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1

The Inflammation-associated Protein TSG-6 Cross-links Hyaluronan via Hyaluronan-induced TSG-6 Oligomers  

PubMed Central

Tumor necrosis factor-stimulated gene-6 (TSG-6) is a hyaluronan (HA)-binding protein that plays important roles in inflammation and ovulation. TSG-6-mediated cross-linking of HA has been proposed as a functional mechanism (e.g. for regulating leukocyte adhesion), but direct evidence for cross-linking is lacking, and we know very little about its impact on HA ultrastructure. Here we used films of polymeric and oligomeric HA chains, end-grafted to a solid support, and a combination of surface-sensitive biophysical techniques to quantify the binding of TSG-6 into HA films and to correlate binding to morphological changes. We find that full-length TSG-6 binds with pronounced positive cooperativity and demonstrate that it can cross-link HA at physiologically relevant concentrations. Our data indicate that cooperative binding of full-length TSG-6 arises from HA-induced protein oligomerization and that the TSG-6 oligomers act as cross-linkers. In contrast, the HA-binding domain of TSG-6 (the Link module) alone binds without positive cooperativity and weaker than the full-length protein. Both the Link module and full-length TSG-6 condensed and rigidified HA films, and the degree of condensation scaled with the affinity between the TSG-6 constructs and HA. We propose that condensation is the result of protein-mediated HA cross-linking. Our findings firmly establish that TSG-6 is a potent HA cross-linking agent and might hence have important implications for the mechanistic understanding of the biological function of TSG-6 (e.g. in inflammation). PMID:21596748

Baranova, Natalia S.; Nilebäck, Erik; Haller, F. Michael; Briggs, David C.; Svedhem, Sofia; Day, Anthony J.; Richter, Ralf P.

2011-01-01

2

Incorporation of pentraxin 3 into hyaluronan matrices is tightly regulated and promotes matrix cross-linking.  

PubMed

Mammalian oocytes are surrounded by a highly hydrated hyaluronan (HA)-rich extracellular matrix with embedded cumulus cells, forming the cumulus cell·oocyte complex (COC) matrix. The correct assembly, stability, and mechanical properties of this matrix, which are crucial for successful ovulation, transport of the COC to the oviduct, and its fertilization, depend on the interaction between HA and specific HA-organizing proteins. Although the proteins inter-?-inhibitor (I?I), pentraxin 3 (PTX3), and TNF-stimulated gene-6 (TSG-6) have been identified as being critical for COC matrix formation, its supramolecular organization and the molecular mechanism of COC matrix stabilization remain unknown. Here we used films of end-grafted HA as a model system to investigate the molecular interactions involved in the formation and stabilization of HA matrices containing TSG-6, I?I, and PTX3. We found that PTX3 binds neither to HA alone nor to HA films containing TSG-6. This long pentraxin also failed to bind to products of the interaction between I?I, TSG-6, and HA, among which are the covalent heavy chain (HC)·HA and HC·TSG-6 complexes, despite the fact that both I?I and TSG-6 are ligands of PTX3. Interestingly, prior encounter with I?I was required for effective incorporation of PTX3 into TSG-6-loaded HA films. Moreover, we demonstrated that this ternary protein mixture made of I?I, PTX3, and TSG-6 is sufficient to promote formation of a stable (i.e. cross-linked) yet highly hydrated HA matrix. We propose that this mechanism is essential for correct assembly of the COC matrix and may also have general implications in other inflammatory processes that are associated with HA cross-linking. PMID:25190808

Baranova, Natalia S; Inforzato, Antonio; Briggs, David C; Tilakaratna, Viranga; Enghild, Jan J; Thakar, Dhruv; Milner, Caroline M; Day, Anthony J; Richter, Ralf P

2014-10-31

3

Solution Cross-Linked Poly(isobutylene) Gels: Synthesis and Swelling Behavior  

Microsoft Academic Search

We prepared several series of PIB gels starting from butyl rubber in dilute toluene solutions using sulfur monochloride as a cross-linking agent. By using solution and suspension cross-linking techniques, PIB gels in the form of rods or beads in the size range of 0.1-2 mm were prepared and subjected to swelling in solvent-nonsolvent mixtures. The swelling capacity of the gels

Oguz Okay; Selda Durmaz; Burak Erman

2000-01-01

4

Photo-initiated cross-linked polyacrylamide gels for microdevice electrophoresis  

E-print Network

Photo-polymerized cross-linked polyacrylamide gels are becoming increasingly important for use in micro-fabricated DNA electrophoresis systems because they allow a concentrated sieving matrix to be precisely positioned at any location within a...

Agrawal, Shilpa

2005-08-29

5

Cross-linking cellulose nanofibrils for potential elastic cryo-structured gels  

NASA Astrophysics Data System (ADS)

Cellulose nanofibrils were produced from P. radiata kraft pulp fibers. The nanofibrillation was facilitated by applying 2,2,6,6-tetramethylpiperidinyl-1-oxyl-mediated oxidation as pretreatment. The oxidized nanofibrils were cross-linked with polyethyleneimine and poly N-isopropylacrylamide- co-allylamine- co-methylenebisacrylamide particles and were frozen to form cryo-structured gels. Samples of the gels were critical-point dried, and the corresponding structures were assessed with scanning electron microscopy. It appears that the aldehyde groups in the oxidized nanofibrils are suitable reaction sites for cross-linking. The cryo-structured materials were spongy, elastic, and thus capable of regaining their shape after a given pressure was released, indicating a successful cross-linking. These novel types of gels are considered potential candidates in biomedical and biotechnological applications.

Syverud, Kristin; Kirsebom, Harald; Hajizadeh, Solmaz; Chinga-Carrasco, Gary

2011-12-01

6

Ionically cross-linked hyaluronic acid: wetting, lubrication, and viscoelasticity of a modified adhesion barrier gel  

PubMed Central

Hyaluronic acid (HA), in linear or cross-linked form, is a common component of cosmetics, personal care products, combination medical products, and medical devices. In all cases, the ability of the HA solution or gel to wet surfaces and/or disrupt and lubricate interfaces is a limiting feature of its mechanism of action. We synthesized ferric ion–cross-linked networks of HA based on an adhesion barrier, varied the degree of cross-linking, and performed wetting goniometry, viscometry, and dynamic mechanical analysis. As cross-linking increases, so do contact angle, viscosity, storage modulus, and loss modulus; thus, wetting and lubrication are compromised. These findings have implications in medical device materials, such as adhesion barriers and mucosal drug delivery vehicles. PMID:22915924

Vorvolakos, Katherine; Isayeva, Irada S; Luu, Hoan-My Do; Patwardhan, Dinesh V; Pollack, Steven K

2011-01-01

7

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

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

8

Swelling Properties of Physically Cross-linked PVA Gels Prepared by a Cast-drying Method  

NASA Astrophysics Data System (ADS)

We report the swelling properties of physically cross-linked polyvinyl alcohol (PVA) hydrogels prepared by a cast-drying method. The swelling ratio of PVA cast gel in its swollen state decreased after repeated processes of water exchange with drying. The measurements using a Fourier Transform Infrared Spectroscopy and X-ray diffraction suggested that the hydrogen bonds were additionally formed during the process of water exchange with drying. We concluded that non-cross-linked polymers with low molecular weight eluted into the solvent by water exchange and additional hydrogen bonds were formed during the dehydration, which resulted in the decrement of the water content in the swollen state.

Otsuka, Emiko; Suzuki, Atsushi

9

Preparation of single or double-network chitosan/poly(vinyl alcohol) gel films through selective cross-linking method  

Technology Transfer Automated Retrieval System (TEKTRAN)

A selective cross-linking method was developed to create single or double network chitosan/poly(vinyl alcohol) gel films. The cross-linking is based on the hydrogen bonding between PVA and borate and the strong electrostatic interaction between chitosan and tripolyphosphate. The resultant gel films ...

10

Protein determination of cells immobilized in cross-linked synthetic gels  

Microsoft Academic Search

An assay for the determination of the protein content of whole cells immobilized in cross-linked synthetic gels was developed. The assay is based on a three step procedure: a) methanol dehydration, b) protein extraction by 1.0 M alkali at 125°C c) colorimetric assay of the extracted protein according to Bradford's procedure (Bradford M. M. (1976), Anal. Biochem. 72:248–254). The procedure

A. Freeman; T. Blank; Y. Aharonowitz

1982-01-01

11

Swelling Properties of Physically Cross-linked PVA Gels Prepared by a Cast-drying Method  

Microsoft Academic Search

\\u000a We report the swelling properties of physically cross-linked polyvinyl alcohol (PVA) hydrogels prepared by a cast-drying method.\\u000a The swelling ratio of PVA cast gel in its swollen state decreased after repeated processes of water exchange with drying.\\u000a The measurements using a Fourier Transform Infrared Spectroscopy and X-ray diffraction suggested that the hydrogen bonds were\\u000a additionally formed during the process of

Emiko Otsuka; Atsushi Suzuki

2009-01-01

12

Phase diagram of selectively cross-linked block copolymers shows chemically microstructured gel  

NASA Astrophysics Data System (ADS)

We study analytically the intricate phase behavior of cross-linked AB diblock copolymer melts, which can undergo two main phase transitions due to quenched random constraints. Gelation, i.e., spatially random localisation of polymers forming a system-spanning cluster, is driven by increasing the number parameter ? of irreversible, type-selective cross-links between random pairs of A blocks. Self-assembly into a periodic pattern of A/B-rich microdomains (microphase separation) is controlled by the AB incompatibility ? inversely proportional to temperature. Our model aims to capture the system's essential microscopic features, including an ensemble of random networks that reflects spatial correlations at the instant of cross-linking. We identify suitable order parameters and derive a free-energy functional in the spirit of Landau theory that allows us to trace a phase diagram in the plane of ? and ?. Selective cross-links promote microphase separation at higher critical temperatures than in uncross-linked diblock copolymer melts. Microphase separation in the liquid state facilitates gelation, giving rise to a novel gel state whose chemical composition density mirrors the periodic AB pattern.

von der Heydt, Alice; Zippelius, Annette

2015-02-01

13

Phase diagram of selectively cross-linked block copolymers shows chemically microstructured gel  

E-print Network

We study analytically the intricate phase behavior of cross-linked $AB$ diblock copolymer melts, which can undergo two main phase transitions due to quenched random constraints: Gelation, i.e., spatially random localization of polymers forming a system-spanning cluster, is driven by increasing the number parameter $\\mu$ of irreversible, type-selective cross-links between random pairs of $A$ blocks. Self-assembly into a periodic pattern of $A$/$B$-rich microdomains (microphase separation) is controlled by the $AB$ incompatibility $\\chi$ inversely proportional to temperature. Our model aims to capture the system's essential microscopic features, including an ensemble of random networks that reflects spatial correlations at the instant of cross-linking. We identify suitable order parameters and derive a free-energy functional in the spirit of Landau theory that allows us to trace a phase diagram in the plane of $\\mu$ and $\\chi$. Selective cross-links promote microphase separation at higher critical temperatures than in uncross-linked diblock copolymer melts. Microphase separation in the liquid state facilitates gelation, giving rise to a novel gel state whose chemical composition density mirrors the periodic $AB$ pattern.

Alice von der Heydt; Annette Zippelius

2014-09-29

14

Oxidation increases mucin polymer cross-links to stiffen airway mucus gels.  

PubMed

Airway mucus in cystic fibrosis (CF) is highly elastic, but the mechanism behind this pathology is unclear. We hypothesized that the biophysical properties of CF mucus are altered because of neutrophilic oxidative stress. Using confocal imaging, rheology, and biochemical measures of inflammation and oxidation, we found that CF airway mucus gels have a molecular architecture characterized by a core of mucin covered by a web of DNA and a rheological profile characterized by high elasticity that can be normalized by chemical reduction. We also found that high levels of reactive oxygen species in CF mucus correlated positively and significantly with high concentrations of the oxidized products of cysteine (disulfide cross-links). To directly determine whether oxidation can cross-link mucins to increase mucus elasticity, we exposed induced sputum from healthy subjects to oxidizing stimuli and found a marked and thiol-dependent increase in sputum elasticity. Targeting mucin disulfide cross-links using current thiol-amino structures such as N-acetylcysteine (NAC) requires high drug concentrations to have mucolytic effects. We therefore synthesized a thiol-carbohydrate structure (methyl 6-thio-6-deoxy-?-d-galactopyranoside) and found that it had stronger reducing activity than NAC and more potent and fast-acting mucolytic activity in CF sputum. Thus, oxidation arising from airway inflammation or environmental exposure contributes to pathologic mucus gel formation in the lung, which suggests that it can be targeted by thiol-modified carbohydrates. PMID:25717100

Yuan, Shaopeng; Hollinger, Martin; Lachowicz-Scroggins, Marrah E; Kerr, Sheena C; Dunican, Eleanor M; Daniel, Brian M; Ghosh, Sudakshina; Erzurum, Serpel C; Willard, Belinda; Hazen, Stanley L; Huang, Xiaozhu; Carrington, Stephen D; Oscarson, Stefan; Fahy, John V

2015-02-25

15

Oxidation increases mucin polymer cross-links to stiffen airway mucus gels  

PubMed Central

Airway mucus in cystic fibrosis (CF) is highly elastic, but the mechanism behind this pathology is unclear. We hypothesized that the biophysical properties of CF mucus are altered because of neutrophilic oxidative stress. Using confocal imaging, rheology, and biochemical measures of inflammation and oxidation, we found that CF airway mucus gels have a molecular architecture characterized by a core of mucin covered by a web of DNA and a rheological profile characterized by high elasticity that can be normalized by chemical reduction. We also found that high levels of reactive oxygen species in CF mucus correlated positively and significantly with high concentrations of the oxidized products of cysteine (disulfide cross-links). To directly determine whether oxidation can cross-link mucins to increase mucus elasticity, we exposed induced sputum from healthy subjects to oxidizing stimuli and found a marked and thiol-dependent increase in sputum elasticity. Targeting mucin disulfide cross-links using current thiol-amino structures such as N-acetylcysteine (NAC) requires high drug concentrations to have mucolytic effects. We therefore synthesized a thiol-carbohydrate structure (methyl 6-thio-6-deoxy-?-D-galactopyranoside) and found that it had stronger reducing activity than NAC and more potent and fast-acting mucolytic activity in CF sputum. Thus, oxidation arising from airway inflammation or environmental exposure contributes to pathologic mucus gel formation in the lung, which suggests that it can be targeted by thiol-modified carbohydrates. PMID:25717100

Yuan, Shaopeng; Hollinger, Martin; Lachowicz-Scroggins, Marrah E.; Kerr, Sheena C.; Dunican, Eleanor M.; Daniel, Brian M.; Ghosh, Sudakshina; Erzurum, Serpel C.; Willard, Belinda; Hazen, Stanley L.; Huang, Xiaozhu; Carrington, Stephen D.; Oscarson, Stefan; Fahy, John V.

2015-01-01

16

Chitin microfibers reinforce soy protein gels cross-linked by transglutaminase.  

PubMed

To improve the gel strength, we attempt to introduce the microcomposite concept into the food gel system. A stable positively charged chitin microfibers (CMFs) suspension was fabricated by a facile microfluidizer approach without changing its chemical structure. The obtained CMFs bearing width of about 0.5-5 ?m and length of more than 500 ?m were then developed in a transglutaminase cross-linked ?-conglycinin (7S) gel. The morphological and rheological characterizations of the 7S-CMF composited gels were done as a function of the protein and CMFs concentrations. Results showed that the presence of the CMFs network improved the gel strength significantly. This effect was CMFs content dependent and was related to the formation of a sponge-like porous microstructure. We inferred that the CMFs provided an initial framework for gel formation and added structural rigidity to the protein gel. The role of protein was to participate in network development as an electrostatic coating and gelation component. PMID:24766388

Yuan, Yang; Sun, Ying-En; Wan, Zhi-Li; Yang, Xiao-Quan; Wu, Jun-Feng; Yin, Shou-Wei; Wang, Jin-Mei; Guo, Jian

2014-05-14

17

MALDI analysis of proteins after extraction from dissolvable ethylene glycol diacrylate cross-linked polyacrylamide gels.  

PubMed

Although the extraction of intact proteins from polyacrylamide gels followed by mass spectrometric molecular mass determination has been shown to be efficient, there is room for alternative approaches. Our study evaluates ethylene glycol diacrylate, a cleavable cross-linking agent used for a new type of dissolvable gels. It attains an ester linkage that can be hydrolyzed in alkali conditions. The separation performance of the new gel system was tested by 1D and 2D SDS-PAGE using the outer chloroplast envelope of Pisum sativum as well as a soluble protein fraction of human lymphocytes, respectively. Gel spot staining (CBB), dissolving, and extracting were conducted using a custom-developed workflow. It includes protein extraction with an ammonia-SDS buffer followed by methanol treatment to remove acrylamide filaments. Necessary purification for MALDI-TOF analysis was implemented using methanol-chloroform precipitation and perfusion HPLC. Both cleaning procedures were applied to several standard proteins of different molecular weight as well as 'real' biological samples (8-75 kDa). The protein amounts, which had to be loaded on the gel to detect a peak in MALDI-TOF MS, were in the range of 0.1 to 5 ?g, and the required amount increased with increasing mass. PMID:23775326

Papasotiriou, Dimitrios G; Markoutsa, Stavroula; Gorka, Jan; Schleiff, Enrico; Karas, Michael; Meyer, Bjoern

2013-09-01

18

Citrate cross-linked gels with strain reversibility and viscoelastic behavior accelerate healing of osteochondral defects in a rabbit model.  

PubMed

Most living tissues are viscoelastic in nature. Self-repair due to the dissipation of energy by reversible bonds prevents the rupture of the molecular backbone in these tissues. Recent studies, therefore, have aimed to synthesize biomaterials that approximate the mechanical performance of biological materials with self-recovery properties. We report an environmentally friendly method for the development of ionotropically cross-linked viscoelastic chitosan gels with a modulus comparable to that of living tissues. The strain recovery property was found to be highest for the gels with the lowest cross-linking density. The force-displacement curve showed significant hysteresis due to the presence of reversible bonds in the cross-linked gels. Nanoindentation studies demonstrated the creep phenomenon for the cross-linked chitosan gels. Creep, hysteresis, and plasticity index confirmed the viscoelastic behavior of the cross-linked gels. The viscoelastic gels were implanted at osteochondral defect sites to assess the tissue regeneration ability. In vivo results demonstrated early cartilage formation and woven bone deposition for defects filled with the gels compared to nontreated defects. PMID:24971647

Ghosh, Paulomi; Rameshbabu, Arun Prabhu; Dhara, Santanu

2014-07-22

19

Properties of collagen gels cross-linked by N-hydroxysuccinimide activated adipic acid deriviate.  

PubMed

In order to improve the properties of collagen gel, N-hydroxysuccinimide activated adipic acid derivative (NHS-AA) was introduced into the formation of collagen fibrils. NHS-AA with different [NHS-AA]/[NH2] ratios (0.1-1.5, calculated by [ester group] of NHS-AA and [NH2] of lysine and hydroxylysine residues of collagen) was added after, simultaneously with or before the formation of collagen fibrils (abbreviated CAF, CSF and CBF, respectively) to obtain different collagen gels. With the same dose of NHS-AA, the cross-linking degree for CAF was lower than those for CSF and CBF. The formation of collagen fibrils was restrained by NHS-AA for CSF and CBF while that for CAF was unaffected. When the dose of NHS-AA increased from 0.1 to 1.5, the water contents of CSF and CBF increased while that of CAF had no obvious change. With lower dose of NHS-AA (0.1), CAF possessed higher value of G' (87.3Pa) and the best thermal stability (47.6°C). As the ratio of [NHS-AA]/[NH2] increased to 1.5, CSF had the maximum value of G' (288.8Pa) and CAF had the best thermal stability (52.9°C). These results showed collagen gels with different properties could be prepared by adding NHS-AA with different adding sequence and dose. PMID:24933521

Duan, Lian; Liu, Wentao; Tian, Zhenhua; Li, Conghu; Li, Guoying

2014-08-01

20

Cross-linking by protein oxidation in the rapidly setting gel-based glues of slugs  

PubMed Central

SUMMARY The terrestrial slug Arion subfuscus secretes a glue that is a dilute gel with remarkable adhesive and cohesive strength. The function of this glue depends on metals, raising the possibility that metal-catalyzed oxidation plays a role. The extent and time course of protein oxidation was measured by immunoblotting to detect the resulting carbonyl groups. Several proteins, particularly one with a relative molecular mass (Mr) of 165×103, were heavily oxidized. Of the proteins known to distinguish the glue from non-adhesive mucus, only specific size variants were oxidized. The oxidation appears to occur within the first few seconds of secretion. Although carbonyls were detected by 2,4-dinitrophenylhydrazine (DNPH) in denatured proteins, they were not easily detected in the native state. The presence of reversible cross-links derived from carbonyls was tested for by treatment with sodium borohydride, which would reduce uncross-linked carbonyls to alcohols, but stabilize imine bonds formed by carbonyls and thus lead to less soluble complexes. Consistent with imine bond formation, sodium borohydride led to a 20–35% decrease in the amount of soluble protein with a Mr of 40–165 (×103) without changing the carbonyl content per protein. In contrast, the nucleophile hydroxylamine, which would competitively disrupt imine bonds, increased protein solubility in the glue. Finally, the primary amine groups on a protein with a Mr of 15×103 were not accessible to acid anhydrides. The results suggest that cross-links between aldehydes and primary amines contribute to the cohesive strength of the glue. PMID:21525316

Bradshaw, Andrew; Salt, Michael; Bell, Ashley; Zeitler, Matt; Litra, Noelle; Smith, Andrew M.

2011-01-01

21

Gels of hydrophobically modified hydroxyethyl cellulose cross-linked by amylose. Competition with cyclodextrin.  

PubMed

Previous work has shown that amylose (AM) can cross-link hydrophobically modified polymers by inclusion complexation, whereby thermoreversible cold-setting gels are formed. In this work, the competition between AM and cyclodextrin (CD) for the formation of inclusion complexes with hydrophobically modified hydroxyethyl cellulose (HMHEC) is investigated. A detailed study of viscosity, NMR self-diffusion, and chemical shifts of the two-component mixture, CD and HMHEC, was performed. The results imply that 2:1 (CD:polymer hydrophobe) complexes may be formed. The three-component mixtures, HMHEC/AM/CD, were investigated by rheology, NMR self-diffusion, and intensities of the NMR resonance peaks. The CD molecules competed efficiently with the AM molecules, as seen by a decreased storage modulus, an increased self-diffusion of AM and HMHEC, and increased NMR intensities of the HMHEC hydrophobes, as the concentration of CD increased in the solution. A high concentration of CD is needed in the mixtures to inhibit all interactions between HMHEC and AM, and it was shown that there still is an effect of AM at excess CD concentration in the mixtures. PMID:16489813

Karlberg, Maria; Piculell, Lennart; Ragout, Sylvaine

2006-02-28

22

Pig vitreous gel: macromolecular composition with particular reference to hyaluronan-binding proteoglycans  

Microsoft Academic Search

The aim of this study was to examine the macromolecular composition of pig vitreous body with particular emphasis on hyaluronan-binding proteoglycans. The whole pig vitreous gel was found to contain 76 ?g of hyaluronan-derived uronic acid, 700 ?g of total protein and 150 ?g of collagen per ml of gel. The contents of neutral hexoses and sialic acids were 80 and 22 ?g\\/ml of vitreous

Argiris V Noulas; Achilleas D Theocharis; Elias Feretis; Nickoletta Papageorgakopoulou; Nikos K Karamanos; Dimitrios A Theocharis

2002-01-01

23

Gels of hydrophobically modified ethyl(hydroxyethyl) cellulose cross-linked by amylose: effects of hydrophobe architecture.  

PubMed

Previous work has shown that amylose (AM) can cross-link hydrophobically modified polymers by inclusion complexation, whereby thermoreversible cold-setting gels are formed. Here we investigate the complexation of AM with different samples of hydrophobically modified ethyl(hydroxyethyl) cellulose (HMEHEC), distinguished by differences in the architecture of the hydrophobes (the hydrophobic side chains). All hydrophobes, except one, were based on linear alkyl chains, but with varying chain lengths (C12-C14). In addition, some samples contained short hydrophilic "spacers", consisting of 2-5 ethylene oxide units, between the alkyl chains and the EHEC backbone. Gels of varying strength were obtained for the different AM/HMEHEC samples. The alkyl chain length seemed to be the major factor affecting the gel strength, with longer alkyl chains giving stronger gels. For similar alkyl chain lengths, stronger gels were obtained when a spacer was present. Addition of AM caused a small increase of the cloud points of HMEHECs with C14 hydrophobes in water. Time-dependent effects and effects of the sample preparation procedure were also investigated. The reversibility of the gelation with respect to shear was confirmed. A gel destroyed by added surfactant was shown to reform on removal of the surfactant by dialysis. PMID:15835672

Egermayer, Monica; Karlberg, Maria; Piculell, Lennart

2004-03-16

24

Mixed photo-cross-linked polyvinyl alcohol and calcium-alginate gels for cell entrapment  

Microsoft Academic Search

Living cells may be immobilized by gel entrapment under very mild conditions. The ionotropic gelation of alginate with bivalent cations such as Ca2+, as well as photo-induced gelation of polyvinyl alcohol (PVA) bearing photosensitive stilbazolium (SbQ) groups, are procedures that are compatible with most bioactive materials. In the search for more stable and stronger alginate gel beads, experiments have been

S. Hertzberg; E. Moen; C. Vogelsang; K. Østgaard

1995-01-01

25

Calcium-alginate gel bead cross-linked with gelatin as microcarrier for anchorage-dependent cell culture.  

PubMed

Valuable products obtainedfrom the cultivation of anchorage-dependent mammalian cells require large-scale processes to obtain commercially useful quantities. It is generally accepted that suspension culture is the ideal mode of operation. Because anchorage-dependent cells need surfaces to be able to attach and spread, the incorporation of microcarriers to suspension culture is indispensable. Since the dextran-based microcarrier wasfirst introduced, many different types of microcarriers have been developed and commercialized. In this study, alginate-based microcarriers were made in the following order: (i) calcium-alginate gel beads prepared by dropping a blend of sodium alginate and propylene glycol alginate (PGA) into calcium chloride solution, (ii) the PGA section of gel beads cross-linked with gelatin in alkaline solution (i.e., via the transacylation reaction between the ester group of PGA and amino group of gelatin), and (iii) gelatin membrane around the beads further cross-linked by glutaraldehyde. The glutaraldehyde-treated gelatintransacylated PGA/alginate microcarrier showed superior features in high stability under phosphate-containing solution, density close to that of culture medium, and transparency. Moreover, the Chinese hamster ovary CHO-KI and amphotropic retrovirus producer PA317 cells cultivated on the newly synthesized microcarriers exhibited similar growth kinetics of these two types of cell lines cultured on commercial polystyrene microcarriers. However, cell morphology was easily monitored on the transparent microcarriers made in this study. PMID:12139248

Kwon, Young Jik; Peng, Ching-An

2002-07-01

26

Applicability of a particularly simple model to nonlinear elasticity of slide-ring gels with movable cross-links as revealed by unequal biaxial deformation  

NASA Astrophysics Data System (ADS)

The strain energy density function (F) of the polyrotaxane-based slide-ring (SR) gels with movable cross-links along the network strands is characterized by unequal biaxial stretching which can achieve various types of deformation. The SR gels as prepared without any post-preparation complication exhibit considerably smaller values of the ratio of the stresses (?y/?x) in the stretched (x) and constrained (y) directions in planar extension than classical chemical gels with heterogeneous and nearly homogeneous network structures do. This feature of the SR gels leads to the peculiar characteristic that the strain energy density function (F) has no explicit cross term of strains in different directions, which is in contrast to F with explicit strain cross terms for most chemical gels and elastomers. The biaxial stress-strain data of the SR gels are successfully described by F of the Gent model with only two parameters (small-strain shear modulus and a parameter representing ultimate elongation), which introduces the finite extensibility effect into the neo-Hookean model with no explicit cross term of strain. The biaxial data of the deswollen SR gels examined in previous study, which underwent a considerable reduction in volume from the preparation state, are also well described by the Gent model, which is in contrast to the case of the classical chemical gels that the stress-strain relations before and after large deswelling are not described by a common type of F due to a significant degree of collapse of the network strands in the deswollen state. These intriguing features of nonlinear elasticity of the SR gels originate from a novel function of the slidable cross-links that can maximize the arrangement entropy of cross-linked and non-cross-linked cyclic molecules in the deformed networks.

Kondo, Yuuki; Urayama, Kenji; Kidowaki, Masatoshi; Mayumi, Koichi; Takigawa, Toshikazu; Ito, Kohzo

2014-10-01

27

Applicability of a particularly simple model to nonlinear elasticity of slide-ring gels with movable cross-links as revealed by unequal biaxial deformation.  

PubMed

The strain energy density function (F) of the polyrotaxane-based slide-ring (SR) gels with movable cross-links along the network strands is characterized by unequal biaxial stretching which can achieve various types of deformation. The SR gels as prepared without any post-preparation complication exhibit considerably smaller values of the ratio of the stresses (?y/?x) in the stretched (x) and constrained (y) directions in planar extension than classical chemical gels with heterogeneous and nearly homogeneous network structures do. This feature of the SR gels leads to the peculiar characteristic that the strain energy density function (F) has no explicit cross term of strains in different directions, which is in contrast to F with explicit strain cross terms for most chemical gels and elastomers. The biaxial stress-strain data of the SR gels are successfully described by F of the Gent model with only two parameters (small-strain shear modulus and a parameter representing ultimate elongation), which introduces the finite extensibility effect into the neo-Hookean model with no explicit cross term of strain. The biaxial data of the deswollen SR gels examined in previous study, which underwent a considerable reduction in volume from the preparation state, are also well described by the Gent model, which is in contrast to the case of the classical chemical gels that the stress-strain relations before and after large deswelling are not described by a common type of F due to a significant degree of collapse of the network strands in the deswollen state. These intriguing features of nonlinear elasticity of the SR gels originate from a novel function of the slidable cross-links that can maximize the arrangement entropy of cross-linked and non-cross-linked cyclic molecules in the deformed networks. PMID:25296836

Kondo, Yuuki; Urayama, Kenji; Kidowaki, Masatoshi; Mayumi, Koichi; Takigawa, Toshikazu; Ito, Kohzo

2014-10-01

28

Influence of cross-linking density on volume phase transition of liquid crystalline gels in a nematogenic solvent  

Microsoft Academic Search

The effect of cross-linking density (Cx) on volume phase transition of two liquid crystalline (LC) networks comprising dissimilar mesogens in a low molar mass LC has been investigated. Cross-linking density alters the modulus and nematicity of LC network each of which directly influence one of the three governing forces (elastic force, nematic interaction, isotropic mixing interaction) for the equilibrium swelling:

Yuko Okuno; Kenji Urayama; Shinzo Kohjiya

2003-01-01

29

Oxygen diffusion in cross-linked, ethanol-swollen poly(vinyl alcohol) gels: counter-intuitive results reflect microscopic heterogeneities.  

PubMed

Oxygen diffusion coefficients have been determined in ethanol-swollen poly(vinyl alcohol), PVA, gels using a technique wherein oxygen sorption is optically monitored using singlet oxygen phosphorescence. Data were recorded as a function of the extent to which the PVA chains are chemically cross-linked using glutaraldehyde. Contrary to conventional expectation, the diffusion coefficients obtained increase with an increase in the extent of cross-linking. This observation is interpreted in terms of a cross-link-dependent increase in the microscopic heterogeneity of the polymer wherein dense cross-linked domains coexist with more fluid domains. It is expected that, in the latter domains, segmental motions of the macromolecule that facilitate oxygen diffusion are more readily achieved. This model of cross-link-dependent heterogeneity is supported by the results of small-angle X-ray scattering experiments. Among other things, the data reported herein provide an informative foundation for studies of small molecule diffusion in biological cells, particularly during photoinduced cell death where the hydrogel-like nature of the cell can change due to cross-linking reactions. PMID:19099533

Schack, Nickolass Bitsch; Oliveira, Cristiano L P; Young, Niall W G; Pedersen, Jan Skov; Ogilby, Peter R

2009-01-20

30

Transformation of metal-organic framework to polymer gel by cross-linking the organic ligands preorganized in metal-organic framework.  

PubMed

Until now, seamless fusion of metal-organic frameworks (MOFs) and covalently cross-linked polymer gels (PG) at molecular level has been extremely rare, since these two matters have been regarded as opposite, that is, hard versus soft. In this report, we demonstrate transformation of cubic MOF crystals to PG via inner cross-linking of the organic linkers in the void space of MOF, followed by decomposition of the metal coordination. The obtained PG behaved as a polyelectrolyte gel, indicating the high content of ionic groups inside. Metal ions were well adsorbed in the PG due to its densely packed carboxylate groups. A chimera-type hybrid material consisting of MOF and PG was obtained by partial hydrolysis of resulting cross-linked MOF. The shape of resulting PG network well reflected the crystal structure of MOF employed as a template. Our results will connect the two different network materials that have been ever studied in the two different fields to provide new soft and hard hybrid materials, and the unique copolymerization in the large void space of the MOF will open a new horizon toward "ideal network polymers" never prepared before now. PMID:23472763

Ishiwata, Takumi; Furukawa, Yuki; Sugikawa, Kouta; Kokado, Kenta; Sada, Kazuki

2013-04-10

31

Facile one-pot synthesis of iron oxide nanoparticles cross-linked magnetic poly(vinyl alcohol) gel beads for drug delivery.  

PubMed

In this paper, a facile one-pot strategy for scalable synthesis of robust magnetic poly(vinyl alcohol) (mPVA) gel beads is developed. Through dropwise addition of mixed aqueous solution of iron salts and PVA solution into alkaline (e.g., ammonia, NaOH, and KOH) solution, mPVA gel beads with uniform size and excellent superparamagnetic property can be fabricated based on the simultaneous formation of magnetic iron oxide nanoparticles (MIONs) and cross-link of PVA chains. Moreover, this approach can be extended to prepare dual- or multiresponsive gel beads through simply adding functional fillers into PVA solution (e.g., mPVA-PNIPAM gel beads that possess both magnetic and temperature responsibilities can be readily prepared by adding temperature responsive poly(N-isopropylacrylamide) (PNIPAM) into PVA solution). It is found that that the obtained mPVA gel beads exhibit high drug loading level (e.g., above 70%) after the treatment of freezing-thawing. Drug release experiments reveal that the drug release rate and amount of the mPVA gel beads can be tuned by operating the external magnetic field and adjusting the concentration of iron oxide nanoparticles and temperature (for mPVA-PNIPAM gel beads). The present work is of interest for opening up enormous opportunities to make full use of magnetic gel beads in drug delivery and other applications, because of their facile availability, cost-effective productivity, and tunable drug release performance. PMID:22191417

Zhou, Li; He, Benzhao; Zhang, Faai

2012-01-01

32

Ultraviolet-B radiation induced cross-linking improves physical properties of cold- and warm-water fish gelatin gels and films.  

PubMed

Cold- and warm-water fish gelatin granules were exposed to ultraviolet-B radiation for doses up to 29.7 J/cm(2). Solutions and films were prepared from the granules. Gel electrophoresis and refractive index were used to examine changes in molecular weight of the samples. Also, the gel strength and rheological properties of the solutions as well as the tensile and water vapor barrier properties of the films were characterized. SDS-PAGE and refractive index results indicated cross-linking of gelatin chains after exposure to radiation. Interestingly, UV-B treated samples displayed higher gel strengths, with cold- and warm-water fish gelatin having gel strength increases from 1.39 to 2.11 N and from 7.15 to 8.34 N, respectively. In addition, both gelatin samples exhibited an increase in viscosity for higher UV doses. For gelatin films, the cold-water fish gelatin samples made from irradiated granules showed greater tensile strength. In comparison, the warm-water gelatin films made from irradiated granules had lower tensile strength, but better water vapor barrier properties. This might be due to the UV induced cross-linking in warm-water gelatin that disrupted helical structures. PMID:22900795

Otoni, Caio G; Avena-Bustillos, Roberto J; Chiou, Bor-Sen; Bilbao-Sainz, Cristina; Bechtel, Peter J; McHugh, Tara H

2012-09-01

33

A Technique for High-Throughput Protein Crystallization in Ionically Cross-Linked Polysaccharide Gel Beads for X-Ray Diffraction Experiments  

PubMed Central

A simple technique for high-throughput protein crystallization in ionically cross-linked polysaccharide gel beads has been developed for contactless handling of crystals in X-ray crystallography. The method is designed to reduce mechanical damage to crystals caused by physical contact between crystal and mount tool and by osmotic shock during various manipulations including cryoprotection, heavy-atom derivatization, ligand soaking, and diffraction experiments. For this study, protein crystallization in alginate and ?-carrageenan gel beads was performed using six test proteins, demonstrating that proteins could be successfully crystallized in gel beads. Two complete diffraction data sets from lysozyme and ID70067 protein crystals in gel beads were collected at 100 K without removing the crystals; the results showed that the crystals had low mosaicities. In addition, crystallization of glucose isomerase was carried out in alginate gel beads in the presence of synthetic zeolite molecular sieves (MS), a hetero-epitaxic nucleant; the results demonstrated that MS can reduce excess nucleation of this protein in beads. To demonstrate heavy-atom derivatization, lysozyme crystals were successfully derivatized with K2PtBr6 within alginate gel beads. These results suggest that gel beads prevent serious damage to protein crystals during such experiments. PMID:24740192

Sugahara, Michihiro

2014-01-01

34

Migration of glial cells differentiated from neurosphere-forming neural stem/progenitor cells depends on the stiffness of the chemically cross-linked collagen gel substrate.  

PubMed

Substrate stiffness affects cell migration and spreading. Our study revealed that the stiffness of the cell-adhesive substrate affected the migration pattern of neural cells. We observed the migration of neural cells differentiated from neurosphere-forming neural stem/progenitor cells (NSPCs) on collagen gels with various degrees of stiffness achieved by chemical cross-linking. Both glial and neuronal cells broadly spread and migrated when stiff collagen gels (G'=5.5kPa, G?=0.2kPa) were used as the substrate. In contrast, the migration of glial cells was suppressed within the limited area on the soft collagen gels (G'=0.8kPa, G?=0.2kPa). Filopodia were rarely observed in glial cells on the soft collagen gels. Analysis of the intercellular distance between the closest neural cells after differentiation from NSPCs indicated that glial cells more broadly spread on the stiff collagen gels than on the soft gels. Immunocytochemical analysis showed that most of the migrated cells were glial cells, suggesting that migration of glial cells was dependent on the stiffness of substrate. PMID:24041935

Mori, Hideki; Takahashi, Ayumi; Horimoto, Ayano; Hara, Masayuki

2013-10-25

35

Gel electrophoretic studies of photochemical cross-linking of type I collagen with brominated 1,8-naphthalimide dyes and visible light  

NASA Astrophysics Data System (ADS)

Insoluble Type I collagen from bovine Achilles tendon (Sigma C9879) was suspended in a 3 mM solution of the dye diEd66Br dissolved in Cremophor ELR (BASF) to give a molecular concentration ratio. Fifty-microliter aliquots in 5-mm-diameter wells were exposed to 458 J/cm2 (225 mW/cm2, 1800 sec) of 457.9-nm light from an argon ion laser; similar aliquots with and without dye were kept in the dark to serve as controls. Following pelleting of the collagen by centrifugation and 3x washing in phosphate-buffered saline, aliquots of light-treated and control sample pellets were (1) digested in collagenase (Sigma C9891) or (2) extracted in 0.5 M acetic acid, followed by centrifugative ultrafiltration (10-kd cutoff) in 0.01 M acetic acid. Aliquots of the supernatant of the acid-extracted collagen also were digested in pepsin. Electrophoretic protein migration in 8% to 25% gradient polyacrylamide gels following SDS solubilization disclosed numerous, densely packed, essentially contiguous protein bands. These studies indicate that the dye and light treatment of insoluble Type I collagen (1) results in cross-linking of collagen molecules and (2) does not denature the trimer conformation sufficiently to enable significant digestion by pepsin.

Judy, Millard M.; Fuh, L.; Matthews, James Lester; Lewis, David E.; Utecht, Ronald E.

1994-09-01

36

Efficacy of auto-crosslinked hyaluronan gel for adhesion prevention in laparoscopy and hysteroscopy: a systematic review and meta-analysis of randomized controlled trials.  

PubMed

Prevention of postoperative adhesions is a clinical need. We undertook a systematic review to explore the available clinical evidence of the efficacy of auto-crosslinked hyaluronan gel for postoperative adhesion prevention following endoscopic gynecological surgery. An electronic database search of MEDLINE, Cochrane Database of Systematic Reviews and EMBASE, and a comprehensive hand-search of reference lists of published and review articles were performed. No language restrictions were applied. Randomized controlled trials (RCTs) on the use of auto-crosslinked hyaluronan gel for the prevention of postoperative adhesions in gynecological surgery were included in the meta-analysis if they reported outcomes as evaluated at a blind second-look assessment. Three authors independently selected studies and extracted data on study characteristics, quality and accuracy. The Jadad scoring system was used for validity assessment. Meta-analysis was performed following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. The outcome was the incidence of postoperative adhesions based on a binary response (present or not present). Only five RCTs were eligible for inclusion in the meta-analysis. The incidence of postoperative adhesions in patients who received auto-crosslinked hyaluronan gel was significantly lower than in patients who underwent standard surgery only. The gel prevented both intraperitoneal adhesions after laparoscopic myomectomy (OR 0.248, 95% CI 0.098, 0.628) and intrauterine adhesions after hysteroscopic surgery (OR 0.408, 95% CI 0.217, 0.766). Further RCTs are needed to assess the efficacy of auto-crosslinked hyaluronan gel in women undergoing different laparoscopic intra-abdominal surgical procedures. PMID:21945572

Mais, Valerio; Cirronis, Maria G; Peiretti, Michele; Ferrucci, Giuliano; Cossu, Ester; Melis, Gian B

2012-01-01

37

Application of NMR spectroscopy and multidimensional imaging to the gelcasting process and in-situ real-time monitoring of cross-linking polyacrylamide gels  

SciTech Connect

In the gelcasting process, a slurry of ceramic powder in a solution of organic monomers is cast in a mold. The process is different from injection molding in that it separates mold-filling from setting during conversion of the ceramic slurry to a formed green part. In this work, NMR spectroscopy and imaging have been conducted for in-situ monitoring of the gelation process and for mapping the polymerization. {sup 1}H nuclear magnetic resonance spectra have been obtained during polymerization of a premix of soluble reactive methacrylamide (monomer) and N, N`-methylene bisacrylamide (cross-linking molecules). The premix was polymerized by adding ammonium persulfate (initiator) and tetramethyl-ethylene-diamine (accelerator) to form long-chain, cross-linked polymers. The time-varying spin-lattice relaxation times T{sub 1} during polymerization have been studied at 25 and 35{degrees}C, and the variation of spectra and T{sub 1} with respect to extent of polymerization has been determined. To verify homogeneous polymerization, multidimensional NMR imaging was utilized for in-situ monitoring of the process. The intensities from the images are modeled and the correspondence shows a direct extraction of T{sub 1} data from the images.

Ahuja, S.; Dieckman, S.L.; Gopalsami, N. [and others

1995-04-01

38

Monitoring the Cross-Linking of a HPAm\\/Cr(III) Acetate Polymer Gel Using H NMR, UV Spectrophotometry, Bottle Testing, and Rheology  

Microsoft Academic Search

The gelation of a polymer gel formulated at 40°C with 7500 mg\\/L of partly hydrolyzed polyacrylamide (HPAm) and 3000 mg\\/L of Cr(III) acetate 50% active was monitored for 72 h using H nuclear magnetic resonance (NMR) techniques, oscillatory rheology, bottle testing, and UV spectrophotometry. During the first 5 h, H NMR techniques detected changes in the polymer gel signal intensity and transverse relaxation that

Silvia Magnolia Vargas-Vasquez; Laura Beatriz Romero-Zerón; Rodney Macgregor; Senthil Gopalakrishnan

2007-01-01

39

Kinetics of the swelling of a gel of cross-linked polyvinyl alcohol during the synthesis of copper-containing composite based on it  

NASA Astrophysics Data System (ADS)

The kinetics of processes that occur during the chemical reduction of copper in a gel of polyvinyl alcohol (PVA) are described. It is shown that we can assess the processes occurring in the polymer from changes in the degree of swelling. The effects the nature of the precursor (precursor compound) has on the conditions of reduction are analyzed. It is found that crystals of reduced copper do not change the volume of PVA gel, which has a positive effect on the mechanical stability of the resulting composite.

Khudyakova, S. N.; Tokmachev, M. G.; Ferapontov, N. B.

2013-07-01

40

Polymeric C-terminal cross-linked material from type-I collagen. A modified method for purification, anomalous behaviour on gel filtration, molecular weight estimation, carbohydrate content and lipid content.  

PubMed Central

Polymeric cross-linked C-terminal peptide material (poly-alpha 1CB6) from mature bovine tendon type-I collagen was prepared and purified by a modification of the method previously described [Light & Bailey (1980) Biochem. J. 185, 373-381]. Poly-alpha 1CB6 was shown to exhibit concentration-dependent aggregation effects on gel filtration due to interaction with a filtration medium. The material had an amino acid content that was very similar to a mixture of alpha 1CB6 and alpha 1CB5. The material was shown to be polydisperse with a mol.wt. range of 50 000-350 000, but chromatographic fractions were relatively homogeneous over this molecular weight range with respect to amino-acid composition. The heterogeneity of the material was not due to incomplete CNBr peptide cleavage, as poly-alpha 1CB6 did not contain detectable quantities of methionine. The material showed no discrete bands on sodium dodecyl sulphate/polyacrylamide-gel electrophoresis but gave a constant blue stain throughout the molecular weight range described above. Lipid analysis showed that the partially purified material contained elevated levels of stearate when compared to the crude CNBr-digested starting material. This may indicate the specific association of a stearic-acid-rich lipid with the peptide material. On carbohydrate analysis poly-alpha 1CB6 was shown to contain only galactose and glucose at levels of 0.72 and 0.28% respectively. The carbohydrate and amino acid analyses indicated that (alpha 1CB6)2-(alpha 1CB5)1 may be the basic cross-linked structural unit of poly-alpha 1CB6)2-(alpha 1CB5)1 units, although the carbohydrate analysis indicated that the higher molecular weight oligomers may be enriched in alpha 1CB6. PMID:7458897

Light, N D; Bailey, A J

1980-01-01

41

In situ cross-linkable hyaluronan hydrogel enhances chondrogenesis.  

PubMed

The present work describes the feasibility of a cross-linkable injectable hyaluronan hydrogel for cartilage repair. The hydrogel used is a two-component system based on aldehyde-modified hyaluronan and hydrazide-modified polyvinyl alcohol, which are rapidly cross-linked in situ upon mixing. The in vitro study showed that chondrocytes and mesenchymal cells cultured in the gel form cartilage-like tissue, rich in glycosaminoglycans, collagen type II and aggrecan. In a rabbit animal model the injection of the hydrogel improved the healing of a full-thickness cartilage defect created in the knee as compared to non-treated controls. This rabbit study showed that the regenerated cartilage defects stained more intensely for type II collagen upon treatment with the hydrogel. The hyaluronan-based hydrogel may be used as a delivery vehicle for both growth factors and/or cells for cartilage repair. The in vivo study also indicated that the hydrogel alone has a beneficial effect on cartilage regeneration. PMID:21394931

Aulin, Cecilia; Bergman, Kristoffer; Jensen-Waern, Marianne; Hedenqvist, Patricia; Hilborn, Jöns; Engstrand, Thomas

2011-08-01

42

Hyaluronan scaffolds: a balance between backbone functionalization and bioactivity.  

PubMed

Development of biomaterials that provide mechanical and molecular cues for wound healing and regeneration must meet several design parameters. In addition to high biocompatibility, biomaterials should possess suitable porosity as well as the ability to be chemically tailored to control parameters including biodegradability and bioactivity. These characteristics were studied in hyaluronan (HA), a natural polymer found in the body. HA was modified with thiol cross-linking sites to form a stable hydrogel scaffold to examine effects in in vitro cortical cell growth. HA with 20% and 44% thiolation was used to make gels at 0.5%, 0.75%, 1%, and 1.25% (w/v). Results indicate that the bioactivity of the HA after functionalization, as determined by degree of substitution (HA thiolation), has a greater effect on neurite outgrowth than does gel stiffness. The lower substituted HA (20%) promoted greater neurite growth as compared to the higher substituted HA (44%). PMID:20051273

Eng, Doris; Caplan, Michael; Preul, Mark; Panitch, Alyssa

2010-07-01

43

Radiation cross-linked carboxymethyl sago pulp hydrogels loaded with ciprofloxacin: Influence of irradiation on gel fraction, entrapped drug and in vitro release  

NASA Astrophysics Data System (ADS)

Carboxymethyl sago pulp (CMSP) with 0.4 DS, viscosity 184 dl/g and molecular weight 76,000 g/mol was synthesized from sago waste. 10 and 20% w/v solutions of CMSP were irradiated at 10-30 kGy to form hydrogels and were characterized by % gel fraction (GF). Irradiation of 20% CMSP using 25 kGy has produced stable hydrogels with the highest % GF and hence loaded with ciprofloxacin HCl. Drug-loaded hydrogels were produced by irradiating the mixture of drug and 20% CMSP solution at 25 kGy. After irradiation, the hydrogels were cut into circular discs with a diameter of 6±1 mm and evaluated for physicochemical properties as well as drug release kinetics. The ciprofloxacin loading in the disc was 14.7%±1 w/w with an entrapment efficiency of 73.5% w/w. The low standard deviation of drug-loaded discs indicated uniform thickness (1.5±0.3 mm). The unloaded discs were thinner (1±0.4 mm) and more brittle than the drug-loaded discs. FESEM, FT-IR, XRD, DSC and TGA analysis revealed the absence of polymer-drug interaction and transformation of crystalline to amorphous form of ciprofloxacin in the discs. The disc sustained the drug release in phosphate buffer pH 7.4 over 36 h in a first-order manner. The mechanism of the drug release was found to be swelling controlled diffusion and matrix erosion. The anti-bacterial effect of ciprofloxacin was retained after irradiation and CMSP disc could be a promising device for ocular drug delivery.

Lam, Yi Lyn; Muniyandy, Saravanan; Kamaruddin, Hashim; Mansor, Ahmad; Janarthanan, Pushpamalar

2015-01-01

44

Sealing effects of cross-linked gelatin.  

PubMed

Surgical sealants form gel when applied to tissues. Currently, fibrin sealant has been successfully used in many surgical fields, but it has several disadvantages, including possible virus transmission, low adhesive strength, and high cost. In this study, gelatin and glutaraldehyde (GA) solutions were chosen to demonstrate the effectiveness of cross-linked gelatin gel as sealant and barrier, both of which have long been used in medical applications. It was found that the gelatin gel prepared from 26?wt% gelatin and 1?wt% GA solutions exhibited bonding strength almost three times higher than that of fibrin glue. The bonding strength increased with the increasing gelatin and GA concentrations. When a needle hole on PTFE vascular grafts was sealed with the gelatin gel, the water-resistant pressure significantly increased upon rubbing and was twice higher than that of fibrin glue. The cytotoxicity of gelatin gel was found to be much lower than that of albumin glue prepared at the same composition as commercially available BioGlue®. The gelatin gel was found to be also effective as barrier to prevent adhesion in a rat cecum abrasion model. PMID:22274878

Suzuki, S; Ikada, Y

2013-03-01

45

Microrheology of cross-linked polyacrylamide networks Bivash R. Dasgupta and D. A. Weitz  

E-print Network

the frequency- independent plateau shear modulus of cross-linked polyvinyl alcohol and polyacrylamide gelsMicrorheology of cross-linked polyacrylamide networks Bivash R. Dasgupta and D. A. Weitz Department; published 24 February 2005 Experiments investigating the local viscoelastic properties of a chemically cross-linked

46

Cross-Linked Polymers Video  

NSDL National Science Digital Library

This video explains an activity related to cross-linked polymers. The topic is covered in relation to nanotechnology and requires background knowledge in eight grade science. The 1:27 minute video details the materials needed and steps required to complete this lesson. Visitors must complete a quick and free registration to access the materials.

47

Low temperature cross linking polyimides  

NASA Technical Reports Server (NTRS)

A polyimide is formed by cross linking a prepolymer formed by reacting a polyfunctional ester, a polyfunctional amine, and an end-capping unit. By providing an end-capping unit, the prepolymer is curable at a relatively low temperature of about 175 to 245 C.

Serafini, T. T.; Delvigs, P. (inventors)

1982-01-01

48

Hyaluronan in human malignancies  

SciTech Connect

Hyaluronan, a major macropolysaccharide in the extracellular matrix of connective tissues, is intimately involved in the biology of cancer. Hyaluronan accumulates into the stroma of various human tumors and modulates intracellular signaling pathways, cell proliferation, motility and invasive properties of malignant cells. Experimental and clinicopathological evidence highlights the importance of hyaluronan in tumor growth and metastasis. A high stromal hyaluronan content is associated with poorly differentiated tumors and aggressive clinical behavior in human adenocarcinomas. Instead, the squamous cell carcinomas and malignant melanomas tend to have a reduced hyaluronan content. In addition to the stroma-cancer cell interaction, hyaluronan can influence stromal cell recruitment, tumor angiogenesis and epithelial-mesenchymal transition. Hyaluronan receptors, hyaluronan synthases and hyaluronan degrading enzymes, hyaluronidases, are involved in the modulation of cancer progression, depending on the tumor type. Furthermore, intracellular signaling and angiogenesis are affected by the degradation products of hyaluronan. Hyaluronan has also therapeutic implications since it is involved in multidrug resistance.

Sironen, R.K. [Institute of Clinical Medicine, Pathology and Forensic Medicine, University of Eastern Finland, P.O. Box 1627, FI-70211 Kuopio (Finland) [Institute of Clinical Medicine, Pathology and Forensic Medicine, University of Eastern Finland, P.O. Box 1627, FI-70211 Kuopio (Finland); Department of Pathology, Kuopio University Hospital, P.O. Box 1777, FI-70211 Kuopio (Finland); Tammi, M.; Tammi, R. [Institute of Biomedicine, Anatomy, University of Eastern Finland, P.O. Box 1627, FI-70211 Kuopio (Finland)] [Institute of Biomedicine, Anatomy, University of Eastern Finland, P.O. Box 1627, FI-70211 Kuopio (Finland); Auvinen, P.K. [Department of Oncology, Kuopio University Hospital, P.O. Box 1777, FI-70211 Kuopio (Finland)] [Department of Oncology, Kuopio University Hospital, P.O. Box 1777, FI-70211 Kuopio (Finland); Anttila, M. [Institute of Clinical Medicine, Pathology and Forensic Medicine, University of Eastern Finland, P.O. Box 1627, FI-70211 Kuopio (Finland) [Institute of Clinical Medicine, Pathology and Forensic Medicine, University of Eastern Finland, P.O. Box 1627, FI-70211 Kuopio (Finland); Department of Gynecology and Obstetrics, Kuopio University Hospital, P.O. Box 1777, FI-70211 Kuopio (Finland); Kosma, V-M., E-mail: Veli-Matti.Kosma@uef.fi [Institute of Clinical Medicine, Pathology and Forensic Medicine, University of Eastern Finland, P.O. Box 1627, FI-70211 Kuopio (Finland); Department of Pathology, Kuopio University Hospital, P.O. Box 1777, FI-70211 Kuopio (Finland)

2011-02-15

49

Comparative DNA cross-linking by activated pyrrolizidine alkaloids.  

PubMed

The toxicity and bioactivity of pyrrolizidine alkaloids (PAs), common constituents of hundreds of plant species, and in herbal remedies and folk medicines prepared thereof, are probably due to their ability to form DNA cross-linking. We investigated DNA cross-linking activity by chemically-activated PAs from four different structural classes in Madin-Darby bovine kidney (MDBK) cells and in pBR322 DNA. In cell culture, alpha,beta-unsaturated macrocyclic diester pyrroles dehydrosenecionine (DHSN), dehydroriddelliine (DHRD) and the saturated macrocyclic diester pyrrole dehydromonocrotaline (DHMO) were significantly more potent cross-linkers than the simple necine base (retronecine) and an N-oxide (indicine N-oxide; INO) as determined by alkaline elution. The proportion of total DNA cross-links that were proteinase K-resistant (DNA-DNA cross-links) induced by the various pyrroles ranged from 0.08 (DHRN) to 0.67 (DHSN). Those pyrroles that were potent cross-linkers of cellular DNA also cross-linked, in a dose-dependent manner, Bam HI-digested pBR322 DNA as assessed by a gel retardation assay. The possible functional relevance of pyrrole-DNA cross-links was determined by their ability to interrupt PCR amplification of a 1.129 kb segment of pBR322. Dehydrosenecionine completely inhibited amplification, while DHMO was of intermediate potency, while DHRN and INO had no effect. Taken together, these studies suggest that structural features, most notably the presence of a macrocyclic diester, confer potent cross-link activity to PAs. In any event, DNA-DNA cross-linking is probably biologically relevant as indicated by their interference with DNA replication. PMID:10478830

Kim, H Y; Stermitz, F R; Li, J K; Coulombe, R A

1999-06-01

50

Electrospinning formaldehyde cross-linked zein solutions  

Technology Transfer Automated Retrieval System (TEKTRAN)

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

51

N(4)C-ethyl-N(4)C cross-linked DNA: synthesis and characterization of duplexes with interstrand cross-links of different orientations.  

PubMed

The preparation and physical properties of short DNA duplexes that contain a N(4)C-ethyl-N(4)C interstrand cross-link are described. Duplexes that contain an interstrand cross-link between mismatched C-C residues and duplexes in which the C residues of a -CG- or -GC- step are linked to give "staggered" interstrand cross-links were prepared using a novel N(4)C-ethyl-N(4)C phosphoramidite reagent. Duplexes with the C-C mismatch cross-link have UV thermal transition temperatures that are 25 degrees C higher than the melting temperatures of control duplexes in which the cross-link is replaced with a G-C base pair. It appears that this cross-link stabilizes adjacent base pairs and does not perturb the structure of the helix, a conclusion that is supported by the CD spectrum of this duplex and by molecular models. An even higher level of stabilization, 49 degrees C, is seen with the duplex that contains a -CG- staggered cross-link. Molecular models suggest that this cross-link may induce propeller twisting in the cross-linked base pairs, and the CD spectrum of this duplex exhibits an unusual negative band at 298 nm, although the remainder of the spectrum is similar to that of B-form DNA. Mismatched C-C or -CG- staggered cross-linked duplexes that have complementary overhanging ends can undergo self-ligation catalyzed by T4 DNA ligase. Analysis of the ligated oligomers by nondenaturing polyacrylamide gel electrophoresis shows that the resulting oligomers migrate in a manner similar to that of a mixture of non-cross-linked control oligomers and suggests that these cross-links do not result in significant bending of the helix. However, the orientation of the staggered cross-link can have a significant effect on the structure and stability of the cross-linked duplex. Thus, the thermal stability of the duplex that contains a -GC- staggered cross-link is 10 degrees C lower than the melting temperature of the control, non-cross-linked duplex. Unlike the -CG- staggered cross-link, in which the cross-linked base pairs can still maintain hydrogen bond contacts, molecular models suggest that formation of the -GC- staggered cross-link disrupts hydrogen bonding and may also perturb adjacent base pairs leading to an overall reduction in helix stability. Duplexes with specifically positioned and oriented cross-links can be used as substrates to study DNA repair mechanisms. PMID:11790097

Noronha, Anne M; Noll, David M; Wilds, Christopher J; Miller, Paul S

2002-01-22

52

Controlled Compaction with Ruthenium-catalyzed Photochemical Cross-linking of Fibrin-based Engineered Connective Tissue  

PubMed Central

Tissue engineering utilizing fibrin gel as a scaffold has the advantage of creating a completely biological replacement. Cells seeded in a fibrin gel can induce fibril alignment by traction forces when subjected to appropriate mechanical constraints. While gel compaction is key to successful tissue fabrication, excessive compaction can result due to low gel stiffness. This study investigated using ruthenium-catalyzed photo-cross-linking as a method to increase gel stiffness in order to minimize over-compaction. Cross-links between the abundant tyrosine molecules that comprise fibrin were created upon exposure to blue light. Cross-linking was effective in increasing the stiffness of the fibrin gel by 93% with no adverse effects on cell viability. Long-term culture of cross-linked tubular constructs revealed no detrimental effects on cell proliferation or collagen deposition due to cross-linking. After 4 weeks of cyclic distension, the cross-linked samples were more than twice as long as non-cross-linked controls, with similar cell and collagen contents. However, the cross-linked samples required a longer incubation period to achieve a UTS and modulus comparable to controls. This study shows that photo-cross-linking is an attractive option to stiffen the initial fibrin gel and thereby reduce cell-induced compaction, which can allow for longer incubation periods and thus more tissue growth without compaction below a useful size. PMID:19782397

Syedain, Zeeshan H.; Bjork, Jason; Sando, Lillian; Tranquillo, Robert T.

2009-01-01

53

Clinical evaluation of a hyaluronan-based gel following microsurgical reconstruction of peripheral nerves of the hand.  

PubMed

A controlled clinical trial was performed to investigate the safety and efficacy of the hyaluronate-based gel polymer Hyaloglide after microsurgical reconstruction of peripheral nerves of the hand. Thirty patients were randomized to receive either no postsurgical treatment (n = 16) or Hyaloglide (n = 14) and were clinically evaluated at various intervals for 1 year. The application of Hyaloglide posed no safety concerns. Efficacy was assessed by the recovery of sensitivity, measurement of pain, and progression of Tinel's sign. The Hyaloglide-treated group showed better improvement in recovery from pain, approaching statistical significance during the first 3 months postsurgery. Likewise, recovery of sensitivity was also higher in the Hyaloglide-treated group throughout the entire follow-up period, and the distance of Tinel's sign was longer in the Hyaloglide-treated group (P < 0.05 at day 30). The application of Hyaloglide may improve recovery of sensitivity and decrease pain following microsurgical repair of the peripheral nerves of the hand. PMID:17205576

Atzei, Andrea; Calcagni, Maurizio; Breda, Bruno; Fasolo, Giampaolo; Pajardi, Giorgio; Cugola, Landino

2007-01-01

54

Porous Cross-Linked Polyimide-Urea Networks  

NASA Technical Reports Server (NTRS)

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.

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

2015-01-01

55

Hyaluronan: A Matrix Component  

NASA Astrophysics Data System (ADS)

The glucosaminoglycan hyaluronan is a key component of the extracellular matrix. It is a large, negatively charged molecule that can act as an ion exchange reservoir for positive ions. Hyaluronan is involved in renomedullary water handling through its water-binding capacity. In the renal medulla, the main source for hyaluronan production is the renomedullary interstitial cells. Hyaluronan synthases are found in the inner part of the plasma membrane and polymerize hyaluronan chains which are extruded into the extracellular space. Hyaluronidases are a family of enzymes involved in the degradation of hyaluronan. They have a wide range of properties, including differences in size, inhibitor sensitivities, catalytic mechanisms, substrate specificities and pH optima.

Rügheimer, Louise

2008-09-01

56

Highly cross-linked nanoporous polymers  

DOEpatents

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

Steckle, Jr., Warren P. (Los Alamos, NM); Apen, Paul G. (Los Alamos, NM); Mitchell, Michael A. (Los Alamos, NM)

1997-01-01

57

Highly cross-linked nanoporous polymers  

DOEpatents

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

Steckle, Jr., Warren P. (Los Alamos, NM); Apen, Paul G. (Los Alamos, NM); Mitchell, Michael A. (Los Alamos, NM)

1998-01-01

58

Hyaluronan Synthesis and Myogenesis  

PubMed Central

Exogenous hyaluronan is known to alter muscle precursor cell proliferation, migration, and differentiation, ultimately inhibiting myogenesis in vitro. The aim of the current study was to investigate the role of endogenous hyaluronan synthesis during myogenesis. In quantitative PCR studies, the genes responsible for synthesizing hyaluronan were found to be differentially regulated during muscle growth, repair, and pathology. Although all Has genes (Has1, Has2, and Has3) were differentially regulated in these models, only Has2 gene expression consistently associated with myogenic differentiation. During myogenic differentiation in vitro, Has2 was the most highly expressed of the synthases and increased after induction of differentiation. To test whether this association between Has2 expression and myogenesis relates to a role for Has2 in myoblast differentiation and fusion, C2C12 myoblasts were depleted of Has2 by siRNA and induced to differentiate. Depletion of Has2 inhibited differentiation and caused a loss of cell-associated hyaluronan and the hyaluronan-dependent pericellular matrix. The inhibition of differentiation caused by loss of hyaluronan was confirmed with the hyaluronan synthesis inhibitor 4-methylumbelliferone. In hyaluronan synthesis-blocked cultures, restoration of the pericellular matrix could be achieved through the addition of exogenous hyaluronan and the proteoglycan versican, but this was not sufficient to restore differentiation to control levels. These data indicate that intrinsic hyaluronan synthesis is necessary for myoblasts to differentiate and form syncytial muscle cells, but the hyaluronan-dependent pericellular matrix is not sufficient to support differentiation alone; additional hyaluronan-dependent cell functions that are yet unknown may be required for myogenic differentiation. PMID:23493399

Hunt, Liam C.; Gorman, Chris; Kintakas, Christopher; McCulloch, Daniel R.; Mackie, Eleanor J.; White, Jason D.

2013-01-01

59

Characterization of Hyaluronan-Protein Microstructures and Polymer Solutions  

NASA Astrophysics Data System (ADS)

Evidence is mounting that mechanical and topographical features of biomaterials can be as critical for cellular behavior as chemical properties. A case in point is hyaluronan (HA), a large polysaccharide with unique mechanical and hydrodynamic properties, found in many tissues and bodily fluids. Thanks to a large variety of accessible conformations and aggregation states, this remarkable polymer can impart on its biological environment a diverse range of structural and viscoelastic properties with far-reaching consequences for cell physiology (migration, inflammation, cancer). Supramolecular assembly of HA is typically mediated by HA-binding proteins. These specialized molecules are known to assist the formation of organized structures, such as cross-linked bundles, gels, or the all-important pericellular coat, a polymer network anchored to many cell surfaces. Precisely how the material properties of HA-rich matrices and aggregates are modified by the associated proteins, however, is largely a matter of speculation. We will present new insights concerning the cell coat and HA-protein solutions characterized using passive microrheology, fluorescence recovery after photobleaching (FRAP), and optical force probe microscopy.

Curtis, J. E.; McLane, L.; Bedoya, M.; Beatty, R.; Kramer, A.; Boehm, H.; Scrimgeour, J.

2010-03-01

60

Cross-linked biopolymer bundles: Cross-link reversibility leads to cooperative binding/unbinding phenomena  

NASA Astrophysics Data System (ADS)

We consider a biopolymer bundle consisting of filaments that are cross-linked together. The cross-links are reversible: they can dynamically bind and unbind adjacent filament pairs as controlled by a binding enthalpy. The bundle is subjected to a bending deformation and the corresponding distribution of cross-links is measured. For a bundle consisting of two filaments, upon increasing the bending amplitude, a first-order transition is observed. The transition is from a state where the filaments are tightly coupled by many bound cross-links, to a state of nearly independent filaments with only a few bound cross-links. For a bundle consisting of more than two filaments, a series of first-order transitions is observed. The transitions are connected with the formation of an interface between regions of low and high cross-link densities. Combining umbrella sampling Monte Carlo simulations with analytical calculations, we present a detailed picture of how the competition between cross-link shearing and filament stretching drives the transitions. We also find that, when the cross-links become soft, collective behavior is not observed: the cross-links then unbind one after the other leading to a smooth decrease of the average cross-link density.

Vink, Richard L. C.; Heussinger, Claus

2012-01-01

61

Tuning chemical and physical cross-links in silk electrogels for morphological analysis and mechanical reinforcement.  

PubMed

Electrochemically controlled, reversible assembly of biopolymers into hydrogel structures is a promising technique for on-demand cell or drug encapsulation and release systems. An electrochemically sol-gel transition has been demonstrated in regenerated Bombyx mori silk fibroin, offering a controllable way to generate biocompatible and reversible adhesives and other biomedical materials. Despite the involvement of an electrochemically triggered electrophoretic migration of the silk molecules, the mechanism of the reversible electrogelation remains unclear. It is, however, known that the freshly prepared silk electrogels (e-gels) adopt a predominantly random coil conformation, indicating a lack of cross-linking as well as thermal, mechanical, and morphological stabilities. In the present work, the tuning of covalent and physical ?-sheet cross-links in silk hydrogels was studied for programming the structural properties. Scanning electron microscopy (SEM) revealed delicate morphology, including locally aligned fibrillar structures, in silk e-gels, preserved by combining glutaraldehyde-cross-linking and ethanol dehydration. Fourier transform infrared (FTIR) spectroscopic analysis of either electrogelled, vortex-induced or spontaneously formed silk hydrogels showed that the secondary structure of silk e-gels was tunable between non-?-sheet-dominated and ?-sheet-dominated states. Dynamic oscillatory rheology confirmed the mechanical reinforcement of silk e-gels provided by controlled chemical and physical cross-links. The selective incorporation of either chemical or physical or both cross-links into the electrochemically responsive, originally unstructured silk e-gel should help in the design for electrochemically responsive protein polymers. PMID:23859710

Lin, Yinan; Xia, Xiaoxia; Shang, Ke; Elia, Roberto; Huang, Wenwen; Cebe, Peggy; Leisk, Gary; Omenetto, Fiorenzo; Kaplan, David L

2013-08-12

62

Polyimide Aerogels with Three-Dimensional Cross-Linked Structure  

NASA Technical Reports Server (NTRS)

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

Panek, John

2010-01-01

63

Firming of Bread Crumb with Cross-Linked Waxy Barley Starch Substituted for Wheat Starch  

Microsoft Academic Search

Cereal Chem. 69(3):321-325 White pan bread was baked from flour that had been fractionated a higher enthalpy of melting than that of control bread crumb, except and reconstituted using cross-linked waxy barley starch (5.9% amylose at 6 hr after baking. Furthermore, a 50% gel of cross-linked waxy barley content) in place of prime wheat starch (28.3% amylose content). starch in

TOSHIKI INAGAKI; PAUL A. SEIB

1992-01-01

64

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

PubMed Central

Protein–nucleic acid complexes are commonly studied by photochemical cross-linking. UV-induced cross-linking of protein to nucleic acid may be followed by structural analysis of the conjugated protein to localize the cross-linked amino acids and thereby idey the nucleic acid binding site. Mass spectrometry is becoming increasingly popular for characterization of purified peptide–nucleic acid heteroconjugates derived from UV cross-linked protein–nucleic acid complexes. The efficiency of mass spectrometry-based methods is, however, hampered by the contrasting physico-chemical properties of nucleic acid and peptide entities present in such heteroconjugates. Sample preparation of the peptide–nucleic acid heteroconjugates is, therefore, a crucial step in any mass spectrometry-based analytical procedure. This study demonstrates the performance of four different MS-based strategies to characterize E. coli single-stranded DNA binding protein (SSB) that was UV-cross-linked to a 5-iodouracil containing DNA oligomer. Two methods were optimized to circumvent the need for standard liquid chromatography and gel electrophoresis, thereby dramatically increasing the overall sensitivity of the analysis. Enzymatic degradation of protein and oligonucleotide was combined with miniaturized sample preparation methods for enrichment and desalting of cross-linked peptide–nucleic acid heteroconjugates from complex mixtures prior to mass spectrometric analysis. Detailed characterization of the peptidic component of two different peptide–DNA heteroconjugates was accomplished by matrix-assisted laser desorption/ionization mass spectrometry and allowed assignment of tryptophan-54 and tryptophan-88 as candidate cross-linked residues. Sequencing of those peptide–DNA heteroconjugates by nanoelectrospray quadrupole time-of-flight tandem mass spectrometry ideied tryptophan-54 and tryptophan-88 as the sites of cross-linking. Although the UV-cross-linking yield of the protein–DNA complex did not exceed 15%, less than 100 pmole of SSB protein was required for detailed structural analysis by mass spectrometry. PMID:11567090

Steen, Hanno; Petersen, JøRgen; Mann, Matthias; Jensen, Ole N.

2001-01-01

65

Some peculiar properties of cross-linked polyvinyl alcohol (CL-PVA) related to the reticulation degree  

Microsoft Academic Search

Unlike usual polyhydroxilic packing materials for liquid chromatography based on cross-linked agarose, CL-amylose and CL-dextrans (Sephadex), the cross-linked PVA gels exhibit an increase of swelling properties with the reticulation degree, up to a certain limit. Afterwards more advanced reticulation degrees induce a decrease in swelling capacities just as in case of other cross-linked polyhydroxilic polymers. This abnormal behaviour of CL-PVA

M. A. Mateescu; H. D. Schell; M. Dimonie; S. Todireanu; O. Maior

1984-01-01

66

Cross-Linked Structure of Network Evolution  

E-print Network

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, and 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.

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

2014-08-05

67

RHEOLOGY OF CROSS-LINKING FISH GELATINS  

Technology Transfer Automated Retrieval System (TEKTRAN)

We extracted gelatin from Alaskan pollock (Theragra chalcogramma) and Alaskan pink salmon (Oncorhynchus gorbuscha) for potential use in biomedical applications, such as bioadhesives and microspheres for drug delivery. To improve their mechanical properties, we cross-linked the gelatins using genipin...

68

Cross-linked structure of network evolution  

SciTech Connect

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.

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)] [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) [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) [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

69

Physicochemical Properties of Calcium Caseinate Films Cross-Linked by Gamma-Irradiation  

Microsoft Academic Search

Gamma-irradiation was used to produce freestanding, sterilized, cross-linked caseinate films and gels. Mechanical properties of gels and films and water vapor permeability of dried films were determined. Irradiated films were significantly ( p ?0.05) more resistant to puncture and moisture. Also, gels were formed when protein solutions received radiation doses ?16 kGy. The addition of CaCl 2 in the solution

M. Lacroix; M. Ressouany; B. Ouattara; H.-L. Yu; M. A. Mateescu; G. Delmas Patterson

2002-01-01

70

Cross-Linking Studies of Lysozyme Nucleation  

NASA Technical Reports Server (NTRS)

Tetragonal chicken egg white crystals consist of 4(sub 3) helices running in alternating directions, the helix rows having a two fold symmetry with each other. The unit cell consists of one complete tetrameric turn from each of two adjacent helices (an octamer). PBC analysis indicates that the helix intermolecular bonds are the strongest in the crystal, therefore likely formed first. AFM analysis of the (110) surface shows only complete helices, no half steps or bisected helices being found, while AFM line scans to measure the growth step increments show that they are multiples of the 4(sub 3) helix tetramer dimensions. This supports our thesis that the growth units are in fact multiples of the four molecule 4(sub 3) helix unit, the "average" growth unit size for the (110) face being an octamer (two turns about the helix) and the (101) growth unit averaging about the size of a hexamer. In an effort to better understand the species involved in the crystal nucleation and growth process, we have initiated an experimental program to study the species formed in solution compared to what is found in the crystal through covalent cross-linking studies. These experiments use the heterobifunctional cross-linking agent aminoethyl-4-azidonitroanaline (AEANA). An aliphatic amine at one end is covalently attached to the protein by a carbodiimide-mediated reaction, and a photo reactive group at the other can be used to initiate crosslinking. Modifications to the parent structure can be used to alter the distance between the two reactive groups and thus the cross-linking agents "reach". In practice, the cross-linking agent is first coupled to the asp101 side chain through the amine group. Asp101 lies within the active site cleft, and previous work with fluorescent probes had shown that derivatives at this site still crystallize in the tetragonal space group. This was also found to be the case with the AEANA derivative, which gave red tetragonal crystals. The protein now has a reactive group that can be photoactivated at a specific point in the nucleation or crystal growth process to "capture" protein molecules bound within reach of the crosslinking agent. If those bound protein molecules have a defined geometric relationship with the capturing molecule, such as would be found in a crystal, then the photoreacted cross-linking site should be consistent. Random protein interactions, typical of an amorphous precipitate or interaction, would show a random cross-linking reaction. The results of these and other experiments will be presented.

Forsythe, Elizabeth; Pusey, Marc

2000-01-01

71

Method of Cross-Linking Aerogels Using a One-Pot Reaction Scheme  

NASA Technical Reports Server (NTRS)

A document discusses a new, simplified method for cross-linking silica and other oxide aerogels, with a polymeric material to increase strength of such materials without adversely affecting porosity or low density. This innovation introduces the polymer precursor into the sol before gelation either as an agent, which co-reacts with the oxide gel, or as soluble polymer precursors, which do not interact with the oxide gel in any way. Subsequent exposure to heat, light, catalyst or other method of promoting polymerization causes cross-linking without any additional infiltration steps.

Meador, Ann B.; Capadona, Lynn A.

2008-01-01

72

Enzymatically cross-linked alginic-hyaluronic acid composite hydrogels as cell delivery vehicles.  

PubMed

An injectable composite gel was developed from alginic and hyaluronic acid. The enzymatically cross-linked injectable gels were prepared via the oxidative coupling of tyramine modified sodium algiante and sodium hyaluronate in the presence of horse radish peroxidase (HRP) and hydrogen peroxide (H2O2). The composite gels were prepared by mixing equal parts of the two tyraminated polymer solutions in 10U HRP and treating with 1.0% H2O2. The properties of the alginate gels were significantly affected by the addition of hyaluronic acid. The percentage water absorption and storage modulus of the composite gels were found to be lower than the alginate gels. The alginate and composite gels showed lower protein release compared to hyaluronate gels in the absence of hyaluronidase. Even hyaluronate gels showed only approximately 10% protein release after 14 days incubation in phosphate buffer solution. ATDC-5 cells encapsulated in the injectable gels showed high cell viability. The composite gels showed the presence of enlarged spherical cells with significantly higher metabolic activity compared to cells in hyaluronic and alginic acid gels. The results suggest the potential of the composite approach to develop covalently cross-linked hydrogels with tuneable physical, mechanical, and biological properties. PMID:23357799

Ganesh, Nitya; Hanna, Craig; Nair, Shantikumar V; Nair, Lakshmi S

2013-04-01

73

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

PubMed

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. PMID:22655797

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

2012-06-20

74

?-Irradiation Effect on the Non-Cross-Linked and Cross-Linked Polyvinyl Alcohol Films  

Microsoft Academic Search

The non-cross-linked and cross-linked polyvinyl alcohol (PVA) films were prepared by the casting 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) and X-ray diffraction (XRD). Swelling behaviour was also investigated. Mechanical properties have been examined with respect to the absorbed

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

2010-01-01

75

Positive tone cross-linked resists based on photoacid inhibition of cross linking  

NASA Astrophysics Data System (ADS)

A resist imaging design that utilizes photoacid inhibition of cationic polymerization and cross-linking during a postexposure bake step has been studied. The key to the design approach is the use of two different polymerization catalysts/initiators: (1) a photoacid produced from a photoacid generator (PAG) upon exposure of the resist that can result in polymerization and cross-linking of the resist matrix and (2) a thermal cross-linking catalyst (TCC) designed to thermally catalyze epoxide-phenol cross-linking. The TCC can be chosen from a variety of compounds such as triphenylphosphine (TPP) or imidazole. When only one of these catalysts (e.g TPP or photoacid) is present in an epoxide and phenol containing resist matrix, it will individually catalyze cross-linking. When they are present together, they effectively quench one another and little to no cross-linking occurs. This approach can be used to switch the tone of a resist from negative (photoacid catalyzed) to positive (TCC catalyzed and photoacid inhibited). The effect of the ratio of TCC:PAG was examined and the optimal ratio for positive tone behavior was determined. Resist contrast can be modified by optimization of epoxide:phenol ratio in the formulation. Dual tone behavior with positive tone at low dose and negative tone at higher doses can be observed in certain formulation conditions. Initial EUV patterning shows poor results, but the source of the poor imaging is not yet understood.

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

2014-03-01

76

Tea Derived Galloylated Polyphenols Cross-Link Purified Gastrointestinal Mucins  

PubMed Central

Polyphenols derived from tea are thought to be important for human health. We show using a combination of particle tracking microrheology and small-angle neutron scattering that polyphenols acts as cross-linkers for purified gastrointestinal mucin, derived from the stomach and the duodenum. Both naturally derived purified polyphenols, and green and black tea extracts are shown to act as cross-linkers. The main active cross-linking component is found to be the galloylated forms of catechins. The viscosity, elasticity and relaxation time of the mucin solutions experience an order of magnitude change in value upon addition of the polyphenol cross-linkers. Similarly small-angle neutron scattering experiments demonstrate a sol-gel transition with the addition of polyphenols, with a large increase in the scattering at low angles, which is attributed to the formation of large scale (>10 nm) heterogeneities during gelation. Cross-linking of mucins by polyphenols is thus expected to have an impact on the physicochemical environment of both the stomach and duodenum; polyphenols are expected to modulate the barrier properties of mucus, nutrient absorption through mucus and the viscoelastic microenvironments of intestinal bacteria. PMID:25162539

Georgiades, Pantelis; Pudney, Paul D. A.; Rogers, Sarah; Thornton, David J.; Waigh, Thomas A.

2014-01-01

77

Modelling of cross-linked actin networks - Influence of geometrical parameters and cross-link compliance.  

PubMed

A major structural component of the cell is the actin cytoskeleton, in which actin subunits are polymerised into actin filaments. These networks can be cross-linked by various types of ABPs (Actin Binding Proteins), such as Filamin A. In this paper, the passive response of cross-linked actin filament networks is evaluated, by use of a numerical and continuum network model. For the numerical model, the influence of filament length, statistical dispersion, cross-link compliance (including that representative of Filamin A) and boundary conditions on the mechanical response is evaluated and compared to experimental results. It is found that the introduction of statistical dispersion of filament lengths has a significant influence on the computed results, reducing the network stiffness by several orders of magnitude. Actin networks have previously been shown to have a characteristic transition from an initial bending-dominated to a stretching-dominated regime at larger strains, and the cross-link compliance is shown to shift this transition. The continuum network model, a modified eight-chain polymer model, is evaluated and shown to predict experimental results reasonably well, although a single set of parameters cannot be found to predict the characteristic dependence of filament length for different types of cross-links. Given the vast diversity of cross-linking proteins, the dependence of mechanical response on cross-link compliance signifies the importance of incorporating it properly in models to understand the roles of different types of actin networks and their respective tasks in the cell. PMID:24491254

Fallqvist, B; Kulachenko, A; Kroon, M

2014-06-01

78

Cross-linked carbon nanotube heat spreader  

NASA Astrophysics Data System (ADS)

Isolated individual carbon nanotubes (CNTs) have shown exceptional thermal conductivity along their axis, but have poor thermal transfer between adjacent CNTs. Thick bundles of aligned CNTs have been used as heat pipes, but the thermal input and output areas are the same, providing no heat spreading effect. Energetic argon ion beams are used to join, or cross-link overlapping CNTs in a thick film to form an interpenetrating network with an isotropic thermal conductivity of 2150 W/m-K. Such thick films may be used as heat spreaders to enlarge the thermal footprint of various electronic and semiconductor devices, laser diodes and CPU chips, for example, to enhance cooling.

Konesky, Gregory

2014-09-01

79

Developing fluorescent hyaluronan analogs for hyaluronan studies.  

PubMed

Two kinds of fluorescent hyaluronan (HA) analogs, one serving as normal imaging agent and the other used as a biosensitive contrast agent, were developed for the investigation of HA uptake and degradation. Our approach of developing HA imaging agents depends on labeling HA with varying molar percentages of a near-infrared (NIR) dye. At low labeling ratios, the hyaluronan uptake can be directly imaged while at high labeling ratios, the fluorescent signal is quenched and signal generation occurs only after degradation. It is found that the conjugate containing 1%-2% NIR dye can be used as a normal optical imaging agent, while bioactivable imaging agents are formed at 6% to 17% dye loading. It was determined that the conjugation of dye to HA with different loading percentages does not impact HA biodegradation by hyaluronidase (Hyal). The feasibility of using these two NIR fluorescent hyaluronan analogs for HA investigation was evaluated in vivo with optical imaging. The data demonstrates that the 1% dye loaded fluorescent HA can be used to monitor the behavior of HA and its fragments, whereas bioactivatable HA imaging agent (17% dye in HA) is more suitable for detecting HA fragments. PMID:22314377

Wang, Wei; Cameron, Arlin G; Ke, Shi

2012-01-01

80

Volume change of double cross-linked poly(aspartic acid) hydrogels induced by cleavage of one of the crosslinks.  

PubMed

In the present paper we report for the first time the development of redox-responsive biocompatible polymer gels. Double cross-linked poly(aspartic acid) hydrogels were prepared using two different cross-linking agents simultaneously. One of the cross-linkers was diaminobutane (DAB), the other cystamine (CYS). The relative amounts of DAB and CYS molecules were varied over a wide range while the total amount of cross-linker molecules (DAB+CYS) was kept constant. DAB provides stable cross-links, whereas CYS contains disulfide bonds, which can be broken by reduction. The cleavage of disulfide cross-links results in enhanced swelling and a significant decrease in the elastic modulus of the gels. These novel types of stimuli-responsive gels are promising candidates for new swelling controlled release matrices. PMID:22975627

Zrinyi, Miklos; Gyenes, Tamas; Juriga, David; Kim, Ji-Heung

2013-02-01

81

Corneal collagen cross-linking: A review  

PubMed Central

The aim was to review the published literature on corneal collagen cross-linking. The emphasis was on the seminal publications, systemic reviews, meta-analyses and randomized controlled trials. Where such an evidence did not exist, selective large series cohort studies, case controlled studies and case series with follow-up preferably greater than 12 months were included. Riboflavin/Ultraviolet A (UVA) corneal collagen cross-linking appears to be the first treatment modality to halt the progression of keratoconus and other corneal ectatic disorders with improvement in visual, keratometric and topographic parameters documented by most investigators. Its precise mechanism of action at a molecular level is as yet not fully determined. Follow-up is limited to 4–6 years at present but suggests continued stability and improvement in corneal shape with time. Most published data are with epithelium-off techniques. Epithelium-on studies suggest some efficacy but less than with the epithelium-off procedures and long-term data are not currently available. The use of Riboflavin/UVA CXL for the management of infectious and non-infectious keratitis appears very promising. Its use in the management of bullous keratopathy is equivocal. Investigation of other methodologies for CXL are under investigation. PMID:25000866

O’Brart, David P.S.

2014-01-01

82

Chicken Corneocyte Cross-Linked Proteome  

PubMed Central

Shotgun proteomic analysis was performed of epidermal scale, feather, beak and claw from the domestic chicken. To this end, the samples were separated first into solubilized and particulate fractions, the latter enriched in isopeptide cross-linking, by exhaustive extraction in sodium dodecyl sulfate under reducing conditions. Among the 205 proteins identified were 17 keratins (types ? and ?), 51 involved in protein synthesis, 8 junctional, 8 histone, 5 heat shock and 5 14-3-3 proteins. Considerable overlap among the beak, claw, feather and scale samples was observed in protein profiles, but those from beak and claw were the most similar. Scale and feather profiles were the most distinctive, each exhibiting specific proteins. Less than 20% of the proteins were found only in the detergent solubilized fraction, while 34-57% were found only in the particulate fraction, depending on the source, and the rest in both fractions. The results provide the first comprehensive analysis of the content of these cornified structures, reveal the efficient use of available proteins in conferring mechanical and chemical stability to them and emphasize the importance of isopeptide cross-linking in avian epithelial cornification. PMID:23256538

Rice, Robert H.; Winters, Brett R.; Durbin-Johnson, Blythe P.; Rocke, David M.

2013-01-01

83

Corneal collagen cross-linking: a review.  

PubMed

The aim was to review the published literature on corneal collagen cross-linking. The emphasis was on the seminal publications, systemic reviews, meta-analyses and randomized controlled trials. Where such an evidence did not exist, selective large series cohort studies, case controlled studies and case series with follow-up preferably greater than 12 months were included. Riboflavin/Ultraviolet A (UVA) corneal collagen cross-linking appears to be the first treatment modality to halt the progression of keratoconus and other corneal ectatic disorders with improvement in visual, keratometric and topographic parameters documented by most investigators. Its precise mechanism of action at a molecular level is as yet not fully determined. Follow-up is limited to 4-6 years at present but suggests continued stability and improvement in corneal shape with time. Most published data are with epithelium-off techniques. Epithelium-on studies suggest some efficacy but less than with the epithelium-off procedures and long-term data are not currently available. The use of Riboflavin/UVA CXL for the management of infectious and non-infectious keratitis appears very promising. Its use in the management of bullous keratopathy is equivocal. Investigation of other methodologies for CXL are under investigation. PMID:25000866

O'Brart, David P S

2014-01-01

84

Interactions between colloids induced by a soft cross-linked polymer substrate.  

PubMed

Using videomicroscopy imaging, we demonstrate the existence of a short-ranged equilibrium attraction between heavy silica colloids diffusing on soft surfaces of cross-linked polymer gels. The intercolloid potential can be tuned by changing the gel stiffness or by coating the colloids with a polymer layer. On sufficiently soft substrates, the interaction induced by the polymer matrix leads to large-scale colloidal aggregation. We correlate the in-plane interaction with a colloid-surface attraction. PMID:22026874

Di Michele, Lorenzo; Yanagishima, Taiki; Brewer, Anthony R; Kotar, Jurij; Eiser, Erika; Fraden, Seth

2011-09-23

85

In situ forming chitosan hydrogels prepared via ionic/covalent co-cross-linking.  

PubMed

In situ forming chitosan hydrogels have been prepared via coupled ionic and covalent cross-linking. Thus, different amounts of genipin (0.05, 0.10, 0.15, and 0.20% (w/w)), used as a chemical cross-linker, were added to a solution of chitosan that was previously neutralized with a glycerol-phosphate complex (ionic cross-linker). In this way, it was possible to overcome the pH barrier of the chitosan solution, to preserve its thermosensitive character, and to enhance the extent of cross-linking in the matrix simultaneously. To investigate the contributions of the ionic cross-linking and the chemical cross-linking, separately, we prepared the hydrogels without the addition of either genipin or the glycerol-phosphate complex. The addition of genipin to the neutralized solution disturbs the ionic cross-linking process and the chemical cross-linking becomes the dominant process. Moreover, the genipin concentration was used to modulate the network structure and performance. The more promising formulations were fully characterized, in a hydrated state, with respect to any equilibrium swelling, the development of internal structure, the occurrence of in vitro degradability and cytotoxicity, and the creation of in vivo injectability. Each of the hydrogel systems exhibited a notably high equilibrium water content, arising from the fact that their internal structure (examined by conventional SEM, and environmental SEM) was highly porous with interconnecting pores. The porosity and the pore size distribution were quantified by mercury intrusion porosimetry. Although all gels became degraded in the presence of lysozyme, their degradation rate greatly depended on the genipin load. Through in vitro viability tests, the hydrogel-based formulations were shown to be nontoxic. The in vivo injection of a co-cross-linking formulation revealed that the gel was rapidly formed and localized at the injection site, remaining in position for at least 1 week. PMID:21774479

Moura, M José; Faneca, H; Lima, M Pedroso; Gil, M Helena; Figueiredo, M Margarida

2011-09-12

86

Gelation of Covalently Cross-Linked PEG–Heparin Hydrogels  

PubMed Central

We study PEG–heparin hydrogels to identify compositions that lead to gel formation and measure the corresponding gelation kinetics. The material consists of a maleimide-functionalized high molecular weight heparin (HMWH) backbone covalently cross-linked with bis-thiol poly(ethylene glycol) (PEG). Using multiple particle tracking microrheology, we investigate a broad composition space, defined by the number of maleimide functional sites per HMWH (f = 3.9–11.8), the molecular weight of the PEG cross-linker (Mn = 2000, 5000, and 10 000), and the concentrations of the heparin and PEG polymers. Gelation kinetics are characterized by time–cure superposition, yielding the gel time, tc, and the critical relaxation exponent, n. Gelation times range from 5 < tc ? 45 min, with the fastest kinetics occurring for the highest HMWH maleimide functionalities. tc depends nonmonotonically on the PEG cross-linker molecular weight, suggesting that gelation is affected by the length of the cross-linker relative to intermolecular interactions between heparin molecules. The critical relaxation exponent decreases from n = 0.52 for PEG 2000 to n = 0.39 for PEG 10 000. Finally, 219 equilibrated samples taken over the entire composition space are identified as liquid or solid, defining the “gelation envelope”. The boundaries of this empirical gelation envelope are in good agreement with Flory–Stockmayer theory. In all, microrheological measurements enable characterization over a large parameter space and provide crucial insight into the gelation of complex, multifunctional hydrogelators used in therapeutic applications. PMID:21494422

Schultz, Kelly M.; Baldwin, Aaron D.; Kiick, Kristi L.; Furst, Eric M.

2010-01-01

87

Hyaluronan and Stone Disease  

NASA Astrophysics Data System (ADS)

Kidney stones cannot be formed as long as crystals are passed in the urine. However, when crystals are retained it becomes possible for them to aggregate and form a stone. Crystals are expected to be formed not earlier than the distal tubules and collecting ducts. Studies both in vitro and in vivo demonstrate that calcium oxalate monohydrate crystals do not adhere to intact distal epithelium, but only when the epithelium is proliferating or regenerating, so that it possesses dedifferentiated cells expressing hyaluronan, osteopontin (OPN) and their mutual receptor CD44 at the apical cell membrane. The polysaccharide hyaluronan is an excellent crystal binding molecule because of its negative ionic charge. We hypothesized that the risk for crystal retention in the human kidney would be increased when tubular cells express hyaluronan at their apical cell membrane. Two different patient categories in which nephrocalcinosis frequently occurs were studied to test this hypothesis (preterm neonates and kidney transplant patients). Hyaluronan (and OPN) expression at the luminal membrane of tubular cells indeed was observed, which preceded subsequent retention of crystals in the distal tubules. Tubular nephrocalcinosis has been reported to be associated with decline of renal function and thus further studies to extend our knowledge of the mechanisms of retention and accumulation of crystals in the kidney are warranted. Ultimately, this may allow the design of new strategies for the prevention and treatment of both nephrocalcinosis and nephrolithiasis in patients.

Asselman, Marino

2008-09-01

88

Composition effects on the EB-induced cross-linking of some acrylate and methacrylate copolymers  

NASA Astrophysics Data System (ADS)

Copolymers of n-butyl acrylate (BuA) were irradiated with accelerated electrons to study the effect of chemical composition on their cross-linking behavior. The polymer reactivity was quantified by applying the Charlesby-Pinner method to the dose dependence of gel fraction. In copolymers including the degrading methyl methacrylate (MMA) unit and the chain linking BuA unit, the composition dependence of the yield for cross-linking G( X) has a monotonous variation, its value increasing gradually with the BuA content. The efficiency for chain scission G( S) showed another type of composition dependence, with the occurrence of a minimum when a small amount of MMA units is present in a BuA rich copolymer. Partial transesterification of the butyl side-groups of poly(BuA) by allyl alcohol yields unsaturated modified polymers with enhanced tendency for cross-linking under radiation.

Turgis, Jean-Dominique; Vergé, Christophe; Coqueret, Xavier

2003-06-01

89

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

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

90

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

PubMed

In designing a tissue engineering strategy for cartilage repair, selection of both the bioreactor, and scaffold is important to the development of a mechanically functional tissue. The hydrodynamic environment associated with many bioreactors enhances nutrient transport, but also introduces fluid shear stress, which may influence cellular response. This study examined the combined effects of hydrogel cross-linking and the hydrodynamic environment on early chondrocyte response. Specifically, chondrocytes were encapsulated in poly(ethylene glycol) (PEG) hydrogels having two different cross-linked structures, corresponding to a low and high cross-linking density. Both cross-linked gels yielded high water contents (92% and 79%, respectively) and mesh sizes of 150 and 60 A respectively. Cell-laden PEG hydrogels were cultured in rotating wall vessels (RWV) or under static cultures for up to 5 days. Rotating cultures yielded low fluid shear stresses (< or = 0.11 Pa) at the hydrogel periphery indicating a laminar hydrodynamic environment. Chondrocyte response was measured through total DNA content, total nitric oxide (NO) production, and matrix deposition for glycosaminoglycans (GAG). In static cultures, gel cross-linking had no effect on DNA content, NO production, or GAG production; although GAG production increased with culture time for both cross-linked gels. In rotating cultures, DNA content increased, NO production decreased, and overall GAG production decreased when compared to static controls for the low cross-linked gels. For the high cross-linked gels, the hydrodynamic environment had no effect on DNA content, but exhibited similar results to the low cross-linked gel for NO production, and matrix production. Our findings demonstrated that at early culture times, when there is limited matrix production, the hydrodynamic environment dramatically influences cell response in a manner dependent on the gel cross-linking, which may impact long-term tissue development. PMID:18949761

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

2009-03-01

91

Dependence of Invadopodia Function on Collagen Fiber Spacing and Cross-Linking: Computational Modeling and Experimental Evidence  

PubMed Central

Invadopodia are subcellular organelles thought to be critical for extracellular matrix (ECM) degradation and the movement of cells through tissues. Here we examine invadopodia generation, turnover, and function in relation to two structural aspects of the ECM substrates they degrade: cross-linking and fiber density. We set up a cellular automaton computational model that simulates ECM penetration and degradation by invadopodia. Experiments with denatured collagen (gelatin) were used to calibrate the model and demonstrate the inhibitory effect of ECM cross-linking on invadopodia degradation and penetration. Incorporation of dynamic invadopodia behavior into the model amplified the effect of cross-linking on ECM degradation, and was used to model feedback from the ECM. When the model was parameterized with spatial fibrillar dimensions that closely matched the organization, in real life, of native ECM collagen into triple-helical monomers, microfibrils, and macrofibrils, little or no inhibition of invadopodia penetration was observed in simulations of sparse collagen gels, no matter how high the degree of cross-linking. Experimental validation, using live-cell imaging of invadopodia in cells plated on cross-linked gelatin, was consistent with simulations in which ECM cross-linking led to higher rates of both invadopodia retraction and formation. Analyses of invadopodia function from cells plated on cross-linked gelatin and collagen gels under standard concentrations were consistent with simulation results in which sparse collagen gels provided a weak barrier to invadopodia. These results suggest that the organization of collagen, as it may occur in stroma or in vitro collagen gels, forms gaps large enough so as to have little impact on invadopodia penetration/degradation. By contrast, dense ECM, such as gelatin or possibly basement membranes, is an effective obstacle to invadopodia penetration and degradation, particularly when cross-linked. These results provide a novel framework for further studies on ECM structure and modifications that affect invadopodia and tissue invasion by cells. PMID:18515372

Enderling, Heiko; Alexander, Nelson R.; Clark, Emily S.; Branch, Kevin M.; Estrada, Lourdes; Crooke, Cornelia; Jourquin, Jérôme; Lobdell, Nichole; Zaman, Muhammad H.; Guelcher, Scott A.; Anderson, Alexander R. A.; Weaver, Alissa M.

2008-01-01

92

Dependence of invadopodia function on collagen fiber spacing and cross-linking: computational modeling and experimental evidence.  

PubMed

Invadopodia are subcellular organelles thought to be critical for extracellular matrix (ECM) degradation and the movement of cells through tissues. Here we examine invadopodia generation, turnover, and function in relation to two structural aspects of the ECM substrates they degrade: cross-linking and fiber density. We set up a cellular automaton computational model that simulates ECM penetration and degradation by invadopodia. Experiments with denatured collagen (gelatin) were used to calibrate the model and demonstrate the inhibitory effect of ECM cross-linking on invadopodia degradation and penetration. Incorporation of dynamic invadopodia behavior into the model amplified the effect of cross-linking on ECM degradation, and was used to model feedback from the ECM. When the model was parameterized with spatial fibrillar dimensions that closely matched the organization, in real life, of native ECM collagen into triple-helical monomers, microfibrils, and macrofibrils, little or no inhibition of invadopodia penetration was observed in simulations of sparse collagen gels, no matter how high the degree of cross-linking. Experimental validation, using live-cell imaging of invadopodia in cells plated on cross-linked gelatin, was consistent with simulations in which ECM cross-linking led to higher rates of both invadopodia retraction and formation. Analyses of invadopodia function from cells plated on cross-linked gelatin and collagen gels under standard concentrations were consistent with simulation results in which sparse collagen gels provided a weak barrier to invadopodia. These results suggest that the organization of collagen, as it may occur in stroma or in vitro collagen gels, forms gaps large enough so as to have little impact on invadopodia penetration/degradation. By contrast, dense ECM, such as gelatin or possibly basement membranes, is an effective obstacle to invadopodia penetration and degradation, particularly when cross-linked. These results provide a novel framework for further studies on ECM structure and modifications that affect invadopodia and tissue invasion by cells. PMID:18515372

Enderling, Heiko; Alexander, Nelson R; Clark, Emily S; Branch, Kevin M; Estrada, Lourdes; Crooke, Cornelia; Jourquin, Jérôme; Lobdell, Nichole; Zaman, Muhammad H; Guelcher, Scott A; Anderson, Alexander R A; Weaver, Alissa M

2008-09-01

93

Hyaluronan in intra-operative edema of NF1-associated neurofibromas.  

PubMed

The tumor suppressor disorder neurofibromatosis type 1 (NF1) is associated with development of multiple neurofibromas which may grow intraneurally as plexiform neurofibromas (PNF) or intracutaneously (CNF). Upon surgery neurofibromas may show prominent swelling hindering skin-edge approximation. To assess whether the water binding glycosaminoglycan hyaluronan is involved in intra-operative swelling, 51 neurofibromas from 33 NF1-patients were investigated. Hyaluronan was histologically demonstrated and was quantified by ELISA. Molecular weight of hyaluronan was determined by gel filtration. Further, hyaluronan content was measured in cultivated Schwann cells and fibroblasts. Clinically, 67% of PNF were associated with moderate or severe intra-operative swelling, whereas only 36% of CNF showed this feature. Significantly higher levels of hyaluronan content were found in PNF compared to CNF (P?hyaluronan in PNF and CNF ranged from higher than 10? Da to approximately 10? Da. Fibroblasts produced less hyaluronan than Schwann cells. The findings support the view that hyaluronan plays an important role in intra-operative swelling in neurofibroma surgery. PMID:22129111

Hagel, Christian; Behrens, Timo; Prehm, Peter; Schnabel, Claudia; Glatzel, Markus; Friedrich, Reinhard E

2012-08-01

94

Intra-articular hyaluronans in knee osteoarthritis: rationale and practical considerations.  

PubMed

Intra-articular hyaluronans are used to treat pain associated with osteoarthritis of the knee. Many controlled clinical studies have demonstrated their efficacy for this indication. The rationale for the use of hyaluronans therapeutically is based on observations that hyaluronic acid is an important component of the synovial fluid acting as a cushion and lubricant for the joint and also serving as a major component of the extracellular matrix of the cartilage, helping to enhance the ability of cartilage to resist shear and maintain a resiliency to compression. While intra-articular hyaluronans are indicated at this time only for the treatment of pain in osteoarthritis of the knee, there are data to suggest that they may also be useful in treating degenerative disease of other articular joints, as well as have an impact on disease progression. The mechanisms by which hyaluronans mediate their clinical benefit seem to be multifactorial and biologically related, in contrast to the notion that they provide only viscous fluid replacement. The safety profile of intra-articular hyaluronans is very favorable and, because they are used as a local therapy, there are no known drug interactions-an advantage for patients receiving treatment for comorbid conditions. Some adverse effects, such as pseudosepsis, have been associated with cross-linked hyaluronan agents and do not appear to be class related. PMID:15005296

Kelly, Michael A; Kurzweil, Peter R; Moskowitz, Roland W

2004-02-01

95

Chemistry of the collagen cross-links. Origin and partial characterization of a putative mature cross-link of collagen.  

PubMed Central

The conversion of the reducible divalent cross-links in collagen to non-reducible multivalent cross-links in mature collagen has resulted in the identification of several new amino acids as the putative mature cross-link. None of these compounds has completely satisfied the necessary criteria. We have now isolated an amino acid of high Mr, derived from lysine, that is only present in high-Mr peptides derived from mature collagen. Its increase with age of the tissue correlates with the decrease in the reducible cross-links, and it is present both in mature skin and bone, which are initially cross-linked through the aldimine and oxo-imine divalent cross-link respectively. We propose that this amino acid, as yet incompletely characterized and designated compound M, is a major cross-link of mature collagen. PMID:3117039

Barnard, K; Light, N D; Sims, T J; Bailey, A J

1987-01-01

96

Cross-Link Guided Molecular Modeling with ROSETTA  

PubMed Central

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. PMID:24069194

Leitner, Alexander; Rosenberger, George; Aebersold, Ruedi; Malmström, Lars

2013-01-01

97

Cross-linked polyvinyl alcohol films as alkaline battery separators  

Microsoft Academic Search

Cross-linking methods have been investigated to determine their effect on the performance of polyvinyl alcohol (PVA) films as alkaline battery separators. The following types of cross-linked PVA films are discussed: PVA-dialdehyde blends post-treated with an acid or acid periodate solution and PVA-dialdehyde blends cross-linked during film formation (drying) by using a reagent with both aldehyde and acid functionality. Laboratory samples

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

1983-01-01

98

Cross-linked polyvinyl alcohol films as alkaline battery separators  

Microsoft Academic Search

Cross-linking methods were investigated to determine their effect on the performance of polyvinyl alcohol (PVA) films as alkaline battery separators. The following types of cross-linked PVA films are discussed: (1) PVA-dialdehyde blends post-treated with an acid or acid periodate solution (two-step method) and (2) PVA-dialdehyde blends cross-linked during film formation (drying) by using a reagent with both aldehyde and acid

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

1982-01-01

99

Effects of Composition of Iron-Cross-Linked Alginate Hydrogels for Cultivation of Human Dermal Fibroblasts  

PubMed Central

We investigated the suitability of ferric-ion-cross-linked alginates (Fe-alginate) with various proportions of L-guluronic acid (G) and D-mannuronic acid (M) residues as a culture substrate for human dermal fibroblasts. High-G and high-M Fe-alginate gels showed comparable efficacy in promoting initial cell adhesion and similar protein adsorption capacities, but superior cell proliferation was observed on high-G than on high-M Fe-alginate as culture time progressed. During immersion in culture medium, high-G Fe-alginate showed little change in gel properties in terms of swelling and polymer content, but the properties of high-M Fe-alginate gel were altered due to loss of ion cross-linking. However, the degree of cell proliferation on high-M Fe-alginate gel was improved after it had been stabilized by immersion in culture medium until no further changes occurred. These results suggest that the mode of cross-linkage between ferric ions and alginate differs depending on alginate composition and that the major factor giving rise to differences in cell growth on the two types of Fe-alginate films is gel stability during culture, rather than swelling of the original gel, polymer content, or protein adsorption ability. Our findings may be useful for extending the application of Fe-alginate to diverse biomedical fields. PMID:23304153

Machida-Sano, Ikuko; Ogawa, Sakito; Ueda, Hiroyuki; Kimura, Yoshitaka; Satoh, Nao; Namiki, Hideo

2012-01-01

100

Swelling and Reswelling Characteristics of Cross-Linked Poly(vinyl alcohol)\\/Chitosan Hydrogel Film  

Microsoft Academic Search

Poly(vinyl alcohol) (PVA), hydrogel was prepared by using glutaraldehyde as a cross-linking agent. The blend semi-synthetic hydrogel film, consisting of PVA and chitosan, was prepared from a solvent-casting technique and characterized for their intermolecular interactions using infrared method. The swelling and reswelling behaviors, as well as mechanical properties of the synthetic and semi-synthetic gels were examined by weighing and tensile

Z. Abdeen

2011-01-01

101

Hyaluronan-mediated cellular adhesion  

NASA Astrophysics Data System (ADS)

Many cells surround themselves with a cushioning halo of polysaccharides that is further strengthened and organized by proteins. In fibroblasts and chrondrocytes, the primary component of this pericellular matrix is hyaluronan, a large linear polyanion. Hyaluronan production is linked to a variety of disease, developmental, and physiological processes. Cells manipulate the concentration of hyaluronan and hyaluronan receptors for numerous activities including modulation of cell adhesion, cell motility, and differentiation. Recent investigations by identify hyaluronan's role in mediating early-stage cell adhesion. An open question is how the cell removes the 0.5-10 micron thick pericellular matrix to allow for further mature adhesion events requiring nanometer scale separations. In this investigation, holographic optical tweezers are used to study the adhesion and viscoelastic properties of chondrocytes' pericellular matrix. Ultimately, we aim to shed further light on the spatial and temporal details of the dramatic transition from micron to nanometer gaps between the cell and its adhesive substrate.

Curtis, Jennifer

2005-03-01

102

Structural Analysis and Mechanical Characterization of Hyaluronic Acid-Based Doubly Cross-Linked Networks  

PubMed Central

We have created a new class of hyaluronic acid (HA)-based hydrogel materials with HA hydrogel particles (HGPs) embedded in and covalently cross-linked to a secondary network. HA HGPs with an average diameter of ?900 nm and narrow particle size distribution were synthesized using a refined reverse micelle polymerization technique. The average mesh size of the HGPs was estimated to be approximately 5.5 to 7.0 nm by a protein uptake experiment. Sodium periodate oxidation not only introduced aldehyde groups to the particles but also reduced the average particle size. The aldehyde groups generated were used as reactive handles for subsequent cross-linking with an HA derivative containing hydrazide groups. The resulting macroscopic gels contain two distinct hierarchical networks (doubly cross-linked networks, DXNs): one within individual particles and another among different particles. Bulk gels (BGs) formed by direct mixing of HA derivatives with mutually reactive groups were included for comparison. The hydrogel microstructures were collectively characterized by microscopy and neutron scattering techniques. Their viscoelasticity was quantified at low frequencies (0.1?10 Hz) using a controlled stress rheometer and at high frequencies (up to 200 Hz) with a home-built torsional wave apparatus. Both BGs and DXNs are stable elastic gels that become stiffer at higher frequencies. The HA-based DXN offers unique structural hierarchy and mechanical properties that are suitable for soft tissue regeneration. PMID:20046226

Jha, Amit K.; Hule, Rohan A.; Jiao, Tong; Teller, Sean S.; Clifton, Rodney J.; Duncan, Randall L.; Pochan, Darrin J.; Jia, Xinqiao

2009-01-01

103

Pyrrolizidine alkaloid-induced DNA-protein cross-links.  

PubMed

Pyrrolizidine alkaloids (PAs) are potent carcinogenic and anti-mitotic compounds produced by a large number of plant species. In this study, we investigated in vitro the DNA-protein cross-linking activity of several structurally diverse PAs. The DNA cross-linked proteins induced by PAs were also isolated and characterized in mammalian cells. At 300 and 500 microM, the pyrrolic PAs (dehydrosenecionine, dehydromonocrotaline, dehydroseneciphylline, dehydroriddelliine) induced potent DNA cross-links. Protein-associated DNA cross-links accounted for approximately 50% of the total cellular DNA cross-links at 300 microM. The simple necine pyrrole dehydroretronecine induced few DNA--protein cross-links and none were detected with indicine N-oxide. The major proteins cross-linked to DNA from either PA-exposed cells or pyrrolic PA-exposed nuclei were in the molecular weight 40-60 kDa range and were primarily acidic in nature (Ca. pI 4.2-5.0). The patterns of the proteins cross-linked to DNA were similar to that induced by standard bifunctional alkylating agents mitomycin C, cisdichlorodiammine platinum(II) and nitrogen mustard. The macrocyclic pyrrole dehydrosenecionine induced DNA cross-links in pBR322 plasmid DNA with BSA as a protein target. Our data indicated that pyrrolic PAs with a macrocyclic diester such as dehydrosenecionine, dehydroseneciphylline, dehydroriddelliine and dehydromonocrotaline were more potent cross-linkers than the simple necine pyrrolic dehydroretronecine. Cross-linking potency of the PAs examined here coincides with known potency differences in animal toxicity and led us to conclude that DNA--protein cross-linking activity is probably involved in PA-related PMID:7586188

Kim, H Y; Stermitz, F R; Coulombe, R A

1995-11-01

104

Identification of cross-linked peptides from large  

E-print Network

pairs based on the presence of a characteristic isotopic shift. MS2 spectra from these pairsIdentification of cross- linked peptides from large sequence databases Oliver Rinner1, Jan & Ruedi Aebersold1,2,4 We describe a method to identify cross-linked peptides from complex samples

Cai, Long

105

Multi-Scale Modeling of Cross-Linked Nanotube Materials  

NASA Technical Reports Server (NTRS)

The effect of cross-linking single-walled carbon nanotubes on the Young's modulus of a nanotube-reinforced composite is modeled with a multi-scale method. The Young's modulus is predicted as a function of nanotube volume fraction and cross-link density. In this method, the constitutive properties of molecular representative volume elements are determined using molecular dynamics simulation and equivalent-continuum modeling. The Young's modulus is subsequently calculated for cross-linked nanotubes in a matrix which consists of the unreacted cross-linking agent. Two different cross-linking agents are used in this study, one that is short and rigid (Molecule A), and one that is long and flexible (Molecule B). Direct comparisons between the predicted elastic constants are made for the models in which the nanotubes are either covalently bonded or not chemically bonded to the cross-linking agent. At a nanotube volume fraction of 10%, the Young's modulus of Material A is not affected by nanotube crosslinking, while the Young's modulus of Material B is reduced by 64% when the nanotubes are cross-linked relative to the non-cross-linked material with the same matrix.

Frankland, S. J. V.; Odegard, G. M.; Herzog, M. N.; Gates, T. S.; Fay, C. C.

2005-01-01

106

A photolithographic approach to spatially resolved cross-linked nanolayers.  

PubMed

The preparation of cross-linked nanosheets with 1-2 nm thickness and predefined shape was achieved by lithographic immobilization of trimethacryloyl thioalkanoates onto the surface of Si wafers, which were functionalized with 2-(phenacylthio)acetamido groups via a photoinduced reaction. Subsequent cross-linking via free radical polymerization as well as a phototriggered Diels-Alder reaction under mild conditions on the surface led to the desired nanosheets. Electrospray ionization mass spectrometry (ESI-MS), X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), as well as infrared reflection-absorption spectroscopy (IRRAS) confirmed the success of individual surface-modification and cross-linking reactions. The thickness and lateral size of the cross-linked structures were determined by atomic force microscopy (AFM) for samples prepared on Si wafers functionalized with a self-assembled monolayer of 1H,1H,2H,2H-perfluorodecyl groups bearing circular pores obtained via a polymer blend lithographic approach, which led to the cross-linking reactions occurring in circular nanoareas (diameter of 50-640 nm) yielding an average thickness of 1.2 nm (radical cross-linking), 1.8 nm (radical cross-linking in the presence of 2,2,2-trifluoroethyl methacrylate as a comonomer), and 1.1 nm (photochemical cross-linking) of the nanosheets. PMID:25705846

Fuchise, Keita; Lindemann, Peter; Heißler, Stefan; Gliemann, Hartmut; Trouillet, Vanessa; Welle, Alexander; Berson, Jonathan; Walheim, Stefan; Schimmel, Thomas; Meier, Michael A R; Barner-Kowollik, Christopher

2015-03-17

107

Cross-linked polyvinyl alcohol films as alkaline battery separators  

NASA Technical Reports Server (NTRS)

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

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

1982-01-01

108

Cross-linked polyvinyl alcohol films as alkaline battery separators  

NASA Technical Reports Server (NTRS)

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

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

1983-01-01

109

Cross-linked polyvinyl alcohol and method of making same  

NASA Technical Reports Server (NTRS)

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

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

1981-01-01

110

Cross-linked polyvinyl alcohol films as alkaline battery separators  

SciTech Connect

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

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

1982-03-01

111

Cross-linked polyvinyl alcohol films as alkaline battery separators  

SciTech Connect

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

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

1983-02-01

112

Fabrication of cross-linked polyethyleneimine microfibers by reactive electrospinning with in situ photo-cross-linking by UV radiation.  

PubMed

The objective of this work is to demonstrate the feasibility of fabrication of cross-linked polyethyleneimine microfibers by a reactive photo-electrospinning technology. Linear polyethyleneimine (L-PEI) has been grafted with cross-linkable methacrylate moiety by reaction with glycidyl methacrylate (GMA), enabling the polymer to cross-link upon UV exposure. The photo-cross-linking reaction was characterized by a photo-rheometer. Neat L-PEI or methacrylated L-PEI tends to aggregate rendering it very difficult to electrospin into microfibers. A high molecular weight polyvinylpyrrolidone (PVP) is an efficient chain entanglement enhancer for both L-PEI and methacrylated L-PEI and helpful to maintain fibrous structure. An optimized composition consisted of 10% methacrylated L-PEI (less than 14.8% methacrylation of total L-PEI) combined with 2% PVP and 1% photoinitiator in ethanol was successfully electrospun into smooth cross-linked microfibers using the reactive electrospinning device. Diameters of cross-linked fibers can be controlled from 419 nm to 2 ?m depending on methacrylation degree and UV irradiation intensity. The resultant cross-linked L-PEI microfibers have demonstrated significantly improved solvent resistance, thermal stability, and mechanical properties. The distinguished characteristics of this novel reactive electrospinning technology are the high cross-linking efficiency and minimal toxic chemical residues in the products. The stability of the fibers can be readily modified and controlled by the cross-linking degree, which is of great importance for biomedical applications. PMID:20690594

Xu, Xiaoming; Zhang, Jian-Feng; Fan, Yuwei

2010-09-13

113

Controlled uptake and release of lysozyme from glycerol diglycidyl ether cross-linked oxidized starch microgel.  

PubMed

A biodegradable microgel system based on glycerol-1,3-diglycidyl ether (GDGE) cross-linked TEMPO-oxidized potato starch polymers was developed for controlled uptake and release of proteins. A series of microgels were prepared with a wide range of charge density and cross-link density. We found both swelling capacity (SWw) and lysozyme uptake at saturation (?sat) increased with increasing degree of oxidation (DO) and decreasing cross-link density. Microgel of DO100% with a low cross-link density (RGDGE/polymer (w/w) of 0.025) was selected to be the optimum gel type for lysozyme absorption; ?sat increased with increasing pH and decreasing ionic strength. It suggests that the binding strength was the strongest at high pH and low ionic strength, which was recognized as the optimum absorption conditions. The lysozyme release was promoted at low pH and high ionic strength, which were considered to be the most suitable conditions for triggering protein release. These results may provide useful information for the controlled uptake and release of proteins by oxidized starch microgels. PMID:25659699

Zhao, Luhai; Chen, Yuying; Li, Wei; Lu, Meiling; Wang, Shanshan; Chen, Xiaodong; Shi, Mengxuan; Wu, Jiande; Yuan, Qipeng; Li, Yuan

2015-05-01

114

Chemoselective cross-linking and functionalization of alginate via Staudinger ligation  

PubMed Central

In this study, we demonstrate the applicability of functionalized alginate to serve as a platform for the covalent cross-linking or immobilization of complimentary phosphine functionalized groups via the chemoselective Staudinger ligation scheme. Azide groups were covalently linked to alginate through a heterobifunctional polyethylene glycol (PEG) linker and carbodiimide. Degree of azide functionalization was varied as a function of carbodiimide concentration and determined by proton nuclear magnetic resonance (1H NMR) and infrared spectroscopy. Spontaneous and covalently cross-linked alginate-PEG gels were generated via the Staudinger ligation scheme upon incubation of the azide functionalized alginate with PEG chains having 1-methyl-2-diphenylphosphino-terephthalate (MDT) as end groups. Modulation of the MDT to N3 ratio resulted in variability of gel characteristics. In addition, azide functionalized alginate retained its capacity to instantaneously form hydrogels via electrostatic interaction with multivalent cations such as Ca2+ and Ba2+. Subsequently, covalent linkage of phosphine functionalized agents post-gelation of the alginate was feasible, as illustrated via linkage of MDT-PEG-carboxyfluorescein. Capitalization of the chemoselective and cell compatible Staudinger ligation scheme for covalent cross-linking of alginate hydrogels may enhance the utility of this polymer for the stable encapsulation of various cell types, in addition to their use in the immobilization of labeling agents, proteins, and other bioactive molecules. PMID:19848408

Gattás-Asfura, Kerim M.; Stabler, Cherie L.

2010-01-01

115

Interactions of linear and cross-linked polyacrylic acid with polyvinyl ether of ethyleneglycol in some aliphatic alcohols  

Microsoft Academic Search

Summary  \\u000a The interaction of linear and cross-linked polyacrylic acid (PAA) with polyvinyl ether of ethyleneglycol (PVEEG) has been\\u000a studied in ethanol, isopropanol and their mixture. Formation of interpolymer complexes (IPC) in solutions is accompanied by\\u000a aggregation of compact particles. Gels of PAA undergo shrinking in solutions of PVEEG.

Zauresh S. Nurkeeva; Grigoriy A. Mun; Vitaliy V. Khutoryanskiy; Victor A. Kan; Alexei A. Zotov; Erengaip M. Shaikhutdinov

2000-01-01

116

Chemistry of the collagen cross-links. Isolation and characterization of two intermediate intermolecular cross-links in collagen  

PubMed Central

This paper describes the isolation from reduced collagen of two new amino acids believed to be involved, in their non-reduced form, as intermolecular cross-links stabilizing the collagen fibre. The reduction of intact collagen fibrils with tritiated sodium borohydride was found to stabilize the aldehyde-mediated cross-links to acid hydrolysis and thus allowed their location and isolation from acid hydrolysates on an automatic amino acid analyser. Comparison of the radioactive elution patterns from the autoanalyser of collagen treated in various ways before reduction permitted a preliminary classification of the peaks into cross-link precursors, intramolecular and intermolecular cross-links. The techniques employed to isolate the purified components on a large scale and to identify them structurally are described in detail. Two labile intermolecular cross-links were isolated in their reduced forms, one of which was identified by high-resolution mass spectrometry as N?-(5-amino-5-carboxypentyl)hydroxylysine. The structure of this compound was confirmed by chemical synthesis. The cross-link precursor ?-aminoadipic ?-semialdehyde was isolated in its reduced form, ?-hydroxynorleucine, together with its acid degradation product ?-chloronorleucine. A relatively stable intermolecular cross-link was isolated and partially characterized by mass spectrometry as an aldol resulting from the reaction of the ?-semialdehyde derived from lysine and hydroxylysine. PMID:5451907

Bailey, A. J.; Peach, Catherine M.; Fowler, L. J.

1970-01-01

117

21 CFR 177.2420 - Polyester resins, cross-linked.  

Code of Federal Regulations, 2012 CFR

...of this section 6. Miscellaneous materials: Castor oil, hydrogenated ?-Methylstyrene Polyethylene glycol 6000 Silicon dioxide Wax, petroleum Complying with § 178.3710 of this chapter. (c) The cross-linked polyester...

2012-04-01

118

21 CFR 177.2420 - Polyester resins, cross-linked.  

Code of Federal Regulations, 2014 CFR

...of this section 6. Miscellaneous materials: Castor oil, hydrogenated ?-Methylstyrene Polyethylene glycol 6000 Silicon dioxide Wax, petroleum Complying with § 178.3710 of this chapter. (c) The cross-linked polyester...

2014-04-01

119

21 CFR 177.2420 - Polyester resins, cross-linked.  

Code of Federal Regulations, 2013 CFR

...of this section 6. Miscellaneous materials: Castor oil, hydrogenated ?-Methylstyrene Polyethylene glycol 6000 Silicon dioxide Wax, petroleum Complying with § 178.3710 of this chapter. (c) The cross-linked polyester...

2013-04-01

120

Dynamic Role of Cross-Linking Proteins in Actin Rheology  

E-print Network

We develop a computational model to compare the relative importance of unbinding and unfolding of actin cross-linking proteins (ACPs) in the dynamic properties of the actin cytoskeleton. We show that in the strain-stiffening ...

Kim, Taeyoon

121

Swelling of model polymer networks with different cross-link densities: A computer simulation study  

NASA Astrophysics Data System (ADS)

The swelling of model polymer networks with different cross-link densities is studied via molecular dynamics simulation. During the simulation, the solvent particles, consisting of one interaction center or six interaction centers, respectively, are transfered between two coupled simulation boxes. The gel box includes both network and solvent particles, whereas the solvent box contains solvent only. The particle transfer is controlled by the solvent chemical potential difference in the two boxes, which is calculated via the Widom test particle method for the one-site solvent and via Rosenbluth sampling for the chainlike solvent. The equilibrium swelling ratio of the network as well as the solvent diffusion coefficient under subcritical and supercritical conditions are computed as functions of the network cross-link density for a wide range of temperatures and pressures. In addition, the simulated swelling behavior is compared to a Flory-Huggins-type theory, which yields qualitative agreement for the systems studied here.

Lu, Z.-Y.; Hentschke, R.

2002-10-01

122

Thermomechanical Behavior of Collagen-Cross-Linked Porcine Cornea  

Microsoft Academic Search

Purpose: Collagen cross-linking using combined riboflavin\\/UVA treatment has been shown to increase the biomechanical rigidity of the cornea and has been used successfully for the treatment of progressive keratoconus. From morphological and biochemical investigations, a different degree of cross-linking for the anterior and posterior stroma by the treatment is suggested. The present study was undertaken to better evaluate this effect

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

2004-01-01

123

Adsorption of chromium onto cross-linked chitosan  

Microsoft Academic Search

While chitosan biopolymer from crustacean shells is recognized as a good adsorbent of metals from aqueous solutions, chemical cross-linking is necessary to avoid biopolymer solubility in acidic medium. Adsorption of chromium onto cross-linked chitosan is realized by means of analysis of pH influence, particle size, adsorbent weight, concentration and oxidation state of metal. Concentrations of chromium in solution are determined

Graciela Rojas; Jorge Silva; Jaime A. Flores; Angélica Rodriguez; Martha Ly; Holger Maldonado

2005-01-01

124

Cross-linked polyvinyl alcohol and method of making same  

Microsoft Academic Search

A film-forming polyvinyl alcohol polymer is mixed with a polyaldehyde-polysaccharide cross-linking agent having at least two monosaccharide units and a plurality of aldehyde groups per molecule, preferably an average of at least one aldehyde group per monosaccharide units. The cross-linking agent, such as a polydialdehyde starch, is used in an amount of about 2.5 to 20% of the theoretical amount

L. Hsu; W. H. Philipp; D. W. Sheibley

1981-01-01

125

Comparative DNA Cross-linking by Activated Pyrrolizidine Alkaloids  

Microsoft Academic Search

The toxicity and bioactivity of pyrrolizidine alkaloids (PAs), common constituents of hundreds of plant species, and in herbal remedies and folk medicines prepared thereof, are probably due to their ability to form DNA cross-linking. We investigated DNA cross-linking activity by chemically-activated PAs from four different structural classes in Madin–Darby bovine kidney (MDBK) cells and in pBR322 DNA. In cell culture,

H.-Y. Kim; F. R. Stermitz; J. K.-K. Li; R. A. Coulombe

1999-01-01

126

Cross-linking and the molecular packing of corneal collagen  

NASA Technical Reports Server (NTRS)

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

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

1996-01-01

127

Cross-linked polyelectrolyte multilayers for marine antifouling applications.  

PubMed

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 stabilization of LbL films in a harsh environment. Covalent cross-linking was confirmed by FTIR and XPS spectroscopy. AFM was used to observe film morphology and its variation because of cross-linking, as well as to measure the thickness of the LbL films. Cross-linking improved the stability of the LbL film when it was immersed in artificial seawater, natural seawater, and in a polar organic solvent (DMSO). No changes in the thickness and topography of the film were observed in these media. The LbL films prevented settlement of Amphibalanus amphitrite barnacle cyprids and reduced adhesion of the benthic diatom Amphora coffeaeformis. Assay results indicated that the cross-linking process did not weaken the antifouling effect of LbL films. The high stability and low degree of fouling make these coatings potentially promising candidates in marine applications. PMID:23781913

Zhu, Xiaoying; Ja?czewski, Dominik; Lee, Serina Siew Chen; Teo, Serena Lay-Ming; Vancso, G Julius

2013-07-10

128

??? Cross-Links Increase Fibrin Fiber Elasticity and Stiffness  

PubMed Central

Fibrin fibers, which are ?100 nm in diameter, are the major structural component of a blood clot. The mechanical properties of single fibrin fibers determine the behavior of a blood clot and, thus, have a critical influence on heart attacks, strokes, and embolisms. Cross-linking is thought to fortify blood clots; though, the role of ?–? cross-links in fibrin fiber assembly and their effect on the mechanical properties of single fibrin fibers are poorly understood. To address this knowledge gap, we used a combined fluorescence and atomic force microscope technique to determine the stiffness (modulus), extensibility, and elasticity of individual, uncross-linked, exclusively ?–? cross-linked (?Q398N/Q399N/K406R fibrinogen variant), and completely cross-linked fibrin fibers. Exclusive ?–? cross-linking results in 2.5× stiffer and 1.5× more elastic fibers, whereas full cross-linking results in 3.75× stiffer, 1.2× more elastic, but 1.2× less extensible fibers, as compared to uncross-linked fibers. On the basis of these results and data from the literature, we propose a model in which the ?-C region plays a significant role in inter- and intralinking of fibrin molecules and protofibrils, endowing fibrin fibers with increased stiffness and elasticity. PMID:22225811

Helms, Christine C.; Ariëns, Robert A.S.; Uitte de Willige, S.; Standeven, Kristina F.; Guthold, Martin

2012-01-01

129

Cross-linked polyvinyl alcohol and method of making same  

SciTech Connect

A film-forming polyvinyl alcohol polymer is mixed with a polyaldehyde-polysaccharide cross-linking agent having at least two monosaccharide units and a plurality of aldehyde groups per molecule, preferably an average of at least one aldehyde group per monosaccharide units. The cross-linking agent, such as a polydialdehyde starch, is used in an amount of about 2.5 to 20% of the theoretical amount required to cross-link all of the available hydroxyl groups of the polyvinyl alcohol polymer. Reaction between the polymer and cross-linking agent is effected in aqueous acidic solution to produce the cross-linked polymer. The polymer product has low electrical resistivity and other properties rendering it suitable for making separators for alkaline batteries. In that event, the mixture of polymer and cross-linking agent is formed into a sheet or film or the like and the film is cut to size and otherwise fabricated into a configuration suitable for a particular end use. The crosslinking reaction is then carried out to produce the final product.

Hsu, L.; Philipp, W.H.; Sheibley, D.W.

1981-06-09

130

Preparation of water-soluble\\/insoluble derivatives of hyaluronic acid by cross-linking with epichlorohydrin in aqueous NaOH\\/NH 4OH solution  

Microsoft Academic Search

Hyaluronan (HA; 0.1 or 1mmol) was cross-linked by using epichlorohydrin (E; 0.005–0.25mol) in the presence of NaOH (0.005–0.25mol) and without or with NH4OH (0.005 or 0.01mol). The deacetylation of the N-acetyl-d-glucosamine units and a degradation of the product was confirmed in solution by NMR and the static light-scattering (LS) analysis. The products prepared with 0.005–0.1mol of NaOH, at the presence

I Šimkovic; M Hricov??ni; L Šoltés; R Mendichi; C Cosentino

2000-01-01

131

Role of hyaluronan in acute pancreatitis  

Microsoft Academic Search

Background: The connective tissue component hyaluronan is accumulated locally in the damaged tissue during various inflammatory conditions. Owing to the strong water-binding capacity of this glycosaminoglycan, increased tissue content of hyaluronan is paralleled by the development of interstitial edema. The aim with the current experiment was to investigate whether hyaluronan is accumulated in acute pancreatitis and if increased levels of

Cecilia Johnsson; Roger Hällgren; Gunnar Tufveson

2000-01-01

132

Enzymatically cross-linked bovine lactoferrin as injectable hydrogel for cell delivery.  

PubMed

Lactoferrin (LF), a 78?kDa glycoprotein, has recently been recognized as an effector molecule in the skeleton due to its ability to decrease osteoclastogenesis and increase osteoblast proliferation, survival, and differentiation. The objective of the study is to investigate the feasibility of developing an injectable hydrogel from bovine lactoferrin (bLF) as a cell delivery vehicle. The study demonstrated the feasibility of cross-linking tyramine substituted bLF in the presence of horse radish peroxidase and hydrogen peroxide (H2O2). The gel presented a mild environment to maintain mouse bone marrow-derived stromal cell (mBMSC) viability and proliferation. Stromal cells derived from multiple gene reporter transgenic mouse (Ibsp-Topaz/Dmp1-mCherry) line showed the ability of the cells to undergo osteogenic differentiation in the hydrogel when cultured in mineralization media. The cross-linked gel supported protein phosphorylation/de-phosphorylation in the encapsulated MC3T3-E1 cells. bLF and bLF gel also showed the ability to modulate growth factor production in mBMSCs. PMID:24802947

Amini, Ashley A; Kan, Ho-Man; Cui, Zhanwu; Maye, Peter; Nair, Lakshmi S

2014-11-01

133

Using pLink to Analyze Cross-Linked Peptides.  

PubMed

pLink is a search engine for high-throughput identification of cross-linked peptides from their tandem mass spectra, which is the data-analysis step in chemical cross-linking of proteins coupled with mass spectrometry analysis. pLink has accumulated more than 200 registered users from all over the world since its first release in 2012. After 2 years of continual development, a new version of pLink has been released, which is at least 40 times faster, more versatile, and more user-friendly. Also, the function of the new pLink has been expanded to identifying endogenous protein cross-linking sites such as disulfide bonds and SUMO (Small Ubiquitin-like MOdifier) modification sites. Integrated into the new version are two accessory tools: pLabel, to annotate spectra of cross-linked peptides for visual inspection and publication, and pConfig, to assist users in setting up search parameters. Here, we provide detailed guidance on running a database search for identification of protein cross-links using the 2014 version of pLink. © 2015 by John Wiley & Sons, Inc. PMID:25754995

Fan, Sheng-Bo; Meng, Jia-Ming; Lu, Shan; Zhang, Kun; Yang, Hao; Chi, Hao; Sun, Rui-Xiang; Dong, Meng-Qiu; He, Si-Min

2015-01-01

134

Spectroscopic characterization of collagen cross-links in bone  

NASA Technical Reports Server (NTRS)

Collagen is the most abundant protein of the organic matrix in mineralizing tissues. One of its most critical properties is its cross-linking pattern. The intermolecular cross-linking provides the fibrillar matrices with mechanical properties such as tensile strength and viscoelasticity. In this study, Fourier transform infrared (FTIR) spectroscopy and FTIR imaging (FTIRI) analyses were performed in a series of biochemically characterized samples including purified collagen cross-linked peptides, demineralized bovine bone collagen from animals of different ages, collagen from vitamin B6-deficient chick homogenized bone and their age- and sex-matched controls, and histologically stained thin sections from normal human iliac crest biopsy specimens. One region of the FTIR spectrum of particular interest (the amide I spectral region) was resolved into its underlying components. Of these components, the relative percent area ratio of two subbands at approximately 1660 cm(-1) and approximately 1690 cm(-1) was related to collagen cross-links that are abundant in mineralized tissues (i.e., pyridinoline [Pyr] and dehydrodihydroxylysinonorleucine [deH-DHLNL]). This study shows that it is feasible to monitor Pyr and DHLNL collagen cross-links spatial distribution in mineralized tissues. The spectroscopic parameter established in this study may be used in FTIRI analyses, thus enabling the calculation of relative Pyr/DHLNL amounts in thin (approximately 5 microm) calcified tissue sections with a spatial resolution of approximately 7 microm.

Paschalis, E. P.; Verdelis, K.; Doty, S. B.; Boskey, A. L.; Mendelsohn, R.; Yamauchi, M.

2001-01-01

135

Mapping of psoralen cross-linked nucleotides in RNA.  

PubMed Central

A method is described for using the cross-linking reagent 4'-(hydroxy-methyl)-4,5',8-trimethylpsoralen (HMT) to map base paired regions and higher-order structure within RNA molecules. Applying this method to yeast tRNAPhe, we have specifically identified cross-links within the acceptor stem between U6 X U68, in the D-stem between C11 X C25, and in the T psi-stem between U50 X C63 and U52 X C63. We have also identified a unique cross-link between U8 X C48 which are trans pyrimidines in the core region due to tertiary interactions between U8:A14 and C48:G15. The precise point of cross-linking was deduced in every case by using purine-specific U2 ribonuclease along with cytidine-specific CL3 ribonuclease which will anomalously cleave after photoreversed pyrimidines. The ability to map the precise point of cross-linking should prove invaluable in identifying nucleotides in close proximity within the tertiary structure of other RNA molecules. Images PMID:6425802

Garrett-Wheeler, E; Lockard, R E; Kumar, A

1984-01-01

136

Spectroscopic characterization of collagen cross-links in bone.  

PubMed

Collagen is the most abundant protein of the organic matrix in mineralizing tissues. One of its most critical properties is its cross-linking pattern. The intermolecular cross-linking provides the fibrillar matrices with mechanical properties such as tensile strength and viscoelasticity. In this study, Fourier transform infrared (FTIR) spectroscopy and FTIR imaging (FTIRI) analyses were performed in a series of biochemically characterized samples including purified collagen cross-linked peptides, demineralized bovine bone collagen from animals of different ages, collagen from vitamin B6-deficient chick homogenized bone and their age- and sex-matched controls, and histologically stained thin sections from normal human iliac crest biopsy specimens. One region of the FTIR spectrum of particular interest (the amide I spectral region) was resolved into its underlying components. Of these components, the relative percent area ratio of two subbands at approximately 1660 cm(-1) and approximately 1690 cm(-1) was related to collagen cross-links that are abundant in mineralized tissues (i.e., pyridinoline [Pyr] and dehydrodihydroxylysinonorleucine [deH-DHLNL]). This study shows that it is feasible to monitor Pyr and DHLNL collagen cross-links spatial distribution in mineralized tissues. The spectroscopic parameter established in this study may be used in FTIRI analyses, thus enabling the calculation of relative Pyr/DHLNL amounts in thin (approximately 5 microm) calcified tissue sections with a spatial resolution of approximately 7 microm. PMID:11585346

Paschalis, E P; Verdelis, K; Doty, S B; Boskey, A L; Mendelsohn, R; Yamauchi, M

2001-10-01

137

Viscoelastic and mechanical properties of hyaluronan films and hydrogels modified by carbodiimide.  

PubMed

This study investigated an effect of different ways of the preparation of insoluble hyaluronan material on its mechanical and viscoelastic properties. Hyaluronan (NaHy) of molecular weight Mw=500,000 g mol(-1) was modified with N-(3-dimethylaminopropyl-N'-ethylcarbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS), to be able absorb liquid without changing its mechanical properties. The modified, water insoluble NaHy materials were prepared in different geometry; as modified films and modified cylinders with exact dimensions. The occurrence of modification was confirmed by FT-IR (Fourier transform infrared spectroscopy) and (1)H NMR (proton nuclear magnetic resonance) spectroscopy and swelling test. The determined mechanical and viscoelastic properties of unmodified and modified hyaluronan revealed the high dependency of elasticity changes depending on the gel processing method. Moreover, NaHy gels in the cylindrical form with the sponge-like structure predominant them as a convenient geometry for application in a humid environment. PMID:25563954

G?und?lová, Lenka; Gregorova, Adriana; Mrá?ek, Aleš; Vícha, Robert; Smolka, Petr; Mina?ík, Antonín

2015-03-30

138

A structural model for desmosine cross-linked peptides.  

PubMed Central

Desmosine-enriched peptides were isolated from a thermolysin digest of bovine ligamentum nuchae elastin and a partial sequence was determined. A 'two-cross-link' model is proposed in which a second cross-link, perhaps lysinonorleucine, joins two peptide chains approx. 35 amino acid residues removed from the desmosine. Implied in this model is a certain asymmetry or directionality which places restrictions on the 'sense' of the peptide chains (either always parallel or anti-parallel) in order to align the cross-linking sites. Imposing such restrictions raises the possibility of specific alignment of elastin precursor molecules by microfibrillar proteins and/or aligning peptides on the precursor molecules themselves. PMID:697739

Mecham, R P; Foster, J A

1978-01-01

139

Functional polymer laminates from hyperthermal hydrogen induced cross-linking.  

PubMed

The use of a hyperthermal hydrogen induced cross-linking process to prepare laminates comprising polypropylene, poly(isobutylene-co-isoprene), and poly(vinyl acetate) is described. In this new, milder alternative to conventional plasma techniques, neutral molecular hydrogen projectiles were used to create carbon radicals on impacted surfaces by collision-induced dissociation of C-H bonds, and this process was used to cross-link polymers on a polypropylene surface. It was demonstrated that multiple layers of cross-linked materials could be added, creating polymer laminates with each layer introducing new functionalities and properties. In particular, the present work shows that the process is largely nondestructive toward ester functionalities. First, the esters were grafted to become nonleachable. Then, the esters were subsequently hydrolyzed to convert the surface from hydrophobic to hydrophilic. Afterward, the esters could be recovered by simple esterification demonstrating that further chemical transformations were possible. PMID:22060118

Thompson, David B; Trebicky, Tomas; Crewdson, Patrick; McEachran, Matthew J; Stojcevic, Goran; Arsenault, Gilles; Lau, Woon M; Gillies, Elizabeth R

2011-12-20

140

Enhanced retention of encapsulated ions in cross-linked polymersomes.  

PubMed

Polymer vesicles (polymersomes) composed of poly(butadiene-b-poly(ethylene oxide)) (PB-b-PEO) are known for their stability and limited permeability. However, when these vesicles are diluted, substances, such as ions, encapsulated in the aqueous cavity can be released due to vesicle disruption. In previous studies, we have shown that these vesicles can be loaded efficiently with sufficient quantities of radionuclides to allow application in radionuclide therapy and pharmacokinetics evaluation, provided that there is no loss of the encapsulated radionuclides when diluted in the bloodstream. In this paper, in order to stabilize the carriers, we propose to cross-link the hydrophobic part of the polymersome membrane and to investigate whether such cross-linking induced by ? radiation can enhance the retention of ions (radionuclides). Retention of ions encapsulated in the lumen in such cross-linked carriers has not been previously quantitatively evaluated, although it is of ultimate importance in any medical application. Here, we also investigate how cross-linking affects the transport of radionuclides (loading) through the membrane of the vesicles. The integrity of the vesicles as a function of the radiation dose is also investigated, including morphological changes. The results show that cross-linking hinders the transport of ions through the membrane, which also leads to higher retention of ions encapsulated prior to cross-linking in the vesicles. Electron micrographs show that the shape of the polymersomes is not greatly affected by ? radiation when left in the original solvent (phosphate buffered saline (PBS) or Milli-Q water), but when diluted in a good solvent for both blocks, i.e., tetrahydrofuran (THF), disintegration of the vesicles and the appearance of droplet-like structures is observed, which had not been reported previously. The results of the present study help to formulate polymersomes as carriers for radionuclide therapy, demonstrating a way to prevent in vivo release of radionuclides, caused by dilution-induced destabilization of the nanocarriers. PMID:25734478

Wang, Guanglin; Hoornweg, Arentien; Wolterbeek, Hubert T; Franken, Linda E; Mendes, Eduardo; Denkova, Antonia G

2015-03-19

141

Cross-Linked Nanotube Materials with Variable Stiffness Tethers  

NASA Technical Reports Server (NTRS)

The constitutive properties of a cross-linked single-walled carbon nanotube material are predicted with a multi-scale model. The material is modeled as a transversely isotropic solid using concepts from equivalent-continuum modeling. The elastic constants are determined using molecular dynamics simulation. Some parameters of the molecular force field are determined specifically for the cross-linker from ab initio calculations. A demonstration of how the cross-linked nanotubes may affect the properties of a nanotube/polyimide composite is included using a micromechanical analysis.

Frankland, Sarah-Jane V.; Odegard, Gregory M.; Herzog, Matthew N.; Gates, Thomas S.; Fay, Catherine C.

2004-01-01

142

Cross-linking of two antiparallel vortex tubes  

NASA Technical Reports Server (NTRS)

The detailed mechanisms in vortex cross-linking are unveiled by adequately resolved, direct numerical simulation of two viscous vortex tubes. There are three characteristic phases: (1) inviscid induction followed by core flattening and stretching; (2) bridging of the two vortices by accumulation of annihilated and then cross-linked vortex lines; and (3) threading of the remnants of the initial vortex pair in between the two bridges as they pull apart. These phases and the role of threading (along with bridging) in the mixing and the enstrophy cascade are explained, and it is shown that the mechanism is insensitive to asymmetries.

Melander, M. V.; Hussain, F.

1989-01-01

143

Simulation of Fracture Nucleation in Cross-Linked Polymer Networks  

NASA Astrophysics Data System (ADS)

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

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

2013-02-01

144

Cross-Linked Protein Crystals for Vaccine Delivery  

NASA Astrophysics Data System (ADS)

The progress toward subunit vaccines has been limited by their poor immunogenicity and limited stability. To enhance the immune response, subunit vaccines universally require improved adjuvants and delivery vehicles. In the present paper, we propose the use of cross-linked protein crystals (CLPCs) as antigens. We compare the immunogenicity of CLPCs of human serum albumin with that of soluble protein and conclude that there are marked differences in the immune response to the different forms of human serum albumin. Relative to the soluble protein, crystalline forms induce and sustain over almost a 6-month study a 6- to 10-fold increase in antibody titer for highly cross-linked crystals and an approximately 30-fold increase for lightly cross-linked crystals. We hypothesize that the depot effect, the particulate structure of CLPCs, and highly repetitive nature of protein crystals may play roles in the enhanced production of circulating antibodies. Several features of CLPCs, such as their remarkable stability, purity, biodegradability, and ease of manufacturing, make them highly attractive for vaccine formulations. This work paves the way for a systematic study of protein crystallinity and cross-linking on enhancement of humoral and T cell responses.

St. Clair, Nancy; Shenoy, Bhami; Jacob, Lawrence D.; Margolin, Alexey L.

1999-08-01

145

Immobilization of enzymes in photochemically cross-linked polyvinyl alcohol  

Microsoft Academic Search

Invertase and amyloglucosidase were entrapped in polyvinyl alcohol membranes through UV irradiation of pendent styrylpyridinium groups. The influence of cross-linking on immobilization efficiency was studied using prepolymers with varied cross-linker density, the above mentioned enzymes of different molecular weight, and various substrates. It was found that the larger enzyme invertase is effectively immobilized even in polymers with very low contents

Thomas Uhlich; Mathias Ulbricht; Georg Tomaschewski

1996-01-01

146

Citric-acid-derived photo-cross-linked biodegradable elastomers.  

PubMed

Citric-acid-derived thermally cross-linked biodegradable elastomers (CABEs) have recently received significant attention in various biomedical applications, including tissue-engineering orthopedic devices, bioimaging and implant coatings. However, citric-acid-derived photo-cross-linked biodegradable elastomers are rarely reported. Herein, we report a novel photo-cross-linked biodegradable elastomer, referred to as poly(octamethylene maleate citrate) (POMC), which preserves pendant hydroxyl and carboxylic functionalities after cross-linking for the potential conjugation of biologically active molecules. Pre-POMC is a low-molecular-mass pre-polymer with an average molecular mass between 701 and 1291 Da. POMC networks are soft and elastic with an initial modulus of 0.07 to 1.3 MPa and an elongation-at-break between 38 and 382%. FT-IR-ATR results confirmed the successful surface immobilization of type-I collagen onto POMC films, which enhanced in vitro cellular attachment and proliferation. Photo-polymerized POMC films implanted subcutaneously into Sprague-Dawley rats demonstrated minimal in vivo inflammatory responses. The development of POMC enriches the family of citric-acid-derived biodegradable elastomers and expands the available biodegradable polymers for versatile needs in biomedical applications. PMID:20557687

Gyawali, Dipendra; Tran, Richard T; Guleserian, Kristine J; Tang, Liping; Yang, Jian

2010-01-01

147

Enzymatically cross-linked hydrogels and their adhesive  

E-print Network

), and as surgical sealants and adhesives (4­6). An emerging approach to formation of hydrogels relies on enzymaticEnzymatically cross-linked hydrogels and their adhesive strength to biosurfaces B-H Hu PB-linked hydrogels were compared with commercial fibrin tissue adhesive. Outcome Measure ­ The shear strength between

148

INJECTABLE IN SITU CROSS-LINKING HYDROGELS FOR LOCAL ANTIFUNGAL THERAPY  

PubMed Central

Invasive fungal infections can be devastating, particularly in immunocompromised patients, and difficult to treat with systemic drugs. Furthermore, systemic administration of those medications can have severe side effects. We have developed an injectable local antifungal treatment for direct administration into existing or potential sites of fungal infection. Amphotericin B (AmB), a hydrophobic, potent, and broad-spectrum antifungal agent, was rendered water-soluble by conjugation to a dextran-aldehyde polymer. The dextran-aldehyde-AmB conjugate retained antifungal efficacy against C. albicans. Mixing carboxymethylcellulose-hydrazide with dextran-aldehyde formed a gel that cross-linked in situ by formation of hydrazone bonds. The gel provided in vitro release of antifungal activity for 11 days, and contact with the gel killed Candida for three weeks. There was no apparent tissue toxicity in the murine peritoneum and the gel caused no adhesions. Gels produced by entrapment of a suspension of AmB in CMC-dextran without conjugation of drug to polymers did not release fungicidal activity, but did kill on contact. Injectable systems of these types, containing soluble or insoluble drug formulations, could be useful for treatment of local antifungal infections, with or without concurrent systemic therapy. PMID:19942285

Hudson, Sarah; Langer, Robert; Fink, Gerald R.; Kohane, Daniel S.

2009-01-01

149

Hyaluronan in Tubular and Interstitial Nephrocalcinosis  

NASA Astrophysics Data System (ADS)

Hyaluronan (HA) is the major glycosaminoglycan (GAG) component of the renal medullary interstitium. HA is extremely large (up to 104 kDa) and composed of thousands repeating disaccharides of glucuronic acid (GlcUA) and N-acetylglucosamine (GlcNAc). HA is synthesized by hyaluronan synthases (HASs) and degraded by hyaluronidases (Hyals). The production of HA by renomedullary interstitial cells is mediated by local osmolality. When excess water needs to be excreted, increased interstitial HA seems to antagonize water reabsorption, while the opposite occurs during water conservation. Hence, papillary interstitial HA is low and Hyal high during anti-diuresis, whereas during diuresis HA is high and Hyal low. The polyanion HA plays a role in the reabsorption of hypotonic fluid by immobilizing cations (Na+) via the carboxylate (COO-) groups of GlcUA. The binding of Ca2+ to anionic HA is probably also responsible for the fact that the papilla does not become a stone despite the extremely high interstitial phosphate and oxalate. HA is also an excellent crystal binding molecule. The expression of HA at the luminal surface of renal tubular cells leads to tubular nephrocalcinosis (tubular NC). Calcium staining methods (Von Kossa, Yasue) demonstrated that crystallization inhibitors cannot avoid the occasional precipitation of calcium phosphate in the papillary interstitium (interstitial NC). These crystals are probably immediately immobilized by the gel-like HA matrix. After ulcerating through the pelvic wall the calcified matrix becomes a Randall's plaque. The attachment of calcium oxalate crystals from the primary urine to plaque may ultimately lead to the development of clinical stones in the renal calyces (nephrolithiasis).

Verkoelen, Carl F.

2007-04-01

150

Swelling and Re-Swelling Characteristics of Cross-Linked Poly (Vinyl Alcohol)\\/Chitosan Hydrogel Film  

Microsoft Academic Search

Poly(vinyl alcohol)(PVA), hydrogel was prepared by using glutaraldehyde as a cross-linking agent. The blend semi-synthetic hydrogel film, consisting of PVA and chitosan, was prepared from a solvent-casting technique and characterized for their intermolecular interactions using infrared method. The swelling and re-swelling behaviors, as well as mechanical properties of the synthetic and semi-synthetic gels were examined by weighing and tensile testing,

Z. Abdeen

2011-01-01

151

Graft copolymerization onto polybutadiene: Cross-linking and thermal degradation of vinyl polymers and copolymers  

NASA Astrophysics Data System (ADS)

This work consists of three parts. In Part I, the graft copolymerization of methyl methacrylate, methyl acrylate, methacylic acid and acrylic acid onto polybutadiene and its copolymers by benzoyl peroxide, BPO, or 2, 2'azobis(2-methylpropionitrile), AIBN, initiation were explored. The results show that these monomers can be grafted onto butadiene region of butadiene-containing polymers. The extent of both graft copolymerization and homopolymerization are dependent on the time and temperature of the reaction and the concentration of all of the reactants. One must specify the monomer, initiator and solvent for the efficient graft copolymerization. The methyl methacrylate adds directly to the radical sites which are formed on the backbone by the interaction of the polymer and the primary radical form the initiator, while for the other three monomers, the graft copolymerization occurs by addition of macro-radical to the double bonds. In Part II, the cross-linking of polybutadiene, butadiene-styrene copolymers, and polystyrene by irradiation, thermal and chemical processes, and Friedel-Crafts chemistry and the effect of cross-linking on the thermal stability were investigated. The proof of cross-linking of the polymer comes from the insolubility of the product after the cross-linking reaction and is characterized by gel content and swelling ratio. The results show that the thermal stability of the polymer can be improved by cross-linking. In Part III, the thermal degradation of three vinyl polymers, poly(vinylsulfonic acid) and its sodium salt and poly(vinylphosphonic acid) were studied by combination technique: TGA/FTIR. The results show that TGA/FTIR combined with analysis of residues provides an excellent opportunity to understand the degradation pathway of the compounds. The observation of foaming indicates that the char which is formed contains carbon as well as the inorganic salts which have been observed. The carbon is in a partially graphitized form. The salts produce a very large amount of char and may prove useful to impart increased flame retardance to other polymers if they can be incorporated in a convenient manner into these polymers.

Jiang, Dayue (David)

152

Direct quantification of the rupture force of single hyaluronan\\/hyaluronan binding protein bonds  

Microsoft Academic Search

The non-covalent bond between aggrecan and hyaluronan is critical for maintaining the normal structure and function of the extracellular matrix in articular cartilage. The failure of this bond can cause the loss of aggrecan and destruction of the extracellular matrix of articular cartilage. In this study, the rupture force of the single bond between hyaluronan and hyaluronan binding protein –

Xuhui Liu; Jian Q. Sun; Michael H. Heggeness; Ming-Long Yeh; Zong-Ping Luo

2004-01-01

153

Transient Anisocoria after Corneal Collagen Cross-Linking  

PubMed Central

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

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

2014-01-01

154

Transparent Humidity Sensor Using Cross-Linked Polyelectrolyte Membrane  

SciTech Connect

This paper describes the fabrication of a porous cross-linked polyelectrolyte membrane and the characterization of its humidity sensitivity performance. Electrostatic self-assembly, combined with acid treatment, and post-deposition annealing produced the membrane. The fabrication process offers the ability to control the thickness of the membrane, as well as enabling the engineering of the humidity sensitivity properties. A transparent humidity sensor was fabricated by integrating the membrane between two parallel electrodes. In order to improve the moisture absorption and diffusion, both the polyelectrolyte layer and the electrode were made porous. The membrane was cross-linked to enhance the durability in high humid environments. Such a polyelectrolyte membrane showed high sensitivity to relative humidity variation over a range of 25%–99%. The see-through property of the structure adds extra features and benefits to the sensor.

Zhang, Q.; Smith, James R.; Saraf, Laxmikant V.; Hua, Feng

2009-07-02

155

Cross-Linked Fiber Network Embedded in Elastic Matrix  

PubMed Central

The mechanical behavior of a three-dimensional cross-linked fiber network embedded in matrix is studied in this work. The network is composed from linear elastic fibers which store energy only in the axial deformation mode, while the matrix is also isotropic and linear elastic. Such systems are encountered in a broad range of applications, from tissue to consumer products. As the matrix modulus increases, the network is constrained to deform more affinely. This leads to internal forces acting between the network and the matrix, which produce strong stress concentration at the network cross-links. This interaction increases the apparent modulus of the network and decreases the apparent modulus of the matrix. A model is developed to predict the effective modulus of the composite and its predictions are compared with numerical data for a variety of networks. PMID:24089623

Zhang, L.; Lake, S.P.; Barocas, V.H.; Shephard, M.S.; Picu, R.C.

2013-01-01

156

Cross-linked filamentous phage as an affinity matrix  

Microsoft Academic Search

Filamentous phage can be cross-linked to make a hydrophilic aggregate that is pelleted by low-speed centrifugation. The aggregate is stable at near-neutral pHs, and withstands exposure to the acid buffers (pH down to 2.2) that are often used as eluents in immunoaffinity purification. If a peptide epitope is genetically fused to a coat protein on the virion surface, the aggregate

George P Smith; Valery A Petrenko; Leslie J Matthews

1998-01-01

157

Estimating the Degree of Cross-Linking in Rubber  

NASA Technical Reports Server (NTRS)

Degree of cross-linking or network chain concentration of rubber estimated with aid of new method. Quantity is needed in studies of mechanical behavior of rubber. New method is based on finding rubber follows different stress/ strain relationships in extension and retraction. When rubber specimen is stretched to given extension ration and released. Stress-vs-strain curve follows two paths: one for extension and other for retraction.

Fedors, R. F.

1983-01-01

158

Reversible PH Lability of Cross-Linked Vault Nanocapsules  

SciTech Connect

Vaults are ubiquitous, self-assembled protein nanocapsules with dimension in the sub-100 nm range that are conserved across diverse phyla from worms to humans. Their normal presence in humans at a copy number of over 10 000/cell makes them attractive as potential drug delivery vehicles. Toward this goal, bifunctional amine-reactive reagents are shown to be useful for the reversible cross-linking of recombinant vaults such that they may be closed and opened in a controllable manner.

Yu, M.; Ng, B.C.; Rome, L.H.; Tolbert, S.H.; Monbouquette, H.G.

2009-05-28

159

Ion exchange selectivity for cross-linked polyacrylic acid  

NASA Technical Reports Server (NTRS)

The ion separation factors for 21 common metal ions with cross-linked polyacrylic acid were determined as a function of pH and the percent of the cross-linked polyacrylic acid neutralized. The calcium ion was used as a reference. At a pH of 5 the decreasing order of affinity of the ions for the cross-linked polyacrylic acid was found to be: Hg++, Fe+++, Pb++, Cr+++, Cu++, Cd++, Al+++, Ag+, Zn++, Ni++, Mn++, Co++, Ca++, Sr++, Ba++, Mg++, K+, Rb+, Cs+, Na+, and Li+. Members of a chemical family exhibited similar selectivities. The Hg++ ion appeared to be about a million times more strongly bound than the alkali metal ions. The relative binding of most of the metal ions varied with pH; the very tightly and very weakly bound ions showed the largest variations with pH. The calcium ion-hydrogen ion equilibrium was perturbed very little by the presence of the other ions. The separation factors and selectivity coefficients are discussed in terms of equilibrium and thermodynamic significance.

May, C. E.; Philipp, W. H.

1983-01-01

160

Fiber optic immunosensor for cross-linked fibrin concentration  

NASA Astrophysics Data System (ADS)

Working with calcium ions in the blood, platelets produce thromboplastin which transforms prothrombin into thrombin. Removing peptides, thrombin changes fibrinogen into fibrin. Cross-linked insoluble fibrin polymers are solubilized by enzyme plasmin found in blood plasma. Resulting D-dimers are elevated in patients with intravascular coagulation, deep venous thrombosis, pulmonary embolism, myocardial infarction, multiple trauma, cancer, impaired renal and liver functions, and sepsis. Consisting principally of a NIR 780 nm GaAlAs laser diode and a 800 nm avalanche photodiode (APD), the fiber-optic immunosensor can determined D-dimer concentration to levels <0.1 ng/ml. A capture monoclonal antibody to the antigen soluble cross-linked fibrin is employed. Immobilized at the tip of an optical fiber by avidin-biotin, the captured antigen is detected by a second antibody which is labeled with NN 382 fluorescent dye. An evanescent wave traveling on an excitation optical fiber excites the antibody-antigen fluorophore complex. Concentration of cross-linked fibrin is directly proportional to the APD measured intensity of fluorescence. NIR fluorescence has advantages of low background interference, short fluorescence lifetime, and large difference between excitation and emission peaks. Competitive ELISA test for D-dimer concentration requires trained personnel performing a time consuming operation.

Moskowitz, Samuel E.

2000-08-01

161

Homogeneous UVA system for corneal cross-linking treatment  

NASA Astrophysics Data System (ADS)

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

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

2010-02-01

162

Structural characterization of Y1 and Y2 receptors for neuropeptide Y and peptide YY by affinity cross-linking  

SciTech Connect

Pharmacological studies indicate that peptide YY (PYY) and neuropeptide Y interact with multiple binding sites, categorized as Y1 and Y2 subtypes. In order to identify and structurally characterize the Y1 and Y2 receptors we covalently cross-linked (125I-Tyr36)PYY to its receptors. The Y2 receptor in rat hippocampus and rabbit kidney membranes was affinity labeled using different homo- and heterobifunctional cross-linking reagents. Analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiography resulted in a major labeled protein band of Mr = 50,000 in both hippocampal and kidney membranes, which was unaffected by reducing agents. The Y1 receptor was analyzed in membranes from the MC-IXC human neuroblastoma cell line. Autoradiography revealed two labeled bands at Mr = 70,000 and 45,000. As the intensity of the Mr = 45,000 band was reduced by protease inhibitors, it is likely that this band is a degradation product of the larger band. Labeling of these proteins was obtained only when N-5-azido-2-nitrobenzoyloxysuccinimide was employed for cross-linking followed by exposure to UV light. Labeling of the two cross-linked bands was unaffected by reducing agents. The binding of radiolabeled PYY and the intensity of the cross-linked bands, for both the Y1 and Y2 receptors, were inhibited similarly in a dose-dependent manner by increasing concentrations of unlabeled PYY. When exposed to agarose-coupled lectins, the detergent-solubilized Y1 receptor-hormone complex was completely adsorbed by wheat germ agglutinin and partially by ricin communis II. The cross-linked Y2 receptor was almost totally adsorbed by wheat germ agglutinin-agarose and partially adsorbed by concanavalin A. The adsorptions were in all cases blocked by the appropriate hapten sugar.

Sheikh, S.P.; Williams, J.A. (Univ. of Michigan, Ann Arbor (USA))

1990-05-15

163

Algorithms for Identifying Protein Cross-links via Tandem Mass Spectrometry  

E-print Network

Algorithms for Identifying Protein Cross-links via Tandem Mass Spectrometry Ting Chen Jake Ja e y George M. Church z Abstract Cross-linking technology combined with tandem mass spectrometry is a powerful structures. We studied the problem of detecting the cross-linked peptides and cross-linked amino acids from

Church, George M.

164

Surface grafted chitosan gels. Part II. Gel formation and characterization.  

PubMed

Responsive biomaterial hydrogels attract significant attention due to their biocompatibility and degradability. In order to make chitosan based gels, we first graft one layer of chitosan to silica, and then build a chitosan/poly(acrylic acid) multilayer using the layer-by-layer approach. After cross-linking the chitosan present in the polyelectrolyte multilayer, poly(acrylic acid) is partly removed by exposing the multilayer structure to a concentrated carbonate buffer solution at a high pH, leaving a surface-grafted cross-linked gel. Chemical cross-linking enhances the gel stability against detachment and decomposition. The chemical reaction between gluteraldehyde, the cross-linking agent, and chitosan was followed in situ using total internal reflection Raman (TIRR) spectroscopy, which provided a molecular insight into the complex reaction mechanism, as well as the means to quantify the cross-linking density. The amount of poly(acrylic acid) trapped inside the surface grafted films was found to decrease with decreasing cross-linking density, as confirmed in situ using TIRR, and ex situ by Fourier transform infrared (FTIR) measurements on dried films. The responsiveness of the chitosan-based gels with respect to pH changes was probed by quartz crystal microbalance with dissipation (QCM-D) and TIRR. Highly cross-linked gels show a small and fully reversible behavior when the solution pH is switched between pH 2.7 and 5.7. In contrast, low cross-linked gels are more responsive to pH changes, but the response is fully reversible only after the first exposure to the acidic solution, once an internal restructuring of the gel has taken place. Two distinct pKa's for both chitosan and poly(acrylic acid), were determined for the cross-linked structure using TIRR. They are associated with populations of chargeable groups displaying either a bulk like dissociation behavior or forming ionic complexes inside the hydrogel film. PMID:25006685

Liu, Chao; Thormann, Esben; Claesson, Per M; Tyrode, Eric

2014-07-29

165

Probing actin polymerization by intermolecular cross-linking  

PubMed Central

We have used N,N'-1,4-phenylenebismaleimide, a bifunctional sulfhydryl cross-linking reagent, to probe the oligomeric state of actin during the early stages of its polymerization into filaments. We document that one of the first steps in the polymerization of globular monomeric actin (G-actin) under a wide variety of ionic conditions is the dimerization of a significant fraction of the G-actin monomer pool. As polymerization proceeds, the yield of this initial dimer ("lower" dimer with an apparent molecular mass of 86 kD by SDS-PAGE [LD]) is attenuated, while an actin filament dimer ("upper" dimer with an apparent molecular mass of 115 kD by SDS-PAGE [UD] as characterized [Elzinga, M., and J. J. Phelan. 1984. Proc. Natl. Acad. Sci. USA. 81:6599-6602]) is formed. This shift from LD to UD occurs concomitant with formation of filaments as assayed by N-(1-pyrenyl)iodoacetamide fluorescence enhancement and electron microscopy. Isolated cross-linked LD does not form filaments, while isolated cross-linked UD will assemble into filaments indistinguishable from those polymerized from unmodified G-actin under typical filament-forming conditions. The presence of cross-linked LD does not effect the kinetics of polymerization of actin monomer, whereas cross-linked UD shortens the "lag phase" of the polymerization reaction in a concentration-dependent fashion. Several converging lines of evidence suggest that, although accounting for a significant oligomeric species formed during early polymerization, the LD is incompatible with the helical symmetry defining the mature actin filament; however, it could represent the interfilament dimer found in paracrystalline arrays or filament bundles. Furthermore, the LD is compatible with the unit cell structure and symmetry common to various types of crystalline actin arrays (Aebi, U., W. E. Fowler, G. Isenberg, T. D. Pollard, and P. R. Smith. 1981. J. Cell Biol. 91:340-351) and might represent the major structural state in which a mutant beta-actin (Leavitt, J., G. Bushar, T. Kakunaga, H. Hamada, T. Hirakawa, D. Goldman, and C. Merril. 1982. Cell. 28:259-268) is arrested under polymerizing conditions. PMID:3346326

1988-01-01

166

Effect of chemical cross-linking on gelatin membrane solubility with a non-toxic and non-volatile agent: Terephthalaldehyde.  

PubMed

In this paper, terephthalaldehyde (TPA) is proposed as non-toxic and non-volatile gelatin cross-linker. Optimal cross-linking parameters (TPA/gelatin ratio, temperature) were first determined from in situ rheological measurements on gelatin solutions and from chemical tests with 2,4,6-trinitrobenzenesulfonic acid (TNBS assays) on gelatin gel. The highest cross-linking ratio was achieved for a concentration of 0.005g TPA/g gelatin at 60°C. The impact of TPA cross-linking on gelatin membrane functional properties (water swelling ratio, water vapor sorption and mechanical properties) was measured. TPA cross-linking increased 17 times the liquid water resistance duration of gelatin films, and delayed the entry of vapor water in the polymer matrix for 7 days, indicating that TPA increased the hydrophobic character of the gelatin matrix. PMID:25478961

Biscarat, Jennifer; Galea, Benjamin; Sanchez, José; Pochat-Bohatier, Celine

2015-03-01

167

Tissue integrity signals communicated by high-molecular weight hyaluronan and the resolution of inflammation  

PubMed Central

The extracellular matrix polysaccharide hyaluronan (HA) exerts size-dependent effects on leukocyte behavior. Low-molecular weight HA is abundant at sites of active tissue catabolism and promotes inflammation via effects on Toll-like receptor signaling. Conversely, high-molecular weight HA is prevalent in uninjured tissues and is anti-inflammatory. We propose that the ability of high-molecular weight but not low-molecular weight HA to cross-link CD44 functions as a novel form of pattern recognition that recognizes intact tissues and communicates “tissue integrity signals” that promote resolution of local immune responses. PMID:24614953

Ruppert, S. M.; Hawn, T. R.; Arrigoni, A.; Wight, T. N.

2014-01-01

168

Tissue integrity signals communicated by high-molecular weight hyaluronan and the resolution of inflammation.  

PubMed

The extracellular matrix polysaccharide hyaluronan (HA) exerts size-dependent effects on leukocyte behavior. Low-molecular weight HA is abundant at sites of active tissue catabolism and promotes inflammation via effects on Toll-like receptor signaling. Conversely, high-molecular weight HA is prevalent in uninjured tissues and is anti-inflammatory. We propose that the ability of high-molecular weight but not low-molecular weight HA to cross-link CD44 functions as a novel form of pattern recognition that recognizes intact tissues and communicates "tissue integrity signals" that promote resolution of local immune responses. PMID:24614953

Ruppert, S M; Hawn, T R; Arrigoni, A; Wight, T N; Bollyky, P L

2014-05-01

169

Degradation of Cross-Linked and Non-Cross-Linked Arabinoxylans by the Intestinal Microbiota in Children  

PubMed Central

In humans, nonstarch polysaccharides (NSP), such as arabinoxylans (AX), are not digested in the upper gut and provide fermentable carbon sources for bacteria growing in the large bowel. Despite the ubiquity of AX in nature, the microbiologic and physiologic consequences of AX digestion in the gut are poorly understood. In this study, we investigated the breakdown of ferulic acid-cross-linked AX (AXF) and non-cross-linked AX in children's intestinal microbiotas, using starch as a readily fermentable polysaccharide for comparative purposes. The experiments were performed using pH-controlled fermentation vessels under anaerobic conditions. The results demonstrated that there was variation in the metabolism of these polysaccharides by colonic microbiotas. AX was always degraded more slowly than starch, while ferulic acid cross-linking reduced the rate of AX fermentation, as shown by fermentation product measurements. Starch digestion was associated with significant acetate and butyrate production, whereas AX breakdown resulted in increased propionate formation. In general, the presence of fermentable carbohydrate significantly increased the total anaerobe counts and eubacterial rRNA concentrations (P < 0.01), while non-cross-linked AX digestion was principally associated with increased viable counts of Bacteroides fragilis group organisms, which was supported by increases in Bacteroides-Porphyromonas-Prevotella group rRNA (P < 0.01). Starch was considerably more bifidogenic than AX in these fermentations. In conclusion, in this study we found that the effects of AX and AXF on the microbial ecology and metabolism of intestinal microbiotas are similar in children and adults. PMID:14602586

Hopkins, Mark J.; Englyst, Hans N.; Macfarlane, Sandra; Furrie, Elizabeth; Macfarlane, George T.; McBain, Andrew J.

2003-01-01

170

Enzymatically cross-linked injectable alginate-g-pyrrole hydrogels for neovascularization.  

PubMed

Microparticles capable of releasing protein drugs are often incorporated into injectable hydrogels to minimize their displacement at an implantation site, reduce initial drug burst, and further control drug release rates over a broader range. However, there is still a need to develop methods for releasing drug molecules over extended periods of time, in order to sustain the bioactivity of drug molecules at an implantation site. In this study, we hypothesized that a hydrogel formed through the cross-linking of pyrrole units linked to a hydrophilic polymer would release protein drugs in a more sustained manner, because of an enhanced association between cross-linked pyrrole groups and the drug molecules. To examine this hypothesis, we prepared hydrogels of alginate substituted with pyrrole groups, alginate-g-pyrrole, through a horse-radish peroxidase (HRP)-activated cross-linking of the pyrrole groups. The hydrogels were encapsulated with poly(lactic-co-glycolic acid) (PLGA) microparticles loaded with vascular endothelial growth factor (VEGF). The resulting hydrogel system released VEGF in a more sustained manner than Ca(2+) alginate or Ca(2+) alginate-g-pyrrole gel systems. Finally, implantations of the VEGF-releasing HRP-activated alginate-g-pyrrole hydrogel system on chicken chorioallantoic membranes resulted in the formation of blood vessels in higher densities and with larger diameters, compared to other control conditions. Overall, the drug releasing system developed in this study will be broadly useful for regulating release rates of a wide array of protein drugs, and further enhance the quality of protein drug-based therapies. PMID:23886705

Devolder, Ross; Antoniadou, Eleni; Kong, Hyunjoon

2013-11-28

171

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

PubMed

Casein micelles are porous colloidal particles, constituted of casein molecules, water, and minerals. The vulnerability of the supramolecular structure of casein micelles face to changes in the environmental conditions restrains their applications in other domains besides food. Thus, redesigning casein micelles is a challenge to create new functionalities for these biosourced particles. The objective of this work was to create stable casein microgels from casein micelles using a natural cross-linker, named genipin. Suspensions of purified casein micelles (25 g L(-1)) were mixed with genipin solutions to have final concentrations of 5, 10, and 20 mM genipin. Covalently linked casein microgels were formed via cross-linking of lysyl and arginyl residues of casein molecules. The reacted products exhibited blue color. The cross-linking reaction induced gradual changes on the colloidal properties of the particles. The casein microgels were smaller and more negatively charged and presented smoother surfaces than casein micelles. These results were explained based on the cross-linking of free NH2 present in an external layer of ?-casein. Light scattering and rheological measurements showed that the reaction between genipin and casein molecules was intramicellar, as one single population of particles was observed and the values of viscosity (and, consequently, the volume fraction of the particles) were reduced. Contrary to the casein micelles, the casein microgels were resistant to the presence of dissociating agents, e.g., citrate (calcium chelating) and urea, but swelled as a consequence of internal electrostatic repulsion and the disruption of hydrophobic interactions between protein chains. The casein microgels did not dissociate at the air-solution interface and formed solid-like interfaces rather than a viscoelastic gel. The potential use of casein microgels as adaptable nanocarriers is proposed in the article. PMID:25117401

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

2014-09-01

172

Surface Cross-Linked Poly (Vinyl Alcohol) Hydrogel for Colon Targeted Drug Release  

Microsoft Academic Search

A series of surface cross-linked PVA hydrogels (previously bulk cross-linked with maleic anhydride) were prepared for different cross-linker (glutaraldehyde) concentration. FTIR-ATR study revealed the cross-linking reaction. Surface cross-linking results in contraction of pores and increase in hydrophobicity, pore tortuosity around the surface of the membrane. As a result swelling, drug release decreases with increasing glutaraldehyde concentration. After surface cross-linking swelling

Piyali Basak; Basudam Adhikari; Alok Kumar Sen

2011-01-01

173

Effect of hydrogen atmosphere on the cross-linking of vinyl polymers  

NASA Astrophysics Data System (ADS)

Numerous mechanisms have been proposed for cross-linking during irradiation, but at present the free radical mechanism has gained widest acceptance. According this mechanism a lateral bond is formed during the interaction of two polymerical radicals sufficiently close to each other; the formation of this radical pair as a result of two independent primary events is in practice impossible because of the randon distribution of the ionization and exitation in the substance. It is natural to assume that after the hydrogen atom has split off from the polymer molecule, it splits another hydrogen atom forming the second polymeric radical; this position becomes much simpler, if one allows for the possibility of intra and intermolecular migration of the polymeric radical, favoring the mutual interaction of these radicals. In this paper different vinyl polymers such as polystyrene, polypropylene, polyvinyl alcohol and polyethylen glycol were irradiated with gamma rays under hydrogen atmosphere and the increasing in gel formation was compared with air or vacuum irradiation in order to determine the importance of H 2 in cross-linking.

Burillo, G.; Carreon, M. P.; Charlesby, A.

174

Thiomer nanoparticles: stabilization via covalent cross-linking.  

PubMed

The purpose of this study was the development of stable thiomer nanoparticles for mucosal drug delivery. Chitosan-thioglycolic acid (chitosan-TGA) nanoparticles (NP) were formed via ionic gelation with tripolyphosphate (TPP). In order to stabilize the NP inter- and intra-molecular disulfide bonds were formed via controlled oxidation with hydrogen peroxide (H?O?). Thereafter, stability was investigated in saline and simulated body fluids at pH 2 and pH 5.5 via optical density measurements. The mucoadhesive properties were evaluated in vitro on freshly excised porcine intestinal mucosa via the rotating cylinder method. Particles had a mean size of 158?±?8?nm and a zeta potential of ~?+?16 mV. Three different degrees of oxidation were adjusted by the addition of H?O? in final concentrations of 10.60 µmol (chitosan-TGA (ox1)), 21.21 µmol (chitosan-TGA (ox2)), and 31.81 µmol (chitosan-TGA (ox3)) leading to 60%, 75%, and 83% of oxidized thiol groups, respectively. More than 99% of chitosan-TGA (ox3) NP, 70% of chitosan-TGA (ox2) NP, and 50% of chitosan-TGA (ox1) NP were stable over a 60-min period in simulated gastric fluid. In contrast, only 10% of unmodified chitosan and chitosan-TGA NP which were just ionically cross-linked remained stable in the same experiment. The adhesion times of covalently cross-linked chitosan-TGA (ox1), chitosan-TGA (ox2), and chitosan-TGA (ox3) were ~?41-fold, 31-fold, and 25-fold longer in comparison to unmodified ionically cross-linked chitosan. The method described here might be useful for the preparation of stable nanoparticulate drug delivery systems. PMID:22111974

Barthelmes, Jan; Dünnhaupt, Sarah; Hombach, Juliane; Bernkop-Schnürch, Andreas

2011-11-01

175

Deregulation of hyaluronan synthesis, degradation and binding promotes breast cancer.  

PubMed

Clinical and experimental data indicate that hyaluronan accumulates in breast cancer compared with normal breast epithelium, which correlates to poor prognosis. In this review, we discuss the expression of genes encoding enzymes that synthesize or degrade hyaluronan, i.e. hyaluronan synthases and hyaluronidases or bind hyaluronan, i.e. CD44 and receptor for hyaluronan-mediated motility (RHAMM, also designated as HMMR or CD168), in relation to breast cancer progression. Hyaluronan and hyaluronan receptors have multi-faceted roles in signalling events in breast cancer. A better understanding of the molecular mechanisms underlying these signalling pathways is highly warranted and may lead to improvement of cancer treatment. PMID:24092768

Heldin, Paraskevi; Basu, Kaustuv; Olofsson, Berit; Porsch, Helena; Kozlova, Inna; Kahata, Kaoru

2013-11-01

176

Swelling enhanced remanent magnetization of hydrogels cross-linked with magnetic nanoparticles.  

PubMed

Hydrogels that are pH-sensitive and partially cross-linked by cobalt ferrite nanoparticles exhibit remarkable remanent magnetization behavior. The magnetic fields measured outside our thin disks of ferrogel are weak, but in the steady state, the field dependence on the magnetic content of the gels and the measurement geometry is as expected from theory. In contrast, the time-dependent behavior is surprisingly complicated. During swelling, the remanent field first rapidly increases and then slowly decreases. We ascribe the swelling-induced field enhancement to a change in the average orientation of magnetic dipolar structures, while the subsequent field drop is due to the decreasing concentration of nanoparticles. During shrinking, the field exhibits a much weaker time dependence that does not mirror the values found during swelling. These observations provide original new evidence for the markedly different spatial profiles of the pH during swelling and shrinking of hydrogels. PMID:25485553

van Berkum, Susanne; Biewenga, Pieter D; Verkleij, Suzanna P; van Zon, J Hans B A; Boere, Kristel W M; Pal, Antara; Philipse, Albert P; Erné, Ben H

2015-01-13

177

Biodegradable Elastomeric Networks: Highly Efficient Cross-Linking of Poly(trimethylene carbonate) by Gamma Irradiation in the Presence of Pentaerythritol Triacrylate  

Microsoft Academic Search

Biodegradable elastomeric poly(trimethylene carbonate) (PTMC) networks were efficiently formed by gamma irradiating the linear polymer in the presence of pentaerythritol triacrylate (PETA). The properties of networks formed upon irradiation of PTMC films containing (0, 1, 5 wt %) PETA as a cross-linking aid were evaluated. The gel contents and network densities increased with increasing PETA contents, irradiation dose, and initial

Erhan Bat; Jan Feijen; Dirk W. Grijpma

2010-01-01

178

Conventional versus accelerated collagen cross-linking for keratoconus.  

PubMed

: Collagen cross-linking (CXL) is a procedure that primarily aims to increase corneal stiffness. Although used for a variety of conditions, it is most commonly applied to the treatment of keratoconus. Collagen cross-linking involves irradiation of the cornea with ultraviolet A (UVA) irradiation after it has been soaked with riboflavin (vitamin B), a photosensitizer. In conventional treatment, based on the Dresden protocol, a minimum corneal thickness threshold of 400 ?m is recommended and UVA (370 nm) irradiation of 3 mW/cm irradiance is applied for 30 min, resulting in a cumulative dose of 5.4 J/cm. Evidence presented in this review shows that conventional CXL stabilizes the vision and corneal topographic parameters in the majority of treated patients, with only a small failure rate. It has a good safety profile with no endothelial cell loss and a small risk of corneal infiltration and infection. To reduce the treatment duration, accelerated protocols of similar efficacy have been sought. In accelerated protocols, UVA irradiation of higher irradiance, typically 9 mW/cm, is applied for a shorter time, typically 10 min. The evidence, limited to small studies with short follow-up, shows that they may also stabilize the vision and the ectasia, with no additional safety concerns highlighted. Randomized controlled studies are, however, required to confirm the encouraging results and noninferiority to conventional treatment. PMID:25503903

Konstantopoulos, Aris; Mehta, Jodhbir S

2015-03-01

179

Thermoset-cross-linked lignocellulose: a moldable plant biomass.  

PubMed

The present work demonstrates a high biomass content (i.e., up to 90% by weight) and moldable material by controlled covalent cross-linking of lignocellulosic particles by a thermoset through epoxide-hydroxyl reactions. As an example for lignocellulosic biomass, Eastern redcedar was employed. Using scanning fluorescence microscopy and vibrational spectroscopy, macroscopic to molecular scale interactions of the thermoset with the lignocellulose have been revealed. Impregnation of the polymer resin into the biomass cellular network by capillary action as well as applied pressure results in a self-organizing structure in the form of thermoset microrods in a matrix of lignocellulose. We also infer permeation of the thermoset into the cell walls from the reaction of epoxides with the hydroxyls of the lignin. Compression tests reveal, at 30% thermoset content, thermoset-cross-linked lignocellulose has superior mechanical properties over a commercial wood plastic composite while comparable stiffness and strength to bulk epoxy and wood, respectively. The failure mechanism is understood to be crack propagation along the particle-thermoset interface and/or interparticle thermoset network. PMID:25734539

Karumuri, Sriharsha; Hiziroglu, Salim; Kalkan, A Kaan

2015-04-01

180

Damage and fatigue in cross-linked rubbers  

NASA Astrophysics Data System (ADS)

Damage and fatigue of elastomers have not been fundamentally understood because of the complex nature of these materials. All currently existing models are completely phenomenological. Therefore two problems have been investigated in this research to address those fundamental issues. The first problem was creating an innovative concept with a mathematical modeling, which would be able to describe the damage using molecular characteristics of elastomers. The second problem is developing new approaches to study fatigue, and especially impact fatigue of elastomers. The following results have been obtained in this research. A theoretical model of damage has been developed which involves the basic molecular characteristics of cross-linked elastomers and takes into account the effects of viscoelasticity and stress-induced crystallization. This model was found very reliable and successful in description of numerous quasi-static simple extension experiments for monotonous and repeating loadings. It also roughly predicts in molecular terms the failure of elastomers with various degrees of cross-linking. Quasi-impact fatigue tests with different geometry of an indenter have also been performed. Some microscopic features of rubber damage have been investigated using optical microscopy and SEM. In particular, the accumulation of a completely de-vulcanized, liquid-like substance was observed under intense, multi-cycle impacts. All the findings discovered in quasi-impact experiments are consistent with the damage model predictions.

Melnikov, Alexei

181

Optimization model for UV-Riboflavin corneal cross-linking  

NASA Astrophysics Data System (ADS)

Nowadays UV-cross-linking is an established method for the treatment of keraectasia. Currently a standardized protocol is used for the cross-linking treatment. We will now present a theoretical model which predicts the number of induced crosslinks in the corneal tissue, in dependence of the Riboflavin concentration, the radiation intensity, the pre-treatment time and the treatment time. The model is developed by merging the difussion equation, the equation for the light distribution in dependence on the absorbers in the tissue and a rate equation for the polymerization process. A higher concentration of Riboflavin solution as well as a higher irradiation intensity will increase the number of induced crosslinks. However, performed stress-strain experiments which support the model showed that higher Riboflavin concentrations (> 0.125%) do not result in a further increase in stability of the corneal tissue. This is caused by the inhomogeneous distribution of induced crosslinks throughout the cornea due to the uneven absorption of the UV-light. The new model offers the possibility to optimize the treatment individually for every patient depending on their corneal thickness in terms of efficiency, saftey and treatment time.

Schumacher, S.; Wernli, J.; Scherrer, S.; Bueehler, M.; Seiler, T.; Mrochen, M.

2011-03-01

182

Mechanical properties of tough hydrogels synthesized with a facile simultaneous radiation polymerization and cross-linking method  

NASA Astrophysics Data System (ADS)

Radiation-induced polymerization and cross-linking method has been applied to hydrogel preparations for decades, but less attention has been paid to the mechanical properties of the hydrogels. In this work, we provide a systematic study on the mechanical properties of hydrogels synthesized with the simultaneous radiation polymerization and cross-linking method. The prepared polyacrylamide (PAAm) had very good mechanical properties, namely high compressive strengths (several to more than 10 MPa), high tensile strengths (up to 260 kPa), high fracture strains (up to 12) and high fracture energies (10-160 J/m2). Absorbed dose and monomer concentration were the two important factors affecting the mechanical properties of the gels. The compressive strength and elastic modulus of the gels increased with increasing absorbed dose and monomer concentration, while the tensile strength, fracture strain and fracture energy of the gels decreased with increasing absorbed dose. The gels also showed excellent elastic recovery property, as indicated by the low stress-strain hysteresis ratios in cyclic tensile tests as well as the small loss factors measured with dynamic mechanical analysis (DMA).

Jiang, Fangzhi; Wang, Xuezhen; He, Changcheng; Saricilar, Sureyya; Wang, Huiliang

2015-01-01

183

New Aptes Cross-linked Polymers from Poly(ethylene oxide)s and Cyanuric Chloride for Lithium Batteries  

NASA Technical Reports Server (NTRS)

A new series of polymer electrolytes for use as membranes for lithium batteries are described. Electrolytes were made by polymerization between cyanuric chloride and diamino-terminated poly(ethylene oxide)s, followed by cross-linking via a sol-gel process. Thermal analysis and lithium conductivity of freestanding polymer films were studied. The effects of several variables on conductivity were investigated, such as length of backbone PEO chain, length of branching PEO chain, extent of branching, extent of cross-linking, salt content, and salt counterion. Polymer films with the highest percentage of PEO were found to be the most conductive, with a maximum lithium conductivity of 3.9 x 10(exp -5) S/cm at 25 C. Addition of plasticizer to the dry polymers increased conductivity by an order of magnitude.

Tigelaar, Dean M.; Meador, Mary Ann B.; Kinder, James D.; Bennett, William R.

2005-01-01

184

Doubling the cross-linking interface of a rationally designed beta roll peptide for calcium-dependent proteinaceous hydrogel formation.  

PubMed

We have rationally engineered a stimulus-responsive cross-linking domain based on a repeats-in-toxin (RTX) peptide to enable calcium-dependent formation of supramolecular hydrogel networks. The peptide isolated from the RTX domain is intrinsically disordered in the absence of calcium. In calcium rich environments, the peptide binds Ca(2+) ions and folds into a beta roll (?-roll) secondary structure composed to two parallel ?-sheet faces. Previously, we mutated one of the faces to contain solvent exposed leucine side chains which are localized only in the calcium-bound ?-roll conformation. We demonstrated the ability of this mutant peptide to self-assemble into hydrogels in the presence of calcium with the aid of additional peptide-based cross-linking moieties. Here, we have expanded this approach by engineering both ?-roll faces to contain leucine residues, thereby doubling the cross-linking interface for each monomeric building block. These leucine rich surfaces impart a hydrophobic driving force for self-assembly. Extensive characterization was performed on this double-faced mutant to ensure the retention of calcium affinity and subsequent structural rearrangement similar to that of the wild type domain. We genetically fused an ?-helical leucine zipper capable of forming tetrameric coiled-coil bundles to the peptide and the resulting chimeric protein self-assembles into a hydrogel only in calcium rich environments. Since this new mutant peptide enables cross-linking on both surfaces simultaneously, a higher oligomerization state was achieved. To further investigate the cross-linking capability, we constructed concatemers of the ?-roll with maltose binding protein (MBP), a monomeric globular protein, without the leucine zipper domains. These concatemers show a similar sol-gel transition in response to calcium. Several biophysical techniques were used to probe the structural and mechanical properties of the mutant ?-roll domain and the resulting supramolecular networks including circular dichroism, fluorescence resonance energy transfer, bis-ANS binding, and microrheology. These results demonstrate that the engineered ?-roll peptides can mediate calcium-dependent cross-linking for protein hydrogel formation without the need for any other cross-linking moieties. PMID:25226243

Dooley, Kevin; Bulutoglu, Beyza; Banta, Scott

2014-10-13

185

Dynamic Role of Cross-Linking Proteins in Actin Rheology  

PubMed Central

We develop a computational model to compare the relative importance of unbinding and unfolding of actin cross-linking proteins (ACPs) in the dynamic properties of the actin cytoskeleton. We show that in the strain-stiffening regime with typical physiological and experimental strain rates, unbinding events are predominant with negligible unfolding. ACPs unbound by greater forces experience larger displacements, with a tendency to rebind to different filaments. At constant strain, stress relaxes to physiological levels by unbinding only—not unfolding—of ACPs, which is consistent with experiments. Also, rebinding of ACPs dampens full relaxation of stress. When the network is allowed to return to a stress-free state after shear deformation, plastic deformation is observed only with unbinding. These results suggest that despite the possibility of unfolding, unbinding of ACPs is the major determinant for the rheology of the actin network. PMID:21961585

Kim, Taeyoon; Hwang, Wonmuk; Kamm, Roger D.

2011-01-01

186

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

PubMed

Keratoconus is a disease of the cornea that usually begins during puberty and progressively weakens its biomechanical structure. Keratoconic eyes show a conic shape and progressive thinning, both leading to irregular astigmatism and reduced vision that cannot be corrected by glasses. In early cases, special contact lens can partly compensate for the visual loss while they do not stop disease progression. Until recently, the only treatment option was a corneal transplant. In 1999, a technique called corneal collagen cross-linking (CXL) was used in human corneas suffering from keratoconus for the first time. CXL uses a process called photopolymerization to halt the progression of keratoconus with an efficacy of more than 95%. Today our challenge is to screen and identify patients early enough to offer a treatment on time before irreversible vision loss develops. PMID:25004773

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

2014-06-01

187

Encapsulation of cobalt nanoparticles in cross-linked-polymer cages  

NASA Astrophysics Data System (ADS)

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

Hatamie, Shadie; Dhole, S. D.; Ding, J.; Kale, S. N.

2009-07-01

188

Novel Magnetic Cross-Linked Lipase Aggregates for Improving the Resolution of (R, S)-2-octanol.  

PubMed

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. Chirality 27:199-204, 2015. © 2014 Wiley Periodicals, Inc. PMID:25482205

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

2015-12-01

189

Peptidoglycan Cross-Linking in Glycopeptide-Resistant Actinomycetales  

PubMed Central

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

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

2014-01-01

190

Thermal fluctuations in chemically cross-linked polymers of cyclodextrins.  

PubMed

The extent and nature of thermal fluctuations in the innovative class of cross-linked polymers called cyclodextrin nanosponges (CDNS) are investigated, on the picosecond time scale, through elastic and quasielastic neutron scattering experiments. Nanosponges are complex 3D polymer networks where covalent bonds connecting different cyclodextrin (CD) units and intra- and inter-molecular hydrogen-bond interactions cooperate to define the molecular architecture and fast dynamics of the polymer. The study presented here aims to clarify the nature of the conformational rearrangements activated by increasing temperature in the nanosponge polymer, and the constraints imposed by intra- and inter-molecular hydrogen-bond patterns on the internal dynamics of the macromolecule. The results suggest a picture, in which conformational rearrangements involving the torsion of the OH groups around the C-O bonds dominate the internal dynamics of the polymer over the picosecond time scale. Moreover, the estimated values of mean square displacements reveal that the motions of the hydrogen atoms in the nanosponges are progressively hampered as the cross-linking degree of the polymer is increased. Finally, the study of the molecular relaxations suggests a dynamical rearrangement of the hydrogen-bond networks, which is characterized by a jump diffusion motion of the more mobile hydrogen atoms belonging to the OH groups of the CD units. All these findings add further contribution to the rational comprehensive view of the dynamics of these macromolecules, which may be particularly beneficial in designing new drug-delivery systems with tuneable inclusion/release properties. PMID:25639345

Rossi, Barbara; Venuti, Valentina; Paciaroni, Alessandro; Mele, Andrea; Longeville, Stéphane; Natali, Francesca; Crupi, Vincenza; Majolino, Domenico; Trotta, Francesco

2015-03-01

191

Cross-linked polyethylenimine–tripolyphosphate nanoparticles for gene delivery  

PubMed Central

The high transfection efficiency of polyethylenimine (PEI) makes it an attractive potential nonviral genetic vector for gene delivery and therapy. However, the highly positive charge of PEI leads to cytotoxicity and limits its application. To reduce the cytotoxicity of PEI, we prepared anion-enriched nanoparticles that combined PEI with tripolyphosphate (TPP). We then characterized the PEI-TPP nanoparticles in terms of size, zeta potential, and Fourier-transform infrared (FTIR) spectra, and assessed their transfection efficiency, cytotoxicity, and ability to resist deoxyribonuclease (DNase) I digestion. The cellular uptake of PEI-TPP with phosphorylated internal ribosome entry site–enhanced green fluorescent protein C1 or FAM (fluorouracil, Adriamycin [doxorubicin] and mitomycin)-labeled small interfering ribonucleic acids (siRNAs) was monitored by fluorescence microscopy and confocal laser microscopy. The efficiency of transfected delivery of plasmid deoxyribonucleic acid (DNA) and siRNA in vitro was 1.11- to 4.20-fold higher with the PEI-TPP particles (7.6% cross-linked) than with the PEI, at all N:P ratios (nitrogen in PEI to phosphorus in DNA) tested. The cell viability of different cell lines was more than 90% at the chosen N:P ratios of PEI-TPP/DNA complexes. Moreover, PEI-TPP nanoparticles resisted digestion by DNase I for more than 2 hours. The time-dependent absorption experiment showed that 7.6% of cross-linked PEI-TPP particles were internalized by 293T cells within 1 hour. In summary, PEI-TPP nanoparticles effectively transfected cells while conferring little or no toxicity, and thus have potential application in gene delivery. PMID:25342902

Huang, Xianzhang; Shen, Sujing; Zhang, Zhanfeng; Zhuang, Junhua

2014-01-01

192

Effect of modified starch and nanoclay particles on biodegradability and mechanical properties of cross-linked poly lactic acid.  

PubMed

Mechanical properties and biodegradation of cross-linked poly(lactic acid) (PLA)/maleated thermoplastic starch (MTPS)/montmorillonite (MMT) nanocomposite were studied. Crosslinking was carried out by adding di-cumyl peroxide (DCP) in the presence of triallyl isocyanurate (TAIC) as coagent. At first, MTPS was prepared by grafting maleic anhydride (MA) to thermoplastic starch in internal mixer. Experimental design was performed by using Box-Behnken method at three variables: MTPS, nanoclay and TAIC at three levels. Results showed that increasing TAIC amount substantially increased the gel fraction, enhanced tensile strength, and caused a decrease in elongation at break. Biodegradation was prevented by increasing TAIC amount in nanocomposite. Increasing MTPS amount caused a slight increase in gel fraction and decreased the tensile strength of nanocomposite. Also, MTPS could increase the elongation at break of nanocomposite and improve the biodegradation. Nanoclay had no effect on the gel fraction, but it improved tensile strength. PMID:25839817

Shayan, M; Azizi, H; Ghasemi, I; Karrabi, M

2015-06-25

193

Chemical cross-linking/mass spectrometry targeting acidic residues in proteins and protein complexes  

PubMed Central

The study of proteins and protein complexes using chemical cross-linking followed by the MS identification of the cross-linked peptides has found increasingly widespread use in recent years. Thus far, such analyses have used almost exclusively homobifunctional, amine-reactive cross-linking reagents. Here we report the development and application of an orthogonal cross-linking chemistry specific for carboxyl groups. Chemical cross-linking of acidic residues is achieved using homobifunctional dihydrazides as cross-linking reagents and a coupling chemistry at neutral pH that is compatible with the structural integrity of most protein complexes. In addition to cross-links formed through insertion of the dihydrazides with different spacer lengths, zero-length cross-link products are also obtained, thereby providing additional structural information. We demonstrate the application of the reaction and the MS identification of the resulting cross-linked peptides for the chaperonin TRiC/CCT and the 26S proteasome. The results indicate that the targeting of acidic residues for cross-linking provides distance restraints that are complementary and orthogonal to those obtained from lysine cross-linking, thereby expanding the yield of structural information that can be obtained from cross-linking studies and used in hybrid modeling approaches. PMID:24938783

Leitner, Alexander; Joachimiak, Lukasz A.; Unverdorben, Pia; Walzthoeni, Thomas; Frydman, Judith; Förster, Friedrich; Aebersold, Ruedi

2014-01-01

194

Cytoskeletal Polymer Networks: Viscoelastic Properties are Determined by the Microscopic Interaction Potential of Cross-links  

E-print Network

Interaction Potential of Cross-links O. Lieleg, K. M. Schmoller, M. M. A. E. Claessens,§ and A. R. Bausch, Enschede, The Netherlands ABSTRACT Although the structure of cross-linking molecules mainly determines, it is largely unknown how the biochemical characteristics of tran- siently cross-linking proteins (actin

Bausch, Andreas

195

Comparison of Cross-linked and Non–Cross-linked Acellular Porcine Dermal Scaffolds for Long-term Full-Thickness Hernia Repair in a Small Animal Model  

PubMed Central

Background: This study compared the strength of incorporation and biocompatibility of 2 porcine-derived grafts (cross-linked and non–cross-linked) in a rat hernia model. Methods: A standardized 2 × 4 cm2 fascial defect was created in 30 Wistar rats and repaired with either a cross-linked or a non–cross-linked graft. The rats were killed 3, 6, and 12 months later. The strength of incorporation, vascularization, cellular invasion, foreign body reaction, and capsule formation were evaluated. Results: Both graft materials showed cellular ingrowth and neovascularization by 3 months postimplantation. The average level of cellularization was significantly higher in the non–cross-linked grafts than in the cross-linked grafts at 6 months (2 vs 1; P = .029). Vascularization was significantly higher in the non–cross-linked grafts than in the cross-linked grafts at 6 months postimplantation (2 vs 1; P = .029) and insignificant at 3 months (2 vs 1.75; P = .311) and 12 months (1 vs 0.67; P = 1). The maximum load and breaking strength of both biomaterials increased during the study period. Overall, the strength of incorporation of the non–cross-linked grafts increased from 3 months (0.75 MPa) to 12 months (3.06 MPa) postimplantation. The strength of incorporation of the cross-linked grafts also increased from 3 months (0.59 MPa) to 12 months (1.58 MPa) postimplantation. Conclusions: The results of our study suggest that non–cross-linked grafts may be slightly more biocompatible and allow a more rapid and higher degree of cellular penetration and vascularization, resulting in stronger attachment to the tissues. PMID:24966996

Mestak, Ondrej; Spurkova, Zuzana; Benkova, Kamila; Vesely, Pavel; Hromadkova, Veronika; Miletin, Jakub; Juzek, Robert; Molitor, Martin; Sukop, Andrej

2014-01-01

196

Analysis of the interaction between hyaluronan and hyaluronan-binding proteins by capillary affinity electrophoresis: significance of hyaluronan molecular size on binding reaction  

Microsoft Academic Search

We developed a method for the analysis of the interaction between hyaluronan (HA) oligosaccharides and hyaluronan-binding proteins (HABPs) using capillary affinity electrophoresis (CAE). The method is based on high-resolution separation of fluorescent-labeled HA molecules in the presence of hyaluronan-binding proteins at different concentrations by capillary electrophoresis (CE) with laser-induced fluorescent detection. Hyaluronan-binding protein from bovine nasal cartilage interacts strongly with

Mitsuhiro Kinoshita; Kazuaki Kakehi

2005-01-01

197

Tailoring Elastic Properties of Silica Aerogels Cross-Linked with Polystyrene  

NASA Technical Reports Server (NTRS)

The effect of incorporating an organic linking group, 1,6-bis(trimethoxysilyl)hexane (BTMSH), into the underlying silica structure of a styrene cross-linked silica aerogel is examined. Vinyltrimethoxysilane (VTMS) is used to provide a reactive site on the silica backbone for styrene polymerization. Replacement of up to 88 mol 1 of the silicon from tetramethoxyorthosilicate with silicon derived from BTMSH and VTMS during the making of silica gels improves the elastic behavior in some formulations of the crosslinked aerogels, as evidenced by measurement of the recovered length after compression of samples to 251 strain. This is especially true for some higher density formulations, which recover nearly 100% of their length after compression to 251 strain twice. The compressive modulus of the more elastic monoliths ranged from 0.2 to 3 MPa. Although some of these monoliths had greatly reduced surface areas, changing the solvent used to produce the gels from methanol to ethanol increased the surface area in one instance from 6 to 220 sq m2/g with little affect on the modulus, elastic recovery, porosity, or density.

Nguyen, Baochau N.; Meador, Mary Ann B.; Tousley, Marissa E.; Shonkwiler, Brian; McCorkle, Linda; Scheiman, Daniel A.; Palczer, Anna

2009-01-01

198

Mechanically strong, flexible polyimide aerogels cross-linked with aromatic triamine.  

PubMed

Polyimide gels are produced by cross-linking anhydride capped polyamic acid oligomers with aromatic triamine in solution and chemically imidizing. The gels are then supercritically dried to form nanoporous polyimide aerogels with densities as low as 0.14 g/cm(3) and surface areas as high as 512 m(2)/g. To understand the effect of the polyimide backbone on properties, aerogels from several combinations of diamine and dianhydride, and formulated oligomer chain length are examined. Formulations made from 2,2'-dimethylbenzidine as the diamine shrink the least but have among the highest compressive modulus. Formulations made using 4,4'-oxydianiline or 2,2'dimethylbenzidine can be fabricated into continuous thin films using a roll to roll casting process. The films are flexible enough to be rolled or folded back on themselves and recover completely without cracking or flaking, and have tensile strengths of 4-9 MPa. Finally, the highest onset of decomposition (above 600 °C) of the polyimide aerogels was obtained using p-phenylene diamine as the backbone diamine with either dianhydride studied. All of the aerogels are suitable candidates for high-temperature insulation with glass transition temperatures ranging from 270-340 °C and onsets of decomposition from 460-610 °C. PMID:22233638

Meador, Mary Ann B; Malow, Ericka J; Silva, Rebecca; Wright, Sarah; Quade, Derek; Vivod, Stephanie L; Guo, Haiquan; Guo, Jiao; Cakmak, Miko

2012-02-01

199

Standard versus trans-epithelial collagen cross-linking in keratoconus patients suitable for standard collagen cross-linking  

PubMed Central

Purpose Evaluating the clinical results of trans-epithelial collagen cross-linking (CXL) and standard CXL in patients with progressive keratoconus. Methods This prospective study comprised 20 eyes of 20 patients with progressive keratoconus. Ten eyes were treated by standard CXL and ten by trans-epithelial cross-linking (TE-CXL, epithelium on) with 1 year of follow-up. All patients underwent complete ophthalmologic testing that included pre- and postoperative uncorrected visual acuity, corrected visual acuity, spherical error, spherical equivalent, corneal astigmatism, simulated maximum, minimum, and average keratometry, coma and spherical aberration, optical pachymetry, and endothelial cell density. Intra-and postoperative complications were recorded. The solution used for standard CXL comprised riboflavin 0.1% and dextran 20.0% (Ricrolin), while the solution for TE-CXL (Ricrolin, TE) comprised riboflavin 0.1%, dextran 15.0%, trometamol (Tris), and ethylenediaminetetraacetic acid. Ultraviolet-A treatment was performed with UV-X System at 3 mW/cm2. Results In both the standard CXL group (ten patients, ten eyes; mean age, 30.4±7.3 years) and the TE-CXL group (ten patients, ten eyes; mean age, 28±3.8 years), uncorrected visual acuity and corrected visual acuity improved significantly after treatment. Furthermore, a significant improvement in topographic outcomes, spherical error, and spherical equivalent was observed in both groups at month 12 posttreatment. No significant variations were recorded in other parameters. No complications were noted. Conclusion A 1-year follow-up showed stability of clinical and refractive outcomes after standard CXL and TE-CXL.

Rossi, S; Orrico, A; Santamaria, C; Romano, V; De Rosa, L; Simonelli, F; De Rosa, G

2015-01-01

200

Synthesis of poly(N-isopropylacrylamide) hydrogels by radiation polymerization and cross-linking  

SciTech Connect

Poly(N-isopropylacrylamide) [poly(NIPAAm)] shows a typical thermal reversibility of phase transition in aqueous solutions. That is, it precipitates from solution above a critical temperature called the lower critical solution temperature (LCST) and dissolves below this temperature. When it is cross-linked, the obtained hydrogel collapses above LCST, while it swells and expands below LCST. This hydrogel has received much attention recently and has been used as a model system to demonstrate the validity of theories describing the coil-globule transition, swelling of networks, and folding and unfolding of biopolymers. It has also been proposed for various applications ranging from controlled drug delivery to solute separation. Poly(NIPAAm) hydrogel is usually synthesized at room temperature from an aqueous solution of the monomer by using a redox initiator composed of ammonium persulfate and N,N,N{prime},N{prime}-tetramethylethylenediamine in the presence of N,N{prime}-methylenebisacrylamide as a cross-linker. Since the LCST of poly(NIPAAm) is around 32 C, the polymerization at room temperature proceeds in a homogeneous solution. Recently, poly(NIPAAm) hydrogels were synthesized by starting the polymerization below the LCST and then elevating the temperature above it, by which method macroporous gels with fast temperature response were obtained. The idea is to apply a radiation--induced polymerization method for the synthesis of poly(NIPAAm) hydrogels. This method offers unique advantages for synthesis: it is a simple and additive-free process at all temperatures, and the degree of cross-linking can be easily controlled by irradiation conditions. Therefore, radiation methods are especially attractive for the synthesis of hydrogels with potential biomedical application where the residual chemical initiators may contaminate the product. It is possible to combine into one step the synthesis and sterilization of the product, and it is economically competitive.

Nagaoka, Noriyasu; Kubota, Hitoshi; Katakai, Ryoichi [Gunma Univ. (Japan). Dept. of Chemistry; Safranj, Agneza; Yoshida, Masaru; Omichi, Hideki [Japan Atomic Energy Research Inst., Gunma (Japan). Dept. of Material Development

1993-12-20

201

An Investigation of Siloxane Cross-linked Hydroxyapatite-Gelatin/Copolymer Composites for Potential Orthopedic Applications†  

PubMed Central

Causes of bone deficiency are numerous, but biomimetic alloplastic grafts provide an alternative to repair tissue naturally. Previously, a hydroxyapatite-gelatin modified siloxane (HAp-Gemosil) composite was prepared by cross-linking (N, N?-bis[(3-trimethoxysilyl)propyl]ethylene diamine (enTMOS) around the HAp-Gel nanocomposite particles, to mimic the natural composition and properties of bone. However, the tensile strength remained too low for many orthopedic applications. It was hypothesized that incorporating a polymer chain into the composite could help improve long range interaction. Furthermore, designing this polymer to interact with the enTMOS siloxane cross-linked matrix would provide improved adhesion between the polymer and the ceramic composite, and improve mechanical properties. To this end, copolymers of L-Lactide (LLA), and a novel alkyne derivatized trimethylene carbonate, propargyl carbonate (PC), were synthesized. Incorporation of PC during copolymerization affects properties of copolymers such as molecular weight, Tg, and % PC incorporation. More importantly, PC monomers bear a synthetic handle, allowing copolymers to undergo post-polymerization functionalization with graft monomers to specifically tailor the properties of the final composite. For our investigation, P(LLA-co-PC) copolymers were functionalized by an azido-silane (AS) via copper catalyzed azide-alkyne cycloaddition (CuAAC) through terminal alkyne on PC monomers. The new functionalized polymer, P(LLA-co-PC)(AS) was blended with HAp-Gemosil, with the azido-silane linking the copolymer to the silsesquioxane matrix within the final composite. These HAp-Gemosil/P(LLA-co-PC)(AS) composites were subjected to mechanical and biological testing, and the results were compared with those from the HAp-Gemosil composites. This study revealed that incorporating a cross-linkable polymer served to increase the flexural strength of the composite by 50%, while maintaining the biocompatibility of HAp-Gemosil ceramics. PMID:23139457

Dyke, Jason Christopher; Knight, Kelly Jane; Zhou, Huaxing; Chiu, Chi-Kai; Ko, Ching-Chang; You, Wei

2012-01-01

202

Trifunctionally Cross-Linked Liquid Single Crystal Elastomers: Swelling Dynamics and Electromechanical Effects  

NASA Astrophysics Data System (ADS)

Here, we study the influence of cross-linking density, X, on the swelling, thermal and electric field response of trifunctionally cross-linked liquid single crystal elastomers (V3 LSCEs) swollen with low molecular weight liquid crystals, 4-n-pentyl-4-cyanobiphenyl (5CB). The cross-linker concentrations are X3V3=3.3 mol %, X5V3=5 mol %, and X7V3=7 mol %. LSCE networks are characterized by frozen-in orientation order, P. Xc is a constitutional critical point for LSCE networks. When XXc (P>0), supercritical behavior prevails over a range of temperatures, ? Ts. Taking ? Ts\\propto(X-Xc)1/2, we find a critical cross-linking density, Xc? 3%, for V3 LSCEs. 5CB diffuses {\\perp}n into V3 similar to isotropic gels with typical times, ?\\perpn in minutes, that decreases with increasing (X-Xc). Swelling with reorientation effects is initiated by 5CB propagating into V3 followed by relaxation of the front profile with ?\\bot(2) (twist), and ?\\|(13) (splay-bend) that both increase nearly parabolically with increasing (X-Xc). Front speeds are 50% faster in 5V3 than in 7V3 but no fronts were observed in 3V3. Compared to dry V3 LSCE volumes, Vd, the swollen volumes, Vs, increased as X? Xc: Vs/Vd˜(X-Xc)-0.27 reducing the frozen-in orientational order at X to \\tilde{X}=X(Vd/Vs). The maximum electromechanical effect found in swollen V3 was ?MAX˜(\\tilde{X}-\\tilde{X}c) with \\tilde{X}c˜ 0.25%. The size of the effect is much smaller than observed in 8A2 which has a larger P. For 7V3 the effect is about 4 times smaller and for 5V3, it is an order of magnitude smaller.

Cho, Dong-Uk; Yusuf, Yusril; Cladis, P. E.; Brand, Helmut R.; Finkelmann, Heino; Kai, Shoichi

2007-03-01

203

The Leaving Group Strongly Affects H2O2-Induced DNA Cross-Linking by Arylboronates  

PubMed Central

We evaluated the effects of the benzylic leaving group and core structure of arylboronates on H2O2-induced formation of bisquinone methides for DNA interstrand cross-linking. The mechanism of DNA cross-linking induced by these arylboronates involves generation of phenol intermediates followed by departure of benzylic leaving group leading to QMs which directly cross-link DNA via alkylation. The QM formation is the rate-determining step for DNA cross-linking. A better leaving group (Br) and stepwise bisquinone methide formation increased interstrand cross-linking efficiency. These findings provide essential guidelines for designing novel anticancer prodrugs. PMID:24378073

Cao, Sheng; Wang, Yibin; Peng, Xiaohua

2014-01-01

204

Effect of cross-linking on physicochemical properties of tapioca starch and its application in soup product.  

PubMed

Physicochemical properties of cross-linked tapioca starch (CLTS) with different cross-linking levels and their application as a thickening agent in soups were studied. The CLTS was prepared by cross-linking native tapioca starch suspended in alkaline solution (41.67% (w/w), pH 11) using a mixture (99:1 (w/w) ratio) of sodium trimetaphosphate (STMP) and sodium tripolyphosphate (STPP) at different concentrations ranged from 0.25% to 6.0% (w/w of starch) at 45°C for 3h. Starch paste clarity decreased with increasing concentration of STMP/STPP mixture. Variations of swelling power, solubility, pasting, gelatinization, and rheological properties of the CLTS were found. Thermogravimetric analysis exhibited higher thermal stability for the CLTS granules compared to the native one. Among the samples, the CLTS prepared using 1.0% STMP/STPP (1.0%-CLTS) and soup containing the 1.0%-CLTS exhibited the strongest gel characteristic and the greatest shear resistant properties. The 1.0%-CLTS improved the textural properties and sensory quality of soups. PMID:24299823

Wongsagonsup, Rungtiwa; Pujchakarn, Thamonwan; Jitrakbumrung, Suparat; Chaiwat, Weerawut; Fuongfuchat, Asira; Varavinit, Saiyavit; Dangtip, Somsak; Suphantharika, Manop

2014-01-30

205

Synthesis of building blocks and oligonucleotides containing {t}o(4)-alkylene-o(4){t} interstrand cross-links.  

PubMed

This protocol describes the preparation of O(4)-thymidine-alkylene-O(4)-thymidine dimer bis-phosphoramidites and precursors for incorporation into DNA sequences to produce site-specific DNA interstrand cross-links. Linkers are introduced at the 4-position of thymidine by reacting the sodium salt of a diol with a pyrimidinyl-convertible nucleoside to produce mono-adducts, which then undergo reaction with a stoichiometric equivalent of a pyrimidinyl-convertible nucleoside under basic conditions to form O(4)-thymidine-alkylene-O(4)-thymidine dimers. Bis-phosphoramidites are incorporated into oligonucleotides by solid-phase synthesis, and mild conditions for deprotection and cleavage from the solid support are employed to prevent degradation of the thymidine modifications. Purification of these cross-linked oligonucleotides is performed by denaturing polyacrylamide gel electrophoresis. This approach allows for the preparation of cross-linked DNA substrates in quantities and purity sufficient for a wide range of biophysical experiments and biochemical studies as substrates to investigate DNA repair pathways. Curr. Protoc. Nucleic Acid Chem. 55:5.13.1-5.13.19. © 2014 by John Wiley & Sons, Inc. PMID:25631535

O'Flaherty, Derek K; McManus, Francis P; Noronha, Anne M; Wilds, Christopher J

2014-01-01

206

Photochemical cross-linking of type I collagen with hydrophobic and hydrophilic 1,8-naphthalimide dyes  

NASA Astrophysics Data System (ADS)

This study extends our previous studies of the photochemical cross-linking of collagen and bonding of collagenous sheets of dura mater using the hydrophobic 1,8-naphthalimide N,N'- bis-(2-({hexylamino)-5-bromo-1H-benz [de]isoquinolin-1,3(2H)-dion-6- yl]amino}ethyl)hexanediamide. We have obtained hydrophilic forms of the bifunctional molecule introducing a spacer and ligands containing alternating carbon-oxygen bonds (polyethers) wherein the oxygen moieties form hydrogen bonds. Additional hydrophilicity is attained by incorporating of an amino group (positive charge) at the end of each ligand. Ongoing studies with these forms of the bifunctional 1,8 naphthalimides have demonstrated welding of meniscal cartilage, articular cartilage, and cornea. These results suggest that the hydrophilic form of the dyes is able to penetrate readily the anionically charged proteoglycan matrix of these tissues and cross-link collagen molecules and possibly the protein cores of the proteoglycans. Gel electrophoretic studies have been performed to assess the photochemical cross-linking of these connective tissue proteins with these new forms of the paththalimide dyes.

Judy, Millard M.; Chen, Li; Fuh, L.; Nosir, Hany R.; Jackson, Robert W.; Matthews, James Lester; Lewis, David E.; Utecht, Ronald E.; Yuan, Dongwu

1996-05-01

207

RHEOLOGICAL AND MECHANICAL PROPERTIES OF CROSS-LINKED FISH GELATINS  

Technology Transfer Automated Retrieval System (TEKTRAN)

Gelatin was extracted from the skins of Alaska pollock (Theragra chalcogramma) and Alaska pink salmon (Oncorhynchus gorbuscha). Amino acid analysis and gel electrophoresis were used to determine their amino acid composition and molecular weight profiles, respectively. Dynamic rheology was also used ...

208

Synthesis and properties of polymerized, diaspirin cross-linked hemoglobins.  

PubMed

During the course of our studies it became clear that there were therapeutic applications for which a polymeric hemoglobin having an extended half-life in circulation would be appropriate. Therefore, a process for the glutaraldehyde-polymerization of diaspirin cross-linked hemoglobin (DCLHb) was developed and used to prepare glutaraldehyde-polymerized DCLHb (GP-DCLHb) in lactated Ringer's solution in sufficient quantities for biological testing. Both isovolemic exchange-transfusion and "top-load" studies (rats; primates and swine, respectively) were completed in which a broad spectrum of physiologic, histopathologic and analytical parameters were monitored and assessed. In general, GP-DCLHb in lactated Ringer's solution was well-tolerated physiologically. When compared to DCLHb, GP-DCLHb offers the advantages of reduced renal clearance of hemoglobin and an extended half-life in circulation. GP-DCLHb has the disadvantages that (1) glutaraldehyde is an ineffective virucidal agent under the conditions of the polymerization reaction and a separate virus inactivation step is required; (2) low-endotoxin (LAL-negative) GP-DCLHb solutions are pyrogenic (rabbits); and (3) unusual deposition of hemoglobin-containing material in the small arterioles of the liver and kidney (rats) was sometimes seen even after a period of time (2 weeks) during which treatment-related organ pathologies are usually resolved, a finding peculiar to GP-DCLHb among the various hemoglobin derivatives we have tested. PMID:1391439

Nelson, D; Hai, T; Srnak, A; Ebeling, A; Kunas, G; Catarello, J; Burhop, K

1992-01-01

209

Profile of Microbial Keratitis after Corneal Collagen Cross-Linking  

PubMed Central

Purpose. To report the profile of microbial keratitis occurring after corneal collagen cross-linking (CXL) in keratoconus patients. Methods. A retrospective analysis of 2350 patients (1715 conventional CXL, 310 transepithelial CXL, and 325 accelerated CXL) over 7 years (from January 2007 to January 2014) of progressive keratoconus, who underwent CXL at a tertiary eye care centre, was performed. Clinical findings, treatment, and course of disease of four eyes that developed postprocedural moxifloxacin resistant Staphylococcus aureus (MXRSA) infectious keratitis are highlighted. Results. Four eyes that underwent CXL (0.0017%) had corneal infiltrates. All eyes that developed keratitis had conventional CXL. Corneal infiltrates were noted on the third postoperative day. Gram's stain as well as culture reported MXRSA as the causative agent in all cases. Polymerase chain reaction (PCR) in each case was positive for eubacterial genome. All patients were treated with fortified antibiotic eye drops, following which keratitis resolved over a 6-week period with scarring. All these patients were on long-term preoperative oral/topical steroids for chronic disorders (chronic vernal keratoconjunctivitis, bronchial asthma, and chronic eczema). Conclusion. The incidence of infectious keratitis after CXL is a rare complication (0.0017%). MXRSA is a potential organism for causing post-CXL keratitis and should be identified early and treated aggressively with fortified antibiotics. PMID:25302296

Shetty, Rohit; Kaweri, Luci; Nuijts, Rudy M. M. A.; Nagaraja, Harsha; Arora, Vishal; Kumar, Rajesh S.

2014-01-01

210

Transepithelial corneal collagen cross-linking in ultrathin keratoconic corneas  

PubMed Central

Background The purpose of this paper was to report the results of transepithelial corneal collagen cross-linking (CXL) with modified riboflavin and ultraviolet A irradiation in patients affected by keratoconus, each with thinnest pachymetry values of less than 400 ?m (with epithelium) and not treatable using standard de-epithelialization techniques. Methods Sixteen patients affected by progressive keratoconus with thinnest pachymetry values ranging from 331 ?m to 389 ?m underwent transepithelial CXL in one eye using a riboflavin 0.1% solution in 15% Dextran T500 containing ethylenediamine tetra-acetic acid 0.01% and trometamol to enhance epithelial penetration. The patients underwent complete ophthalmological examination, including endothelial cell density measurements and computerized videokeratography, before CXL and at one day, one week, and one, 6, and 12 months thereafter. Results Epithelial healing was complete in all patients after one day of use of a soft bandage contact lens. No side effects or damage to the limbal region was observed during the follow-up period. All patients showed slightly improved uncorrected and spectacle-corrected visual acuity; keratometric astigmatism showed reductions (up to 5.3 D) and apical ectasia power decreased (Kmax values reduced up to 4.3 D). Endothelial cell density was unchanged. Conclusion Application of transepithelial CXL using riboflavin with substances added to enhance epithelial permeability was safe, seemed to be moderately effective in keratoconic eyes with ultrathin corneas, and applications of the procedure could be extended to patients with advanced keratoconus. PMID:23152657

Spadea, Leopoldo; Mencucci, Rita

2012-01-01

211

Mechanism of Calponin Stabilization of Cross-Linked Actin Networks  

PubMed Central

The actin-binding protein calponin has been previously implicated in actin cytoskeletal regulation and is thought to act as an actin stabilizer, but the mechanism of its function is poorly understood. To investigate this underlying physical mechanism, we studied an in vitro model system of cross-linked actin using bulk rheology. Networks with basic calponin exhibited a delayed onset of strain stiffening (10.0% without calponin, 14.9% with calponin) and were able to withstand a higher maximal strain before failing (35% without calponin, 56% with calponin). Using fluorescence microscopy to study the mechanics of single actin filaments, we found that calponin increased the flexibility of actin filaments, evident as a decrease in persistence length from 17.6 ?m without to 7.7 ?m with calponin. Our data are consistent with current models of affine strain behavior in semiflexible polymer networks, and suggest that calponin stabilization of actin networks can be explained purely by changes in single-filament mechanics. We propose a model in which calponin stabilizes actin networks against shear through a reduction of persistence length of individual filaments. PMID:24559982

Jensen, Mikkel Herholdt; Morris, Eliza J.; Gallant, Cynthia M.; Morgan, Kathleen G.; Weitz, David A.; Moore, Jeffrey R.

2014-01-01

212

Zinc cross-linked hydroxamated alginates for pulsed drug release  

PubMed Central

Introduction: Alginates can be tailored chemically to improve solubility, physicochemical, and biological properties and its complexation with metal ion is useful for controlling the drug release. Materials And Methods: Synthesized N,O-dimethyl, N-methyl, or N-Benzyl hydroxylamine derivatives of sodium alginate were subsequently complexed with zinc to form beads. Hydroxamation of sodium alginate was confirmed by Fourier transform infra-red spectroscopy (FTIR) and differential scanning calorimetry (DSC). Results: The synthesized polymeric material exhibited reduced aqueous, HCl and NaOH solubility. The hydroxamated derivatives demonstrated pulsed release where change in pH of the dissolution medium stimulated the atenolol release. Conclusion: Atenolol loaded Zn cross-linked polymeric beads demonstrated the sustained the plasma drug levels with increased half-life. Although the synthesized derivatives greatly altered the aqueous solubility of sodium alginate, no significant differences in in vitro and in vivo atenolol release behavior amongst the N,O-dimethyl, N-methyl, or N-Benzyl hydroxylamine derivatives of sodium alginate were observed. PMID:24350039

Raut, Neha S; Deshmukh, Prasad R; Umekar, Milind J; Kotagale, Nandkishor R

2013-01-01

213

Cross-linking of polytetrafluoroethylene during room-temperature irradiation  

SciTech Connect

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

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

2008-01-01

214

Chain gangs: new aspects of hyaluronan metabolism.  

PubMed

Hyaluronan is a matrix polymer prominent in tissues undergoing rapid growth, development, and repair, in embryology and during malignant progression. It reaches 10(7) Daltons in size but also exists in fragmented forms with size-specific actions. It has intracellular forms whose functions are less well known. Hyaluronan occurs in all vertebrate tissues with 50% present in skin. Hyaluronan provides a scaffold on which sulfated proteoglycans and matrix proteins are organized. These supramolecular structures are able to entrap water and ions to provide tissues with hydration and turgor. Hyaluronan is recognized by membrane receptors that trigger intracellular signaling pathways regulating proliferation, migration, and differentiation. Cell responses are often dependent on polymer size. Catabolic turnover occurs by hyaluronidases and by free radicals, though proportions between these have not been determined. New aspects of hyaluronan biology have recently become realized: involvement in autophagy, in the pathology of diabetes., the ability to modulate immune responses through effects on T regulatory cells and, in its fragmented forms, by being able to engage several toll-like receptors. It is also apparent that hyaluronan synthases and hyaluronidases are regulated at many more levels than previously realized, and that the several hyaluronidases have functions in addition to their enzymatic activities. PMID:22216413

Erickson, Michael; Stern, Robert

2012-01-01

215

A Structural Approach to Establishing a Platform Chemistry for the Tunable, Bulk Electron Beam Cross-Linking of Shape Memory Polymer Systems.  

PubMed

The synthetic design and thermomechanical characterization of shape memory polymers (SMPs) built from a new polyurethane chemistry that enables facile, bulk and tunable cross-linking of low-molecular weight thermoplastics by electron beam irradiation is reported in this study. SMPs exhibit stimuli-induced geometry changes and are being proposed for applications in numerous fields. We have previously reported a polyurethane SMP system that exhibits the complex processing capabilities of thermoplastic polymers and the mechanical robustness and tunability of thermomechanical properties that are often characteristic of thermoset materials. These previously reported polyurethanes suffer practically because the thermoplastic molecular weights needed to achieve target cross-link densities severely limit high-throughput thermoplastic processing and because thermally unstable radiation-sensitizing additives must be used to achieve high enough cross-link densities to enable desired tunable shape memory behavior. In this study, we demonstrate the ability to manipulate cross-link density in low-molecular weight aliphatic thermoplastic polyurethane SMPs (M w as low as ~1.5 kDa) without radiation-sensitizing additives by incorporating specific structural motifs into the thermoplastic polymer side chains that we hypothesized would significantly enhance susceptibility to e-beam cross-linking. A custom diol monomer was first synthesized and then implemented in the synthesis of neat thermoplastic polyurethane SMPs that were irradiated at doses ranging from 1 to 500 kGy. Dynamic mechanical analysis (DMA) demonstrated rubbery moduli to be tailorable between 0.1 and 55 MPa, and both DMA and sol/gel analysis results provided fundamental insight into our hypothesized mechanism of electron beam cross-linking, which enables controllable bulk cross-linking to be achieved in highly processable, low-molecular weight thermoplastic shape memory polymers without sensitizing additives. PMID:25411511

Hearon, Keith; Besset, Celine J; Lonnecker, Alexander T; Ware, Taylor; Voit, Walter E; Wilson, Thomas S; Wooley, Karen L; Maitland, Duncan J

2013-11-26

216

A Structural Approach to Establishing a Platform Chemistry for the Tunable, Bulk Electron Beam Cross-Linking of Shape Memory Polymer Systems  

PubMed Central

The synthetic design and thermomechanical characterization of shape memory polymers (SMPs) built from a new polyurethane chemistry that enables facile, bulk and tunable cross-linking of low-molecular weight thermoplastics by electron beam irradiation is reported in this study. SMPs exhibit stimuli-induced geometry changes and are being proposed for applications in numerous fields. We have previously reported a polyurethane SMP system that exhibits the complex processing capabilities of thermoplastic polymers and the mechanical robustness and tunability of thermomechanical properties that are often characteristic of thermoset materials. These previously reported polyurethanes suffer practically because the thermoplastic molecular weights needed to achieve target cross-link densities severely limit high-throughput thermoplastic processing and because thermally unstable radiation-sensitizing additives must be used to achieve high enough cross-link densities to enable desired tunable shape memory behavior. In this study, we demonstrate the ability to manipulate cross-link density in low-molecular weight aliphatic thermoplastic polyurethane SMPs (Mw as low as ~1.5 kDa) without radiation-sensitizing additives by incorporating specific structural motifs into the thermoplastic polymer side chains that we hypothesized would significantly enhance susceptibility to e-beam cross-linking. A custom diol monomer was first synthesized and then implemented in the synthesis of neat thermoplastic polyurethane SMPs that were irradiated at doses ranging from 1 to 500 kGy. Dynamic mechanical analysis (DMA) demonstrated rubbery moduli to be tailorable between 0.1 and 55 MPa, and both DMA and sol/gel analysis results provided fundamental insight into our hypothesized mechanism of electron beam cross-linking, which enables controllable bulk cross-linking to be achieved in highly processable, low-molecular weight thermoplastic shape memory polymers without sensitizing additives. PMID:25411511

Hearon, Keith; Besset, Celine J.; Lonnecker, Alexander T.; Ware, Taylor; Voit, Walter E.; Wilson, Thomas S.; Wooley, Karen L.; Maitland, Duncan J.

2014-01-01

217

Microemulsions as nanoreactors to produce whey protein nanoparticles with enhanced heat stability by sequential enzymatic cross-linking and thermal pretreatments.  

PubMed

Sequential enzymatic cross-linking and heat pretreatments were used in this work to enhance the heat stability of whey protein isolate (WPI). In the first route, WPI was cross-linked by transglutaminase before incorporation in microemulsions for heat pretreatment at 90 degrees C for 20 min. In the second route, WPI was cross-linked by transglutaminase within microemulsions before thermal pretreatment. Particles produced from the two routes were different in dimension and heat stability and were also affected by the ratio of WPI and enzyme and cross-linking duration. At appropriate conditions, for example, 10 h of cross-linking by transglutaminase equivalent to 5% mass of WPI using the first route, a 5% dispersion (pH 6.8 and 100 mM NaCl) of the produced nanoparticles remained clear after heating at 90 degrees C for 20 min. In comparison, nanoparticles produced by thermal pretreatment only in a microemulsion corresponded to a translucent, flowable dispersion, whereas native WPI formed a gel. This novel approach can be used to manufacture heat-stable whey protein ingredients for clear beverage applications. PMID:19807163

Zhang, Weinong; Zhong, Qixin

2009-10-14

218

Structure-Property Relationships in Porous 3-D Nanostructures as a Function of Preparation Conditions: Isocyanate Cross-Linked Silica Aerogels  

NASA Technical Reports Server (NTRS)

Sol-gel derived silica aerogels are attractive candidates for many unique thermal, optical, catalytic, and chemical applications because of their low density and high mesoporosity. However, their inherent fragility has restricted use of aerogel monoliths to applications where they are not subject to any load. We have previously reported cross-linking the mesoporous silica structure of aerogels with di-isocyanates, styrenes or epoxies reacting with amine decorated silica surfaces. These approaches have been shown to significantly increase the strength of aerogels with only a small effect on density or porosity. Though density is a prime predictor of properties such as strength and thermal conductivity for aerogels, it is becoming clear from previous studies that varying the silica backbone and size of the polymer cross-link independently can give rise to combinations of properties which cannot be predicted from density alone. Herein, we examine the effects of four processing parameters for producing this type of polymer cross-linked aerogel on properties of the resulting monoliths. We focus on the results of C-13 CP-MAS NMR which gives insight to the size and structure of polymer cross-link present in the monoliths, and relates the size of the cross-links to microstructure, mechanical properties and other characteristics of the materials obtained.

Meador, Mary Ann B.; Capadona, Lynn A.; McCorkle, Linda; Padadopoulos, Demetrios S.; Leventis, Nicholas

2007-01-01

219

Structure-Property Relationships in Porous 3-D Nanostructures as a Function of Preparation Conditions: Isocyanate Cross-Linked Silica Aerogels  

NASA Technical Reports Server (NTRS)

Sol-gel derived silica aerogels are attractive candidates for many unique thermal, optical, catalytic, and chemical applications because of their low density and high mesoporosity. However, their inherent fragility has restricted use of aerogel monoliths to applications where they are not subject to any load. We have previously reported cross-linking the mesoporous silica structure of aerogels with di-isocyanates, styrenes or epoxies reacting with amine decorated silica surfaces. These approaches have been shown to significantly increase the strength of aerogels with only a small effect on density or porosity. Though density is a prime predictor of properties such as strength and thermal conductivity for aerogels, it is becoming clear from previous studies that varying the silica backbone and size of the polymer cross-link independently can give rise to combinations of properties which cannot be predicted from density alone. Herein, we examine the effects of four processing parameters for producing this type of polymer cross-linked aerogel on properties of the resulting monoliths. We focus on the results of 13C CP-MAS NMR which gives insight to the size and structure of polymer cross-link present in the monoliths, and relates the size of the cross-links to microstructure, mechanical properties and other characteristics of the materials obtained.

Meador, Mary Ann B.; Capadona, Lynn A.; McCorkle, Linda; Papadopoulos, Demetrios S.; Leventis, Nicholas

2007-01-01

220

Customized epithelial debridement for thin ectatic corneas undergoing corneal cross-linking: epithelial island cross-linking technique  

PubMed Central

Thin corneas with a minimum corneal thickness less than 400 ?m after epithelial removal represent a contraindication to standard epithelium-off cross-linking (CXL) treatment due to a significant endothelial cell density decrease and potentiality of permanent haze development. Preoperative swelling of the cornea with hypoosmolar riboflavin solutions broadens the spectrum of CXL indications to thin corneas. However the iatrogenic swelling effect might not be durable throughout the CXL procedure increasing the risk of postoperative complications. The transepithelial CXL technique proposed for thin corneas demonstrated poor clinical results and mid- to long-term keratoconus instability. The epithelial island CXL technique with customized pachymetry-guided epithelial debridement was evaluated by means of in vivo laser scanning confocal microscopy, corneal topography, and clinical examination in a 1-year follow-up, in order to assess if it may be considered an alternative surgical option for keratoconic patients with thin corneas undergoing corneal collagen CXL. According to our clinical and in-vivo micro-morphological results the technique results safe, and efficacious in stabilizing progressive keratoconus and may be considered a valid option in the treatment of thin ectatic corneas alone or in combination with hypoosmolar or dextran-free riboflavin solutions. PMID:25114495

Mazzotta, Cosimo; Ramovecchi, Vincenzo

2014-01-01

221

Mechanism of Hyaluronan Degradation by Streptococcus pneumoniae Hyaluronate Lyase  

E-print Network

Mechanism of Hyaluronan Degradation by Streptococcus pneumoniae Hyaluronate Lyase STRUCTURES structures of Streptococcus pneumoniae hyaluro- nate lyase with tetra- and hexasaccharide hyaluronan may facilitate the binding of the negatively charged hyaluro- nan to the enzyme. Streptococcus

de Groot, Bert

222

Corneal cross-linking in 9 horses with ulcerative keratitis  

PubMed Central

Background Corneal ulcers are one of the most common eye problems in the horse and can cause varying degrees of visual impairment. Secondary infection and protease activity causing melting of the corneal stroma are always concerns in patients with corneal ulcers. Corneal collagen cross-linking (CXL), induced by illumination of the corneal stroma with ultraviolet light (UVA) after instillation of riboflavin (vitamin B2) eye drops, introduces crosslinks which stabilize melting corneas, and has been used to successfully treat infectious ulcerative keratitis in human patients. Therefore we decided to study if CXL can be performed in sedated, standing horses with ulcerative keratitis with or without stromal melting. Results Nine horses, aged 1 month to 16 years (median 5 years) were treated with a combination of CXL and medical therapy. Two horses were diagnosed with mycotic, 5 with bacterial and 2 with aseptic ulcerative keratitis. A modified Dresden-protocol for CXL could readily be performed in all 9 horses after sedation. Stromal melting, diagnosed in 4 horses, stopped within 24 h. Eight of nine eyes became fluorescein negative in 13.5 days (median time; range 4–26 days) days after CXL. One horse developed a bacterial conjunctivitis the day after CXL, which was successfully treated with topical antibiotics. One horse with fungal ulcerative keratitis and severe uveitis was enucleated 4 days after treatment due to panophthalmitis. Conclusions CXL can be performed in standing, sedated horses. We did not observe any deleterious effects attributed to riboflavin or UVA irradiation per se during the follow-up, neither in horses with infectious nor aseptic ulcerative keratitis. These data support that CXL can be performed in the standing horse, but further studies are required to compare CXL to conventional medical treatment in equine keratitis and to optimize the CXL protocol in this species. PMID:23803176

2013-01-01

223

Unconventional metal organic frameworks: porous cross-linked phosphonates.  

PubMed

The past decade has witnessed an exponential growth of metal organic framework compounds (MOFs). The defining character of these compounds is their porosity. However, in many cases no effort was made to show evidence that a stable porous structure has been achieved and that the pores may be accessed. In the present paper we describe recent work on porous pillared zirconium diphosphonates, and the newer and in many respects different characteristics of tin(iv) phosphonates. The Sn(IV) monophosphonates form spherical globules that exhibit very high surface areas. The surface area arises from their nano-sized particles that pack in a "house of cards" arrangement. Also, it is shown that the 1,4-monophenyldiphosphonic acid forms highly porous (250-400 m2 g(-1)) materials with Sn(IV) when prepared in alcohol-water media. This is not the case with analogous Zr(IV) compounds. The many variations in the syntheses of both the zirconium and tin aryl- and alkyldiphosphonate pillars and their combinations with spacers such as methyl- and monophenylphosphonic acid have created a variety of highly porous materials that are stable to 400 degrees C in air, highly stable in acid media, do not collapse when de-solvated, and can be post and presynthesis altered to include functional groups. Several new directions taken by other researchers are also described. However, it is emphasized in this presentation that the cross-linked compounds form particles that precipitate rapidly into nanoparticles that exhibit only short range order. Therefore, they differ from the more conventional MOFs in that they are not amenable to structure solution by X-ray or neutron diffraction techniques. Rather, they must be understood on the basis of modeling and indirect data from EM, NMR, and additional spectroscopic and textural studies. PMID:18985237

Clearfield, Abraham

2008-11-28

224

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

PubMed

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. PMID:15329442

Rieben, W Kurt; Coulombe, Roger A

2004-12-01

225

Sequence context effect on the structure of nitrous acid induced DNA interstrand cross-links  

PubMed Central

In the preceding paper in this journal, we described the solution structure of the nitrous acid cross-linked dodecamer duplex [d(GCATCCGGATGC)]2 (the cross-linked guanines are underlined). The structure revealed that the cross-linked guanines form a nearly planar covalently linked ‘G:G base pair’, with the complementary partner cytidines flipped out of the helix. Here we explore the flanking sequence context effect on the structure of nitrous acid cross-links in [d(CG)]2 and the factors allowing the extrahelical cytidines to adopt such fixed positions in the minor groove. We have used NMR spectroscopy to determine the solution structure of a second cross-linked dodecamer duplex, [d(CGCTACGTAGCG)]2, which shows that the identity of the flanking base pairs significantly alters the stacking patterns and phosphate backbone conformations. The cross-linked guanines are now stacked well on adenines preceding the extrahelical cytidines, illustrating the importance of purine– purine base stacking. Observation of an imino proton resonance at 15.6 p.p.m. provides evidence for hydrogen bonding between the two cross-linked guanines. Preliminary structural studies on the cross-linked duplex [d(CGCGACGTCGCG)]2 show that the extrahelical cytidines are very mobile in this sequence context. We suggest that favorable van der Waals interactions between the cytidine and the adenine 2 bp away from the cross-link localize the cytidines in the previous cross-linked structures. PMID:15155848

Edfeldt, N. B. Fredrik; Harwood, Eric A.; Sigurdsson, Snorri Th.; Hopkins, Paul B.; Reid, Brian R.

2004-01-01

226

Food gels: Gelling process and new applications  

Microsoft Academic Search

Food gels are viscoelastic substances and several gelled products are manufactured throughout the world. The gelling agents in foods are usually polysaccharides and proteins. In food gels, the polymer molecules are not cross-linked by covalent bonds with the exception of disulphide bonds in some protein gels. Instead, the molecules are held together by a combination of weak inter-molecular forces like

SOUMYA BANERJEE; SUVENDU BHATTACHARYA

2011-01-01

227

Food Gels: Gelling Process and New Applications  

Microsoft Academic Search

Food gels are viscoelastic substances and several gelled products are manufactured throughout the world. The gelling agents in foods are usually polysaccharides and proteins. In food gels, the polymer molecules are not cross-linked by covalent bonds with the exception of disulphide bonds in some protein gels. Instead, the molecules are held together by a combination of weak inter-molecular forces like

Soumya Banerjee; Suvendu Bhattacharya

2012-01-01

228

Maleimide cross-linked bioactive PEG hydrogel exhibits improved reaction kinetics and cross-linking for cell encapsulation and in-situ delivery  

PubMed Central

Engineered polyethylene glycol-maleimide matrices for regenerative medicine exhibit improved reaction efficiency and wider range of Young’s moduli by utilizing maleimide cross-linking chemistry. This hydrogel chemistry is advantageous for cell delivery due to the mild reaction that occurs rapidly enough for in situ delivery, while easily lending itself to “plug-and-play” design variations such as incorporation of enzyme-cleavable cross-links and cell-adhesion peptides. PMID:22174081

Phelps, Edward A.; Enemchukwu, Nduka O.; Fiore, Vincent F.; Sy, Jay C.; Murthy, Niren; Sulchek, Todd A.; Barker, Thomas H.

2012-01-01

229

Informatics Strategies for Large-Scale Novel Cross-linking Analysis  

Microsoft Academic Search

The analysis of protein interactions in biological systems represents a significant challenge for today's technology. Chemical cross-linking provides the potential to impart new chemical bonds in a complex system that result in mass changes in the analysis of a set of tryptic peptides. However, system complexity and cross-linking product heterogeneity have precluded widespread chemical cross-linking use for large-scale identification of

Gordon A. Anderson; Nikola Tolic; Xiaoting Tang; Chunxiang Zheng; James E. Bruce

2007-01-01

230

Molecular simulations predict novel collagen conformations during cross-link loading  

PubMed Central

Collagen cross-linking mechanically strengthens tissues during development and aging, but there is limited data describing how force transmitted across cross-links affects molecular conformation. We used Steered Molecular Dynamics (SMD) to model perpendicular force through a side chain. Results predicted collagen peptides have negligible bending resistance and that mechanical force causes helix disruption below covalent bond failure strength, suggesting alternative molecular conformations precede cross-link rupture and macroscopic damage during mechanical loading. PMID:21620686

Bourne, Jonathan W.; Torzilli, Peter A.

2011-01-01

231

The chemistry of natural enzyme-induced cross-links of proteins  

Microsoft Academic Search

The cross-linking of protein molecules to form stable supramolecular aggregates capable of acting as protective and supporting structures is a common feature of organisms coping with the stresses of life. These new polymeric forms range from thick rigid structures to thin flexible membranes. The formation of such cross-links must be carefully controlled since more or less than optimal cross-linking could

A. J. Bailey

1991-01-01

232

Slime Away: Cross-Linking Poly (Vinyl Alcohol) with Sodium Borate  

NSDL National Science Digital Library

The Materials Science and Technology Teacher's Workshop (MAST) provides this lesson plan for students learning about polymers. The module will "explore the change in physical properties of a polymer as a result of cross-linking. The result of adding more cross-linking agents to a polymer is considered and another model of cross-linking is viewed."A step by step laboratory procedure is provided. Discussion questions, teacher notes and a link to a video clip are also included.

233

Dense silicon carbonitride ceramics by pyrolysis of cross-linked and warm pressed polysilazane powders  

Microsoft Academic Search

This study reports on the pyrolysis and densifaction behavior of cross-linked poly(hydridomethylsilazane) powders. The influence of the cross-linking procedure such as temperature and annealing time of the polymer powders on the compaction behavior under cold and warm pressing conditions is discussed. The degree of cross-linking is determined by thermal mechanical analysis (TMA). In addition to particle sliding which is assumed

Christoph Konetschny; Dusan Galusek; Stefan Reschke; Claudia Fasel; Ralf Riedel

1999-01-01

234

Synthesis and Characterization of Cross-linked Polymer Electrolyte Membranes for Supercapacitor  

Microsoft Academic Search

Cross-linked polyvinyl alcohol (PVA) electrolyte membranes have been synthesized by using a solution casting method. In this study, PVA was blended with oxidative cross-linked agent (zinc acetate) and nano-sized silica as filler to stabilize PVA matrix and enhance conductivity. The cross-linked membranes were immersed into lithium hydroxide (LiOH) aqueous solution to increase their ionic conductivity. Two techniques were used to

Memoria Rosi; Muhamad Prama Ekaputra; Mikrajuddin Abdullah; Khairurrijal

2010-01-01

235

High efficiency mixing by the use of cross-linked micro capillary fluid filter  

Microsoft Academic Search

A novel type passive mixing device that causes the three-dimensional flow was proposed. This mixer consists of the integrated\\u000a capillary bundle structure. And the capillaries ware cross-linked each other. So it is called cross-linked micro capillary\\u000a filter. The mixing effect of the cross-linked micro capillary filter was calculated by the computational fluid dynamics (CFD).\\u000a The fluid behaviour in the fine

K. Fujiwara; Y. Ukita; M. Takeo; S. Negoro; T. Kanie; M. Katayama; Y. Utsumi

2008-01-01

236

Synthesis of a disulfide cross-linked polygalacturonic acid hydrogel for biomedical applications.  

PubMed

Polygalacturonic acid (PGA) hydrogel cross-linked via disulfide bonds was synthesized using a thiol oxidation reaction. PGA was grafted with cysteine to yield thiolated PGA (denoted PGAcys). Per gram, PGA-conjugated cysteine was 725 ± 77 ?mol, and the degree of modification was 16.24 %. A PGAcys hydrogel film was fabricated under physiological conditions, with gel content 91.6 % and water content 43.3 %. The PGAcys hydrogel was used as a drug carrier for rosmarinic acid (RA) (denoted PGAcys/RA) and to prevent postsurgical adhesion. The in vitro dynamic release behavior of RA from the PGAcys hydrogel was analyzed. The profiles showed that 80 % of the total RA was released from the hydrogel within 15 min, followed by zero-order kinetic release. Animal implant studies showed that PGAcys and PGAcys/RA hydrogel films reduced adhesion incidence by over 90 %, significantly higher than did Hyaluronate/Carboxymethylcellulose (analogous Seprafilm™) (42 %). The PGAcys/RA hydrogel film also reduced the early inflammatory reaction. PMID:23468164

Peng, Hsiu-Hui; Chen, Yi-Min; Lee, Chen-I; Lee, Ming-Wei

2013-06-01

237

Direct imaging of fluctuations in a cross-linked biopolymer network  

NASA Astrophysics Data System (ADS)

Cross-linked networks are ubiquitous in synthetic and biological polymer systems, such as rubbers and cytoskeletons. To model cross-linked networks, several theories have been developed on the basis of different assumptions as to fluctuations in the networks. Here we put these theories to direct test. This talk will describe direct single-molecule imaging of the dynamic fluctuations of junction points in a cross-linked semiflexible polymer (F-actin) network. The actin filaments are cross linked by biotin/avidin. The junction points are selectively labeled to allow nm spatial imaging resolution. The surprising results point to limitations of the prevailing network models.

Wang, Bo; Jiang, Lingxiang; Tsang, Boyce; Granick, Steve

2013-03-01

238

Covalent cross-links in polyampholytic chitosan fibers enhances bone regeneration in a rabbit model.  

PubMed

Chitosan fibers were prepared in citric acid bath, pH 7.4 and NaOH solution at pH 13, to form ionotropically cross-linked and uncross-linked fibers, respectively. The fibers formed in citric acid bath were further cross-linked via carbodiimide chemistry; wherein the pendant carboxyl moieties of citric acid were used for new amide bond formation. Moreover, upon covalent cross-linking in the ionically gelled citrate-chitosan fibers, incomplete conversion of the ion pairs to amide linkages took place resulting in the formation of a dual network structure. The dual cross-linked fibers displayed improved mechanical property, higher stability against enzymatic degradation, hydrophobicity and superior bio-mineralization compared to the uncross-linked and native citrate cross-linked fibers. Additionally, upon cyclic loading, the ion pairs in the dual cross-linked fibers dissociated by dissipating energy and reformed during the relaxation period. The twin property of elasticity and energy dissipation mechanism makes the dual cross-linked fiber unique under dynamic mechanical conditions. The differences in the physico-chemical characteristics were reflected in protein adsorption, which in turn influenced the cellular activities on the fibers. Compared to the uncross-linked and ionotropically cross-linked fibers, the dual cross-linked fibers demonstrated higher proliferation and osteogenic differentiation of the MSCs in vitro as well as better osseous tissue regeneration in a rabbit model. PMID:25483844

Ghosh, Paulomi; Rameshbabu, Arun Prabhu; Das, Dipankar; Francis, Nimmy K; Pawar, Harpreet Singh; Subramanian, Bhuvaneshwaran; Pal, Sagar; Dhara, Santanu

2015-01-01

239

Effect of radiation cross-linking on the abrasive wear behaviour of polyethylenes  

NASA Astrophysics Data System (ADS)

This study explores the differences in the dry abrasive wear behavior of different polyethylenes, and compares the effect of radiation cross-linking on the wear behavior. Four different types of polyethylenes: LDPE, LLDPE, HDPE and UHMWPE were studied. Cross-linking was carried out by high energy electron beam with radiation dose of 200 kGy. The results show that in unirradiated state UHMWPE has excellent wear resistance, with HDPE showing comparable wear properties; both LDPE and LLDPE exhibit high wear rate. Cross-linking improves wear rate of LDPE and UHMWPE, however, the wear rate of HDPE and LLDPE increases with cross-linking.

Gul, Rizwan M.; Khan, Tahir I.

2014-06-01

240

Structural, mechanical and osmotic properties of injectable hyaluronan-based composite hydrogels  

PubMed Central

The osmotic and scattering properties of hyaluronan-based composite hydrogels composed of stiff biopolymer chains (carboxymethylated thiolated hyaluronan (CMHA-S)) crosslinked by a flexible polymer (polyethylene glycol diacrylate (PEGDA)) are investigated and analyzed in terms of the scaling theory. The total pre-gel polymer weight concentration is varied between 0.5 wt.% and 3.2 wt.%, while the mole ratio between the reactive PEG chain ends and the thiolated HA moieties is changed between 0.15 and 1.0. The shear modulus G of the fully swollen gels exhibits a stronger dependence on pre-gel concentration than on the crosslink density. Osmotic deswelling measurements reveal that the osmotic mixing pressure depends on the weight ratio CMHA-S/PEGDA, and is practically unaffected by the pre-gel concentration. Small-angle neutron scattering observations indicate that the thermodynamic properties of these composite gels are governed by total polymer concentration, i.e., specific interactions between the two polymeric components do not play a significant role. PMID:20824199

Horkay, Ferenc; Magda, Jules; Alcoutlabi, Mataz; Atzet, Sarah; Zarembinski, Thomas

2010-01-01

241

Hyaluronan and phospholipid association in biolubrication.  

PubMed

It is becoming increasingly clear that the outstanding lubrication of synovial joints is achieved by a sophisticated hierarchical structure of cartilage combined with synergistic actions of surface-active components present in the synovial fluid. In this work we focus on the association of two components of the synovial fluid, hyaluronan and dipalmitoyl phosphatidyl choline (DPPC), in bulk solution and at interfaces. We demonstrate that hyaluronan associates with DPPC vesicles and adsorbs to supported DPPC bilayers. The association structures formed at the interface are sufficiently stable to allow sequential adsorption of DPPC and hyaluronan, whereby promoting the formation of thick composite layers of these two components. The lubricating ability of such composite layers was probed by the AFM colloidal probe technique and found to be very favorable with low friction coefficients and high load bearing capacity. With DPPC as the last adsorbed component, a friction coefficient of 0.01 was found up to pressures significantly above what is encountered in healthy synovial joints. Hyaluronan as the last added component increases the friction coefficient to 0.03 and decreases the load bearing capacity somewhat (but still above what is needed in the synovial joint). Our data demonstrate that self-assembly structures formed by hyaluronan and phospholipids at interfaces are efficient aqueous lubricants, and it seems plausible that such self-assembly structures contribute to the exceptional lubrication of synovial joints. PMID:24171653

Wang, Min; Liu, Chao; Thormann, Esben; D?dinait?, Andra

2013-12-01

242

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

PubMed Central

Purpose: To compare the outcome of Collagen cross-linking (CXL) with that following topography-guided customized ablation treatment (T-CAT) with simultaneous CXL in eyes with progressive keratoconus. Materials and Methods: This was a prospective, non-randomized single centre study of 66 eyes with progressive keratoconus. Of these, 40 eyes underwent CXL and 26 eyes underwent T-CAT + CXL. The refractive, topographic, tomographic and aberrometric changes measured at baseline, 1, 3 and 6 months post-operatively were compared between both groups. Results: After a mean follow-up of 7.7 ± 1.3 months, the mean retinoscopic cylinder decreased by 1.02 ± 3.16 D in the CXL group (P = 0.1) and 2.87 ± 3.22 D in the T-CAT + CXL group (P = 0.04). The Best corrected visual acuity increased by 2 lines or more in 10% of eyes in the CXL group and in 23.3% of eyes in the T-CAT + CXL group. The mean steepest-K reduced by 0.40 ± 3.71 D (P = 0.77) in the CXL group and by 2.91 ± 2.01D (P = 0.03) in the T-CAT + CXL group. The sag factor and surface asymmetry index showed no significant change in the CXL group but reduced by 3.59 ± 5.94 D (P = 0.01) and 0.72 ± 1.18 (P = 0.02) respectively in the T-CAT + CXL group. There was a significant increase in the highest posterior corneal elevation in both groups (9.57 ± 14.93 ? in the CXL group and 7.85 ± 9.25 ? in the T-CAT + CXL group, P ? 0.001 for both). There was significantly greater reduction of mean coma (P < 0.001) and mean higher-order aberrations (P = 0.01) following T-CAT + CXL compared to CXL. Conclusions: CAT + CXL is an effective approach to confer biomechanical stability and to improve the corneal contour in eyes with keratoconus and results in better refractive, topographic and aberrometric outcomes than CXL alone. PMID:23619500

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

2014-01-01

243

Isocyanate Cross-Linked Silica: Structurally Strong Aerogels  

NASA Technical Reports Server (NTRS)

Molecular-level synergism between the silica nanoparticles of pre-formed monoliths and molecular cross-linkers inverts the relative host-guest roles in glass-polymer composites, leading to new strong low-density materials. Attempts to load gels with variable amounts of polyurethane precursors such as di-ISO and diol end-capped polybutylene adipate followed by heat treatment, washing, and supercritical drying led to opaque materials, somewhat stronger than silica but still quite brittle and much inferior to the materials described above. Direct mixing of a diisocyanate and an alcohol-free sol has been attempted recently by Yim et al. Reportedly, that procedure leads to week-long gelation times and requires an at least equally long aging period. In our attempt to add various amounts of di-ISO in a base-catalyzed sol in PC, we also noticed a week-long gelation time. The resulting aerogels were translucent but no less brittle than native silica. According to more recent studies, if propylene carbonate is replaced with acetone, it leads not only to shorter processing times, but also to much stronger gels that can tolerate loads in excess of 40 kg in the arrangement presented. We attribute that behavior to the lower viscosity of acetone, that allows faster diffusion of the di-ISO solution within the pores before di-ISO has time to react with the surface of silica. Further studies are underway to vary the chemical identity of the diisocyanate, as well as the composition and density of silica.

Leventis, Nicholas; Sotiriou-Leventis, Chariklia; Zhang, Guo-Hui; Rawashdeh, Abdel-Monem M.

2002-01-01

244

pH-induced metal-ligand cross-links inspired by mussel yield self-healing polymer networks with near-covalent elastic moduli  

PubMed Central

Growing evidence supports a critical role of metal-ligand coordination in many attributes of biological materials including adhesion, self-assembly, toughness, and hardness without mineralization [Rubin DJ, Miserez A, Waite JH (2010) Advances in Insect Physiology: Insect Integument and Color, eds Jérôme C, Stephen JS (Academic Press, London), pp 75–133]. Coordination between Fe and catechol ligands has recently been correlated to the hardness and high extensibility of the cuticle of mussel byssal threads and proposed to endow self-healing properties [Harrington MJ, Masic A, Holten-Andersen N, Waite JH, Fratzl P (2010) Science 328:216–220]. Inspired by the pH jump experienced by proteins during maturation of a mussel byssus secretion, we have developed a simple method to control catechol-Fe3+ interpolymer cross-linking via pH. The resonance Raman signature of catechol-Fe3+ cross-linked polymer gels at high pH was similar to that from native mussel thread cuticle and the gels displayed elastic moduli (G?) that approach covalently cross-linked gels as well as self-healing properties. PMID:21278337

Holten-Andersen, Niels; Harrington, Matthew J.; Birkedal, Henrik; Lee, Bruce P.; Messersmith, Phillip B.; Lee, Ka Yee C.; Waite, J. Herbert

2011-01-01

245

pH-induced metal-ligand cross-links inspired by mussel yield self-healing polymer networks with near-covalent elastic moduli.  

PubMed

Growing evidence supports a critical role of metal-ligand coordination in many attributes of biological materials including adhesion, self-assembly, toughness, and hardness without mineralization [Rubin DJ, Miserez A, Waite JH (2010) Advances in Insect Physiology: Insect Integument and Color, eds Jérôme C, Stephen JS (Academic Press, London), pp 75-133]. Coordination between Fe and catechol ligands has recently been correlated to the hardness and high extensibility of the cuticle of mussel byssal threads and proposed to endow self-healing properties [Harrington MJ, Masic A, Holten-Andersen N, Waite JH, Fratzl P (2010) Science 328:216-220]. Inspired by the pH jump experienced by proteins during maturation of a mussel byssus secretion, we have developed a simple method to control catechol-Fe(3+) interpolymer cross-linking via pH. The resonance Raman signature of catechol-Fe(3+) cross-linked polymer gels at high pH was similar to that from native mussel thread cuticle and the gels displayed elastic moduli (G') that approach covalently cross-linked gels as well as self-healing properties. PMID:21278337

Holten-Andersen, Niels; Harrington, Matthew J; Birkedal, Henrik; Lee, Bruce P; Messersmith, Phillip B; Lee, Ka Yee C; Waite, J Herbert

2011-02-15

246

J-integral fracture toughness and tearing modulus measurement of radiation cross-linked UHMWPE.  

PubMed

Radiation and chemical cross-linking of medical grade ultrahigh molecular weight polyethylene (UHMWPE) has recently been utilized in an effort to improve wear performance of total joint replacement components. However, reductions in mechanical properties with cross-linking are cause for concern regarding the use of cross-linked UHMWPE for high-stress applications such as in total knee replacement prostheses. In this study, the fracture behavior of radiation cross-linked UHMWPE was compared to that of uncross-linked UHMWPE. The Rice and Sorensen model that utilizes mechanical parameters obtained from uniaxial tensile and compact tension tests was used to calculate the steady state J-integral fracture toughness, Jss, for radiation cross-linked UHMWPE. Jss decreased monotonically with increase in radiation dose. UHMWPE exhibited tough, ductile tearing behavior with stable crack growth when it was cross-linked using a gamma radiation dose of 0-50 kGy. However, in cross-linked UHMWPE irradiated to a dose of 100 and 200 kGy, unstable fracture occurred spontaneously upon attaining the initial crack driving force, J1c. This indicates that a high degree of cross-linking is less desirable for high-stress applications in orthopaedic implants. However, a substantial increase in J1c, even at a low degree of cross-linking, suggests that a low degree of cross-linking may be beneficial for resistance to delamination and catastrophic failure, both of which require an initiation step for the fracture to propagate in the material. This mechanical test should, however, be considered along with fatigue tests and joint simulator testing before determination of an appropriate amount of cross-linking for total joint replacement prostheses that experience high stresses. PMID:12472222

Gomoll, A; Wanich, T; Bellare, A

2002-11-01

247

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

PubMed Central

Chemical cross-linking mass spectrometry identifies interacting surfaces within a protein assembly through labeling with bifunctional reagents and identifying the covalently modified peptides. These yield distance constraints that provide a powerful means to model the three-dimensional structure of the assembly. Bioinformatic analysis of cross-linked data resulting from large protein assemblies is challenging because each cross-linked product contains two covalently linked peptides, each of which must be correctly identified from a complex matrix of potential confounders. Protein Prospector addresses these issues through a complementary mass modification strategy in which each peptide is searched and identified separately. We demonstrate this strategy with an analysis of RNA polymerase II. False discovery rates (FDRs) are assessed via comparison of cross-linking data to crystal structure, as well as by using a decoy database strategy. Parameters that are most useful for positive identification of cross-linked spectra are explored. We find that fragmentation spectra generally contain more product ions from one of the two peptides constituting the cross-link. Hence, metrics reflecting the quality of the spectral match to the less confident peptide provide the most discriminatory power between correct and incorrect matches. A support vector machine model was built to further improve classification of cross-linked peptide hits. Furthermore, the frequency with which peptides cross-linked via common acylating reagents fragment to produce diagnostic, cross-linker-specific ions is assessed. The threshold for successful identification of the cross-linked peptide product depends upon the complexity of the sample under investigation. Protein Prospector, by focusing the reliability assessment on the least confident peptide, is better able to control the FDR for results as larger complexes and databases are analyzed. In addition, when FDR thresholds are calculated separately for intraprotein and interprotein results, a further improvement in the number of unique cross-links confidently identified is achieved. These improvements are demonstrated on two previously published cross-linking datasets. PMID:24335475

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

2014-01-01

248

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

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

249

Hyaluronan as an Immune Regulator in Human Diseases  

PubMed Central

Accumulation and turnover of extracellular matrix components are the hallmarks of tissue injury. Fragmented hyaluronan stimulates the expression of inflammatory genes by a variety of immune cells at the injury site. Hyaluronan binds to a number of cell surface proteins on a variety of cell types. Hyaluronan fragments signal through both Toll-like receptor (TLR) 4 and TLR2 as well as CD44 to stimulate inflammatory genes in inflammatory cells. Hyaluronan is also present on the cell surface of epithelial cells and provides protection against tissue damage by interacting with TLR2 and TLR4 on these parenchymal cells. Hyaluronan and hyaluronan-binding proteins regulate inflammation, tissue injury and repair through regulating inflammatory cell recruitment, release of inflammatory cytokines, and stem cell migration. This review focuses on the role of hyaluronan as an immune regulator in human diseases. PMID:21248167

NOBLE, PAUL W.; LIANG, JIURONG; JIANG, DIANHUA

2010-01-01

250

IQGAP1 regulates hyaluronan-mediated fibroblast motility and proliferation.  

PubMed

IQGAP1, an essential scaffolding protein, forms a complex with the hyaluronan receptor CD44. In this study, we have examined the importance of IQGAP1 for hyaluronan-mediated fibroblast migration and proliferation. Hyaluronan induced formation of F-actin fibers and focal adhesions, which was dependent on IQGAP1. IQGAP1 was required for hyaluronan- but not for platelet-derived growth factor (PDGF)-BB-induced cell migration, and was required for both hyaluronan- and PDGF-BB-mediated fibroblast proliferation, but not for proliferation induced by 10% fetal bovine serum. Depletion of IQGAP1 suppressed hyaluronan-induced activation of Rac1 and enhanced the activation of RhoA. Taken together, these findings indicate important roles for IQGAP1 in hyaluronan-stimulated migration and proliferation of fibroblasts. PMID:22634185

Kozlova, Inna; Ruusala, Aino; Voytyuk, Oleksandr; Skandalis, Spyros S; Heldin, Paraskevi

2012-09-01

251

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

NASA Technical Reports Server (NTRS)

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

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

1985-01-01

252

Chemistry and Physical Properties of Melt Processed- and Solution- Cross Linked Corn Zein  

Technology Transfer Automated Retrieval System (TEKTRAN)

Corn zein was cross linked with the glutaraldehyde (GDA) using glacial acetic acid (HAc) as catalyst. The objectives are to enhance the mechanical properties of poured films and to compare them with compression molded tensile bars from melt processed zein. Chemistry of the cross linking reaction w...

253

Cross-linked polyvinyl chloride resin foam and method of manufacturing the same  

Microsoft Academic Search

This invention provides a method of continuously manufacturing a cross-linked polyvinyl chloride resin foam sheet which has a low density, uniformly fine cell, excellent thermal moldability and high heat resistance and is neither deformed nor deteriorated even by long storage characterized by uniformly kneading the polyvinyl chloride resin with a blowing agent, stabilizer, plasticizer and cross-linking promoter without causing the

J. Sasajima; K. Mogi; H. Nagai; A. Nojiri; N. Shiina

1984-01-01

254

Cross-Linking and Rheological Changes of Whey Proteins Treated with Microbial Transglutaminase  

Microsoft Academic Search

Modification of the functionality of whey proteins using microbial transglutaminase (TGase) has been the subject of recent studies. However, changes in rheological properties of whey proteins as affected by extensive cross-linking with TGase are not well studied. The factors affecting cross-linking of whey protein isolate (WPI) using both soluble and immobilized TGase were examined, and the rheological properties of the

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

2004-01-01

255

Virtual synthesis of thermally cross-linked copolymers from a novel implementation of polymatic.  

PubMed

Because of the complex connectivity of cross-linked polymers, generating structures for molecular simulations is a nontrivial task. In this work, a general methodology is presented for constructing post-cross-linked polymers by a new two-stage implementation of the Polymatic simulated polymerization algorithm, where linear polymers are first polymerized and then cross-linked. It is illustrated here for an example system of thermally cross-linked octene-styrene-divinylbenzene (OS-DVB) copolymers. In the molecular models, the degree of cross-linking is ranged from 0 to 100%, and the resulting structural and thermal properties are examined. The simulations reveal an increase in the free volume with higher cross-linking degrees. Shifts in the peaks of the structure factors, which are assigned to contributions from the backbone and side-chain atoms, correspond to the formation of larger free volume elements. Furthermore, the glass transition temperatures increase with higher degrees of cross-linking, while the thermal expansivity decreases. Comparisons with experimental results for similar systems are made when available. As demonstrated here, the presented methodology will provide an effective route to simulating post-cross-linked polymers for a variety of applications, which will enable an improved understanding of their structure-property relationships. PMID:24502582

Abbott, Lauren J; Hughes, Justin E; Colina, Coray M

2014-02-20

256

Formation and characterization of superparamagnetic cross-linked high amylose starch  

E-print Network

Formation and characterization of superparamagnetic cross-linked high amylose starch V. Veigaa , D cross-linked high amylose starch matrix with magnetic properties was synthesized via in situ formation reserved. Keywords: Amylose; X-ray diffractograms; Mo¨ssbauer spectra 1. Introduction Starch is one

Ryan, Dominic

257

Electrospun zein fibers using glyoxal or formaldehyde as the cross-linking reagent  

Technology Transfer Automated Retrieval System (TEKTRAN)

Glyoxal or formaldehyde was used as a cross-linking reagent for zein (corn protein) to provide electrospun fibers with improved physical properties and solvent resistance. These reagents were used between 2 and 6%. The cross-linking reaction was carried out in acetic acid for various lengths of ti...

258

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

EPA Science Inventory

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

259

A novel cross-linked human amniotic membrane for corneal implantations.  

PubMed

The aim of this study was to evaluate the efficacy of Al2(SO4)3 cross-linked human amniotic membrane for ocular surface reconstruction using tissue culture techniques. The human amniotic membrane was cross-linked with Al2(SO4)3, and the cross-linked human amniotic membrane was characterized for its mechanical properties, percentage of swelling in water, sterility, infrared spectroscopy and scanning electron microscopy. The potential of cross-linked human amniotic membrane to support the attachment and proliferation of corneal limbal epithelial cells was assessed in vitro, using static culture system. About 125% increase in the tensile strength was observed in the cross-linked human amniotic membrane compared to human amniotic membrane. Infrared spectroscopy studies have confirmed the cross-linking of human amniotic membrane with Al2(SO4)3. The cross-linked human amniotic membrane was found to be sterile up to 1 year. In culture studies, confluent sheets of epithelial cells were seen at the end of 14th day resembling the morphological features of limbal epithelia. The cross-linked human amniotic membrane has exhibited improved mechanical properties, and the tissue culture studies have shown its feasibility to be used as a limbal transplant. It was concluded that the crosslinked human amniotic membrane with its improved mechanical properties could be used on par with human amniotic membrane. PMID:23662337

Sekar, S; Sasirekha, K; Krishnakumar, S; Sastry, T P

2013-03-01

260

Measurement of cross linked fibrin derivatives in plasma: an immunoassay using monoclonal antibodies  

Microsoft Academic Search

Fibrinogen degradation, fibrin polymerisation, and the insertion of cross links into fibrin by fibrin stabilising factor lead to the appearance of new antigenic determinants. Antibodies against these antigenic sites may react specifically with the derivatives but not with the parent molecules. We have utilised a monoclonal antibody, which interacts with the cross linked fragment D dimer and related high molecular

A N Whitaker; M J Elms; P P Masci; P G Bundesen; D B Rylatt; A J Webber; I H Bunce

1984-01-01

261

Ingested hyaluronan moisturizes dry skin  

PubMed Central

Hyaluronan (HA) is present in many tissues of the body and is essential to maintain moistness in the skin tissues, which contain approximately half the body’s HA mass. Due to its viscosity and moisturizing effect, HA is widely distributed as a medicine, cosmetic, food, and, recently marketed in Japan as a popular dietary supplement to promote skin moisture. In a randomized, double-blind, placebo-controlled clinical study it was found that ingested HA increased skin moisture and improved treatment outcomes for patients with dry skin. HA is also reported to be absorbed by the body distributed, in part, to the skin. Ingested HA contributes to the increased synthesis of HA and promotes cell proliferation in fibroblasts. These effects show that ingestion of HA moisturizes the skin and is expected to improve the quality of life for people who suffer from dry skin. This review examines the moisturizing effects of dry skin by ingested HA and summarizes the series of mechanisms from absorption to pharmacological action. PMID:25014997

2014-01-01

262

Molybdate sorption by cross-linked chitosan beads: Dynamic studies  

SciTech Connect

Recent trends in environmental monitoring have induced increasing development of new wastewater treatment techniques. Membrane processes, electrochemical techniques, or ion-exchange systems are widely used, but biosorption has been recognized in the last 30 years as a promising way to reduce the contamination of surface water issued from industrial effluent. Chitosan, a biopolymer extracted from crustacean shells, exhibits high sorption capacities for metal ion recovery. Sorption efficiency and removal rates are controlled by several diffusion mechanisms. Chitosan gel beads have been prepared and have shown enhanced sorption performance in batch systems. This study shows that, in continuous systems, sorption capacities can reach 700 mg/g, a level close to that obtained in batch studies. The effects of metal concentration, flow velocity, and column size are investigated and demonstrate that, because of diffusion mechanisms, the optimum concentration range is approximately 50 to 100 mg/L. In column systems, the Biot number, though greater than 1, is lower than the Biot number obtained in batch systems, indicating that external mass transfer influences mass transfer at the low superficial velocity investigated in this work.

Guibal, E.; Milot, C.; Roussy, J.

1999-01-01

263

Covalently cross-linked sulfone polybenzimidazole membranes with poly(vinylbenzyl chloride) for fuel cell applications.  

PubMed

Covalently cross-linked polymer membranes were fabricated from poly(aryl sulfone benzimidazole) (SO(2)PBI) and poly(vinylbenzyl chloride) (PVBCl) as electrolytes for high-temperature proton-exchange-membrane fuel cells. The cross-linking imparted organo insolubility and chemical stability against radical attack to the otherwise flexible SO(2)PBI membranes. Steady phosphoric acid doping of the cross-linked membranes was achieved at elevated temperatures with little swelling. The acid-doped membranes exhibited increased mechanical strength compared to both pristine SO(2)PBI and poly[2,2'-(m-phenylene)-5,5'-bibenzimidazole] (mPBI). The superior characteristics of the cross-linked SO(2)PBI membranes allowed higher acid doping levels and, therefore, higher proton conductivity. Fuel-cell tests with the cross-linked membranes demonstrated a high open circuit voltage and improved power performance and durability. PMID:23303655

Yang, Jingshuai; Aili, David; Li, Qingfeng; Cleemann, Lars N; Jensen, Jens Oluf; Bjerrum, Niels J; He, Ronghuan

2013-02-01

264

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

NASA Technical Reports Server (NTRS)

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

Ono, S.; Yamauchi, M.

1992-01-01

265

Comparison of chitosan/starch composite film properties before and after cross-linking.  

PubMed

Unmodified and cross-linked chitosan/starch composite films were prepared using the solvent evaporation method. The properties of the films were studied to obtain useful information about the possible applications of composite films. FT-IR, SEM, and swelling property investigations show that the cross-linking agent glutaraldehyde reacts in the chitosan and starch blend. The compatibility of chitosan and starch blends before and after cross-linking was studied by UV-vis spectroscopy. The compatibility of the blends deteriorated after cross-linking. This finding was confirmed by the results of mechanical properties. The films show improved water barrier performance after cross-linking. The use of trace concentrations of glutaraldehyde in chitosan/starch films allows for possible application in the biomedical field. PMID:23107802

Li, Haihong; Gao, Xiaochen; Wang, Yan; Zhang, Xiaobo; Tong, Zhiwei

2013-01-01

266

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

PubMed

The purpose of this study was to investigate the carbodiimide cross-linking of amniotic membrane (AM) in the presence of amino acid bridges. The biological tissues were treated with glycine, lysine, or glutamic acid and chemically cross-linked to examine the role of amino acid types in collagenous biomaterial processing. Results of zeta potential measurements showed that the use of uncharged, positively and negatively charged amino acids dictates the charge state of membrane surface. Tensile strength and water content measurements demonstrated that the addition of lysine molecules to the cross-linking system can increase the cross-linking efficiency and dehydration degree while the introduction of glutamic acid in the AM samples decreases the number of cross-links per unit mass of chemically modified tissue collagen. The differences in the cross-linking density further determined the thermal and biological stability by differential scanning calorimetry and in vitro degradation tests. As demonstrated in matrix permeability studies, the improved formation of covalent cross-linkages imposed by lysine facilitated construction of stronger cross-linking structures. In contrast, the added glycine molecules were insufficient to enhance the resistances of the proteinaceous matrices to thermal denaturation and enzymatic degradation. The cytocompatibility of these biological tissue membranes was evaluated by using human corneal epithelial cell cultures. Results of cell viability, metabolic activity, and pro-inflammatory gene expression level showed that the AM materials cross-linked with carbodiimide in the presence of different types of amino acids are well tolerated without evidence of detrimental effect on cell growth. In addition, the amino acid treated and carbodiimide cross-linked AM implants had good biocompatibility in the anterior chamber of the rabbit eye model. Our findings suggest that amino acid type is a very important engineering parameter to mediate carbodiimide cross-linking of AM collagen. PMID:25842104

Lai, Jui-Yang

2015-06-01

267

Facile synthesis of core-shell/hollow anisotropic particles via control of cross-linking during one-pot dispersion polymerization.  

PubMed

Preparation of anisotropic particles based on seed phase separation involves multiple processes, and asymmetrical structures and surfaces cannot be produced when anisotropic shapes emerge. In conventional one-pot dispersion polymerization (Dis.P) using cross-linker, only spherical particles are prepared due to rapid and high cross-linking. Herein, monodisperse snowman-like particles with core-shell/hollow structures and partially rough surface were synthesized straightforward by a modified one-pot Dis.P, in which ethylene glycol and water (6/4, vol.) were used as medium, and ammonium persulfate (APS) aqueous solution, vinyl acetate (VA) and/or acrylic acid (AA), divinylbenzene (DVB) and styrene (St) were added at 6h. The cross-linking of growing particles was confined to exterior (forming cross-linked shell), and gel contents were low, leading to phase separation. Asymmetrical morphologies, structures, sizes and surface roughness were flexibly tuned by varying amounts of APS, VA and/or AA, water and DVB, and DVB adding speed. At low APS contents or high DVB amounts, the inhomogeneous cross-linking of head enabled its phase to separate, producing elongated head. With addition of VA and AA, phase separations inside head and body were induced, generating hollow structure. Adding DVB very slowly, nonlinear growth of third compartment occurred, forming bowed head. PMID:25626132

Liu, Yanan; Ma, Yuhong; Liu, Lianying; Yang, Wantai

2015-05-01

268

Preparation and characterization of a magneto-polymeric nanocomposite: Fe 3O 4 nanoparticles in a grafted, cross-linked and plasticized poly(vinyl chloride) matrix  

NASA Astrophysics Data System (ADS)

In this work two kind of materials: (1) grafted, cross-linked and plasticized poly(vinyl chloride) (PVC) "plastic films" and (2) magnetic plastic films "magneto-polymeric nanocomposites" were prepared. Precursor solutions or "plastisols" used to obtain the plastic films were obtained by mixing PVC (emulsion grade) as polymeric matrix, di(2-ethylhexyl)phthalate (DOP) as plasticizer, a thermal stabilizer based in Ca/Zn salts, and a cross-linking agent, 3-mercaptopropyltrimethoxysilane (MTMS) or 3-aminopropyltriethoxysilane (ATES), at several concentrations. Flexible films were obtained from the plastisols using static casting. The stress-strain behavior and the gel content (determined by Soxhlet extraction with boiling THF) of the flexible films were measured in order to evaluate the effect of the cross-linking agent and their content on the degree of cross-linking. The magneto-polymeric nanocomposites were obtained by mixing the optimum composition of the plastisols (analyzed previously) with magnetite (Fe 3O 4)-based ferrofluid and DOP. Later, flexible films were obtained by static casting of the plastisol/ferrofluid systems. The magnetic films were characterized by the above-mentioned techniques and X-ray diffraction, vibrating sample magnetometry and thermogravimetrical analysis.

Rodríguez-Fernández, Oliverio S.; Rodríguez-Calzadíaz, C. A.; Yáñez-Flores, Isaura G.; Montemayor, Sagrario M.

269

Determination of protein conformation by isotopically labelled cross-linking and dedicated software  

NASA Astrophysics Data System (ADS)

Chemical cross-linking in conjunction with mass spectrometry (MS) can be used for sensitive and rapid investigation of the three-dimensional structure of proteins at low resolution. However, the resulting data are very complex, and on the bioinformatic side, there still exists an urgent need for improving computer software for (semi-) automated cross-linking data analysis. In this study, we have developed dedicated software for rapid and confident identification and validation of cross-linked species using an isotopic labelled cross-linker approach in combination with MS. Deuterated (+4 Da) and non-deuterated (+0 Da) bis(sulfosuccinimidyl)suberate, BS3, was used as homobifunctional cross-linker to tag the cross-linked regions. Peptides generated from proteolysis were separated using high performance liquid chromatography, and peptide mass fingerprinting was obtained for the individual fractions using matrix-assisted laser-desorption ionisation time-of-flight (MALDI TOF) MS. The resulting peptide mass lists were combined and transferred to the program, ProteinXXX, which generated the theoretical mass values of all combinations of cross-linked peptides and dead-end cross-links and compared this to the obtained mass lists. In addition, screening for 4 Da-separated signals aided the identification of potential cross-linked species. Sequence information of these candidates was then obtained using MALDI TOF TOF. The cross-linked peptides could then be validated based on the match of the fragmentation pattern and the theoretical values produced by ProteinXXX. This semi-automated interpretation provided a high analysis speed of cross-linking data, with efficient and confident identification of cross-linked species. Four experiments using different conditions showed a high degree of reproducibility as only 1 and 2 cross-links out of 36 identified was not observed in two experiments. The method was tested using human placenta calreticulin (CRT). Based on the identified cross-links, a few corrections to a model of calreticulin obtained by homology modelling using calnexin as template can be suggested. Furthermore, the cross-links show that the C-terminal of the protein continues along the core region opposite the P-domain for at least 11 residues beyond the known structure. In addition, it was observed that the conformation of CRT does not change significantly in the presence or absence of the divalent ions, Ca2+ and Zn2+.

Nielsen, Tina; Thaysen-Andersen, Morten; Larsen, Nanna; Jørgensen, Flemming S.; Houen, Gunnar; Højrup, Peter

2007-12-01

270

Highly Efficient Copper(II) Ion Sorbents Obtained by Calcium Carbonate Mineralization on Functionalized Cross-Linked Copolymers.  

PubMed

A new type of Cu(II) ion sorbents is presented. These are obtained by CaCO3 mineralization from supersaturated solutions on gel-like cross-linked polymeric beads as insoluble templates. A divinylbenzene-ethylacrylate-acrylonitrile cross-linked copolymer functionalized with weakly acidic, basic, or amphoteric functional groups has been used, as well as different initial inorganic concentrations and addition procedures for CaCO3 crystal growth. The morphology of the new composites was investigated by SEM and compared to that of the unmodified beads, and the polymorph content was established by X-ray diffraction. The beads, before and after CaCO3 mineralization, were tested as sorbents for Cu(II) ions. The newly formed patterns on the bead surface after Cu(II) sorption were observed by SEM, and the elemental distribution on the composites and the chemical structure of crystals after interaction with Cu(II) were investigated by EDAX elemental mapping and by FTIR-ATR spectroscopy, respectively. The sorption capacity increased significantly after CaCO3 crystals growth on the weak anionic bead surface (up to 1041.5?mg Cu(II) /g sample) compared to that of unmodified beads (491.5?mg Cu(II) /g sample). PMID:25675892

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

2015-03-23

271

The RecQ helicase RECQL5 participates in psoralen-induced interstrand cross-link repair.  

PubMed

Interstrand cross-links (ICLs) are very severe lesions as they are absolute blocks of replication and transcription. This property of interstrand cross-linking agents has been exploited clinically for the treatment of cancers and other diseases. ICLs are repaired in human cells by specialized DNA repair pathways including components of the nucleotide excision repair pathway, double-strand break repair pathway and the Fanconi anemia pathway. In this report, we identify the role of RECQL5, a member of the RecQ family of helicases, in the repair of ICLs. Using laser-directed confocal microscopy, we demonstrate that RECQL5 is recruited to ICLs formed by trioxalen (a psoralen-derived compound) and ultraviolet irradiation A. Using single-cell gel electrophoresis and proliferation assays, we identify the role of RECQL5 in the repair of ICL lesions. The domain of RECQL5 that recruits to the site of ICL was mapped to the KIX region between amino acids 500 and 650. Inhibition of transcription and of topoisomerases did not affect recruitment, which was inhibited by DNA-intercalating agents, suggesting that the DNA structure itself may be responsible for the recruitment of RECQL5 to the sites of ICLs. PMID:23715498

Ramamoorthy, Mahesh; May, Alfred; Tadokoro, Takashi; Popuri, Venkateswarlu; Seidman, Michael M; Croteau, Deborah L; Bohr, Vilhelm A

2013-10-01

272

Chemistry of collagen cross-links: glucose-mediated covalent cross-linking of type-IV collagen in lens capsules.  

PubMed Central

The incubation of lens capsules with glucose in vitro resulted in changes in the mechanical and thermal properties of type-IV collagen consistent with increased cross-linking. Differential scanning calorimetry (d.s.c.) of fresh lens capsules showed two major peaks at melting temperatures Tm 1 and Tm 2 at approx. 54 degrees C and 90 degrees C, which can be attributed to the denaturation of the triple helix and 7S domains respectively. Glycosylation of lens capsules in vitro for 24 weeks caused an increase in Tm 1 from 54 degrees C to 61 degrees C, while non-glycosylated, control incubated capsules increased to a Tm 1 of 57 degrees C. The higher temperature required to denature the type-IV collagen after incubation in vitro suggested increased intermolecular cross-linking. Glycosylated lens capsules were more brittle than fresh samples, breaking at a maximum strain of 36.8 +/- 1.8% compared with 75.6 +/- 6.3% for the fresh samples. The stress at maximum strain (or 'strength') was dramatically reduced from 12.0 to 4.7 N.mm.mg-1 after glycosylation in vitro. The increased constraints within the system leading to loss of strength and increased brittleness suggested not only the presence of more cross-links but a difference in the location of these cross-links compared with the natural lysyl-aldehyde-derived cross-links. The chemical nature of the fluorescent glucose-derived cross-link following glycosylation was determined as pentosidine, at a concentration of 1 pentosidine molecule per 600 collagen molecules after 24 weeks incubation. Pentosidine was also determined in the lens capsules obtained from uncontrolled diabetics at a level of about 1 per 100 collagen molecules. The concentration of these pentosidine cross-links is far too small to account for the observed changes in the thermal and mechanical properties following incubation in vitro, clearly indicating that another as yet undefined, but apparently more important cross-linking mechanism mediated by glucose is taking place. PMID:8257442

Bailey, A J; Sims, T J; Avery, N C; Miles, C A

1993-01-01

273

Electrospun gelatin nanofibers: a facile cross-linking approach using oxidized sucrose.  

PubMed

Gelatin nanofibers were fabricated via electrospinning with minimal toxicity from solvents and cross-linking agents. Electrospinning was carried out using a solvent system based on water and acetic acid (8:2, v/v). Acetic acid concentration was kept as minimum as possible to reduce the toxic effects. Electrospun gelatin nanofibers were cross-linked with oxidized sucrose. Sucrose was oxidized by periodate oxidation to introduce aldehyde functionality. Cross-linking with oxidized sucrose could be achieved without compromising the nanofibrous architecture. Cross-linked gelatin nanofibers maintained the fibrous morphology even after keeping in contact with aqueous medium. The morphology of the cross-linked nanofibrous mats was examined by scanning electron microscopy (SEM). Oxidized sucrose cross-linked gelatin nanofibers exhibited improved thermal and mechanical properties. The nanofibrous mats were evaluated for cytotoxicity and cell viability using L-929 fibroblast cells. The results confirmed that oxidized sucrose cross-linked gelatin nanofibers were non-cytotoxic towards L-929 cells with good cell viability. PMID:25478965

Jalaja, K; James, Nirmala R

2015-02-01

274

Anomalous normal stresses in biopolymer networks with compliant cross-links  

NASA Astrophysics Data System (ADS)

Cross-linked biopolymer filament networks that constitute the cytoskeleton in living cells show rich mechanical response including large strain stiffening and negative normal stresses. Here, we have studied these phenomena in the case where the cross-links act as flexible worm-like chain springs. We find that in contrast to the well-studied case of sparse networks with rigid cross-links that display negative normal stresses when subject to shear loading, flexible cross-links give rise to positive normal stresses during early stages of deformation. With increased loading, we observe a transition where the normal stresses become negative. In this regime, the ratio of the normal stresses to the shear stress is found to increase with increase in the density of cross-links, in distinct contrast to the behavior observed for rigid cross-links. We show that these anomalous properties can be understood by considering the way in which the applied load is shared by the extension of the cross-links and the bending and stretching of the filaments.

Chen, P.

2014-02-01

275

Cross-linking of SPINK6 by transglutaminases protects from epidermal proteases.  

PubMed

Extracellular kallikrein-related peptidases (KLKs) are involved in the desquamation process and the initiation of epidermal inflammation by different mechanisms. Their action is tightly controlled by specific protease inhibitors. Recently, we have identified the serine protease inhibitor of Kazal-type (SPINK) 6 as a selective inhibitor of KLKs in human stratum corneum extracts. As SPINK6 is expressed in the same localization as transglutaminases (TGM) and contains TGM substrate motifs, SPINK6 was tested to be cross-linked in the epidermis. Recombinant SPINK6 was shown to be cross-linked to fibronectin (FN) by TGM1 by western blot analyses. Moreover, SPINK6 was cross-linked in epidermal extracts and cultured keratinocytes by immunoblotting analyses. The use of TGM1 and TGM3 resulted in different immunoreactivities in western blot analyses of SPINK6 and epidermal extracts, suggesting substrate specifities of different TGMs for SPINK6 cross-linking in the epidermis. Conjugated SPINK6 exhibited protease inhibitory activity in keratinocytes and stratum corneum extracts; cross-linked SPINK6 protected FN from KLK5-mediated cleavage, whereas a lower KLK-inhibiting SPINK6-GM mutation did not. In conclusion, we demonstrated that SPINK6 is cross-linked in keratinocytes and human epidermis and remains inhibitory active. Thus, cross-linked SPINK6 might protect specific substrates such as FN from KLK cleavage and contributes to the regulation of proteases in the epidermis. PMID:23303447

Fischer, Jan; Koblyakova, Yulia; Latendorf, Ties; Wu, Zhihong; Meyer-Hoffert, Ulf

2013-05-01

276

Synthesis and Characterization of Cross-linked Polymer Electrolyte Membranes for Supercapacitor  

NASA Astrophysics Data System (ADS)

Cross-linked polyvinyl alcohol (PVA) electrolyte membranes have been synthesized by using a solution casting method. In this study, PVA was blended with oxidative cross-linked agent (zinc acetate) and nano-sized silica as filler to stabilize PVA matrix and enhance conductivity. The cross-linked membranes were immersed into lithium hydroxide (LiOH) aqueous solution to increase their ionic conductivity. Two techniques were used to characterize the resulted membranes including Fourier transform infra red (FTIR) and AC impedance spectroscopies. The results showed that absorption peaks of C-O-C group and Si-O-Si are presence in the FTIR spectra attributed to the cross-linking process. Impedance spectra indicated that the contribution of ionic dopant (LiOH) to enhance conductivity is insignificant. The highest conductivity of the studied cross-linked PVA membrane is 1.34×10-3 S cm-1 corresponding to 5% LiOH dopant concentration of cross-linked PVA-zinc acetate-nano silica membrane. The present study also suggested that the solution casting is appropriate for cross-linked membrane synthesis.

Rosi, Memoria; Ekaputra, Muhamad Prama; Abdullah, Mikrajuddin; Khairurrijal

2010-10-01

277

Chemosensitivity of primary human fibroblasts with defective unhooking of DNA interstrand cross-links  

SciTech Connect

Xeroderma pigmentosum (XP) is characterised by defects in nucleotide excision repair, ultraviolet (UV) radiation sensitivity and increased skin carcinoma. Compared to other complementation groups, XP-F patients show relatively mild cutaneous symptoms. DNA interstrand cross-linking agents are a highly cytotoxic class of DNA damage induced by common cancer chemotherapeutics such as cisplatin and nitrogen mustards. Although the XPF-ERCC1 structure-specific endonuclease is required for the repair of ICLs cellular sensitivity of primary human XP-F cells has not been established. In clonogenic survival assays, primary fibroblasts from XP-F patients were moderately sensitive to both UVC and HN2 compared to normal cells (2- to 3-fold and 3- to 5-fold, respectively). XP-A fibroblasts were considerably more sensitive to UVC (10- to 12-fold) but not sensitive to HN2. The sensitivity of XP-F fibroblasts to HN2 correlated with the defective incision or 'unhooking' step of ICL repair. Using the comet assay, XP-F cells exhibited only 20% residual unhooking activity over 24 h. Over the same time, normal and XP-A cells unhooked greater than 95% and 62% of ICLs, respectively. After HN2 treatment, ICL-associated DNA double-strand breaks (DSBs) are detected by pulse field gel electrophoresis in dividing cells. Induction and repair of DNA DSBs was normal in XP-F fibroblasts. These findings demonstrate that in primary human fibroblasts, XPF is required for the unhooking of ICLs and not for the induction or repair of ICL-associated DNA DSBs induced by HN2. In terms of cancer chemotherapy, people with mild DNA repair defects affecting ICL repair may be more prevalent in the general population than expected. Since cellular sensitivity of primary human fibroblasts usually reflects clinical sensitivity such patients with cancer would be at risk of increased toxicity.

Clingen, Peter H. [Cancer Research UK Drug-DNA Interactions Research Group, Department of Oncology, Royal Free and University College Medical School, 91 Riding House Street, London, W1W 7BS (United Kingdom)]. E-mail: p.clingen@ucl.ac.uk; Arlett, Colin F. [Brunel Institute for Cancer Genetics and Pharmacogenomics, Division of Biosciences, School of Health Sciences and Social Care, Brunel University, Middlesex, UB8 3PH (United Kingdom); Hartley, John A. [Cancer Research UK Drug-DNA Interactions Research Group, Department of Oncology, Royal Free and University College Medical School, 91 Riding House Street, London, W1W 7BS (United Kingdom); Parris, Christopher N. [Brunel Institute for Cancer Genetics and Pharmacogenomics, Division of Biosciences, School of Health Sciences and Social Care, Brunel University, Middlesex, UB8 3PH (United Kingdom)

2007-02-15

278

A composite dermal filler comprising cross-linked hyaluronic Acid and human collagen for tissue reconstruction.  

PubMed

In this study, we developed a composite filler comprising cross-linked hyaluronic acid (HA) and human collagen (COL) derived from the human umbilical cord with the aim of improving its biocompatibility and longevity compared with commercially available fillers. After HA/ COL composite fillers were made in two different ratios (10:1 and 5:1), the physical properties of the fillers were evaluated. The interior morphologies and in vivo weight change of these hydrogels were also characterized at 1-16 weeks after injection into mice. To evaluate their biocompatibility and durability in vivo, we injected the composite fillers into nude mice subcutaneously. The variations of injected gel weight were measured and compared with the commercial dermal fillers (Restylane and TheraFill). The composites showed improved or similar physical properties (complex viscosity of 19-22 × 10(5) cP, and injection force of 10- 12 N) over the commercial dermal fillers. Sixteen weeks following the injection, the ratio of remaining composite filler weight to initial weight (75.5 ± 16.9%; 10:1) was shown to be greater than that of the commercial fillers (43.2 ± 8.1%, Restylane; 12.3 ± 5.3%, TheraFill). In addition, immunohistochemical analysis with angiogenesis-related markers such as isolectin and vWF revealed newly formed blood vessels and cellular influx into the composite filler, which were not observed in the other fillers. These results clearly suggest that the HA/COL composite filler is a superior candidate for soft tissue reconstruction. The filler we developed may be a suitable candidate as an injectable dermal filler for tissue augmentation in humans. PMID:25502824

Kim, Z-Hun; Lee, Yongjun; Kim, Sun-Mi; Kim, Hojin; Yun, Chang-Koo; Choi, Yong-Soo

2015-03-28

279

Cross-linked Bioreducible Layer-by-layer Films for Increased Cell Adhesion and Transgene Expression  

PubMed Central

The effect of cross-linking layer-by-layer (LbL) films consisting of bioreducible poly(2-dimethylaminoethyl methacrylate) (rPDMAEMA) and DNA is examined with regards to rigidity, biodegradability, cell adhesion, and transfection activity using 1,5-diiodopentane (DIP) cross-linker. DIP chemically reacts with the tertiary amines of rPDMAEMA, altering the chemical composition of these LbL films. The result is a change in surface morphology, film swelling behavior and film rigidity, measured with AFM and ellipsometry. It is found that the apparent Young’s modulus is increased more than four times its original value upon cross-linking. Cross-linking mass is additionally confirmed with quartz crystal microbalance with dissipation (QCM-D). Comprehensive analyses of these experimental values were investigated to calculate the degree of cross-linking using the rubber elasticity theory and the Flory-Rehner theory. Additionally, the Flory-Huggins parameter, ?, was calculated. Good agreement in the two methods yields a cross-linking density of ~0.82 mmol/cm3. The Flory-Huggins parameter increased upon cross-linking from 1.07 to 1.2, indicating increased hydrophobicity of the network and formation of bulk water droplets within the films. In addition, the effects of cross-linking on film disassembly by 1,4-dithiothreitol (DTT) is found to be insignificant despite the alteration in film rigidity. Mouse fibroblast cells and smooth muscle cells are used to study the effect of cross-linking on cell adhesion and cell transfection activity. In vitro transfection activity up to seven days is quantified using secreted alkaline phosphatase (SEAP) DNA. Film cross-linking is found to enhance cell adhesion and prolong the duration of cellular transfection. These results contribute to the development of bioreducible polymer coatings for localized gene delivery. PMID:20369813

Blacklock, Jenifer; Sievers, Torsten K.; Handa, Hitesh; You, Ye-Zi; Oupický, David; Mao, Guangzhao; Möhwald, Helmuth

2010-01-01

280

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

PubMed

In the present study, we developed photo-cross-linked amniotic membrane (AM) as a limbal stem cell niche. After ultraviolet (UV) irradiation for varying time periods, the biological tissues were studied by determinations of cross-linking structure, degradability, and nutrient permeation ability. Our results showed that the number of cross-links per unit mass of AM significantly increased with increasing illumination time from 5 to 50 min. However, the cross-link formation was inhibited by longer irradiation time (i.e., 150 min), probably due to the scission of tissue collagen chains through irradiation. The biological stability and matrix permeability of photo-cross-linked AM materials strongly depended on their cross-linking densities affected by the UV irradiation. In vitro biocompatibility studies including cell viability and pro-inflammatory gene expression analyses demonstrated that, irrespective of the irradiation time employed, the physically cross-linked biological tissues exhibited negligible cytotoxicity and similar interleukin-6 (IL-6) mRNA levels. The data clearly indicate that these AM matrices do not cause potential harm to the corneal epithelial cells. After the growth of limbal epithelial cells (LECs) on AM substrates, Western blot analyses were conducted to examine the expression of ABCG2. It was found that the ability of UV-irradiated AM to maintain the undifferentiated precursor cell phenotype was significantly enhanced with increasing extent of photo-cross-linking. In summary, the UV irradiation time may have a profound influence on the fabrication of photo-cross-linked AM matrices for LEC cultivation. PMID:25491834

Lai, Jui-Yang

2014-12-01

281

Degradation of Newly Synthesized High Molecular Mass Hyaluronan in the Epidermal and Dermal Compartments of Human Skin in Organ Culture  

Microsoft Academic Search

Human whole skin was labeled for 24 h with [6-3H]-glucosamine in organ culture and epidermis, dermis and culture medium were separately analyzed for the molecular mass and content of the [3H]-labeled hyaluronan (HA). Gel filtration on Sephacryl S-1000 of HA purified by HPLC showed a large proportion of the newly synthesized HA to be of a very high molecular mass

Raija Tammi; Anna-Marja Säämänen; Howard I. Maibach; Markku Tammi

1991-01-01

282

Fabrication of a novel pH-sensitive glutaraldehyde cross-linked pectin nanogel for drug delivery.  

PubMed

A novel pH-sensitive nanogel based on pectin cross-linked with glutaraldehyde (PT-GA) was designed and synthesized for drug delivery. Transmission electron microscope observation shows that the nano-sized gel particles exhibit a spherical morphology. The optical absorbance study of nanogel suspension reveals its pH sensitivity. Cytotoxicity study shows that the nanogel has no apparent inhibitory effect on cells. The in vitro drug-release behavior of the drug-loaded nanogel particles in three kinds of media, i.e., simulated gastric fluid, simulated intestine fluid and simulated colon fluid, was studied. PT-GA nanogel exhibits a faster release at a high pH, and the release could be further accelerated in the presence of pectinolytic enzyme, indicating that the nanogel may be used for colon-specific drug delivery. PMID:17988522

Chang, Cong; Wang, Zong-Chun; Quan, Chang-Yun; Cheng, Han; Cheng, Si-Xue; Zhang, Xian-Zheng; Zhuo, Ren-Xi

2007-01-01

283

Chances and pitfalls of chemical cross-linking with amine-reactive N-hydroxysuccinimide esters.  

PubMed

In this report we summarize our experiences with the reaction products of N-hydroxysuccinimide (NHS) esters, which are widely used for chemical cross-linking of lysine residues in proteins. We describe the products, which should be scrutinized during data analysis using customized software when NHS esters are employed for chemical cross-linking. Reaction products of NHS esters were observed not only with lysines, but also with serines, tyrosines, and threonines. This report is intended to be a practical guide for those working in the field of chemical cross-linking and mass spectrometry. PMID:18724398

Kalkhof, Stefan; Sinz, Andrea

2008-09-01

284

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

PubMed Central

The motivation for radiation cross-linking of ultra-high molecular weight polyethylene (UHMWPE) is to increase its wear resistance to be used as bearing surfaces for total joint arthroplasty. However, radiation also leaves behind long-lived residual free radicals in this polymer, the reactions of which can detrimentally affect mechanical properties. In this review, we focus on the radiation cross-linking and oxidative stability of first and second generation highly cross-linked UHMWPEs developed in our laboratory. PMID:19050735

Oral, Ebru; Muratoglu, Orhun K.

2007-01-01

285

Cross-linked polyvinyl alcohols and oil reservoir permeability control therewith  

SciTech Connect

This patent describes an improved method of recovering oil under steam flooding conditions from an oil-bearing subterranean formation penetrated by an injection well and a production well, in which an aqueous fluid is injected into the formation through the injection well to displace oil to the production well. The improvement comprising employing, in at least a portion of the aqueous fluid injected into the formation, a cross-linked polymer obtained by cross-linking polyvinyl alcohol with a cross-linking agent which is a mixture of a phenolic component and an aldehyde or a mixture of a naphtholic component and an aldehyde.

Hoskin, D.H.; Shu, P.

1990-01-30

286

HcRed, a Genetically Encoded Fluorescent Binary Cross-Linking Agent for Cross-Linking of Mitochondrial ATP Synthase in Saccharomyces cerevisiae  

PubMed Central

Genetically encoded fluorescent cross-linking agents represent powerful tools useful both for visualising and modulating protein interactions in living cells. The far-red fluorescent protein HcRed, which is fluorescent only in a dimer form, can be used to promote the homo-dimerisation of target proteins, and thereby yield useful information about biological processes. We have in yeast cells expressed HcRed fused to a subunit of mitochondrial ATP synthase (mtATPase). This resulted in cross-linking of the large multi-subunit mtATPase complex within the inner-membrane of the mitochondrion. Fluorescence microscopy revealed aberrant mitochondrial morphology, and mtATPase complexes isolated from mitochondria were recovered as fluorescent dimers under conditions where complexes from control mitochondria were recovered as monomers. When viewed by electron microscopy normal cristae were absent from mitochondria in cells in which mATPase complexes were cross-linked. mtATPase dimers are believed to be the building blocks that are assembled into supramolecular mtATPase ribbons that promote the formation of mitochondrial cristae. We propose that HcRed cross-links mATPase complexes in the mitochondrial membrane hindering the normal assembly/disassembly of the supramolecular forms of mtATPase. PMID:22496895

Gong, Lan; Ramm, Georg; Devenish, Rodney J.; Prescott, Mark

2012-01-01

287

A thermodynamic model of physical gels  

NASA Astrophysics Data System (ADS)

Physical gels are characterized by dynamic cross-links that are constantly created and broken, changing its state between solid and liquid under influence of environmental factors. This restructuring ability of physical gels makes them an important class of materials with many applications, such as in drug delivery. In this article, we present a thermodynamic model for physical gels that considers both the elastic properties of the network and the transient nature of the cross-links. The cross-links' reformation is captured through a connectivity tensor M at the microscopic level. The macroscopic quantities, such as the volume fraction of the monomer ?, number of monomers per cross-link s, and the number of cross-links per volume q, are defined by statistic averaging. A mean-field energy functional for the gel is constructed based on these variables. The equilibrium equations and the stress are obtained at the current state. We study the static thermodynamic properties of physical gels predicted by the model. We discuss the problems of un-constrained swelling and stress driven phase transitions of physical gels and describe the conditions under which these phenomena arise as functions of the bond activation energy Ea, polymer/solvent interaction parameter ?, and external stress p.

An, Yonghao; Solis, Francisco J.; Jiang, Hanqing

2010-12-01

288

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

PubMed Central

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

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

2014-01-01

289

Cross-linking proteins with bimetallic tetracarboxylate compounds of transition metals  

DOEpatents

Stable cross-linked complexes of transition-metal tetracarboxylates and proteins are formed. The preferred transition-metal is rhodium. The protein may be collagen or an enzyme such as a proteolytic enzyme.

Kostic, Nenad M. (Ames, IA); Chen, Jian (Ames, IA)

1991-03-05

290

Activation energies control the macroscopic properties of physically cross-linked materials.  

PubMed

Here we show the preparation of a series of water-based physically cross-linked polymeric materials utilizing cucurbit[8]uril (CB[8]) ternary complexes displaying a range of binding, and therefore cross-linking, dynamics. We determined that the mechanical strength of these materials is correlated directly with a high energetic barrier for the dissociation of the CB[8] ternary complex cross-links, whereas facile and rapid self-healing requires a low energetic barrier to ternary complex association. The versatile CB[8] ternary complex has, therefore, proven to be a powerful asset for improving our understanding of challenging property-structure relationships in supramolecular systems and their associated influence on the bulk behavior of dynamically cross-linked materials. PMID:25056596

Appel, Eric A; Forster, Rebecca A; Koutsioubas, Alexandros; Toprakcioglu, Chris; Scherman, Oren A

2014-09-15

291

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

PubMed

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

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

2014-05-01

292

Vapor deposition of cross-linked fluoropolymer barrier coatings onto pre-assembled microfluidic devices.  

PubMed

The interior surfaces of pre-assembled poly(dimethylsiloxane) (PDMS) microfluidic devices were modified with a cross-linked fluoropolymer barrier coating that significantly increased the chemical compatibility of the devices. PMID:21850298

Riche, Carson T; Marin, Brandon C; Malmstadt, Noah; Gupta, Malancha

2011-09-21

293

Host-dependent optical dephasing of dye molecules doped in cross-linked polyvinyl alcohols  

NASA Astrophysics Data System (ADS)

Host-dependent optical dephasing of the zero-phonon line of two organic dye molecules doped in several cross-linked polyvinyl alcohol (PVA) derivatives was studied by using an incoherent photon echo technique. It was found that the optical dephasing time of the zero-phonon line increases with increasing the length of the cross-link introduced to the PVA backbone. Our results indicate that, by the introduction of the cross-link, the effect of the two-level tunneling system in PVA on optical dephasing of a doped dye is greatly reduced and the dephasing time of the dye becomes longer than that in the PVA without the cross-link. The decrease of the optical dephasing can be interpreted by assuming a void space in PVA, which is created near to an introduced cross-linker.

Kawase, M.; Fujiwara, S.; Nakanishi, S.; Itoh, H.

1992-07-01

294

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

PubMed

Polyvinyl alcohol (PVA) nanofibrous mat can be easily prepared via electrospinning its aqueous solution. However, the obtained nanofibrous mat is instantaneously dissolved in water. Therefore, rendering the environmentally friendly nanofibrous mat water insoluble by cross-linking mechanism is of great interest. The electrospun PVA nanofibrous mat with an average fiber diameter of ca. 400 nm could be effectively cross-linked by glutaraldehyde vapor at room temperature. The cross-linking not only resulted in a water-insoluble nanofibrous mat but also generated an excess amount of unreacted aldehyde functional groups that could reduce silver salts into silver nanoparticles. The in situ formed silver nanoparticles along the fibrous surface showed excellent antimicrobial activity against Escherichia coli. The vapor cross-linked nanofibrous mat shows a high potential to be used for efficiently capturing and killing pathogenic bacteria. PMID:23668250

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

2013-06-12

295

Cross-linking proteins with bimetallic tetracarboxylate compounds of transition metals  

DOEpatents

Stable cross-linked complexes of transition-metal tetracarboxylates and proteins are formed. The preferred transition-metal is rhodium. The protein may be collagen or an enzyme such as a proteolytic enzyme. No Drawings

Kostic, N.M.; Chen, J.

1991-03-05

296

Distribution and Processing of ADAMTS-4, Aggrecan, Versican and Hyaluronan in the Equine Digital Laminae  

PubMed Central

Objective Determine the expression and distribution of A Disintegrin And Metalloproteinase with ThromboSpondin motifs-4 (ADAMTS-4), its substrates aggrecan and versican, and their binding partner hyaluronan in laminae of healthy horses as a step towards determining the role of ADAMTS-4 in laminar pathology. Sample population Front hoof laminae from 8 healthy horses. Procedures Real-time quantitative polymerase chain reaction was used for gene expression analysis. Hyaluronidase, chondroitinase and keratanase digestion of lamina extracts together with sodium dodecylsulfate polyacrylamide gel electrophoresis and Western blotting were used for protein and proteoglycan analysis. Immunofluorescent and immunohistochemical staining of tissue sections were used for protein and hyaluronan localization. Results Genes encoding ADAMTS-4, aggrecan, versican and hyaluronan synthase II are expressed in laminae. ADAMTS-4 is predominantly present as a 51 kDa protein bearing a catalytic site neoepitope indicative of active enzyme and in situ activity is inferred from the presence of aggrecan and versican fragments bearing ADAMTS-4 cleavage neoepitopes in laminar protein extracts. Aggrecan, versican and hyaluronan localize to basal epithelial cells within the secondary dermal laminae. ADAMTS-4 also localizes to these cells, but in addition, is present in some cells in the dermal laminae. Conclusions and clinical relevance Within the digital laminae, versican exclusively and aggrecan primarily localizes within basal epithelial cells and both are constitutively cleaved by ADAMTS-4 which therefore contributes to their turnover. Based on known properties of these proteoglycans, it is possible that they protect the basal epithelial cells from biomechanical and concussive stress. PMID:22738056

Pawlak, Erica; Wang, Le; Johnson, Philip J.; Nuovo, Gerard; Taye, Almaz; Belknap, James K.; Alfandari, Dominique; Black, Samuel J.

2012-01-01

297

IgE Cross-linking Critically Impairs Human Monocyte Function by Blocking Phagocytosis  

PubMed Central

Background IgE cross-linking triggers many cellular processes that drive allergic disease. While the role of IgE in mediating allergic responses is best described on basophils and mast cells, expression of the high-affinity IgE receptor on other innate immune cells, including monocytes, suggests that it may impact the function of these cells in allergic environments. Objectives To determine the effect of IgE cross-linking on the function of human monocytes. Methods Monocytes purified from healthy donor blood samples were cultured for 4–96 hr with media alone, a cross-linking anti-IgE antibody, or control IgG. Surface CD14 and CD64 expression and secreted cytokine concentrations were determined. Monocyte function was determined by assessing: 1) phagocytosis of E. coli or apoptotic HEp2 cells and 2) killing of intracellular E. coli. Select experiments were performed on monocytes obtained from participants with elevated versus normal serum IgE concentrations. Results IgE cross-linking on monocytes increased CD14 expression and induced secretion of TNF-á, IL-6, and autoregulatory IL-10. These effects were greatest in individuals with elevated serum IgE concentrations. In contrast, IgE cross-linking reduced CD64 expression and significantly impaired phagocytic function without disrupting the capacity of monocytes to kill bacteria. Conclusion IgE cross-linking drives monocyte pro-inflammatory processes and autoregulatory IL-10 in a serum IgE-dependent manner. In contrast, monocyte phagocytic function is critically impaired by IgE cross-linking. Our findings suggest that IgE cross-linking on monocytes may contribute to allergic disease by both enhancing detrimental inflammatory responses and concomitantly crippling phagocytosis, a primary mechanism utilized by these cells to resolve inflammation. PMID:23374271

Pyle, David M; Yang, Victoria S; Gruchalla, Rebecca S; Farrar, J David; Gill, Michelle A

2012-01-01

298

In vivo formaldehyde cross-linking: it is time for black box analysis.  

PubMed

Formaldehyde cross-linking is an important component of many technologies, including chromatin immunoprecipitation and chromosome conformation capture. The procedure remains empirical and poorly characterized, however, despite a long history of its use in research. Little is known about the specificity of in vivo cross-linking, its efficiency and chemical adducts induced by the procedure. It is time to search this black box. PMID:25241225

Gavrilov, Alexey; Razin, Sergey V; Cavalli, Giacomo

2015-03-01

299

Formation and fate of cross-links induced by polyfunctional anticancer drugs in yeast  

Microsoft Academic Search

A method to detect low levels of interstrand cross-links in DNA of Saccharomyces cerevisiae is described. Isopycnic ultracentrifugation of alkali-treated, unpurified Eaton press homogenates allows the detection of less than one cross-link per yeast chromosome. Efficient separation of single-and double-stranded DNA requires low cell density and addition of glycerol during homogenization. Using a yeast strain defective in excision repair, a

Reinhard Fleer; Martin Brendel

1979-01-01

300

The measurement of cross-linked fracture fluid viscosity using a pipe viscometer  

E-print Network

THE MEASUREMENT OF CROSS-LINKED FRACTURE FLUID VISCOSITY USING A PIPE VISCOMETER A Thesis by JOHN DOUGLAS VERMAELEN Submitted to the Graduate College of Texas A&M University in partial fulfillment of the requirements for the degr ee... of MASTER OF SCIENCE December 1985 Major Subject: Petr oleum Engineering THE MEASUREMENT OF CROSS-LINKED FRACTURE FLUID VISCOSITY USING A PIPE VISCOMETER A Thesis by JOHN DOUGLAS VERMAELEN Approved as to style and content by: Stephen A. Holditch...

Vermaelen, John Douglas

1985-01-01

301

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

SciTech Connect

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

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

2008-04-24

302

Protective effect of Withania somnifera (Solanaceae) on collagen glycation and cross-linking  

Microsoft Academic Search

Modification of collagen such as non-enzymatic glycation and cross-linking plays an important role in diabetic complications and age-related diseases. We evaluate the effect of Withania somnifera on glucose-mediated collagen glycation and cross-linking in vitro. Extent of glycation, viscosity, collagen-linked fluorescence and pepsin solubility were assessed in different experimental procedures to investigate the effect of W. somnifera. Tail tendons obtained from

Pon Velayutham Anandh Babu; Adikesavan Gokulakrishnan; Rajendra Dhandayuthabani; Dowlath Ameethkhan; Chandrasekara Vimal Pradeep Kumar

2007-01-01

303

The transport of octamethylcyclotetrasiloxane (D4) and polydimethylsiloxane (PDMS) in lightly cross-linked silicone rubber  

Microsoft Academic Search

The transport of octamethylcyclotetrasiloxane (D4), one of the major constituents of silicone fluids and rubbers, and low viscosity polydimethylsiloxane oil into a silica filled cross-linked silicone elastomeric rubber was measured as a function of temperature, cross-link density of the rubber, and concentration of the D4 in methanol solution. A small amount of material, approximately 3 wt%, is extracted from the

Clarence J. Wolf; Kenneth L. Jerina; Harold J. Brandon; V. L. Young

2001-01-01

304

A fast and activatable cross-linking strategy for hydrogel formation.  

PubMed

Strain-promoted oxidation-controlled cyclo-octyne-1,2-quinone cycloaddition (SPOCQ) is a fast and activatable cross-linking strategy for hydrogel formation. Gelation is induced by oxidation, which is performed both chemically using sodium periodate and enzymatically using mushroom tyrosinase. Due to the fast reaction kinetics, SPOCQ-formed hydrogels can be functionalized in one-pot with an azido-containing moiety using SPAAC cross-linking. PMID:25535032

Jonker, Anika M; Borrmann, Annika; van Eck, Ernst R H; van Delft, Floris L; Löwik, Dennis W P M; van Hest, Jan C M

2015-02-01

305

DNA cross-linking in mammalian cells by pyrrolizidine alkaloids: structure-activity relationships.  

PubMed

Pyrrolizidine alkaloids (PAs) are common constituents of many species of flowering plants which possess carcinogenic as well as anticarcinogenic activity in vivo. Pyrrolizidine alkaloids are genotoxic in various short-term assays. The mechanisms by which these compounds exert these effects is still unclear. In this study, we characterized the ability of eight bifunctional PAs, with differing stereochemistry and functional groups, to cross-link cellular DNA in cultured bovine kidney epithelial cells. PAs representative of three major structural classes, the macrocycles (seneciphylline, riddelline, retrorsine, senecionine, monocrotaline), the open diesters (heliosupine, latifoline), and pyrrolizidine base (retronecine) were cultured for 2 hr with cells and an external metabolizing system. Every PA induced DNA cross-links which consisted primarily of proteinase-sensitive cross-links (DPC), but also to a smaller extent, DNA interstrand cross-links (ISC). None of the PAs induced detectable amounts of DNA single-strand breaks. The PAs which produced DPC and/or ISC (ranked from most potent to least) were: seneciphylline (DPC greater than ISC); riddelline (DPC greater than ISC); retrorsine (DPC greater than ISC); senecionine (DPC greater than ISC); heliosupine (DPC greater than ISC); monocrotaline (ISC = DPC); latifoline (DPC greater than ISC); and retronecine (ISC greater than DPC). Although the PAs induced DNA cross-linking to varying degrees, cell viabilities for all treatment groups were greater than 90% as determined by trypan blue dye exclusion. Since the cross-linking ability of these PAs paralleled their ability to inhibit colony formation, cross-link formation may be involved in the biological activity of these compounds. Two structural determinants of biological activity appear to be the presence of both a macrocyclic necic acid ester and an alpha,beta-unsaturated ester function since the cross-linking ability of seneciphylline, riddelline, retrorsine, and senecionine far exceeded that of monocrotaline, heliosupine, latifoline, and retronecine. In addition, the stereochemical orientation of the ester linkage was found to have no effect on biological activity. PMID:1949039

Hincks, J R; Kim, H Y; Segall, H J; Molyneux, R J; Stermitz, F R; Coulombe, R A

1991-10-01

306

Structure–release rate correlation in collagen gels containing fluorescent drug analog  

Microsoft Academic Search

The paper examines the release properties of collagen gels that contain covalently bound fluorescent drug analogs. Collagen gels were prepared by fibrilogenesis. The gels were stabilized by cross linking with EDAC\\/NHS. SEM studies showed that increasing the cross-linking time with EDAC\\/NHS resulted in decreasing pore size and increasing gel density. Fluorescence spectroscopy measurements showed a clear correlation between decreasing pore

Silvia H. De Paoli Lacerda; Bruce Ingber; Nitsa Rosenzweig

2005-01-01

307

Bifunctional Electrophiles Cross-Link Thioredoxins with Redox Relay Partners in Cells  

PubMed Central

Thioredoxin protects cells against oxidative damage by reducing disulfide bonds in improperly oxidized proteins. Previously, we found that the baker's yeast cytosolic thioredoxin Trx2 undergoes cross-linking to form several protein-protein complexes in cells treated with the bifunctional electrophile divinyl sulfone (DVSF). Here, we report that the peroxiredoxin Tsa1 and the thioredoxin reductase Trr1, both of which function in a redox relay network with thioredoxin, become cross-linked in complexes with Trx2 upon DVSF treatment. Treatment of yeast with other bifunctional electrophiles, including diethyl acetylenedicarboxylate (DAD), mechlorethamine (HN2), and 1,2,3,4-diepoxybutane (DEB), resulted in the formation of similar cross-linked complexes. Cross-linking of Trx2 and Tsa1 to other proteins by DVSF and DAD is dependent on modification of the active site Cys residues within these proteins. In addition, the human cytosolic thioredoxin, cytosolic thioredoxin reductase, and peroxiredoxin 2 form cross-linked complexes to other proteins in the presence of DVSF, although each protein shows different susceptibilities to modification by DAD, HN2, and DEB. Taken together, our results indicate that bifunctional electrophiles potentially disrupt redox homeostasis in yeast and human cells by forming cross-linked complexes between thioredoxins and their redox partners. PMID:23414292

Naticchia, Matthew R.; Brown, Haley A.; Garcia, Francisco J.; Lamade, Andrew M.; Justice, Samantha L.; Herrin, Rachelle P.; Morano, Kevin A.; West, James D.

2013-01-01

308

Structural studies on mitochondrial NADH dehydrogenase using chemical cross-linking.  

PubMed Central

The structure of bovine heart mitochondrial NADH dehydrogenase was investigated by cross-linking constituent subunits with disuccinimidyl tartrate, (ethylene glycol)yl bis(succinimidyl succinate) and dimethyl suberimidate. Cross-linked products were identified by Western blotting with monospecific antisera to nine subunits of the enzyme. Cross-links between subunits within the flavoprotein, iron-protein and hydrophobic domains of the enzyme were identified. Cross-linking between the 75 kDa iron-protein-domain subunit and the 51 kDa flavoprotein-domain subunit was modulated by the substrate NADH. Cross-linking of subunits of the iron-protein and flavoprotein domains to constituents of the hydrophobic domain was also found. This was further substantiated by photolabelling subunits of the latter region, which were in contact with the membrane lipid, with 3-(trifluoromethyl)-3-(m-[125I]iodophenyl)diazirine. One such subunit of Mr 19,000 could be cross-linked to components of the iron-protein domain. Images Fig. 1. Fig. 2. Fig. 3. Fig. 4. Fig. 5. Fig. 6. Fig. 7. Fig. 8. PMID:3223927

Patel, S D; Ragan, C I

1988-01-01

309

xComb: a cross-linked peptide database approach to protein-protein interaction analysis  

PubMed Central

We developed an informatic method to identify tandem mass spectra composed of chemically cross-linked peptides from those of linear peptides and to assign sequence to each of the two unique peptide sequences. For a given set of proteins the key software tool, xComb, combs through all theoretically feasible cross-linked peptides to create a database consisting of a subset of all combinations represented as peptide FASTA files. The xComb library of select theoretical cross-linked peptides may then be used as a database that is examined by a standard proteomic search engine to match tandem mass spectral datasets to identify cross-linked peptides. The database search may be conducted against as many as 50 proteins with a number of common proteomic search engines, e.g. Phenyx, Sequest, OMSSA, Mascot and X!Tandem. By searching against a peptide library of linearized, cross-linked peptides, rather than a linearized protein library, search times are decreased and the process is decoupled from any specific search engine. A further benefit of decoupling from the search engine is that protein cross-linking studies may be conducted with readily available informatics tools for which scoring routines already exist within the proteomic community. PMID:20302351

Panchaud, Alexandre; Singh, Pragya; Shaffer, Scott A.; Goodlett, David R.

2010-01-01

310

Formation mechanism and structure of a guanine-uracil DNA intrastrand cross-link.  

PubMed

The formation and structure of the 5'-G[8-5]U-3' intrastrand cross-link are studied using density functional theory and molecular dynamics simulations due to the potential role of this lesion in the activity of 5-halouracils in antitumor therapies. Upon UV irradiation of 5-halouracil-containing DNA, a guanine radical cation reacts with the uracil radical to form the cross-link, which involves phosphorescence or an intersystem crossing and a rate-determining step of bond formation. Following ionizing radiation, guanine and the uracil radical react, with a rate-limiting step involving hydrogen atom removal. Although cross-link formation from UV radiation is favored, comparison of calculated reaction thermokinetics with that for related experimentally observed purine-pyrimidine cross-links suggests this lesion is also likely to form from ionizing radiation. For the first time, the structure of 5'-G[8-5]U-3' within DNA is identified by molecular dynamics simulations. Furthermore, three conformations of cross-linked DNA are revealed, which differ in the configuration of the complementary bases. Distortions, such as unwinding, are localized to the cross-linked dinucleotide and complementary nucleotides, with minimal changes to the flanking bases. Global changes to the helix, such as bending and groove alterations, parallel cisplatin-induced distortions, which indicate 5'-G[8-5]U-3', may contribute to the cytotoxicity of halouracils in tumor cell DNA using similar mechanisms. PMID:22060045

Churchill, Cassandra D M; Eriksson, Leif A; Wetmore, Stacey D

2011-12-19

311

The role of glycation cross-links in diabetic vascular stiffening.  

PubMed

Previous studies have shown that biomechanical analysis of aorta from diabetic subjects reveals a marked increase in stiffness compared to aorta from age-matched control subjects. In the present paper we have proposed that this increased stiffness can be attributed to glycation-induced inter-molecular cross-links based on a direct analysis of the two known glycation cross-links, the fluorescent pentosidine and the non-fluorescent NFC-1. There was a significant difference in the increase in concentration of both cross-links with increasing age for both the intima (p < 0.0025) and the media (p < 0.0005) from the diabetic compared to the control subjects, but no correlation with the mature enzymic cross-link hy droxylysyl-pyridinoline. Finally, we have obtained a significant correlation of stiffness with both glycation cross-links (NFC-1, r = 0.86; p < 0.005 and pentosidine r = 0.75, p < 0.05), but the concentration of NFC-1 is about 50 times greater than that of pentosidine, indicating that it is the major glycation cross-link responsible for the stiffening of the aorta. PMID:8858217

Sims, T J; Rasmussen, L M; Oxlund, H; Bailey, A J

1996-08-01

312

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

PubMed

In our previous papers I and II (D. Y. Lando et al, J. Biomol. Struct. Dynam. (1997) v. 15, N1, p. 129-140, p. 141-150), two methods were developed for calculation of melting curves of cross-linked DNA. One of them is based on Poland's and another on the Fixman-Freire approach. In the present communication, III, a new theoretical method is developed for computation of differential melting curves of DNAs cross-linked by anticancer drugs and their inactive analogs. As Poland's approach, the method allows study of the influence of the loop entropy factor, delta(n), on melting behavior (n is the length of a loop in base pairs). However the method is much faster and requires computer time that inherent for the most rapid Fixman-Freire calculation approach. In contrast to the computation procedures described before in communications I and II, the method is suitable for computation of differential melting curves in the case of long DNA chains, arbitrary loop entropy factors of melted regions and arbitrary degree of cross-linking including very low values that occur in vivo after administration of antitumor drugs. The method is also appropriate for DNAs without cross-links. The results of calculation demonstrate that even very low degree of cross-linking alters the DNA differential melting curve. Cross-linking also markedly strengthens the influence of particular function delta(n) upon melting behavior. PMID:9745895

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

1998-08-01

313

Enabling Thermoreversible Physically Cross-Linked Polymerized Colloidal Array Photonic Crystals  

PubMed Central

We physically cross-linked a thermoreversible poly(vinyl alcohol) (PVA) hydrogel (TG) within a crystalline colloidal array (CCA) to form an enabling photonic crystal material. The TG consists of a physically cross-linked network formed in a process reminiscent of the well-known freeze-thaw physically cross-linking process, but which avoids solvent freezing which invariably disorders the CCA. These TGCCA can be inexpensively fabricated in any large volume and shape by avoiding the previous covalently polymerized CCA constraints that required thin sheet geometries to enable penetration of the UV light used to photopolymerize the system. This TG hydrogel enables rigidificaton of CCA crystals and subsequent chemical functionalization. In addition, an additional interpenetrating hydrogel can be polymerized within the TGPCCA. The TG can then be dissolved away by simply increasing the temperature. The TGCCA photonic crystal diffraction is highly efficient and similar to previously demonstrated PCCA with covalent cross-links. These TGCCA are stable for weeks or longer at room temperature and can be utilized as photonic crystal materials. They also can be irreversibly covalently cross-linked by using gluteraldehyde. These gluteraldehyde cross-linked TGCCA can be made into chemically responsive sensor photonic crystals by functionalizing the PVA hydroxyl groups with chemical recognition agents. We demonstrate low and high pH sensing by functionalizing with carboxylates and phenol derivatives, respectively. PMID:19966904

Asher, Sanford A.; Kimble, Kyle W.; Walker, Jeremy P.

2009-01-01

314

Bi-functional cross-linking reagents efficiently capture protein-DNA complexes in Drosophila embryos  

PubMed Central

Chromatin immunoprecipitation (ChIP) is widely used for mapping DNA-protein interactions across eukaryotic genomes in cells, tissues or even whole organisms. Critical to this procedure is the efficient cross-linking of chromatin-associated proteins to DNA sequences that are in close proximity. Since the mid-nineties formaldehyde fixation has been the method of choice. However, some protein-DNA complexes cannot be successfully captured for ChIP using formaldehyde. One such formaldehyde refractory complex is the developmentally regulated insulator factor, Elba. Here we describe a new embryo fixation procedure using the bi-functional cross-linking reagents DSG (disuccinimidyl glutarate) and DSP (dithiobis[succinimidyl propionate). We show that unlike standard formaldehyde fixation protocols, it is possible to capture Elba association with insulator elements in 2–5 h embryos using this new cross-linking procedure. We show that this new cross-linking procedure can also be applied to localize nuclear proteins that are amenable to ChIP using standard formaldehyde cross-linking protocols, and that in the cases tested the enrichment was generally superior to that achieved using formaldehyde cross-linking. PMID:24135698

Aoki, Tsutomu; Wolle, Daniel; Preger-Ben Noon, Ella; Dai, Qi; Lai, Eric C; Schedl, Paul

2014-01-01

315

Dynamic OCT measurements of corneal biomechanical properties after UV cross-linking in the rabbit  

NASA Astrophysics Data System (ADS)

Structural properties of the cornea determine the shape and optical quality of the eye. Keratoconus, a structural degeneration of the cornea, is often treated with UV-induced collagen cross-linking to increase tissue resistance to further deformation and degeneration. Optimal treatments would be customized to the individual and consider preexisting structural properties as well as the effects induced by treatment and this requires the capability to noninvasively measure tissue properties. The purpose of this study is to use novel methods of optical elastography to study the effects of UV-induced corneal collagen cross-linking in the rabbit eye. Low-amplitude (<1?m) elastic flexural waves were generated using focused air-pulse stimulation. Elastic wave propagation was measured over a 10x10mm area using Phase Stabilized Swept Source Optical Coherence Elastography (PhS-SSOCE) with a sensitivity of ~ 10 nm. Wave amplitude and velocity were computed and compared in tissues before and after UV cross-linking. Wave amplitude was decreased by the cross-linking treatment, while wave velocity was greater in cross-linked tissue than it was in the untreated cornea. Decreased wave amplitude and increased wave velocity after cross-linking is consistent with increased tissue stiffness. This was confirmed by conventional mechanical tension testing. These results demonstrate that the combination of the PhS-SSOCE and focused air pulse stimulation is capable of measuring low amplitude tissue motion and quantifying corneal stiffness.

Twa, Michael D.; Li, Jiasong; Manapuram, Ravi K.; Menodiado, Floredes M.; Singh, Manmohan; Aglyamov, Salavat; Emelianov, Stanislav; Larin, Kirill V.

2013-03-01

316

Enhanced apoptotic effects of dihydroartemisinin-aggregated gelatin and hyaluronan nanoparticles on human lung cancer cells.  

PubMed

Recent studies suggest that dihydroartemisinin (DHA), a derivative of artemisinin isolated from the traditional Chinese herb Artemisia annua L., has anticancer properties. Due to poor water solubility, poor oral activity, and a short plasma half-life, large doses of DHA have to be injected to achieve the necessary bioavailability. This study examined increasing DHA bioavailability by encapsulating DHA within gelatin (GEL) or hyaluronan (HA) nanoparticles via an electrostatic field system. Observations from transmission electron microscopy show that DHA in GEL and HA nanoparticles formed GEL/DHA and HA/DHA aggregates that were approximately 30-40 nm in diameter. The entrapment efficiencies for DHA were approximately 13 and 35% for the GEL/DHA and HA/DHA aggregates, respectively. The proliferation of A549 cells was inhibited by the GEL/DHA and HA/DHA aggregates. Fluorescent annexin V-fluorescein isothiocyanate (FITC) and propidium iodide (PI) staining displayed low background staining with annexin V-FITC or PI on DHA-untreated cells. In contrast, annexin V-FITC and PI stains dramatically increased when the cells were incubated with GEL/DHA and HA/DHA aggregates. These results suggest that DHA-aggregated GEL and HA nanoparticles exhibit higher anticancer proliferation activities than DHA alone in A549 cells most likely due to the greater aqueous dispersion after hydrophilic GEL or HA nanoparticles aggregation. These results demonstrate that DHA can aggregate with nanoparticles in an electrostatic field environment to form DHA nanosized aggregates. PMID:24039154

Sun, Qian; Teong, Benjamin; Chen, I-Fen; Chang, Shwu Jen; Gao, Jimin; Kuo, Shyh-Ming

2014-04-01

317

Collagen Cross-Linking Using Riboflavin and Ultraviolet-A for Corneal Thinning Disorders  

PubMed Central

Executive Summary Objective The main objectives for this evidence-based analysis were to determine the safety and effectiveness of photochemical corneal collagen cross-linking with riboflavin (vitamin B2) and ultraviolet-A radiation, referred to as CXL, for the management of corneal thinning disease conditions. The comparative safety and effectiveness of corneal cross-linking with other minimally invasive treatments such as intrastromal corneal rings was also reviewed. The Medical Advisory Secretariat (MAS) evidence-based analysis was performed to support public financing decisions. Subject of the Evidence-Based Analysis The primary treatment objective for corneal cross-linking is to increase the strength of the corneal stroma, thereby stabilizing the underlying disease process. At the present time, it is the only procedure that treats the underlying disease condition. The proposed advantages for corneal cross-linking are that the procedure is minimally invasive, safe and effective, and it can potentially delay or defer the need for a corneal transplant. In addition, corneal cross-linking does not adversely affect subsequent surgical approaches, if they are necessary, or interfere with corneal transplants. The evidence for these claims for corneal cross-linking in the management of corneal thinning disorders such as keratoconus will be the focus of this review. The specific research questions for the evidence review were as follows: Technical: How technically demanding is corneal cross-linking and what are the operative risks? Safety: What is known about the broader safety profile of corneal cross-linking? Effectiveness - Corneal Surface Topographic Affects: What are the corneal surface remodeling effects of corneal cross-linking? Do these changes interfere with subsequent interventions, particularly corneal transplant known as penetrating keratoplasty (PKP)? Effectiveness -Visual Acuity: What impacts does the remodeling have on visual acuity? Are these impacts predictable, stable, adjustable and durable? Effectiveness - Refractive Outcomes: What impact does remodeling have on refractive outcomes? Effectiveness - Visual Quality (Symptoms): What impact does corneal cross-linking have on vision quality such as contrast vision, and decreased visual symptoms (halos, fluctuating vision)? Effectiveness - Contact lens tolerance: To what extent does contact lens intolerance improve after corneal cross-linking? Vision-Related QOL: What is the impact of corneal cross-linking on functional visual rehabilitation and quality of life? Patient satisfaction: Are patients satisfied with their vision following the procedure? Disease Process: What impact does corneal cross-linking have on the underling corneal thinning disease process? Does corneal cross-linking delay or defer the need for a corneal transplant? What is the comparative safety and effectiveness of corneal cross-linking compared with other minimally invasive treatments for corneal ectasia such as intrastromal corneal rings? Clinical Need: Target Population and Condition Corneal ectasia (thinning) disorders represent a range of disorders involving either primary disease conditions, such as keratoconus (KC) and pellucid marginal corneal degeneration, or secondary iatrogenic conditions, such as corneal thinning occurring after laser in situ keratomileusis (LASIK) refractive surgery. Corneal thinning is a disease that occurs when the normally round dome-shaped cornea progressively thins causing a cone-like bulge or forward protrusion in response to the normal pressure of the eye. The thinning occurs primarily in the stroma layers and is believed to be a breakdown in the collagen process. This bulging can lead to irregular astigmatism or shape of the cornea. Because the anterior part of the cornea is responsible for most of the focusing of the light on the retina, this can then result in loss of visual acuity. The reduced visual acuity can make even simple daily tasks, such as driving, watching television or reading, difficult to perform. Keratoconus is the most common form of cor

Pron, G; Ieraci, L; Kaulback, K

2011-01-01

318

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

PubMed

Recent in vitro findings suggest that UHMWPE wear particles containing vitamin E (VE) may have reduced biologic activity and decreased osteolytic potential. We hypothesized that particles from VE-stabilized, radiation cross-linked UHMWPE would cause less osteolysis in a murine calvarial bone model when compared to virgin gamma irradiated cross-linked UHMWPE. Groups received equal amount of particulate debris overlaying the calvarium for 10 days. Calvarial bone was examined using high resolution micro-CT and histomorphometric analyses. There was a statistically significant difference between virgin (12.2%±8%) and VE-UHMWPE (3%±1.4%) groups in regards to bone resorption (P=0.005) and inflammatory fibrous tissue overlaying the calvaria (0.48 vs. 0.20, P<0.0001). These results suggest that VE-UHMWPE particles have reduced osteolytic potential in vivo when compared to virgin UHMWPE. PMID:24998319

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

2014-09-01

319

Thermally reversible cross-links in a healable polymer: Estimating the quantity, rate of formation, and effect on viscosity  

E-print Network

Thermally reversible cross-links in a healable polymer: Estimating the quantity, rate of formation with thermally reversible DielseAlder cross-links, is modeled. A processing method is developed to create small of the mono- mers is determined to be inadequate to obtain a maximum level of cross-linking. Viscosity measure

Nemat-Nasser, Sia

320

Effective-medium approach for stiff polymer networks with flexible cross-links C. P. Broedersz,1  

E-print Network

Effective-medium approach for stiff polymer networks with flexible cross-links C. P. Broedersz,1 C remain poorly understood. Here we describe an effective- medium theory of flexibly cross-linked stiff polymer networks. We argue that the response of the cross-links can be fully attributed to entropic

MacKintosh, F.C.

321

Cross-linking of wheat gluten proteins during production of hard pretzels.  

PubMed

The impact of the hot alkaline dip, prior to pretzel-baking, on the types and levels of cross-links between wheat proteins was studied. Protein extractability of pretzel dough in sodium dodecyl sulfate containing buffer decreased during alkaline dipping [45 s, 1.0% (w/v) NaOH, 90°C], and even more during baking (3 min at 250°C) and drying (10 min at 135°C). Reducing agent increased the extractability partly, indicating that both reducible (disulfide, SS) and non-reducible (non-SS) protein cross-links had been formed. The decrease in cystine levels suggested ?-elimination of cystine releasing Cys and dehydroalanine (DHA). Subsequent reaction of DHA with Lys and Cys, induced the unusual and potentially cross-linking amino acids lysinoalanine (LAL) and lanthionine (LAN), respectively, in alkaline dipped dough (7 ?mol LAN/g protein) and in the end product (9 ?mol LAL and 50 ?mol LAN/g protein). The baking/drying step increased sample redness, decreased Lys levels more than expected based on LAL formation (57 ?mol/g protein), and induced a loss of reducing sugars (99 ?mol/g protein), which suggested the potential contribution of Maillard-derived cross-links to the observed extractability loss. However, levels of Maillard products which possibly cross-link proteins, are small compared to DHA-derived cross-links. Higher dipping temperatures, longer dipping times, and higher NaOH concentrations increased protein extractability losses and redness, as well as LAL and LAN levels in the end product. No indications for Maillard-derived cross-links or LAL in pretzel dough immediately after dipping were found, even when severe dipping conditions were used. PMID:21822731

Rombouts, Ine; Lagrain, Bert; Brijs, Kristof; Delcour, Jan A

2012-06-01

322

Pharmacologic Alternatives to Riboflavin Photochemical Corneal Cross-Linking: A Comparison Study of Cell Toxicity Thresholds  

PubMed Central

Purpose. The efficacy of therapeutic cross-linking of the cornea using riboflavin photochemistry (commonly abbreviated as CXL) has caused its use to become widespread. Because there are known chemical agents that cross-link collagenous tissues, it may be possible to cross-link tissue pharmacologically. The present study was undertaken to compare the cell toxicity of such agents. Methods. Nine topical cross-linking agents (five nitroalcohols, glyceraldehyde [GLYC], genipin [GP], paraformaldehyde [FA], and glutaraldehyde [GLUT]) were tested with four different cell lines (immortalized human corneal epithelial cells, human skin fibroblasts, primary bovine corneal endothelial cells, and immortalized human retinal pigment epithelial cells [ARPE-19]). The cells were grown in planar culture and exposed to each agent in a range of concentrations (0.001 mM to 10 mM) for 24 hours followed by a 48-hour recovery phase. Toxicity thresholds were determined by using the trypan blue exclusion method. Results. A semiquantitative analysis using five categories of toxicity/fixation was carried out, based on plate attachment, uptake of trypan blue stain, and cellular fixation. The toxicity levels varied by a factor of 103 with the least toxic being mononitroalcohols and GLYC, intermediate toxicity for a nitrodiol and nitrotriol, and the most toxic being GLUT, FA, GP, and bronopol, a brominated nitrodiol. When comparing toxicity between different cell lines, the levels were generally in agreement. Conclusions. There are significant differences in cell toxicity among potential topical cross-linking compounds. The balance between cross-linking of tissue and cell toxicity should be borne in mind as compounds and strategies to improve mechanical tissue properties through therapeutic tissue cross-linking continue to develop. PMID:24722697

Kim, MiJung; Takaoka, Anna; Hoang, Quan V.; Trokel, Stephen L.; Paik, David C.

2014-01-01

323

Cross-linking methionine and amine residues with reactive halogen species.  

PubMed

Irreversible cross-links are increasingly being recognized as important posttranslational oxidative protein modifications that contribute to tissue injury during oxidative stress and inflammation. They also have a structural function in extracellular matrix proteins such as collagen IV. Likely contenders for forming such cross-links are the reactive halogen species that are generated by neutrophils and eosinophils, including hypochlorous acid, hypobromous acid, and their related haloamines. Methionine residues are kinetically preferred targets for these oxidants and oxidation can potentially result in sulfilimine (>S=N-) bonds with amines. Therefore, we investigated whether oxidation of methionine in the model peptide formyl-Met-Leu-Phe-Lys (fMLFK) produces cross-links with lysine residues, using mass spectrometry to characterize the products. As expected, the sulfoxide was the major product with each reactive halogen species. However, intra- and intermolecular cross-linked products were also formed. Isomers of an intramolecular sulfilimine were readily produced by hypobromous acid and bromamines, with hypochlorous acid forming lesser amounts. The predominant cross-link with chloramines was an intermolecular bond between the sulfur of fMLFK and the amine derived from the chloramine. Reactive halogen species also formed these sulfilimine cross-links in other peptides that contain methionine. We propose that protein cross-links involving methionine and amine residues will form via this mechanism when granulocytes are activated at sites of inflammation. Our results also support the proposal that reactive halogen species generated by the peroxidase peroxidasin could be responsible for the sulfilimine bonds that are integral to the structure of collagen IV. PMID:24486343

Ronsein, Graziella E; Winterbourn, Christine C; Di Mascio, Paolo; Kettle, Anthony J

2014-05-01

324

Immune Focusing and Enhanced Neutralization Induced by HIV-1 gp140 Chemical Cross-Linking  

PubMed Central

Experimental vaccine antigens based upon the HIV-1 envelope glycoproteins (Env) have failed to induce neutralizing antibodies (NAbs) against the majority of circulating viral strains as a result of antibody evasion mechanisms, including amino acid variability and conformational instability. A potential vaccine design strategy is to stabilize Env, thereby focusing antibody responses on constitutively exposed, conserved surfaces, such as the CD4 binding site (CD4bs). Here, we show that a largely trimeric form of soluble Env can be stably cross-linked with glutaraldehyde (GLA) without global modification of antigenicity. Cross-linking largely conserved binding of all potent broadly neutralizing antibodies (bNAbs) tested, including CD4bs-specific VRC01 and HJ16, but reduced binding of several non- or weakly neutralizing antibodies and soluble CD4 (sCD4). Adjuvanted administration of cross-linked or unmodified gp140 to rabbits generated indistinguishable total gp140-specific serum IgG binding titers. However, sera from animals receiving cross-linked gp140 showed significantly increased CD4bs-specific antibody binding compared to animals receiving unmodified gp140. Moreover, peptide mapping of sera from animals receiving cross-linked gp140 revealed increased binding to gp120 C1 and V1V2 regions. Finally, neutralization titers were significantly elevated in sera from animals receiving cross-linked gp140 rather than unmodified gp140. We conclude that cross-linking favors antigen stability, imparts antigenic modifications that selectively refocus antibody specificity and improves induction of NAbs, and might be a useful strategy for future vaccine design. PMID:23843636

Schiffner, T.; Kong, L.; Duncan, C. J. A.; Back, J. W.; Benschop, J. J.; Shen, X.; Huang, P. S.; Stewart-Jones, G. B.; DeStefano, J.; Seaman, M. S.; Tomaras, G. D.; Montefiori, D. C.; Schief, W. R.

2013-01-01

325

A comparative cross-linking strategy to probe conformational changes in protein complexes  

PubMed Central

Chemical cross-linking, together with mass spectrometry, is established as a powerful combination for probing subunit interactions within static protein assemblies. To probe conformational changes in response to stimuli we have developed a comparative cross-linking strategy, employing lysine-specific deuterated and non-deuterated BS3 cross-linking reagents. Here we describe the experimental procedures as well as the data analysis, validation and interpretation. Briefly the protocol involves first assigning cross-linked peptides in the complex without ligand binding, or with post-translational modifications (PTMs) at natural abundance, using a standard procedure employing labeled cross-linkers, proteolysis and subsequent assignment of cross-linked peptides following LC-MS/MS and database searching. An aliquot of the protein complex is then exposed to the stimulus, either ligand binding, or incubation with a phosphatase or kinase to bring about changes in PTMs. Two solutions, one containing the apo/untreated complex the other the enzymatically modified/ligand-bound complex, are then cross-linked independently. Typically non-deuterated BS3-d0 is used or the untreated complex and deuterated BS3-d4 is used for the experiment. The two aliquots are then incubated at equal concentration, digested and processed as before. The ratios of labeled and unlabeled cross-linked peptides then provide a direct readout of the effect of the stimulus. We exemplify our method by quantifying changes in subunit interactions induced by dephosphorylation of an ATP synthase. The protocol is however widely applicable for determining conformational changes in protein complexes induced by various stimuli including ligand/drug binding, oligomerization and other PTMs. Application of the established protocol takes ~9 days, including protein complex purification. PMID:25144272

Schmidt, Carla; Robinson, Carol V.

2014-01-01

326

Cross-linked poly(acrylic acids) microgels and agarose as semi-interpenetrating networks for resveratrol release.  

PubMed

Carbomers, cross-linked poly(acrylic acid) microgels, have been widely used in pharmaceutical formulations as swollen hydrogels. Agarose, whose thermoreversibility may be exploited for drug loading, forms a gel with a mechanism involving coil-helix transition at about 36 °C. In this work carbomer microgels were combined with agarose networks in a semi-interpenetrating polymer network structure, aiming at obtaining suitable delivery systems for the loading and release of molecules with poor bioavailability but high therapeutic interest, like resveratrol. The rheological properties of the formulations and their in vitro cytocompatibility were studied and optimized acting on the neutralizing agent (triethylamine (N,N-diethylethanamine), triethanolamine (tris(2-hydroxyethyl)amine) and sodium hydroxide) and amount of OH donors (1,2-propanediol and glycerol). As a preparation method, autoclaving was introduced to simultaneously obtain heating and sterilising. Among the different neutralizing agents, NaOH was chosen to avoid the use of amines, considering the final application. Without the addition of alcohols as typical OH donors to induce Carbomer gelification, gels with appropriate rheological properties and stability were produced. For this formulation, the release of resveratrol after 7 days was about 80 % of the loaded mass, suggesting it is an interesting approach to be exploited for the development of innovative resveratrol delivery systems. PMID:25577210

Tunesi, Marta; Prina, Elisabetta; Munarin, Fabiola; Rodilossi, Serena; Albani, Diego; Petrini, Paola; Giordano, Carmen

2015-01-01

327

Emodin-mediated cross-linking enhancement for extracellular matrix homeostasis.  

PubMed

The extracellular matrix (ECM) is an essential element of mammalian organisms, and its cross-linking formation plays a vital role in ECM development and postnatal homeostasis. Defects in cross-link formation caused by aging, genetic, or environmental factors are known to cause numerous diseases in mammals. To augment the cross-linking formation of ECM, the present study established a ZsGreen reporter system controlled by the promoter of lysyl oxidase-like 1 gene (LOXL1), which serves as both a scaffold element and a cross-linking enzyme in the ECM. By using this system in a drug screen, we identified emodin as a strong enhancer of LOXL1 expression that promoted cross-linking formation of ECM in all the tested systems, including human fibroblast cells, cultured human skin tissues, and animals that received long-term emodin treatment. Collectively, the results suggest that emodin may serve as an effective drug or supplement for ECM homeostasis. PMID:24680685

Jian, Lihua; Zhang, Chen; Chen, Guangfeng; Shi, Xiujuan; Qiu, Yu; Xue, Yunyun; Yang, Shuzhang; Lu, Lixia; Yuan, Qionglan; Xu, Guotong; Ying, Ming; Liu, Xiaoqing

2014-04-18

328

Polyimide aerogels with amide cross-links: a low cost alternative for mechanically strong polymer aerogels.  

PubMed

Polyimide aerogels combine high porosity, low thermal conductivity, flexibility, and low density with excellent mechanical properties. However, previously used cross-linkers, such as 1,3,5-triaminophenoxybenzene (TAB), 2,4,6-tris(4-aminophenyl)pyridine (TAPP), or octa(aminophenoxy)silsesquioxane (OAPS), either are not commercially available or are prohibitively expensive. Finding more cost efficient cross-linkers that are commercially available to synthesize these aerogels is crucial for making large scale manufacturing attractive. Herein, we describe an approach to making polyimide aerogels starting with amine capped oligomers that are cross-linked with 1,3,5-benzenetricarbonyl trichloride (BTC). BTC is a lower cost, commercially available alternative to TAB, TAPP, or OAPS. Aerogels made in this way have the same or higher modulus and higher surface area compared to those previously reported with either TAB or OAPS cross-links at the same density. While the cross-link structure is an amide, the thermal stability is not compromised most likely because the cross-link is only a small part of the composition of the aerogel. Onset of decomposition depends primarily on the backbone chemistry with 4,4'-oxidianiline (ODA) being more thermally stable than 2,2'-dimethylbenzidine (DMBZ), similar to those previously reported with other cross-links. PMID:25564878

Meador, Mary Ann B; Alemán, Christian R; Hanson, Katrina; Ramirez, Nakaira; Vivod, Stephanie L; Wilmoth, Nathan; McCorkle, Linda

2015-01-21

329

Dependence of nanomechanical modification of polymers on plasma-induced cross-linking  

NASA Astrophysics Data System (ADS)

The nanomechanical properties of low-density polyethylene (LDPE) modified by inductively coupled, radio-frequency Ar plasma were investigated by surface force microscopy. The polymer surface was modified under plasma conditions of different ion energy fluences and radiation intensities obtained by varying the sample distance from the plasma power source. Nanoindentation results of the surface stiffness versus maximum penetration depth did not reveal discernible differences between untreated and plasma-treated LDPE, presumably due to the small thickness of the modified surface layer that resulted in a substrate effect. On the contrary, nanoscratching experiments demonstrated a significant increase in the surface shear resistance of plasma-modified LDPE due to chain cross-linking. These experiments revealed an enhancement of cross-linking with increasing ion energy fluence and radiation intensity, and a tip size effect on the friction force and dominant friction mechanisms (adhesion, plowing, and microcutting). In addition, LDPE samples with a LiF crystal shield were exposed to identical plasma conditions to determine the role of vacuum ultraviolet (VUV) and ultraviolet (UV) radiation in the cross-linking process. The cross-linked layer of plasma-treated LDPE exhibited much higher shear strength than that of VUV/UV-treated LDPE. Plasma-induced surface modification of the nanomechanical properties of LDPE is interpreted in the context of molecular models of the untreated and cross-linked polymer surfaces derived from experimental findings.

Tajima, S.; Komvopoulos, K.

2007-01-01

330

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

PubMed Central

This present study deals with synthesis, characterization and antibacterial activity of cross-linked chitosan-glutaraldehyde. Results from this study indicated that cross-linked chitosan-glutaraldehyde markedly inhibited the growth of antibiotic-resistant Burkholderia cepacia complex regardless of bacterial species and incubation time while bacterial growth was unaffected by solid chitosan. Furthermore, high temperature treated cross-linked chitosan-glutaraldehyde showed strong antibacterial activity against the selected strain 0901 although the inhibitory effects varied with different temperatures. In addition, physical-chemical and structural characterization revealed that the cross-linking of chitosan with glutaraldehyde resulted in a rougher surface morphology, a characteristic Fourier transform infrared (FTIR) band at 1559 cm?1, a specific X-ray diffraction peak centered at 2? = 15°, a lower contents of carbon, hydrogen and nitrogen, and a higher stability of glucose units compared to chitosan based on scanning electron microscopic observation, FTIR spectra, X-ray diffraction pattern, as well as elemental and thermo gravimetric analysis. Overall, this study indicated that cross-linked chitosan-glutaraldehyde is promising to be developed as a new antibacterial drug. PMID:23670533

Li, Bin; Shan, Chang-Lin; Zhou, Qing; Fang, Yuan; Wang, Yang-Li; Xu, Fei; Han, Li-Rong; Ibrahim, Muhammad; Guo, Long-Biao; Xie, Guan-Lin; Sun, Guo-Chang

2013-01-01

331

Availability of fluorescence spectroscopic in the accompaniment of formation of corneal cross-linking  

NASA Astrophysics Data System (ADS)

The corneal cross-linking is a method that associates riboflavin and ultraviolet light to induce a larger mechanical resistance at cornea. This method has been used for the treatment of Keratoconus. Since cross-linking is recent as treatment, there is a need to verify the effectiveness of the method. Therefore, the viability of the fluorescence spectroscopy technique to follow the cross-linking formation at cornea was studied. Corneas were divided in two measuring procedures: M1 (cornea + riboflavin), and M2 (cornea + riboflavina + light irradiation, 365nm). For fluorescence measurements, a spectrofluorimeter was used, where several wavelengths were selected (between 320nm and 370nm) for cornea excitation. Several fluorescence spectra were collected, at 10 min-interval, during 60 min. Spectra allowed one to observe two very well defined bands of fluorescence: the first one at 400nm (collagen), and the second one at 520nm (riboflavin). After spectra analyses, a decrease of collagen fluorescence was observed for both groups. For riboflavin, on the other hand, there was a fluorescence increase for M1, and a decrease for M2. Thus, it is possible to conclude that it this technique is sensitive for the detection of tissue structural changes during cross-linking treatment, encouraging subsequent studies on quantification of cross-linking promotion in tissue.

Costa, M. M.; Kurachi, C.; Bagnato, V. S.; Faria e Sousa, S. J.; Ventura, L.

2010-02-01

332

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

PubMed

Structured xylan-based hydrogels, reinforced with cellulose nanocrystals (CNCs), have successfully been prepared from water suspensions by cross-linking during freeze-casting. In order to induce cross-linking during the solidification/sublimation operation, xylan was first oxidized using sodium periodate to introduce dialdehydes. The oxidized xylan was then mixed with CNCs after which the suspension was frozen unidirectionally in order to control the ice crystal formation and by that the pore morphology of the material. Finally the ice crystal templates were removed by freeze-drying. During the freeze-casting process hemiacetal bonds are formed between the aldehyde groups and hydroxyl groups, either on other xylan molecules or on CNCs, which cross-links the system. The proposed cross-linking reaction was confirmed by using cross-polarization magic angle spinning (CP/MAS) nuclear magnetic resonance (NMR) spectroscopy. The pore morphology of the obtained materials was analyzed by scanning electron microscopy (SEM). The materials were also tested for compressive strength properties, both in dry and water swollen state. All together this study describes a novel combined freeze-casting/cross-linking process which enables fabrication of nanoreinforced biopolymer-based hydrogels with controlled porosity and 3-D architecture. PMID:24188834

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

2014-01-16

333

Preparation and characterization of in situ ionic cross-linked pectin films: unique biodegradable polymers.  

PubMed

The study aimed to investigate the swelling and degradation of calcium pectinate (CaP) films that were cross-linked by the innovative approach of adding aqueous calcium chloride (CaCl2) to pre-formed pectin films in situ. The films, cast from low methoxy pectin, were dried and cross-linked by immersion in a selected CaCl2 solution for a selected period. It was found that CaCl2 concentration, immersion time, and temperature affected the films' dissolution and swelling behaviors in simulated intestinal fluid. With lower CaCl2 concentration, more time was needed to form a proper film. Heat accelerated the cross-linking reaction, probably by elevating the cross-linked solution flux into the matrix. Depending upon cross-linking conditions, similar calcium contents in the CaP films resulted in different swelling and degradation behaviors. The degree of pectin esterification (DE) affected the films' degradation rate. The role of pectin molecular weight and DE on the films' mechanical properties was determined by stress/strain analysis. PMID:24507280

Penhasi, Adel; Meidan, Victor M

2014-02-15

334

Cross-linking connectivity in bone collagen fibrils: the COOH-terminal locus of free aldehyde  

NASA Technical Reports Server (NTRS)

Quantitative analyses of the chemical state of the 16c residue of the alpha 1 chain of bone collagen were performed on samples from fetal (4-6-month embryo) and mature (2-3 year old) bovine animals. All of this residue could be accounted for in terms of three chemical states, in relative amounts which depended upon the age of the animal. Most of the residue was incorporated into either bifunctional or trifunctional cross-links. Some of it, however, was present as free aldehyde, and the content increased with maturation. This was established by isolating and characterizing the aldehyde-containing peptides generated by tryptic digestion of NaB3H4-reduced mature bone collagen. We have concluded that the connectivity of COOH-terminal cross-linking in bone collagen fibrils changes with maturation in the following way: at first, each 16c residue in each of the two alpha 1 chains of the collagen molecule is incorporated into a sheet-like pattern of intermolecular iminium cross-links, which stabilizes the young, nonmineralized fibril as a whole. In time, some of these labile cross-links maturate into pyridinoline while others dissociate back to their precursor form. The latter is likely due to changes in the molecular packing brought about by the mineralization of the collagen fibrils. The resultant reduction in cross-linking connectivity may provide a mechanism for enhancing certain mechanical characteristics of the skeleton of a mature animal.

Otsubo, K.; Katz, E. P.; Mechanic, G. L.; Yamauchi, M.

1992-01-01

335

Hyaluronan Breakdown Contributes to Immune Defense against Group A Streptococcus*  

E-print Network

Hyaluronan Breakdown Contributes to Immune Defense against Group A Streptococcus* Received, La Jolla, California 92093 Background: The role of hyaluronan catabolism in group A Streptococcus be a previously unrecognized mechanism for host defense. Group A Streptococcus (GAS) commonly infects human skin

Nizet, Victor

336

Transport of a hyaluronan-binding protein in brain tissue  

Microsoft Academic Search

Hyaluronan is an unsulfated linear glycosaminoglycan with the ability to nucleate extracellular matrices by the formation of aggregates with lecticans. These matrices are essential during development of the central nervous system. In the prospective white matter of the developing brain hyaluronan is organized into fiber-like structures according to confocal microscopy of fixed slices which may guide the migration of neural

Joachim Kappler; Oliver Hegener; Stephan L. Baader; Sebastian Franken; Volkmar Gieselmann; Hanns Häberlein; Uwe Rauch

2009-01-01

337

Bacterial cellulose gels with high mechanical strength.  

PubMed

A composite structure was formed between polyethylene glycol diacrylate (PEGDA) and bacterial cellulose (BC) gels swollen in polyethylene glycol (PEG) as a solvent (BC/PEG gel) to improve the mechanical strength of the gels. The mechanical strength under compression and the rheostatic properties of the gels were evaluated. The compression test results indicated that the mechanical strength of the gels depended on the weight percent of cross-linked PEGDA in the gel, the chain length between the cross-linking points, and the cross-linking density of PEGDA polymers. The PEGDA polymers around the cellulose fibers were resistant to pressure; thus, the BC/PEG-PEGDA gel was stronger than the BC/PEG gel under compression. The results of transmittance measurements and thermomechanical analysis showed that the rheostatic properties of the gels were retained even after composite structure formation. BC/PEG-PEGDA gels, which are expected to be biocompatible, may be useful for clinical applications as a soft material. PMID:25492172

Numata, Yukari; Sakata, Tadanori; Furukawa, Hidemitsu; Tajima, Kenji

2015-02-01

338

Characterization of the enzymatic activity of the actin cross-linking domain from the Vibrio cholerae MARTX Vc toxin.  

PubMed

Vibrio cholerae is a Gram-negative bacterial pathogen that exports enterotoxins, which alter host cells through a number of mechanisms resulting in diarrheal disease. Among the secreted toxins is the multifunctional, autoprocessing RTX toxin (MARTX(Vc)), which disrupts actin cytoskeleton by covalently cross-linking actin monomers into oligomers. The region of the toxin responsible for cross-linking activity is the actin cross-linking domain (ACD). In this study, we demonstrate unambiguously that ACD utilizes G- and not F-actin as a substrate for the cross-linking reaction and hydrolyzes one molecule of ATP per cross-linking event. Furthermore, major actin-binding proteins that regulate actin cytoskeleton in vivo do not block the cross-linking reaction in vitro. Cofilin inhibits the cross-linking of G- and F-actin, at a high mole ratio to actin but accelerates F-actin cross-linking at low mole ratios. DNase I completely blocks the cross-linking of actin, likely due to steric hindrance with one of the cross-linking sites on actin. In the context of the holotoxin, the inhibition of Rho by the Rho-inactivating domain of MARTX(Vc) (Sheahan, K. L., and Satchell, K. J. F. (2007) Cell. Microbiol. 9, 1324-1335) would accelerate F-actin depolymerization and provide G-actin, alone or in complex with actin-binding proteins, for cross-linking by ACD, ultimately leading to the observed rapid cell rounding. PMID:17951576

Kudryashov, Dmitri S; Cordero, Christina L; Reisler, Emil; Satchell, Karla J Fullner

2008-01-01

339

xiNET: Cross-link Network Maps With Residue Resolution*  

PubMed Central

xiNET is a visualization tool for exploring cross-linking/mass spectrometry results. The interactive maps of the cross-link network that it generates are a type of node-link diagram. In these maps xiNET displays: (1) residue resolution positional information including linkage sites and linked peptides; (2) all types of cross-linking reaction product; (3) ambiguous results; and, (4) additional sequence information such as domains. xiNET runs in a browser and exports vector graphics which can be edited in common drawing packages to create publication quality figures. Availability: xiNET is open source, released under the Apache version 2 license. Results can be viewed by uploading data to http://crosslinkviewer.org/ or by downloading the software from http://github.com/colin-combe/crosslink-viewer and running it locally. PMID:25648531

Combe, Colin W.; Fischer, Lutz; Rappsilber, Juri

2015-01-01

340

Carbon Nanofiber Incorporated Silica Based Aerogels with Di-Isocyanate Cross-Linking  

NASA Technical Reports Server (NTRS)

Lightweight materials with excellent thermal insulating properties are highly sought after for a variety of aerospace and aeronautic applications. (1) Silica based aerogels with their high surface area and low relative densities are ideal for applications in extreme environments such as insulators for the Mars Rover battery. (2) However, the fragile nature of aerogel monoliths prevents their widespread use in more down to earth applications. We have shown that the fragile aerogel network can be cross-linked with a di-isocyanate via amine decorated surfaces to form a conformal coating. (3) This coating reinforces the neck regions between secondary silica particles and significantly strengthens the aerogels with only a small effect on density or porosity. Scheme 1 depicts the cross-linking reaction with the di-isocyanate and exhibits the stages that result in polymer cross-linked aerogel monoliths.

Vivod, Stephanie L.; Meador, Mary Ann B.; Capadona, Lynn A.; Sullivan, Roy M.; Ghosn, Louis J.; Clark, Nicholas; McCorkle, Linda

2008-01-01

341

Abrasive wear and metallosis associated with cross-linked polyethylene in total hip arthroplasty.  

PubMed

A 34-year-old female patient received a cobalt-chromium (CoCr) alloy femoral head on cross-linked polyethylene total hip replacement for the revision of her fractured ceramic-on-ceramic total hip replacement. The CoCr alloy femoral head became severely worn due to third-body abrasive wear by ceramic particles that could not be removed by synovectomy or irrigation at revision surgery. Ceramic particles were found embedded in the cross-linked polyethylene liner. The CoCr alloy femoral head exhibited a total mass loss of 14.2 g and the generated wear particles triggered metallosis in the patient. The present case study suggests not revising a fractured ceramic-on-ceramic total hip replacement with a CoCr alloy femoral head and a cross-linked polyethylene liner to avoid metallosis due to third-body abrasive wear. PMID:22770854

O'Brien, Sean T; Burnell, Colin D; Hedden, David R; Brandt, Jan-M

2013-01-01

342

Tuning of cross-linking and mechanical properties of laser-deposited poly (methyl methacrylate) films  

NASA Astrophysics Data System (ADS)

The chemical composition, amount of cross-linking and its influence on the mechanical properties of poly(methyl methacrylate) (PMMA) thin films produced by pulsed laser deposition (PLD) at a wavelength of 248nm under ultrahigh vacuum were investigated by infrared spectroscopy, scanning electron microscopy, size-exclusion chromatography, thermogravimetric analysis, and nanoindentation experiments. The films consist of two components, one fraction with a molecular weight well below that of the target material and a second fraction, which is cross-linked. Compared to bulk material, the Young's modulus of the film is increased. The amount of cross-linking in the film can be tuned by the applied laser fluence leading to changes of the mechanical properties.

Süske, Erik; Scharf, Thorsten; Krebs, Hans-Ulrich; Panchenko, Elena; Junkers, Thomas; Egorov, Mark; Buback, Michael; Kijewski, Harald

2005-03-01

343

Fracture Behavior of High-Toughness, Ionically Cross-linked Triblock Copolymer Hydrogels  

NASA Astrophysics Data System (ADS)

Mechanisms for enhancing energy dissipation and hence toughness are important for the generation of robust synthetic soft materials for biomedical applications. Ionic cross-linking in particular has been explored in triblock copolymer hydrogels and affords a remarkable change in mechanical performance comparable to non-cross-linked analogs. Here we employ a physically associated base triblock copolymer network composed of hydrophobic poly(methyl methacrylate) endblocks and a hydrophilic poly(methacrylic acid) midblock capable of complexing with divalent cations. Increases in stiffness and strength have previously been reported, with the extent dependent upon the identity, concentration, and pH of a cross-linking cation solution. We delineate the measured toughness in such systems using tensile tear tests and relate the mechanical performance to a damage zone model reminiscent of loading behavior observed in double network hydrogels.

Henderson, Kevin; Otim, Kathryn; Shull, Kenneth

2011-03-01

344

Three-dimensional multimodal microscopy of rabbit cornea after cross-linking treatment  

NASA Astrophysics Data System (ADS)

Cross-linking of stromal collagen with Riboflavin and UVA radiation is an alternative treatment of keratoconus. After the cross-linking a wound healing process starts with the regeneration of the abraded epithelial layer and the stromal keratocyte-network. To clarify possible side effects by visualization we established an imaging platform for the multimodal three-dimensional imaging of the cornea and looked for differences between normal and cross-linked rabbit corneae. The microscopy system utilizes femtosecond laser light for two photon excitation of autofluorescent metabolic compounds, second harmonic imaging in forward and backward direction for the study of stromal collagen-I structure and confocal detection of the backscattered femtosecond laser light for cell detection. Preliminary results show signatures of treatment 5 weeks after the intervention in all imaging modalities.

Krüger, A.; Hovakimyan, M.; Ramírez, D. F.; Lorbeer, R.-A.; Kröger, M.; Stachs, O.; Wree, A.; Guthoff, R. F.; Lubatschowski, H.; Heisterkamp, A.

2010-02-01

345

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

SciTech Connect

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

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

2009-01-01

346

Preparation of cross-linked maize (Zea mays L.) starch in different reaction media.  

PubMed

Granular normal maize starch was reacted with sodium trimetaphosphate in deionized water ( [Formula: see text] ), aqueous sodium sulfate solution ( [Formula: see text] ), aqueous ethanol (MSethanol) or aqueous acetone (MSacetone) under otherwise identical reaction conditions. Analysis of the resultant starches by Rapid Visco Analysis (RVA) showed that the starch was cross-linked to a higher degree in aqueous ethanol or aqueous acetone than in water or sodium sulfate solution, and with minimal starch leaching. While MSacetone and MSethanol had incorporated similar levels of phosphorous, RVA analysis and microscopic analysis showed that MSacetone granules were more effectively stabilized by cross-linking than MSethanol granules. Cross-linking in aqueous acetone is believed to either contain the greater numbers of distarch monophosphate (versus monostarch monophosphate), or occur more intensively at the granule outer layers than that in aqueous ethanol and, at the same time, to account for the greater granular strength of MSethanol than that of MSacetone. PMID:25839824

Hong, Jung Sun; Gomand, Sara V; Delcour, Jan A

2015-06-25

347

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

PubMed

The aim of this study was to determine the effects of the concentration of paste used to produce retrograded starch, and esterification degree, on selected properties of the resultant distarch adipate. Starch paste was prepared from native potato starch (1, 4, 10, 18 or 30 g/100g), frozen, defrosted and dried. Thus produced preparations of retrograded starch were cross-linked with various doses of a cross-linking agent (0.125, 0.25, 0.5, 1.0 or 2.0 ml per 100g of starch). Properties of the produced adipates depended on both the concentration of paste used to produce retrograded starch and the degree of substitution with adipic acid residues. Solubility in water and swelling power of the cross-linked preparations of retrograded starch, as well as pasting temperature and viscosity of produced pastes, all decreased along with the increasing degree of substitution with adipic acid residues. PMID:25148968

Kapelko, M; Zi?ba, T; Michalski, A; Gryszkin, A

2015-01-15

348

Proteomic Analysis of DNA-Protein Cross-Linking by Antitumor Nitrogen Mustards  

PubMed Central

Nitrogen mustards are antitumor agents used clinically for the treatment of a variety of neoplastic conditions. The biological activity of these compounds is typically attributed to their ability to induce DNA-DNA cross-links. However, nitrogen mustards are able to produce a variety of other lesions, including DNA-protein cross-links (DPCs). DPCs induced by nitrogen mustards are not well characterized because of their structural complexity and the insufficient specificity and sensitivity of previously available experimental methodologies. In the present work, affinity capture methodology in combination with mass spectrometry-based proteomics was employed to identify mammalian proteins that form covalent cross-links to DNA in the presence of a simple nitrogen mustard, mechlorethamine. Following incubation of 5?-biotinylated DNA duplexes with nuclear protein extracts, DPCs were isolated by affinity capture on streptavidin beads, and the cross-linked proteins were identified by HPLC-ESI+-MS/MS of tryptic peptides. Mechlorethamine treatment resulted in the formation of DPCs with nuclear proteins involved in chromatin regulation, DNA replication and repair, cell cycle control, transcriptional regulation, and cell architecture. Western blot analysis was employed to confirm protein identification and to quantify the extent of drug-mediated cross-linking. Mass spectrometry of amino acid-nucleobase conjugates found in total proteolytic digests revealed that mechlorethamine-induced DPCs are formed via alkylation of the N7 position of guanine in duplex DNA and cysteine thiols within the proteins to give N-[2-[S-cysteinyl]ethyl]-N-[2-(guan-7-yl)ethyl]methylamine lesions. The results described herein suggest that cellular exposure to nitrogen mustards leads to cross-linking of a large spectrum of nuclear proteins to chromosomal DNA, potentially contributing to the cytotoxic and mutagenic effects of these drugs. PMID:19480393

Loeber, Rachel L.; Michaelson-Richie, Erin D.; Codreanu, Simona G.; Liebler, Daniel C.; Campbell, Colin R.; Tretyakova, Natalia Y.

2009-01-01

349

Stress generation by solvent absorption and wrinkling of a cross-linked coating atop a viscous or elastic base.  

PubMed

An in-plane constrained cross-linked gel layer absorbs an equilibrium amount of solvent and experiences in-plane compressive stress. A stability analysis of such an elastic gel layer that is attached to either a viscous or an elastic bottom layer atop a rigid substrate is considered. The effects of the top and bottom layer moduli (E(t) and E(b)), the bottom-to-top layer thickness ratio (H/h), and the polymer solvent interaction parameter (chi) on the critical condition of wrinkling, wrinkle wavelength, and amplitude are examined. When the bottom layer is viscous, the compressed top layer is always unstable, and wrinkling is rate-controlled. The viscous flow of the bottom layer governs the rate and determines the fastest growing wavelength. As E(t) rises, the bending stiffness of the elastic layer does as well, and so the fastest growing wavelength (lambda(m)) rises and the equilibrium amplitude (A(e)) falls. As H/h rises, the constraint of the rigid substrate diminishes, and so lambda(m) and A(e) rise. As chi falls or as the solvent has higher affinity for the polymeric gel, lambda(m) falls and A(e) rises because better solvents create higher compressive strain that promote low-wavelength, high-amplitude wrinkles. When the bottom layer is elastic, a critical compressive stress exists. If the generated compressive stress by solvent absorption is greater than the critical stress, the top layer wrinkles. It was found that wrinkling is most likely at intermediate E(t), low E(b), high H/h, and low chi. Further, lower chi, higher H/h, and lower E(b) were found to promote higher equilibrium amplitude and higher wavelength wrinkles. PMID:16768530

Basu, Soumendra K; McCormick, Alon V; Scriven, L E

2006-06-20

350

The effects of different crossing-linking conditions of genipin on type I collagen scaffolds: an in vitro evaluation.  

PubMed

The purpose of this paper is to analyze the properties of fabricating rat tail type I collagen scaffolds cross-linked with genipin under different conditions. The porous genipin cross-linked scaffolds are obtained through a two step freeze-drying process. To find out the optimal cross-link condition, we used different genipin concentrations and various cross-linked temperatures to prepare the scaffolds in this study. The morphologies of the scaffolds were characterized by scanning electron microscope, and the mechanical properties of the scaffolds were evaluated under dynamic compression. Additionally, the cross-linking degree was assessed by ninhydrin assay. To investigate the swelling ratio and the in vitro degradation of the collagen scaffold, the tests were also carried out by immersion of the scaffolds in a PBS solution or digestion in a type I collagenase respectively. The morphologies of the non-cross-linked scaffolds presented a lattice-like structure while the cross-linked ones displayed a sheet-like framework. The morphology of the genipin cross-linked scaffolds could be significantly changed by either increasing genipin concentration or the temperature. The swelling ratio of each cross-linked scaffold was much lower than that of the control (non-cross-linked).The ninhydrin assay demonstrated that the higher temperature and genipin concentration could obviously increase the cross-linking efficiency. The in vitro degradation studies indicated that genipin cross-linking can effectively elevate the biostability of the scaffolds. The biocompatibility and cytotoxicity of the scaffolds was evaluated by culturing rat chondrocytes on the scaffold in vitro and by MTT. The results of MTT and the fact that the chondrocytes adhered well to the scaffolds demonstrated that genipin cross-linked scaffolds possessed an excellent biocompatibility and low cytotoxicity. Based on these results, 0.3 % genipin concentrations and 37 °C cross-linked temperatures are recommended. PMID:24442821

Zhang, Xiujie; Chen, Xueying; Yang, Ting; Zhang, Naili; Dong, Li; Ma, Shaoying; Liu, Xiaoming; Zhou, Mo; Li, Baoxing

2014-12-01

351

Oral administration of hyaluronan reduces bone turnover in ovariectomized rats.  

PubMed

The effect of oral hyaluronan (HA) on bone loss in ovariectomized (OVX) 3-month-old rats was measured using serum markers of bone turnover and bone mineral density. OVX rats were administered 1 mg/kg HA (OVX + HA) or phosphate-buffered saline (PBS) (OVX + PBS) by oral gavage (5 days/week for 54 days). Additional controls included sham ovariectomy with PBS gavage (Sham + PBS) and no treatment. Oral administration of HA resulted in approximately 50% (p < 0.05) increases in serum HA. Gel filtration analyses showed this was high molecular weight HA (300-500 kDa). Osteopenia was mild due to the young age of the animals. Thus, ovariectomy resulted in a 30% increase in serum collagen N-terminal telopeptides (p < 0.001), a 20% increase in serum nitrate/nitrite levels (p = 0.05), and a 5-6% decrease in femur bone mineral density/content (p < 0.05). HA gavage blunted the development of osteopenia in this model as determined by preventing the 30% increase in serum collagen N-terminal telopeptide levels (p < 0.001) and by reducing bone mineral content loss from 6 to 4%. These results show that oral supplements of HA (gavage solution, 0.12% solution) significantly reduce bone turnover associated with mild osteopenia in rats. PMID:23256527

Ma, Jenny; Granton, Patrick V; Holdsworth, David W; Turley, Eva A

2013-01-16

352

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

PubMed

Work on enzymatic cross-linking of globular food proteins has mainly focused on food functional effects such as improvements of gelation and enhanced stabilization of emulsions and foams, and on the detailed biochemical characterization of the cross-linking chemistry. What is still lacking is a physical characterization of cluster formation and gelation, as has been done for example, for cluster formation and gelation during heat-induced protein aggregation. Here we present preliminary results along these lines. We propose that enzymatic cross-linking of apo-alpha-lactalbumin is a good model system for studying the problem of cluster formation and gelation during enzymatic cross-linking of globular proteins. We present initial results on cluster sizes produced when crosslinking dilute solutions of apo-alpha-lactalbumin with a range of cross-linking enzymes: microbial transglutaminase, horseradish peroxidase, and mushroom tyrosinase. These results are used to highlight similarities and differences between different enzymes, when acting on the same substrate. Next we consider cluster growth and gelation in somewhat more detail for the specific case of cross-linking by horseradish peroxidase, under the periodic addition of H2O2. Upon increasing the initial concentration of apo-alpha-lactalbumin, at a fixed enzyme-to-substrate ratio and fixed reaction time, the size of the clusters at the end of the reaction increases rapidly, and above a critical concentration, gelation occurs. For the conditions that we have used, gelation occurred at very low initial apo-alpha-lactalbumin concentrations of 34% (w/v), indicating a very dilute cross-linked protein network, with a low average number of cross-links per protein. It is found that reactive protein monomers are first rapidly (1-2 h) incorporated into small covalent clusters. This is followed by a much slower phase (up to about 12 h) in which the small clusters are coupled together to form much larger covalent protein clusters. Consistent with this two-step mechanism, atomic force microscopy shows that the covalent protein clusters are very heterogeneous and seem to consist of smaller subclusters. PMID:23234160

Saricay, Yunus; Dhayal, Surender Kumar; Wierenga, Peter Alexander; de Vries, Renko

2012-01-01

353

Swelling studies of chitosan-gelatin films cross-linked by sulfate  

Microsoft Academic Search

Swelling properties of chitosan-gelatin films cross-linked by sulfate were investigated. Sulfate cross-linked chitosan-gelatin\\u000a films (SCG) were prepared simply by dipping chitosan-gelatin films into sodium sulfate solution. The swelling behavior of\\u000a SCG was investigated as a function of pH and ionic strength. Under acidic conditions pH less than 4, SCG swelled less than\\u000a 120%, while under the conditions pH larger than

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

2004-01-01

354

Increasing Thermal Stability of Gelatin by UV-Induced Cross-Linking with Glucose  

PubMed Central

The effects of ultraviolet (254?nm) radiation on a hydrated gelatin-glucose matrix were investigated for the development of a physiologically thermostable substrate for potential use in cell scaffold production. Experiments conducted with a differential scanning calorimeter indicate that ultraviolet irradiation of gelatin-glucose hydrogels dramatically increases thermal stability such that no melting is observed at temperatures of at least 90°C. The addition of glucose significantly increases the yield of cross-linked product, suggesting that glucose has a role in cross-link formation. Comparisons of lyophilized samples using scanning electron microscopy show that irradiated materials have visibly different densities. PMID:24963297

Masutani, Evan M.; Kinoshita, Christopher K.; Tanaka, Travis T.; Ellison, Andrew K. D.; Yoza, Brandon A.

2014-01-01

355

An Essential Role for the Interaction Between Hyaluronan and Hyaluronan Binding Proteins During Joint Development  

Microsoft Academic Search

SUMMARY We studied the expression of hyaluronan binding proteins (HABPs) during the development of embryonic chick joints, using immunocytochemistry and biotinylated HA. The expression of actin capping proteins and of actin itself was also studied because the cy- toskeleton is important in controlling HA-HABP interactions. Three cell surface HABPs were localized in the epiphyseal cartilage, articular fibrocartilage, and interzone that

Gary P. Dowthwaite; Jo C. W. Edwards; Andrew A. Pitsillides

1998-01-01

356

Graph algorithms for NMR resonance assignment and cross-link experiment planning  

E-print Network

of using randomized graph to solve the NMR resonance assignment problem. Without his help, this work could develops such graph representations and algorithms for two novel applications: structure-based NMRGraph algorithms for NMR resonance assignment and cross-link experiment planning Dartmouth Computer

357

Water photolysis with a cross-linked titanium dioxide nanowire anode Mingzhao Liu,a  

E-print Network

anatase and rutile phases. Under simulated AM 1.5 G illumination, the peak solar energy conversion maximum energy conversion efficiency at 2.2%.4 Most TiO2- based cells make insufficient use of even the UV surface area architecture afforded by the cross-linked TiO2 nanowires enables both long optical path

Heller, Eric

358

Molecular Dynamic Simulations of Cisplatin-and Oxaliplatin-d(GG) Intrastand Cross-links Reveal  

E-print Network

Molecular Dynamic Simulations of Cisplatin- and Oxaliplatin-d(GG) Intrastand Cross-links Reveal Pt-GG adducts containing cis- diammine ligands (formed by cisplatin (CP) and carboplatin) and trans molecular dynamics simulations to explore differences in the conforma- tional dynamics between OX-DNA, CP

Dokholyan, Nikolay V.

359

Highly conductive carbon nanotube buckypapers with improved doping stability via conjugational cross-linking  

NASA Astrophysics Data System (ADS)

Carbon nanotube (CNT) sheets or buckypapers have demonstrated promising electrical conductivity and mechanical performance. However, their electrical conductivity is still far below the requirements for engineering applications, such as using as a substitute for copper mesh, which is currently used in composite aircraft structures for lightning strike protection. In this study, different CNT buckypapers were stretched to increase their alignment, and then subjected to conjugational cross-linking via chemical functionalization. The conjugationally cross-linked buckypapers (CCL-BPs) demonstrated higher electrical conductivity of up to 6200 S cm - 1, which is more than one order increase compared to the pristine buckypapers. The CCL-BPs also showed excellent doping stability in over 300 h in atmosphere and were resistant to degradation at elevated temperatures. The tensile strength of the stretched CCL-BPs reached 220 MPa, which is about three times that of pristine buckypapers. We attribute these property improvements to the effective and stable conjugational cross-links of CNTs, which can simultaneously improve the electrical conductivity, doping stability and mechanical properties. Specifically, the electrical conductivity increase resulted from improving the CNT alignment and inter-tube electron transport capability. The conjugational cross-links provide effective 3D conductive paths to increase the mobility of electrons among individual nanotubes. The stable covalent bonding also enhances the thermal stability and load transfer. The significant electrical and mechanical property improvement renders buckypaper a multifunctional material for various applications, such as conducting composites, battery electrodes, capacitors, etc.

Chen, I.-Wen Peter; Liang, Richard; Zhao, Haibo; Wang, Ben; Zhang, Chuck

2011-12-01

360

Highly conductive carbon nanotube buckypapers with improved doping stability via conjugational cross-linking.  

PubMed

Carbon nanotube (CNT) sheets or buckypapers have demonstrated promising electrical conductivity and mechanical performance. However, their electrical conductivity is still far below the requirements for engineering applications, such as using as a substitute for copper mesh, which is currently used in composite aircraft structures for lightning strike protection. In this study, different CNT buckypapers were stretched to increase their alignment, and then subjected to conjugational cross-linking via chemical functionalization. The conjugationally cross-linked buckypapers (CCL-BPs) demonstrated higher electrical conductivity of up to 6200 S cm( - 1), which is more than one order increase compared to the pristine buckypapers. The CCL-BPs also showed excellent doping stability in over 300 h in atmosphere and were resistant to degradation at elevated temperatures. The tensile strength of the stretched CCL-BPs reached 220 MPa, which is about three times that of pristine buckypapers. We attribute these property improvements to the effective and stable conjugational cross-links of CNTs, which can simultaneously improve the electrical conductivity, doping stability and mechanical properties. Specifically, the electrical conductivity increase resulted from improving the CNT alignment and inter-tube electron transport capability. The conjugational cross-links provide effective 3D conductive paths to increase the mobility of electrons among individual nanotubes. The stable covalent bonding also enhances the thermal stability and load transfer. The significant electrical and mechanical property improvement renders buckypaper a multifunctional material for various applications, such as conducting composites, battery electrodes, capacitors, etc. PMID:22072011

Chen, I-Wen Peter; Liang, Richard; Zhao, Haibo; Wang, Ben; Zhang, Chuck

2011-12-01

361

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

PubMed

Programmed cell death regulating protein motifs play an essential role in the development of an organism, its immune response, and disease-related cellular mechanisms. Among those motifs the BH3 domain of the BCL-2 family is found to be of crucial importance. Recent experiments showed how the isolated, otherwise unstructured BH3 peptide can be modified by a hydrocarbon linkage to regain function. We parametrized a reduced, dynamic model for the stability effects of such covalent cross-linking and confirmed that the model reproduces the reinforcement of the structural stability of the BH3 motif by cross-linking. We show that an analytically solvable model for thermostability around the native state is not capable of reproducing the stabilization effect. This points to the crucial importance of the peptide dynamics and the fluctuations neglected in the analytic model for the cross-linking system to function properly. This conclusion is supported by a thorough analysis of a simulated Go model. The resulting model is suitable for rational design of generic cross-linking systems in silicio. PMID:16674170

Hamacher, K; Hübsch, A; McCammon, J A

2006-04-28

362

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

NASA Astrophysics Data System (ADS)

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

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

2006-04-01

363

Reduced calcification of bioprostheses, cross-linked via an improved carbodiimide based method.  

PubMed

Glutaraldehyde fixation of bioprosthetic tissue has been used successfully for almost 40 years. However, it is generally recognized that glutaraldehyde fixation of bioprostheses is associated with the occurrence of calcification. Accordingly, many efforts have been undertaken to develop techniques for the fixation of bioprostheses, which will not lead to calcification. Here we describe a new improved carbodiimide based cross-linking method. Rather than cross-linking the tissue through its free primary amine groups, these groups were first blocked with butanal and the tissue was then cross-linked by means of carbodiimide activation of tissue carboxylic acid groups followed by a reaction with a poly(propylene glycol)bis 2-(aminopropyl) ether, (Jeffamine trade mark ). It was demonstrated that cross-linked porcine leaflets had a calcification of less than 1mg/g tissue after 8 weeks sub-dermal implantion in rats. Furthermore, aortic wall calcification was reduced to 50mg/g, compared to standard glutaraldehyde fixed tissue, which showed 120mg/g tissue calcification in the 8 weeks calcification model used. PMID:15142734

Everaerts, Frank; Torrianni, Mark; van Luyn, Marja; van Wachem, Pauline; Feijen, Jan; Hendriks, Mark

2004-11-01

364

Endogenous and enhanced oxidative cross-linking in wheat flour mill streams  

Technology Transfer Automated Retrieval System (TEKTRAN)

The oxidative cross-linking of arabinoxylan and protein polymers is partially responsible for variation in end-use quality of wheat flour; specifically, differences in batter viscosity as well as variation in bread and cookie quality. A better understanding of the variation in oxidative cross-linkin...

365

Hierarchically porous polymers from hyper-cross-linked block polymer precursors.  

PubMed

We report synthesis of hierarchically porous polymers (HPPs) consisting of micropores and well-defined 3D continuous mesopores by combination of hyper-cross-linking and block polymer self-assembly. Copolymerization of 4-vinylbenzyl chloride (VBzCl) with divinylbenzene (DVB) in the presence of polylactide (PLA) macro-chain-transfer agent produced a cross-linked block polymer precursor PLA-b-P(VBzCl-co-DVB) via reversible addition-fragmentation chain transfer polymerization. A nanoscopic bicontinuous morphology containing PLA and P(VBzCl-co-DVB) microdomains was obtained as a result of polymerization-induced microphase separation. While a basic treatment of the precursor selectively removed PLA to yield a reticulated mesoporous polymer, hyper-cross-linking of the precursor by FeCl3 generated micropores in the P(VBzCl-co-DVB) microdomain via Friedel-Crafts alkylation and simultaneously degraded PLA to produce the HPP containing micropores in the mesoporous framework. The mesopore size of the HPP could be precisely controlled from 6 to 15 nm by controlling the molar mass of PLA. We demonstrate acceleration in adsorption rate in the HPP compared to a hyper-cross-linked microporous polymer. PMID:25551291

Seo, Myungeun; Kim, Soobin; Oh, Jaehoon; Kim, Sun-Jung; Hillmyer, Marc A

2015-01-21

366

Multiple rounds of transcription by RNA polymerase II at covalently cross-linked templates.  

PubMed Central

An important control point for gene regulation is the frequency of initiations leading to different numbers of RNA polymerases simultaneously transcribing the same gene. To date, the only direct assay for multiple-round transcription by RNA polymerase II in vitro required G-free cassette-containing templates and GTP-free conditions and was thus restricted in application. Here we used instead templates containing a triplex-directed interstrand psoralen-DNA cross-link to block RNA polymerase II elongation at a specific location. Covalently cross-linked templates allowed simultaneous detection of both specific initiation and reinitiation with any combination of promoter and transcribed sequence. In reconstituted systems, identical stacking of RNA polymerases was observed when the first polymerase was halted by GTP deprivation at the end of a G-free cassette or by a covalent cross-link downstream of different transcribed sequences. In contrast to transcription of G-free cassettes, reinitiation was unaffected by the transcription factor SII on sequences containing all four nucleotides. In crude nuclear extracts, transcription of covalently cross-linked templates yielded a reinitiation pattern with a wider spacing than in more purified fractions, indicating that the elongation complexes from nuclear extract contained a different form of RNA polymerase II or a different complement of associated factors. PMID:9592165

Szentirmay, M N; Musso, M; Van Dyke, M W; Sawadogo, M

1998-01-01

367

Corneal collagen cross-linking in a late-onset graft infectious ulcer: a case report  

PubMed Central

Introduction Infectious keratitis following penetrating keratoplasty is a common postoperative complication. Intensive topical and systemic treatments do not always prevent the risk of graft failure. In this report we demonstrate the beneficial anti-microbial effect of corneal collagen cross-linking in a late-onset, sight-threatening, corneal graft ulcer. Case presentation A 57-year old Caucasian man underwent penetrating keratoplasty in his left eye, due to corneal bullosa after cataract extraction surgery. Twelve months after the penetrating keratoplasty, he visited our emergency service complaining of burning and foreign body sensation in his operated eye. Slit-lamp examination revealed a central, round-shaped ulcer of the graft. Due to poor response to the intensive topical antibiotic therapy, corneal collagen cross-linking was applied 3 days after admission, in an attempt to control the infection. Cultures indicated the predominance of methicillin-resistant Staphylococcus aureus infection. Five days after corneal collagen cross-linking treatment, the epithelium was completely re-epithelized, while the transparency of the transplanted cornea was gradually restored within the 12-month follow-up period. No relapses occurred. Conclusion Corneal collagen cross-linking seems to be a safe and effective therapeutic alternative in resistant cases of infectious keratitis following penetrating keratoplasty. PMID:24908420

2014-01-01

368

Role of collagen content and cross-linking in large pulmonary arterial stiffening after chronic hypoxia  

E-print Network

et al. 2003), cystic fibrosis (Fraser et al. 1999), and sleep apnea (Hiestand and Phillips 2008 collagen content and cross-linking and BAPN treatment prevented these increases. Similar trends were observed in Col1a1R/R mice except that collagen content further increased with BAPN treatment. Mechanical

Chesler, Naomi C.

369

Energy dissipation and recovery in a simple model with reversible cross-links  

NASA Astrophysics Data System (ADS)

Reversible cross-linking is a method of enhancing the mechanical properties of polymeric materials. The inspiration for this kind of cross-linking comes from nature, which uses this strategy in a large variety of biological materials to dramatically increase their toughness. Recently, first attempts were made to transfer this principle to technological applications. In this study, Monte Carlo simulations are used to investigate the effect of the number and the topology of reversible cross-links on the mechanical performance of a simple model system. Computational cyclic loading tests are performed, and the work to fracture and the energy dissipation per cycle are determined, which both increase when the density of cross-links is increased. Furthermore, a different topology of the bonds may increase the work to fracture by a factor of more than 2 for the same density. This dependence of the mechanical properties on the topology of the bonds has important implications on the self-healing properties of such systems, because only a fast return of the system to its unloaded state after release of the load ensures that the optimal topology may form.

Nabavi, S. Soran; Fratzl, Peter; Hartmann, Markus A.

2015-03-01

370

Association between collagen cross-links and trabecular microarchitecture properties of human vertebral bone  

E-print Network

the relationships among trabecular bone volume fraction (BV/TV), microarchitecture, collagen cross-link content collected from 51 recently deceased donors (54­95 years of age; 20 men and 30 women). Trabecular bone volume volume fraction (BV/TV ranges from 5% to 30%) [2­5]. With such a small amount of trabecular material

Paris-Sud XI, Université de

371

Structural and Viscoelastic Properties of Actin/Filamin Networks: Cross-Linked versus Bundled Networks  

E-print Network

Structural and Viscoelastic Properties of Actin/Filamin Networks: Cross-Linked versus Bundled as their viscoelastic properties in the linear and the nonlinear regime. INTRODUCTION Actin is a major component viscoelastic behavior of the network. The complex microstructure of such branched bundle networks may

Bausch, Andreas

372

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

SciTech Connect

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

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

2014-05-15

373

Cross-Linked Nanoporous Materials from Reactive and Multifunctional Block Polymers  

SciTech Connect

Polylactide-b-poly(styrene-co-2-hydroxyethylmethacrylate) (PLA-b-P(S-co-HEMA)) and polylactide-b-poly(styrene-co-2-hydroxyethylacrylate) (PLA-b-P(S-co-HEA)) were synthesized by combination of ring-opening polymerization and reversible addition-fragmentation chain transfer polymerization. {sup 1}H nuclear magnetic resonance spectroscopy and size exclusion chromatography data indicated that the polymerizations were controlled and that hydroxyl groups were successfully incorporated into the block polymers. The polymers were reacted with 4,4{prime}-methylenebis(phenyl isocyanate) (MDI) to form the corresponding cross-linked materials. The materials were annealed at 150 C to complete the coupling reaction. Robust nanoporous materials were obtained from the cross-linked polymers by treatment with aqueous base to hydrolyze the PLA phase. Small-angle X-ray scattering study combined with scanning electron microscopy showed that MDI-cross-linked PLA-b-P(S-co-HEMA)/PLA-b-P(S-co-HEA) can adopt lamellar, hexagonally perforated lamellar, and hexagonally packed cylindrical morphologies after annealing. In particular, the HPL morphology was found to evolve from lamellae due to increase in volume fraction of PS phase as MDI reacted with hydroxyl groups. The reaction also kinetically trapped the morphology by cross-linking. Bicontinuous morphologies were also observed when dibutyltin dilaurate was added to accelerate reaction between the polymer and MDI.

Seo, Myungeun; Amendt, Mark A.; Hillmyer, Marc A. (UMM)

2012-10-10

374

DNA-Protein Cross-Linking by 1,2,3,4-Diepoxybutane  

PubMed Central

1,2,3,4-Diepoxybutane (DEB) is a strongly genotoxic diepoxide hypothesized to be the ultimate carcinogenic metabolite of the common industrial chemical and environmental carcinogen 1,3-butadiene. DEB is a bis-electrophile capable of cross-linking cellular biomolecules to form DNA-DNA and DNA-protein cross-links (DPCs), which are thought to play a central role in its biological activity. Previous studies with recombinant proteins have shown that the biological outcomes of DEB-induced DPCs are strongly influenced by protein identities. The present work combines affinity capture methodology with mass spectrometry-based proteomics and immunological detection to identify the proteins which form DPCs in nuclear extracts from human cervical carcinoma (HeLa) cells. We identified 39 human proteins that form covalent DPCs in the presence of DEB. DNA-protein cross-linking efficiency following treatment with 25 mM DEB was 2–12%, depending on protein identity. HPLC-ESI+-MS/MS analysis of the total proteolytic digests of cross-linked proteins revealed the presence of 1-(S-cysteinyl)-4-(guan-7-yl)-2,3-butanediol conjugates, suggesting that DEB forms DPCs between cysteine thiols within proteins and the N-7 guanine positions within DNA. PMID:20666492

Michaelson-Richie, Erin D.; Loeber, Rachel L.; Codreanu, Simona G.; Ming, Xun; Liebler, Daniel C.; Campbell, Colin; Tretyakova, Natalia Y.

2010-01-01

375

Polarization and charge trapping in cross-linked polyethylene (XLPE) cables AC aged in humid environment  

Microsoft Academic Search

The authors report the results of TSDC (thermally stimulated discharge current) and TTC measurements of XLPE (cross-linked polyethylene) cables AC aged in water for a period up to 4000 h. Absorption and resorption current measurements were also performed during the aging to get more information about the penetration of water and ions into the cable. The results suggest that initially

A. Svatik; P. C. N. Scarpa; D. K. Das-Gupta; D. E. Cooper

1992-01-01

376

Self-assembly of biopolymeric structures below the threshold of random cross-link percolation.  

PubMed Central

Self-assembly of extended structures via cross-linking of individual biomolecules often occurs in solutions at concentrations well below the estimated threshold for random cross-link percolation. This requires solute-solute correlations. Here we study bovine serum albumin. Its unfolding causes the appearance of an instability region of the sol, not observed for native bovine serum albumin. As a consequence, spinodal demixing of the sol is observed. The thermodynamic phase transition corresponding to this demixing is the determinative symmetry-breaking step allowing the subsequent occurrence of (correlated) cross-linking and its progress up to the topological phase transition of gelation. The occurrence of this sequence is of marked interest to theories of spontaneous symmetry-breaking leading to morphogenesis, as well as to percolation theories. The present results extend the validity of conclusions drawn from our previous studies of other systems, by showing in one single case, system features that we have hitherto observed separately in different systems. Time-resolved experimental observations of the present type also bring kinetic and diffusional processes and solute-solvent interactions into the picture of cross-link percolation. Images FIGURE 3 PMID:8770227

San Biagio, P L; Bulone, D; Emanuele, A; Palma, M U

1996-01-01

377

Cytotoxicity and internalization of Pluronic micelles stabilized by core cross-linking.  

PubMed

A UV-cross-linkable agent was incorporated and polymerized in Pluronic micelle core to create an interpenetrating polymer network (IPN) of poly(pentaerythritol tetraacrylate). This stabilization prevented micelle disruption below the critical micelle temperature (CMT) and concentration (CMC), while maintaining the integrity of the PEO corona and the hydrophobic properties of the PPO core. The prepared stabilized spherical micelles of Pluronic P94 and F127 presented hydrodynamic diameters ranging from 40 to 50 nm. The stability of cross-linked Pluronic micelles at 37 °C in the presence of serum proteins was studied and no aggregation of the micelles was observed, revealing the colloidal stability of the system. Cytotoxicity experiments in NIH/3T3 mouse fibroblasts revealed that the presence of the cross-linking agent did not induce any further toxicity in comparison to the respective pure polymer solutions. Furthermore, stabilized micelles of Pluronic P94 were shown to be less toxic than the polymer itself. A hydrophobic fluorescent probe (Nile red) was absorbed in the cross-linked core of pre-stabilized micelles to mimic the incorporation of a poorly water-soluble drug, and the internalization and intracellular localization of Nile red was studied by confocal microscopy at different incubation times. Overall, the results indicate that Pluronic micelles stabilized by core cross-linking are capable of delivering hydrophobic components physically entrapped in the micelles, thus making them a potential candidate as a delivery platform for imaging or therapy of cancer. PMID:25307996

Arranja, Alexandra; Schroder, André P; Schmutz, Marc; Waton, Gilles; Schosseler, François; Mendes, Eduardo

2014-12-28

378

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

NASA Astrophysics Data System (ADS)

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.

Ding, Rui

379

Encapsulation and controlled release of hydrophilic pesticide in shell cross-linked nanocapsules containing aqueous core.  

PubMed

In this study, amphiphilic biocopolymers, synthesized by mixing azidobenzaldehyde (Az) and an aqueous solution of carboxymethyl chitosan (CMCS), which self-assemble into nanocapsules with a aqueous core (ACN) in aqueous media followed by photo-cross-linking to obtain shell cross-linked nanocapsules, were used to develop a controlled release pesticide system. The system was characterized by TEM and DLS. Its encapsulation efficiency was determined. The obtained result showed that it is efficient to encapsulate methomyl reaching encapsulation efficiency as high as 90% in an aqueous medium at pH 4.0, which is mainly attributed to the hydrogen bonding adsorption between methomyl molecules and the inner surface of nanocapsules. Release profiles of methomyl from methomyl-loaded nanocapsules in an aqueous solution at pH 6.0 were shown to be diffusion controlled with a half-release time (t(½)) of 36.3-69.5h from different samples. The shell cross-linking and its degree of cross-linking are assumed to be responsible for this diffusion behavior. The insecticidal activity test in laboratory showed that the control efficacy of methomyl-loaded nanocapsules against the armyworm larvae was significantly superior to the original. The relative control efficacy still maintained 100% over 7 days. PMID:24406673

Sun, Chuxiang; Shu, Ke; Wang, Wei; Ye, Zhao; Liu, Ting; Gao, Yuxiang; Zheng, Hua; He, Guanghua; Yin, Yihua

2014-03-10

380

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

Microsoft Academic Search

The use of biological materials in the construction of bioprostheses requires the application of different chemical or physical procedures to improve the mechanical performance of the material without producing any undesirable effects. A number of cross-linking methods have been tested in biological tissues composed mainly of collagen. The basis for most of them is the use of glutaraldehyde (GA), which

E Jorge-Herrero; P Fernández; J Turnay; N Olmo; P Calero; R Garc??a; I Freile; J. L Castillo-Olivares

1999-01-01

381

Reflective confocal laser scanning microscopy and nonlinear microscopy of cross-linked rabbit cornea  

NASA Astrophysics Data System (ADS)

Cross-linking of the cornea with application of Ribovlavin and UV-A light is an evolving clinical treatment of the eye disease keratoconus. Despite the positive clinical track record of corneal cross-linking, the complex wound healing process after the treatment is still under investigation. In this study an animal model was used to clarify the state of wound healing 5 weeks after treatment. Cross-linked rabbit corneae were imaged with reflective confocal laser scanning and nonlinear microscopy, namely second harmonic imaging microscopy (SHIM) and two-photon excited autofluorescence. First results show that the NAD(P) H-autofluorescence of the corneal keratocytes and their scattering signal still show a signature of the treatment five weeks after the cross-linking procedure. The SHIM signals show the structural morphology of the fibrous collagen sheets in the stroma of the cornea. SHIM detected in the forward direction differs substantially from backward SHIM, but no signature of treatment was found in both detection channels of the SHIM signal.

Krueger, Alexander; Hovakimyan, Marina; Ramirez, Diego F.; Stachs, Oliver; Guthoff, Rudolf F.; Heisterkamp, Alexander

2009-07-01

382

Prestressed F-actin networks cross-linked by hinged filamins replicate mechanical properties of cells  

Microsoft Academic Search

We show that actin filaments, shortened to physiological lengths by gelsolin and cross-linked with recombinant human filamins (FLNs), exhibit dynamic elastic properties similar to those reported for live cells. To achieve elasticity values of comparable magnitude to those of cells, the in vitro network must be subjected to external prestress, which directly controls network elasticity. A molecular requirement for the

M. L. Gardel; F. Nakamura; J. H. Hartwig; J. C. Crocker; T. P. Stossel; D. A. Weitz

2006-01-01

383

Prestressed F-actin networks cross-linked by hinged filamins replicate mechanical properties of cells  

E-print Network

magnitude to those of cells, the in vitro network must be subjected to external prestress, which directlyPrestressed F-actin networks cross-linked by hinged filamins replicate mechanical properties yet resist externally or internally generated high shear forces. cytoskeleton cell mechanics nonlinear

Gardel, Margaret

384

Effect of Microwave Irradiation on the Cross-Linking of Polyvinyl Alcohol  

Microsoft Academic Search

The possibility of dehydration (cross-linking) of polyvinyl alcohol upon microwave irradiation of thin polymer films was examined. The properties of polyvinyl alcohol samples treated by convection heating and irradiation were compared. Immobilization of polyvinyl alcohol on polymer matrices by microwave irradiation was studied.

N. V. Petrova; A. M. Evtushenko; I. P. Chikhacheva; V. P. Zubov; I. V. Kubrakova

2005-01-01

385

Reconstitution of Peptidoglycan Cross-Linking Leads to Improved Fluorescent Probes of Cell Wall Synthesis  

E-print Network

-linking activity of penicillin-binding proteins (PBPs) that assemble peptidoglycan in cells has not been glycosyl- transferases polymerize Lipid II into glycan strands and enzymes known as penicillin-binding proteins (PBPs) cross- link and process the peptide side chains to produce mature PG.2 Because PG is highly

Rudner, David

386

Synthesis, Enhanced Fusogenicity, and Solid State NMR Measurements of Cross-Linked HIV-1 Fusion Peptides  

E-print Network

Synthesis, Enhanced Fusogenicity, and Solid State NMR Measurements of Cross-Linked HIV-1 Fusion or trimers. C-terminal trimerization is their likely topology in the fusogenic form of the intact gp41 protein. The fusogenicity of the peptides was then measured in an intervesicle lipid mixing assay

Weliky, David

387

In vivo actin cross-linking induced by Vibrio cholerae type VI secretion system is associated  

E-print Network

with intestinal inflammation Amy T. Ma and John J. Mekalanos1 Department of Microbiology and Molecular Genetics uptake of bacteria into host cells. VgrG-1-induced actin cross-linking impaired phagocytic activity activation and immune cell infiltration in the intestinal lumen. The T6SS-dependent inflammatory response

Mekalanos, John

388

CHEMISTRY AND PHYSICAL PROPERTIES OF MELT PROCESSED- AND SOLUTION-CROSS LINKED CORN ZEIN  

Technology Transfer Automated Retrieval System (TEKTRAN)

Corn zein was cross linked with glutaraldehyde (GDA) and with glacial acetic acid (HAc) as catalyst with the objective to enhance the mechanical properties of poured films which were compared with the physical properties of compression molded tensile bars from melt processed zein with GDA. A reacti...

389

Digestibility of transglutaminase cross-linked caseinate versus native caseinate in an in vitro multicompartmental model simulating young child and adult gastrointestinal conditions.  

PubMed

Aim of this study was to investigate the digestion of transglutaminase cross-linked caseinate (XLC) versus native caseinate (NC) in solution and in cheese spread under digestive conditions for adults and children mimicked in a gastrointestinal model. Samples were collected for gel electrophoresis and nitrogen analysis. The results showed no relevant differences between XLC and NC for total and ?-amino nitrogen in digested fraction under adult and child conditions. However, the rate of digestion was depending on the food matrix. Gel electrophoresis showed the gastric breakdown of XLC without formation of pepsin resistant peptides larger than 4 kDa. NC was slowly digested in the stomach with formation of pepsin resistant fragments and was still detectable in the stomach after 90 min. In the small intestine the proteins were rapidly digested. XLC was digested to small peptides, while NC was resistant against pepsin digestion under gastric conditions of adults and children. PMID:23822864

Havenaar, Robert; de Jong, Aard; Koenen, Marjorie E; van Bilsen, Jolanda; Janssen, Armand M; Labij, Erik; Westerbeek, Hans J M

2013-08-01

390

Single-molecule imaging of hyaluronan in human synovial fluid  

NASA Astrophysics Data System (ADS)

Human synovial fluid contains a high concentration of hyaluronan, a high molecular weight glycosaminoglycan that provides viscoelasticity and contributes to joint lubrication. In osteoarthritis synovial fluid, the concentration and molecular weight of hyaluronan decrease, thus impairing shock absorption and lubrication. Consistently, substitution of hyaluronan (viscosupplementation) is a widely used treatment for osteoarthritis. So far, the organization and dynamics of hyaluronan in native human synovial fluid and its action mechanism in viscosupplementation are poorly characterized at the molecular level. Here, we introduce highly sensitive single molecule microscopy to analyze the conformation and interactions of fluorescently labeled hyaluronan molecules in native human synovial fluid. Our findings are consistent with a random coil conformation of hyaluronan in human synovial fluid, and point to specific interactions of hyaluronan molecules with the synovial fluid matrix. Furthermore, single molecule microscopy is capable of detecting the breakdown of the synovial fluid matrix in osteoarthritis. Thus, single molecule microscopy is a useful new method to probe the structure of human synovial fluid and its changes in disease states like osteoarthritis.

Kappler, Joachim; Kaminski, Tim P.; Gieselmann, Volkmar; Kubitscheck, Ulrich; Jerosch, Jörg

2010-11-01

391

Ratiometric fluorescent biosensor for hyaluronidase with hyaluronan as both nanoparticle scaffold and substrate for enzymatic reaction.  

PubMed

Hyaluronidases (HAase) are involved in various physiological and pathological processes and have been reported as urinary marker for bladder cancer. In this study, a novel ratiometric fluorescent sensing system based on both aggregation-induced emission (AIE) and aggregation-induced quenching (ACQ) was developed to quantitatively assess hyaluronidase level. First, a tetraphenylethylene derivative with positive charges (TPE-2N(+), typical AIE molecule) at both ends and an anthracene derivative with positive charge at one end (AN-N(+), typical ACQ molecule) was synthesized. These two positively charged compounds were then mixed with a negatively charged hyaluronan (HA), which induced the aggregation of the compounds as well as the nanoparticles formation as a result of electrostatic complexation, with TPE-2N(+) acting as cross-linking agent. The aggregation also caused the efficient quenching of the emission of AN-N(+) due to ACQ effect, as well as the fluorescence enhancement of TPE-2N(+) due to AIE effect. In the presence of HAase, the enzymatic reaction led to the degradation of HA and triggered disassembly of the nanoparticles; as a result, the emission of AN-N(+) was restored and that of TPE-2N(+) was suppressed. This fluorescence variation affords the system a robust ratiometric biosensor for HAase, and the ratio of fluorescence intensity for AN-N(+) (I414) to that for TPE-2N(+) (I474) can be used as the sensing signal for detecting HAase activity. In this system, hyaluronan serves not only as the scaffold for nanoparticle formation but also as the substrate for enzymatic reaction. This assay system is operable in aqueous media with very low detection limit of 0.0017 U/mL and is capable of detecting HAase in biological fluids such as serum and urine. This strategy may provide a new and effective approach for developing other enzyme assays. PMID:25068551

Xie, Huafei; Zeng, Fang; Wu, Shuizhu

2014-09-01

392

Expression of hyaluronan and the hyaluronan-binding proteoglycans neurocan, aggrecan, and versican by neural stem cells and neural cells derived from embryonic stem cells  

Microsoft Academic Search

We have examined the expression and localization patterns of hyaluronan and hyaluronan-binding chondroitin sulfate proteoglycans in neural stem cells and differentiated neural cells derived from mouse embryonic stem cells. Expression of proteoglycans and hyaluronan was weak in the SSEA1-positive embryonic stem cells but increased noticeably after retinoic acid induction to nestin-positive neural stem cells. After subsequent plating, the hyaluronan-binding chondroitin

Mary Abaskharoun; Marie Bellemare; Elizabeth Lau; Richard U. Margolis

2010-01-01

393

Tissue-specific distribution of cross-linked somatostatin receptor proteins in the rat.  

PubMed Central

Pharmacological studies have suggested that the somatostatin (SS) receptor is heterogeneous and exhibits SS-14-and SS-28-selective subtypes. Whether such subtypes arise from molecular heterogeneity of the receptor protein has not been definitively established. Previous reports characterizing the molecular properties of the SS receptor by the cross-linking approach have yielded divergent size estimates ranging from 27 kDa to 200 kDa. In order to resolve this discrepancy, as well as to determine whether SS-14 and SS-28 interact with specific receptor proteins, we have cross-linked radioiodinated derivatives of [125I-Tyr11]SS-14 (T*-SS-14) and [Leu8,D-Trp22,125I-Tyr25]SS-28 (LTT*-SS-28) to membrane SS receptors in rat brain, pituitary, exocrine pancreas and adrenal cortex using a number of chemical and photoaffinity cross-linking agents. The labelled cross-linked receptor proteins were analysed by SDS/PAGE under reducing conditions followed by autoradiography. Our findings indicate that the pattern of specifically labelled cross-linked SS receptor proteins is sensitive to the concentration of chemical cross-linking agents such as disuccinimidyl suberate and dithiobis-(succinimidyl propionate). Labelled high-molecular-mass complexes of cross-linked receptor-ligand proteins were observed only when high concentrations of these cross-linkers were employed. Using optimized low concentrations of cross-linkers, however, two major labelled bands of 58 +/- 3 kDa and 27 +/- 2 kDa were detected. These two bands were identified as specifically labelled SS receptor proteins subsequent to cross-linking with a number of photoaffinity cross-linking agents as well. We demonstrate here that the 58 kDa protein is the major SS receptor protein in the rat pituitary, adrenal and exocrine pancreas, whereas the 27 kDa moiety represents the principal form in the brain. Additionally, the presence of a minor specifically labelled band of 32 kDa was detected uniquely in the brain, and a minor labelled protein of 42 kDa was observed in the pancreas. The labelling pattern obtained with LTT*-SS-28 was identical to that observed with T*-SS-14. Labelling of the 27 kDa band by either ligand was inhibited by SS-14 and SS-28 in a dose-dependent manner. Densitometric quantification showed that SS-14 exhibited greater than 2-fold greater potency than SS-28 for inhibiting the labelling of the 27 kDa species. These findings emphasize the need for careful interpretation of cross-linking data obtained for SS receptors, and provide evidence for molecular heterogeneity and for a tissue-specific distribution of the two principal SS receptor proteins. Images Fig. 1. Fig. 2. Fig. 3. Fig. 4. Fig. 5. Fig. 6. PMID:1312325

Srikant, C B; Murthy, K K; Patel, Y C

1992-01-01

394

Dextrin and Poly(acrylic acid)-Based Biodegradable, Non-Cytotoxic, Chemically Cross-Linked Hydrogel for Sustained Release of Ornidazole and Ciprofloxacin.  

PubMed

Herein, novel biodegradable, stimulus-responsive, chemically cross-linked and porous hydrogel has been synthesized to evaluate its applicability as an efficient carrier for sustained release of ornidazole and ciprofloxacin. The cross-linked hydrogel (c-Dxt/pAA) has been developed from dextrin and poly(acrylic acid) using N,N'-methylene bis(acrylamide) cross-linker via Michael-type addition reaction. With the variation of reaction parameters, various c-Dxt/pAA hydrogels have been synthesized to optimize the best one. c-Dxt/pAA hydrogel has been characterized using various physicochemical characterization techniques. The hydrogel demonstrates significant pH and temperature sensitivity. Gel characteristics and gel kinetics have been performed through the measurement of rheological parameters. The hydrogel shows noncytotoxic behavior toward human mesenchymal stem cells. Biodegradation study predicts that c-Dxt/pAA is degradable in nature. The in vitro release of ornidazole and ciprofloxacin suggests that the hydrogel released both the drugs in a controlled manner with extensive stability up to 3 months. The results suggest that c-Dxt/pAA is probably a promising candidate for controlled release of ornidazole and ciprofloxacin. PMID:25654747

Das, Dipankar; Ghosh, Paulomi; Dhara, Santanu; Panda, Asit Baran; Pal, Sagar

2015-03-01

395

Evaluation of the Efficacy of Excimer Laser Ablation of Cross-Linked Porcine Cornea  

PubMed Central

Background Combination of riboflavin/UVA cross-linking (CXL) and excimer laser ablation is a promising therapy for treating corneal ectasia. The cornea is strengthened by cross-linking, while the irregular astigmatism is reduced by laser ablation. This study aims to compare the efficacy of excimer laser ablation on porcine corneas with and without cross-linking. Methods and Findings The porcine cornea was de-epithelialized and treated with 0.1% riboflavin solution for 30 minutes. A half of the cornea was exposed to UVA-radiation for another 30 minutes while the controlled half of the cornea was protected from the UVA using a metal shield. Photo therapeutic keratectomy (PTK) was then performed on the central cornea. Corneal thickness of 5 paired locations on the horizontal line, ±0.5, ±1.0, ±1.5, ±2.0, and ±2.5 mm from the central spot, were measured using optical coherence tomography prior to and after PTK. The ablation depth was then determined by the corneal thickness. There was a 9% difference (P<0.001) in the overall ablation depth between the CXL-half corneas (158±22 µm) and the control-half corneas (174±26 µm). The ablation depths of all 5 correspondent locations on the CXL-half were significantly smaller (P<0.001). Conclusion The efficacy of the laser ablation seems to be lower in cross-linked cornea. Current ablation algorithms may need to be modified for cross-linked corneas. PMID:23056269

Chen, Shihao; Li, Yini; Stojanovic, Aleksander; Zhang, Jia; Wang, Yibo; Wang, Qinmei; Seiler, Theo

2012-01-01

396

Temporal changes in collagen cross-links in spontaneous articular cartilage repair  

PubMed Central

Objective Little is known about how the biochemical properties of collagen change during tissue regeneration following cartilage damage. In the current study, temporal changes in cartilage repair tissue biochemistry were assessed in a rabbit osteochondral defect. Design Bilateral full thickness 3mm osteochondral trochlear groove defects were created in 54 adult male skeletally mature New Zealand white rabbits and tissue repair monitored over 16 weeks. Collagen content, cross-links, lysyl hydroxylation, gene expression, histological grading, and FTIR analyses were performed at 2, 4, 6, 8, 12, and 16 weeks. Results Defect fill occurred at ~4 weeks post-injury, however, histological grading showed that the repair tissue never became normal, primarily due to the presence of fibrocartilage. Gene expression levels of Col1a1 and Col1a2 were higher in the defect compared to adjacent regions. Collagen content in the repair tissue reached the level of normal cartilage at 6 weeks, but it took 12 weeks for the extent of lysine hydroxylation to return to normal. Divalent immature cross-links markedly increased in the early stages of repair. Though the levels gradually diminished thereafter, they never returned to the normal levels. The mature cross-link, pyridinoline, gradually increased with time and nearly reached normal levels by week 16. Infrared imaging data of protein content paralleled the biochemical data. However, collagen maturity, a parameter previously shown to reflect collagen cross-link ratios in bone, did not correlate with the biochemical determination of cross-links in the repair tissue.. Conclusion Collagen biochemical data could provide markers for clinical monitoring in a healing defect. PMID:23272271

Masahiko, Terajima; Damle, Sheela; Penmatsa, Madhuri; West, Paul; Yang, Xu; Bostrom, Mathias; Hidaka, Chisa; Yamauchi, Mitsuo; Pleshko, Nancy

2012-01-01

397

Hybrid sol-gel optical materials  

DOEpatents

Hybrid sol-gel materials comprise silicate sols cross-linked with linear polysilane, polygermane, or poly(silane-germane). The sol-gel materials are useful as optical identifiers in tagging and verification applications and, in a different aspect, as stable, visible light transparent non-linear optical materials. Methyl or phenyl silicones, polyaryl sulfides, polyaryl ethers, and rubbery polysilanes may be used in addition to the linear polysilane. The linear polymers cross-link with the sol to form a matrix having high optical transparency, resistance to thermooxidative aging, adherence to a variety of substrates, brittleness, and a resistance to cracking during thermal cycling.

Zeigler, J.M.

1993-04-20

398

Hybrid sol-gel optical materials  

DOEpatents

Hybrid sol-gel materials comprise silicate sols cross-linked with linear polysilane, polygermane, or poly(silane-germane). The sol-gel materials are useful as optical identifiers in tagging and verification applications and, in a different aspect, as stable, visible light transparent non-linear optical materials. Methyl or phenyl silicones, polyaryl sulfides, polyaryl ethers, and rubbery polysilanes may be used in addition to the linear polysilane. The linear polymers cross-link with the sol to form a matrix having high optical transparency, resistance to thermooxidative aging, adherence to a variety of substrates, brittleness, and a resistance to cracking during thermal cycling.

Zeigler, John M. (Albuquerque, NM)

1993-01-01

399

Hybrid sol-gel optical materials  

DOEpatents

Hybrid sol-gel materials comprise silicate sols cross-linked with linear polysilane, polygermane, or poly(silane-germane). The sol-gel materials are useful as optical identifiers in tagging and verification applications and, in a different aspect, as stable, visible light transparent non-linear optical materials. Methyl or phenyl silicones, polyaryl sulfides, polyaryl ethers, and rubbery polysilanes may be used in addition to the linear polysilane. The linear polymers cross-link with the sol to form a matrix having high optical transparency, resistance to thermooxidative aging, adherence to a variety of substrates, brittleness, and a resistance to cracking during thermal cycling.

Zeigler, John M. (Albuquerque, NM)

1992-01-01

400

Use of Proteinase K Nonspecific Digestion for Selective and Comprehensive Identification of Interpeptide Cross-links: Application to Prion Proteins*  

PubMed Central

Chemical cross-linking combined with mass spectrometry is a rapidly developing technique for structural proteomics. Cross-linked proteins are usually digested with trypsin to generate cross-linked peptides, which are then analyzed by mass spectrometry. The most informative cross-links, the interpeptide cross-links, are often large in size, because they consist of two peptides that are connected by a cross-linker. In addition, trypsin targets the same residues as amino-reactive cross-linkers, and cleavage will not occur at these cross-linker-modified residues. This produces high molecular weight cross-linked peptides, which complicates their mass spectrometric analysis and identification. In this paper, we examine a nonspecific protease, proteinase K, as an alternative to trypsin for cross-linking studies. Initial tests on a model peptide that was digested by proteinase K resulted in a “family” of related cross-linked peptides, all of which contained the same cross-linking sites, thus providing additional verification of the cross-linking results, as was previously noted for other post-translational modification studies. The procedure was next applied to the native (PrPC) and oligomeric form of prion protein (PrP?). Using proteinase K, the affinity-purifiable CID-cleavable and isotopically coded cross-linker cyanurbiotindipropionylsuccinimide and MALDI-MS cross-links were found for all of the possible cross-linking sites. After digestion with proteinase K, we obtained a mass distribution of the cross-linked peptides that is very suitable for MALDI-MS analysis. Using this new method, we were able to detect over 60 interpeptide cross-links in the native PrPC and PrP? prion protein. The set of cross-links for the native form was used as distance constraints in developing a model of the native prion protein structure, which includes the 90–124-amino acid N-terminal portion of the protein. Several cross-links were unique to each form of the prion protein, including a Lys185–Lys220 cross-link, which is unique to the PrP? and thus may be indicative of the conformational change involved in the formation of prion protein oligomers. PMID:22438564

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

2012-01-01

401

Hyaluronan and synovial joint: function, distribution and healing  

PubMed Central

Synovial fluid is a viscous solution found in the cavities of synovial joints. The principal role of synovial fluid is to reduce friction between the articular cartilages of synovial joints during movement. The presence of high molar mass hyaluronan (HA) in this fluid gives it the required viscosity for its function as lubricant solution. Inflammation oxidation stress enhances normal degradation of hyaluronan causing several diseases related to joints. This review describes hyaluronan properties and distribution, applications and its function in synovial joints, with short review for using thiol compounds as antioxidants preventing HA degradations under inflammation conditions. PMID:24678248

2013-01-01

402

Keratinocyte growth factor stimulates migration and hyaluronan synthesis in the epidermis by activation of keratinocyte hyaluronan synthases 2 and 3.  

PubMed

Keratinocyte growth factor (KGF) activates keratinocyte migration and stimulates wound healing. Hyaluronan, an extracellular matrix glycosaminoglycan that accumulates in wounded epidermis, is known to promote cell migration, suggesting that increased synthesis of hyaluronan might be associated with the KGF response in keratinocytes. Treatment of monolayer cultures of rat epidermal keratinocytes led to an elongated and lifted cell shape, increased filopodial protrusions, enhanced cell migration, accumulation of intermediate size hyaluronan in the culture medium and within keratinocytes, and a rapid increase of hyaluronan synthase 2 (Has2) mRNA, suggesting a direct influence on this gene. In stratified, organotypic cultures of the same cell line, both Has2 and Has3 with the hyaluronan receptor CD44 were up-regulated and hyaluronan accumulated in the epidermis, the spinous cell layer in particular. At the same time the expression of the early differentiation marker keratin 10 was inhibited, whereas filaggrin expression and epidermal permeability were less affected. The data indicate that Has2 and Has3 belong to the targets of KGF in keratinocytes, and support the idea that enhanced hyaluronan synthesis acts an effector for the migratory response of keratinocytes in wound healing, whereas it may delay keratinocyte terminal differentiation. PMID:14506240

Karvinen, Susanna; Pasonen-Seppänen, Sanna; Hyttinen, Juha M T; Pienimäki, Juha-Pekka; Törrönen, Kari; Jokela, Tiina A; Tammi, Markku I; Tammi, Raija

2003-12-01

403

The study of cell-death proteins in the outer mitochondrial membrane by chemical cross-linking.  

PubMed Central

Chemical cross-linking was used to study the interactions of the anti-cell-death protein Bcl2 with other proteins in the outer mitochondrial membrane. Cross-linking of mitochondrial surface proteins produced a large Bcl2-containing complex (>200 kDa), and a Bcl2-derived peptide was shown to cross-link specifically with a mitochondrial protein identified by immunoblotting as Raf-1 kinase. PMID:9230109

Ali, S T; Coggins, J R; Jacobs, H T

1997-01-01

404

Effect of heparin coating on epichlorohydrin cross-linked chitosan microspheres on the adsorption of copper (II) ions  

Microsoft Academic Search

Epichlorohydrin cross-linked chitosan microspheres (CS) and chitosan–heparin polyelectrolyte complex microspheres (CSH) were used in the adsorption of copper (II) ions in aqueous solution. The chitosan microspheres were prepared by the phase inversion method. The use of a cross-linking agent improved the resistance to acidic medium. Polyelectrolyte complex microspheres were prepared by impregnating heparin in cross-linked chitosan microspheres. The microspheres were

Thalia C. Coelho; Rogério Laus; Antonio S. Mangrich; Valfredo T. de Fávere; Mauro C. M. Laranjeira

2007-01-01

405

Effect of electron-irradiation on cross-link density and crystalline structure of low- and high-density polyethylene  

Microsoft Academic Search

Low- and high-density polyethylenes (LDPE and HDPE) were cross-linked in solid state by electron beam irradiation. Molar mass between cross-link joints, Mc, and cross-link density,?, were calculated using rubber elasticity theory and hot set data. The results showed that the ? and creep modulus increased and creep strain and Mc decreased with increasing irradiation dose. As compared to HDPE, the

H. A. a Khonakdar; S.H.b Jafari; U. c Wagenknecht; D. c Jehnichen

2006-01-01

406

Emission characteristics of laser dyes C1 and Rh6G in cross-linked polyvinyl alcohol solutions  

Microsoft Academic Search

The lifetimes and the relative quantum yields for fluorescence of two laser dyes Coumarin 1 and Rhodamine 6G have been determined\\u000a in cross-linked polyvinyl alcohol matrix. The cross-linking has been achieved using gamma radiation. The relative fluorescence\\u000a quantum yields of the dyes increased with increasing cross-linking of the polymer, but the fluorescence lifetimes remained\\u000a unchanged within experimental error. The results

K. I. Priyadarsini; T. P. Balan; C. Gopinathan

1993-01-01

407

Immobilization of Quantum Dots in the Photo-Cross-Linked Poly(ethylene glycol)-Based Hydrogel  

SciTech Connect

An inorganic/organic composite hybrid nano-system has been successfully synthesized in which nanocrystalline quantum dots (QDs) were effectively immobilized within a photo-cross-linked poly(ethylene glycol) hydrogel. Organometallic synthesis of CdTe and CdSe QDs was accomplished with a trioctylphosphine oxide (TOPO) cap. Replacing the TOPO cap with mercaptoacetic acid groups further yielded modified water-soluble nanocrystals. The immobilization of these functionalized CdTe and CdSe QDs within PEG hydrogel network has been shown to be effective through utilization of physical trapping. The CdTe and CdSe QDs had a particle diameter of 4.5 and 2.5-6.0 nm, respectively. The most efficiently trapped QDs had a size of 4.5 nm or larger. Particle size determination was derived from spectroscopic (absorption and photoluminescence) and high-resolution transmission electron microscopic techniques. These QD-immobilized gel systems demonstrated photoluminescence characteristics unique to semiconductor QD nanocrystals. The authors have envisioned the utilization of the unique photophysical properties of this material as a convenient signal transducer for in vivo biosensing. The most promising application of the described QD/PEG-NC hybrid system is in the fields of in vivo fluorescence microscopy and as a monitoring system for drug delivery and wound healing.

Gattas-Asfura, Kerim M.(Miami University) [Miami University; Zheng, Yujun (Miami University) [Miami University; Micic, Miodrag (BATTELLE (PACIFIC NW LAB)) [BATTELLE (PACIFIC NW LAB); Snedaker, Michael J.(Miami University) [Miami University; Ji, Xiaojun (Miami University) [Miami University; Sui, Guodong (Miami University) [Miami University; Orbulescu, Jhony (Miami University) [Miami University; Andreopoulos, Fotios M.(Miami University) [Miami University; Pham, Si M.(Miami University) [Miami University; Wang, Chong M.(BATTELLE (PACIFIC NW LAB)) [BATTELLE (PACIFIC NW LAB)

2003-09-25

408

Preparation and characterization of highly cross-linked polyimide aerogels based on polyimide containing trimethoxysilane side groups.  

PubMed

In this study, highly cross-linked and completely imidized polyimide aerogels were prepared from polyimide containing trimethoxysilane side groups, which was obtained as the condensation product of polyimide containing acid chloride side groups and 3-aminopropyltrimethoxysilane. After adding water and acid catalyst, the trimethoxysilane side groups hydrolyzed and condensed one another, and a continuous increase in the complex viscosities of the polyimide solutions with time was observed. The formed polyimide gels were dried by freeze-drying from tert-butyl alcohol to obtain polyimide aerogels, which consisted of a three-dimensional network of polyimide fibers tangled together. By varying the solution concentration of the polyimide containing trimethoxysilane side groups, polyimide aerogels with different densities (ranging from 0.19 to 0.42 g/cm(3)) were obtained. The resulting polyimide aerogels had small pore diameter (ranging from 20.7 to 58.3 nm), high surface area (ranging from 310 to 344 m(2)/g), high 5% weight loss temperature in air (at about 440 °C), and an excellent mechanical property. In addition, the glass transition temperature (349 °C) of the polyimide aerogels was much higher than that (210 °C) of the corresponding linear polyimide. So, even after being heated at 300 °C for 30 min, the porous structure of the polyimide aerogels was not completely destroyed. PMID:25340747

Pei, Xueliang; Zhai, Wentao; Zheng, Wenge

2014-11-11

409

Rheology and Confocal Reflectance Microscopy as Probes of Mechanical Properties and Structure during Collagen and Collagen\\/Hyaluronan Self-Assembly  

Microsoft Academic Search

In this work, the gelation of three-dimensional collagen and collagen\\/hyaluronan (HA) composites is studied by time sweep rheology and time lapse confocal reflectance microscopy (CRM). To investigate the complementary nature of these techniques, first collagen gel formation is investigated at concentrations of 0.5, 1.0, and 1.5 mg\\/mL at 37°C and 32°C. The following parameters are used to describe the self-assembly

Ya-Li Yang; Laura J. Kaufman

2009-01-01

410

Bone fracture toughness and strength correlate with collagen cross-link maturity in a dose-controlled lathyrism mouse model.  

PubMed

Collagen cross-linking is altered in many diseases of bone, and enzymatic collagen cross-links are important to bone quality, as evidenced by losses of strength after lysyl oxidase inhibition (lathyrism). We hypothesized that cross-links also contribute directly to bone fracture toughness. A mouse model of lathyrism using subcutaneous injection of up to 500?mg/kg ?-aminopropionitrile (BAPN) was developed and characterized (60 animals across 4 dosage groups). Three weeks of 150 or 350?mg/kg BAPN treatment in young, growing mice significantly reduced cortical bone fracture toughness, strength, and pyridinoline cross-link content. Ratios reflecting relative cross-link maturity were positive regressors of fracture toughness (HP/[DHLNL?+?HLNL] r(2) ?=?0.208, p?cross-links were significant positive regressors of tissue strength (lysyl pyridinoline r(2) ?=?0.159, p?=?0.014; hydroxylysyl pyridinoline r(2) ?=?0.112, p?cross-links, which were not significantly reduced by BAPN, did not correlate with mechanical properties. The effect of BAPN treatment on mechanical properties was dose specific, with the greatest impact found at the intermediate (350?mg/kg) dose. Calcein labeling was used to define locations of new bone formation, allowing for the identification of regions of normally cross-linked (preexisting) and BAPN-treated (newly formed, cross-link-deficient) bone. Raman spectroscopy revealed spatial differences attributable to relative tissue age and effects of cross-link inhibition. Newly deposited tissues had lower mineral/matrix, carbonate/phosphate, and Amide I cross-link (matrix maturity) ratios compared with preexisting tissues. BAPN treatment did not affect mineral measures but significantly increased the cross-link (matrix maturity) ratio compared with newly formed control tissue. Our study reveals that spatially localized effects of short-term BAPN cross-link inhibition can alter the whole-bone collagen cross-link profile to a measureable degree, and this cross-link profile correlates with bone fracture toughness and strength. Thus, cross-link profile perturbations associated with bone disease may provide insight into bone mechanical quality and fracture risk. © 2014 American Society for Bone and Mineral Research. PMID:25213475

McNerny, Erin Mb; Gong, Bo; Morris, Michael D; Kohn, David H

2015-03-01

411

Polymer gel dosimetry  

NASA Astrophysics Data System (ADS)

Polymer gels are chemical dosimeters based on dose dependent radiation-induced polymerization and cross-linking of monomers in an irradiated volume. The changes are spatially localized in the volume by incorporating the initial monomers in an aqueous gel matrix in the dosimeter and can be probed by various imaging techniques such as magnetic resonance imaging (MRI), x-ray computed tomography (CT), and optical CT. As they are chemical dosimeters, polymer gels are sensitive to preparation conditions. The three dimensional dose readout is sensitive to the imaging modality and also to the technical conditions in use during specific scans. This brief article is intended to present an introduction to these points which need to be taken into account as one attempts to establish this dosimetry in the clinic.

Schreiner, L. J.; Olding, T.; McAuley, K. B.

2010-11-01

412

The boundary lubrication of chemically grafted and cross-linked hyaluronic acid in phosphate buffered saline and lipid solutions measured by the surface forces apparatus.  

PubMed

High molecular weight hyaluronic acid (HA) is present in articular joints and synovial fluid at high concentrations; yet despite numerous studies, the role of HA in joint lubrication is still not clear. Free HA in solution does not appear to be a good lubricant, being negatively charged and therefore repelled from most biological, including cartilage, surfaces. Recent enzymatic experiments suggested that mechanically or physically (rather than chemically) trapped HA could function as an "adaptive" or "emergency" boundary lubricant to eliminate wear damage in shearing cartilage surfaces. In this work, HA was chemically grafted to a layer of self-assembled amino-propyl-triethoxy-silane (APTES) on mica and then cross-linked. The boundary lubrication behavior of APTES and of chemically grafted and cross-linked HA in both electrolyte and lipid 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) solutions was tested with a surface forces apparatus (SFA). Despite the high coefficient of friction (COF) of ? ? 0.50, the chemically grafted HA gel significantly improved the lubrication behavior of HA, particularly the wear resistance, in comparison to free HA. Adding more DOPC lipid to the solution did not improve the lubrication of the chemically grafted and cross-linked HA layer. Damage of the underlying mica surface became visible at higher loads (pressure >2 MPa) after prolonged sliding times. It has generally been assumed that damage caused by or during sliding, also known as "abrasive friction", which is the main biomedical/clinical/morphological manifestation of arthritis, is due to a high friction force and, therefore, a large COF, and that to prevent surface damage or wear (abrasion) one should therefore aim to reduce the COF, which has been the traditional focus of basic research in biolubrication, particularly in cartilage and joint lubrication. Here we combine our results with previous ones on grafted and cross-linked HA on lipid bilayers, and lubricin-mediated lubrication, and conclude that for cartilage surfaces, a high COF can be associated with good wear protection, while a low COF can have poor wear resistance. Both of these properties depend on how the lubricating molecules are attached to and organized at the surfaces, as well as the structure and mechanical, viscoelastic, elastic, and physical properties of the surfaces, but the two phenomena are not directly or simply related. We also conclude that to provide both the low COF and good wear protection of joints under physiological conditions, some or all of the four major components of joints-HA, lubricin, lipids, and the cartilage fibrils-must act synergistically in ways (physisorbed, chemi