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Sample records for cross-linked hyaluronan gel

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

    SciTech Connect

    Wilder, Richard B.; Barme, Greg A.; Gilbert, Ronald F.; Holevas, Richard E.; Kobashi, Luis I.; Reed, Richard R.; Solomon, Ronald S.; Walter, Nancy L.; Chittenden, Lucy; Mesa, Albert V.; Agustin, Jeffrey; Lizarde, Jessica; Macedo, Jorge; Ravera, John; Tokita, Kenneth M.

    2010-07-01

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

  2. Microfabrication of Photo-Cross-Linked Hyaluronan Hydrogels by Single- and Two-Photon Tyramine Oxidation.

    PubMed

    Loebel, Claudia; Broguiere, Nicolas; Alini, Mauro; Zenobi-Wong, Marcy; Eglin, David

    2015-09-14

    Photo-cross-linking of tyramine-substituted hyaluronan (HA-Tyr) hydrogels is demonstrated for the first time. HA-Tyr hydrogels are fabricated via a rapid photosensitized process using visible light illumination. Nontoxic conditions offer photoencapsulation of human mesenchymal stromal cells (hMSCs) with high viability. Macroscopic gels can be formed in less than 10 s, and one- and two-photon photopatterning enable 2D and 3D microfabrication. Different degrees of cross-linking induce different swelling/shrinking, allowing for light-induced microactuation. These new tools are complementary to the previously reported horseradish peroxidase/hydrogen peroxide cross-linking and allow sequential cross-linking of HA-Tyr matrices. PMID:26222128

  3. Novel enzymatically cross-linked hyaluronan hydrogels support the formation of 3D neuronal networks.

    PubMed

    Broguiere, Nicolas; Isenmann, Luca; Zenobi-Wong, Marcy

    2016-08-01

    Hyaluronan (HA) is an essential component of the central nervous system's extracellular matrix and its high molecular weight (MW) form has anti-inflammatory and anti-fibrotic properties relevant for regenerative medicine. Here, we introduce a new hydrogel based on high MW HA which is cross-linked using the transglutaminase (TG) activity of the activated blood coagulation factor XIII (FXIIIa). These HA-TG gels have significant advantages for neural tissue engineering compared to previous HA gels. Due to their chemical inertness in the absence of FXIIIa, the material can be stored long-term, is stable in solution, and shows no cytotoxicity. The gelation is completely cell-friendly due to the specificity of the enzyme and the gelation rate can be tuned from seconds to hours at physiological pH and independently of stiffness. The gels are injectable, and attach covalently to fibrinogen and fibrin, two common bioactive components in in vitro tissue engineering, as well as proteins present in vivo, allowing the gels to covalently bind to brain or spinal cord defects. These optimal chemical and bioactive properties of HA-TG gels enabled the formation of 3D neuronal cultures of unprecedented performance, showing fast neurite outgrowth, axonal and dendritic speciation, strong synaptic connectivity in 3D networks, and rapidly-occurring and long-lasting coordinated electrical activity. PMID:27209262

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

    PubMed Central

    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

    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-α-inhibitor (IαI), 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, IαI, 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 IαI, TSG-6, and HA, among which are the covalent heavy chain (HC)·HA and HC·TSG-6 complexes, despite the fact that both IαI and TSG-6 are ligands of PTX3. Interestingly, prior encounter with IαI was required for effective incorporation of PTX3 into TSG-6-loaded HA films. Moreover, we demonstrated that this ternary protein mixture made of IαI, 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

  5. Inter-α-inhibitor Impairs TSG-6-induced Hyaluronan Cross-linking*

    PubMed Central

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

    2013-01-01

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

  6. Inter-α-inhibitor impairs TSG-6-induced hyaluronan cross-linking.

    PubMed

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

    2013-10-11

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

  7. Preparation and characterization of cross-linked collagen-phospholipid polymer hybrid gels.

    PubMed

    Nam, Kwangwoo; Kimura, Tsuyoshi; Kishida, Akio

    2007-01-01

    2-methacryloyloxyethyl phosphorylcholine (MPC)-immobilized collagen gel was developed. Using 1-ethyl-3-(3-dimethyl aminopropyl)-1-carbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS), we cross-linked a collagen film in 2-morpholinoethane sulfonic acid (MES) buffer (EN gel). EN gel was prepared under both pH 4.5 and pH 9.0 in order to observe changes in cross-linking ability. To cross-link MPC to collagen gel, poly(MPC-co-methacrylic acid) (PMA) having a carboxyl group side chain was chosen. E/N gel was added to the MES buffer having pre-NHS activated PMA to make MPC-immobilized collagen gel (MiC gel). MiC gel was prepared under both acidic and alkaline conditions to observe the changes in the cross-linking ability of PMA. X-ray photoelectron spectroscopy showed that the PMA was cross-linked with collagen under both acidic and alkaline conditions. Differential scanning calorimetry (DSC) results showed that the shrinkage temperature increased for the MiC gels and that the increase would be greater for the MiC gel prepared under alkaline conditions. The data showed that swelling would be less when the MiC gel was prepared under alkaline conditions. The biodegradation caused by collagenase was suppressed for the MiC gel prepared under alkaline conditions due to stable inter- and intrahelical networks. PMID:16959313

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

    NASA Technical Reports Server (NTRS)

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

    1991-01-01

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

  9. Sodium dodecyl sulfate-capillary gel electrophoresis of proteins using non-cross-linked polyacrylamide.

    PubMed

    Wu, D; Regnier, F E

    1992-09-11

    Proteins with relative molecular masses of 14,000 to 205,000 were separated by sodium dodecyl sulfate-capillary gel electrophoresis (SDS-CGE) using non-cross-linked linear polyacrylamide gels on both coated and uncoated fused-silica capillaries. It was determined that viscosity of the acrylamide solution was a major factor affecting column stability with linear acrylamide gels. When the viscosity of the acrylamide solution reaches 100 cP, electro-osmotically driven displacement of the gels is insignificant. Uncoated capillaries provided better resolution, stability, and reproducibility than surface coated capillaries when the concentration of linear polyacrylamide was greater than 4%. At lower gel concentrations, non-cross-linked polyacrylamide is easily displaced from the columns. A calibration plot of log molecular mass vs. mobility with non-linear polyacrylamide was linear, which indicated that resolution was equivalent to that obtained with cross-linked acrylamide. Separations with model proteins indicated that baseline resolution between protein species that vary 10% in molecular mass can be achieved. PMID:1430034

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

    Technology Transfer Automated Retrieval System (TEKTRAN)

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

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

    PubMed

    von der Heydt, Alice; Zippelius, Annette

    2015-02-01

    We study analytically the intricate phase behavior of cross-linked AB diblock copolymer melts, which can undergo two main phase transitions due to quenched random constraints. Gelation, i.e., spatially random localisation of polymers forming a system-spanning cluster, is driven by increasing the number parameter μ of irreversible, type-selective cross-links between random pairs of A blocks. Self-assembly into a periodic pattern of A/B-rich microdomains (microphase separation) is controlled by the AB incompatibility χ inversely proportional to temperature. Our model aims to capture the system's essential microscopic features, including an ensemble of random networks that reflects spatial correlations at the instant of cross-linking. We identify suitable order parameters and derive a free-energy functional in the spirit of Landau theory that allows us to trace a phase diagram in the plane of μ and χ. Selective cross-links promote microphase separation at higher critical temperatures than in uncross-linked diblock copolymer melts. Microphase separation in the liquid state facilitates gelation, giving rise to a novel gel state whose chemical composition density mirrors the periodic AB pattern. PMID:25662662

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

    NASA Astrophysics Data System (ADS)

    von der Heydt, Alice; Zippelius, Annette

    2015-02-01

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

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

    PubMed Central

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

    2015-01-01

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

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

    PubMed

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

    2015-02-25

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

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

    PubMed

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

    2013-01-01

    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

  16. A covalently cross-linked gel derived from the epidermis of the pilot whale Globicephala melas.

    PubMed

    Baum, C; Fleischer, L-G; Roessner, D; Meyer, W; Siebers, D

    2002-01-01

    The rheological properties of the stratum corneum of the pilot whale (Globicephala melas) were investigated with emphasis on their significance to the self-cleaning abilities of the skin surface smoothed by a jelly material enriched with various hydrolytic enzymes. The gel formation of the collected fluid was monitored by applying periodic-harmonic oscillating loads using a stress-controlled rheometer. In the mechanical spectrum of the gel, the plateau region of the storage modulus G' (<1200 Pa) and the loss modulus G" (>120 Pa) were independent of frequency (omega = 43.98 to 0.13 rad x s(-1), tau = 15 Pa, T = 20 degrees C), indicating high elastic performance of a covalently cross-linked viscoelastic solid. In addition, multi-angle laser light scattering experiments (MALLS) were performed to analyse the potential time-dependent changes in the weight-average molar mass of the samples. The observed increase showed that the gel formation is based on the assembly of covalently cross-linked aggregates. The viscoelastic properties and the shear resistance of the gel assure that the enzyme-containing jelly material smoothing the skin surface is not removed from the stratum corneum by shear regimes during dolphin jumping. The even skin surface is considered to be most important for the self-cleaning abilities of the dolphin skin against biofouling. PMID:12454437

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

    PubMed Central

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

    2010-01-01

    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

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

    PubMed

    Tanaka, Fumihiko

    2014-10-01

    Stationary crack propagation in rubbers and chemically cross-linked gels is studied by a new molecular theory of fracture in polymer networks. The fracture energy G (energy required to create a unit free surface by fracture) as a function of the crack velocity V is shown to obey, when measured in the unit of νlkBT, a master curve as a function of the dimensionless velocity 2tan θV/lβ0(T), where ν is the number density of the network chains, T is absolute temperature, θ is the angle of the crack tip, l is the mean distance between the adjacent cross-links, and β0(T) is the scission rate of the chains. The slope of the master curve in logarithmic scale depends on the nature of chain rupture; it takes a small value 0.16-0.2 in the low velocity region, and exhibits a crossover to the three times larger value 0.5-0.6 in the high velocity region. The ultimate strength G0 as defined by the fracture energy in the limit of zero crack velocity is obtained as a function of the molecular weight of the network chain, the bond energy, and temperature. The theoretical model is applied specifically to peeling and tearing experiments of rubbers and gels to study how the velocity affects the fracture energy in different geometry of network breakage. All results are qualitatively compared with the data reported in the literature. PMID:25296834

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

    NASA Astrophysics Data System (ADS)

    Tanaka, Fumihiko

    2014-10-01

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

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

    PubMed

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

    2014-07-22

    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

  1. Separation performance of single-stranded DNA electrophoresis in photopolymerized cross-linked polyacrylamide gels.

    PubMed

    Lo, Roger C; Ugaz, Victor M

    2006-02-01

    Considerable effort has been directed toward optimizing performance and maximizing throughput in ssDNA electrophoresis because it is a critical analytical step in a variety of genomic assays. Ultimately, it would be desirable to quantitatively determine the achievable level of separation resolution directly from measurements of fundamental physical properties associated with the gel matrix rather than by the trial and error process often employed. Unfortunately, this predictive capability is currently lacking, due in large part to the need for a more detailed understanding of the fundamental parameters governing separation performance (mobility, diffusion, and dispersion). We seek to address this issue by systematically characterizing electrophoretic mobility, diffusion, and dispersion behavior of ssDNA fragments in the 70-1,000 base range in a photopolymerized cross-linked polyacrylamide matrix using a slab gel DNA sequencer. Data are collected for gel concentrations of 6, 9, and 12%T at electric fields ranging from 15 to 40 V/cm, and resolution predictions are compared with corresponding experimentally measured values. The data exhibit a transition from behavior consistent with the Ogston model for small fragments to behavior in agreement with the biased reptation model at larger fragment sizes. Mobility data are also used to estimate the mean gel pore size and compare the predictions of several models. PMID:16331587

  2. Austin Chalk: cross-link gel water, slick water fracs common in Giddings field

    SciTech Connect

    Mickey, V.

    1981-05-01

    Of the approx. 600 wells drilled in the Giddings field, Austin Chalk trend in the last year, most were probably completed by cross-link gel fracs or slick water fracs. Although open hole completions are not uncommon in the chalk, they are not really practical in most situations, given the 600 to 800 ft of gross pay usually encountered in the Austin Chalk trend. Most of the open hole completions occur when an operator takes a kick while drilling and decides to drop a mud pill over the zone, run casing above it, cement it in and produce the interval open hole. Chalk wells are subject to kick at any time during drilling because of natural fracturing systems throughout the trend. Mud weights are generally fairly light for faster drilling, approx. 9.4 to 9.8 lb, depending on the particular area.

  3. 1,4-Butanediol diglycidyl ether-cross-linked hyaluronan inhibits fibrosis in rat primary tenocytes by down-regulating autophagy modulation.

    PubMed

    Hsu, Dur-Zong; Jou, I-Ming

    2016-05-01

    Epidural fibrosis, an inevitable part of the postoperative healing process, is one of the important causes of failed back surgery syndrome after spinal surgery. The aim of this study was to examine the inhibitory effect of a novel material 1,4-butanediol diglycidyl ether-cross-linked hyaluronan (cHA) on fibrosis in primary tenocytes. cHA inhibited migration, cell proliferation, and suppressed the expression of fibronectin, but not transforming growth factor-β, in primary tenocytes. cHA significantly increased matrix metalloproteinase-3 but decreased collagen-1 and microtubule-associated protein light chain 3-II expression in a dose-dependent manner compared with control groups. We therefore concluded that suppressing autophagy activity may be involved in the anti-fibrotic effect of cHA in primary tenocytes. Further, cHA may have the potential for preventing epidural fibrosis and subsequent failed back syndrome in patients with laminectomy in the future. PMID:26968759

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

    PubMed

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

    2005-01-01

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

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

    PubMed

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

    2015-04-13

    Small-angle neutron scattering (SANS) was used to characterize the nanoscale structure of enzymatically cross-linked chitosan/gelatin hydrogels obtained from two protocols: a pure chemical cross-linking process (C), which uses the natural enzyme microbial transglutaminase, and a physical-co-chemical (PC) hybrid process, where covalent cross-linking is combined with the temperature-triggered gelation of gelatin, occurring through the formation of triple-helices. SANS measurements on the final and evolving networks provide a correlation length (ξ), which reflects the average size of expanding clusters. Their growth in PC gels is restricted by the triple-helices (ξ ∼ 10s of Å), while ξ in pure chemical gels increases with cross-linker concentration (∼100s of Å). In addition, the shear elastic modulus in PC gels is higher than in pure C gels. Our results thus demonstrate that gelatin triple helices provide a template to guide the cross-linking process; overall, this work provides important structural insight to improve the design of biopolymer-based gels. PMID:25772227

  6. Gel-based chemical cross-linking analysis of 20S proteasome subunit-subunit interactions in breast cancer.

    PubMed

    Song, Hai; Xiong, Hua; Che, Jing; Xi, Qing-Song; Huang, Liu; Xiong, Hui-Hua; Zhang, Peng

    2016-08-01

    The ubiquitin-proteasome system plays a pivotal role in breast tumorigenesis by controlling transcription factors, thus promoting cell cycle growth, and degradation of tumor suppressor proteins. However, breast cancer patients have failed to benefit from proteasome inhibitor treatment partially due to proteasome heterogeneity, which is poorly understood in malignant breast neoplasm. Chemical crosslinking is an increasingly important tool for mapping protein three-dimensional structures and proteinprotein interactions. In the present study, two cross-linkers, bis (sulfosuccinimidyl) suberate (BS(3)) and its water-insoluble analog disuccinimidyl suberate (DSS), were used to map the subunit-subunit interactions in 20S proteasome core particle (CP) from MDA-MB-231 cells. Different types of gel electrophoresis technologies were used. In combination with chemical cross-linking and mass spectrometry, we applied these gel electrophoresis technologies to the study of the noncovalent interactions among 20S proteasome subunits. Firstly, the CP subunit isoforms were profiled. Subsequently, using native/SDSPAGE, it was observed that 0.5 mmol/L BS(3) was a relatively optimal cross-linking concentration for CP subunit-subunit interaction study. 2-DE analysis of the cross-linked CP revealed that α1 might preinteract with α2, and α3 might pre-interact with α4. Moreover, there were different subtypes of α1α2 and α3α4 due to proteasome heterogeneity. There was no significant difference in cross-linking pattern for CP subunits between BS(3) and DSS. Taken together, the gel-based characterization in combination with chemical cross-linking could serve as a tool for the study of subunit interactions within a multi-subunit protein complex. The heterogeneity of 20S proteasome subunit observed in breast cancer cells may provide some key information for proteasome inhibition strategy. PMID:27465334

  7. Physicochemical studies on polyurethane/siloxane cross-linked films for hydrophobic surfaces by the sol-gel process.

    PubMed

    Seeni Meera, Kamal Mohamed; Murali Sankar, Rajavelu; Jaisankar, Sellamuthu N; Mandal, Asit Baran

    2013-03-01

    A series of castor oil based polyurethane/siloxane cross-linked films were prepared using castor oil, isophorone diisocyanate, and 3-aminopropyl trimethoxysilane by the sol-gel process. Fourier transform infrared (FT-IR) spectra reveal the cross-linking interaction between polyurethane and siloxane moieties, thereby shifting the peak position of characteristic N-H and C═O groups to higher wavenumber. (29)Si (silica) solid state nuclear magnetic resonance spectra were used to prove the formation of siloxane network linkage in the polyurethane system, thereby analyzing the Si environment present in the polyurethane/siloxane cross-linked films. The activation energy values at two stages (Tmax1 and Tmax2) for the degradation of polyurethane films were increased with increasing silane ratio. The calculated activation energy values for the higher silane ratio (1.5) are 136 and 170 kJ/mol at Tmax1 and Tmax2, respectively. From contact angle measurements, we observed that increasing siloxane cross-linking increased the hydrophobicity of the films. The optical transmittance obtained from ultraviolet-visible spectra indicated that the film samples are transparent in the region 300-800 nm. The moisture sorption/desorption isotherm curve shows a characteristic behavior of type III isotherm corresponds to hydrophobic materials. Dynamic mechanical studies show that the increase in storage modulus reveals siloxane cross-linking gives rigidity to the films. Atomic force microscopic images show that the introduction of siloxane changes the surface roughness of the polyurethane films. It is found that the siloxane cross-linking can be used to obtain hydrophobic surface films having good thermal stability and optical transmittance. PMID:23394610

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

    PubMed

    Baumberger, T; Ronsin, O

    2010-06-14

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

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

    PubMed

    Kwon, Young Jik; Peng, Ching-An

    2002-07-01

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

  10. Stable Lithium Deposition Generated from Ceramic-Cross-Linked Gel Polymer Electrolytes for Lithium Anode.

    PubMed

    Tsao, Chih-Hao; Hsiao, Yang-Hung; Hsu, Chun-Han; Kuo, Ping-Lin

    2016-06-22

    In this work, a composite gel electrolyte comprising ceramic cross-linker and poly(ethylene oxide) (PEO) matrix is shown to have superior resistance to lithium dendrite growth and be applicable to gel polymer lithium batteries. In contrast to pristine gel electrolyte, these nanocomposite gel electrolytes show good compatibility with liquid electrolytes, wider electrochemical window, and a superior rate and cycling performance. These silica cross-linkers allow the PEO to form the lithium ion pathway and reduce anion mobility. Therefore, the gel not only features lower polarization and interfacial resistance, but also suppresses electrolyte decomposition and lithium corrosion. Further, these nanocomposite gel electrolytes increase the lithium transference number to 0.5, and exhibit superior electrochemical stability up to 5.0 V. Moreover, the lithium cells feature long-term stability and a Coulombic efficiency that can reach 97% after 100 cycles. The SEM image of the lithium metal surface after the cycling test shows that the composite gel electrolyte with 20% silica cross-linker forms a uniform passivation layer on the lithium surface. Accordingly, these features allow this gel polymer electrolyte with ceramic cross-linker to function as a high-performance lithium-ionic conductor and reliable separator for lithium metal batteries. PMID:27247991

  11. Cross-linked Composite Gel Polymer Electrolyte using Mesoporous Methacrylate-Functionalized SiO2 Nanoparticles for Lithium-Ion Polymer Batteries

    PubMed Central

    Shin, Won-Kyung; Cho, Jinhyun; Kannan, Aravindaraj G.; Lee, Yoon-Sung; Kim, Dong-Won

    2016-01-01

    Liquid electrolytes composed of lithium salt in a mixture of organic solvents have been widely used for lithium-ion batteries. However, the high flammability of the organic solvents can lead to thermal runaway and explosions if the system is accidentally subjected to a short circuit or experiences local overheating. In this work, a cross-linked composite gel polymer electrolyte was prepared and applied to lithium-ion polymer cells as a safer and more reliable electrolyte. Mesoporous SiO2 nanoparticles containing reactive methacrylate groups as cross-linking sites were synthesized and dispersed into the fibrous polyacrylonitrile membrane. They directly reacted with gel electrolyte precursors containing tri(ethylene glycol) diacrylate, resulting in the formation of a cross-linked composite gel polymer electrolyte with high ionic conductivity and favorable interfacial characteristics. The mesoporous SiO2 particles also served as HF scavengers to reduce the HF content in the electrolyte at high temperature. As a result, the cycling performance of the lithium-ion polymer cells with cross-linked composite gel polymer electrolytes employing methacrylate-functionalized mesoporous SiO2 nanoparticles was remarkably improved at elevated temperatures. PMID:27189842

  12. Cross-linked Composite Gel Polymer Electrolyte using Mesoporous Methacrylate-Functionalized SiO2 Nanoparticles for Lithium-Ion Polymer Batteries.

    PubMed

    Shin, Won-Kyung; Cho, Jinhyun; Kannan, Aravindaraj G; Lee, Yoon-Sung; Kim, Dong-Won

    2016-01-01

    Liquid electrolytes composed of lithium salt in a mixture of organic solvents have been widely used for lithium-ion batteries. However, the high flammability of the organic solvents can lead to thermal runaway and explosions if the system is accidentally subjected to a short circuit or experiences local overheating. In this work, a cross-linked composite gel polymer electrolyte was prepared and applied to lithium-ion polymer cells as a safer and more reliable electrolyte. Mesoporous SiO2 nanoparticles containing reactive methacrylate groups as cross-linking sites were synthesized and dispersed into the fibrous polyacrylonitrile membrane. They directly reacted with gel electrolyte precursors containing tri(ethylene glycol) diacrylate, resulting in the formation of a cross-linked composite gel polymer electrolyte with high ionic conductivity and favorable interfacial characteristics. The mesoporous SiO2 particles also served as HF scavengers to reduce the HF content in the electrolyte at high temperature. As a result, the cycling performance of the lithium-ion polymer cells with cross-linked composite gel polymer electrolytes employing methacrylate-functionalized mesoporous SiO2 nanoparticles was remarkably improved at elevated temperatures. PMID:27189842

  13. Cross-linked Composite Gel Polymer Electrolyte using Mesoporous Methacrylate-Functionalized SiO2 Nanoparticles for Lithium-Ion Polymer Batteries

    NASA Astrophysics Data System (ADS)

    Shin, Won-Kyung; Cho, Jinhyun; Kannan, Aravindaraj G.; Lee, Yoon-Sung; Kim, Dong-Won

    2016-05-01

    Liquid electrolytes composed of lithium salt in a mixture of organic solvents have been widely used for lithium-ion batteries. However, the high flammability of the organic solvents can lead to thermal runaway and explosions if the system is accidentally subjected to a short circuit or experiences local overheating. In this work, a cross-linked composite gel polymer electrolyte was prepared and applied to lithium-ion polymer cells as a safer and more reliable electrolyte. Mesoporous SiO2 nanoparticles containing reactive methacrylate groups as cross-linking sites were synthesized and dispersed into the fibrous polyacrylonitrile membrane. They directly reacted with gel electrolyte precursors containing tri(ethylene glycol) diacrylate, resulting in the formation of a cross-linked composite gel polymer electrolyte with high ionic conductivity and favorable interfacial characteristics. The mesoporous SiO2 particles also served as HF scavengers to reduce the HF content in the electrolyte at high temperature. As a result, the cycling performance of the lithium-ion polymer cells with cross-linked composite gel polymer electrolytes employing methacrylate-functionalized mesoporous SiO2 nanoparticles was remarkably improved at elevated temperatures.

  14. Cross-Linking the Fibers of Supramolecular Gels Formed from a Tripodal Terpyridine Derived Ligand with d-Block Metal Ions.

    PubMed

    Kotova, Oxana; Daly, Ronan; dos Santos, Cidália M G; Kruger, Paul E; Boland, John J; Gunnlaugsson, Thorfinnur

    2015-08-17

    The tripodal terpyridine ligand, L, forms 1D helical supramolecular polymers/gels in H2O-CH3OH solution mediated through hydrogen bonding and π-π interactions. These gels further cross-link into 3D supramolecular metallogels with a range of metal ions (M) such as Fe(II), Ni(II), Cu(II), Zn(II), and Ru(III); the cross-linking resulting in the formation of colored or colorless gels. The fibrous morphology of these gels was confirmed using scanning electron microscopy (SEM); while the self-assembly processes between L and M were investigated by absorbance and emission spectroscopy from which their binding constants were determined by using a nonlinear regression analysis. PMID:26222397

  15. Fabrication of Collagen Gel Hollow Fibers by Covalent Cross-Linking for Construction of Bioengineering Renal Tubules.

    PubMed

    Shen, Chong; Zhang, Guoliang; Wang, Qichen; Meng, Qin

    2015-09-01

    Collagen, the most used natural biomacromolecule, has been extensively utilized to make scaffolds for cell cultures in tissue engineering, but has never been fabricated into the configuration of a hollow fiber (HF) for cell culture due to its poor mechanical properties. In this study, renal tubular cell-laden collagen hollow fiber (Col HF) was fabricated by dissolving sacrificial Ca-alginate cores from collagen shells strengthened by carbodiimide cross-linking. The inner/outer diameters of the Col HF were precisely controlled by the flow rates of core alginate/shell collagen solution in the microfluidic device. As found, the renal tubular cells self-assembled into renal tubules with diameters of 50-200 μm post to the culture in Col HF for 10 days. According to the 3D reconstructed confocal images or HE staining, the renal cells appeared as a tight tubular monolayer on the Col HF inner surface, sustaining more 3D cell morphology than the cell layer on the 2D flat collagen gel surface. Moreover, compared with the cultures in either a Transwell or polymer HF membrane, the renal tubules in Col HF exhibited at least 1-fold higher activity on brush border enzymes of alkaline phosphatase and γ-glutamyltransferase, consistent with their gene expressions. The enhancement occurred similarly on multidrug resistance protein 2 and glucose uptake. Such bioengineered renal tubules in Col HF will present great potential as alternatives to synthetic HF in both clinical use and pharmaceutical investigation. PMID:26280545

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

    NASA Astrophysics Data System (ADS)

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

    2011-07-01

    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.

  17. Layer-by-layer films from hyaluronan and amine modified hyaluronan

    PubMed Central

    Schneider, Aurore; Senger, Bernard; Schaaf, Pierre; Voegel, Jean-Claude; Frisch, Benoit

    2008-01-01

    Hyaluronan is a polysaccharide that is increasingly investigated for its role in cellular adhesion and for the preparation of biomimetic matrices for tissue engineering. Hyaluronan gels are prepared for application as space fillers whereas hyaluronan films are usually obtained by adsorbing or grafting a single hyaluronan layer onto a biomaterial surface. Here, we examine the possibility to employ the layer-by-layer technique to deposit thin films of cationic modified hyaluronan (HA+) and hyaluronan (HA) of controlled thicknesses. The buildup conditions are investigated and growth is compared to that of other polyelectrolyte multilayer films containing either HA as polyanion or HA+ as polycation. The films could be formed in a low ionic strength medium but required to be cross-linked prior to be put in contact with physiological medium. NIH3T3 fibroblasts were perfectly viable on self-assembled hyaluronan films with however a preference for hyaluronan ending films. These findings point out the possibility to tune the thickness of thin hyaluronan films at the nanometer scale. Such architectures could be employed for investigating cell/substrate interactions or for functionalizing biomaterial surfaces. PMID:17309215

  18. Hyaluronan

    PubMed Central

    Bogdani, Marika; Nagy, Nadine; Johnson, Pamela Y.; Wight, Thomas N.

    2015-01-01

    Hyaluronan (HA) is an extracellular matrix (ECM) component that is present in mouse and human islet ECM. HA is localized in peri-islet and intra-islet regions adjacent to microvessels. HA normally exists in a high molecular weight form, which is anti-inflammatory. However, under inflammatory conditions, HA is degraded into fragments that are proinflammatory. HA accumulates in islets of human subjects with recent onset type 1 diabetes (T1D), and is associated with myeloid and lymphocytic islet infiltration, suggesting a possible role for HA in insulitis. A similar accumulation of HA, in amount and location, occurs in non-obese diabetic (NOD) and DORmO mouse models of T1D. Furthermore, HA accumulates in follicular germinal centers and in T-cell areas in lymph nodes and spleen in both human and mouse models of T1D, as compared with control tissues. Whether HA accumulates in islets in type 2 diabetes (T2D) or models thereof has not been previously described. Here we show evidence that HA accumulates in a mouse model of islet amyloid deposition, a well-known component of islet pathology in T2D. In summary, islet HA accumulation is a feature of both T1D and a model of T2D, and may represent a novel inflammatory mediator of islet pathology. PMID:26216136

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

    PubMed

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

    2013-04-10

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

  20. CO2/light gas separation performance of cross-linked poly(vinylimidazolium) gel membranes as a function of ionic liquid loading and cross-linker content

    SciTech Connect

    Carlisle, TK; Nicodemus, GD; Gin, DL; Noble, RD

    2012-04-15

    A series of cross-linked poly(vinylimidazolium)-RTIL gel membranes was synthesized and evaluated for room-temperature, ideal CO2/N-2, CO2/CH4, and CO2/H-2 separation performance. The membranes were formed by photo-polymerization of oligo(ethylene glycol)-functionalized cross-linking (i.e., di-functional) and non-cross-linking (i.e., mono-functional) vinylimidazolium RTIL monomers with nonpolymerizable, "free RTIL." The effect of free RTIL ([emim][Tf2N]) loading on CO2 separation performance was evaluated by varying RTIL loading at three levels (45, 65, and 75 wt.%). The effect of cross-linker content on CO2 separation performance was also evaluated by varying the copolymer composition of cross-linked membranes from 5 to 100 mol% di-functional monomer. The substituent on the monofunctional RTIL monomer was also varied to investigate the effect of substituent structure and chemistry on CO2 separation performance. CO2 permeability was dramatically increased with higher loading of free RTIL. Increased RTIL loading had no effect on CO2/N-2 or CO2/CH4 permeability selectivity, but significantly improved CO2/H-2 permeability selectivity. Reducing the cross-linking monomer concentration generally improved CO2 permeability. However, anomalous permeability and selectivity behavior was observed below critical concentrations of cross-linker. The effect of the substituent on the monofunctional monomer on CO2 separation performance was minimal compared to the effects of RTIL loading and copolymer composition. (C) 2012 Elsevier B.V. All rights reserved.

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

    PubMed

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

    2013-07-01

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

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

    PubMed

    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

    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

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

    PubMed

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

    2014-03-01

    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

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

    NASA Astrophysics Data System (ADS)

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

    1994-09-01

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

  5. Chemical cross-linking of Chlamydia trachomatis.

    PubMed Central

    Birkelund, S; Lundemose, A G; Christiansen, G

    1988-01-01

    Purified elementary bodies (EBs) of Chlamydia trachomatis serovar L2 were analyzed by chemical cross-linking with disuccinimidyl selenodipropionate. The effect of the cross-linking was analyzed by immunoblotting sodium dodecyl sulfate-polyacrylamide gel electrophoresis-separated components which were reacted with monoclonal antibodies against major outer membrane protein (MOMP) and lipopolysaccharide (LPS). It was shown that in EBs, MOMP was cross-linked to the LPS component of the outer membrane. Migration analysis of the cross-linked components showed that with extensive cross-linking, most of the MOMP became cross-linked to LPS, changing the migration rate from 40 to 42.5 kilodaltons. A small fraction of MOMP associated with LPS was shown to be present in bands with migration rates of 100 and 110 kilodaltons. No association of MOMP or LPS to other proteins, or to dimer or multimer forms of MOMP without LPS, was observed. A totally different membrane structure must be present in reticulate bodies, since there, MOMP was so heavily cross-linked that it did not enter the polyacrylamide gel and thus became impossible to analyze. Furthermore, the monoclonal antibody, which reacted with LPS associated with MOMP in the cross-linked EBs, did not react with reticulate bodies. Images PMID:2449399

  6. Corneal cross-linking.

    PubMed

    Randleman, J Bradley; Khandelwal, Sumitra S; Hafezi, Farhad

    2015-01-01

    Since its inception in the late 1990s, corneal cross-linking has grown from an interesting concept to a primary treatment for corneal ectatic disease worldwide. Using a combination of ultraviolet-A light and a chromophore (vitamin B2, riboflavin), the cornea can be stiffened, usually with a single application, and progressive thinning diseases such as keratoconus arrested. Despite being in clinical use for many years, some of the underlying processes, such as the role of oxygen and the optimal treatment times, are still being worked out. More than a treatment technique, corneal cross-links represent a physiological principle of connective tissue, which may explain the enormous versatility of the method. We highlight the history of corneal cross-linking, the scientific underpinnings of current techniques, evolving clinical treatment parameters, and the use of cross-linking in combination with refractive surgery and for the treatment of infectious keratitis. PMID:25980780

  7. Cross-linked informofers.

    PubMed Central

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

    1979-01-01

    The proteins of 30S RNP particles containing pre-mRNA (hnRNA) were cross-linked with bifunctional reagents (dimethyl-suberimidate and dimethyl-3,3'-dithiobispropionimidate). Further treatment with 1 or 2 M NaCl dissociates all RNA from protein. However, a significant part of protein particles--informofers being cross-linked survived high salt treatment. Their sedimentation coefficients were close to those of original particles. No RNA could be detected in the informofers even after labeling the cells with a precursor for a long period of time. Sodium dodecylsulfate or urea dissociated cross-linked informofers into oligomeric polypeptides. They could be dissociated by beta-mercaptoethanol treatment if a reversible cross-linked reagent had been used. The resulting polypeptides were represented by informatin. RNP particles (30S RNP or poly-particles) were reconstituted upon mixing of cross-linked informofers with pre-mRNA and removal of 2 M NaCl. PMID:503864

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

    PubMed Central

    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

    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

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

    SciTech Connect

    Ahuja, S.; Dieckman, S.L.; Gopalsami, N.

    1995-04-01

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

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

    NASA Technical Reports Server (NTRS)

    Meador, Mary Ann B. (Inventor)

    2016-01-01

    A method for creating a three dimensional cross-linked polyimide structure includes dissolving a diamine, a dianhydride, and a triamine in a solvent, imidizing a polyamic acid gel by heating the gel, extracting the gel in a second solvent, supercritically drying the gel, and removing the solvent to create a polyimide aerogel.

  11. Highly Conductive Ionic-Liquid Gels Prepared with Orthogonal Double Networks of a Low-Molecular-Weight Gelator and Cross-Linked Polymer.

    PubMed

    Kataoka, Toshikazu; Ishioka, Yumi; Mizuhata, Minoru; Minami, Hideto; Maruyama, Tatsuo

    2015-10-21

    We prepared a heterogeneous double-network (DN) ionogel containing a low-molecular-weight gelator network and a polymer network that can exhibit high ionic conductivity and high mechanical strength. An imidazolium-based ionic liquid was first gelated by the molecular self-assembly of a low-molecular-weight gelator (benzenetricarboxamide derivative), and methyl methacrylate was polymerized with a cross-linker to form a cross-linked poly(methyl methacrylate) (PMMA) network within the ionogel. Microscopic observation and calorimetric measurement revealed that the fibrous network of the low-molecular-weight gelator was maintained in the DN ionogel. The PMMA network strengthened the ionogel of the low-molecular-weight gelator and allowed us to handle the ionogel using tweezers. The orthogonal DNs produced ionogels with a broad range of storage elastic moduli. DN ionogels with low PMMA concentrations exhibited high ionic conductivity that was comparable to that of a neat ionic liquid. The present study demonstrates that the ionic conductivities of the DN and single-network, low-molecular-weight gelator or polymer ionogels strongly depended on their storage elastic moduli. PMID:26426303

  12. Flexible all-solid-state supercapacitors based on graphene/carbon black nanoparticle film electrodes and cross-linked poly(vinyl alcohol)-H2SO4 porous gel electrolytes

    NASA Astrophysics Data System (ADS)

    Fei, Haojie; Yang, Chongyang; Bao, Hua; Wang, Gengchao

    2014-11-01

    Flexible all-solid-state supercapacitors (SCs) are fabricated using graphene/carbon black nanoparticle (GCB) film electrodes and cross-linked poly(vinyl alcohol)-H2SO4 porous gel electrolytes (gPVAP-H2SO4). The GCB composite films, with carbon black (CB) nanoparticles uniformly distributed in the graphene nanosheets, greatly improve the active surface areas and ion transportation of pristine graphene film. The porous structure of as-prepared gPVAP-H2SO4 membrane improves the equilibrium swelling ratio in electrolyte and provides interconnected ion transport channels. The chemical crosslinking solves the fluidity problem of PVA-H2SO4 gel electrolyte at high temperature. As-fabricated GCB//gPVAP(20)-H2SO4//GCB flexible SC displays an increased specific capacitance (144.5 F g-1 at 0.5 A g-1) and a higher specific capacitance retention (67.9% from 0.2 to 4 A g-1). More importantly, the flexible SC possesses good electrochemical performance at high temperature (capacitance retention of 78.3% after 1000 cycles at 70 °C).

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

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

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

  14. Electrospinning formaldehyde cross-linked zein solutions

    Technology Transfer Automated Retrieval System (TEKTRAN)

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

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

    PubMed

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

    2011-04-01

    The properties of alginate films modified using two cross-linker ions (Ca(2+) and Ba(2+)), comparing two separate cross-linking techniques (the traditional immersion (IM) method and a new strategy in a pressure-assisted diffusion (PD) method), are evaluated. This was achieved through measuring metal ion content, water uptake and film stability in an ionic solution ([Ca(2+)] = 2 mM). Characterization of the internal structure and mechanical properties of hydrated films were established by cryogenic scanning electron microscopy and tensile testing, respectively. It was found that gels formed by the PD technique possessed greater stability and did not exhibit any delamination after 21 day immersion as compared to gels formed by the IM technique. The Ba(2+) cross-linked gels possessed significantly higher cross-linking density as reflected in lower water content, a more dense internal structure and higher Young's modulus compared to Ca(2+) cross-linked gels. For the Ca(2+) cross-linked gels, a large improvement in the mechanical properties was observed in gels produced by the PD technique and this was attributed to thicker pore walls observed within the hydrogel structure. In contrast, for the Ba(2+) cross-linked gels, the PD technique resulted in gels that had lower tensile strength and strain energy density and this was attributed to phase separation and larger macropores in this gel. PMID:21436510

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

    PubMed

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

    2004-06-01

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

  17. Ocular biocompatibility of carbodiimide cross-linked hyaluronic acid hydrogels for cell sheet delivery carriers.

    PubMed

    Lai, Jui-Yang; Ma, David Hui-Kang; Cheng, Hsiao-Yun; Sun, Chi-Chin; Huang, Shu-Jung; Li, Ya-Ting; Hsiue, Ging-Ho

    2010-01-01

    Due to its innocuous nature, hyaluronic acid (HA) is one of the most commonly used biopolymers for ophthalmic applications. We recently developed a cell sheet delivery system using carbodiimide cross-linked HA carriers. Chemical cross-linking provides an improvement in stability of polymer gels, but probably causes toxic side-effects. The aim of this study was to investigate the ocular biocompatibility of HA hydrogels cross-linked by 1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide (EDC). HA discs without cross-linking and glutaraldehyde (GTA) cross-linked HA samples were used for comparison. The disc implants were inserted in the anterior chamber of rabbit eyes for 24 weeks and characterized by slit-lamp biomicroscopy, histology and scanning electron microscopy. The ophthalmic parameters obtained from biomicroscopic examinations were also scored to provide a quantitative grading system. Results of this study showed that the HA discs cross-linked with EDC had better ocular biocompatibility than those with GTA. The continued residence of GTA cross-linked HA implants in the intraocular cavity elicited severe tissue responses and significant foreign body reactions, whereas no adverse inflammatory reaction was observed after contact with non-cross-linked HA or EDC cross-linked HA samples. It is concluded that the cross-linking agent type gives influence on ocular biocompatibility of cell carriers and the EDC-HA hydrogel is an ideal candidate for use as an implantable material in cell sheet delivery applications. PMID:20178691

  18. In vitro degradation of covalently cross-linked arabinoxylan hydrogels by bifidobacteria.

    PubMed

    Martínez-López, Ana L; Carvajal-Millan, Elizabeth; Micard, Valérie; Rascón-Chu, Agustín; Brown-Bojorquez, Francisco; Sotelo-Cruz, Norberto; López-Franco, Yolanda L; Lizardi-Mendoza, Jaime

    2016-06-25

    Arabinoxylan gels with different cross-linking densities, swelling ratios, and rheological properties were obtained by increasing the concentration of arabinoxylan from 4 to 6% (w/v) during oxidative gelation by laccase. The degradation of these covalently cross-linked gels by a mixture of two Bifidobacterium strains (Bifidobacterium longum and Bifidobacterium adolescentis) was investigated. The kinetics of the evolution of structural morphology of the arabinoxylan gel, the carbohydrate utilization profiles and the bacterial production of short-acid fatty acid (SCFA) were measured. Scanning electron microscopy analysis of the degraded gels showed multiple cavity structures resulting from the bacterial action. The total SCFA decreased when the degree of cross-linking increased in the gels. A slower fermentation of arabinoxylan chains was obtained for arabinoxylan gels with more dense network structures. These results suggest that the differences in the structural features and properties studied in this work affect the degradation time of the arabinoxylan gels. PMID:27083795

  19. Corneal Collagen Cross-Linking

    PubMed Central

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

    2010-01-01

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

  20. Porous Cross-Linked Polyimide-Urea Networks

    NASA Technical Reports Server (NTRS)

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

    2015-01-01

    Porous cross-linked polyimide-urea networks are provided. The networks comprise a subunit comprising two anhydride end-capped polyamic acid oligomers in direct connection via a urea linkage. The oligomers (a) each comprise a repeating unit of a dianhydride and a diamine and a terminal anhydride group and (b) are formulated with 2 to 15 of the repeating units. The subunit was formed by reaction of the diamine and a diisocyanate to form a diamine-urea linkage-diamine group, followed by reaction of the diamine-urea linkage-diamine group with the dianhydride and the diamine to form the subunit. The subunit has been cross-linked via a cross-linking agent, comprising three or more amine groups, at a balanced stoichiometry of the amine groups to the terminal anhydride groups. The subunit has been chemically imidized to yield the porous cross-linked polyimide-urea network. Also provided are wet gels, aerogels, and thin films comprising the networks, and methods of making the networks.

  1. [Biocompatibility analysis of hyaluronic acid sodium gels for medical application].

    PubMed

    Wang, Yaning; Yuan, Tun; Jia, Lifang; Zou, Wen; Liang, Jie

    2012-08-01

    Hyaluronan acid sodium gels are used in ophthalmic surgery, orthopedic treatment and cosmetic surgery. In 2009,there were 12 domestic manufacturers in China producing 33 kinds of products. 23 kinds of imported products were allowed by SFDA to sale in the meantime. Since manufacturers use different production processes, product performances are quite different. According to the GB/T 16886. 1-2001, we designed a pilot program to evaluate the sodium hyaluronate gel products comprehensively in this paper. The results showed that, except chromosome aberration test of gel A and subchronic systemic toxicity of gel C appeared positive, the remaining samples of the test results were negative. This article provides a reference to write standard of cross-linked hyaluronic sodium gel and the revision of standard YY0308-2004. PMID:23016423

  2. Porous Cross-Linked Polyimide Networks

    NASA Technical Reports Server (NTRS)

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

    2015-01-01

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

  3. Histone cross-linking by transglutaminase.

    PubMed

    Kim, Jae-Hong; Nam, Kang Hoon; Kwon, Oh-Seok; Kim, In Gyu; Bustin, Michael; Choy, Hyon E; Park, Sang Chul

    2002-05-24

    Transglutaminases irreversibly catalyze covalent cross-linking of proteins by forming isopeptide bonds between peptide-bound glutamine and lysine residues. Among several transglutaminases, tissue-type transglutaminase (tTGase) is most ubiquitously found in every type of cells and tissues in animals, but its natural substrate has yet to be identified. In an attempt to identify the natural substrate for tTGase, we examined in vitro if core histones were subject to cross-linking by tTGase. We found core histone subunits, H2A and H2B, were specifically cross-linked by tTGase. The cross-linking was between either one or both glutamines at C-terminal end of H2A (-VTIAQ104 GGVLPNTQ112 SVLLPKKTESSKSK-C' end) and the first and/or third lysine from C-terminal end of H2B (-AVESEGK116 AVTKYTSSK125-C' end). The cross-linking occurred only when these subunits were released from nucleosome but not when these were organized in nucleosome. Most interestingly, in chicken erythrocyte the cross-linked H2A-H2B was present in a significant amount. From these results, it can be proposed that tTGase-mediated cross-linking is an another form of core histone modification and it may play a role of chromatin condensation during erythrocyte differentiation. PMID:12054678

  4. Hyaluronan in human malignancies

    SciTech Connect

    Sironen, R.K.; Tammi, M.; Tammi, R.; Auvinen, P.K.; Anttila, M.; Kosma, V-M.

    2011-02-15

    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.

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

    PubMed Central

    Kim, Min Hee; Park, Won Ho

    2016-01-01

    In this study, the synthesis of silk fibroin (SF) hydrogel via chemical cross-linking reactions of SF due to gamma-ray (γ-ray) irradiation was investigated, as were the resultant hydrogel’s properties. Two different hydrogels were investigated: physically cross-linked SF hydrogel and chemically cross-linked SF hydrogel irradiated at different doses of γ-rays. The effects of the irradiation dose and SF concentration on the hydrogelation of SF were examined. The chemically cross-linked SF hydrogel was compared with the physically cross-linked one with regard to secondary structure and gel strength. Furthermore, the swelling behavior, crystallinity, and biodegradation of the SF hydrogels were characterized. To assay cell proliferation, the cell viability of human mesenchymal stem cells on the lyophilized SF hydrogel scaffolds was evaluated, and no significant cytotoxicity against human mesenchymal stem cells was observed. PMID:27382283

  6. Physicochemical properties of collagen solutions cross-linked by glutaraldehyde.

    PubMed

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

    2014-06-01

    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 η* 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

  7. Highly cross-linked nanoporous polymers

    DOEpatents

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

    1997-01-01

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

  8. Highly cross-linked nanoporous polymers

    DOEpatents

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

    1998-01-01

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

  9. Chemistry and physical properties of melt-processed and solution-cross-linked corn zein.

    PubMed

    Sessa, David J; Mohamed, Abdellatif; Byars, Jeffrey A

    2008-08-27

    Corn zein was cross-linked with glutaraldehyde (GDA) using glacial acetic acid (HAc) as catalyst. The objectives are to evaluate the swelling characteristics of GDA cross-linked zein gels in water, ethanol, and their combinations. Similar formulations, upon solvent evaporation, form films. The mechanical properties of the films are compared to compression molded tensile bars from GDA melt-processed zein as a second objective. Chemistry of the cross-linking reaction was based on the aldehyde binding characteristics defined by use of fluorescence spectroscopy; sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) to demonstrate the cross-linking reaction; FTIR to observe absorption differences of the cross-linked product; differential scanning calorimetry, dynamic mechanical analysis and thermogravimetric analysis to assess thermal properties; and the use of Instron Universal Testing Machine to evaluate mechanical properties. A reaction mechanism for acid catalyzed GDA cross-linking of zein is proposed. Thermal and mechanical properties of tensile bars cut from either film or formed by compression molding were similar, where both showed increased tensile strengths, ductility and stiffness when compared with unmodified controls. Samples that were reacted with 8% GDA by weight based on weight of zein from either process retained their integrity when tensile bars from each were subjected to boiling water for 10 min or soaking in either water or HAc for 24 h. The melt-processed, cross-linked zein is a more environmentally friendly method that would eliminate the need for HAc recovery. PMID:18636736

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

    NASA Technical Reports Server (NTRS)

    Panek, John

    2010-01-01

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

  11. Supersaturated lysozyme solution structure studied by chemical cross-linking.

    PubMed

    Hall, Clayton L; Clemens, John R; Brown, Amanda M; Wilson, Lori J

    2005-06-01

    Glutaraldehyde cross-linking followed by separation has been used to detect aggregates of chicken egg-white lysozyme (CEWL) in supersaturated solutions. In solutions of varying NaCl content, the number of aggregates was found to be related to the ionic strength of the solution. Separation by SDS-PAGE showed that percentage of dimer in solution ranged from 25.3% for no NaCl to 27.1% at 15% NaCl, and the aggregates larger than dimer increased from 1.9% for no NaCl to 36.8% at 15% NaCl. Conversely, the percentage of monomers decreased from 72.8% without NaCl to 36.1% at 15% NaCl. Molecular weights by capillary electrophoresis (SDS-CE) were found to be multiples of the monomer molecular weights, with the exception of trimer, which indicates a very compact structure. Native separation was accomplished using size-exclusion chromatography (SEC) and gave a lower monomer concentration and higher aggregate concentration than SDS-CE, which is a denaturing separation method. Most noticeably, trimers were absent in the SEC separation. The number of aggregates did not change with increased time between addition of NaCl and addition of cross-linking agent when separated by gel electrophoresis (SDS-PAGE). The results suggest that high ionic strength CEWL solutions are highly aggregated and that denaturing separation methods disrupt cross-linked products. PMID:15930646

  12. Polymorphism of Cross-Linked Actin Networks in Giant Vesicles

    NASA Astrophysics Data System (ADS)

    Limozin, Laurent; Sackmann, Erich

    2002-09-01

    Actin networks cross-linked by natural linkers α-actinin and filamin are generated in giant vesicles by polymerization through ionophore-mediated influx of Mg2+. α-actinin induces the formation of randomly linked networks at 25 °C which transform at <15 °C into spiderweblike gels or ringlike bundles depending on the vesicle size. Muscle filamin forms ringlike structures under all experimental conditions which can supercoil by subsequent Mg2+ addition. The polymorphism is rationalized in terms of recent models of bivalent ion coupled semiflexible polyelectrolytes and by considering the topology of the linkers.

  13. Cross-linking Chemistry of Squid Beak*

    PubMed Central

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

    2010-01-01

    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

  14. Cross-linking chemistry of squid beak.

    PubMed

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

    2010-12-01

    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

  15. Hybridization triggered cross-linking of deoxyoligonucleotides.

    PubMed Central

    Webb, T R; Matteucci, M D

    1986-01-01

    This paper reports details of the synthesis of oligodeoxynucleotides containing the modified base 5-methyl-N4,N4-ethanocytosine (Ce). The 9-fluorenylmethoxycarbonyl group is used as a protecting group for the exocyclic amines of dA and dC. This group can be removed rapidly under very mild conditions. Oligomers containing the Ce base form a cross-link when hybridized to their complementary deoxyoligonucleotides. Some of the scope and limitations of these cross-link forming oligonucleotides are reported. Images PMID:3774542

  16. Physical properties of pectin-high amylose starch mixtures cross-linked with sodium trimetaphosphate.

    PubMed

    Carbinatto, Fernanda M; de Castro, Ana Dóris; Cury, Beatriz S F; Magalhães, Alviclér; Evangelista, Raul C

    2012-02-28

    Pectin-high amylose starch mixtures (1:4; 1:1; 4:1) were cross-linked at different degrees and characterized by rheological, thermal, X-ray diffraction and NMR analyses. For comparison, samples without cross-linker addition were also prepared and characterized. Although all samples behaved as gels, the results evidenced that the phosphorylation reaction promotes the network strengthening, resulting in covalent gels (highest critical stress, G' and recovery %). Likewise, cross-linked samples presented the highest thermal stability. However, alkaline treatment without cross-linker allowed a structural reorganization of samples, as they also behaved as covalent gels, but weaker than those gels from cross-linked samples, and presented higher thermal stability than the physical mixtures. X-ray diffractograms also evidenced the occurrence of physical and chemical modifications due to the cross-linking process and indicated that samples without cross-linker underwent some structural reorganization, resulting in a decrease of crystallinity. The chemical shift of resonance signals corroborates the occurrence of structural modifications by both alkaline treatment and cross-linking reaction. PMID:22178896

  17. Arabinosylation Plays a Crucial Role in Extensin Cross-linking In Vitro

    PubMed Central

    Chen, Yuning; Dong, Wen; Tan, Li; Held, Michael A; Kieliszewski, Marcia J

    2015-01-01

    Extensins (EXTs) are hydroxyproline-rich glycoproteins (HRGPs) that are structural components of the plant primary cell wall. They are basic proteins and are highly glycosylated with carbohydrate accounting for >50% of their dry weight. Carbohydrate occurs as monogalactosyl serine and arabinosyl hydroxyproline, with arabinosides ranging in size from ~1 to 4 or 5 residues. Proposed functions of EXT arabinosylation include stabilizing the polyproline II helix structure and facilitating EXT cross-linking. Here, the involvement of arabinosylation in EXT cross-linking was investigated by assaying the initial cross-linking rate and degree of cross-linking of partially or fully de-arabinosylated EXTs using an in vitro cross-linking assay followed by gel permeation chromatography. Our results indicate that EXT arabinosylation is required for EXT cross-linking in vitro and the fourth arabinosyl residue in the tetraarabinoside chain, which is uniquely α-linked, may determine the initial cross-linking rate. Our results also confirm the conserved structure of the oligoarabinosides across species, indicating an evolutionary significance for EXT arabinosylation. PMID:26568683

  18. Cross-linked structure of network evolution

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

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

  19. Highly cross-linked nanoporous polymers

    DOEpatents

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

    1998-01-20

    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.

  20. Cross-linked structure of network evolution

    SciTech Connect

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

    2014-03-15

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

  1. Supermacroporous chemically cross-linked poly(aspartic acid) hydrogels.

    PubMed

    Gyarmati, Benjámin; Mészár, E Zsuzsanna; Kiss, Lóránd; Deli, Mária A; László, Krisztina; Szilágyi, András

    2015-08-01

    Chemically cross-linked poly(aspartic acid) (PASP) gels were prepared by a solid-liquid phase separation technique, cryogelation, to achieve a supermacroporous interconnected pore structure. The precursor polymer of PASP, polysuccinimide (PSI) was cross-linked below the freezing point of the solvent and the forming crystals acted as templates for the pores. Dimethyl sulfoxide was chosen as solvent instead of the more commonly used water. Thus larger temperatures could be utilized for the preparation and the drawback of increase in specific volume of water upon freezing could be eliminated. The morphology of the hydrogels was characterized by scanning electron microscopy and interconnectivity of the pores was proven by the small flow resistance of the gels. Compression tests also confirmed the interconnected porous structure and the complete re-swelling and shape recovery of the supermacroporous PASP hydrogels. The prepared hydrogels are of interest for several biomedical applications as scaffolding materials because of their cytocompatibility, controllable morphology and pH-responsive character. PMID:25922304

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

    NASA Technical Reports Server (NTRS)

    Meador, Ann B.; Capadona, Lynn A.

    2008-01-01

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

  3. Encapsulation of volatiles by homogenized partially-cross linked alginates.

    PubMed

    Inguva, Pavan K; Ooi, Shing Ming; Desai, Parind M; Heng, Paul W S

    2015-12-30

    Cross-linked calcium alginate gels are too viscous to be efficaciously incorporated into spray dried formulations. Thus, viscosity reduction is essential to ensure the processability of calcium alginate gels to be sprayed. Viscosity reduction by high pressure homogenization can open new formulation possibilities. Presently, testing of microcapsule integrity is also limited because either single particle tests neglect collective particle behaviours in bulk or bulk testing methods are often associated with single compressions which may not fully characterize individual particle strengths. The aim of this study was sub-divided into three objectives. First objective was to evaluate the impact of high pressure homogenization on gel viscosity. Second objective was to explore the use of the homogenized gels with modified starch for microencapsulation by spray drying. The final objective was to develop a stamping system as microcapsule strength tester that can assess microcapsules in bulk and evaluate the impact of multiple compressions. Collectively, this study would lead towards developing a pressure-activated patch of microcapsules with encapsulated volatiles and the method to assess the patch efficacy. The alginate gels largely experienced an exponential decay in viscosity when homogenized. Furthermore, the homogenized gels were successfully incorporated in spray drying formulations for microencapsulation. The custom-designed microcapsule strength tester was successfully used and shown to possess the required sensitivity to discern batches of microcapsules containing volatiles to have different release profiles. Addition of homogenized gels strengthened the microcapsules only at high wall to core ratios with low mass-load alginate gels. High mass-load gels weaken the microcapsules, exhibiting a higher release at low stamping pressures and wrinkling on the microcapsules surface. PMID:26581772

  4. Cross-Linking Studies of Lysozyme Nucleation

    NASA Technical Reports Server (NTRS)

    Forsythe, Elizabeth; Pusey, Marc

    2000-01-01

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

  5. Characterization of Hyaluronan-Protein Microstructures and Polymer Solutions

    NASA Astrophysics Data System (ADS)

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

    2010-03-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

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

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

    PubMed

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

    2013-04-01

    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

  8. Synthesis of a duplex oligonucleotide containing a nitrogen mustard interstrand DNA-DNA cross-link.

    PubMed

    Ojwang, J O; Grueneberg, D A; Loechler, E L

    1989-12-01

    Many cancer chemotherapeutic agents react with DNA and give adducts that block DNA replication, which is thought to result in cytotoxicity, especially in rapidly proliferating cells such as cancer cells. One class of these agents is bifunctionally reactive (e.g., the nitrogen mustards) and forms DNA-DNA cross-links. It is unknown whether inter- or intrastrand cross-links are more effective at blocking DNA replication. To evaluate this, a DNA shuttle vector is being constructed with an interstrand cross-link at a unique site. In the first step of this project, a duplex oligonucleotide containing an interstrand cross-link is isolated by denaturing polyacrylamide gel electrophoresis from the reaction of nitrogen mustard with two partially complementary oligodeoxynucleotides. The purified oligonucleotide product is characterized and shown to be cross-linked in a 5'-GAC-3' 3'-CTG-5' sequence by a nitrogen mustard moiety that is bound at the N(7)-position of the guanines in the opposing strands; the glycosylic bonds of these guanine adducts are stabilized in their corresponding imidazole ring-opened form. Nitrogen mustard is shown to react with a variety of oligonucleotides and, based upon these results, its preferred targets for interstrand cross-linking are 5'-GXC-3' sequences, where X can be any of the four deoxyribonucleotide bases. PMID:2819709

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

    PubMed

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

    2013-06-26

    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 (ΔHm). 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

  10. Characterization of receptors for VIP on pancreatic acinar cell plasma membranes using covalent cross-linking

    SciTech Connect

    McArthur, K.E.; Wood, C.L.; O'Dorisio, M.S.; Zhou, Z.C.; Gardner, J.D.; Jensen, R.T.

    1987-03-01

    Vasoactive intestinal peptide (VIP) receptors on guinea pig pancreatic acini differ from those on all other tissues in containing a high-affinity VIP receptor and a low-affinity VIP receptor that has a high affinity for secretin. To characterize the molecular components of these receptors, /sup 125/I-VIP was covalently cross-linked to these receptors by four different cross-linking agents: disuccinimidyl suberate, ethylene glycol bis (succinimidyl succinate), dithiobis (succinimidylpropionate), and m-maleimidobenzoyl N-hydroxysuccinimide ester. Analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis demonstrated a single major polypeptide band of M/sub r/ 45,000 and a minor polypeptide band of M/sub r/ 30,000 were cross-linked to /sup 125/I-VIP. Covalent cross-linking only occurred when a cross-linking agent was added, was inhibited by GTP, was inhibited by VIP receptor agonist or antagonists that interact with VIP receptors, and not by other pancreatic secretagogues that interact with difference receptors. Thus the high-affinity VIP receptor on pancreatic acinar cell membranes consists of a single major polypeptide of M/sub r/ 45,000, and this polypeptide is not a subunit of a larger disulfide-linked structure. Furthermore, either the low-affinity VIP/secretin-preferring receptor was not covalently cross-linked under the experimental conditions or it consist of a major polypeptide with the same molecular weight as the high-affinity VIP receptor.

  11. Polyimide aerogels cross-linked through amine functionalized polyoligomeric silsesquioxane.

    PubMed

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

    2011-02-01

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

  12. Tea derived galloylated polyphenols cross-link purified gastrointestinal mucins.

    PubMed

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

    2014-01-01

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

  13. Stretching and bending in cross-linked biopolymer networks

    NASA Astrophysics Data System (ADS)

    Heussinger, Claus; Frey, Erwin

    2007-03-01

    The elastic response of cross-linked biopolymer networks is usually interpreted in terms of affine stretching models, adopted from the theory of rubber-elasticity valid for flexible polymer gels. Unlike flexible polymers, however, stiff polymers have a highly anisotropic elastic response, where the low-energy elastic excitations are actually of bending nature. As a consequence, similar to springs connected in series, one would expect the softer bending mode to dominate the elastic energy rather than the stiff stretching mode. We propose a theory that, unlike recent affine models, properly accounts for the soft bending response of stiff polymers. It allows calculating the macroscopic elastic moduli starting from a microscopic characterization of the (non-affine) deformation field. The calculated scaling properties for the shear modulus are in excellent agreement with the results of recent simulations obtained in simple two-dimensional model networks, and can also be applied to rationalize bulk rheological data in reconstituted actin networks.

  14. Contraction of cross-linked actomyosin bundles

    NASA Astrophysics Data System (ADS)

    Yoshinaga, Natsuhiko; Marcq, Philippe

    2012-08-01

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

  15. Sulfhydryl site-specific cross-linking and labeling of monoclonal antibodies by a fluorescent equilibrium transfer alkylation cross-link reagent.

    PubMed

    del Rosario, R B; Wahl, R L; Brocchini, S J; Lawton, R G; Smith, R H

    1990-01-01

    The site-specific intramolecular cross-linking of sulfhydryls of monoclonal antibodies via a new class of "equilibrium transfer alkylation cross-link (ETAC) reagents" is described. Following complete or partial reduction of interchain disulfides with dithiothreitol (DTT), two murine IgG2a monoclonal antibodies, 225.28S and 5G6.4, were reacted with alpha,alpha-bis[(p-tolylsulfonyl)methyl]-m-aminoacetophenone (ETAC 1a) and a fluorescent conjugated derivative, sulforhodamine B m-(alpha,alpha-bis(p-tolysulfonylmethyl)acetyl)anilide derivative (ETAC 1b). Reducing SDS-polyacrylamide gel electrophoresis analysis of the products from 1b indicated the formation of S-ETAC-S interchain heavy and light chain cross-links (approximately 23-34% overall yield by video-camera densitometry) which do not undergo disulfide-thiol exchange with DTT at 100 degrees C. In contrast, no interchain cross-links were observed upon reaction of unreduced or reduced antibody wherein the thiols have been previously alkylated with iodoacetamide. These results indicated site-specific cross-linking of interchain sulfhydryls and places their distance within 3-4 A. Flow cytometry of the ETAC 1b 5G6.4 cross-linked product using 77 IP3 human ovarian carcinoma target cells showed positive binding and retention of immunoreactivity. The in vivo biodistributions of 131I-labeled intact 5G6.4 and 125I-labeled reduced 5G6.4 + ETAC 1a product in rats were essentially identical over a period of 24 h. The present study illustrates the potential applications of labelable ETAC reagents as thiol-specific probes for a wide variety of immunological studies. PMID:2128870

  16. Corneal Collagen Cross-Linking Outcomes: Review

    PubMed Central

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

    2011-01-01

    Keratoconus is a condition characterized by biomechanical instability of the cornea, presenting in a progressive, asymmetric and bilateral way. Corneal collagen cross-linking with riboflavin and UVA (CXL) is a new technique of corneal tissue strengthening that combines the use of riboflavin as a photo sensitizer and UVA irradiation. The studies showed that CXL was effective in halting the progression of keratoconus over a period of up to four years. The published studies also revealed a reduction of max K readings by more than 2 D, while the postoperative SEQ was reduced by an average of more than 1 D, and refractive cylinder decreased by about 1 D. No eyes lost any line of BCDVA. Moreover, there was no significant decrease in endothelial cell density. It was also found that CXL treatment was effective with reducing corneal and total wavefront aberrations. Corneal cross-linking has also led to an arrest and/or even a partial reversal of keratectasia in the treatment of iatrogenic ectasia after excimer laser ablation. A primary intervention such as CXL should be considered to potentially increase the biomechanical stability of the corneal tissue and postpone the need of lamellar or penetrating keratoplasty. PMID:21448301

  17. Corneal collagen cross-linking: a review.

    PubMed

    O'Brart, David P S

    2014-01-01

    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

  18. Corneal collagen cross-linking: A review

    PubMed Central

    O’Brart, David P.S.

    2014-01-01

    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

  19. To Cross-Link or Not to Cross-Link? Cross-Linking Associated Foreign Body Response of Collagen-Based Devices

    PubMed Central

    Delgado, Luis M.; Bayon, Yves; Pandit, Abhay

    2015-01-01

    Collagen-based devices, in various physical conformations, are extensively used for tissue engineering and regenerative medicine applications. Given that the natural cross-linking pathway of collagen does not occur in vitro, chemical, physical, and biological cross-linking methods have been assessed over the years to control mechanical stability, degradation rate, and immunogenicity of the device upon implantation. Although in vitro data demonstrate that mechanical properties and degradation rate can be accurately controlled as a function of the cross-linking method utilized, preclinical and clinical data indicate that cross-linking methods employed may have adverse effects on host response, especially when potent cross-linking methods are employed. Experimental data suggest that more suitable cross-linking methods should be developed to achieve a balance between stability and functional remodeling. PMID:25517923

  20. Preparation and characterization of electrospun in-situ cross-linked gelatin-graphite oxide nanofibers.

    PubMed

    Zhan, Jianchao; Morsi, Yosry; Ei-Hamshary, Hany; Al-Deyab, Salem S; Mo, Xiumei

    2016-04-01

    Electrospun gelatin(Gel) nanofibers scaffold has such defects as poor mechanical property and quick degradation due to high solubility. In this study, the in situ cross-linked electrospinning technique was used for the production of gelatin nanofibers. Deionized water was chosen as the spinning solvent and graphite oxide (GO) was chosen as the enhancer. The morphological structure, porosity, thermal property, moisture absorption, and moisture retention performance, hydrolysis resistance, mechanical property, and biocompatibility of the produced nanofibers were investigated. Compared with in situ cross-linked gelatin nanofibers scaffold, in situ cross-linked Gel-GO nanofibers scaffold has the following features: (1) the hydrophilicity, moisture absorption, and moisture retention performance slightly reduce, while the hydrolysis resistance is improved; (2) the breaking strength, breaking elongation, and Young's modulus are significantly improved; (3) the porosity slightly reduces while the biocompatibility considerably increases. The in situ cross-linked Gel-GO nanofibers scaffold is likely to be applied in such fields as drug delivery and scaffold for skin tissue engineering. PMID:26733331

  1. Hyaluronan: A Matrix Component

    NASA Astrophysics Data System (ADS)

    Rügheimer, Louise

    2008-09-01

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

  2. Hyaluronan Synthesis and Myogenesis

    PubMed Central

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

    2013-01-01

    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

  3. Nitrocinnamate-functionalized gelatin: synthesis and "smart"hydrogel formation via photo-cross-linking.

    PubMed

    Gattás-Asfura, Kerim M; Weisman, Eric; Andreopoulos, Fotios M; Micic, Miodrag; Muller, Bill; Sirpal, Sanjeev; Pham, Si M; Leblanc, Roger M

    2005-01-01

    Gelatin having p-nitrocinnamate pendant groups (Gel-NC) was prepared via an efficient one-pot synthesis, yield >87%. (1)H NMR data indicated that 1 mol of gelatin was modified with 18 +/- 6 mol of the photosensitive group. Upon exposure to low-intensity 365 nm UV light and in the absence of photoinitiators or catalysts, Gel-NC cross-linked within minutes into a gelatin-based hydrogel as monitored by UV-vis spectroscopy. The degree of swelling of this biodegradable hydrogel in aqueous solutions responded to changes in Gel-NC concentration levels, the ionic strength of the aqueous solutions, and photo-cross-linking time. Topography changes associated with phase transition resulting from "photocleavage" of the hydrogel network with 254 nm UV light were studied with AFM. Both Gel-NC and its hydrogel expressed low toxicity to human neonatal fibroblast cells. In addition, gelatin-based microgels were prepared via the photo-cross-linking of Gel-NC within inverse micelles. PMID:15877371

  4. Kojak: Efficient analysis of chemically cross-linked protein complexes

    PubMed Central

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

    2015-01-01

    Protein chemical cross-linking and mass spectrometry enable the analysis of protein-protein interactions and protein topologies, however complicated cross-linked peptide spectra require specialized algorithms to identify interacting sites. The Kojak cross-linking software application is a new, efficient approach to identify cross-linked peptides, enabling large-scale analysis of protein-protein interactions by chemical cross-linking techniques. The algorithm integrates spectral processing and scoring schemes adopted from traditional database search algorithms, and can identify cross-linked peptides using many different chemical cross-linkers, with or without heavy isotope labels. Kojak was used to analyze both novel and existing datasets, and was compared with existing cross-linking algorithms. The algorithm provided increased cross-link identifications over existing algorithms, and equally importantly, the results in a fraction of computational time. The Kojak algorithm is open-source, cross-platform, and freely available. This software provides both existing and new cross-linking researchers alike an effective way to derive additional cross-link identifications from new or existing datasets. For new users, it provides a simple analytical resource resulting in more cross-link identifications than other methods. PMID:25812159

  5. Riboflavin for corneal cross-linking.

    PubMed

    O'Brart, D P S

    2016-06-01

    Corneal collagen cross-linking (CXL) with riboflavin and ultraviolet A (UVA) radiation is the first therapeutic modality that appears to arrest the progression of keratoconus and other corneal ectasias. Riboflavin is central to the process, acting as a photosensitizer for the production of oxygen singlets and riboflavin triplets. These free radicals drive the CXL process within the proteins of the corneal stroma, altering its biomechanical properties. Riboflavin also absorbs the majority of the UVA radiation, which is potentially cytotoxic and mutagenic, within the anterior stroma, preventing damage to internal ocular structures, such as the corneal endothelium, lens and retina. Clinical studies report cessation of ectatic progression in over 90% of cases and the majority document significant improvements in visual, keratometric and topographic parameters. Clinical follow-up is limited to 5-10 years, but suggests sustained stability and enhancement in corneal shape. Sight-threatening complications are rare. The optimal stromal riboflavin dosage for CXL is as yet undetermined. PMID:27458610

  6. Quinone cross-linked polysaccharide hybrid fiber.

    PubMed

    Kuboe, Yoshiko; Tonegawa, Hitomi; Ohkawa, Kousaku; Yamamoto, Hiroyuki

    2004-01-01

    The present article describes the synthesis of the N-(Lys-Gly-Tyr-Gly)-chitosan using the water-soluble active ester method, the preparation of the N-(Lys-Gly-Tyr-Gly)-chitosan-gellan hybrid fibers, and the reinforcement of the hybrid fibers by enzymatic cross-linking between the N-grafted peptides chains of chitosan. The cationic polysaccharide chitosan was treated with Boc-Lys(Z)-Gly-Tyr(Bzl)-Gly (4-hydroxyphenyl)dimethylsulfonium methyl sulfate ester in DMF-0.15 M acetic acid to incorporate the peptides into the side chain amino groups of chitosan followed by the acidic removals of the Z and Bzl groups. The degrees of N substitution were estimated to be 2.0 and 10 molar % by changing the molar ratios of the amino groups of the parent chitosan and the active ester. The resulting cationic N-(Lys-Gly-Tyr-Gly)-chitosan was spun into the hybrid fibers with the anionic polysaccharide gellan in water. The tensile strengths of the N-(Lys-Gly-Tyr-Gly)-chitosan hybrid fibers were superior to those of the original chitosan-gellan fibers. The mechanical strengths of the hybrid fibers further increased upon enzymatic oxidation using tyrosinase. Based on these results, we concluded that the covalent cross-linking due to the enzyme oxidation between the grafted peptides significantly contributed to reinforcement of the polysaccharide hybrid fibers. The present results afford a new methodology for the reinforcement achieved by the polymer modification inspired by a biological process. PMID:15002994

  7. Organization of photosystem I polypeptides examined by chemical cross-linking

    NASA Technical Reports Server (NTRS)

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

    1996-01-01

    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.

  8. The Adhesion and Neurite Outgrowth of Neurons on Poly(D-lysine)/Hyaluronan Multilayer Films.

    PubMed

    Shi, Haifei; Sheng, Guoping

    2016-06-01

    Poly(D-lysine)/hyaluronan (PDL/HA) films were prepared using layer-by-layer assembly technique and chemically cross-linked with a water soluble carbodiimide (EDC) in combination with N-hydroxysuccinimide (NHS) through formation of amide bonds. Quartz crystal microbalance with dissipation (QCM-D) was used to follow the cross-linking reaction. Atomic force measurement, ellipsometry, and Fourier transform infrared (FTIR) spectroscopy were performed to study the chemical structure, topography, thickness and mechanical properties of the cross-linked films. QCM-D and Frictional force study were used to reveal the viscoelasticity of the films after cross-linking treatment. The stability of the films was studied via incubating the films in physiological environment. Finally, the neurons were used to evaluate the interaction between films and cells. The results indicated that the neurons were preferably proliferating and outgrowth neurite on cross-linked films while uncross-linked films are highly cell resistant. PMID:27427590

  9. Formation and properties of hyaluronan/nano Ag and hyaluronan-lecithin/nano Ag films.

    PubMed

    Khachatryan, Gohar; Khachatryan, Karen; Grzyb, Jacek; Fiedorowicz, Maciej

    2016-10-20

    A facile and environmentally friendly method of the preparation of silver nanoparticles embedded in hyaluronan (Hyal/Ag) and hyaluronan-lecithin (Hyal-L/Ag) matrix was developed. Thin, elastic foils were prepared from gels by an in situ synthesis of Ag in an aqueous solution of sodium hyaluronate (Hyal), using aq. d-(+)-xylose solution as a reducing agent. The gels were applied to a clean, smooth, defatted Teflon surface and left for drying in the air. The dry foils were stored in a closed container. UV-vis spectroscopy, transmission electron microscopy (TEM) and Fourier transform infrared (FTIR) spectra confirmed formation of about 10nm ball-shaped Ag nanoparticles situated within the polysaccharide template. Thermal properties of the composites were characterized involving differential scanning calorimetry (DSC) and thermogravimetric (TGA) analyses, whereas molecular weights of polysaccharide chains of the matrix were estimated with the size exclusion chromatography coupled with multiangle laser light scattering and refractometric detectors (HPSEC-MALLS-RI). An increase in the molecular weight of the hyaluronate after generation of Ag nanoparticles was observed. The foils showed specific properties. The study confirmed that silver nanoparticles can be successfully prepared with environmentally friendly method, using hyaluronan as a stabilizing template. Hyaluronan and hyaluronan-lecithin matrices provide nanocrystals uniform in size and shape. The composites demonstrated a bacteriostatic activity. PMID:27474588

  10. Hyaluronan Hydrogels for a Biomimetic Spongiosa Layer of Tissue Engineered Heart Valve Scaffolds.

    PubMed

    Puperi, Daniel S; O'Connell, Ronan W; Punske, Zoe E; Wu, Yan; West, Jennifer L; Grande-Allen, K Jane

    2016-05-01

    Advanced tissue engineered heart valves must be constructed from multiple materials to better mimic the heterogeneity found in the native valve. The trilayered structure of aortic valves provides the ability to open and close consistently over a full human lifetime, with each layer performing specific mechanical functions. The middle spongiosa layer consists primarily of proteoglycans and glycosaminoglycans, providing lubrication and dampening functions as the valve leaflet flexes open and closed. In this study, hyaluronan hydrogels were tuned to perform the mechanical functions of the spongiosa layer, provide a biomimetic scaffold in which valve cells were encapsulated in 3D for tissue engineering applications, and gain insight into how valve cells maintain hyaluronan homeostasis within heart valves. Expression of the HAS1 isoform of hyaluronan synthase was significantly higher in hyaluronan hydrogels compared to blank-slate poly(ethylene glycol) diacrylate (PEGDA) hydrogels. Hyaluronidase and matrix metalloproteinase enzyme activity was similar between hyaluronan and PEGDA hydrogels, even though these scaffold materials were each specifically susceptible to degradation by different enzyme types. KIAA1199 was expressed by valve cells and may play a role in the regulation of hyaluronan in heart valves. Cross-linked hyaluronan hydrogels maintained healthy phenotype of valve cells in 3D culture and were tuned to approximate the mechanical properties of the valve spongiosa layer. Therefore, hyaluronan can be used as an appropriate material for the spongiosa layer of a proposed laminate tissue engineered heart valve scaffold. PMID:27120017

  11. Synthesis and Properties of Cross-Linked Polyamide Aerogels

    NASA Technical Reports Server (NTRS)

    Williams, Jarrod C.; Meador, Mary Ann; McCorkle, Linda

    2015-01-01

    We report the first synthesis of cross-linked polyamide aerogels through step growth polymerization using a combination of diamines, diacid chloride and triacid chloride. Polyamide oligomers endcapped with amines are prepared as stable solutions in N-methylpyrrolidinone from several different diamine precursors and 1,3-benzenedicarbonyl dichloride. Addition of 1,3,5-benzenetricarbonyl trichloride yields gels which form in under five minutes according to the scheme shown. Solvent exchange of the gels into ethanol, followed by drying using supercritical CO2 extraction gives colorless aerogels with densities around 0.1 to 0.2 gcm3. Thicker monolithes of the polyamide aerogels are stiff and strong, while thin films of certain formulations are highly flexible, durable, and even translucent. These materials may have use as insulation for deployable space structures, rovers, habitats or extravehicular activity suits as well as in many terrestrial applications. Strucure property relationships of the aerogels, including surface area, mechanical properties, and thermal conductivity will be discussed.

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

    NASA Astrophysics Data System (ADS)

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

    2007-12-01

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

  13. Nonlinear behavior of ionically and covalently cross-linked alginate hydrogels

    NASA Astrophysics Data System (ADS)

    Hashemnejad, Seyedmeysam; Zabet, Mahla; Kundu, Santanu

    2015-03-01

    Gels deform differently under applied load and the deformation behavior is related to their network structures and environmental conditions, specifically, strength and density of crosslinking, polymer concentration, applied load, and temperature. Here, we investigate the mechanical behavior of both ionically and covalent cross-linked alginate hydrogel using large amplitude oscillatory shear (LAOS) and cavitation experiments. Ionically-bonded alginate gels were obtained by using divalent calcium. Alginate volume fraction and alginate to calcium ratio were varied to obtain gels with different mechanical properties. Chemical gels were synthesized using adipic acid dihdrazide (AAD) as a cross-linker. The non-linear rheological parameters are estimated from the stress responses to elucidate the strain softening behavior of these gels. Fracture initiation and propagation mechanism during shear rheology and cavitation experiments will be presented. Our results provide a better understanding on the deformation mechanism of alginate gel under large-deformation.

  14. Collagen cross-linking and resorption: effect of glutaraldehyde concentration.

    PubMed

    Roe, S C; Milthorpe, B K; Schindhelm, K

    1990-12-01

    Cross-linked collagen bioprostheses usually are designed to be inert and nonresorbable, resulting in fatigue and wear failure in high-stress environments. Eventual replacement of the implant, although minimizing strength loss during resorption, would result in a graft with reparative ability. Kangaroo tail tendon (KTT) partially cross-linked with glutaraldehyde (GA) was evaluated in vitro for resistance to bacterial collagenase digestion and in vivo for biocompatibility and resorbability in an intramuscular implant assay. Cross-linking was quantified by thermal denaturation studies. Incomplete cross-linking was achieved with concentrations of GA less than 0.1% (w/v). KTT cross-linked in greater than or equal to 0.05% GA were collagenase resistant being incompletely digested after 240 h. Cross-linking of KTT with low concentrations of GA resulted in partial collagenase resistance and slowed resorption. PMID:2126427

  15. Nonlinear elasticity of cross-linked networks

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

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

  16. Corneal Cross-Linking and Safety Issues

    PubMed Central

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

    2011-01-01

    Purpose: To compile the safety aspects of the corneal collagen cross-linking (CXL) by means of the riboflavin/UVA (370 nm) approach. Materials and Methodology: Analysis of the current treatment protocol with respect to safety during CXL. Results: The currently used UVA dose density of 5.4 J/cm2 and the corresponding irradiance of 3 mW/cm2 are below the known damage thresholds of UVA for the corneal endothelium, lens, and retina. Regarding the photochemical damages due to the free radicals the damage threshold for endothelial cells is 0.35 mW/cm2. In a 400μm thick corneal stroma saturated with riboflavin, the irradiance at the endothelial level is about 0.18 mW/cm2, which is a factor of 2 smaller than the damage threshold. Conclusion: As long as the corneal stroma treated has a minimal thickness of 400 microns (as recommended), neither corneal endothelium nor deeper structures such as lens and retina will suffer any damages. The light source should provide a homogenous irradiance avoiding hot spots. PMID:21399770

  17. Identification of neighbouring protein pairs in the rat liver 40-S ribosomal subunits cross-linked with dimethyl suberimidate.

    PubMed

    Terao, K; Uchiumi, T; Kobayashi, Y; Ogata, K

    1980-01-24

    (1) The 40-S ribosomal subunits of rat liver were treated with a bifunctional cross-linking reagent, dimethyl suberimidate. Cross-linked protein-protein dimers were separated by two-dimensional acrylamide gel electrophoresis. The stained cross-linked complexes within the gel were radioiodinated without the elution of proteins from the gel and were cloven into the original monomeric protein constituents by ammonolysis. The proteins in each dimer were finally identified by two-dimensional acrylamide gel electrophoresis of the cloven monomeric proteins, followed by radioautography of the stained gel. (2) The molecular weights of cross-linked complexes were determined by SDS-polyacrylamide gel electrophoresis and were compared with those of their constituent proteins. (3) The following dimers were proposed from these results: S3-S12 (S3 or S3a-S11), S4-S12 (S3b-S11, S5-S7 (S4-S6), S5-S22 (S4-S23 or S24), S6-S8 (S5-S7), S8-S16 (S7-S18), S17-S21 (S16--S19) and S22A-S22B (S23-S24), designated according to our numbering system [1]. The designations according to the proposed uniform nomenclature [2] are described in parentheses. PMID:7353033

  18. Cross-linking of histone proteins to DNA by UV illumination of chromatin stained with Hoechst 33342.

    PubMed

    Davis, Sara K; Bardeen, Christopher J

    2003-06-01

    The photochemical effects of near-UV light on chromatin labeled with the vital DNA dye Hoechst 33342 (H33342) are studied. Several types of experiments demonstrate that illumination at both 365 and 410 nm results in significant cross-linking of proteins with the DNA. Fluorescence microscopy of dye-stained Xenopus XTC-2 nuclei shows that UV illumination has effects similar to chemical fixation by formaldehyde. At 365 nm a dose of approximately 70 J/cm2 results in 50% of the DNA being cross-linked, as measured by chloroform-sodium dodecyl sulfate extraction. At 410 nm the efficiency of cross-linking was smaller by a factor of 3. Gel electrophoresis of the cross-linked proteins shows them to be predominantly core histones. The implications of these results for experiments on live cells stained with H33342, for example, fluorescence microscopy of nuclear dynamics or cell sorting, are discussed. PMID:12870855

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

    PubMed

    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

    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

  20. Enzymatic Cross-Linking of Resilin-Based Proteins for Vascular Tissue Engineering Applications.

    PubMed

    Kim, Yeji; Gill, Emily E; Liu, Julie C

    2016-08-01

    Protein-based biomaterials have received significant attention for tissue engineering applications. For example, resilin-based protein gels have been produced with different cross-linking chemistries for applications in cartilage, cardiovascular, and vocal fold engineering. In this study, we investigate an alternative cross-linking chemistry to form resilin-based protein hydrogels and demonstrate the versatility of the gels for investigating cell response to matrix stiffness. Specifically, transglutaminase was used to cross-link proteins and resulted in gel surfaces more suitable for long-term cell attachment compared to those formed by a Mannich-type condensation reaction. Since matrix stiffness is an important determinant in modulating cell response, we first tuned matrix stiffness by varying total protein concentration. Next, we observed that matrix stiffness modulated cell spreading and endothelial differentiation of human mesenchymal stem cells. In particular, our results show that cells differentiated on our matrices, which have a stiffness similar to subendothelial layers, had statistically equivalent endothelial function compared to cells differentiated on hard glass surfaces. Thus, our protein-based matrix system is a promising tool to provide substrates favorable for long-term cell attachment and better mimics the native subendothelial environment compared to conventional hard culture substrates. PMID:27400383

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

    PubMed Central

    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

    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

  2. Cross-linked hyaluronate hydrogel prevents adhesion formation and reformation in mouse uterine horn model.

    PubMed

    Sawada, T; Tsukada, K; Hasegawa, K; Ohashi, Y; Udagawa, Y; Gomel, V

    2001-02-01

    The aim of this study was to evaluate the efficacy of cross-linked hyaluronate hydrogel (HA gel) as an adjuvant for postoperative adhesion prevention, in a mouse uterine horn model. In experiment 1 uterine horns were abrased with iodine. HA gel was applied to the injured surface before closure in the treatment group. In experiment 2, after injuring the uterine horns, three stitches were placed at equal distances around the uterine horns to appose the injured medial surfaces of the two horns during healing. HA gel was inserted between the uterine horns in the treatment group. In experiment 3 prevention of adhesion reformation was assessed. After lysis of adhesions that were induced as in experiment 2, HA gel was introduced between the serosal surfaces of apposing uterine horns. Untreated animals served as controls in each experiment. Statistical analysis was carried out using Student's t-test. The adhesion score was significantly lower in the HA gel group on the 14th day compared with controls in all the experiments: in experiment 1, 0.3 +/- 0.4 versus 1.7 +/- 1.2; in experiment 2, 0.9 +/- 1.0 versus 2.6 +/- 0.5; and in experiment 3, 1.5 +/- 0.9 versus 2.2 +/- 0.6 respectively. Cross-linked HA gel significantly reduced de-novo adhesions (P< 0.03) and adhesion reformation (P < 0.03). PMID:11157833

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

    SciTech Connect

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

    1987-08-15

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

  4. A photolithographic approach to spatially resolved cross-linked nanolayers.

    PubMed

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

    2015-03-17

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

  5. Multi-Scale Modeling of Cross-Linked Nanotube Materials

    NASA Technical Reports Server (NTRS)

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

    2005-01-01

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

  6. Gelation of Covalently Cross-Linked PEG–Heparin Hydrogels

    PubMed Central

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

    2010-01-01

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

  7. Inhibiting Hexamer Disassembly of Human UDP-Glucose Dehydrogenase by Photoactivated Amino Acid Cross-Linking.

    PubMed

    Grady, George; Thelen, Ashley; Albers, Jaleen; Ju, Tong; Guo, Jiantao; Barycki, Joseph J; Simpson, Melanie A

    2016-06-01

    The enzyme UDP-glucose dehydrogenase (UGDH) catalyzes the reaction of UDP-glucose to UDP-glucuronate through two successive NAD(+)-dependent oxidation steps. Human UGDH apoprotein is purified as a mixture of dimeric and hexameric species. Addition of substrate and cofactor stabilizes the oligomeric state to primarily the hexameric form. To determine if the dynamic conformations of hUGDH are required for catalytic activity, we used site-specific unnatural amino acid incorporation to facilitate cross-linking of monomeric subunits into predominantly obligate oligomeric species. Optimal cross-linking was achieved by encoding p-benzoyl-l-phenylalanine at position 458, normally a glutamine located within the dimer-dimer interface, and exposing the enzyme to long wavelength ultraviolet (UV) radiation in the presence of substrate and cofactor. Hexameric complexes were purified by gel filtration chromatography and found to contain significant fractions of dimer and trimer (approximately 50%) along with another 10% higher-molecular mass species. The activity of the cross-linked enzyme was reduced by almost 60% relative to that of the un-cross-linked UGDH mutant, and UV exposure had no effect on the activity of the wild-type enzyme. These results support a model for catalysis in which the ability to dissociate the dimer-dimer interface is as important for maximal enzyme function as has been previously shown for the formation of the hexamer. PMID:27198584

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

    NASA Technical Reports Server (NTRS)

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

    1982-01-01

    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.

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

    NASA Technical Reports Server (NTRS)

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

    1983-01-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1981-01-01

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

  11. Comparison of cross-linked polyethylene materials for orthopaedic applications.

    PubMed

    Collier, John P; Currier, Barbara H; Kennedy, Francis E; Currier, John H; Timmins, Graham S; Jackson, Simon K; Brewer, Robin L

    2003-09-01

    Cross-linked polyethylenes are being marketed by orthopaedic manufacturers to address the problem of osteolysis caused by polyethylene particulate wear debris. Wear testing of these cross-linked polyethylenes in hip simulators has shown dramatic reduction in wear rate compared with standard ultrahigh molecular weight polyethylene, either gamma irradiated in air or nitrogen - or ethylene oxide-sterilized. However, this reduction in wear rate is not without cost. The cross-linking processes can result in materials with lower mechanical properties than standard ultrahigh molecular weight polyethylene. To evaluate the effect of the various cross-linking processes on physical and mechanical properties of ultrahigh molecular weight polyethylene, commercially available cross-linked polyethylenes from six orthopaedic manufacturers were tested. This study was the culmination of collaboration with these manufacturers, who provided cross-linked polyethylene for this study, wear characteristics of the material they provided, and review of the physical and mechanical properties measure for their polyethylene. Cross-linked materials were evaluated as received and after an accelerated aging protocol. Free radical identity and concentration, oxidation, crystallinity, melt temperature, ultimate tensile strength, elongation at break, tensile stress at yield, and toughness are reported for each material. By comparing these physical and mechanical properties, surgeons can evaluate the trade-off that results from developing materials with substantially lower wear rates. PMID:12966304

  12. Fluorescent cross-linked supramolecular polymers constructed from a novel self-complementary AABB-type heteromultitopic monomer.

    PubMed

    Fang, Le; Hu, Yuanli; Li, Qiang; Xu, Shutao; Dhinakarank, Manivannan Kalavathi; Gong, Weitao; Ning, Guiling

    2016-04-26

    A novel AABB-type heteromultitopic monomer (), having a self-complementary perpendicular structure, could solely self-assemble to fluorescent cross-linked supramolecular polymers. Interestingly, the supramolecular gel film shows a sensitive fluorescence change on exposure to acid and base vapor, endowing this system with a potential application in gas detection. PMID:27005489

  13. Chemoselective cross-linking and functionalization of alginate via Staudinger ligation

    PubMed Central

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

    2010-01-01

    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

  14. Cross-linked carbon nanotubes buckygel actuators: an in-depth study

    NASA Astrophysics Data System (ADS)

    Gendron, David; Bubak, Grzegorz; Ceseracciu, Luca; Ansaldo, Alberto; Ricci, Davide

    2015-04-01

    Recently, materials that can convert electrical energy into mechanical work have drawn great attention. Applications in robotics, tactile or optical displays and microelectrochemical systems are currently investigated. Likewise, interest in actuators devices is increasing toward applications where low voltage and low weight properties are required. One way to achieve such prerequisites is to combine the mechanical and electronic properties of carbon nanotubes (CNTs) with the stability and conductivity of ionic liquids. Indeed, the CNTs can be dispersed in ionic liquids to form hybrid composites also named bucky gels, thanks to the non-covalent (π-π stacking and cation-π) interactions. In our previous studies, we demonstrated an improvement in actuator performance whilst using cross-linked CNTs. Indeed, our preliminary results showed an increase in the capacitance together with a faster response of the actuator. At the time, these results were explained by an actuation mechanism model. Herein, we designed new experiments in order to allow us to get a deeper insight in the effect the crosslinking process on the carbon nanotubes properties. Thus, we present a set of electromechanical and electrochemical data that shed light on the chemical modification of the CNTs, the different cross-linking strategies and also on the uses of cross-linked CNTS polymer blends. Finally, corresponding bucky gels actuators performances will also be discussed.

  15. Mitochondrial permeability transition as induced by cross-linking of the adenine nucleotide translocase.

    PubMed

    Zazueta, C; Reyes-Vivas, H; Zafra, G; Sánchez, C A; Vera, G; Chávez, E

    1998-04-01

    Mitochondrial permeability transition is caused by the opening of a transmembrane pore whose chemical nature has not been well established yet. The present work was aimed to further contribute to the knowledge of the membrane entity comprised in the formation of the non-specific channel. The increased permeability was established by analyzing the inability of rat kidney mitochondria to take up and accumulate Ca2+, as well as their failure to build up a transmembrane potential, after the cross-linking of membrane proteins by copper plus ortho-phenanthroline. To identify the cross-linked proteins, polyacrylamide gel electrophoresis was performed. The results are representative of at least three separate experiments. It is indicated that 30 microM Cu2+ induced the release of 4.3 nmol Ca2+ per mg protein. However, in the presence of 100 microM ortho-phenanthroline only 2 microM Cu2+ was required to attain the total release of the accumulated Ca2+; it should be noted that such a reaction is not inhibited by cyclosporin. The increased permeability corresponds to cross-linking of membrane proteins in which approximately 4 nmol thiol groups per mg protein appear to be involved. Such a linking process is inhibited by carboxyatractyloside. By using the fluorescent probe eosin-5-maleimide the label was found in a cross-linking 60 kDa dimer of two 30 kDa monomers. From the data presented it is concluded that copper-o-phenanthroline induces the intermolecular cross-linking of the adenine nucleotide translocase which in turn is converted to non-specific pore. PMID:9675885

  16. Improving the creep resistance and tensile property of UHMWPE sheet by radiation cross-linking and annealing

    NASA Astrophysics Data System (ADS)

    Wang, Honglong; Xu, Lu; Li, Rong; Hu, Jiangtao; Wang, Mouhua; Wu, Guozhong

    2016-08-01

    Ultra-high molecular weight polyethylene (UHMWPE) sheet was cross-linked by γ irradiation in air with a dose of up to 300 kGy at a dose rate of 5 kGy/h and further treated by post-annealing at 120 °C for 4 h in vacuum. Variations in chemical structure, thermostability, crystallinity, creep resistance, and tensile properties were investigated and compared mainly by gel content, TGA, DSC, and creep and tensile measurements. Gel content measurements indicated that cross-linking was predominant over chain scission during irradiation and post-annealing. Radiation cross-linking resulted in an obvious improvement in the creep resistance and tensile properties of UHMWPE. Through cross-linking, the operational temperature and yield strength of the irradiated and subsequently annealed UHMWPE sheet were improved by more than 100 °C and 14%, respectively, at a dose of 300 kGy. Simultaneously, Young's modulus was increased to 1413 MPa, compared with 398 MPa of pristine UHMWPE. Annealing after irradiation further improved the creep resistance and Young's modulus. Highly cross-linked UHMWPE can even be maintained at 250 °C for a long time without any obvious deformation.

  17. Redox-Responsive, Core Cross-Linked Polyester Micelles

    PubMed Central

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

    2013-01-01

    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

  18. Physically and chemically cross-linked cellulose cryogels: Structure, properties and application for controlled release.

    PubMed

    Ciolacu, Diana; Rudaz, Cyrielle; Vasilescu, Mihai; Budtova, Tatiana

    2016-10-20

    Porous cellulose matrices were prepared via cellulose dissolution in 8wt% NaOH-water, physical gelation and chemical cross-linking with epichlorohydrin (ECH), coagulation in water and lyophilisation. Cellulose and cross-linker concentration were varied. The behaviour of gels upon coagulation and the swelling of cryogels in water were analysed. An anomalous high swelling at cross-linker concentration around stoichiometric molar ratio with cellulose was observed. Cellulose cryogel morphology, crystallinity and density were studied. The influence of chemical cross-linking on cellulose swelling was explained by suggesting that ECH acts as a spacer preventing cellulose chains tight packing during coagulation. Cellulose was loaded with a model drug, procaine hydrochloride, and the kinetics of its release was investigated. PMID:27474581

  19. Copolymers from unsaturated macrolactones: toward the design of cross-linked biodegradable polyesters.

    PubMed

    van der Meulen, Inge; Li, Yingyuan; Deumens, Ronald; Joosten, Elbert A J; Koning, Cor E; Heise, Andreas

    2011-03-14

    The enzymatic synthesis of a series of random copolyesters by ring-opening polymerization of unsaturated macrolactones like globalide and ambrettolide with 1,5-dioxepan-2-one (DXO) and 4-methyl caprolactone (4MeCL) was investigated. (13)C NMR diad analysis confirmed the randomness of all copolymers irrespective of the comonomer ratios. Thermal investigation showed that incorporating the comonomers lowered the melting points of the polymers as compared with the macrolactone homopolymers. The decrease was dependent on the comonomer ratio. The unsaturated copolymers were thermally cross-linked using dicumyl peroxide, which resulted in completely amorphous insoluble networks. It was found that 10% incorporation of the unsaturated macolactone was sufficient to obtain a gel content of 95 wt %. Preliminary degradation tests confirm that the cross-linked copolymers are enzymatically degradable and that the incorporation of hydrophilic comonomers like DXO enhances degradation. PMID:21319813

  20. Photo-cross-linked hydrogels from thermoresponsive PEGMEMA-PPGMA-EGDMA copolymers containing multiple methacrylate groups: mechanical property, swelling, protein release, and cytotoxicity.

    PubMed

    Tai, Hongyun; Howard, Daniel; Takae, Seiji; Wang, Wenxin; Vermonden, Tina; Hennink, Wim E; Stayton, Patrick S; Hoffman, Allan S; Endruweit, Andreas; Alexander, Cameron; Howdle, Steven M; Shakesheff, Kevin M

    2009-10-12

    Photo-cross-linked hydrogels from thermoresponsive polymers can be used as advanced injectable biomaterials via a combination of physical interaction (in situ thermal gelation) and covalent cross-links (in situ photopolymerization). This can lead to gels with significantly enhanced mechanical properties compared to non-photo-cross-linked thermoresponsive hydrogels. Moreover, the thermally phase-separated gels have attractive advantages over non-thermoresponsive gels because thermal gelation upon injection allows easy handling and holds the shape of the gels prior to photopolymerization. In this study, water-soluble thermoresponsive copolymers containing multiple methacrylate groups were synthesized via one-step deactivation enhanced atom transfer radical polymerization (ATRP) of poly(ethylene glycol) methyl ether methacrylate (PEGMEMA, M(n) = 475), poly(propylene glycol) methacrylate (PPGMA, M(n) = 375), and ethylene glycol dimethacrylate (EGDMA) and were used to form covalent cross-linked hydrogels by photopolymerization. The cross-linking density was found to have a significant influence on the mechanical and swelling properties of the photo-cross-linked gels. Release studies using lysozyme as a model protein demonstrated a sustained release profile that varied dependent on the copolymer composition, cross-linking density, and the temperature. Mouse C2C12 myoblast cells were cultured in the presence of the copolymers at concentrations up to 1 mg/mL. It was found that the majority of the cells remained viable, as assessed by Alamar Blue, lactate dehydrogenase (LDH), and Live/Dead cell viability/cytotoxicity assays. These studies demonstrate that thermoresponsive PEGMEMA-PPGMA-EGDMA copolymers offer potential as in situ photopolymerizable materials for tissue engineering and drug delivery applications through a combination of facile synthesis, enhanced mechanical properties, tunable cross-linking density, low cytotoxicity, and accessible functionality for further

  1. Hydrogels of collagen/chondroitin sulfate/hyaluronan interpenetrating polymer network for cartilage tissue engineering.

    PubMed

    Guo, Yan; Yuan, Tun; Xiao, Zhanwen; Tang, Pingping; Xiao, Yumei; Fan, Yujiang; Zhang, Xingdong

    2012-09-01

    The network structure of a three-dimensional hydrogel scaffold dominates its performance such as mechanical strength, mass transport capacity, degradation rate and subsequent cellular behavior. The hydrogels scaffolds with interpenetrating polymeric network (IPN) structure have an advantage over the individual component gels and could simulate partly the structure of native extracellular matrix of cartilage tissue. In this study, to develop perfect cartilage tissue engineering scaffolds, IPN hydrogels of collagen/chondroitin sulfate/hyaluronan were prepared via two simultaneous processes of collagen self-assembly and cross linking polymerization of chondroitin sulfate-methacrylate (CSMA) and hyaluronic acid-methacrylate. The degradation rate, swelling performance and compressive modulus of IPN hydrogels could be adjusted by varying the degree of methacrylation of CSMA. The results of proliferation and fluorescence staining of rabbit articular chondrocytes in vitro culture demonstrated that the IPN hydrogels possessed good cytocompatibility. Furthermore, the IPN hydrogels could upregulate cartilage-specific gene expression and promote the chondrocytes secreting glycosaminoglycan and collagen II. These results suggested that IPN hydrogels might serve as promising hydrogel scaffolds for cartilage tissue engineering. PMID:22639153

  2. Chemical Cross-linking of Neighboring Thylakoid Membrane Polypeptides 12

    PubMed Central

    Novak-Hofer, Ilse; Siegenthaler, Paul-Andre

    1978-01-01

    Cross-linking between protein components of whole spinach (Spinacia oleracea var. Nobel) thylakoids and of photosystem I- and II-enriched thylakoid fractions has been produced by reaction with the bifunctional imidoester dimethyl-3,3′-dithiobispropionimidate dihydrochloride as well as by the oxidation of intrinsic sulfydryl groups with an orthophenanthrolinecupric ion complex. The mixture of membrane proteins and their cross-linked products has been analyzed by two-dimensional sodium dodecyl sulfate electrophoresis, with a reductive cleavage step of the cross-linkages before the second dimension. Cross-linked aggregates up to a molecular weight of about 130 kilodaltons (kD) were analyzed, and it was inferred that the polypeptides appearing together in the same aggregates were neighbors within the membrane. In thylakoids as well as in isolated photosystem fractions, oligomers were formed by cross-linking polypeptides of the 60 to 90 kD range, among them the polypeptides of the chlorophyll-protein complex I. Polypeptides of 46, 19, and 12 kD were cross-linked to these complexes. Polypeptides of 25 and 22 kD, which are related to the chlorophyll-protein complex II, were cross-linked in thylakoids as well as in photosystem II fractions, suggesting that in the membrane these molecules are close together. In photosystem II fractions an oligomer having a molecular weight of about 60 kD was formed by cross-linking several polypeptides of different molecular weights: 40, 25, and 22 kD. Our cross-linking experiments show that protein interactions in the thylakoid membrane occurred mainly among the polypeptides of the two chlorophyll-protein complexes, thus suggesting an oligomeric nature of these apoproteins. ImagesFig. 1Fig. 2Fig. 3 PMID:16660519

  3. Large Scale Chemical Cross-linking Mass Spectrometry Perspectives

    PubMed Central

    Zybailov, Boris L.; Glazko, Galina V.; Jaiswal, Mihir; Raney, Kevin D.

    2014-01-01

    The spectacular heterogeneity of a complex protein mixture from biological samples becomes even more difficult to tackle when one’s attention is shifted towards different protein complex topologies, transient interactions, or localization of PPIs. Meticulous protein-by-protein affinity pull-downs and yeast-two-hybrid screens are the two approaches currently used to decipher proteome-wide interaction networks. Another method is to employ chemical cross-linking, which gives not only identities of interactors, but could also provide information on the sites of interactions and interaction interfaces. Despite significant advances in mass spectrometry instrumentation over the last decade, mapping Protein-Protein Interactions (PPIs) using chemical cross-linking remains time consuming and requires substantial expertise, even in the simplest of systems. While robust methodologies and software exist for the analysis of binary PPIs and also for the single protein structure refinement using cross-linking-derived constraints, undertaking a proteome-wide cross-linking study is highly complex. Difficulties include i) identifying cross-linkers of the right length and selectivity that could capture interactions of interest; ii) enrichment of the cross-linked species; iii) identification and validation of the cross-linked peptides and cross-linked sites. In this review we examine existing literature aimed at the large-scale protein cross-linking and discuss possible paths for improvement. We also discuss short-length cross-linkers of broad specificity such as formaldehyde and diazirine-based photo-cross-linkers. These cross-linkers could potentially capture many types of interactions, without strict requirement for a particular amino-acid to be present at a given protein-protein interface. How these shortlength, broad specificity cross-linkers be applied to proteome-wide studies? We will suggest specific advances in methodology, instrumentation and software that are needed to

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

    PubMed Central

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

    2012-01-01

    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

  5. Photocontrolled Cargo Release from Dual Cross-Linked Polymer Particles.

    PubMed

    Tan, Shereen; Cui, Jiwei; Fu, Qiang; Nam, Eunhyung; Ladewig, Katharina; Ren, Jing M; Wong, Edgar H H; Caruso, Frank; Blencowe, Anton; Qiao, Greg G

    2016-03-01

    Burst release of a payload from polymeric particles upon photoirradiation was engineered by altering the cross-linking density. This was achieved via a dual cross-linking concept whereby noncovalent cross-linking was provided by cyclodextrin host-guest interactions, and irreversible covalent cross-linking was mediated by continuous assembly of polymers (CAP). The dual cross-linked particles (DCPs) were efficiently infiltrated (∼80-93%) by the biomacromolecule dextran (molecular weight up to 500 kDa) to provide high loadings (70-75%). Upon short exposure (5 s) to UV light, the noncovalent cross-links were disrupted resulting in increased permeability and burst release of the cargo (50 mol % within 1 s) as visualized by time-lapse fluorescence microscopy. As sunlight contains UV light at low intensities, the particles can potentially be incorporated into systems used in agriculture, environmental control, and food packaging, whereby sunlight could control the release of nutrients and antimicrobial agents. PMID:26862769

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

    NASA Technical Reports Server (NTRS)

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

    1996-01-01

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

  7. Structural and mechanical properties of UV-photo-cross-linked poly(N-vinyl-2-pyrrolidone) hydrogels.

    PubMed

    D'Errico, Gerardino; De Lellis, Marco; Mangiapia, Gaetano; Tedeschi, Annamaria; Ortona, Ornella; Fusco, Sabato; Borzacchiello, Assunta; Ambrosio, Luigi

    2008-01-01

    Biocompatible poly( N-vinyl-2-pyrrolidone) (PVP) hydrogels have been produced by UV irradiation of aqueous polymer mixtures, using a high-pressure mercury lamp. The resulting materials have been characterized by a combination of experimental techniques, including rheology, small-angle neutron scattering (SANS), electron paramagnetic resonance (EPR), and pulsed gradient spin-echo nuclear magnetic resonance (PGSE-NMR), to put in evidence the relationship between the microstructural properties and the macrofunctional behavior of the gels. Viscoelastic measurements showed that UV photo-cross-linked PVP hydrogels present a strong gel mechanical behavior and viscoelastic moduli values similar to those of biological gels. The average distance between the cross-linking points of the polymer network was estimated from the hydrogels elastic modulus. However, SANS measurements showed that the network microstructure is highly inhomogeneous, presenting polymer-rich regions more densely cross-linked, surrounded by a water-rich environment. EPR and PGSE-NMR data further support the existence of these water-rich domains. Inclusion of a third component, such as glycerol, in the PVP aqueous mixture to be irradiated has been also investigated. A small amount of glycerol (<3% w/w) can be added keeping satisfactory properties of the hydrogel, while higher amounts significantly affect the cross-linking process. PMID:18163572

  8. Elasticity, biodegradability and cell adhesive properties of chitosan/hyaluronan multilayer films

    NASA Astrophysics Data System (ADS)

    Schneider, Aurore; Richert, Ludovic; Francius, Gregory; Voegel, Jean-Claude; Picart, Catherine

    2007-03-01

    In the bioengineering field, a recent and promising approach to modifying biomaterial surfaces is the layer-by-layer (LbL) technique used to build thin polyelectrolyte multilayer films. In this work, we focused on polyelectrolyte multilayer films made of two polysaccharides, chitosan (CHI) and hyaluronan (HA), and on the control of their physico-chemical and cell adhesive properties by chemical cross-linking. CHI/HA films were cross-linked using a water soluble carbodiimide and observed by confocal laser scanning microscopy (CLSM) with a fluorescently labeled CHI. Film thicknesses were similar for native and cross-linked films. The film nanometer roughness was measured by atomic force microscopy and was found to be higher for cross-linked films. Cross-linking the films also leads to a drastic change in film stiffness. The elastic modulus of the films (Young's modulus) as measured by AFM nano-indentation was about tenfold increased for cross-linked films as compared to native ones. From a biological point of view, cross-liked films are more resistant to enzymatic degradation by hyaluronidase. Furthermore, the increase in film stiffness has a favorable effect on the adhesion and spreading of chondrosarcoma cells. Thus, the CHI/HA cross-linked films could be used for various applications due to their adhesive properties and to their mechanical properties (including stability in enzymatic media).

  9. Coarse-Grained Molecular Dynamics Study of the Curing and Properties of Highly Cross-Linked Epoxy Polymers.

    PubMed

    Aramoon, Amin; Breitzman, Timothy D; Woodward, Christopher; El-Awady, Jaafar A

    2016-09-01

    In this work, a coarse-grained model is developed for highly cross-linked bisphenol A diglycidyl ether epoxy resin with diaminobutane hardener. In this model, all conformationally relevant coarse-grained degrees of freedom are accounted for by sampling over the free-energy surfaces of the atomic structures using quantum mechanical simulations. The interaction potentials between nonbonded coarse-grained particles are optimized to accurately predict the experimentally measured density and glass-transition temperature of the system. In addition, a new curing algorithm is also developed to model the creation of highly cross-linked epoxy networks. In this algorithm, to create a highly cross-linked network, the reactants are redistributed from regions with an excessive number of reactive molecules to regions with a lower number of reactants to increase the chances of cross-linking. This new algorithm also dynamically controls the rate of cross-linking at each local region to ensure uniformity of the resulting network. The curing simulation conducted using this algorithm is able to develop polymeric networks having a higher average degree of cross-linking, which is more uniform throughout the simulation cell as compared to that in the networks cured using other curing algorithms. The predicted gel point from the current curing algorithm is in the acceptable theoretical and experimental range of measured values. Also, the resulting cross-linked microstructure shows a volume shrinkage of 5%, which is close to the experimentally measured volume shrinkage of the cured epoxy. Finally, the thermal expansion coefficients of materials in the glassy and rubbery states show good agreement with the experimental values. PMID:27504803

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

    PubMed

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

    2014-10-01

    Viscoelasticity is a useful parameter for characterizing the intrinsic properties of the cross-linked polyacrylate hydrogel used in cataplasm bases. The aim of this study was to investigate the effects of various formulation parameters on the rheological characteristics of polyacrylate hydrogel. The hydrogel layers were formed using a partially neutralized polyacrylate (Viscomate(™)), which contained acrylic acid and sodium acrylate in different copolymerization ratios, as the cross-linked gel 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

  11. Enzymatically Cross-Linked Bovine Lactoferrin as Injectable Hydrogel for Cell Delivery

    PubMed Central

    Amini, Ashley A.; Kan, Ho-Man; Cui, Zhanwu; Maye, Peter

    2014-01-01

    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

  12. Cross-linking of Ordered Pluronic/Ionic Liquid Blends for Solid Polymer Electrolytes

    NASA Astrophysics Data System (ADS)

    Miranda, Daniel; Versek, Craig; Tuominen, Mark; Watkins, James; Russell, Thomas

    2012-02-01

    Ion gels were fabricated by cross-linking PPO-PEO-PPO triblock copolymers swollen in a room temperature ionic liquid (IL). The copolymers are modified by esterification to replace the terminal hydroxyl endgroups with methacrylate endgroups. This allows the copolymer/IL blends to be cross-linked by a UV cure, forming a gel. The strong interaction of the IL with the PEO block suppresses PEO crystallization which is necessary for good ion conduction. In addition, the interaction between the IL and PEO is strongly selective for PEO, strengthening microphase separation. Despite this, the low molecular weight copolymers remain disordered in the melt even when blended with the IL. However, high molecular weight copolymers are capable of microphase separating into highly ordered block copolymer morphologies. This difference allows the effect of microphase separation on ion transport to be studied. The effect of block copolymer composition is also studied, by varying the PEO fraction of the copolymer. The resultant gels show high ionic conductivity and solid-like behavior, indicating that these materials may be effective as solid polymer electrolytes.

  13. Textural and cargo release attributes of trisodium citrate cross-linked starch hydrogel.

    PubMed

    Abhari, Negar; Madadlou, Ashkan; Dini, Ali; Hosseini Naveh, Ozra

    2017-01-01

    An alkaline starch suspension was charged with citric acid and incubated for different durations (0, 8.5 or 17h). The suspension was then supplemented with caffeine and gelatinized to fabricate hydrogels which were subsequently stored for varying periods (0, 24 or 48h). Charging of the well-dissolved alkaline starch suspension with citric acid decreased at first both the flow index and consistency coefficient (K); however, starch cross-linking over time by the generated trisodium citrate increased the K value. The latter also inhibited gel syneresis and increased its water-holding capacity. Trisodium citrate did not nonetheless influence the gel hardness except for the sample incubated for maximum duration and stored for the longest period. The amount of the caffeine released from hydrogel decreased by citrate cross-linking and was higher at neutral pH than pH 2.0. Fourier-transform infra-red spectroscopy suggested that caffeine was enclosed within the gel network via non-covalent interactions. PMID:27507442

  14. Thermally Reversible Physically Cross-Linked Hybrid Network Hydrogels Formed by Thermosensitive Hairy Nanoparticles.

    PubMed

    Wright, Roger A E; Henn, Daniel M; Zhao, Bin

    2016-08-18

    This Article reports on thermally induced reversible formation of physically cross-linked, three-dimensional network hydrogels from aqueous dispersions of thermosensitive diblock copolymer brush-grafted silica nanoparticles (hairy NPs). The hairy NPs consisted of a silica core, a water-soluble polyelectrolyte inner block of poly(2-(methacryloyloxy)ethyltrimethylammonium iodide), and a thermosensitive poly(methoxydi(ethylene glycol) methacrylate) (PDEGMMA) outer block synthesized by sequential surface-initiated atom transfer radical polymerizations and postpolymerization quaternization of tertiary amine moieties. Moderately concentrated dispersions of these hairy nanoparticles in water underwent thermally induced reversible transitions between flowing liquids to self-supporting gels upon heating. The gelation was driven by the lower critical solution temperature (LCST) transition of the PDEGMMA outer block, which upon heating self-associated into hydrophobic domains acting as physical cross-linking points for the gel network. Rheological studies showed that the sol-gel transition temperature decreased with increasing hairy NP concentration, and the gelation was achieved at concentrations as low as 3 wt %. PMID:27455167

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

    PubMed

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

    2014-11-01

    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

  16. Photo-induced cross-linking of unmodified proteins (PICUP) applied to amyloidogenic peptides.

    PubMed

    Rahimi, Farid; Maiti, Panchanan; Bitan, Gal

    2009-01-01

    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 oligomerization(1). Mechanistically, PICUP involves photo-oxidation of Ru(2+) in a tris(bipyridyl)Ru(II) complex (RuBpy) to Ru(3+) by irradiation with visible light in the presence of an electron acceptor. Ru(3+) is a strong one-electron oxidizer capable of abstracting an electron from a neighboring protein molecule, generating a protein radical(1,2). 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

  17. Self-Consistent Field Approach for Cross-Linked Copolymer Materials

    NASA Astrophysics Data System (ADS)

    Schmid, Friederike

    2013-07-01

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

  18. Collagen/elastin hydrogels cross-linked by squaric acid.

    PubMed

    Skopinska-Wisniewska, J; Kuderko, J; Bajek, A; Maj, M; Sionkowska, A; Ziegler-Borowska, M

    2016-03-01

    Hydrogels based on collagen and elastin are very valuable materials for medicine and tissue engineering. They are biocompatible; however their mechanical properties and resistance for enzymatic degradation need to be improved by cross-linking. Up to this point many reagents have been tested but more secure reactants are still sought. Squaric acid (SqAc), 3,4-dihydroxy 3-cyclobutene 1,2-dione, is a strong, cyclic acid, which reacts easily with amine groups. The properties of hydrogels based on collagen/elastin mixtures (95/5, 90/10) containing 5%, 10% and 20% of SqAc and neutralized via dialysis against deionized water were tested. Cross-linked, 3-D, transparent hydrogels were created. The cross-linked materials are stiffer and more resistant to enzymatic degradation than those that are unmodified. The pore size, swelling ability and surface polarity are reduced due to 5% and 10% of SqAc addition. At the same time, the cellular response is not significantly affected by the cross-linking. Therefore, squaric acid would be regarded as a safe, effective cross-linking agent. PMID:26706512

  19. Spectroscopic characterization of collagen cross-links in bone

    NASA Technical Reports Server (NTRS)

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

    2001-01-01

    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.

  20. Hyaluronan and Stone Disease

    NASA Astrophysics Data System (ADS)

    Asselman, Marino

    2008-09-01

    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.

  1. Photoaffinity labeling and photoaffinity cross-linking of phosphofructokinase-1 from Saccharomyces cerevisiae by 8-azidoadeninenucleotides.

    PubMed

    Knoche, M; Mönnich, K; Schäfer, H J; Kopperschläger, G

    2001-01-15

    Phosphofructokinase-1 from Saccharomyces cerevisiae is composed of four alpha- and four beta-subunits, each of them carrying catalytic and regulatory bindings sites for MgATP. In this paper, various photoaffinity labels, such as 8-azidoadenosine 5'-triphosphate, 8-azido-1,N6-ethenoadenosine 5'-triphosphate, and 8-N3-3'(2')-O-biotinyl-8-azidoadenosine 5'-triphosphate have been used to study their interaction with the enzyme in the dark and during irradiation. All nucleotidetriphosphates function as phosphate donor forming fructose 1,6-bisphosphate from fructose 6-phosphate. However, the kinetic analysis revealed distinctly differences between them. Photolabeling causes a decrease in enzyme activity to a similar extent, and ATP acts as competitive effector to inactivation. Three bifunctional diazidodiadeninedinucleotides (8-diN3AP4A, monoepsilon-8-diN3AP4A, and diepsilon-8-diN3AP4A) were applied for studying the spatial arrangement of the nucleotide binding sites. No cross-linking of the subunits was obtained by irradiation of the enzyme with 8-diN3AP4A. Photolabeling with diepsilon-8-diN3AP4A resulted in the formation of two alpha-beta cross-links with different mobilities in the SDS-polyacrylamide gel electrophoresis, while monoepsilon-8-diN3AP4A yielded only one alpha-beta cross-link. Because an interfacial location of the catalytic sites between two subunits is less likely, we suggest that the formation of cross-linked subunits may be the result of specific interactions of the bifunctional photolabels with regulatory sites at the interface of both subunits. PMID:11368011

  2. Biotinylated hyaluronan: a versatile and highly sensitive probe capable of detecting nanogram levels of hyaluronan binding proteins (hyaladherins) on electroblots by a novel affinity detection procedure.

    PubMed

    Melrose, J; Numata, Y; Ghosh, P

    1996-01-01

    Hyaluronan influences cellular proliferation and migration in developing, regenerating and remodelling tissues and in tissues undergoing malignant tumour-cell invasion. The widespread occurrence of hyaluronan-binding proteins indicates that the recognition of hyaluronan is important to tissue organisation and the control of cellular behaviour. A number of extracellular matrix and cellular proteins, which have been termed the hyaladherins, have specific affinities for hyaluronan. These include cartilage link-protein, hyaluronectin, neurocan, versican and aggrecan, which all bind to HA within the extracellular matrix. Cellular receptors for hyaluronan such as CD44 and RHAMM (receptor for hyaluronate-mediated motility) have also been identified. In the present study biotinylated hyaluronan (bHA) was prepared by reacting adipic dihydrazide with a 170 kDa hyaluronan sample using the bifunctional reagent 1-ethyl-3-[3-(dimethylamino) propyl] carbodiimide. The resultant free amine moeity of the hydrazido-hyaluronan was then reacted with biotin succinimidyl ester (sulfo-NHS-biotin) to prepare the bHA. After 4-20% gradient sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and electroblotting to nitrocellulose membranes, bHA and avidin alkaline phosphatase conjugate could be used in conjunction with nitroblue tetrazolium/5-bromo-4-chloro-3-indolyl phosphate substrates to specifically visualise with high sensitivity (> or = 2 ng), bovine nasal cartilage link-protein, aggrecan hyaluronan binding region, and human fibroblast hyaluronan receptors such as CD-44. Conventional Western blotting using specific monoclonal antibodies to these proteins was also used to confirm the identities of these proteins. PMID:8907541

  3. Emergence of large chiroptical responses by ligand exchange cross-linking of monolayer-protected gold clusters with chiral dithiol.

    PubMed

    Yao, Hiroshi; Yaomura, Shota

    2013-05-28

    We here present a study of cross-linking chemistry of optically inactive monothiol-protected gold clusters by chiral bidentate dithiol with two stereogenic centers, (2R,3R)-1,4-dimercapto-2,3-butanediol (L-dithiothreitol; L-DTT), and explore the impacts of the cross-linking on their chiroptical responses. The pristine protective ligand is racemic penicillamine (rac-Pen), and the products of the ligand exchange reactions include clusters containing both rac-Pen and L-DTT (partial exchange). Electrophoresis using polyacrylamide gel with a very low gel concentration (3%) can make the products separable into two components, each of which has the similar mean core diameter of 0.78 and 0.83 nm, so the difference in the relative mobility is mainly ascribed to the size of the cluster assembly. In addition, very large optical activity with the maximum anisotropy factors of about 1.0 × 10(-3) is found for the assemblies. In comparison with chiral 1,3-dithiol protection incapable of cross-linking between gold clusters, we propose that the observed optical activity is due to surface intrinsic handedness caused by a cyclic cross-linking with at least two L-DTT molecules. PMID:23635318

  4. Cross-Linked Nanotube Materials with Variable Stiffness Tethers

    NASA Technical Reports Server (NTRS)

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

    2004-01-01

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

  5. Molecular mechanisms in deformation of cross-linked hydrogel nanocomposite.

    PubMed

    Mathesan, Santhosh; Rath, Amrita; Ghosh, Pijush

    2016-02-01

    The self-folding behavior in response to external stimuli observed in hydrogels is potentially used in biomedical applications. However, the use of hydrogels is limited because of its reduced mechanical properties. These properties are enhanced when the hydrogels are cross-linked and reinforced with nanoparticles. In this work, molecular dynamics (MD) simulation is applied to perform uniaxial tension and pull out tests to understand the mechanism contributing towards the enhanced mechanical properties. Also, nanomechanical characterization is performed using quasi static nanoindentation experiments to determine the Young's modulus of hydrogels in the presence of nanoparticles. The stress-strain responses for chitosan (CS), chitosan reinforced with hydroxyapatite (HAP) and cross-linked chitosan are obtained from uniaxial tension test. It is observed that the Young's modulus and maximum stress increase as the HAP content increases and also with cross-linking process. Load displacement plot from pullout test is compared for uncross-linked and cross-linked chitosan chains on hydroxyapatite surface. MD simulation reveals that the variation in the dihedral conformation of chitosan chains and the evolution of internal structural variables are associated with mechanical properties. Additional results reveal that the formation of hydrogen bonds and electrostatic interactions is responsible for the above variations in different systems. PMID:26652360

  6. 21 CFR 177.1211 - Cross-linked polyacrylate copolymers.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... weight of aqueous sodium chloride solution at 20 °C for 24 hours. The low molecular weight extractives... applied mass). The solvent used shall be at least 60 milliliters aqueous sodium chloride solution per gram... polyacrylate copolymers consist of: (1) The grafted copolymer of cross-linked sodium polyacrylate identified...

  7. 21 CFR 177.1211 - Cross-linked polyacrylate copolymers.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... weight of aqueous sodium chloride solution at 20 °C for 24 hours. The low molecular weight extractives... applied mass). The solvent used shall be at least 60 milliliters aqueous sodium chloride solution per gram... polyacrylate copolymers consist of: (1) The grafted copolymer of cross-linked sodium polyacrylate identified...

  8. 21 CFR 177.1211 - Cross-linked polyacrylate copolymers.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... weight of aqueous sodium chloride solution at 20 °C for 24 hours. The low molecular weight extractives... applied mass). The solvent used shall be at least 60 milliliters aqueous sodium chloride solution per gram... polyacrylate copolymers consist of: (1) The grafted copolymer of cross-linked sodium polyacrylate identified...

  9. 21 CFR 177.1211 - Cross-linked polyacrylate copolymers.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ...). The solvent used shall be at least 60 milliliters aqueous sodium chloride solution per gram of... grafted copolymer of cross-linked sodium polyacrylate identified as 2-propenoic acid, polymers with N,N-di-2-propenyl-2-propen-1-amine and hydrolyzed polyvinyl acetate, sodium salts, graft (CAS Reg....

  10. 21 CFR 177.1211 - Cross-linked polyacrylate copolymers.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... weight of aqueous sodium chloride solution at 20 °C for 24 hours. The low molecular weight extractives... applied mass). The solvent used shall be at least 60 milliliters aqueous sodium chloride solution per gram... polyacrylate copolymers consist of: (1) The grafted copolymer of cross-linked sodium polyacrylate identified...

  11. Femtosecond laser collagen cross-linking without traditional photosensitizers

    NASA Astrophysics Data System (ADS)

    Guo, Yizang; Wang, Chao; Celi, Nicola; Vukelic, Sinisa

    2015-03-01

    Collagen cross-linking in cornea has the capability of enhancing its mechanical properties and thereby providing an alternative treatment for eye diseases such as keratoconus. Currently, riboflavin assisted UVA light irradiation is a method of choice for cross-link induction in eyes. However, ultrafast pulsed laser interactions may be a powerful alternative enabling in-depth treatment while simultaneously diminishing harmful side effects such as, keratocyte apoptosis. In this study, femtosecond laser is utilized for treatment of bovine cornea slices. It is hypothesized that nonlinear absorption of femtosecond laser pulses plays a major role in the maturation of immature cross-links and the promotion of their growth. Targeted irradiation with tightly focused laser pulses allows for the absence of a photosensitizing agent. Inflation test was conducted on half treated porcine cornea to identify the changes of mechanical properties due to laser treatment. Raman spectroscopy was utilized to study subtle changes in the chemical composition of treated cornea. The effects of treatment are analyzed by observing shifts in Amide I and Amide III bands, which suggest deformation of the collagen structure in cornea due to presence of newly formed cross-links.

  12. 21 CFR 177.2420 - Polyester resins, cross-linked.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 21 Food and Drugs 3 2012-04-01 2012-04-01 false Polyester resins, cross-linked. 177.2420 Section 177.2420 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) FOOD FOR HUMAN CONSUMPTION (CONTINUED) INDIRECT FOOD ADDITIVES: POLYMERS Substances for Use Only as Components of Articles Intended for...

  13. 21 CFR 177.2420 - Polyester resins, cross-linked.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 3 2010-04-01 2009-04-01 true Polyester resins, cross-linked. 177.2420 Section 177.2420 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) FOOD FOR HUMAN CONSUMPTION (CONTINUED) INDIRECT FOOD ADDITIVES: POLYMERS Substances for Use Only as Components of Articles Intended for...

  14. 21 CFR 177.2420 - Polyester resins, cross-linked.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 21 Food and Drugs 3 2014-04-01 2014-04-01 false Polyester resins, cross-linked. 177.2420 Section 177.2420 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) INDIRECT FOOD ADDITIVES: POLYMERS Substances for Use Only as Components of Articles Intended for Repeated Use § 177.2420 Polyester...

  15. Viscoelastic Nanomechanics of Ionically Cross-linked Polyelectrolyte Networks

    NASA Astrophysics Data System (ADS)

    Han, Biao; Lee, Daeyeon; Han, Lin

    2015-03-01

    Understanding the mechanics of ionic polyelectrolyte networks is critical for applications where nm-to-um mechanics is the key to success. This study aims to reveal the roles of ionic cross-links and fixed charges in the viscoelasticity of layer-by-layer poly(allylamine hydrochloride)/poly(acrylic acid) microfilms, PAH/PAA, a complex held by pH-sensitive amine-carboxyl links. AFM-nanoindentation and force relaxation (tip R =12.5um) was performed at ionic strength(IS) =0.01-1.0M, pH =5.5-2.0 (pKa of PAA =2.3). When pH changes from 5.5 to 2.0, the films swell for 4x from densely linked, net neutral state to loosely linked, positively charged one. A >100x reduction in indentation modulus was observed at all IS, suggesting the dominance of decrease in cross-link density. In most states, more than 90% force relaxation was observed, where cross-link breaking/reformation likely dominates viscoelasticity. However, at pH =2.5 and IS =0.01M, when electrical double layer repulsion is important (Debye length =3nm), relaxation was about 60%, highlighting the contribution of fixed charges. In summary, this study revealed unique viscoelastic behaviors of PAH/PAA due to the pH- and IS-dependent cross-link and charge densities.

  16. Load transfer mechanisms in cross-linked DWNT fibers

    NASA Astrophysics Data System (ADS)

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

    2011-03-01

    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.

  17. Glutaraldehyde-cross-linked meniscal allografts: mechanical properties.

    PubMed

    Wisnewski, P J; Powers, D L; Kennedy, J M

    1988-01-01

    Removal of a severely damaged medial meniscus has been shown to lead to degradation of the articular cartilage and formation of degenerative arthritis. To counter this degenerative effect, meniscal prostheses, including glutaraldehyde-cross-linked allografts, have been evaluated in dogs. The purpose of this research was to quantify the mechanical properties of both fresh and glutaraldehyde-cross-linked canine medial menisci. Mechanical properties quantified were tensile strength, tensile modulus, and compressive stiffness. In addition, water content of compressive test samples was measured. Analysis of variance showed significantly lower tensile strength and tensile modulus and significantly higher compressive stiffness for the glutaraldehyde-cross-linked menisci, as compared to fresh specimens. Measurement of the weight percentage of water in fresh and cross-linked samples revealed no significant differences in water content. When implanted into a joint, the increased compressive stiffness could increase the peripheral tensile load. Due to the decreased tensile strength in this region, the prosthetic meniscus could be susceptible to peripheral tears. PMID:3155295

  18. Specific covalent immobilization of proteins through dityrosine cross-links.

    PubMed

    Endrizzi, Betsy J; Huang, Gang; Kiser, Patrick F; Stewart, Russell J

    2006-12-19

    Dityrosine cross-links are widely observed in nature in structural proteins such as elastin and silk. Natural oxidative cross-linking between tyrosine residues is catalyzed by a diverse group of metalloenzymes. Dityrosine formation is also catalyzed in vitro by metal-peptide complexes such as Gly-Gly-His-Ni(II). On the basis of these observations, a system was developed to specifically and covalently surface immobilize proteins through dityrosine cross-links. Methacrylate monomers of the catalytic peptide Gly-Gly-His-Tyr-OH (GGHY) and the Ni(II)-chelating group nitrilotriacetic acid (NTA) were copolymerized with acrylamide into microbeads. Green fluorescent protein (GFP), as a model protein, was genetically tagged with a tyrosine-modified His6 peptide on its carboxy terminus. GFP-YGH6, specifically associated with the NTA-Ni(II) groups, was covalently coupled to the bead surface through dityrosine bond formation catalyzed by the colocalized GGHY-Ni(II) complex. After extensive washing with EDTA to disrupt metal coordination bonds, we observed that up to 75% of the initially bound GFP-YGH6 remained covalently bound to the bead while retaining its structure and activity. Dityrosine cross-linking was confirmed by quenching the reaction with free tyrosine. The method may find particular utility in the construction and optimization of protein microarrays. PMID:17154619

  19. Spectral Library Searching To Identify Cross-Linked Peptides.

    PubMed

    Schweppe, Devin K; Chavez, Juan D; Navare, Arti T; Wu, Xia; Ruiz, Bianca; Eng, Jimmy K; Lam, Henry; Bruce, James E

    2016-05-01

    Methods harnessing protein cross-linking and mass spectrometry (XL-MS) offer high-throughput means to identify protein-protein interactions (PPIs) and structural interfaces of protein complexes. Yet, specialized data dependent methods and search algorithms are often required to confidently assign peptide identifications to spectra. To improve the efficiency of matching high confidence spectra, we developed a spectral library based approach to search cross-linked peptide data derived from Protein Interaction Reporter (PIR) methods using the spectral library search algorithm, SpectraST. Spectral library matching of cross-linked peptide data from query spectra increased the absolute number of confident peptide relationships matched to spectra and thereby the number of PPIs identified. By matching library spectra from bona fide, previously established PIR-cross-linked peptide relationships, spectral library searching reduces the need for continued, complex mass spectrometric methods to identify peptide relationships, increases coverage of relationship identifications, and improves the accessibility of XL-MS technologies. PMID:27089058

  20. Simple, High-Yield Syntheses of DNA Duplexes Containing Interstrand DNA-DNA Cross-Links Between an N(4) -Aminocytidine Residue and an Abasic Site.

    PubMed

    Gamboa Varela, Jacqueline; Gates, Kent S

    2016-01-01

    The protocol describes the preparation and purification of interstrand DNA-DNA cross-links derived from the reaction of an N(4) -aminocytidine residue with an abasic site in duplex DNA. The procedures employ inexpensive, commercially available chemicals and enzymes to carry out post-synthetic modification of commercially available oligodeoxynucleotides. The yield of cross-linked duplex is typically better than 90%. If purification is required, the cross-linked duplex can be readily separated from single-stranded DNA starting materials by denaturing gel electrophoresis. The resulting covalent hydrazone-based cross-links are stable under physiologically relevant conditions and may be useful for biophysical studies, structural analyses, DNA repair studies, and materials science applications. © 2016 by John Wiley & Sons, Inc. PMID:27248783

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

    SciTech Connect

    Sheikh, S.P.; Williams, J.A. )

    1990-05-15

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

  2. Processing of targeted psoralen cross-links in Xenopus oocytes.

    PubMed Central

    Segal, D J; Faruqi, A F; Glazer, P M; Carroll, D

    1997-01-01

    Psoralen cross-links have been shown to be both mutagenic and recombinagenic in bacterial, yeast, and mammalian cells. Double-strand breaks (DSBs) have been implicated as intermediates in the removal of psoralen cross-links. Recent work has suggested that site-specific mutagenesis and recombination might be achieved through the use of targeted psoralen adducts. The fate of plasmids containing psoralen adducts was evaluated in Xenopus oocytes, an experimental system that has well-characterized recombination capabilities and advantages in the analysis of intermediates in DNA metabolism. Psoralen adducts were delivered to a specific site by a triplex-forming oligonucleotide. These lesions are clearly recognized and processed in oocytes, since mutagenesis was observed at the target site. The spectrum of induced mutations was compared with that found in similar studies in mammalian cells. Plasmids carrying multiple random adducts were preferentially degraded, perhaps due to the introduction of DSBs. However, when DNAs carrying site-specific adducts were examined, no plasmid loss was observed and removal of cross-links was found to be very slow. Sensitive assays for DSB-dependent homologous recombination were performed with substrates with one or two cross-link sites. No adduct-stimulated recombination was observed with a single lesion, and only very low levels were observed with paired lesions, even when a large proportion of the cross-links was removed by the oocytes. We conclude that DSBs or other recombinagenic structures are not efficiently formed at psoralen adducts in Xenopus oocytes. While psoralen is not a promising reagent for stimulating site-specific recombination, it is effective in inducing targeted mutations. PMID:9343428

  3. INJECTABLE IN SITU CROSS-LINKING HYDROGELS FOR LOCAL ANTIFUNGAL THERAPY

    PubMed Central

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

    2009-01-01

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

  4. Characterization of the somatogenic receptor in rat liver. Hydrodynamic properties and affinity cross-linking

    SciTech Connect

    Husman, B.; Haldosen, L.A.; Andersson, G.; Gustafsson, J.A.

    1988-03-15

    Rat liver somatogenic receptors have been characterized by gel permeation chromatography, sucrose density gradients in H/sub 2/O and D/sub 2/O, and affinity cross-linking using /sup 125/I-bovine growth hormone (bGH) as a specific somatogenic receptor ligand. Cross-linking of /sup 125/I-bovine growth hormone to a Triton X-100-treated low density fraction isolated from livers of late pregnant rats followed by sodium dodecylsulfate-polyacrylamide gel electrophoresis under reducing conditions showed three major binders with Mr 95,000, 86,000, and 43,000 and a minor binder of Mr 55,000, after correction for bound ligand assuming a 1:1 binding ratio of ligand-receptor. The Mr 86,000, 55,000, and 43,000 species were recovered in the detergent-soluble supernatant after high-speed centrifugation, whereas the Mr 95,000 species remained Triton X-100 insoluble. Detergent-soluble /sup 125/I-bGH-receptor complexes were further analyzed by sedimentation into sucrose density gradients. The sedimentation coefficient was S20,w = 5.2 S and the partial specific volume v = 0.72 ml/g. Gel permeation chromatography on a Sepharose S-400 column indicated a Stokes radius of 61 A for the /sup 125/I-bGH-receptor-Triton X-100 complex. Based on these figures, the molecular weight of the complex was calculated as 131,100. The molecular weight of the ligand-free receptor-Triton X-100 complex was calculated as Mr 109,100. Affinity cross-linking and sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the 61 A peak from Sephacryl S-400 chromatography (cf. above) showed two binding entities, one major and one minor with Mr values 86,000 and 43,000, respectively, in the absence of reductant. When electrophoresis was run in the presence of reductant the Mr 43,000 species was the major binding entity.

  5. Hyaluronan-mediated cellular adhesion

    NASA Astrophysics Data System (ADS)

    Curtis, Jennifer

    2005-03-01

    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.

  6. Microscopic examination in vivo and in vitro of natural and cross-linked polyunsaturated mclPHA.

    PubMed

    Bassas, M; Diaz, J; Rodriguez, E; Espuny, M J; Prieto, M J; Manresa, A

    2008-03-01

    Pseudomonas aeruginosa 42A2 produces a polyunsaturated polyhydroxyalkanoates (PHA-L) when grown on linseed oil as a substrate. Its high unsaturation content (36.5%) provides highly reactive PHA-L, generating a cross-linked biopolymer after ultraviolet (UV) irradiation. Both PHAs (PHA-L and uvPHA-L) were characterized by nuclear magnetic resonance, Fourier transform infrared spectroscopy, gel permeation chromatography, gas chromatography-mass spectrometry and differential scanning calorimetry-thermogravimetric analysis. The structural analysis of the new polymer revealed a dramatic decrease in unsaturated monomer content (8.5%), due to the complete disappearance of the polyunsaturated monomers (C(12:2), C(14:2), and C(14:3)). The cross-linking reaction was also confirmed by atomic force microscopy (AFM) and transmission electron microscopy. AFM showed morphological changes in bacteria cells with and without PHA granules. The microscope techniques provided us with micrographs of the native and cross-linked polymers, showing the formation of a reticular structure as the consequence of the cross-linking reaction. PMID:18224316

  7. Cross-Linked Fiber Network Embedded in Elastic Matrix

    PubMed Central

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

    2013-01-01

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

  8. Hydration and swelling of amorphous cross-linked starch microspheres.

    PubMed

    Wojtasz, Joanna; Carlstedt, Jonas; Fyhr, Peter; Kocherbitov, Vitaly

    2016-01-01

    Hydration of cross-linked starch microspheres, commercially available as a medical device, was investigated using a multi-method approach. We found that the uptake of water is accompanied by substantial swelling and changes of the polymer structure. Sorption calorimetry provided information about thermodynamics of water sorption, revealed presence of isothermal glass transition and absence of hydration-induced crystallization, observed in non-cross linked starch material. The changes in the surface and bulk properties of microspheres at different water-starch concentrations were investigated using synchrotron radiation X-ray scattering and analyzed using concept of fractals. The obtained information, combined with the results of differential scanning calorimetry, was used to construct a phase diagram of the studied material. Finally, hydration induced evolution of polymer structure revealed by the X-ray scattering was linked to the changes observed during swelling with optical microscopy. PMID:26453872

  9. Cross-linking Measurements of In Vivo Protein Complex Topologies*

    PubMed Central

    Zheng, Chunxiang; Yang, Li; Hoopmann, Michael R.; Eng, Jimmy K.; Tang, Xiaoting; Weisbrod, Chad R.; Bruce, James E.

    2011-01-01

    Identification and measurement of in vivo protein interactions pose critical challenges in the goal to understand biological systems. The measurement of structures and topologies of proteins and protein complexes as they exist in cells is particularly challenging, yet critically important to improve understanding of biological function because proteins exert their intended function only through the structures and interactions they exhibit in vivo. In the present study, protein interactions in E. coli cells were identified in our unbiased cross-linking approach, yielding the first in vivo topological data on many interactions and the largest set of identified in vivo cross-linked peptides produced to date. These data show excellent agreement with protein and complex crystal structures where available. Furthermore, our unbiased data provide novel in vivo topological information that can impact understanding of biological function, even for cases where high resolution structures are not yet available. PMID:21697552

  10. Biology of hyaluronan: Insights from genetic disorders of hyaluronan metabolism.

    PubMed

    Triggs-Raine, Barbara; Natowicz, Marvin R

    2015-08-26

    Hyaluronan is a rapidly turned over component of the vertebrate extracellular matrix. Its levels are determined, in part, by the hyaluronan synthases, HAS1, HAS2, and HAS3, and three hyaluronidases, HYAL1, HYAL2 and HYAL3. Hyaluronan binding proteins also regulate hyaluronan levels although their involvement is less well understood. To date, two genetic disorders of hyaluronan metabolism have been reported in humans: HYAL1 deficiency (Mucopolysaccharidosis IX) in four individuals with joint pathology as the predominant phenotypic finding and HAS2 deficiency in a single person having cardiac pathology. However, inherited disorders and induced mutations affecting hyaluronan metabolism have been characterized in other species. Overproduction of hyaluronan by HAS2 results in skin folding and thickening in shar-pei dogs and the naked mole rat, whereas a complete deficiency of HAS2 causes embryonic lethality in mice due to cardiac defects. Deficiencies of murine HAS1 and HAS3 result in a predisposition to seizures. Like humans, mice with HYAL1 deficiency exhibit joint pathology. Mice lacking HYAL2 have variably penetrant developmental defects, including skeletal and cardiac anomalies. Thus, based on mutant animal models, a partial deficiency of HAS2 or HYAL2 might be compatible with survival in humans, while complete deficiencies of HAS1, HAS3, and HYAL3 may yet be recognized. PMID:26322170

  11. Biology of hyaluronan: Insights from genetic disorders of hyaluronan metabolism

    PubMed Central

    Triggs-Raine, Barbara; Natowicz, Marvin R

    2015-01-01

    Hyaluronan is a rapidly turned over component of the vertebrate extracellular matrix. Its levels are determined, in part, by the hyaluronan synthases, HAS1, HAS2, and HAS3, and three hyaluronidases, HYAL1, HYAL2 and HYAL3. Hyaluronan binding proteins also regulate hyaluronan levels although their involvement is less well understood. To date, two genetic disorders of hyaluronan metabolism have been reported in humans: HYAL1 deficiency (Mucopolysaccharidosis IX) in four individuals with joint pathology as the predominant phenotypic finding and HAS2 deficiency in a single person having cardiac pathology. However, inherited disorders and induced mutations affecting hyaluronan metabolism have been characterized in other species. Overproduction of hyaluronan by HAS2 results in skin folding and thickening in shar-pei dogs and the naked mole rat, whereas a complete deficiency of HAS2 causes embryonic lethality in mice due to cardiac defects. Deficiencies of murine HAS1 and HAS3 result in a predisposition to seizures. Like humans, mice with HYAL1 deficiency exhibit joint pathology. Mice lacking HYAL2 have variably penetrant developmental defects, including skeletal and cardiac anomalies. Thus, based on mutant animal models, a partial deficiency of HAS2 or HYAL2 might be compatible with survival in humans, while complete deficiencies of HAS1, HAS3, and HYAL3 may yet be recognized. PMID:26322170

  12. Estimating the Degree of Cross-Linking in Rubber

    NASA Technical Reports Server (NTRS)

    Fedors, R. F.

    1983-01-01

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

  13. Reversible PH Lability of Cross-Linked Vault Nanocapsules

    SciTech Connect

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

    2009-05-28

    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.

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

    PubMed

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

    2016-08-16

    Cross-linking/mass spectrometry has evolved into a robust technology that reveals structural insights into proteins and protein complexes. We leverage a new tribrid instrument with improved fragmentation capacities in a systematic comparison to identify which fragmentation method would be best for the identification of cross-linked peptides. Specifically, we explored three fragmentation methods and two combinations: collision-induced dissociation (CID), beam-type CID (HCD), electron-transfer dissociation (ETD), ETciD, and EThcD. Trypsin-digested, SDA-cross-linked human serum albumin (HSA) served as a test sample, yielding over all methods and in triplicate analysis in total 2602 matched PSMs and 1390 linked residue pairs at 5% false discovery rate, as confirmed by the crystal structure. HCD wins in number of matched peptide-spectrum-matches (958 PSMs) and identified links (446). CID is most complementary, increasing the number of identified links by 13% (58 links). HCD wins together with EThcD in cross-link site calling precision, with approximately 62% of sites having adjacent backbone cleavages that unambiguously locate the link in both peptides, without assuming any cross-linker preference for amino acids. Overall quality of spectra, as judged by sequence coverage of both peptides, is best for EThcD for the majority of peptides. Sequence coverage might be of particular importance for complex samples, for which we propose a data dependent decision tree, else HCD is the method of choice. The mass spectrometric raw data has been deposited in PRIDE (PXD003737). PMID:27454319

  15. Cytokines and growth factors cross-link heparan sulfate

    PubMed Central

    Migliorini, Elisa; Thakar, Dhruv; Kühnle, Jens; Sadir, Rabia; Dyer, Douglas P.; Li, Yong; Sun, Changye; Volkman, Brian F.; Handel, Tracy M.; Coche-Guerente, Liliane; Fernig, David G.; Lortat-Jacob, Hugues; Richter, Ralf P.

    2015-01-01

    The glycosaminoglycan heparan sulfate (HS), present at the surface of most cells and ubiquitous in extracellular matrix, binds many soluble extracellular signalling molecules such as chemokines and growth factors, and regulates their transport and effector functions. It is, however, unknown whether upon binding HS these proteins can affect the long-range structure of HS. To test this idea, we interrogated a supramolecular model system, in which HS chains grafted to streptavidin-functionalized oligoethylene glycol monolayers or supported lipid bilayers mimic the HS-rich pericellular or extracellular matrix, with the biophysical techniques quartz crystal microbalance (QCM-D) and fluorescence recovery after photobleaching (FRAP). We were able to control and characterize the supramolecular presentation of HS chains—their local density, orientation, conformation and lateral mobility—and their interaction with proteins. The chemokine CXCL12α (or SDF-1α) rigidified the HS film, and this effect was due to protein-mediated cross-linking of HS chains. Complementary measurements with CXCL12α mutants and the CXCL12γ isoform provided insight into the molecular mechanism underlying cross-linking. Fibroblast growth factor 2 (FGF-2), which has three HS binding sites, was also found to cross-link HS, but FGF-9, which has just one binding site, did not. Based on these data, we propose that the ability to cross-link HS is a generic feature of many cytokines and growth factors, which depends on the architecture of their HS binding sites. The ability to change matrix organization and physico-chemical properties (e.g. permeability and rigidification) implies that the functions of cytokines and growth factors may not simply be confined to the activation of cognate cellular receptors. PMID:26269427

  16. Homogeneous UVA system for corneal cross-linking treatment

    NASA Astrophysics Data System (ADS)

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

    2010-02-01

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

  17. Ion exchange selectivity for cross-linked polyacrylic acid

    NASA Technical Reports Server (NTRS)

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

    1983-01-01

    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.

  18. Fiber optic immunosensor for cross-linked fibrin concentration

    NASA Astrophysics Data System (ADS)

    Moskowitz, Samuel E.

    2000-08-01

    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.

  19. Magnetic macromolecular cross linked enzyme aggregates (CLEAs) of glucoamylase.

    PubMed

    Nadar, Shamraja S; Rathod, Virendra K

    2016-02-01

    This work illustrates the preparation of magnetic macromolecular glucoamylase CLEAs using dialdehydic pectin, as a cross linker instead of traditional glutaraldehyde. The effect of precipitators type and amount, cross linker concentration, cross linking time and amount of amino functionalized magnetic nanoparticles (AFMNs) on glucoamylase activity was studied. Glucoamylase magnetic macromolecular CLEAs prepared by precipitation in presence of AFMNs by ammonium sulfate were subsequently cross linked by dialdehydic pectin. After cross-linked by pectin, 95.4% activity recovery was achieved in magnetic macromolecular CLEAs, whereas in case of glutaraldehyde cross linker, 85.3% activity recovery was achieved. Magnetic macromolecular CLEAs showed 2.91 and 1.27 folds higher thermal stability as compared to free and magnetic glutaraldehyde CLEAs. In kinetics study, magnetic macromolecular CLEAs retained same Km values, whereas magnetic glutaraldehyde CLEAs showed higher Km value than free enzyme. The porous structure of magnetic macromolecular CLEAs was not only enhanced mass transfer toward macromolecular substrates, but also showed compression resistance for 5 consecutive cycles which was checked in terms of effectiveness factor. At the end, in reusability study; magnetic macromolecular CLEAs were retained 84% activity after 10(th) cycle without leaching of enzyme which is 22% higher than traditional magnetic CLEAs. PMID:26777253

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

    PubMed

    Devolder, Ross; Antoniadou, Eleni; Kong, Hyunjoon

    2013-11-28

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

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

    SciTech Connect

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

    1983-06-01

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

  2. A Robust Cross-Linking Strategy for Block Copolymer Worms Prepared via Polymerization-Induced Self-Assembly

    PubMed Central

    2016-01-01

    A poly(glycerol monomethacrylate) (PGMA) chain transfer agent is chain-extended by reversible addition–fragmentation chain transfer (RAFT) statistical copolymerization of 2-hydroxypropyl methacrylate (HPMA) with glycidyl methacrylate (GlyMA) in concentrated aqueous solution via polymerization-induced self-assembly (PISA). A series of five free-standing worm gels is prepared by fixing the overall degree of polymerization of the core-forming block at 144 while varying its GlyMA content from 0 to 20 mol %. 1H NMR kinetics indicated that GlyMA is consumed much faster than HPMA, producing a GlyMA-rich sequence close to the PGMA stabilizer block. Temperature-dependent oscillatory rheological studies indicate that increasing the GlyMA content leads to progressively less thermoresponsive worm gels, with no degelation on cooling being observed for worms containing 20 mol % GlyMA. The epoxy groups in the GlyMA residues can be ring-opened using 3-aminopropyltriethoxysilane (APTES) in order to prepare core cross-linked worms via hydrolysis-condensation with the siloxane groups and/or hydroxyl groups on the HPMA residues. Perhaps surprisingly, 1H NMR analysis indicates that the epoxy–amine reaction and the intermolecular cross-linking occur on similar time scales. Cross-linking leads to stiffer worm gels that do not undergo degelation upon cooling. Dynamic light scattering studies and TEM analyses conducted on linear worms exposed to either methanol (a good solvent for both blocks) or anionic surfactant result in immediate worm dissociation. In contrast, cross-linked worms remain intact under such conditions, provided that the worm cores comprise at least 10 mol % GlyMA. PMID:27134311

  3. Cross linking molecular systems to form ultrathin dielectric layers

    NASA Astrophysics Data System (ADS)

    Feng, Danqin

    Dehydrogenation leads to cross linking of polymer or polymer like formation in very different systems: self-assembled monolayers and in closo -carboranes leading to the formation of semiconducting and dielectric boron carbide. We find evidence of intermolecular interactions for a self-assembled monolayer (SAM) formed from a large molecular adsorbate, [1,1';4',1"-terphenyl]-4,4"-dimethanethiol, from the dispersion of the molecular orbitals with changing the wave vector k and from the changes with temperature. With the formation self assembled molecular (SAM) layer, the molecular orbitals hybridize to electronic bands, with indications of significant band dispersion of the unoccupied molecular orbitals. Although organic adsorbates and thin films are generally regarded as "soft" materials, the effective Debye temperature, indicative of the dynamic motion of the lattice normal to the surface, can be very high, e.g. in the multilayer film formed from [1,1'-biphenyl]-4,4'-dimethanethiol (BPDMT). Depending on molecular orientation, the effective Debye temperature can be comparable to that of graphite due to the 'stiffness' of the benzene rings, but follows the expected Debye-Waller behavior for the core level photoemission intensities with temperature. This is not always the case. We find that a monomolecular film formed from [1,1';4',1"-terphenyl]-4,4"-dimethanethiol deviates from Debye-Waller temperature behavior and is likely caused by temperature dependent changes in molecular orientation. We also find evidence for the increase in dielectric character with polymerization (cross-linking) in spite of the decrease in the HOMO-LUMO gap upon irradiation of TPDMT. The changes in the HOMO-LUMO gap, with cross-linking, are roughly consistent with the band dispersion. The decomposition and cross-linking processes are also accompanied by changes in molecular orientation. The energetics of the three isomeric carborane cage compounds [ closo-1,2-orthocarborane, closo-1

  4. Spontaneous Cross-linking for Fabrication of Nanohybrids Embedded with Size-Controllable Particles.

    PubMed

    Kang, Danmiao; Liu, Qinglei; Chen, Min; Gu, Jiajun; Zhang, Di

    2016-01-26

    This paper reports a versatile method to fabricate robust carbon/metal hybrids with ultrasmall particle and highly developed porous structure through a scalable and facile way. Alginate is used as the precursor for it could perform cross-linking reaction with different polyvalent metal ions to form gels. After simple freeze-drying and carbonization of the alginate-derived gels, we obtained the carbon/metal hybrids with fine nanostructure. Eleven kinds of metal ions were introduced to form gels and five kinds of the gels were carbonized to produce the carbon/metal hybrids. By adjusting the reaction condition, we could tune the size of the nanoparticles in the obtained hybrids. The obtained SnO2/C hybrid shows outstanding specific capacity, rate performance, and long cycle life when it is used as the anode materials of lithium ion batteries. The ultrasmall active nanoparticles were uniformly dispersed within an interconnected pore framework. It ensured a short diffusion and transportation distance of electrolyte ions to the surfaces of active nanoparticles. In addition, the robust carbon framework comprises of quasigraphitic carbon layers. It contributed to the high rate performance by providing excellent conductive pathways for electrons within the electrodes. This work provides a general method for fabrication of carbon/metal (oxide) hybrids with fine nanostructure for application in energy storage. PMID:26650902

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

    PubMed

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

    2010-04-01

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

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

    PubMed

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

    2014-09-01

    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

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

    PubMed

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

    2012-03-01

    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

  8. Physicochemical, antimicrobial, and cytotoxic characteristics of a chitosan film cross-linked by a naturally occurring cross-linking agent, aglycone geniposidic acid.

    PubMed

    Mi, Fwu-Long; Huang, Chin-Tsung; Liang, Hsiang-Fa; Chen, Mei-Chin; Chiu, Ya-Ling; Chen, Chun-Hung; Sung, Hsing-Wen

    2006-05-01

    The purpose of this study was to evaluate the characteristics of a chitosan film cross-linked by a naturally occurring compound, aglycone geniposidic acid (aGSA). This newly developed aGSA-cross-linked chitosan film may be used as an edible film. The chitosan film without cross-linking (fresh) and the glutaraldehyde-cross-linked chitosan film were used as controls. The characteristics of test chitosan films evaluated were their degree of cross-linking, swelling ratio, mechanical properties, water vapor permeability, antimicrobial capability, cytotoxicity, and enzymatic degradability. It was found that cross-linking of chitosan films by aGSA (at a concentration up to 0.8 mM) significantly increased its ultimate tensile strength but reduced its strain at fracture and swelling ratio. There was no significant difference in the antimicrobial capability between the cross-linked chitosan films and their fresh counterpart. However, the aGSA-cross-linked chitosan film had a lower cytotoxicity, a slower degradation rate, and a relatively lower water vapor permeability as compared to the glutaraldehyde-cross-linked film. These results suggested that the aGSA-cross-linked chitosan film may be a promising material as an edible film. PMID:16637687

  9. Hyaluronan-binding properties of human serum hemopexin.

    PubMed

    Hrkal, Z; Kuzelová, K; Muller-Eberhard, U; Stern, R

    1996-03-25

    Hemopexin, the heme-binding serum glycoprotein, exhibits a complex electrophoretic pattern on two-dimensional immunoelectrophoresis on agarose gels into which hyaluronic acid is incorporated in the first and monospecific anti-hemopexin in the second dimension. This heterogeneity reflects a range of interactions of hemopexin isoforms with hyaluronic acid. Electrophoretic patterns of individual human sera greatly differ in their contents of hyaluronan-interacting hemopexin species. Hemopexin itself has no hyaluronidase activity. PMID:8612795

  10. Hyaluronan in cancer - from the naked mole rat to nanoparticle therapy.

    PubMed

    Rankin, Kenneth S; Frankel, Daniel

    2016-05-01

    Hyaluronan, a glycosaminoglycan, abundant in the tumour microenvironment, is a key player in many processes associated with cancer. Recently the cancer resistance of the naked mole rat has been attributed to the presence of an ultra-high molecular weight form of this molecule. The physical properties of this multifunctional biopolymer have been extensively studied in the context of synovial joints. However, relatively little has been reported with regard to the soft matter properties of hyaluronan in relation to cancer. In this review we examine the role of hyaluronan in cancer, paying particular attention to its mechanical interactions with malignant cells and its soft matter properties. In addition we discuss the use of hyaluronan based gels to study cancer invasion as well as nanoparticle based strategies for disease treatment. PMID:27079782

  11. Role of hyaluronan and hyaluronan synthase in endometrial cancer.

    PubMed

    Yabushita, Hiromitsu; Kishida, Tameko; Fusano, Kanako; Kanyama, Kouhei; Zhuo, Lisheng; Itano, Naoki; Kimata, Koji; Noguchi, Masayoshi

    2005-06-01

    The aim of this study was to determine if the immunohistochemical expression of hyaluronan synthase (HAS) and serum levels of hyaluronan correlate with the clinicopathological manifestations of endometrial carcinoma. Sera were obtained from 59 endometrial cancer patients and 22 post-menopausal healthy women. Concentration of hyaluronan in sera was measured by an inhibitory ELISA using a hyaluronan-binding protein. Tissues obtained from 59 endometrial cancer patients were immunostained by the avidin-biotin-peroxidase complex method using anti-HAS1, anti-HAS2, anti-HAS3 and anti-CD44 antibody. A section was defined as having positive expression when >50% of the tumor cells were intensely stained. The expression of HAS1 was related to the depth of myometrial invasion, histological grade and lymph-vascular space involvement, but the expression of HAS2 and HAS3 was unrelated to these parameters. CD44 expression occurred more frequently in the HAS2- or HAS3-positive groups than in the HAS2- or HAS3-negative groups, and the expression of HAS1 was unrelated to CD44 expression. Serum levels of hyaluronan were higher in the endometrial cancer group than in the healthy control group, and increased with depth of myometrial invasion, histological grade and lymph-vascular space involvement. Serum hyaluronan levels were higher in the HAS1-positive group than in the HAS1-negative group, but the expression of HAS2 and HAS3 was unrelated to serum hyaluronan levels. HAS1 expression and an increase in serum hyaluronan in endometrial cancer may be associated with disease progression through myometrial invasion and lymph-vascular space involvement. PMID:15870928

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

    NASA Technical Reports Server (NTRS)

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

    2005-01-01

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

  13. Cross-linked high amylose starch derivatives as matrices for controlled release of high drug loadings.

    PubMed

    Mulhbacher, J; Ispas-Szabo, P; Lenaerts, V; Mateescu, M A

    2001-09-11

    Selection of hydrogels as excipients in controlled drug release systems depends on the characteristics of the gel and of the drug. Three types of derivatives were synthesized from cross-linked high amylose starch (HASCL-6) by substitution of hydroxylic groups with cationic (carboxymethyl: CM), anionic (aminoethyl: AE) and acetate (Ac) groups. These new polymeric excipients are able to control the release over 20 h from monolithic tablets loaded with 20 to 60% drug. Three drugs were used as model tracer: acetaminophen (uncharged), acetylsalicylic acid (having an acidic group) and metformin (having a basic group). It was found that the release of ionic drugs from CM-HASCL-6 and AE-HASCL-6 matrices can be partially controlled by ionic interaction between pendant groups of polymer and drugs. The substitution degree of HASCL-6 derivatives can also be varied to modulate the drug's release time. These derivatives represent a novel generation of pharmaceutical excipients, recommended for high loading dosage formulations. PMID:11532312

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

    PubMed

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

    2015-01-01

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

  15. Blends of cross-linked high amylose starch/pectin loaded with diclofenac.

    PubMed

    Soares, Grazielle Arantes; de Castro, Ana Dóris; Cury, Beatriz S F; Evangelista, Raul C

    2013-01-01

    Polymers blends represent an important approach to obtain materials with modulated properties to reach different and desired properties in designing drug delivery systems in order to fulfill therapeutic needs. The aim of this work was to evaluate the influence of drug loading and polymer ratio on the physicochemical properties of microparticles of cross-linked high amylose starch-pectin blends loaded with diclofenac for further application in controlled drug delivery systems. Thermal analysis and X-ray diffractograms evidenced the occurrence of drug-polymer interactions and the former pointed also to an increase in thermal stability due to drug loading. The rheological properties demonstrated that drug loading resulted in formation of weaker gels while the increase of pectin ratio contributes to origin stronger structures. PMID:23044114

  16. Getting a grip: hyaluronan-mediated cellular adhesion

    NASA Astrophysics Data System (ADS)

    Curtis, Jennifer E.; Spatz, Joachim P.

    2004-10-01

    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.

  17. LET dependence of DNA-protein cross-links

    SciTech Connect

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

    1995-08-01

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

  18. Homologous Recombination Assay for Interstrand Cross-Link Repair

    PubMed Central

    Nakanishi, Koji; Cavallo, Francesca; Brunet, Erika; Jasin, Maria

    2012-01-01

    DNA interstrand cross-links (ICLs) covalently link both strands of the DNA duplex, impeding cellular processes like DNA replication. Homologous recombination (HR) is considered to be a major pathway for the repair of ICLs in mammalian cells as mutants for HR components are highly sensitive to DNA-damaging agents that cause ICLs. This chapter describes GFP assays to measure HR following site-specific ICL formation with psoralen through DNA triplex technology. This approach can be used to determine the genetic requirements for ICL-induced HR in relation to those involved in HR repair of other DNA lesions such as double-strand breaks. PMID:21660700

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

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

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

  20. Gelatin hydrogels cross-linked with bis(vinylsulfonyl)methane (BVSM): 1. The chemical networks.

    PubMed

    Hellio-Serughetti, Dominique; Djabourov, Madeleine

    2006-09-26

    This paper deals with chemical gelation of gelatin in the presence of a cross-linker, bis(vinylsulfonyl)methane (BVSM), which is able to create covalent C-N bonds with amine groups. The investigation is performed at 40 degrees C, where no triple helices are present. Gelatin is in random coil conformation. The influence of various parameters (gelatin concentration, cross-linker concentration, and pH (number of reacting sites along the gelatin chain)) was examined. Gel formation was followed by rheological and thermodynamic measurements (microcalorimetry) versus time (kinetic measurements). Furthermore, the storage moduli were compared to the number of links formed in the course of gelation. The experiments show that, within the experimental range investigated, a fully homogeneous network is not reached; the chemical gels, even upon completion of the reactions, are still in the critical domain, near the threshold. A power law behavior was put in evidence for the shear modulus versus the distance to the gel point, expressed as the concentration of links per gelatin chain. The exponent (f = 3.4 +/- 0.3) is close to that expected for the vulcanization of long chains. The storage moduli can be superposed on a single curve where the abscissa is the product of the number of C-N links per unit volume and the gelatin concentration at an exponent equal to -0.76 +/- 0.03. This exponent suggests the role of entanglements for interchain cross-linking. PMID:16981770

  1. Optimization model for UV-Riboflavin corneal cross-linking

    NASA Astrophysics Data System (ADS)

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

    2011-03-01

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

  2. Troponin T cross-linking in human apoptotic cardiomyocytes.

    PubMed Central

    Gorza, L.; Menabó, R.; Di Lisa, F.; Vitadello, M.

    1997-01-01

    Intracellular calcium overload of guinea pig cardiomyocytes is accompanied by troponin T cross-linking, which is revealed by changes in immunoreactivity of anti-troponin T antibodies. We presently investigated whether the same process is detectable in the human heart. Immunohistochemistry shows myofibrillar staining with BN-59 anti-troponin T antibody with rare cardiomyocytes in samples obtained at surgery, whereas approximately 50% of myocytes are labeled in heart samples taken at autopsy within 3 hours of death, and every cardiomyocyte is stained after exposure of biopsy sections to 10 mmol/L calcium. Western blot analysis shows reactive polypeptides of approximately 70 and 85 to 90 kd in addition to troponin T in both treated and autopsy heart sections. Neither reactivity in immunohistochemistry nor additional reactive polypeptides in Western blot are detectable when calpain or transglutaminase is inhibited during exposure of sections to high calcium. Troponin T crosslinking occurs also in isolated myofibrils, which show staining with BN-59 at either sarcomeric A or I bands. Labeling with TdT-mediated dUTP nick and labeling (TUNEL) to demonstrate apoptosis reveals DNA fragmentation in BN-59-positive myocytes. Thus, troponin T cross-linking occurs in human cardiac myocytes concomitantly with apoptosis and autopsy autolysis, suggesting that similar cytosolic alterations can be produced by different types of myocyte death. Images Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 PMID:9176400

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

    PubMed Central

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

    2012-01-01

    Collagen cross-linking (CXL) using UVA light and riboflavin (vitamin B2) was introduced as a clinical application to stabilize the cornea by inducing cross-links within and between collagen fibers. CXL has been investigated extensively and has been shown clinically to arrest the progression of keratoconic or post-LASIK ectasia. With its minimal cost, simplicity, and proven positive clinical outcome, CXL can be regarded as a useful approach to reduce the number of penetrating keratoplasties performed. Small case series have also indicated that CXL is beneficial in corneal edema by reducing stromal swelling behavior and in keratitis by inhibiting pathogen growth. Despite these encouraging results, CXL remains a relatively new method that is potentially associated with complications. Aspects such as side effects and recurrence rates have still to be elucidated. In light of the growing interest in CXL, our paper summarizes present knowledge about this promising approach. We have intentionally endeavored to include the more relevant studies from the recent literature to provide an overview of the current status of CXL. PMID:22288005

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

    PubMed

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

    2015-04-01

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

  5. One-step electrospinning of cross-linked chitosan fibers.

    PubMed

    Schiffman, Jessica D; Schauer, Caroline L

    2007-09-01

    Chitin is a nitrogen-rich polysaccharide that is abundant in crustaceans, mollusks, insects, and fungi and is the second most abundant organic material found in nature next to cellulose. Chitosan, the N-deacetylated derivative of chitin, is environmentally friendly, nontoxic, biodegradable, and antibacterial. Fibrous mats are typically used in industries for filter media, catalysis, and sensors. Decreasing fiber diameters within these mats causes many beneficial effects such as increased specific surface area to volume ratios. When the intrinsically beneficial effects of chitosan are combined with the enhanced properties of nanofibrous mats, applications arise in a wide range of fields, including medical, packaging, agricultural, and automotive. This is particularly important as innovative technologies that focus around bio-based materials are currently of high urgency, as they can decrease dependencies on fossil fuels. We have demonstrated that Schiff base cross-linked chitosan fibrous mats can be produced utilizing a one-step electrospinning process that is 25 times faster and, therefore, more economical than a previously reported two-step vapor-cross-linking method. These fibrous mats are insoluble in acidic, basic, and aqueous solutions for 72 h. Additionally, this improved production method results in a decreased average fiber diameter, which measures 128 +/- 40 nm. Chemical and structural analyses were conducted utilizing Fourier transform infrared spectroscopy, solubility studies, and scanning electron microscopy. PMID:17696400

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

    PubMed

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

    2014-07-01

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

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

    PubMed Central

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

    2014-01-01

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

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

    SciTech Connect

    Phillips, P.J.

    1981-03-01

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

  9. Enzymatic production of specifically distributed hyaluronan oligosaccharides.

    PubMed

    Yuan, Panhong; Lv, Mengxian; Jin, Peng; Wang, Miao; Du, Guocheng; Chen, Jian; Kang, Zhen

    2015-09-20

    High-molecular-mass hyaluronan (HA) was controllably depolymerized in pure aqueous solution with recombinant leech hyaluronidase (HAase). The HAase concentration per unit HA and hydrolysis time played important roles in molecular mass distribution. By modulating the concentrations of HAase and controlling the hydrolysis time, any molar-mass-defined HA oligomers could be efficiently and specifically produced on a large scale (40 g/L), such as HA oligosaccharides with weight-average molar mass of 4000, 10,000, and 30,000Da and end hydrolysates containing only HA6 and HA4. High performance liquid chromatography-size exclusion chromatography, polyacrylamide gel electrophoresis, capillary zone electrophoresis, and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry confirmed low polydispersity of the produced molar-mass-defined HA oligosaccharides. Therefore, large-scale production of defined HA oligosaccharides with narrow molecular mass distribution will significantly promote progress in related research and its potential applications. PMID:26050905

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

    PubMed

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

    2015-06-25

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

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

    PubMed Central

    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

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

  12. [Cross-links of collagen and bone quality].

    PubMed

    Banse, X

    2010-01-01

    Bone tissue is a marvellous material. Basic bone function is to be structurally stiff and strong. Stiffness allows vertebrates to maintain their shape, to protect the organs and to move. Being strong, bone only breaks in exceptional circumstances. Osteoporosis is a disease where fractures happen too often, because of abnormal bone fragility. In this situation, bone--especially cancellous bone--does not take up its first duty. Trabeculae are scarce and thin, leading to very low tissue density. Biomechanical tests and clinical evidence have shown that some subjects have, with equal bone density, stronger or weaker bone tissue. This led to the concept of bone quality. Even if other hypotheses have been systematically explored, it seems that bone collagen chemical nature, especially its cross-link profile, significantly influences human bone quality. PMID:21513097

  13. Protein cross-linking tools for the construction of nanomaterials.

    PubMed

    Domeradzka, Natalia E; Werten, Marc Wt; Wolf, Frits A de; de Vries, Renko

    2016-06-01

    Across bioengineering there is a need to couple proteins to other proteins, or to peptides. Although traditional chemical conjugations have dominated in the past, more and more highly specific coupling strategies are becoming available that are based on protein engineering. Here we review the use of protein modification approaches such as enzymatic and autocatalytic protein-protein coupling, as well as the use of hetero-dimerizing (or hetero-oligomerizing) modules, applied to the specific case of linking together de novo designed recombinant polypeptides into precisely structured nanomaterials. Such polypeptides are increasingly being investigated for biomedical and other applications. In this review, we describe the protein-engineering based cross-linking strategies that dramatically expand the repertoire of possible molecular structures and, hence, the range of materials that can be produced from them. PMID:26871735

  14. Studies on N-vinylformamide cross-linked copolymers

    NASA Astrophysics Data System (ADS)

    Świder, Joanna; Tąta, Agnieszka; Sokołowska, Katarzyna; Witek, Ewa; Proniewicz, Edyta

    2015-12-01

    Copolymers of N-vinylformamide (NVF) cross-linked with three multifunctional monomers, including divinylbenzene (DVB), ethylene glycol dimethacrylate (EGDMA), and N,N‧-methylenebisacrylamide (MBA) were synthetized by a three-dimensional free radical polymerization in inverse suspension using 2,2‧-azobis(2-methylpropionamide) dihydrochloride (AIBA) as an initiator. Methyl silicon oil was used as the continuous phase during the polymerization processes. Fourier-transform adsorption infrared (FT-IR) spectra revealed the presence of silicone oil traces and suggested that silicone oil strongly interacted with the copolymers surface. Purification procedure allowed to completely remove the silicon oil traces from P(NVF-co-DVB) only. The morphology and the structure of the investigated copolymers were examined by optical microscopy, FT-IR, and FT-Raman (Fourier-transform Raman spectroscopy) methods.

  15. Conventional Versus Cross-Linked Polyethylene for Total Hip Arthroplasty.

    PubMed

    Surace, Michele F; Monestier, Luca; Vulcano, Ettore; Harwin, Steven F; Cherubino, Paolo

    2015-09-01

    The clinical and radiographic outcomes of 88 patients who underwent primary total hip arthroplasty with either conventional polyethylene or cross-linked polyethylene (XLPE) from the same manufacturer were compared. There were no significant differences between the 2 subpopulations regarding average age, gender, side affected, or prosthetic stem and cup size. The average follow-up was 104 months (range, 55 to 131 months). To the authors' knowledge, this is the longest follow-up for this particular insert. Clinical and radiographic evaluations were performed at 1, 3, 6, and 12 months and then annually. Results showed that XLPE has a significantly greater wear reduction than that of standard polyethylene in primary total hip arthroplasty. At the longest available follow-up for these specific inserts, XLPE proved to be effective in reducing wear. PMID:26375527

  16. Hyaluronan viscosupplementation: state of the art and insight into the novel cooperative hybrid complexes based on high and low molecular weight HA of potential interest in osteoarthritis treatment

    PubMed Central

    Schiraldi, Chiara; Stellavato, Antonietta; de Novellis, Francesca; La Gatta, Annalisa; De Rosa, Mario

    2016-01-01

    Summary Osteoarthritis (OA) represents a group of chronic, painful, disabling conditions affecting synovial joints. It is characterized by degeneration of articular cartilage, alterations of peri-articular and subchondral bone, low-grade synovial inflammation (synovitis). Despite OA is commonly described as a non-inflammatory disease, it is known that its progression and the subsequent increment of symptoms correlate to the production of inflammatory factors that induce the secretion of enzymes responsible for cartilage degradation. In clinical practice, to alleviate pain and stiffness, not only during acute phases but also as maintenance therapy, intra-articular injections of corticosteroids or similar drugs are used, besides it is well diffused the viscosupplementation procedure based on hyaluronan gel. There are many different products containing high molecular weight linear HA or cross-linked derivatives, however the novelty in the field consist in the hybrid cooperative complexes derived from high and low molecular weight HA through a patented processing. This technique permit to double the amount of HA delivered to the injured site without increasing the injected volume, beside in vitro assay on human chondrocytes suggested hybrid complexes as effective in the modulation of several inflammatory cytokines in joints. PMID:27252742

  17. Cross-linked polyethylenimine-tripolyphosphate nanoparticles for gene delivery.

    PubMed

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

    2014-01-01

    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

  18. Peptidoglycan cross-linking in glycopeptide-resistant Actinomycetales.

    PubMed

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

    2014-01-01

    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

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

    NASA Technical Reports Server (NTRS)

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

    2007-01-01

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

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

    NASA Technical Reports Server (NTRS)

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

    2007-01-01

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

  1. Characterization of rat leydig cell gonadotropin receptor structure by affinity cross-linking

    SciTech Connect

    Zhang, Q.Y.; Hwang, J.; Menon, K.M.J.

    1986-05-01

    The gonadotropin receptor from rat leydig cell has been characterized with respect to binding kinetics and physiological regulation. The present study was intended to examine the structure of the receptor. Leydig cell suspension was prepared by either collagenase digestion or by mechanical disruption of the testis. The cells were incubated with /sup 125/I-hCG and the unreacted hCG was removed by centrifugation. The /sup 125/I-hCG was then covalently linked to the cell surface receptor using cleavable (dithiobis (succinimidyl propionate)) and non-cleavable (disuccinimidyl suberate) cross-linking reagents. The extracted cross-linked membrane proteins were resolved on SDS-polyacrylamide gels under reducing and non-reducing conditions and subjected to autoradiographic analysis. Under non-reducing conditions, two labeled species with M/sub r/ = 87,000 and 120,000 were detected. However, only one labeled band was detected under reducing conditions with M/sub r/ = 64,000. The binding of /sup 125/I-hCG to the receptor was inhibited by hCG and LH, but not by a number of peptides and proteins. The data suggest that hCG receptor in leydig cell is an oligomeric complex consisting of four subunits, ..cap alpha cap alpha beta gamma... The ..beta.. and ..gamma.. subunits are each linked to an ..cap alpha.. subunit through disulfide linkage and the hormone binds to each ..cap alpha.. subunit. The two dimers formed (..cap alpha beta cap alpha gamma..) are associated by noncovalent interactions.

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

    PubMed

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

    2012-01-01

    Causes of bone deficiency are numerous, but biomimetic alloplastic grafts provide an alternative to repair tissue naturally. Previously, a hydroxyapatite-gelatin modified siloxane (HAp-Gemosil) composite was prepared by cross-linking (N, N'-bis[(3-trimethoxysilyl)propyl]ethylene diamine (enTMOS) around the HAp-Gel nanocomposite particles, to mimic the natural composition and properties of bone. However, the tensile strength remained too low for many orthopedic applications. It was hypothesized that incorporating a polymer chain into the composite could help improve long range interaction. Furthermore, designing this polymer to interact with the enTMOS siloxane cross-linked matrix would provide improved adhesion between the polymer and the ceramic composite, and improve mechanical properties. To this end, copolymers of L-Lactide (LLA), and a novel alkyne derivatized trimethylene carbonate, propargyl carbonate (PC), were synthesized. Incorporation of PC during copolymerization affects properties of copolymers such as molecular weight, T(g), and % PC incorporation. More importantly, PC monomers bear a synthetic handle, allowing copolymers to undergo post-polymerization functionalization with graft monomers to specifically tailor the properties of the final composite. For our investigation, P(LLA-co-PC) copolymers were functionalized by an azido-silane (AS) via copper catalyzed azide-alkyne cycloaddition (CuAAC) through terminal alkyne on PC monomers. The new functionalized polymer, P(LLA-co-PC)(AS) was blended with HAp-Gemosil, with the azido-silane linking the copolymer to the silsesquioxane matrix within the final composite.These HAp-Gemosil/P(LLA-co-PC)(AS) composites were subjected to mechanical and biological testing, and the results were compared with those from the HAp-Gemosil composites. This study revealed that incorporating a cross-linkable polymer served to increase the flexural strength of the composite by 50%, while maintaining the biocompatibility of HAp

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

    SciTech Connect

    Nagaoka, Noriyasu; Kubota, Hitoshi; Katakai, Ryoichi; Safranj, Agneza; Yoshida, Masaru; Omichi, Hideki

    1993-12-20

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

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

    PubMed Central

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

    2012-01-01

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

  5. Cross-linking and 1H n.m.r. spectroscopy of the pyruvate dehydrogenase complex of Escherichia coli

    PubMed Central

    Packman, Leonard C.; Perham, Richard N.; Roberts, Gordon C. K.

    1982-01-01

    The pyruvate dehydrogenase complex of Escherichia coli was treated with o-phenylene bismaleimide in the presence of the substrate pyruvate, producing almost complete cross-linking of the lipoate acetyltransferase polypeptide chains as judged by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis. This took place without effect on the catalytic activities of the other two component enzymes and with little evidence of cross-links being formed with other types of protein subunit. Limited proteolysis with trypsin indicated that the cross-links were largely confined to the lipoyl domains of the lipoate acetyltransferase component of the same enzyme particle. This intramolecular cross-linking had no effect on the very sharp resonances observed in the 1H n.m.r. spectrum of the enzyme complex, which derive from regions of highly mobile polypeptide chain in the lipoyl domains. Comparison of the spin–spin relaxation times, T2, with the measured linewidths supported the idea that the highly mobile region is best characterized as a random coil. Intensity measurements in spin-echo spectra showed that it comprises a significant proportion (probably not less than one-third) of a lipoyl domain and is thus much more than a small hinge region, but there was insufficient intensity in the resonances to account for the whole lipoyl domain. On the other hand, no evidence was found in the 1H n.m.r. spectrum for a substantial structured region around the lipoyl-lysine residues that was free to move on the end of this highly flexible connection. If such a structured region were bound to other parts of the enzyme complex for a major part of its time, its resonances might be broadened sufficiently to evade detection by 1H n.m.r. spectroscopy. ImagesFig. 2.Fig. 3. PMID:6753833

  6. Tailoring Elastic Properties of Silica Aerogels Cross-Linked with Polystyrene

    NASA Technical Reports Server (NTRS)

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

    2009-01-01

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

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

    PubMed

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

    2012-02-01

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

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

    PubMed Central

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

    2015-01-01

    Purpose Evaluating the clinical results of trans-epithelial collagen cross-linking (CXL) and standard CXL in patients with progressive keratoconus. Methods This prospective study comprised 20 eyes of 20 patients with progressive keratoconus. Ten eyes were treated by standard CXL and ten by trans-epithelial cross-linking (TE-CXL, epithelium on) with 1 year of follow-up. All patients underwent complete ophthalmologic testing that included pre- and postoperative uncorrected visual acuity, corrected visual acuity, spherical error, spherical equivalent, corneal astigmatism, simulated maximum, minimum, and average keratometry, coma and spherical aberration, optical pachymetry, and endothelial cell density. Intra-and postoperative complications were recorded. The solution used for standard CXL comprised riboflavin 0.1% and dextran 20.0% (Ricrolin), while the solution for TE-CXL (Ricrolin, TE) comprised riboflavin 0.1%, dextran 15.0%, trometamol (Tris), and ethylenediaminetetraacetic acid. Ultraviolet-A treatment was performed with UV-X System at 3 mW/cm2. Results In both the standard CXL group (ten patients, ten eyes; mean age, 30.4±7.3 years) and the TE-CXL group (ten patients, ten eyes; mean age, 28±3.8 years), uncorrected visual acuity and corrected visual acuity improved significantly after treatment. Furthermore, a significant improvement in topographic outcomes, spherical error, and spherical equivalent was observed in both groups at month 12 posttreatment. No significant variations were recorded in other parameters. No complications were noted. Conclusion A 1-year follow-up showed stability of clinical and refractive outcomes after standard CXL and TE-CXL. PMID:25834386

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

    PubMed

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

    2003-10-22

    Cross-linked hydroxypropylmethylcellulose (HPMC) cast films with citric acid as polycarboxylic cross-linker were elaborated to study the effect of cross-linking level on various properties. Increased amounts of cross-linking agent were not connected to statistically different tensile strength and Young's modulus. Whatever the cross-linking level of the film was, the ultimate elongation parameter decreased by approximately 60% compared to the HMPC control film. Moisture sorption isotherms and water contact angle meter showed that the effect of cross-linking degree tends to reduce the hygroscopic and hydrophilic characteristics of films. In addition, to control bacteria growth on food surfaces, the antimicrobial activity of both 98% cross-linked HPMC-nisin and control HPMC-nisin films was tested on Micrococcus luteus. Despite the incorporation of a significant content of nisin, cross-linked HPMC-nisin films were completely inactive on the microbial strain compared to the HPMC-nisin control films. Cross-linking conditions likely either denatured the nisin or irreversibly bound nisin to the cross-linked HPMC. However, nisin adsorbed into films made from previously cross-linked HPMC maintained its activity. PMID:14558764

  10. Tuning nanoscale viscoelasticity of polyelectrolyte complexes with multiple types of cross-links

    NASA Astrophysics Data System (ADS)

    Ma, Tianzhu; Han, Biao; Lee, Daeyeon; Han, Lin

    Mechanical properties of hydrogels are manifestation of cross-link type and density, fixed charges and water-polymer interactions. In this study, we revealed how different types of cross-links regulate the nanoscale viscoelasticity of polyelectrolyte networks. Ionically cross-linked PAH/PAA layer-by-layer complexes were modified to include covalent cross-links using EDC. AFM-nanoindentation and force relaxation were performed at various ionic strength (0.01-1M) and pH (1.5-5.5). As-assembled networks, held only by ionic cross-links, underwent >95% relaxation, dominated by cross-link breaking and re-formation. Addition of covalent cross-links increased the instantaneous modulus by 1.6-fold and attenuated relaxation to ~80% of net neutral states (pH >=3.5), as covalent cross-links provide additional elastic components. The network remained stabilized when all ionic cross-links were dissociated at pH <=1.5, whereby further attenuation to 31% in relaxation could be due to viscoelastic polymer conformational changes and fluid flow-induced poroelasticity. Taken together, this study demonstrates the potential of using multiple cross-linking types to tune the viscoelastic mechanisms in polyelectrolyte complexes.