WorldWideScience

Sample records for chemical cross-linking reagent

  1. Chemical cross-linking with thiol-cleavable reagents combined with differential mass spectrometric peptide mapping--a novel approach to assess intermolecular protein contacts

    DEFF Research Database (Denmark)

    Bennett, K L; Kussmann, M; Björk, P

    2000-01-01

    with the thiol-cleavable cross-linker 3,3'-dithio-bis(succinimidylproprionate) (DTSSP), proteolytically digested with trypsin and analyzed by MALDI-MS peptide mapping. Comparison of the peptide maps obtained from digested cross-linked ParR dimers in the presence and absence of a thiol reagent strongly supported...... a "head-to-tail" arrangement of the monomers in the dimeric complex. Glycoprotein fusion constructs CD28-IgG and CD80-Fab were cross-linked in vitro by DTSSP, characterized by nonreducing SDS-PAGE, digested in situ with trypsin and analyzed by MALDI-MS peptide mapping (+/- thiol reagent). The data......-linking combined with differential MALDI-MS peptide mapping (+ thiol reagent) enabled localization of the interface region(s) of the complexes studied and clearly demonstrates the utility of such an approach to obtain structural information on interacting noncovalent complexes....

  2. 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...

  3. An amino acid-based heterofunctional cross-linking reagent.

    Science.gov (United States)

    Lelle, Marco; Peneva, Kalina

    2014-05-01

    We describe the synthesis and characterization of a new lysine-based heterofunctional cross-linking reagent. It carries two readily available aminooxy functionalities and an activated and protected thiol group that is capable of generating reducible disulfides, the former enable bioorthogonal modification of ketones and aldehydes by the formation of an oxime bond. The efficacy of the linker was proven by coupling two doxorubicin molecules to the functionalized amino acid core and the subsequent bioconjugation of this drug conjugate with a thiolated antibody.

  4. Cross-linking of the electron-transfer flavoprotein to electron-transfer flavoprotein-ubiquinone oxidoreductase with heterobifunctional reagents.

    OpenAIRE

    Steenkamp, D J

    1988-01-01

    The mitochondrial electron-transfer flavoprotein (ETF) is a heterodimer containing only one FAD. In previous work on the structure-function relationships of ETF, its interaction with the general acyl-CoA dehydrogenase (GAD) was studied by chemical cross-linking with heterobifunctional reagents [D. J. Steenkamp (1987) Biochem. J. 243, 519-524]. GAD whose lysine residues were substituted with 3-(2-pyridyldithio)propionyl groups was preferentially cross-linked to the small subunit of ETF, the ly...

  5. Kojak: efficient analysis of chemically cross-linked protein complexes.

    Science.gov (United States)

    Hoopmann, Michael R; Zelter, Alex; Johnson, Richard S; Riffle, Michael; MacCoss, Michael J; Davis, Trisha N; Moritz, Robert L

    2015-05-01

    Protein chemical cross-linking and mass spectrometry enable the analysis of protein-protein interactions and protein topologies; however, complicated cross-linked peptide spectra require specialized algorithms to identify interacting sites. The Kojak cross-linking software application is a new, efficient approach to identify cross-linked peptides, enabling large-scale analysis of protein-protein interactions by chemical cross-linking techniques. The algorithm integrates spectral processing and scoring schemes adopted from traditional database search algorithms and can identify cross-linked peptides using many different chemical cross-linkers with or without heavy isotope labels. Kojak was used to analyze both novel and existing data sets and was compared to existing cross-linking algorithms. The algorithm provided increased cross-link identifications over existing algorithms and, equally importantly, the results in a fraction of computational time. The Kojak algorithm is open-source, cross-platform, and freely available. This software provides both existing and new cross-linking researchers alike an effective way to derive additional cross-link identifications from new or existing data sets. For new users, it provides a simple analytical resource resulting in more cross-link identifications than other methods.

  6. Thermoresponsive Injectable Hydrogels Cross-Linked by Native Chemical Ligation

    NARCIS (Netherlands)

    Boere, Kristel W M; Soliman, Bram G.; Rijkers, Dirk T S; Hennink, Wim E.; Vermonden, Tina

    2014-01-01

    Temperature-induced physical gelation was combined with native chemical ligation (NCL) as a chemical cross-linking mechanism to yield rapid network formation and mechanically strong hydrogels. To this end, a novel monomer N-(2-hydroxypropyl)methacrylamide-cysteine (HPMA-Cys) was synthesized that

  7. Adding chemical cross-links to a physical hydrogel

    National Research Council Canada - National Science Library

    Paradossi, Gaio; Finelli, Ivana; Cerroni, Barbara; Chiessi, Ester

    2009-01-01

    ... hydrogels. Introduction of chemical cross-links in the 3D structure of the synergistic hydrogel removes this behaviour, adding new features to the swelling and to the viscoelastic properties of the cured hydrogel. The use of epichlorohydrin as low molecular weight cross-linker does not impact unfavourably on the viability of NIH 3T3 fibroblasts.

  8. 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. Copyright © 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

  9. Adding Chemical Cross-Links to a Physical Hydrogel

    Directory of Open Access Journals (Sweden)

    Ester Chiessi

    2009-09-01

    Full Text Available Synergistic hydrogels are often encountered in polysaccharide mixtures widely used in food and biopharma products. The xanthan and konjac glucomannan pair provides one of the most studied synergistic hydrogels. Recently we showed that the junction zones stabilizing the 3D structure of this gel are present as macromolecular complexes in solution formed by the partially depolymerised polysaccharidic chains. The non-covalent interactions stabilizing the structure of the polysaccharidic complex cause the melting of the ordered structure of the complex in the solution and of the hydrogels. Introduction of chemical cross-links in the 3D structure of the synergistic hydrogel removes this behaviour, adding new features to the swelling and to the viscoelastic properties of the cured hydrogel. The use of epichlorohydrin as low molecular weight cross-linker does not impact unfavourably on the viability of NIH 3T3 fibroblasts.

  10. Chemically cross-linked and grafted cyclodextrin hydrogels: from nanostructures to drug-eluting medical devices.

    Science.gov (United States)

    Concheiro, Angel; Alvarez-Lorenzo, Carmen

    2013-08-01

    The unique ability of cyclodextrins (CDs) to form inclusion complexes can be transmitted to polymeric networks in which CDs are chemically grafted or cross-linked. Combination of CDs and hydrogels in a single material leads to synergic properties: the hydrophilic network enhances biocompatibility and prevents dilution in the physiological medium increasing the stability of the inclusion complexes, while CDs finely tune the mechanical features and the stimuli-responsiveness and provide affinity-based regulation of drug loading and release. Therefore, CD-functionalized materials are opening new perspectives in pharmacotherapy, emerging as advanced delivery systems (DDS) for hydrophobic and hydrophilic drugs to be administered via almost any route. Medical devices (catheters, prosthesis, vascular grafts, bone implants) can also benefit from surface grafting or thermofixation of CDs. The present review focuses on the approaches tested to synthesize nano- to macro-size covalently cross-linked CD networks: i) direct cross-linking through condensation with di- or multifunctional reagents, ii) copolymerization of CD derivatives with acrylic/vinyl monomers, and iii) grafting of CDs to preformed medical devices. Examples of the advantages of having the CDs chemically bound among themselves and to substrates are provided and their applicability in therapeutics discussed. Copyright © 2013 Elsevier B.V. All rights reserved.

  11. Structure and dynamics of dark-state bovine rhodopsin revealed by chemical cross-linking and high-resolution mass spectrometry.

    Science.gov (United States)

    Jacobsen, Richard B; Sale, Kenneth L; Ayson, Marites J; Novak, Petr; Hong, Joohee; Lane, Pamela; Wood, Nichole L; Kruppa, Gary H; Young, Malin M; Schoeniger, Joseph S

    2006-06-01

    Recent work using chemical cross-linking to define interresidue distance constraints in proteins has shown that these constraints are useful for testing tertiary structural models. We applied this approach to the G-protein-coupled receptor bovine rhodopsin in its native membrane using lysine- and cysteine-targeted bifunctional cross-linking reagents. Cross-linked proteolytic peptides of rhodopsin were identified by combined liquid chromatography and FT-ICR mass spectrometry with automated data-reduction and assignment software. Tandem mass spectrometry was used to verify cross-link assignments and locate the exact sites of cross-link attachment. Cross-links were observed to form between 10 pairs of residues in dark-state rhodopsin. For each pair, cross-linkers with a range of linker lengths were tested to determine an experimental distance-of-closest-approach (DCA) between reactive side-chain atoms. In all, 28 cross-links were identified using seven different cross-linking reagents. Molecular mechanics procedures were applied to published crystal structure data to calculate energetically achievable theoretical DCAs between reactive atoms without altering the position of the protein backbone. Experimentally measured DCAs are generally in good agreement with the theoretical DCAs. However, a cross-link between C316 and K325 in the C-terminal region cannot be rationalized by DCA simulations and suggests that backbone reorientation relative to the crystal coordinates occurs on the timescale of cross-linking reactions. Biochemical and spectroscopic data from other studies have found that the C-terminal region is highly mobile in solution and not fully represented by X-ray crystallography data. Our results show that chemical cross-linking can provide reliable three-dimensional structural information and insight into local conformational dynamics in a membrane protein.

  12. Influence of different chemical cross-linking treatments on the properties of bovine pericardium and collagen.

    Science.gov (United States)

    Jorge-Herrero, E; Fernández, P; Turnay, J; Olmo, N; Calero, P; García, R; Freile, I; Castillo-Olivares, J L

    1999-03-01

    The use of biological materials in the construction of bioprostheses requires the application of different chemical or physical procedures to improve the mechanical performance of the material without producing any undesirable effects. A number of cross-linking methods have been tested in biological tissues composed mainly of collagen. The basis for most of them is the use of glutaraldehyde (GA), which acts on the Lys or Hyl residues. We have studied the effects of alternative chemical treatments: diphenylphosphorylazide (DPPA) and ethyldimethylaminopropyl carbodiimide (EDAC). Their mechanism of action is based on the activation of the carboxyl groups, which then permits their cross-linking to amino groups. As a control, we employed conventional treatment with GA, applying it to bovine pericardium and collagen membranes removed from bovine pericardium. The analysis of the Lys and Hyl residues showed that DPPA and EDAC produced 50% of the chemical change provoked by GA. This value was even lower in the trials with collagen. In terms of the resistance to collagenase degradation, chemical cross-linking with GA provided much greater protection in both materials (3.81 +/- 3.47 nmol of amino acid/mg dry tissue for pericardium and 4.41 +/- 1.13 nmol of amino acid/mg dry tissue for collagen). Treatment with DPPA also protected pericardium (13.11 +/- 6.57 nmol amino acid/mg dry tissue) although the values for collagen was lower (50.0 +/- 32.4 nmol amino acid/mg dry tissue). Treatment with EDAC was much less protective than the other two chemical reagents (43.28 +/- 17.4 and 55.85 +/- 14.57 nmol amino acid/mg dry tissue for pericardium and collagen, respectively). The degree of tissue calcification after implantation of the chemically treated materials into young rats was considerably greater for GA and DPPA (32.9 +/- 18.8 and 36.3 +/- 13.3 mg g(-1) dry tissue, respectively) than with EDAC (18.0 +/- 7.2 mg g(-1) dry tissue; P collagen levels in samples treated with GA or

  13. Chemically cross-linked silk fibroin hydrogel with enhanced elastic properties, biodegradability, and biocompatibility.

    Science.gov (United States)

    Kim, Min Hee; Park, Won Ho

    2016-01-01

    In this study, the synthesis of silk fibroin (SF) hydrogel via chemical cross-linking reactions of SF due to gamma-ray (γ-ray) irradiation was investigated, as were the resultant hydrogel's properties. Two different hydrogels were investigated: physically cross-linked SF hydrogel and chemically cross-linked SF hydrogel irradiated at different doses of γ-rays. The effects of the irradiation dose and SF concentration on the hydrogelation of SF were examined. The chemically cross-linked SF hydrogel was compared with the physically cross-linked one with regard to secondary structure and gel strength. Furthermore, the swelling behavior, crystallinity, and biodegradation of the SF hydrogels were characterized. To assay cell proliferation, the cell viability of human mesenchymal stem cells on the lyophilized SF hydrogel scaffolds was evaluated, and no significant cytotoxicity against human mesenchymal stem cells was observed.

  14. DNA-protein cross-links produced by various chemicals in cultured human lymphoma cells.

    Science.gov (United States)

    Costa, M; Zhitkovich, A; Harris, M; Paustenbach, D; Gargas, M

    1997-04-11

    Chemicals such as cis-platinum, formaldehyde, chromate, copper, and certain arsenic compounds have been shown to produce DNA-protein cross-links in human in vitro cell systems at high doses, such as those in the cytotoxic range. Thus far there have only been a limited number of other chemicals evaluated for their ability to produce cross-links. The purpose of the work described here was to evaluate whether select industrial chemicals can form DNA-protein cross-links in human cells in vitro. We evaluated acetaldehyde, acrolein, diepoxybutane, paraformaldehyde, 2-furaldehyde, propionaldehyde, chloroacetaldehyde, sodium arsenite, and a deodorant tablet [Mega Blue; hazardous component listed as tris(hydroxymethyl)nitromethane]. Short- and long-term cytotoxicity was evaluated and used to select appropriate doses for in vitro testing. DNA-protein cross-linking was evaluated at no fewer than three doses and two cell lysate washing temperatures (45 and 65 degrees C) in Epstein-Barr virus (EBV) human Burkitt's lymphoma cells. The two washing temperatures were used to assess the heat stability of the DNA-protein cross-link, 2-Furaldehyde, acetaldehyde, and propionaldehyde produced statistically significant increases in DNA-protein cross-links at washing temperatures of 45 degrees C, but not 65 degrees C, and at or above concentrations of 5, 17.5, and 75 mM, respectively. Acrolein, diepoxybutane, paraformaldehyde, and Mega Blue produced statistically significant increases in DNA-protein cross-links washed at 45 and 65 degrees C at or above concentrations of 0.15 mM, 12.5 mM, 0.003%, and 0.1%, respectively. Sodium arsenite and chloroacetaldehyde did not produce significantly increased DNA-protein cross-links at either temperature nor at any dose tested. Excluding paraformaldehyde and 2-furaldehyde treatments, significant increases in DNA-protein cross-links were observed only at doses that resulted in complete cell death within 4 d following dosing. This work demonstrates that

  15. Xlink-identifier: an automated data analysis platform for confident identifications of chemically cross-linked peptides using tandem mass spectrometry.

    Science.gov (United States)

    Du, Xiuxia; Chowdhury, Saiful M; Manes, Nathan P; Wu, Si; Mayer, M Uljana; Adkins, Joshua N; Anderson, Gordon A; Smith, Richard D

    2011-03-04

    Chemical cross-linking combined with mass spectrometry provides a powerful method for identifying protein-protein interactions and probing the structure of protein complexes. A number of strategies have been reported that take advantage of the high sensitivity and high resolution of modern mass spectrometers. Approaches typically include synthesis of novel cross-linking compounds, and/or isotopic labeling of the cross-linking reagent and/or protein, and label-free methods. We report Xlink-Identifier, a comprehensive data analysis platform that has been developed to support label-free analyses. It can identify interpeptide, intrapeptide, and deadend cross-links as well as underivatized peptides. The software streamlines data preprocessing, peptide scoring, and visualization and provides an overall data analysis strategy for studying protein-protein interactions and protein structure using mass spectrometry. The software has been evaluated using a custom synthesized cross-linking reagent that features an enrichment tag. Xlink-Identifier offers the potential to perform large-scale identifications of protein-protein interactions using tandem mass spectrometry.

  16. Immunogenic Display of Purified Chemically Cross-Linked HIV-1 Spikes

    Science.gov (United States)

    Leaman, Daniel P.; Lee, Jeong Hyun; Ward, Andrew B.

    2015-01-01

    ABSTRACT HIV-1 envelope glycoprotein (Env) spikes are prime vaccine candidates, at least in principle, but suffer from instability, molecular heterogeneity and a low copy number on virions. We anticipated that chemical cross-linking of HIV-1 would allow purification and molecular characterization of trimeric Env spikes, as well as high copy number immunization. Broadly neutralizing antibodies bound tightly to all major quaternary epitopes on cross-linked spikes. Covalent cross-linking of the trimer also stabilized broadly neutralizing epitopes, although surprisingly some individual epitopes were still somewhat sensitive to heat or reducing agent. Immunodepletion using non-neutralizing antibodies to gp120 and gp41 was an effective method for removing non-native-like Env. Cross-linked spikes, purified via an engineered C-terminal tag, were shown by negative stain EM to have well-ordered, trilobed structure. An immunization was performed comparing a boost with Env spikes on virions to spikes cross-linked and captured onto nanoparticles, each following a gp160 DNA prime. Although differences in neutralization did not reach statistical significance, cross-linked Env spikes elicited a more diverse and sporadically neutralizing antibody response against Tier 1b and 2 isolates when displayed on nanoparticles, despite attenuated binding titers to gp120 and V3 crown peptides. Our study demonstrates display of cross-linked trimeric Env spikes on nanoparticles, while showing a level of control over antigenicity, purity and density of virion-associated Env, which may have relevance for Env based vaccine strategies for HIV-1. IMPORTANCE The envelope spike (Env) is the target of HIV-1 neutralizing antibodies, which a successful vaccine will need to elicit. However, native Env on virions is innately labile, as well as heterogeneously and sparsely displayed. We therefore stabilized Env spikes using a chemical cross-linker and removed non-native Env by immunodepletion with non

  17. Construction and application of a photo-cross-linked chemical array.

    Science.gov (United States)

    Kondoh, Yasumitsu; Honda, Kaori; Osada, Hiroyuki

    2015-01-01

    Chemical array technology is a powerful tool for high-throughput screening of small-molecule ligand-protein interactions. A chemical array is a collection of small-molecule compounds spotted and immobilized on a glass slide surface, providing a multiplex platform to identify small-molecule compounds binding to a protein of interest in high-throughput screening. Several research groups have developed a variety of methods for the immobilization of small molecules onto a solid matrix. We have developed a unique photo-cross-linked chemical array for immobilizing small molecules in a functional-group-independent manner. In this chapter, we describe in detail a protocol for the construction of a photo-cross-linked chemical array and its application for ligand screening by using a tag-fused protein.

  18. Mitochondrial protein interactome elucidated by chemical cross-linking mass spectrometry.

    Science.gov (United States)

    Schweppe, Devin K; Chavez, Juan D; Lee, Chi Fung; Caudal, Arianne; Kruse, Shane E; Stuppard, Rudy; Marcinek, David J; Shadel, Gerald S; Tian, Rong; Bruce, James E

    2017-02-14

    Mitochondrial protein interactions and complexes facilitate mitochondrial function. These complexes range from simple dimers to the respirasome supercomplex consisting of oxidative phosphorylation complexes I, III, and IV. To improve understanding of mitochondrial function, we used chemical cross-linking mass spectrometry to identify 2,427 cross-linked peptide pairs from 327 mitochondrial proteins in whole, respiring murine mitochondria. In situ interactions were observed in proteins throughout the electron transport chain membrane complexes, ATP synthase, and the mitochondrial contact site and cristae organizing system (MICOS) complex. Cross-linked sites showed excellent agreement with empirical protein structures and delivered complementary constraints for in silico protein docking. These data established direct physical evidence of the assembly of the complex I-III respirasome and enabled prediction of in situ interfacial regions of the complexes. Finally, we established a database and tools to harness the cross-linked interactions we observed as molecular probes, allowing quantification of conformation-dependent protein interfaces and dynamic protein complex assembly.

  19. Chemical and structural characterization of interstrand cross-links formed between abasic sites and adenine residues in duplex DNA

    Science.gov (United States)

    Price, Nathan E.; Catalano, Michael J.; Liu, Shuo; Wang, Yinsheng; Gates, Kent S.

    2015-01-01

    A new type of interstrand DNA–DNA cross-link between abasic (Ap) sites and 2′-deoxyadenosine (dA) residues was recently reported, but the chemical structure and properties of this lesion were not rigorously established. Here we characterized the nucleoside cross-link remnant released by enzymatic digestion of duplex DNA containing the dA-Ap cross-link. A synthetic standard was prepared for the putative nucleoside cross-link remnant 6 in which the anomeric carbon of the 2-deoxyribose residue was connected to the exocyclic N6-amino group of dA. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis showed that the synthetic material 6 matched the authentic cross-link remnant released by enzymatic digestion of cross-linked DNA. These findings establish the chemical structure of the dA-Ap cross-link released from duplex DNA and may provide methods for the detection of this lesion in cellular DNA. Both the nucleoside cross-link remnant 6 and the cross-link in duplex DNA were quite stable at pH 7 and 37°C, suggesting that the dA-Ap cross-link could be a persistent lesion with the potential to block the action of various DNA processing enzymes. PMID:25779045

  20. 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 ...

  1. Cross-link formation between mutant galectins of Caenorhabditis elegans with a substituted cysteine residue and asialofetuin via a photoactivatable bifunctional reagent.

    Science.gov (United States)

    Tamura, Mayumi; Takeuchi, Tomoharu; Nonaka, Takamasa; Kasai, Ken-Ichi; Arata, Yoichiro

    2011-01-01

    LEC-1 is the first tandem repeat-type galectin isolated from an animal system; this galectin has two carbohydrate recognition domains in a single polypeptide chain. Because its two lectin domains have different sugar-binding profiles, these domains are thought to interact with different carbohydrate ligands. In our previous study, we showed that a mutant of LEC-1 in which a cysteine residue was introduced at a unique position in the N-terminal lectin domain (Nh) can be cross-linked with a model glycoprotein ligand, bovine asialofetuin, by using a bifunctional photoactivatable cross-linking reagent, benzophenone-4-maleimide. In the present work, we applied the same procedure to the C-terminal lectin domain (Ch) of LEC-1. Cross-linked products were formed in the cases of two mutants in which a cysteine residue was introduced at Lys¹⁷⁷ and Ser²⁶⁸, respectively. This method is very useful for capturing and assigning endogenous ligand glycoconjugates with relatively low affinities to each carbohydrate recognition domain of the whole tandem repeat-type galectin molecule.

  2. Identification of PDGF-BB binding to thymosin β4 by chemical cross-linking.

    Science.gov (United States)

    Knop, Jana; App, Christine; Huff, Thomas; Iavarone, Federica; Castagnola, Massimo; Hannappel, Ewald

    2015-01-01

    The purpose of our work was to identify unknown interaction partners of thymosin β4 (Tβ4). It was suggested that Tβ4 could be an antifibrotic drug for treatment of liver fibrogenesis, because Tβ4 prevents the platelet-derived growth factor-BB (PDGF-BB)-induced activation of hepatic stellate cells (HSCs). Very little information is available how Tβ4 counteracts the PDGF-BB-induced activation of HSCs. We propose the hypothesis that Tβ4 could bind directly to PDGF-BB and thereby reduce the concentration of free PDGF-BB available for binding to the PDGF-β receptor. To prove our suggestion of a direct interaction between Tβ4 and PDGF-BB, we carried out chemical as well as photochemical cross-linking experiments between the two pure proteins in vitro. We identified an interaction between Tβ4 and PDGF-BB by 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) cross-linking as well as through biotin label transfer using a bifunctional photoactivatable derivative of Tβ4. In an in vitro system, PDGF-BB was identified as the first extracellular partner interacting with Tβ4. This interaction could influence PDGF-BB binding to its receptor and abolish PDGF-BB-related effects. Direct interaction of Tβ4 with extracellular factors should be considered as a potential mechanism to explain the pleiotropic effects of β-thymosins.

  3. Rate effect in the fracture of rubbers and chemically cross-linked gels.

    Science.gov (United States)

    Tanaka, Fumihiko

    2014-10-07

    Stationary crack propagation in rubbers and chemically cross-linked gels is studied by a new molecular theory of fracture in polymer networks. The fracture energy G (energy required to create a unit free surface by fracture) as a function of the crack velocity V is shown to obey, when measured in the unit of νlkBT, a master curve as a function of the dimensionless velocity 2tan θV/lβ0(T), where ν is the number density of the network chains, T is absolute temperature, θ is the angle of the crack tip, l is the mean distance between the adjacent cross-links, and β0(T) is the scission rate of the chains. The slope of the master curve in logarithmic scale depends on the nature of chain rupture; it takes a small value 0.16-0.2 in the low velocity region, and exhibits a crossover to the three times larger value 0.5-0.6 in the high velocity region. The ultimate strength G0 as defined by the fracture energy in the limit of zero crack velocity is obtained as a function of the molecular weight of the network chain, the bond energy, and temperature. The theoretical model is applied specifically to peeling and tearing experiments of rubbers and gels to study how the velocity affects the fracture energy in different geometry of network breakage. All results are qualitatively compared with the data reported in the literature.

  4. Characterization of Protein Complexes Using Chemical Cross-Linking Coupled Electrospray Mass Spectrometry.

    Science.gov (United States)

    Cummins, Timothy D; Sapkota, Gopal P

    2017-10-25

    Identification and characterization of large protein complexes is a mainstay of biochemical toolboxes. Utilization of cross-linking chemicals can facilitate the capture and identification of transient or weak interactions of a transient nature (Huang and Kim, PloS One 8:e61430, 2013; Gao et al., J Vis Exp doi: 10.3791/51387, 2014). Here we describe a detailed methodology for a cell culture-based proteomic approach. We describe the generation of cells stably expressing green fluorescent protein (GFP)-tagged proteins under the tetracycline-inducible promoter and subsequent proteomic analysis of GFP-interacting proteins. We include a list of proteins that were identified as interactors of GFP.

  5. Ligand-induced movements of inner transmembrane helices of Glut1 revealed by chemical cross-linking of di-cysteine mutants.

    Directory of Open Access Journals (Sweden)

    Mike Mueckler

    Full Text Available The relative orientation and proximity of the pseudo-symmetrical inner transmembrane helical pairs 5/8 and 2/11 of Glut1 were analyzed by chemical cross-linking of di-cysteine mutants. Thirteen functional di-cysteine mutants were created from a C-less Glut1 reporter construct containing cysteine substitutions in helices 5 and 8 or helices 2 and 11. The mutants were expressed in Xenopus oocytes and the sensitivity of each mutant to intramolecular cross-linking by two homobifunctional thiol-specific reagents was ascertained by protease cleavage followed by immunoblot analysis. Five of 9 mutants with cysteine residues predicted to lie in close proximity to each other were susceptible to cross-linking by one or both reagents. None of 4 mutants with cysteine substitutions predicted to lie on opposite faces of their respective helices was susceptible to cross-linking. Additionally, the cross-linking of a di-cysteine pair (A70C/M420C, helices 2/11 predicted to lie near the exoplasmic face of the membrane was stimulated by ethylidene glucose, a non-transported glucose analog that preferentially binds to the exofacial substrate-binding site, suggesting that the binding of this ligand stimulates the closure of helices at the exoplasmic face of the membrane. In contrast, the cross-linking of a second di-cysteine pair (T158C/L325, helices 5/8, predicted to lie near the cytoplasmic face of the membrane, was stimulated by cytochalasin B, a glucose transport inhibitor that competitively inhibits substrate efflux, suggesting that this compound recruits the transporter to a conformational state in which closure of inner helices occurs at the cytoplasmic face of the membrane. This observation provides a structural explanation for the competitive inhibition of substrate efflux by cytochalasin B. These data indicate that the binding of competitive inhibitors of glucose efflux or influx induce occluded states in the transporter in which substrate is excluded from

  6. Identification and characterization of a pituitary corticotropin-releasing factor binding protein by chemical cross-linking

    DEFF Research Database (Denmark)

    Nishimura, E; Billestrup, Nils; Perrin, M

    1987-01-01

    A corticotropin-releasing factor (CRF) binding protein has been identified based on the chemical cross-linking of ovine [Nle21,m-125I-Tyr32]CRF (125I-oCRF) to bovine anterior pituitary membranes using disuccinimidyl suberate (DSS). The apparent molecular weight of the cross-linked complex...... appeared to have a molecular weight of approximately 70,000. The cross-linking was specific since an excess (1 microM) of an unrelated peptide (insulin) did not affect the appearance of the Mr 75,000 band. The concentration of CRF required to inhibit cross-linking by 50% was found to be similar...... to that determined for bovine pituitary CRF receptors by radioreceptor assay. The nonhydrolyzable GTP analogue 5'-guanylylimidodiphosphate dose dependently inhibited the cross-linking of 125I-oCRF to the Mr 70,000 protein. 50 nM of the inactive CRF analogue, [Ala14]oCRF, had no effect on the cross-linking...

  7. Effect of cross-linking with riboflavin and ultraviolet A on the chemical bonds and ultrastructure of human sclera.

    Science.gov (United States)

    Jung, Gyeong-Bok; Lee, Hui-Jae; Kim, Ji-Hye; Lim, Jin Ik; Choi, Samjin; Jin, Kyung-Hyun; Park, Hun-Kuk

    2011-12-01

    This study examined the effect of the cross-linking with riboflavin-ultraviolet A (UVA) irradiation on the chemical bonds and ultrastructural changes of human sclera tissues using Raman spectroscopy and atomic force microscopy (AFM). Raman spectroscopy of the normal and cross-linked human sclera tissue revealed different types of the riboflavin-UVA and collagen interactions, which could be identified from their unique peaks, intensity, and shape. Raman spectroscopy can prove to be a powerful tool for examining the chemical bond of collagenous tissues at the molecular level. After riboflavin-UVA treatment, unlike a regular parallel arrangement of normal collagen fibrils, the AFM image revealed interlocking arrangements of collagen fibrils. The observed changes in the surface topography of the collagen fibrils, as well as in their chemical bonds in the sclera tissue, support the formation of interfibrilar cross-links in sclera tissues.

  8. 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...

  9. The release behavior and kinetic evaluation of tramadol HCl from chemically cross linked Ter polymeric hydrogels

    Directory of Open Access Journals (Sweden)

    Malana Muhammad A

    2013-01-01

    Full Text Available Abstract Background and the purpose of the study Hydrogels, being stimuli responsive are considered to be effective for targeted and sustained drug delivery. The main purpose for this work was to study the release behavior and kinetic evaluation of Tramadol HCl from chemically cross linked ter polymeric hydrogels. Methods Ter-polymers of methacrylate, vinyl acetate and acrylic acid cross linked with ethylene glycol dimethacrylate (EGDMA were prepared by free radical polymerization. The drug release rates, dynamic swelling behavior and pH sensitivity of hydrogels ranging in composition from 1-10 mol% EGDMA were studied. Tramadol HCl was used as model drug substance. The release behavior was investigated at pH 8 where all formulations exhibited non-Fickian diffusion mechanism. Results and major conclusion Absorbency was found to be more than 99% indicating good drug loading capability of these hydrogels towards the selected drug substance. Formulations designed with increasing amounts of EGDMA had a decreased equilibrium media content as well as media penetrating velocity and thus exhibited a slower drug release rate. Fitting of release data to different kinetic models indicate that the kinetic order shifts from the first to zero order as the concentration of drug was increased in the medium, showing gradual independency of drug release towards its concentration. Formulations with low drug content showed best fitness with Higuchi model whereas those with higher concentration of drug followed Hixson-Crowell model with better correlation values indicating that the drug release from these formulations depends more on change in surface area and diameter of tablets than that on concentration of the drug. Release exponent (n derived from Korse-Meyer Peppas equation implied that the release of Tramadol HCl from these formulations was generally non-Fickian (n > 0.5 > 1 showing swelling controlled mechanism. The mechanical strength and controlled

  10. The Release Behavior and Kinetic Evaluation of Tramadol HCl from Chemically Cross Linked Ter Polymeric Hydrogels

    Directory of Open Access Journals (Sweden)

    Muhammad A Malana

    2013-01-01

    Full Text Available Background and the purpose of the study: Hydrogels, being stimuli responsive are considered to be effective for targeted and sustained drug delivery. The main purpose for this work was to study the release behavior and kinetic evaluation of Tramadol HCl from chemically cross linked ter polymeric hydrogels.MethodsTer-polymers of methacrylate, vinyl acetate and acrylic acid cross linked with ethylene glycol dimethacrylate (EGDMA were prepared by free radical polymerization. The drug release rates, dynamic swelling behavior and pH sensitivity of hydrogels ranging in composition from 1-10 mol % EGDMA were studied. Tramadol HCl was used as model drug substance. The release behavior was investigated at pH 8 where all formulations exhibited non-Fickian diffusion mechanism.Results and major conclusion: Absorbency was found to be more than 99% indicating good drug loading capability of these hydrogels towards the selected drug substance. Formulations designed with increasing amounts of EGDMA had a decreased equilibrium media content as well as media penetrating velocity and thus exhibited a slower drug release rate. Fitting of release data to different kinetic models indicate that the kinetic order shifts from the first to zero order as the concentration of drug was increased in the medium, showing gradual independency of drug release towards its concentration. Formulations with low drug content showed best fitness with Higuchi model whereas those with higher concentration of drug followed Hixson-Crowell model with better correlation values indicating that the drug release from these formulations depends more on change in surface area and diameter of tablets than that on concentration of the drug. Release exponent (n derived from Korse-Meyer Peppas equation implied that the release of Tramadol HCl from these formulations was generally non-Fickian (n>0.5>1 showing swelling controlled mechanism. The mechanical strength and controlled release capability of

  11. Quaternary structure of the ATPase complex of human 26S proteasomes determined by chemical cross-linking

    DEFF Research Database (Denmark)

    Hartmann-Petersen, R; Tanaka, K; Hendil, K B

    2001-01-01

    and substrate specificity. Among the approximately 18 subunits of PA700 regulator, six are ATPases. The ATPases presumably recognize, unfold, and translocate substrates into the interior of the 26S proteasome. It is generally believed that the ATPases form a hexameric ring. By means of chemical cross-linking......, immunoprecipitation, and blotting, we have determined that the ATPases are organized in the order S6-S6'-S10b-S8-S4-S7. Additionally, we found cross-links between the ATPase S10b and the 20S proteasome subunit alpha6. Together with the previously known interaction between S8 and alpha1 and between S4 and alpha7...

  12. Advancements in mass spectrometry for biological samples: Protein chemical cross-linking and metabolite analysis of plant tissues

    Energy Technology Data Exchange (ETDEWEB)

    Klein, Adam [Iowa State Univ., Ames, IA (United States)

    2015-01-01

    This thesis presents work on advancements and applications of methodology for the analysis of biological samples using mass spectrometry. Included in this work are improvements to chemical cross-linking mass spectrometry (CXMS) for the study of protein structures and mass spectrometry imaging and quantitative analysis to study plant metabolites. Applications include using matrix-assisted laser desorption/ionization-mass spectrometry imaging (MALDI-MSI) to further explore metabolic heterogeneity in plant tissues and chemical interactions at the interface between plants and pests. Additional work was focused on developing liquid chromatography-mass spectrometry (LC-MS) methods to investigate metabolites associated with plant-pest interactions.

  13. Surface modification of sulfur electrodes by chemically anchored cross-linked polymer coating for lithium-sulfur batteries.

    Science.gov (United States)

    Lim, Sanghyun; Thankamony, Roshni Lilly; Yim, Taeeun; Chu, Hodong; Kim, Young-Jun; Mun, Junyoung; Kim, Tae-Hyun

    2015-01-28

    Lithium-sulfur batteries suffer from severe self-discharge due to polysulfide dissolution into electrolytes. In this work, a chemically anchored polymer-coated (CAPC) sulfur electrode was prepared, through chemical bonding by coordinated Cu ions and cross-linking, to improve cyclability for Li/S batteries. This electrode retained specific capacities greater than 665 mAh g(-1) at high current density of 3.35 A g(-1) (2C rate) after 100 cycles with an excellent Coulombic efficiency of 100%.

  14. Chemical, Physical, and Mechanical Characterization of Isocyanate Cross-linked Amine-Modified Silica Aerogels

    Science.gov (United States)

    Katti, Atul; Shimpi, Nilesh; Roy, Samit; Lu, Hongbing; Fabrizio, Eve F.; Dass, Amala; Capadona, Lynn A.; Leventis, Nicholas

    2006-01-01

    We describe a new mechanically strong lightweight porous composite material obtained by encapsulating the skeletal framework of amine-modified silica aerogels with polyurea. The conformal polymer coating preserves the mesoporous structure of the underlying silica framework and the thermal conductivity remains low at 0.041 plus or minus 0.001 W m(sup -1 K(sup -1). The potential of the new cross-linked silica aerogels for load-carrying applications was determined through characterization of their mechanical behavior under compression, three-point bending, and dynamic mechanical analysis (DMA). A primary glass transition temperature of 130 C was identified through DMA. At room temperature, results indicate a hyperfoam behavior where in compression cross-linked aerogels are linearly elastic under small strains (less than 4%) and then exhibit yield behavior (until 40% strain), followed by densification and inelastic hardening. At room temperature the compressive Young's modulus and the Poisson's ratio were determined to be 129 plus or minus 8 MPa and 0.18, respectively, while the strain at ultimate failure is 77% and the average specific compressive stress at ultimate failure is 3.89 x 10(exp 5) N m kg(sup -1). The specific flexural strength is 2.16 x 10(exp 4) N m kg(sup -1). Effects on the compressive behavior of strain rate and low temperature were also evaluated.

  15. Effect of Chemical Reagents in Foam Decontamination

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Han Beom; Yoonm Inho; Jung, Chonghun; Choi, Wangkyu [Korea Atomic Energy research Institute, Daejeon (Korea, Republic of)

    2014-05-15

    The decontamination foam comprises at least one surfactant to generate the foam and one or more chemical reactants to achieve the dissolution of the contaminants at the solid surface. In order to improve the efficiency of decontamination foam, the present study attempts to find the optimum condition of chemical reagents to the foaming solution. This paper deals with understanding the effects of chemical reagents involved in foam decontamination efficiency, evaluation of side effect on foam stability and finally the improvement brought by formulation science. Basic experiments using the nanoparticle-based complex fluid decontamination foam have been performed in order to development of decontamination foam technology. Results show that in the case of coexistence of chemical reagents, for the purpose of the good foam ability and foam stability, it is necessary to increase the concentration of surfactant. In corrosion test, metal materials including carbon steel, stainless steel 304, aluminum, inconel 600 and cupper, generally corrosion solubility percent in nitric acid solution were higher than in phosphoric acid solution. Bench-scale testing was used to evaluate the efficacy of three decontamination formulations on contaminant carbon steel component of dry oven. The results shows decontamination factor was in the range of 6.1∼13.4. Results suggest that our foam formulations have a feasibility potential to removal of about 83∼93% total radioactivity in contaminant.

  16. Multifactor analysis on the effect of collagen concentration, cross-linking and fiber/pore orientation on chemical, microstructural, mechanical and biological properties of collagen type I scaffolds.

    Science.gov (United States)

    Suesca, E; Dias, A M A; Braga, M E M; de Sousa, H C; Fontanilla, M R

    2017-08-01

    This work evaluates the effect of processing variables on some physicochemical and mechanical properties of multi- and unidirectional laminar collagen type I scaffolds. The processing variables considered in this study included microstructure orientation (uni- and multidirectional fiber/pore controlled by freeze-drying methodology), cross-linking (chemical - using genipin and glutaraldehyde, and physical - using a dehydrothermal method), and collagen concentration (2, 5 and 8mg/ml). The biocompatibility of the scaffolds obtained in each of the evaluated manufacturing processes was also assessed. Despite previous research on collagen-based platforms, the effects that these processing variables have on the properties of collagen scaffolds are still not completely understood. Unidirectional scaffolds presented higher resistance to failure under stress than multidirectional ones. The cross-linking degree was found to decrease when the concentration of collagen increased whilst using chemical cross-linkers, and to increase with the concentration of collagen for the dehydrothermal cross-linked scaffolds. Pore orientation indexes of both unidirectional and multidirectional scaffolds were not influenced by collagen concentration. Cross-linked scaffolds were more hydrophobic than non-cross-linked ones, and presented water vapor permeability adequate for use in low-to-moderate exuding wounds. Pore size ranges were compatible with cell in-growth, independently of the employed cross-linking and freezing methodologies. Moreover, scaffolds cross-linked with glutaraldehyde presented higher in-growth of primary oral mucosa fibroblasts than those cross-linked with genipin or with the dehydrothermal treatment. This multi-factor analysis is expected to contribute to the design of collagen type I platforms, which are usable on several potential soft tissue-engineering applications. Copyright © 2017 Elsevier B.V. All rights reserved.

  17. Synthesis of chemical cross-linked gelatin hydrogel reinforced with cellulose nanocrystals (CNC)

    Science.gov (United States)

    Yin, Ooi Shok; Ahmad, Ishak; Amin, Mohd. Cairul Iqbal Mohd

    2014-09-01

    A novel method was performed to obtain hydrogel with superior sensitivity towards changes in pH and temperature by incorporation of CNC into gelatin based hydrogel. Glutaraldehyde was used as cross-linker due to its high chemical reactivity towards NH2 group on gelatin. Different ratio of gelatin / CNC hydrogel was produced in order to study the effects of CNC towards the swelling behaviour of hydrogel at different pH and temperature. Swelling tests were performed at different pH range from pH 3 to pH 11. Temperature swelling tests were performed at 25 °C and 37 °C. The hydrogel showed impressive pH sensitivity and maximum swelling was obtained at pH 3. Higher swelling ratio was observed at higher temperature. SEM micrographs showed that the pore size of hydrogel decreased with increasing CNC content due to formation of more rigid hydrogel structure. The characteristics of the hydrogel to respond to different pH and temperature suggest that gelatin / CNC hydrogel are promising candidates to be developed as drug carrier.

  18. In-line formation of chemically cross-linked P84® co-polyimide hollow fibre membranes for H2/CO2 separation

    KAUST Repository

    Choi, Seung Hak

    2010-12-13

    In this study, chemically cross-linked asymmetric P84® co-polyimide hollow fibre membranes with enhanced separation performance were fabricated, using a dry-wet spinning process with an innovative in-line cross-linking step. The chemical modification was conducted by controlled immersion of the coagulated fibre in an aqueous 1,5-diamino-2-methylpentane (DAMP) cross-linker solution before the take-up. The effect of the cross-linker concentration on the thermal, mechanical, chemical and gas transport properties of the membranes was investigated. FT-IR/ATR analysis was used to identify the chemical changes in the polymer, while DSC analysis confirmed the changes in the Tg and the specific heat of the polymer upon cross-linking. Chemical cross-linking with a 10 wt.% aqueous DAMP solution strongly enhanced the H2/CO2 ideal selectivity from 5.3 to 16.1, while the H2 permeance of the membranes decreased from 7.06 × 10−3 to 1.01 × 10−3 m3(STP) m−2 h−1 bar−1 for a feed pressure of 1 bar at 25 °C. The increase of selectivity with decreasing permeance is somewhat higher than the slope in the Robeson upper bound, evidencing the positive effect of the cross-linking on the separation performance of the fibres. Simultaneously, the cross-linking leads to improved mechanical resistance of the membranes, which could be further enhanced by an additional thermal treatment. The produced membranes are therefore more suitable for use under harsh conditions and have a better overall performance than the uncross-linked ones.

  19. Formulation of in situ chemically cross-linked hydrogel depots for protein release: from the blob model perspective.

    Science.gov (United States)

    Yu, Yu; Chau, Ying

    2015-01-12

    The fast release rate and the undesirable covalent binding are two major problems often encountered in formulating in situ chemically cross-linked hydrogel as protein release depot, particularly when prolonged release over months is desirable. In this study, we applied the De Gennes' blob theory to analyze and tackle these two problems using a vinylsulfone-thiol (VS-SH) reaction based in situ hydrogel system. We showed that the simple scaling relation ξb ≈ Rg(c/c*)(-v/(3v-1)) is applicable to the in situ hydrogel and the mesh size estimated from the precursor polymer parameters is a reasonable match to experimental results. On the other hand, as predicted by the theory and confirmed by experiments, the drug diffusion within hydrogel depends mainly on polymer concentration but not the degree of modification (DM). The covalent binding was found to be caused by the mismatch of location between the reactive groups and the entanglement points. The mismatch and, thus, the protein binding were minimized by increasing the DM and concentration of the SH polymer relative to the VS polymer, as predicted by theory. Using these principles, an in situ hydrogel system for the controlled release of an antiangiogenic antibody therapeutics bevacizumab for 3 months was developed.

  20. Matching Cross-linked Peptide Spectra: Only as Good as the Worse Identification*

    Science.gov (United States)

    Trnka, Michael J.; Baker, Peter R.; Robinson, Philip J. J.; Burlingame, A. L.; Chalkley, Robert J.

    2014-01-01

    Chemical cross-linking mass spectrometry identifies interacting surfaces within a protein assembly through labeling with bifunctional reagents and identifying the covalently modified peptides. These yield distance constraints that provide a powerful means to model the three-dimensional structure of the assembly. Bioinformatic analysis of cross-linked data resulting from large protein assemblies is challenging because each cross-linked product contains two covalently linked peptides, each of which must be correctly identified from a complex matrix of potential confounders. Protein Prospector addresses these issues through a complementary mass modification strategy in which each peptide is searched and identified separately. We demonstrate this strategy with an analysis of RNA polymerase II. False discovery rates (FDRs) are assessed via comparison of cross-linking data to crystal structure, as well as by using a decoy database strategy. Parameters that are most useful for positive identification of cross-linked spectra are explored. We find that fragmentation spectra generally contain more product ions from one of the two peptides constituting the cross-link. Hence, metrics reflecting the quality of the spectral match to the less confident peptide provide the most discriminatory power between correct and incorrect matches. A support vector machine model was built to further improve classification of cross-linked peptide hits. Furthermore, the frequency with which peptides cross-linked via common acylating reagents fragment to produce diagnostic, cross-linker-specific ions is assessed. The threshold for successful identification of the cross-linked peptide product depends upon the complexity of the sample under investigation. Protein Prospector, by focusing the reliability assessment on the least confident peptide, is better able to control the FDR for results as larger complexes and databases are analyzed. In addition, when FDR thresholds are calculated separately

  1. Probing the structure of human protein disulfide isomerase by chemical cross-linking combined with mass spectrometry

    DEFF Research Database (Denmark)

    Peng, Li; Rasmussen, Morten Ib; Chailyan, Anna

    2014-01-01

    the sample contained soluble calnexin and ERp72. Extensive cross-linking was observed within the PDI molecule, both intra- and inter-domain, as well as between the different components in the mixture. The high sensitivity of the analysis in the current experiments, combined with a likely promiscuous...

  2. Immunogenicity of self-associated aggregates and chemically cross-linked conjugates of the 42 kDa Plasmodium falciparum merozoite surface protein-1.

    Directory of Open Access Journals (Sweden)

    Feng Qian

    Full Text Available Self-associated protein aggregates or cross-linked protein conjugates are, in general, more immunogenic than oligomeric or monomeric forms. In particular, the immunogenicity in mice of a recombinant malaria transmission blocking vaccine candidate, the ookinete specific Plasmodium falciparum 25 kDa protein (Pfs25, was increased more than 1000-fold when evaluated as a chemical cross-linked protein-protein conjugate as compared to a formulated monomer. Whether alternative approaches using protein complexes improve the immunogenicity of other recombinant malaria vaccine candidates is worth assessing. In this work, the immunogenicity of the recombinant 42 kDa processed form of the P. falciparum merozoite surface protein 1 (MSP1(42 was evaluated as a self-associated, non-covalent aggregate and as a chemical cross-linked protein-protein conjugate to ExoProtein A, which is a recombinant detoxified form of Pseudomonas aeruginosa exotoxin A. MSP1(42 conjugates were prepared and characterized biochemically and biophysically to determine their molar mass in solution and stoichiometry, when relevant. The immunogenicity of the MSP1(42 self-associated aggregates, cross-linked chemical conjugates and monomers were compared in BALB/c mice after adsorption to aluminum hydroxide adjuvant, and in one instance in association with the TLR9 agonist CPG7909 with an aluminum hydroxide formulation. Antibody titers were assessed by ELISA. Unlike observations made for Pfs25, no significant enhancement in MSP1(42 specific antibody titers was observed for any conjugate as compared to the formulated monomer or dimer, except for the addition of the TLR9 agonist CPG7909. Clearly, enhancing the immunogenicity of a recombinant protein vaccine candidate by the formation of protein complexes must be established on an empirical basis.

  3. 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.

  4. Initiated Chemical Vapor Deposition (iCVD) of Highly Cross-Linked Polymer Films for Advanced Lithium-Ion Battery Separators.

    Science.gov (United States)

    Yoo, Youngmin; Kim, Byung Gon; Pak, Kwanyong; Han, Sung Jae; Song, Heon-Sik; Choi, Jang Wook; Im, Sung Gap

    2015-08-26

    We report an initiated chemical vapor deposition (iCVD) process to coat polyethylene (PE) separators in Li-ion batteries with a highly cross-linked, mechanically strong polymer, namely, polyhexavinyldisiloxane (pHVDS). The highly cross-linked but ultrathin pHVDS films can only be obtained by a vapor-phase process, because the pHVDS is insoluble in most solvents and thus infeasible with conventional solution-based methods. Moreover, even after the pHVDS coating, the initial porous structure of the separator is well preserved owing to the conformal vapor-phase deposition. The coating thickness is delicately controlled by deposition time to the level that the pore size decreases to below 7% compared to the original dimension. The pHVDS-coated PE shows substantially improved thermal stability and electrolyte wettability. After incubation at 140 °C for 30 min, the pHVDS-coated PE causes only a 12% areal shrinkage (versus 90% of the pristine separator). The superior wettability results in increased electrolyte uptake and ionic conductivity, leading to significantly improved rate performance. The current approach is applicable to a wide range of porous polymeric separators that suffer from thermal shrinkage and poor electrolyte wetting.

  5. Characterization of the functional epitope on the urokinase receptor. Complete alanine scanning mutagenesis supplemented by chemical cross-linking

    DEFF Research Database (Denmark)

    Gårdsvoll, Henrik; Gilquin, Bernard; Le Du, Marie Hélène

    2006-01-01

    a comprehensive alanine scanning mutagenesis of uPAR combined with low resolution distance constraints defined within the complex using chemical cross-linkers as molecular rulers. The kinetic rate constants for the interaction between pro-uPA and 244 purified uPAR mutants with single-site replacements were...

  6. Porous Cross-Linked Polyimide Networks

    Science.gov (United States)

    Meador, Mary Ann B. (Inventor); Guo, Haiquan (Inventor)

    2015-01-01

    Porous cross-linked polyimide networks are provided. The networks comprise an anhydride end-capped polyamic acid oligomer. The oligomer (i) comprises a repeating unit of a dianhydride and a diamine and terminal anhydride groups, (ii) has an average degree of polymerization of 10 to 50, (iii) 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, and (iv) has been chemically imidized to yield the porous cross-linked polyimide network. Also provided are porous cross-linked polyimide aerogels comprising a cross-linked and imidized anhydride end-capped polyamic acid oligomer, wherein the oligomer comprises a repeating unit of a dianhydride and a diamine, and the aerogel has a density of 0.10 to 0.333 g/cm.sup.3 and a Young's modulus of 1.7 to 102 MPa. Also provided are thin films comprising aerogels, and methods of making porous cross-linked polyimide networks.

  7. Comparison of cross-linked and non-cross-linked porcine acellular dermal matrices for ventral hernia repair.

    Science.gov (United States)

    Butler, Charles E; Burns, Nadja K; Campbell, Kristin Turza; Mathur, Anshu B; Jaffari, Mona V; Rios, Carmen N

    2010-09-01

    Porcine acellular dermal matrices (PADMs) have been used clinically for abdominal wall repair. The newer non-cross-linked PADMs, however, have not been directly compared with cross-linked PADMs. We hypothesized that chemical cross-linking affects the biologic host response to PADMs used to repair ventral hernias. Fifty-eight guinea pigs underwent inlay repair of surgically created ventral hernias using cross-linked or non-cross-linked PADM. After animals were sacrificed at 1, 2, or 4 weeks, the tenacity of and surface area involved by adhesions to the repair sites were measured. Sections of the repair sites, including the bioprosthesis-musculofascia interface, underwent histologic analysis of cellular and vascular infiltration plus mechanical testing. Compared with cross-linked PADM repairs, non-cross-linked PADM repairs had a significantly lower mean tenacity grade of adhesions at all timepoints and mean adhesion surface area at week 1. Mean cellular and vascular densities were significantly higher in non-cross-linked PADM at all timepoints. Cells and vessels readily infiltrated into the center of non-cross-linked PADM, but encapsulated cross-linked PADM, with a paucity of penetration into it. Mechanical properties were similar for the two PADMs (in isolation) at all timepoints; however, at the bioprosthesis-musculofascia interface, both elastic modulus and ultimate tensile strength were significantly higher at weeks 1 and 2 for non-cross-linked PADM. Non-cross-linked PADM is rapidly infiltrated with host cells and vessels; cross-linked PADM becomes encapsulated. Non-cross-linked PADM causes weaker adhesions to repair sites while increasing the mechanical strength of the bioprosthesis-musculofascia interface at early timepoints. Non-cross-linked PADM may have early clinical advantages over cross-linked PADM for bioprosthetic abdominal wall reconstruction. Copyright 2010 American College of Surgeons. Published by Elsevier Inc. All rights reserved.

  8. Cross-linked polyvinyl alcohol films as alkaline battery separators

    Science.gov (United States)

    Sheibley, D. W.; Manzo, M. A.; Gonzalez-Sanabria, O. D.

    1983-01-01

    Cross-linking methods have been investigated to determine their effect on the performance of polyvinyl alcohol (PVA) films as alkaline battery separators. The following types of cross-linked PVA films are discussed: (1) PVA-dialdehyde blends post-treated with an acid or acid periodate solution (two-step method) and (2) PVA-dialdehyde blends cross-linked during film formation (drying) by using a reagent with both aldehyde and acid functionality (one-step method). Laboratory samples of each cross-linked type of film were prepared and evaluated in standard separator screening tests. Then pilot-plant batches of films were prepared and compared to measure differences due to the cross-linking method. The pilot-plant materials were then tested in nickel oxide-zinc cells to compare the two methods with respect to performance characteristics and cycle life. Cell test results are compared with those from tests with Celgard.

  9. Exploring the Potential for Using Inexpensive Natural Reagents Extracted from Plants to Teach Chemical Analysis

    Science.gov (United States)

    Hartwell, Supaporn Kradtap

    2012-01-01

    A number of scientific articles report on the use of natural extracts from plants as chemical reagents, where the main objective is to present the scientific applications of those natural plant extracts. The author suggests that natural reagents extracted from plants can be used as alternative low cost tools in teaching chemical analysis,…

  10. Utilization of cross-linked laccase aggregates in a perfusion basket reactor for the continuous elimination of endocrine-disrupting chemicals.

    Science.gov (United States)

    Cabana, Hubert; Jones, J Peter; Agathos, Spiros N

    2009-04-15

    A perfusion basket reactor (BR) was developed for the continuous utilization of insolubilized laccase as cross-linked enzyme aggregates (CLEAs). The BR consisted of an unbaffled basket made of a metallic filtration module filled with CLEAs and continuously agitated by a 3-blade marine propeller. The agitation conditions influenced both the apparent laccase activity in the reactor and the stability of the biocatalyst. Optimal laccase activity was obtained at a rotational speed of 12.5 rps and the highest stability was reached at speeds of 1.7 rps or lower. The activity and stability of the biocatalyst were affected drastically upon the appearance of vortices in the reaction medium. This reactor was used for the continuous elimination of the endocrine disrupting chemicals (EDCs) nonylphenol (NP), bisphenol A (BPA), and triclosan (TCS). Optimization of EDC elimination by laccase CLEAs as a function of temperature and pH was achieved by response surface methodology using a central composite factorial design. The optimal conditions of pH and temperature were, respectively, 4.8 and 40.3 degrees C for the elimination of p353NP (a branched isomer of NP), 4.7 and 48.0 degrees C for BPA, and 4.9 and 41.2 degrees C for TCS. Finally, the BR was used for the continuous elimination of these EDCs from a 5 mg L(-1) aqueous solution using 1 mg of CLEAs at pH 5 and room temperature. Our results showed that at least 85% of these EDCs could be eliminated with a hydraulic retention time of 325 min. The performances of the BR were quite stable over a 7-day period of continuous treatment. Furthermore, this system could eliminate the same EDCs from a 100 mg L(-1) solution. Finally, a mathematical model combining the Michaelis-Menten kinetics of the laccase CLEAs and the continuous stirred tank reactor behavior of the BR was developed to predict the elimination of these xenobiotics. 2008 Wiley Periodicals, Inc.

  11. Optimizing Transfection of Primary Human Umbilical Vein Endothelial Cells Using Commercially Available Chemical Transfection Reagents

    OpenAIRE

    Hunt, Michelle A.; Currie, Margaret J.; Robinson, Bridget A.; Dachs, Gabi U.

    2010-01-01

    Primary cells, such as HUVEC, are notoriously difficult to transfect and are susceptible to the toxic effects of transfection reagents. A transfection reagent with a high transfection efficiency and low cytotoxicity was sought to retain sufficient viability of transfected HUVEC for subsequent assays. Nine chemical transfection reagents, currently commercially available, were compared for their ability to transfect HUVEC in vitro. A plasmid expressing the enhanced GFP (EGFP) was used for trans...

  12. Supramolecular chemical shift reagents inducing conformational transitions: NMR analysis of carbohydrate homooligomer mixtures

    DEFF Research Database (Denmark)

    Beeren, Sophie; Meier, Sebastian

    2015-01-01

    We introduce the concept of supramolecular chemical shift reagents as a tool to improve signal resolution for the NMR analysis of homooligomers. Non-covalent interactions with the shift reagent can constrain otherwise flexible analytes inducing a conformational transition that results in signal...

  13. Architecture of a Full-length Retroviral Integrase Monomer and Dimer, Revealed by Small Angle X-ray Scattering and Chemical Cross-linking

    Energy Technology Data Exchange (ETDEWEB)

    Bojja, Ravi S.; Andrake, Mark D.; Weigand, Steven; Merkel, George; Yarychkivska, Olya; Henderson, Adam; Kummerling, Marissa; Skalka, Anna Marie (Fox Chase); (NWU)

    2012-02-07

    We determined the size and shape of full-length avian sarcoma virus (ASV) integrase (IN) monomers and dimers in solution using small angle x-ray scattering. The low resolution data obtained establish constraints for the relative arrangements of the three component domains in both forms. Domain organization within the small angle x-ray envelopes was determined by combining available atomic resolution data for individual domains with results from cross-linking coupled with mass spectrometry. The full-length dimer architecture so revealed is unequivocally different from that proposed from x-ray crystallographic analyses of two-domain fragments, in which interactions between the catalytic core domains play a prominent role. Core-core interactions are detected only in cross-linked IN tetramers and are required for concerted integration. The solution dimer is stabilized by C-terminal domain (CTD-CTD) interactions and by interactions of the N-terminal domain in one subunit with the core and CTD in the second subunit. These results suggest a pathway for formation of functional IN-DNA complexes that has not previously been considered and possible strategies for preventing such assembly.

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

    OpenAIRE

    Feng-Xiang Yu; Gao-Qiang Liu; Hua-Xi Xiao; Qin-Lu Lin

    2012-01-01

    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 sta...

  15. 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.

  16. 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.

  17. Reagent based DOS: a "Click, Click, Cyclize" strategy to probe chemical space.

    Science.gov (United States)

    Rolfe, Alan; Lushington, Gerald H; Hanson, Paul R

    2010-05-07

    The synthesis of small organic molecules as probes for discovering new therapeutic agents has been an important aspect of chemical-biology. Herein we report a reagent-based, diversity-oriented synthetic (DOS) strategy to probe chemical and biological space via a "Click, Click, Cyclize" protocol. In this DOS approach, three sulfonamide linchpins underwent cyclization protocols with a variety of reagents to yield a collection of structurally diverse S-heterocycles. In silico analysis is utilized to evaluate the diversity of the compound collection against chemical space (PC analysis), shape space (PMI) and polar surface area (PSA) calculations.

  18. Single Molecule Source Reagents for Chemical Vapor Deposition of B- Silicon Carbide

    Science.gov (United States)

    1992-12-10

    Phase I conclusively showed the feasibility of rational design of single molecule -source reagents that could lead to improvements in the chemical...vapor deposition of stoichiometric Beta silicon carbide. Four single molecule sources were synthesized, their decomposition pathways studied, and their

  19. Chemically Cross-Linked MOF Membrane Generated from Imidazolium-Based Ionic Liquid-Decorated UiO-66 Type NMOF and Its Application toward CO2 Separation and Conversion.

    Science.gov (United States)

    Yao, Bing-Jian; Ding, Luo-Gang; Li, Fei; Li, Jiang-Tao; Fu, Qi-Juan; Ban, Yujie; Guo, Ang; Dong, Yu-Bin

    2017-10-25

    Carbon dioxide capture and transformation are of great importance to make cuts in greenhouse gas emissions. Nanometal-organic frameworks (NMOFs) could serve as ideal fillers for polymer membranes owing to their structural diversity and regulable microenvironment of the nanocage. Herein, a bifunctional, robust, and chemically cross-linked NMOF-based membrane was successfully constructed by the postsynthetic polymerization of imidazolium-based ionic liquid (IL)-decorated UiO-66 type nanoparticles (NPs) and the isocyanate-terminated polyurethane oligomer under mild conditions. The IL-modified MOF-polymer membranes exhibit a highly selective adsorption for CO2 over N2 and CH4. In addition, the obtained membrane can also be a highly active heterogeneous catalyst for CO2 transformation by cycloaddition with epoxide under an ambient pressure.

  20. 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

  1. Reagents for the chemical development of latent fingerprints: synthesis and properties of some ninhydrin analogues.

    Science.gov (United States)

    Almog, J; Hirshfeld, A; Klug, J T

    1982-10-01

    In an attempt to design new reagents for the chemical development of latent fingerprints, a number of ninhydrin analogues were synthesized and their reactions with latent fingerprints on paper were studied. The ring-fused and substituted ninhydrins developed latent fingerprints with a sensitivity similar to that of ninhydrin. The most promising of the group was 2,2-dihydroxybenz[f]indane-1,3-dione, which developed latent fingerprints as dark green images with excellent resolution.

  2. Molecular model for HNBR with tunable cross-link density

    OpenAIRE

    Khawaja; Molinari; Sutton, AP; Mostofi, AA

    2016-01-01

    We introduce a chemically-inspired, all-atom model of HNBR and assess its perfor- mance by computing the mass density and glass transition temperature as a function of cross-link density in the structure. Our HNBR structures are created by a procedure that mimics the real process used to produce HNBR, i.e., saturation of the carbon- carbon double bonds in NBR, either by hydrogenation or by cross-linking. The atomic interactions are described by the all-atom ?Optimized Potentials for Liquid Si...

  3. Conformational Entropy of an Ideal Cross-Linking Polymer Chain.

    Science.gov (United States)

    Vorov, Oleg K; Livesay, Dennis R; Jacobs, Donald J

    2008-09-20

    We present a novel analytical method to calculate conformational entropy of ideal cross-linking polymers from the configuration integral by employing a Mayer series expansion. Mayer-functions describing chemical bonds within the chain and for cross-links are sharply peaked over the temperature range of interest, and, are well approximated as statistically weighted Dirac delta-functions that enforce distance constraints. All geometrical deformations consistent with a set of distance constraints are integrated over. Exact results for a contiguous series of connected loops are employed to substantiate the validity of a previous phenomenological distance constraint model that describes protein thermodynamics successfully based on network rigidity.

  4. Conformational Entropy of an Ideal Cross-Linking Polymer Chain

    Directory of Open Access Journals (Sweden)

    Donald J. Jacobs

    2008-09-01

    Full Text Available We present a novel analytical method to calculate conformational entropy of ideal cross-linking polymers from the configuration integral by employing a Mayer series expansion. Mayer-functions describing chemical bonds within the chain and for cross-links are sharply peaked over the temperature range of interest, and, are well approximated as statistically weighted Dirac delta-functions that enforce distance constraints. All geometrical deformations consistent with a set of distance constraints are integrated over. Exact results for a contiguous series of connected loops are employed to substantiate the validity of a previous phenomenological distance constraint model that describes protein thermodynamics successfully based on network rigidity.

  5. Nanostructure development during peroxidase catalysed cross-linking of a-lactalbumin

    NARCIS (Netherlands)

    Saricay, Y.; Wierenga, P.A.; Vries, de R.J.

    2013-01-01

    Whereas extensive work has been done on the food functional and chemical aspects of enzymatic protein cross-linking, relatively little is known about the nanostructure and physical-chemical properties of enzymatically cross-linked protein. We investigate how nanostructure develops during enzymatic

  6. 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, Hanno; Petersen, Jørgen; Mann, Matthias

    2001-01-01

    . 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......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...... spectrometry is becoming increasingly popular for characterization of purified peptide-nucleic acid heteroconjugates derived from UV cross-linked protein-nucleic acid complexes. The efficiency of mass spectrometry-based methods is, however, hampered by the contrasting physico-chemical properties of nucleic...

  7. Highly cross-linked nanoporous polymers

    Science.gov (United States)

    Steckle, Jr., Warren P.; Apen, Paul G.; Mitchell, Michael A.

    1997-01-01

    Condensation polymerization followed by a supercritical extraction step can be used to obtain highly cross-linked nanoporous polymers with high surface area, controlled pore sizes and rigid structural integrity. The invention polymers are useful for applications requiring separation membranes.

  8. Synthesis and evaluation of physicochemical properties of cross-linked sago starch.

    Science.gov (United States)

    Singh, Akhilesh V; Nath, Lila K

    2012-01-01

    Highly substituted sago starch phosphate was synthesized using POCl(3) as cross-linking reagent. Titrimetric and Fourier transform infra red (FT-IR) spectral analysis were used to characterize the substitution. Studying the different factors affecting the reaction parameters showed that the optimal conditions for starch phosphorylation were: 4h reaction time and reagent concentration 1.5% (w/w). The physicochemical properties of cross-linked sago starch (CLSS) were done using Scanning electron micrograph (SEM), X-ray powder diffractometer (XRD and Thermogravimetric analysis (TGA). The results revealed that crystalline nature of native sago starch was transformed after cross-linking. TGA report exhibited higher thermal stability, which makes it suitable for various industrial applications. Swelling behavior showed high swelling at low temperature (30 and 60°C) as compared to high temperature (90°C). Copyright © 2011 Elsevier B.V. All rights reserved.

  9. 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 agains...

  10. Molecular Model for HNBR with Tunable Cross-Link Density.

    Science.gov (United States)

    Molinari, N; Khawaja, M; Sutton, A P; Mostofi, A A

    2016-12-15

    We introduce a chemically inspired, all-atom model of hydrogenated nitrile butadiene rubber (HNBR) and assess its performance by computing the mass density and glass-transition temperature as a function of cross-link density in the structure. Our HNBR structures are created by a procedure that mimics the real process used to produce HNBR, that is, saturation of the carbon-carbon double bonds in NBR, either by hydrogenation or by cross-linking. The atomic interactions are described by the all-atom "Optimized Potentials for Liquid Simulations" (OPLS-AA). In this paper, first, we assess the use of OPLS-AA in our models, especially using NBR bulk properties, and second, we evaluate the validity of the proposed model for HNBR by investigating mass density and glass transition as a function of the tunable cross-link density. Experimental densities are reproduced within 3% for both elastomers, and qualitatively correct trends in the glass-transition temperature as a function of monomer composition and cross-link density are obtained.

  11. 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.

  12. Enrichment of Cross-Linked Peptides Using Charge-Based Fractional Diagonal Chromatography (ChaFRADIC).

    Science.gov (United States)

    Tinnefeld, Verena; Venne, A Saskia; Sickmann, Albert; Zahedi, René P

    2017-02-03

    Chemical cross-linking of proteins is an emerging field with huge potential for the structural investigation of proteins and protein complexes. Owing to the often relatively low yield of cross-linking products, their identification in complex samples benefits from enrichment procedures prior to mass spectrometry analysis. So far, this is mainly accomplished by using biotin moieties in specific cross-linkers or by applying strong cation exchange chromatography (SCX) for a relatively crude enrichment. We present a novel workflow to enrich cross-linked peptides by utilizing charge-based fractional diagonal chromatography (ChaFRADIC). On the basis of two-dimensional diagonal SCX separation, we could increase the number of identified cross-linked peptides for samples of different complexity: pure cross-linked BSA, cross-linked BSA spiked into a simple protein mixture, and cross-linked BSA spiked into a HeLa lysate. We also compared XL-ChaFRADIC with size exclusion chromatography-based enrichment of cross-linked peptides. The XL-ChaFRADIC approach is straightforward, reproducible, and independent of the cross-linking chemistry and cross-linker properties.

  13. Interrelation of electret properties of polyethylene foam from the method of cross-linking

    Science.gov (United States)

    Gilmanov, I. R.; Galikhanov, M. F.; Gilmanova, A. R.

    2017-09-01

    The electret properties of chemically cross-linked polyethylene foam and physically cross-linked polyethylene foam have been studied. It has been shown that chemically cross-linked polyethylene foam has higher surface potential, effective surface charge density and electric field strength compared to physically bonded polyethylene foam. This is due to the presence of molecules and fragments of dicumyl peroxide, which can play the role of traps for injection charge carriers, a greater degree of cross-linking and with the oxidation of polyethylene, which occurs during irradiation during physical cross-linking. When the foam is deformed, its electret properties are reduced, and when the volume is relaxed, they are restored. This is due to the partial mutual compensation of homo- and heterocharge during compression and the return of the structure of the gas-filled polymer to its former position when the load is removed.

  14. 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.

  15. Cross-linking Enset Starch Microspheres, Physicochemical ...

    African Journals Online (AJOL)

    Enset starch was cross-linked in solid phase systems using sodium hexametaphosphate (SHMP) as crosslinking agent under different microwave powers and reaction times to investigate its drug-release-sustaining ability. Paracetamol was used as a model drug. The swelling and water-binding capacities and the peak ...

  16. 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.

  17. Carbodiimide cross-linking of amniotic membranes in the presence of amino acid bridges.

    Science.gov (United States)

    Lai, Jui-Yang

    2015-06-01

    The purpose of this study was to investigate the carbodiimide cross-linking of amniotic membrane (AM) in the presence of amino acid bridges. The biological tissues were treated with glycine, lysine, or glutamic acid and chemically cross-linked to examine the role of amino acid types in collagenous biomaterial processing. Results of zeta potential measurements showed that the use of uncharged, positively and negatively charged amino acids dictates the charge state of membrane surface. Tensile strength and water content measurements demonstrated that the addition of lysine molecules to the cross-linking system can increase the cross-linking efficiency and dehydration degree while the introduction of glutamic acid in the AM samples decreases the number of cross-links per unit mass of chemically modified tissue collagen. The differences in the cross-linking density further determined the thermal and biological stability by differential scanning calorimetry and in vitro degradation tests. As demonstrated in matrix permeability studies, the improved formation of covalent cross-linkages imposed by lysine facilitated construction of stronger cross-linking structures. In contrast, the added glycine molecules were insufficient to enhance the resistances of the proteinaceous matrices to thermal denaturation and enzymatic degradation. The cytocompatibility of these biological tissue membranes was evaluated by using human corneal epithelial cell cultures. Results of cell viability, metabolic activity, and pro-inflammatory gene expression level showed that the AM materials cross-linked with carbodiimide in the presence of different types of amino acids are well tolerated without evidence of detrimental effect on cell growth. In addition, the amino acid treated and carbodiimide cross-linked AM implants had good biocompatibility in the anterior chamber of the rabbit eye model. Our findings suggest that amino acid type is a very important engineering parameter to mediate

  18. Correlation of Thermal Stability and Structural Distortion of DNA Interstrand Cross-Links Produced from Oxidized Abasic Sites with Their Selective Formation and Repair.

    Science.gov (United States)

    Ghosh, Souradyuti; Greenberg, Marc M

    2015-10-13

    C4'-oxidized (C4-AP) and C5'-oxidized abasic sites (DOB) that are produced following abstraction of a hydrogen atom from the DNA backbone reversibly form cross-links selectively with dA opposite a 3'-adjacent nucleotide, despite the comparable proximity of an opposing dA. A previous report on UvrABC incision of DNA substrates containing stabilized analogues of the ICLs derived from C4-AP and DOB also indicated that the latter is repaired more readily by nucleotide excision repair [Ghosh, S., and Greenberg, M. M. (2014) Biochemistry 53, 5958-5965]. The source for selective cross-link formation was probed by comparing the reactivity of ICL analogues of C4-AP and DOB that mimic the preferred and disfavored cross-links with that of reagents that indirectly detect distortion by reacting with the nucleobases. The disfavored C4-AP and DOB analogues were each more reactive than the corresponding preferred cross-link substrates, suggesting that the latter are more stable, which is consistent with selective ICL formation. In addition, the preferred DOB analogue is more reactive than the respective C4-AP ICL, which is consistent with its more efficient incision by UvrABC. The conclusions drawn from the chemical probing experiments are corroborated by UV melting studies. The preferred ICLs exhibit melting temperatures higher than those of the corresponding disfavored isomers. These studies suggest that oxidized abasic sites form reversible interstrand cross-links with dA opposite the 3'-adjacent thymidine because these products are more stable and the thermodynamic preference is reflected in the transition states for their formation.

  19. 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

  20. Treatment of textile effluent by chemical (Fenton's Reagent) and biological (sequencing batch reactor) oxidation.

    Science.gov (United States)

    Rodrigues, Carmen S D; Madeira, Luis M; Boaventura, Rui A R

    2009-12-30

    The removal of organic compounds and colour from a synthetic effluent simulating a cotton dyeing wastewater was evaluated by using a combined process of Fenton's Reagent oxidation and biological degradation in a sequencing batch reactor (SBR). The experimental design methodology was first applied to the chemical oxidation process in order to determine the values of temperature, ferrous ion concentration and hydrogen peroxide concentration that maximize dissolved organic carbon (DOC) and colour removals and increase the effluent's biodegradability. Additional studies on the biological oxidation (SBR) of the raw and previously submitted to Fenton's oxidation effluent had been performed during 15 cycles (i.e., up to steady-state conditions), each one with the duration of 11.5h; Fenton's oxidation was performed either in conditions that maximize the colour removal or the increase in the biodegradability. The obtained results allowed concluding that the combination of the two treatment processes provides much better removals of DOC, BOD(5) and colour than the biological or chemical treatment alone. Moreover, the removal of organic matter in the integrated process is particularly effective when Fenton's pre-oxidation is carried out under conditions that promote the maximum increase in wastewater biodegradability.

  1. [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.

  2. 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.

  3. Corneal Collagen Cross-Linking Outcomes: Review

    OpenAIRE

    Jankov II,Mirko R.; Jovanovic,Vesna; Delevic, Sladjana; Coskunseven, Efekan

    2011-01-01

    Keratoconus is a condition characterized by biomechanical instability of the cornea, presenting in a progressive, asymmetric and bilateral way. Corneal collagen cross-linking with riboflavin and UVA (CXL) is a new technique of corneal tissue strengthening that combines the use of riboflavin as a photo sensitizer and UVA irradiation. The studies showed that CXL was effective in halting the progression of keratoconus over a period of up to four years. The published studies also revealed a reduc...

  4. 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.

  5. Collagen cross-linking in thin corneas

    Science.gov (United States)

    Padmanabhan, Prema; Dave, Abhishek

    2013-01-01

    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. PMID:23925328

  6. In vivo covalent cross-linking of photon-converted rare-earth nanostructures for tumour localization and theranostics

    Science.gov (United States)

    Ai, Xiangzhao; Ho, Chris Jun Hui; Aw, Junxin; Attia, Amalina Binte Ebrahim; Mu, Jing; Wang, Yu; Wang, Xiaoyong; Wang, Yong; Liu, Xiaogang; Chen, Huabing; Gao, Mingyuan; Chen, Xiaoyuan; Yeow, Edwin K. L.; Liu, Gang; Olivo, Malini; Xing, Bengang

    2016-01-01

    The development of precision nanomedicines to direct nanostructure-based reagents into tumour-targeted areas remains a critical challenge in clinics. Chemical reaction-mediated localization in response to tumour environmental perturbations offers promising opportunities for rational design of effective nano-theranostics. Here, we present a unique microenvironment-sensitive strategy for localization of peptide-premodified upconversion nanocrystals (UCNs) within tumour areas. Upon tumour-specific cathepsin protease reactions, the cleavage of peptides induces covalent cross-linking between the exposed cysteine and 2-cyanobenzothiazole on neighbouring particles, thus triggering the accumulation of UCNs into tumour site. Such enzyme-triggered cross-linking of UCNs leads to enhanced upconversion emission upon 808 nm laser irradiation, and in turn amplifies the singlet oxygen generation from the photosensitizers attached on UCNs. Importantly, this design enables remarkable tumour inhibition through either intratumoral UCNs injection or intravenous injection of nanoparticles modified with the targeting ligand. Our strategy may provide a multimodality solution for effective molecular sensing and site-specific tumour treatment.

  7. 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....... 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...... 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...

  8. Total organic carbon removal from a chemical lab’s wastewater using Fenton’s reagent

    Directory of Open Access Journals (Sweden)

    Oscar Mauricio Martínez Ávila

    2013-05-01

    Full Text Available Treating industrial wastewater represents a serious problem nowadays; it requires a strong understanding of the particular systems and (in most of cases ad hoc solutions. This work describes the use of Fenton’s reagent (reaction between H2O2 and Fe(II for removing total organic carbon (TOC from a particular chemical laboratory’s lab-scale batch reactor wastewater. Some operating variables (hydrogen peroxide and ferrous ion concentration, temperature and pH were evaluated regarding final TOC removal. An economic optimisation was made by means of a second order polynomial model representing these variables’ behaviour regarding TOC removal (0.94 R2. The highest experimentally reached TOC removal was 88.8% at 50 mg/L [Fe(II]0, 50 mM [H2O2]0 , pH=2.8 at 80oC, while 53.9% was obtained in optimised conditions, i.e. 36 mg/L [Fe(II]0 , 45.5 mM [H2O2]0 , pH=2.6 at 20°C. It was found that the Fenton process could achieve 41% removal, even in adverse conditions (pH close to 6. It was noted from the analysis that both H2O2 concentration and temperature had a powerful effect on organic matter degradation efficiency, as well as on total treatment cost.

  9. Total organic carbon removal from a chemical lab’s wastewater using Fenton’s reagent

    Directory of Open Access Journals (Sweden)

    Oscar Mauricio Martínez Ávila

    2012-10-01

    Full Text Available Treating industrial wastewater represents a serious problem nowadays; it requires a strong understanding of the particular systems and (in most of cases ad hoc solutions. This work describes the use of Fenton’s reagent (reaction between H2O2 and Fe(II for removing total organic carbon (TOC from a particular chemical laboratory’s lab-scale batch reactor wastewater. Some operating variables (hydrogen peroxide and ferrous ion concentration, temperature and pH were evaluated regarding final TOC removal. An economic optimisation was made by means of a second order polynomial model representing these variables’ behaviour regarding TOC removal (0.94 R2. The highest experimentally reached TOC removal was 88.8% at 50 mg/L [Fe(II]0, 50 mM [H2O2]0 , pH=2.8 at 80oC, while 53.9% was obtained in optimised conditions, i.e. 36 mg/L [Fe(II]0 , 45.5 mM [H2O2]0 , pH=2.6 at 20°C. It was found that the Fenton process could achieve 41% removal, even in adverse conditions (pH close to 6. It was noted from the analysis that both H2O2 concentration and temperature had a powerful effect on organic matter degradation efficiency, as well as on total treatment cost.

  10. Automated HPLC assay for urinary collagen cross-links: effect of age, menopause, and metabolic bone diseases.

    Science.gov (United States)

    Kraenzlin, Marius E; Kraenzlin, Claude A; Meier, Christian; Giunta, Cecilia; Steinmann, Beat

    2008-09-01

    The pyridinium cross-links pyridinoline (PYD) and deoxypyridinoline (DPD) are established markers of bone resorption. We evaluated the analytical and clinical performance of a commercially available PYD HPLC assay and established reference intervals in children and adults. We used a commercially available reagent set (Chromsystems Instruments & Chemicals) to measure PYD and DPD in 319 healthy controls (156 premenopausal women, 80 healthy men, and 83 healthy children age 1 month to 14 years) and 397 patients with metabolic bone diseases (postmenopausal osteoporosis, n = 175; male osteoporosis, n = 176; hyperparathyroidism, n = 17; hyperthyroidism, n = 19; Paget disease, n = 10). The mean intraassay and interassay CVs were link values peaked at 20-29 years and decreased thereafter. Women with postmenopausal osteoporosis had significantly higher PYD (51%) and DPD (58%) values compared to premenopausal women. Similar results were found in osteoporotic men. In children the highest values were found in the first weeks and months after birth, followed by a decrease of 50%-60% at age 11-14 years. In metabolic bone diseases cross-link concentrations were significantly increased. The DPD:PYD ratio (mean value approximately 0.2) was remarkably constant in all populations evaluated. The automated HPLC assay is a precise and convenient method for PYD and DPD measurement. We established reference intervals for adult women and men and for children up to 14 years old. The cross-link concentrations we determined by use of this HPLC method confirm its clinical value in enabling identification of increased bone resorption in patients with metabolic bone diseases.

  11. Investigations of the application of Fenton's reagent for chemical oxidation in waste-water treatment

    Energy Technology Data Exchange (ETDEWEB)

    Feuerstein, W.

    1982-02-01

    The reactions of Fenton's reagent (H/sub 2/O/sub 2//Fe(II)) with model compounds for refractory aromatic waste water components (p-toluenesulfonic acid, aniline, 4-nitrophenol, 2,4-dichlorophenol) and a waste water from the chemical industry were investigated. The highest reaction rate in presence and in absence of aromatic substrates and best results with respect to the sum parameters of water chemistry are observed at pH 3. Feeding of oxygen or air into the reaction mixture improves considerably the oxidation efficiency. The specific hydrogen peroxide consumption for 50% reduction in COD (chemical oxygen demand) was 0.5 to 0.9 mg H/sub 2/O/sub 2/ per mg of COD. 90% elimination of model compounds needs 1.7 to 2.4 mmole H/sub 2/O/sub 2/ per mmole of aromatic compound. Formation of nonbiodegradable intermediate products were detected with aniline as long as the compound itself was not quantitatively eliminated. Fenton's reagent in combination with feeding pure oxygen or air seems to be a promising oxidation reagent for the conversion of refractory aromatics into biodegradable substances. The specific oxygen reagent consumption is remarkably less than in the case of ozone.

  12. 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.

  13. Convenient analysis of protein modification by chemical blotting with fluorogenic “click” reagents

    Science.gov (United States)

    Ohata, Jun; Farrukh, Vohidov; Ball, Zachary T.

    2015-01-01

    Direct visualization of bioorthogonal alkyne or azide handles using fluorogenic azide-alkyne cycloaddition conducted on the surface of a blot membrane. The method eliminates the need for separation steps to remove excess small molecule reagents before attachment of antigen molecules or other visualization handles, and is especially useful for the analysis of peptides and small proteins. A variety of potential fluorogenic reagents are assessed, and sensitivity (<0.1 picomole) similar to current commercially available fluorescence imaging methods is possible. PMID:26325302

  14. Rapid yeast DNA extraction by boiling and freeze-thawing without using chemical reagents and DNA purification

    Directory of Open Access Journals (Sweden)

    Gildo Almeida da Silva

    2012-04-01

    Full Text Available The purpose of this work was to study a rapid yeast DNA extraction by boiling and freeze-thawing processes without using chemical reagents or any purification procedures, to obtain a high grade PCR-product. A specific DNA fragment of the 18S region of Dekkera bruxellensis and Saccharomyces cerevisiae was chosen. The described boiling and freeze-thawing protocols generated the PCR-grade product preparations and could be used to process many samples. The amplification of the fragments could be observed after 30 and 35 cycles. These processes of extraction without using any kind of chemical reagents, especial water, and purification procedures proved to be efficient, reproducible, simple, fast, and inexpensive.

  15. A combined photocatalytic determination system for chemical oxygen demand with a highly oxidative reagent.

    Science.gov (United States)

    Zhang, Aiyong; Zhou, Minghua; Zhou, Qixing

    2011-02-07

    This study focuses on the proposal and validation of a combined photocatalytic (PC) system and a three-parameterized procedure for the determination of chemical oxygen demand (COD; PcCOD(combined)), with a highly oxidative reagent utilized as a photoelectron scavenger and signal indicator. The PcCOD(combined) was the functional combination of photon-efficient thin-layer photocatalytic oxidation, conventional bulk-phase photocatalytic oxidation and photocarrier-efficient high-activity photocatalytic reduction in one single photodigestion system, and consequently, this system possessed high photon-utilization efficiency, automatic stirring function and satisfactory determination characteristics. In comparison with the conventional one-parameterized procedure, the three-parameterized procedure introduces the blank and total photocatalytic reduction responses as two of the three significant analytical parameters. Under the optimized pH value of 3.0-4.5 and a rotating rate of 40 rpm, the representative KMnO(4) species was used for the PcCOD(combined) system as the combined high-activity oxidant, and a narrow and reliable analytical linear range of 0-260 mg L(-1) was achieved during the 10 min duration of the determinations. No observable interference of Cl(-) was found at concentration of the ion up to 2000 mg L(-1). A real sample analysis indicated that the measured values for the PcCOD(combined) were all within a relative deviation below 5% of COD(Cr) of the standard method, which further validates the practical feasibility of the proposed PcCOD(combined) system. Copyright © 2010 Elsevier B.V. All rights reserved.

  16. CF3+ and CF2H+: new reagents for n-alkane determination in chemical ionisation reaction mass spectrometry.

    Science.gov (United States)

    Blake, Robert S; Ouheda, Saleh A; Evans, Corey J; Monks, Paul S

    2016-11-28

    Alkanes provide a particular analytical challenge to commonly used chemical ionisation methods such as proton-transfer from water owing to their basicity. It is demonstrated that the fluorocarbon ions CF3+ and CF2H+, generated from CF4, as reagents provide an effective means of detecting light n-alkanes in the range C2-C6 using direct chemical ionisation mass spectrometry. The present work assesses the applicability of the reagents in Chemical Ionisation Mass Spectrometric (CI-TOF-MS) environments with factors such as high moisture content, operating pressures of 1-10 Torr, accelerating electric fields (E/N) and long-lived intermediate complex formation. Of the commonly used chemical ionisation reagents, H3O+ and NO+ only react with hexane and higher while O2+ reacts with all the target samples, but creates significant fragmentation. By contrast, CF3+ and CF2H+ acting together were found to produce little or no fragmentation. In dry conditions with E/N = 100 Td or higher the relative intensity of CF2H+ to CF3+ was mostly less than 1% but always less than 3%, making CF3+ the main reagent ion. Using O2+ in a parallel series of experiments, a substantially greater degree of fragmentation was observed. The detection sensitivities of the alkanes with CF3+ and CF2H+, while relatively low, were found to be better than those observed with O2+. Experiments using alkane mixtures in the ppm range have shown the ionisation technique based on CF3+ and CF2H+ to be particularly useful for measurements of alkane/air mixtures found in polluted environments. As a demonstration of the technique's effectiveness in complex mixtures, the detection of n-alkanes in a smoker's breath is demonstrated.

  17. Single-sided NMR for the measurement of the degree of cross-linking and curing

    Directory of Open Access Journals (Sweden)

    N. Halmen

    2018-01-01

    Full Text Available The degree of cross-linking and curing is one of the most important values concerning the quality of cross-linked polyethylene (PE-X and the functionality of adhesives and resin-based components. Up to now, the measurement of this property has mostly been time-consuming and usually destructive. Within the shown work the feasibility of single-sided nuclear magnetic resonance (NMR for the non-destructive determination of the degree of cross-linking and curing as process monitoring was investigated. First results indicate the possibility of distinguishing between PE-X samples with different degrees of cross-linking. The homogeneity of the samples and the curing kinetics of adhesives can also be monitored. The measurements show good agreement with reference tests (wet chemical analysis, differential scanning calorimetry, dielectric analysis. Furthermore, the influence of sample temperature on the characteristic relaxation times can be observed.

  18. 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...... 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...... 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....

  19. Corneal collagen cross-linking outcomes: review.

    Science.gov (United States)

    Jankov Ii, Mirko R; Jovanovic, Vesna; Delevic, Sladjana; Coskunseven, Efekan

    2011-02-11

    Keratoconus is a condition characterized by biomechanical instability of the cornea, presenting in a progressive, asymmetric and bilateral way. Corneal collagen cross-linking with riboflavin and UVA (CXL) is a new technique of corneal tissue strengthening that combines the use of riboflavin as a photo sensitizer and UVA irradiation. The studies showed that CXL was effective in halting the progression of keratoconus over a period of up to four years. The published studies also revealed a reduction of max K readings by more than 2 D, while the postoperative SEQ was reduced by an average of more than 1 D, and refractive cylinder decreased by about 1 D. No eyes lost any line of BCDVA. Moreover, there was no significant decrease in endothelial cell density. It was also found that CXL treatment was effective with reducing corneal and total wavefront aberrations. Corneal cross-linking has also led to an arrest and/or even a partial reversal of keratectasia in the treatment of iatrogenic ectasia after excimer laser ablation. A primary intervention such as CXL should be considered to potentially increase the biomechanical stability of the corneal tissue and postpone the need of lamellar or penetrating keratoplasty.

  20. Functional polyketones for the removal of calcium and magnesium from water (Part II) : cross-linking and functional characterization

    NARCIS (Netherlands)

    Figaroa, Patrick; Miedema, Henk; Euverink, Gerrit; Picchioni, Francesco

    Functional polyketones were chemically cross-linked for the softening of hard water, i.e. for the removal of the divalent cations Ca2+ and Mg2+. Elemental analysis, FT-IR spectroscopy, solubility- and swelling-experiments were used to demonstrate the occurrence of the cross-link reaction. Testing

  1. 21 CFR 177.2420 - Polyester resins, cross-linked.

    Science.gov (United States)

    2010-04-01

    ... 21 Food and Drugs 3 2010-04-01 2009-04-01 true Polyester resins, cross-linked. 177.2420 Section... as Components of Articles Intended for Repeated Use § 177.2420 Polyester resins, cross-linked. Cross-linked polyester resins may be safely used as articles or components of articles intended for repeated...

  2. 21 CFR 177.1211 - Cross-linked polyacrylate copolymers.

    Science.gov (United States)

    2010-04-01

    ... polyacrylate copolymers consist of: (1) The grafted copolymer of cross-linked sodium polyacrylate identified as... 21 Food and Drugs 3 2010-04-01 2009-04-01 true Cross-linked polyacrylate copolymers. 177.1211... Basic Components of Single and Repeated Use Food Contact Surfaces § 177.1211 Cross-linked polyacrylate...

  3. A novel pyrroleninone cross-link from bovine dentine

    NARCIS (Netherlands)

    Kleter, G.A.; Damen, J.J.M.; Kettenes-Bosch, J.J. van den; Bank, R.A.; Koppele, J.M. te; Veraart, J.R.; Cate, J.M. ten

    1998-01-01

    The aim was to identify suspect collagen cross-links in dentine, eluting close to known cross-links in ion-exchange HPLC. Bovine tooth roots as source of dentine were powdered, demineralised, reduced, and acid-hydrolysed. Cross-linking amino acids were isolated from the acid hydrolysate by size

  4. 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

    spectrometry is becoming increasingly popular for characterization of purified peptide-nucleic acid heteroconjugates derived from UV cross-linked protein-nucleic acid complexes. The efficiency of mass spectrometry-based methods is, however, hampered by the contrasting physico-chemical properties of nucleic...

  5. [Treatment of keratoconus by collagen cross linking].

    Science.gov (United States)

    Wollensak, G; Spörl, E; Seiler, T

    2003-01-01

    We were able to show a significant increase in corneal stiffness of rabbit and porcine eyes after combined riboflavin/UVA-induced collagen cross-linking. In this study,we tried to treat keratoconus patients with this method to stop the progression of corneal ectasia. We treated 16 eyes of 15 patients with progressive keratoconus and mostly moderate keratectasia (48-56 dpt). After removal of the epithelium (7 mm X), riboflavin solution was applied on the cornea, which was irradiated with UVA (370 nm,3 mW/cm(2)) at a distance of 1 cm for 30 min.Post-operative follow-up controls were conducted every 3 months in the first year and then every 6 months, always including visual acuity testing, corneal topography and measurements of endothelial cell density. The follow-up time was between 1 and 3 years. Progression of keratectasia was stopped in all patients. Best corrected visual acuity and the maximal keratometry values improved slightly in about 50% of the cases. In all patients corneal transparency, the degree of keratectasia registered by corneal topography and the density of endothelial cells remained unchanged within the follow-up time. No negative side-effects were observed. Our results show that collagen cross linking might be a useful conservative treatment modality to stop the progression of keratoconus. By this means the need for keratoplasty might be significantly reduced. Given the simplicity of the technique and minimal costs of the treatment it might also be well suited for developing countries.Further studies are envisaged to exclude long-term side effects and to evaluate the long term durability of the mechanical stiffness effect.

  6. Cross-linked Collagen Hydrogel Matrix Resisting Contraction To Facilitate Full-Thickness Skin Equivalents.

    Science.gov (United States)

    Lotz, Christian; Schmid, Freia F; Oechsle, Eva; Monaghan, Michael G; Walles, Heike; Groeber-Becker, Florian

    2017-06-21

    Full-thickness skin equivalents are gathering increased interest as skin grafts for the treatment of large skin defects or chronic wounds or as nonanimal test platforms. However, their fibroblast-mediated contraction and poor mechanical stability lead to disadvantages toward their reproducibility and applicability in vitro and in vivo. To overcome these pitfalls, we aimed to chemically cross-link the dermal layer of a full-thickness skin model composed of a collagen type I hydrogel. Using a noncytotoxic four-arm succinimidyl glutarate polyethylene glycol (PEG-SG), cross-linking could be achieved in cell seeded collagen hydrogels. A concentration of 0.5 mg of PEG-SG/mg of collagen led to a viability comparable to non-cross-linked collagen hydrogels and no increased release of intracellular lactate dehydrogenase. Cross-linked collagen hydrogels were more mechanically stable and less prone to enzymatic degradation via collagenase when compared with non-cross-linked collagen hydrogels. Remarkably, during 21 days, cross-linked collagen hydrogels maintain their initial surface area, whereas standard dermal models contracted up to 50%. Finally, full-thickness skin equivalents were generated by seeding human epidermal keratinocytes on the surface of the equivalents and culturing these equivalents at an air-liquid interface. Immunohistochemical stainings of the cross-linked model revealed well-defined epidermal layers including an intact stratum corneum and a dermal part with homogeneously distributed human dermal fibroblasts. These results indicate that cross-linking of collagen with PEG-SG reduces contraction of collagen hydrogels and thus increases the applicability of these models as an additional tool for efficacy and safety assessment or a new generation of skin grafts.

  7. Students' Dilemmas in Reaction Stoichiometry Problem Solving: Deducing the Limiting Reagent in Chemical Reactions

    Science.gov (United States)

    Chandrasegaran, A. L.; Treagust, David F.; Waldrip, Bruce G.; Chandrasegaran, Antonia

    2009-01-01

    A qualitative case study was conducted to investigate the understanding of the limiting reagent concept and the strategies used by five Year 11 students when solving four reaction stoichiometry problems. Students' written problem-solving strategies were studied using the think-aloud protocol during problem-solving, and retrospective verbalisations…

  8. Nanoporous magnesium aluminometasilicate tablets for precise, controlled, and continuous dosing of chemical reagents and catalysts

    DEFF Research Database (Denmark)

    Ruhland, T.; Nielsen, S.D.; Holm, P.

    2007-01-01

    Mechanically robust tablets of nanoporous magnesium aluminometasilicate with high surface area and porosity can be loaded with a variety of organic and inorganic reagents and catalysts. The scope of this novel dosing methodology is demonstrated through the evaluation of 14 diverse organic reactions...

  9. 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…

  10. (S)-(-)-N-(pentafluorobenzylcarbamoyl)prolyl chloride: a chiral derivatisation reagent designed for gas chromatography/negative ion chemical ionisation mass spectrometry of amino compounds.

    Science.gov (United States)

    Leis, Hans J; Windischhofer, Werner

    2012-03-30

    The synthesis of a novel chiral derivatisation reagent, (S)-(-)-N-(pentafluorobenzylcarbamoyl)prolyl chloride is described which is preferably useful for negative-ion chemical ionisation mass spectrometry. Preparation of the reagent followed a general strategy used to prepare enantioselective reagents based on the N-substitution of L-proline. Pentafluorobenzyl chloroformate smoothly reacted with L-proline to give the desired derivatisation reagent after conversion into the acyl chloride. The product was sufficiently pure to be used in the following steps without any additional purification. The reagent was tested against selected chiral and non-chiral analytical targets. Chromatographic enantioseparation was at least equal to the commonly used (S)-(-)-N-(heptafluorobutyryl)prolyl derivatives. The derivatives exhibit excellent mass spectral properties under negative ion chemical ionisation, i.e. reduced fragmentation and thus high ion current for the targeted m/z during analysis. With electron ionisation, the fragmentation that occurs is mainly directed by the introduced group. Enantioseparation with gas chromatography/negative-ion chemical ionisation mass spectrometry of the derivatives was demonstrated for the enantiomers of amphetamine, α-aminocaprylic acid methyl ester and threo-methylphenidate. The new derivatisation reagent shows highly improved mass spectral properties for negative-ion chemical ionisation mass spectrometry and is thus suitable for sensitive chiral detection of amino compounds. The reagent extends the applicability of dissociative resonance electron capture using pentafluorobenzyl derivatives to chiral analysis. Copyright © 2012 John Wiley & Sons, Ltd.

  11. Simultaneous processing of fibril formation and cross-linking improves mechanical properties of collagen.

    Science.gov (United States)

    Yunoki, Shunji; Matsuda, Takehisa

    2008-03-01

    In vitro "simultaneous processing" was investigated in which fibril formation of collagen and cross-linking occur simultaneously in the presence of 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDC) as a cross-linking reagent. Fibril formation in simultaneous processing was monitored using turbidity. The EDC in simultaneous processing increased T(1/2) (time required for half of the plateau value in turbidity) and decreased the degree of the fibril formation dose dependently. The reduced fibril formation rate (T(1/2) > 60 s) suggests the introduction of intrafibrillar cross-linking during fibril formation. The collagen gels prepared using simultaneous processing had a compressive modulus that was 6-fold higher than that using sequential processing, which is an advantage of simultaneous processing. Atomic force microscopy images acquired under water on the wet gels demonstrated that the simultaneous processing provided a unique double-network structure: intrafibrillarly cross-linked collagen fibrils among which nonfibrous collagens act as interfibrillar cross-linkages.

  12. Cross-linking for microbial keratitis.

    Science.gov (United States)

    Chan, Tommy C Y; Agarwal, Tushar; Vajpayee, Rasik B; Jhanji, Vishal

    2016-07-01

    Microbial keratitis is one of the leading causes of ocular morbidity. The standard treatment consists of antibiotics, which is intensive and is fraught with risks of antibiotic resistance. Corneal collagen cross-linking (CXL) has recently been advocated as an adjunctive therapy for management of microbial keratitis. The addition of CXL to ongoing antimicrobial treatment can have a potential effect on overall duration of the disease, need for corneal transplantation, final visual outcome, and long-term impact on drug resistance pattern. CXL has been used in cases with bacterial, fungal as well as amoebic keratitis. However, so far the reported results have been variable and the evidence is largely anecdotal. The debate over the safety and efficacy of this modality continues especially with regards to its utilization in early phases of the disease when the corneal involvement is limited to the anterior stroma. CXL appears to be a promising adjunctive treatment in selective cases of mild to moderate bacterial keratitis. Its efficacy in fungal and amoebic keratitis is questionable. Treatment protocols in microbial keratitis need to be individualized. Long-term, prospective, randomized trials are needed to determine its usefulness in microbial keratitis.

  13. Riboflavin for corneal cross-linking.

    Science.gov (United States)

    O'Brart, D P S

    2016-06-01

    Corneal collagen cross-linking (CXL) with riboflavin and ultraviolet A (UVA) radiation is the first therapeutic modality that appears to arrest the progression of keratoconus and other corneal ectasias. Riboflavin is central to the process, acting as a photosensitizer for the production of oxygen singlets and riboflavin triplets. These free radicals drive the CXL process within the proteins of the corneal stroma, altering its biomechanical properties. Riboflavin also absorbs the majority of the UVA radiation, which is potentially cytotoxic and mutagenic, within the anterior stroma, preventing damage to internal ocular structures, such as the corneal endothelium, lens and retina. Clinical studies report cessation of ectatic progression in over 90% of cases and the majority document significant improvements in visual, keratometric and topographic parameters. Clinical follow-up is limited to 5-10 years, but suggests sustained stability and enhancement in corneal shape. Sight-threatening complications are rare. The optimal stromal riboflavin dosage for CXL is as yet undetermined. Copyright 2016 Prous Science, S.A.U. or its licensors. All rights reserved.

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

    Directory of Open Access Journals (Sweden)

    Juan D Chavez

    Full Text Available 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.

  15. Cross-linking of dermal sheep collagen with tannic acid.

    Science.gov (United States)

    Heijmen, F H; du Pont, J S; Middelkoop, E; Kreis, R W; Hoekstra, M J

    1997-05-01

    The purpose of this study was to investigate cross-linking of (damaged) collagen by tannic acid, with a view to reconsider its use as a possible therapeutical agent in the treatment of burn wounds. Because of contradictory reports in the literature, and increased purity of tannic acid, this method has again become valuable for re-evaluation. A laboratory study using dermal sheep collagen was conducted to analyse the influence of several metal ions on collagen cross-linking with tannic acid. The tannic acid concentration vs degree of cross-linking, tannic acid uptake and release, influence of the addition of metal ions, and the rate of degradation of treated collagen were established. We have shown that tannic acid mediated collagen cross-linking in a concentration-dependent manner. Cross-linking was influenced by the presence of metal ions: Fe3+ and Ag+ were shown to exert a stimulatory effect on the degree of cross-linking by a 2% tannic acid solution, whereas Zn2+ had an inhibitory effect Ce3+ Ca2+ and Na+ did not influence the degree of cross-linking. The degree of cross-linking was proportional to the uptake of tannic acid, which variod between 6 and 35 wt%. Reversibility of cross-linking was established. Tannic acid-treated dermal sheep collagen showed a slow degradation rate relative to differently cross-linked collagen materials when subjected to collagenase or pancreatic proteolytic enzymes. The results of this study suggest that tannic acid could have a function in vivo in burn treatment by binding burn toxins and inhibiting degradation of the (remaining) dermal matrix, and allows combination with metal ions as antimicrobials. Optimal cross-linking was obtained using a 2 wt% tannic acid solution; combination with Ce3+ as a potential antimicrobial agent is possible without diminishing cross-linking.

  16. Experimental research of the impact of the dosing of chemical reagents on the dynamic behavior of regulation system of cycle chemistry

    Science.gov (United States)

    Yegoshina, O. V.; Bolshakova, N. A.

    2017-11-01

    Organization of reliable chemical control for maintaining cycle chemistry is one of the most important problems to be solved at the present time the design and operation of thermal power plants. To maintain optimal parameters of cycle chemistry are used automated chemical control system and regulation system of dosing chemical reagents. Reliability and stability analyzer readings largely determine the reliability of the water cycle chemistry. Now the most common reagents are ammonia, alkali and film-forming amines. In this paper are presented the results of studies of the impact of concentration and composition of chemical reagents for readings stability of automatic analyzers and transients time of control systems for cycles chemistry. Research of the impact of chemical reagents on the dynamic behavior of regulation system for cycle chemistry was conducted at the experimental facility of the Department of thermal power stations of the Moscow Engineering Institute. This experimental facility is model of the work of regulation system for cycle chemistry close to the actual conditions on the energy facilities CHP. Analysis of results of the impact of chemical reagent on the dynamic behavior of ammonia and film forming amines dosing systems showed that the film-forming amines dosing system is more inertia. This emphasizes the transition process of the system, in which a half times longer dosing of ammonia. Results of the study can be used to improve the monitoring systems of water chemical treatment.

  17. Evaluation of the degree of cross-linking in UV irradiated porcine valves.

    Science.gov (United States)

    Suh, H; Lee, W K; Park, J C; Cho, B K

    1999-04-01

    A porcine heart valve was irradiated by Ultraviolet (UV) rays (10 W, 254 nm) for 2, 4, 8 and 24 hours at 4 degrees C to cross-link the structural collagen matrix. The degree of cross-linking was evaluated by assaying the released amount of hydroxyproline (Hyp) from the matrix, and comparing it with the positive controls of valves treated by glutaraldehyde (GA) solution (0.625 wt%) and the negative controls of non-treated fresh valves. The undigested weight ratio of the specimens increased by increasing the UV irradiation time. The undigested weight of the leaflets, tunica interna and tunica externa of the fresh, GA-treated and UV-irradiated specimens after collagenase digestion was compared. As UV irradiation increased, the amount of released hydroxyproline was gradually decreased until 8 hours of irradiation, after which the released hydroxyproline-reduction occurred slightly until 24 hours of irradiation time in this system. A total 47.68% of the hydroxyproline in the valve was cross-linked by UV irradiation after 24 hours, while 73.74% of the hydroxyproline in the positive control was crossed-linked. Light microscopic observation revealed that the typical crimp pattern of collagen fibers decreased and was rearranged into a dense flattened pattern as the UV irradiation induced interfibrilar cross-linking. GA-treated valves demonstrated a denser matrix pattern than the UV-irradiated specimens. Cross-linked collagenous tissue prepared by UV irradiation would be useful for improving durability and reducing the disadvantages related to using a chemical cross-linking agent.

  18. Second-generation method for analysis of chromatin binding with formaldehyde-cross-linking kinetics.

    Science.gov (United States)

    Zaidi, Hussain; Hoffman, Elizabeth A; Shetty, Savera J; Bekiranov, Stefan; Auble, David T

    2017-11-24

    Formaldehyde-cross-linking underpins many of the most commonly used experimental approaches in the chromatin field, especially in capturing site-specific protein-DNA interactions. Extending such assays to assess the stability and binding kinetics of protein-DNA interactions is more challenging, requiring absolute measurements with a relatively high degree of physical precision. We previously described an experimental framework called the cross-linking kinetics (CLK) assay, which uses time-dependent formaldehyde-cross-linking data to extract kinetic parameters of chromatin binding. Many aspects of formaldehyde behavior in cells are unknown or undocumented, however, and could potentially affect CLK data analyses. Here, we report biochemical results that better define the properties of formaldehyde-cross-linking in budding yeast cells. These results have the potential to inform interpretations of "standard" chromatin assays, including chromatin immunoprecipitation. Moreover, the chemical complexity we uncovered resulted in the development of an improved method for measuring binding kinetics with the CLK approach. Optimum conditions included an increased formaldehyde concentration and more robust glycine-quench conditions. Notably, we observed that formaldehyde-cross-linking rates can vary dramatically for different protein-DNA interactions in vivo Some interactions were cross-linked much faster than the in vivo macromolecular interactions, making them suitable for kinetic analysis. For other interactions, we found the cross-linking reaction occurred on the same time scale or slower than binding dynamics; for these interactions, it was sometimes possible to compute the in vivo equilibrium-binding constant but not binding on- and off-rates. This improved method yields more accurate in vivo binding kinetics estimates on the minute time scale. © 2017 by The American Society for Biochemistry and Molecular Biology, Inc.

  19. Heavy Grignard Reagents: Synthesis, Physical and Structural Properties, Chemical Behavior, and Reactivity.

    Science.gov (United States)

    Westerhausen, Matthias; Koch, Alexander; Görls, Helmar; Krieck, Sven

    2017-01-31

    The Grignard reaction offers a straight forward atom-economic synthesis of organomagnesium halides, which undergo redistribution reactions (Schlenk equilibrium) yielding diorganylmagnesium and magnesium dihalides. The homologous organocalcium complexes (heavy Grignard reagents) gained interest only quite recently owing to several reasons. The discrepancy between the inertness of this heavy alkaline earth metal and the enormous reactivity of its organometallics hampered a vast and timely development after the first investigation more than 100 years ago. In this overview the synthesis of organocalcium reagents is described as is the durability in ethereal solvents. Aryl-, alkenyl-, and alkylcalcium halides are prepared by direct synthesis. Characteristic structural features and NMR parameters are discussed. Ligand redistribution reactions can be performed by addition of potassium tert-butanolate to ethereal solutions of arylcalcium iodides yielding soluble diarylcalcium, whereas sparingly soluble potassium iodide and calcium bis(tert-butanolate) precipitate. Furthermore, reactivity studies with respect to metalation and addition to unsaturated organic compounds and metal-based Lewis acids, leading to the formation of heterobimetallic complexes, are presented. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  20. Kinetic-quantum chemical model for catalytic cycles: the Haber-Bosch process and the effect of reagent concentration.

    Science.gov (United States)

    Kozuch, Sebastian; Shaik, Sason

    2008-07-03

    A combined kinetic-quantum chemical model is developed with the goal of estimating in a straightforward way the turnover frequency (TOF) of catalytic cycles, based on the state energies obtained by quantum chemical calculations. We describe how the apparent activation energy of the whole cycle, so-called energetic span (delta E), is influenced by the energy levels of two species: the TOF determining transition state (TDTS) and the TOF determining intermediate (TDI). Because these key species need not be adjoining states, we conclude that for catalysis there are no rate-determining steps, only rate determining states. In addition, we add here the influence of reactants concentrations. And, finally, the model is applied to the Haber-Bosch process of ammonia synthesis, for which we show how to calculate which catalyst will be the most effective under specific reagents conditions.

  1. 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......-linked by an amidation reaction using 3,6,9-trioxaundecandioic acid cross-linker. The cross-linked micelle was functionalized with two pH sensitive fluorophores and one reference fluorophore, which resulted in a highly uniform ratiometric pH nanosensor with a diameter of 29 nm. The use of two sensor fluorophores...

  2. An unprecedented single platform via cross-linking of zeolite and MOFs.

    Science.gov (United States)

    Lim, Dae-Woon; Lee, Heeju; Kim, Sungjune; Cho, In Hwa; Yoon, Minyoung; Choi, Yong Nam

    2016-05-21

    The unprecedented ternary nanocomposites have been synthesized as a single platform via cross-linking of two nanoporous materials, MOFs and Pt nanoparticle (NP) loaded zeolite. The heterojunction of the novel nanocomposites is anticipated to work as a chemical platform for size selective catalytic hydrogenation or deuteration of small molecules.

  3. Baking Performance of Phosphorylated Cross-Linked Resistant Starch in Low-Moisture Bakery Goods

    Science.gov (United States)

    Phosphorylated cross-linked resistant starch (RS) is a type 4 RS, which can be used for enhancing the benefits of dietary fiber. The baking performance of the RS was explored using wire-cut cookie baking and benchtop chemically-leavened cracker baking methods to produce low-moisture baked goods (coo...

  4. Thermogelling and chemoselectively cross-linked hydrogels with controlled mechanical properties and degradation behavior

    NARCIS (Netherlands)

    Boere, Kristel W M; Van Den Dikkenberg, Joep; Gao, Yuan; Visser, Jetze; Hennink, Wim E.; Vermonden, Tina

    2015-01-01

    Chemoselectively cross-linked hydrogels have recently gained increasing attention for the development of novel, injectable biomaterials given their limited side reactions. In this study, we compared the properties of hydrogels obtained by native chemical ligation (NCL) and its recently described

  5. Mechanical Strength Improvements of Carbon Nanotube Threads through Epoxy Cross-Linking

    Directory of Open Access Journals (Sweden)

    Qingyue Yu

    2016-01-01

    Full Text Available Individual Carbon Nanotubes (CNTs have a great mechanical strength that needs to be transferred into macroscopic fiber assemblies. One approach to improve the mechanical strength of the CNT assemblies is by creating covalent bonding among their individual CNT building blocks. Chemical cross-linking of multiwall CNTs (MWCNTs within the fiber has significantly improved the strength of MWCNT thread. Results reported in this work show that the cross-linked thread had a tensile strength six times greater than the strength of its control counterpart, a pristine MWCNT thread (1192 MPa and 194 MPa, respectively. Additionally, electrical conductivity changes were observed, revealing 2123.40 S·cm−1 for cross-linked thread, and 3984.26 S·cm−1 for pristine CNT thread. Characterization suggests that the obtained high tensile strength is due to the cross-linking reaction of amine groups from ethylenediamine plasma-functionalized CNT with the epoxy groups of the cross-linking agent, 4,4-methylenebis(N,N-diglycidylaniline.

  6. Synthesis of surface protein-imprinted nanoparticles endowed with reversible physical cross-links.

    Science.gov (United States)

    Yang, Chongchong; Yan, Xianming; Guo, Hao; Fu, Guoqi

    2016-01-15

    Researches on protein molecularly imprinted polymers have been challenged by the difficulties in facilitating biomacromolecular transfer, in particular upon the template removal step, and enhancing their recognition performance. Addressing these issues, herein we report synthesis of core–shell structured surface protein-imprinted nanoparticles with reversible physical cross-links formed in the imprinted nanoshells. The imprinted layers over nanoparticle supports are fabricated via aqueous precipitation polymerization (PP) of di(ethylene glycol) methyl ether methacrylate (MEO2MA), a thermo-responsive monomer bearing no strong H-bond donor, and other functional and cross-linking monomers. During polymerization, physical cross-links together with chemical cross-links are in site produced within the imprinted shells based on hydrophobic association among the PMEO2MA, favoring formation of high-quality imprints. While cooled appropriately below the polymerization temperature, these physical cross-links can be dissociated rapidly, thus facilitating removal of the embedded template. For proof of this concept, lysozyme-imprinted nanoparticles were synthesized at 37 °C over the nanoparticles functionalized with carboxylic and vinyl groups. The template removal from the imprinted nanoparticles was readily achieved by washing with a dilute acidic detergent solution at 4 °C. As-prepared imprinted nanoparticles showed greatly higher imprinting factor and specific rebinding than obtained with the same recipe but by solution polymerization (SP). Moreover, such imprinted nanomaterials exhibited satisfactory rebinding selectivity, kinetics and reusability.

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

    CSIR Research Space (South Africa)

    Luo, H

    2009-05-01

    Full Text Available The proton exchange membrane was prepared by covalent cross-linking sulfonated-sulfinated polyetheretherketone. The cross-linked membrane showed high proton conductivity (0.04 S/cm) with suitable water uptake, low methanol permeability (2.21 × 10...

  8. Hydrogels Prepared from Cross-Linked Nanofibrillated Cellulose

    Science.gov (United States)

    Sandeep S. Nair; J.Y. Zhu; Yulin Deng; Arthur J. Ragauskas

    2014-01-01

    Nanocomposite hydrogels were developed by cross-linking nanofibrillated cellulose with poly(methyl vinyl ether-co-maleic acid) and polyethylene glycol. The cross-linked hydrogels showed enhanced water absorption and gel content with the addition of nanocellulose. In addition, the thermal stability, mechanical strength, and modulus increased with an increase in the...

  9. Preparation and adsorption property of aminated cross linking ...

    Indian Academy of Sciences (India)

    Administrator

    gas bath (Boxun Medical Treatment Equipment Fac- tory of Shanghai), 438VP Scanning Electron Micro- scope (SEM, England LEO Company). 2.2 Synthesis and characteristic of cross linking microbeads GMA/EGDMA. The cross linking microbeads were prepared by sus- pension polymerization of GMA and EGDMA with.

  10. Cross-linked polyelectrolyte multilayers for marine antifouling applications

    NARCIS (Netherlands)

    Zhu, X.; Janczewski, D.; Lee, S.S.C.; Teo, S.L-M.; Vancso, Gyula J.

    2013-01-01

    A polyionic multilayer film was fabricated by layer-by-layer (LbL) sequential deposition followed by cross-linking under mild conditions on a substrate surface to inhibit marine fouling. A novel polyanion, featuring methyl ester groups for an easy cross-linking was used as a generic solution for

  11. Preparation of the Reagent

    Indian Academy of Sciences (India)

    Srimath

    D-glucose and D-fructose. It is the easiest to perform among all the distinguishing tests available in the literature [2,3] for these two sugars, gives unambiguous results and uses ordinary chemicals such as NaOH and potassium ferricyanide. Preparation of the Reagent. The alkaline potassium ferricyanide reagent is prepared ...

  12. Cross-linked agarose for separation of low molecular weight natural products in hydrophilic interaction liquid chromatography.

    Science.gov (United States)

    Tan, Tianwei; Su, Zhi-Guo; Gu, Ming; Xu, Jun; Janson, Jan-Christer

    2010-05-01

    Following its market introduction in 1982, the cross-linked 12% agarose gel media Superose 12 has become widely known as a tool for size exclusion chromatography of proteins and other biological macromolecules. In this review it is shown that, when appropriate mobile phases are used, Superose possesses adsorption properties similar to that of traditional media for hydrophilic interaction liquid chromatography (HILIC). This is illustrated by the separation and purification of low molecular weight compounds such as polyphenols including active components of traditional Chinese medicinal herbs and green tea. Structural features of the cross-linked agarose that likely cause the observed adsorption effects are discussed as well. These are identified as being primarily ether bonds acting as strong hydrogen bond acceptors as well as hydrophobic residues originating from the cross-linking reagents.

  13. Recent advances in corneal collagen cross-linking

    Directory of Open Access Journals (Sweden)

    Gitansha Shreyas Sachdev

    2017-01-01

    Full Text Available Corneal collagen cross-linking has become the preferred modality of treatment for corneal ectasia since its inception in late 1990s. Numerous studies have demonstrated the safety and efficacy of the conventional protocol. Our understanding of the cross-linking process is ever evolving, with its wide implications in the form of accelerated and pulsed protocols. Newer advancements in technology include various riboflavin formulations and the ability to deliver higher fluence protocols with customised irradiation patterns. A greater degree of customisation is likely the path forward, which will aim at achieving refractive improvements along with disease stability. The use of cross-linking for myopic correction is another avenue under exploration. Combination of half fluence cross-linking with refractive correction for high errors to prevent post LASIK regression is gaining interest. This review aims to highlight the various advancements in the cross-linking technology and its clinical applications.

  14. Recent advances in corneal collagen cross-linking.

    Science.gov (United States)

    Sachdev, Gitansha Shreyas; Sachdev, Mahipal

    2017-09-01

    Corneal collagen cross-linking has become the preferred modality of treatment for corneal ectasia since its inception in late 1990s. Numerous studies have demonstrated the safety and efficacy of the conventional protocol. Our understanding of the cross-linking process is ever evolving, with its wide implications in the form of accelerated and pulsed protocols. Newer advancements in technology include various riboflavin formulations and the ability to deliver higher fluence protocols with customised irradiation patterns. A greater degree of customisation is likely the path forward, which will aim at achieving refractive improvements along with disease stability. The use of cross-linking for myopic correction is another avenue under exploration. Combination of half fluence cross-linking with refractive correction for high errors to prevent post LASIK regression is gaining interest. This review aims to highlight the various advancements in the cross-linking technology and its clinical applications.

  15. Cross-linked polyvinyl alcohol and method of making same

    Science.gov (United States)

    Hsu, L. C.; Sheibley, D. W.; Philipp, W. H. (Inventor)

    1981-01-01

    A film-forming polyvinyl alcohol polymer is mixed with a polyaldehyde-polysaccharide cross-linking agent having at least two monosaccharide units and a plurality of aldehyde groups per molecule, perferably an average of at least one aldehyde group per monosaccharide units. The cross-linking agent, such as a polydialdehyde starch, is used in an amount of about 2.5 to 20% of the theoretical amount required to cross-link all of the available hydroxyl groups of the polyvinyl alcohol polymer. Reaction between the polymer and cross-linking agent is effected in aqueous acidic solution to produce the cross-linked polymer. The polymer product has low electrical resistivity and other properties rendering it suitable for making separators for alkaline batteries.

  16. 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.

  17. Radiation cross-linked collagen/dextran dermal scaffolds: effects of dextran on cross-linking and degradation.

    Science.gov (United States)

    Zhang, Yaqing; Zhang, Xiangmei; Xu, Ling; Wei, Shicheng; Zhai, Maolin

    2015-01-01

    Ionizing radiation effectively cross-links collagen into network with enhanced anti-degradability and biocompatibility, while radiation-cross-linked collagen scaffold lacks flexibility, satisfactory surface appearance, and performs poor in cell penetration and ingrowth. To make the radiation-cross-linked collagen scaffold to serve as an ideal artificial dermis, dextran was incorporated into collagen. Scaffolds with the collagen/dextran (Col/Dex) ratios of 10/0, 7/3, and 5/5 were fabricated via (60)Co γ-irradiation cross-linking, followed by lyophilization. The morphology, microstructure, physicochemical, and biological properties were investigated. Compared with pure collagen, scaffolds with dextran demonstrated more porous appearance, enhanced hydrophilicity while the cross-linking density was lower with the consequence of larger pore size, higher water uptake, as well as reduced stiffness. Accelerated degradation was observed when dextran was incorporated in both the in vitro and in vivo assays, which led to earlier integration with cell and host tissue. The effect of dextran on degradation was ascribed to the decreased cross-linking density, looser microstructure, more porous and hydrophilic surface. Considering the better appearance, softness, moderate degradation rate due to controllable cross-linking degree and good biocompatibility as well, radiation-cross-linked collagen/dextran scaffolds are expected to serve as promising artificial dermal substitutes.

  18. Simple, High-Yield Syntheses of DNA Duplexes Containing Interstrand DNA-DNA Cross-links Between an N4-Aminocytidine Residue and an Abasic Site

    OpenAIRE

    Gamboa Varela, Jacqueline; Gates, Kent S.

    2016-01-01

    The protocol describes the preparation and purification of interstrand DNA-DNA cross-links derived from the reaction of an N4-aminocytidine residue with an abasic site in duplex DNA. The procedures employ inexpensive, commercially-available chemicals and enzymes to carry out post-synthetic modification of commercially-available oligodeoxynucleotides. The yield of cross-linked duplex is typically better than 90%. If purification is required, the cross-linked duplex can be readily separated fro...

  19. 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.

  20. Controlled Light Cross-Linking Technique to Prepare Healable Materials

    Directory of Open Access Journals (Sweden)

    Soliman Abdalla

    2017-06-01

    Full Text Available Detection of defects, damages and cracks in structural polymers is very difficult, and even if they are detected, they will be very hard to be repaired. This is because different kinds of stress can reduce the mechanical efficiency of structural and functional thermosetting composite materials and they can damage the polymer matrix, thus reducing the purposed properties. General healing processes use thermal energy “alone” to heal these materials, thus impairing the intended properties of the materials. Therefore, we present a thermal healing ability that can be switched-on and/or -off at desire using illumination by photon energy (visible and ultra violet. By this technique, one can control local heal while keeping the efficiency of the material nearly unchanged. Furan-based cross-linker chemically reacts (forward- and reverse-reaction with short-chains of maleimide-substituted poly(lauryl methacrylate to form robust chemical bonds. This permits us to perform local control over thermally induced de- and/or re-cross-linking techniques. One can extend and apply this technique to cover micro-devices, coating-techniques, fine lithography, micro- and nano-fabrication processes, etc. Therefore, the present work developed a suitable technology with structural polymeric material, which has the ability to self-heal cracks (and damages and recover structural function.

  1. Arabinosylation Plays a Crucial Role in Extensin Cross-linking

    Directory of Open Access Journals (Sweden)

    Yuning Chen

    2015-01-01

    Full Text Available Extensins (EXTs are hydroxyproline-rich glycoproteins (HRGPs that are structural components of the plant primary cell wall. They are basic proteins and are highly glycosylated with carbohydrate accounting for >50% of their dry weight. Carbohydrate occurs as monoga-lactosyl serine and arabinosyl hydroxyproline, with arabinosides ranging in size from ~1 to 4 or 5 residues. Proposed functions of EXT arabinosylation include stabilizing the polyproline II helix structure and facilitating EXT cross-linking. Here, the involvement of arabinosylation in EXT cross-linking was investigated by assaying the initial cross-linking rate and degree of cross-linking of partially or fully dearabinosylated EXTs using an in vitro cross-linking assay followed by gel permeation chromatography. Our results indicate that EXT arabinosylation is required for EXT cross-linking in vitro and the fourth arabinosyl residue in the tetraarabinoside chain, which is uniquely α-linked, may determine the initial cross-linking rate. Our results also confirm the conserved structure of the oligoarabinosides across species, indicating an evolutionary significance for EXT arabinosylation.

  2. “Zero-length” Cross-linking in Solid State as an Approach for Analysis of Protein -Protein Interactions

    Energy Technology Data Exchange (ETDEWEB)

    Elshafey, Ahmed; Tolic, Nikola; Young, Malin M.; Sale, Kenneth L.; Smith, Richard D.; Kery, Vladimir

    2006-03-01

    Analyzing the architecture of protein complexes is a difficult task. Chemical cross-linking is often used in combination with mass spectrometric analysis to elucidate the interaction interfaces between proteins. We have developed a new approach for the analysis of interacting interfaces in protein complexes based on cross-linking in the solid state. Protein complexes are freeze-dried under vacuum and cross-links are introduced in the solid phase by dehydrating the protein in a non-water solvent, thus, creating peptide bonds between amino and carboxyl groups of the interacting peptides. Cross-linked proteins are digested into peptides with trypsin in both H216O and H218O and then readily distinguished in mass spectra by characteristic 8 atomic mass unit (amu) shifts reflecting incorporation of two 18O atoms into each C-terminus of proteolytic peptides. Computer analysis of mass spectrometry (MS) and MS/MS data is used to identify the cross-linked peptides.We demonstrated our method by cross-linking homooligomeric protein complexes alone or in a mixture of many other proteins. Cross-linking in the solid state was shown to be specific and reproducible. Glutathione-S-transferase (GST) from Schistosoma japonicum was studied in more detail. Twenty-seven unique intra-molecular and two inter-molecular cross-linked peptides were identified using tryptic mapping followed by LTQ-MS analysis. Identified cross-links were predominantly of amide origin, but six esters and thioesters were also found. Identified cross-linked peptides were validated by computational (visualization of cross-links in the three-dimensional [3D] structure of GST) and experimental (MS/MS) analyses. Most of the identified cross-links matched interacting peptides in the native 3D structure of GST indicating that the structure of GST and its oligomeric complex remained primarily intact after freeze drying. The pattern of oligomeric GST obtained in solid state was the same as that obtained in solution by Ru

  3. Use of Specific Chemical Reagents for Detection of Modified Nucleotides in RNA

    Directory of Open Access Journals (Sweden)

    Isabelle Behm-Ansmant

    2011-01-01

    Full Text Available Naturally occurring cellular RNAs contain an impressive number of chemically distinct modified residues which appear posttranscriptionally, as a result of specific action of the corresponding RNA modification enzymes. Over 100 different chemical modifications have been identified and characterized up to now. Identification of the chemical nature and exact position of these modifications is typically based on 2D-TLC analysis of nucleotide digests, on HPLC coupled with mass spectrometry, or on the use of primer extension by reverse transcriptase. However, many modified nucleotides are silent in reverse transcription, since the presence of additional chemical groups frequently does not change base-pairing properties. In this paper, we give a summary of various chemical approaches exploiting the specific reactivity of modified nucleotides in RNA for their detection.

  4. CLMSVault: A Software Suite for Protein Cross-Linking Mass-Spectrometry Data Analysis and Visualization.

    Science.gov (United States)

    Courcelles, Mathieu; Coulombe-Huntington, Jasmin; Cossette, Émilie; Gingras, Anne-Claude; Thibault, Pierre; Tyers, Mike

    2017-07-07

    Protein cross-linking mass spectrometry (CL-MS) enables the sensitive detection of protein interactions and the inference of protein complex topology. The detection of chemical cross-links between protein residues can identify intra- and interprotein contact sites or provide physical constraints for molecular modeling of protein structure. Recent innovations in cross-linker design, sample preparation, mass spectrometry, and software tools have significantly improved CL-MS approaches. Although a number of algorithms now exist for the identification of cross-linked peptides from mass spectral data, a dearth of user-friendly analysis tools represent a practical bottleneck to the broad adoption of the approach. To facilitate the analysis of CL-MS data, we developed CLMSVault, a software suite designed to leverage existing CL-MS algorithms and provide intuitive and flexible tools for cross-platform data interpretation. CLMSVault stores and combines complementary information obtained from different cross-linkers and search algorithms. CLMSVault provides filtering, comparison, and visualization tools to support CL-MS analyses and includes a workflow for label-free quantification of cross-linked peptides. An embedded 3D viewer enables the visualization of quantitative data and the mapping of cross-linked sites onto PDB structural models. We demonstrate the application of CLMSVault for the analysis of a noncovalent Cdc34-ubiquitin protein complex cross-linked under different conditions. CLMSVault is open-source software (available at https://gitlab.com/courcelm/clmsvault.git ), and a live demo is available at http://democlmsvault.tyerslab.com/ .

  5. Thermomechanical behavior of collagen-cross-linked porcine cornea.

    Science.gov (United States)

    Spoerl, Eberhard; Wollensak, Gregor; Dittert, Dag-Daniel; Seiler, Theo

    2004-01-01

    Collagen cross-linking using combined riboflavin/UVA treatment has been shown to increase the biomechanical rigidity of the cornea and has been used successfully for the treatment of progressive keratoconus. From morphological and biochemical investigations, a different degree of cross-linking for the anterior and posterior stroma by the treatment is suggested. The present study was undertaken to better evaluate this effect by testing the thermomechanical behavior. Ten 10 x 5 mm corneal strips from porcine cadaver eyes enucleated within 5 h post mortem were cross-linked using the photosensitizer riboflavin and UVA irradiation (370 nm, irradiance = 3 mW/cm(2)) for 30 min and compared to ten untreated corneal strips and ten corneal strips cross-linked with 0.1% glutaraldehyde. The temperature in a water bath was raised from 60 to 95 degrees C with temperature increments of 1 degrees C per minute. The hydrothermal shrinkage of the corneal strips was measured in 2.5 degrees C steps using a micrometer. In addition, six 10-mm whole corneal buttons were cross-linked with riboflavin/UVA and immersed into water at 70 or 75 degrees C. The maximal hydrothermal shrinkage for the untreated control specimens and the posterior portion of the riboflavin/UVA-treated corneas was at 70 degrees C, for the anterior portion of the cornea cross-linked by riboflavin/UVA at 75 degrees C and for glutaraldehyde-cross-linked cornea at 90 degrees C. In the cross-linked corneal buttons, a typical mushroom-like shape was observed at 70 degrees C and a cylinder shape at 75 degrees C. The different degree of collagen cross-linking in the corneal stroma after riboflavin/UVA treatment is reflected by the differences in the maximal shrinkage temperature of the anterior and posterior portion. Therefore, in the corneas cross-linked with riboflavin/UVA a higher shrinkage temperature was observed for the anterior portion of the cornea (75 degrees C) compared to the posterior stroma (70 degrees C) due to

  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. Effect of nordihydroguaiaretic acid cross-linking on fibrillar collagen: in vitro evaluation of fibroblast adhesion strength and migration

    Directory of Open Access Journals (Sweden)

    Ana Y. Rioja

    2017-04-01

    Full Text Available Fixation is required to reinforce reconstituted collagen for orthopedic bioprostheses such as tendon or ligament replacements. Previous studies have demonstrated that collagen fibers cross-linked by the biocompatible dicatechol nordihydroguaiaretic acid (NDGA have mechanical strength comparable to native tendons. This work focuses on investigating fibroblast behavior on fibrillar and NDGA cross-linked type I collagen to determine if NDGA modulates cell adhesion, morphology, and migration. A spinning disk device that applies a range of hydrodynamic forces under uniform chemical conditions was employed to sensitively quantify cell adhesion strength, and a radial barrier removal assay was used to measure cell migration on films suitable for these quantitative in vitro assays. The compaction of collagen films, mediated by the drying and cross-linking fabrication process, suggests a less open organization compared to native fibrillar collagen that likely allowed the collagen to form more inter-chain bonds and chemical links with NDGA polymers. Fibroblasts strongly adhered to and migrated on native and NDGA cross-linked fibrillar collagen; however, NDGA modestly reduced cell spreading, adhesion strength and migration rate. Thus, it is hypothesized that NDGA cross-linking masked some adhesion receptor binding sites either physically, chemically, or both, thereby modulating adhesion and migration. This alteration in the cell-material interface is considered a minimal trade-off for the superior mechanical and compatibility properties of NDGA cross-linked collagen compared to other fixation approaches.

  8. 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.

  9. 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.

  10. A simple, cross-linked collagen tissue substitute for corneal implantation.

    Science.gov (United States)

    Liu, Yuwen; Gan, Lisha; Carlsson, David J; Fagerholm, Per; Lagali, Neil; Watsky, Mitchell A; Munger, Rejean; Hodge, William G; Priest, David; Griffith, May

    2006-05-01

    To develop a simple corneal substitute from cross-linked collagen. Porcine type I collagen (10%; pH 5), was mixed with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) and N-hydroxysuccinimide (NHS). The final homogenous solution was molded to corneal dimensions, cured, and then implanted into rabbits and minipigs by lamellar keratoplasty. The implants were followed for up to 6 months after surgery. Clinical examinations of the cornea included detailed slit lamp biomicroscopy, in vivo confocal microscopy, topography and esthesiometry for nerve function. Histopathologic examinations were also performed on rabbit corneas harvested after 6 months. Cross-linked collagen (refractive index, 1.35) had optical clarity superior to human corneas. Implanted into rabbit and porcine corneas, only 1 of 24 of the surgical corneas showed a slight haze at 6 months after surgery. All other implants showed no adverse reactions and remained optically clear. Topography showed a smooth surface and a profile similar to that of the contralateral nonsurgical eye. The implanted matrices promoted regeneration of corneal cells, tear film, and nerves. Touch sensitivity was restored, indicating some restoration of function. The corneas with implants showed no significant loss of thickness and demonstrated stable host-graft integration. Collagen can be adequately stabilized, using water soluble carbodiimides as protein cross-linking reagents, in the fabrication of corneal matrix substitutes for implantation. The simple cross-linking methodology would allow for easy fabrication of matrices for transplantation in centers where there is a shortage of corneas, or where there is need for temporary patches to repair perforations in emergency situations.

  11. Exogenous collagen cross-linking reduces scleral permeability: modeling the effects of age-related cross-link accumulation.

    Science.gov (United States)

    Stewart, Jay M; Schultz, David S; Lee, On-Tat; Trinidad, Monique L

    2009-01-01

    To investigate the relationship between scleral permeability and nonenzymatic cross-link density. Scleral discs 18 mm in diameter were dissected from the medial and lateral equatorial regions of 60 cadaveric porcine eyes. Samples were incubated for 24 hours with control solution or methylglyoxal at concentrations of 0.001%, 0.01%, 0.10%, and 1.00%. Nonenzymatic cross-link density in treated and control groups was quantified with the use of papain digest and fluorescence spectrophotometry. Treated scleral discs were mounted in a customized Ussing-type chamber connected to vertical tubing, and specific hydraulic conductivity was determined according to the descent of a column of degassed saline at room temperature. Permeability to diffusion of fluorescein in a static chamber was determined for another set of treated scleral samples. Methylglyoxal treatment effectively increased nonenzymatic cross-link content, as indicated by the average fluorescence for each group. Specific hydraulic conductivity (m(2)) was reduced with increasing cross-link density. Similarly, the permeability coefficient for the fluorescein solute consistently decreased with increasing methylglyoxal concentration, indicating diffusion impedance from the treatment. Nonenzymatic cross-link density can be significantly increased by treatment with methylglyoxal. Porcine sclera showed a nonlinear reduction in solute permeability and specific hydraulic conductivity with increasing cross-link density. This model indicates that age-related nonenzymatic cross-link accumulation can have a substantial impact on scleral permeability.

  12. 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.

  13. O6-2'-Deoxyguanosine-butylene-O6-2'-deoxyguanosine DNA Interstrand Cross-Links Are Replication-Blocking and Mutagenic DNA Lesions.

    Science.gov (United States)

    Xu, Wenyan; Kool, Daniel; O'Flaherty, Derek K; Keating, Ashley M; Sacre, Lauralicia; Egli, Martin; Noronha, Anne; Wilds, Christopher J; Zhao, Linlin

    2016-11-21

    DNA interstrand cross-links (ICLs) are cytotoxic DNA lesions derived from reactions of DNA with a number of anti-cancer reagents as well as endogenous bifunctional electrophiles. Deciphering the DNA repair mechanisms of ICLs is important for understanding the toxicity of DNA cross-linking agents and for developing effective chemotherapies. Previous research has focused on ICLs cross-linked with the N7 and N2 atoms of guanine as well as those formed at the N6 atom of adenine; however, little is known about the mutagenicity of O 6 -dG-derived ICLs. Although less abundant, O 6 -alkylated guanine DNA lesions are chemically stable and highly mutagenic. Here, O 6 -2'-deoxyguanosine-butylene-O 6 -2'-deoxyguanosine (O 6 -dG-C4-O 6 -dG) is designed as a chemically stable ICL, which can be induced by the action of bifunctional alkylating agents. We investigate the DNA replication-blocking and mutagenic properties of O 6 -dG-C4-O 6 -dG ICLs during an important step in ICL repair, translesion DNA synthesis (TLS). The model replicative DNA polymerase (pol) Sulfolobus solfataricus P2 DNA polymerase B1 (Dpo1) is able to incorporate a correct nucleotide opposite the cross-linked template guanine of ICLs with low efficiency and fidelity but cannot extend beyond the ICLs. Translesion synthesis by human pol κ is completely inhibited by O 6 -dG-C4-O 6 -dG ICLs. Moderate bypass activities are observed for human pol η and S. solfataricus P2 DNA polymerase IV (Dpo4). Among the pols tested, pol η exhibits the highest bypass activity; however, 70% of the bypass products are mutagenic containing substitutions or deletions. The increase in the size of unhooked repair intermediates elevates the frequency of deletion mutation. Lastly, the importance of pol η in O 6 -dG-derived ICL bypass is demonstrated using whole cell extracts of Xeroderma pigmentosum variant patient cells and those complemented with pol η. Together, this study provides the first set of biochemical evidence for the

  14. Comparison of glutaraldehyde and procyanidin cross-linked scaffolds for soft tissue engineering.

    Science.gov (United States)

    Yang, Yang; Ritchie, Alastair Campbell; Everitt, Nicola M

    2017-11-01

    Soft tissue injuries are among the most difficult orthopaedic conditions to treat, and regenerative medicine holds the promise of better treatments of these injuries. There is therefore a requirement for substrates and porous scaffolds which provide an appropriate chemical and mechanical environment for cell attachment, growth, proliferation and differentiation. In this study, cross-linked porous gelatin-chitosan (Gel/Chi) scaffolds with high porosity (>90%) were fabricated and their internal morphology, pore sizes and porosities were characterized using scanning electron microscopy (SEM), micro computed tomography (micro-CT) and mercury intrusion porosimetry. The cross-linking agents chosen for this study were Procyanidin (PA), chosen for its biocompatibility, and glutaraldehyde (GA), chosen for comparison as a highly effective cross-linker. Concentrations of these cross-linkers varied from 0.1% to 1% (w/v) and controls had the same gelatin-chitosan blend but were untreated. It was found that the water absorption of cross-linked scaffolds decreased as the cross-linker concentration increased and in vitro collagenase degradation test showed both cross-linkers increased the biostability of the scaffolds. Scaffolds were also tested under compressive load to investigate their resistance to deformation. The results indicated that both cross-linkers increase the stiffness of the scaffolds both initially and at higher strains, but GA cross-linked scaffolds had a higher compressive stiffness than scaffolds cross-linked with PA for a given concentration. Results from cyclic compression and stress relaxation tests showed that PA cross-linked scaffolds recover more rapidly after deformation. 3T3 fibroblasts were cultured on the scaffolds to assess cytotoxicity and biocompatibility. The results indicated that PA was non-cytotoxic and promoted the attachment and proliferation of the seeded cells, while fewer cells were seen on GA cross-linked scaffolds, indicating that the GA

  15. AUTOCLAVABLE HIGHLY CROSS-LINKED POLYURETHANE NETWORKS IN OPHTHALMOLOGY

    NARCIS (Netherlands)

    BRUIN, P; MEEUWSEN, EAJ; VANANDEL, MV; WORST, JGF; PENNINGS, AJ

    1993-01-01

    Highly cross-linked aliphatic polyurethane networks have been prepared by the bulk step reaction of low molecular weight polyols and hexamethylenediisocyanate (HDI). These polyurethane networks are optically transparent, colourless and autoclavable amorphous glassy thermosets, which are suited for

  16. Polymeric Nanoparticles via Noncovalent Cross-Linking of Linear Chains

    NARCIS (Netherlands)

    Seo, Myungeun; Beck, Benjamin J.; Paulusse, Jos Marie Johannes; Hawker, Craig J.; Kim, Sang Youl

    2008-01-01

    Novel polymeric nanoparticles were prepared through the chain collapse of linear polymers driven by noncovalent cross-linking of dendritic self-complementary hydrogen-bonding units (SHB). Random copolymers containing SHB units, poly[(methyl

  17. 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.

  18. Recent advances in corneal collagen cross-linking

    OpenAIRE

    Sachdev, Gitansha Shreyas; Sachdev, Mahipal

    2017-01-01

    Corneal collagen cross-linking has become the preferred modality of treatment for corneal ectasia since its inception in late 1990s. Numerous studies have demonstrated the safety and efficacy of the conventional protocol. Our understanding of the cross-linking process is ever evolving, with its wide implications in the form of accelerated and pulsed protocols. Newer advancements in technology include various riboflavin formulations and the ability to deliver higher fluence protocols with cust...

  19. Modulation by propranolol of the lysyl cross-links in aortic elastin and collagen of the aneurysm-prone turkey.

    Science.gov (United States)

    Boucek, R J; Gunja-Smith, Z; Noble, N L; Simpson, C F

    1983-01-15

    dl-Propranolol (propranolol) fed to immature and mature aneurysm-prone turkeys (Broad-Breasted White, BBW) for 6 weeks significantly raised the tensile strength of tissue rings from the abdominal aorta. The drug-mediated increase in tensile strength values was dose-related and independent of its heart rate- and arterial pressure-lowering effects. Propranolol acts, in part, by (a) stimulating lysyl oxidase to produce greater amounts of reactive aldehydes for intermolecular cross-links, (b) enhancing the progression of chemically unstable to stable forms of intermolecular elastin cross-links (lysinonorleucine and the desmosines), and (c) reducing the density of the age-related intermolecular cross-linking of collagen (pyridinoline). These propranolol effects on the lysyl cross-links were demonstrated in both the immature and mature animals and suggest a heretofore unrecognized potential for this widely used cardiovascular drug.

  20. Cross-linking and the molecular packing of corneal collagen

    Science.gov (United States)

    Yamauchi, M.; Chandler, G. S.; Tanzawa, H.; Katz, E. P.

    1996-01-01

    We have quantitatively characterized, for the first time, the cross-linking in bovine cornea collagen as a function of age. The major iminium reducible cross-links were dehydro-hydroxylysinonorleucine (deH-HLNL) and dehydro-histidinohydroxymerodesmosine (deH-HHMD). The former rapidly diminished after birth; however, the latter persisted in mature animals at a level of 0.3 - 0.4 moles/mole of collagen. A nonreducible cross-link, histidinohydroxylysinonorleucine (HHL), previously found only in skin, was also found to be a major mature cross-link in cornea. The presence of HHL indicates that cornea fibrils have a molecular packing similar to skin collagen. However, like deH-HHMD, the HHL content in corneal fibrils only reaches a maximum value with time about half that of skin. These data suggest that the corneal fibrils are comprised of discrete filaments that are internally stabilized by HHL and deH-HHMD cross-links. This pattern of intermolecular cross-linking would facilitate the special collagen swelling property required for corneal transparency.

  1. Controlled release of vancomycin from cross-linked gelatine.

    Science.gov (United States)

    Tigani, Domenico; Zolezzi, Carola; Trentani, Federico; Ragaini, Alessandro; Iafisco, Michele; Manara, Silvia; Palazzo, Barbara; Roveri, Norberto

    2008-03-01

    This paper explores the possibility of using biodegradable cross-linked gelatines as antibiotic devices for a long-term elution (80 days). Capillary electrophoresis (CE) has been utilized to evaluate the mass percentage of vancomycin and gelatine contemporary released from differently cross-linked vancomycin loaded gelatine samples in an elution time ranging from 24 to 1920 h. While the solubilization kinetic of gelatine samples differently cross-linked can be very close described by the simplified Higuchi model, the vancomycin release kinetic is contemporary governed by both the Fickian diffusion process trough the gelatine matrix network and the dissolution process of the matrix due to its degradation. Comparing the antibiotic eluting kinetics from gelatine at diverse cross-linking degree we observed that the degradation of the proteic matrix appears to have a minor influence in the drug release control. Vancomycin released from all the gelatine partially cross-linked samples results active against Staphylococcus aureus and Streptococcus faecalis which represent the most pathogens commonly isolated in orthopaedic infections. Vancomycin overcomes the minimum inhibitory concentration for both the bacteria in the whole range of elution time. Cross-linked gelatine devices appear to represent a useful biodegradable delivery system for local anti-infective therapy in arthoplasty.

  2. Reduction of Cr(VI) to Cr(III) in Artificially-Contaminated Soil using Chemical Reagents

    Science.gov (United States)

    Kostarelos, Konstantinos; Rao, Ennio; Reale, Daniela

    2010-05-01

    The presence of hexavalent chromium (CrVI) in soil is an environmental concern due to its effect on human health. The concern arises from the leaching and the seepage of Cr(VI) from soil to groundwater. A remediation approach that has been studied in the literature is that of reducing the hexavalent chromium to its trivalent form using a chemical reagent, namely ferrous sulfate heptahydrate (FeSO4.7H20). In this study, we compared performance of ferrous sulfate heptahydrate to sodium thiosulfate (Na2S2O3), a less costly reductant. The means of measuring the performance of the reductants is the US EPA's Toxicity Characteristic Leaching Procedure (TCLP), which states that the total chromium release from the soil must be less than 5 ppm. Because this treatment approach is pH sensitive and thus, susceptible to acid rain effects, it was studied with the intention that it be coupled with a stabilization/fixation approach so as to provide a second level of treatment; i.e., it is not intended to be the stand-alone treatment approach. In this study, the reductants were initially used to treat a contaminated, artificial soil and allowed to cure for varying time periods to determine the minimum curing time. Contaminated artificial soil were then prepared using the same percentage of white sand, kaolinite clay and potassium chromate and varying amount of water as a function of the humidity of the specimens in order to illucidate the effect of moisture on the reductant performance. Finally, the reductant (either ferrous sulfate heptahydrate or sodium thiosulfate) was added in varying doses to determine the best ratio Cr/reagent dose. Chromium release from the soil was evaluated with a modified Toxicity Characteristic Leaching Procedure (TCLP) test after allowing the samples to cure. Results indicated that chromium(VI) released from the specimens was less than 5 ppm for the samples treated with either ferrous sulfate heptahydrate (99.9% of reduction) and sodium thiosulfate (98

  3. Comparação de bulas de duas marcas de tiras reagentes utilizadas no exame químico de urina Comparison of product labelings of two marks of reagent strips for the chemical examination of urine

    Directory of Open Access Journals (Sweden)

    Adriana Scotti da Silva Colombeli

    2006-04-01

    Full Text Available INTRODUÇÃO: O exame de urina proporciona informações sobre patologias renais e do trato urinário, bem como algumas moléstias extra-renais. Usualmente o exame químico de urina é feito com tiras reagentes, objetivando tornar a determinação mais rápida, simples e econômica. OBJETIVOS: Comparar bulas de duas marcas de tiras amplamente utilizadas em laboratórios de urinálise (Roche Combur10 Test® UX e Bayer Multistix® 10 SG. MATERIAL E MÉTODO: Compararam-se as bulas quanto aos princípios utilizados nas determinações de pH, proteínas, glicose, cetonas, hemoglobina, bilirrubina, urobilinogênio, nitrito, densidade e leucócitos, além das informações sobre possíveis interferências. RESULTADOS: Foram verificadas diferenças nos reagentes utilizados para detecção dos parâmetros, como é o caso do urobilinogênio (a tira Multistix usa o reagente de Ehrlich, menos específico e mais propenso a interferências analíticas que o sal de diazônio derivado de metoxibenzeno, utilizado na tira Roche; para nitrito, proteína, glicose, bilirrubina e hemoglobina as diferenças foram mais sutis. DISCUSSÃO: Detectou-se diversidade de informações quanto a possíveis interferentes, o que talvez possa ser justificado parcialmente pelas diferenças nos reagentes. Também foram verificadas diferenças nas informações sobre interferências de um idioma para outro, destacando-se a omissão de algumas delas na bula em português. Observou-se grande disparidade na avaliação da intensidade da reação e sua expressão em cruzes, como, por exemplo, no parâmetro glicose, o que pode levar a erros na interpretação do laudo laboratorial. CONCLUSÃO: As observações registradas reforçam a importância de padronizações no exame parcial de urina.BACKGROUND: The urinalysis provides information about renal and urinary diseases, as well as about some extra renal diseases. The chemical examination of urine is done with reagent strips, which allows

  4. Water Processable Polythiophene Nanowires by Photo-Cross-Linking and Click-Functionalization.

    Science.gov (United States)

    Kim, Hyeong Jun; Skinner, Matthew; Yu, Hojeong; Oh, Joon Hak; Briseno, Alejandro L; Emrick, Todd; Kim, Bumjoon J; Hayward, Ryan C

    2015-09-09

    Replacing or minimizing the use of halogenated organic solvents in the processing and manufacturing of conjugated polymer-based organic electronics has emerged as an important issue due to concerns regarding toxicity, environmental impact, and high cost. To date, however, the processing of well-ordered conjugated polymer nanostructures has been difficult to achieve using environmentally benign solvents. In this work, we report the development of water and alcohol processable nanowires (NWs) with well-defined crystalline nanostructure based on the solution assembly of azide functionalized poly(3-hexylthiophene) (P3HT-azide) and subsequent photo-cross-linking and functionalization of these NWs. The solution-assembled P3HT-azide NWs were successfully cross-linked by exposure to UV light, yielding good thermal and chemical stability. Residual azide units on the photo-cross-linked NWs were then functionalized with alkyne terminated polyethylene glycol (PEG-alkyne) using copper catalyzed azide-alkyne cycloaddition chemistry. PEG functionalization of the cross-linked P3HT-azide NWs allowed for stable dispersion in alcohols and water, while maintaining well-ordered NW structures with electronic properties suitable for the fabrication of organic field effect transistors (OFETs).

  5. 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.

  6. Mutagenicity of Some Munitions Wastewater Chemicals and Chlorine Test Kit Reagents

    Science.gov (United States)

    1977-05-01

    standard iodometric titration .3 Final chlorine concentrations after reaction with the test chemical were adjusted to 0.1 to 0.2 mg/l with sodium thiosulfate...times of 10 minutes were used. Ozone concentrations were monitored by standard iodometric titrations . 3 14 0 0 W U. U 0 -1 ~ 2 U.4L TLTA cI 03 I.- W2 Wi

  7. Treatment of textile effluent by chemical (Fenton's Reagent) and biological (sequencing batch reactor) oxidation

    Energy Technology Data Exchange (ETDEWEB)

    Rodrigues, Carmen S.D. [LSRE - Laboratory of Separation and Reaction Engineering, Department of Chemical Engineering, Faculty of Engineering, University of Porto, R. Dr. Roberto Frias, s/n, 4200-465 Porto (Portugal); Madeira, Luis M. [LEPAE - Laboratory for Process, Environmental and Energy Engineering, Department of Chemical Engineering, Faculty of Engineering, University of Porto, R. Dr. Roberto Frias, s/n, 4200-465 Porto (Portugal); Boaventura, Rui A.R., E-mail: bventura@fe.up.pt [LSRE - Laboratory of Separation and Reaction Engineering, Department of Chemical Engineering, Faculty of Engineering, University of Porto, R. Dr. Roberto Frias, s/n, 4200-465 Porto (Portugal)

    2009-12-30

    The removal of organic compounds and colour from a synthetic effluent simulating a cotton dyeing wastewater was evaluated by using a combined process of Fenton's Reagent oxidation and biological degradation in a sequencing batch reactor (SBR). The experimental design methodology was first applied to the chemical oxidation process in order to determine the values of temperature, ferrous ion concentration and hydrogen peroxide concentration that maximize dissolved organic carbon (DOC) and colour removals and increase the effluent's biodegradability. Additional studies on the biological oxidation (SBR) of the raw and previously submitted to Fenton's oxidation effluent had been performed during 15 cycles (i.e., up to steady-state conditions), each one with the duration of 11.5 h; Fenton's oxidation was performed either in conditions that maximize the colour removal or the increase in the biodegradability. The obtained results allowed concluding that the combination of the two treatment processes provides much better removals of DOC, BOD{sub 5} and colour than the biological or chemical treatment alone. Moreover, the removal of organic matter in the integrated process is particularly effective when Fenton's pre-oxidation is carried out under conditions that promote the maximum increase in wastewater biodegradability.

  8. 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.

  9. The theory and art of corneal cross-linking.

    Science.gov (United States)

    McQuaid, Rebecca; Cummings, Arthur B; Mrochen, Michael

    2013-08-01

    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.

  10. Inactivation of SARS coronavirus by means of povidone-iodine, physical conditions, and chemical reagents

    OpenAIRE

    Kariwa, Hiroaki; Fujii, Nobuhiro; TAKASHIMA, Ikuo

    2004-01-01

    products, a number of other chemical agents, and various physical conditions were evaluated for their ability to inactivate the severe acute respiratory syndrome coronavirus (SARS-CoV). Treatment of SARS-CoV with PVP-I products for 2 min reduced the virus infectivity from 1.17 x 10⁶ TCID₅₀/ml to below the detectable level. The efficacy of 70% ethanol was equivalent to that of PVP-I products. Fixation of SARS-CoV-infected Vero E6 cells with a fixative including formalin, glutaraldehyde, methan...

  11. Chemical crosslinking and mass spectrometry studies of the structure and dynamics of membrane proteins and receptors.

    Energy Technology Data Exchange (ETDEWEB)

    Haskins, William E.; Leavell, Michael D.; Lane, Pamela; Jacobsen, Richard B.; Hong, Joohee; Ayson, Marites J.; Wood, Nichole L.; Schoeniger, Joseph S.; Kruppa, Gary Hermann; Sale, Kenneth L.; Young, Malin M.; Novak, Petr

    2005-03-01

    Membrane proteins make up a diverse and important subset of proteins for which structural information is limited. In this study, chemical cross-linking and mass spectrometry were used to explore the structure of the G-protein-coupled photoreceptor bovine rhodopsin in the dark-state conformation. All experiments were performed in rod outer segment membranes using amino acid 'handles' in the native protein sequence and thus minimizing perturbations to the native protein structure. Cysteine and lysine residues were covalently cross-linked using commercially available reagents with a range of linker arm lengths. Following chemical digestion of cross-linked protein, cross-linked peptides were identified by accurate mass measurement using liquid chromatography-fourier transform mass spectrometry and an automated data analysis pipeline. Assignments were confirmed and, if necessary, resolved, by tandem MS. The relative reactivity of lysine residues participating in cross-links was evaluated by labeling with NHS-esters. A distinct pattern of cross-link formation within the C-terminal domain, and between loop I and the C-terminal domain, emerged. Theoretical distances based on cross-linking were compared to inter-atomic distances determined from the energy-minimized X-ray crystal structure and Monte Carlo conformational search procedures. In general, the observed cross-links can be explained by re-positioning participating side-chains without significantly altering backbone structure. One exception, between C3 16 and K325, requires backbone motion to bring the reactive atoms into sufficient proximity for cross-linking. Evidence from other studies suggests that residues around K325 for a region of high backbone mobility. These findings show that cross-linking studies can provide insight into the structural dynamics of membrane proteins in their native environment.

  12. Spray-dried chitosan microspheres cross-linked with d, l-glyceraldehyde as a potential drug delivery system: preparation and characterization

    Directory of Open Access Journals (Sweden)

    B. F Oliveira

    2005-09-01

    Full Text Available Chitosan microspheres of a small particle size and with good sphericity were prepared by a spray-drying method followed by treatment with a cross-linking agent. Owing to restrictions on the use of cross-linked chitosan microspheres in the pharmaceutical field, d,l-glyceraldehyde, a biocompatible reatant was used. The parameters studied affecting extent of cross-linking were cross-linking time and concentration of the cross-linking agent. Glutaraldehyde, the aldehyde most frequently employed as chemical cross-linking agent for proteins, was also used as a control. The cross-linked spray-dried chitosan microspheres were analyzed with respect to their morphological aspects, particle size, zeta potential and water uptake capacity. It was found that an increase either in d,l-glyceraldehyde concentration or in duration of cross-linking caused a decrease in both the swelling capacity and the zeta potential of the chitosan microspheres. Compared to glutaraldehyde, d,l-glyceraldehyde appears to be a good cross-linking agent for chitosan microspheres with the advantage that it is nontoxic.

  13. Small unilamellar vesicles as reagents: a chemically defined, quantitative assay for lectins

    Energy Technology Data Exchange (ETDEWEB)

    Rando, R.R.

    1981-01-01

    Samll unilamellar vesicles containing synthetic glycolipids can be prepared. These vesicles are aggregated by the appropriate lectin (Orr et al., 1979; Rando and Bangerter, 1979; Slama and Rando, 1980). It is shown here that extent of aggregation of these vesicles as measured by light scattering at 360 nm, is, under certain conditions, linear with amount of lectin added. This forms the basis of a rapid and simple quantitative assay for lectins using the modified vesicles as a defined chemical substrate. The assay is sensitive to lectin concentrations in the low ..mu..g range. The assay is applied here to studies on concanavalin A, Ricinus communis agglutinin and the ..cap alpha..-fucosyl binding lectin from Ulex europaeus (Type I).

  14. In vivo oxidation in remelted highly cross-linked retrievals.

    Science.gov (United States)

    Currier, B H; Van Citters, D W; Currier, J H; Collier, J P

    2010-10-20

    Elimination of free radicals to prevent oxidation has played a major role in the development and product differentiation of the latest generation of highly cross-linked ultra-high molecular weight polyethylene bearing materials. In the current study, we (1) examined oxidation in a series of retrieved remelted highly cross-linked ultra-high molecular weight polyethylene bearings from a number of device manufacturers and (2) compared the retrieval results with findings for shelf-stored control specimens. The hypothesis was that radiation-cross-linked remelted ultra-high molecular weight polyethylene would maintain oxidative stability in vivo comparable with the stability during shelf storage and in published laboratory aging tests. Fifty remelted highly cross-linked ultra-high molecular weight polyethylene acetabular liners and nineteen remelted highly cross-linked ultra-high molecular weight polyethylene tibial inserts were received after retrieval from twenty-one surgeons from across the U.S. Thirty-two of the retrievals had been in vivo for two years or more. Each was measured for oxidation with use of Fourier transform infrared spectroscopy. A control series of remelted highly cross-linked ultra-high molecular weight polyethylene acetabular liners from three manufacturers was analyzed with electron paramagnetic resonance spectroscopy to measure free radical content and with Fourier transform infrared spectroscopy to measure oxidation initially and after eight to nine years of shelf storage in air. The never-implanted, shelf-aged controls had no measurable free-radical content initially or after eight to nine years of shelf storage. The never-implanted controls showed no increase in oxidation during shelf storage. Oxidation measurements showed measurable oxidation in 22% of the retrieved remelted highly cross-linked liners and inserts after an average of two years in vivo. Because never-implanted remelted highly cross-linked ultra-high molecular weight

  15. Cross-Linking Chemistry of Tyramine-Modified Hyaluronan Hydrogels Alters Mesenchymal Stem Cell Early Attachment and Behavior.

    Science.gov (United States)

    Loebel, Claudia; Szczesny, Spencer E; Cosgrove, Brian D; Alini, Mauro; Zenobi-Wong, Marcy; Mauck, Robert L; Eglin, David

    2017-03-13

    Given the significance of hydrogels as cell-instructive materials, it is important to understand how differences in their chemical and physical properties are able to direct cell fate. For example, it remains unclear how different hydrogel cross-linking chemistries and gelation mechanisms influence cell behavior. Here, we report on hyaluronan-tyramine (HA-Tyr) hydrogels prepared either with enzymatic cross-linking using horseradish peroxidase and H2O2 or with visible light (500 nm) triggered gelation. We demonstrate that when hydrogels are polymerized to equivalent Young's moduli, the specific cross-linking chemistry of HA-Tyr hydrogels can have a substantial impact on mesenchymal stem cell (MSC) behavior. MSCs cultured on HA-Tyr hydrogels exhibit increased cell spread areas on enzymatically formed substrates relative to photo-cross-linked matrices. While enzymatically formed hydrogels led to MSCs exhibiting greater cell focal adhesion length, MSCs cultured on the photo-cross-linked matrices exhibited smaller cell spread area and shorter focal adhesion length but generated increased traction stress. These findings highlight the importance of understanding hydrogel cross-linking chemistries when the role of biophysical cues in regulating stem cell fate is investigated.

  16. Conformational analysis of site-specific DNA cross-links of cisplatin-distamycin conjugates.

    Science.gov (United States)

    Kostrhunova, H; Brabec, V

    2000-10-17

    The requirement for novel platinum antitumor drugs led to the concept of synthesis of novel platinum drugs based on targeting cisplatin to various carrier molecules. We have shown [Loskotova, H., and Brabec, V. (1999) Eur. J. Biochem. 266, 392-402] that attachment of DNA minor-groove-binder distamycin to cisplatin changes several features of DNA-binding mode of the parent platinum drug. Major differences comprise different conformational changes in DNA and a considerably higher interstrand cross-linking efficiency. The studies of the present work have been directed to the analysis of oligodeoxyribonucleotide duplexes containing single, site-specific adducts of platinum-distamycin conjugates. These uniquely modified duplexes were analyzed by Maxam-Gilbert footprinting, phase-sensitive gel electrophoresis bending assay and chemical probes of DNA conformation. The results have indicated that the attachment of distamycin to cisplatin mainly affects the sites involved in the interstrand cross-links so that these adducts are preferentially formed between complementary guanine and cytosine residues. This interstrand cross-link bends the helix axis by approximately 35 degrees toward minor groove, unwinds DNA by approximately 95 degrees and distorts DNA symmetrically around the adduct. In addition, CD spectra of restriction fragments modified by the cisplatin-distamycin conjugates have demonstrated that distamycin moiety in the interstrand cross-links of these compounds interacts with DNA. This interaction facilitates the formation of these adducts. Hence, the structural impact of the specific interstrand cross-link detected in this study deserves attention when biological behavior of cisplatin derivatives targeted by oligopeptide DNA minor-groove-binders is evaluated.

  17. Cross-Linked Collagen Triple Helices by Oxime Ligation.

    Science.gov (United States)

    Hentzen, Nina B; Smeenk, Linde E J; Witek, Jagna; Riniker, Sereina; Wennemers, Helma

    2017-09-13

    Covalent cross-links are crucial for the folding and stability of triple-helical collagen, the most abundant protein in nature. Cross-linking is also an attractive strategy for the development of synthetic collagen-based biocompatible materials. Nature uses interchain disulfide bridges to stabilize collagen trimers. However, their implementation into synthetic collagen is difficult and requires the replacement of the canonical amino acids (4R)-hydroxyproline and proline by cysteine or homocysteine, which reduces the preorganization and thereby stability of collagen triple helices. We therefore explored alternative covalent cross-links that allow for connecting triple-helical collagen via proline residues. Here, we present collagen model peptides that are cross-linked by oxime bonds between 4-aminooxyproline (Aop) and 4-oxoacetamidoproline placed in coplanar Xaa and Yaa positions of neighboring strands. The covalently connected strands folded into hyperstable collagen triple helices (Tm ≈ 80 °C). The design of the cross-links was guided by an analysis of the conformational properties of Aop, studies on the stability and functionalization of Aop-containing collagen triple helices, and molecular dynamics simulations. The studies also show that the aminooxy group exerts a stereoelectronic effect comparable to fluorine and introduce oxime ligation as a tool for the functionalization of synthetic collagen.

  18. Mechanical properties of the equine superficial digital flexor tendon relate to specific collagen cross-link levels.

    Science.gov (United States)

    Thorpe, C T; Stark, R J F; Goodship, A E; Birch, H L

    2010-11-01

    Damage to the flexor tendons, particularly the superficial digital flexor tendon (SDFT), is one of the most common musculoskeletal injuries sustained by horses competing in all disciplines. Our previous work has shown that SDFTs from different individuals show a wide variation in mechanical strengths; this is important clinically as it may relate to predisposition to injury. The high mechanical strength of tendon relies on the correct orientation of collagen molecules within fibrils and stabilisation by the formation of chemical cross-links between collagen molecules. It is not known whether the variation in SDFT mechanical properties between individuals relates to differences in collagen cross-link levels. Enzyme-derived, intermolecular cross-linking of tendon collagen correlates with mechanical properties of the SDFT. SDFTs were collected from 38 horses and mechanically tested to failure. Structural and material properties were calculated from the load/deformation plot and cross-sectional area for each tendon. Following mechanical testing, pyrrolic cross-link levels were measured using a spectrophotometric assay for Ehrlich's reactivity and pyridinoline levels were quantified by HPLC. Cross-link levels were correlated with mechanical properties and statistical significance tested using a Pearson's correlation test. Pyrrole cross-link levels showed a significant positive correlation with ultimate stress (P = 0.004), yield stress (P = 0.003) and elastic modulus (P = 0.018) of the tendons, despite being a minor cross-link in these tendons. There was no significant correlation of mechanical properties with either hydroxylysyl- or lysyl-pyridinoline levels. Given the low absolute levels of pyrrole, we suggest that the correlation with high mechanical strength is through an indirect mechanism. Understanding the nature of the relationships between pyrrole cross-links, other matrix characteristics and tendon material properties may allow development of strategies to

  19. 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.

  20. Mechanisms of corneal tissue cross-linking in response to treatment with topical riboflavin and long-wavelength ultraviolet radiation (UVA).

    Science.gov (United States)

    McCall, A Scott; Kraft, Stefan; Edelhauser, Henry F; Kidder, George W; Lundquist, Richard R; Bradshaw, Helen E; Dedeic, Zinaida; Dionne, Megan J C; Clement, Ethan M; Conrad, Gary W

    2010-01-01

    Treatment of de-epithelialized human corneas with riboflavin (RF) + long-wavelength ultraviolet light (UVA; RFUVA) increases corneal stroma tensile strength significantly. RFUVA treatment retards the progression of keratoconus, perhaps by cross-linking of collagen molecules, but exact molecular mechanisms remain unknown. Research described here tested possible chemical mechanisms of cross-linking. Corneas of rabbits and spiny dogfish sharks were de-epithelialized mechanically, subjected to various chemical pretreatments, exposed to RFUVA, and then subjected to destructive tensile stress measurements. Tensile strength was quantified with a digital force gauge to measure degree of tissue cross-linking. For both rabbit and shark corneas, RFUVA treatment causes significant cross-linking by mechanism(s) that can be blocked by the presence of sodium azide. Conversely, such cross-linking is greatly enhanced in the presence of deuterium oxide (D(2)O), even when RF is present at only one tenth the currently used clinical concentrations. Blocking carbonyl groups preexisting in the stroma with 2,4-dinitrophenylhydrazide or hydroxylamine blocks essentially all corneal cross-linking. In contrast, blocking free amine groups preexisting in the stroma with acetic anhydride or ethyl acetimidate does not affect RFUVA corneal cross-linking. When both carbonyl groups are blocked and singlet oxygen is quenched, no RFUVA cross-linking occurs, indicating the absence of other cross-linking mechanisms. RFUVA catalyzes cross-linking reactions that require production of singlet oxygen ((1)O(2)), whose half-life is extended by D(2)O. Carbonyl-based cross-linking reactions dominate in the corneal stroma, but other possible reaction schemes are proposed. The use of D(2)O as solution media for RF would enable concentration decreases or significant strength enhancement in treated corneas.

  1. Spectrophotometric determination of aminomethylbenzoic acid using sodium 1,2-naphthoquinone-4-sulfonate as the chemical derivative chromogenic reagent

    Science.gov (United States)

    Li, Quan-Min; Yang, Zhan-Jun

    2007-03-01

    A new method has been established for the determination of aminomethylbenzoic acid using sodium 1,2-naphthoquinone-4-sulfonate as the chemical derivative chromogenic reagent. This method is based on the formation of a pink compound from the reaction of aminomethylbenzoic acid and sodium 1,2-naphthoquinone-4-sulfonate. The nucleophilic substitution reaction proceeds quantitatively in pH 12.0 buffer solution. The stoichiometric ratio of the reaction, maximum absorption wavelength and the value of ɛ430 were 1:1, 430 nm, and 2.87 × 10 3 L mol -1 cm -1, respectively. Beer's law was obeyed in the range of 0.80-80 mg/L of aminomethylbenzoic acid. The data have been filled to a linear regression equation A = 0.03183 + 0.01658 C (mg/L), with a correlation coefficient of 0.9996. The detection limit is 0.11 mg/L, R.S.D. is 0.54%, and average recovery is over 99.6%. This paper further improves the determination of aminomethylbenzoic acid compared to the previous methods. The kinetic property and reaction mechanism have also been discussed. This proposed method has been successfully applied to the determination of aminomethylbenzoic acid in injection of aminomethylbenzoic acid with satisfactory results.

  2. 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...

  3. Formaldehyde cross-linking and structural proteomics: Bridging the gap.

    Science.gov (United States)

    Srinivasa, Savita; Ding, Xuan; Kast, Juergen

    2015-11-01

    Proteins are dynamic entities constantly moving and altering their structures based on their functions and interactions inside and outside the cell. Formaldehyde cross-linking combined with mass spectrometry can accurately capture interactions of these rapidly changing biomolecules while maintaining their physiological surroundings. Even with its numerous established uses in biology and compatibility with mass spectrometry, formaldehyde has not yet been applied in structural proteomics. However, formaldehyde cross-linking is moving toward analyzing tertiary structure, which conventional cross-linkers have already accomplished. The purpose of this review is to describe the potential of formaldehyde cross-linking in structural proteomics by highlighting its applications, characteristics and current status in the field. Copyright © 2015 Elsevier Inc. All rights reserved.

  4. Developing a Multiplexed Quantitative Cross-Linking Mass Spectrometry Platform for Comparative Structural Analysis of Protein Complexes.

    Science.gov (United States)

    Yu, Clinton; Huszagh, Alexander; Viner, Rosa; Novitsky, Eric J; Rychnovsky, Scott D; Huang, Lan

    2016-10-18

    Cross-linking mass spectrometry (XL-MS) represents a recently popularized hybrid methodology for defining protein-protein interactions (PPIs) and analyzing structures of large protein assemblies. In particular, XL-MS strategies have been demonstrated to be effective in elucidating molecular details of PPIs at the peptide resolution, providing a complementary set of structural data that can be utilized to refine existing complex structures or direct de novo modeling of unknown protein structures. To study structural and interaction dynamics of protein complexes, quantitative cross-linking mass spectrometry (QXL-MS) strategies based on isotope-labeled cross-linkers have been developed. Although successful, these approaches are mostly limited to pairwise comparisons. In order to establish a robust workflow enabling comparative analysis of multiple cross-linked samples simultaneously, we have developed a multiplexed QXL-MS strategy, namely, QMIX (Quantitation of Multiplexed, Isobaric-labeled cross (X)-linked peptides) by integrating MS-cleavable cross-linkers with isobaric labeling reagents. This study has established a new analytical platform for quantitative analysis of cross-linked peptides, which can be directly applied for multiplexed comparisons of the conformational dynamics of protein complexes and PPIs at the proteome scale in future studies.

  5. Study of Rigid Cross-Linked PVC Foams with Heat Resistance

    Directory of Open Access Journals (Sweden)

    Chenhui Zhao

    2012-12-01

    Full Text Available Three heat resistant cross-linked PVC foam plastics were prepared and their performances were compared with universal cross-linked PVC structural foam. The results show that these three heat resistant foams have higher glass transition temperatures (close to 100 °C than universal structural foam (83.2 °C. Compared with the universal structural foam, the three heat resistant foams show much higher decomposition temperature and better chemical stability due to the crosslinking of PVC macromolecular chains. The heat distortion temperature (HDT values of the three heat resistant foam plastics are just a little higher than that of universal structural foam. The three heat resistant foam plastics have good dimensional stability at 140 °C, and when used as core material can closely adhere to the face plates in medium temperature curing processes. Compared with universal structural foam, the three heat resistant foam plastics have slightly better mechanical properties.

  6. 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

    and the change of bulk viscosity due to network developing was determined. For delivering of local derivatives smoothing techniques were applied on creep data. The rate of increment of viscosity increased with increasing the temperature, and the major of this increment took place in the first stages of reaction.......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...

  7. Clasificación de reactivos químicos en los laboratorios de la Universidad Nacional Classification of chemical reagents in the laboratories of National University

    Directory of Open Access Journals (Sweden)

    José Carlos Mora Barrantes

    2012-11-01

    Full Text Available Durante el periodo 2008-2010 se realizaron inventarios de los reactivos químicos utilizados y almacenados en los laboratorios de los campus Omar Dengo y Benjamín Núñez de la Universidad Nacional. Se le solicitó a cada coordinador de laboratorio completar un formulario que incluía el nombre, la cantidad y el número CAS de los reactivos químicos almacenados y utilizados en cada laboratorio. Con estos datos, se clasificaron los reactivos de acuerdo con su categoría de peligro, utilizando el Código IMDG de la Organización de las Naciones Unidas (ONU. La clasificación de los reactivos químicos permitió el desarrollo de sus patrones de distribución en las diferentes unidades, institutos y centros de investigación de la Universidad Nacional. Además, se identificaron las clases de reactivos de mayor y menor uso en los laboratorios de la institución. El adecuado manejo de los reactivos químicos, con su correspondiente clasificación basada en la categoría de riesgo, es la base principal para la implementación de un ambiente seguro de trabajo en los laboratorios. La clasificación de los reactivos químicos permite minimizar los costos administrativos, económicos, legales, de seguridad y técnicos asociados con la atención de emergencias químicas; permitiendo además el desarrollo y aplicación de prácticas de trabajo preventivas por parte de funcionarios y estudiantes durante la manipulación de estas sustancias.During 2008-2010 inventories of chemical reagents used and stored in teaching and research laboratories of Omar Dengo and Benjamín Núñez campuses of National University were generated. E ach laboratory coordinator was asked to fill out a form that included name, quantity and CAS number of every chemical reagent stored and utilized in the laboratories. Chemical reagents were then classified according to the risk categories described by the United Nations IMDG Code. Such a classification process allowed the development

  8. Continuous Sensing Photonic Lab-on-a-Chip Platform Based on Cross-Linked Enzyme Crystals.

    Science.gov (United States)

    Conejero-Muriel, Mayte; Rodríguez-Ruiz, Isaac; Verdugo-Escamilla, Cristóbal; Llobera, Andreu; Gavira, José A

    2016-12-06

    Microfluidics or lab-on-a-chip technology offer clear advantages over conventional systems such as a dramatic reduction of reagent consumption or a shorter analysis time, which are translated into cost-effective systems. In this work, we present a photonic enzymatic lab-on-a-chip reactor based on cross-linked enzyme crystals (CLECs), able to work in continuous flow, as a highly sensitive, robust, reusable, and stable platform for continuous sensing with superior performance as compared to the state of the art. The microreactor is designed to facilitate the in situ crystallization and crystal cross-linking generating enzymatically active material that can be stored for months/years. Thus, and by means of monolithically integrated micro-optics elements, continuous enzymatic reactions can be spectrophotometrically monitored. Lipase, an enzyme with industrial significance for catalyzed transesterification, hydrolysis, and esterification reactions, is used to demonstrate the potential of the microplatforms as both a continuous biosensor and a microreactor for the synthesis of high value compounds.

  9. Physically Cross-linked Polymer Binder Induced by Reversible Acid-Base Interaction for High-Performance Silicon Composite Anodes.

    Science.gov (United States)

    Lim, Sanghyun; Chu, Hodong; Lee, Kukjoo; Yim, Taeeun; Kim, Young-Jun; Mun, Junyoung; Kim, Tae-Hyun

    2015-10-28

    Silicon is greatly promising for high-capacity anode materials in lithium-ion batteries (LIBs) due to their exceptionally high theoretical capacity. However, it has a big challenge of severe volume changes during charge and discharge, resulting in substantial deterioration of the electrode and restricting its practical application. This conflict requires a novel binder system enabling reliable cyclability to hold silicon particles without severe disintegration of the electrode. Here, a physically cross-linked polymer binder induced by reversible acid-base interaction is reported for high performance silicon-anodes. Chemical cross-linking of polymer binders, mainly based on acidic polymers including poly(acrylic acid) (PAA), have been suggested as effective ways to accommodate the volume expansion of Si-based electrodes. Unlike the common chemical cross-linking, which causes a gradual and nonreversible fracturing of the cross-linked network, a physically cross-linked binder based on PAA-PBI (poly(benzimidazole)) efficiently holds the Si particles even after the large volume changes due to its ability to reversibly reconstruct ionic bonds. The PBI-containing binder, PAA-PBI-2, exhibited large capacity (1376.7 mAh g(-1)), high Coulombic efficiency (99.1%) and excellent cyclability (751.0 mAh g(-1) after 100 cycles). This simple yet efficient method is promising to solve the failures relating with pulverization and isolation from the severe volume changes of the Si electrode, and advance the realization of high-capacity LIBs.

  10. Practical application of thermoreversibly Cross-linked rubber products

    Science.gov (United States)

    Polgar, L. M.; Picchioni, F.; de Ruiter, E.; van Duin, M.

    2017-07-01

    Currently, rubber products cannot simply be reprocessed after their product life, due to the irreversible cross-linking methods traditionally applied. The purpose of this work is to investigate how thermoreversible cross-linking of rubbers via Diels Alder chemistry can be used for the development of recyclable rubber products. Unfortunately, the applicability of the thermoreversible EPM-g-furan/BM system appears to be limited to room temperature applications, because of the rapid deterioration of the compression set at elevated temperatures compared to irreversibly cross-linked EPM. However, the use of EPM rubber modified with thiophene or cyclopentadiene moieties may extend the temperature application range and results in rubber products with acceptable properties. Finally, rubber products generally comprise fillers such as silica, carbon black or fibers. In this context, the reinforcing effect of short cut aramid fibers on the material properties of the newly developed thermoreversibly cross-linked EPM rubbers was also studied. The material properties of the resulting products were found to be comparable to those of a fiber reinforced, peroxide cured reference sample.

  11. Lactoferrin binding to transglutaminase cross-linked casein micelles

    NARCIS (Netherlands)

    Anema, S.G.; de Kruif, C.G.|info:eu-repo/dai/nl/073609609

    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

  12. 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.

  13. Functionalisation of cross-linked polyethylenimine for the removal of ...

    African Journals Online (AJOL)

    Functionalisation of cross-linked polyethylenimine for the removal of As from mining wastewater. ... The Freundlich isotherm was found to best fit and describe the experimental data. The thermodynamic study of the adsorption process indicated high activation energies (55.91 kJ mol-1) which confirms chemisorption as a ...

  14. UV laser-induced cross-linking in peptides

    Science.gov (United States)

    Leo, Gabriella; Altucci, Carlo; Bourgoin-Voillard, Sandrine; Gravagnuolo, Alfredo M.; Esposito, Rosario; Marino, Gennaro; Costello, Catherine E.; Velotta, Raffaele; Birolo, Leila

    2013-01-01

    RATIONALE The aim of this study was to demonstrate, and to characterize by high resolution mass spectrometry, that it is possible to preferentially induce covalent cross-links in peptides by using high energy femtosecond UV laser pulses. The cross-link is readily formed only when aromatic amino acids are present in the peptide sequence. METHODS Three peptides, xenopsin, angiotensin I, interleukin, individually or in combination, were exposed to high energy femtosecond UV laser pulses, either alone or in the presence of spin trapping molecules, the reaction products being characterized by high resolution mass spectrometry. RESULTS High resolution mass spectrometry and spin trapping strategies showed that cross-linking occurs readily, proceeds via a radical mechanism, and is the highly dominant reaction, proceeding without causing significant photo-damage in the investigated range of experimental parameters. CONCLUSIONS High energy femtosecond UV laser pulses can be used to induce covalent cross-links between aromatic amino acids in peptides, overcoming photo-oxidation processes, that predominate as the mean laser pulse intensity approaches illumination conditions achievable with conventional UV light sources. PMID:23754800

  15. 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

  16. Thermoreversibly Cross-Linked EPM Rubber Nanocomposites with Carbon Nanotubes

    NARCIS (Netherlands)

    Polgar, Lorenzo Massimo; Criscitiello, Francesco; van Essen, Machiel; Araya-Hermosilla, Rodrigo; Migliore, Nicola; Lenti, Mattia; Raffa, Patrizio; Picchioni, Francesco; Pucci, Andrea

    2018-01-01

    Conductive rubber nanocomposites were prepared by dispersing conductive nanotubes (CNT) in thermoreversibly cross-linked ethylene propylene rubbers grafted with furan groups (EPM-g-furan) rubbers. Their features were studied with a strong focus on conductive and mechanical properties relevant for

  17. 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...... tests at 130 °C. The relationships between PA uptake, chemical composition and mechanical stability are reported. Proton conductivity and mechanical properties only depend on the phosphoric acid content, which, however is a function of the chemical composition....

  18. 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.

  19. Comparative performance of electrospun collagen nanofibers cross-linked by means of different methods.

    Science.gov (United States)

    Torres-Giner, Sergio; Gimeno-Alcañiz, Jose V; Ocio, Maria J; Lagaron, Jose M

    2009-01-01

    Collagen, as the major structural protein of the extracellular matrix in animals, is a versatile biomaterial of great interest in various engineering applications. Electrospun nanofibers of collagen are regarded as very promising materials for tissue engineering applications because they can reproduce the morphology of the natural bone but have as a drawback a poor structural consistency in wet conditions. In this paper, a comparative study between the performance of different cross-linking methods such as a milder enzymatic treatment procedure using transglutaminase, the use of N-[3-(dimethylamino)propyl]-N'-ethylcarbodiimide hydrochloride/N-hydroxysuccinimide, and genipin, and the use of a physical method based on exposure to ultraviolet light was carried out. The chemical and enzymatic treatments provided, in this order, excellent consistency, morphology, cross-linking degree, and osteoblast viability for the collagen nanofibers. Interestingly, the enzymatically cross-linked collagen mats, which are considered to be a more biological treatment, promoted adequate cell adhesion, making the biomaterial biocompatible and with an adequate degree of porosity for cell seeding and in-growth.

  20. Self-Healing Gelatin Hydrogels Cross-Linked by Combining Multiple Hydrogen Bonding and Ionic Coordination.

    Science.gov (United States)

    Zhang, Guangzhao; Lv, Lei; Deng, Yonghong; Wang, Chaoyang

    2017-06-01

    Self-healing hydrogels have been studied by many researchers via multiple cross-linking approaches including physical and chemical interactions. It is an interesting project in multifunctional hydrogel exploration that a water soluble polymer matrix is cross-linked by combining the ionic coordination and the multiple hydrogen bonds to fabricate self-healing hydrogels with injectable property. This study introduces a general procedure of preparing the hydrogels (termed gelatin-UPy-Fe) cross-linked by both ionic coordination of Fe3+ and carboxyl group from the gelatin and the quadruple hydrogen bonding interaction from the ureido-pyrimidinone (UPy) dimers. The gelatin-UPy-Fe hydrogels possess an excellent self-healing property. The effects of the ionic coordination of Fe3+ and quadruple hydrogen bonding of UPy on the formation and mechanical behavior of the prepared hydrogels are investigated. In vitro drug release of the gelatin-UPy-Fe hydrogels is also observed, giving an intriguing glimpse into possible biological applications. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  1. Seed-mediated synthesis of cross-linked Pt-NiO nanochains for methanol oxidation

    Energy Technology Data Exchange (ETDEWEB)

    Gu, Zhulan; Bin, Duan; Feng, Yue; Zhang, Ke; Wang, Jin; Yan, Bo; Li, Shumin; Xiong, Zhiping; Wang, Caiqin; Shiraishi, Yukihide; Du, Yukou, E-mail: duyk@suda.edu.cn

    2017-07-31

    Highlights: • Cross-linked Pt-NiO nanochains using seed-mediated growth method are synthesized. • The as-prepared catalysts exhibit higher electrocatalytic activity than Pt/C for MOR. • The Pt-NiO(1:1 by molar) catalyst shows the best electrocatalytic property towards MOR. - Abstract: A simple method was reported for employing NiO nanoparticles act as seeds and then different amounts of Pt{sup 2+} were reduced on the NiO nanoparticles, forming a cross-linked Pt-NiO nanocatalysts. These as-prepared catalysts were characterized using different physical-chemical techniques, including X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The results indicate that the morphology of the cross-linked Pt-NiO nanochain was successfully produced regardless of the molar ratio of Pt{sup 2+} to NiO precursors. The electrochemical characteristics of Pt-NiO nanochain catalysts were evaluated for the oxidation of methanol as a model reaction, which verify that the Pt-NiO catalysts show enhanced activity and high stability in comparison with the commercial Pt/C catalyst. The optimized ratio of Pt to NiO is 1:1, then tuned by simple adjusting the feed ratio of the precursors as well. The synthesized nanocatalysts will be found the great potential applications as electrocatalysts for fuel cells owe to their enhanced catalytic performance and long-term stability.

  2. An attempt to cast light into starch nanocrystals preparation and cross-linking.

    Science.gov (United States)

    Jivan, Mehdi Jalali; Madadlou, Ashkan; Yarmand, Mohamadsaeed

    2013-12-01

    Potato starch was hydrolyzed with 2.2 or 3.7 M hydrochloric acid in order to obtain the nanocrystals which afterwards were chemically cross-linked with sodium hexametaphosphate. The stronger acidity resulted in smaller nanocrystals with mean size of 48 nm in a shorter time. X-ray diffraction confirmed the dominant crystalline nature of particles and Fourier transform infrared spectroscopy suggested the presence of lower number of free hydroxyl groups in nanocrystals after cross-linking. Starch nanocrystals showed two distinctive differential scaning colorimetry endotherms at 26 and 125 °C, attributed to destruction of nanocrystals lattice and moblizing of each nanocrystal's structure, respectively. Cross-linking resulted in a tenacious spatial arrangement of nanocrystals, strengthening the crystals lattice against phase transitions induced by heating. Scanning electron microscopy images confirmed the particle size measured for nanocrystals by light scattering. Atomic force microscopy topographic images suggested that starch nanocrystals were originated from small amylopectin blocklets in granular assembly of starch. Copyright © 2013 Elsevier Ltd. All rights reserved.

  3. 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. Copyright © 2015, American Association for the Advancement of Science.

  4. 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.

  5. 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.

  6. A Redox-Active, Compact Molecule for Cross-Linking Amyloidogenic Peptides into Nontoxic, Off-Pathway Aggregates: In Vitro and In Vivo Efficacy and Molecular Mechanisms

    Energy Technology Data Exchange (ETDEWEB)

    Derrick, Jeffrey S.; Kerr, Richard A.; Nam, Younwoo; Oh, Shin Bi; Lee, Hyuck Jin; Earnest, Kaylin G.; Suh, Nayoung; Peck, Kristy L.; Ozbil, Mehmet; Korshavn, Kyle J.; Ramamoorthy, Ayyalusamy; Prabhakar, Rajeev; Merino, Edward J.; Shearer, Jason; Lee, Joo-Yong; Ruotolo, Brandon T.; Lim, Mi Hee

    2015-11-25

    Chemical reagents targeting and controlling amyloidogenic peptides have received much attention for helping identify their roles in the pathogenesis of protein-misfolding disorders. Herein, we report a novel strategy for redirecting amyloidogenic peptides into nontoxic, off-pathway aggregates, which utilizes redox properties of a small molecule (DMPD, N,N-dimethyl-p-phenylenediamine) to trigger covalent adduct formation with the peptide. In addition, for the first time, biochemical, biophysical, and molecular dynamics simulation studies have been performed to demonstrate a mechanistic understanding for such an interaction between a small molecule (DMPD) and amyloid-β (Aβ) and its subsequent anti-amyloidogenic activity, which, upon its transformation, generates ligand–peptide adducts via primary amine-dependent intramolecular cross-linking correlated with structural compaction. Furthermore, in vivo efficacy of DMPD toward amyloid pathology and cognitive impairment was evaluated employing 5xFAD mice of Alzheimer’s disease (AD). Such a small molecule (DMPD) is indicated to noticeably reduce the overall cerebral amyloid load of soluble Aβ forms and amyloid deposits as well as significantly improve cognitive defects in the AD mouse model. Overall, our in vitro and in vivo studies of DMPD toward Aβ with the first molecular-level mechanistic investigations present the feasibility of developing new, innovative approaches that employ redox-active compounds without the structural complexity as next-generation chemical tools for amyloid management.

  7. Newer protocols and future in collagen cross-linking.

    Science.gov (United States)

    Cummings, Arthur B; McQuaid, Rebecca; Mrochen, Michael

    2013-08-01

    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.

  8. Cross-linking of starch with bifunctional precursors of nitroalkenes

    NARCIS (Netherlands)

    Heeres, A.; Doren, H.A. van; Gotlieb, K.F.; Bleeker, I.P.; Kellogg, R.M.

    1998-01-01

    Granular starch was cross-linked with 1,3-di-O-acetyl-2-nitro-1,3-propanediol (1), 1,3-di-O-pivaloyl-2-nitro-1,3-propanediol (2), 2-nitro-3-O-pivaloyl-1-propene-3-ol (3), 1,3-di-O-acetyl-aci-2-nitro-1,3-propanediol (4), 1,3-di-O-pivaloyl-aci-2-nitro-1,3-propanediol (5) and

  9. Cross-linking of starch with bifunctional precursors of nitroalkenes

    NARCIS (Netherlands)

    Heeres, André; Doren, Henk A. van; Gotlieb, Kees F.; Bleeker, Ido P.; Kellogg, R.M.

    Granular starch was cross-linked with 1,3-di-O-acetyl-2-nitro-1,3-propanediol (1), 1,3-di-O-pivaloyl-2-nitro-1,3-propanediol (2), 2-nitro-3-O-pivaloyl-1-propene-3-ol (3), 1,3-di-O-acetyl-aci-2-nitro-1,3-propanediol (4), 1,3-di-O-pivaloyl-aci-2-nitro-1,3-propanediol (5) and

  10. Induced collagen cross-links enhance cartilage integration.

    Directory of Open Access Journals (Sweden)

    Aristos A Athens

    Full Text Available Articular cartilage does not integrate due primarily to a scarcity of cross-links and viable cells at the interface. The objective of this study was to test the hypothesis that lysyl-oxidase, a metalloenzyme that forms collagen cross-links, would be effective in improving integration between native-to-native, as well as tissue engineered-to-native cartilage surfaces. To examine these hypotheses, engineered cartilage constructs, synthesized via the self-assembling process, as well as native cartilage, were implanted into native cartilage rings and treated with lysyl-oxidase for varying amounts of time. For both groups, lysyl-oxidase application resulted in greater apparent stiffness across the cartilage interface 2-2.2 times greater than control. The construct-to-native lysyl-oxidase group also exhibited a statistically significant increase in the apparent strength, here defined as the highest observed peak stress during tensile testing. Histology indicated a narrowing gap at the cartilage interface in lysyl-oxidase treated groups, though this alone is not sufficient to indicate annealing. However, when the morphological and mechanical data are taken together, the longer the duration of lysyl-oxidase treatment, the more integrated the interface appeared. Though further data are needed to confirm the mechanism of action, the enhancement of integration may be due to lysyl-oxidase-induced pyridinoline cross-links. This study demonstrates that lysyl-oxidase is a potent agent for enhancing integration between both native-to-native and native-to-engineered cartilages. The fact that interfacial strength increased manifold suggests that cross-linking agents should play a significant role in solving the difficult problem of cartilage integration. Future studies must examine dose, dosing regimen, and cellular responses to lysyl-oxidase to optimize its application.

  11. Flexible Optical Waveguides for Uniform Periscleral Cross-Linking

    OpenAIRE

    Kwok, Sheldon J. J.; Kim, Moonseok; Lin, Harvey H.; Seiler, Theo G.; Beck, Eric; Shao, Peng; Kochevar, Irene E.; Seiler, Theo; Yun, Seok-Hyun

    2017-01-01

    Purpose Scleral cross-linking (SXL) with a photosensitizer and light is a potential strategy to mechanically reinforce the sclera and prevent progressive axial elongation responsible for severe myopia. Current approaches for light delivery to the sclera are cumbersome, do not provide uniform illumination, and only treat a limited area of sclera. To overcome these challenges, we developed flexible optical waveguides optimized for efficient, homogeneous light delivery. Methods: Waveguides were ...

  12. The theory and art of corneal cross-linking

    OpenAIRE

    Rebecca McQuaid; Cummings, Arthur B; Michael Mrochen

    2013-01-01

    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 ...

  13. [Complications and postoperative therapeutic strategies in cross-linking].

    Science.gov (United States)

    Kohlhaas, M

    2017-05-24

    The reduced corneal mechanical stability in keratoconus and similar collagen diseases can lead to a progressive and irregular corneal shape and decrease of visual acuity. A progression of keratectatic diseases can be shown with corneal topography. Keratoconus can be treated by photo-oxidative cross-linking of the corneal collagen. In order to achieve a high absorption of irradiation energy in the cornea, riboflavin at a concentration of 0.1% and UVA light at a wavelength of 370 nm corresponding to the relative maximum absorption of riboflavin (vitamin B2) are used. Evidence for corneal cross-linking are the increase of biomechanical stiffness, the increased resistance against enzymatic degradation, a higher shrinkage temperature, a lower swelling rate and an increased diameter of collagen fibers. The currently available data demonstrate that the therapeutic cross-linking procedure is safe when respecting the important theoretical and clinical parameters and that a progression of the keratoconus can be avoided. In 80% of cases an average levelling of the curvature of approximately 2 dpt can be achieved, which leads not only to stabilization but also to an increase in visual acuity of approximately 1.2 lines. In a Cochrane review from 2015 publications about complications and results were reviewed. Complication rates ranged from 1-10% depending on the initial situation, comorbidities and stage of the keratoconus. The most important complications are early epithelial wound healing problems as well as extremely rare perforations. Corneal cross-linking is a well-established and safe procedure but is not free of complications.

  14. Newer protocols and future in collagen cross-linking

    OpenAIRE

    Cummings, Arthur B; Rebecca McQuaid; Michael Mrochen

    2013-01-01

    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 proc...

  15. Optimized Fragmentation Regime for Diazirine Photo-Cross-Linked Peptides.

    Science.gov (United States)

    Giese, Sven H; Belsom, Adam; Rappsilber, Juri

    2016-08-16

    Cross-linking/mass spectrometry has evolved into a robust technology that reveals structural insights into proteins and protein complexes. We leverage a new tribrid instrument with improved fragmentation capacities in a systematic comparison to identify which fragmentation method would be best for the identification of cross-linked peptides. Specifically, we explored three fragmentation methods and two combinations: collision-induced dissociation (CID), beam-type CID (HCD), electron-transfer dissociation (ETD), ETciD, and EThcD. Trypsin-digested, SDA-cross-linked human serum albumin (HSA) served as a test sample, yielding over all methods and in triplicate analysis in total 2602 matched PSMs and 1390 linked residue pairs at 5% false discovery rate, as confirmed by the crystal structure. HCD wins in number of matched peptide-spectrum-matches (958 PSMs) and identified links (446). CID is most complementary, increasing the number of identified links by 13% (58 links). HCD wins together with EThcD in cross-link site calling precision, with approximately 62% of sites having adjacent backbone cleavages that unambiguously locate the link in both peptides, without assuming any cross-linker preference for amino acids. Overall quality of spectra, as judged by sequence coverage of both peptides, is best for EThcD for the majority of peptides. Sequence coverage might be of particular importance for complex samples, for which we propose a data dependent decision tree, else HCD is the method of choice. The mass spectrometric raw data has been deposited in PRIDE (PXD003737).

  16. Mechanism of DNA-protein cross-linking by chromium.

    Science.gov (United States)

    Macfie, Andrea; Hagan, Elizabeth; Zhitkovich, Anatoly

    2010-02-15

    Hexavalent chromium is a known inducer of DNA-protein cross-links (DPCs) that contribute to repression of inducible genes and genotoxicity of this metal. Lymphocytic DPCs have also shown potential utility as biomarkers of human exposure to Cr(VI). Here, we examined the mechanism of DPC formation by Cr(VI) and the impact of its main cellular reducers. In vitro reactions of Cr(VI) with one-electron reducing thiols (glutathione and cysteine) or two-electron donating ascorbate were all efficient at DPC production, indicating a dispensable role of Cr(V). No Cr(VI) reducer was able to generate DPC in the presence of Cr(III)-chelating EDTA or phosphate. A critical role of Cr(III) in DNA-protein linkages was further confirmed by dissociation of Cr(VI)-induced DPC by phosphate. EDTA was very inefficient in DPC dissociation, indicating its poor suitability for testing of Cr(III)-mediated bridging and reversal of complex DPC. Reactions containing only one Cr-modified component (protein or DNA) showed that Cr(III)-DNA adduction was the initial step in DPC formation. Cross-linking proceeded slowly after the rapid formation of Cr-DNA adducts, indicating that protein conjugation was the rate-limiting step in DPC generation. Experiments with depletion of glutathione and restoration of ascorbate levels in human lung A549 cells showed that high cellular reducing capacity promotes DPC yield. Overall, our data provide evidence for a three-step cross-linking mechanism involving (i) reduction of Cr(VI) to Cr(III), (ii) Cr(III)-DNA binding, and (iii) protein capture by DNA-bound Cr(III) generating protein-Cr(III)-DNA cross-links.

  17. Differential base stacking interactions induced by trimethylene interstrand DNA cross-links in the 5'-CpG-3' and 5'-GpC-3' sequence contexts.

    Science.gov (United States)

    Huang, Hai; Dooley, Patricia A; Harris, Constance M; Harris, Thomas M; Stone, Michael P

    2009-11-01

    Synthetically derived trimethylene interstrand DNA cross-links have been used as surrogates for the native cross-links that arise from the 1,N(2)-deoxyguanosine adducts derived from alpha,beta-unsaturated aldehydes. The native enal-mediated cross-linking occurs in the 5'-CpG-3' sequence context but not in the 5'-GpC-3' sequence context. The ability of the native enal-derived 1,N(2)-dG adducts to induce interstrand DNA cross-links in the 5'-CpG-3' sequence as opposed to the 5'-GpC-3' sequence is attributed to the destabilization of the DNA duplex in the latter sequence context. Here, we report higher accuracy solution structures of the synthetically derived trimethylene cross-links, which are refined from NMR data with the AMBER force field. When the synthetic trimethylene cross-links are placed into either the 5'-CpG-3' or the 5'-GpC-3' sequence contexts, the DNA duplex maintains B-DNA geometry with structural perturbations confined to the cross-linked base pairs. Watson-Crick hydrogen bonding is conserved throughout the duplexes. Although different from canonical B-DNA stacking, the cross-linked and the neighbor base pairs stack in the 5'-CpG-3' sequence. In contrast, the stacking at the cross-linked base pairs in the 5'-GpC-3' sequence is greatly perturbed. The pi-stacking interactions between the cross-linked and the neighbor base pairs are reduced. This is consistent with remarkable chemical shift perturbations of the C(5) H5 and H6 nucleobase protons that shifted downfield by 0.4-0.5 ppm. In contrast, these chemical shift perturbations in the 5'-CpG-3' sequence are not remarkable, consistent with the stacked structure. The differential stacking of the base pairs at the cross-linking region probably explains the difference in stabilities of the trimethylene cross-links in the 5'-CpG-3' and 5'-GpC-3' sequence contexts and might, in turn, account for the sequence selectivity of the interstrand cross-link formation induced by the native enal-derived 1,N(2)-d

  18. Cross-linked polymeric membranes for carbon dioxide separation

    Energy Technology Data Exchange (ETDEWEB)

    Hong, Tao; Chatterjee, Sabornie; Mahurin, Shannon Mark; Long, Brian Keith; Jiang, De-en; Mays, Jimmy Wayne; Sokolov, Alexei P.; Saito, Tomonori

    2018-01-23

    A membrane useful in gas separation, the membrane comprising a cross-linked polysiloxane structure having a cross-link density of about 0.1.times.10.sup.-5 mol/cm.sup.3 to about 6.times.10.sup.-5 mol/cm.sup.3, where, in particular embodiments, the cross-linked polysiloxane structure has the following general structure: ##STR00001## wherein R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5, and R.sup.6 are independently selected from hydrocarbon groups having at least 1 and up to 6 carbon atoms; A.sup.1 and A.sup.2 are independently selected from cyclic hydrocarbon groups; L.sup.1 and L.sup.2 are linking groups or covalent bonds; n is an integer of at least 1; r and s are independently selected from integers of at least 1; and p is an integer of at least 10. The invention also includes methods for making and using the above-described membranes for gas separation.

  19. Homogeneous UVA system for corneal cross-linking treatment

    Science.gov (United States)

    Ayres Pereira, Fernando R.; Stefani, Mario A.; Otoboni, José A.; Richter, Eduardo H.; Ventura, Liliane

    2010-02-01

    The treatment of keratoconus and corneal ulcers by collagen cross-linking using ultraviolet type A irradiation, combined with photo-sensitizer Riboflavin (vitamin B2), is a promising technique. The standard protocol suggests instilling Riboflavin in the pre-scratched cornea every 5min for 30min, during the UVA irradiation of the cornea at 3mW/cm2 for 30 min. This process leads to an increase of the biomechanical strength of the cornea, stopping the progression, or sometimes, even reversing Keratoconus. The collagen cross-linking can be achieved by many methods, but the utilization of UVA light, for this purpose, is ideal because of its possibility of a homogeneous treatment leading to an equal result along the treated area. We have developed a system, to be clinically used for treatment of unhealthy corneas using the cross-linking technique, which consists of an UVA emitting delivery device controlled by a closed loop system with high homogeneity. The system is tunable and delivers 3-5 mW/cm2, at 365nm, for three spots (6mm, 8mm and 10mm in diameter). The electronics close loop presents 1% of precision, leading to an overall error, after the calibration, of less than 10% and approximately 96% of homogeneity.

  20. Massive corneal edema treated with corneal cross-linking.

    Science.gov (United States)

    Laborante, A; Buzzonetti, L; Longo, C

    2012-01-01

    Massive corneal edema disrupts the fine architecture of corneal stroma that guarantees its transparency, causing opacities that seriously impair clear vision and are usually solved by corneal transplant. Corneal cross-linking, a treatment developed to halt keratoconus progression, results in a loss of water and a compaction of corneal stroma. It might therefore be useful to improve the pathologic edematous condition of some corneas, ameliorating visual acuity and allowing more time for a surgical procedure of keratoplasty. Six patients with visual impairing corneal edemas further to lens phacoemulsification, penetrating keratoplasty, or post-infective neovascularization were treated with corneal cross-linking alone, or in combination with amniotic membrane apposition with or without anti-angiogenic therapy. All patients partly resolved the edematous condition, improving both corneal transparency and visual acuity. Corneal cross-linking appears to be a useful method to treat massive corneal edemas, so that keratoplasty can be at least delayed, and need not to be an emergency treatment in these cases.

  1. Exploring the kinetics of gelation and final architecture of enzymatically cross-linked chitosan/gelatin gels.

    Science.gov (United States)

    da Silva, Marcelo A; Bode, Franziska; Grillo, Isabelle; Dreiss, Cécile A

    2015-04-13

    Small-angle neutron scattering (SANS) was used to characterize the nanoscale structure of enzymatically cross-linked chitosan/gelatin hydrogels obtained from two protocols: a pure chemical cross-linking process (C), which uses the natural enzyme microbial transglutaminase, and a physical-co-chemical (PC) hybrid process, where covalent cross-linking is combined with the temperature-triggered gelation of gelatin, occurring through the formation of triple-helices. SANS measurements on the final and evolving networks provide a correlation length (ξ), which reflects the average size of expanding clusters. Their growth in PC gels is restricted by the triple-helices (ξ ∼ 10s of Å), while ξ in pure chemical gels increases with cross-linker concentration (∼100s of Å). In addition, the shear elastic modulus in PC gels is higher than in pure C gels. Our results thus demonstrate that gelatin triple helices provide a template to guide the cross-linking process; overall, this work provides important structural insight to improve the design of biopolymer-based gels.

  2. Induction and repair of DNA cross-links induced by sulfur mustard in the A-549 cell line followed by a comet assay.

    Science.gov (United States)

    Jost, Petr; Svobodova, Hana; Stetina, Rudolf

    2015-07-25

    Sulfur mustard is a highly toxic chemical warfare agent with devastating impact on intoxicated tissues. DNA cross-links are probably the most toxic DNA lesions induced in the cell by sulfur mustard. The comet assay is a very sensitive method for measuring DNA damage. In the present study using the A-549 lung cell line, the comet assay protocol was optimized for indirect detection of DNA cross-links induced by sulfur mustard. The method is based on the additional treatment of the assayed cells containing cross-links with the chemical mutagen, styrene oxide. Alkali-labile adducts of styrene oxide cause DNA breaks leading to the formation of comets. A significant dose-dependent reduction of DNA migration of the comet's tail was found after exposing cells to sulfur mustard, indicative of the amount of sulfur mustard induced cross-links. The remarkable decrease of % tail DNA could be observed as early as 5min following exposure to sulfur mustard and the maximal effect was found after 30min, when DNA migration was reduced to the minimum. Sulfur mustard preincubated in culture medium without cells lost its ability to induce cross-links and had a half-life of about 15min. Pre-incubation longer than 30min does not lead to a significant increase in cross-links when applied to cells. However, the amount of cross-links is decreased during further incubation due to repair. The current modification of the comet assay provides a useful tool for detecting DNA cross-links induced by sulfur mustard and could be used for detection of other DNA cross-linking agents such as chemotherapeutic drugs. Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.

  3. Treatment of Refractory Keratitis After a Boston Type I Keratoprosthesis With Corneal Collagen Cross-Linking.

    Science.gov (United States)

    Zarei-Ghanavati, Siamak; Irandoost, Fatemeh

    2015-09-01

    To report a patient with refractory keratitis after a Boston type I keratoprosthesis treated with corneal collagen cross-linking (CXL). Case report. A 29-year-old man with a history of chemical burn in the left eye underwent keratoprosthesis implantation. He developed infectious keratitis 4 months after surgery, which did not respond to topical antibiotics. The patient underwent corneal CXL with a shield covering the keratoprosthesis optic. Three weeks after CXL, the infiltration completely resolved. Corneal CXL might be beneficial in the treatment of refractory keratitis in patients with the Boston type I keratoprosthesis.

  4. 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.

  5. Evaluation of nanohydroxyapaptite (nano-HA) coated epigallocatechin-3-gallate (EGCG) cross-linked collagen membranes.

    Science.gov (United States)

    Chu, Chenyu; Deng, Jia; Man, Yi; Qu, Yili

    2017-09-01

    Collagen is the main component of extracellular matrix (ECM) with desirable biological activities and low antigenicity. Collagen materials have been widely utilized in guided bone regeneration (GBR) surgery due to its abilities to maintain space for hard tissue growth. However, pure collagen lacks optimal mechanical properties. In our previous study, epigallocatechin-3-gallate (EGCG) cross-linked collagen membranes, with better biological activities and enhanced mechanical properties, may promote osteoblast proliferation, but their effect on osteoblast differentiation is not very significant. Nanohydroxyapatite (nano-HA) is the main component of mineral bone, which possesses exceptional bioactivity properties including good biocompatibility, high osteoconductivity and osteoinductivity, non-immunogenicity and non-inflammatory behavior. Herein, by analyzing the physical and chemical properties as well as the effects on promoting bone regeneration, we have attempted to present a novel EGCG-modified collagen membrane with nano-HA coating, and have found evidence that the novel collagen membrane may promote bone regeneration with a better surface morphology, without destroying collagen backbone. To evaluate the surface morphologies, chemical and mechanical properties of pure collagen membranes, epigallocatechin-3-gallate (EGCG) cross-linked collagen membranes, nano-HA coated collagen membranes, nano-HA coated EGCG-collagen membranes, (ii) to evaluate the bone regeneration promoted by theses membranes. In the present study, collagen membranes were divided into 4 groups: (1) untreated collagen membranes (2) EGCG cross-linked collagen membranes (3) nano-HA modified collagen membranes (4) nano-HA modified EGCG-collagen membranes. Scanning electron microscope (SEM) and Fourier transform infrared spectroscopy (FTIR) were used to evaluate surface morphologies and chemical properties, respectively. Mechanical properties were determined by differential scanning calorimeter (DSC

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

    Science.gov (United States)

    Panek, John

    2010-01-01

    Polyimide aerogels with three-dimensional cross-linked structure are made using linear oligomeric segments of polyimide, and linked with one of the following into a 3D structure: trifunctional aliphatic or aromatic amines, latent reactive end caps such as nadic anhydride or phenylethynylphenyl amine, and silica or silsesquioxane cage structures decorated with amine. Drying the gels supercritically maintains the solid structure of the gel, creating a polyimide aerogel with improved mechanical properties over linear polyimide aerogels. Lightweight, low-density structures are desired for acoustic and thermal insulation for aerospace structures, habitats, astronaut equipment, and aeronautic applications. Aerogels are a unique material for providing such properties because of their extremely low density and small pore sizes. However, plain silica aerogels are brittle. Reinforcing the aerogel structure with a polymer (X-Aerogel) provides vast improvements in strength while maintaining low density and pore structure. However, degradation of polymers used in cross-linking tends to limit use temperatures to below 150 C. Organic aerogels made from linear polyimide have been demonstrated, but gels shrink substantially during supercritical fluid extraction and may have lower use temperature due to lower glass transition temperatures. The purpose of this innovation is to raise the glass transition temperature of all organic polyimide aerogel by use of tri-, tetra-, or poly-functional units in the structure to create a 3D covalently bonded network. Such cross-linked polyimides typically have higher glass transition temperatures in excess of 300 400 C. In addition, the reinforcement provided by a 3D network should improve mechanical stability, and prevent shrinkage on supercritical fluid extraction. The use of tri-functional aromatic or aliphatic amine groups in the polyimide backbone will provide such a 3D structure.

  7. 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

  8. LET dependence of DNA-protein cross-links

    Energy Technology Data Exchange (ETDEWEB)

    Blakely, E.A.; Chang, P.Y.; Bjornstad, K.A.

    1995-08-01

    We have preliminary data indicating a fluence-dependent yield of particle-induced protein cross-links (DPC`s) with a dependency on LET and particle residual energy. Our data indicate that the DPC yield for hamster fibroblasts in vitro irradiated at 32 keV/{mu}m is similar to that reported for hamster cells irradiated with cobalt-60 gamma rays. At 100-120 keV/{mu}m there is some evidence for an enhanced DPC yield with increasing particle fluence, but there are differences in the yields that are dependent on particle track structure.

  9. Novel magnetic cross-linked lipase aggregates for improving the resolution of (R, S)-2-octanol.

    Science.gov (United States)

    Liu, Ying; Guo, Chen; Liu, Chun-Zhao

    2015-03-01

    Novel magnetic cross-linked lipase aggregates were fabricated by immobilizing the cross-linked lipase aggregates onto magnetic particles with a high number of -NH2 terminal groups using p-benzoquinone as the cross-linking agent. At the optimal fabrication conditions, 100% of immobilization efficiency and 139% of activity recovery of the magnetic cross-linked lipase aggregates were achieved. The magnetic cross-linked lipase aggregates were able to efficiently resolve (R, S)-2-octanol, and retained 100% activity and 100% enantioselectivity after 10 cycles of reuse, whereas the cross-linked lipase aggregates only retained about 50% activity and 70% enantioselectivity due to insufficient cross-linking. These results provide a great potential for industrial applications of the magnetic cross-linked lipase aggregates. © 2014 Wiley Periodicals, Inc.

  10. Lysyl hydroxylase 2 induces a collagen cross-link switch in tumor stroma

    National Research Council Canada - National Science Library

    Chen, Yulong; Terajima, Masahiko; Yang, Yanan; Sun, Li; Ahn, Young-Ho; Pankova, Daniela; Puperi, Daniel S; Watanabe, Takeshi; Kim, Min P; Blackmon, Shanda H; Rodriguez, Jaime; Liu, Hui; Behrens, Carmen; Wistuba, Ignacio I; Minelli, Rosalba; Scott, Kenneth L; Sanchez-Adams, Johannah; Guilak, Farshid; Pati, Debananda; Thilaganathan, Nishan; Burns, Alan R; Creighton, Chad J; Martinez, Elisabeth D; Zal, Tomasz; Grande-Allen, K Jane; Yamauchi, Mitsuo; Kurie, Jonathan M

    2015-01-01

    .... However, the biochemical nature of collagen cross-links in cancer is still unclear. Here, we postulated that epithelial tumorigenesis is accompanied by changes in the biochemical type of collagen cross-links...

  11. Electrospinning of Cross-Linked Magnetic Chitosan Nanofibers for Protein Release

    National Research Council Canada - National Science Library

    Nicknejad, Ehsan Tayerani; Ghoreishi, Seyyed Mohammad; Habibi, Neda

    2015-01-01

    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...

  12. 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.

  13. Collagen Cross-Linking: Current Status and Future Directions

    Directory of Open Access Journals (Sweden)

    Marine Hovakimyan

    2012-01-01

    Full Text Available Collagen cross-linking (CXL using UVA light and riboflavin (vitamin B2 was introduced as a clinical application to stabilize the cornea by inducing cross-links within and between collagen fibers. CXL has been investigated extensively and has been shown clinically to arrest the progression of keratoconic or post-LASIK ectasia. With its minimal cost, simplicity, and proven positive clinical outcome, CXL can be regarded as a useful approach to reduce the number of penetrating keratoplasties performed. Small case series have also indicated that CXL is beneficial in corneal edema by reducing stromal swelling behavior and in keratitis by inhibiting pathogen growth. Despite these encouraging results, CXL remains a relatively new method that is potentially associated with complications. Aspects such as side effects and recurrence rates have still to be elucidated. In light of the growing interest in CXL, our paper summarizes present knowledge about this promising approach. We have intentionally endeavored to include the more relevant studies from the recent literature to provide an overview of the current status of CXL.

  14. 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.

  15. Matrix cross-linking-mediated mechanotransduction promotes posttraumatic osteoarthritis.

    Science.gov (United States)

    Kim, Jin-Hong; Lee, Gyuseok; Won, Yoonkyung; Lee, Minju; Kwak, Ji-Sun; Chun, Churl-Hong; Chun, Jang-Soo

    2015-07-28

    Osteoarthritis (OA) is characterized by impairment of the load-bearing function of articular cartilage. OA cartilage matrix undergoes extensive biophysical remodeling characterized by decreased compliance. In this study, we elucidate the mechanistic origin of matrix remodeling and the downstream mechanotransduction pathway and further demonstrate an active role of this mechanism in OA pathogenesis. Aging and mechanical stress, the two major risk factors of OA, promote cartilage matrix stiffening through the accumulation of advanced glycation end-products and up-regulation of the collagen cross-linking enzyme lysyl oxidase, respectively. Increasing matrix stiffness substantially disrupts the homeostatic balance between chondrocyte catabolism and anabolism via the Rho-Rho kinase-myosin light chain axis, consequently eliciting OA pathogenesis in mice. Experimental enhancement of nonenzymatic or enzymatic matrix cross-linking augments surgically induced OA pathogenesis in mice, and suppressing these events effectively inhibits OA with concomitant modulation of matrix degrading enzymes. Based on these findings, we propose a central role of matrix-mediated mechanotransduction in OA pathogenesis.

  16. Collagen cross-linking: Strengthening the unstable cornea

    Directory of Open Access Journals (Sweden)

    Oren Tomkins

    2008-05-01

    Full Text Available Oren Tomkins, Hanna J GarzoziDepartment of Ophthalmology, Bnai Zion Medical Center, Haifa, IsraelAbstract: Corneal ectasia, a weakening of corneal integrity, occurs both due to acquired and congenital conditions such as keratoconus. It is a progressing condition that affects both visual acuity, and corneal stability. Various methods exist for correcting this impairment, however none address the inherit pathology, an increase laxity of the corneal stroma. Collagen crosslinking, a new, minimally invasive method, aims to strengthen the stroma by inducing cross links between neighboring collagen fibers. This method results in an increase in corneal tensile strength, with no medium term adverse effects on its normal architecture. Clinically, treated patients display improvement in both visual acuity and keratometric readings. This method may provide clinicians with easily accessible tools to stop the progression, and even correct visual deterioration due to corneal ectasia. Here we review the current information regarding this new method, as well as discuss its potential benefits and downfalls.Keywords: corneal cross-linking, corneal ectasia, keratoconus, stroma, cornea

  17. 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

  18. Thermoreversibly Cross-Linked EPM Rubber Nanocomposites with Carbon Nanotubes

    Directory of Open Access Journals (Sweden)

    Lorenzo Massimo Polgar

    2018-01-01

    Full Text Available Conductive rubber nanocomposites were prepared by dispersing conductive nanotubes (CNT in thermoreversibly cross-linked ethylene propylene rubbers grafted with furan groups (EPM-g-furan rubbers. Their features were studied with a strong focus on conductive and mechanical properties relevant for strain-sensor applications. The Diels-Alder chemistry used for thermoreversible cross-linking allows for the preparation of fully recyclable, homogeneous, and conductive nanocomposites. CNT modified with compatible furan groups provided nanocomposites with a relatively large tensile strength and small elongation at break. High and low sensitivity deformation experiments of nanocomposites with 5 wt % CNT (at the percolation threshold displayed an initially linear sensitivity to deformation. Notably, only fresh samples displayed a linear response of their electrical resistivity to deformations as the resistance variation collapsed already after one cycle of elongation. Notwithstanding this mediocre performance as a strain sensor, the advantages of using thermoreversible chemistry in a conductive rubber nanocomposite were highlighted by demonstrating crack-healing by welding due to the joule effect on the surface and the bulk of the material. This will open up new technological opportunities for the design of novel strain-sensors based on recyclable rubbers.

  19. [Corneal collagen cross-linking in keratoconus management].

    Science.gov (United States)

    Bikbov, M M; Bikbova, G M; Khabibullin, A F

    2011-01-01

    Functional results of collagen UV cross-linking in keratoconus management are evaluated. 77 patients (87 eyes) with keratoconus stage I-II (Amsler classification) were under observation. All the patients received UV radiation (370 3m, 3mW/sm2) for 30 min with simultaneous instillation of "Dextralink" solution. Besides routine ophthalmological examination confocal biomicroscopy (HRT III, Heidelberg, Germany) and optical coherent tomography (Vizante-OCT, Carl Zeis, Germany) were performed before, in 1, 3, 6 and 12 months, 2 and 3 years after the procedure. By the 6th month the best corrected visual acuity showed improvement from 0.41 + 0.12 (M+m) till 0.52 + 0.01. Corneal refractive power decreased to 49.41 + 1.69 dpt by the last examination. UV cross-linking is a minimally invasive and effective option for management of keratoconus at the early stages, that let achieve biomechanical stabilization of the cornea and reduce progression rate.

  20. UV Radiation Induced Cross-Linking of Whey Protein Isolate-Based Films

    OpenAIRE

    Schmid, Markus; Prinz, Tobias Konrad; Müller, Kerstin; Haas, Andreas

    2017-01-01

    Casted whey protein films exposed to ultraviolet irradiation were analyzed for their cross-linking properties and mechanical and barrier performance. Expected mechanical and barrier improvements are discussed with regard to quantification of the cross-linking in the UV-treated whey protein films. Swelling tests were used to determine the degree of swelling, degree of cross-linking, and cross-linking density. When the UV radiation dosage was raised, a significant increase of the tensile streng...

  1. 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.

  2. Chemical electron-transfer reactions in electrospray mass spectrometry: Effective oxidation potentials of electron-transfer reagents in methylene chloride

    Energy Technology Data Exchange (ETDEWEB)

    Van Berkel, G.J.; Zhou, F. (Oak Ridge National Lab., TN (United States))

    1994-10-15

    Cyclic voltammetry (CV), UV/visible absorption spectroscopy, and electrospray mass spectrometry (ES-MS) are used in conjunction to study the mono- and /or dications produced in solution from the reaction of three model compounds ([beta]-carotene, cobalt(II) octaethylporphyrin (Co[sup II]OEP), nickel(II) octaethylporphyrin (Ni[sup II]OEP), in three different solvent/electron-transfer reagent systems (methylene chloride/0.1% trifluoroacetic acid (TFA) (v/v), methylene chloride/0.1% TFA/2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) v/v/200 [mu]M), methylene chloride/0.1% TFA/0.1% antimony pentafluoride (SbF[sub 5]) (v/v/v)). The reactions were carried out on-line with ES-MS by means of flow injection. Correlation of the CV data for these analytes with the ionic species determined to be in the solution on the basis of UV/visible absorption spectra and/or on the basis of the ionic species observed in the gas phase by ES-MS, along with our previously published data on these solvent/reagent systems, allowed an effective oxidation potential range, E, to be assigned to these solvent/reagent systems: methylene chloride/0.1% TFA (v/v), 0.6V [le] E[sub TFA] < 0.7 V; methylene chloride/0.1% TFA/DDQ (v/v/200 [mu]M), 0.8 [le] E[sub TFA/DDQ] < 1.0 V; methylene chloride/0.1% TFA/0.1% SbF[sub 5] (v/v/v), 1.3 [le] E[sub TFA/SbF(5)] < 1.5. 40 refs., 7 figs.

  3. Reagents for the chemical development of latent fingerprints: scope and limitations of benzo[f]ninhydrin in comparison to ninhydrin.

    Science.gov (United States)

    Almog, J; Sears, V G; Springer, E; Hewlett, D F; Walker, S; Wiesner, S; Lidor, R; Bahar, E

    2000-05-01

    Benzo[f]ninhydrin was compared to ninhydrin for fingerprint development on paper. Overall, the performance of ninhydrin on exhibits was slightly better than that of benzo[f]ninhydrin. The significant advantages of the benzo[f]ninhydrin over ninhydrin were the much stronger fluorescence it gave after treatment with zinc salts and a slightly quicker reaction under ambient conditions. This fluorescence is, however, similar to that obtained with other reagents, such as DFO or ninhydrin analogs. These advantages apparently are not sufficient to justify regular usage of benzo[f]ninhydrin, especially when one considers its low solubility and high cost.

  4. Oxidative cross-linking of casein by horseradish peroxidase and its ...

    African Journals Online (AJOL)

    The cross-linking of food proteins is an interesting topic of food science in recent years and served successfully as an approach to modify protein functional properties. In the presented work, horseradish peroxidase (HRP, EC 1.11.1.7) was used to oxidative cross-link casein in presence of H2O2. The cross-linking of casein ...

  5. 21 CFR 177.2710 - Styrene-divinylbenzene resins, cross-linked.

    Science.gov (United States)

    2010-04-01

    ... 21 Food and Drugs 3 2010-04-01 2009-04-01 true Styrene-divinylbenzene resins, cross-linked. 177.2710 Section 177.2710 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN... resins, cross-linked. Styrene-divinylbenzene cross-linked copolymer resins may be safely used as articles...

  6. Cross-linking of LDPE/wax Blends in the Presence of Dicumyl ...

    African Journals Online (AJOL)

    The analyses of cross-link density of the samples indicated that increased amounts of peroxide gives rise to more efficient cross-linking, but only the PE phase in the blends is cross-linked. The DSC results indicated that LDPE and wax are probably miscible in the crystalline phase at low wax concentrations, but at higher ...

  7. Thermodynamic stability and energetics of DNA duplexes containing major intrastrand cross-links of second-generation antitumor dinuclear Pt(II) complexes.

    Science.gov (United States)

    Florian, Jakub; Kasparkova, Jana; Farrell, Nicholas P; Brabec, Viktor

    2012-02-01

    The effects of major DNA intrastrand cross-links of antitumor dinuclear Pt(II) complexes [{trans-PtCl(NH(3))(2)}(2)-μ-{trans-(H(2)N(CH(2))(6)NH(2)(CH(2))(2)NH(2)(CH(2))(6)NH(2))}](4+) (1) and [{PtCl(DACH)}(2)-μ-{H(2)N(CH(2))(6)NH(2)(CH(2))(2)NH(2)(CH(2))(6)NH(2))}](4+) (2) (DACH is 1,2-diaminocyclohexane) on DNA stability were studied with emphasis on thermodynamic origins of that stability. Oligodeoxyribonucleotide duplexes containing the single 1,2, 1,3, or 1,5 intrastrand cross-links at guanine residues in the central TGGT, TGTGT, or TGTTTGT sequences, respectively, were prepared and analyzed by differential scanning calorimetry. The unfolding of the platinated duplexes was accompanied by unfavorable free energy terms. The efficiency of the cross-links to thermodynamically destabilize the duplex depended on the number of base pairs separating the platinated bases. The trend was 1,5→1,2→1,3 cross-link of 1 and 1,5→1,3→1,2 cross-link of 2. Interestingly, the results showed that the capability of the cross-links to reduce the thermodynamic stability of DNA (ΔG(298)(0)) correlated with the extent of conformational distortions induced in DNA by various types of intrastrand cross-links of 1 or 2 determined by chemical probes of DNA conformation. We also examined the efficiency of the mammalian nucleotide excision repair systems to remove from DNA the intrastrand cross-links of 1 or 2. The efficiency of the excinucleases to remove the cross-links from DNA depended on the length of the cross-link; the trend was identical to that observed for the efficiency of the intrastrand cross-links to thermodynamically destabilize the duplex. Thus, the results are consistent with the thesis that an important factor that determines the susceptibility of the intrastrand cross-links of dinuclear platinum complexes 1 and 2 to be removed from DNA by nucleotide excision repair is the efficiency of these lesions to thermodynamically destabilize DNA.

  8. Polyacrylamide thickened slurry explosive with particular cross-linking combination

    Energy Technology Data Exchange (ETDEWEB)

    Sheeran, H.W.; Oriard, M.H.

    1973-02-20

    In manufacturing slurry blasting agents, it is commonly very important to produce a uniform and stable suspension of the liquid and nonexplosive solid ingredients along with a desired amount of fine entrained air bubbles in order to obtain optimum density and reactivity. Slurry explosives require the same type of uniform stable suspension of the liquid and explosive solid ingredients for optimum performance. In addition, it is very important that the suspending medium, the liquid or continuous phase of the slurries, be stable for extended periods of time at all normally encountered storage and use conditions. Further, it is very desirable that this liquid phase must resist penetration or dilution by water when the slurry is loaded in drill holes prior to a blast. Water-resistant gels are described which are produced by cross linking water-soluble polyacrylamide resins in an aqueous nitrate solution. (15 claims)

  9. Collagen cross-linking therapy in patients with keratoconus

    Directory of Open Access Journals (Sweden)

    Lokman Aslan

    2012-12-01

    Full Text Available Keratoconus affecting young population is a progressiveeye disease. This disease may remain silent untilcomplain of visual impairment is appeared. By using thehigh-quality imaging techniques disease now can be diagnosedearlier. The goal of keratoconus treatment is toimprove visual acuity and to prevent the progression ofthe disease. Although the previous treatment methods initiallyprovided slightly improvement of visual acuity, couldnot prevent keratoconus progression. However, collagencross-link (CCL treatment both halts the progression ofthe disease and provides an increased vision. Since theside effect of the treatment is less and implementation iseasier, CCL provides an important advantage for thesepatients and this technique becomes common day by day.Key words: Keratoconus, cross-linking, cornea.

  10. [Keratoconus treatment by corneal cross-linking (CLX)].

    Science.gov (United States)

    Hammer, Arthur; Tabibian, David; Richoz, Olivier; Hafezi, Farhad

    2014-06-04

    Keratoconus is a disease of the cornea that usually begins during puberty and progressively weakens its biomechanical structure. Keratoconic eyes show a conic shape and progressive thinning, both leading to irregular astigmatism and reduced vision that cannot be corrected by glasses. In early cases, special contact lens can partly compensate for the visual loss while they do not stop disease progression. Until recently, the only treatment option was a corneal transplant. In 1999, a technique called corneal collagen cross-linking (CXL) was used in human corneas suffering from keratoconus for the first time. CXL uses a process called photopolymerization to halt the progression of keratoconus with an efficacy of more than 95%. Today our challenge is to screen and identify patients early enough to offer a treatment on time before irreversible vision loss develops.

  11. Thermally reversible cross-linked poly(ether-urethanes

    Directory of Open Access Journals (Sweden)

    V. Gaina

    2013-07-01

    Full Text Available Cross-linked poly(ether-urethanes were prepared by Diels-Alder (DA reaction of the furan-containing poly(ether-urethane to bismaleimides and showed thermal reversibility evidenced by differential scanning calorimetry and attenuated total reflectance in conjunction with Fourier transform infrared spectroscopy (ATR-FTIR. The furan-containing poly(ether-urethanes were synthesized by the polyaddition reaction of 1,6-hexamethylene diisocyanate (HMDI or 4,4'- dibenzyl diisocyanate (DBDI to poly(tetramethylene ether glycol (PTMEG having Mn = 250, 650, 1000, 1500 and 2000 and 2-[N,N-bis(2-methyl-2-hydroxyethylamino]furfuryl as chain extender by the solution prepolymer method. The molar ratio of isocyanate: PTMEG:chain extender varied from 2:1:1 to 4:1:3, which produces a molar concentration of furyl group ranging between 3.65•10–4 and 1.25•10–3 mol/g.

  12. Encapsulation of cobalt nanoparticles in cross-linked-polymer cages

    Energy Technology Data Exchange (ETDEWEB)

    Hatamie, Shadie [Department of Electronic-Science, Fergusson College, Pune 411 004 (India); Dhole, S.D. [Department of Physics, University of Pune, Pune 411 007 (India); Ding, J. [Department of Materials Science and Engineering, National University of Singapore, 7, Engineering Drive 1, Singapore 117574 (Singapore); Kale, S.N. [Department of Electronic-Science, Fergusson College, Pune 411 004 (India)], E-mail: sangeetakale2004@gmail.com

    2009-07-15

    Nanoparticles embedded in polymeric cages give rise to interesting applications ranging from nanocatalysis to drug-delivery systems. In this context, we report on synthesis of cobalt (Co) nanoparticles trapped in polyvinyl alcohol (PVA) matrix to yield self-supporting magnetic films in PVA slime. A 20 nm, Co formed in FCC geometry encapsulated with a weak citrate coat when caged in PVA matrix exhibited persistence of magnetism and good radio-frequency response. Cross-linking of PVA chains to form cage-like structures to arrest Co nanoparticles therein, is believed to be the reason for oxide-free nature of Co, promising applications in biomedicine as well as in radio-frequency shielding.

  13. Synthesis and Catalytic Properties of Non-Cross-Linked and Cross-Linked Poly(alkylmethyldiallylammonium bromides) Having Decyl, Octyl, and Hexyl Side Chains

    NARCIS (Netherlands)

    Wang, G.J; Engberts, J.B.F.N.

    1995-01-01

    A family of non-cross-linked and cross-linked copolymers containing decyl, octyl, and hexyl groups as side chains ((CL)-CopolC1-10, (CL)-CopolC1-8, and (CL)-CopolC1-6, respectively) were synthesized by radical-initiated cyclocopolymerization of alkylmethyldiallylammonium bromide monomers without and

  14. Corneal collagen cross-linking effects on pseudophakic bullous keratopathy

    Directory of Open Access Journals (Sweden)

    Mohammad Mirzaei

    2014-05-01

    Full Text Available AIM: To evaluate the efficacy of riboflavin administration and ultraviolet A(UVAcross-linking on advanced symptomatic bullous keratopathy. METHODS: Fifteen patients with symptomatic pseudophakic bullous keratopathy(PBKwere included. Slit-lamp examination, visual acuity, foreign body sensation(FBSquestionnaire, corneal clarity grading, ocular pain intensity scale and corneal thickness measures with Pentacam and ultrasound pachymetry(UP, were performed before corneal cross-linking and 1 and 6mo thereafter. After using sodium chloride solution, for one week, the central 8mm(diameterof the corneal epithelium was removed, and cross-linking, with riboflavin instillation every 3min for 30min, and UVA irradiation for 30min was performed. RESULTS: Five males and 10 females with mean age of 66±13y were included. Mean follow up time was 6.2mo. Corneal transparency in all eyes was statistically significantly better 1 month after treatment than preoperatively(PP= 0.218. Foreign body sensation subsided in 70% of patients. The average CCT decreased within 1mo after the procedure(PP=0.006. The improvement in mean CDVA from preoperatively to 1mo postoperatively was statistically significant(P=0.010. At 6mo, no significant differences were observed(P=0.130. The pain scores at 1mo were statistically significantly better than preoperatively(P=0.007. At 6mo, however the mean pain score was higher than at 1mo and not statistically significantly different from the preoperative score(P=0.070. CONCLUSION: Corneal CXL significantly improved corneal transparency, corneal thickness, and ocular pain 1 month postoperatively. However, it did not seem to have a long-lasting effect in decreasing pain and maintaining corneal transparency in patients with PBK. This procedure extends the time interval for corneal transplantation and increases visualization at DSAEK procedure.

  15. Transepithelial corneal collagen cross-linking in ultrathin keratoconic corneas

    Directory of Open Access Journals (Sweden)

    Spadea L

    2012-11-01

    Full Text Available Leopoldo Spadea,1 Rita Mencucci21University of L'Aquila, Department of Biotechnological and Applied Clinical Sciences, Eye Clinic, L'Aquila, 2University of Florence, Department of Oto-Neuro-Ophthalmological Surgical Sciences, Eye Clinic, Florence, ItalyBackground: The purpose of this paper was to report the results of transepithelial corneal collagen cross-linking (CXL with modified riboflavin and ultraviolet A irradiation in patients affected by keratoconus, each with thinnest pachymetry values of less than 400 µm (with epithelium and not treatable using standard de-epithelialization techniques.Methods: Sixteen patients affected by progressive keratoconus with thinnest pachymetry values ranging from 331 µm to 389 µm underwent transepithelial CXL in one eye using a riboflavin 0.1% solution in 15% Dextran T500 containing ethylenediamine tetra-acetic acid 0.01% and trometamol to enhance epithelial penetration. The patients underwent complete ophthalmological examination, including endothelial cell density measurements and computerized videokeratography, before CXL and at one day, one week, and one, 6, and 12 months thereafter.Results: Epithelial healing was complete in all patients after one day of use of a soft bandage contact lens. No side effects or damage to the limbal region was observed during the follow-up period. All patients showed slightly improved uncorrected and spectacle-corrected visual acuity; keratometric astigmatism showed reductions (up to 5.3 D and apical ectasia power decreased (Kmax values reduced up to 4.3 D. Endothelial cell density was unchanged.Conclusion: Application of transepithelial CXL using riboflavin with substances added to enhance epithelial permeability was safe, seemed to be moderately effective in keratoconic eyes with ultrathin corneas, and applications of the procedure could be extended to patients with advanced keratoconus.Keywords: keratoconus, pachymetry, topography, transepithelial corneal collagen

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

    Science.gov (United States)

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

    2016-01-01

    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

  17. 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.

  18. Oral delivery of exenatide via microspheres prepared by cross-linking of alginate and hyaluronate.

    Directory of Open Access Journals (Sweden)

    Baojie Zhang

    Full Text Available Exenatide is an FDA-approved glucose-lowering peptide drug for the treatment of type 2 diabetes by subcutaneous injection. To address the issues on the inconvenience for patient use and the difficulty of oral administration of peptide drugs, chemical cross-linking of two pH-responsive biomaterials, alginate and hyaluronate, was carried out to prepare a new material for the encapsulation of exenatide as a form of microspheres. The exenatide-loaded microspheres exhibited spherical structures with excellent loading and release behaviors in the simulated gastrointestinal tract environments. After oral administration of the microspheres in db/db mice, maximum plasma concentration of exenatide appeared at 4 hours, and blood glucose was effectively reduced to a normal level within 2 hours and maintained for another 4 hours. The bioavailability of the exenatide-loaded microspheres, relative to subcutaneous injection of exenatide, reached 10.2%. Collectively, the present study demonstrated the feasibility of orally delivering exenatide with the new cross-linked biomaterial and formulation, and showed therapeutic potential for clinical applications.

  19. Seed-mediated synthesis of cross-linked Pt-NiO nanochains for methanol oxidation

    Science.gov (United States)

    Gu, Zhulan; Bin, Duan; Feng, Yue; Zhang, Ke; Wang, Jin; Yan, Bo; Li, Shumin; Xiong, Zhiping; Wang, Caiqin; Shiraishi, Yukihide; Du, Yukou

    2017-07-01

    A simple method was reported for employing NiO nanoparticles act as seeds and then different amounts of Pt2+ were reduced on the NiO nanoparticles, forming a cross-linked Pt-NiO nanocatalysts. These as-prepared catalysts were characterized using different physical-chemical techniques, including X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The results indicate that the morphology of the cross-linked Pt-NiO nanochain was successfully produced regardless of the molar ratio of Pt2+ to NiO precursors. The electrochemical characteristics of Pt-NiO nanochain catalysts were evaluated for the oxidation of methanol as a model reaction, which verify that the Pt-NiO catalysts show enhanced activity and high stability in comparison with the commercial Pt/C catalyst. The optimized ratio of Pt to NiO is 1:1, then tuned by simple adjusting the feed ratio of the precursors as well. The synthesized nanocatalysts will be found the great potential applications as electrocatalysts for fuel cells owe to their enhanced catalytic performance and long-term stability.

  20. Study the adsorption of sulfates by high cross-linked polystyrene divinylbenzene anion-exchange resin

    Science.gov (United States)

    Fathy, Mahmoud; Moghny, Th. Abdel; Awadallah, Ahmed E.; El-Bellihi, Abdel-Hameed A.-A.

    2017-03-01

    In response to rising concerns about the effect of sulfate on water quality, human health, and agriculture, many jurisdictions around the world are imposing tighter regulations for sulfate discharge. This is driving the need for environmental compliance in industries like mining, metal processing, pulp and paper, sewage treatment, and chemical manufacturing. The sulfate removal from synthetic water by high cross-linked polystyrene divinylbenzene resin was studied at batch experiments in this study. The effect of pH, contact time, sulfates concentration, and adsorbent dose on the sulfate sequestration was investigated. The optimum conditions were studied on Saline water as a case study. The results showed that with increasing of the absorbent amount; contact time, and pH improve the efficiency of sulfate removal. The maximum sulfates uptake was obtained in pH and contact time 3.0 and 120 min, respectively. Also, with increasing initial concentration of sulfates in water, the efficiency of sulfate removal decreased. The obtained results in this study were matched with Freundlich isotherm and pseudo-second-order kinetic. The maximum adsorption capacity (Qm) and constant rate were found 0.318 (mg/g) and 0.21 (mg/g.min), respectively. This study also showed that in the optimum conditions, the sulfate removal efficiency from Saline water by 0.1 mg/L sulfates was 65.64 %. Eventually, high cross-linked polystyrene divinylbenzene resin is recommended as a suitable and low cost absorbent to sulfate removal from aqueous solutions.

  1. Spermidine cross-linked hydrogels as a controlled release biomimetic approach for cloxacillin.

    Science.gov (United States)

    López-Cebral, Rita; Romero-Caamaño, Vanessa; Seijo, Begoña; Alvarez-Lorenzo, Carmen; Martín-Pastor, Manuel; Concheiro, Ángel; Landin, Mariana; Sanchez, Alejandro

    2014-07-07

    The intrinsic ability of albumin to bind active substances in the physiological fluids has been explored to endow hydrogels with improved capability to regulate drug release. To develop such biomimetic-functional hydrogels, it is critical that albumin conformation is not altered and that the protein remains retained inside the hydrogel keeping its conformational freedom, i.e., it should be not chemically cross-linked. Thus, the hydrogels were prepared with various proportions of albumin by physical cross-linking of anionic polysaccharides (gellan gum and chondroitin sulfate) with the cationic endogen polyamine spermidine under mild conditions in order to prevent albumin denaturation. Texture and swelling properties of hydrogels with various compositions were recorded, and the effect of the preparation variables was evaluated applying neurofuzzy logic tools for hydrogels prepared with and without albumin and associating the antibiotic cloxacillin. Developed hydrogel systems were extensively analyzed by means of nuclear magnetic resonance (NMR) to determine weak-to-medium and strong binding modes and the equilibrium constants of the albumin-cloxacillin association. NMR techniques were also employed to demonstrate the successful modulation of the cloxacillin release from the albumin-containing hydrogels. In vitro microbiological tests carried out with Staphylococcus aureus and Staphylococcus epidermidis confirmed the interest of the albumin-containing hydrogels as efficient platforms for cloxacillin release in its bioactive form.

  2. Effects of Genipin Concentration on Cross-Linked Chitosan Scaffolds for Bone Tissue Engineering: Structural Characterization and Evidence of Biocompatibility Features

    Directory of Open Access Journals (Sweden)

    Simona Dimida

    2017-01-01

    Full Text Available Genipin (GN is a natural molecule extracted from the fruit of Gardenia jasminoides Ellis according to modern microbiological processes. Genipin is considered as a favorable cross-linking agent due to its low cytotoxicity compared to widely used cross-linkers; it cross-links compounds with primary amine groups such as proteins, collagen, and chitosan. Chitosan is a biocompatible polymer that is currently studied in bone tissue engineering for its capacity to promote growth and mineral-rich matrix deposition by osteoblasts in culture. In this work, two genipin cross-linked chitosan scaffolds for bone repair and regeneration were prepared with different GN concentrations, and their chemical, physical, and biological properties were explored. Scanning electron microscopy and mechanical tests revealed that nonremarkable changes in morphology, porosity, and mechanical strength of scaffolds are induced by increasing the cross-linking degree. Also, the degradation rate was shown to decrease while increasing the cross-linking degree, with the high cross-linking density of the scaffold disabling the hydrolysis activity. Finally, basic biocompatibility was investigated in vitro, by evaluating proliferation of two human-derived cell lines, namely, the MG63 (human immortalized osteosarcoma and the hMSCs (human mesenchymal stem cells, as suitable cell models for bone tissue engineering applications of biomaterials.

  3. CO2 capture by nitrogen-doped porous carbons derived from nitrogen-containing hyper-cross-linked polymers.

    Science.gov (United States)

    Shao, Lishu; Liu, Mingqiang; Huang, Jianhan; Liu, You-Nian

    2017-11-15

    The N-containing hyper-cross-linked polymers with different porosity and polarity were prepared from 4-vinylbenzyl chloride and 4-vinyl pyridine by the suspension polymerization and Friedel-Crafts reaction. A carbonization process by KOH chemical activation was carried out for the N-containing hyper-cross-linked polymers, and hence a series of N-doped porous carbons (NDPC) was easily fabricated. These porous materials were comparatively evaluated for CO2 adsorption. The NDPC were much more efficient than the N-containing hyper-cross-linked polymers for the CO2 capture and the CO2 uptake had a linear correlation to the ultramicropore volume (d ≤ 0.8 nm) with R2 = 0.9737. NDPC-10% possessed the highest CO2 uptake around 270 mg/g, and had the sufficient CO2/N2 selectivity of 20.2 at 273 K and 1.0 bar. The CO2/N2 selectivity of the N-containing hyper-cross-linked polymers was much higher than the NDPC due to the higher nitrogen content. The isosteric heat of adsorption on the N-containing hyper-cross-linked polymers ranged 29.0-41.2 kJ/mol while that on the NDPC was much lower (24.6-29.2 kJ/mol). The NDPC developed in this study may provide promising candidates for the CO2 capture. Copyright © 2017 Elsevier Inc. All rights reserved.

  4. Cross-linking affects cellular condensation and chondrogenesis in type II collagen-GAG scaffolds seeded with bone marrow-derived mesenchymal stem cells.

    Science.gov (United States)

    Vickers, Scott M; Gotterbarm, Tobias; Spector, Myron

    2010-09-01

    The formation of cartilaginous tissue by chondroprogenitor cells, whether in vivo or in vitro, appears to require a critical initial stage of "condensation" in which intercellular space is reduced through an aggregation of cells, leading to development of cell-to-cell junctions followed by chondrocytic differentiation. The objective of this study was to investigate the association of aggregation (condensation) of mesenchymal stem cell (MSCs) and chondrogenesis in vitro. Previous work with chondrocytes indicated that the cross-link density and related cell-mediated contraction of collagen scaffolds significantly affects cartilaginous tissue formation within the cell-seeded construct. Based on this finding, we hypothesized that the cell-aggregating effect of the contraction of MSC-seeded collagen scaffolds of lower cross-link density favors chondrogenesis; scaffolds of higher cross-link density, which resist cell-mediated contraction, would demonstrate a lower cell number density (i.e., subcritical packing density) and less cartilage formation. Type II collagen-GAG scaffolds, chemically cross-linked to achieve a range of cross-link densities, were seeded with caprine MSCs and cultured for 4 weeks. Constructs with low cross-link densities experienced cell-mediated contraction, increased cell number densities, and a greater degree of chondrogenesis (indicated by the chondrocytic morphology of cells, and synthesis of GAG and type II collagen) compared to more highly cross-linked scaffolds that resisted cellular contraction. These results provide a foundation for further investigation of the mechanisms by which condensation of mesenchymal cells induces chondrogenesis in this in vitro model, and may inform cross-linking protocols for collagen scaffolds for use in cartilage tissue engineering. (c) 2010 Orthopaedic Research Society. Published by Wiley Periodicals, Inc.

  5. Mussel-inspired new approach for polymerization and cross-linking of peptides and proteins containing tyrosines by Fremy's salt oxidation.

    Science.gov (United States)

    Wilchek, Meir; Miron, Talia

    2015-03-18

    Our objective was to develop a method mimicking the natural process of coherence in marine mollusks, by direct chemical conversion of protein tyrosine residues to DOPA-o-quinones, which consequently generates polymerization and cross-linking. Fremy's salt, (ON(SO3K)2, was used to convert tyrosine residues in peptides and proteins to reactive o-quinones. The conversion of tyrosines to DOPA-o-quinones, and their ability to polymerize or cross-link, was tested on tyramine, peptides, and proteins. The peptides tested were as follows: biotin-PEG4-tyramine (PEG-BT), and two decapeptides (identical to the repeating units comprising the mussel's adhesive protein). The proteins tested were as follows: bovine pancreatic ribonuclease A (RNase), lysozyme, IgG, avidin, and streptavidin. The oxidized peptides and proteins were all shown to incorporate oxygen atoms and undergo polymerization and cross-linking, depending on the availability of nucleophiles, mostly lysine amino groups of proteins. All the peptides and the noninteracting proteins such as RNase and lysozyme underwent homopolymerization upon Fremy's salt oxidation. When Fremy's salt oxidaized PEG-BT was mixed with the above proteins, it did not react with any of these proteins because PEG-BT underwent fast self-polymerization. Conversely, streptavidin or avidin cross-linked with PEG-BT after preincubation, thus showing that biorecognition is a prerequisite for cross-linking. Polymerization and cross-linking also occurred, following Fremy's salt oxidation of interacting proteins such as avidin and strepavidin with biotinyilated lysozyme or biotinylated RNase. This indicates that only proteins in very close proximity readily cross-link and polymerize via tyrosine residues. Attempts to convert DOPA-quinone to DOPA by reduction with sodium dithionite (Na2S2O4), was successful as far as small peptides were used. Fremy's salt oxidation can serve as an easy and useful tool to polymerize and cross-link proteins, for

  6. 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.

  7. Reduced cross-linking demarcation line depth at the peripheral cornea after corneal collagen cross-linking.

    Science.gov (United States)

    Yam, Jason C S; Cheng, Arthur C K

    2013-01-01

    To compare the corneal collagen cross-linking (CXL) demarcation line depth between the central and peripheral cornea after cross-linking using anterior segment optical coherence tomography. Retrospective interventional case series of 38 eyes with keratoconus or postoperative LASIK ectasia treated with riboflavin ultraviolet A CXL (UV-X, IROC). CXL demarcation line depth, corneal thickness, and the ratio of the CXL demarcation line depth to the corneal thickness were measured using anterior segment optical coherence tomography at the central cornea and at 2 and 4 mm from the corneal center in four regions: temporal, nasal, superior, and inferior. The CXL demarcation line depths at the center and periphery were compared using the Friedman test. The CXL demarcation line was deepest in the central cornea (302 μm; range: 180 to 397 μm) and was reduced progressively toward the peripheral cornea, at nasal 2 mm (289.5 μm; range: 125 to 370 μm), at nasal 4 mm (206.5 μm; range: 100 to 307 μm), at temporal 2 mm (278.5 μm; range: 128 to 375 μm), and at temporal 4 mm (194 μm; range: 80 to 325 μm) (Pcornea (64.8%; range: 44% to 80%) and was decreased toward the periphery, at nasal 2 mm (53.8%; range: 30% to 74%), at nasal 4 mm (33.8%; range: 19% to 53%), at temporal 2 mm (54.1%; range: 29% to 77%), and at temporal 4 mm (34.1%; range: 15% to 54%) (P⩽.001). Both the CXL demarcation line depth and its proportion over the corneal thickness were greater at the central cornea than the peripheral cornea. Copyright 2013, SLACK Incorporated.

  8. Stimuli-responsive hydrogels cross-linked by magnetic nanoparticles

    OpenAIRE

    Ilg Patrick

    2013-01-01

    Embedding magnetic nanoparticles into soft host media offers the opportunity to externally control material properties via a magnetic field. Choosing a hydrogel as host medium allows to modify not only the elastic properties but also the degree of swelling of the gel and the shape changes of the sample. Hydrogels where magnetic nanoparticles serve as the only crosslinking reagent of the network are a promising new class of such stimuli responsive gels. The well defined magneto mechanical coup...

  9. Digestibilidade do bagaço de cana-de-açúcar tratado com reagentes químicos e pressão de vapor Digestibility of sugar cane bagasse treated with chemical reagents and steam pressure

    Directory of Open Access Journals (Sweden)

    Ricardo Pereira Manzano

    2000-08-01

    Full Text Available Com o objetivo de elevar a digestibilidade do bagaço de cana-de-açúcar, este resíduo agro-industrial foi tratado com inúmeros reagentes químicos acompanhados ou não de tratamento físico. Após ensaios preliminares, nos quais diversos agentes deslignificantes foram avaliados, dez tratamentos foram selecionados para serem melhor estudados em ensaios de digestibilidade in vitro da matéria seca e da matéria orgânica. Em seguida, para o ensaio de digestibilidade in vivo, foram feitas quatro dietas à base de: 1 - Bagaço auto-hidrolisado (BAH, pressão de 17 kgf/cm² por 5 min; 2 - Bagaço tratado com 4% Na2S + 6% NaOH, pressão de 12 kgf/cm² por 8 min; 3 - Bagaço tratado com 2% Na2S + 3% NaOH, pressão de 12 kgf/cm² por 8 min; e 4 - Bagaço tratado com 9% H2O2 + 7% NaOH, a 70ºC por 8 min. Bagaço tratado com 4% Na2S + 6% NaOH e submetido a 12 kgf/cm² de pressão apresentou os melhores coeficientes de digestibilidade da matéria seca, matéria orgânica, fibra em detergente neutro e fibra em detergente ácido e o maior valor de nutrientes digestíveis totais. Em seguida, o bagaço tratado com 9% H2O2 + 7% NaOH a 70ºC por 8 min apresentou os melhores resultados. Piores resultados foram observados para o bagaço hidrolizado. A melhor digestibilidade de algumas das dietas, particularmente das frações fibrosas, sugere a exiqüibilidade do emprego de menores quantidades de alimento concentrado em dietas à base de bagaço de cana tratado química/fisicamente.In order to increase the sugar cane bagasse digestibility, this agricultural by-product was treated with several chemical reagents with or without physical treatment. After preliminary evaluation, where several delignificant agents were evaluated, ten treatments were selected for more detailed in vitro dry and organic matter disappearance trials. Then, for the in vivo digestibility trial, four sugar cane bagasse based diets were made: 1 - Hydrolyzed sugar cane bagasse, pressure of

  10. Pinning Down the Mechanism of Transport: Probing the Structure and Function of Transporters Using Cysteine Cross-Linking and Site-Specific Labeling.

    Science.gov (United States)

    Mulligan, Christopher; Mindell, Joseph A

    2017-01-01

    Transporters are crucial in a number of cellular functions, including nutrient uptake, cell signaling, and toxin removal. As such, transporters are important drug targets and their malfunction is related to several disease states. Treating transporter-related diseases and developing pharmaceuticals targeting transporters require an understanding of their mechanism. Achieving a detailed understanding of transporter mechanism depends on an integrative approach involving structural and computational approaches as well as biochemical and biophysical methodologies. Many of the elements of this toolkit exploit the unique and useful chemistry of the amino acid cysteine. Cysteine offers researchers a specific molecular handle with which to precisely modify the protein, which enables the introduction of biophysical probes to assess ligand binding and the conformational ensemble of the transporter, to topologically map transporters and validate structural models, and to assess essential conformational changes. Here, we summarize several uses for cysteine-based labeling and cross-linking in the pursuit of understanding transporter mechanism, the common cysteine-reactive reagents used to probe transporter mechanism, and strategies that can be used to confirm cysteine cross-link formation. In addition, we provide methodological considerations for each approach and a detailed procedure for the cross-linking of introduced cysteines, and a simple screening method to assess cross-link formation. 2017 Published by Elsevier Inc.

  11. Physicochemical properties and bioactivity of nisin-containing cross-linked hydroxypropylmethylcellulose films.

    Science.gov (United States)

    Sebti, Issam; Delves-Broughton, John; Coma, Véronique

    2003-10-22

    Cross-linked hydroxypropylmethylcellulose (HPMC) cast films with citric acid as polycarboxylic cross-linker were elaborated to study the effect of cross-linking level on various properties. Increased amounts of cross-linking agent were not connected to statistically different tensile strength and Young's modulus. Whatever the cross-linking level of the film was, the ultimate elongation parameter decreased by approximately 60% compared to the HMPC control film. Moisture sorption isotherms and water contact angle meter showed that the effect of cross-linking degree tends to reduce the hygroscopic and hydrophilic characteristics of films. In addition, to control bacteria growth on food surfaces, the antimicrobial activity of both 98% cross-linked HPMC-nisin and control HPMC-nisin films was tested on Micrococcus luteus. Despite the incorporation of a significant content of nisin, cross-linked HPMC-nisin films were completely inactive on the microbial strain compared to the HPMC-nisin control films. Cross-linking conditions likely either denatured the nisin or irreversibly bound nisin to the cross-linked HPMC. However, nisin adsorbed into films made from previously cross-linked HPMC maintained its activity.

  12. Understanding of the viscoelastic response of the human corneal stroma induced by riboflavin/UV-a cross-linking at the nano level.

    Directory of Open Access Journals (Sweden)

    Cristina Labate

    Full Text Available 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.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.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.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.

  13. Mussel-Inspired Self-Healing Double-Cross-Linked Hydrogels by Controlled Combination of Metal Coordination and Covalent Cross-Linking

    DEFF Research Database (Denmark)

    Andersen, Amanda; Krogsgaard, Marie; Birkedal, Henrik

    2017-01-01

    the degree of catechol oxidation that occurs under alkaline conditions in air and has a great impact on the aforementioned properties because it introduces irreversible covalent cross-links to the system, which stiffens the hydrogels but consume catechols needed for self-healing. Herein, we present...... a catechol-based hydrogel design that allows for the degree of oxidative covalent cross-linking to be controlled. Double cross-linked hydrogels with tunable stiffness are constructed by adding the oxidizable catechol analogue, tannic acid, to an oxidation-resistant hydrogel construct held together...

  14. Krebs cycle metabolon: structural evidence of substrate channeling revealed by cross-linking and mass spectrometry.

    Science.gov (United States)

    Wu, Fei; Minteer, Shelley

    2015-02-02

    It has been hypothesized that the high metabolic flux in the mitochondria is due to the self-assembly of enzyme supercomplexes (called metabolons) that channel substrates from one enzyme to another, but there has been no experimental confirmation of this structure or the channeling. A structural investigation of enzyme organization within the Krebs cycle metabolon was accomplished by in vivo cross-linking and mass spectrometry. Eight Krebs cycle enzyme components were isolated upon chemical fixation, and interfacial residues between mitochondrial malate dehydrogenase, citrate synthase, and aconitase were identified. Using constraint protein docking, a low-resolution structure for the three-enzyme complex was achieved, as well as the two-fold symmetric octamer. Surface analysis showed formation of electrostatic channeling upon protein-protein association, which is the first structural evidence of substrate channeling in the Krebs cycle metabolon. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  15. pH-Sensitive micelles with cross-linked cores formed from polyaspartamide derivatives for drug delivery.

    Science.gov (United States)

    Lin, Wang; Kim, Dukjoon

    2011-10-04

    A series of polyaspartamide derivatives were synthesized by grafting O-(2-aminoethyl)-O'-methylpoly(ethylene glycol) 5000 (MPEG), 1-(3-aminopropyl) imidazole (API), and cinnamate onto polysuccinimide (PSI) with the respective degrees of substitution adjusted by the feed molar ratio. The chemical structure of the prepared polymer was confirmed using FT-IR and (1)H NMR spectroscopy. A new pH-sensitive polymeric micelle based on the synthesized polymer was prepared and characterized, and its pH-sensitive properties were characterized by the measurement of light transmittance and particle sizes at varying pH values. pH-dependent aggregation and deaggregation behavior was clearly observed in the polymer aqueous dispersion system. Photo-cross-linking of the cinnamate branches cross-linked the core of the micelles. The core cross-linked micelles showed high stability over a wider pH range and displayed obvious pH-dependent swelling-shrinking behavior instead of micelle-unimer transition behavior. This micelle system overcame the drawback of the facile disintegration of normal polymeric micelles and showed obvious delayed paclitaxel release in in vitro drug delivery experiments. © 2011 American Chemical Society

  16. 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.

  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. 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.

  19. 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.

  20. Microfluidic formation of ionically cross-linked polyamine gels.

    Science.gov (United States)

    Kini, Gautam C; Lai, Justin; Wong, Michael S; Biswal, Sibani Lisa

    2010-05-04

    In this article, we discuss in situ polymer gelation in microfluidic channels from electrostatically mediated interactions when reactant streams of a linear cationic polymer (poly(allylamine hydrochloride, PAH) and a multivalent anion (sodium citrate) are subjected to shear flow. We find that the polyamine exhibits shear-thickening behavior as it is ionically cross-linked by citrate ions to form viscoelastic gel phases. These gels form at room temperature and remain stable and intact after the cessation of flow. Gelation is found to occur in the polymer stream and not the citrate stream because of an appreciably higher diffusivity of citrate ions when compared to the gel and PAH and because of laminar flow conditions in the microfluidic environment. Gel formation occurred when the pH of the PAH stream was below the PAH pK(a) value of 8.38 and when citrate was either in a disodium or trisodium state. The formation of aggregates, gels, and droplets was found to depend strongly on the charge ratio and flow conditions. The gelation of PAH begins with the formation of colloidal aggregates of PAH and citrate, which then combine under shear flow to form noncontinuous or continuous gels. Droplets of citrate can form within regions of continuous gels as excess citrate anions diffuse into the gel stream.

  1. [Corneal Cross-Linking with Riboflavin and UVA in Keratoconus].

    Science.gov (United States)

    Raiskup, F; Terai, N; Veliká, V; Spörl, E

    2016-08-01

    Changes in the biomechanical properties of the human cornea play an important role in the pathogenesis of corneal ectatic diseases. Many different pathological conditions in the cornea may reduce its biomechanical resistance. Corneal collagen cross-linking (CXL) has emerged as a promising technique to slow or even to stop the progression of ectasia. In this procedure, riboflavin (vitamin B2) is administered in conjunction with ultraviolet A light (UVA, 365 nm). This interaction causes the formation of reactive oxygen species, leading to additional covalent bonds between collagen molecules, with consequent biomechanical stiffening of the cornea. Although this method is not yet accepted as an evidence-based treatment of corneal ectasia, the results of prospective, randomised studies of CXL used in the treatment of this pathological entity show significant changes in the properties of corneal tissue. This procedure is currently the only aetiopathogenetic treatment of ectatic eyes that can delay or stop the process of cornea destabilisation, reducing the necessity for keratoplasty. Despite promising results, CXL is associated with issues that include long-term safety and duration of the stabilising effect. Georg Thieme Verlag KG Stuttgart · New York.

  2. 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.

  3. Corneal Collagen Cross-Linking for Keratoconus: Systematic Review

    Directory of Open Access Journals (Sweden)

    Hidenaga Kobashi

    2017-01-01

    Full Text Available Purpose. To evaluate the efficacy of collagen cross-linking (CXL one year after treatment for keratoconus compared to no treatment by summarizing randomized controlled trials (RCTs using a systematic review. Methods. Trials meeting the selection criteria were quality appraised, and the data were extracted by two independent authors. The outcome parameters included maximum keratometry (Kmax, corneal thickness at the thinnest point, best spectacle-corrected visual acuity (BSCVA, uncorrected visual acuity (UCVA, spherical equivalent (SE refraction, and cylindrical refraction one year after CXL. We compared the changes in the above parameters with the control group. Results. We identified five RCTs involving 289 eyes that met the eligibility criteria for this systematic review. The changes in BSCVA from baseline to one year exhibited a significant difference between the two groups. There was no statistically significant difference between the two groups for changes in corneal thickness and cylindrical refraction. We did not conduct a meta-analysis in Kmax, UCVA, and SE refraction because their I2 values were greater than 50%. Conclusions. According to the systematic review, CXL may be effective in halting the progression of keratoconus for one year under certain conditions, although evidence is limited due to the significant heterogeneity and paucity of RCTs.

  4. Transepithelial corneal cross-linking in pediatric patients: early results.

    Science.gov (United States)

    Buzzonetti, Luca; Petrocelli, Gianni

    2012-11-01

    To report 18-month follow-up after transepithelial cross-linking (CXL) in young patients. Thirteen eyes with keratoconus were evaluated (mean patient age: 14.4 ± 3.7 years [range: 8 to 18 years]). Corrected distance visual acuity (CDVA); spherical equivalent refraction; keratometry (K); coma, spherical aberration, and higher order aberrations (HOAs) for a 5.0-mm pupil; and thinnest point were measured preoperatively and 1, 3, 6, 9, 12, and 18 months postoperatively by Scheimplflug camera. Endothelial cell density and anterior segment optical coherence tomography were also evaluated. Paired Student t test was used to compare preoperative and 12- and 18-month postoperative data. P.05). The mean demarcation line depth was 105 μm. No side effects were observed. Transepithelial CXL appears to be a safe treatment in children. Although improved CDVA was noted 18 months after treatment, this technique does not effectively halt keratoconus progression in children compared to standard CXL. Copyright 2012, SLACK Incorporated.

  5. Enzymatic cross-linking of a phenolic polymer extracted from the marine alga Fucus serratus.

    Science.gov (United States)

    Berglin, Mattias; Delage, Ludovic; Potin, Philippe; Vilter, Hans; Elwing, Hans

    2004-01-01

    We have shown that a phenolic polymer (PP) extracted from Fucus serratus can be cross-linked using a vanadium-dependent bromoperoxidase (BPO). The methanol extracted PP was adsorbed to a quartz crystal sensor and the cross-linking was initiated by the addition of BPO, KBr, and H2O2. The decreased dissipation upon addition of the cross-linking agents, as measured with the quartz crystal microbalance with dissipation monitoring (QCM-D) method, was interpreted as intramolecular cross-links were formed between different phloroglucinol units in the PP. With surface plasmon resonance, it was shown that no desorption occurred from the sensor surface during the cross-linking. UV/vis spectroscopy verified the results achieved with QCM-D that all components, i.e., BPO, KBr, and H2O2, were necessary in order to achieve intramolecular oxidative cross-linking of the polymer.

  6. UV Radiation Induced Cross-Linking of Whey Protein Isolate-Based Films

    Directory of Open Access Journals (Sweden)

    Markus Schmid

    2017-01-01

    Full Text Available Casted whey protein films exposed to ultraviolet irradiation were analyzed for their cross-linking properties and mechanical and barrier performance. Expected mechanical and barrier improvements are discussed with regard to quantification of the cross-linking in the UV-treated whey protein films. Swelling tests were used to determine the degree of swelling, degree of cross-linking, and cross-linking density. When the UV radiation dosage was raised, a significant increase of the tensile strength as well as an increase in Young’s modulus was observed. No significant changes in water vapor and oxygen barrier properties between the UV-treated films and an untreated reference sample could be observed. The cross-linking density and the degree of cross-linking significantly increased due to UV radiation. Combined results indicate a disordered protein network in cast films showing locally free volume and therefore only minor mechanical and barrier improvements.

  7. FT-IR and FT-Raman studies of cross-linking processes with Ca(2+) ions, glutaraldehyde and microwave radiation for polymer composition of poly(acrylic acid)/sodium salt of carboxymethyl starch--part I.

    Science.gov (United States)

    Grabowska, Beata; Sitarz, Maciej; Olejnik, Ewa; Kaczmarska, Karolina

    2015-01-25

    FT-IR and FT-Raman spectroscopic methods allowed to identify the cross-linking process of the aqueous composition of poly(acrylic acid)/sodium salt of carboxymethyl starch (PAA/CMS-Na) applied as a binder for moulding sands. The cross-linking was performed by chemical methods by introducing cross-linking substances with Ca(2+) ions or glutaraldehyde and by physical way, applying the microwave radiation. It was found that Ca(2+) ions cause formation of cross-linking ionic bonds within carboxyl and carboxylate groups. Glutaraldehyde generates formation of cross-linking bonds with hemiacetal and acetal structures. Whereas in the microwave radiation field, due to dehydration, lattices are formed by anhydride bonds. Copyright © 2014 Elsevier B.V. All rights reserved.

  8. 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.

  9. Covalent Cross-Linking of Porous Poly(ionic liquid) Membrane via a Triazine Network

    OpenAIRE

    Täuber, K.; Dani, A.; Yuan, J.

    2017-01-01

    Porous poly(ionic liquid) membranes that were prepared via electrostatic cross-linking were subsequently covalently cross-linked via formation of a 1,3,5-triazine network. The additional covalent cross-links do not affect the pore size and pore size distribution of the membranes and stabilize them towards salt solutions of high ionic strength, enabling the membranes to work in a broader environmental window.

  10. 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.

  11. Study on the preparation process of cross-linked porous cassava starch

    Science.gov (United States)

    Yin, Xiulian; You, Qinghong; Wan, Miaomiao; Zhang, Xuejuan; Dai, Chunhua

    2017-04-01

    Using cassava starch as raw material, preparation process of porous cross-linked cassava starch was studied. Using TSTP as cross-linking agents, Orthogonal design was applied for the optimization of cross-linked porous starch preparation process. The results showed that the opitmal conditions of cross-linked porous cassava starch were as follows: reaction temperature 45°C, reaction time 20 h, 1% of the amount of the enzyme, the enzyme ratio of 1:5, pH 5.50, substrate concentration of 40%.

  12. Polypeptide modification and cross-linking by oxidized 3-hydroxykynurenine.

    Science.gov (United States)

    Aquilina, J A; Carver, J A; Truscott, R J

    2000-12-26

    3-Hydroxykynurenine (3OHKyn) is present in the mammalian lens as a UV filter and is formed from kynurenine in the tryptophan metabolic pathway. 3OHKyn is a readily autoxidized o-aminophenol which binds to proteins in vitro. The lens, particularly its central region, the nucleus, becomes increasingly oxidized with age. Under such conditions, the oxidation products of 3OHKyn may bind to lens proteins and contribute to nuclear cataract formation. The purpose of this study was to determine the structures of in vitro reaction products of 3OHKyn with model peptides as a general model for 3OHKyn modification of proteins. 3OHKyn was incubated with the dipeptide glycylglycine (GG) and the tetrapeptide tuftsin (sequence TKPR) under oxidizing conditions, and the reaction products were characterized by a variety of spectroscopic techniques. The major 3OHKyn-GG reaction product involves formation of a benzimidazole moiety between the GG N-terminus and the oxidized amino and/or phenol groups of 3OHKyn. In contrast, tuftsin, which has an N-terminal threonine, forms predominantly a cross-linked dimer with oxidized 3OHKyn. This product is analogous in structure to the dimeric reaction product, quinilinobenzoxamine, formed between oxidized 3OHKyn and glycyllysine [Aquilina, J. A., et al. (1999) Biochemistry 38, 11455-11464], which contains a benzoxazole moiety. The identification of a tuftsin dimer suggests that 3OHKyn can react with any peptide having a free alpha-amino group, via a general side chain elimination mechanism. The identification of both benzimidazole and benzoxazole adducts in peptides with a free N-terminus suggests that peptide amino groups can react initially at either the aromatic amino or hydroxyl group of oxidized 3OHKyn. The proportion of each adduct may change, however, depending on the amino acid sequence at the N-terminus.

  13. Study of bacteriophage T4-encoded Dam DNA (adenine-N6)-methyltransferase binding with substrates by rapid laser UV cross-linking.

    Science.gov (United States)

    Evdokimov, Alexey A; Sclavi, Bianca; Zinoviev, Victor V; Malygin, Ernst G; Hattman, Stanley; Buckle, Malcolm

    2007-09-07

    DNA methyltransferases of the Dam family (including bacteriophage T4-encoded Dam DNA (adenine-N(6))-methyltransferase (T4Dam)) catalyze methyl group transfer from S-adenosyl-L-methionine (AdoMet), producing S-adenosyl-L-homocysteine (AdoHcy) and methylated adenine residues in palindromic GATC sequences. In this study, we describe the application of direct (i.e. no exogenous cross-linking reagents) laser UV cross-linking as a universal non-perturbing approach for studying the characteristics of T4Dam binding with substrates in the equilibrium and transient modes of interaction. UV irradiation of the enzyme.substrate complexes using an Nd(3+):yttrium aluminum garnet laser at 266 nm resulted in up to 3 and >15% yields of direct T4Dam cross-linking to DNA and AdoMet, respectively. Consequently, we were able to measure equilibrium constants and dissociation rates for enzyme.substrate complexes. In particular, we demonstrate that both reaction substrates, specific DNA and AdoMet (or product AdoHcy), stabilized the ternary complex. The improved substrate affinity for the enzyme in the ternary complex significantly reduced dissociation rates (up to 2 orders of magnitude). Several of the parameters obtained (such as dissociation rate constants for the binary T4Dam.AdoMet complex and for enzyme complexes with a nonfluorescent hemimethylated DNA duplex) were previously inaccessible by other means. However, where possible, the results of laser UV cross-linking were compared with those of fluorescence analysis. Our study suggests that rapid laser UV cross-linking efficiently complements standard DNA methyltransferase-related tools and is a method of choice to probe enzyme-substrate interactions in cases in which data cannot be acquired by other means.

  14. Use of cross-linked carboxymethyl cellulose for soft-tissue augmentation: preliminary clinical studies

    Directory of Open Access Journals (Sweden)

    Mauro Leonardis

    2010-11-01

    Full Text Available Mauro Leonardis1, Andrea Palange2, Rodrigo FV Dornelles3, Felipe Hund41Department of Plastic Surgery, Salvator Mundi International Hospital, Roma, Italy; 2Department of Aesthetic Medicine, Fisiobios, Roma, Italy; 3Department of Plastic Surgery, Núcleo de Plástica Avançada, São Paulo, SP, Brazil; 4Department of Plastic Surgery, Consultorio de Cirurgia Plastica, Criciuma, SC, BrazilPurpose: The continual search for new products for soft-tissue augmentation has in recent years led to the introduction of long lasting alternatives to hyaluronic acids and collagen that are composed of other polymers able to improve clinical persistence over time. This is the first report in which sodium carboxymethyl cellulose (CMC has been chemically treated by the cross-linking process and thus used as a hydrogel for soft-tissue augmentation through injection with thin needles. The study evaluates, from a clinical point of view, the behavior of cross-linked carboxymethyl cellulose hydrogel used in the aesthetic field and its side effects so as to check the safety and performance of the polymer following intradermal injections.Patients and methods: This work shows the preliminary results of an ongoing clinical study conducted between 2006 and 2009, performed on 84 healthy volunteers (62 females, 22 males aged between 18 and 72 years, for the treatment of 168 nasolabial folds, 45 perioral wrinkles, and 39 lip volume.Results: Study results show an excellent correction of facial defects. Tolerance and aesthetic quality of the correction obtained indicate considerable safety features and absence of side effects. From a clinical point of view, hydrogel is gradually absorbed into the injection site without migration issues.Conclusion: Cross-linked CMC hydrogel proves to be an ideal agent for soft tissue augmentation with regard to safety and ease of application. It did not cause infection, extrusion, migration, or adverse reactions in the patients who have been

  15. Changes in collagen cross-linking in degenerative disc disease and scoliosis.

    Science.gov (United States)

    Duance, V C; Crean, J K; Sims, T J; Avery, N; Smith, S; Menage, J; Eisenstein, S M; Roberts, S

    1998-12-01

    Biochemical study of the changes in the collagen cross-link profile of human intervertebral discs collected at surgery from patients with either low back pain associated with disc degeneration or scoliosis. To determine whether changes occur in the collagen cross-link profile in the disc of patients with either low back pain associated with disc degeneration or scoliosis, which may well influence matrix integrity. Such changes in the cross-link profile of a tissue indicates increased matrix turnover and tissue remodeling and may have implications for the progression of these disorders. The diseases of the intervertebral disc, degenerative disc disease and scoliosis, are both characterized by changes in the extracellular matrix components that will affect the mechanical function of the tissue. The stability of the collagenous components and hence the mechanical integrity of connective tissues such as the disc is dependent on the degree and type of cross-links between the collagen molecules. This article reports results on the distribution of the different cross-links in the disc and the changes that occur with age, degenerative disc disease, and scoliosis. Thirty-three discs were obtained from patients with degenerative disc disease and 29 discs from patients with scoliosis. Samples were acid hydrolyzed and the collagen cross-links analyzed by either fractionation on an amino acid analyzer configured for cross-link analysis using ninhydrin postcolumn detection or fractionation by high-pressure liquid chromatography with fluorescence detection. The reducible cross-links and the mature cross-link all increased from the outer anulus fibrosus through into the nucleus pulposus. The highest levels of the mature cross-link were found in the cartilage end-plate. The nonenzymic derived cross-link, pentosidine, in contrast, showed little difference across the disc, but did show the expected age-related increase. In degenerative disc disease, no change in the levels of the

  16. Order-Disorder Transitions in Cross-Linked Block Copolymer Solids

    Energy Technology Data Exchange (ETDEWEB)

    Das, J.

    2005-01-12

    With a view toward creating solid block copolymers wherein the order-disorder transition can be accessed many times they investigated the nature of order-disorder transitions in cross-linked diblock copolymer melts using synergistic theory and experiment. A mean-field theory based on a coarse grained free-energy and the Random Phase Approximation (RPA) is developed for the system of interest. The quenched distribution of cross-links is averaged using the replica method. The phase behavior of a particular A-B block copolymer melt with a randomly cross-linked B-Block is determined as a function of the Florry-Huggins interaction parameter ({chi}) and the average number of cross-links per chain N{sub c}. They find for a cross-link density greater than N*{sub c} the B monomers are localized within a region of size {zeta} {approx} (N{sub c} - N*{sub c}){sup -1/2}. The cross-links strongly oppose ordering in the system as {zeta} becomes comparable to the radius of gyration of the block copolymer chain. As such the order-disorder transition temperature T{sub ODT} decreases precipitously when N{sub c} > N*{sub c}. When N{sub c} < N*{sub c}, T{sub ODT} increases weakly with N{sub c}. Experiments were conducted on cross-linked polystyrene-block-polyisoprene copolymer samples wherein the polyisoprene block was selectively cross-linked at a temperature well above the order-disorder transition temperature of the pure block copolymer. Small angle X-ray scattering (SAXS) and birefringence measurements on the cross-linked samples are consistent with the theoretical prediction. T{sub ODT} decreases rapidly when the cross-linking density exceeds the critical cross-linking density.

  17. Core cross-linked block ionomer micelles as pH-responsive carriers for cis-diamminedichloroplatinum(II).

    Science.gov (United States)

    Oberoi, Hardeep S; Laquer, Frederic C; Marky, Luis A; Kabanov, Alexander V; Bronich, Tatiana K

    2011-07-15

    Benefits of the frequently prescribed platinum (II) chemotherapy drugs are compromised by undesirable side effects, poor pharmacokinetics and development of drug resistance. Polymer micelles derived from amphiphilic block copolymers, offer a novel macromolecular platform for carrier based delivery of such compounds. Soft polymeric nanocarriers were synthesized by template-assisted method involving condensation of the poly(ethylene oxide)-b-polymethacrylate anions by metal ions into core-shell block ionomer complex micelles followed by chemical cross-linking of the polyion chains in the micelle cores. The resulting micelles can efficiently incorporate cisplatin with a high loading capacity (up to 42% w/w). Core cross-linking stabilized the micelles against structural disintegration and prevented premature drug release. The reversible cisplatin entrapment involved the carboxylate groups of the micellar core. The drug was released in a pH-responsive manner, without loss of its biological activity. The stable cross-linked polymer micelles can potentially improve platinum (II) drug disposition with improved therapeutic potential. Copyright © 2011 Elsevier B.V. All rights reserved.

  18. Xlink Analyzer: software for analysis and visualization of cross-linking data in the context of three-dimensional structures.

    Science.gov (United States)

    Kosinski, Jan; von Appen, Alexander; Ori, Alessandro; Karius, Kai; Müller, Christoph W; Beck, Martin

    2015-03-01

    Structural characterization of large multi-subunit protein complexes often requires integrating various experimental techniques. Cross-linking mass spectrometry (XL-MS) identifies proximal protein residues and thus is increasingly used to map protein interactions and determine the relative orientation of subunits within the structure of protein complexes. To fully adapt XL-MS as a structure characterization technique, we developed Xlink Analyzer, a software tool for visualization and analysis of XL-MS data in the context of the three-dimensional structures. Xlink Analyzer enables automatic visualization of cross-links, identifies cross-links violating spatial restraints, calculates violation statistics, maps chemically modified surfaces, and allows interactive manipulations that facilitate analysis of XL-MS data and aid designing new experiments. We demonstrate these features by mapping interaction sites within RNA polymerase I and the Rvb1/2 complex. Xlink Analyzer is implemented as a plugin to UCSF Chimera, a standard structural biology software tool, and thus enables seamless integration of XL-MS data with, e.g. fitting of X-ray structures to EM maps. Xlink Analyzer is available for download at http://www.beck.embl.de/XlinkAnalyzer.html. Copyright © 2015 The Authors. Published by Elsevier Inc. All rights reserved.

  19. Effects of granule size of cross-linked and hydroxypropylated sweet potato starches on their physicochemical properties.

    Science.gov (United States)

    Zhao, Jianwei; Chen, Zhenghong; Jin, Zhengyu; Buwalda, Piet; Gruppen, Harry; Schols, Henk A

    2015-05-13

    Sweet potato starch was modified by cross-linking, hydroxypropylation, and combined cross-linking and hydroxypropylation, and the starches were subsequently sieved to obtain differently sized granule fractions. The effects of granule size of native and modified sweet potato starch fractions and all fractions were investigated with respect to their physicochemical properties. The large-size granule fraction (27-30 μm) showed a 16-20% higher chemical phosphorylation and a 4-7% higher hydroxypropylation than the small-size granule fraction (14-16 μm). The large-size granule fractions of native and modified sweet potato starches showed lower transition temperatures (0.7-3.1 °C for peak temperature of gelatinization) and lower enthalpy changes (0.6-1.9 J/g) during gelatinization than the small-size granule fractions, making the sweet potato starch different from cereal starches. The large-size granule fraction of native starch showed a higher paste viscosity (78-244 cP) than the corresponding small-size granule fraction. In addition, cross-linking and hydroxypropylation affected the paste viscosity of the large-size granule fraction significantly more than that of the small-size granule fraction when compared to the corresponding parental starch fractions. The large-size granule fraction of native and dual-modified starches showed a lower syneresis after freeze-thaw treatments than the small-size granule fractions. The difference in swelling power between large- and small-size granule fractions was not significant. In general, the large-size granule fraction of sweet potato starch was more susceptible for cross-linking and hydroxypropylation and the physicochemical properties were changed to a higher extent compared to the corresponding small-size granule fraction.

  20. 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.

  1. Cross-linked type I and type II collagenous matrices for the repair of full-thickness articular cartilage defects--a study in rabbits.

    NARCIS (Netherlands)

    Buma, P.; Pieper, J.S.; Tienen, Tony van; Susante, J.L.C. van; Kraan, P.M. van der; Veerkamp, J.H.; Berg, W.B. van den; Veth, R.P.H.; Kuppevelt, A.H.M.S.M. van

    2003-01-01

    The physico-chemical properties of collagenous matrices may determine the tissue response after insertion into full-thickness articular cartilage defects. In this study, cross-linked type I and type II collagen matrices, with and without attached chondroitin sulfate, were implanted into

  2. Phenol red-silk tyrosine cross-linked hydrogels.

    Science.gov (United States)

    Sundarakrishnan, Aswin; Herrero Acero, Enrique; Coburn, Jeannine; Chwalek, Karolina; Partlow, Benjamin; Kaplan, David L

    2016-09-15

    Phenol red is a cytocompatible pH sensing dye that is commonly added to cell culture media, but removed from some media formulations due to its structural mimicry of estrogen. Phenol red free media is also used during live cell imaging, to avoid absorbance and fluorescence quenching of fluorophores. To overcome these complications, we developed cytocompatible and degradable phenol red-silk tyrosine cross-linked hydrogels using horseradish peroxidase (HRP) enzyme and hydrogen peroxide (H2O2). Phenol red added to silk during tyrosine crosslinking accelerated di-tyrosine formation in a concentration-dependent reaction. Phenol red diffusion studies and UV-Vis spectra of phenol red-silk tyrosine hydrogels at different pHs showed altered absorption bands, confirming entrapment of dye within the hydrogel network. LC-MS of HRP-reacted phenol red and N-acetyl-l-tyrosine reaction products confirmed covalent bonds between the phenolic hydroxyl group of phenol red and tyrosine on the silk. At lower phenol red concentrations, leak-proof hydrogels which did not release phenol red were fabricated and found to be cytocompatible based on live-dead staining and alamar blue assessments of encapsulated fibroblasts. Due to the spectral overlap between phenol red absorbance at 415nm and di-tyrosine fluorescence at 417nm, phenol red-silk hydrogels provide both absorbance and fluorescence-based pH sensing. With an average pKa of 6.8 and good cytocompatibiltiy, phenol red-silk hydrogels are useful for pH sensing in phenol red free systems, cellular microenvironments and bioreactors. Phenol red entrapped within hydrogels facilitates pH sensing in phenol red free environments. Leak-proof phenol red based pH sensors require covalent binding techniques, but are complicated due to the lack of amino or carboxyl groups on phenol red. Currently, there is no simple, reliable technique to covalently link phenol red to hydrogel matrices, for real-time pH sensing in cell culture environments. Herein

  3. Cross-linking of LDPE/wax blends by using dicumyl peroxide

    African Journals Online (AJOL)

    Igor Krupa

    Abstract. Thermal properties of cross-linked and uncross-linked LDPE/wax blends were investigated. The blends were prepared by thoroughly mixing the powdery ingredients, followed by pressing at 180 °C for ten minutes. The extent of cross-linking was determined by means of gravimetric analysis of the gel content of the ...

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

    NARCIS (Netherlands)

    Everaerts, F.; 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

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

    Science.gov (United States)

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

    2014-01-01

    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...

  6. Covalent-ionically cross-linked polyetheretherketone proton exchange membrane for direct methanol fuel cell

    CSIR Research Space (South Africa)

    Luo, H

    2010-08-01

    Full Text Available cross-linked PEEK-WC membrane, this covalent-ionically cross-linked PEEK-WC membrane exhibits extremely reduced water uptake and methanol permeability, but just slightly sacrificed proton conductivity. The proton conductivity of the covalent...

  7. Protein cluster formation during enzymatic cross-linking of globular proteins

    NARCIS (Netherlands)

    Saricay, Y.; Dhayal, S.K.; Wierenga, P.A.; Vries, de R.J.

    2012-01-01

    Work on enzymatic cross-linking of globular food proteins has mainly focused on food functional effects such as improvements of gelation and enhanced stabilization of emulsions and foams, and on the detailed biochemical characterization of the cross-linking chemistry. What is still lacking is a

  8. Oxidative cross-linking of casein by horseradish peroxidase and its ...

    African Journals Online (AJOL)

    STORAGESEVER

    2009-10-19

    Oct 19, 2009 ... composite design using response surface methodology was used to optimize cross-linking conditions of casein. The optimal cross-linking .... according to a central composite face-centered design. The ranges ..... Liquid chromatographic assay of dityrosine in human cerebrospinal fluid. J. Chromatogr.

  9. 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.

  10. 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

  11. Lysyl Oxidase-like-2 Cross-links Collagen IV of Glomerular Basement Membrane*

    Science.gov (United States)

    Añazco, Carolina; López-Jiménez, Alberto J.; Rafi, Mohamed; Vega-Montoto, Lorenzo; Zhang, Ming-Zhi; Hudson, Billy G.; Vanacore, Roberto M.

    2016-01-01

    The 7S dodecamer is recognized as an important structural cross-linking domain of collagen IV networks that provide mechanical stability to basement membranes, a specialized form of extracellular matrix essential for the development and maintenance of tissue architecture. Although the 7S dodecamer is stabilized by covalent cross-linking, the molecular mechanism by which such cross-links are formed has not been revealed. Here, we aimed to identify the enzyme(s) that cross-links the 7S dodecamer and characterize its expression in the kidney glomerulus. Pharmacological inhibition of candidate extracellular matrix enzymes revealed that lysyl oxidase activity is required for cross-linking of 7S polypeptides. Among all lysyl oxidase family members, lysyl oxidase-like-2 (LOXL2) was identified as the isoform cross-linking collagen IV in mouse embryonal PFHR-9 cells. Biochemical analyses revealed that LOXL2 readily promoted the formation of lysyl-derived cross-links in the 7S dodecamer but not in the NC1 domain. We also established that LOXL2 is the main lysyl oxidase family member present in the glomerular extracellular matrix. Altogether, we demonstrate that LOXL2 is a novel component of the molecular machinery that forms cross-linked collagen IV networks, which are essential for glomerular basement membrane stability and molecular ultrafiltration function. PMID:27770022

  12. Lysyl Oxidase-like-2 Cross-links Collagen IV of Glomerular Basement Membrane.

    Science.gov (United States)

    Añazco, Carolina; López-Jiménez, Alberto J; Rafi, Mohamed; Vega-Montoto, Lorenzo; Zhang, Ming-Zhi; Hudson, Billy G; Vanacore, Roberto M

    2016-12-09

    The 7S dodecamer is recognized as an important structural cross-linking domain of collagen IV networks that provide mechanical stability to basement membranes, a specialized form of extracellular matrix essential for the development and maintenance of tissue architecture. Although the 7S dodecamer is stabilized by covalent cross-linking, the molecular mechanism by which such cross-links are formed has not been revealed. Here, we aimed to identify the enzyme(s) that cross-links the 7S dodecamer and characterize its expression in the kidney glomerulus. Pharmacological inhibition of candidate extracellular matrix enzymes revealed that lysyl oxidase activity is required for cross-linking of 7S polypeptides. Among all lysyl oxidase family members, lysyl oxidase-like-2 (LOXL2) was identified as the isoform cross-linking collagen IV in mouse embryonal PFHR-9 cells. Biochemical analyses revealed that LOXL2 readily promoted the formation of lysyl-derived cross-links in the 7S dodecamer but not in the NC1 domain. We also established that LOXL2 is the main lysyl oxidase family member present in the glomerular extracellular matrix. Altogether, we demonstrate that LOXL2 is a novel component of the molecular machinery that forms cross-linked collagen IV networks, which are essential for glomerular basement membrane stability and molecular ultrafiltration function. © 2016 by The American Society for Biochemistry and Molecular Biology, Inc.

  13. Cross-linked PEEK-WC proton exchange membrane for fuel cell

    CSIR Research Space (South Africa)

    Lou, H

    2009-10-01

    Full Text Available The low cost proton exchange membrane was prepared by cross-linking water soluble sulfonated-sulfinated poly(oxa-p-phenylene-3,3-phthalido-p-phenylene-oxa-p-phenylene-oxyphenylene) (SsPEEK-WC). The prepared cross-linked membrane became insoluble...

  14. SECONDARY CYTOTOXICITY OF CROSS-LINKED DERMAL SHEEP COLLAGENS DURING REPEATED EXPOSURE TO HUMAN FIBROBLASTS

    NARCIS (Netherlands)

    VANLUYN, MJA; VANWACHEM, PB; DAMINK, LHHO; DIJKSTRA, PJ; FEIJEN, J; NIEUWENHUIS, P

    1992-01-01

    We investigated commercially available dermal sheep collagen either cross-linked with hexamethylenedlisocyanate, or cross-linked with glutaraldehyde. In previous in vitro studies we could discriminate primary, i.e. extractable, and secondary cytotoxicity, due to cell-biomaterial interactions, i.e.

  15. 21 CFR 864.4020 - Analyte specific reagents.

    Science.gov (United States)

    2010-04-01

    ... reagents. (a) Identification. Analyte specific reagents (ASR's) are antibodies, both polyclonal and... application for identification and quantification of an individual chemical substance or ligand in biological... practitioners, e.g., forensic, academic, research, and other nonclinical laboratories. (b) Classification. (1...

  16. 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......, a fraction (quantified by the stress transfer function ) of the second-stage cross-links contribute to the effective first-stage cross-link density. The stress transfer functions extracted from the MD simulations of the reacting networks are found to be in very...

  17. Collagen cross-linking of skin in patients with amyotrophic lateral sclerosis

    Science.gov (United States)

    Ono, S.; Yamauchi, M.

    1992-01-01

    Collagen cross-links of skin tissue (left upper arm) from 11 patients with amyotrophic lateral sclerosis (ALS) and 9 age-matched control subjects were quantified. It was found that patients with ALS had a significant reduction in the content of an age-related, stable cross-link, histidinohydroxylysinonorleucine, that was negatively correlated with the duration of illness. The contents of sodium borohydride-reducible labile cross-links, dehydro-hydroxylysinonorleucine and dehydro-histidinohydroxymerodesmosine, were significantly increased and were positively associated with the duration of illness (r = 0.703, p less than 0.05 and r = 0.684, p less than 0.05, respectively). The results clearly indicate that during the course of ALS, the cross-linking pathway of skin collagen runs counter to its normal aging, resulting in a "rejuvenation" phenomenon of skin collagen. Thus, cross-linking of skin collagen is affected in ALS.

  18. A Study into the Collision-induced Dissociation (CID) Behavior of Cross-Linked Peptides*

    Science.gov (United States)

    Giese, Sven H.; Fischer, Lutz; Rappsilber, Juri

    2016-01-01

    Cross-linking/mass spectrometry resolves protein–protein interactions or protein folds by help of distance constraints. Cross-linkers with specific properties such as isotope-labeled or collision-induced dissociation (CID)-cleavable cross-linkers are in frequent use to simplify the identification of cross-linked peptides. Here, we analyzed the mass spectrometric behavior of 910 unique cross-linked peptides in high-resolution MS1 and MS2 from published data and validate the observation by a ninefold larger set from currently unpublished data to explore if detailed understanding of their fragmentation behavior would allow computational delivery of information that otherwise would be obtained via isotope labels or CID cleavage of cross-linkers. Isotope-labeled cross-linkers reveal cross-linked and linear fragments in fragmentation spectra. We show that fragment mass and charge alone provide this information, alleviating the need for isotope-labeling for this purpose. Isotope-labeled cross-linkers also indicate cross-linker-containing, albeit not specifically cross-linked, peptides in MS1. We observed that acquisition can be guided to better than twofold enrich cross-linked peptides with minimal losses based on peptide mass and charge alone. By help of CID-cleavable cross-linkers, individual spectra with only linear fragments can be recorded for each peptide in a cross-link. We show that cross-linked fragments of ordinary cross-linked peptides can be linearized computationally and that a simplified subspectrum can be extracted that is enriched in information on one of the two linked peptides. This allows identifying candidates for this peptide in a simplified database search as we propose in a search strategy here. We conclude that the specific behavior of cross-linked peptides in mass spectrometers can be exploited to relax the requirements on cross-linkers. PMID:26719564

  19. Trivalent manganese as an environmentally friendly oxidizing reagent for microwave- and ultrasound-assisted chemical oxygen demand determination.

    Science.gov (United States)

    Domini, Claudia E; Vidal, Lorena; Canals, Antonio

    2009-06-01

    In the present work manganese(III) has been used as oxidant and microwave radiation and ultrasound energy have been assessed to speed up and to improve the efficiency of digestion step for the determination of chemical oxygen demand (COD). Microwave (MW) and ultrasound-assisted COD determination methods have been optimized by means of experimental design and the optimum conditions are: 40psi pressure, 855W power and 1min irradiation time; and 90% of maximum nominal power (180W), 0.9s (s(-1)) cycles and 1min irradiation time for microwaves and ultrasound, respectively. Chloride ion interference is removed as hydrochloric acid gas from acidified sample solutions at 150 degrees C in a closed reaction tube and captured by bismuth-based adsorbent suspended above the heated solution. Under optimum conditions, the evaluated assisted digestion methods have been successfully applied, with the exception of pyridine, to several pure organic compounds and two reference materials. COD recoveries obtained with MW and ultrasound-assisted digestion for five real wastewater samples were ranged between 86-97% and 68-91%, respectively, of the values obtained with the classical method (open reflux) used as reference, with relative standard deviation lower than 4% in most cases. Thus, the Mn(III) microwave-assisted digestion method seems to be an interesting and promising alternative to conventional COD digestion methods since it is faster and more environmentally friendly than the ones used for the same purpose.

  20. Mitochondrial Dysfunction Causes Oxidative Stress and Tapetal Apoptosis in Chemical Hybridization Reagent-Induced Male Sterility in Wheat

    Directory of Open Access Journals (Sweden)

    Shuping Wang

    2018-01-01

    Full Text Available Male sterility in plants has been strongly linked to mitochondrial dysfunction. Chemical hybridization agent (CHA-induced male sterility is an important tool in crop heterosis. Therefore, it is important to better understand the relationship between mitochondria and CHA-induced male sterility in wheat. This study reports on the impairment of mitochondrial function duo to CHA-SQ-1, which occurs by decreasing cytochrome oxidase and adenosine triphosphate synthase protein levels and theirs activities, respiratory rate, and in turn results in the inhibition of the mitochondrial electron transport chain (ETC, excessive production of reactive oxygen species (ROS and disruption of the alternative oxidase pathway. Subsequently, excessive ROS combined with MnSOD defects results in damage to the mitochondrial membrane, followed by ROS release into the cytoplasm. The microspores underwent severe oxidative stress during pollen development. Furthermore, chronic oxidative stress, together with the overexpression of type II metacaspase, triggered premature tapetal apoptosis, which resulted in pollen abortion. Accordingly, we propose a metabolic pathway for mitochondrial-mediated male sterility in wheat, which provides information on the molecular events underlying CHA-SQ-1-induced abortion of anthers and may serve as an additional guide to the practical application of hybrid breeding.

  1. 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.

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

    Science.gov (United States)

    Padmanabhan, Prema; Radhakrishnan, Aishwaryah; Venkataraman, Abinaya Priya; Gupta, Nidhi; Srinivasan, Bhaskar

    2014-01-01

    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. PMID:23619500

  3. Iontophoretic collagen cross-linking versus epithelium-off collagen cross-linking for early stage of progressive keratoconus - 3 years follow-up study.

    Science.gov (United States)

    Cantemir, Alina; Alexa, Anisia-Iuliana; Galan, Bogdan Gabriel; Anton, Nicoleta; Ciuntu, Roxana Elena; Danielescu, Ciprian; Chiselita, Dorin; Costin, Danut

    2017-11-01

    To compare 3-year iontophoretic corneal collagen cross-linking (I-CXL) outcomes with epithelium-off corneal collagen cross-linking (epi-off CXL) for early stage of progressive keratoconus. Eighty eyes of 80 patients with early progressive keratoconus treated by I-CXL (n = 40) or epi-off CXL (n = 40) were included in this study. Uncorrected (UDVA) and corrected (CDVA) distance visual acuities, refraction, corneal topography and pachymetry were assessed at baseline and at 1, 3, 6, 12, 24 and 36 months of follow-up. Visual acuity (VA) showed a significant improvement (p collagen cross-linking (I-CXL) is non-inferior to epi-off CXL for stopping the progression of keratoconus in its early stages with a higher degree of safety for the patients and a faster recovery of VA. © 2017 Acta Ophthalmologica Scandinavica Foundation. Published by John Wiley & Sons Ltd.

  4. Optimization of protein cross-linking in bicomponent electrospun scaffolds for therapeutic use

    Energy Technology Data Exchange (ETDEWEB)

    Papa, Antonio [Institute for Polymers, Composites and Biomaterials, National Research Council of Italy (IPCB-CNR), V.le Kennedy 54, Naples 80125 (Italy); IMAST SCaRL, Piazza Bovio 22, 80133 Naples (Italy); Guarino, Vincenzo, E-mail: vincenzo.guarino@cnr.it; Cirillo, Valentina; Oliviero, Olimpia; Ambrosio, Luigi [Institute for Polymers, Composites and Biomaterials, National Research Council of Italy (IPCB-CNR), V.le Kennedy 54, Naples 80125 (Italy)

    2015-12-17

    Bio-instructive electrospun scaffolds based on the combination of synthetic polymers, such as PCL or PLLA, and natural polymers (e.g., collagen) have been extensively investigated as temporary extracellular matrix (ECM) analogues able to support cell proliferation and stem cell differentiation for the regeneration of several tissues. The growing use of natural polymers as carrier of bioactive molecules is introducing new ideas for the design of polymeric drug delivery systems based on electrospun fibers with improved bioavailability, therapeutic efficacy and programmed drug release. In particular, the release mechanism is driven by the use of water soluble proteins (i.e., collagen, gelatin) which fully degrade in in vitro microenvironment, thus delivering the active principles. However, these protein are generally rapidly digested by enzymes (i.e., collagenase) produced by many different cell types, both in vivo and in vitro with significant drawbacks in tissue engineering and controlled drug delivery. Here, we aim at investigating different chemical strategies to improve the in vitro stability and mechanical strength of scaffolds against enzymatic degradation, by modifying the biodegradation rates of proteins embedded in bicomponent fibers. By comparing scaffolds treated by different cross-linking agents (i.e., GC, EDC, BDDGE), we have provided an extensive morphological/chemical/physical characterization via SEM and TGA to identify the best conditions to control drug release via protein degradation from bicomponent fibers without compromising in vitro cell response.

  5. Optimization of protein cross-linking in bicomponent electrospun scaffolds for therapeutic use

    Science.gov (United States)

    Papa, Antonio; Guarino, Vincenzo; Cirillo, Valentina; Oliviero, Olimpia; Ambrosio, Luigi

    2015-12-01

    Bio-instructive electrospun scaffolds based on the combination of synthetic polymers, such as PCL or PLLA, and natural polymers (e.g., collagen) have been extensively investigated as temporary extracellular matrix (ECM) analogues able to support cell proliferation and stem cell differentiation for the regeneration of several tissues. The growing use of natural polymers as carrier of bioactive molecules is introducing new ideas for the design of polymeric drug delivery systems based on electrospun fibers with improved bioavailability, therapeutic efficacy and programmed drug release. In particular, the release mechanism is driven by the use of water soluble proteins (i.e., collagen, gelatin) which fully degrade in in vitro microenvironment, thus delivering the active principles. However, these protein are generally rapidly digested by enzymes (i.e., collagenase) produced by many different cell types, both in vivo and in vitro with significant drawbacks in tissue engineering and controlled drug delivery. Here, we aim at investigating different chemical strategies to improve the in vitro stability and mechanical strength of scaffolds against enzymatic degradation, by modifying the biodegradation rates of proteins embedded in bicomponent fibers. By comparing scaffolds treated by different cross-linking agents (i.e., GC, EDC, BDDGE), we have provided an extensive morphological/chemical/physical characterization via SEM and TGA to identify the best conditions to control drug release via protein degradation from bicomponent fibers without compromising in vitro cell response.

  6. Novel thermally cross-linked polyimide membranes for ethanol dehydration via pervaporation

    KAUST Repository

    Xu, Sheng

    2015-12-01

    © 2015 Elsevier B.V. In this work, two novel carboxyl-containing polyimides, 2,2\\'-bis(3,4-dicarboxyphenyl) hexafluoropropane dianhydride-4,4\\'-diaminodiphenylmethane/3,5-diaminobenzoic acid (6FDA-MDA/DABA, FMD) and 3,3\\',4,4\\'-benzophenone tetracarboxylic dianhydride-4,4\\'-diaminodiphenylmethane/3,5-diaminobenzoic acid (BTDA-MDA/DABA, BMD), are synthesized via chemical and thermal imidization methods, respectively, and employed as pervaporation membranes for ethanol dehydration. Chemical structures of the two polyimides are examined by FTIR and TGA to confirm the successful synthesis. A post thermal treatment of the polyimide membranes with the temperature range of 250 to 400. °C is applied, and its effects on the membrane morphology and separation performance are studied and characterized by FTIR, TGA, WXRD, solubility and sorption test. It is believed that the thermal treatment of the carboxyl-containing polyimide membrane at a relative low temperature only leads to the physical annealing, while it may cause the decarboxylation-induced cross-linking at a higher temperature. In addition, the operation temperature in pervaporation is also varied and shown to be an important factor to affect the final membrane performance. Performance benchmarking shows that the developed polyimide membranes both have superior pervaporation performance to most other flat-sheet dense membranes. This work is believed to shed useful insights on polyimide membranes for pervaporation applications.

  7. [Comparative evaluation of different corneal cross-linking techniques with respect to biomechanical stability of the cornea].

    Science.gov (United States)

    Pashtaev, N P; Pozdeeva, N A; Sinitsyn, M V; Zotov, V V; Gagloev, B V

    2016-01-01

    To perform a comparative analysis of the following cross-linking techniques: standard cross-linking (SCXL), local transepithelial femto cross-linking (LTF) and transepithelial intrastromal femto cross-linking with MyoRing implantation (TIF+MyoRing) in experimental animals and patients with progressive stage II--III keratoconus (KC), paying particular attention to the changes in biomechanical stability of the cornea. The experimental series was performed on 20 eyes of 10 rabbits. The animals were divided into 4 groups of 5. Group 1 served as the control, group 2 consisted of animals that underwent SCXL, group 3 -- of those after LTF, and group 4 -- of those after TIF+MyoRing. Femto step was performed using the IntraLase FS 60 kHz femtosecond laser, cross-linking - with the Evolution machine. The follow-up period was 1 month. Clinical study enrolled 48 patients (45 eyes) with stage II-III KC. Depending on the surgical technique all the patients were divided into 3 groups. In group I (14 eyes, 9 patients), TIF+MyoRing was performed, in group II (16 eyes, 20 patients) --SCXL, in group III (15 eyes, 19 patients) -- LTF. The follow-up period was 6 months. The experiment showed a significant increase in rupture resistance of the cornea in all three groups. Six months after surgery, patients from group I demonstrated a 1.0±0.22 mmHg higher corneal resistance factor (CRF) and a 1.0±0.12 mmHg higher corneal hysteresis (CH). In group II, the said parameters increased by 0.8±0.10 mmHg and 0.6±0.16 mmHg, respectively; in group III -- by 0.8±0.25 mmHg and 0.6±0.26 mmHg, respectively. In neither group the density of endothelial cells has reduced significantly over the follow-up period. C-ONCLUSION: All three methods (LTF, TIF and SCXL) equally increase the biomechanical strength of the cornea and are safe. In patients with progressive stage II-III KC, TIF+MyoRing surgery has yielded an even higher improvement of biomechanical parameters in a 6-month follow-up period, which

  8. On the Reproducibility of Label-Free Quantitative Cross-Linking/Mass Spectrometry

    Science.gov (United States)

    Müller, Fränze; Fischer, Lutz; Chen, Zhuo Angel; Auchynnikava, Tania; Rappsilber, Juri

    2017-12-01

    Quantitative cross-linking/mass spectrometry (QCLMS) is an emerging approach to study conformational changes of proteins and multi-subunit complexes. Distinguishing protein conformations requires reproducibly identifying and quantifying cross-linked peptides. Here we analyzed the variation between multiple cross-linking reactions using bis[sulfosuccinimidyl] suberate (BS3)-cross-linked human serum albumin (HSA) and evaluated how reproducible cross-linked peptides can be identified and quantified by LC-MS analysis. To make QCLMS accessible to a broader research community, we developed a workflow that integrates the established software tools MaxQuant for spectra preprocessing, Xi for cross-linked peptide identification, and finally Skyline for quantification (MS1 filtering). Out of the 221 unique residue pairs identified in our sample, 124 were subsequently quantified across 10 analyses with coefficient of variation (CV) values of 14% (injection replica) and 32% (reaction replica). Thus our results demonstrate that the reproducibility of QCLMS is in line with the reproducibility of general quantitative proteomics and we establish a robust workflow for MS1-based quantitation of cross-linked peptides. [Figure not available: see fulltext.

  9. FT-IR study for hydroxyapatite/collagen nanocomposite cross-linked by glutaraldehyde.

    Science.gov (United States)

    Chang, Myung Chul; Tanaka, Junzo

    2002-12-01

    FT-IR analysis was performed for the hydroxyapatite (HAp)/collagen (COL) nanocomposite cross-linked by glutaraldehyde (GA). The amide bands I, II and III from COL matrix, and phosphate and carbonate bands from HAp were identified. The amide B band arising from C-H stretching mode showed a sensitive conformation by the degree of cross-linking. The amide I band showed a complicate conformational change by the degree of cross-linking. The characteristic amide I band at 1685 cm(-1), which is known as an aging parameter in the biological bone, did not show a monotonous tendency by the degree of cross-linking. The relative contents of the organics in the cross-linked HAp/COL nanocomposite were evaluated as an integration ratio between the amide I band at 1600-1700 cm(-1) and PO(4)(3-) band at 900-1200 cm(-1). The increase of the organics content by the cross-linking is enabled by the further organization of Ca(2+) ions of HAp crystals in HAp/COL nanocomposite. The complicate conformational behavior in the amide I, II and III bands seems to be affected by the cross-linking induced directional arrangement of HAp/COL nanocomposite fibrils. Copyright 2002 Elsevier Science Ltd.

  10. 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.

  11. Lysyl hydroxylase 2 induces a collagen cross-link switch in tumor stroma.

    Science.gov (United States)

    Chen, Yulong; Terajima, Masahiko; Yang, Yanan; Sun, Li; Ahn, Young-Ho; Pankova, Daniela; Puperi, Daniel S; Watanabe, Takeshi; Kim, Min P; Blackmon, Shanda H; Rodriguez, Jaime; Liu, Hui; Behrens, Carmen; Wistuba, Ignacio I; Minelli, Rosalba; Scott, Kenneth L; Sanchez-Adams, Johannah; Guilak, Farshid; Pati, Debananda; Thilaganathan, Nishan; Burns, Alan R; Creighton, Chad J; Martinez, Elisabeth D; Zal, Tomasz; Grande-Allen, K Jane; Yamauchi, Mitsuo; Kurie, Jonathan M

    2015-03-02

    Epithelial tumor metastasis is preceded by an accumulation of collagen cross-links that heighten stromal stiffness and stimulate the invasive properties of tumor cells. However, the biochemical nature of collagen cross-links in cancer is still unclear. Here, we postulated that epithelial tumorigenesis is accompanied by changes in the biochemical type of collagen cross-links. Utilizing resected human lung cancer tissues and a p21CIP1/WAF1-deficient, K-rasG12D-expressing murine metastatic lung cancer model, we showed that, relative to normal lung tissues, tumor stroma contains higher levels of hydroxylysine aldehyde-derived collagen cross-links (HLCCs) and lower levels of lysine aldehyde-derived cross-links (LCCs), which are the predominant types of collagen cross-links in skeletal tissues and soft tissues, respectively. Gain- and loss-of-function studies in tumor cells showed that lysyl hydroxylase 2 (LH2), which hydroxylates telopeptidyl lysine residues on collagen, shifted the tumor stroma toward a high-HLCC, low-LCC state, increased tumor stiffness, and enhanced tumor cell invasion and metastasis. Together, our data indicate that LH2 enhances the metastatic properties of tumor cells and functions as a regulatory switch that controls the relative abundance of biochemically distinct types of collagen cross-links in the tumor stroma.

  12. Interrelation of Hydration, Collagen Cross-Linking Treatment, and Biomechanical Properties of the Cornea.

    Science.gov (United States)

    Hatami-Marbini, Hamed; Rahimi, Abdolrasol

    2016-05-01

    The present study was designed to investigate the effects of hydration and collagen cross-linking treatment on biomechanical properties of the cornea. The original corneal collagen cross-linking protocol was used to induce cross-links in bovine corneas. The thickness of samples was used as a measure of their hydration and five different thickness groups (n = 5 each) were considered. The cross-linked corneal strips were allowed to hydrate/dehydrate until their thickness reached 500, 700, 900, 1100, and 1500 μm. The tensile behavior of specimens in each thickness group was characterized by conducting uniaxial tensile experiments. The experiments were done in mineral oil in order to keep the thickness of samples constant and minimize hydration changes. It was observed that collagen cross-linking treatment significantly increased both the maximum tensile stress and the equilibrium (relaxed) stress of the bovine cornea (p  0.99), respectively. Hydration and collagen cross-linking treatment concomitantly affect biomechanical properties of the cornea. Therefore, an accurate estimate of stiffening effects of collagen cross-linking treatment option using uniaxial tensile experiments is only possible if the hydration of specimens is fully controlled.

  13. 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. Copyright © 2015 Elsevier B.V. All rights reserved.

  14. Silica/organosilica cross-linked block copolymer micelles: a versatile theranostic platform.

    Science.gov (United States)

    Niu, Dechao; Li, Yongsheng; Shi, Jianlin

    2017-02-06

    As a member of the organic-inorganic hybrid family, silica/organosilica cross-linked block copolymer micelles are becoming increasingly attractive due to the combined features of excellent self-assembly properties of amphiphilic block copolymers and the high stability and the easy surface modification of silica/organosilica components. Compared to the traditional cross-linking route with organic components, the silica/organosilica cross-linking approach could offer more advantages, such as quick reaction under mild conditions, a much stronger barrier to the diffusion of both encapsulated small molecules and functional nanoparticles and the substantial improvement in the stability of the whole micelles against the ambient environment. In this tutorial review, we will focus on the recent developments in the design, synthesis and biomedical applications of silica/organosilica cross-linked block copolymer micelles based on the self-assembly of amphiphilic block copolymers and the hydrolysis and condensation of silanes in aqueous solution. First, we will summarize the synthesis of three typical kinds of silica/organosilica cross-linked block copolymer micelles based on the self-assembly of non-ionic polyethylene oxide (PEO)-based, cationic and anionic poly(acrylic acid) (PAA)-based block copolymer micelles. Then, a series of multifunctional silica/organosilica cross-linked block copolymer micelles by encapsulating various functional nanoparticles/molecules in the hydrophobic polymer cores or hydrophilic silica/organosilica cross-linked shells are introduced and their biomedical applications in controlled drug delivery, bio-imaging (magnetic resonance, fluorescence and multimodal imaging) and imaging-guided therapies (photothermal and high intensity focused ultrasound therapies) will be discussed. Finally, the challenges and prospects of silica/organosilica cross-linked micellar nanostructures and their biological applications are discussed and assessed. It is highly

  15. Stiffening effects of riboflavin/UVA corneal collagen cross-linking is hydration dependent.

    Science.gov (United States)

    Hatami-Marbini, H; Rahimi, A

    2015-04-13

    The collagen cross-linking is a relatively new treatment option for strengthening the cornea, delaying, and in some cases stopping the progression of keratoconus. The uniaxial tensile experiments are among the most commonly used techniques to assess the effectiveness of this therapeutic option in enhancing tensile properties. In the present study, we investigated the possible effects of hydration on stiffening effects of corneal collagen cross-linking procedure, as measured by the uniaxial tensile testing method. For this purpose, after cross-linking bovine corneas, we let the strips to dehydrate in air or swell in a solution until their thickness reached an average thickness of 0.5, 0.7, 0.9, 1.1, and 1.5 mm. Using thickness as a representative of hydration, we divided corneal strips into five different groups and measured their stress-strain behavior by conducting uniaxial tensile experiments in mineral oil. It was observed that the collagen cross-linking treatment and hydration together affect the tensile behavior of the bovine cornea. While corneal collagen cross-linking resulted in a significant increase in the tensile stress-strain response of each thickness group (Pcollagen cross-linked samples showed a significantly stiffer response (Pcollagen cross-linked bovine cornea at different levels of hydration. The results of the present research confirmed that the amount of mechanical stiffening of the corneal collagen cross-linking, as measured by uniaxial tensile testing, strongly depends on the hydration. Therefore, it is concluded that uniaxial tensile experiments could only be used to assess stiffening effects of the collagen cross-linking treatment if the hydration of specimens is fully controlled. Copyright © 2015 Elsevier Ltd. All rights reserved.

  16. Riboflavin/UVA collagen cross-linking-induced changes in normal and keratoconus corneal stroma.

    Directory of Open Access Journals (Sweden)

    Sally Hayes

    Full Text Available PURPOSE: To determine the effect of Ultraviolet-A collagen cross-linking with hypo-osmolar and iso-osmolar riboflavin solutions on stromal collagen ultrastructure in normal and keratoconus ex vivo human corneas. METHODS: Using small-angle X-ray scattering, measurements of collagen D-periodicity, fibril diameter and interfibrillar spacing were made at 1 mm intervals across six normal post-mortem corneas (two above physiological hydration (swollen and four below (unswollen and two post-transplant keratoconus corneal buttons (one swollen; one unswollen, before and after hypo-osmolar cross-linking. The same parameters were measured in three other unswollen normal corneas before and after iso-osmolar cross-linking and in three pairs of swollen normal corneas, in which only the left was cross-linked (with iso-osmolar riboflavin. RESULTS: Hypo-osmolar cross-linking resulted in an increase in corneal hydration in all corneas. In the keratoconus corneas and unswollen normal corneas, this was accompanied by an increase in collagen interfibrillar spacing (p<0.001; an increase in fibril diameter was also seen in two out of four unswollen normal corneas and one unswollen keratoconus cornea (p<0.001. Iso-osmolar cross-linking resulted in a decrease in tissue hydration in the swollen normal corneas only. Although there was no consistent treatment-induced change in hydration in the unswollen normal samples, iso-osmolar cross-linking of these corneas did result in a compaction of collagen fibrils and a reduced fibril diameter (p<0.001; these changes were not seen in the swollen normal corneas. Collagen D-periodicity was not affected by either treatment. CONCLUSION: The observed structural changes following Ultraviolet-A cross-linking with hypo-osmolar or iso-osmolar riboflavin solutions are more likely a consequence of treatment-induced changes in tissue hydration rather than cross-linking.

  17. Alkaline phosphatase-fused repebody as a new format of immuno-reagent for an immunoassay

    Energy Technology Data Exchange (ETDEWEB)

    Seo, Hyo-Deok; Lee, Joong-jae [Department of Biological Sciences, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon, 305-701 (Korea, Republic of); Kim, Yu Jung [Industrial Biotechnology and Bioenergy Research Center, Korea Research Institute of Bioscience and Biotechnology (KRIBB), Daejeon (Korea, Republic of); Hantschel, Oliver [School of Life Sciences, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne (Switzerland); Lee, Seung-Goo [Industrial Biotechnology and Bioenergy Research Center, Korea Research Institute of Bioscience and Biotechnology (KRIBB), Daejeon (Korea, Republic of); Kim, Hak-Sung, E-mail: hskim76@kaist.ac.kr [Department of Biological Sciences, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon, 305-701 (Korea, Republic of)

    2017-01-15

    Enzyme-linked immunoassays based on an antibody-antigen interaction are widely used in biological and medical sciences. However, the conjugation of an enzyme to antibodies needs an additional chemical process, usually resulting in randomly cross-linked molecules and a loss of the binding affinity and enzyme activity. Herein, we present the development of an alkaline phosphatase-fused repebody as a new format of immuno-reagent for immunoassays. A repebody specifically binding to human TNF-α (hTNF-α) was selected through a phage display, and its binding affinity was increased up to 49 nM using a modular engineering approach. A monomeric alkaline phosphatase (mAP), which was previously isolated from a metagenome library, was genetically fused to the repebody as a signal generator, and the resulting repebody-mAP fusion protein was used for direct and sandwich immunoassays of hTNF-α. We demonstrate the utility and potential of the repebody-mAP fusion protein as an immuno-reagent by showing the sensitivity of 216 pg mL{sup −1} for hTNF-α in a sandwich immunoassay. Furthermore, this repebody-mAP fusion protein enabled the detection of hTNF-α spiked in a serum-supplemented medium with high accuracy and reproducibility. It is thus expected that a mAP-fused repebody can be broadly used as an immuno-reagent in immunoassays. - Highlights: • A human TNF-α (hTNF-α)-specific repebody was selected using a phage display. • A monomeric alkaline phosphatase (mAP) was genetically fused to the repebody. • mAP-fused repebody enabled detection of hTNF-α with high sensitivity and accuracy. • mAP-fused repebody can be widely used as a new immuno-reagent in immunoassays.

  18. 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 (Physteresis 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

  19. 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)

  20. Single-sided NMR for the measurement of the degree of cross-linking and curing

    OpenAIRE

    Halmen, Norbert; Kugler, Christoph; Kraus, Eduard; Baudrit, Benjamin; Hochrein, Thomas; Bastian, Martin

    2018-01-01

    The degree of cross-linking and curing is one of the most important values concerning the quality of cross-linked polyethylene (PE-X) and the functionality of adhesives and resin-based components. Up to now, the measurement of this property has mostly been time-consuming and usually destructive. Within the shown work the feasibility of single-sided nuclear magnetic resonance (NMR) for the non-destructive determination of the degree of cross-linking and curing as process moni...

  1. Double-helical nucleic acids with cross-linked strands: synthesis and applications in molecular biology

    Energy Technology Data Exchange (ETDEWEB)

    Antsypovitch, Sergei I; Oretskaya, Tat' yana S [Department of Chemistry, M.V. Lomonosov Moscow State University, Moscow (Russian Federation)

    1998-03-31

    Data on the methods employed for cross-linking of DNA strands and for the synthesis of oligonucleotide duplexes with cross-links between strands are summarised. Existing methods are systematised; their advantages and drawbacks are discussed. The examples of applications of DNA duplexes with covalently cross-linked chains for the study of protein-nucleic acid recognition and mechanisms of action of nucleic acid-binding proteins for gaining information about the spatial structure of nucleic acids, and for the solution of other problems of molecular biology are given. The bibliography includes 131 references.

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

    DEFF Research Database (Denmark)

    Heinz, Andrea; Ruttkies, Christoph K H; Jahreis, Günther

    2013-01-01

    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...... 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. GENERAL SIGNIFICANCE: The study provides important insight into the formation of native elastin cross...

  3. 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...

  4. 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.

  5. Handling Pyrophoric Reagents

    Energy Technology Data Exchange (ETDEWEB)

    Alnajjar, Mikhail S.; Haynie, Todd O.

    2009-08-14

    Pyrophoric reagents are extremely hazardous. Special handling techniques are required to prevent contact with air and the resulting fire. This document provides several methods for working with pyrophoric reagents outside of an inert atmosphere.

  6. Corneal collagen cross-linking for treating keratoconus.

    Science.gov (United States)

    Sykakis, Evripidis; Karim, Rushmia; Evans, Jennifer R; Bunce, Catey; Amissah-Arthur, Kwesi N; Patwary, Showrob; McDonnell, Peter J; Hamada, Samer

    2015-03-24

    Keratoconus is a condition of the eye that affects approximately 1 in 2000 people. The disease leads to a gradual increase in corneal curvature and decrease in visual acuity with consequent impact on quality of life. Collagen cross-linking (CXL) with ultraviolet A (UVA) light and riboflavin (vitamin B2) is a relatively new treatment that has been reported to slow or halt the progression of the disease in its early stages. The objective of this review was to assess whether there is evidence that CXL is an effective and safe treatment for halting the progression of keratoconus compared to no treatment. We searched the Cochrane Central Register of Controlled Trials (CENTRAL; 2014, Issue 7), Ovid MEDLINE, Ovid MEDLINE In-Process and Other Non-Indexed Citations, Ovid MEDLINE Daily, Ovid OLDMEDLINE (January 1946 to August 2014), EMBASE (January 1980 to August 2014), Latin American and Caribbean Health Sciences Literature Database (LILACS) (1982 to August 2014), Cumulative Index to Nursing and Allied Health Literature (CINAHL) (1982 to August 2014), OpenGrey (System for Information on Grey Literature in Europe) (www.opengrey.eu/), the metaRegister of Controlled Trials (mRCT) (www.controlled-trials.com), ClinicalTrials.gov (www.clinicaltrials.gov) and the World Health Organisation International Clinical Trials Registry Platform (ICTRP) (www.who.int/ictrp/search/en). We used no date or language restrictions in the electronic searches for trials. We last searched the electronic databases on 28 August 2014. We included randomised controlled trials (RCTs) where CXL with UVA light and riboflavin was used to treat people with keratoconus and was compared to no treatment. Two review authors independently screened the search results, assessed trial quality, and extracted data using standard methodological procedures expected by Cochrane. Our primary outcomes were two indicators of progression at 12 months: increase in maximum keratometry of 1.5 dioptres (D) or more and

  7. Imade-imide cross-linked PEEK proton exchange membrane.

    CSIR Research Space (South Africa)

    Luo, H

    2009-08-01

    Full Text Available based membrane. Because of its high proton conductivity and good chemical stability, it has been widely used as the proton exchange membrane in PEMFC. However, the high cost of fluorinated polymers limits the large-scale commercialization of PEMFC...

  8. Preparation and adsorption property of aminated cross linking ...

    Indian Academy of Sciences (India)

    The adsorption property of aminated microbeads for bilirubin was investigated, and the effects of various factors, such as the chemical structures of the aminating agents, pH values of the medium and the presence of bovine serum albumin in the adsorption medium, on the adsorption property were examined.

  9. Molecular weight and galloylation affect grape seed extract constituents' ability to cross-link dentin collagen in clinically relevant time.

    Science.gov (United States)

    Liu, Yi; Bai, Xinyan; Li, Shaohua; Liu, Ying; Keightley, Andrew; Wang, Yong

    2015-07-01

    To investigate the relationship between the structures of polyphenolic compounds found in grape seed extract (GSE) and their activity in cross-linking dentin collagen in clinically relevant settings. Representative monomeric and dimeric GSE constituents including (+)-catechin (pCT), (-)-catechin (CT), (-)-epicatechin (EC), (-)-epigallocatechin (EGC), (-)-epicatechin gallate (ECG), (-)-epigallocatechin gallate (EGCG), procyanidin B2 and a pCT-pCT dimer were purchased or synthesized. GSE was separated into low (PALM) and high molecular weight (PAHM) fractions. Human molars were processed into dentin films and beams. After demineralization, 11 groups of films (n=5) were treated for 1min with the aforementioned reagents (1wt% in 50/50 ethanol/water) and 1 group remained untreated. The films were studied by Fourier transform infrared spectroscopy (FTIR) followed by a quantitative mass spectroscopy-based digestion assay. Tensile properties of demineralized dentin beams were evaluated (n=7) after treatments (2h and 24h) with selective GSE species that were found to protect dentin collagen from collagenase. Efficacy of GSE constituents in cross-linking dentin collagen was dependent on molecular size and galloylation. Non-galloylated species with degree of polymerization up to two, including pCT, CT, EC, EGC, procyanidin B2 and pCT-pCT dimer were not active. Galloylated species were active starting from monomeric form, including ECG, EGCG, PALM, GSE and PAHM. PALM induced the best overall improvement in tensile properties of dentin collagen. Identification under clinically relevant settings of structural features that contribute to GSE constituents' efficacy in stabilizing demineralized dentin matrix has immediate impact on optimizing GSE's use in dentin bonding. Copyright © 2015 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

  10. Cross-linking of rubber in the presence of multi-functional cross-linking aids via thermoreversible Diels-Alder chemistry

    NARCIS (Netherlands)

    Polgar, L. M.; Fortunato, G.; Araya-Hermosilla, R.; van Duin, M.; Pucci, A.; Picchioni, F.

    Furan-functionalized polyketone (PK-FU) was added to a furan-functionalized ethylene-propylene rubber (EPM-FU). The mixture was subsequently cross-linked with a bismaleimide through Diels-Alder chemistry in order to improve the mechanical properties of the rubber. Infrared spectroscopy showed the

  11. Cross-Linked Conjugated Polymer Fibrils: Robust Nanowires from Functional Polythiophene Diblock Copolymers

    Energy Technology Data Exchange (ETDEWEB)

    Hammer, Brenton A. G.; Bokel, Felica A.; Hayward, Ryan C.; Emrick, Todd

    2011-09-27

    A series of poly(3-hexyl thiophene) (P3HT)-based diblock copolymers were prepared and examined in solution for their assembly into fibrils, and post-assembly cross-linking into robust nanowire structures. P3HT-b-poly(3-methanol thiophene) (P3MT), and P3HT-b-poly(3-aminopropyloxymethyl thiophene) (P3AmT) diblock copolymers were synthesized using Grignard metathesis (GRIM) polymerization. Fibrils formed from solution assembly of these copolymers are thus decorated with hydroxyl and amine functionality, and cross-linking is achieved by reaction of diisocyanates with the hydroxyl and amine groups. A variety of cross-linked structures, characterized by transmission electron microscopy (TEM), were produced by this method, including dense fibrillar sheets, fibril bundles, or predominately individual fibrils, depending on the chosen reaction conditions. In solution, the cross-linked fibrils maintained their characteristic vibronic structure in solvents that would normally disrupt (dissolve) the structures.

  12. 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.

  13. In vivo Confocal Microscopy Report after Lasik with Sequential Accelerated Corneal Collagen Cross-Linking Treatment

    National Research Council Canada - National Science Library

    Mazzotta, Cosimo; Balestrazzi, Angelo; Traversi, Claudio; Caragiuli, Stefano; Caporossi, Aldo

    2014-01-01

    ...) treatment combined with sequential high-fluence accelerated corneal collagen cross-linking, denominated Lasik XTra, by means of HRT II laser scanning in vivo confocal microscopy after a 6-month follow-up...

  14. Identification of peptide-cross-linked trisdisaccharide peptide trimers in murein of Escherichia coli.

    OpenAIRE

    Gmeiner, J

    1980-01-01

    Purified murein from Escherichia coli K-12 was degraded into disaccharide peptide fragments by endo-N-acetylmuramidase from Chalaropsis. About 5% of the total murein fragments were recovered as peptide-cross-linked trisdisaccharide peptide trimers.

  15. 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.

  16. 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...

  17. Absorbed Pb2+ and Cd2+ Ions in Water by Cross-Linked Starch Xanthate

    National Research Council Canada - National Science Library

    Feng, Kai; Wen, Guohua

    2017-01-01

    ...]-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...

  18. 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.

  19. Gamma-irradiated cross-linked LDPE foams: Characteristics and properties

    Science.gov (United States)

    Cardoso, E. C. L.; Scagliusi, S. R.; Parra, D. F.; Lugão, A. B.

    2013-03-01

    Foamed polymers are future materials, as they are increasingly considered "green materials" due to their interesting properties at very low consumption of raw materials. They can be used to improve appearance of insulation structures, thermal and acoustic insulation, core materials for sandwich panels, fabrication of furniture and flotation materials or to reduce costs involving materials. Low-density polyethylene is widely used because of its excellent properties, such as softness, elasticity, processibility and insulation. In general, cross-linking is often applied to improve the thermal and mechanical properties of polyethylene products, due to the formation of a three-dimensional network. In particular for the production of PE foams, cross-linking is applied prior the expansion to control bubble formation, cell characteristics and final properties of the foam. However, the usual production process of PE foams is a process in which a gaseous blowing agent is injected into a melted thermoplastic polymer, under pressure, to form a solution between blowing agent and melted polymer. An extrusion system is provided for foaming the polymer, supplied to an extruder and moving through a rotating screw. The pressure must be high enough to keep the gas blowing agent (or foaming agent) in the solution with the melt. The foaming agent is then diffused and dissolved in the molten material to form a single-phase solution. In the present work carbon dioxide was used as the bowing agent, a chemically stable and non-toxic gas, with good diffusion coefficient; gas pressure used varied within a 20-40 bar range. Some requirements for physical foaming are required, as low friction heat generation, homogeneous melt temperature distribution, melt temperature at die exit just above crystallization temperature (die) and high melt strength during expansion. This work studied foams properties gamma-irradiated within 0, 10, 15, 20, 25, and 30 kGy, from a LDPE exhibiting 2.6 g/10 min Melt

  20. 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

    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...... structural data are rapidly accumulating in databases, we envision that many protein-nucleic acid assemblies will be initially characterized by combinations of cross-linking methods, MS, and computational molecular modeling....

  1. Tracer diffusion through F-actin: effect of filament length and cross-linking

    OpenAIRE

    Jones, J.D.; Luby-Phelps, K.

    1996-01-01

    We have determined diffusion coefficients for small (50- to 70-nm diameter) fluorescein-thiocarbamoyl-labeled Ficoll tracers through F-actin as a function of filament length and cross-linking. fx45 was used to regulate filament length and avidin/biotinylated actin or ABP-280 was used to prepare cross-linked actin gels. We found that tracer diffusion was generally independent of filament length in agreement with theoretical predictions for diffusion through solutions of rods. However, in some ...

  2. Mechanical properties of cross-linked collagen meshes after human adipose derived stromal cells seeding

    OpenAIRE

    Ochoa, I. (Ignacio); Peña, E. (Estefanía); Andreu, E.J. (Enrique José); Perez-Ilzarbe, M. (Maitane); Robles, J.E. (José Enrique); Alcaine, C. (C.); Lopez, T. (Tania); Prosper, F. (Felipe); Doblare, M. (M.)

    2010-01-01

    The main goal of this study was to evaluate the potential of collagen meshes derived from porcine dermis as scaffolds for repairing pelvic organ prolapses. Mechanical properties of collagen meshes with different cross-linking percentages before and after Adipose Derived Stromal Cells (ADSC) seeding were studied as well as the cell-scaffold interaction. Uniaxial tensile tests of the collagen meshes with three different cross-linking percentages (full-, partial-, and non...

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

    OpenAIRE

    Seciu A-M.; Gaspar A.; Stefan L.M.; Moldovan L.; Craciunescu O.; Zarnescu O.

    2016-01-01

    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....

  4. Influence of reversible cross-link coordination on the mechanical behavior of a linear polymer chain

    Science.gov (United States)

    Shabbir, H.; Hartmann, M. A.

    2017-09-01

    In this work, we investigate the effect of the coordination of cross-links (i.e., the number of monomers participating in one cross-link) on the mechanical performance of a single polymeric chain. The framework provided by the reactive empirical bond order potential is used to generically describe the ability of certain monomers to form cross-links of different coordination. A systematic investigation of the influence of the coordination of cross-links on the mechanical properties of single polymeric chains is presented by comparing systems that contain cross-links in the classical form between two monomers (dimer) and such where the cross-links are formed by three monomers (trimer). The results show that the mechanical performance crucially depends on the coordination of cross-links. The overall shape of the load-displacement curves as well as mechanical parameters like stiffness, strength and work-to-straighten the molecule are different for the different systems. While the load-displacement curve shows an overall more continuous shape for the system containing trimers compared to the system including dimers only, the mechanical parameters are consistently lower for the first system. On the other hand, in contrast to the dimer case a trimer remains stable upon detachment of one of the monomers and the bonds are more mobile. This will be of importance in the case of fiber bundles, where the loading situation is even more complicated than in the single chain system due to the presence of inter-chain cross-links.

  5. Rheological Characterization of Cataplasm Bases Composed of Cross-Linked Partially Neutralized Polyacrylate Hydrogel

    OpenAIRE

    Wang, Jian(PRISMA Cluster of Excellence & Mainz Institute for Theoretical Physics, Johannes Gutenberg University, D-55099, Mainz, Germany); Zhang, Hongqin; An, Dianyun; Yu, Jian; Li, Wei; Shen, Teng; Wang, Jianxin

    2014-01-01

    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 ...

  6. 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.

  7. Design of triple-shape memory polyurethane with photo-cross-linking of cinnamon groups.

    Science.gov (United States)

    Wang, Lin; Yang, Xifeng; Chen, Hongmei; Gong, Tao; Li, Wenbing; Yang, Guang; Zhou, Shaobing

    2013-11-13

    A triple-shape memory polyurethane (TSMPU) with poly(ε-caprolactone) -diols (PCL-diols) as the soft segments and diphenyl methane diisocyanate (MDI), N,N-bis (2-hydroxyethyl) cinnamamide (BHECA) as the hard segments was synthesized via simple photo-crosslinking of cinnamon groups irradiated under λ > 280 nm ultraviolet (UV) light. Fourier transform infrared spectroscopy (FT-IR), proton nuclear magnetic resonance ((1)H-NMR) and ultraviolet-visible absorption spectrum (UV-vis) confirmed the chemical structure of the material. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) results demonstrated that the photo-crosslinked polymer possessed two transition temperatures, one is due to the melting point of the soft segment PCL-diols, and the other is due to the glass transition temperature. All these contributed to the cross-linked structure of the hard segments and resulted in an excellent triple-shape memory effect. Alamar blue assay showed that the material has good non-cytotoxicity and can be potentially used in biomaterial devices.

  8. Structure of a DNA glycosylase that unhooks interstrand cross-links

    Energy Technology Data Exchange (ETDEWEB)

    Mullins, Elwood A.; Warren, Garrett M.; Bradley, Noah P.; Eichman, Brandt F. (Vanderbilt)

    2017-04-10

    DNA glycosylases are important editing enzymes that protect genomic stability by excising chemically modified nucleobases that alter normal DNA metabolism. These enzymes have been known only to initiate base excision repair of small adducts by extrusion from the DNA helix. However, recent reports have described both vertebrate and microbial DNA glycosylases capable of unhooking highly toxic interstrand cross-links (ICLs) and bulky minor groove adducts normally recognized by Fanconi anemia and nucleotide excision repair machinery, although the mechanisms of these activities are unknown. Here we report the crystal structure of Streptomyces sahachiroi AlkZ (previously Orf1), a bacterial DNA glycosylase that protects its host by excising ICLs derived from azinomycin B (AZB), a potent antimicrobial and antitumor genotoxin. AlkZ adopts a unique fold in which three tandem winged helix-turn-helix motifs scaffold a positively charged concave surface perfectly shaped for duplex DNA. Through mutational analysis, we identified two glutamine residues and a β-hairpin within this putative DNA-binding cleft that are essential for catalytic activity. Additionally, we present a molecular docking model for how this active site can unhook either or both sides of an AZB ICL, providing a basis for understanding the mechanisms of base excision repair of ICLs. Given the prevalence of this protein fold in pathogenic bacteria, this work also lays the foundation for an emerging role of DNA repair in bacteria-host pathogenesis.

  9. Resveratrol cross-linked chitosan loaded with phospholipid for controlled release and antioxidant activity.

    Science.gov (United States)

    Jeong, Hun; Samdani, Kunda J; Yoo, Dong Hyuck; Lee, Dong Won; Kim, Nam Hoon; Yoo, Il-Soo; Lee, Joong Hee

    2016-12-01

    Despite the therapeutic effects of resveratrol, its clinical application is restricted by its poor oral bioavailability and low water solubility. To overcome these physicochemical and pharmacokinetic limitations, encapsulation of resveratrol (RV) into nanodevices has been explored. Resveratrol cross-linked chitosan nanoparticles modified with phospholipids (RVC-lipid) were synthesized using a double emulsion technique. The surface morphology of RVC-lipid nanoparticles was evaluated with field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). Particle size was measured using dynamic light scattering technique (DLS), X-ray diffraction (XRD) was performed to identify the crystallographic nature and Fourier transform infrared spectroscopy (FTIR) was used to measure changes in the chemical structures of the resveratrol and RVC-lipid nanoparticles. Results showed RVC-lipid nanoparticle had a characteristic amorphous structure, a mean particle sizes of 570nm in DI water and 950nm in ethanol, and an encapsulation efficiency of 63.82% in aqueous medium and 85.59% in ethanol medium. In-vitro release studies demonstrated a slow and sustained release of resveratrol governed by diffusion. Based on assays of antioxidant activity the scavenging activity of RVC-lipid nanoparticles was inferior to that of resveratrol due to its prolonged release. We concluded that phospholipids are the potential carriers for resveratrol. Copyright © 2016 Elsevier B.V. All rights reserved.

  10. Novel Magnetic Cross-Linked Cellulase Aggregates with a Potential Application in Lignocellulosic Biomass Bioconversion

    Directory of Open Access Journals (Sweden)

    Junqi Jia

    2017-02-01

    Full Text Available The utilization of renewable biomass resources to produce high-value chemicals by enzymatic processes is beneficial for alternative energy production, due to the accelerating depletion of fossil fuels. As immobilization techniques can improve enzyme stability and reusability, a novel magnetic cross-linked cellulase aggregate has been developed and applied for biomass bioconversion. The crosslinked aggregates could purify and immobilize enzymes in a single operation, and could then be combined with magnetic nanoparticles (MNPs, which provides easy separation of the materials. The immobilized cellulase showed a better activity at a wider temperature range and pH values than that of the free cellulase. After six cycles of consecutive reuse, the immobilized cellulase performed successful magnetic separation and retained 74% of its initial activity when carboxylmethyl cellulose (CMC was used as the model substrate. Furthermore, the structure and morphology of the immobilized cellulase were studied by Fourier transform infrared spectroscopy (FTIR and scanning electron microscopy (SEM. Moreover, the immobilized cellulase was shown to hydrolyze bamboo biomass with a yield of 21%, and was re-used in biomass conversion up to four cycles with 38% activity retention, which indicated that the immobilized enzyme has good potential for biomass applications.

  11. Functional properties of a cross-linked soy protein-gelatin composite towards limited tryptic digestion of two extents.

    Science.gov (United States)

    Sheng, Wen-Wen; Zhao, Xin-Huai

    2013-12-01

    Both enzymatic cross-linking and hydrolysis are used to treat food proteins for functionality modification. The present study aimed to reveal the impact of limited tryptic digestion on some functional properties of a cross-linked composite generated from soy protein isolate and gelatin by transglutaminase. The composite was digested by trypsin for 1.5 and 4 h to produce two hydrolyzed composites with degrees of hydrolysis of 1% and 2%, respectively. Electrophoretic and chemical analysis showed that only part of the composite was degraded, and the gelatin fraction in the composite was more sensitive to tryptic digestion than the soy protein fraction. The hydrolyzed composites exhibited higher protein dispersion index at pH 4.5 or 7.0 and surface hydrophobicity, better digestibility in vitro, emulsifying property and oil absorption capacity, but lower water holding capacity and rheological properties (apparent viscosity, storage and loss modulus) than the composite. Compared to soy protein isolate, the hydrolyzed composites had better rheological properties, and higher water-holding capacity and emulsion stability index. The applied tryptic digestion conferred some improved properties on the hydrolyzed composites compared with the composite or soy protein isolate, and has potential for obtaining a new functional ingredient for processed foods. © 2013 Society of Chemical Industry.

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

    Energy Technology Data Exchange (ETDEWEB)

    He, Kongduo [Department of Light Sources and Illuminating Engineering, Fudan University, Shanghai 200433 (China); Liu, Yang [Department of Light Sources and Illuminating Engineering, Fudan University, Shanghai 200433 (China); Engineering Research Center of Advanced Lighting Technology, Ministry of Education, Shanghai 200433 (China); Gong, Junyi; Zeng, Pan; Kong, Xun; Yang, Xilu; Yang, Cheng; Yu, Yan [Department of Light Sources and Illuminating Engineering, Fudan University, Shanghai 200433 (China); Liang, Rongqing [Department of Light Sources and Illuminating Engineering, Fudan University, Shanghai 200433 (China); Engineering Research Center of Advanced Lighting Technology, Ministry of Education, Shanghai 200433 (China); Ou, Qiongrong, E-mail: qrou@fudan.edu.cn [Department of Light Sources and Illuminating Engineering, Fudan University, Shanghai 200433 (China); Engineering Research Center of Advanced Lighting Technology, Ministry of Education, Shanghai 200433 (China)

    2016-09-30

    Highlights: • Mixed acetylene and Ar plasma treatment makes the organic film surface cross-linked. • The plasma treatment for 30 s does not affect the performance of OLEDs. • Cross-linking surface can resist rinsing and corrosion of organic solvent. • The surface morphology is nearly unchanged after plasma treatment. • The plasma cross-linking method can realize solution processed multilayer OLEDs. - Abstract: 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.

  13. 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.

  14. Corneal melting after collagen cross-linking for keratoconus: a case report

    Directory of Open Access Journals (Sweden)

    Zissimopoulos Athanassios

    2011-04-01

    Full Text Available Abstract Introduction Corneal collagen cross-linking is a rather new technique that uses riboflavin and ultraviolet A light for collagen fiber stabilization in keratoconus corneas. Other than reversible side effects, the preliminary results of corneal collagen cross-linking studies suggest that it is a rather safe technique. In this report, we demonstrate a case of corneal melting after corneal collagen cross-linking for keratoconus corneas associated with an acute inflammatory response. Case presentation A 23-year-old Caucasian man with keratoconus cornea stage 1 to 2 underwent uneventful corneal collagen cross-linking treatment according to the Dresden protocol. The next day the patient had intense photophobia, watering and redness of the eye, and his visual acuity was limited to counting fingers. Slit lamp biomicroscopy revealed severe corneal haze accompanied by non-specific endothelial precipitates following an acute inflammatory response. Mild inflammation could be detected in the anterior chamber. Moreover, the re-epithelialization process could barely be detected. His corneal state gradually deteriorated, resulting in descemetocele and finally perforation. Conclusion In this report, we present a case of a patient with corneal melting after standard corneal collagen cross-linking treatment for keratoconus corneas following an acute inflammatory response. Despite modifying postoperative treatment, elaboration of all apparent associated causes by the treating physicians and undergoing extensive laboratory testing, the patient developed descemetocele, which led to perforation. Our report suggests that further research is necessary regarding the safety of corneal collagen cross-linking in keratoconus corneas.

  15. Current status of corneal collagen cross-linking for keratoconus: a review.

    Science.gov (United States)

    Chan, Elsie; Snibson, Grant R

    2013-03-01

    Over the past decade, corneal collagen cross-linking has become commonplace as a treatment option for individuals with progressive keratoconus. This is based on laboratory data suggesting that cross-linking using riboflavin and ultraviolet-A irradiation increases collagen diameter and the biomechanical strength of the treated cornea. Case series and limited randomised controlled trials support these findings with data demonstrating that cross-linking slows and possibly halts the progression of keratoconus. In some patients cross-linking results in an improvement in maximum corneal curvature, visual acuity, spherical equivalent and higher-order aberrations. The number of reported complications is small. More recently, variations in the treatment protocol have been described, although they have not yet been subject to comparative studies. While the published data indicate cross-linking is effective in modifying the natural history of keratoconus, the long-term impact of this treatment is still unknown. This paper reviews the theoretical basis, pre-clinical research and clinical results of corneal collagen cross-linking in keratoconus. © 2013 The Authors. Clinical and Experimental Optometry © 2013 Optometrists Association Australia.

  16. Mechanical properties of cross-linked collagen meshes after human adipose derived stromal cells seeding.

    Science.gov (United States)

    Ochoa, Ignacio; Peña, Estefania; Andreu, Enrique J; Pérez-Ilzarbe, Maitane; Robles, Jose E; Alcaine, Clara; López, Tania; Prósper, Felipe; Doblaré, Manuel

    2011-02-01

    The main goal of this study was to evaluate the potential of collagen meshes derived from porcine dermis as scaffolds for repairing pelvic organ prolapses. Mechanical properties of collagen meshes with different cross-linking percentages before and after Adipose Derived Stromal Cells (ADSC) seeding were studied as well as the cell-scaffold interaction. Uniaxial tensile tests of the collagen meshes with three different cross-linking percentages (full-, partial-, and noncross-linked) were carried out along orthogonal directions. Their mechanical properties were studied with the same tests before and after seeding with human derived adipose stem cells (ADSC) after 1 and 7 days. Histological analyses were performed to determine adhesion and proliferation of ADSC. Significant differences in mechanical properties of the unseeded meshes were observed between each orthogonal direction independently of the cross-linking percentage. A better cell adhesion rate was observed in the cross-linked meshes. An increase in the mechanical properties after cell seeding was observed with a direct relation with the degree of cross-linking. All meshes analyzed showed a marked anisotropy that should be taken into account during the surgical procedure. The cross-linking treatment increased cell adhesion and the mechanical properties of the collagen meshes after seeding. These results suggest that the mechanical properties of this type of collagen mesh could be useful as scaffolds for repair of pelvic organ prolapse. 2010 Wiley Periodicals, Inc.

  17. Formulation development and evaluation of lamivudine controlled release tablets using cross-linked sago starch.

    Science.gov (United States)

    Singh, Akhilesh Vikram; Nath, Lila Kanta

    2013-02-01

    Modified starches based polymeric substances find utmost applicability in pharmaceutical formulation development. Cross-linked starches showed very promising results in drug delivery application. The present investigation concerns with the development of controlled release tablets of lamivudine using cross-linked sago starch. The cross-linked derivative was synthesized with phosphorous oxychloride and native sago starch in basic pH medium. The cross-linked sago starch was tested for acute toxicity and drug-excipient compatibility study. The formulated tablets were evaluated for various physical characteristics, in vitro dissolution release study and in vivo pharmacokinetic study in rabbit model. In vitro release study showed that the optimized formulation exhibited highest correlation (R) in case of zero order kinetic model and the release mechanism followed a combination of diffusion and erosion process. There was a significant difference in the pharmacokinetic parameters (T(max), C(max), AUC, V(d), T(1/2), and MDT) of the optimized formulation as compared to the marketed conventional tablet Lamivir®. The cross-linked starch showed promising results in terms of controlling the release behavior of the active drug from the matrix. The hydrophilic matrix synthesized by cross-linking could be used with a variety of active pharmaceutical ingredients for making their controlled/sustained release formulations.

  18. 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.

  19. Corneal collagen cross-linking. A review of its clinical applications.

    Science.gov (United States)

    Balparda, K; Maldonado, M J

    2017-04-01

    To perform a literature review of the current clinical applications of corneal collagen cross-linking. An exhaustive literature search was made, including the main biomedical databases, and encompassing all years since the introduction of cross-linking in ophthalmology practice. Corneal collagen cross-linking using UVA irradiation and riboflavin is a surgical technique that is currently being optimised, and is supported by a good amount of pre-clinical and clinical studies. These papers found show the beneficial effect of the surgery on preventing the progression of corneal ectasia, especially keratoconus, but also on pellucid marginal degeneration and keratectasia after refractive surgery. The effect of cross-linking on avoiding the occurrence of iatrogenic keratectasia when combined with a photo-ablative procedure is less clear to date. Additionally, it appears that cross-linking may have a considerable beneficial effect on controlling corneal infection caused by fungi, bacteria and amoebae. However, its effect on viral keratitis can be detrimental. The benefit on bullous keratopathy seems to be rather transient. Corneal collagen cross-linking may be used with relative safety and efficacy in patients with progressive keratoconus. Its use could also be considered in patients with other corneal ectasias or with corneal infections of non-viral origin. Currently, there is still a need for more studies as regards its effect on preventing iatrogenic keratectasia. Copyright © 2016 Sociedad Española de Oftalmología. Publicado por Elsevier España, S.L.U. All rights reserved.

  20. Fibromodulin Interacts with Collagen Cross-linking Sites and Activates Lysyl Oxidase.

    Science.gov (United States)

    Kalamajski, Sebastian; Bihan, Dominique; Bonna, Arkadiusz; Rubin, Kristofer; Farndale, Richard W

    2016-04-08

    The hallmark of fibrotic disorders is a highly cross-linked and dense collagen matrix, a property driven by the oxidative action of lysyl oxidase. Other fibrosis-associated proteins also contribute to the final collagen matrix properties, one of which is fibromodulin. Its interactions with collagen affect collagen cross-linking, packing, and fibril diameter. We investigated the possibility that a specific relationship exists between fibromodulin and lysyl oxidase, potentially imparting a specific collagen matrix phenotype. We mapped the fibromodulin-collagen interaction sites using the collagen II and III Toolkit peptide libraries. Fibromodulin interacted with the peptides containing the known collagen cross-linking sites and the MMP-1 cleavage site in collagens I and II. Interestingly, the interaction sites are closely aligned within the quarter-staggered collagen fibril, suggesting a multivalent interaction between fibromodulin and several collagen helices. Furthermore, we detected an interaction between fibromodulin and lysyl oxidase (a major collagen cross-linking enzyme) and mapped the interaction site to 12 N-terminal amino acids on fibromodulin. This interaction also increases the activity of lysyl oxidase. Together, the data suggest a fibromodulin-modulated collagen cross-linking mechanism where fibromodulin binds to a specific part of the collagen domain and also forms a complex with lysyl oxidase, targeting the enzyme toward specific cross-linking sites. © 2016 by The American Society for Biochemistry and Molecular Biology, Inc.

  1. Fibromodulin Interacts with Collagen Cross-linking Sites and Activates Lysyl Oxidase*

    Science.gov (United States)

    Bihan, Dominique; Bonna, Arkadiusz; Rubin, Kristofer; Farndale, Richard W.

    2016-01-01

    The hallmark of fibrotic disorders is a highly cross-linked and dense collagen matrix, a property driven by the oxidative action of lysyl oxidase. Other fibrosis-associated proteins also contribute to the final collagen matrix properties, one of which is fibromodulin. Its interactions with collagen affect collagen cross-linking, packing, and fibril diameter. We investigated the possibility that a specific relationship exists between fibromodulin and lysyl oxidase, potentially imparting a specific collagen matrix phenotype. We mapped the fibromodulin-collagen interaction sites using the collagen II and III Toolkit peptide libraries. Fibromodulin interacted with the peptides containing the known collagen cross-linking sites and the MMP-1 cleavage site in collagens I and II. Interestingly, the interaction sites are closely aligned within the quarter-staggered collagen fibril, suggesting a multivalent interaction between fibromodulin and several collagen helices. Furthermore, we detected an interaction between fibromodulin and lysyl oxidase (a major collagen cross-linking enzyme) and mapped the interaction site to 12 N-terminal amino acids on fibromodulin. This interaction also increases the activity of lysyl oxidase. Together, the data suggest a fibromodulin-modulated collagen cross-linking mechanism where fibromodulin binds to a specific part of the collagen domain and also forms a complex with lysyl oxidase, targeting the enzyme toward specific cross-linking sites. PMID:26893379

  2. Role of special cross-links in structure formation of bacterial DNA polymer

    Science.gov (United States)

    Agarwal, Tejal; Manjunath, G. P.; Habib, Farhat; Lakshmi Vaddavalli, Pavana; Chatterji, Apratim

    2018-01-01

    Using data from contact maps of the DNA-polymer of Escherichia coli (E. Coli) (at kilobase pair resolution) as an input to our model, we introduce cross-links between monomers in a bead-spring model of a ring polymer at very specific points along the chain. Via suitable Monte Carlo simulations, we show that the presence of these cross-links leads to a particular organization of the chain at large (micron) length scales of the DNA. We also investigate the structure of a ring polymer with an equal number of cross-links at random positions along the chain. We find that though the polymer does get organized at the large length scales, the nature of the organization is quite different from the organization observed with cross-links at specific biologically determined positions. We used the contact map of E. Coli bacteria which has around 4.6 million base pairs in a single circular chromosome. In our coarse-grained flexible ring polymer model, we used 4642 monomer beads and observed that around 80 cross-links are enough to induce the large-scale organization of the molecule accounting for statistical fluctuations caused by thermal energy. The length of a DNA chain even of a simple bacterial cell such as E. Coli is much longer than typical proteins, hence we avoided methods used to tackle protein folding problems. We define new suitable quantities to identify the large scale structure of a polymer chain with a few cross-links.

  3. 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.

  4. Biomechanical Changes of Collagen Cross-Linking on Human Keratoconic Corneas Using Scanning Acoustic Microscopy.

    Science.gov (United States)

    Beshtawi, Ithar M; Akhtar, Riaz; Hillarby, M Chantal; O'Donnell, Clare; Zhao, Xuegen; Brahma, Arun; Carley, Fiona; Derby, Brian; Radhakrishnan, Hema

    2016-05-01

    To assess the biomechanical changes of collagen cross-linking on keratoconic corneas in vitro. Six keratoconic corneal buttons were included in this study. Each cornea was divided into two halves, where one half was cross-linked and the other half was treated with riboflavin only and served as control. The biomechanical changes of the corneal tissue were measured across the stroma using scanning acoustic microscopy (SAM). In the cross-linked corneas, there was a steady decrease in the magnitude of speed of sound from the anterior region through to the posterior regions of the stroma. The speed of sound was found to decrease slightly across the corneal thickness in the control corneas. The increase in speed of sound between the cross-linked and control corneas in the anterior region was by a factor of 1.039×. A higher speed of sound was detected in cross-linked keratoconic corneal tissue when compared with their controls, using SAM. This in vitro model can be used to compare to the cross-linking results obtained in vivo, as well as comparing the results obtained with different protocols.

  5. Recyclable cross-linked anion exchange membrane for alkaline fuel cell application

    Science.gov (United States)

    Hou, Jianqiu; Liu, Yazhi; Ge, Qianqian; Yang, Zhengjin; Wu, Liang; Xu, Tongwen

    2018-01-01

    Cross-linking can effectively solve the conductivity-swelling dilemma in anion exchange membranes (AEMs) but will generate solid wastes. To address this, we developed an AEM cross-linked via disulfide bonds, bearing quaternary ammonium groups, which can be easily recycled. The membrane (RC-QPPO) with IEC of 1.78 mmol g-1, when cross-linked, showed enhanced mechanical properties and good hydroxide conductivity (24.6 mS cm-1 at 30 °C). Even at higher IEC value (2.13 mmol g-1), it still has low water uptake, low swelling ratio and delivers a peak power density of 150 mW cm-2 at 65 °C. Exploiting the formation of disulfide bonds from -SH groups, the membrane can be readily cross-linked in alkaline condition and recycled by reversibly breaking disulfide bonds with dithiothreitol (DTT). The recycled membrane solution can be directly utilized to cast a brand-new AEM. By washing away the residual DTT with water and exposure to air, it can be cross-linked again and this process is repeatable. During the recycling and cross-linking processes, the membrane showed a slight IEC decrease of 5% due to functional group degradation. The strategy presented here is promising in enhancing AEM properties and reducing the impact of artificial polymers on the environment.

  6. Melting of cross-linked DNA. III. Calculation of differential melting curves.

    Science.gov (United States)

    Lando, D Y; Fridman, A S; Krot, V I; Akhrem, A A

    1998-08-01

    In our previous papers I and II (D. Y. Lando et al, J. Biomol. Struct. Dynam. (1997) v. 15, N1, p. 129-140, p. 141-150), two methods were developed for calculation of melting curves of cross-linked DNA. One of them is based on Poland's and another on the Fixman-Freire approach. In the present communication, III, a new theoretical method is developed for computation of differential melting curves of DNAs cross-linked by anticancer drugs and their inactive analogs. As Poland's approach, the method allows study of the influence of the loop entropy factor, delta(n), on melting behavior (n is the length of a loop in base pairs). However the method is much faster and requires computer time that inherent for the most rapid Fixman-Freire calculation approach. In contrast to the computation procedures described before in communications I and II, the method is suitable for computation of differential melting curves in the case of long DNA chains, arbitrary loop entropy factors of melted regions and arbitrary degree of cross-linking including very low values that occur in vivo after administration of antitumor drugs. The method is also appropriate for DNAs without cross-links. The results of calculation demonstrate that even very low degree of cross-linking alters the DNA differential melting curve. Cross-linking also markedly strengthens the influence of particular function delta(n) upon melting behavior.

  7. Catalytic Systems for the Cross-Linking of Organosilicon Polymers.

    Science.gov (United States)

    Wang, Dengxu; Klein, Johann; Mejía, Esteban

    2017-06-01

    Silicones and silicone rubbers are omnipresent in household and industrial products such as lubricants, coatings, sealants, insulators, medical devices, etc. This plethora of applications arises from their unparalleled properties including hydrophobicity, low surface energy, chemical inertness, extreme temperature stability, elasticity, and biocompatibility. Even though silicones have been known for more than five decades, their chemistry is still far from fully understood. Industrially, the vast majority of processes for their synthesis, transformation, and use are based on rather well established, alas outdated technologies, which are frequently empirical and poorly investigated. This review attempts to summarize the different approaches for the synthesis of silicone rubbers by vulcanization or curing of silicone polymers, the catalysts used, and the corresponding reaction mechanisms. Apart from the well-known methods (radical, hydrosilylation, and metal-based condensation), novel approaches such as organo- and bio-catalysis are also addressed. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  8. Simultaneous wastewater treatment and bioelectricity production in microbial fuel cells using cross-linked chitosan-graphene oxide mixed-matrix membranes.

    Science.gov (United States)

    Holder, Shima L; Lee, Ching-Hwa; Popuri, Srinivasa R

    2017-05-01

    Microbial fuel cells (MFCs) are emerging technology for wastewater treatment by chemical oxygen demand (COD) reduction and simultaneous bioelectricity production. Fabrication of an effective proton exchange membrane (PEM) is a vital component for MFC performance. In this work, green chitosan-based (CS) PEMs were fabricated with graphene oxide (GO) as filler material (CS-GO) and cross-linked with phosphoric acid (CS-GO-P(24)) or sulfuric acid (CS-GO-S(24)) to determine their effect on PEM properties. Interrogation of the physicochemical, thermal, and mechanical properties of the cross-linked CS-GO PEMs demonstrated that ionic cross-linking based on the incorporation of PO43- groups in the CS-GO mixed-matrix composites, when compared with sulfuric acid cross-linking commonly used in proton exchange membrane fuel cell (PEMFC) studies, generated additional density of ionic cluster domains, rendered enhanced sorption properties, and augmented the thermal and mechanical stability of the composite structure. Consequently, bioelectricity performance analysis in MFC application showed that CS-GO-P(24) membrane produced 135% higher power density than the CS-GO-S(24) MFC system. Simultaneously, 89.52% COD removal of primary clarifier municipal wastewater was achieved in the MFC operated with the CS-GO-P(24) membrane.

  9. Immunofluoresence of rabbit corneas following collagen cross-linking treatment with Riboflavin and Ultraviolet A

    Science.gov (United States)

    Esquenazi, Salomon; He, Jiucheng; Li, Na; Bazan, Haydee E.P.

    2009-01-01

    Purpose To assess ultrastructural modifications in keratocytes and inflammatory cell response in rabbit corneas after riboflavin and ultraviolet A (UVA) exposure using immunoflurescence microscopy. Methods Twenty adult New Zealand albino rabbits weighing 2.0 to 3.0 kg were used in this study. Two rabbits served as controls. The animals had their epithelia removed and were cross-linked with riboflavin 0.1% solution (10mgs riboflavin-5-phosphate in 10ml 20% dextran-T-500) applied every 3 minutes for 30 minutes, and exposed to UVA (360 nm, 3 mW/cm2) for 30 minutes. Four rabbits were humanely euthanized at each time point of 1, 3 and 11 days and at 3 and 5 weeks after the procedure. Immunohistochemestry studies of thin sections of each cornea were performed using TUNEL staining, Alpha smooth muscle actin (α-SMA), CD-3, myeloperoxidase (MPO) antibodies and DAPI counterstaining. In another experiment six additional rabbits were treated as above, and after 10 days of cross-linking, 5 μl of lipopolysaccharide (LPS) endotoxin (1μg/ml) was injected in the mid stroma. Results Cross-linked corneas showed early stromal edema. By 5 weeks, complete resolution of the edema and a pronounced highly organized anterior 200 μm fluorescent zone was observed. TUNEL staining showed keratocyte death by both necrosis and apoptosis between day 1 and 3 after cross-linking. At day 1 the limbal area close to the cross linking zone showed some inflammatory cells as well as α-SMA positive cells, indicative of the presence of myofibroblasts. By day 3 some myofibroblasts had migrated to the area beneath the cross linked stroma. Between day 3 and 5 weeks there was an increase in α-SMA staining in the area surrounding the cross linked stroma. The area of cross linking remained acellular up to 5 weeks. Conclusions Collagen cross-linking results in early edema, keratocyte apoptosis and necrosis, appearance of inflammatory cells in the surrounding area of treatment and transformation of

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

    Science.gov (United States)

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

    2007-12-15

    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 obtained by measuring the concentration of residual amine groups, which is frequently carried out with the 2,4,6 trinitrobenzene sulphonic acid (TNBS) assay. Cross-linked tissue and collagen matrices are usually further characterized by determining their physical properties (such as the shrinkage temperature), biological properties (such as resistance to enzymatic degradation), and mechanical properties before in vivo evaluation takes place. In an effort to improve the properties of cross-linked tissue and collagen, alternative cross-linking methods have been developed. One of these methods is based on the use of water soluble carbodiimides (CDI). It is generally accepted that this cross-linking method leads only to the formation of amide linkages between tissue carboxyl and amine groups. Therefore, until recently the TNBS assay was also used to determine the degree of cross-linking of CDI cross-linked tissue and collagen. However, it cannot be excluded that after activation of carboxyl groups of tissue and collagen by CDI, these groups can react with other nucleophiles (like hydroxyl groups) present in the matrix. To obtain a better insight in the degree of cross-linking of CDI cross-linked matrices a reliable assay for quantification of residual carboxyl groups is required. Up to now such an assay was not available. In this study a new assay to determine residual carboxyl groups in CDI cross-linked collagen matrices is presented. Reconstituted dermal bovine collagen matrices (RDBC) were cross-linked with a water soluble CDI and N-hydroxysuccinimide (NHS) and residual carboxyl groups were labeled using 5-bromomethyl fluorescein. Subsequently, the fluorescent label was released

  11. Mesoscopic simulations of hydrophilic cross-linked polycarbonate polyurethane networks: structure and morphology.

    Science.gov (United States)

    Iype, E; Esteves, A C C; de With, G

    2016-06-14

    Polyurethane (PU) cross-linked networks are frequently used in biomedical and marine applications, e.g., as hydrophilic polymer coatings with antifouling or low-friction properties and have been reported to exhibit characteristic phase separation between soft and hard segments. Understanding this phase-separation behavior is critical to design novel hydrophilic polymer coatings. However, most of the studies on the structure and morphology of cross-linked coatings are experimental, which only assess the phase separation via indirect methods. Herein we present a mesoscopic simulation study of the network characteristics of model hydrophilic polymer networks, consisting of PU with and without methyl-polyethylene glycol (mPEG) dangling chains. The systems are analyzed using a number of tools, such as the radial distribution function, the cross-link point density distribution and the Voronoi volume distribution (of the cross-linking points). The combined results show that the cross-linked networks without dangling chains are rather homogeneous but contain a small amount of clustering of cross-linker molecules. A clear phase separation is observed when introducing the dangling chains. In spite of that, the amount of cross-linker molecules connected to dangling chains only, i.e., not connected to the main network, is relatively small, leading to about 3 wt% extractables. Thus, these cross-linked polymers consist of a phase-separated, yet highly connected network. This study provides valuable guidelines towards new self-healing hydrophilic coatings based on the molecular design of cross-linked networks in direct contact with water or aqueous fluids, e.g., as anti-fouling self-repairing coatings for marine applications.

  12. Genipin-cross-linked collagen/chitosan biomimetic scaffolds for articular cartilage tissue engineering applications.

    Science.gov (United States)

    Yan, Le-Ping; Wang, Ying-Jun; Ren, Li; Wu, Gang; Caridade, Sofia G; Fan, Jia-Bing; Wang, Ling-Yun; Ji, Pei-Hong; Oliveira, Joaquim M; Oliveira, João T; Mano, João F; Reis, Rui L

    2010-11-01

    In this study, genipin-cross-linked collagen/chitosan biodegradable porous scaffolds were prepared for articular cartilage regeneration. The influence of chitosan amount and genipin concentration on the scaffolds physicochemical properties was evaluated. The morphologies of the scaffolds were characterized by scanning electron microscope (SEM) and cross-linking degree was investigated by ninhydrin assay. Additionally, the mechanical properties of the scaffolds were assessed under dynamic compression. To study the swelling ratio and the biostability of the collagen/chitosan scaffold, in vitro tests were also carried out by immersion of the scaffolds in PBS solution or digestion in collagenase, respectively. The results showed that the morphologies of the scaffolds underwent a fiber-like to a sheet-like structural transition by increasing chitosan amount. Genipin cross-linking remarkably changed the morphologies and pore sizes of the scaffolds when chitosan amount was less than 25%. Either by increasing the chitosan ratio or performing cross-linking treatment, the swelling ratio of the scaffolds can be tailored. The ninhydrin assay demonstrated that the addition of chitosan could obviously increase the cross-linking efficiency. The degradation studies indicated that genipin cross-linking can effectively enhance the biostability of the scaffolds. The biocompatibility of the scaffolds was evaluated by culturing rabbit chondrocytes in vitro. This study demonstrated that a good viability of the chondrocytes seeded on the scaffold was achieved. The SEM analysis has revealed that the chondrocytes adhered well to the surface of the scaffolds and contacted each other. These results suggest that the genipin-cross-linked collagen/chitosan matrix may be a promising formulation for articular cartilage scaffolding.

  13. Optimizing the Parameters Governing the Fragmentation of Cross-Linked Peptides in a Tribrid Mass Spectrometer.

    Science.gov (United States)

    Kolbowski, Lars; Mendes, Marta L; Rappsilber, Juri

    2017-05-16

    We compared the five different ways of fragmentation available on a tribrid mass spectrometer and optimized their collision energies with regard to optimal sequence coverage of cross-linked peptides. We created a library of bis(sulfosuccinimidyl)suberate (BS3/DSS) cross-linked precursors, derived from the tryptic digests of three model proteins (Human Serum Albumin, creatine kinase, and myoglobin). This enabled in-depth targeted analysis of the fragmentation behavior of 1065 cross-linked precursors using the five fragmentation techniques: collision-induced dissociation (CID), beam-type CID (HCD), electron-transfer dissociation (ETD), and the combinations ETciD and EThcD. EThcD gave the best sequence coverage for cross-linked m/z species with high charge density, while HCD was optimal for all others. We tested the resulting data-dependent decision tree against collision energy-optimized single methods on two samples of differing complexity (a mix of eight proteins and a highly complex ribosomal cellular fraction). For the high complexity sample the decision tree gave the highest number of identified cross-linked peptide pairs passing a 5% false discovery rate (on average ∼21% more than the second best, HCD). For the medium complexity sample, the higher speed of HCD proved decisive. Currently, acquisition speed plays an important role in allowing the detection of cross-linked peptides against the background of linear peptides. Enrichment of cross-linked peptides will reduce this role and favor methods that provide spectra of higher quality. Data are available via ProteomeXchange with identifier PXD006131.

  14. 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.

  15. CHARACTERIZATION OF SORBENT PRODUCED THROUGH IMMOBILIZATION OF HUMIC ACID ON CHITOSAN USING GLUTARALDEHYDE AS CROSS-LINKING AGENT AND Pb(II ION AS ACTIVE SITE PROTECTOR

    Directory of Open Access Journals (Sweden)

    Uripto Trisno Santoso

    2010-12-01

    Full Text Available Sorbent produced through immobilization of humic acid (HA on chitosan using glutaraldehyde as cross-linking agent and Pb(II ions as active site protector has been characterized. Active sorption site of HA was protected by reacting HA with Pb(II ion, and the protected-HA was then activated by glutaraldehyde, crosslinked onto chitosan, and deprotected by 0.1 M disodium ethylenediamine tetra-acetic acid (Na2EDTA. The protected-crosslinking method enhanced the content of immobilized-HA and its chemical stability. Based on the FTIR spectra, crosslinking of HA on chitosan probably occurred through a chemical reaction. The sorption capacity of sorbent still remains unchanged after the second regeneration, but some of HA start to be soluble. The latter shows that cross-linking reaction between HA and chitosan is through formation an unstable product. The effectiveness of sorbent regeneration can also be identified by the XRD pattern.

  16. Hemostatic porous sponges of cross-linked hyaluronic acid/cationized dextran by one self-foaming process.

    Science.gov (United States)

    Liu, Jia-Ying; Li, Yang; Hu, Yang; Cheng, Gang; Ye, Enyi; Shen, Chuanan; Xu, Fu-Jian

    2018-02-01

    Effective hemostatic materials are very important for treating trauma cases. Natural polysaccharides have been particularly appealing in the development of new hemostatic materials due to their unique functions in human bodies. In this work, different polysaccharide-based hemostatic porous sponges (SHDP or SHDQ) of cross-linked hyaluronic acid (HA)/cationized dextran were readily prepared by the self-foaming process of HA and poly((2-dimethyl amino)-ethyl methacrylate)-grafted dextran (Dex-PDM) or partially-quaternized Dex-PDM in the presence of sodium trimetaphosphate crosslinkers. SHDP and SHDQ sponges were investigated in terms of liquid-absorption ability, hemolysis, whole-blood clotting and hemostatic activity in hemorrhaging-liver models. Compared with HA/Dex-PDM sponges (HDP) without chemical cross-linking, SHDP and SHDQ sponges displayed higher porosity (>70.0% vs. 48.9%) and swelling ratios (>1000% vs. 520%). Meanwhile, hemolysis assay revealed the good blood compatibility of SHDP and SHDQ with low hemolysis ratio (below 0.5%). Furthermore, in vitro and in vivo hemostatic assay showed that SHDQ possessed better hemostatic properties than SHDP, owing to the higher cationic charges of partially-quaternized Dex-QPDM than Dex-PDM. The present study demonstrated that the self-foaming process of HA/Dex-PDM under a 'green' condition is an effective means to produce new hemostatic materials. Copyright © 2017 Elsevier B.V. All rights reserved.

  17. Highly efficient copper(II) ion sorbents obtained by calcium carbonate mineralization on functionalized cross-linked copolymers.

    Science.gov (United States)

    Mihai, Marcela; Bunia, Ion; Doroftei, Florica; Varganici, Cristian-Dragos; Simionescu, Bogdan C

    2015-03-23

    A new type of Cu(II) ion sorbents is presented. These are obtained by CaCO3 mineralization from supersaturated solutions on gel-like cross-linked polymeric beads as insoluble templates. A divinylbenzene-ethylacrylate-acrylonitrile cross-linked copolymer functionalized with weakly acidic, basic, or amphoteric functional groups has been used, as well as different initial inorganic concentrations and addition procedures for CaCO3 crystal growth. The morphology of the new composites was investigated by SEM and compared to that of the unmodified beads, and the polymorph content was established by X-ray diffraction. The beads, before and after CaCO3 mineralization, were tested as sorbents for Cu(II) ions. The newly formed patterns on the bead surface after Cu(II) sorption were observed by SEM, and the elemental distribution on the composites and the chemical structure of crystals after interaction with Cu(II) were investigated by EDAX elemental mapping and by FTIR-ATR spectroscopy, respectively. The sorption capacity increased significantly after CaCO3 crystals growth on the weak anionic bead surface (up to 1041.5 mg Cu(II) /g sample) compared to that of unmodified beads (491.5 mg Cu(II) /g sample). © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  18. The bis-electrophile diepoxybutane cross-links DNA to human histones but does not result in enhanced mutagenesis in recombinant systems.

    Science.gov (United States)

    Loecken, Elisabeth M; Dasari, Surendra; Hill, Salisha; Tabb, David L; Guengerich, F Peter

    2009-06-01

    1,2-Dibromoethane and 1,3-butadiene are cancer suspects present in the environment and have been used widely in industry. The mutagenic properties of 1,2-dibromoethane and the 1,3-butadiene oxidation product diepoxybutane are thought to be related to the bis-electrophilic character of these chemicals. The discovery that overexpression of O(6)-alkylguanine alkyltransferase (AGT) enhances bis-electrophile-induced mutagenesis prompted a search for other proteins that may act by a similar mechanism. A human liver screen for nuclear proteins that cross-link with DNA in the presence of 1,2-dibromoethane identified histones H2b and H3 as candidate proteins. Treatment of isolated histones H2b and H3 with diepoxybutane resulted in DNA-protein cross-links and produced protein adducts, and DNA-histone H2b cross-links were identified (immunochemically) in Escherichia coli cells expressing histone H2b. However, heterologous expression of histone H2b in E. coli failed to enhance bis-electrophile-induced mutagenesis. These results are similar to those found with the cross-link candidate glyceraldehyde 3-phosphate dehydrogenase (GAPDH) [ Loecken , E. M. and Guengerich , F. P. ( 2008 ) Chem. Res. Toxicol. 21 , 453 - 458 ], but in contrast to GAPDH, histone H2b bound DNA with even higher affinity than AGT. The extent of DNA cross-linking of isolated histone H2b was similar to that of AGT, suggesting that differences in postcross-linking events explain the difference in mutagenesis.

  19. Effects of cross-linking type II collagen-GAG scaffolds on chondrogenesis in vitro: dynamic pore reduction promotes cartilage formation.

    Science.gov (United States)

    Vickers, Scott M; Squitieri, Lee S; Spector, Myron

    2006-05-01

    Articular cartilage tissue-engineering investigations often implement bioassays for chondrogenesis in vitro using articular chondrocytes or mesenchymal stem cells in cell pellets that contract with time in culture, suggesting an association between the processes of contraction of the cell pellet and cartilage formation. The objective of the present study was to investigate this relationship further using adult canine articular chondrocyte-seeded type II collagen-GAG scaffolds. The collagen-GAG scaffolds were chemically cross-linked to achieve a range of cross-link densities. Chondrocyte-seeded scaffolds of varying cross-link densities were then cultured for 2 weeks to evaluate the effect of crosslink density on scaffold contraction and chondrogenesis. Scaffolds with low cross-link densities experienced cell-mediated contraction, increased cell number densities, a greater degree of chondrogenesis (viz., chondrocytic morphology of cells, synthesis of type II collagen), and an apparent increase in the rate of degradation of the scaffold compared to more highly cross-linked scaffolds that resisted cellular contraction. The results of this study suggest the promise of "dynamic pore reduction" for scaffolds for articular cartilage tissue engineering. In this approach, scaffolds would have an initial pore diameter large enough to facilitate cell seeding and a mechanical stiffness low enough to allow for cell-mediated contraction to yield a reduced pore volume to favor chondrogenesis. This approach may provide a useful alternative to traditional means of increasing cell number density and retention of synthesized molecules that promote cartilage formation in tissue-engineered constructs.

  20. Analysis of nidogen-1/laminin γ1 interaction by cross-linking, mass spectrometry, and computational modeling reveals multiple binding modes.

    Directory of Open Access Journals (Sweden)

    Philip Lössl

    Full Text Available We describe the detailed structural investigation of nidogen-1/laminin γ1 complexes using full-length nidogen-1 and a number of laminin γ1 variants. The interactions of nidogen-1 with laminin variants γ1 LEb2-4, γ1 LEb2-4 N836D, γ1 short arm, and γ1 short arm N836D were investigated by applying a combination of (photo-chemical cross-linking, high-resolution mass spectrometry, and computational modeling. In addition, surface plasmon resonance and ELISA studies were used to determine kinetic constants of the nidogen-1/laminin γ1 interaction. Two complementary cross-linking strategies were pursued to analyze solution structures of laminin γ1 variants and nidogen-1. The majority of distance information was obtained with the homobifunctional amine-reactive cross-linker bis(sulfosuccinimidylglutarate. In a second approach, UV-induced cross-linking was performed after incorporation of the diazirine-containing unnatural amino acids photo-leucine and photo-methionine into laminin γ1 LEb2-4, laminin γ1 short arm, and nidogen-1. Our results indicate that Asn-836 within laminin γ1 LEb3 domain is not essential for complex formation. Cross-links between laminin γ1 short arm and nidogen-1 were found in all protein regions, evidencing several additional contact regions apart from the known interaction site. Computational modeling based on the cross-linking constraints indicates the existence of a conformational ensemble of both the individual proteins and the nidogen-1/laminin γ1 complex. This finding implies different modes of interaction resulting in several distinct protein-protein interfaces.

  1. The basis for a second-generation highly cross-linked UHMWPE.

    Science.gov (United States)

    Dumbleton, John H; D'Antonio, James A; Manley, Michael T; Capello, William N; Wang, Aiguo

    2006-12-01

    Highly cross-linked ultra-high molecular weight polyethylene (UHMWPE) decreases wear at the hip by more than 50% compared with conventional UHMWPE. However, melted highly cross-linked polyethylene may be susceptible to fatigue cracking, and annealed highly cross-linked polyethylene may be susceptible to in vivo oxidation. The second-generation highly cross-linked UHMWPE (X3 HXPE) uses a sequential irradiation and annealing process. It preserves mechanical strength properties and has the highest survivorship in functional fatigue testing. The free radical content is low, and its performance under accelerated aging is the same as virgin UHMWPE. Hip simulator studies with 32-mm acetabular components demonstrated 97% wear reduction compared with conventional UHMWPE, and 62% compared with a clinically successful first-generation annealed highly cross-linked polyethylene. The crystallinity, density, and tensile strength of the X3 HXPE material was unchanged by oxidative challenge. X3 HXPE material articulating on cobalt-chromium alloy yields a volumetric wear rate very similar to that of metal-on-metal articulations, but eliminates the concerns of metal ion release. Wear particles generated from the X3 HXPE were the same size as those produced from conventional UHMWPE. Preliminary results suggest X3 HXPE can be used for cups larger than 36 mm.

  2. 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. Copyright © 2015 Elsevier Ltd. All rights reserved.

  3. Mechanical properties and biocompatibility of in situ enzymatically cross-linked gelatin hydrogels.

    Science.gov (United States)

    Alarake, Nada Z; Frohberg, Patrick; Groth, Thomas; Pietzsch, Markus

    2017-05-09

    Gelatin, a degraded collagen, has been widely used as a scaffolding material in tissue engineering applications. In this work, we aimed at the development of in situ, cross-linking, cytocompatible hydrogels by the use of transglutaminase as a cross-linker for potential application in the regeneration of tissues. Hydrogels were prepared from gelatin of different concentrations and bloom degree (175 (G175) or 300 (G300) bloom gelatin) and cross-linked with various amounts of microbial transglutaminase (mTG) at 37°C. Mechanical properties and cross-linking degree were studied by rheology and swelling experiments. Four hydrogels with different stiffness were selected for studies with embedded human adipose-derived stem cells (hASCs). Hydrogels were obtained with storage modulus (G') values between 11 (±1) Pa and 1,800 (±200) Pa with gelation times between 80 (±6) and 450 (±36) seconds. G300 cross-linked gelatin hydrogels displayed higher gel stiffness, lower swelling ratio and gelled more rapidly compared to the hydrogels prepared from G175. Stiffer hydrogels (50 and 200 Pa) showed greater ability to support the proliferation of hASCs than softer ones (11 and 30 Pa). The highest cell proliferation was observed with a hydrogel of 200 Pa modulus. Overall, transglutaminase cross-linked gelatin hydrogels might be suitable as injectable hydrogels for the engineering of musculoskeletal and other types of connective tissues.

  4. Usage of polarization-sensitive optical coherence tomography for investigation of collagen cross-linking

    Science.gov (United States)

    Ju, Myeong Jin; Tang, Shuo

    2015-04-01

    To investigate morphological alternation in corneal stroma induced by collagen cross-linking (CXL) treatment, polarization-sensitive optical coherence tomography (PS-OCT) capable of providing scattering, phase retardation, and degree of polarization uniformity (DOPU) images were employed on fresh bovine cornea. Significant corneal thickness reduction was observed after the CXL procedure, and its variation was quantitatively analyzed. From the scattering contrast, a hyperscattering region was observed in the anterior of the cornea immediately after the CXL procedure and its range increased with time. Within the scattering region, a slow increase was observed in the phase retardation image, and a discriminable characteristic was found in the DOPU image. A global threshold value was empirically determined from the averaged DOPU depth profile in order to locate the effective cross-linking depth. In addition to the standard protocol, an accelerated CXL procedure shortening the treatment time with higher intensity of ultraviolet-A (UV-)A power was also performed. From the measurement results after the two different CXL protocols, different cross-linking aspects were found and their difference was discussed in terms of the effectiveness of cross-linking. Based on this study, we believe that PS-OCT could be a promising optical imaging modality to evaluate the progression and effectiveness of the riboflavin/UV-A induced corneal collagen cross-linking.

  5. Regeneration of rat calvarial defects using a bioabsorbable membrane technique: influence of collagen cross-linking.

    Science.gov (United States)

    Brunel, G; Piantoni, P; Elharar, F; Benqué, E; Marin, P; Zahedi, S

    1996-12-01

    The aim of the present study was to examine the influence of cross-linking on collagen membranes used for guided bone regeneration of calvarial defects in rats. In 48 Wistar rats, divided equally into 4 groups, 1 control and 3 experimental, standardized transosseous circular calvarial defects were made midparietally. In the control group, the defect was only covered by the soft tissue flap while in the 3 experimental groups, 3 differently cross-linked collagen membranes were interposed between the osseous defect and the overlying flap before suturing. The healing was assessed at 10, 20, and 30 days after surgery. The results showed that augmenting the degree of collagen cross-linking diminished the membrane resorption rate. Compared to the sham-operated sites, the membrane protected defects showed significantly more bone regeneration (on average 4 times more) as attested by histology and measured by histomorphometric analysis. Although the bone gain seemed to augment with increasing degrees of cross-linking, the results within the 3 experimental groups were not statistically different. Since longer healing periods might have been necessary to substantiate results within experimental groups, a study is currently undertaken to evaluate this aspect. This study demonstrated the efficacy of collagen membranes in guiding bone regeneration, as well as the importance of the type and degree of cross-linking.

  6. Cross-linked collagen sponges loaded with plant polyphenols with inhibitory activity towards chronic wound enzymes.

    Science.gov (United States)

    Antonio, Francesko; Guillem, Rocasalbas; Sonia, Touriño; Clara, Mattu; Piergiorgio, Gentile; Valeria, Chiono; Gianluca, Ciardelli; Tzanov, Tzanko

    2011-10-01

    Collagen sponges loaded with polyphenols from Hamamelis virginiana were investigated as active materials for chronic wound dressings, evaluating in vitro the inhibition of two major enzymes that impair the wound healing process - myeloperoxidase (MPO) and collagenase. Prior to polyphenols loading, collagen was cross-linked with genipin to improve its biostability. The effect of genipin cross-linking and polyphenol concentration in the development of mechanically and enzymatically stable sponges was studied. The tensile strength of the cross-linked collagen increased with the increase of the cross-linking degree, coupled to decrease in the elongation and the swelling capacity of the sponges. The stability of the sponges to collagenase digestion reached maximum when 1 mM genipin was used. However, the biostability decreased more than 10-fold after loading the sponges with polyphenols (0.5 mg/mL), nevertheless, this effect was partially overcome using higher concentration of polyphenols (1 and 2 mg/mL) to inhibit collagenase. Moreover, the polyphenols released from the sponges were sufficient for complete inhibition of MPO activity. No considerable cytotoxicity of the genipin cross-linked collagen loaded with polyphenols was observed evaluating the NIH 3T3 fibroblasts viability. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  7. p-Stilbazole moieties as artificial base pairs for photo-cross-linking of DNA duplex.

    Science.gov (United States)

    Kashida, Hiromu; Doi, Tetsuya; Sakakibara, Takumi; Hayashi, Takamitsu; Asanuma, Hiroyuki

    2013-05-29

    In this study, we report a photo-cross-linking reaction between p-stilbazole moieties. p-Stilbazoles were introduced into base-paring positions of complementary DNA strands. The [2 + 2] photocycloaddition reaction occurred rapidly upon light irradiation at 340 nm. Consequently, duplex was cross-linked and highly stabilized after 3 min irradiation. The CD spectrum of the cross-linked duplex indicated that the B-form double-helical structure was not severely distorted. NMR analysis revealed only one conformation of the duplex prior to UV irradiation, whereas two diastereomers were detected after the photo-cross-linking reaction. Before UV irradiation, p-stilbazole can adopt two different stacking modes because of rotation around the single bond between the phenyl and vinyl groups; these conformations cannot be discriminated on the NMR time scale due to rapid interconversion. However, photo-cross-linking fixed the conformation and enabled discrimination both by NMR and HPLC. The artificial base pair of p-methylstilbazolium showed almost the same reactivity as p-stilbazole, indicating that positive charge does not affect the reactivity. When a natural nucleobase was present in the complementary strand opposite p-stilbazole, the duplex was significantly destabilized relative to the duplex with paired p-stilbazole moieties and no photoreaction occurred between p-stilbazole and the nucleobase. The p-stilbazole pair has potential as a "third base pair" for nanomaterials due to its high stability and superb orthogonality.

  8. Cross-Linked Amylose Bio-Plastic: A Transgenic-Based Compostable Plastic Alternative

    Science.gov (United States)

    Sagnelli, Domenico; Kemmer, Gerdi Christine; Holse, Mette; Hebelstrup, Kim H.; Bao, Jinsong; Stelte, Wolfgang; Bjerre, Anne-Belinda; Blennow, Andreas

    2017-01-01

    Bio-plastics and bio-materials are composed of natural or biomass derived polymers, offering solutions to solve immediate environmental issues. Polysaccharide-based bio-plastics represent important alternatives to conventional plastic because of their intrinsic biodegradable nature. Amylose-only (AO), an engineered barley starch with 99% amylose, was tested to produce cross-linked all-natural bioplastic using normal barley starch as a control. Glycerol was used as plasticizer and citrate cross-linking was used to improve the mechanical properties of cross-linked AO starch extrudates. Extrusion converted the control starch from A-type to Vh- and B-type crystals, showing a complete melting of the starch crystals in the raw starch granules. The cross-linked AO and control starch specimens displayed an additional wide-angle diffraction reflection. Phospholipids complexed with Vh-type single helices constituted an integrated part of the AO starch specimens. Gas permeability tests of selected starch-based prototypes demonstrated properties comparable to that of commercial Mater-Bi© plastic. The cross-linked AO prototypes had composting characteristics not different from the control, indicating that the modified starch behaves the same as normal starch. The data shows the feasibility of producing all-natural bioplastic using designer starch as raw material. PMID:28973963

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

    Science.gov (United States)

    Yang, Chen-Guang; Wang, Mou-Hua; Zhang, Ming-Xing; Li, Xiao-Hu; Wang, Hong-Long; Xing, Zhe; Ye, Lin-Feng; Wu, Guo-Zhong

    2016-12-07

    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.

  10. Cross-Linked Amylose Bio-Plastic: A Transgenic-Based Compostable Plastic Alternative

    Directory of Open Access Journals (Sweden)

    Domenico Sagnelli

    2017-09-01

    Full Text Available Bio-plastics and bio-materials are composed of natural or biomass derived polymers, offering solutions to solve immediate environmental issues. Polysaccharide-based bio-plastics represent important alternatives to conventional plastic because of their intrinsic biodegradable nature. Amylose-only (AO, an engineered barley starch with 99% amylose, was tested to produce cross-linked all-natural bioplastic using normal barley starch as a control. Glycerol was used as plasticizer and citrate cross-linking was used to improve the mechanical properties of cross-linked AO starch extrudates. Extrusion converted the control starch from A-type to Vh- and B-type crystals, showing a complete melting of the starch crystals in the raw starch granules. The cross-linked AO and control starch specimens displayed an additional wide-angle diffraction reflection. Phospholipids complexed with Vh-type single helices constituted an integrated part of the AO starch specimens. Gas permeability tests of selected starch-based prototypes demonstrated properties comparable to that of commercial Mater-Bi© plastic. The cross-linked AO prototypes had composting characteristics not different from the control, indicating that the modified starch behaves the same as normal starch. The data shows the feasibility of producing all-natural bioplastic using designer starch as raw material.

  11. Cross-Linked Amylose Bio-Plastic: A Transgenic-Based Compostable Plastic Alternative.

    Science.gov (United States)

    Sagnelli, Domenico; Hooshmand, Kourosh; Kemmer, Gerdi Christine; Kirkensgaard, Jacob J K; Mortensen, Kell; Giosafatto, Concetta Valeria L; Holse, Mette; Hebelstrup, Kim H; Bao, Jinsong; Stelte, Wolfgang; Bjerre, Anne-Belinda; Blennow, Andreas

    2017-09-30

    Bio-plastics and bio-materials are composed of natural or biomass derived polymers, offering solutions to solve immediate environmental issues. Polysaccharide-based bio-plastics represent important alternatives to conventional plastic because of their intrinsic biodegradable nature. Amylose-only (AO), an engineered barley starch with 99% amylose, was tested to produce cross-linked all-natural bioplastic using normal barley starch as a control. Glycerol was used as plasticizer and citrate cross-linking was used to improve the mechanical properties of cross-linked AO starch extrudates. Extrusion converted the control starch from A-type to Vh- and B-type crystals, showing a complete melting of the starch crystals in the raw starch granules. The cross-linked AO and control starch specimens displayed an additional wide-angle diffraction reflection. Phospholipids complexed with Vh-type single helices constituted an integrated part of the AO starch specimens. Gas permeability tests of selected starch-based prototypes demonstrated properties comparable to that of commercial Mater-Bi© plastic. The cross-linked AO prototypes had composting characteristics not different from the control, indicating that the modified starch behaves the same as normal starch. The data shows the feasibility of producing all-natural bioplastic using designer starch as raw material.

  12. The effect of ionotropic gelation residence time on alginate cross-linking and properties.

    Science.gov (United States)

    Patel, Mitulkumar A; AbouGhaly, Mohamed H H; Schryer-Praga, Jacqueline V; Chadwick, Keith

    2017-01-02

    The ability to engineer biocompatible polymers with controllable properties is highly desirable. One such approach is to cross-link carbohydrate polymers using ionotropic gelation (IG). Previous studies have investigated the effect of curing time on alginate cross-linking. Herein, we discuss a novel study detailing the effect of IG residence time (IGRT) on the cross-linking of alginate with calcium ions (Ca2+) along with water migration (syneresis) and their subsequent impact on the pharmaceutical properties of alginate particles. IGRT was shown to have a significant effect on particle size, porosity, density, mechanical strength and swelling of calcium alginate particles as well as drug release mechanism. Furthermore, we describe a novel application of electron dispersive spectroscopy (EDS), in conjunction with Fourier Transform- infra red (FT-IR) spectroscopy, to analyze and monitor the changes in Ca2+ concentration during cross-linking. A simple procedure to determine the concentration and distribution of the surface and internal Ca2+ involved in alginate cross-linking was successfully developed. Copyright © 2016 Elsevier Ltd. All rights reserved.

  13. Biodegradable Chitosan-Based Ambroxol Hydrochloride Microspheres: Effect of Cross-Linking Agents

    Science.gov (United States)

    Gangurde, HH; Chavan, NV; Mundada, AS; Derle, DV; Tamizharasi, S

    2011-01-01

    The objective of this study was to investigate the influence of type of cross-linking method used on the properties of ambroxol hydrochloride microspheres such as encapsulation efficiency, particle size, and drug release. Microspheres were prepared by solvent evaporation technique using chitosan as a matrix-forming agent and cross-linked using formaldehyde and heat treatment. Morphological and physicochemical properties of microspheres were then investigated by scanning electron microscopy (SEM), X-ray diffractometry (XRD), differential scanning calorimetry (DSC), and Fourier-transform infrared spectroscopy (FTIR) spectroscopy. The cross-linking of chitosan takes place at the free amino group because of formation of imine bond as evidenced by FTIR. The DSC, XRD, and FTIR analysis showed that chitosan microspheres cross linked by heating were superior in properties and performance as compared to the microspheres cross-linked using formaldehyde. SEM results revealed that heat-treated microspheres were spherical, discrete having smooth, and porous structure. The particle size and encapsulation efficiencies of the prepared chitosan microspheres ranged between 10.83–24.11 μm and 39.73μ80.56%, respectively. The drug release was extended up to 12 h, and the kinetics of the drug release was obeying Higuchi kinetic proving diffusion-controlled drug release. PMID:21607049

  14. Influence of cross-linked arabinoxylans on the postprandial blood glucose response in rats.

    Science.gov (United States)

    Vogel, Barbara; Gallaher, Daniel D; Bunzel, Mirko

    2012-04-18

    Viscous dietary fibers are well established to reduce the blood glucose response to a meal. In this study, arabinoxylans, the most abundant dietary fiber in most cereals, were extracted under alkaline conditions and cross-linked by using laccase. Cross-linking of the arabinoxylans led to gel formation and increased in vitro viscosity almost 100-fold after drying and rehydration. To determine the ability of these cross-linked arabinoxylans to blunt the postprandial blood glucose curve of a meal, arabinoxylans, either native or cross-linked, and either prehydrated or not, were fed to rats as part of a meal, and blood glucose was monitored at intervals after the meal. Cellulose, a nonviscous fiber, served as a control. Cross-linked, but not native, arabinoxylans significantly reduced the area under the blood glucose time curve 5-9% relative to cellulose, indicating that they remained viscous within the gastrointestinal tract, and thus likely provide the health benefits found with other viscous fibers.

  15. Modification mechanism of sesbania gum, and preparation, property, adsorption of dialdehyde cross-linked sesbania gum.

    Science.gov (United States)

    Tang, Hongbo; Gao, Shiqi; Li, Yanping; Dong, Siqing

    2016-09-20

    This paper studied the modification mechanism of Sesbania gum (SG) by means of the variations in the numbers of surface hydroxyl groups on the granules, Schiff's agent coloration of aldehyde groups, Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD), energy dispersive spectrum (EDS), etc., and also examined the preparation, property and adsorption of dialdehyde cross-linked sesbania gum (DCLSG). The results showed that the surface hydroxyl numbers of cross-linked sesbania gum (CLSG) decreased with increasing the cross-linking degree. The distribution of the aldehyde groups on the DCLSG particles was nonuniform because most of aldehyde groups mainly located on the edge of particles. The cross-linking occurred only on the surface of SG particles. The oxidization occurred not only on the surface of SG particles, but also in the interior of particles. The cross-linking or oxidization changed the thermal properties, and reduced the swelling power, viscosity, alkali and acid resistance of SG. Copyright © 2016 Elsevier Ltd. All rights reserved.

  16. DNA-protein, DNA interstrand cross-links induced by camphoramine chloroacetic platinum in vitro.

    Science.gov (United States)

    Wang, L G; Zeng, H

    1989-05-01

    Effects of camphoramine chloroacetic platinum (CCP) on DNA migration and transcription, DNA-protein and DNA interstrand cross-links induced by CCP were investigated by using agarose gel electrophoresis, alkaline elution and enzymatic techniques, respectively. Chromosome break down and migration alteration of DNa modified by CCP were observed. Plasmid pAR 436 DNA transcription was also blocked when the DNA was treated with CCP. The cross-links took place 8 h after HeLa cells were exposed to CCP 10 mumol/L and higher number of cross-links were obtained after treatment with the agent 20 mumol/L. The number of cross-links was also found to be decreased when the cell lysis was digested with proteinase K. These results suggest that CCP can also induce DNA-protein cross links. Enzymatic studies indicated that CCP preferentially attacks guanine in DNA and restriction enzymes are unable to cleave G-platinated at interval of one base to the restriction sequence.

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

    Science.gov (United States)

    Sarika, P R; Cinthya, Kuriakose; Jayakrishnan, A; Anilkumar, P R; James, Nirmala Rachel

    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. Copyright © 2014 Elsevier B.V. All rights reserved.

  18. 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.

  19. 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. Copyright © 2014 Elsevier Ltd. All rights reserved.

  20. Effects of collagen cross-linking on the interlamellar cohesive strength of porcine cornea.

    Science.gov (United States)

    Tao, Chen; Sun, Yong; Zhou, Chuanqing; Han, Zhaolong; Ren, Qiushi

    2013-02-01

    To determine the interlamellar cohesive strength (ICS) of porcine cornea before and after collagen cross-linking using riboflavin and ultraviolet A (UVA) irradiation. Corneal flaps, 130 μm thick, were created with a microkeratome. Cross-linking was accomplished with 0.1% riboflavin and UVA irradiation for 30 minutes (3 mW/cm, 5.4 J/cm) at a distance of 10 mm. Two experiments were performed. (1) The maximal ICS between corneal flap and the stroma was determined and histological examination was performed. (2) The mean stromal ICS was measured. Untreated eyes served as controls in all experiments. The mean maximum flap-stroma ICS was 0.088 ± 0.046 N/mm in the experimental group and 0.012 ± 0.004 N/mm in the control group (P = 0.009). In experiment 2, incomplete (2 mm long) corneal flaps were used and the mean stromal ICS was 0.750 ± 0.077 N/mm in the experimental group and 0.338 ± 0.046 N/mm in the control group (P cornea with cross-linking, but a smooth separation surface in the cornea without cross-linking. Collagen cross-linking activated by riboflavin/UVA increases ICS in porcine corneas.

  1. 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.

  2. The effects of different crossing-linking conditions of genipin on type I collagen scaffolds: an in vitro evaluation.

    Science.gov (United States)

    Zhang, Xiujie; Chen, Xueying; Yang, Ting; Zhang, Naili; Dong, Li; Ma, Shaoying; Liu, Xiaoming; Zhou, Mo; Li, Baoxing

    2014-12-01

    The purpose of this paper is to analyze the properties of fabricating rat tail type I collagen scaffolds cross-linked with genipin under different conditions. The porous genipin cross-linked scaffolds are obtained through a two step freeze-drying process. To find out the optimal cross-link condition, we used different genipin concentrations and various cross-linked temperatures to prepare the scaffolds in this study. The morphologies of the scaffolds were characterized by scanning electron microscope, and the mechanical properties of the scaffolds were evaluated under dynamic compression. Additionally, the cross-linking degree was assessed by ninhydrin assay. To investigate the swelling ratio and the in vitro degradation of the collagen scaffold, the tests were also carried out by immersion of the scaffolds in a PBS solution or digestion in a type I collagenase respectively. The morphologies of the non-cross-linked scaffolds presented a lattice-like structure while the cross-linked ones displayed a sheet-like framework. The morphology of the genipin cross-linked scaffolds could be significantly changed by either increasing genipin concentration or the temperature. The swelling ratio of each cross-linked scaffold was much lower than that of the control (non-cross-linked).The ninhydrin assay demonstrated that the higher temperature and genipin concentration could obviously increase the cross-linking efficiency. The in vitro degradation studies indicated that genipin cross-linking can effectively elevate the biostability of the scaffolds. The biocompatibility and cytotoxicity of the scaffolds was evaluated by culturing rat chondrocytes on the scaffold in vitro and by MTT. The results of MTT and the fact that the chondrocytes adhered well to the scaffolds demonstrated that genipin cross-linked scaffolds possessed an excellent biocompatibility and low cytotoxicity. Based on these results, 0.3 % genipin concentrations and 37 °C cross-linked temperatures are

  3. 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. Copyright © 2014. Published by Elsevier SAS.

  4. Dialing in the Ratio of Covalent and Coordination Cross-links in Self-healing Hydrogels

    DEFF Research Database (Denmark)

    Andersen, Amanda; Krogsgaard, Marie; Birkedal, Henrik

    and as these impacts the abovementioned properties, it is of great interest to control the degree of which these are present; i.e. controlling the degree of catechol oxidation. Until now, the catechols participating in the two cross-linking types have been the same. This way the actual ratio between the two types......Supported by the diverse chemistry of the catechol group, pH-responsive, mussel-inspired hydrogels has drawn considerable attention due to the presence of reversible catecholato–metal bonds, which incorporates self-healing properties. Through oxidation, catechols also participates in covalent cross-linking...... cannot be either predefined or controlled, as it is determined by the oxidation rate within the hydrogel. Here, we report hydrogels in which the catechols participating in reversible (oxidation resistant catechol) and irreversible (classical catechol) cross-links are separated, enabling one to predefine...

  5. xiNET: Cross-link Network Maps With Residue Resolution*

    Science.gov (United States)

    Combe, Colin W.; Fischer, Lutz; Rappsilber, Juri

    2015-01-01

    xiNET is a visualization tool for exploring cross-linking/mass spectrometry results. The interactive maps of the cross-link network that it generates are a type of node-link diagram. In these maps xiNET displays: (1) residue resolution positional information including linkage sites and linked peptides; (2) all types of cross-linking reaction product; (3) ambiguous results; and, (4) additional sequence information such as domains. xiNET runs in a browser and exports vector graphics which can be edited in common drawing packages to create publication quality figures. Availability: xiNET is open source, released under the Apache version 2 license. Results can be viewed by uploading data to http://crosslinkviewer.org/ or by downloading the software from http://github.com/colin-combe/crosslink-viewer and running it locally. PMID:25648531

  6. xiNET: cross-link network maps with residue resolution.

    Science.gov (United States)

    Combe, Colin W; Fischer, Lutz; Rappsilber, Juri

    2015-04-01

    xiNET is a visualization tool for exploring cross-linking/mass spectrometry results. The interactive maps of the cross-link network that it generates are a type of node-link diagram. In these maps xiNET displays: (1) residue resolution positional information including linkage sites and linked peptides; (2) all types of cross-linking reaction product; (3) ambiguous results; and, (4) additional sequence information such as domains. xiNET runs in a browser and exports vector graphics which can be edited in common drawing packages to create publication quality figures. xiNET is open source, released under the Apache version 2 license. Results can be viewed by uploading data to http://crosslinkviewer.org/ or by downloading the software from http://github.com/colin-combe/crosslink-viewer and running it locally. © 2015 by The American Society for Biochemistry and Molecular Biology, Inc.

  7. 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.

  8. 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.

  9. Novel polymer electrolytes for lithium ion batteries based on cross linked polysiloxanes

    Energy Technology Data Exchange (ETDEWEB)

    Kloss, S.; Gentschev, A.C.; Hiller, M.; Hoffmann-zu Hoene, A.; Jeschke, S.; Kogel, M.; Schuermann, T.; Stolina, R.; Burjanadze, M. [Muenster Univ. (Germany). Inst. fuer Anorganische und Analytische Chemie; Wiemhoefer, H.D.

    2010-07-01

    In this work we present a promising salt-in-polymer system for application as safe electrolyte in lithium ion batteries. It ws based on a cross linked polysiloxane with good mechanical and thermal stability. We used a particular cross-linking variant based on the introduction of 15% of the side groups at the siloxane backbone with terminal alcohol functions. These are easily cross linked by transesterification with alkoxysilanes. Impedance spectroscopy served to measure the ionic conductivity of the corresponding membranes as a function of temperature and salt concentration. The maximum room temperature conductivity of 3.2.10{sup -5} S/cm was observed at a doping level of 20 wt.% LiTFSI (lithium bis(trifluoromethanesulfonyl)imide). (orig.)

  10. Carbon Nanofiber Incorporated Silica Based Aerogels with Di-Isocyanate Cross-Linking

    Science.gov (United States)

    Vivod, Stephanie L.; Meador, Mary Ann B.; Capadona, Lynn A.; Sullivan, Roy M.; Ghosn, Louis J.; Clark, Nicholas; McCorkle, Linda

    2008-01-01

    Lightweight materials with excellent thermal insulating properties are highly sought after for a variety of aerospace and aeronautic applications. (1) Silica based aerogels with their high surface area and low relative densities are ideal for applications in extreme environments such as insulators for the Mars Rover battery. (2) However, the fragile nature of aerogel monoliths prevents their widespread use in more down to earth applications. We have shown that the fragile aerogel network can be cross-linked with a di-isocyanate via amine decorated surfaces to form a conformal coating. (3) This coating reinforces the neck regions between secondary silica particles and significantly strengthens the aerogels with only a small effect on density or porosity. Scheme 1 depicts the cross-linking reaction with the di-isocyanate and exhibits the stages that result in polymer cross-linked aerogel monoliths.

  11. Measuring NLR Oligomerization I: Size Exclusion Chromatography, Co-immunoprecipitation, and Cross-Linking.

    Science.gov (United States)

    Khare, Sonal; Radian, Alexander D; Dorfleutner, Andrea; Stehlik, Christian

    2016-01-01

    Oligomerization of nod-like receptors (NLRs) can be detected by several biochemical techniques dependent on the stringency of protein-protein interactions. Some of these biochemical methods can be combined with functional assays, such as caspase-1 activity assay. Size exclusion chromatography (SEC) allows separation of native protein lysates into different sized complexes by fast protein liquid chromatography (FPLC) for follow-up analysis. Using co-immunoprecipitation (co-IP), combined with SEC or on its own, enables subsequent antibody-based purification of NLR complexes and associated proteins, which can then be analyzed by immunoblot and/or subjected to functional caspase-1 activity assay. Chemical cross-linking covalently joins two or more molecules, thus capturing the oligomeric state with high sensitivity and stability. Apoptosis-associated speck-like protein containing a caspase activation domain (ASC) oligomerization has been successfully used as readout for NLR or AIM2-like receptor (ALR) inflammasome activation in response to various pathogen- or damage-associated molecular patterns (PAMPs or DAMPs) in human and mouse macrophages and THP-1 cells. Here, we provide a detailed description of the methods used for NLRP7 oligomerization in response to infection with Staphylococcus aureus (S. aureus) in primary human macrophages, co-immunoprecipitation and immunoblot analysis of NLRP7 and NLRP3 inflammasome complexes, as well as caspase-1 activity assays. Also, ASC oligomerization is shown in response to dsDNA, LPS/ATP, and LPS/nigericin in mouse bone marrow-derived macrophages (BMDMs) and/or THP-1 cells or human primary macrophages.

  12. Efficient Gene Transfection into Mammalian Cells Mediated by Cross-linked Polyethylenimine

    Directory of Open Access Journals (Sweden)

    Zichun Hua

    2007-02-01

    Full Text Available 25 kDa branched polyethylenimine (PEI has successfully been used for in vitroand in vivo gene delivery approaches, but it is cytotoxic. Smaller PEIs are usually non-cytotoxic but less efficient. In order to enhance the gene delivery efficiency and minimizecytotoxicity of PEI, we explored to synthesize cross-linked PEIs with degradable bonds byreacting amines of small branched 2000 Da PEI with small diacrylate (1,4-butanedioldiacrylate or ethyleneglycol dimethacrylate for 2-6 hours. The efficiency of the cross-linkedPEIs during in vitro delivering plasmid containing enhanced green fluorescent protein(EGFP gene reporter and their cytotoxicity were assessed in melanoma B16F10 cell andother cell lines. In vivo gene delivery efficiency was evaluated by direct injection delivery ofthe EGFP plasmid/ cross-linked PEI complexes into mice and by estimating the EGFPexpression in animal muscles. Compared to commercially available 25-kDa branched PEI,the cross-linked PEIs reported here could mediate more efficient expression of reporter genethan the 25-kDa PEI control, 19-fold more efficiently in B16F10 cells, 17-fold in 293T cells, 2.3-fold in 3T3 cells, and they exhibited essentially nontoxic at their optimized condition for gene delivery. Furthermore the transfection activity of polyplexs was preserved in the presence of serum proteins. The muscle transfected with the cross-linked PEI prepared here exhibited normal morphology and excellent gene expression. The cross-linked PEIs reported here were evidently more efficient than the commercial 25-kD PEI control and had less cytotoxicity in gene delivery in vitro and in vivo.

  13. Cross-Linked and Biodegradable Polymeric System as a Safe Magnetic Resonance Imaging Contrast Agent.

    Science.gov (United States)

    Luo, Qiang; Xiao, Xueyang; Dai, Xinghang; Duan, Zhenyu; Pan, Dayi; Zhu, Hongyan; Li, Xue; Sun, Ling; Luo, Kui; Gong, Qiyong

    2018-01-17

    Owing to the low efficacy of clinically used small-molecule gadolinium (Gd)-based magnetic resonance imaging (MRI) agents, we designed and explored biodegradable macromolecular conjugates as MRI contrast agents. The linear polymeric structure and core-cross-linked formulation possessed different characteristics and features, so we prepared and comparatively studied the two kinds of Gd-based N-(2-hydroxypropyl) methacrylamide (HPMA) polymeric systems (the core-cross-linked pHPMA-DOTA-Gd and the linear one) using the clinical agent diethylene-triamine pentaacetic acid-Gd(III) (DTPA-Gd) as a control. This study was aimed to find the optimal polymeric formulation as a biocompatible and efficient MRI contrast agent. The high molecular weight (MW, 181 kDa) and core-cross-linked copolymer was obtained via the cross-linked block linear copolymer and could be degraded to low-MW segments (29 kDa) in the presence of glutathione (GSH) and cleaned from the body. Both core-cross-linked and linear pHPMA-DOTA-Gd copolymers displayed 2-3-fold increased relaxivity (r1 value) than that of DTPA-Gd. Animal studies demonstrated that two kinds of macromolecular systems led to much longer blood circulation time, higher tumor accumulation, and much higher signal intensity compared with the linear and clinical ones. Finally, in vivo and in vitro toxicity studies indicated that the two macromolecular agents had great biocompatibility. Therefore, we performed preliminary but important studies on the Gd-based HPMA polymeric systems as biocompatible and efficient MRI contrast agents and found that the biodegradable core-cross-linked pHPMA-DOTA-Gd copolymer might have greater benefits for the foreground.

  14. 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

  15. 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

  16. Thermal conductivity of cross-linked polyethylene from molecular dynamics simulation

    Science.gov (United States)

    Xiong, Xue; Yang, Ming; Liu, Changlin; Li, Xiaobo; Tang, Dawei

    2017-07-01

    The thermal conductivity of cross-linked bulk polyethylene is studied using molecular dynamics simulation. The atomic structure of the cross-linked polyethylene (PEX) is generated through simulated bond formation using LAMMPS. The thermal conductivity of PEX is studied with different degrees of crosslinking, chain length, and tensile strain. Generally, the thermal conductivity increases with the increasing degree of crosslinking. When the length of the primitive chain increases, the thermal conductivity increases linearly. When the polymer is stretched along one direction, the thermal conductivity increases in the stretched direction and decreases in the direction perpendicular to it. However, the thermal conductivity varies slightly when the polymer is stretched in three directions simultaneously.

  17. Intrastromal keratoplasy with segment implantation in combination with corneal collagen cross-linking

    OpenAIRE

    Z.I. Moroz; S.B. Izmaylova; S.L. Legkikh; D.E. Merzlov

    2013-01-01

    ABSTRACT Purpose. To evaluate the efficacy of intrastromal keratoplasy with intra-corneal ring segment (ICRS) implantation in combination with corneal collagen cross-linking in the treatment of early and advanced keratoconus. Material and methods. In the study 183 eyes with keratoconus were included: 87 eyes (47.5%) with the stage II and 96 eyes (32.5%) with stage III. The ICRS were implanted as a first step of treatment in 98 cases (53.5%), cross-linking was performed 3 months late...

  18. Dynamic OCT measurements of corneal biomechanical properties after UV cross-linking in the rabbit

    Science.gov (United States)

    Twa, Michael D.; Li, Jiasong; Manapuram, Ravi K.; Menodiado, Floredes M.; Singh, Manmohan; Aglyamov, Salavat; Emelianov, Stanislav; Larin, Kirill V.

    2013-03-01

    Structural properties of the cornea determine the shape and optical quality of the eye. Keratoconus, a structural degeneration of the cornea, is often treated with UV-induced collagen cross-linking to increase tissue resistance to further deformation and degeneration. Optimal treatments would be customized to the individual and consider preexisting structural properties as well as the effects induced by treatment and this requires the capability to noninvasively measure tissue properties. The purpose of this study is to use novel methods of optical elastography to study the effects of UV-induced corneal collagen cross-linking in the rabbit eye. Low-amplitude (corneal stiffness.

  19. 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...

  20. 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

    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....

  1. 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.

  2. A Hyper-cross-linked Polynaphthalene Semiconductor with Excellent Visible-Light Photocatalytic Performance in the Degradation of Organic Dyes.

    Science.gov (United States)

    Zhang, Lei; Huang, Xin-Hua; Hu, Jin-Song; Song, Jian; Kim, Il

    2017-02-28

    Hyper-cross-linked polynaphthalene nanoparticles (PNNs) capable of catalyzing the degradation of organic pollutants upon exposure to visible light have been developed. The nascent and metal-free PNNs with a porous structure, high specific surface area, and narrow bandgap are chemically and thermally stable in the catalytic system, which make it promising as a kind of excellent photocatalytic material compared to conventional photocatalysts. The photocatalytic activity of the as-obtained PNNs exhibits remarkable photocatalytic performance for the degradation of rhodamine B (RhB) and methyl blue (MB) under the irradiation of visible light. The easy preparation, high catalytic activity, and recyclability of the PNNs open new opportunities in the visible-light-promoted degradation of organic pollutants.

  3. Polydopamine Wrapping Silicon Cross-linked with Polyacrylic Acid as High-Performance Anode for Lithium-Ion Batteries.

    Science.gov (United States)

    Bie, Yitian; Yang, Jun; Liu, Xiaolin; Wang, Jiulin; Nuli, Yanna; Lu, Wei

    2016-02-10

    A robust silicon electrode for lithium-ion battery has been developed via prepolymerizing dopamine on silicon particle surface and then chemical binding with poly(acrylic acid) (PAA). In this favorable electrode, silicon nanoparticles are covered by a thin layer of polydopamine (PD) through firm hydrogen bonds between phenolic hydroxyl and hydroxyl, while the elastic polymer layer reacts with PAA binder to form three-dimensional cross-linked binding system. The Si@PD/PAA electrode exhibits more stable cycle performance than conventional electrodes. In the case of thick electrode, a capacity of 3.69 mA h cm(-2) and fairly good rechargeability for 80 cycles can be achieved.

  4. Polymeric molecular sieve membranes via in situ cross-linking of non-porous polymer membrane templates.

    Science.gov (United States)

    Qiao, Zhen-An; Chai, Song-Hai; Nelson, Kimberly; Bi, Zhonghe; Chen, Jihua; Mahurin, Shannon M; Zhu, Xiang; Dai, Sheng

    2014-04-16

    High-performance polymeric membranes for gas separation are attractive for molecular-level separations in industrial-scale chemical, energy and environmental processes. Molecular sieving materials are widely regarded as the next-generation membranes to simultaneously achieve high permeability and selectivity. However, most polymeric molecular sieve membranes are based on a few solution-processable polymers such as polymers of intrinsic microporosity. Here we report an in situ cross-linking strategy for the preparation of polymeric molecular sieve membranes with hierarchical and tailorable porosity. These membranes demonstrate exceptional performance as molecular sieves with high gas permeabilities and selectivities for smaller gas molecules, such as carbon dioxide and oxygen, over larger molecules such as nitrogen. Hence, these membranes have potential for large-scale gas separations of commercial and environmental relevance. Moreover, this strategy could provide a possible alternative to 'classical' methods for the preparation of porous membranes and, in some cases, the only viable synthetic route towards certain membranes.

  5. Polymeric molecular sieve membranes via in situ cross-linking of non-porous polymer membrane templates

    Science.gov (United States)

    Qiao, Zhen-An; Chai, Song-Hai; Nelson, Kimberly; Bi, Zhonghe; Chen, Jihua; Mahurin, Shannon M.; Zhu, Xiang; Dai, Sheng

    2014-04-01

    High-performance polymeric membranes for gas separation are attractive for molecular-level separations in industrial-scale chemical, energyand environmental processes. Molecular sieving materials are widely regarded as the next-generation membranes to simultaneously achieve high permeability and selectivity. However, most polymeric molecular sieve membranes are based on a few solution-processable polymers such as polymers of intrinsic microporosity. Here we report an in situ cross-linking strategy for the preparation of polymeric molecular sieve membranes with hierarchical and tailorable porosity. These membranes demonstrate exceptional performance as molecular sieves with high gas permeabilities and selectivities for smaller gas molecules, such as carbon dioxide and oxygen, over larger molecules such as nitrogen. Hence, these membranes have potential for large-scale gas separations of commercial and environmental relevance. Moreover, this strategy could provide a possible alternative to ‘classical’ methods for the preparation of porous membranes and, in some cases, the only viable synthetic route towards certain membranes.

  6. In vivo covalent cross-linking of photon-converted rare-earth nanostructures for tumour localization and theranostics

    OpenAIRE

    Ai, Xiangzhao; Ho, Chris Jun Hui; Aw, Junxin; Attia, Amalina Binte Ebrahim; Mu, Jing; Wang, Yu; Wang, Xiaoyong; Wang, Yong; Liu, Xiaogang; Chen, Huabing; Gao, MingYuan; Chen, Xiaoyuan; Yeow, Edwin K.L.; Liu, Gang; Olivo,Malini

    2016-01-01

    The development of precision nanomedicines to direct nanostructure-based reagents into tumour-targeted areas remains a critical challenge in clinics. Chemical reaction-mediated localization in response to tumour environmental perturbations offers promising opportunities for rational design of effective nano-theranostics. Here, we present a unique microenvironment-sensitive strategy for localization of peptide-premodified upconversion nanocrystals (UCNs) within tumour areas. Upon tumour-specif...

  7. DNA Release from Fe3+ -Cross-Linked Alginate Films Triggered by Logically Processed Biomolecular Signals: Integration of Biomolecular Computing and Actuation.

    Science.gov (United States)

    Gamella, Maria; Privman, Marina; Bakshi, Saira; Melman, Artem; Katz, Evgeny

    2017-07-05

    Signal-controlled release of DNA from Fe3+ -cross-linked alginate hydrogel electrochemically deposited on an electrode surface was studied. The multiple input signals were logically processed with the help of the enzyme-biocatalyzed reactions. Boolean logic gates, OR, AND, INH, were realized with the biocatalytic reactions performed by the enzymes entrapped in the alginate film. Hydrogen peroxide produced by the enzymatic reactions resulted in the degradation of the alginate hydrogel and DNA release. The alginate degradation was facilitated by the formation of free radicals in the Fenton-type reaction catalyzed by iron cations cross-linking the alginate hydrogel. The studied approach is versatile and can be adapted to various chemical signals processed by various enzymes with differently implemented Boolean logic. This work illustrates a novel concept of functional integration of biomolecular computing and actuation. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  8. Characterization and in vitro and in vivo evaluation of cross-linked ...

    Indian Academy of Sciences (India)

    ... there is no evidence of any inflammation, any foreign body granuloma or any necrosis or hemorrhage. Tissue configuration remains unaltered after 30 days of implantation. So, it can be suggested that cross-linked CH films of above said composition can be used as implant for long term application in depression and ...

  9. 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

  10. 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

  11. Cross-Linking Treatment and Corneal Transplant in Refractory Acremonium Keratitis: Case Report.

    Science.gov (United States)

    Yagci, Ayse; Palamar, Melis; Polat Hilmioglu, Suleyha; Irkec, Murat

    2016-10-01

    To report a case of Acremonium keratitis treated with voriconazole, corneal collagen cross-linking, and corneal transplant. Case report. A 42-year-old woman who wore contact lenses daily was referred for refractory keratitis. Her main complaints were gritty sensation and pain. At slit lamp biomicroscopy, an infiltrate on the inferior paracentral cornea and an arcuate conjunctival ulceration were evident. The rest of the cornea was clear with no anterior chamber reaction. Scrapings from the corneal ulcer showed Candida parapsilosis and Acremonium species, which were sensitive to voriconazole. Despite the administration of topical, systemic, and intrastromal voriconazole for 1 month, repeat corneal scraping was positive for Acremonium, and clinical appearance and pain did not resolve. Therefore, corneal collagen cross-linking was applied. Although the pain resolved immediately after the procedure, the lesion showed no improvement. After a month of cross-linking, corneal transplant was performed for visual rehabilitation and treatment of the refractory lesion. The excised corneal button was negative for any microorganisms. Although corneal collagen cross-linking may be an effective treatment for Acremonium keratitis refractory to medical therapy, corneal transplant was required for visual gain and recovery.

  12. Preparation and characterization of cross-linked carboxymethyl chitin porous membrane scaffold for biomedical applications.

    Science.gov (United States)

    Zhao, Liqing; Wu, Yiguang; Chen, Shu; Xing, Tao

    2015-08-01

    Porous dermal scaffold membrane (PDSM) was successfully prepared by using a so-called sol-gel freeze-drying method. In this method, the carboxymethyl chitin (CMC) hydrosol was first cross-linked by 1-ethyl-3-[3-dimethylaminopropyl] carbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS), and then lyophilized to form the PDSM. For the first time, this research focused on the cross-linked CMC as the only component for three-dimensional PDSM. The effects of cross-linking conditions on the performance of the PDSM were investigated. And PDSM with optimal performance was obtained through 4-h cross-linking at 4 wt% of CMC concentration in the hydrosol, where the mass ratio of EDC to NHS to CMC was 5:3:10. The porosity of the optimized PDSM was more than 90% and the water swelling rate was above 4000%. The pore size was well distributed and was between 100 μm and 200 μm. And the tensile strength was above 0.09 MPa. The as-made PDSM could be degraded above 80% in 12 days in the presence of a 0.2mg/mL lysozyme solution. Very importantly, the PDSM had no cytotoxicity and good biocompatibility from MTT assays. Our results showed the application possibility of the as-prepared PDSM as dermal scaffold for skin tissue engineering. Copyright © 2015 Elsevier Ltd. All rights reserved.

  13. 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

  14. Interactions of cross-linked and uncross-linked chitosan hydrogels ...

    African Journals Online (AJOL)

    The swelling equilibrium of Chitosan and sodium tripolyphosphate (NaTPP) cross-linked chitosan hydrogels in aqueous solutions of surfactants differing in structure and hydrophobicity at 250C is reported. Anionic surfactant sodium dodecylsulfate (SDS), the cationic surfactant hexadecyltrimethylammonium bromide (HTAB) ...

  15. 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...

  16. EGDMA–cross-linked polystyrene resin: An efficient support for gel ...

    Indian Academy of Sciences (India)

    Unknown

    acetone followed by methanol to remove linear polymers and low molecular weight products. The beads were meshed to 200–400 range. Yield of the polymer obtained was. 85%. For preparation of the divinylbenzene–cross-linked polystyrene (DVB–PS), the same procedure was employed and the yield polymer obtained ...

  17. 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

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

    African Journals Online (AJOL)

    STORAGESEVER

    2009-12-15

    Dec 15, 2009 ... taminase would improve the rheological properties of stirred yoghurt with no syneresis (Bonisch et al., 2007), or could incorporate whey proteins into cheese curd to obtain whey- protein- enriched dairy products (Cozzolino et al., 2003). There are other enzyme systems that are capable of cross-linking side ...

  19. Preparation and characterization of electrospun in-situ cross-linked gelatin-graphite oxide nanofibers.

    Science.gov (United States)

    Zhan, Jianchao; Morsi, Yosry; Ei-Hamshary, Hany; Al-Deyab, Salem S; Mo, Xiumei

    2016-01-01

    Electrospun gelatin(Gel) nanofibers scaffold has such defects as poor mechanical property and quick degradation due to high solubility. In this study, the in situ cross-linked electrospinning technique was used for the production of gelatin nanofibers. Deionized water was chosen as the spinning solvent and graphite oxide (GO) was chosen as the enhancer. The morphological structure, porosity, thermal property, moisture absorption, and moisture retention performance, hydrolysis resistance, mechanical property, and biocompatibility of the produced nanofibers were investigated. Compared with in situ cross-linked gelatin nanofibers scaffold, in situ cross-linked Gel-GO nanofibers scaffold has the following features: (1) the hydrophilicity, moisture absorption, and moisture retention performance slightly reduce, while the hydrolysis resistance is improved; (2) the breaking strength, breaking elongation, and Young's modulus are significantly improved; (3) the porosity slightly reduces while the biocompatibility considerably increases. The in situ cross-linked Gel-GO nanofibers scaffold is likely to be applied in such fields as drug delivery and scaffold for skin tissue engineering.

  20. Enzymatic cross-linking of a-lactalbumin to produce nanoparticles with increased foam stability

    NARCIS (Netherlands)

    Dhayal, S.K.; Delahaije, R.J.B.M.; Vries, de R.J.; Gruppen, H.; Wierenga, P.A.

    2015-01-01

    Hard colloidal nanoparticles (e.g. partly hydrophobised silica), are known to make foams with very high foam-stability. Nanoparticles can also be produced from proteins by enzymatic cross-linking. Such protein based particles are more suitable for food applications, but it is not known if they

  1. 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.

  2. 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

  3. Collagen cross-linking treatment effects on corneal dynamic biomechanical properties.

    Science.gov (United States)

    Hatami-Marbini, Hamed; Rahimi, Abdolrasol

    2015-06-01

    Cornea is a soft tissue with the principal function of transmitting and refracting light rays. The objective of the current study was to characterize possible effects of the riboflavin/UVA collagen cross-linking on corneal dynamic properties. The original corneal cross-linking protocol was used to induce cross-links in the anterior portion of the bovine cornea. A DMA machine was used to conduct mechanical tensile experiments at different levels of tensile strains. The samples were divided into a control group (n = 5) and a treated group (n = 5). All specimens were first stretched to a strain of 5% and allowed to relax for twenty minutes. After completion of the stress-relaxation experiment, a frequency sweep test with oscillations ranging from 0.01 to 10 Hz was performed. The same procedure was repeated to obtain the stress-relaxation and dynamic properties at 10% strain. It was observed that the collagen cross-linking therapy significantly increased the immediate and equilibrium tensile behavior of the bovine cornea (P corneal stiffness, it decreased significantly its damping capability and deformability. This reduced damping ability might adversely interfere with corneal mechanical performance. Copyright © 2015 Elsevier Ltd. All rights reserved.

  4. A molecular characterization of hyper-cross-linked hybrid polyPOSS-imide networks

    NARCIS (Netherlands)

    Neyertz, Sylvie; Brown, David; Raaijmakers, Michiel; Benes, Nieck Edwin

    2016-01-01

    Hybrid hyper-cross-linked membranes based on inorganic polyhedral oligomeric silsesquioxanes (POSS) covalently bonded with organic imides have been shown to maintain remarkable molecular sieving abilities and gas separation performances up to 300 C. These films are obtained through the interfacial

  5. 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.

  6. 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.

  7. 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

  8. 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

  9. Double cross-linked polyetheretherketone proton exchange membrane for fuel cell

    CSIR Research Space (South Africa)

    Luo, H

    2012-04-01

    Full Text Available . The performance of direct methanol fuel cell was slightly improved as compared to Nafion® 117 due to its low methanol permeability. The results indicated that the double cross-linked membrane is a promising candidate for the polymer electrolyte membrane fuel cell...

  10. Nodular Epithelial Hyperplasia after Photorefractive Keratectomy Followed by Corneal Collagen Cross-Linking

    Directory of Open Access Journals (Sweden)

    Ayla Bogoni

    2013-01-01

    Full Text Available This study describes a case of nodular epithelial hyperplasia and stromal alterations in a patient with keratoconus who was submitted to topography-guided photorefractive keratectomy (PRK followed by corneal collagen cross-linking. Debridement of the epithelial nodule was performed. After a 2-year followup, a new topography-guided PRK was indicated.

  11. Calcium-Mediated Secondary Cross-Linking of Bisphosphonated Oligo(poly(ethylene glycol) Fumarate) Hydrogels

    NARCIS (Netherlands)

    Reza Nejadnik, M.; Yang, X.; Mimura, T.; Tahmasebi Birgani, Zeinab; Habibovic, Pamela; Itatani, K.; Jansen, J.A.; Hilborn, J.; Ossipov, D.; Mikos, A.G.; Leeuwenburgh, S.C.G.

    2013-01-01

    This study demonstrates, for the first time, that synthetic PEG-based hydrogels can be cross-linked reversibly by calcium upon functionalization of the polymer backbone with bisphosphonate groups (BPs) that allow for the formation of strong coordination bonds with divalent metal ions such as Mg2+

  12. 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.

  13. Can para-aryl-dithiols cross-link two plasmonic noble nanoparticles as monolayer dithiolate spacers

    Science.gov (United States)

    Para-aryl-dithiols (PADTs, HS-(C6H4)n-SH, n = 1, 2, and 3) have been used extensively in molecular electronics, surface-enhanced Raman spectroscopy (SERS), and quantum electron tunneling between two gold or silver nanoparticles (AuNPs and AgNPs). One popular belief is that these dithiols cross-link ...

  14. [Long-term efficacy of corneal collagen cross-linking in patients with progressive keratoconus].

    Science.gov (United States)

    Bubnova, I A; Kuznetsov, A V; Zelyanina, E V; Bubnova, I A; Kuznetsov, A V; Zelyanina, E V

    2015-01-01

    to study the efficacy of corneal collagen cross-linking in patients with progressive keratoconus over longer (up to 2 years) follow-up periods. A total of 52 patients (104 eyes) aged 23-34 years with stage I-III progressive keratoconus were enrolled. Besides routine examinations (automatic refractometry, uncorrected and best corrected visual acuity (UCVA and BCVA) evaluation, pneumatic tonometry), Pentacam keratotopography and pachymetry ("Oculus", Germany) were performed in all cases. Corneal biomechanical properties were assessed with an Ocular Response Analyzer ("Reichert", USA). In all patients cross-linking procedure was carried out in the eye with more advanced keratoconus, the fellow eye being used as the control. Judging from the results of UCVA and BCVA evaluation, keratotopography, and pachymetry obtained 2 years after the standard corneal cross-linking procedure, stabilization has been achieved in 97% of cases. In the remaining 3% of eyes corresponding parameters declined, although to a lesser extent than in the controls. Indices describing biomechanical properties of the cornea, such as corneal hysteresis, corneal resistance factor, as well as elastonometry results did not differ significantly throughout the whole observation period, which agrees with literature data. Corneal collagen cross-linking has been proved capable of stopping keratoconus progression in most of the patients (97%). Further studies with even longer follow-up periods are needed.

  15. An integrated cross-linking-MS approach to investigate cell penetrating peptides interacting partners

    Directory of Open Access Journals (Sweden)

    Séverine Clavier

    2014-06-01

    Biological significance: The robust and efficient cross-linking-MS workflow presented here can easily be adapted to any CPP-protein interacting system and could thus contribute to a better understanding of CPPs activity as cell-specific drug delivery tools. We validated the relevancy of this cross-linking-MS approach with two biologically active CPPs, (R/W9 and (R/W16, and two interacting protein partners, actin and albumin, previously reported using isothermal titration calorimetry (ITC and NMR. Cross-linking-MS results obtained on these previous studies allowed us to go further by providing a detailed mapping of the interaction zones. The identified interaction zones between actin and CPPs (R/W9 and (R/W16 are biologically meaningful. Two cross-linked zones [46–57] and [202–210] of actin are indeed involved in the modulation of its dynamics. Moreover, [46–57] domain has also been described as one interaction domain for thymosin β4 whose actin binding can be displaced by competition with (R/W16 (NMR experiments.

  16. Cross-linked gelatin microspheres with continuously tunable degradation profiles for renal tissue regeneration.

    Science.gov (United States)

    Serban, Monica A; Knight, Toyin; Payne, Richard G; Basu, Joydeep; Rivera, Elias A; Robbins, Neil; McCoy, Darell; Halberstadt, Craig; Jain, Deepak; Bertram, Timothy A

    2014-01-01

    Collagen and gelatin-based biomaterials are widely used in tissue engineering applications. Various methods have been reported for the cross-linking of these macromolecules for the purpose of delaying their biodegradation to prolong their in vivo residence (in tissue engineering applications) or tailoring their drug releasing capacity (when used as drug carriers). In this study, a carbodiimide-based cross-linking method, also used in the production of United States Food and Drug Administration-approved products, was employed to obtain differentially cross-linked gelatin beads. The colorimetric determination of the in vitro enzymatic susceptibility of the beads indicated that the resistance to degradation linearly correlated with the concentration of carbodiimide used for the cross-linking reaction. This result was also confirmed in vivo by the histological evaluation of the residence time of orthotopically injected cell-seeded beads. These data would indicate that the production of gelatin-based microbeads with tunable degradation profiles might be applicable toward the development of products that catalyze regeneration of kidney and other solid organs. © 2013 International Union of Biochemistry and Molecular Biology, Inc.

  17. Characterization and in vitro and in vivo evaluation of cross-linked ...

    Indian Academy of Sciences (India)

    Abstract. The aim of the present study is to develop cross-linked chitosan (CH) films that can release drug over an extended period of time and that too in a controlled manner. A solution of different percentages of CH, is prepared in 1% lactic acid, followed by addition of citalopram (CTP) and then reacted with increasing ...

  18. 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

  19. Evaluation of Native and Cross-Linked Acacia Senegal Gums as ...

    African Journals Online (AJOL)

    Fourier transform infrared spectroscopy (FTIR) studies indicated the compatibility of the gums with the model drug, theophylline. Dissolution studies showed AS, Cross-linked var. karensis (CAS) and var. senegal (CAH) can sustain the release of the drug beyond 12 h at higher gum concentrations (p < 0.05) indicating the ...

  20. Crown ether activation of cross-linked subtilisin Carlsberg crystals in organic solvents

    NARCIS (Netherlands)

    van Unen, D.J.; Sakodinskaya, I.K.; Sakodinskaya, Inna K.; Engbersen, Johannes F.J.; Reinhoudt, David

    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

  1. Impact of treatment on myocardial lysyl oxidase expression and collagen cross-linking in patients with heart failure

    OpenAIRE

    Lopez, B. (Begoña); Querejeta, R. (Ramón); Gonzalez, A. (Arantxa); Beaumont, J. (Javier); Larman, M. (Mariano); Diez, J. (Javier)

    2009-01-01

    The aim of this study was to investigate whether torasemide modifies collagen cross-linking in the failing human heart. We analyzed the degree of cross-linking and the expression of the enzyme lysyl oxidase, which regulates cross-linking, in the myocardium of patients with chronic heart failure at baseline and after 8 months of treatment with either torasemide or furosemide in addition to their standard heart failure therapy. Whereas lysyl oxidase protein expression was very scarce in normal ...

  2. Evaluation of the efficacy of excimer laser ablation of cross-linked porcine cornea.

    Directory of Open Access Journals (Sweden)

    Shihao Chen

    Full Text Available BACKGROUND: Combination of riboflavin/UVA cross-linking (CXL and excimer laser ablation is a promising therapy for treating corneal ectasia. The cornea is strengthened by cross-linking, while the irregular astigmatism is reduced by laser ablation. This study aims to compare the efficacy of excimer laser ablation on porcine corneas with and without cross-linking. METHODS AND FINDINGS: The porcine cornea was de-epithelialized and treated with 0.1% riboflavin solution for 30 minutes. A half of the cornea was exposed to UVA-radiation for another 30 minutes while the controlled half of the cornea was protected from the UVA using a metal shield. Photo therapeutic keratectomy (PTK was then performed on the central cornea. Corneal thickness of 5 paired locations on the horizontal line, ± 0.5, ± 1.0, ± 1.5, ± 2.0, and ± 2.5 mm from the central spot, were measured using optical coherence tomography prior to and after PTK. The ablation depth was then determined by the corneal thickness. There was a 9% difference (P<0.001 in the overall ablation depth between the CXL-half corneas (158 ± 22 µm and the control-half corneas (174 ± 26 µm. The ablation depths of all 5 correspondent locations on the CXL-half were significantly smaller (P<0.001. CONCLUSION: The efficacy of the laser ablation seems to be lower in cross-linked cornea. Current ablation algorithms may need to be modified for cross-linked corneas.

  3. Cancer-associated Fibroblasts Induce a Collagen Cross-link Switch in Tumor Stroma

    Science.gov (United States)

    Pankova, Daniela; Chen, Yulong; Terajima, Masahiko; Schliekelman, Mark J.; Baird, Brandi N.; Fahrenholtz, Monica; Sun, Li; Gill, Bartley J.; Vadakkan, Tegy J.; Kim, Min P.; Ahn, Young-Ho; Roybal, Jonathon D.; Liu, Xin; Parra Cuentas, Edwin Roger; Rodriguez, Jaime; Wistuba, Ignacio I.; Creighton, Chad J.; Gibbons, Don L.; Hicks, John M.; Dickinson, Mary E.; West, Jennifer L.; Grande-Allen, K. Jane; Hanash, Samir M.; Yamauchi, Mitsuo; Kurie, Jonathan M.

    2015-01-01

    Intratumoral collagen cross-links heighten stromal stiffness and stimulate tumor cell invasion, but it is unclear how collagen cross-linking is regulated in epithelial tumors. To address this question, we used KrasLA1 mice, which develop lung adenocarcinomas from somatic activation of a KrasG12D allele. The lung tumors in KrasLA1 mice were highly fibrotic and contained cancer-associated fibroblasts (CAFs) that produced collagen and generated stiffness in collagen gels. In xenograft tumors generated by injection of wild-type mice with lung adenocarcinoma cells alone or in combination with CAFs, the total concentration of collagen cross-links was the same in tumors generated with or without CAFs, but co-injected tumors had higher hydroxylysine aldehyde-derived collagen cross-links (HLCCs) and lower lysine-aldehyde-derived collagen cross-links (LCCs). Therefore, we postulated that an LCC-to-HLCC switch induced by CAFs promotes the migratory and invasive properties of lung adenocarcinoma cells. To test this hypothesis, we created co-culture models in which CAFs are positioned interstitially or peripherally in tumor cell aggregates, mimicking distinct spatial orientations of CAFs in human lung cancer. In both contexts, CAFs enhanced the invasive properties of tumor cells in 3-dimensional (3D) collagen gels. Tumor cell aggregates that attached to CAF networks on a Matrigel surface dissociated and migrated on the networks. Lysyl hydroxylase 2 (PLOD2/LH2), which drives HLCC formation, was expressed in CAFs, and LH2 depletion abrogated the ability of CAFs to promote tumor cell invasion and migration. PMID:26631572

  4. Acoustic radiation force for noninvasive evaluation of corneal biomechanical changes induced by cross-linking therapy.

    Science.gov (United States)

    Urs, Raksha; Lloyd, Harriet O; Silverman, Ronald H

    2014-08-01

    To noninvasively measure changes in corneal biomechanical properties induced by ultraviolet-activated riboflavin cross-linking therapy using acoustic radiation force (ARF). Cross-linking was performed on the right eyes of 6 rabbits, with the left eyes serving as controls. Acoustic radiation force was used to assess corneal stiffness before treatment and weekly for 4 weeks after treatment. Acoustic power levels were within US Food and Drug Administration guidelines for ophthalmic safety. Strain, determined from ARF-induced displacement of the front and back surfaces of the cornea, was fit to the Kelvin-Voigt model to determine the elastic modulus (E) and coefficient of viscosity (η). The stiffness factor, the ratio of E after treatment to E before treatment, was calculated for treated and control eyes. At the end of 4 weeks, ex vivo thermal shrinkage temperature analysis was performed for comparison with in vivo stiffness measurements. One-way analysis of variance and Student t tests were performed to test for differences in E, η, the stiffness factor, and corneal thickness. Biomechanical stiffening was immediately evident in cross-linking-treated corneas. At 4 weeks after treatment, treated corneas were 1.3 times stiffer and showed significant changes in E (P= .006) and η (P= .007), with no significant effect in controls. Corneal thickness increased immediately after treatment but did not differ significantly from the pretreatment value at 4 weeks. Our findings demonstrate a statistically significant increase in stiffness in cross-linking-treated rabbit corneas based on in vivo axial stress/strain measurements obtained using ARF. The capacity to noninvasively monitor corneal stiffness offers the potential for clinical monitoring of cross-linking therapy. © 2014 by the American Institute of Ultrasound in Medicine.

  5. Elucidation of a novel polypeptide cross-link involving 3-hydroxykynurenine.

    Science.gov (United States)

    Aquilina, J A; Carver, J A; Truscott, R J

    1999-08-31

    3-Hydroxykynurenine, a metabolite of tryptophan, is a powerful antioxidant and neurotoxin. The neurotoxicity results from the oxidation of 3-hydroxykynurenine, and hydroxyl radicals, formed via H(2)O(2), may also be implicated [Okuda, S., Nishiyama, N., Saito, H. , and Katsuki, H. (1996) Proc. Natl. Acad. Sci. U.S.A. 93, 12553-12558]. Oxidation of o-aminophenols, such as 3-hydroxykynurenine, also results in the formation of highly reactive quinonimines. Thus, one possible consequence of 3-hydroxykynurenine oxidation may be covalent modification of cellular macromolecules. Such a process could contribute to the neurotoxicity and may potentially be important in other tissues, such as the human lens, where 3-hydroxykynurenine functions as a UV filter. In this work, we demonstrate that 3-hydroxykynurenine can bind to protein amino groups and, further, that under oxidative conditions, 3-hydroxykynurenine can function to cross-link polypeptide chains. The structure of the cross-linked moiety, using the peptide glycyllysine, has been elucidated. The cross-link, which is both colored and fluorescent, involves the peptide alpha-amino groups. Proteins modified by 3-hydroxykynurenine become colored and fluorescent as well as cross-linked. LC-MS studies indicate that the cross-link is also present in gamma-crystallin, following incubation of this lens protein in the presence of 3-hydroxykynurenine. Similar posttranslational modifications of lens proteins accompany cataract formation, and knowledge of the precise mode of reaction of 3-hydroxykynurenine with proteins will assist in determining if 3-hydroxykynurenine is involved in degenerative conditions in which oxidation of such aminophenols is implicated.

  6. Bone fracture toughness and strength correlate with collagen cross-link maturity in a dose-controlled lathyrism mouse model.

    Science.gov (United States)

    McNerny, Erin M B; Gong, Bo; Morris, Michael D; Kohn, David H

    2015-03-01

    Collagen cross-linking is altered in many diseases of bone, and enzymatic collagen cross-links are important to bone quality, as evidenced by losses of strength after lysyl oxidase inhibition (lathyrism). We hypothesized that cross-links also contribute directly to bone fracture toughness. A mouse model of lathyrism using subcutaneous injection of up to 500 mg/kg β-aminopropionitrile (BAPN) was developed and characterized (60 animals across 4 dosage groups). Three weeks of 150 or 350 mg/kg BAPN treatment in young, growing mice significantly reduced cortical bone fracture toughness, strength, and pyridinoline cross-link content. Ratios reflecting relative cross-link maturity were positive regressors of fracture toughness (HP/[DHLNL + HLNL] r(2)  = 0.208, p cross-links were significant positive regressors of tissue strength (lysyl pyridinoline r(2)  = 0.159, p = 0.014; hydroxylysyl pyridinoline r(2)  = 0.112, p cross-links, which were not significantly reduced by BAPN, did not correlate with mechanical properties. The effect of BAPN treatment on mechanical properties was dose specific, with the greatest impact found at the intermediate (350 mg/kg) dose. Calcein labeling was used to define locations of new bone formation, allowing for the identification of regions of normally cross-linked (preexisting) and BAPN-treated (newly formed, cross-link-deficient) bone. Raman spectroscopy revealed spatial differences attributable to relative tissue age and effects of cross-link inhibition. Newly deposited tissues had lower mineral/matrix, carbonate/phosphate, and Amide I cross-link (matrix maturity) ratios compared with preexisting tissues. BAPN treatment did not affect mineral measures but significantly increased the cross-link (matrix maturity) ratio compared with newly formed control tissue. Our study reveals that spatially localized effects of short-term BAPN cross-link inhibition can alter the whole-bone collagen cross-link profile to a

  7. ProXL (Protein Cross-Linking Database): A Platform for Analysis, Visualization, and Sharing of Protein Cross-Linking Mass Spectrometry Data.

    Science.gov (United States)

    Riffle, Michael; Jaschob, Daniel; Zelter, Alex; Davis, Trisha N

    2016-08-05

    ProXL is a Web application and accompanying database designed for sharing, visualizing, and analyzing bottom-up protein cross-linking mass spectrometry data with an emphasis on structural analysis and quality control. ProXL is designed to be independent of any particular software pipeline. The import process is simplified by the use of the ProXL XML data format, which shields developers of data importers from the relative complexity of the relational database schema. The database and Web interfaces function equally well for any software pipeline and allow data from disparate pipelines to be merged and contrasted. ProXL includes robust public and private data sharing capabilities, including a project-based interface designed to ensure security and facilitate collaboration among multiple researchers. ProXL provides multiple interactive and highly dynamic data visualizations that facilitate structural-based analysis of the observed cross-links as well as quality control. ProXL is open-source, well-documented, and freely available at https://github.com/yeastrc/proxl-web-app .

  8. Influence of 1,2-PB matrix cross-linking on structure and properties of selectively etched 1,2-PB-b-PDMS block copolymers

    DEFF Research Database (Denmark)

    Guo, Fengxiao; Andreasen, Jens Wenzel; Vigild, Martin Etchells

    2007-01-01

    of the cross-linked samples in toluene was converted into a degree of cross-linking following the Flory scheme; a simple relation between the Flory cross-linking degree and the fraction of consumed double bonds during the cross-linking reaction followed. The structure of the block copolymer at different stages...

  9. Efeito terapêutico do "cross-linking" corneano na ceratopatia bolhosa sintomática Therapeutic effect of corneal cross-linking on symptomatic bullous keratophaty

    Directory of Open Access Journals (Sweden)

    Diego Nery Benevides Gadelha

    2009-08-01

    Full Text Available OBJETIVO: Avaliar o efeito do "cross-linking" corneano na ceratopatia bolhosa sintomática e seu impacto na acuidade visual, espessura corneana e sintomatologia dolorosa. MÉTODOS: Doze pacientes com ceratopatia bolhosa sintomática foram incluídos. Exame clínico com questionário específico para a pesquisa com escala de dor (escala visual analógica numérica, acuidade visual e mensuração da espessura corneana foi realizada pré "cross-linking" corneano, 7, 30 e 60 dias após. Em todos os pacientes o tratamento com UVA-crosslinking foi realizado após abrasão do epitélio corneano na lâmpada de fenda e instilação de solução de riboflavina 0,1% a cada 5 minutos por 30 minutos. Após esse período o paciente foi submetido à exposição à luz ultravioleta A (UVA, utilizando riboflavina e anestesia tópica a cada 5 minutos por 30 minutos. O paciente utilizou colírios de ofloxacina 0,3% e lágrima artificial até completa reepitelização. O teste de Friedman foi usado para comparar as médias das frequências da acuidade visual, sintomatologia dolorosa e espessura central da córnea. Os valores de "p" menor que 0,05 foram considerados como estatisticamente significantes. RESULTADOS: Doze olhos de 12 pacientes com erosões epiteliais recorrentes foram tratados. O tempo de seguimento foi de dois meses. Foi observada redução significante da dor (pPURPOSE: To evaluate the corneal cross-linking (CXL effect on symptomatic bullous keratopathy, and its impact on the visual acuity, corneal thickness and pain symptomatology. METHODS: Twelve patients with symptomatic bullous keratophaty were included. A clinical examination with a specific questionnaire (pain scale - visual numeric analog scale, visual acuity, and corneal thickness measures was performed before corneal cross-linking and 7, 30 and 60 days after the procedure. In all patients, the treatment with the UVA-crosslinking was done after corneal abrasion on the slit-lamp and

  10. Enhancing the mechanical properties of collagen by photo-chemical cross-linking

    OpenAIRE

    Shahban, S. A.; Brown, R. A.; Bozec, L.; Cheema, U.

    2009-01-01

    Cell survival within mechanically strong scaffolds is critical in the design of tissue engineered constructs. Collagen type I gels tend to be mechanically weak due to the low percentage of collagen with limited orientation and crosslinking. To enhance the properties of collagen type I gels we used the following approaches: a) plastically compress the collagen gel to increase the density and b) photochemically crosslink the gel using riboflavin as a photoinitiator and high intensity blue light...

  11. Insights in luteovirid structural biology guided by chemical cross-linking and high resolution mass spectrometry

    Science.gov (United States)

    Interactions among plant pathogenic viruses in the family /react-text Luteoviridae react-text: 233 and their plant hosts and insect vectors are governed by the topology of the viral capsid, which is the sole vehicle for long distance movement of the viral genome. Previous application of a mass spect...

  12. Chemical Cross-Linking Stabilizes Native-Like HIV-1 Envelope Glycoprotein Trimer Antigens

    NARCIS (Netherlands)

    Schiffner, Torben; de Val, Natalia; Russell, Rebecca A.; de Taeye, Steven W.; de la Peña, Alba Torrents; Ozorowski, Gabriel; Kim, Helen J.; Nieusma, Travis; Brod, Florian; Cupo, Albert; Sanders, Rogier W.; Moore, John P.; Ward, Andrew B.; Sattentau, Quentin J.

    2016-01-01

    Major neutralizing antibody immune evasion strategies of the HIV-1 envelope glycoprotein (Env) trimer include conformational and structural instability. Stabilized soluble trimers such as BG505 SOSIP.664 mimic the structure of virion-associated Env but nevertheless sample different conformational

  13. New reagents for coal desulfurization. Final technical report, September 1, 1990--August 31, 1991

    Energy Technology Data Exchange (ETDEWEB)

    Buchanan, D.H.; Kalembasa, S.; Olson, D.; Wang, S.; Warfel, L.

    1991-12-31

    The primary goal of this project was development and exploration of potential new desulfurization reagents for the removal of ``organic sulfur`` from Illinois coals by mild chemical methods. Potential new desulfurization reagents were investigated using organic sulfur compounds of the types thought to be present in coals. Reagents included low-valent metal complexes based on nickel and on iron as well as possible Single Electron Transfer reagents. Soluble coal extracts served as second generation model compounds during this reagent development project.

  14. Fluorescence spectroscopic study of the aggregation behavior of non-cross-linked and cross-linked poly(alkylmethyldiallylammonium bromides) having decyl, octyl, and hexyl side chains in aqueous solution

    NARCIS (Netherlands)

    Wang, G.J; Engberts, J.B.F.N.

    1996-01-01

    The conformational state of a series of non-cross-linked and cross-linked poly(alkylmethyldiallylammonium bromides) bearing decyl, octyl, and hexyl side chains ((CL)-CopolC1-10, (CL)-CopolC1-8, and (CL)-CopolC1-6, respectively) in aqueous solutions were investigated by fluorescence spectroscopy

  15. Antibody cross-linking and target elution protocols used for immunoprecipitation significantly modulate signal-to noise ratio in downstream 2D-PAGE analysis

    Directory of Open Access Journals (Sweden)

    Slupphaug Geir

    2011-08-01

    Full Text Available Abstract Background Immunoprecipitation and subsequent 2D-PAGE/mass spectrometry are powerful tools to study post-translational protein modifications. Often disregarded in this workflow is the impact of the chemical cross-linker upon antibody affinity, as well as incomplete elution of primary target protein in buffers commonly used in 2D-PAGE. This may impede detection of non-abundant protein isoforms. Results Here we have compared cross-linking of antibodies to Dynabeads® Protein A by using DMP or BS3, as well as the efficiency of various target elution buffers prior to 2D-PAGE separation. BS3 cross-linking generally resulted in less non-specific binding than DMP, whereas DMP cross-linking gave overall higher yield of target protein. Regardless of the cross-linker used, incomplete elution of target protein was observed with conventional glycine- or urea-based buffers. Conversely, complete elution was obtained with 2% hot SDS and subsequent dilution in urea buffer containing 4% CHAPS, to 0.2% final SDS yielded perfectly focused gels suitable for mass spectrometry analysis. Conclusion Careful choice of Ig cross-linker as well as efficient elution of target protein in SDS prior to downstream 2D-PAGE may be key factors to analyze low-abundance proteins enriched by magnetic bead immunoprecipitation.

  16. Optical properties of thin films of zinc oxide quantum dots and polydimethylsiloxane: UV-blocking and the effect of cross-linking.

    Science.gov (United States)

    Eita, Mohamed; El Sayed, Ramy; Muhammed, Mamoun

    2012-12-01

    Thin films of polydimethylsiloxane (PDMS) and ZnO quantum dots (QDs) were built up as multilayers by spin-coating. The films are characterized by a UV-blocking ability that increases with increasing number of bilayers. Photoluminescence (PL) emission spectra of the thin films occur at 522 nm, which is the PL wavelength of the ZnO QDs dispersion, but with a lower intensity and a quantum yield (QY) less than 1% that of the dispersion. Cross-linking has introduced new features to the absorption spectra in that the absorption peak was absent. These changes were attributed to the morphological and structural changes revealed by transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR), respectively. TEM showed that the ZnO particle size in the film increased from 7 (±2.7) nm to 16 (±7.8) upon cross-linking. The FTIR spectra suggest that ZnO QDs are involved in the cross-linking of PDMS and that the surface of the ZnO QDs has been chemically modified. Copyright © 2012 Elsevier Inc. All rights reserved.

  17. Chromium (VI) ion adsorption by grafted cross-linked chitosan beads in aqueous solution - a mathematical and statistical modeling study.

    Science.gov (United States)

    Igberase, E; Osifo, P; Ofomaja, A

    2017-12-01

    Chitosan outstanding qualities and efficient way of binding metal ions even to near zero concentration is the major reason for special attention. Modification of chitosan allows the polymer to be applied in numerous field of research. Depending on the modification techniques, chitosan possesses increased adsorption capacity. In this study chitosan beads (CS) were formulated from chitosan flakes, the beads were cross-linked with glutaraldehyde and thereafter grafted with ethyldiaminetetraacetic acid. The stability and amine concentration of the beads were determined. The chemical functionalities of the beads were obtained by Fourier transform infrared spectroscopy, X-ray diffraction and thermogravimetric analysis (TGA). However, in the adsorption studies with Cr(VI), the number of runs in the experiment was obtained by response surface methodology (RSM), and the maximum adsorption capacity (Qm) from each run was determined from the Langmuir model. The results of the experiment showed that the non-modified beads were soluble at pH 1-4 and insoluble at pH 5, while the modified beads were insoluble at pH 1-6. The amine concentration of CS, CCS and grafted cross-linked chitosan beads (GCCS) were 4.4, 3.8 and 5.0 mmol/g, respectively. The point of zero charge (pHPZC) of GCCS was found to be 4.4. The quadratic model was significant and adequate in describing the experimental data. The difference between experimental and predicted Qm was negligible. From the design matrix and results, increased Qm was achieved at pH 5, contact time 70 min, temperature 45°C, adsorbent dosage 5 g and initial concentration 70 mg/l. The desorption of the beads loaded with Cr(VI) was successful with 0.5 M HCl eluant and contact time of 180 min, leading to cost minimization.

  18. 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...

  19. Higher number of pentosidine cross-links induced by ribose does not alter tissue stiffness of cancellous bone

    NARCIS (Netherlands)

    Willems, N.M.B.K.; Langenbach, G.E.J.; Stoop, R.; Toonder, J.M.J. den; Mulder, L.; Zentner, A.; Everts, V.

    2014-01-01

    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

  20. 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