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1

Cross-Linked Hyaluronan Gel Reduces the Acute Rectal Toxicity of Radiotherapy for Prostate Cancer  

SciTech Connect

Purpose: To prospectively analyze whether cross-linked hyaluronan gel reduces the mean rectal dose and acute rectal toxicity of radiotherapy for prostate cancer. Methods and Materials: Between September 2008 and March 2009, we transperitoneally injected 9mL of cross-linked hyaluronan gel (Hylaform; Genzyme Corporation, Cambridge, MA) into the anterior perirectal fat of 10 early-stage prostate cancer patients to increase the separation between the prostate and rectum by 8 to 18mm at the start of radiotherapy. Patients then underwent high-dose rate brachytherapy to 2,200cGy followed by intensity-modulated radiation therapy to 5,040cGy. We assessed acute rectal toxicity using the National Cancer Institute Common Terminology Criteria for Adverse Events v3.0 grading scheme. Results: Median follow-up was 3 months. The anteroposterior dimensions of Hylaform at the start and end of radiotherapy were 13 {+-} 3mm (mean {+-} SD) and 10 {+-} 4mm, respectively. At the start of intensity-modulated radiation therapy, daily mean rectal doses were 73 {+-} 13cGy with Hylaform vs. 106 {+-} 20cGy without Hylaform (p = 0.005). There was a 0% incidence of National Cancer Institute Common Terminology Criteria for Adverse Events v3.0 Grade 1, 2, or 3 acute diarrhea in 10 patients who received Hylaform vs. a 29.7% incidence (n = 71) in 239 historical controls who did not receive Hylaform (p = 0.04). Conclusions: By increasing the separation between the prostate and rectum, Hylaform decreased the mean rectal dose. This led to a significant reduction in the acute rectal toxicity of radiotherapy for prostate cancer.

Wilder, Richard B., E-mail: richardbwilder@yahoo.co [Cancer Center of Irvine, Irvine, CA (United States); Barme, Greg A.; Gilbert, Ronald F.; Holevas, Richard E.; Kobashi, Luis I.; Reed, Richard R.; Solomon, Ronald S.; Walter, Nancy L.; Chittenden, Lucy; Mesa, Albert V.; Agustin, Jeffrey; Lizarde, Jessica; Macedo, Jorge; Ravera, John; Tokita, Kenneth M. [Cancer Center of Irvine, Irvine, CA (United States)

2010-07-01

2

The inflammation-associated protein TSG-6 cross-links hyaluronan via hyaluronan-induced TSG-6 oligomers.  

PubMed

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

2011-05-19

3

Rheological Properties of Cross-Linked Hyaluronan-Gelatin Hydrogels for Tissue Engineering  

PubMed Central

Hydrogels that mimic the natural extracellular matrix (ECM) are used in three-dimensional cell culture, cell therapy, and tissue engineering. A semi-synthetic ECM based on cross-linked hyaluronana offers experimental control of both composition and gel stiffness. The mechanical properties of the ECM in part determine the ultimate cell phenotype. We now describe a rheological study of synthetic ECM hydrogels with storage shear moduli that span three orders of magnitude, from 11 to 3 500 Pa, a range important for engineering of soft tissues. The concentration of the chemically modified HA and the cross-linking density were the main determinants of gel stiffness. Increase in the ratio of thiol-modified gelatin reduced gel stiffness by diluting the effective concentration of the HA component.

Vanderhooft, Janssen L.; Alcoutlabi, Mataz; Magda, Jules J.; Prestwich, Glenn D.

2009-01-01

4

Inter-?-inhibitor Impairs TSG-6-induced Hyaluronan Cross-linking*  

PubMed Central

Under inflammatory conditions and in the matrix of the cumulus-oocyte complex, the polysaccharide hyaluronan (HA) becomes decorated covalently with heavy chains (HCs) of the serum glycoprotein inter-?-inhibitor (I?I). This alters the functional properties of the HA as well as its structural role within extracellular matrices. The covalent transfer of HCs from I?I to HA is catalyzed by TSG-6 (tumor necrosis factor-stimulated gene-6), but TSG-6 is also known as a HA cross-linker that induces condensation of the HA matrix. Here, we investigate the interplay of these two distinct functions of TSG-6 by studying the ternary interactions of I?I and TSG-6 with well defined films of end-grafted HA chains. We demonstrate that TSG-6-mediated cross-linking of HA films is impaired in the presence of I?I and that this effect suppresses the TSG-6-mediated enhancement of HA binding to CD44-positive cells. Furthermore, we find that the interaction of TSG-6 and I?I in the presence of HA gives rise to two types of complexes that independently promote the covalent transfer of heavy chains to HA. One type of complex interacts very weakly with HA and is likely to correspond to the previously reported covalent HC·TSG-6 complexes. The other type of complex is novel and binds stably but noncovalently to HA. Prolonged incubation with TSG-6 and I?I leads to HA films that contain, in addition to covalently HA-bound HCs, several tightly but noncovalently bound molecular species. These findings have important implications for understanding how the biological activities of TSG-6 are regulated, such that the presence or absence of I?I will dictate its function.

Baranova, Natalia S.; Foulcer, Simon J.; Briggs, David C.; Tilakaratna, Viranga; Enghild, Jan J.; Milner, Caroline M.; Day, Anthony J.; Richter, Ralf P.

2013-01-01

5

Inter-?-inhibitor Impairs TSG-6-induced Hyaluronan Cross-linking.  

PubMed

Under inflammatory conditions and in the matrix of the cumulus-oocyte complex, the polysaccharide hyaluronan (HA) becomes decorated covalently with heavy chains (HCs) of the serum glycoprotein inter-?-inhibitor (I?I). This alters the functional properties of the HA as well as its structural role within extracellular matrices. The covalent transfer of HCs from I?I to HA is catalyzed by TSG-6 (tumor necrosis factor-stimulated gene-6), but TSG-6 is also known as a HA cross-linker that induces condensation of the HA matrix. Here, we investigate the interplay of these two distinct functions of TSG-6 by studying the ternary interactions of I?I and TSG-6 with well defined films of end-grafted HA chains. We demonstrate that TSG-6-mediated cross-linking of HA films is impaired in the presence of I?I and that this effect suppresses the TSG-6-mediated enhancement of HA binding to CD44-positive cells. Furthermore, we find that the interaction of TSG-6 and I?I in the presence of HA gives rise to two types of complexes that independently promote the covalent transfer of heavy chains to HA. One type of complex interacts very weakly with HA and is likely to correspond to the previously reported covalent HC·TSG-6 complexes. The other type of complex is novel and binds stably but noncovalently to HA. Prolonged incubation with TSG-6 and I?I leads to HA films that contain, in addition to covalently HA-bound HCs, several tightly but noncovalently bound molecular species. These findings have important implications for understanding how the biological activities of TSG-6 are regulated, such that the presence or absence of I?I will dictate its function. PMID:24005673

Baranova, Natalia S; Foulcer, Simon J; Briggs, David C; Tilakaratna, Viranga; Enghild, Jan J; Milner, Caroline M; Day, Anthony J; Richter, Ralf P

2013-09-04

6

Effect of electron beam-cross-linked gels on the rheological properties of raw natural rubber  

Microsoft Academic Search

Electron beam (EB)-cross-linked natural rubber (NR) gels were prepared from latex and characterized by various techniques. The addition of a small amount of these gels to raw NR was found to reduce the apparent shear viscosity and die swell remarkably. This effect was further enhanced with the addition of butyl acrylate as a sensitizer. The apparent shear viscosity first decreased

Suman Mitra; Santanu Chattopadhyay; Y. K. Bharadwaj; S. Sabharwal; Anil K. Bhowmick

2008-01-01

7

Effect of electron beam-cross-linked gels on the rheological properties of raw natural rubber  

NASA Astrophysics Data System (ADS)

Electron beam (EB)-cross-linked natural rubber (NR) gels were prepared from latex and characterized by various techniques. The addition of a small amount of these gels to raw NR was found to reduce the apparent shear viscosity and die swell remarkably. This effect was further enhanced with the addition of butyl acrylate as a sensitizer. The apparent shear viscosity first decreased up to 8 phr of gel loading and then increased. However, the percent die swell value decreased steadily upon gel loading. These were explained by calculating principal normal stress difference, the activation energy of melt flow and characteristics of EB-cross-linked gels. These effects were also reflected in the changes of mechanical and dynamic mechanical properties of gel-filled raw NR. Tailoring of the above properties could be done with the help of these gels.

Mitra, Suman; Chattopadhyay, Santanu; Bharadwaj, Y. K.; Sabharwal, S.; Bhowmick, Anil K.

2008-05-01

8

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

9

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

PubMed Central

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.

2011-01-01

10

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.

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

2011-01-01

11

Robust cross-links in molluscan adhesive gels: testing for contributions from hydrophobic and electrostatic interactions.  

PubMed

The cross-linking interactions that provide cohesive strength to molluscan adhesive gels were investigated. Metal-based interactions have been shown to play an important role in the glue of the slug Arion subfuscus (Draparnaud), but other types of interactions may also contribute to the glue's strength and their role has not been investigated. This study shows that treatments that normally disrupt hydrophobic or electrostatic interactions have little to no effect on the slug glue. High salt concentrations and non-ionic detergent do not affect the solubility of the proteins in the glue or the ability of the glue proteins to stiffen gels. In contrast, metal chelation markedly disrupts the gel. Experiments with gel filtration chromatography identify a 40 kDa protein that is a central component of the cross-links in the glue. This 40 kDa protein forms robust macromolecular aggregations that are stable even in the presence of high concentrations of salt, non-ionic detergent, urea or metal chelators. Metal chelation during glue secretion, however, may block some of these cross-links. Such robust, non-specific interactions in an aqueous environment are highly unusual for hydrogels and reflect an intriguing cross-linking mechanism. PMID:18952190

Smith, A M; Robinson, T M; Salt, M D; Hamilton, K S; Silvia, B E; Blasiak, R

2008-10-15

12

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

13

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 ...

14

Cross-linked sodium hyaluronate, an anti-adhesion barrier gel in gynaecological endoscopic surgery.  

PubMed

Abstract Objectives: In the context of common adhesion prevention in laparotomic, laparoscopic and hysteroscopic surgery this article details the effects of a cross-linked sodium hyaluronate anti-adhesion barrier gel. The observed adhesion score is expressed in the following three measurements: Severity, extent and incidents of adhesions. Material and methods: From a total of 85 patients treated by laparoscopy and hysteroscopy, a second look endoscopic procedure could be performed in 35 cases. Results: Our preliminary, short evaluation of 35 patients submitted to a second look laparoscopy or hysteroscopy revealed the beneficial effect of the applied HYAcorp endo gel, showing only a minimal amount of adhesions at the second look observation. Conclusion: Cross-linked sodium hyaluronate is highly effective in the prevention of adhesions at laparoscopic and hysteroscopic surgery. PMID:23289513

Mettler, Liselotte; Sammur, Wael; Schollmeyer, Thoralf; Alkatout, Ibrahim

2013-01-06

15

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

16

Preparation of porous, chemically cross-linked, PVdF-based gel polymer electrolytes for rechargeable lithium batteries  

Microsoft Academic Search

This study reports the development of a new system of porous, chemically cross-linked, gel polymer electrolytes based on poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF–HFP) copolymer as a polymer matrix, polyethylene glycol (PEG) as a plasticizer, and polyethylene glycol dimethacrylate (PEGDMA) as a chemical cross-linking oligomer. The electrolytes are prepared by a combination of controlled evaporation and thermal polymerization of PEGDMA. PVdF–HFP\\/PEG\\/PEGDMA gel polymer

C. L Cheng; C. C Wan; Y. Y Wang

2004-01-01

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

2013-08-01

18

Model and field studies of the degradation of cross-linked polyacrylamide gels used during the revegetation of slate waste.  

PubMed

Cross-linked polyacrylamide gels are increasingly being used in environmental restoration schemes and horticulture as a means of enhancing water supply to plants. However, the environmental impact of cross-linked polyacrylamide gel deployment in soil remains poorly understood. This study assessed the chemical, physical and biological properties of new and field-conditioned cross-linked polyacrylamide gels. Both monomeric acrylamide (11 microg l(-1)) and acrylic acid (285 microg l(-1)) were observed in new gel; however, the levels of monomers in field-conditioned gels (1-6 years old) were very low (acrylamide <1 microg l(-1); acrylic acid <7 microg l(-1)). Generally, freeze-thaw processes and exposure to UV radiation had little effect on gel acrylic acid and acrylamide concentrations. However, elevated temperatures (35 degrees C) caused a significant release of up to 144 mug l(-1) of acrylamide and 453 microg l(-1) of acrylic acid in new gel and up to 25 microg l(-1) of acrylamide and 157 microg l(-1) of acrylic acid in field-conditioned gels. In contrast, gel water holding capacity was highly dependent upon environmental conditions (UV exposure and freeze/thaw cycles produced the greatest loss of water holding in new gels) and gel age. Optical microscopy revealed that after placement in the field the gels became increasingly colonised over time by fungi and bacteria. In enrichment cultures, we were unable, however, to demonstrate microbial growth when cross-linked polyacrylamide was used as the sole nitrogen source. In summary, under a range of conditions cross-linked polyacrylamide did not release acrylamide above legally permitted limits, with the exception of gel subjected to elevated temperatures. However, their capacity for holding water decreased sharply within 18 months. We therefore conclude that cross-linked polyacrylamide placed in soil is relatively stable with respect to the production of potentially toxic acrylamide, a species with a short half-life, which degrades to the much less toxic acrylic acid. However, the loss of water holding capacity raises questions about its long-term effectiveness in land restoration schemes as this is the main reason it is used in this role. PMID:15589246

Holliman, Peter J; Clark, Jennifer A; Williamson, Julie C; Jones, Davey L

2005-01-01

19

In vitro release of lysozyme from gelatin microspheres: effect of cross-linking agents and thermoreversible gel as suspending medium.  

PubMed

This study was aimed to characterize the microstructure and the performance of gelatin microspheres (GMs) cross-linked by two different cross-linkers viz. d-glucose and glutaraldehyde. New formulations were obtained, suspending the GMs in a thermoreversible Pluronic F127 (PF127) liquid-crystalline gel. Lysozyme was used as a model biomacromolecular drug to evaluate release features. Both types of cross-linked GMs were prepared by thermal gelation method. The lysozyme-loaded microspheres were characterized by scanning electron microscopy (SEM) for size distribution, shape, and surface texture. SEM revealed that both types of lysozyme-loaded GMs were spherical in shape and that the surface of glutaraldehyde cross-linked GMs was smoother than that of the glucose cross-linked GMs. The degree of cross-linking of microspheres was investigated using ATR-FTIR technique. The prepared GMs were suspended in 20% w/v aqueous PF127 gel for which the usual sol-gel transition temperature of 22 °C did not change in the presence of GMs, as indicated by rheological measurements. SAXS study of the PF127 gel confirmed the occurrence of a discrete cubic liquid-crystalline phase of the Fm3m type whose lattice parameter slightly decreased as a result of GMs addition. The in vitro release of lysozyme from both types of cross-linked GMs was successfully controlled when they were suspended in PF127 gel, thus suggesting the potential use of this new combined formulation as a drug-depot system. PMID:21809827

Hiwale, Pradip; Lampis, Sandrina; Conti, Gabriele; Caddeo, Carla; Murgia, Sergio; Fadda, Anna M; Monduzzi, Maura

2011-08-11

20

Cooperative effect of stress and ion displacement on the dynamics of cross-link unzipping and rupture of alginate gels.  

PubMed

We study the effect of nonbinding Na(+) ions on the kinetics of rupture of alginate gels cross-linked by Ca(2+). Wetting a crack tip with a saline solution at physiological concentrations is found to be able to induce a quasi-instantaneous, 10-fold velocity jump. This effect is analyzed with a phenomenological model for the rate-dependent fracture energy in physical gels, extended here to account for the role of ions on the rate of cross-link "unzipping". Ionic interaction is found to act cooperatively with mechanical tension, leading to an enhanced rate of rupture. The kinetics turns out to be second order in counterion concentration. The definition of the reference state requires to take into account counterion condensation due to long-range interactions in the polyelectrolyte gel. Surprisingly, the contribution of the Na(+) ions to the free energy of the activated state is essentially entropic, suggesting that the displacement of Ca(2+) is primarily a steric process, electrostatic interactions being reduced to the constraint of charge conservation. This phenomenon may have important consequences on the rate of degradation of alginate based scaffolds for in vivo tissue regeneration. PMID:20499914

Baumberger, T; Ronsin, O

2010-06-14

21

Cross-linked redox gels containing glucose oxidase for amperometric biosensor applications.  

PubMed

Oxidoreductases, such as glucose oxidase, can be electrically "wired" to electrodes by electrostatic complexing or by covalent binding of redox polymers so that the electrons flow from the enzyme, through the polymer, to the electrode. We describe two materials for amperometric biosensors based on a cross-linkable poly(vinylpyridine) complex of [Os-(bpy)2Cl]+2+ that communicates electrically with flavin adenine dinucleotide redox centers of enzymes such as glucose oxidase. The uncomplexed pyridines of the poly(vinylpyridine) are quaternized with two types of groups, one promoting hydrophilicity (2-bromoethanol or 3-bromopropionic acid), the other containing an active ester (N-hydroxysuccinimide) that forms amide bonds with both lysines on the enzyme surface and with an added polyamine cross-linking agent (triethylenetetraamine, trien). In the presence of glucose oxidase and trien this polymer forms rugged, cross-linked, electroactive films on the surface of electrodes, thereby eliminating the requirement for a membrane for containing the enzyme and redox couple. The glucose response time of the resulting electrodes is less than 10 s. The glucose response under N2 shows an apparent Michaelis constant, Km' = 7.3 mM, and limiting current densities, jmax, between 100 and 800 microA/cm2. Currents are decreased by 30-50% in air-saturated solutions because of competition between O2 and the Os(III) complex for electrons from the reduced enzyme. Rotating ring desk experiments in air-saturated solutions containing 10 mM glucose show that about 20% of the active enzyme is electrooxidized via the Os(III) complex, while the rest is oxidized by O2. These results suggest that only part of the active enzyme is in electrical contact with the electrode. PMID:2305956

Gregg, B A; Heller, A

1990-02-01

22

Cross-linked redox gels containing glucose oxidase for amperometric biosensor applications  

SciTech Connect

Oxidoreductases, such as glucose oxidase, can be electrically wired to electrodes by electrostatic complexing or by covalent binding of redox polymers so that the electrons flow from the enzyme, through the polymer, to the electrode. We describe two materials for amperometric biosensors based on a cross-linkable poly(vinylpyridine) complex of (Os-(bpy){sub 2}Cl){sup +/2+} that communicates electrically with flavin adenine dinucleiotide redox centers of enzymes such as glucose oxidase. The uncomplexed pyridines of the poly(vinylpyridine) are quaternized with two types of groups, one promoting hydrophilicity (2-bromoethanol or 3-bromopropionic acid), the other containing an active ester (N-hydroxysuccinimide) that forms amide bonds with both lysines on the enzyme surface and with an added polyamine cross-linking agent (tri-ethylenetetraamine, trien). In the presence of glucose oxidase and trien this polymer forms rugged, cross-linked, electroactive films on the surface of electrodes, thereby eliminating the requirement for a membrane for containing the enzyme and redox couple. The glucose response time of the resulting electrodes is less than 10 s. The glucose response under N{sub 2} shows an apparent Michaelis constant, K{sub m}{prime} = 7.3 mM, and limiting current densities, j{sub max}, between 100 and 800 {mu}A/cm{sup 2}. Currents are decreased by 30-50% in air-saturated solutions because of competition between O{sub 2} and the Os(III) complex for electrons from the reduced enzyme. Rotating ring disk experiments in air-saturated solutions containing 10 mM glucose show that about 20% of the active enzyme is electrooxidized via the Os(III) complex, while the rest is oxidized by O{sub 2}. These results suggest that only part of the active enzyme is in electrical contact with the electrode.

Gregg, B.A.; Heller, A. (Univ. of Texas, Austin (USA))

1990-02-01

23

Liquid crystal gels cross-linked with 1,3,5-tris-(?-methacryloyloxyalkyloxy)benzenes  

Microsoft Academic Search

A mixture of ?-(4-cyanobiphenyl-4?-yloxy)alkyl methacrylate and 1,3,5-tris-(?-methacryloyloxyalkyloxy)benzene was heated to\\u000a 200 °C at 5–10 °C\\/min. A large, broad exothermic transition peak was observed by differential scanning calorimetry during\\u000a the first heating process. The transition indicated the formation of a networked polymer, which was then immersed for 24 h\\u000a in various nematic liquid crystals, such as 4-cyano-4?-pentylbiphenyl, to give liquid crystal gels. The networked

Toshio Itahara; Mayumi Morimoto; Yusuke Iemura

2011-01-01

24

Design principles for cytokine-neutralizing gels: Cross-linking effects.  

PubMed

Constructs composed of cytokine-neutralizing antibodies conjugated to high-molecular-weight hyaluronic acid have been shown to be effective at controlling inflammatory responses in vivo. A critical question in the development of this new class of biomaterial is whether crosslinked conjugates have similar anti-inflammatory effects, which would open up a broad range of tissue engineering applications in which the material would have intrinsic inflammation-controlling function. To test this, high-molecular-weight hyaluronic acid was conjugated with monoclonal antibodies to the pro-inflammatory cytokines interleukin-1? and tumor necrosis factor-? in two forms of the material: viscous, non-crosslinked polymer-antibody conjugates and crosslinked, elastomeric polymer-antibody conjugates. The cytokine affinities of both constructs were validated using molecular characterization methods, and the biological activities were tested through subcutaneous implantation in Sprague-Dawley rats. In vitro, both forms of these constructs are capable of binding cytokines, but in vivo only the non-crosslinked polymer significantly reduces markers of acute inflammation compared to controls that lack the antibodies. We propose that these materials function by retarding cytokine diffusion, with the non-crosslinked polymers being capable of retarding the diffusion of cytokines in the extracellular matrix and preventing engagement with receptors. In contrast, crosslinked materials have long diffusion lengths into the gel compared with those between cells on the surface of the material, which may make them ineffective at sequestering pro-inflammatory cytokines on biologically relevant timescales. These results suggest an important design principle for preparing cytokine-regulating materials based on consideration of transport phenomena. PMID:20601239

Sun, Liang Tso; Bencherif, Sidi A; Gilbert, Thomas W; Lotze, Michael T; Washburn, Newell R

2010-06-30

25

Cross-linking properties of alginate gels determined by using advanced NMR imaging and Cu(2+) as contrast agent.  

PubMed

The entrapment of enzymes, drugs, cells or tissue fragments in alginates cross-linked with Ca(2+) or Ba(2+) has great potential in basic research, biotechnology and medicine. The swelling properties and, in turn, the mechanical stability are key factors in designing an optimally cross-linked hydrogel matrix. These parameters depend critically on the cross-linking process and seemingly minor modifications in manufacture have a large impact. Thus, sensitive and non-invasive tools are required to determine the spatial homogeneity and efficacy of the cross-linking process. Here, we show for alginate microcapsules (between 400 microm and 600 microm in diameter) that advanced (1)H NMR imaging, along with paramagnetic Cu(2+) as contrast agent, can be used to validate the cross-linking process. Two- and three-dimensional images and maps of the spin-lattice relaxation time T(1) of Ba(2+) cross-linked microcapsules exposed to external Cu(2+) yielded qualitative as well as quantitative information about the accumulation of Cu(2+) within and removal from microcapsules upon washing with Cu(2+) free saline solution. The use of Cu(2+) (having a slightly higher affinity constant to alginate than Ba(2+)) for gelling gave a complementary insight into the spatial homogeneity of the cross-linking process together with information about the mechanical stability of the microcapsules. The potential of this technique was demonstrated for alginates extracted from two different algal sources and cross-linked either externally by the conventional air-jet dropping method or internally by the "crystal gun" method. PMID:13680210

Manz, B; Hillgärtner, M; Zimmermann, H; Zimmermann, D; Volke, F; Zimmermann, U

2003-09-16

26

Topical diclofenac in hyaluronan gel for the treatment of solar keratoses.  

PubMed

This randomized, double-blind, placebo-controlled study assessed the efficacy and safety of a topical gel containing 3% diclofenac in 2.5% hyaluronan in 150 patients with solar keratoses (SK). The active treatment was compared with the vehicle only, hyaluronan gel, as placebo over a 12-week period. Patients in both groups applied the active treatment or placebo to a targeted area of skin (0.25 g b.d.). At 12 weeks the mean lesion-count reduction in the targeted area was not significantly different between treatments. However, at post-termination follow up (16 weeks), there was a highly significant decrease in the number of lesions, 6.2 +/- 7.5 standard deviations (SD) (56.1% reduction) in the active treatment group compared with 2.4 +/- 4.3 SD (23.6% reduction) in the placebo group (P < 0.001). Other efficacy measures (complete lesion resolution, >50% lesion reduction) were also significantly different (P < 0.01) between treatments at 16 weeks. In conclusion, topical 3% diclofenac in 2.5% hyaluronan gel was effective and well tolerated in this study, suggesting a role for this therapy in the treatment of SK. PMID:12581080

Gebauer, Kurt; Brown, Pam; Varigos, George

2003-02-01

27

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

2012-08-17

28

Evaluation of the matrix-synthesis potential of crosslinked hyaluronan gels for tissue engineering of aortic heart valves  

Microsoft Academic Search

Our goal is to fabricate continuous sheets of elastin atop non-biodegradable hydrogels (hylans) containing crosslinked hyaluronan, a glycosaminoglycan. Such elastin–hyaluronan composites may be useful to tissue engineer replacements for the glycosaminoglycan- and elastin-rich layers of the native aortic valve cusp. Neonatal rat aortic smooth muscle cells were cultured atop hylan gels with micro-textured surfaces, and on plastic, and the components

A. Ramamurthi; I. Vesely

2005-01-01

29

A method to resolve the composition of heterogeneous affinity-purified protein complexes assembled around a common protein by chemical cross-linking, gel electrophoresis and mass spectrometry.  

PubMed

Protein complexes form, dissociate and re-form in order to perform specific cellular functions. In this two-pronged protocol, noncovalent protein complexes are initially isolated by affinity purification for subsequent identification of the components by liquid chromatography high-resolution mass spectrometry (LC-MS) on a hybrid LTQ Orbitrap Velos. In the second prong of the approach, the affinity-purification strategy includes a chemical cross-linking step to 'freeze' a series of concurrently formed, heterogeneous protein subcomplex species that are visualized by gel electrophoresis. This branch of the methodology amalgamates standard and well-practiced laboratory methods to reveal compositional changes that occur in protein complex architecture. By using mouse N-terminally tagged streptavidin-binding peptide-hemagglutinin-TANK-binding kinase 1 (SH-TBK1), we chemically cross-linked the affinity-purified complex of SH-TBK1 with the homobifunctional lysine-specific reagent bis(sulfosuccinimidyl) suberate (BS(3)), and we separated the resultant protein complexes by denaturation and by silver-stained one- and two-dimensional SDS-PAGE. We observed a range of cross-linked TBK1 complexes of variable pI and M(r) and confirmed them by immunoblotting. LC-MS analysis of in situ-digested cross-linked proteins shows differences in the composition of the TBK1 subcomplexes. The protocol is inherently simple and can be readily extended to the investigation of a range of protein complexes. From cell lysis to data generation by LC-MS, the protocol takes approximately 2.5 to 5.5 d to perform. PMID:23237831

Rudashevskaya, Elena L; Sacco, Roberto; Kratochwill, Klaus; Huber, Marie L; Gstaiger, Matthias; Superti-Furga, Giulio; Bennett, Keiryn L

2012-12-13

30

Synthesis of nanocomposites from Pd(0) and a hyper-cross-linked functional resin obtained from a conventional gel-type precursor.  

PubMed

Hyper-cross-linked resins stemming from a gel-type poly-chloromethylated poly(styrene-co-divinylbenzene) resin (GT) have been investigated by a multi-methodological approach based on elemental analysis, scanning electron microscopy, X-ray microanalysis, and solvent absorption. The hyper-cross-linking of the parent resin was accomplished by Friedel-Crafts alkylation of the phenyl rings of the resins with the chloromethyl groups. This produced a permanent pore system comprising both micropores (<2.0 nm in diameter) and mesopores (2.2 nm). The chloromethyl groups that did not react in the hyper-cross-linking step were transformed into methylmercaptan groups and the latter were then converted into sulfonic groups by oxidation with hydrogen peroxide. By this procedure the extensive permanent porosity of the parent unsulfonated hyper-cross-linked polymer (HGT) was retained by the sulfonated polymer (HGTS). The final exchange capacity of HGTS was determined to be 0.36 mmol g(-1). HGTS was easily metalated with Pd(II) and the subsequent reduction of the metal centers with either aqueous sodium borohydride, formaldehyde, or dihydrogen produced three Pd(0)/HGTS nanocomposites. The metal nanoparticles had diameters in the 1-6 nm range for all the nanocomposites, as determined by TEM, but with somewhat different distributions. When formaldehyde was used, more than 90% of the nanoparticles were less than 3 nm and their radial distribution throughout the polymer beads was quite homogeneous. These findings show that with this reducing agent the metal nanoparticles are generated within the pore system of the polymer matrix, hence their size is controlled by the dimensions of the pores of the polymeric support. PMID:23728964

Je?ábek, Karel; Zecca, Marco; Centomo, Paolo; Marchionda, Federico; Peruzzo, Luca; Canton, Patrizia; Negro, Enrico; Di Noto, Vito; Corain, Benedetto

2013-05-31

31

In vitro hemocompatibility testing of UV-modified hyaluronan hydrogels  

Microsoft Academic Search

Hydrogels (hylans) based on cross-linked hyaluronan (HA) are potentially good biomaterials for vascular tissue engineering applications because they are highly non-antigenic and -immunogenic. To facilitate surface endothelialization, vital to vascular deployment, we irradiated the gel surface with low wavelength UV light. This process micro-textures the smooth gel surface to provide sites for cell anchorage and causes limited scission of native

Leena Pravina Amarnath; Arvind Srinivas; Anand Ramamurthi

2006-01-01

32

NMR relaxation enhancement in gels polymerized and cross-linked by ionizing radiation: a new approach to 3D dosimetry by MRI.  

PubMed

A new type of tissue-equivalent medium for magnetic resonance imaging of the dose distributions produced by ionizing radiation has been developed. Agarose gel is infused with acrylamide and N,N'-methylene-bis-acrylamide (Bis) comonomers, which are readily polymerized by free radical initiators in de-aerated aqueous solutions. Polymerization and cross-linking induced locally by free radical products of water radiolysis increase the rate of water proton spin relaxation gradually up to doses of about 15 Gy. The slopes of the dose-response curves at 64 MHz are 0.015 and 0.28 s-1 Gy-1 for R1 and R2, respectively. The agarose matrix as well as the high (50% by weight) relative concentration of the cross-linker (Bis) per total comonomer limit the spread of polymerization so that the spatial distribution of the radiation dose is faithfully represented in the resultant spatial distribution of relaxation rates. The gel can be imaged with conventional magnetic resonance imaging devices with high spatial resolution and accuracy. In addition, due to the well established effect of the precipitation of insoluble agglomerates of highly cross-linked acrylamide, the optical turbidity of the gel increases gradually with the absorbed dose. This may provide an additional means of visualizing the dose distribution in three dimensions. The major advantage of the acrylamide-Bis-agarose gels over those that depend on ionic chemical dosimeters, for example, Fricke-infused gels, lies in the lack of diffusion of radiation-induced chemical changes subsequent to or concurrent with irradiation. PMID:8455435

Maryanski, M J; Gore, J C; Kennan, R P; Schulz, R J

1993-01-01

33

Cross-linking casein micelles by a microbial transglutaminase conditions for formation of transglutaminase-induced gels  

Microsoft Academic Search

The conditions for obtaining transglutaminase-induced casein gels have been studied by rheological measurements. The experiments have been performed with pure micellar casein. Different parameters were investigated including enzyme concentration, protein concentration, pH, ways of acidification, gelation temperature, etc. The conditions of gel formation are clearly based on a compromise between the conditions required for casein gelation and those controlling the

C Schorsch; H Carrie; A. H Clark; I. T Norton

2000-01-01

34

One-step separation and purification of hydrolysable tannins from Geranium wilfordii Maxim by adsorption chromatography on cross-linked 12% agarose gel.  

PubMed

The hydrolysable tannins corilagin and geraniin, the major active components of the traditional Chinese medicine Geranium wilfordii Maxim, have been separated and purified from crude extracts in one step by adsorption chromatography on cross-linked 12% agarose gel (Superose 12 10/300 GL). The separation was achieved by gradient elution using mobile phase A composed of 5% ethanol and 5% acetic acid and mobile phase B composed of 30% ethanol and 30% acetic acid. The gradients were composed as follows: 0-240?mL, 0-25% B; 240-480?mL, 25-40% B; after 480?mL, 100% B. The purities of the collected corilagin and geraniin were 92.4 and 87.2%, and the corresponding yields were 88.0 and 76.8%, respectively. PMID:21442751

Liu, Dan; Ma, Yan; Wang, Ye; Su, Zhiguo; Gu, Ming; Janson, Jan-Christer

2011-03-25

35

Noncovalently and covalently cross-linked polyurethane gels as alignment media and the suppression of residual polymer signals using diffusion-filtered spectroscopy.  

PubMed

With polyurethane (PU), a novel alignment medium for organic solvents is introduced and characterized, which is very robust and easy to produce on a large scale. Linear PU already constitutes an elastomer gel with several solvents based on its ability to form hydrogen bonds. Covalent cross-linking of the polymer with accelerated electrons provides an alignment medium with different properties. However, PU exhibits a number of undesired polymer signals in corresponding spectra, which ideally have to be removed spectroscopically. Within this context, we demonstrate the applicability of diffusion-filtered experiments for removal of the polymer signals. Example spectra for the usefulness of PU alignment media are provided for the common test molecules strychnine and norcamphor. PMID:23280657

Kaden, Peter; Freudenberger, J Christoph; Luy, Burkhard

2012-12-01

36

Influence of titanium oxide and titanium peroxy gel on the breakdown of hyaluronan by reactive oxygen species  

Microsoft Academic Search

The molecular events occuring at the interface between titanium and connective tissue were investigated in order to help explain the unique biocompatible properties of titanium implants and their successful osseointegration into bone tissue. In this study the influence of commercially pure titanium and titanium peroxy gels on the breakdown of the connective tissue component and serum derived factor, hyaluronan, by

G. C. Taylor; R. J. Waddington; R. Moseley; K. R. Williams; G. Embery

1996-01-01

37

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, D. E.; Utecht, Ronald E.

1994-09-01

38

Cross-linked informofers.  

PubMed Central

The proteins of 30S RNP particles containing pre-mRNA (hnRNA) were cross-linked with bifunctional reagents (dimethyl-suberimidate and dimethyl-3,3'-dithiobispropionimidate). Further treatment with 1 or 2 M NaCl dissociates all RNA from protein. However, a significant part of protein particles--informofers being cross-linked survived high salt treatment. Their sedimentation coefficients were close to those of original particles. No RNA could be detected in the informofers even after labeling the cells with a precursor for a long period of time. Sodium dodecylsulfate or urea dissociated cross-linked informofers into oligomeric polypeptides. They could be dissociated by beta-mercaptoethanol treatment if a reversible cross-linked reagent had been used. The resulting polypeptides were represented by informatin. RNP particles (30S RNP or poly-particles) were reconstituted upon mixing of cross-linked informofers with pre-mRNA and removal of 2 M NaCl.

Prosvirnin, V V; Ruzidic, S; Samarina, O P

1979-01-01

39

The Determination of Hyaluronan Molecular Weight Distribution by Means of High-Performance Size Exclusion Chromatography  

Microsoft Academic Search

The high-performance liquid chromatographic (HPLC) method relevant to the size exclusion chromatographic mode (SEC) used for the distribution analysis of high-molecular-weight hyaluronans is described. The HPLC fillings used, to which was applied a phosphate buffer (50 mM, pH 7.8) effluent, consisted of a cross-linked hydroxyethylmethacrylate derivative gel (HEMA-BIO), which is commercially available, and a highly porous aminopropyl-silica sorbent (SG-10-6000-NH2), which

E. Orviský; L. Šoltés; P. Chabr?ek; I. Novák; V. Kéry; M. Stan?íková; I. Vinš

1992-01-01

40

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

41

Reduction of postoperative adhesions with an auto-crosslinked hyaluronan gel in gynaecological laparoscopic surgery: a blinded, controlled, randomized, multicentre study  

Microsoft Academic Search

BACKGROUND: Following myomectomy, postoperative adhesions occur in many patients with adverse effects on fertility. This study investigated the applicability, safety and efficacy of an auto-crosslinked hyaluronan gel in pre- venting adhesion formation after laparoscopic myomectomy. METHODS: Fifty-two patients aged 22-42 years, undergoing surgery at four centres, were randomly allocated to receive either the gel or no adhesion prevention. The incidence

V. Mais; G. L. Bracco; P. Litta; T. Gargiulo; G. B. Melis

2006-01-01

42

DNA Interstrand Cross-Linking by Epichlorohydrin  

PubMed Central

Epichlorohydrin (ECH), an important industrial chemical, is a bifunctional alkylating agent with the potential to form DNA cross-links. Occupational exposure to this suspect carcinogen leads to chromosomal aberrations, and ECH has been shown previously to undergo reaction with DNA in vivo and in vitro.We used denaturing polyacrylamide gel electrophoresis to monitor the possible formation of interstrand cross-links within DNA oligomers by ECH and the related compound, epibromohydrin (EBH). Although both compounds did indeed form cross-links between deoxyguanosine residues, EBH was a more efficient cross-linker than ECH. The optimal pH for cross-linking also varied, with ECH more efficient at pH 5.0 and EBH more efficient at pH 7.0. Both agents were relatively flexible in the sequences targeted, with comparable efficiencies for 5?-GGC and 5?GC sites. Furthermore, interstrand cross-linking by the two optical isomers of ECH correlated with their relative cytotoxicities, with R-ECH about twice as potent as S-ECH.

Romano, Keith P.; Newman, Adam G.; Zahran, Rami W.; Millard, Julie T.

2008-01-01

43

Phase separation of weakly cross-linked polymer blends  

Microsoft Academic Search

We consider the microphase separation that occurs when a mixture of two different polymers is brought to phase separation after being cross-linked. For deep quenching, microphase separation takes place, related to the competition that exists between demixion and elasticity. We consider more carefully very weak cross-linking in two cases. If the gel is assumed to be regular, the effect is

A. Bettachy; A. Derouiche; M. Benhamou; M. Daoud

1991-01-01

44

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

2011-09-25

45

Modified Dendrimer Cross-Linked Collagen-Based Matrices.  

PubMed

Dendrimer cross-linking has been achieved with pepsin digested over 80% type-I bovine collagen to create strong hydrogels with good cell compatibility. Herein we investigate the use of commercially available collagen-based products with the dendrimer cross-linking technology. Specifically PureCol(®) (PC), a 97% bovine type-I collagen, human collagen (HC) and human extracellular matrix (hECM) were concentrated, and then cross-linked with polypropyleneimine octaamine generation two dendrimers using 1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) chemistry. PC gels with 30 and 20 mg/ml bovine collagen were fabricated, and despite similar concentrations to >80% type-I bovine collagen dendrimer cross-linked gels (CG), PC gels demonstrated increased swelling and decreased stability, as determined with collagenase digestion. The highly purified bovine (PC) and human sourced-collagen (HC) gels were similar in performance, but not as stable as the CG gels, which may correlate to the manufacturer's collagen purification and storage. Finally, the addition of hECM components to PC to create PC-hECM gels, resulted in a looser gel network, compared to heparinized dendrimer cross-linked bovine >80% type-I collagen gels (CHG). However, all collagen-based gels supported 3T3 fibroblast cell growth over 4 days, indicating these gels may be suitable for tissue-engineering applications. PMID:22137239

Princz, M A; Sheardown, H

2011-12-01

46

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.

Light, N D; Bailey, A J

1980-01-01

47

Ionic conductivity and electrochemical properties of cross-linked poly[siloxane- g-oligo(ethylene oxide)] gel-type polymer electrolyte  

Microsoft Academic Search

Poly[siloxane-g-oligo(ethylene oxide)] tetraacrylate cross-linker was synthesized, and the gel polymer electrolytes (GPE) was prepared by thermal curing using them. Increase of conductivity with decrease of Tg was observed as the content of liquid electrolyte increased. Maximum conductivity was found to be 3.92 × 10?3S\\/cm at 30°C with a 70wt.% 1M LiPF6 in EC\\/PC (1:1). The electrochemical stability of the resulting

Junkyoung Lee; Yongku Kanga; Dong Hack Suh; Changjin Lee

2004-01-01

48

Cross-linking casein micelles by a microbial transglutaminase: influence of cross-links in acid-induced gelation  

Microsoft Academic Search

Mechanical and structural properties of transglutaminase-induced casein gels are described here and compared with those of traditional acid casein gels. These gels were characterised by rheology and microscopy (confocal laser scanning microscopy and transmission electron microscopy). Unlike traditional casein gels produced by acidification and\\/or renneting which lead to gels cross-linked by weak physical interactions, gels formed using transglutaminase are covalently

C Schorsch; H Carrie; I. T Norton

2000-01-01

49

Photoreactivities and thermal properties of psoralen cross-links  

SciTech Connect

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

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

1988-05-03

50

Collagen cross linking: Current perspectives  

PubMed Central

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

Rao, Srinivas K

2013-01-01

51

Microrheology of cross-linked polymers  

NASA Astrophysics Data System (ADS)

We use different microrheological techniques to investigate the elastic and viscous properties of polyacrylamide, a chemically cross-linked polymer. We have already shown^1 that a localized probe of the mechanical properties using light scattering compares very well with macrorheology measurements for polyethylene oxide, a simple flexible polymer. The addition of cross-linkers to a polymeric system is the next level of complexity that needs to be investigated using this technique. We probe both the sol and the gel phases of polyacrylamide. The two different phases are obtained by changing the concentration of acrylamide and methylenebisacrylamide, the cross-linking agent. We employ single scattering, diffusing wave spectroscopy and multi-particle tracking to measure the dynamics of the probe particles that are embedded in the polymer and compare it with bulk measurements. Light scattering probes the ensemble averaged response of the beads at higher frequencies while particle tracking can measure a local response of the polymer. ^1Bivash R. Dasgupta, Shang-You Tee, John C. Crocker, B.J. Frisken, and D.A. Weitz, PRE 65 051505 (2002).

Dasgupta, Bivash R.; Weitz, D. A.

2003-03-01

52

Diepoxybutane and diepoxyoctane interstrand cross-linking of the 5S DNA nucleosomal core particle.  

PubMed

Diepoxyalkanes form interstrand cross-links in DNA oligomers preferentially at 5'-GNC sites. We have examined cross-linking by 1,2,3,4-diepoxybutane (DEB) and 1,2,7,8-diepoxyoctane (DEO) within a fragment of the 5S RNA gene of Xenopus borealis in both the free and nucleosomal states. Sites and efficiencies of interstrand cross-linking were probed through denaturing polyacrylamide gel electrophoresis and quantitative phosphorimagery. Both agents targeted 5'-GNC sites for cross-linking in the restriction fragment in its free state, and DEO also targeted 5'-GNNC sites. Monoalkylation occurred at all deoxyguanosines. The sites for both monoalkylation and interstrand cross-linking were similar in nucleosomal and free DNA, and cross-linked DNA was cleanly incorporated into the core particle structure. These findings suggest that the 5S core particle is able to tolerate any structural abnormalities induced by diepoxide cross-linking. PMID:11524013

Millard, J T; Wilkes, E E

2001-09-01

53

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...

54

Electrospun cross linked rosin fibers  

NASA Astrophysics Data System (ADS)

In this study, we describe the first reported preparation of rosin in fiber form through use of an electrospinning technique utilizing various solvent systems. The polymer concentration of the formed fiber was studied by using various solvents such as chloroform, ethanol, N-N dimethylformamide (DMF), tetrahydrofuran (THF), acetone, and methylene chloride (MC). An electrospray of the solution resulted in the beaded form of the rosin. By varying the polymer concentration with MC, we were then able to obtain uniform fibers. However, the fibers exhibited large diameter. We believe that it is possible to reduce the diameter of the rosin fibers through appropriate selection of electrospinning parameters. In addition, the morphological transitions from beads, to beaded fiber, to fiber were studied at different polymer concentrations. We propose a possible physical cross linking mechanism for the formation of rosin fibers during the electrospinning process. Our results demonstrate the feasibility of producing fiber nanostructures of rosin by using an electrospinning technique.

Baek, Woo-il; Nirmala, R.; Barakat, Nasser A. M.; El-Newehy, Mohamed H.; Al-Deyab, Salem S.; Kim, Hak Yong

2011-12-01

55

Graphene oxide cross-linked chitosan nanocomposite membrane  

NASA Astrophysics Data System (ADS)

Graphene oxide (GO) cross-linked chitosan (CS) nanocomposite membrane is firstly reported in this study. At elevated temperatures, the cross-linking reaction between amino groups of CS and epoxy groups of GO happens which significantly affects the properties of membranes. The physicochemical properties of nanocomposite membranes have been examined by various methods including the gel content test, Fourier transform infrared (FTIR), differential scanning calorimeter (DSC), scanning electron microscope (SEM), transmission electron microscope (TEM) and tensile strength test. Interestingly, the tensile strength of chitosan membranes is greatly improved by GO incorporation. The 1 wt% loading of GO can improve the tensile strength from 43.2 MPa to 104.2 MPa with the increment of 141%. This should be attributed to the effective load transfer between GO and CS arising from the good interfacial properties after cross-linking reactions. Therefore, the biocompatible nanocomposite membranes with enhanced physicochemical properties are promising for diverse applications.

Shao, Lu; Chang, Xiaojing; Zhang, Yongling; Huang, Yifeng; Yao, Yuhuan; Guo, Zhanhu

2013-09-01

56

Poly(ethylene oxide) induced cross-linking modification of Matrimid membranes for selective separation of CO 2  

Microsoft Academic Search

The novel cross-linker, poly(propylene glycol) block poly(ethylene glycol) block poly(propylene glycol) diamine (PPG\\/PEG\\/PPGDA), was employed to chemically cross-link Matrimid 5218 at room temperature. The cross-linking reaction process was monitored by FTIR. The XRD was used to indicate the changing of the polymer structure by cross-linking reaction. The effects of the cross-linking reaction on mechanical performance, gel content and H2, CO2,

Hong-Yong Zhao; Yi-Ming Cao; Xiao-Li Ding; Mei-Qing Zhou; Jian-Hui Liu; Quan Yuan

2008-01-01

57

Influence of cross-linking degree on shape memory effect of styrene copolymer  

NASA Astrophysics Data System (ADS)

This paper is concerned about the synthesis of shape memory styrene copolymer and the investigation of the influence of cross-linking degree on its shape memory effect. As one of novel actuators in smart materials, shape memory polymers (SMPs) have been investigated intensively. Styrene copolymer with proper cross-linking degree can exhibit shape memory effect (SME). In this paper, the influence of cross-linking degree on shape memory effect of styrene copolymer was investigated through altering the dosage of cross-linking agent. The cross-linking degree of styrene copolymer was determined by measuring the gel content. The glass transition temperature (Tg) of styrene copolymer, which is determined the cross-linking degree, was measured by Dynamic Mechanical Analysis (DMA). The shape memory performance of styrene copolymer with different cross-linking degrees was also evaluated. Results indicated that the shape memory polymer (SMP) was synthesized successfully. The Tg increased from 55°C to 80.7°C followed by increasing the gel content from 0% to 80% through increasing the dosage of cross-linking agent from 0% to 4%. Moreover, the SMP experienced good SME and the largest reversible strain of the SMP reached as high as 150%. When heating above Tg+30°C (different copolymers performed different Tg), the shape recovery speed of the copolymers increased with increasing the gel content. However, the recovery speed decreased with increasing the gel content at the same temperature of 95°C.

Zhang, Dawei; Lan, Xin; Liu, Yanju; Leng, Jinsong

2007-04-01

58

Corneal collagen cross-linking.  

PubMed

Corneal collagen cross-linking (CXL) with riboflavin and ultraviolet-A (UVA) is a new technique of corneal tissue strengthening by using riboflavin as a photosensitizer and UVA to increase the formation of intra and interfibrillar covalent bonds by photosensitized oxidation.Keratocyte apoptosis in the anterior segment of the corneal stroma all the way down to a depth of about 300 microns has been described and a demarcation line between the treated and untreated cornea has been clearly shown. It is important to ensure that the cytotoxic threshold for the endothelium has not been exceeded by strictly respecting the minimal corneal thickness. Confocal microscopy studies show that repopulation of keratocytes is already visible 1 month after the treatment, reaching its pre-operative quantity and quality in terms of functional morphology within 6 months after the treatment. The major indication for the use of CXL is to inhibit the progression of corneal ectasias, such as keratoconus and pellucid marginal degeneration. CXL may also be effective in the treatment and prophylaxis of iatrogenic keratectasia, resulting from excessively aggressive photoablation. This treatment has also been used to treat infectious corneal ulcers with apparent favorable results. Combination with other treatments, such as intracorneal ring segment implantation, limited topography-guided photoablation and conductive keratoplasty have been used with different levels of success. PMID:20543933

Jankov Ii, Mirko R; Jovanovic, Vesna; Nikolic, Ljubisa; Lake, Jonathan C; Kymionis, Georgos; Coskunseven, Efekan

2010-01-01

59

Controlled compaction with ruthenium-catalyzed photochemical cross-linking of fibrin-based engineered connective tissue.  

PubMed

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

2009-09-25

60

Controlled degradation of hydrogels using multi-functional cross-linking molecules.  

PubMed

Hydrogels, chemically cross-linked or physically entangled, have found a number of applications as novel delivery vehicles of drugs and cells. However, the narrow ranges of degradation rates and mechanical strength currently available from many hydrogels limits their applications. We have hypothesized that utilization of multi-functional cross-linking molecules to form hydrogels could provide a wider range and tighter control over the degradation rates and mechanical stiffness of gels than bi-functional cross-linking molecules. To address the possibility, we isolated alpha-L-guluronate residues of sodium alginate, and oxidized them to prepare poly(aldehyde guluronate) (PAG). Hydrogels were formed with either poly(acrylamide-co-hydrazide) (PAH) as a multi-functional cross-linking molecule or adipic acid dihydrazide (AAD) as a bi-functional cross-linking molecule. The initial properties and degradation behavior of both PAG gel types were monitored. PAG/PAH hydrogels showed higher mechanical stiffness before degradation and degraded more slowly than PAG/AAD gels, at the same concentration of cross-linking functional groups. The enhanced mechanical stiffness and prolonged degradation behavior could be attributed to the multiple attachment points of PAH in the gel at the same concentration of functional groups. This approach to regulating gel properties with multifunctional cross-linking molecules could be broadly used in hydrogels. PMID:14751730

Lee, Kuen Yong; Bouhadir, Kamal H; Mooney, David J

2004-06-01

61

Cross-Linked Poly(Ester-Acetals).  

National Technical Information Service (NTIS)

The cross-linked products have utility as bonding agents for glass laminates. Certain novel soluble poly(ester-acetal) resins initially formed under alkaline conditions, under which the acetal groups appear to be inactive, may be crossed-linked by the add...

E. H. Pryde

1965-01-01

62

Genipin-Cross-linked Electrospun Collagen Fibers.  

PubMed

The fabrication of a fibrous collagen scaffold using electrospinning is desirable for tissue-engineering applications. Previously, electrospun collagen fibers were shown to be unstable in aqueous environments and, therefore, cross-linking is essential to stabilize these fibers. In this study genipin, a significantly less cytotoxic cross-linking agent compared to glutaraldehyde, was used to cross-link electrospun collagen fibers. The significance of this research lies in the use of four alcohol/water solvent systems to carry out the cross-linking reaction to maintain fibrous morphology during cross-linking. The four cross-linking conditions established were: (1) ethanol, 5% water and 3 days, (2) ethanol, 3% water and 5 days, (3) ethanol, 5% water and 5 days, and (4) isopropanol, 5% water and 5 days at a genipin concentration of 0.03 M. Results illustrated that genipin-cross-linking was effective in maintaining collagen fiber integrity in aqueous and cell culture media environments for up to 7 days. In addition, it was shown that fiber swelling could be controlled by using different cross-linking conditions. Swelling of cross-linked fibers immersed in Dulbecco's modified eagle medium for 7 days ranged from 0 to 59±4%. The cross-linked fibers were analyzed using scanning electron microscopy, Fourier transform infrared spectroscopy and ninhydrin assay. Finally, studies using primary human fibroblasts indicated good cell adhesion to these scaffolds. Overall, our data suggest that these stabilized fibrous collagen scaffolds provide a promising environment for tissue-regeneration applications. PMID:21083975

Mekhail, Mina; Wong, Kenneth Kar Ho; Padavan, Donna Teresa; Wu, Yan; O'Gorman, David B; Wan, Wankei

2010-11-17

63

Cross-Linked Antioxidant Nanozymes for Improved Delivery to CNS  

PubMed Central

Formulations of antioxidant enzymes, superoxide dismutase 1 (SOD1, also known as Cu/Zn SOD) and catalase were prepared by electrostatic coupling of enzymes with cationic block copolymers, polyethyleneimine-poly(ethylene glycol) or poly(L-lysine)-poly(ethylene glycol), followed by covalent cross-linking to stabilize nanoparticles. Different cross-linking strategies (using glutaraldehyde, bis-(sulfosuccinimidyl)suberate sodium salt or 1-Ethyl-3-[3-dimethylaminopropyl]carbodiimide hydrochloride with N-hydroxysulfosuccinimide) and reaction conditions (pH and polycation/protein charge ratio) were investigated that allowed immobilizing active enzymes in cross-linked nanoparticles, termed “nanozymes”. Bi-enzyme nanoparticles, containing both SOD1 and catalase were also formulated. Formation of complexes was confirmed using denaturing gel electrophoresis and western blotting and physicochemical characterization was conducted using dynamic light scattering and atomic force microscopy. In vivo studies of 125I-labeled SOD1-containing nanozymes in mice demonstrated its increased stability in both blood and brain and increased accumulation in brain tissues, compared to non-cross-linked complexes and native SOD1. Future studies will evaluate potential of these formulations for delivery of antioxidant enzymes to central nervous system to attenuate oxidative stress associated with neurological diseases.

Klyachko, Natalia L.; Manickam, Devika S.; Brynskikh, Anna M.; Uglanova, Svetlana V.; Li, Shu; Higginbotham, Sheila M.; Bronich, Tatiana K.; Batrakova, Elena V.; Kabanov, Alexander V.

2011-01-01

64

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

NASA Astrophysics Data System (ADS)

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

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

2013-07-01

65

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

66

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

67

Thermal Stability of Cross-Linked Polyethylene.  

National Technical Information Service (NTIS)

The investigation demonstrated the fact that many different forms of polymerized trimethyl dihydro quinoline are available and that the 150C. oven aging characteristics of cross-linked polyethylene are sometimes affected by which of the various forms is e...

A. C. Bluestein J. C. Henderson

1966-01-01

68

Phenol Oxidase Mediated Protein Cross-Linking.  

National Technical Information Service (NTIS)

This project is examining the mechanisms of protein cross linking induced by phenol oxidase mediated processes in the schistosome eggshell. Synthetic peptides are being used as models for this process. Physical and chemical techniques are being used to ex...

C. R. Middaugh J. S. Cordingley

1988-01-01

69

Intramolecular cross-linking in the native JHBP molecule.  

PubMed

Juvenile hormone binding protein (JHBP) acts as a shuttle, carrying one of the most crucial hormones for insect development to target tissues. We have found that although the JHBP molecule does not contain tryptophan residues, it exhibits a weak fluorescence maximum near 420nm upon excitation at 315nm. Gel filtration experiments performed in denaturing conditions and ESI-MS analyses excluded the possibility that some low molecular ligand was bound to the protein molecules. Further UV and CD spectroscopy studies, as well as immunoblotting, showed that the unusual JHBP optical properties were due to dityrosine intramolecular cross-linking. These bridges were detected both in native and recombinant protein molecules. We believe that in Galleria mellonella hemolymph the DT generation occurs via ROS-mediated oxidation leading to the formation of cross-linked JHBP monomers. MS analyses of peptides generated after JHBP proteolysis indicated, that the dityrosine bridge occurs between the Y128 and Y130 residues. PMID:22086120

Bystranowska, Dominika; Szewczuk, Zbigniew; Lisowski, Marek; Sitkiewicz, Ewa; Dobryszycki, Piotr; O?yhar, Andrzej; Kochman, Marian

2011-11-09

70

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

2013-07-16

71

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.

Steen, Hanno; Petersen, J?Rgen; Mann, Matthias; Jensen, Ole N.

2001-01-01

72

The 5'-GNC Site for DNA Interstrand Cross-Linking is Conserved for Diepoxybutane Stereoisomers  

PubMed Central

The bifunctional alkylating agent 1,2,3,4-diepoxybutane forms interstrand DNA-DNA cross-links between the N7 positions of deoxyguanosine residues on opposite strands of the duplex. For racemic diepoxybutane, these cross-links predominate within 5’-GNC/3’CNG sequences, where N is any nucleotide. We used denaturing polyacrylamide gel electrophoresis (dPAGE) to examine the role of stereochemistry in the cross-linking reaction, subjecting a restriction fragment to cross-linking with S,S DEB, R,R DEB, or meso DEB. DNA cross-links generated by each isomer were isolated by dPAGE, and the sites of cross-linking were identified by sequencing gel analysis of DNA fragments generated by hot piperidine cleavage. We found that the 5’-GNC consensus sequence of racemic DEB is conserved, but the efficiencies of cross-linking vary, with S,S > R,R > meso DEB. These results help explain the observed differences between the biological activities of DEB stereoisomers.

Millard, Julie T.; Hanly, Trevor C.; Murphy, Kris; Tretyakova, Natalia

2006-01-01

73

Composition of cross-linked 125I-follitropin-receptor complexes  

SciTech Connect

Both of the alpha and beta subunits of intact human follitropin (FSH) were radioiodinated with SVI-sodium iodide and chloramine-T and could be resolved on sodium dodecyl sulfate-polyacrylamide gels. Radioiodinated FSH was affinity-cross-linked with a cleavable (nondisulfide) homobifunctional reagent to its membrane receptor on the porcine granulosa cell surface as well as to a Triton X-100-solubilized form of the receptor. Cross-linked samples revealed three additional bands of slower electrophoretic mobility, corresponding to 65, 83, and 117 kDa, in addition to the hormone bands. The hormone alpha beta dimer band corresponded to 43 kDa. Formation of the three bands requires the SVI-hormone to bind specifically to the receptor with subsequent cross-linking. Binding was prevented by an excess of the native hormone but not by other hormones. A monofunctional analog of the cross-linking reagent failed to produce the three bands. Reagent concentration-dependent cross-linking revealed that their formation was sequential; smaller complexes formed first and then larger ones. When gels of cross-linked complexes were treated to cleave covalent cross-links and then electrophoresed in a second dimension, 18-, 22-, and 34-kDa components were released, in addition to the alpha and beta subunits of the hormone.

Shin, J.; Ji, T.H.

1985-10-15

74

Susceptibility of an industrial ?-lactalbumin concentrate to cross-linking by microbial transglutaminase  

Microsoft Academic Search

The susceptibility of an industrial ?-lactalbumin concentrate to cross-linking with a microbial transglutaminase from Streptoverticillium mobaraense was investigated. At a protein concentration of 0.5% wv?1, the maximum cross-linking was observed at 50°C, pH 5 and at 5h of incubation time. Results from sodium dodecyl sulphate (SDS)-polyacrylamide gel electrophoresis showed that most of the monomeric form of ?-lactalbumin was converted to

Ranjan Sharma; Mila Zakora; Karsten B Qvist

2002-01-01

75

Actin Filament Length Tunes Elasticity of Flexibly Cross-Linked Actin Networks  

PubMed Central

Networks of the cytoskeletal biopolymer actin cross-linked by the compliant protein filamin form soft gels that stiffen dramatically under shear stress. We demonstrate that the elasticity of these networks shows a strong dependence on the mean length of the actin polymers, unlike networks with small, rigid cross-links. This behavior is in agreement with a model of rigid filaments connected by multiple flexible linkers.

Kasza, K.E.; Broedersz, C.P.; Koenderink, G.H.; Lin, Y.C.; Messner, W.; Millman, E.A.; Nakamura, F.; Stossel, T.P.; MacKintosh, F.C.; Weitz, D.A.

2010-01-01

76

Cross-linking of bacteriorhodopsin using specific carboxyl modifications and proteolytic cleavage  

Microsoft Academic Search

Specific carboxyl modification of purple membrane using a water-soluble carbodiimide yielded a mixture of oligomers, revealed by gel electrophoresis. Purple membrane pre-treated with papain or trypsin, cleaving the C-terminal tail, showed the same pattern of cross-linked products. Chymotryptic cleavage released amino acids 1-72 (7kD fragment) from the cross-linked products, as it did with native membrane. The tail and helices A

S. Wu-Chou; A. E. Robinson; E. Hrabeta; L. Packer

1984-01-01

77

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. 1 fig.

Steckle, W.P. Jr.; Apen, P.G.; Mitchell, M.A.

1998-01-20

78

Phenol Oxidase Mediated Protein Cross-Linking.  

National Technical Information Service (NTIS)

The aim of this research is to investigate the secondary structure of the highly repetitive schistosome eggshell protein known in our laboratory as F4. The schistosome eggshell is cross-linked by 'quinone tanning' apparently catalyzed by a copper dependen...

C. R. Middaugh J. S. Cordingley

1989-01-01

79

The effects of shear and proppant on the viscosity of cross-linked fracturing fluids  

SciTech Connect

Several frequently used cross-linked fracturing fluids, hereafter referred to as gels, have been evaluated as to the effects that shear and that 20/40 mesh sand proppant have on their rheological properties. A closed-loop pipe viscometer was used to evaluate the shear resistance and post-shear recovery of various gels as a function of pH, cross-linker type, polymer concentration, shear intensity (shear stress and shear rate), and shear duration. The aqueous-base gels that were tested included those made with guar, hydroxypropyl guar (HPG), and carboxymethyl hydroxyethyl cellulose (CMHEC) polymers. Selected aqueous-base gels were also evaluated as to the effect on slurry viscosity of varying concentrations of 20/40 mesh sand proppant. Test results indicate that when cross-linked with borate ions, guar and HPG gels have the greatest resistance to shear. Yet when cross-linked with various titanates, HPG gels showed significantly lower resistance to induced shear. Tests on CMHEC gels which were cross-linked with trivalent aluminum (A1+++) indicate a shear resistance between that of the HPG-borate gels and that of the HPG-titanate gels. Also tested was post-shear recovery or the percentage of viscosity increase following high shear exposure as correlated to field tubular pumping conditions. The HPG-borate gels and the CMHEC-A1+++ gels demonstrated considerably higher post-shear recoveries than those attained with HPG-titanate gels. In addition, the effect of 20/40 mesh sand on the viscosity of gels is a larger increase in slurry viscosity in the fracture than that predicted from Newtonian slurry mathematical models.

Gardner, D.

1982-09-01

80

Collagen cross-linking influences osteoblastic differentiation.  

PubMed

Osteoblasts synthesize collagen matrix, which itself regulates the differentiation of precursor cells into mature osteoblasts. They express lysyl oxidase (LOX), which is involved in the collagen cross-linking process. Lathyrogens, like ss-aminopropionitrile (ssAPN), inhibit the formation of a stable matrix. The aim of the present study was to investigate the influence of cross-linking on osteoblastic differentiation. MC3T3-E1 cells were seeded and treated with or without 400 muM ssAPN for 1 week. Thereafter, living cells were removed and, on this extracellular matrix, new MC3T3-E1 cells were seeded and cultured for 1 week without ssAPN. RNA was isolated, and expression of specific marker genes was determined by quantitative reverse transcription-polymerase chain reaction. Changes in specific cross-links after ssAPN treatment were measured with Fourier-transform infrared spectroscopy. The collagen matrix that formed showed a significant reduction of two major cross-links of bone collagen, deH-DHLNL and pyr, compared to control cultures. Gene expression studies showed an increase of collagen alpha1 (I) (COL1A1) to 150%. Expression of LOX and osteocalcin (OCN) mRNA was significantly downregulated to about 75%. When fresh MC3T3-E1 cells were seeded on this altered matrix without ssAPN, COL1A1 mRNA expression was upregulated (140%), OCN was downregulated (60%), and LOX mRNA expression remained unaffected. These results indicate that ssAPN treatment not only disrupts collagen cross-link formation but also affects osteoblastic activity and expression. In conclusion, the disrupted matrix produced in the presence of lathyrogen influences, even in its absence, the expression of osteoblastic genes. PMID:18488133

Turecek, C; Fratzl-Zelman, N; Rumpler, M; Buchinger, B; Spitzer, S; Zoehrer, R; Durchschlag, E; Klaushofer, K; Paschalis, E P; Varga, F

2008-05-17

81

Hydrogels Cross-Linked by Native Chemical Ligation  

PubMed Central

We describe the use of native chemical ligation (NCL) reaction to covalently cross-link soluble polymers into hydrogels. Macromonomers consisting of a four-armed poly(ethylene glycol) (PEG) core end-functionalized with either thioester or N-terminal cysteine peptide were designed and synthesized. Upon mixing aqueous solutions of the thioester and N-terminal cysteine macromonomers, rigid hydrogels formed within minutes. The gelation time was affected by choice of buffer, pH, polymer concentration, reaction temperature, and chemical composition of the N-terminal cysteine conjugate. The kinetics of gel formation and the viscoelastic behavior of selected hydrogels were further studied by oscillatory rheology, which demonstrated a minimum gel formation time of approximately two minutes and the formation of an elastic cross-linked hydrogel via the NCL reaction. A useful feature of this hydrogel strategy is the regeneration of thiol functional groups as a result of the NCL reaction, thereby allowing functionalization of the polymer hydrogel with biomolecules. This was demonstrated by conjugation of a maleimide-GRGDSPG-NH2 peptide to an NCL hydrogel, permitting the attachment of human mesenchymal stem cells (hMSCs) on the hydrogel. Due to the mild reaction conditions, chemoselectivity, and potential for biological functionalization, our approach may prove useful as a general method for hydrogel formation, including hydrogels intended for biomedical applications.

Hu, Bi-Huang; Su, Jing; Messersmith, Phillip B.

2009-01-01

82

Hydrogels cross-linked by native chemical ligation.  

PubMed

We describe the use of native chemical ligation (NCL) reaction to covalently cross-link soluble polymers into hydrogels. Macromonomers consisting of a four-armed poly(ethylene glycol) (PEG) core end-functionalized with either thioester or N-terminal cysteine peptide were designed and synthesized. Upon mixing aqueous solutions of the thioester and N-terminal cysteine macromonomers, rigid hydrogels formed within minutes. The gelation time was affected by choice of buffer, pH, polymer concentration, reaction temperature, and chemical composition of the N-terminal cysteine conjugate. The kinetics of gel formation and the viscoelastic behavior of selected hydrogels were further studied by oscillatory rheology, which demonstrated a minimum gel formation time of approximately two minutes and the formation of an elastic cross-linked hydrogel via the NCL reaction. A useful feature of this hydrogel strategy is the regeneration of thiol functional groups as a result of the NCL reaction, thereby allowing functionalization of the polymer hydrogel with biomolecules. This was demonstrated by conjugation of a maleimide-GRGDSPG-NH(2) peptide to an NCL hydrogel, permitting the attachment of human mesenchymal stem cells (hMSCs) on the hydrogel. Due to the mild reaction conditions, chemoselectivity, and potential for biological functionalization, our approach may prove useful as a general method for hydrogel formation, including hydrogels intended for biomedical applications. PMID:19601644

Hu, Bi-Huang; Su, Jing; Messersmith, Phillip B

2009-08-10

83

Cross-Linked Poled Polymer: Poling and Thermal Stability  

NASA Astrophysics Data System (ADS)

Cross-linked poled polymers were studied with a methacrylate polymer containing chromophores and epoxide groups as side chains. The cross-linking and poling processes were monitored by electrooptic (EO) measurement. Contribution of molecular motions of the chromophores was observed with low-frequency AC electric field. This contribution decreased as the cross-linking reaction proceeded, and was found to be a good monitor of poling with cross-linking. The resultant cross-linked poled polymers showed significant improvement of thermal stability. The stability was studied by changing the concentrations of cross-linking agents, curing temperatures, and type of cross-linking agent.

Aramaki, Shinji; Okamoto, Yuko; Murayama, Tetsuo

1994-10-01

84

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

NASA Astrophysics Data System (ADS)

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

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

2010-06-01

85

Complications of Corneal Collagen Cross-Linking  

PubMed Central

Cross-linking of corneal collagen (CXL) is a promising approach for the treatment of keratoconus and secondary ectasia. Several long-term and short-term complications of CXL have been studied and documented. The possibility of a secondary infection after the procedure exists because the patient is subjected to epithelial debridement and the application of a soft contact lens. Formation of temporary corneal haze, permanent scars, endothelial damage, treatment failure, sterile infiltrates, and herpes reactivation are the other reported complications of this procedure. Cross-linking is a low-invasive procedure with low complication and failure rate but it may have direct or primary complications due to incorrect technique application or incorrect patient's inclusion and indirect or secondary complications related to therapeutic soft contact lens, patient's poor hygiene, and undiagnosed concomitant ocular surface diseases.

Dhawan, Shikha; Rao, Kavita; Natrajan, Sundaram

2011-01-01

86

Cross-linked crystals of chloroperoxidase  

Microsoft Academic Search

Chloroperoxidase from Caldariomyces fumago was crystallized. The crystals were modified with several cross-linkers, but only glurataldehyde was able to produce catalytically active and insoluble crystals. Unlike other immobilized chloroperoxidase preparations, these catalytic crystals are more thermostable than the unmodified soluble enzyme. The enhanced stability is probably due to the structure conservation in the crystalline matrix. In addition, non-cross-linked chloroperoxidase crystals

Marcela Ayala; Eduardo Horjales; Michael A. Pickard; Rafael Vazquez-Duhalt

2002-01-01

87

Heparin-modified dendrimer cross-linked collagen matrices for the delivery of basic fibroblast growth factor (FGF-2).  

PubMed

Tissue integration between a tissue-engineered corneal equivalent and the host eye is of critical importance in ensuring long-term implant success. A novel dendrimer cross-linked collagen scaffold has previously shown good corneal epithelial cell compatibility in vitro particularly when the highly functional dendrimer cross-linkers were functionalized to introduce additional biological groups. Herein we investigated heparinization of these materials and their potential to facilitate the delivery of basic fibroblast growth factor (FGF-2) in an active form, ultimately for use as a corneal tissue scaffold. Collagen gels cross-linked with 1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) chemistry, and varying amounts of polypropyleneimine octaamine generation 2 (G2) dendimer and heparin were synthesized. Swelling studies and differential scanning calorimetry characterization indicated higher gel stability with the introduction of dendrimer cross-linking, which was not compromised by heparin integration. Dendrimer cross-linked gels with or without heparin gave multiple denaturation peaks, as did the heparinized EDC gels. This is thought to be the result of the heterogeneous cross-linking possible between collagen, the dendrimer and heparin. Release of FGF-2 from collagen gels showed typical first-order kinetics, with an initial burst followed by a prolonged gradual release. Heparinized dendrimer cross-linked gels released approx. 40% of the growth factor over a 2-week period, with significance maintenance of growth factor activity. Incorporation of heparin resulted in somewhat prolonged release from these systems. PMID:18727861

Princz, M A; Sheardown, H

2008-01-01

88

Collagen cross-linking in thin corneas  

PubMed Central

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

Padmanabhan, Prema; Dave, Abhishek

2013-01-01

89

Serologic and Histologic Findings in Patients with Capsular Contracture After Breast Augmentation with Smooth Silicone Gel Implants: Is Serum Hyaluronan a Potential Predictor?  

Microsoft Academic Search

Background: In this study, breast implant capsular tissues and blood samples from 25 cases were studied to characterize the relationship between capsular findings and serum analysis. The serum fibrosis indexes hyaluronan and the aminoterminal propeptide of procollagen type III (PIIINP) are fairly well correlated in several other studies with the inflammation grade and fibrosis in patients with progressive fibrotic disorders

L. Prantl; N. Pöppl; N. Horvat; N. Heine; M. Eisenmann-Klein

2005-01-01

90

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

2012-09-10

91

Design of Zero-Birefringence Cross-Linked Polymers  

NASA Astrophysics Data System (ADS)

We analyzed thermoplastic methacrylate polymers and found that their birefringence during polymerization is due to both orientational and photoelastic birefringence. We designed zero-birefringence cross-linked polymers that do not exhibit birefringence during the polymerization process or elastic deformation, and deduced the contributions of cross-linking agents to photoelastic coefficient by analyzing binary cross-linked polymers. When photoelastic coefficient values of ternary cross-linked polymers were almost zero, their average in-plane birefringence was linearly related with the concentration of cross-linking agents. Finally, we designed and demonstrated two types of zero-birefringence cross-linked polymers.

Yamazaki, Sayuri; Tagaya, Akihiro; Koike, Yasuhiro

2010-02-01

92

Polyimide aerogels cross-linked through amine functionalized polyoligomeric silsesquioxane.  

PubMed

We report the first synthesis of polyimide aerogels cross-linked through a polyhedral oligomeric silsesquioxane, octa(aminophenyl)silsesquioxane (OAPS). Gels formed from polyamic acid solutions of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), bisaniline-p-xylidene (BAX) and OAPS were chemically imidized and dried using supercritical CO(2) extraction to give aerogels having density around 0.1 g/cm(3). The aerogels are greater than 90 % porous, have high surface areas (230 to 280 m(2)/g) and low thermal conductivity (14 mW/m-K at room temperature). Notably, the polyimide aerogels cross-linked with OAPS have higher modulus than polymer reinforced silica aerogels of similar density and can be fabricated as both monoliths and thin films. Thin films of the aerogel are flexible and foldable making them an ideal insulation for space suits, and inflatable structures for habitats or decelerators for planetary re-entry, as well as more down to earth applications. PMID:21294517

Guo, Haiquan; Meador, Mary Ann B; McCorkle, Linda; Quade, Derek J; Guo, Jiao; Hamilton, Bart; Cakmak, Miko; Sprowl, Guilherme

2011-02-04

93

Triple shape memory effects of cross-linked polyethylene/polypropylene blends with cocontinuous architecture.  

PubMed

In this paper, the triple shape memory effects (SMEs) observed in chemically cross-linked polyethylene (PE)/polypropylene (PP) blends with cocontinuous architecture are systematically investigated. The cocontinuous window of typical immiscible PE/PP blends is the volume fraction of PE (v(PE)) of ca. 30-70 vol %. This architecture can be stabilized by chemical cross-linking. Different initiators, 2,5-dimethyl-2,5-di(tert-butylperoxy)-hexane (DHBP), dicumylperoxide (DCP) coupled with divinylbenzene (DVB) (DCP-DVB), and their mixture (DHBP/DCP-DVB), are used for the cross-linking. According to the differential scanning calorimetry (DSC) measurements and gel fraction calculations, DHBP produces the best cross-linking and DCP-DVB the worst, and the mixture, DHBP/DCP-DVB, is in between. The chemical cross-linking causes lower melting temperature (Tm) and smaller melting enthalpy (?Hm). The prepared triple shape memory polymers (SMPs) by cocontinuous immiscible PE/PP blends with v(PE) of 50 vol % show pronounced triple SMEs in the dynamic mechanical thermal analysis (DMTA) and visual observation. This new strategy of chemically cross-linked immiscible blends with cocontinuous architecture can be used to design and prepare new SMPs with triple SMEs. PMID:23713446

Zhao, Jun; Chen, Min; Wang, Xiaoyan; Zhao, Xiaodong; Wang, Zhenwen; Dang, Zhi-Min; Ma, Lan; Hu, Guo-Hua; Chen, Fenghua

2013-06-07

94

Contraction of cross-linked actomyosin bundles  

NASA Astrophysics Data System (ADS)

Cross-linked actomyosin bundles retract when severed in vivo by laser ablation, or when isolated from the cell and micromanipulated in vitro in the presence of ATP. We identify the timescale for contraction as a viscoelastic time ?, where the viscosity is due to (internal) protein friction. We obtain an estimate of the order of magnitude of the contraction time ? ? 10-100 s, consistent with available experimental data for circumferential microfilament bundles and stress fibers. Our results are supported by an exactly solvable, hydrodynamic model of a retracting bundle as a cylinder of isotropic, active matter, from which the order of magnitude of the active stress is estimated.

Yoshinaga, Natsuhiko; Marcq, Philippe

2012-08-01

95

Chemically Cross-Linked Heat-Shrinkable Polyethylene Tubes.  

National Technical Information Service (NTIS)

The memory effect of heat-shrinkable tubes made of low density polyethylene obtained by irradiation with accelerated electrons is presented. The dependence of the cross-linked polyethylene contraction force on time, temperature, degree of cross-linking, e...

C. Cazac I. Mihalcea S. Ilie S. Jipa V. Contineanu

1986-01-01

96

21 CFR 177.2420 - Polyester resins, cross-linked.  

Code of Federal Regulations, 2010 CFR

... Asbestos Glass fiber Polyester fiber produced by the... (c) The cross-linked polyester resins, with or...In accordance with good manufacturing practice, finished articles containing the cross-linked polyester resins shall be...

2009-04-01

97

21 CFR 177.2420 - Polyester resins, cross-linked.  

Code of Federal Regulations, 2010 CFR

... Asbestos Glass fiber Polyester fiber produced by the... (c) The cross-linked polyester resins, with or...In accordance with good manufacturing practice, finished articles containing the cross-linked polyester resins shall be...

2010-01-01

98

Chicken corneocyte cross-linked proteome.  

PubMed

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

2013-01-04

99

Cross-Linked Polyvinyl Alcohol and Method of Making Same.  

National Technical Information Service (NTIS)

A method is described for producing cross-linked polyvinyl alcohol battery separators. A film-forming polyvinyl alcohol resin is admixed, in aqueous solution, with a dialdehyde cross-linking agent which is capable of cross-linking the polyvinyl alcohol re...

D. W. Sheibley L. L. Rieker L. C. Hsu M. A. Manzo

1981-01-01

100

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

101

Genipin cross-linked alginate-chitosan microcapsules: membrane characterization and optimization of cross-linking reaction.  

PubMed

The genipin cross-linked alginate-chitosan (GCAC) microcapsule, composed of an alginate core and a genipin cross-linked chitosan membrane, was recently proposed for live cell encapsulation and other delivery applications. This article for the first time describes the details of the microcapsule membrane characterization using a noninvasive and in situ method without any physical or chemical modifications on the samples. Results showed that the cross-linking reaction generated the fluorescent chitosan-genipin conjugates. The cross-linked chitosan membrane was clearly visualized by confocal laser scanning microscopy (CLSM). A straightforward assessment on the membrane thickness and relative intensity was successfully achieved. CLSM studies showed that the shell-like cross-linked chitosan membranes of approximately 37 microm in thickness were formed surrounding the microcapsule. The reaction variables, including cross-linking temperature and time significantly affected the fluorescence intensity of the membranes. Elevating the cross-linking temperature from 4 to 37 degrees C drastically intensified the membrane fluorescence, suggesting the attainment of a high degree of cross-linking on the chitosan membrane. Extended cross-linking time altered the cross-linked membranes in modulation. Although genipin concentration and cross-linking time had little effects on the membrane thickness, cross-linking at higher temperatures tended to form relatively thinner membranes. PMID:16827575

Chen, Hongmei; Ouyang, Wei; Lawuyi, Bisi; Prakash, Satya

2006-07-01

102

[Riboflavin UVA cross-linking for keratoconus].  

PubMed

Keratoconus is a progressive, ectatic disease of the cornea leading to thinning and highly irregular astigmatism. Until recently all treatment options, such as prescription of glasses or contact lenses were symptomatic and neither keratoplasty nor the implantation of intracorneal rings can heal the disease. Riboflavin ultraviolet A (UVA) collagen cross-linking (CXL) cannot heal keratoconus either but promises to halt the progression. The therapeutic principle is a photochemical reaction of riboflavin and UVA light leading to free oxygen radicals in the corneal stroma that induce covalent linking of the collagen fibrils. This stiffening effect should stop the progression. After the first reports at the end of the 1990s the treatment was widely used and many case series show that CXL can be effective in stopping disease progression in some patients. However, randomized, controlled multicenter trials showing high evidence of the treatment effectiveness are rare. This report includes a review of the literature regarding treatment effectiveness, indications and new developments. PMID:23760423

Maier, P; Reinhard, T

2013-09-01

103

TGFbeta affects collagen cross-linking independent of chondrocyte phenotype but strongly depending on physical environment.  

PubMed

Transforming growth factor beta (TGFbeta) is often used in cartilage tissue engineering to increase matrix formation by cells with various phenotypes. However, adverse effects of TGFbeta, such as extensive crosslinking in cultured fibroblasts, have also been reported. Our goal was to study effects of TGFbeta on collagen cross-linking and evaluating the role of cellular phenotype and physical environment. We therefore used four different cell populations in two very different physical environments: primary and expanded chondrocytes and fibroblasts embedded in alginate gel and attached to tissue culture plastic. Matrix production, collagen cross-linking, and alpha-smooth muscle actin (alphaSMA) were analyzed during 4 weeks with or without 2.5 ng/ mL TGFbeta2. TGFbeta2 did not affect collagen deposition by primary cells. In expanded cells, TGFbeta2 increased collagen deposition. Chondrocytes and fibroblasts in monolayer produced more collagen cross-links with TGFbeta2. In alginate, primary and expanded cells displayed an unexpected decrease in collagen cross-linking with TGFbeta2. alphaSMA was not present in alginate cultures and barely upregulated by TGFbeta2. Organized alphaSMA fibers were present in all monolayer cultures and became more pronounced with TGFbeta2. This study demonstrates that the physical environment determined by the substrate used co-determines the response of cells to TGFbeta. The presence of mechanical stress, determined with alphaSMA-staining, is probably responsible for the increase in collagen cross-linking upon addition of TGFbeta. PMID:19230128

Bastiaansen-Jenniskens, Yvonne Maria; Koevoet, Wendy; De Bart, Anton C W; Zuurmond, Anne-Marie; Bank, Ruud A; Verhaar, Jan A N; DeGroot, Jeroen; van Osch, Gerjo J V M

2008-06-01

104

Chemical model for the rheological behavior of cross-linked fluid systems  

SciTech Connect

The use of cross-linking agents to improve viscosity in polysaccharide polymer fluids is a widespread practice in hydraulic fracturing. The viscosity obtained from the use of a particular cross-linking agent depends entirely on the parameters of the in-situ chemical reaction to be performed at the well site. The major parameters encountered, such as concentration of polymer and cross-linking agent, pH, temperature, and shear regimen, will dictate the apparent viscosity of the product generated by the reaction. A mechanistic model for this cross-linking reaction is presented along with a description of the general effects of concentration, pH, temperature, and shear levels. Macroscopic observation of an ideal ''complexed'' gel is discussed using the most significant reaction parameters. Data show that the rheological properties of a cross-linked fracturing fluid are time-dependent and vary widely, depending on the reaction parameters to be encountered at the well site during a fracture treatment.

Conway, M.W.; Almond, S.W.; Briscoe, J.E.; Harris, L.E.

1983-02-01

105

Cross-Link Guided Molecular Modeling with ROSETTA.  

PubMed

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

Kahraman, Abdullah; Herzog, Franz; Leitner, Alexander; Rosenberger, George; Aebersold, Ruedi; Malmström, Lars

2013-09-17

106

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.

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

2013-01-01

107

Vitamin C hinders radiation cross-linking in aqueous poly(vinyl alcohol) solutions  

NASA Astrophysics Data System (ADS)

Poly(vinyl alcohol) (PVA) is a promising semi-crystalline material for biomedical applications. It is soluble in water and can be formed into hydrogels by freezing and thawing or crystallizing from an aqueous theta solution such as that of polyethylene glycol (PEG). Radiation cross-linking caused by sterilization or high dose irradiation of concentrated PVA solutions could compromise some properties of these hydrogels. Therefore, we hypothesized that radiation cross-linking of PVA solutions and PVA PEG theta gels could be prevented by using the antioxidant vitamin C as an anticross-linking agent. Our hypothesis tested positive. Vitamin C concentrations of 0.75 and 4.5 mol/mol of PVA repeating unit could prevent cross-linking in 17.5 wt/v% PVA solutions made with PVA molecular weight of 115,000 g/mol irradiated to 25 and 100 kGy, respectively. Vitamin C also prevented cross-linking in 25 kGy irradiated PVA PEG theta gels containing up to 5 wt% PEG and decreased the viscosity of those up to 39 wt%.

Oral, Ebru; Bodugoz-Senturk, Hatice; Macias, Celia; Muratoglu, Orhun K.

2007-12-01

108

Corneal Cross-Linking and Safety Issues  

PubMed Central

Purpose: To compile the safety aspects of the corneal collagen cross-linking (CXL) by means of the riboflavin/UVA (370 nm) approach. Materials and Methodology: Analysis of the current treatment protocol with respect to safety during CXL. Results: The currently used UVA dose density of 5.4 J/cm2 and the corresponding irradiance of 3 mW/cm2 are below the known damage thresholds of UVA for the corneal endothelium, lens, and retina. Regarding the photochemical damages due to the free radicals the damage threshold for endothelial cells is 0.35 mW/cm2. In a 400?m thick corneal stroma saturated with riboflavin, the irradiance at the endothelial level is about 0.18 mW/cm2, which is a factor of 2 smaller than the damage threshold. Conclusion: As long as the corneal stroma treated has a minimal thickness of 400 microns (as recommended), neither corneal endothelium nor deeper structures such as lens and retina will suffer any damages. The light source should provide a homogenous irradiance avoiding hot spots.

Spoerl, Eberhard; Hoyer, Anne; Pillunat, Lutz E; Raiskup, Frederik

2011-01-01

109

Nonlinear elasticity of cross-linked networks  

NASA Astrophysics Data System (ADS)

Cross-linked semiflexible polymer networks are omnipresent in living cells. Typical examples are actin networks in the cytoplasm of eukaryotic cells, which play an essential role in cell motility, and the spectrin network, a key element in maintaining the integrity of erythrocytes in the blood circulatory system. We introduce a simple mechanical network model at the length scale of the typical mesh size and derive a continuous constitutive law relating the stress to deformation. The continuous constitutive law is found to be generically nonlinear even if the microscopic law at the scale of the mesh size is linear. The nonlinear bulk mechanical properties are in good agreement with the experimental data for semiflexible polymer networks, i.e., the network stiffens and exhibits a negative normal stress in response to a volume-conserving shear deformation, whereby the normal stress is of the same order as the shear stress. Furthermore, it shows a strain localization behavior in response to an uniaxial compression. Within the same model we find a hierarchy of constitutive laws depending on the degree of nonlinearities retained in the final equation. The presented theory provides a basis for the continuum description of polymer networks such as actin or spectrin in complex geometries and it can be easily coupled to growth problems, as they occur, for example, in modeling actin-driven motility.

John, Karin; Caillerie, Denis; Peyla, Philippe; Raoult, Annie; Misbah, Chaouqi

2013-04-01

110

Clinical fracture of cross-linked UHMWPE acetabular liners  

Microsoft Academic Search

Highly cross-linked ultrahigh molecular weight polyethylene (UHMWPE) is increasingly used as a bearing material in total hip replacements. Cross-linking of UHMWPE has been shown to increase wear resistance but decrease its fracture resistance. We analyzed the clinical fracture failure of four cross-linked UHMWPE total hip replacement components of four different designs via microscopic observation of the fracture surfaces, and found

Jevan Furmanski; Martin Anderson; Sonny Bal; A. Seth Greenwald; David Halley; Brad Penenberg; Michael Ries; Lisa Pruitt

2009-01-01

111

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

112

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

113

Rheological Characteristics of Adjustable Cross-Linked Fracturing Fluids  

Microsoft Academic Search

A study was done evaluating apparent viscosity and fluid stability by allowing cross-linking to occur at varying times during and after a period of high shear. A high temperature closed-loop pipe viscometer was used for this process. To observe the interdependencies of shear history, cross-linking time, and apparent viscosity, two adjustable cross-linked fracturing fluid systems were employed. As part of

T. N. Royce; L. M. Beck; A. R. Rickards

1984-01-01

114

Current status of accelerated corneal cross-linking  

PubMed Central

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

Mrochen, Michael

2013-01-01

115

Filamin Cross-Linked Semiflexible Networks: Fragility under Strain  

Microsoft Academic Search

The semiflexible F-actin network of the cytoskeleton is cross-linked by a variety of proteins including filamin, which contains Ig domains that unfold under applied tension. We examine a simple filament network model cross-linked by such unfolding linkers that captures the main mechanical features of F-actin networks cross-linked by filamin proteins and show that, under sufficient strain, the network spontaneously self-organizes

B. A. Didonna; Alex J. Levine

2006-01-01

116

Isolation of Proteins Cross-linked to DNA by Formaldehyde  

Microsoft Academic Search

\\u000a Formaldehyde is a reversible cross-linker that will cross-link protein to DNA, RNA, or protein (1). Because of its high-resolution (2 Å) cross-linking, formaldehyde is a useful agent to cross-link a DNA binding protein\\u000a of interest to DNA. For example, formaldehyde has been used to cross-link proteins to DNA in studies fine-mapping the distribution\\u000a of particular DNA binding proteins along specific

Virginia A. Spencer; James R. Davie

117

Cross-Linked Poly(acrylic acid) Microgels from Precipitation Polymerization  

Microsoft Academic Search

Cross-linked poly(acrylic acid) microgels were prepared via thermally initiated free-radical precipitation polymerization in a binary organic solvent. N,N?-Methylenebisacrylamide (MBA) and 2,2?-azobisisobutyronitrile were used as cross-linker and initiator, respectively. The effect of (MAB) concentration on different features of sample (i.e., spectral characteristics, glass transition temperature, equilibrium swelling, gel content and rheological properties) was investigated. The Flory-Rehner equation and rubber elasticity theory

H. Es-haghi; H. Bouhendi; Gh. Bagheri-Marandi; M. J. Zohurian-Mehr; K. Kabiry

2010-01-01

118

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.

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

119

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

120

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

121

Identification of the bombesin receptor on murine and human cells by cross-linking experiments  

SciTech Connect

The bombesin receptor present on the surface of murine and human cells was identified using /sup 125/I-labeled gastrin-releasing peptide as a probe, the cross-linking agent disuccinimidyl suberate, and sodium dodecyl sulfate gels. A clone of NIH-3T3 cells which possesses approximately 80,000 bombesin receptors/cell with a single binding constant of approximately 1.9 X 10(-9) M was used in these studies. In addition, we used Swiss 3T3 cells and a human glioma cell line which possesses approximately 100,000 and approximately 55,000 bombesin receptors/cell, respectively. Under conditions found optimal for binding, it is demonstrated that /sup 125/I-labeled gastrin-releasing peptide can be cross-linked specifically to a glycoprotein of apparent molecular mass of 65,000 daltons on the surface of the NIH-3T3 cells. Similar results were obtained when the cross-linked product was analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis under reducing or non-reducing conditions. Moreover, the cross-linking reaction is specific and saturable and the 65,000-dalton polypeptide is not observed when the cross-linking experiments were performed with a NIH-3T3 cell line which is devoid of bombesin receptors. Interestingly, glycoproteins with apparent molecular weights of 75,000 were labeled specifically by /sup 125/I-labeled gastrin-releasing peptide when similar experiments were performed with Swiss 3T3 cells and with human glioma cell line GM-340. These different molecular weights may indicate differential glycosylation as treatment with the enzyme N-glycanase reduced the apparent molecular weight of the cross-linked polypeptide to 45,000. On the basis of these results it is concluded that the cross-linked polypeptides represent the bombesin receptor or the ligand-binding subunit of a putative larger bombesin receptor expressed on the surface of these cells.

Kris, R.M.; Hazan, R.; Villines, J.; Moody, T.W.; Schlessinger, J.

1987-08-15

122

Quantitative evaluation of protein conformation in pharmaceuticals using cross-linking reactions coupled with LC-MS/MS analysis.  

PubMed

The need for a simple and high-throughput method for identifying the tertiary structure of protein pharmaceuticals has increased. In this study, a simple method for mapping the protein fold is proposed for use as a complementary quality test. This method is based on cross-linking a protein using a [bis(sulfosuccinimidyl)suberate (BS(3))], followed by peptide mapping by LC-MS. Consensus interferon (CIFN) was used as the model protein. The tryptic map obtained via liquid chromatography tandem mass spectroscopy (LC-MS/MS) and the mass mapping obtained via matrix-assisted laser desorption/ionization time-of-flight mass spectroscopy were used to identify cross-linked peptides. While LC-MS/MS analyses found that BS(3) formed cross-links in the loop region of the protein, which was regarded as the biologically active site, sodium dodecyl-sulfate polyacrylamide gel electrophoresis demonstrated that cross-linking occurred within a protein molecule, but not between protein molecules. The occurrence of cross-links at the active site depends greatly on the conformation of the protein, which is determined by the denaturing conditions. Quantitative evaluation of the tertiary structure of CIFN was thus possible by monitoring the amounts of cross-linked peptides generated. Assuming that background information is available at the development stage, this method may be applicable to process development as a complementary test for quality control. PMID:21367553

Yamaguchi, Hideto; Hirakura, Yutaka; Shirai, Hiroki; Mimura, Hisashi; Toyo'oka, Toshimasa

2011-03-01

123

DNA interstrand cross-links of trans-diamminedichloroplatinum(II) are preferentially formed between guanine and complementary cytosine residues.  

PubMed Central

Bases in the opposite strands of DNA cross-linked by clinically ineffective trans-diamminedichloroplatinum(II) (trans-[Pt(NH3)2Cl2]) have been identified by means of three experimental approaches. These include HPLC analysis of enzymatic digests of synthetic oligonucleotide duplexes containing the interstrand cross-link, footprinting experiments on the interstrand cross-linked oligonucleotide duplexes, and termination of the duplex transcription on trans-[Pt(NH3)2Cl2]-treated fragments of plasmid DNA. The results reveal that deoxyguanine and complementary deoxycytosine residues are preferential binding sites of trans-[Pt(NH3)2Cl2] in the interstrand adducts. The interstrand cross-linking reaction was studied by means of gel electrophoresis for the cis and trans isomers. The rate of formation of interstrand cross-links was lower for the trans isomer; however, trans-[Pt(NH3)2Cl2] formed about twice the amount of interstrand cross-links as compared with the cis isomer after 48 hr. The present results are suggested to be relevant to differences in clinical activity of the two platinum(II) isomers. Images Fig. 2 Fig. 3 Fig. 4

Brabec, V; Leng, M

1993-01-01

124

Deformation of Cross-Linked Semiflexible Polymer Networks  

NASA Astrophysics Data System (ADS)

Networks of filamentous proteins play a crucial role in cell mechanics. These cytoskeletal networks, together with various cross-linking and other associated proteins largely determine the (visco)elastic response of cells. In this Letter we study a model system of cross-linked, stiff filaments in order to explore the connection between the microstructure under strain and the macroscopic response of cytoskeletal networks. We find two distinct regimes as a function primarily of cross-link density and filament rigidity: one characterized by affine deformation and one by nonaffine deformation. We characterize the crossover between these two.

Head, David A.; Levine, Alex J.; Mackintosh, F. C.

2003-09-01

125

Current status of accelerated corneal cross-linking.  

PubMed

Corneal cross-linking with riboflavin is a technique to stabilize or reduce corneal ectasia, in diseases such as keratoconus and post-laser-assisted in situ keratomileusis (LASIK) ectasia. There is an interest by patient as well as clinicians to reduce the overall treatment time. Especially, the introduction of corneal cross-linking in combination with corneal laser surgery demands a shorter treatment time to assure a sufficient patient flow. The principles and techniques of accelerated corneal cross-linking is discussed. PMID:23925330

Mrochen, Michael

2013-08-01

126

Cross-Link-Governed Dynamics of Biopolymer Networks  

NASA Astrophysics Data System (ADS)

Recent experiments show that networks of stiff biopolymers cross-linked by transient linker proteins exhibit complex stress relaxation, enabling network flow at long times. We present a model for the dynamics controlled by cross-links in such networks. We show that a single microscopic time scale for cross-linker unbinding leads to a broad spectrum of macroscopic relaxation times and a shear modulus G˜?1/2 for low frequencies ?. This model quantitatively describes the measured rheology of actin networks cross-linked with ?-actinin-4 over more than four decades in frequency.

Broedersz, Chase P.; Depken, Martin; Yao, Norman Y.; Pollak, Martin R.; Weitz, David A.; Mackintosh, Frederick C.

2010-12-01

127

Fast DNA interstrand cross-linking reaction by 6-vinylpurine.  

PubMed

Oligonucleotides that incorporate a reactive moiety to form an interstrand cross-link have been widely studied for their potential toward inhibiting gene expression or as basic tools for chemical biology studies. The 6-vinylpurine (2) newly designed in the current study serves well as a new purine-base moiety for increasing cross-link reactivity to target cytosine. Thus, oligonucleotides containing 6-vinylpurine exhibit a more selective and much smoother DNA cross-linking ability to cytosine than the oligonucleotide analogs derived from 2-amino-6-vinylpurine (1) previously explored. PMID:23067126

Imoto, Shuhei; Chikuni, Tomoko; Kansui, Hisao; Kunieda, Takehisa; Nagatsugi, Fumi

2012-01-01

128

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.

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

2010-01-01

129

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.

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

1970-01-01

130

Quantitative affinity electrophoresis of RNA-small molecule interactions by cross-linking the ligand to acrylamide.  

PubMed

We show that the affinity electrophoresis analysis of RNA-small molecule interactions can be made quantifiable by cross-linking the ligand to the gel matrix. Using an RNA-aminoglycoside model system to verify our method, we attached an acryloyl chloride molecule to the aminoglycosides paromomycin and neomycin B to synthesize an acrylamide-aminoglycoside monomer. This molecule was then used as a component in gel polymerization for affinity electrophoresis, covalently attaching an aminoglycoside molecule to the gel matrix. To test RNA binding to the cross-linked aminoglycosides, we used the aminoglycoside binding RNA molecule derived from thymidylate synthase messenger RNA (mRNA) that contains a C-C mismatch. Binding is indicated by the difference in RNA mobility between gels with cross-linked ligand, with ligand embedded during polymerization, and with no ligand present. Critically, the predicted straight line relationship between the reciprocal of the relative migration of the RNA and the ligand concentration is obtained when using cross-linked aminoglycosides, whereas a straight line is not obtained using embedded aminoglycosides. Average apparent dissociation constants are determined from the slope of the line from these plots. This method allows an easy quantitative comparison between different nucleic acid molecules for a small molecule ligand. PMID:23928050

Boodram, Sherry N; McCann, Lucas C; Organ, Michael G; Johnson, Philip E

2013-08-06

131

Neohemoglobins and Cross-Linked Hemoglobins as Blood Substitutes.  

National Technical Information Service (NTIS)

We have investigated the effect of specific cross-linking of beta subunits in bovine hemoglobins. It appears that both techniques can be utilized for obtaining products potentially useful as oxygen carriers in resuscitative fluids.

E. Bucci

1985-01-01

132

Macrophage response to cross-linked and conventional UHMWPE  

Microsoft Academic Search

To prevent wear debris-induced osteolysis and aseptic loosening, cross-linked ultra-high molecular weight polyethylene's (UHMWPE) with improved wear resistance have been developed. Hip simulator studies have demonstrated very low wear rates with these new materials leading to their widespread clinical use. However, the biocompatibility of this material is not known. We studied the macrophage response to cross-linked UHMWPE (XLPE) and compared

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

2003-01-01

133

Cross-linked growth hormone dimers have enhanced biological activity  

Microsoft Academic Search

In this study we have investigated the effect on the bioactivity of pituitary-derived human growth hormone (hGH) and recombinant bovine (b) GH after the addition of various concentrations of the water soluble cross-linking agent 1-ethyl-3(3-dimethylaminopropyl) carbodiimide (EDC; 6.25- 100 mg\\/ml). The biological activity of resulting cross-linked reactions were determined by its ability to promote incorporation of 35SO 2? 4 into

James W Mockridge; Roger Aston; David J Morrell; Andrew T Holder

1998-01-01

134

Optimization model for UV-Riboflavin corneal cross-linking  

Microsoft Academic Search

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

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

2011-01-01

135

Transglutaminases: multifunctional cross-linking enzymes that stabilize tissues  

Microsoft Academic Search

Transglutaminases catalyze the posttrans- lational modification of proteins by transamidation of available glutamine residues. This action results primarily in the formation of e-('y-glutamyl)lysine cross-links but includes the incorporation of polyamines into suitable protein substrates as well. The covalent isopeptide cross- link is stable and resistant to proteolysis, thereby increas- ing the resistance of tissue to chemical, enzymatic, and mechanical disruption.

CHARLES S. GREENBERG; PAUL J. BIRCKBICHLER; ROBERT H. RICEt

136

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

137

Rheological characteristics of adjustable cross-linked fracturing fluids  

SciTech Connect

A study was done evaluating apparent viscosity and fluid stability by allowing cross-linking to occur at varying times during and after a period of high shear. A high temperature closed-loop pipe viscometer was used for this process. To observe the interdependencies of shear history, cross-linking time, and apparent viscosity, two adjustable cross-linked fracturing fluid systems were employed. As part of the study, a plexiglass parallel plate fracture and wellbore model was used to observe proppant transport for both fluid systems at ambient temperature. Results of these studies indicate that when cross-linking time is less than the high shear duration period, both the maximum viscosity and the fluid's stability are reduced. The amount of reduction is shown to be related to the difference between the high shear duration period and the cross-link time. Also, from observations made on the plexiglassfracture model, a better understanding of the relationships among treating string residence time, cross-link time, fluid stability, and proppant transport in the vicinity of the wellbore can be developed.

Royce, T.N.; Beck, L.M.; Rickards, A.R.

1984-09-01

138

System for Gel Electrophoretic Immunoassay.  

National Technical Information Service (NTIS)

A micro-analytical platform for performing electrophoresis-based immunoassays was developed by integrating photopolymerized cross-linked polyacrylamide gels within a microfluidic device. The microfluidic immunoassays are performed by gel electrophoretic s...

A. E. Herr A. K. Singh D. J. Throckmorton

2005-01-01

139

Cross-Linking of Methyl Silicone Rubbers. Part II. Analysis of Extractables from Samples Cross-Linked under Various Conditions  

Microsoft Academic Search

During the cross-linking under themal conditions of two pre-polymers, a variety of compounds may be formed in addition to the desired cross-linked network, i.e., branched chain, large ring, and linear chain of twice pre-polymer molecular weight. In order to evaluate these processes with as little chemical complication as possible, a series of two component methyl silicone pre-polymers (Sylgard 184, 186,

Philip M. James; Edward M. Barrall II; Barbara Dawson; J. A. Logan

1974-01-01

140

Synthesis and use of bifunctional chloromethylalkanedione derivatives of variable chain length for cross-linking thiol groups in oligomeric proteins. Specific cross-linking in glyceraldehyde 3-phosphate dehydrogenase.  

PubMed

Bischloromethylpentanedione, bischloromethylhexanedione, bischloromethyloctanedione and bischloromethyldecanedione were synthesized from their corresponding dicarboxylic acids via the bis-acyl chloride and the bisdiazomethylketone derivatives. These compounds proved to be highly specific cross-linking reagents for rabbit skeletal-muscle glyceraldehyde 3-phosphate dehydrogenase. Incubation of the enzyme with cross-linking reagents resulted in both a time- and concentration-dependent formation of covalently linked oligomeric structures. The major cross-linked product detected by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis was the dimer (mol. wt. 72000). Sepharose 6B chromatography of the cross-linked enzyme showed that it still existed as the tetramer. Cross-linking was dependent on the native structure of the enzyme, since it was abolished on denaturation of the enzyme. The actual covalently linked product depends on the conditions of modification and the chain length of the reagent. The maximum yield of dimer (70-80%) was obtained with bischloromethylhexanedione, and the yield decreased with either shorter- or longer-chain compounds. The calculated distance between the two reactive points in bischloromethylhexanedione is 1.21-1.45nm. Bischloromethylhexanedione modified at least two thiol groups per monomer. Modification of the active-site thiol, cysteine-149, was not essential for cross-linking, since glyceraldehyde 3-phosphate dehydrogenase carboxymethylated on cysteine-149 still reacted to form the dimer. The rate of chemical cross-linking was markedly decreased by increasing the NAD(+) occupancy of the enzyme active sites. These experiments are discussed in terms of the asymmetry of the enzyme structure in solution. PMID:588252

Bloxham, D P

1977-10-01

141

Radiation cross-linked polymers: Recent developments and new applications  

NASA Astrophysics Data System (ADS)

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

Rouif, Sophie

2005-07-01

142

Characterization of radiation-cross-linked, high-density polyethylene for thermal energy storage  

SciTech Connect

Electron beam cross-linked high-density polyethylene (HDPE) pellets (DuPont Alathon, 0.93 MI) have been characterized for potential utility in thermal energy storage applications, before and after up to 500 melt-freeze cycles in ethylene glycol. Up to 95% of the HDPE's initial DSC differential scanning calorimetry ..delta.. H/sub f/ value (44.7 cal/g) (at 1.25/sup 0/C/min cooling rates) was retained up to 9.0 Mrad radiation dosage. Form-stability after 500 melt-freeze cycles was very good at this dosage level. X-ray diffraction measurements showed little difference between irradiated HDPE's and the unirradiated control, indicating that cross-linking occurred primarily in the amorphous regions. FTIR spectroscopy showed the pellets to be uniformly reacted. The ratios of the 965-cm/sup -1/ absorption band (trans RCH=CRH') to the 909-cm/sup -1/ band (RCH=CH/sub 2/) increased with increasing radiation dosage, up to 18 Mrad. Gel contents reached a maximum of 75% at the 13.5 Mrad dosage, indicating that other reactions, in addition to cross-linking, occurred at the highest (18 Mrad) dosage level. 15 references, 5 figures, 4 tables.

Whitaker, R.B.; Craven, S.M.; Etter, D.E.; Jendrek, E.F.; Nease, A.B.

1983-01-01

143

Moulded cross-linked chitosan matrix systems for controlled drug release.  

PubMed

Matrix-type drug delivery systems were prepared by moulding and drying cross-linked chitosan gels in 24-well plates and they were evaluated in terms of their physical properties, drug content, surface morphology and swelling. Furthermore, the in vitro drug release profiles were subjected to kinetic modelling at two different pH values. In general, the moulded matrix systems showed statistically significantly slower drug release compared to immediate release tablets as measured by the mean dissolution time. Drug release from the moulded matrix systems prepared from chitosan cross-linked with tripolyphosphate was pH-dependent as can be seen from the release exponent value (n) of 0.75 at pH 5.8 (anomalous transport, erosion), while the n value was only 0.40 at pH 7.4 (Fickian diffusion). The matrix systems obtained from chitosan cross-linked with sodium lauryl sulphate showed higher swelling but mostly Fickian diffusional release (n?=?0.25 at pH 7.4, n?=?0.41 at pH 5.8). PMID:20214415

Tarirai, Clemence; Enslin, Gill M; Steenekamp, Jan H; Hamman, Josias H

2010-03-09

144

Cross-linking of apoproteins in high density lipoprotein by dimethylsuberimidate inhibits specific lipoprotein binding to membranes  

SciTech Connect

Apoprotein E-free high density lipoproteins (HDL) bind to various cells and cell membrane preparations with properties typical of ligand-receptor interactions. This specific binding can be inhibited by treatment of HDL with tetranitromethane (TNM). During treatment of HDL with TNM, in addition to the expected nitration of tyrosine residues, cross-linking of lipids to apoproteins and of apoproteins to each other occurs. We have recently shown that cross-linking of phospholipids to apoproteins is not responsible for the inhibition of binding. To determine the role of cross-linking of apoproteins to each other in the inhibition, we used the bifunctional reagent dimethylsuberimidate (DMS) to cross-link the apoproteins in HDL3. Over 80% of apoproteins in DMS-HDL3 were cross-linked, as analyzed by SDS-polyacrylamide gel electrophoresis. DMS-HDL3 was similar to control HDL3 in its lipid composition. Gel filtration chromatography did not reveal any significant difference in size between DMS-HDL3 and control HDL3. As determined by competitive binding with 125I-labeled HDL3, DMS-HDL3 was almost completely unable to bind specifically to rat liver plasma membranes and human skin fibroblasts. It is concluded from these results that TNM inhibits the specific binding of HDL3 to membranes by a mechanism that involves cross-linking of apoproteins to each other in HDL3 particles. This observation implies that the specific binding of HDL3 to cells may depend on the native quaternary structure of apoproteins in the HDL particle. Because of its reduced ability to bind to the specific binding sites, DMS-HDL3 may be useful for studies related to the functional aspects of HDL binding sites.

Chacko, G.K.; Mahlberg, F.H.; Johnson, W.J.

1988-03-01

145

The relative contribution of calcium, zinc and oxidation-based cross-links to the stiffness of Arion subfuscus glue.  

PubMed

Metal ions are present in many different biological materials, and are capable of forming strong cross-links in aqueous environments. The relative contribution of different metal-based cross-links was measured in the defensive glue produced by the terrestrial slug Arion subfuscus. This glue contains calcium, magnesium, zinc, manganese, iron and copper. These metals are essential to the integrity of the glue and to gel stiffening. Removal of all metals caused at least a 15-fold decrease in the storage modulus of the glue. Selectively disrupting cross-links involving hard Lewis acids such as calcium reduced the stiffness of the glue, while disrupting cross-links involving borderline Lewis acids such as zinc did not. Calcium is the most common cation bound to the glue (40 mmol l(-1)), and its charge is balanced primarily by sulphate at 82-84 mmol l(-1). Thus these ions probably play a primary role in bringing polymers together directly. Imine bonds formed as a result of protein oxidation also contribute substantially to the stiffness of the glue. Disrupting these bonds with hydroxylamine caused a 33% decrease in storage modulus of the glue, while stabilizing them by reduction with sodium borohydride increased the storage modulus by 40%. Thus a combination of metal-based bonds operates in this glue. Most likely, cross-links directly involving calcium play a primary role in bringing together and stabilizing the polymer network, followed by imine bond formation and possible iron coordination. PMID:23264483

Braun, M; Menges, M; Opoku, F; Smith, A M

2012-12-21

146

Self-Consistent Field Approach for Cross-Linked Copolymer Materials  

NASA Astrophysics Data System (ADS)

A generalized self-consistent field approach for polymer networks with a fixed topology is developed. It is shown that the theory reproduces the localization of cross-links, which is characteristic for gels. The theory is then used to study the order-disorder transition in regular networks of end-linked diblock copolymers. Compared to diblock copolymer melts, the transition is shifted towards lower values of the incompatibility parameter ? (the Flory- Huggins parameter). Moreover, the transition becomes strongly first order already at the mean-field level. If stress is applied, the transition is further shifted and finally vanishes in a critical point.

Schmid, Friederike

2013-07-01

147

CRACK INITIATION IN RETRIEVED CROSS-LINKED UHMWPE ACETABULAR LINERS  

PubMed Central

Nine cross-linked UHMWPE acetabular liners were retrieved at revision surgery. Eight of the liners were fully intact and functional at retrieval. Six cases contained shallow initiated cracks at the root of rim notches; one crack had propagated several millimeters. Optical and electron microscopic inspection of the crack surfaces revealed clam shell markings, which are characteristic of fatigue crack initiation. Crack initiation at notches has been identified in reports of catastrophic cross-linked liner failures, with cracks initiation sites exhibiting similar morphology and clam shell markings. Thus, we believe the shallow cracks identified in this case series are precursors to catastrophic rim fracture. The results of this study recommend further investigations to clarify the etiology and prevalence of crack initiation in cross-linked acetabular liners.

Furmanski, Jevan; Kraay, Matthew J.; Rimnac, Clare M.

2010-01-01

148

In vitro progesterone release from ?-irradiated cross-linked polydimethylsiloxane  

NASA Astrophysics Data System (ADS)

Instead of conventional method such as thermal cross-linking method, ?-irradiation is used to improve the properties of polydimethylsiloxane (PDMS) as a matrix containing progesterone. The thermal cross-linking of PDMS monolithic systems containing drug is deleterious to the drug. Usually, all drugs are unstable both at high vulcanizing temperature and in the presence of peroxide catalysts. This novel method is found to be effective for the stability of the controlled drug delivery systems. The PDMS (three medical grades) matrices were exposed to ?-irradiation in ambient conditions with total doses of 50, 75 and 100 kGy. The mechanical properties confirmed that the samples are cross-linked. It is found that the progesterone release rate is affected by irradiation treatment. It is deduced, however that there is no significant difference in the release profile of progesterone by increasing the irradiation dose from 50 to 100 kGy.

Mashak, Arezou; Taghizadeh, S. Mojtaba

2006-02-01

149

Boundary lubricant polymer films: effect of cross-linking.  

PubMed

We have studied the adsorption and lubricant properties of a multifunctional triblock copolymer poly(l-lysine)-b-poly(acrylic acid)-b-poly(l-lysine). In particular, we investigated the nature of the layer adsorbed under different conditions of polymer and salt concentration and the lubricant properties of the polymer layer before and after its chemical cross-linking by bridging the poly(acrylic acid) blocks. We found that the amount of polymer adsorbed is controlled by the ionic strength and the polymer concentration in the solution. In all cases, the self-assembled polymer layer is a poor lubricant before cross-linking, but the cohesion and load-carrying ability of the layer are substantially improved by this reaction. However, the chemically cross-linked coating has a limited deformation capacity as a consequence of its permanent network nature, and irreversible damage is observed after excessive strain of the film. PMID:24053315

Giasson, Suzanne; Lagleize, Jeanne-Marie; Rodríguez-Hernández, Juan; Drummond, Carlos

2013-10-09

150

Biodegradable binders and cross-linking agents from renewable resources  

Microsoft Academic Search

Conclusions  Recently, epoxidised vegetable oils have found industrial application as cross-linking agents in environment-friendly solvent-free\\u000a powder coatings. A variety of vegetable oil-based epoxidised cross-linking agents is available by both chemical and enzymatic\\u000a routes with high chemical purities.\\u000a \\u000a Furthermore, it was shown that functionalised vegetable oils can serve as building blocks for the preparation of biodegradable\\u000a hydrophobic plastics poly-hydroxy alkanoates (PHAs) exhibiting

G J H Buisman

1999-01-01

151

Filamin Cross-Linked Semiflexible Networks: Fragility under Strain  

Microsoft Academic Search

The semiflexible F-actin network of the cytoskeleton is cross-linked by a\\u000avariety of proteins including filamin, which contain Ig-domains that unfold\\u000aunder applied tension. We examine a simple semiflexible network model\\u000across-linked by such unfolding linkers that captures the main mechanical\\u000afeatures of F-actin networks cross-linked by filamin proteins and show that\\u000aunder sufficiently high strain the network spontaneously self-organizes

B. A. DiDonna; Alex J. Levine

2006-01-01

152

cis- and trans-diamminedichloroplatinum(II) interstrand cross-linking of a defined sequence nucleosomal core particle.  

PubMed

Interstrand cross-linking studies with the antitumor drug cis-diamminedichloroplatinum(II) and its clinically inactive isomer, trans-diamminedichloroplatinum(II), were performed on a fragment of the 5S rRNA gene of Xenopus borealis in the free and nucleosomal state. 5S nucleosomes were formed via histone octamer exchange from chicken erythrocyte core particles. Native polyacrylamide gel electrophoresis was used to probe the ability of platinated DNA to reconstitute into core particles. Both isomers negatively impacted reconstitution when histones were present during incubation with the drug. When histones were not present during the drug treatment, platinated DNA was successfully reconstituted into core particles. These results suggest that platination of histones impedes reconstitution of free DNA. However, already-formed core particles were not disrupted upon platination. Sites of interstrand cross-linking were probed through denaturing polyacrylamide gel electrophoresis and quantitative phosphorimagery. We found both site-specific enhancement and depression of cis-diamminedichloroplatinum(II) cross-linking in the nucleosomal samples relative to free DNA at both drug concentrations that were tested (0.01 and 0.0025 mM). trans-Diamminedichloroplatinum(II) exhibited no detectable differences in the interstrand cross-linking of free and nucleosomal samples. PMID:11123932

Millard, J T; Wilkes, E E

2000-12-26

153

Photochemical cross-linking of histones to DNA nucleosomes.  

PubMed Central

Ultraviolet (UV)-induced cross-linking was utilized in order to identify histone-DNA interacting regions in the chromatin repeating unit. Fractionated mononucleosomes which contained 185 base pairs of DNA and a full complement of the histones, including histone H1, were irradiated with light of lambda greater than 290nm in the presence of a photosensitizer. Equimolar amounts of histones H2A and H2B were found, by two independent labeling experiments, to be cross-linked to the DNA. Based on previous finding that the UV irradiation specifically cross-links residues which are in close proximity, irrespective of the nature of the amino acid side chain or the nucleotide involved, our results indicate that the four core histones are not positioned equivalently with respect to the DNA. This arrangement allows histones H2A and H2B to preferentially cross-link to the DNA. A water soluble covalent complex of DNA and histones was isolated. This complex was partially resistant to mild nuclease digestion, it exhibited a CD spectrum similar to that of chromatin, and was found to contain histone H1. These results are compatible with a model which suggests that histone H1, though anchored to the linker, is bound to the DNA at additional sites. By doing so it spans the whole length of the nucleosome and clamps together the DNA fold around the histone core. Images

Sperling, J; Sperling, R

1978-01-01

154

Synthesis and applications of heterobifunctional photocleavable cross-linking reagents.  

PubMed

This study designed, synthesized, and characterized a number of new heterobifunctional photocleavable cross-linking reagents that may be used to photomodulate the activity of proteins or to prepare caged fluorescent dyes. Biomolecules or fluorophores caged via a thiol group with the BNBASE reagent can be covalently linked to a second protein, ligand, or derivatized surface through the activated carboxyl group. Members of the new class of photocleavable cross-linking reagent can be used to cage amino groups in the molecule of interest, which can then be covalently linked to a second molecule through the thiol-reactive oxirane group. These crosslinking reagents may be used for the following applications: (1) to cage the activity of a protein by masking its active site with a second macromolecule, e.g., aminodextran; (2) to prepare a protein conjugate exhibiting an enhanced or new activity that is lost on irradiation with near-ultraviolet light, e.g., cross-linked actin dimer; (3) to target the caged compound to a specific site by cross linking to a specific antibody; (4) to attach the caged compound to a thiol or amino derivatized surface; and (5) to render the caged compound fluorescent in order to image or to quantify the yield of the photoactivation reaction. PMID:9661150

Marriott, G; Ottl, J

1998-01-01

155

Tuft protein: protein cross-linking in enamel development.  

PubMed

Tuft protein is a material associated with enamel tufts, and resides in dental enamel primarily at the enamel-dentine junction. It is located primarily at prism peripheries and extends in a very attenuated form towards the enamel outer surface. While it appears to be a mixture of components, partial sequencing and antibody studies have demonstrated the presence of amelin, a protein associated with prism boundaries. Biochemical investigations have been seriously hampered by the fact that tuft protein is extremely insoluble in a range of solvents, including mineral acids, EDTA, chaotropic agents, and detergents including SDS. This raised the question as to whether it could be chemically cross-linked. Antibodies to ?-glutamyl cross-linking peptide were used to determine the presence of a cross-linking isopeptide. In all cases examined, a positive response indicated that tuft protein does display chemical cross-linking, which may explain the insoluble nature of this material. This may be a mechanism to prevent protein degradation at the enamel-dentine junction during the degradation of enamel matrix, which occurs during amelogenesis. PMID:22243226

Robinson, Colin; Hudson, Jackie

2011-12-01

156

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

157

Cross linking molecular systems to form ultrathin dielectric layers  

Microsoft Academic Search

Dehydrogenation leads to cross linking of polymer or polymer like formation in very different systems: self-assembled monolayers and in closo -carboranes leading to the formation of semiconducting and dielectric boron carbide. We find evidence of intermolecular interactions for a self-assembled monolayer (SAM) formed from a large molecular adsorbate, [1,1';4',1\\

Danqin Feng

2007-01-01

158

Cross-linked protein crystals for vaccine delivery  

PubMed Central

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.

1999-01-01

159

Advanced Corneal Cross-Linking System with Fluorescence Dosimetry  

PubMed Central

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

Friedman, Marc D.; Pertaub, Radha; Usher, David; Sherr, Evan; Kamaev, Pavel; Muller, David

2012-01-01

160

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

Microsoft Academic Search

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

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

2003-01-01

161

Stabilization of human prostate acid phosphatase by cross-linking with diimidoesters.  

PubMed

1. Modification of dimeric human prostate acid phosphatase (EC 3.1.3.2) by diimidoesters leads to the formation of water-soluble preparations of high enzymatic activity, resistant to denaturing agents. 2. Monomeric, dimeric, trimeric and tetrameric species were found in SDS-polyacrylamide gel electrophoresis of the phosphatase cross-linked with dimethyl-suberimidate, and dimeric, trimeric and tetrameric enzymatically active species on thin-layer Sephadex 200 gel filtration. This molecular pattern evidenced formation of the inter-subunit covalent linkages. All molecular forms are immunoreactive against the polyclonal rabbit anti-phosphatase antibodies. 3. The catalytic properties of the modified phosphatase are almost the same as those of the native enzyme. Differences in the optical properties between the modified and the native enzymes point to slight conformational transitions in the modified enzyme. PMID:3673438

Wasylewska, E; Duli?ska, J; Trubetskoy, V S; Torchilin, V P; Ostrowski, W S

1987-01-01

162

Hyaluronan-Dependent Pericellular Matrix  

PubMed Central

Hyaluronan is a multifunctional glycosaminoglycan that forms the structural basis of the pericellular matrix. Hyaluronan is extruded directly through the plasma membrane by one of three hyaluronan synthases and anchored to the cell surface by the synthase or cell surface receptors such as CD44 or RHAMM. Aggregating proteoglycans and other hyaluronan-binding proteins, contribute to the material and biological properties of the matrix and regulate cell and tissue function. The pericellular matrix plays multiple complex roles in cell adhesion/de-adhesion, and cell shape changes associated with proliferation and locomotion. Time-lapse studies show that pericellular matrix formation facilitates cell detachment and mitotic cell rounding. Hyaluronan crosslinking occurs through various proteins, such as tenascin, TSG-6, inter-alpha-trypsin inhibitor, pentraxin and TSP-1. This creates higher order levels of structured hyaluronan that may regulate inflammation and other biological processes. Microvillous or filopodial membrane protrusions are created by active hyaluronan synthesis, and form the scaffold of hyaluronan coats in certain cells. The importance of the pericellular matrix in cellular mechanotransduction and the response to mechanical strain are also discussed.

Evanko, Stephen P.; Tammi, Markku I.; Tammi, Raija H.; Wight, Thomas N.

2007-01-01

163

Reversible chemical cross-linking and ribonuclease digestion analysis of the organization of proteins in ribonucleoprotein particles  

Microsoft Academic Search

The organization of select proteins within ribonucleoprotein particles containing heterogeneous nuclear and uridine-rich small nuclear RNAs (hnRNP and UsnRNP respectively) was examined by chemical cross-linking and ribonuclease digestion using diagonal two dimensional PAGE and immunoblotting detection systems. Monoclonal antibodies specific for A2, C1 and C2 hnRNP proteins, detected these proteins at gel coordinates which suggested homotypic dimers and trimers of

Stanley G. Harris; Terence E. Martin; Harold C. Smith

1988-01-01

164

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

165

Injectable in situ cross-linking hydrogels for local antifungal therapy.  

PubMed

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 Candida 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 P; Langer, Robert; Fink, Gerald R; Kohane, Daniel S

2009-11-26

166

Dynamics of cross linking fronts in alkyd coatings  

NASA Astrophysics Data System (ADS)

The dynamics of the curing process of alkyd coatings is an important aspect for coating performance. The formation of cross links in an alkyd coating film has been followed in time using a microimaging nuclear magnetic resonance setup, having a spatial resolution of 5 ?m perpendicular to the film. During this cross-linking process a front has been observed inside the coating film. The position of this front varied with the square root of time. With the help of a simple reaction model, we have proven that this dynamics results from the fact that the curing rate is limited by the oxygen flux into the coating. This model can also explain, the differences in curing rates observed for various coatings.

Erich, S. J. F.; Laven, J.; Pel, L.; Huinink, H. P.; Kopinga, K.

2005-03-01

167

Elasticity in Ionically Cross-Linked Neurofilament Networks  

PubMed Central

Abstract Neurofilaments are found in abundance in the cytoskeleton of neurons, where they act as an intracellular framework protecting the neuron from external stresses. To elucidate the nature of the mechanical properties that provide this protection, we measure the linear and nonlinear viscoelastic properties of networks of neurofilaments. These networks are soft solids that exhibit dramatic strain stiffening above critical strains of 30–70%. Surprisingly, divalent ions such as Mg2+, Ca2+, and Zn2+ act as effective cross-linkers for neurofilament networks, controlling their solidlike elastic response. This behavior is comparable to that of actin-binding proteins in reconstituted filamentous actin. We show that the elasticity of neurofilament networks is entropic in origin and is consistent with a model for cross-linked semiflexible networks, which we use to quantify the cross-linking by divalent ions.

Yao, Norman Y.; Broedersz, Chase P.; Lin, Yi-Chia; Kasza, Karen E.; MacKintosh, Frederick C.; Weitz, David A.

2010-01-01

168

[Epidemiological studies on the manufacture of cross-linked polyethylene].  

PubMed

In the production of cross-linked polyethylene in the air of the working environment above the norm concentrations of acetophenon, dicumyl peroxide and antioxidant are established, which create unfavourable working conditions. During clinical and laboratory examinations of 55 workers, engaged in the production of cross-linked polyethylene, are registered subjective complaints from the irritating effect of the chemical noxae on the mucous membranes and skin. Methaemoglobinaemia is found in 4 workers. There are deviations in the functional state of the liver (transaminase, APh, GGTP and triglycerides) in the group "maintaining staff". The same workers have also increased quantity of metabolite hippuric acid in the urine. On the grounds of the results, the group "maintaining staff" is determined as risk group. Recommendations are made for follow-up care and work in controlled parameters of the working environment. PMID:2099468

Khankova, L; Mikha?lova, A; Khristeva, V; Mukhtarova, M; Benchev, I; Matakieva, M; Kolarova, S

1990-01-01

169

Model selection for athermal cross-linked fiber networks.  

PubMed

Athermal random fiber networks are usually modeled by representing each fiber as a truss, a Euler-Bernoulli or a Timoshenko beam, and, in the case of cross-linked networks, each cross-link as a pinned, rotating, or welded joint. In this work we study the effect of these various modeling options on the dependence of the overall network stiffness on system parameters. We conclude that Timoshenko beams can be used for the entire range of density and beam stiffness parameters, while the Euler-Bernoulli model can be used only at relatively low network densities. In the high density-high bending stiffness range, strain energy is stored predominantly in the axial and shear deformation modes, while in the other extreme range of parameters, the energy is stored in the bending mode. The effect of the model size on the network stiffness is also discussed. PMID:23005468

Shahsavari, A; Picu, R C

2012-07-24

170

Model selection for athermal cross-linked fiber networks  

NASA Astrophysics Data System (ADS)

Athermal random fiber networks are usually modeled by representing each fiber as a truss, a Euler-Bernoulli or a Timoshenko beam, and, in the case of cross-linked networks, each cross-link as a pinned, rotating, or welded joint. In this work we study the effect of these various modeling options on the dependence of the overall network stiffness on system parameters. We conclude that Timoshenko beams can be used for the entire range of density and beam stiffness parameters, while the Euler-Bernoulli model can be used only at relatively low network densities. In the high density-high bending stiffness range, strain energy is stored predominantly in the axial and shear deformation modes, while in the other extreme range of parameters, the energy is stored in the bending mode. The effect of the model size on the network stiffness is also discussed.

Shahsavari, A.; Picu, R. C.

2012-07-01

171

Induced Collagen Cross-Links Enhance Cartilage Integration  

PubMed Central

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

Athens, Aristos A.; Makris, Eleftherios A.; Hu, Jerry C.

2013-01-01

172

Photoresponsive cross-linked polymeric particles for phototriggered burst release.  

PubMed

We synthesized a series of cross-linked photoresponsive polymeric particles with photolabile monomers and cross-linkers through miniemulsion polymerization. These particles are quite stable in dark, while light irradiation caused the breakage of particles and the efficient release of encapsulated contents up to 95% based on Nile red fluorescence. Photoswitches of particle systems were confirmed by fluorescence spectroscopy, SEM and colorimetry. Particle uptake and triggered release in RAW264.7 cells were confirmed by fluorescein diacetate loaded particles. PMID:23294131

Wang, Zhen; Yu, Lili; Lv, Cong; Wang, Peng; Chen, Yedong; Tang, Xinjing

2013-01-29

173

Antiviral activity of carbopol, a cross-linked polycarboxylate  

Microsoft Academic Search

Summary Carbopol, a polymer of acrylic acid cross-linked with allylsucrose, was found to impart resistance to virus infection in mice which received an intraperitoneal injection of the polycarboxylate 1 or 4 days before either intravenous vaccinia virus challenge or intranasal herpes simplex virus challenge. An interferon-like substance was detected in the blood stream 20–40 hours after the intraperitoneal injection of

E. de Clercq; M. Luczak

1976-01-01

174

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

175

Rheology of core cross-linked star polymers  

Microsoft Academic Search

The rheological characterization for a set of structurally diverse core cross-linked star (CCS) polymers is presented. The influence of arm molecular weight (Mw(arm)) and CCS polymer molecular weight (Mw(CCSP)) on the steady- and dynamic-shear properties determined by plate rheometry will be discussed. Both these parameters dramatically affect the CCS polymer solution properties and determine its “molecular softness”; a key feature

Tor Kit Goh; Kristopher D. Coventry; Anton Blencowe; Greg G. Qiao

2008-01-01

176

Newer protocols and future in collagen cross-linking  

PubMed Central

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

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

2013-01-01

177

Multi-gigabit laser communications for satellite cross-links  

Microsoft Academic Search

Nd:YAG space laser communications systems are being developed with multi-gigabit capability. A 1 Gbps system Engineering Feasibility Model which has been tested successfully both functionally and environmentally, has led to further designs for space qualified multi-gigabit packages. A system configuration for a 2 Gbps duplex cross-link between synchronous satellites is described. The 2 Gbps transceiver characteristics are addressed in detail

J. A. Maynard; M. Ross; J. D. Wolf

1979-01-01

178

Hydrogels of collagen hydrolysate cross-linked with dialdehyde starch  

Microsoft Academic Search

Processing hydrogels of collagen hydrolysate (H) cross-linked with dialdehyde starch (DAS) by dipping or casting into biodegradable\\u000a materials for various applications, is complicated by their marked tendency to aging. One-hour action by temperatures at 60–90 °C\\u000a reduces sorbed water content in hydrogels by approx. 12%; dependence of the extent of this reduction on temperature (within\\u000a the mentioned range) was not detected.

F. Langmaier; M. Mládek; P. Mokrejš

2009-01-01

179

Synthesis and Properties of Titanium Oxide Cross-Linked Montmorillonite  

Microsoft Academic Search

Abstract-- Titanium was introduced into the montmorillonite structure by cation exchange with polymeric Ti cations, formed by partial hydrolysis of TIC1, in HC1. On further hydrolysis and heating, TiO2 pillars in the form of anastase were formed between the montmorillonite layers. The resulting TiOE-Cross-linked montmorillonites possessed surface areas in the range 200-350 m2\\/g and pore volumes of about 0.2 cm3\\/g

Johan Sterte

1986-01-01

180

Plasma cross linked fibrin degradation products in pulmonary embolism.  

PubMed Central

Plasma concentrations of cross linked fibrin degradation products, a marker of intravascular thrombosis and fibrinolysis, were measured in 495 patients with suspected pulmonary embolism referred for ventilation-perfusion lung scanning to determine whether concentrations are increased in pulmonary embolism and their potential use in diagnosis. Lung scans were described as normal (n = 66) or as showing a low (n = 292), indeterminate (n = 58), or high probability (n = 79) of pulmonary embolism. There was a difference between the mean levels of cross linked fibrin degradation products in each scan category: normal scans, 142 ng/ml; low probability scans, 295 ng/ml; indeterminate probability scans, 510 ng/ml; high probability scans, 952 ng/ml (p less than 0.001). Of the patients with high probability scans, 96% had raised concentrations. Explanations for discrepant low results include incorrect scan diagnosis, delay in blood sampling, and anticoagulation. Of the patients with a low or indeterminate probability of pulmonary embolism, 43% had increased concentrations of cross linked fibrin degradation products that could be attributed in most cases to another illness. Owing to the wide range of values in each lung scan diagnostic category, raised concentrations of these fibrin degradation products cannot be used without reference to the patient's clinical state as a discriminatory test for pulmonary embolism. Further evaluation of the significance of normal concentrations in excluding a diagnosis of pulmonary embolism appears to be warranted.

Rowbotham, B J; Egerton-Vernon, J; Whitaker, A N; Elms, M J; Bunce, I H

1990-01-01

181

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

182

Elasticity in Ionically Cross-Linked Neurofilament Networks  

NASA Astrophysics Data System (ADS)

Neurofilaments are found in abundance in the cytoskeleton of neurons, where they act as an intracellular framework protecting the neuron from external stresses. To elucidate the nature of the mechanical properties that provide this protection, we measure the linear and nonlinear viscoelastic properties of networks of neurofilaments. These networks are soft solids that exhibit dramatic strain stiffening above critical strains of 30-70%. Surprisingly, divalent ions, such as Mg^2+, Ca^2+, and Zn^2+, act as effective cross-linkers for neurofilament networks, controlling their solid-like elastic response. This behavior is comparable to that of actin-binding proteins in reconstituted filamentous actin. We show that the elasticity of neurofilament networks is entropic in origin and is consistent with a model for cross-linked semiflexible networks, which we use to quantify the cross-linking by divalent ions. Ultimately, we are able to extract microstructural network parameters such as the persistence length and the average distance between cross-links directly from bulk rheology.

Yao, Norman; Lin, Yi-Chia; Broedersz, Chase; Kasza, Karen; Mackintosh, Frederick; Weitz, David

2009-03-01

183

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

184

Method and Apparatus for Gel Electrophoretic Immunoassay.  

National Technical Information Service (NTIS)

A micro-analytical platform for performing electrophoresis-based immunoassays was developed by integrating photopolymerized cross-linked polyacrylamide gels within a microfluidic device. The microfluidic immunoassays are performed by gel electrophoretic s...

A. E. Herr A. K. Singh D. J. Throckmorton

2005-01-01

185

A vaccinia virus DNase preparation which cross-links superhelical DNA.  

PubMed

Multiple DNA-dependent enzyme activities have been detected in highly purified preparations of a single-strand-specific nuclease from vaccinia virus. These enzyme preparations were extensively purified and characterized by using superhelical DNAs as substrates. In particular, the nuclease activity was monitored by the extent of conversion of supercoiled closed duplex DNA (DNA I) to nicked circular DNA (DNA II), which could subsequently be converted to duplex linear DNA (DNA III) by prolonged incubation with the enzyme. DNA species which were not substrates for the enzyme included relaxed closed duplex DNA, DNA II which had been prepared by nuclease S1 treatment or by photochemical nicking of DNA I, and DNA III. With plasmid pSM1 DNA as substrate, the extent of cleavage of DNA I to DNA II was found to increase with superhelix density above a threshold value of about -0.06. The linear reaction products were examined by gel electrophoresis after restriction enzyme digestion of the DNAs from plasmids pSM1 and pBR322 and of the viral DNAs from bacteriophage phi X174 (replicative form) and simian virus 40, and the map coordinate locations of the scissions were determined. These products were further examined by electron microscopy and by gel electrophoresis under denaturing conditions. Electron micrographs taken under partially denaturing conditions revealed molecules with terminal loops or hairpins such as would result from the introduction of cross-links at the cutting sites. These species exhibited snapback renaturation. The denaturing gel electrophoresis experiments revealed the appearance of new bands at locations consistent with terminal cross-linking. With pSM1 and pBR322 DNAs, this band was shown to contain DNA that was approximately twice the length of a linear single strand. The terminal regions of the cross-linked linear duplex reaction products were sensitive to nuclease S1 but insensitive to proteinase K, suggesting that the structure is a hairpin loop not maintained by a protein linker. A similar structure is found in mature vaccinia virus DNA. PMID:3871865

Lakritz, N; Foglesong, P D; Reddy, M; Baum, S; Hurwitz, J; Bauer, W R

1985-03-01

186

Wet cross-linking gliadin fibers with citric acid and a quantitative relationship between cross-linking conditions and mechanical properties.  

PubMed

This paper reports the wet cross-linking of gliadin fibers using citric acid without using phosphorus-containing catalysts or high temperatures. Carboxylic acids such as citric acid are inexpensive and nontoxic chemicals preferred for cross-linking proteins and cellulose. However, previous studies have shown that carboxylic acid cross-linked materials experience substantial strength loss and/or yellowing when cross-linked using phosphorus-containing catalysts after drying and curing at high temperatures. In this research, citric acid has been used to cross-link gliadin fibers and the effects of various cross-linking conditions on the breaking tenacity and breaking elongation have been studied. A mathematical relationship that can predict the breaking tenacity of the fibers at various cross-linking conditions has also been developed. This research shows that citric acid in aqueous solutions can cross-link gliadin fibers at low temperatures using alkali as catalyst. The method of cross-linking developed in this research could be useful to cross-link plant proteins for food, fiber, and other applications. PMID:19061311

Reddy, Narendra; Li, Ying; Yang, Yiqi

2009-01-14

187

Cross-linking with bifunctional reagents and its application to the study of the molecular symmetry and the arrangement of subunits in hexameric protein oligomers.  

PubMed

Cross-linking with a bifunctional reagent and subsequent SDS gel electrophoresis is a simple but effective method to study the symmetry and arrangement of subunits in oligomeric proteins. In this study, theoretical expressions for the description of cross-linking patterns were derived for protein homohexamers through extension of the method used for tetramers by Hajdu et al. (1976). The derived equations were used for the analysis of cross-linking by glutardialdehyde of four protein hexamers: beef liver glutamate dehydrogenase (GDH), jack bean urease, hemocyanin from the spiny lobster Panulirus pencillatus (PpHc), Escherichia coli glutamate decarboxylase (GDC) and for analysis of published data on the cross-linking of hexameric E. coli rho by dimethyl suberimidate. Best fit models showed that the subunits in the first four proteins are arranged according to D(3) symmetry in two layers, each subunit able to cross-link to three neighboring subunits for GDH and urease, or to four for PpHc and GDC. The findings indicate a dimer-of-trimers eclipsed arrangement of subunits for GDH and urease and a trimer-of-dimers staggered one for PpHc and GDC. In rho, the subunits are arranged according to D(3) symmetry in a trimer-of-dimers ring. The conclusions from cross-linking of GDH and GDC, PpHc and rho are consistent with results from X-ray crystal structure, those for urease with findings from electron microscopy. PMID:20005307

Azem, Abdussalam; Tsfadia, Yossi; Hajouj, Omar; Shaked, Isabella; Daniel, Ezra

2009-12-11

188

Development of a novel photoreactive calmodulin derivative: Cross-linking of purified adenylate cyclase from bovine brain  

SciTech Connect

A novel photoreactive calmodulin (CaM) derivative was developed and used to label the purified CaM-sensitive adenylate cyclase from bovine cortex. {sup 125}I-CaM was conjugated with the heterobifunctional cross-linking agent p-nitrophenyl 3-diazopyruvate (DAPpNP). Spectral data indicated that diazopyruvoyl (DAP) groups were incorporated into the CaM molecule. Iodo-CaM-DAPs behaved like native CaM with respect to (1) Ca{sup 2+}-dependent enhanced mobility on sodium dodecyl sulfate-polyacrylamide gels and (2) Ca{sup 2+}-dependent stimulation of adenylate cyclase activity. {sup 125}I-CaM-DAP photochemically cross-linked to CaM-binding proteins in a manner that was both Ca{sup 2+} dependent and CaM specific. Photolysis of forskolin-agarose-purified adenylate cyclase from bovine cortex with {sup 125}I-CaM-DAP produced a single cross-linked product which migrates on sodium dodecyl sulfate-polyacrylamide gels with an apparent molecular weight of approximately 140,000.

Harrison, J.K.; Lawton, R.G.; Gnegy, M.E. (Univ. of Michigan, Ann Arbor (USA))

1989-07-11

189

A novel hydrogel crosslinked hyaluronan with glycol chitosan  

Microsoft Academic Search

A novel hydrogel was prepared by crosslinking hyaluronan with glycol chitosan in aqueous solution using water soluble carbodiimide\\u000a at nearly neutral pH and room temperature. The products can be easily formulated into injectable gels, various films, membranes\\u000a and sponges for soft tissue augmentation, viscosupplementation, drug delivery, preventing adhesion of post operation, wound\\u000a dressing and tissue engineering scaffolds. The said hydrogel

Wei Wang

2006-01-01

190

LET dependence of DNA-protein cross-links  

SciTech Connect

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

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

1995-08-01

191

Pericellular Hyaluronan and Prostate Cancer.  

National Technical Information Service (NTIS)

The working hypothesis of the present project is that hyaluronan (HA) is responsible for maintaining pericellular spaces between nests of prostate tumor cells that are vital for the diffusion of nutrients required for tumor growth. To test this hypothesis...

C. B. Underhill

2000-01-01

192

Hyaluronan Biosynthesis in Prostate Carcinoma.  

National Technical Information Service (NTIS)

Despite advances in the diagnosis and treatment of prostate cancer in the last several years, metastasis represents the major cause of frustration and failure in the successful treatment of prostate cancer patients. Hyaluronan (HA) is polymeric anionic ca...

J. B. McCarthy

2004-01-01

193

Hyaluronan Biosynthesis in Prostate Carcinoma.  

National Technical Information Service (NTIS)

Despite advances in the diagnosis and treatment of prostate cancer in the last several years, metastasis represents the major cause of frustration and failure in the successful treatment of prostate cancer patients. Hyaluronan (HA) is polymeric anionic ca...

J. B. McCarthy

2007-01-01

194

Hyaluronan Biosynthesis in Prostate Carcinoma.  

National Technical Information Service (NTIS)

Despite advances in the diagnosis and treatment of prostate cancer in the last several years, metastasis represents the major cause of frustration and failure in the successful treatment of prostate cancer patients. Hyaluronan (HA) is polymeric anionic ca...

J. B. McCarthy

2003-01-01

195

Probing Native Protein Structures by Chemical Cross-linking, Mass Spectrometry, and Bioinformatics*  

PubMed Central

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

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

2010-01-01

196

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

Microsoft Academic Search

Cross-linked elastomers have numerous applications including automobiles, sporting goods, and biomedical devices. During both their processing and application, these materials experience large mechanical stresses and thermal gradients. In this study, we investigate the mechanical and thermal transport behavior of cross-linked polybutadienes. These materials have been prepared by cross linking well-entangled polybutadienes using an organic peroxide cross-linking agent at low concentration.

David C. Venerus; Dimitre Kolev

2008-01-01

197

Emulsifying Properties of Milk Proteins Cross-linked with Microbial Transglutaminase  

Microsoft Academic Search

Oil-in-water emulsions containing 20% oil were prepared with n-tetradecane and sodium caseinate or ?-lactoglobulin in the aqueous phase. The proteins had been cross-linked with microbial transglutaminase prior to emulsification or were cross-linked in the emulsions after emulsification. Extensive cross-linking reduced the stability of the emulsions to coalescence or strong flocculation, as determined by droplet size measurements, whereas limited cross-linking improved

Merete Færgemand; Jeanette Otte; Karsten Bruun Qvist

1998-01-01

198

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

Microsoft Academic Search

The aim of the present study was to compare the biodegradation of differently cross-linked collagen membranes in rats. Five commercially available and three experimental membranes (VN) were included: (1) BioGide (BG) (non-cross-linked porcine type I and III collagens), (2) BioMend (BM), (3) BioMendExtend (BME) (glutaraldehyde cross-linked bovine type I collagen), (4) Ossix (OS) (enzymatic-cross-linked bovine type I collagen), (5) TutoDent

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

2005-01-01

199

Formation of composites comprised of calcium deficient HAp and cross-linked gelatin  

Microsoft Academic Search

Cross-linked gelatin\\/calcium deficient hydroxyapatite (CDHAp) composites were prepared at or near physiologic temperature.\\u000a ?-tricalcium phosphate (?-TCP) or a mixture of tetracalcium phosphate and dicalcium phosphate were used as CDHAp precursors.\\u000a Glutaraldehyde was used to cross-link the gelatin fibers. CDHAp formation reached completion in the presence of cross-linked\\u000a gelatin fibers. Effects of cross-linking concentrations, proportions of gelatin fiber, molecular weight of

Ahmed H. Touny; Cato Laurencin; Lakshmi Nair; Harry Allcock; Paul W. Brown

2008-01-01

200

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

201

[Corneal collagen cross-linking in keratoconus management].  

PubMed

Functional results of collagen UV cross-linking in keratoconus management are evaluated. 77 patients (87 eyes) with keratoconus stage I-II (Amsler classification) were under observation. All the patients received UV radiation (370 3m, 3mW/sm2) for 30 min with simultaneous instillation of "Dextralink" solution. Besides routine ophthalmological examination confocal biomicroscopy (HRT III, Heidelberg, Germany) and optical coherent tomography (Vizante-OCT, Carl Zeis, Germany) were performed before, in 1, 3, 6 and 12 months, 2 and 3 years after the procedure. By the 6th month the best corrected visual acuity showed improvement from 0.41 + 0.12 (M+m) till 0.52 + 0.01. Corneal refractive power decreased to 49.41 + 1.69 dpt by the last examination. UV cross-linking is a minimally invasive and effective option for management of keratoconus at the early stages, that let achieve biomechanical stabilization of the cornea and reduce progression rate. PMID:22165094

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

202

Characterization of soybean lipoxygenase immobilized in cross-linked phyllosilicates.  

PubMed

Lipoxygenase (LOX) is an enzyme that regioselectively introduces the hydroperoxide functionality into polyunsaturated fatty acids, such as linoleic acid (LA). Hydroperoxide derivatives of polyunsaturated fatty acids are of interest because they can serve as important intermediates in the synthesis of chemical and pharmaceutical compounds. In this study, LOX was immobilized in dispersed phyllosilicate layers that were cross-linked with silicate polymers formed by the hydrolysis of tetramethyl orthosilicates. The effects of substrate concentration, reaction temperature and solvent participation were studied on the oxidation of LA by LOX. The temperature optimum for the oxidation of LA by immobilized LOX was 25 degrees C and values of Km and Vmax for this reaction were 1.7 mM and 0.023 micromol/min respectively. Enzymic activity was stimulated by the addition of 10% (v/v) iso-octane to the reaction mixture. The immobilized LOX preparation showed a degree of substrate preference that demonstrated that 1,3-dilinolein was a better substrate than LA in the oxidation reaction, followed in order by 1-monolinolein, methyl oleate and trilinolein. In general, LOX immobilized in cross-linked phyllosilicates retained the physical and chemical characteristics of free LOX. PMID:9693089

Hsu, A F; Shen, S; Wu, E; Foglia, T A

1998-08-01

203

Structurally Cross-Linked Composite Proton Exchange Membranes  

SciTech Connect

Composite proton exchange membranes (PEMs) with a thermally cross-linked polymer backbone for high-temperature fuel cell applications were fabricated by casting tetrahydrofuran solution mixtures of tetraethoxysilane, a functional silane, a proton conductor, a molecular cross-linker (MXL), and an ethylene-methylacrylate copolymer with glycidyl methacrylate groups (PMG). The proton conductors used were commercial Keggin-structured silicotungstic acid (H4SiW12O40-26H2O, W12-STA) and lacunary W10- and W11-STA. The 3D cross-linked membranes were dense with in-situ formed SiO2 nanoparticles and showed high thermal stability, high chemical resistance to the Fenton's reagent, and moderate mechanical strength and flexibility. The corresponding proton conductivity was affected by formulation, membrane quality, loading level of W12-STA, temperature, and relative humidity, and was in the 20-25 mS/cm range at 80 C/100%RH with proton diffusion coefficients of 2.5-3.5 x 10-6 cm/s peaked in the {approx}90-110 C range for PEMs having a loading level of W12-STA >150 wt% (ratio to the weight sum of PMG and MXL).

Pern, J.; Turner, J.; Dec, S.; Yan, Y.; To, B.; Lipfert, D.; Meng, F.; Herring, A. M.

2007-01-01

204

Preparation and characterization of cross-linked composite polymer electrolytes  

SciTech Connect

Cross-linkable composite electrolytes were prepared from poly(ethylene glycol) dimethyl ether (PEGDME)-500, LiClO{sub 4}, fumed silica, and 10 wt % methyl, butyl, or octyl methacrylate. The silicas used were chemically modified by attaching methacrylate groups to the silica surface through C{sub 8} and C{sub 3} tethers. Before cross-linking, the electrolytes were thixotropic and had ionic conductivities of >2 {times} 10{sup {minus}4} S/cm. After ultraviolet (UV)-induced cross-linking, the electrolytes were rubbery and dimensionally stable, and the conductivities were unchanged. Conductivity, extraction, and thermal analysis data all support a model where the added methacrylate monomer and growing polymer chains phase separate from the electrolyte phase during photopolymerization to yield a methacrylate-rich silica/polymer phase and little or no polymer in the PEGDME-500 phase. Thus, the mechanical properties of the composite electrolyte and its ionic conductivity are decoupled and can be optimized independently.

Hou, J.; Baker, G.L. [Michigan State Univ., East Lansing, MI (United States)

1998-11-01

205

Collagen Cross-Linking: Current Status and Future Directions  

PubMed Central

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

Hovakimyan, Marine; Guthoff, Rudolf F.; Stachs, Oliver

2012-01-01

206

Effects of processing conditions on the reliability of cross-linked polyethylene cable insulation. Progress report  

SciTech Connect

Crystallization and morphology were investigated in cross-linked PE. /sup 13/C NMR was used to quantify the cross-links. Production of cable is being studied. Dielectric constant and loss of cross-linked PE are being measured. (DLC)

Phillips, P.J.

1981-03-01

207

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

208

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.

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

2011-01-01

209

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

NASA Astrophysics Data System (ADS)

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

Venerus, David C.; Kolev, Dimitre

2008-07-01

210

Influence of Chemical Cross-Linking on the Over Voltage Positive Temperature Coefficient of Linear Low Density Polyethylene/carbon Black/aluminum Hydroxide Nano Composites  

NASA Astrophysics Data System (ADS)

The effect of cross-linking of blends on the stability of positive temperature coefficient (PTC) and the elimination of negative temperature coefficient (NTC) were investigated. Linear low density polyethylene (LLDPE) was chemically cross-linking with various amounts of dicumyl peroxide (DCP). The resulting of cross-linking structure of composites was analyzed by gel content, differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA). By the effect of DCP, not only a high PTC intensity appeared, but also was the NTC effect of the composite eliminated. The PTC intensity reached six orders of magnitude for the LLDPE/DCP(0.10 wt%)/CB/Al(OH)3 composite, and successfully passed the test of over-voltage resistance.

Huang, C. Y.; Tsai, C. S.; Tsao, K. Y.

2008-08-01

211

The many ways to cleave hyaluronan.  

PubMed

Hyaluronan is being used increasingly as a component of artificial matrices and in bioengineering for tissue scaffolding. The length of hyaluronan polymer chains is now recognized as informational, involving a wide variety of size-specific functions. Inadvertent scission of hyaluronan can occur during the process of preparation. On the other hand, certain size-specific hyaluronan fragments may be desirable, endowing the finished bioengineered product with specific properties. In this review, the vast arrays of reactions that cause scission of hyaluronan polymers is presented, including those on an enzymatic, free radical, and chemical basis. PMID:17716848

Stern, Robert; Kogan, Grigorij; Jedrzejas, Mark J; Soltés, Ladislav

2007-07-18

212

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

PubMed

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, T(g), 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

2012-09-01

213

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.

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

2012-01-01

214

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

215

A Negative Ion Mass Spectrometry Approach to Identify Cross-Linked Peptides Utilizing Characteristic Disulfide Fragmentations  

NASA Astrophysics Data System (ADS)

Chemical cross-linking combined with mass spectrometry (MS) is an analytical tool used to elucidate the topologies of proteins and protein complexes. However, identification of the low abundance cross-linked peptides and modification sites amongst a large quantity of proteolytic fragments remains challenging. In this work, we present a strategy to identify cross-linked peptides by negative ion MS for the first time. This approach is based around the facile cleavages of disulfide bonds in the negative mode, and allows identification of cross-linked products based on their characteristic fragmentations. MS3 analysis of the cross-linked peptides allows for their sequencing and identification, with residue specific location of cross-linking sites. We demonstrate the applicability of the commercially available cystine based cross-linking reagent dithiobis(succinimidyl) propionate (DSP) and identify cross-linked peptides from ubiquitin. In each instance, the characteristic fragmentation behavior of the cross-linked species is described. The data presented here indicate that this negative ion approach may be a useful tool to characterize the structures of proteins and protein complexes, and provides the basis for the development of high throughput negative ion MS chemical cross-linking strategies.

Calabrese, Antonio N.; Good, Nikki J.; Wang, Tianfang; He, Jingjia; Bowie, John H.; Pukala, Tara L.

2012-08-01

216

Pyridinium cross-links in heritable disorders of collagen  

SciTech Connect

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

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

1995-12-01

217

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

218

Segmental dynamics and cross-linking in ion containing polymers  

NASA Astrophysics Data System (ADS)

We present Quasi Elastic Neutron Scattering (QENS) data for characterizing proton dynamics in ion containing polymers (ionomers) with varying ion content and ion identity. The anion is immobilized by covalently bonding it to the PEO backbone through an `ionizable' isophthalate co-monomer unit and only the cation contributes to the conductivity, thereby isolating cation-polymer interaction for study. The ion content is varied in two ways: changing the ratio of neutral to ionized co-monomer units, and changing the length of the PEO spacer separating the co-monomer units. In neutral ionomers, we observe two segmental processes: PEO segments in the spacer midpoint are one order of magnitude faster than those near the isophthalate groups. In ionized samples, cross-linking between ionic groups considerably slows the dynamics of PEO segments near the isophthalate group. This effect is ion dependent, which indicates that cations have different binding capacities and formation of this complex determines the availability of free cations for conduction.

Sinha, Kokonad; Maranas, Janna

2010-03-01

219

Stability of chitosan nanoparticles cross-linked with tripolyphosphate.  

PubMed

The physical stability of chitosan nanoparticles cross-linked with sodium tripolyphosphate (TPP) was investigated over a period of 1 month. Special emphasis was placed on changes in the particle size and the particle compactness, which are two important physicochemical parameters of nanoparticulate drug delivery systems. The chitosan-TPP particles were prepared at different ionic strengths, chitosan chloride concentrations, and TPP-to-chitosan ratios. In the presence of monovalent salt, the positive ? potential of the particles was reduced. In spite of this, the particles were more stable when prepared and stored under saline conditions compared to water. This could be attributed to the smaller particle sizes found in the presence of sodium chloride. Most of the particles prepared in saline solvents were stable with respect to changes in the size and the compactness of the particles. However, instability was observed at the highest cross-linker-to-polymer ratios. Generally, a reduction in the ? potential and an increase in the particle compactness were observed at increasing TPP-to-chitosan ratios. This combined with the size increase induced by a high concentration of chitosan, increased the aggregation and sedimentation tendency of the particles and reduced the colloidal stability of the particles. PMID:23046433

Jonassen, Helene; Kjøniksen, Anna-Lena; Hiorth, Marianne

2012-10-09

220

Preparation and characterization of macromolecule cross-linked collagen hydrogels for chondrocyte delivery.  

PubMed

Collagen hydrogels are widely used in cartilage tissue engineering for their mimicked chondrogenic environment. Due to the rapid degradation nature and weak mechanical property, collagen hydrogels are often cross-linked in application. In this work, collagen hydrogels were soaked into oxidized alginate solution which used as macromolecular cross-linker to prepare the cross-linked hydrogels. Soaking method could retain the self-assemble property of collagen and also bring in a cross-linking network. The compressive modulus and degradation properties of collagen hydrogels were ameliorated after cross-linked, and chondrocytes encapsulated in the cross-linked hydrogels proliferated well and maintained the cell phenotype. This study implied that collagen hydrogels cross-linked by oxidized alginate may have a great potential for application in cartilage tissue engineering. PMID:23916642

Yang, Xiaoqin; Guo, Likun; Fan, Yujiang; Zhang, Xingdong

2013-08-03

221

Cross-linking of streptomycin to the 16S ribosomal RNA of Escherichia coli  

Microsoft Academic Search

(³H)Dihydrostreptomycin was cross-linked to the 30S ribosomal subunit from Escherichia coli with the bifunctional reagent nitrogen mustard. The cross-linking primarily involved the 16S RNA. To localize the site of cross-linking of streptomycin to the 16S RNA, the authors hybridized RNA labeled with streptomycin to restriction fragments of the 16S RNA gene. Labeled RNA hybridized to DNA fragments corresponding to bases

Michel Gravel; Pierre Melancon; L. Barkier-Gingras

1987-01-01

222

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

223

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.

Oral, Ebru; Muratoglu, Orhun K.

2007-01-01

224

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

NASA Astrophysics Data System (ADS)

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.

Oral, Ebru; Muratoglu, Orhun K.

2007-12-01

225

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

Microsoft Academic Search

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

A. Gomoll; T. Wanich; A. Bellare

2002-01-01

226

Adsorption behavior of reactive dye in aqueous solution on chemical cross-linked chitosan beads  

Microsoft Academic Search

A batch system was applied to study the adsorption of reactive dye (reactive red 189) from aqueous solutions by cross-linked chitosan beads. The ionic cross-linking reagent sodium tripolyphosphate was used to obtain more rigid chitosan beads. To stabilize chitosan in acid solutions, chemical cross-linking reagent epichlorohydrin (ECH), glutaraldehyde and ethylene glycol diglycidyl ether was used and ECH shows a higher

M. S Chiou; H. Y Li

2003-01-01

227

Urinary excretion of pyridinium cross-links of collagen in infancy  

Microsoft Academic Search

This cross-sectional study evaluated urinary excretion of pyridinium cross-links of collagen, specific markers of ongoing bone resorption, in infants aged 1 week to 7 months and examined the relationship between urinary cross-links and individual renal function. Spot urines from a total of 100 infants were analyzed. The collagen cross-links, pyridinoline (Pyd) and deoxypyridinoline (D-Pyd), were assayed by fluorescence detection after

Hirokazu Tsukahara; Masakazu Miura; Chikahide Hori; Masahiro Hiraoka; Kazuhiko Nosaka; Keishi Hata; Yukuo Konishi; Masakatsu Sudo

1996-01-01

228

Different Pattern of Collagen Cross-Links in Two Sclerotic Skin Diseases: Lipodermatosclerosis and Circumscribed Scleroderma  

Microsoft Academic Search

Changes in the process of cross-linking of collagen molecules are associated with defects in the biomechanical stability of the extracellular matrix. Fibrosis of skin is characterized by an increase in pyridinolines, which are hydroxylysine aldehyde derived cross-links usually absent in healthy skin. In this study, we analyzed cross-links in lipodermatosclerosis and localized scleroderma to address the question whether all the

J Brinckmann; C. M Neess; Y Gaber; H Sobhi; H Notbohm; N Hunzelmann; P. P Fietzek; P. K Muller; J Risteli; R Gebker; K Scharffetter-Kochanek; med. Jürgen Brinckmann

2001-01-01

229

Yield of DNA-Protein Cross-Links in 7-Irradiated Chinese Hamster Cells1  

Microsoft Academic Search

•y-Irradiation of Chinese hamster V79 cells increases the percentage of nuclear DNA cross-linked to proteins. Studies were carried out to ascertain whether the radiation-induced increase in DNA-protein cross links (DPC) is due to an increase in the number of DNA fragments which are cross-linked to protein or to an increase in the size of bound DNA fragments. Cells were prelabeled

Narayani Ramakrishnan; Nancy L. Oleinick

230

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.

2012-12-17

231

Rheology and Convective Heat Transfer Properties of Borate Cross-Linked Nitrogen Foam Fracturing Fluid  

Microsoft Academic Search

This article considers the rheology and convective heat transfer characteristics of borate cross-linked guar and borate cross-linked foam fracturing fluid by conducting experiments on a large-scale test loop at 30 MPa. The results show that severe chemical degradation of borate cross-linked guar occurred as temperature increased. When temperature was higher than the threshold value, the cross-linker was almost disabled and

Xiao Sun; Shuzhong Wang; Yu Bai; Shuangshuang Liang

2011-01-01

232

Effects of cross-linking modification on gas separation performance of Matrimid membranes  

Microsoft Academic Search

A room-temperature chemical cross-linking modification has been performed on Matrimid® 5218, a material that has received pervasive attention in membrane separation. The cross-linking reaction was conducted by simply immersing the membrane in a p-xylenediamine solution at ambient temperature for a stipulated period of time. The influence of cross-linking modification on thermal and gas transport properties of Matrimid membrane were studied.

P. S. Tin; T. S. Chung; Y. Liu; R. Wang; S. L. Liu; K. P. Pramoda

2003-01-01

233

In vivo behaviour of rat band 3 cross-linked carrier erythrocytes.  

PubMed

Rat band 3 cross-linked carrier erythrocytes have been prepared. Iodinated carbonic anhydrase has been encapsulated into rat erythrocytes. Then, carrier erythrocytes were labeled with 51chromium. Eventually, these doubly labeled rat RBCs were treated with a band 3 cross-linking reagent, namely bis(sulfosuccinimidyl)suberate (BS3). 51Chromium labeling and 125I CA showed to have cytosolic localization in cross-linked carrier erythrocytes. Estimation of the band 3 cross-linking induced by BS3 on rat carrier erythrocytes has been done rendering values around 25% of band 3 monomer reduction. BS3-cross-linked carrier erythrocytes when injected into rats are mainly targeted to liver as shown by chromium labeling localization. Also, encapsulated CA radioactivity carried by cross-linked carrier rat erythrocytes when injected into rats is localized predominantly in liver as shown by in vivo experiments. Accordingly, cross-linked carrier erythrocytes are highly recognized by peritoneal macrophages as detected by in vitro analyses of macrophage recognition. Thus, our data revealed a targeting of carrier rat erythrocytes induced by cross-linking of band 3 protein by BS3. These results support claims in favor of this animal model as a feasible system to analyze cross-linked carrier erythrocytes survival and targeting as well as the in vivo efficacy of targeting of loaded compounds to liver. PMID:9672753

Jordán, J A; Alvarez, F J; Lotero, L A; Tejedor, M C; Díez, J C

1998-04-01

234

Hyaluronan in Limb Morphogenesis  

PubMed Central

Hyaluronan (HA) is a large glycosaminoglycan that is not only a structural component of extracellular matrices, but also interacts with cell surface receptors to promote cell proliferation, migration, and intracellular signaling. HA is a major component of the extracellular matrix of the distal subapical mesenchymal cells of the developing limb bud that are undergoing proliferation, directed migration, and patterning in response to the apical ectodermal ridge (AER), and has the functional potential to be involved in these processes. Here we show that the HA synthase Has2 is abundantly expressed by the distal subridge mesodermal cells of the chick limb bud and also by the AER itself. Has2 expression and HA production are downregulated in the proximal central core of the limb bud during the formation of the precartilage condensations of the skeletal elements, suggesting downregulation of HA may be necessary for the close juxtaposition of cells and the resulting cell-cell interactions that trigger cartilage differentiation during condensation. Overexpression of Has2 in the mesoderm of the chick limb bud in vivo results in the formation of shortened and severely malformed limbs that lack one or more skeletal elements. Skeletal elements that do form in limbs overexpressing Has2 are reduced in length, exhibit abnormal morphology, and are positioned inappropriately. We also demonstrate that sustained HA production in micromass cultures of limb mesenchymal cells inhibits formation of precartilage condensations and subsequent chondrogenesis, indicating that downregulation of HA is indeed necessary for formation of the precartilage condensations that trigger cartilage differentiation. Taken together these results suggest involvement of HA in various aspects of limb morphogenesis.

Li, Yingcui; Toole, Bryan P.; Dealy, Caroline N.; Kosher, Robert A.

2007-01-01

235

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.

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

2012-01-01

236

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.

2013-01-01

237

The theory and art of corneal cross-linking.  

PubMed

Before the discovery of corneal cross-linking (CXL), patients with keratoconus would have had to undergo corneal transplantation, or wear rigid gas permeable lenses (RGPs) that would temporarily flatten the cone, thereby improving the vision. The RGP contact lens (CL) would not however alter the corneal stability and if the keratoconus was progressive, the continued steepening of the cone would occur under the RGP CL. To date, the Siena Eye has been the largest study to investigate long term effects of standard CXL. Three hundred and sixty-three eyes were treated and monitored over 4 years, producing reliable long-term results proving long-term stability of the cornea by halting the progression of keratoconus, and proving the safety of the procedure. Traditionally, CXL requires epithelial removal prior to corneal soakage of a dextran-based 0.1% riboflavin solution, followed by exposure of ultraviolet-A (UV-A) light for 30 min with an intensity of 3 mW/cm2. A series of in vitro investigations on human and porcine corneas examined the best treatment parameters for standard CXL, such as riboflavin concentration, intensity, wavelength of UV-A light, and duration of treatment. Photochemically, CXL is achieved by the generation of chemical bonds within the corneal stroma through localized photopolymerization, strengthening the cornea whilst minimizing exposure to the surrounding structures of the eye. In vitro studies have shown that CXL has an effect on the biomechanical properties of the cornea, with an increased corneal rigidity of approximately 70%. This is a result of the creation of new chemical bonds within the stroma. PMID:23925326

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

2013-08-01

238

Molecular Recognition in Gels, Monolayers, and Solids.  

National Technical Information Service (NTIS)

This paper describes work in four area:affinity electrophoresis of carbonic anhydrase in cross-linked polyacrylamide-derived gels containing immobilized derivatives of aryl sulfonamides; inhibition of the hemagglutination of erythrocytes induced by influe...

K. L. Prime Y. H. Chu W. Schmid C. T. Seto J. K. Chen

1991-01-01

239

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 ...

240

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

241

Viscoelasticity of cross-linked actin networks: experimental tests, mechanical modeling and finite-element analysis.  

PubMed

Filamentous actin is one of the main constituents of the eukaryotic cytoskeleton. The actin cortex, a densely cross-linked network, resides underneath the lipid bilayer. In the present work we propose a continuum mechanical formulation for describing the viscoelastic properties of in vitro actin networks, which serve as model systems for the cortex, by including the microstructure, i.e. the behavior of a single filament and its spatial arrangement. The modeling of the viscoelastic response in terms of physically interpretable parameters is conducted using a multiscale approach consisting of two steps: modeling of the single filament response of F-actin by a worm-like chain model including the extensibility of the filament, and assembling the three-dimensional biopolymer network by using the microsphere model which accounts for filaments equally distributed in space. The viscoelastic effects of the network are taken into account using a generalized Maxwell model. The Cauchy stress and elasticity tensors are obtained within a continuum mechanics framework and implemented into a finite-element program. The model is validated on the network level using large strain experiments on reconstituted actin gels. Comparisons of the proposed model with rheological experiments recover reasonable values for the material parameters. Finite-element simulations of the indentation of a sphere on a network slab and the aspiration of a droplet in a micropipette allow for further insights of the viscoelastic behavior of actin networks. PMID:23523535

Unterberger, Michael J; Schmoller, Kurt M; Wurm, Christine; Bausch, Andreas R; Holzapfel, Gerhard A

2013-03-21

242

Fibrinogen influx and accumulation of cross-linked fibrin in healing wounds and in tumor stroma.  

PubMed Central

Fibrinogen enters wounds and solid tumors, where it is clotted to fibrin that may subsequently be replaced by collagenous stroma. If, as has been suggested, the pathogenesis of wound healing and tumor stroma generation is similar and dependent on fibrin deposition, then the types and amounts of fibrin deposited in wounds and tumors might also be expected to be similar. To test this hypothesis, the authors injected homologous tracer fibrinogen (125I-GPF) intravenously into guinea pigs and measured its influx and accumulation in skin wounds and syngeneic carcinomas. In support of their hypothesis, the urea-insoluble product deposited in both wounds and tumors was identified as cross-linked fibrin by gel electrophoresis. Accumulation of both total and urea-insoluble 125I-GPF was quantitatively similar in wounds and tumors. However, influx and initial clotting of 125I-GPF in tumors exceeded that in wounds; given equivalent accumulation, these data suggest that fibrin turnover is more rapid in tumors than in wounds. Fibrinogen influx and fibrin accumulation declined toward normal a few days after wounding but remained consistently elevated in tumors. Thus, the magnitude and the persistence of microvascular hyperpermeability, as well as fibrin turnover, are major points of difference that distinguish tumors from healing wounds. Images Figure 3 Figure 4 Figure 5

Brown, L. F.; Van de Water, L.; Harvey, V. S.; Dvorak, H. F.

1988-01-01

243

Oxidation-induced unfolding facilitates Myosin cross-linking in myofibrillar protein by microbial transglutaminase.  

PubMed

Myofibrillar protein from pork Longissimus muscle was oxidatively stressed for 2 and 24 h at 4 °C with mixed 10 ?M FeCl(3)/100 ?M ascorbic acid/1, 5, or 10 mM H(2)O(2) (which produces hydroxyl radicals) and then treated with microbial transglutaminase (MTG) (E:S = 1:20) for 2 h at 4 °C. Oxidation induced significant protein structural changes (P < 0.05) as evidenced by suppressed K-ATPase activity, elevated Ca-ATPase activity, increased carbonyl and disulfide contents, and reduced conformational stability, all in a H(2)O(2) dose-dependent manner. The structural alterations, notably with mild oxidation, led to stronger MTG catalysis. More substantial amine reductions (19.8-27.6%) at 1 mM H(2)O(2) occurred as compared to 11.6% in nonoxidized samples (P < 0.05) after MTG treatment. This coincided with more pronounced losses of myosin in oxidized samples (up to 33.2%) as compared to 21.1% in nonoxidized (P < 0.05), which was attributed to glutamine-lysine cross-linking as suggested by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. PMID:22809283

Li, Chunqiang; Xiong, Youling L; Chen, Jie

2012-07-31

244

Proteins cross-linked to U1 RNA by ultraviolet irradiation  

SciTech Connect

Proteins associated to U1 RNA react with antinuclear antibodies obtained from sera of patients with autoimmune diseases. K.B. cells were labeled with /sup 3/H-amino acids of /sup 3/H-uridine. The U1 RNA particles were immunoprecipitated. Protein and RNA analysis was by electrophoresis and fluorography. The ratio of material at the top of the RNA gel to the U1 RNA band was 0.79. After exposure of the cells to UV irradiation, the ratio was 5.04. A substantial amount of U1 RNA was cross-linked to proteins or other nuclear components. Protein patterns obtained from U1 RNP particles subjected to UV irradiation revealed a change in electrophoretic mobility by four proteins in the molecular range of 14,000 to 28,000 daltons. The 33,000 dalton protein was reduced by 50% but its electrophoretic mobility was unchanged. The protein band at 68,000 daltons was unchanged in amount or mobility by UV irradiation. It is concluded that the low molecular weight proteins (14,000 - 28,000) and the protein of 33,000 daltons are in close proximity to U1 RNA and possibly play a role in the molecular function(s) attributed to U1 RNA.

Marti, A.; Jimenez, R.; Matos, J.

1987-05-01

245

Cross-linked tyrosinase aggregates for elimination of phenolic compounds from wastewater.  

PubMed

A novel, practical and inexpensive immobilization method has been developed for mushroom tyrosinase to be used for enzymatic treatment of phenolic wastewater. Catalyzed by the enzyme immobilized in the form of cross-linked enzyme aggregates (CLEAs), phenolic compounds such as phenol, p-cresol, p-chlorophenol and bisphenol A can be efficiently eliminated, with a complete conversion obtained within 0.5-3h, superior to other processes catalyzed by the same enzyme which is either free or immobilized with traditional carrier-bound immobilization methods. The effects of reaction time, pH, enzyme dosage and initial concentration of the phenol solution were examined. The sequence of dephenolization rate (p-cresol>p-chlorophenol>phenol) was in accordance with the substrate selectivity of the enzyme. The reusability of the CLEAs has been tested in a batch reactor for each phenol. In a continuous stirred tank reactor, the CLEAs encapsulated into calcium alginate gels were effective for removing phenol for at least 26h. The toxicity of the phenol-containing solution was remarkably diminished after treatment with the tyrosinase CLEAs, as demonstrated by the Hydra sinensis test. PMID:23411085

Xu, Da-You; Yang, Zhen

2013-02-11

246

Radiation cross-linking of small electrical wire insulator fabricated from NR/LDPE blends  

NASA Astrophysics Data System (ADS)

A low voltage, radiation-crosslinked wire insulator has been fabricated from blends of natural rubber block (STR-5L) and LDPE with phthalic anhydride (PA) as a compatibilizer. Physical properties of the NR/LDPE blend ratios of 50/50 and 60/40 with 0.5, 1.0, and 1.5 wt% PA were evaluated. The gel content increased as the radiation dose increased. Tensile at break exhibited a maximum value of 12 MPa at 120 kGy for 1.0 and 1.5 wt% PA of both blend ratios. A higher PA content yielded a higher modulus for the same blend ratio. Blends of 60/40 ratio with 1.0 wt% PA and 0.8 wt% antimony oxide flame retardant gave the highest limiting oxygen index (LOI) of >30% at above 150 kGy. Other electrical properties of the wire insulator were investigated. It was found that an insulator fabricated from a PA content of 1.0 wt% in the NR/LDPE blend ratio of 50/50, after gamma ray cross-linked at a dose of 180 kGy in low vacuum (1 mm Hg), met the Thai Industrial Standard 11-2531 for low voltage wire below 1.0 kV. To comply with the standard for vertical flame test, a more suitable flame retardant was needed for the insulator.

Siri-Upathum, Chyagrit; Punnachaiya, Suvit

2007-12-01

247

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

248

Studies on the oxidative cross-linking of feruloylated arabinoxylans from wheat flour and wheat bran  

Microsoft Academic Search

Feruloylated arabinoxylans isolated from wheat flour and wheat bran were compared in their cross-linking behaviour with respect to viscosity properties and cross-linking products formed when various oxidative agents were applied to dilute solutions. Optimal conditions for each oxidative agent were investigated. In case of hydrogen peroxide and peroxidase, similar conditions were found for both types of arabinoxylans but wheat bran

M. E. F. Schooneveld-Bergmans; M. J. W. Dignum; J. H. Grabber; G. Beldman; A. G. J. Voragen

1999-01-01

249

Characterization of Aziridinylbenzoquinone DNA Cross-links by LC-IRMPD-MS  

PubMed Central

DNA cross-linking was evaluated by LC-MS/MS to determine the relative cross-linking abilities of two aziridinylbenzoquinones. Reactivities of RH1 (2,5-diaziridinyl-3-[hydroxymethyl]-6-methyl-1,4-benzoquinone), a clinically studied anti-tumor cross-linking agent, and an analog containing a phenyl group (PhRH1) rather than a methyl group was compared. The bulky phenyl substituent was added to determine the impact of steric hindrance on the formation of cross-links within a double helical structure. Cross-links formed by RH1 and PhRH1 (2,5-diaziridinyl-3-[hydroxymethyl]-6-phenyl-1,4-benzoquinone) were observed at 5’-dGNC sites as well as 5’-dGAAC/dGTTC sites. RH1 was more effective at forming cross-links than PhRH1 for a variety of duplexes. Infrared multiphoton dissociation (IRMPD) and collision induced dissociation (CID) results confirmed the presence and the location of the cross-links within the duplexes, and IRMPD was used to identify the dissociation pathways of the cross-linked duplexes.

Pierce, Sarah E.; Guziec, Lynn J.; Guziec, Frank S.; Brodbelt, Jennifer S.

2010-01-01

250

The type of collagen cross-link determines the reversibility of experimental skin fibrosis.  

PubMed

Fibrotic processes in humans are characterised by an excessive accumulation of collagen containing increased levels of hydroxyallysine-derived cross-links. The occurrence of these cross-links appears to be an important criterion in assessing the irreversibility of fibrosis. We hypothesise that increased hydroxyallysine cross-linking results in a collagenous matrix that is less susceptible to proteolytic degradation and therefore the collagen deposition is no longer reversible. In this report, we show that collagen matrices with increased hydroxyallysine cross-link levels were less susceptible to matrix metalloproteinase 1 degradation than are collagen matrices containing low hydroxyallysine levels. These data indicate that the type of collagen cross-link influences collagen catabolism. In vivo evidence for the importance of the cross-linking type in determining the reversibility of the fibrotic process was found using the bleomycin-induced skin fibrosis mouse model. The analysis of the accumulated collagen in the fibrotic skin of bleomycin-treated mice did not reveal an increase in hydroxyallysine cross-link levels. In concurrence with our hypothesis, the collagen accumulation resolved in time when the mice were no longer receiving bleomycin treatment, showing the reversibility of the fibrosis. In conclusion, our data indicate that the type of collagen cross-linking is an important factor in determining whether the outcome of the fibrotic process is reversible or not. PMID:15878742

van der Slot-Verhoeven, Annemarie J; van Dura, Ernst A; Attema, Joline; Blauw, Bep; Degroot, Jeroen; Huizinga, Tom W J; Zuurmond, Anne-Marie; Bank, Ruud A

2005-03-05

251

Determination of the cross-linking effect of adipic acid dihydrazide on glycoconjugate preparation  

Microsoft Academic Search

The cross-linking effect of adipic acid dihydrazide (ADH) on polysaccharide derivatization can be evaluated by applying combination of elemental analysis and colorimetric assay. Elemental analysis is used for estimation of total ADH bound to polysaccharide and a colorimetric trinitrobenzene sulfonic acid assay is used to determine the part of ADH not involved in cross-linking. The difference of values expressed as

Slavomír Bystrický; Eva Machová; Anna Malovíková; Grigorij Kogan

1999-01-01

252

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...

253

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

254

A comparison of thermally and photochemically cross-linked polymers for nanoimprinting  

Microsoft Academic Search

The characteristics and benefits of two types of cross-linking prepolymers with low glass transition temperature (Tg) for nanoimprinting are reported. They are soluble in organic solvents and their solutions can be processed like those of common thermoplastics. The imprinted patterns receive high thermal and mechanical stability through cross-linking polymerization. The course of the polymerization was investigated to determine the appropriate

K. Pfeiffer; F. Reuther; M. Fink; G. Gruetzner; P. Carlberg; I. Maximov; L. Montelius; J. Seekamp; S. Zankovych; C. M. Sotomayor-Torres; H. Schulz; H.-C. Scheer

2003-01-01

255

Dielectric behavior of filled silicone rubbers: effects of cross-linking agent and surface modified fillers  

Microsoft Academic Search

The influence of amount of cross-linking agent and surface modification of alumina trihydrate (ATH) fillers on dielectric properties of silica filled silicone rubber were investigated. It was found that the cross-linking agent did not affect the dielectric properties of the silica filled silicone rubber if the samples were electrically aged before. There were two clear processes in these systems, relaxation

E. Tuncer; S. M. Gubanski; B. Nettelblad; H. Hillborg; K. Dowling

2000-01-01

256

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...

257

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

2013-01-09

258

pH- and voltage-responsive chitosan hydrogel through covalent cross-linking with catechol.  

PubMed

A new method for covalently cross-linking chitosan is developed by chemically oxidizing catechol to o-quinone which subsequently reacts with and cross-links chitosan through Michael addition and Schiff base formation. The cross-linked chitosan film shows a pH-responsive, switchlike behavior toward the negatively charged redox probe, Fe(CN)(6)(3-/4-), and withstands harsh acidic conditions. The negative Fe(CN)(6)(3-/4-) is found to be trapped and enriched in the catechol-cross-linked chitosan film under acidic conditions and released into solution by either increasing pH or applying a negative voltage. Chitosan films made with different techniques, i.e., solvent evaporation (simple deposition), electrodeposition, and covalent cross-linking, are examined using cyclic voltammetry and electrochemical impedance spectroscopy (EIS), and the results demonstrate that fabrication methods greatly affect the properties of the chitosan films. PMID:22229705

Zhang, Yongchao; Thomas, Yanique; Kim, Eunkyoung; Payne, Gregory F

2012-01-24

259

Analysis of Secondary Structure in Proteins by Chemical Cross-Linking Coupled to Mass Spectrometry  

PubMed Central

Chemical cross-linking is an attractive technique for the study of the structure of protein complexes due to its low sample consumption and short analysis time. Furthermore, distance constraints obtained from the identification of cross-linked peptides by mass spectrometry can be used to construct and validate protein models. If a sufficient number of distance constraints are obtained, then determining the secondary structure of a protein can allow inference of the protein’s fold. In this work, we show how the distance constraints obtained from cross-linking experiments can identify secondary structures within the protein sequence. Molecular modeling of alpha helices and beta sheets indicate cross-linking patterns based on the topological distances between reactive residues. DSS[1] cross-linking experiments with model alpha helix containing proteins corroborated the molecular modeling predictions. The patterns established here can be extended to other cross-linkers with known spacing lengths.

Fioramonte, Mariana; dos Santos, Aline Mara; McIlwain, Sean; Noble, William S.; Franchini, Kleber Gomes; Gozzo, Fabio Cesar

2013-01-01

260

Thermal energy storage material comprising hydrated compound and water-swollen cross-linked polymer  

SciTech Connect

The thermal energy storage material comprises at least one hydrated compound (Such as an inorganic salt) having a reversible transition to the anhydrous or a less hydrated form and a hydrogel, comprising a water-swollen cross-linked polymer formed by cross-linking a synthetic hydrophilic polymer by a covalent cross-linking mechanism, throughout which the compound is dispersed. The hydrogel is made by reacting a water-soluble or water-dispersible synthetic hydrophilic polymer, which is preferably linear and thermoplastic, with a cross-linking agent therefor in an aqueous medium containing the hydrated compound. The hydrophilic polymer, the aqueous medium and the hydrated compound are used in such amounts that the storage material contains a major proportion, by weight, of the hydrated compound and a minor proportion, by weight, of the cross-linked polymer.

Kent, P.J.; Page, J.K.

1981-06-16

261

Block Ionomer Complex Micelles with Cross-Linked Cores for Drug Delivery1,2  

PubMed Central

Soft polymeric nanomaterials were synthesized by template-assisted method involving condensation of the poly(ethylene oxide)-b-polycarboxylate anions by metal ions into core-shell block ionomer complex micelles followed by chemical cross-linking of the polyion chains in the micelle cores. The resulting materials represent nanogels and are capable of swelling in a pH-dependent manner. The structural determinants that guide the self-assembly of the initial micelle templates and the swelling behavior of the cross-linked micelles include the block ionomer structure, the chemical nature of metal ions, the structure of the cross-links and the degree of cross-linking. The application of these materials for loading and release of a drug, cisplatin, is evaluated. These cross-linked block ionomer micelles have promise for delivery of pharmaceutical agents.

Kim, Jong Oh; Nukolova, Nataliya V.; Oberoi, Hardeep S.; Kabanov, Alexander V.; Bronich, Tatiana K.

2010-01-01

262

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

2012-10-26

263

Gels with magnetic properties  

Microsoft Academic Search

Materials producing strain in magnetic field are known as magnetoelastic or magneto strictive materials. A new type has been\\u000a developed by preparing magnetic field sensitive gels, called ferrogels. Single domain, magnetic particles of colloidal size\\u000a are incorporated into chemically cross-linked polyvinyl-alcohol hydrogels. The finely distributed colloidal particles having\\u000a superparamgnetic behavior couple the shape of the gel to the nonuniform external

L. Barsi; A. Biiki; D. Szabó; M. Zrinyi

264

Design principles for cytokine-neutralizing gels: Cross-linking effects  

Microsoft Academic Search

Constructs composed of cytokine-neutralizing antibodies conjugated to high-molecular-weight hyaluronic acid have been shown to be effective at controlling inflammatory responses in vivo. A critical question in the development of this new class of biomaterial is whether crosslinked conjugates have similar anti-inflammatory effects, which would open up a broad range of tissue engineering applications in which the material would have intrinsic

Liang Tso Sun; Sidi A. Bencherif; Thomas W. Gilbert; Michael T. Lotze; Newell R. Washburn

2010-01-01

265

Cross-Linked Functionalized Poly(3-hexylthiophene) Nanofibers with Tunable Excitonic Coupling.  

PubMed

We show that mechanically and chemically robust functionalized poly(3-hexylthiophene) (P3HT) nanofibers can be made via chemical cross-linking. Dramatically different photophysical properties are observed depending on the choice of functionalizing moiety and cross-linking strategy. Starting with two different nanofiber families formed from (a) P3HT-b-P3MT or (b) P3HT-b-P3ST diblock copolymers, cross-linking to form robust nanowire structures was readily achieved by either a third-party cross-linking agent (hexamethylene diisocyanate, HDI) which links methoxy side chains on the P3MT system, or direct disulfide cross-link for the P3ST system. Although the nanofiber families have similar gross structure (and almost identical pre-cross-linked absorption spectra), they have completely different photophysics as signaled by ensemble and single nanofiber wavelength- and time-resolved photoluminescence as well as transient absorption (visible and near-IR) probes. For the P3ST diblock nanofibers, excitonic coupling appears to be essentially unchanged before and after cross-linking. In contrast, cross-linked P3MT nanofibers show photoluminescence similar in electronic origin, vibronic structure, and lifetime to unaggregated P3HT molecules, e.g., dissolved in an inert polymer matrix, suggesting almost complete extinction of excitonic coupling. We hypothesize that the different photophysical properties can be understood from structural perturbations resulting from the cross-linking: For the P3MT system, the DIC linker induces a high degree of strain on the P3HT aggregate block, thus disrupting both intra- and interchain coupling. For the P3ST system, the spatial extent of the cross-linking is approximately commensurate with the interlamellar spacing, resulting in a minimally perturbed aggregate structure. PMID:24004252

Baghgar, Mina; Pentzer, Emily; Wise, Adam J; Labastide, Joelle A; Emrick, Todd; Barnes, Michael D

2013-09-12

266

Influence of intramolecular cross-links on the molecular, structural and functional properties of PEGylated haemoglobin  

PubMed Central

The influence of intramolecular cross-links on the molecular, structural and functional properties of PEGylated {PEG [poly(ethylene glycol)]-conjugated} haemoglobin has been investigated. The sites and the extent of PEGylation of haemoglobin by reductive alkylation are not influenced by the presence of an ??-fumaryl cross-link at Lys-99(?). The propylated hexaPEGylated cross-linked haemoglobin, (propyl-PEG5K)6-??-Hb, exhibits a larger molecular radius and lower colloidal osmotic pressure than propylated hexaPEGylated non-cross-linked haemoglobin, (propyl-PEG5K)6-Hb. Perturbation of the haem microenvironment and the ?1?2 interface by PEGylation of haemoglobin is reduced by intramolecular cross-linking. Sedimentation velocity analysis established that PEGylation destabilizes the tetrameric structure of haemoglobin. (Propyl-PEG5K)6-Hb and (propyl-PEG5K)6-??-Hb sediment as stable dimeric and tetrameric molecules, respectively. The ??-succinimidophenyl PEG-2000 cross-link at Cys-93(?) outside the central cavity also influences the molecular properties of haemoglobin, comparable to that by the ??-fumaryl cross-link within the central cavity. However, the influence of the two cross-links on the oxygen affinity of PEGylated haemoglobin are very distinct, indicating that the high oxygen affinity of PEGylated haemoglobin is not a direct consequence of the dissociation of the haemoglobin tetramers into dimers. ??-Fumaryl cross-linking is preferred to modulate both oxygen affinity and molecular properties of PEGylated haemoglobin, and cross-linking outside the central cavity could only modulate molecular properties of PEGylated haemoglobin. It is suggested that PEGylation induces a hydrodynamic drag on haemoglobin and this plays a role in the microcirculatory properties of PEGylated haemoglobin.

Hu, Tao; Manjula, Belur N.; Li, Dongxia; Brenowitz, Michael; Acharya, Seetharama A.

2006-01-01

267

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

268

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

269

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

270

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

271

Stabilized nanocarriers for plasmids based upon cross-linked poly(ethylene imine).  

PubMed

Stabilized PEI/DNA polyplexes were generated by cross-linking PEI with biodegradable disulfide bonds. The reaction conversion of different PEIs with the amine reactive cross-linker dithiobis(succinimidyl propionate) (DSP) was investigated, and the molecular weight of the reaction products was identified. Light scattering and microelectrophoresis were employed to assess size and zeta potential of the resulting polyplexes. Polyplex morphology and mechanic stability were investigated using atomic force microscopy. Finally, albumin and erythrocyte interactions and stability against polyanions and high ionic strength were checked. Polyplexes of PEI and DNA were prepared by two different formulation methods, either using pre-cross-linked polymers or by cross-linking polyplexes after complexation. Only the latter method yielded small (100-300 nm) polyplexes with a positive zeta potential when HMW PEI was used, whereas cross-linked LMW PEI resulted in polyplexes with increased size (>1000 nm) and zeta potentials down to -20 mV. In addition, only cross-linking after polyplex formation was able to enhance resistance against polyanion exchange and high ionic strength. AFM images revealed no changes in the morphology of cross-linked HWM PEI polyplexes, and indentation force measurements using AFM significantly increased mechanical stability of cross-linked HMW PEI polyplexes. These polyplexes also displayed significantly reduced interactions with major blood components like albumin and erythrocytes. The resulting biocompatible particles offer a means of combining enhanced polyplex stability with redox-triggered activation for in vivo application. PMID:17154471

Neu, Michael; Sitterberg, Johannes; Bakowsky, Udo; Kissel, Thomas

2006-12-01

272

Surface cross-linked UHMWPE can enable the use of larger femoral heads in total joints.  

PubMed

Limiting cross-linking to the articular surfaces of ultrahigh molecular weight polyethylene (UHMWPE) to increase wear resistance while preventing detrimental effects of cross-linking on mechanical strength has been a desirable goal. A surface cross-linked UHMWPE can be achieved by blending UHMWPE with a free radical scavenger, such as vitamin E, consolidating the blend into an implant shape, extracting the vitamin E from the surface, and radiation cross-linking the surface extracted blend. This process results in high cross-link density in the vitamin E-depleted surface region because vitamin E hinders cross-linking during irradiation. In this study, we described the properties of successful extraction media and the manipulation of the wear and mechanical properties of extracted, irradiated blends. We showed that these formulations could have similar wear and significantly improved mechanical properties compared to currently available highly cross-linked UHMWPEs. We believe that these materials can enable thinner implant forms and more anatomical designs in joint arthroplasty and may provide a feasible alternative to metal-on-metal implants. PMID:22847503

Oral, Ebru; Neils, Andrew L; Lyons, Chelsea; Fung, Mitchell; Doshi, Brinda; Muratoglu, Orhun K

2012-07-30

273

Actin Cross-link Assembly and Disassembly Mechanics for ?-Actinin and Fascin*  

PubMed Central

Self-assembly of complex structures is commonplace in biology but often poorly understood. In the case of the actin cytoskeleton, a great deal is known about the components that include higher order structures, such as lamellar meshes, filopodial bundles, and stress fibers. Each of these cytoskeletal structures contains actin filaments and cross-linking proteins, but the role of cross-linking proteins in the initial steps of structure formation has not been clearly elucidated. We employ an optical trapping assay to investigate the behaviors of two actin cross-linking proteins, fascin and ?-actinin, during the first steps of structure assembly. Here, we show that these proteins have distinct binding characteristics that cause them to recognize and cross-link filaments that are arranged with specific geometries. ?-Actinin is a promiscuous cross-linker, linking filaments over all angles. It retains this flexibility after cross-links are formed, maintaining a connection even when the link is rotated. Conversely, fascin is extremely selective, only cross-linking filaments in a parallel orientation. Surprisingly, bundles formed by either protein are extremely stable, persisting for over 0.5 h in a continuous wash. However, using fluorescence recovery after photobleaching and fluorescence decay experiments, we find that the stable fascin population can be rapidly competed away by free fascin. We present a simple avidity model for this cross-link dissociation behavior. Together, these results place constraints on how cytoskeletal structures assemble, organize, and disassemble in vivo.

Courson, David S.; Rock, Ronald S.

2010-01-01

274

Actin cross-link assembly and disassembly mechanics for alpha-Actinin and fascin.  

PubMed

Self-assembly of complex structures is commonplace in biology but often poorly understood. In the case of the actin cytoskeleton, a great deal is known about the components that include higher order structures, such as lamellar meshes, filopodial bundles, and stress fibers. Each of these cytoskeletal structures contains actin filaments and cross-linking proteins, but the role of cross-linking proteins in the initial steps of structure formation has not been clearly elucidated. We employ an optical trapping assay to investigate the behaviors of two actin cross-linking proteins, fascin and alpha-actinin, during the first steps of structure assembly. Here, we show that these proteins have distinct binding characteristics that cause them to recognize and cross-link filaments that are arranged with specific geometries. alpha-Actinin is a promiscuous cross-linker, linking filaments over all angles. It retains this flexibility after cross-links are formed, maintaining a connection even when the link is rotated. Conversely, fascin is extremely selective, only cross-linking filaments in a parallel orientation. Surprisingly, bundles formed by either protein are extremely stable, persisting for over 0.5 h in a continuous wash. However, using fluorescence recovery after photobleaching and fluorescence decay experiments, we find that the stable fascin population can be rapidly competed away by free fascin. We present a simple avidity model for this cross-link dissociation behavior. Together, these results place constraints on how cytoskeletal structures assemble, organize, and disassemble in vivo. PMID:20551315

Courson, David S; Rock, Ronald S

2010-06-15

275

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

PubMed

Chemical cross-linking, combined with mass spectrometry, has been applied to map three-dimensional protein structures and protein-protein interactions. Proper choice of the cross-linking agent, including its reactive groups and spacer arm length, is of great importance. However, studies to understand the details of reactivity of the chemical cross-linkers with proteins are quite sparse. In this study, we investigated chemical cross-linking from the aspects of the protein structures and the cross-linking reagents involved, by using two structurally well-known proteins, glyceraldehyde 3-phosohate dehydrogenase and ribonuclease S. Chemical cross-linking reactivity was compared using a series of homo- and hetero-bifunctional cross-linkers, including bis(sulfosuccinimidyl) suberate, dissuccinimidyl suberate, bis(succinimidyl) penta (ethylene glycol), bis(succinimidyl) nona (ethylene glycol), m-maleimidobenzoyl-N-hydroxysulfosuccinimide ester, 2-pyridyldithiol-tetraoxaoctatriacontane-N-hydrosuccinimide and succinimidyl-[(N-maleimidopropionamido)-tetracosaethyleneglycol]ester. The protein structure itself, especially the distances between target amino acid residues, was found to be a determining factor for the cross-linking efficiency. Moreover, the reactive groups of the chemical cross-linker also play an important role; a higher cross-linking reaction efficiency was found for maleimides compared to 2-pyrimidyldithiols. The reaction between maleimides and sulfhydryl groups is more favorable than that between N-hydroxysuccinimide esters and amine groups, although cysteine residues are less abundant in proteins compared to lysine residues. PMID:23832936

Chen, Fan; Nielsen, Simone; Zenobi, Renato

2013-07-01

276

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

PubMed

FT-IR analysis was performed for the hydroxyapatite (HAp)/collagen (COL) nanocomposite cross-linked by glutaraldehyde (GA). The amide bands I, II and III from COL matrix, and phosphate and carbonate bands from HAp were identified. The amide B band arising from C-H stretching mode showed a sensitive conformation by the degree of cross-linking. The amide I band showed a complicate conformational change by the degree of cross-linking. The characteristic amide I band at 1685 cm(-1), which is known as an aging parameter in the biological bone, did not show a monotonous tendency by the degree of cross-linking. The relative contents of the organics in the cross-linked HAp/COL nanocomposite were evaluated as an integration ratio between the amide I band at 1600-1700 cm(-1) and PO(4)(3-) band at 900-1200 cm(-1). The increase of the organics content by the cross-linking is enabled by the further organization of Ca(2+) ions of HAp crystals in HAp/COL nanocomposite. The complicate conformational behavior in the amide I, II and III bands seems to be affected by the cross-linking induced directional arrangement of HAp/COL nanocomposite fibrils. PMID:12361620

Chang, Myung Chul; Tanaka, Junzo

2002-12-01

277

Differences between binding of one-chain and two-chain tissue plasminogen activators to non-cross-linked and cross-linked fibrin clots  

SciTech Connect

Interaction of tissue plasminogen activator (t-PA) with fibrin plays a key role in regulation of plasminogen activation and clot dissolution. Previous investigations of t-PA-fibrin interaction, using incorporation of t-PA into polymerizing fibrin clots, have suggested that no significant differences exist in the binding of one-chain or two-chain t-PA to non-cross-linked or cross-linked fibrin. In the present study, binding of 125I-labeled and affinity-purified one-chain and two-chain forms of t-PA to preformed non-cross-linked or cross-linked, sonicated suspension of fibrin was investigated. Interaction of one-chain t-PA with cross-linked fibrin involved a single type of binding site with dissociation constant (kd) of 0.58 mumol/L and a stoichiometry (n) of 1.5. Interaction of one-chain t-PA with non-cross-linked fibrin, however, involved two classes of binding sites with dissociation constants of 0.32 and 1.5 mumol/L and corresponding number of binding sites equal to 0.57 and 2.0, respectively. In contrast to the binding of one-chain t-PA to cross-linked fibrin by a limited number of sites, two-chain t-PA appeared to involve a considerably greater number of sites (minimum six) whose dissociation constant was 3.2 mumol/L. Interaction of two-chain t-PA with non-cross-linked fibrin also showed the presence of many binding sites (minimum seven) with approximate dissociation constant of 6.4 mumol/L, as well as a few (n = 0.012) high-affinity sites with a kd of 0.011 mumol/L epsilon-Aminocaproic acid did not completely reverse the binding of either one-chain t-PA or two-chain t-PA to fibrin. The present findings suggest that the fibrin-binding properties of t-PA undergo considerable changes on proteolytic conversion from one-chain to two-chain t-PA, catalyzed under physiologic conditions by plasmin.

Husain, S.S.; Hasan, A.A.; Budzynski, A.Z. (Temple Univ. School of Medicine, Philadelphia, PA (USA))

1989-08-15

278

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.

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

2010-01-01

279

Cross-linked bioreducible layer-by-layer films for increased cell adhesion and transgene expression.  

PubMed

The effect of cross-linking layer-by-layer (LbL) films consisting of bioreducible poly(2-dimethylaminoethyl methacrylate) (rPDMAEMA) and DNA is examined with regard 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 4 times its original value upon cross-linking. Cross-linking mass is additionally confirmed with a 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, chi, was calculated. Good agreement in the two methods yields a cross-linking density of approximately 0.82 mmol/cm(3). 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) are 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

2010-04-29

280

Interstrand DNA Cross-links Induced by ?,?-Unsaturated Aldehydes Derived from Lipid Peroxidation and Environmental Sources  

PubMed Central

Conspectus Significant levels of the 1,N2-?-hydroxypropano-dG adducts of the ?,?-unsaturated aldehydes acrolein, crotonaldehyde, and 4-hydroxy-2E-nonenal (HNE) have been identified in human DNA, arising from both exogenous and endogenous exposure. They yield interstrand DNA cross-links between guanines in the neighboring C•G and G•C base pairs located in 5?-CpG-3? sequences, as a result of opening of the 1,N2-?-hydroxypropano-dG adducts to form reactive aldehydes that are positioned within the minor groove of duplex DNA. Using a combination of chemical, spectroscopic, and computational methods, we have elucidated the chemistry of cross-link formation in duplex DNA. NMR spectroscopy revealed that, at equilibrium, the acrolein and crotonaldehyde cross-links consist primarily of interstrand carbinolamine linkages between the exocyclic amines of the two guanines located in the neighboring C•G and G•C base pairs located in 5?-CpG-3? sequences, that maintain the Watson–Crick hydrogen bonding of the cross-linked base pairs. The ability of crotonaldehyde and HNE to form interstrand cross-links depends upon their common relative stereochemistry at the C6 position of the 1,N2-?-hydroxypropano-dG adduct. The stereochemistry at this center modulates the orientation of the reactive aldehyde within the minor groove of the double-stranded DNA, either facilitating or hindering the cross-linking reactions; it also affects the stabilities of the resulting diastereoisomeric cross-links. The presence of these cross-links in vivo is anticipated to interfere with DNA replication and transcription, thereby contributing to the etiology of human disease. Reduced derivatives of these cross-links are useful tools for studying their biological processing.

Stone, Michael P.; Cho, Young-Jin; Huang, Hai; Kim, Hye-Young; Kozekov, Ivan D.; Kozekova, Albena; Wang, Hao; Minko, Irina G.; Lloyd, R. Stephen; Harris, Thomas M.; Rizzo, Carmelo J.

2009-01-01

281

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

2013-05-28

282

Catabolism of hyaluronan: involvement of transition metals  

PubMed Central

One of the very complex structures in the vertebrates is the joint. The main component of the joint is the synovial fluid with its high-molar-mass glycosaminoglycan hyaluronan, which turnover is approximately twelve hours. Since the synovial fluid does not contain any hyaluronidases, the fast hyaluronan catabolism is caused primarily by reductive-oxidative processes. Eight transition metals – V23, Mn25, Fe26, Co27, Ni28, Cu29, Zn30, and Mo42 – naturally occurring in living organism are essential for the control of various metabolic and signaling pathways. They are also the key elements in catabolism of hyaluronan in the joint. In this overview, the role of these metals in physiological and pathophysiological catabolism of hyaluronan is described. The participation of these metals in the initiation and propagation of the radical degradation hyaluronan is critically reviewed.

Soltes, Ladislav; Kogan, Grigorij

2009-01-01

283

Catabolism of hyaluronan: involvement of transition metals.  

PubMed

One of the very complex structures in the vertebrates is the joint. The main component of the joint is the synovial fluid with its high-molar-mass glycosaminoglycan hyaluronan, which turnover is approximately twelve hours. Since the synovial fluid does not contain any hyaluronidases, the fast hyaluronan catabolism is caused primarily by reductive-oxidative processes.Eight transition metals - V(23), Mn(25), Fe(26), Co(27), Ni(28), Cu(29), Zn(30), and Mo(42) - naturally occurring in living organism are essential for the control of various metabolic and signaling pathways. They are also the key elements in catabolism of hyaluronan in the joint.In this overview, the role of these metals in physiological and pathophysiological catabolism of hyaluronan is described. The participation of these metals in the initiation and propagation of the radical degradation hyaluronan is critically reviewed. PMID:21217859

Soltés, Ladislav; Kogan, Grigorij

2009-12-28

284

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

285

Release of toluene from micron-sized, monodispersed, cross-linked, hollow polymer particles  

Microsoft Academic Search

The release behavior of toluene from the hollow-inside, micron-sized, monodispersed, cross-linked, polystyrene\\/polydivinylbenzene\\u000a composite particles which had various cross-linking densities and shell thicknesses was examined. The hollow particles were\\u000a produced by seeded polymerization utilizing the dynamic swelling method which we proposed in 1991. In comparison with that\\u000a from hollow-free particles, there was a clear difference. The cross-linking density and shell thickness

M. Okubo; H. Minami; Y. Yamamoto

2001-01-01

286

The Fanconi anemia/BRCA pathway: a coordinator of cross-link repair.  

PubMed

Fanconi anemia (FA) is a rare inherited disease characterized by genomic instability and markedly increased cancer risk. Efforts to elucidate the molecular basis of FA have unearthed a novel DNA damage response pathway, the integrity of which is critical for cellular resistance to DNA cross-linking agents. Despite significant progress in uncovering the molecular events underlying FA, the precise function of this pathway in DNA repair is unknown. This article will review evidence implicating FA proteins in multiple aspects of DNA cross-link repair and propose a model to explain the selectivity of the FA pathway toward DNA cross-linking agents. PMID:16859679

Mirchandani, Kanchan D; D'Andrea, Alan D

2006-06-21

287

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.

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

2012-01-01

288

HcRed, a genetically encoded fluorescent binary cross-linking agent for cross-linking of mitochondrial ATP synthase in Saccharomyces cerevisiae.  

PubMed

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

2012-04-04

289

Probing DNA interstrand cross-link formation by an oxidized abasic site using nonnative nucleotides  

PubMed Central

The C4'-oxidized abasic site (C4-AP) forms two types of interstrand cross-links with the adjacent nucleotides in DNA. Previous experiments revealed that dG does not react with the lesion and that formation of one type of cross-link is catalyzed by the opposing dA. Iso-guanosine•dC and 2-aminopurine•dT base pairs were used to determine why dG does not cross-link with C4-AP despite its well known reactivity with other bis-electrophiles. 7-Deaza-2'-deoxyadenosine was used to probe the role of the nucleotide opposite C4-AP in the catalysis of interstrand cross-link formation.

Sczepanski, Jonathan T.; Hiemstra, Christine N.; Greenberg, Marc M.

2011-01-01

290

Five-year comparative study of highly cross-linked (crossfire) and traditional polyethylene.  

PubMed

The purpose of this study was to compare the linear penetration rates of a highly cross-linked ultra-high-molecular-weight polyethylene to traditional polyethylene. Twenty-seven highly cross-linked components were matched to 27 traditional polyethylene components with respect to age, sex, body mass index, and activity level. Each group was followed up for a mean of approximately 6 years. Linear penetration was measured using Martell's computerized technique (J Bone Joint Surg Am 1997;79:1635). The mean total penetration was 0.283 mm (SD, 0.253) for the highly cross-linked group. The mean total penetration for the traditional polyethylene was 0.696 mm (SD, 0.402). This difference was highly significant (P < or = .001). Our experience demonstrates a 59% reduction in total penetration of highly cross-linked polyethylene when compared with traditional polyethylene at a minimum of 5 years. PMID:18534491

Rajadhyaksha, Amar D; Brotea, Cristian; Cheung, Yeukkei; Kuhn, Courtney; Ramakrishnan, Rama; Zelicof, Steven B

2008-03-04

291

Dynamic Mechanical Properties of Cross-Linked Rubbers. VII. Butyl Rubber Networks.  

National Technical Information Service (NTIS)

The linear viscoelastic properties of seven samples of butyl rubber, cross-linked by sulfur to different extents, have been studied in shear by dynamic and creep measurements. The creep data were converted to the corresponding dynamic viscoelastic functio...

J. F. Sanders J. D. Ferry

1974-01-01

292

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

293

Identification of cyanogen bromide peptides involved in intermolecular cross-linking of bovine type III collagen.  

PubMed Central

Cyanogn bromide peptides derived from bovine type III collagen and containing reducible cross-links were isolated and identified. Two peptides, alpha 1 (III)CB7 and alpha 1 (III)CB9B, from within the helical portion of the molecule were shown to contain the 'amino donor' residues cross-linked to non-helical 'aldehyde donor' residues in the formation of cross-links. This information, in conjunction with previously published data for the order of the cyanogen bromide peptides [Fietzek, Allman, Rauterberg & Wachter (1977) Proc. Natl. Acad. Sci. U.S.A. 74, 84-86], suggests that in type III collagen intermolecular cross-links are located in the end-overlap regions, so as to stabilize a quarter-stagger arrangement of molecules within the fibre in a similar manner to that proposed for type I and type II collagens.

Nicholls, A C; Bailey, A J

1980-01-01

294

Cross-Linking of Polymers from PerfluOrodiamidines and Perfluoromonoamidines.  

National Technical Information Service (NTIS)

The elastomeric dielectric compounds are capable of withstanding the high temperatures encountered in high speed space flights. The fluorocarbonamidine polymers have active groups in the polymer segments which may serve as cross-linking sites, and when cr...

A. D. Delman A. E. Ruff B. B. Simms

1965-01-01

295

Intra-molecular cross-linking of acidic residues for protein structure studies.  

SciTech Connect

Intra-molecular cross-linking has been suggested as a method of obtaining distance constraints that would be useful in developing structural models of proteins. Recent work published on intra-molecular cross-linking for protein structural studies has employed commercially available primary amine selective reagents that can cross-link lysine residues to other lysine residues or the amino terminus. Previous work using these cross-linkers has shown that for several proteins of known structure, the number of cross-links that can be obtained experimentally may be small compared to what would be expected from the known structure, due to the relative reactivity, distribution, and solvent accessibility of the lysines in the protein sequence. To overcome these limitations we have investigated the use of cross-linking reagents that can react with other reactive sidechains in proteins. We used 1-Ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) to activate the carboxylic acid containing residues, aspartic acid (D), glutamic acid (E), and the carboxy terminus (O), for cross-linking reactions. Once activated, the DEO sidechains can react to form 'zero-length' cross-links with nearby primary amine containing resides, lysines (K) and the amino terminus (X), via the formation of a new amide bond. We also show that the EDC-activated DEO sidechains can be cross-linked to each other using dihydrazides, two hydrazide moieties connected by an alkyl cross-linker ann of variable length. Using these reagents, we have found three new 'zero-length' cross-links in ubiquitin consistent with its known structure (M1-E16, M1-E18, and K63-E64). Using the dihydrazide cross-linkers, we have identified 2 new cross-links (D21-D32 and E24-D32) unambiguously. Using a library of dihydrazide cross-linkers with varying arm length, we have shown that there is a minimum arm length required for the DEO-DEO cross-links of 5.8 angstroms. These results show that additional structural information can be obtained by exploiting new cross-linker chemistry, increasing the probability that the protein target of choice will yield sufficient distance constraints to develop a structural model.

Kruppa, Gary Hermann; Young, Malin M.; Novak, Petr; Schoeniger, Joseph S.

2005-03-01

296

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

297

Improved cross-linked enzyme aggregates for the production of desacetyl ?-lactam antibiotics intermediates  

Microsoft Academic Search

Cross-linked enzyme aggregates (CLEAs) are reported for the first time for a recombinant acetyl xylan esterase (AXE) from Bacillus pumilus. With this enzyme, CLEAs production was most effective using 3.2M (80%-saturation) ammonium sulfate, followed by cross-linking for 3h with 1% (v\\/v) glutaraldehyde. Particle size was a key determinant of the CLEAs activity. The usual method for generating particles, by short-time

Silvia Montoro-García; Fernando Gil-Ortiz; José Navarro-Fernández; Vicente Rubio; Francisco García-Carmona; Álvaro Sánchez-Ferrer

2010-01-01

298

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

Microsoft Academic Search

FT-IR analysis was performed for the hydroxyapatite (HAp)\\/collagen (COL) nanocomposite cross-linked by glutaraldehyde (GA). The amide bands I, II and III from COL matrix, and phosphate and carbonate bands from HAp were identified. The amide B band arising from C–H stretching mode showed a sensitive conformation by the degree of cross-linking. The amide I band showed a complicate conformational change

Myung Chul Chang; Junzo Tanaka

2002-01-01

299

Mechanical Properties of Retrieved Highly Cross-Linked Crossfire Liners After Short-Term Implantation  

Microsoft Academic Search

This study reports on detailed analyses of retrieved, annealed cross-linked liners. Twelve cross-linked liners (Crossfire, Stryker Orthopaedics, Mahwah, NJ) of the same Omnifit design were retrieved at revision surgery by one institution after an average 1.9 years (0.02-4.8 years) in vivo. In each case, the revision surgery was performed for reasons unrelated to wear. The mechanical properties and extent of

Steven M. Kurtz; William Hozack; Joseph Turner; James Purtill; Daniel MacDonald; Peter Sharkey; Javad Parvizi; Michael Manley; Richard Rothman

2005-01-01

300

Five-Year Comparative Study of Highly Cross-Linked (Crossfire) and Traditional Polyethylene  

Microsoft Academic Search

The purpose of this study was to compare the linear penetration rates of a highly cross-linked ultra–high-molecular-weight polyethylene to traditional polyethylene. Twenty-seven highly cross-linked components were matched to 27 traditional polyethylene components with respect to age, sex, body mass index, and activity level. Each group was followed up for a mean of approximately 6 years. Linear penetration was measured using

Amar D. Rajadhyaksha; Cristian Brotea; Yeukkei Cheung; Courtney Kuhn; Rama Ramakrishnan; Steven B. Zelicof

2009-01-01

301

Adsorption of anionic dyes in acid solutions using chemically cross-linked chitosan beads  

Microsoft Academic Search

One kind of adsorbents with high adsorption capacity of anionic dyes was prepared using ionically and chemically cross-linked chitosan beads. A batch system was applied to study the adsorption of four reactive dyes (RB2, RR2, RY2, RY86), three acid dyes (AO12, AR14, AO7) and one direct dye (DR81) from aqueous solutions by the cross-linked chitosan beads. The adsorption capacities had

Ming-Shen Chiou; Pang-Yen Ho; Hsing-Ya Li

2004-01-01

302

Double clathrate hydrates of cross-linked tetrabutylammonium polyacrylate and noble gases at high pressures  

Microsoft Academic Search

Temperatures of hydrate decomposition were measured by means of the differential thermal analysis at a pressures up to 800–900 Mpa\\u000a in the systems: cross-linked tetrabutylammonium polyacrylate–water and cross-linked tetrabutylammonium polyacrylate–water–noble\\u000a gas (He, Ne, Ar, Kr, Xe). The effect of the deformation of D- cavities of the hydrates on the temperature of their decomposition is discussed on the basis of the experimental

E. Ya. Aladko; E. G. Larionov; A. Yu. Manakov; I. S. Terekhova

2010-01-01

303

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

304

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

NASA Astrophysics Data System (ADS)

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

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

2011-07-01

305

Uranyl ion adsorption using novel cross-linked maleic anhydride–allyl propionate–styrene terpolymer  

Microsoft Academic Search

Maleic anhydride–allyl propionate–styren? terpolymer has been modified with tri-ethanolamine in order to prepare a new cross-linked functional polymer sorbent. The sorption behaviors of UO22+ ions on the optimum sorption conditions were determined. The synthesized cross-linked polymer has a network structure that contains carboxylic acid, carbonyl, hydroxyl, amine and ester groups; all of which are capable of interacting with metal ions.

E. O. Akperov; A. M. Maharramov; O. G. Akperov

2009-01-01

306

Synthesis of cross-linked magnetic composite microspheres containing carboxyl groups  

Microsoft Academic Search

Fe3O4 magnetic nano-particles were prepared by a co-precipitation method and were modified using oleic acid. Then, the cross-linked\\u000a magnetic compsoite microspheres containing a carboxyl group were prepared by using an improved emulsion polymerization with\\u000a divinylbenzene (DVB) as the cross-linking agent. The composite microspheres comprised the Fe3O4 magnetic nano-particles as cores and the copolymer of styrene and acrylic acid as shells.

Jili Zhao; Zhaorang Han; Qiang Song; Ying Wang; Dan Sun

2008-01-01

307

Edible films produced with gelatin and casein cross-linked with transglutaminase  

Microsoft Academic Search

In this study, transglutaminase was used to produce cross-linked casein, gelatin and casein–gelatin blend (100:0, 75:25, 50:50, 25:75 and 0:100) edible films. Cross-linking was investigated by SDS–PAGE. Mechanical and water vapor barrier properties of the films were characterized using ASTM procedures, and the film morphology was evaluated using scanning electron microscopy. The casein–gelatin film showed significant greater elongation values (P<0.05)

Hulda Chambi; Carlos Grosso

2006-01-01

308

Removal of hexavalent chromium using a novel cross linked xanthated chitosan  

Microsoft Academic Search

Suitability of a novel cross linked, chemically modified chitosan as highly efficient adsorbent for the recovery of toxic chromium(VI) was studied. After cross linking with glutaraldehyde, xanthate group was grafted onto the back bone of chitosan. Sorption was found to be both pH and concentration dependent, with pH 3 being the optimum value. Both, chemically modified beads (CMCB) and flakes

Nalini Sankararamakrishnan; Awantika Dixit; Leela Iyengar; Rashmi Sanghi

2006-01-01

309

Cross-linking of Phospholipid Membranes is a Conserved Property of Calcium-sensitive Synaptotagmins  

Microsoft Academic Search

Synaptotagmins are vesicular proteins implicated in many membrane trafficking events. They are highly conserved in evolution and the mammalian family contains 16 isoforms. We now show that the tandem C2 domains of several calcium-sensitive synaptotagmin isoforms tested, including Drosophila synaptotagmin, rapidly cross-link phospholipid membranes. In contrast to the tandem structure, individual C2 domains failed to trigger membrane cross-linking in several

Emma Connell; Asiya Giniatullina; Joséphine Lai-Kee-Him; Richard Tavare; Enrico Ferrari; Alan Roseman; Dan Cojoc; Alain R. Brisson; Bazbek Davletov

2008-01-01

310

Bio-inspired high-performance and recyclable cross-linked polymers.  

PubMed

Bio-inspired molecular design and synthesis of high-performance and recyclable cross-linked polymers is reported. Reversible cross-links between hard segments are incorporated into linear segmented polyurethane via Diels-Alder reaction between maleimide pendant group and furan cross-linker. The materials form hierarchical structure and exhibit excellent properties with high stiffness, strength and toughness, and can be easily thermally reshaped and re-mended. PMID:23861235

Yu, Shen; Zhang, Rongchun; Wu, Qiang; Chen, Tiehong; Sun, Pingchuan

2013-07-17

311

Synthesis and sorption ability of telogenated hyper-cross-linked polydivinylbenzene networks  

Microsoft Academic Search

Synthesis and properties of hyper-cross-linked polymer networks prepared by radical polymerization of commercial divinylbenzene\\u000a in oxylene, a good solvent and a powerful telogen, are reported. The permeability of hyper-cross-linked networks is evaluated\\u000a by adsorption of bioactive molecules significantly differing in size. High sorption capacity for Cephalosporin C makes the\\u000a polymers prepared promising for pharmacology and biotechnology.

L. A. Pavlova; M. P. Tsyurupa; M. A. Papkov; V. A. Davankov

2010-01-01

312

Proteins of rough microsomal membranes related to ribosome binding. II. Cross-linking of bound ribosomes to specific membrane proteins exposed at the binding sites  

PubMed Central

Two proteins (ribophorins I and II), which are integral components of rough microsomal membranes and appear to be related to the bound ribosomes, were shown to be exposed on the surface of rat liver rough microsomes (RM) and to be in close proximity to the bound ribosomes. Both proteins were labeled when intact RM were incubated with a lactoperoxidase iodinating system, but only ribophorin I was digested during mild trypsinization of intact RM. Ribophorin II (63,000 daltons) was only proteolyzed when the luminal face of the microsomal vesicles was made accessible to trypsin by the addition of sublytical detergent concentrations. Only 30--40% of the bound ribosomes were released during trypsinization on intact RM, but ribosome release was almost complete in the presence of low detergent concentrations. Very low glutaraldehyde concentrations (0.005--0.02%) led to the preferential cross-linking of large ribosomal subunits of bound ribosomes to the microsomal membranes. This cross-linking prevented the release of subunits caused by puromycin in media of high ionic strength, but not the incorporation of [3H]puromycin into nascent polypeptide chains. SDS- acrylamide gel electrophoresis of cross-linked samples a preferential reduction in the intensity of the bands representing the ribophorins and the formation of aggregates which did not penetrate into the gels. At low methyl-4-mercaptobutyrimidate (MMB) concentrations (0.26 mg/ml) only 30% of the ribosomes were cross-linked to the microsomal membranes, as shown by the puromycin-KCl test, but membranes could still be solubilized with 1% DOC. This allowed the isolation of the ribophorins together with the sedimentable ribosomes, as was shown by electrophoresis of the sediments after disruption of the cross-links by reduction. Experiments with RM which contained only inactive ribosomes showed that the presence of nascent chains was not necessary for the reversible cross-linking of ribosomes to the membranes. These observations suggest that ribophorins are in close proximity to the bound ribosomes, as may be expected from components of the ribosome- binding sites.

1978-01-01

313

Tradeoffs amongst fatigue, wear, and oxidation resistance of cross-linked ultra-high molecular weight polyethylene  

Microsoft Academic Search

This study evaluated the tradeoffs amongst fatigue crack propagation resistance, wear resistance, and oxidative stability in a wide variety of clinically-relevant cross-linked ultra-high molecular weight polyethylene. Highly cross-linked re-melted materials showed good oxidation and wear performance, but diminished fatigue crack propagation resistance. Highly cross-linked annealed materials showed good wear and fatigue performance, but poor oxidation resistance. Moderately cross-linked re-melted materials

Sara A. Atwood; Douglas W. Van Citters; Eli W. Patten; Jevan Furmanski; Michael D. Ries; Lisa A. Pruitt

2011-01-01

314

Does chemical cross-linking with NHS esters reflect the chemical equilibrium of protein-protein noncovalent interactions in solution?  

Microsoft Academic Search

Chemical cross-linking in combination with mass spectrometry has emerged as a powerful tool to study noncovalent protein complexes.\\u000a Nevertheless, there are still many questions to answer. Does the amount of detected cross-linked complex correlate with the\\u000a amount of protein complex in solution? In which concentration and affinity range is specific cross-linking possible? To answer\\u000a these questions, we performed systematic cross-linking

Stefanie Mädler; Markus Seitz; John Robinson; Renato Zenobi

2010-01-01

315

Effect of nucleosome structure on DNA interstrand cross-linking reactions.  

PubMed

Antitumor agents of the nitrogen mustard family and mitomycin C form interstrand cross-links in duplex DNA. To provide information about the cellular mechanism by which these compounds exert their cytotoxic effects, we examined cross-linking of a nucleosomal core particle formed on a fragment of the 5S RNA gene of Xenopus borealis. For the mustards mechlorethamine, chlorambucil, and melphalan, both sites of monoalkylation and interstrand cross-linking were similar in nucleosomal and free DNA. Some small (two- to three- fold) differences in intensity of cross-linking at some sites were apparent. However, these differences did not appear to correlate with rotational or translational positioning. For mitomycin C, cross-linking was inhibited five- to ten-fold at the nucleosomal dyad and showed attenuation of inhibition toward the ends. Furthermore, rotational positioning also appeared to be a factor, with sites facing inward in the nucleosome less accessible for mitomycin cross-linking. None of these agents demonstrated the 10-base pair periodicity exhibited by hydroxyl radical cleavage of nucleosomal DNA. PMID:9548752

Millard, J T; Spencer, R J; Hopkins, P B

1998-04-14

316

Neurofilaments are the major neuronal target of hydroxynonenal-mediated protein cross-links.  

PubMed

Lipid peroxidation generates reactive aldehydes, most notably hydroxynonenal (HNE), which covalently binds amino acid residue side chains leading to protein inactivation and insolubility. Specific adducts of lipid peroxidation have been demonstrated to be intimately associated with pathological lesions of Alzheimer's disease (AD), suggesting that oxidative stress is a major component in the disease. Here, we examined the HNE-cross-linking modifications by using an antibody specific for a lysine-lysine cross-link. Since in a prior study we noted no immunolabeling of neuritic plaques or neurofibrillary tangles but instead found strong labeling of axons, we focused this study on axons. Axonal labeling was examined in mouse sciatic nerve, and immunoblotting showed the cross-link was restricted to neurofilament heavy and medium subunits, which while altering migration, did not indicate larger NF aggregates, indicative of intermolecular cross-links. Examination of mice at various ages showed the extent of modification remaining relatively constant through the life span. These findings demonstrate lipid-cross-linking peroxidation primarily involves lysine-rich neurofilaments and is restricted to intramolecular cross-links. PMID:23566300

Perry, E A; Castellani, R J; Moreira, P I; Nunomura, A; Lui, Q; Harris, P L R; Sayre, L M; Szweda, P A; Szweda, L I; Zhu, X; Smith, M A; Perry, G

2013-05-10

317

Dimethyl suberimidate cross-linked pericardium tissue: Raman spectroscopic and atomic force microscopy investigations  

NASA Astrophysics Data System (ADS)

Chemically stabilized pericardium tissue is widely used as a tissue-derived biomaterial for the preparation of bioprostheses such as heart valves or vascular grafts. The bifunctional imidoester dimethyl suberimidate (DMS) belongs to the wide class of the cross-linking reagents and is often used to cross-link a variety of proteins, including collagen matrices and collagen-based tissues. Raman spectroscopy in the wide frequency range 200 4000 cm-1 and contact mode atomic force microscopy (AFM) have been employed to investigate the structural changes and chemical bonds in DMS cross-linked porcine pericardium tissue. It has been found, that in addition to the commonly accepted reaction with the ?-amine groups of lysine or hydroxylysine residues, DMS may interact also with the carbonyl CO and amide NH groups of the peptide bond in collagen. Our paper presents for the first time spectral evidence for the peptide contribution to the formation of DMS collagen cross-links. The results confirm also possible competition between the hydrolysis of the free imidoester group and cross-linking reaction. Products of the partial alkaline hydrolysis of DMS have been found in the spectra. The observed changes in the surface topography of the fibrils as well as in their spatial organization in the tissue support the formation of both intra- and interfibrillar cross-links in DMS-stabilized tissue.

Jastrzebska, Maria; Zalewska-Rejdak, Justyna; Wrzalik, Roman; Kocot, Antoni; Barwi?ski, Bogdan; Mróz, Iwona; Cwalina, Beata

2005-06-01

318

Rapid cross-linking of elastin-like polypeptides with (hydroxymethyl)phosphines in aqueous solution.  

PubMed

In situ gelation of injectable polypeptide-based materials is attractive for minimally invasive in vivo implantation of biomaterials and tissue engineering scaffolds. We demonstrate that chemically cross-linked elastin-like polypeptide (ELP) hydrogels can be rapidly formed in aqueous solution by reacting lysine-containing ELPs with an organophosphorous cross-linker, beta-[tris(hydroxymethyl)phosphino]propionic acid (THPP) under physiological conditions. The mechanical properties of the cross-linked ELP hydrogels were largely modulated by the molar concentration of lysine residues in the ELP and the pH at which the cross-linking reaction was carried out. Fibroblasts embedded in ELP hydrogels survived the cross-linking process and were viable after in vitro culture for 3 days. DNA quantification of ELP hydrogels with encapsulated fibroblasts indicated that there was no significant difference in DNA content between day 0 and day 3 when ELP hydrogels were formed with an equimolar ratio of THPP and lysine residues of the ELPs. These results suggest that THPP cross-linking may be a biocompatible strategy for the in situ formation of cross-linked hydrogels. PMID:17411091

Lim, Dong Woo; Nettles, Dana L; Setton, Lori A; Chilkoti, Ashutosh

2007-04-06

319

Interstrand Cross-Links Induce DNA Synthesis in Damaged and Undamaged Plasmids in Mammalian Cell Extracts  

PubMed Central

Mammalian cell extracts have been shown to carry out damage-specific DNA repair synthesis induced by a variety of lesions, including those created by UV and cisplatin. Here, we show that a single psoralen interstrand cross-link induces DNA synthesis in both the damaged plasmid and a second homologous unmodified plasmid coincubated in the extract. The presence of the second plasmid strongly stimulates repair synthesis in the cross-linked plasmid. Heterologous DNAs also stimulate repair synthesis to variable extents. Psoralen monoadducts and double-strand breaks do not induce repair synthesis in the unmodified plasmid, indicating that such incorporation is specific to interstrand cross-links. This induced repair synthesis is consistent with previous evidence indicating a recombinational mode of repair for interstrand cross-links. DNA synthesis is compromised in extracts from mutants (deficient in ERCC1, XPF, XRCC2, and XRCC3) which are all sensitive to DNA cross-linking agents but is normal in extracts from mutants (XP-A, XP-C, and XP-G) which are much less sensitive. Extracts from Fanconi anemia cells exhibit an intermediate to wild-type level of activity dependent upon the complementation group. The DNA synthesis deficit in ERCC1- and XPF-deficient extracts is restored by addition of purified ERCC1-XPF heterodimer. This system provides a biochemical assay for investigating mechanisms of interstrand cross-link repair and should also facilitate the identification and functional characterization of cellular proteins involved in repair of these lesions.

Li, Lei; Peterson, Carolyn A.; Lu, Xiaoyan; Wei, Ping; Legerski, Randy J.

1999-01-01

320

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

PubMed Central

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

2011-01-01

321

Chemical synthesis of cross-linked poly(KGGVG), an elastin-like biopolymer.  

PubMed

Previous studies afforded on peptides and polypeptides containing repetitive sequences of elastin have largely demonstrated that their molecular and supramolecular properties are fully representative of those of tropoelastin, the soluble, linear precursor of elastin itself. In the attempt to synthesize cross-linked elastin-mimetic polypeptides, the repeating sequence VGGVG (V: valine; G: glycine), typical of elastin, was modified to incorporate lysine residues, yielding the polymer poly(KGGVG) (K: lysine). This imparts primary amine functionality susceptible to cross-linking reaction with appropriate bifunctional cross-linking reagents. We report herein the chemical synthesis and cross-linking of poly(KGGVG) with glutaraldehyde (GTA) and with disuccinimidyl glutarate (DSG). In both cases, the characterization of the polymers, both linear and cross-linked, has been carried out by CD spectroscopy and transmission electron microscopy measurements. The obtained results, although not conclusive, demonstrate that poly(KGGVG), both linear and cross-linked, may be considered very similar to tropoelastin and mature elastin, as concerns its molecular and supramolecular properties. PMID:11343278

Martino, M; Tamburro, A M

2001-07-01

322

Cross-linking of DNA through HMGA1 suggests a DNA scaffold  

PubMed Central

Binding of proteins to DNA is usually considered 1D with one protein bound to one DNA molecule. In principle, proteins with multiple DNA binding domains could also bind to and thereby cross-link different DNA molecules. We have investigated this possibility using high-mobility group A1 (HMGA1) proteins, which are architectural elements of chromatin and are involved in the regulation of multiple DNA-dependent processes. Using direct stochastic optical reconstruction microscopy (dSTORM), we could show that overexpression of HMGA1a-eGFP in Cos-7 cells leads to chromatin aggregation. To investigate if HMGA1a is directly responsible for this chromatin compaction we developed a DNA cross-linking assay. We were able to show for the first time that HMGA1a can cross-link DNA directly. Detailed analysis using point mutated proteins revealed a novel DNA cross-linking domain. Electron microscopy indicates that HMGA1 proteins are able to create DNA loops and supercoils in linearized DNA confirming the cross-linking ability of HMGA1a. This capacity has profound implications for the spatial organization of DNA in the cell nucleus and suggests cross-linking activities for additional nuclear proteins.

Vogel, Benjamin; Loschberger, Anna; Sauer, Markus; Hock, Robert

2011-01-01

323

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

PubMed

The main goal of this study was to evaluate the potential of collagen meshes derived from porcine dermis as scaffolds for repairing pelvic organ prolapses. Mechanical properties of collagen meshes with different cross-linking percentages before and after Adipose Derived Stromal Cells (ADSC) seeding were studied as well as the cell-scaffold interaction. Uniaxial tensile tests of the collagen meshes with three different cross-linking percentages (full-, partial-, and noncross-linked) were carried out along orthogonal directions. Their mechanical properties were studied with the same tests before and after seeding with human derived adipose stem cells (ADSC) after 1 and 7 days. Histological analyses were performed to determine adhesion and proliferation of ADSC. Significant differences in mechanical properties of the unseeded meshes were observed between each orthogonal direction independently of the cross-linking percentage. A better cell adhesion rate was observed in the cross-linked meshes. An increase in the mechanical properties after cell seeding was observed with a direct relation with the degree of cross-linking. All meshes analyzed showed a marked anisotropy that should be taken into account during the surgical procedure. The cross-linking treatment increased cell adhesion and the mechanical properties of the collagen meshes after seeding. These results suggest that the mechanical properties of this type of collagen mesh could be useful as scaffolds for repair of pelvic organ prolapse. PMID:21171153

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

2010-11-29

324

T3 affects expression of collagen I and collagen cross-linking in bone cell cultures  

PubMed Central

Thyroid hormones (T3, T4) have a broad range of effects on bone, however, its role in determining the quality of bone matrix is poorly understood. In-vitro, the immortalized mouse osteoblast-like cell line MC3T3-E1 forms a tissue like structure, consisting of several cell layers, whose formation is affected by T3 significantly. In this culture system, we investigated the effects of T3 on cell multiplication, collagen synthesis, expression of genes related to the collagen cross-linking process and on the formation of cross-links. T3 compared to controls modulated cell multiplication, up-regulated collagen synthesis time and dose dependently, and stimulated protein synthesis. T3 increased mRNA expressions of procollagen-lysine-1,2-oxoglutarate 5-dioxygenase 2 (Plod2) and of lysyloxidase (Lox), both genes involved in post-translational modification of collagen. Moreover, it stimulated mRNA expression of bone morphogenetic protein 1 (Bmp1), the processing enzyme of the lysyloxidase-precursor and of procollagen. An increase in the collagen cross-link-ratio Pyr/deDHLNL indicates, that T3 modulated cross-link maturation in the MC3T3-E1 culture system. These results demonstrate that T3 directly regulates collagen synthesis and collagen cross-linking by up-regulating gene expression of the specific cross-link related enzymes, and underlines the importance of a well-balanced concentration of thyroid hormones for maintenance of bone quality.

Varga, F.; Rumpler, M.; Zoehrer, R.; Turecek, C.; Spitzer, S.; Thaler, R.; Paschalis, E.P.; Klaushofer, K.

2010-01-01

325

[Characterization of cross-linked quaternary chitosan salt and its adsorption of perchlorate from water].  

PubMed

Cross-linked quaternary chitosan salt was prepared and used to adsorb perchlorate from water. Parameters of cross-linking agent, temperature and pH were investigated to optimize the reaction conditions. The adsorption and regeneration ability of the adsorbent were also conducted. Quaternary chitosan salt could be fixed by cross-linking with glutaraldehyde using ethanol as dispersant. The optimal glutaraldehyde dosage and temperature were 6.82% and 45 degrees C, respectively. The cross-linked reaction was independent of pH with the range from 3 to 12. Quaternary chitosan salt was cross-linked mainly through the reaction between the methyl groups of ammonium on quaternary chitosan salt and the -C=O groups on glutaraldehyde. The optimal pH(zpc) of the adsorbent was about 10.6. The adsorbent showed high efficiency for perchlorate removal, and the adsorption capacity varied from 12.321 mg/g to 117.819 mg/g with the ClO4(-) concentration range from 5 mg/L to 200 mg/L. The spent adsorbents could be effectively regenerated by NaCl brine with the concentration more than 0.3%. The results suggest that the cross-linked chitosan quaternary ammonium salt would be a promising method for perchlorate removal from water. PMID:22165217

Xie, Yan-Hua; Li, Shi-Yu; Liu, Guang-Li

2011-09-01

326

SiRNA delivery systems based on neutral cross-linked dendrimers.  

PubMed

A neutral cross-linked dendritic system is described for use of delivering small interfering RNA (siRNA) for targeted gene silencing. By replacing the terminal amines with hydrazide groups and N-acetylgalactosamine (GalNAc) ligands, cationic polyamidoamine (PAMAM) dendrimers were transformed into neutral glycosylated carriers for siRNA delivery. Mainly owing to the pH sensitivity and the proton-absorption capability of the tertiary amines within the interior branches, these PAMAM derivatives showing neutrality under physiological conditions (pH 7.4) formed complexes with siRNA through electrostatic interactions at pH 5. Cross-linking procedures via reactions with glutaraldehyde were established, and cytocompatible cross-linked systems loaded with siRNA obtained, with the particulate properties variable with the cross-linking condition and the GalNAc level in the dendritic carrier. In vitro cellular uptake and RNAi experiments showed that the cross-linked dendritic systems with an appropriate level of GalNAc composition effectively interacted with HepG2 cells and inhibited the expression of a luciferase reporter gene. Neutral cross-linked dendritic systems provide a new paradigm for designing siRNA delivery systems with biocompatibility and targeting capability. PMID:22292572

Liu, Jie; Zhou, Jihan; Luo, Ying

2012-01-31

327

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

PubMed

We investigated the hypothesis that exogenous collagen cross-linking can augment intact regions of tendon to mitigate mechanical propagation of partial tears. We first screened the low toxicity collagen cross-linkers genipin, methylglyoxal and ultra-violet (UV) light for their ability to augment tendon stiffness and failure load in rat tail tendon fascicles (RTTF). We then investigated cross-linking effects in load bearing equine superficial digital flexor tendons (SDFT). Data indicated that all three cross-linking agents augmented RTTF mechanical properties but reduced native viscoelasticity. In contrast to effects observed in fascicles, methylglyoxal treatment of SDFT detrimentally affected tendon mechanical integrity, and in the case of UV did not alter tendon mechanics. As in the RTTF experiments, genipin cross-linking of SDFT resulted in increased stiffness, higher failure loads and reduced viscoelasticity. Based on this result we assessed the efficacy of genipin in arresting tendon tear propagation in cyclic loading to failure. Genipin cross-linking secondary to a mid-substance biopsy-punch significantly reduced tissue strains, increased elastic modulus and increased resistance to fatigue failure. We conclude that genipin cross-linking of injured tendons holds potential for arresting tendon tear progression, and that implications of the treatment on matrix remodeling in living tendons should now be investigated. PMID:22102295

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

2011-11-18

328

Hyaluronan: from biomimetic to industrial business strategy.  

PubMed

Hyaluronan (hyaluronic acid) is a naturally occurring polysaccharide of a linear repeating disaccharide unit consisting of beta-(1-->4)-linked D-glucopyranuronic acid and beta-(1-->3)-linked 2-acetamido-2-deoxy-D-glucopyranose, which is present in extracellular matrices, the synovial fluid of joints, and scaffolding that comprises cartilage. In its mechanism of synthesis, its size, and its physico-chemical properties, hyaluronan is unique amongst other glycosaminoglycans. The network-forming, viscoelastic and its charge characteristics are important to many biochemical properties of living tissues. It is an important pericellular and cell surface constituent; its interaction with other macromolecules such as proteins, participates in regulating cell behavior during numerous morphogenic, restorative, and pathological processes in the body. The knowledge of HA in diseases such as various forms of cancers, arthritis and osteoporosis has led to new impetus in research and development in the preparation of biomaterials for surgical implants and drug conjugates for targeted delivery. A concise and focused review on hyaluronan is timely. This review will cover the following important aspects of hyaluronan: (i) biological functions and synthesis in nature; (ii) current industrial production and potential biosynthetic processes of hyaluronan; (iii) chemical modifications of hyaluronan leading to products of commercial significance; and (iv) and the global market position and manufacturers of hyaluronan. PMID:21560767

Murano, Erminio; Perin, Danilo; Khan, Riaz; Bergamin, Massimo

2011-04-01

329

A comparative study of the characteristics of cross-linked, oxidized and dual-modified rice starches.  

PubMed

Rice starch was cross-linked with epichlorohydrin (0.3%, w/w, on a dry starch basis) and oxidized with sodium hypochlorite (2.5% w/w), respectively. Two dual-modified rice starch samples (oxidized cross-linked rice starch and cross-linked oxidized rice starch) were obtained by the oxidation of cross-linked rice starch and the cross-linking of oxidized rice starch at the same level of reagents. The physicochemical properties of native rice starch, cross-linked rice starch and oxidized rice starch were also studied parallel with those of the two dual-modified rice starch samples using rapid visco analysis (RVA), differential scanning calorimetry (DSC), dynamic rheometry and scanning electron microscopy (SEM). It was found that the levels of cross-linking and oxidation used in this study did not cause any significant changes in the morphology of rice starch granules. Cross-linked oxidized starch showed lower swelling power (SP) and solubility, and higher paste clarity in comparison with native starch. Cross-linked oxidized rice starch also had the lowest tendency of retrogradation and highest ability to resistant to shear compared with native, cross-linked, oxidized and oxidized cross-linked rice starches. These results suggest that the undesirable properties in native, cross-linked and oxidized rice starch samples could be overcome through dual-modification. PMID:22971580

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

2012-09-12

330

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

331

Domain motions of hyaluronan lyase underlying processive hyaluronan translocation.  

PubMed

Hyaluronan lyase (Hyal) is a surface enzyme occurring in many bacterial organisms including members of Streptococcus species. Streptococcal Hyal primarily degrades hyaluronan-substrate (HA) of the extracellular matrix. This degradation appears to facilitate the spread of this bacterium throughout host tissues. Unlike purely endolytic degradation of its other substrates, unsulfated chondroitin or some chondroitin sulfates, the degradation of HA by Hyal proceeds by processive exolytic cleavage of one disaccharide at a time following an initial endolytic cut. Molecular dynamics (MD) studies of Hyal from Streptococcus pneumoniae are presented that address the enzyme's molecular mechanism of action and the role of domain motions for processive functionality. The analysis of extensive sub-microsecond MD simulations of this enzyme action on HA-substrates of different lengths and the connection between the domain dynamics of Hyal and the translocation of the HA-substrate reveals that opening/closing and twisting domain motions of the Hyal are intimately linked to processive HA degradation. Enforced simulations confirmed this finding as the domain motions in SpnHyal were found to be induced by enforced substrate translocation. These results establish the dynamic interplay between Hyal flexibility and substrate translocation and provide insight into the processive mechanism of Hyal. PMID:19089975

Joshi, Harshad V; Jedrzejas, Mark J; de Groot, Bert L

2009-07-01

332

Antisense inhibition of hyaluronan synthase-2 in human osteosarcoma cells inhibits hyaluronan retention and tumorigenicity  

SciTech Connect

Osteosarcoma is a common malignant bone tumor associated with childhood and adolescence. The results of numerous studies have suggested that hyaluronan plays an important role in regulating the aggressive behavior of various types of cancer cells. However, no studies have addressed hyaluronan with respect to osteosarcomas. In this investigation, the mRNA expression copy number of three mammalian hyaluronan synthases (HAS) was determined using competitive RT-PCR in the osteoblastic osteosarcoma cell line, MG-63. MG-63 are highly malignant osteosarcoma cells with an abundant hyaluronan-rich matrix. The results demonstrated that HAS-2 is the predominant HAS in MG-63. Accumulation of intracellular hyaluronan increased in association with the proliferative phase of these cells. The selective inhibition of HAS-2 mRNA in MG-63 cells by antisense phosphorothioate oligonucleotides resulted in reduced hyaluronan accumulation by these cells. As expected, the reduction in hyaluronan disrupted the assembly of cell-associated matrices. However, of most interest, coincident with the reduction in hyaluronan, there was a substantial decrease in cell proliferation, a decrease in cell motility and a decrease in cell invasiveness. These data suggest that hyaluronan synthesized by HAS-2 in MG-63 plays a crucial role in osteosarcoma cell proliferation, motility, and invasion.

Nishida, Yoshihiro [Department of Orthopaedic Surgery, Nagoya University School of Medicine, 65 Tsurumai, Showa-ku, Nagoya 466-8550 (Japan)]. E-mail: ynishida@med.nagoya-u.ac.jp; Knudson, Warren [Department of Biochemistry, Rush Medical College, Rush University Medical Center, 1653 W. Congress Parkway, Chicago, IL 60612 (United States); Knudson, Cheryl B. [Department of Biochemistry, Rush Medical College, Rush University Medical Center, 1653 W. Congress Parkway, Chicago, IL 60612 (United States); Ishiguro, Naoki [Department of Orthopaedic Surgery, Nagoya University School of Medicine, 65 Tsurumai, Showa-ku, Nagoya 466-8550 (Japan)

2005-07-01

333

Cyclodextrin-cross-linked diaminotriazine-based hydrogen bonding strengthened hydrogels for drug and reverse gene delivery.  

PubMed

A hydrogen bonding strengthened hydrogel was prepared by radical copolymerization of poly(ethylene glycol) methacrylated ?-cyclodextrin (PEG-?-CD) and 2-vinyl-4,6-diamino-1,3,5-triazine (VDT) monomer. PEG-?-CD served not only as a cross-linker, but also as a built-in solubilizing agent of the hydrophobic drug in the gel. Increasing VDT content resulted in a notable enhancement in the mechanical strengths of hydrogels whose equilibrium water contents could be modulated from 75% to 85% by varying the ratio of PEG-?-CD cross-linker. It was shown that copolymerizing more PEG-?-CDs could load higher amount of ibuprofen (IBU) in the gels and contribute to a slower release rate of IBU. Plasmid DNA could be anchored onto the surface of hydrogels due to the hydrogen bonding between the base pairs and diaminotriazine, thereby mediating efficient reverse gene transfection of luciferase gene in COS-7 cells cultured on the gel surface. The cytocompatible PEG-?-CD-cross-linked PVDT hydrogels with multifunction of drug and gene delivery hold a potential as tissue engineering scaffold. PMID:23862694

Hu, Xiufeng; Wang, Ning; Liu, Lu; Liu, Wenguang

2013-07-17

334

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

PubMed Central

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

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

2009-01-01

335

Diffusion of linear deuterated polystyrene chains in cross-linked polystyrene networks  

SciTech Connect

The diffusion of linear deuterated polystyrene (DPS) chains into a cross-linked polystyrene matrix has been studied by secondary ion mass spectrometry (SIMS). The cross-linked matrices were prepared by radiation cross-linking with {gamma}-rays from a {sup 60}Co source. The doses used were 40, 75, and 156 Mrad, which resulted in an approximate network density, N{sub c} (number of monomer units between cross-linking points), of 9,300, 4,900, and 2,400. The homopolymer DPS chains were of molecular weight M{sub w} = 85,000, 104,000, 303,000, and 550,000 (corresponding to degrees of polymerization of N{sub b} = 759, 929, 2,705, and 4,910). Diffusion of the linear chains into the cross-linked matrix was observed at all molecular weights and cross-linking densities studied. Diffusion was significantly slower into the cross-linked systems than into the matrix chains before cross-linking (M{sub w} = 1,030,000). A free energy expression for the system calculated by assuming additivity of Gaussian rubber elasticity and the Flory-Huggins energy of mixing was used in combination with the Hartley-Crank equation to calculate concentration profiles for linear chains diffusing into the matrix. The predictions were then compared with the data obtained by SIMS. The only free parameter used in fitting the data was the relaxed or reference state network volume fraction. Good fits to the data were obtained when the relaxed state of the networks accounted for the free sol chains still present after cross-linking. The diffusion of the linear chains became very slow when N{sub b} {approximately} N{sub c}, but no distinct halt to the diffusion was observed at this linear chain length. The tracer diffusion coefficients for the linear chains, which were measured separately, were found to be independent of the cross-linking density and to scale with M{sub w}{sup {minus}2.0}, in agreement with the repetition model prediction.

Zheng, X.; Rafailovich, M.H.; Sokolov, J. [State Univ. of New York, Stony Brook, NY (United States). Dept. of Materials Science and Engineering; Zhao, X. [Queens Coll., Flushing, NY (United States). Physics Dept.; Briber, R.M. [Univ. of Maryland, College Park, MD (United States). Dept. of Materials and Nuclear Engineering; Schwarz, S.A. [Bellcore, Red Bank, NJ (United States)

1993-11-22

336

Structural interactions between retroviral Gag proteins examined by cysteine cross-linking.  

PubMed Central

We have examined structural interactions between Gag proteins within Moloney murine leukemia virus (M-MuLV) particles by making use of the cysteine-specific cross-linking agents iodine and bis-maleimido hexane. Virion-associated wild-type M-MuLV Pr65Gag proteins in immature particles were intermolecularly cross-linked at cysteines to form Pr65Gag oligomers, from dimers to pentamers or hexamers. Following a systematic approach of cysteine-to-serine mutagenesis, we have shown that cross-linking of Pr65Gag occurred at cysteines of the nucleocapsid (NC) Cys-His motif, suggesting that the Cys-His motifs within virus particles are packed in close proximity. The M-MuLV Pr65Gag protein did not cross-link to the human immunodeficiency virus Pr55Gag protein when the two molecules were coexpressed, indicating either that they did not coassemble or that heterologous Gag proteins were not in close enough proximity to be cross-linked. Using an assembly-competent, protease-minus, cysteine-minus Pr65Gag protein as a template, novel cysteine residues were generated in the M-MuLV capsid domain major homology region (MHR). Cross-linking of proteins containing MHR cysteines showed above-background levels of Gag-Gag dimers but also identified a novel cellular factor, present in virions, that cross-linked to MHR residues. Although the NC cysteine mutation was compatible with M-MuLV particle assembly, deletions of the NC domain were not tolerated. These results suggest that the Cys-His motif is held in close proximity within immature M-MuLV particles by interactions between CA domains and/or non-Cys-His motif domains of the NC.

Hansen, M S; Barklis, E

1995-01-01

337

Mapping the cofilin binding site on yeast G-actin by chemical cross-linking  

PubMed Central

Cofilin is a major cytoskeletal protein that binds to both monomeric (G-) and polymeric (F-) actin and is involved in microfilament dynamics. Although an atomic structure of the G-actin-cofilin complex does not exist, models of the complex have been built using molecular dynamics simulations, structural homology considerations, and synchrotron radiolytic footprinting data. The hydrophobic cleft between actin subdomains 1 and 3 and, alternatively, the cleft between actin subdomains 1 and 2 have been proposed as possible high affinity cofilin binding sites. In this study, the proposed binding of cofilin to the subdomain 1/3 region on G-actin has been probed using site-directed mutagenesis, fluorescence labeling, and chemical cross-linking with yeast actin mutants containing single reactive cysteines in the actin hydrophobic cleft and cofilin mutants carrying reactive cysteines in the regions predicted to bind to G-actin. Mass spectrometric analysis of the cross-linked complex revealed that cysteine 345 in subdomain 1 of mutant G-actin was cross-linked to native cysteine 62 on cofilin. A cofilin mutant that carried a cysteine substitution in the ?3 helix (residue 95) formed a cross-link with residue 144 in actin subdomain 3. Distance constraints imposed by these cross-links provide experimental evidence for cofilin binding between actin subdomains 1 and 3 and fit a corresponding, docking-based structure of the complex. The cross-linking of the N-terminal region of recombinant yeast cofilin to actin residues 346 and 374 with dithio-bis-maleimidoethane (DTME, 12.4 Å) and via disulfide bond formation was also documented. This set of cross-linking data confirms the important role the N-terminal segment of cofilin in the interactions with G-actin.

Grintsevich, Elena E.; Benchaar, Sabrina A.; Warshaviak, Dora; Boontheung, Pinmanee; Halgand, Frederic; Whitelegge, Julian P.; Faull, Kym F.; Ogorzalek Loo, Rachel R.; Sept, David; Loo, Joseph A.

2009-01-01

338

Oxidative cross-linking of immune complexes by human polymorphonuclear leukocytes.  

PubMed Central

Incubation of human serum albumin-anti-human serum albumin immune complexes bound to a plastic surface, with human polymorphonuclear leukocytes for 1 h at 37 degrees C resulted in covalent cross-linking of 8.5% +/- 0.5 of the complexes, corresponding to a minimum rate of 700 antibody molecules per cell per minute. Similar results were obtained with IgG-anti-IgG and type II collagen-anticollagen II human antibodies. Cross-linking was defined as the antibody remaining attached to plastic-bound antigen after extraction with 3 M MgCl2 and 0.1 N HCl solutions. The effects of addition of oxygen radical scavengers, heme-enzyme inhibitors, and omission of Cl- indicated that the cross-linking process was mediated by the myeloperoxidase-H2O2-Cl- system. Cross-linking was also obtained with cell lysates, polymorphonuclear granules, and purified human myeloperoxidase in the presence of a steady flux of H2O2 provided by glucose oxidase-glucose. Cross-linking by the cell-free systems was also abolished by sodium azide or omission of chloride ions. Cross-linked immune complexes were also generated by incubation with 20 to 50 microM solutions of freshly distilled hypochlorous acid. Addition of 10 mM hypochlorous acid to soluble IgG resulted in the formation of protein precipitates insoluble in 5 M guanidine, 0.1 N HCl, or boiling 2.3 M sodium dodecyl sulfate-1.4 M 2-mercaptoethanol. The remaining soluble IgG contained fluorescent high molecular aggregates (ex: 360 nm; em: 454 nm). Oxidative cross-linking of antigen-antibody molecules, and of immune complexes to connective tissue macromolecules may play a pathogenic role in acute and chronic inflammatory processes.

Jasin, H E

1988-01-01

339

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

SciTech Connect

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

Gajewski, E.; Dizdaroglu, M. (National Institute of Standards and Technology, Gaithersburg, MD (USA))

1990-01-30

340

Chromium(VI) Causes Interstrand DNA Cross-Linking in Vitro but Shows No Hypersensitivity in Cross-Link Repair-Deficient Human Cells.  

PubMed

Hexavalent chromium is a human carcinogen activated primarily by direct reduction with cellular ascorbate and to a lesser extent, by glutathione. Cr(III), the final product of Cr(VI) reduction, forms six bonds allowing intermolecular cross-linking. In this work, we investigated the ability of Cr(VI) to cause interstrand DNA cross-links (ICLs) whose formation mechanisms and presence in human cells are currently uncertain. We found that in vitro reduction of Cr(VI) with glutathione showed a sublinear production of ICLs, the yield of which was less than 1% of total Cr-DNA adducts at the optimal conditions. Formation of ICLs in fast ascorbate-Cr(VI) reactions occurred during a short reduction interval and displayed a linear dose dependence with the average yield of 1.3% of total adducts. In vitro production of ICLs was strongly suppressed by increasing buffer molarity, indicating inhibitory effects of ligand-Cr(III) binding on the formation of cross-linking species. The presence of ICLs in human cells was assessed from the impact of ICL repair deficiencies on Cr(VI) responses. We found that ascorbate-restored FANCD2-null and isogenic FANCD2-complemented cells showed similar cell cycle inhibition and toxicity by Cr(VI). XPA-null cells are defective in the repair of Cr-DNA monoadducts, but stable knockdowns of ERCC1 or XPF in these cells with extended time for the completion of cross-linking reactions did not produce any sensitization to Cr(VI). Our results together with chemical and steric considerations of Cr(III) reactivity suggest that ICL generation by chromate is probably an in vitro phenomenon occurring at conditions permitting the formation of Cr(III) oligomers. PMID:24059640

Morse, Jessica L; Luczak, Michal W; Zhitkovich, Anatoly

2013-10-08

341

Hyaluronan fragments: An information-rich system  

Microsoft Academic Search

Hyaluronan is a straight chain, glycosaminoglycan polymer of the extracellular matrix composed of repeating units of the disaccharide [-d-glucuronic acid-?1,3-N-acetyl-d-glucosamine-?1,4-]n. Hyaluronan is synthesized in mammals by at least three synthases with products of varying chain lengths. It has an extraordinary high rate of turnover with polymers being funneled through three catabolic pathways. At the cellular level, it is degraded progressively

Robert Stern; Akira A. Asari; Kazuki N. Sugahara

2006-01-01

342

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.

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

2012-01-01

343

Purification and characterization of a hyaluronan-binding protein from rat chondrosarcoma.  

PubMed Central

Swarm rat chondrosarcoma contains a hyaluronan-binding protein of molecular mass 102 kDa (HABP102). The protein is present in 4 M-guanidinium chloride extracts of the chondrosarcoma and can be incorporated into reconstituted proteoglycan aggregates, but it is not present in native proteoglycan aggregates or in 0.5 M-guanidinium chloride extracts. HABP102 is unlikely to be an integral membrane protein, as it does not require detergent for extraction, is not enriched in hydrophobic amino acids and does not bind avidly to octyl-Sepharose. The protein stains poorly with Coomassie Blue and is only visible on PAGE gels after staining with silver. Disulphide bonds are essential for the binding of HABP102 to hyaluronan, and bivalent cations are not required for this interaction. HABP102 can be purified from dissociative chondrosarcoma extracts by sequential density-gradient centrifugation, hyaluronan-Sepharose affinity chromatography and hydrophobic-interaction chromatography. The amino acid composition is similar to that of domains 1-4 of the chondrosarcoma proteoglycan core protein, but peptide analysis after digestion with Staphylococcus aureus V8 proteinase and chymotrypsin and different immunoreactivity suggest that HABP102 is not closely related to proteoglycan hyaluronan-binding region. HABP102 is a glycoprotein containing N-acetylgalactosamine, N-acetylglucosamine, mannose and galactose. Images Fig. 1. Fig. 2. Fig. 3. Fig. 4. Fig. 5.

Crossman, M V; Mason, R M

1990-01-01

344

Activation of T Cells by Cross-Linking Qa-2, the Ped Gene Product, Requires Fyn  

PubMed Central

Problem Qa-2, the product of the Ped (preimplantation development) gene, regulates the rate of cell division of preimplantation mouse embryos by an unknown mechanism. Due to the limited availability of preimplantation embryos, T cells were used as a model system to assess the possible roles of Fyn and Lck, and two downstream effectors, PI-3 kinase and Akt, in Qa-2 induced cell proliferation. Method of study Resting T cells were stimulated to proliferate by treating with mouse anti-Qa-2 antibody, cross-linking with anti-mouse immunoglobulin, and adding PMA. The effects of kinase inhibitors on this proliferation were studied. Co-immunoprecipitates of T-cell lysates were analyzed for possible associations between Qa-2 and Fyn or Lck. Fyn knockout mice (Fyn?/?) were used to determine whether Fyn is required for T-cell activation induced by cross-linking Qa-2. Results An inhibitor of Src family kinases and inhibitors of PI-3 kinase and Akt suppressed proliferation of resting T cells induced by cross-linking Qa-2. Fyn, but not Lck, co-immunoprecipitated with Qa-2. Fyn?/? T cells failed to proliferate in response to Qa-2 cross-linking. Conclusion Fyn, PI-3 kinase, and Akt are required for the activation of T cells by cross-linking Qa-2.

De Fazio, Sally R.; Warner, Carol M.

2008-01-01

345

F actin bundles in Drosophila bristles. I. Two filament cross-links are involved in bundling  

PubMed Central

Transverse sections though Drosophila bristles reveal 7-11 nearly round, plasma membrane-associated bundles of actin filaments. These filaments are hexagonally packed and in a longitudinal section they show a 12-nm periodicity in both the 1.1 and 1.0 views. From earlier studies this periodicity is attributable to cross-links and indicates that the filaments are maximally cross-linked, singed mutants also have 7-11 bundles, but the bundles are smaller, flattened, and the filaments within the bundles are randomly packed (not hexagonal); no periodicity can be detected in longitudinal sections. Another mutant, forked (f36a), also has 7-11 bundles but even though the bundles are very small, the filaments within them are hexagonally packed and display a 12-nm periodicity in longitudinal section. The singed-forked double mutant lacks filament bundles. Thus there are at least two species of cross-links between adjacent actin filaments. Hints of why two species of cross-links are necessary can be gleaned by studying bristle formation. Bristles sprout with only microtubules within them. A little later in development actin filaments appear. At early stages the filaments in the bundles are randomly packed. Later the filaments in the bundles become hexagonally packed and maximally cross-linked. We consider that the forked proteins may be necessary early in development to tie the filaments together in a bundle so that they can be subsequently zippered together by fascin (the singed gene product).

1995-01-01

346

Highly cross-linked polyethylene in total knee arthroplasty: in the affirmative.  

PubMed

Polyethylene bearing failure has been cited as one of the leading causes of knee arthroplasty revision surgery. In 1998, highly cross-linked polyethylene was introduced for clinical use in total hip arthroplasty. Altered mechanical properties in first-generation highly cross-linked polyethylene did exhibit clinical failures, such as post fractures in total knee arthroplasty. Remelting alters the integrity of polyethylene. Some approaches to mitigate this include mechanical deformation, vitamin E incorporation, and sequential irradiation and annealing. Forces and stresses in total knee arthroplasty differ substantially from the wear mechanisms and forces seen in total hip arthroplasty. There is now considerable interest in the clinical use of highly cross-linked polyethylene for the knee. The use of sequentially annealed, highly cross-linked polyethylene, based on bench top data, appears to be promising for use in total knee arthroplasty. One should be aware that all highly cross-linked polyethylenes are not manufactured, nor processed, in the same manner. Marked and significant differences may exist between products. PMID:18701237

Jacofsky, David J

2008-08-12

347

Small strain deformation measurements of konjac glucomannan solutions and the influence of borate cross-linking.  

PubMed

The dynamic rheology of aqueous solutions of konjac glucomannan has been evaluated over a range of concentrations up to 2.35%, and the effect of borate cross-linking of such solutions evaluated in the range 0.02-40 mM borate. In preliminary work, conventional parallel plate geometries were employed and in situ cross-linking was investigated. For borate cross-linked samples a superior method, however, was found to be measurement of pre-formed cores of cross-linked polymer into which a four-bladed vane geometry was introduced. In order to compare with other associating polymer systems, rheological data were analysed by defining plateau moduli, corresponding relaxation times and zero shear viscosities and the scaling behaviour of these parameters with polymer and cross-linker concentrations was established. Maxwell fits and time-concentration superposition procedures were investigated. The rheological properties of the cross-linked polymer were shown to be the result of both increased network connectivity and retarded network dynamics. PMID:23618269

Ratcliffe, Ian; Williams, Peter A; English, Robert J; Meadows, John

2013-02-27

348

Cross-linking the protein precursor of marine mussel adhesives: bulk measurements and reagents for curing.  

PubMed

Marine mussels affix themselves to surfaces by use of a highly cross-linked, protein-based adhesive. Metal levels (e.g., Fe, Zn, Cu, Mn) of the cured glue are significantly concentrated relative to surrounding waters. Specific details on the reagents used by mussels to induce protein cross-linking are not known at this time. To provide insight on the cross-linking agents and reactions taking place while curing mussel glues, we performed a study in which various compounds were tested for the ability to bring about protein curing. A precursor to adhesion, with proteins containing the unusual amino acid 3,4-dihydroxyphenylalanine, was extracted from mussel feet. Potential cross-linking agents were mixed with this gelatinous pellet. The compressibility and shear properties of the resulting material were investigated by use of a penetration test. The reagents examined included simple metal ions (e.g., Na+, Zn2+), oxidizing transition metals (e.g., Fe3+, Cr2O7(2-)), nonmetallic oxidants (e.g., H2O2,IO4-), and oxidizing enzymes (e.g., tyrosinase). We found that protein curing was brought about by simple oxidants and transition metal ions. The results show that optimal curing occurs when the reagent is an oxidizing metal ion (e.g., MnO4-, Fe3+). We conclude that marine mussels are likely to employ Mn3+ and Fe3+ for protein cross-linking and adhesive synthesis. PMID:15875406

Monahan, Jennifer; Wilker, Jonathan J

2004-04-27

349

Glutaraldehyde and glyoxal cross-linked chitosan microspheres for controlled delivery of centchroman.  

PubMed

Glutaraldehyde and glyoxal cross-linked microspheres were prepared using chitosan with different molecular weights (MWs) and degrees of deacetylation (DDAs) for sustained release of centchroman under physiological conditions. The DDA in chitosan was determined by different methods, and the samples were categorized as chitosan with low (48%), medium (62%), and high (75%) DDA. The size and shape of the microspheres were determined by scanning electron microscopy (SEM), and hydrophobicity was determined by adsorption of Rose Bengal dye on microspheres cross-linked with glutaraldehyde or glyoxal. The effect of MW, DDA, and degree of cross-linking in microspheres was studied on the degree of swelling, as well as by the loading and release of centchroman. The glyoxal cross-linked microspheres were more compact and hydrophobic and showed better sustained release in companion to chitosan microspheres and glutaraldehyde cross-linked microspheres. The linear fractional release of centchroman with the square root of time indicated a Fickian behavior of centchroman, and the microspheres also showed zero-order release kinetics for centchroman. PMID:16499893

Gupta, K C; Jabrail, Fawzi Habeeb

2006-02-24

350

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

SciTech Connect

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. [Department of Mechanical Engineering, University of California, Berkeley, California 94720 (United States)

2007-01-01

351

Structural Investigation of Supertough Polymer Gels by Small-Angle Neutron Scattering Measurement  

NASA Astrophysics Data System (ADS)

Various types of supertough polymer gels capable of high recoverable deformability and/or with high shear/compressive moduli are investigated by small-angle neutron scattering (SANS) and mechanical measurements. These gels have unique structures, such as sliding cross-links (slide-ring gels), plane cross-links by clay platelets (nanocomposite gels; NC gels), and tetrahedral networks (tetra-PEG gels). One of the common features of these gels is that frozen inhomogeneities inherent to polymer gels are negligible. This fact, observed by SANS measurements, indicates that cross-links are introduced very effectively. Hence, the mechanical properties of these gels are expected to be well predicted by the theories of rubber elasticity. In this review, we discuss the relationship between the structure and mechanical properties of supertough polymer gels. Furthermore, we address the necessary conditions for high-performance polymer gels in the analogy of rubber.

Shibayama, Mitsuhiro

2009-04-01

352

[Hyaluronan-mediated regulation of inflammation].  

PubMed

Hyaluronan is high-molecular-weight biopolymer. Its linear structure is created by repeating disaccharide units. A single unit is composed of N-acetyl-D-glucosamine and D-glucuronic acid. Hyaluronan is the main component of the extracellular matrix. Apart from its structural role, hyaluronan can influence cell proliferation, differentiation, and migration, angiogenesis, as well as inflammation and immune cell function. During inflammation, high-molecular-weight hyaluronan is broken down under the influence of free radicals and enzymes to smaller fragments. Numerous literature data show that the effect of haluronan on immune cells is closely dependent on its molecular mass. High-molecular-weight hyaluronan can participate in restraining inflammation, while the low-molecular-weight form possesses a proinflammatory effect and activates immune cells. Through interaction with surface receptors (CD44, RHAMM, TLR4), hyaluronan fragments stimulate immune cells and enhance cytokine and reactive oxygen species production as well as other factors participating in inflammation. Hyaluronate can thus be an important regulator of the inflammatory process. Low-molecular-weight fragments deliver signal about tissue damage and mobilize immune cells, while the high-molecular-form suppresses immune cell function and prevents excessive exacerbation of inflammation. PMID:18033205

Krasi?ski, Rafa?; Tchórzewski, Henryk

2007-11-19

353

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

2011-12-18

354

Chain Gangs: New Aspects of Hyaluronan Metabolism  

PubMed Central

Hyaluronan is a matrix polymer prominent in tissues undergoing rapid growth, development, and repair, in embryology and during malignant progression. It reaches 107 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.

Erickson, Michael; Stern, Robert

2012-01-01

355

Photo-Cross-Linking of a Purified Preinitiation Complex Reveals Central Roles for the RNA Polymerase II Mobile Clamp and TFIIE in Initiation Mechanisms  

PubMed Central

The topological organization of a TATA binding protein-TFIIB-TFIIF-RNA polymerase II (RNAP II)-TFIIE-promoter complex was analyzed using site-specific protein-DNA photo-cross-linking of gel-purified complexes. The cross-linking results for the subunits of RNAP II were used to determine the path of promoter DNA against the structure of the enzyme. The results indicate that promoter DNA wraps around the mobile clamp of RNAP II. Cross-linking of TFIIF and TFIIE both upstream of the TATA element and downstream of the transcription start site suggests that both factors associate with the RNAP II mobile clamp. TFIIE? closely approaches promoter DNA at nucleotide ?10, a position immediately upstream of the transcription bubble in the open complex. Increased stimulation of transcription initiation by TFIIE? is obtained when the DNA template is artificially premelted in the ?11/?1 region, suggesting that TFIIE? facilitates open complex formation, possibly through its interaction with the upstream end of the partially opened transcription bubble. These results support the central roles of the mobile clamp of RNAP II and TFIIE in transcription initiation.

Forget, Diane; Langelier, Marie-France; Therien, Cynthia; Trinh, Vincent; Coulombe, Benoit

2004-01-01

356

Overexpression of Hyaluronan Synthase 2 Alters Hyaluronan Distribution and Function in Proximal Tubular Epithelial Cells  

Microsoft Academic Search

The functional consequences of increased renal cortical hyaluronan that is associated with both acute injury and progressive scarring are unclear. The aim of this study was to characterize hyaluronan synthase-2 (HAS2)-driven HA synthesis and determine its effect on renal proximal tubular epithelial cell (PTC) function, because this is known to be the inducible form of HA synthase in this cell

Wisam Selbi; Anthony J. Day; Marilyn S. Rugg; Csaba Fulop; Carol A. de la Motte; Timothy Bowen; Vincent C. Hascall; Aled O. Phillips

2006-01-01

357

Protein oxidation at different salt concentrations affects the cross-linking and gelation of pork myofibrillar protein catalyzed by microbial transglutaminase.  

PubMed

In a fabricated then restructured meat product, protein gelation plays an essential role in producing desirable binding and fat-immobilization properties. In the present study, myofibrillar protein (MFP) suspended in 0.15, 0.45, and 0.6 M NaCl was subjected to hydroxyl radical stress for 2 or 24 h and then treated with microbial transglutaminase (MTGase) in 0.6 M NaCl (E?:?S = 1?:?20) at 4 and 15 °C for 2 h. Protein cross-linking and dynamic rheological tests were performed to assess the efficacy of MTGase for mediating the gelation of oxidized MFP. MTGase treatments affected more remarkable polymerization of myosin in oxidized MFP than in nonoxidized, especially for samples oxidized at 0.6 M NaCl. Notably, the extent of MTGase-induced myosin cross-linking at 15 °C in oxidized MFP improved up to 46.8%, compared to 31.6% in nonoxidized MFP. MTGase treatment at 4 °C for MFP oxidized in 0.6 M NaCl, but not MFP oxidized in 0.15 M NaCl, produced stronger gels than nonoxidized MFP (P < 0.05). The final (75 °C) storage modulus (G') of oxidized MFP gels was significantly greater than that of nonoxidized, although the G' of the transient peak (?44.5 °C) showed the opposite trend. Overall, oxidation at high salt concentrations significantly improved MTGase-mediated myosin cross-linking and MFP gelation. This might be because under this condition, MTGase had an increased accessibility to glutamine and lysine residues to effectively initiate protein-protein interactions and gel network formation. PMID:23627930

Li, Chunqiang; Xiong, Youling L; Chen, Jie

2013-04-29

358

Chitosan-hyaluronan/nano chondroitin sulfate ternary composite sponges for medical use.  

PubMed

In this work chitosan-hyaluronan composite sponge incorporated with chondroitin sulfate nanoparticle (nCS) was developed. The fabrication of hydrogel was based on simple ionic cross-linking using EDC, followed by lyophilization to obtain the composite sponge. nCS suspension was characterized using DLS and SEM and showed a size range of 100-150 nm. The composite sponges were characterized using SEM, FT-IR and TG-DTA. Porosity, swelling, biodegradation, blood clotting and platelet activation of the prepared sponges were also evaluated. Nanocomposites showed a porosity of 67% and showed enhanced swelling and blood clotting ability. Cytocompatibility and cell adhesion studies of the sponges were done using human dermal fibroblast (HDF) cells and the nanocomposite sponges showed more than 90% viability. Nanocomposite sponges also showed enhanced proliferation of HDF cells within two days of study. These results indicated that this nanocomposite sponges would be a potential candidate for wound dressing. PMID:23399178

Anisha, B S; Sankar, Deepthi; Mohandas, Annapoorna; Chennazhi, K P; Nair, Shantikumar V; Jayakumar, R

2012-11-09

359

Oil recovery process using a polyacrylamide gel  

SciTech Connect

A polymer gel is formulated by adding a cross-linking agent containing a polyvalent metal cation to an aqueous solution of undried partially hydrolyzed polyacrylamide. The resulting gel is dissolved or suspended in an aqueous medium and injected via a well into a subterranean hydrocarbon-bearing formation to improve oil recovery from the formation.

Norton, C. J.; Falk, D. O.; Hill, A. D.

1985-12-31

360

Cross-linking of streptomycin to the 16S ribosomal RNA of Escherichia coli  

SciTech Connect

(/sup 3/H)Dihydrostreptomycin was cross-linked to the 30S ribosomal subunit from Escherichia coli with the bifunctional reagent nitrogen mustard. The cross-linking primarily involved the 16S RNA. To localize the site of cross-linking of streptomycin to the 16S RNA, the authors hybridized RNA labeled with streptomycin to restriction fragments of the 16S RNA gene. Labeled RNA hybridized to DNA fragments corresponding to bases 892-917 and bases 1394-1415. These two segments of the ribosomal RNA must by juxtaposed in the ribosome, since there is a single binding site for streptomycin. This region has been implicated both in the decoding site and in the binding of initiation factor IF-3, indicating its functional importance.

Gravel, M.; Melancon, P.; Barkier-Gingras, L.

1987-09-22

361

Poly(vinyl alcohol)/CNT composites: An effect of cross-linking with glutaraldehyde  

NASA Astrophysics Data System (ADS)

We propose a new method of preparation of the cross-linked composites of poly(vinyl alcohol) (PVA) with carbon nanotubes (CNTs), in which the formation of new covalent bonds does not involve the nanotube entities, but instead PVA macromolecules only. The method consists in the addition of glutaraldehyde to PVA/CNT dispersions in order to cross-link PVA chains via an acetalization reaction. The composites prepared were studied by scanning electron microscopy, atomic force microscopy, Fourier-transform infrared spectroscopy, Raman spectroscopy and thermogravimetric analysis. The addition of 0.5 and 1% of single-walled and multi-walled CNTs (SWNTs and MWNTs, respectively) considerably changes the morphology and thermal stability characteristics of the glutaraldehyde cross-linked PVA. The use of SWNTs is believed to be more advantageous due to their better dispersion within the PVA phase as compared to MWNTs.

Basiuk, Elena V.; Anis, Arfat; Bandyopadhyay, Sri; Alvarez-Zauco, Edgar; Chan, Sammy L. I.; Basiuk, Vladimir A.

2009-07-01

362

In vitro calcification and in vivo biocompatibility of the cross-linked polypentapeptide of elastin  

SciTech Connect

The in vitro calcifiability and molecular weight dependence of calcification of the polypentapeptide, (L X Val1-L X Pro2-Gly3-L X Val4-Gly5)n, which had been gamma-irradiation cross-linked have been determined when exposed to dialyzates of normal, nonaugmented fetal bovine serum. The material was found to calcify: calcifiability was found to be highly molecular weight dependent and to be most favored when the highest molecular weight polymers (n approximately equal to 240) had been used for cross-linking. The in vivo biocompatibility, biodegradability, and calcifiability of the gamma-irradiation cross-linked polypentapeptide were examined in rabbits in both soft and hard tissue sites. The material was found to be biocompatible irrespective of its physical form and to be biodegradable but with n of 200 or less it was not shown to calcify or ossify in the rabbit tibial nonunion model.

Wood, S.A.; Lemons, J.E.; Prasad, K.U.; Urry, D.W.

1986-03-01

363

In vivo wear and migration of highly cross-linked polyethylene cups a radiostereometry analysis study.  

PubMed

In 50 cemented hip arthroplasties, wear and migration of the polyethylene (PE) cups were measured with radiostereometric analysis for a period of 2 years. Twenty had a normal gamma-in-air-sterilized PE, another 20 had a PE sterilized with 30000 Gy followed by heat stabilization (Duration; Stryker Orthopaedics, Mahwah, NJ), and 10 had highly cross-linked PE cups irradiated with 100000 Gy (Crossfire; Stryker Orthopaedics). In the initial 2 months, head penetration (creep) was 63 microm on average for the 3 groups. From 2 to 24 months, the mean proximal head penetration (wear) was 156 microm for standard PE, 138 microm for stabilized PE (P = .45), and 23 microm for highly cross-linked PE (P < .001; analysis of variance). The low in vivo wear rate for highly cross-linked cups was not at the expense of higher migration or less favorable clinical outcome and looks promising. PMID:16124954

Röhrl, Stephan; Nivbrant, Bo; Mingguo, Li; Hewitt, Ben

2005-06-01

364

Bioinert solution-cross-linked hydrogen-bonded multilayers on colloidal particles.  

PubMed

Bioinert polyelectrolyte multilayers comprised of poly(acrylic acid) and polyacrylamide were deposited on colloidal particles (1.7 microm in diameter) at low pH conditions by layer-by-layer assembly using hydrogen-bonding interactions. The multilayer films were coated uniformly on the colloidal particles without causing any flocculation of the colloids, and the deposited films were subsequently cross-linked by a single treatment of a carbodiimide aqueous solution. The lightly cross-linked multilayer films show excellent stability at physiological conditions (pH 7.4, phosphate-buffered saline), whereas untreated multilayer films dissolved. The multilayer-coated surfaces, both on flat substrates and on colloidal particles, exhibit excellent resistance toward mammalian cell adhesion. With this new solution-based cross-linking method, bioinert H-bonded multilayer coatings offer potential for biomedical applications. PMID:16459619

Yang, Sung Yun; Lee, Daeyeon; Cohen, Robert E; Rubner, Michael F

2004-07-01

365

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

366

Photochemical cross-linking of proteins with visible-light-absorbing 1,8-naphthalamides  

NASA Astrophysics Data System (ADS)

We have newly synthesized a class of photochemical 1,8-naphthalimide dyes. Photochemical investigation strongly suggests that these dyes function as photoalkylation agents following activation to an intermediate state by visible light (circa 420 nm) excitation. The activated species reacts readily with nucleophilic amino acid residues, e.g., tryptophan, cysteine, and methionine. One dye, 1,14-bis-(N-hexyl-3'-bromo-1,8'-naphthalimid-4'-yl)-1,4,11,14- tetraazatetradecane-5,10-dione, which incorporates two reactive 1,8-naphthalimide groups at each end of an intervening structural bridge has been used to cross-link the protein monomers of F-actin, thus preventing its natural depolymerization at low salt concentrations, and to cross-link Apolipoprotein I of human high-density lipoprotein. These observations suggest continued study of these dyes as agents for protein cross-linking, tissue bonding, and inactivation of infectious agents.

Judy, Millard M.; Matthews, James Lester; Boriak, Richard L.; Burlacu, A.; Lewis, D. E.; Utecht, Ronald E.

1993-07-01

367

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

PubMed Central

Although the structure of cross-linking molecules mainly determines the structural organization of actin filaments and with that the static elastic properties of the cytoskeleton, it is largely unknown how the biochemical characteristics of transiently cross-linking proteins (actin-binding proteins (ABPs)) affect the viscoelasticity of actin networks. In this study, we show that the macroscopic network response of reconstituted actin networks can be traced back to the microscopic interaction potential of an individual actin/ABP bond. The viscoelastic response of cross-linked actin networks is set by the cross-linker off-rate, the binding energy, and the characteristic bond length of individual actin/ABP interactions.

Lieleg, O.; Schmoller, K.M.; Claessens, M.M.A.E.; Bausch, A.R.

2009-01-01

368

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

369

Galanin receptor in the rat pancreatic beta cell line Rin m 5F. Molecular characterization by chemical cross-linking.  

PubMed

125I-Galanin was cross-linked to receptor in Rin m 5F cell membranes using the bifunctional reagent disuccinimidyl tartarate. Regardless of the presence of reducing agents, sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of cross-linked galanin-receptor complexes revealed the presence of a radioactive band at Mr 57,000. Excess unlabeled galanin completely inhibited the labeling of the band while other regulatory peptides had no effect. Labeling of the Mr 57,000 complex was abolished by galanin concentration from 10(-9) to 10(-6) M (IC50 = 5 X 10(-9) M). Initial incubation with 125I-galanin in the presence of increasing concentrations of guanyl-5'-yl imidodiphosphate (GMP-P(NH)P) (10(-7) to 10(-4) M) also inhibited the labeling of the Mr 57,000 complex. Moreover, pretreatment of membranes with pertussis toxin before formation of the covalent galanin-receptor complex, dramatically reduced the labeling of the Mr 57,000 species. Covalent Mr 57,000 galanin-receptor complexes solubilized by Triton X-100 bound specifically to wheat germ agglutinin-concanavalin A-, and soybean-coupled Sepharose, supporting the glycoproteic nature of the galanin receptor. Assuming one molecule of 125I-galanin (Mr 3,000) was bound per molecule of protein, these results suggest that the pancreatic galanin receptor is a glycoprotein with a Mr of 54,000 bearing the recognition site for the ligand and which is coupled with a pertussis toxin-sensitive G protein in the plasma membrane. PMID:2479648

Amiranoff, B; Lorinet, A M; Laburthe, M

1989-12-01

370

Preparation of covalently linked complexes between DNA and O(6)-alkylguanine-DNA alkyltransferase using interstrand cross-linked DNA.  

PubMed

O(6)-alkylguanine-DNA alkyltransferases (AGT) are responsible for the removal of alkylation at both the O(6) atom of guanine and O(4) atom of thymine. AGT homologues show vast substrate differences with respect to the size of the adduct and which alkylated atoms they can restore. The human AGT (hAGT) has poor capabilities for removal of methylation at the O(4) atom of thymidine, which is not the case in most homologues. No structural data are available to explain this poor hAGT repair. We prepared and characterized O(6)G-butylene-O(4)T (XLGT4) and O(6)G-heptylene-O(4)T (XLGT7) interstrand cross-linked (ICL) DNA as probes for hAGT and the Escherichia coli homologues, OGT and Ada-C, for the formation of DNA-AGT covalent complexes. XLGT7 reacted only with hAGT and did so with a cross-linking efficiency of 25%, while XLGT4 was inert to all AGT tested. The hAGT mediated repair of XLGT7 occurred slowly, on the order of hours as opposed to the repair of O(6)-methyl-2'-deoxyguanosine which requires seconds. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis of the repair reaction revealed the formation of a covalent complex with an observed migration in accordance with a DNA-AGT complex. The identity of this covalent complex, as determined by mass spectrometry, was composed of a heptamethylene bridge between the O(4) atom of thymidine (in an 11-mer DNA strand) to residue Cys145 of hAGT. This procedure can be applied to produce well-defined covalent complexes between AGT with DNA. PMID:23347328

McManus, Francis P; Khaira, Amardeep; Noronha, Anne M; Wilds, Christopher J

2013-01-24

371

T3 affects expression of collagen I and collagen cross-linking in bone cell cultures.  

PubMed

Thyroid hormones (T3,T4) have a broad range of effects on bone, however, its role in determining the quality of bone matrix is poorly understood. In-vitro, the immortalized mouse osteoblast-like cell line MC3T3-E1 forms a tissue like structure, consisting of several cell layers, whose formation is affected by T3 significantly. In this culture system, we investigated the effects of T3 on cell multiplication, collagen synthesis, expression of genes related to the collagen cross-linking process and on the formation of cross-links. T3 compared to controls modulated cell multiplication, up-regulated collagen synthesis time and dose dependently, and stimulated protein synthesis. T3 increased mRNA expressions of procollagen-lysine-1,2-oxoglutarate 5-dioxygenase 2 (Plod2) and of lysyloxidase (Lox), both genes involved in post-translational modification of collagen. Moreover, it stimulated mRNA expression of bone morphogenetic protein 1 (Bmp1), the processing enzyme of the lysyloxidase-precursor and of procollagen. An increase in the collagen cross-link-ratio Pyr/deDHLNL indicates, that T3 modulated cross-link maturation in the MC3T3-E1 culture system. These results demonstrate that T3 directly regulates collagen synthesis and collagen cross-linking by up-regulating gene expression of the specific cross-link related enzymes, and underlines the importance of a well-balanced concentration of thyroid hormones for maintenance of bone quality. PMID:20707983

Varga, F; Rumpler, M; Zoehrer, R; Turecek, C; Spitzer, S; Thaler, R; Paschalis, E P; Klaushofer, K

2010-08-11

372

Cross-linked Compared with Historical Polyethylene in THA: An 8-year Clinical Study  

PubMed Central

Wear particle-induced osteolysis is a major cause of aseptic loosening in THA. Increasing wear resistance of polyethylene (PE) occurs by increasing the cross-link density and early reports document low wear rates with such implants. To confirm longer-term reductions in wear we compared cross-linked polyethylene (irradiation in nitrogen, annealing) with historical polyethylene (irradiation in air) in a prospective, randomized clinical study involving 48 patients who underwent THAs with a minimum followup of 7 years (mean, 8 years; range, 7–9 years). The insert material was the only variable. The Harris hip score, radiographic signs of osteolysis, and polyethylene wear were recorded annually. Twenty-three historical and 17 moderately cross-linked polyethylene inserts were analyzed (five patients died, three were lost to followup). At 8 years, the wear rate was lower for cross-linked polyethylene (0.088 ± 0.03 mm/year) than for the historical polyethylene (0.142 ± 0.07 mm/year). This reduction (38%) did not diminish with time (33% at 5 years). Acetabular cyst formation was less frequent (39% versus 12%), affected fewer DeLee and Charnley zones (17% versus 4%), and was less severe for the cross-linked polyethylene. The only revision was for an aseptically loose cup in the historical polyethylene group. Moderately cross-linked polyethylene maintained its wear advantage with time and produced less osteolysis, showing no signs of aging at mid-term followup. Level of Evidence: Level I, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

Grimm, Bernd; Vencken, Wendy; Heyligers, Ide C.; Tonino, Alphons J.

2008-01-01

373

Defective DNA cross-link removal in Chinese hamster cell mutants hypersensitive to bifunctional alkylating agents  

SciTech Connect

DNA repair-deficient mutants from five genetic complementation groups isolated previously from Chinese hamster cells were assayed for survival after exposure to the bifunctional alkylating agents mitomycin C or diepoxybutane. Groups 1, 3, and 5 exhibited 1.6- to 3-fold hypersensitivity compared to the wild-type cells, whereas Groups 2 and 4 exhibited extraordinary hypersensitivity. Mutants from Groups 1 and 2 were exposed to 22 other bifunctional alkylating agents in a rapid assay that compared cytotoxicity of the mutants to the wild-type parental strain, AA8. With all but two of the compounds, the Group 2 mutant (UV4) was 15- to 60-fold more sensitive than AA8 or the Group 1 mutant (UV5). UV4 showed only 6-fold hypersensitivity to quinacrine mustard. Alkaline elution measurements showed that this compound produced few DNA interstrand cross-links but numerous strand breaks. Therefore, the extreme hypersensitivity of mutants from Groups 2 and 4 appeared specific for compounds the main cytotoxic lesions of which were DNA cross-links. Mutant UV5 was only 1- to 4-fold hypersensitive to all the compounds. Although the initial number of cross-links was similar for the three cell lines, the efficiency of removal of cross-links was lowest in UV4 and intermediate in UV5. These results suggest that the different levels of sensitivity are specifically related to different efficiencies of DNA cross-link removal. The phenotype of hypersensitivity to both UV radiation and cross-link damage exhibited by the mutants in Groups 2 and 4 appears to differ from those of the known human DNA repair syndromes.

Hoy, C.A.; Thompson, L.H.; Mooney, C.L.; Salazar, E.P.

1985-04-01

374

Concentration-dependent oligomerization of cross-linked complexes between ferredoxin and ferredoxin-NADP+ reductase.  

PubMed

Ferredoxin-NADP(+) reductase (FNR) forms a 1:1 complex with ferredoxin (Fd), and catalyzes the electron transfer between Fd and NADP(+). In our previous study, we prepared a series of site-specifically cross-linked complexes of Fd and FNR, which showed diverse electron transfer properties. Here, we show that X-ray crystal structures of the two different Fd-FNR cross-linked complexes form oligomers by swapping Fd and FNR moieties across the molecules; one complex is a dimer from, and the other is a successive multimeric form. In order to verify whether these oligomeric structures are formed only in crystal, we investigated the possibility of the oligomerization of these complexes in solution. The mean values of the particle size of these cross-linked complexes were shown to increase with the rise of protein concentration at sub-milimolar order, whereas the size of dissociable wild-type Fd:FNR complex was unchanged as analyzed by dynamic light scattering measurement. The oligomerization products were detected by SDS-PAGE after chemical cross-linking of these complexes at the sub-milimolar concentrations. The extent and concentration-dependent profile of the oligomerizaion were differentiated between the two cross-linked complexes. These results show that these Fd-FNR cross-linked complexes exhibit concentration-dependent oligomerization, possibly through swapping of Fd and FNR moieties also in solution. These findings lead to the possibility that some native multi-domain proteins may present similar phenomenon in vivo. PMID:23618857

Kimata-Ariga, Yoko; Kubota-Kawai, Hisako; Lee, Young-Ho; Muraki, Norifumi; Ikegami, Takahisa; Kurisu, Genji; Hase, Toshiharu

2013-04-22

375

Retention of conditioning agent hyaluronan on hydrogel contact lenses  

Microsoft Academic Search

Hyaluronan, a member of the glycosaminoglycan family of biological polysaccharides, is a high-molecular-weight disaccharide polymer found throughout the human body, particularly in the eye. Bausch+Lomb Biotrue™ multi-purpose solution contains hyaluronan as a lens conditioning agent. The retention of hyaluronan from Biotrue multi-purpose solution to a variety of hydrogel contact lenses was evaluated over time. Fluorescein-tagged hyaluronan was allowed to adhere

C. A. Scheuer; K. M. Fridman; V. L. Barniak; S. E. Burke; S. Venkatesh

376

Preparation of cross-linked carboxymethyl chitosan for repairing sciatic nerve injury in rats  

Microsoft Academic Search

A successful nerve regeneration process was achieved with nerve repair tubes made up of 1-ethyl-3(3-dimethylaminopropyl) carbodiimide\\u000a hydrochloride (EDC) cross-linked carboxymethyl chitosan (CM-chitosan) with improved biodegradability. Chitosan has a very\\u000a slow degradation rate, while the EDC cross-linked CM-chitosan tubes degraded to 30% of original weight during 8 weeks of incubation\\u000a in lysozyme solution. In vitro cell culture indicated that the CM-chitosan films

Gan Wang; Guangyuan Lu; Qiang Ao; Yandao Gong; Xiufang Zhang

2010-01-01

377

Femtosecond-UVA-riboflavin (FUR) cross-linking approach to penetrating keratoplasty and anterior lamellar keratoplasty?  

PubMed Central

Purpose To introduce femtosecond laser wound design combined with riboflavin/ultraviolet light-A (UVA) collagen cross-linking at the wound for penetrating (PKP) and anterior lamellar keratoplasty (ALK). Primary outcomes were intraocular pressure (IOP in mmHg) at burst point for the PKP group, and tensile strength (kPa) until dehiscence for the ALK group. Methods Human corneoscleral rims (N = 20) were mounted on artificial anterior chambers. PKP specimens underwent FUR, femtosecond laser-cut without cross-linking, or conventional corneal transplantation. PKP maximum burst IOP with progressive suture removal was assessed by a digital manometer, in triplicate and by three observers. ALK involved whole human globes (N = 10) divided into three groups using a 200-micron, 8 mm diameter donor lenticule, with or without cross-linking. Cross-linked specimens were exposed to UVA light (3 mW/cm2 irradiance, 3.4 J, 370 nm wavelength) for 30 min with 0.1% riboflavin (20% Dextran) applied every 2-min. ALK tensile strength was determined using a digital tensiometer. Results In PKP, burst IOP was 31.32 mmHg greater for corneas that underwent the UVA-riboflavin treatment than for those that did not (p < 0.05). There was no significant relationship (p = 0.719) established between cut design (femtosecond versus conventional). On multivariate analysis, there was a mean of 15.82 mmHg higher sustainable pressure for each stabilization suture present (p < 0.0001). In ALK, specimens comprised of human donor and human recipient tissue combined with UVA-riboflavin therapy experienced the greatest level of adhesion strength (954.7 ± 290.4 kPa) as shown by the force required to separate the tissues, and compared to non-cross-linked specimens. Electron microscopy of ALK specimens showed non-fused and fused longitudinal cross-linked collagen fibers as well as bridges, densities, attachment plaques and primitive plasmalemmal densities. Conclusions Cross-linking effects of the FUR technique enable a stronger graft-recipient adhesion compared to conventional penetrating and anterior lamellar keratoplasty. Electron microscopy enabled visualization of cross-linked interface and potential bonding. The FUR approach may further lead to sutureless transplantation techniques in the future. Setting/venue ImagePlus Laser Eye Centre, Winnipeg, and University of Ottawa Eye Institute, Ottawa, Canada.

Rocha, Guillermo; Butler, Michael; Butler, Andrea; Hackett, Joanne M.

2011-01-01

378

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

379

Cysteine-based cross-linking approach to study inter-domain interactions in ion channels.  

PubMed

Cysteine contains a highly reactive thiol group and therefore under oxidizing conditions a disulfide bond can form between a pair of cysteines that are juxtaposed in the close vicinity, which can be only reversed by reducing agents. These attributes have been elegantly exploited to study the functional role of an interaction or contact between two adjacent domains that are present in ion channels or virtually in any proteins, by introducing double cysteine substitutions at the domain interface and measuring changes in the ion channel functions arising from cross-linking the two substituted cysteines via formation of a disulfide bond. Here I describe this cysteine-based cross-linking approach. PMID:23529437

Jiang, Lin-Hua

2013-01-01

380

Use of a hyperdried cross-linked amniotic membrane as initial therapy for corneal perforations  

Microsoft Academic Search

Purpose  To report the use of hyperdried cross-linked (HDCL) amniotic membrane (AM) patching with tissue adhesive as an initial therapy\\u000a for corneal perforations.\\u000a \\u000a \\u000a \\u000a \\u000a Methods  Cryopreserved AM was cross-linked with 0.1% glutaraldehyde and then dried using far-infrared rays and microwaves (hyperdry\\u000a method). Three eyes of three patients with corneal perforations of up to 3 mm in diameter were included in this study. They

Kiyotaka Kitagawa; Motonori Okabe; Shuichiro Yanagisawa; Xue-Yun Zhang; Toshio Nikaido; Atsushi Hayashi

2011-01-01

381

DNA Cross-Linking Responses of Human Malignant Glioma Cell Strains to Chloroethylnitrosoureas, Cisplatin, and Diaziquone  

Microsoft Academic Search

Cell strains derived by culture of malignant glioma (astrocytoma grade III IV) surgical specimens were tested for the production of DNA interstrand cross-links (ISC) and DNA-protein cross-links following treatment in vitro with l-(2-ch!oroethyl)-l-nitrosourea, l,3-bis(2-chlo- roethylH-nitrosourea (BCNU, carmustine), l-(2-chloroethyl)-3-{2,6- dioxo-l-piperidyl)-l-nitrosourea (PCNU), c\\/s-dichlorodiamminepla- tinum(II) (cisplatin), and 3,6-diaziridinyl-2,5-bis(carboethoxyamino)- 1,4-benzoquinone (diaziquone). ISC and DNA-protein crosslinks were measured by means of the DNA alkaline elution

Eric Sariban; Kurt W. Kohn; Chana Zlotogorski; Guy Laurent; Mauricio D'Incaici; Rufus Day III; Barry H. Smith; Paul L. Kornblith; Leonard C. Erickson

1987-01-01

382

Fracture of a cross-linked polyethylene liner: a multifactorial issue.  

PubMed

A limited number of reports have detailed the cause of fracture of a highly cross-linked polyethylene liner. Typically, the fractures have occurred in a region of thin and/or unsupported polyethylene, in association with superiorly directed edge loading conditions secondary to an excessively inclinated acetabular component. This case report details an unusual fracture mechanism of a 5-mrad cross-linked liner caused by horizontal loading conditions. The report details several factors that were felt to be etiologic including the specific liner locking mechanism. The treatment options are discussed. PMID:20851563

Blumenfeld, Thomas J; McKellop, Harry A; Schmalzried, Thomas P; Billi, Fabrizio

2010-09-18

383

Unique dynamic properties of DNA duplexes containing interstrand cross-links.  

PubMed

Bifunctional DNA alkylating agents form a diverse assortment of covalent DNA interstrand cross-linked (ICL) structures that are potent cytotoxins. Because it is implausible that cells could possess distinct DNA repair systems for each individual ICL, it is believed that common structural and dynamic features of ICL damage are recognized, rather than specific structural characteristics of each cross-linking agent. Investigation of the structural and dynamic properties of ICLs that might be important for recognition has been complicated by heterogeneous incorporation of these lesions into DNA. To address this problem, we have synthesized and characterized several homogeneous ICL DNAs containing site-specific staggered N4-cytosine-ethyl-N4-cytosine cross-links. Staggered cross-links were introduced in two ways, in a manner that preserves the overall structure of B-form duplex DNA and in a manner that highly distorts the DNA structure, with the goal of understanding how structural and dynamic properties of diverse ICL duplexes might flag these sites for repair. Measurements of base pair opening dynamics in the B-form ICL duplex by (1)H NMR line width or imino proton solvent exchange showed that the guanine base opposite the cross-linked cytosine opened at least 1 order of magnitude more slowly than when in a control matched normal duplex. To a lesser degree, the B-form ICL also induced a decrease in base pair opening dynamics that extended from the site of the cross-link to adjacent base pairs. In contrast, the non-B-form ICL showed extensive conformational dynamics at the site of the cross-link, which extended over the entire DNA sequence. Because DNA duplexes containing the B-form and non-B-form ICL cross-links have both been shown to be incised when incubated in mammalian whole cell extracts, while a matched normal duplex is not, we conclude that intrinsic DNA dynamics is not a requirement for specific damage incision of these ICLs. Instead, we propose a general model in which destabilized ICL duplexes serve to energetically facilitate binding of DNA repair factors that must induce bubbles or other distortions in the duplex. However, the essential requirement for incision is an immobile Y-junction where the repair factors are stably bound at the site of the ICL, and the two DNA strands are unpaired. PMID:21174443

Friedman, Joshua I; Jiang, Yu Lin; Miller, Paul S; Stivers, James T

2011-01-11

384

Mutational Analysis of a Conserved Glutamic Acid Required for Self-Catalyzed Cross-Linking of Bacteriophage HK97 Capsids?  

PubMed Central

The capsid of bacteriophage HK97 is stabilized by ?400 covalent cross-links between subunits which form without any action by external enzymes or cofactors. Cross-linking only occurs in fully assembled particles after large-scale structural changes bring together side chains from three subunits at each cross-linking site. Isopeptide cross-links form between asparagine and lysine side chains on two subunits. The carboxylate of glutamic acid 363 (E363) from a third subunit is found ?2.4 Å from the isopeptide bond in the partly hydrophobic pocket that contains the cross-link. It was previously reported without supporting data that changing E363 to alanine abolishes cross-linking, suggesting that E363 plays a role in cross-linking. This alanine mutant and six additional substitutions for E363 were fully characterized and the proheads produced by the mutants were tested for their ability to cross-link under a variety of conditions. Aspartic acid and histidine substitutions supported cross-linking to a significant extent, while alanine, asparagine, glutamine, and tyrosine did not, suggesting that residue 363 acts as a proton acceptor during cross-linking. These results support a chemical mechanism, not yet fully tested, that incorporates this suggestion, as well as features of the structure at the cross-link site. The chemically identical isopeptide bonds recently documented in bacterial pili have a strikingly similar chemical geometry at their cross-linking sites, suggesting a common chemical mechanism with the phage protein, but the completely different structures and folds of the two proteins argues that the phage capsid and bacterial pilus proteins have achieved shared cross-linking chemistry by convergent evolution.

Dierkes, Lindsay E.; Peebles, Craig L.; Firek, Brian A.; Hendrix, Roger W.; Duda, Robert L.

2009-01-01

385

Hyaluronan Facilitates Corneal Epithelial Wound Healing in Diabetic Rats  

Microsoft Academic Search

We investigated the effect of hyaluronan on corneal epithelial wound healing in rats affected by diabetes. Furthermore, because hyaluronan is thought to affect corneal epithelial wound healing through the mechanism of binding of hyaluronan to provisional fibronectin in the wounded area, we compared the localization of fibronectin immunohistochemically during corneal epithelial wound healing in diabetic and non-diabetic rats. Streptozotocin was

MASATSUGU NAKAMURA; NORIAKI SATO; TAI-ICHIRO CHIKAMA; YASUSHI HASEGAWA; TERUO NISHIDA

1997-01-01

386

Prevention of peritoneal adhesions with an in situ cross-linkable hyaluronan hydrogel delivering budesonide.  

PubMed

Peritoneal adhesions are tissue connections that form within the abdominopelvic cavity following surgery or other injuries. They can cause major medical complications. Barrier devices and pharmacological agents have been used to prevent adhesion formation, with mixed success. We hypothesize that an adhesion barrier which also delivers anti-adhesion drugs can address both physical and physiological causes for adhesion formation. Here, we describe an in situ cross-linking hyaluronan hydrogel (barrier device) containing the glucocorticoid receptor agonist budesonide. Budesonide was chosen because of the known role of inflammation in adhesion formation, hyaluronan because of its known biocompatibility in the peritoneum. The system, consisting of two cross-linkable precursor liquids, was applied using a double-barreled syringe, forming a flexible and durable hydrogel in less than 5 s. We applied this formulation or controls to the injured sites after the second injury in a severe repeat sidewall defect-cecum abrasion model of peritoneal adhesion formation in the rabbit. Large adhesions (median area 15.4 cm(2)) developed in all saline-treated animals. Adhesion formation and area were slightly mitigated in animals treated with budesonide in saline (median area 5.0 cm(2)) or the hydrogel without budesonide (median area 4.9 cm(2)). The incidence and area of adhesions were dramatically reduced in animals treated with budesonide in the hydrogel (median area 0.0 cm(2)). In subcutaneous injections in rats, budesonide in hydrogel reduced inflammation compared to hydrogel alone. In summary, budesonide in a hyaluronan hydrogel is easy to use and highly effective in preventing adhesions in our severe repeated injury model. It is a potentially promising system for post-surgical adhesion prevention, and suggests that the effectiveness of barrier devices can be greatly enhanced by concurrent drug delivery. PMID:17582645

Yeo, Yoon; Adil, Maroof; Bellas, Evangelia; Astashkina, Anna; Chaudhary, Nilika; Kohane, Daniel S

2007-05-03

387

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.

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

2012-01-01

388

A Novel Micromixer with Three-Dimensionally Cross-Linked Capillary Array Structure Fabricated by Deep X-ray Lithography  

NASA Astrophysics Data System (ADS)

A novel micromixer is proposed, fabricated and verified. The new concept of the micromixere is to cross-link the many capillaries in three-dimensional structure. The characteristic flow behaviors are simulated by using computational fluid dynamics(CFD) software “FLUENT”. The results of the CFD shows unique mixing behavior in three-dimensionally cross-linked capillaries. The mixing performance of the micromixer is strongly influenced by controlling the three-dimensional crossing condition. The micromixer is fabricated by means of deep X-ray lithography with multi step exposure. The cross-linked capillary structures are successfully fabricated with controlled cross-link conditions. The performance of micromixer is evaluated by using a kind of enzyme reaction. By comparing mixture, mixed with cross-linked fluid filter and fluid filter without cross-linked capillaries, we found out the speeding up of the reaction by using new micromixer.

Kondo, Saki; Ukita, Yoshiaki; Fujiwara, Kuniyo; Utsumi, Yuichi

389

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

Technology Transfer Automated Retrieval System (TEKTRAN)

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

390

Cross-Linking of Lens Crystallins in a Photodynamic System: A Process Mediated by Singlet Oxygen  

Microsoft Academic Search

In a dye-sensitized photooxidation system, lens crystallin polypeptides become cross-linked, and a blue fluorescence that is associated with the proteins is produced. These changes are similar to those seen in vivo in the aging human lens. Evidence implicating singlet oxygen as the causative agent of the effects in vitro is presented, and the possibility that this species may play a

John D. Goosey; J. Samuel Zigler; Jin H. Kinoshita

1980-01-01

391

Nodular Epithelial Hyperplasia after Photorefractive Keratectomy Followed by Corneal Collagen Cross-Linking  

PubMed Central

This study describes a case of nodular epithelial hyperplasia and stromal alterations in a patient with keratoconus who was submitted to topography-guided photorefractive keratectomy (PRK) followed by corneal collagen cross-linking. Debridement of the epithelial nodule was performed. After a 2-year followup, a new topography-guided PRK was indicated.

Salerno, Liberdade Cezaro; Ghanem, Vinicius Coral; Ghanem, Ramon Coral

2013-01-01

392

C. elegans FANCD2 responds to replication stress and functions in interstrand cross-link repair  

Microsoft Academic Search

One of the least well understood DNA repair processes in cells is the repair of DNA interstrand cross-links (ICLs) which present a major obstacle to DNA replication and must be repaired or bypassed to allow fork progression. Fanconi anemia (FA) is an inherited genome instability syndrome characterized by hypersensitivity to ICL damage. Central to the FA repair pathway is FANCD2

Spencer J. Collis; Louise J. Barber; Jordan D. Ward; Julie S. Martin; Simon J. Boulton

2006-01-01

393

Evaluation of cross-linked chitosan microparticles containing metronidazole for periodontitis treatment.  

PubMed

The aims of this study were to find the optimal formulation for the preparation of metronidazole-loaded chitosan microparticles (MTZ-MPs) via an emulsion cross-linking process, and to compare the in vitro release of MTZ from hydrogels and films containing the drug in forms of MTZ-MPs and raw powders. The effects of emulsifier type and concentration, amount of cross-linking agent, cross-linking time, drug:chitosan ratio, form of drug adding and washing method on the properties of the MTZ-MPs were investigated. The results indicated that the optimal conditions for round and free-flowing MTZ-MPs with a high percentage of entrapped drug and preferable release profile were 1% of Span80 in soybean oil, 5% of glutaraldehyde based on chitosan solution, 30 min of cross-linking time, 1:1 drug:chitosan ratio, drug adding in form of ethanol solution and washing with hexane only. MTZ-MPs prepared from the optimal formulation were incorporated in mucoadhesive hydrogel and film. The release profiles of the drug from hydrogel and film containing MTZ-MPs were in prolong pattern compared with those containing drug powders. However, the hydrogels exhibited higher preferable pattern of release profile than the films. Therefore, the hydrogel containing MTZ-MPs was possible to be further clinically investigated for peridontitis treatment. PMID:23827560

Pichayakorn, Wiwat; Boonme, Prapaporn

2012-12-08

394

Effect of cross-linking ultrahigh molecular weight polyethylene: Surface molecular orientation and wear characteristics  

SciTech Connect

Molecular orientation at the surface layer of cross-linked ultrahigh molecular weight polyethylene (UHMWPE) has been examined. Molecular orientation has been shown to affect the wear resistance and surface mechanical properties of UHMWPE under biomechanical loading conditions. This study utilizes a nondestructive synchrotron based soft x-ray technique; near edge x-ray absorption fine structure at the carbon K-edge to examine the degree of surface molecular orientation of UHMWPE subjected to various cross-linking/sterilization techniques as a function of stress and wear. UHMWPE samples prepared under gamma irradiation, ethylene-oxide (EtO) treatment, and electron beam irradiation were worn in a wear tester systematically. Results suggest that the cross-linking resists surface orientation when the samples were under tensile and biomechanical stresses. The molecular orientation in the C-C chains in the polymer showed a monotonic decrease with an increase in gamma irradiation dosage levels. EtO sterilized samples showed more C-C chain orientation than the electron beam irradiated samples, but lower than the 30 kGy gamma irradiated samples. Ordered C-C chains in UHMWPE samples have been associated with more crystallinity or large strain plastic deformation of the polymer. Higher levels of gamma irradiation appear to induce cross-linking of C-C chains and render a polymer with more amorphous phase which resists orientation after wear and imparts wear resistance to the polymer.

Sambasivan, Sharadha; Fischer, Daniel A.; Hsu, Stephen M. [Ceramics Division, Material Science and Engineering Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States)

2007-07-15

395

Cross-linked metalloproteins: Novel systems for the study of intraprotein electron-transfer reactions.  

National Technical Information Service (NTIS)

My initial research shows, for the first time, that proteins can be cross-linked selectively via transition-metal compounds to form stable protein complexes. Incubation of horse heat cytochrome c (designated cyt) with reagents PtCl(sub 4)(sup 2(minus)) an...

L. M. Peerey

1990-01-01

396

Enhancement of the DNA cross-linking activity of melphalan by misonidazole in vivo.  

PubMed Central

The technique of alkaline elution has been adapted for the study of drug-induced DNA cross-link formation in vivo. Pretreatment with misonidazole (MISO) enhances the number of cross-links formed in a fibrosarcoma and in the spleen and gut of mice for periods up to 48 h following a single injection of melphalan (MEL). The tumour was sensitized by a greater factor (2.05) than either of the normal tissues (enhancement factor 1.4-1.5). This enhancement did not appear to be related to inhibition of the repair of actual cross-links. Rather, the effect was explicable in terms of one of two alternative models. Firstly, MISO pretreatment could result in a greater amount of binding of MEL to DNA at early times after injection. This may be the result of altered pharmacokinetics of MEL, or of enhanced intracellular uptake of MEL due to MISO pretreatment. Secondly, MISO may exert its affect by inhibition of the repair of cross-links or monoadducts at early times post-injection, which would not be observed in this study. The possible involvement of glutathione depletion in chemosensitization by MISO was investigated by comparison with the effect of diethyl maleate (DEM), a known thiol-depleting reagent. Glutathione depletion, while perhaps being important, could not account for all of the effects observed.

Murray, D.; Meyn, R. E.

1983-01-01

397

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

2011-11-09

398

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

399

Thermal stability and flammability of butadiene- acrylonitrile rubber cross-linked with iodoform  

Microsoft Academic Search

Summary The paper discusses the  results of thermal analysis and flammability of butadiene-acrylonitrile rubber, Perbunan NT 1845 of Bayer, cross-linked with iodoform. The properties of the iodoform vulcanizate have been compared with those of peroxide vulcanizate. The thermal analysis has been performed in air with use of a derivatograph under air and nitrogen atmosphere as well as dynamic scanning calorimetry

P. Rybi?ski; G. Janowska; W. Antkowicz; S. Krauze

2005-01-01

400

In situ Self Cross-Linking of Polyvinyl Alcohol Battery Separators.  

National Technical Information Service (NTIS)

The method disclosed is used to produce a polyvinyl alcohol sheet material wherein the polyvinyl alcohol is substantially free of 1,2 diol units, and has an acetal self cross-linked structure wherein the acetal content is determined by the 1,2 diol conten...

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

1978-01-01

401

Pseudo-Spherulite Structures in Cross-Linked Low-Density Polyethylene  

Microsoft Academic Search

This paper describes evidence for the formation of secondary fissure structures, in low-density polyethylene (PE), and in cross-linked polyethylene (XLPE). These structures can be observed by optical and by scanning electron microscope techniques. The secondary fissures are not a volume effect like spherulites, but are associated with the fracture surface only. An explanation of this effect is given, as well

Heinz Wagner

1978-01-01

402

Cross-linked poly (ether ether ketone) as a proton exchange membrane for fuel cell applications  

Microsoft Academic Search

Sulfonated poly (ether ether ketone) with pendant carboxylic acid groups was directly synthesized and used to prepare cross-linked polymer electrolyte membrane. The direct synthesis of the sulfonated polymer provided the opportunity to control the degree of sulfonation and the distribution of the sulfonic acid groups within the polymer. The pendant carboxylic acid groups were functionalized by unsaturated groups in order

Shuhua Zhou; Nguyenthi Que Chi; Dukjoon Kim

2010-01-01

403

Cross-linked soy protein as material for biodegradable films: Synthesis, characterization and biodegradation  

Microsoft Academic Search

The modification of soy protein isolate (SPI) with different amounts of a naturally occurring cross-linking agent (genipin, Gen) and glycerol used as plasticizer was carried out in this work. The films yielded were cast from heated and alkaline aqueous solution of SPI, glycerol and Gen and then dried in an oven. Total soluble matter, water vapor permeability and mechanical properties

Agustín González; Miriam Cristina Strumia; Cecilia Ines Alvarez Igarzabal

2011-01-01

404

Effects of Mechanical Stretch on Collagen and Cross-Linking in Engineered Blood Vessels  

PubMed Central

It has been shown that mechanical stimulation affects the physical properties of multiple types of engineered tissues. However, the optimum regimen for applying cyclic radial stretch to engineered arteries is not well understood. To this end, the effect of mechanical stretch on the development of engineered blood vessels was analyzed in constructs grown from porcine vascular smooth muscle cells. Cyclic radial distension was applied during vessel culture at three rates: 0 beats per minute (bpm), 90 bpm, and 165 bpm. At the end of the 7-week culture period, harvested vessels were analyzed with respect to physical characteristics. Importantly, mechanical stretch at 165 bpm resulted in a significant increase in rupture strength in engineered constructs over nonstretched controls. Stress–strain data and maximal elastic moduli from vessels grown at the three stretch rates indicate enhanced physical properties with increasing pulse rate. In order to investigate the role of collagen cross-linking in the improved mechanical characteristics, collagen cross-link density was quantified by HPLC. Vessels grown with mechanical stretch had somewhat more collagen and higher burst pressures than nonpulsed control vessels. Pulsation did not increase collagen cross-link density. Thus, increased wall thickness and somewhat elevated collagen concentrations, but not collagen cross-link density, appeared to be responsible for increased burst strength.

Solan, Amy; Dahl, Shannon L. M.; Niklason, Laura E.

2009-01-01

405

The counterbend phenomenon in flagellar axonemes and cross-linked filament bundles.  

PubMed

Recent observations of flagellar counterbend in sea urchin sperm show that the mechanical induction of curvature in one part of a passive flagellum induces a compensatory countercurvature elsewhere. This apparent paradoxical effect cannot be explained using the standard elastic rod theory of Euler and Bernoulli, or even the more general Cosserat theory of rods. Here, we develop a geometrically exact mechanical model to describe the statics of microtubule bundles that is capable of predicting the curvature reversal events observed in eukaryotic flagella. This is achieved by allowing the interaction of deformations in different material directions, by accounting not only for structural bending, but also for the elastic forces originating from the internal cross-linking mechanics. Large-amplitude static configurations can be described analytically, and an excellent match between the model and the observed counterbend deformation was found. This allowed a simultaneous estimation of multiple sperm flagellum material parameters, namely the cross-linking sliding resistance, the bending stiffness, and the sperm head junction compliance ratio. We further show that small variations on the empirical conditions may induce discrepancies for the evaluation of the flagellar material quantities, so that caution is required when interpreting experiments. Finally, our analysis demonstrates that the counterbend emerges as a fundamental property of sliding resistance in cross-linked filamentous polymer bundles, which also suggests that cross-linking proteins may contribute to the regulation of the flagellar waveform in swimming sperm via counterbend mechanics. PMID:23824293

Gadêlha, Hermes; Gaffney, Eamonn A; Goriely, Alain

2013-07-03

406

Lung collagen cross-links in rats with experimentally induced pulmonary fibrosis  

Microsoft Academic Search

Rats were intratracheally instilled with bleomycin or with silica (quartz) dust to induce lung fibrosis. Several weeks later, purified collagen chains (or collagen digests) were isolated from the lungs of these animals and from age-matched controls instilled intratracheally with saline solution, and the ratios of hydroxylysine to lysine and of the difunctional cross-links DHLNL to HLNL were quantified. Collagen from

Joan E. Gerriets; Karen M. Reiser; Jerold A. Last

1996-01-01

407

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

PubMed

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 rats (Rattus norvegicus) weighing 250-275 g were incubated with 50 mM glucose and 100 mg of metformin or Withania root powder or ethanolic extract of Withania under physiological conditions of temperature and pH for 30 days. Formation of advanced glycation end products (AGE) was measured by fluorescent method whereas the cross-linking of collagen was assessed by pepsin digestion and viscosity measurements. Tendon collagen incubated with glucose showed an increase in glycation, AGE and cross-linking of collagen. The collagen incubated with W. somnifera and metformin ameliorates these modifications. The ethanolic extract of Withania showed more prominent effect than Withania root powder. The activity of ethanolic extract of Withania is comparable to metformin, a known antiglycating agent. In conclusion, Withania could have therapeutic role in the prevention of glycation induced pathogenesis in diabetes mellitus and aging. PMID:17329138

Babu, Pon Velayutham Anandh; Gokulakrishnan, Adikesavan; Dhandayuthabani, Rajendra; Ameethkhan, Dowlath; Kumar, Chandrasekara Vimal Pradeep; Ahamed, Md Iqbal Niyas

2007-01-31

408

Interstrand Cross-Links Induce DNA Synthesis in Damaged and Undamaged Plasmids in Mammalian Cell Extracts  

Microsoft Academic Search

Mammalian cell extracts have been shown to carry out damage-specific DNA repair synthesis induced by a variety of lesions, including those created by UV and cisplatin. Here, we show that a single psoralen interstrand cross-link induces DNA synthesis in both the damaged plasmid and a second homologous unmodified plasmid coincubated in the extract. The presence of the second plasmid strongly

LEI LI; CAROLYN A. PETERSON; XIAOYAN LU; PING WEI; RANDY J. LEGERSKI

1999-01-01

409

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...

410

Cross-linking carbon nanotubes by glycidyl azide polymer via click chemistry.  

PubMed

Functionalization and cross linking of carbon nanotubes was necessary to fabricate nanotube composites with good interfacial properties and mechanical performance. Glycidyl azide polymer was used as cross-linker of carbon nanotubes via a simple clickable one step reaction initiated by decomposition of azide groups. Both heating and UV irradiation were used to carry out the reaction. FTIR and Raman spectra confirmed the decomposition of azide groups and the anchoring of glycidyl azide polymer onto the surface of carbon nanotubes. Thermal gravity analysis showed that the polymer anchored onto carbon nanotubes was about 10% of the total mass in the solid product, but the efficiency of the reaction was low. The result of tensile test using bulky paper infiltrated with 10% GAP showed that cross linking could bring forth a higher strength, about 4 times higher than the not cross linked. The success of cross linking carbon nanotubes by glycidyl azide polymer paves a new way to fabrication of ultra strong carbon nanotube composites. PMID:22524058

Wei, Zhong; Du, Liang; Wang, Lin

2012-01-01

411

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 Go 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

412

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

413

Vinylsulfonamide and Acrylamide Modification of DNA for Cross-linking with Proteins.  

PubMed

Bioorthogonal covalent cross-linking of DNA-binding proteins (p53) to DNA was achieved through novel DNA probes bearing a reactive vinylsulfonamide (VS) group. The VS-modified dCTP served as building block for polymerase synthesis of modified DNA, which was readily conjugated with cysteine-containing peptides and proteins by Michael addition. PMID:23939933

Dadová, Jitka; Orság, Petr; Pohl, Radek; Brázdová, Marie; Fojta, Miroslav; Hocek, Michal

2013-08-12

414

Capacity of Cognitive Radio under imperfect secondary and cross link Channel State Information  

Microsoft Academic Search

In this paper, we study the ergodic capacity of secondary user channel in a spectrum sharing scenario in which the secondary transmitter is instantaneously aware of estimated versions of the cross link (between the secondary transmitter and the primary receiver) and the secondary link Channel State Information (CSI). The secondary link optimal power profile along with the ergodic capacity are

Lokman Sboui; Zouheir Rezki; Mohamed-Slim Alouini

2011-01-01

415

Promoting peptide ?-helix formation with dynamic covalent oxime side-chain cross-links.  

PubMed

Covalent side-chain cross-linking has been shown to be a viable strategy to control peptide folding. We report here that an oxime side-chain linkage can elicit ?-helical folds from peptides in aqueous solution. The bio-orthogonal bridge is formed rapidly under neutral buffered conditions, and the resulting cyclic oximes are capable of dynamic covalent exchange. PMID:21691623

Haney, Conor M; Loch, Matthew T; Horne, W Seth

2011-06-20

416

Use of crossed-linked hyaluronic acid in the anterior segment  

Microsoft Academic Search

We evaluated the use of cross-linked hyaluronic acid (CLHA) in the anterior segment of the rabbit's eye. Subconjunctival injection of less than 0.1ml of CLHA was well tolerated. Intracameral injection containing more than 0.05 ml of CLHA produced severe inflammatory reaction.

Gholam A. Peyman; Grace W. Kao

1987-01-01

417

Ionically cross-linked chitosan microspheres for controlled release of bioactive nerve growth factor.  

PubMed

Controlled release of neurotrophic factors to target tissue via microsphere-based delivery systems is critical for the treatment strategies of diverse neurodegenerative disorders. The present study aims to investigate the feasibility of the controlled release of bioactive nerve growth factor (NGF) with ionically cross-linked chitosan microspheres (NGF-CMSs). The microspheres were prepared by the emulsion-ionic cross-linking method with sodium tripolyphosphate (STPP) as an ionic cross-linking agent. The size and distribution of the microspheres, SEM images, Fourier transform infra red spectroscopy (FT-IR), encapsulation efficiency, in vitro release tests and bioactivity assay were subsequently evaluated. We found that the microspheres had relatively rough surfaces with mean sizes between 20 and 31?m. FT-IR results provided evidence of ionic interaction between amino groups and phosphoric groups of chitosan and STPP. The NGF encapsulation efficiency ranged from 63% to 88% depending on the concentration of STPP. The in vitro release profiles of NGF from NGF-CMSs were influenced by the concentration of STPP. NGF-CMSs which were cross-linked with higher concentration of STPP showed slower but sustained release of NGF. In addition, the released NGF from NGF-CMSs was capable of maintaining the viability of PC12 cells, as well as promoting their differentiation. Taken together, our findings suggest that NGF-CMSs are capable of releasing bioactive NGF over 7 days, thus having potential application in nerve injury repair. PMID:22001532

Zeng, Wen; Huang, Jinghui; Hu, Xueyu; Xiao, Wei; Rong, Mengyao; Yuan, Zhi; Luo, Zhuojing

2011-10-06

418

In-vitro fermentability of cell walls as influenced by lignin composition and cross-linking.  

Technology Transfer Automated Retrieval System (TEKTRAN)

We assessed how diverse modifications in lignin composition and reductions in ferulate-lignin cross-linking influence the degradability of cell walls. Cell walls from nonlignified maize cell suspensions were artificially lignified with varying ratios of normal monolignols (coniferyl and sinapyl alco...

419

Comparison of diamino cross-linking in different polyimide solutions and membranes by precipitation observation and gas transport  

Microsoft Academic Search

Matrimid and 6FDA-durene polyimides (PI) are chosen to investigate diamino cross-linking processes in solution and dense membrane forms. The cross-linking process (precipitation) of polyimide solutions is visually monitored by a digital camera to provide visual evidence for the chemical reaction. By comparing the reaction of different diamines with the polyimide solutions, we inferred that the cross-linking rate is an indication

Lu Shao; Li Liu; Si-Xue Cheng; Yu-Dong Huang; Jun Ma

2008-01-01

420

Preparation, characterization and dielectric properties of 4,4-diphenylmethane diisocyanate (MDI) based cross-linked polyimide films  

Microsoft Academic Search

Four different types of cross-linked polyimides based on 4,4-diphenylmethane diisocyanate (MDI) were prepared by the reaction of different types of conventional poly(amic acid) intermediates with MDI as a cross-linking agent. Subsequently, they were thermally imidized in order to obtain corresponding cross-linked polyimide structure. The results of FTIR-ATR showed that MDI can effectively react with carboxylic acid groups of PAA to

Hüseyin Deligöz; Tuncer Yalcinyuva; Saadet Özgümüs; Saffettin Yildirim

2006-01-01