markus C.

    2014-01-01

    We have developed a hole-blocking layer for bulk-heterojunction solar cells based on cross-linked polyethylenimine (PEI). We tested five different ether-based cross-linkers and found that all of them give comparable solar cell efficiencies. The initial idea that a cross-linked layer is more solvent resistant compared to a pristine PEI layer could not be confirmed. With and without cross-linking, the PEI layer sticks very well to the surface of the indium–tin–oxide electrode and cannot be removed by solvents used to process PEI or common organic semiconductors. The cross-linked PEI hole-blocking layer functions for multiple donor–acceptor blends. We found that using cross-linkers improves the reproducibility of the device fabrication process. PMID:24817837

  8. Elasticity of cross-linked semiflexible biopolymers under tension

    CERN Document Server

    von der Heydt, Alice; Benetatos, Panayotis; Zippelius, Annette

    2013-01-01

    Aiming at the mechanical properties of cross-linked biopolymers, we set up and analyze a model of two weakly bending wormlike chains subjected to a tensile force, with regularly spaced inter-chain bonds (cross-links) represented by harmonic springs. Within this model, we compute the force-extension curve and the differential stiffness exactly and discuss several limiting cases. Cross-links effectively stiffen the chain pair by reducing thermal fluctuations transverse to the force and alignment direction. The extra alignment due to cross-links increases both with growing number and with growing strength of the cross-links, and is most prominent for small force f. For large f, the additional, cross-link-induced extension is subdominant except for the case of linking the chains rigidly and continuously along their contour. In this combined limit, we recover asymptotically the elasticity of a weakly bending wormlike chain without constraints, stiffened by a factor four. The increase in differential stiffness can ...

  9. Fiber optic immunosensor for cross-linked fibrin concentration

    Science.gov (United States)

    Moskowitz, Samuel E.

    2000-08-01

    Working with calcium ions in the blood, platelets produce thromboplastin which transforms prothrombin into thrombin. Removing peptides, thrombin changes fibrinogen into fibrin. Cross-linked insoluble fibrin polymers are solubilized by enzyme plasmin found in blood plasma. Resulting D-dimers are elevated in patients with intravascular coagulation, deep venous thrombosis, pulmonary embolism, myocardial infarction, multiple trauma, cancer, impaired renal and liver functions, and sepsis. Consisting principally of a NIR 780 nm GaAlAs laser diode and a 800 nm avalanche photodiode (APD), the fiber-optic immunosensor can determined D-dimer concentration to levels detected by a second antibody which is labeled with NN 382 fluorescent dye. An evanescent wave traveling on an excitation optical fiber excites the antibody-antigen fluorophore complex. Concentration of cross-linked fibrin is directly proportional to the APD measured intensity of fluorescence. NIR fluorescence has advantages of low background interference, short fluorescence lifetime, and large difference between excitation and emission peaks. Competitive ELISA test for D-dimer concentration requires trained personnel performing a time consuming operation.

  10. Covalently cross-linked polyetheretherketone proton exchange membrane for DMFC

    CSIR Research Space (South Africa)

    Luo, H

    2009-05-01

    Full Text Available -7 cm2/s) and good electrochemical stability. The results suggested that cross-linked polyetheretherketone membrane is particularly promising to be used as proton exchange membrane for the direct methanol fuel cell application....

  11. Gelation threshold of cross-linked polymer brushes.

    Science.gov (United States)

    Hoffmann, Max; Lang, Michael; Sommer, Jens-Uwe

    2011-02-01

    The cross-linking of polymer brushes is studied using the bond-fluctuation model. By mapping the cross-linking process into a two-dimensional (2D) percolation problem within the lattice of grafting points, we investigate the gelation transition in detail. We show that the particular properties of cross-linked polymer brushes can be reduced to the distribution of bonds which are formed between the grafted chains, and we propose scaling arguments to relate the gelation threshold to the chain length and the grafting density. The gelation threshold is lower than the percolation threshold for 2D bond percolation because of the longer range and broad distribution of bonds formed by the cross-linking process. We term this type of percolation problem star percolation. We observe a broad crossover from mean-field to critical percolation behavior by analyzing the cluster size distribution near the gelation threshold.

  12. Cross-linked aromatic cationic polymer electrolytes with enhanced stability for high temperature fuel cell applications

    DEFF Research Database (Denmark)

    Ma, Wenjia; Zhao, Chengji; Yang, Jingshuai

    2012-01-01

    Diamine-cross-linked membranes were prepared from cross-linkable poly(arylene ether ketone) containing pendant cationic quaternary ammonium group (QPAEK) solution by a facile and general thermal curing method using 4,4′-diaminodiphenylmethane with rigid framework and 1,6-diaminohexane with flexible...... framework as cross-linker, respectively. Self-cross-linked cationic polymer electrolytes membranes were also prepared for comparison. The diamines were advantageously distributed within the polymeric matrix and its amine function groups interacted with the benzyl bromide of QPAEK, resulting in a double...... that the diamine-cross-linked membranes using the rigid cross-linker show much improved properties than that using the flexible cross-linker. More properties relating to the feasibility in high temperature proton exchange membrane fuel cell applications were investigated in detail....

  13. Photochemical Patterning of Ionically Cross-Linked Hydrogels

    Directory of Open Access Journals (Sweden)

    Marion Bruchet

    2013-08-01

    Full Text Available Iron(III cross-linked alginate hydrogel incorporating sodium lactate undergoes photoinduced degradation, thus serving as a biocompatible positive photoresist suitable for photochemical patterning. Alternatively, surface etching of iron(III cross-linked hydrogel contacting lactic acid solution can be used for controlling the thickness of the photochemical pattering. Due to biocompatibility, both of these approaches appear potentially useful for advanced manipulation with cell cultures including growing cells on the surface or entrapping them within the hydrogel.

  14. Grass Cell Walls: A Story of Cross-Linking

    Science.gov (United States)

    Hatfield, Ronald D.; Rancour, David M.; Marita, Jane M.

    2017-01-01

    Cell wall matrices are complex composites mainly of polysaccharides, phenolics (monomers and polymers), and protein. We are beginning to understand the synthesis of these major wall components individually, but still have a poor understanding of how cell walls are assembled into complex matrices. Valuable insight has been gained by examining intact components to understand the individual elements that make up plant cell walls. Grasses are a prominent group within the plant kingdom, not only for their important roles in global agriculture, but also for the complexity of their cell walls. Ferulate incorporation into grass cell wall matrices (C3 and C4 types) leads to a cross-linked matrix that plays a prominent role in the structure and utilization of grass biomass compared to dicot species. Incorporation of p-coumarates as part of the lignin structure also adds to the complexity of grass cell walls. Feruoylation results in a wall with individual hemicellulosic polysaccharides (arabinoxylans) covalently linked to each other and to lignin. Evidence strongly suggests that ferulates not only cross-link arabinoxylans, but may be important factors in lignification of the cell wall. Therefore, the distribution of ferulates on arabinoxylans could provide a means of structuring regions of the matrix with the incorporation of lignin and have a significant impact upon localized cell wall organization. The role of other phenolics in cell wall formation such as p-coumarates (which can have concentrations higher than ferulates) remains unknown. It is possible that p-coumarates assist in the formation of lignin, especially syringyl rich lignin. The uniqueness of the grass cell wall compared to dicot sepcies may not be so much in the gross composition of the wall, but how the distinctive individual components are organized into a functional wall matrix. These features are discussed and working models are provided to illustrate how changing the organization of feruoylation and p

  15. Grafted, cross-linked carbon black as a double-layer capacitor electrode material

    Energy Technology Data Exchange (ETDEWEB)

    Richner, R.; Mueller, S.; Wokaun, A.

    2001-03-01

    Isocyanate prepolymers readily react with oxidic functional groups on carbon black. On carbon black grafted with diisocyanates, reactive isocyanate groups are available for cross-linking to a polyurethane system. This cross-linked carbon black was considered as a new active material for electrochemical electrodes. Active material for electric double-layer capacitor electrodes was produced which had values of specific capacitance of up to 200 F/g. Cross-linking efficiencies of up to 58 % of the polymers utilised were achieved. (author)

  16. Permanent Set of Cross-Linking Networks: Comparison of Theory with Molecular Dynamics Simulations

    DEFF Research Database (Denmark)

    Rottach, Dana R.; Curro, John G.; Budzien, Joanne

    2006-01-01

    The permanent set of cross-linking networks is studied by molecular dynamics. The uniaxial stress for a bead-spring polymer network is investigated as a function of strain and cross-link density history, where cross-links are introduced in unstrained and strained networks. The permanent set...... is found from the strain of the network after it returns to the state-of-ease where the stress is zero. The permanent set simulations are compared with theory using the independent network hypothesis, together with the various theoretical rubber elasticity theories: affine, phantom, constrained junction...

  17. A genetic anomaly of oriented collagen biosynthesis and cross-linking: Keratoconus.

    Science.gov (United States)

    Bourges, J L; Robert, A M; Robert, L

    2015-02-01

    Oriented collagen biosynthesis is one of the major mechanisms involved in tissue and organ formation during development. Corneal biogenesis is one example. Defects in this process lead to anomalies in tissue structure and function. The transparency of cornea and its achievement are a good example as well as its pathological modifications. Keratoconus is one example of this type of pathologies, involving also inappropriate cross-linking of collagen fibers. Among the tentatives to correct this anomaly, the riboflavin-potentiated UV-cross-linking (CXL) of keratoconus corneas appears clinically satisfactory, although none of the experiments and clinical results published prove effective cross-linking. The published results are reviewed in this article.

  18. Permanent Set of Cross-Linking Networks: Comparison of Theory with Molecular Dynamics Simulations

    DEFF Research Database (Denmark)

    Rottach, Dana R.; Curro, John G.; Budzien, Joanne;

    2006-01-01

    is found from the strain of the network after it returns to the state-of-ease where the stress is zero. The permanent set simulations are compared with theory using the independent network hypothesis, together with the various theoretical rubber elasticity theories: affine, phantom, constrained junction......The permanent set of cross-linking networks is studied by molecular dynamics. The uniaxial stress for a bead-spring polymer network is investigated as a function of strain and cross-link density history, where cross-links are introduced in unstrained and strained networks. The permanent set...

  19. Molecular Dynamics Simulations of Polymer Networks Undergoing Sequential Cross-Linking and Scission Reactions

    DEFF Research Database (Denmark)

    Rottach, Dana R.; Curro, John G.; Budzien, Joanne;

    2007-01-01

    The effects of sequential cross-linking and scission of polymer networks formed in two states of strain are investigated using molecular dynamics simulations. Two-stage networks are studied in which a network formed in the unstrained state (stage 1) undergoes additional cross-linking in a uniaxia......The effects of sequential cross-linking and scission of polymer networks formed in two states of strain are investigated using molecular dynamics simulations. Two-stage networks are studied in which a network formed in the unstrained state (stage 1) undergoes additional cross...... good agreement with the predictions of Flory and Fricker. It was found that the fractional stress reduction upon removal of the first-stage cross-links could be accurately calculated from the slip tube model of Rubinstein and Panyukov modified to use the theoretical transfer functions of Fricker.  ...

  20. The wear of cross-linked polyethylene against itself.

    Science.gov (United States)

    Joyce, T J; Ash, H E; Unsworth, A

    1996-01-01

    Cross-linked polyethylene (XLPE) may have an application as a material for an all-plastic surface replacement finger joint. It is inexpensive, biocompatible and can be injection-moulded into the complex shapes that are found on the ends of the finger bones. Further, the cross-linking of polyethylene has significantly improved its mechanical properties. Therefore, the opportunity exists for an all-XLPE joint, and so the wear characteristics of XLPE sliding against itself have been investigated. Wear tests were carried out on both reciprocating pin-on-plate machines and a finger function simulator. The reciprocating pin-on-plate machines had pins loaded at 10 N and 40 N. All pin-on-plate tests show wear factors from the plates very much greater than those of the pins. After 349 km of sliding, a mean wear factor of 0.46 x 10(-6) mm3/N m was found for the plates compared with 0.021 x 10(-6) mm3/N m for the pins. A fatigue mechanism may be causing this phenomenon of greater plate wear. Tests using the finger function simulator give an average wear rate of 0.22 x 10(-6) mm3/N m after 368 km. This sliding distance is equivalent to 12.5 years of use in vivo. The wear factors found were comparable with those of ultra-high molecular weight polyethylene (UHMWPE) against a metallic counterface and, therefore, as the loads across the finger joint are much less than those across the knee or the hip, it is probable that an all-XLPE finger joint will be viable from a wear point of view.

  1. Collagen/elastin hydrogels cross-linked by squaric acid.

    Science.gov (United States)

    Skopinska-Wisniewska, J; Kuderko, J; Bajek, A; Maj, M; Sionkowska, A; Ziegler-Borowska, M

    2016-03-01

    Hydrogels based on collagen and elastin are very valuable materials for medicine and tissue engineering. They are biocompatible; however their mechanical properties and resistance for enzymatic degradation need to be improved by cross-linking. Up to this point many reagents have been tested but more secure reactants are still sought. Squaric acid (SqAc), 3,4-dihydroxy 3-cyclobutene 1,2-dione, is a strong, cyclic acid, which reacts easily with amine groups. The properties of hydrogels based on collagen/elastin mixtures (95/5, 90/10) containing 5%, 10% and 20% of SqAc and neutralized via dialysis against deionized water were tested. Cross-linked, 3-D, transparent hydrogels were created. The cross-linked materials are stiffer and more resistant to enzymatic degradation than those that are unmodified. The pore size, swelling ability and surface polarity are reduced due to 5% and 10% of SqAc addition. At the same time, the cellular response is not significantly affected by the cross-linking. Therefore, squaric acid would be regarded as a safe, effective cross-linking agent.

  2. Extreme dryness and DNA-protein cross-links

    Science.gov (United States)

    Bieger-Dose, A.; Dose, K.; Meffert, R.; Mehler, M.; Risi, S.

    Exposure of fungal conidia (Aspergillus ochraceus) or spores of Bacillus subtilis to extreme dryness or vacuum induces DNA lesions, including strand breaks and the formation of DNA-protein cross-links. In wet cells only a small amount of protein is bound to DNA, but exposure to conditions of lowered water activity results in an increasing number of cross-links between DNA and proteins. In fungal conidia these cross-links are detected after selective iodination (125J) of the DNA-bound proteins followed by gel electrophoresis and subsequent autoradiography. Another approach is the labelling of DNA with 32p by means of nick translation and the detection of differences in the electrophoretic mobility of DNA before and after digestion with proteinase K of proteins bound to DNA.

  3. Computer simulation of randomly cross-linked polymer networks

    CERN Document Server

    Williams, T P

    2002-01-01

    In this work, Monte Carlo and Stochastic Dynamics computer simulations of mesoscale model randomly cross-linked networks were undertaken. Task parallel implementations of the lattice Monte Carlo Bond Fluctuation model and Kremer-Grest Stochastic Dynamics bead-spring continuum model were designed and used for this purpose. Lattice and continuum precursor melt systems were prepared and then cross-linked to varying degrees. The resultant networks were used to study structural changes during deformation and relaxation dynamics. The effects of a random network topology featuring a polydisperse distribution of strand lengths and an abundance of pendant chain ends, were qualitatively compared to recent published work. A preliminary investigation into the effects of temperature on the structural and dynamical properties was also undertaken. Structural changes during isotropic swelling and uniaxial deformation, revealed a pronounced non-affine deformation dependant on the degree of cross-linking. Fractal heterogeneiti...

  4. Stabilized sulfonated aromatic polymers by in situ solvothermal cross-linking

    Directory of Open Access Journals (Sweden)

    Maria Luisa eDi Vona

    2014-10-01

    Full Text Available The cross-link reaction via sulfone bridges of sulfonated polyetheretherketone (SPEEK by thermal treatment at 180 °C in presence of dimethylsulfoxide (DMSO is discussed. The modifications of properties subsequent to the cross-linking are presented. The mechanical strength as well as the hydrolytic stability increased with the thermal treatment time, i.e., with the degree of cross-linking. The proton conductivity was determined as function of temperature, IEC, degree of cross-linking and hydration number. The memory effect, which is the membrane ability to remember the water uptake reached at high temperature also at lower temperature, is exploited in order to achieve high values of conductivity. Membranes swelled at 110 °C can reach a conductivity of 0.14 S/cm at 80°C with a hydration number ( of 73.

  5. Glutaraldehyde vapor cross-linked nanofibrous PVA mat with in situ formed silver nanoparticles.

    Science.gov (United States)

    Destaye, Addisu Getachew; Lin, Cheng-Keng; Lee, Cheng-Kang

    2013-06-12

    Polyvinyl alcohol (PVA) nanofibrous mat can be easily prepared via electrospinning its aqueous solution. However, the obtained nanofibrous mat is instantaneously dissolved in water. Therefore, rendering the environmentally friendly nanofibrous mat water insoluble by cross-linking mechanism is of great interest. The electrospun PVA nanofibrous mat with an average fiber diameter of ca. 400 nm could be effectively cross-linked by glutaraldehyde vapor at room temperature. The cross-linking not only resulted in a water-insoluble nanofibrous mat but also generated an excess amount of unreacted aldehyde functional groups that could reduce silver salts into silver nanoparticles. The in situ formed silver nanoparticles along the fibrous surface showed excellent antimicrobial activity against Escherichia coli. The vapor cross-linked nanofibrous mat shows a high potential to be used for efficiently capturing and killing pathogenic bacteria.

  6. Directing the oligomer size distribution of peroxidase-mediated cross-linked bovine alpha-lactalbumin.

    Science.gov (United States)

    Heijnis, Walter H; Wierenga, Peter A; van Berkel, Willem J H; Gruppen, Harry

    2010-05-12

    Enzymatic protein cross-linking is a powerful tool to change protein functionality. For optimal functionality in gel formation, the size of the cross-linked proteins needs to be controlled, prior to heating. In the current study, we addressed the optimization of the horseradish peroxidase-mediated cross-linking of calcium-depleted bovine alpha-lactalbumin. To characterize the formed products, the molecular weight distribution of the cross-linked protein was determined by size exclusion chromatography. At low ionic strength, more dimers of alpha-lactalbumin are formed than at high ionic strength, while the same conversion of monomers is observed. Similarly, at pH 5.9 more higher oligomers are formed than at pH 6.8. This is proposed to be caused by local changes in apo alpha-lactalbumin conformation as indicated by circular dichroism spectroscopy. A gradual supply of hydrogen peroxide improves the yield of cross-linked products and increases the proportion of higher oligomers. In conclusion, this study shows that the size distribution of peroxidase-mediated cross-linked alpha-lactalbumin can be directed toward the protein oligomers desired.

  7. Cross-linking proteins by laccase-catalyzed oxidation: importance relative to other modifications.

    Science.gov (United States)

    Steffensen, Charlotte L; Andersen, Mogens L; Degn, Peter E; Nielsen, Jacob H

    2008-12-24

    Laccase-catalyzed oxidation was able to induce intermolecular cross-links in beta-lactoglobulin, and ferulic acid-mediated laccase-catalyzed oxidation was able to induce intermolecular cross-links in alpha-casein, whereas transglutaminase cross-linked only alpha-casein. In addition, different patterns of laccase-induced oxidative modifications were detected, including dityrosine formation, formation of fluorescent tryptophan oxidation products, and carbonyls derived from histidine, tryptophan, and methionine. Laccase-catalyzed oxidation as well as transglutaminase induced only minor changes in surface tension of the proteins, and the changes could not be correlated to protein cross-linking. The presence of ferulic acid was found to influence the effect of laccase, allowing laccase to form irreducible intermolecular cross-links in beta-lactoglobulin and resulting in proteins exercising higher surface tensions due to cross-linking as well as other oxidative modifications. The outcome of using ferulic acid-mediated laccase-catalyzed oxidation to modify the functional properties of proteinaceous food components or other biosystems is expected to be highly dependent on the protein composition, resulting in different changes of the functional properties.

  8. FTIR Spectroscopic Studies on Cross Linking of SU-8 Photoresist

    Science.gov (United States)

    Kalaiselvi, S. M. P.; Tan, T. L.; Rawat, R. S.; Lee, P.; Heussler, S. P.; Breese, M. B. H.

    2013-11-01

    The usage of chemically-amplified, negative tone SU-8 photoresist is numerous, spanning industrial, scientific and medical fields. Hence, in this study, some preliminary studies were conducted to understand the dosage and heat treatment requirements of the SU-8 photoresist essential for pattern generation using X-ray lithography. In this work, using Synchrotron as the X-ray source, SU-8 photoresist was characterized for X-ray lithography in terms of its process parameters such as X-ray exposure dose, post exposure bake (PEB) time and temperature for various photoresist thicknesses which is considered worthwhile in view of applications of SU-8 for the fabrication of very high aspect ratio micro structures. The process parameters were varied and the resultant cross linking of the molecular chains of the photoresist was accurately monitored using a Fourier Transform Infra-Red (FTIR) spectrometer and the results are discussed. The infrared absorption peak at 914 cm-1 in the spectrum of the SU-8 photoresist was found to be a useful indicator for the completion of cross linking in the SU-8 photoresist. Results show that the cross linking of the SU-8 photoresist is at a higher rate from 0 J/cm3 to 30 J/cm3 after which the peak almost saturates regardless of the PEB time. It is a good evidence for the validation of dosage requirement of SU-8 photoresist for effective completion of cross linking, which in turn is a requirement for efficient fabrication of micro and nano structures. An analogous behavior was also observed between the extent of cross linking and the PEB time and temperature. The rate of cross linking declines after a certain period of PEB time regardless of PEB temperature. The obtained results also show a definite relation between variation of the absorbance area of the peak at 914 cm-1 and the X-ray exposure dose.

  9. DNA interstrand cross-linking by a mycotoxic diepoxide.

    Science.gov (United States)

    Millard, J T; Katz, J L; Goda, J; Frederick, E D; Pierce, S E; Speed, T J; Thamattoor, D M

    2004-06-01

    The diepoxide mycotoxin (2R, 3R, 8R, 9R)-4,6-decadiyne-2,3:8,9-diepoxy-1,10-diol (repandiol) was both isolated from the mushroom Hydnum repandum and synthesized de novo. Repandiol was found to form interstrand cross-links within a restriction fragment of DNA, linking deoxyguanosines on opposite strands primarily within the 5'-GNC and 5'-GNNC sequences preferred by diepoxyoctane. However, repandiol was a significantly less efficient cross-linker than either of the diepoxyalkanes (diepoxyoctane and diepoxybutane) to which it was compared.

  10. Molecular mechanisms in deformation of cross-linked hydrogel nanocomposite.

    Science.gov (United States)

    Mathesan, Santhosh; Rath, Amrita; Ghosh, Pijush

    2016-02-01

    The self-folding behavior in response to external stimuli observed in hydrogels is potentially used in biomedical applications. However, the use of hydrogels is limited because of its reduced mechanical properties. These properties are enhanced when the hydrogels are cross-linked and reinforced with nanoparticles. In this work, molecular dynamics (MD) simulation is applied to perform uniaxial tension and pull out tests to understand the mechanism contributing towards the enhanced mechanical properties. Also, nanomechanical characterization is performed using quasi static nanoindentation experiments to determine the Young's modulus of hydrogels in the presence of nanoparticles. The stress-strain responses for chitosan (CS), chitosan reinforced with hydroxyapatite (HAP) and cross-linked chitosan are obtained from uniaxial tension test. It is observed that the Young's modulus and maximum stress increase as the HAP content increases and also with cross-linking process. Load displacement plot from pullout test is compared for uncross-linked and cross-linked chitosan chains on hydroxyapatite surface. MD simulation reveals that the variation in the dihedral conformation of chitosan chains and the evolution of internal structural variables are associated with mechanical properties. Additional results reveal that the formation of hydrogen bonds and electrostatic interactions is responsible for the above variations in different systems.

  11. Computational exploration of polymer nanocomposite mechanical property modification via cross-linking topology

    Energy Technology Data Exchange (ETDEWEB)

    Lacevic, N; Gee, R; Saab, A; Maxwell, R

    2008-04-24

    Molecular dynamics simulations have been performed in order to study the effects of nanoscale filler cross-linking topologies and loading levels on the mechanical properties of a model elastomeric nanocomposite. The model system considered here is constructed from octa-functional polyhedral oligomeric silsesquioxane (POSS) dispersed in a poly(dimethylsiloxane) (PDMS) matrix. Shear moduli, G, have been computed for pure and for filled and unfilled PDMS as a function of cross-linking density, POSS fill loading level, and polymer network topology. The results reported here show that G increases as the cross-linking (covalent bonds formed between the POSS and the PDMS network) density increases. Further, G is found to have a strong dependence on cross-linking topology. The increase in shear modulus, G, for POSS filled PDMS is significantly higher than that for unfilled PDMS cross-linked with standard molecular species, suggesting an enhanced reinforcement mechanism for POSS. In contrast, in blended systems (POSS/PDMS mixture with no cross-linking) G was not observed to significantly increase with POSS loading. Finally, we find intriguing differences in the structural arrangement of bond strains between the cross-linked and the blended systems. In the unfilled PDMS the distribution of highly strained bonds appears to be random, while in the POSS filled system, the strained bonds form a net-like distribution that spans the network. Such a distribution may form a structural network 'holding' the composite together and resulting in increases in G compared to an unfilled, cross-linked system. These results are of importance for engineering of new POSS-based multifunctional materials with tailor-made mechanical properties.

  12. Chloroacetamide-Linked Nucleotides and DNA for Cross-Linking with Peptides and Proteins.

    Science.gov (United States)

    Olszewska, Agata; Pohl, Radek; Brázdová, Marie; Fojta, Miroslav; Hocek, Michal

    2016-09-21

    Nucleotides, 2'-deoxyribonucleoside triphosphates (dNTPs), and DNA probes bearing reactive chloroacetamido group linked to nucleobase (cytosine or 7-deazadaenine) through a propargyl tether were prepared and tested in cross-linking with cysteine- or histidine-containing peptides and proteins. The chloroacetamide-modifed dNTPs proved to be good substrates for DNA polymerases in the enzymatic synthesis of modified DNA probes. Modified nucleotides and DNA reacted efficiently with cysteine and cysteine-containing peptides, whereas the reaction with histidine was sluggish and low yielding. The modified DNA efficiently cross-linked with p53 protein through alkylation of cysteine and showed potential for cross-linking with histidine (in C277H mutant of p53).

  13. Conductive Polymeric Composites Based on Multiwalled Carbon Nanotubes and Linseed Oil Functionalized and Cross-Linked with Diacetylenes from Propargyl Alcohol

    Directory of Open Access Journals (Sweden)

    Alejandro Ramírez-Jiménez

    2015-01-01

    Full Text Available Diacetylene-functionalized epoxidized linseed oil (DAELO matrix was synthesized in order to improve the dispersion of multiwalled carbon nanotubes (MWCNTs without the necessity of some chemical or physical modification of them. That fact was evidenced by the low critical concentration of DAELO-based composites in comparison (1.0 wt% MWCNTs with the epoxidized linseed oil- (ELO- based composites (5 wt% MWCNTs. For this, both series of composites were prepared by the ultrasonic dispersion method using the same conditions of solvent, dilution, and sonication time. It was shown that, tailoring the polymer matrix with groups rich in nonpolar electric density, as diacetylene, and capable of interacting by van der Waals forces, it is possible to improve the dispersion of carbon nanotubes (CNTs without necessity of some modification knowing that those treatments usually affect lowering their electrical properties.

  14. Advanced Corneal Cross-Linking System with Fluorescence Dosimetry

    Directory of Open Access Journals (Sweden)

    Marc D. Friedman

    2012-01-01

    Full Text Available Purpose. This paper describes an advanced system that combines corneal cross-linking with riboflavin with fluorescence dosimetry, the ability to measure riboflavin diffusion within the cornea both before and during UVA treatment. Methods and Results. A corneal cross-linking system utilizing a digital micromirror device (DMD was assembled and used to measure diffusion coefficients of 0.1% riboflavin in 20% dextran in porcine eyes. A value of (3.3±0.2×10−7 cm2/s was obtained for the stroma. Diffusion coefficients for the transepithelial formulation of 0.1% riboflavin in 0.44% saline and 0.02% BAK were also measured to be 4.7±0.3×10−8 cm2/s for epithelium only and (4.6±0.4×10−7 cm2/s for stroma only. Riboflavin consumption during a UVA treatment was also demonstrated. Conclusion. A new advanced corneal cross-linking system with fluorescence dosimetry of riboflavin has been demonstrated. It is hoped that this method may play a significant role in determining the underlying mechanisms of corneal cross-linking and assist with the development of additional riboflavin formulations. Moreover, dosimetry may prove valuable in providing a method to account for the biological differences between individuals, potentially informing cornea-specific UVA treatment doses in real time.

  15. Simulation of Fracture Nucleation in Cross-Linked Polymer Networks

    Science.gov (United States)

    Moller, J. C.; Barr, S. A.; Schultz, E. J.; Breitzman, T. D.; Berry, R. J.

    2013-02-01

    A novel atomistic simulation method is developed whereby polymer systems can undergo strain-rate-controlled deformation while bond scission is enabled. The aim is to provide insight into the nanoscale origins of fracture. Various highly cross-linked epoxy systems including various resin chain lengths and levels of nonreactive dilution were examined. Consistent with the results of physical experiments, cured resin strength increased and ductility decreased with increasing cross-link density. An analysis of dihedral angle activity shows the locations in the molecular network that are most absorptive of mechanical energy. Bond scission occurred principally at cross-link sites as well as between phenyl rings in the bisphenol moiety. Scissions typically occurred well after yield and were accompanied by steady increases in void size and dihedral angle motion between bisphenol moieties and at cross-link sites. The methods developed here could be more broadly applied to explore and compare the atomistic nature of deformation for various polymers such that mechanical and fracture properties could be tuned in a rational way. This method and its results could become part of a solution system that spans multiple length and time scales and that could more completely represent such mechanical events as fracture.

  16. The Database of Ribosomal Cross-links: an update.

    OpenAIRE

    Baranov, P V; Kubarenko, A V; Gurvich, O L; Shamolina, T A; Brimacombe, R

    1999-01-01

    The Database of Ribosomal Cross-links (DRC) was created in 1997. Here we describe new data incorporated into this database and several new features of the DRC. The DRC is freely available via World Wide Web at http://visitweb.com/database/ or http://www. mpimg-berlin-dahlem.mpg.de/ approximately ag_ribo/ag_brimacombe/drc/

  17. Elasticity of Rigidly Cross-Linked Networks of Athermal Filaments

    NARCIS (Netherlands)

    Zagar, Goran; Onck, Patrick R.; Van der Giessen, Erik

    2011-01-01

    Actin filaments assemble into network-like structures and play an important role in various cellular mechanical processes. It is known that the response of actin networks cross-linked by stiff proteins is characterized by two distinct regimes: (i) a linear stress strain response for small deformatio

  18. Porous Cross-Linked Polyimide-Urea Networks

    Science.gov (United States)

    Meador, Mary Ann B. (Inventor); Nguyen, Baochau N. (Inventor)

    2015-01-01

    Porous cross-linked polyimide-urea networks are provided. The networks comprise a subunit comprising two anhydride end-capped polyamic acid oligomers in direct connection via a urea linkage. The oligomers (a) each comprise a repeating unit of a dianhydride and a diamine and a terminal anhydride group and (b) are formulated with 2 to 15 of the repeating units. The subunit was formed by reaction of the diamine and a diisocyanate to form a diamine-urea linkage-diamine group, followed by reaction of the diamine-urea linkage-diamine group with the dianhydride and the diamine to form the subunit. The subunit has been cross-linked via a cross-linking agent, comprising three or more amine groups, at a balanced stoichiometry of the amine groups to the terminal anhydride groups. The subunit has been chemically imidized to yield the porous cross-linked polyimide-urea network. Also provided are wet gels, aerogels, and thin films comprising the networks, and methods of making the networks.

  19. Femtosecond laser collagen cross-linking without traditional photosensitizers

    Science.gov (United States)

    Guo, Yizang; Wang, Chao; Celi, Nicola; Vukelic, Sinisa

    2015-03-01

    Collagen cross-linking in cornea has the capability of enhancing its mechanical properties and thereby providing an alternative treatment for eye diseases such as keratoconus. Currently, riboflavin assisted UVA light irradiation is a method of choice for cross-link induction in eyes. However, ultrafast pulsed laser interactions may be a powerful alternative enabling in-depth treatment while simultaneously diminishing harmful side effects such as, keratocyte apoptosis. In this study, femtosecond laser is utilized for treatment of bovine cornea slices. It is hypothesized that nonlinear absorption of femtosecond laser pulses plays a major role in the maturation of immature cross-links and the promotion of their growth. Targeted irradiation with tightly focused laser pulses allows for the absence of a photosensitizing agent. Inflation test was conducted on half treated porcine cornea to identify the changes of mechanical properties due to laser treatment. Raman spectroscopy was utilized to study subtle changes in the chemical composition of treated cornea. The effects of treatment are analyzed by observing shifts in Amide I and Amide III bands, which suggest deformation of the collagen structure in cornea due to presence of newly formed cross-links.

  20. Scleral lens tolerance after corneal cross-linking for keratoconus

    NARCIS (Netherlands)

    Visser, Esther Simone; Soeters, Nienke; Tahzib, Nayyirih G.

    2015-01-01

    Purpose. Subjective and objective evaluation of scleral lens tolerance and fitting before and after corneal cross-linking (CXL) for progressive keratoconus. Methods. In this prospective cohort, evaluations were made of 18 unilateral eyes in patients who underwent CXL and had been wearing scleral len

  1. Lactoferrin binding to transglutaminase cross-linked casein micelles

    NARCIS (Netherlands)

    Anema, S.G.; de Kruif, C.G.

    2012-01-01

    Casein micelles in skim milk were either untreated (untreated milk) or were cross-linked using transglutaminase (TGA-milk). Added lactoferrin (LF) bound to the casein micelles and followed Langmuir adsorption isotherms. The adsorption level was the same in both milks and decreased the micellar zeta

  2. Polyimide Aerogels with Three-Dimensional Cross-Linked Structure

    Science.gov (United States)

    Meador, Mary Ann B. (Inventor)

    2016-01-01

    A method for creating a three dimensional cross-linked polyimide structure includes dissolving a diamine, a dianhydride, and a triamine in a solvent, imidizing a polyamic acid gel by heating the gel, extracting the gel in a second solvent, supercritically drying the gel, and removing the solvent to create a polyimide aerogel.

  3. 21 CFR 177.2420 - Polyester resins, cross-linked.

    Science.gov (United States)

    2010-04-01

    .... Pentaerythritol. Polyoxypropylene ethers of 4,4′-isopropylide-nediphenol (containing an average of 2-7.5 moles of...-pentanediol. (3) Cross-linking agents: Butyl acrylate. Butyl methacrylate. Ethyl acrylate. Ethylhexyl acrylate... the production of the resins or added thereto to impart desired technical or physical...

  4. Cross-linked enzyme aggregates (CLEAs): stable and recyclable biocatalysts

    NARCIS (Netherlands)

    Sheldon, R.A.

    2007-01-01

    The key to obtaining an optimum performance of an enzyme is often a question of devising an effective method for its immobilization. In the present review, we describe a novel, versatile and effective methodology for enzyme immobilization as CLEAs (cross-linked enzyme aggregates). The method is

  5. Hyper-cross-linked, hybrid membranes via interfacial polymerization

    NARCIS (Netherlands)

    Raaijmakers, M.J.T.

    2015-01-01

    Hyper-cross-linked, hybrid membranes consist of covalent networks of alternating organic and inorganic, or biological groups. This thesis reports on the preparation of such hybrid networks via interfacial polymerization. The structure-property relationships of the hybrid networks depend strongly on

  6. Digestibility of β-lactoglobulin following cross-linking by Trametes versicolor laccase and apple polyphenols

    Directory of Open Access Journals (Sweden)

    DRAGANA STANIĆ-VUČINIĆ

    2011-06-01

    Full Text Available β-Lactoglobulin (BLG is an important nutrient of dairy products and an important allergen in cow’s milk allergy. The aim of this study was to investigate the potential of laccase to cross-link BLG in the presence of an apple phenolic extract (APE and to characterize the obtained products for their digestibility by pepsin and pancreatin. The composition of the apple phenolics used for cross-linking was determined by liquid chromatography–electrospray ionization-mass spectrometry (LC–ESI-MS. The apple phenolic extract contained significant amounts of quercetin glycosides, catechins and chlorogenic acid. The laccase cross-linked BLG in the presence of apple phenolics. The polymerization rendered the protein insoluble in the reaction mixture. Sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS-PAGE analysis of the cross-linking reaction mixture revealed a heterogeneous mixture of high molecular masses (cross-linked BLG, with a fraction of the BLG remaining monomeric. Enzymatic processing of BLG by laccase and apple polyphenols as mediators can decrease the biphasal pepsin–pancreatin digestibility of the monomeric and cross-linked protein, thus decreasing its nutritional value. In addition, reduced BLG digestibility can decrease its allergenic potential. Apple polyphenols can find usage in the creation of new, more functional food products, designed to prevent obesity and hypersensitivity-related disorders.

  7. Computational exploration of polymer nanocomposite mechanical property modification via cross-linking topology.

    Science.gov (United States)

    Lacevic, Naida; Gee, Richard H; Saab, Andrew; Maxwell, Robert

    2008-09-28

    Molecular dynamics simulations have been performed in order to study the effects of nanoscale filler cross-linking topologies and loading levels on the mechanical properties of a model elastomeric nanocomposite. The model system considered here is constructed from octafunctional polyhedral oligomeric silsesquioxane (POSS) dispersed in a poly(dimethylsiloxane) (PDMS) matrix. Shear moduli, G, have been computed for pure and for filled and unfilled PDMS as a function of cross-linking density, POSS fill loading level, and polymer network topology. The results reported here show that G increases as the cross-linking (covalent bonds formed between the POSS and the PDMS network) density increases. Further, G is found to have a strong dependence on cross-linking topology. The increase in shear modulus, G, for POSS filled PDMS is significantly higher than that for unfilled PDMS cross-linked with standard molecular species, suggesting an enhanced reinforcement mechanism for POSS. In contrast, in blended systems (POSS/PDMS mixture with no cross-linking) G was not observed to significantly increase with POSS loading. Finally, we find intriguing differences in the structural arrangement of bond strains between the cross-linked and the blended systems. In the unfilled PDMS the distribution of highly strained bonds appears to be random, while in the POSS filled system, the strained bonds form a netlike distribution that spans the network. Such a distribution may form a structural network "holding" the composite together and resulting in increases in G compared to an unfilled, cross-linked system. These results are of importance for engineering of new POSS-based multifunctional materials with tailor-made mechanical properties.

  8. Crossing Hazard Functions in Common Survival Models.

    Science.gov (United States)

    Zhang, Jiajia; Peng, Yingwei

    2009-10-15

    Crossing hazard functions have extensive applications in modeling survival data. However, existing studies in the literature mainly focus on comparing crossed hazard functions and estimating the time at which the hazard functions cross, and there is little theoretical work on conditions under which hazard functions from a model will have a crossing. In this paper, we investigate crossing status of hazard functions from the proportional hazards (PH) model, the accelerated hazard (AH) model, and the accelerated failure time (AFT) model. We provide and prove conditions under which the hazard functions from the AH and the AFT models have no crossings or a single crossing. A few examples are also provided to demonstrate how the conditions can be used to determine crossing status of hazard functions from the three models.

  9. Tea derived galloylated polyphenols cross-link purified gastrointestinal mucins.

    Directory of Open Access Journals (Sweden)

    Pantelis Georgiades

    Full Text Available Polyphenols derived from tea are thought to be important for human health. We show using a combination of particle tracking microrheology and small-angle neutron scattering that polyphenols acts as cross-linkers for purified gastrointestinal mucin, derived from the stomach and the duodenum. Both naturally derived purified polyphenols, and green and black tea extracts are shown to act as cross-linkers. The main active cross-linking component is found to be the galloylated forms of catechins. The viscosity, elasticity and relaxation time of the mucin solutions experience an order of magnitude change in value upon addition of the polyphenol cross-linkers. Similarly small-angle neutron scattering experiments demonstrate a sol-gel transition with the addition of polyphenols, with a large increase in the scattering at low angles, which is attributed to the formation of large scale (>10 nm heterogeneities during gelation. Cross-linking of mucins by polyphenols is thus expected to have an impact on the physicochemical environment of both the stomach and duodenum; polyphenols are expected to modulate the barrier properties of mucus, nutrient absorption through mucus and the viscoelastic microenvironments of intestinal bacteria.

  10. Conserved C272/278 in b domain regulate the function of PDI-P5 to make lysozymes trypsin-resistant forms via significant intermolecular disulfide cross-linking.

    Science.gov (United States)

    Miyakawa, Miho; Zukeran, Gosuke; Wada, Yuko; Akama, Kuniko

    2015-05-01

    Protein disulfide isomerase-P5 (P5) is thought to have important functions as an oxidoreductase, however, molecular functions of P5 have not been fully elucidated. We have reported that P5 has insulin reductase activity and inhibits lysozyme refolding by formation of lysozyme multimers with hypermolecular mass inactivated by intermolecular disulfides (hyLYS) in oxidative refolding of reduced denatured lysozyme. To explore the role of each domain of P5, we investigated the effects of domain deletion and Cys-Ala mutants of P5 on insulin reduction and the oxidative refolding of the lysozyme. The mutants of catalytic cysteines, C36/39A, C171/174A, and C36/39/171/174A inhibited the lysozyme refolding almost similarly to P5, and even b domain without catalytic cysteines showed moderate inhibitory effect, suggesting that the b domain played a key role in the inhibition. Western blotting analysis of the refolding products indicated that the catalytic cysteines in both the a and a' domains cross-linked lysozyme comparably to form hyLYS resistant to trypsin, in which b domain was suggested to capture lysozyme for the significant sulfhydryl oxidation. The mutant of the conserved cysteines in b domain, C272/278A, did not form hyLYS, however, showed predominant reductase activity, implying that P5 functioned as a potent sulfhydryl oxidase and a predominant reductase depending on the circumstance around C272/278. These results provide new insight into the molecular basis of P5 function.

  11. Transient Anisocoria after Corneal Collagen Cross-Linking

    Science.gov (United States)

    Kymionis, George D.; Grentzelos, Michael A.; Stojanovic, Nela; Paraskevopoulos, Theodore A.; Detorakis, Efstathios T.

    2014-01-01

    Purpose. To report a case with transient anisocoria after corneal collagen cross-linking (CXL). Methods. Case report. Results. A 24-year-old male underwent corneal collagen cross-linking (CXL) in his right eye for keratoconus. At the end of the procedure, the pupil of the treated eye was irregular and dilated, while the pupil of the fellow eye was round, regular, and reactive (anisocoria). The following day, pupils were round, regular, and reactive in both eyes. Conclusion. Anisocoria may be a transient and innocuous complication after CXL. A possible cause for this complication might be the anesthetic drops used before and during the surgical procedure or/and the ultraviolet A irradiation during the treatment. PMID:25276451

  12. Transient Anisocoria after Corneal Collagen Cross-Linking

    Directory of Open Access Journals (Sweden)

    George D. Kymionis

    2014-01-01

    Full Text Available Purpose. To report a case with transient anisocoria after corneal collagen cross-linking (CXL. Methods. Case report. Results. A 24-year-old male underwent corneal collagen cross-linking (CXL in his right eye for keratoconus. At the end of the procedure, the pupil of the treated eye was irregular and dilated, while the pupil of the fellow eye was round, regular, and reactive (anisocoria. The following day, pupils were round, regular, and reactive in both eyes. Conclusion. Anisocoria may be a transient and innocuous complication after CXL. A possible cause for this complication might be the anesthetic drops used before and during the surgical procedure or/and the ultraviolet A irradiation during the treatment.

  13. Click Cross-Linking-Improved Waterborne Polymers for Environment-Friendly Coatings and Adhesives.

    Science.gov (United States)

    Hu, Jianqing; Peng, Kaimei; Guo, Jinshan; Shan, Dingying; Kim, Gloria B; Li, Qiyao; Gerhard, Ethan; Zhu, Liang; Tu, Weiping; Lv, Weizhong; Hickner, Michael A; Yang, Jian

    2016-07-13

    Waterborne polymers, including waterborne polyurethanes (WPU), polyester dispersions (PED), and polyacrylate emulsions (PAE), are employed as environmentally friendly water-based coatings and adhesives. An efficient, fast, stable, and safe cross-linking strategy is always desirable to impart waterborne polymers with improved mechanical properties and water/solvent/thermal and abrasion resistance. For the first time, click chemistry was introduced into waterborne polymer systems as a cross-linking strategy. Click cross-linking rendered waterborne polymer films with significantly improved tensile strength, hardness, adhesion strength, and water/solvent resistance compared to traditional waterborne polymer films. For example, click cross-linked WPU (WPU-click) has dramatically improved the mechanical strength (tensile strength increased from 0.43 to 6.47 MPa, and Young's modulus increased from 3 to 40 MPa), hardness (increased from 59 to 73.1 MPa), and water resistance (water absorption percentage dropped from 200% to less than 20%); click cross-linked PED (PED-click) film also possessed more than 3 times higher tensile strength (∼28 MPa) than that of normal PED (∼8 MPa). The adhesion strength of click cross-linked PAE (PAE-click) to polypropylene (PP) was also improved (from 3 to 5.5 MPa). In addition, extra click groups can be preserved after click cross-linking for further functionalization of the waterborne polymeric coatings/adhesives. In this work, we have demonstrated that click modification could serve as a convenient and powerful approach to significantly improve the performance of a variety of traditional coatings and adhesives.

  14. Electrochemical Characterization of Ultrathin Cross-Linked Metal Nanoparticle Films.

    Science.gov (United States)

    Han, Chu; Percival, Stephen J; Zhang, Bo

    2016-09-06

    Here we report the preparation, characterization, and electrochemical study of conductive, ultrathin films of cross-linked metal nanoparticles (NPs). Nanoporous films ranging from 40 to 200 nm in thickness composed of gold and platinum NPs of ∼5 nm were fabricated via a powerful layer-by-layer spin coating process. This process allows preparation of uniform NP films as large as 2 × 2 cm(2) with precise control over thickness, structure, and electrochemical and electrocatalytic properties. Gold, platinum, and bimetallic NP films were fabricated and characterized using cyclic voltammetry, scanning electron microscopy, and conductance measurements. Their electrocatalytic activity toward the oxygen reduction reaction (ORR) was investigated. Our results show that the electrochemical activity of such NP films is initially hindered by the presence of dense thiolate cross-linking ligands. Both electrochemical cycling and oxygen plasma cleaning are effective means in restoring their electrochemical activity. Gold NP films have higher electric conductivity than platinum possibly due to more uniform film structure and closer particle-particle distance. The electrochemical and electrocatalytic performance of platinum NP films can be greatly enhanced by the incorporation of gold NPs. This work focuses on electrochemical characterization of cross-linked NP films and demonstrates several unique properties. These include quick and easy preparation, ultrathin and uniform film thickness, tunable structure and composition, and transferability to many other substrates.

  15. Phosphate uptake studies of cross-linked chitosan bead materials.

    Science.gov (United States)

    Mahaninia, Mohammad H; Wilson, Lee D

    2017-01-01

    A systematic experimental study is reported that provides a molecular based understanding of cross-linked chitosan beads and their adsorption properties in aqueous solution containing phosphate dianion (HPO4(2-)) species. Synthetically modified chitosan using epichlorohydrin and glutaraldehyde cross-linkers result in surface modified beads with variable hydrophile-lipophile character and tunable HPO4(2-) uptake properties. The kinetic and thermodynamic adsorption properties of cross-linked chitosan beads with HPO4(2-) species were studied in aqueous solution. Complementary structure and physicochemical characterization of chitosan beads via potentiometry, Raman spectroscopy, DSC, and dye adsorption measurements was carried out to establish structure-property relationships. The maximum uptake (Qm) of bead systems with HPO4(2-) at equilibrium was 52.1mgg(-1); whereas, kinetic uptake results for chitosan bead/phosphate systems are relatively rapid (0.111-0.113min(-1)) with an intraparticle diffusion rate-limiting step. The adsorption process follows a multi-step pathway involving inner- and outer-sphere complexes with significant changes in hydration. Phosphate uptake strongly depends on the composition and type of cross-linker used for preparation of chitosan beads. The adsorption isotherms and structural characterization of bead systems illustrate the role of surface charge, hydrophile-lipophile balance, adsorption site accessibility, and hydration properties of the chitosan bead surface. Copyright © 2016 Elsevier Inc. All rights reserved.

  16. Sensitizing potential of enzymatically cross-linked peanut proteins in a mouse model of peanut allergy.

    NARCIS (Netherlands)

    Smit, Joost|info:eu-repo/dai/nl/250600706

    2014-01-01

    SCOPE: The cross-linking of proteins by enzymes to form high-molecular-weight protein, aggregates can be used to tailor the technological or physiological functionality of food products. Aggregation of dietary proteins by food processing may promote allergic sensitization, but the effects of enzymat

  17. Dynamically vulcanized biobased polylactide/natural rubber blend material with continuous cross-linked rubber phase.

    Science.gov (United States)

    Chen, Yukun; Yuan, Daosheng; Xu, Chuanhui

    2014-03-26

    We prepared a biobased material, dynamically vulcanized polylactide (PLA)/natural rubber (NR) blend in which the cross-linked NR phase owned a continuous network-like dispersion. This finding breaks the traditional concept of a sea-island morphology formed after dynamic vulcanization of the blends. The scan electron microscopy and dissolution/swell experiments provided the direct proof of the continuous cross-linked NR phase. This new biobased PLA/NR blend material with the novel structure is reported for the first time in the field of dynamic vulcanization and shows promise for development for various functional applications.

  18. Integrated Cryogenic Satellite Communications Cross-Link Receiver Experiment

    Science.gov (United States)

    Romanofsky, R. R.; Bhasin, K. B.; Downey, A. N.; Jackson, C. J.; Silver, A. H.; Javadi, H. H. S.

    1995-01-01

    An experiment has been devised which will validate, in space, a miniature, high-performance receiver. The receiver blends three complementary technologies; high temperature superconductivity (HTS), pseudomorphic high electron mobility transistor (PHEMT) monolithic microwave integrated circuits (MMIC), and a miniature pulse tube cryogenic cooler. Specifically, an HTS band pass filter, InP MMIC low noise amplifier, HTS-sapphire resonator stabilized local oscillator (LO), and a miniature pulse tube cooler will be integrated into a complete 20 GHz receiver downconverter. This cooled downconverter will be interfaced with customized signal processing electronics and integrated onto the space shuttle's 'HitchHiker' carrier. A pseudorandom data sequence will be transmitted to the receiver, which is in low Earth orbit (LEO), via the Advanced Communication Technology Satellite (ACTS) on a 20 GHz carrier. The modulation format is QPSK and the data rate is 2.048 Mbps. The bit error rate (BER) will be measured in situ. The receiver is also equipped with a radiometer mode so that experiment success is not totally contingent upon the BER measurement. In this mode, the receiver uses the Earth and deep space as a hot and cold calibration source, respectively. The experiment closely simulates an actual cross-link scenario. Since the receiver performance depends on channel conditions, its true characteristics would be masked in a terrestrial measurement by atmospheric absorption and background radiation. Furthermore, the receiver's performance depends on its physical temperature, which is a sensitive function of platform environment, thermal design, and cryocooler performance. This empirical data is important for building confidence in the technology.

  19. Macrophage response to cross-linked and conventional UHMWPE.

    Science.gov (United States)

    Sethi, Rajiv K; Neavyn, Mark J; Rubash, Harry E; Shanbhag, Arun S

    2003-07-01

    To prevent wear debris-induced osteolysis and aseptic loosening, cross-linked ultra-high molecular weight polyethylene's (UHMWPE) with improved wear resistance have been developed. Hip simulator studies have demonstrated very low wear rates with these new materials leading to their widespread clinical use. However, the biocompatibility of this material is not known. We studied the macrophage response to cross-linked UHMWPE (XLPE) and compared it to conventional UHMWPE (CPE) as well as other clinically used orthopaedic materials such as titanium-alloy (TiAlV) and cobalt-chrome alloy (CoCr). Human peripheral blood monocytes and murine macrophages, as surrogates for cells mediating peri-implant inflammation, were cultured onto custom designed lipped disks fabricated from the test materials to isolate cells. Culture supernatants were collected at 24 and 48h and analyzed for cytokines such as IL-1alpha, IL-1beta, TNF-alpha and IL-6. Total RNA was extracted from adherent cells and gene expression was analyzed using qualitative RT-PCR. In both in vitro models, macrophages cultured on cross-linked and conventional polyethylene released similar levels of cytokines, which were also similar to levels on control tissue culture dishes. Macrophages cultured on TiAlV and CoCr-alloy released significantly higher levels of cytokines. Human monocytes from all donors varied in the magnitude of cytokines released when cultured on identical surfaces. The variability in individual donor responses to TiAlV and CoCr surfaces may reflect how individuals respond differently to similar stimuli and perhaps reveal a predisposed sensitivity to particular materials.

  20. Polymer-additive extraction via pressurized fluids and organic solvents of variously cross-linked poly(methylmethacrylates).

    Science.gov (United States)

    Nazem, N; Taylor, L T

    2002-04-01

    Variously cross-linked poly(methylmethacrylates) (PMMAs) are synthesized with three additives incorporated at theoretically 1000 microg of the additive per gram of prepared polymer. The additives are Irganox 1010, Irganox 1076, and Irgafos 168. The in-house" synthesized polyacrylates are then subjected to supercritical fluid extraction (SFE) to determine if additive recovery is a function of percent cross-linking. Although considerable work in this regard has been performed with non-cross-linked polyolefins, the literature is lacking regarding polyacrylates. Some additive degradation apparently occurs during the synthesis, as judged by the increased complexity of the extract high-performance liquid chromatographic trace and the low percent recoveries observed especially for the Irganoxes. For low polymer cross-linking (1%), it appears that both PMMA synthetic reproducibility and readily observed polymer swelling during SFE are serious issues that adversely affect additive percent recovery and precision of results. Higher percent cross-linking yields more consistent analytical data than low percent cross-linking, even though the amount of additive extracted in all PMMA samples (regardless of cross-linking percentage) is essentially the same whether the extraction is via SFE or liquid-solid extraction with methylene chloride. Results for comparably cross-linked poly(ethylmethacrylate) and poly(butylmethacrylate) are similar to PMMA.

  1. Newer protocols and future in collagen cross-linking

    Directory of Open Access Journals (Sweden)

    Arthur B Cummings

    2013-01-01

    Full Text Available Corneal Cross-Linking (CXL is an established surgical procedure for the treatment of corneal disorders such as corneal ectasia and keratoconus. This method of treatment stabilises the corneal structure and increases rigidity, reducing the requirement for corneal transplantation. Since its development, many scientific studies have been conducted to investigate ways of improving the procedure. Biomechanical stability of the cornea after exposure to UV-A light, and the effect of shortening procedure time has been some of the many topics explored

  2. Cross-linking and rheological changes of whey proteins treated with microbial transglutaminase.

    Science.gov (United States)

    Truong, Van-Den; Clare, Debra A; Catignani, George L; Swaisgood, Harold E

    2004-03-10

    Modification of the functionality of whey proteins using microbial transglutaminase (TGase) has been the subject of recent studies. However, changes in rheological properties of whey proteins as affected by extensive cross-linking with TGase are not well studied. The factors affecting cross-linking of whey protein isolate (WPI) using both soluble and immobilized TGase were examined, and the rheological properties of the modified proteins were characterized. The enzyme was immobilized on aminopropyl glass beads (CPG-3000) by selective adsorption of the biotinylated enzyme on avidin that had been previously immobilized. WPI (4 and 8% w/w) in deionized water, pH 7.5, containing 10 mM dithiothreitol was cross-linked using enzyme/substrate ratios of 0.12-10 units of activity/g WPI. The reaction was carried out in a jacketed bioreactor for 8 h at 40 degrees C with continuous circulation. The gel point temperature of WPI solutions treated with 0.12 unit of immobilized TGase/g was slightly decreased, but the gel strength was unaffected. However, increasing the enzyme/substrate ratio resulted in extensive cross-linking of WPI that was manifested by increases in apparent viscosity and changes in the gelation properties. For example, using 10 units of soluble TGase/g resulted in extensive cross-linking of alpha-lactalbumin and beta-lactoglobulin in WPI, as evidenced by SDS-PAGE and Western blotting results. Interestingly, the gelling point of WPI solutions increased from 68 to 94 degrees C after a 4-h reaction, and the gel strength was drastically decreased (lower storage modulus, G'). Thus, extensive intra- and interchain cross-linking probably caused formation of polymers that were too large for effective network development. These results suggest that a process could be developed to produce heat-stable whey proteins for various food applications.

  3. ROMP-based thermosetting polymers from modified castor oil with various cross-linking agents

    Science.gov (United States)

    Ding, Rui

    Polymers derived from bio-renewable resources are finding an increase in global demand. In addition, polymers with distinctive functionalities are required in certain advanced fields, such as aerospace and civil engineering. In an attempt to meet both these needs, the goal of this work aims to develop a range of bio-based thermosetting matrix polymers for potential applications in multifunctional composites. Ring-opening metathesis polymerization (ROMP), which recently has been explored as a powerful method in polymer chemistry, was employed as a unique pathway to polymerize agricultural oil-based reactants. Specifically, a novel norbornyl-functionalized castor oil alcohol (NCA) was investigated to polymerize different cross-linking agents using ROMP. The effects of incorporating dicyclopentadiene (DCPD) and a norbornene-based crosslinker (CL) were systematically evaluated with respect to curing behavior and thermal mechanical properties of the polymers. Isothermal differential scanning calorimetry (DSC) was used to investigate the conversion during cure. Dynamic DSC scans at multiple heating rates revealed conversion-dependent activation energy by Ozawa-Flynn-Wall analysis. The glass transition temperature, storage modulus, and loss modulus for NCA/DCPD and NCA/CL copolymers with different cross-linking agent loading were compared using dynamic mechanical analysis. Cross-link density was examined to explain the very different dynamic mechanical behavior. Mechanical stress-strain curves were developed through tensile test, and thermal stability of the cross-linked polymers was evaluated by thermogravimetric analysis to further investigate the structure-property relationships in these systems.

  4. A minimal model for stabilization of biomolecules by hydrocarbon cross-linking

    Science.gov (United States)

    Hamacher, K.; Hübsch, A.; McCammon, J. A.

    2006-04-01

    Programmed cell death regulating protein motifs play an essential role in the development of an organism, its immune response, and disease-related cellular mechanisms. Among those motifs the BH3 domain of the BCL-2 family is found to be of crucial importance. Recent experiments showed how the isolated, otherwise unstructured BH3 peptide can be modified by a hydrocarbon linkage to regain function. We parametrized a reduced, dynamic model for the stability effects of such covalent cross-linking and confirmed that the model reproduces the reinforcement of the structural stability of the BH3 motif by cross-linking. We show that an analytically solvable model for thermostability around the native state is not capable of reproducing the stabilization effect. This points to the crucial importance of the peptide dynamics and the fluctuations neglected in the analytic model for the cross-linking system to function properly. This conclusion is supported by a thorough analysis of a simulated Gō model. The resulting model is suitable for rational design of generic cross-linking systems in silicio.

  5. Enzymatic characterization of transglutaminase from Streptomyces mobaraensis DSM 40587 in high salt and effect of enzymatic cross-linking of yak milk proteins on functional properties of stirred yogurt.

    Science.gov (United States)

    Zhang, L; Zhang, L; Yi, H; Du, M; Ma, C; Han, X; Feng, Z; Jiao, Y; Zhang, Y

    2012-07-01

    Streptomyces transglutaminase (TGase) purified from high-salt medium was characterized and applied into yak yogurts. The purified enzyme presented a Michaelis constant of 40.47 mmol and a maximum velocity of 44.44 U/mg of protein for N-carboxybenzoyl-l-glutaminyl-glycine in the hydroxamate procedure. The purified TGase exhibited optimum activity at 55°C and pH 6.0. The enzyme was not stable above 50°C and was stable within a pH range of 5.0 to 10.0 at 4°C for 12h and pH 5.0 to 9.0 at 37°C for 30 min. The TGase activity was not affected by Ca(2+), K(+), Ba(2+), or Na(+), but slightly inhibited by Fe(2+), Mg(2+), and Mn(2+), and strongly by Cu(2+) and Zn(2+). To explore yak milk products, it was used to produce yogurt and TGase was used. It was found that TGase-catalyzed cross-linking was effective in improving functional properties of stirred yak yogurt. Treated yogurt produced a strong acid gel, higher consistency, cohesiveness, index of viscosity, and creamier mouth feel than the untreated product. Furthermore, yak yogurt treated with TGase presented lower wet yak hair or sweat odor, or both. Therefore, TGase can be used to pave the way for exploration of novel yak products to overcome the issues of peculiar wet yak hair or sweat odor, or both.

  6. Probing native protein structures by chemical cross-linking, mass spectrometry, and bioinformatics.

    Science.gov (United States)

    Leitner, Alexander; Walzthoeni, Thomas; Kahraman, Abdullah; Herzog, Franz; Rinner, Oliver; Beck, Martin; Aebersold, Ruedi

    2010-08-01

    Chemical cross-linking of reactive groups in native proteins and protein complexes in combination with the identification of cross-linked sites by mass spectrometry has been in use for more than a decade. Recent advances in instrumentation, cross-linking protocols, and analysis software have led to a renewed interest in this technique, which promises to provide important information about native protein structure and the topology of protein complexes. In this article, we discuss the critical steps of chemical cross-linking and its implications for (structural) biology: reagent design and cross-linking protocols, separation and mass spectrometric analysis of cross-linked samples, dedicated software for data analysis, and the use of cross-linking data for computational modeling. Finally, the impact of protein cross-linking on various biological disciplines is highlighted.

  7. Cross-linked comb-shaped anion exchange membranes with high base stability

    Energy Technology Data Exchange (ETDEWEB)

    Li, NW; Wang, LZ; Hickner, M

    2014-01-01

    A unique one-step cross-linking strategy that connects quaternary ammonium centers using Grubbs II-catalyzed olefin metathesis was developed. The cross-linked anion exchange membranes showed swelling ratios of less than 10% and hydroxide conductivities of 18 to 40 mS cm(- 1). Cross-linking improved the membranes' stability to hydroxide degradation compared to their non-cross-linked analogues.

  8. Investigation of anisotropic thermal transport in cross-linked polymers

    Science.gov (United States)

    Simavilla, David Nieto

    Thermal transport in lightly cross-linked polyisoprene and polybutadine subjected to uniaxial elongation is investigated experimentally. We employ two experimental techniques to assess the effect that deformation has on this class of materials. The first technique, which is based on Forced Rayleigh Scattering (FRS), allows us to measure the two independent components of the thermal diffusivity tensor as a function of deformation. These measurements along with independent measurements of the tensile stress and birefringence are used to evaluate the stress-thermal and stress-optic rules. The stress-thermal rule is found to be valid for the entire range of elongations applied. In contrast, the stress-optic rule fails for moderate to large stretch ratios. This suggests that the degree of anisotropy in thermal conductivity depends on both orientation and tension in polymer chain segments. The second technique, which is based on infrared thermography (IRT), allows us to measure anisotropy in thermal conductivity and strain induced changes in heat capacity. We validate this method measurements of anisotropic thermal conductivity by comparing them with those obtained using FRS. We find excellent agreement between the two techniques. Uncertainty in the infrared thermography method measurements is estimated to be about 2-5 %. The accuracy of the method and its potential application to non-transparent materials makes it a good alternative to extend current research on anisotropic thermal transport in polymeric materials. A second IRT application allows us to investigate the dependence of heat capacity on deformation. We find that heat capacity increases with stretch ratio in polyisoprene specimens under uniaxial extension. The deviation from the equilibrium value of heat capacity is consistent with an independent set of experiments comparing anisotropy in thermal diffusivity and conductivity employing FRS and IRT techniques. We identify finite extensibility and strain

  9. Cross-linking e segmento de anel corneano intraestromal

    Directory of Open Access Journals (Sweden)

    Adimara da Candelaria Renesto

    2011-02-01

    Full Text Available O cross-linking corneano é um procedimento usado para a estabilização mecânica e aumento da rigidez corneana em pacientes com ceratocone (reduzindo a possibilidade de progressão, e também em processos inflamatórios de afinamento corneano. Os segmentos de anéis corneanos intraestromais têm como princípio o aplanamento central da córnea. Inicialmente utilizados para correção de baixa miopia, a principal indicação atual é em pacientes com ceratocone, para melhorar a acuidade visual não corrigida, a acuidade visual corrigida e permitir uma melhor tolerância ao uso de lentes de contato como também retardar a necessidade de um transplante de córnea. O objetivo deste artigo é revisar algumas publicações relacionadas ao cross-linking corneano e à inserção do segmento de anel intraestromal, apresentando suas indicações, resultados e complicações relatadas até o momento.

  10. Adsorption of methyl orange onto protonated cross-linked chitosan

    Directory of Open Access Journals (Sweden)

    Ruihua Huang

    2017-01-01

    Full Text Available The adsorption of methyl orange (MO from aqueous solutions on protonated cross-linked chitosan was studied in a batch system. The results showed that the adsorption of MO onto protonated cross-linked chitosan was affected significantly by initial MO concentration, adsorbent dosage, adsorption temperature, and contact time. The pH value of solution had a minor impact on the adsorption of MO in a pH range of 1.0–9.1. The equilibrium isotherms at different temperatures (293, 303, and 313 K and pH values (4.5, 6.7, and 9.1 were investigated. Langmuir model was able to describe these Equilibrium data fitted perfectly. The maximum monolayer adsorption capacities obtained from the Langmuir model were 89.29, 130.9, and 180.2 mg/g at 293, 303, and 313 K, respectively. Adsorption kinetics at different concentrations (100, 200 and 300 mg/L and pH values (4.5, 6.7 and 9.1 were also studied. The kinetics was correlated well with the pseudo second-order model.

  11. Supermacroporous chemically cross-linked poly(aspartic acid) hydrogels.

    Science.gov (United States)

    Gyarmati, Benjámin; Mészár, E Zsuzsanna; Kiss, Lóránd; Deli, Mária A; László, Krisztina; Szilágyi, András

    2015-08-01

    Chemically cross-linked poly(aspartic acid) (PASP) gels were prepared by a solid-liquid phase separation technique, cryogelation, to achieve a supermacroporous interconnected pore structure. The precursor polymer of PASP, polysuccinimide (PSI) was cross-linked below the freezing point of the solvent and the forming crystals acted as templates for the pores. Dimethyl sulfoxide was chosen as solvent instead of the more commonly used water. Thus larger temperatures could be utilized for the preparation and the drawback of increase in specific volume of water upon freezing could be eliminated. The morphology of the hydrogels was characterized by scanning electron microscopy and interconnectivity of the pores was proven by the small flow resistance of the gels. Compression tests also confirmed the interconnected porous structure and the complete re-swelling and shape recovery of the supermacroporous PASP hydrogels. The prepared hydrogels are of interest for several biomedical applications as scaffolding materials because of their cytocompatibility, controllable morphology and pH-responsive character.

  12. Microbial Keratitis After Collagen Cross-linking Treatment

    Directory of Open Access Journals (Sweden)

    Banu Torun Acar

    2012-07-01

    Full Text Available A 33-year-old woman presented with pain, redness, and diminution of vision that occurred 2 days after collagen cross-linking had been performed for keratoconus in the right eye. Culture results from the patient's contact lens and corneal scrapings were positive for Staphylococcus epidermidis. According to the results of antibiotic susceptibility testing, the patient was treated with hourly topical fortified vancomycin and exocin. Before collagen cross-linking, the best-corrected visual acuity (BCVA was 4/10, the manifest refraction was -7.00 -1.755 3°. Four months after the procedure, the BCVA was 4/10, the manifest refraction was -5.50 -1.75 10°. Slit-lamp examination revealed a mild residual haze in the upper midperipheral cornea, and stromal opacities had disappeared. Collagen crosslinking is less invasive compared to other methods for treatment of keratoconus, but epithelial debridement and bandage contact lens wearing may lead to the development of bacterial keratitis. (Turk J Oph thal mol 2012; 42: 300-2

  13. One-step electrospinning of cross-linked chitosan fibers.

    Science.gov (United States)

    Schiffman, Jessica D; Schauer, Caroline L

    2007-09-01

    Chitin is a nitrogen-rich polysaccharide that is abundant in crustaceans, mollusks, insects, and fungi and is the second most abundant organic material found in nature next to cellulose. Chitosan, the N-deacetylated derivative of chitin, is environmentally friendly, nontoxic, biodegradable, and antibacterial. Fibrous mats are typically used in industries for filter media, catalysis, and sensors. Decreasing fiber diameters within these mats causes many beneficial effects such as increased specific surface area to volume ratios. When the intrinsically beneficial effects of chitosan are combined with the enhanced properties of nanofibrous mats, applications arise in a wide range of fields, including medical, packaging, agricultural, and automotive. This is particularly important as innovative technologies that focus around bio-based materials are currently of high urgency, as they can decrease dependencies on fossil fuels. We have demonstrated that Schiff base cross-linked chitosan fibrous mats can be produced utilizing a one-step electrospinning process that is 25 times faster and, therefore, more economical than a previously reported two-step vapor-cross-linking method. These fibrous mats are insoluble in acidic, basic, and aqueous solutions for 72 h. Additionally, this improved production method results in a decreased average fiber diameter, which measures 128 +/- 40 nm. Chemical and structural analyses were conducted utilizing Fourier transform infrared spectroscopy, solubility studies, and scanning electron microscopy.

  14. Thermally Cross-Linked Anion Exchange Membranes from Solvent Processable Isoprene Containing Ionomers

    Science.gov (United States)

    2015-01-15

    capacities (IECs). Solution cast membranes were thermally cross- linked to form anion exchange membranes. Cross-linking was achieved by taking advantage...distribution is unlimited. Thermally Cross-Linked Anion Exchange Membranes from Solvent Processable Isoprene Containing Ionomers The views...Box 12211 Research Triangle Park, NC 27709-2211 Anion Exchnage Membrane, Polymer synthesis, Morphology, Anion Conductivity REPORT DOCUMENTATION PAGE

  15. Small Strain Topological Effects of Biopolymer Networks with Rigid Cross-Links

    NARCIS (Netherlands)

    Zagar, G.; Onck, P. R.; Van der Giessen, E.; Garikipati, K; Arruda, EM

    2010-01-01

    Networks of cross-linked filamentous biopolymers form topological structures characterized by L, T and X cross-link types of connectivity 2, 3 and 4, respectively. The distribution of cross-links over these three types proofs to be very important for the initial elastic shear stiffness of isotropic

  16. Cross-linking of dermal sheep collagen using a water-soluble carbodiimide

    NARCIS (Netherlands)

    Olde Damink, L.H.H.; Dijkstra, P.J.; Luyn, van M.J.A.; Wachem, van P.B.; Nieuwenhuis, P.; Feijen, J.

    1996-01-01

    A cross-linking method for collagen-based biomaterials was developed using the water-soluble carbodiimide 1-ethyl-3-(3-dimethyl aminopropyl)carbodiimide hydrochloride (EDC). Cross-linking using EDC involves the activation of carboxylic acid groups to give O-acylisourea groups, which form cross-links

  17. Structure and kinetics of chemically cross-linked protein gels from small-angle X-ray scattering

    CERN Document Server

    Kaieda, Shuji; Halle, Bertil

    2014-01-01

    Glutaraldehyde (GA) reacts with amino groups in proteins, forming intermolecular cross-links that, at sufficiently high protein concentration, can transform a protein solution into a gel. Although GA has been used as a cross-linking reagent for decades, neither the cross-linking chemistry nor the microstructure of the resulting protein gel have been clearly established. Here we use small-angle X-ray scattering (SAXS) to characterise the microstructure and structural kinetics of gels formed by cross-linking of pancreatic trypsin inhibitor, myoglobin or intestinal fatty acid-binding protein. By comparing the scattering from gels and dilute solutions, we extract the structure factor and the pair correlation function of the gel. The protein gels are spatially heterogeneous, with dense clusters linked by sparse networks. Within the clusters, adjacent protein molecules are almost in contact, but the protein concentration in the cluster is much lower than in a crystal. At the $\\sim$ 1 nm SAXS resolution, the native ...

  18. Temperature dependence of creep compliance of highly cross-linked epoxy: A molecular simulation study

    Energy Technology Data Exchange (ETDEWEB)

    Khabaz, Fardin, E-mail: rajesh.khare@ttu.edu; Khare, Ketan S., E-mail: rajesh.khare@ttu.edu; Khare, Rajesh, E-mail: rajesh.khare@ttu.edu [Department of Chemical Engineering, Texas Tech University, Lubbock, TX 79409 (United States)

    2014-05-15

    We have used molecular dynamics (MD) simulations to study the effect of temperature on the creep compliance of neat cross-linked epoxy. Experimental studies of mechanical behavior of cross-linked epoxy in literature commonly report creep compliance values, whereas molecular simulations of these systems have primarily focused on the Young’s modulus. In this work, in order to obtain a more direct comparison between experiments and simulations, atomistically detailed models of the cross-linked epoxy are used to study their creep compliance as a function of temperature using MD simulations. The creep tests are performed by applying a constant tensile stress and monitoring the resulting strain in the system. Our results show that simulated values of creep compliance increase with an increase in both time and temperature. We believe that such calculations of the creep compliance, along with the use of time temperature superposition, hold great promise in connecting the molecular insight obtained from molecular simulation at small length- and time-scales with the experimental behavior of such materials. To the best of our knowledge, this work is the first reported effort that investigates the creep compliance behavior of cross-linked epoxy using MD simulations.

  19. Cross-linked hyaluronic acid in pressure ulcer prevention.

    Science.gov (United States)

    Beniamino, P; Vadalà, M; Laurino, C

    2016-07-02

    Long-term bedridden patients are at high risk of acquring pressure ulcers (PUs). In this group of patients, prevention is necessary to cut the health costs, improve quality of life and reduce the mortality. Here, we evaluated the effectiveness of a cross-linked hyaluronic acid (HA) as plastic bulking-agent filling and remodelling the deep dermis and subcutaneous space of the skin areas exposed to the risk of necrosis. Our work hypothesis has been to inflate a sub-dermal elastic cushion, filled with a natural ECM component, with the aim to induce a stronger tissue background resistant to the ulcerative process. All the patients had an increased risk of PUs, at the sacral, ileum or heel skin. Patients were being nursed accordingly to the standard orthopaedic ward management with a pressure relieveing air mattress. The standard protocol consisted in body mobilisation every 3 hours, 24 hours a day and accurate cleaning of the skin with liquid soap and water without any towel friction and without adding any cream or lotion for the skin protection. Our filling protocol enclosed: accurate disinfection of the skin to be injected with povidone-iodine solution, followed by a local anaesthesia with 28G 13 mm needle, injecting 1.5 ml of 1% xylocaine. Then slow, deep, subcutaneous injection of cross-linked HA was performed with a 18G long needle, in order to deliver a homogeneous, soft gel layer underneath and around the whitish erythematous skin edges at risk of ulceration. Patients' tolerability of the compound and adverse events were also recorded. There were 15 patients (78-94 years old) who participated in the study. All tolerated the procedure very well and no serious side effects were declared. No skin pressure ulceration was detected in the four weeks follow-up Conclusion: We have demonstrated the safety and tolerability of a cross-linked HA subdermal injection in PUs prevention. The compound stratifies in a soft, elastic, interstitial bulk into the deep dermis, thus

  20. Riboflavin-UVA-induced corneal collagen cross-linking in pediatric patients.

    Science.gov (United States)

    Caporossi, Aldo; Mazzotta, Cosimo; Baiocchi, Stefano; Caporossi, Tomaso; Denaro, Rosario; Balestrazzi, Angelo

    2012-03-01

    Evaluation of stability and functional response after riboflavin-UVA–induced cross-linking in a population of patients younger than 18 years with progressive keratoconus after 36 months of follow-up. Prospective nonrandomized phase II open trial conducted at the Department of Ophthalmology, Siena University, Italy. The "Siena CXL Pediatrics" trial involved 152 patients aged 18 years or younger (10–18 years) with clinical and instrumental evidence of keratoconus progression. The population was divided into 2 groups according to corneal thickness (>450 and 450 μm) and +0.14 and +0.15 Snellen lines, respectively, in the thinner group (corneal thickness <450 μm). Patients in the latter group already showed a better and faster functional recovery than the thicker group at 3-month follow-up. Topographic results showed statistically significant improvement in K readings and asymmetry index values. Coma reduction was also statistically significant. The study demonstrated significant and rapid functional improvement in pediatric patients younger than 18 years with progressive keratoconus, undergoing riboflavin-UVA–induced cross-linking. In pediatric age, a good functional response and keratoconus stability was obtained after corneal cross-linking in a 36-month follow-up.

  1. Functional links and robustness in food webs.

    Science.gov (United States)

    Allesina, Stefano; Bodini, Antonio; Pascual, Mercedes

    2009-06-27

    The robustness of ecosystems to species losses is a central question in ecology, given the current pace of extinctions and the many species threatened by human impacts, including habitat destruction and climate change. Robustness from the perspective of secondary extinctions has been addressed in the context of food webs to consider the complex network of species interactions that underlie responses to perturbations. In-silico removal experiments have examined the structural properties of food webs that enhance or hamper the robustness of ecosystems to species losses, with a focus on the role of hubs, the most connected species. Here we take a different approach and focus on the role of the connections themselves. We show that trophic links can be divided into functional and redundant based on their contribution to robustness. The analysis of empirical webs shows that hubs are not necessarily the most important species as they may hold many redundant links. Furthermore, the fraction of functional connections is high and constant across systems regardless of size and interconnectedness. The main consequence of this scaling pattern is that ecosystem robustness can be considerably reduced by species extinctions even when these do not result in any secondary extinctions. This introduces the possibility of tipping points in the collapse of ecosystems.

  2. Synthesis of Cross-Linked Polymeric Micelle pH Nanosensors

    DEFF Research Database (Denmark)

    Ek, Pramod Kumar; Jølck, Rasmus Irming; Andresen, Thomas Lars

    2015-01-01

    at the micelle shell using CuAAC results in a stabilized micelle pH nanosensor. Compared to the postmicelle modification strategy, the mixed-micellization approach increases the control of the overall composition of the nanosensors.Both approaches provide stable nanosensors with similar pKa profiles and thereby......The design flexibility that polymeric micelles offer in the fabrication of optical nanosensors for ratiometric pH measurements is investigated. pH nanosensors based on polymeric micelles are synthesized either by a mixed-micellization approach or by a postmicelle modification strategy. In the mixed......-micellization approach, self-assembly of functionalized unimers followed by shell cross-linking by copper-catalyzed azide-alkyne cycloaddition (CuAAC) results in stabilized cRGD-functionalized micelle pH nanosensors. In the postmicelle modification strategy, simultaneous cross-linking and fluorophore conjugation...

  3. Stiffening of semiflexible biopolymers and cross-linked networks

    CERN Document Server

    Van Dillen, T; Van der Giessen, E

    2006-01-01

    We study the mechanical stiffening behavior in two-dimensional (2D) cross-linked networks of semiflexible biopolymer filaments under simple shear. Filamental constituents immersed in a fluid undergo thermally excited bending motions. Pulling out these undulations results in an increase in the axial stiffness. We analyze this stiffening behavior of 2D semiflexible filaments in detail: we first investigate the average, {static} force-extension relation by considering the initially present undulated configuration that is pulled straight under a tensile force, and compare this result with the average response in which undulation dynamics is allowed during pulling, as derived earlier by MacKintosh and coworkers. We will show that the resulting mechanical behavior is rather similar, but with the axial stiffness being a factor 2 to 4 larger in the dynamic model. Furthermore, we study the stretching contribution in case of extensible filaments and show that, for 2D filaments, the mechanical response is dominated by {...

  4. Swelling properties of cross-linked DNA gels.

    Science.gov (United States)

    Costa, Diana; Miguel, M Graça; Lindman, Björn

    2010-07-12

    This work represents our contribution to the field of physical chemistry of DNA gels, and concerns the synthesis and study of novel chemically cross-linked DNA gels. The use of covalent DNA gels is a very promising way to study DNA-cosolute interactions, as well as the dynamic behaviour of DNA and cationic compacting agents, like lipids, surfactants and polycations. Manipulating DNA in new ways, like DNA networks, allows a better understanding and characterization of DNA-cosolute complexes at the molecular level, and also allows us to follow the assembly structures of these complexes. The use of responsive polymer gels for targeted delivery of toxic and/or labile drugs has, during the past few years, shown to be a promising concept. The features found in the proposed system would find applications in a broader field of gel/drug interaction, for the development of controlled release and targeted delivery devices.

  5. Conventional Versus Cross-Linked Polyethylene for Total Hip Arthroplasty.

    Science.gov (United States)

    Surace, Michele F; Monestier, Luca; Vulcano, Ettore; Harwin, Steven F; Cherubino, Paolo

    2015-09-01

    The clinical and radiographic outcomes of 88 patients who underwent primary total hip arthroplasty with either conventional polyethylene or cross-linked polyethylene (XLPE) from the same manufacturer were compared. There were no significant differences between the 2 subpopulations regarding average age, gender, side affected, or prosthetic stem and cup size. The average follow-up was 104 months (range, 55 to 131 months). To the authors' knowledge, this is the longest follow-up for this particular insert. Clinical and radiographic evaluations were performed at 1, 3, 6, and 12 months and then annually. Results showed that XLPE has a significantly greater wear reduction than that of standard polyethylene in primary total hip arthroplasty. At the longest available follow-up for these specific inserts, XLPE proved to be effective in reducing wear.

  6. Studies on N-vinylformamide cross-linked copolymers

    Science.gov (United States)

    Świder, Joanna; Tąta, Agnieszka; Sokołowska, Katarzyna; Witek, Ewa; Proniewicz, Edyta

    2015-12-01

    Copolymers of N-vinylformamide (NVF) cross-linked with three multifunctional monomers, including divinylbenzene (DVB), ethylene glycol dimethacrylate (EGDMA), and N,N‧-methylenebisacrylamide (MBA) were synthetized by a three-dimensional free radical polymerization in inverse suspension using 2,2‧-azobis(2-methylpropionamide) dihydrochloride (AIBA) as an initiator. Methyl silicon oil was used as the continuous phase during the polymerization processes. Fourier-transform adsorption infrared (FT-IR) spectra revealed the presence of silicone oil traces and suggested that silicone oil strongly interacted with the copolymers surface. Purification procedure allowed to completely remove the silicon oil traces from P(NVF-co-DVB) only. The morphology and the structure of the investigated copolymers were examined by optical microscopy, FT-IR, and FT-Raman (Fourier-transform Raman spectroscopy) methods.

  7. Polyanionic collagen membranes for guided tissue regeneration: Effect of progressive glutaraldehyde cross-linking on biocompatibility and degradation.

    Science.gov (United States)

    Veríssimo, D M; Leitão, R F C; Ribeiro, R A; Figueiró, S D; Sombra, A S B; Góes, J C; Brito, G A C

    2010-10-01

    The ultimate goal of periodontal therapy is to control periodontal tissue inflammation and to produce predictable regeneration of that part of the periodontium which has been lost as a result of periodontal disease. In guided tissue regeneration membranes function as mechanical barriers, excluding the epithelium and gingival corium from the root surface and allowing regeneration by periodontal ligament cells. This report aims to study the effect of glutaraldehyde (GA) cross-linking on mineralized polyanionic collagen (PAC) membranes by conducting a histological evaluation of the tissue response (biocompatibility) and by assessing the biodegradation of subcutaneous membrane implants in rats. We studied six different samples: a PAC, a PAC mineralized by alternate soaking processes for either 25 or 75 cycles (PAC 25 and PAC 75, respectively) and these films cross-linked by GA. Inflammatory infiltrate, cytokine dosage, fibrosis capsule thickness, metalloproteinase immunohistochemistry and membrane biodegradation after 1, 7, 15 and 30 days were measured. The inflammatory response was found to be more intense in membranes without cross-linking, while the fibrosis capsules became thicker in cross-linked membranes after 30 days. The membranes without cross-linking suffered intense biodegradation, while the membranes with cross-linking remained intact after 30 days. The cross-linking with GA reduced the inflammatory response and prevented degradation of the membranes over the entire course of the observation period. These membranes are thus an attractive option when the production of new bone depends on the prolonged presence of a mechanical barrier.

  8. Peptidoglycan Cross-Linking in Glycopeptide-Resistant Actinomycetales

    Science.gov (United States)

    Hugonnet, Jean-Emmanuel; Haddache, Nabila; Veckerlé, Carole; Dubost, Lionel; Marie, Arul; Shikura, Noriyasu; Mainardi, Jean-Luc; Rice, Louis B.

    2014-01-01

    Synthesis of peptidoglycan precursors ending in d-lactate (d-Lac) is thought to be responsible for glycopeptide resistance in members of the order Actinomycetales that produce these drugs and in related soil bacteria. More recently, the peptidoglycan of several members of the order Actinomycetales was shown to be cross-linked by l,d-transpeptidases that use tetrapeptide acyl donors devoid of the target of glycopeptides. To evaluate the contribution of these resistance mechanisms, we have determined the peptidoglycan structure of Streptomyces coelicolor A(3)2, which harbors a vanHAX gene cluster for the production of precursors ending in d-Lac, and Nonomuraea sp. strain ATCC 39727, which is devoid of vanHAX and produces the glycopeptide A40296. Vancomycin retained residual activity against S. coelicolor A(3)2 despite efficient incorporation of d-Lac into cytoplasmic precursors. This was due to a d,d-transpeptidase-catalyzed reaction that generated a stem pentapeptide recognized by glycopeptides by the exchange of d-Lac for d-Ala and Gly. The contribution of l,d-transpeptidases to resistance was limited by the supply of tetrapeptide acyl donors, which are essential for the formation of peptidoglycan cross-links by these enzymes. In the absence of a cytoplasmic metallo-d,d-carboxypeptidase, the tetrapeptide substrate was generated by hydrolysis of the C-terminal d-Lac residue of the stem pentadepsipeptide in the periplasm in competition with the exchange reaction catalyzed by d,d-transpeptidases. In Nonomuraea sp. strain ATCC 39727, the contribution of l,d-transpeptidases to glycopeptide resistance was limited by the incomplete conversion of pentapeptides into tetrapeptides despite the production of a cytoplasmic metallo-d,d-carboxypeptidase. Since the level of drug production exceeds the level of resistance, we propose that l,d-transpeptidases merely act as a tolerance mechanism in this bacterium. PMID:24395229

  9. Cross-linking staphylococcal enterotoxin A bound to major histocompatibility complex class I is required for TNF-alpha secretion

    Science.gov (United States)

    Wright, A. D.; Chapes, S. K.

    1999-01-01

    The mechanism of how superantigens function to activate cells has been linked to their ability to bind and cross-link the major histocompatibility complex class II (MHCII) molecule. Cells that lack the MHCII molecule also respond to superantigens, however, with much less efficiency. Therefore, the purpose of this study was to confirm that staphylococcal enterotoxin A (SEA) could bind the MHCI molecule and to test the hypothesis that cross-linking SEA bound to MHCII-deficient macrophages would induce a more robust cytokine response than without cross-linking. We used a capture enzyme-linked immunosorbent assay and an immunprecipitation assay to directly demonstrate that MHCI molecules bind SEA. Directly cross-linking MHCI using monoclonal antibodies or cross-linking bound SEA with an anti-SEA antibody or biotinylated SEA with avidin increased TNF-alpha and IL-6 secretion by MHCII(-/-) macrophages. The induction of a vigorous macrophage cytokine response by SEA/anti-SEA cross-linking of MHCI offers a mechanism to explain how MHCI could play an important role in superantigen-mediated pathogenesis. Copyright 1999 Academic Press.

  10. Yield and Failure Behavior Investigated for Cross-Linked Phenolic Resins Using Molecular Dynamics

    Science.gov (United States)

    Monk, Joshua D.; Lawson, John W.

    2016-01-01

    Molecular dynamics simulations were conducted to fundamentally evaluate the yield and failure behavior of cross-linked phenolic resins at temperatures below the glass transition. Yield stress was investigated at various temperatures, strain rates, and degrees of cross-linking. The onset of non-linear behavior in the cross-linked phenolic structures was caused by localized irreversible molecular rearrangements through the rotation of methylene linkers followed by the formation or annihilation of neighboring hydrogen bonds. The yield stress results, with respect to temperature and strain rate, could be fit by existing models used to describe yield behavior of amorphous glasses. The degree of cross-linking only indirectly influences the maximum yield stress through its influence on glass transition temperature (Tg), however there is a strong relationship between the degree of cross-linking and the failure mechanism. Low cross-linked samples were able to separate through void formation, whereas the highly cross-linked structures exhibited bond scission.

  11. Mass spectrometric analysis of a UV-cross-linked protein-DNA complex: tryptophans 54 and 88 of E. coli SSB cross-link to DNA

    DEFF Research Database (Denmark)

    Steen, H; Petersen, J; Mann, M

    2001-01-01

    Protein-nucleic acid complexes are commonly studied by photochemical cross-linking. UV-induced cross-linking of protein to nucleic acid may be followed by structural analysis of the conjugated protein to localize the cross-linked amino acids and thereby identify the nucleic acid binding site. Mass....... coli single-stranded DNA binding protein (SSB) that was UV-cross-linked to a 5-iodouracil containing DNA oligomer. Two methods were optimized to circumvent the need for standard liquid chromatography and gel electrophoresis, thereby dramatically increasing the overall sensitivity of the analysis....... Enzymatic degradation of protein and oligonucleotide was combined with miniaturized sample preparation methods for enrichment and desalting of cross-linked peptide-nucleic acid heteroconjugates from complex mixtures prior to mass spectrometric analysis. Detailed characterization of the peptidic component...

  12. Photo-cross-linking of amniotic membranes for limbal epithelial cell cultivation

    Energy Technology Data Exchange (ETDEWEB)

    Lai, Jui-Yang, E-mail: jylai@mail.cgu.edu.tw

    2014-12-01

    In the present study, we developed photo-cross-linked amniotic membrane (AM) as a limbal stem cell niche. After ultraviolet (UV) irradiation for varying time periods, the biological tissues were studied by determinations of cross-linking structure, degradability, and nutrient permeation ability. Our results showed that the number of cross-links per unit mass of AM significantly increased with increasing illumination time from 5 to 50 min. However, the cross-link formation was inhibited by longer irradiation time (i.e., 150 min), probably due to the scission of tissue collagen chains through irradiation. The biological stability and matrix permeability of photo-cross-linked AM materials strongly depended on their cross-linking densities affected by the UV irradiation. In vitro biocompatibility studies including cell viability and pro-inflammatory gene expression analyses demonstrated that, irrespective of the irradiation time employed, the physically cross-linked biological tissues exhibited negligible cytotoxicity and similar interleukin-6 (IL-6) mRNA levels. The data clearly indicate that these AM matrices do not cause potential harm to the corneal epithelial cells. After the growth of limbal epithelial cells (LECs) on AM substrates, Western blot analyses were conducted to examine the expression of ABCG2. It was found that the ability of UV-irradiated AM to maintain the undifferentiated precursor cell phenotype was significantly enhanced with increasing extent of photo-cross-linking. In summary, the UV irradiation time may have a profound influence on the fabrication of photo-cross-linked AM matrices for LEC cultivation. - Highlights: • We report the development of photo-cross-linked AM as a limbal stem cell niche. • Cross-linked structure of tissue materials was controlled by UV irradiation time. • Biostability and matrix permeability of AM depended on cross-linking density. • All the studied photo-cross-linked AM showed good in vitro biocompatibility.

  13. Blind testing of cross-linking/mass spectrometry hybrid methods in CASP11.

    Science.gov (United States)

    Schneider, Michael; Belsom, Adam; Rappsilber, Juri; Brock, Oliver

    2016-09-01

    Hybrid approaches combine computational methods with experimental data. The information contained in the experimental data can be leveraged to probe the structure of proteins otherwise elusive to computational methods. Compared with computational methods, the structures produced by hybrid methods exhibit some degree of experimental validation. In spite of these advantages, most hybrid methods have not yet been validated in blind tests, hampering their development. Here, we describe the first blind test of a specific cross-link based hybrid method in CASP. This blind test was coordinated by the CASP organizers and utilized a novel, high-density cross-linking/mass-spectrometry (CLMS) approach that is able to collect high-density CLMS data in a matter of days. This experimental protocol was developed in the Rappsilber laboratory. This approach exploits the chemistry of a highly reactive, photoactivatable cross-linker to produce an order of magnitude more cross-links than homobifunctional cross-linkers. The Rappsilber laboratory generated experimental CLMS data based on this protocol, submitted the data to the CASP organizers which then released this data to the CASP11 prediction groups in a separate, CLMS assisted modeling experiment. We did not observe a clear improvement of assisted models, presumably because the properties of the CLMS data-uncertainty in cross-link identification and residue-residue assignment, and uneven distribution over the protein-were largely unknown to the prediction groups and their approaches were not yet tailored to this kind of data. We also suggest modifications to the CLMS-CASP experiment and discuss the importance of rigorous blind testing in the development of hybrid methods. Proteins 2016; 84(Suppl 1):152-163. © 2016 The Authors Proteins: Structure, Function, and Bioinformatics Published by Wiley Periodicals, Inc.

  14. Linking microarray reporters with protein functions

    Directory of Open Access Journals (Sweden)

    Gaj Stan

    2007-09-01

    Full Text Available Abstract Background The analysis of microarray experiments requires accurate and up-to-date functional annotation of the microarray reporters to optimize the interpretation of the biological processes involved. Pathway visualization tools are used to connect gene expression data with existing biological pathways by using specific database identifiers that link reporters with elements in the pathways. Results This paper proposes a novel method that aims to improve microarray reporter annotation by BLASTing the original reporter sequences against a species-specific EMBL subset, that was derived from and crosslinked back to the highly curated UniProt database. The resulting alignments were filtered using high quality alignment criteria and further compared with the outcome of a more traditional approach, where reporter sequences were BLASTed against EnsEMBL followed by locating the corresponding protein (UniProt entry for the high quality hits. Combining the results of both methods resulted in successful annotation of > 58% of all reporter sequences with UniProt IDs on two commercial array platforms, increasing the amount of Incyte reporters that could be coupled to Gene Ontology terms from 32.7% to 58.3% and to a local GenMAPP pathway from 9.6% to 16.7%. For Agilent, 35.3% of the total reporters are now linked towards GO nodes and 7.1% on local pathways. Conclusion Our methods increased the annotation quality of microarray reporter sequences and allowed us to visualize more reporters using pathway visualization tools. Even in cases where the original reporter annotation showed the correct description the new identifiers often allowed improved pathway and Gene Ontology linking. These methods are freely available at http://www.bigcat.unimaas.nl/public/publications/Gaj_Annotation/.

  15. THE EFFECTS OF HIGH DOSE IRRADIATION ON THE CROSS-LINKING OF VITAMIN E-BLENDED ULTRAHIGH MOLECULAR WEIGHT POLYETHYLENE

    Science.gov (United States)

    Oral, Ebru; Beckos, Christine Godleski; Malhi, Arnaz S.; Muratoglu, Orhun K.

    2008-01-01

    Vitamin E-stabilized, highly cross-linked ultrahigh molecular weight polyethylene (UHMWPE) is a promising oxidation and wear resistant UHMWPE with improved mechanical strength in comparison with the first generation, irradiated and melted UHMWPE. One approach of incorporating vitamin E in UHMWPE is through blending of vitamin E in UHMWPE powder followed by consolidation and radiation crosslinking. However radiation crosslinking efficiency of UHMWPE decreases in the presence of vitamin E. Therefore an optimum vitamin E concentration and radiation dose level needs to be determined to achieve a cross-link density comparable to 100-kGy irradiated and melted UHMWPE, which has shown excellent wear properties in vivo. We investigated the cross-link density and mechanical properties of vitamin E-blended UHMWPEs as a function of vitamin E concentration in the blend and gamma irradiation doses up to 200 kGy. We found that 0.3 wt% vitamin E-blended UHMWPE could not be cross-linked above a cross-link density achieved at a radiation dose of 65 kGy for virgin UHMWPE and 1.0 wt% vitamin E-blended UHMWPE could not be cross-linked above a cross-link density achieved at a radiation dose of 25 kGy for virgin UHMWPE even when the former were irradiated to a radiation dose of 200 kGy. In addition, higher plasticity at vitamin E concentrations at and above 0.3 wt% indicated that increased chain scissioning may be prevalent. Since the wear resistance of this irradiated UHMWPE would be expected to be low, vitamin E concentrations equal to or above 0.3 wt% are not recommended for subsequent irradiation to achieve a wear resistant cross-linked UHMWPE. The long–term oxidative stability of irradiated blends with low vitamin E concentrations has yet to be studied to determine an optimum between cross-link density and long-term oxidative stability. PMID:18514813

  16. Characterizing RNA-protein interaction using cross-linking and metabolite supplemented nuclear RNA-immunoprecipitation.

    Science.gov (United States)

    Au, Phil Chi Khang; Helliwell, Chris; Wang, Ming-Bo

    2014-05-01

    RNA-immunoprecipitation (RNA-IP) is a method used to isolate and identify RNA molecules specifically associated with an RNA-binding protein. Non-coding RNAs are emerging as key regulators of many biological and developmental pathways and RNA-IP has become an important tool in studying their function(s). While RNA-IP is successfully used to determine protein-RNA interaction, specific details regarding the level of this association and the metabolic requirement of this interaction which can influence the success of RNA-IP remain unclear. Here, we investigate the conditions required for efficient nuclear RNA-IP using Arabidopsis AGO4 (Argonaute 4) and siRNA binding as the study model. We showed that formaldehyde cross-linking, but not UV cross-linking, allowed for efficient pull-down of 24-nt siRNAs, suggesting that AGO4-siRNA interaction involves other protein(s). We also showed that, while formaldehyde cross-linking could also be performed on purified nuclei, ATP supplementation to the nuclei isolation buffer was needed to efficiently pull down 24-nt siRNAs. This result indicates that ATP is required for efficient siRNA loading onto AGO4. As most of the known RNA-mediated regulatory processes occur in the nucleus, our findings on cross-linking conditions and metabolite requirement for successful AGO4 nuclear RNA-IP provide a valuable insight and future consideration when studying the function of protein-RNA interactions in plants.

  17. Epoxy Cross-Linked Collagen and Collagen-Laminin Peptide Hydrogels as Corneal Substitutes

    Directory of Open Access Journals (Sweden)

    May Griffith

    2013-08-01

    Full Text Available A bi-functional epoxy-based cross-linker, 1,4-Butanediol diglycidyl ether (BDDGE, was investigated in the fabrication of collagen based corneal substitutes. Two synthetic strategies were explored in the preparation of the cross-linked collagen scaffolds. The lysine residues of Type 1 porcine collagen were directly cross-linked using l,4-Butanediol diglycidyl ether (BDDGE under basic conditions at pH 11. Alternatively, under conventional methodology, using both BDDGE and 1-Ethyl-3-(3-dimethyl aminopropyl carbodiimide (EDC/N-hydroxysuccinimide (NHS as cross-linkers, hydrogels were fabricated under acidic conditions. In this latter strategy, Cu(BF42·XH2O was used to catalyze the formation of secondary amine bonds. To date, we have demonstrated that both methods of chemical cross-linking improved the elasticity and tensile strength of the collagen implants. Differential scanning calorimetry and biocompatibility studies indicate comparable, and in some cases, enhanced properties compared to that of the EDC/NHS controls. In vitro studies showed that human corneal epithelial cells and neuronal progenitor cell lines proliferated on these hydrogels. In addition, improvement of cell proliferation on the surfaces of the materials was observed when neurite promoting laminin epitope, IKVAV, and adhesion peptide, YIGSR, were incorporated. However, the elasticity decreased with peptide incorporation and will require further optimization. Nevertheless, we have shown that epoxy cross-linkers should be further explored in the fabrication of collagen-based hydrogels, as alternatives to or in conjunction with carbodiimide cross-linkers.

  18. Evaluation of ultrasonic atomization as a new approach to prepare ionically cross-linked chitosan microparticles.

    Science.gov (United States)

    Albertini, Beatrice; Passerini, Nadia; Rodriguez, Lorenzo

    2005-07-01

    Ultrasonic atomization was evaluated as a new approach for the preparation of ionically cross-linked controlled-release chitosan microparticles loaded with theophylline as the model drug, using tripolyphosphate (TPP) as counter-ion. It was possible to nebulize both 2% and 3% (w/v) chitosan solutions as a function of their viscosity, usually not processed by employing the conventional nebulizer. The results of the chitosan molecular characterization using the SEC-MALS analysis revealed that ultrasonic atomization caused a certain depolymerization, probably due to the main chain scission of the 1,4-glycosidic bond; however, Fourier transform-infrared spectroscopy revealed the absence of other chemical modifications. The ultrasonic atomization allowed preparation of TPP cross-linked chitosan microparticles mostly ranging between 50 and 200 mum. As regards manufacturing parameters, the linking time and washing medium were found to affect the properties of the microparticles, while the stirring rate of the TPP solution did not show any influence. The evaluation of the formulation variables revealed that chitosan concentration strongly affected both the feasibility of the ultrasonic atomization and the drug release. All the microparticles showed an encapsulation efficiency of > 50 % and, after an initial burst effect, a controlled release of drug for 48 h. In conclusion, the ultrasonic atomization could be proposed as a robust and innovative single-step procedure with scale-up potential to successfully prepare ionically cross-linked chitosan microparticles.

  19. Preparation of novel ferrocene-based shell cross-linked thermoresponsive hybrid micelles with antitumor efficacy.

    Science.gov (United States)

    Wei, Hua; Quan, Chang-Yun; Chang, Cong; Zhang, Xian-Zheng; Zhuo, Ren-Xi

    2010-04-29

    The shell cross-linked (SCL) thermoresponsive hybrid poly(N-isopropylacrylamide-co-aminoethyl methacrylate)-b-polymethyl methacrylate (P(NIPAAm-co-AMA)-b-PMMA) micelle consisting of a cross-linked thermoresponsive hybrid shell and a hydrophobic core domain was fabricated via a two-step process: micellization of P(NIPAAm-co-AMA)-b-PMMA in aqueous solution followed by cross-linking of the hydrophilic shell layer via the amidation reaction between the amine groups of AMA units and the carboxylic acid functions of 1,1'-ferrocenedicarboxylic acid. The SCL micelle showed reversible dispersion/aggregation in response to the temperature cycles through the lower critical solution temperature (LCST) of the thermoresponsive hybrid shell at around 36 degrees C, observed by turbidity measurements and dynamic light scattering (DLS). Besides the usage as an inorganic difunctional cross-linker, the inorganic ferrocene segment further endowed the SCL hybrid micelle with the antitumor efficacy, namely, the resulting SCL micelle exhibited a remarkable cytotoxic effect for HeLa cells with a very low IC50. The results showed that the SCL hybrid micelle developed in this study could be potentially used as an antitumor agent, which is unique compared to the conventional tumor therapy by using the antitumor drug loaded in the micellar core.

  20. Oegylated and cross-linking carbazole dendrons and dendrimers: Synthesis, characterization, assembly and thin film fabrication

    Science.gov (United States)

    Felipe, Mary Jane Legaspi

    2011-12-01

    Dendrimers and dendrons (fractional dendrimers) are macromolecular structures that have well-defined molecular weights and precise number of functional groups. Tailoring these structures has provided designer molecules that can be used for various applications including drug delivery, sensors, and anti-biofouling surfaces. Overall, this dissertation provides novel protocols for the understanding of molecular design, synthesis, and structure-property relationship of OEGylated and conjugated carbazole dendrons and dendrimers. In this design, the use of oligo(ethylene glycol) (OEG) allows for the fabrication of biocompatible materials and imparts hydrophilicity on the structure while the carbazole functionality allows the cross-linking of these designer molecules. Such fine-tuning of macromolecular structures leading to the fabrication of anti-biofouling thin films, nanostructuring at the air-water interface, and assembly into supramolecular superstructures are considered in this dissertation. Chapter 2 details the synthesis, characterization, and electrochemical cross-linking of OEGylated linear dendrons and "Janus-type" dendrimers. Cross-linking the carbazole moieties enables the deposition of these films on Au, indium tin oxide-coated glass, and doped silicon through cyclic voltammetry and provides films with secondary level of organization imparted by the inter- and intra-molecular interaction among the carbazole units. Chapter 3 describes the fabrication of nonspecific protein adsorption resistant surfaces through electrochemical grafting of three different dendrons on SAM carbazole-coated gold substrates. The predictable shape of each dendron and the ability to cross-link the carbazole units have enabled parametrization of OEG conformation and density on these interfaces. Chapter 4 demonstrates the fundamental architectural requirements for obtaining stable films with OEGylated linear dendron molecules providing a new architectural design of nanostructuring

  1. Thermo-responsive shell cross-linked PMMA-b-P(NIPAAm-co-NAS) micelles for drug delivery.

    Science.gov (United States)

    Chang, Cong; Wei, Hua; Wu, De-Qun; Yang, Bin; Chen, Ni; Cheng, Si-Xue; Zhang, Xian-Zheng; Zhuo, Ren-Xi

    2011-11-28

    Thermo-responsive amphiphilic poly(methyl methacrylate)-b-poly(N-isopropylacrylamide-co-N-acryloxysuccinimide) (PMMA-b-P(NIPAAm-co-NAS)) block copolymer was synthesized by successive RAFT polymerizations. The uncross-linked micelles were facilely prepared by directly dissolving the block copolymer in an aqueous medium, and the shell cross-linked (SCL) micelles were further fabricated by the addition of ethylenediamine as a di-functional cross-linker into the micellar solution. Optical absorption measurements showed that the LCST of uncross-linked and cross-linked micelles was 31.0°C and 40.8°C, respectively. Transmission electron microscopy (TEM) showed that both uncross-linked and cross-linked micelles exhibited well-defined spherical shape in aqueous phase at room temperature, while the SCL micelles were able to retain the spherical shape with relatively smaller dimension even at 40°C due to the cross-linked structure. In vitro drug release study demonstrated a slower and more sustained drug release behavior from the SCL micelles at high temperature as compared with the release profile of uncross-linked micelles, indicating the great potential of SCL micelles developed herein as novel smart carriers for controlled drug release.

  2. X-linked genes and mental functioning

    National Research Council Canada - National Science Library

    Skuse, David H

    2005-01-01

    ... (as indicated by the large number of X-linked mental retardation syndromes). In addition, there is evidence for relatively specific effects of X-linked genes on social-cognition and emotional regulation...

  3. Cross-linked polyethylenimine–tripolyphosphate nanoparticles for gene delivery

    Directory of Open Access Journals (Sweden)

    Huang XZ

    2014-10-01

    Full Text Available Xianzhang Huang,1 Sujing Shen,2 Zhanfeng Zhang,1 Junhua Zhuang1 1Department of Laboratory Science, Second Affiliated Hospital of Guangzhou University of Chinese Medicine, 2Department of Laboratory Science, Guangdong Second Provincial Traditional Chinese Medicine Hospital, Guangzhou, People’s Republic of China Abstract: The high transfection efficiency of polyethylenimine (PEI makes it an attractive potential nonviral genetic vector for gene delivery and therapy. However, the highly positive charge of PEI leads to cytotoxicity and limits its application. To reduce the cytotoxicity of PEI, we prepared anion-enriched nanoparticles that combined PEI with tripolyphosphate (TPP. We then characterized the PEI-TPP nanoparticles in terms of size, zeta potential, and Fourier-transform infrared (FTIR spectra, and assessed their transfection efficiency, cytotoxicity, and ability to resist deoxyribonuclease (DNase I digestion. The cellular uptake of PEI-TPP with phosphorylated internal ribosome entry site–enhanced green fluorescent protein C1 or FAM (fluorouracil, Adriamycin [doxorubicin] and mitomycin-labeled small interfering ribonucleic acids (siRNAs was monitored by fluorescence microscopy and confocal laser microscopy. The efficiency of transfected delivery of plasmid deoxyribonucleic acid (DNA and siRNA in vitro was 1.11- to 4.20-fold higher with the PEI-TPP particles (7.6% cross-linked than with the PEI, at all N:P ratios (nitrogen in PEI to phosphorus in DNA tested. The cell viability of different cell lines was more than 90% at the chosen N:P ratios of PEI-TPP/DNA complexes. Moreover, PEI-TPP nanoparticles resisted digestion by DNase I for more than 2 hours. The time-dependent absorption experiment showed that 7.6% of cross-linked PEI-TPP particles were internalized by 293T cells within 1 hour. In summary, PEI-TPP nanoparticles effectively transfected cells while conferring little or no toxicity, and thus have potential application in gene

  4. Riboflavin-ultraviolet a corneal cross-linking for keratoconus

    Directory of Open Access Journals (Sweden)

    El-Raggal Tamer

    2009-01-01

    Full Text Available Purpose: To evaluate the safety, efficacy of riboflavin-ultraviolet A irradiation (UVA corneal cross-linking and present refractive changes induced by the treatment in cases of keratoconus. Materials and Methods: The study includes 15 eyes of 9 patients with keratoconus with an average keratometric (K reading less than 54 D and minimal corneal thickness greater than 420 microns. The corneal epithelium was removed manually within the central 8.5 mm diameter area and the cornea was soaked with riboflavin eye drops (0.1% in 20% dextran t-500 for 30 minutes followed by exposure to UVA radiation (365 nm, 3 mW/cm 2 for 30 minutes. During the follow-up period, uncorrected visual acuity (UCVA, best spectacle-corrected visual acuity (BSCVA, manifest refraction, slit lamp examination and topographic changes were recorded at the first week, first month, 3 and 6 months. Results: There was statistically significant improvement of UCVA from a preoperative mean of 0.11 ± 0.07 (range 0.05-0.3 to a postoperative mean of 0.15 ± 0.06 (range 0.1-0.3 (P < 0.05. None of the eyes lost lines of preoperative UCVA but 1 eye lost 1 line of preoperative BSCVA. The preoperative mean K of 49.97 ± 2.81 D (range 47.20-51.75 changed to 48.34 ± 2.64 D (range 45.75-50.40. This decrease in K readings was statistically significant (P < 0.05. All eyes developed minimal faint stromal haze that cleared in 14 eyes within 1 month. In only 1 eye, this resulted in a very faint corneal scar. Other sight threatening complications were not encountered in this series. Progression of the original disease was not seen in any of the treated eyes within 6 months of follow-up. Conclusion: Riboflavin-UVA corneal cross-linking is a safe and promising method for keratoconus. Larger studies with longer follow up are recommended.

  5. Thermally Conductive-Silicone Composites with Thermally Reversible Cross-links.

    Science.gov (United States)

    Wertz, J T; Kuczynski, J P; Boday, D J

    2016-06-08

    Thermally conductive-silicone composites that contain thermally reversible cross-links were prepared by blending diene- and dienophile-functionalized polydimethylsiloxane (PDMS) with an aluminum oxide conductive filler. This class of thermally conductive-silicones are useful as thermal interface materials (TIMs) within Information Technology (IT) hardware applications to allow rework of valuable components. The composites were rendered reworkable via retro Diels-Alder cross-links when temperatures were elevated above 130 °C and required little mechanical force to remove, making them advantageous over other TIM materials. Results show high thermal conductivity (0.4 W/m·K) at low filler loadings (45 wt %) compared to other TIM solutions (>45 wt %). Additionally, the adhesion of the material was found to be ∼7 times greater at lower temperatures (25 °C) and ∼2 times greater at higher temperatures (120 °C) than commercially available TIMs.

  6. Mechanical properties and collagen cross-linking of the patellar tendon in old and young men

    DEFF Research Database (Denmark)

    Couppé, C; Hansen, P; Kongsgaard, M

    2009-01-01

    Age-related loss in muscle mass and strength impairs daily life function in the elderly. However, it remains unknown whether tendon properties also deteriorate with age. Cross-linking of collagen molecules provides structural integrity to the tendon fibrils and has been shown to change with age...... in animals but has never been examined in humans in vivo. In this study, we examined the mechanical properties and pyridinoline and pentosidine cross-link and collagen concentrations of the patellar tendon in vivo in old (OM) and young men (YM). Seven OM (67 +/- 3 years, 86 +/- 10 kg) and 10 YM (27 +/- 2...... contractions. Percutaneous tendon biopsies were taken and analyzed for hydroxylysyl pyridinoline (HP), lysyl pyridinoline (LP), pentosidine, and collagen concentrations. We found no significant differences in the dimensions or mechanical properties of the tendon between OM and YM. Collagen concentrations were...

  7. [Use of native and cross-linked collagen membranes for guided tissue and bone regeneration].

    Science.gov (United States)

    Schwarz, Frank; Sager, Martin; Rothamel, Daniel; Herten, Monika; Sculean, Anton; Becker, Jürgen

    2006-01-01

    A material which is used as a barrier for GBR/GTR procedures has to satisfy several physicochemical characteristics such as biocompatibility, tissue integration, barrier function, and dimensional stability. Recently, many investigations reported on the use of products derived from type I and type III porcine or bovine collagen. Collagen membranes are predominantly resorbed by enzymatic activity (protease and collagenase). To decrease resorption, various physical and chemical cross-linking techniques have been used. Although nowadays cross-linking of collagen seems to be a commonly used procedure, its impact on physicochemical properties of the membrane is still unknown. The aim of the present literature review is to evaluate the potential use of different collagen membranes for GBR/GTR procedures.

  8. APP Function and Lipids: A Bidirectional Link.

    Science.gov (United States)

    Grimm, Marcus O W; Mett, Janine; Grimm, Heike S; Hartmann, Tobias

    2017-01-01

    Extracellular neuritic plaques, composed of aggregated amyloid-β (Aβ) peptides, are one of the major histopathological hallmarks of Alzheimer's disease (AD), a progressive, irreversible neurodegenerative disorder and the most common cause of dementia in the elderly. One of the most prominent risk factor for sporadic AD, carrying one or two aberrant copies of the apolipoprotein E (ApoE) ε4 alleles, closely links AD to lipids. Further, several lipid classes and fatty acids have been reported to be changed in the brain of AD-affected individuals. Interestingly, the observed lipid changes in the brain seem not only to be a consequence of the disease but also modulate Aβ generation. In line with these observations, protective lipids being able to decrease Aβ generation and also potential negative lipids in respect to AD were identified. Mechanistically, Aβ peptides are generated by sequential proteolytic processing of the amyloid precursor protein (APP) by β- and γ-secretase. The α-secretase appears to compete with β-secretase for the initial cleavage of APP, preventing Aβ production. All APP-cleaving secretases as well as APP are transmembrane proteins, further illustrating the impact of lipids on Aβ generation. Beside the pathological impact of Aβ, accumulating evidence suggests that Aβ and the APP intracellular domain (AICD) play an important role in regulating lipid homeostasis, either by direct effects or by affecting gene expression or protein stability of enzymes involved in the de novo synthesis of different lipid classes. This review summarizes the current literature addressing the complex bidirectional link between lipids and AD and APP processing including lipid alterations found in AD post mortem brains, lipids that alter APP processing and the physiological functions of Aβ and AICD in the regulation of several lipid metabolism pathways.

  9. Fluorescence imaging of tryptophan and collagen cross-links to evaluate wound closure ex vivo

    Science.gov (United States)

    Wang, Ying; Ortega-Martinez, Antonio; Farinelli, Bill; Anderson, R. R.; Franco, Walfre

    2016-02-01

    Wound size is a key parameter in monitoring healing. Current methods to measure wound size are often subjective, time-consuming and marginally invasive. Recently, we developed a non-invasive, non-contact, fast and simple but robust fluorescence imaging (u-FEI) method to monitor the healing of skin wounds. This method exploits the fluorescence of native molecules to tissue as functional and structural markers. The objective of the present study is to demonstrate the feasibility of using variations in the fluorescence intensity of tryptophan and cross-links of collagen to evaluate proliferation of keratinocyte cells and quantitate size of wound during healing, respectively. Circular dermal wounds were created in ex vivo human skin and cultured in different media. Two serial fluorescence images of tryptophan and collagen cross-links were acquired every two days. Histology and immunohistology were used to validate correlation between fluorescence and epithelialization. Images of collagen cross-links show fluorescence of the exposed dermis and, hence, are a measure of wound area. Images of tryptophan show higher fluorescence intensity of proliferating keratinocytes forming new epithelium, as compared to surrounding keratinocytes not involved in epithelialization. These images are complementary since collagen cross-links report on structure while tryptophan reports on function. HE and immunohistology show that tryptophan fluorescence correlates with newly formed epidermis. We have established a fluorescence imaging method for studying epithelialization processes during wound healing in a skin organ culture model, our approach has the potential to provide a non-invasive, non-contact, quick, objective and direct method for quantitative measurements in wound healing in vivo.

  10. Energy harvesting from vibration with cross-linked polypropylene piezoelectrets

    Directory of Open Access Journals (Sweden)

    Xiaoqing Zhang

    2015-07-01

    Full Text Available Piezoelectret films are prepared by modification of the microstructure of polypropylene foam sheets cross-linked by electronic irradiation (IXPP, followed by proper corona charging. Young’s modulus, relative permittivity, and electromechanical coupling coefficient of the fabricated films, determined by dielectric resonance spectra, are about 0.7 MPa, 1.6, and 0.08, respectively. Dynamic piezoelectric d33 coefficients up to 650 pC/N at 200 Hz are achieved. The figure of merit (FOM, d33 ⋅ g33 for a more typical d33 value of 400 pC/N is about 11.2 GPa−1. Vibration-based energy harvesting with one-layer and two-layer stacks of these films is investigated at various frequencies and load resistances. At an optimum load resistance of 9 MΩ and a resonance frequency of 800 Hz, a maximum output power of 120 μW, referred to the acceleration g due to gravity, is obtained for an energy harvester consisting of a one-layer IXPP film with an area of 3.14 cm2 and a seismic mass of 33.7 g. The output power can be further improved by using two-layer stacks of IXPP films in electric series. IXPP energy harvesters could be used to energize low-power electronic devices, such as wireless sensors and LED lights.

  11. Cross-linking da cornea: protocolo padrão

    Directory of Open Access Journals (Sweden)

    Marcony R. Santhiago

    Full Text Available RESUMO O objetivo desta revisão é de determinar as indicações e eficácia da cirurgia que promove novas ligações covalentes entre as fibras de colágeno da córnea, conhecida como Cross-Linking (CXL, assim como esclarecer seus objetivos. O ceratocone é uma doença ectasica da córnea, bilateral, assimétrica, que, principalmente, cursa com encurvamento e afinamentos progressivo, e se inicia em geral na segunda década de vida. O uso primário do CXL tem sido na interrupção da progressão do Ceratocone. Apesar do conhecido encurvamento no estroma da córnea ocorrer nesses pacientes, a fisiopatologia por trás do ceratocone ainda é desconhecida e parece ser multifatorial. Pela evidencia literária disponível até o momento, o CXL da córnea esta, portanto indicado nos pacientes com doença em progressão. Concluímos que existe evidencia suficiente para afirmar que o CXL da córnea é eficaz na estabilização da doença ectásica da cornea.

  12. Cross-linking of polytetrafluoroethylene during room-temperature irradiation

    Energy Technology Data Exchange (ETDEWEB)

    Pugmire, David L [Los Alamos National Laboratory; Wetteland, Chris J [Los Alamos National Laboratory; Duncan, Wanda S [Los Alamos National Laboratory; Lakis, Rollin E [Los Alamos National Laboratory; Schwartz, Daniel S [Los Alamos National Laboratory

    2008-01-01

    Exposure of polytetrafluoroethylene (PTFE) to {alpha}-radiation was investigated to detennine the physical and chemical effects, as well as to compare and contrast the damage mechanisms with other radiation types ({beta}, {gamma}, or thermal neutron). A number of techniques were used to investigate the chemical and physical changes in PTFE after exposure to {alpha}-radiation. These techniques include: Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and fluorescence spectroscopy. Similar to other radiation types at low doses, the primary damage mechanism for the exposure of PTFE to {alpha}-radiation appears to be chain scission. Increased doses result in a change-over of the damage mechanism to cross-linking. This result is not observed for any radiation type other than {alpha} when irradiation is performed at room temperature. Finally, at high doses, PTFE undergoes mass-loss (via smallfluorocarbon species evolution) and defluorination. The amount and type of damage versus sample depth was also investigated. Other types of radiation yield damage at depths on the order of mm to cm into PTFE due to low linear energy transfer (LET) and the correspondingly large penetration depths. By contrast, the {alpha}-radiation employed in this study was shown to only induce damage to a depth of approximately 26 {mu}m, except at very high doses.

  13. Synthesis and Properties of Cross-Linked Polyamide Aerogels

    Science.gov (United States)

    Williams, Jarrod C.; Meador, Mary Ann; McCorkle, Linda

    2015-01-01

    We report the first synthesis of cross-linked polyamide aerogels through step growth polymerization using a combination of diamines, diacid chloride and triacid chloride. Polyamide oligomers endcapped with amines are prepared as stable solutions in N-methylpyrrolidinone from several different diamine precursors and 1,3-benzenedicarbonyl dichloride. Addition of 1,3,5-benzenetricarbonyl trichloride yields gels which form in under five minutes according to the scheme shown. Solvent exchange of the gels into ethanol, followed by drying using supercritical CO2 extraction gives colorless aerogels with densities around 0.1 to 0.2 gcm3. Thicker monolithes of the polyamide aerogels are stiff and strong, while thin films of certain formulations are highly flexible, durable, and even translucent. These materials may have use as insulation for deployable space structures, rovers, habitats or extravehicular activity suits as well as in many terrestrial applications. Strucure property relationships of the aerogels, including surface area, mechanical properties, and thermal conductivity will be discussed.

  14. Energy harvesting from vibration with cross-linked polypropylene piezoelectrets

    Science.gov (United States)

    Zhang, Xiaoqing; Wu, Liming; Sessler, Gerhard M.

    2015-07-01

    Piezoelectret films are prepared by modification of the microstructure of polypropylene foam sheets cross-linked by electronic irradiation (IXPP), followed by proper corona charging. Young's modulus, relative permittivity, and electromechanical coupling coefficient of the fabricated films, determined by dielectric resonance spectra, are about 0.7 MPa, 1.6, and 0.08, respectively. Dynamic piezoelectric d33 coefficients up to 650 pC/N at 200 Hz are achieved. The figure of merit (FOM, d33 ṡ g33) for a more typical d33 value of 400 pC/N is about 11.2 GPa-1. Vibration-based energy harvesting with one-layer and two-layer stacks of these films is investigated at various frequencies and load resistances. At an optimum load resistance of 9 MΩ and a resonance frequency of 800 Hz, a maximum output power of 120 μW, referred to the acceleration g due to gravity, is obtained for an energy harvester consisting of a one-layer IXPP film with an area of 3.14 cm2 and a seismic mass of 33.7 g. The output power can be further improved by using two-layer stacks of IXPP films in electric series. IXPP energy harvesters could be used to energize low-power electronic devices, such as wireless sensors and LED lights.

  15. Energy harvesting from vibration with cross-linked polypropylene piezoelectrets

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Xiaoqing [Shanghai Key Laboratory of Special Artificial Microstructure Materials and Technology & School of Physics Science and Engineering, Tongji University, Shanghai 200092 (China); Institute for Telecommunications Technology, Merckstrasse 25, 64283 Darmstadt (Germany); Wu, Liming [Shanghai Key Laboratory of Special Artificial Microstructure Materials and Technology & School of Physics Science and Engineering, Tongji University, Shanghai 200092 (China); Sessler, Gerhard M., E-mail: g.sessler@nt.tu-darmstadt.de [Institute for Telecommunications Technology, Merckstrasse 25, 64283 Darmstadt (Germany)

    2015-07-15

    Piezoelectret films are prepared by modification of the microstructure of polypropylene foam sheets cross-linked by electronic irradiation (IXPP), followed by proper corona charging. Young’s modulus, relative permittivity, and electromechanical coupling coefficient of the fabricated films, determined by dielectric resonance spectra, are about 0.7 MPa, 1.6, and 0.08, respectively. Dynamic piezoelectric d{sub 33} coefficients up to 650 pC/N at 200 Hz are achieved. The figure of merit (FOM, d{sub 33} ⋅ g{sub 33}) for a more typical d{sub 33} value of 400 pC/N is about 11.2 GPa{sup −1}. Vibration-based energy harvesting with one-layer and two-layer stacks of these films is investigated at various frequencies and load resistances. At an optimum load resistance of 9 MΩ and a resonance frequency of 800 Hz, a maximum output power of 120 μW, referred to the acceleration g due to gravity, is obtained for an energy harvester consisting of a one-layer IXPP film with an area of 3.14 cm{sup 2} and a seismic mass of 33.7 g. The output power can be further improved by using two-layer stacks of IXPP films in electric series. IXPP energy harvesters could be used to energize low-power electronic devices, such as wireless sensors and LED lights.

  16. Subclinical inflammatory response after accelerated corneal cross-linking

    Institute of Scientific and Technical Information of China (English)

    Hassan Hashemi; Nahid Ashraf; Ebrahim Jafarzadehpur; Alireza Hedayatfar; Soheila Asgari

    2016-01-01

    Background: To evaluate the inlfammatory response after accelerated collagen cross-linking (CXL) in eyes with keratoconus. Methods: Consecutive eyes with keratoconus undergoing CXL surgery were included in this non-randomized interventional study. Aqueous lfare was measured pre- and post-operatively with a laser lfare photometer at 1 week, 1, 3 and 6 months after CXL. Results: Sixty eyes of 60 patients were entered into the study. Before CXL, the mean lfare value was 4.5 photons per millisecond (ph/ms). The lfare values observed at week 1 (7.1 ph/ms; P=0.008), month 1 (6.5 ph/ms; P=0.04), month 3 (6.7 ph/ms; P=0.004) and month 6 (6.7 ph/ms; P=0.004) were signiifcantly higher compared to baseline. Flare values were not signiifcantly different from week 1 up to 6 months after CXL (P=0.930). No statistically significant correlation was detected between the amount of inlfammation and keratometric indices. Conclusions: Accelerated CXL in patients with keratoconus may cause a subclinical inflammatory response which is evident as slight but rather long-lasting rise of aqueous lfare.

  17. Pyridinium cross-links in heritable disorders of collagen

    Energy Technology Data Exchange (ETDEWEB)

    Pasquali, M.; Still, M.J.; Dembure, P.P. [Emory Univ., Atlanta, GA (United States)] [and others

    1995-12-01

    Ehlers-Danlos syndrome (EDS) is a heterogeneous group of inherited disorders of collagen that is characterized by skin fragility, skin hyperextensibility, and joint hypermobility. EDS type VI is caused by impaired collagen lysyl hydroxylase (procollagen-lysine, 2-oxoglutarate 5-dioxygenase; E.C.1.14.11.4), the ascorbate-dependent enzyme that hydroxylates lysyl residues on collagen neopeptides. Different alterations in the gene for collagen lysyl hydroxylase have been reported in families with EDS type VI. In EDS type VI, impairment of collagen lysyl hydroxylase results in a low hydroxylysine content in mature collagen. Hydroxylysine is a precursor of the stable, covalent, intermolecular cross-links of collagen, pyridinoline (Pyr), and deoxypyridinoline (Dpyr). Elsewhere we reported in preliminary form that patients with EDS type VI had a distinctive alteration in the urinary excretion of Pyr and Dpyr. In the present study, we confirm that the increased Dpyr/Pyr ratio is specific for EDS type VI and is not observed in other inherited or acquired collagen disorders. In addition, we find that skin from patients with EDS type VI has reduced Pyr and increased Dpyr, which could account for the organ pathology. 19 refs., 1 tab.

  18. Analysis of protein-nucleic acid interactions by photochemical cross-linking and mass spectrometry

    DEFF Research Database (Denmark)

    Steen, Hanno; Jensen, Ole Nørregaard

    2002-01-01

    Photochemical cross-linking is a commonly used method for studying the molecular details of protein-nucleic acid interactions. Photochemical cross-linking aids in defining nucleic acid binding sites of proteins via subsequent identification of cross-linked protein domains and amino acid residues....... Mass spectrometry (MS) has emerged as a sensitive and efficient analytical technique for determination of such cross-linking sites in proteins. The present review of the field describes a number of MS-based approaches for the characterization of cross-linked protein-nucleic acid complexes...... and for sequencing of peptide-nucleic acid heteroconjugates. The combination of photochemical cross-linking and MS provides a fast screening method to gain insights into the overall structure and formation of protein-oligonucleotide complexes. Because the analytical methods are continuously refined and protein...

  19. Characterization of the deoxyguanosine-lysine cross-link of methylglyoxal.

    Science.gov (United States)

    Petrova, Katya V; Millsap, Amy D; Stec, Donald F; Rizzo, Carmelo J

    2014-06-16

    Methylglyoxal is a mutagenic bis-electrophile that is produced endogenously from carbohydrate precursors. Methylglyoxal has been reported to induce DNA-protein cross-links (DPCs) in vitro and in cultured cells. Previous work suggests that these cross-links are formed between guanine and either lysine or cysteine side chains. However, the chemical nature of the methylglyoxal induced DPC have not been determined. We have examined the reaction of methylglyoxal, deoxyguanosine (dGuo), and Nα-acetyllysine (AcLys) and determined the structure of the cross-link to be the N2-ethyl-1-carboxamide with the lysine side chain amino group (1). The cross-link was identified by mass spectrometry and the structure confirmed by comparison to a synthetic sample. Further, the cross-link between methylglyoxal, dGuo, and a peptide (AcAVAGKAGAR) was also characterized. The mechanism of cross-link formation is likely to involve an Amadori rearrangement.

  20. Fabrication of patterned calcium cross-linked alginate hydrogel films and coatings through reductive cation exchange.

    Science.gov (United States)

    Bruchet, Marion; Melman, Artem

    2015-10-20

    Calcium cross-linked alginate hydrogels are widely used in targeted drug delivery, tissue engineering, wound treatment, and other biomedical applications. We developed a method for preparing homogeneous alginate hydrogels cross-linked with Ca(2+) cations using reductive cation exchange in homogeneous iron(III) cross-linked alginate hydrogels. Treatment of iron(III) cross-linked alginate hydrogels with calcium salts and sodium ascorbate results in reduction of iron(III) cations to iron(II) that are instantaneously replaced with Ca(2+) cations, producing homogeneous ionically cross-linking hydrogels. Alternatively, the cation exchange can be performed by photochemical reduction in the presence of calcium chloride using a sacrificial photoreductant. This approach allows fabrication of patterned calcium alginate hydrogels through photochemical patterning of iron(III) cross-linked alginate hydrogel followed by the photochemical reductive exchange of iron cations to calcium.

  1. ROLE OF CORNEAL COLLAGEN CROSS LINKING IN KERATOCONUS

    Directory of Open Access Journals (Sweden)

    Atul

    2015-09-01

    Full Text Available To evaluate the outcome of collagen cross linkage using riboflavin 0.1% and ultraviolet A radiation of a wavelength 370nm . PURPOSE : To determine the effect of collagen cross linking for keratoconus on pachymetry , corneal topography, uncorrected visual acuity, specular count, IOP at 1, 3, 6 months . METHODS : The current study was designed as a prospective interventional trial of corneal collagen cross - linking in subjects with progressive keratoconus between a period of J anuary 2013 to J uly 2014 including 50 eyes of 30 patients. This study rece ived approval from Ethics committee. Informed written consent was obtained from all patients prior to treatment. RESULTS: Mean follow up period of 6 months. There was statistically significant decline in effective k readings from mean pre op (51.7D to pos t op value (49.65D . Pachymetry showed initial increase post operatively followed by reduction in corneal thickness in 3 month s follow up , followed by gradual increase in thickness over a period of 6 months though it was not equivalent to pre - operative values. paired t test p value was 0.00 1 in 1 n 3 month and 0. 043 in 6 month, concluding significant reduction in early post op period with im provement over time . Specular count reduced from pre - op (2673.80 levels to post - op (2654.60 levels ,the reduction in specular count was not statistically significant P value (0.014 The uncorrected visual acuity showed decrease in refractive error with in crease in visual acuity gradually over 6 months, log MAR scale visual acuity was used for statistical analysis with P value (0.001 which was statistically significant .visual acuity improved by 1.5 lines in snellens equivalence or from 0.5 to 0.4 in log MA R char y ± 20cells/mm 3 , P value(0. 001 . IOP statically show ed no significant change in pre - operative and post operatively , paired t test p value was 0. 44 showing it was not significant . CONCLUSIONS : 1. Visual acuity improved in

  2. Effect of the cross-linking silane concentration in a novel silane system on bonding resin-composite cement

    NARCIS (Netherlands)

    Matinlinna, Jukka; Ozcan, Mutlu; Lassila, Lippo; Kalk, Warner; Vallittu, Pekka

    2008-01-01

    Objective. Four experimental blends of an organo-functional silane monomer with a non-functional cross-linking silane monomer (a novel silane system) were evaluated as adhesion promoters in an experiment in which a resin-composite cement was bonded to silica-coated titanium. Material and Methods. 3-

  3. Radiation cross-linking in ultra-high molecular weight polyethylene for orthopaedic applications

    OpenAIRE

    Oral, Ebru; Muratoglu, Orhun K.

    2007-01-01

    The motivation for radiation cross-linking of ultra-high molecular weight polyethylene (UHMWPE) is to increase its wear resistance to be used as bearing surfaces for total joint arthroplasty. However, radiation also leaves behind long-lived residual free radicals in this polymer, the reactions of which can detrimentally affect mechanical properties. In this review, we focus on the radiation cross-linking and oxidative stability of first and second generation highly cross-linked UHMWPEs develo...

  4. Quantitative assessment of fibrinogen cross-linking by epsilon aminocaproic acid in patients with end-stage liver disease.

    Science.gov (United States)

    Quach, Thien; Tippens, Melissa; Szlam, Fania; Van Dyke, Rebecca; Levy, Jerrold H; Csete, Marie

    2004-01-01

    Analysis of the effectiveness of antifibrinolytic therapy for liver transplant recipients is hampered by lack of quantitative assays for assessing drug effects. We adapted chemical engineering tools used in polymerization studies to quantify fibrinogen cross-linking by plasma from liver transplant patients obtained before and after epsilon aminocaproic acid (EACA) therapy. A target fluorescein isothiocyanate-fibrinogen (FITC-fibrinogen) molecule was constructed; it fluoresces in a quantifiable pattern when in solution, and undergoes cross-linking in the presence of plasmin inhibitors. Cross-linking quenches the fluorescent signal, and the quenching is a quantifiable endpoint. Thus fluorescence from this reporter molecule can be used to assess functional improvement in fibrinogen cross-linking as a result of antifibrinolytic therapies, and it is sensitive to picomolar amounts of plasmin inhibitors and activators. Cross-linking of FITC-fibrinogen by patient plasma, before and after EACA therapy, was assessed using fluorescence spectrometry. Fluorescence patterns from FITC-fibrinogen indicated no significant cross-linking of the target fibrinogen as a consequence of EACA in posttreatment plasma. When the fibrinogen-FITC target was assayed without plasma in the presence of EACA at concentrations that bracket therapeutic levels (100 and 400 microg/ml), significant fluorescence quenching (target FITC-fibrinogen cross-linking) was achieved. These results suggest that fibrinogen-FITC fluorescence is sensitive enough to detect EACA activity in clinically relevant ranges, but that EACA given in usual doses is insufficient to promote fibrinogen cross-linking in patients with end-stage liver disease.

  5. Parenting Stress and Dimensions of Parenting Behavior : Cross-Sectional and Longitudinal Links with Adolescents' Somatization

    NARCIS (Netherlands)

    Rousseau, Sofie; Grietens, Hans; Vanderfaeillie, Johan; Hoppenbrouwers, Karel; Wiersema, Jan Roelf; Van Leeuwen, Karla

    2013-01-01

    Objective: This study explored direct and indirect associations between adolescents' somatization, parenting stress, and three parenting dimensions (warmth, psychological control, and harsh punishment). First, the associations were explored cross-sectionally. Second, significant cross-sectional link

  6. Fluorescent and cross-linked organic-inorganic hybrid nanoshells for monitoring drug delivery.

    Science.gov (United States)

    Sun, Lijuan; Liu, Tianhui; Li, Hua; Yang, Liang; Meng, Lingjie; Lu, Qinghua; Long, Jiangang

    2015-03-04

    Functionalized and monodisperse nanoshells have attracted significant attention owing to their well-defined structure, unique properties, and wide range of potential applications. Here, the synthesis of cross-linked organic-inorganic hybrid nanoshells with strong fluorescence properties was reported via a facile precipitation polymerization of hexachlorocyclotriphosphazene (HCCP) and fluorescein on silica particles used as templates. The resulting poly(cyclotriphosphazene-co-fluorescein) (PCTPF) nanoshells were firm cross-linked shells with ∼2.2 nm mesopores that facilitated the transport of drug molecules. The fluorescent nanoshells also exhibited excellent water dispersibility and biocompatibility; thus, they can be considered as ideal drug vehicles with high doxorubicin storage capacity (26.2 wt %) and excellent sustained release (up to 14 days). Compared to doxorubicin (DOX) alone, the PCTPF nanoshells more efficiently delivered DOX into and killed cancer cells. Moreover, the PCTPF nanoshells also exhibited remarkable fluorescent emission properties and improved photobleaching stability in both suspension and solid state owing to the covalent immobilization of fluorescein in the highly cross-linked organic-inorganic hybrids. The exceptional fluorescent properties enabled the release of DOX as well as the distribution of nanoshells and DOX to be monitored.

  7. Synthesis of cross-linked carbon nanotube mats and their applications

    Science.gov (United States)

    Ventura, Darryl N.

    2011-12-01

    Carbon nanotubes (CNTs) possess excellent tensile strength and electron transport properties that make them a promising component in future materials and technologies. The covalent cross-linking of carbon nanotubes is one avenue of producing thin, flexible mats that can be used in a variety of applications. Here we describe the cross-linking of functionalized CNTs through the Michael addition and imine formation reaction schemes. Our method of cross-linking is an improvement over traditional techniques such as laser irradiation because it is not detrimental to the nanotube structure. Our method also does not rely on weak van der Waals interactions that are sometimes used in the synthesis of nanotube mats. Furthermore, our filtration-from-suspension procedure can be readily scaled up for industrial use and does not require high pressure or high temperature reaction chambers. Such CNT-based composites can be used in a wide variety of applications. We demonstrate their use in a hydrogen sensor and a dye-sensitized solar cell.

  8. Optimizing performance in cross-linking negative-tone molecular resists

    Science.gov (United States)

    Lawson, Richard A.; Narcross, Hannah; Sharp, Brandon; Chun, Jun Sung; Neisser, Mark; Tolbert, Laren M.; Henderson, Clifford L.

    2015-03-01

    Many different types of non-traditional resist designs have shown promise for future generations of patterning, but there is a greater need for understanding and developing additives and ancillary materials for these novel resists compared to traditional polymeric positive tone systems which are quite mature. With the goal of meeting some of these needs, we carried out multiple different studies of negative tone molecular resists based on epoxide cross-linking. We have developed methods for controlling cross-linking in these materials using photo-decomposable nucleophiles (PDNs) which have shown resolution improvements in one resist from 26 nm down to 18 nm so far. Aqueous base developed systems have been made by introducing phenol groups to these resists. Although the first molecule designed successfully patterns in aqueous base, its performance is limited compared to organic solvent development. A series of di-functional epoxide molecular resists have been made and generally show much worse sensitivity than a fourfunctional epoxide resist. Underlayers (ULs) have been designed specifically to leverage the high reactivity of epoxides to create ULs that can cross-link to the resist. These ULs improve the adhesion of some of these molecular resists, but also show significant sensitivity improvements compared to imaging on bare silicon. Sensitivity in one resist was improved by 5-12 mJ/cm2 simply by using the UL.

  9. Fracture mechanics of collagen fibrils: influence of natural cross-links.

    Science.gov (United States)

    Svensson, Rene B; Mulder, Hindrik; Kovanen, Vuokko; Magnusson, S Peter

    2013-06-04

    Tendons are important load-bearing structures, which are frequently injured in both sports and work. Type I collagen fibrils are the primary components of tendons and carry most of the mechanical loads experienced by the tissue, however, knowledge of how load is transmitted between and within fibrils is limited. The presence of covalent enzymatic cross-links between collagen molecules is an important factor that has been shown to influence mechanical behavior of the tendons. To improve our understanding of how molecular bonds translate into tendon mechanics, we used an atomic force microscopy technique to measure the mechanical behavior of individual collagen fibrils loaded to failure. Fibrils from human patellar tendons, rat-tail tendons (RTTs), NaBH₄ reduced RTTs, and tail tendons of Zucker diabetic fat rats were tested. We found a characteristic three-phase stress-strain behavior in the human collagen fibrils. There was an initial rise in modulus followed by a plateau with reduced modulus, which was finally followed by an even greater increase in stress and modulus before failure. The RTTs also displayed the initial increase and plateau phase, but the third region was virtually absent and the plateau continued until failure. The importance of cross-link lability was investigated by NaBH₄ reduction of the rat-tail fibrils, which did not alter their behavior. These findings shed light on the function of cross-links at the fibril level, but further studies will be required to establish the underlying mechanisms.

  10. Effects of polymerization on the oxygen carrying and redox properties of diaspirin cross-linked hemoglobin.

    Science.gov (United States)

    Rogers, M S; Ryan, B B; Cashon, R E; Alayash, A I

    1995-04-27

    Human hemoglobin site specifically cross-linked with bis(3,5-dibromosalicyl)fumarate results in a low oxygen affinity hemoglobin-based red cell substitute (alpha-DBBF). Polymerization of alpha-DBBF by bis(maleoylglycylamide) polyethylene glycol (BMAA-PEG) yields poly alpha-DBBF which offers the added benefits of reduced renal clearance and increased retention in the vascular circulation. Oxygen equilibrium curves for poly alpha-DBBF are slightly left-shifted (higher O2 affinity) compared to those of alpha-DBBF; with a diminished cooperativity and a reduced Bohr effect. In rapid mixing experiments (oxygen dissociation and carbon monoxide binding), poly alpha-DBBF exhibits a several fold increase in the overall rate of deoxygenation and carbon monoxide binding kinetics over its cross-linked counterpart. The rate of nitric oxide binding to the oxidized form of poly alpha-DBBF shows little or no change compared to the intramolecularly cross-linked derivative. The reduction of cyanomet poly alpha-DBBF by dithionite is several fold faster than that of HbA0 and alpha-DBBF whereas the slow subsequent cyanide dissociation from the ferrous iron remained unchanged among all proteins. The propensity of poly alpha-DBBF for auto-oxidation is slightly enhanced over alpha-DBBF whereas the extent of oxidative modification by hydrogen peroxide is very similar. Polymerization appears to selectively modify ligand interactions and redox kinetics of the tetrameric cross-linked form which reflects a possibly more open heme pocket. The data suggests that changes in oxygenation properties of hemoglobin brought about by a given modification are not necessarily predictive of other functional changes.

  11. A copper-hydrogen peroxide redox system induces dityrosine cross-links and chemokine oligomerisation.

    Science.gov (United States)

    MacGregor, Helen J; Kato, Yoji; Marshall, Lindsay J; Nevell, Thomas G; Shute, Janis K

    2011-12-01

    The activity of the chemoattractant cytokines, the chemokines, in vivo is enhanced by oligomerisation and aggregation on glycosaminoglycan (GAG), particularly heparan sulphate, side chains of proteoglycans. The chemokine RANTES (CCL5) is a T-lymphocyte and monocyte chemoattractant, which has a minimum tetrameric structure for in vivo activity and a propensity to form higher order oligomers. RANTES is unusual among the chemokines in having five tyrosine residues, an amino acid susceptible to oxidative cross-linking. Using fluorescence emission spectroscopy, Western blot analysis and LCMS-MS, we show that a copper/H2O2 redox system induces the formation of covalent dityrosine cross-links and RANTES oligomerisation with the formation of tetramers, as well as higher order oligomers. Amongst the transition metals tested, namely copper, nickel, mercury, iron and zinc, copper appeared unique in this respect. At high (400 μM) concentrations of H2O2, RANTES monomers, dimers and oligomers are destroyed, but heparan sulphate protects the chemokine from oxidative damage, promoting dityrosine cross-links and multimer formation under oxidative conditions. Low levels of dityrosine cross-links were detected in copper/H2O2-treated IL-8 (CXCL8), which has one tyrosine residue, and none were detected in ENA-78 (CXCL5), which has none. Redox-treated RANTES was fully functional in Boyden chamber assays of T-cell migration and receptor usage on activated T-cells following RANTES oligomerisation was not altered. Our results point to a protective, anti-oxidant, role for heparan sulphate and a previously unrecognised role for copper in chemokine oligomerisation that may offer an explanation for the known anti-inflammatory effect of copper-chelators such as penicillamine and tobramycin.

  12. Development of casein microgels from cross-linking of casein micelles by genipin.

    Science.gov (United States)

    Silva, Naaman F Nogueira; Saint-Jalmes, Arnaud; de Carvalho, Antônio F; Gaucheron, Frédéric

    2014-09-02

    Casein micelles are porous colloidal particles, constituted of casein molecules, water, and minerals. The vulnerability of the supramolecular structure of casein micelles face to changes in the environmental conditions restrains their applications in other domains besides food. Thus, redesigning casein micelles is a challenge to create new functionalities for these biosourced particles. The objective of this work was to create stable casein microgels from casein micelles using a natural cross-linker, named genipin. Suspensions of purified casein micelles (25 g L(-1)) were mixed with genipin solutions to have final concentrations of 5, 10, and 20 mM genipin. Covalently linked casein microgels were formed via cross-linking of lysyl and arginyl residues of casein molecules. The reacted products exhibited blue color. The cross-linking reaction induced gradual changes on the colloidal properties of the particles. The casein microgels were smaller and more negatively charged and presented smoother surfaces than casein micelles. These results were explained based on the cross-linking of free NH2 present in an external layer of κ-casein. Light scattering and rheological measurements showed that the reaction between genipin and casein molecules was intramicellar, as one single population of particles was observed and the values of viscosity (and, consequently, the volume fraction of the particles) were reduced. Contrary to the casein micelles, the casein microgels were resistant to the presence of dissociating agents, e.g., citrate (calcium chelating) and urea, but swelled as a consequence of internal electrostatic repulsion and the disruption of hydrophobic interactions between protein chains. The casein microgels did not dissociate at the air-solution interface and formed solid-like interfaces rather than a viscoelastic gel. The potential use of casein microgels as adaptable nanocarriers is proposed in the article.

  13. Alkaline battery containing a separator of a cross-linked copolymer of vinyl alcohol and unsaturated carboxylic acid

    Science.gov (United States)

    Hsu, L. C.; Philipp, W. H.; Sheibley, D. W.; Gonzalez-Sanabria, O. D. (Inventor)

    1985-01-01

    A battery separator for an alkaline battery is described. The separator comprises a cross linked copolymer of vinyl alcohol units and unsaturated carboxylic acid units. The cross linked copolymer is insoluble in water, has excellent zincate diffusion and oxygen gas barrier properties and a low electrical resistivity. Cross linking with a polyaldehyde cross linking agent is preferred.

  14. Encapsulation of volatiles by homogenized partially-cross linked alginates.

    Science.gov (United States)

    Inguva, Pavan K; Ooi, Shing Ming; Desai, Parind M; Heng, Paul W S

    2015-12-30

    Cross-linked calcium alginate gels are too viscous to be efficaciously incorporated into spray dried formulations. Thus, viscosity reduction is essential to ensure the processability of calcium alginate gels to be sprayed. Viscosity reduction by high pressure homogenization can open new formulation possibilities. Presently, testing of microcapsule integrity is also limited because either single particle tests neglect collective particle behaviours in bulk or bulk testing methods are often associated with single compressions which may not fully characterize individual particle strengths. The aim of this study was sub-divided into three objectives. First objective was to evaluate the impact of high pressure homogenization on gel viscosity. Second objective was to explore the use of the homogenized gels with modified starch for microencapsulation by spray drying. The final objective was to develop a stamping system as microcapsule strength tester that can assess microcapsules in bulk and evaluate the impact of multiple compressions. Collectively, this study would lead towards developing a pressure-activated patch of microcapsules with encapsulated volatiles and the method to assess the patch efficacy. The alginate gels largely experienced an exponential decay in viscosity when homogenized. Furthermore, the homogenized gels were successfully incorporated in spray drying formulations for microencapsulation. The custom-designed microcapsule strength tester was successfully used and shown to possess the required sensitivity to discern batches of microcapsules containing volatiles to have different release profiles. Addition of homogenized gels strengthened the microcapsules only at high wall to core ratios with low mass-load alginate gels. High mass-load gels weaken the microcapsules, exhibiting a higher release at low stamping pressures and wrinkling on the microcapsules surface.

  15. The theory and art of corneal cross-linking

    Directory of Open Access Journals (Sweden)

    Rebecca McQuaid

    2013-01-01

    Full Text Available Before the discovery of corneal cross-linking (CXL, patients with keratoconus would have had to undergo corneal transplantation, or wear rigid gas permeable lenses (RGPs that would temporarily flatten the cone, thereby improving the vision. The RGP contact lens (CL would not however alter the corneal stability and if the keratoconus was progressive, the continued steepening of the cone would occur under the RGP CL. To date, the Siena Eye has been the largest study to investigate long term effects of standard CXL. Three hundred and sixty-three eyes were treated and monitored over 4 years, producing reliable long-term results proving long-term stability of the cornea by halting the progression of keratoconus, and proving the safety of the procedure. Traditionally, CXL requires epithelial removal prior to corneal soakage of a dextran-based 0.1% riboflavin solution, followed by exposure of ultraviolet-A (UV-A light for 30 min with an intensity of 3 mW/cm2. A series of in vitro investigations on human and porcine corneas examined the best treatment parameters for standard CXL, such as riboflavin concentration, intensity, wavelength of UV-A light, and duration of treatment. Photochemically, CXL is achieved by the generation of chemical bonds within the corneal stroma through localized photopolymerization, strengthening the cornea whilst minimizing exposure to the surrounding structures of the eye. In vitro studies have shown that CXL has an effect on the biomechanical properties of the cornea, with an increased corneal rigidity of approximately 70%. This is a result of the creation of new chemical bonds within the stroma.

  16. Transglutaminases: widespread cross-linking enzymes in plants.

    Science.gov (United States)

    Serafini-Fracassini, Donatella; Del Duca, Stefano

    2008-08-01

    Transglutaminases have been studied in plants since 1987 in investigations aimed at interpreting some of the molecular mechanisms by which polyamines affect growth and differentiation. Transglutaminases are a widely distributed enzyme family catalysing a myriad of biological reactions in animals. In plants, the post-translational modification of proteins by polyamines forming inter- or intra-molecular cross-links has been the main transglutaminase reaction studied. The few plant transglutaminases sequenced so far have little sequence homology with the best-known animal enzymes, except for the catalytic triad; however, they share a possible structural homology. Proofs of their catalytic activity are: (a) their ability to produce glutamyl-polyamine derivatives; (b) their recognition by animal transglutaminase antibodies; and (c) biochemical features such as calcium-dependency, etc. However, many of their fundamental biochemical and physiological properties still remain elusive. It has been detected in algae and in angiosperms in different organs and sub-cellular compartments, chloroplasts being the best-studied organelles. Possible roles concern the structural modification of specific protein substrates. In chloroplasts, transglutaminases appear to stabilize the photosynthetic complexes and Rubisco, being regulated by light and other factors, and possibly exerting a positive effect on photosynthesis and photo-protection. In the cytosol, they modify cytoskeletal proteins. Preliminary reports suggest an involvement in the cell wall construction/organization. Other roles appear to be related to fertilization, abiotic and biotic stresses, senescence and programmed cell death, including the hypersensitive reaction. The widespread occurrence of transglutaminases activity in all organs and cell compartments studied suggests a relevance for their still incompletely defined physiological roles. At present, it is not possible to classify this enzyme family in plants owing to

  17. Development and characterization of films based on chemically cross-linked gliadins.

    Science.gov (United States)

    Hernández-Muñoz, Pilar; Kanavouras, Antonis; Lagaron, José M; Gavara, Rafael

    2005-10-19

    The aim of the present work has been to study the possibility of obtaining modified gliadin films with improved water resistance and mechanical properties by means of promoting intermolecular covalent bonds between polypeptide chains. Prior to casting films, formaldehyde, glutaraldehyde, and glyoxal were used to cross-link proteins at concentrations ranging from 1% to 4% (grams per 100 g of protein). Mechanical properties (tensile strength and elongation at break), water vapor permeability, moisture sorption isotherms, and optical properties of the films produced were evaluated as a function of the cross-linker used. Experimental results showed that some properties of gliadin films were considerably modified. Cross-linking improved the water resistance of films, avoiding their disintegration. Their water barrier properties were also enhanced, but their moisture sorption properties remained unchanged. Formaldehyde imparted greater mechanical strength to films than glutaraldehyde or glyoxal, increasing tensile strength values 10-fold. Addition of the cross-linkers at concentrations in excess of 2.5% did not further improve the mechanical or barrier properties. However, modification with glutaraldehyde or glyoxal imparted an increasingly yellowish tint to the films.

  18. Effects of Supercritical CO 2 Conditioning on Cross-Linked Polyimide Membranes

    KAUST Repository

    Kratochvil, Adam M.

    2010-05-25

    The effects of supercritical CO2 (scCO2) conditioning on high-performance cross-linked polyimide membranes is examined through gas permeation and sorption experiments. Under supercritical conditions, the cross-linked polymers do not exhibit a structural reorganization of the polymer matrix that was observed in the non-cross-linkable, free acid polymer. Pure gas permeation isotherms and mixed gas permeabilities and selectivities show the cross-linked polymers to be much more stable to scCO2 conditioning than the free acid polymer. In fact, following scCO2 conditioning, the mixed gas CO2 permeabilities of the cross-linked polymers increased while the CO2/CH4 separation factors remained relatively unchanged. This response highlights the stability and high performance of these cross-linked membranes in aggressive environments. In addition, this response reveals the potential for the preconditioning of cross-linked polymer membranes to enhance productivity without sacrificing efficiency in practical applications which, in effect, provides another tool to \\'tune\\' membrane properties for a given separation. Finally, the dual mode model accurately describes the sorption and dilation characteristics of the cross-linked polymers. The changes in the dual mode sorption model parameters before and after the scCO2 exposure also provide insights into the alterations in the different glassy samples due to the cross-linking and scCO2 exposure. © 2010 American Chemical Society.

  19. Investigation of cross-linking characteristics of novel hole-transporting materials for solution-processed phosphorescent OLEDs

    Science.gov (United States)

    Lee, Jaemin; Ameen, Shahid; Lee, Changjin

    2016-04-01

    After the success of commercialization of the vacuum-evaporated organic light-emitting diodes (OLEDs), solutionprocessing or printing of OLEDs are currently attracting much research interests. However, contrary to various kinds of readily available vacuum-evaporable OLED materials, the solution-processable OLED materials are still relatively rare. Hole-transporting layer (HTL) materials for solution-processed OLEDs are especially limited, because they need additional characteristics such as cross-linking to realize multilayer structures in solution-processed OLEDs, as well as their own electrically hole-transporting characteristics. The presence of such cross-linking characteristics of solutionprocessable HTL materials therefore makes them more challenging in the development stage, and also makes them essence of solution-processable OLED materials. In this work, the structure-property relationships of thermally crosslinkable HTL materials were systematically investigated by changing styrene-based cross-linking functionalities and modifying the carbazole-based hole-transporting core structures. The temperature dependency of the cross-linking characteristics of the HTL materials was systematically investigated by the UV-vis. absorption spectroscopy. The new HTL materials were also applied to green phosphorescent OLEDs, and their device characteristics were also investigated based on the chemical structures of the HTL materials. The device configuration was [ITO / PEDOT:PSS / HTL / EML / ETL / CsF / Al]. We found out that the chemical structures of the cross-linking functionalities greatly affect not only the cross-linking characteristics of the resultant HTL materials, but also the resultant OLED device characteristics. The increase of the maximum luminance and efficiency of OLEDs was evident as the cross-linking temperature decreases from higher than 200°C to at around 150°C.

  20. Feruloylated arabinoxylans are oxidatively cross-linked by extracellular maize peroxidase but not by horseradish peroxidase.

    Science.gov (United States)

    Burr, Sally J; Fry, Stephen C

    2009-09-01

    Covalent cross-linking of soluble extracellular arabinoxylans in living maize cultures, which models the cross-linking of wall-bound arabinoxylans, is due to oxidation of feruloyl esters to oligoferuloyl esters and ethers. The oxidizing system responsible could be H2O2/peroxidase, O2/laccase, or reactive oxygen species acting non-enzymically. To distinguish these possibilities, we studied arabinoxylan cross-linking in vivo and in vitro. In living cultures, exogenous, soluble, extracellular, feruloylated [pentosyl-3H]arabinoxylans underwent cross-linking, beginning abruptly 8 d after sub-culture. Cross-linking was suppressed by iodide, an H2O2 scavenger, indicating dependence on endogenous H2O2. However, exogenous H2O2 did not cause precocious cross-linking, despite the constant presence of endogenous peroxidases, suggesting that younger cultures contained natural cross-linking inhibitors. Dialysed culture-filtrates cross-linked [3H]arabinoxylans in vitro only if H2O2 was also added, indicating a peroxidase requirement. This cross-linking was highly ionic-strength-dependent. The peroxidases responsible were heat-labile, although relatively heat-stable peroxidases (assayed on o-dianisidine) were also present. Surprisingly, added horseradish peroxidase, even after heat-denaturation, blocked the arabinoxylan-cross-linking action of maize peroxidases, suggesting that the horseradish protein was a competing substrate for [3H]arabinoxylan coupling. In conclusion, we show for the first time that cross-linking of extracellular arabinoxylan in living maize cultures is an action of apoplastic peroxidases, some of whose unusual properties we report.

  1. Feruloylated Arabinoxylans Are Oxidatively Cross-Linked by Extracellular Maize Peroxidase but Not by Horseradish Peroxidase

    Institute of Scientific and Technical Information of China (English)

    Sally J. Burr; Stephen C. Fry

    2009-01-01

    Covalent cross-linking of soluble extraceUular arabinoxylans in living maize cultures, which models the cross-linking of wall-bound arabinoxylans, is due to oxidation of feruloyl esters to oligoferuloyl esters and ethers. The oxidizing system responsible could be H_2O_2/peroxidase, O_2/laccase, or reactive oxygen species acting non-enzymically. To distinguish these possibilities, we studied arabinoxylan cross-linking in vivo and in vitro. In living cultures, exogenous, soluble, extra-cellular, feruloylated [pentosyl-~3H]arabinoxylans underwent cross-linking, beginning abruptly 8 d after sub-culture. Cross-linking was suppressed by iodide, an H_2O_2 scavenger, indicating dependence on endogenous H2O2. However, exogenous H_2O_2 did not cause precocious cross-linking, despite the constant presence of endogenous peroxidases, suggesting that younger cultures contained natural cross-linking inhibitors. Dialysed culture-filtrates cross-linked [~3H]arabinoxylans in vitro only if H_20_2 was also added, indicating a peroxiclase requirement. This cross-linking was highly ionic-strength-dependent. The peroxidases responsible were heat-labile, although relatively heat-stable peroxidases (assayed on o-dianisidine) were also present, Surprisingly, added horseradish peroxidase, even after heat-denaturation, blocked the arabinoxylan-cross-linking action of maize peroxidases, suggesting that the horseradish protein was a competing substrate for [~3H]arabino-xylan coupling. In conclusion, we show for the first time that cross-linking of extracellular arabinoxylan in living maize cultures is an action of apoplastic peroxidases, some of whose unusual properties we report.

  2. Understanding chemical reactivity for homo- and heterobifunctional protein cross-linking agents.

    Science.gov (United States)

    Chen, Fan; Nielsen, Simone; Zenobi, Renato

    2013-07-01

    Chemical cross-linking, combined with mass spectrometry, has been applied to map three-dimensional protein structures and protein-protein interactions. Proper choice of the cross-linking agent, including its reactive groups and spacer arm length, is of great importance. However, studies to understand the details of reactivity of the chemical cross-linkers with proteins are quite sparse. In this study, we investigated chemical cross-linking from the aspects of the protein structures and the cross-linking reagents involved, by using two structurally well-known proteins, glyceraldehyde 3-phosohate dehydrogenase and ribonuclease S. Chemical cross-linking reactivity was compared using a series of homo- and hetero-bifunctional cross-linkers, including bis(sulfosuccinimidyl) suberate, dissuccinimidyl suberate, bis(succinimidyl) penta (ethylene glycol), bis(succinimidyl) nona (ethylene glycol), m-maleimidobenzoyl-N-hydroxysulfosuccinimide ester, 2-pyridyldithiol-tetraoxaoctatriacontane-N-hydrosuccinimide and succinimidyl-[(N-maleimidopropionamido)-tetracosaethyleneglycol]ester. The protein structure itself, especially the distances between target amino acid residues, was found to be a determining factor for the cross-linking efficiency. Moreover, the reactive groups of the chemical cross-linker also play an important role; a higher cross-linking reaction efficiency was found for maleimides compared to 2-pyrimidyldithiols. The reaction between maleimides and sulfhydryl groups is more favorable than that between N-hydroxysuccinimide esters and amine groups, although cysteine residues are less abundant in proteins compared to lysine residues. Copyright © 2013 John Wiley & Sons, Ltd.

  3. Plasmodium falciparum liver stage antigen-1 is cross-linked by tissue transglutaminase

    Directory of Open Access Journals (Sweden)

    Doerig Christian

    2011-01-01

    Full Text Available Abstract Background Plasmodium falciparum sporozoites injected by mosquitoes into the blood rapidly enter liver hepatocytes and undergo pre-erythrocytic developmental schizogony forming tens of thousands of merozoites per hepatocyte. Shortly after hepatocyte invasion, the parasite starts to produce Liver Stage Antigen-1 (LSA-1, which accumulates within the parasitophorous vacuole surrounding the mass of developing merozoites. The LSA-1 protein has been described as a flocculent mass, but its role in parasite development has not been determined. Methods Recombinant N-terminal, C-terminal or a construct containing both the N- and C- terminal regions flanking two 17 amino acid residue central repeat sequences (LSA-NRC were subjected to in vitro modification by tissue transglutaminase-2 (TG2 to determine if cross-linking occurred. In addition, tissue sections of P. falciparum-infected human hepatocytes were probed with monoclonal antibodies to the isopeptide ε-(γ-glutamyllysine cross-bridge formed by TG2 enzymatic activity to determine if these antibodies co-localized with antibodies to LSA-1 in the growing liver schizonts. Results This study identified a substrate motif for (TG2 and a putative casein kinase 2 phosphorylation site within the central repeat region of LSA-1. The function of TG2 is the post-translational modification of proteins by the formation of a unique isopeptide ε-(γ-glutamyllysine cross-bridge between glutamine and lysine residues. When recombinant LSA-1 protein was crosslinked in vitro by purified TG2 in a calcium dependent reaction, a flocculent mass of protein was formed that was highly resistant to degradation. The cross-linking was not detectably affected by phosphorylation with plasmodial CK2 in vitro. Monoclonal antibodies specific to the very unique TG2 catalyzed ε- lysine cross-bridge co-localized with antibodies to LSA-1 in infected human hepatocytes providing visual evidence that LSA-1 was cross-linked in vivo

  4. Comparative studies on performance of radiation-induced and thermal cross-linked ion-exchange membrane for water electrolysis

    Energy Technology Data Exchange (ETDEWEB)

    Chakrabarty, Tina; Jasti, Amaranadh [Electro-Membrane Processes Division, Central Salt and Marine Chemicals Research Institute, Council of Scientific and Industrial Research (CSIR), G. B. Marg, Bhavnagar 364002, Gujarat (India); Goel, N.K. [Radiation Technology Division, Bhabha Atomic Research Center, Trombay, Mumbai (India); Shahi, Vinod K., E-mail: vkshahi@csmcri.or [Electro-Membrane Processes Division, Central Salt and Marine Chemicals Research Institute, Council of Scientific and Industrial Research (CSIR), G. B. Marg, Bhavnagar 364002, Gujarat (India); Sabharwal, Sunil [Radiation Technology Division, Bhabha Atomic Research Center, Trombay, Mumbai (India)

    2011-07-15

    Radiation-induced and thermal cross-linked sulfonated poly(ether sulfone) (SPS)-sulfonated poly(ether ether ketone) (SPK) composite ion-exchange membranes (SPS/SPK({gamma}) and SPS/SPK(T), respectively) were prepared. Their performances for water electrolysis were comparatively assessed. Thermal cross-linked membrane (SPS/SPK(T)) showed cross-linking of part functional groups (-SO{sub 3}H) and thus deterioration in membrane conductivity. While, radiation-induced cross-linked membrane (SPS/SPK({gamma})) avoided any cross-linking between functional groups and thus conductivity. Electrolysis performances of these membranes were evaluated in comparison with Nafion117 membrane. Relatively low current efficiency (CE) for SPS/SPK and SPS/SPK(T) membranes was due to their high mass transfer (water) via electro-osmotic drag, which was negligible for SPS/SPK({gamma}) membrane. SPS/SPK({gamma}) membrane exhibited comparable stabilities and water splitting performance with Nafion117 membrane, which revealed its suitability as substitute for electrochemical applications.

  5. Comparative studies on performance of radiation-induced and thermal cross-linked ion-exchange membrane for water electrolysis

    Science.gov (United States)

    Chakrabarty, Tina; Jasti, Amaranadh; Goel, N. K.; Shahi, Vinod K.; Sabharwal, Sunil

    2011-07-01

    Radiation-induced and thermal cross-linked sulfonated poly(ether sulfone) (SPS)-sulfonated poly(ether ether ketone) (SPK) composite ion-exchange membranes (SPS/SPK(γ) and SPS/SPK(T), respectively) were prepared. Their performances for water electrolysis were comparatively assessed. Thermal cross-linked membrane (SPS/SPK(T)) showed cross-linking of part functional groups (-SO 3H) and thus deterioration in membrane conductivity. While, radiation-induced cross-linked membrane (SPS/SPK(γ)) avoided any cross-linking between functional groups and thus conductivity. Electrolysis performances of these membranes were evaluated in comparison with Nafion117 membrane. Relatively low current efficiency (CE) for SPS/SPK and SPS/SPK(T) membranes was due to their high mass transfer (water) via electro-osmotic drag, which was negligible for SPS/SPK(γ) membrane. SPS/SPK(γ) membrane exhibited comparable stabilities and water splitting performance with Nafion117 membrane, which revealed its suitability as substitute for electrochemical applications.

  6. Link prediction boosted psychiatry disorder classification for functional connectivity network

    Science.gov (United States)

    Li, Weiwei; Mei, Xue; Wang, Hao; Zhou, Yu; Huang, Jiashuang

    2017-02-01

    Functional connectivity network (FCN) is an effective tool in psychiatry disorders classification, and represents cross-correlation of the regional blood oxygenation level dependent signal. However, FCN is often incomplete for suffering from missing and spurious edges. To accurate classify psychiatry disorders and health control with the incomplete FCN, we first `repair' the FCN with link prediction, and then exact the clustering coefficients as features to build a weak classifier for every FCN. Finally, we apply a boosting algorithm to combine these weak classifiers for improving classification accuracy. Our method tested by three datasets of psychiatry disorder, including Alzheimer's Disease, Schizophrenia and Attention Deficit Hyperactivity Disorder. The experimental results show our method not only significantly improves the classification accuracy, but also efficiently reconstructs the incomplete FCN.

  7. Progress of corneal collagen cross-linking combined with refractive surgery

    Directory of Open Access Journals (Sweden)

    Na Li

    2014-02-01

    Full Text Available As a photochemical reaction that can stiffen the cornea, corneal collagen cross-linking (CXL is the only promising method of preventing the progress of keratectasia, such as keratoconus and secondary ectasia following refractive surgery. The aim of CXL is to stabilize the underlying condition, with a small chance of visual improvement. Combining CXL with refractive surgery targeting both stabilization and reshaping of the corneal tissue for visual function improvement is a good treatment option. This review aims to provide a comprehensive and unbiased summary of the published research regarding combined CXL and refractive surgery, including measures and results, to help elucidate the future direction of CXL.

  8. SYNTHESIS AND CATALYTIC PROPERTIES OF CROSS-LINKED HYDROPHOBICALLY ASSOCIATING POLY(ALKYLMETHYLDIALLYLAMMONIUM BROMIDES)

    NARCIS (Netherlands)

    WANG, GJ; ENGBERTS, JBFN

    1994-01-01

    Cross-linked, hydrophobically associating homo- and copolymers were synthesized by free-radical cyclo(co)polymerization of alkylmethyldiallylammonium bromide monomers with a small amount of N,N'-methylenebisacrylamide in aqueous solution using ammonium persulfate as the initiator. The cross-linked h

  9. Rheological properties of dispersions of enzymatically cross-linked apo-α-lactalbumin

    NARCIS (Netherlands)

    Saricay, Yunus; Wierenga, Peter A.; Vries, de Renko

    2016-01-01

    The enzymatic cross-linking of apo-α-lactalbumin (α-LA) with horseradish peroxidase (HRP) leads to the formation of hydrophilic protein aggregates with controlled size and architecture. We explore the rheological properties of dispersions of these HRP-cross-linked α-LA aggregates with a hydrodyna

  10. Covalently Cross-Linked Sulfone Polybenzimidazole Membranes with Poly(Vinylbenzyl Chloride) for Fuel Cell Applications

    DEFF Research Database (Denmark)

    Yang, Jingshuai; Aili, David; Li, Qingfeng;

    2013-01-01

    Covalently cross-linked polymer membranes were fabricated from poly(aryl sulfone benzimidazole) (SO(2) PBI) and poly(vinylbenzyl chloride) (PVBCl) as electrolytes for high-temperature proton-exchange-membrane fuel cells. The cross-linking imparted organo insolubility and chemical stability against...

  11. PREPARATION OF NOVEL METALLIC AND BIMETALLIC CROSS-LINKED POLY (VINYL ALCOHOL) NANOCOMPOSITES UNDER MICROWAVE IRRADIATION

    Science.gov (United States)

    A facile method utilizing microwave irradiation is described that accomplishes the cross-linking reaction of PVA with metallic and bimetallic systems. Nanocomposites of PVA-cross-linked metallic systems such as Pt, Cu, and In and bimetallic systems such as Pt-In, Ag-Pt, Pt-Fe, Cu...

  12. NOVEL METALLIC AND BIMETALLIC CROSS-LINKED POLY (VINYL ALCOHOL) NANOCOMPOSITES PREPARED UNDER MICROWAVE IRRADIATION

    Science.gov (United States)

    A facile microwave irradiation approach that results in a cross-linking reaction of poly (vinyl alcohol) (PVA) with metallic and bimetallic systems is described. Nanocomposites of PVA cross-linked metallic systems such as Pt, Cu, and In and bimetallic systems such as Pt-In, Ag-P...

  13. Quantification of carboxyl groups in carbodiimide cross-linked collagen sponges

    NARCIS (Netherlands)

    Everaerts, Frank; Torrianni, Mark; Hendriks, Marc; Feijen, Jan

    2007-01-01

    Glutaraldehyde (GA) fixation of bioprosthetic tissue is a well adapted technique, with commercial products on the market for almost 40 years. Amine groups present in tissue react with GA to form different types of cross-links. An estimation of the degree of cross-linking of the tissue can be obtaine

  14. Infrared microspectroscopic determination of collagen cross-links in articular cartilage

    Science.gov (United States)

    Rieppo, Lassi; Kokkonen, Harri T.; Kulmala, Katariina A. M.; Kovanen, Vuokko; Lammi, Mikko J.; Töyräs, Juha; Saarakkala, Simo

    2017-03-01

    Collagen forms an organized network in articular cartilage to give tensile stiffness to the tissue. Due to its long half-life, collagen is susceptible to cross-links caused by advanced glycation end-products. The current standard method for determination of cross-link concentrations in tissues is the destructive high-performance liquid chromatography (HPLC). The aim of this study was to analyze the cross-link concentrations nondestructively from standard unstained histological articular cartilage sections by using Fourier transform infrared (FTIR) microspectroscopy. Half of the bovine articular cartilage samples (n=27) were treated with threose to increase the collagen cross-linking while the other half (n=27) served as a control group. Partial least squares (PLS) regression with variable selection algorithms was used to predict the cross-link concentrations from the measured average FTIR spectra of the samples, and HPLC was used as the reference method for cross-link concentrations. The correlation coefficients between the PLS regression models and the biochemical reference values were r=0.84 (p<0.001), r=0.87 (p<0.001) and r=0.92 (p<0.001) for hydroxylysyl pyridinoline (HP), lysyl pyridinoline (LP), and pentosidine (Pent) cross-links, respectively. The study demonstrated that FTIR microspectroscopy is a feasible method for investigating cross-link concentrations in articular cartilage.

  15. Glucose-mediated cross-linking of collagen in rat tendon and skin

    NARCIS (Netherlands)

    Mentink, CJAL; Hendriks, M; Levels, AAG; Wolffenbuttel, BHR

    2002-01-01

    Back-ground: Cross-linking of macromolecules like collagen plays an important role in the development of complications in diabetes and ageing. One of the underlying mechanisms of this cross-linking is the formation of advanced glycation endproducts (AGEs). Methods: In this study, we assessed the use

  16. Peroxidase-mediated cross-linking of a tyrosine-containing peptide with ferulic acid

    NARCIS (Netherlands)

    Oudgenoeg, G.; Hilhorst, R.; Piersma, S.R.; Boeriu, C.G.; Gruppen, H.; Hessing, M.; Voragen, A.G.J.; Laane, C.

    2001-01-01

    The tyrosine-containing peptide Gly-Tyr-Gly (GYG) was oxidatively cross-linked by horseradish peroxidase in the presence of hydrogen peroxide. As products, covalently coupled di- to pentamers of the peptide were identified by LC-MS. Oxidative cross-linking of ferulic acid with horseradish peroxidase

  17. Biodegradation of differently cross-linked collagen membranes: an experimental study in the rat.

    NARCIS (Netherlands)

    Rothamel, D.; Schwarz, F.; Sager, M.; Herten, M. van; Sculean, A.; Becker, J.M.

    2005-01-01

    The aim of the present study was to compare the biodegradation of differently cross-linked collagen membranes in rats. Five commercially available and three experimental membranes (VN) were included: (1) BioGide (BG) (non-cross-linked porcine type I and III collagens), (2) BioMend (BM), (3) BioMendE

  18. Novel antimicrobial superporous cross-linked chitosan/pyromellitimide benzoyl thiourea hydrogels.

    Science.gov (United States)

    Mohamed, Nadia A; Abd El-Ghany, Nahed A; Fahmy, Mona M

    2016-01-01

    In this work, chitosan (CS) was cross-linked with different amounts of pyromellitimide benzoyl thiourea moieties. The structure of the cross-linked CS was confirmed by elemental analyses, FTIR and (1)H- NMR spectroscopy. The cross-linking process proceeds via reacting of the amino groups of CS with the isothiocyanate groups of the N,N'-bis [4-(isothiocyanate carbonyl)phenyl] pyromellitimide cross-linker. The amount of the cross-linker was varied with respect to CS to produce four new pyromellitimide benzoyl thiourea cross-linked CS (PIBTU-CS) hydrogels designated as PIBTU-CS-1, PIBTU-CS-2, PIBTU-CS-3, and PIBTU-CS-4 of increasing cross-linking degree percent of 11, 22, 44 and 88%, respectively. The scanning electron microscopy observation indicates the extremely porous structure of the hydrogels. XRD results showed that the crystallinity of CS was decreased upon cross-linking. The four hydrogels exhibit a higher antibacterial activity on Bacillus subtilis and Streptococcus pneumoniae as Gram positive bacteria and against Escherichia coli as Gram negative bacteria and higher antifungal activity on Aspergillus fumigatus, Syncephalastrum racemosum and Geotricum candidum than that of the parent CS as shown from their higher inhibition zone diameters and their lower MIC values. The swell ability of the hydrogel as well as their antimicrobial activity increased with increasing cross-linking density.

  19. Cross-covariance functions for multivariate geostatistics

    KAUST Repository

    Genton, Marc G.

    2015-05-01

    Continuously indexed datasets with multiple variables have become ubiquitous in the geophysical, ecological, environmental and climate sciences, and pose substantial analysis challenges to scientists and statisticians. For many years, scientists developed models that aimed at capturing the spatial behavior for an individual process; only within the last few decades has it become commonplace to model multiple processes jointly. The key difficulty is in specifying the cross-covariance function, that is, the function responsible for the relationship between distinct variables. Indeed, these cross-covariance functions must be chosen to be consistent with marginal covariance functions in such a way that the second-order structure always yields a nonnegative definite covariance matrix. We review the main approaches to building cross-covariance models, including the linear model of coregionalization, convolution methods, the multivariate Matérn and nonstationary and space-time extensions of these among others. We additionally cover specialized constructions, including those designed for asymmetry, compact support and spherical domains, with a review of physics-constrained models. We illustrate select models on a bivariate regional climate model output example for temperature and pressure, along with a bivariate minimum and maximum temperature observational dataset; we compare models by likelihood value as well as via cross-validation co-kriging studies. The article closes with a discussion of unsolved problems. © Institute of Mathematical Statistics, 2015.

  20. Characteristic of hyaluronic acid derivative films cross-linked by polyethylene glycol of low water content

    Institute of Scientific and Technical Information of China (English)

    Chen Jinghua; Chen Jingtao; Xu Zheng; Gu Qisheng

    2008-01-01

    Objective: To test the characteristics of byaluronic acid (HA) derivative cross-linked by polyethylene glycol films of low water content. Methods: The cross-linked HA film with 200 μm thickness was got at atmospheric pressure at 25℃ for 5 d. After dried, cross-linked films of 10 mm×10 mm were weighed and immersed in phosphate buffered saline (PBS pH 7.45) at 37℃ for 24 h. Then the solution fraction and water content were estimated. Meanwhile, cross-linked HA derivative films were immersed in phosphate buffered saline (PBS: pH 7.45) at 37℃ for determined time and then implanted subcutaneously in the back of white rats to test in vitro or in vivo degradation characteristic. Results and Conclusion: HA hydrogel cross-linked by polyethylene glycol with water content is as low as 60% and this kind of HA derivative has a slow degradation rate.

  1. The peroxyl radical-induced oxidation of Escherichia coli FtsZ and its single tryptophan mutant (Y222W) modifies specific side-chains, generates protein cross-links and affects biological function.

    Science.gov (United States)

    Escobar-Álvarez, Elizabeth; Leinisch, Fabian; Araya, Gissela; Monasterio, Octavio; Lorentzen, Lasse G; Silva, Eduardo; Davies, Michael J; López-Alarcón, Camilo

    2017-11-01

    FtsZ (filamenting temperature-sensitive mutant Z) is a key protein in bacteria cell division. The wild-type Escherichia coli FtsZ sequence (FtsZwt) contains three tyrosine (Tyr, Y) and sixteen methionine (Met, M) residues. The Tyr at position 222 is a key residue for FtsZ polymerization. Mutation of this residue to tryptophan (Trp, W; mutant Y222W) inhibits GTPase activity resulting in an extended time in the polymerized state compared to FtsZwt. Protein oxidation has been highlighted as a determinant process for bacteria resistance and consequently oxidation of FtsZwt and the Y222W mutant, by peroxyl radicals (ROO•) generated from AAPH (2,2'-azobis(2-methylpropionamidine) dihydrochloride) was studied. The non-oxidized proteins showed differences in their polymerization behavior, with this favored by the presence of Trp at position 222. AAPH-treatment of the proteins inhibited polymerization. Protein integrity studies using SDS-PAGE revealed the presence of both monomers and oligomers (dimers, trimers and high mass material) on oxidation. Western blotting indicated the presence of significant levels of protein carbonyls. Amino acid analysis showed that Tyr, Trp (in the Y222W mutant), and Met were consumed by ROO•. Quantification of the number of moles of amino acid consumed per mole of ROO• shows that most of the initial oxidant can be accounted for at low radical fluxes, with Met being a major target. Western blotting provided evidence for di-tyrosine cross-links in the dimeric and trimeric proteins, confirming that oxidation of Tyr residues, at positions 339 and/or 371, are critical to ROO•-mediated crosslinking of both the FtsZwt and Y222W mutant protein. These findings are in agreement with di-tyrosine, N-formyl kynurenine, and kynurenine quantification assessed by UPLC, and with LC-MS data obtained for AAPH-treated protein samples. Copyright © 2017 Elsevier Inc. All rights reserved.

  2. Disuccinimidyl suberate cross-linked hemoglobin as a novel red blood cell substitute

    Institute of Scientific and Technical Information of China (English)

    LU; Xiuling; ZHENG; Chunyang; XU; Yuhong; SU; Zhiguo

    2005-01-01

    Disuccinimidyl suberate (DSS) intramolecularly cross-linked hemoglobin (Hb) was developed as a novel red blood cell substitute. A multi-angle laser light scattering detector coupled with size exclusion HPLC was applied to determine the molecular weight of the modified Hb. SDS-PAGE was also used as a complement. It was proved that 83.8% of the product was intramolecularly cross-linked Hb with weight-average molecular weights (Mw) of 67.5 kD, 12% was dimeric Hb with Mw of 146.6 kD, and 4.2% was trimeric Hb with Mw of 306.4 kD. The tetramer structure of the cross-linked Hb was stable as shown in size-exclusion chromatography using a mobile phase containing 1 mol/L MgCl2. Analysis by LC-MS demonstrated that the reaction of DSS with Hb mainly took place between the twoα subunits within a Hb molecule, resulting in stabilization of the tetramer structure. However, the cross-linking was not site-specific. The P50 of the cross-linked Hb decreased from 21.8 mmHg to 14.3 mmHg, and the Hill coefficient decreased from 2.22 to 1.41. Result of isoelectric focusing showed that the pI of DSS cross-linked Hb was in the range of 4.6-5.2, similar to that of serum albumin. The safety of DSS cross-linked Hb was favored by animal tests on rats and guinea pigs. Exchange transfusion experiment with DSS cross-linked Hb using rats as a model indicated no pressor effect or other significant side effects. The characteristics and properties of DSS cross-linked Hb were also compared with that of diaspirin cross-linked Hb reported in the literature.

  3. Multi-Functional Fibre-Optic Microwave Links

    DEFF Research Database (Denmark)

    Gliese, Ulrik Bo

    1998-01-01

    The multi-functionality of microwave links based on remote heterodyne detection of signals from a dual-frequency laser transmitter is discussed and experimentally demonstrated in this paper. Typically, direct detection in conjunction with optical intensity modulation is used to implement fibre......-optic microwave links. The resulting links are inherently transparent and mainly used for signal transmission. As opposed to direct detection links, remote heterodyne detection links can directly perform functionalities such as modulation, frequency conversion, and transparent signal recovery in addition...

  4. Corneal changes following collagen cross linking and simultaneous topography guided photoablation with collagen cross linking for keratoconus

    Directory of Open Access Journals (Sweden)

    Prema Padmanabhan

    2014-01-01

    Full Text Available Purpose: To compare the outcome of Collagen cross-linking (CXL with that following topography-guided customized ablation treatment (T-CAT with simultaneous CXL in eyes with progressive keratoconus. Materials and Methods: This was a prospective, non-randomized single centre study of 66 eyes with progressive keratoconus. Of these, 40 eyes underwent CXL and 26 eyes underwent T-CAT + CXL. The refractive, topographic, tomographic and aberrometric changes measured at baseline, 1, 3 and 6 months post-operatively were compared between both groups. Results: After a mean follow-up of 7.7 ± 1.3 months, the mean retinoscopic cylinder decreased by 1.02 ± 3.16 D in the CXL group ( P = 0.1 and 2.87 ± 3.22 D in the T-CAT + CXL group ( P = 0.04. The Best corrected visual acuity increased by 2 lines or more in 10% of eyes in the CXL group and in 23.3% of eyes in the T-CAT + CXL group. The mean steepest-K reduced by 0.40 ± 3.71 D ( P = 0.77 in the CXL group and by 2.91 ± 2.01D ( P = 0.03 in the T-CAT + CXL group. The sag factor and surface asymmetry index showed no significant change in the CXL group but reduced by 3.59 ± 5.94 D ( P = 0.01 and 0.72 ± 1.18 ( P = 0.02 respectively in the T-CAT + CXL group. There was a significant increase in the highest posterior corneal elevation in both groups (9.57 ± 14.93 μ in the CXL group and 7.85 ± 9.25 μ in the T-CAT + CXL group, P ≤ 0.001 for both. There was significantly greater reduction of mean coma ( P < 0.001 and mean higher-order aberrations ( P = 0.01 following T-CAT + CXL compared to CXL. Conclusions: CAT + CXL is an effective approach to confer biomechanical stability and to improve the corneal contour in eyes with keratoconus and results in better refractive, topographic and aberrometric outcomes than CXL alone.

  5. Photo-cross-linked poly(ethylene carbonate) elastomers: synthesis, in vivo degradation, and determination of in vivo degradation mechanism.

    Science.gov (United States)

    Cornacchione, L A; Qi, B; Bianco, J; Zhou, Z; Amsden, B G

    2012-10-01

    Low-molecular-weight poly(ethylene carbonate) diols of varying molecular weight were generated through catalyzed thermal degradation of high-molecular-weight poly(ethylene carbonate). These polymers were then end functionalized with acrylate groups. The resulting α,ω-diacrylates were effectively photo-cross-linked upon exposure to long-wave UV light in the presence of a photoinitiator to yield rubbery networks of low sol content. The degree of cross-linking effectively controlled the in vivo degradation rate of the networks by adherent macrophages; higher cross-link densities yielded slower degradation rates. The cross-link density did not affect the number of adherent macrophages at the elastomer/tissue interface, indicating that cross-linking affected the susceptibility of the elastomer to degradative species released by the macrophages. The reactive species likely responsible for in vivo degradation appears to be superoxide anion, as the in vivo results were in agreement with in vitro degradation via superoxide anion, while cholesterol esterase, known to degrade similar poly(alkylene carbonate)s, had no affect on elastomer degradation.

  6. Cross-Linking and Mass Spectrometry Methodologies to Facilitate Structural Biology: Finding a Path through the Maze

    Energy Technology Data Exchange (ETDEWEB)

    Merkley, Eric D.; Cort, John R.; Adkins, Joshua N.

    2013-09-01

    Multiprotein complexes, rather than individual proteins, make up a large part of the biological macromolecular machinery of a cell. Understanding the structure and organization of these complexes is critical to understanding cellular function. Chemical cross-linking coupled with mass spectrometry is emerging as a complementary technique to traditional structural biology methods and can provide low-resolution structural information for a multitude of purposes, such as distance constraints in computational modeling of protein complexes. In this review, we discuss the experimental considerations for successful application of chemical cross-linking-mass spectrometry in biological studies and highlight three examples of such studies from the recent literature. These examples (as well as many others) illustrate the utility of a chemical cross-linking-mass spectrometry approach in facilitating structural analysis of large and challenging complexes.

  7. Study of temperature dependence of thermal conductivity in cross-linked epoxies using molecular dynamics simulations with long range interactions

    Science.gov (United States)

    Kumar, A.; Sundararaghavan, V.; Browning, A. R.

    2014-03-01

    In this work, we demonstrate the use of the Green-Kubo integral of the heat flux autocorrelation function, incorporating long-range corrections to model the thermal conductivity versus temperature relationship of cross-linked polymers. The simulations were performed on a cross-linked epoxy made from DGEBA and a curing agent (diamino diphenyl sulfone) using a consistent valence force field (CVFF). A dendrimeric approach was utilized for building equilibrated cross-linked structures that allowed replication of the experimental dilatometric curve for the epoxy system. We demonstrate that the inclusion of a long-range correction within the Ewald/PPPM approach brings the results close to experimentally measured conductivity within an error of 10% while providing a good prediction of the relationship of thermal conductivity versus temperature. This method shows significant promise towards the computation of thermal conductivity from simulations even before synthesis of the polymer for purposes of materials by design.

  8. Cross-linking and mass spectrometry methodologies to facilitate structural biology: finding a path through the maze.

    Science.gov (United States)

    Merkley, Eric D; Cort, John R; Adkins, Joshua N

    2013-09-01

    Multiprotein complexes, rather than individual proteins, make up a large part of the biological macromolecular machinery of a cell. Understanding the structure and organization of these complexes is critical to understanding cellular function. Chemical cross-linking coupled with mass spectrometry is emerging as a complementary technique to traditional structural biology methods and can provide low-resolution structural information for a multitude of purposes, such as distance constraints in computational modeling of protein complexes. In this review, we discuss the experimental considerations for successful application of chemical cross-linking-mass spectrometry in biological studies and highlight three examples of such studies from the recent literature. These examples (as well as many others) illustrate the utility of a chemical cross-linking-mass spectrometry approach in facilitating structural analysis of large and challenging complexes.

  9. [A Method for Protein Photo-cross-linking in Living Cells Facilitating Analysis of Physiological Interactions of Proteins].

    Science.gov (United States)

    Hino, Nobumasa

    2015-01-01

    In living cells, most proteins form complexes with other proteins to exert their functions. Since protein functions are regulated in response to changes in the cellular environment, the components of the complexes can vary; therefore, proteins often interact in a weak and transient manner. To capture such labile protein interactions, we have developed a method for photo-cross-linking of proteins directly interacting in mammalian cells; this method involves expansion of the genetic code and site-specific incorporation of photoreactive amino acids into proteins. Upon cross-linking, protein complexes are stabilized by a covalent bond and can be readily isolated from cell extracts without the problems usually associated with simple affinity purification methods such as co-immunoprecipitation. Photo-cross-linkers have another benefit: they react exclusively with molecules within a range defined by the linker length. This property becomes useful for determining the binding interface of two proteins because the linkers can be introduced in a site-directed manner with our method. In this review, we first describe the expansion of the genetic code of mammalian cells for the incorporation of non-natural amino acids into proteins. Then, we introduce our recent applications and developments of the cross-linking method: identification of intracellular binding partners of the signaling protein growth factor receptor binding protein 2; analysis of the binding between membrane proteins on the cell surface; and a novel photoreactive amino acid that enables wide-ranging photo-cross-linking.

  10. Quantitative Raman characterization of cross-linked collagen thin films as a model system for diagnosing early osteoarthritis

    Science.gov (United States)

    Wang, Chao; Durney, Krista M.; Fomovsky, Gregory; Ateshian, Gerard A.; Vukelic, Sinisa

    2016-03-01

    The onset of osteoarthritis (OA)in articular cartilage is characterized by degradation of extracellular matrix (ECM). Specifically, breakage of cross-links between collagen fibrils in the articular cartilage leads to loss of structural integrity of the bulk tissue. Since there are no broadly accepted, non-invasive, label-free tools for diagnosing OA at its early stage, Raman spectroscopyis therefore proposed in this work as a novel, non-destructive diagnostic tool. In this study, collagen thin films were employed to act as a simplified model system of the cartilage collagen extracellular matrix. Cross-link formation was controlled via exposure to glutaraldehyde (GA), by varying exposure time and concentration levels, and Raman spectral information was collected to quantitatively characterize the cross-link assignments imparted to the collagen thin films during treatment. A novel, quantitative method was developed to analyze the Raman signal obtained from collagen thin films. Segments of Raman signal were decomposed and modeled as the sum of individual bands, providing an optimization function for subsequent curve fitting against experimental findings. Relative changes in the concentration of the GA-induced pyridinium cross-links were extracted from the model, as a function of the exposure to GA. Spatially resolved characterization enabled construction of spectral maps of the collagen thin films, which provided detailed information about the variation of cross-link formation at various locations on the specimen. Results showed that Raman spectral data correlate with glutaraldehyde treatment and therefore may be used as a proxy by which to measure loss of collagen cross-links in vivo. This study proposes a promising system of identifying onset of OA and may enable early intervention treatments that may serve to slow or prevent osteoarthritis progression.

  11. Plasticizer migration from cross-linked flexible PVC. 1. Effects on tribology

    Science.gov (United States)

    Pannico, M.; Persico, P.; Ambrogi, V.; Carfagna, C.

    2010-06-01

    Utilization of soft PVC is restricted by plasticizer migration that can affect material properties, as well as its toxicity. Modifying the chemical structure of PVC is one of the most effective tool to reduce the diffusion of plasticizer. In this work, a soft cross-linked PVC was obtained using a difunctional amine, namely isophoron diamine (IPDA) as the cross-linking agent. The gel content (wt %) was evaluated by weighting the insoluble portion obtained through solvent extraction technique. Thermogravimetric analysis (TGA) revealed that cross-linking reactions promote thermal degradation phenomena in the polymer matrix. Tribological properties of soft uncross-linked, cross-linked and rigid PVC were determined. Soft formulations were held in contact for 32 days with rigid PVC sheets. Plasticizer migration towards the interface causes an increase of dynamic friction compared to that of the reference rigid PVC.

  12. Chemistry and physical properties of melt-processed and solution-cross-linked corn zein.

    Science.gov (United States)

    Sessa, David J; Mohamed, Abdellatif; Byars, Jeffrey A

    2008-08-27

    Corn zein was cross-linked with glutaraldehyde (GDA) using glacial acetic acid (HAc) as catalyst. The objectives are to evaluate the swelling characteristics of GDA cross-linked zein gels in water, ethanol, and their combinations. Similar formulations, upon solvent evaporation, form films. The mechanical properties of the films are compared to compression molded tensile bars from GDA melt-processed zein as a second objective. Chemistry of the cross-linking reaction was based on the aldehyde binding characteristics defined by use of fluorescence spectroscopy; sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) to demonstrate the cross-linking reaction; FTIR to observe absorption differences of the cross-linked product; differential scanning calorimetry, dynamic mechanical analysis and thermogravimetric analysis to assess thermal properties; and the use of Instron Universal Testing Machine to evaluate mechanical properties. A reaction mechanism for acid catalyzed GDA cross-linking of zein is proposed. Thermal and mechanical properties of tensile bars cut from either film or formed by compression molding were similar, where both showed increased tensile strengths, ductility and stiffness when compared with unmodified controls. Samples that were reacted with 8% GDA by weight based on weight of zein from either process retained their integrity when tensile bars from each were subjected to boiling water for 10 min or soaking in either water or HAc for 24 h. The melt-processed, cross-linked zein is a more environmentally friendly method that would eliminate the need for HAc recovery.

  13. Modified gum arabic cross-linked gelatin scaffold for biomedical applications

    Energy Technology Data Exchange (ETDEWEB)

    Sarika, P.R. [Department of Chemistry, Indian Institute of Space Science and Technology, Valiamala, Thiruvananthapuram, Kerala 695 547 (India); Cinthya, Kuriakose [Tissue Culture Laboratory, Biomedical Technology Wing, Sree Chitra Tirunal Institute for Medical Sciences and Technology, Poojappura, Thiruvananthapuram, Kerala 695 012 (India); Jayakrishnan, A. [Department of Biotechnology, Indian Institute of Technology Madras, Chennai 600 036 (India); Anilkumar, P.R., E-mail: anilkumarpr@sctimst.ac.in [Tissue Culture Laboratory, Biomedical Technology Wing, Sree Chitra Tirunal Institute for Medical Sciences and Technology, Poojappura, Thiruvananthapuram, Kerala 695 012 (India); James, Nirmala Rachel, E-mail: nirmala@iist.ac.in [Department of Chemistry, Indian Institute of Space Science and Technology, Valiamala, Thiruvananthapuram, Kerala 695 547 (India)

    2014-10-01

    The present work deals with development of modified gum arabic cross-linked gelatin scaffold for cell culture. A new biocompatible scaffold was developed by cross-linking gelatin (Gel) with gum arabic, a polysaccharide. Gum arabic was subjected to periodate oxidation to obtain gum arabic aldehyde (GAA). GAA was reacted with gelatin under appropriate pH to prepare the cross-linked hydrogel. Cross-linking occurred due to Schiff's base reaction between aldehyde groups of oxidized gum arabic and amino groups of gelatin. The scaffold prepared from the hydrogel was characterized by swelling properties, degree of cross-linking, in vitro degradation and scanning electron microscopy (SEM). Cytocompatibility evaluation using L-929 and HepG2 cells confirmed non-cytotoxic and non-adherent nature of the scaffold. These properties are essential for generating multicellular spheroids and hence the scaffold is proposed to be a suitable candidate for spheroid cell culture. - Highlights: • Gum arabic cross-linked gelatin scaffold was developed for tissue engineering. • Cross-linking was achieved by Schiff's base reaction. • The scaffold is non-cytotoxic and non adherent to fibroblast and hepatocytes. • The scaffolds are potential candidates for spheroid cell culture.

  14. Shell and core cross-linked poly(L-lysine)/poly(acrylic acid) complex micelles.

    Science.gov (United States)

    Hsieh, Yi-Hsuan; Hsiao, Yung-Tse; Jan, Jeng-Shiung

    2014-12-21

    We report the versatility of polyion complex (PIC) micelles for the preparation of shell and core cross-linked (SCL and CCL) micelles with their surface properties determined by the constituent polymer composition and cross-linking agent. The negatively and positively charged PIC micelles with their molecular structure and properties depending on the mixing weight percentage and polymer molecular weight were first prepared by mixing the negatively and positively charged polyions, poly(acrylic acid) (PAA) and poly(L-lysine) (PLL). The feasibility of preparing SCL micelles was demonstrated by cross-linking the shell of the negatively and positively charged micelles using cystamine and genipin, respectively. The core of the micelles can be cross-linked by silica deposition to stabilize the assemblies. The shell and/or core cross-linked micelles exhibited excellent colloid stability upon changing solution pH. The drug release from the drug-loaded SCL micelles revealed that the controllable permeability of the SCL micelles can be achieved by tuning the cross-linking degree and the SCL micelles exhibited noticeable pH-responsive behavior with accelerated release under acidic conditions. With the versatility of cross-linking strategies, it is possible to prepare a variety of SCL and CCL micelles from PIC micelles.

  15. New insights into the pros and cons of cross-linking decellularized bioartificial organs.

    Science.gov (United States)

    Hussein, Kamal H; Park, Kyung-Mee; Lee, Yun-Suk; Woo, Jae-Seok; Kang, Byung-Jae; Choi, Ki-Young; Kang, Kyung-Sun; Woo, Heung-Myong

    2017-01-25

    ABSTRACTDecellularization is an attractive method for scaffold designing in regenerative medicine. The resulting extracellular matrix (ECM) consists of structural proteins such as collagen and elastin, growth factors, and glycosaminoglycans, which can direct site-appropriate remodeling after in vivo implantation. Mainly, collagen and elastin of ECM are exposed to the enzymatic biodegradation in the host. To control the biodegradation process, treatment of decellularized tissue by a cross-linking agent is required. Cross-linking also reduces antigenicity and increases the storage properties. Cross-linkers should be nontoxic, with the ability to preserve the ECM components, especially glycosaminoglycans and associated growth factors for retention of scaffold bioactivity. In this review, we describe the different cross-linking agents and methods of evaluation of cross-linking efficiency.

  16. Cross-linked survey analysis is an approach for separating cause and effect in survey research.

    Science.gov (United States)

    Redelmeier, Donald A; Thiruchelvam, Deva; Lustig, Andrew J

    2015-01-01

    We developed a new research approach, called cross-linked survey analysis, to explore how an acute exposure might lead to changes in survey responses. The goal was to identify associations between exposures and outcomes while reducing some ambiguities related to interpreting cause and effect in survey responses from a population-based community questionnaire. Cross-linked survey analysis differs from a cross-sectional, longitudinal, and panel survey analysis by individualizing the timeline to the unique history of each respondent. Cross-linked survey analysis, unlike a repeated-measures self-matching design, does not track changes in a repeated survey question given to the same respondent at multiple time points. Pilot data from three analyses (n = 1,177 respondents) illustrate how a cross-linked survey analysis can control for population shifts, temporal trends, and reverse causality. Accompanying graphs provide an intuitive display to readers, summarize results, and show differences in response distributions. Population-based individual-level linkages also reduce selection bias and increase statistical power compared with a single-center cross-sectional survey. Cross-linked survey analysis has limitations related to unmeasured confounding, pragmatics, survivor bias, statistical models, and the underlying artifacts in survey responses. We suggest that a cross-linked survey analysis may help in epidemiology science using survey data. Copyright © 2015 Elsevier Inc. All rights reserved.

  17. Protein structure prediction guided by cross-linking restraints - A systematic evaluation of the impact of the cross-linking spacer length

    CERN Document Server

    Hofmann, Tommy; Meiler, Jens; Kalkhof, Stefan

    2015-01-01

    Recent development of high-resolution mass spectrometry (MS) instruments enables chemical cross-linking (XL) to become a high-throughput method for obtaining structural information about proteins. Restraints derived from XL-MS experiments have been used successfully for structure refinement and protein-protein docking. However, one formidable question is under which circumstances XL-MS data might be sufficient to determine a protein's tertiary structure de novo? Answering this question will not only include understanding the impact of XL-MS data on sampling and scoring within a de novo protein structure prediction algorithm, it must also determine an optimal cross-linker type and length for protein structure determination. While a longer cross-linker will yield more restraints, the value of each restraint for protein structure prediction decreases as the restraint is consistent with a larger conformational space. In this study, the number of cross-links and their discriminative power was systematically analyz...

  18. Tissue-specific effects of aldose reductase inhibition on fluorescence and cross-linking of extracellular matrix in chronic galactosemia. Relationship to pentosidine cross-links.

    Science.gov (United States)

    Richard, S; Tamas, C; Sell, D R; Monnier, V M

    1991-08-01

    Chronic experimental hyperglycemia mediated by galactose has been shown to induce browning and cross-linking of rat tail tendon collagen that could be duplicated in vitro by nonenzymatic galactosylation. To investigate the nature of these changes, Sprague-Dawley rats were placed on a 33% galactose diet without and with sorbinil for 6 and 12 mo. Collagen-linked fluorescence and pentosidine cross-links increased with age and galactosemia in tail tendons (P less than 0.001) and skin but were essentially unresponsive to aldose reductase inhibition (ARI). In contrast, tendon breaking time in urea, a likely parameter of cross-linking, was markedly improved (P less than 0.001) by ARI. Fluorescence that was inhibited by sorbinil treatment was increased in pepsin and proteinase K digest of aortic tissue from galactosemic rats (P less than 0.001), but impaired enzymatic digestibility was not observed. Systolic blood pressure as potential consequence of aortic stiffening was not increased in galactosemia. These data suggest that fluorescence in skin and tendon might be in part due to advanced glycosylation and pentosidine formation because these were not decreased by ARI. However, they also suggest that nonfluorescent cross-links may also be forming because, in contrast to fluorescence, tail tendon breaking time was partly corrected by ARI. Thus, it appears that extracellular matrix changes in chronic galactosemia are complex, being partly attributable to advanced glycosylation and partly to polyol-pathway activation.

  19. Characterization of solid UV cross-linked PEGDA for biological applications

    KAUST Repository

    Castro, David

    2013-10-20

    This paper reports on solid UV cross-linked Poly(ethylene)-glycol-diacrylate (PEGDA) as a material for microfluidic devices for biological applications. We have evaluated biocompatibility of PEGDA through two separate means: 1) by examining cell viability and attachment on cross-linked PEGDA surfaces for cell culture applications, and 2) by determining if cross-linked PEGDA inhibits the polymerase chain reaction (PCR) processes for on-chip PCR. Through these studies a correlation has been found between degree of curing and cell viability, attachment, as well as on PCR outcome.

  20. Strategics links between purchases and logistics functions

    OpenAIRE

    2016-01-01

    This thesis is meant to global companies that would implement purchasing and logistics strategies in order to win a competitive edge and increase their performance. The purpose of this thesis is to learn about the organization of purchasing and logistics functions within global companies. Not only to discover their organization but also to understand their operational principal and realize how strategic and important those function can be to an international company. The Case Stu...

  1. Cross-linked chitosan improves the mechanical properties of calcium phosphate-chitosan cement.

    Science.gov (United States)

    Aryaei, Ashkan; Liu, Jason; Jayatissa, Ahalapitiya H; Jayasuriya, A Champa

    2015-09-01

    Calcium phosphate (CaP) cements are highly applicable and valuable materials for filling bone defects by minimally invasive procedures. The chitosan (CS) biopolymer is also considered as one of the promising biomaterial candidates in bone tissue engineering. In the present study, some key features of CaP-CS were significantly improved by developing a novel CaP-CS composite. For this purpose, CS was the first cross-linked with tripolyphosphate (TPP) and then mixed with CaP matrix. A group of CaP-CS samples without cross-linking was also prepared. Samples were fabricated and tested based on the known standards. Additionally, the effect of different powder (P) to liquid (L) ratios was also investigated. Both cross-linked and uncross-linked CaP-CS samples showed excellent washout resistance. The most significant effects were observed on Young's modulus and compressive strength in wet condition as well as surface hardness. In dry conditions, the Young's modulus of cross-linked samples was slightly improved. Based on the presented results, cross-linking does not have a significant effect on porosity. As expected, by increasing the P/L ratio of a sample, ductility and injectability were decreased. However, in the most cases, mechanical properties were enhanced. The results have shown that cross-linking can improve the mechanical properties of CaP-CS and hence it can be used for bone tissue engineering applications.

  2. Characterization of the receptor for endothelial cell growth factor (ECGF) by affinity cross-linking

    Energy Technology Data Exchange (ETDEWEB)

    Friesel, R.; Burgess, W.H.; Mehlman, T.; Maciag, T.

    1986-05-01

    The authors have demonstrated high affinity receptors for ECGF on endothelial cells by covalent cross-linking of (/sup 125/I)-ECGF with disuccinimidyl suberate and observe a single chain cross-linked polypeptide species with an apparent M/sub r/ of 170K. The M/sub r/ 170K species represents (/sup 125/I)-ECGF bound to its receptor since (i) excess unlabeled ECGF inhibits the cross-linking of (/sup 125/I)-ECGF, (ii) labeling of the M/sub r/170K species does not take place in the absence of cross-linker, (iii) cells previously shown to be refractory to ECGF and lack ECGF receptors do not yield a cross-linked species, (iv) the cross-linked species can be immunoprecipitated with anti-ECGF antibodies, and (v) preincubation of cells with ECGF at 37/sup 0/C significantly reduces cross-linking while incubation at 4/sup 0/C does not. These data demonstrate that ECGF induced cell proliferation occurs through the occupancy of a specific cell surface polypeptide receptor with an apparent M/sub r/ of 150K, and suggests that internalization of the receptor-ligand complex may be relevant to ECGF-induced signal transduction.

  3. A novel strategy for preparing mechanically robust ionically cross-linked alginate hydrogels

    Energy Technology Data Exchange (ETDEWEB)

    Jejurikar, Aparna; Lawrie, Gwen; Groendahl, Lisbeth [School of Chemistry and Molecular Biosciences, University of Queensland, Brisbane, Queensland 4072 (Australia); Martin, Darren, E-mail: l.grondahl@uq.edu.au [Australian Institute for Bioengineering and Nanotechnology, University of Queensland, Brisbane, Queensland 4072 (Australia)

    2011-04-15

    The properties of alginate films modified using two cross-linker ions (Ca{sup 2+} and Ba{sup 2+}), comparing two separate cross-linking techniques (the traditional immersion (IM) method and a new strategy in a pressure-assisted diffusion (PD) method), are evaluated. This was achieved through measuring metal ion content, water uptake and film stability in an ionic solution ([Ca{sup 2+}] = 2 mM). Characterization of the internal structure and mechanical properties of hydrated films were established by cryogenic scanning electron microscopy and tensile testing, respectively. It was found that gels formed by the PD technique possessed greater stability and did not exhibit any delamination after 21 day immersion as compared to gels formed by the IM technique. The Ba{sup 2+} cross-linked gels possessed significantly higher cross-linking density as reflected in lower water content, a more dense internal structure and higher Young's modulus compared to Ca{sup 2+} cross-linked gels. For the Ca{sup 2+} cross-linked gels, a large improvement in the mechanical properties was observed in gels produced by the PD technique and this was attributed to thicker pore walls observed within the hydrogel structure. In contrast, for the Ba{sup 2+} cross-linked gels, the PD technique resulted in gels that had lower tensile strength and strain energy density and this was attributed to phase separation and larger macropores in this gel.

  4. Incorporation of Decanethiol-Passivated Gold Nanoparticles into Cross-Linked Poly(Dimethylsiloxane Films

    Directory of Open Access Journals (Sweden)

    Motohiro Tagaya

    2011-01-01

    Full Text Available Cross-linking degree of a poly(dimethylsiloxane (PDMS film was controlled, and the incorporation of hydrophobic decanethiol-passivated gold (Au nanoparticles into the film was investigated. FT-IR spectra indicated that the hydrosilylation reaction between a vinyl group and a hydrosilyl group occurred with the cross-linking. The swelling degree of the film in toluene changed with a cross-linker concentration, indicating the control of the cross-linking degree of PDMS film. By EDX analysis, the amount of incorporated Au nanoparticles increased with decreasing a cross-linker concentration, indicating the enlarged free volume of the film. The Au nanoparticle-PDMS composite film containing a cross-linker at 6 wt% showed brown color attributed to plasmon resonance of Au nanoparticles, suggesting the Au nanoparticles in the film at monodispersion state. The UV-visible absorbance of the composite film decreased without spectralshift by swelling with toluene, and the changes were reversible. The aggregation among Au nanoparticles in the composite film after calcination also depended on the cross-linking degree. Thus, the control of cross-linking degree of PDMS film successfully leaded to a simple way of fabricating the Au nanoparticle-PDMS composite film at the mono-dispersion state.

  5. Preparation of Thermo-Responsive and Cross-Linked Fluorinated Nanoparticles via RAFT-Mediated Aqueous Polymerization in Nanoreactors.

    Science.gov (United States)

    Ma, Jiachen; Zhang, Luqing; Geng, Bing; Azhar, Umair; Xu, Anhou; Zhang, Shuxiang

    2017-01-25

    In this work, a thermo-responsive and cross-linked fluoropolymer poly(2,2,2-Trifluoroethyl) methacrylate (PTFEMA) was successfully prepared by reversible addition-fragmentation chain transfer (RAFT) mediated aqueous polymerization with a thermo-responsive diblock poly(dimethylacrylamide-b-N-isopropylacrylamide) (PDMA-b-PNIPAM) that performed a dual function as both a nanoreactor and macro-RAFT agent. The cross-linked polymer particles proved to be in a spherical-like structure of about 50 nm in diameter and with a relatively narrow particle size distribution. ¹H-NMR and (19)F-NMR spectra showed that thermo-responsive diblock P(DMA-b-NIPAM) and cross-linked PTFEMA particles were successfully synthesized. Influence of the amount of ammonium persulfate (APS), the molar ratio of monomers to RAFT agent, influence of the amount of cross-linker on aqueous polymerization and thermo-responsive characterization of the particles are investigated. Monomer conversion increased from 44% to 94% with increasing the molar ratio of APS and P(DMA-b-NIPAM) from 1:9 to1:3. As the reaction proceeded, the particle size increased from 29 to 49 nm due to the consumption of TFEMA monomer. The size of cross-linked nanoparticles sharply decreased from 50.3 to 40.5 nm over the temperature range 14-44 °C, suggesting good temperature sensitivity for these nanoparticles.

  6. Neutron scattering and ab initio molecular dynamics study of cross-linking in biomedical phosphate glasses

    Energy Technology Data Exchange (ETDEWEB)

    Parsons, A J; Ahmed, I; Rudd, C D [Division of Materials, Mechanics and Structures, Faculty of Engineering, University of Nottingham, Nottingham NG7 2RD (United Kingdom); Cuello, G J; Pellegrini, E; Richard, D; Johnson, M R, E-mail: andrew.parsons@nottingham.ac.uk [Institut Laue-Langevin, BP 156, 38042 Grenoble (France)

    2010-12-08

    Details of the microscopic structure of phosphate glasses destined for biomedical applications, which include sodium, magnesium and calcium cations, have been obtained from the static structure factor measured by means of neutron scattering. A complementary, molecular dynamics study has been performed on a range of phosphate glasses using density functional theory methods, which allow structural fluctuations, including bond breaking, in the liquid phase before quenching to the glass phase. Good agreement between experiment and simulation allows the molecular dynamics trajectories to be analysed in detail. In particular, attention is focused on the cross-linking of divalent cations in contrast with the structural aspects associated with monovalent cations. Magnesium cations are found equidistant and bridging between the phosphorus atoms of different phosphate chains, leading to a shorter phosphorus-phosphorus second neighbour distance (that is, a more compact packing of neighbouring phosphate chains) compared to the effect of sodium cations. Calcium cations show behaviour intermediate between those of magnesium and sodium. Molecular dynamics simulations give access to the cation mobility, which is lowest for magnesium, reflecting its structural, cross-linking role.

  7. Swelling Studies of Chitosan-Gelatin Films Cross-Linked by Sulfate

    Institute of Scientific and Technical Information of China (English)

    Xiao Ling; Yu Zu-yu; Yang Chao; Zhu Hua-yue; Du Yu-min

    2004-01-01

    Swelling properties of chitosan-gelatin films cross-linked by sulfate were investigated. Sulfate cross-linked chitosan-gelatin films (SCG) were prepared simply by dipping chitosan-gelatin films into sodium sulfate solution. The swelling behavior of SCG was investigated as a function of pH and ionic strength. Under acidic conditions pH less than 4, SCG swelled less than 120%, while under the conditions pH larger than 7.4, SCG swelled very significantly, the swelling ratio was over 350%. Sodium chloride weakened the electrostatic interaction between sulfate and amine ions of chitosan and gelatin, therefore facilitated the film swelling. The swelling ratio increased with increasing sodium chloride concentration, the SCG dissociated in the sodium chloride concentration of 0.20 mol·L-1. The parameters of film preparation such as sulfate concentration, dipping time, sulfate solution pH, influenced the film swelling behavior. The lower concentration and the higher pH of sulfate solution resulted in a larger swelling ratio.

  8. Laser cross-linking protein captures for living cells on a biochip

    Science.gov (United States)

    Lin, Chih-Lang; Pan, Ming-Jeng; Chen, Hai-Wen; Lin, Che-Kuan; Lin, Chuen-Fu; Baldeck, Patrice L.

    2014-03-01

    In this study, bio-sensing pads are proposed to capture living cells, which are fabricated on cover glasses by cross-linking proteins/antibodies using laser induced photochemistry. The biological functions of the cross-linked protein/antibody were verified by capturing Staphylococcus aureus (S. aureus), Leptospira, and red blood cells (RBCs), separately, with associated protein/antibody sensing pads. The experimental results show that S. aureus were bound on GFP-AcmA' pad after minutes of incubation and phosphate buffered saline (PBS) rinsing. No binding was observed with reference pad made of neutral bovine serum albumin (BSA). Second, A-type RBCs were chosen as the model cell to demonstrate the blood typing feasibility of the anti-A pad in microchannel. The A-type RBCs were captured only by the anti-A pad, but not the reference pad made of BSA. The same experimental model was carried out on the Leptospira, which stuck on the blood serum pad after PBS rinsing, but not BSA pad. This study provides a potential platform for simple and direct detection of living full cells without culture that could be used in point-of-care settings.

  9. Multivalent anchoring and cross-linking of mussel-inspired antifouling surface coatings.

    Science.gov (United States)

    Wei, Qiang; Becherer, Tobias; Mutihac, Radu-Cristian; Noeske, Paul-Ludwig Michael; Paulus, Florian; Haag, Rainer; Grunwald, Ingo

    2014-08-11

    In this work, we combine nature's amazing bioadhesive catechol with the excellent bioinert synthetic macromolecule hyperbranched polyglycerol (hPG) to prepare antifouling surfaces. hPG can be functionalized by different amounts of catechol groups for multivalent anchoring and cross-linking because of its highly branched architecture. The catecholic hPGs can be immobilized on various surfaces including metal oxides, noble metals, ceramics, and polymers via simple incubation procedures. The effect of the catechol amount on the immobilization, surface morphology, stability, and antifouling performance of the coatings was studied. Both anchoring and cross-linking interactions provided by catechols can enhance the stability of the coatings. When the catechol groups on the hPG are underrepresented, the tethering of the coating is not effective; while an overrepresentation of catechol groups leads to protein adsorption and cell adhesion. Thus, only a well-balanced amount of catechols as optimized and described in this work can supply the coatings with both good stability and antifouling ability.

  10. Synthesis of Covalently Cross-Linked Colloidosomes from Peroxidized Pickering Emulsions

    Directory of Open Access Journals (Sweden)

    Nadiya Popadyuk

    2016-10-01

    Full Text Available A new approach to the formation of cross-linked colloidosomes was developed on the basis of Pickering emulsions that were stabilized exclusively by peroxidized colloidal particles. Free radical polymerization and a soft template technique were used to convert droplets of a Pickering emulsion into colloidosomes. The peroxidized latex particles were synthesized in the emulsion polymerization process using amphiphilic polyperoxide copolymers poly(2-tert-butylperoxy-2-methyl-5-hexen-3-ine-co-maleic acid (PM-1-MAc or poly[N-(tert-butylperoxymethylacrylamide]-co-maleic acid (PM-2-MAc, which were applied as both initiators and surfactants (inisurfs. The polymerization in the presence of the inisurfs results in latexes with a controllable amount of peroxide and carboxyl groups at the particle surface. Peroxidized polystyrene latex particles with a covalently grafted layer of inisurf PM-1-MAc or PM-2-MAc were used as Pickering stabilizers to form Pickering emulsions. A mixture of styrene and/or butyl acrylate with divinylbenzene and hexadecane was applied as a template for the synthesis of colloidosomes. Peroxidized latex particles located at the interface are involved in the radical reactions of colloidosomes formation. As a result, covalently cross-linked colloidosomes were obtained. It was demonstrated that the structure of the synthesized (using peroxidized latex particles colloidosomes depends on the amount of functional groups and pH during the synthesis. Therefore, the size and morphology of colloidosomes can be controlled by latex particle surface properties.

  11. In situ cross-linking of stimuli-responsive hemicellulose microgels during spray drying.

    Science.gov (United States)

    Zhao, Weifeng; Nugroho, Robertus Wahyu N; Odelius, Karin; Edlund, Ulrica; Zhao, Changsheng; Albertsson, Ann-Christine

    2015-02-25

    Chemical cross-linking during spray drying offers the potential for green fabrication of microgels with a rapid stimuli response and good blood compatibility and provides a platform for stimuli-responsive hemicellulose microgels (SRHMGs). The cross-linking reaction occurs rapidly in situ at elevated temperature during spray drying, enabling the production of microgels in a large scale within a few minutes. The SRHMGs with an average size range of ∼ 1-4 μm contain O-acetyl-galactoglucomannan as a matrix and poly(acrylic acid), aniline pentamer (AP), and iron as functional additives, which are responsive to external changes in pH, electrochemical stimuli, magnetic field, or dual-stimuli. The surface morphologies, chemical compositions, charge, pH, and mechanical properties of these smart microgels were evaluated using scanning electron microscopy, IR, zeta potential measurements, pH evaluation, and quantitative nanomechanical mapping, respectively. Different oxidation states were observed when AP was introduced, as confirmed by UV spectroscopy and cyclic voltammetry. Systematic blood compatibility evaluations revealed that the SRHMGs have good blood compatibility. This bottom-up strategy to synthesize SRHMGs enables a new route to the production of smart microgels for biomedical applications.

  12. Mass spectrometric analysis of a UV-cross-linked protein-DNA complex: tryptophans 54 and 88 of E. coli SSB cross-link to DNA

    DEFF Research Database (Denmark)

    Steen, H; Petersen, J; Mann, M

    2001-01-01

    of two different peptide-DNA heteroconjugates was accomplished by matrix-assisted laser desorption/ionization mass spectrometry and allowed assignment of tryptophan-54 and tryptophan-88 as candidate cross-linked residues. Sequencing of those peptide-DNA heteroconjugates by nanoelectrospray quadrupole...

  13. An Investigation on Rheology of Peroxide Cross-linking of Low Density Polyethylene

    DEFF Research Database (Denmark)

    Ghasemi, Ismaeil; Rasmussen, Henrik K.; Szabo, Peter

    2005-01-01

    One of the most important post-reactor modifications of polyethylene is cross-linking. It improves some properties of polyethylene such as environmental stress cracking resistance, chemical and abrasion resistance, and service temperature. In this study, the effect of peroxide cross-linking on th......One of the most important post-reactor modifications of polyethylene is cross-linking. It improves some properties of polyethylene such as environmental stress cracking resistance, chemical and abrasion resistance, and service temperature. In this study, the effect of peroxide cross......-linking on the rheological behaviour of low density polyethylene was investigated by using a combination of creep test and differential scanning calorimeter (DSC) in isotherm condition. The used peroxide was di-cumyl peroxide and its concentration was 2 wt%. The experiments were carried out at 150,160, and 170 degrees C...

  14. PROSPECTS OF HIGH-CURRENT ELECTRON BEAMS APPLICATION TO RADIATION POLYETHYLENE CROSS-LINKING

    Directory of Open Access Journals (Sweden)

    A.G. Gurin

    2013-09-01

    Full Text Available A possibility of applying a pulse-periodic high-current induction electron accelerators to radiation polyethylene cross-linking is considered in the article. A comparative analysis with other devices used for irradiation is made.

  15. Comparative study of PBI Cross Linked Utilizing Agents of Varying Steric Configurations

    DEFF Research Database (Denmark)

    Kirkebcek, Andreas; Aili, David; Li, Qingfeng;

    2016-01-01

    The high thermal and chemical stability of poly[2,2'-(m-phenylene)-5,5' bibenzimidazole] (PBI) accounts for its wise spread use in high temperature polymer electrolyte membrane fuel cells (HT- PEMFC). By doping the membrane with phosphoric acid (PA) ionic conductivity is obtained. Thus conductivity...... ionic or covalent cross linking. When considering such, little attention is devoted to explore the effect of the sterical configuration of the cross linking agent. In this contribution three different cross linking agents are utilized to evaluate how these affects final membrane properties....... is dependent on the amount of PA present within the membrane. However mechanical properties are reduced are significantly reduced due to the plasticizing effect shown by PA [1]. This effect is due to PBI chain displacement. This effect can be lessened by use of cross linking [2-4]. This can be obtained using...

  16. Riboflavin cross-linking of collagen porous scaffolds for periodontal regeneration

    Directory of Open Access Journals (Sweden)

    Seciu A-M.

    2016-05-01

    Full Text Available Periodontitis treatment using occlusive membranes presented variable efficacy due to their rapid degradation in the complex biologic environment of the damaged periodontium. The aim of this study was to prepare novel composites based on collagen, chondroitin sulfate and fibronectin, and to establish the optimal parameters for their photochemical cross-linking using riboflavin and UV exposure. The degree of cross-linking, biodegradability and density of all scaffold variants were investigated. Their cytotoxicity was evaluated in a culture of gingival fibroblasts by MTT assay and light microscopy. The results indicated that the higher the cross-linking degree, the lower was the scaffold biodegradation. Cell culture studies showed that composite scaffolds were favorable for cellular survival. In conclusion, the cross-linking method using riboflavin and UV exposure resulted in stable and biocompatible collagen-based composite scaffolds that could be used for periodontitis treatment.

  17. A Review of Collagen Cross-Linking in Cornea and Sclera

    Directory of Open Access Journals (Sweden)

    Xiao Zhang

    2015-01-01

    Full Text Available Riboflavin/UVA cross-linking is a technique introduced in the past decades for the treatment of keratoconus, keratectasia, and infectious keratitis. Its efficacy and safety have been investigated with clinical and laboratory studies since its first clinical application by Wollensak for the treatment of keratoconus. Although its complications are encountered during clinical practice, such as infection inducing risk, minimal invasion merits a further investigation on its future application in clinical practice. Recently, collagen cross-linking in sclera shows a promising prospect. In present study, we summarized the representative studies describing the clinical and laboratory application of collagen cross-linking published in past decades and provided our opinion on the positive and negative results of cross-linking in the treatment of ophthalmic disorders.

  18. The level of cross-linking and the structure of anisotropic magnetorheological elastomers

    Energy Technology Data Exchange (ETDEWEB)

    Borin, Dmitry, E-mail: dmitry.borin@tu-dresden.de [Institute of Fluid Mechanics, Technische Universitaet Dresden, Dresden 01062 (Germany); Guenther, David [Institute of Fluid Mechanics, Technische Universitaet Dresden, Dresden 01062 (Germany); Hintze, Christian; Heinrich, Gert [Leibniz Institute of Polymer Research, Dresden 01069 (Germany); Odenbach, Stefan [Institute of Fluid Mechanics, Technische Universitaet Dresden, Dresden 01062 (Germany)

    2012-10-15

    The influence of the concentration of the magnetic powder on the level of cross-linking of magnetorheological elastomers (MREs) has been studied. Afterwards the structural characterisation of manufactured MREs has been performed by using non-destructive method, specifically the computed tomography. The correlation between internal structures of MREs and the developing of its cross-linking level during the curing was found. It was shown that changes in the concentration of the powder significantly affect morphologies of the sample.

  19. Novel thermoplastic vulcanizates (TPVs based on silicone rubber and polyamide exploring peroxide cross-linking

    Directory of Open Access Journals (Sweden)

    K. Naskar

    2014-04-01

    Full Text Available Novel thermoplastic vulcanizates (TPVs based on silicone rubber (PDMS and polyamide (PA12 have been prepared by dynamic vulcanization process. The effect of dynamic vulcanization and influence of various types of peroxides as cross-linking agents were studied in detail. All the TPVs were prepared at a ratio of 50/50 wt% of silicone rubber and polyamide. Three structurally different peroxides, namely dicumyl peroxide (DCP, 3,3,5,7,7-pentamethyl 1,2,4-trioxepane (PMTO and cumyl hydroperoxide (CHP were taken for investigation. Though DCP was the best option for curing the silicone rubber, at high temperature it suffers from scorch safety. An inhibitor 2,2,6,6-tetramethylpiperidinyloxyl (TEMPO was added with DCP to stabilize the radicals in order to increase the scorch time. Though CHP (hydroperoxide had higher half life time than DCP at higher temperature, it has no significant effect on cross-linking of silicone rubber. PMTO showed prolonged scorch safety and better cross-linking efficiency rather than the other two. TPVs of DCP and PMTO were made up to 11 minutes of mixing. Increased values of tensile strength and elongation at break of PMTO cross-linked TPV indicate the superiority of PMTO. Scanning electron micrographs correlate with mechanical properties of the TPVs. High storage modulus (E' and lower loss tangent value of the PMTO cross-linked TPV indicate the higher degree of cross-linking which is also well supported by the overall cross-link density value. Thus PMTO was found to be the superior peroxide for cross-linking of silicone rubber at high temperature.

  20. Sorption of substituted indoles on highly cross-linked polystyrene from water-acetonitrile solutions

    Science.gov (United States)

    Shafigulin, R. V.; Myakishev, A. A.; Il'Ina, E. A.; Il'in, M. M.; Davankov, V. A.; Bulanova, A. V.

    2011-07-01

    The sorption of first synthesized indole derivatives by highly cross-linked polystyrenes from water-acetonitrile solutions was studied by high-performance liquid chromatography. The retention factors and differences in the Gibbs energy of adsorption from infinite diluted solutions were calculated, and the applicability of the Snyder-Soczewinski and Scott-Kucera models for describing the chromatographic retention of sorbates on a polymer network of highly cross-linked polystyrene was shown.

  1. Analysis of glycation induced protein cross-linking inhibitory effects of some antidiabetic plants and spices

    OpenAIRE

    Perera, Handunge Kumudu Irani; Handuwalage, Charith Sandaruwan

    2015-01-01

    Background Protein cross-linking which occurs towards the latter part of protein glycation is implicated in the development of chronic diabetic complications. Glycation induced protein cross-linking inhibitory effects of nine antidiabetic plants and three spices were evaluated in this study using a novel, simple, electrophoresis based method. Methods Methanol extracts of thirteen plants including nine antidiabetic plants and three spices were used. Lysozyme and fructose were incubated at 37 °...

  2. Porphyrin-induced photodynamic cross-linking of hepatic heme-binding proteins.

    Science.gov (United States)

    Vincent, S H; Holeman, B; Cully, B C; Muller-Eberhard, U

    1986-01-27

    Three types of hepatic proteins, a heme-binding Z protein, a mixture of the glutathione S-transferases and a cytochrome P450 isozyme, were shown to be susceptible to photodynamic cross-linking and loss in antigenicity by naturally occurring porphyrins. At 50 microM, uroporphyrin caused the most and protoporphyrin the least photodecomposition. Hemopexin, a specific serum heme carrier, was photodecomposed but no cross-linking was detected. Heme and scavengers of singlet oxygen partially prevented protein photodecomposition.

  3. Optimizing end-group cross-linking polymer electrolytes for fuel cell applications

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Yu Seung [Los Alamos National Laboratory; Lee, Kwan Soo [Los Alamos National Laboratory; Jeong, Myung - Hwan [GIST, KOREA; Lee, Jae - Suk [GIST, KOREA

    2009-01-01

    This paper demonstrates the optimization of proton conductivity and water uptake for cross-linkable polymer electrolytes through synthesis and characterization of end-group cross-linkable sulfonated poly(arylene ether) copolymers (ESF-BPs). The extent of reaction of cross-linking was controlled by reaction time resulting in a series of polymers with two, independent tunable parameters, degree of sulfonation (DS) and degree of cross-linking (DC). For the polymers presented, cross-linking improved proton conductivity while reducing water uptake, an uncommon trend in polymer electrolytes where water is critical for proton conduction. Other trends relating to changes are reported and the results yield insight into the role of DS and DC and how to optimize electrochemical properties and performance of polymer electrolytes through these tunable parameters. Select polymer electrolytes were tested in fuel cells where performance and durability with accelerated relative humidity cycling were compared with Nafion{reg_sign}.

  4. Smooth muscle cell phenotype modulation and contraction on native and cross-linked polyelectrolyte multilayers.

    Science.gov (United States)

    Moussallem, Maroun D; Olenych, Scott G; Scott, Shannon L; Keller, Thomas C S; Schlenoff, Joseph B

    2009-11-09

    Smooth muscle cells convert between a motile, proliferative "synthetic" phenotype and a sessile, "contractile" phenotype. The ability to manipulate the phenotype of aortic smooth muscle cells with thin biocompatible polyelectrolyte multilayers (PEMUs) with common surface chemical characteristics but varying stiffness was investigated. The stiffness of (PAH/PAA) PEMUs was varied by heating to form covalent amide bond cross-links between the layers. Atomic force microscopy (AFM) showed that cross-linked PEMUs were thinner than those that were not cross-linked. AFM nanoindentation demonstrated that the Young's modulus ranged from 6 MPa for hydrated native PEMUs to more than 8 GPa for maximally cross-linked PEMUs. Rat aortic A7r5 smooth muscle cells cultured on native PEMUs exhibited morphology and motility of synthetic cells and expression of the synthetic phenotype markers vimentin, tropomyosin 4, and nonmuscle myosin heavy chain IIB (nmMHCIIB). In comparison, cells cultured on maximally cross-linked PEMUs exhibited the phenotype markers calponin, smooth muscle myosin heavy chain (smMHC), myocardin, transgelin, and smooth muscle alpha-actin (smActin) that are characteristic of the smooth muscle "contractile" phenotype. Consistent with those cells being "contractile", A7r5 cells grown on cross-linked PEMUs produced contractile force when stimulated with a Ca(2+) ionophore.

  5. A General Method for Targeted Quantitative Cross-Linking Mass Spectrometry

    Science.gov (United States)

    Chavez, Juan D.; Eng, Jimmy K.; Schweppe, Devin K.; Cilia, Michelle; Rivera, Keith; Zhong, Xuefei; Wu, Xia; Allen, Terrence; Khurgel, Moshe; Kumar, Akhilesh; Lampropoulos, Athanasios; Larsson, Mårten; Maity, Shuvadeep; Morozov, Yaroslav; Pathmasiri, Wimal; Perez-Neut, Mathew; Pineyro-Ruiz, Coriness; Polina, Elizabeth; Post, Stephanie; Rider, Mark; Tokmina-Roszyk, Dorota; Tyson, Katherine; Vieira Parrine Sant'Ana, Debora; Bruce, James E.

    2016-01-01

    Chemical cross-linking mass spectrometry (XL-MS) provides protein structural information by identifying covalently linked proximal amino acid residues on protein surfaces. The information gained by this technique is complementary to other structural biology methods such as x-ray crystallography, NMR and cryo-electron microscopy[1]. The extension of traditional quantitative proteomics methods with chemical cross-linking can provide information on the structural dynamics of protein structures and protein complexes. The identification and quantitation of cross-linked peptides remains challenging for the general community, requiring specialized expertise ultimately limiting more widespread adoption of the technique. We describe a general method for targeted quantitative mass spectrometric analysis of cross-linked peptide pairs. We report the adaptation of the widely used, open source software package Skyline, for the analysis of quantitative XL-MS data as a means for data analysis and sharing of methods. We demonstrate the utility and robustness of the method with a cross-laboratory study and present data that is supported by and validates previously published data on quantified cross-linked peptide pairs. This advance provides an easy to use resource so that any lab with access to a LC-MS system capable of performing targeted quantitative analysis can quickly and accurately measure dynamic changes in protein structure and protein interactions. PMID:27997545

  6. A Comparative Study of the Characteristics of Cross-Linked, Oxidized and Dual-Modified Rice Starches

    Directory of Open Access Journals (Sweden)

    Feng-Xiang Yu

    2012-09-01

    Full Text Available Rice starch was cross-linked with epichlorohydrin (0.3%, w/w, on a dry starch basis and oxidized with sodium hypochlorite (2.5% w/w, respectively. Two dual-modified rice starch samples (oxidized cross-linked rice starch and cross-linked oxidized rice starch were obtained by the oxidation of cross-linked rice starch and the cross-linking of oxidized rice starch at the same level of reagents. The physicochemical properties of native rice starch, cross-linked rice starch and oxidized rice starch were also studied parallel with those of the two dual-modified rice starch samples using rapid visco analysis (RVA, differential scanning calorimetry (DSC, dynamic rheometry and scanning electron microscopy (SEM. It was found that the levels of cross-linking and oxidation used in this study did not cause any significant changes in the morphology of rice starch granules. Cross-linked oxidized starch showed lower swelling power (SP and solubility, and higher paste clarity in comparison with native starch. Cross-linked oxidized rice starch also had the lowest tendency of retrogradation and highest ability to resistant to shear compared with native, cross-linked, oxidized and oxidized cross-linked rice starches. These results suggest that the undesirable properties in native, cross-linked and oxidized rice starch samples could be overcome through dual-modification.

  7. [Study on the effect of temperature on the conformation of cross-linked collagen by two-dimensional infrared correlation spectroscopy].

    Science.gov (United States)

    Chen, Yi-Hui; Tian, Hui-Lin; Li, Ji-Heng; Li, Guo-Ying

    2012-06-01

    The Fourier transform infrared spectroscopy and two dimensional correlation analysis method were applied to study a denaturing process of uncross-linked collagen and cross-linked collagen during varying temperature. It was found that the intensity of typically characteristic absorptions of collagen decreased and its peak shifted to low frequency, The amide II central absorbance peak moved to a lower frequency by about 10 cm(-1), which indicated that the inter-chain hydrogen bonds which stabilized the triple helix conformation of collagen were disrupted during thermal denaturation, resulting in a conformational change. The intensity of auto-peak at 1 515 cm(-1) was maximum, which suggested that the temperature had a big impact on amide II. In comparison with uncross-linked collagen, the intensity of cross-peaks of cross-linked collagen was weaker, which demonstrated that the effect of temperature on the structure of cross-linked collagen was smaller, and the thermal stability properties of collagen solution could be improved by cross-linking. While the order of second structure changes of cross-linked collagen was different. These fundamental data should provide available information for understanding the relationship between the structure and function of cross-linked collagen.

  8. Cross-linking density alters early metabolic activities in chondrocytes encapsulated in poly(ethylene glycol) hydrogels and cultured in the rotating wall vessel.

    Science.gov (United States)

    Villanueva, Idalis; Klement, Brenda J; von Deutsch, Daniel; Bryant, Stephanie J

    2009-03-01

    In designing a tissue engineering strategy for cartilage repair, selection of both the bioreactor, and scaffold is important to the development of a mechanically functional tissue. The hydrodynamic environment associated with many bioreactors enhances nutrient transport, but also introduces fluid shear stress, which may influence cellular response. This study examined the combined effects of hydrogel cross-linking and the hydrodynamic environment on early chondrocyte response. Specifically, chondrocytes were encapsulated in poly(ethylene glycol) (PEG) hydrogels having two different cross-linked structures, corresponding to a low and high cross-linking density. Both cross-linked gels yielded high water contents (92% and 79%, respectively) and mesh sizes of 150 and 60 A respectively. Cell-laden PEG hydrogels were cultured in rotating wall vessels (RWV) or under static cultures for up to 5 days. Rotating cultures yielded low fluid shear stresses (production, and matrix deposition for glycosaminoglycans (GAG). In static cultures, gel cross-linking had no effect on DNA content, NO production, or GAG production; although GAG production increased with culture time for both cross-linked gels. In rotating cultures, DNA content increased, NO production decreased, and overall GAG production decreased when compared to static controls for the low cross-linked gels. For the high cross-linked gels, the hydrodynamic environment had no effect on DNA content, but exhibited similar results to the low cross-linked gel for NO production, and matrix production. Our findings demonstrated that at early culture times, when there is limited matrix production, the hydrodynamic environment dramatically influences cell response in a manner dependent on the gel cross-linking, which may impact long-term tissue development.

  9. Corneal Cross-Linking for Pediatric Keratoconus : Long-Term Results

    NARCIS (Netherlands)

    Godefrooij, Daniel A; Soeters, Nienke; Imhof, Saskia M; Wisse, Robert P L

    2016-01-01

    PURPOSE: To assess the efficacy and safety of cross-linking in pediatric patients with keratoconus and to provide a systematic literature overview regarding this subject. METHODS: In this prospective cohort, 54 eyes of 36 pediatric patients with keratoconus underwent standard epithelium-off cross-li

  10. Kinetics of enzyme-catalyzed cross-linking of feruloylated arabinan from sugar beet

    DEFF Research Database (Denmark)

    Abang Zaidel, Dayang Norulfairuz; Arnous, Anis; Holck, Jesper

    2011-01-01

    the kinetics of HRP catalyzed cross-linking of FA esterified to α-(1,5)-linked arabinans are affected by the length of the arabinan chains carrying the feruloyl substitutions. The kinetics of the HRP-catalyzed cross-linking of four sets of arabinan samples from sugar beet pulp, having different molecular...... weights and hence different degrees of polymerization, were monitored by the disappearance of FA absorbance at 316 nm. MALDI-TOF/TOF-MS analysis confirmed that the sugar beet arabinans were feruloyl-substituted, and HPLC analysis verified that the amounts of diFAs increased when FA levels decreased...

  11. Preparation of shell cross-linked nano-objects from hybrid-peptide block copolymers.

    Science.gov (United States)

    Rodríguez-Hernández, Juan; Babin, Jérôme; Zappone, Bruno; Lecommandoux, Sébastien

    2005-01-01

    Supramolecular structures formed by self-assembly of diblock copolymers in solution are stable over restricted environmental conditions: concentration, temperature, pH, or ion strength among others. To enlarge their domain of application, it appears necessary to develop stabilization strategies. We report here different strategies to stabilize the shell of micelles formed by self-assembly of amphiphilic polydiene-b-polypeptide diblock copolymers. For this purpose, covalent bonds can be formed between either amine or carboxylic acid groups distributed along the soluble peptide block and a cross-linking agent that contains respectively aldehyde or amine functions. Shell stabilization affords systems with unique properties that combine three main advantages: shape persistence, control of the porosity, and stimuli-responsive behavior. The covalent capture of such macromolecular objects has been studied by light scattering, AFM, and conductimetry measurements.

  12. Iontophoresis-Assisted Corneal Collagen Cross-Linking with Epithelial Debridement: Preliminary Results

    Science.gov (United States)

    Legrottaglie, Emanuela F.

    2016-01-01

    Purpose. To report the early outcomes of iontophoresis-assisted corneal collagen cross-linking procedure with epithelial debridement (I-SCXL). Methods. Twenty eyes of twenty patients with progressive keratoconus were included in this prospective clinical study. Best spectacle corrected visual acuity (BSCVA), sphere and cylinder refraction, corneal topography, Scheimpflug tomography, aberrometry, anterior segment optical coherence tomography (AS-OCT), and endothelial cell count were assessed at baseline and at 1, 3, and 6 months of follow-up. The parameters considered to establish keratoconus progression were always proven with differential maps as change in curvature in the cone area of at least 1 diopter obtained with an instantaneous map. Results. Functional parameters showed a significant improvement (p 0.05). Conclusion. The early results indicate that the I-SCXL may be able to reduce the treatment time and improve the riboflavin diffusion. PMID:27547758

  13. Physicochemical characterization of chitosan/nylon6/polyurethane foam chemically cross-linked ternary blends.

    Science.gov (United States)

    Jayakumar, S; Sudha, P N

    2013-03-15

    Chitosan/nylon6/polyurethane foam (CS/Ny6/PUF) ternary blend was prepared and chemically cross-linked with glutaraldehyde. Structural, thermal and morphological studies were performed for the prepared ternary blends. Characterizations of the ternary blends were investigated by Fourier transform infrared spectroscopy (FTIR), thermo gravimetric analysis (TGA), differential scanning calorimetry (DSC), X-ray diffraction (XRD) and scanning electron microscope (SEM). The FTIR results showed that the strong intermolecular hydrogen bonds took place between CS, Ny6 and PUF. TGA and DSC studies reveal that the thermal stability of the blend is enhanced by glutaraldehyde as crosslinking agent. Results of XRD indicated that the relative crystalline of pure CS film was reduced when the polymeric network was reticulated by glutaraldehyde. Finally, the results of scanning electron microscopy (SEM) indicated that the morphology of the blend is rough and heterogeneous, further it confirms the interaction between the functional groups of the blend components.

  14. Iontophoresis-Assisted Corneal Collagen Cross-Linking with Epithelial Debridement: Preliminary Results

    Directory of Open Access Journals (Sweden)

    Paolo Vinciguerra

    2016-01-01

    Full Text Available Purpose. To report the early outcomes of iontophoresis-assisted corneal collagen cross-linking procedure with epithelial debridement (I-SCXL. Methods. Twenty eyes of twenty patients with progressive keratoconus were included in this prospective clinical study. Best spectacle corrected visual acuity (BSCVA, sphere and cylinder refraction, corneal topography, Scheimpflug tomography, aberrometry, anterior segment optical coherence tomography (AS-OCT, and endothelial cell count were assessed at baseline and at 1, 3, and 6 months of follow-up. The parameters considered to establish keratoconus progression were always proven with differential maps as change in curvature in the cone area of at least 1 diopter obtained with an instantaneous map. Results. Functional parameters showed a significant improvement (p0.05. Conclusion. The early results indicate that the I-SCXL may be able to reduce the treatment time and improve the riboflavin diffusion.

  15. Physicochemical characterization of chitosan/nylon6/polyurethane foam chemically cross-linked ternary blends

    Science.gov (United States)

    Jayakumar, S.; Sudha, P. N.

    2013-03-01

    Chitosan/nylon6/polyurethane foam (CS/Ny6/PUF) ternary blend was prepared and chemically cross-linked with glutaraldehyde. Structural, thermal and morphological studies were performed for the prepared ternary blends. Characterizations of the ternary blends were investigated by Fourier transform infrared spectroscopy (FTIR), thermo gravimetric analysis (TGA), differential scanning calorimetry (DSC), X-ray diffraction (XRD) and scanning electron microscope (SEM). The FTIR results showed that the strong intermolecular hydrogen bonds took place between CS, Ny6 and PUF. TGA and DSC studies reveal that the thermal stability of the blend is enhanced by glutaraldehyde as crosslinking agent. Results of XRD indicated that the relative crystalline of pure CS film was reduced when the polymeric network was reticulated by glutaraldehyde. Finally, the results of scanning electron microscopy (SEM) indicated that the morphology of the blend is rough and heterogeneous, further it confirms the interaction between the functional groups of the blend components.

  16. 1,3-Diphenylethenylcarbazolyl-Based Monomer for Cross-Linked Hole Transporting Layers

    Directory of Open Access Journals (Sweden)

    Maryte Daskeviciene

    2015-05-01

    Full Text Available A new cross-linkable monomer containing 1,3-diphenylethenylcarbazolyl-based hole-transporting moieties and four reactive epoxy groups, was prepared by a multistep synthesis route from 1,3-bis(2,2-diphenylethenyl-9H-carbazol-2-ol and its application for the in situ formation of cross-linked hole transporting layers was investigated. A high concentration of flexible aliphatic epoxy chains ensures good solubility and makes this compound an attractive cross-linking agent. The synthesized compounds were characterized by various techniques, including differential scanning calorimetry, xerographic time of flight, and electron photoemission in air methods.

  17. Characterization of Cross-linked Alkaline Lignin/Poly (Vinyl Alcohol Film with a Formaldehyde Cross-linker

    Directory of Open Access Journals (Sweden)

    Ling Su

    2014-06-01

    Full Text Available On the basis of previous experiments, industrial alkaline lignin/poly (vinyl alcohol (PVOH cross-linked films, industrial alkaline lignin/poly (vinyl alcohol blend films, and neat poly (vinyl alcohol films were prepared by casting. The films were investigated by Fourier transform infra-red spectroscopy (FTIR, X-ray diffraction (XRD, thermogravimetry analysis (TGA, and dynamic mechanical analysis (DMA. The water contact angles for the three kinds of films were studied as well. The crosslinking reaction between alkaline lignin and PVOH was strong, which was attributed to the high hydrolysis degree of PVOH and the high reactivity of formaldehyde. Compared with the neat PVOH film, the crystallinity of the cross-linked film decreased slightly; the thermal stability of the cross-linked film was higher; DMA analysis showed that the Tg and the tanδ magnitude of the alkaline lignin/PVOH reaction film both decreased slightly. Lignin and the cross-linking reaction both improved the water resistance of films. Therefore, this research has provided a detailed analysis of the characterization of the films while exploring the potential of direct usage of industrial alkaline lignin in polymer materials.

  18. Multifunctional Hydrogels Prepared by Dual Ion Cross-Linking for Chronic Wound Healing.

    Science.gov (United States)

    Li, Yonghui; Han, Yan; Wang, Xiaoya; Peng, Jinliang; Xu, Yuhong; Chang, Jiang

    2017-05-17

    The creation of a moist environment and promotion of blood vessel formation are critical for wound healing. Sodium alginate (SA) hydrogel, which has good biocompatibility and is able to provide a moist environment, has been widely used as a wound dressing. However, it lacks antibacterial ability and bioactivities, which would facilitate chronic wound healing. On the basis of the gelation characteristics of SA and the bioactive hardystonite (HS) bioceramic, we designed a unique, bioactive, injectable composite hydrogel through double ion cross-linking, in which divalent ions, such as Ca(2+) and Zn(2+) function as cross-linkers; Zn(2+) also functions as an antibacterial component and as nutrition for wound healing, and Si ions play a key role in determining the bioactivity of the hydrogel. With the controlled release of divalent ions, such as Ca(2+) and Zn(2+) from HS, the gelation process of the composite hydrogel could be efficiently controlled. In addition, in vitro results reveal that the composite hydrogel stimulated proliferation and migration of both human dermal fibroblasts and human umbilical vein endothelial cells, and the in vivo results show that the wound-healing process is obviously enhanced, and the formation of epithelium and blood vessels are evidently advanced. This study indicates the potential of the SA/HS hydrogel as a multifunctional injectable wound dressing with the ability to inhibit bacterial growth and stimulate angiogenesis and wound healing.

  19. Stable Bioactive Enzyme-Containing Multilayer Films Based on Covalent Cross-Linking from Mussel-Inspired Adhesives.

    Science.gov (United States)

    Longo, Johan; Garnier, Tony; Mateescu, Mihaela; Ponzio, Florian; Schaaf, Pierre; Jierry, Loïc; Ball, Vincent

    2015-11-17

    The use of immobilized enzymes is mandatory for the easy separation of the enzyme, the unreacted substrates, and the obtained products to allow repeated enzymatic assays without cumbersome purification steps. The immobilization procedure is however critical to obtain a high fraction of active enzyme. In this article, we present an enzyme immobilization strategy based on a catechol functionalized alginate. We demonstrate that alkaline phosphatase (ALP) remains active in multilayered films made with alginate modified with catechol moieties (AlgCat) for long duration, that is, up to 7 weeks, provided the multilayered architecture is cross-linked with sodium periodate. This cross-linking reaction allows to create covalent bonds between the amino groups of ALP and the quinone group carried by the modified alginate. In the absence of cross-linking, the enzymatic activity is rapidly lost and this reduction is mainly due to enzyme desorption. We also show that NaIO4 cross-linked (AlgCat-Alp)n films can be freeze-dried and reused at least 3 weeks later without lost in enzymatic activity.

  20. Ice templated and cross-linked xylan/nanocrystalline cellulose hydrogels.

    Science.gov (United States)

    Köhnke, Tobias; Elder, Thomas; Theliander, Hans; Ragauskas, Arthur J

    2014-01-16

    Structured xylan-based hydrogels, reinforced with cellulose nanocrystals (CNCs), have successfully been prepared from water suspensions by cross-linking during freeze-casting. In order to induce cross-linking during the solidification/sublimation operation, xylan was first oxidized using sodium periodate to introduce dialdehydes. The oxidized xylan was then mixed with CNCs after which the suspension was frozen unidirectionally in order to control the ice crystal formation and by that the pore morphology of the material. Finally the ice crystal templates were removed by freeze-drying. During the freeze-casting process hemiacetal bonds are formed between the aldehyde groups and hydroxyl groups, either on other xylan molecules or on CNCs, which cross-links the system. The proposed cross-linking reaction was confirmed by using cross-polarization magic angle spinning (CP/MAS) nuclear magnetic resonance (NMR) spectroscopy. The pore morphology of the obtained materials was analyzed by scanning electron microscopy (SEM). The materials were also tested for compressive strength properties, both in dry and water swollen state. All together this study describes a novel combined freeze-casting/cross-linking process which enables fabrication of nanoreinforced biopolymer-based hydrogels with controlled porosity and 3-D architecture.

  1. DNA-Protein Cross-Links: Formation, Structural Identities, and Biological Outcomes.

    Science.gov (United States)

    Tretyakova, Natalia Y; Groehler, Arnold; Ji, Shaofei

    2015-06-16

    Noncovalent DNA-protein interactions are at the heart of normal cell function. In eukaryotic cells, genomic DNA is wrapped around histone octamers to allow for chromosomal packaging in the nucleus. Binding of regulatory protein factors to DNA directs replication, controls transcription, and mediates cellular responses to DNA damage. Because of their fundamental significance in all cellular processes involving DNA, dynamic DNA-protein interactions are required for cell survival, and their disruption is likely to have serious biological consequences. DNA-protein cross-links (DPCs) form when cellular proteins become covalently trapped on DNA strands upon exposure to various endogenous, environmental and chemotherapeutic agents. DPCs progressively accumulate in the brain and heart tissues as a result of endogenous exposure to reactive oxygen species and lipid peroxidation products, as well as normal cellular metabolism. A range of structurally diverse DPCs are found following treatment with chemotherapeutic drugs, transition metal ions, and metabolically activated carcinogens. Because of their considerable size and their helix-distorting nature, DPCs interfere with the progression of replication and transcription machineries and hence hamper the faithful expression of genetic information, potentially contributing to mutagenesis and carcinogenesis. Mass spectrometry-based studies have identified hundreds of proteins that can become cross-linked to nuclear DNA in the presence of reactive oxygen species, carcinogen metabolites, and antitumor drugs. While many of these proteins including histones, transcription factors, and repair proteins are known DNA binding partners, other gene products with no documented affinity for DNA also participate in DPC formation. Furthermore, multiple sites within DNA can be targeted for cross-linking including the N7 of guanine, the C-5 methyl group of thymine, and the exocyclic amino groups of guanine, cytosine, and adenine. This structural

  2. A novel method for immobilization of proteins via entrapment of magnetic nanoparticles through epoxy cross-linking.

    Science.gov (United States)

    Iype, Tessy; Thomas, Jaiby; Mohan, Sangeetha; Johnson, Kochurani K; George, Ligi E; Ambattu, Lizebona A; Bhati, Aniruddha; Ailsworth, Kristen; Menon, Bindu; Rayabandla, Sunayana M; Jesudasan, Rachel A; Santhosh, Sam; Ramchand, Chaniyilparampu N

    2017-02-15

    A method for immobilization of functional proteins by chemical cross-linking of the protein of interest and uncoated iron oxide nanoparticles in the presence of Epichlorohydrin is described. As a result of the cross-linking, the proteins form a matrix in which the particles get entrapped. The optimum concentration of Epichlorohydrin that facilitates immobilization of protein without affecting the functional properties of the protein was determined. This method was used to immobilize several functional proteins and the development and functional activity of Protein A-magnetic nanoparticles (MNPs) is described here in detail. The Protein A-MNPs possess high binding capacity due to the increased surface area of uncoated nanoparticles and robust magnetic separation due to the absence of polymeric coating materials. Protein A-MNPs were successfully used for purification of antibodies and also for immunoprecipitation. We also immobilized enzymes such as horse radish peroxidase and esterase and found that by providing the optimum incubation time, temperature and protein to nanoparticle ratio, we can retain the activity and improve the stability of the enzyme. This study is the first demonstration that Epichlorohydrin can be used to entrap nanoparticles in a cross-linked matrix of protein without impairing the activity of immobilized protein.

  3. Selective adsorption of metoprolol enantiomers using 2-hydroxypropyl-β-cyclodextrin cross-linked multiwalled carbon nanotube.

    Science.gov (United States)

    Farhadian, Nafiseh; Sharifi, Arezoo; Lashgari, Elmira

    2015-03-01

    This study investigates the ability of functionalized multiwalled carbon nanotubes (MWCNTs) for enantio-separation of metoprolol chiral forms. 2Hydroxypropyl-β-cyclodextrin (2HP-β-CD) was applied as a chiral selector to functionalize carbon nanotubes (CNTs). The modified multiwalled CNT samples were characterized using scanning electron microscopy and Fourier transform infrared spectroscopy. The results of analyses showed that CNTs were successfully cross-linked with 2HP-β-CD. To evaluate the enantio-separation property of the products, the separation of metoprolol chiral forms on the initial and final products was examined. Further, UV-visible spectroscopy and polarimeter analyses were used for characterization. The results indicate that MWCNT does not have any intrinsic enantio-separation ability, although its selectivity for enantio-separation can be enhanced by cross-linking it to 2HP-β-CD. Moreover, the optimal mass of adsorbent as well as optimal mass of functional groups is estimated to achieve maximum enantio-separation efficiency. The results indicate that applying large amounts of 2HP-β-CD to CNTs functionalization decreases the cross-linking efficiency, which consequently reduces enantio-separation efficiency. Copyright © 2014 John Wiley & Sons, Ltd.

  4. Designing of superporous cross-linked hydrogels containing acrylic-based polymer network

    Directory of Open Access Journals (Sweden)

    Ray Debajyoti

    2008-01-01

    Full Text Available Biodegradable cross-linked polymer, 2-hydroxyethyl methacrylate-co-acrylic acid was synthesized by free radical polymerization technique using N,N"-methylene-bis-acrylamide as cross-linker and benzoyl peroxide as reaction initiator. FT-IR, 1 H-NMR, scanning electron microscopy (SEM, and thermogravimetric analysis (TGA studies of the copolymer along with homopolymers were carried out. FT-IR studies showed no interactions on copolymerization. SEM studies of the copolymer were carried out and mean particle size was found to be 50 µm. TGA analysis indicated an increase in thermal stability by cross-linking the polymer network. Swelling behavior of the copolymer showed more swelling by increasing pH of the medum and the prepared polymer was found to be biodegradable. The prepared cross-linked polymer system holds good for further drug delivery studies in connection to its super swelling and biodegradability.

  5. EFFICIENCY MODELS OF THE CROSS-FUNCTIONAL TEAMS

    OpenAIRE

    Dinca Laura; Criveanu Radu

    2013-01-01

    Cross-functional teams represent a characteristic of the new organization form of the enterprises, imposed by the complexity of the present environment. Regardless their kind, the new organization forms are based on the cross-functional teams as an innovation source and reunion of competences. Only by the medium of the cross-functional teams, the new organizational partnerships obtain flexibility in their actions and fastness in their reactions. By their features, the cross-functional teams s...

  6. Biodegradation of differently cross-linked collagen membranes: an experimental study in the rat.

    Science.gov (United States)

    Rothamel, Daniel; Schwarz, Frank; Sager, Martin; Herten, Monika; Sculean, Anton; Becker, Jürgen

    2005-06-01

    The aim of the present study was to compare the biodegradation of differently cross-linked collagen membranes in rats. Five commercially available and three experimental membranes (VN) were included: (1) BioGide (BG) (non-cross-linked porcine type I and III collagens), (2) BioMend (BM), (3) BioMendExtend (BME) (glutaraldehyde cross-linked bovine type I collagen), (4) Ossix (OS) (enzymatic-cross-linked bovine type I collagen), (5) TutoDent (TD) (non-cross-linked bovine type I collagen, and (6-8) VN(1-3) (chemical cross-linked porcine type I and III collagens). Specimens were randomly allocated in unconnected subcutaneous pouches separated surgically on the back of 40 wistar rats, which were divided into five groups (2, 4, 8, 16, and 24 weeks), including eight animals each. After 2, 4, 8, 16, and 24 weeks of healing, the rats were sacrificed and explanted specimens were prepared for histologic and histometric analysis. The following parameters were evaluated: biodegradation over time, vascularization, tissue integration, and foreign body reaction. Highest vascularization and tissue integration was noted for BG followed by BM, BME, and VN(1); TD, VN(2), and VN(3) showed prolongated, while OS exhibited no vascularization. Subsequently, biodegradation of BG, BM, BME and VN(1) was faster than TD, VN(2), and VN(3). OS showed only a minute amount of superficial biodegradation 24 weeks following implantation. Biodegradation of TD, BM, BME, VN(2), and VN(3) was associated with the presence of inflammatory cells. Within the limits of the present study, it was concluded that cross-linking of bovine and porcine-derived collagen types I and III was associated with (i) prolonged biodegradation, (ii) decreased tissue integration and vascularization, and (iii) in case of TD, BM, BME, VN(2), and VN(3) foreign body reactions.

  7. Vitamin E-diffused highly cross-linked UHMWPE particles induce less osteolysis compared to highly cross-linked virgin UHMWPE particles in vivo.

    Science.gov (United States)

    Bichara, David A; Malchau, Erik; Sillesen, Nanna H; Cakmak, Selami; Nielsen, G Petur; Muratoglu, Orhun K

    2014-09-01

    Recent in vitro findings suggest that UHMWPE wear particles containing vitamin E (VE) may have reduced biologic activity and decreased osteolytic potential. We hypothesized that particles from VE-stabilized, radiation cross-linked UHMWPE would cause less osteolysis in a murine calvarial bone model when compared to virgin gamma irradiated cross-linked UHMWPE. Groups received equal amount of particulate debris overlaying the calvarium for 10 days. Calvarial bone was examined using high resolution micro-CT and histomorphometric analyses. There was a statistically significant difference between virgin (12.2%±8%) and VE-UHMWPE (3%±1.4%) groups in regards to bone resorption (P=0.005) and inflammatory fibrous tissue overlaying the calvaria (0.48 vs. 0.20, PUHMWPE particles have reduced osteolytic potential in vivo when compared to virgin UHMWPE.

  8. Vitamin E-diffused highly cross-linked UHMWPE particles induce less osteolysis compared to highly cross-linked virgin UHMWPE particles in vivo

    DEFF Research Database (Denmark)

    Bichara, David A; Malchau, Erik; Sillesen, Nanna H

    2014-01-01

    when compared to virgin gamma irradiated cross-linked UHMWPE. Groups received equal amount of particulate debris overlaying the calvarium for 10 days. Calvarial bone was examined using high resolution micro-CT and histomorphometric analyses. There was a statistically significant difference between...... virgin (12.2%±8%) and VE-UHMWPE (3%±1.4%) groups in regards to bone resorption (P=0.005) and inflammatory fibrous tissue overlaying the calvaria (0.48 vs. 0.20, P

  9. Fast Computation of Cross-Ambiguity Function

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    A novel method based on zoom fast Fourier transform(FFT) is proposed for minimizing the burden processing of cross-ambiguity functions without affecting performance. The low-pass anti-aliasing filter in zoom FFT is realized by using the multistage filtering technique and the weighting processing is employed in the first stage filter to get rid of the redundancy of the computation. In practical systems, the input data is divided into overlapped data frames to avoid loss of detection ability which results in the rapid increase of computational complexity. A segment technique is also proposed in which CAF calculation of overlapped data frames is viewed as slide window FFT to decrease the computational complexity. The experimental results show that compared to the conventional methods, the proposed method can lower computational complexity and is consistent with the real time implementation in existing high-speed digital processors.

  10. Introduction: Links between Social Interaction and Executive Function

    Science.gov (United States)

    Lewis, Charlie; Carpendale, Jeremy I. M.

    2009-01-01

    The term executive function is used increasingly within developmental psychology and is often taken to refer to unfolding brain processes. We trace the origins of research on executive function to show that the link with social interaction has a long history. We suggest that a recent frenzy of research exploring methods for studying individual…

  11. Introduction: Links between Social Interaction and Executive Function

    Science.gov (United States)

    Lewis, Charlie; Carpendale, Jeremy I. M.

    2009-01-01

    The term executive function is used increasingly within developmental psychology and is often taken to refer to unfolding brain processes. We trace the origins of research on executive function to show that the link with social interaction has a long history. We suggest that a recent frenzy of research exploring methods for studying individual…

  12. Preparation of cross-linked hen-egg white lysozyme crystals free of cracks

    Science.gov (United States)

    Yan, Er-Kai; Lu, Qin-Qin; Zhang, Chen-Yan; Liu, Ya-Li; He, Jin; Chen, Da; Wang, Bo; Zhou, Ren-Bin; Wu, Ping; Yin, Da-Chuan

    2016-01-01

    Cross-linked protein crystals (CLPCs) are very useful materials in applications such as biosensors, catalysis, and X-ray crystallography. Hence, preparation of CLPCs is an important research direction. During the preparation of CLPCs, an often encountered problem is that cracks may appear in the crystals, which may finally lead to shattering of the crystals into small pieces and cause problem in practical applications. To avoid cross-link induced cracking, it is necessary to study the cracking phenomenon in the preparation process. In this paper, we present an investigation on how to avoid cracking during preparation of CLPCs. An orthogonal experiment was designed to study the phenomenon of cross-link induced cracking of hen-egg white lysozyme (HEWL) crystals against five parameters (temperature, solution pH, crystal growth time, glutaraldehyde concentration, and cross-linking time). The experimental results showed that, the solution pH and crystal growth time can significantly affect cross-link induced cracking. The possible mechanism was studied, and optimized conditions for obtaining crack-free CLPCs were obtained and experimentally verified. PMID:27703210

  13. Supercritical CO2 Foaming of Radiation Cross-Linked Isotactic Polypropylene in the Presence of TAIC

    Directory of Open Access Journals (Sweden)

    Chen-Guang Yang

    2016-12-01

    Full Text Available Since the maximum foaming temperature window is only about 4 °C for supercritical CO2 (scCO2 foaming of pristine polypropylene, it is important to raise the melt strength of polypropylene in order to more easily achieve scCO2 foaming. In this work, radiation cross-linked isotactic polypropylene, assisted by the addition of a polyfunctional monomer (triallylisocyanurate, TAIC, was employed in the scCO2 foaming process in order to understand the benefits of radiation cross-linking. Due to significantly enhanced melt strength and the decreased degree of crystallinity caused by cross-linking, the scCO2 foaming behavior of polypropylene was dramatically changed. The cell size distribution, cell diameter, cell density, volume expansion ratio, and foaming rate of radiation-cross-linked polypropylene under different foaming conditions were analyzed and compared. It was found that radiation cross-linking favors the foamability and formation of well-defined cell structures. The optimal absorbed dose with the addition of 2 wt % TAIC was 30 kGy. Additionally, the foaming temperature window was expanded to about 8 °C, making the handling of scCO2 foaming of isotactic polypropylene much easier.

  14. Mapping of the dimer interface of the Escherichia coli mannitol permease by cysteine cross-linking.

    Science.gov (United States)

    van Montfort, Bart A; Schuurman-Wolters, Gea K; Wind, Joyce; Broos, Jaap; Robillard, George T; Poolman, Bert

    2002-04-26

    A cysteine cross-linking approach was used to identify residues at the dimer interface of the Escherichia coli mannitol permease. This transport protein comprises two cytoplasmic domains and one membrane-embedded C domain per monomer, of which the latter provides the dimer contacts. A series of single-cysteine His-tagged C domains present in the native membrane were subjected to Cu(II)-(1,10-phenanthroline)(3)-catalyzed disulfide formation or cysteine cross-linking with dimaleimides of different length. The engineered cysteines were at the borders of the predicted membrane-spanning alpha-helices. Two residues were found to be located in close proximity of each other and capable of forming a disulfide, while four other locations formed cross-links with the longer dimaleimides. Solubilization of the membranes did only influence the cross-linking behavior at one position (Cys(73)). Mannitol binding only effected the cross-linking of a cysteine at the border of the third transmembrane helix (Cys(134)), indicating that substrate binding does not lead to large rearrangements in the helix packing or to dissociation of the dimer. Upon mannitol binding, the Cys(134) becomes more exposed but the residue is no longer capable of forming a stable disulfide in the dimeric IIC domain. In combination with the recently obtained projection structure of the IIC domain in two-dimensional crystals, a first proposal is made for alpha-helix packing in the mannitol permease.

  15. Effects of partial hydrolysis and subsequent cross-linking on wheat gluten physicochemical properties and structure.

    Science.gov (United States)

    Wang, Kaiqiang; Luo, Shuizhong; Cai, Jing; Sun, Qiaoqiao; Zhao, Yanyan; Zhong, Xiyang; Jiang, Shaotong; Zheng, Zhi

    2016-04-15

    The rheological behavior and thermal properties of wheat gluten following partial hydrolysis using Alcalase and subsequent microbial transglutaminase (MTGase) cross-linking were investigated. The wheat gluten storage modulus (G') and thermal denaturation temperature (Tg) were significantly increased from 2.26 kPa and 54.43°C to 7.76 kPa and 57.69°C, respectively, by the combined action of partial hydrolysis (DH 0.187%) and cross-linking. The free SH content, surface hydrophobicity, and secondary structure analysis suggested that an appropriate degree of Alcalase-based hydrolysis allowed the compact wheat gluten structure to unfold, increasing the β-sheet content and surface hydrophobicity. This improved its molecular flexibility and exposed additional glutamine sites for MTGase cross-linking. SEM images showed that a compact 3D network formed, while SDS-PAGE profiles revealed that excessive hydrolysis resulted in high-molecular-weight subunits degrading to smaller peptides, unsuitable for cross-linking. It was also demonstrated that the combination of Alcalase-based partial hydrolysis with MTGase cross-linking might be an effective method for modifying wheat gluten rheological behavior and thermal properties.

  16. Site specificity of psoralen-DNA interstrand cross-linking determined by nuclease Bal31 digestion

    DEFF Research Database (Denmark)

    Zhen, W P; Buchardt, O; Nielsen, Henrik

    1986-01-01

    A novel method for determination of psoralen photo-cross-linking sites in double-stranded DNA is described, which is based on a pronounced inhibition of Bal31 exonuclease activity by psoralen-DNA interstrand cross-links. The results using a 51 base pair fragment of plasmid pUC19 and a 346 base pair...... fragment of pBR322 show that 5'-TA sequences are preferred cross-linking sites compared to 3'-TA sequences. They also indicate that sequences flanking the 5'-TA site influence the cross-linking efficiency at the site. The DNA photo-cross-linking by 4,5',8-trimethylpsoralen and 8-methoxypsoralen...... was analyzed, and these two psoralens showed identical site specificity. The 5'-TA preference is rationalized on the basis of the local DNA structure in terms of the pi-pi electronic interaction between the thymines and the intercalated psoralens, as well as on the base tilt angles of the DNA....

  17. Effects of alginate hydrogel cross-linking density on mechanical and biological behaviors for tissue engineering.

    Science.gov (United States)

    Jang, Jinah; Seol, Young-Joon; Kim, Hyeon Ji; Kundu, Joydip; Kim, Sung Won; Cho, Dong-Woo

    2014-09-01

    An effective cross-linking of alginate gel was made through reaction with calcium carbonate (CaCO3). We used human chondrocytes as a model cell to study the effects of cross-linking density. Three different pore size ranges of cross-linked alginate hydrogels were fabricated. The morphological, mechanical, and rheological properties of various alginate hydrogels were characterized and responses of biosynthesis of cells encapsulated in each gel to the variation in cross-linking density were investigated. Desired outer shape of structure was maintained when the alginate solution was cross-linked with the applied method. The properties of alginate hydrogel could be tailored through applying various concentrations of CaCO3. The rate of synthesized GAGs and collagens was significantly higher in human chondrocytes encapsulated in the smaller pore structure than that in the larger pore structure. The expression of chondrogenic markers, including collagen type II and aggrecan, was enhanced in the smaller pore structure. It was found that proper structural morphology is a critical factor to enhance the performance and tissue regeneration.

  18. Synthesis, Characterization, and Antibacterial Activity of Cross-Linked Chitosan-Glutaraldehyde

    Directory of Open Access Journals (Sweden)

    Long-Biao Guo

    2013-05-01

    Full Text Available This present study deals with synthesis, characterization and antibacterial activity of cross-linked chitosan-glutaraldehyde. Results from this study indicated that cross-linked chitosan-glutaraldehyde markedly inhibited the growth of antibiotic-resistant Burkholderia cepacia complex regardless of bacterial species and incubation time while bacterial growth was unaffected by solid chitosan. Furthermore, high temperature treated cross-linked chitosan-glutaraldehyde showed strong antibacterial activity against the selected strain 0901 although the inhibitory effects varied with different temperatures. In addition, physical-chemical and structural characterization revealed that the cross-linking of chitosan with glutaraldehyde resulted in a rougher surface morphology, a characteristic Fourier transform infrared (FTIR band at 1559 cm−1, a specific X-ray diffraction peak centered at 2θ = 15°, a lower contents of carbon, hydrogen and nitrogen, and a higher stability of glucose units compared to chitosan based on scanning electron microscopic observation, FTIR spectra, X-ray diffraction pattern, as well as elemental and thermo gravimetric analysis. Overall, this study indicated that cross-linked chitosan-glutaraldehyde is promising to be developed as a new antibacterial drug.

  19. Cross-Linking Poly(lactic acid) Film Surface by Neutral Hyperthermal Hydrogen Molecule Bombardment.

    Science.gov (United States)

    Du, Wangli; Shao, Hong; He, Zhoukun; Tang, Changyu; Liu, Yu; Shen, Tao; Zhu, Yan; Lau, Woon-ming; Hui, David

    2015-12-16

    Constructing a dense cross-linking layer on a polymer film surface is a good way to improve the water resistance of poly(lactic acid) (PLA). However, conventional plasma treatments have failed to achieve the aim as a result of the unavoidable surface damage arising from the charged species caused by the uncontrolled high energy coming from colliding ions and electrons. In this work, we report a modified plasma method called hyperthermal hydrogen-induced cross-linking (HHIC) technology to construct a dense cross-linking layer on PLA film surfaces. This method produces energy-controlled neutral hyperthermal hydrogen, which selectively cleaves C-H bonds by molecule collision from the PLA film without breaking other bonds (e.g., C-C bonds in the polymer backbone), and results in subsequent cross-linking of the carbon radicals generated from the organic molecules. The formation of a dense cross-linking layer can serve as a barrier layer to significantly improve both the hydrophobicity and water vapor barrier property of the PLA film. Because of the advantage of selective cleavage of C-H bonds by HHIC treatment, the original physical properties (e.g., mechanical strength and light transmittance) of the PLA films are well-preserved.

  20. Studies on Cross-linking of succinic acid with chitosan/collagen

    Directory of Open Access Journals (Sweden)

    Tapas Mitra

    2013-01-01

    Full Text Available The present study summarizes the cross-linking property of succinic acid with chitosan /collagen. In detail, the chemistry behind the cross-linking and the improvement in mechanical and thermal properties of the cross-linked material were discussed with suitable instruments and bioinformatics tools. The concentration of succinic acid with reference to the chosen polymers was optimized. A 3D scaffold prepared using an optimized concentration of succinic acid (0.2% (w/v with chitosan (1.0% (w/v and similarly with collagen (0.5% (w/v, was subjected to surface morphology, FT-IR analysis, tensile strength assessment, thermal stability and biocompatibility. Results revealed, cross-linking with succinic acid impart appreciable mechanical strength to the scaffold material. In silico analysis suggested the prevalence of non-covalent interactions, which played a crucial role in improving the mechanical and thermal properties of the cross-linked scaffold. The resultant 3D scaffold may find application as wound dressing material, as an implant in clinical applications and as a tissue engineering material.

  1. Mechanical and biocompatible characterization of a cross-linked collagen-hyaluronic acid wound dressing.

    Science.gov (United States)

    Kirk, James F; Ritter, Gregg; Finger, Isaac; Sankar, Dhyana; Reddy, Joseph D; Talton, James D; Nataraj, Chandra; Narisawa, Sonoko; Millán, José Luis; Cobb, Ronald R

    2013-01-01

    Collagen scaffolds have been widely employed as a dermal equivalent to induce fibroblast infiltrations and dermal regeneration in the treatment of chronic wounds and diabetic foot ulcers. Cross-linking methods have been developed to address the disadvantages of the rapid degradation associated with collagen-based scaffolds. To eliminate the potential drawbacks associated with glutaraldehyde cross-linking, methods using a water soluble carbodiimide have been developed. In the present study, the glycosaminoglycan (GAG) hyaluronic acid (HA), was covalently attached to an equine tendon derived collagen scaffold using 1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide (EDC) to create ntSPONGE The HA was shown to be homogeneously distributed throughout the collagen matrix. In vitro analyses of the scaffold indicated that the cross-linking enhanced the biological stability by decreasing the enzymatic degradation and increasing the thermal denaturation temperature. The material was shown to support the attachment and proliferation of mouse L929 fibroblast cells. In addition, the cross-linking decreased the resorption rate of the collagen as measured in an intramuscular implant model in rabbits. The material was also shown to be biocompatible in a variety of in vitro and in vivo assays. These results indicate that this cross-linked collagen-HA scaffold, ntSPONGE has the potential for use in chronic wound healing.

  2. Novel Technique of Transepithelial Corneal Cross-Linking Using Iontophoresis in Progressive Keratoconus

    Science.gov (United States)

    Raffa, Paolo; Rosati, Marianna

    2016-01-01

    In this work, the authors presented the techniques and the preliminary results at 6 months of a randomized controlled trial (NCT02117999) comparing a novel transepithelial corneal cross-linking protocol using iontophoresis with the Dresden protocol for the treatment of progressive keratoconus. At 6 months, there was a significant average improvement with an average flattening of the maximum simulated keratometry reading of 0.72 ± 1.20 D (P = 0.01); in addition, corrected distance visual acuity improved significantly (P = 0.08) and spherical equivalent refraction was significantly less myopic (P = 0.02) 6 months after transepithelial corneal cross-linking with iontophoresis. The novel protocol using iontophoresis showed comparable results with standard corneal cross-linking to halt progression of keratoconus during 6-month follow-up. Investigation of the long-term RCT outcomes are ongoing to verify the efficacy of this transepithelial corneal cross-linking protocol and to determine if it may be comparable with standard corneal cross-linking in the management of progressive keratoconus. PMID:27597895

  3. Novel Technique of Transepithelial Corneal Cross-Linking Using Iontophoresis in Progressive Keratoconus

    Directory of Open Access Journals (Sweden)

    Marco Lombardo

    2016-01-01

    Full Text Available In this work, the authors presented the techniques and the preliminary results at 6 months of a randomized controlled trial (NCT02117999 comparing a novel transepithelial corneal cross-linking protocol using iontophoresis with the Dresden protocol for the treatment of progressive keratoconus. At 6 months, there was a significant average improvement with an average flattening of the maximum simulated keratometry reading of 0.72±1.20 D (P=0.01; in addition, corrected distance visual acuity improved significantly (P=0.08 and spherical equivalent refraction was significantly less myopic (P=0.02 6 months after transepithelial corneal cross-linking with iontophoresis. The novel protocol using iontophoresis showed comparable results with standard corneal cross-linking to halt progression of keratoconus during 6-month follow-up. Investigation of the long-term RCT outcomes are ongoing to verify the efficacy of this transepithelial corneal cross-linking protocol and to determine if it may be comparable with standard corneal cross-linking in the management of progressive keratoconus.

  4. Cross-linking study on skeletal muscle actin: properties of suberimidate-treated actin.

    Science.gov (United States)

    Ohara, O; Takahashi, S; Ooi, T; Fujiyoshi, Y

    1982-06-01

    Cross-linking experiments were performed on muscle skeletal actin, using imidoesters of various chain lengths. Chemical analyses on all products except one (derived from succinimidate) show evidence of the presence of intramolecular cross-links in the molecule. The detailed properties of suberimidate-treated actin (SA) are as follows: SA contains nearly 1 mol of intramolecular cross-link per mol of actin and less than 15% of intermolecularly cross-linked products. Even at a low salt concentration, SA is polymeric, exchanges slowly its bound nucleotide with free nucleotides in solution, and shows an F-actin-type CD spectrum. Electron micrographs of SA reveal that SA exists actually as fibrous polymers in solutions of low ionic strength, although the fibers seem to be less rigid than those at high salt concentration. The F-form of SA at a high salt concentration is indistinguishable from intact F-actin. SA can bind heavy meromyosin and activate the ATPase of heavy meromyosin as observed for intact F-actin. Tropomyosin binds SA only at a high salt concentration. These results show that SA possesses the properties of F-actin even in media of low salt concentration, which are favorable for depolymerization of F-actin. Thus, we may infer that the conformation of SA is frozen in the F-state of actin by the introduction of intramolecular cross-links in the protein.

  5. DNA interstrand cross-link induced by estrogens as well as their complete and synergic carcinogenesis

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    The estrogens show negative activity in Ames test, but estrodiol and diethylstilbestrol in estrogens both are carcinogens based upon animal experiments and epidemiological investigation. It is concluded from the di-region theory, a mechanism conception put forward by one of the present authors, that the carcinogenesis of estrogens is switched on by the covalent cross-link between complementary DNA bases induced by them. We verified for the first time by the DNA alkaline elution method that both estrodiol and diethylstilbestrol cause covalent cross-link between DNA-protein and DNA interstrands after metabolic activation with dosage correlation, but neither the non-carcinogens cholesterol nor pyrene can lead to these sorts of cross-link in the same condition. It has been known that there is a synergetic effect between estrogen and pollution of polycyclic aromatic hydrocarbons. Although non-carcinogenic pyrene alone cannot induce cross-link, its addition with equal molar quantity to estrodiol culture causes synergically the total and DNA interstrand cross-link ratios to be respectively four and three times more than the ones in the cultivation with estrodiol only. It is shown that not only the estrodiol set off the formation of pyrene bi-radicals, but also the pyrene radicals arouse conversely the production of estrodiol bi-radicals.

  6. UV-Induced DNA Interstrand Cross-Linking and Direct Strand Breaks from a New Type of Binitroimidazole Analogue.

    Science.gov (United States)

    Han, Yanyan; Chen, Wenbing; Kuang, Yunyan; Sun, Huabing; Wang, Zhiqiang; Peng, Xiaohua

    2015-05-18

    Four novel photoactivated binitroimidazole prodrugs were synthesized. These agents produced DNA interstrand cross-links (ICLs) and direct strand breaks (DSB) upon UV irradiation, whereas no or very few DNA ICLs and DSBs were observed without UV treatment. Although these four molecules (1-4) contain the same binitroimidazole moiety, they bear four different leaving groups, which resulted in their producing different yields of DNA damage. Compound 4, with nitrogen mustard as a leaving group, showed the highest ICL yield. Surprisingly, compounds 1-3, without any alkylating functional group, also induced DNA ICL formation, although they did so with lower yields, which suggested that the binitroimidazole moiety released from UV irradiation of 1-3 is capable of cross-linking DNA. The DNA cross-linked products induced by these compounds were completely destroyed upon 1.0 M piperidine treatment at 90 °C (leading to cleavage at dG sites), which revealed that DNA cross-linking mainly occurred via alkylation of dGs. We proposed a possible mechanism by which alkylating agents were released from these compounds. HRMS and NMR analysis confirmed that free nitrogen mustards were generated by UV irradiation of 4. Suppression of DNA ICL and DSB formation by a radical trap, TEMPO, indicated the involvement of free radicals in the photo reactions of 3 and 4 with DNA. On the basis of these data, we propose that UV irradiation of compounds 1-4 generated a binitroimidazole intermediate that cross-links DNA. The higher ICL yield observed with 4 resulted from the amine effector nitrogen mustard released from UV irradiation.

  7. Mass spectrometric identification of formaldehyde-induced peptide modifications under in vivo protein cross-linking conditions.

    Science.gov (United States)

    Toews, Judy; Rogalski, Jason C; Clark, Thomas J; Kast, Juergen

    2008-06-23

    Formaldehyde cross-linking of proteins is emerging as a novel approach to study protein-protein interactions in living cells. It has been shown to be compatible with standard techniques used in functional proteomics such as affinity-based protein enrichment, enzymatic digestion, and mass spectrometric protein identification. So far, the lack of knowledge on formaldehyde-induced protein modifications and suitable mass spectrometric methods for their targeted detection has impeded the identification of the different types of cross-linked peptides in these samples. In particular, it has remained unclear whether in vitro studies that identified a multitude of amino acid residues reacting with formaldehyde over the course of several days are suitable substitutes for the much shorter reaction times of 10-20 min used in cross-linking experiments in living cells. The current study on model peptides identifies amino-termini as well as lysine, tryptophan, and cysteine side chains, i.e. a small subset of those modified after several days, as the major reactive sites under such conditions, and suggests relative position in the peptide sequence as well as sequence microenvironment to be important factors that govern reactivity. Using MALDI-MS, mass increases of 12 Da on amino groups and 30 Da on cysteines were detected as the major reaction products, while peptide fragment ion analysis by tandem mass spectrometry was used to localize the actual modification sites on a peptide. Non-specific cross-linking was absent, and could only be detected with low yield at elevated peptide concentrations. The detailed knowledge on the constraints and products of the formaldehyde reaction with peptides after short incubation times presented in this study is expected to facilitate the targeted mass spectrometric analysis of proteins after in vivo formaldehyde cross-linking.

  8. Cross-linking Electrospun Polydioxanone-Soluble Elastin Blends: Material Characterization

    Directory of Open Access Journals (Sweden)

    Michael J. McClure

    2008-03-01

    Full Text Available The purpose of this study was to establish whether material properties of elastin co-electrospun with polydioxanone (PDO would change over time in both the uncross-linked state and the cross-linked state. First, uncross-linked scaffolds were placed in phosphate buffered saline (PBS for three separate time periods: 15 minutes, 1 hour, and 24 hours, and subsequently tested using uniaxial materials testing. Several cross-linking reagents were then investigated to verify their ability to crosslink elastin: 1-ethyl-3-(dimethylaminopropyl-carbodiimide (EDC, ethylene glycol diglycidyl ether (EGDE, and genipin. Uniaxial tensile testing was performed on scaffolds cross-linked with EDC and genipin, yielding results that warranted further investigation for PDO-elastin blends. Material properties of the cross-linked scaffolds were then found within range of both pig femoral artery and human femoral artery. These results demonstrate PDO-elastin blends could potentially be favorable as vascular grafts, thus warranting future in vitro and in vivo studies.

  9. Use of proteinase K nonspecific digestion for selective and comprehensive identification of interpeptide cross-links: application to prion proteins.

    Science.gov (United States)

    Petrotchenko, Evgeniy V; Serpa, Jason J; Hardie, Darryl B; Berjanskii, Mark; Suriyamongkol, Bow P; Wishart, David S; Borchers, Christoph H

    2012-07-01

    Chemical cross-linking combined with mass spectrometry is a rapidly developing technique for structural proteomics. Cross-linked proteins are usually digested with trypsin to generate cross-linked peptides, which are then analyzed by mass spectrometry. The most informative cross-links, the interpeptide cross-links, are often large in size, because they consist of two peptides that are connected by a cross-linker. In addition, trypsin targets the same residues as amino-reactive cross-linkers, and cleavage will not occur at these cross-linker-modified residues. This produces high molecular weight cross-linked peptides, which complicates their mass spectrometric analysis and identification. In this paper, we examine a nonspecific protease, proteinase K, as an alternative to trypsin for cross-linking studies. Initial tests on a model peptide that was digested by proteinase K resulted in a "family" of related cross-linked peptides, all of which contained the same cross-linking sites, thus providing additional verification of the cross-linking results, as was previously noted for other post-translational modification studies. The procedure was next applied to the native (PrP(C)) and oligomeric form of prion protein (PrPβ). Using proteinase K, the affinity-purifiable CID-cleavable and isotopically coded cross-linker cyanurbiotindipropionylsuccinimide and MALDI-MS cross-links were found for all of the possible cross-linking sites. After digestion with proteinase K, we obtained a mass distribution of the cross-linked peptides that is very suitable for MALDI-MS analysis. Using this new method, we were able to detect over 60 interpeptide cross-links in the native PrP(C) and PrPβ prion protein. The set of cross-links for the native form was used as distance constraints in developing a model of the native prion protein structure, which includes the 90-124-amino acid N-terminal portion of the protein. Several cross-links were unique to each form of the prion protein, including

  10. Cross-linking methods of electrospun fibrinogen scaffolds for tissue engineering applications

    Energy Technology Data Exchange (ETDEWEB)

    Sell, Scott A; Garg, Koyal; McClure, Michael J; Bowlin, Gary L [Department of Biomedical Engineering, Virginia Commonwealth University, Richmond, VA 23284-3067 (United States); Francis, Michael P [Department of Pathology, Virginia Commonwealth University, Richmond, VA 23298-0709 (United States); Simpson, David G [Department of Anatomy and Neurobiology, Virginia Commonwealth University, Richmond, VA 23298-0709 (United States)], E-mail: glbowlin@vcu.edu

    2008-12-15

    The purpose of this study was to enhance the mechanical properties and slow the degradation of an electrospun fibrinogen scaffold, while maintaining the scaffold's high level of bioactivity. Three different cross-linkers were used to achieve this goal: glutaraldehyde vapour, 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) in ethanol and genipin in ethanol. Scaffolds with a fibrinogen concentration of 120 mg ml{sup -1} were electrospun and cross-linked with one of the aforementioned cross-linkers. Mechanical properties were determined through uniaxial tensile testing performed on scaffolds incubated under standard culture conditions for 1 day, 7 days and 14 days. Cross-linked scaffolds were seeded with human foreskin fibroblasts (BJ-GFP-hTERT) and cultured for 7, 14 and 21 days, with histology and scanning electron microscopy performed upon completion of the time course. Mechanical testing revealed significantly increased peak stress and modulus values for the EDC and genipin cross-linked scaffolds, with significantly slowed degradation. However, cross-linking with EDC and genipin was shown to have some negative effect on the bioactivity of the scaffolds as cell migration throughout the thickness of the scaffold was slowed.

  11. Fixed Links and Vague Discourses About Culture and the Making of Cross-border Regions

    Directory of Open Access Journals (Sweden)

    Birgit Stöber

    2011-06-01

    Full Text Available It has been en vogue for official bodies to focus on ‘culture’ as a strategic factor for the development of spatial entities such as cross-border regions in the making. This focus places high expectations and a strong belief in the power of ‘culture’. In this paper I will argue that in region building processes the focus on ‘culture’ is often due to an overriding wish to develop an economic well-functioning region. Moreover, it seems like ‘culture’ is used as a tool to distract people from a critique of bigger infrastructure projects that such developments entail. In order to strengthen these arguments, the paper will focus on two examples from Northern Europe, the existing Danish-Swedish Øresund link as well as the planned link between Denmark and Germany across the Femernbelt. In the course of the paper, focus will be on central bodies or actors that are taking up the issue of culture within a regional context. Hence, the concept of governance, particularly that of networked governance structures as well co-governance will be briefly discussed. All in all, the paper shows the ‘fragmented complexity of agency and the multitude of actors related to region building’ (Paasi 2010:2300.

  12. Short duration gluteraldehyde cross linking of decellularized bovine pericardium improves biological response.

    Science.gov (United States)

    Umashankar, P R; Arun, T; Kumari, T V

    2011-06-01

    Gluteraldehyde stabilized bovine pericardium is used for clinical application since 1970s because of its desirable features such as less immunogenicity and acceptable durability. However, a propensity for calcification and long term implant failure is reported because of gluteraldehyde treatment. There is also failure of implant to integrate into host tissue because of its resistance to tissue remodeling. Decellularized bovine pericardium, a potential alternative allows tissue remodeling but it has problems such as immunogenicity and chronic inflammatory response. In this study, decellularized bovine pericardium was subjected to short duration, low concentration gluteraldehyde cross-linking at two levels and its biological response (both in vitro and in vivo) was compared with un-crosslinked decellularized bovine pericardium and fully crosslinked normal bovine pericardium. It was observed that both un-crosslinked and partially crosslinked decellularized bovine pericardium to be non-cytotoxic and it caused significantly less inflammatory cytokine release such as TNF alpha and IL1beta from activated macrophages. Among all groups, short duration 0.2% Gluteraldehyde treated decellularized bovine pericardium showed significantly less antibody response and inflammatory response compared to un-crosslinked decellularized pericardium, short duration 0.6% gluteraldehyde treated decellularized bovine pericardium or completely cross linked bovine pericardium in juvenile rat subcutaneous implantation model. Moreover, short duration 0.2% gluteraldehyde crosslinked decellularized bovine pericardium showed minimum calcification, better host fibroblast incorporation, new collagen deposition and angiogenesis within the implant. These attributes may finally lead to better implant remodeling and sustained implant function during clinical use. Copyright © 2011 Wiley Periodicals, Inc.

  13. Effect of base sequence on the DNA cross-linking properties of pyrrolobenzodiazepine (PBD) dimers.

    Science.gov (United States)

    Rahman, Khondaker M; James, Colin H; Thurston, David E

    2011-07-01

    Pyrrolo[2,1-c][1,4]benzodiazepine (PBD) dimers are synthetic sequence-selective DNA minor-groove cross-linking agents that possess two electrophilic imine moieties (or their equivalent) capable of forming covalent aminal linkages with guanine C2-NH(2) functionalities. The PBD dimer SJG-136, which has a C8-O-(CH(2))(3)-O-C8'' central linker joining the two PBD moieties, is currently undergoing phase II clinical trials and current research is focused on developing analogues of SJG-136 with different linker lengths and substitution patterns. Using a reversed-phase ion pair HPLC/MS method to evaluate interaction with oligonucleotides of varying length and sequence, we recently reported (JACS, 2009, 131, 13 756) that SJG-136 can form three different types of adducts: inter- and intrastrand cross-linked adducts, and mono-alkylated adducts. These studies have now been extended to include PBD dimers with a longer central linker (C8-O-(CH(2))(5)-O-C8'), demonstrating that the type and distribution of adducts appear to depend on (i) the length of the C8/C8'-linker connecting the two PBD units, (ii) the positioning of the two reactive guanine bases on the same or opposite strands, and (iii) their separation (i.e. the number of base pairs, usually ATs, between them). Based on these data, a set of rules are emerging that can be used to predict the DNA-interaction behaviour of a PBD dimer of particular C8-C8' linker length towards a given DNA sequence. These observations suggest that it may be possible to design PBD dimers to target specific DNA sequences.

  14. Preparation and characterization of resistant starch type IV nanoparticles through ultrasonication and miniemulsion cross-linking.

    Science.gov (United States)

    Ding, Yongbo; Zheng, Jiong; Xia, Xuejuan; Ren, Tingyuan; Kan, Jianquan

    2016-05-05

    This study aimed to assess the properties of resistant starch type IV (chemically modified starch, RS4) prepared from a new and convenient synthesis route by using ultrasonication combined with water-in-oil miniemulsion cross-linking technique. A three-factor Box-Behnken design and optimization was used to minimize particle size through the developed RS4 nanoparticles. The predicted minimized Z-Avel (576.1nm) under the optimum conditions of the process variables (ultrasonic power, 214.57W; sonication time, 114.73min; and oil/water ratio, 10.54:1) was very close to the experimental value (651.0nm) determined in a batch experiment. After preparing the RS4 nanoparticles, morphological, physical, chemical, and functional properties were assessed. Results revealed that RS4 nanoparticle size reached about 600nm. Scanning electron microscopy images showed that ultrasonication induced notches and grooves on the surface. Under polarized light, the polarized cross was impaired. X-ray diffraction results revealed that the crystalline structure was disrupted. Smaller or no endotherms were exhibited in DSC analysis. In the FTIR graph, new peaks at 1532.91 and 1451.50cm(-1) were observed, and pasting properties were reduced. Amylose content, solubility, and SP increased, but RS content decreased. Anti-digestibility remained after ultrasonication. The prepared RS4 nanoparticles could be extensively used in biomedical applications and in the development of new medical materials. Copyright © 2016 Elsevier Ltd. All rights reserved.

  15. Protein-Sized Bright Fluorogenic Nanoparticles Based on Cross-Linked Calixarene Micelles with Cyanine Corona.

    Science.gov (United States)

    Shulov, Ievgen; Rodik, Roman V; Arntz, Youri; Reisch, Andreas; Kalchenko, Vitaly I; Klymchenko, Andrey S

    2016-12-19

    The key challenge in the field of fluorescent nanoparticles (NPs) for biological applications is to achieve superior brightness for sizes equivalent to single proteins (3-7 nm). We propose a concept of shell-cross-linked fluorescent micelles, in which PEGylated cyanine 3 and 5 bis-azides form a covalently attached corona on micelles of amphiphilic calixarene bearing four alkyne groups. The fluorescence quantum yield of the obtained monodisperse NPs, with a size of 7 nm, is a function of viscosity and reached up to 15 % in glycerol. In the on-state they are circa 2-fold brighter than quantum dots (QD-585), which makes them the smallest PEGylated organic NPs of this high brightness. FRET between cyanine 3 and 5 cross-linkers at the surface of NPs suggests their integrity in physiological media, organic solvents, and living cells, in which the NPs rapidly internalize, showing excellent imaging contrast. Calixarene micelles with a cyanine corona constitute a new platform for the development of protein-sized ultrabright fluorescent NPs.

  16. Mechanically Strong, Polymer Cross-linked Aerogels (X-Aerogels)

    Science.gov (United States)

    Leventis, Nicholas

    2006-01-01

    Aerogels comprise a class of low-density, high porous solid objects consisting of dimensionally quasi-stable self-supported three-dimensional assemblies of nanoparticles. Aerogels are pursued because of properties above and beyond those of the individual nanoparticles, including low thermal conductivity, low dielectric constant and high acoustic impedance. Possible applications include thermal and vibration insulation, dielectrics for fast electronics, and hosting of functional guests for a wide variety of optical, chemical and electronic applications. Aerogels, however, are extremely fragile materials, hence they have found only limited application in some very specialized environments, for example as Cerenkov radiation detectors in certain types of nuclear reactors, aboard spacecraft as collectors of hypervelocity particles (refer to NASA's Stardust program) and as thermal insulators on planetary vehicles on Mars (refer to Sojourner Rover in 1997 and Spirit and Opportunity in 2004). Along these lines, the X-Aerogel is a new NASA-developed strong lightweight material that has resolved the fragility problem of traditional (native) aerogels. X-Aerogels are made by applying a conformal polymer coating on the surfaces of the skeletal nanoparticles of native aerogels (see Scanning Electron Micrographs). Since the relative amounts of the polymeric crosslinker and the backbone are comparable, X-Aerogels can be viewed either as aerogels modified by the templated accumulation of polymer on the skeletal nanoparticles, or as nanoporous polymers made by remplated casting of polymer on a nanostructured framework. The most striking feature of X-Aerogels is that for a nominal 3-fold increase in density (still a ultralighweight material), the mechanical strength can be up to 300 times higher than the strength of the underlying native aerogel. Thus, X-Aerogels combine a multiple of the specific compressive strength of steel, with the the thermal conductivity of styrofoam. X

  17. Synthesis of cross-linked magnetic composite microspheres containing carboxyl groups

    Institute of Scientific and Technical Information of China (English)

    Jili ZHAO; Zhaorang HAN; Qiang SONG; Ying WANG; Dan SUN

    2008-01-01

    Fe3O4 magnetic nano-particles were prepared by a co-precipitation method and were modified using oleic acid. Then, the cross-linked magnetic composite microspheres containing a carboxyl group were prepared by using an improved emulsion polymerization with divinylbenzene (DVB) as the cross-linking agent. The composite microspheres comprised the Fe3O4 magnetic nano-partictes as cores and the copolymer of styrene and acrylic acid as shells. The morphology and structure of the composite microsphere were characterized by FT-IR, transmission electron microscopy (TEM), X-ray diffrac-tion (XRD), X-ray photoelectron spectrum (XPS) and so on. The results show that the composite microspheres were well dispersed in emulsion with uniform sizes and carboxyl groups on their surface. They were cross-linked and stable in 1 mol/L of HCl and DMF.

  18. Photochromic cross-link polymer for color changing and sensing surface

    Science.gov (United States)

    Fu, Richard; Shi, Jianmin; Forsythe, Eric; Srour, Merric

    2016-12-01

    Photochromic cross-link polymers were developed using patented ultraviolet (UV) photoinitiator and commercial photochromic dyes. The photochromic dyes have been characterized by measuring absorbance before and after UV activation using UV-visible (Vis) spectrometry with varying activation intensities and wavelengths. Photochromic cross-link polymers were characterized by a dynamic xenon and UV light activation and fading system. The curing processes on cloth were established and tested to obtain effective photochromic responses. Both PulseForge photonic curing and PulseForge plus heat surface curing processes had much better photochromic responses (18% to 19%, 16% to 25%, respectively) than the xenon lamp treatment (8%). The newly developed photochromic cross-link polymer showed remarkable coloration contrasts and fast and comparable coloration and fading rates. Those intelligent, controlled color changing and sensing capabilities will be used on flexible and "drapeable" surfaces, which will incorporate ultra-low power sensors, sensor indicators, and identifiers.

  19. Genipin Cross-Linked Polymeric Alginate-Chitosan Microcapsules for Oral Delivery: In-Vitro Analysis

    Directory of Open Access Journals (Sweden)

    Hongmei Chen

    2009-01-01

    Full Text Available We have previously reported the preparation of the genipin cross-linked alginate-chitosan (GCAC microcapsules composed of an alginate core with a genipin cross-linked chitosan membrane. This paper is the further investigation on their structural and physical characteristics. Results showed that the GCAC microcapsules had a smooth and dense surface and a networked interior. Cross-linking by genipin substantially reduced swelling and physical disintegration of microcapsules induced by nongelling ions and calcium sequestrants. Strong resistance to mechanical shear forces and enzymatic degradation was observed. Furthermore, the GCAC membranes were permeable to bovine serum albumin and maintained a molecular weight cutoff at 70 KD, analogous to the widely studied alginate-chitosan, and alginate-poly-L-lysine-alginate microcapsules. The release features and the tolerance of the GCAC microcapsules in the stimulated gastrointestinal environment were also investigated. This GCAC microcapsule formulation offers significant potential as a delivery vehicle for many biomedical applications.

  20. Cross-linked PAN-based thin-film composite membranes for non-aqueous nanofiltration

    KAUST Repository

    Pérez-Manríquez, Liliana

    2015-01-01

    A new approach on the development of cross-linked PAN based thin film composite (TFC) membranes for non-aqueous application is presented in this work. Polypropylene backed neat PAN membranes fabricated by phase inversion process were cross-linked with hydrazine to get excellent solvent stability toward dimethylformamide (DMF). By interfacial polymerization a selective polyamide active layer was coated over the cross-linked PAN using N,N′-diamino piperazine (DAP) and trimesoyl chloride (TMC) as monomers. Permeation and molecular weight cut off (MWCO) experiments using various dyes were done to evaluate the performance of the membranes. Membranes developed by such method show excellent solvent stability toward DMF with a permeance of 1.7 L/m2 h bar and a molecular weight cut-off of less than 600 Da.

  1. Light-triggered cross-linking of alginates with caged Ca2+.

    Science.gov (United States)

    Cui, Jiaxi; Wang, Miao; Zheng, Yijun; Rodríguez Muñiz, Gemma Maria; del Campo, Aránzazu

    2013-05-13

    A strategy to light-trigger ionic cross-linking of alginates by incorporating a photosensitive Ca2+ cage (nitr-T) is presented. Upon irradiation, free Ca2+ was released, and this caused gelation of the alginate solution. Addition of Ca2+ "on-demand" allowed us to obtain homogeneous alginate (ALG) gels using concentrated initial ALG solutions (10%), not possible with other ionic gelation approaches. The cross-linking degree and derived mechanical properties of the hydrogel were modulated by the exposure dose. The light-mediated cross-linked alginate hydrogel displayed a significant improvement in the mechanical properties and homogeneity when compared to mixtures of alginate and soluble Ca2+ at comparable concentrations.

  2. Synthesis of acrylic and allylic bifunctional cross-linking monomers derived from PET waste

    Science.gov (United States)

    Cruz-Aguilar, A.; Herrera-González, A. M.; Vázquez-García, R. A.; Navarro-Rodríguez, D.; Coreño, J.

    2013-06-01

    An acrylic and two novel allylic monomers synthesized from bis (hydroxyethyl) terephthalate, BHET, are reported. This was obtained by glycolysis of post-consumer PET with boiling ethylene glycol. The bifunctional monomer bis(2-(acryloyloxy)ethyl) terephthalate was obtained from acryloyl chloride, while the allylic monomers 2-(((allyloxi)carbonyl)oxy) ethyl (2-hydroxyethyl) terephthalate and bis(2-(((allyloxi)carbonyl)oxy)ethyl) terephthalate, from allyl chloroformate. Cross-linking was studied in bulk polymerization using two different thermal initiators. Monomers were analyzed by means of 1H NMR and the cross-linked polymers by infrared spectroscopy. Gel content higher than 90% was obtained for the acrylic monomer. In the case of the mixture of the allylic monomers, the cross-linked polymer was 80 % using BPO initiator, being this mixture 24 times less reactive than the acrylic monomer.

  3. Effect of cross-linking degree on selected properties of retrograded starch adipate.

    Science.gov (United States)

    Kapelko, M; Zięba, T; Michalski, A; Gryszkin, A

    2015-01-15

    The aim of this study was to determine the effects of the concentration of paste used to produce retrograded starch, and esterification degree, on selected properties of the resultant distarch adipate. Starch paste was prepared from native potato starch (1, 4, 10, 18 or 30 g/100g), frozen, defrosted and dried. Thus produced preparations of retrograded starch were cross-linked with various doses of a cross-linking agent (0.125, 0.25, 0.5, 1.0 or 2.0 ml per 100g of starch). Properties of the produced adipates depended on both the concentration of paste used to produce retrograded starch and the degree of substitution with adipic acid residues. Solubility in water and swelling power of the cross-linked preparations of retrograded starch, as well as pasting temperature and viscosity of produced pastes, all decreased along with the increasing degree of substitution with adipic acid residues.

  4. Cheese whey protein recovery by ultrafiltration through transglutaminase (TG) catalysis whey protein cross-linking.

    Science.gov (United States)

    Wen-Qiong, Wang; Lan-Wei, Zhang; Xue, Han; Yi, Lu

    2017-01-15

    In whey ultrafiltration (UF) production, two main problems are whey protein recovery and membrane fouling. In this study, membrane coupling protein transglutaminase (TG) catalysis protein cross-linking was investigated under different conditions to find out the best treatment. We found that the optimal conditions for protein recovery involved catalyzing whey protein cross-linking with TG (40U/g whey proteins) at 40°C for 60min at pH 5.0. Under these conditions, the recovery rate was increased 15-20%, lactose rejection rate was decreased by 10%, and relative permeate flux was increase 30-40% compared to the sample without enzyme treatment (control). It was noticeable that the total resistance and cake resistance were decreased after enzyme catalysis. This was mainly due to the increased particle size and decreased zeta potential. Therefore, membrane coupling enzyme catalysis protein cross-linking is a potential means for further use.

  5. Solution processed organic light-emitting diodes using the plasma cross-linking technology

    Science.gov (United States)

    He, Kongduo; Liu, Yang; Gong, Junyi; Zeng, Pan; Kong, Xun; Yang, Xilu; Yang, Cheng; Yu, Yan; Liang, Rongqing; Ou, Qiongrong

    2016-09-01

    Solution processed multilayer organic light-emitting diodes (OLEDs) present challenges, especially regarding dissolution of the first layer during deposition of a second layer. In this work, we first demonstrated a plasma cross-linking technology to produce a solution processed OLED. The surfaces of organic films can be cross-linked after mixed acetylene and Ar plasma treatment for several tens of seconds and resist corrosion of organic solvent. The film thickness and surface morphology of emissive layers (EMLs) with plasma treatment and subsequently spin-rinsed with chlorobenzene are nearly unchanged. The solution processed triple-layer OLED is successfully fabricated and the current efficiency increases 50% than that of the double-layer OLED. Fluorescent characteristics of EMLs are also observed to investigate factors influencing the efficiency of the triple-layer OLED. Plasma cross-linking technology may open up a new pathway towards fabrication of all-solution processed multilayer OLEDs and other soft electronic devices.

  6. Improvement on Physical Properties of Pullulan Films by Novel Cross-Linking Strategy.

    Science.gov (United States)

    Chen, Chieh-Ting; Chen, Kuan-I; Chiang, Hsin-Han; Chen, Yu-Kuo; Cheng, Kuan-Chen

    2017-01-01

    Pullulan based films possess several advantages, including high transparency, low toxicity, good biodegradability, good mechanical properties, and low oxygen permeability, are preferable for food packaging. The application of pullulan films on food packaging, however, has inherent disadvantage of high water solubility. In this study, glutaraldehyde and glycerol were used as the cross-linking reagent and the plasticizer respectively to improve water resistance and physical properties of the pullulan films. Effects of cross-linking degree on physical properties, including water absorptions, swelling behaviors, water vapor permeability and tensile strengths of films were evaluated. FTIR results demonstrated that the pullulan films were successfully cross-linked by glutaraldehyde. The tensile strength of pullulan films could be enhanced significantly (P glycerol as a plasticizer enhanced the extensibility of films as well as the hydrophilicity, resulting in higher water vapor permeability.

  7. Study on Chemical Cross-linking Modification of Hyaluronan and the Biocompatibility of its Derivatives

    Institute of Scientific and Technical Information of China (English)

    HU Guo-ying; LIU Xin; GU Han-qing

    2006-01-01

    Objective: Prepare cross-linked HA gels with higher mechanical stability,lower degradation velocity and desirable biocompatibility,so as to extend the usage of HA.Method: 1.Test molecular weight of HA (MrHA) by viscosimetry;2.Prepare cross-linked HA gels by DVS,GTA,DEC;3.Discuss the cross-linking and degradation procedure;4,evaluate the biocompatibility of the best HA gels.Results: The mechanical stability and durability to degradation of HA-DVS gels are superior to those of other gels,and when HA :DVS = 40:1 (g/g),at 35℃ and in 0.2M NaOH solution,the HA-DVS gel shows the best mechanical stability,and its cytotoxicity reaches class I,hemolysis ratio is lower than 5 %.Conclusion:Our HADVS gel can be used to prepare biologic scaffolds.

  8. Comparison of Wear and Oxidation in Retrieved Conventional and Highly Cross-Linked UHMWPE Tibial Inserts.

    Science.gov (United States)

    Currier, Barbara H; Currier, John H; Franklin, Katherine J; Mayor, Michael B; Reinitz, Steven D; Van Citters, Douglas W

    2015-12-01

    Two groups of retrieved tibial inserts from one manufacturer's knee system were analyzed to evaluate the effect of a highly cross-linked bearing surface on wear and in vivo oxidation. The two groups ((1) conventional gamma-inert sterilized and (2) highly cross-linked, coupled with the same rough (Ra=0.25) Ti-6Al-4V tray) were matched with statistically similar in vivo duration and patient variables. The retrieved inserts were analyzed for ketone oxidation and wear in the form of dimensional change. The difference in oxidation rate between highly cross-linked and conventional gamma-inert sterilized inserts did not reach statistical significance. Observations suggest that the majority of wear can be accounted for by the backside interface with the rough Ti-6Al-4V tray; however, wear measured by thickness-change rate was statistically indistinguishable between the two bearing materials.

  9. Biomimetic acellular detoxified glutaraldehyde cross-linked bovine pericardium for tissue engineering

    Energy Technology Data Exchange (ETDEWEB)

    Mathapati, Santosh; Bishi, Dillip Kumar [Stem Cell and Molecular Biology Laboratory, Department of Biotechnology, Indian Institute of Technology Madras, Chennai (India); Frontier Lifeline Pvt Ltd. and Dr. K. M. Cherian Heart Foundation, Mogappair, Chennai (India); Healthcare and Energy Materials Laboratory, NUSNNI, Faculty of Engineering, National University of Singapore (Singapore); Guhathakurta, Soma [Departmet of Engineering Design, Indian Institute of Technology Madras, Chennai (India); Cherian, Kotturathu Mammen [Frontier Lifeline Pvt Ltd. and Dr. K. M. Cherian Heart Foundation, Mogappair, Chennai (India); Venugopal, Jayarama Reddy; Ramakrishna, Seeram [Healthcare and Energy Materials Laboratory, NUSNNI, Faculty of Engineering, National University of Singapore (Singapore); Verma, Rama Shanker, E-mail: vermars@iitm.ac.in [Stem Cell and Molecular Biology Laboratory, Department of Biotechnology, Indian Institute of Technology Madras, Chennai (India)

    2013-04-01

    Glutaraldehyde (GLUT) processing, cellular antigens, calcium ions in circulation, and phospholipids present in the native tissue are predominantly responsible for calcification, degeneration, and lack of natural microenvironment for host progenitor cell migration in tissue implants. The study presents an improved methodology for adhesion and proliferation of endothelial progenitor cells (EPCs) without significant changes in biomechanical and biodegradation properties of the processed acellular bovine pericardium. The anti-calcification potential of the processed tissue was enhanced by detoxification of GLUT-cross-linked bovine pericardium by decellularization, pretreating it with ethanol or removing the free aldehydes by citric acid treatment and lyophilization. The treated tissues were assessed for biomechanical properties, GLUT ligand quantification, adhesion, proliferation of EPCs, and biodegradability. The results indicate that there was no significant change in biomechanical properties and biodegradability when enzymatic hydrolysis (p > 0.05) is employed in detoxified acellular GLUT cross-linked tissue (DBP–G–CA–ET), compared with the native detoxified GLUT cross-linked bovine pericardium (NBP–G–CA–ET). DBP–G–CA–ET exhibited a significant (p > 0.05) increase in the viability of EPCs and cell adhesion as compared to acellular GLUT cross-linked bovine pericardium (p < 0.05). Lyophilized acellular detoxified GLUT cross-linked bovine pericardium, employed in our study as an alternative to conventional GLUT cross-linked bovine pericardium, might provide longer durability and better biocompatibility, and reduce calcification. The developed bovine pericardium patches could be used in cardiac reconstruction and repair, arteriotomy, soft tissue repair, and general surgical procedures with tissue regeneration dimensions. - Highlights: ► We improved the quality of patch biomaterial for cardiovascular surgical procedures. ► Bovine pericardium was

  10. Solvent Composition is Critical for Carbodiimide Cross-Linking of Hyaluronic Acid as an Ophthalmic Biomaterial

    Directory of Open Access Journals (Sweden)

    Jui-Yang Lai

    2012-10-01

    Full Text Available Hyaluronic acid (HA is one of the most important ophthalmic biomaterials, while also being used for tissue engineering and drug delivery. Although chemical cross-linking is an effective way to improve the material performance, it may as a consequence be detrimental to the living cells/tissues. Given that the cross-linking efficiency is mediated by the solvent composition during the chemical modification, this study aims to explore the stability and biocompatibility of carbodiimide cross-linked HA in relation to material processing conditions by varying the acetone/water volume ratio (from 70:30 to 95:5 at a constant 1-ethyl-3-(3-dimethyl aminopropyl carbodiimide (EDC concentration of 100 mM. Our results indicated that after the EDC treatment in the presence of an acetone/water mixture (85:15, v/v, the HA hydrogel membranes have the lowest equilibrium water content, the highest stress at break and the greatest resistance to hyaluronidase digestion. Live/Dead assays and pro-inflammatory cytokine expression analyses showed that the cross-linked HA hydrogel membranes, irrespective of the solvent composition, are compatible with human RPE cell lines without causing toxicity and inflammation. However, it should be noted that the test samples prepared by the cross-linking in the presence of acetone/water mixtures containing 70, 75, and 95 vol % of acetone slightly inhibit the metabolic activity of viable ARPE-19 cultures, probably due to the alteration in the ionic interaction between the medium nutrients and polysaccharide biomaterials. In summary, the water content, mechanical strength and RPE cell proliferative capacity strongly depends on the solvent composition for carbodiimide cross-linking of HA materials.

  11. Collagen telopeptides (cross-linking sites) play a role in collagen gel lattice contraction

    Science.gov (United States)

    Woodley, D. T.; Yamauchi, M.; Wynn, K. C.; Mechanic, G.; Briggaman, R. A.

    1991-01-01

    Solubilized interstitial collagens will form a fibrillar, gel-like lattice when brought to physiologic conditions. In the presence of human dermal fibroblasts the collagen lattice will contract. The rate of contraction can be determined by computer-assisted planemetry. The mechanisms involved in contraction are as yet unknown. Using this system it was found that the rate of contraction was markedly decreased when collagen lacking telopeptides was substituted for native collagen. Histidinohydroxylysinonorleucine (HHL) is a major stable trifunctional collagen cross-link in mature skin that involves a carboxyl terminal, telopeptide site 16c, the sixteenth amino acid residue from the carboxy terminal of the telopeptide region of alpha 1 (I) in type I collagen. Little, if any, HHL was present in native, purified, reconstituted, soluble collagen fibrils from 1% acetic acid-extracted 2-year-old bovine skin. In contrast, HHL cross-links were present (0.22 moles of cross-link per mole of collagen) in lattices of the same collagen contracted by fibroblasts. However, rat tail tendon does not contain HHL cross-links, and collagen lattices made of rat tail tendon collagen are capable of contraction. This suggests that telopeptide sites, and not mature HHL cross-links per se, are essential for fibroblasts to contract collagen lattices. Beta-aminopropionitrile fumarate (BAPN), a potent lathyrogen that perturbs collagen cross-linking by inhibition of lysyl oxidase, also inhibited the rate of lattice cell contraction in lattices composed of native collagen. However, the concentrations of BAPN that were necessary to inhibit the contraction of collagen lattices also inhibited fibroblast growth suggestive of cellular toxicity. In accordance with other studies, we found no inhibition of the rate of lattice contraction when fibronectin-depleted serum was used. Electron microscopy of contracted gels revealed typical collagen fibers with a characteristic axial periodicity. The data

  12. Bioreducible cross-linked nanoshell enhances gene transfection of polycation/DNA polyplex in vivo.

    Science.gov (United States)

    Piao, Ji-Gang; Ding, Sheng-Gang; Yang, Lu; Hong, Chun-Yan; You, Ye-Zi

    2014-08-11

    In this study, we have prepared a self-cross-linking PEG-based branched polymer, which easily forms a bioreducible nanoshell around polyplexes of cationic polymer and DNA, simply via heating the polyplex dispersions in the presence of this self-cross-linking branched polymer. This nanoshell can prevent the polyplex from dissociation and aggregation in physiological fluids without inhibiting the electrostatic interactions between the polymer and DNA. Furthermore, glutathione (GSH) can act as a stimulus to open the nanoshell after it has entered the cell. The polyplexes coated with the bioreducible nanoshell show an obvious enhancement in gene transfection in vivo compared with bare polyplexes.

  13. Increasing Thermal Stability of Gelatin by UV-Induced Cross-Linking with Glucose

    Directory of Open Access Journals (Sweden)

    Evan M. Masutani

    2014-01-01

    Full Text Available The effects of ultraviolet (254 nm radiation on a hydrated gelatin-glucose matrix were investigated for the development of a physiologically thermostable substrate for potential use in cell scaffold production. Experiments conducted with a differential scanning calorimeter indicate that ultraviolet irradiation of gelatin-glucose hydrogels dramatically increases thermal stability such that no melting is observed at temperatures of at least 90°C. The addition of glucose significantly increases the yield of cross-linked product, suggesting that glucose has a role in cross-link formation. Comparisons of lyophilized samples using scanning electron microscopy show that irradiated materials have visibly different densities.

  14. A novel DTPA cross-linking of hyaluronic acid and metal complexation thereof.

    Science.gov (United States)

    Buffa, Radovan; Běťák, Jiří; Kettou, Sofiane; Hermannová, Martina; Pospíšilová, Lucie; Velebný, Vladimír

    2011-09-27

    Macromolecular conjugates of a natural polysaccharide, hyaluronic acid, with diethylenetriaminepentaacetic acid (DTPA)-metal complexes were synthesized and characterized by FTIR, NMR, SEC-MALLS and ICP analysis. Several parameters of the cross-linking reaction as molecular weight of starting HA, temperature, equivalent of DTPA bis-anhydride, concentration of HA, presence of transacylation catalyst DMAP and reaction time were studied. The mechanism for the reaction was suggested and relationship between the molecular weight assigned by SEC-MALLS, reaction parameters and rheological properties of the final cross-linked products were investigated. Copyright © 2011 Elsevier Ltd. All rights reserved.

  15. Preparation and in vitro evaluation of chitosan matrices cross-linked by formaldehyde vapors.

    Science.gov (United States)

    Rao, B S; Murthy, K V

    2000-10-01

    Rifampicin-chitosan matrices were prepared by a chemical cross-linking method to develop a sustained-release form. The effects of cross-linking agent (formaldehyde) on the drug release rate and release kinetics were investigated in this study. Moreover, the kinetics of rifampicin released from chitosan matrices exposed to formaldehyde vapors for predetermined time intervals were analyzed using Ritger and Peppas exponential equation. The in vitro release kinetics exhibited a non-Fickian transport model. Increasing the exposure time to formaldehyde vapors decreased the release rate of rifampicin from chitosan matrices as a result of formation of greater structural strength and tighter texture.

  16. Reinforced films based on cross-linked water-soluble sulfonated carbon nanotubes with sulfonated polystyrene.

    Science.gov (United States)

    Dai, Ying; Haiping, Hong; Guiver, Michael; Welsh, Jeffry S

    2009-09-01

    Reinforced films based on sulfonated polystyrene cross-linked with water-soluble sulfonated carbon nanotubes were fabricated using a free-standing film-making method. Transmission and scanning electron microscopy (TEM and SEM), and X-ray photoelectron spectroscopy (XPS) were used to verify the cross-linking reaction. The mechanical properties of these films demonstrated that the tensile strength increases with an increase in the sulfonated nanotube concentration. At 5 wt% nanotube loading, the tensile strength increased 84% compared with polymer containing no nanotube loading. The relationships between structure and mechanical properties are discussed and a possible direction for making ultra thin and ultra lightweight film is proposed.

  17. In Situ Cross-Linking of Stimuli-Responsive Hemicellulose Microgels during Spray Drying

    OpenAIRE

    Zhao, Weifeng; Nugroho, Robertus Wahyu N.; Odelius, Karin; Edlund, Ulrica; Zhao, Changsheng; Albertsson, Ann-Christine

    2015-01-01

    Chemical cross-linking during spray drying offers the potential for green fabrication of microgels with a rapid stimuli response and good blood compatibility and provides a platform for stimuli-responsive hemicellulose microgels (SRHMGs). The cross-linking reaction occurs rapidly in situ at elevated temperature during spray drying, enabling the production of microgels in a large scale within a few minutes. The SRHMGs with an average size range of ∼1–4 μm contain O-acetyl-galactoglucomannan as...

  18. Preparation of Nanocellulose Reinforced Chitosan Films, Cross-Linked by Adipic Acid.

    Science.gov (United States)

    Falamarzpour, Pouria; Behzad, Tayebeh; Zamani, Akram

    2017-02-13

    Adipic acid, an abundant and nontoxic compound, was used to dissolve and cross-link chitosan. After the preparation of chitosan films through casting technique, the in situ amidation reaction was performed at 80-100 °C as verified by Fourier transform infrared (FT-IR). The reaction was accompanied by the release of water which was employed to investigate the reaction kinetics. Accordingly, the reaction rate followed the first-order model and Arrhenius equation, and the activation energy was calculated to be 18 kJ/mol. Furthermore, the mechanical properties of the chitosan films were comprehensively studied. First, optimal curing conditions (84 °C, 93 min) were introduced through a central composite design. In order to evaluate the effects of adipic acid, the mechanical properties of physically cross-linked (uncured), chemically cross-linked (cured), and uncross-linked (prepared by acetic acid) films were compared. The use of adipic acid improved the tensile strength of uncured and chemically cross-linked films more than 60% and 113%, respectively. Finally, the effect of cellulose nanofibrils (CNFs) on the mechanical performance of cured films, in the presence of glycerol as a plasticizer, was investigated. The plasticized chitosan films reinforced by 5 wt % CNFs showed superior properties as a promising material for the development of chitosan-based biomaterials.

  19. Preparation of Nanocellulose Reinforced Chitosan Films, Cross-Linked by Adipic Acid

    Directory of Open Access Journals (Sweden)

    Pouria Falamarzpour

    2017-02-01

    Full Text Available Adipic acid, an abundant and nontoxic compound, was used to dissolve and cross-link chitosan. After the preparation of chitosan films through casting technique, the in situ amidation reaction was performed at 80–100 °C as verified by Fourier transform infrared (FT-IR. The reaction was accompanied by the release of water which was employed to investigate the reaction kinetics. Accordingly, the reaction rate followed the first-order model and Arrhenius equation, and the activation energy was calculated to be 18 kJ/mol. Furthermore, the mechanical properties of the chitosan films were comprehensively studied. First, optimal curing conditions (84 °C, 93 min were introduced through a central composite design. In order to evaluate the effects of adipic acid, the mechanical properties of physically cross-linked (uncured, chemically cross-linked (cured, and uncross-linked (prepared by acetic acid films were compared. The use of adipic acid improved the tensile strength of uncured and chemically cross-linked films more than 60% and 113%, respectively. Finally, the effect of cellulose nanofibrils (CNFs on the mechanical performance of cured films, in the presence of glycerol as a plasticizer, was investigated. The plasticized chitosan films reinforced by 5 wt % CNFs showed superior properties as a promising material for the development of chitosan-based biomaterials.

  20. Mutational Analysis of a Conserved Glutamic Acid Required for Self-Catalyzed Cross-Linking of Bacteriophage HK97 Capsids▿

    Science.gov (United States)

    Dierkes, Lindsay E.; Peebles, Craig L.; Firek, Brian A.; Hendrix, Roger W.; Duda, Robert L.

    2009-01-01

    The capsid of bacteriophage HK97 is stabilized by ∼400 covalent cross-links between subunits which form without any action by external enzymes or cofactors. Cross-linking only occurs in fully assembled particles after large-scale structural changes bring together side chains from three subunits at each cross-linking site. Isopeptide cross-links form between asparagine and lysine side chains on two subunits. The carboxylate of glutamic acid 363 (E363) from a third subunit is found ∼2.4 Å from the isopeptide bond in the partly hydrophobic pocket that contains the cross-link. It was previously reported without supporting data that changing E363 to alanine abolishes cross-linking, suggesting that E363 plays a role in cross-linking. This alanine mutant and six additional substitutions for E363 were fully characterized and the proheads produced by the mutants were tested for their ability to cross-link under a variety of conditions. Aspartic acid and histidine substitutions supported cross-linking to a significant extent, while alanine, asparagine, glutamine, and tyrosine did not, suggesting that residue 363 acts as a proton acceptor during cross-linking. These results support a chemical mechanism, not yet fully tested, that incorporates this suggestion, as well as features of the structure at the cross-link site. The chemically identical isopeptide bonds recently documented in bacterial pili have a strikingly similar chemical geometry at their cross-linking sites, suggesting a common chemical mechanism with the phage protein, but the completely different structures and folds of the two proteins argues that the phage capsid and bacterial pilus proteins have achieved shared cross-linking chemistry by convergent evolution. PMID:19091865

  1. Dynamic Heterogeneity in Highly Cross-linked Epoxy in the Vicinity of Glass Transition

    Science.gov (United States)

    Lin, Po-Han; Khare, Rajesh

    2010-03-01

    Cross-linked epoxy has been widely used in aerospace and electronics industries. The highly cross-linked nature of these systems leads to different chain dynamics as compared to the linear polymeric systems. In this work, we have used molecular dynamics (MD) simulations to study the dynamic heterogeneity in cross-linked epoxy near the glass transition temperature. Well-relaxed atomistic models of cross-linked epoxy were first created by employing the simulated annealing polymerization approach. The specific epoxy system studied consisted of diglycidyl ether of bisphenol-A (DGEBA) as the epoxy monomer and trimethylene glycol di-p-aminobenzoate (TMAB) as the cross-linker. The glass transition temperature of these model structures was determined from MD simulation by monitoring their volume-temperature behaviour in a stepwise cooling run. The chain dynamics of these systems were characterized by their local translational and orientational mobility. Furthermore, dynamic heterogeneity was studied by analyzing the spatial distribution of the mobile and immobile atoms in the system near the glass transition temperature.

  2. Altered Cross-linking of HSP27 by Zerumbone as a Novel Strategy for Overcoming HSP27- mediated Resistance

    Energy Technology Data Exchange (ETDEWEB)

    Choi, Seo Hyun; Lee, Yoon Jin; Lee, Hae June; Lee, Yun Sil [Korea Institue of Radiological and Medical Sciences, Seoul (Korea, Republic of); Kim, Joon [Korea University, Seoul (Korea, Republic of); Seo, Woo Duck [National Institute of Crop Science, Miryang (Korea, Republic of); Nam, Joo Won; Lee, Yoo Jin; Seo, Eun Kyung [Ewha Womans University, Seoul (Korea, Republic of)

    2010-05-15

    HSPs have diverse roles in the regulation of signal transduction and in numerous aspects of cell growth and death. Indeed, HSP90, HSP70, and HSP27 have each been implicated in promoting cancer. Most HSP27 exists as large oligomeric complexes ranging from 100- 800 kDa, which are probably stabilized by complex interactions between dimeric building blocks. The functional properties of HSP27 are dependent on the quaternary structure of the protein. For example, HSP27 acts as a chaperone and binds to cytochrome c or Daxx as a dimer. Therefore, the oligomerization pattern of HPS27 is believed to have HSP27-mediated protective functions. In this study, zerumbone (ZER), the cytotoxic component isolated from Zingiber zerumbet Smith, induced cross-linking of HSP27 protein by its insertion between the disulfide bond of HSP27, and ZERmediated altered cross-linking of HSP27 modified normal HSP27 dimerization, which resulted in a sensitizing effect to tumors after treatment with radiation. Therefore, altered cross-linking by ZER may be a novel strategy for inhibition of HSP27-mediated resistance

  3. Assessment of using laponite cross-linked poly(ethylene oxide) for controlled cell adhesion and mineralization.

    Science.gov (United States)

    Gaharwar, Akhilesh K; Schexnailder, Patrick J; Kline, Benjamin P; Schmidt, Gudrun

    2011-02-01

    The in vitro cytocompatibility of silicate (Laponite clay) cross-linked poly(ethylene oxide) (PEO) nanocomposite films using MC3T3-E1 mouse preosteoblast cells was investigated while cell adhesion, spreading, proliferation and mineralization were assessed as a function of film composition. By combining the advantageous characteristics of PEO polymer (hydrophilic, prevents protein and cell adhesion) with those of a synthetic and layered silicate (charged, degradable and potentially bioactive) some of the physical and chemical properties of the resulting polymer nanocomposites could be controlled. Hydration, dissolution and mechanical properties were examined and related to cell adhesion. Overall, this feasibility study demonstrates the ability of using model Laponite cross-linked PEO nanocomposites to create bioactive scaffolds.

  4. Electrospinning of Cross-Linked Magnetic Chitosan Nanofibers for Protein Release.

    Science.gov (United States)

    Nicknejad, Ehsan Tayerani; Ghoreishi, Seyyed Mohammad; Habibi, Neda

    2015-12-01

    A poly(vinylalcohol) (PVA) electrospun/magnetic/chitosan nanocomposite fibrous cross-linked network was fabricated using in situ cross-linking electrospinning technique and used for bovine serum albumin (BSA) loading and release applications. Sodium tripolyphosphate (TPP) and glutaraldehyde (GA) were used as cross-linkers which modified magnetic-Fe3O4 chitosan as Fe3O4/CS/TPP and Fe3O4/CS/GA, respectively. BSA was used as a model protein drugs which was encapsulated to form Fe3O4/CS/TPP/BSA and Fe3O4/CS/GA/BSA nanoparticles. The composites were electrospun with PVA to form nanofibers. Nanofibers were characterized by field emission scanning electron microscopy (FESEM) and Fourier transform infrared spectroscopy (FTIR). The characterization results suggest that Fe3O4 nanoparticles with average size of 45 nm were successfully bound on the surface of chitosan. The cross-linked nanofibers were found to contain uniformly dispersed Fe3O4 nanoparticles. The size and morphology of the nanofibers network was controlled by varying the cross-linker type. FTIR data show that these two polymers have intermolecular interactions. The sample with TPP cross-linker showed an enhancement of the controlled release properties of BSA during 30-h experimental investigation. Graphical Abstract ᅟ.

  5. Preoperative cross functional teams improve OR performance.

    Science.gov (United States)

    Bitter, Justin; van Veen-Berkx, Elizabeth; van Amelsvoort, Pierre; Gooszen, Hein

    2015-01-01

    The purpose of this paper is to present the effect of the introduction of cross-functional team (CFT)-based organization, rather than, on planning and performance of OR teams. In total, two surgical departments of the Radboud University Nijmegen Medical Center (RUNMC) in the Netherlands were selected to illustrate the effect on performance. Data were available for a total of seven consecutive years from 2005 until 2012 and consisted of 4,046 OR days for surgical Department A and 1,154 OR days for surgical Department B on which, respectively 8,419 and 5,295 surgical cases were performed. The performance indicator "raw utilization" of the two surgical Departments was presented as box-and-whisker plots per year (2005-2011). The relationship between raw utilization (y) and years (x) was analyzed with linear regression analysis, to observe if performance changed over time. Based on the linear regression analysis, raw utilization of surgical Department A showed a statistically significant increase since 2006. The variation in raw utilization reduced from IQR 33 percent in 2005 to IQR 8 percent in 2011. Surgical Department B showed that raw utilization increased since 2005. The variation in raw utilization reduced from IQR 21 percent in 2005 to IQR 8 percent in 2011. Hospitals need to improve their productivity and efficiency in response to higher societal demands and rapidly escalating costs. The RUNMC increased their OR performance significantly by introduction of CFT-based organization in the operative process and abandoning the so called functional silos. The stepwise reduction of variation - a decrease of IQR during the years - indicates an organizational learning effect. This study demonstrates that introducing CFTs improve OR performance by working together as a team.

  6. Synthesis, Optimization, Property, Characterization, and Application of Dialdehyde Cross-Linking Guar Gum

    Directory of Open Access Journals (Sweden)

    Tang Hongbo

    2016-01-01

    Full Text Available Dialdehyde cross-linking guar gum (DCLGG, as a novel material, was synthesized using phosphorus oxychloride as a cross-linking reagent, sodium periodate as an oxidant, and ethanol as a solvent through keeping the original particle form of guar gum. The process parameters such as the reaction temperature, reaction time, pH, amount of sodium periodate, and amount of ethanol were optimized by the response surface methodology in order to obtain the regression model of the oxidization. The covalent binding of L-asparagine onto the surfaces of DCLGG was further investigated. The results showed that the best technological conditions for preparing DCLGG were as follows: reaction temperature = 40°C, reaction time = 3.0 h, pH = 4.0, and amount of ethanol = 74.5%. The swelling power of DCLGG was intermediate between cross-linking guar gum and dialdehyde guar gum. The cross-linking and dialdehyde oxidization reduced the viscosity of GG. The cross-liking reduced the melting enthalpy of GG. However, the oxidization increased melting enthalpy of ACLGG. The thermal stability of GG was increased by cross-linking or oxidization. The variation of the onset decomposition temperature and end decomposition temperature of GG was not consistent with thermal stability of GG. L-asparagine could be chemically bound well by DCLGG through forming Schiff base under the weak acidity. The maximum adsorption capacity of L-asparagine on DCLGG with aldehyde content of 56.2% reached 21.9 mg/g.

  7. Proteins cross-linked to U1 RNA by ultraviolet irradiation

    Energy Technology Data Exchange (ETDEWEB)

    Marti, A.; Jimenez, R.; Matos, J.

    1987-05-01

    Proteins associated to U1 RNA react with antinuclear antibodies obtained from sera of patients with autoimmune diseases. K.B. cells were labeled with /sup 3/H-amino acids of /sup 3/H-uridine. The U1 RNA particles were immunoprecipitated. Protein and RNA analysis was by electrophoresis and fluorography. The ratio of material at the top of the RNA gel to the U1 RNA band was 0.79. After exposure of the cells to UV irradiation, the ratio was 5.04. A substantial amount of U1 RNA was cross-linked to proteins or other nuclear components. Protein patterns obtained from U1 RNP particles subjected to UV irradiation revealed a change in electrophoretic mobility by four proteins in the molecular range of 14,000 to 28,000 daltons. The 33,000 dalton protein was reduced by 50% but its electrophoretic mobility was unchanged. The protein band at 68,000 daltons was unchanged in amount or mobility by UV irradiation. It is concluded that the low molecular weight proteins (14,000 - 28,000) and the protein of 33,000 daltons are in close proximity to U1 RNA and possibly play a role in the molecular function(s) attributed to U1 RNA.

  8. Synthesis and properties of reprocessable sulfonated polyimides cross-linked via acid stimulation for use as proton exchange membranes

    Science.gov (United States)

    Zhang, Boping; Ni, Jiangpeng; Xiang, Xiongzhi; Wang, Lei; Chen, Yongming

    2017-01-01

    Cross-linked sulfonated polyimides are one of the most promising materials for proton exchange membrane (PEM) applications. However, these cross-linked membranes are difficult to reprocess because they are insoluble. In this study, a series of cross-linkable sulfonated polyimides with flexible pendant alkyl side chains containing trimethoxysilyl groups is successfully synthesized. The cross-linkable polymers are highly soluble in common solvents and can be used to prepare tough and smooth films. Before the cross-linking reaction is complete, the membranes can be reprocessed, and the recovery rate of the prepared films falls within an acceptable range. The cross-linked membranes are obtained rapidly when the cross-linkable membranes are immersed in an acid solution, yielding a cross-linking density of the gel fraction of greater than 90%. The cross-linked membranes exhibit high proton conductivities and tensile strengths under hydrous conditions. Compared with those of pristine membranes, the oxidative and hydrolytic stabilities of the cross-linked membranes are significantly higher. The CSPI-70 membrane shows considerable power density in a direct methanol fuel cell (DMFC) test. All of these results suggest that the prepared cross-linked membranes have great potential for applications in proton exchange membrane fuel cells.

  9. The Effect of Glutaraldehyde Cross-Linking on the Enzyme Activity of Immobilized &beta-Galactosidase on Chitosan Bead

    Directory of Open Access Journals (Sweden)

    He Chen

    2013-07-01

    Full Text Available The effect of glutaraldehyde solution concentration, cross-linking time, cross-linking pH and cross-linking temperature on the enzyme activity of the immobilized &beta-galactosidase on Chitosan beads were studied. The enzyme activity was measured after immobilized by detecting the absorbance value at 420 nm.The results were as follows: the immobilized enzyme activity reached the maximum when the concentration of glutaraldehyde solution was 0.3%.The immobilized enzyme had optimal cross-linking time of 3h, optimal cross-linking pH of 6.5, optimal cross-linking temperature of 25°C, under these conditions, the immobilized enzyme activity reached 101, 96, 90 U/g, respectively.

  10. Physicochemical properties and micro-structural characteristics in starch from kudzu root as affected by cross-linking.

    Science.gov (United States)

    Chen, Boru; Dang, Leping; Zhang, Xiao; Fang, Wenzhi; Hou, Mengna; Liu, Tiankuo; Wang, Zhanzhong

    2017-03-15

    Kudzu starch was cross-linked with sodium trimetaphosphate (STMP) at different temperatures, time and of STMP concentrations in this work. The cross-linked starches (CLSs) were fractionated further into cross-linked amylose and amylopectin in order to compare the effect of cross-linking on the microstructure. According to scanning electron microscope (SEM), CLSs displayed the resemble appearance of spherical and polygonal shapes like NS. X-ray diffraction (XRD) revealed that amylose of native starch (A), NS and CLS displayed a combination of A-type and B-type structure, while that was not found in amylose of cross-linked starch (CLA). The deconvoluted fourier transform infrared (FT-IR) indicated that crystal structure of kudzu starch was losing with the proceeding of cross-linking reaction. The CLSs exhibited a higher retrogradation and freeze-thaw stability than NS. This was accompanied by a significant decrease in sedimentation, transparency, swelling power and solubility.

  11. Thermally cross-linked superparamagnetic iron oxide nanoparticles: synthesis and application as a dual imaging probe for cancer in vivo.

    Science.gov (United States)

    Lee, Haerim; Yu, Mi Kyung; Park, Sangjin; Moon, Sungmin; Min, Jung Jun; Jeong, Yong Yeon; Kang, Hae-Won; Jon, Sangyong

    2007-10-24

    We report the fabrication and characterization of thermally cross-linked superparamagnetic iron oxide nanoparticles (TCL-SPION) and their application to the dual imaging of cancer in vivo. Unlike dextran-coated cross-linked iron oxide nanoparticles, which are prepared by a chemical cross-linking method, TCL-SPION are prepared by a simple, thermal cross-linking method using a Si-OH-containing copolymer. The copolymer, poly(3-(trimethoxysilyl)propyl methacrylate-r-PEG methyl ether methacrylate-r-N-acryloxysuccinimide), was synthesized by radical polymerization and used as a coating material for as-synthesized magnetite (Fe3O4) SPION. The polymer-coated SPION was further heated at 80 degrees C to induce cross-linking between the -Si(OH)3 groups in the polymer chains, which finally generated TCL-SPION bearing a carboxyl group as a surface functional group. The particle size, surface charge, presence of polymer-coating layers, and the extent of thermal cross-linking were characterized and confirmed by various measurements, including dynamic light scattering, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The carboxyl TCL-SPION was converted to amine-modified TCL-SPION and then finally to Cy5.5 dye-conjugated TCL-SPION for use in dual (magnetic resonance/optical) in vivo cancer imaging. When the Cy5.5 TCL-SPION was administered to Lewis lung carcinoma tumor allograft mice by intravenous injection, the tumor was unambiguously detected in T2-weighted magnetic resonance images as a 68% signal drop as well as in optical fluorescence images within 4 h, indicating a high level of accumulation of the nanomagnets within the tumor site. In addition, ex vivo fluorescence images of the harvested tumor and other major organs further confirmed the highest accumulation of the Cy5.5 TCL-SPION within the tumor. It is noteworthy that, despite the fact that TCL-SPION does not bear any targeting ligands on its surface, it was highly effective for tumor

  12. Design of phosphated cross-linked microspheres of bael fruit gum as a biodegradable carrier.

    Science.gov (United States)

    Mahammed, Nawaz; Gowda, D V; Deshpande, Rohan D; Thirumaleshwar, Shailesh

    2015-01-01

    Present work was aimed at designing of phosphated cross-linked microspheres of bael fruit gum (BFG) by emulsification method using sodium-tri-meta phosphate as a cross-linking agent for treatment of colon cancer using 5-fluorouracil as model drug. Stirring speed was found to be 1,000 rpm for about 5 h to be optimal to obtain reproducible microspheres. It was found that there is an increase in particle size as polymer concentration is increased whereas a reduction in particle size was observed as there is increase in stirring speed. Cross-linked BFG microspheres were successfully prepared by emulsification method. Optimum surfactant concentration was found to be 2 % w/w. Scanning electron microscopy studies showed that the drug-loaded microspheres were non-aggregated and in spherical shape. Differential scanning calorimetry and Fourier transform infrared-spectroscopy studies showed that drug and excipients are compatible. Release studies showed that drug release was more profound in cecal medium induced with enzymes causing degradation of the cross linked BFG than that of the release showed in simulated intestinal fluid. Stability studies showed that there were no significant changes in the drug content and physical appearance of microspheres.

  13. Elevated carboxy terminal cross linked telopeptide of type I collagen in alcoholic cirrhosis

    DEFF Research Database (Denmark)

    Møller, S; Hansen, M; Hillingsø, Jens

    1999-01-01

    BACKGROUND: The carboxy terminal cross linked telopeptide of type I collagen (ICTP) has been put forward as a marker of bone resorption. Patients with alcoholic liver disease may have osteodystrophy. AIMS: To assess circulating and regional concentrations of ICTP in relation to liver dysfunction...

  14. TGFβ affects collagen cross-linking independent of chondrocyte phenotype but strongly depending on physical environment

    NARCIS (Netherlands)

    Bastiaansen-Jenniskens, Y.M.; Koevoet, W.; Bart, A.C.W. de; Zuurmond, A.-M.; Bank, R.A.; Verhaar, J.A.N.; Groot, J. de; Osch, G.J.V.M. van

    2008-01-01

    Transforming growth factor beta (TGFβ) is often used in cartilage tissue engineering to increase matrix formation by cells with various phenotypes. However, adverse effects of TGFβ, such as extensive cross-linking in cultured fibroblasts, have also been reported. Our goal was to study effects of

  15. Ionically cross-linked hyaluronic acid: wetting, lubrication, and viscoelasticity of a modified adhesion barrier gel

    Directory of Open Access Journals (Sweden)

    Katherine Vorvolakos

    2010-12-01

    Full Text Available Katherine Vorvolakos1, Irada S Isayeva1, Hoan-My Do Luu1, Dinesh V Patwardhan1, Steven K Pollack21Division of Chemistry and Material Science, 2Office of Science and Engineering Laboratories, Center for Devices and Radiological Health, Food and Drug Administration, Silver Spring, MD, USAAbstract: Hyaluronic acid (HA, in linear or cross-linked form, is a common component of cosmetics, personal care products, combination medical products, and medical devices. In all cases, the ability of the HA solution or gel to wet surfaces and/or disrupt and lubricate interfaces is a limiting feature of its mechanism of action. We synthesized ferric ion–cross-linked networks of HA based on an adhesion barrier, varied the degree of cross-linking, and performed wetting goniometry, viscometry, and dynamic mechanical analysis. As cross-linking increases, so do contact angle, viscosity, storage modulus, and loss modulus; thus, wetting and lubrication are compromised. These findings have implications in medical device materials, such as adhesion barriers and mucosal drug delivery vehicles.Keywords: hyaluron, adhesion barrier, wetting, contact angle, viscosity, lubrication, elasticity, viscoelastic, hydrogel, ferric

  16. Characteristic features and biotechnological applications of cross-linked enzyme aggregates (CLEAs)

    NARCIS (Netherlands)

    Sheldon, R.A.

    2011-01-01

    Cross-linked enzyme aggregates (CLEAs) have many economic and environmental benefits in the context of industrial biocatalysis. They are easily prepared from crude enzyme extracts, and the costs of (often expensive) carriers are circumvented. They generally exhibit improved storage and operational

  17. Grafted Cross-Linked Polyolefin Substrates for Peptide Synthesis and Assays

    DEFF Research Database (Denmark)

    1999-01-01

    suited for use in solid-phase biosystems, notably bioassays, such as immunoassays, DNA hybridization assays or PCR amplification. The grafted chains may bear substituents which are such that the polymer-grafted cross-linked polyolefin substrate is swellable by water or aqueous media, in other words...

  18. Mocaf cross-linking with gluten to improve the quality of mocaf dough

    Science.gov (United States)

    Raharja, Sapta; Udin, Faqih; Suparno, Ono; Febrianti, Faricha Helfi; Nuraisyah, Ani

    2017-03-01

    Crosslink between mocaf and gluten is conducted to increase the using of mocaf which has very big potential in Indonesia. The effort of cross-linking between mocaf and gluten is to get mocaf flour with better dough quality. This study aims to produce a cross-linked mocaf-gluten flour and to evaluate the influence of heating temperature (X1) and the addition of gluten concentration (X2) using completely randomized design factorial (RAFL). The cross-linking is carried out in alkaline solution with 10%, 20%, and 30% gluten addition and heating temperature at 50, 55, and 60 °C. The result showed that mocaf - gluten flour with the treatment of 30% gluten addition at 55 °C had the largest amount of protein and baking expansion (i.e 19.77% and 2.78 mL/g). Swelling power of the flour was increasing along with the increasing of water absorbing capacity of the mocaf - gluten flour. Birefringence properties of mocaf - gluten flour tended to be reduced as the increasing heating temperature. FTIR analysis of mocaf - gluten flour showed that there was peak strengthening of the infrared spectrum of the C - N bond at 1167-1159 cm-1 which was presumably resulted from the gluten addition and the cross-linking properties.

  19. Design and Preparation of Cross-Linked Polystyrene Nanoparticles for Elastomer Reinforcement

    Directory of Open Access Journals (Sweden)

    Ming Lu

    2010-01-01

    Full Text Available Cross-linked polystyrene (PS particles in a latex form were synthesized by free radical emulsion polymerization. The nano-PS-filled elastomer composites were prepared by the energy-saving latex compounding method. Results showed that the PS particles took a spherical shape in the size of 40–60 nm with a narrow size distribution, and the glass-transition temperature of the PS nanoparticles increased with the cross-linking density. The outcomes from the mechanical properties demonstrated that when filled into styrene-butadiene rubber (SBR, nitrile-butadiene rubber (NBR, and natural rubber (NR, the cross-linked PS nano-particles exhibited excellent reinforcing capabilities in all the three matrices, and the best in the SBR matrix. In comparison with that of the carbon black filled composites, another distinguished advantage of the cross-linked PS particles filled elastomer composites was found to be light weight in density, which could help to save tremendous amount of energy when put into end products.

  20. Polymers and Cross-Linking: A CORE Experiment to Help Students Think on the Submicroscopic Level

    Science.gov (United States)

    Bruce, Mitchell R. M.; Bruce, Alice E.; Avargil, Shirly; Amar, Francois G.; Wemyss, Thomas M.; Flood, Virginia J.

    2016-01-01

    The Polymers and Cross-Linking experiment is presented via a new three phase learning cycle: CORE (Chemical Observations, Representations, Experimentation), which is designed to model productive chemical inquiry and to promote a deeper understanding about the chemistry operating at the submicroscopic level. The experiment is built on two familiar…

  1. 21 CFR 177.2710 - Styrene-divinylbenzene resins, cross-linked.

    Science.gov (United States)

    2010-04-01

    ... SERVICES (CONTINUED) FOOD FOR HUMAN CONSUMPTION (CONTINUED) INDIRECT FOOD ADDITIVES: POLYMERS Substances..., preparing, treating, packaging, transporting, or holding food, in accordance with the following prescribed... 21 Food and Drugs 3 2010-04-01 2009-04-01 true Styrene-divinylbenzene resins, cross-linked....

  2. Substituent distribution within cross-linked and hydroxypropylated sweet potato starch and potato starch

    NARCIS (Netherlands)

    Zhao, J.; Schols, H.A.; Chen Zenghong,; Jin Zhengyu,; Buwalda, P.L.; Gruppen, H.

    2012-01-01

    Revealing the substituents distribution within starch can help to understand the changes of starch properties after modification. The distribution of substituents over cross-linked and hydroxypropylated sweet potato starch was investigated and compared with modified potato starch. The starches were

  3. EVA交联机理的研究%The Research of EVA Cross-linking Mechanism

    Institute of Scientific and Technical Information of China (English)

    王川艳; 苑会林

    2011-01-01

    研究了过氧化二异丙苯(DCP)对乙烯-醋酸乙烯共聚物(EVA)交联的影响,分析交联过程的反应机理.对交联的EVA样品进行紫外光辐照,分析在该过程中所发生的反应,并研究加入紫外线吸收剂2-羟基-4-正辛氧基-二苯甲酮(UV-531)后,对交联EVA样品在紫外光辐照下交联的影响.%The effect of peroxide (DCP) on Ethylene-Vinyl Acetate (EVA) cross-linking were studied, the reaction mechanism of EVA cross-linking were analyzed. Upon the exposure of cross-linked EVA samples to ultraviolet light, the reaction during this process were analyzed, and also, after adding the ultraviolet absorber (UV-531) , the influences to cross-linked EVA samples during the ultraviolet radiation process were researched.

  4. Laccase-Based CLEAs: Chitosan as a Novel Cross-Linking Agent

    Directory of Open Access Journals (Sweden)

    Alexandre Arsenault

    2011-01-01

    Full Text Available Laccase from Coriolopsis Polyzona was insolubilized as cross-linked enzyme aggregates (CLEAs for the first time with chitosan as the cross-linking agent. Concentrations between 0.01 and 1.867 g/L of chitosan were used and between 0.05 and 600 mM of 1-ethyl-3-(3-dimethylaminopropylcarbodiimide hydrochloride. The laccase was precipitated using ammonium sulphate and cross-linked simultaneously. Specific activity and thermal stability of these biocatalysts were measured. Activities of up to 737 U/g were obtained when 2,2-azino-bis-(3-ethylbenzthiazoline-6-sulfonic acid (ABTS was used as a substrate. Moreover, the stability of these biocatalysts was improved with regards to thermal degradation compared to free laccase when exposed to denaturing conditions of high temperature and low pH. The CLEAs stability against chemical denaturants was also tested but no significant improvement was detected. The total amount of ABTS to be oxidized during thermal degradation by CLEAs and free laccase was calculated and the insolubilized enzymes were reported to oxidize more substrate than free laccase. The formation conditions were analyzed by response surface methodology in order to determine an optimal environment for the production of efficient laccase-based CLEAs using chitosan as the cross-linking agent. After 24 hours of formation at pH 3 and at 4°C without agitation, the CLEAs exhibit the best specific activity.

  5. Standard and hypoosmolar corneal cross-linking in various pachymetry groups

    NARCIS (Netherlands)

    Soeters, Nienke; Tahzib, Nayyirih G

    2015-01-01

    PURPOSE: To investigate the influence of corneal thickness on the outcome of corneal cross-linking (CXL) for progressive keratoconus. METHODS: In this cohort study, 72 unilateral eyes were treated by CXL and divided into three groups according to central corneal thickness (CCT) measured by ultrasoun

  6. The peptidoglycan of Mycobacterium abscessus is predominantly cross-linked by L,D-transpeptidases.

    Science.gov (United States)

    Lavollay, Marie; Fourgeaud, Martine; Herrmann, Jean-Louis; Dubost, Lionel; Marie, Arul; Gutmann, Laurent; Arthur, Michel; Mainardi, Jean-Luc

    2011-02-01

    Few therapeutic alternatives remain for the treatment of infections due to multiresistant Mycobacterium abscessus. Here we show that the peptidoglycans of the "rough" and "smooth" morphotypes contain predominantly 3→3 cross-links generated by l,d-transpeptidases, indicating that these enzymes are attractive targets for the development of efficient drugs.

  7. Is dialdehyde starch a valuable cross-linking agent for collagen/elastin based materials?

    Science.gov (United States)

    Skopinska-Wisniewska, J; Wegrzynowska-Drzymalska, K; Bajek, A; Maj, M; Sionkowska, A

    2016-04-01

    Collagen and elastin are the main structural proteins in mammal bodies. They provide mechanical support, strength, and elasticity to various organs and tissues, e.g. skin, tendons, arteries, and bones. They are readily available, biodegradable, biocompatible and they stimulate cell growth. The physicochemical properties of collagen and elastin-based materials can be modified by cross-linking. Glutaraldehyde is one of the most efficient cross-linking agents. However, the unreacted molecules can be released from the material and cause cytotoxic reactions. Thus, the aim of our work was to investigate the influence of a safer, macromolecular cross-linking agent--dialdehyde starch (DAS). The properties of hydrogels based on collagen/elastin mixtures (95/5, 90/10) containing 5 and 10% of DAS and neutralized via dialysis against deionized water were tested. The homogenous, transparent, stiff hydrogels were obtained. The DAS addition causes the formation of intermolecular cross-linking bonds but does not affect the secondary structure of the proteins. As a result, the thermal stability, mechanical strength, and, surprisingly, swelling ability increased. At the same time, the surface properties test and in vitro study show that the materials are attractive for 3T3 cells. Moreover, the materials containing 10% of DAS are more resistant to enzymatic degradation.

  8. Pickering emulsions stabilized by whey protein nanoparticles prepared by thermal cross-linking

    NARCIS (Netherlands)

    Wu, Jiande; Shi, Mengxuan; Li, Wei; Zhao, Luhai; Wang, Ze; Yan, Xinzhong; Norde, Willem; Li, Yuan

    2015-01-01

    A Pickering (o/w) emulsion was formed and stabilized by whey protein isolate nanoparticles (WPI NPs). Those WPI NPs were prepared by thermal cross-linking of denatured WPI proteins within w/o emulsion droplets at 80. °C for 15. min. During heating of w/o emulsions containing 10% (w/v) WPI protein

  9. Detection of DNA cross-links in tumor cells with the ethidium bromide fluorescence assay

    NARCIS (Netherlands)

    de Jong, Steven; Zijlstra, J G; Timmer-Bosscha, H; Mulder, N H; de Vries, Liesbeth

    1986-01-01

    Until now the fluorescence assay with ethidium bromide has only been used on pure DNA. This assay depends on the difference in fluorescence between single- and double-stranded DNA (dsDNA). Cross-links in DNA are measured by the return of fluorescence of dsDNA after heat denaturation at pH 12. Under

  10. Horseradish peroxidase-catalyzed cross-linking of feruloylated arabinoxylans with β-casein

    NARCIS (Netherlands)

    Boeriu, C.G.; Oudgenoeg, G.; Spekking, W.T.J.; Berendsen, L.B.J.M.; Vancon, L.; Boumans, H.; Gruppen, H.; Berkel, W.J.H. van; Laane, C.; Voragen, A.G.J.

    2004-01-01

    Heterologous conjugates of wheat arabinoxylan and β-casein were prepared via enzymatic cross-linking, using sequential addition of the arabinoxylan to a mixture of β-casein, peroxidase, and hydrogen peroxide. The maximal formation of adducts between the β-casein and the feruloylated arabinoxylan was

  11. Mature enzymatic collagen cross-links, hydroxylysylpyridinoline and lysylpyridinoline, in the aging human vitreous

    NARCIS (Netherlands)

    Ponsioen, T.L.; van Deemter, M.; Bank, R.A.; Snabel, J.M.; Zijlstra, G.S.; van der Worp, R.J.; Hooymans, J.M.M.; Los, L.I.

    2009-01-01

    Purpose. The vitreous body of the human eye undergoes progressive morphologic changes with aging. Since the enzymatic collagen cross-links hydroxylysylpyridinoline (HP) and lysylpyridinoline (LP) are known to be important for the integrity of the collagen matrix, the presence in the vitreous on agin

  12. Mature Enzymatic Collagen Cross-Links, Hydroxylysylpyridinoline and Lysylpyridinoline, in the Aging Human Vitreous

    NARCIS (Netherlands)

    Ponsioen, Theodorus L.; van Deemter, Marielle; Bank, Rudolf A.; Snabel, Johanna M.; Zijlstra, Gerrit S.; van der Worp, Roelofje J.; Hooymans, Johanna M. M.; Los, Leonoor I.

    2009-01-01

    PURPOSE. The vitreous body of the human eye undergoes progressive morphologic changes with aging. Since the enzymatic collagen cross-links hydroxylysylpyridinoline (HP) and lysylpyridinoline (LP) are known to be important for the integrity of the collagen matrix, the presence in the vitreous on agin

  13. Formation and Distribution of Space-Charge in Cross-Linked Polyethylene

    Science.gov (United States)

    Zhang, Ye-Wen; Li, Ji-Xiao; Zheng, Fei-Hu; Peng, Zong-Ren; Wu, Chang-Shun; Xia, Zhong-Fu

    2002-08-01

    The formation and distribution of space-charge in a cross-linked polyethylene (XLPE) sample are investigated by means of pressure wave propagation, infrared spectroscopy and electrostatic force microscopy (EFM). The related mechanism of space-charge distribution and the structure of XLPE are discussed. The EFM images show that quite large quantitative space-charges locate at the surface of spherulites.

  14. Crown ether activation of cross-linked subtilisin Carlsberg crystals in organic solvents

    NARCIS (Netherlands)

    Unen, van Dirk-Jan; Sakodinskaya, Inna K.; Engbersen, Johan F.J.; Reinhoudt, David N.

    1998-01-01

    The activity of cross-linked subtilisin Carlsberg crystals in the catalysis of peptide bond formation can be significantly enhanced by pretreatment of the enzyme crystals with crown ethers. Soaking of the enzyme crystals in a solution of crown ether in acetonitrile followed by evaporation of the sol

  15. Phosphoric acid doped polysulfone membranes with aminopyridine pendant groups and imidazole cross-links

    DEFF Research Database (Denmark)

    Hink, Steffen; Elsøe, Katrine; Cleemann, Lars Nilausen;

    2015-01-01

    Udel polysulfone based membranes with 4-aminopyridine pendant groups and cross-linking imidazole units are synthesized in a simple two step reaction. The ratio of 4-aminopyridine and imidazole is varied and the materials are extensively characterized. The average phosphoric acid uptake (in 85 wt...

  16. Cross-Linked Nanoporous Materials from Reactive and Multifunctional Block Polymers

    Energy Technology Data Exchange (ETDEWEB)

    Seo, Myungeun; Amendt, Mark A.; Hillmyer, Marc A. (UMM)

    2012-10-10

    Polylactide-b-poly(styrene-co-2-hydroxyethylmethacrylate) (PLA-b-P(S-co-HEMA)) and polylactide-b-poly(styrene-co-2-hydroxyethylacrylate) (PLA-b-P(S-co-HEA)) were synthesized by combination of ring-opening polymerization and reversible addition-fragmentation chain transfer polymerization. {sup 1}H nuclear magnetic resonance spectroscopy and size exclusion chromatography data indicated that the polymerizations were controlled and that hydroxyl groups were successfully incorporated into the block polymers. The polymers were reacted with 4,4{prime}-methylenebis(phenyl isocyanate) (MDI) to form the corresponding cross-linked materials. The materials were annealed at 150 C to complete the coupling reaction. Robust nanoporous materials were obtained from the cross-linked polymers by treatment with aqueous base to hydrolyze the PLA phase. Small-angle X-ray scattering study combined with scanning electron microscopy showed that MDI-cross-linked PLA-b-P(S-co-HEMA)/PLA-b-P(S-co-HEA) can adopt lamellar, hexagonally perforated lamellar, and hexagonally packed cylindrical morphologies after annealing. In particular, the HPL morphology was found to evolve from lamellae due to increase in volume fraction of PS phase as MDI reacted with hydroxyl groups. The reaction also kinetically trapped the morphology by cross-linking. Bicontinuous morphologies were also observed when dibutyltin dilaurate was added to accelerate reaction between the polymer and MDI.

  17. Effect of dual modification with hydroxypropylation and cross-linking on physicochemical properties of taro starch.

    Science.gov (United States)

    Hazarika, Bidyut Jyoti; Sit, Nandan

    2016-04-20

    Dual modification of taro starch by hydroxypropylation and cross-linking was carried out and the properties of the modified starches were investigated. Two different levels of hydroxypropylation (5 and 10%) and cross-linking (0.05 and 0.10%) were used in different sequences. The amylose contents of the starch decreased due to single and dual modification. For the dual-modified starches, the swelling, solubility and clarity was found to increase with level of hydroxypropylation and decrease with level of cross-linking. The freeze-thaw stability of the dual-modified starches was also affected by the sequence of modification. The viscosities of the cross-linked and dual-modified starches were more than native and hydroxypropylated starches. The firmness of the dual-modified starches was also higher than native and single modified starches. The dual-modified starches have benefits of both type of modifications and could be used for specific purposes e.g. food products requiring high viscosity as well as freeze-thaw stability.

  18. Vitamin E diffused highly cross-linked polyethylene in total hip arthroplasty at five years

    DEFF Research Database (Denmark)

    Nebergall, Audrey K; Greene, M. E.; Laursen, M B

    2017-01-01

    AIMS: The objective of this five-year prospective, blinded, randomised controlled trial (RCT) was to compare femoral head penetration into a vitamin E diffused highly cross-linked polyethylene (HXLPE) liner with penetration into a medium cross-linked polyethylene control liner using radiostereome......AIMS: The objective of this five-year prospective, blinded, randomised controlled trial (RCT) was to compare femoral head penetration into a vitamin E diffused highly cross-linked polyethylene (HXLPE) liner with penetration into a medium cross-linked polyethylene control liner using...... radiostereometric analysis. PATIENTS AND METHODS: Patients scheduled for total hip arthroplasty (THA) were randomised to receive either the study E1 (32 patients) or the control ArComXL polyethylene (35 patients). The median age (range) of the overall cohort was 66 years (40 to 76). RESULTS: The five-year median...... (interquartile range) proximal femoral head penetration into the E1 was -0.05 mm (-0.13 to -0.02) and 0.07 mm (-0.03 to 0.16) for ArComXL. At three and five years, the penetration was significantly greater in the ArComXL group compared with the E1 group (p = 0.029 and p = 0.019, respectively). All patient...

  19. EFFICIENCY MODELS OF THE CROSS-FUNCTIONAL TEAMS

    Directory of Open Access Journals (Sweden)

    Dinca Laura

    2013-04-01

    Full Text Available Cross-functional teams represent a characteristic of the new organization form of the enterprises, imposed by the complexity of the present environment. Regardless their kind, the new organization forms are based on the cross-functional teams as an innovation source and reunion of competences. Only by the medium of the cross-functional teams, the new organizational partnerships obtain flexibility in their actions and fastness in their reactions. By their features, the cross-functional teams should be differentiated from any kind of work-group. What makes them different is the common effort carried to reach the common objective of the team. The present paper presents two research models for the efficiency of the cross-functional teams, respectively input-process-output and input-mediator-outcome models. These show the factors on which cross-functional teams’ managers should action to obtain superior economic performances.

  20. Capacity of cognitive radio under imperfect secondary and cross link channel state information

    KAUST Repository

    Sboui, Lokman

    2011-09-01

    In this paper, we study the ergodic capacity of secondary user channel in a spectrum sharing scenario in which the secondary transmitter is instantaneously aware of estimated versions of the cross link (between the secondary transmitter and the primary receiver) and the secondary link Channel State Information (CSI). The secondary link optimal power profile along with the ergodic capacity are derived for a class of fading channels, under an average power constraint and an instantaneous interference outage constraint. We also show that our framework is rather general as it encompasses several previously studied spectrum sharing settings as special cases. In order to gain some insights on the capacity behavior, numerical results are shown for independent Rayleigh fading channels where it is found for instance, that at low SNR regime, only the secondary channel estimation matters and that the cross link CSI has no effect on the ergodic capacity; whereas at high SNR regime, the capacity is rather driven by the cross link CSI. © 2011 IEEE.

  1. Organizing Innovation Complementarities between Cross-Functional Teams

    OpenAIRE

    James H. Love; Stephen Roper; Giovanni Mangiarotti

    2006-01-01

    Cross-functional teams play a potentially important part in the innovation process enabling knowledge sharing, the development of trust and overcoming spatial and organizational barriers. Using a supermodularity approach, we focus on potential complementarities which may arise when cross-functional teams are used in different elements of the innovation process in UK and German manufacturing plants. Using optimal combinations of cross-functional teams in the innovation process increases innova...

  2. Organizing innovation: complementarities between cross-functional teams

    OpenAIRE

    James H Love; Roper, Stephen

    2009-01-01

    Cross-functional teams play a potentially important part in the innovation process enabling knowledge sharing, the development of trust and overcoming spatial and organizational barriers. Using a supermodularity approach, we focus on potential complementarities which may arise when cross-functional teams are used in different elements of the innovation process in UK and German manufacturing plants. Using optimal combinations of cross-functional teams in the innovation process increases innova...

  3. CROSS-FUNCTIONAL MANAGEMENT – EFFECTIVE ORGANIZATION FORM OF ENTERPRISES

    OpenAIRE

    2012-01-01

    Today, cross-functional management is a challenging research topic given the multitude of the cross-functional organizations that are founded and whose advantages are unanimous recognized. The old hierarchical pyramid was suitable for companies a long while during the industrial era. But nowadays they are not at all seen as profitable organizations. The aim of this paper is to present the main features of the cross-functional organizations, their advantages and limits. Cooperation is also pre...

  4. Cross-functional team processes and patient functional improvement.

    Science.gov (United States)

    Alexander, Jeffrey A; Lichtenstein, Richard; Jinnett, Kimberly; Wells, Rebecca; Zazzali, James; Liu, Dawei

    2005-10-01

    To test the hypothesis that higher levels of participation and functioning in cross-functional psychiatric treatment teams will be related to improved patient outcomes. Primary data were collected during the period 1992-1999. The study was conducted in 40 teams within units treating seriously mentally ill patients in 16 Veterans Affairs hospitals across the U.S. A longitudinal, multilevel analysis assessed the relationship between individual- and team-level variables and patients' ability to perform activities of daily living (ADL) over time. Team data were collected in 1992, 1994, and 1995. The number of times patient data were collected was dependent on the length of time the patient was treated and varied from 1 to 14 between 1992 and 1999. Key variables included: patients' ADL scores (the dependent variable); measures of team participation and team functioning; the number of days from baseline on which a patient's ADLs were assessed; and several control variables. Team data were obtained via self-administered questionnaires distributed to staff on the study teams. Additional team data were obtained via questionnaires completed by unit directors contemporaneously with the staff survey. Patient data were collected by trained clinicians at regular intervals using a standard assessment instrument. Results indicated that patients treated in teams with higher levels of staff participation experienced greater improvement in ADL over time. No differences in ADL change were noted for patients treated in teams with higher levels of team functioning. Findings support our premise that team process has important implications for patient outcomes. The results suggest that the level of participation by the team as a whole may be a more important process attribute, in terms of patient improvements in ADLs, than the team's smooth functioning. These findings indicate the potential appropriateness of managerial interventions to encourage member investment in team processes.

  5. Metal cation cross-linked nanocellulose hydrogels as tissue engineering substrates.

    Science.gov (United States)

    Zander, Nicole E; Dong, Hong; Steele, Joshua; Grant, John T

    2014-01-01

    The use of cellulose materials for biomedical applications is attractive due to their low cost, biocompatibility, and biodegradability. Specific processing of cellulose to yield nanofibrils further improves mechanical properties and suitability as a tissue engineering substrate due to the similarity to the fibrous structure, porosity, and size-scale of the native extracellular matrix. In order to generate the substrate, nanocellulose hydrogels were fabricated from carboxylated cellulose nanofibrils via hydrogelation using metal salts. Hydrogels cross-linked with Ca(2+) and Fe(3+) were investigated as tissue culture substrates for C3H10T1/2 fibroblast cells. Control substrates as well as those with physically adsorbed and covalently attached fibronectin protein were evaluated with X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR), and enzyme linked immunosorbent assay (ELISA). Significantly more cells were attached to surfaces modified with protein, with the highest number of cells adhered to the calcium cross-linked hydrogels with covalently attached protein.

  6. Polymeric Nanocapsule from Silica Nanoparticle@Cross-linked Polymer Nanoparticles via One-Pot Approach

    Directory of Open Access Journals (Sweden)

    Shen Ruoping

    2009-01-01

    Full Text Available Abstract A facile strategy was developed here to prepare cross-linked polymeric nanocapsules (CP nanocapsules with silica nanoparticles as templates. The silica nanoparticle@cross-linked polymer nanoparticles were prepared by the encapsulation of the silica nanoparticles by the one-pot approach via surface-initiated atom transfer radical polymerization of hydroxyethyl acrylate in the presence ofN,N′-methylenebisacrylamide as a cross-linker from the initiator-modified silica nanoparticles. After the silica nanoparticle templates were etched with hydrofluoric acid, the CP nanocapsules with particle size of about 100 nm were obtained. The strategy developed was confirmed with Fourier transform infrared, thermogravimetric analysis and transmission electron microscopy.

  7. The cross-linking influence of electromagnetic radiation on water-soluble polyacrylan compositions with biopolymers

    Directory of Open Access Journals (Sweden)

    B. Grabowska

    2009-01-01

    Full Text Available The results of examinations of the cross-linking influence of electromagnetic radiation - in a microwave range – on polyacrylancompositions with biopolymers, are presented in the hereby paper. The cross-linking process of the tested compositions was determined on the basis of the FT-IR spectroscopic methods. It was shown that microwave operations can lead to the formation of new cross-linkedstructures with strong covalent bonds. The adsorption process and formation of active centres in polymer molecules as well as in highsilica sand were found due to microwave radiations. In this process hydroxyl groups (-OH - present in a polymer - and silane groups (Si- O-H - present in a matrix - are mainly taking part. Spectroscopic and strength tests performed for the system: biopolymer binding agent – matrix indicate that the microwave radiation can be applied for hardening moulding sands with biopolymer binders.

  8. Biochemical properties of bioplastics made from wheat gliadins cross-linked with cinnamaldehyde.

    Science.gov (United States)

    Balaguer, M Pau; Gómez-Estaca, Joaquín; Gavara, Rafael; Hernandez-Munoz, Pilar

    2011-12-28

    The aim of this work has been to study the modification of gliadin films with cinnamaldehyde as a potential cross-linker agent. The molecular weight profile and cross-linking density showed that cinnamaldehyde increased reticulation in the resulting films. The participation of free amino groups of the protein in the newly created entanglements could be a possible mechanism of connection between the polypeptidic chains. The combination of a Schiff base and a Michael addition is a feasible approach to understanding this mechanism. The protein solubility in different media pointed to lower participation by both noncovalent and disulfide bonds in stabilizing the structure of the cross-linked films. The new covalent bonds formed by the cinnamaldehyde treatment hampered water absorption and weight loss, leading to more water-resistant matrices which had not disintegrated after 5 months. The properties of this novel bioplastic could be modified to suit the intended application by using cinnamaldehyde, a naturally occurring compound.

  9. pH-sensitive genipin-cross-linked chitosan microspheres for heparin removal.

    Science.gov (United States)

    Kamiński, Kamil; Zazakowny, Karolina; Szczubiałka, Krzysztof; Nowakowska, Maria

    2008-11-01

    Chitosan hydrogel microspheres were obtained by cross-linking chitosan in its inverse emulsion using genipin as cross-linker. The genipin-cross-linked chitosan microspheres (ChGp) swell significantly in water at pH values below 6.5 and shrink to a smaller extent at pH values above 6.5. ChGp microspheres bind heparin in water. The kinetics of heparin binding was found to be pH dependent and was faster and more efficient at a lower pH. That can be also controlled by the weight of ChGp microspheres used. Rate and efficiency of heparin adsorption at pH 7.4, which is typical of blood, could be increased by quaternization of ChGp microspheres using glycidyltrimethylammonium chloride (GTMAC). The polymeric material obtained thus can be potentially useful for heparin removal in biomedical applications.

  10. Biomimetic acellular detoxified glutaraldehyde cross-linked bovine pericardium for tissue engineering.

    Science.gov (United States)

    Mathapati, Santosh; Bishi, Dillip Kumar; Guhathakurta, Soma; Cherian, Kotturathu Mammen; Venugopal, Jayarama Reddy; Ramakrishna, Seeram; Verma, Rama Shanker

    2013-04-01

    Glutaraldehyde (GLUT) processing, cellular antigens, calcium ions in circulation, and phospholipids present in the native tissue are predominantly responsible for calcification, degeneration, and lack of natural microenvironment for host progenitor cell migration in tissue implants. The study presents an improved methodology for adhesion and proliferation of endothelial progenitor cells (EPCs) without significant changes in biomechanical and biodegradation properties of the processed acellular bovine pericardium. The anti-calcification potential of the processed tissue was enhanced by detoxification of GLUT-cross-linked bovine pericardium by decellularization, pretreating it with ethanol or removing the free aldehydes by citric acid treatment and lyophilization. The treated tissues were assessed for biomechanical properties, GLUT ligand quantification, adhesion, proliferation of EPCs, and biodegradability. The results indicate that there was no significant change in biomechanical properties and biodegradability when enzymatic hydrolysis (p>0.05) is employed in detoxified acellular GLUT cross-linked tissue (DBP-G-CA-ET), compared with the native detoxified GLUT cross-linked bovine pericardium (NBP-G-CA-ET). DBP-G-CA-ET exhibited a significant (p>0.05) increase in the viability of EPCs and cell adhesion as compared to acellular GLUT cross-linked bovine pericardium (ppericardium, employed in our study as an alternative to conventional GLUT cross-linked bovine pericardium, might provide longer durability and better biocompatibility, and reduce calcification. The developed bovine pericardium patches could be used in cardiac reconstruction and repair, arteriotomy, soft tissue repair, and general surgical procedures with tissue regeneration dimensions. Copyright © 2012 Elsevier B.V. All rights reserved.

  11. Wear measurement of highly cross-linked UHMWPE using a 7Be tracer implantation technique.

    Science.gov (United States)

    Wimmer, Markus A; Laurent, Michel P; Dwiwedi, Yasha; Gallardo, Luis A; Chipps, Kelly A; Blackmon, Jeffery C; Kozub, Raymond L; Bardayan, Daniel W; Gross, Carl J; Stracener, Daniel W; Smith, Michael S; Nesaraja, Caroline D; Erikson, Luke; Patel, Nidhi; Rehm, Karl E; Ahmad, Irshad; Greene, John P; Greife, Uwe

    2013-04-01

    The very low wear rates achieved with the current highly cross-linked ultrahigh molecular weight polyethylenes (UHMWPE) used in joint prostheses have proven to be difficult to measure accurately by gravimetry. Tracer methods are therefore being explored. The purpose of this study was to perform a proof-of-concept experiment on the use of the radioactive tracer beryllium-7 ((7)Be) for the determination of in vitro wear in a highly cross-linked orthopedic UHMWPE. Three cross-linked and four conventional UHMWPE pins made from compression-molded GUR 1050, were activated with 10(9) to 10(10) (7)Be nuclei using a new implantation setup that produced a homogenous distribution of implanted nuclei up to 8.5 μm below the surface. The pins were tested for wear in a six-station pin-on-flat apparatus for up to 7.1 million cycles (178 km). A Germanium gamma detector was employed to determine activity loss of the UHMWPE pins at preset intervals during the wear test. The wear of the cross-linked UHMWPE pins was readily detected and estimated to be 17 ± 3 μg per million cycles. The conventional-to-cross-linked ratio of the wear rates was 13.1 ± 0.8, in the expected range for these materials. Oxidative degradation damage from implantation was negligible; however, a weak dependence of wear on implantation dose was observed limiting the number of radioactive tracer atoms that can be introduced. Future applications of this tracer technology may include the analysis of location-specific wear, such as loss of material in the post or backside of a tibial insert.

  12. Identification of dityrosine cross-linked sites in oxidized human serum albumin.

    Science.gov (United States)

    Annibal, Andrea; Colombo, Graziano; Milzani, Aldo; Dalle-Donne, Isabella; Fedorova, Maria; Hoffmann, Ralf

    2016-04-15

    Reactive oxygen species (ROS) can oxidize virtually all cellular components. In proteins cysteine, methionine, tryptophan, and tyrosine residues are most prone to oxidation and their oxidized forms are thus considered as biomarkers of oxidative protein damages. Ultraviolet radiation and some endogenous ROS can produce tyrosine radicals reacting with other tyrosine residues yielding intra- or intermolecular cross-links in proteins. These 3,3'-dityrosines can be quantified by their characteristic fluorescence, but analytical methods to identify the modification sites in proteins are still missing. Although mass spectrometry (MS) is routinely used to map other post-translational modifications, the analysis of dityrosines is challenged by simultaneous fragmentations of both cross-linked peptide chains producing complex tandem mass spectra. Additionally, the fragmentation patterns differ from linear peptides. Here, we studied the fragmentation behavior of dityrosine cross-linked peptides obtained by incubating three peptides (AAVYHHFISDGVR, TEVSSNHVLIYLDK, and LVAYYTLIGASGQR) with horseradish peroxidase in the presence of hydrogen peroxide. Homo- and hetero-dimerization via dityrosine was monitored by fluorescence spectroscopy and MS. The fragmentation characteristics of dityrosine-linked peptides were studied on an ESI-LTQ-Orbitrap-MS using collision induced dissociation, which allowed localizing the cross-linked positions and provided generic rules to identify this oxidative modification. When human serum albumin oxidized with 50-fold molar excess of HOCl in phosphate buffer saline was analyzed by nanoRPC-ESI-MS/MS, an automatic database search considering all possible (in-silico generated) tyrosine-containing peptides as dynamic modifications revealed four different types of oxidatively modified tyrosine residues including dityrosines linking ten different Tyr residues. The automatic database search was confirmed by manual interpretation of each tandem mass spectrum.

  13. A Novel Learning Scheme for Chebyshev Functional Link Neural Networks

    Directory of Open Access Journals (Sweden)

    Satchidananda Dehuri

    2011-01-01

    dimensional-space where linear separability is possible. Moreover, the proposed HCFLNN combines the best attribute of particle swarm optimization (PSO, back propagation learning (BP learning, and functional link neural networks (FLNNs. The proposed method eliminates the need of hidden layer by expanding the input patterns using Chebyshev orthogonal polynomials. We have shown its effectiveness of classifying the unknown pattern using the publicly available datasets obtained from UCI repository. The computational results are then compared with functional link neural network (FLNN with a generic basis functions, PSO-based FLNN, and EFLN. From the comparative study, we observed that the performance of the HCFLNN outperforms FLNN, PSO-based FLNN, and EFLN in terms of classification accuracy.

  14. Flour mill stream blending affects sugar snap cookie and Japanese sponge cake quality and oxidative cross-linking potential of soft white wheat.

    Science.gov (United States)

    Ramseyer, Daniel D; Bettge, Arthur D; Morris, Craig F

    2011-01-01

    The purpose of this research was to study the functional differences between straight grade (75% extraction rate) and patent (60% extraction rate) flour blends from 28 genetically pure soft white and club wheat grain lots, as evidenced by variation in sugar snap cookie and Japanese sponge cake quality. Functional differences were examined relative to arabinoxylan content, protein content, and oxidative cross-linking potential of flour slurries. Oxidative cross-linking measurements were obtained on flour slurries with a low shear Bostwick consistometer and considered endogenous oxidative cross-linking potential (water alone) or enhanced oxidative cross-linking potential (with added hydrogen peroxide-peroxidase). A 2-way ANOVA indicated that flour blend was the greater source of variation compared to grain lot for all response variables except water-extractable arabinoxylan content. Patent flours produced larger sugar snap cookies and Japanese sponge cakes, and contained significantly less total and water-unextractable arabinoxylans, protein, and ash than did straight grade flours. Patent flours produced more viscous slurries for endogenous and enhanced cross-linking measurements compared to the straight grade flours. The functional differences between patent and straight grade flours appear to be related to the particular mill streams that were utilized in the formulation of the 2 flour blends and compositional differences among those streams.

  15. The design of equipment for optical power measurement in FSO link beam cross-section

    Science.gov (United States)

    Latal, Jan; David, Tomas; Wilfert, Otakar; Kolka, Zdenek; Koudelka, Petr; Hanacek, Frantisek; Vitasek, Jan; Siska, Petr; Skapa, Jan; Vasinek, Vladimir

    2012-06-01

    The free space optical links have found their major application in today's technological society. The demand for quality broadband is a must for all types of end users in these times. Because of the large jamming from wireless radio networks in non-licensed ISM bands, the free space optical links provide bridging of some densely populated urban areas. Their advantage is the high transmission rate for relatively long distances. However, the disadvantage is the dependence of free space optical links on atmospheric influences. Aired collimated optical beam passes through the atmospheric transmission environment and by its influence cause the deformation of the optical beam. Author's team decided to construct a special measuring device for measurement of optical power in FSO link beam cross-section. The equipment is mobile and can be rearranged and adjust according to the given location and placement of the FSO link at any time. The article describes the individual structural elements of the measuring equipment, its controlling and application for evaluation and adjustment of measuring steps. The graphs from optical power measurements in the beam cross-section of professional FSO links are presented at the end.

  16. Preparation and Characterization of Epoxy Resin Cross-Linked with High Wood Pyrolysis Bio-Oil Substitution by Acetone Pretreatment

    Directory of Open Access Journals (Sweden)

    Yi Liu

    2017-03-01

    Full Text Available The use of cost effective solvents may be necessary to store wood pyrolysis bio-oil in order to stabilize and control its viscosity, but this part of the production system has not been explored. Conversely, any rise in viscosity during storage, that would occur without a solvent, will add variance to the production system and render it cost ineffective. The purpose of this study was to modify bio-oil with a common solvent and then react the bio-oil with an epoxy for bonding of wood without any loss in properties. The acetone pretreatment of the bio-oil/epoxy mixture was found to improve the cross-linking potential and substitution rate based on its mechanical, chemical, and thermal properties. Specifically, the bio-oil was blended with epoxy resin at weight ratios ranging from 2:1 to 1:5 and were then cured. A higher bio-oil substitution rate was found to lower the shear bond strength of the bio-oil/epoxy resins. However, when an acetone pretreatment was used, it was possible to replace the bio-oil by as much as 50% while satisfying usage requirements. Extraction of the bio-oil/epoxy mixture with four different solvents demonstrated an improvement in cross-linking after acetone pretreatment. ATR-FTIR analysis confirmed that the polymer achieved a higher cross-linked structure. DSC and TGA curves showed improved thermal stability with the addition of the acetone pretreatment. UV-Vis characterization showed that some functional groups of the bio-oil to epoxy system were unreacted. Finally, when the resin mixture was utilized to bond wood, the acetone pretreatment coupled with precise tuning of the bio-oil:epoxy ratio was an effective method to control cross-linking while ensuring acceptable bond strength.

  17. Molecular contacts for chlorosome envelope proteins revealed by cross-linking studies with chlorosomes from Chlorobium tepidum

    DEFF Research Database (Denmark)

    Li, Hui; Frigaard, Niels-Ulrik; Bryant, Donald A

    2006-01-01

    type and mutants lacking a single chlorosome protein were cross-linked with the zero-length cross-linker 1-ethyl-3-[3-(dimethylamino)propyl]carbodiimide (EDC) and analyzed by gel electrophoresis. Similar cross-linking products were observed when the time and temperature were varied or when EDC...... was replaced with glutaraldehyde. Specific interactions between chlorosome proteins in cross-linked products were identified by immunoblotting with polyclonal antibodies raised against recombinant chlorosome proteins. We confirmed these interactions by demonstrating that these products were missing...... in appropriate mutants. Confirming the location of CsmA in the paracrystalline baseplate, cross-linking showed that CsmA forms dimers, trimers, and homomultimers as large as dodecamers and that CsmA directly interacts with the Fenna-Matthews-Olson protein. Cross-linking further suggests that the precursor form...

  18. Silica cross-linked micelles loading with silicon nanoparticles: preparation and characterization.

    Science.gov (United States)

    Pan, Guo-Hui; Barras, Alexandre; Boussekey, Luc; Boukherroub, Rabah

    2013-08-14

    A new family of luminescent and stable silicon-based nanoparticles (NPs), silica cross-linked pluronic F127 (PF127) micelles loaded with decyl capped silicon nanoparticles (decyl-SiNPs), were synthesized in aqueous media. The decyl-SiNPs were prepared by first liberating hydride terminated SiNPs (H-SiNPs) from a porous silicon matrix followed by their functionalization via hydrosilylation with 1-decene under photochemical activation. The silicon-based NPs exhibit bright photoluminescence (PL) with a quantum yield of ∼3.8% and peaking at ∼2.0 eV, which lies within the transmission window that is useful for biological imaging. They display a hydrodynamic size of ∼25 nm with exterior polyethylene oxide (PEO) blocks stretching out in aqueous media. Chloroform was found to quench the excitation at energy above 4.9 eV by shielding the incident light or relaxing the charge carriers, which highlights that caution against solvent interference should be taken when performing the studies on PL origin and luminescence efficiency of SiNPs. For PF127, the blocks of hydrophilic PEO participate in the PL quenching, while poly(propylene oxide) (PPO) does not. The colloidal solution displays excellent PL stability against salt (NaCl) and temperature but is susceptible to basic solution at pH above 9.

  19. Preparation and characterization of a microencapsulated polyethylene glycol cross-linked polyhemoglobin.

    Science.gov (United States)

    Knirsch, Marcos C; Dell'Anno, Filippo; Chicoma, Dennis; Stephano, Marco Antonio; Bou-Chacra, Nádia A; Palombo, Domenico; Converti, Attilio; Polakiewicz, Bronislaw

    2015-11-01

    Many complications are associated to the therapeutic use of blood, among which are not only transfusion adverse events but also other issues such as lack of donors and high costs for collecting, testing, preserving, and distributing blood packages. Therefore, a clinically viable "blood substitute" is considered the holy grail of traumatology and may greatly benefit medicine. One of the most successful approaches to date is conjugating hemoglobin with polyethylene glycol (PEG). This conjugation aims mainly at overcoming free cell hemoglobin toxicity, which makes its use as oxygen carrier in pure form unfeasible. To improve PEG-hemoglobin conjugates feasibility, we propose applying dual functional PEG cross-linking hemoglobin molecules encapsulated by a protein carrier. The new oxygen carrier showed mean values of the hydrodynamic diameter, dispersity, and zeta potential of 1370 nm, 0.029 and -36 mV, respectively, evidencing the successful synthesis of PEG bis(N-succinimidyl succinate) and polyhemoglobin as well as the structuring of protein carrier.

  20. Graphene oxide-reinforced biodegradable genipin-cross-linked chitosan fluorescent biocomposite film and its cytocompatibility

    Directory of Open Access Journals (Sweden)

    Li JH

    2013-09-01

    Full Text Available Jianhua Li,1 Na Ren1, Jichuan Qiu,1 Xiaoning Mou,2 Hong Liu1,21Center of Bio and Micro/Nano Functional Materials, State Key Laboratory of Crystal Materials, Shandong University, Jinan, People's Republic of China; 2Beijing Institute of Nanoenergy and Nanosystems, Chinese Academy of Sciences, Beijing, People's Republic of ChinaAbstract: A genipin-cross-linked chitosan/graphene oxide (GCS/GO composite film was prepared using a solution casting method. Fourier transform infrared (FTIR and ultraviolet-visible (UV-Vis spectroscopy of the composite films showed that the interactions between the CS and oxygen-containing groups of GO resulted in good dispersion of the GO sheets in the CS network. The addition of GO decreased the expansion ratio of the composite films in physiological conditions and increased the resistance to degradation by lysozymes in vitro. As well, the tensile strength values of the GCS/GO films were significantly increased with the increasing load of GO. Moreover, the GCS/GO composite film also maintained the intrinsic fluorescence of GCS. The in vitro cell study results revealed that the composite films were suitable for the proliferation and adhesion of mouse preosteoblast (MC3T3-E1 cells. The GCS/GO biocomposite films might have a potential use in tissue engineering, bioimaging, and drug delivery.Keywords: chitosan film degradation, fluorescence, cytocompatibility

  1. Characterization of receptor proteins using affinity cross-linking with biotinylated ligands.

    Science.gov (United States)

    Shinya, Tomonori; Osada, Tomohiko; Desaki, Yoshitake; Hatamoto, Masahiro; Yamanaka, Yuko; Hirano, Hisashi; Takai, Ryota; Che, Fang-Sik; Kaku, Hanae; Shibuya, Naoto

    2010-02-01

    The plant genome encodes a wide range of receptor-like proteins but the function of most of these proteins is unknown. We propose the use of affinity cross-linking of biotinylated ligands for a ligand-based survey of the corresponding receptor molecules. Biotinylated ligands not only enable the analysis of receptor-ligand interactions without the use of radioactive compounds but also the isolation and identification of receptor molecules by a simple affinity trapping method. We successfully applied this method for the characterization, isolation and identification of the chitin elicitor binding protein (CEBiP). A biocytin hydrazide conjugate of N-acetylchitooctaose (GN8-Bio) was synthesized and used for the detection of CEBiP in the plasma or microsomal membrane preparations from rice and carrot cells. Binding characteristics of CEBiP analyzed by inhibition studies were in good agreement with the previous results obtained with the use of a radiolabeled ligand. The biotin-tagged CEBiP could be purified by avidin affinity chromatography and identified by LC-MALDI-MS/MS after tryptic digestion. We also used this method to detect OsFLS2, a rice receptor-like kinase for the perception of the peptide elicitor flg22, in membrane preparations from rice cells overexpressing OsFLS2. This work demonstrates the applicability of this method to the purification and identification of plant receptor proteins.

  2. The pH sensitive properties of carboxymethyl chitosan nanoparticles cross-linked with calcium ions.

    Science.gov (United States)

    Kalliola, Simo; Repo, Eveliina; Srivastava, Varsha; Heiskanen, Juha P; Sirviö, Juho Antti; Liimatainen, Henrikki; Sillanpää, Mika

    2017-05-01

    In environmental applications the applied materials are required to be non-toxic and biodegradable. Carboxymethyl chitosan nanoparticles cross-linked with Ca(2+) ions (CMC-Ca) fulfill these requirements, and they are also renewable. These nanoparticles were applied to oil-spill treatment in our previous study and here we focused on enhancing their properties. It was found that while the divalent Ca(2+) ions are crucial for the formation of the CMC-Ca, the attractive interaction between NH3(+) and COO(-) groups contributed significantly to the formation and stability of the CMC-Ca. The stability decreased as a function of pH due to the deprotonation of the amino groups. Therefore, the nanoparticles were found to be fundamentally pH sensitive in solution, if the pH deviated from the pH (7-9) that was used in the synthesis of the nanoparticles. The pH sensitive CMC-Ca synthesized in pH 7 and 8 were most stable in the studied conditions and could find applications in oil-spill treatment or controlled-release of substances.

  3. Dehydration of an ethanol/water azeotrope through alginate-DNA membranes cross-linked with metal ions by pervaporation.

    Science.gov (United States)

    Uragami, Tadashi; Banno, Masashi; Miyata, Takashi

    2015-12-10

    To obtain high dehydration membranes for an ethanol/water azeotrope, dried blend membranes prepared from mixtures of sodium alginate (Alg-Na) and sodium deoxyribonucleate (DNA-Na) were cross-linked by immersing in a methanol solution of CaCl2 or MaCl2. In the dehydration of an ethanol/water azeotropic mixture by pervaporation, the effects of immersion time in methanol solution of CaCl2 or MaCl2 on the permeation rate and water/ethanol selectivity through Alg-DNA/Ca(2+) and Alg-DNA/Mg(2+) cross-linked membranes were investigated. Alg-DNA/Mg(2+) cross-linked membrane immersed for 12h in methanol solution of MaCl2 exhibited the highest water/ethanol selectivity. This results from depressed swelling of the membranes by formation of a cross-linked structure. However, excess immersion in solution containing cross-linker led to an increase in the hydrophobicity of cross-linked membrane. Therefore, the water/ethanol selectivity of Alg-DNA/Mg(2+) cross-linked membranes with an excess immersion in cross-linking solution was lowered. The relationship between the structure of Alg-DNA/Ca(2+) and Alg-DNA/Mg(2+) cross-linked membranes and their permeation and separation characteristics during pervaporation of an ethanol/water azeotropic mixture is discussed in detail.

  4. Light-harvesting cross-linked polymers for efficient heterogeneous photocatalysis.

    Science.gov (United States)

    Wang, Cheng; Xie, Zhigang; deKrafft, Kathryn E; Lin, Wenbin

    2012-04-01

    Nonporous, phosphorescent cross-linked polymers (Ru-CP and Ir-CP) were synthesized via Pd-catalyzed Sonogashira cross-coupling reactions between tetra(p-ethynylphenyl)methane and dibrominated Ru(bpy)(3)(2+) or Ir(ppy)(2)(bpy)(+), respectively. The resultant particulate cross-linked polymer (CP) materials have very high catalyst loadings (76.3 wt % for Ru-CP and 71.6 wt % for Ir-CP), and are nonporous with negligibly small surface areas (2.9 m(2)/g for Ru-CP and 2.7 m(2)/g for Ir-CP). Despite their nonporous nature, the insoluble CP materials serve as highly active and recyclable heterogeneous photocatalysts for a range of organic transformations such as aza-Henry reaction, aerobic amine coupling, and dehalogenation of benzyl bromoacetate. An efficient light-harvesting mechanism, which involves collection of photons by exciting the (3)MLCT states of the phosphors and migration of the excited states to the particle surface, is proposed to account for the very high catalytic activities of these nonporous CPs. Steady-state and time-resolved emission data, as well as the reduced catalytic activity of Os(bpy)(3)(2+)-doped Ru-CPs supports efficient excited state migration for the CP frameworks. This work uncovers a new strategy in designing highly efficient photocatalysts based on light-harvesting cross-linked polymers.

  5. Reasons for revision of first-generation highly cross-linked polyethylenes.

    Science.gov (United States)

    Kurtz, Steven M; Medel, Francisco J; MacDonald, Daniel W; Parvizi, Javad; Kraay, Matthew J; Rimnac, Clare M

    2010-09-01

    Over a 10-year period, we prospectively evaluated the reasons for revision of contemporary and highly cross-linked polyethylene formulations in amulticenter retrieval program. Two hundred twelve consecutive retrievals were classified as conventional gamma inert sterilized (n = 37), annealed (Cross fire,[Stryker Orthopedics, Mahwah, NJ] n = 72), or remelted (Longevity [Zimmer ,Warsaw, Ind], XLPE[Smith and Nephew, Memphis, Tenn], Durasul [Zimmer,Warsaw, Ind] n = 103) liners. The most frequent reasons for revision were loosening (35%), instability(28%), and infection (21%) and were not related to polyethylene formulation (P = .17). Annealed and remelted liners had comparable linear penetration rates(0.03 and 0.04 mm/y, respectively, on average), and these were significantly lower than the rate in conventional retrievals (0.11 mm/y, P ≤ .0005). This retrieval study including first-generation highly cross linked liners demonstrated lower wear than conventional polyethylene. Although loosening remained as the most prevalent reason for revision, we could not demonstrate a relationship between wear and loosening.The long-term clinical performance of first-generation highly cross-linked liners remains promising based on the midterm outcomes of the components documented in this study [corrected].

  6. Azide-based cross-linking of polymers of intrinsic microporosity (PIMs) for condensable gas separation

    KAUST Repository

    Du, Naiying

    2011-03-11

    Cross-linked polymers of intrinsic microporosity (PIM)s for gas separation membranes, were prepared by a nitrene reaction from a representative PIM in the presence of two different diazide cross-linkers. The reaction temperature was optimized using TGA. The homogenous membranes were cast from THF solutions of different ratios of PIM to azides. The resulting cross-linked structures of the PIMs membranes were formed at 175 °C after 7.5 h and confirmed by TGA, XPS, FT-IR spectroscopy and gel content analysis. These resulting cross-linked polymeric membranes showed excellent gas separation performance and can be used for O 2/N 2 and CO 2/N 2 gas pairs, as well as for condensable gases, such as CO 2/CH 4, propylene/propane separation. Most importantly, and differently from typical gas separation membranes derived from glassy polymers, the crosslinked PIMs showed no obvious CO 2 plasticization up to 20 atm pressure of pure CO 2 and CO 2/CH 4 mixtures. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  7. Advertising and Marketing in Cross-Functional Instruction.

    Science.gov (United States)

    Treise, Debbie; Schumann, David

    1995-01-01

    States that advertising educators have been concerned with the lack of cooperation between advertising and marketing disciplines. Describes a cross-functional educational experiment in which two instructors (one from marketing and one from advertising) formed cross-functional teams for two projects. Concludes that the experiment was successful,…

  8. Fabrication of Redox-Responsive Degradable Capsule Particles by a Shell-Selective Photoinduced Cross-Linking Approach from Spherical Polymer Particles.

    Science.gov (United States)

    Kitayama, Yukiya; Takeuchi, Toshifumi

    2017-09-18

    In this study, a fabrication route towards functional capsule particles was successfully developed by means of a self-templating shell-selective cross-linking strategy that enables us to prepare shell-cross-linked hollow polymer particles directly from homogeneous spherical polymer particles. To prepare redox-responsive degradable capsule particles, a newly designed monomer bearing a photoinduced post-cross-linking group (cinnamoyl group) and a redox-environment-responsive cleavable group (disulfide group), N-cinnamoyl-N'-methyacryloylcystamine (MCC), was synthesized. Redox-responsive degradable capsule particles were successfully prepared from homogeneous spherical poly(MCC)-based particles by a self-templating shell-selective photoinduced cross-linking approach. Moreover, the cargo loading capability of the shell-cross-linked hollow particles was confirmed through a solvent exchange procedure using dyes, polymer precursors and anticancer reagents. Furthermore, redox-responsive degradability of the capsule polymer particles was also confirmed by adding a reducing agent for cleavage of the disulfide linkage. We hope that the efficient fabrication route of functional capsule particles directly from spherical polymer particles opens efficient routes for the fabrication of a wide range of capsule particles; in particular, this technique is robust, productive, and facile because neither additional sacrificial template particles nor toxic solvents are required. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  9. Molecular dynamics simulation of cross-linked urea-formaldehyde polymers for self-healing nanocomposites: prediction of mechanical properties and glass transition temperature.

    Science.gov (United States)

    Arab, Behrouz; Shokuhfar, Ali

    2013-11-01

    Urea-formaldehyde polymers, which are utilized in the adhesives industry, have recently been shown to be suitable materials for synthesizing micro/nanocapsules for use in self-healing (nano)composites. In this study, molecular dynamics was employed to simulate the process in which urea and formaldehyde are cross-linked via methylene and ether cross linkers, and to study the structure and mechanical/thermal properties of simulated poly(urea-formaldehyde)s (PUFs). The elastic stiffness constants of the simulated materials were calculated using the constant-strain (static) method. A temperature cycle was applied to the cross-linked PUFs, and the glass transition behavior of each material was investigated through the mean squared displacement (MSD) and temperature evolution of the energy and the specific volume of the polymer. The simulation results confirmed that there was considerable improvement in the properties of the poly(UF) materials upon cross linking. The radial distribution function was also used to study the local structures of the polymers, and this revealed that increasing the temperature and cross linking density results in a significant drop in hydrogen bonding intensity in the cross-linked PUF systems.

  10. Wheat gluten films cross-linked with 1-ethyl-3-(3-demethylaminopropyl) carbodiimide and N-hydroxysuccinimide

    NARCIS (Netherlands)

    Tropini, V.; Lens, J.P.; Mulder, W.J.; Silvestre, F.

    2004-01-01

    Wheat gluten films were cast from aqueous dispersions containing 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) and N-hydroxysuccinimide (NHS) as cross-linking reagents and glycerol as a plasticizer. Cross-linking was carried out to improve film properties such as water sensitivity and tensile

  11. Simulation and theory of self-assembly and network formation in reversibly cross-linked equilibrium polymers

    Science.gov (United States)

    Kindt, James T.

    2005-10-01

    A simulation model of hard spheres capable of reversible assembly into chains, which then may reversibly cross-link into networks, has been studied through grand canonical Monte Carlo simulation. Effects of varying intra- and interchain bond strengths, chain flexibilities, and restrictions on cross-linking angle were investigated. Observations including chain-length distributions and phase separation could be captured in most cases using a simple model theory. The coupling of chain growth to cross-linking was shown to be highly sensitive to the treatment of cross-linking by chain ends. In some systems, ladderlike domains of several cross-links joining two chains were common, resulting from cooperativity in the cross-linking. Extended to account for this phenomenon, the model theory predicts that such cooperativity will suppress phase separation in weakly polymerizing chains and at high cross-link concentration. In the present model, cross-linking stabilizes the isotropic phase with respect to the nematic phase, causing a shift in the isotropic-nematic transition to higher monomer concentration than in simple equilibrium polymers.

  12. Comparative studies of photochemical cross-linking methods for stabilizing the bulk hetero-junction morphology in polymer solar cells

    DEFF Research Database (Denmark)

    Carlé, Jon Eggert; Andreasen, Birgitta; Tromholt, Thomas;

    2012-01-01

    -light illumination to give solvent resistant films and reduced phase separation and growth of PCBM crystallites in polymer:PCBM films. The stability of solar cells based on the cross-linked polymers was tested under various conditions. This study showed that cross-linking can improve morphological stability...

  13. Effect of PDMS cross-linking degree on the permeation performance of PAN/PDMS composite nanofiltration membranes

    NARCIS (Netherlands)

    Stafie, N.; Stamatialis, Dimitrios; Wessling, Matthias

    2006-01-01

    This work focuses on the effect of poly(dimethyl siloxane) (PDMS) cross-linking on the permeation performance of the poly(acrylonitrile) (PAN)/PDMS nanofiltration (NF) composite membrane. PDMS membrane of various cross-linking degrees could be obtained by changing the ratio of a vinyl-terminated

  14. Insights into the swelling process and drug release mechanisms from cross-linked pectin/high amylose starch matrices

    Directory of Open Access Journals (Sweden)

    Fernanda M. Carbinatto

    2014-02-01

    Full Text Available Cross-linked pectin/high amylose mixtures were evaluated as a new excipient for matrix tablets formulations, since the mixing of polymers and cross-linking reaction represent rational tools to reach materials with modulated and specific properties that meet specific therapeutic needs. Objective: In this work the influence of polymer ratio and cross-linking process on the swelling and the mechanism driving the drug release from swellable matrix tablets prepared with this excipient was investigated. Methods: Cross-linked samples were characterized by their micromeritic properties (size and shape, density, angle of repose and flow rate and liquid uptake ability. Matrix tablets were evaluated according their physical properties and the drug release rates and mechanisms were also investigated. Results: Cross-linked samples demonstrated size homogeneity and irregular shape, with liquid uptake ability insensible to pH. Cross-linking process of samples allowed the control of drug release rates and the drug release mechanism was influenced by both polymer ratio and cross-linking process. The drug release of samples with minor proportion of pectin was driven by an anomalous transport and the increase of the pectin proportion contributed to the erosion of the matrix. Conclusion: The cross-linked mixtures of high amylose and pectin showed a suitable excipient for slowing the drug release rates.

  15. Corneal cross-linking in a 10-year-old child with stage III keratoconus.

    Science.gov (United States)

    Abbondanza, Marco; Felice, Valentina De; Abbondanza, Gabriele

    2016-07-01

    Keratoconus is a corneal dystrophy characterized by progressive thinning, conical shape of the cornea and irregular astigmatism. It is particularly insidious when it occurs in very young patients. We report the case of a 10-year-old child with an aggressive stage III keratoconus, who was suggested to undergo a Penetrating Keratoplasty. We performed Corneal Collagen Cross-linking with epithelium removal instead, which was successful in arresting the rapid progression of keratoconus. Eighteen months later, Kmax had decreased by 1.3 D, astigmatism by 0.8 D, thinnest pachimetry had improved by 69 μm and CDVA was 20/32. This case confirms that Corneal Collagen Cross-linking is a safe and effective procedure for the treatment of keratoconus even in its aggressive forms. We encourage ophthalmic surgeons to favor conservative treatments when dealing with very young patients. © NEPjOPH.

  16. Development and Evaluation of Dual Cross-Linked Pulsatile Beads for Chronotherapy of Rheumatoid Arthritis

    Directory of Open Access Journals (Sweden)

    Abanesh kumar Bansal

    2013-01-01

    Full Text Available In the present investigation, pulsatile release beads were prepared by ionic gelation technique. Lornoxicam dual cross-linked beads were prepared by dropping dispersed phase of lornoxicam, pectin, and sodium alginate into the dispersion phase of different concentrations of calcium chloride solution followed by aluminium chloride solution. The formulated beads were further coated by Eudragit L & S 100 in the ratio 1 : 2 w/w in order to achieve desired lag time. In vitro release study showed lag time of 5–8 h before release of lornoxicam from the formulated beads. Thus, formulated dual cross-linked beads when administered at bed time may release lornoxicam when needed most for chronotherapeutics of early morning rheumatoid arthritis attacks in chronic patients.

  17. Anisotropic nanoparticles with controllable morphologies from non-cross-linked seeded emulsion polymerization.

    Science.gov (United States)

    Niu, Qun; Pan, Mingwang; Yuan, Jinfeng; Liu, Xiao; Wang, Xiaomei; Yu, Haifeng

    2013-09-01

    A simple and elegant approach to fabricate anisotropic P(VC-co-AAEM)/PS nanoparticles with controllable morphologies via emulsifier-free seeded emulsion polymerization is presented. Non-cross-linked P(VC-co-AAEM) seeds with hydrophilic surface are first synthesized through copolymerization of vinyl chloride (VC) and acetoacetoxyethyl methacrylate (AAEM), which are used to prepare P(VC-co-AAEM)/PS NPs with multiple bulges by SEP of styrene. Electron microscopy observation indicates that the content of AAEM in seeds is crucial to control the phase separation and morphology of the composite NPs. Moreover, the thermodynamic immiscibility between PVC and PS is the driving force for the formation of PS bulges onto the P(VC-co-AAEM) seeds. The resultant anisotropic NPs with non-cross-linked feature may promisingly serve as compatibilizers for further polymer processing. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  18. Preparation of bioimprinting cross-linked enzyme aggregates of phenylalanine ammonia lyase and it's partial properties

    Directory of Open Access Journals (Sweden)

    Jiandong CUI

    2015-12-01

    Full Text Available Phenylalanine ammonia lyase (PAL is a key enzyme for production of L-phenylalanine. Currently, PAL is mainly obtained from Rhodotorula PAL However, Rhodotorula PAL exhibits poor stability, which limits its industrial application. In this study, bioimprinting cross-linked enzyme aggregates of PAL (PAL-iCLEAs is developed by combining cross-linked enzyme aggregates technology and imprinted enzyme method. The most optimal imprinting molecule substrate is screened. Moreover, some characteristics of the PAL-iCLEAs are examined. The results show that the most suitable substrates for preparing PAL-iCLEAs is tran-cinnamic acid. The optimal temperature and pH was 50 ℃ and 10.5, respectively. In addition, PAL-iCLEAs shows good reusability, the recovery of PAL activity still remained 32% after reusing 9 times.

  19. Acute corneal hydrops during pregnancy with spontaneous resolution after corneal cross-linking for keratoconus: a case report.

    Science.gov (United States)

    Stock, Ricardo Alexandre; Thumé, Thaís; Bonamigo, Elcio Luiz

    2017-02-25

    Keratoconus may progress to acute corneal hydrops even after cross-linking. In some cases, keratoconus progresses during pregnancy. In this report, we present a case of a patient with increased anterior stromal resistance after cross-linking that would favor nonprogression of keratoconus during pregnancy. We report that cross-linking is likely to have had a protective effect in a white pregnant patient with acute corneal hydrops who showed rapid improvement, as documented by corneal topography. Improvement occurred within 8 days, whereas up to 250 days are reported in the literature. No keratoconus progression occurred in the 20-month follow-up period. Cross-linking failed to prevent the occurrence of acute corneal hydrops after rupture of Descemet's membrane but most likely helped to accelerate the resolution of the condition. Corneal hardening resulting from cross-linking may have also contributed to stabilizing keratoconus during pregnancy.

  20. The process of EDC-NHS cross-linking of reconstituted collagen fibres increases collagen fibrillar order and alignment

    Directory of Open Access Journals (Sweden)

    D. V. Shepherd

    2015-01-01

    Full Text Available We describe the production of collagen fibre bundles through a multi-strand, semi-continuous extrusion process. Cross-linking using an EDC (1-ethyl-3-(3-dimethylaminopropylcarbodiimide, NHS (N-hydroxysuccinimide combination was considered. Atomic Force Microscopy and Raman spectroscopy focused on how cross-linking affected the collagen fibrillar structure. In the cross-linked fibres, a clear fibrillar structure comparable to native collagen was observed which was not observed in the non-cross-linked fibre. The amide III doublet in the Raman spectra provided additional evidence of alignment in the cross-linked fibres. Raman spectroscopy also indicated no residual polyethylene glycol (from the fibre forming buffer or water in any of the fibres.

  1. The process of EDC-NHS cross-linking of reconstituted collagen fibres increases collagen fibrillar order and alignment

    Science.gov (United States)

    Shepherd, D. V.; Shepherd, J. H.; Ghose, S.; Kew, S. J.; Cameron, R. E.; Best, S. M.

    2015-01-01

    We describe the production of collagen fibre bundles through a multi-strand, semi-continuous extrusion process. Cross-linking using an EDC (1-ethyl-3-(3-dimethylaminopropyl)carbodiimide), NHS (N-hydroxysuccinimide) combination was considered. Atomic Force Microscopy and Raman spectroscopy focused on how cross-linking affected the collagen fibrillar structure. In the cross-linked fibres, a clear fibrillar structure comparable to native collagen was observed which was not observed in the non-cross-linked fibre. The amide III doublet in the Raman spectra provided additional evidence of alignment in the cross-linked fibres. Raman spectroscopy also indicated no residual polyethylene glycol (from the fibre forming buffer) or water in any of the fibres.

  2. Synthesis and Characterisation of Novel Cross Linked Biopolyesters from Olive Oil as Eco-friendly Biodegradable Materials

    Directory of Open Access Journals (Sweden)

    J. Shakina

    2012-01-01

    Full Text Available Novel cross linked biopolyesters were synthesised from naturally available olive oil, oligomeric polytriglyceride fumarate (o-PTF was prepared by glycerolysis of the olive oil followed by condensation with maleic anhydride. The (o-PTF was characterised by spectral (FTIR, UV, NMR and physicochemical properties (specific gravity, viscosity, saponification value, iodine value. The molecular weight of o-PTF was estimated using gel permeation chromatography (GPC. The cross linked biopolyesters were prepared by treating o-PTF of olive with N-vinyl-2-pyrrolidone and vinyl acetate. The cross linked biopolyesters were evaluated for spectral properties (FT IR, cross linked density, thermal properties, mechanical properties and biodegradation. The potential antifungal and anti bacterial activities of the newly prepared biopolyesters were evaluated. The environment degradation was assessed by soil burial test. The outcome of the studies has revealed that the newly prepared cross linked biopolyesters are potential biodegradable material for various consumer application like package materials and agricultural applications.

  3. Progress of research on corneal collagen cross-linking for corneal melting

    Directory of Open Access Journals (Sweden)

    Ke-Ren Xiao

    2016-06-01

    Full Text Available Corneal collagen cross-linking(CXLcould increase the mechanical strength, biological stability and halt ectasia progression due to covalent bond formed by photochemical reaction between ultraviolet-A and emulsion of riboflavin between collagen fibers in corneal stroma. Corneal melting is an autoimmune related noninfectious corneal ulcer. The mechanism of corneal melting, major treatment, the basic fundamental of ultraviolet-A riboflavin induced CXL and the clinical researches status and experiment in CXL were summarized in the study.

  4. Histological response to injected gluteraldehyde cross-linked bovine collagen based implant in a rat model

    Directory of Open Access Journals (Sweden)

    Cağlar Melda

    2006-02-01

    Full Text Available Abstract Background The aim of present study is to investigate the short and long term histopathological alterations caused by submucosal injection of gluteraldehyde cross-linked bovine collagen based on an experimental rat model. Methods Sixty Sprague-Dawley rats were assigned into two groups as group I and II each containing 30 rats. 0.1 ml of saline solution and 0.1 ml of gluteraldehyde cross-linked bovine collagen were injected into the submucosa of bladder of first (control and second groups, respectively. Both group I and II were further subdivided into 3 other groups as Group IA, IB, IC and Group IIA, IIB, IIC according to the sacrification period. Group IA and IIA, IB and IIB, IC and IIC rats (10 rats for each group were sacrificed 3, 6, and 12 months after surgical procedure, respectively. Two slides prepared from injection site of the bladder were evaluated completely for each rat by being unaware of the groups and at random by two independent senior pathologists to determine the fibroblast invasion, collagen formation, capillary ingrowth and inflammatory reaction. Additionally, randomized brain sections from each rat were also examined to detect migration of the injection material. The measurements were made using an ocular micrometer at ×10 magnification. The results were assessed using t-tests for paired and independent samples, with p Results Migration to the brain was not detected in any group. Significant histopathological changes in the gluteraldehyde cross-linked bovine collagen injected groups were fibroblast invasion in 93.3%, collagen formation in 73.3%, capillary ingrowth in 46.6%, inflamatory reaction in 20%. Conclusion We emphasize that the usage of gluteraldehyde cross-linked bovine collagen in children appears to be safe for endoscopic treatment of vesicoureteral reflux.

  5. Synthesis and Properties of Lactic Acid-based Cross-linked Poly(ester-amide)

    Institute of Scientific and Technical Information of China (English)

    Yue Ying HE; Cong Ming XIAO

    2006-01-01

    A novel lactic acid-based cross-linked poly(ester-amide) (LCPEA) was synthesized. The gel fraction of the LCPEA could be modulated by the reaction conditions and it affected the mechanical and thermal properties of the LCPEA. The tensile strength, elastic modulus and bend strength of the LCPEA of 65% gel fraction were 4.65, 136.55 and 39.63 MPa, respectively. The thermal decomposition temperature (50 wt%) of the LCPEA was around 410 ℃.

  6. Long-term results of cornea collagen cross-linking with riboflavin for keratoconus

    Directory of Open Access Journals (Sweden)

    Vinay Agrawal

    2013-01-01

    Full Text Available Corneal collagen cross-linking with riboflavin and UVA light (CXL is the only method designed to arrest the progression of keratoconus. Visual improvement generally starts 3 months after treatment. Reduction is coma seen on aberrometry in early postoperative phase is also responsible for the improvement in visual acuity. In the light of currently available data we can thus say that CXL is a safe procedure that is successful in arresting keratoconus.

  7. Comparative study between novel self cross-linking and conventional fluorinated acrylic latex

    Institute of Scientific and Technical Information of China (English)

    Li Jun Chen

    2011-01-01

    Novel self cross-linking fluorinated acrylic latex (SCLFAL) has been successfully prepared via starved seeded semi-batch emulsion polymerization. The resultant SCLFAL is characterized by Fourier transform infrared (FTTR) spectrometry. Contact angle (CA) and glass transition temperature (Tg) of the film are investigated. Results show that CA and Tg of the film can be improved when the moderate amount of HPMA is introduced into the mixed monomers.

  8. Porous chitosan scaffold cross-linked by chemical and natural procedure applied to investigate cell regeneration

    Energy Technology Data Exchange (ETDEWEB)

    Yao, Chih-Kai [Department of Materials Science and Engineering, National Cheng Kung University, No. 1, University Road, Tainan 70101, Taiwan (China); Liao, Jiunn-Der, E-mail: jdliao@mail.ncku.edu.tw [Department of Materials Science and Engineering, National Cheng Kung University, No. 1, University Road, Tainan 70101, Taiwan (China); Center of Micro/Nano Science and Technology, National Cheng Kung University, No. 1, University Road, Tainan 70101, Taiwan (China); Chung, Chia-Wei; Sung, Wei-I. [Department of Materials Science and Engineering, National Cheng Kung University, No. 1, University Road, Tainan 70101, Taiwan (China); Chang, Nai-Jen [Institute of Biomedical Engineering, National Cheng Kung University, No. 1, University Road, Tainan 70101, Taiwan (China)

    2012-12-01

    Highlights: Black-Right-Pointing-Pointer Polymeric scaffolds, made from chitosan-based films fixed by chemical (citrate) or natural method (genipin), were developed. Black-Right-Pointing-Pointer Nano-indentation with a constant harmonic frequency was applied on porous scaffolds to explore their surface mechanics. Black-Right-Pointing-Pointer The relationship between surface mechanical property and cell-surface interactions of scaffold materials was demonstrated. Black-Right-Pointing-Pointer Porous scaffolds cross-linked by genipin showed adequate cell affinity, non-toxicity, and suitable mechanical properties. - Abstract: Porous chitosan scaffold is used for tissue engineering and drug delivery, but is limited as a scaffold material due to its mechanical weakness, which restrains cell adhesion on the surface. In this study, a chemical reagent (citrate) and a natural reagent (genipin) are used as cross-linkers for the formation of chitosan-based films. Nanoindentation technique with a continuous stiffness measurement system is particularly applied on the porous scaffold surface to examine the characteristic modulus and nanohardness of a porous scaffold surface. The characteristic modulus of a genipin-cross-linked chitosan surface is Almost-Equal-To 2.325 GPa, which is significantly higher than that of an uncross-linked one ( Almost-Equal-To 1.292 GPa). The cell-scaffold surface interaction is assessed. The cell morphology and results of an MTS assay of 3T3-fibroblast cells of a genipin-cross-linked chitosan surface indicate that the enhancement of mechanical properties induced cell adhesion and proliferation on the modified porous scaffold surface. The pore size and mechanical properties of porous chitosan film can be tuned for specific applications such as tissue regeneration.

  9. Generation of Guanine – Thymidine Cross-links in DNA by Peroxynitrite/Carbon Dioxide

    OpenAIRE

    Yun, Byeong Hwa; Geacintov, Nicholas E.; Shafirovich, Vladimir

    2011-01-01

    Nitrosoperoxycarbonate derived from the combination of carbon dioxide and peroxynitrite, is an important chemical mediator of inflammation. In aqueous solutions, it rapidly decomposes to the reactive species CO3•− and •NO2 radicals that are known to initiate the selective oxidation and nitration of guanine in DNA. We have previously demonstrated that the reactions of carbonate radical anions with guanine in 2′-deoxyoligoribonucleotides generate a previously unknown intrastrand cross-linked gu...

  10. Polymer Composition and Substrate Influences on the Adhesive Bonding of a Biomimetic, Cross-Linking Polymer

    OpenAIRE

    Matos-Pérez, Cristina R.; White, James D.; Wilker, Jonathan J.

    2012-01-01

    Hierarchical biological materials such as bone, sea shells, and marine bioadhesives are providing inspiration for the assembly of synthetic molecules into complex structures. The adhesive system of marine mussels has been the focus of much attention in recent years. Several catechol-containing polymers are being developed to mimic the cross-linking of proteins containing 3,4-dihydroxyphenylalanine (DOPA) used by shellfish for sticking to rocks. Many of these biomimetic polymer systems have be...

  11. Sorption of adamantane phenylamide derivatives on hyper-cross-linked polystyrene from water-acetonitrile eluents

    Science.gov (United States)

    Shafigulin, R. V.; Konstantinov, A. V.; Bulanova, A. V.; Il'in, M. M.; Davankov, V. A.

    2016-11-01

    Study of the main physicochemical features of the sorption of phenylamide adamantane derivatives on hyper-cross-linked polystyrene from water-acetonitrile solutions shows that both hydrophobic and electronic interactions make a large contribution to retention, especially for a chlorine-containing derivative in which there are π- p and π- d interactions between the outer-shell electrons of the chlorine atom in addition to π- π interactions between aromatic fragments of the sorbate and sorbent.

  12. Fabrication and properties of irradiation-cross-linked poly(vinyl alcohol)/clay aerogel composites.

    Science.gov (United States)

    Chen, Hong-Bing; Liu, Bo; Huang, Wei; Wang, Jun-Sheng; Zeng, Guang; Wu, Wen-Hao; Schiraldi, David A

    2014-09-24

    Poly(vinyl alcohol) (PVOH)/clay aerogel composites were fabricated by an environmentally friendly freeze-drying of the aqueous precursor suspensions, followed by cross-linking induced by gamma irradiation without chemical additives. The influences of cross-linking conditions, i.e., absorbed dose and polymer loading as well as density on the aerogel structure and properties, were investigated. The absorbed dose of 30 kGy was found to be the optimum dose for fabricating strong PVOH composites; the compressive modulus of an aerogel prepared from an aqueous suspension containing 2 wt % PVOH/8 wt % clay increased 10-fold, and that containing 1 wt % PVOH/9 wt % clay increased 12 times upon cross-linking with a dose of 30 kGy. Increasing the solids concentration led to an increase in the mechanical strength, in accordance with the changes in microstructure from layered structure to network structure. The increase of absorbed dose also led to decreased porous size of the network structure. Cross-linking and the increase of the PVOH lead to decreased thermal stability. The strengthened PVOH/clay aerogels possess very low flammability, as measured by cone calorimetry, with heat, smoke, and volatile products release value decreasing as increasing clay content. The mechanism of flame retardation in these materials was investigated with weight loss, FTIR, WAXD, and SEM of the burned residues. The proposed mechanism is that with decreasing fuel content (increasing clay content), increased heat and mass transport barriers are developed; simultaneously low levels of thermal conductivity are maintained during the burning.

  13. Aspergillus Galactomannan Enzyme-Linked Immunosorbent Assay Cross-Reactivity Caused by Invasive Geotrichum capitatum

    Science.gov (United States)

    Giacchino, Mareva; Chiapello, Nadia; Bezzio, Stefania; Fagioli, Franca; Saracco, Paola; Alfarano, Alda; Martini, Vincenza; Cimino, Giuseppe; Martino, Pietro; Girmenia, Corrado

    2006-01-01

    We report three cases of invasive Geotrichum capitatum infection in patients with acute leukemia for which an enzyme-linked immunosorbent assay (ELISA) for Aspergillus galactomannan was positive, with no evidence of aspergillosis. Supernatants obtained from suspensions of 17 G. capitatum strains gave positive reactions with the Aspergillus galactomannan ELISA. These clinical and laboratory data seem to suggest that G. capitatum produces a soluble antigen that is cross-reactive with Aspergillus galactomannan. PMID:16954294

  14. Effects of cross-linking molecular weights in a hyaluronic acid-poly(ethylene oxide) hydrogel network on its properties

    Energy Technology Data Exchange (ETDEWEB)

    Noh, Insup [Department of Chemical Engineering, Seoul National University of Technology, 172 Gongnung-dong, Nowon-gu, Seoul 139-743 (Korea, Republic of); Kim, Gun-Woo [Department of Chemical Engineering, Seoul National University of Technology, 172 Gongnung-dong, Nowon-gu, Seoul 139-743 (Korea, Republic of); Choi, Yoon-Jeong [Department of Chemical Engineering, Seoul National University of Technology, 172 Gongnung-dong, Nowon-gu, Seoul 139-743 (Korea, Republic of); Kim, Mi-Sook [Department of Chemical Engineering, Seoul National University of Technology, 172 Gongnung-dong, Nowon-gu, Seoul 139-743 (Korea, Republic of); Park, Yongdoo [Korea Artificial Organ Center, Korea University, Seoul 136-705 (Korea, Republic of); Lee, Kyu-Back [Korea Artificial Organ Center, Korea University, Seoul 136-705 (Korea, Republic of); Kim, In-Sook [Dental Research Institute, Seoul National University, Seoul 110-749 (Korea, Republic of); Hwang, Soon-Jung [Dental Research Institute, Seoul National University, Seoul 110-749 (Korea, Republic of); Tae, Giyoong [Department of Materials Science and Engineering, Gwangju Institute of Science and Technology, Gwangju 500-712 (Korea, Republic of)

    2006-09-15

    We examined the effects of cross-linking molecular weights on the properties of a hyaluronic acid (HA)-poly(ethylene oxide) (PEO) hydrogel. Swelling behaviors, mechanical strength and rheological behaviors of the HA-PEO hydrogel were evaluated by employing different cross-linking molecular weights (100 kDa and 1.63 mDa) of the HAs in the hydrogel networks. The low molecular weight of HA was obtained in advance by treating high molecular weight HA with a hydrogen chloride solution. Methacrylation of HA was obtained by grafting aminopropylmethacrylate to its caroboxylic acid functional groups. While reduction of the HA molecular weights was confirmed by gel permeation chromatography, the degree of methacrylate grafting to the HA was measured by {sup 1}H-nuclear magnetic resonance. Synthesis of the HA-PEO hydrogel was successfully achieved via the Michael-type addition reaction between the methacrylate arm groups in the HA and the six thiol groups in PEO. The hydrogel formation was not dependent upon the HA molecular weights and its gelation behaviors were markedly different. Compared to the properties of the high molecular weight HA-based PEO one, the low molecular weight HA-based hydrogel induced quicker hydrogelation, as observed from the behaviors of the elastic and viscous modulus. Furthermore, the low molecular weight HA-based hydrogel demonstrated stronger mechanical properties as measured with a texture analyzer, lower water absorption as measured with a microbalance and smaller pore sizes on its surface and cross section as observed with scanning electron microscopy. The information about the effects of the cross-linking molecular weights of the gel network on the properties of the HA-based PEO hydrogel may lead to better design of hydrogels, especially in tissue engineering applications.

  15. Understanding of the Viscoelastic Response of the Human Corneal Stroma Induced by Riboflavin/UV-A Cross-Linking at the Nano Level

    Science.gov (United States)

    Labate, Cristina; De Santo, Maria Penelope; Lombardo, Giuseppe; Lombardo, Marco

    2015-01-01

    Purpose To investigate the viscoelastic changes of the human cornea induced by riboflavin/UV-A cross-linking using Atomic Force Microscopy (AFM) at the nano level. Methods Seven eye bank donor corneas were investigated, after gently removing the epithelium, using a commercial AFM in the force spectroscopy mode. Silicon cantilevers with tip radius of 10 nm and spring elastic constants between 26- and 86-N/m were used to probe the viscoelastic properties of the anterior stroma up to 3 µm indentation depth. Five specimens were tested before and after riboflavin/UV-A cross-linking; the other two specimens were chemically cross-linked using glutaraldehyde 2.5% solution and used as controls. The Young’s modulus (E) and the hysteresis (H) of the corneal stroma were quantified as a function of the application load and scan rate. Results The Young’s modulus increased by a mean of 1.1-1.5 times after riboflavin/UV-A cross-linking (P<0.05). A higher increase of E, by a mean of 1.5-2.6 times, was found in chemically cross-linked specimens using glutaraldehyde 2.5% (P<0.05). The hysteresis decreased, by a mean of 0.9-1.5 times, in all specimens after riboflavin/UV-A cross-linking (P<0.05). A substantial decrease of H, ranging between 2.6 and 3.5 times with respect to baseline values, was observed in glutaraldehyde-treated corneas (P<0.05). Conclusions The present study provides the first evidence that riboflavin/UV-A cross-linking induces changes of the viscoelastic properties of the cornea at the scale of stromal molecular interactions. PMID:25830534

  16. Corneal Cross-Linking: An Example of Photoinduced Polymerization as a Treatment Modality in Keratoconus.

    Science.gov (United States)

    Kubrak-Kisza, Magdalena; Kisza, Krystian Jerzy; Misiuk-Hojło, Marta

    2016-01-01

    The cornea is one of the principal refractive elements in the human eye and plays a crucial role in the process of vision. Keratoconus is the most common corneal dystrophy, found mostly among young adults. It is characterized by a reduced number of collagen cross-links in the corneal stroma, resulting in reduced biomechanical stability and an abnormal shape of the cornea. These changes lead to progressive myopia, corneal thinning, central scarring and irregular astigmatism, causing severely impaired vision. Hard contact lenses, photorefractive keratectomy or intracorneal rings are the most common treatment options for refractive error caused by keratoconus. However, these techniques do not treat the underlying cause of the corneal ectasia and therefore are not able to stop the progression of the disease. Riboflavin photoinduced polymerization of corneal collagen, also known as corneal cross-linking (CXL), has been introduced as the first therapy which, by stabilizing the structure of the cornea, prevents the progression of keratoconus. It stiffens the cornea using the photo-sensitizer riboflavin in combination with ultraviolet irradiation. This is a current review of the CXL procedure as a therapy for keratoconus, which relies on photoinduced polymerization of human tissue. We have focused on its biomechanical and physiological influences on the human cornea and have reviewed the previous and current biochemical theories behind cross-linking reactions in the cornea.

  17. An Update on the Safety and Efficacy of Corneal Collagen Cross-Linking in Pediatric Keratoconus

    Science.gov (United States)

    El Rami, Hala; Chelala, Elias; Fakhoury, Henry; Cherfan, Carole; Cherfan, George; Jarade, Elias

    2015-01-01

    Keratoconus is a degenerative disease that affects adolescents and young adults and presents with variable thinning and conical deformation of the corneal apex. The resultant irregular astigmatism can progress to levels that can significantly affect everyday activities and overall quality of life. Therefore, stopping the progression of the disease is an essential part in managing patients with keratoconus. Corneal collagen cross-linking is a minimally invasive procedure that stiffens the anterior corneal stroma by creating strong covalent bonds between collagen fibrils. Over the past decade, many studies have proved its safety and efficacy in halting keratoconus progression in adults. This review of the literature highlights the growing trend towards using this treatment in pediatric keratoconic patients. In children, keratoconus tends to be more severe and fast progression is often encountered requiring closer follow-up intervals. Standard cross-linking shows comparable results in children with a good safety-efficacy profile during follow-up periods of up to three years. Further research is needed to standardize and evaluate transepithelial and accelerated cross-linking protocols as these could be of tremendous help in a population where cooperation and compliance are major issues. PMID:26491663

  18. Analysis of the effective dose of ultraviolet light in corneal cross-linking.

    Science.gov (United States)

    Zhang, Yong; Wang, Kuan-Chen; Chang, Chao-Kai; Lin, Jui-Teng

    2016-01-01

    To analyze the efficacy of ultraviolet (UV) light initiating corneal cross-linking (CXL). The time-dependent absorption of UV light due to the depletion of the initiator (riboflavin) was calculated. The effective dose of CXL with corneal surface covered by a thin layer of riboflavin was derived analytically. The cross linking time was calculated by the depletion level of the riboflavin concentration. A comprehensive method was used to derive analytic formulas. The effective dose of CXL was reduced by a factor (R) which was proportional to the thickness (d) and concentrations (C0) of the riboflavin surface layer. Our calculations showed that the conventional dose of 5.4 J/cm(2) had a reduced effective dose of 4.3 and 3.45 J/cm(2), for d was 100 and 200 µm, respectively, and C0=0.1%. The surface cross linking time was calculated to be T*=10.75s, for a depletion level of 0.135 and UV initial intensity of 30 mW/cm(2). The volume T* was exponentially increasing and proportional to exp (bdC0), with b being the steady state absorption coefficient. The effective dose of CXL is reduced by a factor proportional to the thickness and concentrations of the riboflavin surface layer. The wasted dose should be avoided by washing out the extra riboflavin surface layer prior to the UV light exposure.

  19. Preparation and Characterization of a pH-Responsive Core Cross-linked Polymer Micelle

    Energy Technology Data Exchange (ETDEWEB)

    Kousaka, Shouta; Sugahara, Makoto; Endo, Tatsuya; Yusa, Shin-ichi, E-mail: yusa@eng.u-hyogo.ac.jp [Department of Materials Science and Chemistry, Graduate School of Engineering, University of Hyogo, 2167 Shosha, Himeji, Hyogo 671-2280 (Japan)

    2011-01-01

    Poly(ethylene glycol)-b-poly(2-(diethylamino) ethyl methacrylate-co-2-cinnamoyl-oxyethyl acrylate) (PEG-b-P(DEA/CEA)) was prepared by reversible addition-fragmentation chain transfer (RAFT) controlled radical polymerization. pH-responsive association behaviour of PEG-b-P(DEA/CEA) in 0.1 M NaCl was characterized by dynamic light scattering (DLS). As solution pH is increased from an acidic pH, the hydrodynamic radius (R{sub h}) increases, indicative of the polymer micelle formation. The formation of a micelle was also supported by static light scattering (SLS) data. The cinnamoyl groups in the core of the polymer micelle undergo photodimerization, yielding cross-links between polymer chains. The core of the polymer micelle was fixed, which was confirmed by DLS, SLS, and small angle X-ray scattering (SAXS) techniques. When pH is decreased to 3, R{sub h} of the core cross-linked (CCL) polymer micelle slightly increases due to the protonation of the DEA unit in the cross-linked core. The reversible pH-induced swelling and shrinking behaviour can be observed.

  20. EGDMA-cross-linked polystyrene resin: An efficient support for gel phase peptide synthesis

    Indian Academy of Sciences (India)

    P K Ajikumar; K S Devaky

    2000-08-01

    This article illustrates the application of a 2% ethyleneglycol dimethacrylate-cross-linked polystyrene support (EGDMA-PS) in manual solid phase peptide synthesis. This copolymer has been characterised and optimised for peptide synthesis by performing the synthesis of a few model peptides and two biologically important peptides. EGDMA-cross-linked polystyrene support was prepared by the suspension polymerisation of the monomers EGDMA and styrene. EGDMA-PS resin undergoes facile swelling in a variety of solvents, both polar and nonpolar, used in peptide synthesis. The polymer was functionalised by Friedel-Crafts chloromethylation reaction. Peptides were assembled on a 2% cross-linked chloromethyl polymer support of capacity 1.63 mmol Cl/g. The biological peptides synthesised are an 11-residue peptide ATP binding site of the CDC2 kinase and a difficult sequence-a nineresidue peptide 34-42 corresponding to a portion of the hydrophobic terminus of the-amyloid protein 1-42. After synthesis, the peptides were cleaved from the support by treating with neat TFA. Purity of the peptides obtained in good yield was checked by TLC and HPLC methods and found to be fairly high.

  1. Core Cross-linked Star Polymers for Temperature/pH Controlled Delivery of 5-Fluorouracil

    Directory of Open Access Journals (Sweden)

    Elizabeth Sánchez-Bustos

    2016-01-01

    Full Text Available RAFT polymerization with cross-linking was used to prepare core cross-linked star polymers bearing temperature sensitive arms. The arms consisted of a diblock copolymer containing N-isopropylacrylamide (NIPAAm and 4-methacryloyloxy benzoic acid (4MBA in the temperature sensitive block and poly(hexyl acrylate forming the second hydrophobic block, while ethyleneglycol dimethacrylate was used to form the core. The acid comonomer provides pH sensitivity to the arms and also increases the transition temperature of polyNIPAAm to values in the range of 40 to 46°C. Light scattering and atomic force microscopy studies suggest that loose core star polymers were obtained. The star polymers were loaded with 5-fluorouracil (5-FU, an anticancer agent, in values of up to 30 w/w%. In vitro release experiments were performed at different temperatures and pH values, as well as with heating and cooling temperature cycles. Faster drug release was obtained at 42°C or pH 6, compared to normal physiological conditions (37°C, pH 7.4. The drug carriers prepared acted as nanopumps changing the release kinetics of 5-FU when temperatures cycles were applied, in contrast with release rates at a constant temperature. The prepared core cross-linked star polymers represent advanced drug delivery vehicles optimized for 5-FU with potential application in cancer treatment.

  2. Molecular dynamics simulations of highly cross-linked polymer networks: prediction of thermal and mechanical properties

    Science.gov (United States)

    Shenogina, Natalia; Tsige, Mesfin; Mukhopadhyay, Sharmila; Patnaik, Soumya

    2012-02-01

    We use all-atom molecular dynamics (MD) simulations to predict the mechanical and thermal properties of thermosetting polymers. Atomistic simulation is a promising tool which can provide detailed structure-property relationships of densely cross-linked polymer networks. In this work we study the thermo-mechanical properties of thermosetting polymers based on amine curing agents and epoxy resins and have focused on the DGEBA/DETDA epoxy system. At first we describe the modeling approach to construction of realistic all-atom models of densely cross-linked polymer matrices. Subsequently, a series of atomistic simulations was carried out to examine the simulation cell size effect as well as the role of cross-linking density and chain length of the resin strands on thermo-mechanical properties at different temperatures. Two different methods were used to deform the polymer networks. Both static and dynamic approaches to calculating the mechanical properties were considered and the thermo-mechanical properties obtained from our simulations were found in reasonable agreement with experimental values.

  3. Application of cross-linked and hydrolyzed arabinoxylans in baking of model rye bread.

    Science.gov (United States)

    Buksa, Krzysztof; Nowotna, Anna; Ziobro, Rafał

    2016-02-01

    The role of water extractable arabinoxylan with varying molar mass and structure (cross-linked vs. hydrolyzed) in the structure formation of rye bread was examined using a model bread. Instead of the normal flour, the dough contained starch, arabinoxylan and protein, which were isolated from rye wholemeal. It was observed that the applied mixes of these constituents result in a product closely resembling typical rye bread, even if arabinoxylan was modified (by cross-linking or hydrolysis). The levels of arabinoxylan required for bread preparation depended on its modification and mix composition. At 3% protein, the maximum applicable level of poorly soluble cross-linked arabinoxylan was 3%, as higher amounts of this preparation resulted in an extensively viscous dough and diminished bread volume. On the other hand highly soluble, hydrolyzed arabinoxylan could be used at a higher level (6%) together with larger amounts of rye protein (3% or 6%). Further addition of arabinoxylan leads to excessive water absorption, resulting in a decreased viscosity of the dough during baking and insufficient gas retention. Copyright © 2015 Elsevier Ltd. All rights reserved.

  4. Wood Sawdust/Natural Rubber Ecocomposites Cross-Linked by Electron Beam Irradiation

    Directory of Open Access Journals (Sweden)

    Elena Manaila

    2016-06-01

    Full Text Available The obtaining and characterization of some polymeric eco-composites based on wood sawdust and natural rubber is presented. The natural rubber was cross-linked using the electron beam irradiation. The irradiation doses were of 75, 150, 300 and 600 kGy and the concentrations of wood sawdust were of 10 and 20 phr, respectively. As a result of wood sawdust adding, the physical and mechanical properties such as hardness, modulus at 100% elongation and tensile strength, showed significant improvements. The presence of wood sawdust fibers has a reinforcing effect on natural rubber, similar or better than of mineral fillers. An increase in the irradiation dose leads to the increasing of cross-link density, which is reflected in the improvement of hardness, modulus at 100% elongation and tensile strength of blends. The cross-linking rates, appreciated using the Flory-Rehner equation, have increased with the amount of wood sawdust in blends and with the irradiation dose. Even if the gel fraction values have varied irregularly with the amount of wood sawdust and irradiation dose it was over 90% for all blends, except for the samples without wood sawdust irradiated with 75 kGy. The water uptake increased with increasing of fiber content and decreased with the irradiation dose.

  5. Oxidation increases mucin polymer cross-links to stiffen airway mucus gels.

    Science.gov (United States)

    Yuan, Shaopeng; Hollinger, Martin; Lachowicz-Scroggins, Marrah E; Kerr, Sheena C; Dunican, Eleanor M; Daniel, Brian M; Ghosh, Sudakshina; Erzurum, Serpel C; Willard, Belinda; Hazen, Stanley L; Huang, Xiaozhu; Carrington, Stephen D; Oscarson, Stefan; Fahy, John V

    2015-02-25

    Airway mucus in cystic fibrosis (CF) is highly elastic, but the mechanism behind this pathology is unclear. We hypothesized that the biophysical properties of CF mucus are altered because of neutrophilic oxidative stress. Using confocal imaging, rheology, and biochemical measures of inflammation and oxidation, we found that CF airway mucus gels have a molecular architecture characterized by a core of mucin covered by a web of DNA and a rheological profile characterized by high elasticity that can be normalized by chemical reduction. We also found that high levels of reactive oxygen species in CF mucus correlated positively and significantly with high concentrations of the oxidized products of cysteine (disulfide cross-links). To directly determine whether oxidation can cross-link mucins to increase mucus elasticity, we exposed induced sputum from healthy subjects to oxidizing stimuli and found a marked and thiol-dependent increase in sputum elasticity. Targeting mucin disulfide cross-links using current thiol-amino structures such as N-acetylcysteine (NAC) requires high drug concentrations to have mucolytic effects. We therefore synthesized a thiol-carbohydrate structure (methyl 6-thio-6-deoxy-α-D-galactopyranoside) and found that it had stronger reducing activity than NAC and more potent and fast-acting mucolytic activity in CF sputum. Thus, oxidation arising from airway inflammation or environmental exposure contributes to pathologic mucus gel formation in the lung, which suggests that it can be targeted by thiol-modified carbohydrates.

  6. Cross-linked polystyrene sulfonic acid and polyethylene glycol as a low-fouling material.

    Science.gov (United States)

    Alghunaim, Abdullah; Zhang Newby, Bi-min

    2016-04-01

    A negatively charged hydrophilic low fouling film was prepared by thermally cross-linking a blend consisting of polystyrene sulfonic acid (PSS) and polyethylene glycol (PEG). The film was found to be stable by dip-washing. The fouling resistance of this material toward bacterial (Escherichia coli) and colloidal (polystyrene particles) attachment, non-specific protein (fibronectin) adsorption and cell (3T3 NIH) adhesion was evaluated and was compared with glass slides modified with polyethylene glycol (PEG) brushes, oxidized 3-mercaptopropyltrimethoxysilane (sulfonic acid, SA), and n-octadecyltrichlorosilane (OTS). The extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory and thermodynamic models based on surface energy were used to explain the interaction behaviors of E. coli/polystyrene particles-substrate and protein-substrate interactions, respectively. The cross-linked PSS-PEG film was found to be slightly better than SA and PEG toward resisting non-specific protein adsorption, and showed comparable low attachment results as those of PEG toward particle, bacterial and NIH-3T3 cells adhesion. The low-fouling performance of PSS-PEG, a cross-linked film by a simple thermal curing process, could allow this material to be used for applications in aqueous environments, where most low fouling hydrophilic polymers, such as PSS or PEG, could not be easily retained.

  7. Cross-linked carbon nanotubes buckygel actuators: an in-depth study

    Science.gov (United States)

    Gendron, David; Bubak, Grzegorz; Ceseracciu, Luca; Ansaldo, Alberto; Ricci, Davide

    2015-04-01

    Recently, materials that can convert electrical energy into mechanical work have drawn great attention. Applications in robotics, tactile or optical displays and microelectrochemical systems are currently investigated. Likewise, interest in actuators devices is increasing toward applications where low voltage and low weight properties are required. One way to achieve such prerequisites is to combine the mechanical and electronic properties of carbon nanotubes (CNTs) with the stability and conductivity of ionic liquids. Indeed, the CNTs can be dispersed in ionic liquids to form hybrid composites also named bucky gels, thanks to the non-covalent (π-π stacking and cation-π) interactions. In our previous studies, we demonstrated an improvement in actuator performance whilst using cross-linked CNTs. Indeed, our preliminary results showed an increase in the capacitance together with a faster response of the actuator. At the time, these results were explained by an actuation mechanism model. Herein, we designed new experiments in order to allow us to get a deeper insight in the effect the crosslinking process on the carbon nanotubes properties. Thus, we present a set of electromechanical and electrochemical data that shed light on the chemical modification of the CNTs, the different cross-linking strategies and also on the uses of cross-linked CNTS polymer blends. Finally, corresponding bucky gels actuators performances will also be discussed.

  8. An atomistic model for cross-linked HNBR elastomers used in seals

    Science.gov (United States)

    Molinari, Nicola; Sutton, Adrian; Stevens, John; Mostofi, Arash

    2015-03-01

    Hydrogenated nitrile butadiene rubber (HNBR) is one of the most common elastomeric materials used for seals in the oil and gas industry. These seals sometimes suffer ``explosive decompression,'' a costly problem in which gases permeate a seal at the elevated temperatures and pressures pertaining in oil and gas wells, leading to rupture when the seal is brought back to the surface. The experimental evidence that HNBR and its unsaturated parent NBR have markedly different swelling properties suggests that cross-linking may occur during hydrogenation of NBR to produce HNBR. We have developed a code compatible with the LAMMPS molecular dynamics package to generate fully atomistic HNBR configurations by hydrogenating initial NBR structures. This can be done with any desired degree of cross-linking. The code uses a model of atomic interactions based on the OPLS-AA force-field. We present calculations of the dependence of a number of bulk properties on the degree of cross-linking. Using our atomistic representations of HNBR and NBR, we hope to develop a better molecular understanding of the mechanisms that result in explosive decompression.

  9. Scheimpflug imaged corneal changes on anterior and posterior surfaces after collagen cross-linking

    Directory of Open Access Journals (Sweden)

    Ziad Hassan

    2014-04-01

    Full Text Available AIM: To compare the anterior and posterior corneal parameters before and after collagen cross-linking therapy for keratoconus.METHODS: Collagen cross-linking was performed in 31 eyes of 31 keratoconus patients (mean age 30.6±8.9y. Prior to treatment and an average 7mo after therapy, Scheimpflug analysis was performed using Pentacam HR. In addition to corneal thickness assessments, corneal radius, elevation, and aberrometric measurements were performed both on anterior and posterior corneal surfaces. Data obtained before and after surgery were statistically analyzed.RESULTS: In terms of horizontal and vertical corneal radius, and central corneal thickness no deviations were observed an average 7mo after operation. Corneal higher order aberration showed no difference neither on anterior nor on posterior corneal surfaces. During follow-up period, no significant deviation was detected regarding elevation values obtained by measurement in mm units between the 3.0-8.0 mm-zones.CONCLUSION: Corneal stabilization could be observed in terms of anterior and posterior corneal surfaces, elevation and higher order aberration values 7mo after collagen cross-linking therapy for keratoconus.

  10. Crosslink density, oxidation and chain scission in retrieved, highly cross-linked UHMWPE tibial bearings.

    Science.gov (United States)

    Reinitz, Steven D; Currier, Barbara H; Levine, Rayna A; Van Citters, Douglas W

    2014-05-01

    Irradiated, thermally stabilized, highly cross-linked UHMWPE bearings have demonstrated superior wear performance and improved in vitro oxidation resistance compared with terminally gamma-sterilized bearings, yet retrieval analysis reveals unanticipated in vivo oxidation in these materials despite fewer or no measurable free radicals. There has been little evidence to date that the oxidation mechanism in thermally stabilized materials is the same as that in conventional materials, and so it is unknown whether oxidation in these materials is leading to chain scission and a degradation of mechanical properties, molecular weight, and crosslink density. The aim of this study was to determine whether measured in vivo oxidation in retrieved, highly cross-linked tibial bearings corresponds with a decreasing crosslink density. Analysis of three tibial bearing materials revealed that crosslink density decreased following in vivo duration, and that the change in crosslink density was strongly correlated with oxidation. The results suggest that oxidation in highly cross-linked materials is causing chain scissions that may, in time, impact the material properties. If in vivo oxidation continues over longer durations, there is potential for a clinically significant degradation of mechanical properties.

  11. Cross-linked multilayer-dye films deposited onto silica surfaces with high affinity for pepsin

    Science.gov (United States)

    Bucatariu, Florin; Ghiorghita, Claudiu-Augustin; Cocarta, Ana-Irina; Dragan, Ecaterina Stela

    2016-12-01

    Cross-linked thin films based on pH-responsive polymers with a specific ligand inside the organic layer are useful materials in separation processes or in fabrication of controlled delivery systems. Herein, we report the step-by-step deposition of polymer multilayers based on poly(ethyleneimine) (PEI), poly(acrylic acid) (PAA) and poly(sodium methacrylate) (PMAA) followed by the Congo red (CR) immobilization onto composite Daisogel silica microparticles and silicon wafers. The non-crosslinked composites were not stable in extreme basic medium (pH = 13), while thermal and chemical cross-linked samples with CR inside were stable over a wide range of pH. The interaction properties of different proteins [pepsin (PEP), lysozyme, trypsin, bovine serum albumin] with modified solid surfaces were followed by potentiometric titrations, UV and AFM measurements. Only the PEP macromolecules were sorbed onto the Daisogel composite microparticles with CR inside the cross-linked multilayer. The maximum sorbed amount was nearly 200 mg PEP/g Daisogel//(PEI/PAA)4.5 + CR. This high sorbed amount was in accordance with the AFM images, the average high and roughness increased drastically after the sorption of PEP.

  12. Rheological characterization of cataplasm bases composed of cross-linked partially neutralized polyacrylate hydrogel.

    Science.gov (United States)

    Wang, Jian; Zhang, Hongqin; An, Dianyun; Yu, Jian; Li, Wei; Shen, Teng; Wang, Jianxin

    2014-10-01

    Viscoelasticity is a useful parameter for characterizing the intrinsic properties of the cross-linked polyacrylate hydrogel used in cataplasm bases. The aim of this study was to investigate the effects of various formulation parameters on the rheological characteristics of polyacrylate hydrogel. The hydrogel layers were formed using a partially neutralized polyacrylate (Viscomate(™)), which contained acrylic acid and sodium acrylate in different copolymerization ratios, as the cross-linked gel framework. Dihydroxyaluminum aminoacetate (DAAA), which produces aluminum ions, was used as the cross-linking agent. Rheological analyses were performed using a "stress amplitude sweep" and a "frequency sweep". The results showed that greater amounts of acrylic acid in the structure of Viscomate as well as higher concentrations of DAAA and Viscomate led to an increase in the elastic modulus (G'). However, greater amounts of acrylic acid in the structure of Viscomate and higher concentrations of DAAA had an opposite on the viscous modulus (G″); this might be owing to higher steric hindrance. The results of this study can serve as guidelines for the optimization of formulations for cataplasms.

  13. Single-molecule dynamics of lysozyme processing distinguishes linear and cross-linked peptidoglycan substrates.

    Science.gov (United States)

    Choi, Yongki; Moody, Issa S; Sims, Patrick C; Hunt, Steven R; Corso, Brad L; Seitz, David E; Blaszczak, Larry C; Blaszcazk, Larry C; Collins, Philip G; Weiss, Gregory A

    2012-02-01

    The dynamic processivity of individual T4 lysozyme molecules was monitored in the presence of either linear or cross-linked peptidoglycan substrates. Single-molecule monitoring was accomplished using a novel electronic technique in which lysozyme molecules were tethered to single-walled carbon nanotube field-effect transistors through pyrene linker molecules. The substrate-driven hinge-bending motions of lysozyme induced dynamic electronic signals in the underlying transistor, allowing long-term monitoring of the same molecule without the limitations of optical quenching or bleaching. For both substrates, lysozyme exhibited processive low turnover rates of 20-50 s(-1) and rapid (200-400 s(-1)) nonproductive motions. The latter nonproductive binding events occupied 43% of the enzyme's time in the presence of the cross-linked peptidoglycan but only 7% with the linear substrate. Furthermore, lysozyme catalyzed the hydrolysis of glycosidic bonds to the end of the linear substrate but appeared to sidestep the peptide cross-links to zigzag through the wild-type substrate.

  14. Cross ambiguity functions on the MasPar MP-2

    Energy Technology Data Exchange (ETDEWEB)

    Carlson, D.A.; Pryor, D.V. [Superconducting Research Center, Bowie, MD (United States); Frock, C.K. [and others

    1995-12-01

    In a signal processing environment, cross ambiguity functions are often used to detect when one signal is a time and/or frequency shift of another. They consist of multiple cross-correlations, which can be computed efficiently using complex valued FFTs. This paper discusses the implementation of cross ambiguity functions on the MasPar MP-2, a SIMD processor array. Two different implementations are developed. The first computes each cross ambiguity function serially, using FFT code that parallelizes across the complete set of processors. The second uses the MasPar IORAM to realign the data so that the cross ambiguity functions can be computed in parallel. In this case, multiple FFTs are executed in parallel on subsets of the processors, which lowers the overall amount of communication required.

  15. The algebraic crossing number and the braid index of knots and links

    CERN Document Server

    Kawamuro, Keiko

    2009-01-01

    It has been conjectured that the algebraic crossing number of a link is uniquely determined in minimal braid representation. This conjecture is true for many classes of knots and links. The Morton-Franks-Williams inequality gives a lower bound for braid index. And sharpness of the inequality on a knot type implies the truth of the conjecture for the knot type. We prove that there are infinitely many examples of knots and links for which the inequality is not sharp but the conjecture is still true. We also show that if the conjecture is true for K and L, then it is also true for the (p,q)-cable of K and for the connect sum of K and L.

  16. Internal acetylene unit as a cross-link site for polyimides

    Energy Technology Data Exchange (ETDEWEB)

    Takeichi, T.; Tanikawa, M. [Toyohashi Univ. of Technology (Japan)

    1995-12-01

    We have been studying on the cross-linking behavior of internal acetylenes linked meta-meta to aromatic connecting units which were introduced into the polyimide backbone utilizing 3,3`-diaminodiphenylacetylene (m-intA). In this study, we studied on the cross-linking behavior of internal acetylenes linked para-para to aromatic connecting units. The internal acetylene units were introduced into the polyimide backbone by the reaction of 4,4`-diaminodiphenylacetylene (p-intA) with such acid anhydrides as biphenyltetracarboxylic dianhydride (BPDA), pyromellitic dianhydride (PMDA), and 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA). The polyimides showed exotherm on DSC: The onset of the exotherm of p-intA appeared at around 330-390{degrees}C, which is 10-50{degrees}C higher than that of m-intA. The exotherm disappeared after thermal treatment at 400{degrees}C, suggesting the progress of crosslinking between acetylene units. The polyimides cured at 350{degrees}C or 400{degrees}C showed increased Tg and improved physical properties at high temperatures as confirmed by viscoelastic analyses. It was also made clear that polyimides containing p-intA showed higher modulus compared with polyimides containing m-intA, especially when coupled with BPDA and PMDA.

  17. Core Cross-Linked Multiarm Star Polymers with Aggregation-Induced Emission and Temperature Responsive Fluorescence Characteristics

    KAUST Repository

    Zhang, Zhen

    2017-05-19

    Aggregation-induced emission (AIE) active core cross-linked multiarm star polymers, carrying polystyrene (PS), polyethylene (PE), or polyethylene-b-polycaprolactone (PE-b-PCL) arms, have been synthesized through an “arm-first” strategy, by atom transfer radical copolymerization (ATRP) of a double styrene-functionalized tetraphenylethene (TPE-2St) used as a cross-linker with linear arm precursors possessing terminal ATRP initiating moieties. Polyethylene macroinitiator (PE–Br) was prepared via the polyhomologation of dimethylsulfoxonium methylide with triethylborane followed by oxidation/hydrolysis and esterification of the produced PE–OH with 2-bromoisobutyryl bromide; polyethylene-block-poly(ε-caprolactone) diblock macroinitiator was derived by combining polyhomologation with ring-opening polymerization (ROP). All synthesized star polymers showed AIE-behavior either in solution or in bulk. At high concentration in good solvents (e.g., THF, or toluene) they exhibited low photoluminescence (PL) intensity due to the inner filter effect. In sharp contrast to the small molecule TPE-2St, the star polymers were highly emissive in dilute THF solutions. This can be attributed to the cross-linked structure of poly(TPE-2St) core which restricts the intramolecular rotation and thus induces emission. In addition, the PL intensity of PE star polymers in THF(solvent)/n-hexane(nonsolvent) mixtures, due to their nearly spherical shape, increased when the temperature decreased from 55 to 5 °C with a linear response in the range 40–5 °C.

  18. Low-Temperature Cross-Linking of PEDOT:PSS Films Using Divinylsulfone.

    Science.gov (United States)

    Mantione, Daniele; Del Agua, Isabel; Schaafsma, Wandert; ElMahmoudy, Mohammed; Uguz, Ilke; Sanchez-Sanchez, Ana; Sardon, Haritz; Castro, Begoña; Malliaras, George G; Mecerreyes, David

    2017-05-31

    Recent interest in bioelectronics has prompted the exploration of properties of conducting polymer films at the interface with biological milieus. Poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate) (PEDOT:PSS) from a commercially available source has been used as a model system for these studies. Different cross-linking schemes have been used to stabilize films of this material against delamination and redispersion, but the cost is a decrease in the electrical conductivity and/or additional heat treatment. Here we introduce divinylsulfone (DVS) as a new cross-linker for PEDOT:PSS. Thanks to the higher reactiveness of the vinyl groups of DVS, the cross-linking can be performed at room temperature. In addition, DVS does not reduce electronic conductivity of PEDOT:PSS but rather increases it by acting as a secondary dopant. Cell culture studies show that PEDOT:PSS:DVS films are cytocompatible and support neuroregeneration. As an example, we showed that this material improved the transconductance value and stability of an organic electrochemical transistor (OECT) device. These results open the way for the utilization of DVS as an effective cross-linker for PEDOT:PSS in bioelectronics applications.

  19. Nondestructive fluorescence-based quantification of threose-induced collagen cross-linking in bovine articular cartilage

    Science.gov (United States)

    Kinnunen, Jussi; Kokkonen, Harri T.; Kovanen, Vuokko; Hauta-Kasari, Markku; Vahimaa, Pasi; Lammi, Mikko J.; Töyräs, Juha; Jurvelin, Jukka S.

    2012-09-01

    Extensive collagen cross-linking affects the mechanical competence of articular cartilage: it can make the cartilage stiffer and more brittle. The concentrations of the best known cross-links, pyridinoline and pentosidine, can be accurately determined by destructive high-performance liquid chromatography (HPLC). We explore a nondestructive evaluation of cross-linking by using the intrinsic fluorescence of the intact cartilage. Articular cartilage samples from bovine knee joints were incubated in threose solution for 40 and 100 h to increase the collagen cross-linking. Control samples without threose were also prepared. Excitation-emission matrices at wavelengths of 220 to 950 nm were acquired from the samples, and the pentosidine and pyridinoline cross-links and the collagen concentrations were determined using HPLC. After the threose treatment, pentosidine and lysyl pyridinole (LP) concentrations increased. The intrinsic fluorescence, excited below 350 nm, decreased and was related to pentosidine [r=-0.90, 240/325 nm (excitation/emission)] or LP (r=-0.85, 235/285 nm) concentrations. Due to overlapping, the changes in emission could not be linked specifically to the recorded cross-links. However, the fluorescence signal enabled a nondestructive optical estimate of changes in the pentosidine and LP cross-linking of intact articular cartilage.

  20. Automated Assignment of MS/MS Cleavable Cross-Links in Protein 3D-Structure Analysis

    Science.gov (United States)

    Götze, Michael; Pettelkau, Jens; Fritzsche, Romy; Ihling, Christian H.; Schäfer, Mathias; Sinz, Andrea

    2015-01-01

    CID-MS/MS cleavable cross-linkers hold an enormous potential for an automated analysis of cross-linked products, which is essential for conducting structural proteomics studies. The created characteristic fragment ion patterns can easily be used for an automated assignment and discrimination of cross-linked products. To date, there are only a few software solutions available that make use of these properties, but none allows for an automated analysis of cleavable cross-linked products. The MeroX software fills this gap and presents a powerful tool for protein 3D-structure analysis in combination with MS/MS cleavable cross-linkers. We show that MeroX allows an automatic screening of characteristic fragment ions, considering static and variable peptide modifications, and effectively scores different types of cross-links. No manual input is required for a correct assignment of cross-links and false discovery rates are calculated. The self-explanatory graphical user interface of MeroX provides easy access for an automated cross-link search platform that is compatible with commonly used data file formats, enabling analysis of data originating from different instruments. The combination of an MS/MS cleavable cross-linker with a dedicated software tool for data analysis provides an automated workflow for 3D-structure analysis of proteins. MeroX is available at www.StavroX.com .

  1. Cross-kingdom similarities in microbiome functions

    NARCIS (Netherlands)

    Mendes, R.; Raaijmakers, J.M.

    2015-01-01

    Recent advances in medical research have revealed how humans rely on their microbiome for diverse traits and functions. Similarly, microbiomes of other higher organisms play key roles in disease, health, growth and development of their host. Exploring microbiome functions across kingdoms holds enorm

  2. Cross-kingdom similarities in microbiome functions

    NARCIS (Netherlands)

    Mendes, R.; Raaijmakers, J.M.

    2016-01-01

    Recent advances in medical research have revealed how humans rely on their microbiome for diverse traits and functions. Similarly, microbiomes of other higher organisms play key roles in disease, health, growth and development of their host. Exploring microbiome functions across kingdoms holds enorm

  3. Cross-kingdom similarities in microbiome functions

    NARCIS (Netherlands)

    Mendes, R.; Raaijmakers, J.M.

    2015-01-01

    Recent advances in medical research have revealed how humans rely on their microbiome for diverse traits and functions. Similarly, microbiomes of other higher organisms play key roles in disease, health, growth and development of their host. Exploring microbiome functions across kingdoms holds

  4. Preliminary clinical and radiographic results of large ceramic heads on highly cross-linked polyethylene.

    Science.gov (United States)

    Meftah, Morteza; Ebrahimpour, Prouskeh Bruce; He, Chuan; Ranawat, Amar S; Ranawat, Chitranjan S

    2011-06-14

    Data are limited regarding large ceramic femoral heads with highly cross-linked polyethylene. We hypothesized that large ceramic head articulation with highly cross-linked polyethylene is safe with a low wear rate, comparable to metal-on-highly cross-linked polyethylene.The study group comprised 63 patients (72 hips) who had undergone total hip replacement (THR) with ceramic-on-highly cross-linked polyethylene between April 2006 and March 2007 with a minimum 2-year follow-up. Postoperative Western Ontario and Mc-Master Universities Arthritis Index (WOMAC) and Hospital for Special Surgery (HSS) scores were used for clinical assessment. Six-week and 2-year radiographs were analyzed by 2 independent observers using Roman 1.70 software. Twenty-six patients (29 hips) had 32-mm and 37 patients (43 hips) had 36-mm Biolox delta ceramic femoral heads (Ceramtec, Plochingen, Germany). Mean patient age was 60.9 ± 8.9 years, and mean follow-up was 2.9 ± 0.5 years. Mean postoperative WOMAC and HSS hip scores were 30.4 and 36.6, respectively. Mean wear at 1 and 2 years postoperatively was 0.06 ± 0.28 and 0.006 ± 0.12 mm/yr for all hips, respectively. Mean wear at 1 and 2 years postoperatively for the 32-mm femoral head was 0.063 ± 0.278 and 0.007 ± 0.126 mm/yr, respectively, and for the 36-mm femoral head was 0.057 ± 0.292 and 0.006 ± 0.118 mm/yr, respectively. No patient had any clinical complications, such as reoperation, infection, fractures, or radiographic evidence of osteolysis or loosening. The early results of THR with large ceramic heads demonstrate high safety and efficacy. Our data with 2-year follow-up show low wear rates, similar to published data for metal-on-highly cross-linked polyethylene.

  5. Graft copolymerization onto polybutadiene: Cross-linking and thermal degradation of vinyl polymers and copolymers

    Science.gov (United States)

    Jiang, Dayue (David)

    This work consists of three parts. In Part I, the graft copolymerization of methyl methacrylate, methyl acrylate, methacylic acid and acrylic acid onto polybutadiene and its copolymers by benzoyl peroxide, BPO, or 2, 2'azobis(2-methylpropionitrile), AIBN, initiation were explored. The results show that these monomers can be grafted onto butadiene region of butadiene-containing polymers. The extent of both graft copolymerization and homopolymerization are dependent on the time and temperature of the reaction and the concentration of all of the reactants. One must specify the monomer, initiator and solvent for the efficient graft copolymerization. The methyl methacrylate adds directly to the radical sites which are formed on the backbone by the interaction of the polymer and the primary radical form the initiator, while for the other three monomers, the graft copolymerization occurs by addition of macro-radical to the double bonds. In Part II, the cross-linking of polybutadiene, butadiene-styrene copolymers, and polystyrene by irradiation, thermal and chemical processes, and Friedel-Crafts chemistry and the effect of cross-linking on the thermal stability were investigated. The proof of cross-linking of the polymer comes from the insolubility of the product after the cross-linking reaction and is characterized by gel content and swelling ratio. The results show that the thermal stability of the polymer can be improved by cross-linking. In Part III, the thermal degradation of three vinyl polymers, poly(vinylsulfonic acid) and its sodium salt and poly(vinylphosphonic acid) were studied by combination technique: TGA/FTIR. The results show that TGA/FTIR combined with analysis of residues provides an excellent opportunity to understand the degradation pathway of the compounds. The observation of foaming indicates that the char which is formed contains carbon as well as the inorganic salts which have been observed. The carbon is in a partially graphitized form. The salts

  6. Generation of Guanine – Thymidine Cross-links in DNA by Peroxynitrite/Carbon Dioxide

    Science.gov (United States)

    Yun, Byeong Hwa; Geacintov, Nicholas E.; Shafirovich, Vladimir

    2011-01-01

    Nitrosoperoxycarbonate derived from the combination of carbon dioxide and peroxynitrite, is an important chemical mediator of inflammation. In aqueous solutions, it rapidly decomposes to the reactive species CO3•− and •NO2 radicals that are known to initiate the selective oxidation and nitration of guanine in DNA. We have previously demonstrated that the reactions of carbonate radical anions with guanine in 2′-deoxyoligoribonucleotides generate a previously unknown intrastrand cross-linked guanine-thymine product G*-T* with a covalent bond between the C8 (G*) and thymine N3 (T*) atoms (Crean et al., Nucleic Acids Res., 2008, 36, 742–755). In this work we demonstrate that G*-T* cross-linked products are also formed when peroxynitrite (0.1 mM) reacts with native DNA in aqueous solutions (pH 7.5–7.7) containing 25 mM carbon dioxide/bicarbonate, in addition to the well known nitration/oxidation products of guanine such as 8-nitroguanine (8-nitroG), 5-guanidino-4-nitroimidazole (NIm), 8-oxo-7,8-dehydroguanine (8-oxoG) and spiroiminodihydantoin (Sp). The yields of these products, after enzymatic digestion with P1 nuclease and alkaline phosphatase to the nucleotide level, and reversed phase HPLC separation, were compared with those obtained with the uniformly, isotopically labeled 15N,13C-labeled 2′-deoxy oligoribonucleotides 5′-dGpT and 5′-dGpCpT. The d(G*pT*) and d(G*-T*) cross-linked products derived from the di- and tri-oligonucleotides, respectively, were used as standards for identifying the analogous lesions in calf thymus DNA by isotope dilution LC-MS/MS methods in the selected reaction-monitoring mode. The Nim and 8nitroG are the major products formed (~ 0.05% each), and lesser amounts of 8-oxoG (~ 0.02%), and d(G*pT*) and d(G*-T*) enzymatic digestion products (~ 0.002% each) were found. It is shown that the formation of d(G*pT*) enzyme digestion product can arise only from intrastrand cross-links, whereas d(G*-T*) can arise from both

  7. Generation of guanine-thymidine cross-links in DNA by peroxynitrite/carbon dioxide.

    Science.gov (United States)

    Yun, Byeong Hwa; Geacintov, Nicholas E; Shafirovich, Vladimir

    2011-07-18

    Nitrosoperoxycarbonate derived from the combination of carbon dioxide and peroxynitrite is an important chemical mediator of inflammation. In aqueous solutions, it rapidly decomposes to the reactive species CO(3)(•-) and (•)NO(2) radicals that are known to initiate the selective oxidation and nitration of guanine in DNA. We have previously demonstrated that the reactions of carbonate radical anions with guanine in 2'-deoxyoligoribonucleotides generate a previously unknown intrastrand cross-linked guanine-thymine product G*-T* with a covalent bond between the C8 (G*) and the thymine N3 (T*) atoms (Crean Nucleic Acids Res. 2008, 36, 742-755). In this work, we demonstrate that G*-T* cross-linked products are also formed when peroxynitrite (0.1 mM) reacts with native DNA in aqueous solutions (pH 7.5-7.7) containing 25 mM carbon dioxide/bicarbonate, in addition to the well-known nitration/oxidation products of guanine such as 8-nitroguanine (8-nitro-G), 5-guanidino-4-nitroimidazole (NIm), 8-oxo-7,8-dehydroguanine (8-oxo-G), and spiroiminodihydantoin (Sp). The yields of these products, after enzymatic digestion with P1 nuclease and alkaline phosphatase to the nucleotide level and reversed phase HPLC separation, were compared with those obtained with the uniformly, isotopically labeled (15)N,(13)C-labeled 2'-deoxy oligoribonucleotides 5'-dGpT and 5'-dGpCpT. The d(G*pT*) and d(G*-T*) cross-linked products derived from the di- and trioligonucleotides, respectively, were used as standards for identifying the analogous lesions in calf thymus DNA by isotope dilution LC-MS/MS methods in the selected reaction monitoring mode. The NIm and 8-nitro-G are the major products formed (∼0.05% each), and lesser amounts of 8-oxo-G (∼0.02%) and d(G*pT*) and d(G*-T*) enzymatic digestion products (∼0.002% each) were found. It is shown that the formation of d(G*pT*) enzyme digestion product can arise only from intrastrand cross-links, whereas d(G*-T*) can arise from both interstrand

  8. Cross-linking immunoprecipitation-MS (xIP-MS): Topological Analysis of Chromatin-associated Protein Complexes Using Single Affinity Purification.

    Science.gov (United States)

    Makowski, Matthew M; Willems, Esther; Jansen, Pascal W T C; Vermeulen, Michiel

    2016-03-01

    In recent years, cross-linking mass spectrometry has proven to be a robust and effective method of interrogating macromolecular protein complex topologies at peptide resolution. Traditionally, cross-linking mass spectrometry workflows have utilized homogenous complexes obtained through time-limiting reconstitution, tandem affinity purification, and conventional chromatography workflows. Here, we present cross-linking immunoprecipitation-MS (xIP-MS), a simple, rapid, and efficient method for structurally probing chromatin-associated protein complexes using small volumes of mammalian whole cell lysates, single affinity purification, and on-bead cross-linking followed by LC-MS/MS analysis. We first benchmarked xIP-MS using the structurally well-characterized phosphoribosyl pyrophosphate synthetase complex. We then applied xIP-MS to the chromatin-associated cohesin (SMC1A/3), XRCC5/6 (Ku70/86), and MCM complexes, and we provide novel structural and biological insights into their architectures and molecular function. Of note, we use xIP-MS to perform topological studies under cell cycle perturbations, showing that the xIP-MS protocol is sufficiently straightforward and efficient to allow comparative cross-linking experiments. This work, therefore, demonstrates that xIP-MS is a robust, flexible, and widely applicable methodology for interrogating chromatin-associated protein complex architectures.

  9. Linking community size structure and ecosystem functioning using metabolic theory.

    Science.gov (United States)

    Yvon-Durocher, Gabriel; Allen, Andrew P

    2012-11-05

    Understanding how biogeochemical cycles relate to the structure of ecological communities is a central research question in ecology. Here we approach this problem by focusing on body size, which is an easily measured species trait that has a pervasive influence on multiple aspects of community structure and ecosystem functioning. We test the predictions of a model derived from metabolic theory using data on ecosystem metabolism and community size structure. These data were collected as part of an aquatic mesocosm experiment that was designed to simulate future environmental warming. Our analyses demonstrate significant linkages between community size structure and ecosystem functioning, and the effects of warming on these links. Specifically, we show that carbon fluxes were significantly influenced by seasonal variation in temperature, and yielded activation energies remarkably similar to those predicted based on the temperature dependencies of individual-level photosynthesis and respiration. We also show that community size structure significantly influenced fluxes of ecosystem respiration and gross primary production, particularly at the annual time-scale. Assessing size structure and the factors that control it, both empirically and theoretically, therefore promises to aid in understanding links between individual organisms and biogeochemical cycles, and in predicting the responses of key ecosystem functions to future environmental change.

  10. Fluxomics links cellular functional analyses to whole-plant phenotyping.

    Science.gov (United States)

    Salon, Christophe; Avice, Jean-Christophe; Colombié, Sophie; Dieuaide-Noubhani, Martine; Gallardo, Karine; Jeudy, Christian; Ourry, Alain; Prudent, Marion; Voisin, Anne-Sophie; Rolin, Dominique

    2017-04-01

    Fluxes through metabolic pathways reflect the integration of genetic and metabolic regulations. While it is attractive to measure all the mRNAs (transcriptome), all the proteins (proteome), and a large number of the metabolites (metabolome) in a given cellular system, linking and integrating this information remains difficult. Measurement of metabolome-wide fluxes (termed the fluxome) provides an integrated functional output of the cell machinery and a better tool to link functional analyses to plant phenotyping. This review presents and discusses sets of methodologies that have been developed to measure the fluxome. First, the principles of metabolic flux analysis (MFA), its 'short time interval' version Inst-MFA, and of constraints-based methods, such as flux balance analysis and kinetic analysis, are briefly described. The use of these powerful methods for flux characterization at the cellular scale up to the organ (fruits, seeds) and whole-plant level is illustrated. The added value given by fluxomics methods for unravelling how the abiotic environment affects flux, the process, and key metabolic steps are also described. Challenges associated with the development of fluxomics and its integration with 'omics' for thorough plant and organ functional phenotyping are discussed. Taken together, these will ultimately provide crucial clues for identifying appropriate target plant phenotypes for breeding. © The Author 2017. Published by Oxford University Press on behalf of the Society for Experimental Biology. All rights reserved. For permissions, please email: journals.permissions@oup.com.

  11. Probing Protein 3D Structures and Conformational Changes Using Electrochemistry-Assisted Isotope Labeling Cross-Linking Mass Spectrometry

    Science.gov (United States)

    Zheng, Qiuling; Zhang, Hao; Wu, Shiyong; Chen, Hao

    2016-05-01

    This study presents a new chemical cross-linking mass spectrometry (MS) method in combination with electrochemistry and isotope labeling strategy for probing both protein three-dimensional (3D) structures and conformational changes. For the former purpose, the target protein/protein complex is cross-linked with equal mole of premixed light and heavy isotope labeled cross-linkers carrying electrochemically reducible disulfide bonds (i.e., DSP-d0 and DSP-d8 in this study, DSP = dithiobis[succinimidyl propionate]), digested and then electrochemically reduced followed with online MS analysis. Cross-links can be quickly identified because of their reduced intensities upon electrolysis and the presence of doublet isotopic peak characteristics. In addition, electroreduction converts cross-links into linear peptides, facilitating MS/MS analysis to gain increased information about their sequences and modification sites. For the latter purpose of probing protein conformational changes, an altered procedure is adopted, in which the protein in two different conformations is cross-linked using DSP-d0 and DSP-d8 separately, and then the two protein samples are mixed in 1:1 molar ratio. The merged sample is subjected to digestion and electrochemical mass spectrometric analysis. In such a comparative cross-linking experiment, cross-links could still be rapidly recognized based on their responses to electrolysis. More importantly, the ion intensity ratios of light and heavy isotope labeled cross-links reveal the conformational changes of the protein, as exemplified by examining the effect of Ca2+ on calmodulin conformation alternation. This new cross-linking MS method is fast and would have high value in structural biology.

  12. Integrated Workflow for Structural Proteomics Studies Based on Cross-Linking/Mass Spectrometry with an MS/MS Cleavable Cross-Linker.

    Science.gov (United States)

    Arlt, Christian; Götze, Michael; Ihling, Christian H; Hage, Christoph; Schäfer, Mathias; Sinz, Andrea

    2016-08-16

    Cross-linking combined with mass spectrometry (MS) has evolved as an alternative strategy in structural biology for characterizing three-dimensional structures of protein assemblies and for mapping protein-protein interactions. Here, we describe an integrated workflow for an automated identification of cross-linked products that is based on the use of a tandem mass spectrometry (MS/MS) cleavable cross-linker (containing a 1,3-bis-(4-oxo-butyl)-urea group, BuUrBu) generating characteristic doublet patterns upon fragmentation. We evaluate different fragmentation methods available on an Orbitrap Fusion mass spectrometer for three proteins and an E. coli cell lysate. An updated version of the dedicated software tool MeroX was employed for a fully automated identification of cross-links. The strength of our cleavable cross-linker is that characteristic patterns of the cross-linker as well as backbone fragments of the connected peptides are already observed at the MS/MS level, eliminating the need for conducting MS(3) or sequential CID (collision-induced dissociation)- and ETD (electron transfer dissociation)-MS/MS experiments. This makes our strategy applicable to a broad range of mass spectrometers with MS/MS capabilities. For purified proteins and protein complexes, our workflow using CID-MS/MS acquisition performs with high confidence, scoring cross-links at 0.5% false discovery rate (FDR). The cross-links provide structural insights into the intrinsically disordered tetrameric tumor suppressor protein p53. As a time-consuming manual inspection of cross-linking data is not required, our workflow will pave the way for making the cross-linking/MS approach a routine technique for structural proteomics studies.

  13. Neural Cross-Frequency Coupling Functions

    Directory of Open Access Journals (Sweden)

    Tomislav Stankovski

    2017-06-01

    Full Text Available Although neural interactions are usually characterized only by their coupling strength and directionality, there is often a need to go beyond this by establishing the functional mechanisms of the interaction. We introduce the use of dynamical Bayesian inference for estimation of the coupling functions of neural oscillations in the presence of noise. By grouping the partial functional contributions, the coupling is decomposed into its functional components and its most important characteristics—strength and form—are quantified. The method is applied to characterize the δ-to-α phase-to-phase neural coupling functions from electroencephalographic (EEG data of the human resting state, and the differences that arise when the eyes are either open (EO or closed (EC are evaluated. The δ-to-α phase-to-phase coupling functions were reconstructed, quantified, compared, and followed as they evolved in time. Using phase-shuffled surrogates to test for significance, we show how the strength of the direct coupling, and the similarity and variability of the coupling functions, characterize the EO and EC states for different regions of the brain. We confirm an earlier observation that the direct coupling is stronger during EC, and we show for the first time that the coupling function is significantly less variable. Given the current understanding of the effects of e.g., aging and dementia on δ-waves, as well as the effect of cognitive and emotional tasks on α-waves, one may expect that new insights into the neural mechanisms underlying certain diseases will be obtained from studies of coupling functions. In principle, any pair of coupled oscillations could be studied in the same way as those shown here.

  14. Neural Cross-Frequency Coupling Functions

    Science.gov (United States)

    Stankovski, Tomislav; Ticcinelli, Valentina; McClintock, Peter V. E.; Stefanovska, Aneta

    2017-01-01

    Although neural interactions are usually characterized only by their coupling strength and directionality, there is often a need to go beyond this by establishing the functional mechanisms of the interaction. We introduce the use of dynamical Bayesian inference for estimation of the coupling functions of neural oscillations in the presence of noise. By grouping the partial functional contributions, the coupling is decomposed into its functional components and its most important characteristics—strength and form—are quantified. The method is applied to characterize the δ-to-α phase-to-phase neural coupling functions from electroencephalographic (EEG) data of the human resting state, and the differences that arise when the eyes are either open (EO) or closed (EC) are evaluated. The δ-to-α phase-to-phase coupling functions were reconstructed, quantified, compared, and followed as they evolved in time. Using phase-shuffled surrogates to test for significance, we show how the strength of the direct coupling, and the similarity and variability of the coupling functions, characterize the EO and EC states for different regions of the brain. We confirm an earlier observation that the direct coupling is stronger during EC, and we show for the first time that the coupling function is significantly less variable. Given the current understanding of the effects of e.g., aging and dementia on δ-waves, as well as the effect of cognitive and emotional tasks on α-waves, one may expect that new insights into the neural mechanisms underlying certain diseases will be obtained from studies of coupling functions. In principle, any pair of coupled oscillations could be studied in the same way as those shown here. PMID:28663726

  15. Cross-functional teams in health care organizations.

    Science.gov (United States)

    McKenzie, L

    1994-03-01

    Cross-functional teams in health care organizations provide a comprehensive view of problems and are highly useful in designing and implementing improvements in work processes. Several potential obstacles may impede team progress, but these can be overcome. Cross-functional teams must develop norms that guide the interactions of team members. Individual team members must display behaviors that serve task accomplishment and team spirit. The promise of cross-functional teams for health care organizations is great. These promises, however, will not be fulfilled without the positive support of health care supervisors.

  16. Characteristics of highly cross-linked polyethylene wear debris in vivo.

    Science.gov (United States)

    Baxter, Ryan M; MacDonald, Daniel W; Kurtz, Steven M; Steinbeck, Marla J

    2013-04-01

    Despite the widespread implementation of highly cross-linked polyethylene (HXLPE) liners to reduce the clinical incidence of osteolysis, it is not known if the improved wear resistance will outweigh the inflammatory potential of HXLPE wear debris generated in vivo. Thus, we asked: What are the differences in size, shape, number, and biological activity of polyethylene wear particles obtained from primary total hip arthroplasty revision surgery of conventional polyethylene (CPE) versus remelted or annealed HXLPE liners? Pseudocapsular tissue samples were collected from revision surgery of CPE and HXLPE (annealed and remelted) liners, and digested using nitric acid. The isolated polyethylene wear particles were evaluated using scanning electron microscopy. Tissues from both HXLPE cohorts contained an increased percentage of submicron particles compared to the CPE cohort. However, the total number of particles was lower for both HXLPE cohorts, as a result there was no significant difference in the volume fraction distribution and specific biological activity (SBA; the relative biological activity per unit volume) between cohorts. In contrast, based on the decreased size and number of HXLPE wear debris there was a significant decrease in total particle volume (mm(3)/g of tissue). Accordingly, when the SBA was normalized by total particle volume (mm(3)/gm tissue) or by component wear volume rate (mm(3)/year), functional biological activity of the HXLPE wear debris was significantly decreased compared to the CPE cohort. Indications for this study are that the osteolytic potential of wear debris generated by HXLPE liners in vivo is significantly reduced by improvements in polyethylene wear resistance. Copyright © 2013 Wiley Periodicals, Inc.

  17. Characteristics of highly cross-linked polyethylene wear debris in vivo

    Science.gov (United States)

    Baxter, Ryan M.; MacDonald, Daniel W.; Kurtz, Steven M.; Steinbeck, Marla J.

    2014-01-01

    Despite the widespread implementation of highly cross-linked polyethylene (HXLPE) liners to reduce the clinical incidence of osteolysis, it is not known if the improved wear resistance will outweigh the inflammatory potential of HXLPE wear debris generated in vivo. Thus, we asked: What are the differences in size, shape, number, and biological activity of polyethylene wear particles obtained from primary total hip arthroplasty revision surgery of conventional polyethylene (CPE) versus remelted or annealed HXLPE liners? Pseudocapsular tissue samples were collected from revision surgery of CPE and HXLPE (annealed and remelted) liners, and digested using nitric acid. The isolated polyethylene wear particles were evaluated using scanning electron microscopy. Tissues from both HXLPE cohorts contained an increased percentage of submicron particles compared to the CPE cohort. However, the total number of particles was lower for both HXLPE cohorts, as a result there was no significant difference in the volume fraction distribution and specific biological activity (SBA; the relative biological activity per unit volume) between cohorts. In contrast, based on the decreased size and number of HXLPE wear debris there was a significant decrease in total particle volume (mm3/g of tissue). Accordingly, when the SBA was normalized by total particle volume (mm3/gm tissue) or by component wear volume rate (mm3/year), functional biological activity of the HXLPE wear debris was significantly decreased compared to the CPE cohort. Indications for this study are that the osteolytic potential of wear debris generated by HXLPE liners in vivo is significantly reduced by improvements in polyethylene wear resistance. PMID:23436587

  18. Inhibiting effect of [HOEmim][BF4] and [Amim]Cl ionic liquids on the cross-linking reaction of bituminous coal

    Institute of Scientific and Technical Information of China (English)

    Wang Lanyun; Xu Yongliang; Wang Shaokun; Song Zhipeng

    2016-01-01

    In order to reduce the hazard of coal spontaneous combustion, the cross-linking reaction between O-containing functional groups of coal should be inhibited. So the inhibitory effect of an ionic liquid (IL) on the cross-linking reaction was studied. The O-containing functional groups change the weight loss and H2O, CO2, CO yields of bituminous coal before and after [HOEmim][BF4] and [Amim]Cl pre-treatment and were detected by Fourier Transform Infrared spectroscopy (FTIR) and Thermo Gravimetric (TG) anal-ysis. The results show that [Amim]Cl has a weaker ability to inhibit the cross-linking reaction of bitumi-nous coal compared to [HOEmim][BF4]. Besides, based on Quantum Chemistry calculation, it was found that the different inhibiting effects of [HOEmim][BF4] and [Amim]Cl are greatly related to their anions and the H linked with C2 atom on the imidazole ring. The H-donor ability of coal will be enhanced by [HOEmim][BF4] leading to a weaker cross-linking reaction of coal.

  19. A FUZZY LOGIC CONTROLLERFORA TWO-LINK FUNCTIONAL MANIPULATOR

    Directory of Open Access Journals (Sweden)

    Sherif Kamel Hussein

    2014-12-01

    Full Text Available This paper presents a new approach for designing a Fuzzy Logic Controller "FLC"for a dynamically multivariable nonlinear coupling system. The conventional controller with constant gains for different operating points may not be sufficient to guarantee satisfactory performance for Robot manipulator. The Fuzzy Logic Controller utilizes the error and the change of error as fuzzy linguistic inputs to regulate the system performance. The proposed controller have been developed to simulate the dynamic behavior of A Two-Link Functional Manipulator. The new controller uses only the available information of the inputoutput for controlling the position and velocity of the robot axes of the motion of the end effectors

  20. X-linked adrenoleukodystrophy in women: a cross-sectional cohort study.

    Science.gov (United States)

    Engelen, Marc; Barbier, Mathieu; Dijkstra, Inge M E; Schür, Remmelt; de Bie, Rob M A; Verhamme, Camiel; Dijkgraaf, Marcel G W; Aubourg, Patrick A; Wanders, Ronald J A; van Geel, Bjorn M; de Visser, Marianne; Poll-The, Bwee T; Kemp, Stephan

    2014-03-01

    X-linked adrenoleukodystrophy is the most common peroxisomal disorder. The disease is caused by mutations in the ABCD1 gene that encodes the peroxisomal transporter of very long-chain fatty acids. A defect in the ABCD1 protein results in elevated levels of very long-chain fatty acids in plasma and tissues. The clinical spectrum in males with X-linked adrenoleukodystrophy has been well described and ranges from isolated adrenocortical insufficiency and slowly progressive myelopathy to devastating cerebral demyelination. As in many X-linked diseases, it was assumed that female carriers remain asymptomatic and only a few studies addressed the phenotype of X-linked adrenoleukodystrophy carriers. These studies, however, provided no information on the prevalence of neurological symptoms in the entire population of X-linked adrenoleukodystrophy carriers, since data were acquired in small groups and may be biased towards women with symptoms. Our primary goal was to investigate the symptoms and their frequency in X-linked adrenoleukodystrophy carriers. The secondary goal was to determine if the X-inactivation pattern of the ABCD1 gene was associated with symptomatic status. We included 46 X-linked adrenoleukodystrophy carriers in a prospective cross-sectional cohort study. Our data show that X-linked adrenoleukodystrophy carriers develop signs and symptoms of myelopathy (29/46, 63%) and/or peripheral neuropathy (26/46, 57%). Especially striking was the occurrence of faecal incontinence (13/46, 28%). The frequency of symptomatic women increased sharply with age (from 18% in women 60 years of age). Virtually all (44/45, 98%) X-linked adrenoleukodystrophy carriers had increased very long-chain fatty acids in plasma and/or fibroblasts, and/or decreased very long-chain fatty acids beta-oxidation in fibroblasts. We did not find an association between the X-inactivation pattern and symptomatic status. We conclude that X-linked adrenoleukodystrophy carriers develop an

  1. Modeling behavior: the quest to link mechanisms to function.

    Science.gov (United States)

    Janus, C; Dubnau, J

    2003-02-01

    T. Dobzhansky (1973) has been credited with saying: 'nothing in biology makes sense, except in the light of evolution'. The evolutionary conservation of gene function, as well as remarkable conservation of elemental behavioral mechanisms, guarantees that much of what we learn in one organism will inform our understanding of behavior in all animals, including humans. This insight has permitted behavior-geneticists to choose organisms based on experimental tractability for a given scientific question. IBANGS as a society has clearly embraced this Dobzhanskian worldview. As a result, the intellectual synergy of cross-species behavior-genetic analysis was palpable at the IBANGS meeting in Tours, France.

  2. Relationship between cross-linking conditions of ethylene vinyl acetate and potential induced degradation for crystalline silicon photovoltaic modules

    Science.gov (United States)

    Jonai, Sachiko; Hara, Kohjiro; Tsutsui, Yuji; Nakahama, Hidenari; Masuda, Atsushi

    2015-08-01

    In this study, we investigated the relationship in crystalline silicon (c-Si) photovoltaic (PV) modules between the cross-linking level of copolymer of ethylene and vinyl acetate (EVA) as the encapsulant and the degree of degradation due to potential induced degradation (PID) phenomenon. We used three methods for the determination of cross-linking level of EVA: xylene method, which is one of the solvent extraction methods (SEM), curing degree by differential scanning calorimetry (DSC), and viscoelastic properties by dynamic mechanical analysis (DMA). The results indicate that degradation of PV modules by PID test depends on the cross-linking level of EVA. The PV modules encapsulated by EVA with higher cross-linking level show lower degradation degree due to PID phenomenon. Also we showed that EVA with higher cross-linking level tended to be higher volume resistivity. This tendency is similar to that for electrical resistance value during the PID test. The PID test was also done by changing thickness of EVA between front cover glass and c-Si with the same cross-linking level. The PV modules encapsulated by thicker EVA between front cover glass and c-Si cell show lower degradation by PID. From these results, the PV modules encapsulated by EVA with higher cross-linking level, higher volume resistivity and increased thickness would be tolerant of PID phenomenon.

  3. Evaluation of epigallocatechin-3-gallate (EGCG) cross-linked collagen membranes and concerns on osteoblasts

    Energy Technology Data Exchange (ETDEWEB)

    Chu, Chenyu; Deng, Jia [State Key Laboratory of Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu 610041 (China); Xiang, Lin; Wu, Yingying [State Key Laboratory of Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu 610041 (China); Department of Oral Implantology, West China Hospital of Stomatology, Sichuan University, Chengdu 610041 (China); Wei, Xiawei [State Key Laboratory of Biotherapy and Laboratory for Aging Research, West China Hospital, Sichuan University, and Collaborative Innovation Center for Biotherapy, Chengdu, Sichuan 610041 (China); Qu, Yili [State Key Laboratory of Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu 610041 (China); Department of Oral Implantology, West China Hospital of Stomatology, Sichuan University, Chengdu 610041 (China); Man, Yi, E-mail: manyi780203@126.com [State Key Laboratory of Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu 610041 (China); Department of Oral Implantology, West China Hospital of Stomatology, Sichuan University, Chengdu 610041 (China)

    2016-10-01

    Collagen membranes have ideal biological and mechanical properties for supporting infiltration and proliferation of osteoblasts and play a vital role in guided bone regeneration (GBR). However, pure collagen can lead to inflammation, resulting in progressive bone resorption. Therefore, a method for regulating the level of inflammatory cytokines at surgical sites is paramount for the healing process. Epigallocatechin-3-gallate (EGCG) is a component extracted from green tea with numerous biological activities including an anti-inflammatory effect. Herein, we present a novel cross-linked collagen membrane containing different concentrations of EGCG (0.0064%, 0.064%, and 0.64%) to regulate the level of inflammatory factors secreted by pre-osteoblast cells; improve cell proliferation; and increase the tensile strength, wettability, and thermal stability of collagen membranes. Scanning electron microscope images show that the surfaces of collagen membranes became smoother and the collagen fiber diameters became larger with EGCG treatment. Measurement of the water contact angle demonstrated that introducing EGCG improved membrane wettability. Fourier transform infrared spectroscopy analyses indicated that the backbone of collagen was intact, and the thermal stability was significant improved in differential scanning calorimetry. The mechanical properties of 0.064% and 0.64% EGCG-treated collagen membranes were 1.5-fold greater than those of the control. The extent of cross-linking was significantly increased, as determined by a 2,4,6-trinitrobenzenesulfonic acid solution assay. The Cell Counting Kit-8 (CCK-8) and live/dead assays revealed that collagen membrane cross-linked by 0.0064% EGCG induced greater cell proliferation than pure collagen membranes. Additionally, real-time polymerase chain reaction and enzyme-linked immunosorbent assay results showed that EGCG significantly affected the production of inflammatory factors secreted by MC3T3-E1 cells. Taken together, our

  4. Absorbed Pb2+ and Cd2+ Ions in Water by Cross-Linked Starch Xanthate

    Directory of Open Access Journals (Sweden)

    Kai Feng

    2017-01-01

    Full Text Available A cross-linked starch xanthate was prepared by graft copolymerization of acrylamide and sodium acrylate onto starch xanthate using potassium persulfate and sodium hydrogen sulfite initiating system and N,N′-methylenebisacrylamide as a cross-linker. As this kind of cross-linked potato starch xanthate can effectively absorb heavy metal ions, it was dispersed in aqueous solutions of divalent heavy metal ions (Pb2+ and Cd2+ to investigate their absorbency by the polymer. Factors that can influence absorbency were investigated, such as the ratio of matrix to monomers, the amount of initiator and cross-linker, pH, and the concentration of metal ions. Results were reached and conclusion was drawn that the best synthetic conditions for the polymer adsorbing Pb2+ and Cd2+ were as follows: the quality ratio of matrix to monomers was 1 : 12 and 1 : 11, the amount of initiator was 2.4% and 3.2% of matrix, and the amount of cross-linker was 12 mg and 13 mg. When the initial concentration of ions was 10 mg/L, the highest quantities of adsorption of Pb2+ and Cd2+ were 47.11 mg/g and 36.55 mg/g. Adsorption mechanism was discussed by using Fourier transform infrared (FTIR spectroscopy, X-ray diffraction (XRD, scanning electron microscope (SEM, Energy Dispersive X-Ray Spectroscopy (EDS test, and adsorption kinetic simulation.

  5. Higher number of pentosidine cross-links induced by ribose does not alter tissue stiffness of cancellous bone

    Energy Technology Data Exchange (ETDEWEB)

    Willems, Nop M.B.K., E-mail: n.willems@acta.nl [Dept. of Orthodontics, Academic Centre for Dentistry Amsterdam (ACTA), University of Amsterdam and VU University, Gustav Mahlerlaan 3004, 1081 LA Amsterdam (Netherlands); Dept. of Oral Cell Biology and Functional Anatomy, MOVE Research Institute, Academic Centre for Dentistry Amsterdam (ACTA), University of Amsterdam and VU University, Gustav Mahlerlaan 3004, 1081 LA Amsterdam (Netherlands); Langenbach, Geerling E.J. [Dept. of Oral Cell Biology and Functional Anatomy, MOVE Research Institute, Academic Centre for Dentistry Amsterdam (ACTA), University of Amsterdam and VU University, Gustav Mahlerlaan 3004, 1081 LA Amsterdam (Netherlands); Stoop, Reinout [Dept. of Metabolic Health Research, TNO, P.O. Box 2215, 2301 CE Leiden (Netherlands); Toonder, Jaap M.J. den [Dept. of Mechanical Engineering, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven (Netherlands); Mulder, Lars [Dept. of Biomedical Engineering, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven (Netherlands); Zentner, Andrej [Dept. of Orthodontics, Academic Centre for Dentistry Amsterdam (ACTA), University of Amsterdam and VU University, Gustav Mahlerlaan 3004, 1081 LA Amsterdam (Netherlands); Everts, Vincent [Dept. of Oral Cell Biology and Functional Anatomy, MOVE Research Institute, Academic Centre for Dentistry Amsterdam (ACTA), University of Amsterdam and VU University, Gustav Mahlerlaan 3004, 1081 LA Amsterdam (Netherlands)

    2014-09-01

    The role of mature collagen cross-links, pentosidine (Pen) cross-links in particular, in the micromechanical properties of cancellous bone is unknown. The aim of this study was to examine nonenzymatic glycation effects on tissue stiffness of demineralized and non-demineralized cancellous bone. A total of 60 bone samples were derived from mandibular condyles of six pigs, and assigned to either control or experimental groups. Experimental handling included incubation in phosphate buffered saline alone or with 0.2 M ribose at 37 °C for 15 days and, in some of the samples, subsequent complete demineralization of the sample surface using 8% EDTA. Before and after experimental handling, bone microarchitecture and tissue mineral density were examined by means of microcomputed tomography. After experimental handling, the collagen content and the number of Pen, hydroxylysylpyridinoline (HP), and lysylpyridinoline (LP) cross-links were estimated using HPLC, and tissue stiffness was assessed by means of nanoindentation. Ribose treatment caused an up to 300-fold increase in the number of Pen cross-links compared to nonribose-incubated controls, but did not affect the number of HP and LP cross-links. This increase in the number of Pen cross-links had no influence on tissue stiffness of both demineralized and nondemineralized bone samples. These findings suggest that Pen cross-links do not play a significant role in bone tissue stiffness. - Highlights: • The assessment of effects of glycation in bone using HPLC, microCT, and nanoindentation • Ribose incubation: 300‐fold increase in the number of pentosidine cross-links • 300‐fold increase in the number of pentosidine cross-links: no changes in bone tissue stiffness.

  6. Sub- T g Cross-Linking of a Polyimide Membrane for Enhanced CO 2 Plasticization Resistance for Natural Gas Separation

    KAUST Repository

    Qiu, Wulin

    2011-08-09

    Decarboxylation-induced thermal cross-linking occurs at elevated temperatures (∼15 °C above glass transition temperature) for 6FDA-DAM:DABA polyimides, which can stabilize membranes against swelling and plasticization in aggressive feed streams. Despite this advantage, such a high temperature might result in collapse of substructure and transition layers in the asymmetric structure of a hollow fibers based on such a material. In this work, the thermal cross-linking of the 6FDA-DAM:DABA at temperatures much below the glass transition temperature (∼387 °C by DSC) was demonstrated. This sub-Tg cross-linking capability enables extension to asymmetric structures useful for large scale membranes. The resulting polymer membranes were characterized by swelling in known solvents for the un-cross-linked materials, TGA analysis, and permeation tests of aggressive gas feed stream at higher pressure. The annealing temperature and time clearly influence the degree of cross-linking of the membranes, and results in a slight difference in selectivity for membranes under various cross-linking conditions. Results indicate that the sub-Tg thermal cross-linking of 6FDA-DAM:DABA dense film membrane can be carried out completely even at a temperature as low as 330 °C. Permeabilities were tested for the polyimide membranes using both pure gases (He, O2, N2, CH4, CO2) and mixed gases (CO2/CH4). The selectivity of the cross-linked membrane can be maintained even under very aggressive CO2 operating conditions that are not possible without cross-linking. Moreover, the plasticization resistance was demonstrated up to 700 psia for pure CO 2 gas or 1000 psia for 50% CO2 mixed gas feeds. © 2011 American Chemical Society.

  7. Influence of cross-link structure, density and mechanical properties in the mesoscale deformation mechanisms of collagen fibrils.

    Science.gov (United States)

    Depalle, Baptiste; Qin, Zhao; Shefelbine, Sandra J; Buehler, Markus J

    2015-12-01

    Collagen is a ubiquitous protein with remarkable mechanical properties. It is highly elastic, shows large fracture strength and enables substantial energy dissipation during deformation. Most of the connective tissue in humans consists of collagen fibrils composed of a staggered array of tropocollagen molecules, which are connected by intermolecular cross-links. In this study, we report a three-dimensional coarse-grained model of collagen and analyze the influence of enzymatic cross-links on the mechanics of collagen fibrils. Two representatives immature and mature cross-links are implemented in the mesoscale model using a bottom-up approach. By varying the number, type and mechanical properties of cross-links in the fibrils and performing tensile test on the models, we systematically investigate the deformation mechanisms of cross-linked collagen fibrils. We find that cross-linked fibrils exhibit a three phase behavior, which agrees closer with experimental results than what was obtained using previous models. The fibril mechanical response is characterized by: (i) an initial elastic deformation corresponding to the collagen molecule uncoiling, (ii) a linear regime dominated by molecule sliding and (iii) the second stiffer elastic regime related to the stretching of the backbone of the tropocollagen molecules until the fibril ruptures. Our results suggest that both cross-link density and type dictate the stiffness of large deformation regime by increasing the number of interconnected molecules while cross-links mechanical properties determine the failure strain and strength of the fibril. These findings reveal that cross-links play an essential role in creating an interconnected fibrillar material of tunable toughness and strength.

  8. Linking Design to Business Strategy Through Functional Analysis

    DEFF Research Database (Denmark)

    Simonsen, Jesper

    1997-01-01

    The paper discusses how designers, conducting design projects in specific organization's, can assure that the design of IT is appropriately linked to the organizations overall business strategy. A case study is presented in the form of a design project in a small public organization. Functional...... analysis was used as a means to clarify how a specific needed information system could support the organization's new business strategy. Using functional analysis in the design project had a powerful effect: it seriously challenged the organization's business strategy and revealed that the system...... to the relation between an organization's IT-projects and its business strategy and by suggesting that it is the responsibility of the designers, conducting design projects, to assure that this task is taken proper care of. Practical guidelines for this purpose are given....

  9. Comparison of hydrazone heterobifunctional cross-linking agents for reversible conjugation of thiol-containing chemistry.

    Science.gov (United States)

    Christie, R James; Anderson, Diana J; Grainger, David W

    2010-10-20

    Reversible covalent conjugation chemistries that allow site- and condition-specific coupling and uncoupling reactions are attractive components in nanotechnologies, bioconjugation methods, imaging, and drug delivery systems. Here, we compare three heterobifunctional cross-linkers, containing both thiol- and amine-reactive chemistries, to form pH-labile hydrazones with hydrazide derivatives of the known and often published water-soluble polymer, poly[N-(2-hydroxypropyl methacrylamide)] (pHPMA), while subsequently coupling thiol-containing molecules to the cross-linker via maleimide addition. Two novel cross-linkers were prepared from the popular heterobifunctional cross-linking agent, succinimidyl-4-(N-maleimidomethyl) cyclohexane-1-carboxylate (SMCC), modified to contain either terminal aldehyde groups (i.e., 1-(N-3-propanal)-4-(N-maleimidomethyl) cyclohexane carboxamide, PMCA) or methylketone groups (i.e., 1-(N-3-butanone)-4-(N-maleimidomethyl) cyclohexane carboxamide, BMCA). A third cross-linking agent was the commercially available N-4-acetylphenyl maleimide (APM). PMCA and BMCA exhibited excellent reactivity toward hydrazide-derivatized pHPMA with essentially complete hydrazone conjugation to polymer reactive sites, while APM coupled only ∼60% of available reactive sites on the polymer despite a 3-fold molar excess relative to polymer hydrazide groups. All polymer hydrazone conjugates bearing these bifunctional agents were then further reacted with thiol-modified tetramethylrhodamine dye, confirming cross-linker maleimide reactivity after initial hydrazone polymer conjugation. Incubation of dye-labeled polymer conjugates in phosphate buffered saline at 37 °C showed that hydrazone coupling resulting from APM exhibited the greatest difference in stability between pH 7.4 and 5.0, with hydrolysis and dye release increased at pH 5.0 over a 24 h incubation period. Polymer conjugates bearing hydrazones formed from cross-linker BMCA exhibited intermediate stability

  10. Viability, Apoptosis, Proliferation, Activation, and Cytokine Secretion of Human Keratoconus Keratocytes after Cross-Linking

    Directory of Open Access Journals (Sweden)

    Xuefei Song

    2015-01-01

    Full Text Available Purpose. The purpose of this study was to determine the impact of cross-linking (CXL on viability, apoptosis, proliferation, activation, and cytokine secretion of human keratoconus (KC keratocytes, in vitro. Methods. Primary KC keratocytes were cultured in DMEM/Ham’s F12 medium supplemented with 10% FCS and underwent UVA illumination (370 nm, 2 J/cm2 during exposure to 0.1% riboflavin and 20% Dextran in PBS. Twenty-four hours after CXL, viability was assessed using Alamar blue assay; apoptosis using APO-DIRECT Kit; proliferation using ELISA-BrdU kit; and CD34 and alpha-smooth muscle actin (α-SMA expression using flow cytometry. Five and 24 hours after CXL, FGFb, HGF, TGFβ1, VEGF, KGF, IL-1β, IL-6, and IL-8 secretion was measured using enzyme-linked-immunoabsorbent assay (ELISA. Results. Following CXL, cell viability and proliferation decreased (P0.06. Five hours after CXL, FGFb secretion increased significantly (P=0.037; however no other cytokine secretion differed significantly from controls after 5 or 24 hours (P>0.12. Conclusions. Cross-linking decreases viability, triggers apoptosis, and inhibits proliferation, without an impact on multipotent hematopoietic stem cell transformation and myofibroblastic transformation of KC keratocytes. CXL triggers FGFb secretion of KC keratocytes transiently (5 hours, normalizing after 24 hours.

  11. Size-dependent release of fluorescent macromolecules and nanoparticles from radically cross-linked hydrogels.

    Science.gov (United States)

    Henke, Matthias; Brandl, Ferdinand; Goepferich, Achim M; Tessmar, Joerg K

    2010-02-01

    Hydrogels play an important role in drug delivery and tissue engineering applications due to their excellent biocompatibility and their variable mechanical and physical properties, which allow their optimization for many different aspects of the intended use. In this study, we examined the suitability of poly(ethylene glycol) (PEG)-based hydrogels as release systems for nanometer-sized drugs or drug carriers, like nanoparticles, using the radically cross-linkable oligo(poly(ethylene glycol)fumarate) (OPF) together with two cross-linking agents. Different fluorescent nanoparticulate probes with respect to size and physical structure were incorporated in the cross-linked hydrogels, and the obtained release profiles were correlated with the physical properties and the chemical structure of the gels, indicating a strong dependence of the release on the chosen PEG prepolymers. The prepared hydrogels were characterized by oscillatory rheometry and swelling experiments. Release experiments as well as diffusion measurements using fluorescence recovery after photobleaching showed the great potential of this type of hydrogels for the preparation of adjustable release systems by altering the molecular weights of the used PEG molecules.

  12. Polymeric redox-responsive delivery systems bearing ammonium salts cross-linked via disulfides

    Directory of Open Access Journals (Sweden)

    Christian Dollendorf

    2013-08-01

    Full Text Available A redox-responsive polycationic system was synthesized via copolymerization of N,N-diethylacrylamide (DEAAm and 2-(dimethylaminoethyl methacrylate (DMAEMA. N,N’-bis(4-chlorobutanoylcystamine was used as disulfide-containing cross-linker to form networks by the quaternization of tertiary amine groups. The insoluble cationic hydrogels become soluble by reduction of disulfide to mercaptanes by use of dithiothreitol (DTT, tris(2-carboxyethylphosphine (TCEP or cysteamine, respectively. The soluble polymeric system can be cross-linked again by using oxygen or hydrogen peroxide under basic conditions. The redox-responsive polymer networks can be used for molecular inclusion and controlled release. As an example, phenolphthalein, methylene blue and reactive orange 16 were included into the network. After treatment with DTT a release of the dye could be recognized. Physical properties of the cross-linked materials, e.g., glass transition temperature (Tg, swelling behavior and cloud points (Tc were investigated. Redox-responsive behavior was further analyzed by rheological measurements.

  13. Biomolecule-recognition gating membrane using biomolecular cross-linking and polymer phase transition.

    Science.gov (United States)

    Kuroki, Hidenori; Ito, Taichi; Ohashi, Hidenori; Tamaki, Takanori; Yamaguchi, Takeo

    2011-12-15

    We present for the first time a biomolecule-recognition gating system that responds to small signals of biomolecules by the cooperation of biorecognition cross-linking and polymer phase transition in nanosized pores. The biomolecule-recognition gating membrane immobilizes the stimuli-responsive polymer, including the biomolecule-recognition receptor, onto the pore surface of a porous membrane. The pore state (open/closed) of this gating membrane depends on the formation of specific biorecognition cross-linking in the pores: a specific biomolecule having multibinding sites can be recognized by several receptors and acts as the cross-linker of the grafted polymer, whereas a nonspecific molecule cannot. The pore state can be distinguished by a volume phase transition of the grafted polymer. In the present study, the principle of the proposed system is demonstrated using poly(N-isopropylacrylamide) as the stimuli-responsive polymer and avidin-biotin as a multibindable biomolecule-specific receptor. As a result of the selective response to the specific biomolecule, a clear permeability change of an order of magnitude was achieved. The principle is versatile and can be applied to many combinations of multibindable analyte-specific receptors, including antibody-antigen and lectin-sugar analogues. The new gating system can find wide application in the bioanalytical field and aid the design of novel biodevices.

  14. Dual Cross-Linked Carboxymethyl Sago Pulp-Gelatine Complex Coacervates for Sustained Drug Delivery

    Directory of Open Access Journals (Sweden)

    Saravanan Muniyandy

    2015-06-01

    Full Text Available In the present work, we report for the first time the complex coacervation of carboxymethyl sago pulp (CMSP with gelatine for sustained drug delivery. Toluene saturated with glutaraldehyde and aqueous aluminum chloride was employed as cross-linkers. Measurements of zeta potential confirm neutralization of two oppositely charged colloids due to complexation, which was further supported by infrared spectroscopy. The coacervates encapsulated a model drug ibuprofen and formed microcapsules with a loading of 29%–56% w/w and an entrapment efficiency of 85%–93% w/w. Fresh coacervates loaded with drug had an average diameter of 10.8 ± 1.93 µm (n = 3 ± s.d.. The coacervates could encapsulate only the micronized form of ibuprofen in the absence of surfactant. Analysis through an optical microscope evidenced the encapsulation of the drug in wet spherical coacervates. Scanning electron microscopy revealed the non-spherical geometry and surface roughness of dried drug-loaded microcapsules. X-ray diffraction, differential scanning calorimetry and thermal analysis confirmed intact and crystalline ibuprofen in the coacervates. Gas chromatography indicated the absence of residual glutaraldehyde in the microcapsules. Dual cross-linked microcapsules exhibited a slower release than mono-cross-linked microcapsules and could sustain the drug release over the period of 6 h following Fickian diffusion.

  15. Cross-linked self-assembled micelle based nanosensor for intracellular pH measurements

    DEFF Research Database (Denmark)

    Ek, Pramod Kumar; Søndergaard, Rikke Vicki; Windschiegl, Barbara

    2014-01-01

    A micelle based nanosensor was synthesized and investigated as a ratiometric pH sensor for use in measurements in living cells by fluorescent microscopy. The nanosensor synthesis was based on self-assembly of an amphiphilic triblock copolymer, which was chemically cross-linked after micelle forma...... provided a sensor with a very broad measurement range that seems to be influenced by the chemical design of the sensor. Cell experiments show that the sensor is capable of monitoring the pH distributions in HeLa cells.......A micelle based nanosensor was synthesized and investigated as a ratiometric pH sensor for use in measurements in living cells by fluorescent microscopy. The nanosensor synthesis was based on self-assembly of an amphiphilic triblock copolymer, which was chemically cross-linked after micelle...... formation. The copolymer, poly(ethylene glycol)-b-poly(2-aminoethyl methacrylate)-b-poly(styrene) (PEG-b-PAEMA-b-PS), was synthesized by isolated macroinitiator atom transfer radical polymerization that forms micelles spontaneously in water. The PAEMA shell of the micelle was hereafter cross...

  16. Effects of Composition of Iron-Cross-Linked Alginate Hydrogels for Cultivation of Human Dermal Fibroblasts

    Directory of Open Access Journals (Sweden)

    Ikuko Machida-Sano

    2012-01-01

    Full Text Available We investigated the suitability of ferric-ion-cross-linked alginates (Fe-alginate with various proportions of L-guluronic acid (G and D-mannuronic acid (M residues as a culture substrate for human dermal fibroblasts. High-G and high-M Fe-alginate gels showed comparable efficacy in promoting initial cell adhesion and similar protein adsorption capacities, but superior cell proliferation was observed on high-G than on high-M Fe-alginate as culture time progressed. During immersion in culture medium, high-G Fe-alginate showed little change in gel properties in terms of swelling and polymer content, but the properties of high-M Fe-alginate gel were altered due to loss of ion cross-linking. However, the degree of cell proliferation on high-M Fe-alginate gel was improved after it had been stabilized by immersion in culture medium until no further changes occurred. These results suggest that the mode of cross-linkage between ferric ions and alginate differs depending on alginate composition and that the major factor giving rise to differences in cell growth on the two types of Fe-alginate films is gel stability during culture, rather than swelling of the original gel, polymer content, or protein adsorption ability. Our findings may be useful for extending the application of Fe-alginate to diverse biomedical fields.

  17. Nanomechanical characterization and molecular mechanism study of nanoparticle reinforced and cross-linked chitosan biopolymer.

    Science.gov (United States)

    Rath, Amrita; Mathesan, Santhosh; Ghosh, Pijush

    2015-03-01

    Chitosan (CS) is a biomaterial that offers many sophisticated and innovative applications in the biomedical field owing to its excellent characteristics of biodegradability, biocompatibility and non-toxicity. However, very low mechanical properties of chitosan polymer impose restriction on its further development. Cross-linking and nanoparticle reinforcement are the two possible methods to improve the mechanical properties of chitosan films. In this research, these two methods are adopted individually by using tripolyphosphate as cross-linker and nano-hydroxyapatite as particle reinforcement. The nanomechanical characterizations under static loading conditions are performed on these modified chitosan films. It is observed that nanoparticle reinforcement provided necessary mechanical properties such as ductility and modulus. The mechanisms involved in improvement of mechanical properties due to particle reinforcement are studied by molecular dynamics (MD). Further, improvement in mechanical properties due to combination of particle reinforcement and cross-linking agent with chitosan is investigated. The stress relaxation behavior for all these types of films is characterized under dynamic loading conditions using dynamic mechanical analysis (nanoDMA) experiment. A viscoelastic solid like response is observed for all types of film with modulus relaxing by 3-6% of its initial value. A suitable generalized Maxwell model is fitted with the obtained viscoelastic response of these films. The response to nano-scratch behavior is also studied for particle reinforced composite films.

  18. Comparative Study of One-Step Cross-Linked Electrospun Chitosan-Based Membranes

    Directory of Open Access Journals (Sweden)

    Yanet E. Aguirre-Chagala

    2017-01-01

    Full Text Available Chitosan membranes are widely applied for tissue engineering; however, a major drawback is their low resistance in aqueous phases and therefore the structure collapses impeding their long-term use. Although there is extensive research, because of chitosan’s importance as a biomaterial, studies involving chitosan-based membranes are still needed. Herein, a detailed investigation of diverse chemical routes to cross-link fibers in situ by electrospinning process is described. In case of using genipin as cross-linker, a close relationship with the content and the mean diameter values is reported, suggesting a crucial effect over the design of nanostructures. Also, the physical resistance is enhanced for the combination of two types of methods, such as chemical and physical methods. Cross-linked fibers upon exposure to long wave ultraviolet A (UVA light change their morphology, but not their chemical composition. When they are incubated in aqueous phase for 70 days, they show an extensive improvement of their macrostructural integrity which makes them attractive candidates for tissue engineering application. As a result, the thermal properties of these materials reveal less crystallinity and higher temperature of degradation.

  19. 1,2,3,4-Diepoxybutane-Induced DNA-Protein Cross-Linking in Human Fibrosarcoma (HT1080) Cells

    OpenAIRE

    2013-01-01

    1,2,3,4-diepoxybutane (DEB) is the key carcinogenic metabolite of 1,3-butadiene (BD), an important industrial and environmental chemical present in urban air and in cigarette smoke. DEB is a genotoxic bis-electrophile capable of cross-linking cellular biomolecules to form DNA-DNA and DNA-protein cross-links (DPCs). In the present work, mass spectrometry-based proteomics was employed to characterize DEB-mediated DNA-protein cross-linking in human fibrosarcoma (HT1080) cells. Over 150 proteins ...

  20. Syntheses of DNA Duplexes That Contain a N4C-alkyl-N4C Interstrand Cross-Link

    Science.gov (United States)

    Miller, Paul S.

    2011-01-01

    A simple procedure is described for preparing short DNA duplexes that contain a single N4C-alkyl-N4C interstrand cross-link. The synthesis is carried out on an automated DNA synthesizer using standard phosphoramidite chemistry. The cross-link is introduced during the synthesis of the duplex. The method can be used to prepare mg quantities of cross-linked duplexes suitable for physical studies and for the preparation of larger DNA molecules that can be used as substrates to study DNA repair in whole cell extracts and in living cells in culture. PMID:21400705