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1

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

PubMed Central

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

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

2011-01-01

2

Incorporation of Pentraxin 3 into Hyaluronan Matrices Is Tightly Regulated and Promotes Matrix Cross-linking  

PubMed Central

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

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

2014-01-01

3

Slide-ring gel: Topological gel with freely movable cross-links  

NASA Astrophysics Data System (ADS)

The structure of “slide-ring (SR) gel” was investigated by means of small angle neutron scattering (SANS). The SR gel was synthesized by coupling of ?-cyclodextrin molecules on polyrotaxane chains. A cross-linking point of SR gel has a shape of “figure-of-eight”. Two-dimensional SANS patterns for uniaxially stretched SR gels showed a “normal” butterfly pattern. This result indicates that the cross-links slide along the polymer chain so as to minimize the local strain as a “pulley”. The pulley effect was found to be significant to reduce spatial inhomogeneities inherent in polymer gels.

Karino, Takeshi; Shibayama, Mitsuhiro; Ito, Kohzo

2006-11-01

4

Enzymatically cross-linked gelatin/chitosan hydrogels: tuning gel properties and cellular response.  

PubMed

This work investigates the effect of combining physical and chemical gelation processes in a biopolymer blend: chitosan and tilapia fish gelatin. Chemical (C) gels are obtained by cross-linking with the microbial enzyme transglutaminase at 37?°C. Hybrid physical-co-chemical (PC) gels are cross-linked at 21?°C, below gelatin gelation temperature. These protocols provide two microenvironments for the gelation process: in C gels, both gelatin and chitosan are present as single strands; in PC gels, cross-linking proceeds within a transient physical gel of gelatin, filled by chitosan strands. The chitosan/gelatin chemical networks generated in PC gels show a consistently higher shear modulus than pure C gels; they are also less turbid than their C gels counterparts, suggesting a more homogeneous network. Finally, chitosan enhances the gels' shear modulus in all gels. Proliferation assays show that MC3T3 cells proliferate in these mixed, hybrid gels and better so on PC gels than in C mixed gels. PMID:24550134

da Silva, Marcelo A; Bode, Franziska; Drake, Alex F; Goldoni, Silvia; Stevens, Molly M; Dreiss, Cécile A

2014-06-01

5

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

6

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

Microsoft Academic Search

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 ?g l?1) and acrylic

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

2005-01-01

7

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

PubMed Central

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.

2009-01-01

8

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

2009-02-01

9

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

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

10

Surface characteristics determining the cell compatibility of ionically cross-linked alginate gels.  

PubMed

In this study we investigated differences in the characteristics determining the suitability of five types of ion (Fe(3+), Al(3+), Ca(2+), Ba(2+) and Sr(2+))-cross-linked alginate films as culture substrates for cells. Human dermal fibroblasts were cultured on each alginate film to examine the cell affinity of the alginates. Since cell behavior on the surface of a material is dependent on the proteins adsorbed to it, we investigated the protein adsorption ability and surface features (wettability, morphology and charge) related to the protein adsorption abilities of alginate films. We observed that ferric, aluminum and barium ion-cross-linked alginate films supported better cell growth and adsorbed higher amounts of serum proteins than other types. Surface wettability analysis demonstrated that ferric and aluminum ion-cross-linked alginates had moderate hydrophilic surfaces, while other types showed highly hydrophilic surfaces. The roughness was exhibited only on barium ion-cross-linked alginate surface. Surface charge measurements revealed that alginate films had negatively charged surfaces, and showed little difference among the five types of gel. These results indicate that the critical factors of ionically cross-linked alginate films determining the protein adsorption ability required for their cell compatibility may be surface wettability and morphology. PMID:24496019

Machida-Sano, Ikuko; Hirakawa, Makoto; Matsumoto, Hiroki; Kamada, Mitsuki; Ogawa, Sakito; Satoh, Nao; Namiki, Hideo

2014-04-01

11

Iodopropyl-branched polysiloxane gel electrolytes with improved ionic conductivity upon cross-linking.  

PubMed

We here report the implementation of poly[(3-N-methylimidazoliumpropyl)methylsiloxane-co-dimethylsiloxane]iodides as suitable polymeric hosts for a novel class of in situ cross-linkable iodine/iodide-based gel-electrolytes for dye-sensitized solar cells. The polymers are first partially quaternized and then subjected to a thermal cross-linking which allows the formation of a 3D polymeric network which is accompanied by a dramatic enhancement of the ionic conductivity. PMID:25266064

De Gregorio, G L; Giannuzzi, R; Cipolla, M P; Agosta, R; Grisorio, R; Capodilupo, A; Suranna, G P; Gigli, G; Manca, M

2014-10-16

12

The enhanced stability of the cross-linked hylan structure to hydroxyl (OH) radicals compared with the uncross-linked hyaluronan  

NASA Astrophysics Data System (ADS)

A comparison has been made of the relative stabilities of hyaluronan and hylan to degradation by OH radicals produced by ?-irradiation of aqueous solutions in N 2O, when G (yield per 100 eV) for OH radicals is 5.6 and H atoms 0.6. Using low angle light scattering and viscometric methods, the change in molecular weight of the polysaccharides was measured with increasing dose. From the yield/dose curves (expressed as breaks per molecule), the initial G value for hyaluronan degradation is ˜ 4. A further slow post-irradiation decrease in molecular weight is observed, which can be brought to completion by incubating the solutions for 1 h at 60°C. Thereafter, the G value for degradation is ˜ 6. A similar post-irradiation degradation was found for hylan. A technique using tetranitromethane (TNM) has been used to distinguish between two types of radicals formed on the hyaluronan backbone. Radicals of the 1-hydroxy-2-alkoxy type (C-2, C-4, C-2 and C3 of the glucuronic acid) would induce strand breakage by alkoxy elimination. For the equivalent alkoxy radical at C6 of the acetamido monosaccharide, ring opening would occur with formation of a hemi-acetal, leading also to strand breakage. The C-2 and C-3 radicals would eliminate water rather than produce breaks by ?-alkoxy elimination. Thus three out of the initially formed radicals would produce breaks by ?-alkoxy formation. These can be stabilised with TNM and distinguished. It is concluded that these are the radicals involved in the post-irradiation thermal degradation process. Comparison of hylan and hyaluronan is, therefore, most valid when this post-irradiation process has been completed. Therefore, all G values for degradation were measured after incubation for 1 h at 60°. This investigation establishes the greater stability of hylan ( Gdegradation = 2) compared to hylan ( Gdegradation = 6). Therefore, in an environment such as supplementation of an inflammed joint where OH radicals are released, hylan is able to retain its integrity as a viscoelastic macromolecule three times better than hyaluronan. Its potential as a viscosupplementation material, or as an inflammatory drug release matrix inserted within the joint is, therefore, greater than non-cross-linked hyaluronan.

Al-Assaf, Saphwan; Phillips, Glyn O.; Deeble, D. J.; Parsons, Barry; Starnes, Hazel; Von Sonntag, C.

1995-08-01

13

Immobilization of Cross-Linked Phenylalanine Ammonia Lyase Aggregates in Microporous Silica Gel  

PubMed Central

A separable and highly-stable enzyme system was developed by adsorption of phenylalanine ammonia lyase (PAL) from Rhodotorula glutinis in amino-functionalized macroporous silica gel and subsequent enzyme crosslinking. This resulted in the formation of cross-linked enzyme aggregates (PAL-CLEAs) into macroporous silica gel (MSG-CLEAs). The effect of adsorptive conditions, type of aggregating agent, its concentration as well as that of cross-linking agent was studied. MSG-CLEAs production was most effective using ammonium sulfate (40%-saturation), followed by cross-linking for 1 h with 1.5% (v/v) glutaraldehyde. The resulting MSG-CLEAs extended the optimal temperature and pH range compared to free PAL and PAL-CLEAs. Moreover, MSG-CLEAs exhibited the excellent stability of the enzyme against various deactivating conditions such as temperature and denaturants, and showed higher storage stability compared to the free PAL and the conventional PAL-CLEAs. Such as, after 6 h incubation at 60°C, the MSG-CLEAs still retained more than 47% of the initial activity whereas PAL-CLEAs only retained 7% of the initial activity. Especially, the MSG-CLEAs exhibited good reusability due to its suitable size and active properties. These results indicated that PAL-CLEAs on MSG might be used as a feasible and efficient solution for improving properties of immobilized enzyme in industrial application. PMID:24260425

Cui, Jian Dong; Li, Lian Lian; Bian, Hong Jie

2013-01-01

14

Immobilization of cross-linked phenylalanine ammonia lyase aggregates in microporous silica gel.  

PubMed

A separable and highly-stable enzyme system was developed by adsorption of phenylalanine ammonia lyase (PAL) from Rhodotorula glutinis in amino-functionalized macroporous silica gel and subsequent enzyme crosslinking. This resulted in the formation of cross-linked enzyme aggregates (PAL-CLEAs) into macroporous silica gel (MSG-CLEAs). The effect of adsorptive conditions, type of aggregating agent, its concentration as well as that of cross-linking agent was studied. MSG-CLEAs production was most effective using ammonium sulfate (40%-saturation), followed by cross-linking for 1 h with 1.5% (v/v) glutaraldehyde. The resulting MSG-CLEAs extended the optimal temperature and pH range compared to free PAL and PAL-CLEAs. Moreover, MSG-CLEAs exhibited the excellent stability of the enzyme against various deactivating conditions such as temperature and denaturants, and showed higher storage stability compared to the free PAL and the conventional PAL-CLEAs. Such as, after 6 h incubation at 60°C, the MSG-CLEAs still retained more than 47% of the initial activity whereas PAL-CLEAs only retained 7% of the initial activity. Especially, the MSG-CLEAs exhibited good reusability due to its suitable size and active properties. These results indicated that PAL-CLEAs on MSG might be used as a feasible and efficient solution for improving properties of immobilized enzyme in industrial application. PMID:24260425

Cui, Jian Dong; Li, Lian Lian; Bian, Hong Jie

2013-01-01

15

Microencapsulation of islets within alginate/poly(ethylene glycol) gels cross-linked via Staudinger ligation  

PubMed Central

Functionalized alginate and PEG polymers were used to generate covalently linked alginate-PEG (XAlgPEG) microbeads of high stability. The cell-compatible Staudinger ligation scheme was used to chemoselectively cross-link phosphine-terminated poly(ethylene glycol) (PEG) to azide-functionalized alginate, resulting in XAlgPEG hydrogels. XAlgPEG microbeads were formed by co-incubation of the two polymers, followed by ionic cross-linking of the alginate using barium ions. The enhanced stability and gel properties of the resulting XAlgPEG microbeads, as well as the compatibility of these polymers for the encapsulation of islets and beta cells lines, were investigated. Our data show that XAlgPEG microbeads exhibit superior resistance to osmotic swelling compared to traditional barium cross-linked alginate (Ba-Alg) beads, with a 5-fold reduction in observed swelling, as well as resistance to dissolution via chelation solution. Diffusion and porosity studies found XAlgPEG beads to exhibit properties comparable to standard Ba-Alg. Our data found XAlgPEG microbeads to be highly cell compatible with insulinoma cell lines, as well as rat and human pancreatic islets, where the viability and functional assessment of cells within XAlgPEG were comparable to Ba-Alg controls. The remarkable improved stability, as well as demonstrated cellular compatibility, of XAlgPEG hydrogels makes them an appealing option for a wide variety of tissue engineering applications. PMID:20654745

Hall, Kristina K.; Gattás-Asfura, Kerim M.; Stabler, Cherie L.

2010-01-01

16

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

NASA Astrophysics Data System (ADS)

Stationary crack propagation in rubbers and chemically cross-linked gels is studied by a new molecular theory of fracture in polymer networks. The fracture energy G (energy required to create a unit free surface by fracture) as a function of the crack velocity V is shown to obey, when measured in the unit of ?lkBT, a master curve as a function of the dimensionless velocity 2tan ?V/l?0(T), where ? is the number density of the network chains, T is absolute temperature, ? is the angle of the crack tip, l is the mean distance between the adjacent cross-links, and ?0(T) is the scission rate of the chains. The slope of the master curve in logarithmic scale depends on the nature of chain rupture; it takes a small value 0.16-0.2 in the low velocity region, and exhibits a crossover to the three times larger value 0.5-0.6 in the high velocity region. The ultimate strength G0 as defined by the fracture energy in the limit of zero crack velocity is obtained as a function of the molecular weight of the network chain, the bond energy, and temperature. The theoretical model is applied specifically to peeling and tearing experiments of rubbers and gels to study how the velocity affects the fracture energy in different geometry of network breakage. All results are qualitatively compared with the data reported in the literature.

Tanaka, Fumihiko

2014-10-01

17

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

PubMed

Stationary crack propagation in rubbers and chemically cross-linked gels is studied by a new molecular theory of fracture in polymer networks. The fracture energy G (energy required to create a unit free surface by fracture) as a function of the crack velocity V is shown to obey, when measured in the unit of ?lkBT, a master curve as a function of the dimensionless velocity 2tan??V/l?0(T), where ? is the number density of the network chains, T is absolute temperature, ? is the angle of the crack tip, l is the mean distance between the adjacent cross-links, and ?0(T) is the scission rate of the chains. The slope of the master curve in logarithmic scale depends on the nature of chain rupture; it takes a small value 0.16-0.2 in the low velocity region, and exhibits a crossover to the three times larger value 0.5-0.6 in the high velocity region. The ultimate strength G0 as defined by the fracture energy in the limit of zero crack velocity is obtained as a function of the molecular weight of the network chain, the bond energy, and temperature. The theoretical model is applied specifically to peeling and tearing experiments of rubbers and gels to study how the velocity affects the fracture energy in different geometry of network breakage. All results are qualitatively compared with the data reported in the literature. PMID:25296834

Tanaka, Fumihiko

2014-10-01

18

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

PubMed

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

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

2014-07-22

19

Enzymatic cross-linking of soy proteins within non-fat set yogurt gel.  

PubMed

Soy proteins as the health-promoting ingredients and candidate fat substitutes in dairy products are good substrates for the cross-linking action of the enzyme transglutaminase. Non-fat set yogurt samples were prepared from the milks enriched with soy protein isolate (SPI) and/or treated with the enzyme transglutaminase. The highest titrable acidity was recorded for the yogurt enriched with SPI and treated with the enzyme throughout the cold storage for 21 d. SPI-enrichment of yogurt milk increased the water holding capacity. Although enrichment with SPI did not influence the count of Streptococcus themophilus, increased that of Lactobacillus bulgaricus ?3 log cycles. The enzymatic treatment of SPI-enriched milk however, suppressed the bacteria growth-promoting influence of SPI due probably to making the soy proteins inaccessible for Lactobacillus. SPI-enrichment and enzymatic treatment of milk decreased the various organic acids content in yoghurt samples; influence of the former was more significant. The cross-linking of milk proteins to soy proteins was confirmed with the gel electrophoresis results. PMID:25052439

Soleymanpuori, Rana; Madadlou, Ashkan; Zeynali, Fariba; Khosrowshahi, Asghar

2014-08-01

20

Cross-linked gel polymer electrolyte containing multi-wall carbon nanotubes for application in dye-sensitized solar cells  

NASA Astrophysics Data System (ADS)

A cross-linked gel polymer electrolyte composed of poly (ethylene oxide-co-2-(2-methoxyethoxy) ethyl glycidyl ether-co-allyl glycidyl ether, ?-butyrolactone, LiI and I2, mixed with functionalized multi-wall carbon nanotubes (MWCNT), was applied in dye-sensitized solar cells (DSSC). The electrolyte was characterized by differential scanning calorimetry, conductivity measurements and Raman spectroscopy. Due to its nature, the terpolymer was chemically cross-linked during DSSC assembly to give rise to quasi-solid state solar cells. The gel polymer electrolyte containing 1 wt% of MWCNT exhibited conductivity values higher than 10-3 S cm-1. An increase in MWCNT content provided a smaller concentration of polyiodide species, as confirmed by Raman spectroscopy. The highest photocurrent (8.74 mA cm-2) was achieved by DSSC based on the cross-linked gel polymer electrolyte containing 1 wt% of MWCNT compared to DSSC based on non-cross-linked gel polymer electrolytes (7.93 mA cm-2). The incorporation of 3 wt% of MWCNT into the gel polymer electrolyte promoted a decrease in both Jsc and Voc, probably due to poorer light transmittance of the electrolyte in the visible range and higher charge recombination losses, respectively. Thus, the highest efficiency in this work was achieved by using electrolyte containing 1 wt% of MWCNT. After the cross-linking process, the dimensional stability of the gel composite electrolyte was improved and the conversion efficiency of DSSC was only slightly affected, changing from 3.37% (before cross-linking) to 3.35%.

Benedetti, João E.; Corrêa, Aline A.; Carmello, Mayara; Almeida, Luiz C. P.; Gonçalves, Agnaldo S.; Nogueira, Ana F.

2012-06-01

21

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

PubMed

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

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

2011-05-15

22

Photo-initiated cross-linked polyacrylamide gels for microdevice electrophoresis  

E-print Network

complex micro-channel network. The rate of photo-initiation in the free radical gel polymerization reaction, however, can exert a strong influence on the resulting gel structure. Experimental data on separation resolution of single stranded DNA (ss...

Agrawal, Shilpa

2005-08-29

23

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

PubMed Central

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.

2012-01-01

24

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

PubMed

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

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

2014-10-01

25

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

26

A Study of Cross-linked Regions of Poly(Vinyl Alcohol) Gels by Small-Angle Neutron Scattering  

NASA Astrophysics Data System (ADS)

A poly(vinyl alcohol)-borax cross-linked hydrogel has been studied by Small Angle Neutron Scattering as a function of borax concentration in the wave-vector transfer (Q) range of 0.017 Å-1 to 0.36 Å-1. It is found that as the concentration of borax increases, so does the intensity of scattering in this range. Beyond a borax concentration of 2 mg/ml, the increase in cross-linked PVA chains leads to cross-linked units larger than 150 Å as evidenced by a reduction in intensity in the lower Q region.

Lawrence, Mathias B.; Desa, J. A. E.; Aswal, V. K.

2011-07-01

27

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

PubMed Central

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

Sugahara, Michihiro

2014-01-01

28

Cross-linked supramolecular polymer gels constructed from discrete multi-pillar[5]arene metallacycles and their multiple stimuli-responsive behavior.  

PubMed

A new family of discrete hexakis-pillar[5]arene metallacycles with different sizes have been successfully prepared via coordination-driven self-assembly, which presented very few successful examples of preparation of discrete multiple pillar[n]arene derivatives. These newly designed hexakis-pillar[5]arene metallacycles were well characterized with one-dimensional (1-D) multinuclear NMR ((1)H and (31) P NMR), two-dimensional (2-D) (1)H-(1)H COSY and NOESY, ESI-TOF-MS, elemental analysis, and PM6 semiempirical molecular orbital methods. Furthermore, the host-guest complexation of such hexakis-pillar[5]arene hosts with a series of different neutral ditopic guests G1-6 were well investigated. Through host-guest interactions of hexakis-pillar[5]arene metallacycles H2 or H3 with the neutral dinitrile guest G5, the cross-linked supramolecular polymers H2?(G5)3 or H3?(G5)3 were successfully constructed at the high-concentration region, respectively. Interestingly, these cross-linked supramolecular polymers transformed into the stable supramolecular gels upon increasing the concentrations to a relatively high level. More importantly, by taking advantage of the dynamic nature of metal-ligand bonds and host-guest interactions, the reversible multiple stimuli-responsive gel-sol phase transitions of such polymer gels were successfully realized under different stimuli, such as temperature, halide, and competitive guest, etc. The mechanism of such multiple stimuli-responsive processes was well illustrated by in situ multinuclear NMR investigation. This research not only provides a highly efficient approach to the preparation of discrete multiple pillar[n]arene derivatives but also presents a new family of multiple stimuli-responsive "smart" soft matters. PMID:24571308

Li, Zhong-Yu; Zhang, Yanyan; Zhang, Chang-Wei; Chen, Li-Jun; Wang, Chao; Tan, Hongwei; Yu, Yihua; Li, Xiaopeng; Yang, Hai-Bo

2014-06-18

29

Increasing the maximum achievable strain of a covalent polymer gel through the addition of mechanically invisible cross-links.  

PubMed

Hydrogels and organogels made from polymer networks are widely used in biomedical applications and soft, active devices for which the ability to sustain large deformations is required. The strain at which polymer networks fracture is typically improved through the addition of elements that dissipate energy, but these materials require extra work to achieve a given, desired level of deformation. Here, the addition of mechanically "invisible" supramolecular crosslinks causes substantial increases in the ultimate gel properties without incurring the added energetic costs of dissipation. PMID:25044398

Kean, Zachary S; Hawk, Jennifer L; Lin, Shaoting; Zhao, Xuanhe; Sijbesma, Rint P; Craig, Stephen L

2014-09-10

30

Gold nanoparticle mediated designing of non-hydrolytic sol-gel cross-linked metformin imprinted polymer network: a theoretical and experimental study.  

PubMed

A sensitive and selective electrochemical sensor based on molecularly imprinted polymers was developed for trace level detection of metformin-an antidiabetic drug. For the first time, we have applied non-hydrolytic sol-gel matrix as a cross-linking agent in the field of molecular imprinting. To create the sol-gel matrix and enhance the electro-conductivity of the proposed sensor citrate-capped gold nanoparticle were used. The morphologies and properties of the sensor were characterized by scanning electron microscopy, cyclic voltammetry, electron impedance spectroscopy, chronocoulometry and differential pulse voltammetry. Energy of the HOMO and LUMO orbitals and Mülliken's atomic charges of template molecule were also calculated using density functional theory utilizing B3LYP with 3-21G-basis set. The theoretical results allied to the diagnostic criteria of the cyclic voltammetry indicate that the metformin redox mechanism is associated to the irreversible oxidation process of metformin-imino-group to N-hydroxyimino-group. The results demonstrated that the prepared sensor had excellent selectivity and high sensitivity for metformin in the linear range from 0.02 to 80 ng ml(-1) with a detection limit of 0.005 ng ml(-1) (S/N=3). The sensor was also successfully employed to detect metformin in pharmaceutical sample. PMID:24468360

Roy, Ekta; Patra, Santanu; Madhuri, Rashmi; Sharma, Prashant K

2014-03-01

31

Oxidative cross-linking of casein by horseradish peroxidase and its impacts on emulsifying properties and the microstructure of acidified gel  

Microsoft Academic Search

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

Junwen Li; Xinhuai Zhao

32

Agarose and Polyacrylamide Gel Electrophoresis Methods for Molecular Mass Analysis of 5–500 kDa Hyaluronan  

PubMed Central

Agarose and polyacrylamide gel electrophoresis systems for the molecular mass-dependent separation of hyaluronan (HA) in the size range of approximately 5–500 kDa have been investigated. For agarose-based systems, the suitability of different agarose types, agarose concentrations, and buffers systems were determined. Using chemoenzymatically synthesized HA standards of low polydispersity, the molecular mass range was determined for each gel composition, over which the relationship between HA mobility and logarithm of the molecular mass was linear. Excellent linear calibration was obtained for HA molecular mass as low as approximately 9 kDa in agarose gels. For higher resolution separation, and for extension to molecular masses as low as approximately 5 kDa, gradient polyacrylamide gels were superior. Densitometric scanning of stained gels allowed analysis of the range of molecular masses present in a sample, and calculation of weight-average and number-average values. The methods were validated for polydisperse HA samples with viscosity-average molecular masses of 112, 59, 37, and 22 kDa, at sample loads of 0.5 µg (for polyacrylamide) to 2.5 µg (for agarose). Use of the methods for electrophoretic mobility shift assays was demonstrated for binding of the HA-binding region of aggrecan (recombinant human aggrecan G1-IGD-G2 domains) to a 150 kDa HA standard. PMID:21684248

Bhilocha, Shardul; Amin, Ripal; Pandya, Monika; Yuan, Han; Tank, Mihir; LoBello, Jaclyn; Shytuhina, Anastasia; Wang, Wenlan; Wisniewski, Hans-Georg; de la Motte, Carol; Cowman, Mary K.

2011-01-01

33

Functional Properties of Hydroxypropylated, Cross-Linked, and Hydroxypropylated Cross-Linked Tuber and Root Starches  

Microsoft Academic Search

Cereal Chem. 84(1):30-37 Functional properties of some underexploited tuber and root starches (true yam, gourd yam, taro, lotus, and sweet potato) were investigated before and after hydroxypropylation, cross-linking, and hydroxypropylation and cross-linking using potato starch as the reference. Low swelling ability, poor viscosity development but high shear stability, gel hardness, and resistance to enzyme hydrolysis was observed in starches from

Anil Gunaratne; Harold Corke

2007-01-01

34

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. PMID:17441735

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

2008-01-01

35

Hyaluronan: from extracellular glue to pericellular cue  

Microsoft Academic Search

Hyaluronan is an extracellular and cell-surface-associated polysaccharide that is traditionally regarded as a biological 'goo' that participates in lubricating joints or holding together gel-like connective tissues. Although these are common physiological roles of hyaluronan in adult organisms, hyaluronan also functions as a microenvironmental cue that co-regulates cell behaviour during embryonic development, healing processes, inflammation and tumour development. Recent work highlights

Bryan P. Toole

2004-01-01

36

Absorption of Hyaluronan Applied to the Surface of Intact Skin  

Microsoft Academic Search

Hyaluronan has recently been introduced as a vehicle for topical application of drugs to the skin. We sought to determine whether hyaluronan acts solely as a hydrophilic reservoir on the surface of intact skin or might partly penetrate it. Drug-free hyaluronan gels were applied to the intact skin of hairless mice and human forearm in situ, with and without [3H

Tracey J Brown; Daine Alcorn; J RoberT E Fraser; Robert Fraser

1999-01-01

37

Cross-Linked Polymers Video  

NSDL National Science Digital Library

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

2014-09-04

38

Hyaluronan in human malignancies  

SciTech Connect

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

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

2011-02-15

39

p-NN'-phenylenebismaleimide, a specific cross-linking agent for F-actin.  

PubMed Central

Covalent cross-links can be inserted between the subunits of F-actin by using p-NN'-phenylenebismaleimide. Cross-linking reaches its maximum value when one molecule of reagent has reacted with each actin subunit. p-NN'-Phenylenebismaleimide reacts initially with a cysteine residue on one subunit, the slower cross-linking reaction involving a lysine residue on a neighbouring subunit. Hydrolysis of the actin-bound reagent limits the extent of cross-linking. Quantitative analysis of the amounts of cross-linked oligomers seen on polyacrylamide gels containing sodium dodecyl sulphate suggests that neither the binding of the reagent to actin nor the formation of cross-links introduces strain into the structure. The cross-links do not join together different F-actin filaments, and evidence is presented that suggests that the cross-links join subunits of the same long-pitched helix. Images Fig. 1. PMID:743226

Knight, P; Offer, G

1978-01-01

40

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. PMID:23925327

Rao, Srinivas K

2013-01-01

41

DNA Interstrand Cross-Linking Activity of (1-Chloroethenyl)oxirane, a Metabolite of ?-chloroprene  

PubMed Central

With the goal of elucidating the molecular and cellular mechanisms of chloroprene toxicity, we examined the potential DNA cross-linking of the bifunctional chloroprene metabolite, (1-chloroethenyl)oxirane (CEO). We used denaturing polyacrylamide gel electrophoresis to monitor possible formation of interstrand cross-links by CEO within synthetic DNA duplexes. Our data suggest interstrand cross-linking at deoxyguanosine residues within 5?-GC and 5?-GGC sites, with the rate of cross-linking depending on pH (pH 5.0 > pH 6.0 > pH 7.0). A comparison of the cross-linking efficiencies of CEO and the structurally similar cross-linkers diepoxybutane (DEB) and epichlorohydrin (ECH) revealed that DEB > CEO ? ECH. Furthermore, we found that cytotoxicity correlates with cross-linking efficiency, supporting a role for interstrand cross-links in the genotoxicology of chloroprene. PMID:20030381

Wadugu, Brian A.; Ng, Christopher; Bartley, Bethany L.; Rowe, Rebecca J.; Millard, Julie T.

2010-01-01

42

Molecular structure of citric acid cross-linked starch films.  

PubMed

The effect of citric acid (CA) on starch films has been examined. A new method to detect cross-linking of starch by CA in solution-cast films by molecular weight measurements is described. Furthermore, we managed to distinguished between free, mono- and di-esterified CA and quantify di-ester content within starch films by using a modification in the method of complexometric titration with copper(II)-sulfate. Cross-linking of starch by CA occurred at low temperature, 70°C, which we assumed is so far the lowest temperature reported where cross-linking reaction occurred. This is essential for starch coating applications within paper industry since no high temperatures for curing will be required. However, curing at 150°C and high CA concentrations, 30 pph, increased cross-linking reaction. Furthermore, the physical properties like water solubility, gel content and glass transition temperature, were highly reflected by changes in the molecular structure i.e. cross-linking and hydrolysis, as well as CA content and curing temperature. PMID:23688480

Menzel, Carolin; Olsson, Erik; Plivelic, Tomás S; Andersson, Roger; Johansson, Caisa; Kuktaite, Ramune; Järnström, Lars; Koch, Kristine

2013-07-01

43

Comparative analysis of hyaluronan gel and xanthan-based chlorhexidine gel, as adjunct to scaling and root planing with scaling and root planing alone in the treatment of chronic periodontitis: A preliminary study  

PubMed Central

Aim: The aim of this study was to evaluate the effects of hyaluronan (HA) and chlorhexidine (CHX) gels as adjunct to scaling and root planing (SRP) in the treatment of chronic periodontitis. Materials and Methods: Sixty patients within the age group of 30-65 years recruited to participate in the study were randomly equally divided into three groups. Complete SRP and subgingival debridement were performed within 6 h in all the patients. For control (Group I) patients, SRP was the only treatment modality given; for Group II and III patients, at least 8 teeth with 4-8 mm probing pocket depth (PPD) were selected for subgingival application of HA gel and CHX gel, respectively. Clinical periodontal parameters such as gingival index, PPD, and clinical attachment level (CAL) were recorded at baseline and 3 months, whereas plaque index was recorded at baseline, 1 month, and 3 months. For measuring systemic/hematological parameters, blood samples for laboratory tests for total leucocyte count (TLC), differential leucocyte count (DLC), and C-reactive protein (CRP) were obtained using standard 2-mL syringe from each subject in all the three groups at baseline, 24 h, and on the 1 month and 3 months post-baseline. Results: In all the three groups, a significant reduction in PPD and gain in CAL were observed between baseline and 3 months follow-up (P< 0.05); however, at 3 months, change in PPD and CAL was more in Group II than Group III, but the difference was non-significant, and Group I (control) showed less changes in PPD and CAL than both experimental groups. Only one patient revealed positive value for CRP at baseline only, and hence could not be statistically analyzed. In all the three groups, the peak values for TLC count were observed at 24 h. At 1-month and 3-month intervals, a significant improvement in TLC and DLC counts was observed among the experimental (HA gel/SRP and Xan-CHX gel) groups as compared to control group (SRP alone). PMID:23853453

Chauhan, Avinash Singh; Bains, Vivek K.; Gupta, Vivek; Singh, G. P.; Patil, Sudhir S.

2013-01-01

44

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. PMID:21703990

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

45

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

46

Hyaluronan Synthesis and Myogenesis  

PubMed Central

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

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

2013-01-01

47

Variation of polyelectrolyte film stiffness by photo-cross-linking: a new way to control cell adhesion.  

PubMed

We report on the preparation of polyelectrolyte films based on biopolymers whose nanomechanical properties can be tuned by photo-cross-linking. Cationic poly(L-lysine) was layer-by-layer assembled with anionic hyaluronan (HA) derivatives modified by photoreactive vinylbenzyl (VB) groups. The study of the multilayer buildup by quartz crystal microbalance with dissipation monitoring showed that the presence of VB groups does not influence significantly the multilayer growth. Then the VB-modified HA incorporated into the films was cross-linked upon UV irradiation. UV spectroscopy measurements showed that the cross-linking rate of the multilayers increases with the amount of VB groups grafted onto HA chains. Force measurements performed by atomic force microscopy with a colloidal probe proved that the rigidity of the cross-linked films increases with the grafting degree of HA chains and consequently the number of cross-links. Cell culture assays performed on non-cross-linked and photo-cross-linked films with myoblast cells demonstrated that cell adhesion and proliferation are considerably improved with increasing film rigidity. PMID:19275180

Vázquez, Cuauhtémoc Pozos; Boudou, Thomas; Dulong, Virginie; Nicolas, Claire; Picart, Catherine; Glinel, Karine

2009-04-01

48

Physicochemical properties of collagen solutions cross-linked by glutaraldehyde.  

PubMed

The physicochemical properties of collagen solutions (5 mg/ml) cross-linked by various amounts of glutaraldehyde (GTA) [GTA/collagen (w/w)?= 0-0.5] under acidic condition (pH 4.00) were examined. Based on the results of the determination of residual amino group content, sodium dodecyl sulphate-polyacrylamide gel electrophoresis, dynamic rheological measurements, differential scanning calorimetry and atomic force microscopy (AFM), it was proved that the collagen solutions possessed strikingly different physicochemical properties depending on the amount of GTA. At low GTA amounts [GTA/collagen (w/w)?? 0.1], the residual amino group contents of the cross-linked collagens decreased largely from 100% to 32.76%, accompanied by an increase in the molecular weight. Additionally, increases of the fiber diameter and the values of G', G? and ?* were measured, while the thermal denaturation temperature (Td) did not change visibly and the fluidity of collagen samples was still retained with increasing the GTA amount. When the ratio of GTA to collagen exceeded 0.1, although the residual amino group content only decreased by ~8.2%, the cross-linked collagen solution [GTA/collagen (w/w)?= 0.3] displayed a clear loss of flow and a sudden rise (~2.0 °C) of the Td value compared to the uncross-linked collagen solution, probably illustrating that the collagen solution was converted into a gel with mature network structure-containing nuclei observed in AFM image. It was conjectured that the physicochemical properties of the collagen solutions might be in connection with the cross-linking between collagen molecules from the same aggregate or different aggregates. PMID:24564765

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

2014-06-01

49

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

NASA Astrophysics Data System (ADS)

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

Vink, Richard L. C.; Heussinger, Claus

2012-01-01

50

Cross-linking reconsidered: binding and cross-linking fields and the cellular response.  

PubMed Central

We analyze a model for the reversible cross-linking of cell surface receptors by a collection of bivalent ligands with different affinities for the receptor as would be found in a polyclonal anti-receptor serum. We assume that the amount of cross-linking determines, via a monotonic function, the rate at which cells become activated and divide. In addition to the density of receptors on the cell surface, two quantities, the binding field and the cross-linking field, are needed to characterize the cross-linking curve, i.e., the equilibrium concentration of cross-linked receptors plotted as a function of the total ligand site concentration. The binding field is the sum of all ligand site concentrations weighted by their respective binding affinities, and the cross-linking field is the sum of all ligand site concentrations weighted by the product of their respective binding and cross-linking affinity and the total receptor density. Assuming that the cross-linking affinity decreases if the binding affinity decreases, we find that the height of the cross-linking curve decreases, its width narrows, and its center shifts to higher ligand site concentrations as the affinities decrease. Moreover, when we consider cross-linking-induced proliferation, we find that there is a minimum cross-linking affinity that must be surpassed before a clone can expand. We also show that under many circumstances a polyclonal antiserum would be more likely than a monoclonal antibody to lead to cross-linking-induced proliferation. Images FIGURE 1 FIGURE 2 FIGURE 5 PMID:8785275

Sulzer, B; De Boer, R J; Perelson, A S

1996-01-01

51

Phased psoralen cross-links do not bend the DNA double helix  

SciTech Connect

Although the chemical reaction of psoralens with nucleic acids is well understood, the structure of psoralen-DNA cross-linked products is still not clear. Model building studies based on the crystal structure of the psoralen-thymine monoadduct suggest that each cross-link bends the DNA double helix by 46.5/sup 0/. Here the authors use gel electrophoresis to test the validity of the current models. They have synthesized a series of DNA fragments (21-24 base pairs in length), each containing one unique T-A site for 4'-(hydroxymethyl)-4,5'8-trimethylpsoralen (HMT) cross-linking. Because of an estimated 28/sup 0/ unwinding of the helix by HMT, one expects that the 22-bp cross-linked fragment will be repeated nearly in phase with the average helical screw when multimerized. In that sequence ligation will maximally amplify any deformation to the double helix. They find that the ligated multimers of cross-linked DNA migrate close to the multimers of non-cross-linked DNA on polyacrylamide gels. These observations place an upper limit of 10/sup 0/ on DNA bending induced by psoralen cross-linking and indicate unwinding by about 1 bp, as well as stiffening of the double helix. These properties are not unexpected for classical intercalators.

Haran, T.E.; Crothers, D.M.

1988-09-06

52

Cross-linking between histones and DNA following treatment with a series of dimethane sulphonate esters  

Microsoft Academic Search

The cross-linking on the nucleohistone to the associated DNA by a series of methaneusulphonates of the busulphan series (CH3SO2O(CH2)nOSO2CH3) from n=4–9 has been studied by gel electrophoresis, by the use of 35S labelling and by pyrenemaleimide competition. It has been shown that all the dimethanesulphonates react with the Cys 114 of histone H3, and that octamethylene dimethanesulphonate (n=8) cross-links histone

J. A. Hartley; B. W. Fox

1986-01-01

53

Cross-linking chemistry of squid beak.  

PubMed

In stark contrast to most aggressive predators, Dosidicus gigas (jumbo squids) do not use minerals in their powerful mouthparts known as beaks. Their beaks instead consist of a highly sclerotized chitinous composite with incremental hydration from the tip to the base. We previously reported l-3,4-dihydroxyphenylalanine (dopa)-histidine (dopa-His) as an important covalent cross-link providing mechanical strengthening to the beak material. Here, we present a more complete characterization of the sclerotization chemistry and describe additional cross-links from D. gigas beak. All cross-links presented in this report share common building blocks, a family of di-, tri-, and tetra-histidine-catecholic adducts, that were separated by affinity chromatography and high performance liquid chromatography (HPLC) and identified by tandem mass spectroscopy and proton nuclear magnetic resonance ((1)H NMR). The data provide additional insights into the unusually high cross-link density found in mature beaks. Furthermore, we propose both a low molecular weight catechol, and peptidyl-dopa, to be sclerotization agents of squid beak. This appears to represent a new strategy for forming hard tissue in animals. The interplay between covalent cross-linking and dehydration on the graded properties of the beaks is discussed. PMID:20870720

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

2010-12-01

54

Cross-linking Chemistry of Squid Beak*  

PubMed Central

In stark contrast to most aggressive predators, Dosidicus gigas (jumbo squids) do not use minerals in their powerful mouthparts known as beaks. Their beaks instead consist of a highly sclerotized chitinous composite with incremental hydration from the tip to the base. We previously reported l-3,4-dihydroxyphenylalanine (dopa)-histidine (dopa-His) as an important covalent cross-link providing mechanical strengthening to the beak material. Here, we present a more complete characterization of the sclerotization chemistry and describe additional cross-links from D. gigas beak. All cross-links presented in this report share common building blocks, a family of di-, tri-, and tetra-histidine-catecholic adducts, that were separated by affinity chromatography and high performance liquid chromatography (HPLC) and identified by tandem mass spectroscopy and proton nuclear magnetic resonance (1H NMR). The data provide additional insights into the unusually high cross-link density found in mature beaks. Furthermore, we propose both a low molecular weight catechol, and peptidyl-dopa, to be sclerotization agents of squid beak. This appears to represent a new strategy for forming hard tissue in animals. The interplay between covalent cross-linking and dehydration on the graded properties of the beaks is discussed. PMID:20870720

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

2010-01-01

55

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

56

Cross-linked structure of network evolution.  

PubMed

We study the temporal co-variation of network co-evolution via the cross-link structure of networks, for which we take advantage of the formalism of hypergraphs to map cross-link structures back to network nodes. We investigate two sets of temporal network data in detail. In a network of coupled nonlinear oscillators, hyperedges that consist of network edges with temporally co-varying weights uncover the driving co-evolution patterns of edge weight dynamics both within and between oscillator communities. In the human brain, networks that represent temporal changes in brain activity during learning exhibit early co-evolution that then settles down with practice. Subsequent decreases in hyperedge size are consistent with emergence of an autonomous subgraph whose dynamics no longer depends on other parts of the network. Our results on real and synthetic networks give a poignant demonstration of the ability of cross-link structure to uncover unexpected co-evolution attributes in both real and synthetic dynamical systems. This, in turn, illustrates the utility of analyzing cross-links for investigating the structure of temporal networks. PMID:24697374

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

2014-03-01

57

A new, mild cross-linking methodology to prepare cross-linked enzyme aggregates.  

PubMed

Cross-linked enzyme aggregates (CLEAs) were prepared from several enzymes (penicillin G acylase, hydroxynitrile lyase, alcohol dehydrogenase, and two different nitrilases) by precipitation and subsequent cross-linking using dextran polyaldehyde. In most cases, higher immobilization yields were obtained using the latter cross-linker as compared with the commonly used glutaraldehyde. Active site titration of penicillin acylase CLEAs showed that the higher activity originated from a significantly lower loss in active sites using dextran polyaldehyde as a cross-linking agent. It is proposed that macromolecular cross-linkers are too large to penetrate the protein active site and react with catalytically essential amino acid residues. PMID:15083507

Mateo, Cesar; Palomo, José M; van Langen, Luuk M; van Rantwijk, Fred; Sheldon, Roger A

2004-05-01

58

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. PMID:23925328

Padmanabhan, Prema; Dave, Abhishek

2013-01-01

59

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

PubMed

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

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

2013-04-01

60

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

PubMed

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

Fallqvist, B; Kulachenko, A; Kroon, M

2014-06-01

61

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

2013-06-26

62

Cross-linking for microbial keratitis  

PubMed Central

The success of collagen cross-linking as a clinical modality to modify the clinical course in keratoconus seems to have fueled the search for alternative applications for this treatment. Current clinical data on its efficacy is limited and laboratory data seems to indicate that it performs poorly against resistant strains of bacteria and against slow growing organisms. However, the biological plausibility of crosslinking and the lack of effective strategies in managing infections with these organisms continue to focus attention on this potential treatment. Well-conducted experimental and clinical studies with controls are required to answer the questions of its efficacy in future. PMID:23925334

Vazirani, Jayesh; Vaddavalli, Pravin K

2013-01-01

63

General protein-protein cross-linking.  

PubMed

This protocol describes a general protein-to-protein cross-linking procedure using the water-soluble amine-reactive homobifunctional BS(3) (bis[sulfosuccinimidyl] suberate); however, the protocol can be easily adapted using other cross-linkers of similar properties. BS(3) is composed of two sulfo-NHS ester groups and an 11.4 Å linker. Sulfo-NHS ester groups react with primary amines in slightly alkaline conditions (pH 7.2-8.5) and yield stable amide bonds. The reaction releases N-hydroxysuccinimide (see an application of NHS esters on Labeling a protein with fluorophores using NHS ester derivitization). PMID:24581440

Alegria-Schaffer, Alice

2014-01-01

64

Cross-linked carbon nanotube heat spreader  

NASA Astrophysics Data System (ADS)

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

Konesky, Gregory

2014-09-01

65

The properties of water in swollen cross-linked polystyrene sulfo acids  

NASA Astrophysics Data System (ADS)

The properties of water in polystyrene sulfo acid gels with various cross-linking degrees were studied by optical volumetry and dynamic desorption porosimetry. The isotherms of water desorption obtained by dynamic desorption porosimetry coincided with isopiestic isotherms, which allowed this method to be recommended for the determination of the amount of water in polymer gels. Joint optical volumetry and dynamic desorption porosimetry studies showed that the interphase boundary in the cross-liked hydrophilic polymer-water system did not coincide with the visible gel boundary, because gels were two-phase systems, which contained water of two types, “free” and “bound.” The influence of the degree of polymer cross-linking on the amounts and properties of water of the two types was studied. It was shown that constants of water distribution in the polymer could be calculated from the dynamic desorption porosimetry data.

Gagarin, A. N.; Tokmachev, M. G.; Kovaleva, S. S.; Ferapontov, N. B.

2008-11-01

66

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

PubMed

An effective cross-linking of alginate gel was made through reaction with calcium carbonate (CaCO3). We used human chondrocytes as a model cell to study the effects of cross-linking density. Three different pore size ranges of cross-linked alginate hydrogels were fabricated. The morphological, mechanical, and rheological properties of various alginate hydrogels were characterized and responses of biosynthesis of cells encapsulated in each gel to the variation in cross-linking density were investigated. Desired outer shape of structure was maintained when the alginate solution was cross-linked with the applied method. The properties of alginate hydrogel could be tailored through applying various concentrations of CaCO3. The rate of synthesized GAGs and collagens was significantly higher in human chondrocytes encapsulated in the smaller pore structure than that in the larger pore structure. The expression of chondrogenic markers, including collagen type II and aggrecan, was enhanced in the smaller pore structure. It was found that proper structural morphology is a critical factor to enhance the performance and tissue regeneration. PMID:24880568

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

2014-09-01

67

Chicken Corneocyte Cross-Linked Proteome  

PubMed Central

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

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

2013-01-01

68

Corneal collagen cross-linking: A review  

PubMed Central

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

O'Brart, David P.S.

2014-01-01

69

Hyaluronan and Stone Disease  

NASA Astrophysics Data System (ADS)

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

Asselman, Marino

2008-09-01

70

Inhibition of blood coagulation factor XIIIa-mediated cross-linking between fibronectin and collagen by polyamines.  

PubMed

Soluble fibronectin is found in body fluids and media of cultured adherent cells. Insoluble fibronectin is found in tissue stroma and in extracellular matrices of cultured cells. Fibronectin is a substrate for factor XIIIa (plasma transglutaminase) and can be cross-linked to collagen and to the alpha chain of fibrin. We have used sodium dodecyl sulfate-polyacrylamide gel electrophoresis to investigate the possibility that factor XIIIa-mediated cross-linking is influenced by polyamines. Spermidine inhibited cross-linking between fibronectin and type I collagen, isolated alpha 1 (I) collagen chains, or iodinated cyanogen bromide fragment 7 of alpha 1 (I) chains (125I-alpha 1 (I)-CB7). Half-maximal inhibition of cross-linking between 125I-alpha (I)-CB7 and fibronectin was observed when 0.1 mM spermine or spermidine was present. Spermidine, 0.7 mM, partially inhibited cross-linking between fibronectin and the alpha chain of fibrin but failed to inhibit cross-linking between the fibrin monomers of a fibrin clot. Spermidine also failed to inhibit cross-linking between fibronectin molecules when aggregation of fibronectin was induced with dithiothreitol. In contrast, 0.7 mM monodanyslcadaverine inhibited fibronectin-collagen, fibronectin-fibrin, fibronectin-fibronectin, and fibrin-fibrin cross-linking. Spermidine or spermine, 0.7 mM, enhanced the cross-linking between molecules of partially amidinated fibronectin, suggesting that N1,8-(di-gamma-glutamyl)-polyamine cross-linkages were formed. Spermidine and spermine failed to enhance cross-linking between monomers of amidinated fibrin. These results indicate that physiologic concentrations of polyamines specifically disturb transglutaminase-catalyzed cross-linking between fibronectin and collagen. PMID:548650

Mosher, D F; Schad, P E; Kleinman, H K

1979-01-01

71

Additional Applications of Corneal Cross Linking  

PubMed Central

Corneal collagen cross-linking (CxL) is a prevalent surgical method for the management of keratoconus. However, literature suggests that, further to keratoconus, CxL has a beneficial impact on a series of corneal related diseases and states. This article attempts to provide a contemporary review for all additional applications of CxL. Specifically, it outlines the most recent studies that demonstrate the beneficial impact of CxL for iatrogenic ectasias, pellucid marginal degeneration, infectious keratitis, bullous keratitopathy, and for ulcerative keratitis. The outcome of this review indicates that CxL could serve as a primary or adjuvant therapeutic modality for all aforementioned corneal-related pathologic states. PMID:21448300

Kozobolis, Vassilios; Labiris, Georgios; Gkika, Maria; Sideroudi, Haris

2011-01-01

72

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

Microsoft Academic Search

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).

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

2008-01-01

73

Improved stability and cell response by intrinsic cross-linking of multilayers from collagen I and oxidized glycosaminoglycans.  

PubMed

Stability of surface coatings against environmental stress, such as pH, high ionic strength, mechanical forces, and so forth, is crucial for biomedical application of implants. Here, a novel extracellular-matrix-like polyelectrolyte multilayer (PEM) system composed of collagen I (Col I) and oxidized glycosaminoglycans (oGAGs) was stabilized by intrinsic cross-linking due to formation of imine bonds between aldehydes of oxidized chondroitin sulfate (oCS) or hyaluronan (oHA) and amino groups of Col I. It was also found that Col I contributed significantly more to overall mass in CS-Col I than in HA-Col I multilayer systems and fibrillized particularly in the presence of native and oxidized CS. Adhesion and proliferation studies with murine C3H10T1/2 embryonic fibroblasts demonstrated that covalent cross-linking of oGAG with Col I had no adverse effects on cell behavior. By contrast, it was found that cell size and polarization was more pronounced on oGAG-based multilayer systems, which corresponded also to the higher stiffness of cross-linked multilayers as observed by studies with quartz crystal microbalance (QCM). Overall, PEMs prepared from oGAG and Col I give rise to stable PEM constructs due to intrinsic cross-linking that may be useful for making bioactive coatings of implants and tissue engineering scaffolds. PMID:25246006

Zhao, Mingyan; Li, Lihua; Zhou, Changren; Heyroth, Frank; Fuhrmann, Bodo; Maeder, Karsten; Groth, Thomas

2014-11-10

74

Hyaluronan (HA) Interacting Proteins RHAMM and Hyaluronidase Impact Prostate Cancer Cell Behavior and Invadopodia Formation in 3D HA-Based Hydrogels  

PubMed Central

To study the individual functions of hyaluronan interacting proteins in prostate cancer (PCa) motility through connective tissues, we developed a novel three-dimensional (3D) hyaluronic acid (HA) hydrogel assay that provides a flexible, quantifiable, and physiologically relevant alternative to current methods. Invasion in this system reflects the prevalence of HA in connective tissues and its role in the promotion of cancer cell motility and tissue invasion, making the system ideal to study invasion through bone marrow or other HA-rich connective tissues. The bio-compatible cross-linking process we used allows for direct encapsulation of cancer cells within the gel where they adopt a distinct, cluster-like morphology. Metastatic PCa cells in these hydrogels develop fingerlike structures, “invadopodia”, consistent with their invasive properties. The number of invadopodia, as well as cluster size, shape, and convergence, can provide a quantifiable measure of invasive potential. Among candidate hyaluronan interacting proteins that could be responsible for the behavior we observed, we found that culture in the HA hydrogel triggers invasive PCa cells to differentially express and localize receptor for hyaluronan mediated motility (RHAMM)/CD168 which, in the absence of CD44, appears to contribute to PCa motility and invasion by interacting with the HA hydrogel components. PCa cell invasion through the HA hydrogel also was found to depend on the activity of hyaluronidases. Studies shown here reveal that while hyaluronidase activity is necessary for invadopodia and inter-connecting cluster formation, activity alone is not sufficient for acquisition of invasiveness to occur. We therefore suggest that development of invasive behavior in 3D HA-based systems requires development of additional cellular features, such as activation of motility associated pathways that regulate formation of invadopodia. Thus, we report development of a 3D system amenable to dissection of biological processes associated with cancer cell motility through HA-rich connective tissues. PMID:23166824

Gurski, Lisa A.; Nguyen, Ngoc T.; Xiao, Longxi; van Golen, Kenneth L.; Jia, Xinqiao; Farach-Carson, Mary C.

2012-01-01

75

Organization of photosystem I polypeptides examined by chemical cross-linking  

NASA Technical Reports Server (NTRS)

Photosystem I from the cyanobacterium Synechocystis sp. PCC 6803 was examined using the chemical cross-linkers glutaraldehyde and N-ethyl-1-3-[3-(dimethylamino)propyl]carbodiimide to investigate the organization of the polypeptide subunits. Thylakoid membranes and photosystem I, which was isolated by Triton X-100 fractionation, were treated with cross-linking reagents and were resolved using a Tricine/urea low-molecular-weight resolution gel system. Subunit-specific antibodies and western blotting analysis were used to identify the components of cross-linked species. These analyses identified glutaraldehyde-dependent cross-linking products composed of small amounts of PsaD and PsaC, PsaC and PsaE, and PsaE and PsaF. The novel cross-link between PsaE and PsaF was also observed following treatment with N-ethyl-1-3-[3-(dimethylamino)propyl]carbodiimide. These cross-linking results suggest a structural interaction between PsaE and PsaF and predict a transmembrane topology for PsaF.

Armbrust, T. S.; Chitnis, P. R.; Guikema, J. A.; Spooner, B. S. (Principal Investigator)

1996-01-01

76

Revisiting the mystery of fibronectin multimers: The fibronectin matrix is composed of fibronectin dimers cross-linked by non-covalent bonds  

E-print Network

dimers cross-linked by non-covalent bonds Tomoo Ohashi , Harold P. Erickson Department of Cell Biology that are further cross-linked by non-covalent protein­protein bonds. © 2009 Elsevier B.V. All rights reserved. 1 Keywords: Fibronectin Disulfide bond Matrix SDS gel Fibrillin Fibronectin (FN) matrix fibrils have long

Erickson, Harold P.

77

Cross-Link Guided Molecular Modeling with ROSETTA  

PubMed Central

Chemical cross-links identified by mass spectrometry generate distance restraints that reveal low-resolution structural information on proteins and protein complexes. The technology to reliably generate such data has become mature and robust enough to shift the focus to the question of how these distance restraints can be best integrated into molecular modeling calculations. Here, we introduce three workflows for incorporating distance restraints generated by chemical cross-linking and mass spectrometry into ROSETTA protocols for comparative and de novo modeling and protein-protein docking. We demonstrate that the cross-link validation and visualization software Xwalk facilitates successful cross-link data integration. Besides the protocols we introduce XLdb, a database of chemical cross-links from 14 different publications with 506 intra-protein and 62 inter-protein cross-links, where each cross-link can be mapped on an experimental structure from the Protein Data Bank. Finally, we demonstrate on a protein-protein docking reference data set the impact of virtual cross-links on protein docking calculations and show that an inter-protein cross-link can reduce on average the RMSD of a docking prediction by 5.0 Å. The methods and results presented here provide guidelines for the effective integration of chemical cross-link data in molecular modeling calculations and should advance the structural analysis of particularly large and transient protein complexes via hybrid structural biology methods. PMID:24069194

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

2013-01-01

78

High-resolution HPLC-ESI-MS characterization of the contact sites of the actin-thymosin ?(4) complex by chemical and enzymatic cross-linking.  

PubMed

Thymosin ?4 sequesters actin by formation of a 1:1 complex. This transient binding in the complex was stabilized by formation of covalent bonds using the cross-linking agents 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and a microbial transglutaminase. The localization of cross-linking sites was determined after separating the products using SDS-PAGE by tryptic in-gel digestion and high-resolution HPLC-ESI-MS. Three cross-linked fragments were identified after chemical cross-linking, indicating three contact sites. Because the cross-linked fragments were detected simultaneously with the corresponding non-cross-linked fragments, the three contact sites were not formed in parallel. K3 of thymosin ?4 was cross-linked to E167 of actin, K18 or K19 of thymosin ?4 to one of the first three amino acids of actin (DDE), and S43 of thymosin ?4 to H40 of actin. The imidazole ring of histidine was proven to be an acyl acceptor for carbodiimide-mediated cross-linking. Molecular modeling proved an extended conformation of thymosin ?4 along the subdomains 1 to 3 of actin. The enzymatic cross-linking using a microbial transglutaminase led to the formation of three cross-linking sites. Q41 of actin was cross-linked to K19 of thymosin ?4, and K61 of actin to Q39 of thymosin ?4. The third cross-linking site was identified between Q41 of actin and Q39 of thymosin ?4, which are simultaneously cross-linked to K16, K18, or K19 of thymosin ?4. When both cross-linking reactions are taken together, the complex formation of actin by thymosin ?4 is more likely to be flexible than rigid and is localized along the subdomains 1 to 3 of actin. PMID:23924371

Knop, Jana; App, Christine; Horn, Anselm H C; Iavarone, Federica; Castagnola, Massimo; Hannappel, Ewald

2013-08-20

79

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

80

Radiation cross-linked polymers: Recent developments and new applications  

Microsoft Academic Search

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

Sophie Rouif

2005-01-01

81

Cross-Linking Aromatic Polymers With Ionizing Radiation  

NASA Technical Reports Server (NTRS)

Resistance to heat and solvents increased. Certain aromatic polymers containing radiation-sensitive methylene groups cross-linked through methylene groups upon exposure to ionizing radiation. Cross-linked polymers resistant to most organic solvents and generally more resistant to high temperatures, with less tendency to creep under load. No significant embrittlement of parts fabricated from these polymers when degree of cross-linking, as controlled by irradiation dose, kept at moderate level.

Bell, Vernon L.; Havens, Stephen J.

1987-01-01

82

Hyaluronan-mediated cellular adhesion  

NASA Astrophysics Data System (ADS)

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

Curtis, Jennifer

2005-03-01

83

Transient binding and dissipation in cross-linked actin networks.  

PubMed

In contrast with entangled actin solutions, transiently cross-linked actin networks can provide highly elastic properties while still allowing for local rearrangements in the microstructure-on biological relevant time scales. Here, we show that thermal unbinding of transient cross-links entails local stress relaxation and energy dissipation in an intermediate elasticity dominated frequency regime. We quantify the viscoelastic response of an isotropically cross-linked actin network by experimentally tuning the off rate of the transiently cross-linking molecules, their density, and the solvent viscosity. We reproduce the measured frequency response by a semiphenomenological model that is predicated on microscopic unbinding events. PMID:18851260

Lieleg, O; Claessens, M M A E; Luan, Y; Bausch, A R

2008-09-01

84

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

PubMed Central

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

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

2009-01-01

85

Cross-linked polyvinyl alcohol films as alkaline battery separators  

NASA Technical Reports Server (NTRS)

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

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

1982-01-01

86

Cross-linked polyvinyl alcohol films as alkaline battery separators  

NASA Technical Reports Server (NTRS)

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

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

1983-01-01

87

Cross-linked polyvinyl alcohol and method of making same  

NASA Technical Reports Server (NTRS)

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

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

1981-01-01

88

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. PMID:23925330

Mrochen, Michael

2013-01-01

89

Redox-Responsive, Core Cross-Linked Polyester Micelles  

PubMed Central

Monomethoxy poly(ethylene glycol)-b-poly(Tyr(alkynyl)-OCA), a biodegradable amphiphilic block copolymer, was synthesized by means of ring-opening polymerization of 5-(4-(prop-2-yn-1-yloxy)benzyl)-1,3-dioxolane-2,4-dione (Tyr(alkynyl)-OCA) and used to prepare core cross-linked polyester micelles via click chemistry. Core cross-linking not only improved the structural stability of the micelles but also allowed controlled release of cargo molecules in response to the reducing reagent. This new class of core cross-linked micelles can potentially be used in controlled release and drug delivery applications. PMID:23536920

Zhang, Zhonghai; Yin, Lichen; Tu, Chunlai; Song, Ziyuan; Zhang, Yanfeng; Xu, Yunxiang; Tong, Rong; Zhou, Qin; Ren, Jie; Cheng, Jianjun

2013-01-01

90

Chemoselective cross-linking and functionalization of alginate via Staudinger ligation  

PubMed Central

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

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

2010-01-01

91

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

2013-11-15

92

Remarkable swelling capability of amino acid based cross-linked polymer networks in organic and aqueous medium.  

PubMed

This work reports design and synthesis of side chain amino acid based cross-linked polymeric gels, able to switch over from organogel to hydrogel by a simple deprotection reaction and showing superabsorbancy in water. Amino acid based methacrylate monomers, tert-butoxycarbonyl (Boc)-l/d-alanine methacryloyloxyethyl ester (Boc-l/d-Ala-HEMA), have been polymerized in the presence of a cross-linker via conventional free radical polymerization (FRP) and the reversible addition-fragmentation chain transfer (RAFT) technique for the synthesis of cross-linked polymer gels. The swelling behaviors of these organogels are investigated in organic solvents, and they behave as superabsorbent materials for organic solvents such as dichloromethane, acetone, tetrahydrofuran, etc. Swollen cross-linked polymer gels release the absorbed organic solvent rapidly. After Boc group deprotection from the pendant alanine moiety, the organogels transform to the hydrogels due to the formation of side chain ammonium (-NH3(+)) groups, and these hydrogels showed a significantly high swelling ratio (?560 times than their dry volumes) in water. The morphology of organogels and hydrogels is studied by field emission scanning electron microscopy (FE-SEM). Amino acid based cross-linked gels could find applications as absorbents for oil spilled on water as well as superabsorbent hydrogels. PMID:24556036

Roy, Saswati Ghosh; Haldar, Ujjal; De, Priyadarsi

2014-03-26

93

Getting a grip: hyaluronan-mediated cellular adhesion  

NASA Astrophysics Data System (ADS)

Holographic optical tweezers (HOTs) techniques are further developed to study hyaluronan-mediated adhesion of chondrocyte cells. We present a calibration scheme and address fundamental issues concerning the use of HOTs for quantitative force measurements. Influence of SLM pixelation on trap stiffness is observed and can be utilized to design calibrated HOTs more effectively. It is also shown that the HOTs trapping stiffness can vary significantly over short distances. Then we use HOTs cell adhesion assays investigate the viscoelastic and adhesive nature of chondrocytes' pericellular matrix (PCM) at two different time steps (30 minute and 24 hour incubation periods). Surprisingly, no physical influence of the large, presumably gel-like PCM is observed. However, a difference is discerned in the adhesiveness of the two sets of cells. The early-stage cells have reversible adhesion with negatively-charged and fibronectin-coated microspheres even after they are held at the cell surface for 10 seconds. In contrast, late stage cells stick irreversibly to all types of beads: positive, negative, fibronectin and hyaluronan-coated. Additionally, only the late stage cells produce membrane tethers. These observations suggest that the late-stage chondrocytes have less surface-associated hyaluronan and have interesting implications for the role of hyaluronan in the early stages of cell adhesion.

Curtis, Jennifer E.; Spatz, Joachim P.

2004-10-01

94

Effectiveness of trimethylopropane trimethacrylate for the electron-beam-irradiation-induced cross-linking of polylactic acid  

NASA Astrophysics Data System (ADS)

The purpose of this research was to investigate the effects of various loading levels of trimethylopropane trimethacrylate (TMPTMA) on the properties of polylactic acid (PLA) cross-linked via electron-beam irradiation. PLA was compounded with 3-5 wt.% of TMPTMA to induce cross-linking upon subjection to electron-beam irradiation doses of 25-250 kGy. The physical properties of the PLA samples were characterised by means of X-ray diffraction, gel fraction and scanning electron microscopy analyses on fractured surfaces after tensile tests. The presence of TMPTMA in PLA was found to effectively increase the crystallite size and gel fraction. However, higher loading levels of TMPTMA could compromise the properties of the PLA/TMPTMA samples, indicating that a larger amount of monomer free radicals might promote degradation within the substantially cross-linked amorphous phase. Irradiation-induced cross-linking in the samples could improve the cross-linking density while decreasing the elongation and interfering with the crystallisation. These effects are caused by the intensive irradiation-induced chain scission that is responsible for the deterioration of the mechanical and crystalline properties of the samples.

Ng, Hon-Meng; Bee, Soo-Tueen; Ratnam, C. T.; Sin, Lee Tin; Phang, Yee-Yao; Tee, Tiam-Ting; Rahmat, A. R.

2014-01-01

95

Cross-link induced shrinkage of grafted Gaussian chains  

E-print Network

The statistical mechanics of polymers grafted on surfaces has been the subject of intense research activity because of many potential applications. In this paper, we analytically investigate the conformational changes caused by a single cross-link on two ideal (Gaussian) chains grafted on a rigid planar surface. Both the cross-link and the surface reduce the number of allowed configurations. In the absence of the hard substrate, the sole effect of the cross-link is a reduction in the effective Kuhn length of a tethered chain. The cross-link induced shrinkage (collapse) of the grafted chains (mushrooms) turns out to be a reduction in the variance of the distribution of the height of the chain rather than a reduction of the height itself.

Panayotis Benetatos

2014-04-04

96

21 CFR 177.2420 - Polyester resins, cross-linked.  

...an average of 2-7.5 moles of propylene oxide). Propylene glycol. Sorbitol. Trimethylol ethane. Trimethylol propane. 2,2,4-Trimethyl-1,3-pentanediol. (3) Cross-linking agents: Butyl acrylate. Butyl...

2014-04-01

97

Humidity sensor using cross-linked poly(chloromethyl styrene)  

Microsoft Academic Search

A resistive-type humidity sensor was prepared using a poly(chloromethyl styrene) (PCMS) film which was simultaneously cross-linked and quaternized. The impedance dependence on humidity for samples with various reaction degrees was measured. The sorption isotherm curves of water vapor in the cross-linked films were obtained using the quartz crystal microbalance method for the various samples. It was found that the degree

Y. Sakai; M. Matsuguchi; T. Hurukawa

2000-01-01

98

Influence of cross-linking degree of a biodegradable genipin-cross-linked gelatin guide on peripheral nerve regeneration  

Microsoft Academic Search

We evaluated peripheral nerve regeneration using biodegradable genipin-cross-linked gelatin nerve conduits (GGCs) with three different cross-linking degrees, 24, 36 and 51%. Biocompatibility and biodegradability of the GGC and its efficiency as a guidance channel were examined based on the repair process of a 10-mm gap in the rat sciatic nerve. From this pilot study we concluded that GGCs with a

Ming-Chin Lu; Shih-Wei Hsiang; Tung-Yuan Lai; Chun-Hsu Yao; Li-Yu Lin; Yueh-Sheng Chen

2007-01-01

99

The formation of a disulfide cross-link between the two subunits demonstrates the dimeric structure of the mitochondrial oxoglutarate carrier.  

PubMed

Isolated oxoglutarate carrier (OGC) can be cross-linked to dimers by disulfide-forming reagents such as Cu2+-phenanthroline and diamide. Acetone and other solvents increase the extent of Cu2+ -phenanthroline-induced cross-linking of OGC. Cross-linked OGC re-incorporated in proteoliposomes fully retains the oxoglutarate transport activity. The amount of cross-linked OGC calculated by densitometry of scanned gels depends on the method of staining, since cross-linked OGC exhibits a higher sensitivity to Coomassie brilliant blue as compared to silver nitrate. Under optimal conditions the formation of cross-linked OGC dimer (stained with Coomassie brilliant blue) amounts to 75% of the total protein. Approximately the same cross-linking efficiency was evaluated from Western blots. Cross-linking of OGC is prevented by SH reagents and reversed by SH-reducing reagents, which shows that it is mediated by disulfide bridge(s). The formation of S-S bridge(s) requires the native state of the protein, since it is suppressed by SDS and by heating. Furthermore, the extent of cross-linking is independent of OGC concentration indicating that disulfide bridge(s) must be formed between the two subunits of native dimers. The number and localization of disulfide bridge(s) in the cross-linked OGC were examined by peptide fragmentation and subsequent cleavage of disulfide bond(s) by beta-mercaptoethanol. Our experimental results show that cross-linking of OGC is accomplished by a single disulfide bond between the cysteines 184 of the two subunits and suggest that these residues in the putative transmembrane helix four are fairly close to the twofold axis of the native dimer structure. PMID:8597574

Bisaccia, F; Zara, V; Capobianco, L; Iacobazzi, V; Mazzeo, M; Palmieri, F

1996-02-01

100

Spectroscopic characterization of collagen cross-links in bone  

NASA Technical Reports Server (NTRS)

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

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

2001-01-01

101

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

PubMed

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

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

2014-11-01

102

Rheological characterization of cataplasm bases composed of cross-linked partially neutralized polyacrylate hydrogel.  

PubMed

Viscoelasticity is a useful parameter for characterizing the intrinsic properties of the cross-linked polyacrylate hydrogel used in cataplasm bases. The aim of this study was to investigate the effects of various formulation parameters on the rheological characteristics of polyacrylate hydrogel. The hydrogel layers were formed using a partially neutralized polyacrylate (Viscomate(™)), which contained acrylic acid and sodium acrylate in different copolymerization ratios, as the cross-linked gel framework. Dihydroxyaluminum aminoacetate (DAAA), which produces aluminum ions, was used as the cross-linking agent. Rheological analyses were performed using a "stress amplitude sweep" and a "frequency sweep". The results showed that greater amounts of acrylic acid in the structure of Viscomate as well as higher concentrations of DAAA and Viscomate led to an increase in the elastic modulus (G'). However, greater amounts of acrylic acid in the structure of Viscomate and higher concentrations of DAAA had an opposite on the viscous modulus (G?); this might be owing to higher steric hindrance. The results of this study can serve as guidelines for the optimization of formulations for cataplasms. PMID:24865937

Wang, Jian; Zhang, Hongqin; An, Dianyun; Yu, Jian; Li, Wei; Shen, Teng; Wang, Jianxin

2014-10-01

103

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

2011-08-01

104

Photo-Induced Cross-Linking of Unmodified Proteins (PICUP) Applied to Amyloidogenic Peptides  

PubMed Central

The assembly of amyloidogenic proteins into toxic oligomers is a seminal event in the pathogenesis of protein misfolding diseases, including Alzheimer's, Parkinson's, and Huntington's diseases, hereditary amyotrophic lateral sclerosis, and type 2 diabetes. Owing to the metastable nature of these protein assemblies, it is difficult to assess their oligomer size distribution quantitatively using classical methods, such as electrophoresis, chromatography, fluorescence, or dynamic light scattering. Oligomers of amyloidogenic proteins exist as metastable mixtures, in which the oligomers dissociate into monomers and associate into larger assemblies simultaneously. PICUP stabilizes oligomer populations by covalent cross-linking and when combined with fractionation methods, such as sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) or size-exclusion chromatography (SEC), PICUP provides snapshots of the oligomer size distributions that existed before cross-linking. Hence, PICUP enables visualization and quantitative analysis of metastable protein populations and can be used to monitor assembly and decipher relationships between sequence modifications and oligomerization1. Mechanistically, PICUP involves photo-oxidation of Ru2+ in a tris(bipyridyl)Ru(II) complex (RuBpy) to Ru3+ by irradiation with visible light in the presence of an electron acceptor. Ru3+ is a strong one-electron oxidizer capable of abstracting an electron from a neighboring protein molecule, generating a protein radical1,2. Radicals are unstable, highly-reactive species and therefore disappear rapidly through a variety of intra- and intermolecular reactions. A radical may utilize the high energy of an unpaired electron to react with another protein monomer forming a dimeric radical, which subsequently loses a hydrogen atom and forms a stable, covalently-linked dimer. The dimer may then react further through a similar mechanism with monomers or other dimers to form higher-order oligomers. Advantages of PICUP relative to other photo- or chemical cross-linking methods3,4 include short (?1 s) exposure to non-destructive visible light, no need for pre facto modification of the native sequence, and zero-length covalent cross-linking. In addition, PICUP enables cross-linking of proteins within wide pH and temperature ranges, including physiologic parameters. Here, we demonstrate application of PICUP to cross-linking of three amyloidogenic proteins the 40- and 42-residue amyloid ?-protein variants (A?40 and A?42), and calcitonin, and a control protein, growth-hormone releasing factor (GRF). PMID:19229175

Rahimi, Farid; Maiti, Panchanan; Bitan, Gal

2009-01-01

105

Cross-linking and degradation of step-growth hydrogels formed by thiol-ene photoclick chemistry.  

PubMed

Thiol-ene photoclick hydrogels have been used for a variety of tissue engineering and controlled release applications. In this step-growth photopolymerization scheme, four-arm poly(ethylene glycol) norbornene (PEG4NB) was cross-linked with dithiol containing cross-linkers to form chemically cross-linked hydrogels. While the mechanism of thiol-ene gelation was well described in the literature, its network ideality and degradation behaviors are not well-characterized. Here, we compared the network cross-linking of thiol-ene hydrogels to Michael-type addition hydrogels and found thiol-ene hydrogels formed with faster gel points and higher degree of cross-linking. However, thiol-ene hydrogels still contained significant network nonideality, demonstrated by a high dependency of hydrogel swelling on macromer contents. In addition, the presence of ester bonds within the PEG-norbornene macromer rendered thiol-ene hydrogels hydrolytically degradable. Through validating model predictions with experimental results, we found that the hydrolytic degradation of thiol-ene hydrogels was not only governed by ester bond hydrolysis, but also affected by the degree of network cross-linking. In an attempt to manipulate network cross-linking and degradation of thiol-ene hydrogels, we incorporated peptide cross-linkers with different sequences and characterized the hydrolytic degradation of these PEG-peptide hydrogels. In addition, we incorporated a chymotrypsin-sensitive peptide as part of the cross-linkers to tune the mode of gel degradation from bulk degradation to surface erosion. PMID:22708824

Shih, Han; Lin, Chien-Chi

2012-07-01

106

Preparation of hyaluronan-DNA matrices and films.  

PubMed

Natural carbohydrate is a class of underexplored polymers for gene delivery. The noninflammatory and nonimmunogenic properties of hyaluronan (hyaluronic acid, HA) are important in clinical situations. It has a role in wound repair and has great lubricating ability. Moreover, the presence of hyaluronidase in vivo enables any vehicle fabricated from HA to be degraded by enzyme-mediated erosion. When DNA is entrapped in a cross-linked HA vehicle, HA-DNA fragments are released on digestion by hyaluronidase. These fragments could serve both as microcarriers of DNA and its protective mechanism. This protocol describes preparation of water-insoluble HA-DNA matrices and films designed for clinical applications, and assays for verification of their bioactivities. Plasmid DNA (pDNA) encoding platelet-derived growth factor (PDGF) is coupled to the matrices that could be implanted into chronic wounds to accelerate their healing. pDNA encoding hyaluronan synthase 2 (HAS2) is coupled to the film that could initially serve as a physical barrier and subsequently a pDNA reservoir for sustaining HAS2 transfection. This would lead to continual HA production for preventing postsurgical adhesion. PMID:23028077

Chen, Weiliam

2012-10-01

107

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

2013-04-15

108

Cross-linking of micelles by gemini surfactants  

E-print Network

We investigate the effects of gemini surfactants, telechelic chain and lipids on the nature of micelles formed by conventional single-tail surfactants in water by carrying out Monte Carlo simulations. In a mixture of gemini and single-tail surfactants in water we find direct evidence of micelles of predominantly single-tail surfactants some of which are dynamically cross-linked by gemini surfactants when the concentrations of the geminis is only a few mole percent and their spacers are {\\it hydrophilic}. In contrast, mixtures of lipids and single-tail surfactants in water form only isolated micelles, each consisting of a mixture of both species, without cross-links.

Prabal K. Maiti; Kurt Kremer; Oliver Flimm; Debashish Chowdhury; Dietrich Stauffer

1999-12-01

109

Diepoxybutane Interstrand Cross-Links Induce DNA Bending  

PubMed Central

The bifunctional alkylating agent 1,2,3,4-diepoxybutane (DEB) is thought to be a major contributor to the carcinogenicity of 1,3-butadiene, from which it is derived in vivo. DEB forms DNA interstrand cross-links primarily between distal deoxyguanosine residues at the duplex sequence 5’-GNC. In order for the short butanediol tether to span this distance, distortion of the DNA target has been postulated. We determined that the electrophoretic mobility of ligated DNA oligomers containing DEB cross-links was retarded in comparison with control, uncross-linked DNA. Our data are consistent with DNA bending of ~34° per lesion towards the major groove. PMID:21839139

Millard, Julie T.; McGowan, Erin E.; Bradley, Sharonda Q.

2011-01-01

110

Histidinoalanine, a naturally occurring cross-link derived from phosphoserine and histidine residues in mineral-binding phosphoproteins.  

PubMed

Native mineral-containing phosphoprotein particles were isolated from the Heterodont bivalve Macrocallista nimbosa. The native particles are discrete structures about 40 nm in diameter which migrate as a single band during electrophoresis in agarose gels. Removal of the mineral component with ethylenediaminetetraacetic acid dissociates the native protein into nonidentical subunits. The lower molecular weight subunits, representing 8% of the total protein, were obtained by differential centrifugation. The native protein is characterized by a high content of aspartic acid, phosphoserine, phosphothreonine, histidine, and the bifunctional cross-linking residue histidinoalanine. The low molecular weight subunits have the same amino acid composition except for a reduction in histidinoalanine and a corresponding increase in phosphoserine and histidine residues, demonstrating that the alanine portion of the cross-link is derived from phosphoserine residues. Ion-exchange chromatography and molecular sieve chromatography show that the low molecular weight subunits have a similar charge density but differ in molecular weight, and the relative mobilities of the subunits on agarose gels indicate that they are polymers of a single phosphoprotein molecule. The minimum molecular weight of the monomer is about 140 000 on the basis of the amino acid composition. The high molecular weight subunits are rich in histidinoalanine and too large to be resolved by either molecular sieve chromatography or gel electrophoresis. On the basis of the ultrastructural, electrophoretic, chromatographic, and compositional evidence, native phosphoprotein particles are composed of subunits ionically cross-linked via divalent cations. These subunits are variable molecular weight aggregates of a single phosphoprotein molecule covalently cross-linked via histidinoalanine residues. Evidence for a nonenzymatic cross-linking mechanism is discussed. PMID:3087418

Marsh, M E

1986-05-01

111

Load transfer mechanisms in cross-linked DWNT fibers  

NASA Astrophysics Data System (ADS)

The application of carbon nanotubes (CNT) to macroscopic composite fibers has been limited by weak shear interfaces between adjacent CNT shells and composite matrix elements. A fundamental understanding of load transfer at multiple length-scales is needed to identify how the exceptional mechanical properties of CNTs can be scaled to produce high-performance fibers. Through in-situ electron microscopy tensile testing we have elucidated load transfer mechanisms across multiple scales of cross-linked double-walled nanotube (DWNT) fibers. A low density of polymer cross-links is found to increase the total energy dissipated at failure and ductility of fibers by 5 and 10X, respectively, without reducing strength. This mutiscale approach has identified a need to enhance shear interactions between individual DWNTs within the hierarchical DWNT fiber structures. Through in-situ TEM electron irradiation studies we have shown that load can be effectively transferred to inner DWNTs within bundles by covalently cross-linking the interfaces of adjacent DWNTs and shells. We have observed order of magnitude increases in strength and modulus and identified their dependence on irradiation dose. In future a combined approach of irradiation induced covalent and polymer cross-linking may lead to high-performance DWNT-based fibers and composites with tunable mechanical properties.

Filleter, T.; Naraghi, M.; Moravsky, A.; Bernal, R.; Loutfy, R. O.; Espinosa, H. D.

2011-03-01

112

Enzymatically cross-linked hydrogels and their adhesive  

E-print Network

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

113

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

PubMed Central

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

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

2014-01-01

114

Hyaluronan in Tubular and Interstitial Nephrocalcinosis  

NASA Astrophysics Data System (ADS)

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

Verkoelen, Carl F.

2007-04-01

115

The packing of the transmembrane segments of human multidrug resistance P-glycoprotein is revealed by disulfide cross-linking analysis.  

PubMed

Residues from several transmembrane (TM) segments of P-glycoprotein (P-gp) likely form the drug-binding site(s). To determine the organization of the TM segments, pairs of cysteine residues were introduced into the predicted TM segments of a Cys-less P-gp, and the mutant protein was subjected to oxidative cross-linking. In SDS gels, the cross-linked product migrated with a slower mobility than the native protein. The cross-linked products were not detected in the presence of dithiothreitol. Cross-linking was observed in 12 of 125 mutants. The pattern of cross-linking suggested that TM6 is close to TMs 10, 11, and 12, while TM12 is close to TMs 4, 5, and 6. In some mutants the presence of drug substrate colchicine, verapamil, cyclosporin A, or vinblastine either enhanced or inhibited cross-linking. Cross-linking was inhibited in the presence of ATP plus vanadate. These results suggest that the TM segments critical for drug binding must be close to each other and exhibit different conformational changes in response to binding of drug substrate or vanadate trapping of nucleotide. Based on these results, we propose a model for the arrangement of the TM segments. PMID:10681495

Loo, T W; Clarke, D M

2000-02-25

116

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

NASA Astrophysics Data System (ADS)

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

Jiang, Dayue (David)

117

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

118

Enzymatic degradation of cross-linked high amylose starch tablets and its effect on in vitro release of sodium diclofenac  

Microsoft Academic Search

The influence of several physicochemical parameters on enzymatic hydrolysis and the in vitro release of sodium diclofenac (SDic) from cross-linked high amylose starch (Contramid) (CLA) tablets was evaluated. These parameters included pH, ionic strength of the medium, enzyme concentration, compression force and incorporation of gel-forming polymers such as hydroxypropyl methylcellulose (HPMC), poly(ethylene oxide) (PEO) and poly(vinyl alcohol) into the tablet.

M Rahmouni; F Chouinard; F Nekka; V Lenaerts; J. C Leroux

2001-01-01

119

Chemical cross-linking reveals a dimeric structure for CTP:phosphocholine cytidylyltransferase.  

PubMed

CTP:phosphacholine cytidylyltransferase (EC 2.7.7.15) was purified from rat liver according to the method of Weinhold et al. (Weinhold, P. A., Rounsifer, M. E., and Feldman, D. A. (1986) J. Biol. Chem. 261, 5104-5110). Sodium dodecyl sulfate-polyacrylamide gel electrophoresis with or without beta-mercaptoethanol revealed a single major band of 42,000 daltons. This band corresponds to the 45-kDa catalytic subunit isolated by Feldman and Weinhold (Feldman, D. A., and Weinhold, P. A. (1987) J. Biol. Chem. 262, 9075-9081). A minor component of 84,000 daltons was intensified in nonreducing gels when the sulfhydryl reducing agent, dithiothreitol, was removed from the enzyme preparation by dialysis. Reduction with dithiothreitol and electrophoresis in the second dimension showed that this 84-kDa protein was derived from the 42-kDa protein. This result suggested that the 42 kDa protein can be converted to an 84-kDa protein by disulfide bond formation. Reaction with the thiol-cleavable cross-linking reagents, dithiobis(succimidyl propionate) or dimethyl-3,3'-dithiobispropionimidate, converted the 42-kDa cytidylyltransferase subunit into a diffuse band approximately twice its molecular mass. Disulfide reduction and electrophoresis in the second dimension showed that this band was derived exclusively from the 42-kDa subunit. This cross-linking pattern was observed when cytidylyltransferase was bound to a Triton X-100 micelle or when bound to a membrane vesicle containing phosphatidylcholine, oleic acid, and Triton X-100. Reaction of the fully reduced enzyme with glutaraldehyde also generated a cross-linked dimer. All three cross-linking reagents inactivated the enzyme. Reduction of the disulfide cross-linkers with dithiothreitol partially reactivated the transferase. When Triton was removed from the enzyme preparation by DEAE-Sepharose chromatography, reaction of the detergent-depleted enzyme with glutaraldehyde generated a band corresponding to a hexamer and higher molecular weight aggregates. The dimeric form was regenerated by addition of either Triton X-100 or phosphatidylcholine-oleic acid vesicles. We conclude that the purified, native cytidylyltransferase, when bound to a detergent micelle or membrane vesicle, is a dimer composed of two noncovalently linked 42-kDa subunits. In the absence of a membrane or micelle, the dimers self-aggregate in a reversible manner. PMID:2542297

Cornell, R

1989-05-25

120

Drug-stimulated ATPase activity of human P-glycoprotein is blocked by disulfide cross-linking between the nucleotide-binding sites.  

PubMed

P-glycoprotein (P-gp) is an ATP-dependent drug pump that contains two nucleotide-binding domains (NBDs). Disulfide cross-linking analysis was done to determine if the two NBDs are close to each other. Residues within or close to the Walker A (GNSGCGKS in NDB1 and GSSGCGKS in NBD2) sequences for nucleotide binding were replaced with cysteine, and the mutant P-gps were subjected to oxidative cross-linking. Cross-linking was detected in two mutants, G427C(NBD1)/Cys-1074(NBD2) and L439C(NBD1)/Cys-1074(NBD2), because the cross-linked proteins migrated slower in SDS gels. Mutants G427C(NBD1)/Cys-1074(NBD2) and L439C(NBD1)/Cys-1074(NBD2) retained 10% and 82%, respectively, of the drug-stimulated ATPase activity relative to that of Cys-less P-gp. The cross-linking properties of the more active mutant L439C(NBD1)/Cys-1074(NBD2) were then studied. Cross-linking was reversed by addition of dithiothreitol and could be prevented by pretreatment of the mutant with N-ethylmaleimide. Cross-linking was also inhibited by MgATP, but not by the verapamil. Oxidative cross-linking of mutant L439C(NBD1)/Cys-1074(NBD2) resulted in almost complete inhibition of drug-stimulated ATPase activity. More than 60% of the drug-stimulated ATPase activity, however, was recovered after treatment with dithiothreitol. The results indicate that the two predicted nucleotide-binding sites are close to each other and that cross-linking inhibits ATP hydrolysis. PMID:10806188

Loo, T W; Clarke, D M

2000-06-30

121

Collagen cross-linking: Strengthening the unstable cornea  

PubMed Central

Corneal ectasia, a weakening of corneal integrity, occurs both due to acquired and congenital conditions such as keratoconus. It is a progressing condition that affects both visual acuity, and corneal stability. Various methods exist for correcting this impairment, however none address the inherit pathology, an increase laxity of the corneal stroma. Collagen cross-linking, a new, minimally invasive method, aims to strengthen the stroma by inducing cross links between neighboring collagen fibers. This method results in an increase in corneal tensile strength, with no medium term adverse effects on its normal architecture. Clinically, treated patients display improvement in both visual acuity and keratometric readings. This method may provide clinicians with easily accessible tools to stop the progression, and even correct visual deterioration due to corneal ectasia. Here we review the current information regarding this new method, as well as discuss its potential benefits and downfalls. PMID:19668440

Tomkins, Oren; Garzozi, Hanna J

2008-01-01

122

Transient Anisocoria after Corneal Collagen Cross-Linking  

PubMed Central

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

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

2014-01-01

123

[Cross-linking and intrastromal corneal ring segment].  

PubMed

Corneal cross-linking is a procedure used for stabilizing the cornea in patients with progressive keratoconus by increasing corneal rigidity, and it is also used in corneal inflammatory melting process. The intrastromal corneal ring segments act by flattening the center of the cornea. Originally designed for the correction of mild myopia, the segments are now being used for reduction of keratoconus in order to improve the uncorrected visual acuity, the best spectacle corrected visual acuity, to allow good tolerance to the use of contact lenses and delay the need for corneal grafting procedures. The present text presents a review of corneal cross-linking and insertion of intrastromal corneal ring segments, emphasizing their indications, results and complications related until now. PMID:21670914

Renesto, Adimara da Candelaria; Sartori, Marta; Campos, Mauro

2011-01-01

124

Repair of 8-methoxypsoralen photoinduced cross-links in yeast  

Microsoft Academic Search

The repair of interstrand cross-links induced by 8-methoxypsoralen plus UVA (365 nm) radiation DNA was analyzed in diploid strains of the yeast Saccharomyces cerevisiae. The strains employed were the wild-type D7 and derivatives homozygous for the rad18-1 or the rad3-12 mutation. Alkaline step-elution and electron microscopy were performed to follow the process of induction and removal of photoinduced crosslinks. In

E. Cundari; M. Dardalhon; S. Rousset; D. Averbeck

1991-01-01

125

UV cross-linking of unmodified DNA on glass surfaces  

Microsoft Academic Search

The performance of DNA microarrays strongly depends on their surface properties. Furthermore, the immobilization method of\\u000a the capture molecules is of importance for the efficiency of the microarray in terms of sensitivity and specificity. This\\u000a work describes the immobilization of single-stranded capture oligonucleotides by UV cross-linking on silanated (amino and\\u000a epoxy) glass surfaces. Thereby we used amino (NH2) and poly

Thomas Schüler; Alla Nykytenko; Andrea Csaki; Robert Möller; Wolfgang Fritzsche; Jürgen Popp

2009-01-01

126

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

127

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

128

Chain length dependent termination in radical cross-linking polymerization  

Microsoft Academic Search

The work presents an evidence in support of chain length dependent termination during cross-linking polymerization. It is based on the behavior of the ratio of the bimolecular termination coefficient ktb to propagation rate coefficient kp during the after-effect of a photo-induced polymerization. The chain-length dependence was manifested by a decrease of the ktb\\/kp ratio with the increase in dark reaction

Ewa Andrzejewska; El?bieta Socha; Mariusz Bogacki; Maciej Andrzejewski

2005-01-01

129

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

130

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

131

Ion exchange selectivity for cross-linked polyacrylic acid  

NASA Technical Reports Server (NTRS)

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

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

1983-01-01

132

Lymphocyte mechanical response triggered by cross-linking surface receptors  

PubMed Central

Using a recently developed method (Petersen, N. O., W. B. McConnaughey, and E. L. Elson, 1982, Proc. Natl. Acad. Sci. USA., 79:5327-5331), we have measured changes in the deformability of lymphocytes triggered by cross-linking cell surface proteins. Our study was motivated by two previously demonstrated phenomena: the redistribution ("capping") of cross-linked surface immunoglobulin (sIg) on B lymphocytes and the inhibition of capping and lateral diffusion ("anchorage modulation") of sIg by the tetravalent lectin Concanavalin A (Con A). Both capping and anchorage modulation are initiated by cross-linking cell surface proteins and both require participation of the cytoskeleton. We have shown that the resistance of lymphocytes to deformation strongly increased when sIg or Con A acceptors were cross-linked. We have measured changes in deformability in terms of an empirical "stiffness" parameter, defined as the rate at which the force of cellular compression increases with the extent of compression. For untreated cells the stiffness was approximately 0.15 mdyn/micron; for cells treated with antibodies against sIg or with Con A the stiffness increased to approximately 0.6 or 0.4 mdyn/micron, respectively. The stiffness decreased after completion of the capping of sIg. The increases in stiffness could be reversed to various extents by cytochalasin D and by colchicine. The need for cross-linking was demonstrated by the failure both of monovalent Fab' fragments of the antibodies against sIg and of succinylated Con A (a poor cross-linker) to cause an increase in stiffness. We conclude that capping and anchorage modulation involve changes in the lymphocyte cytoskeleton and possibly other cytoplasmic properties, which increase the cellular viscoelastic resistance to deformation. Similar increases in cell stiffness could be produced by exposing cells to hypertonic medium, azide ions, and to a calcium ionophore in the presence of calcium ions. These results shed new light on the capabilities of the lymphocyte cytoskeleton and its role in capping and anchorage modulation. They also demonstrate that measurements of cellular deformability can characterize changes in cytoskeletal functions initiated by signals originating at the cell surface. PMID:4038710

1985-01-01

133

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

PubMed

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

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

2014-07-29

134

Semisynthetic resorbable materials from hyaluronan esterification  

Microsoft Academic Search

In recent years, research on new, biocompatible, degradable materials has seen the development of a series of modified natural polymers. Among these, a new class of materials consisting of different hyaluronan derivatives promises to be useful in a whole range of clinical applications thanks to their varied biological properties. These new materials are obtained by chemical modification of purified hyaluronan

Davide Campoccia; Patrick Doherty; Marco Radice; Paola Brun; Giovanni Abatangelo; David F. Williams

1998-01-01

135

Binding and covalent cross-linking of purified von Willebrand factor to native monomeric collagen.  

PubMed Central

We have analyzed the interaction of the adhesive glycoprotein, von Willebrand factor (vWF), with native monomeric collagen monolayers by adsorbing acid soluble Types I and III collagen derived from calf skin to polystyrene microtiter wells and incubating the wells with purified human 125I-vWF. The binding of 125I-vWF was saturable, reversible, specific, and was abolished by heat denaturation of the collagen monomers. Binding was half-maximal at 5 micrograms/ml, and, at saturation, 7.5 ng 125I-vWF were bound to each microgram of immobilized collagen. 125I-vWF did not bind to wells coated with other extracellular matrix or plasma proteins such as fibronectin, fibrinogen, gelatin, or the q subunit of the first component of complement (C1q). In addition, bound 125I-vWF could not be displaced from collagen by the addition of either fibronectin or fibrinogen. After incubation with Factor XIIIa, plasma transglutaminase, 125I-vWF bound to collagen could no longer be displaced by vWF, which suggests covalent cross-linking of vWF to collagen monomers. Factor XIIIa-dependent covalent cross-linking of vWF to collagen, but not to fibronectin or laminin, was also demonstrated by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. Images PMID:2874156

Bockenstedt, P; McDonagh, J; Handin, R I

1986-01-01

136

Cross-linked hybrid nanofiltration membrane with antibiofouling properties and self-assembled layered morphology.  

PubMed

A new siloxane monomer, 3-(3-(diethoxy(2-(5-(4-(10-ethoxy-4-hydroxy-2,2-dimethyl-11-oxa-2-ammonio-6-aza-10-silatridecan-10-yl)phenyl)-1,3,4-oxadi azol-2-ylthio)ethyl)silyl)propylamino)-2-hydroxy-N,N,N-trimethylpropan-1-aminium chloride (OA), was synthesized by reported 3-((4-(5-(2-((3-aminopropyl) diethoxysilyl)ethylthio)-1,3,4-oxadiazol-2-yl)phenyl) diethoxysilyl)propan-1-amine (APDSMO) and glycidyltrimethylammonium chloride (GDTMAC) by epoxide ring-opening reaction. OA-poly(vinyl alcohol) (PVA) hybrid antibiofouling nanofilter (NF) membranes were prepared by acid-catalyzed sol-gel followed by formal cross-linking. Membranes showed wormlike arrangement and self-assembled layered morphology with varying OA content. Hybrid NF membrane, especially OA-6, showed low surface roughness, high hydrophilic nature, low biofouling, high cross-linking density, thermal and mechanical stablility, solvent- and chlorine-tolerant nature, along with good permeability and salt rejection. Prepared OA-6 hybrid NF membrane can be used efficiently for desalting and purification of water with about 2.0 g/L salt content (groundwater in major part of India). The described method provides novel route for producing antibiofouling membranes of diversified applications. PMID:22360398

Singh, Ajay K; Prakash, S; Kulshrestha, Vaibhav; Shahi, Vinod K

2012-03-01

137

Stable biocompatible cross-linked fluorescent polymeric nanoparticles based on AIE dye and itaconic anhydride.  

PubMed

Self-assembly of polymeric materials to form nanoparticles is a particularly promising strategy for various biomedical applications, however, these self-assembling systems often encounter the critical micelle concentration (CMC) issue, as the nanoparticles is usually unstable at low concentration. Therefore, stable cross-linked fluorescent polymeric nanoparticles (FPNs) were covalently constructed from an aggregation induced emission (AIE) dye, itaconic anhydride, poly(ethylene glycol) monomethyl ether methacylate and polyethylenimine. These obtained PhE-ITA-20%(80%) FPNs were fully characterized by a series of techniques including (1)H NMR spectra, UV-vis absorption spectra, fluorescence spectra, FT-IR spectra, transmission electron microscopy, gel permeation chromatography, and dynamic light scattering. Such FPNs emitted intense fluorescence due to the introduction of aggregation induced emission dye. More importantly, the FPNs were found extremely stable in physiological solution even below the CMC owing to their cross-linked architectures. Biocompatibility evaluation and cell uptake behavior of the FPNs were further investigated to explore their potential biomedical applications, the demonstrated excellent biocompatibility made them promising for cell imaging. PMID:24973146

Li, Haiyin; Zhang, Xiqi; Zhang, Xiaoyong; Yang, Bin; Wei, Yen

2014-09-01

138

Novel polymers with thermally controlled covalent cross-linking  

NASA Astrophysics Data System (ADS)

The exploration of re-mending and self-healing of polymeric materials has become increasingly more exciting in the recent past. However, no highly cross-linked polymeric material could be healed in the absence of additional ingredients such as a catalyst, additional monomer, or special surface treatment of the fractured interface until the materials that are the subject of this dissertation were discovered. Thermally reversible Diels-Alder (DA) cycloadditions of multi-dienes and multi-dienophiles were used as cross-linking to prepare thermally re-mendable highly cross-linked polymers, in which the thermal reversibility can be accomplished by the retro DA reaction. The bulk polymeric materials are tough solids at room temperature but at temperatures above 90 to 120°C, a number of "intermonomer" linkages disconnect, yet reconnect upon cooling. This process is fully reversible and can be used to restore a fractured part multiple times. DSC, TMDSC, TMA, DMA and solid state NMR were applied to study the thermal and mechanical properties of the polymers. To determine the fracture-healing efficiencies of these polymers, tests were performed using compact tension specimens. Representative recoveries were obtained between 57% and 83% of the original fracture load, after the thermal treatment of failed pieces. Scanning electron microscope (SEM) was also used to characterize healing efficiency. Efficient multiple-time healing was also observed. Novel shape memory materials with Diels-Alder groups were also developed. The shapes of materials can be changed and restored after being heated to elevated temperatures (60 to 80°C). Water-soluble cationic poly(p-phenylene vinylene) were synthesized for bio-sensing purposes.

Chen, Xiangxu

139

Tethered Lubricant Films Based On Cross-linked Polydimethylsiloxane  

NASA Astrophysics Data System (ADS)

We report on the interfacial friction and wear properties of surface-tethered cross-linked polymer thin films. We show that thin, two-tiered films produced by covalently tethering polydimethylsiloxane (PDMS) networks to self-assembled monolayers manifest the lowest friction coefficient (mu = 0.0039) recorded for a dry lubricant film. Using a combination of lateral force microscopy, equilibrium swelling, and adhesion measurements we determine the physical processes responsible for these low friction coefficients. We also investigate the effect of free (unattached) and pendent polymer chains dispersed in thin PDMS network films on transient mechanical properties, interfacial friction, and wear characteristics.

Landherr, Lucas; Cohen, Claude; Archer, Lynden

2009-03-01

140

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 PMID:23925329

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

2013-01-01

141

Effect of transglutaminase-induced cross-linking on gelation of myofibrillar/soy protein mixtures.  

PubMed

Microbial transglutaminase (MTGase)-catalyzed interaction and gelation of mixed myofibrillar (MPI)/soy (SPI) protein isolates were investigated at varying ionic strengths and MPI:SPI ratios, with or without SPI being preheated (80 °C). MTGase treatments in deionized water converted myosin heavy chain and actin into lower molecular-weight polypeptides, which gradually diminished as the ionic strength increased up to 0.6 M NaCl. A reduced intensity in the electrophoretic bands of soy proteins (7S and 11S except the basic subunits) was observed in all treatments, suggesting cross-linking with MPI. The enzyme treatment slightly increased the thermal transition (denaturation) temperatures of MPI/SPI but greatly enhanced (P<0.05) the elasticity of the mixed protein gels when compared with untreated samples, independent of incubation time. PMID:22063454

Ramírez-Suárez, J C; Xiong, Y L

2003-10-01

142

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

PubMed

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

Dooley, Kevin; Bulutoglu, Beyza; Banta, Scott

2014-10-13

143

Association between collagen cross-links and trabecular microarchitecture properties of human vertebral bone  

E-print Network

Association between collagen cross-links and trabecular microarchitecture properties of human Keywords: Microarchitecture Collagen cross-links Pentosidine Vertebrae Trabecular bone It has been suggested that age-related deterioration in trabecular microarchitecture and changes in collagen cross

Paris-Sud XI, Université de

144

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

145

The role of cross-linking in epidermal differentiation.  

PubMed

Cultured bovine keratinocytes contain two major classes of transglutaminase substrate proteins. These may be separated on Sephadex G-75 into a 30,000-to-50,000-dalton fraction and a fraction which is heavier than 75,000 daltons. By SDS-electrophoresis, the lighter fraction consists of two components of molecular weights 9,000 and 18,000 daltons, while the heavier fraction consists of a doublet of about 100,000 daltons. Bovine epidermis contains substrate proteins which apparently correspond to the two components of the lighter class. The 2 classes of substrate proteins may be analogous to two substrate proteins isolated from cultured human keratinocytes which are thought to be precursors of cornified envelope. The major transglutaminase substrate present in both newborn rat epidermis and cultured keratinocytes has a native molecular weight of greater than 75,000 daltons but an SDS-dissociated molecular weight of 22,000 daltons. The sera of 5 of 6 rabbits react immunologically with a protein present in cultured human keratinocytes which is a poor or minor substrate of transglutaminase. The cross-linking of keratins may play a role in epidermal differentiation since keratins from more differentiated areas of epidermis may contain a higher level of interchain isopeptide bonds. Keratin may be cross-linked itself or to stratum corneum basic protein, in vitro, to form both soluble and insoluble aggregates. No adducts between keratin and purified cornified envelope were formed when both were treated with active epidermal transglutaminase. PMID:6197245

Kubilus, J; Baden, H P

1983-01-01

146

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

147

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

148

Customized pachymetric guided epithelial debridement for corneal collagen cross linking  

PubMed Central

Backround We describe a modified method for deepitheliazation prior to corneal cross linking (CXL). The technique may overcome the current corneal pachymetric limitation parameter (over 400 microns) that is necessary for the safety of the procedure without affecting the overall benefits. Methods In a series of two patients, with inferior topographic steepening and regional thinning (less than 400 microns corresponding to the area of corneal steepening), CXL after customized epithelial removal was performed. Results There were no intra- or postoperative adverse events seen by the nine month follow up examination. Stabilization of the corneal ectasia was observed up to nine months post-costumized pachymetric-guided epithelial removal. Conclusion The technique of customized pachymetric-guided epithelial removal is easy to perform and may overcome the limitations of the preoperative corneal pachymetry expanding the application of the procedure in patients with regional corneal thinning. PMID:19715585

Kymionis, George D; Diakonis, Vasilios F; Coskunseven, Efekan; Jankov, Mirco; Yoo, Sonia H; Pallikaris, Ioannis G

2009-01-01

149

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

PubMed

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

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

2014-06-01

150

Peptidoglycan Cross-Linking in Glycopeptide-Resistant Actinomycetales  

PubMed Central

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

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

2014-01-01

151

Cross-linked polyethylenimine-tripolyphosphate nanoparticles for gene delivery  

PubMed Central

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

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

2014-01-01

152

Cross-linked polynorbornene-coated gold nanoparticles: dependence of particle stability on cross-linking position and cross-linker structure.  

PubMed

This paper describes the preparation of cross-linked polynorbornene coated gold nanoparticles. The polymer was grown radially from the particle surface using a ring opening metathesis polymerization of norbornene and an electrophilic norbornene ester, which was cross-linked using a variety of diamines. The stability of the cross-linked nanoparticles toward oxidative etching by cyanide was evaluated. The rate of etching decreases as diamines with fewer degrees of conformational freedom are used as cross-linkers. The distance of the cross-linking block from the nanoparticle surface was systematically varied. Nanoparticles with the cross-linked block furthest from the surface were etched most slowly. This is suggested to arise as a result of the polymers adopting a mushroom conformation when the cross-linking block is close to the particle surface, while more distal cross-linking results in more rigid polymer chains that are less permeable to the cyanide etchant. These results provide new insight into how fine-tuning the polymer cross-linking architecture can modulate nanoparticle stability. PMID:18729530

Liu, Xiang; Basu, Amit

2008-10-01

153

Molecular structure of hyaluronan: an introduction  

Microsoft Academic Search

Hyaluronan is an unbranched polysaccharide of repeating disaccharides consisting of d-glucuronic acid and N-acetyl-d-glucosamine. Its strong water-retaining ability and visco-elastic properties have been broadly utilized in medical applications.\\u000a Hyaluronan is an important constituent of the extracellular matrix whose physiological functions are manifested both as the\\u000a substance is by itself as well as when it is being linked to various proteins.

István Hargittai; Magdolna Hargittai

2008-01-01

154

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

PubMed Central

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

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

2014-01-01

155

Cross-linking of collagen. Location of pyridinoline in bovine articular cartilage at two sites of the molecule.  

PubMed Central

The location of pyridinoline in 18-month-old bovine articular cartilage was investigated by fractionation of CNBr-derived peptides by ion-exchange chromatography and gel filtration. Two peptides, PCP1 and PCP2, were isolated and were shown to contain stoichiometric amounts of pyridinoline. From its amino acid composition and sequence studies, peptide PCP1 was shown to comprise two C-terminal non-helical chains (CB14) linked through pyridinoline to the alpha 1(II)-CB12 portion of the helix. The CB14 chains appeared to be labile at their C-terminal ends, resulting in lower-than-expected amounts of homoserine, and only the N-terminal portion of the peptide was sequenced. Similar studies of peptide PCP2 showed that it contained two N-terminal non-helical chains (CB4) linked to the alpha 1(II)-CB9,7 portion of the helix. The isolated peptides therefore confirmed the function of pyridinoline in stabilizing the 4D stagger of adjacent molecules. The possibility that the cross-link could act both as an intra- and an inter-microfibrillar cross-link was considered. A mechanism of formation of pyridinoline was postulated that, together with other evidence, appears to support the view that, in cartilage, pyridinoline acts primarily as an intramicrofibrillar cross-link and does not contribute to increased stability during maturation through lateral aggregation and bonding of filaments. PMID:6626173

Robins, S P; Duncan, A

1983-01-01

156

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

PubMed

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

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

2014-01-30

157

Photoresponsive DNA-cross-linked hydrogels for controllable release and cancer therapy.  

PubMed

We have developed a photoresponsive DNA-cross-linked hydrogel that can be photoregulated by two wavelengths with a reversible sol-gel conversion. This photoinduced conversion can be further utilized for precisely controllable encapsulation and release of multiple loads. Specifically, photosensitive azobenzene moieties are incorporated into DNA strands as cross-linkers, such that their hybridization to complementary DNAs (cDNAs) responds differently to different wavelengths of light. On the basis of the rheology variation of hydrogels, it is possible to utilize this material for storing and releasing molecules and nanoparticles. To prove the concept, three different materials--fluorescein, horseradish peroxidase, and gold nanoparticles--were encapsulated inside the gel at 450 nm and then released by photons at 350 nm. Further experiments were carried out to deliver the chemotherapy drug doxorubicin in a similar manner in vitro. Our results show a net release rate of 65% within 10 min, and the released drug maintained its therapeutic effect. This hydrogel system provides a promising platform for drug delivery in targeted therapy and in biotechnological applications. PMID:21126095

Kang, Huaizhi; Liu, Haipeng; Zhang, Xiaoling; Yan, Jilin; Zhu, Zhi; Peng, Lu; Yang, Huanghao; Kim, Youngmi; Tan, Weihong

2011-01-01

158

Hyaluronan regulation of vascular integrity  

PubMed Central

Vascular integrity or the maintenance of blood vessel continuity is a fundamental process regulated, in part, by the endothelial glycocalyx and cell-cell junctions. Defects in endothelial barrier function are an initiating factor in several disease processes including atherosclerosis, ischemia/reperfusion, tumor angiogenesis, cancer metastasis, diabetes, sepsis and acute lung injury. The glycosaminoglycan, hyaluronan (HA), maintains vascular integrity through endothelial glycocalyx modulation, caveolin-enriched microdomain regulation and interaction with endothelial HA binding proteins. Certain disease states increase hyaluronidase activity and reactive oxygen species (ROS) generation which break down high molecular weight HA to low molecular weight fragments causing damage to the endothelial glycocalyx. Further, these HA fragments can activate specific HA binding proteins upregulated in vascular disease to promote actin cytoskeletal reorganization and inhibition of endothelial cell-cell contacts. This review focuses on the crucial role of HA in vascular integrity and how HA degradation promotes vascular barrier disruption. PMID:22254199

Lennon, Frances E; Singleton, Patrick A

2011-01-01

159

Cross-linking of fibrinogen and fibrin by fibrin-stablizing factor (factor XIIIa).  

PubMed

Factor XIIIa catalyzed intermolecular cross-linking of fibrinogen at initial rates that varied in direct (first order) proportion to the fibrinogen concentration, which differed from the well known zero order relationship in fibrin cross-linking. Preferential cross-linking of gamma-chains occurred with both substrates. The differences in rates and order of reaction were attributed mainly to effect of self-alignment of the gamma-chains in fibrin which enabled the cross-linking enzyme to interact with paired chains as a single rather than two independent entities. Studies on mixtures of fibrinogen and fibrin indicated factor XIIIa had near equal affinities for the two substrates. At low concentrations with which cross-linking of fibrinogen proceeded sluggishly compared to fibrin, fibrinogen inhibited stabilization of fibrin clots by competitively partitioning factor XIIIa away from the fribin. Additional inhibition arose from cross-linking of fibrin in soluble combination with fibrinogen in mixtures containing fibrinogen in large excess over fibrin. The observations demonstrate ways in which fibrinogen normally helps to suppress both polymerization and cross-linking of small amounts of fibrin produced within the circulation. At very high concentrations above 30 mg. per milliliter, fibrinogen underwent cross-linking at faster initial rates than the cross-linking of fibrin. Rapid cross-linking of concentrated fibrogen raises the possibility that filtration enrichment may be a factor contributing to abnormal formation of the highly insoluble fibrinogen deposits occurring in atheromatous tissue. PMID:1168234

Kanaide, H; Shainoff, J R

1975-04-01

160

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

161

Zinc cross-linked hydroxamated alginates for pulsed drug release  

PubMed Central

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

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

2013-01-01

162

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

163

Immobilized Thylakoids in a Cross-Linked Albumin Matrix  

PubMed Central

Immobilization of lettuce (Lactuca sativa) thylakoids has been performed by using glutaraldehyde and bovine serum albumin. Confirming previous reports, a stabilization of the O2 evolution activity of the photosystem II (PSII) under storage and functional conditions has been observed. The present work is devoted to the role played by mono-and divalent cations, during the immobilization process itself, on the O2 production. Four types of measurements have been employed: kinetic measurements, low temperature (77 K) fluorescence emission, photoacoustic (PA) spectroscopy, and electron microscopy observations. We show that the effect of glutaraldehyde is complex because it acts as an inhibitor, a stabilizing agent, and a cross-linking reactive. In the present studies, the thylakoids are immobilized within a polymeric insoluble albumin matrix. The highest activity yield and the best storage conditions are obtained when 0.15 mm Na+ (or K+), 1 mm Mg2+, and 0.1 mm Mn2+ are present in the resuspending media before the immobilization. Due to modifications of the ionic content during such a process, structural differences are observed on the stacking degree of thylakoids. No modification of the fluorescence and PA spectra after the immobilization are found. Furthermore, a correlation between activities and spectral changes have been shown: when the activities increase, the F735 to F695 ratio increases and the PA676 to PA440 ratio decreases. Images Fig. 2 Fig. 5 PMID:16662563

Thomasset, Brigitte; Thomasset, Thierry; Vejux, Alain; Jeanfils, Joseph; Barbotin, Jean-Noel; Thomas, Daniel

1982-01-01

164

Grafting of cross-linked hydrogel networks to titanium surfaces.  

PubMed

The performance of medical implants and devices is dependent on the biocompatibility of the interfacial region between tissue and the implant material. Polymeric hydrogels are attractive materials for use as biocompatible surface coatings for metal implants. In such systems, a factor that is critically important for the longevity of an implant is the formation of a robust bond between the hydrogel layer and the implant metal surface and the ability for this assembly to withstand physiological conditions. Here, we describe the grafting of cross-linked hydrogel networks to titanium surfaces using grit-blasting and subsequent chemical functionalization using a silane-based adhesion promoter. Metal surface characterization was carried out using profilometry, scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX) analysis. Hydrogel layers composed of poly(ethylene glycol)-dimethacrylate (PEG-DMA), poly(2-hydroxyethylmethacrylate) (PHEMA), or poly(ethylene glycol)/poly(acrylic acid) (PEG/PAA) semi-interpenetrating polymer networks (semi-IPNs) have been prepared. The mechanical properties of these hydrogel-metal assemblies have been characterized using lap-shear measurements, and the surface morphology was studied by SEM and EDX. We have shown that both high surface roughness and chemical functionalization are critical for adhesion of the hydrogel layer to the titanium substrate. PMID:24364560

Muir, Beinn V O; Myung, David; Knoll, Wolfgang; Frank, Curtis W

2014-01-22

165

Profile of Microbial Keratitis after Corneal Collagen Cross-Linking  

PubMed Central

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

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

2014-01-01

166

Aminoguanidine Prevents Diabetes-Induced Arterial Wall Protein Cross-Linking  

Microsoft Academic Search

Age-associated increases in collagen cross-linking and accumulation of advanced glycosylation products are both accelerated by diabetes, suggesting that glucose-derived cross-link formation may contribute to the development of chronic diabetic complications as well as certain physical changes of aging. Aminoguanidine, a nucleophilic hydrazine compound, prevented both the formation of fluorescent advanced nonenzymatic glycosylation products and the formation of glucose-derived collagen cross-links

M. Brownlee; H. Vlassara; A. Kooney; P. Ulrich; A. Cerami

1986-01-01

167

Multiple Repair Pathways Mediate Tolerance to Chemotherapeutic Cross-linking Agents in Vertebrate Cells  

Microsoft Academic Search

Cross-linking agents that induce DNA interstrand cross-links (ICL) are widely used in anticancer chemotherapy. Yeast genetic studies show that nucleotide excision repair (NER), Rad6\\/Rad18-dependent postreplication repair, homologous recombination, and cell cycle checkpoint pathway are involved in ICL repair. To study the contribution of DNA damage response pathways in tolerance to cross-linking agents in vertebrates, we made a panel of gene-disrupted

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

2005-01-01

168

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

Microsoft Academic Search

Introduction  Corneal collagen cross-linking is a rather new technique that uses riboflavin and ultraviolet A light for collagen fiber stabilization\\u000a in keratoconus corneas. Other than reversible side effects, the preliminary results of corneal collagen cross-linking studies\\u000a suggest that it is a rather safe technique. In this report, we demonstrate a case of corneal melting after corneal collagen\\u000a cross-linking for keratoconus corneas

Georgios Labiris; Eleni Kaloghianni; Stavrenia Koukoula; Athanassios Zissimopoulos; Vassilios P Kozobolis

2011-01-01

169

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

170

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

PubMed Central

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

Mazzotta, Cosimo; Ramovecchi, Vincenzo

2014-01-01

171

Biologically relevant oxidants cause bound proteins to readily oxidatively cross-link at Guanine.  

PubMed

Oxidative DNA-protein cross-links have received less attention than other types of DNA damage and remain as one of the least understood types of oxidative lesion. A model system using ribonuclease A and a 27-nucleotide DNA was used to determine the propensity of oxidative cross-linking to occur in the presence of oxidants. Cross-link formation was examined using four different oxidation systems that generate singlet oxygen, superoxide, and metal-based Fenton reactions. It is shown that oxidative cross-linking occurs in yields ranging from 14% to a maximal yield of 61% in all oxidative systems when equivalent concentrations of DNA and protein are present. Because singlet oxygen is the most efficient oxidation system in generating DNA-protein cross-links, it was chosen for further analyses. Cross-linking occurred with single-stranded DNA binding protein and not with bovine serum albumin. Addition of salt lowered nonspecific binding affinity and lowered cross-link yield by up to 59%. The yield of cross-linking increased with increased ratios of protein compared with DNA. Cross-linking was highly dependent on the number of guanines in a DNA sequence. Loss of guanine content on the 27-nucleotide DNA led to nearly complete loss in cross-linking, while primer extension studies showed cross-links to predominantly occur at guanine base on a 100-nucleotide DNA. The chemical species generated were examined using two peptides derived from the ribonuclease A sequence, N-acetyl-AAAKF and N-acetyl-AYKTT, which were cross-linked to 2'-deoxyguanosine. The cross-link products were spiroiminodihydantoin, guanidinohydantoin, and tyrosyl-based adducts. Formation of tyrosine-based adducts may be competitive with the more well-studied lysine-based cross-links. We conclude that oxidative cross-links may be present at high levels in cells since the propensity to oxidatively cross-link is high and so much of the genomic DNA is coated with protein. PMID:22216745

Solivio, Morwena J; Nemera, Dessalegn B; Sallans, Larry; Merino, Edward J

2012-02-20

172

Synthesis of cross-linked DNA containing oxidized abasic site analogues.  

PubMed

DNA interstrand cross-links are an important family of DNA damage that block replication and transcription. Recently, it was discovered that oxidized abasic sites react with the opposing strand of DNA to produce interstrand cross-links. Some of the cross-links between 2'-deoxyadenosine and the oxidized abasic sites, 5'-(2-phosphoryl-1,4-dioxobutane) (DOB) and the C4-hydroxylated abasic site (C4-AP), are formed reversibly. Chemical instability hinders biochemical, structural, and physicochemical characterization of these cross-linked duplexes. To overcome these limitations, we developed methods for preparing stabilized analogues of DOB and C4-AP cross-links via solid-phase oligonucleotide synthesis. Oligonucleotides of any sequence are attainable by synthesizing phosphoramidites in which the hydroxyl groups of the cross-linked product were orthogonally protected using photochemically labile and hydrazine labile groups. Selective unmasking of a single hydroxyl group precedes solid-phase synthesis of one arm of the cross-linked DNA. The method is compatible with commercially available phosphoramidites and other oligonucleotide synthesis reagents. Cross-linked duplexes containing as many as 54 nt were synthesized on solid-phase supports. Subsequent enzyme ligation of one cross-link product provided a 60 bp duplex, which is suitable for nucleotide excision repair studies. PMID:24949656

Ghosh, Souradyuti; Greenberg, Marc M

2014-07-01

173

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

NASA Astrophysics Data System (ADS)

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

Gul, Rizwan M.; Khan, Tahir I.

2014-06-01

174

Controlled sparse and percolating cross-linking in waterborne soft adhesives.  

PubMed

The effect of low levels of cross-linking on the adhesive and mechanical properties of waterborne pressure-sensitive adhesives was investigated. We have taken advantage of a core-shell latex particle morphology obtained by emulsion polymerization to create a heterogeneous structure of cross-links without major modification of the monomer composition. The latex particles comprise a shell containing cross-linkable diacetone acrylamide (DAAM) repeat units localized on the periphery of a slightly softer core copolymer of very similar composition. Adipic acid dihydrazide was added to the latex prior to film formation to react with DAAM repeat units and affect interfacial cross-linking between particles in the adhesive films. The honeycomb-like structure obtained after drying of the latex results in a good balance between the dissipative properties required for adhesion and the resistance to creep. The characterization of the mechanical properties of the films shows that the chosen cross-linking method creates a percolating lightly cross-linked network, swollen with a nearly un-cross-linked component. With this cross-linking method, the linear viscoelastic properties of the soft films are nearly unaffected by the cross-linking while the nonlinear tensile properties are greatly modified. As a result, the long-term shear resistance of the adhesive film improves very significantly while the peel force remains nearly the same. A simple rheological model is used to interpret qualitatively the changes in the material parameters induced by cross-linking. PMID:20355828

Deplace, F; Carelli, C; Langenfeld, A; Rabjohns, M A; Foster, A B; Lovell, P A; Creton, C

2009-09-01

175

Hyaluronan and phospholipid association in biolubrication.  

PubMed

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

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

2013-12-01

176

The theory and art of corneal cross-linking  

PubMed Central

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

2013-01-01

177

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

178

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

PubMed Central

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

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

2012-01-01

179

Use of Hyaluronan-Derived Hydrogels for Three-Dimensional Cell Culture and Tumor Xenografts  

PubMed Central

The practice of in vitro three-dimensional (3-D) cell culture has lagged behind the realization that classical two-dimensional (2-D) culture on plastic surfaces fails to mirror normal cell biology. Biologically, a complex network of proteins and proteoglycans that constitute the extracellular matrix (ECM) surrounds every cell. To recapitulate the normal cellular behavior, scaffolds (ECM analogs) that reconstitute the essential biological cues are required. This unit describes the 3-D cell culture and tumor engineering applications of Extracel, a novel semisynthetic ECM (sECM), based on cross-linked derivatives of hyaluronan and gelatin. A simplified cell encapsulation and pseudo-3-D culturing (on top of hydrogels) protocol is provided. In addition, the use of this sECM as a vehicle to obtain tumor xenografts with improved take rates and tumor growth is presented. These engineered tumors can be used to evaluate anticancer therapies under physiologically relevant conditions. PMID:18819087

Serban, Monica A.; Scott, Anna; Prestwich, Glenn D.

2012-01-01

180

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

NASA Technical Reports Server (NTRS)

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

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

1985-01-01

181

Hyaluronan as an Immune Regulator in Human Diseases  

PubMed Central

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

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

2010-01-01

182

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

183

IQGAP1, a Rac- and Cdc42-binding Protein, Directly Binds and Cross-links Microfilaments  

PubMed Central

Activated forms of the GTPases, Rac and Cdc42, are known to stimulate formation of microfilament-rich lamellipodia and filopodia, respectively, but the underlying mechanisms have remained obscure. We now report the purification and characterization of a protein, IQGAP1, which is likely to mediate effects of these GTPases on microfilaments. Native IQGAP1 purified from bovine adrenal comprises two ?190-kD subunits per molecule plus substoichiometric calmodulin. Purified IQGAP1 bound directly to F-actin and cross-linked the actin filaments into irregular, interconnected bundles that exhibited gel-like properties. Exogenous calmodulin partially inhibited binding of IQGAP1 to F-actin, and was more effective in the absence, than in the presence of calcium. Immunofluorescence microscopy demonstrated cytochalasin D–sensitive colocalization of IQGAP1 with cortical microfilaments. These results, in conjunction with prior evidence that IQGAP1 binds directly to activated Rac and Cdc42, suggest that IQGAP1 serves as a direct molecular link between these GTPases and the actin cytoskeleton, and that the actin-binding activity of IQGAP1 is regulated by calmodulin. PMID:9199170

Bashour, Anne-Marie; Fullerton, Aaron T.; Hart, Matthew J.; Bloom, George S.

1997-01-01

184

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

2012-08-15

185

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

2013-07-01

186

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

2013-07-01

187

Ingested hyaluronan moisturizes dry skin  

PubMed Central

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

2014-01-01

188

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

EPA Science Inventory

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

189

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...

190

Effect of the nature of cross-linking acrylamides on structurization of gelatin by laser irradiation  

Microsoft Academic Search

We consider the characteristics of photochemical reactions in gelatin-cross-linking agent systems under the influence of emission from a helium-neon laser. We show that the degree of structural transformations is determined by the nature of the cross-linking agents and depends on their structure and reactivity.

A. V. Botsman; S. V. Volkov; V. I. Lutoshkin

1990-01-01

191

Preparation and Structures of Ethyl-Cyanoethyl Cellulose/Cross-Linked Polystyrene Composites.  

National Technical Information Service (NTIS)

Ethyl-cyanoethyl cellulose ((E-CE)C)/cross-linked polystyrene (PS) composites were prepared via polymerization of styrene in (E-CE)C/styrene solutions with glycol diacrylate as a cross-linking reagent. The polymerization of the solution, morphology, and m...

S. H. Jiang, Y. Huang

1995-01-01

192

Cross-linking electrochemical mass spectrometry for probing protein three-dimensional structures.  

PubMed

Chemical cross-linking combined with mass spectrometry (MS) is powerful to provide protein three-dimensional structure information but difficulties in identifying cross-linked peptides and elucidating their structures limit its usefulness. To tackle these challenges, this study presents a novel cross-linking MS in conjunction with electrochemistry using disulfide-bond-containing dithiobis[succinimidyl propionate] (DSP) as the cross-linker. In our approach, electrolysis of DSP-bridged protein/peptide products, as online monitored by desorption electrospray ionization mass spectrometry is highly informative. First, as disulfide bonds are electrochemically reducible, the cross-links are subject to pronounced intensity decrease upon electrolytic reduction, suggesting a new way to identify cross-links. Also, mass shift before and after electrolysis suggests the linkage pattern of cross-links. Electrochemical reduction removes disulfide bond constraints, possibly increasing sequence coverage for tandem MS analysis and yielding linear peptides whose structures are more easily determined than their cross-linked precursor peptides. Furthermore, this cross-linking electrochemical MS method is rapid, due to the fast nature of electrochemical conversion (much faster than traditional chemical reduction) and no need for chromatographic separation, which would be of high value for structural proteomics research. PMID:25141260

Zheng, Qiuling; Zhang, Hao; Tong, Lingying; Wu, Shiyong; Chen, Hao

2014-09-16

193

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

PubMed Central

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

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

2010-01-01

194

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

NASA Technical Reports Server (NTRS)

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

Ono, S.; Yamauchi, M.

1992-01-01

195

Modified dextran cross-linked electrospun gelatin nanofibres for biomedical applications.  

PubMed

Electrospun gelatin nanofibres attract attention of bioengineering arena because of its excellent biocompatibility and structural resemblance with native extracellular matrix. In this study, we have developed gelatin nanofibres using an innovative cross-linking approach to minimize cytotoxic effects. Gelatin was dissolved in water:acetic acid (8:2, v/v) solution and electrospun to form nanofibres with diameter in the range of 156±30nm. The nanofibres were cross-linked with a modified polysaccharide, namely, dextran aldehyde (DA). Cross-linking with DA could be achieved without compromising the fibrous architecture. DA cross-linked gelatin nanofibres maintained the fibrous morphology in aqueous medium. These mats exhibit improved mechanical properties and gradual degradation behaviour. The nanofibres were evaluated for cytotoxicity, cell adhesion, viability, morphology and proliferation using L-929 fibroblast cells. The results confirmed that DA cross-linked mats were non cytotoxic towards L-929 cells with good cell adhesion, spreading and proliferation. PMID:25263915

Jalaja, K; Kumar, P R Anil; Dey, Tuli; Kundu, Subhas C; James, Nirmala R

2014-12-19

196

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

197

Characterization of the bombesin receptor on mouse pancreatic acini by chemical cross-linking  

SciTech Connect

Bombesin (BN), gastrin-releasing peptide (GRP) and GRP(18-27) (neuromedin C) were equipotent and 30-fold more potent than neuromedin B (NMB) in inhibiting binding of {sup 125}I-GRP to and in stimulating amylase release from mouse pancreatic acini. In the present study we used {sup 125}I-GRP and chemical cross-linking techniques to characterize the mouse pancreatic BN receptor. After binding of {sup 125}I-GRP to membranes, and incubation with various chemical cross-linking agents, cross-linked radioactivity was analyzed by SDS-PAG electrophoresis and autoradiography. With each of 4 different chemical cross-linking agents, there was a single broad polypeptide band of Mr 80,000. Cross-linking did not occur in the absence of the cross-linking agent. Cross-linking was inhibited only by peptides that interact with the BN receptor such as GRP, NMB, GRP(18-27) or BN. Dose-inhibition curves for the ability of BN or NMB to inhibit binding of {sup 125}I-GRP to membranes or cross-linking to the 80,000 polypeptide demonstrated for both that BN was 15-fold more potent than NMB. The apparent molecular weight of the cross-linked polypeptide was unchanged by adding dithiothreitol. N-Glycanase treatment reduced the molecular weight of the cross-linked peptide to 40,000. The present results indicate that the BN receptor on mouse pancreatic acinar cell membranes resembles that recently described on various tumor cells in being a single glycoprotein with a molecular weight of 76,000. Because dithiothreitol had no effect, this glycoprotein is not a subunit of a larger disulfide-linked structure.

Huang, S.C.; Yu, D.H.; Wank, S.A.; Gardner, J.D.; Jensen, R.T. (National Institutes of Health, Bethesda, MD (USA))

1990-11-01

198

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

NASA Astrophysics Data System (ADS)

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

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

199

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

200

Retention of the original LLC structure in a cross-linked poly(ethylene glycol) diacrylate hydrogel with reinforcement from a silica network.  

PubMed

Cross-linked poly(ethylene glycol) diacrylate (PEGDA) hydrogels with uniformly controlled nanoporous structures templated from hexagonal lyotropic liquid crystals (LLC) represent separation membrane materials with potentially high permeability and selectivity due to their high pore density and narrow pore size distribution. However, retaining LLC templated nanostructures is a challenge as the polymer gels are not strong enough to sustain the surface tension during the drying process. In the current study, cross-linked PEGDA gels were reinforced with a silica network synthesized via an in situ sol-gel method, which assists in the retention of the hexagonal LLC structure. The silica precursor does not obstruct the formation of hexagonal phases. After surfactant removal and drying, these hexagonal structures in samples with a certain amount of tetraethoxysilane (TEOS) loading are well retained while the nanostructures are collapsed in samples without silica reinforcement, leading to the hypothesis that the reinforcement provided by the silica network stabilizes the LLC structure. The study examines the conditions necessary for a sufficient and well dispersed silica network in PEGDA gels that contributes to the retention of original LLC structures, which potentially enables broad applications of these gels as biomedical and membrane materials. PMID:24916196

Zhang, Juan; Xie, Zongli; Hoang, Manh; Hill, Anita J; Cong, Weiwei; She, Feng Hua; Gao, Weimin; Kong, Ling Xue

2014-07-28

201

Anomalous normal stresses in biopolymer networks with compliant cross-links  

NASA Astrophysics Data System (ADS)

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

Chen, P.

2014-02-01

202

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

PubMed

We report the versatility of polyion complex (PIC) micelles for the preparation of shell and core cross-linked (SCL and CCL) micelles with their surface properties determined by the constituent polymer composition and cross-linking agent. The negatively and positively charged PIC micelles with their molecular structure and properties depending on the mixing weight percentage and polymer molecular weight were first prepared by mixing the negatively and positively charged polyions, poly(acrylic acid) (PAA) and poly(l-lysine) (PLL). The feasibility of preparing SCL micelles was demonstrated by cross-linking the shell of the negatively and positively charged micelles using cystamine and genipin, respectively. The core of the micelles can be cross-linked by silica deposition to stabilize the assemblies. The shell and/or core cross-linked micelles exhibited excellent colloid stability upon changing solution pH. The drug release from the drug-loaded SCL micelles revealed that the controllable permeability of the SCL micelles can be achieved by tuning the cross-linking degree and the SCL micelles exhibited noticeable pH-responsive behavior with accelerated release under acidic conditions. With the versatility of cross-linking strategies, it is possible to prepare a variety of SCL and CCL micelles from PIC micelles. PMID:25357089

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

2014-12-21

203

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

PubMed

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

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

2013-05-01

204

Characterization of protein cross-links via mass spectrometry and an open-modification search strategy.  

PubMed

Protein-protein interactions are key to function and regulation of many biological pathways. To facilitate characterization of protein-protein interactions using mass spectrometry, a new data acquisition/analysis pipeline was designed. The goal for this pipeline was to provide a generic strategy for identifying cross-linked peptides from single LC/MS/MS data sets, without using specialized cross-linkers or custom-written software. To achieve this, each peptide in the pair of cross-linked peptides was considered to be "post-translationally" modified with an unknown mass at an unknown amino acid. This allowed use of an open-modification search engine, Popitam, to interpret the tandem mass spectra of cross-linked peptides. False positives were reduced and database selectivity increased by acquiring precursors and fragments at high mass accuracy. Additionally, a high-charge-state-driven data acquisition scheme was utilized to enrich data sets for cross-linked peptides. This open-modification search based pipeline was shown to be useful for characterizing both chemical as well as native cross-links in proteins. The pipeline was validated by characterizing the known interactions in the chemically cross-linked CYP2E1-b5 complex. Utility of this method in identifying native cross-links was demonstrated by mapping disulfide bridges in RcsF, an outer membrane lipoprotein involved in Rcs phosphorelay. PMID:18947195

Singh, Pragya; Shaffer, Scott A; Scherl, Alexander; Holman, Carol; Pfuetzner, Richard A; Larson Freeman, Theodore J; Miller, Samuel I; Hernandez, Patricia; Appel, Ron D; Goodlett, David R

2008-11-15

205

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. PMID:20551315

Courson, David S.; Rock, Ronald S.

2010-01-01

206

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

207

Riboflavin/UVA Collagen Cross-Linking-Induced Changes in Normal and Keratoconus Corneal Stroma  

PubMed Central

Purpose To determine the effect of Ultraviolet-A collagen cross-linking with hypo-osmolar and iso-osmolar riboflavin solutions on stromal collagen ultrastructure in normal and keratoconus ex vivo human corneas. Methods Using small-angle X-ray scattering, measurements of collagen D-periodicity, fibril diameter and interfibrillar spacing were made at 1 mm intervals across six normal post-mortem corneas (two above physiological hydration (swollen) and four below (unswollen)) and two post-transplant keratoconus corneal buttons (one swollen; one unswollen), before and after hypo-osmolar cross-linking. The same parameters were measured in three other unswollen normal corneas before and after iso-osmolar cross-linking and in three pairs of swollen normal corneas, in which only the left was cross-linked (with iso-osmolar riboflavin). Results Hypo-osmolar cross-linking resulted in an increase in corneal hydration in all corneas. In the keratoconus corneas and unswollen normal corneas, this was accompanied by an increase in collagen interfibrillar spacing (p<0.001); an increase in fibril diameter was also seen in two out of four unswollen normal corneas and one unswollen keratoconus cornea (p<0.001). Iso-osmolar cross-linking resulted in a decrease in tissue hydration in the swollen normal corneas only. Although there was no consistent treatment-induced change in hydration in the unswollen normal samples, iso-osmolar cross-linking of these corneas did result in a compaction of collagen fibrils and a reduced fibril diameter (p<0.001); these changes were not seen in the swollen normal corneas. Collagen D-periodicity was not affected by either treatment. Conclusion The observed structural changes following Ultraviolet-A cross-linking with hypo-osmolar or iso-osmolar riboflavin solutions are more likely a consequence of treatment-induced changes in tissue hydration rather than cross-linking. PMID:21850225

Hayes, Sally; Boote, Craig; Kamma-Lorger, Christina S.; Rajan, Madhavan S.; Harris, Jonathan; Dooley, Erin; Hawksworth, Nicholas; Hiller, Jennifer; Terill, Nick J.; Hafezi, Farhad; Brahma, Arun K.; Quantock, Andrew J.; Meek, Keith M.

2011-01-01

208

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

PubMed Central

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

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

2010-01-01

209

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

PubMed Central

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

Oral, Ebru; Muratoglu, Orhun K.

2007-01-01

210

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

211

Target-Responsive DNAzyme Cross-Linked Hydrogel for Visual Quantitative Detection of Lead.  

PubMed

Because of the severe health risks associated with lead pollution, rapid, sensitive, and portable detection of low levels of Pb(2+) in biological and environmental samples is of great importance. In this work, a Pb(2+)-responsive hydrogel was prepared using a DNAzyme and its substrate as cross-linker for rapid, sensitive, portable, and quantitative detection of Pb(2+). Gold nanoparticles (AuNPs) were first encapsulated in the hydrogel as an indicator for colorimetric analysis. In the absence of lead, the DNAzyme is inactive, and the substrate cross-linker maintains the hydrogel in the gel form. In contrast, the presence of lead activates the DNAzyme to cleave the substrate, decreasing the cross-linking density of the hydrogel and resulting in dissolution of the hydrogel and release of AuNPs for visual detection. As low as 10 nM Pb(2+) can be detected by the naked eye. Furthermore, to realize quantitative visual detection, a volumetric bar-chart chip (V-chip) was used for quantitative readout of the hydrogel system by replacing AuNPs with gold-platinum core-shell nanoparticles (Au@PtNPs). The Au@PtNPs released from the hydrogel upon target activation can efficiently catalyze the decomposition of H2O2 to generate a large volume of O2. The gas pressure moves an ink bar in the V-chip for portable visual quantitative detection of lead with a detection limit less than 5 nM. The device was able to detect lead in digested blood with excellent accuracy. The method developed can be used for portable lead quantitation in many applications. Furthermore, the method can be further extended to portable visual quantitative detection of a variety of targets by replacing the lead-responsive DNAzyme with other DNAzymes. PMID:25340621

Huang, Yishun; Ma, Yanli; Chen, Yahong; Wu, Xuemeng; Fang, Luting; Zhu, Zhi; Yang, Chaoyong James

2014-11-18

212

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

213

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

PubMed Central

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

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

2014-01-01

214

Transcription Inhibition by Platinum DNA Cross-links in Live Mammalian Cells  

E-print Network

We have investigated the processing of site-specific Pt?DNA cross-links in live mammalian cells to enhance our understanding of the mechanism of action of platinum-based anticancer drugs. The activity of platinum drugs ...

Ang, Wee Han

215

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. PMID:6769428

Nicholls, A C; Bailey, A J

1980-01-01

216

Cross-linking proteins with bimetallic tetracarboxylate compounds of transition metals  

DOEpatents

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

Kostic, N.M.; Chen, J.

1991-03-05

217

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

PubMed

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

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

2013-06-12

218

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

PubMed

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

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

2014-09-15

219

Reversible, self cross-linking nanowires from thiol-functionalized polythiophene diblock copolymers.  

PubMed

Poly(3-hexylthiophene)-block-poly(3-(3-thioacetylpropyl) oxymethylthiophene) (P3HT)-b-(P3TT) diblock copolymers were synthesized and manipulated by solvent-induced crystallization to afford reversibly cross-linked semiconductor nanowires. To cross-link the nanowires, we deprotected the thioacetate groups to thiols and they subsequently oxidized to disulfides. Cross-linked nanowires maintained their structural integrity in solvents that normally dissolve the polymers. These robust nanowires could be reduced to the fully solvated polymer, representing a novel, reversible cross-linking procedure for functional P3HT-based nanowire fibrils. Field-effect transistor measurements were carried out to determine the charge transport properties of these nanostructures. PMID:24735371

Hammer, Brenton A G; Reyes-Martinez, Marcos A; Bokel, Felicia A; Liu, Feng; Russell, Thomas P; Hayward, Ryan C; Briseno, Alejandro L; Emrick, Todd

2014-05-28

220

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

221

Effects of cross-linking and low molecular amylose on pasting characteristics of waxy corn starch  

Microsoft Academic Search

The action of amylose within the granule of normal corn starch is investigated by changes in pasting characteristics of waxy corn starch in a Rapid Visco Analyzer (RVA), using addition of soluble amylose (DP=18) and cross-linking with epichlorohydrin. Although waxy corn starch, containing no amylose, did not show an effect of addition of amylose on pasting characteristics, by cross-linking with

Masahiro Kurakake; Yoshio Akiyama; Hiroshi Hagiwara; Toshiaki Komaki

2009-01-01

222

Photocurable hard and porous biomaterials from ROMP precursors cross-linked with diyl radicals.  

PubMed

A combination of (ROMP) ring-opening metathesis polymerization and diradical (diyl) cross-linking provides a new access to hard biomaterials and potential artificial bone replacements. ROMP was used to construct soft and pliable linear polymers bearing photolabile diazene functions. After treatment with light, a nitrogen aerosol is released throughout the polymer to create desirable porosity, cross-linking, and hardening in a single step. Nonpolymeric mechanistic work supporting these studies was also examined. PMID:16203146

Enholm, Eric; Joshi, Aarti; Wright, Dennis L

2005-12-01

223

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

E-print Network

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

Vermaelen, John Douglas

2012-06-07

224

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

Microsoft Academic Search

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

Reinhard Fleer; Martin Brendel

1979-01-01

225

Chemical and thermal cross-linking of collagen and elastin hydrolysates  

Microsoft Academic Search

Chemical and thermal cross-linking of collagen soluble in acetic acid and elastin hydrolysates soluble in water have been studied. Solutions of collagen and elastin hydrolysates were treated using variable concentrations of 1-ethyl-3(3-dimethyl aminopropyl) carbodiimide (EDC) and N-hydroxysuccinimide (NHS). Moreover, diepoxypropylether (DEPE) has been used as cross-linking agent. Films made of collagen and elastin hydrolysates were also treated with temperature at

A. Sionkowska; J. Skopinska-Wisniewska; M. Gawron; J. Kozlowska; A. Planecka

2010-01-01

226

Cross-linked crystals of hydroxynitrile lyase as catalyst for the synthesis of optically active cyanohydrins  

Microsoft Academic Search

Purified hydroxynitrile lyase (HNL) from Manihot esculenta was crystallized by the sitting-drop vapour-diffusion method. The bipyramidal crystals formed (10–20 ?m) were cross-linked with different amounts of glutaraldehyde and used as biocatalyst for the synthesis of optically active cyanohydrins. The cross-linked crystals were more stable than Celite-immobilized enzymes when incubated in organic solvents, especially in polar solvents. After six consecutive batch

David Costes; Ernst Wehtje; Patrick Adlercreutz

2001-01-01

227

Dextran cross-linked gelatin microspheres as a drug delivery system  

Microsoft Academic Search

This paper describes the use of oxidized dextran as a cross-linker for the preparation of gelatin microspheres. Microspheres were obtained by a thermal gelation method and their dissolution kinetic was examined. In order to find evidence of sugar mediated cross-linking, swelling tests and gelatin microspheres dissolution experiments were performed. The obtained results indicated that oxidized dextran can form a cross-linked

Rita Cortesi; Elisabetta Esposito; Maria Osti; Enea Menegatti; Giacomo Squarzoni; Stanley Spencer Davis; Claudio Nastruzzi

1999-01-01

228

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

229

Facile fabrication of core cross-linked micelles by RAFT polymerization and enzyme-mediated reaction.  

PubMed

Polymeric micelles formed in aqueous solution by assembly of amphiphilic block copolymers have been extensively investigated due to their great potential as drug carriers. However, the stability of polymeric assembly is still one of the major challenges in delivering drugs to tissues and cells. Here, we report a facile route to fabricate core cross-linked (CCL) micelles using an enzymatic polymerization as the cross-linking method. We present synthesis of poly(ethylene glycol)-block-poly(N-isopropyl acrylamide-co-N-(4-hydroxyphenethyl) acrylamide) diblock copolymer PEG-b-P(NIPAAm-co-NHPAAm) via reversible addition-fragmentation chain transfer (RAFT) polymerization. The diblock copolymer was then self-assembled into non-cross-linked (NCL) micelles upon heating above the lower critical solution temperature (LCST), and subsequently cross-linked using horseradish peroxidase (HRP) and hydrogen peroxide (H2O2) as enzyme and oxidant. The characterization of the diblock copolymer and micelles were studied by NMR, DLS, UV-vis, and fluorescence spectroscopy. The fluorescence study reveals that the cross-linking process endows the micelles with much lower critical micelle concentration (CMC). In addition, the drug release study shows that the CCL micelles have lower release amount of doxorubicin (DOX) than the NCL micelles due to the enhanced stability of the CCL micelles by core cross-linking process. PMID:24768266

Wu, Yukun; Lai, Quanyong; Lai, Shuqi; Wu, Jing; Wang, Wei; Yuan, Zhi

2014-06-01

230

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

231

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. PMID:21496288

2011-01-01

232

Structural change of ?-carrageenan gel near sol-gel transition point  

NASA Astrophysics Data System (ADS)

The structural change of ?-carrageenan gel in the gel-to-sol transition was observed with the small-angle neutron scattering (SANS). The SANS intensity decreases on approaching to the transition point from the gel phase. On the other hand, the observed gyration radius does not change in the whole region of the gel phase. The fact means that the number of the cross link points decreases but their size keeps almost unchanged in the gel-to-sol transition.

Masaaki Sugiyama; Chikanori Yuasa; Kazuhiro Hara; Nobuyasu Hiramatsu; Atsushi Nakamura; Yasushi Hayakawa; Yutaka Maeda

233

Hyaluronidase and Hyaluronan in Insect Venom Allergy  

Microsoft Academic Search

Background: Insect venoms contain an allergen hyaluronidase that catalyzes the hydrolysis of hyaluronan (HA), a polymer of disaccharide GlcUA-GlcNAc in skin. HAs depending on their size have variable function in inflammation and immunity. This paper reports on whether hyaluronidase, HA polymers and oligomers can promote antibody response in mice. Methods: HA oligomers (8- to 50-mer; 3–20 kDa) were obtained by

Te Piao King; Knut M. Wittkowski

2011-01-01

234

Hyaluronan microspheres for sustained gene delivery and site-specific targeting  

Microsoft Academic Search

Hyaluronan is a naturally occurring polymer that has enjoyed wide successes in biomedical and cosmetic applications as coatings, matrices, and hydrogels. For controlled delivery applications, formulating native hyaluronan into microspheres could be advantageous but has been difficult to process unless organic solvents are used or hyaluronan has been modified by etherification. Therefore, we present a novel method of preparing hyaluronan

Yang H. Yun; Douglas J. Goetz; Paige Yellen; Weiliam Chen

2004-01-01

235

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

PubMed Central

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

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

2013-01-01

236

Tau protein is cross-linked by transglutaminase in P301L tau transgenic mice.  

PubMed

The microtubule-associated protein tau is highly soluble under physiological conditions. However, in tauopathies, tau protein aggregates into insoluble filaments and neurofibrillary tangles (NFTs). The mechanisms underlying the formation of tau filaments and NFTs in tauopathies remain unclear. Several lines of evidence suggest that transglutaminase may cross-link tau into stable, insoluble aggregates, leading to the formation of NFTs in Alzheimer's disease and progressive supranuclear palsy. To further determine the contribution of transglutaminase in the formation of NFTs, we compared the levels of cross-linked tau protein from P301L tau transgenic mice that develop NFTs to four-repeat wild-type (4RWT) tau transgenic and nontransgenic mice that do not develop NFT pathology. Immunoprecipitation and immunoblotting experiments show that transglutaminase cross-links phosphorylated tau in the hindbrain of P301L tau transgenic mice but not in mice overexpressing 4RWT tau and nontransgenic mice. Cross-linked, phosphorylated tau from P301L tau transgenic mice runs as high-molecular mass aggregates on Western blots, similar to cross-linked tau from paired helical filaments of Alzheimer's disease. We also used double-label immunofluorescence to demonstrate colocalization of PHF-1-immunoreactive tau and the transglutaminase-catalyzed cross-link in the hindbrain, spinal cord, and cortex of P301L tau transgenic mice. In the spinal cord, 87% of PHF-1-labeled cells colocalize with the transglutaminase-catalyzed cross-link. Additionally, transglutaminase enzymatic activity is significantly elevated in the spinal cord of P301L tau transgenic mice. These studies further implicate transglutaminase in the formation and/or stabilization of NFT and paired helical filaments and provide a model system to investigate the therapeutic potential of transglutaminase inhibitors in tauopathies. PMID:15689560

Halverson, Robyn A; Lewis, Jada; Frausto, Shanti; Hutton, Mike; Muma, Nancy A

2005-02-01

237

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

PubMed Central

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

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

2014-01-01

238

Mechanism of Hyaluronan Degradation by Streptococcus pneumoniae Hyaluronate Lyase  

E-print Network

Mechanism of Hyaluronan Degradation by Streptococcus pneumoniae Hyaluronate Lyase STRUCTURES§¶, Luciane V. Mello , Bert L. de Groot**, and Songlin Li§ From the Children's Hospital Oakland Research structures of Streptococcus pneumoniae hyaluro- nate lyase with tetra- and hexasaccharide hyaluronan

de Groot, Bert

239

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

PubMed

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

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

2014-09-01

240

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

2013-10-21

241

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

2013-06-01

242

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

PubMed Central

Collagen scaffolds have been widely employed as a dermal equivalent to induce fibroblast infiltrations and dermal regeneration in the treatment of chronic wounds and diabetic foot ulcers. Cross-linking methods have been developed to address the disadvantages of the rapid degradation associated with collagen-based scaffolds. To eliminate the potential drawbacks associated with glutaraldehyde cross-linking, methods using a water soluble carbodiimide have been developed. In the present study, the glycosaminoglycan (GAG) hyaluronic acid (HA), was covalently attached to an equine tendon derived collagen scaffold using 1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide (EDC) to create ntSPONGE™. The HA was shown to be homogeneously distributed throughout the collagen matrix. In vitro analyses of the scaffold indicated that the cross-linking enhanced the biological stability by decreasing the enzymatic degradation and increasing the thermal denaturation temperature. The material was shown to support the attachment and proliferation of mouse L929 fibroblast cells. In addition, the cross-linking decreased the resorption rate of the collagen as measured in an intramuscular implant model in rabbits. The material was also shown to be biocompatible in a variety of in vitro and in vivo assays. These results indicate that this cross-linked collagen-HA scaffold, ntSPONGE™, has the potential for use in chronic wound healing. PMID:23896569

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

2013-01-01

243

Alkali reversal of psoralen cross-link for the targeted delivery of psoralen monoadduct lesion  

SciTech Connect

Psoralen intercalates into double-stranded DNA and photoreacts mainly with thymines to form monoadducts and interstrand cross-links. The authors used an oligonucleotide model to demonstrate a novel mechanism: the reversal of psoralen cross-links by base-catalyzed rearrangement at 90/sup 0/C (BCR). The BCR reaction is more efficient than the photoreversal reaction. They show that the BCR occurs predominantly on the furan side of a psoralen cross-link. The cleavage does not result in the breaking of the DNA backbone, and the thymine based freed from the cross-link by the cleavage reaction appears to be unmodified. Similarly, BCR of the furan-side monoadduct of psoralen removed the psoralen molecule and regenerated the unaltered native oligonucleotide. The pyrone-side psoralen monoadduct is relatively resistant to BCR. One can use BCR to perform efficient oligonucleotide-directed, site-specific delivery of a psoralen monoadduct. As a demonstration of this approach, they have hybridized a 19 base long oligonucleotide vehicle containing a furan-side psoralen monoadduct to a 56 base long complementary oligonucleotide target strand and formed a specific cross-link at the target site with 365-nm UV. Subsequent BCR released the oligonucleotide vehicle and deposited the psoralen at the target site.

Yeung, A.T.; Dinehart, W.J.; Jones, B.K.

1988-08-23

244

Osteopontin: its transglutaminase-catalyzed posttranslational modifications and cross-linking to fibronectin.  

PubMed

Osteopontin (OP) is a component of extracellular, bone, and urinary stone matrices, but the mechanism by which it is stably incorporated into such matrices remains unknown. By SDS-PAGE analysis of [125I]OP, treated with a catalytic amount of TG, we first demonstrate both intra- and intermolecular covalent cross-linking of OP. Most importantly, the analysis of the products generated from reactions containing OP, Fn, and TG by SDS-PAGE, autoradiography, and Western blotting using either OP or Fn antibody, and quantitation of TG-catalyzed epsilon-(gamma-glutamyl)lysine isopeptide formation between OP and Fn demonstrate, for the first time, covalent cross-linking between these two proteins. Similar reactions in the presence of polyamine substrates of TG show OP-Fn intermolecular cross-linking via N,N-bis-(gamma-glutamyl)polyamine formation. Finally, immunoprecipitation of 125I-labeled NRK cell surface proteins with anti-OP and anti-Fn antibodies, SDS-PAGE analysis, and autoradiography provides critical evidence for nonreducible OP-Fn cross-linking in vivo. These results clearly suggest that TG-mediated cross-linking between OP and Fn represents one of the most likely mechanisms by which OP becomes covalently linked to bone matrix, urinary stone matrix, and to ECM. PMID:7916341

Beninati, S; Senger, D R; Cordella-Miele, E; Mukherjee, A B; Chackalaparampil, I; Shanmugam, V; Singh, K; Mukherjee, B B

1994-04-01

245

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

PubMed Central

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

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

2013-01-01

246

Knee-simulator testing of conventional and cross-linked polyethylene tibial inserts.  

PubMed

We compared the resistance to delamination and to adhesive/abrasive wear of conventional and highly cross-linked polyethylene tibial inserts of a cruciate-retaining total knee design using a knee simulator. Both groups were tested after aggressive, accelerated aging, and 1 set of conventional inserts was studied without aging. Aging oxidized the conventional, but not the highly cross-linked, inserts. The simulated normal gait testing lasted for 5 and 10 million cycles for the conventional and highly cross-linked inserts, respectively. Aged conventional inserts showed delaminations, whereas none were observed in the unaged conventional and aged cross-linked inserts. Wear rates measured by the gravimetric method were 9 +/- 2 mm3, 10 +/- 4 mm3, and 1 +/- 0 mm3 per million cycles; by the metrologic method, they were 8 +/- 1 mm3, 9 +/- 2 mm3, and 3 +/- 0 mm3 for the unaged conventional, aged conventional, and aged highly crosslinked inserts, respectively. In the test model used, oxidation led to delamination, whereas increased cross-link density resulted in reduced adhesive/abrasive wear of tibial inserts. PMID:15483806

Muratoglu, Orhun K; Bragdon, Charles R; Jasty, Murali; O'Connor, Daniel O; Von Knoch, Rebecca S; Harris, William H

2004-10-01

247

Cross-linked acrylic hydrogel for the controlled delivery of hydrophobic drugs in cancer therapy  

PubMed Central

Objective: To investigate cross-linked hydrogels prepared via inverse emulsion polymerization to entrap poorly aqueous soluble drugs. Polyethylene glycol cross-linked acrylic polymers were synthesized and the loading and release of curcumin, a model hydrophobic drug, was investigated. Methods: Physicochemical characteristics of hydrogels were studied with 13C nuclear magnetic resonance, Fourier transform infrared spectroscopy, transmission electron microscopy, scanning electron microscopy, differential scanning calorimetry, and swelling. Polymerization of the acrylic acid with cross-linked polyethylene glycol diacrylate was characterized with 13C nuclear magnetic resonance imaging and Fourier transform infrared spectroscopy. Results: The in vitro release rate of curcumin showed that there was a sustained release from the hydrogel with increased cross-linking; the release rate depended on the pH of the releasing medium. Intracellular and cytotoxicity studies were carried out in human cervical cancer cell lines. Conclusion: The results suggest cross-linked acrylic polymers can be used as efficient vectors for pH-sensitive, controlled delivery of hydrophobic drugs. PMID:22888244

Deepa, G; Thulasidasan, Arun Kumar T; Anto, Ruby John; Pillai, J Jisha; Kumar, GS Vinod

2012-01-01

248

Reversible Inter- and Intra-Microgel Cross-Linking using Disulfides  

PubMed Central

Thermoresponsive hydrogel nanoparticles composed of poly(N-isopropylmethacrylamide) (pNIPMAm) and the disulfide-based cross-linker N,N’-bis(acryloyl)cystamine (BAC) have been prepared using a redox-initiated, aqueous precipitation polymerization approach, leading to improved stability of the disulfide bond compared to traditional thermally-initiated methods. The resultant particles demonstrate complete erosion in response to reducing conditions or thiol competition. This stands in contrast to the behavior of thermally-initiated particles, which retain a cross-linked network following disulfide cleavage due to uncontrolled chain-branching and self-cross-linking side reactions. The synthetic strategy has also been combined with the non-degradable cross-linker N,N-methylenebisacrylamide (BIS) to generate “co-cross-linked” pNIPMAm-BAC-BIS microgels. These particles are redox-responsive, swell upon BAC cross-link scission and present reactive thiols. This pendant thiol functionality was demonstrated to be useful for conjugation of thiol-reactive probes and in reversible network formation by assembling particles cross-linked by disulfide linkages. PMID:22287810

Gaulding, Jeffrey C.; Smith, Michael H.; Hyatt, John S.; Fernandez-Nieves, Alberto; Lyon, L. Andrew

2012-01-01

249

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

NASA Astrophysics Data System (ADS)

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

Tajima, S.; Komvopoulos, K.

2007-01-01

250

Accumulation of Extracellular Hyaluronan by Hyaluronan Synthase 3 Promotes Tumor Growth and Modulates the Pancreatic Cancer Microenvironment  

PubMed Central

Extensive accumulation of the glycosaminoglycan hyaluronan is found in pancreatic cancer. The role of hyaluronan synthases 2 and 3 (HAS2, 3) was investigated in pancreatic cancer growth and the tumor microenvironment. Overexpression of HAS3 increased hyaluronan synthesis in BxPC-3 pancreatic cancer cells. In vivo, overexpression of HAS3 led to faster growing xenograft tumors with abundant extracellular hyaluronan accumulation. Treatment with pegylated human recombinant hyaluronidase (PEGPH20) removed extracellular hyaluronan and dramatically decreased the growth rate of BxPC-3 HAS3 tumors compared to parental tumors. PEGPH20 had a weaker effect on HAS2-overexpressing tumors which grew more slowly and contained both extracellular and intracellular hyaluronan. Accumulation of hyaluronan was associated with loss of plasma membrane E-cadherin and accumulation of cytoplasmic ?-catenin, suggesting disruption of adherens junctions. PEGPH20 decreased the amount of nuclear hypoxia-related proteins and induced translocation of E-cadherin and ?-catenin to the plasma membrane. Translocation of E-cadherin was also seen in tumors from a transgenic mouse model of pancreatic cancer and in a human non-small cell lung cancer sample from a patient treated with PEGPH20. In conclusion, hyaluronan accumulation by HAS3 favors pancreatic cancer growth, at least in part by decreasing epithelial cell adhesion, and PEGPH20 inhibits these changes and suppresses tumor growth. PMID:25147816

Zhao, Chunmei; Singha, Netai C.; Osgood, Ryan J.; Symons, Rebecca; Jiang, Ping; Li, Xiaoming; Thompson, Curtis B.; Infante, Jeffrey R.; Jacobetz, Michael A.; Tuveson, David A.; Frost, Gregory I.; Shepard, H. Michael; Huang, Zhongdong

2014-01-01

251

Enzymatic Method for the Simultaneous Determination of Hyaluronan and Chondroitin Sulfates Using High-Performance Liquid Chromatography  

Microsoft Academic Search

A chromatographic method for the simultaneous determination of hyaluronan and chondroitin sulfates was examined. Hyaluronan differs from chondroitin sulfates in the susceptibility to chondroitinase ABC under alkaline conditions. When hyaluronan and chondroitin sulfates were treated with chondroitinase ABC in the buffered solution (pH 9.1), chondroitin sulfates were selectively degraded to the unsaturated disaccharides, whereas hyaluronan was not. Subsequently, hyaluronan in

Ichiro Koshiishi; Michinari Takenouchi; Takashi Hasegawa; Toshio Imanari

1998-01-01

252

The effects of different crossing-linking conditions of genipin on type I collagen scaffolds: an in vitro evaluation.  

PubMed

The purpose of this paper is to analyze the properties of fabricating rat tail type I collagen scaffolds cross-linked with genipin under different conditions. The porous genipin cross-linked scaffolds are obtained through a two step freeze-drying process. To find out the optimal cross-link condition, we used different genipin concentrations and various cross-linked temperatures to prepare the scaffolds in this study. The morphologies of the scaffolds were characterized by scanning electron microscope, and the mechanical properties of the scaffolds were evaluated under dynamic compression. Additionally, the cross-linking degree was assessed by ninhydrin assay. To investigate the swelling ratio and the in vitro degradation of the collagen scaffold, the tests were also carried out by immersion of the scaffolds in a PBS solution or digestion in a type I collagenase respectively. The morphologies of the non-cross-linked scaffolds presented a lattice-like structure while the cross-linked ones displayed a sheet-like framework. The morphology of the genipin cross-linked scaffolds could be significantly changed by either increasing genipin concentration or the temperature. The swelling ratio of each cross-linked scaffold was much lower than that of the control (non-cross-linked).The ninhydrin assay demonstrated that the higher temperature and genipin concentration could obviously increase the cross-linking efficiency. The in vitro degradation studies indicated that genipin cross-linking can effectively elevate the biostability of the scaffolds. The biocompatibility and cytotoxicity of the scaffolds was evaluated by culturing rat chondrocytes on the scaffold in vitro and by MTT. The results of MTT and the fact that the chondrocytes adhered well to the scaffolds demonstrated that genipin cross-linked scaffolds possessed an excellent biocompatibility and low cytotoxicity. Based on these results, 0.3 % genipin concentrations and 37 °C cross-linked temperatures are recommended. PMID:24442821

Zhang, Xiujie; Chen, Xueying; Yang, Ting; Zhang, Naili; Dong, Li; Ma, Shaoying; Liu, Xiaoming; Zhou, Mo; Li, Baoxing

2014-12-01

253

Ketene functionalized polyethylene: control of cross-link density and material properties.  

PubMed

The functionalization and cross-linking of polyethylene is synthetically challenging, commonly relying on highly optimized radical based postpolymerization strategies. To address these difficulties, a norbornene monomer containing Meldrum's acid is shown to be effectively copolymerized with polyethylene using a nickel ?-iminocarbaxamidato complex, providing high-melting, semicrystalline polymers with a tunable incorporation of the functional comonomer. Upon heating the copolymer to common polyethylene processing temperatures, the thermolysis of Meldrum's acid to ketene provides the desired reactive group. This simple and versatile methodology does not require small molecule radical sources or catalysts, and the dimerization of the in situ generated ketenes is shown to provide tunable cross-linking densities in polyethylene. Subsequent rheological and tensile experiments illustrate the ability to tune cross-linked polyethylene properties by comonomer incorporation and elucidate valuable structure/property relationships in these materials. This study illustrates the power of well-defined and synthetically accessible functional groups in polyolefin synthesis and functionalization. PMID:20923158

Leibfarth, Frank A; Schneider, Yanika; Lynd, Nathaniel A; Schultz, Alison; Moon, Bongjin; Kramer, Edward J; Bazan, Guillermo C; Hawker, Craig J

2010-10-27

254

Spray assembled, cross-linked polyelectrolyte multilayer membranes for salt removal.  

PubMed

The present study reports the synthesis of spray-coated cross-linked polyelectrolyte multilayer membranes. Membrane cross-linking was performed using alkyne-azide "click" chemistry, where alkyne and azide functional groups were used to modify the poly(acrylic acid) (PAA) and the poly(allylamine) hydrochloride (PAH) polyelectrolytes. The results demonstrate that deposition at lower ionic strength produced smoother and denser membrane structures. Pore size analysis using neutral poly(ethylene glycol) revealed a decrease in the membrane pore size as the degree of cross-linking was increased, resulting in the membrane rejecting divalent CaCl2 at levels of up to 80%, and 50% rejection of monovalent NaCl. When poly(sodium-4-styrenesulfonate) (PSS) was combined with small amounts of cross-linkable PAA, significant flux increases were observed in the multilayer membranes with no observable reduction in ion rejection. PMID:25036367

Cho, Kwun Lun; Lomas, Hannah; Hill, Anita J; Caruso, Frank; Kentish, Sandra E

2014-07-29

255

Laccase-catalyzed cross-linking of amino acids and peptides with dihydroxylated aromatic compounds.  

PubMed

In order to design potential biomaterials, we investigated the laccase-catalyzed cross-linking between L-lysine or lysine-containing peptides and dihydroxylated aromatics. L-Lysine is one of the major components of naturally occurring mussel adhesive proteins (MAPs). Dihydroxylated aromatics are structurally related to 3,4-dihydroxyphenyl-L-alanine, another main component of MAPs. Mass spectrometry and nuclear magnetic resonance analyses show that the epsilon-amino group of L-lysine is able to cross-link dihydroxylated aromatics. Additional oligomer and polymer cross-linked products were obtained from di- and oligopeptides containing L-lysine. Potential applications in medicine or industry for biomaterials synthesised via the three component system consisting of the oligopeptide [Tyr-Lys]10, dihydroxylated aromatics and laccase are discussed. PMID:20143113

Mikolasch, Annett; Hahn, Veronika; Manda, Katrin; Pump, Judith; Illas, Nicole; Gördes, Dirk; Lalk, Michael; Gesell Salazar, Manuela; Hammer, Elke; Jülich, Wolf-Dieter; Rawer, Stephan; Thurow, Kerstin; Lindequist, Ulrike; Schauer, Frieder

2010-08-01

256

Simple, clean preparation method for cross-linked ?-cyclodextrin nanoparticles via inclusion complexation.  

PubMed

A simple, clean method was presented in this letter to prepare cross-linked ?-cyclodextrin (?-CD) nanoparticles with a low dispersion. The nanoparticles were synthesized in water by cross-linking the inclusion complex of ?-CDs and poly(ethylene glycol) (PEG). The structure of the nanoparticles was characterized by (1)H NMR, nuclear overhauser enhancement spectroscopy (NOESY), and wide-angle X-ray diffraction (XRD). Spherical morphology was observed by scanning electron microscopy (SEM) for these nanoparticles. Their average hydrodynamic radius was determined to be 67 nm by dynamic light scattering (DLS). Small guest molecules could be included in the cross-linked ?-CD nanoparticles, and anticancer drug cisplatin was used to evaluate the drug release behavior. PMID:23472675

Zhu, Wen; Zhang, Ke; Chen, Yongming; Xi, Fu

2013-05-21

257

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

258

Carbodiimide cross-linked amniotic membranes for cultivation of limbal epithelial cells.  

PubMed

In ophthalmic tissue engineering, amniotic membrane (AM) is one of the most prevalent natural matrices used for limbal epithelial cell (LEC) cultivation and transplantation. However, the application of AM as a scaffold is limited by its low biomechanical strength and rapid biodegradation. The present study reports the development of 1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide hydrochloride (EDC)/N-hydroxysuccinimide (NHS) cross-linked AM as an LEC carrier. The collagenous tissue materials were modified with varying cross-linker concentrations (0-0.25 mmol EDC/mg AM) and were characterized by attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR), differential scanning calorimetry (DSC), ninhydrin assays, electron microscopy, light transmission measurements, mechanical and in vitro degradation tests, as well as diffusion permeability and cell culture studies. Our results showed that chemical cross-linking approaches saturation at concentrations of 0.05 mmol EDC/mg AM. The formation of cross-links (i.e., amide bonds) in the samples treated with 0.05 mmol EDC/mg AM may cause significant aggregation of tropocollagen molecules and collagen microfibrils without affecting cell morphology of biological tissues. With the optimum concentration of 0.05 mmol EDC/mg AM, chemical cross-linker could significantly enhance the mechanical and thermal stability, optical transparency, and resistance to collagenase digestion. Continuous permeation of albumin through the cross-linked AM would be helpful to cell growth over the matrix surface. In addition, the EDC cross-linked samples were able to support LEC proliferation and preserve epithelial progenitor cells in vitro and in vivo. It is concluded that the AM cross-linked with 0.05 mmol EDC/mg AM may be a potential biomaterial for regenerative medicine. PMID:20541801

Ma, David Hui-Kang; Lai, Jui-Yang; Cheng, Hsiao-Yun; Tsai, Chen-Chi; Yeh, Lung-Kun

2010-09-01

259

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

PubMed

Glutaraldehyde (GLUT) processing, cellular antigens, calcium ions in circulation, and phospholipids present in the native tissue are predominantly responsible for calcification, degeneration, and lack of natural microenvironment for host progenitor cell migration in tissue implants. The study presents an improved methodology for adhesion and proliferation of endothelial progenitor cells (EPCs) without significant changes in biomechanical and biodegradation properties of the processed acellular bovine pericardium. The anti-calcification potential of the processed tissue was enhanced by detoxification of GLUT-cross-linked bovine pericardium by decellularization, pretreating it with ethanol or removing the free aldehydes by citric acid treatment and lyophilization. The treated tissues were assessed for biomechanical properties, GLUT ligand quantification, adhesion, proliferation of EPCs, and biodegradability. The results indicate that there was no significant change in biomechanical properties and biodegradability when enzymatic hydrolysis (p>0.05) is employed in detoxified acellular GLUT cross-linked tissue (DBP-G-CA-ET), compared with the native detoxified GLUT cross-linked bovine pericardium (NBP-G-CA-ET). DBP-G-CA-ET exhibited a significant (p>0.05) increase in the viability of EPCs and cell adhesion as compared to acellular GLUT cross-linked bovine pericardium (p<0.05). Lyophilized acellular detoxified GLUT cross-linked bovine pericardium, employed in our study as an alternative to conventional GLUT cross-linked bovine pericardium, might provide longer durability and better biocompatibility, and reduce calcification. The developed bovine pericardium patches could be used in cardiac reconstruction and repair, arteriotomy, soft tissue repair, and general surgical procedures with tissue regeneration dimensions. PMID:23827609

Mathapati, Santosh; Bishi, Dillip Kumar; Guhathakurta, Soma; Cherian, Kotturathu Mammen; Venugopal, Jayarama Reddy; Ramakrishna, Seeram; Verma, Rama Shanker

2013-04-01

260

Tuning the Coulomb charging energy in cross-linked nanoparticle films  

NASA Astrophysics Data System (ADS)

We have systematically tuned the Coulomb charging energy in cross-linked gold nanoparticle films by varying both the nanoparticle size and the length of the cross-linker molecules. We show that at low temperatures (T?100K) , the observed conduction behavior can be closely described with a classical percolation model for interacting metal particles embedded in an effective dielectric medium. The ease and precision with which one can control the geometrical parameters make these cross-linked nanoparticle systems attractive as model systems for the study of electronic conduction in granular materials.

Herrmann, J.; Bray, D. J.; Müller, K.-H.; Wei, G.; Lindoy, L. F.

2007-12-01

261

The effect of pressure upon the equilibrium swelling of cross-linked polymers in nonpolar solvents  

E-print Network

of the reguirements for the degree of MASTER OF SCIENCE August 1960 Major Subjecti PhFsics THE EFFECT OF PRESSURE UPON THE ECUILTfSIUM SWELLING OF CROSS-LINKED POLYMERS IN NONPOLAR SOLVENTS A Thesis James Kenneth Hughes Approved as to style ALnd potent by... of the reguirements for the degree of MASTER OF SCIENCE August 1960 Major Subjecti PhFsics THE EFFECT OF PRESSURE UPON THE ECUILTfSIUM SWELLING OF CROSS-LINKED POLYMERS IN NONPOLAR SOLVENTS A Thesis James Kenneth Hughes Approved as to style ALnd potent by...

Hughes, James Kenneth

2012-06-07

262

The oligomeric structure of rat liver microsomal glutathione transferase studied by chemical cross-linking.  

PubMed

The oligomeric structure of rat liver microsomal glutathione transferase was investigated using four different chemical cross-linking reagents. Studies were performed with the isolated enzyme, with the enzyme incorporated into phosphatidyl choline liposomes and with rat liver microsomes. Cross-linking was analyzed by use of SDS-PAGE combined with Western blotting. Our results strongly suggest that the microsomal glutathione transferase is a trimer in situ in the endoplasmic reticulum, as well as in the purified state and in proteoliposomes. These results lend strong support to previous studies, involving hydrodynamic characterization and radiation inactivation, indicating that the microsomal glutathione transferase is a trimeric enzyme. PMID:1390907

Lundqvist, G; Yücel-Lindberg, T; Morgenstern, R

1992-09-01

263

Increasing Thermal Stability of Gelatin by UV-Induced Cross-Linking with Glucose  

PubMed Central

The effects of ultraviolet (254?nm) radiation on a hydrated gelatin-glucose matrix were investigated for the development of a physiologically thermostable substrate for potential use in cell scaffold production. Experiments conducted with a differential scanning calorimeter indicate that ultraviolet irradiation of gelatin-glucose hydrogels dramatically increases thermal stability such that no melting is observed at temperatures of at least 90°C. The addition of glucose significantly increases the yield of cross-linked product, suggesting that glucose has a role in cross-link formation. Comparisons of lyophilized samples using scanning electron microscopy show that irradiated materials have visibly different densities. PMID:24963297

Masutani, Evan M.; Kinoshita, Christopher K.; Tanaka, Travis T.; Ellison, Andrew K. D.; Yoza, Brandon A.

2014-01-01

264

Fracture of highly cross-linked all-polyethylene patella after total knee arthroplasty.  

PubMed

Recent advances in polyethylene fabrication have led to the introduction of highly cross-linked polyethylene tibial and patellar components for use in total knee arthroplasty (TKA) with the goal of reducing wear-related osteolysis. However, some reports suggest decreased mechanical strength as a result of the additional thermal and sterilization treatments in the manufacturing of implants. Complications related to the patella are among the most common causes of failure in TKA, but patellar component fracture is rare. The authors report a case of a highly cross-linked all-polyethylene patellar component that failed as a result of fracture in vivo in a patient 3 years after TKA. PMID:21446631

Hambright, Dustin S; Watters, Tyler Steven; Kaufman, Adam M; Lachiewicz, Paul F; Bolognesi, Michael P

2010-12-01

265

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

PubMed

We prepared a biobased material, dynamically vulcanized polylactide (PLA)/natural rubber (NR) blend in which the cross-linked NR phase owned a continuous network-like dispersion. This finding breaks the traditional concept of a sea-island morphology formed after dynamic vulcanization of the blends. The scan electron microscopy and dissolution/swell experiments provided the direct proof of the continuous cross-linked NR phase. This new biobased PLA/NR blend material with the novel structure is reported for the first time in the field of dynamic vulcanization and shows promise for development for various functional applications. PMID:24621374

Chen, Yukun; Yuan, Daosheng; Xu, Chuanhui

2014-03-26

266

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

267

Single-molecule imaging of hyaluronan in human synovial fluid  

NASA Astrophysics Data System (ADS)

Human synovial fluid contains a high concentration of hyaluronan, a high molecular weight glycosaminoglycan that provides viscoelasticity and contributes to joint lubrication. In osteoarthritis synovial fluid, the concentration and molecular weight of hyaluronan decrease, thus impairing shock absorption and lubrication. Consistently, substitution of hyaluronan (viscosupplementation) is a widely used treatment for osteoarthritis. So far, the organization and dynamics of hyaluronan in native human synovial fluid and its action mechanism in viscosupplementation are poorly characterized at the molecular level. Here, we introduce highly sensitive single molecule microscopy to analyze the conformation and interactions of fluorescently labeled hyaluronan molecules in native human synovial fluid. Our findings are consistent with a random coil conformation of hyaluronan in human synovial fluid, and point to specific interactions of hyaluronan molecules with the synovial fluid matrix. Furthermore, single molecule microscopy is capable of detecting the breakdown of the synovial fluid matrix in osteoarthritis. Thus, single molecule microscopy is a useful new method to probe the structure of human synovial fluid and its changes in disease states like osteoarthritis.

Kappler, Joachim; Kaminski, Tim P.; Gieselmann, Volkmar; Kubitscheck, Ulrich; Jerosch, Jörg

2010-11-01

268

Hyaluronan, CD44 and Emmprin: Partners in cancer cell chemoresistance  

PubMed Central

Hyaluronan is not only an important structural component of extracellular matrices but also interacts with cells during dynamic cell processes such as occur in cancer. Consequently, interactions of hyaluronan with tumor cells play important cooperative roles in various aspects of malignancy. Hyaluronan binds to several cell surface receptors, including CD44, thus leading to co-regulation of signaling pathways that are important in regulation of multidrug resistance to anticancer drugs, in particular anti-apoptotic pathways induced by activation of receptor tyrosine kinases. Emmprin, a cell surface glycoprotein of the Ig superfamily, stimulates hyaluronan production and downstream signaling consequences. Emmprin and CD44 also interact with various multidrug transporters of the ABC family and monocarboxylate transporters associated with resistance to cancer therapies. Moreover, hyaluronan-CD44 interactions are critical to these properties in the highly malignant, chemotherapy-resistant cancer stem-like cells. Perturbations of the hyaluronan-CD44 interaction at the plasma membrane by various antagonists result in attenuation of receptor tyrosine kinase and transporter activities and inhibition of tumor progression in vivo. These antagonists, especially small hyaluronan oligomers, may be useful in therapeutic strategies aimed at preventing tumor refractoriness or recurrence due to drug-resistant sub-populations within malignant cancers. PMID:18490190

Toole, Bryan P.; Slomiany, Mark G.

2008-01-01

269

Therapeutic Targeting of Hyaluronan in the Tumor Stroma  

PubMed Central

The tumor stroma, consisting of non-malignant cells and the extracellular matrix, undergoes significant quantitative and qualitative changes throughout malignant transformation and tumor progression. With increasing recognition of the role of the tumor microenvironment in disease progression, stromal components of the tumor have become attractive targets for therapeutic intervention. Stromal accumulation of the glycosaminoglycan hyaluronan occurs in many tumor types and is frequently associated with a negative disease prognosis. Hyaluronan interacts with other extracellular molecules as well as cellular receptors to form a complex interaction network influencing physicochemical properties, signal transduction, and biological behavior of cancer cells. In preclinical animal models, enzymatic removal of hyaluronan is associated with remodeling of the tumor stroma, reduction of tumor interstitial fluid pressure, expansion of tumor blood vessels and facilitated delivery of chemotherapy. This leads to inhibition of tumor growth and increased survival. Current evidence shows that abnormal accumulation of hyaluronan may be an important stromal target for cancer therapy. In this review we highlight the role of hyaluronan and hyaluronan-mediated interactions in cancer, and discuss historical and recent data on hyaluronidase-based therapies and the effect of hyaluronan removal on tumor growth. PMID:24213471

Kultti, Anne; Li, Xiaoming; Jiang, Ping; Thompson, Curtis B.; Frost, Gregory I.; Shepard, H. Michael

2012-01-01

270

Reflective confocal laser scanning microscopy and nonlinear microscopy of cross-linked rabbit cornea  

NASA Astrophysics Data System (ADS)

Cross-linking of the cornea with application of Ribovlavin and UV-A light is an evolving clinical treatment of the eye disease keratoconus. Despite the positive clinical track record of corneal cross-linking, the complex wound healing process after the treatment is still under investigation. In this study an animal model was used to clarify the state of wound healing 5 weeks after treatment. Cross-linked rabbit corneae were imaged with reflective confocal laser scanning and nonlinear microscopy, namely second harmonic imaging microscopy (SHIM) and two-photon excited autofluorescence. First results show that the NAD(P) H-autofluorescence of the corneal keratocytes and their scattering signal still show a signature of the treatment five weeks after the cross-linking procedure. The SHIM signals show the structural morphology of the fibrous collagen sheets in the stroma of the cornea. SHIM detected in the forward direction differs substantially from backward SHIM, but no signature of treatment was found in both detection channels of the SHIM signal.

Krueger, Alexander; Hovakimyan, Marina; Ramirez, Diego F.; Stachs, Oliver; Guthoff, Rudolf F.; Heisterkamp, Alexander

2009-07-01

271

Laccase-Based CLEAs: Chitosan as a Novel Cross-Linking Agent  

PubMed Central

Laccase from Coriolopsis Polyzona was insolubilized as cross-linked enzyme aggregates (CLEAs) for the first time with chitosan as the cross-linking agent. Concentrations between 0.01 and 1.867?g/L of chitosan were used and between 0.05 and 600?mM of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride. The laccase was precipitated using ammonium sulphate and cross-linked simultaneously. Specific activity and thermal stability of these biocatalysts were measured. Activities of up to 737?U/g were obtained when 2,2-azino-bis-(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) was used as a substrate. Moreover, the stability of these biocatalysts was improved with regards to thermal degradation compared to free laccase when exposed to denaturing conditions of high temperature and low pH. The CLEAs stability against chemical denaturants was also tested but no significant improvement was detected. The total amount of ABTS to be oxidized during thermal degradation by CLEAs and free laccase was calculated and the insolubilized enzymes were reported to oxidize more substrate than free laccase. The formation conditions were analyzed by response surface methodology in order to determine an optimal environment for the production of efficient laccase-based CLEAs using chitosan as the cross-linking agent. After 24 hours of formation at pH 3 and at 4°C without agitation, the CLEAs exhibit the best specific activity. PMID:21811672

Arsenault, Alexandre; Cabana, Hubert; Jones, J. Peter

2011-01-01

272

Highly conductive carbon nanotube buckypapers with improved doping stability via conjugational cross-linking  

NASA Astrophysics Data System (ADS)

Carbon nanotube (CNT) sheets or buckypapers have demonstrated promising electrical conductivity and mechanical performance. However, their electrical conductivity is still far below the requirements for engineering applications, such as using as a substitute for copper mesh, which is currently used in composite aircraft structures for lightning strike protection. In this study, different CNT buckypapers were stretched to increase their alignment, and then subjected to conjugational cross-linking via chemical functionalization. The conjugationally cross-linked buckypapers (CCL-BPs) demonstrated higher electrical conductivity of up to 6200 S cm - 1, which is more than one order increase compared to the pristine buckypapers. The CCL-BPs also showed excellent doping stability in over 300 h in atmosphere and were resistant to degradation at elevated temperatures. The tensile strength of the stretched CCL-BPs reached 220 MPa, which is about three times that of pristine buckypapers. We attribute these property improvements to the effective and stable conjugational cross-links of CNTs, which can simultaneously improve the electrical conductivity, doping stability and mechanical properties. Specifically, the electrical conductivity increase resulted from improving the CNT alignment and inter-tube electron transport capability. The conjugational cross-links provide effective 3D conductive paths to increase the mobility of electrons among individual nanotubes. The stable covalent bonding also enhances the thermal stability and load transfer. The significant electrical and mechanical property improvement renders buckypaper a multifunctional material for various applications, such as conducting composites, battery electrodes, capacitors, etc.

Chen, I.-Wen Peter; Liang, Richard; Zhao, Haibo; Wang, Ben; Zhang, Chuck

2011-12-01

273

Role of collagen content and cross-linking in large pulmonary arterial stiffening after chronic hypoxia  

E-print Network

hypertension (HPH) occurs in patients with lung diseases such as chronic obstructive pulmonary disease (BarberaRole of collagen content and cross-linking in large pulmonary arterial stiffening after chronic ­ Madison Abstract Chronic hypoxic pulmonary hypertension (HPH) is associated with large pulmonary artery

Chesler, Naomi C.

274

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

E-print Network

Actin Filament Length Tunes Elasticity of Flexibly Cross-Linked Actin Networks K. E. Kasza, C. P, Boston, Massachusetts ABSTRACT Networks of the cytoskeletal biopolymer actin cross that the elasticity of these networks shows a strong dependence on the mean length of the actin polymers, unlike

275

Polyalkylcyanoacrylate nanocapsules: variation of membrane permeability by chemical cross-linking.  

PubMed

The permeability of the polymer walls of polyalkylcyanoacrylate nanocapsules varies by different degrees of chemical cross-linking. For this reason, different amounts of bivalent alkylcyanoacrylates are added to the monovalent alkylcyanoacrylate prior to an interfacial polymerization step in order to generate capsules with various cross-linking densities. The obtained nanocapsules are characterized by observing the water molecules via pulsed field-gradient nuclear magnetic resonance using a stimulated echo sequence. The resulting echo decay plots reveal the exchange rate of the water molecules between the free and encapsulated states. The observed dwell times of water molecules in the encapsulated state are characteristic parameters for the permeability of the given capsule membranes. They show a clear dependence on the degree of cross-linking, proving the potential of this approach for a controlled variation of the capsule permeability. Also, the cross-linked nanocapsules exhibit a significantly decreased solubility in tetrahydrofuran which may lead to new applications for polyalkylcyanoacrylate nanocapsules in organic solvents. PMID:24713086

Gross-Heitfeld, Christoph; Linders, Jürgen; Appel, Ralph; Selbach, Florian; Mayer, Christian

2014-05-01

276

Removal of Cobalt Ions from Aqueous Solution by Adsorption onto Cross-Linked Calcium Alginate Beads  

Microsoft Academic Search

The removal of cobalt ions from dilute aqueous solutions using cross linked calcium alginate beads as the adsorbent is reported in this article. The influence of various experimental parameters such as pH, initial metal ion concentration, contact time and solid to liquid ratio were studied. The adsorption data were applied to Langmuir and Freundlich isotherm equations and various static parameters

Tulika Dewangan; Alka Tiwari; A. K. Bajpai

2009-01-01

277

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

NASA Astrophysics Data System (ADS)

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

Khabaz, Fardin; Khare, Ketan S.; Khare, Rajesh

2014-05-01

278

Corneal collagen cross-linking in a late-onset graft infectious ulcer: a case report  

PubMed Central

Introduction Infectious keratitis following penetrating keratoplasty is a common postoperative complication. Intensive topical and systemic treatments do not always prevent the risk of graft failure. In this report we demonstrate the beneficial anti-microbial effect of corneal collagen cross-linking in a late-onset, sight-threatening, corneal graft ulcer. Case presentation A 57-year old Caucasian man underwent penetrating keratoplasty in his left eye, due to corneal bullosa after cataract extraction surgery. Twelve months after the penetrating keratoplasty, he visited our emergency service complaining of burning and foreign body sensation in his operated eye. Slit-lamp examination revealed a central, round-shaped ulcer of the graft. Due to poor response to the intensive topical antibiotic therapy, corneal collagen cross-linking was applied 3 days after admission, in an attempt to control the infection. Cultures indicated the predominance of methicillin-resistant Staphylococcus aureus infection. Five days after corneal collagen cross-linking treatment, the epithelium was completely re-epithelized, while the transparency of the transplanted cornea was gradually restored within the 12-month follow-up period. No relapses occurred. Conclusion Corneal collagen cross-linking seems to be a safe and effective therapeutic alternative in resistant cases of infectious keratitis following penetrating keratoplasty. PMID:24908420

2014-01-01

279

Immobilization of lipase by ultrafiltration and cross-linking onto the polysulfone membrane surface.  

PubMed

In this study, a biphasic enzymatic membrane reactor was made by immobilizing Candida Rugosa lipase onto the dense surface of polysulfone ultrafiltration membrane by filtration and then cross-linking with glutaraldehyde solution. The reactor was further applied for the hydrolysis of olive oil, the performance of which was evaluated in respect of apparent reaction rate based on the amount of fatty acids extracted into the aqueous phase per minute and per membrane surface. It was found that the ultrafiltration and cross-linking process greatly improved the reaction rate per unit membrane area and the enzyme lifetime. The highest reaction rate reached 0.089 micromol FFA/min cm2 when the enzyme loading density was 0.098 mg/cm2. The results also indicated that the performance of lipase immobilized on the membrane surface was superior to that immobilized in the pores, and the apparent reaction rate and stability of immobilized lipases were improved greatly after cross-linking. It suggested that immobilization of enzymes by filtration and then cross-linking the enzymes onto the membrane surface is a simple and convenient way to prepare a high-activity immobilized enzyme membrane. PMID:17591438

Yujun, Wang; Jian, Xu; Guangsheng, Luo; Youyuan, Dai

2008-05-01

280

Isolation and Structure of a Covalent Cross-Link Adduct between Mitomycin C and DNA  

Microsoft Academic Search

A DNA cross-link adduct of the antitumor agent mitomycin C (MC) to DNA has been isolated and characterized; the results provide direct proof for bifunctional alkylation of DNA by MC. Exposure of MC to Micrococcus luteus DNA under reductive conditions and subsequent nuclease digestion yielded adducts formed between MC and deoxyguanosine residues. In addition to the two known monoadducts, a

Maria Tomasz; Roselyn Lipman; Dondapati Chowdary; Jan Pawlak; Gregory L. Verdine; Koji Nakanishi

1987-01-01

281

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

2013-07-23

282

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. PMID:23691390

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

2013-01-01

283

Carbon Tetrachloride as Thermoporometry Liquid-probe to Study the Cross linking of Styrene Copolymer  

E-print Network

Carbon Tetrachloride as Thermoporometry Liquid-probe to Study the Cross linking of Styrene styrene copolymer networks have been measured by thermoporometry using CCl4 as a probe liquid. All of vinyl monomers bearing benzil pendant groups and their copolymerization with styrene has been described

Paris-Sud XI, Université de

284

Pharmacologic inhibition of transglutaminase-induced cross-linking of Alzheimer's amyloid ?-peptide  

Microsoft Academic Search

The brain of Alzheimer's disease (AD) patients contains deposits of amyloid ?-peptide (A?). Recent studies have shown that A? is a substrate for tissue transglutaminase (TGase), which induces the formation of cross-linked dimers and polymers, and that tacrine, indomethacin and deferoxamine, which have widely different chemical structures, attenuate the progression of symptoms of AD. This report evaluated the potential of

Wei Zhang; Brett R. Johnson; Thorir D. Bjornsson

1997-01-01

285

DNA-Protein Cross-Linking by 1,2,3,4-Diepoxybutane  

PubMed Central

1,2,3,4-Diepoxybutane (DEB) is a strongly genotoxic diepoxide hypothesized to be the ultimate carcinogenic metabolite of the common industrial chemical and environmental carcinogen 1,3-butadiene. DEB is a bis-electrophile capable of cross-linking cellular biomolecules to form DNA-DNA and DNA-protein cross-links (DPCs), which are thought to play a central role in its biological activity. Previous studies with recombinant proteins have shown that the biological outcomes of DEB-induced DPCs are strongly influenced by protein identities. The present work combines affinity capture methodology with mass spectrometry-based proteomics and immunological detection to identify the proteins which form DPCs in nuclear extracts from human cervical carcinoma (HeLa) cells. We identified 39 human proteins that form covalent DPCs in the presence of DEB. DNA-protein cross-linking efficiency following treatment with 25 mM DEB was 2–12%, depending on protein identity. HPLC-ESI+-MS/MS analysis of the total proteolytic digests of cross-linked proteins revealed the presence of 1-(S-cysteinyl)-4-(guan-7-yl)-2,3-butanediol conjugates, suggesting that DEB forms DPCs between cysteine thiols within proteins and the N-7 guanine positions within DNA. PMID:20666492

Michaelson-Richie, Erin D.; Loeber, Rachel L.; Codreanu, Simona G.; Ming, Xun; Liebler, Daniel C.; Campbell, Colin; Tretyakova, Natalia Y.

2010-01-01

286

Aggressive wear testing of a cross-linked polyethylene in total knee arthroplasty.  

PubMed

Recently, highly cross-linked polyethylenes with high wear and oxidation resistance have been developed. These materials may improve the in vivo performance of polyethylene components used in total knee arthroplasty. To date, the in vitro knee wear testing of these new polyethylenes has been done under conditions of normal gait. However, their critical assessment also must include aggressive in vitro fatigue and wear testing. In the current study, an aggressive in vitro knee wear and device fatigue model simulating a tight posterior cruciate ligament balance during stair climbing was developed and used to assess the performance of one type of highly cross-linked polyethylene tibial knee insert in comparison with conventional polyethylene. The highly cross-linked inserts and one group of conventional inserts were tested after sterilization. One additional group of conventional inserts was subjected to accelerated aging before testing. The articular surfaces of the inserts were inspected visually for surface delamination, cracking, and pitting at regular intervals during the test. The aged conventional polyethylene inserts showed extensive delamination and cracking as early as 50,000 cycles. In contrast, the unaged conventional and highly cross-linked polyethylene inserts did not show any subsurface cracking or delamination at 0.5 million cycles. The appearance and location of delamination that occurred in the aged conventional inserts tested with the current model previously have been observed in vivo with posterior cruciate-sparing design knee arthroplasties with a tight posterior cruciate ligament. PMID:12439243

Muratoglu, Orhun K; Bragdon, Charles R; O'Connor, Daniel O; Perinchief, Rebecca S; Jasty, Murali; Harris, William H

2002-11-01

287

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

288

Photoswitchable formation of a DNA interstrand cross-link by a coumarin-modified nucleotide.  

PubMed

A coumarin-modified pyrimidine nucleoside (1) has been synthesized using a Cu(I)-catalyzed click reaction and incorporated into oligodeoxynucleotides (ODNs). Interstrand cross-links are produced upon irradiation of ODNs containing 1 at 350?nm. Cross-linking occurs through a [2+2] cycloaddition reaction with the opposing thymidine, 2'-deoxycytidine, or 2'-deoxyadenosine. A much higher reactivity was observed with dT than dC or dA. Irradiation of the dT-1 and dC-1 cross-linked products at 254?nm leads to a reversible ring-opening reaction, while such phenomena were not observed with dA-1 adducts. The reversible reaction is ultrafast and complete within 50-90?s. Consistent photoswitching behavior was observed over 6 cycles of irradiation at 350?nm and 254?nm. To the best of our knowledge, this is the first example of photoswitchable interstrand cross-linking formation induced by a modified pyrimidine nucleoside. PMID:24840115

Haque, Mohammad Mojibul; Sun, Huabing; Liu, Shuo; Wang, Yinsheng; Peng, Xiaohua

2014-07-01

289

Concentration of collagen cross-links in human dentin bears no relation to the individual age  

Microsoft Academic Search

Lysylpyridinoline (LP) and hydroxylysylpyridinoline (HP) are collagen cross-link residues. HP is present in most tissues, whereas LP is specific for bone and dentin. Based on the current literature there are certain indications that measurement of the concentrations of HP and LP in dentin may be a valuable tool to determine the individual age. The purpose of this investigation was to

Y. Açil; I. N. G. Springer; J. G. Prasse; J. Hedderich; S. Jepsen

2002-01-01

290

THE PHYSICAL AND THERMAL PROPERTIES OF MODIFIED ROTATIONAL MOLDING GRADE SILANE CROSS-LINKED POLYETHYLENE COMPOUND  

Microsoft Academic Search

This study is aimed at investigating the physical and thermal properties of the modified rotational molding grade cross-linked polyethylene compound with respect to process ability..... Rotational molding grade High Density Polyethylene (HDPE) was blended at various compositions with HDPE and Low Density Polyethylene (LDPE) using twin screw extruder. The melt index of the blends was studied according to ASTM D

WAN AIZAN; WAN ABDUL RAHMAN; CHEN CHAN HOONG; AHMAD FAREED

291

Cross-Linked Nanoporous Materials from Reactive and Multifunctional Block Polymers  

SciTech Connect

Polylactide-b-poly(styrene-co-2-hydroxyethylmethacrylate) (PLA-b-P(S-co-HEMA)) and polylactide-b-poly(styrene-co-2-hydroxyethylacrylate) (PLA-b-P(S-co-HEA)) were synthesized by combination of ring-opening polymerization and reversible addition-fragmentation chain transfer polymerization. {sup 1}H nuclear magnetic resonance spectroscopy and size exclusion chromatography data indicated that the polymerizations were controlled and that hydroxyl groups were successfully incorporated into the block polymers. The polymers were reacted with 4,4{prime}-methylenebis(phenyl isocyanate) (MDI) to form the corresponding cross-linked materials. The materials were annealed at 150 C to complete the coupling reaction. Robust nanoporous materials were obtained from the cross-linked polymers by treatment with aqueous base to hydrolyze the PLA phase. Small-angle X-ray scattering study combined with scanning electron microscopy showed that MDI-cross-linked PLA-b-P(S-co-HEMA)/PLA-b-P(S-co-HEA) can adopt lamellar, hexagonally perforated lamellar, and hexagonally packed cylindrical morphologies after annealing. In particular, the HPL morphology was found to evolve from lamellae due to increase in volume fraction of PS phase as MDI reacted with hydroxyl groups. The reaction also kinetically trapped the morphology by cross-linking. Bicontinuous morphologies were also observed when dibutyltin dilaurate was added to accelerate reaction between the polymer and MDI.

Seo, Myungeun; Amendt, Mark A.; Hillmyer, Marc A. (UMM)

2012-10-10

292

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

293

Preparation of Cross-Linked Enzyme Aggregates of Trehalose Synthase via Co-aggregation with Polyethyleneimine.  

PubMed

Trehalose synthase (TreS) from Meiothermus ruber was co-aggregated with polyethyleneimine (PEI) and precipitated with polyethylene glycol (PEG), followed by cross-linking with glutaraldehyde to obtain TreS-polyethyleneimine cross-linked enzyme aggregates (termed as CLEAs-PEI-PEG). The TreS solution at 0.5 mg mL(-1) protein concentration, with PEI at a mass ratio of 1:0.8 (enzyme/PEI, w/w) and 25 % (w/v) PEG concentration were found to be most adequate for the co-aggregation of TreS. CLEAs-PEI-PEG was most active with glutaraldehyde at a mass ratio of 1:0.5 (enzyme/glutaraldehyde, w/w) to cross-link the co-aggregates. The CLEAs-PEI-PEG prepared in this work had an optimum pH of 6.5 and optimum temperature of 60 °C. For lower concentrations of enzyme, using PEI could enhance the cross-linking efficiency of TreS. The thermal stability and pH tolerance of CLEAs-PEI-PEG were significantly improved. Scanning electron microscopy revealed that the main structure of CLEAs-PEI-PEG showed scaffolding morphology which was constituted by structured ball-like particles with a size of 1-2.5 ?m in diameter. PMID:25163880

Zheng, Jianfeng; Chen, Ying; Yang, Liwei; Li, Mingchun; Zhang, Jun

2014-11-01

294

Preparation of cross-linked enzyme aggregates by using bovine serum albumin as a proteic feeder  

Microsoft Academic Search

Addition of bovine serum albumin (BSA) as a proteic feeder facilitates obtaining cross-linked enzyme aggregates (CLEAs) in cases where the protein concentration in the enzyme preparation is low and\\/or the enzyme activity is vulnerable to the high concentration of glutaraldehyde required to obtain aggregates. CLEAs of Pseudomonas cepacia lipase and penicillin acylase were prepared. CLEA of lipase prepared in the

Shweta Shah; Aparna Sharma; Munishwar N. Gupta

2006-01-01

295

Swelling of Olympic Gels  

NASA Astrophysics Data System (ADS)

The swelling equilibrium of Olympic gels, which are composed of entangled cyclic polymers, is studied by Monte Carlo simulations. In contrast to chemically cross-linked polymer networks, we observe that Olympic gels made of chains with a larger degree of polymerization, N, exhibit a smaller equilibrium swelling degree, Q?N-0.28?0-0.72, at the same polymer volume fraction ?0 at network preparation. This observation is explained by a desinterspersion (reorganization with release of nontrapped entanglements) process of overlapping nonconcatenated rings upon swelling.

Lang, M.; Fischer, J.; Werner, M.; Sommer, J.-U.

2014-06-01

296

Effect of electron-irradiation on cross-link density and crystalline structure of low- and high-density polyethylene  

Microsoft Academic Search

Low- and high-density polyethylenes (LDPE and HDPE) were cross-linked in solid state by electron beam irradiation. Molar mass between cross-link joints, Mc, and cross-link density,nu, were calculated using rubber elasticity theory and hot set data. The results showed that the nu and creep modulus increased and creep strain and Mc decreased with increasing irradiation dose. As compared to HDPE, the

H. A. Khonakdar; S. H. Jafari; U. Wagenknecht; D. Jehnichen

2006-01-01

297

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

PubMed

Characterization of protein cross-linking, particularly without prior knowledge of the chemical nature and site of cross-linking, poses a significant challenge, because of their intrinsic structural complexity and the lack of a comprehensive analytical approach. Toward this end, we have developed a generally applicable workflow-XChem-Finder-that involves four stages: (1) detection of cross-linked peptides via (18)O-labeling at C-termini; (2) determination of the putative partial sequences of each cross-linked peptide pair using a fragment ion mass database search against known protein sequences coupled with a de novo sequence tag search; (3) extension to full sequences based on protease specificity, the unique combination of mass, and other constraints; and (4) deduction of cross-linking chemistry and site. The mass difference between the sum of two putative full-length peptides and the cross-linked peptide provides the formulas (elemental composition analysis) for the functional groups involved in each cross-linking. Combined with sequence restraint from MS/MS data, plausible cross-linking chemistry and site were inferred, and ultimately confirmed, by matching with all data. Applying our approach to a stressed IgG2 antibody, 10 cross-linked peptides were discovered and found to be connected via thioethers originating from disulfides at locations that had not been previously recognized. Furthermore, once the cross-link chemistry was revealed, a targeted cross-link search yielded 4 additional cross-linked peptides that all contain the C-terminus of the light chain. PMID:23634697

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

2013-06-18

298

A Collection Method and High-Sensitivity Enzyme Immunoassay for Sweat Pyridinoline and Deoxypyridinoline Cross-Links  

Microsoft Academic Search

Background: Collagen cross-link molecules such as pyridinoline (PYD), deoxypyridinoline (DPD), and N- terminal cross-linked peptides (NTX) have been mea- sured in urine as indices of bone resorption. However, very little is known regarding the excretion of pyridino- lines into other biological fluids. We report a collection device, normalizing analyte, and high-sensitivity immu- noassay for quantitative analysis of free pyridinoline cross-links

Mark Sarno; Helen Powell; Gayle Tjersland; Donald Schoendorfer; Holden Harris; Kimberly Adams; Peggy Ogata; G. Russell Warnick

1999-01-01

299

Structural change of?-carrageenan gel near solgel transition point  

NASA Astrophysics Data System (ADS)

The structural change of ?-carrageenan gel in the gel-to-sol transition was observed with the small-angle neutron scattering (SANS). The SANS intensity decreases on approaching to the transition point from the gel phase. On the other hand, the observed gyration radius does not change in the whole region of the gel phase. The fact means that the number of the cross link points decreases but their size keeps almost unchanged in the gel-to-sol transition.

Sugiyama, Masaaki; Yuasa, Chikanori; Hara, Kazuhiro; Hiramatsu, Nobuyasu; Nakamura, Atsushi; Hayakawa, Yasushi; Maeda, Yutaka

1998-04-01

300

Repair of Laser-localized DNA Interstrand Cross-links in G1 Phase Mammalian Cells*  

PubMed Central

Interstrand cross-links (ICLs) are absolute blocks to transcription and replication and can provoke genomic instability and cell death. Studies in bacteria define a two-stage repair scheme, the first involving recognition and incision on either side of the cross-link on one strand (unhooking), followed by recombinational repair or lesion bypass synthesis. The resultant monoadduct is removed in a second stage by nucleotide excision repair. In mammalian cells, there are multiple, but poorly defined, pathways, with much current attention on repair in S phase. However, many questions remain, including the efficiency of repair in the absence of replication, the factors involved in cross-link recognition, and the timing and demarcation of the first and second repair cycles. We have followed the repair of laser-localized lesions formed by psoralen (cross-links/monoadducts) and angelicin (only monoadducts) in mammalian cells. Both were repaired in G1 phase by nucleotide excision repair-dependent pathways. Removal of psoralen adducts was blocked in XPC-deficient cells but occurred with wild type kinetics in cells deficient in DDB2 protein (XPE). XPC protein was rapidly recruited to psoralen adducts. However, accumulation of DDB2 was slow and XPC-dependent. Inhibition of repair DNA synthesis did not interfere with DDB2 recruitment to angelicin but eliminated recruitment to psoralen. Our results demonstrate an efficient ICL repair pathway in G1 phase cells dependent on XPC, with entry of DDB2 only after repair synthesis that completes the first repair cycle. DDB2 accumulation at sites of cross-link repair is a marker for the start of the second repair cycle. PMID:19684342

Muniandy, Parameswary A.; Thapa, Dennis; Thazhathveetil, Arun Kalliat; Liu, Su-ting; Seidman, Michael M.

2009-01-01

301

Rapid cross-linking of an RNA internal loop by the anticancer drug cisplatin.  

PubMed

Cisplatin is the most prominent member of a series of platinum(II) antitumor drugs that demonstrate activity based on binding to adjacent purines on genomic DNA. The interactions between cisplatin and alternate biomolecules, including chemically similar RNA, are less understood than are those for DNA. In order to investigate potential implications of platinum(II) drug binding to a structurally complex RNA, we have characterized the reaction between cisplatin and the internal loop of a 41-nucleotide subdomain derived from the U2:U6 spliceosomal RNAs. This "BBD" RNA subdomain consists of a hairpin structure containing a purine-rich asymmetric internal loop. Aquated cisplatin is found to cross-link G nucleobases on opposing sides of the internal loop, forming an intramolecular internal loop cross-link in BBD and an analogous intermolecular cross-link in a two-piece construct containing the same internal loop sequence. The two opposing guanine residues involved in the cross-link were identified via limited alkaline hydrolysis. The kinetics of aquated cisplatin binding to the BBD RNA, a related RNA hairpin, and its DNA hairpin analogue were investigated in an ionic background of 0.1 M NaNO(3) and 1 mM Mg(NO(3))(2). Both BBD and the RNA hairpin react 5-6-fold faster than the DNA hairpin, with calculated second-order rate constants of 2.0(2), 1.7(3), and 0.33(3) M(-1) s(-1), respectively, at 37 degrees C, pH 7.8. MALDI-MS data corroborate the biochemical studies and support a model in which kinetically preferred platinum binding sites compete with less reactive sites in these oligonucleotides. Taken together, these data indicate that cisplatin treatment has potential to create internal loop and other unusual cross-links in structurally complex RNAs, on a time scale that is relevant for RNA-dependent biological processes. PMID:19566097

Hostetter, Alethia A; Chapman, Erich G; DeRose, Victoria J

2009-07-01

302

Developing functional musculoskeletal tissues through hypoxia and lysyl oxidase-induced collagen cross-linking.  

PubMed

The inability to recapitulate native tissue biomechanics, especially tensile properties, hinders progress in regenerative medicine. To address this problem, strategies have focused on enhancing collagen production. However, manipulating collagen cross-links, ubiquitous throughout all tissues and conferring mechanical integrity, has been underinvestigated. A series of studies examined the effects of lysyl oxidase (LOX), the enzyme responsible for the formation of collagen cross-links. Hypoxia-induced endogenous LOX was applied in multiple musculoskeletal tissues (i.e., cartilage, meniscus, tendons, ligaments). Results of these studies showed that both native and engineered tissues are enhanced by invoking a mechanism of hypoxia-induced pyridinoline (PYR) cross-links via intermediaries like LOX. Hypoxia was shown to enhance PYR cross-linking 1.4- to 6.4-fold and, concomitantly, to increase the tensile properties of collagen-rich tissues 1.3- to 2.2-fold. Direct administration of exogenous LOX was applied in native cartilage and neocartilage generated using a scaffold-free, self-assembling process of primary chondrocytes. Exogenous LOX was found to enhance native tissue tensile properties 1.9-fold. LOX concentration- and time-dependent increases in PYR content (?16-fold compared with controls) and tensile properties (approximately fivefold compared with controls) of neocartilage were also detected, resulting in properties on par with native tissue. Finally, in vivo subcutaneous implantation of LOX-treated neocartilage in nude mice promoted further maturation of the neotissue, enhancing tensile and PYR content approximately threefold and 14-fold, respectively, compared with in vitro controls. Collectively, these results provide the first report, to our knowledge, of endogenous (hypoxia-induced) and exogenous LOX applications for promoting collagen cross-linking and improving the tensile properties of a spectrum of native and engineered tissues both in vitro and in vivo. PMID:25349395

Makris, Eleftherios A; Responte, Donald J; Paschos, Nikolaos K; Hu, Jerry C; Athanasiou, Kyriacos A

2014-11-11

303

Covalent Cross-Linking of Glutathione and Carnosine to Proteins by 4-Oxo-2-nonenal§  

PubMed Central

The lipid oxidation product 4-oxo-2-nonenal (ONE) derived from peroxidation of polyunsaturated fatty acids is a highly reactive protein cross-linking reagent. The major family of cross-links reflects conjugate addition of side-chain nucleophiles such as sulfhydryl or imidazole groups to the C=C of ONE to give either a 2- or 3-substituted 4-ketoaldehyde, which then undergoes Paal-Knorr condensation with the primary amine of protein lysine side-chains. If ONE is intercepted in biological fluids by antielectrophiles such as glutathione (GSH) or ?-alanylhistidine (carnosine), this would lead to circulating 4-ketoaldehydes that could then bind covalently to the protein Lys residues. This phenomenon was investigated by SDS–PAGE and mass spectrometry (MALDI-TOF and LC-ESI-MS/MS with both tryptic and chymotryptic digestion). Under the reaction conditions of 0.25 mM to 2 mM ONE, 1 mM GSH or carnosine, 0.25 mM bovine ?-lactoglobulin (?-LG), 100 mM phosphate buffer (pH 7.4, 10% ethanol), 24 h, 37 °C, virtually every Lys of ?-LG was found to be fractionally cross-linked to GSH. Cross-linking of Lys to carnosine was slightly less efficient. Using cytochrome c and RNase A, we showed that ONE becomes more protein-reactive in the presence of GSH, whereas protein modification by 4-hydroxy-2-nonenal is inhibited by GSH. Stable antielectrophile–ONE–protein cross-links may serve as biomarkers of oxidative stress and may represent a novel mechanism of irreversible protein glutathionylation. PMID:19480392

Zhu, Xiaochun; Gallogly, Molly M.; Mieyal, John J.; Anderson, Vernon E.; Sayre, Lawrence M.

2010-01-01

304

Development and evaluation of cross-linked collagen-hydroxyapatite scaffolds for tissue engineering.  

PubMed

This study examines the tissue engineering potential of type I collagen cross-linked in the presence of hydroxyapatite (HAp). Scaffolds were prepared by controlled freezing followed by lyophilization of composite mixtures of collagen and HAp in acetic acid, followed by cross-linking with 0.3% glutaraldehyde. Scaffolds of three ratios were prepared, corresponding to collagen/HAp ratios of 1:2, 1:4, and 1:6. The scaffolds were evaluated for their microstructure, chemical and physical properties, swelling behavior, mechanical strength, biodegradability hemocompatability, cytocompatibility, and histopathology following subcutaneous implantation in Sprague Dawley rats. The collagen/HAp matrices showed a smaller pore size of 10-40 ?m compared to 50-100 ?m for pure collagen scaffolds. Pure collagen showed a mechanical strength of 0.25 MPa, and the value almost doubled for cross-linked composites with collagen/HAp ratio 1:6. The improvement in mechanical strength corresponded to a decrease in swelling and enzymatic degradation (measured by resistance to collagenases). FTIR spectra results in conjunction with scanning electron micrographs showed that cross-linking in the presence of HAp did not significantly alter the structure of collagen. MTT assay and calcein AM staining revealed prominent and healthy growth of mesenchymal stem cells in both the pure collagen as well as collagen:HAp composites of ratio 1:2. In vivo implantation in Sprague Dawley rats showed an initial acute inflammatory response during days 3 and 7, followed by a chronic, macrophage-mediated inflammatory response on days 14 and 28. Overall, a cross-linked collagen/HAp composite scaffold of ratio 1:2 was identified as having potential for further development in tissue engineering. PMID:23905722

Panda, Niladri Nath; Jonnalagadda, Sriramakamal; Pramanik, Krishna

2013-01-01

305

Polypeptide Grafted Hyaluronan: Synthesis and Characterization  

PubMed Central

Poly(L-leucine) grafted hyaluronan (HA-g-PLeu) has been synthesized via a Michael addition reaction between primary amine terminated poly(L-leucine) and acrylate functionalized HA (TBAHA-acrylate). The precursor hyaluronan was first functionalized with acrylate groups by reaction with acryloyl chloride in the presence of triethylamine in N,N-dimethylformamide. 1H NMR analysis of the resulting product indicated that an increase in the concentration of acryloylchoride with respect to hydroxyl groups on HA has only a moderate effect on functionalization efficiency, f. A precise control of stoichiometry was not achieved, which could be attributed to partial solubility of intermolecular aggregates and the hygroscopic nature of HA. Michael addition at high [PLeu-NH2]/[acrylate]TBAHA ratios gave a molar grafting ratio of only 0.20 with respect to the repeat unit of HA, indicating grafting limitation due to insolubility of the grafted HA-g-PLeu. Soluble HA-g-PLeu graft copolymers were obtained for low grafting ratios (< 0.039) with < 8.6 % by mass of PLeu and were characterized thoroughly using light scattering, 1H NMR, FT-IR and AFM techniques. Light scattering experiments showed a strong hydrophobic interaction between PLeu chains, resulting in aggregates with segregated non-grafted HA segments. This yields local networks of aggregates as demonstrated by atomic force microscopy. Circular dichroism spectroscopy showed a ?-sheet conformation for aggregates of poly(L-leucine). PMID:20690642

Wang, Xiaojun; Messman, Jamie; Mays, Jimmy W.; Baskaran, Durairaj

2010-01-01

306

Enhancement of copolymerization of itaconic acid with N-vinyl 2-pyrrolidone by radiation in the presence of cross-linking agent  

NASA Astrophysics Data System (ADS)

Enhancement of copolymerization of itaconic acid (IA) with N-vinyl 2-pyrrolidone (VP) by radiation in the presence of cross-linking agent was investigated. Hydrogels with varying IA content were prepared from the ternary systems N-vinyl 2-pyrrolidone/itaconic acid/water by irradiating with gamma-rays in the presence of a chemical cross-linker, ethylene glycol dimethacrylate (EGDMA) at ambient temperature. The incorporation of EGDMA into the ternary mixtures caused an increase in the amount of IA in the gel system up to a mole fraction of 13.7%. Hydrogels showed a typical pH response such as high pH swelling and low pH deswelling. Equilibrium volume swelling ratio at pH 7 was varied from 15-40 with changing the IA content in the gel system and irradiation dose. The equation recently modified by the authors for the determination of M is observed to describe the swelling behaviour of P(VP/IA/EGDMA) networks containing relatively higher amount of charged units very well. In addition to the evaluation of M from swelling data, the measurement of polymer solvent interaction parameter and the determination of the reaction yield of cross-links of the systems were examined.

?en, M.; Yakar, A.

2005-06-01

307

Fusion protein of the hyaluronan binding domain from human TSG-6 with luciferase for assay of hyaluronan.  

PubMed

The gene expression plasmid, pET-Lmluc, for the fusion protein of the hyaluronan binding domain from human TSG-6 [product of tumor necrosis factor (TNF)-stimulated gene-6] and luciferase from Renilla reniformis was constructed. The fused gene was expressed in Escherichia coli and the resulted insoluble Lm-luc fusion protein was purified and refolded to recover both the hyaluronan binding capability and the luciferase activity. Hyaluronan as low as 1 ng ml(-1) was detected by using the indirect enzymatic immunological assay with the refolded Lm-luc fusion protein. PMID:12889811

Chang, Te-Sheng; Wan, Hisao-Ming; Chen, Chien-Chiang; Giridhar, R; Wu, Wen-Teng

2003-07-01

308

Hyaluronan release from Streptococcus pyogenes: export by an ABC transporter.  

PubMed

Capsular hyaluronan of Streptococcus pyogenes is synthesized at the protoplast membrane. It is widely assumed that hyaluronan is exported by the synthase itself and that no additional protein is required for transfer through plasma membranes. However, we produced an insertional mutation that reduced the mucoid phenotype, hyaluronan production, and capsule formation. Nucleotide sequence analysis of the insertion site identified a gene coding for a protein with an ATP-binding cassette (ABC) that belonged to an ABC transporter system and was located next to the hyaluronan synthesis genes. The mucoid phenotype was reconstituted by complementation with DNA encoding the ABC transporter system. These results indicated that an ABC transporter was required for efficient capsule production. PMID:15215229

Ouskova, Galina; Spellerberg, Barbara; Prehm, Peter

2004-10-01

309

Well-defined, Reversible Disulfide Cross-linked Micelles for On-demand Paclitaxel Delivery  

PubMed Central

To minimize premature release of drugs from their carriers during circulation in the blood stream, we have recently developed reversible disulfide cross-linked micelles (DCMs) that can be triggered to release drug at the tumor site or in cancer cells. We designed and synthesized thiolated linear-dendritic polymers (telodendrimers) by introducing cysteines to the dendritic oligo-lysine backbone of our previously reported telodendrimers comprised of linear polyethylene glycol (PEG) and a dendritic cluster of cholic acids. Reversibly cross-linked micelles were then prepared by the oxidization of thiol groups to disulfide bond in the core of micelles after the self-assembly of thiolated telodendrimers. The DCMs were spherical with a uniform size of 28 nm, and were able to load paclitaxel (PTX) in the core with superior loading capacity up to 35.5% (w/w, drug/micelle). Cross-linking of the micelles within the core reduced their apparent critical micelle concentration and greatly enhanced their stability in non-reductive physiological conditions as well as severe micelle-disrupting conditions. The release of PTX from the DCMs was significantly slower than that from non-cross-linked micelles (NCMs), but can be gradually facilitated by increasing the concentration of reducing agent (glutathione) to an intracellular reductive level. The DCMs demonstrated a longer in vivo blood circulation time, less hemolytic activities, and superior toxicity profiles in nude mice, when compared to NCMs. DCMs were found to be able to preferentially accumulate at the tumor site in nude mice bearing SKOV-3 ovarian cancer xenograft. We also demonstrated that the disulfide cross-linked micellar formulation of PTX (PTX-DCMs) was more efficacious than both free drug and the non-cross-linked formulation of PTX at equivalent doses of PTX in the ovarian cancer xenograft mouse model. The anti-tumor effect of PTX-DCMs can be further enhanced by triggering the release of PTX on-demand by the administration of the FDA approved reducing agent, N-acetylcysteine, after PTX-DCMs have reached the tumor site. PMID:21658763

Li, Yuanpei; Xiao, Kai; Luo, Juntao; Xiao, Wenwu; Lee, Joyce S.; Gonik, Abby M.; Kato, Jason; Dong, Tiffany; Lam, Kit S.

2011-01-01

310

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

NASA Astrophysics Data System (ADS)

Dendrimers and dendrons (fractional dendrimers) are macromolecular structures that have well-defined molecular weights and precise number of functional groups. Tailoring these structures has provided designer molecules that can be used for various applications including drug delivery, sensors, and anti-biofouling surfaces. Overall, this dissertation provides novel protocols for the understanding of molecular design, synthesis, and structure-property relationship of OEGylated and conjugated carbazole dendrons and dendrimers. In this design, the use of oligo(ethylene glycol) (OEG) allows for the fabrication of biocompatible materials and imparts hydrophilicity on the structure while the carbazole functionality allows the cross-linking of these designer molecules. Such fine-tuning of macromolecular structures leading to the fabrication of anti-biofouling thin films, nanostructuring at the air-water interface, and assembly into supramolecular superstructures are considered in this dissertation. Chapter 2 details the synthesis, characterization, and electrochemical cross-linking of OEGylated linear dendrons and "Janus-type" dendrimers. Cross-linking the carbazole moieties enables the deposition of these films on Au, indium tin oxide-coated glass, and doped silicon through cyclic voltammetry and provides films with secondary level of organization imparted by the inter- and intra-molecular interaction among the carbazole units. Chapter 3 describes the fabrication of nonspecific protein adsorption resistant surfaces through electrochemical grafting of three different dendrons on SAM carbazole-coated gold substrates. The predictable shape of each dendron and the ability to cross-link the carbazole units have enabled parametrization of OEG conformation and density on these interfaces. Chapter 4 demonstrates the fundamental architectural requirements for obtaining stable films with OEGylated linear dendron molecules providing a new architectural design of nanostructuring OEGylated macromolecules by combining the LB technique and electrochemical cross-linking. The behavior of these OEGylated systems at the air-water interface varies with carbazole dendron generation, the length of the OEG units and the surface pressure applied upon compression. Chapter 5 describes the synthesis and self-assembly behavior of a new series of OEGylated "Janus-type" carbazole dendrimers wherein ordering of these dendrimers was found to depend on the dendrimer generation as well as the solution concentration. Cross-linking the carbazole superstructures was successfully done in situ via chemical oxidation of the carbazole moieties and reduction of the Au ions to zero valent Au.

Felipe, Mary Jane Legaspi

311

Preparation and characterization of highly cross-linked polyimide aerogels based on polyimide containing trimethoxysilane side groups.  

PubMed

In this study, highly cross-linked and completely imidized polyimide aerogels were prepared from polyimide containing trimethoxysilane side groups, which was obtained as the condensation product of polyimide containing acid chloride side groups and 3-aminopropyltrimethoxysilane. After adding water and acid catalyst, the trimethoxysilane side groups hydrolyzed and condensed one another, and a continuous increase in the complex viscosities of the polyimide solutions with time was observed. The formed polyimide gels were dried by freeze-drying from tert-butyl alcohol to obtain polyimide aerogels, which consisted of a three-dimensional network of polyimide fibers tangled together. By varying the solution concentration of the polyimide containing trimethoxysilane side groups, polyimide aerogels with different densities (ranging from 0.19 to 0.42 g/cm(3)) were obtained. The resulting polyimide aerogels had small pore diameter (ranging from 20.7 to 58.3 nm), high surface area (ranging from 310 to 344 m(2)/g), high 5% weight loss temperature in air (at about 440 °C), and an excellent mechanical property. In addition, the glass transition temperature (349 °C) of the polyimide aerogels was much higher than that (210 °C) of the corresponding linear polyimide. So, even after being heated at 300 °C for 30 min, the porous structure of the polyimide aerogels was not completely destroyed. PMID:25340747

Pei, Xueliang; Zhai, Wentao; Zheng, Wenge

2014-11-11

312

Hyaluronan and a cell-associated hyaluronan binding protein regulate the locomotion of ras-transformed cells  

Microsoft Academic Search

Hyaluronan (HA) and one of its cell binding sites, fibroblast hyaluronan binding protein (HABP), is shown to contribute to the regulation of 10T1\\/2 cell locomotion that contain an EJ-ras-metaUo- thionein (MT-1) hybrid gene. Promotion of the ras- hybrid gene with zinc sulfate acutely stimulates, by 6-10-fold, cell locomotion. After 10 h, locomotion drops to two- to threefold above that of

E. A. Turley; L. Austen; K. Vandeligt; C. Clary

1991-01-01

313

Quasi-solid polymer electrolytes using photo-cross-linked polymers. Lithium and divalent cation conductors and their applications  

NASA Astrophysics Data System (ADS)

In this report, we will present the results on the photo-cross-linked poly-(ethylene glycol) diacrylate (PEGDA) based quasi-solid, i.e. gel, polymer electrolyte systems with lithium, magnesium and zinc trifluoromethanesulfonates [triflate; M n(CF 3SO 3) n] and their preliminary applications to primary cells. The Celgard® membrane-impregnated electrolytes were prepared in the same manner as Abraham et al. [K.M. Abraham, M. Alamgir, D.K. Hoffman, J. Electrochem. Soc. 142 (1995) 683]. The precursor solutions were composed of metal triflates, ethylene carbonate, propylene carbonate, and tetraethylene glycol diacrylate. The Celgard® #3401 membrane was soaked overnight in the precursor solution, then clamped between two Pyrex glass plates and irradiated with UV light to form a gel electrolyte. The maxima of the conductivity obtained were 4.5×10 -4 S cm -1 at 12 mol% for LiCF 3SO 3, 1.7×10 -4 S cm -1 at 1 mol% for Mg(CF 3SO 3) 2, and 2.1×10 -4 S cm -1 at 4 mol% for Zn(CF 3SO 3) 2 system, respectively. The Arrhenius plots of the conductivities are almost linear between 268 and 338 K with 15-25 kJ/mol of activation energy for conduction. The cell, Li|LiCF 3SO 3-SPE+Celgard® #3401|(CH 3) 4NI 5+acetylene black, showed 2.86 V of OCV and could discharge up to 25% with respect to the cathode active material at a discharging current of 0.075 mA/cm 2.

Ikeda, Shoichiro; Mori, Yoichi; Furuhashi, Yuri; Masuda, Hideki; Yamamoto, Osamu

314

Isotope-Coded and Affinity-Tagged Cross-Linking (ICATXL): An Efficient Strategy to Probe Protein Interaction Surfaces  

E-print Network

Isotope-Coded and Affinity-Tagged Cross-Linking (ICATXL): An Efficient Strategy to Probe Protein; E-mail: alb@cgl.ucsf.edu Protein bait affinity studies on the yeast proteome have begun to reveal of the cross-linked products sought. Incorporation of affinity tags into cross-linkers can reduce

Craik, Charles S.

315

Cross-Linked Collagen Surface for Cell Culture That Is Stable, Uniform, and Optically Superior to Conventional Surfaces  

E-print Network

Cross-Linked Collagen Surface for Cell Culture That Is Stable, Uniform, and Optically Superior Volume21, Number3, Part I, March1985 © 1985 Tissue CultureAssociation,Inc. CROSS-LINKED COLLAGEN SURFACE (Received 4 November 1983; accepted 14 December 1984) SUMMARY A new type of collagen surface for use

316

DNA interstrand cross-link repair: understanding role of Fanconi anemia pathway and therapeutic implications.  

PubMed

Interstrand cross-links (ICLs) are extremely toxic DNA lesions that prevent DNA double-helix separation due to the irreversible covalent linkage binding of some agents on DNA strands. Agents that induce these ICLs are thus widely used as chemotherapeutic drugs but may also lead to tumor growth. Fanconi anemia (FA) is a rare genetic disorder that leads to ICL sensitivity. This review provides update on current understanding of the role of FA proteins in repairing ICLs at various stages of cell cycle. We also discuss link between DNA cross-link genotoxicity caused by aldehydes in FA pathway. Besides this, we summarize various ICL agents that act as drugs to treat different types of tumors and highlight strategies for modulating ICL sensitivity for therapeutic interventions that may be helpful in controlling cancer and life-threatening disease, FA. PMID:23859405

Shukla, Pallavi; Solanki, Avani; Ghosh, Kanjaksha; Vundinti, Babu Rao

2013-11-01

317

Membrane formation mechanism of cross-linked polyurea microcapsules by phase separation method.  

PubMed

This research was conducted to clarify the membrane formation mechanism of cross-linked polyurea microcapsules by phase separation method, especially the role of polymeric surfactant, such as poly(ethylene-alt-maleic anhydride) (poly(E-MA)) at the interface of O/W emulsion. It was found that poly(E-MA) was necessary for the formation of cross-linked polyurea membrane. The addition of sodium dodecyl sulphate (SDS) prohibited the membrane formation reaction at the interface, even in the case of poly(E-MA) concentration enough for polymeric microcapsule formation. From the results in this study, poly(E-MA) was found to be adsorbed on the O/W emulsion and provide the reaction site for the membrane formation of polymeric microcapsules. PMID:15204592

Yoshizawa, H; Kamio, E; Hirabayashi, N; Jacobson, J; Kitamura, Y

2004-05-01

318

Elastin cross-linking in the skin from patients with amyotrophic lateral sclerosis  

NASA Technical Reports Server (NTRS)

Two cross-links unique to elastin, desmosine and isodesmosine were measured and compared in skin tissue (left upper arm) from 10 patients with amyotrophic lateral sclerosis (ALS) and from seven age-matched controls. The contents of desmosine and isodesmosine were significantly decreased (p < 0.01 and p < 0.01, respectively) in patients with ALS compared with those of controls, and were negatively and significantly associated with duration of illness in ALS patients (r = -0.77, p < 0.01 and r = -0.65, p < 0.05, respectively). The decline in skin desmosine and isodesmosine is more rapid in ALS than in normal ageing. Thus cross-linking of skin elastin is affected in ALS.

Ono, S.; Yamauchi, M.

1994-01-01

319

Cell Growth on In Situ Photo-Cross-Linked Electrospun Acrylated Cellulose Acetate Butyrate.  

PubMed

In this study, electrospinning was combined with UV curing technology for producing in situ photo cross-linked fibers from methacrylated cellulose acetate butyrate (CABIEM). ECV304 and 3T3 cells were seeded on electrospun fibrous scaffolds. Collagen modified CABIEM fibers were also prepared for improving cell adhesion and proliferation. Cross-linking and the morphology of the fibers were characterized by ATR-FT-IR spectrometry and environmental scanning electron microscopy (ESEM). The cytotoxicity of the fibers was examined using the MTT cytotoxicity assay. According to the results, electrospun fibrous scaffolds are non-toxic and cell viability depends on the amount of collagen. It was found that cell adhesion and cell growth were enhanced as the collagen percentage was increased. PMID:21457618

Cakmakç?, Emrah; Güngör, Atilla; Kayaman-Apohan, Nilhan; Kuruca, Serap Erdem; Cetin, Muzaffer Beyza; Dar, Kadriye Akgün

2011-03-31

320

Let there be light: photo-cross-linked block copolymer nanoparticles.  

PubMed

Polymeric nanoparticles are prepared by selectively cross-linking a photo-sensitive dimethylmaleimide-containing block of a diblock copolymer via UV irradiation. A well-defined photo-cross-linkable block copolymer is prepared via reversible addition-fragmentation chain transfer (RAFT) polymerization of a dimethylmaleimide-functional acrylamido monomer containing photoreactive pendant groups with a poly(N,N-dimethylacrylamide) (PDMA) macro-chain transfer agent. The resulting amphiphilic block copolymers form micelles in water with a hydrophilic PDMA shell and a hydrophobic photo-cross-linkable dimethylmaleimide-containing core. UV irradiation results in photodimerization of the dimethylmaleimide groups within the micelle cores to yield core-cross-linked aggregates. Alternatively, UV irradiation of homogeneous solutions of the block copolymer in a non-selective solvent leads to in situ nanoparticle formation. PMID:24127389

Roy, Debashish; Sumerlin, Brent S

2014-01-01

321

In vitro cross-linking of bovine lens proteins photosensitized by promazines  

SciTech Connect

Promazine derivatives induce cross-linking of bovine lens crystallins in vitro by irradiation with near-ultraviolet (UV) light in the presence of O/sub 2/, as revealed by electrophoresis after denaturation. With the five derivatives tested (promazine (PZ), chlorpromazine (CPZ), triflupromazine (TFPZ), methoxypromazine (MTPZ), and acepromazine (ACPZ)), single-hit kinetics are observed. Evidence implicating the cation radicals of the PZ derivatives as the causative agent of this in vitro effect is presented. Hydroxyl radicals do not appear to be involved in the photo-cross-linking reaction. Sodium ascorbate protects against damage induced either by PZ derivatives plus light or by PZ cation radicals in the dark. These findings are discussed with respect to development of cataracts induced by these drugs in vivo.

Merville, M.P.; Decuyper, J.; Piette, J.; Calberg-Bacq, C.M.; Van de Vorst, A.

1984-05-01

322

Metal cation cross-linked nanocellulose hydrogels as tissue engineering substrates.  

PubMed

The use of cellulose materials for biomedical applications is attractive due to their low cost, biocompatibility, and biodegradability. Specific processing of cellulose to yield nanofibrils further improves mechanical properties and suitability as a tissue engineering substrate due to the similarity to the fibrous structure, porosity, and size-scale of the native extracellular matrix. In order to generate the substrate, nanocellulose hydrogels were fabricated from carboxylated cellulose nanofibrils via hydrogelation using metal salts. Hydrogels cross-linked with Ca(2+) and Fe(3+) were investigated as tissue culture substrates for C3H10T1/2 fibroblast cells. Control substrates as well as those with physically adsorbed and covalently attached fibronectin protein were evaluated with X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR), and enzyme linked immunosorbent assay (ELISA). Significantly more cells were attached to surfaces modified with protein, with the highest number of cells adhered to the calcium cross-linked hydrogels with covalently attached protein. PMID:25295848

Zander, Nicole E; Dong, Hong; Steele, Joshua; Grant, John T

2014-11-12

323

Biochemical properties of bioplastics made from wheat gliadins cross-linked with cinnamaldehyde.  

PubMed

The aim of this work has been to study the modification of gliadin films with cinnamaldehyde as a potential cross-linker agent. The molecular weight profile and cross-linking density showed that cinnamaldehyde increased reticulation in the resulting films. The participation of free amino groups of the protein in the newly created entanglements could be a possible mechanism of connection between the polypeptidic chains. The combination of a Schiff base and a Michael addition is a feasible approach to understanding this mechanism. The protein solubility in different media pointed to lower participation by both noncovalent and disulfide bonds in stabilizing the structure of the cross-linked films. The new covalent bonds formed by the cinnamaldehyde treatment hampered water absorption and weight loss, leading to more water-resistant matrices which had not disintegrated after 5 months. The properties of this novel bioplastic could be modified to suit the intended application by using cinnamaldehyde, a naturally occurring compound. PMID:22047158

Balaguer, M Pau; Gómez-Estaca, Joaquín; Gavara, Rafael; Hernandez-Munoz, Pilar

2011-12-28

324

MeV ion beam interaction with polymer films containing cross-linking agents  

SciTech Connect

Polymer films containing cross linking enhancers were irradiated with MeV alpha particles to determine the effects of MeV ion beam interaction on these materials. The contributed effects from the electronic and nuclear stopping powers were separated by irradiating stacked thin films of polyvinyl chloride (PVC), polystyrene (PS) and polyethersulfone (PES). This layered system allowed most of the effects of the electronic energy deposited to be experienced by the first layers and the last layers to receive most of the effects of the nuclear stopping power. RGA, Raman microprobe analysis, RBS and FTIR measured changes in the chemical structures of the irradiated films. The characterization resolved the effects of the stopping powers on the PVC, PS and PES and the results were compared with those from previously studied polymers that did not contain any cross linking agents.

Evelyn, A. L. [Center for Irradiation of Materials, Alabama A and M University, P.O. Box 1447, Normal, Alabama 35762-1447 (United States)

1999-06-10

325

A cross-linked electro-optic polymer for second order nonlinear optical applications  

NASA Astrophysics Data System (ADS)

Electro-optic properties of a cross-linked second order nonlinear optical polymer were reported. This polymer was synthesized via the crosslinking reaction with cross linker Trimethylolmelamine by doping the chromophores into the cellulose diacetate system. The crosslinking temperature is 144°C. The electro-optic coefficient was measured to be 7.12 pm/v at 1550 nm after poling. The stability characteristic of electro-optic effects was studied by a combination of the electro-optic coefficient and dielectric relaxation measurements. Results show that the cross-linked electro-optic polymer system possesses an excellent long-time stability. The average relaxation time is as large as 5880 days and the relaxation was modeled by KWW equation. The dielectric analyses show that the temperature dependence of the relaxation time follows Arrhenius law.

Hong, Jianxun; Li, Chengjun; Zhou, Jianxin; Zhou, Limin; Chen, Shuiping; Chen, Wei

2008-11-01

326

Reversible cross-linking, microdomain structure, and heterogeneous dynamics in thermally reversible cross-linked polyurethane as revealed by solid-state NMR.  

PubMed

Polyurethane material is widely utilized in industry and daily life due to its versatile chemistry and relatively easy handling. Here, we focused on a novel thermally reversible cross-linked polyurethane with comprehensive remarkable mechanical properties as reported in our recent work (Adv. Mater. 2013, 25, 4912). The microphase-separated structure and heterogeneous segmental dynamics were well revealed by T2 relaxometry experiments, which was also first utilized to in situ monitor the reversible cross-linking associated with Diels-Alder (DA) and retro-Diels-Alder (RDA) reactions. On the basis of T2 relaxometry results, we determined the actual temperature of the (R)DA reaction as well as the corresponding activation energies of the motion of soft segments. Besides, the roles of the temperature and cross-linker contents on the microdomain structure and dynamics are discussed in detail. It is found that the microphase separation is enhanced by the increase of temperature as well as the incorporation of cross-linkers. Also, the polyurethane samples are still thermal-stable even at a high temperature beyond the disassociation of the cross-linkages. Furthermore, Baum-Pines and three-pulse multiple-quantum NMR experiments are utilized to investigate the heterogeneous structures and dynamics of the mobile and rigid segments, respectively. Both the results obtained from the T2 relaxometry and multiple-quantum NMR experiments are in good agreement with the macroscopic mechanical properties of the polyurethane. Finally, it is also well demonstrated that proton T2 relaxometry combined with multiple-quantum NMR is a powerful method to study the heterogeneous structures and dynamics of a multiphase polymer system. PMID:24400980

Zhang, Rongchun; Yu, Shen; Chen, Shengli; Wu, Qiang; Chen, Tiehong; Sun, Pingchuan; Li, Baohui; Ding, Datong

2014-01-30

327

Effect of functionalized silica particles on cross-linked poly(vinyl alcohol) proton conducting membranes  

Microsoft Academic Search

A family of proton conducting membranes based on cross-linked poly(vinyl alcohol), PVA, has been synthesized and characterized.\\u000a The influence of surface-functionalized silica particles on the membrane properties has been evaluated by means of 1H-NMR, vibrational spectroscopy, thermal analysis and electrochemical characterization. The study revealed that the crystallinity\\u000a of the polymer, the proton diffusivity and the water retention are strongly affected

M. A. Navarra; A. Fernicola; S. Panero; A. Martinelli; A. Matic

2008-01-01

328

Quartz Crystal Microbalance Measurements of Protein Deposition onto Cross-linked polyHEMA Hydrogel  

NASA Astrophysics Data System (ADS)

The adsorption of various concentrations of several opthalmologically relevant proteins was measured using Quartz Crystal Microbalance (QCM). Hen egg white lysozyme HEWL, bovine serum albumin BSA, and lactoferrin were measured both individually and in various combinations as they adsorbed onto cross-linked polyHEMA substrate. Results are discussed in terms of the concentration and time dependence of total adhered protein, as well as the amount of desorbable protein. Variations seen during competitive adsorption are also presented.

Teichroeb, Jonathan; Forrest, James; Jones, Lyndon

2006-03-01

329

A review: Non-cross-linked polystyrene bound reagents, catalysts and syntheses  

Microsoft Academic Search

Non-cross-linked polystyrene (NCPS), as a type of soluble polymer having remarkable properties, has attracted more and more attention. Many organic synthetic applications based on NCPS have been shown great success. NCPS is easily functionalized and can be used as supports in organic synthesis. Comparing to classical liquid-phase synthesis, their advantages involve simplified isolation, cycling procedures and increasing stereoselectivity. This review

Jianian Chen; Guichun Yang; Haiqing Zhang; Zuxing Chen

2006-01-01

330

Transglutaminase 2 cross-linking of matrix proteins: biological significance and medical applications  

Microsoft Academic Search

This review summarises the functions of the enzyme tissue transglutaminase (TG2) in the extracellular matrix (ECM) both as\\u000a a matrix stabiliser through its protein cross-linking activity and as an important cell adhesion protein involved in cell\\u000a survival. The contribution of extracellular TG2 to the pathology of important diseases such as cancer and fibrosis are discussed\\u000a with a view to the

R. J. Collighan; M. Griffin

2009-01-01

331

Cross-Linked Thermoplastic Blends of Polyethylene with an Elastomer. 1. Deformation and Strength Characteristics  

Microsoft Academic Search

Results of an experimental investigation into changes of some mechanical characteristics of binary blends of high- and low-density polyethylenes with an elastomer (ethylene-propylene-dicyclopentadiene terpolymer) in the course of ?-radiation and chemical cross-linking are reported for a wide range of component ratios. Data on changes in the tensile strength and total, residual, and reversible strains at break, as well the microhardness

T. Bocok; J. Zicans; M. Kalnins

2005-01-01

332

Radiation cross-linked plastics: a versatile material solution for packaging, automotive, Electrotechnic and Electronics  

Microsoft Academic Search

Used since the beginning of the 1970s for the production of halogen-free and heat-resistant cables and wires, for conditioning polyethylene hot-water pipes or for the manufacture of heat shrinkable tubes and of tyres, radiation cross-linking is developing fastly today on the scale of plastic-moulded parts, and not only by the mean of EB, but also under gamma rays.Indeed, it improves

Sophie Rouif

2004-01-01

333

Quantitative evaluation of fracture, healing and re-healing of a reversibly cross-linked polymer  

Microsoft Academic Search

The repeated fracture–healing characteristics of 2MEP4F polymer, a cross-linked polymer based on Diels–Alder cycloaddition, are systematically and quantitatively evaluated using a sample geometry that allows for controlled incremental crack growth so that the cracked sample remains in one piece after the test, improving our ability to realign the fracture surfaces prior to healing. The specimens have been pre-cracked to a

Thomas A. Plaisted; Sia Nemat-Nasser

2007-01-01

334

Cross-linked polyvinylpyrrolidone nanoparticles: a potential carrier for hydrophilic drugs  

Microsoft Academic Search

Injectable hydrogel polymeric nanoparticles of polyvinylpyrrolidone cross-linked with N,N?-methylene bis-acrylamide and encapsulating water-soluble macromolecules such as FITC–dextran (FITC–Dx) have been prepared in the aqueous cores of reverse micellar droplets. These particles are 100 nm and below in diameter with a narrow size distribution. When dispersed in aqueous buffer these particles appear to be transparent and give an optically clear solution. Lyophilized

Dhruba Jyoti Bharali; Sanjeeb Kumar Sahoo; Subho Mozumdar; Amarnath Maitra

2003-01-01

335

Hypoxia-Selective DNA Interstrand Cross-Link Formation by Two Modified Nucleosides  

PubMed Central

Two nitroimidazole modified thymidines 1a and 1b have been synthesized and incorporated into DNA oligomers. The 350 nm photolysis of 1a and 1b generated a 5-(2?-deoxyuridinyl)methyl radical that induced DNA interstrand cross-links (ICL). Higher ICL yield was observed under hypoxic conditions than aerobic conditions. The photoproducts of monomers or DNA oligomers were isolated and characterized by NMR and/or mass spectroscopy. PMID:22936396

Kuang, Yunyan; Sun, Huabing; Blain, J. Craig

2012-01-01

336

Hypoxia-selective DNA interstrand cross-link formation by two modified nucleosides.  

PubMed

The clean crossed code: Two nitroimidazole-modified thymidines 1 a and 1 b were synthesized and incorporated into DNA oligomers. The 350 nm photolysis of 1 a and 1 b generated a 5-(2'-deoxyuridinyl)methyl radical that induced DNA interstrand cross-links (ICL; see scheme). A higher ICL yield was observed under hypoxic conditions than under aerobic conditions. PMID:22936396

Kuang, Yunyan; Sun, Huabing; Blain, J Craig; Peng, Xiaohua

2012-10-01

337

Studies on the enzymatic and fungal degradation of cross-linked gelatin and its graft copolymers  

Microsoft Academic Search

Glutaraldehyde cross-linked gelatin was graft copolymerized with acrylic acid, acrylamide, vinyl acetate, methyl acrylate, and methyl methacrylate either individually or in combination. The enzymatic and fungal degradation of these graft copolymers with trypsin, pepsin, and mixed cultures ofAspergillus niger, Penicillium ochrochloron, Penicillium funiculosum, andTrichoderma viride was studied for short and extended periods. The weight loss suffered by the samples, the

D. Satyanarayana; P. R. Chatterji

1995-01-01

338

Non-cross-linking gold nanoparticle aggregation as a detection method for single-base substitutions  

Microsoft Academic Search

Aggregation of DNA-modified gold nanoparticles in a non-cross-linking configuration has extraordinary selectivity against terminal mismatch of the surface- bound duplex. In this paper, we demonstrate the utility of this selectivity for detection of single-base substi- tutions. The samples were prepared through stand- ard protocols: DNA extraction, PCR amplification and single-base primer extension. Oligonucleotide- modified nanoparticles correctly responded to the unpurified

Kae Sato; Kazuo Hosokawa; Mizuo Maeda

2005-01-01

339

XPS study for the microstructure development of hydroxyapatite–collagen nanocomposites cross-linked using glutaraldehyde  

Microsoft Academic Search

X-ray photoelectron spectroscopy (XPS) was measured for the dry body of hydroxyapatite (HAP)–collagen (COL) nanocomposites cross-linked using glutaraldehyde (GA). Survey scan XPS showed the elemental spectra of N, C, O, Ca and P, which came from HAP and COL. The covalent bond formation between Ca2+ of HAP and RCOO? of COL molecule was confirmed by XPS. The bridge formation between

Myung Chul Chang; Junzo Tanaka

2002-01-01

340

A Role for Collagen IV Cross-links in Conferring Immune Privilege to the Goodpasture Autoantigen  

PubMed Central

The detailed structural basis for the cryptic nature (crypticity) of a B cell epitope harbored by an autoantigen is unknown. Because the immune system may be ignorant of the existence of such “cryptic” epitopes, their exposure could be an important feature in autoimmunity. Here we investigated the structural basis for the crypticity of the epitopes of the Goodpasture autoantigen, the ?3?4?5 noncollagenous-1 (NC1) hexamer, a globular domain that connects two triple-helical molecules of the ?3?4?5 collagen IV network. The NC1 hexamer occurs in two isoforms as follows: the M-isoform composed of monomer subunits in which the epitopes are accessible to autoantibodies, and the D-isoform composed of both monomer and dimer subunits in which the epitopes are cryptic. The D-isoform was characterized with respect to quaternary structure, as revealed by mass spectrometry of dimer subunits, homology modeling, and molecular dynamics simulation. The results revealed that the D-isoform contains two kinds of cross-links as follows: S-hydroxylysyl-methionine and S-lysyl-methionine cross-links, which stabilize the ?3?5-heterodimers and ?4?4-homodimers, respectively. Construction and analysis of a three-dimensional model of the D-isoform of the ?3?4?5 NC1 hexamer revealed that crypticity is a consequence of the following: (a) sequestration of key residues between neighboring subunits that are stabilized by domain-swapping interactions, and (b) by cross-linking of subunits at the trimer-trimer interface, which stabilizes the structural integrity of the NC1 hexamer and protects against binding of autoantibodies. The sequestrated epitopes and cross-linked subunits represent a novel structural mechanism for conferring immune privilege at the level of quaternary structure. Perturbation of the quaternary structure may be a key factor in the etiology of Goodpasture disease. PMID:18499662

Vanacore, Roberto M.; Ham, Amy-Joan L.; Cartailler, Jean-Philippe; Sundaramoorthy, Munirathinam; Todd, Parvin; Pedchenko, Vadim; Sado, Yoshikazu; Borza, Dorin-Bogdan; Hudson, Billy G.

2008-01-01

341

Fabrication and properties of irradiation-cross-linked poly(vinyl alcohol)/clay aerogel composites.  

PubMed

Poly(vinyl alcohol) (PVOH)/clay aerogel composites were fabricated by an environmentally friendly freeze-drying of the aqueous precursor suspensions, followed by cross-linking induced by gamma irradiation without chemical additives. The influences of cross-linking conditions, i.e., absorbed dose and polymer loading as well as density on the aerogel structure and properties, were investigated. The absorbed dose of 30 kGy was found to be the optimum dose for fabricating strong PVOH composites; the compressive modulus of an aerogel prepared from an aqueous suspension containing 2 wt % PVOH/8 wt % clay increased 10-fold, and that containing 1 wt % PVOH/9 wt % clay increased 12 times upon cross-linking with a dose of 30 kGy. Increasing the solids concentration led to an increase in the mechanical strength, in accordance with the changes in microstructure from layered structure to network structure. The increase of absorbed dose also led to decreased porous size of the network structure. Cross-linking and the increase of the PVOH lead to decreased thermal stability. The strengthened PVOH/clay aerogels possess very low flammability, as measured by cone calorimetry, with heat, smoke, and volatile products release value decreasing as increasing clay content. The mechanism of flame retardation in these materials was investigated with weight loss, FTIR, WAXD, and SEM of the burned residues. The proposed mechanism is that with decreasing fuel content (increasing clay content), increased heat and mass transport barriers are developed; simultaneously low levels of thermal conductivity are maintained during the burning. PMID:25164075

Chen, Hong-Bing; Liu, Bo; Huang, Wei; Wang, Jun-Sheng; Zeng, Guang; Wu, Wen-Hao; Schiraldi, David A

2014-09-24

342

Models of shear-thickening behavior in physically cross-linked networks  

SciTech Connect

Shear-thickening effects are often observed in physically cross-linked networks formed by polymeric chains having a few localized, energetically favored interactions. The authors find that a possible explanation for these effects is the non-Gaussian behavior of the chains stretched by the shear flow. Two network models for unentangled telechelic chains are proposed, which differ in the way unattached chains relax after deformation. One of the models correctly portrays the qualitative shear-thickening features commonly observed.

Marrucci, G.; Bhargava, S.; Cooper, S.L. [Univ. of Delaware, Newark, DE (United States). Dept. of Chemical Engineering

1993-11-22

343

Informatics Strategies for Large-Scale Novel Cross-Linking Analysis  

PubMed Central

The detection of protein interactions in biological systems represents a significant challenge for today’s technology. Chemical cross-linking provides the potential to impart new chemical bonds in a complex system that result in mass changes in a set of tryptic peptides detected by mass spectrometry. However, system complexity and cross-linking product heterogeneity have precluded widespread chemical cross-linking use for large-scale identification of protein–protein interactions. The development of mass spectrometry identifiable cross-linkers called protein interaction reporters (PIRs) has enabled on-cell chemical cross-linking experiments with product type differentiation. However, the complex datasets resultant from PIR experiments demand new informatics capabilities to allow interpretation. This manuscript details our efforts to develop such capabilities and describes the program X-links, which allows PIR product type differentiation. Furthermore, we also present the results from Monte Carlo simulation of PIR-type experiments to provide false discovery rate estimates for the PIR product type identification through observed precursor and released peptide masses. Our simulations also provide peptide identification calculations based on accurate masses and database complexity that can provide an estimation of false discovery rates for peptide identification. Overall, the calculations show a low rate of false discovery of PIR product types due to random mass matching of approximately 12% with 10 ppm mass measurement accuracy and spectral complexity resulting from 100 peptides. In addition, consideration of a reduced database resulting from stage 1 analysis of Shewanella oneidensis MR-1 containing 367 proteins resulted in a significant reduction of expected identification false discovery rate estimation compared to that from the entire Shewanella oneidensis MR-1 proteome. PMID:17676784

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

2008-01-01

344

Engineering of biomaterials surfaces by hyaluronan.  

PubMed

This review addresses the area of study that defines the field of surface modification of biomedical materials and devices by hyaluronan (HA), as related to the exploitation of HA biological properties. To provide a comprehensive view of the subject matter, initial sections give a quick introduction to basic information on HA-protein and HA-cell interactions, together with some discussion on the bioactive role of HA in wound healing and related phenomena. This is followed by a description of current theories that correlate HA properties to its molecular structure in aqueous media, underlying how HA molecular details are crucial for its biological interaction and role. Finally, existing approaches to surface modification by HA are reviewed, stressing the need for HA-surface engineering founded on the knowledge and control of the surface-linked HA molecular conformation at the solid/aqueous interface. PMID:15877335

Morra, Marco

2005-01-01

345

Hyaluronan, neural stem cells and tissue reconstruction after acute ischemic stroke  

PubMed Central

Focal stroke is a disabling disease with lifelong sensory, motor and cognitive impairments. Given the paucity of effective clinical treatments, basic scientists are developing novel options for protection of the affected brain and regeneration of lost tissue. Tissue bioengineering and stem/progenitor cell treatments have both been individually pursued for stroke neural repair therapies, with some benefit in tissue recovery. Emerging directions in stroke neural repair approaches combine these two therapies to use biopolymers with stem/progenitor transplants to promote greater cell survival in the transplant and directed delivery of bioactive molecules to the transplanted cells and the adjacent injured tissue. In this review the background literature on a combined use of neural stem/progenitor cells encapsulated in hyaluronan gels is discussed and the way this therapeutic approach can affect the important processes involved in brain tissue reconstruction, such as angiogenesis, axon regeneration, neural differentiation and inflammation is clarified. The glycosaminoglycan hyaluronan can optimize those processes and be employed in a successful neural tissue engineering approach. PMID:23507922

Moshayedi, Pouria; Carmichael, S. Thomas

2013-01-01

346

Well-defined cross-linked antioxidant nanozymes for treatment of ischemic brain injury  

PubMed Central

Development of well-defined nanomedicines is critical for their successful clinical translation. A simple synthesis and purification procedure is established for chemically cross-linked polyion complexes of Cu/Zn superoxide dismutase (SOD1) or catalase with a cationic block copolymer, methoxy-poly(ethylene glycol)-block-poly(L-lysine hydrochloride) (PEG-pLL50). Such complexes, termed cross-linked nanozymes (cl-nanozymes) retain catalytic activity and have narrow size distribution. Moreover, their cytotoxicity is decreased compared to non-cross-linked complexes due to suppression of release of the free block copolymer. SOD1 cl-nanozymes exhibit prolonged ability to scavenge experimentally induced reactive oxygen species (ROS) in cultured brain microvessel endothelial cells and central neurons. In vivo they decrease ischemia/reperfusion-induced tissue injury and improve sensorimotor functions in a rat middle cerebral artery occlusion (MCAO)model after a single intravenous (i.v.) injection. Altogether, well-defined cl-nanozymes are promising modalities for attenuation of oxidative stress after brain injury. PMID:22902590

Manickam, Devika S.; Brynskikh, Anna M.; Kopanic, Jennifer L.; Sorgen, Paul L.; Klyachko, Natalia L.; Batrakova, Elena V.; Bronich, Tatiana K.; Kabanov, Alexander V.

2013-01-01

347

Collagen cross-linking in sun-exposed and unexposed sites of aged human skin  

NASA Technical Reports Server (NTRS)

A recently described nonreducible, acid-heat stable compound, histidinohydroxylysinonorleucine (HHL), is a collagen cross-link isolated from mature skin tissue. Its abundance is related to chronologic aging of skin. The present communication describes the quantity of HHL from aged human skin of the same individuals in sun-exposed (wrist) and unexposed (buttock) sites. Punch biopsies were obtained from these sites from nine people of age 60 or older. HHL contents (moles/mole of collagen) at these sites were for wrist 0.13 +/- 0.07 and for buttock 0.69 +/- 0.17 (mean +/- SD, p less than 0.001). In addition, it was found that acute irradiation of the cross-linked peptides with UVA (up to 250 J/cm2) and UVB (up to 1 J/cm2) had no effect on HHL structure. The same treatment significantly degraded another nonreducible, stable collagen cross-link, pyridinoline. The results suggest that chronic sunlight exposure may be associated with an impediment to normal maturation of human dermal collagen resulting in tenuous amount of HHL. Thus, the process of photoaging in dermal collagen is different from that of chronologic aging in human skin.

Yamauchi, M.; Prisayanh, P.; Haque, Z.; Woodley, D. T.

1991-01-01

348

?-Lactalbumin nanoparticles prepared by desolvation and cross-linking: structure and stability of the assembled protein.  

PubMed

A key step in the preparation of cross-linked protein nanoparticles involves the desolvation of proteins with an organic solvent, which is thought to act by modulating hydrophobic interactions. However, to date, no study has examined the conformational changes that proteins undergo during the assembly process. In this work, by using several biophysical techniques (CD spectroscopy, DSC, TEM, etc.), we studied spheroidal nanoparticles made from bovine ?-lactalbumin cross-linked with glutaraldehyde in the presence of acetone. Within the nanoparticle, the polypeptide chain acquires a ?-strand-like conformation (completely different from the native protein in secondary and tertiary structure) in which several side chains likely become available for reacting with glutaraldehyde. A multiplicity of cross-linking sites, together with the polymeric nature of glutaraldehyde, may thus explain the low dry-weight fraction of protein that was found in the nanoparticles. Although covalent bonds undoubtedly constitute the main source for nanoparticle stability, noncovalent interactions also appear to play a role in this regard. PMID:25105879

Arroyo-Maya, Izlia J; Hernández-Sánchez, Humberto; Jiménez-Cruz, Esmeralda; Camarillo-Cadena, Menandro; Hernández-Arana, Andrés

2014-01-01

349

Comparative wear tests of ultra-high molecular weight polyethylene and cross-linked polyethylene.  

PubMed

Wear particle-induced osteolysis is a major concern in hip implant failure. Therefore, recent research work has focussed on wear-resistant materials, one of the most important of which is cross-linked polyethylene. In view of this, the objective of this study was to compare the in vitro wear performance of cross-linked polyethylene to traditional ultra-high molecular weight polyethylene. In order to mimic appropriate in vivo conditions, a novel high-capacity wear tester called a circularly translating pin-on-disc was used. The results of this in vitro study demonstrated that the wear rate for cross-linked polyethylene was about 80% lower than that of conventional ultra-high molecular weight polyethylene. This difference closely matches in vivo results reported in the literature for total hip replacements that use the two biopolymers. The in vitro results were also verified against ASTM F732-00 (standard test method for wear testing of polymeric materials for use in total joint prostheses). The 50-station circularly translating pin-on-disc proved to be a reliable device for in vitro wear studies of orthopaedic biopolymers. PMID:23637270

Harsha, A P; Joyce, Tom J

2013-05-01

350

Micro- and Macrorheological Properties of Isotropically Cross-linked Actin Networks  

E-print Network

Cells make use of semi-flexible biopolymers such as actin or intermediate filaments to control their local viscoelastic response by dynamically adjusting the concentration and type of cross-linker molecules. The microstructure of the resulting networks mainly determines their mechanical properties. It remains an important challenge to relate structural transitions to both the molecular properties of the cross-linking molecules and the mechanical response of the network. This can be achieved best by well-defined in vitro model systems in combination with microscopic techniques. Here, we show that with increasing concentrations of the cross-linker HMM (heavy meromyosin) a transition in the mechanical network response occurs. At low cross-linker densities the network elasticity is dominated by the entanglement length of the polymer, while at high HMM densities the cross-linker distance determines the elastic behavior. Using microrheology the formation of heterogeneous networks is observed at low cross-linker concentrations. Micro- and macrorheology both report the same transition to a homogeneous cross-linked phase. This transition is set by a constant average cross-linker distance. Thus, the micro- and macromechanical properties of isotropically cross-linked in vitro actin networks are determined by only one intrinsic network parameter.

Yuxia Luan; Oliver Lieleg; Bernd Wagner; Andreas R. Bausch

2007-06-04

351

Hyaluronic acid and alginate covalent nanogels by template cross-linking in polyion complex micelle nanoreactors.  

PubMed

Hyaluronic acid (HA) and alginate (AL) covalent nanogels cross-linked with l-lysine ethyl ester were prepared by template chemical cross-linking of the polysaccharide in polyion complex micelle (PIC) nanoreactors. By using this method we were able to prepare HA and AL nanogels without organic solvents. PICs were prepared by using poly(ethylene oxide)-block-poly[(3-acrylamidopropyl)-trimethylammonium chloride] (PEO-b-PAMPTMA) or poly[(N-isopropylacrylamide)-block-PAMPTMA] (PNIPAAM-b-PAMPTMA). Only PNIPAAM-b-PAMPTMA block copolymers allowed to prepare PIC with small and controlled size. Short polysaccharide chains (Xn=50 and 63 for AL and HA, respectively, where Xn is the number of monosaccharidic units present in the polysaccharide) where used to optimize PIC formation. The remarkable difference in charge density and rigidity of HA and AL did not have a significant influence on the formation of PICs. PICs with small size (diameter of about 50-80 nm) and low polydispersity were obtained up to 5mg/mL of polymer. After cross-linking with l-lysine ethyl ester, the nanoreactors were dissociated by adding NaCl. The nanogels were easily purified and isolated by dialysis. The dissociation of the nanoreactors and the formation of the nanogels were confirmed by (1)H NMR, DLS, TEM and ?-potential measurements. The size of the smallest nanogels in solution in the swollen state was 50-70 nm in presence of salt and 80-100 nm in water. PMID:24299754

De Santis, Serena; Diociaiuti, Marco; Cametti, Cesare; Masci, Giancarlo

2014-01-30

352

Tunable High Performance Cross-Linked Alkaline Anion Exchange Membranes for Fuel Cell Applications  

SciTech Connect

Fuel cells are energy conversion devices that show great potential in numerous applications ranging from automobiles to portable electronics. However, further development of fuel cell components is necessary for them to become commercially viable. One component critical to their performance is the polymer electrolyte membrane, which is an ion conductive medium separating the two electrodes. While proton conducting membranes are well established (e.g., Nafion), hydroxide conducting membranes (alkaline anion exchange membranes, AAEMs) have been relatively unexplored by comparison. Operating under alkaline conditions offers significant efficiency benefits, especially for the oxygen reduction reaction; therefore, effective AAEMs could significantly advance fuel cell technologies. Here we demonstrate the use of ring-opening metathesis polymerization to generate new cross-linked membrane materials exhibiting high hydroxide ion conductivity and good mechanical properties. Cross-linking allows for increased ion incorporation, which, in turn supports high conductivities. This facile synthetic approach enables the preparation of cross-linked materials with the potential to meet the demands of hydrogen-powered fuel cells as well as direct methanol fuel cells.

Robertson, Nicholas J.; Kostalik, IV, Henry A.; Clark, Timothy J.; Mutolo, Paul F.; Abruña, Héctor D.; Coates, Geoffrey W.

2010-01-01

353

Surface cross linking and functionalization of poly(ethylene terephthalate) in a helium discharge  

NASA Astrophysics Data System (ADS)

Films of poly(ethylene terephthalate) (PET) have been subjected to a low frequency (70 kHz) helium discharge, with a non-symmetrical configuration of electrodes, in order to study the treatment conditions for which the `ageing' effect is slowed down. Treatments were made for different gas flow rates (40, 70 and 100 sccm) and different exposure times (1, 10 and 30 s). Emission spectroscopy and mass spectrometry were used to characterize the discharge plasma. The resulting modifications to the polymer surface were analysed via contact angle measurements and the XPS technique. It is pointed out that treatments on an He discharge induce both a functionalization and a cross linking of the uppermost layers of the polymer film. The residual oxygen, which partially originates within the polymer, induces surface oxidation. The cross-linked content critically depends on the residence time and concentration of implicated species. It seems that a change in the surface work function takes place as a result of a surface restructuring in the earliest stages of the reactions. This could involve an increase in the rate constant for the surface de-excitation of the helium metastables in the presence of the polymer. A contribution to the understanding of the competitive processes of cross linking and functionalization, as a function of the helium flow rate, is accomplished.

Gheorghiu, Mariana; Arefi, F.; Amouroux, J.; Placinta, G.; Popa, G.; Tatoulian, M.

1997-02-01

354

Radiation cross-linked plastics: a versatile material solution for packaging, automotive, Electrotechnic and Electronics  

NASA Astrophysics Data System (ADS)

Used since the beginning of the 1970s for the production of halogen-free and heat-resistant cables and wires, for conditioning polyethylene hot-water pipes or for the manufacture of heat shrinkable tubes and of tyres, radiation cross-linking is developing fastly today on the scale of plastic-moulded parts, and not only by the mean of EB, but also under gamma rays. Indeed, it improves considerably the performances of a great number of plastics among thermoplastics, elastomers and thermoplastic elastomers (TPE). Radiation cross-linking reinforces the dimensional stability of polymers in chemically aggressive and high-temperature conditions. Radiation cross-linked-based engineering plastics offers OEM and end users in many branches of industry both technical and economical advantages in comparison with high-performances plastics. They constitute a technical and economical compromise between engineering plastics that failed and high-performances plastic, often over-tailored and expensive. This modern industrial technology gives way to new applications and perspectives in various sectors (packaging, automotive, electrotechnic and electronics, including connectors, surface-mounted devices, integrated circuits, 3D-MID, etc.) that are described in the paper.

Rouif, Sophie

2004-09-01

355

Nonprotein Based Enrichment Method to Analyze Peptide Cross-Linking in Protein Complexes  

PubMed Central

Cross-linking analysis of protein complexes and structures by tandem mass spectrometry (MS/MS) has advantages in speed, sensitivity, specificity, and the capability of handling complicated protein assemblies. However, detection and accurate assignment of the cross-linked peptides are often challenging due to their low abundance and complicated fragmentation behavior in collision-induced dissociation (CID). To simplify the MS analysis and improve the signal-to-noise ratio of the cross-linked peptides, we developed a novel peptide enrichment strategy that utilizes a cross-linker with a cryptic thiol group and using beads modified with a photocleavable cross-linker. The functional cross-linkers were designed to react with the primary amino groups in proteins. Human serum albumin was used as a model protein to detect intra- and intermolecular cross-linkages. Use of this protein-free selective retrieval method eliminates the contamination that can result from avidin–biotin based retrieval systems and simplifies data analysis. These features may make the method suitable to investigate protein–protein interactions in biological samples. PMID:19642656

Yan, Funing; Che, Fa-Yun; Rykunov, Dmitry; Nieves, Edward; Fiser, Andras; Weiss, Louis M.; Angeletti, Ruth Hogue

2009-01-01

356

Thermal diffusivity of hexagonal boron nitride composites based on cross-linked liquid crystalline polyimides.  

PubMed

Hexagonal boron nitride (h-BN) composites with the oriented cross-linked liquid crystalline (LC) polyimide have been developed as high thermally conductive materials. Well-dispersed h-BN composite films were obtained, as observed by scanning electron microscopy. The morphology of the composite films was further investigated in detail by the wide-angle X-ray diffraction. The obtained composite films based on the cross-linked LC polyimide showed that the polymer chains vertically aligned in the direction parallel to the films, while those based on the amorphous polyimide showed an isotropic nature. Moreover, the alignment of the cross-linked LC polyimides was maintained, even after increasing the volume fraction of h-BN. This alignment plays an important role in the effective phonon conduction between h-BN and the matrices. Indeed, the thermal diffusivity in the thickness direction of the composite films based on the LC polyimide measured by a temperature wave analysis method was increased to 0.679 mm(2) s(-1) at a 30 vol % h-BN loading, which was higher than that based on the amorphous polyimide. PMID:23506319

Shoji, Yu; Higashihara, Tomoya; Tokita, Masatoshi; Morikawa, Junko; Watanabe, Junji; Ueda, Mitsuru

2013-04-24

357

Fracture Mechanics of Collagen Fibrils: Influence of Natural Cross-Links  

PubMed Central

Tendons are important load-bearing structures, which are frequently injured in both sports and work. Type I collagen fibrils are the primary components of tendons and carry most of the mechanical loads experienced by the tissue, however, knowledge of how load is transmitted between and within fibrils is limited. The presence of covalent enzymatic cross-links between collagen molecules is an important factor that has been shown to influence mechanical behavior of the tendons. To improve our understanding of how molecular bonds translate into tendon mechanics, we used an atomic force microscopy technique to measure the mechanical behavior of individual collagen fibrils loaded to failure. Fibrils from human patellar tendons, rat-tail tendons (RTTs), NaBH4 reduced RTTs, and tail tendons of Zucker diabetic fat rats were tested. We found a characteristic three-phase stress-strain behavior in the human collagen fibrils. There was an initial rise in modulus followed by a plateau with reduced modulus, which was finally followed by an even greater increase in stress and modulus before failure. The RTTs also displayed the initial increase and plateau phase, but the third region was virtually absent and the plateau continued until failure. The importance of cross-link lability was investigated by NaBH4 reduction of the rat-tail fibrils, which did not alter their behavior. These findings shed light on the function of cross-links at the fibril level, but further studies will be required to establish the underlying mechanisms. PMID:23746520

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

2013-01-01

358

Interfacial friction and adhesion of cross-linked polymer thin films swollen with linear chains.  

PubMed

The preparation and interfacial properties of a new type of tethered, thin-film lubricant coating are presented. These coatings are composed of three components: a dense self-assembled monolayer (SAM) underlayer that presents reactive vinyl groups at its surface; a cross-linked polydimethylsiloxane (PDMS) overlayer that is covalently tethered to the SAM; and free, mobile linear PDMS chains dispersed in the network. We investigate the influence of the molecular weight (Ms) and concentration of the free PDMS chains on the structure and equilibrium swelling properties of the cross-linked films. Using a bead-probe lateral force microscopy measurement technique, we also quantify the interfacial friction and adhesion characteristics of surfaces functionalized with these coatings. We find that both the volume fraction and the molecular weight of free PDMS molecules in the coatings influence their interfacial friction and adhesion properties. For example, the addition of short PDMS chains in dry, cross-linked PDMS thin films yields tethered surface coatings with ultralow friction coefficients (mu = 5.2 x 10(-3)). An analysis based on classical lubrication theory suggests that the reduction in friction force produced by free polymer is a consequence of the gradual separation of asperities on opposing surfaces and the consequent substitution of solid-solid friction by viscous drag of the free polymer chains in the network. PMID:17552545

Zhang, Qing; Archer, Lynden A

2007-07-01

359

Cross-linked polymer nanofibers for hyperthermophilic enzyme immobilization: approaches to improve enzyme performance.  

PubMed

We report an enzyme immobilization method effective at elevated temperatures (up to 105 °C) and sufficiently robust for hyperthermophilic enzymes. Using a model hyperthermophilic enzyme, ?-galactosidase from Thermotoga maritima, immobilization within chemically cross-linked poly(vinyl alcohol) (PVA) nanofibers to provide high specific surface area is achieved by (1) electrospinning a blend of a PVA and enzyme and (2) chemically cross-linking the polymer to entrap the enzyme within a water insoluble PVA fiber. The resulting enzyme-loaded nanofibers are water-insoluble at elevated temperatures, and enzyme leaching is not observed, indicating that the cross-linking effectively immobilizes the enzyme within the fibers. Upon immobilization, the enzyme retains its hyperthermophilic nature and shows improved thermal stability indicated by a 5.5-fold increase in apparent half-life at 90 °C, but with a significant decrease in apparent activity. The loss in apparent activity is attributed to enzyme deactivation and mass transfer limitations. Improvements in the apparent activity can be achieved by incorporating a cryoprotectant during immobilization to prevent enzyme deactivation. For example, immobilization in the presence of trehalose improved the apparent activity by 10-fold. Minimizing the mat thickness to reduce interfiber diffusion was a simple and effective method to further improve the performance of the immobilized enzyme. PMID:25058141

Tang, Christina; Saquing, Carl D; Morton, Stephen W; Glatz, Brittany N; Kelly, Robert M; Khan, Saad A

2014-08-13

360

Crosslink density, oxidation and chain scission in retrieved, highly cross-linked UHMWPE tibial bearings.  

PubMed

Irradiated, thermally stabilized, highly cross-linked UHMWPE bearings have demonstrated superior wear performance and improved in vitro oxidation resistance compared with terminally gamma-sterilized bearings, yet retrieval analysis reveals unanticipated in vivo oxidation in these materials despite fewer or no measurable free radicals. There has been little evidence to date that the oxidation mechanism in thermally stabilized materials is the same as that in conventional materials, and so it is unknown whether oxidation in these materials is leading to chain scission and a degradation of mechanical properties, molecular weight, and crosslink density. The aim of this study was to determine whether measured in vivo oxidation in retrieved, highly cross-linked tibial bearings corresponds with a decreasing crosslink density. Analysis of three tibial bearing materials revealed that crosslink density decreased following in vivo duration, and that the change in crosslink density was strongly correlated with oxidation. The results suggest that oxidation in highly cross-linked materials is causing chain scissions that may, in time, impact the material properties. If in vivo oxidation continues over longer durations, there is potential for a clinically significant degradation of mechanical properties. PMID:24589360

Reinitz, Steven D; Currier, Barbara H; Levine, Rayna A; Van Citters, Douglas W

2014-05-01

361

Initiation of DNA Interstrand Cross-link Repair in Mammalian Cells  

PubMed Central

Interstrand cross-links (ICLs) are among the most cytotoxic DNA lesions to cells because they prevent the two DNA strands from separating, thereby precluding replication and transcription. Even though chemotherapeutic cross-linking agents are well established in clinical use, and numerous repair proteins have been implicated in the initial events of mammalian ICL repair, the precise mechanistic details of these events remain to be elucidated. This review will summarize our current understanding of how ICL repair is initiated with an emphasis on the context (replicating, transcribed or quiescent DNA) in which the ICL is recognized, and how the chemical and physical properties of ICLs influence repair. Although most studies have focused on replication-dependent repair because of the relation to highly replicative tumor cells, replication-independent ICL repair is likely to be important in the circumvention of cross-link cytotoxicity in non-dividing, terminally differentiated cells that may be challenged with exogenous or endogenous sources of ICLs. Consequently, the ICL repair pathway that should be considered ‘dominant’ appears to depend on the cell type and the DNA context in which the ICL is encountered. The ability to define and inhibit distinct pathways of ICL repair in different cell cycle phases may help in developing methods that increase cytotoxicity to cancer cells while reducing side-effects in non-dividing normal cells. This may also lead to a better understanding of pathways that protect against malignancy and aging. PMID:20658650

Hlavin, Erica M.; Smeaton, Michael B.; Miller, Paul S.

2010-01-01

362

Adsorption of allura red dye by cross-linked chitosan from shrimp waste.  

PubMed

The present study was designed to evaluate the chitosan, which has been obtained by deacetylation of chitin, as a biosorbent. The chitin was isolated from fermented shrimp waste by an important local industrial food biopolymer. The aim of this work was the characterization of chitosan and preparation of cross-linked chitosan- tripolyphosphate (chitosan-TPP) beads for the removal of allura red food dye from aqueous solutions. Conditions of batch adsorption such as pH, time and adsorbent dose were examined. The effectiveness of cross-linked chitosan beads for dye removal was found to be higher for pH 2 (98%, percentage of dye removal) and tends to decrease at pHs of 3 to 11 (up to 49%). The values of percentage removal show that the adsorption capacity increases with time of contact and dosage of chitosan-TPP, but red dye adsorption is mainly influenced by pH level. The cross-linked chitosan-TPP beads can significantly adsorb allura red monoazo dye from aqueous solutions even at acidic pHs unlike raw chitosan beads that tend to dissolve in acidic solutions. Consequently, this modified chitosan has characteristics that allow minimization of environmental pollution and widening the valorization of shrimp waste. PMID:22277220

Sánchez-Duarte, Reyna G; Sánchez-Machado, Dalia I; López-Cervantes, Jaime; Correa-Murrieta, Ma A

2012-01-01

363

Characterization and antibacterial properties of N-halamine-derivatized cross-linked polymethacrylamide nanoparticles.  

PubMed

N-halamine-derivatized cross-linked polymethacrylamide nanoparticles with sizes ranging between 18 ± 2.0 and 460 ± 60 nm were prepared via surfactant-free dispersion co-polymerization of methacrylamide (MAA) and the cross-linking monomer N,N-methylenebisacrylamide (MBAA) in an aqueous continuous phase, followed by a chlorination process using sodium hypochlorite. The effect of various polymerization parameters (monomer concentration, initiator type and concentration, polymerization duration, polymerization temperature, and the weight ratio [MBAA]/[MAA]) on the size and size distribution of the produced cross-linked P(MAA-MBAA) nanoparticles was elucidated. The effect of various chlorination parameters (hypochlorite concentration, chlorination period and temperature) on the bound oxidative chlorine atom (Cl) content of the P(MAA-MBAA) nanoparticles was also investigated. The bactericidal activity of these chloramine-derivatized nanoparticles was tested against two common bacterial pathogens (Escherichia coli and Staphylococcus aureus), and they were found to be highly potent. Furthermore, these nanoparticles also exerted their antimicrobial activity against multi-drug resistant (MDR) bacteria, further demonstrating their efficacy. PMID:24695094

Gutman, Ori; Natan, Michal; Banin, Ehud; Margel, Shlomo

2014-06-01

364

Enzyme catalyzed cross-linking of spruce galactoglucomannan improves its applicability in barrier films.  

PubMed

Hemicelluloses are one of the main constituents of plant cell walls and thereby one of the most abundant biopolymers on earth. They can be obtained as by-products from different wood based processes, most importantly from the mechanical pulping. Hemicelluloses have interesting properties in e.g. barrier film applications. However, their relatively low molecular weight after isolation and co-extraction with lignin has limited their use. In this work, we present a novel technique for increasing the molecular weight of different wood hemicelluloses from mechanical pulping process waters as well as from pre-hydrolysis extracts. This is achieved by enzyme-catalyzed cross-linking of aromatic moieties bound to the hemicelluloses. The cross-linking treatment resulted in significantly improved mechanical properties in barrier films made with spruce galactoglucomannan. To our knowledge, this is the first time that wood hemicelluloses have been cross-linked by utilizing the bound aromatic moieties and creates new possibilities for utilizing this raw material source. PMID:23648031

Oinonen, Petri; Areskogh, Dimitri; Henriksson, Gunnar

2013-06-20

365

Performance of differently cross-linked, partially fluorinated proton exchange membranes in polymer electrolyte fuel cells  

SciTech Connect

A series of differently cross-linked FEP-g-polystyrene proton exchange membranes has been synthesized by the preirradiation grafting method [FEP: poly(tetrafluoroethylene-co-hexafluoropropylene)]. Divinylbenzene (DVB) and/or triallyl cyanurate (TAC) were used as cross-linkers in the membranes. It was found that the physical properties of the membranes, such as water-uptake and specific resistance, are strongly influenced by the nature of the cross-linker. Generally it can be stated that DVB decreases water-uptake and increases specific resistance; on the other hand TAC increases swelling and decreases specific resistance to values as low as 5.0 {Omega} cm at 60 C. The membranes were tested in H{sub 2}/O{sub 2} fuel cells for stability and performance. It was found that thick (170 {micro}m) DVB cross-linked membranes showed stable operation for 1,400 h at temperatures up to 80 C. The highest power density in the fuel cell was found for the DVB and TAC double-cross-linked membrane; it exceeded the value of a cell with a Nafion{reg_sign} 117 membrane by more than 60%.

Buechi, F.N.; Gupta, B.; Haas, O.; Scherer, G.G. [Paul Scherrer Inst., Villigen (Switzerland). Lab. for Energy and Process Technology

1995-09-01

366

Synthesis of a cross-linked branched polymer network in the interior of a protein cage.  

PubMed

A goal of biomimetic chemistry is to use the hierarchical architecture inherent in biological systems to guide the synthesis of functional three-dimensional structures. Viruses and other highly symmetrical protein cage architectures provide defined scaffolds to initiate hierarchical structure assembly. Here we demonstrate that a cross-linked branched polymer can be initiated and synthesized within the interior cavity of a protein cage architecture. Creating this polymer network allows for the spatial control of pendant reactive sites and dramatically increases the stability of the cage architecture. This material was generated by the sequential coupling of multifunctional monomers using click chemistry to create a branched cross-linked polymer network. Analysis of polymer growth by mass spectrometry demonstrated that the polymer was initiated at the interior surface of the cage at genetically introduced cysteine reactive sites. The polymer grew as expected to generation 2.5 where it was limited by the size constraints of the cavity. The polymer network was fully cross-linked across protein subunits that make up the cage and extended the thermal stability for the cage to at least 120 degrees C. The introduced reactive centers were shown to be active and their number density increased with increasing generation. This synthetic approach provides a new avenue for creating defined polymer networks, spatially constrained by a biological template. PMID:19317506

Abedin, Md Joynal; Liepold, Lars; Suci, Peter; Young, Mark; Douglas, Trevor

2009-04-01

367

Collagen cross-link excretion during space flight and bed rest  

NASA Technical Reports Server (NTRS)

Extended exposure to weightlessness results in bone loss. However, little information exists as to the precise nature or time course of this bone loss. Bone resorption results in the release of collagen breakdown products, including N-telopeptide and the pyridinium (PYD) cross-links, pyridinoline and deoxypyridinoline. Urinary pyridinoline and deoxypyridinoline are known to increase during bed rest. We assessed excretion of PYD cross-links and N-telopeptide before, during, and after long (28-day, 59-day, and 84-day) Skylab missions, as well as during short (14-day) and long (119-day) bed-rest studies. During space flight, the urinary cross-link excretion level was twice those observed before flight. Urinary excretion levels of the collagen breakdown products were also 40-50% higher, during short and long bed rest, than before. These results clearly show that the changes in bone metabolism associated with space flight involve increased resorption. The rate of response (i.e. within days to weeks) suggests that alterations in bone metabolism are an early effect of weightlessness. These studies are important for a better understanding of bone metabolism in space crews and in those who are bedridden.

Smith, S. M.; Nillen, J. L.; Leblanc, A.; Lipton, A.; Demers, L. M.; Lane, H. W.; Leach, C. S.; LeBlanc, A. (Principal Investigator)

1998-01-01

368

Keratoconus corneal architecture after riboflavin/ultraviolet A cross-linking: Ultrastructural studies  

PubMed Central

Purpose Study to investigate the effects of collagen cross-linking on the ultrastructural organization of the corneal stroma in the human keratoconus cornea (KC). Methods Three normal, three keratoconus (KC1, KC2, KC3), and three cross-linked keratoconus (CXL1, CXL2, CXL3) corneas were analyzed. The KC corneas were treated with a riboflavin-ultraviolet A (UVA) treatment (CXL) method described by Wollensak et al. Penetrating keratoplasty (PKP) was performed 6 months after treatment. All samples were processed for electron microscopy. Results The riboflavin-UVA-treated CXL corneal stroma showed interlacing lamellae in the anterior stroma followed by well-organized parallel running lamellae. The lamellae contained uniformly distributed collagen fibrils (CFs) decorated with normal proteoglycans (PGs). The CF diameter and interfibrillar spacing in the CXL cornea were significantly increased compared to those in the KC cornea. The PG area in the CXL corneas were significantly smaller than the PGs in the KC cornea. The epithelium and Bowman’s layer were also normal. On rare occasions, a thick basement membrane and collagenous pannus were also observed. Conclusions Corneal cross-linking leads to modifications of the cornea stroma. The KC corneal structure showed a modification in the CF diameter, interfibrillar spacing, and PG area. This resulted in a more uniform distribution of collagen fibrils, a key feature for corneal transparency. PMID:23878503

Almubrad, Turki; Paladini, Iacopo; Mencucci, Rita

2013-01-01

369

Scheimpflug imaged corneal changes on anterior and posterior surfaces after collagen cross-linking  

PubMed Central

AIM To compare the anterior and posterior corneal parameters before and after collagen cross-linking therapy for keratoconus. METHODS Collagen cross-linking was performed in 31 eyes of 31 keratoconus patients (mean age 30.6±8.9y). Prior to treatment and an average 7mo after therapy, Scheimpflug analysis was performed using Pentacam HR. In addition to corneal thickness assessments, corneal radius, elevation, and aberrometric measurements were performed both on anterior and posterior corneal surfaces. Data obtained before and after surgery were statistically analyzed. RESULTS In terms of horizontal and vertical corneal radius, and central corneal thickness no deviations were observed an average 7mo after operation. Corneal higher order aberration showed no difference neither on anterior nor on posterior corneal surfaces. During follow-up period, no significant deviation was detected regarding elevation values obtained by measurement in mm units between the 3.0-8.0 mm-zones. CONCLUSION Corneal stabilization could be observed in terms of anterior and posterior corneal surfaces, elevation and higher order aberration values 7mo after collagen cross-linking therapy for keratoconus. PMID:24790876

Hassan, Ziad; Modis, Laszlo; Szalai, Eszter; Berta, Andras; Nemeth, Gabor

2014-01-01

370

Statistical physics of polymer gels  

NASA Astrophysics Data System (ADS)

This work presents a comprehensive analysis of the statistical mechanics of randomly cross-linked polymer gels, starting from a microscopic model of a network made of instantaneously cross-linked Gaussian chains with excluded volume, and ending with the derivation of explicit expressions for the thermodynamic functions and for the density correlation functions which can be tested by experiments. Using replica field theory we calculate the mean field density in replica space and show that this solution contains statistical information about the behavior of individual chains in the network. The average monomer positions change affinely with macroscopic deformation and fluctuations about these positions are limited to length scales of the order of the mesh size. We prove that a given gel has a unique state of microscopic equilibrium which depends on the temperature, the solvent, the average monomer density and the imposed deformation. This state is characterized by the set of the average positions of all the monomers or, equivalently, by a unique inhomogeneous monomer density profile. Gels are thus the only known example of equilibrium solids with no long-range order. We calculate the RPA density correlation functions that describe the statistical properties of small deviations from the average density, due to both static spatial heterogeneities (which characterize the inhomogeneous equilibrium state) and thermal fluctuations (about this equilibrium). We explain how the deformation-induced anisotropy of the inhomogeneous equilibrium density profile is revealed by small angle neutron scattering and light scattering experiments, through the observation of the butterfly effect. We show that all the statistical information about the structure of polymer networks is contained in two parameters whose values are determined by the conditions of synthesis: the density of cross-links and the heterogeneity parameter. We find that the structure of instantaneously cross-linked gels becomes increasingly inhomogeneous with the approach to the cross-link saturation threshold at which the heterogeneity parameter diverges. Analytical expressions for the correlators of deformed gels are derived in both the long wavelength and the short wavelength limits and an exact expression for the total static structure factor, valid for arbitrary wavelengths, is obtained for gels in the state of preparation. We adapt the RPA results to gels permeated by free labelled chains and to gels in good solvents (in the latter case, excluded volume effects are taken into account exactly) and make predictions which can be directly tested by scattering and thermodynamic experiments. Finally, we discuss the limitations and the possible extensions of our work.

Panyukov, Sergei; Rabin, Yitzhak

1996-05-01

371

Molecular mass dependence of hyaluronan detection by sandwich ELISA-like assay and membrane blotting using biotinylated hyaluronan binding protein  

PubMed Central

Hyaluronan (HA) is widely detected in biological samples and its concentration is most commonly determined by the use of a labeled specific HA binding protein (aggrecan G1-IGD-G2, HABP), employing membrane blotting and sandwich enzyme-linked immunosorbent assay (ELISA)-like methods. However, the detected signal intensity or the quantified value obtained by using these surface-based methods is related to the molecular mass (M) of HA, especially for HA in the low M range below ?150 kDa. At the same mass or mass concentration, higher M HA gives a higher signal than lower M HA. We have experimentally determined the quantitative relationship between the M of HA (in the range 20–150 kDa) and the relative signal intensity in comparison with a standard HA, in a sandwich ELISA-like assay. An M-dependent signal correction factor (SCF) was calculated and used to correct the signal intensity, so that the corrected concentration value would more accurately reflect the true HA concentration in solution. The SCF for polydisperse low M HA was also calculated and compared with experimental results. When the molecular mass distribution of an HA sample is determined by a method such as gel electrophoresis, then its appropriately averaged SCF can be calculated and used to correct the signal in sandwich ELISA to obtain a more accurate concentration estimation. The correction method works for HA with M between ?150 and 20 kDa, but lower M HA is too poorly detected for useful analysis. The physical basis of the M-dependent detection is proposed to be the increase in detector-accessible fraction of each surface-bound molecule as M increases. PMID:23964097

Yuan, Han; Tank, Mihir; Alsofyani, Abeer; Shah, Naman; Talati, Nishant; LoBello, Jaclyn C; Kim, Jin Ryoun; Oonuki, Yoji; de la Motte, Carol A; Cowman, Mary K

2013-01-01

372

Characterization of spray-dried microalgal oil encapsulated in cross-linked sodium caseinate matrix induced by microbial transglutaminase.  

PubMed

Sodium caseinate (SC) cross-linked by microbial transglutaminase (MTGase) for encapsulating microalgal oil was investigated. Protein cross-linking was evidenced in the SDS-PAGE graph. The emulsifying properties of SC depended on the cross-linked time with MTGase. The emulsifying activity and stability indexes of SC increased with the cross-linking time of 30 to 90 min (P30 to P90), and then declined with longer cross-linked time of 180 to 420 min (P180 to P420). The P30 to P90 as wall material for microencapsulation was superior to P180 to P420 and control sample. The microcapsules prepared with P30 to P90 showed more than 97% of microencapsulation efficiency in contrast to about 90% with the P180 to P420. During storage, the microcapsules prepared with P30 to P90 exhibited higher oxidative stability as compared with other microcapsules. A sustained release of microalgal oil was observed, and core release was time dependent and affected by cross-linking degree. Results showed that the powdered microalgal oil prepared with P30 to P90 demonstrated enhanced physicochemical properties and oxidative stability. Practical Application: The novel method using cross-linked proteins as wall material induced by microbial transglutaminase in food industry for sensitive ingredients could convert microcapsules into a stable form, which would lead to its more widespread utilization as a kind of food additive. PMID:21535662

Bao, Shan-Shan; Hu, Xue-Chao; Zhang, Ka; Xu, Xiao-Kang; Zhang, Hong-Man; Huang, He

2011-01-01

373

A new cross-linking strategy: protein interaction reporter (PIR) technology for protein–protein interaction studies  

PubMed Central

Chemical cross-linking coupled with mass spectrometry, an emerging approach for protein topology and interaction studies, has gained increasing interest in the past few years. A number of recent proof-of-principle studies on model proteins or protein complex systems with improved cross-linking strategies have shown great promise. However, the heterogeneity and low abundance of the cross-linked products as well as data complexity continue to pose enormous challenges for large-scale application of cross-linking approaches. A novel mass spectrometry-cleavable cross-linking strategy embodied in Protein Interaction Reporter (PIR) technology, first reported in 2005, was recently successfully applied for in vivo identification of protein–protein interactions as well as actual regions of the interacting proteins that share close proximity while present within cells. PIR technology holds great promise for achieving the ultimate goal of mapping protein interaction network at systems level using chemical cross-linking. In this review, we will briefly describe the recent progress in the field of chemical cross-linking development with an emphasis on the PIR concepts, its applications and future directions. PMID:20485738

Tang, Xiaoting; Bruce, James E.

2011-01-01

374

Versatile supramolecular cross-linker: a rotaxane cross-linker that directly endows vinyl polymers with movable cross-links.  

PubMed

A supramolecular cross-linked cross-linker, capable of introducing rotaxane cross-links to vinyl polymers, has been developed for the rational synthesis of polyrotaxane networks. The experimental results reveal that the combination of an oligocyclodextrin (OCD) and a terminal bulky group-tethering macromonomer (TBM) forms a polymer-network structure having polymerizable moieties through supramolecular cross-linking. Radical polymerization of a variety of typical vinyl monomers in the presence of the vinylic supramolecular cross-linker (VSC) afforded the corresponding vinyl polymers cross-linked through the rotaxane cross-links (RCP) as transparent stable films in high yields under both photoinitiated and thermal polymerization conditions. A poly(N,N-dimethylacrylamide)-based hydrogel synthesized by using VSC, RCPDMAAm , displayed a unique mechanical property. The small-angle X-ray scattering (SAXS) results, indicating patterns characteristic of a polyrotaxane network, clearly suggested the presence and role of the rotaxane cross-links. The confirmation of the introduction of rotaxane-cross-links into vinyl polymers strongly reveals the significant usefulness of VSC. PMID:23495049

Arai, Takayuki; Jang, Keumhee; Koyama, Yasuhito; Asai, Shigeo; Takata, Toshikazu

2013-05-01

375

Characterization of cross-links between cellulose microfibrils, and their occurrence during elongation growth in pea epicotyl.  

PubMed

The occurrence and chemical nature of the cross-links between cellulose microfibrils in outer epidermal cell walls in Pisum sativum cv. Alaska was investigated by rapid-freezing and deep-etching techniques coupled with chemical and enzymatic treatments. The cell wall in the elongating region of epidermal cells was characterized by the absence of the cross-links, while in the elongated region, the cell wall was characterized by the presence of cross-links. The cross-links remained in the cell wall of the elongated region after treatment with SDS electrophoresis sample buffer and treatment with 4% potassium hydroxide. After treatment with endo-1,4-beta-glucanase, which fragments xyloglucan, the cross-links were remarkably reduced from the cell wall of the elongated region. The endoglucanase treatment also reduced immunogold labeling of xyloglucan in the cell wall. The endoglucanase hydrolysate from the cell wall fraction of the elongated region gave spots of oligosaccharides in thin layer chromatography, which were identical to the spots of xyloglucan oligosaccharides produced by xyloglucanase from both the cell wall fraction and tamarind xyloglucan. These results indicate that the cross-links are made of xyloglucan. We discussed the possibility of cross-links involved in the control of mechanical properties of the cell wall. PMID:10845462

Fujino, T; Sone, Y; Mitsuishi, Y; Itoh, T

2000-04-01

376

Higher number of pentosidine cross-links induced by ribose does not alter tissue stiffness of cancellous bone.  

PubMed

The role of mature collagen cross-links, pentosidine (Pen) cross-links in particular, in the micromechanical properties of cancellous bone is unknown. The aim of this study was to examine nonenzymatic glycation effects on tissue stiffness of demineralized and non-demineralized cancellous bone. A total of 60 bone samples were derived from mandibular condyles of six pigs, and assigned to either control or experimental groups. Experimental handling included incubation in phosphate buffered saline alone or with 0.2M ribose at 37°C for 15 days and, in some of the samples, subsequent complete demineralization of the sample surface using 8% EDTA. Before and after experimental handling, bone microarchitecture and tissue mineral density were examined by means of microcomputed tomography. After experimental handling, the collagen content and the number of Pen, hydroxylysylpyridinoline (HP), and lysylpyridinoline (LP) cross-links were estimated using HPLC, and tissue stiffness was assessed by means of nanoindentation. Ribose treatment caused an up to 300-fold increase in the number of Pen cross-links compared to nonribose-incubated controls, but did not affect the number of HP and LP cross-links. This increase in the number of Pen cross-links had no influence on tissue stiffness of both demineralized and nondemineralized bone samples. These findings suggest that Pen cross-links do not play a significant role in bone tissue stiffness. PMID:25063086

Willems, Nop M B K; Langenbach, Geerling E J; Stoop, Reinout; den Toonder, Jaap M J; Mulder, Lars; Zentner, Andrej; Everts, Vincent

2014-09-01

377

Cofilin-Induced Changes in F-Actin Detected via Cross-Linking with Benzophenone-4-maleimide  

PubMed Central

Cofilin is a member of the actin depolymerizing factor (ADF)/cofilin family of proteins. It plays a key role in actin dynamics by promoting disassembly and assembly of actin filaments. Upon its binding, cofilin has been shown to bridge two adjacent protomers in filamentous actin (F-actin) and promote the displacement and disordering of subdomain 2 of actin. Here, we present evidence for cofilin promoting a new structural change in the actin filament, as detected via a switch in cross-linking sites. Benzophenone-4-maleimide, which normally forms intramolecular cross-linking in F-actin, cross-links F-actin intermolecularly upon cofilin binding. We mapped the cross-linking sites and found that in the absence of cofilin intramolecular cross-linking occurred between residues Cys374 and Asp11. In contrast, cofilin shifts the cross-linking by this reagent to intermolecular, between residue Cys374, located within subdomain 1 of the upper protomer, and Met44, located in subdomain 2 of the lower protomer. The intermolecular cross-linking of F-actin slows the rate of cofilin dissociation from the filaments and decreases the effect of ionic strength on cofilin?actin binding. These results are consistent with a significant role of filament flexibility in cofilin?actin interactions. PMID:23862734

Chen, Christine K.; Benchaar, Sabrina A.; Phan, Mai; Grintsevich, Elena E.; Loo, Rachel R. Ogorzalek; Loo, Joseph A.; Reisler, Emil

2014-01-01

378

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

PubMed Central

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

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

2008-01-01

379

"Zero-length" cross-linking in solid state as an approach for analysis of protein-protein interactions  

PubMed Central

We have developed a new approach for the analysis of interacting interfaces in protein complexes and protein quaternary structure based on cross-linking in the solid state. Protein complexes are freeze-dried under vacuum, and cross-links are introduced in the solid phase by dehydrating the protein in a nonaqueous solvent creating peptide bonds between amino and carboxyl groups of the interacting peptides. Cross-linked proteins are digested into peptides with trypsin in both H216O and H218O and then readily distinguished in mass spectra by characteristic 8 atomic mass unit (amu) shifts reflecting incorporation of two 18O atoms into each C terminus of proteolytic peptides. Computer analysis of mass spectrometry (MS) and MS/MS data is used to identify the cross-linked peptides. We demonstrated specificity and reproducibility of our method by cross-linking homo-oligomeric protein complexes of glutathione-S-transferase (GST) from Schistosoma japonicum alone or in a mixture of many other proteins. Identified cross-links were predominantly of amide origin, but six esters and thioesters were also found. The cross-linked peptides were validated against the GST monomer and dimer X-ray structures and by experimental (MS/MS) analyses. Some of the identified cross-links matched interacting peptides in the native 3D structure of GST, indicating that the structure of GST and its oligomeric complex remained primarily intact after freeze-drying. The pattern of oligomeric GST obtained in solid state was the same as that obtained in solution by Ru (II) Bpy32+ catalyzed, oxidative “zero-length” cross-linking, confirming that it is feasible to use our strategy for analyzing the molecular interfaces of interacting proteins or peptides. PMID:16501223

El-Shafey, Ahmed; Tolic, Nikola; Young, Malin M.; Sale, Kenneth; Smith, Richard D.; Kery, Vladimir

2006-01-01

380

On the limiting pore size of hydrophilic gels for electrophoresis and isoelectric focusing.  

PubMed

The maximum pore diameter that can be obtained in hydrophilic gels, either highly diluted agarose (0.16%C) or highly cross-linked polyacrylamide (45%CBis or 60%C DHEBA) is around 500 nm. An empirical equation has been derived linking the mean pore diameter (mean p) to gel concentration (C) in dilute agarose gels: mean p = 140.7 x C(-0.7). It is suggested that other equations hold for concentrated gels and for highly cross-linked polyacrylamides, since the matrix structure is different. Most of the cross linkers for polymerizing polyacrylamide gels have been tabulated and their properties studied. A new gel matrix is described: a highly cross-linked N,N'-(1,2-dihydroxyethylene)bisacrylamide gel, which is hydrophilic, highly porous and can be conveniently used for electrophoresis in horizontal, ultrathin layers cast on silanized glass surfaces. PMID:7252045

Righetti, P G; Brost, B C; Snyder, R S

1981-06-01

381

Studies on the formation and characterization of macroporous electron-beam generated hyaluronan cryogels  

NASA Astrophysics Data System (ADS)

Macroporous cryogels from methacrylated hyaluronan were synthesized at sub-zero temperatures using a novel electron-beam based approach with and without the use of tetra(ethylene glycol) diacrylate as additional cross-linker. Mechanically stable materials possessing a spongy morphology with pore diameters ranging from 50 ?m to 70 ?m were obtained and characterized by scanning electron microscopy. The excellent cytocompatibility was proven by seeding and cultivation of 3T3 mouse cells on top of the gels. The primary reaction and the chain growth radicals were investigated by quantum chemical calculation and electron paramagnetic resonance spectroscopy and experimentally verified by X-ray photoelectron spectroscopy. The additional cross-linker enhances the reaction efficiency of the cryogel formation.

Reichelt, Senta; Naumov, Sergej; Knolle, Wolfgang; Prager, Andrea; Decker, Ulrich; Becher, Jana; Weisser, Jürgen; Schnabelrauch, Matthias

2014-12-01

382

Investigation on chemical cross-linked collagen phosphoric acid hydrolysates with cyanuric chloride by differential scanning calorimetry  

Microsoft Academic Search

The process of cross-linking of collagen phosphoric acid hydrolysates (CH) with cyanuric chloride (CY) was studied by the\\u000a increase in the denaturation temperature using differential scanning calorimetry (DSC). This measurement gave indications\\u000a concerning the efficiency of the treatment, i.e., the extent of cross-linking of the collagen hydrolysates. The optimal conditions\\u000a for cross-linking were determined: CH\\/CY in a ratio 1:1, reaction

I. Chakarska; S. Todinova; K. Idakieva

2010-01-01

383

Cross-linking in the silks of bees, ants and hornets.  

PubMed

Silk production is integral to the construction of nests or cocoons for many Aculeata, stinging Hymenopterans such as ants, bees and wasps. Here we report the sequences of new aculeate silk proteins and compare cross-linking among nine native silks from three bee species (Apis mellifera, Bombus terrestris and Megachile rotundata), three ant species (Myrmecia forficata, Oecophylla smaragdina and Harpegnathos saltator) and three hornets (Vespa analis, Vespa simillima and Vespa mandarinia). The well studied silks of spiders and silkworms are comprised of large proteins that are cross-linked and stabilized predominantly by intra and intermolecular beta sheet structure. In contrast, the aculeate silks are comprised of relatively small proteins that contain central coiled coil domains and comparatively reduced amounts of beta sheet structure. The hornet silks, which have the most beta sheet structure and the greatest amount of amino acid sequence outside the coiled-coil domains, dissolve in concentrated LiBr solution and appear to be stabilized predominantly by beta sheet structure like the classic silks. In contrast, the ant and bee silks, which have less beta sheet and less sequence outside the coiled-coil domains, could not be dissolved in LiBr and appear to be predominantly stabilized by covalent cross-linking. The iso-peptide cross-linker, ?-(?-glutamyl)-lysine that is produced by transglutaminase enzymes, was demonstrated to be present in all silks by mass spectrometry, but at greater levels in silks of ants and bees. The bee silks and ant cocoons, but not the Oecophylla nest silks, appeared to be further stabilized by tanning reactions. PMID:24607851

Campbell, Peter M; Trueman, Holly E; Zhang, Qiang; Kojima, Katsura; Kameda, Tsunenori; Sutherland, Tara D

2014-05-01

384

Alteration of glomerular permeability to macromolecules induced by cross-linking of beta 1 integrin receptors.  

PubMed Central

Altered glomerular epithelial cell attachment to the glomerular basement membrane is an important pathogenetic factor in increased glomerular permeability to proteins. We have previously presented evidence that antibodies reactive with integrin matrix receptors on glomerular epithelial cells inhibit adhesion of these cells and may be involved in the production of proteinuria in vivo. Therefore, we utilized intact glomeruli in an in vitro system to directly assess the effect of anti-beta 1-integrin antibody on glomerular permeability. Permeability to albumin (Palb) was calculated from the volume response of glomeruli to a transcapillary oncotic gradient. Anti-beta 1-integrin increased Palb in a dose- and time-dependent manner. Palb was increased to 0.70 +/- 0.05 whereas normal rabbit IgG had no effect (0.10 +/- 0.04). F(ab')2 fragments of antibody increased Palb to a similar degree whereas Fab fragments had no effect (0.10 +/- 0.06). Cross-linking of Fab fragments, however, with a second antibody restored their ability to increase Palb (0.60 +/- 0.09), demonstrating the importance of integrin cross-linking in producing the observed effect. Intact, F(ab')2 and Fab fragments of anti-beta 1 antibody all inhibited adhesion of glomerular epithelial cells to fibronectin, laminin, and types I and IV collagen, although the degree of inhibition by Fab fragments was significantly less on collagens. No cytotoxic effects were observed with anti-beta 1 antibody or its fragments. These results suggest that antibodies to integrin matrix receptors on glomerular cells alter cell interactions with the glomerular basement membrane and lead to increased glomerular permeability to proteins via a process that is initiated by integrin cross-linking rather than through simple interference with cell adhesion per se. Images Figure 1 Figure 7 PMID:8780402

Adler, S.; Sharma, R.; Savin, V. J.; Abbi, R.; Eng, B.

1996-01-01

385

Block Copolymer Cross-linked Nanoassemblies Improve Particle Stability and Biocompatibility of Superparamagnetic Iron Oxide Nanoparticles  

PubMed Central

Purpose To develop cross-linked nanoassemblies (CNAs) as carriers for superparamagnetic iron oxide nanoparticles (IONPs). Methods Ferric and ferrous ions were co-precipitated inside core-shell type nanoparticles prepared by cross-linking poly(ethylene glycol)-poly(aspartate) block copolymers to prepare CNAs entrapping Fe3O4 IONPs (CNA-IONPs). Particle stability and biocompatibility of CNA-IONPs were characterized in comparison to citrate-coated Fe3O4 IONPs (Citrate-IONPs). Results CNA-IONPs, approximately 30 nm in diameter, showed no precipitation in water, PBS, or a cell culture medium after 3 or 30 h, at 22, 37, and 43 °C, and 1, 2.5, and 5 mg/mL, whereas Citrate-IONPs agglomerated rapidly (> 400 nm) in all aqueous media tested. No cytotoxicity was observed in a mouse brain endothelial-derived cell line (bEnd.3) exposed to CNA-IONPs up to 10 mg/mL for 30 h. Citrate-IONPs (> 0.05 mg/mL) reduced cell viability after 3 h. CNA-IONPs retained the superparamagnetic properties of entrapped IONPs, enhancing T2-weighted magnetic resonance images (MRI) at 0.02 mg/mL, and generating heat at a mild hyperthermic level (40 ~ 42 °C) with an alternating magnetic field (AMF). Conclusion Compared to citric acid coating, CNAs with a cross-linked anionic core improved particle stability and biocompatibility of IONPs, which would be beneficial for future MRI and AMF-induced remote hyperthermia applications. PMID:23080062

Dan, Mo; Scott, Daniel F.; Hardy, Peter A.; Wydra, Robert J.; Hilt, J. Zach; Yokel, Robert A.; Bae, Younsoo

2014-01-01

386

Multinuclear NMR and Kinetic Analysis of DNA Interstrand Cross-link Formation  

PubMed Central

Recently, a phenyl selenyl modified thymidine (2) was shown to produce DNA interstrand cross-links (ICLs) via two mechanisms. Photolysis of 2 generates 5-(2?-deoxyuridinyl)methyl radical (1), the reactive intermediate that results from formal hydrogen atom abstraction from the thymine methyl group. This reactive intermediate reacts with the opposing dA, and is the first example of a DNA radical to produce ICLs. Kinetic competition studies described below support the proposal that the rate limiting step in ICL formation from 1 involves rotation about the glycosidic bond, and that the rate constant for this process is influenced by flanking sequence. Cross-links also form with the opposing dA when 2 is treated with mild oxidants that result in the formation of an intermediate methide-like species (4). Kinetic experiments described below reveal that 4 reacts with azide, a model nucleophile, via a SN2? pathway. Previous experiments suggested that the same product is produced via 1 or 4, but that the initially formed cross-link rearranges during the enzyme digestion and isolation procedures. In situ product analysis by NMR using synthetic, doubly labeled duplex DNA containing 13C-2 and 15N1-dA provides definitive evidence that the kinetic ICL product formed via the radical and oxidative pathways is the same and corresponds to that arising from formal alkylation of N1-dA. Furthermore, analysis of the thermodynamic product formed upon rearrangement indicates that the primary product isomerizes via an associative mechanism in DNA. PMID:19053196

Ding, Hui; Majumdar, Ananya; Tolman, Joel R.; Greenberg, Marc M.

2009-01-01

387

Multinuclear NMR and kinetic analysis of DNA interstrand cross-link formation.  

PubMed

Recently, a phenylselenyl-modified thymidine (2) was shown to produce DNA interstrand cross-links (ICLs) via two mechanisms. Photolysis of 2 generates 5-(2'-deoxyuridinyl)methyl radical (1), the reactive intermediate that results from formal hydrogen atom abstraction from the thymine methyl group. This reactive intermediate reacts with the opposing dA and is the first example of a DNA radical that produces ICLs. Kinetic competition studies support the proposal that the rate-limiting step in ICL formation from 1 involves rotation about the glycosidic bond and that the rate constant for this process is influenced by the flanking sequence. Cross-links also form with the opposing dA when 2 is treated with mild oxidants that result in the formation of an intermediate methide-like species (4). Kinetic experiments reveal that 4 reacts with azide, a model nucleophile, via an S(N)2' pathway. Previous experiments suggested that the same product is produced via 1 or 4 but that the initially formed cross-link rearranges during the enzyme digestion and isolation procedures. In situ product analysis by NMR using synthetic, doubly labeled duplex DNA containing (13)C-2 and (15)N(1)-dA provides definitive evidence that the kinetic ICL products formed via the radical and oxidative pathways are the same and correspond to that arising from formal alkylation of N(1)-dA. Furthermore, analysis of the thermodynamic product formed upon rearrangement indicates that the primary product isomerizes via an associative mechanism in DNA. PMID:19053196

Ding, Hui; Majumdar, Ananya; Tolman, Joel R; Greenberg, Marc M

2008-12-31

388

Cross-Linking with Ultraviolet-A and Riboflavin Reduces Corneal Permeability  

PubMed Central

Purpose. To investigate the effect of cross-linking treatment on corneal permeability in a live animal model. Methods. Rabbit eyes were selected at random to be left unoperated or to undergo epithelial debridement with or without treatment consisting of cross-linking (CXL) with riboflavin and ultraviolet-A. Nine eyes received a total dose of 3.6 J/cm2 and after epithelial healing the corneas were placed in a two-chamber system for quantification of the diffusion of fluorescein compared with controls. Thirty eyes received a total dose of 5.4 J/cm2 and, after epithelial healing, in vivo corneal permeability was quantified as the pupillary response over a 30-minute period to a dose of topical pilocarpine compared with controls. Results. In the ex vivo assay, the mean permeability coefficient in the CXL group (2.42 × 10?7) was reduced when compared with the unoperated controls (3.73 × 10?7; P = 0.007) and to the eyes that received epithelial debridement alone (3.74 × 10?7; P = 0.01). In the in vivo permeability assay, the change in pupillary diameter at 30 minutes after pilocarpine administration was smaller in the CXL group (?1.9 mm), compared with the epithelial debridement group (?2.6 mm; P < 0.001) and with the unoperated controls (?2.7 mm; P = 0.003). Conclusions. Corneal cross-linking with ultraviolet-A and riboflavin results in a statistically significant reduction in corneal permeability. These findings suggest that dosing of topical medications may need to be increased in eyes with a history of CXL to achieve expected therapeutic effects, and they may have implications for the long-term health of the cornea. PMID:22064989

Lee, On-Tat; Wong, Fergus F.; Schultz, David S.; Lamy, Ricardo

2011-01-01

389

Disruption of heme-peptide covalent cross-linking in mammalian peroxidases by hypochlorous acid.  

PubMed

Myeloperoxidase (MPO), lactoperoxidase (LPO) and eosinophil peroxidase (EPO) play a central role in oxidative damage in inflammatory disorders by utilizing hydrogen peroxide and halides/pseudo halides to generate the corresponding hypohalous acid. The catalytic sites of these enzymes contain a covalently modified heme group, which is tethered to the polypeptide chain at two ester linkages via the methyl group (MPO, EPO and LPO) and one sulfonium bond via the vinyl group (MPO only). Covalent cross-linking of the catalytic site heme to the polypeptide chain in peroxidases is thought to play a protective role, since it renders the heme moiety less susceptible to the oxidants generated by these enzymes. Mass-spectrometric analysis revealed the following possible pathways by which hypochlorous acid (HOCl) disrupts the heme-protein cross-linking: (1) the methyl-ester bond is cleaved to form an alcohol; (2) the alcohol group undergoes an oxygen elimination reaction via the formation of an aldehyde intermediate or undergoes a demethylation reaction to lose the terminal CH2 group; and (3) the oxidative cleavage of the vinyl-sulfonium linkage. Once the heme moiety is released it undergoes cleavage at the carbon-methyne bridge either along the ?-? or a ?-? axis to form different pyrrole derivatives. These results indicate that covalent cross-linking is not enough to protect the enzymes from HOCl mediated heme destruction and free iron release. Thus, the interactions of mammalian peroxidases with HOCl modulates their activity and sets a stage for initiation of the Fenton reaction, further perpetuating oxidative damage at sites of inflammation. PMID:25193127

Abu-Soud, Husam M; Maitra, Dhiman; Shaeib, Faten; Khan, Sana N; Byun, Jaeman; Abdulhamid, Ibrahim; Yang, Zhe; Saed, Ghassan M; Diamond, Michael P; Andreana, Peter R; Pennathur, Subramaniam

2014-11-01

390

Cross-Linked Peptidoglycan Mediates Lysostaphin Binding to the Cell Wall Envelope of Staphylococcus aureus†  

PubMed Central

Staphylococcus simulans bv. staphylolyticus secretes lysostaphin, a bacteriocin that cleaves pentaglycine cross bridges in the cell wall of Staphylococcus aureus. The C-terminal cell wall-targeting domain (CWT) of lysostaphin is required for selective binding of this bacteriocin to S. aureus cells; however, the molecular target for this was unknown. We used purified green fluorescent protein fused to CWT (GFP-CWT) to reveal species-specific association of the reporter with staphylococci. GFP-CWT bound S. aureus cells as well as purified peptidoglycan sacculi. The addition of cross-linked murein, disaccharides linked to interconnected wall peptides, blocked GFP-CWT binding to staphylococci, whereas murein monomers or lysostaphin-solubilized cell wall fragments did not. S. aureus strain Newman variants lacking the capacity for synthesizing polysaccharide capsule (capFO), poly-N-acetylglucosamine (icaAC), lipoprotein (lgt), cell wall-anchored proteins (srtA), or the glycolipid anchor of lipoteichoic acid (ypfP) bound GFP-CWT similar to wild-type staphylococci. A tagO mutant strain, defective in the synthesis of polyribitol wall teichoic acid attached to the cell wall envelope, displayed increased GFP-CWT binding. In contrast, a femAB mutation, reducing both the amount and the length of peptidoglycan cross-linking (monoglycine cross bridges), showed a dramatic reduction in GFP-CWT binding. Thus, the CWT domain of lysostaphin directs the bacteriocin to cross-linked peptidoglycan, which also serves as the substrate for its glycyl-glycine endopeptidase domain. PMID:16547033

Grundling, Angelika; Schneewind, Olaf

2006-01-01

391

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

PubMed Central

A bi-functional epoxy-based cross-linker, 1,4-Butanediol diglycidyl ether (BDDGE), was investigated in the fabrication of collagen based corneal substitutes. Two synthetic strategies were explored in the preparation of the cross-linked collagen scaffolds. The lysine residues of Type 1 porcine collagen were directly cross-linked using l,4-Butanediol diglycidyl ether (BDDGE) under basic conditions at pH 11. Alternatively, under conventional methodology, using both BDDGE and 1-Ethyl-3-(3-dimethyl aminopropyl) carbodiimide (EDC)/N-hydroxysuccinimide (NHS) as cross-linkers, hydrogels were fabricated under acidic conditions. In this latter strategy, Cu(BF4)2·XH2O was used to catalyze the formation of secondary amine bonds. To date, we have demonstrated that both methods of chemical cross-linking improved the elasticity and tensile strength of the collagen implants. Differential scanning calorimetry and biocompatibility studies indicate comparable, and in some cases, enhanced properties compared to that of the EDC/NHS controls. In vitro studies showed that human corneal epithelial cells and neuronal progenitor cell lines proliferated on these hydrogels. In addition, improvement of cell proliferation on the surfaces of the materials was observed when neurite promoting laminin epitope, IKVAV, and adhesion peptide, YIGSR, were incorporated. However, the elasticity decreased with peptide incorporation and will require further optimization. Nevertheless, we have shown that epoxy cross-linkers should be further explored in the fabrication of collagen-based hydrogels, as alternatives to or in conjunction with carbodiimide cross-linkers. PMID:24956085

Koh, Li Buay; Islam, Mohammad Mirazul; Mitra, Debbie; Noel, Christopher W.; Merrett, Kimberley; Odorcic, Silvia; Fagerholm, Per; Jackson, William. Bruce; Liedberg, Bo; Phopase, Jaywant; Griffith, May

2013-01-01

392

Successive epoxy and carbodiimide cross-linking of dermal sheep collagen  

Microsoft Academic Search

Cross-linking of dermal sheep collagen (N-DSC, Ts=46°C, numberofaminegroups=31(n\\/1000)) with 1,4-butanediol diglycidyl ether (BDDGE) at pH 9.0 resulted in a material (BD90) with a high Ts(69°C), a decreased number of amine groups of 15 (n\\/1000) and a high resistance towards collagenase and pronase degradation. Reaction of DSC with BDDGE at pH 4.5 yielded a material (BD45) with a Ts of 64°C,

Raymond Zeeman; Pieter J. Dijkstra; Pauline B. van Wachem; Marja J. A. van Luyn; Marc Hendriks; Patrick T. Cahalan; Jan Feijen

1999-01-01

393

Inexpensive cross-linked polymeric separators made from water-soluble polymers  

SciTech Connect

Polyvinyl alcohol (PVA) cross-linked chemically with aldehyde reagents produces membranes which demonstrate oxidation resistance, dimensional stability, low ionic resistivity (<0.8 /OMEGA/-cm/sup 2/), low zincate diffusivity (1x10/sup -7/ mols/cm/sup 2//-min), and low zinc dendrite penetration rate (>350 min) which make them suitable for use as alkaline battery separators. They are intrinsically low in cost, and environmental health and safety problems associated with commercial production appear minimal. Preparation, property measurements, and cell test results in Ni/Zn and Ag/Zn cells are described and discussed. 4 refs.

Hsu, L.C.; Sheibley, D.W.

1982-02-01

394

Spatial characterization of corneal biomechanical properties with optical coherence elastography after UV cross-linking  

PubMed Central

Corneal collagen cross-linking (CXL) is a clinical treatment for keratoconus that structurally reinforces degenerating ocular tissue, thereby limiting disease progression. Clinical outcomes would benefit from noninvasive methods to assess tissue material properties in affected individuals. Regional variations in tissue properties were quantified before and after CXL in rabbit eyes using optical coherence elastography (OCE) imaging. Low-amplitude (<1µm) elastic waves were generated using micro air-pulse stimulation and the resulting wave amplitude and speed were measured using phase-stabilized swept-source OCE. OCE imaging following CXL treatment demonstrates increased corneal stiffness through faster elastic wave propagation speeds and lower wave amplitudes. PMID:24877005

Twa, Michael D.; Li, Jiasong; Vantipalli, Srilatha; Singh, Manmohan; Aglyamov, Salavat; Emelianov, Stanislav; Larin, Kirill V.

2014-01-01

395

Progress of corneal collagen cross-linking combined with refractive surgery  

PubMed Central

As a photochemical reaction that can stiffen the cornea, corneal collagen cross-linking (CXL) is the only promising method of preventing the progress of keratectasia, such as keratoconus and secondary ectasia following refractive surgery. The aim of CXL is to stabilize the underlying condition, with a small chance of visual improvement. Combining CXL with refractive surgery targeting both stabilization and reshaping of the corneal tissue for visual function improvement is a good treatment option. This review aims to provide a comprehensive and unbiased summary of the published research regarding combined CXL and refractive surgery, including measures and results, to help elucidate the future direction of CXL. PMID:24634883

Li, Na; Peng, Xiu-Jun; Fan, Zheng-Jun

2014-01-01

396

INTRAMOLECULAR LOCALIZATION OF THE ACCEPTOR CROSS-LINKING SITES IN FIBRIN*  

PubMed Central

Using 1-14C-glycine ethyl ester to titrate and label the acceptor cross-linking sites in fibrin, it was possible to localize and characterize the reactivity of these sites. In terms of sulfitolyzed chain fragments, both ? and ? chains were shown to act as amine-acceptors, the site in ? being more reactive. Identification and isolation of the acceptor loci were also achieved after cyanogen bromide fragmentation. It is interesting that the “N-terminal disulfide knot” portion of fibrin does not seem to contain acceptor functions. PMID:5260927

Lorand, L.; Chenoweth, D.

1969-01-01

397

Identification of the polypeptide chains involved in the cross-linking of fibrin.  

PubMed

The stabilization of fibrin clots by activated factor XIII involves two different sets of cross-linked chains. In one case (type I) two gamma-chains are linked to each other, indicating that gamma-chains have both donor (suitable lysyl-) and acceptor (suitable glutaminyl-) functions. A second system (type II) consists of a gamma-chain linked to an alpha-chain. Experiments with a substitute donor (glycine ethylester) indicate that only gamma-chains have enzyme-accessible acceptor sites, suggesting that alpha-chain participation is limited to lysyl side chains. A model molecular arrangement for fibrin has been suggested which accommodates all the data. PMID:5257132

Chen, R; Doolittle, R F

1969-06-01

398

IDENTIFICATION OF THE POLYPEPTIDE CHAINS INVOLVED IN THE CROSS-LINKING OF FIBRIN*  

PubMed Central

The stabilization of fibrin clots by activated factor XIII involves two different sets of cross-linked chains. In one case (type I) two ?-c