Optimization of Formaldehyde Cross-Linking for Protein Interaction Analysis of Non-Tagged Integrin β1

Science.gov (United States)

Klockenbusch, Cordula; Kast, Juergen

2010-01-01

Formaldehyde cross-linking of protein complexes combined with immunoprecipitation and mass spectrometry analysis is a promising technique for analysing protein-protein interactions, including those of transient nature. Here we used integrin β1 as a model to describe the application of formaldehyde cross-linking in detail, particularly focusing on the optimal parameters for cross-linking, the detection of formaldehyde cross-linked complexes, the utility of antibodies, and the identification of binding partners. Integrin β1 was found in a high molecular weight complex after formaldehyde cross-linking. Eight different anti-integrin β1 antibodies were used for pull-down experiments and no loss in precipitation efficiency after cross-linking was observed. However, two of the antibodies could not precipitate the complex, probably due to hidden epitopes. Formaldehyde cross-linked complexes, precipitated from Jurkat cells or human platelets and analyzed by mass spectrometry, were found to be composed of integrin β1, α4 and α6 or β1, α6, α2, and α5, respectively. PMID:20634879

Molecular and macro-scale analysis of enzyme-crosslinked silk hydrogels for rational biomaterial design.

Science.gov (United States)

McGill, Meghan; Coburn, Jeannine M; Partlow, Benjamin P; Mu, Xuan; Kaplan, David L

2017-11-01

Silk fibroin-based hydrogels have exciting applications in tissue engineering and therapeutic molecule delivery; however, their utility is dependent on their diffusive properties. The present study describes a molecular and macro-scale investigation of enzymatically-crosslinked silk fibroin hydrogels, and demonstrates that these systems have tunable crosslink density and diffusivity. We developed a liquid chromatography tandem mass spectroscopy (LC-MS/MS) method to assess the quantity and order of covalent tyrosine crosslinks in the hydrogels. This analysis revealed between 28 and 56% conversion of tyrosine to dityrosine, which was dependent on the silk concentration and reactant concentration. The crosslink density was then correlated with storage modulus, revealing that both crosslinking and protein concentration influenced the mechanical properties of the hydrogels. The diffusive properties of the bulk material were studied by fluorescence recovery after photobleaching (FRAP), which revealed a non-linear relationship between silk concentration and diffusivity. As a result of this work, a model for synthesizing hydrogels with known crosslink densities and diffusive properties has been established, enabling the rational design of silk hydrogels for biomedical applications. Hydrogels from naturally-derived silk polymers offer versitile opportunities in the biomedical field, however, their design has largely been an empirical process. We present a fundamental study of the crosslink density, storage modulus, and diffusion behavior of enzymatically-crosslinked silk hydrogels to better inform scaffold design. These studies revealed unexpected non-linear trends in the crosslink density and diffusivity of silk hydrogels with respect to protein concentration and crosslink reagent concentration. This work demonstrates the tunable diffusivity and crosslinking in silk fibroin hydrogels, and enables the rational design of biomaterials. Further, the characterization methods

pH and temperature dual-sensitive liposome gel based on novel cleavable mPEG-Hz-CHEMS polymeric vaginal delivery system

Directory of Open Access Journals (Sweden)

Chen D

2012-05-01

Full Text Available Daquan Chen,1,2 Kaoxiang Sun,1,2 Hongjie Mu,1 Mingtan Tang,3 Rongcai Liang,1,2 Aiping Wang,1,2 Shasha Zhou,1 Haijun Sun,1 Feng Zhao,1 Jianwen Yao,1 Wanhui Liu1,21School of Pharmacy, Yantai University, 2State Key Laboratory of Longacting and Targeting Drug Delivery Systems, Yantai, 3School of Pharmaceutical Sciences, Shandong University, Jinan, People's Republic of ChinaBackground: In this study, a pH and temperature dual-sensitive liposome gel based on a novel cleavable hydrazone-based pH-sensitive methoxy polyethylene glycol 2000-hydrazone-cholesteryl hemisuccinate (mPEG-Hz-CHEMS polymer was used for vaginal administration.Methods: The pH-sensitive, cleavable mPEG-Hz-CHEMS was designed as a modified pH-sensitive liposome that would selectively degrade under locally acidic vaginal conditions. The novel pH-sensitive liposome was engineered to form a thermogel at body temperature and to degrade in an acidic environment.Results: A dual-sensitive liposome gel with a high encapsulation efficiency of arctigenin was formed and improved the solubility of arctigenin characterized by Fourier transform infrared spectroscopy and differential scanning calorimetry. The dual-sensitive liposome gel with a sol-gel transition at body temperature was degraded in a pH-dependent manner, and was stable for a long period of time at neutral and basic pH, but cleavable under acidic conditions (pH 5.0. Arctigenin encapsulated in a dual-sensitive liposome gel was more stable and less toxic than arctigenin loaded into pH-sensitive liposomes. In vitro drug release results indicated that dual-sensitive liposome gels showed constant release of arctigenin over 3 days, but showed sustained release of arctigenin in buffers at pH 7.4 and pH 9.0.Conclusion: This research has shed some light on a pH and temperature dual-sensitive liposome gel using a cleavable mPEG-Hz-CHEMS polymer for vaginal delivery.Keywords: mPEG-Hz-CHEMS polymer, pH-sensitive liposomes, thermosensitive

Evaluation of ¹¹¹in-labelled exendin-4 derivatives containing different meprin β-specific cleavable linkers.

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Andreas Jodal

Full Text Available Cleavable linkers, which are specifically cleaved by defined conditions or enzymes, are powerful tools that can be used for various purposes. Amongst other things, they have been successfully used to deliver toxic payloads as prodrugs into target tissues. In this work novel linker sequences targeting meprin β, a metalloprotease expressed in the kidney brush-border membrane, were designed and included in the sequence of three radiolabelled exendin-4 derivatives. As radiolabelled exendin-4 derivatives strongly accumulate in the kidneys, we hypothesised that specific cleavage of the radiolabelled moiety at the kidney brush-border membrane would allow easier excretion of the activity into the urine and therefore improve the pharmacological properties of the peptide.The insertion of a cleavable linker did not negatively influence the in vitro properties of the peptides. They showed a good affinity to the GLP-1 receptor expressed in CHL cells, a high internalisation and sufficiently high stability in fresh human blood plasma. In vitro digestion with recombinant meprin β rapidly metabolised the corresponding linker sequences. After 60 min the majority of the corresponding peptides were digested and at the same time the anticipated fragments were formed. The peptides were also quickly metabolised in CD1 nu/nu mouse kidney homogenates. Immunofluorescence staining of meprin β in kidney sections confirmed the expression of the protease in the kidney brush-border membrane. Biodistribution in GLP-1 receptor positive tumour-xenograft bearing mice revealed high specific uptake of the 111In-labelled tracers in receptor positive tissue. Accumulation in the kidneys, however, was still high and comparable to the lead compound 111In-Ex4NOD40.In conclusion, we show that the concept of cleavable linkers specific for meprin β is feasible, as the peptides are rapidly cleaved by the enzyme while retaining their biological properties.

Characterization of the degree of cross-linking in radiation cross-linked low and high density polyethylenes

International Nuclear Information System (INIS)

Posselt, K.; Haedrich, W.

1986-01-01

In practice the cross-linking of irradiated polyethylene is mostly characterized by solubility and thermomechanical data. The irradiation of samples of a LDPE and a HDPE yields very different gel-dose curves. But for a quantitative comparison the complicated connection between the gel values and the corresponding densities of cross-links, especially the dependence on the initial molecular size distribution, has to take into consideration. The analysis of the solubility data according to the statistical theory of cross-linking developed by Inokuti and Saito shows that at equal doses in both investigated PE types in spite of the different gel values nearly the same densities of cross-links are present. That result is confirmed by the densities of cross-links determined from stress-strain measurements at 423 K. (author)

Microfabrication of crosslinked PTFE by synchrotron radiation

International Nuclear Information System (INIS)

Sato, Yasunori; Yamaguchi, Daichi; Oshima, Akihiro; Washio, Masakazu; Katoh, Takanori; Aoki, Yasushi; Ikeda, Shigetoshi; Tanaka, Shigeru

2003-01-01

Microfabrication of crosslinked polytetrafluoroethylene (PTFE) using synchrotron radiation (SR) has been demonstrated for production of micro-components applicable to radiation fields. The method of microfabrication was readily capable of obtaining a microstructure with aspect-ratio of 25 made of crosslinked PTFE. The etching rate of crosslinked PTFE was higher than that of non-crosslinked PTFE. The results show that the etching rate of crosslinked PTFE depends only on the degree of crosslinking. The effect of molecular motion on etching process was discussed from temperature dependence on etching rate. Moreover, in order to examine whether any change of chemical structures and crystallinity would be induced by SR-irradiation on PTFE, SR-irradiated PTFE was measured by NMR spectroscopy and DSC analysis. The results showed that the crosslinking reaction of PTFE would be induced by SR-irradiation in the solid state. (author)

Characterisation of radiation crosslinked polydimethylsiloxane

International Nuclear Information System (INIS)

Preston, C.M.L.; Hill, D.J.T.; Pomery, P.J.; Whittaker, A.K.

1998-01-01

Polysiloxanes, or silicones, are used widely in industry, as lubricants and process additives, as well as in many household products. The most common of the silicones is polydimethylsiloxane (PDMS). The fact that silicones crosslink during exposure to high energy radiation is well established. However, despite the number of studies performed on these systems, the exact mechanism of crosslinking has yet to be determined. Nuclear Magnetic Resonance spectroscopy (NMR) provides a useful method for the analysis of crosslinked polymer systems. Linear uncrosslinked PDMS is easily characterised in the solution state by NMR, as PDMS is readily soluble in common organic solvents. However, the onset of gelation caused by crosslinking results in an insoluble polymer network. The use of cross-polarisation (CP) and magic-angle spinning (MAS) in conjunction with high power decoupling has been shown to greatly enhance sensitivity of the NMR technique in solids. The true mechanism of crosslinking between polymer chains will be discussed

Cross-link guided molecular modeling with ROSETTA.

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Abdullah Kahraman

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

Development of a UV-Cleavable Protecting Group for Hydroxylamines, Synthesis of a StructurallyWide Variety of Hydroxamic Acids, and Identification of Histone Deacetylase Inhibitors

DEFF Research Database (Denmark)

Mortensen, Kim Thollund

Photo-cleavable protecting groups are highly applicable for the synthesis of structural complex and sensitive compounds, including biological important molecules. Herein, we present the development of a novel O-hydroxylamine photo-cleavable protecting group, based on the methyl-6-nitroveratryl...... moiety. We demonstrate the application of the protected hydroxylamine derivative for the synthesis of N-alkylated hydroxamic acids. We have shown that the construct is stable toward a diverse set of reaction conditions, as well as orthogonal with conventional protection groups. The O......-protected hydroxylamine derivative was applied to synthesize a small collection of N-alkylated hydroxamic acids as inhibitors of the histone deacetylase enzymes, an important class of enzymes for the treatment of a range of diseases, most importantly cancer. During my external stay at Nanyang Technological University...

Gamma irradiation Effect on the Non-Crosslinked and Crosslinked Poly(vinyl alcohol) Films

International Nuclear Information System (INIS)

El-Sawy, N.M.; El-Arnaouty, M.B.; Abdel Ghaffar, A.M.

2008-01-01

The non-crosslinked and crosslinked poly(vinyl alcohol) (PVA) films were prepared by the cast method then irradiated with gamma rays for various doses up to 300 kGy. The structure and characterization of PVA were determined by using Infrared spectroscopy (FTIR), ultraviolet spectroscopy (UV). Swelling behaviour was also investigated. Mechanical properties have been examined with respect to the absorbed dose. The color of the films changed to yellowish-white after irradiation. Additional changes were observed using FTIR analysis on the degradation products demonstrated that the radiolysis of PVA was initiated by liberation of H and OH groups leading to scission of the main chains and formation of carbonyl and double bond groups. Thermogravimetric analysis (TGA) was performed

Crosslinkable coatings from phosphorylcholine-based polymers.

Science.gov (United States)

Lewis, A L; Cumming, Z L; Goreish, H H; Kirkwood, L C; Tolhurst, L A; Stratford, P W

2001-01-01

2-Methacryloyloxyethyl phosphorylcholine (MPC) was synthesised and then used in the preparation of crosslinked polymer membranes with lauryl methacrylate, hydroxypropyl methacrylate and trimethoxysilylpropyl methacrylate (crosslinker) comonomers. Some physical aspects of the membrane properties were evaluated in order to establish the basis for the synthesis of a series of post-crosslinkable polymers. These materials were made by copolymerisation of the constituent monomers via a free radical method, and characterised using NMR, FT-IR, viscometry and elemental analysis. The optimum crosslink density and conditions required for curing coatings of these polymers were investigated using atomic force microscopy (AFM) and showed the inclusion of 5 mol% silyl crosslinking agent to be ideal. A nanoindentation technique was employed to determine if the coating developed elasticity upon crosslinking. The biological properties of the coatings were evaluated using a variety of protein adsorption assays and blood contacting experiments, and an enzyme immunoassay was developed to detect E. coli in order to assess the level of bacterial adhesion to these biomaterials. Polymers of this type were shown to be very useful as coating materials for improving the biocompatibility of, or reducing the levels of adherent bacteria to medical devices.

Alginate/PEG based microcarriers with cleavable crosslinkage for expansion and non-invasive harvest of human umbilical cord blood mesenchymal stem cells

Energy Technology Data Exchange (ETDEWEB)

Li, Chunge [Tianjin Key Laboratory of Composite and Functional Materials, School of Materials Science and Engineering, Tianjin University, No. 92, Weijin Road, Tianjin 300072 (China); Qian, Yufeng [Department of Chemistry and Biochemistry, University of Texas at Austin, 2500 Speedway, Austin, TX 78712 (United States); Zhao, Shuang [Tianjin Key Laboratory of Composite and Functional Materials, School of Materials Science and Engineering, Tianjin University, No. 92, Weijin Road, Tianjin 300072 (China); Yin, Yuji, E-mail: yinyuji@tju.edu.cn [Tianjin Key Laboratory of Composite and Functional Materials, School of Materials Science and Engineering, Tianjin University, No. 92, Weijin Road, Tianjin 300072 (China); Li, Junjie, E-mail: li41308@tju.edu.cn [Tianjin Key Laboratory of Composite and Functional Materials, School of Materials Science and Engineering, Tianjin University, No. 92, Weijin Road, Tianjin 300072 (China); Department of Advanced Interdisciplinary Studies, Institute of Basic Medical Sciences and Tissue Engineering Research Center, Academy of Military Medical Sciences, No. 27, Taiping Road, Beijing 100850 (China)

2016-07-01

Porous microcarriers are increasingly used to expand and harvest stem cells. Generally, the cells are harvested via proteolytic enzyme treatment, which always leads to damages to stem cells. To address this disadvantage, a series of alginate/PEG (AL/PEG) semi-interpenetrating network microcarriers are prepared in this study. In this AL/PEG system, the chemically cross-linked alginate networks are formed via the reaction between carboxylic acid group of alginate and di-terminated amine groups of cystamine. PEG is introduced to modulate the degradation of microcarriers, which does not participate in this cross-linked reaction, while it interpenetrates in alginate network via physical interactions. In addition, chitosan are coated on the surface of AL/PEG to improve the mechanical strength via the electrostatic interactions. Biocompatible fibronectin are also coated on these microcarriers to modulate the biological behaviors of cells seeded in microcarriers. Results suggest that the size of AL/PEG microcarriers can be modulated via adjusting the contents and molecular weight of PEG. Moreover, the microcarriers are designed to be degraded with cleavage of disulfide crosslinkage. By changing the type and concentration of reductant, the ratio of AL to PEG, and the magnitude of chitosan coating, the degradation ability of AL/PEG microcarriers can be well controlled. In addition, AL/PEG microcarriers can support the attachment and proliferation of human umbilical cord blood mesenchymal stem cells (hUCB-MSCs). More importantly, the expanded hUCB-MSCs can be detached from microcarriers after addition of reductant, which indeed reduce the cell damage caused by proteolytic enzyme treatment. Therefore, it is convinced that AL/PEG based microcarriers will be a promising candidate for large-scale expansion of hUCB-MSCs. - Graphical abstract: Alginate/PEG IPN microcarriers can support the attachment and expansion of hUCB-MSCs. More importantly, the expanded cells can be harvested

Alginate/PEG based microcarriers with cleavable crosslinkage for expansion and non-invasive harvest of human umbilical cord blood mesenchymal stem cells

International Nuclear Information System (INIS)

Li, Chunge; Qian, Yufeng; Zhao, Shuang; Yin, Yuji; Li, Junjie

2016-01-01

Porous microcarriers are increasingly used to expand and harvest stem cells. Generally, the cells are harvested via proteolytic enzyme treatment, which always leads to damages to stem cells. To address this disadvantage, a series of alginate/PEG (AL/PEG) semi-interpenetrating network microcarriers are prepared in this study. In this AL/PEG system, the chemically cross-linked alginate networks are formed via the reaction between carboxylic acid group of alginate and di-terminated amine groups of cystamine. PEG is introduced to modulate the degradation of microcarriers, which does not participate in this cross-linked reaction, while it interpenetrates in alginate network via physical interactions. In addition, chitosan are coated on the surface of AL/PEG to improve the mechanical strength via the electrostatic interactions. Biocompatible fibronectin are also coated on these microcarriers to modulate the biological behaviors of cells seeded in microcarriers. Results suggest that the size of AL/PEG microcarriers can be modulated via adjusting the contents and molecular weight of PEG. Moreover, the microcarriers are designed to be degraded with cleavage of disulfide crosslinkage. By changing the type and concentration of reductant, the ratio of AL to PEG, and the magnitude of chitosan coating, the degradation ability of AL/PEG microcarriers can be well controlled. In addition, AL/PEG microcarriers can support the attachment and proliferation of human umbilical cord blood mesenchymal stem cells (hUCB-MSCs). More importantly, the expanded hUCB-MSCs can be detached from microcarriers after addition of reductant, which indeed reduce the cell damage caused by proteolytic enzyme treatment. Therefore, it is convinced that AL/PEG based microcarriers will be a promising candidate for large-scale expansion of hUCB-MSCs. - Graphical abstract: Alginate/PEG IPN microcarriers can support the attachment and expansion of hUCB-MSCs. More importantly, the expanded cells can be harvested

Radiation induced crosslinking of polytetrafluoroethylene

International Nuclear Information System (INIS)

Oshima, Akihiro; Tabata, Yoneho; Ikeda, Shigetoshi; Otsuhata, Kazushige; Kudoh, Hisaaki; Seguchi, Tadao.

1995-01-01

The Irradiation temperature effect on polytetrafluoroethylene (PTFE) from room temperature to 380degC was investigated by tensile test and thermal analysis. The behavior of tensile properties and changes of crystallinity on irradiation indicated the formation of a network structure in PTFE by radiation induced crosslinking in inert gas in the molten state just above the melting temperature of PTFE (327degC). The crosslinked PTFE showed a much improved radiation resistance in an atmospheric radiation field. (author)

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.

Clickable prodrugs bearing potent and hydrolytically cleavable nicotinamide phosphoribosyltransferase inhibitors

Directory of Open Access Journals (Sweden)

Sadrerafi K

2018-04-01

release at various rates in serum presumably owing to the presence of several different classes of esterase. The biological activities of the drug conjugates correlate with the stability of their cleavable linkers observed in serum.Conclusion: The targeted and selective delivery of potent Nampt inhibitors to cancer cells is a potentially new route for the treatment of many cancers. These prodrugs linked to small cancer-associated peptides may be optimum for their use as targetable Nampt inhibitors. Keywords: carboranes, Nampt, cancer, prodrugs, cleavable linker

Carboxymethylcellulose hydrogel crosslinked with citric acid for biomedical application

International Nuclear Information System (INIS)

Capanema, Nadia S.V.; Mansur, Alexandra A.P.; Mansur, Herman S.; Universidade Federal de Minas Gerais

2016-01-01

The carboxymethylcellulose (CMCel) has been extensively used in order application as flexible polymer membrane. Biopolymers crosslinked have been studied to optimize their performance in biomedical applications. In this work, CMCel films with a degree of substitution (DS = 0.77) were prepared by evaporation of solvent and crosslinked with different concentrations of citric acid (CA). The synthesized CMCel was characterized by Infrared Spectroscopy by Fourier Transform X-ray spectroscopy (FTIR), and morphology assessed by scanning electron microscopy (SEM). Morphological analysis performed using the SEM indicated the crosslinked CMCel and not crosslinked with a very smooth and uniform appearance. The FTIR results indicated the modification of existing bands and appearance of a new band 1715 cm"-"1 suggesting that there has been change in the structure of the crosslinked CMCel. (author)

Thermo-cleavable solvents for printing conjugated polymers: Application in polymer solar cells

DEFF Research Database (Denmark)

Jørgensen, Mikkel; Hagemann, Ole; Alstrup, Jan

2009-01-01

large-scale production of polymer solar cells using screen printing. Screen-printed solar cells are still very inferior to state of the art P3HT/PCBM technology, but it is our view that it is necessary to explore these printing technologies if polymer solar cells are to ever become commercial products.......The synthesis and characterization of a number of so-called thermo-cleavable solvents are described with their application in all-air, all-solution and all-screen-printed polymer solar cells. These solvents were developed to meet some requirements for printing techniques such as long “open time...... (TGA) and high-temperature NMR established the onset temperature of decomposition, the rate of the reaction and the nature of the products. Printing experiments with inks based on these solvents together with conjugated polymers are exemplified for polymer solar cell devices to show how they enable...

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

Directory of Open Access Journals (Sweden)

Tapas Mitra

2013-01-01

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

Quantitative protein expression analysis of CLL B cells from mutated and unmutated IgV(H) subgroups using acid-cleavable isotope-coded affinity tag reagents.

Science.gov (United States)

Barnidge, David R; Jelinek, Diane F; Muddiman, David C; Kay, Neil E

2005-01-01

Relative protein expression levels were compared in leukemic B cells from two patients with chronic lymphocytic leukemia (CLL) having either mutated (M-CLL) or unmutated (UM-CLL) immunoglobulin variable heavy chain genes (IgV(H)). Cells were separated into cytosol and membrane protein fractions then labeled with acid-cleavable ICAT reagents (cICAT). Labeled proteins were digested with trypsin then subjected to SCX and affinity chromatography followed by LC-ESI-MS/MS analysis on a linear ion trap mass spectrometer. A total of 9 proteins from the cytosol fraction and 4 from the membrane fraction showed a 3-fold or greater difference between M-CLL and UM-CLL and a subset of these were examined by Western blot where results concurred with cICAT abundance ratios. The abundance of one of the proteins in particular, the mitochondrial membrane protein cytochrome c oxidase subunit COX G was examined in 6 M-CLL and 6 UM-CLL patients using western blot and results showed significantly greater levels (P < 0.001) in M-CLL patients vs UM-CLL patients. These results demonstrate that stable isotope labeling and mass spectrometry can complement 2D gel electrophoresis and gene microarray technologies for identifying putative and perhaps unique prognostic markers in CLL.

The role of crosslinkers in epoxy-amine crosslinked silicon sol-gel barrier protection coatings

International Nuclear Information System (INIS)

Vreugdenhil, A.J.; Gelling, V.J.; Woods, M.E.; Schmelz, J.R.; Enderson, B.P.

2008-01-01

The search for chromate replacements in corrosion prevention materials has identified the use of hybrid sol-gel coatings as one, very promising approach. Appropriately functionalized hybrid sol-gel materials can be crosslinked to enhance their chemical durability and mechanical strength. In this work, we evaluate three crosslinkers used in a tetramethoxysilane-glycidoxypropyltrimethoxysilane binary sol-gel system in order to identify the role of the crosslinkers in corrosion protection. The crosslinkers examined were ethylenediamine, N-aminethylepiperazine, and diethylenetriamine. The sol-gel coatings were examined by contact angle, atomic force microscopy, and electrochemical impedance spectroscopy (EIS). Circuit modeling of the EIS results yielded valuable insights into the significant differences between the durabilities of the variously crosslinked coatings. Crosslinker hydrophobicity was identified as not playing a significant role whereas the number of reactive sites per crosslinker and the resulting morphology of the material may be an important parameter

DNA cross-linking by dehydromonocrotaline lacks apparent base sequence preference.

Science.gov (United States)

Rieben, W Kurt; Coulombe, Roger A

2004-12-01

Pyrrolizidine alkaloids (PAs) are ubiquitous plant toxins, many of which, upon oxidation by hepatic mixed-function oxidases, become reactive bifunctional pyrrolic electrophiles that form DNA-DNA and DNA-protein cross-links. The anti-mitotic, toxic, and carcinogenic action of PAs is thought to be caused, at least in part, by these cross-links. We wished to determine whether the activated PA pyrrole dehydromonocrotaline (DHMO) exhibits base sequence preferences when cross-linked to a set of model duplex poly A-T 14-mer oligonucleotides with varying internal and/or end 5'-d(CG), 5'-d(GC), 5'-d(TA), 5'-d(CGCG), or 5'-d(GCGC) sequences. DHMO-DNA cross-links were assessed by electrophoretic mobility shift assay (EMSA) of 32P endlabeled oligonucleotides and by HPLC analysis of cross-linked DNAs enzymatically digested to their constituent deoxynucleosides. The degree of DNA cross-links depended upon the concentration of the pyrrole, but not on the base sequence of the oligonucleotide target. Likewise, HPLC chromatograms of cross-linked and digested DNAs showed no discernible sequence preference for any nucleotide. Added glutathione, tyrosine, cysteine, and aspartic acid, but not phenylalanine, threonine, serine, lysine, or methionine competed with DNA as alternate nucleophiles for cross-linking by DHMO. From these data it appears that DHMO exhibits no strong base preference when forming cross-links with DNA, and that some cellular nucleophiles can inhibit DNA cross-link formation.

Reactive electrospinning and biodegradation of cross-linked methacrylated polycarbonate nanofibers

Energy Technology Data Exchange (ETDEWEB)

Wu Ruizhi; Zhang Jianfeng; Fan Yuwei; Xu Xiaoming [Department of Comprehensive Dentistry and Biomaterials, Louisiana State University Health Sciences Center, 1100 Florida Avenue, Box 137, New Orleans, LA 70119 (United States); Stoute, Diana; Lallier, Thomas, E-mail: xxu@lsuhsc.edu [Department of Cell Biology and Anatomy, Louisiana State University Health Science Center, 1100 Florida Avenue, Box 137, New Orleans, LA 70119 (United States)

2011-06-15

The objectives of this study were to fabricate cross-linked biodegradable polycarbonate nanofibers and to investigate their biodegradability by different enzymes. Poly(2,3-dihydroxycarbonate) was synthesized from naturally occurring l-tartaric acid. The hydroxyl groups on the functional polycarbonate were converted to methacrylate groups to enable the polymer to cross-link under UV irradiation. Smooth cross-linked methacrylated polycarbonate nanofibers (300-1800 nm) were fabricated by a reactive electrospinning process with in situ UV radiation from a mixed solution of linear methacrylated polycarbonate (MPC) and poly(ethylene oxide) (PEO) (MPC:PEO = 9:1) in methanol/chloroform (50/50). These cross-linked nanofibers have shown excellent solvent resistance and their solubility decreases with increasing degree of cross-linking. The thermal properties of linear and cross-linked polycarbonate nanofibers were investigated by differential scanning calorimetry and thermogravimetric analysis. The cross-linked polycarbonate nanofibers show no melting point below 200 {sup 0}C and their decomposition temperature increases with increasing cross-linking degree. Their biodegradation products by five different enzymes were analyzed using liquid chromatography-mass spectrometry (LC-MS). The biodegradability of the polycarbonate nanofibers decreases with increasing cross-linking degree. These nanofibers were found to support human fibroblast survival and to promote cell attachment. This study demonstrates that cross-linked biodegradable polycarbonate nanofibers with different chemical properties and biodegradability can be fabricated using the novel reactive electrospinning technology to meet the needs of different biomedical applications.

Crosslinked electrospun PVA nanofibrous membranes: elucidation of their physicochemical, physicomechanical and molecular disposition

International Nuclear Information System (INIS)

Shaikh, Rubina P; Kumar, Pradeep; Choonara, Yahya E; Du Toit, Lisa C; Pillay, Viness

2012-01-01

The effects of modifying electrospun poly(vinyl alcohol) (PVA) nanofibers through crosslinking using glutaraldehyde (GA) are explored in this paper. Various concentrations of PVA solutions containing model drugs rifampicin (RIF) and isoniazid (INH) were electrospun and thereafter crosslinked using GA vapors. PVA nanofibers demonstrated high drug entrapment efficiency of 98.77% ± 1.384% and 95.07% ± 1.988% for the INH- and RIF-loaded PVA nanofibers, respectively. The surface morphology, molecular vibrational transitions, tensile attributes and in vitro drug release were characterized and supported by in silico molecular mechanics simulations. Results indicated that crosslinking caused a significant reduction in the rate of drug release where 81.11% ± 2.35% of INH and 59.31% ± 2.57% of RIF were released after 12 h. Tensile properties such as the ultimate strength and Young's modulus increased after crosslinking, caused by crosslinks forming between PVA nanofibers as was revealed through scanning electron microscopy analysis. Fourier Transform infrared analysis was conducted to further support the mode of crosslinking. Additionally, image processing analysis was carried out to quantify the effect of formulation variables on the morphology of nanofibers. Furthermore, the effect of GA-induced crosslinking and addition of drugs on the performance of electrospun fibers was further elucidated and conceptualized using a molecular mechanics assisted model building and energy refinement approach via molecular mechanics energy relationships by exploring the spatial disposition of energy-minimized molecular structures of the polymer, crosslinker and the drugs. (paper)

Donor cross-linking for keratoplasty: a laboratory evaluation.

Science.gov (United States)

Mukherjee, Achyut; Hayes, Sally; Aslanides, Ioannis; Lanchares, Elena; Meek, Keith M

2015-12-01

This laboratory-based investigation compares the topographic outcomes of conventional penetrating keratoplasty with that of a novel procedure in which donor corneas are cross-linked prior to keratoplasty. Penetrating keratoplasty procedures with continuous running sutures were carried out in a porcine whole globe model. Sixty eyes were randomly paired as 'donor' and 'host' tissue before being assigned to one of two groups. In the cross-linked group, donor corneas underwent riboflavin/UVA cross-linking prior to being trephined and sutured to untreated hosts. In the conventional keratoplasty group, both host and donor corneas remained untreated prior to keratoplasty. Topographic and corneal wavefront measurements were performed following surgery, and technical aspects of the procedure evaluated. Mean keratometric astigmatism was significantly lower in the cross-linked donor group at 3.67D (SD 1.8 D), vs. 8.43 D (SD 2.4 D) in the conventional keratoplasty group (p < 0.005). Mean wavefront astigmatism was also significantly reduced in the cross-linked donor group 4.71 D (SD 2.1) vs. 8.29D (SD 3.6) in the conventional keratoplasty group (p < 0.005). Mean RMS higher order aberration was significantly lower in the cross-linked donor group at 1.79 um (SD 0.98), vs. 3.05 um (SD 1.9) in the conventional keratoplasty group (P = 0.02). Qualitative analysis revealed less tissue distortion at the graft-host junction in the cross-linked group. Cross-linking of donor corneas prior to keratoplasty reduces intraoperative induced astigmatism and aberrations in an animal model. Further studies are indicated to evaluate the implications of this potential modification of keratoplasty surgery.

Fabrication of homobifunctional crosslinker stabilized collagen for biomedical application

International Nuclear Information System (INIS)

Lakra, Rachita; Kiran, Manikantan Syamala; Sai, Korrapati Purna

2015-01-01

Collagen biopolymer has found widespread application in the field of tissue engineering owing to its excellent tissue compatibility and negligible immunogenicity. Mechanical strength and enzymatic degradation of the collagen necessitates the physical and chemical strength enhancement. One such attempt deals with the understanding of crosslinking behaviour of EGS (ethylene glycol-bis (succinic acid N-hydroxysuccinimide ester)) with collagen to improve the physico-chemical properties. The incorporation of a crosslinker during fibril formation enhanced the thermal and mechanical stability of collagen. EGS crosslinked collagen films exhibited higher denaturation temperature (T d ) and the residue left after thermogravimetric analysis was about 16  ±  5.2%. Mechanical properties determined by uniaxial tensile tests showed a threefold increase in tensile strength and Young’s modulus at higher concentration (100 μM). Water uptake capacity reduced up to a moderate extent upon crosslinking which is essential for the transport of nutrients to the cells. Cell viability was found to be 100% upon treatment with 100 μM EGS whereas only 30% viability could be observed with glutaraldehyde. Rheological studies of crosslinked collagen showed an increase in shear stress and shear viscosity at 37 °C. Crosslinking with EGS resulted in the formation of a uniform fibrillar network. Trinitrobenzene sulfonate (TNBS) assay confirmed that EGS crosslinked collagen by forming a covalent interaction with ε-amino acids of collagen. The homobifunctional crosslinker used in this study enhanced the effectiveness of collagen as a biomaterial for biomedical application. (paper)

Molecular analysis by electron microscopy of the removal of psoralen-photoinduced DNA cross-links in normal and Fanconi's anemia fibroblasts

International Nuclear Information System (INIS)

Rousset, S.; Nocentini, S.; Revet, B.; Moustacchi, E.

1990-01-01

The induction and fate of psoralen-photoinduced DNA interstrand cross-links in the genome of Fanconi's anemia (FA) fibroblasts of complementation groups A and B, and of normal human fibroblasts, were investigated by quantitative analysis of totally denatured DNA fragments visualized by electron microscopy. 8-Methoxypsoralen (5 x 10(-5) M) interstrand cross-links were induced as a function of the near ultraviolet light dose. With time of postexposure incubation, a fraction of interstrand cross-links disappeared in all cell lines. However, 24 h after treatment, this removal was significantly lower in the two FA group A cell lines examined (34-39%) than in the FA group B and normal cell lines (43-53 and 47-57%, respectively). These data indicate that FA cells are at least able to recognize and incise interstrand cross-links, as normal cells do, although group A cells seem somewhat hampered in this process. This is in accord with data obtained on the same cell lines using another biochemical assay. Since the fate of cross-links in FA constituted a controversial matter, it is important to stress that two different methodologies applied to genetically well defined cell lines led to the same conclusions

Shell-crosslinked knedel-like nanoparticles induce lower immunotoxicity than their non-crosslinked analogs.

Science.gov (United States)

Elsabahy, Mahmoud; Samarajeewa, Sandani; Raymond, Jeffery E; Clark, Corrie; Wooley, Karen L

2013-10-21

The development of stable nanoparticles that can withstand the changing conditions experienced in a biological setting and also be of low toxicity and immunogenicity is of particular importance to address the problems associated with currently utilized nanotechnology-based therapeutics and diagnostics. The use of crosslinked nanoparticles continues to receive special impetus, due to their robust structure and high kinetic stability, and they have recently been shown to induce lower cytotoxicity than their non-crosslinked micellar counterparts. In the current study, poly(acrylamidoethylamine)- block -poly(DL-lactide) (PAEA 90 - b -PDLLA 40 ) copolymers were synthesized, self-assembled in water to yield nanoscopic polymeric micelles, and the effects of decorating the micellar surface with poly(ethylene glycol) ( i.e. PEGylation) and crosslinking the PAEA layer to varying extents on the physicochemical characteristics, cytotoxicity and immunotoxicity of the nanoparticles were studied. Herein, we report for the first time that crosslinking can efficiently reduce the immunotoxicity of polymeric nanomaterials. In addition, increasing the degree of crosslinking further reduced the accessibility of biomolecules to the core of the nanoparticles and decreased their cytotoxicity and immunotoxicity. It is also highlighted that crosslinking can be more efficient than PEGylation in reducing the immunotoxicity of nanomaterials. Shell-crosslinking of block copolymer micelles, therefore, is expected to advance their clinical development beyond the earlier known effects, and to broaden the implications in the field of nanomedicine.

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

. Mass spectrometry (MS) has emerged as a sensitive and efficient analytical technique for determination of such cross-linking sites in proteins. The present review of the field describes a number of MS-based approaches for the characterization of cross-linked protein-nucleic acid complexes...

Radiation crosslinking of polymer materials

International Nuclear Information System (INIS)

Yoshii, Fumio

2004-01-01

It was found that some polyfunctional monomers (PFM) like triallyl isocyanurate (TAIC) and trimethallyl isocyanurate (TMAIC) when incorporated at low concentrations, are effective for promotion of crosslinking of biodegradable polymers such as polycaprolactone (PCL), poly(butylene succinate-co-adipate) (PBS) and poly(lactic acid) (PLA). PFM are kneaded with biodegradable polymers at molten condition before irradiation. Radiation crosslinking of PBS and PCL with 1% TAIC gave gel fractions of 80% at 20 kGy. This crosslinking is effective to improve deformation of biodegradable polymers at high temperature. The irradiated materials retained their biodegradability even after crosslinking when subjected to soil burial test. Irradiation at molten state (melting temperature, 340degC) led to crosslinking structures for polytetrafluoroethylene (PTFE). Crosslinked PTFE forms transparent films with high abrasion property and high radiation resistance. High-density polyethylene (HDPE) has a higher gel fraction in irradiation at molten state than irradiation at ordinary temperature. Crosslinked HDPE has been applied as knee joints in order to have high abrasion. Radiation crosslinked polycarbosilane (PCS) fiber gives high heat resistant silicon carbide (SiC) after firing. EB irradiation of PCS is effective to improve strength of product and to inhibit flow during carbonization. SiC, being resistant to high temperature will be applied in turbine and body of rockets. (author)

Radiation crosslinking of polymer blends

International Nuclear Information System (INIS)

Spenadel, L.

1979-01-01

Rocked by the one-two punch of rising energy costs and tougher pollution controls, a growing number of companies are looking to radiation crosslinking as a cheaper, cleaner alternative to heat and costly chemical crosslinking agents such as peroxides. With the development of larger, more powerful electron beam machines it is now possible to irradiate parts as thick as 400 mils in a single pass. Two application areas which have been investigated at our laboratory are the electron beam processing of thermoplastic elastomeric automotive parts and EPDM electrical insulation. This paper covers work carried out to develop the necessary technology base for the radiation crosslinking of ethylene propylene/polyolefin blends. Initial results indicate that EP/PE blends of electrical insulation quality cross-link quite readily when irradiated. On the other hand, EP/PP blends developed for automotive fascia require the addition of crosslinking monomers such as trimethylol propane trimethacrylate in order for crosslinking to predominate over chain scission. Crosslinking EP/PP blends improve mar resistance, flexural set and deformation at elevated temperatures. These are all key properties for automotive fascia. (author)

Influences of poly (vinyl alcohol molecular weight and carbon nanotubes on radiation crosslinking shape memory polymers

Directory of Open Access Journals (Sweden)

Aamer A.M. Alfayyadh

2017-06-01

Full Text Available Polyvinyl alcohol (PVA of two molecular weights was used to prepare shape memory polymers based on chemical-crosslinking by glutaraldehyde. The chemical-crosslinking was done in the presence of 2-carboxyethyl acrylate oligomers (CEA and nano-filler [multi-wall carbon nanotubes (MWCNT and functionalized carbon nanotubes (MWCNT-NH2] followed by radiation-induced crosslinking. The analysis of the material revealed an increase in the gel fraction and a significant reduction in swelling of the nanocomposite material that was crosslinked with both glutaraldehyde and ionizing radiation. The radiation crosslinked nanocomposites demonstrated approximately a 90% gelation over a range of 50–300 kGy irradiation doses. The scanning electron microscopy (SEM analysis showed a homogeneous distribution of nanocomposites in the composite matrix. The thermal properties of radiation crosslinked (PVA/CEA and (PVA-CEA-nano-fillers were investigated by a thermogravimetric analysis (TGA. The mechanical properties were examined via dynamic mechanical analysis (DMA which showed significant variation because of the addition of nanocomposites. This radiation crosslinked materials show good shape memory behavior that may be useful in many applications based on the range of temperatures at which Tan δ appears.

Radiation crosslinking of polypropylene

International Nuclear Information System (INIS)

Nojiri, A.; Sawasaki, T.

1984-01-01

The radiation crosslinking of polypropylene with several kinds of polyfunctional monomers has been examined, and it has been clarified that the enhanced crosslinking may be classified into two types. In particular, the irradiation crosslinking process of polypropylene containing a polyfunctional monomer having an acryloyloxy group giving a specific gel - dose curve has been studied by infrared absorption spectrum and oxygen absorptivity measurement in comparison with the non-enhanced system. (author)

Crosslinking of viral nanoparticles with “clickable” fluorescent crosslinkers at the interface

Institute of Scientific and Technical Information of China (English)

KAUR; Gagandeep; BARNHILL; Hannah

2010-01-01

Cu (I) catalyzed alkyne-azide cycloaddition (CuAAC) reaction,a typical "click" reaction,is one of the modular synthetic approaches which has been broadly used in various organic syntheses,medicinal chemistry,materials development and bioconjugation applications.We have for the first time synthesized two dialkyne derivatized fluorescent crosslinkers which could be applied to crosslink two biomolecules using CuAAC reaction.Turnip yellow mosaic virus,a plant virus with unique structural and chemical properties,was used as a prototypical scaffold to form a 2D single layer at the interface of two immiscible liquids and crosslinked with these two linkers by the CuAAC reaction.Upon crosslinking,the fluorescence of both linkers diminished,likely due to the distortion of the polymethylene backbone,which therefore could be used to indicate the completion of the reaction.

Crosslinked poly(ether block amide) composite membranes for organic solvent nanofiltration applications

KAUST Repository

Aburabie, Jamaliah; Peinemann, Klaus-Viktor.

2016-01-01

Poly(ether block amide) – Pebax® – based membranes are well described for gas separation applications. But only a few publications exist for their application in pressure driven liquid applications like ultrafiltration and nanofiltration. Here we use the commercially available Pebax® 1657 for the preparation of membranes for the filtration of organic solvents. Porous polyacrylonitrile membranes were coated with Pebax® 1657 which was then crosslinked. Toluene diisocyanate (TDI) was used as a crosslinker agent for the coating. Reaction time and crosslinker concentration were optimized for the aimed application. The Pebax® coating and the impact of the TDI on the resulting crosslinked membranes were investigated by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). SEM analysis shows a uniform thin coating of the PEBAX that covers the pores of the PAN membranes. FTIR and DSC analysis confirm the crosslinking reaction. Crosslinked Pebax® membranes show high stability toward ethanol propanol, acetone and even dimethylformamide (DMF). In the case of DMF applications, the standard PAN was replaced by crosslinked PAN developed in our laboratory. In order to increase the membranes permeances, graphene oxide (GO) nanosheets were incorporated in the Pebax® coating. These GO containing membranes showed strongly increased permeances for selected solvents. © 2016 Elsevier B.V.

Crosslinked poly(ether block amide) composite membranes for organic solvent nanofiltration applications

KAUST Repository

Aburabie, Jamaliah

2016-10-01

Poly(ether block amide) – Pebax® – based membranes are well described for gas separation applications. But only a few publications exist for their application in pressure driven liquid applications like ultrafiltration and nanofiltration. Here we use the commercially available Pebax® 1657 for the preparation of membranes for the filtration of organic solvents. Porous polyacrylonitrile membranes were coated with Pebax® 1657 which was then crosslinked. Toluene diisocyanate (TDI) was used as a crosslinker agent for the coating. Reaction time and crosslinker concentration were optimized for the aimed application. The Pebax® coating and the impact of the TDI on the resulting crosslinked membranes were investigated by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). SEM analysis shows a uniform thin coating of the PEBAX that covers the pores of the PAN membranes. FTIR and DSC analysis confirm the crosslinking reaction. Crosslinked Pebax® membranes show high stability toward ethanol propanol, acetone and even dimethylformamide (DMF). In the case of DMF applications, the standard PAN was replaced by crosslinked PAN developed in our laboratory. In order to increase the membranes permeances, graphene oxide (GO) nanosheets were incorporated in the Pebax® coating. These GO containing membranes showed strongly increased permeances for selected solvents. © 2016 Elsevier B.V.

Gamma-radiation induced cross-links in ethylene-propylene rubber studied by CP-MAS NMR

International Nuclear Information System (INIS)

Sohma, J.; Shiotani, M.; Murakami, S.

1983-01-01

A new technique of 13 C-NMR, the CP-MAS method, was applied to study a chemistry of cross-links induced by #betta#-irradiation of ethylene-propylene rubber. The chemical species of cross-linking points were specified with their relative concentrations by the analysis of the CP-MAS spectra obtained before and after the irradiation. It was found that the short branches were also formed by the irradiation. A comparison was made between the cross-links detected by the CP-MAS method and those obtained by the Charlesby-Pinner analysis of the gelation caused by the #betta#-irradiation. The conventional 13 C-NMR of the cross-linked and swollen EPR provided us an information on the sol parts of the sample but little information on the cross-links in the gel parts. (author)

Effects of the nature of the antioxidant on the radiation crosslinking of polyethylene

Energy Technology Data Exchange (ETDEWEB)

Gal, O S; Markovic, V M; Novakovic, L R; Stannett, V T

1985-01-01

The effects of three antioxidants, a hindered phenolic, a secondary amine and a thioester on the radiation crosslinking efficiency of low-density polyethylene were studied. Both gel content and thermomechanical analysis were used to follow the crosslinking. All three antioxidants decreased the amount of crosslinking at a given dose, the thioester being the most effective. The ratios of G (scission) to G (X linking) increased with all three antioxidants. This is attributed to the antioxidants only interfering with the crosslinking reaction. (author).

Cross-linking of polymeric materials

International Nuclear Information System (INIS)

Bloom, L.I.; Du Plessis, T.A.; Meij, G.O.

1991-01-01

The invention provides a method of producing a cured polymeric artifact from a polymeric thermoplastic starting material, the material of the artifact having reduced thermoplasticity relative to the starting material and exhibiting an enhanced degree of cross-linking relative to the starting material. The method includes subjecting a polymeric thermoplastic starting material, which is capable of being cross-linked by irradiation, to sufficient irradiation partially to cross-linked the starting material to produce a thermoplastic partially cross-linked intermediate material. The thermoplasticity of the intermediate material is then reduced by heating it to raise its melting point. The invention also provides a method of making a partially cross-linked feedstocks and a master batch for use in making such artifacts

Crosslinking of agarose bioplastic using citric acid.

Science.gov (United States)

Awadhiya, Ankur; Kumar, David; Verma, Vivek

2016-10-20

We report chemical crosslinking of agarose bioplastic using citric acid. Crosslinking was confirmed using Fourier transform infrared (FTIR) spectroscopy. The effects of crosslinking on the tensile strength, swelling, thermal stability, and degradability of the bioplastic were studied in detail. The tensile strength of the bioplastic films increased from 25.1MPa for control films up to a maximum of 52.7MPa for citric acid crosslinked films. At 37°C, the amount of water absorbed by crosslinked agarose bioplastic was only 11.5% of the amount absorbed by non-crosslinked controls. Thermogravimetric results showed that the crosslinked samples retain greater mass at high temperature (>450°C) than control samples. Moreover, while the crosslinked films were completely degradable, the rate of degradation was lower compared to non-crosslinked controls. Copyright © 2016 Elsevier Ltd. All rights reserved.

Photo-crosslinkable cyanoacrylate bioadhesive: shrinkage kinetics, dynamic mechanical properties, and biocompatibility of adhesives containing TMPTMA and POSS nanostructures as crosslinking agents.

Science.gov (United States)

Ghasaban, S; Atai, M; Imani, M; Zandi, M; Shokrgozar, M-A

2011-11-01

The study investigates the photo-polymerization shrinkage behavior, dynamic mechanical properties, and biocompatibility of cyanoacrylate bioadhesives containing POSS nanostructures and TMPTMA as crosslinking agents. Adhesives containing 2-octyl cyanoacrylate (2-OCA) and different percentages of POSS nanostructures and TMPTMA as crosslinking agents were prepared. The 1-phenyl-1, 2-propanedione (PPD) was incorporated as photo-initiator into the adhesive in 1.5, 3, and 4 wt %. The shrinkage strain of the specimens was measured using bonded-disk technique. Shrinkage strain, shrinkage strain rate, maximum and time at maximum shrinkage strain rate were measured and compared. Mechanical properties of the adhesives were also studied using dynamic mechanical thermal analysis (DMTA). Biocompatibility of the adhesives was examined by MTT method. The results showed that shrinkage strain increased with increasing the initiator concentration up to 3 wt % in POSS-containing and 1.5 wt % in TMPTMA-containing specimens and plateaued out at higher concentrations. By increasing the crosslinking agent, shrinkage strain, and shrinkage strain rate increased and the time at maximum shrinkage strain rate decreased. The study indicates that the incorporation of crosslinking agents into the cyanoacrylate adhesives resulted in improved mechanical properties. Preliminary MTT studies also revealed better biocompatibility profile for the adhesives containing crosslinking agents comparing to the neat specimens. Copyright © 2011 Wiley Periodicals, Inc.

Radiation-crosslinking of shape memory polymers based on poly(vinyl alcohol) in the presence of carbon nanotubes

Science.gov (United States)

Basfar, A. A.; Lotfy, S.

2015-01-01

Shape memory polymers based on poly(vinyl alcohol) (SM-PVA) in the presence of 2-carboxyethyl acrylate oligomers (CEA) and multi-wall carbon nanotubes (MWCNTs) crosslinked by ionizing radiation were investigated. Chemical-crosslinking of PVA by glutaraldehyde in the presence of CEA and MWCNTs was also studied. The swelling and gel fraction of the radiation-crosslinked SM-PVA and chemically crosslinked systems were evaluated. Analysis of the swelling and gel fraction revealed a significant reduction in swelling and an increase in the gel fraction of the material that was chemically crosslinked with glutaraldehyde. The radiation-crosslinked SM-PVA demonstrated 100% gelation at an irradiation dose of 50 kGy. In addition, radiation-crosslinked SM-PVA exhibited good temperature responsive shape-memory behavior. A scanning electron microscopy (SEM) analysis was performed. The thermal properties of radiation-crosslinked SM-PVA were investigated by a thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA). The ability of the material to return or store energy (E‧), to its ability to lose energy (E″), and the ratio of these effects (Tanδ), which is called damping were examined via DMA. The temperature of Tanδ in the radiation-crosslinked SM-PVA decreased significantly by 6 and 13 °C as a result of the addition of MWCNTs. In addition, the temperature of Tanδ for SM-PVA increased as the irradiation dose increased. These radiation-crosslinked SM-PVA materials show promising shape-memory behavior based on the range of temperatures at which Tanδ appears.

Synthesis of a cleavable heterobifunctional photolabelling reagent: ring-labelled 3-((4-azidophenyl)dithio)propionic acid- sup 14 C

Energy Technology Data Exchange (ETDEWEB)

Ramaswami, Varadarajan (Carnegie-Mellon Univ., Pittsburgh, PA (USA). Dept. of Chemistry); Tirrell, D.A. (Massachusetts Univ., Amherst, MA (USA). Dept. of Polymer Science and Engineering)

1989-08-01

An efficient synthesis of ring-labelled 3-((4-azidophenyl)dithio)propionic acid-{sup 14}C is described. Chlorosulfonation of uniformly ring-labelled acetanilide-{sup 14}C followed by reductive dimerization of the sulfonyl chloride with HI afforded 4-acetamidophenyl disulfide. Hydrolysis and diazotization then gave 4-azidophenyl disulfide, which was converted to the title compound via the sulfur transfer reagent N-(4-azidophenylthio)phthalimide. The overall yield of 3-((4-azidophenyl)dithio)propionic acid-{sup 14}C was 22%. 3-((4-Azidophenyl)dithio)propionic acid-{sup 14}C is a cleavable heterobifunctional photolabelling reagent of potential utility in studies of biomembrane structure and intermacromolecular interaction. (author).

Conformational analysis of a covalently cross-linked Watson-Crick base pair model.

Science.gov (United States)

Jensen, Erik A; Allen, Benjamin D; Kishi, Yoshito; O'Leary, Daniel J

2008-11-15

Low-temperature NMR experiments and molecular modeling have been used to characterize the conformational behavior of a covalently cross-linked DNA base pair model. The data suggest that Watson-Crick or reverse Watson-Crick hydrogen bonding geometries have similar energies and can interconvert at low temperatures. This low-temperature process involves rotation about the crosslink CH(2)C(5') (psi) carbon-carbon bond, which is energetically preferred over the alternate CH(2)N(3) (phi) carbon-nitrogen bond rotation.

Computational investigation of kinetics of cross-linking reactions in proteins: importance in structure prediction.

Science.gov (United States)

Bandyopadhyay, Pradipta; Kuntz, Irwin D

2009-01-01

The determination of protein structure using distance constraints is a new and promising field of study. One implementation involves attaching residues of a protein using a cross-linking agent, followed by protease digestion, analysis of the resulting peptides by mass spectroscopy, and finally sequence threading to detect the protein folds. In the present work, we carry out computational modeling of the kinetics of cross-linking reactions in proteins using the master equation approach. The rate constants of the cross-linking reactions are estimated using the pKas and the solvent-accessible surface areas of the residues involved. This model is tested with fibroblast growth factor (FGF) and cytochrome C. It is consistent with the initial experimental rate data for individual lysine residues for cytochrome C. Our model captures all observed cross-links for FGF and almost 90% of the observed cross-links for cytochrome C, although it also predicts cross-links that were not observed experimentally (false positives). However, the analysis of the false positive results is complicated by the fact that experimental detection of cross-links can be difficult and may depend on specific experimental conditions such as pH, ionic strength. Receiver operator characteristic plots showed that our model does a good job in predicting the observed cross-links. Molecular dynamics simulations showed that for cytochrome C, in general, the two lysines come closer for the observed cross-links as compared to the false positive ones. For FGF, no such clear pattern exists. The kinetic model and MD simulation can be used to study proposed cross-linking protocols.

Theoretical studies of ionic conductivity of crosslinked chitosan membranes

Energy Technology Data Exchange (ETDEWEB)

Chavez, Ernesto Lopez [Programa de Ingenieria Molecular y Nuevos Materiales, Universidad Autonoma de la Ciudad de Mexico, Fray Servando Teresa de Mier 92, 1er. Piso, Col Centro, Mexico D.F. CP 06080 (Mexico); Oviedo-Roa, R.; Contreras-Perez, Gustavo; Martinez-Magadan, Jose Manuel [Instituto Mexicano del Petroleo, Eje Central Lazaro Cardenas Norte 152, Col. San Bartolo Atepehuacan, CP 07730 Mexico D.F. (Mexico); Castillo-Alvarado, F.L. [Escuela Superior de Fisica y Matematicas del Instituto Politecnico Nacional, Edificio 9 de la UPALM, Colonia Lindavista, Mexico D.F. CP 07738 (Mexico)

2010-11-15

Ionic conductivity of crosslinked chitosan membranes was studied using techniques of molecular modeling and simulation. The COMPASS force field was used. The simulation allows the description of the mechanism of ionic conductivity along the polymer matrix. The theoretical results obtained are compared with experimental results for chitosan membranes. The analysis suggests that the conduction mechanism is portrayed by the overlapping large Polaron tunneling model. In addition, when the chitosan membrane was crosslinked with an appropriate degree of crosslinking its ionic conductivity, at room temperature, was increased by about one order of magnitude. The chitosan membranes can be used as electrolytes in solid state batteries, electric double layer capacitors and fuel cells. (author)

Conformational Analysis of a Covalently Cross-Linked Watson-Crick Base Pair Model

OpenAIRE

Jensen, Erik A.; Allen, Benjamin D.; Kishi, Yoshito; O'Leary, Daniel J.

2008-01-01

Low temperature NMR experiments and molecular modeling have been used to characterize the conformational behavior of a covalently cross-linked DNA base pair model. The data suggest that Watson-Crick or reverse Watson-Crick hydrogen bonding geometries have similar energies and can interconvert at low temperatures. This low-temperature process involves rotation about the crosslink CH2–C(5′) (ψ) carbon-carbon bond, which is energetically preferred over the alternate CH2–N(3) (ϕ) carbon-nitrogen ...

Analysis of structural changes influence on radiation crosslinking of unsaturated polyester resins

International Nuclear Information System (INIS)

Pucic, I.; Ranogajec, F.

1998-01-01

Complete text of publication follows. DC-electrical conductivity has shown high sensitivity toward structural changes, especially to some low intensity transitions such as liquid-liquid transitions that are difficult to observe. It also showed favorable properties for monitoring of crosslinking of unsaturated polyester resins. However, when the rates were calculated using commonly applied formula: k lnσ =ln[(ln σ t - ln σ o )/(ln σ ∞ - ln σ o )] the sensitivity decreased. The extents of the reaction were shifted on time axis compared to non-logarithmic conductivity data and extraction analysis results. The logarithmic data had pronounced scattering at the end of the reaction so it was very difficult to determine end point of reaction and almost impossible to detect vitrification point. Some other features that can be seen on conductivity plot were lost. Therefore the results of DC-electrical conductivity monitoring of radiation and thermally initiated crosslinking of unsaturated polyester resins were interpreted in the same manner as the data collected by other non-electrical methods, using 'raw' data instead of its logarithmic form: k σ = ln [(σ t - σ o )/(σ ∞ - σ o )]. By this modification of data analysis the full sensitivity of electrical conductivity method to structural changes in reacting system was proven. Lower data scattering allowed observation of dose rate influences. The apparent rate constants calculated from conductivity itself showed the influence of upper liquid-liquid transition on the rate of radiation induced reaction that could not be seen if the logarithm of conductivity was used

Crosslink Radio Occultation for the Remote Sensing of Planetary Atmospheres

Science.gov (United States)

Mannucci, A. J.; Ao, C. O.; Asmar, S.; Edwards, C. D.; Kahan, D. S.; Paik, M.; Pi, X.; Williamson, W.

2015-12-01

Radio occultation utilizing deep space telecommunication signals has been used with great success in the profiling of planetary atmospheres and ionospheres since the 1960s. A shortcoming of this technique, however, is the limited temporal and spatial sampling that it provides. We consider a different approach where radio occultation measurements are taken between two spacecraft orbiting an extra-terrestrial body. Such "crosslink" radio occultations between the Global Positioning System satellites and low-earth orbiting spacecraft have been routinely acquired to provide global observations of the Earth's atmosphere and ionosphere that are used for weather forecast, climate analysis, and space weather applications. The feasibility of applying this concept to other planets has recently been demonstrated for the first time, where crosslink occultation measurements have been acquired between the Mars Odyssey and Mars Reconnaissance Orbiter spacecraft. These measurements leverage the proximity link telecommunication payloads on each orbiter, which are nominally used to provide relay communication and navigation services to Mars landers and rovers. In this presentation, we will describe the Mars crosslink experiments and the corresponding data analysis in detail. In addition, we will discuss how the crosslink occultation concepts can be effectively applied in future space exploration missions.

The effects of the nature of the antioxidant on the radiation crosslinking of polyethylene

International Nuclear Information System (INIS)

Gal, O.S.; Markovic, V.M.; Novakovic, L.R.; Stannett, V.T.

1985-01-01

The effects of three antioxidants, a hindered phenolic, a secondary amine and a thioester on the radiation crosslinking efficiency of low-density polyethylene were studied. Both gel content and thermomechanical analysis were used to follow the crosslinking. All three antioxidants decreased the amount of crosslinking at a given dose, the thioester being the most effective. The ratios of G (scission) to G (X linking) increased with all three antioxidants. This is attributed to the antioxidants only interfering with the crosslinking reaction. (author)

Structure-based non-canonical amino acid design to covalently crosslink an antibody–antigen complex

Science.gov (United States)

Xu, Jianqing; Tack, Drew; Hughes, Randall A.; Ellington, Andrew D.; Gray, Jeffrey J.

2014-01-01

Engineering antibodies to utilize non-canonical amino acids (NCAA) should greatly expand the utility of an already important biological reagent. In particular, introducing crosslinking reagents into antibody complementarity determining regions (CDRs) should provide a means to covalently crosslink residues at the antibody–antigen interface. Unfortunately, finding the optimum position for crosslinking two proteins is often a matter of iterative guessing, even when the interface is known in atomic detail. Computer-aided antibody design can potentially greatly restrict the number of variants that must be explored in order to identify successful crosslinking sites. We have therefore used Rosetta to guide the introduction of an oxidizable crosslinking NCAA, l-3,4-dihydroxyphenylalanine (l-DOPA), into the CDRs of the anti-protective antigen scFv antibody M18, and have measured crosslinking to its cognate antigen, domain 4 of the anthrax protective antigen. Computed crosslinking distance, solvent accessibility, and interface energetics were three factors considered that could impact the efficiency of l-DOPA-mediated crosslinking. In the end, 10 variants were synthesized, and crosslinking efficiencies were generally 10% or higher, with the best variant crosslinking to 52% of the available antigen. The results suggest that computational analysis can be used in a pipeline for engineering crosslinking antibodies. The rules learned from l-DOPA crosslinking of antibodies may also be generalizable to the formation of other crosslinked interfaces and complexes. PMID:23680795

Hyaluronan microgel as a potential carrier for protein sustained delivery by tailoring the crosslink network

Energy Technology Data Exchange (ETDEWEB)

Luo, Chunhong [Department of Materials Science and Engineering, College of Science and Engineering, Jinan University, Guangzhou 510632 (China); Zhao, Jianhao, E-mail: jhzhao@jnu.edu.cn [Department of Materials Science and Engineering, College of Science and Engineering, Jinan University, Guangzhou 510632 (China); Engineering Research Center of Artificial Organs and Materials, Ministry of Education, Guangzhou 510632 (China); Tu, Mei; Zeng, Rong; Rong, Jianhua [Department of Materials Science and Engineering, College of Science and Engineering, Jinan University, Guangzhou 510632 (China); Engineering Research Center of Artificial Organs and Materials, Ministry of Education, Guangzhou 510632 (China)

2014-03-01

Hyaluronan (HA) microgels with different crosslink network, i.e. HGPs-1, HGPs-1.5, HGPs-3, HGPs-6 and HGPs-15, were synthesized using divinyl sulfone (DVS) as the crosslinker in an inverse microemulsion system for controlling the sustained delivery of bovine serum albumin (BSA). With increasing the crosslinker content, the average particle size slightly increased from 1.9 ± 0.3 μm to 3.6 ± 0.5 μm by dynamic laser scattering analysis. However, the crosslinker content had no significant effect on the morphology of HA microgels by scanning and transmission electron microscopes. Fourier transform infrared spectroscopy and elemental analysis proved more sulfur participated in the crosslink reaction when raising the crosslinker amount. The water swelling test confirmed the increasing crosslink density with the crosslinker content by calculating the average molecular weight between two crosslink points to be 8.25 ± 2.51 × 10{sup 5}, 1.26 ± 0.43 × 10{sup 5}, 0.96 ± 0.09 × 10{sup 5}, 0.64 ± 0.03 × 10{sup 5}, and 0.11 ± 0.01 × 10{sup 5} respectively. The degradation of HA microgels by hyaluronidase slowed down by enhancing the crosslink density, only about 5% of HGPs-15 was degraded as opposed to over 90% for HGPs-1. BSA loading had no obvious influence on the surface morphology of HA microgels but seemed to induce their aggregation. The increase of crosslink density decreased the BSA loading capacity but facilitated its long-term sustained delivery. When the molar ratio of DVS to repeating unit of HA reached 3 or higher, similar delivery profiles were obtained. Among all these HA microgels, HGPs-3 was the optimal carrier for BSA sustained delivery in this system because it possessed both high BSA loading capacity and long-term delivery profile simultaneously. - Highlights: • HA microgels with different crosslink densities were prepared. • The crosslinker content had little effect on the morphology and size of HA microgels. • The crosslink density

Rational design of molecularly imprinted polymer: the choice of cross-linker.

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Muhammad, Turghun; Nur, Zohre; Piletska, Elena V; Yimit, Osmanjan; Piletsky, Sergey A

2012-06-07

The paper describes a rational approach for the selection of cross-linkers during the development of molecularly imprinted polymers (MIPs). As a model system for this research MIPs specific for the drug zidovudine (AZT) were designed and tested. Three cross-linkers trimethylolpropane trimethacrylate (TRIM), ethylene glycol dimethacrylate (EGDMA) and divinylbenzene (DVB) were studied. The analogue of zidovudine (AZT) ester (AZT-ES) was used as a dummy template. The imprinting factors for all of the polymers in the static adsorption experiments were calculated. The data on the AZT adsorption by control polymers (CP), which were prepared with different cross-linkers without a functional monomer, was also analyzed. DVB was found to be more inert towards zidovudine than EGDMA and TRIM, which was confirmed by both molecular modelling and adsorption experiments. It was demonstrated that DVB-based polymers had a higher imprinting factor (I = 1.85) compared with other tested cross-linked polymers. It was suggested that the selection of the cross-linker should be based on the strength of the interaction with the template: the cross-linker which displays lower binding of the template should be preferential because it generates MIPs with lower non-specific binding and a higher imprinting factor, and therefore specificity. Which cross-linker to use for the preparation of any particular MIP can be determined by analysis of the interactions between the cross-linker and template. This could be done either virtually using computational modelling or by template adsorption using a small library of polymers prepared using different cross-linkers.

Adenoviral vectors expressing fusogenic membrane glycoproteins activated via matrix metalloproteinase cleavable linkers have significant antitumor potential in the gene therapy of gliomas.

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Allen, Cory; McDonald, Cari; Giannini, Caterina; Peng, Kah Whye; Rosales, Gabriela; Russell, Stephen J; Galanis, Evanthia

2004-11-01

Fusogenic membrane glycoproteins (FMG) such as the gibbon ape leukemia virus envelope (GALV) glycoprotein are potent therapeutic transgenes with potential utility in the gene therapy of gliomas. Transfection of glioma cell lines with FMG expression constructs results in fusion with massive syncytia formation followed by cytotoxic cell death. Nevertheless, ubiquitous expression of the GALV receptor, Pit-1, makes targeting desirable in order to increase the specificity of the observed cytopathic effect. Here we report on use of matrix metalloproteinase (MMP)-cleavable linkers to target the cytotoxicity of FMG-expressing adenoviral vectors against gliomas. Replication-defective adenoviruses (Ad) were constructed expressing the hyperfusogenic version of the GALV glycoprotein linked to a blocking ligand (C-terminal extracellular domain of CD40 ligand) through either an MMP-cleavable linker (AdM40) or a non-cleavable linker (AdN40). Both viruses also co-expressed the green fluorescent protein (GFP) via an internal ribosomal entry site. The glioma cell lines U87, U118, and U251 characterized by zymography and MMP-2 activity assay as high, medium and low MMP expressors, respectively, the MMP-poor cell lines TE671 and normal human astrocytes were infected with AdM40 and AdN40 at different multiplicities of infection (MOIs) from 1-30. Fusion was quantitated by counting both number and size of syncytia. Infection of these cell lines with AdN40 did not result in fusion or cytotoxic cell death, despite the presence of infection, as demonstrated by GFP positivity, therefore indicating that the displayed CD40 ligand blocked GALV-induced fusion. Fusion was restored after infection of glioma cells with AdM40 at an MOI as low as 1 to an extent dependent on MMP expression and coxsackie adenovirus receptor (CAR) expression in the specific cell line. Western immunoblotting demonstrated the presence of the cleaved CD40 ligand in the supernatant of fused glioma cells. Use of the MMP

Link establishment criterion and topology optimization for hybrid GPS satellite communications with laser crosslinks

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Li, Lun; Wei, Sixiao; Tian, Xin; Hsieh, Li-Tse; Chen, Zhijiang; Pham, Khanh; Lyke, James; Chen, Genshe

2018-05-01

In the current global positioning system (GPS), the reliability of information transmissions can be enhanced with the aid of inter-satellite links (ISLs) or crosslinks between satellites. Instead of only using conventional radio frequency (RF) crosslinks, the laser crosslinks provide an option to significantly increase the data throughput. The connectivity and robustness of ISL are needed for analysis, especially for GPS constellations with laser crosslinks. In this paper, we first propose a hybrid GPS communication architecture in which uplinks and downlinks are established via RF signals and crosslinks are established via laser links. Then, we design an optical crosslink assignment criteria considering the practical optical communication factors such as optical line- of-sight (LOS) range, link distance, and angular velocity, etc. After that, to further improve the rationality of establishing crosslinks, a topology control algorithm is formulated to optimize GPS crosslink networks at both physical and network layers. The RF transmission features for uplink and downlink and optical transmission features for crosslinks are taken into account as constraints for the optimization problem. Finally, the proposed link establishment criteria are implemented for GPS communication with optical crosslinks. The designs of this paper provide a potential crosslink establishment and topology control algorithm for the next generation GPS.

Fabrication and characterization of hydrothermal cross-linked chitosan porous scaffolds for cartilage tissue engineering applications.

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Shamekhi, Mohammad Amin; Rabiee, Ahmad; Mirzadeh, Hamid; Mahdavi, Hamid; Mohebbi-Kalhori, Davod; Baghaban Eslaminejad, Mohamadreza

2017-11-01

The use of various chemical cross-linking agents for the improvement of scaffolds physical and mechanical properties is a common practical method, which is limited by cytotoxicity effects. Due to exerting contract type forces, chondrocytes are known to implement shrinkage on the tissue engineered constructs, which can be avoided by the scaffold cross-linking. In the this research, chitosan scaffolds are cross-linked with hydrothermal treatment with autoclave sterilization time of 0, 10, 20 and 30min, to avoid the application of the traditional chemical toxic materials. The optimization studies with gel content and crosslink density measurements indicate that for 20min sterilization time, the gel content approaches to ~80%. The scaffolds are fully characterized by the conventional techniques such as SEM, porosity and permeability, XRD, compression, thermal analysis and dynamic mechanical thermal analysis (DMTA). FT-IR studies shows that autoclave inter-chain cross-linking reduces the amine group absorption at 1560cm -1 and increase the absorption of N-acetylated groups at 1629cm -1 . It is anticipated, that this observation evidenced by chitosan scaffold browning upon autoclave cross-linking is an indication of the familiar maillard reaction between amine moieties and carbonyl groups. The biodegradation rate analysis shows that chitosan scaffolds with lower concentrations, possess suitable degradation rate for cartilage tissue engineering applications. In addition, cytotoxicity analysis shows that fabricated scaffolds are biocompatible. The human articular chondrocytes seeding into 3D cross-linked scaffolds shows a higher viability and proliferation in comparison with the uncross-linked samples and 2D controls. Investigation of cell morphology on the scaffolds by SEM, shows a more spherical morphology of chondrocytes on the cross-linked scaffolds for 21days of in vitro culture. Copyright © 2017. Published by Elsevier B.V.

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

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Perera, Handunge Kumudu Irani; Handuwalage, Charith Sandaruwan

2015-06-09

Protein cross-linking which occurs towards the latter part of protein glycation is implicated in the development of chronic diabetic complications. Glycation induced protein cross-linking inhibitory effects of nine antidiabetic plants and three spices were evaluated in this study using a novel, simple, electrophoresis based method. Methanol extracts of thirteen plants including nine antidiabetic plants and three spices were used. Lysozyme and fructose were incubated at 37 °C in the presence or absence of different concentrations of plant extracts up to 31 days. Standard glycation inhibitor aminoguanidine and other appropriate controls were included. A recently established sodium dodecyl polyacrylamide gel electrophoresis (SDS-PAGE) method was used to detect the products of protein cross-linking in the incubation mixtures. High molecular weight protein products representing the dimer, trimer and tetramer of lysozyme were detected in the presence of fructose. Among the nine antidiabetic plants, seven showed glycation induced protein cross-linking inhibitory effects namely Ficus racemosa (FR) stem bark, Gymnema sylvestre (GS) leaves, Musa paradisiaca (MP) yam, Phyllanthus debilis (PD) whole plant, Phyllanthus emblica (PE) fruit, Pterocarpus marsupium (PM) latex and Tinospora cordifolia (TC) leaves. Inhibition observed with Coccinia grandis (CG) leaves and Strychnos potatorum (SP) seeds were much low. Leaves of Gymnema lactiferum (GL), the plant without known antidiabetic effects showed the lowest inhibition. All three spices namely Coriandrum sativum (CS) seeds, Cinnamomum zeylanicum (CZ) bark and Syzygium aromaticum (SA) flower buds showed cross-link inhibitory effects with higher effects in CS and SA. PD, PE, PM, CS and SA showed almost complete inhibition on the formation of cross-linking with 25 μg/ml extracts. Methanol extracts of PD, PE, PM, CS and SA have shown promising inhibitory effects on glycation induced protein cross-linking.

Automobile parts by radiation crosslinking

International Nuclear Information System (INIS)

Yoshii, Fumio

2008-01-01

Radiation crosslinking, graft polymerization and degradation are useful technologies to improve polymer materials. The crosslinking causes improvement in strength, heat stability and processability to gives network structure for polymer materials and hence crosslinked materials are used in various fields, especially car parts. Electron beam (EB) of short time irradiation is used for these modifications. Irradiated (pre-vulcanized) before sulfur vulcanization rubber tires, heat resistant wires/cables, shrinkable tubes and foams of car parts are achieved by EB crosslinking. Polyethylene and polyvinyl chloride are used in cables and wires, polypropylene in plastic foams and natural rubber etc. In this paper radiation processing of tire, wire/cables, foams, shrinkable tubes and circuit protection devices (CPT) are explained. (author)

Crosslinked anion exchange membranes with primary diamine-based crosslinkers for vanadium redox flow battery application

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Cha, Min Suc; Jeong, Hwan Yeop; Shin, Hee Young; Hong, Soo Hyun; Kim, Tae-Ho; Oh, Seong-Geun; Lee, Jang Yong; Hong, Young Taik

2017-09-01

A series of polysulfone-based crosslinked anion exchange membranes (AEMs) with primary diamine-based crosslinkers has been prepared via simple a crosslinking process as low-cost and durable membranes for vanadium redox flow batteries (VRFBs). Chloromethylated polysulfone is used as a precursor polymer for crosslinked AEMs (CAPSU-x) with different degrees of crosslinking. Among the developed AEMs, CAPSU-2.5 shows outstanding dimensional stability and anion (Cl-, SO42-, and OH-) conductivity. Moreover, CAPSU-2.5 exhibits much lower vanadium ion permeability (2.72 × 10-8 cm2 min-1) than Nafion 115 (2.88 × 10-6 cm2 min-1), which results in an excellent coulombic efficiency of 100%. The chemical and operational stabilities of the membranes have been investigated via ex situ soaking tests in 0.1 M VO2+ solution and in situ operation tests for 100 cycles, respectively. The excellent chemical, physical, and electrochemical properties of the CAPSU-2.5 membrane make it suitable for use in VRFBs.

Desmosine-Inspired Cross-Linkers for Hyaluronan Hydrogels

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Hagel, Valentin; Mateescu, Markus; Southan, Alexander; Wegner, Seraphine V.; Nuss, Isabell; Haraszti, Tamás; Kleinhans, Claudia; Schuh, Christian; Spatz, Joachim P.; Kluger, Petra J.; Bach, Monika; Tussetschläger, Stefan; Tovar, Günter E. M.; Laschat, Sabine; Boehm, Heike

2013-06-01

We designed bioinspired cross-linkers based on desmosine, the cross-linker in natural elastin, to prepare hydrogels with thiolated hyaluronic acid. These short, rigid cross-linkers are based on pyridinium salts (as in desmosine) and can connect two polymer backbones. Generally, the obtained semi-synthetic hydrogels are form-stable, can withstand repeated stress, have a large linear-elastic range, and show strain stiffening behavior typical for biopolymer networks. In addition, it is possible to introduce a positive charge to the core of the cross-linker without affecting the gelation efficiency, or consequently the network connectivity. However, the mechanical properties strongly depend on the charge of the cross-linker. The properties of the presented hydrogels can thus be tuned in a range important for engineering of soft tissues by controlling the cross-linking density and the charge of the cross-linker.

Triethyl orthoformate mediated a novel crosslinking method for the preparation of hydrogels for tissue engineering applications: characterization and in vitro cytocompatibility analysis

Energy Technology Data Exchange (ETDEWEB)

Yar, Muhammad, E-mail: drmyar@ciitlahore.edu.pk [Interdisciplinary Research Center in Biomedical Materials, COMSATS Institute of Information Technology, Lahore 54000 (Pakistan); Shahzad, Sohail [Interdisciplinary Research Center in Biomedical Materials, COMSATS Institute of Information Technology, Lahore 54000 (Pakistan); Department of Chemistry, The Islamia University of Bahawalpur, Bahawalpur 63100 (Pakistan); Siddiqi, Saadat Anwar [Interdisciplinary Research Center in Biomedical Materials, COMSATS Institute of Information Technology, Lahore 54000 (Pakistan); Mahmood, Nasir [Department of Allied Health Sciences and Chemical Pathology, Department of Human Genetics and Molecular Biology, University of Health Sciences, Lahore (Pakistan); Rauf, Abdul [Department of Chemistry, The Islamia University of Bahawalpur, Bahawalpur 63100 (Pakistan); Anwar, Muhammad Sabieh [Department of Physics, Syed Babar Ali School of Science and Engineering, Lahore University of Management Sciences (LUMS), Opposite Sector U, D.H.A., Lahore 54792 (Pakistan); Chaudhry, Aqif Anwar [Interdisciplinary Research Center in Biomedical Materials, COMSATS Institute of Information Technology, Lahore 54000 (Pakistan); Rehman, Ihtesham ur [Interdisciplinary Research Center in Biomedical Materials, COMSATS Institute of Information Technology, Lahore 54000 (Pakistan); Department of Materials Science and Engineering, The Kroto Research Institute, The University of Sheffield, North Campus, Broad Lane, Sheffield S3 7HQ (United Kingdom)

2015-11-01

This paper describes the development of a new crosslinking method for the synthesis of novel hydrogel films from chitosan and PVA for potential use in various biomedical applications. These hydrogel membranes were synthesized by blending different ratios of chitosan (CS) and poly(vinyl alcohol) (PVA) solutions and were crosslinked with 2.5% (w/v) triethyl orthoformate (TEOF) in the presence of 17% (w/v) sulfuric acid. The physical/chemical interactions and the presence of specific functional groups in the synthesized materials were evaluated by Fourier transform infrared (FT-IR) spectroscopy. The morphology, structure and pore size of the materials were investigated by scanning electron microscopy (SEM). Thermal gravimetric analysis (TGA) proved that these crosslinked hydrogel films have good thermal stability which was decreased as the CS ratio was increased. Differential scanning calorimetry (DSC) exhibited that CS and PVA were present in the amorphous form. The solution absorption properties were performed in phosphate buffer saline (PBS) solution of pH 7.4. The 20% PVA–80% CS crosslinked hydrogel films showed a greater degree of solution absorption (183%) as compared to other compositions. The hydrogels with greater CS concentration (60% and 80%) demonstrated relatively more porous structure, better cell viability and proliferation and also revealed good blood clotting ability even after crosslinking. Based on the observed facts these hydrogels can be tailored for their potential utilization in wound healing and skin tissue engineering applications. - Highlights: • A new method for covalently crosslinking of chitosan and PVA. • Triethyl orthoformate (TEOF) a new polymer–polymer crosslinking agent. • Hydrogels displayed a good solution absorption capacity. • Hydrogels demonstrated good cytocompatibility. • Good blood clotting potential was shown by these scaffolds.

Triethyl orthoformate mediated a novel crosslinking method for the preparation of hydrogels for tissue engineering applications: characterization and in vitro cytocompatibility analysis

International Nuclear Information System (INIS)

Yar, Muhammad; Shahzad, Sohail; Siddiqi, Saadat Anwar; Mahmood, Nasir; Rauf, Abdul; Anwar, Muhammad Sabieh; Chaudhry, Aqif Anwar; Rehman, Ihtesham ur

2015-01-01

This paper describes the development of a new crosslinking method for the synthesis of novel hydrogel films from chitosan and PVA for potential use in various biomedical applications. These hydrogel membranes were synthesized by blending different ratios of chitosan (CS) and poly(vinyl alcohol) (PVA) solutions and were crosslinked with 2.5% (w/v) triethyl orthoformate (TEOF) in the presence of 17% (w/v) sulfuric acid. The physical/chemical interactions and the presence of specific functional groups in the synthesized materials were evaluated by Fourier transform infrared (FT-IR) spectroscopy. The morphology, structure and pore size of the materials were investigated by scanning electron microscopy (SEM). Thermal gravimetric analysis (TGA) proved that these crosslinked hydrogel films have good thermal stability which was decreased as the CS ratio was increased. Differential scanning calorimetry (DSC) exhibited that CS and PVA were present in the amorphous form. The solution absorption properties were performed in phosphate buffer saline (PBS) solution of pH 7.4. The 20% PVA–80% CS crosslinked hydrogel films showed a greater degree of solution absorption (183%) as compared to other compositions. The hydrogels with greater CS concentration (60% and 80%) demonstrated relatively more porous structure, better cell viability and proliferation and also revealed good blood clotting ability even after crosslinking. Based on the observed facts these hydrogels can be tailored for their potential utilization in wound healing and skin tissue engineering applications. - Highlights: • A new method for covalently crosslinking of chitosan and PVA. • Triethyl orthoformate (TEOF) a new polymer–polymer crosslinking agent. • Hydrogels displayed a good solution absorption capacity. • Hydrogels demonstrated good cytocompatibility. • Good blood clotting potential was shown by these scaffolds

Cleavable DNA-protein hybrid molecular beacon: A novel efficient signal translator for sensitive fluorescence anisotropy bioassay.

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Hu, Pan; Yang, Bin

2016-01-15

Due to its unique features such as high sensitivity, homogeneous format, and independence on fluorescent intensity, fluorescence anisotropy (FA) assay has become a hotspot of study in oligonucleotide-based bioassays. However, until now most FA probes require carefully customized structure designs, and thus are neither generalizable for different sensing systems nor effective to obtain sufficient signal response. To address this issue, a cleavable DNA-protein hybrid molecular beacon was successfully engineered for signal amplified FA bioassay, via combining the unique stable structure of molecular beacon and the large molecular mass of streptavidin. Compared with single DNA strand probe or conventional molecular beacon, the DNA-protein hybrid molecular beacon exhibited a much higher FA value, which was potential to obtain high signal-background ratio in sensing process. As proof-of-principle, this novel DNA-protein hybrid molecular beacon was further applied for FA bioassay using DNAzyme-Pb(2+) as a model sensing system. This FA assay approach could selectively detect as low as 0.5nM Pb(2+) in buffer solution, and also be successful for real samples analysis with good recovery values. Compatible with most of oligonucleotide probes' designs and enzyme-based signal amplification strategies, the molecular beacon can serve as a novel signal translator to expand the application prospect of FA technology in various bioassays. Copyright © 2015 Elsevier B.V. All rights reserved.

WICH, a member of WASP-interacting protein family, cross-links actin filaments

International Nuclear Information System (INIS)

Kato, Masayoshi; Takenawa, Tadaomi

2005-01-01

In yeast, Verprolin plays an important role in rearrangement of the actin cytoskeleton. There are three mammalian homologues of Verprolin, WIP, CR16, and WICH, and all of them bind actin and Wiskott-Aldrich syndrome protein (WASP) and/or neural-WASP. Here, we describe a novel function of WICH. In vitro co-sedimentation analysis revealed that WICH not only binds to actin filaments but also cross-links them. Fluorescence and electron microscopy detected that this cross-linking results in straight bundled actin filaments. Overexpression of WICH alone in cultured fibroblast caused the formation of thick actin fibers. This ability of WICH depended on its own actin cross-linking activity. Importantly, the actin cross-linking activity of WICH was modified through a direct association with N-WASP. Taken together, these data suggest that WICH induces a bundled form of actin filament with actin cross-linking activity and the association with N-WASP suppresses that activity. WICH thus appears to be a novel actin bundling protein

Genipin cross-linked electrospun chitosan-based nanofibrous mat as tissue engineering scaffold

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Esmaeil Mirzaei

2014-04-01

Full Text Available   Objective(s: To improve water stability of electrospun chitosan/ Polyethylene oxide (PEO nanofibers, genipin, a biocompatible and nontoxic agent, was used to crosslink chitosan based nanofibers.   Materials and Methods: Different amounts of genipin were added to the chitosan/PEO solutions, chitosan/PEO weight ratio 90/10 in 80 % acetic acid, and the solutions were then electrospun to form nanofibers. The spun nanofibers were exposed to water vapor to complete crosslinking. The nanofibrous membranes were subjected to detailed analysis by scanning electron microscopy (SEM, Fourier transform infrared-attenuated total reflection (FTIR-ATR spectroscopy, swelling test, MTT cytotoxicity, and cell attachment. Results: SEM images of electrospun mats showed that genipin-crosslinked nanofibers retained their fibrous structure after immerging in PBS (pH=7.4 for 24 hours, while the uncrosslinked samples lost their fibrous structure, indicating the water stability of genipin-crosslinked nanofibers. The genipin-crosslinked mats also showed no significant change in swelling ratio in comparison with uncrosslinked ones. FTIR-ATR spectrum of uncrosslinked and genipin-crosslinked chitosan nanofibers revealed the reaction between genipin and amino groups of chitosan. Cytotoxicity of genipin-crosslinked nanofibers was examined by MTT assay on human fibroblast cells in the presence of nanofibers extraction media. The genipin-crosslinked nanofibers did not show any toxic effects on fibroblast cells at the lowest and moderate amount of genipin. The fibroblast cells also showed a good adhesion on genipin-crosslinked nanofibers. Conclusion: This electrospun matrix would be used for biomedical applications such as wound dressing and scaffold for tissue engineering without the concern of toxicity.

Porcine skin as a source of biodegradable matrices: alkaline treatment and glutaraldehyde crosslinking

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Fabiana T. Rodrigues

2010-06-01

Full Text Available In this work, the modifications promoted by alkaline hydrolysis and glutaraldehyde (GA crosslinking on type I collagen found in porcine skin have been studied. Collagen matrices were obtained from the alkaline hydrolysis of porcine skin, with subsequent GA crosslinking in different concentrations and reaction times. The elastin content determination showed that independent of the treatment, elastin was present in the matrices. Results obtained from in vitro trypsin degradation indicated that with the increase of GA concentration and reaction time, the degradation rate decreased. From thermogravimetry and differential scanning calorimetry analysis it can be observed that the collagen in the matrices becomes more resistant to thermal degradation as a consequence of the increasing crosslink degree. Scanning electron microscopy analysis indicated that after the GA crosslinking, collagen fibers become more organized and well-defined. Therefore, the preparations of porcine skin matrices with different degradation rates, which can be used in soft tissue reconstruction, are viable.

Carboxymethyl starch cross-linked by electron beam radiation in presence of acrylic acid sensitizer

International Nuclear Information System (INIS)

Doan Binh; Nguyen Thanh Duoc; Pham Thi Thu Hong

2013-01-01

Carboxymethyl starch (CMS) can be cross-linked by electron beam radiation to form a biocompatible and environment-friendly hydrogel at a high absorbed dose and a condensed CMS concentration. Acrylic acid (AAc) can be used as a sensitizer in order to reduce the absorbed doses to an acceptable certain level. At an absorbed dose of 3-4 kGy, the gel content of crosslinked CMS can be obtained about 50% with 5% (w/w) AAc concentration used. The compressive strength of CMS samples increased with increasing their cross-linked densities due to raising absorbed doses. The swelling ratio of cross-linked CMS was also attainable at a maximum of 50 times in the distilled water. The enzymatic degradation of cross-linked CMS was carried out in acetate buffer pH 4.6 with 0.1% α-amylase enzymatic solution incubated at 40℃ for 6 h. The crosslinked CMS samples were degraded slower than uncrosslinked CMS ones. The results indicated that the highly cross-linked CMS was almost fully degradable when the enzymatic hydrolysis was performed during 6 h. The FT IR spectra of cross-linked CMS in the presence of AAc were examined to observe the carboxyl group of AAc in the structure of cross-linked CMS. The hydrophilic of cross-linked CMS surface was determined by a contact-angle analysis. (authors)

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

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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.

Radiostereometric analysis comparison of wear of highly cross-linked polyethylene against 36- vs 28-mm femoral heads.

Science.gov (United States)

Bragdon, Charles R; Greene, Meridith E; Freiberg, Andrew A; Harris, William H; Malchau, Henrik

2007-09-01

This study used radiostereometric analysis (RSA) to compare the femoral head penetration of 28- vs 36-mm-diameter femoral heads into highly cross-linked polyethylene in 2 groups of total hip arthroplasty patients. Thirty patients were enrolled in this RSA study using highly cross-linked polyethylene (Longevity, Zimmer Inc, Warsaw, Idaho) against either 28- or 36-mm-diameter cobalt chrome femoral heads. At 3-year follow-up, there was no significant difference in the total average femoral head penetration, including both creep and wear, using 3 methods of RSA measurement between the 2 groups. Importantly, after bedding-in, there was no further significant increase in the amount of femoral head penetration (ie, wear) with either head size between years 1 and 3. There were no radiographic signs of lysis or radiolucencies at a minimum 3-year follow-up.

HPLC-UV, MALDI-TOF-MS and ESI-MS/MS analysis of the mechlorethamine DNA crosslink at a cytosine-cytosine mismatch pair.

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Pornchai Rojsitthisak

Full Text Available Mechlorethamine [ClCH(2CH(2N(CH(3CH(2CH(2Cl], a nitrogen mustard alkylating agent, has been proven to form a DNA interstrand crosslink at a cytosine-cytosine (C-C mismatch pair using gel electrophoresis. However, the atomic connectivity of this unusual crosslink is unknown.HPLC-UV, MALDI-TOF-MS, and ESI-MS/MS were used to determine the atomic connectivity of the DNA C-C crosslink formed by mechlorethamine, MALDI-TOF-MS of the HPLC-purified reaction product of mechlorethamine with the DNA duplex d[CTCACACCGTGGTTC]•d[GAACCACCGTGTGAG] (underlined bases are a C-C mismatch pair indicated formation of an interstrand crosslink at m/z 9222.088 [M-2H+Na](+. Following enzymatic digestion of the crosslinked duplex by snake venom phosphodiesterase and calf intestinal phosphatase, ESI-MS/MS indicated the presence of dC-mech-dC [mech = CH(2CH(2N(CH(3CH(2CH(2] at m/z 269.2 [M](2+ (expected m/z 269.6, exact mass 539.27 and its hydrolytic product dC-mech-OH at m/z 329.6 [M](+ (expected m/z 329.2. Fragmentation of dC-mech-dC gave product ions at m/z 294.3 and 236.9 [M](+, which are both due to loss of the 4-amino group of cytosine (as ammonia, in addition to dC and dC+HN(CH(3CH = CH(2, respectively. The presence of m/z 269.2 [M](2+ and loss of ammonia exclude crosslink formation at cytosine N(4 or O(2 and indicate crosslinking through cytosine N(3 with formation of two quaternary ammonium ions.Our results provide an important addition to the literature, as the first example of the use of HPLC and MS for analysis of a DNA adduct at the N(3 position of cytosine.

Analysis of growth hormone and lactogenic binding sites cross-linked to iodinated human growth hormone

International Nuclear Information System (INIS)

Hughes, J.P.; Simpson, J.S.; Friesen, H.G.

1983-01-01

GH (GHR) and lactogenic receptors were analyzed after use of the cross-linking reagent ethylene glycol bis-(succinimidyl succinate) to attach covalently iodinated human GH (hGH) to binding proteins 1) on intact IM-9 lymphocytes, 2) in a partially purified GHR preparation from rabbit liver, and 3) in crude microsomal fractions from rabbit liver, rabbit mammary gland, and rat liver. The latter two microsomal preparations contain primarily lactogenic receptors, whereas in IM-9 lymphocytes and the rabbit liver preparations, GHR predominate. Cross-linked [125I]hGH-receptor complexes were solubilized, reduced, and separated on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Analysis of proteins cross-linked to [125I]hGH in the microsomal fraction from rabbit liver showed a specifically labeled complex with an estimated molecular weight (mol wt) of 75K. A slightly lower mol wt (71K) was determined for the complex labeled in the purified GHR preparation. In contrast to the relatively low mol wt complexes in rabbit liver, a complex that migrated with an apparent mol wt of 130K was identified in IM-9 lymphocytes. Labeled complexes were identified at 66K from rat liver and 61K from rabbit mammary gland. If it is assumed that hGH contributes 21K to the mol wt of the radiolabeled complexes, then the approximate mol wts of hGH-binding sites are 50-54K from rabbit liver, 109K from IM-9 lymphocytes, 45K from rat liver, and 40K from rabbit mammary gland

Thermal enhancement of x-ray induced DNA crosslinking

International Nuclear Information System (INIS)

Bowden, G.T.; Kasunic, M.; Cress, A.E.

1982-01-01

Ionizing radiation appears to crosslink nuclear DNA with chromosomal proteins. Important cellular processes such as transcription and DNA replication are likely to be compromised as a result of the DNA crosslinking. Heat treatment (43/sup o/C) of mouse leukemia cells (L1210) before X irradiation (50 Gy) was found to cause a doubling of the radiation-induced DNA crosslinking as measured by alkaline elution technique. By using proteinase K, a very active protease, to eliminate DNA-protein crosslinking in the alkaline elution assay, it was shown that the thermally enhanced DNA crosslinking was attributed to an increase in DNA-protein crosslinking. However, utilizing a protein radiolabel technique under conditions of increased DNA-protein crosslinking, the amount of protein left on the filter in the elution assay was not increased. These data suggest that qualitative rather than large quantitative differences in the crosslinked chromosomal proteins exist between irradiated cells and cells treated with heat prior to irradiation

Transglutaminase catalyzed cross-linking of sodium caseinate improves oxidative stability of flaxseed oil emulsion.

Science.gov (United States)

Ma, Hairan; Forssell, Pirkko; Kylli, Petri; Lampi, Anna-Maija; Buchert, Johanna; Boer, Harry; Partanen, Riitta

2012-06-20

Sodium caseinate was modified by transglutaminase catalyzed cross-linking reaction prior to the emulsification process in order to study the effect of cross-linking on the oxidative stability of protein stabilized emulsions. The extent of the cross-linking catalyzed by different dosages of transglutaminase was investigated by following the ammonia production during the reaction and using SDS-PAGE gel. O/W emulsions prepared with the cross-linked and non-cross-linked sodium caseinates were stored for 30 days under the same conditions. Peroxide value measurement, oxygen consumption measurement, and headspace gas chromatography analysis were used to study the oxidative stability of the emulsions. The emulsion made of the cross-linked sodium caseinate showed an improved oxidative stability with reduced formation of fatty acid hydroperoxides and volatiles and a longer period of low rate oxygen consumption. The improving effect of transglutaminase catalyzed cross-linking could be most likely attributed to the enhanced physical stability of the interfacial protein layer against competitive adsorption by oil oxidation products.

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

Science.gov (United States)

Ding, Rui

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

Poly(tetramethyleneterephthalate) crosslinked by irradiation

International Nuclear Information System (INIS)

Nyberg, D.D.

1978-01-01

Crosslinking, e.g., by irradiation, of a polymer comprising poly(tetramethyleneterephthalate) is made possible by the addition of a member selected from the group consisting of triallyl cyanurate and N,N'-m-phenylenedimaleimide. The resulting crosslinked modified polymer may be rendered heat recoverable

DNA Photolithography with Cinnamate Crosslinkers

Science.gov (United States)

Feng, Lang (Inventor); Chaikin, Paul Michael (Inventor)

2016-01-01

The present invention relates generally to cinnamate crosslinkers. Specifically, the present invention relates to gels, biochips, and functionalized surfaces useful as probes, in assays, in gels, and for drug delivery, and methods of making the same using a newly-discovered crosslinking configuration.

The radiation crosslinking of ethylene copolymers

International Nuclear Information System (INIS)

Burns, N.M.

1979-01-01

The enhanced radiation crosslinking tendency of ethylene-vinyl acetate and ethylene-ethyl acrylate copolymers over ethylene homopolymer is proportional to the comonomer content. This is caused by an increase in the amorphous polymer content and by structure-related factors. The copolymers crosslink by a random process that for ethylene-vinyl acetate copolymer involves some crosslinking through the acetoxy group of the comonomer. While knowledge of the process for the crosslinking of ethylene-ethyl acrylate copolymer is less certain, it is currently believed to occur primarily at the branch point on the polymer backbone. Data relating comonomer content and the molecular weight of the copolymers to the radiation crosslinking levels realized were developed to aid in resin selection by the formulator. Triallyl cyanurate cure accelerator was found to be less effective in ethylene-vinyl acetate copolymer than in homopolymer and to have no effect on gel development in ethylene-ethyl acrylate copolymer. (author)

Lithium polymer cell assembled by in situ chemical cross-linking of ionic liquid electrolyte with phosphazene-based cross-linking agent

International Nuclear Information System (INIS)

Choi, Ji-Ae; Kang, Yongku; Kim, Dong-Won

2013-01-01

Highlights: ► Ionic liquid-based cross-linked gel polymer electrolytes were synthesized and their electrochemical properties were investigated. ► Lithium polymer cells with in situ cross-linked gel polymer electrolytes exhibited reversible cycling behavior with good capacity retention. ► The use of ionic liquid-based cross-linked gel polymer electrolytes significantly improved the thermal stability of the cells. -- Abstract: Ionic liquid-based cross-linked gel polymer electrolytes were prepared with a phosphazene-based cross-linking agent, and their electrochemical properties were investigated. Lithium polymer cells composed of lithium anode and LiCoO 2 cathode were assembled with ionic liquid-based cross-linked gel polymer electrolyte and their cycling performance was evaluated. The interfacial adhesion between the electrodes and the electrolyte by in situ chemical cross-linking resulted in stable capacity retention of the cell. A reduction in the ionic mobility in both the electrolyte and the electrode adversely affected discharge capacity and high rate performance of the cell. DSC studies demonstrated that the use of ionic liquid-based cross-linked gel polymer electrolytes provided a significant improvement in the thermal stability of the cell

Crosslinking of thermoplastic composites using electron beam radiation

International Nuclear Information System (INIS)

Strong, A.B.; Black, S.R.; Bryce, G.R.; Olcott, D.D.

1991-01-01

The crosslinking of thermoset materials has been clearly demonstrated to improve many desirable physical and chemical properties for composite applications. While thermoplastic resins also offer many advantages for composite applications, they are not crosslinked and, therefore, may not meet the same property criteria as crosslinked thermosets. Electron beams have been used successfully for crosslinking non-reinforced thermoplastic materials. Electron beams have also been used for curing composite thermoset materials. This research utilizes electron beams to crosslink high performance thermoplastic composite materials (PEEK and PPS with glass and carbon fibers). The tensile strength and tensile modulus are compared under various crosslinking conditions. The method is found to have some advantages in potentially improving physical properties of thermoplastic composite materials

Radiation crosslinking of poly(butyl acrylate) during polymerization and grafted copolymerization with Cr(III) crosslinked collagen

International Nuclear Information System (INIS)

Pietrucha, K.; Kroh, J.

1984-01-01

Enhanced crosslinking of synthetic polymer simultaneous with grafting and homopolymerization processes have been observed in irradiated leather tanned with Cr(III) and embedded with aqueous emulsions of butyl acrylate. Extent of poly(butyl acrylate) crosslinking during copolymerization was found to be approximately one order higher than in the case of radiation polymerization of butyl acrylate in emulsion. New method for isolation of grafted copolymer based on degradation of collagen has been developed. The extent of crosslinking was calculated from the swelling data. (author)

Collagen crosslink location: a molecular marker for fibrosis in lungs of rats with experimental silicosis

International Nuclear Information System (INIS)

Gerriets, J.E.; Reiser, K.M.; Last, J.A.

1986-01-01

Collagen content is increased in lungs of animals with experimental silicosis. They hypothesize that the collagen deposited in such fibrotic lungs differs structurally from normal lung collagen. Silicotic lung collagen shows an increase in lysine hydroxylation. In addition, the ratio of the difunctional crosslinks DHLNL (dihydroxylysinonorleucine) to HLNL (hydroxylysinonorleucine) is sharply elevated compared to that in control lungs. The peptide α1(I)CB7 x α2(I)CB1 crosslinked by HLNL was demonstrated in NaB 3 H 4 -reduced, CNBr-digested collagen from rat tail tendon by peptide purification, followed by periodate oxidation and amino acid analysis. Further structural analysis of this peptide was obtained by digestion of the crosslinked peptide with trypsin and purification of the tryptic peptide containing this crosslink followed by amino acid analysis. They then examined the analogous collagenous peptide in normal and silicotic lungs and analyzed the crosslink it contained. They observed that DHLNL was present at specific sites previously containing HLNL; that is, the collagen in fibrotic lungs is altered at specific sites by post-translational modification of a lysine residue by hydroxylation in a predictable way. They conclude that such unusual hydroxylation of a specific lysine residue in the α2 chain provides a molecular marker for fibrotic lung collagen

ESR study on free radicals trapped in crosslinked polytetrafluoroethylene (PTFE)

International Nuclear Information System (INIS)

Oshima, Akihiro; Tabata, Yoneho; Seguchi, Tadao

1997-01-01

Free radicals in crosslinked PTFE which formed by 60 Co γ-rays irradiation at 77 K and at room temperature were studied by electron spin resonance (ESR) spectroscopy. The crosslinked PTFE specimens with different crosslinking density were prepared by electron beam irradiation in the molten state. The ESR spectra observed in the irradiated crosslinked PTFE are much different from those in non-crosslinked PTFE (virgin); a broad singlet component increases with increasing the crosslinking density, G-value of radicals is much higher in crosslinked PTFE than in non-crosslinked one. Free radicals related to the broad component are trapped in the non-crystalline region of crosslinked PTFE and rather stable at room temperature, whereas radicals trapped in amorphous non-crosslinked PTFE are unstable at room temperature. It is thought that most of free radicals trapped in the crosslinked PTFE are formed in the crosslinked amorphous region. The trapped radicals decays around 383 K (110 o C) due to the molecular motion of α-relaxation. (Author)

Photosensitized UVA-Induced Cross-Linking between Human DNA Repair and Replication Proteins and DNA Revealed by Proteomic Analysis

Science.gov (United States)

2016-01-01

Long wavelength ultraviolet radiation (UVA, 320–400 nm) interacts with chromophores present in human cells to induce reactive oxygen species (ROS) that damage both DNA and proteins. ROS levels are amplified, and the damaging effects of UVA are exacerbated if the cells are irradiated in the presence of UVA photosensitizers such as 6-thioguanine (6-TG), a strong UVA chromophore that is extensively incorporated into the DNA of dividing cells, or the fluoroquinolone antibiotic ciprofloxacin. Both DNA-embedded 6-TG and ciprofloxacin combine synergistically with UVA to generate high levels of ROS. Importantly, the extensive protein damage induced by these photosensitizer+UVA combinations inhibits DNA repair. DNA is maintained in intimate contact with the proteins that effect its replication, transcription, and repair, and DNA–protein cross-links (DPCs) are a recognized reaction product of ROS. Cross-linking of DNA metabolizing proteins would compromise these processes by introducing physical blocks and by depleting active proteins. We describe a sensitive and statistically rigorous method to analyze DPCs in cultured human cells. Application of this proteomics-based analysis to cells treated with 6-TG+UVA and ciprofloxacin+UVA identified proteins involved in DNA repair, replication, and gene expression among those most vulnerable to cross-linking under oxidative conditions. PMID:27654267

Shape memory behaviour of radiation-crosslinked PCL/PMVS blends

International Nuclear Information System (INIS)

Zhu Guangming; Xu Shuogui; Wang Jinhua; Zhang Longbin

2006-01-01

The performance and radiation crosslinking of polycaprolactone (PCL) and polymethylvinylsiloxane (PMVS) blends has been investigated. Radiation crosslinking of PCL/PMVS blends followed the Charlesby-Pinner equation, and PMVS promoted the radiation crosslinking of the blends. As the concentration of PMVS increased, the gelation dose and the ratio of degradation to crosslinking (p 0 /q 0 ) decreased and the efficiency of radiation crosslinking increased. The elastic modulus below the melting point of PCL of radiation-crosslinked PCL/PMVS blends decreased with the increase of PMVS, and increased above the melting point. The crosslinked PCL/PMVS blends exhibited excellent shape memory effects, and the ratios of deformation to recovery were more than 95%

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.

Effect of polyfunctional monomers on properties of radiation crosslinked EPDM/waste tire dust blend

International Nuclear Information System (INIS)

Yasin, Tariq; Khan, Sajid; Nho, Young-Chang; Ahmad, Rashid

2012-01-01

In this study, waste tire dust is recycled as filler and blended with ethylene-propylene diene monomer (EPDM) rubber. Three different polyfuntional monomers (PFMs) are incorporated into the standard formulation and irradiated under electron beam at different doses up to maximum of 100 kGy. The combined effects of PFMs and absorbed dose on the physical properties of EPDM/WTD blend are measured and compared with sulfur crosslinked formulation. Thermogravimetric analysis showed that radiation developed better crosslinked network with higher thermal stability than sulfur crosslinked structure. The physical properties of radiation crosslinked blend are similar to the sulfur crosslinked blend. The absence of toxic chemicals/additives in radiation crosslinked blends made them an ideal candidate for many applications such as roof sealing sheets, water retention pond, playground mat, sealing profile for windows etc. - Highlights: ► We have recycled waste tire dust and blended it with EPDM. ► EB crosslinking is carried in the presence of polyfuntional monomers. ► Radiation gave better network with higher thermal stability than sulfur. ► The absence of toxic chemicals in EB blends will increase its acceptability.

Radiation crosslinking of poly(butyl acrylate) during polymerization and grafted copolymerization with Cr(III) crosslinked collagen

International Nuclear Information System (INIS)

Pietrucha, K.; Kroh, J.

1986-01-01

Enhanced crosslinking of synthetic polymer simultaneously with grafting and homopolymerization processes has been observed in irradiated leather tanned with Cr(III) and embedded with aqueous emulsions of butyl acrylate. The extent of poly(butyl acrylate) crosslinking during copolymerization was found to be approximately one order higher than in the case of radiation polymerization of butyl acrylate in emulsion. A new method for isolation of grafted copolymer based on degradation of collagen has been developed. The extent of crosslinking was calculated from the swelling data. (author)

Characterization of Aldehyde Crosslinked Kenaf Regenerated Cellulose Film

Directory of Open Access Journals (Sweden)

Hatika Kaco

2015-08-01

Full Text Available Regenerated cellulose film with better mechanical properties was successfully produced by introducing aldehyde crosslinker during the regeneration process. The cellulose source material was derived from kenaf core powder and dissolved in LiOH/urea solvent at −13 °C to form a cellulose solution. The cellulose solution was cast and coagulated in a crosslinker bath at different percentages of glutaraldehyde (GA and glyoxal (GX to form a regenerated cellulose film. According to Fourier transform infrared spectroscopy (FTIR spectra, the hydroxyl group of the cellulose was reduced, reducing the percentage of swelling as the percentage of crosslinker was increased. X-ray diffraction (XRD patterns showed that the crystallinity index of the crosslinked film was decreased. The pore size of the films decreased as the percentage of crosslinker was increased, resulting in decreased film transparency. The pore volume and percentage of swelling in water of the films also increased with decreases in the pore size as the percentage of crosslinker was increased. The tensile strengths of the GA- and GX-crosslinked films increased by 20 and 15% with the addition of 20% of each crosslinker, respectively.

Crosslinking of wire and cable insulation using electron accelerators

International Nuclear Information System (INIS)

Feng Yongxiang; Ma Zueteh

1992-01-01

Radiation crosslinking of wire and cable insulation is a well-established technology that is widely used in industry. The advantages of radiation crosslinking over chemical crosslinking have helped maintain its steady growth. Since successful utilization of electron beam processing relies on the formulation of compounds used in insulation, the radiation crosslinking of various polymers is reviewed. The handling technology for crosslinking wire and cable insulation and the throughput capacity of electron beam processors are also discussed. More than 30% of the industrial electron accelerators in the world are used for the radiation crosslinking of wire and cable insulation. Prospects of increased use of electron accelerators for crosslinking of wire and cable insulation are very good. (orig.)

Radiation crosslinking of highly plasticized PVC

Science.gov (United States)

Mendizabal, E.; Cruz, L.; Jasso, C. F.; Burillo, G.; Dakin, V. I.

1996-02-01

To improve the physical properties of highly plasticized PVC, the polymer was crosslinked by gamma irradiation using a dose rate of 91 kGy/h. The effect of plasticizer type was studied by using three different plasticizers, 2,2,4-trimethyl-1,3-pentanediol diisobutyrate (TXIB), di(2-ethyl hexyl) phthalate (DOP), and di(2-ethylhexyl terephthalate) (DOTP), and varying irradiation doses. Gel content was determined by soxhlet extraction, tensile measurements were made on a universal testing machine and the mechano-dynamic measurements were made in a dynamic rheometer. It was found that a considerable bonding of plasticizer molecules to macromolelcules takes place along with crosslinking, so that the use of the solvent extraction method for measuring the degree of crosslinking can give erroneous information. Radiation-chemical crosslinking yield ( Gc) and molecular weight of interjunctions chains ( Mc), were calculated for different systems studied. Addition of ethylene glycol dimethacrylate (EGDM) as a crosslinking coagent and dioctyl tin oxide (DOTO) as a stabilizer was also studied. Plasticizers extraction resistance was increased by irradiation treatment.

Radiation crosslinking of highly plasticized PVC

International Nuclear Information System (INIS)

Mendizabal, E.; Cruz, L.; Jasso, C.F.; Burillo, G.; Dakin, V.I.

1996-01-01

To improve the physical properties of highly plasticized PVC, the polymer was crosslinked by gamma irradiation using a dose rate of 91 kGy/h. The effect of plasticizer type was studied by using three different plasticizers, 2,2,4-trimethyl-1,3-pentanediol diisobutyrate (TXIB), di(2-ethyl hexyl) phthalate (DOP), and di(2-ethylhexyl terephthalate) (DOTP), and varying irradiation doses. Gel content was determined by soxhlet extraction, tensile measurements were made on a universal testing machine and the mechano-dynamic measurements were made in a dynamic rheometer. It was found that a considerable bonding of plasticizer molecules to macromolecules takes place along with crosslinking, so that the use of the solvent extraction method for measuring the degree of crosslinking can give erroneous information. Radiation-chemical crosslinking yield (G c ) and molecular weight of interjunctions chains (M c ), were calculated for different systems studied. Addition of ethylene glycol dimethyacrylate (EGDM) as a crosslinking coagent and dioctyl tin oxide (DOTO) as a stabilizer was also studied. Plasticizers extraction resistance was increased by irradiation treatment. (author)

UV-crosslinkable photoreactive self-adhesive hydrogels based on acrylics

Directory of Open Access Journals (Sweden)

Czech Zbigniew

2016-06-01

Full Text Available Hydrogels are a unique class of macromolecular networks that can hold a large fraction of an aqueous solvent within their structure. They are suitable for biomedical area including controlled drug delivery and for technical applications as self-adhesive materials for bonding of wet surfaces. This paper describes photoreactive self-adhesive hydrogels based on acrylics crosslinked using UV radiation. They are prepared in ethyl acetate through radical polymerization of monomers mixture containing 2-ethylhexyl acrylate (2-EHA, butyl acrylate (BA, acrylic acid (AA and copolymerizable photoinitiator 4-acryloyloxy benzophenone (ABP at presence of radical starter 2.2’-azobis-diisobutyronitrile AIBN. The synthesized acrylic copolymers were determined by viscosity and GPC analysis and later modified using ethoxylated amines. 4-acryloyloxy benzophenone (ABP was used as crosslinking monomer. After UV crosslinking the properties of these novel synthesized hydrogels, such as tack, peel adhesion, shears strength, elongation and water adsorption were also studied.

Endothelial cell seeding on crosslinked collagen : Effects of crosslinking on endothelial cell proliferation and functional parameters

NARCIS (Netherlands)

Wissink, MJB; van Luyn, MJA; Dijk, F; Poot, AA; Engbers, GHM; Beugeling, T; van Aken, WG; Feijen, J

Endothelial cell seeding, a promising method to improve the performance of small-diameter vascular grafts, requires a suitable substrate, such as crosslinked collagen. Commonly used crosslinking agents such as glutaraldehyde and formaldehyde cause, however, cytotoxic reactions and thereby hamper

A Molecular Dynamics Study of Crosslinked Phthalonitrile Polymers: The Effect of Crosslink Density on Thermomechanical and Dielectric Properties

Directory of Open Access Journals (Sweden)

Janel Chua

2018-01-01

Full Text Available In this work, molecular dynamics (MD and molecular mechanics (MM simulations are used to study well-equilibrated models of 4,4′-bis(3,4-dicyanophenoxybiphenyl (BPh–1,3-bis(3-aminophenoxybenzene (m-APB phthalonitrile (PN system with a range of crosslink densities. A cross-linking technique is introduced to build a series of systems with different crosslink densities; several key properties of this material, including thermal expansion, mechanical properties and dielectric properties are studied and compared with experimental results. It is found that the coefficient of linear thermal expansion predicted by the model is in good agreement with experimental results and indicative of the good thermal stability of the PN polymeric system. The simulation also shows that this polymer has excellent mechanical property, whose strength increases with increasing crosslink density. Lastly and most importantly, the calculated dielectric constant—which shows that this polymer is an excellent insulating material—indicates that there is an inverse relation between cross-linking density and dielectric constant. The trend gave rise to an empirical quadratic function which can be used to predict the limits of attainable dielectric constant for highly crosslinked polymer systems. The current computational work provides strong evidence that this polymer is a promising material for aerospace applications and offers guidance for experimental studies of the effect of cross-linking density on the thermal, mechanical and dielectric properties of the material.

Dehydration of an azeotrope of ethanol/water by sodium carboxymethylcellulose membranes cross-linked with organic or inorganic cross-linker

Directory of Open Access Journals (Sweden)

2010-11-01

Full Text Available To control the swelling of sodium carboxymethylcellulose (CMCNa membranes, mixtures of CMCNa and glutaraldehyde (GA and mixtures of CMCNa as an organic component and tetraethoxysilane (TEOS as an inorganic component were prepared, and CMCNa/GA cross-linked membranes and CMCNa/TEOS hybrid membranes were formed. In the separation of an ethanol/water azeotrope by pervaporation (PV, the effects of the GA or TEOS content on the water/ethanol selectivity and permeability of these CMCNa/GA cross-linked and CMCNa/TEOS hybrid membranes were investigated. Cross-linked and hybrid membranes containing up to 10 wt% GA or 10 wt% TEOS exhibited higher water/ethanol selectivity than CMCNa membrane without any cross-linker. This resulted from both increased density and depressed swelling of the membranes by the formation of a cross-linked structure. The relationship between the structure of the CMCNa/GA cross-linked membranes and CMCNa/TEOS hybrid membranes and their permeation and separation characteristics for an ethanol/water azeotrope during PV is discussed in detail.

Radiation-induced crosslinking of poly(vinylidene fluoride)

International Nuclear Information System (INIS)

Makuuchi, Keizo

1977-07-01

The factors influencing radiation-induced crosslinking efficiency of poly(vinylidene fluoride) (PVdF) have been studied. Results of the basic research on irradiation conditions (dose rate and atmosphere) and initial physical properties of PVdF (structure of molecular chain and molecular mobility of chain segment) showed that crosslinking efficiency is raised in irradiation at high temperature above 50 0 C under vacuum in the presence of an absorbent for the evolved hydrogen fluoride. The crosslinking reaction is also accelerated with irregular molecular structure such as head-to-head bond in main chain. High crosslinking efficiency is obtained by addition of a polyfunctional monomer having good solubility with PVdF. Mechanical properties of PVdF, the strength at high temperature near the melting point in particular, are improved by crosslinking in the presence of a polyfunctional monomer. (auth.)

The effects of crosslinkers on physical, mechanical, and cytotoxic properties of gelatin sponge prepared via in-situ gas foaming method as a tissue engineering scaffold.

Science.gov (United States)

Poursamar, S Ali; Lehner, Alexander N; Azami, Mahmoud; Ebrahimi-Barough, Somayeh; Samadikuchaksaraei, Ali; Antunes, A P M

2016-06-01

In this study porous gelatin scaffolds were prepared using in-situ gas foaming, and four crosslinking agents were used to determine a biocompatible and effective crosslinker that is suitable for such a method. Crosslinkers used in this study included: hexamethylene diisocyanate (HMDI), poly(ethylene glycol) diglycidyl ether (epoxy), glutaraldehyde (GTA), and genipin. The prepared porous structures were analyzed using Fourier Transform Infrared Spectroscopy (FT-IR), thermal and mechanical analysis as well as water absorption analysis. The microstructures of the prepared samples were analyzed using Scanning Electron Microscopy (SEM). The effects of the crosslinking agents were studied on the cytotoxicity of the porous structure indirectly using MTT analysis. The affinity of L929 mouse fibroblast cells for attachment on the scaffold surfaces was investigated by direct cell seeding and DAPI-staining technique. It was shown that while all of the studied crosslinking agents were capable of stabilizing prepared gelatin scaffolds, there are noticeable differences among physical and mechanical properties of samples based on the crosslinker type. Epoxy-crosslinked scaffolds showed a higher capacity for water absorption and more uniform microstructures than the rest of crosslinked samples, whereas genipin and GTA-crosslinked scaffolds demonstrated higher mechanical strength. Cytotoxicity analysis showed the superior biocompatibility of the naturally occurring genipin in comparison with other synthetic crosslinking agents, in particular relative to GTA-crosslinked samples. Copyright © 2016 Elsevier B.V. All rights reserved.

Development of new materials by utilizing radiation crosslinking

International Nuclear Information System (INIS)

Ueno, Keiji; Uda, Yujiro; Suzuki, Shizuo

1989-01-01

About 30 years have elapsed since the cables by electron beam crosslinking were developed as the first industrial utilization of radiation in Japan. At present about 200 electron beam accelerators are used industrially in Japan, and cable industry ranks at the top, followed by foaming polyethylene and curing, and the preliminary vulcanization of tires. The effect of these irradiations is the reforming of polymers by radiation crosslinking. In cables, the heat resistance and chemical resistance of insulators are improved by radiation crosslinking. By applying radiation crosslinking to polyurethane elastomer, its weakest point, waterproof property, was improved. Moreover, by using this crosslinked polyurethane elastomer for cable coating, the reliability of the sensor cables for brake system was able to be remarkably improved. As another new application of radiation crosslinking process, the improvement of the heat resistance of engineering plasties was examined. The structure of radiation crosslinked urethane elastomer cables, their endurance in hot water and oil, and the life, and the characteristics of sensor cables are reported. Multi-functional monomers, the molecular structure, and the various characteristics of engineering plastics are described. (K.I.)

Chitosan coatings crosslinked with genipin for corrosion protection of AZ31 magnesium alloy sheets.

Science.gov (United States)

de Y Pozzo, Ludmila; da Conceição, Thiago F; Spinelli, Almir; Scharnagl, Nico; Pires, Alfredo T N

2018-02-01

In this study, coatings of chitosan crosslinked with genipin were prepared on sheets of AZ31 magnesium alloy and their corrosion protection properties were characterized by means of potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The coatings were also characterized by means of FTIR and XPS. It was observed that the crosslinking process decreases the corrosion current and shifts the corrosion potential of the alloy to less negative values. The EIS analysis demonstrated that the crosslinking process increases the maximum impedance after short and long exposure times. The superior performance of the crosslinked coatings is related to a lower degree of swelling, as observed in the swelling tests carried out on free-standing films. Copyright © 2017 Elsevier Ltd. All rights reserved.

Nuclear magnetic resonance structure investigations on crosslinked polyesters

International Nuclear Information System (INIS)

Grobelny, J.

1999-01-01

Styrene-crosslinked mixed polyesters derived from maleic anhydride, 2,2-di(4-hydroxypropoxyphenyl)propane, oligo(propylene oxide) and 1,2-propylene glycol were investigated by high-resolution solid-state 13 C NMR spectroscopy. The structural modifications accompanying crosslinking were characterized in terms of spin-lattice relaxation times as a function of unsaturated polyester composition. Copolymerization and crosslinking effects were individually evaluated and the latter effect was related to variations in crosslinking density associated with the chemical structure of the unsaturated prepolymer. As the crosslinking effect is suppressed, the mechanical properties undergo expected changes, e.g., impact strength is increased and modulus of elasticity in tension is decreased. (author)

The effects of crosslinkers on physical, mechanical, and cytotoxic properties of gelatin sponge prepared via in-situ gas foaming method as a tissue engineering scaffold

Energy Technology Data Exchange (ETDEWEB)

Poursamar, S. Ali [Institute for Creative Leather Technologies, Park Campus, The University of Northampton, Boughton Green Road, Northampton NN2 7AL (United Kingdom); Lehner, Alexander N. [Centre for Physical Activity and Chronic Disease and the Aging Research Centre, Institute for Health and Wellbeing, School of Health, Park Campus, The University of Northampton, Boughton Green Road, Northampton NN2 7AL (United Kingdom); Azami, Mahmoud; Ebrahimi-Barough, Somayeh [Department of Tissue Engineering, School of Advanced Technologies in Medicine, Tehran University of Medical Sciences, Tehran (Iran, Islamic Republic of); Samadikuchaksaraei, Ali [Cellular and Molecular Research Centre, Iran University of Medical Sciences, Tehran (Iran, Islamic Republic of); Department of Tissue Engineering & Regenerative Medicine, Faculty of Advanced Technologies in Medicine, Iran University of Medical Sciences, Tehran (Iran, Islamic Republic of); Department of Medical Biotechnology, Faculty of Applied Medicine, Iran University of Medical Sciences, Tehran (Iran, Islamic Republic of); Antunes, A.P.M., E-mail: Paula.Antunes@northampton.ac.uk [Institute for Creative Leather Technologies, Park Campus, The University of Northampton, Boughton Green Road, Northampton NN2 7AL (United Kingdom)

2016-06-01

In this study porous gelatin scaffolds were prepared using in-situ gas foaming, and four crosslinking agents were used to determine a biocompatible and effective crosslinker that is suitable for such a method. Crosslinkers used in this study included: hexamethylene diisocyanate (HMDI), poly(ethylene glycol) diglycidyl ether (epoxy), glutaraldehyde (GTA), and genipin. The prepared porous structures were analyzed using Fourier Transform Infrared Spectroscopy (FT-IR), thermal and mechanical analysis as well as water absorption analysis. The microstructures of the prepared samples were analyzed using Scanning Electron Microscopy (SEM). The effects of the crosslinking agents were studied on the cytotoxicity of the porous structure indirectly using MTT analysis. The affinity of L929 mouse fibroblast cells for attachment on the scaffold surfaces was investigated by direct cell seeding and DAPI-staining technique. It was shown that while all of the studied crosslinking agents were capable of stabilizing prepared gelatin scaffolds, there are noticeable differences among physical and mechanical properties of samples based on the crosslinker type. Epoxy-crosslinked scaffolds showed a higher capacity for water absorption and more uniform microstructures than the rest of crosslinked samples, whereas genipin and GTA-crosslinked scaffolds demonstrated higher mechanical strength. Cytotoxicity analysis showed the superior biocompatibility of the naturally occurring genipin in comparison with other synthetic crosslinking agents, in particular relative to GTA-crosslinked samples. - Highlights: • In-situ gas foaming application in the production of sponge-like gelatin structures • The crosslinkers molecular length impacts on the physical and mechanical properties of the structure. • The effect of crosslinkers on the biocompatibility of gelatin scaffolds.

The effects of crosslinkers on physical, mechanical, and cytotoxic properties of gelatin sponge prepared via in-situ gas foaming method as a tissue engineering scaffold

International Nuclear Information System (INIS)

Poursamar, S. Ali; Lehner, Alexander N.; Azami, Mahmoud; Ebrahimi-Barough, Somayeh; Samadikuchaksaraei, Ali; Antunes, A.P.M.

2016-01-01

In this study porous gelatin scaffolds were prepared using in-situ gas foaming, and four crosslinking agents were used to determine a biocompatible and effective crosslinker that is suitable for such a method. Crosslinkers used in this study included: hexamethylene diisocyanate (HMDI), poly(ethylene glycol) diglycidyl ether (epoxy), glutaraldehyde (GTA), and genipin. The prepared porous structures were analyzed using Fourier Transform Infrared Spectroscopy (FT-IR), thermal and mechanical analysis as well as water absorption analysis. The microstructures of the prepared samples were analyzed using Scanning Electron Microscopy (SEM). The effects of the crosslinking agents were studied on the cytotoxicity of the porous structure indirectly using MTT analysis. The affinity of L929 mouse fibroblast cells for attachment on the scaffold surfaces was investigated by direct cell seeding and DAPI-staining technique. It was shown that while all of the studied crosslinking agents were capable of stabilizing prepared gelatin scaffolds, there are noticeable differences among physical and mechanical properties of samples based on the crosslinker type. Epoxy-crosslinked scaffolds showed a higher capacity for water absorption and more uniform microstructures than the rest of crosslinked samples, whereas genipin and GTA-crosslinked scaffolds demonstrated higher mechanical strength. Cytotoxicity analysis showed the superior biocompatibility of the naturally occurring genipin in comparison with other synthetic crosslinking agents, in particular relative to GTA-crosslinked samples. - Highlights: • In-situ gas foaming application in the production of sponge-like gelatin structures • The crosslinkers molecular length impacts on the physical and mechanical properties of the structure. • The effect of crosslinkers on the biocompatibility of gelatin scaffolds

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...

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...

Grafting functional antioxidants on highly crosslinked polyethylene

Science.gov (United States)

Al-Malaika, S.; Riasat, S.; Lewucha, C.

2016-05-01

The problem of interference of antioxidants, such as hindered phenols, with peroxide-initiated crosslinking of polyethylene was addressed through the use of functional (reactive) graftable antioxidants (g-AO). Reactive derivatives of hindered phenol and hindered amine antioxidants were synthesised, characterised and used to investigate their grafting reactions in high density polyethylene; both non-crosslinked (PE) and highly peroxide-crosslinked (PEXa). Assessment of the extent of in-situ grafting of the antioxidants, their retention after exhaustive solvent extraction in PE and PEXa, and the stabilising performance of the grafted antioxidants (g-AO) in the polymer were examined and benchmarked against conventionally stabilised crosslinked & non-crosslinked polyethylene. It was shown that the functional antioxidants graft to a high extent in PEXa, and that the level of interference of the g-AOs with the polymer crosslinking process was minimal compared to that of conventional antioxidants which bear the same antioxidant function. The much higher level of retention of the g-AOs in PEXa after exhaustive solvent extraction, compared to that of the corresponding conventional antioxidants, accounts for their superior long-term thermal stabilising performance under severe extractive conditions.

Crosslinked polytriazole membranes for organophilic filtration

KAUST Repository

Chisca, Stefan

2016-12-30

We report the preparation of crosslinked membranes for organophilic filtration, by reacting a new polytriazole with free OH groups, using non-toxic poly (ethylene glycol) diglycidyl ether (PEGDE). The OH-functionalized polymer was obtained by converting the oxadiazole to triazole rings with high yield (98%). The maximum degree of crosslinking is achieved after 6 h of reaction. The crosslinked polytriazole membranes are stable in a wide range of organic solvents and show high creep recovery, indicating the robustness of crosslinked membranes. The influence of different casting solutions and different crosslinking time on the membrane morphology and membrane performance was investigated. The membranes performance was studied in dimethylformamide (DMF) and (tetrahydrofuran) THF. We achieved a permeance for THF of 49 L m−2 h−1 bar−1 for membranes with molecular weight cut off (MWCO) of 7 kg mol−1 and a permeance for THF of 17.5 L m−2 h−1 bar−1 for membranes with MWCO of 3 kg mol−1. Our data indicate that by using the new polytriazole is possible to adjust the pore dimensions of the membranes to have a MWCO, which covers ultra- and nanofiltration range.

Crosslinked polytriazole membranes for organophilic filtration

KAUST Repository

Chisca, Stefan; Falca, Gheorghe; Musteata, Valentina-Elena; Boi, Cristiana; Nunes, Suzana Pereira

2016-01-01

We report the preparation of crosslinked membranes for organophilic filtration, by reacting a new polytriazole with free OH groups, using non-toxic poly (ethylene glycol) diglycidyl ether (PEGDE). The OH-functionalized polymer was obtained by converting the oxadiazole to triazole rings with high yield (98%). The maximum degree of crosslinking is achieved after 6 h of reaction. The crosslinked polytriazole membranes are stable in a wide range of organic solvents and show high creep recovery, indicating the robustness of crosslinked membranes. The influence of different casting solutions and different crosslinking time on the membrane morphology and membrane performance was investigated. The membranes performance was studied in dimethylformamide (DMF) and (tetrahydrofuran) THF. We achieved a permeance for THF of 49 L m−2 h−1 bar−1 for membranes with molecular weight cut off (MWCO) of 7 kg mol−1 and a permeance for THF of 17.5 L m−2 h−1 bar−1 for membranes with MWCO of 3 kg mol−1. Our data indicate that by using the new polytriazole is possible to adjust the pore dimensions of the membranes to have a MWCO, which covers ultra- and nanofiltration range.

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.

Tumor-activated prodrug (TAP)-conjugated nanoparticles with cleavable domains for safe doxorubicin delivery.

Science.gov (United States)

Guarnieri, Daniela; Biondi, Marco; Yu, Hui; Belli, Valentina; Falanga, Andrea P; Cantisani, Marco; Galdiero, Stefania; Netti, Paolo A

2015-03-01

A major issue in chemotherapy is the lack of specificity of many antitumor drugs, which cause severe side effects and an impaired therapeutic response. Here we report on the design and characterization of model tumor activated prodrug-conjugated polystyrene (PS) nanoparticles (TAP-NPs) for the release of doxorubicin (Dox) triggered by matrix metalloprotease-2 (MMP2) enzyme, which is overexpressed in the extracellular matrix of tumors. In particular, TAP-NPs were produced by attaching Dox to poly(ethylene glycol) (PEG) through two MMP2-cleavable enzymes. The resulting adduct was then tethered to PS NPs. Results showed that Dox release was actually triggered by MMP2 cleavage and was dependent on enzyme concentration, with a plateau around 20 nM. Furthermore, significant cell cytotoxicity was observed towards three cell lines only in the presence of MMP2, but not in cells without enzyme pre-treatment, even after NP internalization by cells. These findings indicate the potential of TAP-NPs as suitable nanocarriers for an on demand, tumor--specific delivery of antitumor drugs after the response to an endogenous stimulus. Further advancements will focus on the translation of this production technology to biodegradable systems for the safe transport of cytotoxic drug to tumor tissues. © 2014 Wiley Periodicals, Inc.

Nitric oxide-induced interstrand cross-links in DNA.

Science.gov (United States)

Caulfield, Jennifer L; Wishnok, John S; Tannenbaum, Steven R

2003-05-01

The DNA damaging effects of nitrous acid have been extensively studied, and the formation of interstrand cross-links have been observed. The potential for this cross-linking to occur through a common nitrosating intermediate derived from nitric oxide is investigated here. Using a HPLC laser-induced fluorescence (LIF) system, the amount of interstrand cross-link formed on nitric oxide treatment of the 5'-fluorescein-labeled oligomer ATATCGATCGATAT was determined. This self-complimentary sequence contains two 5'-CG sequences, which is the preferred site for nitrous acid-induced cross-linking. Nitric oxide was delivered to an 0.5 mM oligomer solution at 15 nmol/mL/min to give a final nitrite concentration of 652 microM. The resulting concentration of the deamination product, xanthine, in this sample was found to be 211 +/- 39 nM, using GC/MS, and the amount of interstrand cross-link was determined to be 13 +/- 2.5 nM. Therefore, upon nitric oxide treatment, the cross-link is found at approximately 6% of the amount of the deamination product. Using this system, detection of the cross-link is also possible for significantly lower doses of nitric oxide, as demonstrated by treatment of the same oligomer with NO at a rate of 18 nmol/mL/min resulting in a final nitrite concentration of 126 microM. The concentration of interstrand cross-link was determined to be 3.6 +/- 0.1 nM in this sample. Therefore, using the same dose rate, when the total nitric oxide concentration delivered drops by a factor of approximately 5, the concentration of cross-link drops by a factor of about 4-indicating a qausi-linear response. It may now be possible to predict the number of cross-links in a small genome based on the number of CpG sequences and the yield of xanthine derived from nitrosative deamination.

Covalent DNA-protein crosslinking occurs after hyperthermia and radiation

International Nuclear Information System (INIS)

Cress, A.E.; Bowden, G.T.

1983-01-01

Covalent DNA-protein crosslinks occur in exponentially growing mouse leukemia cells (L1210) after exposure to ionizing radiation. The amount of DNA-protein crosslinks as measured by a filter binding assay is dose dependent upon X irradiation. Although hyperthermia and radiation in combination are synergistic with respect to cell lethality, the combination does not result in an increase of DNA-protein crosslinks when assayed immediately following treatments. Hyperthermia (43 degrees C/15 min) given prior to radiation does not alter the radiation dose dependency of the amount of initial crosslinking. In addition, the amount of DNA-protein crosslinking produced by heat plus radiation is independent of the length of heating the cells at 43 degrees C. The DNA-protein crosslinks produced by 50-Gy X ray alone are removed after 2 hr at 37 degrees C. However, if hyperthermia (43 degrees C/15 min) is given prior to 100-Gy X ray, the removal of DNA-protein crosslinks is delayed until 4.0 hr after radiation. Phospho-serine and phospho-threonine bonds are not produced with either radiation or the combination of hyperthermia plus radiation as judged by the resistance of the bonds to guanidine hydrochloride. However, hyperthermia plus radiation causes an increase in phosphate to nitrogen type bonding. These results show that radiation alone causes covalent DNA-protein crosslinks. Hyperthermia in combination with radiation does not increase the total amount of the crosslinks but delays the removal of the crosslinks and alters the distribution of the types of chemical bonding. These data suggest that the synergistic action on hyperthermia with radiation is more related to the rate of removal and the type of chemical bonding involved in the covalent DNA-protein crosslinks rather than the amount of DNA-protein crosslinks

Mechanism of melphalan crosslink enhancement by misonidazole pretreatment

International Nuclear Information System (INIS)

Taylor, Y.C.; Sawyer, J.M.; Hsu, B.; Brown, J.M.

1984-01-01

Sensitization of Chinese hamster ovary cells to melphalan (L-PAM) toxicity by prior treatment with misonidazole is associated with increased levels of DNA crosslinks believed to be the critical lesion for bifunctional alkylating agent toxicity. Enhanced L-PAM crosslinking of DNA could occur by a variety of mechanisms in MISO-pretreated cells including: (1) increased transport or binding of L-PAM, (2) decreased repair of L-PAM monoadducts which would allow more time for their conversion to crosslinks, (3) decreased crosslink repair (unhooking of one arm), or (4) chemical modification of the DNA structure, presumably by bound MISO derivatives, such that crosslink formation is facilitated. Previous studies have eliminated mechanisms (1) and (3). Mechanism (4) was investigated by following MISO-pretreatments of whole cells with L-PAM treatments of the isolated DNA from these cells. Treatment of bare DNA with L-PAM modeled very well the crosslinking behavior in whole cells although it was somewhat more efficient. In the presence of double stranded DNA and absence of repair systems during and after the L-PAM exposure, it was determined that MISO-pretreatments did not increase the crosslinking efficiency of L-PAM

Discovery of undefined protein cross-linking chemistry: a comprehensive methodology utilizing 18O-labeling and mass spectrometry.

Science.gov (United States)

Liu, Min; Zhang, Zhongqi; Zang, Tianzhu; Spahr, Chris; Cheetham, Janet; Ren, Da; Zhou, Zhaohui Sunny

2013-06-18

Characterization of protein cross-linking, particularly without prior knowledge of the chemical nature and site of cross-linking, poses a significant challenge, because of their intrinsic structural complexity and the lack of a comprehensive analytical approach. Toward this end, we have developed a generally applicable workflow-XChem-Finder-that involves four stages: (1) detection of cross-linked peptides via (18)O-labeling at C-termini; (2) determination of the putative partial sequences of each cross-linked peptide pair using a fragment ion mass database search against known protein sequences coupled with a de novo sequence tag search; (3) extension to full sequences based on protease specificity, the unique combination of mass, and other constraints; and (4) deduction of cross-linking chemistry and site. The mass difference between the sum of two putative full-length peptides and the cross-linked peptide provides the formulas (elemental composition analysis) for the functional groups involved in each cross-linking. Combined with sequence restraint from MS/MS data, plausible cross-linking chemistry and site were inferred, and ultimately confirmed, by matching with all data. Applying our approach to a stressed IgG2 antibody, 10 cross-linked peptides were discovered and found to be connected via thioethers originating from disulfides at locations that had not been previously recognized. Furthermore, once the cross-link chemistry was revealed, a targeted cross-link search yielded 4 additional cross-linked peptides that all contain the C-terminus of the light chain.

Preparation and properties of silk sericin/cellulose cross-linking films

Directory of Open Access Journals (Sweden)

Wang Kunyan

2017-01-01

Full Text Available Silk sericin/cellulose cross-linked films were successfully prepared using glutaraldehyde as cross-linkinger. FTIR was applied to characterize the chemical structure of films. Cross-linked silk sericin film was found the peak intensity of FTIR for cross-linked film decreased markedly compared to pure silk sericin, which indicating cross-linking reaction has been occurred. The increasing value of swelling ratio also indicated the cross-linking has been happened. The cross-linking reaction increased the thermal decomposition temperature.

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.

Charged Triazole Cross-Linkers for Hyaluronan-Based Hybrid Hydrogels

Directory of Open Access Journals (Sweden)

Maike Martini

2016-09-01

Full Text Available Polyelectrolyte hydrogels play an important role in tissue engineering and can be produced from natural polymers, such as the glycosaminoglycan hyaluronan. In order to control charge density and mechanical properties of hyaluronan-based hydrogels, we developed cross-linkers with a neutral or positively charged triazole core with different lengths of spacer arms and two terminal maleimide groups. These cross-linkers react with thiolated hyaluronan in a fast, stoichiometric thio-Michael addition. Introducing a positive charge on the core of the cross-linker enabled us to compare hydrogels with the same interconnectivity, but a different charge density. Positively charged cross-linkers form stiffer hydrogels relatively independent of the size of the cross-linker, whereas neutral cross-linkers only form stable hydrogels at small spacer lengths. These novel cross-linkers provide a platform to tune the hydrogel network charge and thus the mechanical properties of the network. In addition, they might offer a wide range of applications especially in bioprinting for precise design of hydrogels.

Computer simulation of randomly cross-linked polymer networks

International Nuclear Information System (INIS)

Williams, Timothy Philip

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 heterogeneities were observed in the swollen model networks and were analysed by considering constituent substructures of varying size. The network connectivity determined the length scales at which the majority of the substructure unfolding process occurred. Simulated stress-strain curves and diffraction patterns for uniaxially deformed swollen networks, were found to be consistent with experimental findings. Analysis of the relaxation dynamics of various network components revealed a dramatic slowdown due to the network connectivity. The cross-link junction spatial fluctuations for networks close to the sol-gel threshold, were observed to be at least comparable with the phantom network prediction. The dangling chain ends were found to display the largest characteristic relaxation time. (author)

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.

Covalent DNA-protein crosslinking occurs after hyperthermia and radiation

International Nuclear Information System (INIS)

Cress, A.E.; Bowden, G.T.

1983-01-01

Covalent DNA-protein crosslinks occur in exponentially growing mouse leukemia cells (L1210) after exposure to ionizing radiation. The amount of DNA-protein crosslinks as measured by a filter binding assay is dose dependent upon x irradiation. Although hyperthermia and radiation in combination are synergistic with respect to cell lethality, the combination does not result in an increase of DNA-protein crosslinks when assayed immediately following treatments. Hyperthermia (43 0 C/15 min) given prior to radiation dose not alter the radiation dose dependency of the amount of initial crosslinking. In addition, the amount of DNA-protein crosslinking produced by heat plus radiation is independent of the length of heating the cells at 43 0 C. The DNA-protein crosslinks produced y 50-Gy x ray alone are removed after 2 hr at 37 0 C. However, if hyperthermia (43 0 C/15 min) is given prior to 100-Gy x ray, the removal of DNA-protein crosslinks is delayed until 4.0 hr after radiation. Phospho-serine and phospho-threonine bonds are not produced with either radiation or the combination of hyperthermia plus radiation as judged by the resistance of the bonds to guanidine hydrochloride. However, hyperthermia plus radiation causes an increase in phosphate to nitrogen type bonding. These results show that radiation alone causes covalent DNA-protein crosslinks. Hyperthermia in combination with radiation does not increase the total amount of the crosslinks but delays the removal of the crosslinks and alters the distribution of the types of chemical bonding

Comparison of neat and photo-crosslinked polyvinylidene fluoride-co-hexafluoropropylene thin film dielectrics formed by spin-coating

International Nuclear Information System (INIS)

Iyore, O.D.; Roodenko, K.; Winkler, P.S.; Noriega, J.R.; Vasselli, J.J.; Chabal, Y.J.; Gnade, B.E.

2013-01-01

We report the characterization of photo-crosslinked polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) thin film, metal–insulator–metal capacitors fabricated using standard semiconductor processing techniques. We characterize the capacitors using in-situ vibrational spectroscopy during thermally-assisted poling and correlate the Fourier transform infrared spectroscopy (FTIR) results with X-ray diffraction (XRD) results. FTIR analysis of the neat PVDF-HFP showed α → β transformations during poling at room temperature and at 55 °C. α → β transformations were observed for the crosslinked polymer only during poling at 55 °C. XRD data revealed that photo-crosslinking caused the polymer to partially crystallize into the β-phase. The similar behavior of the neat and crosslinked samples at 55 °C suggests that a higher activation energy was needed for α → β transformations in crosslinked PVDF-HFP during poling. Electrical measurements showed that photo-crosslinking had no significant effect on the dielectric constant and dielectric loss of PVDF-HFP. However, the dielectric strength and maximum energy density of the crosslinked polymer were severely reduced. - Highlights: • Polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) dielectrics were studied. • Phase transformations were observed only at 55 °C for the crosslinked PVDF-HFP. • Crosslinking had no strong effect on the dielectric constant of PVDF-HFP. • Breakdown strengths were 620 MVm −1 and 362 MVm −1 for neat and crosslinked films

Formation of interfacial network structure via photo-crosslinking in carbon fiber/epoxy composites

Directory of Open Access Journals (Sweden)

S. H. Deng

2014-07-01

Full Text Available A series of diblock copolymers (poly(n-butylacrylate-co-poly(2-hydroxyethyl acrylate-b-poly(glycidyl methacrylate ((PnBA-co-PHEA-b-PGMA, containing a random copolymer block PnBA-co-PHEA, were successfully synthesized by atom transfer radical polymerization (ATRP. After being chemically grafted onto carbon fibers, the photosensitive methacrylic groups were introduced into the random copolymer, giving a series of copolymers (poly(n-butylacrylate-co-poly(2-methacryloyloxyethyl acrylate-b-poly(glycidyl methacrylate((PnBA-co-PMEA-b-PGMA. Dynamic mechanical analysis indicated that the random copolymer block after ultraviolet (UV irradiation was a lightly crosslinked polymer and acted as an elastomer, forming a photo-crosslinked network structure at the interface of carbon fiber/epoxy composites. Microbond test showed that such an interfacial network structure greatly improved the cohesive strength and effectively controlled the deformation ability of the flexible interlayer. Furthermore, three kinds of interfacial network structures, i physical crosslinking by H-bonds, ii chemical crosslinking by photopolymerization, and iii interpenetrating crosslinked network by photopolymerization and epoxy curing reaction were received in carbon fiber/epoxy composite, depending on the various preparation processes.

Azide-based cross-linking of polymers of intrinsic microporosity (PIMs) for condensable gas separation

KAUST Repository

Du, Naiying

2011-03-11

Cross-linked polymers of intrinsic microporosity (PIM)s for gas separation membranes, were prepared by a nitrene reaction from a representative PIM in the presence of two different diazide cross-linkers. The reaction temperature was optimized using TGA. The homogenous membranes were cast from THF solutions of different ratios of PIM to azides. The resulting cross-linked structures of the PIMs membranes were formed at 175 °C after 7.5 h and confirmed by TGA, XPS, FT-IR spectroscopy and gel content analysis. These resulting cross-linked polymeric membranes showed excellent gas separation performance and can be used for O 2/N 2 and CO 2/N 2 gas pairs, as well as for condensable gases, such as CO 2/CH 4, propylene/propane separation. Most importantly, and differently from typical gas separation membranes derived from glassy polymers, the crosslinked PIMs showed no obvious CO 2 plasticization up to 20 atm pressure of pure CO 2 and CO 2/CH 4 mixtures. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Azide-based cross-linking of polymers of intrinsic microporosity (PIMs) for condensable gas separation

KAUST Repository

Du, Naiying; Dal-Cin, Mauro M D; Pinnau, Ingo; Nicalek, Andrzej; Robertson, Gilles P.; Guiver, Michael D.

2011-01-01

Cross-linked polymers of intrinsic microporosity (PIM)s for gas separation membranes, were prepared by a nitrene reaction from a representative PIM in the presence of two different diazide cross-linkers. The reaction temperature was optimized using TGA. The homogenous membranes were cast from THF solutions of different ratios of PIM to azides. The resulting cross-linked structures of the PIMs membranes were formed at 175 °C after 7.5 h and confirmed by TGA, XPS, FT-IR spectroscopy and gel content analysis. These resulting cross-linked polymeric membranes showed excellent gas separation performance and can be used for O 2/N 2 and CO 2/N 2 gas pairs, as well as for condensable gases, such as CO 2/CH 4, propylene/propane separation. Most importantly, and differently from typical gas separation membranes derived from glassy polymers, the crosslinked PIMs showed no obvious CO 2 plasticization up to 20 atm pressure of pure CO 2 and CO 2/CH 4 mixtures. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Repair of DNA-polypeptide crosslinks by human excision nuclease

Science.gov (United States)

Reardon, Joyce T.; Sancar, Aziz

2006-03-01

DNA-protein crosslinks are relatively common DNA lesions that form during the physiological processing of DNA by replication and recombination proteins, by side reactions of base excision repair enzymes, and by cellular exposure to bifunctional DNA-damaging agents such as platinum compounds. The mechanism by which pathological DNA-protein crosslinks are repaired in humans is not known. In this study, we investigated the mechanism of recognition and repair of protein-DNA and oligopeptide-DNA crosslinks by the human excision nuclease. Under our assay conditions, the human nucleotide excision repair system did not remove a 16-kDa protein crosslinked to DNA at a detectable level. However, 4- and 12-aa-long oligopeptides crosslinked to the DNA backbone were recognized by some of the damage recognition factors of the human excision nuclease with moderate selectivity and were excised from DNA at relatively efficient rates. Our data suggest that, if coupled with proteolytic degradation of the crosslinked protein, the human excision nuclease may be the major enzyme system for eliminating protein-DNA crosslinks from the genome. damage recognition | nucleotide excision repair

Moisture curable toughened poly(lactide utilizing vinyltrimethoxysilane based crosslinks

Directory of Open Access Journals (Sweden)

J. Schneider

2016-10-01

Full Text Available Vinyltrimethoxysilane (VTMOS was grafted on to the backbone of poly(lactide (PLA through a free radical grafting reaction using reactive extrusion (REX processing. The methoxy groups of the silane provide the modified PLA sites for crosslinking through a moisture induced pathway. VTMOS grafting efficiencies of up to 90% were obtained. The newly created methoxy functionality of the modified PLA readily undergoes hydrolysis and condensation forming siloxane crosslinks in the material. Crosslinking with VTMOS exhibited improved modulus, strength, and impact toughness while showing a decrease in ductility. Incorporating silanol-terminated poly(dimethylsiloxane (OH-PDMS resulted in the formation of longer siloxane crosslinks. These samples showed an increase in modulus and impact toughness due to the crosslinking, while the longer siloxane linkages resulted in improved ductility and tensile toughness. This is unusual for polymers toughened through crosslinking reactions. Scanning Electron Microscopy (SEM of the fractured surfaces showed the presence of these elongated siloxane crosslinks. This enhanced ability for the modified PLA to deform and absorb energy results in the increase in both impact and tensile toughness.

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.

In vivo biocompatibility of carbodiimide-crosslinked collagen matrices : Effects of crosslink density, heparin immobilization, and bFGF loading

NARCIS (Netherlands)

van Wachem, PB; Plantinga, JA; Wissink, MJB; Poot, AA; Engbers, GHM; Beugeling, T; van Aken, WG; Feijen, J; van Luyn, MJA

2001-01-01

Collagen matrices, crosslinked using N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide (E) and N-hydroxvsuccinimide (N), were previously developed as a substrate for endothelial cell seeding of small-diameter vascular grafts. In the present study, the biocompatibility of various EN-crosslinked collagen

Shaped articles of cross-linked fluorocarbon polymers

International Nuclear Information System (INIS)

Gotcher, A.J.; Germeraad, P.B.

1981-01-01

A process is described which comprises (1) contacting (a) a shaped article of a polymeric composition wherein the polymer is a fluorocarbon polymer having a melting point of at least 200 0 C, the article having a tensile strength of at least 3,000 psi, with (b) a fluid composition comprising a cross-linking agent, until the article contains at least 2.5% by weight of the cross-linking agent; and (2) irradiating the shaped article with ionising radiation to a dosage not exceeding 50 Mrads under conditions such that the composition is cross-linked sufficiently to impart thereto an M 100 value of at least 300 psi, while maintaining a tensile strength of at least 3000 psi, the shaped article containing a specified proportion of the cross-linking agent. (author)

Biocatalytic cross-linking of pectic polysaccharides for designed food functionality

DEFF Research Database (Denmark)

Zaidel, Dayang Norulfairuz Abang; Meyer, Anne S.

2012-01-01

the mechanisms of formation of functional pectic polysaccharide cross-links, including covalent cross-links (notably phenolic esters and uronyl ester linkages) and non-covalent, ionic cross-links (which involve calcium and borate ester links). The treatise examines how such cross-links can be designed via......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...... specific enzymatic reactions, and highlights the most recent data concerning enzyme catalyzed engineering of cross-links for in situ structural design of functional properties of foods....

Preparation and Enzymatic Degradation of Porous Crosslinked Polylactides of Biomass Origin

Directory of Open Access Journals (Sweden)

Yuya Kido

2014-06-01

Full Text Available To understand the enzymatic degradation behavior of crosslinked polylactide (PLA, the preparation and enzymatic degradation of both thermoplastic (linear and crosslinked PLAs that have pore structures with different dimensions were carried out. The porous structures of the linear PLA samples were of micro and nanoporous nature, and prepared by batch foaming with supercritical CO2 and compared with the porous structures of crosslinked PLA (Lait-X created by the salt leaching method. The surface and cross-sectional morphologies of the porous structures were investigated by using scanning electron microscopy. The morphological analysis of porous Lait-X showed a rapid loss of physical features within 120 h of exposure to proteinase-K enzymatic degradation at 37 °C. Due to the higher affinity for water, enhanced enzymatic activity as compared to the linear PLA porous structures in the micro and nanoporous range was observed.

Nitrile crosslinked polyphenyl-quinoxaline/graphite fiber composites

Science.gov (United States)

Alston, W. B.

1976-01-01

Studies were performed to reduce the 600 F thermoplasticity of polyphenylquinoxaline (PPQ) matrix resins by introducing crosslinking by the reaction of terminal nitrile groups. Seven solvents and solvent mixtures were studied as the crosslinking catalysts and used to fabricate crosslinked PPQ/HMS graphite fiber composites. The room temperature and 600 F composite mechanical properties after short time and prolonged 600 F air exposure and the 600 F composite weight loss were determined and compared to those properties of high molecular weight, linear PPQ/HMS graphite fiber composites.

Comparison of neat and photo-crosslinked polyvinylidene fluoride-co-hexafluoropropylene thin film dielectrics formed by spin-coating

Energy Technology Data Exchange (ETDEWEB)

Iyore, O.D.; Roodenko, K.; Winkler, P.S. [Materials Science and Engineering Department, The University of Texas at Dallas, Richardson, TX 75080 (United States); Noriega, J.R.; Vasselli, J.J. [Electrical Engineering Department, The University of Texas at Tyler, Tyler, TX 75799 (United States); Chabal, Y.J. [Materials Science and Engineering Department, The University of Texas at Dallas, Richardson, TX 75080 (United States); Gnade, B.E., E-mail: gnade@utdallas.edu [Materials Science and Engineering Department, The University of Texas at Dallas, Richardson, TX 75080 (United States)

2013-12-02

We report the characterization of photo-crosslinked polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) thin film, metal–insulator–metal capacitors fabricated using standard semiconductor processing techniques. We characterize the capacitors using in-situ vibrational spectroscopy during thermally-assisted poling and correlate the Fourier transform infrared spectroscopy (FTIR) results with X-ray diffraction (XRD) results. FTIR analysis of the neat PVDF-HFP showed α → β transformations during poling at room temperature and at 55 °C. α → β transformations were observed for the crosslinked polymer only during poling at 55 °C. XRD data revealed that photo-crosslinking caused the polymer to partially crystallize into the β-phase. The similar behavior of the neat and crosslinked samples at 55 °C suggests that a higher activation energy was needed for α → β transformations in crosslinked PVDF-HFP during poling. Electrical measurements showed that photo-crosslinking had no significant effect on the dielectric constant and dielectric loss of PVDF-HFP. However, the dielectric strength and maximum energy density of the crosslinked polymer were severely reduced. - Highlights: • Polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) dielectrics were studied. • Phase transformations were observed only at 55 °C for the crosslinked PVDF-HFP. • Crosslinking had no strong effect on the dielectric constant of PVDF-HFP. • Breakdown strengths were 620 MVm{sup −1} and 362 MVm{sup −1} for neat and crosslinked films.

Cross-linked structure of network evolution

International Nuclear Information System (INIS)

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

2014-01-01

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

Cross-linked structure of network evolution

Energy Technology Data Exchange (ETDEWEB)

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

2014-03-15

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

A NOVEL APPROACH TO SYNTHESIZE CHITOSAN BEADS CROSSLINKED BY EPICHLOROHYDRIN

Institute of Scientific and Technical Information of China (English)

WANG Yongjian; BAI Shu; SUN Yan

2001-01-01

The present investigation describes a novel method for preparing spherical chitosan particles based on crosslinking with epichlorohydrin. Certain amount of pre-crosslinking agent was added to form chitosan gels by traditional inverse phase suspension polymerization. Then the gels were crosslinked by epichlorohydrin at basic condition to obtain chitosan beads. The effects of reaction conditions, such as crosslinking time, the amount of crosslinking agent and the NaOtt concentration,on the physical properties of the chitosan beads were investigated. The beads were found to have more amino groups in the polymer chains than the beads crosslinked by glutaraldehyde. The capacity for copper ions is as high as 40mg/g. The beads have good mechanical strength and can be reused.

A NOVEL APPROACH TO SYNTHESIZE CHITOSAN BEADS CROSSLINKED BY EPICHLOROHYDRIN

Institute of Scientific and Technical Information of China (English)

WANGYongjina; BAIShu; 等

2001-01-01

The present investigation describes a novel method for preparing spherical chitosan particles based on crosslinking with epichlorohydrin.Certain amount of pre-crosslinking agent was added to form chitosan gels by traditional inverse phase suspension polymerization.Then the gels were crosslinked by epichlorohydrin at basic condition to obtain chitosan beads.The effects of reaction conditions,such as crosslinking time,the amount of crosslinking agent and the NaOH concentration,on the physical properties of the chitosan beads were investigated.The beads were found to have more amino groups in the polymer chains than the beads crosslinked by glutaraldehyde.The capacity for copper ions in as high as 40mg/g,The beads have good mechanical strength and can be reused.

Formation of DNA-protein crosslinks in gamma-irradiated chromatin

International Nuclear Information System (INIS)

Mee, L.K.

1985-01-01

Gamma-irradiation of chromatin in vitro and in vivo induces DNA-protein crosslinks which are stable to salt and detergent treatment. The efficiency of crosslink formation is 100 times greater in irradiated isolated chromatin than in chromatin irradiated in cells before isolation. Gamma-irradiation of isolated chromatin in the presence of radical scavengers shows that OH . is the most effective radical for the promotion of crosslinking whereas e/sub aq//sup -/ and O/sub 2//sup -/ are essentially ineffective. For chromatin irradiated in the cell before isolation, fewer crosslinks are formed in air than in an atmosphere of nitrogen; the greatest effect is found in cells irradiated in an atmosphere of nitrous oxide, suggesting that OH . may be involved in the formation of crosslinks in vivo. On the basis of comparing radiation-induced crosslinking in whole chromating (DNA, H1 histone, the core histones - H2A, H2B, H3 and H4 - and non-histone chromosomal proteins) and in a chromatin subunit (DNA and the core histones), the authors identified the core histones as the specific chromosomal proteins predominantly involved in crosslinking to DNA

Dissociation Behavior of a TEMPO-Active Ester Cross-Linker for Peptide Structure Analysis by Free Radical Initiated Peptide Sequencing (FRIPS) in Negative ESI-MS.

Science.gov (United States)

Hage, Christoph; Ihling, Christian H; Götze, Michael; Schäfer, Mathias; Sinz, Andrea

2017-01-01

We have synthesized a homobifunctional amine-reactive cross-linking reagent, containing a TEMPO (2,2,6,6-tetramethylpiperidine-1-oxy) and a benzyl group (Bz), termed TEMPO-Bz-linker, to derive three-dimensional structural information of proteins. The aim for designing this novel cross-linker was to facilitate the mass spectrometric analysis of cross-linked products by free radical initiated peptide sequencing (FRIPS). In an initial study, we had investigated the fragmentation behavior of TEMPO-Bz-derivatized peptides upon collision activation in (+)-electrospray ionization collision-induced dissociation tandem mass spectrometry (ESI-CID-MS/MS) experiments. In addition to the homolytic NO-C bond cleavage FRIPS pathway delivering the desired odd-electron product ions, an alternative heterolytic NO-C bond cleavage, resulting in even-electron product ions mechanism was found to be relevant. The latter fragmentation route clearly depends on the protonation of the TEMPO-Bz-moiety itself, which motivated us to conduct (-)-ESI-MS, CID-MS/MS, and MS 3 experiments of TEMPO-Bz-cross-linked peptides to further clarify the fragmentation behavior of TEMPO-Bz-peptide molecular ions. We show that the TEMPO-Bz-linker is highly beneficial for conducting FRIPS in negative ionization mode as the desired homolytic cleavage of the NO-C bond is the major fragmentation pathway. Based on characteristic fragments, the isomeric amino acids leucine and isoleucine could be discriminated. Interestingly, we observed pronounced amino acid side chain losses in cross-linked peptides if the cross-linked peptides contain a high number of acidic amino acids. Graphical Abstract ᅟ.

Multiple repair pathways mediate tolerance to chemotherapeutic cross-linking agents in vertebrate cells.

Science.gov (United States)

Nojima, Kuniharu; Hochegger, Helfrid; Saberi, Alihossein; Fukushima, Toru; Kikuchi, Koji; Yoshimura, Michio; Orelli, Brian J; Bishop, Douglas K; Hirano, Seiki; Ohzeki, Mioko; Ishiai, Masamichi; Yamamoto, Kazuhiko; Takata, Minoru; Arakawa, Hiroshi; Buerstedde, Jean-Marie; Yamazoe, Mitsuyoshi; Kawamoto, Takuo; Araki, Kasumi; Takahashi, Jun A; Hashimoto, Nobuo; Takeda, Shunichi; Sonoda, Eiichiro

2005-12-15

Cross-linking agents that induce DNA interstrand cross-links (ICL) are widely used in anticancer chemotherapy. Yeast genetic studies show that nucleotide excision repair (NER), Rad6/Rad18-dependent postreplication repair, homologous recombination, and cell cycle checkpoint pathway are involved in ICL repair. To study the contribution of DNA damage response pathways in tolerance to cross-linking agents in vertebrates, we made a panel of gene-disrupted clones from chicken DT40 cells, each defective in a particular DNA repair or checkpoint pathway, and measured the sensitivities to cross-linking agents, including cis-diamminedichloroplatinum (II) (cisplatin), mitomycin C, and melphalan. We found that cells harboring defects in translesion DNA synthesis (TLS), Fanconi anemia complementation groups (FANC), or homologous recombination displayed marked hypersensitivity to all the cross-linking agents, whereas NER seemed to play only a minor role. This effect of replication-dependent repair pathways is distinctively different from the situation in yeast, where NER seems to play a major role in dealing with ICL. Cells deficient in Rev3, the catalytic subunit of TLS polymerase Polzeta, showed the highest sensitivity to cisplatin followed by fanc-c. Furthermore, epistasis analysis revealed that these two mutants work in the same pathway. Our genetic comprehensive study reveals a critical role for DNA repair pathways that release DNA replication block at ICLs in cellular tolerance to cross-linking agents and could be directly exploited in designing an effective chemotherapy.

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.

Rheological analysis of irradiated crosslinkable and scissionable polymers used for medical devices under different radiation conditions

Science.gov (United States)

Satti, A. J.; Ressia, J. A.; Cerrada, M. L.; Andreucetti, N. A.; Vallés, E. M.

2018-03-01

The effects on different synthetic polymers of distinct types of radiation, gamma rays and electron beam, under different atmospheres are followed by changes in their viscoelastic behavior. Taking into account the two main radioinduced reactions, crosslinking and scissioning of polymeric chains, liquid polydimethylsiloxane has been used as example of crosslinkable polymer and semi crystalline polypropylene as example of scissionable polymer. Propylene - 1-hexene copolymers have been also evaluated, and the effects of both reactions were clearly noticed. Accordingly, samples of those aforementioned polymers have been irradiated with 60Co gamma irradiation in air and under vacuum, and also with electron beam, at similar doses. Sinusoidal dynamic oscillation experiments showed a significant increase in branching and crosslinking reactions when specimens are irradiated under vacuum, while scissioning reactions were observed for the different polymers when irradiation takes place under air with either gamma irradiation or electron beam.

EB radiation crosslinking of elastomers

International Nuclear Information System (INIS)

Bik, J.; Rzymski, M.; Gluszewski, W.; Zagorski, Z.P.

2002-01-01

Complete text of publication follows. The first paper in the series described by the general title, starts with radiation crosslinking of hydrogenated butadiene-nitrile rubber (HBNR). This high-tech elastomer is obtained by catalytic hydrogenation of >C=C 99.5 and 94.5% of starting double bonds. Samples were irradiated with 10 MeV electrons, monoenergetical, 6 kW power, used as scanned beam over the conveyor, securing homogeneity of dose distribution. The doses were up to 300 kGy, applied in 20 kGy increments to avoid radiation generated heating of the material. The influence of presence or absence of oxygen was considered. Irradiated samples were investigated for the extend of crosslinking in the function of dose and for properties important for understanding of mechanisms. Samples are transparent, what allowed conventional absorption spectrophotometry, also time resolved. The quantitative interpretation of results shows that for 100 crosslinks there are 6-9 acts of chain-scission. It is less, than expected from the participation of multi-ionization spurs, also in the solid state, as announced during the previous, 9th Tihany Conference. However, the apparent lower yield of multi-ionization spurs is explained by partial conversion of products into crosslinks of specific type. Our investigations confirm the usefulness of consideration of radiation spurs in polymers as well as in all, low LET irradiated media

Efficient production of native lunasin with correct N-terminal processing by using the pH-induced self-cleavable Ssp DnaB mini-intein system in Escherichia coli.

Science.gov (United States)

Setrerrahmane, Sarra; Zhang, Yi; Dai, Guangzhi; Lv, Jing; Tan, Shuhua

2014-09-01

To develop an efficient and cost-effective approach for the production of small preventive peptide lunasin with correct natural N terminus, a synthetic gene was designed by OPTIMIZER & Gene Designer and cloned into pTWIN1 vector at SapI and PstI sites. Thus, lunasin was N-terminally fused to the pH-induced self-cleavable Ssp DnaB mini-intein linked to a chitin binding domain (CBD) with no extra residues. The resultant fusion protein was highly expressed by lactose induction in Escherichia coli BL21 (DE3) in a 7-l bioreactor and bound to a chitin affinity column. After washing the impurities, the Ssp DnaB intein mediated on-column self-cleavage was easily triggered by shifting pH and temperature to allow the native lunasin released. The final purified lunasin yielded up to 75 mg/l medium. Tricine/SDS-PAGE and matrix-assisted laser desorption time-of-flight (MALDI-TOF)/mass spectrometry (MS) verified the structural authenticity of the product, implying the correct cleavage at the junction between Ssp DnaB intein and lunasin. MTT assay confirmed its potent proliferation inhibitory activity to human cancer cells HCT-116 and MDA-MB-231; however, no cytotoxicity to normal human lens epithelial cell SRA01/04 and hepatoma HepG2. Taken together, we provide a novel strategy to produce recombinant native lunasin with correct N-terminal processing by using the pH-induced self-cleavable Ssp DnaB mini-intein.

Radiation crosslinking of methylcellulose and hydroxyethylcellulose in concentrated aqueous solutions

International Nuclear Information System (INIS)

Wach, Radoslaw A.; Mitomo, Hiroshi; Nagasawa, Naotsugu; Yoshii, Fumio

2003-01-01

The effects of ionizing radiation on aqueous solutions of cellulose ethers, methylcellulose (MC) and hydroxyethylcellulose (HEC) were investigated. The well-established knowledge states that cellulose and its derivatives belong to degrading type of polymers. However, in our study intermolecular crosslinking initiated by gamma rays or electron beam leaded to the formation of insoluble gel. This is an opposite effect of irradiation to the degradation. Paste-like form of the initial specimen, i.e. concentration 20-30%, when water plasticizes the bulk of polymer; and a high dose rate were favorable for hydrogel formation. Gel fraction up to 60% and 70% was obtained from solutions of HEC and MC, respectively. Produced hydrogels swell markedly in aqueous media by imbibing and holding the solvent. Radiation parameters of irradiation, such as yields of degradation and crosslinking and the gelation dose, were evaluated by sol-gel analysis on the basis of Charlesby-Rosiak equation. Despite of the crosslinked structure, obtained hydrogels can be included into the group of biodegradable materials. They undergo decomposition by the action of cellulase enzyme or microorganisms from compost

Collagen cross-linking: insights on the evolution of metazoan extracellular matrix.

Science.gov (United States)

Rodriguez-Pascual, Fernando; Slatter, David Anthony

2016-11-23

Collagens constitute a large family of extracellular matrix (ECM) proteins that play a fundamental role in supporting the structure of various tissues in multicellular animals. The mechanical strength of fibrillar collagens is highly dependent on the formation of covalent cross-links between individual fibrils, a process initiated by the enzymatic action of members of the lysyl oxidase (LOX) family. Fibrillar collagens are present in a wide variety of animals, therefore often being associated with metazoan evolution, where the emergence of an ancestral collagen chain has been proposed to lead to the formation of different clades. While LOX-generated collagen cross-linking metabolites have been detected in different metazoan families, there is limited information about when and how collagen acquired this particular modification. By analyzing telopeptide and helical sequences, we identified highly conserved, potential cross-linking sites throughout the metazoan tree of life. Based on this analysis, we propose that they have importantly contributed to the formation and further expansion of fibrillar collagens.

Electron beam irradiation crosslinked hydrogels based on tyramine conjugated gum tragacanth.

Science.gov (United States)

Tavakol, Moslem; Dehshiri, Saeedeh; Vasheghani-Farahani, Ebrahim

2016-11-05

In the present study, electron beam irradiation was applied to prepare a chemically crosslinked hydrogel based on tyramine conjugated gum tragacanth. Then, the gel content, swelling behavior and cytotoxicity of the hydrogels were evaluated. The gel content of the hydrogels was in the range of 75-85%. Equilibrium swelling degree of the hydrogels decreased from 51 to 14 with increasing polymer concentration and irradiation dose. Moisture retention capability of the hydrogels after 5h incubation at 37°C was in the range of 45-52 that is comparable with of commercial hydrogels. The cytotoxicity analysis showed the good biocompatibility of hydrogels. These results indicated that electron beam irradiation is a promising method to prepare chemically crosslinked tyramine conjugated gum tragacanth hydrogels for biomedical applications. Also, the versatility of electron beam irradiation for crosslinking of a variety of polymers possessing tyramine groups was demonstrated. Copyright © 2016 Elsevier Ltd. All rights reserved.

Dual Targeting of Intracellular Pathogenic Bacteria with a Cleavable Conjugate of Kanamycin and an Antibacterial Cell-Penetrating Peptide.

Science.gov (United States)

Brezden, Anna; Mohamed, Mohamed F; Nepal, Manish; Harwood, John S; Kuriakose, Jerrin; Seleem, Mohamed N; Chmielewski, Jean

2016-08-31

Bacterial infection caused by intracellular pathogens, such as Mycobacterium, Salmonella, and Brucella, is a burgeoning global health epidemic that necessitates urgent action. However, the therapeutic value of a number of antibiotics, including aminoglycosides, against intracellular pathogenic bacteria is compromised due to their inability to traverse eukaryotic membranes. For this significant problem to be addressed, a cleavable conjugate of the antibiotic kanamycin and a nonmembrane lytic, broad-spectrum antimicrobial peptide with efficient mammalian cell penetration, P14LRR, was prepared. This approach allows kanamycin to enter mammalian cells as a conjugate linked via a tether that breaks down in the reducing environment within cells. Potent antimicrobial activity of the P14KanS conjugate was demonstrated in vitro, and this reducible conjugate effectively cleared intracellular pathogenic bacteria within macrophages more potently than that of a conjugate lacking the disulfide moiety. Notably, successful clearance of Mycobacterium tuberculosis within macrophages was observed with the dual antibiotic conjugate, and Salmonella levels were significantly reduced in an in vivo Caenorhabditis elegans model.

Crosslinking of electrospun poly (VDF-co-HFP) nanofibrous membranes by gamma-ray irradiation

International Nuclear Information System (INIS)

Kim, Yun Hye; Lim, Youn Mook; Choi, Jae Hak; An, Sung Jun; Park, Jong Seok; Nho, Young Chang

2008-01-01

Poly (VDF-co-HFP)/PEGDMA nanofibrous membranes (NFMs) have been prepared by an electrospinning process. Since electrospun NFMs have a nanoporous structure, they have a potential application for a polymer electrolyte or a separator. Poly (VDF-co-HFP) is a polymer electrolyte binder. In order to improve their mechanical properties, poly (VDF-co-HFP)/PEGDMA NFMs were crosslinked by a gamma-ray irradiation. Then the crosslinked NFMs were characterized through an electrolyte uptake, IR structural analysis, and SEM morphological investigation

Natural polyphenols enhance stability of crosslinked UHMWPE for joint implants.

Science.gov (United States)

Shen, Jie; Gao, Guorong; Liu, Xincai; Fu, Jun

2015-03-01

Radiation-crosslinked UHMWPE has been used for joint implants since the 1990s. Postirradiation remelting enhances oxidative stability, but with some loss in strength and toughness. Vitamin E-stabilized crosslinked UHMWPE has shown improved strength and stability as compared with irradiated and remelted UHMWPE. With more active phenolic hydroxyl groups, natural polyphenols are widely used in the food and pharmaceutical industries as potent stabilizers and could be useful for oxidative stability in crosslinked UHMWPE. We asked whether UHMWPE blended with polyphenols would (1) show higher oxidation resistance after radiation crosslinking; (2) preserve the mechanical properties of UHMWPE after accelerated aging; and (3) alter the wear resistance of radiation-crosslinked UHMWPE. The polyphenols, gallic acid and dodecyl gallate, were blended with medical-grade UHMWPE followed by consolidation and electron beam irradiation at 100 kGy. Radiation-crosslinked virgin and vitamin E-blended UHMWPEs were used as reference materials. The UHMWPEs were aged at 120 °C in air with oxidation levels analyzed by infrared spectroscopy. Tensile (n = 5 per group) and impact (n = 3 per group) properties before and after aging as per ASTM F2003 were evaluated. The wear rates were examined by pin-on-disc testing (n = 3 per group). The data were reported as mean ± SDs. Statistical analysis was performed by using Student's t-test for a two-tailed distribution with unequal variance for tensile and impact data obtained with n ≥ 3. A significant difference is defined with p Accelerated aging of these polyphenol-blended UHMWPEs resulted in ultimate tensile strength of 50.4 ± 1.4 MPa and impact strength of 53 ± 5 kJ/m(2) for 100 kGy-irradiated UHMWPE with 0.05 wt% dodecyl gallate, for example, in comparison to 51.2 ± 0.7 MPa (p = 0.75) and 58 ± 5 kJ/m(2) (p = 0.29) before aging. The pin-on-disc wear rates of 100 kGy-irradiated UHMWPE with 0.05 wt% dodecyl gallate and 0.05 wt% gallic acid

Manufacture of polyethylene foam by electron beam cross-linking

International Nuclear Information System (INIS)

Tamai, Isamu

1976-01-01

The manufacturing process of polyethylene foam, comparison between electron beam cross-linking process and chemical cross-linking process, the electron beam irradiation technique for continuous sheets, the characteristics and uses of polyethylene foam are reviewed. The pore diameter can be controlled by selecting the dose rate, because there is strong relationship between the pore diameter and the dose rate. As the dose if higher, the foam becomes finer. The electron accelerators having large capacity show the lowest cost as the radiation source, and are applicable industrially. If the production capacity exceeds about 200 tons per month, the costs of electron beam irradiation process may be more advantageous than that of chemical process according to the circumstances. It is difficult to obtain the uniform distribution of absorption dose in the direction of thickness. General characteristics of cross-linked polyethylene foam are listed. The special feature of electron beam process is that the degree of cross-linking can be controlled arbitrarily before foaming. The products obtained by the electron beam cross-linking process have finer foams and smoother surfaces than those obtained by the chemical process, because the separation of the decomposition of foaming agents from that of cross-linking agents in the chemical cross-linking is difficult. (Iwakiri, K.)

[Biophysical principles of collagen cross-linking].

Science.gov (United States)

Spörl, E; Raiskup-Wolf, F; Pillunat, L E

2008-02-01

The reduced mechanical stability of the cornea in keratoconus or in keratectasia after Lasik may be increased by photooxidative cross-linking of corneal collagen. The biophysical principles are compiled for the safe and effective application of this new treatment method. The setting of the therapy parameters should be elucidated from the absorption behaviour of the cornea. The safety of the method for the endothelium cells and the lens will be discussed. The induced cross-links are shown to be the result of changes in the physico-chemical properties of the cornea. To reach a high absorption of the irradiation energy in the cornea, riboflavin of a concentration of 0.1% and UV light of a wavelength of 370 nm, corresponding to the relative maximum of absorption of riboflavin, were used. An irradiance of 3 mW/cm(2) and an irradiation time of 30 min lead to an increase of the mechanical stiffness. The endothelium cells will be protected due to the high absorption within the cornea, that means the damaging threshold of the endothelium cells will not be reached in a 400 microm thick stroma. As evidence for cross-links we can consider the increase of the biomechanical stiffness, the increased resistance against enzymatic degradation, a higher shrinkage temperature, a lower swelling rate and an increased diameter of collagen fibres. The therapy parameters were tested experimentally and have been proven clinically in the corneal collagen cross-linking. These parameters should be respected to reach a safe cross-linking effect without damage of the adjacent tissues.

Study of the characterization of crosslinking polyethylene foam by irradiation process with electron beam

International Nuclear Information System (INIS)

Dias, Djalma Batista

2007-01-01

The polyethylene foams are widely used. Their main applications are used for both home appliances to medical equipment. Beside that, they have applications in building and automotive industries. The foam properties depend on the density and its cellular structure, that is, the amount of open and closed cells, of the distribution and size of them. The methods of the crosslinking polyethylene foam production are classified in two types, according to the crosslinking method. One method is based on the chemical crosslinking, which utilizes peroxide as crosslinking agent. In the other method, the crosslinking is induced by electron beam radiation. The foams obtained from the crosslinking polyethylene by irradiation process presented a smooth and the homogeneous surface, and are formed basically by closed cells. The aim of this study was to apply the ionizing radiation from electron beam to crosslink low density polyethylene (LDPE), to obtain foams. Their morphological, thermal and mechanical properties were studied to evaluate the obtained samples. The samples of low density polyethylene (0,946 g/cm 3 ), containing 5% of azodicarbonamide (ADCA), as expander agent, were irradiated with electron beam with doses of 10, 20, 30, 40, 50, 60, 80 and 100 kGy. After the irradiation, these LDPE samples were put into an oven to obtain the foams. It was determined the crosslinking degree of the foams. Some samples were also thermally aged. The mechanical performance of the foams samples was evaluated by means of the tensile strength, compression, hardness, permanent deformation by compression and resilience. It was also carried out thermogravimetry and scanning electron microscopy (SEM). The results have shown that, in the interval of radiation doses studied, that the tensile strength increases with the increase of the crosslinking degree. The compression resistance results obtained from with samples with to radiation dose of 40 kGy showed significant decreasing. The resilience

Preparation of flexible PLA/PEG-POSS nanocomposites by melt blending and radiation crosslinking

International Nuclear Information System (INIS)

Jung, Chang-Hee; Hwang, In-Tae; Jung, Chan-Hee; Choi, Jae-Hak

2014-01-01

In this study, poly(lactic acid) (PLA)/poly(ethylene glycol)-functionalized polyhedral oligomeric silsesquioxane (PEG-POSS) nanocomposites with or without triallyl isocyanurate (TAIC) were investigated by melt blending and electron beam irradiation to enhance the flexibility of PLA. Based on the results of the crosslinking degree measurements, the PLA/PEG-POSS nanocomposites were crosslinked by electron beam irradiation in the presence of triallyl isocyanurate (TAIC) and their crosslinking degree reached up to 80% based on the absorbed dose and their compositions. From the results of the FE-SEM and EDX Si-mapping, the crosslinked PLA/PEG-POSS nanocomposites were homogenous without a micro-phase separation or radiation-induced morphological change. Based on the results of the tensile test, the PLA/PEG-POSS nanocomposites containing 15 wt% PEG-POSS exhibited the highest flexibility, and their tensile strength showed a maximum value of 44.5 MPa after electron beam irradiation at an absorbed dose of 100 kGy in the presence of TAIC, which is comparable to non-biodegradable polypropylene. The results of the dynamic mechanical analysis revealed that the crosslinked PLA/PEG-POSS nanocomposites exhibited a higher thermal resistance above their melting temperature in comparison to that of the neat PLA, although their glass transition temperature was lower than that of the neat PLA. The enzymatic biodegradation test revealed that the PLA/PEG-POSS nanocomposites were biodegradable even though their biodegradability was deteriorated in comparison to that of the neat PLA. - Highlights: • PLA/PEG-POSS nanocomposites were prepared by melt blending. • The nanocomposites containing TAIC were crosslinked by electron beam irradiation. • The mechanical properties of the nanocomposites were comparable to polypropylene. • The crosslinked nanocomposites can be biodegradable

Ionically crosslinked alginate–carboxymethyl cellulose beads for the delivery of protein therapeutics

International Nuclear Information System (INIS)

Kim, Min Sup; Park, Sang Jun; Gu, Bon Kang; Kim, Chun-Ho

2012-01-01

Highlights: ► We prepared Fe 3+ crosslinked alginate–carboxymethyl cellulose (AC) beads. ► Different surface and inner morphology of AC beads were observed on volume of CMC. ► AC beads showed minimum swelling degree in acidic condition. ► Protein release from AC beads was to control in gastrointestinal condition. - Abstract: We developed Fe 3+ -crosslinked alginate–carboxymethyl cellulose (AC) beads in various volume ratios by dropping an AC solution into a ferric chloride solution to form protein therapeutic carrier beads. Scanning electron microscopy revealed that the roughness and pore size of the crosslinked beads increased with the volume ratio of the carboxymethyl cellulose. Fourier transform-infrared analysis revealed the formation of a three-dimensional bonding structure between the anionic polymeric chains of AC and the Fe 3+ ions. The degree of swelling and the release profile of albumin from the beads were investigated under simulated gastrointestinal conditions (pH 1.2, 4.5, and 7.4). The Fe 3+ -crosslinked AC beads displayed different degrees of swelling and albumin release for the various AC volume ratios and under various pH conditions. An in vitro release test was used to monitor the controlled release of albumin from the AC beads under simulated gastrointestinal conditions over 24 h. The Fe 3+ -crosslinked AC beads protected and controlled the release of protein, demonstrating that such beads present a promising protein therapeutic carrier for the oral delivery.

Improvement of radiation resistance for polytetrafluoroethylene(PTFE) by radiation cross-linking

International Nuclear Information System (INIS)

Oshima, Akihiro; Tabata, Yoneho; Ikeda, Shigetoshi; Seguchi, Tadao.

1996-01-01

The crosslinked polytetrafluoroethylene(PTFE) was prepared by electron beams irradiation technique in the molten state at 340degC ± 3degC in inert gas atmosphere. The crosslinking density was changed by the irradiation dose. The radiation resistance of crosslinked PTFE was investigated on the mechanical properties after irradiation by γ-rays at room temperature under vacuum and in air. The dose at half value of elongation at break was about 1MGy for 500kGy-crosslinked PTFE, while the dose for non-crosslinked PTFE was only 3.5kGy. It was found that the radiation resistance of PTFE was extremely improved by crosslinking. (author)

Chemical structure and physical properties of radiation-induced crosslinking of polytetrafluoroethylene

International Nuclear Information System (INIS)

Oshima, Akihiro; Ikeda, Shigetoshi; Katoh, Etsuko; Tabata, Yoneho

2001-01-01

The chemical structure and physical properties of polytetrafluoroethylene (PTFE) that has been crosslinked by radiation have been studied by various methods. It has been found that a Y-type crosslinking structure and a Y-type structure incorporating a double bond (modified Y-type) is formed in PTFE by radiation-crosslinking in the molten state. In addition, various types of double bond structures, excluding the crosslinking site, have been identified. The crosslinked PTFE has a good light transparency due to the loss of crystallites, whilst it retains the excellent properties of electrical insulation and heat resistance. The coefficient of abrasion and the permanent creep are also greatly improved by crosslinking

Comparison study of crosslink density determination in cured rubber

International Nuclear Information System (INIS)

El-sabbagh, S.H.; Yehia, A.A.

2005-01-01

The crosslink density is an important property affecting the major characteristics of cured rubber. The crosslink density can be determined by different methods such as: 1. Dynamic mechanical method using the data of stress-strain relationship. 2. Mooney-Rivlin equation 3. Swelling in organic solvents measurements using Flory-Rehner equation. The crosslink density calculated by the previous methods were discussed and compared with each other for cured NR, SBR and NBR. The obtained data showed that the dynamic-mechanical method can be considered as a simple and reliable method for determination of crosslink density for cured rubbers

Radiation crosslinking of elastomers

International Nuclear Information System (INIS)

Pearson, D.S.

1981-01-01

In the first part of this paper a review is presented of recent results which show that the tensile strength and fatigue life of synthetic elastomers cured by radiation are essentially equivalent to those prepared by other crosslinking techniques. An explanation for the conflict of these new results with the earlier studies on natural rubber is presented. Investigations into the mechanisms and kinetics of crosslinking mentioned above have also shown that the irradiation method should be ideal for preparing well characterized networks. Such materials are useful for testing theoretical relationships between the structure of rubber networks and their stress-strain behavior. The second part of this paper is devoted to this aspect. (author)

Vitamin E diffused highly cross-linked polyethylene in total hip arthroplasty at five years

DEFF Research Database (Denmark)

Nebergall, Audrey K; Greene, M. E.; Laursen, M B

2017-01-01

Aims: The objective of this five-year prospective, blinded, randomised controlled trial (RCT) was to compare femoral head penetration into a Vitamin E diffused highly cross-linked polyethylene (HXLPE) liner with penetration into a medium cross-linked polyethylene control liner using......, ArComXL. This is the longest-term RCT comparing the wear performance and clinical outcome of Vitamin E diffused HXLPE with a previous generation of medium cross-linked polyethylene....... radiostereometric analysis. Patients and Methods: Patients scheduled for total hip arthroplasty (THA) were randomised to receive either the study E1 (32 patients) or the control ArComXL polyethylene (35 patients). The median age (range) of the overall cohort was 66 years (40 to 76). Results: The five-year median...

Properties of crosslinked ultra-high-molecular-weight polyethylene.

Science.gov (United States)

Lewis, G

2001-02-01

Substantially reducing the rate of generation of wear particles at the surfaces of ultra-high-molecular-weight polyethylene (UHMWPE) orthopedic implant bearing components, in vivo, is widely regarded as one of the most formidable challenges in modern arthroplasty. In the light of this, much research attention has been paid to the myriad of endogenous and exogenous factors that have been postulated to affect this wear rate, one such factor being the polymer itself. In recent years, there has been a resurgence of interest in crosslinking the polymer as a way of improving its properties that are considered relevant to its use for fabricating bearing components. Such properties include wear resistance, fatigue life, and fatigue crack propagation rate. Although a large volume of literature exists on the topic on the impact of crosslinking on the properties of UHMWPE, no critical appraisal of this literature has been published. This is one of the goals of the present article, which emphasizes three aspects. The first is the trade-off between improvement in wear resistance and depreciation in other mechanical and physical properties. The second aspect is the presentation of a method of estimating the optimal value of a crosslinking process variable (such as dose in radiation-induced crosslinking) that takes into account this trade-off. The third aspect is the description of a collection of under- and unexplored research areas in the field of crosslinked UHMWPE, such as the role of starting resin on the properties of the crosslinked polymer, and the in vitro evaluation of the wear rate of crosslinked tibial inserts and other bearing components that, in vivo, are subjected to nearly unidirectional motion.

Production of radiation crosslinked polymeric compositions using diacetylenes

International Nuclear Information System (INIS)

Patel, G.N.

1979-01-01

Crosslinked polymeric compositions, useful as electrical insulators, heat shrinkable packaging, and lightweight foam plastics, are described. The crosslinked polymeric compositions are produced by admixing a diacetylene monomer, oligomer, polymer or mixture thereof, wherein the monomer has the formula, RNHCO-O-CH 2 -C==C-C==C-CH- 2 -O-OCNHR' in which R and R' are the same or different and are alkyl containing 1 to 20 carbon atoms, with a thermoplastic crosslinkable polymer and then subjecting the resulting mixture to actinic radiation

A novel combined polyphenol-aldehyde crosslinking of collagen film-Applications in biomedical materials.

Science.gov (United States)

Liu, Ting; Shi, Lu; Gu, Zhipeng; Dan, Weihua; Dan, Nianhua

2017-08-01

Despite its crucial role in directing cell fate in healthy and diseased tissues, improvements in physical-chemical properties and biocompatibility of type-I collagen are still needed. In this report, we described combined and facile method to modify collagen. The collagen film was first modified by procyanidins solution, in which, then subjected to further crosslinked by dialdehyde alginate, resulting in collagen-procyanidins-dialdehyde alginate film. The properties of the crosslinked collagen films were investigated and the results were discussed. Results from differential scanning calorimetry and thermo gravimetric analysis suggested that the thermal stabilities of the collagen-procyanidins-dialdehyde alginate film were significantly improved. The mechanical properties of collagen-procyanidins-dialdehyde alginate film in terms of elongation at break and tensile strength increased approximately 2-fold and 3-fold, respectively compare to pure collagen film. In addition, the resistance to collagenase degradation of collagen-procyanidins-dialdehyde alginate film was remarkably promoted. The results from methyltetrazolium assay and confocal laser scanning microscopy showed that no cytotoxicity of collagen film was introduced by the combined crosslinking method. Thus, the novel combined by procyanidins-dialdehyde alginate crosslinking method shown in this study provided a non-toxic and efficient crosslinking method that improved various properties of collagen film, which has great potential applications in biomedical materials. Copyright © 2017 Elsevier B.V. All rights reserved.

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...

New crosslinked polyvinyl chloride insulated wire by electron beam irradiation

International Nuclear Information System (INIS)

Takahata, Norio; Shingyouchi, Kazuo; Sato, Masakatsu; Sasaki, Hidemi; Terunuma, Haruji

1978-01-01

The polyvinyl chloride-coated wires crosslinked by electron beam irradiation have made rapid progress as electric and electronic wiring material and grown to hold a firm position in this field. In response to the requirements for wires with the advance of electronic equipments, Hitachi Cable Ltd. developed a peculiar graft polymer consisting of chlorinated polyethylene and polyvinyl chloride. To this polymer, the characteristics of a very wide range from toughness to flexibility can be given, and the crosslinked polyvinyl chloride wires utilizing these characteristics were put in practical use. Many kinds of the wires were developed as follows; 105 deg. C rating crosslinked vinyl-coated wires authorized by UL and CSA standards, crosslinked vinyl-coated wires with excellent flexibility, high strength crosslinked vinyl-coated wires with thin coating and crosslinked vinyl-coated wires for automobiles. They are expected to be developed into other new fields and applications. (Kobatake, H.)

Crosslinkers of Different Types in Precipitation Polymerization of Acrylic Acid

Directory of Open Access Journals (Sweden)

H. Eshaghi

2013-01-01

Full Text Available Crosslinked poly(acrylic acids were prepared using two types of crosslinker by precipitation polymerization method in a binary organic solvent. N,N’-methylenebisacrylamide (MBA and polyethylene glycol dimethacrylate (PEGDMA-330 were used as low-molecular weight and long-chain crosslinkers, respectively. The effect of various types of crosslinkers on polymer characteristics (i.e., gel content, equilibrium swelling, glass transition temperature, and rheological properties was investigated. Maximum amount of viscosity was obtained by using long-chain crosslinker. The Flory-Rehner equation and rubber elasticity theory were used to discuss the network structure of polymer. It was observed that, the glass transition temperature (Tg of the synthesized polymer containing PEGDMA-330 is higher than that of polymer containing MBA. Apparent and rotational viscosity were used to determine the optimal crosslinker type. In addition, the consistencycoefficient (m and flow behavior index (n parameter of Ostwald equation were investigated as well.

Fabrication of polymer-alloy based on polytetrafluoroethylene by radiation-crosslinking

International Nuclear Information System (INIS)

Oshima, A.; Asano, S.; Hyunga, T.; Ichizuri, S.; Washio, M.

2003-01-01

Perfluoropolymer such as polytetrafluoroethylene (PTFE), tetrafluoroethylene co-perfluoroalkylvinylether (PFA) and tetrafluoroethylene-co-hexafluoropropylene (FFP) have been classified to be a typical polymer of radiation-induced degradation. However, we confirmed that the crosslinking of PTFE, PFA and FEP proceed by irradiation under selective condition where oxygen-free and high temperature above the melting temperature of them. In this study, fabrication of polymer-alloy based on PTFE has been demonstrated by radiation-crosslinking techniques. The polymer alloy, which was PTFE fine powder contained with other polymeric materials, was obtained by electron beams irradiation under oxygen-free atmosphere. Characterization of polymer-alloy based on PTFE has been studied by various measurements such as solid state 19F- and 13C-NMR spectroscopy, thermal analysis (DSC, TGA)

Enzymatically crosslinked silk-hyaluronic acid hydrogels.

Science.gov (United States)

Raia, Nicole R; Partlow, Benjamin P; McGill, Meghan; Kimmerling, Erica Palma; Ghezzi, Chiara E; Kaplan, David L

2017-07-01

In this study, silk fibroin and hyaluronic acid (HA) were enzymatically crosslinked to form biocompatible composite hydrogels with tunable mechanical properties similar to that of native tissues. The formation of di-tyrosine crosslinks between silk fibroin proteins via horseradish peroxidase has resulted in a highly elastic hydrogel but exhibits time-dependent stiffening related to silk self-assembly and crystallization. Utilizing the same method of crosslinking, tyramine-substituted HA forms hydrophilic and bioactive hydrogels that tend to have limited mechanics and degrade rapidly. To address the limitations of these singular component scaffolds, HA was covalently crosslinked with silk, forming a composite hydrogel that exhibited both mechanical integrity and hydrophilicity. The composite hydrogels were assessed using unconfined compression and infrared spectroscopy to reveal of the physical properties over time in relation to polymer concentration. In addition, the hydrogels were characterized by enzymatic degradation and for cytotoxicity. Results showed that increasing HA concentration, decreased gelation time, increased degradation rate, and reduced changes that were observed over time in mechanics, water retention, and crystallization. These hydrogel composites provide a biologically relevant system with controllable temporal stiffening and elasticity, thus offering enhanced tunable scaffolds for short or long term applications in tissue engineering. Copyright © 2017 Elsevier Ltd. All rights reserved.

Mmp-9 responsive PEG cleavable nanovesicles for efficient delivery of chemotherapeutics to pancreatic cancer.

Science.gov (United States)

Kulkarni, Prajakta S; Haldar, Manas K; Nahire, Rahul R; Katti, Preeya; Ambre, Avinash H; Muhonen, Wallace W; Shabb, John B; Padi, Sathish K R; Singh, Raushan K; Borowicz, Pawel P; Shrivastava, D K; Katti, Kalpana S; Reindl, Katie; Guo, Bin; Mallik, Sanku

2014-07-07

Significant differences in biochemical parameters between normal and tumor tissues offer an opportunity to chemically design drug carriers which respond to these changes and deliver the drugs at the desired site. For example, overexpression of the matrix metalloproteinase-9 (MMP-9) enzyme in the extracellular matrix of tumor tissues can act as a trigger to chemically modulate the drug delivery from the carriers. In this study, we have synthesized an MMP-9-cleavable, collagen mimetic lipopeptide which forms nanosized vesicles with the POPC, POPE-SS-PEG, and cholesteryl-hemisuccinate lipids. The lipopeptide retains the triple-helical conformation when incorporated into these nanovesicles. The PEG groups shield the substrate lipopeptides from hydrolysis by MMP-9. However, in the presence of elevated glutathione levels, the PEG groups are reductively removed, exposing the lipopeptides to MMP-9. The resultant peptide-bond cleavage disturbs the vesicles' lipid bilayer, leading to the release of encapsulated contents. These PEGylated nanovesicles are capable of encapsulating the anticancer drug gemcitabine with 50% efficiency. They were stable in physiological conditions and in human serum. Effective drug release was demonstrated using the pancreatic ductal carcinoma cells (PANC-1 and MIAPaCa-2) in two-dimensional and three-dimensional "tumor-like" spheroid cultures. A reduction in tumor growth was observed after intravenous administration of the gemcitabine-encapsulated nanovesicles in the xenograft model of athymic, female nude mice.

Crosslinked polyethylene foams, via eb radiation

International Nuclear Information System (INIS)

Cardoso, E.C.L.; Lugao, A. B.; Andrade e Silva, L. G.

1998-01-01

Polyethylene foams, produced by radio-induced crosslinking, show a smooth and homogeneous surface, when compared to chemical crosslinking method using peroxide as crosslinking agent. This process fosters excellent adhesive and printability properties. Besides that, closed cells, intrinsic to these foams, imparts optimum mechanical, shocks and insulation resistance, indicating these foams to some markets segments as: automotive and transport; buoyancy, flotation and marine; building and insulation; packaging; domestic sports and leisure goods. We were in search of an ideal foam, by adding 5 to 15% of blowing agent in LDPE. A series of preliminary trials defined 203 degree sign C as the right blowing agent decomposition temperature. At a 22.7 kGys/dose ratio, the lowest dose for providing an efficient foam was 30 kGy, for a formulation comprising 10% of azodicarbonamide in LDPE, within a 10 minutes foaming time

Modified gum arabic cross-linked gelatin scaffold for biomedical applications

International Nuclear Information System (INIS)

Sarika, P.R.; Cinthya, Kuriakose; Jayakrishnan, A.; Anilkumar, P.R.; James, Nirmala Rachel

2014-01-01

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

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.

Interstrand DNA crosslinks due to AP (apurinic/apyrimidinic) sites

International Nuclear Information System (INIS)

Goffin, C.; Verly, W.G.

1983-01-01

Storage of a solution of DNA containing apurinic sites, even at 4 0 C leads to the appearance of interstrand crosslinks. Possible consequences of these crosslinks, when they appear in cell DNA, are briefly discussed. Formation of interstrand crosslinks in DNA containing tritium-labelled thymine and kept in an aqueous solution might be due, at least partly, to the loss of bases by the autoirradiated DNA. (Auth.)

Stable and biocompatible genipin-inducing interlayer-crosslinked micelles for sustained drug release

Energy Technology Data Exchange (ETDEWEB)

Dai, Yu; Zhang, Xiaojin, E-mail: zhangxj@cug.edu.cn [China University of Geosciences, Faculty of Materials Science and Chemistry (China)

2017-05-15

To develop the sustained drug release system, here we describe genipin-inducing interlayer-crosslinked micelles crosslinked via Schiff bases between the amines of amphiphilic linear-hyperbranched polymer poly(ethylene glycol)-branched polyethylenimine-poly(ε-caprolactone) (PEG-PEI-PCL) and genipin. The generation of Schiff bases was confirmed by the color changes and UV-Vis absorption spectra of polymeric micelles after adding genipin. The particle size, morphology, stability, in vitro cytotoxicity, drug loading capacity, and in vitro drug release behavior of crosslinked micelles as well as non-crosslinked micelles were characterized. The results indicated that genipin-inducing interlayer-crosslinked micelles had better stability and biocompatibility than non-crosslinked micelles and glutaraldehyde-inducing interlayer-crosslinked micelles. In addition, genipin-inducing interlayer-crosslinked micelles were able to improve drug loading capacity, reduce the initial burst release, and achieve sustained drug release.

Cross-linking of wheat gluten using a water-soluble carbodiimide

NARCIS (Netherlands)

Tropini, V.; Lens, J.P.; Mulder, W.J.; Silvestre, F.

2000-01-01

Wheat gluten was cross-linked using water-soluble 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide HCl (EDC). To enhance cross-linking, N-hydroxysuccinimide (NHS) was added to the reaction mixture. The cross-linking efficiency was evaluated by the decrease in the amount of amino groups, the solubility

Protein cross-linking by chlorinated polyamines and transglutamylation stabilizes neutrophil extracellular traps.

Science.gov (United States)

Csomós, Krisztián; Kristóf, Endre; Jakob, Bernadett; Csomós, István; Kovács, György; Rotem, Omri; Hodrea, Judit; Bagoly, Zsuzsa; Muszbek, Laszlo; Balajthy, Zoltán; Csősz, Éva; Fésüs, László

2016-08-11

Neutrophil extracellular trap (NET) ejected from activated dying neutrophils is a highly ordered structure of DNA and selected proteins capable to eliminate pathogenic microorganisms. Biochemical determinants of the non-randomly formed stable NETs have not been revealed so far. Studying the formation of human NETs we have observed that polyamines were incorporated into the NET. Inhibition of myeloperoxidase, which is essential for NET formation and can generate reactive chlorinated polyamines through hypochlorous acid, decreased polyamine incorporation. Addition of exogenous primary amines that similarly to polyamines inhibit reactions catalyzed by the protein cross-linker transglutaminases (TGases) has similar effect. Proteomic analysis of the highly reproducible pattern of NET components revealed cross-linking of NET proteins through chlorinated polyamines and ɛ(γ-glutamyl)lysine as well as bis-γ-glutamyl polyamine bonds catalyzed by the TGases detected in neutrophils. Competitive inhibition of protein cross-linking by monoamines disturbed the cross-linking pattern of NET proteins, which resulted in the loss of the ordered structure of the NET and significantly reduced capacity to trap bacteria. Our findings provide explanation of how NETs are formed in a reproducible and ordered manner to efficiently neutralize microorganisms at the first defense line of the innate immune system.

Densely crosslinked polycarbosiloxanes .2. Thermal and mechanical properties

NARCIS (Netherlands)

Flipsen, T.A C; Derks, R.; van der Vegt, H.A.; Stenekes, R.; Pennings, A.J; Hadziioannou, G

1997-01-01

The thermal and mechanical properties of two densely crosslinked polycarbosiloxane systems were investigated in relation to the molecular structure. The networks were prepared from functional branched prepolymers and crosslinked via a hydrosilylation curing reaction. The prepolymers having only

Effects of Alkali Treatment and Polyisocyanate Crosslinking on the Mechanical Properties of Kraft Fiber-Reinforced Unsaturated Polyester Composites

Directory of Open Access Journals (Sweden)

Zhenhua Gao

2014-08-01

Full Text Available The effects of alkali treatment and polyisocyanate crosslinking on the mechanical properties of kraft fiber-reinforced UPE composites were investigated by means of tensile evaluation, SEM analysis, and XRD analysis. The results indicated that the alkali treatment decreased the tensile strength of the prepared composite before aging from 121 MPa to 97 MPa due to the decreased degree of crystallinity of the alkali-treated kraft fiber. Polyisocyanate crosslinking could apparently improve the mechanical properties and stability in terms of a 43% increase of non-aged tensile strength and 52% increase of hydrothermal-aged tensile strength compared with the controlled composite without crosslinking modification, which was attributable to the formation of strong chemical bonding between the interfaces of kraft fiber and polyester.

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

Conservation of RNA sequence and cross-linking ability in ribosomes from a higher eukaryote: photochemical cross-linking of the anticodon of P site bound tRNA to the penultimate cytidine of the UACACACG sequence in Artemia salina 18S rRNA

International Nuclear Information System (INIS)

Ciesiolka, J.; Nurse, K.; Klein, J.; Ofengand, J.

1985-01-01

The complex of Artemia salina ribosomes and Escherichia coli acetylvalyl-tRNA could be cross-linked by irradiation with near-UV light. Cross-linking required the presence of the codon GUU, GUA being ineffective. The acetylvalyl group could be released from the cross-linked tRNA by treatment with puromycin, demonstrating that cross-linking had occurred at the P site. This was true both for pGUU- and also for poly(U2,G)-dependent cross-linking. All of the cross-linking was to the 18S rRNA of the small ribosomal subunit. Photolysis of the cross-link at 254 nm occurred with the same kinetics as that for the known cyclobutane dimer between this tRNA and Escherichia coli 16S rRNA. T1 RNase digestion of the cross-linked tRNA yielded an oligonucleotide larger in molecular weight than any from un-cross-linked rRNA or tRNA or from a prephotolyzed complex. Extended electrophoresis showed this material to consist of two oligomers of similar mobility, a faster one-third component and a slower two-thirds component. Each oligomer yielded two components on 254-nm photolysis. The slower band from each was the tRNA T1 oligomer CACCUCCCUVACAAGp, which includes the anticodon. The faster band was the rRNA 9-mer UACACACCGp and its derivative UACACACUG. Unexpectedly, the dephosphorylated and slower moving 9-mer was derived from the faster moving dimer. Deamination of the penultimate C to U is probably due to cyclobutane dimer formation and was evidence for that nucleotide being the site of cross-linking. Direct confirmation of the cross-linking site was obtained by Z-gel analysis

Structure of E. coli 16S RNA elucidated by psoralen crosslinking

International Nuclear Information System (INIS)

Thompson, J.F.; Hearst, J.E.

1983-01-01

E. coli 16S RNA in solution was photoreacted with hydroxymethyltrimethylpsoralen and long wave ultraviolet light. Positions of crosslinks were determined to high resolution by partially digesting the RNA with T 1 RNase, separating the crosslinked fragments by two-dimensional gel electrophoresis, reversing the crosslink, and sequencing the separated fragments. This method yielded the locations of crosslinks to +/-15 nucleotides. Even finer placement has been made on the basis of our knowledge of psoralen reactivity. Thirteen unique crosslinks were mapped. Seven crosslinks confirmed regions of secondary structure which had been predicted in published phylogenetic models, three crosslinks discriminated between phylogenetic models, and three proved the existence of new structures. The new structures were all long-range interactions which appear to be in dynamic equilibrium with local secondary structure. Because this technique yields direct information about the secondary structure of large RNAs, it should prove invaluable in studying the structure of other RNAs of all sizes

Characterization of the UV-crosslinked heterodimer of histones H2B and H4

International Nuclear Information System (INIS)

Johnson, E.R.; Brown, D.M.; DeLange, R.J.

1986-01-01

At relatively high salt concentrations (1.2 M), histone 2B (H2B) and histone 4 (H4) can be covalently crosslinked by irradiation with ultraviolet light to yield a mixture of the three possible dimers: H2B-H2B, H4-H4, and H2B-H4. The formation of the H2B-H4 heterodimer was found to be favored at lower histone concentrations (> 90% H2B-H4 at 0.1 mg/ml total histone protein). CNBr cleavage of the H2B-H4 dimer produced three fragments which were separated by reverse phase HPLC. These fragments were identified by amino acid compositional analysis to be H4(85-102), H2B(62-125), and the crosslinked N-terminal regions H2B(1-59)-H4(1-84). Amino acid sequence analysis of the crosslinked fragment indicated that tyrosine-40 of H2B is likely involved in the covalent crosslinkage which joins the histone monomers to form the heterodimer

Study of the direct detection of crosslinking in hydrocarbons by 13C-NMR. II. Identification of crosslink in model compound and application to irradiate paraffins

International Nuclear Information System (INIS)

Bennett, R.L.; Keller, A.; Stejny, H.H.; Murray, M.

1976-01-01

A 13 C-NMR investigation was carried out in aid of direct detection of crosslinks in hydrocarbons with the future objective of studying radiation-induced crosslinking in polyethylene by a direct method. The resonance signal due to a tertiary carbon atom appropriate to a crosslink far remote from molecular ends has been identified in a definitive manner with the aid of the H-shaped model compound 1,1,2,2-tetra(tridecyl)ethane synthetized in Part I of this study. This identification was then put to use in the examination of the irradiated linear paraffins n-hexadecane and n-eicosane, where it enabled the detection of radiation-induced crosslinks. This crosslinking could then be associated with corresponding changes in molecular weight (dimer, trimer formation) as revealed by discrete peaks in the gel-permeation chromatograms of the same samples and randomness of the crosslinking process in the liquid state of these compounds being inferred

Radiation cross-linked polymers: Recent developments and new applications

International Nuclear Information System (INIS)

Rouif, Sophie

2005-01-01

The purpose of the present paper is to review the innovative and recent applications of radiation cross-linking of polymers that reinforces their dimensional stability in chemically aggressive and high temperature conditions. Radiation cross-linking can be applied to a great number of plastics: thermoplastics, elastomers and thermoplastic elastomers (TPE). Some of them can cross-link on their own, some others need to be formulated with a cross-linking agent (promoter) or to be modified during their polymerization. Some results of chemical and thermomechanical characterizations of radiation cross-linked plastics based on engineering polymers will be described, and their advantages will be emphasized in relation with their applications in various sectors: pipes and cables, packaging, automotive, electrical engineering and electronics, including connectors, surface mounted devices, integrated circuits, 3D-MID technology, etc. The paper will conclude with a short review of the industrial irradiation facilities (EB facilities and gamma plants) adapted to the treatment of such various products

The Fanconi Anemia Pathway in Replication Stress and DNA Crosslink Repair

Science.gov (United States)

Jones, Mathew JK.; Huang, Tony T.

2013-01-01

Interstand crosslinks (ICLs) are DNA lesions where the bases of opposing DNA strands are covalently linked, inhibiting critical cellular processes such as transcription and replication. Chemical agents that generate ICLs cause chromosomal abnormalities including breaks, deletions and rearrangements, making them highly genotoxic compounds. This toxicity has proven useful for chemotherapeutic treatment against a wide variety of cancer types. The majority of our understanding of ICL repair in humans has been uncovered thorough analysis of the rare genetic disorder Fanconi anemia, in which patients are extremely sensitive to crosslinking agents. Here, we discuss recent insights into ICL repair gained through new ICL repair assays and highlight the role of the Fanconi Anemia repair pathway during replication stress. PMID:22744751

Radiolytic crosslinking and chain scission in aliphatic and alkyl-aromatic polyamides: Pt. 2

International Nuclear Information System (INIS)

Lyons, B.J.; Glover, L.C. Jr.

1991-01-01

Regression analysis of the radiation parameters of nine aliphatic polyamides exposed to ionizing radiation leads to the conclusion that the decline in the ratio of chain scission to crosslinking in higher aliphatic polyamides is best related to the linear increase in the methylene content of, or the number of methylene groups in, the polyamide repeat unit. G(crosslink)[G(X)] and G(chain scission) [G(CS)] values, however, do not correlate well with either of these parameters. Rather it is found that the major determinant of yields [about 80-85% of the variation for G(X), 70% for G(CS)] is the number of hydrogen atoms or methylene groups in the amine residue. Although, logically, the yields of crosslinks and chain scissions in polyamides would be expected to tend to that of polyethylene as the number of methylene groups in the repeat unit increases, use of two models assuming an exponential trend to the G(X) value characteristic of polyethylene in the analysis did not provide better fits to the data than the simple linear model referred to above. Indeed, the assumption of a significant exponential trend factor led to a marked drop in the goodness of fit. (author)

Preparation and Characterisation of Crosslinked Natural Rubber (SMR CV 60 and Epoxidised Natural Rubber (ENR-50 Blends

Directory of Open Access Journals (Sweden)

M. SASITARAN

2018-04-01

Full Text Available In this sudy, the influenceof di(tert-butylperoxyisopropylbenzene (DTBPIB on the properties of natural rubber (NR blend with epoxidized natural rubber (ENR was determined. Fourier transform infrared spectroscopy with attenuated total refletance analysis and gel content confired crosslinking occurred in the rubber blends in the presence of peroxide DTBPIB percentage. Studies including tensile properties, dynamic mechanical properties, thermogravimetric analysis (TGA and water absorptivity showed the changes in properties of the crosslinked NR/ENR blends. Tensile properties analysis disclosed the improvements in the modulus at 300% elongation and tensile stength with increasing NR ratios. Dynamic mechanical analysis revealed the blends to be incompatible and immiscible, with ENR showing a more viscous behaviour compared to the polymer blends. Thermal properties improved by blending NR with ENR as the onset temperature of NR/ENR: 50/50 was higher than pure NR by approximately 10oC and ENR by approximately 2oC. Water absorptivity experiment revealed a two-fold reduction in the presence of crosslinking for all blend ratios.

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.

Oxidation resistant peroxide cross-linked UHMWPE produced by blending and surface diffusion

International Nuclear Information System (INIS)

Gul, Rizwan M; Oral, Ebru; Muratoglu, Orhun K

2014-01-01

Ultra-high molecular weight polyethylene (UHMWPE) has been widely used as acetabular cup in total hip replacement (THR) and tibial component in total knee replacement (TKR). Crosslinking of UHMWPE has been successful used to improve its wear performance leading to longer life of orthopedic implants. Crosslinking can be performed by radiation or organic peroxides. Peroxide crosslinking is a convenient process as it does not require specialized equipment and the level of crosslinking can be manipulated by changing the amount of peroxide added. However, there is concern about the long-term stability of these materials due to possible presence of by-products. Vitamin E has been successfully used to promote long-term oxidative stability of UHMWPE. In this study, UHMWPE has been crosslinked using organic peroxide in the presence of Vitamin E to produce an oxidation resistant peroxide crosslinked material. Crosslinking was performed both in bulk by mixing peroxide and resin, and only on the surface using diffusion of peroxides.The results show that UHMWPE can be crosslinked using organic peroxides in the presence of vitamin E by both methods. However, the level of crosslinking decreases with the increase in vitamin E content. The wear resistance increases with the increase in crosslink density, and oxidation resistance significantly increases due to the presence of vitamin E

Oxidation resistant peroxide cross-linked UHMWPE produced by blending and surface diffusion

International Nuclear Information System (INIS)

Gul, R. M.; Oral, E.; Muratoglu, O. K.

2013-01-01

Ultra-high molecular weight polyethylene (UHMWPE) has been widely used as acetabular cup in total hip replacement (THR) and tibial component in total knee replacement (TKR). Crosslinking of UHMWPE has been successful used to improve its wear performance leading to longer life of orthopedic implants. Crosslinking can be performed by radiation or organic peroxides. Peroxide crosslinking is a convenient process as it does not require specialized equipment and the level of crosslinking can be manipulated by changing the amount of peroxide added. However, there is concern about the long-term stability of these materials due to possible presence of by-products. Vitamin E has been successfully used to promote long-term oxidative stability of UHMWPE. In this study, UHMWPE has been crosslinked using organic peroxide in the presence of Vitamin E to produce an oxidation resistant peroxide crosslinked material. Crosslinking was performed both in bulk by mixing peroxide and resin, and only on the surface using diffusion of peroxides.The results show that UHMWPE can be crosslinked using organic peroxides in the presence of vitamin E by both methods. However, the level of crosslinking decreases with the increase in vitamin E content. The wear resistance increases with the increase in crosslink density, and oxidation resistance significantly increases due to the presence of vitamin E. (author)

Irradiation Crosslinking of Polyamides for the Electrical and Automotive Industry

International Nuclear Information System (INIS)

Gehring, J.

2006-01-01

Irradiation crosslinking of electrical cables and heat shrinkable tubes have been widely accepted in the automotive and electrical industry for a long time. Due higher demands regarding temperature resistance, arc resistance and good chemical resistance against oil and greases crosslinked injection moulded parts made out of polyamid and polybutylentherephtalate become also more and more interesting. Crosslinked polyamide can also replace thermosets for switches and offers therefore additional financial benefits. It will be shown on the basis of already realized projects, which basic requirements exist and how irradiation crosslinking can fulfil these demands

Radiation crosslinking of polymer materials and its functional properties

International Nuclear Information System (INIS)

Yoshii, Fumio

2006-01-01

It was found out that radiation crosslinking of biodegradable polymer such as poly (butylene succinate, PBS) and poly(ε-caprolactone, PCL) could be achieved by radiation in the presence of small amount of trimethallyl isocyanurate (TMAIC) or 1% triallyl isocyanurate (TAIC). Such modification is very effective to improve heat resistance for PBS and PCL. Poly (lactic acid, PLA) undergoes crosslinking effectively with 3% TAIC by radiation. Outstanding feature of these polymers is their biodegradability even after crosslinking. Radiation crosslinking of polysaccharide derivatives such as carboxymethyl-cellulose (CMC) is also achieved in aqueous solution at high concentration (paste-like state). The crosslinking behavior was largely affected by the degree of substitution (DS) and polymer concentration. After removal of water the dry CMC gel is used as water absorbent material. This dry gel is the most effective for removal of large amounts of water from organic wastes, resulting in the acceleration of their fermentation. Measurement of swelling ratio of the dry CMC gel in 0.9% NaCl aqueous solution was carried out to expand application fields for this material. Radiation crosslinked poly (vinyl alcohol) hydrogel was successfully commercialized from July 2004 as wound dressing for accelerated healing. Furthermore, this material was also used as gel protector to prevent shore sore and was further commercialized. (author)

Protein analysis by 31p NMR spectroscopy in ionic liquid: quantitative determination of enzymatically created cross-links.

Science.gov (United States)

Monogioudi, Evanthia; Permi, Perttu; Filpponen, Ilari; Lienemann, Michael; Li, Bin; Argyropoulos, Dimitris; Buchert, Johanna; Mattinen, Maija-Liisa

2011-02-23

Cross-linking of β-casein by Trichoderma reesei tyrosinase (TrTyr) and Streptoverticillium mobaraense transglutaminase (Tgase) was analyzed by (31)P nuclear magnetic resonance (NMR) spectroscopy in ionic liquid (IL). According to (31)P NMR, 91% of the tyrosine side chains were cross-linked by TrTyr at high dosages. When Tgase was used, no changes were observed because a different cross-linking mechanism was operational. However, this verified the success of the phosphitylation of phenolics within the protein matrix in the IL. Atomic force microscopy (AFM) in solid state showed that disk-shaped nanoparticles were formed in the reactions with average diameters of 80 and 20 nm for TrTyr and Tgase, respectively. These data further advance the current understanding of the action of tyrosinases on proteins on molecular and chemical bond levels. Quantitative (31)P NMR in IL was shown to be a simple and efficient method for the study of protein modification.

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.

Carboxymethylcellulose hydrogel crosslinked with citric acid for biomedical application; Reticulacao de hidrogeis de carboximetilcelulose com acido citrico para aplicacoes biomedicas

Energy Technology Data Exchange (ETDEWEB)

Capanema, Nadia S.V.; Mansur, Alexandra A.P.; Mansur, Herman S., E-mail: nsvnadia@gmail.com [Centro de Nanociencias, Nanotecnologia e Inovacao (CeNano), MG (Brazil); Universidade Federal de Minas Gerais (UFMG), Belo Horizonte, MG (Brazil). Departamento de Engenharia Metalurgica e Materiais

2016-07-01

The carboxymethylcellulose (CMCel) has been extensively used in order application as flexible polymer membrane. Biopolymers crosslinked have been studied to optimize their performance in biomedical applications. In this work, CMCel films with a degree of substitution (DS = 0.77) were prepared by evaporation of solvent and crosslinked with different concentrations of citric acid (CA). The synthesized CMCel was characterized by Infrared Spectroscopy by Fourier Transform X-ray spectroscopy (FTIR), and morphology assessed by scanning electron microscopy (SEM). Morphological analysis performed using the SEM indicated the crosslinked CMCel and not crosslinked with a very smooth and uniform appearance. The FTIR results indicated the modification of existing bands and appearance of a new band 1715 cm{sup -1} suggesting that there has been change in the structure of the crosslinked CMCel. (author)

In vitro evaluation of crosslinked electrospun fish gelatin scaffolds

International Nuclear Information System (INIS)

Gomes, S.R.; Rodrigues, G.; Martins, G.G.; Henriques, C.M.R.; Silva, J.C.

2013-01-01

Gelatin from cold water fish skin was electrospun, crosslinked and investigated as a substrate for the adhesion and proliferation of cells. Gelatin was first dissolved in either water or concentrated acetic acid and both solutions were successfully electrospun. Cross-linking was achieved via three different routes: glutaraldehyde vapor, genipin and dehydrothermal treatment. Solution's properties (surface tension, electrical conductivity and viscosity) and scaffold's properties (chemical bonds, weight loss and fiber diameters) were measured. Cellular viability was analyzed culturing 3T3 fibroblasts plated on the scaffolds and grown up to 7 days. The cells were fixed and observed with SEM or stained for DNA and F-actin and observed with confocal microscopy. In all scaffolds, the cells attached and spread with varying degrees. The evaluation of cell viability showed proliferation of cells until confluence in scaffolds crosslinked by glutaraldehyde and genipin; however the rate of growth in genipin crosslinked scaffolds was slow, recovering only by day five. The results using the dehydrothermal treatment were the less satisfactory. Our results show that glutaraldehyde treated fish gelatin is the most suitable substrate, of the three studied, for fibroblast adhesion and proliferation. - Highlights: ► Electrospinning of fish gelatin dissolved in both water or concentrated acetic acid ► Glutaraldehyde, genipin and dehydrothermal treatment effectively crosslink the fish gelatin fibers ► Fibroblasts effectively adhere to and propagate on all scaffolds ► Cell population is highest for glutaraldehyde crosslinked scaffolds ► Cells exhibit more filopodia and stress fibers on glutaraldehyde crosslinked scaffolds

In vitro evaluation of crosslinked electrospun fish gelatin scaffolds

Energy Technology Data Exchange (ETDEWEB)

Gomes, S.R. [Centro de Física e Investigação Tecnológica / Departamento de Física, Faculdade de Ciências e Tecnologia, FCT, Universidade Nova de Lisboa, 2829-516 Caparica (Portugal); Rodrigues, G.; Martins, G.G. [Centro de Biologia Ambiental / Departamento de Biologia Animal, Faculdade de Ciências da Universidade de Lisboa, FCUL, 1749-016 Campo Grande, Lisboa (Portugal); Henriques, C.M.R. [Centro de Física e Investigação Tecnológica / Departamento de Física, Faculdade de Ciências e Tecnologia, FCT, Universidade Nova de Lisboa, 2829-516 Caparica (Portugal); Silva, J.C., E-mail: jcs@fct.unl.pt [Centro de Física e Investigação Tecnológica / Departamento de Física, Faculdade de Ciências e Tecnologia, FCT, Universidade Nova de Lisboa, 2829-516 Caparica (Portugal)

2013-04-01

Gelatin from cold water fish skin was electrospun, crosslinked and investigated as a substrate for the adhesion and proliferation of cells. Gelatin was first dissolved in either water or concentrated acetic acid and both solutions were successfully electrospun. Cross-linking was achieved via three different routes: glutaraldehyde vapor, genipin and dehydrothermal treatment. Solution's properties (surface tension, electrical conductivity and viscosity) and scaffold's properties (chemical bonds, weight loss and fiber diameters) were measured. Cellular viability was analyzed culturing 3T3 fibroblasts plated on the scaffolds and grown up to 7 days. The cells were fixed and observed with SEM or stained for DNA and F-actin and observed with confocal microscopy. In all scaffolds, the cells attached and spread with varying degrees. The evaluation of cell viability showed proliferation of cells until confluence in scaffolds crosslinked by glutaraldehyde and genipin; however the rate of growth in genipin crosslinked scaffolds was slow, recovering only by day five. The results using the dehydrothermal treatment were the less satisfactory. Our results show that glutaraldehyde treated fish gelatin is the most suitable substrate, of the three studied, for fibroblast adhesion and proliferation. - Highlights: ► Electrospinning of fish gelatin dissolved in both water or concentrated acetic acid ► Glutaraldehyde, genipin and dehydrothermal treatment effectively crosslink the fish gelatin fibers ► Fibroblasts effectively adhere to and propagate on all scaffolds ► Cell population is highest for glutaraldehyde crosslinked scaffolds ► Cells exhibit more filopodia and stress fibers on glutaraldehyde crosslinked scaffolds.

Simulations of tensile failure in glassy polymers: effect of cross-link density

International Nuclear Information System (INIS)

Panico, M; Narayanan, S; Brinson, L C

2010-01-01

Molecular dynamics simulations are adopted to investigate the failure mechanisms of glassy polymers, particularly with respect to increasing density of cross-links. In our simulations thermosetting polymers, which are cross-linked, exhibit an embrittlement compared with uncross-linked thermoplastics in a similar fashion to several experimental investigations (Levita et al 1991 J. Mater. Sci. 26 2348; Sambasivam et al 1997 J. Appl. Polym. Sci. 65 1001; Iijima et al 1992 Eur. Polym. J. 28 573). We perform a detailed analysis of this phenomenon and propose an interpretation based on the predominance of chain scission process over disentanglement in thermosetting polymers. We also elucidate the brittle fracture response of the thermosetting polymers

The spectra character of photodegraded the pyridinoline cross-links by Hypocrellin B

International Nuclear Information System (INIS)

Zhang Jucheng; Chen Rui; Liu Wei; Chen Zhuo; Shu Lidan; Liu Yingji

2011-01-01

Pyridinoline cross-links is one of the cross-link formation in collagen which in cell matrix, many research shown that this cross-link cause the fibrosis. Hypocrellin B (HB) is one of the nature photosensitizers, this work investigated the pyridinoline cross-link in collagen was photodegraded by HB. The result shown HB can degrade the pyridinoline cross-link with photo. This is to say, HB may be use as the photodynamic reagent to study the fibrosis.

Synthesis and Characterization of Ionically Crosslinked Elastomers

Science.gov (United States)

2016-01-01

was prepared by quaternization of vinyl benzyl chloride, while a  common dicarboxylic RAFT agent was neutralized with  potassium . The ideal structure...polymerization  where each mole of RAFT agent will  produce one mole of crosslink  junctions.  Initial polymerizations of n‐butyl  acrylate  (BA) were...butyl  acrylate  was polymerized  with the RAFT crosslinking agent in  methanol to low conversion to  introduce BA units, but limit the crosslinking

Effect of Crosslinking Agent Concentration on the Properties of Unmedicated Hydrogels

Directory of Open Access Journals (Sweden)

Rachel Shet Hui Wong

2015-09-01

Full Text Available Novel polyethylene oxide (PEO hydrogel films were synthesized via UV crosslinking with varying concentrations of pentaerythritol tetra-acrylate (PETRA as crosslinking agent. The aim was to study the effects of the crosslinking agent on the material properties of hydrogel films intended for dermatological applications. Fabricated film samples were characterized using swelling studies, scanning electron microscopy, tensile testing and rheometry. Films showed rapid swelling and high elasticity. The increase of PETRA concentration resulted in significant increase in the gel fraction and crosslinking density (ρc, while causing a significant decrease in the equilibrium water content (EWC, average molecular weight between crosslinks (\\({\\overline{M}}_{c}\\, and mesh size (ζ of films. From the scanning electron microscopy, cross-linked PEO hydrogel network appeared as cross-linked mesh-like structure with interconnected micropores. Rheological studies showed PEO films required a minimum of 2.5% w/w PETRA to form stable viscoelastic solid gels. Preliminary studies concluded that a minimum of 2.5% w/w PETRA is required to yield films with desirable properties for skin application.

Effect of crosslinking UHMWPE on its tensile and compressive creep performance.

Science.gov (United States)

Lewis, G; Carroll, M

2001-01-01

The in vitro quasi-static tensile and compressive creep properties of three sets of GUR 1050 ultra-high-molecular-weight polyethylene (UHMWPE) specimens were obtained. These sets were: control (as-received stock); "low-gamma" (specimens were crosslinked using gamma radiation, with a minimum dose of 5 Mrad); and "high-gamma" (specimens were crosslinked using gamma radiation, with a minimum dose of 15 Mrad). The % crystallinity (%C) and crosslink density (rho(x)) of the specimens in the three sets were also obtained. It was found that, in both tension and compression, crosslinking resulted in a significant depreciation in the creep properties, relative to control. The trend in the creep results is explained in terms of the impact of crosslinking on the polymer's %C and rho(x). The present results are in contrast to literature reports that show that crosslinking enhances the wear resistance of the polymer. The implications of the present results, taken together with the aforementioned literature results, are fully discussed vis-a-vis the use of crosslinked UHMWPE for fabricating articular components for arthroplasties.

Long-Chain Diacrylate Crosslinkers and Use of PEG Crosslinks in Poly(potassium acrylate-acrylic acid)/Kaolin Composite Superabsorbents

OpenAIRE

Koroush Kabiri; Siavash Nafisi; Mohammad jalaledin Zohuriaan-Mehr; Ali Akbar Yousefi

2013-01-01

Long-chain diacrylate crosslinkers based on linear α,ω-diols were synthesized and characterized using FTIR and 1H NMR spectroscopy. The highest reaction yield (99.5%) was due to polyethylene glycol diacrylate 1000 (PEGDA-1000). Then, kaolin-containing poly(potassium acrylate-acrylic acid) superabsorbent composites and kaolin-free counterparts were synthesized using PEGDA-1000.The effect of the crosslinker concentration on swelling, rheological and thermo-mechanical properties was investigated...

Enzymatic digestibility of peptides cross-linked by ionizing radiation

International Nuclear Information System (INIS)

Dizdaroglu, M.; Gajewski, E.; Simic, M.G.

1984-01-01

Digestibility by proteolytic enzymes of peptides cross-linked by ionizing radiation was investigated. Small peptides of alanine and phenylalanine were chosen as model compounds and aminopeptidases and carboxypeptidases were used as proteolytic enzymes. Peptides exposed to γ-radiation in aqueous solution were analysed by high-performance liquid chromatography before and after hydrolysis by aminopeptidase M, leucine aminopeptidase carboxypeptidase A and carboxypeptidase Y. The results obtained clearly demonstrate the different actions of these enzymes on cross-linked aliphatic and aromatic peptides. Peptide bonds of cross-linked dipeptides of alanine were completely resistant to enzymatic hydrolysis whereas the enzymes, except for carboxypeptidase Y, cleaved all peptide bonds of cross-linked peptides of phenylalanine. The actions of the enzymes on these particular compounds are discussed in detail. (author)

Mechano-responsive hydrogels crosslinked by reactive block copolymer micelles

Science.gov (United States)

Xiao, Longxi

Hydrogels are crosslinked polymeric networks that can swell in water without dissolution. Owing to their structural similarity to the native extracelluar matrices, hydrogels have been widely used in biomedical applications. Synthetic hydrogels have been designed to respond to various stimuli, but mechanical signals have not incorporated into hydrogel matrices. Because most tissues in the body are subjected to various types of mechanical forces, and cells within these tissues have sophisticated mechano-transduction machinery, this thesis is focused on developing hydrogel materials with built-in mechano-sensing mechanisms for use as tissue engineering scaffolds or drug release devices. Self-assembled block copolymer micelles (BCMs) with reactive handles were employed as the nanoscopic crosslinkers for the construction of covalently crosslinked networks. BCMs were assembled from amphiphilic diblock copolymers of poly(n-butyl acrylate) and poly(acrylic acid) partially modified with acrylate. Radical polymerization of acrylamide in the presence of micellar crosslinkers gave rise to elastomeric hydrogels whose mechanical properties can be tuned by varying the BCM composition and concentration. TEM imaging revealed that the covalently integrated BCMs underwent strain-dependent reversible deformation. A model hydrophobic drug, pyrene, loaded into the core of BCMs prior to the hydrogel formation, was dynamically released in response to externally applied mechanical forces, through force-induced reversible micelle deformation and the penetration of water molecules into the micelle core. The mechano-responsive hydrogel has been studied for tissue repair and regeneration purposes. Glycidyl methacrylate (GMA)-modified hyaluronic acid (HA) was photochemically crosslinked in the presence of dexamethasone (DEX)-loaded crosslinkable BCMs. The resultant HA gels (HAxBCM) contain covalently integrated micellar compartments with DEX being sequestered in the hydrophobic core. Compared

General protein-protein cross-linking.

Science.gov (United States)

Alegria-Schaffer, Alice

2014-01-01

This protocol describes a general protein-to-protein cross-linking procedure using the water-soluble amine-reactive homobifunctional BS(3) (bis[sulfosuccinimidyl] suberate); however, the protocol can be easily adapted using other cross-linkers of similar properties. BS(3) is composed of two sulfo-NHS ester groups and an 11.4 Å linker. Sulfo-NHS ester groups react with primary amines in slightly alkaline conditions (pH 7.2-8.5) and yield stable amide bonds. The reaction releases N-hydroxysuccinimide (see an application of NHS esters on Labeling a protein with fluorophores using NHS ester derivitization). © 2014 Elsevier Inc. All rights reserved.

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.

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

African Journals Online (AJOL)

STORAGESEVER

2009-10-19

Oct 19, 2009 ... The cross-linking of casein was demonstrated by capillary zone electrophoresis analysis. .... linking reaction was started by addition of 1.0 ml 3% (w/v) H2O2 and .... by Design Expert Software (Version 7.0), keeping one variable at its ... The emulsion was immediately transferred into a 250 ml capa-.

The effect of plasticiser on the properties of radiation crosslinked poly(vinyl chloride)

International Nuclear Information System (INIS)

Jamaliah Shariff; Roslin Abu Bakar

1996-01-01

A study on the effects of plasticizers in the crosslinking of poly(vinyl chloride), PVC, by an electron beam irradiation was carried out. Different types of plasticizers were used and these, with other additives, were blended with PVC in a Brabender mixer. The blended compound was the irradiated with high energy electron beam. Subsequent analysis of its properties showed that the efficiency of crosslinking was better in the presence of the adipate and trimellitate. The tensile and elongation properties were acceptable. The ageing properties of the compounds with adipate and trimellitate-type plasticizers showed encouraging results

Modification of liposomes with proteins by dansyl-labeled heterobifunctional crosslinker.

Science.gov (United States)

Chen, Tao; Wang, Rutao; Lu, Tingting; Liang, Guozheng; Lu, Tingli

2011-07-01

The introduction of a fluorescent chromaphore into bifunctional crosslinkers results in a molecule with normal crosslinker properties and a fluorescent group for straightforward quantification. This work describes the synthesis of the dansyl-labeled heterobifunctional crosslinker N-succinimidyl ε-N-dansyl α-N-(acetylthio)acetyllysine (dansyl-ATA-lysine-NHS) containing reactive N-hydroxysuccinimidyl (NHS) ester and sulfhydryl groups. The application of this crosslinker to conjugation of bovine serum albumin (BSA) protein to the surface of a liposome containing maleimide functions is also demonstrated. BSA was modified with the dansyl-labeled crosslinker and subsequently conjugated to liposomes containing reactive phospholipid derivative N-[4-(p-maleimidophenyl)butyryl]phosphatidylethanolamine and the degree of modification and conjugation were quantitatively determined by measuring the fluorescence emission of the dansyl group. The reliability of the fluorescence quantification was confirmed by a micro bio-barcode assay protein assay.

Photoreactivities and thermal properties of psoralen cross-links

International Nuclear Information System (INIS)

Yeung, A.T.; Jones, B.K.; Chu, C.T.

1988-01-01

The authors have studied the photoreaction of 8-methoxypsoralen (8-MOP), 4,5',8-trimethylpsoralen (TMP), and 4'-(hydroxymethyl)-4,5',8-trimethylpsoralen (HMT) with a pair of 18-base-long oligonucleotides in which a 14-base region is complementary. Only one 5'TpA site, favored for both monoadduct and cross-link formation with psoralen, is present in this oligonucleotide pair. They have used this model system to demonstrate, for the first time, strand specificity in the photoreaction of psoralen with DNA. They found that the two types of cross-links which form at this site have large differences in thermal stabilities. In addition, the denaturation of each cross-links isomer duplex occurred in at least three stages, which can be visualized as three bands in thermal equilibrium under the conditions of a denaturing polyacrylamide gel. This novel observation suggests that there are several domains differing in thermal stability in a psoralen cross-link

Effect of crosslink torsional stiffness on elastic behavior of semiflexible polymer networks

Science.gov (United States)

Hatami-Marbini, H.

2018-02-01

Networks of semiflexible filaments are building blocks of different biological and structural materials such as cytoskeleton and extracellular matrix. The mechanical response of these systems when subjected to an applied strain at zero temperature is often investigated numerically using networks composed of filaments, which are either rigidly welded or pinned together at their crosslinks. In the latter, filaments during deformation are free to rotate about their crosslinks while the relative angles between filaments remain constant in the former. The behavior of crosslinks in actual semiflexible networks is different than these idealized models and there exists only partial constraint on torques at crosslinks. The present work develops a numerical model in which two intersecting filaments are connected to each other by torsional springs with arbitrary stiffness. We show that fiber networks composed of rigid and freely rotating crosslinks are the limiting case of the present model. Furthermore, we characterize the effects of stiffness of crosslinks on effective Young's modulus of semiflexible networks as a function of filament flexibility and crosslink density. The effective Young's modulus is determined as a function of the mechanical properties of crosslinks and is found to vanish for networks composed of very weak torsional springs. Independent of the stiffness of crosslinks, it is found that the effective Young's modulus is a function of fiber flexibility and crosslink density. In low density networks, filaments primarily bend and the effective Young's modulus is much lower than the affine estimate. With increasing filament bending stiffness and/or crosslink density, the mechanical behavior of the networks becomes more affine and the stretching of filaments depicts itself as the dominant mode of deformation. The torsional stiffness of the crosslinks significantly affects the effective Young's modulus of the semiflexible random fiber networks.

The Effect of Double Crosslinker on Precipitation Polymerization of Poly(acrylic acid

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Hajar Es-haghi

2014-06-01

Full Text Available Cross-linked poly(acrylic acids were prepared by dual cross-linkers via precipitation polymerization method in a binary organic solvent. Polyethylene glycol diacrylate (PEGDA-400 as a long-chain cross-linker and di(trimethylol propane tetraacrylate (DTMPTA as multifunctional cross-linker were used. PEGDA-400 was utilized to increase thickening properties and DTMPTA was used to improve the gel strength. The dual cross-linkers effect on the sample features (i.e., equilibrium swelling, thickening properties and rheological properties was investigated. Maximum amount of swelling was obtained by a high percentage of long-chain cross-linker. The apparent viscosity of the microgels was measured to determine their thickening properties for aqueous media. Maximum viscosity occurred at DT25-PE75 which was dependent on the type of cross-linkers in the polymer structure. The Flory-Rehner equation (from swelling ratio data and rubber elasticity theory (from rheometry data were used to discuss the network structure of the polymer. Increasing density of the network was shown by a sample containing high percentage of a four-functional cross-linker. The rheological properties of the cross-linked polymers were measured to determine storage modulus (strength network. The rheological behaviors demonstrated that the synthesized polymer containing a high amount of four-functional cross-linker had higher storage modulus (G′ than other samples. In addition the consistency coefficient (m and flow behavior index (n parameters of Ostwald equation were investigated as well. As a result, n values in each sample were found to be smaller than 1 and these results were fitted clearly with the pseudoplastic model. Apparent and rotational viscosities were used to determine the optimal cross-linker type (synthesized sample contained a high percentage of long-chain cross-linker.

Quantification of radiation induced crosslinking in a commercial, toughened silicone rubber, TR-55, by 1H MQ-NMR

Energy Technology Data Exchange (ETDEWEB)

Maxwell, R; Chinn, S; Alviso, C; Harvey, C A; Giuliani, J; Wilson, T; Cohenour, R

2008-11-10

Radiation induced degradation in a commercial, filled silicone composite has been studied by SPME/GC-MS, DMA, DSC, swelling, and Multiple Quantum NMR. Analysis of volatile and semivolatile species indicates degradation via decomposition of the peroxide curing catalyst and radiation induced backbiting reactions. DMA, swelling, and spin-echo NMR analysis indicate a increase in crosslink density of near 100% upon exposure to a cumulative dose of 250 kGray. Analysis of the sol-fraction via Charlseby-Pinner analysis indicates a ratio of chain scission to crosslinking yields of 0.38, consistent with the dominance of the crosslinking observed by DMA, swelling and spin-echo NMR and the chain scissioning reactions observed by MS analysis. Multiple Quantum NMR has revealed a bimodal distribution of residual dipolar couplings near 1 krad/sec and 5 krad/sec in an approximately 90:10 ratio, consistent with bulk network chains and chains associated with the filler surface. Upon exposure to radiation, the mean {Omega}{sub d} for both domains and the width of both domains both increased. The MQ NMR analysis provided increase insight into the effects of ionizing radiation on the network structure of silicone polymers.

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

Melt-processable, radiation cross-linkable E--CTFE copolymer compositions

International Nuclear Information System (INIS)

Robertson, A.B.; Schaffhauser, R.J.

1976-01-01

Melt-processable, radiation cross-linkable ethylene/chlorotrifluoroethylene copolymer compositions are provided which contain about 0.1 to 5 percent by weight of the copolymer of a radiation cross-linking promoter, about 0.01 to 5 percent by weight of an anti-oxidant and about 0.1 to 30 precent by weight of an acid scavenger. Such compositions do not give off odors when irradiated to cross-link the copolymer and do not develop bubbles after irradiation. 15 claims, no drawings

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

NARCIS (Netherlands)

Damink, LHHO; Dijkstra, PJ; vanLuyn, MJA; vanWachem, PB; Nieuwenhuis, P; Feijen, J

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

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

NARCIS (Netherlands)

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

1996-01-01

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

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.

Sequence-Dependent Diastereospecific and Diastereodivergent Crosslinking of DNA by Decarbamoylmitomycin C.

Science.gov (United States)

Aguilar, William; Paz, Manuel M; Vargas, Anayatzinc; Clement, Cristina C; Cheng, Shu-Yuan; Champeil, Elise

2018-04-20

Mitomycin C (MC), a potent antitumor drug, and decarbamoylmitomycin C (DMC), a derivative lacking the carbamoyl group, form highly cytotoxic DNA interstrand crosslinks. The major interstrand crosslink formed by DMC is the C1'' epimer of the major crosslink formed by MC. The molecular basis for the stereochemical configuration exhibited by DMC was investigated using biomimetic synthesis. The formation of DNA-DNA crosslinks by DMC is diastereospecific and diastereodivergent: Only the 1''S-diastereomer of the initially formed monoadduct can form crosslinks at GpC sequences, and only the 1''R-diastereomer of the monoadduct can form crosslinks at CpG sequences. We also show that CpG and GpC sequences react with divergent diastereoselectivity in the first alkylation step: 1"S stereochemistry is favored at GpC sequences and 1''R stereochemistry is favored at CpG sequences. Therefore, the first alkylation step results, at each sequence, in the selective formation of the diastereomer able to generate an interstrand DNA-DNA crosslink after the "second arm" alkylation. Examination of the known DNA adduct pattern obtained after treatment of cancer cell cultures with DMC indicates that the GpC sequence is the major target for the formation of DNA-DNA crosslinks in vivo by this drug. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Synthesis and Crosslinking of Polyether-Based Main Chain Benzoxazine Polymers and Their Gas Separation Performance

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Muntazim Munir Khan

2018-02-01

Full Text Available The poly(ethylene glycol-based benzoxazine polymers were synthesized via a polycondensation reaction between Bisphenol-A, paraformaldehyde, and poly(ether diamine/(Jeffamine®. The structures of the polymers were confirmed by proton nuclear magnetic resonance spectroscopy (1H-NMR, indicating the presence of a cyclic benzoxazine ring. The polymer solutions were casted on the glass plate and cross-linked via thermal treatment to produce tough and flexible films without using any external additives. Thermal properties and the crosslinking behaviour of these polymers were studied by thermogravimetric analysis (TGA and differential scanning calorimetry (DSC. Single gas (H2, O2, N2, CO2, and CH4 transport properties of the crosslinked polymeric membranes were measured by the time-lag method. The crosslinked PEG-based polybenzoxazine membranes show improved selectivities for CO2/N2 and CO2/CH4 gas pairs. The good separation selectivities of these PEG-based polybenzoxazine materials suggest their utility as efficient thin film composite membranes for gas and liquid membrane separation technology.

Study of induced cross-linking by ionizing radiation of polyvinylpyrrolidone (PVP)/carboxymethylcellulose (CMC)

International Nuclear Information System (INIS)

Alcantara, Mara T.S.; Chirinos, Hugo; Amaral, Renata H.; Rogero, Sizue O.; Lugao, Ademar B.

2005-01-01

The polymeric hydrogels are materials with capacity to absorb great amount of water. They present interesting characteristics for many applications in the industry and as biomaterials. The hydrogel membrane with PVP, poly ethylene glycol and agar, crosslinked and sterilized simultaneously by radiation was introduced in the European market and now it is reaching other regions. In this work the hydrogel studied was synthesized with PVP and CMC and crosslinked by gamma radiation. It was applied factorial planning methodology using the gel fraction as basic parameter. Antagonistic interaction was observed between PVP and CMC. High concentrations of PVP help the crosslinking and the opposite with CMC. On the other hand, for low concentrations of PVP the dose influences considerable the gel fraction what it does not happen for high concentrations. From these results it was made an analysis of response surface allowing the optimization of the concentrations of the variables PVP and CMC. (author)

Crosslinked pullulan/cellulose acetate fibrous scaffolds for bone tissue engineering

Energy Technology Data Exchange (ETDEWEB)

Atila, Deniz [Department of Engineering Sciences, Middle East Technical University (Turkey); Keskin, Dilek [Department of Engineering Sciences, Middle East Technical University (Turkey); Biomaterials and Tissue Engineering Center of Excellence, Middle East Technical University (Turkey); Tezcaner, Ayşen, E-mail: tezcaner@metu.edu.tr [Department of Engineering Sciences, Middle East Technical University (Turkey); Biomaterials and Tissue Engineering Center of Excellence, Middle East Technical University (Turkey)

2016-12-01

Natural polymer based fibrous scaffolds have been explored for bone tissue engineering applications; however, their inadequate 3-dimensionality and poor mechanical properties are among the concerns for their use as bone substitutes. In this study, pullulan (P) and cellulose acetate (CA), two polysaccharides, were electrospun at various P/CA ratios (P{sub 80}/CA{sub 20}, P{sub 50}/CA{sub 50}, and P{sub 20}/CA{sub 80}%) to develop 3D fibrous network. The scaffolds were then crosslinked with trisodium trimetaphosphate (STMP) to improve the mechanical properties and to delay fast weight loss. The lowest weight loss was observed for the groups that were crosslinked with P/STMP 2/1 for 10 min. Fiber morphologies of P{sub 50}/CA{sub 50} were more uniform without phase separation and this group was crosslinked most efficiently among groups. It was found that mechanical properties of P{sub 20}/CA{sub 80} and P{sub 50}/CA{sub 50} were higher than that of P{sub 80}/CA{sub 20.} After crosslinking strain values of P{sub 50}/CA{sub 50} scaffolds were improved and these scaffolds became more stable. Unlike P{sub 80}/CA{sub 20,} uncrosslinked P{sub 50}/CA{sub 50} and P{sub 20}/CA{sub 80} were not lost in PBS. Among all groups, crosslinked P{sub 50}/CA{sub 50} scaffolds had more uniform pores; therefore this group was used for bioactivity and cell culture studies. Apatite-like structures were observed on fibers after SBF incubation. Human Osteogenic Sarcoma Cell Line (Saos-2) seeded onto crosslinked P{sub 50}/CA{sub 50} scaffolds adhered and proliferated. The functionality of cells was tested by measuring ALP activity of the cells and the results indicated their osteoblastic differentiation. In vitro tests showed that scaffolds were cytocompatible. To sum up, crosslinked P{sub 50}/CA{sub 50} scaffolds were proposed as candidate cell carriers for bone tissue engineering applications. - Highlights: • Crosslinked 3D electrospun P/CA scaffolds were prepared for the first time. • CA

UV cross-linking of polypeptides associated with 3'-terminal exons

International Nuclear Information System (INIS)

Stolow, D.T.; Berget, S.M.

1990-01-01

Association of nuclear proteins with chimeric vertebrate precursor RNAs containing both polyadenylation signals and an intron was examined by UV cross-linking. One major difference in cross-linking pattern was observed between this chimeric precursor RNA and precursors containing only polyadenylation or splicing signals. The heterogeneous nuclear ribonucleoprotein (hnRNP) polypeptide C cross-linked strongly to sequences downstream of the A addition site in polyadenylation precursor RNA containing only the polyadenylation signal from the simian virus 40 (SV40) late transcription unit. In contrast, the hnRNP C polypeptide cross-linked to chimeric RNA containing the same SV40 late poly(A) cassette very poorly, at a level less than 5% of that observed with the precursor RNA containing just the poly(A) site. Observation that cross-linking of the hnRNP C polypeptide to elements within the SV40 late poly(A) site was altered by the presence of an upstream intron suggests differences in the way nuclear factors associate with poly(A) sites in the presence and absence of an upstream intron. Cross-linking of C polypeptide to chimeric RNA increased with RNAs mutated for splicing or polyadenylation consensus sequences and under reaction conditions (high magnesium) that inhibited polyadenylation. Furthermore, cross-linking of hnRNP C polypeptide to precursors containing just the SV40 late poly(A) site was eliminated in the presence of competing poly(U); polyadenylation, however, was unaffected. Correlation of loss of activity with high levels of hnRNP C polypeptide cross-linking raises questions about the specificity of the interaction between the hnRNP C polypeptide and polyadenylation precursor RNAs in vitro

Redundancy and cooperativity in the mechanics of compositely crosslinked filamentous networks.

Directory of Open Access Journals (Sweden)

Moumita Das

Full Text Available The cytoskeleton of living cells contains many types of crosslinkers. Some crosslinkers allow energy-free rotations between filaments and others do not. The mechanical interplay between these different crosslinkers is an open issue in cytoskeletal mechanics. Therefore, we develop a theoretical framework based on rigidity percolation to study a generic filamentous system containing both stretching and bond-bending forces to address this issue. The framework involves both analytical calculations via effective medium theory and numerical simulations on a percolating triangular lattice with very good agreement between both. We find that the introduction of angle-constraining crosslinkers to a semiflexible filamentous network with freely rotating crosslinks can cooperatively lower the onset of rigidity to the connectivity percolation threshold-a result argued for years but never before obtained via effective medium theory. This allows the system to ultimately attain rigidity at the lowest concentration of material possible. We further demonstrate that introducing angle-constraining crosslinks results in mechanical behaviour similar to just freely rotating crosslinked semflexible filaments, indicating redundancy and universality. Our results also impact upon collagen and fibrin networks in biological and bio-engineered tissues.

Effect of carbon nanotube dispersion on glass transition in cross-linked epoxy-carbon nanotube nanocomposites: role of interfacial interactions.

Science.gov (United States)

Khare, Ketan S; Khare, Rajesh

2013-06-20

We have used atomistic molecular simulations to study the effect of nanofiller dispersion on the glass transition behavior of cross-linked epoxy-carbon nanotube (CNT) nanocomposites. Specific chemical interactions at the interface of CNTs and cross-linked epoxy create an interphase region, whose impact on the properties of their nanocomposites increases with an increasing extent of dispersion. To investigate this aspect, we have compared the volumetric, structural, and dynamical properties of three systems: neat cross-linked epoxy, cross-linked epoxy nanocomposite containing dispersed CNTs, and cross-linked epoxy nanocomposite containing aggregated CNTs. We find that the nanocomposite containing dispersed CNTs shows a depression in the glass transition temperature (Tg) by ~66 K as compared to the neat cross-linked epoxy, whereas such a large depression is absent in the nanocomposite containing aggregated CNTs. Our results suggest that the poor interfacial interactions between the CNTs and the cross-linked epoxy matrix lead to a more compressible interphase region between the CNTs and the bulk matrix. An analysis of the resulting dynamic heterogeneity shows that the probability of percolation of immobile domains becomes unity near the Tg calculated from volumetric properties. Our observations also lend support to the conceptual analogy between polymer nanocomposites and the nanoconfinement of polymer thin films.

Intelligent hydrophilic nanoparticles fabricated via alkaline hydrolysis of crosslinked polyacrylonitrile nanoparticles

International Nuclear Information System (INIS)

Zhang, Y.; Wu, Q.; Zhang, H.; Zhao, J.

2013-01-01

Crosslinked polyacrylonitrile (PAN) nanolatex, with an average hydrodynamic diameter of 84 nm and a polydispersity index of 0.06, was successfully synthesized at a high monomer concentration and low surfactant content via a modified emulsion polymerization. Three measurements were adopted to control the nucleation and growth processes. Taking advantage of the chemical activity of nitrile groups, intelligent hydrophilic polymeric nanoparticles were fabricated via simple alkaline hydrolysis treatment of the crosslinked PAN nanolatex. Dynamic light scattering, electrophoretic light scattering, FT-IR spectroscopy, elemental analysis, and TEM observations were used to monitor the changes in the composition, structure, and morphology of the nanoparticles during the hydrolysis process. The sizes, chemical composition, morphology, and pH-responsive behavior of the intelligent hydrophilic nanoparticles could be adjusted by simply changing the hydrolysis time. As the hydrolysis was prolonged, the following nanoparticles could be obtained, crosslinked PAN nanoparticles with hydrophilic surfaces, amphiphilic nanoparticles with a hydrophobic PAN core and a hydrophilic polymeric shell composed of acrylamide and acrylic acid units, or carboxylic polyacrylamide nanoparticles. These modified nanoparticles all display good hydrophilicity, good biocompatibility, pH-sensitivity, as well as carboxyl functional groups, and thus are ideal candidates for various biomedical applications

Intelligent hydrophilic nanoparticles fabricated via alkaline hydrolysis of crosslinked polyacrylonitrile nanoparticles

Energy Technology Data Exchange (ETDEWEB)

Zhang, Y., E-mail: zhyw@dhu.edu.cn; Wu, Q.; Zhang, H.; Zhao, J. [Donghua University, State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, College of Material Science and Engineering, Chemical Fibers Research Institute (China)

2013-07-15

Crosslinked polyacrylonitrile (PAN) nanolatex, with an average hydrodynamic diameter of 84 nm and a polydispersity index of 0.06, was successfully synthesized at a high monomer concentration and low surfactant content via a modified emulsion polymerization. Three measurements were adopted to control the nucleation and growth processes. Taking advantage of the chemical activity of nitrile groups, intelligent hydrophilic polymeric nanoparticles were fabricated via simple alkaline hydrolysis treatment of the crosslinked PAN nanolatex. Dynamic light scattering, electrophoretic light scattering, FT-IR spectroscopy, elemental analysis, and TEM observations were used to monitor the changes in the composition, structure, and morphology of the nanoparticles during the hydrolysis process. The sizes, chemical composition, morphology, and pH-responsive behavior of the intelligent hydrophilic nanoparticles could be adjusted by simply changing the hydrolysis time. As the hydrolysis was prolonged, the following nanoparticles could be obtained, crosslinked PAN nanoparticles with hydrophilic surfaces, amphiphilic nanoparticles with a hydrophobic PAN core and a hydrophilic polymeric shell composed of acrylamide and acrylic acid units, or carboxylic polyacrylamide nanoparticles. These modified nanoparticles all display good hydrophilicity, good biocompatibility, pH-sensitivity, as well as carboxyl functional groups, and thus are ideal candidates for various biomedical applications.

Screening for sequence-specific RNA-BPs by comprehensive UV crosslinking

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Le Meuth-Metzinger Valerie

2002-06-01

Full Text Available Abstract Background Specific cis-elements and the associated trans-acting factors have been implicated in the post-transcriptional regulation of gene expression. In the era of genome wide analyses identifying novel trans-acting factors and cis-regulatory elements is a step towards understanding coordinated gene expression. UV-crosslink analysis is a standard method used to identify RNA-binding proteins. Uridine is traditionally used to radiolabel substrate RNAs, however, proteins binding to cis-elments particularly uridine poor will be weakly or not detected. We evaluate here the possibility of using UV-crosslinking with RNA substrates radiolabeled with each of the four ribonucleotides as an approach for screening for novel sequence specific RNA-binding proteins. Results The radiolabeled RNA substrates were derived from the 3'UTRs of the cloned Eg and c-mos Xenopus laevis maternal mRNAs. Specific, but not identical, uv-crosslinking signals were obtained, some of which corresponded to already identified proteins. A signal for a novel 90 kDa protein was observed with the c-mos 3'UTR radiolabeled with both CTP and GTP but not with UTP. The binding site of the 90 kDa RNA-binding protein was localised to a 59-nucleotide portion of the c-mos 3'UTR. Conclusion That the 90 kDa signal was detected with RNAs radiolabeled with CTP or GTP but not UTP illustrates the advantage of radiolabeling all four nucleotides in a UV-crosslink based screen. This method can be used for both long and short RNAs and does not require knowledge of the cis-acting sequence. It should be amenable to high throughput screening for RNA binding proteins.

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

NARCIS (Netherlands)

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

2010-01-01

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

Physical Characterization Of High Amylose/Pectin Mixtures Cross-Linked With Sodium Trimetaphosphate

International Nuclear Information System (INIS)

Carbinatto, F.M.; Cury, B.S.F.; Evangelista, R.C.

2010-01-01

Some researches have reported that pectin and high amylose mixtures presented superior mechanical properties in relation to those of the isolated polymers. In this work, mixtures at different ratios (1:4; 1:1) of pectin and high amylose were crosslinked with sodium trimetaphosphate at different degrees by varying reaction conditions. All samples were characterized by rheological and X-ray diffraction analyses. Samples without cross-linker were prepared as control. The oscillatory dynamic tests showed that all samples exhibited predominant elastic behavior, although cross-linked samples presented higher G' values, suggesting that crosslinking by phosphorylation resulted in more strength structures. The diffractograms showed that cross-linked samples underwent structural modifications that resulted in increase of crystallinity due to cross-linking process. (author)

Interstrand DNA crosslinking by 4,5',8-trimethylpsoralen plus monochromatic ultraviolet light

International Nuclear Information System (INIS)

Cohen, L.F.; Ewig, R.A.G.; Kohn, K.W.; Glaubiger, D.

1980-01-01

DNA crosslinking by 4,5',8-trimethylpsoralen plus monochromatic ultraviolet light of wavelength 365 nm was studied in mouse L1210 leukemia cells. DNA breaks and crosslinking were evaluated by alkaline elution of DNA from poly(vinyl chloride) filters. Trimethylpsoralen plus 365 nm light produced DNA crosslinks but not breaks. The kinetics of crosslinging were linear with respect to concentration and second-order with respect to light exposure time. The latter finding supports the proposed two photon mechanism for the formation of diadducts. In contrast to DNA crosslinking agents such as nitrogen mustard, nitrosoureas and platinums, trimethylpsoralen crosslinks were resistant to proteolytic digestion. Thus, trimethylpsoralen plus 365 nm light produced interstrand crosslinks, as proposed for a bifunctional agent binding to bases on opposite DNA strands. (Auth.)

Long-Chain Diacrylate Crosslinkers and Use of PEG Crosslinks in Poly(potassium acrylate-acrylic acid/Kaolin Composite Superabsorbents

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Koroush Kabiri

2013-01-01

Full Text Available Long-chain diacrylate crosslinkers based on linear α,ω-diols were synthesized and characterized using FTIR and 1H NMR spectroscopy. The highest reaction yield (99.5% was due to polyethylene glycol diacrylate 1000 (PEGDA-1000. Then, kaolin-containing poly(potassium acrylate-acrylic acid superabsorbent composites and kaolin-free counterparts were synthesized using PEGDA-1000.The effect of the crosslinker concentration on swelling, rheological and thermo-mechanical properties was investigated. Absorption capacity of the composite hydrogels (having ~38% kaolin was unexpectedly higher than that of kaolin-free hydrogels. This was attributed to an interfering effect of kaolin during the polymerization. Glass transition temperature was increased with crosslinker concentration enhancement and addition of kaolin up to about 10oC and 28oC, respectively. Making such K-containing superabsorbents may be taken as an effective action to achieve more durable and cheaper superabsorbents for agricultural uses.

Effective modification of cell death-inducing intracellular peptides by means of a photo-cleavable peptide array-based screening system.

Science.gov (United States)

Kozaki, Ikko; Shimizu, Kazunori; Honda, Hiroyuki

2017-08-01

Intracellular functional peptides that play a significant role inside cells have been receiving a lot of attention as regulators of cellular activity. Previously, we proposed a novel screening system for intracellular functional peptides; it combined a photo-cleavable peptide array system with cell-penetrating peptides (CPPs). Various peptides can be delivered into cells and intracellular functions of the peptides can be assayed by means of our system. The aim of the present study was to demonstrate that the proposed screening system can be used for assessing the intracellular activity of peptides. The cell death-inducing peptide (LNLISKLF) identified in a mitochondria-targeting domain (MTD) of the Noxa protein served as an original peptide sequence for screening of peptides with higher activity via modification of the peptide sequence. We obtained 4 peptides with higher activity, in which we substituted serine (S) at the fifth position with phenylalanine (F), valine (V), tryptophan (W), or tyrosine (Y). During analysis of the mechanism of action, the modified peptides induced an increase in intracellular calcium concentration, which was caused by the treatment with the original peptide. Higher capacity for cell death induction by the modified peptides may be caused by increased hydrophobicity or an increased number of aromatic residues. Thus, the present work suggests that the intracellular activity of peptides can be assessed using the proposed screening system. It could be used for identifying intracellular functional peptides with higher activity through comprehensive screening. Copyright © 2017 The Society for Biotechnology, Japan. Published by Elsevier B.V. All rights reserved.

Sorption characteristics of technetium on crosslinked chitosan from aqueous solution

International Nuclear Information System (INIS)

Pivarciova, L.; Rosskopfova, O.; Galambos, M.; Rajec, P.

2014-01-01

Sorption of technetium on crosslinked chitosan was studied using batch techniques in static arrangement of experiment under aerobic conditions at laboratory temperature. The adsorption of technetium was rapid and the percentage of the technetium sorption was > 98 %. In the pH range of 3-11 adsorption of technetium on crosslinked chitosan was > 98 %. The competition effect of Fe 3+ towards TcO 4 - sorption on crosslinked chitosan was stronger than the competition effect of other observed cations. The selectivity of crosslinked chitosan for these cations in solution with the concentration above 1·10 -3 mol·dm -3 was in the order Fe 3+ > Ca 2+ > Na + > Fe 2+ . The competition effect of (ClO 4 ) - towards TcO 4 - sorption was stronger than the competition effect of (SO 4 ) 2 - ions. From these results it can be expected that crosslinked chitosan could be a suitable sorbent for the immobilization of technetium in the liquid radioactive waste. (authors)

Comparison of Swelling and Mechanical Analysis for the Determination of Crosslink Density of Acrylamide Based Hydrogels Prepared by Ionizing Radiation

International Nuclear Information System (INIS)

Sen, M.

2006-01-01

One of the basic parameters that describes the structure of a hydrogel network is the molecular weight between cross-links or cross-link density of highly swollen network. Several theories have been proposed to calculate the average molecular weight between cross-links. In the highly swollen state, the constrained junction theory indicates that a real network exhibits properties closer to those of the phantom network model and molecular weight between cross-links can be calculated easily by using swelling and polymer-solvent based parameters such as molar volume of the swelling agent, polymer-solvent interaction parameter, functionality, specific volume of the polymer and polymer volume fraction in the relaxed state. Molecular weight between cross-links (M c a ver.) and effective cross-linking density (V e ) of a hydrogel can also be determined from shear modulus data obtained from compression tests. Our previous studies indicated that simple compression analyses and equations derived from Phantom network theory can be used for the determination of effective cross-link density of hydrogels without needing some polymer-solvent based parameters as in the case of swelling based determinations. The M c a ver. and V e values calculated from mechanical tests were found to be very close to the values obtained from swelling experiments. Slight differences observed were attributed to the uncertainty on the value of the χ parameter used in the expression related to swelling data. In this study the uncertainty in the polymer based parameter χ on the M c a ver. was discussed. Poly(acrylamide/methacrylamide) P(AAm/MAAm) and Poly(acrylamide/hydroxyethylmeth acrylate) P(AAm/HEMA) hydrogels were prepared by gamma rays and used as model hydrogel systems. The uniaxial compression was applied to cylindrical samples using the Universal Testing Instrument in the swollen form at pH 7. Stress-strain curves of hydrogels were evaluated to calculate the shear modulus values. The M c a ver

Fabrication of chemically cross-linked porous gelatin matrices.

Science.gov (United States)

Bozzini, Sabrina; Petrini, Paola; Altomare, Lina; Tanzi, Maria Cristina

2009-01-01

The aim of this study was to chemically cross-link gelatin, by reacting its free amino groups with an aliphatic diisocyanate. To produce hydrogels with controllable properties, the number of reacting amino groups was carefully determined. Porosity was introduced into the gelatin-based hydrogels through the lyophilization process. Porous and non-porous matrices were characterized with respect to their chemical structure, morphology, water uptake and mechanical properties. The physical, chemical and mechanical properties of the porous matrices are related to the extent of their cross-linking, showing that they can be controlled by varying the reaction parameters. Water uptake values (24 hours) vary between 160% and 200% as the degree of cross-linking increases. The flexibility of the samples also decreases by changing the extent of cross-linking. Young's modulus shows values between 0.188 KPa, for the highest degree, and 0.142 KPa for the lowest degree. The matrices are potential candidates for use as tissue-engineering scaffolds by modulating their physical chemical properties according to the specific application.

Tunable photonic multilayer sensors from photo-crosslinkable polymers

Science.gov (United States)

Chiappelli, Maria; Hayward, Ryan

2014-03-01

The fabrication of tunable photonic multilayer sensors from stimuli-responsive, photo-crosslinkable polymers will be described. Benzophenone is covalently incorporated as a pendent photo-crosslinker, allowing for facile preparation of multilayer films by sequential spin-coating and crosslinking processes. Copolymer chemistries and layer thicknesses are selected to provide robust multilayer sensors which can show color changes across nearly the full visible spectrum due to the specific stimulus-responsive nature of the hydrated film stack. We will describe how this approach is extended to alternative sensor designs by tailoring the thickness and chemistry of each layer independently, allowing for the preparation of sensors which depend not only on the shift in wavelength of a reflectance peak, but also on the transition between Bragg mirrors and filters. Device design is optimized by photo-patterning sensor arrays on a single substrate, providing more efficient fabrication time as well as multi-functional sensors. Finally, radiation-sensitive multilayers, designed by choosing polymers which will preferentially degrade or crosslink under ionizing radiation, will also be described.

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.

Epoxy Crosslinked Silica Aerogels (X-Aerogels)

Science.gov (United States)

fabrizio, Eve; Ilhan, Faysal; Meador, Mary Ann; Johnston, Chris; Leventis, Nicholas

2004-01-01

NASA is interested in the development of strong lightweight materials for the dual role of thermal insulator and structural component for space vehicles; freeing more weight for useful payloads. Aerogels are very-low density materials (0.010 to 0.5 g/cc) that, due to high porosity (meso- and microporosity), can be, depending on the chemical nature of the network, ideal thermal insulators (thermal conductivity approx. 15 mW/mK). However, aerogels are extremely fragile. For practical application of aerogels, one must increase strength without compromising the physical properties attributed to low density. This has been achieved by templated growth of an epoxy polymer layer that crosslinks the "pearl necklace" network of nanoparticles: the framework of a typical silica aerogel. The requirement for conformal accumulation of the epoxy crosslinker is reaction both with the surface of silica and with itself. After cross-linking, the strength of a typical aerogel monolith increases by a factor of 200, in the expense of only a 2-fold increase in density. Strength is increased further by coupling residual unreacted epoxides with diamine.

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.

Effects of Thermal Cross-Linking on the Structure and Property of Asymmetric Membrane Prepared from the Polyacrylonitrile

Directory of Open Access Journals (Sweden)

Xin Jin

2018-05-01

Full Text Available Improving the thermal and chemical stabilities of classical polymer membranes will be beneficial to extend their applications in the high temperature or aggressive environment. In this work, the asymmetric ultrafiltration membranes prepared from the polyacrylonitrile (PAN were used to fabricate the cross-linking asymmetric (CLA PAN membranes via thermal cross-linking in air to improve their thermal and chemical stabilities. The effects of thermal cross-linking parameters such as temperature and holding time on the structure, gas separation performance, thermal and chemical stabilities of PAN membranes were investigated by Fourier transform infrared spectroscopy (FTIR, X-ray photoelectron spectroscopy (XPS, positron annihilation lifetime spectroscopy (PALS, scanning electron microscopy (SEM, thermogravimetic analysis (TGA and gas permeation test. The thermal cross-linking significantly influences the chemical structure, microstructure and pore structure of PAN membrane. During the thermal cross-linking, the shrinkage of membrane and coalescence or collapse of pore and microstructure make large pores diminish, small pores disappear and pore volumes reduce. The gas permeances of CLA-PAN membranes increase as the increasing of cross-linking temperature and holding time due to the volatilization of small molecules. The CLA-PAN membranes demonstrate excellent thermal and chemical stabilities and present good prospects for application in ultrafiltration for water treatment and for use as a substrate for nanofiltration or gas separation with an aggressive and demanding environment.

Crosslinked polymeric nanocapsules with controllable structure via a 'self-templating' approach

International Nuclear Information System (INIS)

Liu Peng; Liu Guangfeng; Zhang Wei; Jiang Fan

2010-01-01

We developed a novel strategy for the near-monodispersed crosslinked polymeric nanocapsules with controllable structure via the 'self-templating' approach by the following four steps: (i) preparation of the PVAc lattices by the emulsion polymerization of VAc; (ii) surface hydrolysis of the PVAc lattices; (iii) crosslinking the PVA segments on the surface of the surface-hydrolyzed PVAc lattices and (iv) removal of the PVAc core of the core-shell structures by being dissolved by methanol. The strategy developed was confirmed with Fourier-transform infrared, transmission electron microscopy and dynamic light scattering techniques. In the strategy developed, the particle size, the thickness and the crosslinking degree of the nanocapsules could be controlled with the lattice's size, relative molecular weight of PVAc and the crosslinking degree of the crosslinked shell.

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.

Evaluation of cross-linked gelatin membranes as delivery carriers for retinal sheets

Energy Technology Data Exchange (ETDEWEB)

Lai, Jui-Yang, E-mail: jylai@mail.cgu.edu.tw [Institute of Biochemical and Biomedical Engineering, Chang Gung University, Taoyuan, 33302 Taiwan (China); Biomedical Engineering Research Center, Chang Gung University, Taoyuan, 33302 Taiwan (China); Molecular Medicine Research Center, Chang Gung University, Taoyuan, 33302 Taiwan (China); Li, Ya-Ting [Institute of Biochemical and Biomedical Engineering, Chang Gung University, Taoyuan, 33302 Taiwan (China)

2010-06-15

The delivery of intact sheet transplants to the subretinal space can prevent cell loss that is generally associated with the injection of cell suspensions or cell aggregates. The aim of this study was to develop chemically modified gelatin matrices that enhance the delivery efficiency and analyze whether the gelatin membranes cross-linked with 1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide (EDC) can be considered as potential carriers for retinal sheets. The characteristics of EDC cross-linked gelatin membranes were determined by mechanical and in vitro degradation tests, melting point measurements, cell proliferation assays, cytokine expression analyses, and tissue delivery studies. Gelatin membranes without cross-linking and glutaraldehyde cross-linked gelatin samples were used for comparison. Results of this study indicated that introduction of cross-links is capable of rendering the gelatin network more stable against mechanical stresses and deformations as well as rapid hydrolysis during intraocular delivery of delicate tissue sheets. In comparison with the glutaraldehyde treated samples, the EDC cross-linked gelatin membranes showed a better degradation profile and a relatively higher cytocompatibility. In addition, after EDC cross-linking, the gelatin matrices having an acceptable melting point could be used for the fabrication of a sandwich-like carrier with a high transfer and encapsulation efficiency. These findings suggest that the cross-linking agent type gives an influence on delivery functionality of gelatin membranes. In summary, the EDC cross-linked gelatin is an ideal candidate for use as a carrier material in retinal sheet delivery applications.

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

Crosslinking of a Peritrophic Matrix Protein Protects Gut Epithelia from Bacterial Exotoxins

Science.gov (United States)

Shibata, Toshio; Maki, Kouki; Hadano, Jinki; Fujikawa, Takumi; Kitazaki, Kazuki; Koshiba, Takumi; Kawabata, Shun-ichiro

2015-01-01

Transglutaminase (TG) catalyzes protein-protein crosslinking, which has important and diverse roles in vertebrates and invertebrates. Here we demonstrate that Drosophila TG crosslinks drosocrystallin, a peritrophic matrix protein, to form a stable fiber structure on the gut peritrophic matrix. RNA interference (RNAi) of the TG gene was highly lethal in flies and induced apoptosis of gut epithelial cells after oral infection with Pseudomonas entomophila. Moreover, AprA, a metalloprotease secreted by P. entomophila, digested non-crosslinked drosocrystallin fibers, but not drosocrystallin fibers crosslinked by TG. In vitro experiments using recombinant drosocrystallin and monalysin proteins demonstrated that monalysin, a pore-forming exotoxin of P. entomophila, was adsorbed on the crosslinked drosocrystallin fibers in the presence of P. entomophila culture supernatant. In addition, gut-specific TG-RNAi flies had a shorter lifespan than control flies after ingesting P. entomophila, whereas the lifespan after ingesting AprA-knockout P. entomophila was at control levels. We conclude that drosocrystallin fibers crosslinked by TG, but not non-crosslinked drosocrystallin fibers, form an important physical barrier against exotoxins of invading pathogenic microbes. PMID:26506243

Crosslinking of a Peritrophic Matrix Protein Protects Gut Epithelia from Bacterial Exotoxins.

Directory of Open Access Journals (Sweden)

Toshio Shibata

2015-10-01

Full Text Available Transglutaminase (TG catalyzes protein-protein crosslinking, which has important and diverse roles in vertebrates and invertebrates. Here we demonstrate that Drosophila TG crosslinks drosocrystallin, a peritrophic matrix protein, to form a stable fiber structure on the gut peritrophic matrix. RNA interference (RNAi of the TG gene was highly lethal in flies and induced apoptosis of gut epithelial cells after oral infection with Pseudomonas entomophila. Moreover, AprA, a metalloprotease secreted by P. entomophila, digested non-crosslinked drosocrystallin fibers, but not drosocrystallin fibers crosslinked by TG. In vitro experiments using recombinant drosocrystallin and monalysin proteins demonstrated that monalysin, a pore-forming exotoxin of P. entomophila, was adsorbed on the crosslinked drosocrystallin fibers in the presence of P. entomophila culture supernatant. In addition, gut-specific TG-RNAi flies had a shorter lifespan than control flies after ingesting P. entomophila, whereas the lifespan after ingesting AprA-knockout P. entomophila was at control levels. We conclude that drosocrystallin fibers crosslinked by TG, but not non-crosslinked drosocrystallin fibers, form an important physical barrier against exotoxins of invading pathogenic microbes.

Synthesis and characterization of crosslinked gellan/PVA nanofibers for tissue engineering application.

Science.gov (United States)

Vashisth, Priya; Pruthi, Vikas

2016-10-01

Electrospun nanofibers based on gellan are considered as promising biomaterial for tissue engineering and wound healing applications. However, major hurdles in usage of these nanofibers are their poor stability and deprived structural consistency in aqueous medium which is a prerequisite for their application in the biomedical sector. In this investigation, three dimensional nanofibers, consisting of gellan and PVA have been fabricated and then stabilized under various crosslinking conditions in order to improve their physiochemical stability. The impacts of different crosslinking procedures on the gellan/PVA nanofibers were examined in terms of changes in morphological, mechanical, swelling and biological properties. Superior tensile strength and strain was recorded in case of crosslinked nanofibers as compared to non-crosslinked nanofibers. Contact angles and swelling properties of fabricated gellan/PVA nanofibers were found to vary with the crosslinking method. All crosslinking conditions were evaluated with regard to their response towards human dermal fibroblast (3T3L1) cells. Biocompatibility studies suggested that the fabricated crosslinked gellan/PVA nanofibers hold a great prospective in the biomedical engineering arena. Copyright © 2016 Elsevier B.V. All rights reserved.

Effect of the fluorinated groups on nematic liquid crystal alignment on monomer crosslinked film

International Nuclear Information System (INIS)

Yu Tao; Peng Zenghui; Ruan Shengping; Xuan Li

2004-01-01

It was found in this work that photosensitive monomers, bisphenol A dicinnamate ester and hexafluorobiphenol a dicinnamate ester were crosslinked under irradiation of linearly polarized ultraviolet light. The exposed films induced homogeneous and homeotropic alignment of liquid crystals (LC), respectively. We verified through experiments that it was fluorinated groups that caused the generation of LC homeotropic alignment on the crosslinked film. Photoreaction process was revealed by Fourier transform infrared spectra. There was no clear morphological anisotropy on these aligned films observed through atomic force microscope analysis. The surface energies were measured and homeotropic alignment reason was discussed in this work

Syntheses of crosslinked latex nanoparticles using differential microemulsion polymerization

Science.gov (United States)

Hassmoro, N. F.; Rusop, M.; Abdullah, S.

2013-06-01

The differential microemulsion polymerization was used to synthesize latex nanoparticles. In this paper, 1, 3-butylene glycol dimethacrylate (1, 3-BGDMA) was used as a crosslinker respectively 1-5 weight% of monomer total. Butyl acrylate (BA), butyl methacrylate (BMA), and methacrylic acid (MAA) was used as the monomer. The thin film of latex nanoparticles were prepared by using spin coating method and have been dried at 100°C for 5 minutes. The amount of the crosslinker added in the polymerization was optimized and we found that the particle sizes fall in the range of 30-60 nm. The structural morphology of the uncrosslinked latex represented the most homogeneous image compared to the crosslinked latex. The effect of the amount of crosslinker on the particle sizes investigated by the Zeta-sizer Nano series while Atomic Force microscopy (AFM) was used to study the structural properties of latex nanoparticles.

Syntheses of crosslinked latex nanoparticles using differential microemulsion polymerization

International Nuclear Information System (INIS)

Hassmoro, N F; Abdullah, S; Rusop, M

2013-01-01

The differential microemulsion polymerization was used to synthesize latex nanoparticles. In this paper, 1, 3-butylene glycol dimethacrylate (1, 3-BGDMA) was used as a crosslinker respectively 1–5 weight% of monomer total. Butyl acrylate (BA), butyl methacrylate (BMA), and methacrylic acid (MAA) was used as the monomer. The thin film of latex nanoparticles were prepared by using spin coating method and have been dried at 100°C for 5 minutes. The amount of the crosslinker added in the polymerization was optimized and we found that the particle sizes fall in the range of 30–60 nm. The structural morphology of the uncrosslinked latex represented the most homogeneous image compared to the crosslinked latex. The effect of the amount of crosslinker on the particle sizes investigated by the Zeta-sizer Nano series while Atomic Force microscopy (AFM) was used to study the structural properties of latex nanoparticles.

Heating tubes of cross-linked polyethylene

International Nuclear Information System (INIS)

Knoeppler, H.; Hoffmann, M.

1981-01-01

Oxygen permeability of plastic tubes for floor heating systems was measured as a function of the reduced oxygen content of water in plastic tubes at a flow rate of 0.5 m/s and a temperature of 30 0 C and as a function of oxygen uptake of low-oxygen water in floor heating tubes. Pipes of VEP, periodically cross-linked polyethylene (Engels process), polypropylene copolymeride, and polybutene were compared. The permeability of periodically cross-linked polyethylene is twice as high as that of VEP. Measurements, results, and consequences for floor heating systems are discussed. (KH) [de

Fanconi anemia (cross)linked to DNA repair.

Science.gov (United States)

Niedernhofer, Laura J; Lalai, Astrid S; Hoeijmakers, Jan H J

2005-12-29

Fanconi anemia is characterized by hypersensitivity to DNA interstrand crosslinks (ICLs) and susceptibility to tumor formation. Despite the identification of numerous Fanconi anemia (FANC) genes, the mechanism by which proteins encoded by these genes protect a cell from DNA interstrand crosslinks remains unclear. The recent discovery of two DNA helicases that, when defective, cause Fanconi anemia tips the balance in favor of the direct involvement of the FANC proteins in DNA repair and the bypass of DNA lesions.

The role of unsaturations in the Gamma irradiation of crosslinkable polymers

International Nuclear Information System (INIS)

Satti, Angel J.; Ciolino, Andrés E.; Andreucetti, Noemí A.; Vallés, Enrique M.

2015-01-01

Nowadays, the understanding of the interaction of ionizing radiations with polymeric materials is becoming increasingly important. It is well known that many parameters regarding the synthesis of the polymers noticeably affect the irradiation process. In this work, an analysis of the effect of the type and the position of unsaturations in the molecular structure of crosslinkable polymers is performed. For such purpose, two solid semycristalline metallocenic ethylene 1-olefin copolymers (mEOC) which contain a low concentration of unsaturations from the synthesis, and their hydrogenated samples, were irradiated along with liquid poly(dimethylsiloxane) (PDMS) homo and copolymers containing different location and concentration of vinyl groups, which were structurally tailored through anionic synthesis. The source of irradiation was 60 Co, under vacuum at room temperature, in all the cases. The results indicated that terminal vinyls drastically accelerate the crosslinking to lower doses, even at much lower concentrations than other type and location of unsaturations for both, mEOC and PDMS, type of polymers. - Graphical abstract: Irradiated PEX # (ethylene copolymers with an # amount of 1-hexene -H- or 1-octadecene -OD) and their non-vinyl containing hidrogenated samples (PEX #h), along with irradiated vinyl functionalized siloxane polymers. Numbers within parentheses correspond to the number of vinyl groups per polymer chain for each irradiated polymer. Note that PDVi have been crosslinked with the lower dose of irradiation, although it has only one vinyl group. However, that is a terminal vinyl, while for the other polydimethylsiloxane derivatives, vinyls are within the main chain. - Highlights: • Terminal vinyls from metallocenic synthesis accelerate radioinduced crosslinking. • Trans vinyl structures are generated during irradiation, but vinyldenes are reluctant to react. • The position of the vinyl groups noticeably affects the irradiation process. �

Radiation degradation and crosslinking of polytetrafluoroethylene and its application

International Nuclear Information System (INIS)

Wu Guozhong; Wang Mouhua; Tang Zhongfeng

2009-01-01

Polytetrafluoroethylene (PTFE) is a high-performance engineering plastic and known as a typical material of radiation degradation. PTFE can be degraded by radiation under various conditions and PTFE micro-powder is usually fabricated by a combination of radiation and milling. PTFE can also be crosslinked by irradiation in the melt state (330∼340 degree C). The materials can be applied as a special additive due to its excellent wear resistance. Crosslinked PTFE may also be applied in lithography and fuel cell membrane in the future. In this paper, history and application of PTFE degradation and crosslinking products are reviewed. (authors)

Development of new cross-linked polyethylene for atomic energy

International Nuclear Information System (INIS)

Fujimura, Shun-ichi; Ohya, Shingo; Kubo, Masaji; Tsutsumi, Yukihiro; Seguchi, Tadao.

1988-01-01

Cross-linked polyethylene is the material which is used most as the insulating material for electric wires and cables, but for the cables for nuclear power stations and the wiring materials within machinery and equipment, the cross-linked polyethylene which is hard to burn by mixing burning-retarding agent is frequently used as the disaster-preventing countermeasures. As the burning-retarding agent for cross-linked polyethylene, bromine system agent that gives high burning retardation, chlorine system agent that can prevent melting and dripping at the time of burning and so on have been used so as to meet the objective. However by the addition of burning-retarding agents, the electrical and mechanical characteristics of cross-linked polyethylene lower, therefore consideration must be given to the use. In this paper, the results of the examination on the application of condensed acenaphthylene bromide as a new burning-retarding agent to cross-linked polyethylene are reported. White lead was effective for catching HBr. It was confirmed that more than 30 parts of this agent ensured burning retardation. By mixing this agent, the tensile strength increased, but the elongation lowered. It was found that the good radiation resistance was obtained by adding this agent. (K.I.)

Hydroxyl radical induced cross-linking of cytosine and tyrosine in nucleohistone

International Nuclear Information System (INIS)

Gajewski, E.; Dizdaroglu, M.

1990-01-01

Hydroxyl radical induced formation of a DNA-protein cross-link involving cytosine and tyrosine in nucleohistone in buffered aqueous solution is reported. The technique of gas chromatography-mass spectrometry was used for this investigation. A γ-irradiated aqueous mixture of cytosine and tyrosine was first investigated in order to obtain gas chromatographic-mass spectrometric properties of possible cytosine-tyrosine cross-links. One cross-link was observed, and its structure was identified as the product from the formation of a covalent bond between carbon 6 of cytosine and carbon 3 of tyrosine. With the use of gas chromatography-mass spectrometry with selected-ion monitoring, this cytosine-tyrosine cross-link was identified in acidic hydrolysates of calf thymus nucleohistone γ-irradiated in N 2 O-saturated aqueous solution. The yield of this DNA-protein cross-link in nucleohistone was found to be a linear function of the radiation dose in the range of 100-500 Gy (J·kg -1 ). This yield amounted to 0.05 nmol·J -1 . Mechanisms underlying the formation of the cytosine-tyrosine cross-link in nucleohistone were proposed to involve radical-radical and/or radical addition reactions of hydroxyl adduct radicals of cytosine and tyrosine moieties, forming a covalent bond between carbon 6 of cytosine and carbon 3 of tyrosine. When oxygen was present in irradiated solutions, no cytosine-tyrosine cross-links were observed

A review of crosslinked fracturing fluids prepared with produced water

Directory of Open Access Journals (Sweden)

Leiming Li

2016-12-01

Full Text Available The rapidly increasing implementations of oilfield technologies such as horizontal wells and multistage hydraulic fracturing, particularly in unconventional formations, have expanded the need for fresh water in many oilfield locations. In the meantime, it is costly for services companies and operators to properly dispose large volumes of produced water, generated annually at about 21 billion barrels in the United States alone. The high operating costs in obtaining fresh water and dealing with produced water have motivated scientists and engineers, especially in recent years, to use produced water in place of fresh water to formulate well treatment fluids. The objective of this brief review is to provide a summary of the up-to-date technologies of reusing oilfield produced water in preparations of a series of crosslinked fluids implemented mainly in hydraulic fracturing operations. The crosslinked fluids formulated with produced water include borate- and metal-crosslinked guar and derivatized guar fluids, as well as other types of crosslinked fluid systems such as crosslinked synthetic polymer fluids and crosslinked derivatized cellulose fluids. The borate-crosslinked guar fluids have been successfully formulated with produced water and used in oilfield operations with bottomhole temperatures up to about 250 °F. The produced water sources involved showed total dissolved solids (TDS up to about 115,000 mg/L and hardness up to about 11,000 mg/L. The metal-crosslinked guar fluids prepared with produced water were successfully used in wells at bottomhole temperatures up to about 250 °F, with produced water TDS up to about 300,000 mg/L and hardness up to about 44,000 mg/L. The Zr-crosslinked carboxymethyl hydroxypropyl guar (CMHPG fluids have been successfully made with produced water and implemented in operations with bottomhole temperatures at about 250+ °F, with produced water TDS up to about 280,000 mg/L and hardness up to about 91,000�

Development of extremely low wear cross-link polyethylene for 30 years

International Nuclear Information System (INIS)

Oonishi, Hironobu; Fujita, Hiroshi; Kim, Seok-Cheol; Ito, Shigeru; Masuda, Shingo; Clarke, I.C.

2003-01-01

In this report we present our long-term developmental and clinical results with both highly cross-linked and extensively cross-linked polyethylene materials. Beginning in 1970s, we performed wear screening studies on ultra high molecular weight polyethylene (UHMWPE) (GUR412) sterilized by gamma-irradiation in air (range 0 to 10,000 kGy). From these scientific studies the 1,000 kGy dose (100 Mrad) appeared optimal, and so we began clinical use in 1971, and that continued into 1978. The radiographic wear-rates in patients with 1,000 kGy sockets, assessed by radiography, appeared 6-fold reduced compared to our standard UHMWPE sockets. Note also that we had not used any post-sterilization heat treatment for these pioneering extensively cross-linked polyethylene sockets. With clinical use now over 30 years, it was also clear that there was no adverse oxidation created by any free radicals present in our extensively cross-linked polyethylene sockets. With these encouraging clinical results, we further studied laboratory wear results with the modern UHMWPE resins, using the irradiation doses 1,000, 5,000, 10,000 and 15,000 kGy and with both saline and serum lubricants in hip simulators. These more recent studies demonstrated that the wear in extensively cross-linked polyethylene sockets was undetectable, less even than the measurement errors in the simulator techniques. It was unfortunate that the physical properties of such extensively cross-linked polyethylene sockets did not meet the current International Organization for Standardization (ISO) and American Society for Testing and Materials (ASTM) standards. Thus, despite the excellent wear performance of these materials, we decided to investigate also the properties of the 60 kGy irradiated UHMWPE. The polyethylene sheet (GUR1050) was first irradiated with 35 kGy under N2 and then heat treated to remove free radicals. The socket liners were then machined to shape and resterilized with 25 kGy under N2 gas. The

Radiation-induced crosslinking of polyethylene in the presence of bifunctional vinyl monomers

Energy Technology Data Exchange (ETDEWEB)

Joshi, M.S.

1976-10-06

The apparent crosslinking produced by the radiation grafting of two monomers to polyethylene, acrylic acid and acrylonitrile, was investigated. Evidence is presented to show that covalent crosslinks are not produced during the radiation grafting step; covalent crosslinks are produced by the post-irradiation heat treatment associated with measurements of gel; the enhancement in gel fraction and physical properties arises from true crosslinks rather than chain entanglements; and there may be practical value associated with the sensitization of crosslinking produced by the methods employed in this work. The effect of monomer-solvent composition on the graft and gel yield was studied. Viscoelastic properties of grafted films were determined above the melting point of pure polyethylene. The kinetic data, infrared spectra, and viscoelastic properties are the bases for the following mechanism: (1) Acrylic acid-g-PE: Acrylic acid enters the film in the form of a hydrogen bonded dimer and undergoes a grafting reaction that produces hydrogen-bond crosslinks. The heat treatment during the conventional methods for determining of crosslinks convert them into intermolecular anhydride bonds. (2) Acrylonitrile-g-PE: In this, the post-grafting crosslinking is the result of a thermally induced chain reaction leading to an uninterrupted conjugated sequence. The length of the ring structure increases with time and temperature, and the intensity of color increases with the length of the ring structure.

Radiation-induced crosslinking of polyethylene in the presence of bifunctional vinyl monomers

International Nuclear Information System (INIS)

Joshi, M.S.

1976-01-01

The apparent crosslinking produced by the radiation grafting of two monomers to polyethylene, acrylic acid and acrylonitrile, was investigated. Evidence is presented to show that covalent crosslinks are not produced during the radiation grafting step; covalent crosslinks are produced by the post-irradiation heat treatment associated with measurements of gel; the enhancement in gel fraction and physical properties arises from true crosslinks rather than chain entanglements; and there may be practical value associated with the sensitization of crosslinking produced by the methods employed in this work. The effect of monomer-solvent composition on the graft and gel yield was studied. Viscoelastic properties of grafted films were determined above the melting point of pure polyethylene. The kinetic data, infrared spectra, and viscoelastic properties are the bases for the following mechanism: (1) Acrylic acid-g-PE: Acrylic acid enters the film in the form of a hydrogen bonded dimer and undergoes a grafting reaction that produces hydrogen-bond crosslinks. The heat treatment during the conventional methods for determining of crosslinks convert them into intermolecular anhydride bonds. (2) Acrylonitrile-g-PE: In this, the post-grafting crosslinking is the result of a thermally induced chain reaction leading to an uninterrupted conjugated sequence. The length of the ring structure increases with time and temperature, and the intensity of color increases with the length of the ring structure

Separator Membrane from Crosslinked Poly(Vinyl Alcohol and Poly(Methyl Vinyl Ether-alt-Maleic Anhydride

Directory of Open Access Journals (Sweden)

Charu Vashisth Rohatgi

2015-03-01

Full Text Available In this work, we report separator membranes from crosslinking of two polymers, such as poly vinyl alcohol (PVA with an ionic polymer poly(methyl vinyl ether-alt-maleic anhydride (PMVE-MA. Such interpolymer-networked systems were extensively used for biomedical and desalination applications but they were not examined for their potential use as membranes or separators for batteries. Therefore, the chemical interactions between these two polymers and the influence of such crosslinking on physicochemical properties of the membrane are systematically investigated through rheology and by critical gel point study. The hydrogen bonding and the chemical interaction between PMVE-MA and PVA resulted in highly cross-linked membranes. Effect of the molecular weight of PVA on the membrane properties was also examined. The developed membranes were extensively characterized by studying their physicochemical properties (water uptake, swelling ratio, and conductivity, thermal and electrochemical properties using differential scanning calorimetry (DSC, dynamic mechanical analysis (DMA, thermo-gravimetric analysis (TGA and electrochemical impedance spectroscopy (EIS. The DSC study shows the presence of a single Tg in the membranes indicating compatibility of the two polymers in flexible and transparent films. The membranes show good stability and ion conductivity suitable for separator applications.

Separator Membrane from Crosslinked Poly(Vinyl Alcohol) and Poly(Methyl Vinyl Ether-alt-Maleic Anhydride)

Science.gov (United States)

Rohatgi, Charu Vashisth; Dutta, Naba K.; Choudhury, Namita Roy

2015-01-01

In this work, we report separator membranes from crosslinking of two polymers, such as poly vinyl alcohol (PVA) with an ionic polymer poly(methyl vinyl ether-alt-maleic anhydride) (PMVE-MA). Such interpolymer-networked systems were extensively used for biomedical and desalination applications but they were not examined for their potential use as membranes or separators for batteries. Therefore, the chemical interactions between these two polymers and the influence of such crosslinking on physicochemical properties of the membrane are systematically investigated through rheology and by critical gel point study. The hydrogen bonding and the chemical interaction between PMVE-MA and PVA resulted in highly cross-linked membranes. Effect of the molecular weight of PVA on the membrane properties was also examined. The developed membranes were extensively characterized by studying their physicochemical properties (water uptake, swelling ratio, and conductivity), thermal and electrochemical properties using differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), thermo-gravimetric analysis (TGA) and electrochemical impedance spectroscopy (EIS). The DSC study shows the presence of a single Tg in the membranes indicating compatibility of the two polymers in flexible and transparent films. The membranes show good stability and ion conductivity suitable for separator applications. PMID:28347019

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.

Enzymatically crosslinked carboxymethyl-chitosan/gelatin/nano-hydroxyapatite injectable gels for in situ bone tissue engineering application

Energy Technology Data Exchange (ETDEWEB)

Mishra, Debasish; Bhunia, Bibhas; Banerjee, Indranil [Department of Biotechnology, Indian Institute of Technology Kharagpur (India); Datta, Pallab; Dhara, Santanu [School of Medical Science and Technology, Indian Institute of Technology Kharagpur (India); Maiti, Tapas K., E-mail: maititapask@gmail.com [Department of Biotechnology, Indian Institute of Technology Kharagpur (India)

2011-10-10

Present study reports synthesis and characterization of an enzymatically crosslinked injectable gel (iGel) suitable for cell based bone tissue engineering application. The gel comprises of carboxymethyl-chitosan (CMC)/gelatin/nano-hydroxyapatite (nHAp) susceptible to tyrosinase/p-cresol mediated in situ gelling at physiological temperature. Study revealed that a combination of tyrosinase (60U) and p-cresol (2 mM) as crosslinking agents yield rigid gels at physiological temperature when applied to CMC/gelatin within 35 min in presence or absence of nHAp. Rheological study in conjugation with FT-IR analysis showed that an increase in CMC concentration in the gel leads to higher degree of crosslinking and higher strength. Scanning electron microscopy showed that pore sizes of iGels increased with higher gelatin concentration. In vitro study of osteoblast cell proliferation and differentiation showed that, although all iGels are supportive towards the growth of primary osteoblast cells, GC1:1 supported cellular differentiation to the maximum. Application of iGels in mice revealed that stability of the in situ formed gels depends on the degree of crosslinking and CMC concentration. In conclusion, the iGels may be used in treating irregular small bone defects with minimal clinical invasion as well as for bone cell delivery. - Research Highlights: {yields} Enzymatically crosslinked injectable gel made up of CM-chitosan (C)/gelatin (G)/nHAp. {yields} Tyrosinase/p-cresol used for crosslinking and in situ gelling of polymers at 37deg. C. {yields} 60U tyrosinase and 2mM p-cresol is needed for gelation in 35 min. {yields} Higher GC ratio manifests lower crosslinking and gel strength but higher porosity. {yields} GC1:1 shows maximum in vivo gel stability and in vitro osteoblast differentiation.

Effect of Structure Change on Radiation Crosslinking of Unsaturated Polyesters

International Nuclear Information System (INIS)

Ranogajec, F.

2006-01-01

During the course of crosslinking of unsaturated polyesters reacting system, that was liquid prior to reaction, gels, and becomes solid. Crosslinking reaction begins to be controlled by the change of the physical state of the system at an early stage of reaction. The kinetics can not be studied by the usual kinetical methods. In-source 60 C o gamma rays induced crosslinking of unsaturated polyester with styrene was followed directly and continuously by measuring electrical conductivity change. The results of extraction analysis proved good correlation between the change of electrical conductivity and the extent of curing. The gel content was inversely proportional to conductivity and free styrene content directly proportional to conductivity. DC-electrical conductivity has shown high sensitivity toward structural changes and enabled us to detect liquid-liquid transitions in unsaturated polyester. The upper liquid-liquid transition (T l ρ) is less known transition caused by a stepwise decrease of intramolecular short-range local order that remains above the glass and lower liquid-liquid transitions. The local order is based on secondary valent interactions and is enhanced by hydrogen bonding. The linear temperature dependence of the viscosity and dc electrical conductivity of unsaturated polyesters showed a change of slope caused by the (T l ρ). Those changes were the result of the diminishing of the local order (which includes several bond lengths) caused by breaking of the intramolecular interactions. The intramolecular nature of the (T l ρ) in the polyesters under consideration was proved by its insensitivity to crosslinking and dilution with solvents. In the corresponding temperature range, DSC thermograms shoved expected endothermic changes. The structure changes related to the (T l ρ) in the investigated polyesters were determined by 1 H NMR and NIR spectroscopy. The proton NMR indicated that the stepwise change in hydrogen bonding occurred in the

Crosslinkable fumed silica-based nanocomposite electrolytes for rechargeable lithium batteries

Energy Technology Data Exchange (ETDEWEB)

Li, Yangxing; Yerian, Jeffrey A.; Khan, Saad A.; Fedkiw, Peter S. [Department of Chemical & amp; Biomolecular Engineering, North Carolina State University, Raleigh, NC 27695-7905 (United States)

2006-10-27

Electrochemical and rheological properties are reported of composite polymer electrolytes (CPEs) consisting of dual-functionalized fumed silica with methacrylate and octyl groups+low-molecular weight poly(ethylene glycol) dimethyl ether (PEGdm)+lithium bis(trifluoromethanesulfonyl)imide (LiTFSI, lithium imide)+butyl methacrylate (BMA). The role of butyl methacrylate, which aids in formation of a crosslinked network by tethering adjacent fumed silica particles, on rheology and electrochemistry is examined together with the effects of fumed silica surface group, fumed silica weight percent, salt concentration, and solvent molecular weight. Chemical crosslinking of the fumed silica with 20% BMA shows a substantial increase in the elastic modulus of the system and a transition from a liquid-like/flocculated state to an elastic network. In contrast, no change in lithium transference number and only a modest decrease (factor of 2) on conductivity of the CPE are observed, indicating that a crosslinked silica network has minimal effect on the mechanism of ionic transport. These trends suggest that the chemical crosslinks occur on a microscopic scale, as opposed to a molecular scale, between adjacent silica particles and therefore do not impede the segmental mobility of the PEGdm. The relative proportion of the methacrylate and octyl groups on the silica surface displays a nominal effect on both rheology and conductivity following crosslinking although the pre-cure rheology is a function of the surface groups. Chemical crosslinked nanocomposite polymer electrolytes offer significant higher elastic modulus and yield stress than the physical nanocomposite counterpart with a small/negligible penalty of transport properties. The crosslinked CPEs exhibit good interfacial stability with lithium metal at open circuit, however, they perform poorly in cycling of lithium-lithium cells. (author)

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.

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

International Nuclear Information System (INIS)

Sell, Scott A; Garg, Koyal; McClure, Michael J; Bowlin, Gary L; Francis, Michael P; Simpson, David G

2008-01-01

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 -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.

Evaluation of proanthocyanidin-crosslinked electrospun gelatin nanofibers for drug delivering system

International Nuclear Information System (INIS)

Huang, Chiung-Hua; Chi, Chin-Ying; Chen, Yueh-Sheng; Chen, Kuo-Yu; Chen, Pei-Lain; Yao, Chun-Hsu

2012-01-01

Electrospun nanofibers are excellent candidates for various biomedical applications. We successfully fabricated proanthocyanidin‐crosslinked gelatin electrospun nanofibers. Proanthocyanidin, a low cytotoxic collagen crosslinking reagent, increased the gelatin crosslinking percentage in the nanofibers from 53% to 64%. The addition of proanthocyanidin kept the nanofibers from swelling, and, thus, made the fibers more stable in the aqueous state. The compatibility and the release behavior of the drug in the nanofibers were examined using magnesium ascorbyl phosphate as the model drug. Proanthocyanidin also promoted drug loading and kept the drug release rate constant. These properties make the proanthocyanidin‐crosslinked gelatin nanofibers an excellent material for drug delivery. In the cell culture study, L929 fibroblast cells had a significantly higher proliferation rate when cultured with the gelatin/proanthocyanidin blended nanofibers. This characteristic showed that proanthocyanidin‐crosslinked gelatin electrospun nanofibers could potentially be employed as a wound healing material by increasing cell spreading and proliferation. - Highlights: ► Proanthocyanidin‐crosslinked gelatin nanofibers (GEL/PA) is synthesized. ► Proanthocyanidin promoted drug loading and kept the drug release rate constant. ► The GEL/PA nanofibers accelerate fibroblast cell proliferation. ► The GEL/PA nanofibers increase the drug loading efficiency.

CrossWork: Software-assisted identification of cross-linked peptides

DEFF Research Database (Denmark)

Rasmussen, Morten; Refsgaard, Jan; Peng, Li

2011-01-01

Work searches batches of tandem mass-spectrometric data, and identifies cross-linked and non-cross-linked peptides using a standard PC. We tested CrossWork by searching mass-spectrometric datasets of cross-linked complement factor C3 against small (1 protein) and large (1000 proteins) search spaces, and show...

Collagen crosslinks in chondromalacia of the patella.

Science.gov (United States)

Väätäinen, U; Kiviranta, I; Jaroma, H; Arokosi, J; Tammi, M; Kovanen, V

1998-02-01

The aim of the study was to determine collagen concentration and collagen crosslinks in cartilage samples from chondromalacia of the patella. To study the extracellular matrix alterations associated to chondromalacia, we determined the concentration of collagen (hydroxyproline) and its hydroxylysylpyridinoline and lysylpyridinoline crosslinks from chondromalacia foci of the patellae in 12 patients and 7 controls from apparently normal cadavers. The structure of the collagen network in 8 samples of grades II-IV chondromalacia was examined under polarized light microscopy. The full-thickness cartilage samples taken with a surgical knife from chondromalacia lesions did not show changes in collagen, hydroxylysylpyridinoline and lysylpyridinoline concentration as compared with the controls. Polarized light microscopy showed decreased birefringence in the superficial cartilage of chondromalacia lesions, indicating disorganization or disappearance of collagen fibers in this zone. It is concluded that the collagen network shows gradual disorganization with the severity of chondromalacia lesion of the patella without changes in the concentration or crosslinks of collagen.

Stabilized Sulfonated Aromatic Polymers by in situ Solvothermal Cross-Linking

Energy Technology Data Exchange (ETDEWEB)

Di Vona, Maria Luisa, E-mail: divona@uniroma2.it; Sgreccia, Emanuela [Dipartimento di Scienze e Tecnologie Chimiche, Università di Roma Tor Vergata, Rome (Italy); Narducci, Riccardo; Pasquini, Luca [Dipartimento di Scienze e Tecnologie Chimiche, Università di Roma Tor Vergata, Rome (Italy); MAtériaux Divisés, Interfaces, Réactivité, ELectrochimie (MADIREL – UMR 7246), Aix Marseille Université, Marseille (France); Hou, Hongying [Faculty of Material and Engineering, Kunming University of Science and Technology, Kunming (China); Knauth, Philippe [MAtériaux Divisés, Interfaces, Réactivité, ELectrochimie (MADIREL – UMR 7246), Aix Marseille Université, Marseille (France)

2014-10-10

The cross-link reaction via sulfone bridges of sulfonated polyether ether ketone (SPEEK) by thermal treatment at 180°C in presence of dimethylsulfoxide 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 (λ) of 73.

Light-induced cross-linking and post-cross-linking modification of polyglycidol.

Science.gov (United States)

Marquardt, F; Bruns, M; Keul, H; Yagci, Y; Möller, M

2018-02-08

The photoinduced radical generation process has received renewed interest due to its economic and ecological appeal. Herein the light-induced cross-linking of functional polyglycidol and its post-cross-linking modification are presented. Linear polyglycidol was first functionalized with a tertiary amine in a two-step reaction. Dimethylaminopropyl functional polyglycidol was cross-linked in a UV-light mediated reaction with camphorquinone as a type II photoinitiator. The cross-linked polyglycidol was further functionalized by quaternization with various organoiodine compounds. Aqueous dispersions of the cross-linked polymers were investigated by means of DLS and zeta potential measurements. Polymer films were evaluated by DSC and XPS.

Comparison of glutaraldehyde and carbodiimides to crosslink tissue engineering scaffolds fabricated by decellularized porcine menisci

International Nuclear Information System (INIS)

Gao, Shuang; Yuan, Zhiguo; Guo, Weimin; Chen, Mingxue; Liu, Shuyun; Xi, Tingfei; Guo, Quanyi

2017-01-01

The objectives of this study were to fabricate porous scaffolds using decellularized meniscus, and to explore a preferable crosslinking condition to enhance mechanical properties of scaffolds. Moreover, the microstructure, porosity, biodegradation and cytotoxicity were also evaluated. EDAC or GTA in different concentration was used to crosslink scaffolds. FTIR demonstrated functional groups change in crosslinking process. SEM photography showed that crosslinked scaffolds had blurry edges, which resulted scaffolds crosslinked by 1.2 mol/l EDAC had smaller porosity than other groups. The structure change enhanced antidegradation property. After immersing in enzyme solution for 96 h, scaffolds crosslinked by GTA and EDAC could maintain their mass > 70% and 80%. Most importantly, mechanical properties of crosslinked scaffolds were also improved. Uncrosslinked Scaffolds had only 0.49 kPa in compression modulus and 12.81 kPa in tensile modulus. The compression and tensile modulus of scaffolds crosslinked by 1.0% GTA were 1.42 and 567.44 kPa respectively. The same value of scaffolds crosslinked by 1.2 mol/l EDAC were 1.49 and 532.50 kPa. Scaffolds crosslinked by 1.0% and 2.5% GTA were toxic to cells, while EDAC groups showed no cytotoxicity. Chondrocytes could proliferate and infiltrate within scaffolds after seeding. Overall, 1.2 mol/l EDAC was a preferable crosslinking condition. - Highlights: • Porous meniscus scaffolds were fabricated using decellularized meniscus tissue. • Mechanical properties of meniscus scaffolds were enhanced by chemical crosslinking. • The crosslinked scaffold showed enhanced anti-degradation properties. • Chondrocytes could infiltrate and proliferate within crosslinked scaffolds.

Comparison of glutaraldehyde and carbodiimides to crosslink tissue engineering scaffolds fabricated by decellularized porcine menisci

Energy Technology Data Exchange (ETDEWEB)

Gao, Shuang [Center for Biomedical Material and Tissue Engineering, Academy for Advanced Interdisciplinary Studies, Peking University, Beijing 100871 (China); Yuan, Zhiguo; Guo, Weimin; Chen, Mingxue; Liu, Shuyun [Beijing Key Lab of Regenerative Medicine in Orthopaedics, Institute of Orthopaedics, Chinese PLA General Hospital, Beijing 100853 (China); Key Laboratory of Musculoskeletal Trauma & War Injuries, Institute of Orthopaedics, Chinese PLA General Hospital, Beijing 100853 (China); Xi, Tingfei, E-mail: tingfeixi@163.com [Center for Biomedical Material and Tissue Engineering, Academy for Advanced Interdisciplinary Studies, Peking University, Beijing 100871 (China); Shenzhen Institute, Peking University, Shenzhen 518057 (China); Guo, Quanyi, E-mail: doctorguo_301@163.com [Beijing Key Lab of Regenerative Medicine in Orthopaedics, Institute of Orthopaedics, Chinese PLA General Hospital, Beijing 100853 (China); Key Laboratory of Musculoskeletal Trauma & War Injuries, Institute of Orthopaedics, Chinese PLA General Hospital, Beijing 100853 (China)

2017-02-01

The objectives of this study were to fabricate porous scaffolds using decellularized meniscus, and to explore a preferable crosslinking condition to enhance mechanical properties of scaffolds. Moreover, the microstructure, porosity, biodegradation and cytotoxicity were also evaluated. EDAC or GTA in different concentration was used to crosslink scaffolds. FTIR demonstrated functional groups change in crosslinking process. SEM photography showed that crosslinked scaffolds had blurry edges, which resulted scaffolds crosslinked by 1.2 mol/l EDAC had smaller porosity than other groups. The structure change enhanced antidegradation property. After immersing in enzyme solution for 96 h, scaffolds crosslinked by GTA and EDAC could maintain their mass > 70% and 80%. Most importantly, mechanical properties of crosslinked scaffolds were also improved. Uncrosslinked Scaffolds had only 0.49 kPa in compression modulus and 12.81 kPa in tensile modulus. The compression and tensile modulus of scaffolds crosslinked by 1.0% GTA were 1.42 and 567.44 kPa respectively. The same value of scaffolds crosslinked by 1.2 mol/l EDAC were 1.49 and 532.50 kPa. Scaffolds crosslinked by 1.0% and 2.5% GTA were toxic to cells, while EDAC groups showed no cytotoxicity. Chondrocytes could proliferate and infiltrate within scaffolds after seeding. Overall, 1.2 mol/l EDAC was a preferable crosslinking condition. - Highlights: • Porous meniscus scaffolds were fabricated using decellularized meniscus tissue. • Mechanical properties of meniscus scaffolds were enhanced by chemical crosslinking. • The crosslinked scaffold showed enhanced anti-degradation properties. • Chondrocytes could infiltrate and proliferate within crosslinked scaffolds.

Covalent crosslinking of carbon nanostructures

Indian Academy of Sciences (India)

Composites of the binary conjugates with polymer can be readily prepared by using the ... Besides the preparation of crosslinked ... of graphite oxide following the procedure described ... several times to remove the metal nanoparticles and.

A comparison of thiolated and disulfide-crosslinked polyethylenimine for nonviral gene delivery.

Science.gov (United States)

Aravindan, Latha; Bicknell, Katrina A; Brooks, Gavin; Khutoryanskiy, Vitaliy V; Williams, Adrian C

2013-09-01

Branched polyethylenimine (25 kDa) is thiolated and compared with redox-sensitive crosslinked derivatives. Both polymers thiol contents are assessed; the thiolated polymers have 390-2300 mmol SH groups/mol, whereas the crosslinked polymers have lower thiol contents. Cytotoxicity assays show that both modified polymers give lower hemolysis than unmodified PEI. Increased thiol content increases gene transfer efficiency but also elevates cytotoxicity. Crosslinking improves plasmid DNA condensation and enhances transfection efficiency, but extensive crosslinking overstabilizes the polyplexes and decreases transfection, emphasizing the need to balance polyplex stabilization and unpacking. Thus, at low levels of crosslinking, 25 kDa PEI can be an efficient redox-sensitive carrier system. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Crosslinking of commercial polyethylenes by 10 MeV electrons

International Nuclear Information System (INIS)

Singh, A.; Lopata, V.J.; Kremers, W.; Sze, Yu-keung

1995-08-01

Commercial polyethylenes were irradiated with 10 MeV electrons to induce crosslinking. The gel fraction data measured as a function of total dose suggests that crosslinking proceeds on irradiation, as expected. A number of the properties of the irradiated polyethylenes, such as the degree of oxidation, crystallinity and thermal degradation, were studied by Fourier transform infrared/photo acoustic spectroscopy, X-ray diffraction, and a pyrolysis technique coupled with gas chromatography and mass spectrometry. The results of this study suggest that commercial polyethylenes can be crosslinked to a gel fraction of ∼70%, required for wire and cable applications, by 10 MeV electrons. (author). 35 refs., 6 figs

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.

A zwitterionic macro-crosslinker for durable non-fouling coatings.

Science.gov (United States)

Wang, Wei; Lu, Yang; Xie, Jinbing; Zhu, Hui; Cao, Zhiqiang

2016-03-28

A novel zwitterionic macro-crosslinker was developed and applied to fabricate durable non-fouling coatings on a polyurethane substrate. The zwitterionic macro-crosslinker coating exhibited superior durability over the traditional brush polymer coating and was able to retain its non-fouling property even after weeks of shearing in flowing liquid.

Entropic benefit of a cross-link in protein association.

Science.gov (United States)

Zaman, Muhammad H; Berry, R Stephen; Sosnick, Tobin R

2002-08-01

We introduce a method to estimate the loss of configurational entropy upon insertion of a cross-link to a dimeric system. First, a clear distinction is established between the loss of entropy upon tethering and binding, two quantities that are often considered to be equivalent. By comparing the probability distribution of the center-to-center distances for untethered and cross-linked versions, we are able to calculate the loss of translational entropy upon cross-linking. The distribution function for the untethered helices is calculated from the probability that a given helix is closer to its partner than to all other helices, the "Nearest Neighbor" method. This method requires no assumptions about the nature of the solvent, and hence resolves difficulties normally associated with calculations for systems in liquids. Analysis of the restriction of angular freedom upon tethering indicates that the loss of rotational entropy is negligible. The method is applied in the context of the folding of a ten turn helical coiled coil with the tether modeled as a Gaussian chain or a flexible amino acid chain. After correcting for loop closure entropy in the docked state, we estimate the introduction of a six-residue tether in the coiled coil results in an effective concentration of the chain to be about 4 or 100 mM, depending upon whether the helices are denatured or pre-folded prior to their association. Thus, tethering results in significant stabilization for systems with millimolar or stronger dissociation constants. Copyright 2002 Wiley-Liss, Inc.

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.

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

OpenAIRE

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

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...

ISOCT study of collagen crosslinking of collagen in cancer models (Conference Presentation)

Science.gov (United States)

Spicer, Graham; Young, Scott T.; Yi, Ji; Shea, Lonnie D.; Backman, Vadim

2016-03-01

The role of extracellular matrix modification and signaling in cancer progression is an increasingly recognized avenue for the progression of the disease. Previous study of field effect carcinogenesis with Inverse Spectroscopic Optical Coherence Tomography (ISOCT) has revealed pronounced changes in the nanoscale-sensitive mass fractal dimension D measured from field effect tissue when compared to healthy tissue. However, the origin of this difference in tissue ultrastructure in field effect carcinogenesis has remained poorly understood. Here, we present findings supporting the idea that enzymatic crosslinking of the extracellular matrix is an effect that presents at the earliest stages of carcinogenesis. We use a model of collagen gel with crosslinking induced by lysyl oxidase (LOXL4) to recapitulate the difference in D previously reported from healthy and cancerous tissue biopsies. Furthermore, STORM imaging of this collagen gel model verifies the morphologic effects of enzymatic crosslinking at length scales as small as 40 nm, close to the previously reported lower length scale sensitivity threshold of 35 nm for ISOCT. Analysis of the autocorrelation function from STORM images of collagen gels and subsequent fitting to the Whittle-Matérn correlation function shows a similar effect of LOXL4 on D from collagen measured with ISOCT and STORM. We extend this to mass spectrometric study of tissue to directly measure concentrations of collagen crosslink residues. The validation of ISOCT as a viable tool for non-invasive rapid quantification of collagen ultrastructure lends it to study other physiological phenomena involving ECM restructuring such as atherosclerotic plaque screening or cervical ripening during pregnancy.

Process for crosslinking methylene-containing aromatic polymers with ionizing radiation

Science.gov (United States)

Bell, Vernon L. (Inventor); Havens, Stephen J. (Inventor)

1990-01-01

A process for crosslinking aromatic polymers containing radiation-sensitive methylene groups (-CH2-) by exposing the polymers to ionizing radiation thereby causing crosslinking of the polymers through the methylene groups is described. Crosslinked polymers are resistant to most organic solvents such as acetone, alcohols, hydrocarbons, methylene, chloride, chloroform, and other halogenated hydrocarbons, to common fuels and to hydraulic fluids in contrast to readily soluble uncrosslinked polymers. In addition, the degree of crosslinking of the polymers depends upon the percentage of the connecting groups which are methylene which ranges from 5 to 50 pct and preferably from 25 to 50 pct of the connecting groups, and is also controlled by the level of irradiation which ranges from 25 to 1000 Mrads and preferably from 25 to 250 Mrads. The temperature of the reaction conditions ranges from 25 to 200 C and preferably at or slightly above the glass transition temperature of the polymer. The crosslinked polymers are generally more resistant to degradation at elevated temperatures such as greater than 150 C, have a reduced tendency to creep under load, and show no significant embrittlement of parts fabricated from the polymers.

Five-Year Experience of Vitamin E-Diffused Highly Cross-Linked Polyethylene Wear in Total Hip Arthroplasty Assessed by Radiostereometric Analysis

DEFF Research Database (Denmark)

Nebergall, Audrey K; Troelsen, Anders; Rubash, Harry E

2016-01-01

BACKGROUND: Vitamin E-diffused highly cross-linked polyethylene (VEPE) was developed to reduce oxidation without compromising mechanical strength. The purpose of this study was to evaluate VEPE in vivo using radiostereometric analysis (RSA) and patient-reported outcome measures (PROMs). METHODS......: Fifty-one hips were enrolled. Each patient received a VEPE liner, a porous titanium shell, and an uncemented stem with a 32-mm cobalt-chrome femoral head. Tantalum beads were inserted into the VEPE to measure femoral head penetration using RSA. RSA radiographs and PROMs were obtained preoperatively...

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.

Pulsed NMR studies of crosslinking and entanglements in high molecular weight linear polydimethylsiloxanes

International Nuclear Information System (INIS)

Folland, R.; Charlesby, A.

1977-01-01

Pulsed NMR studies of proton spin relaxation are used to investigate both radiation-induced cross linking and entanglements in three high molecular weight linear polydimethylsiloxanes (Msub(w) = 26,000, 63,000 and 110,000). Particular emphasis is placed on the spin-spin relaxation since this is determined by the slower relative translational motions of the polymer chains and hence profoundly affected by the presence of intermolecular couplings such as crosslinks or entanglements. The spin-lattice relaxation times, T 1 , are determined by the fast anisotropic chain rotations and are rather insensitive to such intermolecular couplings. The spin-spin relaxation in these materials is represented by a double exponential decay involving two time constants, Tsub(2S) and Tsub(2L). The shorter component, Tsub(2S), is attributed to network material, which may be either of a dynamic form arising from temporary entanglements or of a permanent nature due to crosslinks. The concentration of entanglements depends on the initial molecular weight of the sample whereas the concentration of crosslinks is a function of the radiation dose. The longer component, Tsub(2L), is attributed to the non-network molecules. On the time scale of the NMR measurements the entanglements are shown to act in the same way as crosslinks. The variation of the relative proportions of network and non-network material with dose is shown to be accounted for by using standard gelation theory when allowance is made for the initial effective crosslink density due to entanglements. The analysis provides a value for the average molecular weight per entanglement point of 27,000 +- 1000 which is consistent with the critical molecular weight for entanglements of 29,000. The dependences of Tsub(2S) and Tsub(2L) on dose and molecular weight are also discussed in terms of the molecular motion. (author)

Anisotropically Swelling Gels Attained through Axis-Dependent Crosslinking of MOF Crystals.

Science.gov (United States)

Ishiwata, Takumi; Kokado, Kenta; Sada, Kazuki

2017-03-01

Anisotropically deforming objects have attracted considerable interest for use in molecular machines and artificial muscles. Herein, we focus on a new approach based on the crystal crosslinking of organic ligands in a pillared-layer metal-organic framework (PLMOF). The approach involves the transformation from crosslinked PLMOF to polymer gels through hydrolysis of the coordination bonds between the organic ligands and metal ions, giving a network polymer that exhibits anisotropic swelling. The anisotropic monomer arrangement in the PLMOF underwent axis-dependent crosslinking to yield anisotropically swelling gels. Therefore, the crystal crosslinking of MOFs should be a useful method for creating actuators with designable deformation properties. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

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.

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.

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

International Nuclear Information System (INIS)

Fuguet, Elisabet; Platerink, Chris van; Janssen, Hans-Gerd

2007-01-01

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 ε-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

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.

Identification of mammalian proteins cross-linked to DNA by ionizing radiation.

Science.gov (United States)

Barker, Sharon; Weinfeld, Michael; Zheng, Jing; Li, Liang; Murray, David

2005-10-07

Ionizing radiation (IR) is an important environmental risk factor for various cancers and also a major therapeutic agent for cancer treatment. Exposure of mammalian cells to IR induces several types of damage to DNA, including double- and single-strand breaks, base and sugar damage, as well as DNA-DNA and DNA-protein cross-links (DPCs). Little is known regarding the biological consequences of DPCs. Identifying the proteins that become cross-linked to DNA by IR would be an important first step in this regard. We have therefore undertaken a proteomics study to isolate and identify proteins involved in IR-induced DPCs. DPCs were induced in AA8 Chinese hamster ovary or GM00637 human fibroblast cells using 0-4 gray of gamma-rays under either aerated or hypoxic conditions. DPCs were isolated using a recently developed method, and proteins were identified by mass spectrometry. We identified 29 proteins as being cross-linked to DNA by IR under aerated and/or hypoxic conditions. The identified proteins include structural proteins, actin-associated proteins, transcription regulators, RNA-splicing components, stress-response proteins, cell cycle regulatory proteins, and GDP/GTP-binding proteins. The involvement of several proteins (actin, histone H2B, and others) in DPCs was confirmed by using Western blot analysis. The dose responsiveness of DPC induction was examined by staining one-dimensional SDS-polyacrylamide gels with SYPRO Tangerine followed by analysis using fluorescence imaging. Quantitation of the fluorescence signal indicated no significant difference in total yields of IR-induced DPCs generated under aerated or hypoxic conditions, although differences were observed for several individual protein bands.

Characterization of Thermally Cross-Linkable Hollow Fiber Membranes for Natural Gas Separation

KAUST Repository

Chen, Chien-Chiang

2013-01-23

The performance of thermally cross-linkable hollow fiber membranes for CO2/CH4 separation and the membrane stability against CO2 plasticization was investigated. The fiber membranes were thermally cross-linked at various conditions. Cross-linking temperature was found to have a significant effect, while shorter soak time and the presence of trace oxidizer (O2 or N2O) had a negligible effect. The cross-linked fibers were tested using high CO2 content feeds (50-70% CO2) at a variety of feed pressures (up to 1000 psia), temperatures, and permeate pressures (up to 100 psia) to evaluate membrane performance under various realistic operating conditions. The results demonstrated that cross-linking improves membrane selectivity and effectively eliminates swelling-induced hydrocarbon loss at high pressures. Excellent stability under aggressive feeds (with CO2 partial pressure up to 700 psia) suggests that cross-linked hollow fiber membranes have great potential for use in diverse aggressive applications, even beyond the CO2/CH4 example explored in this work. © 2012 American Chemical Society.

Radiation-induced crosslinking and post-processing of poly(L-lactic acid) composite

International Nuclear Information System (INIS)

Nagasawa, Naotsugu; Kasai, Noboru; Yagi, Toshiaki; Yoshii, Fumio; Tamada, Masao

2011-01-01

Poly(L-lactic acid), PLLA, was irradiated using electron beams (EBs) in the presence of triallyl isocyanurate (TAIC) at 5% concentration as crosslinking agent. The crosslinked PLLA obtained has heat resistance, as demonstrated by retention of its original shape at glass transition temperature or even higher than 200 o C. As an application of this fact, crosslinked PLLA is applied in spectacle lens to prevent shape deformation of eyeglass frames in displaying and transporting. However, in this application to lens, it is not enough to improve the thermal deformation of PLLA under stress at 70 o C. Radiation-induced crosslinking of a PLLA/silicon dioxide (SiO 2 ) composite with TAIC and post-processing of the crosslinked PLLA composite by heating were further investigated from the viewpoint of thermal deformation. The PLLA materials have several advantages such as high heat resistance and transparency. It is therefore proved that the combination of radiation-induced crosslinking, composition of SiO 2 and post-heating is beneficial for expanding the applications of PLLA.

Radiation-induced crosslinking and post-processing of poly(L-lactic acid) composite

Energy Technology Data Exchange (ETDEWEB)

Nagasawa, Naotsugu, E-mail: nagasawa.naotsugu@jaea.go.j [Japan Atomic Energy Agency (JAEA), Quantum Beam Science Directorate, 1233 Watanuki, Takasaki, Gunma 370-1292 (Japan); Kasai, Noboru; Yagi, Toshiaki; Yoshii, Fumio; Tamada, Masao [Japan Atomic Energy Agency (JAEA), Quantum Beam Science Directorate, 1233 Watanuki, Takasaki, Gunma 370-1292 (Japan)

2011-02-15

Poly(L-lactic acid), PLLA, was irradiated using electron beams (EBs) in the presence of triallyl isocyanurate (TAIC) at 5% concentration as crosslinking agent. The crosslinked PLLA obtained has heat resistance, as demonstrated by retention of its original shape at glass transition temperature or even higher than 200 {sup o}C. As an application of this fact, crosslinked PLLA is applied in spectacle lens to prevent shape deformation of eyeglass frames in displaying and transporting. However, in this application to lens, it is not enough to improve the thermal deformation of PLLA under stress at 70 {sup o}C. Radiation-induced crosslinking of a PLLA/silicon dioxide (SiO{sub 2}) composite with TAIC and post-processing of the crosslinked PLLA composite by heating were further investigated from the viewpoint of thermal deformation. The PLLA materials have several advantages such as high heat resistance and transparency. It is therefore proved that the combination of radiation-induced crosslinking, composition of SiO{sub 2} and post-heating is beneficial for expanding the applications of PLLA.

Antibacterial effect of novel synthesized sulfated β-cyclodextrin crosslinked cotton fabric and its improved antibacterial activities with ZnO, TiO2 and Ag nanoparticles coating.

Science.gov (United States)

Selvam, S; Rajiv Gandhi, R; Suresh, J; Gowri, S; Ravikumar, S; Sundrarajan, M

2012-09-15

Sulfated β-cyclodextrin was synthesized from sulfonation of β-cyclodextrin and sulfated polymer was crosslinked with cotton fabric using ethylenediaminetetraacetic acid as crosslinker. ZnO, TiO(2) and Ag nanoparticles were prepared and characterized by XRD, UV, DLS, SEM and PSA. The prepared nanoparticles were coated on crosslinked cotton fabric. The crosslinking and nanoparticles coating effects of cotton fabrics were studied by FTIR and SEM analysis. The antibacterial test was done against gram positive Staphylococcus aureus and gram negative Escherichia coli bacterium. Copyright © 2012 Elsevier B.V. All rights reserved.

Application of a fast sorting algorithm to the assignment of mass spectrometric cross-linking data.

Science.gov (United States)

Petrotchenko, Evgeniy V; Borchers, Christoph H

2014-09-01

Cross-linking combined with MS involves enzymatic digestion of cross-linked proteins and identifying cross-linked peptides. Assignment of cross-linked peptide masses requires a search of all possible binary combinations of peptides from the cross-linked proteins' sequences, which becomes impractical with increasing complexity of the protein system and/or if digestion enzyme specificity is relaxed. Here, we describe the application of a fast sorting algorithm to search large sequence databases for cross-linked peptide assignments based on mass. This same algorithm has been used previously for assigning disulfide-bridged peptides (Choi et al., ), but has not previously been applied to cross-linking studies. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Study on the kinetics of gel formation in the radiation crosslinking reaction

International Nuclear Information System (INIS)

Wang Mingjun; Liu Yuming

1988-01-01

From the kinetic equation of gel formation obtained by the authors, the mechanism of gel formation may be interpreted clearly as follows: (1) When the degree of crosslinking q g , the system is sol and the crosslinking reaction is only carried out between the sol molecules. (q g is the gel point). (2) When q=q g , there exists a beginning point where the gel is coexisted with the sol, and the system is still sol, and the crosslinking reaction is still carried out between the sol molecules. (3) When q>q g , the crosslinking reaction exceeds the gel point and the gel is coexisted with the sol. The kinetic equation shows clearly that the transformation from sol into gel is caused by crosslinking reaction of the uncrosslinked chain units between the sol and gel molecules. As a result the sol molecules are transformed into the gel molecules gradually, and the sol fraction is reduced. When the chain units P-barw(s)S(1-s)dq in sol are crosslinked with gel, the sol fraction in the system is reduced ds (where P-barw(s) is a function of the radiation dose and s is sol frection). The degree of crosslinking per unit dose (q 0 ) is a reduced function of dose (R). The equation for calculating its value for every irradiation dose is obtained. After knowing the correlation between P-bar W(s) vs R and q 0 vs R, the distribution of gel and sol in the process of radiation crosslinking can be discussed as well

Influence of some crosslinking agents on thermal and mechanical properties of electron beam irradiated polylactide

Energy Technology Data Exchange (ETDEWEB)

Rytlewski, Piotr, E-mail: prytlewski@ukw.edu.p [Department of Materials Engineering, Kazimierz Wielki University, ul. Chodkiewicza 30, 85-064 Bydgoszcz (Poland); Malinowski, RafaL [Institute for Engineering of Polymer Materials and Dyes, ul. M. SkLodowskiej-Curie 55, 87-100 Torun (Poland); Moraczewski, Krzysztof [Department of Materials Engineering, Kazimierz Wielki University, ul. Chodkiewicza 30, 85-064 Bydgoszcz (Poland); Zenkiewicz, Marian [Institute for Engineering of Polymer Materials and Dyes, ul. M. SkLodowskiej-Curie 55, 87-100 Torun (Poland)

2010-10-15

The aim of this article was to determine and compare the influence of trimethylopropane trimethacylate (TMPTA) and trially isocyanurate (TAIC) crosslinking agents on thermal and mechanical properties of electron beam irradiated polylactide (PLA). The blends were made of PLA mixed with 3 wt% of TMPTA (PLA/TMPTA), and PLA mixed with 3 wt% of TAIC (PLA/TAIC). Injection moulded samples were irradiated with the use of high energy (10 MeV) electron beam at various radiation doses to crosslinking PLA macromolecules. Thermal and mechanical properties were investigated by means of differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), tensile strength, and impact strength measurements. The samples were also characterized by Fourier transform infrared spectroscopy (FTIR). It was found that under the influence of electron irradiation PLA/TMPTA samples underwent degradation while PLA/TAIC samples became crosslinked. Tensile and impact strengths of PLA/TMPTA samples decreased with increasing radiation dose while an enhancement of these properties for PLA/TAIC samples was observed.

Influence of some crosslinking agents on thermal and mechanical properties of electron beam irradiated polylactide

International Nuclear Information System (INIS)

Rytlewski, Piotr; Malinowski, RafaL; Moraczewski, Krzysztof; Zenkiewicz, Marian

2010-01-01

The aim of this article was to determine and compare the influence of trimethylopropane trimethacylate (TMPTA) and trially isocyanurate (TAIC) crosslinking agents on thermal and mechanical properties of electron beam irradiated polylactide (PLA). The blends were made of PLA mixed with 3 wt% of TMPTA (PLA/TMPTA), and PLA mixed with 3 wt% of TAIC (PLA/TAIC). Injection moulded samples were irradiated with the use of high energy (10 MeV) electron beam at various radiation doses to crosslinking PLA macromolecules. Thermal and mechanical properties were investigated by means of differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), tensile strength, and impact strength measurements. The samples were also characterized by Fourier transform infrared spectroscopy (FTIR). It was found that under the influence of electron irradiation PLA/TMPTA samples underwent degradation while PLA/TAIC samples became crosslinked. Tensile and impact strengths of PLA/TMPTA samples decreased with increasing radiation dose while an enhancement of these properties for PLA/TAIC samples was observed.

Crosslinked polyurethanes based on hyperbranched polymers

Directory of Open Access Journals (Sweden)

Vuković Jasna

2008-01-01

Full Text Available In this paper, two samples of polyurethane (PU crosslinked with hydroxy -functonal hyperbranched aliphatic polyester of the second pseudo generation were investigated. For the synthesis of these crosslinked PUs two different macrodiols were used: poly(tetramethyleneoxide (PTMO for PUPTMO and ethylene oxide-poly(dimethylsiloxane-ethylene oxide (PDMS-EO for PUPDMS-EO sample. Synthesized samples behave as elastomers and have yellow color. Obtained results show that swelling degree of the sample PUPDMS-EO in N-methyl-2-pyrrolidinon (NMP determined at room temperature is higher than for the sample PUPTMO. It has been also observed that thermal properties of these polyurethane networks can be changed by incorporation of siloxane sequences in their structure.

Thermoreversible covalent crosslinking of maleated ethylene/propylene copolymers with diols

NARCIS (Netherlands)

Mee, van der M.A.J.; Goossens, J.G.P.; Duin, van M.

2008-01-01

Maleated ethylene/propylene copolymer (MAn-g-EPM) was thermoreversibly cross-linked using different routes, i.e. ionic interactions (ionomers), hydrogen bonding and a combination thereof. Microphase separation into polar MAn-rich aggregates occurs for MAn-g-EPM and all cross-linked materials, which

Ultraviolet light-induced crosslinking reveals a unique region of local tertiary structure in potato spindle tuber viroid and HeLa 5S RNA

International Nuclear Information System (INIS)

Branch, A.D.; Benenfeld, B.J.; Robertson, H.D.

1985-01-01

The positions of intramolecular crosslinks induced by irradiation with ultraviolet light were mapped into potato spindle tuber viroid RNA and HeLa 5S rRNA. Crosslinking in each of these molecules occurred at a single major site, which was located by RNA fingerprinting and secondary analysis. Various lines of evidence suggest that these crosslinks identify a previously undescribed element of local tertiary structure common to these two widely divergent RNA molecules: (i) both crosslinks occur in an identical eight-base context, with the sequence 5 GGGAA 3 on one side and the sequence 5 UAC 3 on the other; (ii) both crosslinks connect bases that are not thought to be involved in conventional hydrogen bonding, within regions usually depicted as single-stranded loops flanked by short helical segments; and (iii) both crosslinks connect a purine and a pyrimidine residue, and both may generate the same G-U dimer. Furthermore, it is likely that the crosslinking site is of functional significance because it is located within the most highly conserved region of the viroid sequence and involves bases that are essentially invariant among eukaryotic 5S rRNA molecules

Thermoreversible cross-linking of maleated ethylene/propylene copolymers with diamines and amino-alcohols

NARCIS (Netherlands)

Mee, van der M.A.J.; Goossens, J.G.P.; Duin, van M.

2008-01-01

Maleated ethylene/propylene copolymers (MAn-g-EPM) were thermoreversibly cross-linked using diamines and amino-alcohols. Covalent cross-links are formed via the equilibrium reaction of the grafted anhydride groups with di-functional cross-linkers containing combinations of primary (1°) and secondary

DNA-protein crosslinking by trans-platinum(II)diamminedichloride in mammalian cells, a new method of analysis

International Nuclear Information System (INIS)

Kohn, K.W.; Ewig, R.A.G.

1979-01-01

DNA-protein crosslinks produced in mouse leukemia L1210 cells by trans-Pt(II)diamminedichloride were quantitated using the technique of DNA alkaline elution. DNA single-strand segments that were or were not linked to protein were separable into distinct components by alkaline elution after exposure of the cells to 2-15 kR of X-ray. Protein-linked DNA strands were separated on the basis of their retention on filters at pH 12 while free DNA strands of the size generated by 2-15 kR of X-ray passed rapidly through the filters. The retention of protein-linked DNA strands was attributable to adsorption of protein to the filter under the conditions of alkaline elution. The results obeyed a simple quantitative model according to which the frequency of DNA-protein crosslinks could be calculated. (Auth.)

LFQProfiler and RNP(xl): Open-Source Tools for Label-Free Quantification and Protein-RNA Cross-Linking Integrated into Proteome Discoverer.

Science.gov (United States)

Veit, Johannes; Sachsenberg, Timo; Chernev, Aleksandar; Aicheler, Fabian; Urlaub, Henning; Kohlbacher, Oliver

2016-09-02

Modern mass spectrometry setups used in today's proteomics studies generate vast amounts of raw data, calling for highly efficient data processing and analysis tools. Software for analyzing these data is either monolithic (easy to use, but sometimes too rigid) or workflow-driven (easy to customize, but sometimes complex). Thermo Proteome Discoverer (PD) is a powerful software for workflow-driven data analysis in proteomics which, in our eyes, achieves a good trade-off between flexibility and usability. Here, we present two open-source plugins for PD providing additional functionality: LFQProfiler for label-free quantification of peptides and proteins, and RNP(xl) for UV-induced peptide-RNA cross-linking data analysis. LFQProfiler interacts with existing PD nodes for peptide identification and validation and takes care of the entire quantitative part of the workflow. We show that it performs at least on par with other state-of-the-art software solutions for label-free quantification in a recently published benchmark ( Ramus, C.; J. Proteomics 2016 , 132 , 51 - 62 ). The second workflow, RNP(xl), represents the first software solution to date for identification of peptide-RNA cross-links including automatic localization of the cross-links at amino acid resolution and localization scoring. It comes with a customized integrated cross-link fragment spectrum viewer for convenient manual inspection and validation of the results.

Procyanidins-crosslinked aortic elastin scaffolds with distinctive anti-calcification and biological properties.

Science.gov (United States)

Wang, Xiaoya; Zhai, Wanyin; Wu, Chengtie; Ma, Bing; Zhang, Jiamin; Zhang, Hongfeng; Zhu, Ziyan; Chang, Jiang

2015-04-01

Elastin, a main component of decellularized extracellular matrices and elastin-containing materials, has been used for tissue engineering applications due to their excellent biocompatibility. However, elastin is easily calcified, leading to the decrease of life span for elastin-based substitutes. How to inhibit the calcification of elastin-based scaffolds, but maintain their good biocompatibility, still remains significantly challenging. Procyanidins (PC) are a type of natural polyphenols with crosslinking ability. To investigate whether pure elastin could be crosslinked by PC with anti-calcification effect, PC was first used to crosslink aortic elastin. Results show that PC can crosslink elastin and effectively inhibit elastin-initiated calcification. Further experiments reveal the possible mechanisms for the anti-calcification of PC crosslinking including (1) inhibiting inflammation cell attachment, and secretion of inflammatory factors such as MMPs and TNF-α, (2) preventing elastin degradation by elastase, and (3) direct inhibition of mineral nucleation in elastin. Moreover, the PC-crosslinked aortic elastin maintains natural structure with high pore volume (1111 μL/g), large pore size (10-300 μm) and high porosity (75.1%) which facilitates recellularization of scaffolds in vivo, and displays excellent hemocompatibility, anti-thrombus and anti-inflammatory potential. The advantages of PC-crosslinked porous aortic elastin suggested that it can serve as a promising scaffold for tissue engineering. Copyright © 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

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

International Nuclear Information System (INIS)

Jejurikar, Aparna; Lawrie, Gwen; Groendahl, Lisbeth; Martin, Darren

2011-01-01

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

Crosslinked copolyazoles with a zwitterionic structure for organic solvent resistant membranes

KAUST Repository

Chisca, Stefan

2015-01-01

The preparation of crosslinked membranes with a zwitterionic structure based on a facile reaction between a newly synthesized copolyazole with free OH groups and (3-glycidyloxypropyl)trimethoxysilane (GPTMS) is reported. The new OH-functionalized copolyazole is soluble in common organic solvents, such as tetrahydrofuran (THF), dimethylsulfoxide (DMSO), N,N′-dimethylformamide (DMF) and N-methyl-2-pyrrolidone (NMP) and can be easily processed by phase inversion. After crosslinking with GPTMS, the membranes acquire high solvent resistance. We show the membrane performance and the influence of the crosslinking reaction conditions on the thermal stability, surface polarity, pore morphology, and solvent resistance. By using UV-spectroscopy we monitored the solvent resistance of the membranes in four aggressive solvents (THF, DMSO, DMF and NMP) for 30 days. After this time, only minor changes (less than 2%) were detected for membranes subjected to a crosslinking reaction for 6 hours or longer. Our data suggest that the novel crosslinked membranes can be used for industrial applications in wide harsh environments in the presence of organic solvents.

An Injectable Enzymatically Crosslinked Carboxymethylated Pullulan/Chondroitin Sulfate Hydrogel for Cartilage Tissue Engineering

Science.gov (United States)

Chen, Feng; Yu, Songrui; Liu, Bing; Ni, Yunzhou; Yu, Chunyang; Su, Yue; Zhu, Xinyuan; Yu, Xiaowei; Zhou, Yongfeng; Yan, Deyue

2016-01-01

In this study, an enzymatically cross-linked injectable and biodegradable hydrogel system comprising carboxymethyl pullulan-tyramine (CMP-TA) and chondroitin sulfate-tyramine (CS-TA) conjugates was successfully developed under physiological conditions in the presence of both horseradish peroxidase (HRP) and hydrogen peroxide (H2O2) for cartilage tissue engineering (CTTE). The HRP crosslinking method makes this injectable system feasible, minimally invasive and easily translatable for regenerative medicine applications. The physicochemical properties of the mechanically stable hydrogel system can be modulated by varying the weight ratio and concentration of polymer as well as the concentrations of crosslinking reagents. Additionally, the cellular behaviour of porcine auricular chondrocytes encapsulated into CMP-TA/CS-TA hydrogels demonstrates that the hydrogel system has a good cyto-compatibility. Specifically, compared to the CMP-TA hydrogel, these CMP-TA/CS-TA composite hydrogels have enhanced cell proliferation and increased cartilaginous ECM deposition, which significantly facilitate chondrogenesis. Furthermore, histological analysis indicates that the hydrogel system exhibits acceptable tissue compatibility by using a mouse subcutaneous implantation model. Overall, the novel injectable pullulan/chondroitin sulfate composite hydrogels presented here are expected to be useful biomaterial scaffold for regenerating cartilage tissue.

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...

Epoxides cross-linked hexafluoropropylidene polybenzimidazole membranes for application as high temperature proton exchange membranes

International Nuclear Information System (INIS)

Yang, Jingshuai; Xu, Yixin; Liu, Peipei; Gao, Liping; Che, Quantong; He, Ronghuan

2015-01-01

Covalently cross-linked hexafluoropropylidene polybenzimidazole (F 6 PBI) was prepared and used to fabricate high temperature proton exchange membranes with enhanced mechanical strength against thermoplastic distortion. Three different epoxides, i.e. bisphenol A diglycidyl ether (R 1 ), bisphenol A propoxylate diglycidyl ether (R 2 ) and poly(ethylene glycol) diglycidyl ether (R 3 ), were chosen as the cross-linkers to investigate the influence of their structures on the properties of the cross-linked F 6 PBI membranes. All the cross-linked F 6 PBI membranes displayed excellent stability towards the radical oxidation. Comparing with the pure F 6 PBI membrane, the cross-linked F 6 PBI membranes showed high acid doping level but less swelling after doping phosphoric acid at elevated temperatures. The mechanical strength at 130 °C was improved from 0.4 MPa for F 6 PBI membrane to a range of 0.8–2.0 MPa for the cross-linked F 6 PBI membranes with an acid doping level as high as around 14, especially for that crosslinking with the epoxide (R 3 ), which has a long linear structure of alkyl ether. The proton conductivity of the cross-linked membranes was increased accordingly due to the high acid doping levels. Fuel cell tests demonstrated the technical feasibility of the acid doped cross-linked F 6 PBI membranes for high temperature proton exchange membrane fuel cells

Characterizing the collagen stabilizing effect of crosslinked chitosan nanoparticles against collagenase degradation.

Science.gov (United States)

Kishen, Anil; Shrestha, Suja; Shrestha, Annie; Cheng, Calvin; Goh, Cynthia

2016-08-01

Antibacterial and chelating properties of chitosan has been widely studied for various dental applications. To characterize the interaction between chitosan-nanoparticles (CSnp) and collagen, and understand their stabilizing effect against collagenase degradation for dentin matrix stabilization. Phase-1: a single Type I collagen-fibril model was used to study the interaction with CSnp along with carbodiimides crosslinking treatment. Degradation of the crosslinked fibrils was studied with bacterial collagenase enzyme and monitored using Fourier Transform Infrared (FTIR) spectroscopy, turbidity measurement (400nm), ninhydrin assay and Atomic Force Microscopy (AFM). Interaction of CSnp with collagenase and Type I collagen, were evaluated using SDS-PAGE, and proteolytic cleavage potential of a synthetic peptide. Phase-2: degradation of dentin collagen crosslinked with/without CSnp was evaluated using FTIR, ninhydrin assay and Scanning Electron Microscopy (SEM). Glutaraldehyde crosslinking was used as a positive control. Both native collagen-fibrils and dentin collagen after crosslinking showed higher resistance to collagenase degradation, as observed in turbidity measurements and FTIR spectra. AFM images showed the interaction of CSnp with single collagen-fibril and crosslinked collagen resisted collagenase degradation up to 54h. The collagen and collagenase both formed complexes with CSnp resulting in thickening of bands and reduction in collagen degradation. CSnp treated collagenase showed significantly reduced cleavage of the fluorescent peptides. Dentin collagen was coated with CSnp following crosslinking with significant increase in resistance to collagenase degradation. Crosslinked CSnp on collagen stabilized and enhanced the resistance of dentin matrix against bacterial collagenase degradation due to non-specific interaction with both collagen and collagenase. Copyright © 2016 The Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

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.

Swelling and tensile properties of starch glycerol system with various crosslinking agents

Science.gov (United States)

Mohamed, R.; Mohd, N.; Nurazzi, N.; Siti Aisyah, M. I.; Fauzi, F. Mohd

2017-07-01

Brittle properties of starch had been overcome by the modification process. In this work, sago starch is being modified with variable amount of plasticiser, namely glycerol at 20 and 40% and crosslinking agent had been added to the system. The film of the modification and characterizations of the starch glycerol system with various crosslinking systems were produced by casting method. The film properties of the starch glycerol system were then characterized by tensile strength (mechanical properties) and swelling (physical properties). The modification of the starch glycerol had improved that system by increasing the tensile strength, modulus however lowering its elongation. The increasing in percentage of the water absorption and also swelling are due to the intrinsic hydroxyl groups presence from the starch and glycerol itself that can attract more water to the system. Upon crosslinking, films casted with chemicals namely, glyoxal, malonic acid, borax, PEG were characterised. It was found that, all the film of sago starch crosslinked and undergoing easy film formation. From this modification, borax and malonic acid crosslinking agent had been determined as the best crosslinking agent to the starch glycerol system.

UV-induced cross-linking of abscisic acid to binding proteins

International Nuclear Information System (INIS)

Cornelussen, M.H.M.; Karssen, C.M.; Loon, L.C. van

1995-01-01

Conditions for UV-induced cross-linking of abscisic acid (ABA) through its enone chromophore to binding proteins were evaluated. The effects of a UV-light band between 260 and 530 nm on both unconjugated and protein-conjugated ABA, as well as on anti-ABA antibodies as models of ABA-binding proteins were determined. UV irradiation caused both isomerization and photolysis of ABA, but increasing the lower irradiation boundary to 345 nm strongly reduced photolysis and largely prevented isomerization. When conjugated to alkaline phosphatase (AP), ABA remained stable when using either a 320 or a 345 nm filter. At these wavelengths both binding of ABA to antibodies as well as AP enzymatic activity were maintained. UV-induced cross-linking of monoclonal anti-ABA antibodies to immobilized ABA was analysed by immunoassays. Optimal cross-linking was achieved after a 5 min irradiation period at 0°, using a long pass, cut-on filter to quench wavelengths below 290 nm. This cross-linking faithfully reflected cognate binding activity. (author)

Covalent Crosslinking of Porous Poly(Ionic Liquid) Membrane via a Triazine Network

OpenAIRE

Täuber, Karoline; Dani, Alessandro; Yuan, Jiayin

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.

Cholesterol Removal from Whole Egg by Crosslinked β-Cyclodextrin

Directory of Open Access Journals (Sweden)

H. J. Jeong

2014-04-01

Full Text Available This study was carried out to optimize cholesterol removal in whole egg using crosslinked β-cyclodextrin (β-CD and to recycle the β-CD. Various factors for optimizing conditions were concentration of the β-CD, mixing temperature, mixing time, mixing speed and centrifugal speed. In the result of this study, the optimum conditions of cholesterol removal were 25% crosslinked β-CD, 40°C mixing temperature, 30 min mixing time, 1,200 rpm mixing speed and 2,810×g centrifugal speed. The recycling was repeated five times. The cholesterol removal was 92.76% when treated with the optimum conditions. After determining the optimum conditions, the recyclable yields of the crosslinked β-CD ranged from 86.66% to 87.60% in the recycling and the percentage of cholesterol removal was over 80% until third recycling. However, the cholesterol removal efficiency was decreased when the number of repeated recycling was increased. Based on the result of this study, it was concluded that the crosslinked β-CD was efficient for cholesterol removal in whole egg, and recycling is possible for only limited repeating times due to the interaction of the β-CD and egg protein.

In vitro evaluation of crosslinked electrospun fish gelatin scaffolds.

Science.gov (United States)

Gomes, S R; Rodrigues, G; Martins, G G; Henriques, C M R; Silva, J C

2013-04-01

Gelatin from cold water fish skin was electrospun, crosslinked and investigated as a substrate for the adhesion and proliferation of cells. Gelatin was first dissolved in either water or concentrated acetic acid and both solutions were successfully electrospun. Cross-linking was achieved via three different routes: glutaraldehyde vapor, genipin and dehydrothermal treatment. Solution's properties (surface tension, electrical conductivity and viscosity) and scaffold's properties (chemical bonds, weight loss and fiber diameters) were measured. Cellular viability was analyzed culturing 3T3 fibroblasts plated on the scaffolds and grown up to 7 days. The cells were fixed and observed with SEM or stained for DNA and F-actin and observed with confocal microscopy. In all scaffolds, the cells attached and spread with varying degrees. The evaluation of cell viability showed proliferation of cells until confluence in scaffolds crosslinked by glutaraldehyde and genipin; however the rate of growth in genipin crosslinked scaffolds was slow, recovering only by day five. The results using the dehydrothermal treatment were the less satisfactory. Our results show that glutaraldehyde treated fish gelatin is the most suitable substrate, of the three studied, for fibroblast adhesion and proliferation. Copyright © 2012 Elsevier B.V. All rights reserved.

Mesoscopic Simulations of Crosslinked Polymer Networks

Science.gov (United States)

Megariotis, Grigorios; Vogiatzis, Georgios G.; Schneider, Ludwig; Müller, Marcus; Theodorou, Doros N.

2016-08-01

A new methodology and the corresponding C++ code for mesoscopic simulations of elastomers are presented. The test system, crosslinked ds-1’4-polyisoprene’ is simulated with a Brownian Dynamics/kinetic Monte Carlo algorithm as a dense liquid of soft, coarse-grained beads, each representing 5-10 Kuhn segments. From the thermodynamic point of view, the system is described by a Helmholtz free-energy containing contributions from entropic springs between successive beads along a chain, slip-springs representing entanglements between beads on different chains, and non-bonded interactions. The methodology is employed for the calculation of the stress relaxation function from simulations of several microseconds at equilibrium, as well as for the prediction of stress-strain curves of crosslinked polymer networks under deformation.

Platelet factor XIII increases the fibrinolytic resistance of platelet-rich clots by accelerating the crosslinking of alpha 2-antiplasmin to fibrin

Science.gov (United States)

Reed, G. L.; Matsueda, G. R.; Haber, E.

1992-01-01

Platelet clots resist fibrinolysis by plasminogen activators. We hypothesized that platelet factor XIII may enhance the fibrinolytic resistance of platelet-rich clots by catalyzing the crosslinking of alpha 2-antiplasmin (alpha 2AP) to fibrin. Analysis of plasma clot structure by polyacrylamide gel electrophoresis and immunoblotting revealed accelerated alpha 2AP-fibrin crosslinking in platelet-rich compared with platelet-depleted plasma clots. A similar study of clots formed with purified fibrinogen (depleted of factor XIII activity), isolated platelets, and specific factor XIII inhibitors indicated that this accelerated crosslinking was due to the catalytic activity of platelet factor XIII. Moreover, when washed platelets were aggregated by thrombin, there was evidence of platelet factor XIII-mediated crosslinking between platelet alpha 2AP and platelet fibrin(ogen). Specific inhibition (by a monoclonal antibody) of the alpha 2AP associated with washed platelet aggregates accelerated the fibrinolysis of the platelet aggregate. Thus in platelet-rich plasma clots, and in thrombin-induced platelet aggregates, platelet factor XIII actively formed alpha 2AP-fibrin crosslinks, which appeared to enhance the resistance of platelet-rich clots to fibrinolysis.

Crosslinking of SAVY-4000 O-rings as a Function of Aging Conditions

Energy Technology Data Exchange (ETDEWEB)

Van Buskirk, Caleb Griffith [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

2017-09-08

SAVY-4000 containers were developed as a part of DOE M 441.1-1 to protect workers who handle stored nuclear material from exposure due to loss of containment.1 The SAVY-4000 is comprised of three parts: a lid, a container, and a cross-linked fluoropolymer O-ring. Degradation of the O-ring during use could limit the lifetime of the SAVY-4000. In order to quantify the chemical changes of the Oring over time, the molecular weight between crosslinks was determined as a function of aging conditions using a swelling technique. Because the O-ring is a cross-linked polymer, it will absorb solvent into its matrix without dissolving. The relative amount of solvent uptake can be related to the degree of crosslinking using an equation developed by Paul Flory and John Rehner Jr3. This method was used to analyze O-ring samples aged under thermal and ionizing-radiation conditions. It was found that at the harsher thermal gaining conditions in absence of ionizing-radiation the average molecular weight between crosslinks decreased, indicating a rise in crosslinks, which may be attributable to advanced aging with no ionizing radiation present. Inversely, in the presence of ionizing radiation it was found that material has a higher level of cross-linking with age. This information could be used to help predict the lifetime of the O-rings in SAVY-4000 containers under service conditions.

Rubber mixing process and its relationship with bound rubber and crosslink density

Science.gov (United States)

Hasan, A.; Rochmadi; Sulistyo, H.; Honggokusumo, S.

2017-06-01

This research studied the relationship between bound rubber and crosslink density based on rubber mixing process. Bound rubber was obtained after natural rubber was masticated and mixed with rubber chemicals and filler while crosslink density was collected after rubber compound was vulcanized. Four methods are used and each method refers to four ways of incorporating carbon black during mixing. The first method, after rubber was masticated for 5 minutes, the addition of rubber chemicals and filler was done simultaneously. Rubber was masticated for 1 minute and continued mixing of rubber chemicals and filler where mixing was different from first method. This was the second method. The third method was the same as the second method but the filler used N 660 while in the second method N 330. The last method is not the same as the first and second, the rubber is only masticated for 3 minutes and then mixed with filler and followed by rubber chemicals sequentially. The results showed that bound rubber and crosslink density were influenced by mixing and mastication process. Bound rubber dropped and crosslink density was relatively stable in the first three mixing methods for increasing carbon black at the beginning of the mixing process. Bound rubber and crosslink density stated opposite results in the fourth mixing method. The higher the bound rubber the lower the crosslink density. Without regard to mixing methods, there is a non-linear relationship between bound rubber formation and crosslink density determination

Nanoporous Crosslinked Polyisoprene from Polyisoprene-Polydimethylsiloxane Block Copolymer

DEFF Research Database (Denmark)

Hansen, Michael Steffen; Vigild, Martin Etchells; Berg, Rolf Henrik

2004-01-01

The polyisoprene block of a polyisoprene-polydimethylsiloxane (PI-PDMS) diblock copolymer with 0.68 volume fraction of PI was tightly crosslinked with dicumylperoxide. The PDMS part of the obtained glassy material was subsequently quantitatively etched with anhydrous hydrogen fluoride or tetrabut......The polyisoprene block of a polyisoprene-polydimethylsiloxane (PI-PDMS) diblock copolymer with 0.68 volume fraction of PI was tightly crosslinked with dicumylperoxide. The PDMS part of the obtained glassy material was subsequently quantitatively etched with anhydrous hydrogen fluoride...

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

KAUST Repository

Kratochvil, Adam M.; Koros, William J.

2010-01-01

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

Proton conducting sulphonated fluorinated poly(styrene) crosslinked electrolyte membranes

Energy Technology Data Exchange (ETDEWEB)

Soules, A.; Ameduri, B.; Boutevin, B.; David, G. [Institut Charles Gerhardt UMR CNRS 5253 Equipe, Ingenierie et Architectures Macromoleculaires,' ' Ecole Nationale Superieure de Chimie de Montpellier, 8 rue de l' Ecole Normale, 34296 Montpellier, Cedex 05 (France); Perrin, R. [CEA Le Ripault Departement des Materiaux, DMAT/SCMF/LSTP, BP16 - 37260 Monts (France); Gebel, G. [Structure et Proprietes des Architectures Moleculaires UMR 5819 (CEA-CNRS-UJF), INAC, SPrAM, CEA Grenoble, 17 Rue des Martyrs, 38054 Grenoble, Cedex 9 (France)

2011-10-15

Potential membranes for polymer electrolyte membrane fuel cell based on crosslinked sulphonated fluorinated polystyrenes (PS) were synthesised in two steps. First, azide-telechelic polystyrene was obtained by iodine transfer polymerisation of styrene in the presence of 1,6-diiodoperfluorohexane followed by azido chain-end functionalisation. Then azide-telechelic polystyrene was efficiently crosslinked with 1,10-diazido-1H,1H,2H,2H,9H,9H,10H,10H-perfluorodecane under UV irradiation. After 45 min only, almost completion of azide crosslinking could be achieved, resulting in crosslinked membranes with insoluble fractions higher than 95%. The sulphonation of the crosslinked membranes afforded ionic exchange capacities (IECs) ranging from 2.2 to 3.2 meq g{sup -1}. The hydration number was shown to be very high (from 30 to 75), depending on both the content of perfluorodecane and of sulphonic acid groups. The morphology of the membranes, assessed by small-angle X-ray scattering, was found to be a lamellar-type structure with two types of ionic domains. For the membrane that exhibited an IEC value of 2.2 meq.g{sup -1}, proton conductivity was in the same range as that of Nafion {sup registered} (120-135 mS.cm{sup -1}), whereas the membrane IEC value of 3.2 meq.g{sup -1} showed a proton conductivity higher than that of Nafion {sup registered} in liquid water from 25 to 80 C, though a high water uptake. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Effects of Neutralization and Crosslinking Agents on the Morphology of Chitosan Electrospun Scaffolds

Directory of Open Access Journals (Sweden)

Maryam Mashayekhi

2017-01-01

Full Text Available Chitosan, a natural polymer derived from chitin by deacetylation process of chitin, has gained an enormous interest in tissue engineering due to its unique features such as antibacterial activity and wound healing properties. Electrospinning of acidified chitosan solution is one of the most widely-used approaches in fabrication of 3D scaffolds. Although there are some reports addressing morphology tailoring of the chitosan nanofibers through solution electrospinning, there is no comparative report concerning the neutralization and stabilization conditions of chitosan electrospun fibers. Therefore, this article compares the effects of different neutralizing agents such as aqueous solutions of sodium carbonate (Na2CO3 and potassium carbonate (K2CO3, and crosslinking reagents including glutaraldehyde (GA and genipin on morphology of electrospun chitosan fibers. After neutralization and stabilization processes, Fourier transform infrared spectroscopy (FTIR was employed to investigate the morphology of fibers. Furthermore, the influence of the aforementioned parameters on stability of fibers was probed using scanning electron microscopy. SEM images illustrated that the scaffold resulting from electrospinning of 4 wt% chitosan solution in a mixture of trifluoroacetic acid (TFA and dichloromethane (DCM possessed a well-formed nanofibrous structure. Afterwards, different methods for neutralization and stabilization of the electrospun chitosan nanofiber mats were performed. In this respect, aqueous solutions of both Na2CO3 and K2CO3 salts (1M were employed as neutralization agents and GA and genipin were used as two different crosslinking agents. Based on SEM analysis, the chitosan fibers, crosslinked with genipin, showed better morphology than a scaffold which was crosslinked with glutaraldehyde

Food Simulating Organic Solvents for Evaluating Crosslink Density of Bulk Fill Composite Resin

Directory of Open Access Journals (Sweden)

Neveen M. Ayad

2017-01-01

Full Text Available Objectives. To evaluate crosslink densities of two bulk fill composite resins and determine if the used Food Simulating Organic Solvent (FSOS affected them. Methods. Forty specimens were prepared from SureFill and SonicFill bulk fill composite resins, 20 each. All specimens were stored dry for 24 h. Each group was divided into 2 subgroups: stored in ethanol (E 75% or in methyl ethyl ketone (MEK 100% for 24 h. Crosslink density was evaluated by calculating the difference between the Vickers hardness numbers of the specimens stored dry and after their storage in FSOS. The data were statistically analyzed using t-test. Results. The means of crosslink density in E and MEK were 6.99% and 9.44% for SureFill and 10.54% and 11.92% for SonicFill, respectively. t-test displayed significant differences between crosslink densities of SureFill and SonicFill: (P<0.0001 in E and (P=0.02 in MEK and between crosslink densities of SureFill in E and MEK (P=0.02. Conclusions. Crosslink density of bulk fill composite resin can be evaluated using E or MEK. SureFill has higher crosslink density than SonicFill in both E and MEK.

Influence of crosslinking process on the mechanical behavior of Poly(Dimethylsiloxane) (PDMS)

International Nuclear Information System (INIS)

Fernandes, Barbara Monteiro Pessoa; Weber, Ricardo Ponde; Elzubair, Amal; Suarez, Joao Carlos Miguez

2010-01-01

In the present work was studied the influence of the crosslinking process on the mechanical behavior of a composite with a poly(dimethylsiloxane) (PDMS) matrix filled with inorganic particles, used as dental impression material. The material was crosslinked chemically and by exposition to 400kGy gamma radiation dose. The material properties, before and after crosslinking, were analyzed through physical chemical and mechanical tests and microscopic exam. The results showed that the gamma irradiation, as compared to chemical cure process, produced higher degree of crosslinking, better wettability, adjusted hardness and low fragility. However, the microscopic exam showed that the gamma irradiated PDMS presents, as compared with the chemical cure, a greater number of defaults which resulted from the large concentration of released gases. The results allowed us to conclude that gamma irradiation is an adequate process to crosslink the studied PDMS composite, since we can reduce the quantity of gases formed in this process. (author)

Friedel-Crafts Crosslinked Highly Sulfonated Polyether Ether Ketone (SPEEK) Membranes for a Vanadium/Air Redox Flow Battery.

Science.gov (United States)

Merle, Géraldine; Ioana, Filipoi Carmen; Demco, Dan Eugen; Saakes, Michel; Hosseiny, Seyed Schwan

2013-12-30

Highly conductive and low vanadium permeable crosslinked sulfonated poly(ether ether ketone) (cSPEEK) membranes were prepared by electrophilic aromatic substitution for a Vanadium/Air Redox Flow Battery (Vanadium/Air-RFB) application. Membranes were synthesized from ethanol solution and crosslinked under different temperatures with 1,4-benzenedimethanol and ZnCl2 via the Friedel-Crafts crosslinking route. The crosslinking mechanism under different temperatures indicated two crosslinking pathways: (a) crosslinking on the sulfonic acid groups; and (b) crosslinking on the backbone. It was observed that membranes crosslinked at a temperature of 150 °C lead to low proton conductive membranes, whereas an increase in crosslinking temperature and time would lead to high proton conductive membranes. High temperature crosslinking also resulted in an increase in anisotropy and water diffusion. Furthermore, the membranes were investigated for a Vanadium/Air Redox Flow Battery application. Membranes crosslinked at 200 °C for 30 min with a molar ratio between 2:1 (mol repeat unit:mol benzenedimethanol) showed a proton conductivity of 27.9 mS/cm and a 100 times lower VO2+ crossover compared to Nafion.

Influence of Crosslink Density and Stiffness on Mechanical Properties of Type I Collagen Gel

Directory of Open Access Journals (Sweden)

Shengmao Lin

2015-02-01

Full Text Available The mechanical properties of type I collagen gel vary due to different polymerization parameters. In this work, the role of crosslinks in terms of density and stiffness on the macroscopic behavior of collagen gel were investigated through computational modeling. The collagen fiber network was developed in a representative volume element, which used the inter-fiber spacing to regulate the crosslink density. The obtained tensile behavior of collagen gel was validated against published experimental data. Results suggest that the cross-linked fiber alignment dominated the strain stiffening effect of the collagen gel. In addition, the gel stiffness was enhanced approximately 40 times as the crosslink density doubled. The non-affine deformation was reduced with the increased crosslink density. A positive bilinear correlation between the crosslink density and gel stiffness was obtained. On the other hand, the crosslink stiffness had much less impact on the gel stiffness. This work could enhance our understanding of collagen gel mechanics and shed lights on designing future clinical relevant biomaterials with better control of polymerization parameters.

Cross-linked polymeric membranes for carbon dioxide separation

Science.gov (United States)

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.

Anion exchange membranes based on terminally crosslinked methyl morpholinium-functionalized poly(arylene ether sulfone)s

Science.gov (United States)

Kwon, Sohyun; Rao, Anil H. N.; Kim, Tae-Hyun

2018-01-01

Azide-assisted terminal crosslinking of methyl morpholinium-functionalized poly(arylene ether sulfone) block copolymers yields products (xMM-PESs) suitable for use as anion exchange membranes. By combining the advantages of bulky morpholinium conductors and our unique polymer network crosslinked only at the termini of the polymer chains, we can produce AEMs that after the crosslinking show minimal loss in conductivity, yet with dramatically reduced water uptake. Terminal crosslinking also significantly increases the thermal, mechanical and chemical stability levels of the membranes. A high ion conductivity of 73.4 mS cm-1 and low water uptake of 26.1% at 80 °C are obtained for the crosslinked membrane with higher amount of hydrophilic composition, denoted as xMM-PES-1.5-1. In addition, the conductivity of the crosslinked xMM-PES-1.5-1 membrane exceeds that of its non-crosslinked counterpart (denoted as MM-PES-1.5-1) above 60 °C at 95% relative humidity because of its enhanced water retention capacity caused by the terminally-crosslinked structure.

High Performance Polymer Field-Effect Transistors Based on Thermally Crosslinked Poly(3-hexylthiophene)

International Nuclear Information System (INIS)

Jiang Chun-Xia; Yang Xiao-Yan; Zhao Kai; Wu Xiao-Ming; Yang Li-Ying; Cheng Xiao-Man; Yin Shou-Gen; Wei Jun

2011-01-01

The performance of polymer field-effect transistors is improved by thermal crosslinking ofpoly(3-hexylthiophene), using ditert butyl peroxide as the crosslinker. The device performance depends on the crosslinker concentration significantly. We obtain an optimal on/off ratio of 10 5 and the saturate field-effect mobility of 0.34cm 2 V −1 s −1 , by using a suitable ratios of ditert butyl peroxide, 0.5 wt% ofpoly(3-hexylthiophene). The microstructure images show that the crosslinked poly(3-hexylthiophene) active layers simultaneously possess appropriate crystallinity and smooth morphology. Moreover, crosslinking of poly(3-hexylthiophene) prevents the transistors from large threshold voltage shifts under ambient bias-stressing, showing an advantage in encouraging device environmental and operating stability. (cross-disciplinary physics and related areas of science and technology)

Swelling and mechanical properties of physically crosslinked poly(vinyl alcohol) hydrogels.

Science.gov (United States)

Suzuki, Atsushi; Sasaki, Saori

2015-12-01

Physically crosslinked poly(vinyl alcohol) gels are versatile biomaterials due to their excellent biocompatibility. In the past decades, physically crosslinked poly(vinyl alcohol) and poly(vinyl alcohol)-based hydrogels have been extensively studied for biomedical applications. However, these materials have not yet been implemented due to their mechanical strength. Physically crosslinked poly(vinyl alcohol) gels consist of a swollen amorphous network of poly(vinyl alcohol) physically crosslinked by microcrystallites. Although the mechanical properties can be improved to some extent by controlling the distribution of microcrystallites on the nano- and micro-scales, enhancing the mechanical properties while maintaining high water content remains very difficult. It may be technologically impossible to significantly improve the mechanical properties while keeping the gel's high water absorbance ability using conventional fabrication methods. Physical and chemical understandings of the swelling and mechanical properties of physically crosslinked poly(vinyl alcohol) gels are considered here; some promising strategies for their practical applications are presented. This review focuses more on the recent studies on swelling and mechanical properties of poly(vinyl alcohol) hydrogels, prepared using only poly(vinyl alcohol) and pure water with no other chemicals, as potential biomedical materials. © IMechE 2015.

Physico-chemical/biological properties of tripolyphosphate cross-linked chitosan based nanofibers

Energy Technology Data Exchange (ETDEWEB)

Sarkar, Soumi Dey [School of Medical Science and Technology, Indian Institute of Technology Kharagpur, Kharagpur-721302 (India); Farrugia, Brooke L.; Dargaville, Tim R. [Institute of Health and Biomedical Innovation, Queensland University of Technology, Kelvin Groove, Queensland-4059 (Australia); Dhara, Santanu, E-mail: sdhara@smst.iitkgp.ernet.in [School of Medical Science and Technology, Indian Institute of Technology Kharagpur, Kharagpur-721302 (India)

2013-04-01

In this study, chitosan-PEO blend, prepared in a 15 M acetic acid, was electrospun into nanofibers (∼ 78 nm diameter) with bead free morphology. While investigating physico-chemical parameters of blend solutions, effect of yield stress on chitosan based nanofiber fabrication was clearly evidenced. Architectural stability of nanofiber mat in aqueous medium was achieved by ionotropic cross-linking of chitosan by tripolyphosphate (TPP) ions. The TPP cross-linked nanofiber mat showed swelling up to ∼ 300% in 1 h and ∼ 40% degradation during 30 day study period. 3T3 fibroblast cells showed good attachment, proliferation and viability on TPP treated chitosan based nanofiber mats. The results indicate non-toxic nature of TPP cross-linked chitosan based nanofibers and their potential to be explored as a tissue engineering matrix. - Highlights: ► Chitosan based nanofiber fabrication through electrospinning. ► Roles of solution viscosity and yield stress on spinnability of chitosan evidenced. ► Tripolyphosphate (TPP) cross-linking rendered structural stability to nanofibers. ► TPP cross-linking also improved cellular response on chitosan based nanofibers. ► Thus, chitosan based nanofibers are suitable for tissue engineering application.

Physico-chemical/biological properties of tripolyphosphate cross-linked chitosan based nanofibers

International Nuclear Information System (INIS)

Sarkar, Soumi Dey; Farrugia, Brooke L.; Dargaville, Tim R.; Dhara, Santanu

2013-01-01

In this study, chitosan-PEO blend, prepared in a 15 M acetic acid, was electrospun into nanofibers (∼ 78 nm diameter) with bead free morphology. While investigating physico-chemical parameters of blend solutions, effect of yield stress on chitosan based nanofiber fabrication was clearly evidenced. Architectural stability of nanofiber mat in aqueous medium was achieved by ionotropic cross-linking of chitosan by tripolyphosphate (TPP) ions. The TPP cross-linked nanofiber mat showed swelling up to ∼ 300% in 1 h and ∼ 40% degradation during 30 day study period. 3T3 fibroblast cells showed good attachment, proliferation and viability on TPP treated chitosan based nanofiber mats. The results indicate non-toxic nature of TPP cross-linked chitosan based nanofibers and their potential to be explored as a tissue engineering matrix. - Highlights: ► Chitosan based nanofiber fabrication through electrospinning. ► Roles of solution viscosity and yield stress on spinnability of chitosan evidenced. ► Tripolyphosphate (TPP) cross-linking rendered structural stability to nanofibers. ► TPP cross-linking also improved cellular response on chitosan based nanofibers. ► Thus, chitosan based nanofibers are suitable for tissue engineering application

Swelling of radiation crosslinked acrylamide-based microgels and their potential applications

Energy Technology Data Exchange (ETDEWEB)

Abd El-Rehim, H.A. [National Center for Radiation Research and Technology, Atomic Energy Authority, P.O. Box 29 Nasr City, Cairo (Egypt)]. E-mail: ha_rehim@hotmail.com

2005-10-01

Crosslinked polyacrylamide PAAm and acrylamide-Na-acrylate P(AAm-Na-AAc) microgels were prepared by electron beam irradiation. It was found that the dose required for crosslinking depends on the polymer moisture content, so that the dose to obtain PAAm of maximum gel fraction was over 40 and 20 kGy for dry and moist PAAm, respectively. The structural changes in irradiated PAAm were investigated using FTIR and SEM. The swelling property of such microgels in distilled water and real urine solution was determined and crosslinked polymers reached their equilibrium swelling state in a few minutes. As the gel content and crosslinking density decrease, the swelling of the microgels increases. The ability of the microgels to absorb and retain large amount of solutions suggested their possible uses in horticulture and in hygienic products such as disposable diapers.

Swelling of radiation crosslinked acrylamide-based microgels and their potential applications

International Nuclear Information System (INIS)

Abd El-Rehim, H.A.

2005-01-01

Crosslinked polyacrylamide PAAm and acrylamide-Na-acrylate P(AAm-Na-AAc) microgels were prepared by electron beam irradiation. It was found that the dose required for crosslinking depends on the polymer moisture content, so that the dose to obtain PAAm of maximum gel fraction was over 40 and 20 kGy for dry and moist PAAm, respectively. The structural changes in irradiated PAAm were investigated using FTIR and SEM. The swelling property of such microgels in distilled water and real urine solution was determined and crosslinked polymers reached their equilibrium swelling state in a few minutes. As the gel content and crosslinking density decrease, the swelling of the microgels increases. The ability of the microgels to absorb and retain large amount of solutions suggested their possible uses in horticulture and in hygienic products such as disposable diapers

Driving Chemical Reactions in Plasmonic Nanogaps with Electrohydrodynamic Flow.

Science.gov (United States)

Thrift, William J; Nguyen, Cuong Q; Darvishzadeh-Varcheie, Mahsa; Zare, Siavash; Sharac, Nicholas; Sanderson, Robert N; Dupper, Torin J; Hochbaum, Allon I; Capolino, Filippo; Abdolhosseini Qomi, Mohammad Javad; Ragan, Regina

2017-11-28

Nanoparticles from colloidal solution-with controlled composition, size, and shape-serve as excellent building blocks for plasmonic devices and metasurfaces. However, understanding hierarchical driving forces affecting the geometry of oligomers and interparticle gap spacings is still needed to fabricate high-density architectures over large areas. Here, electrohydrodynamic (EHD) flow is used as a long-range driving force to enable carbodiimide cross-linking between nanospheres and produces oligomers exhibiting sub-nanometer gap spacing over mm 2 areas. Anhydride linkers between nanospheres are observed via surface-enhanced Raman scattering (SERS) spectroscopy. The anhydride linkers are cleavable via nucleophilic substitution and enable placement of nucleophilic molecules in electromagnetic hotspots. Atomistic simulations elucidate that the transient attractive force provided by EHD flow is needed to provide a sufficient residence time for anhydride cross-linking to overcome slow reaction kinetics. This synergistic analysis shows assembly involves an interplay between long-range driving forces increasing nanoparticle-nanoparticle interactions and probability that ligands are in proximity to overcome activation energy barriers associated with short-range chemical reactions. Absorption spectroscopy and electromagnetic full-wave simulations show that variations in nanogap spacing have a greater influence on optical response than variations in close-packed oligomer geometry. The EHD flow-anhydride cross-linking assembly method enables close-packed oligomers with uniform gap spacings that produce uniform SERS enhancement factors. These results demonstrate the efficacy of colloidal driving forces to selectively enable chemical reactions leading to future assembly platforms for large-area nanodevices.

Crosslinked Hexafluoropropylidene Polybenzimidazole Membranes with Chloromethyl Polysulfone for Fuel Cell Applications

DEFF Research Database (Denmark)

Yang, Jingshuai; Li, Qingfeng; Cleemann, Lars Nilausen

2013-01-01

Hexafluoropropylidene polybenzimidazole (F6PBI) was synthesized with excellent chemical stability and improved solubility. When doped with phosphoric acid, however, the F6PBI membranes showed plastic deformation at elevated temperatures. Further efforts were made to covalently crosslink F6PBI...... membranes with chloromethyl polysulfone as a polymeric crosslinker. Comparing with linear F6PBI and mPBI membranes, the polymer crosslinked F6PBI membranes exhibited little organo solubility, excellent stability towards the radical oxidation, high resistance to swelling in concentrated phosphoric acid...... with the linear F6PBI and mPBI membranes....

Electron beam crosslinked PVC : structure property relationships

International Nuclear Information System (INIS)

Gupta, Neeraj K.; Sabharwal, Sunil

2001-01-01

PVC is used extensively for its insulating properties for the manufacture of wires and cables and for other applications. Its gradual degradation, oxidation and even dehydro chlorination restricts use for long lasting period in installations such as high temperature zones, underground cables, communication systems, electro-nuclear facilities, etc. The technological properties and performance characteristics of PVC based insulation can be improved via crosslinking by high-energy electrons. PVC is however a polymer, which on irradiation predominantly undergoes degradation. To avoid degradation, it needs to be compounded with sensitizing agents or multifunctional monomers so that crosslinking is the predominant reaction. Radiation cross linkable formulations are complex mixtures of resin and various additives incorporated for achieving desired technological and performance characteristics, ease of processing and improving quality. The proper choice of additives and sensitizing agents enable low dose requirements for efficient crosslinking and improvements in various technological properties. The purposes of this work was to investigate the effect of using a binary sensitizer blend of a trifunctional monomer and a rubber in PVC, and develop suitable electron beam cross linkable formulations for wire insulation. This paper presents some aspects of the investigations and development of insulation demonstrated at industrial scale

Highly efficient perovskite solar cells with crosslinked PCBM interlayers

KAUST Repository

Qiu, W.

2017-01-09

Commercially available phenyl-C-butyric acid methyl ester (PCBM) is crosslinked with 1,6-diazidohexane (DAZH), resulting in films resistant to common solvents used in perovskite solar cell processing. By using crosslinked PCBM as an interlayer and (HC(NH))(CHNH)PbIBr as the active layer, we achieve small area devices and modules with a maximum steady-state power conversion efficiency of 18.1% and 14.9%, respectively.

a study of the kinetic of synthesis and crosslinking of methylol ...

African Journals Online (AJOL)

Nurudeen

The reaction was carried out in ... temperature of reaction medium reduced the time of formation and subsequent crosslinking to the ... The experiment was repeated using 3, 4, 5 and 6 ... increase the rate of the crosslinking in the formation of.

BIOCOMPATIBILITY AND TISSUE REGENERATING CAPACITY OF CROSS-LINKED DERMAL SHEEP COLLAGEN

NARCIS (Netherlands)

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

The biocompatibility and tissue regenerating capacity of four crosslinked dermal sheep collagens (DSC) was studied. In vitro, the four DSC versions were found to be noncytotoxic or very low in cytoxicity. After subcutaneous implantation in rats, hexamethylenediisocyanate-crosslinked DSC (HDSC)

Friedel–Crafts Crosslinked Highly Sulfonated Polyether Ether Ketone (SPEEK Membranes for a Vanadium/Air Redox Flow Battery

Directory of Open Access Journals (Sweden)

Géraldine Merle

2013-12-01

Full Text Available Highly conductive and low vanadium permeable crosslinked sulfonated poly(ether ether ketone (cSPEEK membranes were prepared by electrophilic aromatic substitution for a Vanadium/Air Redox Flow Battery (Vanadium/Air-RFB application. Membranes were synthesized from ethanol solution and crosslinked under different temperatures with 1,4-benzenedimethanol and ZnCl2 via the Friedel–Crafts crosslinking route. The crosslinking mechanism under different temperatures indicated two crosslinking pathways: (a crosslinking on the sulfonic acid groups; and (b crosslinking on the backbone. It was observed that membranes crosslinked at a temperature of 150 °C lead to low proton conductive membranes, whereas an increase in crosslinking temperature and time would lead to high proton conductive membranes. High temperature crosslinking also resulted in an increase in anisotropy and water diffusion. Furthermore, the membranes were investigated for a Vanadium/Air Redox Flow Battery application. Membranes crosslinked at 200 °C for 30 min with a molar ratio between 2:1 (mol repeat unit:mol benzenedimethanol showed a proton conductivity of 27.9 mS/cm and a 100 times lower VO2+ crossover compared to Nafion.

Friedel–Crafts Crosslinked Highly Sulfonated Polyether Ether Ketone (SPEEK) Membranes for a Vanadium/Air Redox Flow Battery

Science.gov (United States)

Merle, Géraldine; Ioana, Filipoi Carmen; Demco, Dan Eugen; Saakes, Michel; Hosseiny, Seyed Schwan

2014-01-01

Highly conductive and low vanadium permeable crosslinked sulfonated poly(ether ether ketone) (cSPEEK) membranes were prepared by electrophilic aromatic substitution for a Vanadium/Air Redox Flow Battery (Vanadium/Air-RFB) application. Membranes were synthesized from ethanol solution and crosslinked under different temperatures with 1,4-benzenedimethanol and ZnCl2 via the Friedel–Crafts crosslinking route. The crosslinking mechanism under different temperatures indicated two crosslinking pathways: (a) crosslinking on the sulfonic acid groups; and (b) crosslinking on the backbone. It was observed that membranes crosslinked at a temperature of 150 °C lead to low proton conductive membranes, whereas an increase in crosslinking temperature and time would lead to high proton conductive membranes. High temperature crosslinking also resulted in an increase in anisotropy and water diffusion. Furthermore, the membranes were investigated for a Vanadium/Air Redox Flow Battery application. Membranes crosslinked at 200 °C for 30 min with a molar ratio between 2:1 (mol repeat unit:mol benzenedimethanol) showed a proton conductivity of 27.9 mS/cm and a 100 times lower VO2+ crossover compared to Nafion. PMID:24957118

The degree of collagen crosslinks in medical collagen membranes determined by water absorption

International Nuclear Information System (INIS)

Braczko, M.; Tederko, A.; Grzybowski, J.

1994-01-01

Collagen membranes were crosslinked by using three agents: glutaraldehyde, hexametylenediisocyanate, and UV irradiation. The increasing concentrations of above chemical agents or longer time of UV exposition resulted in the higher cross-links degree and in the decrease of collagen membranes swelling (measured as water absorption), their elasticity and mechanical resistance. According to American standards, the degree of collagen biomaterial cross-links is determined by measuring of the digestion time by pepsin. However, that method is very time-consuming. In our study, we have that a simple, linear regression between logarithm of digestion time by pepsin exists and it was identical for all three cross-linking agents used. We have concluded that determination of water absorption can be an alternative, simple and fast method for examination of collagen membrane cross-links degree. (author). 16 refs, 7 figs, 1 tab

All solid supercapacitor based on polyaniline and crosslinked sulfonated poly[ether ether ketone

International Nuclear Information System (INIS)

Sivaraman, P.; Kushwaha, R.K.; Shashidhara, K.; Hande, V.R.; Thakur, A.P.; Samui, A.B.; Khandpekar, M.M.

2010-01-01

All solid supercapacitor based on polyaniline (PANI) and crosslinked sulfonated poly[ether ether ketone] (XSPEEK,) is reported in this paper. The crosslinker used for sulfonated poly[ether ether ketone] (SPEEK) is 1,4-bis(hydroxymethyl) benzene. The XSPEEK is used as both solid electrolyte and separator membrane. Supercapacitors are fabricated using various PANI/XSPEEK weight ratios. These are characterized by cyclic voltammetry and galvanostatic charge-discharge studies. The supercapacitor with PANI/XSPEEK weight ratio 1:0.5, exhibit a specific capacitance of 480 F g -1 of PANI. To the best of authors' knowledge, the value reported here is the highest for a supercapacitor based on a proton conducting solid polymer electrolyte and PANI. Detailed electrochemical impedance spectroscopy analysis is carried out. The analysis shows that the complex capacitance of the supercapacitor depends on the XSPEEK content. The time constant (t 0 ), derived from the imaginary part of complex capacitance decreases with increase in the XSPEEK content in the supercapacitor. Cycle life characteristics of the supercapacitor show a decrease in specific capacitance during initial cycles and get stabilized during later cycles.

Photochemical Acceleration of DNA Strand Displacement by Using Ultrafast DNA Photo-crosslinking.

Science.gov (United States)

Nakamura, Shigetaka; Hashimoto, Hirokazu; Kobayashi, Satoshi; Fujimoto, Kenzo

2017-10-18

DNA strand displacement is an essential reaction in genetic recombination, biological processes, and DNA nanotechnology. In particular, various DNA nanodevices enable complicated calculations. However, it takes time before the output is obtained, so acceleration of DNA strand displacement is required for a rapid-response DNA nanodevice. Herein, DNA strand displacement by using DNA photo-crosslinking to accelerate this displacement is evaluated. The DNA photo-crosslinking of 3-cyanovinylcarbazole ( CNV K) was accelerated at least 20 times, showing a faster DNA strand displacement. The rate of photo-crosslinking is a key factor and the rate of DNA strand displacement is accelerated through ultrafast photo-crosslinking. The rate of DNA strand displacement was regulated by photoirradiation energy. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Preparation and mechanical properties of photo-crosslinked poly(trimethylene carbonate) and nano-hydroxyapatite composites.

Science.gov (United States)

Geven, Mike A; Barbieri, Davide; Yuan, Huipin; de Bruijn, Joost D; Grijpma, Dirk W

2015-01-01

Composite materials of photo-crosslinked poly(trimethylene carbonate) and nanoscale hydroxyapatite were prepared and their mechanical characteristics for application as orbital floor implants were assessed. The composites were prepared by solvent casting poly(trimethylene carbonate) macromers with varying amounts of nano-hydroxyapatite and subsequent photo-crosslinking. The incorporation of the nano-hydroxyapatite into the composites was examined by thermogravimetric analysis, scanning electron microscopy and gel content measurements. The mechanical properties were investigated by tensile testing and trouser tearing experiments. Our results show that nano-hydroxyapatite particles can readily be incorporated into photo-crosslinked poly(trimethylene carbonate) networks. Compared to the networks without nano-hydroxyapatite, incorporation of 36.3 wt.% of the apatite resulted in an increase of the E modulus, yield strength and tensile strength from 2.2 MPa to 51 MPa, 0.5 to 1.4 N/mm2 and from 1.3 to 3.9 N/mm2, respectively. We found that composites containing 12.4 wt.% nano-hydroxyapatite had the highest values of strain at break, toughness and average tear propagation strength (376% , 777 N/mm2 and 3.1 N/mm2, respectively).

Polymeric micelles with ionic cores containing biodegradable cross-links for delivery of chemotherapeutic agents.

Science.gov (United States)

Kim, Jong Oh; Sahay, Gaurav; Kabanov, Alexander V; Bronich, Tatiana K

2010-04-12

Novel functional polymeric nanocarriers with ionic cores containing biodegradable cross-links were developed for delivery of chemotherapeutic agents. Block ionomer complexes (BIC) of poly(ethylene oxide)-b-poly(methacylic acid) (PEO-b-PMA) and divalent metal cations (Ca(2+)) were utilized as templates. Disulfide bonds were introduced into the ionic cores by using cystamine as a biodegradable cross-linker. The resulting cross-linked micelles with disulfide bonds represented soft, hydrogel-like nanospheres and demonstrated a time-dependent degradation in the conditions mimicking the intracellular reducing environment. The ionic character of the cores allowed to achieve a very high level of doxorubicin (DOX) loading (50% w/w) into the cross-linked micelles. DOX-loaded degradable cross-linked micelles exhibited more potent cytotoxicity against human A2780 ovarian carcinoma cells as compared to micellar formulations without disulfide linkages. These novel biodegradable cross-linked micelles are expected to be attractive candidates for delivery of anticancer drugs.

The effect of chain flexibility and chain mobility on radiation crosslinking reactions of polymers

International Nuclear Information System (INIS)

Sun Jiazhen

2003-01-01

Flexibility of polymer chains is an important factor to effects of radiation crosslinking of the polymer. Polymers with flexible chains are easier to be crosslinked, with lower dose of gelation, than polymers with more rigid chains. And it is known that most polymers with abnormal rigidity can be radiation-crosslinked only at high temperatures when the molecular chains get enough mobility. The flexibility of polymer chains also influences the relationship between degree of degradation and radiation dose. A chain flexibility factor β has been introduced to modify the Charlesby-Pinner equation of sol-fraction and radiation dose. The new relationship equation applies to a wider range of polymers in radiation crosslinking. Studies also show that for flexible polymers with lower T g and molecular internal rotating factor, mechanism of radiation crosslinking is mainly in H type, whereas for rigid polymers with higher T g and molecular internal rotating factor, mechanism of radiation crosslinking is mainly in T type

Cross-linked polybenzimidazole membranes for high temperature proton exchange membrane fuel cells with dichloromethyl phosphinic acid as a cross-linker

DEFF Research Database (Denmark)

Noye, Pernille; Li, Qingfeng; Pan, Chao

2008-01-01

Phosphoric acid doped polybenzimidazole (PBI) membranes have been covalently cross-linked with dichloromethyl phosphinic acid (DCMP). FT-IR measurements showed new bands originating from bonds between the hydrogen bearing nitrogen in the imidazole group of PBI and the CH2 group in DCMP. The produ......Phosphoric acid doped polybenzimidazole (PBI) membranes have been covalently cross-linked with dichloromethyl phosphinic acid (DCMP). FT-IR measurements showed new bands originating from bonds between the hydrogen bearing nitrogen in the imidazole group of PBI and the CH2 group in DCMP.......e. within the temperature range of operation of PBI-based fuel cells....

Models for stiffening in cross-linked biopolymer networks : A comparative study

NARCIS (Netherlands)

van Dillen, T.; Onck, P. R.; Van der Giessen, E.

In a recent publication, we studied the mechanical stiffening behavior in two-dimensional (2D) cross-linked networks of semiflexible biopolymer filaments under simple shear [Onck, P.R., Koeman, T., Van Dillen, T., Van der Giessen, E., 2005. Alternative explanation of stiffening in cross-linked

Effects of Surface Modification and Bulk Geometry on the Biotribological Behavior of Cross-Linked Polyethylene: Wear Testing and Finite Element Analysis.

Science.gov (United States)

Watanabe, Kenichi; Kyomoto, Masayuki; Saiga, Kenichi; Taketomi, Shuji; Inui, Hiroshi; Kadono, Yuho; Takatori, Yoshio; Tanaka, Sakae; Ishihara, Kazuhiko; Moro, Toru

2015-01-01

The wear and creep deformation resistances of polymeric orthopedic bearing materials are both important for extending their longevity. In this study, we evaluated the wear and creep deformation resistances, including backside damage, of different polyethylene (PE) materials, namely, conventional PE, cross-linked PE (CLPE), and poly(2-methacryloyloxyethyl phosphorylcholine)- (PMPC-) grafted CLPE, through wear tests and finite element analysis. The gravimetric and volumetric degrees of wear of disks (3 or 6 mm in thickness) of these materials against a cobalt-chromium-molybdenum alloy pin were examined using a multidirectional pin-on-disk tester. Cross-linking and PMPC grafting decreased the gravimetric wear of the PE disks significantly. The volumetric wear at the bearing surface and the volumetric penetration in the backside of the 3-mm thick PE disk were higher than those of the 6-mm thick PE disk, regardless of the bearing material. The geometrical changes induced in the PE disks consisted of creep, because the calculated internal von Mises stress at the bearing side of all disks and that at the backside of the 3-mm thick disks exceeded their actual yield strengths. A highly hydrated bearing surface layer, formed by PMPC grafting, and a cross-linking-strengthened substrate of adequate thickness are essential for increasing the wear and creep deformation resistances.

Fanconi anaemia and the repair of Watson and Crick DNA crosslinks.

Science.gov (United States)

Kottemann, Molly C; Smogorzewska, Agata

2013-01-17

The function of Fanconi anaemia proteins is to maintain genomic stability. Their main role is in the repair of DNA interstrand crosslinks, which, by covalently binding the Watson and the Crick strands of DNA, impede replication and transcription. Inappropriate repair of interstrand crosslinks causes genomic instability, leading to cancer; conversely, the toxicity of crosslinking agents makes them a powerful chemotherapeutic. Fanconi anaemia proteins can promote stem-cell function, prevent tumorigenesis, stabilize replication forks and inhibit inaccurate repair. Recent advances have identified endogenous aldehydes as possible culprits of DNA damage that may induce the phenotypes seen in patients with Fanconi anaemia.

Assessment of UVA-Riboflavin Corneal Cross-Linking Using Small Amplitude Oscillatory Shear Measurements.

Science.gov (United States)

Aslanides, Ioannis M; Dessi, Claudia; Georgoudis, Panagiotis; Charalambidis, Georgios; Vlassopoulos, Dimitris; Coutsolelos, Athanassios G; Kymionis, George; Mukherjee, Achyut; Kitsopoulos, Theofanis N

2016-04-01

The effect of ultraviolet (UV)-riboflavin cross-linking (CXL) has been measured primarily using the strip extensometry technique. We propose a simple and reliable methodology for the assessment of CXL treatment by using an established rheologic protocol based on small amplitude oscillatory shear (SAOS) measurements. It provides information on the average cross-link density and the elastic modulus of treated cornea samples. Three fresh postmortem porcine corneas were used to study the feasibility of the technique, one serving as control and two receiving corneal collagen cross-linking treatment. Subsequently, five pairs of fresh postmortem porcine corneas received corneal collagen cross-linking treatment with riboflavin and UVA-irradiation (370 nm; irradiance of 3 mW/cm2) for 30 minutes (Dresden protocol); the contralateral porcine corneas were used as control samples. After the treatment, the linear viscoelastic moduli of the corneal samples were measured using SAOS measurements and the average cross-linking densities extracted. For all cases investigated, the dynamic moduli of the cross-linked corneas were higher compared to those of the corresponding control samples. The increase of the elastic modulus of the treated samples was between 122% and 1750%. The difference was statistically significant for all tested samples (P = 0.018, 2-tailed t-test). We report a simple and accurate methodology for quantifying the effects of cross-linking on porcine corneas treated with the Dresden protocol by means of SAOS measurements in the linear regime. The measured dynamic moduli, elastic and viscous modulus, represent the energy storage and energy dissipation, respectively. Hence, they provide a means to assess the changing physical properties of the cross-linked collagen networks after CXL treatment.

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.

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

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.

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.

Crosslinking of oriented polyethylene by electron beam radiation. Influence of morphology induced by drawing

International Nuclear Information System (INIS)

Aerle, N.A.J.M. van; Crevecoeur, G.; Lemstra, P.J.

1988-01-01

The influence of drawing on the crosslinking efficiency for electron beam radiation is reported for solution-crystallized ultra-high molecular weight polyethylene. A maximum in crosslinking efficiency is found at a draw ratio of approximately five, indicating an optimum morphology for inducing crosslinks during the hot-drawing process. (author)

Dually cross-linked single network poly(acrylic acid) hydrogels with superior mechanical properties and water absorbency.

Science.gov (United States)

Zhong, Ming; Liu, Yi-Tao; Liu, Xiao-Ying; Shi, Fu-Kuan; Zhang, Li-Qin; Zhu, Mei-Fang; Xie, Xu-Ming

2016-06-28

Poly(acrylic acid) (PAA) hydrogels with superior mechanical properties, based on a single network structure with dual cross-linking, are prepared by one-pot free radical polymerization. The network structure of the PAA hydrogels is composed of dual cross-linking: a dynamic and reversible ionic cross-linking among the PAA chains enabled by Fe(3+) ions, and a sparse covalent cross-linking enabled by a covalent cross-linker (Bis). Under deformation, the covalently cross-linked PAA chains remain intact to maintain their original configuration, while the Fe(3+)-enabled ionic cross-linking among the PAA chains is broken to dissipate energy and then recombined. It is found that the mechanical properties of the PAA hydrogels are significantly influenced by the contents of covalent cross-linkers, Fe(3+) ions and water, which can be adjusted within a substantial range and thus broaden the applications of the hydrogels. Meanwhile, the PAA hydrogels have excellent recoverability based on the dynamic and reversible ionic cross-linking enabled by Fe(3+) ions. Moreover, the swelling capacity of the PAA hydrogels is as high as 1800 times in deionized water due to the synergistic effects of ionic and covalent cross-linkings. The combination of balanced mechanical properties, efficient recoverability, high swelling capacity and facile preparation provides a new method to obtain high-performance hydrogels.

Effect of crosslinking chemistry of albumin/heparin multilayers on FGF-2 adsorption and endothelial cell behavior

Energy Technology Data Exchange (ETDEWEB)

Kumorek, Marta, E-mail: kumorek@imc.cas.cz [Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic v.v.i., Heyrovského Square 2, Prague 162 06 (Czech Republic); Janoušková, Olga, E-mail: janouskova@imc.cas.cz [Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic v.v.i., Heyrovského Square 2, Prague 162 06 (Czech Republic); Höcherl, Anita, E-mail: hocherl@imc.cas.cz [Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic v.v.i., Heyrovského Square 2, Prague 162 06 (Czech Republic); Houska, Milan, E-mail: houska@imc.cas.cz [Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic v.v.i., Heyrovského Square 2, Prague 162 06 (Czech Republic); Mázl-Chánová, Eliška, E-mail: chanova@imc.cas.cz [Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic v.v.i., Heyrovského Square 2, Prague 162 06 (Czech Republic); Kasoju, Naresh, E-mail: naresh.kasoju@eng.ox.ac.uk [Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic v.v.i., Heyrovského Square 2, Prague 162 06 (Czech Republic); Cuchalová, Lucie, E-mail: cuchaloval@gmail.com [Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic v.v.i., Heyrovského Square 2, Prague 162 06 (Czech Republic); and others

2017-07-31

Highlights: • Amine, carboxyl, and induced aldehyde groups of heparin were used for crosslinking of LbL film. • The carbodiimide-mediated cross-linking was the most efficient fixation method. • FGF-2 bound the most effectively to the glutaraldehyde-cross-linked LbL film. • Films cross-linked through carboxyl and aldehyde groups showed a slow FGF-2 release. • FGF-2-loaded LbL films stimulated the HUVECs growth better than the soluble FGF-2. - Abstract: The biomaterials that efficiently deliver growth factors represent an important challenge in cell-based tissue engineering. Layer-by-layer (LbL) thin films are attractive for incorporating controlled amounts of growth factors and releasing them over time. Herein, we investigated the effect of a method of cross-linking of albumin/heparin layer-by-layer (LbL) assembly ((Alb/Hep){sub 3}) on the loading and release of basic fibroblast growth factor (FGF-2), and subsequent proliferation of human endothelial cells (HUVECs). The (Alb/Hep){sub 3} assemblies were cross-linked using glutaraldehyde, reductive amination or carbodiimide chemistries, and then biofunctionalized with FGF-2. The (Alb/Hep){sub 3} assemblies were characterized by the infrared multi-internal reflection spectroscopy, atomic force microscopy, ellipsometry, and surface plasmon resonance (SPR). The FGF-2 loading was quantified by the SPR in situ analysis. Our results showed that the (Alb/Hep){sub 3} cross-linking affected the amount of the bound heparin (from 150 to 315 ng/cm{sup 2}), amount of FGF-2 loaded (from 75 to 125 ng/cm{sup 2}), FGF-2 release (from 15 to 53% over 8 days), and consequently the HUVEC cell proliferation (from 50 to 80 × 10{sup 3} cells/cm{sup 2} at day 5). All FGF-2 loaded assemblies stimulated the cell growth more than a soluble FGF-2 added into the cell media. In particular, the highest HUVECs proliferation was detected on the carbodiimide-cross-linked assembly. Overall, these biocompatible cross-linked assemblies can fine

Adsorption of hexavalent chromium on modified corn stalk using different cross-linking agents

Science.gov (United States)

Chen, Suhong; Zhu, Yi; Han, Zhijun; Feng, Gao; Jia, Yuling; Fu, Kaifang; Yue, Qinyan

2017-12-01

In this study, four different types of adsorbents modified from corn stalk were synthesized after the reaction with epichlorohydrin, N,N-dimethylformamide, triethylamine and different cross-linking agents. The surface functional groups and thermal stability of modified corn stalk (MCSs) were characterized using FTIR and TG analysis, respectively. The feasibility of using MCSs to remove Cr(VI) were evaluated. Adsorption isotherms were determined and modeled with Langmuir, Freundlich and Temkin equations. The experimental results showed that MCS modified using diethylenetriamine (DETA) had the best modification effect, and the adsorption capacity of Cr(VI) reached as high as 227.27 mg/g at 323 K. Thermodynamic study showed that the Cr(VI) adsorption onto MCSs was endothermic processes. As a result, MCS by using DETA as cross-linking agent has good potential for the removal of Cr(VI) from aqueous solutions.

Crosslinked ionic polysaccharides for stimuli-sensitive drug delivery.

Science.gov (United States)

Alvarez-Lorenzo, Carmen; Blanco-Fernandez, Barbara; Puga, Ana M; Concheiro, Angel

2013-08-01

Polysaccharides are gaining increasing attention as components of stimuli-responsive drug delivery systems, particularly since they can be obtained in a well characterized and reproducible way from the natural sources. Ionic polysaccharides can be readily crosslinked to render hydrogel networks sensitive to a variety of internal and external variables, and thus suitable for switching drug release on-off through diverse mechanisms. Hybrids, composites and grafted polymers can reinforce the responsiveness and widen the range of stimuli to which polysaccharide-based systems can respond. This review analyzes the state of the art of crosslinked ionic polysaccharides as components of delivery systems that can regulate drug release as a function of changes in pH, ion nature and concentration, electric and magnetic field intensity, light wavelength, temperature, redox potential, and certain molecules (enzymes, illness markers, and so on). Examples of specific applications are provided. The information compiled demonstrates that crosslinked networks of ionic polysaccharides are suitable building blocks for developing advanced externally activated and feed-back modulated drug delivery systems. Copyright © 2013 Elsevier B.V. All rights reserved.

Thermal and radiation process for nano-/micro-fabrication of crosslinked PTFE

International Nuclear Information System (INIS)

Kobayashi, Akinobu; Oshima, Akihiro; Okubo, Satoshi; Tsubokura, Hidehiro; Takahashi, Tomohiro; Oyama, Tomoko Gowa; Tagawa, Seiichi; Washio, Masakazu

2013-01-01

Nano-/micro-fabrication process of crosslinked poly(tetrafluoroethylene) (RX-PTFE) is proposed as a novel method using combined process which is thermal and radiation process for fabrication of RX-PTFE (TRaf process). Nano- and micro-scale patterns of silicon wafers fabricated by EB lithography were used as the molds for TRaf process. Poly(tetrafluoroethylene) (PTFE) dispersion was dropped on the fabricated molds, and then PTFE was crosslinked with doses from 105 kGy to 1500 kGy in its molten state at 340 °C in nitrogen atmosphere. The obtained nano- and micro-structures by TRaf process were compared with those by the conventional thermal fabrication process. Average surface roughness (R a ) of obtained structures was evaluated with atomic force microscope (AFM) and scanning electron microscope (SEM). R a of obtained structures with the crosslinking dose of 600 kGy showed less than 1.2 nm. The fine nano-/micro-structures of crosslinked PTFE were successfully obtained by TRaf process

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.

Characteristics of heat shrinkable high density polyethylene crosslinked by γ-irradiation

International Nuclear Information System (INIS)

Kang, Phil Hyun; Nho, Young Chang

2001-01-01

The effects of γ-irradiation on the crosslinking of high density polyethylene (HDPE) was investigated for the purpose of obtaining a suitable formulation for heat shrinkable materials. In this study the HDPE specimens were prepared by blending with cross linking agents and pressed into a 0.2 mm sheet at 180 .deg. C. γ-irradiation was conducted at 40 to 100 kGy in nitrogen. The heat shrinkable property and thermal mechanical property of the HDPE sheets have been investigated. It was found that the degree of crosslinking of the irradiated HDPE samples were increased with irradiation dose. Compared with the HDPE containing triallylisocyanurate, the HDPE containing trimethlol propane triacrylate shows a slight increase in crosslinking density. The heat transformation and dimension change of HDPE decreased with increasing radiation dose. The heat shrinkage of the samples increased with increasing annealing temperatures. The thermal resistance of HDPE increased upon the crosslinking of HDPE

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

DEFF Research Database (Denmark)

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

2005-01-01

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

Reduction-responsive interlayer-crosslinked micelles prepared from star-shaped copolymer via click chemistry for drug controlled release

Science.gov (United States)

Dai, Yu; Wang, Hongquan; Zhang, Xiaojin

2017-12-01

To improve the stability of polymeric micelles, here we describe interlayer-crosslinked micelles prepared from star-shaped copolymer via click chemistry. The formation of interlayer-crosslinked micelles was investigated and confirmed by proton nuclear magnetic resonance, Fourier-transform infrared spectroscopy, and fluorescence spectroscopy. The morphology of un-crosslinked micelles and crosslinked micelles observed by transmission electron microscope is both uniform nano-sized spheres (approximately 20 nm). The crosslinking enhances the stability of polymeric micelles and improves the drug loading capacity of polymeric micelles. The interlayer-crosslinked micelles prepared from star-shaped copolymer and a crosslinker containing a disulfide bond are reduction-responsive and can release the drug quickly in the presence of the reducing agents such as glutathione (GSH).

Primary processes in radiation-induced crosslinking of poly(2-phenylbutadiene)

International Nuclear Information System (INIS)

Yamaoka, Hitoshi; Kato, Kazuo; Okamura, Seizo.

1987-01-01

The radiation-induced crosslinking of poly(2-phenylbutadiene)(PPB) in ethylene dichloride solution was studied in vacuum at 303 K. The G value of the crosslinking was estimated to be about 7.2. In order to detect the reaction intermediates under irradiation, optical absorption spectra in rigid matrices and ESR spectra in bulk were measured. The absorption spectra due to radical cation of PPB and due to α,α-disubstituted benzyl cation were observed in butyl chloride glass. ESR spectra owing to polyenyl type radical was found in the irradiated specimens of PPB and Diels-Alder type dimer of 2-phenylbutadiene. The primary processes in radiation-induced crosslinking of PPB were discussed on the basis of the results obtained. (author)

LOX-mediated collagen crosslinking is responsible for fibrosis-enhanced metastasis

DEFF Research Database (Denmark)

Cox, Thomas R; Bird, Demelza; Baker, Ann-Marie

2013-01-01

of metastastic tumor cells. We show that LOX-dependent collagen crosslinking is involved in creating a growth-permissive fibrotic microenvironment capable of supporting metastatic growth by enhancing tumor cell persistence and survival. We show that therapeutic targeting of LOX abrogates not only the extent...... to which fibrosis manifests, but also prevents fibrosis-enhanced metastatic colonization. Finally, we show that the LOX-mediated collagen crosslinking directly increases tumor cell proliferation, enhancing metastatic colonization and growth manifesting in vivo as increased metastasis. This is the first...... time that crosslinking of collagen I has been shown to enhance metastatic growth. These findings provide an important link between ECM homeostasis, fibrosis, and cancer with important clinical implications for both the treatment of fibrotic disease and cancer....

Dipolar cross-linkers for PDMS networks with enhanced dielectric permittivity and low dielectric loss

DEFF Research Database (Denmark)

Bahrt, Frederikke; Daugaard, Anders Egede; Hvilsted, Søren

2013-01-01

-(4-((4-nitrophenyl)diazenyl)phenoxy)-prop-1-yn-1-ylium, with a synthesized silicone compatible azide-functional cross-linker by click chemistry. The thermal, mechanical and electromechanical properties were investigated for PDMS films with 0 to 3.6 wt% of dipole-cross-linker. The relative dielectric permittivity......Dipole grafted cross-linkers were utilized to prepare polydimethylsiloxane (PDMS) elastomers with various chain lengths and with various concentrations of functional cross-linker. The grafted cross-linkers were prepared by reaction of two alkyne-functional dipoles, 1-ethynyl-4-nitrobenzene and 3...

Designing solution-processable air-stable liquid crystalline crosslinkable semiconductors

DEFF Research Database (Denmark)

McCulloch, I.; Bailey, C.; Genevicius, K.

2006-01-01

organic light emitting diode displays, low frequency radio frequency identification tag and other low performance electronics. Organic semiconductors that offer both electrical performance and stability with respect to storage and operation under ambient conditions are required. This work describes...... the development of reactive mesogen semiconductors, which form large crosslinked LC domains on polymerization within mesophases. These crosslinked domains offer mechanical stability and are inert to solvent exposure in further processing steps. Reactive mesogens containing conjugated aromatic cores, designed...

Direct comparison of two albumin-based paclitaxel-loaded nanoparticle formulations: is the crosslinked version more advantageous?

Science.gov (United States)

Li, Chunlei; Li, Yanhui; Gao, Yuqing; Wei, Na; Zhao, Xi; Wang, Caixia; Li, Yongfeng; Xiu, Xian; Cui, Jingxia

2014-07-01

Nanoparticles using albumin as particle matrix have entered the mainstream of drug delivery. It was reported that non-crosslinked albumin nanoparticles were unstable in circulation and could deliver drugs into tumor through gp60/SPARC pathway; in contrast, the delivery of drugs with stable nanoparticles was dependent on enhanced permeability and retention effect. Thus, it is questionable which kind of nanoparticles was more advantageous. Two versions of albumin-bound paclitaxel nanoparticles were prepared. In vitro, the non-crosslinked particles could rapidly disintegrate and the crosslinked was stable. The pharmacokinetics of both formulations was different especially at early time and the non-crosslinked particles were cleared rapidly. After non-crosslinked particle treatment paclitaxel had a tendency to accumulate into heart and kidney and following therapy with the crosslinked particles, paclitaxel was liable to be delivered into lung, spleen and liver. The delivery efficiency of paclitaxel into tumor following the non-crosslinked particle treatment was greater than that of the crosslinked (palbumin nanoparticles. Copyright © 2014 Elsevier B.V. All rights reserved.

Recyclable crosslinked polymer networks with full property recovery made via one-step controlled radical polymerization

Science.gov (United States)

Jin, Kailong; Li, Lingqiao; Torkelson, John

Rubber tires illustrate well the issues ranging from economic loss to environmental problems and sustainability issues that arise with spent, covalently crosslinked polymers. A nitroxide-mediated polymerization (NMP) strategy has been developed that allows for one-step synthesis of recyclable crosslinked polymers from monomers or polymers that contain carbon-carbon double bonds amenable to radical polymerization. Resulting materials possess dynamic alkoxyamine crosslinks that undergo reversible decrosslinking as a function of temperature. Using polybutadiene as starting material, and styrene, an appropriate nitroxide molecule and bifunctional initiator for initial crosslinking, a model for tire rubber can be produced by reaction at temperatures comparable to those employed in tire molding. Upon cooling, the crosslinks are made permanent due to the extraordinarily strong temperature dependence of the reverisible nitroxide capping and uncapping reaction. Based on thermomechanical property characterization, when the original crosslinked model rubber is chopped into bits and remolded in the melt state, a well-consolidated material is obtained which exhibits full recovery of properties reflecting crosslink density after multiple recycling steps.

Intramolecularly Protein-Crosslinked DNA Gels: New Biohybrid Nanomaterials with Controllable Size and Catalytic Activity.

Science.gov (United States)

Zhou, Li; Morel, Mathieu; Rudiuk, Sergii; Baigl, Damien

2017-07-01

DNA micro- and nanogels-small-sized hydrogels made of a crosslinked DNA backbone-constitute new promising materials, but their functions have mainly been limited to those brought by DNA. Here a new way is described to prepare sub-micrometer-sized DNA gels of controllable crosslinking density that are able to embed novel functions, such as an enzymatic activity. It consists of using proteins, instead of traditional base-pairing assembly or covalent approaches, to form crosslinks inside individual DNA molecules, resulting in structures referred to as intramolecularly protein-crosslinked DNA gels (IPDGs). It is first shown that the addition of streptavidin to biotinylated T4DNA results in the successful formation of thermally stable IPDGs with a controllable crosslinking density, forming structures ranging from elongated to raspberry-shaped and pearl-necklace-like morphologies. Using reversible DNA condensation strategies, this paper shows that the gels can be reversibly actuated at a low crosslinking density, or further stabilized when they are highly crosslinked. Finally, by using streptavidin-protein conjugates, IPDGs with various enzymes are successfully functionalized. It is demonstrated that the enzymes keep their catalytic activity upon their incorporation into the gels, opening perspectives ranging from biotechnologies (e.g., enzyme manipulation) to nanomedicine (e.g., vectorization). © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Comparison of femtosecond laser and continuous wave UV sources for protein-nucleic acid crosslinking.

Science.gov (United States)

Fecko, Christopher J; Munson, Katherine M; Saunders, Abbie; Sun, Guangxing; Begley, Tadhg P; Lis, John T; Webb, Watt W

2007-01-01

Crosslinking proteins to the nucleic acids they bind affords stable access to otherwise transient regulatory interactions. Photochemical crosslinking provides an attractive alternative to formaldehyde-based protocols, but irradiation with conventional UV sources typically yields inadequate product amounts. Crosslinking with pulsed UV lasers has been heralded as a revolutionary technique to increase photochemical yield, but this method had only been tested on a few protein-nucleic acid complexes. To test the generality of the yield enhancement, we have investigated the benefits of using approximately 150 fs UV pulses to crosslink TATA-binding protein, glucocorticoid receptor and heat shock factor to oligonucleotides in vitro. For these proteins, we find that the quantum yields (and saturating yields) for forming crosslinks using the high-peak intensity femtosecond laser do not improve on those obtained with low-intensity continuous wave (CW) UV sources. The photodamage to the oligonucleotides and proteins also has comparable quantum yields. Measurements of the photochemical reaction yields of several small molecules selected to model the crosslinking reactions also exhibit nearly linear dependences on UV intensity instead of the previously predicted quadratic dependence. Unfortunately, these results disprove earlier assertions that femtosecond pulsed laser sources provide significant advantages over CW radiation for protein-nucleic acid crosslinking.

Combination of supramolecular cross-linking with covalent cross-linking through epoxide ring-opening including gel studies

NARCIS (Netherlands)

Hofmeier, H.; El-Ghayoury, A.; Schubert, U.S.

2003-01-01

Terpolymers based on poly(methyl methacrylate), containing terpyridinemoieties as well as epoxide groups, were synthesized via free-radical polymerization. The products were cross-linked non-covalently with iron(II) ions and covalently by treatment with AlCl3. Both steps could be combined in

Corneal collagen crosslinking for keratoconus. A review

Directory of Open Access Journals (Sweden)

M. M. Bikbov

2014-10-01

Full Text Available Photochemical crosslinking is widely applied in ophthalmology. Its biochemical effect is due to the release of singlet oxygen that promotes anaerobic photochemical reaction. Keratoconus is one of the most common corneal ectasia affecting 1 in 250 to 250 000 persons. Currently, the rate of iatrogenic ectasia following eximer laser refractive surgery increases due to biomechanical weakening of the cornea. Morphologically and biochemically, ectasia is characterized by corneal layers thinning, contact between the stroma and epithelium resulting from Bowman’s membrane rupture, chromatin fragmentation in keratocyte nuclei, phagocytosis, abnormal staining and arrangement of collagen fibers, enzyme system disorders, and keratocyte apoptosis. In corneal ectasia, altered enzymatic processes result in the synthesis of abnormal collagen. Collagen packing is determined by the activity of various extracellular matrix enzymes which bind amines and aldehydes of collagen fiber amino acids. In the late stage, morphological changes of Descemet’s membrane (i.e., rupture and detachment develop. Abnormal hexagonal-shaped keratocytes and their apoptosis are the signs of endothelial dystrophy. The lack of analogs in domestic ophthalmology encouraged the scientists of Ufa Eye Research Institute to develop a device for corneal collagen crosslinking. The parameters of ultraviolet (i.e., wavelength, exposure time, power to achieve the desired effect were identified. The specifics of some photosensitizers in the course of the procedure were studied. UFalink, a device for UV irradiation of cornea, and photosensitizer Dextralink were developed and adopted. Due to the high risk of endothelial damage, this treatment is contraindicated in severe keratoconus (CCT less than 400 microns. Major effects of corneal collagen crosslinking are the following: Young’s modulus (modulus of elasticity increase by 328.9 % (on average, temperature tolerance increase by 5�

Hydrophilic modification of polyethersulfone porous membranes via a thermal-induced surface crosslinking approach

Energy Technology Data Exchange (ETDEWEB)

Mu Lijun, E-mail: l.j.mu@hotmail.com [School of Material Science and Engineering, Xi' an Jiaotong University, Xi' an 710049 (China); Zhao Wenzhen [School of Material Science and Engineering, Xi' an Jiaotong University, Xi' an 710049 (China)

2009-05-30

A thermal-induced surface crosslinking process was employed to perform a hydrophilic surface modification of PES porous membranes. Difunctional poly(ethylene glycol) diacrylate (PEGDA) was used as the main crosslinking modifier. The addition of trifunctional trimethylolpropane trimethylacrylate (TMPTMA) into the reaction solutions accelerated the crosslinking progress of PEGDA on PES membranes. The membrane surface morphology and chemical composition were characterized by scanning electron microscopy (SEM) and FTIR-ATR spectroscopy. The mass gains (MG) of the modified membranes could be conveniently modulated by varying the PEGDA concentration and crosslinking time. The measurements of water contact angle showed that the hydrophilicity of PES membranes was remarkably enhanced by the coating of crosslinked PEGDA layer. When a moderate mass gain of about 150 {mu}g/cm{sup 2} was reached, both the permeability and anti-fouling ability of PES membranes could be significantly improved. Excessive mass gain not only contributed little to the anti-fouling ability, but also brought a deteriorated permeability to PES membranes.

Hydrophilic modification of polyethersulfone porous membranes via a thermal-induced surface crosslinking approach

International Nuclear Information System (INIS)

Mu Lijun; Zhao Wenzhen

2009-01-01

A thermal-induced surface crosslinking process was employed to perform a hydrophilic surface modification of PES porous membranes. Difunctional poly(ethylene glycol) diacrylate (PEGDA) was used as the main crosslinking modifier. The addition of trifunctional trimethylolpropane trimethylacrylate (TMPTMA) into the reaction solutions accelerated the crosslinking progress of PEGDA on PES membranes. The membrane surface morphology and chemical composition were characterized by scanning electron microscopy (SEM) and FTIR-ATR spectroscopy. The mass gains (MG) of the modified membranes could be conveniently modulated by varying the PEGDA concentration and crosslinking time. The measurements of water contact angle showed that the hydrophilicity of PES membranes was remarkably enhanced by the coating of crosslinked PEGDA layer. When a moderate mass gain of about 150 μg/cm 2 was reached, both the permeability and anti-fouling ability of PES membranes could be significantly improved. Excessive mass gain not only contributed little to the anti-fouling ability, but also brought a deteriorated permeability to PES membranes.

Effect of crosslinking agents on chitosan microspheres in controlled release of diclofenac sodium

OpenAIRE

Gonçalves,Vanessa L.; Laranjeira,Mauro C. M.; Fávere,Valfredo T.; Pedrosa,Rozângela C.

2005-01-01

In this work chitosan microspheres were prepared by the simple coacervation method and crosslinked using epichlorhydrin or glutaraldehyde for the controlled release of diclofenac sodium. The effects of the crosslinking agents on chitosan microspheres over a 12-hour period were assessed with regard to swelling, hydrolysis, porosity, crosslinking, impregnation of diclofenac sodium (DS), and consequently to the release of DS in buffer solutions, simulating the gastrointestinal tract. The degree ...

DNA-protein crosslinks in peripheral lymphocytes of individuals exposed to hexavalent chromium compounds.

Science.gov (United States)

Zhitkovich, A; Lukanova, A; Popov, T; Taioli, E; Cohen, H; Costa, M; Toniolo, P

1996-01-01

Abstract DNA-protein crosslinks were measured in peripheral blood lymphocytes of chrome-platers and controls from Bulgaria in order to evaluate a genotoxic effect of human exposure to carcinogenic Cr(VI) compounds. Chrome-platers and most of the unexposed controls were from the industrial city of Jambol; some additional controls were recruited from the seaside town of Burgas. The chrome-platers had significantly elevated levels of chromium in pre- and post-shift urine, erythrocytes and lymphocytes compared with the control subjects. The largest differences between the two groups were found in erythrocyte chromium concentrations which are considered to be indicative of Cr(VI) exposure. Despite the significant differences in internal chromium doses, levels of DNA-protein crosslinks were not significantly different between the combined controls and exposed workers. Individual DNA-protein crosslinks, however, correlated strongly with chromium in erythrocytes at low and moderate doses but at high exposures, such as among the majority of chrome-platers, these DNA adducts were saturated at maximum levels. The saturation of DNA-protein crosslinks seems to occur at 7-8 μg I-(1) chromium in erythrocytes whereas a mean erythrocyte chromium among the chrome platers was as high as 22.8 μg l(-1). Occupationally unexposed subjects exhibited a significant variability with respect to the erythrocyte chromium concentration, however erythrocyte chromium levels correlated closely with DNA-protein crosslinks in lymphocytes. The controls from Jambol had higher chromium concentrations in erythrocytes and elevated levels of DNA-protein crosslinks compared with Burgas controls. Occupational exposure to formaldehyde among furniture factory workers did not change levels of DNA-protein crosslinks in peripheral lymphocytes. DNA-protein crosslink measurements showed a low intraindividual variability and their levels among both controls and exposed indivduals were not affected by smoking, age

Competition between dewetting and cross-linking in poly(N-vinylpyrrolidone)/polystyrene bilayer films.

Science.gov (United States)

Telford, Andrew M; Thickett, Stuart C; James, Michael; Neto, Chiara

2011-12-06

We investigated the dewetting of metastable poly(N-vinylpyrrolidone) (PNVP) thin films (45 nm) on top of polystyrene (PS) thin films (58 nm) as a function of annealing temperature and molecular weight of PS (96 and 6850 kg/mol). We focused on the competition between dewetting, occurring as a result of unfavorable intermolecular interactions at the PNVP/PS interface, and spontaneous cross-linking of PNVP, occurring during thermal annealing, as we recently reported (Telford, A. M.; James, M.; Meagher, L.; Neto, C. ACS Appl. Mater. Interfaces 2010, 2, 2399-2408). Using optical microscopy, we studied how the dewetting morphology and dynamics at different temperatures depended on the relative viscosity of the top PNVP film, which increased with cross-linking time, and of the bottom PS film. In the PNVP/PS96K system, cross-linking dominated over dewetting at temperatures below 180 °C, reducing drastically nucleated hole density and their maximum size, while above 180 °C the two processes reversed, with complete dewetting occurring at 200 °C. On the other hand, the PNVP/PS6850K system never achieved advanced dewetting stages as the dewetting was slower than cross-linking in the investigated temperature range. In both systems, dewetting of the PNVP films could be avoided altogether by thermally annealing the bilayers at temperatures where cross-linking dominated. The cross-linking was characterized quantitatively using neutron reflectometry, which indicated shrinkage and densification of the PNVP film, and qualitatively through selective removal of the bottom PS film. A simple model accounting for progressive cross-linking during the dewetting process predicted well the observed hole growth profiles and produced estimates of the PNVP cross-linking rate coefficients and of the activation energy of the process, in good agreement with literature values for similar systems. © 2011 American Chemical Society

Low-Temperature Cross-Linking of PEDOT:PSS Films Using Divinylsulfone.

Science.gov (United States)

Mantione, Daniele; Del Agua, Isabel; Schaafsma, Wandert; ElMahmoudy, Mohammed; Uguz, Ilke; Sanchez-Sanchez, Ana; Sardon, Haritz; Castro, Begoña; Malliaras, George G; Mecerreyes, David

2017-05-31

Recent interest in bioelectronics has prompted the exploration of properties of conducting polymer films at the interface with biological milieus. Poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate) (PEDOT:PSS) from a commercially available source has been used as a model system for these studies. Different cross-linking schemes have been used to stabilize films of this material against delamination and redispersion, but the cost is a decrease in the electrical conductivity and/or additional heat treatment. Here we introduce divinylsulfone (DVS) as a new cross-linker for PEDOT:PSS. Thanks to the higher reactiveness of the vinyl groups of DVS, the cross-linking can be performed at room temperature. In addition, DVS does not reduce electronic conductivity of PEDOT:PSS but rather increases it by acting as a secondary dopant. Cell culture studies show that PEDOT:PSS:DVS films are cytocompatible and support neuroregeneration. As an example, we showed that this material improved the transconductance value and stability of an organic electrochemical transistor (OECT) device. These results open the way for the utilization of DVS as an effective cross-linker for PEDOT:PSS in bioelectronics applications.

Comparison between electron-beam and chemical crosslinking of silicone rubber

Energy Technology Data Exchange (ETDEWEB)

Frounchi, Masoud [Polymer Engineering Group, Department of Chemical and Petroleum Engineering, Sharif University of Technology, Azadi Ave, Tehran (Iran, Islamic Republic of)]. E-mail: frounchi@sharif.edu; Dadbin, Susan [Yazd Processing Center, Atomic Energy Organization of Iran, Tehran (Iran, Islamic Republic of); Panahinia, Farhad [Polymer Engineering Group, Department of Chemical and Petroleum Engineering, Sharif University of Technology, Azadi Ave, Tehran (Iran, Islamic Republic of)

2006-02-15

Silicone rubber (SR) was irradiated by electron beam over a dose range of 50-300 kGy in the absence of chemical reagents. Molecular weight between crosslinks (M {sub c}) in the network of SB was determined by two methods of solvent swelling and modulus of elasticity. The network structure of the elastomer crosslinked by electron beam irradiation and chemical vulcanization was compared. Mechanical tests were performed to determine shore hardness, tensile elongation, strength and modulus of the samples. It was found that SR is effectively crosslinked by electron beam irradiation. The tensile strength, hardness, modulus and elongation of irradiated SR were higher than peroxide-crosslinked SR. The optimum dose for the neat rubber was 150 kGy which reduced to 50 kGy with addition of 10 wt.% fumed silica. The synergistic effect of fumed silica was verified by M {sub c} measurements which showed a dramatic decrease in presence of fumed silica in the rubber. The synergism in properties was also verified by comparing the modulus values calculated from the Guth-Smallwood equation and experimental data. Absence of chemical reagents in irradiated SR samples makes them a proper choice for medical applications.

The Evaluation of Corneal Fragility After UVA/Riboflavin Crosslinking.

Science.gov (United States)

Li, Zhiwei; Wang, Yumeng; Xu, Yanyun; Jhanji, Vishal; Zhang, Chunxiao; Mu, Guoying

2017-03-01

To evaluate the fragility of cornea after UVA/riboflavin crosslinking (CXL). Sixty New Zealand rabbits received UVA/riboflavin crosslinking treatment (wavelength 365 nm, irradiance 3.0 mW/cm, and total dose 5.4 J/cm) on right eyes. Animals were sacrificed before and immediately after treatment (day 0), day 1, 3, 7, and 28 after treatment. A 4×10 mm corneal strip for biomechanical evaluation was harvested after sacrifice. The corneal fragility was evaluated by measurement of elongation rate, whereby the elongation rate equals elongation length/baseline length. The Youngs modulus and maximal stress were 1.41±0.51 MPa and 5.56±1.84 MPa before CXL, and increased to 2.31±0.68 MPa (P=0.008) and 9.25±2.74 MPa (P=0.04), respectively, on day 0, then maintained a stable level within a 28 days follow-up. The elongation rate was 62.04±9.34% before CXL and decreased to 48.95%±8.24% (P=0.02) on day 0, then maintained a stable level within a 28 days follow-up. This study showed an increase in the corneal fragility after UVA/riboflavin crosslinking along with an increase in the corneal stiffness. A long-term follow-up should be taken to evaluate the potential deleterious effect of the increasing corneal fragility after UVA/riboflavin crosslinking.

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.

Biohybrid Fibro-Porous Vascular Scaffolds: Effect of Crosslinking on Properties

OpenAIRE

Thomas, Vinoy; Nozik, Danna; Patel, Harsh; Singh, Raj K.; Vohra, Yogesh K.

2015-01-01

Tubular grafts were fabricated from blends of polycaprolactone (PCL) and poly(glycolide -co-caprolactone) (PGC) polymers and coated with an extracellular matrix containing collagens, laminin, and proteoglycans, but not growth factors (HuBiogel™). Multifunctional scaffolds from polymer blends and membrane proteins provide the necessary biomechanics and biological functions for tissue regeneration. Two crosslinking agents, a natural crosslinker namely genipin (Gp) and a carbodiimide reagent nam...

The conformational stability and flexibility of insulin with an additional intramolecular cross-link

International Nuclear Information System (INIS)

Brems, D.N.; Brown, P.L.; Nakagawa, S.H.; Tager, H.S.

1991-01-01

The conformational stability and flexibility of insulin containing a cross-link between the alpha-amino group of the A-chain to the epsilon-amino group of Lys29 of the B-chain was examined. The cross-link varied in length from 2 to 12 carbon atoms. The conformational stability was determined by guanidine hydrochloride-induced equilibrium denaturation and flexibility was assessed by H2O/D2O amide exchange. The cross-link has substantial effects on both conformational stability and flexibility which depend on its length. In general, the addition of a cross-link enhances conformational stability and decreases flexibility. The optimal length for enhanced stability and decreased flexibility was the 6-carbon link. For the 6-carbon link the Gibbs free energy of unfolding was 8.0 kcal/mol compared to 4.5 kcal/mol for insulin, and the amide exchange rate decreased by at least 3-fold. A very short cross-link (i.e. the 2-carbon link) caused conformational strain that was detectable by a lack of stabilization in the Gibbs free energy of unfolding and enhancement in the amide exchange rate compared to insulin. The effect of the cross-link length on insulin hydrodynamic properties is discussed relative to previously obtained receptor binding results

Combination of supramolecular cross-linking with covalent cross-linking through epoxide ring-opening including gel studies

NARCIS (Netherlands)

Hofmeier, H.; El-Ghayoury, A.; Schubert, U.S.

2003-01-01

Terpolymers based on poly(methyl methacrylate), containing terpyridine-moieties as well as epoxide groups, were synthesized via free-radical polymeri-zation. The products were cross-linked non-covalently with iron(II) ions and cova-lently by treatment with AlCl3. Both steps could be combined in

The Effect of Filler-Polymer Interactions on Cold-Crystallization Kinetics in Crosslinked, Silica Filled PDMS/PDPS Copolymer Melts

International Nuclear Information System (INIS)

Chien, A; DeTeresa, S; Thompson, L; Cohenour, R; Balazs, B; Maxwell, R S

2006-01-01

Crystallization in a series of variable crosslink density poly(dimethyl-diphenyl) siloxanes random block copolymers reinforced through a mixture of precipitated and fumed silica fillers has been studied by Differential Scanning Calorimetry (DSC), Dynamic Mechanical Analysis (DMA), and X-ray Diffraction (XRD). The silicone composite studied was composed of 94.6 mol% Dimethoylsiloxane, 5.1 mol% diphenylsiloxane, and 0.3 mol% methyl-vinyl siloxane (which formed crosslinking after a peroxide cure). The polymer was filled with a mixture of 21.6 wt. % fumed silica and 4.0 wt. % precipitated silica previously treated with 6.8 wt. % ethoxy-endblocked siloxane processing aid. The base composite was characterized by a molecular weight between crosslinks in the polymer network of ∼24 kDa and an overall molecular weight (including the influence of the silica fillers) between crosslinks of ∼11 kDa. Molecular weight between crosslinks and filler-polymer interaction strength were then modified by exposure to γ-irradiation in either air or vacuum. The unirradiated material exhibited crystallization at -80 C as measured by DSC with a 16% crystallization as measured by XRD. Isothermal DMA experiments illustrated that crystallization at -85 C occurred over a 1.8 hour period in silica-filled systems and 2.2-2.6 hours in unfilled systems. The onset of crystallization typically occurred after a 30-minute incubation/nucleation period. The crystallization kinetics were dependent on crosslink density. Changes in molecular weight of a factor of two did not, however, change the amount of crystallization. Irradiation in vacuum resulted in faster overall crystallization rates compared to air irradiation for the same crosslink density, likely due to a reduction in the interaction between the polymer chains and the silica filler surface. Modulated differential scanning calorimetry contrasted the crystallization and melting behavior of pure PDMS versus the PDMS/PDPS base copolymer and helped

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.

Hydrophilic crosslinked-polymeric surface capable of effective suppression of protein adsorption

Energy Technology Data Exchange (ETDEWEB)

Kamon, Yuri; Inoue, Naoko; Mihara, Erika; Kitayama, Yukiya; Ooya, Tooru; Takeuchi, Toshifumi, E-mail: takeuchi@gold.kobe-u.ac.jp

2016-08-15

Highlights: • Three hydrophilic crosslinked polymers were examined for protein adsorption. • All polymers showed low nonspecific adsorption of negatively charged proteins. • Poly(MMPC) showed the lowest adsorption for positively charged proteins. • Poly(MMPC) is able to reduce nonspecific adsorption of a wide range of proteins. - Abstract: We investigated the nonspecific adsorption of proteins towards three hydrophilic crosslinked-polymeric thin layers prepared by surface-initiated atom transfer radical polymerization using N,N′-methylenebisacrylamide, 2-(methacryloyloxy)ethyl-[N-(2-methacryloyloxy)ethyl]phosphorylcholine (MMPC), or 6,6′-diacryloyl-trehalose crosslinkers. Protein binding experiments were performed by surface plasmon resonance with six proteins of different pI values including α-lactalbumin, bovine serum albumin (BSA), myoglobin, ribonuclease A, cytochrome C, and lysozyme in buffer solution at pH 7.4. All of the obtained crosslinked-polymeric thin layers showed low nonspecific adsorption of negatively charged proteins at pH 7.4 such as α-lactalbumin, BSA, and myoglobin. Nonspecific adsorption of positively charged proteins including ribonuclease A, cytochrome C, and lysozyme was the lowest for poly(MMPC). These results suggest poly(MMPC) can effectively reduce nonspecific adsorption of a wide range of proteins that are negatively or positively charged at pH 7.4. MMPC is a promising crosslinker for a wide range of polymeric materials requiring low nonspecific protein binding.

Glyoxal Crosslinking of Cell-Seeded Chitosan/Collagen Hydrogels for Bone Regeneration

Science.gov (United States)

Wang, Limin; Stegemann, Jan P.

2011-01-01

Chitosan and collagen are natural biomaterials that have been used extensively in tissue engineering, both separately and as composite materials. Most methods to fabricate chitosan/collagen composites use freeze drying and chemical crosslinking to create stable porous scaffolds, which subsequently can be seeded with cells. In this study, we directly embedded human bone marrow stem cells (hBMSC) in chitosan/collagen materials by initiating gelation using β-glycerophosphate at physiological temperature and pH. We further examined the use of glyoxal, a dialdehyde with relatively low toxicity, to crosslink these materials and characterized the resulting changes in matrix and cell properties. The cytocompatibility of glyoxal and the crosslinked gels were investigated in terms of hBMSC metabolic activity, viability, proliferation, and osteogenic differentiation. These studies revealed that glyoxal was cytocompatible at concentrations below about 1 mM for periods of exposure up to 15 h, though the degree of cell spreading and proliferation were dependent on matrix composition. Glyoxal-crosslinked matrices were stiffer and compacted less than uncrosslinked controls. It was further demonstrated that hBMSC can attach and proliferate in 3D matrices composed of 50/50 chitosan/collagen, and that these materials supported osteogenic differentiation in response to stimulation. Such glyoxal-crosslinked chitosan/collagen composite materials may find utility as cell delivery vehicles for enhancing the repair of bone defects. PMID:21345389

Pressure effects on the crosslinking by gamma radiation of commercial vinil polymers

International Nuclear Information System (INIS)

Lopez V, D.; Burillo, G.

1991-01-01

Gamma-ray induced crosslinking of some commercial polymers was investigated. Polypropylene, polystyrene, polyvinilchloride, polyacrylamide and polyvinilalcohol were compressed to disks and the effect to pressure on the crosslinking was studied. In all the cases, the crosslinking yield increased significantly by compressing the polymers. This is probably because oxygen is removed from polymer by the effect of the pressure and therefore the chain scission is prevented. The effect of pressure is also due to the decrease in the intermolecular distance and thus the coupling of polymer radicals is facilitated. (Author)

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

Recyclable Cu(II)-Coordination Crosslinked Poly(benzimidazolyl pyridine)s as High-Performance Polymers.

Science.gov (United States)

Wang, Cheng; Yang, Li; Chang, Guanjun

2018-03-01

Crosslinked high-performance polymers have many industrial applications, but are difficult to recycle or rework. A novel class of recyclable crosslinking Cu(II)-metallo-supramolecular coordination polymers are successfully prepared, which possess outstanding thermal stability and mechanical property. More importantly, the Cu 2+ coordination interactions can be further removed via external pyrophosphate to recover the linear polymers, which endow the crosslinking polymers with recyclability. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Polymeric Micelles with Ionic Cores Containing Biodegradable Crosslinks for Delivery of Chemotherapeutic Agents

OpenAIRE

Kim, Jong Oh; Sahay, Gaurav; Kabanov, Alexander V.; Bronich, Tatiana K.

2010-01-01

Novel functional polymeric nanocarriers with ionic cores containing biodegradable cross-links were developed for delivery of chemotherapeutic agents. Block ionomer complexes (BIC) of poly(ethylene oxide)-b-poly(methacylic acid) (PEO-b-PMA) and divalent metal cations (Ca2+) were utilized as templates. Disulfide bonds were introduced into the ionic cores by using cystamine as a biodegradable cross-linker. The resulting cross-linked micelles with disulfide bonds represented soft, hydrogel-like n...

Sodium tripolyphosphate cross-linked chitosan based sensor for enhacing sensing properties towards acetone

Science.gov (United States)

Nasution, T. I.; Asrosa, R.; Nainggolan, I.; Balyan, M.; Indah, R.; Wahyudi, A.

2018-02-01

In this report, sensing properties of sodium tripolyphosphate (TPP) cross-linked chitosan based sensor has been successfully enhanced towards acetone. Chitosan solutions were cross-linked with sodium TPP in variation of 0.1%, 0.5%, 1% and 1.5% w/v, respectively. The sensors were fabricated in film form using an electrochemical deposition method. The sensing properties of the sensors were observed by exposing the pure chitosan and sodium TPP cross-linked chitosan sensors towards acetone concentrations of 5, 10, 50, 100 and 200 ppm. The measurement results revealed that the maximum response in output voltage value of pure chitosan sensor was 0.35 V while sodium TPP crosslinked chitosan sensors were above 0.35 V towards 5 ppm acetone concentration. When the sensors were exposed towards acetone concentration of 200 ppm, the maximum response of pure chitosan was 0.45 V while sodium TPP crosslinked chitosan sensors were above 0.45 V. Amongst the variation of sodium TPP, the maximum response of 1% sodium TPP was the highest since the maximum response was 0.4 V and 0.6 V towards 5 ppm and 200 ppm acetone concentration, respectively. While the maximum responses of other sodium TPP concentrations were under 0.4 V and 0.6 V towards 5 ppm and 200 ppm acetone concentration. Moreover, 1% sodium TPP cross-linked chitosan based sensor showed good reproducibility and outstanding lifetime. Therefore, 1% sodium TPP cross-linked chitosan based sensor has exhibited remarkable sensing properties as a novel acetone sensor.

Enhancing the antimony sorption properties of nano titania-chitosan beads using epichlorohydrin as the crosslinker.

Science.gov (United States)

Nishad, Padala Abdul; Bhaskarapillai, Anupkumar; Velmurugan, Sankaralingam

2017-07-15

Antimony is classified as a pollutant of priority importance by USEPA. We have earlier reported the synthesis of nano-titania impregnated epichlorohydrin crosslinked chitosan (TA-Cts-Epi) beads, in a format suitable for large scale applications with high sorption capacity for antimony. To understand the sorption mechanism, and to fine tune the bead composition, the effect of crosslinking density on the swelling and sorption properties of the beads was investigated in detail. Epichlorohydrin effected significant changes in physical and sorption properties of the beads. The antimony sorption capacity of the TA-Cts-Epi beads prepared by crosslinking 0.3g non-crosslinked titania-chitosan beads (TA-Cts-NCL) with 6.4mmol epichlorohydrin was 493μmol/g, while those crosslinked with 0.64mmol showed a capacity of 133μmol/g. Whereas, TA-Cts-NCL beads showed a capacity of 75μmol/g. The increase in uptake capacity with increase in crosslinking demonstrated the active involvement of the epichlorohydrin moieties in antimony binding leading to enhanced sorption. Apart from altering the stability, swelling behaviour and sorption kinetics of the beads, crosslinking significantly increased the uptake of the anionic species via electrostatic interactions. Epichlorohydrin crosslinked chitosan beads prepared without TiO 2 also showed similar behaviour. The results demonstrated the involvement of chitosan, TiO 2 and epichlorohydrin in sorption. Copyright © 2017 Elsevier B.V. All rights reserved.

Novel silicone compatible cross-linkers for controlled functionalization of PDMS networks

DEFF Research Database (Denmark)

Madsen, Frederikke Bahrt; Daugaard, Anders Egede; Hvilsted, Søren

2013-01-01

. In order to improve the dielectric properties of PDMS a novel system is developed where push-pull dipoles are grafted to a new silicone compatible cross-linker. The grafted cross-linkers are prepared by reaction of two different push-pull dipole alkynes as well as a fluorescent alkyne with the new azide...

Photo-crosslinkable polymers for fabrication of photonic multilayer sensors

Science.gov (United States)

Chiappelli, Maria; Hayward, Ryan C.

2013-03-01

We have used photo-crosslinkable polymers to fabricate photonic multilayer sensors. Benzophenone is utilized as a covalently incorporated pendent photo-crosslinker, providing a convenient means of fabricating multilayer films by sequential spin-coating and crosslinking processes. Colorimetric temperature sensors were designed from thermally-responsive, low-refractive index poly(N-isopropylacrylamide) (PNIPAM) and high-refractive index poly(para-methyl styrene) (P pMS). Copolymer chemistries and layer thicknesses were selected to provide robust multilayer sensors which show color changes across nearly the full visible spectrum due to changes in temperature of the hydrated film stack. We have characterized the uniformity and interfacial broadening within the multilayers, the kinetics of swelling and de-swelling, and the reversibility over multiple hydration/dehydration cycles. We also describe how the approach can be extended to alternative sensor designs through the ability to tailor each layer independently, as well as to additional stimuli by selecting alternative copolymer chemistries.

Synthesis and Characterization of Cleavable Core-Cross-Linked Micelles Based on Amphiphilic Block Copolypeptoids as Smart Drug Carriers.

Science.gov (United States)

Li, Ang; Zhang, Donghui

2016-03-14

Amphiphilic block copolypeptoids consisting of a hydrophilic poly(N-ethyl glycine) segment and a hydrophobic poly[(N-propargyl glycine)-r-(N-decyl glycine)] random copolymer segment [PNEG-b-P(NPgG-r-NDG), EPgD] have been synthesized by sequential primary amine-initiated ring-opening polymerization (ROP) of the corresponding N-alkyl N-carboxyanhydride monomers. The block copolypeptoids form micelles in water and the micellar core can be cross-linked with a disulfide-containing diazide cross-linker by copper-mediated alkyne-azide cycloaddition (CuAAC) in aqueous solution. Transmission electron microscopy (TEM) and dynamic light scattering (DLS) analysis revealed the formation of spherical micelles with uniform size for both the core-cross-linked micelles (CCLMs) and non-cross-linked micelles (NCLMs) precursors for selective block copolypeptoid polymers. The CCLMs exhibited increased dimensional stability relative to the NCLMs in DMF, a nonselective solvent for the core and corona segments. Micellar dissociation of CCLMs can be induced upon addition of a reducing agent (e.g., dithiothreitol) in dilute aqueous solutions, as verified by a combination of fluorescence spectroscopy, size exclusion chromatography (SEC), and (1)H NMR spectroscopic measurement. Doxorubicin (DOX), an anticancer drug, can be loaded into the hydrophobic core of CCLMs with a maximal 23% drug loading capacity (DLC) and 37% drug loading efficiency (DLE). In vitro DOX release from the CCLMs can be triggered by DTT (10 mM), in contrast to significantly reduced DOX release in the absence of DTT, attesting to the reductively responsive characteristic of the CCLMs. While the CCLMs exhibited minimal cytotoxicity toward HepG2 cancer cells, DOX-loaded CCLMs inhibited the proliferation of the HepG2 cancer cells in a concentration and time dependent manner, suggesting the controlled release of DOX from the DOX-loaded CCLMS in the cellular environment.

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

International Nuclear Information System (INIS)

Mathapati, Santosh; Bishi, Dillip Kumar; Guhathakurta, Soma; Cherian, Kotturathu Mammen; Venugopal, Jayarama Reddy; Ramakrishna, Seeram; Verma, Rama Shanker

2013-01-01

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

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

Molecular contacts for chlorosome envelope proteins revealed by cross-linking studies with chlorosomes from Chlorobium tepidum

DEFF Research Database (Denmark)

Li, Hui; Frigaard, Niels-Ulrik; Bryant, Donald A

2006-01-01

type and mutants lacking a single chlorosome protein were cross-linked with the zero-length cross-linker 1-ethyl-3-[3-(dimethylamino)propyl]carbodiimide (EDC) and analyzed by gel electrophoresis. Similar cross-linking products were observed when the time and temperature were varied or when EDC...... was replaced with glutaraldehyde. Specific interactions between chlorosome proteins in cross-linked products were identified by immunoblotting with polyclonal antibodies raised against recombinant chlorosome proteins. We confirmed these interactions by demonstrating that these products were missing...... in appropriate mutants. Confirming the location of CsmA in the paracrystalline baseplate, cross-linking showed that CsmA forms dimers, trimers, and homomultimers as large as dodecamers and that CsmA directly interacts with the Fenna-Matthews-Olson protein. Cross-linking further suggests that the precursor form...

Stress-Strain Relation of Tire Rubber Consist of Entangled Polymers, Fillers and Crosslink

Science.gov (United States)

Hagita, Katsumi; Bito, Y.; Minagawa, Y.; Omiya, M.; Morita, H.; Doi, M.; Takano, H.

2009-03-01

We presented a preliminary result of large scale coarse-grained Molecular Dynamics simulation of filled polymer melts with Sulfur-crosslink under an uni-axial deformation by using the Kremer-Grest Model. The size of simulation box under periodic boundary conditions (PBC) is set to about 66nm to consider length of entangled polymer chains, size and structure of fillers, and non-uniform distribution of crosslink. We put 640 polymer chains of 1024 particles and 32 fillers into the PBC box. Each filler consists of 1280 particles of the C1280 fullerene structure. A repulsive force from the center of the filler is applied to the particles. Here, the particles of the fillers are chosen to be the same as the particles of the polymers and the diameter of the filler is about 15nm. The distribution of the fillers used in this simulation is provided by the result of 2d pattern RMC analysis for 2D-USAXS experiments at SPring-8. Sulfur crosslink are randomly distributed in the system. It is found that stress-strain curves estimated by applying a certain uni-axial deformation to the system in simulations are in good agreement with those in experiments. It is successful to show difference on the S-S curve between existence / absence of fillers and qualitative dependence of attractive force between polymer and filler.

Electron beam modification and crosslinking: Influence of nitrile and carboxyl contents and level of unsaturation on structure and properties of nitrile rubber

International Nuclear Information System (INIS)

Vijayabaskar, V.; Tikku, V.K.; Bhowmick, Anil K.

2006-01-01

The structural changes of nitrile rubber with varying nitrile contents, hydrogenated nitrile rubber and carboxylated nitrile rubber in the presence and absence of a polyfunctional monomer, namely trimethylolpropane triacrylate, at different doses of electron beam irradiation, were investigated with the help of FTIR spectroscopy (in the attenuated total reflectance mode), dynamic mechanical thermal analysis and sol-gel analysis. Solid-state NMR with gated high power decoupling technique was used to understand the mechanism of crosslinking of the irradiated samples. The allylic radicals generated in the butadiene chains react to form intermolecular crosslinkages. There was a significant decrease in the concentration of olefinic groups for the nitrile rubber on irradiation. This was also affirmed by the increase in the carbon resonances due to C-C linkages from the NMR technique, indicating more crosslinkages. The spectroscopic crosslink densities were determined and the results were compared with the swelling measurements. The variation in the crosslink clustering for rubbers with different acrylonitrile contents was explained using the NMR technique. The increase in crosslinking was also revealed by the increase in the percent gel content and dynamic storage moduli with radiation doses. The lifetime of spurs formed and the critical dose, an important criterion for overlapping of spurs, were determined for both the grafted and the ungrafted nitrile rubbers of different grades and compared using a mathematical model. The ratio of scissioning to crosslinking for nitrile rubber was determined using Charlesby-Pinner equation. The mechanical properties had also been studied for both the modified and the unmodified systems

Tratamento aditivo do ceratocone por 'crosslinking' do colágeno após implante de anel de Ferrara Addictive treatment of keratoconus with collagen crosslinking after Ferrara ring implant

Directory of Open Access Journals (Sweden)

Edna Almodin

2009-06-01

Full Text Available OBJETIVO: Este trabalho tem como objetivo relatar experiência com utilização do crosslinking após implante de anel intracorneano de Ferrara (Ferrara Ophtalmic visando a melhora refrativa e estabilização corneana. MÉTODOS: Seis pacientes com idade entre 26 e 38 anos foram submetidos ao tratamento com crosslinking após implante de anel de Ferrara. Cinco pacientes receberam 2 segmentos de anel e um paciente recebeu um segmento. Depois de 4 a 55 meses os pacientes foram submetidos a aplicação do "crosslinking" com ultra-violeta de acordo com o protocolo estabelecido por Seiler & cols. RESULTADOS: Quatro olhos apresentaram alteração progressiva da refração e 2 apresentaram refração sem alteração progressiva. A topografia mostrou queda acentuada da curvatura e o estudo da lâmpada de fenda mostrou anel em boa profundidade durante um ano de pós-operatório em 100% dos olhos. A microscopia especular não mostrou alteração significativa e a acuidade visual se mostrou semelhante ao pré-operatório. CONCLUSÃO: O crosslinking poderá ajudar a manter ceratocones estáveis, não-somente nos casos de progressão, mas também nos cones evolutivos com implante de anel.PURPOSE: To describe our experience with crosslinking after Ferrara ring implant for better vision and corneal stabilization. METHODS: six patients with age of 26 - 38 years old had treatment with crosslinking after Ferrara ring implant. Five patients had 2 ring segments implanted and one patient had one segment implanted. After 4 to 55 months the patients were submitted to crosslinking with UVA light according to Seiler et al protocol. RESULTS: Four eyes had progressive alteration of refraction and 2 patients had no alteration of refraction. The topography showed flattener curvature and at the slip lamp 100% of the eyes had good depth after one year post operatively. The specular microscopy didn't show any significant alteration and the visual acuity was similar before the

Biohybrid Fibro-Porous Vascular Scaffolds: Effect of Crosslinking on Properties.

Science.gov (United States)

Thomas, Vinoy; Nozik, Danna; Patel, Harsh; Singh, Raj K; Vohra, Yogesh K

Tubular grafts were fabricated from blends of polycaprolactone (PCL) and poly(glycolide -co-caprolactone) (PGC) polymers and coated with an extracellular matrix containing collagens, laminin, and proteoglycans, but not growth factors (HuBiogel™). Multifunctional scaffolds from polymer blends and membrane proteins provide the necessary biomechanics and biological functions for tissue regeneration. Two crosslinking agents, a natural crosslinker namely genipin (Gp) and a carbodiimide reagent namely 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC), were used for further stabilizing the protein matrix and the effect of crosslinking was evaluated for structural, morphological, mechanical properties using SEM, DSC and DMA. SEM images and fiber diameter distribution showed fiber-size between 0.2 µm to 1 µm with the majority of fiber diameters being under 500 nm, indicating upper range of protein fiber-sizes (for example, collagen fibers in extracellular matrix are in 50 to 500 nm diameter range). HB coating did not affect the mechanical properties, but increased its hydrophilicity of the graft. Overall data showed that PCL/PGC blends with 3:1 mass ratio exhibited mechanical properties comparable to those of human native arteries (tensile strength of 1-2 MPa and Young's modulus of crosslinking on coating stability was investigated to assure the retention of proteins on scaffold for effective cell-matrix interactions.

Effects of genipin corneal crosslinking in rabbit corneas.

Science.gov (United States)

Avila, Marcel Y; Narvaez, Mauricio; Castañeda, Juan P

2016-07-01

To evaluate the effect of genipin, a natural crosslinking agent, in rabbit eyes. Department of Ophthalmology, Universidad Nacional de Colombia Centro de Tecnologia Oftalmica, Bogotá, Colombia. Experimental study. Ex vivo rabbit eyes (16; 8 rabbits) were treated with genipin 1.00%, 0.50%, and 0.25% for 5 minutes with a vacuum device to increase corneal permeability. Penetration was evaluated using Scheimpflug pachymetry (Pentacam). In the in vivo model (20 rabbits; 1 eye treated, 1 eye with vehicle), corneas were crosslinked with genipin as described. Corneal curvature, corneal pachymetry, and intraocular pressure (IOP) assessments as well as slitlamp examinations were performed 0, 7, 30, and 60 days after treatment. In the ex vivo model, Scheimpflug pachymetry showed deep penetration in the rabbit corneas with an increase in corneal density and a dose-dependent relationship. Corneal flattening was observed in treated eyes (mean 4.4 diopters ± 0.5 [SD]) compared with the control eyes. Pachymetry and IOP were stable in all evaluations. No eye showed toxicity in the anterior chamber or in the lens. Corneal crosslinking induced by genipin produced significant flattening of the cornea with no toxicity in rabbit eyes. This crosslinking could be useful in the treatment of corneal ectasia and in the modification of corneal curvature. None of the authors has a financial or proprietary interest in any material or method mentioned. Copyright © 2016 ASCRS and ESCRS. Published by Elsevier Inc. All rights reserved.

177Lu-labeled HPMA copolymers utilizing cathepsin B and S cleavable linkers: Synthesis, characterization and preliminary in vivo investigation in a pancreatic cancer model

International Nuclear Information System (INIS)

Ogbomo, Sunny M.; Shi, Wen; Wagh, Nilesh K.; Zhou, Zhengyuan; Brusnahan, Susan K.; Garrison, Jered C.

2013-01-01

Introduction: A major barrier to the advancement of therapeutic nanomedicines has been the non-target toxicity caused by the accumulation of the drug delivery systems in organs associated with the reticuloendothelial system, particularly the liver and spleen. Herein, we report the development of peptide based metabolically active linkers (MALs) that are enzymatically cleaved by cysteine cathepsin B and S, two proteases highly expressed in the liver and spleen. The overall goal of this approach is to utilize the MALs to lower the non-target retention and toxicity of radiolabeled drug delivery systems, thus resulting in higher diagnostic and radiotherapeutic efficacy. Methods: In this study three MALs (MAL0, MAL1 and MAL2) were investigated. MAL1 and MAL2 are composed of known substrates of cathepsin B and S, respectively, while MAL0 is a non-cleavable control. Both MAL1 and MAL2 were shown to undergo enzymatic cleavage with the appropriate cathepsin protease. Subsequent to conjugation to the HPMA copolymer and radiolabeling with 177 Lu, the peptide–polymer conjugates were renamed 177 Lu-metabolically active copolymers ( 177 Lu-MACs) with the corresponding designations: 177 Lu-MAC0, 177 Lu-MAC1 and 177 Lu-MAC2. Results: In vivo evaluation of the 177 Lu-MACs was performed in an HPAC human pancreatic cancer xenograft mouse model. 177 Lu-MAC1 and 177 Lu-MAC2 demonstrated 3.1 and 2.1 fold lower liver retention, respectively, compared to control ( 177 Lu-MAC0) at 72 h post-injection. With regard to spleen retention, 177 Lu-MAC1 and 177 Lu-MAC2 each exhibited a nearly fourfold lower retention, relative to control, at the 72 h time point. However, the tumor accumulation of the 177 Lu-MAC0 was two to three times greater than 177 Lu-MAC1 and 177 Lu-MAC2 at the same time point. The MAL approach demonstrated the capability of substantially reducing the non-target retention of the 177 Lu-labeled HPMA copolymers. Conclusions: While further studies are needed to optimize the

Bypass of a psoralen DNA interstrand cross-link by DNA polymerases beta, iota, and kappa in vitro

Science.gov (United States)

Smith, Leigh A.; Makarova, Alena V.; Samson, Laura; Thiesen, Katherine E.; Dhar, Alok; Bessho, Tadayoshi

2012-01-01

Repair of DNA inter-strand cross-links in mammalian cells involves several biochemically distinctive processes, including the release of one of the cross-linked strands and translesion DNA synthesis (TLS). In this report, we investigated in vitro TLS activity of psoralen DNA inter-strand cross-link by three DNA repair polymerases, DNA polymerase beta, kappa and iota. DNA polymerase beta is capable of bypassing a psoralen cross-link with a low efficiency. Cell extracts prepared from DNA polymerase beta knockout mouse embryonic fibroblast showed a reduced bypass activity of the psoralen cross-link and purified DNA polymerase beta restored the bypass activity. In addition, DNA polymerase iota mis-incorporated thymine across the psoralen cross-link and DNA polymerase kappa extended these mis-paired primer ends, suggesting that DNA polymerase iota may serve as an inserter and DNA polymerase kappa may play a role as an extender in the repair of psoralen DNA inter-strand cross-links. The results demonstrated here indicate that multiple DNA polymerases could participate in TLS steps in mammalian DNA inter-strand cross-link repair. PMID:23106263

Radiation polymerization and crosslinking of N-isopropylacrylamide in aqueous solution and in solid state

International Nuclear Information System (INIS)

Safranj, A.; Yoshida, Masaru; Omichi, Hideki; Nagaoka, Noriyasu; Kubota, Hitoshi; Katakai, Ryoichi.

1995-01-01

Poly(N-isopropylacrylamide) hydrogels were synthesized by radiation induced simultaneous polymerization and cross-linking. Aqueous monomer solutions and pure monomer, without crosslinker, were irradiated in nitrogen atmosphere at a 60 Co gamma source. The conversion from monomer to polymer and cross-linked gel was investigated as a function of temperature and monomer concentration. The swelling behavior of the gels showed clear dependence on the synthesis conditions. (author)

The comparative safety of genipin versus UVA-riboflavin crosslinking of rabbit corneas

Science.gov (United States)

Song, Wenjing; Tang, Yun; Qiao, Jing; Li, Haili; Rong, Bei; Yang, Songlin; Wu, Yuan

2017-01-01

Purpose To investigate, after 24 h, the safety of genipin or ultraviolet A (UVA)-riboflavin crosslinking of keratocytes and endothelial cells. Methods Fifteen New Zealand white rabbits were selected and divided into a PBS group (five rabbits), a 0.2% genipin crosslinking (GP-CXL) group (five rabbits), and a UVA-riboflavin crosslinking (UVA-CXL) group (five rabbits). In the GP-CXL and PBS groups, 0.2% genipin or PBS was applied to the corneal surface of the right eyes. In the UVA-CXL group, a clinical crosslinking procedure was used. Before and after surgery, the operated eyes of each group were characterized with confocal microscopy, and the corneal buttons were excised for endothelium staining and electron microscopy. Results The corneal endothelial cell density of the GP-CXL, UVA-CLX, and PBS groups changed. There was a statistically significant difference in thickness and changes in corneal endothelial cell density between the UVA-CXL group and the PBS group (pUVA-CXL group and the GP-CXL group (pUVA-CXL group. In the GP-CXL group, only active keratocytes were found and minimal endothelial cell damage. Conclusions Treatment of rabbit corneas with 0.2% genipin showed minimal toxicity toward keratocytes and endothelial cells. Genipin is safer than UVA-CXL for crosslinking of thin corneas. PMID:28761323

CD24 cross-linking induces apoptosis in, and inhibits migration of, MCF-7 breast cancer cells

International Nuclear Information System (INIS)

Kim, Jong Bin; Bae, Ji-Yeon; Jee, Hyeon-Gun; Noh, Dong-Young; Ko, Eunyoung; Han, Wonshik; Lee, Jeong Eon; Lee, Kyung-Min; Shin, Incheol; Kim, Sangmin; Lee, Jong Won; Cho, Jihyoung

2008-01-01

The biological effects of CD24 (FL-80) cross-linking on breast cancer cells have not yet been established. We examined the impact of CD24 cross-linking on human breast cancer cell line MCF-7. MCF-7 and MDA-MB-231 cells were treated with anti-rabbit polyclonal IgG or anti-human CD24 rabbit polyclonal antibodies to induce cross-linking, and then growth was studied. Changes in cell characteristics such as cell cycle modulation, cell death, survival in three-dimensional cultures, adhesion, and migration ability were assayed after CD24 cross-linking in MCF-7. Expression of CD24 was analyzed by flow cytometry in MDA-MB-231 and MCF-7 cells where 2% and 66% expression frequencies were observed, respectively. CD24 cross-linking resulted in time-dependent proliferation reduction in MCF-7 cells, but no reduction in MDA-MB-231 cells. MCF-7 cell survival was reduced by 15% in three-dimensional culture after CD24 cross-linking. Increased MCF-7 cell apoptosis was observed after CD24 cross-linking, but no cell cycle arrest was observed in that condition. The migration capacity of MCF-7 cells was diminished by 30% after CD24 cross-linking. Our results showed that CD24 cross-linking induced apoptosis and inhibited migration in MCF-7 breast cancer cells. We conclude that CD24 may be considered as a novel therapeutic target for breast cancer

The Colibactin Genotoxin Generates DNA Interstrand Cross-Links in Infected Cells

Directory of Open Access Journals (Sweden)

Nadège Bossuet-Greif

2018-03-01

Full Text Available Colibactins are hybrid polyketide-nonribosomal peptides produced by Escherichia coli, Klebsiella pneumoniae, and other Enterobacteriaceae harboring the pks genomic island. These genotoxic metabolites are produced by pks-encoded peptide-polyketide synthases as inactive prodrugs called precolibactins, which are then converted to colibactins by deacylation for DNA-damaging effects. Colibactins are bona fide virulence factors and are suspected of promoting colorectal carcinogenesis when produced by intestinal E. coli. Natural active colibactins have not been isolated, and how they induce DNA damage in the eukaryotic host cell is poorly characterized. Here, we show that DNA strands are cross-linked covalently when exposed to enterobacteria producing colibactins. DNA cross-linking is abrogated in a clbP mutant unable to deacetylate precolibactins or by adding the colibactin self-resistance protein ClbS, confirming the involvement of the mature forms of colibactins. A similar DNA-damaging mechanism is observed in cellulo, where interstrand cross-links are detected in the genomic DNA of cultured human cells exposed to colibactin-producing bacteria. The intoxicated cells exhibit replication stress, activation of ataxia-telangiectasia and Rad3-related kinase (ATR, and recruitment of the DNA cross-link repair Fanconi anemia protein D2 (FANCD2 protein. In contrast, inhibition of ATR or knockdown of FANCD2 reduces the survival of cells exposed to colibactin-producing bacteria. These findings demonstrate that DNA interstrand cross-linking is the critical mechanism of colibactin-induced DNA damage in infected cells.

Hardness enhancement and crosslinking mechanisms in polystyrene irradiated with high energy ion-beams

International Nuclear Information System (INIS)

Lee, E.H.; Rao, G.R.; Mansur, L.K.

1996-01-01

Surface hardness values several times larger than steel were produced using high energy ion beams at several hundred keV to MeV. High LET is important for crosslinking. Crosslinking is studied by analyzing hardness variations in response to irradiation parameter such as ion species, energy, and fluence. Effective crosslinking radii at hardness saturation are derived base on experimental data for 350 keV H + and 1 MeV Ar + irradiation of polystyrene. Saturation value for surface hardness is about 20 GPa

Electrical resistivity of carbon black-filled high-density polyethylene (HDPE) composite containing radiation crosslinked HDPE particles

International Nuclear Information System (INIS)

Lee, M.-G.; Nho, Y.C.

2001-01-01

The room-temperature volume resistivity of high-density polyethylene (HDPE)-carbon black (CB) blends containing previously radiation crosslinked HDPE powder was studied. The results showed that the room-temperature volume resistivity decreases with increasing concentration of crosslinked HDPE powder. It is considered that the crosslinked HDPE particles act as a filler that increases the CB volume fraction in the HDPE matrix. The results of an optical microscope observation indicated that the crosslinked polymer particles are dispersed in the HDPE/CB composite. This effect of the crosslinked particles is attributed to the fact that the crosslinked mesh size of the HDPE particles is so small that the CB particles cannot go inside them. The effect of 60 Co γ-ray and electron beam (EB) irradiation on the positive temperature coefficient, negative temperature coefficient and electrical resistivity behavior of the blends were studied

Mesoscopic simulations of crosslinked polymer networks

NARCIS (Netherlands)

Megariotis, G.; Vogiatzis, G.G.; Schneider, L.; Müller, M.; Theodorou, D.N.

2016-01-01

A new methodology and the corresponding C++ code for mesoscopic simulations of elastomers are presented. The test system, crosslinked ds-1'4-polyisoprene' is simulated with a Brownian Dynamics/kinetic Monte Carlo algorithm as a dense liquid of soft, coarse-grained beads, each representing 5-10 Kuhn

Role of solvent-mediated carbodiimide cross-linking in fabrication of electrospun gelatin nanofibrous membranes as ophthalmic biomaterials

International Nuclear Information System (INIS)

Chou, Shih-Feng; Luo, Li-Jyuan; Lai, Jui-Yang; Ma, David Hui-Kang

2017-01-01

Due to their ability to mimic the structure of extracellular matrix, electrospun gelatin nanofibers are promising cell scaffolding materials for tissue engineering applications. However, the hydrophilic gelatin molecules usually need stabilization before use in aqueous physiological environment. Considering that biomaterials cross-linked via film immersion technique may have a more homogeneous cross-linked structure than vapor phase cross-linking, this work aims to investigate the chemical modification of electrospun gelatin nanofibrous membranes by liquid phase carbodiimide in the presence of ethanol/water co-solvents with varying ethanol concentrations ranging from 80 to 99.5 vol%. The results of characterization showed that increasing water content in the binary reaction solvent system increases the extent of cross-linking of gelatin nanofibers, but simultaneously promotes the effect of biopolymer swelling and distortion in fiber mat structure. As compared to non-cross-linked counterparts, carbodiimide treated gelatin nanofibrous mats exhibited better thermal and biological stability where the shrinkage temperature and resistance to enzymatic degradation varied in response to ethanol/water solvent composition-mediated generation of cross-links. Irrespective of their cross-linking density, all studied membrane samples did not induce any responses in ocular epithelial cell cultures derived from cornea, lens, and retina. Unlike many other cross-linking agents and/or methods (e.g., excessive vapor phase cross-linking) that may pose a risk of toxicity, our study demonstrated that these nanofibrous materials are well tolerated by anterior segment tissues. These findings also indicate the safety of using ethanol/water co-solvents for chemical cross-linking of gelatin to engineer nanofibrous materials with negligible biological effects. In summary, the present results suggest the importance of solvent-mediated carbodiimide cross-linking in modulating structure�

Role of solvent-mediated carbodiimide cross-linking in fabrication of electrospun gelatin nanofibrous membranes as ophthalmic biomaterials

Energy Technology Data Exchange (ETDEWEB)

Chou, Shih-Feng [Department of Mechanical Engineering, University of Texas at Tyler, Tyler, TX 75799 (United States); Luo, Li-Jyuan [Department of Chemical and Materials Engineering, Chang Gung University, Taoyuan 33302, Taiwan, ROC (China); Lai, Jui-Yang, E-mail: jylai@mail.cgu.edu.tw [Institute of Biochemical and Biomedical Engineering, Chang Gung University, Taoyuan 33302, Taiwan, ROC (China); Biomedical Engineering Research Center, Chang Gung University, Taoyuan 33302, Taiwan, ROC (China); Center for Tissue Engineering, Chang Gung Memorial Hospital, Taoyuan 33305, Taiwan, ROC (China); Department of Ophthalmology, Chang Gung Memorial Hospital, Taoyuan 33305, Taiwan, ROC (China); Department of Materials Engineering, Ming Chi University of Technology, New Taipei City 24301, Taiwan, ROC (China); Ma, David Hui-Kang [Center for Tissue Engineering, Chang Gung Memorial Hospital, Taoyuan 33305, Taiwan, ROC (China); Department of Ophthalmology, Chang Gung Memorial Hospital, Taoyuan 33305, Taiwan, ROC (China); Department of Chinese Medicine, Chang Gung University, Taoyuan 33302, Taiwan, ROC (China)

2017-02-01

Due to their ability to mimic the structure of extracellular matrix, electrospun gelatin nanofibers are promising cell scaffolding materials for tissue engineering applications. However, the hydrophilic gelatin molecules usually need stabilization before use in aqueous physiological environment. Considering that biomaterials cross-linked via film immersion technique may have a more homogeneous cross-linked structure than vapor phase cross-linking, this work aims to investigate the chemical modification of electrospun gelatin nanofibrous membranes by liquid phase carbodiimide in the presence of ethanol/water co-solvents with varying ethanol concentrations ranging from 80 to 99.5 vol%. The results of characterization showed that increasing water content in the binary reaction solvent system increases the extent of cross-linking of gelatin nanofibers, but simultaneously promotes the effect of biopolymer swelling and distortion in fiber mat structure. As compared to non-cross-linked counterparts, carbodiimide treated gelatin nanofibrous mats exhibited better thermal and biological stability where the shrinkage temperature and resistance to enzymatic degradation varied in response to ethanol/water solvent composition-mediated generation of cross-links. Irrespective of their cross-linking density, all studied membrane samples did not induce any responses in ocular epithelial cell cultures derived from cornea, lens, and retina. Unlike many other cross-linking agents and/or methods (e.g., excessive vapor phase cross-linking) that may pose a risk of toxicity, our study demonstrated that these nanofibrous materials are well tolerated by anterior segment tissues. These findings also indicate the safety of using ethanol/water co-solvents for chemical cross-linking of gelatin to engineer nanofibrous materials with negligible biological effects. In summary, the present results suggest the importance of solvent-mediated carbodiimide cross-linking in modulating structure�

Radiation-induced crosslinking of short Fiber-filled polytetrafluoroethylene (PTFE)

International Nuclear Information System (INIS)

Oshima, Akihiro; Udagawa, Akira; Morita, Yousuke

1999-02-01

The radiation-induced crosslinking of PTFE mixed with short fibers as glass or carbon fibers was studied for processing the composite materials. The crosslinking behaviors did not change by mixing of the fiber under the irradiation condition in oxygen-free atmosphere at temperature at temperature of 330degC - 350degC. The effect of reinforcement by the fibers in the fabricated composite materials was supposed to be a morphological change of PTFE because and adhesion between PTFE and the fibers was hardly observed in the composite materials. (author)

[Riboflavin UVA crosslinking in progressive keratoconus].

Science.gov (United States)

Maier, P; Reinhard, T

2017-06-01

In patients with keratoconus, a progressive, ectatic disease of the cornea, the shape of the cornea is continuously changing leading to a reduction in visual acuity by progressive myopia and more and more (irregular) astigmatism. The symptomatic treatment consists of the prescription of glasses or special gas-permeable rigid contact lenses. Corneal tomography is generally used for diagnosis. After initial diagnosis of keratoconus, regular tomographic follow-ups should be performed. If clinically significant progression is found and confirmed by repeated measurements, riboflavin UVA collagen crosslinking should be offered to the patients. The aim of riboflavin UVA collagen crosslinking is to halt the progression of the disease to avoid further complications. The therapeutic principle is a combined effect of the photosensitizer riboflavin and UVA light. This stiffening effect of the corneal tissue halts the progression of keratoconus. The efficacy of this treatment has been demonstrated in various randomized, controlled trials.

The involvement of dityrosine crosslinking in α-synuclein assembly and deposition in Lewy Bodies in Parkinson’s disease

Science.gov (United States)

Al-Hilaly, Youssra K.; Biasetti, Luca; Blakeman, Ben J. F.; Pollack, Saskia J.; Zibaee, Shahin; Abdul-Sada, Alaa; Thorpe, Julian R.; Xue, Wei-Feng; Serpell, Louise C.

2016-01-01

Parkinson’s disease (PD) is characterized by intracellular, insoluble Lewy bodies composed of highly stable α-synuclein (α-syn) amyloid fibrils. α-synuclein is an intrinsically disordered protein that has the capacity to assemble to form β-sheet rich fibrils. Oxidiative stress and metal rich environments have been implicated in triggering assembly. Here, we have explored the composition of Lewy bodies in post-mortem tissue using electron microscopy and immunogold labeling and revealed dityrosine crosslinks in Lewy bodies in brain tissue from PD patients. In vitro, we show that dityrosine cross-links in α-syn are formed by covalent ortho-ortho coupling of two tyrosine residues under conditions of oxidative stress by fluorescence and confirmed using mass-spectrometry. A covalently cross-linked dimer isolated by SDS-PAGE and mass analysis showed that dityrosine dimer was formed via the coupling of Y39-Y39 to give a homo dimer peptide that may play a key role in formation of oligomeric and seeds for fibril formation. Atomic force microscopy analysis reveals that the covalent dityrosine contributes to the stabilization of α-syn assemblies. Thus, the presence of oxidative stress induced dityrosine could play an important role in assembly and toxicity of α-syn in PD. PMID:27982082

UV laser-induced histone-DNA crosslinking proceeds via the N-terminal tails

International Nuclear Information System (INIS)

Stefanovski, V.; Dimitrov, S.; Angelov, D.; Keskinova, E.; Pashev, I.

1990-01-01

The covalent crosslinking of histones to DNA by UV laser irradiation is accomplished solely via the N-terminal part of the molecule. Irradiated isolated calfthymus nuclei are treated with clostripain. The crosslinked protein-DNA complexes are isolated and the presence of each core histone analyzed by dot-immunoassay using antibodies, specific to the central globular domain of the respective histone. The reaction is negative for all core histones i.e. the globular domain is absent. It means that this domain has not been crosslinked to DNA and, once cleaved by clostripain, it has been stripped from DNA during the centrigugation in CsCl. This peculiar property of the crosslinked procedure makes it particularly useful in addressing some yet unanswered questions concerning histone-DNA interactions, such as the interaction of the N-terminal tails with linker DNA, the effect of the transient postsynthetic histone acetylation on its interaction with DNA, etc. These questions are now under study. 1 fig., 6 refs