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

    2010-07-01

    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. Microfluidic formation of ionically cross-linked polyamine gels.

    PubMed

    Kini, Gautam C; Lai, Justin; Wong, Michael S; Biswal, Sibani Lisa

    2010-05-01

    In this article, we discuss in situ polymer gelation in microfluidic channels from electrostatically mediated interactions when reactant streams of a linear cationic polymer (poly(allylamine hydrochloride, PAH) and a multivalent anion (sodium citrate) are subjected to shear flow. We find that the polyamine exhibits shear-thickening behavior as it is ionically cross-linked by citrate ions to form viscoelastic gel phases. These gels form at room temperature and remain stable and intact after the cessation of flow. Gelation is found to occur in the polymer stream and not the citrate stream because of an appreciably higher diffusivity of citrate ions when compared to the gel and PAH and because of laminar flow conditions in the microfluidic environment. Gel formation occurred when the pH of the PAH stream was below the PAH pK(a) value of 8.38 and when citrate was either in a disodium or trisodium state. The formation of aggregates, gels, and droplets was found to depend strongly on the charge ratio and flow conditions. The gelation of PAH begins with the formation of colloidal aggregates of PAH and citrate, which then combine under shear flow to form noncontinuous or continuous gels. Droplets of citrate can form within regions of continuous gels as excess citrate anions diffuse into the gel stream. PMID:20078130

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

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

    Microsoft Academic Search

    Kwangwoo Nam; Tsuyoshi Kimura; Akio Kishida

    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

  5. Improved gene transfection efficacy and cytocompatibility of multifunctional polyamidoamine-cross-linked hyaluronan particles.

    PubMed

    Srivastava, Akshay; Cunningham, Claire; Pandit, Abhay; Wall, J Gerard

    2015-05-01

    We describe a multi-functional, cationic hyaluronic acid (HA)-based gene carrier with improved transfection over non-cross-linked HA, and negligible cytotoxicity. Cationized particles are developed by cross-linking HA chain carboxyl groups with polyamidoamine amine termini to produce well segregated particles of 350-400?nm with a surface charge density of +2?mV, compared with -35?mV for non-cationized particles. A tethered antibody fragment retains ligand binding for cell targeting. Cationized and antibody-linked particles complex plasmid DNA efficiently and the cationized particles successfully deliver reporter genes to bovine intervertebral disk cells as an intervertebral disk regeneration model. PMID:25641575

  6. "Out-gel" tryptic digestion procedure for chemical cross-linking studies with mass spectrometric detection.

    PubMed

    Petrotchenko, Evgeniy V; Serpa, Jason J; Cabecinha, Ashley N; Lesperance, Mary; Borchers, Christoph H

    2014-02-01

    SDS-PAGE is one of the most powerful protein separation techniques, and in-gel digestion is the leading method for converting proteins separated by SDS-PAGE into peptides suitable for mass spectrometry-based proteomic studies. In in-gel digestion, proteins are digested within the gel matrix, and the resulting peptides are extracted into an appropriate buffer. Transfer of the digested peptides to the liquid phase for subsequent mass spectrometric analysis, however, may be hampered by peptide-specific characteristics, including size, shape, poor solubility, adsorption to the polyacrylamide, and-in the case of cross-linking applications-by the branched structure of the peptides produced. This can be a limitation in cross-linking studies where efficient recoveries of the cross-linked peptides are critical. To overcome this limitation, we have developed a modification to the standard in-gel digestion procedure for SDS-PAGE-separated cross-linked proteins, based on older passive diffusion methods. By omitting the gel staining and gel fixation steps, intact proteins or cross-linked protein complexes can move through the gel and into the buffer solution. Digestion of the entire protein in the buffer outside the gel increases the probability that most of the proteolytic peptides produced will be present in the final digest solution. The resulting peptide mixture is then freed of SDS and concentrated using SCX (strong cation exchange) zip-tips and analyzed by mass spectrometry. For standard protein identification studies and the recovery of noncross-linked peptides, the in-gel procedure outperformed the out-gel procedure, but for cross-linking studies with enrichable cross-linkers (such as CBDPS), the standard out-gel procedure allowed the recoveries of cross-links not recovered via the in-gel method. Labeling experiments showed that, with an enrichable cross-linker, 93% of the cross-links showed better or equal recoveries with the out-gel procedure, as compared to the in-gel procedure. It should be noted that this method is not designed to replace in-gel digestion for most proteomics applications. However, by using the out-gel method, we were able to detect twice as many interprotein CBDPS cross-links from the histone H2A/H2B complex as were found in the in-gel digested sample. PMID:24354799

  7. Photo-initiated cross-linked polyacrylamide gels for microdevice electrophoresis 

    E-print Network

    Agrawal, Shilpa

    2005-08-29

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

  8. Photo-initiated cross-linked polyacrylamide gels for microdevice electrophoresis

    E-print Network

    Agrawal, Shilpa

    2005-08-29

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

  9. Reverse hyaluronan substrate gel zymography procedure for the detection of hyaluronidase inhibitors.

    PubMed

    Mio, K; Stern, R

    2000-11-01

    Little is known of the ubiquitous inhibitors of hyaluronidase, molecules that may be important for the deposition of hyaluronan. A reverse hyaluronan-substrate gel procedure is described here that detects such inhibitors, even in crude biological extracts, and is independent of the catalytic mechanism of the target enzyme. Following electrophoresis, hyaluronan-containing gels are incubated in a hyaluronidase solution. Alcian blue-staining bands indicate hyaluronan protected from degradation and the location of hyaluronidase inhibitors. Coordinated use of hyaluronan substrate gel and reverse substrate gel procedures provides estimates of the number and relative molecular sizes of both enzymes and their inhibitors. PMID:11443277

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

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

  11. 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 ...

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

    PubMed

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

    2014-11-21

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

  13. Structure and kinetics of chemically cross-linked protein gels from small-angle X-ray scattering

    E-print Network

    Kaieda, Shuji; Halle, Bertil

    2014-01-01

    Glutaraldehyde (GA) reacts with amino groups in proteins, forming intermolecular cross-links that, at sufficiently high protein concentration, can transform a protein solution into a gel. Although GA has been used as a cross-linking reagent for decades, neither the cross-linking chemistry nor the microstructure of the resulting protein gel have been clearly established. Here we use small-angle X-ray scattering (SAXS) to characterise the microstructure and structural kinetics of gels formed by cross-linking of pancreatic trypsin inhibitor, myoglobin or intestinal fatty acid-binding protein. By comparing the scattering from gels and dilute solutions, we extract the structure factor and the pair correlation function of the gel. The protein gels are spatially heterogeneous, with dense clusters linked by sparse networks. Within the clusters, adjacent protein molecules are almost in contact, but the protein concentration in the cluster is much lower than in a crystal. At the $\\sim$ 1 nm SAXS resolution, the native ...

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

    E-print Network

    Alice von der Heydt; Annette Zippelius

    2014-09-29

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

  15. 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 ? of irreversible, type-selective cross-links between random pairs of A blocks. Self-assembly into a periodic pattern of A/B-rich microdomains (microphase separation) is controlled by the AB incompatibility ? inversely proportional to temperature. Our model aims to capture the system's essential microscopic features, including an ensemble of random networks that reflects spatial correlations at the instant of cross-linking. We identify suitable order parameters and derive a free-energy functional in the spirit of Landau theory that allows us to trace a phase diagram in the plane of ? and ?. Selective cross-links promote microphase separation at higher critical temperatures than in uncross-linked diblock copolymer melts. Microphase separation in the liquid state facilitates gelation, giving rise to a novel gel state whose chemical composition density mirrors the periodic AB pattern. PMID:25662662

  16. 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 ? of irreversible, type-selective cross-links between random pairs of A blocks. Self-assembly into a periodic pattern of A/B-rich microdomains (microphase separation) is controlled by the AB incompatibility ? inversely proportional to temperature. Our model aims to capture the system's essential microscopic features, including an ensemble of random networks that reflects spatial correlations at the instant of cross-linking. We identify suitable order parameters and derive a free-energy functional in the spirit of Landau theory that allows us to trace a phase diagram in the plane of ? and ?. Selective cross-links promote microphase separation at higher critical temperatures than in uncross-linked diblock copolymer melts. Microphase separation in the liquid state facilitates gelation, giving rise to a novel gel state whose chemical composition density mirrors the periodic AB pattern.

  17. 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-?-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

  18. 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

  19. Cross-linking patterns and their images in swollen and deformed gels

    E-print Network

    Sergey Panyukov; Yitzhak Rabin

    2015-07-10

    Using the theory of elasticity of polymer gels we show that large-scale cross-link density patterns written into the structure of the network in the melt state, can be revealed upon swelling by monitoring the monomer density patterns. We find that while isotropic deformations in good solvent yield magnified images of the original pattern, anisotropic deformations distort the image (both types of deformation yield affinely stretched images in $\\theta$ solvents). We show that in ordinary solids with spatially inhomogeneous profile of the shear modulus, isotropic stretching leads to distorted density image of this profile under isotropic deformation. Using simple physical arguments we demonstrate that the different response to isotropic stretching stems from fundamental differences between the theory of elasticity of solids and that of gels. Possible tests of our predictions and some potential applications are discussed.

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

    PubMed

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

    2013-09-01

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

  1. Structure and kinetics of chemically cross-linked protein gels from small-angle X-ray scattering.

    PubMed

    Kaieda, Shuji; Plivelic, Tomás S; Halle, Bertil

    2014-03-01

    Glutaraldehyde (GA) reacts with amino groups in proteins, forming intermolecular cross-links that, at sufficiently high protein concentration, can transform a protein solution into a gel. Although GA has been used as a cross-linking reagent for decades, neither the cross-linking chemistry nor the microstructure of the resulting protein gel have been clearly established. Here we use small-angle X-ray scattering (SAXS) to characterise the microstructure and structural kinetics of gels formed by cross-linking of pancreatic trypsin inhibitor, myoglobin or intestinal fatty acid-binding protein. By comparing the scattering from gels and dilute solutions, we extract the structure factor and the pair correlation function of the gels. The protein gels are spatially heterogeneous, with dense clusters linked by sparse networks. Within the clusters, adjacent protein molecules are almost in contact, but the protein concentration in the cluster is much lower than in a crystal. At the ?1 nm SAXS resolution, the native protein structure is unaffected by cross-linking. The cluster radius is in the range 10-50 nm, with the cluster size determined mainly by the availability of lysine amino groups on the protein surface. The development of structure in the gel, on time scales from minutes to hours, appears to obey first-order kinetics. Cross-linking is slower at acidic pH, where the population of amino groups in the reactive deprotonated form is low. These results support the use of cross-linked protein gels in NMR studies of protein dynamics and for modeling NMR relaxation in biological tissue. PMID:24445422

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

    NASA Astrophysics Data System (ADS)

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

    2012-06-01

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

  3. 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 (?), which reflects the average size of expanding clusters. Their growth in PC gels is restricted by the triple-helices (? ? 10s of Å), while ? 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

  4. Investigation of the adsorption behavior of glycine peptides on 12% cross-linked agarose gel media.

    PubMed

    Zhang, Xiaoou; Samuelsson, Jörgen; Janson, Jan-Christer; Wang, Changhai; Su, Zhiguo; Gu, Ming; Fornstedt, Torgny

    2010-03-19

    The highly cross-linked 12% agarose gel Superose 12 10/300 GL causes retardation of glycine peptides when mobile phases containing varying concentrations of acetonitrile in water are used. An investigation has been made into the retention mechanism behind this retardation using the glycine dipeptide (GG) and tripeptide (GGG) as models. The dependence of retention times of analytical-size peaks under different experimental conditions was interpreted such that the adsorption most probably was caused by the formation of hydrogen bonds but that electrostatic interactions cannot be ruled out. Thereafter, a nonlinear adsorption study was undertaken at different acetonitrile content in the eluent, using the elution by characteristic points (ECPs) method on strongly overloaded GG and GGG peaks. With a new evaluation tool, the adsorption energy distribution (AED) could be calculated prior to the model selection. These calculations revealed that when the acetonitrile content in the eluent was varied from 0% to 20% the interactions turned from (i) being homogenous (GG) or mildly heterogeneous (GGG), (ii) via a more or less stronger degree of heterogeneity around one site to (iii) finally a typical bimodal energy interaction comprising of two sites (GG at 20% and GGG at 10% and 20%). The Langmuir, Tóth and bi-Langmuir models described these interesting adsorption trends excellently. Thus, the retardation observed for these glycine peptides is interpreted as being of mixed-mode character composed of electrostatic bonds and hydrogen bonds. PMID:20167326

  5. Study of CO2 Mobility Control Using Cross-linked Gel Conformance Control and CO2 Viscosifiers in Heterogeneous Media 

    E-print Network

    Cai, Shuzong

    2011-10-21

    result, early gas breakthrough has been a very common problem in CO2-related projects, reducing the overall sweep efficiency of CO2 flooding. This research aims at improving the CO2 flood efficiency using cross-linked gel conformance control and CO2...

  6. 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

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

    PubMed

    Gebauer, Kurt; Brown, Pam; Varigos, George

    2003-02-01

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

  8. A study of cross-linked PEO gel polymer electrolytes using bisphenol A ethoxylate diacrylate: ionic conductivity and mechanical properties

    NASA Astrophysics Data System (ADS)

    Kang, Yongku; Cheong, Kwangjo; Noh, Kun-Ae; Lee, Changjin; Seung, Do-Young

    Ionic conductivity, mechanical stability and electrochemical property were examined on the poly ethyleneoxide (PEO) based cross-linked gel polymer electrolyte. Bisphenol A ethoxylate diacrylates (BPAEDA) with different numbers of ethylene oxide units ( n=4, 15) were used as cross-linkers. The curing kinetics of the cross-linker was examined by an FT-IR study with two types of initiators and at different curing temperatures. Higher conductivity was observed for the longer ethylene oxide unit. Conductivity of the polymer electrolyte prepared from BPAEDA ( n=15) and liquid electrolyte (70 wt.%) was 3.47×10 -3 S/cm at 30 °C. Improved tensile strength and elongation at break were realized from the polymer electrolyte using BPAEDA as a cross-linker. Electrolyte having higher cross-linking density showed higher tensile strength, but showed decreased flexibility. The stability of the polymer electrolyte against electrochemical oxidation could be extended to larger than 4.5 V (versus Li/Li +). Lithium cycling efficiency of the polymer electrolyte was about 80%.

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

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

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

  10. Case study: Hydraulic fracturing with cross-linked gels in the Oriskany formation to improve gas storage deliverability

    SciTech Connect

    Stiles, E.K.; Reese, R.R.

    1995-12-31

    During the summer and fall of 1994, CNG Transmission Corporation fracture-stimulated thirty (30) gas storage wells with a cross-linked gel fluid system. The work was done to increase late season field deliverability. Individual well tests taken to date have shown that, on average, per-well deliverability has increased by a factor of five. The text that follows will detail the engineering and geologic aspects, procedures, results, and analysis of the project. A discussion of the strategic placement of the storage fields involved will be presented, along with a review of FERC Order 636 and it`s impact on the current gas storage business mechanics. Overviews are presented on the geology, reservoir properties, and characteristics of the storage fields involved in the project. General well design and well completion configuration are discussed. Fracturing/refracturing candidate selection criteria are presented. Basic fracturing design criteria are discussed including: fluid parameters, geometry, proppant selection, and concentration. Discussions of observations and minor changes in treatment designs which occurred between the different fields are discussed. The treatments are summarized and compared on a pre and post fracturing deliverability test analysis. Explanations are offered for wells with exceptional results, as well as marginally successful treatments.

  11. 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.

  12. Diffusion, conductivity and DSC studies of a polymer gel electrolyte composed of cross-linked PEO, ?-butyrolactone and LiBF 4

    Microsoft Academic Search

    Kikuko Hayamizu; Yuichi Aihara; Shigemasa Arai; William S Price

    1998-01-01

    The gel electrolyte system composed of ?-butyrolactone (GBL), LiBF4, and cross-linked acrylated polyethylene oxide (PEO) with a molecular weight of 4000 (PEO4) was studied using the pulsed field gradient (PFG) NMR method to measure the diffusion coefficients. The NMR spin-lattice relaxation times, ionic conductivities and thermal behaviour were also measured. Seven reference samples were also prepared: pure GBL (sample A),

  13. Isolation and purification of flavonoid and isoflavonoid compounds from the pericarp of Sophora japonica L. by adsorption chromatography on 12% cross-linked agarose gel media

    Microsoft Academic Search

    Yuanying Qi; Ailing Sun; Renmin Liu; Zhaoling Meng; Hongyan Xie

    2007-01-01

    A method for isolation and purification of flavonoid and isoflavonoid compounds in extracts of the pericarp of Sophora japonica L. was established by adsorption chromatography on the 12% cross-linked agarose gel Superose 12. The crude extracts were pre-separated to two parts, sample A and sample B, on a D-101 macroporous resin column by elution with 20% ethanol and 40% ethanol,

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

    PubMed

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

    2012-09-01

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

  15. 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

  16. 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. [and others

    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.

  17. Collagen cross-linking with Au nanoparticles.

    PubMed

    Castaneda, Luciano; Valle, Judith; Yang, Nina; Pluskat, Suzanne; Slowinska, Katarzyna

    2008-12-01

    Tiopronin (N-(2-mercaptopropionyl)glycine)-protected gold nanoparticles (TPAu) were cross-linked to collagen via EDC (1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide) coupling. On average, each TPAu forms eight amide bonds with collagen lysine moieties. The resulting gels were studied with environmental SEM, TEM, micro-DSC, and TNBS assay. The porous structure of collagen was significantly altered by cross-linking, resulting in the reduction of the pore size from ca. 140 to <1 microm depending on the concentration of nanoparticles. The collagenase biodegradation assay showed improved stability of cross-linked material. The cell viability assay, CellTiter96, indicates that the gold nanoparticles are not toxic at the concentrations used in gel synthesis. This new material has potential for the delivery of small molecule drugs as well as Au nanoparticles for photothermal therapies, imaging, and cell targeting. PMID:18959440

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

    Microsoft Academic Search

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

    2007-01-01

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

  19. Comparative evaluation of the swelling and degrees of cross-linking in three organic gel packings for SEC through some geometric parameters

    Microsoft Academic Search

    Rosa Garc??a; Clara M Gómez; Armando Codoñer; Concepción Abad; Agust??n Campos

    2003-01-01

    The size exclusion chromatographic (SEC) behavior of five solvent\\/polymer systems in three organic column packings based on polystyrene\\/divinylbenzene (PS\\/DVB) copolymer, TSK-Gel HHR, ?-styragel and TSK-Gel HXL, has been compared. All the packings offer similar characteristics (pore size, particle size and efficiency) but some differences have been found when eluting the same systems. The different elution behavior observed in both polymeric

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

    NASA Astrophysics Data System (ADS)

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

    2013-07-01

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

  1. Effect of Colloidal Fillers on the Cross-Linking of a UV-Curable Polymer: Gel Point Rheology and the Winter-Chambon Criterion

    E-print Network

    Raghavan, Srinivasa

    -curable polymer systems is their gelation behavior, in particular, the kinetics of gelation as well as the instant of incipient gelation or gel point. Recently, we have systematically elucidated the gelation behavior of a neat that the intersection point of the tan s indeed occurs at the chemical gelation time. In recent years, the validity

  2. DNA Interstrand Cross-Linking by Epichlorohydrin

    PubMed Central

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

    2008-01-01

    Epichlorohydrin (ECH), an important industrial chemical, is a bifunctional alkylating agent with the potential to form DNA cross-links. Occupational exposure to this suspect carcinogen leads to chromosomal aberrations, and ECH has been shown previously to undergo reaction with DNA in vivo and in vitro.We used denaturing polyacrylamide gel electrophoresis to monitor the possible formation of interstrand cross-links within DNA oligomers by ECH and the related compound, epibromohydrin (EBH). Although both compounds did indeed form cross-links between deoxyguanosine residues, EBH was a more efficient cross-linker than ECH. The optimal pH for cross-linking also varied, with ECH more efficient at pH 5.0 and EBH more efficient at pH 7.0. Both agents were relatively flexible in the sequences targeted, with comparable efficiencies for 5?-GGC and 5?GC sites. Furthermore, interstrand cross-linking by the two optical isomers of ECH correlated with their relative cytotoxicities, with R-ECH about twice as potent as S-ECH. PMID:17441735

  3. Hyaluronan in human malignancies

    SciTech Connect

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

    2011-02-15

    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.

  4. Cross-Linked Polymers Video

    NSDL National Science Digital Library

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

  5. Chitosan cross-linked with Mo(VI) polyoxyanions: a new gelling system.

    PubMed

    Draget, K I; Vårum, K M; Moen, E; Gynnild, H; Smidsrød, O

    1992-01-01

    A procedure for preparing homogeneous chitosan gels by in situ molybdate cross-linking is described. The gels are obtained by dispersing solid MoO3 in a buffered chitosan solution and the polymer is cross-linked by formation of heavily negatively charged molybdate polyoxyanions. The resulting ionic gels are very transparent, thermoirreversible and can be made at low polymer concentrations. Depending on the ionic strength, these gels are able to swell several times their original size in aqueous solutions. Estimates of the degree of cross-linking reveal a very open pore structure which is confirmed by electron micrographs of the gel. PMID:1391410

  6. The measurement of the viscosity of cross-linked fracture fluids using a FANN Model 50C rotational viscometer 

    E-print Network

    Bastian, Peter Andrae

    1983-01-01

    which link together the long molecular chains already found in the base gels. The cross-linking mechanism creates even longer molecules, which dramatically increases the viscosity of the fluid. These fluids are commonly called cross-linked... measurement of the viscosity of cross-linked fracture fluids very difficult. 14 EXPERINENTAL PROCEDVRE Introduction This investigation involved the testing of two different types of cross-linking systems, non-delayed and delayed. The base gel was a 40 8...

  7. Electrospun cross linked rosin fibers

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

  8. 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

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

    Microsoft Academic Search

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

    2005-01-01

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

  10. Graphene oxide cross-linked chitosan nanocomposite membrane

    NASA Astrophysics Data System (ADS)

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

    2013-09-01

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

  11. Determination of several variables affecting laboratory measurements of cross-linked fracture fluids 

    E-print Network

    Wilson, Matilda Jane

    1982-01-01

    . . . . . . . . . . . . . . . 55 Effect of Initial RPM Setting on Shear Stress Readings . . . . , . . . . . . . . . . . . . . . . . 5 6 Effect of Different Base Gel Viscosities on Shear Stress Readings of two Cross-linked Samples at Constant 200 RPM Settings 0-1 Variations... and be easy to remove from the formation. The rate of leakoff and the proppant carrying ability are essentially dependent on the viscosity of the fracture fluid. The most common fluids used in fracturing are cross-linked polymer gels. The polymers used...

  12. Dual cross-linking ribonucleoprotein immunoprecipitation assay.

    PubMed

    Khan, Dilshad H; Davie, James R

    2014-08-01

    Ribonucleoprotein immunoprecipitation (RIP) is an antibody-based method to detect RNA-protein interactions in situ. In the assay, UV cross-linking is commonly used to preserve RNA-protein interactions for subsequent target identification. UV light is a zero-length cross linker and thus identifies proteins directly bound to RNAs. Here, we describe a dual cross-linking RIP method that involves sequential protein-protein cross-linking step with a protein-protein cross-linker, followed by protein-RNA fixation by UV irradiation. In this way, proteins that indirectly bound to RNA can be analyzed. PMID:24935679

  13. Sulphilimine cross-links in Goodpasture's disease.

    PubMed

    Vanacore, R; Pedchenko, V; Bhave, G; Hudson, B G

    2011-05-01

    The sulphilimine cross-link of the Goodpasture (GP) autoantigen is a novel molecular mechanism (structural constraint) for conferring immune privilege to a site which otherwise is susceptible to structural changes that induce an immunogenic and pathogenic conformation. Perturbation of the assembly or cleavage of the sulphilimine cross-links could be a key factor in the aetiology of Goodpasture's disease in susceptible individuals. PMID:21447121

  14. Polynucleotide cross-linking by aluminum.

    PubMed

    Karlik, S J; Eichhorn, G L

    1989-12-01

    The observations that there was an increased concentration of Al in the brains of Alzheimer's, Guam-Parkinson, and amyotrophic lateral sclerosis disease patients and that there was an apparent localization of the Al in chromatin led to a study of the interaction of Al(III) with DNA. We have previously shown that Al cross-links calf thymus DNA at low pH (S. J. Karlik, G. L. Eichhorn, P. N. Lewis, and D. R. Crapper, Biochemistry 19, 5991 [1980]). Extended studies indicate that cross-linking occurs in DNAs of all base ratios, including polydAdT and polydGdC. Since Al cross-links prevent renaturation in polydAdT, the decrease in the amount of polymer renatured in the presence of Al becomes a quantitative appraisal of the extent of cross-linking. Saturation of cross-linking occurs at a 0.4 ratio of Al to nucleotide phosphate, indicating that potentially 80% of the base pairs are Al bound. Cross-links are broken at elevated pH and by EDTA. PMID:2560791

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

    PubMed

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

    2013-08-12

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

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

    NASA Astrophysics Data System (ADS)

    Vink, Richard L. C.; Heussinger, Claus

    2012-01-01

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

  17. Modified gum arabic cross-linked gelatin scaffold for biomedical applications.

    PubMed

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

    2014-10-01

    The present work deals with development of modified gum arabic cross-linked gelatin scaffold for cell culture. A new biocompatible scaffold was developed by cross-linking gelatin (Gel) with gum arabic, a polysaccharide. Gum arabic was subjected to periodate oxidation to obtain gum arabic aldehyde (GAA). GAA was reacted with gelatin under appropriate pH to prepare the cross-linked hydrogel. Cross-linking occurred due to Schiff's base reaction between aldehyde groups of oxidized gum arabic and amino groups of gelatin. The scaffold prepared from the hydrogel was characterized by swelling properties, degree of cross-linking, in vitro degradation and scanning electron microscopy (SEM). Cytocompatibility evaluation using L-929 and HepG2 cells confirmed non-cytotoxic and non-adherent nature of the scaffold. These properties are essential for generating multicellular spheroids and hence the scaffold is proposed to be a suitable candidate for spheroid cell culture. PMID:25175214

  18. The effect of substrate stiffness, thickness, and cross-linking density on osteogenic cell behavior.

    PubMed

    Mullen, Conleth A; Vaughan, Ted J; Billiar, Kristen L; McNamara, Laoise M

    2015-04-01

    Osteogenic cells respond to mechanical changes in their environment by altering their spread area, morphology, and gene expression profile. In particular, the bulk modulus of the substrate, as well as its microstructure and thickness, can substantially alter the local stiffness experienced by the cell. Although bone tissue regeneration strategies involve culture of bone cells on various biomaterial scaffolds, which are often cross-linked to enhance their physical integrity, it is difficult to ascertain and compare the local stiffness experienced by cells cultured on different biomaterials. In this study, we seek to characterize the local stiffness at the cellular level for MC3T3-E1 cells plated on biomaterial substrates of varying modulus, thickness, and cross-linking concentration. Cells were cultured on flat and wedge-shaped gels made from polyacrylamide or cross-linked collagen. The cross-linking density of the collagen gels was varied to investigate the effect of fiber cross-linking in conjunction with substrate thickness. Cell spread area was used as a measure of osteogenic differentiation. Finite element simulations were used to examine the effects of fiber cross-linking and substrate thickness on the resistance of the gel to cellular forces, corresponding to the equivalent shear stiffness for the gel structure in the region directly surrounding the cell. The results of this study show that MC3T3 cells cultured on a soft fibrous substrate attain the same spread cell area as those cultured on a much higher modulus, but nonfibrous substrate. Finite element simulations predict that a dramatic increase in the equivalent shear stiffness of fibrous collagen gels occurs as cross-linking density is increased, with equivalent stiffness also increasing as gel thickness is decreased. These results provide an insight into the response of osteogenic cells to individual substrate parameters and have the potential to inform future bone tissue regeneration strategies that can optimize the equivalent stiffness experienced by a cell. PMID:25863052

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

    Microsoft Academic Search

    TOSHIKI INAGAKI; PAUL A. SEIB

    1992-01-01

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

  20. 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

  1. Cross-linked structure of network evolution

    PubMed Central

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

    2014-01-01

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

  2. Cross-linked structure of network evolution

    SciTech Connect

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

    2014-03-15

    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.

  3. 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.

  4. 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.

  5. 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.

  6. Tea Derived Galloylated Polyphenols Cross-Link Purified Gastrointestinal Mucins

    PubMed Central

    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

  7. Contraction of cross-linked actomyosin bundles

    E-print Network

    Yoshinaga, Natsuhiko

    2015-01-01

    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 time scale for contraction as a viscoelastic time tau, where the viscosity is due to (internal) protein friction. We obtain an estimate of the order of magnitude of the contraction time tau ~ 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.

  8. Interactions between Colloids Induced by a Soft Cross-Linked Polymer Substrate

    Microsoft Academic Search

    Lorenzo di Michele; Taiki Yanagishima; Anthony R. Brewer; Jurij Kotar; Erika Eiser; Seth Fraden

    2011-01-01

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

  9. 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

  10. Hyaluronan-Dependent Pericellular Matrix

    PubMed Central

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

    2007-01-01

    Hyaluronan is a multifunctional glycosaminoglycan that forms the structural basis of the pericellular matrix. Hyaluronan is extruded directly through the plasma membrane by one of three hyaluronan synthases and anchored to the cell surface by the synthase or cell surface receptors such as CD44 or RHAMM. Aggregating proteoglycans and other hyaluronan-binding proteins, contribute to the material and biological properties of the matrix and regulate cell and tissue function. The pericellular matrix plays multiple complex roles in cell adhesion/de-adhesion, and cell shape changes associated with proliferation and locomotion. Time-lapse studies show that pericellular matrix formation facilitates cell detachment and mitotic cell rounding. Hyaluronan crosslinking occurs through various proteins, such as tenascin, TSG-6, inter-alpha-trypsin inhibitor, pentraxin and TSP-1. This creates higher order levels of structured hyaluronan that may regulate inflammation and other biological processes. Microvillous or filopodial membrane protrusions are created by active hyaluronan synthesis, and form the scaffold of hyaluronan coats in certain cells. The importance of the pericellular matrix in cellular mechanotransduction and the response to mechanical strain are also discussed. PMID:17804111

  11. 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.

  12. Hybrid cross-linking characteristics of hydrogel control stem cell fate.

    PubMed

    Rajesh Krishnan, G; Cheah, Calvin; Sarkar, Debanjan

    2015-06-01

    Controlling hydrogel structures by combination of physical and chemical cross-links provides a novel system to regulate (stem) cell fate. In this study, we designed a polyethylene glycol (PEG)-based hydrogel where the polymer chains contain both physical and chemical cross-linking units in the same chain with self-assembling L-tyrosine-based dipeptides and photopolymerizable polyacrylate groups, respectively. It is shown that hydrogel architectures derived from this polymer are correlated to the cross-linking mechanisms. Combination of these cross-links controls three-dimensional gel architecture to regulate stem cell behavior in these hydrogels. Particularly, interaction of mesenchymal stem cells with the hydrogel enabled cellular aggregation to enhance chondrogenic differentiation as observed from the deposition of chondrogenic matrix. Increased chondrogenesis was due to enhanced cell-cell adhesion, which was mediated by gel morphology. This study shows the interplay of physical and chemical cross-links in hydrogels to regulate stem cell function and provides a novel molecular engineering tool for controlling hydrogel properties. PMID:25771753

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

    PubMed

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

    2011-09-12

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

  14. Biology and biotechnology of hyaluronan.

    PubMed

    Viola, Manuela; Vigetti, Davide; Karousou, Evgenia; D'Angelo, Maria Luisa; Caon, Ilaria; Moretto, Paola; De Luca, Giancarlo; Passi, Alberto

    2015-05-01

    The hyaluronan (HA) polymer is a critical component of extracellular matrix with a remarkable structure: is a linear and unbranched polymer without sulphate or phosphate groups. It is ubiquitous in mammals showing several biological functions, ranging from cell proliferation and migration to angiogenesis and inflammation. For its critical biological functions the amount of HA in tissues is carefully controlled by different mechanisms including covalent modification of the synthetic enzymes and epigenetic control of their gene expression. The concentration of HA is also critical in several pathologies including cancer, diabetes and inflammation. Beside these biological roles, the structural properties of HA allow it to take advantage of its capacity to form gels even at concentration of 1 % producing scaffolds with very promising applications in regenerative medicine as biocompatible material for advanced therapeutic uses. In this review we highlight the biological aspects of HA addressing the mechanisms controlling the HA content in tissues as well as its role in important human pathologies. In the second part of the review we highlight the different use of HA polymers in the modern biotechnology. PMID:25971701

  15. Formation of dityrosine cross-links in proteins by oxidation of tyrosine residues.

    PubMed

    Aeschbach, R; Amadò, R; Neukom, H

    1976-08-01

    1. Enzymic oxidation of proteins with peroxidase and hydrogenperoxide at a basic pH value leads to an oxidative phenolic coupling of adjacent tyrosine residues forming cross-linked proteins. 2. Dityrosine (3,3'-bityrosine) was identified as the cross-link in oxidised proteins by thin-layer chromatography, amino acid analysis and fluorescence measurements. 3. Gel filtration experiments with oxidised insulin showed that the cross-linkage is predominantly intermolecular. 4. In tetranitromethane treated proteins, dityrosine could be identified after hydrolysis. PMID:952964

  16. Silk Hydrogels of Tunable Structure and Viscoelastic Properties Using Different Chronological Orders of Genipin and Physical Cross-Linking.

    PubMed

    Elliott, Winston H; Bonani, Walter; Maniglio, Devid; Motta, Antonella; Tan, Wei; Migliaresi, Claudio

    2015-06-10

    Catering the hydrogel manufacturing process toward defined viscoelastic properties for intended biomedical use is important to hydrogel scaffolding function and cell differentiation. Silk fibroin hydrogels may undergo "physical" cross-linking through ?-sheet crystallization during high pressure carbon dioxide treatment, or covalent "chemical" cross-linking by genipin. We demonstrate here that time-dependent mechanical properties are tunable in silk fibroin hydrogels by altering the chronological order of genipin cross-linking with ?-sheet formation. Genipin cross-linking before ?-sheet formation affects gelation mechanics through increased molecular weight, affecting gel morphology, and decreasing stiffness response. Alternately, genipin cross-linking after gelation anchored amorphous regions of the protein chain, and increasing stiffness. These differences are highlighted and validated through large amplitude oscillatory strain near physiologic levels, after incorporation of material characterization at molecular and micron length scales. PMID:25978549

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

    PubMed

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

    2014-11-10

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

  18. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2013-06-01

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

  20. 30S ribosomal proteins cross-linked to 16S RNA by periodate oxidation followed by borohydride reduction

    Microsoft Academic Search

    Jutta Rinke; Richard Brimacombe

    1978-01-01

    Gel electrophoretic techniques have been used to reexamine the RNA-protein cross-linking reaction induced by periodate oxidation and borohydride reduction of 30S ribosomal subunits. The results show that a number of 30S ribosomal proteins become attached to intact 16S RNA by this method, in addition to those already published. It follows that this cross-linking technique as it stands is of little

  1. Thermal cross-linking for biologically degradable materials. Preliminary report.

    PubMed

    Ma, X H; Noishiki, Y; Yamane, Y; Iwai, Y; Marato, D; Matsumoto, A

    1996-01-01

    To diminish undesirable side effects of chemical cross-linking of biodegradable materials, the authors developed a thermal cross-linking method that involved esterification by dehydration under dry conditions. The optimal condition for cross-linking was heating at 130-140 degrees C for 40 hr. Efficacy of the cross-linking was evaluated using enzymatic digestion of 0.01% protease in phosphate buffer at pH 7.4. Collagenous materials without cross-linking were digested completely within 30 min. However, with thermal cross-linking, it required 7 days for digestion. The capacity for holding onto water also was tested. Water content decreased when the cross-link density was increased. As an in vivo experiment, six succinylated collagen sealed vascular grafts treated with thermal cross-linking were implanted in the abdominal aortae of dogs and removed 21 days later. These grafts showed no foreign body reaction, and the collagen layer was almost completely absorbed. A collagen sealed graft cross-linked with formaldehyde used as a control showed a strong foreign body reaction. These results suggest that the physical cross-linking method was suitable for biodegradable biologicals, such as collagenous materials, without the undesirable side effects of chemical cross-linking regents. PMID:8945008

  2. 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 400?m thick corneal stroma saturated with riboflavin, the irradiance at the endothelial level is about 0.18 mW/cm2, which is a factor of 2 smaller than the damage threshold. Conclusion: As long as the corneal stroma treated has a minimal thickness of 400 microns (as recommended), neither corneal endothelium nor deeper structures such as lens and retina will suffer any damages. The light source should provide a homogenous irradiance avoiding hot spots. PMID:21399770

  3. Hyaluronan and proximal tubular cell migration

    Microsoft Academic Search

    TAKAFUMI ITO; JOHN D WILLIAMS; SAPHWAN AL-ASSAF; Glyn O. Phillips; Aled O. Phillips

    2004-01-01

    Hyaluronan and proximal tubular cell migration.BackgroundThe ubiquitous polysaccharide hyaluronan has been associated with both acute renal injury and progressive renal disease. The aim of this study was to examine the effect of hyaluronan on proximal tubular cell migration.MethodsThe proximal tubular cell line, HK-2 cells, were grown in monolayer culture, and cell migration following addition of hyaluronan characterized in an in

  4. 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 (40g/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

  5. Hyaluronan and versican in the control of human T-lymphocyte adhesion and migration.

    PubMed

    Evanko, Stephen P; Potter-Perigo, Susan; Bollyky, Paul L; Nepom, Gerald T; Wight, Thomas N

    2012-03-01

    The ability of lymphocytes to migrate freely through connective tissues is vital to efficient immune function. How the extracellular matrix (ECM) may affect T-cell adhesion and migration is not well understood. We have examined the adhesion and migration of activated human T-lymphocytes on ECM made by fibroblast-like synoviocytes and lung fibroblasts. These cells were minimally interactive until treated with a viral mimetic, Poly I:C. This treatment promoted myofibroblast formation and engendered a higher-order structured ECM, rich in versican and hyaluronan, to which T-cells avidly adhered in a hyaluronidase-sensitive manner. This Poly I:C-induced matrix impeded T-cell spreading and migration on and through synoviocyte monolayers, while hyaluronidase treatment or adding versican antibody during matrix formation reversed the effect on T-cell migration. Hyaluronidase also reversed the spread myofibroblast morphology. These data suggest that the viscous hyaluronan- and versican-rich matrix binds and constrains T-lymphocytes. Using purified matrix components and solid state matrices of defined composition, we uncovered a role for versican in modulating hyaluronan-T-cell interactions. Versican prevented T-cell binding to soluble hyaluronan, as well as the amoeboid shape change on hyaluronan-coated dishes and T-cell penetration of collagen gels. Together, these data suggest that hyaluronan and versican play a role in T-cell trafficking and function in inflamed tissues. PMID:22155153

  6. X-Ray Diffraction Studies of Cross Linked Chitosan With Different Cross Linking Agents For Waste Water Treatment Application

    NASA Astrophysics Data System (ADS)

    Julkapli, Nurhidayatullaili Muhd; Ahmad, Zulkifli; Akil, Hazizan Md

    2010-01-01

    Chitosan is a polysaccharide derived from N-deacetylation of chitin and receiving increased attention as metal ion absorbent in wastewater treatment application. To improve the performance of chitosan as an absorbent, the cross linking approach was applied. Introduction of cross-linking agent would break the crystal zone in chitosan system, making it less crystal and consequently enhanced the absorption area. Therefore, in this study, cross-linked chitosan were prepared using different of cross-linking agents. The chitosan powder was weighed, dissolved in acetic acid (0.1 M), and dropped slowly into absolute N-methyl pyyrolidone solvent containing cross-linking agent. The cross linking reaction was carried out in N2 environment at 150° C for 6 hours. X-ray diffraction (XRD) analysis was applied to characterize the crystallinity of native and cross linked chitosan. Generally, the XRD patterns of all types of chitosan show two crystalline peaks approximately at 10° and 20° (2?). However, the cross linked chitosan with longer length of cross linking agents show lower and broader crystalline peaks as compare to those with shorter length. Similarly, the calculated crystalline index (Cr I) also showed this decreasing tendency.

  7. The many ways to cleave hyaluronan.

    PubMed

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

    2007-01-01

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

  8. Rigidity and ergodicity of randomly cross-linked macromolecules

    Microsoft Academic Search

    Paul Goldbart; Nigel Goldenfeld

    1987-01-01

    We consider a system of randomly cross-linked, interacting macromolecules, within the framework of replica field theory. We find that above a critical number of cross links, translational and replica symmetry are simultaneously broken, thus showing that the system is an equilibrium amorphous solid, with many pure phases unrelated by global symmetry. We argue that each symmetry-unrelated pure phase describes a

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

    NASA Technical Reports Server (NTRS)

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

    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.

  10. Preparation and characterization of cross-linked carboxymethyl chitin porous membrane scaffold for biomedical applications.

    PubMed

    Zhao, Liqing; Wu, Yiguang; Chen, Shu; Xing, Tao

    2015-08-01

    Porous dermal scaffold membrane (PDSM) was successfully prepared by using a so-called sol-gel freeze-drying method. In this method, the carboxymethyl chitin (CMC) hydrosol was first cross-linked by 1-ethyl-3-[3-dimethylaminopropyl] carbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS), and then lyophilized to form the PDSM. For the first time, this research focused on the cross-linked CMC as the only component for three-dimensional PDSM. The effects of cross-linking conditions on the performance of the PDSM were investigated. And PDSM with optimal performance was obtained through 4-h cross-linking at 4wt% of CMC concentration in the hydrosol, where the mass ratio of EDC to NHS to CMC was 5:3:10. The porosity of the optimized PDSM was more than 90% and the water swelling rate was above 4000%. The pore size was well distributed and was between 100?m and 200?m. And the tensile strength was above 0.09MPa. The as-made PDSM could be degraded above 80% in 12 days in the presence of a 0.2mg/mL lysozyme solution. Very importantly, the PDSM had no cytotoxicity and good biocompatibility from MTT assays. Our results showed the application possibility of the as-prepared PDSM as dermal scaffold for skin tissue engineering. PMID:25933533

  11. Cross-linked hydroxypropylcellulose films: mechanical behaviour and electro-optical properties of PDLC type cells

    NASA Astrophysics Data System (ADS)

    Almeida, P. L.; Tavares, S.; Martins, A. F.; Godinho, M. H.; Cidade, M. T.; Figueirinhas, J. L.

    2002-09-01

    We study the effect of the amount of cross-linking agent upon the mechanical and electro-optical behaviour of several cells prepared from hydroxypropylcellulose (HPC) cross-linked with 1,4 diisocianatobutane (BDI) (0.0%, 3.1%, 7.6%, 12.3% w/w). The tensile properties and the sol/gel fractions were obtained as a function of the amount of the cross-linking agent used to prepare the solid films. The Young's modulus appears to be constant, over the range of concentrations studied. The electro-optical cells prepared with the nematic liquid crystal (E7) were analysed by light transmission. Several trends were observed, e.g. the cross-linking agent, at the percentages used, has a strong influence on the cells contrast but not on the cell's maximum transmission or turn on voltage, while the film thickness shows preponderantly its influence on the cell's maximum transmission and turn on voltage. The mechanical properties of the HPC films are important for a recent application that is now being developed [Liq. Cryst., in press], where a flexible substrate is used. The results obtained point out ways for the realisation of an optimum electro-optical cell.

  12. Radiation cross-linked collagen/dextran dermal scaffolds: effects of dextran on cross-linking and degradation.

    PubMed

    Zhang, Yaqing; Zhang, Xiangmei; Xu, Ling; Wei, Shicheng; Zhai, Maolin

    2015-01-01

    Ionizing radiation effectively cross-links collagen into network with enhanced anti-degradability and biocompatibility, while radiation-cross-linked collagen scaffold lacks flexibility, satisfactory surface appearance, and performs poor in cell penetration and ingrowth. To make the radiation-cross-linked collagen scaffold to serve as an ideal artificial dermis, dextran was incorporated into collagen. Scaffolds with the collagen/dextran (Col/Dex) ratios of 10/0, 7/3, and 5/5 were fabricated via (60)Co ?-irradiation cross-linking, followed by lyophilization. The morphology, microstructure, physicochemical, and biological properties were investigated. Compared with pure collagen, scaffolds with dextran demonstrated more porous appearance, enhanced hydrophilicity while the cross-linking density was lower with the consequence of larger pore size, higher water uptake, as well as reduced stiffness. Accelerated degradation was observed when dextran was incorporated in both the in vitro and in vivo assays, which led to earlier integration with cell and host tissue. The effect of dextran on degradation was ascribed to the decreased cross-linking density, looser microstructure, more porous and hydrophilic surface. Considering the better appearance, softness, moderate degradation rate due to controllable cross-linking degree and good biocompatibility as well, radiation-cross-linked collagen/dextran scaffolds are expected to serve as promising artificial dermal substitutes. PMID:25431991

  13. Gelation and Cross-Linking in Multifunctional Thiol and Multifunctional Acrylate Systems Involving an in Situ Comonomer

    E-print Network

    Khan, Saad A.

    Gelation and Cross-Linking in Multifunctional Thiol and Multifunctional Acrylate Systems Involving transform infrared spectroscopy (FTIR) is used to examine the gelation kinetics, mechanism, and gel point of novel thiol-acrylate systems containing varying concentrations of an in situ catalyst. Gelation

  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 (?-? stacking and cation-?) 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. High mobility group protein number17 cross-links primarily to histone H2A in the reconstituted HMG 17 - nucleosome core particle complex

    SciTech Connect

    Cook, G.R.; Yau, P.; Yasuda, H.; Traut, R.R.; Bradbury, E.M.

    1986-05-01

    The neighbor relationship of lamb thymus High Mobility Group (HMG) protein 17 to native HeLa nucleosome core particle histones in the reconstituted complex has been studied. /sup 125/I-labeled HMG 17 was cross-linking to core histones using the protein-protein cross-linking reagent 2-iminothiolane. Specific cross-linked products were separated on a two-dimensional Triton-acid-urea/SDS gel system, located by autoradiography, excised and quantified. Disulfide bonds in the cross links were then cleaved and the protein constituents were identified by SDS gel electrophoresis. HMG 17 cross-linked primarily to histone H2A while lower levels of cross-linking occurred between HMG 17 and the other histones. In contrast, cross-linking between two HMG 17 molecules bound on the same nucleosome was relatively rare. It is concluded that the same nucleosome was relatively rare. It is concluded that H2A comprises part of the HMG 17 binding site but that HMG 17 is sufficiently elongated and mobile to permit cross-linking to the other histones and to a second HMG 17 molecule. These results are in agreement with the current model for the structure of the nucleosome and the proposed binding sites for HMG 17.

  16. [Study on 5-carboxyfluorescein N-succinimidyl ester in detecting the degree of cross-linked allogenic tissue].

    PubMed

    Zahng, Jun; Liu, Wenyi; Liu, Luqi

    2010-08-01

    This study was designed to creat a new method for detecting the degree of cross-linked allogenic tissue based on fluorescent technique. The thoracic aorta of New Zealand rabbits were divided randomly into four groups according to the concentration of Glutaraldehyde (GA), which were group A (control group-with no GA), group B (cross-linked with GA of 0.625%), group C (1.25%), and group D (2.5%). Each group was cross-linked with GA and reacted with 5-FAMSE, and then the fluorescence intensity was observed via fluorescence microscopy (analyzed with Image-Pro Plus 6.0, a professional image analysis software). The differences between groups in order of fluorescence intensity were found to be: group A > roup B > group C > group D (P < 0.01). Meanwhile, the tissue proteins extracted from aorta in each group were submitted to conventional polyacrylamide gel electrophoresis (PGE) after being cross-linked with GA; the result from this method was compared with that from the method of 5-FAMSE. In group A, the tissue proteins extracted from the aorta cross-linked with GA were obviously less than those not cross-linked with GA. However, this phenomenom was not clearly seen among the B, C and D groups. Nevertheless, 5-FAMSE can detect the degree of cross-linkage more conveniently and directly. PMID:20842851

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

    PubMed

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

    2011-06-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-01-01

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

  19. 21 CFR 177.2420 - Polyester resins, cross-linked.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

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

  20. Humidity sensor using cross-linked poly(chloromethyl styrene)

    Microsoft Academic Search

    Y. Sakai; M. Matsuguchi; T. Hurukawa

    2000-01-01

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

  1. Large Scale Chemical Cross-linking Mass Spectrometry Perspectives.

    PubMed

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

    2013-02-01

    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 make such a leap. PMID:25045217

  2. 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

  3. Hyaluronan and versican in the control of human T lymphocyte adhesion and migration

    PubMed Central

    Evanko, Stephen P.; Potter-Perigo, Susan; Bollyky, Paul L.; Nepom, Gerald T.; Wight, Thomas N.

    2011-01-01

    The ability of lymphocytes to migrate freely through connective tissues is vital to efficient immune function. How the extracellular matrix (ECM) may affect T cell adhesion and migration is not well understood. We have examined the adhesion and migration of activated human T lymphocytes on extracellular matrix made by fibroblast-like synoviocytes and lung fibroblasts. These cells were minimally interactive until treated with a viral mimetic, Poly I:C. This treatment promoted myofibroblast formation and engendered a higher-order structured ECM rich in versican and hyaluronan to which T cells avidly adhered in a hyaluronidase-sensitive manner. This Poly I:C-induced matrix impeded T-cell spreading and migration on and through synoviocyte monolayers, while hyaluronidase treatment or adding versican antibody during matrix formation reversed the effect on T-cell migration. Hyaluronidase also reversed the spread myofibroblast morphology. These data suggest that the viscous hyaluronan- and versican-rich matrix binds and constrains T lymphocytes. Using purified matrix components and solid state matrices of defined composition we uncovered a role for versican in modulating HA - T-cell interactions. Versican prevented T-cell binding to soluble hyaluronan, as well as the amoeboid shape change on hyaluronan coated dishes and T-cell penetration of collagen gels. Together, these data suggest that hyaluronan and versican play a role in T-cell trafficking and function in inflamed tissues. PMID:22155153

  4. Self-consistent field approach for cross-linked copolymer materials.

    PubMed

    Schmid, Friederike

    2013-07-12

    A generalized self-consistent field approach for polymer networks with a fixed topology is developed. It is shown that the theory reproduces the localization of cross-links, which is characteristic for gels. The theory is then used to study the order-disorder transition in regular networks of end-linked diblock copolymers. Compared to diblock copolymer melts, the transition is shifted towards lower values of the incompatibility parameter ? (the Flory-Huggins parameter). Moreover, the transition becomes strongly first order already at the mean-field level. If stress is applied, the transition is further shifted and finally vanishes in a critical point. PMID:23889451

  5. 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.

  6. 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

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

    PubMed

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

    2011-08-01

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

  8. Hyaluronan: a multifunctional, megaDalton, stealth molecule

    Microsoft Academic Search

    Janet Y Lee; Andrew P Spicer

    2000-01-01

    Hyaluronan has been implicated in biological processes such as cell adhesion, migration and proliferation. Traditionally, it was thought to be associated with the extracellular matrix, but, hyaluronan may also have unimagined roles inside the cell. Investigation of hyaluronan synthesis and degradation, the identification of new receptors and binding proteins, and the elucidation of hyaluronan-dependent signaling pathways are providing novel insights

  9. Enhanced retention of encapsulated ions in cross-linked polymersomes.

    PubMed

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

    2015-03-19

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

  10. Melting of cross-linked DNA v. cross-linking effect caused by local stabilization of the double helix.

    PubMed

    Fridman, Alexander S; Brabec, Viktor; Haroutiunian, Samuel G; Wartell, Roger M; Lando, Dmitri Y

    2003-02-01

    DNA interstrand cross-links are usually formed due to bidentate covalent or coordination binding of a cross-linking agent to nucleotides of different strands. However interstrand linkages can be also caused by any type of chemical modification that gives rise to a strong local stabilization of the double helix. These stabilized sites conserve their helical structure and prevent local and total strand separation at temperatures above the melting of ordinary AT and GC base pairs. This local stabilization makes DNA melting fully reversible and independent of strand concentration like ordinary covalent interstrand cross-links. The stabilization can be caused by all the types of chemical modifications (interstrand cross-links, intrastrand cross-links or monofunctional adducts) if they give rise to a strong enough local stabilization of the double helix. Our calculation demonstrates that an increase in stability by 25 to 30 kcal in the free energy of a single base pair of the double helix is sufficient for this "cross-linking effect" (i.e. conserving the helicity of this base pair and preventing strand separation after melting of ordinary base pairs). For the situation where there is more then one stabilized site in a DNA duplex (e.g., 1 stabilized site per 1000 bp), a lower stabilization per site is sufficient for the "cross-linking effect" (18 - 20 kcal). A substantial increase in DNA stability was found in various experimental studies for some metal-based anti-tumor compounds. These compounds may give rise to the effect described above. If ligand induced stabilization is distributed among several neighboring base pairs, a much lower minimum increase per stabilized base pair is sufficient to produce the cross-linking effect (1 bp- 24.4 kcal; 5 bp- 5.3 kcal; 10 bp- 2.9 kcal, 25 bp- 1.4 kcal; 50 bp- 1.0 kcal). The relatively weak non-covalent binding of histones or protamines that cover long regions of DNA (20- 40 bp) can also cause this effect if the salt concentration of the solution is sufficiently low to cause strong local stabilization of the double helix. Stretches of GC pairs more than 25 bp in length inserted into poly(AT) DNA also exhibit properties of stabilizing interstrand cross-links. PMID:12529152

  11. Cross-linking of micelles by gemini surfactants

    E-print Network

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

    2000-04-12

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

  12. Diepoxybutane Interstrand Cross-Links Induce DNA Bending

    PubMed Central

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

    2011-01-01

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

  13. Cross-linking of two antiparallel vortex tubes

    NASA Technical Reports Server (NTRS)

    Melander, M. V.; Hussain, F.

    1989-01-01

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

  14. Catabolism of hyaluronan: involvement of transition metals.

    PubMed

    Soltés, Ladislav; Kogan, Grigorij

    2009-12-01

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

  15. Catabolism of hyaluronan: involvement of transition metals

    PubMed Central

    Šoltés, Ladislav; Kogan, Grigorij

    2009-01-01

    One of the very complex structures in the vertebrates is the joint. The main component of the joint is the synovial fluid with its high-molar-mass glycosaminoglycan hyaluronan, which turnover is approximately twelve hours. Since the synovial fluid does not contain any hyaluronidases, the fast hyaluronan catabolism is caused primarily by reductive-oxidative processes. Eight transition metals – V23, Mn25, Fe26, Co27, Ni28, Cu29, Zn30, and Mo42 – naturally occurring in living organism are essential for the control of various metabolic and signaling pathways. They are also the key elements in catabolism of hyaluronan in the joint. In this overview, the role of these metals in physiological and pathophysiological catabolism of hyaluronan is described. The participation of these metals in the initiation and propagation of the radical degradation hyaluronan is critically reviewed. PMID:21217859

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

    PubMed

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

    1987-01-01

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

  17. 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

  18. Bacteriophage HK97 structure: wholesale covalent cross-linking between the major head shell subunits.

    PubMed Central

    Popa, M P; McKelvey, T A; Hempel, J; Hendrix, R W

    1991-01-01

    We describe initial genetic and structural characterizations of HK97, a temperate bacteriophage of Escherichia coli. We isolated 28 amber mutants, characterized them with respect to what phage-related structures they make, and mapped many of them to restriction fragments of genomic DNA. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of HK97 virions revealed nine different protein species plus a substantial amount of material that failed to enter the gel, apparently because it is too large. Five proteins are tail components and are assigned functions as tail fiber subunit, tail length template, and major shaft subunit (two and possibly three species). The four remaining proteins and the material that did not enter the gel are head components. One of these proteins is assigned as the portal subunit, and the remaining three head proteins in the gel and the material that did not enter the gel are components of the head shell. All of the head shell protein species have apparent molecular masses well in excess of 100 kDa; they share amino acid sequence with each other and also with a 42-kDa protein that is found in infected lysates and as the major component of prohead structures that accumulate in infections by one of the amber mutants. We propose that all of the head shell species found in mature heads are covalently cross-linked oligomers derived from the 42-kDa precursor during head shell maturation. Images PMID:1709700

  19. 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.

  20. UV laser-induced cross-linking in peptides

    PubMed Central

    Leo, Gabriella; Altucci, Carlo; Bourgoin-Voillard, Sandrine; Gravagnuolo, Alfredo M.; Esposito, Rosario; Marino, Gennaro; Costello, Catherine E.; Velotta, Raffaele; Birolo, Leila

    2013-01-01

    RATIONALE The aim of this study was to demonstrate, and to characterize by high resolution mass spectrometry, that it is possible to preferentially induce covalent cross-links in peptides by using high energy femtosecond UV laser pulses. The cross-link is readily formed only when aromatic amino acids are present in the peptide sequence. METHODS Three peptides, xenopsin, angiotensin I, interleukin, individually or in combination, were exposed to high energy femtosecond UV laser pulses, either alone or in the presence of spin trapping molecules, the reaction products being characterized by high resolution mass spectrometry. RESULTS High resolution mass spectrometry and spin trapping strategies showed that cross-linking occurs readily, proceeds via a radical mechanism, and is the highly dominant reaction, proceeding without causing significant photo-damage in the investigated range of experimental parameters. CONCLUSIONS High energy femtosecond UV laser pulses can be used to induce covalent cross-links between aromatic amino acids in peptides, overcoming photo-oxidation processes, that predominate as the mean laser pulse intensity approaches illumination conditions achievable with conventional UV light sources. PMID:23754800

  1. Water contamination in a cross-linked polyethylene cable joint

    Microsoft Academic Search

    G. W. Rittmann; S. V. Heyer

    1976-01-01

    An analysis of splice failures on a cross-linked polyethylene (XLPE) insulated cable is performed with particular interest in the effects of contaminants and the adsorption of water on surface track resistance of the splice pencil. Many cable users do not give sufficient consideration to the hygroscopic nature of XLPE surfaces when developing splicing procedures. This paper examines some of the

  2. 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.

  3. Advanced Corneal Cross-Linking System with Fluorescence Dosimetry

    PubMed Central

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

    2012-01-01

    Purpose. This paper describes an advanced system that combines corneal cross-linking with riboflavin with fluorescence dosimetry, the ability to measure riboflavin diffusion within the cornea both before and during UVA treatment. Methods and Results. A corneal cross-linking system utilizing a digital micromirror device (DMD) was assembled and used to measure diffusion coefficients of 0.1% riboflavin in 20% dextran in porcine eyes. A value of (3.3 ± 0.2) × 10?7?cm2/s was obtained for the stroma. Diffusion coefficients for the transepithelial formulation of 0.1% riboflavin in 0.44% saline and 0.02% BAK were also measured to be 4.7 ± 0.3 × 10?8?cm2/s for epithelium only and (4.6 ± 0.4) × 10?7?cm2/s for stroma only. Riboflavin consumption during a UVA treatment was also demonstrated. Conclusion. A new advanced corneal cross-linking system with fluorescence dosimetry of riboflavin has been demonstrated. It is hoped that this method may play a significant role in determining the underlying mechanisms of corneal cross-linking and assist with the development of additional riboflavin formulations. Moreover, dosimetry may prove valuable in providing a method to account for the biological differences between individuals, potentially informing cornea-specific UVA treatment doses in real time. PMID:22792444

  4. 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.

  5. Simulation of Fracture Nucleation in Cross-Linked Polymer Networks

    NASA Astrophysics Data System (ADS)

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

    2013-02-01

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

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

    SciTech Connect

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

    2005-07-01

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

  7. Transparent Humidity Sensor Using Cross-Linked Polyelectrolyte Membrane

    SciTech Connect

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

    2009-07-02

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

  8. 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.

  9. Photoresponsive cross-linked polymeric particles for phototriggered burst release.

    PubMed

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

    2013-01-01

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

  10. Multi-gigabit laser communications for satellite cross-links

    Microsoft Academic Search

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

    1979-01-01

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

  11. Hydrogels of collagen hydrolysate cross-linked with dialdehyde starch

    Microsoft Academic Search

    F. Langmaier; M. Mládek; P. Mokrejš

    2009-01-01

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

  12. Synthesis and cross-linking of polyisoprene latexes

    Microsoft Academic Search

    In Woo Cheong; Christopher M. Fellows; Robert G. Gilbert

    2004-01-01

    Seeded and ab initio emulsion polymerizations of isoprene using redox initiation systems were investigated and suitable reaction conditions determined to prepare polyisoprene latexes with minimal cross-linking. Polymerizations initiated with the potassium persulfate\\/sodium bisulfite (KPS\\/SBS) redox couple had a significant inhibition period and low yield. Polymerizations initiated with the tert-butyl hydroperoxide\\/tetraethylene-pentamine redox couple showed reasonable yields and no apparent inhibition. It

  13. Self-cross-linking polyelectrolyte complexes for therapeutic cell encapsulation.

    PubMed

    Mazumder, M A Jafar; Shen, Feng; Burke, Nicholas A D; Potter, Murray A; Stöver, Harald D H

    2008-09-01

    Self-cross-linking polyelectrolytes are used to strengthen the surface of calcium alginate beads for cell encapsulation. Poly([2-(methacryloyloxy)ethyl]trimethylammonium chloride), containing 30 mol % 2-aminoethyl methacrylate, and poly(sodium methacrylate), containing 30 mol % 2-(methacryloyloxy)ethyl acetoacetate, were prepared by radical polymerization. Sequential deposition of these polyelectrolytes on calcium alginate films or beads led to a shell consisting of a covalently cross-linked polyelectrolyte complex that resisted osmotic pressure changes as well as challenges with citrate and high ionic strength. Confocal laser fluorescence microscopy revealed that both polyelectrolytes were concentrated in the outer 7-25 microm of the calcium alginate beads. The thickness of this cross-linked shell increased with exposure time. GPC studies of solutions permeating through analogous flat model membranes showed molecular weight cut-offs between 150 and 200 kg/mol for poly(ethylene glycol), suitable for cell encapsulation. C 2C 12 mouse cells were shown to be viable within calcium alginate capsules coated with the new polyelectrolytes, even though some of the capsules showed fibroid overcoats when implanted in mice due to an immune response. PMID:18665640

  14. 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-1,7-metacarborane, closo-1,12-paracarborane (C2B10H12)] decomposition are investigated. Thermodynamic Born-Haber cycles are constructed for neutral and ionic species in an attempt to systemically characterize closo-carborane decomposition process. The decomposition processes are in favor of lower energy decomposition processes. Among the ionic species the photon induced decomposition is dominated by BH+ and BH 2+ fragment loss, and associated with core to bound excitations. It has been observed that dehydrogenation of the closo-carboranes leads to possible cross-linking and formation of a boron rich semiconductor with good dielectric properties.

  15. Molecular structure of hyaluronan: an introduction

    Microsoft Academic Search

    István Hargittai; Magdolna Hargittai

    2008-01-01

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

  16. Macrophage response to cross-linked and conventional UHMWPE.

    PubMed

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

    2003-07-01

    To prevent wear debris-induced osteolysis and aseptic loosening, cross-linked ultra-high molecular weight polyethylene's (UHMWPE) with improved wear resistance have been developed. Hip simulator studies have demonstrated very low wear rates with these new materials leading to their widespread clinical use. However, the biocompatibility of this material is not known. We studied the macrophage response to cross-linked UHMWPE (XLPE) and compared it to conventional UHMWPE (CPE) as well as other clinically used orthopaedic materials such as titanium-alloy (TiAlV) and cobalt-chrome alloy (CoCr). Human peripheral blood monocytes and murine macrophages, as surrogates for cells mediating peri-implant inflammation, were cultured onto custom designed lipped disks fabricated from the test materials to isolate cells. Culture supernatants were collected at 24 and 48h and analyzed for cytokines such as IL-1alpha, IL-1beta, TNF-alpha and IL-6. Total RNA was extracted from adherent cells and gene expression was analyzed using qualitative RT-PCR. In both in vitro models, macrophages cultured on cross-linked and conventional polyethylene released similar levels of cytokines, which were also similar to levels on control tissue culture dishes. Macrophages cultured on TiAlV and CoCr-alloy released significantly higher levels of cytokines. Human monocytes from all donors varied in the magnitude of cytokines released when cultured on identical surfaces. The variability in individual donor responses to TiAlV and CoCr surfaces may reflect how individuals respond differently to similar stimuli and perhaps reveal a predisposed sensitivity to particular materials. PMID:12726710

  17. 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

    2015-01-13

    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

  18. Biodistribution and magnetic resonance imaging of cross-linked DTPA polysaccharides.

    PubMed

    Gibby, W A; Billings, J; Hall, J; Ovitt, T W

    1990-02-01

    Large polysaccharide complexes, cross-linked with DTPA and chelated with gadolinium have been tested for various potential uses for magnetic resonance imaging (MRI) in rats. Biodistribution and pharmacokinetic data for several of the soluble polymers are presented and compared with Gd-DTPA and GdCl3. By varying the initial polysaccharide length and ratio of DTPA to glucose units, polymers of molecular weights (mol wt) from 17,000 to several million were formed, giving soluble material, gels, or particles. The larger polymers (mol wt greater than 100,000) demonstrate prolonged enhancement of the intravascular space, striking renal enhancement, and moderate hepatic uptake. Small particulate material (less than 10 microns) was also successfully used for intravascular enhancement. The material is metabolized and excreted in urine. PMID:1690184

  19. Humidity sensor using cross-linked copolymers containing viologen moiety

    Microsoft Academic Search

    Myoung-Seon Gong; Myong-Hoon Lee; Hee-Woo Rhee

    2001-01-01

    1-[3-(2-Methacryloxyethyl dimethyl ammono)propyl] 1?-propyl-4,4?-bipyridinium tribromide (MDAPBT) was selected as a humidity-sensing monomer. n-Butyl acrylate (n-BA) and 2-(N,N?-dimethylaminoethyl)methacrylate (DAEMA) were used as a comonomer. The major ingredient of the humid membrane is the copolymers of MDAPBT with n-BA and DAEMA. The cross-linked copolymer of MDAPBT\\/n-BA\\/DAEMA=40\\/30\\/30 showed average resistance of 1000, 52 and 3.1K? at 30, 60 and 90% relative humidity (RH),

  20. 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.

  1. Newer protocols and future in collagen cross-linking.

    PubMed

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

    2013-08-01

    Corneal Cross-Linking (CXL) is an established surgical procedure for the treatment of corneal disorders such as corneal ectasia and keratoconus. This method of treatment stabilises the corneal structure and increases rigidity, reducing the requirement for corneal transplantation. Since its development, many scientific studies have been conducted to investigate ways of improving the procedure. Biomechanical stability of the cornea after exposure to UV-A light, and the effect of shortening procedure time has been some of the many topics explored. PMID:23925329

  2. Newer protocols and future in collagen cross-linking

    PubMed Central

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

    2013-01-01

    Corneal Cross-Linking (CXL) is an established surgical procedure for the treatment of corneal disorders such as corneal ectasia and keratoconus. This method of treatment stabilises the corneal structure and increases rigidity, reducing the requirement for corneal transplantation. Since its development, many scientific studies have been conducted to investigate ways of improving the procedure. Biomechanical stability of the cornea after exposure to UV-A light, and the effect of shortening procedure time has been some of the many topics explored PMID:23925329

  3. Structurally Cross-Linked Composite Proton Exchange Membranes

    SciTech Connect

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

    2007-01-01

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

  4. Loosening of globular structure under alkaline pH affects accessibility of ?-lactoglobulin to tyrosinase-induced oxidation and subsequent cross-linking.

    PubMed

    Partanen, Riitta; Torkkeli, Mika; Hellman, Maarit; Permi, Perttu; Serimaa, Ritva; Buchert, Johanna; Mattinen, Maija-Liisa

    2011-07-10

    Globular proteins such as ?-lactoglobulin (BLG) are poorly accessible to enzymes. We have studied susceptibility of BLG to oxidation by Trichoderma reesei (TrTyr) and Agaricus bisporus (AbTyr) tyrosinases and subsequent intermolecular cross-linking with respect to pH-induced structural changes. We evaluated pH-induced structural changes in BLG using circular dichroism, tryptophan fluorescence and small angle X-ray scattering (SAXS) measurements, where after these results were correlated with the analysis of cross-linking by sodium dodecyl sulphate polyacrylamide gel electrophoresis. Oxygen consumption measurement and changes in radii of gyration determined by SAXS during the enzyme-induced oxidation at the respective reaction conditions were also followed. Intermolecular cross-linking of BLG by TrTyr was found at pH 9 but not at pH 7.5. AbTyr was unable to catalyze cross-linking at pH 7.5 or pH 9. Increased accessibility and cross-linking by TrTyr was addressed to loosening of the three dimensional structure of the protein, increased flexibility of the backbone as well as partial hydrolysis. In addition to basic research of the effect of protein folding on enzymatic cross-linking the research results have significance on the exploitation of TrTyr at alkaline conditions. PMID:22112399

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

    PubMed Central

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

    2010-01-01

    Chemical cross-linking of reactive groups in native proteins and protein complexes in combination with the identification of cross-linked sites by mass spectrometry has been in use for more than a decade. Recent advances in instrumentation, cross-linking protocols, and analysis software have led to a renewed interest in this technique, which promises to provide important information about native protein structure and the topology of protein complexes. In this article, we discuss the critical steps of chemical cross-linking and its implications for (structural) biology: reagent design and cross-linking protocols, separation and mass spectrometric analysis of cross-linked samples, dedicated software for data analysis, and the use of cross-linking data for computational modeling. Finally, the impact of protein cross-linking on various biological disciplines is highlighted. PMID:20360032

  6. Encapsulation of cobalt nanoparticles in cross-linked-polymer cages

    NASA Astrophysics Data System (ADS)

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

    2009-07-01

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

  7. Peptidoglycan Cross-Linking in Glycopeptide-Resistant Actinomycetales

    PubMed Central

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

    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

  8. 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

  9. Thermal fluctuations in chemically cross-linked polymers of cyclodextrins.

    PubMed

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

    2015-03-21

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

  10. 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

  11. Transient Binding and Dissipation in Cross-Linked Actin Networks O. Lieleg,1

    E-print Network

    Bausch, Andreas

    Transient Binding and Dissipation in Cross-Linked Actin Networks O. Lieleg,1 M. M. A. E. Claessens 2008) In contrast with entangled actin solutions, transiently cross-linked actin networks can provide-on biological relevant time scales. Here, we show that thermal unbinding of transient cross-links entails local

  12. 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.

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

    PubMed

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

    2011-01-01

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

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

    PubMed Central

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

    2014-01-01

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

  15. Gel Permeation Chromatography: Gel Preparation and Packing Technique

    Microsoft Academic Search

    F. W. Peaker; C. R. Tweedale

    1967-01-01

    SINCE the original publication by Moore1, gel permeation chromatography has been widely recognized as a rapid means of assessing the molecular weight distributions of polymeric materials soluble in organic solvents. While the use of this technique, principally based on the reliable commercial instrument2, is well established, reference in published work to the preparation of the cross-linked polystyrene gel, and its

  16. 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

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

    SciTech Connect

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

    1993-12-20

    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.

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

    NASA Astrophysics Data System (ADS)

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

    1996-05-01

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

  19. Measuring the Formaldehyde Protein–DNA Cross-Link Reversal Rate

    PubMed Central

    2015-01-01

    Protein–DNA binding interactions play critical roles in important cellular processes such as gene expression, cell division, and chromosomal organization. Techniques to identify and characterize these interactions often utilize formaldehyde cross-linking for stabilization of the complexes. Advantages of formaldehyde as a cross-linking reagent include cell permeability, relatively fast cross-linking kinetics, and short cross-linker length. In addition, formaldehyde cross-links are reversible, which has the advantage of allowing complexes to be dissociated if desired but may also present a problem if undesired dissociation occurs in the course of an experiment. While the kinetics of formaldehyde cross-link formation have been well-established in numerous studies, there have been no reports of the rate of cross-link dissociation, even though it is clearly a critical variable when developing a biochemical protocol involving formaldehyde cross-linking. We present here a method for measurement of the rate of formaldehyde cross-link reversal based upon the Formaldehyde-Assisted Isolation of Regulatory Elements (FAIRE) procedure and use it to determine the rate of cross-link reversal for cross-linked protein–DNA complexes from yeast cell lysate. The half-life of the protein–DNA cross-links varies from 179 h at 4 °C to 11.3 h at 47 °C, with a rate that increases exponentially with temperature and is independent of salt concentration. PMID:24848408

  20. Transepithelial corneal collagen cross-linking in ultrathin keratoconic corneas

    PubMed Central

    Spadea, Leopoldo; Mencucci, Rita

    2012-01-01

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

  1. Zinc cross-linked hydroxamated alginates for pulsed drug release

    PubMed Central

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

    2013-01-01

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

  2. Pyridinium cross-links in heritable disorders of collagen

    SciTech Connect

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

    1995-12-01

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

  3. Grafting of cross-linked hydrogel networks to titanium surfaces.

    PubMed

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

    2014-01-22

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

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

    PubMed

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

    2013-11-26

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

  5. Precise tailoring of tyramine-based hyaluronan hydrogel properties using DMTMM conjugation.

    PubMed

    Loebel, Claudia; D'Este, Matteo; Alini, Mauro; Zenobi-Wong, Marcy; Eglin, David

    2015-01-22

    Injectable tyramine modified hyaluronic acid (HA-Tyr) hydrogels which are bio-orthogonally cross-linked with horseradish peroxidase (HRP) and hydrogen peroxide (H2O2) are excellent candidate biomaterials for drug delivery, regenerative medicine and tissue engineering. Ligation of tyramine to HA has been reported using the very well established N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) chemistry. Here we demonstrate the applicability of 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride (DMTMM) as an alternative coupling agent to synthesize HA-Tyr conjugates. The optimized derivatization process allows accurate control of the degree of substituted Tyr on hyaluronan (DSmol). Hence, viscoelastic properties, in vitro swelling and enzymatic digestion profiles of the crosslinked hydrogels can be precisely tuned via DSmol. Our study demonstrates the advantages of DMTMM conjugation as a powerful tool to synthesize HA-Tyr hydrogels with properties exactly tailored for biomedical applications. PMID:25439901

  6. 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.

  7. 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.

  8. Food Gels: Gelling Process and New Applications

    Microsoft Academic Search

    Soumya Banerjee; Suvendu Bhattacharya

    2012-01-01

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

  9. Food gels: Gelling process and new applications

    Microsoft Academic Search

    SOUMYA BANERJEE; SUVENDU BHATTACHARYA

    2011-01-01

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

  10. Reentrant phase diagram and pH effects in cross-linked gelatin gels

    E-print Network

    T. Abete; E. Del Gado; L. de Arcangelis; D. Hellio Serughetti; M. Djabourov

    2008-10-02

    Experimental results have shown that the kinetics of bond formation in chemical crosslinking of gelatin solutions is strongly affected not only by gelatin and reactant concentrations but also by the solution pH. We present an extended numerical investigation of the phase diagram and of the kinetics of bond formation as a function of the pH, via Monte Carlo simulations of a lattice model for gelatin chains and reactant agent in solution. We find a reentrant phase diagram, namely gelation can be hindered either by loop formation, at low reactant concentrations, or by saturation of active sites of the chains via formation of single bonds with crosslinkers, at high reactant concentrations. The ratio of the characteristic times for the formation of the first and of the second bond between the crosslinker and an active site of a chain is found to depend on the reactant reactivity, in good agreement with experimental data.

  11. Evaluation of High Cross Linked Cation Gel Resins in an MPA Environment at Byron and Braidwood

    Microsoft Academic Search

    John Wilson; Joe Bates

    The use of 3-methoxypropylamine (MPA) has been instrumental in reducing corrosion product transport to steam generators at the Braidwood and Byron units for over 8 years. During this time the blowdown demineralizers have been operated past the amine break. This operation allows for low level leakage of sodium off of the blowdown demineralizer resin, which increases the sodium to chloride

  12. Encoding Hydrogel Mechanics via Network Cross-Linking Structure

    PubMed Central

    2015-01-01

    The effects of mechanical cues on cell behaviors in 3D remain difficult to characterize as the ability to tune hydrogel mechanics often requires changes in the polymer density, potentially altering the material’s biochemical and physical characteristics. Additionally, with most PEG diacrylate (PEGDA) hydrogels, forming materials with compressive moduli less than ?10 kPa has been virtually impossible. Here, we present a new method of controlling the mechanical properties of PEGDA hydrogels independent of polymer chain density through the incorporation of additional vinyl group moieties that interfere with the cross-linking of the network. This modification can tune hydrogel mechanics in a concentration dependent manner from <1 to 17 kPa, a more physiologically relevant range than previously possible with PEG-based hydrogels, without altering the hydrogel’s degradation and permeability. Across this range of mechanical properties, endothelial cells (ECs) encapsulated within MMP-2/MMP-9 degradable hydrogels with RGDS adhesive peptides revealed increased cell spreading as hydrogel stiffness decreased in contrast to behavior typically observed for cells on 2D surfaces. EC-pericyte cocultures exhibited vessel-like networks within 3 days in highly compliant hydrogels as compared to a week in stiffer hydrogels. These vessel networks persisted for at least 4 weeks and deposited laminin and collagen IV perivascularly. These results indicate that EC morphogenesis can be regulated using mechanical cues in 3D. Furthermore, controlling hydrogel compliance independent of density allows for the attainment of highly compliant mechanical regimes in materials that can act as customizable cell microenvironments.

  13. Synthesis of borate cross-linked rhamnogalacturonan II.

    PubMed

    Funakawa, Hiroya; Miwa, Kyoko

    2015-01-01

    In the present review, we describe current knowledge about synthesis of borate crosslinked rhamnogalacturonan II (RG-II) and it physiological roles. RG-II is a portion of pectic polysaccharide with high complexity, present in primary cell wall. It is composed of homogalacturonan backbone and four distinct side chains (A-D). Borate forms ester bonds with the apiosyl residues of side chain A of two RG-II monomers to generate borate dimerized RG-II, contributing for the formation of networks of pectic polysaccharides. In plant cell walls, more than 90% of RG-II are dimerized by borate under boron (B) sufficient conditions. Borate crosslinking of RG-II in primary cell walls, to our knowledge, is the only experimentally proven molecular function of B, an essential trace-element. Although abundance of RG-II and B is quite small in cell wall polysaccharides, increasing evidence supports that RG-II and its borate crosslinking are critical for plant growth and development. Significant advancement was made recently on the location and the mechanisms of RG-II synthesis and borate cross-linking. Molecular genetic studies have successfully identified key enzymes for RG-II synthesis and regulators including B transporters required for efficient formation of RG-II crosslinking and consequent normal plant growth. The present article focuses recent advances on (i) RG-II polysaccharide synthesis, (ii) occurrence of borate crosslinking and (iii) B transport for borate supply to RG-II. Molecular mechanisms underlying formation of borate RG-II crosslinking and the physiological impacts are discussed. PMID:25954281

  14. The theory and art of corneal cross-linking.

    PubMed

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

    2013-08-01

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

  15. The theory and art of corneal cross-linking

    PubMed Central

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

    2013-01-01

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

  16. Unconventional metal organic frameworks: porous cross-linked phosphonates.

    PubMed

    Clearfield, Abraham

    2008-11-28

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

  17. Effect of glucose content on thermally cross-linked fibrous gelatin scaffolds for tissue engineering.

    PubMed

    Siimon, Kaido; Reemann, Paula; Põder, Annika; Pook, Martin; Kangur, Triin; Kingo, Külli; Jaks, Viljar; Mäeorg, Uno; Järvekülg, Martin

    2014-09-01

    Thermally cross-linked glucose-containing electrospun gelatin meshes were studied as possible cell substrate materials. FTIR analysis was used to study the effect of glucose on cross-linking reactions. It was found that the presence of glucose increases the extent of cross-linking of fibrous gelatin scaffolds, which in return determines scaffold properties and their usability in tissue engineering applications. Easy to handle fabric-like scaffolds were obtained from blends containing up to 15% glucose. Maximum extent of cross-linking was reached at nearly 20% glucose content. Cross-linking effectively resulted in decreased solubility and increased resistance to enzymatic degradation. Preliminary short-term cell culture experiments indicate that such thermally cross-linked gelatin-glucose scaffolds are suitable for tissue engineering applications. PMID:25063151

  18. Characterization of the Deoxyguanosine–Lysine Cross-Link of Methylglyoxal

    PubMed Central

    2015-01-01

    Methylglyoxal is a mutagenic bis-electrophile that is produced endogenously from carbohydrate precursors. Methylglyoxal has been reported to induce DNA–protein cross-links (DPCs) in vitro and in cultured cells. Previous work suggests that these cross-links are formed between guanine and either lysine or cysteine side chains. However, the chemical nature of the methylglyoxal induced DPC have not been determined. We have examined the reaction of methylglyoxal, deoxyguanosine (dGuo), and N?-acetyllysine (AcLys) and determined the structure of the cross-link to be the N2-ethyl-1-carboxamide with the lysine side chain amino group (1). The cross-link was identified by mass spectrometry and the structure confirmed by comparison to a synthetic sample. Further, the cross-link between methylglyoxal, dGuo, and a peptide (AcAVAGKAGAR) was also characterized. The mechanism of cross-link formation is likely to involve an Amadori rearrangement. PMID:24801980

  19. Aminoguanidine Prevents Diabetes-Induced Arterial Wall Protein Cross-Linking

    Microsoft Academic Search

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

    1986-01-01

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

  20. Polymer micelles with cross-linked ionic cores for delivery of anticancer drugs

    Microsoft Academic Search

    Satya Bontha; Alexander V. Kabanov; Tatiana K. Bronich

    2006-01-01

    This work reports the design of polymer micelles with cross-linked ionic cores that display high stability. Block ionomer complexes of poly(ethylene oxide)-b-poly(methacrylic acid) copolymer and divalent metal cations were utilized as micellar templates for the synthesis of the cross-linked micelles. Such micelles represent hydrophilic nanospheres of core-shell morphology. The core comprises a network of the cross-linked polyanions, which is surrounded

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

    Microsoft Academic Search

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

    1996-01-01

    A cross-linking method for collagen-based biomaterials was developed using the water-soluble carbodiimide 1-ethyl-3-(3-dimethyl aminopropyl)carbodiimide hydrochloride (EDC). Cross-linking using EDC involves the activation of carboxylic acid groups to give O-acylisourea groups, which form cross-links after reaction with free amine groups. Treatment of dermal sheep collagen (DSC) with EDC (E-DSC) resulted in materials with an increased shrinkage temperature (Ts) and a decreased

  2. Glucose-mediated cross-linking of collagen in rat tendon and skin

    Microsoft Academic Search

    Cyriel J. A. L. Mentink; Marc Hendriks; Bruce H. R. Wolffenbuttel

    2002-01-01

    Background: Cross-linking of macromolecules like collagen plays an important role in the development of complications in diabetes and ageing. One of the underlying mechanisms of this cross-linking is the formation of advanced glycation endproducts (AGEs). Methods: In this study, we assessed the use of differential scanning calorimetry (DSC) for the determination of these cross-links and the effects of an AGE

  3. THA with Highly Cross-linked Polyethylene in Patients 50 Years or Younger

    Microsoft Academic Search

    Derek S. Shia; John C. Clohisy; Mark F. Schinsky; John M. Martell; William J. Maloney

    2009-01-01

    Highly cross-linked polyethylene has been associated with low in vitro wear, but also has decreased in vitro ultimate yield\\u000a strength. We therefore asked whether highly cross-linked polyethylene would result in lower outcome scores, wear, or early\\u000a failure in a young patient population. Seventy THAs in 64 patients were performed using a highly cross-linked (electron beam-irradiated\\u000a to 9 Mrads) acetabular liner

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

    NSDL National Science Digital Library

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

  5. Synthesis of Porous Cross-Linked Grafted Chitosan and Its Application for Metal Ion Adsorption

    Microsoft Academic Search

    Liu Hui

    2009-01-01

    A water-soluble intermediate bi-functional compound with thioureido and carboxyl groups was prepared by reacting chitosan with ammonium thiocyanate and chloroacetic acid. The intermediate compound was then cross-linked by epichlorohydrin to prepare a novel water-insoluble cross-linked chitosan aiming to be used as an adsorbent for heavy metal wastewater treatment. Both the intermediate compound and the cross-linked grafted chitosan (CGCTS) were characterized

  6. Reinforcement of Bacillus subtilis spores by cross-linking of outer coat proteins during maturation.

    PubMed

    Abhyankar, Wishwas; Pandey, Rachna; Ter Beek, Alexander; Brul, Stanley; de Koning, Leo J; de Koster, Chris G

    2015-02-01

    Resistance characteristics of bacterial endospores towards various environmental stresses such as chemicals and heat are in part attributed to their coat proteins. Heat resistance is developed in a late stage of sporulation and during maturation of released spores. Using our gel-free proteomic approach and LC-FT-ICR-MS/MS analysis we have monitored the efficiency of the tryptic digestion of proteins in the coat during spore maturation over a period of eight days, using metabolically (15)N labeled mature spores as reference. The results showed that during spore maturation the loss of digestion efficiency of outer coat and crust proteins synchronized with the increase in heat resistance. This implicates that spore maturation involves chemical cross-linking of outer coat and crust layer proteins leaving the inner coat layer proteins unmodified. It appears that digestion efficiencies of spore surface proteins can be linked to their location within the coat and crust layers. We also attempted to study a possible link between spore maturation and the observed heterogeneity in spore germination. PMID:25481062

  7. Direct imaging of fluctuations in a cross-linked biopolymer network

    NASA Astrophysics Data System (ADS)

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

    2013-03-01

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

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

    NASA Astrophysics Data System (ADS)

    Gul, Rizwan M.; Khan, Tahir I.

    2014-06-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-03-01

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

  10. Characterization of and host response to tyramine substituted-hyaluronan enriched fascia extracellular matrix

    PubMed Central

    Chin, LiKang; Calabro, Anthony; Rodriguez, E. Rene; Tan, Carmela D.; Walker, Esteban

    2011-01-01

    Naturally-occurring biomaterial scaffolds derived from extracellular matrix (ECM) have been previously investigated for soft tissue repair. We propose to enrich fascia ECM with high molecular weight tyramine substituted-hyaluronan (TS-HA) to modulate inflammation associated with implantation and enhance fibroblast infiltration. As critical determinants of constructive remodeling, the host inflammatory response and macrophage polarization to TS-HA enriched fascia were characterized in a rat abdominal wall model. TS-HA treated fascia with cross-linking had a similar lymphocyte (P = 0.11) and plasma cell (P = 0.13) densities, greater macrophage (P = 0.001) and giant cell (P < 0.0001) densities, and a lower density of fibroblast-like cells (P < 0.0001) than water treated controls. Treated fascia, with or without cross-linking, exhibited a predominantly M2 pro-remodeling macrophage profile similar to water controls (P = 0.82), which is suggestive of constructive tissue remodeling. Our findings demonstrated that HA augmentation can alter the host response to an ECM, but the appropriate concentration and molecular weight needed to minimize chronic inflammation within the scaffold remains to be determined. PMID:21553156

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

    NASA Technical Reports Server (NTRS)

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

    1985-01-01

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

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

    EPA Science Inventory

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

  13. The slow folding of cross-linked -helical peptides is due to steric SUPPLEMENTARY MATERIAL

    E-print Network

    Caflisch, Amedeo

    , 2009) Keywords: protein folding, -helix, stretched-exponential kinetics, free-energy landscape #12The slow folding of cross-linked -helical peptides is due to steric hindrance SUPPLEMENTARY;Paoli et al., Slow folding of cross-linked -helix S-1 Contents I. r- and l-conformations of Arginine 10

  14. Alkaline membrane fuel cells with in-situ cross-linked ionomers Yongjun Leng a

    E-print Network

    membranes (AEMs) as the solid polymer electrolyte to facilitate high pH cell operation have garnered recentAlkaline membrane fuel cells with in-situ cross-linked ionomers Yongjun Leng a , Lizhu Wang b membrane fuel cell (AMFC) in-situ cross-linking ionomer net water transport coefficient A B S T R A C

  15. Alignment of fibrillin molecules in elastic microfibrils is defined by transglutaminase-derived cross-links.

    PubMed

    Qian, R Q; Glanville, R W

    1997-12-16

    Microfibrils were extracted from human amnion in the form of a beaded filament and analyzed for the presence of transglutaminase-derived cross-links using acrylonitrile derivatization. The cross-link structure was isolated from protease hydrolysates of beaded filaments and identified as a phenylthiocarbamyl amino acid derivative by comparison to a standard. Acid hydrolysis of the isolated cross-link gave the expected lysine and glutamic acid in a 1:1 ratio. The beaded filaments were also treated with trypsin to produce a fraction that contained the bead structure and a fraction containing fragments of the interbead filaments. Cross-links were detected in the interbead filaments but not in the beads. A large tryptic peptide that contained a cross-link was isolated and sequenced. The two amino acid sequences obtained identified both of the cross-linked molecules as fibrillin-1 and enabled the approximate localization of the cross-link sites within the molecule. The locations of cross-link sites on two adjacent molecules fixed the relative positions of fibrillin monomers within the microfibrils, providing insight into the spatial organization of fibrillin within the elastic microfibrils. PMID:9398316

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

    PubMed

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

    2014-02-20

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

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

    Technology Transfer Automated Retrieval System (TEKTRAN)

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

  18. Lamb and Cow Performance when Fed Corn Silage that has Reduced Ferulate Cross Linking

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Ferulate-mediated lignin/hemicellulose cross linking in grasses reduces in vitro NDF digestibility (IVNDFD). Impact of ferulate cross linking on animal performance was examined in lamb digestibility and dairy cow performance trials using the seedling ferulate ester (sfe) corn mutant that reduces cro...

  19. Microscopic theory for cross-linked macromolecules. I. Broken symmetry, rigidity, and topology

    Microsoft Academic Search

    Paul Goldbart; Nigel Goldenfeld

    1989-01-01

    This paper is concerned with the onset of rigidity in randomly cross-linked macromolecules. We discuss in detail the possible partitionings of configuration space, which may accompany the spontaneous breaking of translational invariance, treating separately the cases of crystals, amorphous solids, and cross-linked macromolecules. We describe the order parameters for these systems, drawing the distinction between solids with discrete translational symmetry

  20. Cross linking and rheological characterization of adsorbed protein layers at the oil-water interface.

    PubMed

    Romoscanu, Alexandre I; Mezzenga, Raffaele

    2005-10-11

    The dilatational rheological properties of cross-linked protein layers adsorbed at the oil-water interface were investigated with help of a modified drop tensiometer allowing successive replacements of the external phase. This setup enables one to perform cross-linking reactions at the interface only, that is, without any contact between the cross-linking agent and protein molecules in solution, under continuous monitoring of the interfacial tension. The mechanical properties of the resulting interface were investigated with dilatational large strain experiments. Measured rheological properties were related to the expected stability of an emulsion against disproportionation by considering the ratio of the interfacial elasticity to the interfacial tension. In an attempt to increase this ratio to improve the resistance against disproportionation, experiments were performed with densified protein layers obtained via reduction of the droplet area prior to cross linking. To highlight the influence of the protein morphology on the dilatational rheological properties of the cross-linked adsorbed layers, experiments were performed with random coil (beta-casein) as well as globular (beta-lactoglobulin) proteins. Glutaraldehyde was used as a cross-linking agent. Experiments were performed at 55 degrees C and pH 7.0 in 20 mM imidazole buffer for later comparison with enzymatically cross-linked adsorbed protein layers. The present work demonstrated substantial qualitative and quantitative differences in the interfacial rheological properties of cross-linked random coil and globular proteins. PMID:16207053

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

    EPA Science Inventory

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

  2. Hydroxyl radical induced cross-linking between phenylalanine and 2-deoxyribose

    SciTech Connect

    Farahani, M.; Simic, M.G.

    1988-06-28

    Hydroxy radicals induce cross-linking between phenylalanine (Phe) and 2-deoxyribose (dR) via formation of corresponding free radical intermediates. The cross-linked products were separated and identified by capillary gas chromatography-mass spectrometry. When phenylalanine and 2-deoxyribose radicals were generated in a 1:1 ratio, the predominant interaction was between Phe and dR radicals while the Phe-Phe and dR-dR cross-links were less abundant. The newly discovered cross-linked between 2-deoxyribose and phenylalanine may serve as a model for radiation or free radical induced cross-linking between DNA and proteins and in general between sugar moieties and amino acids.

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

    NASA Technical Reports Server (NTRS)

    Ono, S.; Yamauchi, M.

    1992-01-01

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

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

    PubMed

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

    2013-01-01

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

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

    PubMed

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

    2014-12-19

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

  6. Mechanical characterization of electrospun gelatin scaffolds cross-linked by glucose.

    PubMed

    Siimon, Kaido; Siimon, Hele; Järvekülg, Martin

    2015-01-01

    Nanofibrous gelatin scaffolds were prepared by electrospinning from aqueous acetic acid and cross-linked thermally by glucose. The effect of the amount of glucose used as cross-linking agent on the mechanical properties of gelatin fibres was studied in this paper. The elastic modulus of gelatin fibres cross-linked by glucose was determined by modelling the behaviour of the meshes during tensile test. The model draws connections between the elastic moduli of a fibrous mesh and the fibre material and allows evaluation of elastic modulus of the fibre material. It was found that cross-linking by glucose increases the elastic modulus of gelatin fibres from 0.3 GPa at 0 % glucose content to 1.1 GPa at 15 % glucose content. This makes fibrous gelatin scaffolds cross-linked by glucose a promising material for biomedical applications. PMID:25578715

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

    PubMed

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

    2015-05-01

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

  8. Mechanical Properties of Tyramine Substituted-Hyaluronan Enriched Fascia Extracellular Matrix

    PubMed Central

    Chin, LiKang; Calabro, Anthony; Walker, Esteban; Derwin, Kathleen A.

    2011-01-01

    Naturally-occurring biomaterial scaffolds derived from extracellular matrix (ECM) have been the topic of recent investigation in the context of rotator cuff tendon repair. We previously reported a method to treat fascia ECM with high molecular weight tyramine substituted-hyaluronan (TS-HA) for use as a tendon augmentation scaffold. The presence of cross-linked TS-HA in fascia was associated with an increased macrophage and giant cell response compared to water treated controls after implantation in a rat abdominal wall model. The objective of this study was to determine the extent to which TS-HA treatment was associated with mechanical property changes of fascia after implantation in the rat model. Fascia samples in all groups demonstrated time-dependent decreases in mechanical properties. TS-HA treated fascia with cross-linking exhibited a lower toe modulus, a trend toward lower toe stiffness, and a higher transition strain than water treated controls not only after implantation, but also at time zero. TS-HA treatment, with or without cross-linking, had no significant effect on time-zero or post-implantation load relaxation ratio, load relaxation rate, linear-region stiffness, or linear-region modulus. Our findings demonstrated that the particular TS-HA treatment employed in this study decreased the low-load elastic mechanical properties of fascia ECM, in keeping with the heightened macrophage and giant cell host response seen previously. This work provides a starting point and guidance for investigating alternative HA treatment strategies. PMID:22238019

  9. Highly efficient copper(II) ion sorbents obtained by calcium carbonate mineralization on functionalized cross-linked copolymers.

    PubMed

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

    2015-03-23

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

  10. On the Formation and Properties of Interstrand DNA-DNA Cross-links Forged by Reaction of an Abasic Site With the Opposing Guanine Residue of 5?-CAp Sequences in Duplex DNA

    PubMed Central

    Johnson, Kevin M.; Price, Nathan E.; Wang, Jin; Fekry, Mostafa I.; Dutta, Sanjay; Seiner, Derrick R.; Wang, Yinsheng; Gates, Kent S.

    2014-01-01

    We recently reported that the aldehyde residue of an abasic (Ap) site in duplex DNA can generate an interstrand cross-link via reaction with a guanine residue on the opposing strand. This finding is intriguing because the highly deleterious nature of interstrand cross-links suggests that even small amounts of Ap-derived cross-links could make a significant contribution to the biological consequences stemming from the generation of Ap sites in cellular DNA. Incubation of 21-bp duplexes containing a central 5?-CAp sequence under conditions of reductive amination (NaCNBH3, pH 5.2) generated much higher yields of cross-linked DNA than reported previously. At pH 7, in the absence of reducing agents, these Ap-containing duplexes also produced cross-linked duplexes that were readily detected on denaturing polyacrylamide gels. Cross-link formation was not highly sensitive to reaction conditions and, once formed, the cross-link was stable to a variety of work-up conditions. Results of multiple experiments including MALDI-TOF mass spectrometry, gel mobility, methoxyamine capping of the Ap aldehyde, inosine-for-guanine replacement, hydroxyl radical footprinting, and LCMS/MS were consistent with a cross-linking mechanism involving reversible reaction of the Ap aldehyde residue with the N2-amino group of the opposing guanine residue in 5?-CAp sequences to generate hemiaminal, imine, or cyclic hemiaminal cross-links (7-10) that were irreversibly converted under conditions of reductive amination (NaCNBH3/pH 5.2) to a stable amine linkage. Further support for the importance of the exocyclic N2-amino group in this reaction was provided by an experiment showing that installation of a 2-aminopurine-thymine base pair at the cross-linking site produced high yields (15-30%) of a cross-linked duplex at neutral pH, in the absence of NaCNBH3. PMID:23215239

  11. Protein cross-linking and oligomerization through dityrosine formation upon exposure to ozone

    NASA Astrophysics Data System (ADS)

    Liu, Fobang; Kampf, Christopher; Reinmuth-Selzle, Kathrin; Berkemeier, Thomas; Shiraiwa, Manabu; Pöschl, Ulrich

    2015-04-01

    Air pollution is a potential factor for the increasing prevalence of allergic diseases. Airborne allergenic proteins can be directly exposed to air pollution promoting post-translational modifications, which can enhance the allergenic potential of proteins. The formation of dimers or oligomers of allergenic proteins has been reported to result in an enhanced allergenicity. However, the oligomerization process for proteins at atmospherically relevant concentration of O3 is still largely unknown. In this study, the kinetics and reaction mechanism of protein oligomerization upon ozone exposure were studied at atmospherically relevant ozone concentrations and relative humidity (RH) in coated-wall flow tube experiments. Bovine Serum Albumin (BSA) was used as a model protein. Protein ozone exposure was studied for different protein phase-states, i.e. amorphous solid (45% RH experiments), semi-solid (96% RH experiments) and liquid (bulk solution experiments) to account for the differences of phase in atmospheric particulates, e.g., aerosol particles and cloud droplets. Product analysis was performed using a size exclusion chromatography-high performance liquid chromatography-diode array detector (SEC-HPLC-DAD). We demonstrate that protein cross-linking upon ozone exposure can be attributed to the formation of covalent intermolecular dityrosine species by gel electrophoretic and fluorescence spectroscopic methods. The exposure experiments indicate that in addition to ozone concentration, the oligomerization process was depending on the phase-state of protein. In liquid-phase experiments, dimer formation was significantly enhanced, thus indicating a potential relevance of in-cloud processes for protein oligomerization. The reactive turnover is higher at 96% RH compared to 45% RH, indicating a higher bulk diffusion coefficient at high RH, which is explicitly resolved by kinetic modeling. Further, the reactive turnover showed a strong correlation to particle surface-to-volume ratio, confirming the bulk diffusion limitation.

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

    SciTech Connect

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

    2007-02-15

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

  13. Cross-linking and fluorescence changes of collagen by glycation and oxidation.

    PubMed

    Fujimori, E

    1989-10-01

    The non-enzymatic glucosylation of collagen in vivo and in vitro produces blue-fluorescent cross-links very slowly. The mechanism of their formation is unknown. We investigated the role of oxidation in glycation. When native fluorescent collagen from old-rat tail tendon and its CNBr peptides were oxidized by chemically generated singlet oxygen, cross-linking occurred immediately, and the cross-linked products showed an increased blue fluorescence. Further cross-linking and development of blue fluorescence also were accelerated by singlet oxygen when oxidizing in vitro glucosylated collagen CNBr peptides. It was noted that the blue fluorescence developed at the expense of a near-UV fluorescence. This near-UV fluorophore, which is also present in native collagen, was found to be produced by the in vitro glucosylation of collagen and during the cross-linking by glucosylation was slowly converted to the blue fluorophore. These changes indicate the autoxidation of near-UV fluorescent intermediates to blue fluorescent cross-links during glucosylation. Non-enzymatic fructosylation, which occurs in vivo in certain proteins, was more effective than glucosylation in forming fluorophores and cross-links with collagen in vitro. Fructosylated fluorophores were found different from glucosylated products in their oxidation reactivities with singlet oxygen. PMID:2506934

  14. Microencapsulation of protein into biodegradable matrix: a smart solution cross-linking technique.

    PubMed

    Bejugam, Naveen K; Gayakwad, Sanjay G; Uddin, Akm N; D'Souza, Martin J

    2013-01-01

    Sustained-release albumin microspheres (MSs) can be obtained by chemically cross-linking albumin. However, a significant challenge is preventing the cross-linking of the active pharmaceutical (protein or small molecule) ingredient (API) with the MS matrix. To prevent cross-linking of the API with the albumin matrix, a smart "solution cross-linking-microencapsulation" method was developed which involves cross-linking albumin solution with glutaraldehyde first, neutralizing any excess glutaraldehyde with sodium bisulphite, followed by the addition of API and finally spray drying. Using lysozyme as model API, MS formulations FL1 and FL2 were prepared and characterized. Physicochemical characterization using FT-IR and bioactivity evaluation indicate that microencapsulated API did not undergo any significant change in its native structure and the bioactivity was preserved during the formulation processing. Preliminary immunogenicity potential of the cross-linked albumin matrix determined by in vivo studies did not show any significant increase in antigen-specific serum-IgG levels, implying safety and biocompatibility of the cross-linked albumin matrix. PMID:23098577

  15. Genipin cross-linked nanocomposite films for the immobilization of antimicrobial agent.

    PubMed

    Khan, Avik; Salmieri, Stéphane; Fraschini, Carole; Bouchard, Jean; Riedl, Bernard; Lacroix, Monique

    2014-09-10

    Cellulose nanocrystal (CNC) reinforced chitosan based antimicrobial films were prepared by immobilizing nisin on the surface of the films. Nanocomposite films containing 18.65 ?g/cm(2) of nisin reduced the count of L. monocytogenes by 6.73 log CFU/g, compared to the control meat samples (8.54 log CFU/g) during storage at 4 °C in a Ready-To-Eat (RTE) meat system. Film formulations containing 9.33 ?g/cm(2) of nisin increased the lag phase of L. monocytogenes on meat by more than 21 days, whereas formulations with 18.65 ?g/cm(2) completely inhibited the growth of L. monocytogenes during storage. Genipin was used to cross-link and protect the activity of nisin during storage. Nanocomposite films cross-linked with 0.05% w/v genipin exhibited the highest bioactivity (10.89 ?g/cm(2)) during the storage experiment, as compared to that of the un-cross-linked films (7.23 ?g/cm(2)). Genipin cross-linked films were able to reduce the growth rate of L. monocytogenes on ham samples by 21% as compared to the un-cross-linked films. Spectroscopic analysis confirmed the formation of genipin-nisin-chitosan heterocyclic cross-linked network. Genipin cross-linked films also improved the swelling, water solubility, and mechanical properties of the nanocomposite films. PMID:25140839

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

    PubMed

    Jalaja, K; James, Nirmala R

    2015-02-01

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

  17. Lysyl hydroxylase 2 induces a collagen cross-link switch in tumor stroma

    PubMed Central

    Chen, Yulong; Terajima, Masahiko; Yang, Yanan; Sun, Li; Ahn, Young-Ho; Pankova, Daniela; Puperi, Daniel S.; Watanabe, Takeshi; Kim, Min P.; Blackmon, Shanda H.; Rodriguez, Jaime; Liu, Hui; Behrens, Carmen; Wistuba, Ignacio I.; Minelli, Rosalba; Scott, Kenneth L.; Sanchez-Adams, Johannah; Guilak, Farshid; Pati, Debananda; Thilaganathan, Nishan; Burns, Alan R.; Creighton, Chad J.; Martinez, Elisabeth D.; Zal, Tomasz; Grande-Allen, K. Jane; Yamauchi, Mitsuo; Kurie, Jonathan M.

    2015-01-01

    Epithelial tumor metastasis is preceded by an accumulation of collagen cross-links that heighten stromal stiffness and stimulate the invasive properties of tumor cells. However, the biochemical nature of collagen cross-links in cancer is still unclear. Here, we postulated that epithelial tumorigenesis is accompanied by changes in the biochemical type of collagen cross-links. Utilizing resected human lung cancer tissues and a p21CIP1/WAF1-deficient, K-rasG12D-expressing murine metastatic lung cancer model, we showed that, relative to normal lung tissues, tumor stroma contains higher levels of hydroxylysine aldehyde–derived collagen cross-links (HLCCs) and lower levels of lysine aldehyde–derived cross-links (LCCs), which are the predominant types of collagen cross-links in skeletal tissues and soft tissues, respectively. Gain- and loss-of-function studies in tumor cells showed that lysyl hydroxylase 2 (LH2), which hydroxylates telopeptidyl lysine residues on collagen, shifted the tumor stroma toward a high-HLCC, low-LCC state, increased tumor stiffness, and enhanced tumor cell invasion and metastasis. Together, our data indicate that LH2 enhances the metastatic properties of tumor cells and functions as a regulatory switch that controls the relative abundance of biochemically distinct types of collagen cross-links in the tumor stroma. PMID:25664850

  18. CrossWork: software-assisted identification of cross-linked peptides.

    PubMed

    Rasmussen, Morten I; Refsgaard, Jan C; Peng, Li; Houen, Gunnar; Højrup, Peter

    2011-09-01

    The increased interest in chemical cross-linking for probing protein structure and interaction has led to a large increase in literature describing new cross-linkers and search programs. However, this has not led to a corresponding increase in the analysis of large and complex proteins. A major obstacle is that the new cross-linkers are either not readily available and/or have a low reactivity. In combination with aging search programs that are slow and have low sensitivity, or new search programs that are described but not released, these efforts do little to advance the field of cross-linking. Here we present a method pipeline for chemical cross-linking, using two standard cross-linkers, BS3 and BS2G, combined with our freely available CrossWork search program. By this approach we generate cross-link data sufficient to derive structural information for large and complex proteins. CrossWork searches batches of tandem mass-spectrometric data, and identifies cross-linked and non-cross-linked peptides using a standard PC. We tested CrossWork by searching mass-spectrometric datasets of cross-linked complement factor C3 against small (1 protein) and large (1000 proteins) search spaces, and show that the resulting distance constraints agree with the established structures. We further investigated the structure of the multi-domain ERp72, and combined the individual domains of ERp72 into a single structure. PMID:21600323

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

    PubMed Central

    Courson, David S.; Rock, Ronald S.

    2010-01-01

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

  20. Lysyl hydroxylase 2 induces a collagen cross-link switch in tumor stroma.

    PubMed

    Chen, Yulong; Terajima, Masahiko; Yang, Yanan; Sun, Li; Ahn, Young-Ho; Pankova, Daniela; Puperi, Daniel S; Watanabe, Takeshi; Kim, Min P; Blackmon, Shanda H; Rodriguez, Jaime; Liu, Hui; Behrens, Carmen; Wistuba, Ignacio I; Minelli, Rosalba; Scott, Kenneth L; Sanchez-Adams, Johannah; Guilak, Farshid; Pati, Debananda; Thilaganathan, Nishan; Burns, Alan R; Creighton, Chad J; Martinez, Elisabeth D; Zal, Tomasz; Grande-Allen, K Jane; Yamauchi, Mitsuo; Kurie, Jonathan M

    2015-03-01

    Epithelial tumor metastasis is preceded by an accumulation of collagen cross-links that heighten stromal stiffness and stimulate the invasive properties of tumor cells. However, the biochemical nature of collagen cross-links in cancer is still unclear. Here, we postulated that epithelial tumorigenesis is accompanied by changes in the biochemical type of collagen cross-links. Utilizing resected human lung cancer tissues and a p21CIP1/WAF1-deficient, K-rasG12D-expressing murine metastatic lung cancer model, we showed that, relative to normal lung tissues, tumor stroma contains higher levels of hydroxylysine aldehyde-derived collagen cross-links (HLCCs) and lower levels of lysine aldehyde-derived cross-links (LCCs), which are the predominant types of collagen cross-links in skeletal tissues and soft tissues, respectively. Gain- and loss-of-function studies in tumor cells showed that lysyl hydroxylase 2 (LH2), which hydroxylates telopeptidyl lysine residues on collagen, shifted the tumor stroma toward a high-HLCC, low-LCC state, increased tumor stiffness, and enhanced tumor cell invasion and metastasis. Together, our data indicate that LH2 enhances the metastatic properties of tumor cells and functions as a regulatory switch that controls the relative abundance of biochemically distinct types of collagen cross-links in the tumor stroma. PMID:25664850

  1. Stiffening effects of riboflavin/UVA corneal collagen cross-linking is hydration dependent.

    PubMed

    Hatami-Marbini, H; Rahimi, A

    2015-04-13

    The collagen cross-linking is a relatively new treatment option for strengthening the cornea, delaying, and in some cases stopping the progression of keratoconus. The uniaxial tensile experiments are among the most commonly used techniques to assess the effectiveness of this therapeutic option in enhancing tensile properties. In the present study, we investigated the possible effects of hydration on stiffening effects of corneal collagen cross-linking procedure, as measured by the uniaxial tensile testing method. For this purpose, after cross-linking bovine corneas, we let the strips to dehydrate in air or swell in a solution until their thickness reached an average thickness of 0.5, 0.7, 0.9, 1.1, and 1.5 mm. Using thickness as a representative of hydration, we divided corneal strips into five different groups and measured their stress-strain behavior by conducting uniaxial tensile experiments in mineral oil. It was observed that the collagen cross-linking treatment and hydration together affect the tensile behavior of the bovine cornea. While corneal collagen cross-linking resulted in a significant increase in the tensile stress-strain response of each thickness group (P<0.01), less hydrated collagen cross-linked samples showed a significantly stiffer response (P<0.01). A master curve was found for representing the tensile behavior of the collagen cross-linked bovine cornea at different levels of hydration. The results of the present research confirmed that the amount of mechanical stiffening of the corneal collagen cross-linking, as measured by uniaxial tensile testing, strongly depends on the hydration. Therefore, it is concluded that uniaxial tensile experiments could only be used to assess stiffening effects of the collagen cross-linking treatment if the hydration of specimens is fully controlled. PMID:25704532

  2. Kinetically controlled patterning of highly cross-linked phosphonium photopolymers using simple anion exchange.

    PubMed

    Guterman, Ryan; Gillies, Elizabeth R; Ragogna, Paul J

    2015-05-12

    A phosphonium salt possessing three methacrylate groups has been incorporated into a photopolymeric system to generate highly cross-linked polyelectrolyte networks. Emergent chemical and physical properties in the polymers were observed and attributed to the tandem increase in cross-link density and ion-content upon incorporation of the self-cross-linking cation. Anion-exchange with bis(trifluoromethylsulfonyl)imide or dodecylbenzenesulfonate resulted in significant differences in wettability and ion-exchange behavior. The passivating effects of dodecylbenzenesulfonate were utilized to selectively pattern fluorescein dye into the polymer network, highlighting a new patterning procedure using ionic-bond forming reactions. PMID:25896478

  3. The nature of the collagen cross-links in bone in the chronic uraemic state.

    PubMed Central

    Russell, J E; Avioli, L V; Mechanic, G

    1975-01-01

    The cross-links from NaB3H4-reduced bone collagen of chronically uraemic rats and pairfed controls were compared. The ratio of the reduced cross-links deltadelta'-dihydroxylysinonorleucine to delta-hydroxylysinonorleucine was significantly increased in the uraemic animals. The observed increment in the dihydroxylysinonorleucine:hydroxylysinonorleucine ratio was accentuated as the uraemic state advanced. The data indicate that osteodystrophy of chronic renal insufficiency is characterized by an alteration of the quantitative relations between cross-links and aldehydic precursors of bone collagen. PMID:1191249

  4. XL-MS: Protein cross-linking coupled with mass spectrometry

    E-print Network

    Holding, Andrew N.

    2015-06-12

    s as they elute from an HPLC directly coupled to the mass spectrometer. (E) The .org/10.1016/j.ymeth.2015.06.010 hydrolysis (or sometimes amination) of the cross-linking reagent to produce modified peptides; depending on the cross-linking reagent used, these can... in vivo cross-linking experiments. The value of these techniques is demonstrated by the current efforts already committed to build a proteome scale static map of interactome using Y2H assays [85,86] and the analy- sis of sequence co-evolution [87]. XL...

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

    PubMed

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

    2014-09-15

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

  6. Role of cross-links in bundle formation, phase separation and gelation of long filaments

    E-print Network

    A. Zilman; S. Safran

    2004-06-01

    We predict the thermodynamic and structural behavior of solutions of long cross-linked filaments. We find that at the mean field level, the entropy of self-assembled junctions induces an effective attraction between the filaments that can result in a phase separation into a connected network, in equilibrium with a dilute phase. A connected network can also be formed in a non-thermodynamic transition upon increase of the chain, or cross link density, or with decreasing temperature. For rigid rods, at low temperatures, we predict a transition from an isotropic network, to anisotropic bundles of rods tightly bound by cross links, that is triggered by the interplay between the configurational entropy of the cross-link distribution among the rods, and the rotational and translational entropy of the rods.

  7. Iba1 is an actin-cross-linking protein in macrophages/microglia.

    PubMed

    Sasaki, Y; Ohsawa, K; Kanazawa, H; Kohsaka, S; Imai, Y

    2001-08-17

    Iba1 is a 17-kDa EF hand protein that is specifically expressed in macrophages/microglia and is upregulated during the activation of these cells. When exposed to macrophage colony-stimulating factor (M-CSF), microglia cell line MG5 immediately produces intense membrane ruffles in which Iba1 accumulates together with filamentous actin. In this study, we investigated the physical interaction between Iba1 and actin by centrifugation assay and electron microscopic examination and showed that Iba1 possesses actin-binding and -cross-linking activities. Inhibitory mutant Iba1 that suppresses M-CSF-induced membrane ruffling had lost the actin-cross-linking activity, and it inhibited the cross-linking activity of intact Iba1. These results indicate that Iba1 is a macrophage/microglia-specific actin-cross-linking protein essential for M-CSF-induced membrane ruffling. PMID:11500035

  8. Preparation and properties of cross-linked fluorescent poly(methyl methacrylate) latex colloids.

    PubMed

    Dullens, R P A; Claesson, E M; Kegel, W K

    2004-02-01

    We report a single step preparation of monodisperse fluorescent poly(methyl)methacrylate (PMMA) lattices cross-linked with ethylene glycol dimethacrylate with radii in the range 150-1000 nm using dispersion polymerization. The particles are applied as fluorescent cores in core-shell PMMA particles for confocal microscopy (Dullens et al. Langmuir 2003, 19, 5963). Contrary to un-cross-linked particles, these cross-linked colloids are stable in good solvents for PMMA as well. Therefore we studied the properties of the cross-linked PMMA particles in the good solvents tetrahydrofuran (THF), chloroform, and toluene using light scattering and confocal scanning laser microscopy. We show that the particles swell instantaneously and that their volume can increase up to more than seven times their volume in poor solvents. Further, it is very likely that the particles are charged in THF. PMID:15773089

  9. Cross-linking proteins with bimetallic tetracarboxylate compounds of transition metals

    DOEpatents

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

    1991-03-05

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

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

    PubMed

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

    2009-02-01

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

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

    E-print Network

    Ang, Wee Han

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

  12. Collagen type IX from human cartilage: a structural profile of intermolecular cross-linking sites.

    PubMed Central

    Diab, M; Wu, J J; Eyre, D R

    1996-01-01

    Type IX collagen, a quantitatively minor collagenous component of cartilage, is known to be associated with and covalently cross-linked to type II collagen fibrils in chick and bovine cartilage. Type IX collagen molecules have also been shown to form covalent cross-links with each other in bovine cartilage. In the present study we demonstrate by structural analysis and location of cross-linking sites that, in human cartilage, type IX collagen is covalently cross-linked to type II collagen and to other molecules of type IX collagen. We also present evidence that, if the proteoglycan form of type IX collagen is present in human cartilage, it can only be a minor component of the matrix, similar to findings with bovine cartilage. PMID:8660302

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

    PubMed Central

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

    2014-01-01

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

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

    PubMed

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

    2014-05-01

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

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

    SciTech Connect

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

    2005-03-01

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

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

    E-print Network

    Vermaelen, John Douglas

    1985-01-01

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

  17. Dextran cross-linked gelatin microspheres as a drug delivery system

    Microsoft Academic Search

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

    1999-01-01

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

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

    SciTech Connect

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

    2008-04-24

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

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

    Microsoft Academic Search

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

    2009-01-01

    Cross-linking of the cornea with application of Ribovlavin and UV-A light is an evolving clinical treatment of the eye disease keratoconus. Despite the positive clinical track record of corneal cross-linking, the complex wound healing process after the treatment is still under investigation. In this study an animal model was used to clarify the state of wound healing 5 weeks after

  20. Collagen and elastin cross-linking is altered during aberrant late lung development associated with hyperoxia.

    PubMed

    Mižíková, Ivana; Ruiz-Camp, Jordi; Steenbock, Heiko; Madurga, Alicia; Vadász, István; Herold, Susanne; Mayer, Konstantin; Seeger, Werner; Brinckmann, Jürgen; Morty, Rory E

    2015-06-01

    Maturation of the lung extracellular matrix (ECM) plays an important role in the formation of alveolar gas exchange units. A key step in ECM maturation is cross-linking of collagen and elastin, which imparts stability and functionality to the ECM. During aberrant late lung development in bronchopulmonary dysplasia (BPD) patients and animal models of BPD, alveolarization is blocked, and the function of ECM cross-linking enzymes is deregulated, suggesting that perturbed ECM cross-linking may impact alveolarization. In a hyperoxia (85% O2)-based mouse model of BPD, blunted alveolarization was accompanied by alterations to lung collagen and elastin levels and cross-linking. Total collagen levels were increased (by 63%). The abundance of dihydroxylysinonorleucine collagen cross-links and the dihydroxylysinonorleucine-to-hydroxylysinonorleucine ratio were increased by 11 and 18%, respectively, suggestive of a profibrotic state. In contrast, insoluble elastin levels and the abundance of the elastin cross-links desmosine and isodesmosine in insoluble elastin were decreased by 35, 30, and 21%, respectively. The lung collagen-to-elastin ratio was threefold increased. Treatment of hyperoxia-exposed newborn mice with the lysyl oxidase inhibitor ?-aminopropionitrile partially restored normal collagen levels, normalized the dihydroxylysinonorleucine-to-hydroxylysinonorleucine ratio, partially normalized desmosine and isodesmosine cross-links in insoluble elastin, and partially restored elastin foci structure in the developing septa. However, ?-aminopropionitrile administration concomitant with hyperoxia exposure did not improve alveolarization, evident from unchanged alveolar surface area and alveoli number, and worsened septal thickening (increased by 12%). These data demonstrate that collagen and elastin cross-linking are perturbed during the arrested alveolarization of developing mouse lungs exposed to hyperoxia. PMID:25840994

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

    Microsoft Academic Search

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

    2009-01-01

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

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

    Microsoft Academic Search

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

    2005-01-01

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

  3. Shear strength and laws of shear deformation of some cross-linked resins

    Microsoft Academic Search

    A. Ya. Gol'dman; A. L. Rabinovich

    1966-01-01

    The authors present the results of an experimental investigation and comparison with theory of certain laws of shear deformation and shear strength for rigid cross-linked resins. The possibility of describing the state of strain of homogeneous isotropic polymers by means of the generalized nonlinear Maxwell equation is considered. The results of an investigation of thin-walled tubular specimens of three cross-linked

  4. T-lymphocytes mediate left ventricular fibrillar collagen cross-linking and diastolic dysfunction in mice

    Microsoft Academic Search

    Qianli Yu; Randy Vazquez; Sherma Zabadi; Ronald R. Watson; Douglas F. Larson

    2010-01-01

    Aberrant concentrations of cardiac extracellular matrix (ECM) fibrillar collagen cross-linking have been proposed to be an underlying cause of cardiac diastolic dysfunction however the role of the adaptive immune system in this process has yet to be investigated. Fibrillar collagen cross-linking is a product of the enzymatic activities of lysyl oxidase (LOX and LOXL-3) released by the cardiac fibroblast and

  5. Positively charged composite nanofiltration membrane from quaternized chitosan by toluene diisocyanate cross-linking

    Microsoft Academic Search

    Ruihua Huang; Guohua Chen; Bingchao Yang; Congjie Gao

    2008-01-01

    2-Hydroxypropyltrimethyl ammonium chloride chitosan\\/polyacrylonitrile (HACC\\/PAN) positively charged composite nanofiltration (NF) membrane was prepared using HACC as active layer, PAN ultrafiltration (UF) membrane as support layer, and toluene diisocyanate (TDI) as cross-linking reagent. FTIR-ATR spectrum was employed to characterize the cross-linking on the resultant membrane surface. Besides, some characteristics such as the permeability of pure water and the rejection performance to

  6. The Equation of State of a Gaussian Phantom Network with Defined Cross Link Functionality

    E-print Network

    Benjamin Paul; Michael Schulz; Harry L. Frisch

    1998-12-24

    A phantom network of Gaussian chains far from the point of gelation can be described as a gas of interacting particles represented by the cross links. The type of particles varies with the network functionality, whereas the type of interaction depends on the properties of the connecting chains. In a mean field approximation the Equation of State can be calculated using Mayer's cluster expansion. The resulting isothermal compressibility is compared for different cross link functionalities.

  7. Chemical and thermal cross-linking of collagen and elastin hydrolysates

    Microsoft Academic Search

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

    2010-01-01

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

  8. Interpretation of experiments on ZDDP anti-wear films through pressure-induced cross-linking

    Microsoft Academic Search

    N. J. Mosey; T. K. Woo; M. Kasrai; P. R. Norton; G. M. Bancroft; M. H. Müser

    2006-01-01

    We review a recently developed molecular-level theory for the formation and functionality of zinc dialkyldithiophosphate anti-wear films [N. J. Mosey, M. H. Müser and T. K. Woo, Science 307 (2005) 1612]. This theory is based on the idea that pressure-induced cross-linking leads to chemically connected networks. The formation of cross-links modifies the mechanical properties of the films such that wear

  9. Hyaluronan and synovial joint: function, distribution and healing

    PubMed Central

    2013-01-01

    Synovial fluid is a viscous solution found in the cavities of synovial joints. The principal role of synovial fluid is to reduce friction between the articular cartilages of synovial joints during movement. The presence of high molar mass hyaluronan (HA) in this fluid gives it the required viscosity for its function as lubricant solution. Inflammation oxidation stress enhances normal degradation of hyaluronan causing several diseases related to joints. This review describes hyaluronan properties and distribution, applications and its function in synovial joints, with short review for using thiol compounds as antioxidants preventing HA degradations under inflammation conditions. PMID:24678248

  10. Structural properties of the D1 and surrounding photosystem II polypeptides as revealed by their interaction with cross-linking reagents.

    PubMed

    Adir, N; Ohad, I

    1988-01-01

    Treatment of Chlamydomonas reinhardtii thylakoids with cross-linking reagents including glutaraldehyde causes polymerization of all thylakoid polypeptides, but not of the reaction center II polypeptide D1 unless the thylakoids are presolubilized by octyl beta-D-glucoside (Adir, N., and Ohad, I. (1986) Biochim. Biophys. Acta 850, 264-274). The results presented here show that this is a general property of D1 as it can be demonstrated in thylakoids of cyanophytes, Dasicladaceae, green algae, and C3 and C4 plants. Solubilization of the membranes by ionic detergents, deoxycholate, lauryl sucrose, or dodecyl beta-D-maltoside is not effective in inducing cross-linking of the D1 polypeptides by glutaraldehyde. The most effective alkyl glucosides were those with 7-9 carbon alkyl chains. The same behavior toward glutaraldehyde was exhibited by the unprocessed D1 precursor and by the palmitoylated D1 protein. Based on the refractility of the D1 protein to cross-linking reagents, a procedure was developed for its isolation from cross-linked thylakoids by lithium dodecyl sulfate-polyacrylamide gel electrophoresis. Isolated D1 retained its behavior toward cross-linking by glutaraldehyde and generated tryptic fragments similar to those obtained following trypsin treatment of intact thylakoids. Denaturation of isolated D1 protein by acetone facilitates cross-linking by glutaraldehyde and extensive degradation by trypsin. The photosystem II polypeptides are differentially cross-linked with increasing concentrations of glutaraldehyde, the most susceptible being the 28- and 23-kDa components of the light-harvesting chlorophyll a-b protein complex and the core complex 44- and 51-kDa polypeptides, and the least affected being the cytochrome b559, the D2 protein, and a 24-kDa component of the light-harvesting chlorophyll a-b protein complex. These results reflect the relative position and interaction of the photosystem II polypeptides within the complex and suggest that strong and specific hydrophobic interactions may be responsible for the tight and stable conformation of D1. This may be based mostly on the conserved amino acid sequences of D1 and possibly plays a role in the process of D1 integration and removal from the reaction center during its light-dependent turnover. PMID:3121610

  11. Cross-linked chitosan improves the mechanical properties of calcium phosphate-chitosan cement.

    PubMed

    Aryaei, Ashkan; Liu, Jason; Jayatissa, Ahalapitiya H; Champa Jayasuriya, A

    2015-09-01

    Calcium phosphate (CaP) cements are highly applicable and valuable materials for filling bone defects by minimally invasive procedures. The chitosan (CS) biopolymer is also considered as one of the promising biomaterial candidates in bone tissue engineering. In the present study, some key features of CaP-CS were significantly improved by developing a novel CaP-CS composite. For this purpose, CS was the first cross-linked with tripolyphosphate (TPP) and then mixed with CaP matrix. A group of CaP-CS samples without cross-linking was also prepared. Samples were fabricated and tested based on the known standards. Additionally, the effect of different powder (P) to liquid (L) ratios was also investigated. Both cross-linked and uncross-linked CaP-CS samples showed excellent washout resistance. The most significant effects were observed on Young's modulus and compressive strength in wet condition as well as surface hardness. In dry conditions, the Young's modulus of cross-linked samples was slightly improved. Based on the presented results, cross-linking does not have a significant effect on porosity. As expected, by increasing the P/L ratio of a sample, ductility and injectability were decreased. However, in the most cases, mechanical properties were enhanced. The results have shown that cross-linking can improve the mechanical properties of CaP-CS and hence it can be used for bone tissue engineering applications. PMID:26046262

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

    PubMed Central

    2011-01-01

    Introduction Corneal collagen cross-linking is a rather new technique that uses riboflavin and ultraviolet A light for collagen fiber stabilization in keratoconus corneas. Other than reversible side effects, the preliminary results of corneal collagen cross-linking studies suggest that it is a rather safe technique. In this report, we demonstrate a case of corneal melting after corneal collagen cross-linking for keratoconus corneas associated with an acute inflammatory response. Case presentation A 23-year-old Caucasian man with keratoconus cornea stage 1 to 2 underwent uneventful corneal collagen cross-linking treatment according to the Dresden protocol. The next day the patient had intense photophobia, watering and redness of the eye, and his visual acuity was limited to counting fingers. Slit lamp biomicroscopy revealed severe corneal haze accompanied by non-specific endothelial precipitates following an acute inflammatory response. Mild inflammation could be detected in the anterior chamber. Moreover, the re-epithelialization process could barely be detected. His corneal state gradually deteriorated, resulting in descemetocele and finally perforation. Conclusion In this report, we present a case of a patient with corneal melting after standard corneal collagen cross-linking treatment for keratoconus corneas following an acute inflammatory response. Despite modifying postoperative treatment, elaboration of all apparent associated causes by the treating physicians and undergoing extensive laboratory testing, the patient developed descemetocele, which led to perforation. Our report suggests that further research is necessary regarding the safety of corneal collagen cross-linking in keratoconus corneas. PMID:21496288

  13. Stabilization of the i-motif structure by the intra-strand cross-link formation.

    PubMed

    Kikuta, Kenji; Piao, Haishun; Brazier, John; Taniguchi, Yosuke; Onizuka, Kazumitsu; Nagatsugi, Fumi; Sasaki, Shigeki

    2015-08-15

    The i-motif structures are formed by oligonucleotides containing cytosine tracts under acidic conditions. The folding of the i-motif under physiological conditions is of great interest because of its biological role. In this study, we investigated the effect of the intra-strand cross-link on the stability of the i-motif structure. The 4-vinyl-substituted analog of thymidine (T-vinyl) was incorporated into the 5'-end of the human telomere complementary strand, which formed the intra-strand cross-link with the internal adenine. The intra-strand cross-linked i-motif displayed CD spectra similar to that of the natural i-motif at acidic pH, which was transformed into a random coil with the increasing pH. The pH midpoint for the transition from the i-motif to random coil increased from pH 6.1 for the natural one to pH 6.8 for the cross-linked one. The thermodynamic parameters were obtained by measuring the thermal melting behaviors by CD and UV, and it was determined that the intra-strand cross-linked i-motif is stabilized due to a favorable entropy effect. Thus, this study has clearly indicated the validity of the intra-strand cross-linking for stabilization of the i-motif structure. PMID:26105193

  14. Ruthenium-catalyzed photo cross-linking of fibrin-based engineered tissue

    PubMed Central

    Bjork, Jason W.; Johnson, Sandra L.; Tranquillo, Robert T.

    2012-01-01

    Most cross-linking methods utilize chemistry or physical processes that are detrimental to cells and tissue development. Those that are not as harmful often do not provide a level of strength that ultimately meets the required application. The purpose of this work was to investigate the use of a ruthenium-sodium persulfate cross-linking system to form dityrosine in fibrin-based engineered tissue. By utilizing the tyrosine residues inherent to fibrin and cell-deposited proteins, at least 3-fold mechanical strength increases and 10-fold stiffness increases were achieved after cross-linking. This strengthening and stiffening effect was found to increase with culture duration prior to cross-linking such that physiologically relevant properties were obtained. Fibrin was not required for this effect as demonstrated by testing with collagen-based engineered tissue. Cross-linked tissues were implanted subcutaneously and shown to have minimal inflammation after 30 days, similar to non-cross-linked controls. Overall, the method employed is rapid, non-toxic, minimally inflammatory, and is capable of increasing strength and stiffness of engineered tissues to physiological levels. PMID:21196047

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

    NASA Astrophysics Data System (ADS)

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

    2005-06-01

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

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

    PubMed Central

    Pron, G; Ieraci, L; Kaulback, K

    2011-01-01

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

  17. Visible-Light Photocatalyzed Cross-Linking of Diacetylene Ligands by Quantum Dots to Improve Their Aqueous Colloidal Stability

    PubMed Central

    2015-01-01

    Ligand cross-linking is known to improve the colloidal stability of nanoparticles, particularly in aqueous solutions. However, most cross-linking is performed chemically, in which it is difficult to limit interparticle cross-linking, unless performed at low concentrations. Photochemical cross-linking is a promising approach but usually requires ultraviolet (UV) light to initiate. Using such high-energy photons can be harmful to systems in which the ligand–nanoparticle bond is fairly weak, as is the case for the commonly used semiconductor quantum dots (QDs). Here, we introduce a novel approach to cross-link thiolated ligands on QDs by utilizing the photocatalytic activity of QDs upon absorbing visible light. We show that using visible light leads to better ligand cross-linking by avoiding the problem of ligand dissociation that occurs upon UV light exposure. Once cross-linked, the ligands significantly enhance the colloidal stability of those same QDs that facilitated cross-linking. PMID:25036275

  18. Polypeptide Grafted Hyaluronan: Synthesis and Characterization

    SciTech Connect

    Wang, Xiaojun [ORNL; Messman, Jamie M [ORNL; Mays, Jimmy [ORNL; Baskaran, Durairaj [University of Tennessee, Knoxville (UTK)

    2010-01-01

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

  19. Bacterial cellulose gels with high mechanical strength.

    PubMed

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

    2015-02-01

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

  20. Nanopod Formation through Gold Nanoparticle Templated and Catalyzed Cross-linking of Polymers Bearing Pendant Propargyl Ethers

    SciTech Connect

    Zhang, Ke [Northwestern Univ., Evanston, IL (United States); Cutler, Joshua I. [Northwestern Univ., Evanston, IL (United States); Zhang, Jian A. [Northwestern Univ., Evanston, IL (United States); Zheng, Dan [Northwestern Univ., Evanston, IL (United States); Auyeung, Evelyn [Northwestern Univ., Evanston, IL (United States); Mirkin, Chad A. [Northwestern Univ., Evanston, IL (United States)

    2010-01-01

    A novel method for synthesizing polymer nanopods from a linear polymer bearing pendant propargyl ether groups, using gold nanoparticles as both the template and the catalyst for the cross-linking reaction, is reported. The transformations involved in the cross-linking process are unprecedented on the surface of a gold particle. A tentative cross-linking mechanism is proposed.

  1. Protein structure prediction guided by cross-linking restraints - A systematic evaluation of the impact of the cross-linking spacer length

    E-print Network

    Hofmann, Tommy; Meiler, Jens; Kalkhof, Stefan

    2015-01-01

    Recent development of high-resolution mass spectrometry (MS) instruments enables chemical cross-linking (XL) to become a high-throughput method for obtaining structural information about proteins. Restraints derived from XL-MS experiments have been used successfully for structure refinement and protein-protein docking. However, one formidable question is under which circumstances XL-MS data might be sufficient to determine a protein's tertiary structure de novo? Answering this question will not only include understanding the impact of XL-MS data on sampling and scoring within a de novo protein structure prediction algorithm, it must also determine an optimal cross-linker type and length for protein structure determination. While a longer cross-linker will yield more restraints, the value of each restraint for protein structure prediction decreases as the restraint is consistent with a larger conformational space. In this study, the number of cross-links and their discriminative power was systematically analyz...

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

    PubMed

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

    2014-09-01

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

  3. Quantitative cross-linking/mass spectrometry using isotope-labelled cross-linkers?

    PubMed Central

    Fischer, Lutz; Chen, Zhuo Angel; Rappsilber, Juri

    2013-01-01

    Dynamic proteins and multi-protein complexes govern most biological processes. Cross-linking/mass spectrometry (CLMS) is increasingly successful in providing residue-resolution data on static proteinaceous structures. Here we investigate the technical feasibility of recording dynamic processes using isotope-labelling for quantitation. We cross-linked human serum albumin (HSA) with the readily available cross-linker BS3-d0/4 in different heavy/light ratios. We found two limitations. First, isotope labelling reduced the number of identified cross-links. This is in line with similar findings when identifying proteins. Second, standard quantitative proteomics software was not suitable for work with cross-linking. To ameliorate this we wrote a basic open source application, XiQ. Using XiQ we could establish that quantitative CLMS was technically feasible. Biological significance Cross-linking/mass spectrometry (CLMS) has become a powerful tool for providing residue-resolution data on static proteinaceous structures. Adding quantitation to CLMS will extend its ability of recording dynamic processes. Here we introduce a cross-linking specific quantitation strategy by using isotope labelled cross-linkers. Using a model system, we demonstrate the principle and feasibility of quantifying cross-linking data and discuss challenges one may encounter while doing so. We then provide a basic open source application, XiQ, to carry out automated quantitation of CLMS data. Our work lays the foundations of studying the molecular details of biological processes at greater ease than this could be done so far. This article is part of a Special Issue entitled: New Horizons and Applications for Proteomics [EuPA 2012]. PMID:23541715

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

    PubMed Central

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

    2014-01-01

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

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

    PubMed Central

    Schmidt, Carla; Robinson, Carol V.

    2014-01-01

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

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

    PubMed

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

    2014-05-01

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

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

    PubMed Central

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

    2013-01-01

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

  8. [Cross-linking and neurodermitis: prolonged re-epithelisation with severe corneal vascularisation after cross-linking in a patient with neurodermitis and keratoconus].

    PubMed

    Görsch, I C; Steinberg, J; Richard, G; Katz, T; Linke, S

    2014-06-01

    This case report describes a patient with keratoconus and neurodermitis suffering from a significantly prolonged postoperative time interval to re-epithelisation after corneal cross-linking. The development of corneal calcifications and vascularisations additionally inhibited proper re-epithelisation. Therefore the patient received four subsequent subconjunctival injections of Bevacizumab and an additional keratectomy to remove the calcifications. This therapeutic scheme led to a significant reduction of corneal vascularisation and finally a full rehabilitation of the epithelium. PMID:24788604

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

    PubMed

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

    2014-01-16

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

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

    PubMed Central

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

    2013-01-01

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

  11. Usage of polarization-sensitive optical coherence tomography for investigation of collagen cross-linking.

    PubMed

    Ju, Myeong Jin; Tang, Shuo

    2015-04-01

    To investigate morphological alternation in corneal stroma induced by collagen cross-linking (CXL) treatment, polarization-sensitive optical coherence tomography (PS-OCT) capable of providing scattering, phase retardation, and degree of polarization uniformity (DOPU) images were employed on fresh bovine cornea. Significant corneal thickness reduction was observed after the CXL procedure, and its variation was quantitatively analyzed. From the scattering contrast, a hyperscattering region was observed in the anterior of the cornea immediately after the CXL procedure and its range increased with time. Within the scattering region, a slow increase was observed in the phase retardation image, and a discriminable characteristic was found in the DOPU image. A global threshold value was empirically determined from the averaged DOPU depth profile in order to locate the effective cross-linking depth. In addition to the standard protocol, an accelerated CXL procedure shortening the treatment time with higher intensity of ultraviolet-A (UV-)A power was also performed. From the measurement results after the two different CXL protocols, different cross-linking aspects were found and their difference was discussed in terms of the effectiveness of cross-linking. Based on this study, we believe that PS-OCT could be a promising optical imaging modality to evaluate the progression and effectiveness of the riboflavin/UV-A induced corneal collagen cross-linking. PMID:25837511

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

    PubMed

    Penhasi, Adel; Meidan, Victor M

    2014-02-15

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

  13. The Non-catalytic B Subunit of Coagulation Factor XIII Accelerates Fibrin Cross-linking.

    PubMed

    Souri, Masayoshi; Osaki, Tsukasa; Ichinose, Akitada

    2015-05-01

    Covalent cross-linking of fibrin chains is required for stable blood clot formation, which is catalyzed by coagulation factor XIII (FXIII), a proenzyme of plasma transglutaminase consisting of catalytic A (FXIII-A) and non-catalytic B subunits (FXIII-B). Herein, we demonstrate that FXIII-B accelerates fibrin cross-linking. Depletion of FXIII-B from normal plasma supplemented with a physiological level of recombinant FXIII-A resulted in delayed fibrin cross-linking, reduced incorporation of FXIII-A into fibrin clots, and impaired activation peptide cleavage by thrombin; the addition of recombinant FXIII-B restored normal fibrin cross-linking, FXIII-A incorporation into fibrin clots, and activation peptide cleavage by thrombin. Immunoprecipitation with an anti-fibrinogen antibody revealed an interaction between the FXIII heterotetramer and fibrinogen mediated by FXIII-B and not FXIII-A. FXIII-B probably binds the ?-chain of fibrinogen with its D-domain, which is near the fibrin polymerization pockets, and dissociates from fibrin during or after cross-linking between ?-chains. Thus, FXIII-B plays important roles in the formation of a ternary complex between proenzyme FXIII, prosubstrate fibrinogen, and activator thrombin. Accordingly, congenital or acquired FXIII-B deficiency may result in increased bleeding tendency through impaired fibrin stabilization due to decreased FXIII-A activation by thrombin and secondary FXIII-A deficiency arising from enhanced circulatory clearance. PMID:25809477

  14. Lignin cross-links with cysteine- and tyrosine-containing peptides under biomimetic conditions.

    PubMed

    Diehl, Brett G; Brown, Nicole R

    2014-10-22

    The work presented here investigates the cross-linking of various nucleophilic amino acids with lignin under aqueous conditions, thus providing insight as to which amino acids might cross-link with lignin in planta. Lignin dehydrogenation polymer (DHP) was prepared in aqueous solutions that contained tripeptides with the general structure XGG, where X represents an amino acid with a nucleophilic side chain. Fourier-transform infrared spectroscopy and energy dispersive X-ray spectroscopy showed that peptides containing cysteine and tyrosine were incorporated into the DHP to form DHP-CGG and DHP-YGG adducts, whereas peptides containing other nucleophilic amino acids were not incorporated. Scanning electron microscopy showed that the physical morphology of DHP was altered by the presence of peptides in the aqueous solution, regardless of peptide incorporation into the DHP. Nuclear magnetic resonance (NMR) spectroscopy showed that cysteine-containing peptide cross-linked with lignin at the lignin ?-position, whereas in the case of the lignin-tyrosine adduct the exact cross-linking pathway could not be determined. This is the first study to use NMR to confirm cross-linking between lignin and peptides under biomimetic conditions. The results of this study may indicate the potential for lignin-protein linkage formation in planta, particularly between lignin and cysteine- and/or tyrosine-rich proteins. PMID:25275918

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

    NASA Technical Reports Server (NTRS)

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

    1992-01-01

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

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

    PubMed Central

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

    2012-01-01

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

  17. The basis for a second-generation highly cross-linked UHMWPE.

    PubMed

    Dumbleton, John H; D'Antonio, James A; Manley, Michael T; Capello, William N; Wang, Aiguo

    2006-12-01

    Highly cross-linked ultra-high molecular weight polyethylene (UHMWPE) decreases wear at the hip by more than 50% compared with conventional UHMWPE. However, melted highly cross-linked polyethylene may be susceptible to fatigue cracking, and annealed highly cross-linked polyethylene may be susceptible to in vivo oxidation. The second-generation highly cross-linked UHMWPE (X3 HXPE) uses a sequential irradiation and annealing process. It preserves mechanical strength properties and has the highest survivorship in functional fatigue testing. The free radical content is low, and its performance under accelerated aging is the same as virgin UHMWPE. Hip simulator studies with 32-mm acetabular components demonstrated 97% wear reduction compared with conventional UHMWPE, and 62% compared with a clinically successful first-generation annealed highly cross-linked polyethylene. The crystallinity, density, and tensile strength of the X3 HXPE material was unchanged by oxidative challenge. X3 HXPE material articulating on cobalt-chromium alloy yields a volumetric wear rate very similar to that of metal-on-metal articulations, but eliminates the concerns of metal ion release. Wear particles generated from the X3 HXPE were the same size as those produced from conventional UHMWPE. Preliminary results suggest X3 HXPE can be used for cups larger than 36 mm. PMID:17016228

  18. Orientation birefringence of cross-linked rubber containing low-mass compound

    NASA Astrophysics Data System (ADS)

    Kiyama, Ayumi; Nobukawa, Shogo; Yamauchi, Masayuki

    2015-05-01

    Molecular orientation of low-mass compounds (LMCs) in a cross-linked rubber is studied in order to obtain the basic information on the dynamics of LMC molecules in a polymer beyond the glass transition temperature. A small amount of LMCs such as 4-cyano-4'-pentylbiphenyl (5CB), tricresylphosphate (TCP), and styrene-based tackifier (TF) is added into polybutadiene rubber (BR). After cross-linking reaction, the sheet samples are used to evaluate the orientation birefringence during stretching and stress relaxation. The rectangular films, cut out from the cross-linked sheets, are set in a uniaxial stretching machine equipped with an optical system to measure both birefringence and tensile stress simultaneously. It is confirmed that orientation birefringence is proportional to the stress for not only pure cross-linked BR, but also cross-linked BR containing an LMC in a wide range of strain. Even after stretching, the birefringence does not change as far as the sample is kept at a constant strain. The results suggest that the LMC molecules are forced to orient with polymer chains by the strong intermolecular orientation correlation. Because of the LMC orientation, the stress-optical coefficient CR is enhanced by the addition of 5CB and TCP, but depressed by TF. Therefore, the LMC doping can be used to control the birefringence of a retardation film.

  19. Biodegradable Chitosan-Based Ambroxol Hydrochloride Microspheres: Effect of Cross-Linking Agents

    PubMed Central

    Gangurde, HH; Chavan, NV; Mundada, AS; Derle, DV; Tamizharasi, S

    2011-01-01

    The objective of this study was to investigate the influence of type of cross-linking method used on the properties of ambroxol hydrochloride microspheres such as encapsulation efficiency, particle size, and drug release. Microspheres were prepared by solvent evaporation technique using chitosan as a matrix-forming agent and cross-linked using formaldehyde and heat treatment. Morphological and physicochemical properties of microspheres were then investigated by scanning electron microscopy (SEM), X-ray diffractometry (XRD), differential scanning calorimetry (DSC), and Fourier-transform infrared spectroscopy (FTIR) spectroscopy. The cross-linking of chitosan takes place at the free amino group because of formation of imine bond as evidenced by FTIR. The DSC, XRD, and FTIR analysis showed that chitosan microspheres cross linked by heating were superior in properties and performance as compared to the microspheres cross-linked using formaldehyde. SEM results revealed that heat-treated microspheres were spherical, discrete having smooth, and porous structure. The particle size and encapsulation efficiencies of the prepared chitosan microspheres ranged between 10.83–24.11 ?m and 39.73?80.56%, respectively. The drug release was extended up to 12 h, and the kinetics of the drug release was obeying Higuchi kinetic proving diffusion-controlled drug release. PMID:21607049

  20. Raloxifene ameliorates detrimental enzymatic and nonenzymatic collagen cross-links and bone strength in rabbits with hyperhomocysteinemia

    Microsoft Academic Search

    M. Saito; K. Marumo; S. Soshi; Y. Kida; C. Ushiku; A. Shinohara

    2010-01-01

    Summary  We demonstrate a reduction in enzymatic divalent immature and trivalent pyridinium cross-links and an increase in the nonenzymatic\\u000a cross-link, pentosidine (Pen), in rabbits with methionine (Met)-induced hyperhomocysteinemia. Such detrimental cross-link\\u000a formation in bone was ameliorated by raloxifene (RLX) treatment.\\u000a \\u000a \\u000a \\u000a \\u000a Introduction  Collagen cross-links are determinants of bone quality. Homocysteine (Hcys) interferes with collagen cross-linking. Because\\u000a RLX is thought to ameliorate bone quality,

  1. Fabrication of robust honeycomb polymer films: a facile photochemical cross-linking process.

    PubMed

    Li, Lei; Chen, Caikang; Zhang, Aijuan; Liu, Xinyu; Cui, Kun; Huang, Jin; Ma, Zhi; Han, Zhaohui

    2009-03-15

    Highly ordered honeycomb films are prepared by breath-figure method using an amphiphilic diblock copolymer of polystyrene-block-polyacrylic acid (PS-b-PAA). By simply cross-linking PS matrix via deep ultraviolet (UV) irradiation, both the solvent and thermal stability of the porous films was significantly improved while retaining the three-dimensional (3D) structures. The film surface wettability was changed from hydrophobicity to hydrophilicity by the formed polar groups during the photochemical process. After 6 h UV cross-linking, the honeycomb structures could be preserved up to 320 degrees C, an increase of more than 200 K as compared to the non-cross-linked films. PMID:19100561

  2. Preparation of cross-linked maize (Zea mays L.) starch in different reaction media.

    PubMed

    Hong, Jung Sun; Gomand, Sara V; Delcour, Jan A

    2015-06-25

    Granular normal maize starch was reacted with sodium trimetaphosphate in deionized water ( [Formula: see text] ), aqueous sodium sulfate solution ( [Formula: see text] ), aqueous ethanol (MSethanol) or aqueous acetone (MSacetone) under otherwise identical reaction conditions. Analysis of the resultant starches by Rapid Visco Analysis (RVA) showed that the starch was cross-linked to a higher degree in aqueous ethanol or aqueous acetone than in water or sodium sulfate solution, and with minimal starch leaching. While MSacetone and MSethanol had incorporated similar levels of phosphorous, RVA analysis and microscopic analysis showed that MSacetone granules were more effectively stabilized by cross-linking than MSethanol granules. Cross-linking in aqueous acetone is believed to either contain the greater numbers of distarch monophosphate (versus monostarch monophosphate), or occur more intensively at the granule outer layers than that in aqueous ethanol and, at the same time, to account for the greater granular strength of MSethanol than that of MSacetone. PMID:25839824

  3. Alterations in physical cross-linking modulate mechanical properties of two-phase protein polymer networks.

    PubMed

    Wu, Xiaoyi; Sallach, Rory; Haller, Carolyn A; Caves, Jeffrey A; Nagapudi, Karthik; Conticello, Vincent P; Levenston, Marc E; Chaikof, Elliot L

    2005-01-01

    Physically cross-linked protein-based materials possess a number of advantages over their chemically cross-linked counterparts, including ease of processing and the ability to avoid the addition or removal of chemical reagents or unreacted intermediates. The investigations reported herein sought to examine the nature of physical cross-links within two-phase elastin-mimetic protein triblock copolymer networks through an analysis of macroscopic viscoelastic properties. Given the capacity of solution processing conditions, including solvent type and temperature to modulate the microstructure of two-phase protein polymer networks, viscoelastic properties were examined under conditions in which interphase block mixing had been either accentuated or diminished during network formation. Protein networks exhibited strikingly different properties in terms of elastic modulus, hysteresis, residual deformability, and viscosity in response to interdomain mixing. Thus, two-phase protein polymer networks exhibit tunable responses that extend the range of application of these materials to a variety of tissue engineering applications. PMID:16283724

  4. Optimizing end-group cross-linking polymer electrolytes for fuel cell applications

    SciTech Connect

    Kim, Yu Seung [Los Alamos National Laboratory; Lee, Kwan Soo [Los Alamos National Laboratory; Jeong, Myung - Hwan [GIST, KOREA; Lee, Jae - Suk [GIST, KOREA

    2009-01-01

    This paper demonstrates the optimization of proton conductivity and water uptake for cross-linkable polymer electrolytes through synthesis and characterization of end-group cross-linkable sulfonated poly(arylene ether) copolymers (ESF-BPs). The extent of reaction of cross-linking was controlled by reaction time resulting in a series of polymers with two, independent tunable parameters, degree of sulfonation (DS) and degree of cross-linking (DC). For the polymers presented, cross-linking improved proton conductivity while reducing water uptake, an uncommon trend in polymer electrolytes where water is critical for proton conduction. Other trends relating to changes are reported and the results yield insight into the role of DS and DC and how to optimize electrochemical properties and performance of polymer electrolytes through these tunable parameters. Select polymer electrolytes were tested in fuel cells where performance and durability with accelerated relative humidity cycling were compared with Nafion{reg_sign}.

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

    PubMed

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

    2005-06-01

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

  6. Localization of the dominant non-enzymatic intermolecular cross-linking sites on fibrous collagen.

    PubMed

    Chiue, Hiroko; Yamazoye, Tsutako; Matsumura, Sueo

    2015-06-01

    Previous studies have shown that fibrous collagen undergoes intermolecular cross-linking at multiple sites of the elongated triple-helical regions among adjacent juxtaposed collagen molecules on incubation with a very high concentration of reducing sugar such as 200 mM ribose, and the similarity of the changes in its physicochemical properties to that of senescent collagen aged in vivo has been emphasized. In the present study, however, it was found that when incubated with less than 30 mM ribose, fibrous collagen underwent intermolecular cross-linking primarily between the telopeptide region of a collagen molecule and the triple-helical region of another adjacent collagen molecule, and intermolecular cross-linking between the triple-helical regions of adjacent collagen molecules was very small. Physiological significance of the previous studies thus needs to be reevaluated. PMID:25892520

  7. Molecular Dynamics Simulation of Cross-linked Graphene-Epoxy Nanocomposites

    E-print Network

    Rahman, R

    2011-01-01

    This paper focuses on molecular dynamics (MD) modeling of graphene reinforced cross-linked epoxy (Gr-Ep) nanocomposite. The goal is to study the influence of geometry, and concentration of reinforcing nanographene sheet (NGS) on interfacial properties and elastic constants such as bulk Young's modulus, and shear modulus of Gr-Ep nanocomposites. The most typical cross-linked configuration was obtained in order to use in further simulations. The mechanical properties of this cross-linked structure were determined using MD simulations and the results were verified with those available in literatures. Graphene with different aspect ratios and concentrations (1%, 3% and 5%) were considered in order to construct amorphous unit cells of Gr-Ep nanocomposites. The Gr-Ep nanocomposites system undergoes NVT (constant number of atoms, volume and temperature) and NPT (constant number of atoms, pressure and temperature) ensemble with applied uniform strain field during MD simulation to obtain bulk Young's modulus and shear...

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

    NASA Astrophysics Data System (ADS)

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

    1993-07-01

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

  9. xiNET: Cross-link Network Maps With Residue Resolution*

    PubMed Central

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

    2015-01-01

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

  10. Revisiting glutaraldehyde cross-linking: the case of the Arg–Lys intermolecular doublet

    PubMed Central

    Salem, Michèle; Mauguen, Yves; Prangé, Thierry

    2010-01-01

    In addition to the common use of glutaraldehyde to nonspecifically cross-link protein crystals through lysine residues disposed on the surface of the protein, the use of gentle vapour diffusion of glutaraldehyde offers a convenient way to limit polymerization and to allow slow diffusion throughout the crystal. In the case of trimeric barnase crystals, a specific cross-link was observed between an lysine side chain and an arginine side chain that were spatially disposed at the ideal distance on the protein surface in the three monomers. Here, the direct observation of a specific Lys–Arg cross-link site is reported and a mechanism is proposed for the reaction. PMID:20208148

  11. Revisiting glutaraldehyde cross-linking: the case of the Arg-Lys intermolecular doublet.

    PubMed

    Salem, Michèle; Mauguen, Yves; Prangé, Thierry

    2010-03-01

    In addition to the common use of glutaraldehyde to nonspecifically cross-link protein crystals through lysine residues disposed on the surface of the protein, the use of gentle vapour diffusion of glutaraldehyde offers a convenient way to limit polymerization and to allow slow diffusion throughout the crystal. In the case of trimeric barnase crystals, a specific cross-link was observed between an lysine side chain and an arginine side chain that were spatially disposed at the ideal distance on the protein surface in the three monomers. Here, the direct observation of a specific Lys-Arg cross-link site is reported and a mechanism is proposed for the reaction. PMID:20208148

  12. Hyaluronan, a Crucial Regulator of Inflammation

    PubMed Central

    Petrey, Aaron C.; de la Motte, Carol A.

    2014-01-01

    Hyaluronan (HA), a major component of the extracellular matrix (ECM), plays a key role in regulating inflammation. Inflammation is associated with accumulation and turnover of HA polymers by multiple cell types. Increasingly through the years, HA has become recognized as an active participant in inflammatory, angiogenic, fibrotic, and cancer promoting processes. HA and its binding proteins regulate the expression of inflammatory genes, the recruitment of inflammatory cells, the release of inflammatory cytokines, and can attenuate the course of inflammation, providing protection against tissue damage. A growing body of evidence suggests the cell responses are HA molecular weight dependent. HA fragments generated by multiple mechanisms throughout the course of inflammatory pathologies, elicit cellular responses distinct from intact HA. This review focuses on the role of HA in the promotion and resolution of inflammation. PMID:24653726

  13. Hyaluronan inhibits BMP-induced osteoblast differentiation.

    PubMed

    Kaneko, Keiko; Higuchi, Chikahisa; Kunugiza, Yasuo; Yoshida, Kiyoshi; Sakai, Takashi; Yoshikawa, Hideki; Nakata, Ken

    2015-02-13

    Hyaluronan (HA), one of the major structural extracellular components in cartilage, regulates cellular responses via receptors such as CD44. However, the direct effects of HA on osteoblastic differentiation has not been studied in detail. Here, we investigated the effects of HA (molecular weight: 900-1200 kDa) on osteoblastic differentiation that was induced by bone morphogenetic protein (BMP) in C2C12 cells (mouse myoblastic cells) and ST2 cells (mouse bone marrow cells). BMP-induced osteoblastic differentiation and Smad1/Smad5/Smad8 phosphorylation were downregulated by HA. Use of the CD44-blocking antibody restored HA-induced inhibition of osteoblastic differentiation and Smad1/Smad5/Smad8 phosphorylation. Our results indicate that HA inhibits BMP-induced osteoblastic differentiation through the CD44 receptor. PMID:25592835

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

    PubMed

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

    2010-09-01

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

  15. Comparison of two proanthocyanidin cross-linked recombinant human collagen-peptide (RHC) - chitosan scaffolds.

    PubMed

    Zhang, Jing; Deng, Aipeng; Zhou, Aimei; Yang, Yang; Gao, Lihu; Zhong, Zhaocai; Yang, Shulin

    2015-07-01

    Cross-linking plays an important role in tissue engineering, which involves the alternative of cross-linker and the way of components interaction. We compared two proanthocyanidin (PA) cross-linked recombinant human collagen-peptide - chitosan scaffolds: immerse cross-linking (I-CLS) and premix cross-linking (P-CLS). Both of the scaffolds presented homogeneous pore structure with mean pore size of 110-115 ?m. The swelling ratio was decreased to 29.6 in I-CLS, but increased to 37.1 in P-CLS while porosity of the two scaffolds was reduced about 8% comparing to 94.3% before cross-linking. The cross-linked scaffolds exhibited enhanced resistance to enzyme degradation and improved compressive modulus (I-CLS > P-CLS). The scaffolds transformed from elastic region to plastic region until the strain reached 60%, and the stress was 40.5, 133.2 and 84.1 kPa of uncross-linking scaffold, I-CLS and P-CLS individually. Thermal stability indicated molecular bonding between PA and the scaffold components, simultaneously, Fourier transform infrared spectroscopy mainly presented hydrogen bonding between the protein amide carbonyl and the phenolic hydroxyl with a particular transform due to pyrrolidine rings of proline in P-CLS. Both of the I-CLS and P-CLS could promote human umbilical vein endothelial cells attachment and proliferation. The characterization suggested in situ biodegradable application of P-CLS, while a potential long-term utilization of I-CLS in tissue engineering. PMID:26053645

  16. Gel formation of lignin and biodegradation of the lignin gels by microorganisms

    Microsoft Academic Search

    Hiroyuki Yamamoto; Masato Amaike; Hideki Saitoh; Yoshiyasu Sano

    2000-01-01

    The multifunctional, polyphenolic nature of isolated lignins invites practical applications in which lignin serves as the principal component of cross-linked network polymers. Unmodified kraft lignin was first condensated with phenols and then further condensated with resorcinol under alkaline conditions, to give lignin–phenol–resorcinol resin (LPR resin). Lignin gels were prepared from the methanol-diluted LPR resin with the use of organic cross-linking

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

    Microsoft Academic Search

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

    2007-01-01

    Here, we study the influence of cross-linking density, X, on the swelling, thermal and electric field response of trifunctionally cross-linked liquid single crystal elastomers (V3 LSCEs) swollen with low molecular weight liquid crystals, 4-n-pentyl-4-cyanobiphenyl (5CB). The cross-linker concentrations are X3V3=3.3 mol %, X5V3=5 mol %, and X7V3=7 mol %. LSCE networks are characterized by frozen-in orientation order, P. Xc is

  18. The cross-linking of tyrosine residues in apo-ovotransferrin by treatment with periodate anions.

    PubMed Central

    Hsuan, J J

    1987-01-01

    The iron-binding ability of apotransferrins is rapidly abolished in the reaction with periodate anions, which destroys 4 mol of tyrosine per mol of protein. Treatment of ovotransferrin with cyanogen bromide and tryptic digestion of the glycopeptide fragment demonstrated the existence of an intramolecular cross-link in the C-terminal domain of the oxidized protein. The cross-linked residues were identified as Tyr-421 and Tyr-524 and the product is similar in structure to 3,3'-dityrosine. PMID:2827629

  19. Cross-linking and modification of cytochrome c with redox-active metal complexes

    SciTech Connect

    Lukes, A.

    1991-05-02

    This thesis consists of two parts. The first part shows that a redox-active trinuclear metal cluster may be used as a cross-linking reagent for proteins. Electron transfer is observed in the protein oligomers. The second part involves labelling the cysteine residue of baker's yeast cytochrome c with chloromercuriferrocene. Chloromercuriferrocene reacts with cytochrome c in two interesting ways. Symmetrization produces two products; two proteins cross-linked with mercury and diferrocenylmercury. Simple substitution of FeHgCl onto the protein followed by the addition of a proton by electrophilic substitution affords ferrocene and the mercuric chloride modified protein. 16 refs., 3 figs.

  20. Chemical cross-linking of polypropylenes towards new shape memory polymers.

    PubMed

    Raidt, Thomas; Hoeher, Robin; Katzenberg, Frank; Tiller, Joerg C

    2015-04-01

    In this work, syndiotactic polypropylene (sPP) as well as isotactic polypropylene (iPP) are cross-linked to gain a shape memory effect. Both prepared PP networks exhibit maximum strains of 700%, stored strains of up to 680%, and recoveries of nearly 100%. While x-iPP is stable for many cycles, x-sPP ruptures after the first shape-memory cycle. It is shown by wide-angle X-ray scattering (WAXS) experiments that cross-linked iPP exhibits homoepitaxy in the temporary, stretched shape but in contrast to previous reports it contains a higher amount of daughter than mother crystals. PMID:25689515

  1. Protein cluster formation during enzymatic cross-linking of globular proteins.

    PubMed

    Saricay, Yunus; Dhayal, Surender Kumar; Wierenga, Peter Alexander; de Vries, Renko

    2012-01-01

    Work on enzymatic cross-linking of globular food proteins has mainly focused on food functional effects such as improvements of gelation and enhanced stabilization of emulsions and foams, and on the detailed biochemical characterization of the cross-linking chemistry. What is still lacking is a physical characterization of cluster formation and gelation, as has been done for example, for cluster formation and gelation during heat-induced protein aggregation. Here we present preliminary results along these lines. We propose that enzymatic cross-linking of apo-alpha-lactalbumin is a good model system for studying the problem of cluster formation and gelation during enzymatic cross-linking of globular proteins. We present initial results on cluster sizes produced when crosslinking dilute solutions of apo-alpha-lactalbumin with a range of cross-linking enzymes: microbial transglutaminase, horseradish peroxidase, and mushroom tyrosinase. These results are used to highlight similarities and differences between different enzymes, when acting on the same substrate. Next we consider cluster growth and gelation in somewhat more detail for the specific case of cross-linking by horseradish peroxidase, under the periodic addition of H2O2. Upon increasing the initial concentration of apo-alpha-lactalbumin, at a fixed enzyme-to-substrate ratio and fixed reaction time, the size of the clusters at the end of the reaction increases rapidly, and above a critical concentration, gelation occurs. For the conditions that we have used, gelation occurred at very low initial apo-alpha-lactalbumin concentrations of 34% (w/v), indicating a very dilute cross-linked protein network, with a low average number of cross-links per protein. It is found that reactive protein monomers are first rapidly (1-2 h) incorporated into small covalent clusters. This is followed by a much slower phase (up to about 12 h) in which the small clusters are coupled together to form much larger covalent protein clusters. Consistent with this two-step mechanism, atomic force microscopy shows that the covalent protein clusters are very heterogeneous and seem to consist of smaller subclusters. PMID:23234160

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

    PubMed Central

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

    2014-01-01

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

  3. Synthesis and cross-linking activities of oligodeoxynucleotides containing a 4-oxoalkenal group.

    PubMed

    Kobori, Akio; Kobuchi, Takashi; Ikeda, Masato; Murakami, Akira

    2006-01-01

    The 4-oxoalkenal group, which has been characterized as part of a novel lipid-peroxidation-derived genotoxin, reacts with dG, dC, and dA, yielding etheno adducts. To develop a new interstrand cross-linking system based on the covalent bond formed between the 4-oxoalkenal group and DNA bases, we prepared 4-oxoalkenal-derivatized oligodeoxynucleotides. The protected 4-oxoalkenal derivative with a primary amino group was synthesized and incorporated to the 5' end of the oligodeoxynucleotide. In the presence of the complementary strand, cross-linking products were observed by HPLC and MALDI-MS analysis. PMID:17150816

  4. Hybrid sol-gel optical materials

    DOEpatents

    Zeigler, John M. (Albuquerque, NM)

    1993-01-01

    Hybrid sol-gel materials comprise silicate sols cross-linked with linear polysilane, polygermane, or poly(silane-germane). The sol-gel materials are useful as optical identifiers in tagging and verification applications and, in a different aspect, as stable, visible light transparent non-linear optical materials. Methyl or phenyl silicones, polyaryl sulfides, polyaryl ethers, and rubbery polysilanes may be used in addition to the linear polysilane. The linear polymers cross-link with the sol to form a matrix having high optical transparency, resistance to thermooxidative aging, adherence to a variety of substrates, brittleness, and a resistance to cracking during thermal cycling.

  5. Hybrid sol-gel optical materials

    DOEpatents

    Zeigler, J.M.

    1993-04-20

    Hybrid sol-gel materials comprise silicate sols cross-linked with linear polysilane, polygermane, or poly(silane-germane). The sol-gel materials are useful as optical identifiers in tagging and verification applications and, in a different aspect, as stable, visible light transparent non-linear optical materials. Methyl or phenyl silicones, polyaryl sulfides, polyaryl ethers, and rubbery polysilanes may be used in addition to the linear polysilane. The linear polymers cross-link with the sol to form a matrix having high optical transparency, resistance to thermooxidative aging, adherence to a variety of substrates, brittleness, and a resistance to cracking during thermal cycling.

  6. Hybrid sol-gel optical materials

    DOEpatents

    Zeigler, John M. (Albuquerque, NM)

    1992-01-01

    Hybrid sol-gel materials comprise silicate sols cross-linked with linear polysilane, polygermane, or poly(silane-germane). The sol-gel materials are useful as optical identifiers in tagging and verification applications and, in a different aspect, as stable, visible light transparent non-linear optical materials. Methyl or phenyl silicones, polyaryl sulfides, polyaryl ethers, and rubbery polysilanes may be used in addition to the linear polysilane. The linear polymers cross-link with the sol to form a matrix having high optical transparency, resistance to thermooxidative aging, adherence to a variety of substrates, brittleness, and a resistance to cracking during thermal cycling.

  7. Fabrication and characterization of ionic polymer gel actuators

    NASA Astrophysics Data System (ADS)

    Jo, Choonghee; In, Eunji; Naguib, Hani E.

    2010-04-01

    Poly-AMPS (PAMPS) gel was fabricated and its electroactive behavior was studied. A weakly cross-linked anionic PAMPS gel was produced by radical polymerization using 2-acrylamido-2-methylpropane sulfonic acid (AMPS) monomers, where N,N'-methlenebisacrylamide (MBAA) and ? -ketoglutaric acid were used as a cross-linking agent and a radical initiator, respectively. The polymerization was carried out at 55°C for at least 24 hours. Density and the degree of swelling of gel samples were investigated as physical properties. Also, swelling experiments were conducted in a surfactant solution using 1-dodecylpyridinium chloride hydrate. The chemo-mechanical properties of PAMPS gel were studied in a dilute surfactant solution under the electric field. The effect of material parameters on the bending deformation was investigated. As design parameters, sample thickness, current density, ion concentration of the surfactant solution, and cross-linking degree of gel were chosen, and the effect of these parameters on the actuation was studied.

  8. Nanoparticles for localized delivery of hyaluronan oligomers towards regenerative repair of elastic matrix.

    PubMed

    Sylvester, Andrew; Sivaraman, Balakrishnan; Deb, Partha; Ramamurthi, Anand

    2013-12-01

    Abdominal aortic aneurysms (AAAs) are rupture-prone progressive dilations of the infrarenal aorta due to a loss of elastic matrix that lead to weakening of the aortic wall. Therapies to coax biomimetic regenerative repair of the elastic matrix by resident, diseased vascular cells may thus be useful to slow, arrest or regress AAA growth. Hyaluronan oligomers (HA-o) have been shown to induce elastic matrix synthesis by healthy and aneurysmal rat aortic smooth muscle cells (SMCs) in vitro but only via exogenous dosing, which potentially has side-effects and limitations to in vivo delivery towards therapy. In this paper, we describe the development of HA-o loaded poly(lactide-co-glycolide) nanoparticles (NPs) for targeted, controlled and sustained delivery of HA-o towards the elastogenic induction of aneurysmal rat aortic SMCs. These NPs were able to deliver HA-o over an extended period (>30 days) at previously determined elastogenic doses (0.2-20 ?g ml(-1)). HA-o released from the NPs led to dose-dependent increases in elastic matrix synthesis, and the recruitment and activity of lysyl oxidase, the enzyme which cross-links elastin precursor molecules into mature fibers/matrix. Therefore, we were able to successfully develop a nanoparticle-based system for controlled and sustained HA-o delivery for the in vitro elastogenic induction of aneurysmal rat aortic smooth muscle cells. PMID:23917150

  9. Chemical and structural characterization of interstrand cross-links formed between abasic sites and adenine residues in duplex DNA.

    PubMed

    Price, Nathan E; Catalano, Michael J; Liu, Shuo; Wang, Yinsheng; Gates, Kent S

    2015-04-20

    A new type of interstrand DNA-DNA cross-link between abasic (Ap) sites and 2'-deoxyadenosine (dA) residues was recently reported, but the chemical structure and properties of this lesion were not rigorously established. Here we characterized the nucleoside cross-link remnant released by enzymatic digestion of duplex DNA containing the dA-Ap cross-link. A synthetic standard was prepared for the putative nucleoside cross-link remnant 6 in which the anomeric carbon of the 2-deoxyribose residue was connected to the exocyclic N(6)-amino group of dA. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis showed that the synthetic material 6: matched the authentic cross-link remnant released by enzymatic digestion of cross-linked DNA. These findings establish the chemical structure of the dA-Ap cross-link released from duplex DNA and may provide methods for the detection of this lesion in cellular DNA. Both the nucleoside cross-link remnant 6: and the cross-link in duplex DNA were quite stable at pH 7 and 37°C, suggesting that the dA-Ap cross-link could be a persistent lesion with the potential to block the action of various DNA processing enzymes. PMID:25779045

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

    NASA Astrophysics Data System (ADS)

    ?en, M.; Yakar, A.

    2005-06-01

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

  11. Structure and dynamics of cross-linked actin networks Oliver Lieleg,a

    E-print Network

    Bausch, Andreas

    Structure and dynamics of cross-linked actin networks Oliver Lieleg,a Mireille M. A. E. Claessensb and dynamics of the resulting networks. This review focuses on the structural polymorphism that can be induced Article on the web 22nd October 2009 DOI: 10.1039/b912163n The actin cytoskeleton, a network of protein

  12. Experimental scleral cross-linking increases glaucoma damage in a mouse model.

    PubMed

    Kimball, Elizabeth C; Nguyen, Cathy; Steinhart, Matthew R; Nguyen, Thao D; Pease, Mary E; Oglesby, Ericka N; Oveson, Brian C; Quigley, Harry A

    2014-11-01

    The purpose of this study was to assess the effect of a scleral cross-linking agent on susceptibility to glaucoma damage in a mouse model.CD1 mice underwent 3 subconjunctival injections of 0.5 M glyceraldehyde (GA) in 1 week, then had elevated intraocular pressure (IOP) induced by bead injection. Degree of cross-linking was measured by enzyme-linked immunosorbent assay (ELISA), scleral permeability was measured by fluorescence recovery after photobleaching (FRAP), and the mechanical effects of GA exposure were measured by inflation testing. Control mice had buffer injection or no injection in 2 separate glaucoma experiments. IOP was monitored by Tonolab and retinal ganglion cell (RGC) loss was measured by histological axon counting. To rule out undesirable effects of GA, we performed electroretinography and detailed histology of the retina. GA exposure had no detectable effects on RGC number, retinal structure or function either histologically or electrophysiologically. GA increased cross-linking of sclera by 37% in an ELISA assay, decreased scleral permeability (FRAP, p = 0.001), and produced a steeper pressure-strain behavior by in vitro inflation testing. In two experimental glaucoma experiments, GA-treated eyes had greater RGC axon loss from elevated IOP than either buffer-injected or control eyes, controlling for level of IOP exposure over time (p = 0.01, and 0.049, multivariable regression analyses). This is the first report that experimental alteration of the sclera, by cross-linking, increases susceptibility to RGC damage in mice. PMID:25285424

  13. Rheological Monitoring of Polyacrylamide Gelation: Importance of Cross-Link Density and Temperature

    E-print Network

    Rheological Monitoring of Polyacrylamide Gelation: Importance of Cross-Link Density and Temperature modulus G and viscous modulus G are measured in real time during the gelation which takes place directly such as elasticity. Kinetics of in situ gelation and resulting rheological properties of different speci

  14. Hierarchically porous polymers from hyper-cross-linked block polymer precursors.

    PubMed

    Seo, Myungeun; Kim, Soobin; Oh, Jaehoon; Kim, Sun-Jung; Hillmyer, Marc A

    2015-01-21

    We report synthesis of hierarchically porous polymers (HPPs) consisting of micropores and well-defined 3D continuous mesopores by combination of hyper-cross-linking and block polymer self-assembly. Copolymerization of 4-vinylbenzyl chloride (VBzCl) with divinylbenzene (DVB) in the presence of polylactide (PLA) macro-chain-transfer agent produced a cross-linked block polymer precursor PLA-b-P(VBzCl-co-DVB) via reversible addition-fragmentation chain transfer polymerization. A nanoscopic bicontinuous morphology containing PLA and P(VBzCl-co-DVB) microdomains was obtained as a result of polymerization-induced microphase separation. While a basic treatment of the precursor selectively removed PLA to yield a reticulated mesoporous polymer, hyper-cross-linking of the precursor by FeCl3 generated micropores in the P(VBzCl-co-DVB) microdomain via Friedel-Crafts alkylation and simultaneously degraded PLA to produce the HPP containing micropores in the mesoporous framework. The mesopore size of the HPP could be precisely controlled from 6 to 15 nm by controlling the molar mass of PLA. We demonstrate acceleration in adsorption rate in the HPP compared to a hyper-cross-linked microporous polymer. PMID:25551291

  15. Molecular origin of strain softening in cross-linked F-actin networks Hyungsuk Lee,1

    E-print Network

    Lang, Matthew

    Molecular origin of strain softening in cross-linked F-actin networks Hyungsuk Lee,1 Jorge M by oscillating an embedded microbead. Second, a microbead is translated at constant rate and transitions provide further evidence that strain softening of F-actin networks is caused by force-induced rupture

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

    Technology Transfer Automated Retrieval System (TEKTRAN)

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

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

    E-print Network

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

    2005-02-02

    . To further determine the contribution of transglutaminase in the formation of NFTs, we compared the levels of cross-linked tau protein from P301L tau transgenic mice that develop NFTs to four-repeat wild-type (4RWT) tau transgenic and nontransgenic mice...

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

    Microsoft Academic Search

    Lokman Sboui; Zouheir Rezki; Mohamed-Slim Alouini

    2011-01-01

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

  19. Energy dissipation and recovery in a simple model with reversible cross-links.

    PubMed

    Nabavi, S Soran; Fratzl, Peter; Hartmann, Markus A

    2015-03-01

    Reversible cross-linking is a method of enhancing the mechanical properties of polymeric materials. The inspiration for this kind of cross-linking comes from nature, which uses this strategy in a large variety of biological materials to dramatically increase their toughness. Recently, first attempts were made to transfer this principle to technological applications. In this study, Monte Carlo simulations are used to investigate the effect of the number and the topology of reversible cross-links on the mechanical performance of a simple model system. Computational cyclic loading tests are performed, and the work to fracture and the energy dissipation per cycle are determined, which both increase when the density of cross-links is increased. Furthermore, a different topology of the bonds may increase the work to fracture by a factor of more than 2 for the same density. This dependence of the mechanical properties on the topology of the bonds has important implications on the self-healing properties of such systems, because only a fast return of the system to its unloaded state after release of the load ensures that the optimal topology may form. PMID:25871137

  20. Can para-aryl-dithiols cross-link two plasmonic noble nanoparticles as monolayer dithiolate spacers

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Para-aryl-dithiols (PADTs, HS-(C6H4)n-SH, n = 1, 2, and 3) have been used extensively in molecular electronics, surface-enhanced Raman spectroscopy (SERS), and quantum electron tunneling between two gold or silver nanoparticles (AuNPs and AgNPs). One popular belief is that these dithiols cross-link ...

  1. Cross-Linked Nanoporous Materials from Reactive and Multifunctional Block Polymers

    SciTech Connect

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

    2012-10-10

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

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

    PubMed Central

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

    2011-01-01

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

  3. Tissue Transglutaminase, Protein Cross-linking and Alzheimer's Disease: Review and Views

    PubMed Central

    Wang, Deng-Shun; Dickson, Dennis W; Malter, James S

    2008-01-01

    Extensive protein cross-linking and aggregation are some of the most common molecular events in the pathogenesis of Alzheimer's disease (AD). Both ?-amyloid (A?) plaques and neurofibrillary tangles, which are extracellular and intracellular proteinaceous aggregates, respectively, contribute to neuronal death and progressive cognitive decline. Although protein cross-linking has been recognized and extensively studied for many years, the underlying mechanisms are largely unknown. Recent data indicates that tissue transglutaminase (tTG), which catalyzes the cross-linking of a wide spectrum of proteins including A?, tau, ?-synuclein and neurofilament proteins, may be involved in protein aggregation in AD. Many AD risk factors, such as trauma, inflammation, ischemia and stress, up-regulate tTG protein and activity levels. In this review, we summarize the evidence that tTG plays a role in AD, especially in cross-linking of A?, tau, ?-synuclein and neurofilament proteins. An experimentally testable hypothesis is that tTG may play a central role in AD pathogenesis and that it provides a conceptual link between sporadic and familial AD through a shared pathogenic pathway. PMID:18784819

  4. Influence of different chemical cross-linking treatments on the properties of bovine pericardium and collagen

    Microsoft Academic Search

    E Jorge-Herrero; P Fernández; J Turnay; N Olmo; P Calero; R Garc??a; I Freile; J. L Castillo-Olivares

    1999-01-01

    The use of biological materials in the construction of bioprostheses requires the application of different chemical or physical procedures to improve the mechanical performance of the material without producing any undesirable effects. A number of cross-linking methods have been tested in biological tissues composed mainly of collagen. The basis for most of them is the use of glutaraldehyde (GA), which

  5. Endogenous and enhanced oxidative cross-linking in wheat flour mill streams

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The oxidative cross-linking of arabinoxylan and protein polymers is partially responsible for variation in end-use quality of wheat flour; specifically, differences in batter viscosity as well as variation in bread and cookie quality. A better understanding of the variation in oxidative cross-linkin...

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

    E-print Network

    Chesler, Naomi C.

    Role of collagen content and cross-linking in large pulmonary arterial stiffening after chronic (PA) stiffening, which is correlated with collagen accumulation. However, the mechanisms by which collagen contributes to PA stiffening remain largely unexplored. Moreover, HPH may alter mechanical

  7. Effect of different cross-linking methods and processing parameters on drug release from hydrogel beads.

    PubMed

    Mitra, Shataneek; Maity, Siddhartha; Sa, Biswanath

    2015-03-01

    The purpose of this work was to evaluate different methods of cross-linking for developing diltiazem-resin complex loaded carboxymethyl xanthan gum (CMXG) hydrogel beads to achieve highest possible drug entrapment and extended release for effective cardio-protection. The hydrogel beads were prepared by ionic cross-linking and dual cross-linking using simultaneous (SIM) and sequential (SEQ) methods. Among the three methods, SEQ method produced smaller sized beads having higher drug entrapment efficacy and prolonged release characteristics as evidenced from mean dissolution time and diffusion coefficient of drug. Keeping the concentration of ionic cross-linker constant, increase in the amount of covalent cross-linker and cross-linking time decreased the drug release. Higher release of the drug in acid solution was attributed to the higher solubility of the basic drug and higher swelling of the matrices in acid solution. Comparison of FTIR spectra, drug content and dissolution profiles indicated that the drug was stable in the beads when kept under stress condition up to 3 months. In conclusion, the sequential method was found superior for producing CMXG hydrogel beads as a prolonged release delivery device in cardiovascular diseases. PMID:25576745

  8. HEMOSTASIS, THROMBOSIS, AND VASCULAR BIOLOGY Enhancement of thrombogenesis by plasma fibronectin cross-linked

    E-print Network

    Mosher, Deane F.

    cross-linked to fibrin and assembled in platelet thrombi Jaehyung Cho and Deane F. Mosher To learn how plasma fibronectin stabi- lizes platelet-rich thrombi in injured mes- enteric arterioles of mice, we studied the impact of plasma fibronectin on platelet thrombus formation ex vivo in a parallel flow chamber

  9. Highly Cross-Linked Ultrahigh Molecular Weight Polyethylene With Improved Fatigue Resistance for Total Joint Arthroplasty

    Microsoft Academic Search

    Ebru Oral; Arnaz S. Malhi; Keith K. Wannomae; Orhun K. Muratoglu

    2008-01-01

    Eliminating postirradiation melting and stabilizing the residual free radicals of radiation cross-linked ultrahigh molecular weight polyethylene (UHMWPE) with vitamin E resulted in improved fatigue crack propagation resistance without compromising wear resistance. We designed a cantilever postbending test to determine the bending fatigue resistance of ?-tocopherol–doped, irradiated UHMWPE (?-TPE) in comparison to conventional UHMWPE. The bending fatigue behavior of ?-TPE was

  10. Reinforcement Mechanisms in Polymer Nanotube Composites: Simulated Non-Bonded and Cross-Linked Systems

    E-print Network

    Bebendorf, Mario

    . The results indicate that the cross-linked system has an enhanced shear yield strength of one to two orders analyzed. In the second set of simulations, a critical shear yield strength was calculated using a simulated "pull-through" experiment. The shear yield strength was in turn used to estimate how long the load

  11. Interstrand cross-linking reaction in triplexes containing a monofunctional transplatin-adduct.

    PubMed Central

    Colombier, C; Lippert, B; Leng, M

    1996-01-01

    Our aim was to determine whether a single transplatin monofunctional adduct, either trans-[Pt(NH3)2(dC)Cl]+ or trans-[Pt(NH3)2(dG)Cl]+ within a homopyrimidine oligonucleotide, could further react and form an interstrand cross-link once the platinated oligonucleotide was bound to the complementary duplex. The single monofunctional adduct was located at either the 5' end or in the middle of the platinated oligonucleotide. In all the triplexes, specific interstrand cross-links were formed between the platinated Hoogsteen strand and the complementary purine-rich strand. No interstrand cross-links were detected between the platinated oligonucleotides and non-complementary DNA. The yield and the rate of the cross-linking reaction depend upon the nature and location of the monofunctional adducts. Half-lives of the monofunctional adducts within the triplexes were in the range 2-6 h. The potential use of the platinated oligonucleotides to modulate gene expression is discussed. PMID:8948644

  12. T-lymphocytes mediate left ventricular fibrillar collagen cross-linking and diastolic dysfunction in mice.

    PubMed

    Yu, Qianli; Vazquez, Randy; Zabadi, Sherma; Watson, Ronald R; Larson, Douglas F

    2010-07-01

    Aberrant concentrations of cardiac extracellular matrix (ECM) fibrillar collagen cross-linking have been proposed to be an underlying cause of cardiac diastolic dysfunction however the role of the adaptive immune system in this process has yet to be investigated. Fibrillar collagen cross-linking is a product of the enzymatic activities of lysyl oxidase (LOX and LOXL-3) released by the cardiac fibroblast and possibly cardiac myocytes. Our hypothesis is that stimulation of the TH1 lymphocytes activates lysyl oxidase mediated ECM cross-linking and thereby alters left ventricular function. Three-month old C57BL/J female mice were treated with selective TH1 lymphocyte inducers - T-cell receptor V? peptides (TCR). After 6 weeks, candidate gene expression, tissue enzymatic activity, ECM composition, and left ventricular mechanics were quantified. Lymphocyte gene expression and cytokine assay revealed TH1 immune polarization with TCR administration which was associated with a 2.6-fold and 3.1-fold increase of LOX and LOXL3 gene expression, respectively, and a 55% increase in cardiac LOX enzymatic activity. The ECM cross-linked fibrillar collagen increased by 95% when compared with the control. Concurrently, there was a 33% increased ventricular stiffness, decreased cardiac output, and normal ejection fraction. These data implicate the TH1 lymphocyte in the pathogenesis of diastolic dysfunction which has potential clinical application in the pathogenesis of diastolic heart failure. PMID:20600894

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

    PubMed

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

    2013-07-23

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

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

    PubMed Central

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

    2013-01-01

    This study describes a case of nodular epithelial hyperplasia and stromal alterations in a patient with keratoconus who was submitted to topography-guided photorefractive keratectomy (PRK) followed by corneal collagen cross-linking. Debridement of the epithelial nodule was performed. After a 2-year followup, a new topography-guided PRK was indicated. PMID:23691390

  15. Effect of the cross-linking density on the thermoresponsive behavior of hollow PNIPAM microgels.

    PubMed

    Contreras-Cáceres, Rafael; Schellkopf, Leonard; Fernández-López, Cristina; Pastoriza-Santos, Isabel; Pérez-Juste, Jorge; Stamm, Manfred

    2015-01-27

    We report on the fabrication of thermally responsive hollow pNIPAM particles through the oxidation of the metal core in an Au@pNIPAM system. The selective oxidation of the Au core is achieved by addition of AuCl4(-) to an aqueous dispersion of Au@pNIPAM particles in the presence of cetyltrimethylammonium bromide (CTAB). We fabricate hollow pNIPAM particles with three cross-linking densities (N,N'-methylenebis(acrylamide), BA, at 5%, 10%, and 17.5%). The study of the effect of the amount of BA within the microgel network was performed by dynamic light scattering (DLS), transmission electron microscopy (TEM), and atomic force microscopy (AFM), showing its key role in determining the final hollow structure and thermal response. While the thermal responsiveness is largely achieved at low cross-linking densities, the hollow structure only remains at larger cross-linking densities. This was further confirmed by cryo-TEM analysis of hollow pNIPAM particles below and above the volume phase transition temperature (VPTT). Thus, it clearly shows (i) the shrinking of particle size with the temperature at low cross-linking density and (ii) the dependence of particle size on the amount of cross-linker for the final hollow pNIPAM structure. Observed differences in the hollow pNIPAM structure are attributed to different elastic contributions (?(elas)), showing higher elasticity for microgels synthesized at lower amount of BA. PMID:25526382

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

    NASA Astrophysics Data System (ADS)

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

    2009-07-01

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

  17. A cross-linked positive resist derived from poly (methacrylonitrileco-Methacrylic acid)

    SciTech Connect

    Suzuki, M.; Furuta, A.; Ohnishi, Y.

    1985-06-01

    Cross-linked positive resists derived from copolymers of methacrylonitrile (MCN) and methacrylic acid (MAA) have been developed based on the theoretical formula which shows that a large M /sub w/ X G /sub s/ value is essential to improve the cross-linked positive resist sensitivity, where M /sub w/ is the weight-average molecular weight and G /sub s/ is the main chain scission efficiency. The cross-linked positive resist consists of P(MCN/sub 92//sup -/MAA/sub 8/) with a viscosity-average molecular weight (M /sub v/ ) of 5.7 x 10/sup 5/ and tripropylene glycol diglycidyl ether (TPG) as a cross-linking agent. It has high sensitivity (3..mu..C/cm/sup 2/) and high dry-etch resistance, reflecting the large M /sub w/ X G /sub s/ value of the copolymer and the high dry-etch resistance of the MCN component. The resist is applied to a trilayer resist system as the top imaging layer. Submicron fine patterns delineated at 3.4 ..mu..C/cm/sup 2/ are transferred to the thick organic layer, and high aspect ratio patterns are obtained.

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

    PubMed

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

    2011-12-01

    Carbon nanotube (CNT) sheets or buckypapers have demonstrated promising electrical conductivity and mechanical performance. However, their electrical conductivity is still far below the requirements for engineering applications, such as using as a substitute for copper mesh, which is currently used in composite aircraft structures for lightning strike protection. In this study, different CNT buckypapers were stretched to increase their alignment, and then subjected to conjugational cross-linking via chemical functionalization. The conjugationally cross-linked buckypapers (CCL-BPs) demonstrated higher electrical conductivity of up to 6200 S cm( - 1), which is more than one order increase compared to the pristine buckypapers. The CCL-BPs also showed excellent doping stability in over 300 h in atmosphere and were resistant to degradation at elevated temperatures. The tensile strength of the stretched CCL-BPs reached 220 MPa, which is about three times that of pristine buckypapers. We attribute these property improvements to the effective and stable conjugational cross-links of CNTs, which can simultaneously improve the electrical conductivity, doping stability and mechanical properties. Specifically, the electrical conductivity increase resulted from improving the CNT alignment and inter-tube electron transport capability. The conjugational cross-links provide effective 3D conductive paths to increase the mobility of electrons among individual nanotubes. The stable covalent bonding also enhances the thermal stability and load transfer. The significant electrical and mechanical property improvement renders buckypaper a multifunctional material for various applications, such as conducting composites, battery electrodes, capacitors, etc. PMID:22072011

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

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

  20. Light-scattering thermal cross-linking material using morphology of nanoparticle free polymer blends

    NASA Astrophysics Data System (ADS)

    Takei, Satoshi

    2015-03-01

    A newly light-scattering thermal cross-linking material based on self-assembly for forming the morphology of nanoparticle free polymer blends was reported. The material design concept to use light-scattering thermal cross-linking material with high uniformity of light on display panel from LED for high quality such as brightness and evenness, mechanical properties, and gas and water barrier properties. The high light scattering rate of 8 % at 350-450 nm of wavelength, fast cure film at 140 ºC and 120 s, and thermal stability at 190 ºC in bake condition for high productivity were indicated in the light-scattering thermal cross-linking material using the nanoparticle free polymers with carboxylic acid functional groups. These novel system using morphology of nanoparticle free polymer blends in light-scattering package material for a LCD using LED was a valuable approach to the design of material formulations for newly light-scattering thermal cross-linking material.

  1. Chemical Probes Reveal an Extraseptal Mode of Cross-Linking in Staphylococcus aureus.

    PubMed

    Gautam, Samir; Kim, Taehan; Spiegel, David A

    2015-06-17

    Staphylococcus aureus is an important human pathogen and a model organism for studying cell wall synthesis in Gram-positive cocci. The prevailing model of cell wall biogenesis in cocci holds that peptidoglycan synthesis (i.e., transglycosylation and cross-linking) is restricted spatially to the septal cross-wall and temporally to cell division. Previously, we developed a method for visualizing cross-linking in S. aureus using fluorescently tagged mimics of the endogenous substrate of penicillin-binding proteins (PBPs). These probes are incorporated into the cell wall of S. aureus specifically by PBP4, allowing localization of the enzyme's cross-linking activity in vivo with precise spatial and temporal resolution. Here, using this methodology, we have discovered that PBP4 is active not only at the septum, but unexpectedly at the peripheral wall as well. These results challenge the long-held belief that peptidoglycan synthesis is restricted to the septum in spherical bacteria, and instead indicate the presence of two spatiotemporally distinct modes of cross-linking in S. aureus: one at the septum during cell division, and another at the peripheral wall between divisions. PMID:26035224

  2. Monitoring the internal structure of poly(N-vinylcaprolactam) microgels with variable cross-link concentration.

    PubMed

    Schneider, Florian; Balaceanu, Andreea; Feoktystov, Artem; Pipich, Vitaliy; Wu, Yaodong; Allgaier, Jürgen; Pyckhout-Hintzen, Wim; Pich, Andrij; Schneider, Gerald J

    2014-12-23

    The combination of a set of complementary techniques allows us to construct an unprecedented and comprehensive picture of the internal structure, temperature dependent swelling behavior, and the dependence of these properties on the cross-linker concentration of microgel particles based on N-vinylcaprolactam (VCL). The microgels were synthesized by precipitation polymerization using different amounts of cross-linking agent. Characterization was performed by small-angle neutron scattering (SANS) using two complementary neutron instruments to cover a uniquely broad Q-range with one probe. Additionally we used dynamic light scattering (DLS), atomic force microscopy (AFM), and differential scanning calorimetry (DSC). Previously obtained nuclear magnetic resonance spectroscopy (NMR) results on the same PVCL particles are utilized to round the picture off. Our study shows that both the particle radius and the cross-link density and therefore also the stiffness of the microgels rises with increasing cross-linker content. Hence, more cross-linker reduces the swelling capability distinctly. These findings are supported by SANS and AFM measurements. Independent DLS experiments also found the increase in particle size but suggest an unchanged cross-link density. The reason for the apparent contradiction is the indirect extraction of the parameters via a model in the evaluation of DLS measurements. The more direct approach in AFM by evaluating the cross section profiles of observed microgel particles gives evidence of significantly softer and more deformable particles at lower cross-linker concentrations and therefore verifies the change in cross-link density. DSC data indicate a minor but unexpected shift of the volume phase transition temperature (VPTT) to higher temperatures and exposes a more heterogeneous internal structure of the microgels with increasing cross-link density. Moreover, a change in the total energy transfer during the VPT gives evidence that the strength of hydrogen bonds is significantly affected by the cross-link density. A strong and reproducible deviation of the material density of the cross-linked microgel polymer chains toward a higher value compared to the respective linear chains has yet to be explained. PMID:25493607

  3. The Dynamic Metabolism of Hyaluronan Regulates the Cytosolic Concentration of UDP-GlcNAc

    PubMed Central

    Hascall, Vincent C.; Wang, Aimin; Tammi, Markku; Oikari, Sanna; Tammi, Raija; Passi, Alberto; Vigetti, Davide; Hanson, Richard W.; Hart, Gerald W.

    2014-01-01

    Hyaluronan, a macromolecular glycosaminoglycan, is normally synthesized by hyaluronan synthases at the plasma membrane using cytosolic UDP-GlcUA and UDP-GlcNAc substrates and extruding the elongating chain into the extracellular space. The cellular metabolism (synthesis and catabolism) of hyaluronan is dynamic. UDP-GlcNAc is also the substrate for O-GlcNAc transferase, which is central to control of many cytosolic pathways. This Perspective outlines recent data for regulation of hyaluronan synthesis and catabolism that support a model that hyaluronan metabolism can be a rheostat for controlling an acceptable normal range of cytosolic UDP-GlcNAc concentrations in order to maintain normal cell functions. PMID:24486448

  4. Triglycidylamine Cross-linking Combined with Ethanol Inhibits Bioprosthetic Heart Valve Calcification

    PubMed Central

    Connolly, Jeanne M.; Bakay, Marina A.; Alferiev, Ivan S.; Gorman, Robert C.; Gorman, Joseph H.; Kruth, Howard S.; Ashworth, Paul E.; Kutty, Jaishankar K.; Schoen, Frederick J.; Bianco, Richard W.; Levy, Robert J.

    2012-01-01

    Background One of the most important factors responsible for the calcific failure of bioprosthetic heart valves is glutaraldehyde cross-linking. Ethanol (EtOH) incubation after glutaraldehyde cross-linking has previously been reported to confer anti-calcification efficacy for bioprostheses. The present studies investigated the anticalcification efficacy in vivo of the novel cross-linking agent, triglycidyl amine (TGA), with or without EtOH incubation, in comparison to glutaraldehyde. Methods TGA cross-linking (+/? EtOH) was used to prepare porcine aortic valves for both rat subdermal implants and sheep mitral valve replacements, for comparisons with glutaraldehyde-fixed controls. Thermal denaturation temperature (Ts), an index of cross-linking, cholesterol extraction, and hydrodynamic properties were quantified. Explant endpoints included quantitative and morphologic assessment of calcification. Results Ts after TGA were intermediate between unfixed and glutaraldehyde-fixed. EtOH incubation resulted in almost complete extraction of cholesterol from TGA or glutaraldehyde-fixed cusps. Rat subdermal explants (90days) demonstrated that TGA-EtOH resulted in a significantly greater level of inhibition of calcification than other conditions. Thus, TGA-ethanol stent mounted porcine aortic valve bioprostheses were fabricated for comparisons with glutaraldehyde-pretreated controls. In hydrodynamic studies, TGA-EtOH bioprostheses had lower pressure gradients than glutaraldehyde-fixed. TGA-ethanol bioprostheses used as mitral valve replacements in juvenile sheep (150 days) demonstrated significantly lower calcium levels in both explanted porcine aortic cusp and aortic wall samples compared to glutaraldehyde-fixed controls. However, TGA-EtOH sheep explants also demonstrated isolated calcific nodules and intracuspal hematomas. Conclusions TGA-EtOH pretreatment of porcine aortic valves confers significant calcification resistance in both rat subdermal and sheep circulatory implants, but with associated structural instability. PMID:21871270

  5. Collagen cross-linking treatment effects on corneal dynamic biomechanical properties.

    PubMed

    Hatami-Marbini, Hamed; Rahimi, Abdolrasol

    2015-06-01

    Cornea is a soft tissue with the principal function of transmitting and refracting light rays. The objective of the current study was to characterize possible effects of the riboflavin/UVA collagen cross-linking on corneal dynamic properties. The original corneal cross-linking protocol was used to induce cross-links in the anterior portion of the bovine cornea. A DMA machine was used to conduct mechanical tensile experiments at different levels of tensile strains. The samples were divided into a control group (n = 5) and a treated group (n = 5). All specimens were first stretched to a strain of 5% and allowed to relax for twenty minutes. After completion of the stress-relaxation experiment, a frequency sweep test with oscillations ranging from 0.01 to 10 Hz was performed. The same procedure was repeated to obtain the stress-relaxation and dynamic properties at 10% strain. It was observed that the collagen cross-linking therapy significantly increased the immediate and equilibrium tensile behavior of the bovine cornea (P < 0.05). Furthermore, for all samples in control and treated groups and throughout the whole range of frequencies, a significantly larger tensile storage modulus was measured at an axial strain of 10% compared to what was obtained at a tensile strain of 5%. Finally, it was noted that although this treatment procedure resulted in a significant increase in the storage and loss modulus at any axial strain and frequency (P < 0.05), it significantly reduced the ratio of the dissipated and stored energy during a single cycle of deformation. Therefore, it was concluded that while the riboflavin/UVA collagen cross-linking increased significantly corneal stiffness, it decreased significantly its damping capability and deformability. This reduced damping ability might adversely interfere with corneal mechanical performance. PMID:25887295

  6. Acoustic Radiation Force for Noninvasive Evaluation of Corneal Biomechanical Changes Induced by Cross-linking Therapy

    PubMed Central

    Urs, Raksha; Lloyd, Harriet O.; Silverman, Ronald H.

    2015-01-01

    Objectives To noninvasively measure changes in corneal biomechanical properties induced by ultraviolet-activated riboflavin cross-linking therapy using acoustic radiation force (ARF). Methods Cross-linking was performed on the right eyes of 6 rabbits, with the left eyes serving as controls. Acoustic radiation force was used to assess corneal stiffness before treatment and weekly for 4 weeks after treatment. Acoustic power levels were within US Food and Drug Administration guidelines for ophthalmic safety. Strain, determined from ARF-induced displacement of the front and back surfaces of the cornea, was fit to the Kelvin-Voigt model to determine the elastic modulus (E) and coefficient of viscosity (?). The stiffness factor, the ratio of E after treatment to E before treatment, was calculated for treated and control eyes. At the end of 4 weeks, ex vivo thermal shrinkage temperature analysis was performed for comparison with in vivo stiffness measurements. One-way analysis of variance and Student t tests were performed to test for differences in E, ?, the stiffness factor, and corneal thickness. Results Biomechanical stiffening was immediately evident in cross-linking–treated corneas. At 4 weeks after treatment, treated corneas were 1.3 times stiffer and showed significant changes in E(P= .006) and ? (P= .007), with no significant effect in controls. Corneal thickness increased immediately after treatment but did not differ significantly from the pretreatment value at 4 weeks. Conclusions Our findings demonstrate a statistically significant increase in stiffness in cross-linking–treated rabbit corneas based on in vivo axial stress/strain measurements obtained using ARF. The capacity to noninvasively monitor corneal stiffness offers the potential for clinical monitoring of cross-linking therapy. PMID:25063407

  7. The effects of high dose irradiation on the cross-linking of vitamin E-blended ultrahigh molecular weight polyethylene

    Microsoft Academic Search

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

    2008-01-01

    Vitamin E-stabilized, highly cross-linked ultrahigh molecular weight polyethylene (UHMWPE) is a promising oxidation and wear resistant UHMWPE with improved mechanical strength in comparison with the first generation, irradiated and melted UHMWPE. One approach of incorporating vitamin E in UHMWPE is through blending of vitamin E in UHMWPE powder followed by consolidation and radiation cross-linking. However, radiation cross-linking efficiency of UHMWPE

  8. Identification of the receptor for erythropoietin by cross-linking to Friend virus-infected erythroid cells

    SciTech Connect

    Sawyer, S.T.; Krantz, S.B.; Luna, J.

    1987-06-01

    Erythropoietin (Epo) is a glycoprotein hormone that regulates erythroid development and interacts with surface receptors on developing erythroid cells. In this laboratory, a cell system with a relatively pure population of erythroid cells that respond to Epo has been developed. Immature erythroid cells are obtained from the spleens of mice infected with the anemia strain of Friend virus. The binding of /sup 125/I-labeled Epo (/sup 125/-Epo) to plasma membranes from these cells was studied in this investigation. /sup 125/I-Epo binding reached equilibrium within 20 min at 37/sup 0/C. Twenty percent of the receptors bound /sup 125/I-Epo with a K/sub d/ of 0.08 x 10/sup -9/ M, while the remaining receptors bound the hormone with a k/sub d/ of 0.6 x 10/sup -9/ M. In this study, a receptor for Epo was identified by cross-linking /sup 125/I-Epo to the receptor in intact cells and plasma membrane preparations using disuccinimidyl suberate. Polyacrylamide gel electrophoresis revealed two labeled bands of 100 and 85 kDa. The 85-kDa band was more heavily labeled (65%) than the 100-kDa band. Both bands were equally decreased when increasing amounts of unlabeled Epo were included in the binding mixture, indicating a specific interaction of /sup 175/I-Epo with the receptor.

  9. Suppression of cell proliferation, DNA protein cross-links, and induction of apoptosis by vanadium in chemical rat mammary carcinogenesis.

    PubMed

    Sankar Ray, Rajarshi; Roy, Souvik; Ghosh, Shilpi; Kumar, Manisenthil; Chatterjee, Malay

    2004-11-18

    Vanadium, a dietary micronutrient, has recently been considered as an important pharmacological agent. The present investigation was carried out to ascertain its anticarcinogenic potential against an experimental rat mammary carcinogenesis. Female Sprague-Dawley rats were treated with 7,12dimethylbenz(alpha)anthracene (DMBA) (0.5 mg/100 g body weight) by a single tail vein injection in an oil emulsion. Vanadium (ammonium monovanadate) at a concentration of 0.5 ppm (4.27 micromol/L) was supplemented in drinking water and given ad libitum to the experimental group. The present study was an attempt to assess the effect of vanadium (ammonium monovanadate) on cell proliferation, apoptosis and histopathology in the mammary tissue. We also have examined DNA fragmentation and DNA protein cross-links (DPC) in the liver of rats as well. Immunohistochemical analysis indicated that early neoplasia in mammary tissue proceeds by a decrease in apoptotic cell death (ACD), which was also examined with TUNEL assay, rather than an increase in cell proliferation (P<0.01). DPC in liver were reduced by vanadium treatment (ANOVA, F=13.7, P<0.01). Agarose gel electrophoresis revealed DNA fragmentation in the vanadium-treated group, confirming apoptosis further. Results of the study indicate that the mammary preneoplasia is sensitive to vanadium intervention whereas normal proliferating cells are not. PMID:15535980

  10. Immobilization of Quantum Dots in the Photo-Cross-Linked Poly(ethylene glycol)-Based Hydrogel

    SciTech Connect

    Gattas-Asfura, Kerim M.(Miami University) [Miami University; Zheng, Yujun (Miami University) [Miami University; Micic, Miodrag (BATTELLE (PACIFIC NW LAB)) [BATTELLE (PACIFIC NW LAB); Snedaker, Michael J.(Miami University) [Miami University; Ji, Xiaojun (Miami University) [Miami University; Sui, Guodong (Miami University) [Miami University; Orbulescu, Jhony (Miami University) [Miami University; Andreopoulos, Fotios M.(Miami University) [Miami University; Pham, Si M.(Miami University) [Miami University; Wang, Chong M.(BATTELLE (PACIFIC NW LAB)) [BATTELLE (PACIFIC NW LAB)

    2003-09-25

    An inorganic/organic composite hybrid nano-system has been successfully synthesized in which nanocrystalline quantum dots (QDs) were effectively immobilized within a photo-cross-linked poly(ethylene glycol) hydrogel. Organometallic synthesis of CdTe and CdSe QDs was accomplished with a trioctylphosphine oxide (TOPO) cap. Replacing the TOPO cap with mercaptoacetic acid groups further yielded modified water-soluble nanocrystals. The immobilization of these functionalized CdTe and CdSe QDs within PEG hydrogel network has been shown to be effective through utilization of physical trapping. The CdTe and CdSe QDs had a particle diameter of 4.5 and 2.5-6.0 nm, respectively. The most efficiently trapped QDs had a size of 4.5 nm or larger. Particle size determination was derived from spectroscopic (absorption and photoluminescence) and high-resolution transmission electron microscopic techniques. These QD-immobilized gel systems demonstrated photoluminescence characteristics unique to semiconductor QD nanocrystals. The authors have envisioned the utilization of the unique photophysical properties of this material as a convenient signal transducer for in vivo biosensing. The most promising application of the described QD/PEG-NC hybrid system is in the fields of in vivo fluorescence microscopy and as a monitoring system for drug delivery and wound healing.

  11. Bone fracture toughness and strength correlate with collagen cross-link maturity in a dose-controlled lathyrism mouse model.

    PubMed

    McNerny, Erin M B; Gong, Bo; Morris, Michael D; Kohn, David H

    2015-03-01

    Collagen cross-linking is altered in many diseases of bone, and enzymatic collagen cross-links are important to bone quality, as evidenced by losses of strength after lysyl oxidase inhibition (lathyrism). We hypothesized that cross-links also contribute directly to bone fracture toughness. A mouse model of lathyrism using subcutaneous injection of up to 500?mg/kg ?-aminopropionitrile (BAPN) was developed and characterized (60 animals across 4 dosage groups). Three weeks of 150 or 350?mg/kg BAPN treatment in young, growing mice significantly reduced cortical bone fracture toughness, strength, and pyridinoline cross-link content. Ratios reflecting relative cross-link maturity were positive regressors of fracture toughness (HP/[DHLNL?+?HLNL] r(2) ?=?0.208, p?cross-links were significant positive regressors of tissue strength (lysyl pyridinoline r(2) ?=?0.159, p?=?0.014; hydroxylysyl pyridinoline r(2) ?=?0.112, p?cross-links, which were not significantly reduced by BAPN, did not correlate with mechanical properties. The effect of BAPN treatment on mechanical properties was dose specific, with the greatest impact found at the intermediate (350?mg/kg) dose. Calcein labeling was used to define locations of new bone formation, allowing for the identification of regions of normally cross-linked (preexisting) and BAPN-treated (newly formed, cross-link-deficient) bone. Raman spectroscopy revealed spatial differences attributable to relative tissue age and effects of cross-link inhibition. Newly deposited tissues had lower mineral/matrix, carbonate/phosphate, and Amide I cross-link (matrix maturity) ratios compared with preexisting tissues. BAPN treatment did not affect mineral measures but significantly increased the cross-link (matrix maturity) ratio compared with newly formed control tissue. Our study reveals that spatially localized effects of short-term BAPN cross-link inhibition can alter the whole-bone collagen cross-link profile to a measureable degree, and this cross-link profile correlates with bone fracture toughness and strength. Thus, cross-link profile perturbations associated with bone disease may provide insight into bone mechanical quality and fracture risk. PMID:25213475

  12. Rheology of mixed alginate-hyaluronan aqueous solutions.

    PubMed

    Travan, Andrea; Fiorentino, Simona; Grassi, Mario; Borgogna, Massimiliano; Marsich, Eleonora; Paoletti, Sergio; Donati, Ivan

    2015-07-01

    The present manuscript addresses the description of binary systems of hyaluronan (HA) and alginate (Alg) in semi-concentrated solution. The two polysaccharides were completely miscible in the entire range of relative weight fraction explored at a total polymer concentration of up to 3% (w/V). The rheological study encompassed steady flow and mechanical spectra for HA/Alg systems at different weight fractions with hyaluronan at different molecular weights. These extensive analyses allowed us to propose a model for the molecular arrangement in solution that envisages a mutual exclusion between the two polysaccharides even though a clear phase separation does not occur. This result may have profound implications when combinations of alginate and hyaluronan are proposed in the field of biomedical materials. PMID:25910645

  13. The boundary lubrication of chemically grafted and cross-linked hyaluronic acid in phosphate buffered saline and lipid solutions measured by the surface forces apparatus.

    PubMed

    Yu, Jing; Banquy, Xavier; Greene, George W; Lowrey, Daniel D; Israelachvili, Jacob N

    2012-01-31

    High molecular weight hyaluronic acid (HA) is present in articular joints and synovial fluid at high concentrations; yet despite numerous studies, the role of HA in joint lubrication is still not clear. Free HA in solution does not appear to be a good lubricant, being negatively charged and therefore repelled from most biological, including cartilage, surfaces. Recent enzymatic experiments suggested that mechanically or physically (rather than chemically) trapped HA could function as an "adaptive" or "emergency" boundary lubricant to eliminate wear damage in shearing cartilage surfaces. In this work, HA was chemically grafted to a layer of self-assembled amino-propyl-triethoxy-silane (APTES) on mica and then cross-linked. The boundary lubrication behavior of APTES and of chemically grafted and cross-linked HA in both electrolyte and lipid 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) solutions was tested with a surface forces apparatus (SFA). Despite the high coefficient of friction (COF) of ? ? 0.50, the chemically grafted HA gel significantly improved the lubrication behavior of HA, particularly the wear resistance, in comparison to free HA. Adding more DOPC lipid to the solution did not improve the lubrication of the chemically grafted and cross-linked HA layer. Damage of the underlying mica surface became visible at higher loads (pressure >2 MPa) after prolonged sliding times. It has generally been assumed that damage caused by or during sliding, also known as "abrasive friction", which is the main biomedical/clinical/morphological manifestation of arthritis, is due to a high friction force and, therefore, a large COF, and that to prevent surface damage or wear (abrasion) one should therefore aim to reduce the COF, which has been the traditional focus of basic research in biolubrication, particularly in cartilage and joint lubrication. Here we combine our results with previous ones on grafted and cross-linked HA on lipid bilayers, and lubricin-mediated lubrication, and conclude that for cartilage surfaces, a high COF can be associated with good wear protection, while a low COF can have poor wear resistance. Both of these properties depend on how the lubricating molecules are attached to and organized at the surfaces, as well as the structure and mechanical, viscoelastic, elastic, and physical properties of the surfaces, but the two phenomena are not directly or simply related. We also conclude that to provide both the low COF and good wear protection of joints under physiological conditions, some or all of the four major components of joints-HA, lubricin, lipids, and the cartilage fibrils-must act synergistically in ways (physisorbed, chemisorbed, grafted and/or cross-linked) that are still to be determined. PMID:22148857

  14. Aliphatic ?-Nitroalcohols for Therapeutic Corneoscleral Cross-linking: Chemical Mechanisms and Higher Order Nitroalcohols

    PubMed Central

    Solomon, Marissa R.; Wen, Quan; Turro, Nicholas J.; Trokel, Stephen L.

    2010-01-01

    Purpose. The recent tissue cross-linking studies indicate that aliphatic ?-nitroalcohols (BNAs) may be useful as pharmacologic corneoscleral cross-linking agents. The present study was performed to identify the specific chemistry involved under physiologic conditions, with the intent of identifying more effective agents. Methods. The mechanism of chemical cross-linking at pH 7.4 and 37°C was studied using three techniques. The colorimetric Griess assay was used to follow the release of nitrite from three mono-nitroalcohols (2-nitroethanol [2ne], 2-nitro-1-propanol [2nprop]), and 3-nitro-2-pentanol [3n2pent]). Second, the evolution of 2nprop in 0.2 M NaH2PO4/Na2HPO4/D2O was studied using 1H-NMR. Third, thermal shrinkage temperature analysis (Ts), a measure of tissue cross-linking, was used to support information from 1the H-NMR studies. Results. A time-dependent release of nitrite was observed for all three mono-nitroalcohols studied. The maximum levels were comparable using either 2ne or 2nprop (?30%). However, much less (?10%) was observed from 3n2pent. Using 1H-NMR, 2nprop evolved into a unique splitting pattern. No match was observed with reference spectra from three possible products of denitration. In contrast, 2-methyl-2-nitro-1,3-propanediol (MNPD), a nitro-diol, was identified, implying the formation of formaldehyde from a retro-nitroaldol (i.e., reverse Henry) reaction. In support of this mechanism, Ts shifts induced by the nitro-triol 2-hydroxymethyl-2-nitro-1,3-propanediol (HNPD) were superior to the nitro-diol MNPD which were superior to the mono nitroalcohol 2nprop. Conclusions. BNAs function as both formaldehyde and nitrite donors under physiologic conditions to cross-link collagenous tissue. Higher order BNAs are more effective than mono nitroalcohols, raising the possibility of using these agents for therapeutic corneoscleral cross-linking. PMID:19797229

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

    NASA Astrophysics Data System (ADS)

    Felipe, Mary Jane Legaspi

    2011-12-01

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

  16. Hypotheses on the evolution of hyaluronan: A highly ironic acid

    PubMed Central

    Csoka, Antonei B; Stern, Robert

    2013-01-01

    Hyaluronan is a high-molecular-weight glycosaminoglycan (GAG) prominent in the extracellular matrix. Emerging relatively late in evolution, it may have evolved to evade immune recognition. Chondroitin is a more ancient GAG and a possible hyaluronan precursor. Epimerization of a 4-hydroxyl in N-acetylgalactosamine in chondroitin to N-acetylglucosamine of hyaluronan is the only structural difference other than chain length between these two polymers. The axial 4-hydroxyl group extends out perpendicular from the equatorial plane of N-acetylgalactosamine in chondroitin. We suspect that this hydroxyl is a prime target for immune recognition. Conversion of a thumbs-up hydroxyl group into a thumbs-down position in the plane of the sugar endows hyaluronan with the ability to avoid immune recognition. Chitin is another potential precursor to hyaluronan. But regardless whether of chondroitin or of chitin origin, an ancient chondroitinase enzyme sequence seems to have been commandeered to catalyze the cleavage of the new hyaluronan substrate. The evolution of six hyaluronidase-like sequences in the human genome from a single chondroitinase as found in Caenorhabditis elegans can now be traced. Confirming our previous predictions, two duplication events occurred, with three hyaluronidase-like sequences occurring in the genome of Ciona intestinalis (sea squirt), the earliest known chordate. This was probably followed by en masse duplication, with six such genes present in the genome of zebra fish onwards. These events occurred, however, much earlier than predicted. It is also apparent on an evolutionary time scale that in several species, this gene family is continuing to evolve. PMID:23315448

  17. Hyaluronan Synthase 1: A Mysterious Enzyme with Unexpected Functions

    PubMed Central

    Siiskonen, Hanna; Oikari, Sanna; Pasonen-Seppänen, Sanna; Rilla, Kirsi

    2015-01-01

    Hyaluronan synthase 1 (HAS1) is one of three isoenzymes responsible for cellular hyaluronan synthesis. Interest in HAS1 has been limited because its role in hyaluronan production seems to be insignificant compared to the two other isoenzymes, HAS2 and HAS3, which have higher enzymatic activity. Furthermore, in most cell types studied so far, the expression of its gene is low and the enzyme requires high concentrations of sugar precursors for hyaluronan synthesis, even when overexpressed in cell cultures. Both expression and activity of HAS1 are induced by pro-inflammatory factors like interleukins and cytokines, suggesting its involvement in inflammatory conditions. Has1 is upregulated in states associated with inflammation, like atherosclerosis, osteoarthritis, and infectious lung disease. In addition, both full length and splice variants of HAS1 are expressed in malignancies like bladder and prostate cancers, multiple myeloma, and malignant mesothelioma. Interestingly, immunostainings of tissue sections have demonstrated the role of HAS1 as a poor predictor in breast cancer, and is correlated with high relapse rate and short overall survival. Utilization of fluorescently tagged proteins has revealed the intracellular distribution pattern of HAS1, distinct from other isoenzymes. In all cell types studied so far, a high proportion of HAS1 is accumulated intracellularly, with a faint signal detected on the plasma membrane and its protrusions. Furthermore, the pericellular hyaluronan coat produced by HAS1 is usually thin without induction by inflammatory agents or glycemic stress and depends on CD44–HA interactions. These specific interactions regulate the organization of hyaluronan into a leukocyte recruiting matrix during inflammatory responses. Despite the apparently minor enzymatic activity of HAS1 under normal conditions, it may be an important factor under conditions associated with glycemic stress like metabolic syndrome, inflammation, and cancer. PMID:25699059

  18. Hyaluronan treatment of interstitial cystitis\\/painful bladder syndrome

    Microsoft Academic Search

    Claus R. Riedl; Paul F. Engelhardt; Kurosch L. Daha; Nike Morakis; Heinz Pflüger

    2008-01-01

    The aim of this study is to evaluate the efficacy of intravesical hyaluronan therapy in interstitial cystitis\\/painful bladder\\u000a syndrome (IC\\/PBS). One hundred twenty-six patients with IC\\/PBS and an average disease duration of 6.1 years were treated with\\u000a weekly instillations of a 50-cm3 phosphate-buffered saline solution containing 40 mg sodium hyaluronate. To be eligible for hyaluronan treatment, a positive\\u000a modified potassium test was

  19. Hyaluronan, Inflammation, and Breast Cancer Progression

    PubMed Central

    Schwertfeger, Kathryn L.; Cowman, Mary K.; Telmer, Patrick G.; Turley, Eva A.; McCarthy, James B.

    2015-01-01

    Breast cancer-induced inflammation in the tumor reactive stroma supports invasion and malignant progression and is contributed to by a variety of host cells including macrophages and fibroblasts. Inflammation appears to be initiated by tumor cells and surrounding host fibroblasts that secrete pro-inflammatory cytokines and chemokines and remodel the extracellular matrix (ECM) to create a pro-inflammatory “cancerized” or tumor reactive microenvironment that supports tumor expansion and invasion. The tissue polysaccharide hyaluronan (HA) is an example of an ECM component within the cancerized microenvironment that promotes breast cancer progression. Like many ECM molecules, the function of native high-molecular weight HA is altered by fragmentation, which is promoted by oxygen/nitrogen free radicals and release of hyaluronidases within the tumor microenvironment. HA fragments are pro-inflammatory and activate signaling pathways that promote survival, migration, and invasion within both tumor and host cells through binding to HA receptors such as CD44 and RHAMM/HMMR. In breast cancer, elevated HA in the peri-tumor stroma and increased HA receptor expression are prognostic for poor outcome and are associated with disease recurrence. This review addresses the critical issues regarding tumor-induced inflammation and its role in breast cancer progression focusing specifically on the changes in HA metabolism within tumor reactive stroma as a key factor in malignant progression.

  20. Nematic Nanotube Gels M. F. Islam, A. M. Alsayed, Z. Dogic, J. Zhang, T. C. Lubensky, and A. G. Yodh

    E-print Network

    Fraden, Seth

    concentration in an N-isopropyl acrylamide gel and then inducing a volume-compression transition. These gels acrylamide monomer that is then polymerized and cross- linked to form a gel [13]. Then the solvent quality bundles of SWNTs. The gel consisted of polymerized N-isopropyl acrylamide polymer (NIPA; 492 mM), N; N0

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

    PubMed

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

    2011-12-28

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

  2. One-pot synthesis and characterization of cross-linked quaternized chitosan microspheres as protein adsorbent.

    PubMed

    Zhang, Weican; Sun, Caiyun; Zhao, Yue; Lu, Xuemei

    2011-11-01

    The one-pot synthesis and characterization of cross-linked quaternized chitosan microspheres (CQCM) as a protein adsorbent are presented. First of all, chitosan particles were prepared by spray drying method, and then they were quaternized and cross-linked in turn with glycidyltrimethylammonium (GTMAC) chloride and glutaraldehyde in isopropanol containing 10% water in one-pot. The effect of the reaction temperature, reaction time and the amounts of added GTMAC and glutaraldehyde on the protein adsorption ability of CQCM was investigated. The adsorption behavior of the CQCM prepared in the optimum synthetic conditions was well described by the Langmuir isotherm with maximum adsorption capacity equal to 1424 mg BSA/g dry weight. The particle size ranged from 7.6 to 48.9 ?m. The mechanism of adsorption-desorption of BSA to the CQCM was ion-exchange. Finally, the extraction of soybean peroxidase from crude soybean peroxidase solution using the CQCM was performed. PMID:21763718

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

    PubMed

    Roy, Debashish; Sumerlin, Brent S

    2014-01-01

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

  4. Hologram formation reconsidered in dichromated polyvinylalcohol: polymer cross-linking around chromium (V)

    NASA Astrophysics Data System (ADS)

    Bolte, Michele; Israeli, Yael; Djouani, Fatma; Rivaton, Agnes; Frezet, Lawrence; Lessard, Roger A.

    2005-04-01

    The photochemical behavior of dichromated polyvinylalcohol (DCPVA) films was analysed upon exposure at 365 nm in connection with the hologram quality recorded in such a photosensitive material. The evolution of both involved species, chromium and polyvinylalcohol, were quantified by implementing an innovative approach. This approach combines the monitoring of the structural modification of the polymeric matrix and the fate of the various chromium species ((VI), (V) and (III)). For the first time, it was established that chromium (V) was at the origin of the cross-linking implied in the hologram formation by acting as a bridge between hydroxyl groups of the polymeric chains. A second unanswered question was also elucidated. The improvement brought by ammonium dichromate with respect to potassium dichromate involves amide groups as additional chelating sites for chromium (V) resulting in the increase of the matrix cross-linking.

  5. Cross-linked sulfonated aromatic ionomers via SO2 bridges: Conductivity properties

    NASA Astrophysics Data System (ADS)

    Di Vona, M. L.; Pasquini, L.; Narducci, R.; Pelzer, K.; Donnadio, A.; Casciola, M.; Knauth, P.

    2013-12-01

    The proton conductivity of SPEEK membranes in situ cross-linked by thermal treatment at 180 °C for various times was investigated by impedance spectroscopy. The conductivity measurements were made on fully humidified membranes between 25 and 65 °C and on membranes exposed to different relative humidity between 80 and 140 °C. The Ionic Exchange Capacity (IEC) was determined by acid-base titration and the water uptake by gravimetry. The proton conductivity was determined as function of temperature, IEC, degree of cross-linking and hydration number. A curve of proton conductivity vs. hydration number allows predicting that in order to reach a value of 0.1 S/cm at 100 °C a hydration number above 20 is necessary. The measured conductivity at this temperature is 0.16 S/cm for a hydration number of 60.

  6. Microglial Fc Receptors Mediate Physiological Changes Resulting From Antibody Cross-Linking of Myelin Oligodendrocyte Glycoprotein

    PubMed Central

    Marta, Cecilia B.; Bansal, Rashmi; Pfeiffer, Steven E.

    2009-01-01

    Antibodies to myelin oligodendrocyte glycoprotein (MOG) have been implicated in Multiple Sclerosis demyelination through activation of complement and/or macrophage-effector processes. We presented a novel mechanism, whereby MOG on oligodendrocytes, when cross-linked with anti-MOG and secondary antibody resulted in its repartitioning into lipid rafts, and changes in protein phosphorylation and morphology. Here, we show that similar events occur when anti-MOG is cross-linked with Fc receptors (FcRs) present on microglia but not with complement. These results indicate that FcRs are endogenous antigen/antibody cross-linkers in vitro, suggesting that FcRs could be physiologically relevant in vivo and possible targets for therapy in Multiple Sclerosis. PMID:18406472

  7. Radiation cross-linking of elastomers in the presence of chlorine-containing and chroman compounds

    SciTech Connect

    Mamedov, S.M.; Zakharova, E.I.; Sarycheva, I.K. [and others

    1992-03-01

    The role of hexachloro-p-xylene (HCPX) and 6-hydroxy-2,2,5, 7,8-pentamethylchroman (HPMC) in butadiene-nitrile rubbers (SKN) in the systems SKN-40+HCPX+ZnO and SKN- 40+HPMC+ZnO exposed to radiation was investigated. A change in the molecular structure of the SKN-40 rubber in the presence of HCPX and HPMC after irradiation with a dose of 150 kGy of {gamma}rays was demonstrated by physicochemical and spectral methods. The cross-linking yields and appearance of cross-links in the elastomers were determined for each system studied as a function of the absorbed dose. A hypothesis was advanced concerning the mechanism of radiation-heterogeneous conversion of elastomers in the presence of HCPX. 17 refs., 3 figs., 1 tab.

  8. Analysis of Epidermal Growth Factor Receptor Dimerization by BS3 Cross-Linking

    PubMed Central

    Turk, Harmony F.; Chapkin, Robert S.

    2015-01-01

    Dimerization of receptor tyrosine kinases is a well-characterized process. It is imperative for the activation of many receptors, including the epidermal growth factor receptor (EGFR). EGFR has been shown to be regulated by a number of factors, including lipid raft localization. For example, alteration of the lipid raft localization of EGFR has been demonstrated to modify receptor dimerization. This protocol describes an assay to quantify EGFR dimers using BS3 cross-linking. BS3 cross-linking is well suited for this purpose because of its length, water solubility, and membrane impermeability. Although this protocol is written specifically for EGFR, the assay can be extrapolated in order to characterize dimerization of other receptor tyrosine kinases. PMID:25319886

  9. Metal-Free Preparation of Linear and Cross-Linked Polydicyclopentadiene.

    PubMed

    Goetz, Adam E; Boydston, Andrew J

    2015-06-24

    Metal-free ring-opening metathesis polymerization (ROMP) utilizes organic photoredox mediators as alternatives to traditional metal-based ROMP initiators to allow the preparation of polymers without residual metal contamination. Herein we report studies exploring the use of endo-dicyclopentadiene (DCPD), a common ROMP monomer, to form linear polyDCPD and copolymers with norbornene. Subsequent cross-linking of the linear polyDCPD using thiol-ene chemistry allows for a completely metal-free preparation of cross-linked polyDCPD. Furthermore, the examination of a number of structurally related monomers offers insights into mechanistic details of this polymerization and demonstrates new monomers that can be utilized for metal-free ROMP. PMID:26053254

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

    SciTech Connect

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

    1984-05-01

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

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

    PubMed

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

    2004-05-01

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

  12. Combined corneal collagen cross-linking and posterior chamber toric implantable collamer lens implantation for keratoconus.

    PubMed

    Kymionis, George D; Grentzelos, Michael A; Karavitaki, Alexandra E; Zotta, Paraskevi; Yoo, Sonia H; Pallikaris, Ioannis G

    2011-01-01

    A 29-year-old woman with keratoconus underwent posterior chamber toric implantable Collamer lens (Visian ICL; STAAR Surgical, Monrovia, CA) implantation 12 months after corneal collagen cross-linking with riboflavin and ultraviolet radiation-A. No intraoperative or postoperative complications were observed. Three months postoperatively, uncorrected distance visual acuity improved from counting fingers to 20/40 and corrected distance visual acuity improved from 20/100 to 20/30. Combined cross-linking treatment and posterior chamber toric phakic Collamer lens implantation in a two-step procedure seems to be an effective method for correcting keratoconus in patients with high myopia and astigmatism. Despite the encouraging results, longer follow-up is necessary to evaluate the outcomes of this approach. PMID:21366205

  13. F-ATPase: forced full rotation of the rotor despite covalent cross-link with the stator.

    PubMed

    Gumbiowski, K; Cherepanov, D; Muller, M; Panke, O; Promto, P; Winkler, S; Junge, W; Engelbrecht, S

    2001-11-01

    In ATP synthase (F(O)F(1)-ATPase) ion flow through the membrane-intrinsic portion, F(O), drives the central "rotor", subunits c(10)epsilongamma, relative to the "stator" ab(2)delta(alphabeta)(3). This converts ADP and P(i) into ATP. Vice versa, ATP hydrolysis drives the rotation backwards. Covalent cross-links between rotor and stator subunits have been shown to inhibit these activities. Aiming at the rotary compliance of subunit gamma we introduced disulfide bridges between gamma (rotor) and alpha or beta (stator). We engineered cysteine residues into positions located roughly at the "top," "center," and "bottom" parts of the coiled-coil portion of gamma and suitable residues on alpha or beta. This part of gamma is located at the center of the (alphabeta)(3) domain with its C-terminal part at the top of F(1) and the bottom part close to the F(O) complex. Disulfide bridge formation under oxidizing conditions was quantitative as shown by SDS-polyacrylamide gel electrophoresis and immunoblotting. As expected both the ATPase activities and the yield of rotating subunits gamma dropped to zero when the cross-link was formed at the center (gammaL262C <--> alphaA334C) and bottom (gammaCys(87) <--> betaD380C) positions. But much to our surprise disulfide bridging impaired neither ATP hydrolysis activity nor the full rotation of gamma and the enzyme-generated torque of oxidized F(1), which had been engineered at the top position (gammaA285C <--> alphaP280C). Apparently the high torque of this rotary engine uncoiled the alpha-helix and forced amino acids at the C-terminal portion of gamma into full rotation around their dihedral (Ramachandran) angles. This conclusion was supported by molecular dynamics simulations: If gammaCys(285)-Val(286) are attached covalently to (alphabeta)(3) and gammaAla(1)-Ser(281) is forced to rotate, gammaGly(282)-Ala(284) can serve as cardan shaft. PMID:11533065

  14. NIR-light-induced deformation of cross-linked liquid-crystal polymers using upconversion nanophosphors.

    PubMed

    Wu, Wei; Yao, Liming; Yang, Tianshe; Yin, Ruoyuan; Li, Fuyou; Yu, Yanlei

    2011-10-12

    When upconversion nanophosphors were incorporated into an azotolane-containing cross-linked liquid-crystal polymer film, the resulting composite film generated fast bending upon exposure to continuous-wave near-IR light at 980 nm. This occurs because the upconversion luminescence of the nanophosphors leads to trans-cis photoisomerization of the azotolane units and an alignment change of the mesogens. The bent film completely reverted to the initial flat state after the light source was removed. PMID:21913658

  15. Defective Removal of DMA Cross-Links in a Repairdeficient Mutant of Chinese Hamster Cells1

    Microsoft Academic Search

    Raymond E. Meyn; Susan F. Jenkins; Larry H. Thompson

    To further understand the relationships between DNA dam age, DNA repair, and cellular end points such as survival and mutation, the repair capacity of a DNA repair-deficient mutant (strain UV-20) of Chinese hamster ovary cells was character ized in response to DNA cross-linking agents. This mutant, previously shown to be hypersensitive to killing by both ultra violet light and the

  16. Adsorption of Cr(VI) on Cross?Linked Chitosan Beads

    Microsoft Academic Search

    Zofia Modrzejewska; Witold Sujka; Ma?gorzata Dorabialska; Roman Zarzycki

    2006-01-01

    A possibility of Cr(VI) removal by the adsorption method is discussed in the paper. An adsorbent were hydrogel chitosan beads are produced by the phase inversion method (by changing pH). The possibility of removing Cr(VI) ions by both pure chitosan hydrogel and its chelate compounds (chitosan cross?linked with Cu(II) and Ag(I) ions) was investigated. The adsorption proceeded from the solutions

  17. Tyrosyl radical generated by myeloperoxidase catalyzes the oxidative cross-linking of proteins.

    PubMed Central

    Heinecke, J W; Li, W; Francis, G A; Goldstein, J A

    1993-01-01

    Phagocytes generate H2O2 for use by a secreted heme enzyme, myeloperoxidase, to kill invading bacteria, viruses, and fungi. We have explored the possibility that myeloperoxidase might also convert L-tyrosine to a radical catalyst that cross-links proteins. Protein-bound tyrosyl residues exposed to myeloperoxidase, H2O2, and L-tyrosine were oxidized to o,o'-dityrosine, a stable product of the tyrosyl radical. The cross-linking reaction required L-tyrosine but was independent of halide and free transition metal ions; the heme poisons azide and aminotriazole were inhibitory. Activated neutrophils likewise converted polypeptide tyrosines to dityrosine. The pathway for oxidation of peptide tyrosyl residues was dependent upon L-tyrosine and was inhibited by heme poisons and catalase. Dityrosine synthesis was little affected by plasma concentrations of Cl- and amino acids, suggesting that the reaction pathway might be physiologically relevant. The requirement for free L-tyrosine and H2O2 for dityrosine formation and the inhibition by heme poisons support the hypothesis that myeloperoxidase catalyzes the cross-linking of proteins by a peroxidative mechanism involving tyrosyl radical. In striking contrast to the pathways generally used to study protein oxidation in vitro, the reaction does not require free metal ions. We speculate that protein dityrosine cross-linking by myeloperoxidase may play a role in bacterial killing or injuring normal tissue. The intense fluorescence and stability of biphenolic compounds may allow dityrosine to act as a marker for proteins oxidatively damaged by myeloperoxidase in phagocyte-rich inflammatory lesions. Images PMID:8390491

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

    Microsoft Academic Search

    R. J. Collighan; M. Griffin

    2009-01-01

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

  19. Injection Molded Optical Lens Using a Heat Resistant Thermoplastic Resin with Electron Beam Cross-Linking

    NASA Astrophysics Data System (ADS)

    Sano, Tomomi; Iyoda, Yoshitomo; Shimazu, Takayuki; Harumoto, Michiko; Inoue, Akira; Nakabayashi, Makoto; Ito, Hiroshi

    2010-05-01

    The poor heat resistant properties of a transparent thermoplastic resin was improved by electron beam irradiation cross-linking. A correcting aspheric lens for a 635-nm laser diode was fabricated using an injection molding machine, and was irradiated with an electron beam. The near field pattern (NFP), the far field pattern (FFP) at the focus position and the transmittance of the lens did not change after exposure to a 260 °C reflow process for 60 s.

  20. Generation of guanine-amino acid cross-links by a free radical combination mechanism.

    PubMed

    Uvaydov, Yuriy; Geacintov, Nicholas E; Shafirovich, Vladimir

    2014-06-21

    A direct method has been developed for the in vitro synthesis of stable DNA-protein cross-links (DPC's) between guanine and amino acids (lysine and arginine). This method employs the combination of guanine neutral radicals, G(-H)?, and side-chain C-centered amino acid radicals. The latter were generated indirectly after first causing the selective photoionization of 2-aminopurine (2AP) embedded in the oligonucleotide, 5'-d(CC[2AP]TCGCTACC), by intense nanosecond 308 nm excimer laser pulses. The 2AP radical cation deprotonates rapidly to form the 2AP(-H)? neutral radical which, in turn, oxidizes the nearby guanine to form the neutral guanine G(-H)? radical, as described previously (Shafirovich et al., J. Phys. Chem. B, 2001, 105, 8431). In parallel, the hydrated electrons, generated by the photoionization of 2AP, are scavenged by nitrous oxide to generate hydroxyl radicals. In the presence of a large excess of the amino acids, the hydroxyl radicals oxidize the latter to produce C-centered amino acid radicals that combine with the G(-H)? radicals to form the guanine-amino acid cross-linked oligonucleotide product. Analogous products were generated by photoionizing the free nucleoside, 2',3',5'-tri-O-acetylguanosine, (tri-O-Ac-Guo), using intense nanosecond 266 nm Nd:YAG laser pulse irradiation. The guanine-amino acid cross-links thus produced site-specifically positioned either in oligonucleotides, or in the free nucleoside tri-O-Ac-Guo were isolated by HPLC methods and identified by high resolution LC-TOF/MS and LC-MS/MS methods. The possibility that analogous guanine-amino acid cross-linked products could be formed in vivo using single hit radical generation mechanisms during oxidative stress is discussed. PMID:24810398

  1. Stabilization of collagen by cross-linking with oxazolidine E-resorcinol

    Microsoft Academic Search

    Hui Chen; Zhi-hua Shana

    2010-01-01

    Cross-linking agents play an important part in the physical properties of collagen based biomaterials. This paper describes the stabilization of type I collagen using an oxazolidine E-resorcinol compound. It is shown by NMR and elemental analysis techniques that oxazolidine E undergoes ring opening to form an N-methylol intermediate form and then reacts with the hydrogen bonds of resorcinol. Oxazolidine E-resorcinol

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

    Microsoft Academic Search

    Sharadha Sambasivan; Daniel A. Fischer; Stephen M. Hsu

    2007-01-01

    Molecular orientation at the surface layer of cross-linked ultrahigh molecular weight polyethylene (UHMWPE) has been examined. Molecular orientation has been shown to affect the wear resistance and surface mechanical properties of UHMWPE under biomechanical loading conditions. This study utilizes a nondestructive synchrotron based soft x-ray technique; near edge x-ray absorption fine structure at the carbon K-edge to examine the degree

  3. Third-Body Wear Testing of a Highly Cross-Linked Acetabular Liner

    Microsoft Academic Search

    Charles R. Bragdon; Murali Jasty; Orhun K. Muratoglu; William H. Harris

    2005-01-01

    The hip simulator wear performance of an electron beam cross-linked and subsequently melted ultrahigh molecular weight polyethylene against femoral heads of 28-, 38-, and 46-mm diameter in the presence of poly(methyl-methacrylate) particulate debris was contrasted with that of conventional polyethylene against a 46-mm diameter head. Over 5 million cycles of testing, the average wear rate of the conventional polyethylene liners

  4. Inhibition of gene expression by triple helix-directed DNA cross-linking at specific sites.

    PubMed Central

    Grigoriev, M; Praseuth, D; Guieysse, A L; Robin, P; Thuong, N T; Hélène, C; Harel-Bellan, A

    1993-01-01

    Synthetic oligodeoxynucleotides represent promising tools for gene inhibition in live systems. Triple helix-forming oligonucleotides, which bind to double-stranded DNA, are of special interest since they are targeted to the gene itself rather than to its mRNA product, as in the antisense strategy. Triple helix-forming oligonucleotides can be coupled to DNA-modifying agents and used to introduce modifications in the DNA target in a highly sequence-specific manner. We have recently designed psoralen-oligonucleotide conjugates, which, upon binding to double-stranded DNA sequences via triple helix formation, may be cross-linked in vitro to both strands of the DNA following UV irradiation. A psoralen-oligonucleotide conjugate was targeted to the promoter of the alpha subunit of the interleukin 2 receptor (IL-2R alpha) gene. The triple helix site overlaps the binding site for the transcription factor NF-kappa B, which activates transcription from the IL-2R alpha promoter. After UV irradiation, the oligonucleotide conjugate becomes cross-linked to the target site and inhibits transcription of reporter plasmids transfected in live cells. Inhibition is observed when UV-induced cross-linking occurs both in vitro (before transfection) and in vivo (after transfection). We directly demonstrate that this inhibitory effect is due to triple helix formation at the target site, since a mutant of the promoter, to which oligonucleotide binding was inhibited, was not affected by the psoralen-oligonucleotide conjugate after UV irradiation. In addition, we demonstrate that site-specific cross-linking upstream of the promoter has no effect on transcription. Images Fig. 2 Fig. 3 Fig. 4 PMID:8475098

  5. The relationship between collagen scaffold cross-linking agents and neutrophils in the foreign body reaction

    Microsoft Academic Search

    Qingsong Ye; Martin C. Harmsen; Marja J. A. van Luyn; Ruud A. Bank

    2010-01-01

    In order to get more insight into the role of neutrophils on the micro-environment and consequently on macrophages in the foreign body reaction in mice, we investigated the fate of the two differently cross-linked dermal sheep collagen disks (glutaraldehyde = GDSC, hexamethylenediisocyanate = HDSC) in mice implanted in one anatomical location, namely subcutaneously. In GDSC massive infiltration of neutrophils is seen at day 2

  6. Informatics strategies for large-scale novel cross-linking analysis.

    PubMed

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

    2007-09-01

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

  7. Pluronic\\/chitosan shell cross-linked nanocapsules encapsulating magnetic nanoparticles

    Microsoft Academic Search

    Ki Hyun Bae; Young Jin Ha; Chunsoo Kim; Kyu-Ri Lee; Tae Gwan Park

    2008-01-01

    We have developed novel Pluronic\\/chitosan nanocapsules encapsulating iron oxide nanoparticles. These nanocapsules were produced by dispersing hydrophobically-modified iron oxide nanoparticles and amine-reactive Pluronic derivatives in an organic solvent, and subsequently emulsification in an aqueous chitosan solution by ultrasonication. The resultant shell cross-linked nanocapsules had a unique core\\/shell type nanoreservoir architecture: an inner core encapsulating magnetic nanoparticles and a hydrophilic Pluronic\\/chitosan

  8. Functionality of Cross-Linked Polyvinylpyrrolidone as a Spheronization Aid: A Promising Alternative to Microcrystalline Cellulose

    Microsoft Academic Search

    Celine V. Liew; Li Gu; Josephine L. P. Soh; Paul W. S. Heng

    2005-01-01

    Purpose. This work seeks to explore and demonstrate the functionality of cross-linked polyvinylpyrrolidone (crospovidone) as a spheronization aid and a promising alternative to microcrystalline cellulose (MCC). Methods. Pellets were prepared with various grades of crospovidone using both small- and large-scale extrusionYspheronization. A Box-Behnken experimental design was employed to elucidate the effects of operating variables on the quality of the pellets.

  9. The influence of the degree of cross-linking on the adsorption properties of chitosan beads

    Microsoft Academic Search

    Peter O. Osifo; Athena Webster; Hein van der Merwe; Hein W. J. P. Neomagus; Marius A. van der Gun; David M. Grant

    2008-01-01

    The influence of the degree of cross-linking (DCL) on chitosan beads was studied. Chitosan was prepared from the exoskeleton of Cape rock-lobsters, collected from the surroundings of Cape Town, South Africa. The chitosan beads were characterized; the beads water contents and pKa varied in the range of 90–96% and 4.3–6.0, respectively, and were found to decrease with increasing DCL (0.0–34.0%).

  10. Nonenzymatic collagen cross-links induced by glycoxidation (pentosidine) predicts vertebral fractures

    Microsoft Academic Search

    Masataka Shiraki; Tatsuhiko Kuroda; Shiro Tanaka; Mitsuru Saito; Masao Fukunaga; Toshitaka Nakamura

    2008-01-01

    Advanced glycation end products (AGE) in collagen have been reported to decrease the mechanical property of bone. However,\\u000a there are no available data on the relation between fracture risk and levels of glycoxidative (nonenzymatic) cross-links of\\u000a collagen in clinical samples. A total of 432 Japanese elderly women who were not receiving any drug treatment for osteoporosis\\u000a were selected and followed

  11. Synthesis, characterization and properties of biodegradable polylactic acid-?-cyclodextrin cross-linked copolymer microgels

    Microsoft Academic Search

    Dedai Lu; Liqiang Yang; Tianhong Zhou; Ziqiang Lei

    2008-01-01

    The novel biodegradable polylactic acid-?-cyclodextrin (PLA-?-CD) cross-linked copolymer microgels were prepared by the radical copolymerization of PLA macromonomer and polymerizable ?-CD derivatives. The ?-CD derivatives with various numbers of polymerizable vinyl groups were synthesized from 1-allyloxy-2,3-epoxy propane (also called allylglycidyl ether, AGE) and ?-CD. The chemical structures of polymerizable monomers were determined by NMR. The thermal properties, size, morphology, in

  12. Evidences for a role of protein cross-links in transglutaminase-related disease

    Microsoft Academic Search

    Claudio Tabolacci; Alessandro Lentini; Bruno Provenzano; Simone Beninati

    Transglutaminases (TGs) are a large family of related and ubiquitous enzymes that catalyze the cross-linking of a glutaminyl\\u000a residue of a protein\\/peptide substrate to a lysyl residue of a protein\\/peptide co-substrate. Considerable and intense progress\\u000a has been made in the understanding of the chemistry, molecular biology and cell biology of TGs. The knowledge that very different\\u000a physiological and pathological processes

  13. Biosorption of uranium by cross-linked and alginate immobilized residual biomass from distillery spent wash

    Microsoft Academic Search

    M. Bustard; A. P. McHale

    1997-01-01

    Residual biomass from a whiskey distillery was examined for its ability to function as a biosorbent for uranium. Biomass recovered and lyophilised exhibited a maximum biosorption capacity of 165-170 mg uranium\\/g dry weight biomass at 15v°C. With a view towards the development of continuous or semi-continuous flow biosorption processes it was decided to immobilize the material by (1) cross-linking with

  14. Biocompatibility of chemically cross-linked gelatin hydrogels for ophthalmic use

    Microsoft Academic Search

    Jui-Yang Lai

    2010-01-01

    Biocompatibility is a major requirement for the development of functional biomaterials for ophthalmic applications. In this\\u000a study, we investigated the effect of cross-linker functionality on ocular biocompatibility of chemically modified gelatin\\u000a hydrogels. The test materials were cross-linked with glutaraldehyde (GTA) or 1-ethyl-3-(3-dimethyl aminopropyl)carbodiimide\\u000a (EDC), and were analyzed using in vitro and in vivo assays. Primary rat iris pigment epithelial cultures

  15. Static Inhomogeneities in Thermoreversible Physical Gels

    NASA Astrophysics Data System (ADS)

    Ikkai, Fumiyoshi; Shibayama, Mitsuhiro

    1999-06-01

    Thermoreversible gels of poly(vinyl alcohol)/Congo red in aqueous solutions have been studied by dynamic light scattering. Below Tgel \\(~ 43 °C\\), a speckle pattern appeared, while it disappeared for T>Tgel. This indicates that nonergodicity observed in chemically cross-linked gels also exists in thermoreversible physical gels. Analogous to the ? and ? relaxations of glasses, the intensity correlation function showed a power-law behavior for T<=Tgel and a stretched exponential behavior for T>=Tgel, respectively, while the thermal fluctuations characteristic of polymer gels were present independent of Tgel.

  16. Modelling of the inhomogeneous interior of polymer gels

    NASA Astrophysics Data System (ADS)

    Shew, Chwen-Yang; Iwaki, Takafumi

    2006-04-01

    A simple model has been investigated to elucidate the mean squared displacement (MSD) of probe molecules in cross-linked polymer gels. In the model, we assume that numerous cavities distribute in the inhomogeneous interior of a gel, and probe molecules are confined within these cavities. The individual probe molecules trapped in a gel are treated as Brownian particles confined to a spherical harmonic potential. The harmonic potential is chosen to model the effective potential experienced by the probe particle in the cavity of a gel. Each field strength is corresponding to the characteristic of one type of effective cavity. Since the statistical distribution of different effective cavity sizes is unknown, several distribution functions are examined. Meanwhile, the calculated averaged MSDs are compared to the experimental data by Nisato et al (2000 Phys. Rev. E 61 2879). We find that the theoretical results of the MSD are sensitive to the shape of the distribution function. For low cross-linked gels, the best fit is obtained when the interior cavities of a gel follow a bimodal distribution. Such a result may be attributed to the presence of at least two distinct classes of cavity in gels. For high cross-linked gels, the cavities in the gel can be depicted by a single-modal uniform distribution function, suggesting that the range of cavity sizes becomes smaller. These results manifest the voids inside a gel, and the shape of distribution functions may provide the insight into the inhomogeneous interior of a gel.

  17. Molecular dynamics simulations of highly cross-linked polymer networks: prediction of thermal and mechanical properties

    NASA Astrophysics Data System (ADS)

    Shenogina, Natalia; Tsige, Mesfin; Mukhopadhyay, Sharmila; Patnaik, Soumya

    2012-02-01

    We use all-atom molecular dynamics (MD) simulations to predict the mechanical and thermal properties of thermosetting polymers. Atomistic simulation is a promising tool which can provide detailed structure-property relationships of densely cross-linked polymer networks. In this work we study the thermo-mechanical properties of thermosetting polymers based on amine curing agents and epoxy resins and have focused on the DGEBA/DETDA epoxy system. At first we describe the modeling approach to construction of realistic all-atom models of densely cross-linked polymer matrices. Subsequently, a series of atomistic simulations was carried out to examine the simulation cell size effect as well as the role of cross-linking density and chain length of the resin strands on thermo-mechanical properties at different temperatures. Two different methods were used to deform the polymer networks. Both static and dynamic approaches to calculating the mechanical properties were considered and the thermo-mechanical properties obtained from our simulations were found in reasonable agreement with experimental values.

  18. Cross-links in carbon nanotube assembly introduced by using polyacrylonitrile as precursor.

    PubMed

    Cui, Yanbin; Zhang, Mei

    2013-08-28

    Individual carbon nanotube (CNT) exhibits extraordinary mechanics. However, the properties of the macroscopic CNT-based structure, such as CNT fibers and films, are far lower than that of individual CNT. One of the main reasons is the weak interaction between tubes and bundles in the CNT assemblies. It is understood that the cross-links in CNT assembly play a key role to improve the performance of CNT-based structure. Different approaches have been taken to create CNT joints. Most of these approaches focus on connecting CNTs by generating new covalent bonding between tubes. In this work, we intend to reinforce the CNT network by locking the contacted CNTs. Polyacrylonitrile (PAN) was used as precursor because PAN can form graphitic structures after carbonization. The freestanding superthin CNT sheet and CNT yarn were used to evaluate the effects of the PAN precursor to form cross-links between CNTs. The tensile strength of CNT yarn is improved when the yarn is partially infiltrated with PAN and consequently carbonated. High-resolution transmission electron microscopy observation of the sheets shows that graphite structures are formed and cross-link CNTs in CNT assembly. PMID:23901778

  19. Deformation responses of a physically cross-linked high molecular weight elastin-like protein polymer.

    PubMed

    Wu, Xiaoyi; Sallach, Rory E; Caves, Jeffrey M; Conticello, Vincent P; Chaikof, Elliot L

    2008-07-01

    Recombinant protein polymers were synthesized and examined under various loading conditions to assess the mechanical stability and deformation responses of physically cross-linked, hydrated, protein polymer networks designed as triblock copolymers with central elastomeric and flanking plastic-like blocks. Uniaxial stress-strain properties, creep and stress relaxation behavior, as well as the effect of various mechanical preconditioning protocols on these responses were characterized. Significantly, we demonstrate for the first time that ABA triblock protein copolymers when redesigned with substantially larger endblock segments can withstand significantly greater loads. Furthermore, the presence of three distinct phases of deformation behavior was revealed upon subjecting physically cross-linked protein networks to step and cyclic loading protocols in which the magnitude of the imposed stress was incrementally increased over time. We speculate that these phases correspond to the stretch of polypeptide bonds, the conformational changes of polypeptide chains, and the disruption of physical cross-links. The capacity to select a genetically engineered protein polymer that is suitable for its intended application requires an appreciation of its viscoelastic characteristics and the capacity of both molecular structure and conditioning protocols to influence these properties. PMID:18558738

  20. Density variant glycan microarray for evaluating cross-linking of mucin-like glycoconjugates by lectins.

    PubMed

    Godula, Kamil; Bertozzi, Carolyn R

    2012-09-26

    Interactions of mucin glycoproteins with cognate receptors are dictated by the structures and spatial organization of glycans that decorate the mucin polypeptide backbone. The glycan-binding proteins, or lectins, that interact with mucins are often oligomeric receptors with multiple ligand binding domains. In this work, we employed a microarray platform comprising synthetic glycopolymers that emulate natural mucins arrayed at different surface densities to evaluate how glycan valency and spatial separation affect the preferential binding mode of a particular lectin. We evaluated a panel of four lectins (Soybean agglutinin (SBA), Wisteria floribunda lectin (WFL), Vicia villosa-B-4 agglutinin (VVA), and Helix pomatia agglutin (HPA)) with specificity for ?-N-acetylgalactosamine (?-GalNAc), an epitope displayed on mucins overexpressed in many adenocarcinomas. While these lectins possess the ability to agglutinate A(1)-blood cells carrying the ?-GalNAc epitope and cross-link low valency glycoconjugates, only SBA showed a tendency to form intermolecular cross-links among the arrayed polyvalent mucin mimetics. These results suggest that glycopolymer microarrays can reveal discrete higher-order binding preferences beyond the recognition of individual glycan epitopes. Our findings indicate that glycan valency can set thresholds for cross-linking by lectins. More broadly, well-defined synthetic glycopolymers enable the integration of glycoconjugate structural and spatial diversity in a single microarray screening platform. PMID:22967056

  1. Fluorescent and cross-linked organic-inorganic hybrid nanoshells for monitoring drug delivery.

    PubMed

    Sun, Lijuan; Liu, Tianhui; Li, Hua; Yang, Liang; Meng, Lingjie; Lu, Qinghua; Long, Jiangang

    2015-03-01

    Functionalized and monodisperse nanoshells have attracted significant attention owing to their well-defined structure, unique properties, and wide range of potential applications. Here, the synthesis of cross-linked organic-inorganic hybrid nanoshells with strong fluorescence properties was reported via a facile precipitation polymerization of hexachlorocyclotriphosphazene (HCCP) and fluorescein on silica particles used as templates. The resulting poly(cyclotriphosphazene-co-fluorescein) (PCTPF) nanoshells were firm cross-linked shells with ?2.2 nm mesopores that facilitated the transport of drug molecules. The fluorescent nanoshells also exhibited excellent water dispersibility and biocompatibility; thus, they can be considered as ideal drug vehicles with high doxorubicin storage capacity (26.2 wt %) and excellent sustained release (up to 14 days). Compared to doxorubicin (DOX) alone, the PCTPF nanoshells more efficiently delivered DOX into and killed cancer cells. Moreover, the PCTPF nanoshells also exhibited remarkable fluorescent emission properties and improved photobleaching stability in both suspension and solid state owing to the covalent immobilization of fluorescein in the highly cross-linked organic-inorganic hybrids. The exceptional fluorescent properties enabled the release of DOX as well as the distribution of nanoshells and DOX to be monitored. PMID:25651861

  2. Maillard reaction and protein cross-linking in relation to the solubility of milk powders.

    PubMed

    Le, Thao T; Bhandari, Bhesh; Holland, John W; Deeth, Hilton C

    2011-12-14

    Protein changes in relation to solubility, Maillard reaction (MR), and protein cross-linking in whole milk powder (WMP), skim milk powder (SMP), and whey protein concentrate (WPC) stored at different relative humidities (RHs) were investigated by chemical and electrophoretic methods. WMP and SMP reached minimum solubility rapidly, while WPC showed no change in solubility. The loss of solubility corresponded with development of high-molecular-weight protein complexes observed by two-dimensional electrophoresis. The maximal MR rate occurred at 66% RH for WMP and SMP (high lactose/protein ratios) and 84% RH for WPC (low lactose/protein ratios) based on the furosine and hydroxymethylfurfural contents. However, browning was greatest at 84% RH in all powders. The minimum solubility corresponded with the casein and fat contents. The retention of solubility and minimal protein cross-linking of WPC compared to casein-containing powders suggest that the casein content and cross-linking strongly influence the decrease in the solubility of milk powder. PMID:22007925

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

    NASA Technical Reports Server (NTRS)

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

    1991-01-01

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

  4. Macroscopic, mesostructured cationic surfactant/neutral polymer films: structure and cross-linking.

    PubMed

    O'Driscoll, Benjamin M D; Fernandez-Martin, Cristina; Wilson, Roland D; Knott, Jessica; Roser, Stephen J; Edler, Karen J

    2007-04-10

    Mesostructured films of alkyltrimethylammonium bromides or cetylpyridinium bromide and polyethylenimines that spontaneously self-assemble at the air/water interface have been examined using a range of surface sensitive techniques. These films are unusual in that they can be micrometers thick and are relatively robust. Here we show that the films can be cross-linked and thus removed from the liquid surface where they form, as solid, mesostructured polymer-surfactant membranes. Cross-linking causes little change in the structure of the films but freezes in the metastable mesostructures, enhancing the potential of these films for future applications. Cross-linked films, dried after removal from the solution surface, retain the ordered nanoscale structure within the film. We also report grazing incidence X-ray diffraction (GID), which shows that most films display scattering consistent with 2D-hexagonal phase crystallites of rodlike surfactant micelles encased in polymer. Polymer branching makes little difference to the film structures; however, polymer molecular weight has a significant effect. Films with lower polymer MW are generally thinner and more ordered, while higher polymer MW films were thicker and less ordered. Increased pH causes formation of thicker films and improves the ordering in low MW films, while high MW films lose order. To rationalize these results, we propose a model for the film formation process that relates the kinetic and thermodynamic limits of phase separation and mesophase ordering to the structures observed. PMID:17371057

  5. Mechanical properties of retrieved highly cross-linked crossfire liners after short-term implantation.

    PubMed

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

    2005-10-01

    This study reports on detailed analyses of retrieved, annealed cross-linked liners. Twelve cross-linked liners (Crossfire, Stryker Orthopaedics, Mahwah, NJ) of the same Omnifit design were retrieved at revision surgery by one institution after an average 1.9 years (0.02-4.8 years) in vivo. In each case, the revision surgery was performed for reasons unrelated to wear. The mechanical properties and extent of oxidation of all inserts were characterized using a standard small punch test and measurement of the oxidation index. Results indicated that there was no association between implantation time and either mechanical properties or extent of oxidation for the inserts near the worn bearing surface. Slight variation in properties was observed as a function of sampling location, with the properties near the unworn surface displaying the greatest relative variability. We conclude that the variability in polyethylene properties observed in this small study was not clinically significant for these short-term-implanted, annealed cross-linked liners. PMID:16230233

  6. Collagen cross-link excretion during space flight and bed rest

    NASA Technical Reports Server (NTRS)

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

    1998-01-01

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

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

    E-print Network

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

    2007-06-04

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

  8. Selective adsorption of metoprolol enantiomers using 2-hydroxypropyl-?-cyclodextrin cross-linked multiwalled carbon nanotube.

    PubMed

    Farhadian, Nafiseh; Sharifi, Arezoo; Lashgari, Elmira

    2015-03-01

    This study investigates the ability of functionalized multiwalled carbon nanotubes (MWCNTs) for enantio-separation of metoprolol chiral forms. 2Hydroxypropyl-?-cyclodextrin (2HP-?-CD) was applied as a chiral selector to functionalize carbon nanotubes (CNTs). The modified multiwalled CNT samples were characterized using scanning electron microscopy and Fourier transform infrared spectroscopy. The results of analyses showed that CNTs were successfully cross-linked with 2HP-?-CD. To evaluate the enantio-separation property of the products, the separation of metoprolol chiral forms on the initial and final products was examined. Further, UV-visible spectroscopy and polarimeter analyses were used for characterization. The results indicate that MWCNT does not have any intrinsic enantio-separation ability, although its selectivity for enantio-separation can be enhanced by cross-linking it to 2HP-?-CD. Moreover, the optimal mass of adsorbent as well as optimal mass of functional groups is estimated to achieve maximum enantio-separation efficiency. The results indicate that applying large amounts of 2HP-?-CD to CNTs functionalization decreases the cross-linking efficiency, which consequently reduces enantio-separation efficiency. PMID:25124099

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

    SciTech Connect

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

    2010-01-01

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

  10. Intermediate closed state for glycine receptor function revealed by cysteine cross-linking

    PubMed Central

    Prevost, Marie S.; Moraga-Cid, Gustavo; Van Renterghem, Catherine; Edelstein, Stuart J.; Changeux, Jean-Pierre; Corringer, Pierre-Jean

    2013-01-01

    Pentameric ligand-gated ion channels (pLGICs) mediate signal transmission by coupling the binding of extracellular ligands to the opening of their ion channel. Agonist binding elicits activation and desensitization of pLGICs, through several conformational states, that are, thus far, incompletely characterized at the structural level. We previously reported for GLIC, a prokaryotic pLGIC, that cross-linking of a pair of cysteines at both sides of the extracellular and transmembrane domain interface stabilizes a locally closed (LC) X-ray structure. Here, we introduced the homologous pair of cysteines on the human ?1 glycine receptor. We show by electrophysiology that cysteine cross-linking produces a gain-of-function phenotype characterized by concomitant constitutive openings, increased agonist potency, and equalization of efficacies of full and partial agonists. However, it also produces a reduction of maximal currents at saturating agonist concentrations without change of the unitary channel conductance, an effect reversed by the positive allosteric modulator propofol. The cross-linking thus favors a unique closed state distinct from the resting and longest-lived desensitized states. Fitting the data according to a three-state allosteric model suggests that it could correspond to a LC conformation. Its plausible assignment to a gating intermediate or a fast-desensitized state is discussed. Overall, our data show that relative movement of two loops at the extracellular-transmembrane interface accompanies orthosteric agonist-mediated gating. PMID:24085847

  11. Reasons for revision of first-generation highly cross-linked polyethylenes.

    PubMed

    Kurtz, Steven M; Medel, Francisco J; MacDonald, Daniel W; Parvizi, Javad; Kraay, Matthew J; Rimnac, Clare M

    2010-09-01

    Over a 10-year period, we prospectively evaluated the reasons for revision of contemporary and highly cross-linked polyethylene formulations in amulticenter retrieval program. Two hundred twelve consecutive retrievals were classified as conventional gamma inert sterilized (n = 37), annealed (Cross fire,[Stryker Orthopedics, Mahwah, NJ] n = 72), or remelted (Longevity [Zimmer ,Warsaw, Ind], XLPE[Smith and Nephew, Memphis, Tenn], Durasul [Zimmer,Warsaw, Ind] n = 103) liners. The most frequent reasons for revision were loosening (35%), instability(28%), and infection (21%) and were not related to polyethylene formulation (P = .17). Annealed and remelted liners had comparable linear penetration rates(0.03 and 0.04 mm/y, respectively, on average), and these were significantly lower than the rate in conventional retrievals (0.11 mm/y, P ? .0005). This retrieval study including first-generation highly cross linked liners demonstrated lower wear than conventional polyethylene. Although loosening remained as the most prevalent reason for revision, we could not demonstrate a relationship between wear and loosening.The long-term clinical performance of first-generation highly cross-linked liners remains promising based on the midterm outcomes of the components documented in this study [corrected]. PMID:20541895

  12. Human Muscle LIM Protein Dimerizes along the Actin Cytoskeleton and Cross-Links Actin Filaments

    PubMed Central

    Hoffmann, Céline; Moreau, Flora; Moes, Michèle; Luthold, Carole; Dieterle, Monika; Goretti, Emeline; Neumann, Katrin; Steinmetz, André

    2014-01-01

    The muscle LIM protein (MLP) is a nucleocytoplasmic shuttling protein playing important roles in the regulation of myocyte remodeling and adaptation to hypertrophic stimuli. Missense mutations in human MLP or its ablation in transgenic mice promotes cardiomyopathy and heart failure. The exact function(s) of MLP in the cytoplasmic compartment and the underlying molecular mechanisms remain largely unknown. Here, we provide evidence that MLP autonomously binds to, stabilizes, and bundles actin filaments (AFs) independently of calcium and pH. Using total internal reflection fluorescence microscopy, we have shown how MLP cross-links actin filaments into both unipolar and mixed-polarity bundles. Quantitative analysis of the actin cytoskeleton configuration confirmed that MLP substantially promotes actin bundling in live myoblasts. In addition, bimolecular fluorescence complementation (BiFC) assays revealed MLP self-association. Remarkably, BiFC complexes mostly localize along actin filament-rich structures, such as stress fibers and sarcomeres, supporting a functional link between MLP self-association and actin cross-linking. Finally, we have demonstrated that MLP self-associates through its N-terminal LIM domain, whereas it binds to AFs through its C-terminal LIM domain. Together our data support that MLP contributes to the maintenance of cardiomyocyte cytoarchitecture by a mechanism involving its self-association and actin filament cross-linking. PMID:24934443

  13. Large diameter femoral heads on highly cross-linked polyethylene: minimum 3-year results.

    PubMed

    Geller, Jeffrey A; Malchau, Henrik; Bragdon, Charles; Greene, Meridith; Harris, William H; Freiberg, Andrew A

    2006-06-01

    Contemporary highly cross-linked polyethylenes have become the most widely used alternative bearing surfaces in total hip replacement and may be paired with large diameter femoral heads (> 32 mm) in patients considered to be at high risk for dislocation. We report on a prospective series of 42 patients (45 hips) who had total hip replacement using large diameter cobalt-chrome femoral heads articulating with a highly cross linked polyethylene after a minimum of 3 years followup (mean 3.3 years). At final followup, the final patient cohort showed excellent clinical results with no radiographic failures or episodes of loosening. There was no evidence of pelvic or femoral osteolysis. One patient sustained a dislocation due to a grossly malpositioned acetabular component necessitating early isolated acetabular revision. The average yearly steady state wear rate was -0.06 +/- 0.41 mm/year. The results of our short-term prospective series indicated total hip replacement with large femoral heads articulating with a highly cross linked polyethylene showed excellent wear characteristics and clinical results and could be considered in patients at increased risk for dislocation. PMID:16741475

  14. Mechanical and Thermal Properties of Cross-Linked Phenolic Resins Using Molecular Dynamics

    NASA Astrophysics Data System (ADS)

    Lawson, John; Monk, Joshua; Haskins, Justin; Bauschlicher, Charles

    2013-03-01

    To gain insight into the design of materials, it is valuable to understand how the chemical make-up at the nano-scale can influence the thermal and mechanical bulk properties. An atomistic computational study allows us to manipulate the structural make-up of individual phenolic chains as well as generate various cross-linked (or cured) systems. In this study, molecular dynamics simulations of bulk phenolic systems were performed with the software LAMMPS. An all-atom force field was chosen to investigate how the strength and thermal conductivity of the phenolic material varies as a function of the degree of cross-linking and chemical make-up of the phenolic chains. Small-scale mechanical tests were performed to compute various moduli for the phenolic systems above and below the glass transition at varied degrees of cross-linking. The thermal conductivity was obtained using the Green-Kubo approach for the virgin phenolic system as well as the strained systems.

  15. Charge regulation and energy dissipation while compressing and sliding a cross-linked chitosan hydrogel layer.

    PubMed

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

    2015-04-01

    Interactions between a silica surface and a surface coated with a grafted cross-linked hydrogel made from chitosan/PAA multilayers are investigated, utilizing colloidal probe atomic force microscopy. Attractive double-layer forces are found to dominate the long-range interaction over a broad range of pH and ionic strength conditions. The deduced potential at the hydrogel/aqueous interface is found to be very low. This situation is maintained in the whole pH-range investigated, even though the degree of protonation of chitosan changes significantly. This demonstrates that pH-variations change the concentration of counterions within the hydrogel to keep the interior close to uncharged, which is similar to what has been observed for polyelectrolyte brushes. Changes in pH and ionic strength affect the adhesion force and the friction force between the silica surface and the hydrogel layer, but not the friction coefficient. This suggests that the main energy dissipation mechanism arises from processes occurring within the hydrogel layer, rather than at the silica/hydrogel interface, and we suggest that it is related to stretching of polymer chains between the cross-linking points. We also find that an increased cross-linking density, from 40% to 100%, in the hydrogel reduces the friction coefficient. PMID:25553574

  16. Magnetoceramics from the bulk pyrolysis of polysilazane cross-linked by polyferrocenylcarbosilanes with hyperbranched topology.

    PubMed

    Kong, Jie; Kong, Minmin; Zhang, Xiaofei; Chen, Lixin; An, Linan

    2013-10-23

    In this contribution, we report a novel strategy for the synthesis of nanocrystal-containing magnetoceramics with an ultralow hysteresis loss by the pyrolysis of commercial polysilazane cross-linked with a functional metallopolymer possessing hyperbranched topology. The usage of hyperbranched polyferrocenylcarbosilane offers either enhanced ceramic yield or magnetic functionality of pyrolyzed ceramics. The ceramic yield was enhanced accompanied by a decreased evolution of hydrocarbons and NH3 because of the cross-linking of precursors and the hyperbranched cross-linker. The nucleation of Fe5Si3 from the reaction of iron atoms with Si-C-N amorphous phase promoted the formation of ?-Si3N4 and SiC crystals. After annealing at 1300 °C, stable Fe3Si crystals were generated from the transformation of the metastable Fe5Si3 phase. The nanocrystal-containing ceramics showed good ferromagnetism with an ultralow (close to 0) hysteresis loss. This method is convenient for the generation of tunable functional ceramics using a commercial polymeric precursor cross-linked by a metallopolymer with a designed topology. PMID:24060298

  17. In situ fabrication of cross-linked protein membranes by using microfluidics.

    PubMed

    Nair, Greeshma; Gargiuli, Joseph F; Shiju, N Raveendran; Rong, Zimei; Shapiro, Evgeniy; Drikakis, Dimitris; Vadgama, Pankaj

    2006-11-01

    We report a novel technique for preparing cross-linked protein membranes within microchannels by using an interfacial cross-linking reaction. Glass microchannels with a Y input were assembled by using a simple adhesive bonding technique to achieve dual, parallel laminar flows. Membrane formation utilised an interfacial reaction at the liquid-liquid interface, which involved bovine serum albumin (aqueous solution with a flow rate of 300 microL min(-1)) and terephthaloyl chloride (xylene solution with a flow rate of 700 microL min(-1)), to form thin ( approximately 25 microm) cross-linked films along the length of the channel under the continuous pressure-driven laminar flow. Such microfabricated membranes could extend the separation potential of any microfluidic structure to provide a stable barrier layer. Furthermore, degradation of the membrane was possible by using an alkali sodium dodecyl sulfate solution, which led to the complete disappearance of the membrane. These membranes could facilitate additional modification to allow for different permeability properties by controlled degradation. The one-step in situ membrane-fabrication methodology reported here generated precisely localised membranes and avoided the complexities of subcomponent assembly, which require complicated alignment of small, preformed membranes. This methodology could become the basis for sophisticated microseparation systems, biosensors and several "lab-on-a-chip" devices. PMID:17051656

  18. Optimizing performance in cross-linking negative-tone molecular resists

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

    Many different types of non-traditional resist designs have shown promise for future generations of patterning, but there is a greater need for understanding and developing additives and ancillary materials for these novel resists compared to traditional polymeric positive tone systems which are quite mature. With the goal of meeting some of these needs, we carried out multiple different studies of negative tone molecular resists based on epoxide cross-linking. We have developed methods for controlling cross-linking in these materials using photo-decomposable nucleophiles (PDNs) which have shown resolution improvements in one resist from 26 nm down to 18 nm so far. Aqueous base developed systems have been made by introducing phenol groups to these resists. Although the first molecule designed successfully patterns in aqueous base, its performance is limited compared to organic solvent development. A series of di-functional epoxide molecular resists have been made and generally show much worse sensitivity than a fourfunctional epoxide resist. Underlayers (ULs) have been designed specifically to leverage the high reactivity of epoxides to create ULs that can cross-link to the resist. These ULs improve the adhesion of some of these molecular resists, but also show significant sensitivity improvements compared to imaging on bare silicon. Sensitivity in one resist was improved by 5-12 mJ/cm2 simply by using the UL.

  19. Biomedical publications of Prof. David N. Nikogosyan, made in UCC UV-induced nucleic acid-protein cross-linking

    E-print Network

    Nikogosyan, David N.

    Biomedical publications of Prof. David N. Nikogosyan, made in UCC UV-induced nucleic acid-protein cross-linking 1. E.N. Dobrov, D.N. Nikogosyan: UV-induced nucleic acid-protein cross-linking: manual acids in collagen. J. Photochem. Photobiol. B: Biol., 47(1), 63-67 (1998) 2. D.N. Nikogosyan, H. Görner

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

    E-print Network

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

  1. Optimization of the efficiency of cross-linking PtII oligonucleotide phosphorothioate complexes to complementary oligonucleotides.

    PubMed Central

    Chu, B C; Orgel, L E

    1990-01-01

    We have investigated the efficiency with which PtII complexes cross-link phosphorothioates of oligonucleotides to complementary DNA targets. The A and G residues 2-5 bases downstream from the 5'-phosphorothioate group are preferred sites for cross-linking. Replacement of residues in this part of the target by T residues results in greatly decreased cross-linking when cis platinum diammine dichloride (cisPtII) or potassium platinous chloride (K2PtCl4) are used. Trans platinum diammine dichloride (transPtII) forms cross-links with T residues if A and G residues are absent from the susceptible region of the target. Oligomers containing an internal phosphorothioate group can also be linked to their templates with transPtII, but not with cisPtII or K2PtCl4. Cross-linking via an internal phosphorothioate group tends to be less efficient than cross-linking via a 5'-terminal phosphorothioate. The Sp isomers of internal phosphorothioates are cross-linked more efficiently than the Rp isomers. Preliminary experiments suggest that the efficiency of cross-linking to RNA targets will prove similar to that found for DNA targets. Images PMID:2402442

  2. The Torque of Rotary F-ATPase Can Unfold Subunit Gamma If Rotor and Stator Are Cross-Linked

    E-print Network

    Junge, Wolfgang

    cross-linked (via an engineered disulfide bridge) with the bearing, the rotary function of F1 persists an artificial disulfide bridge did not impair the rotary ATPase activity. We newly engineered three mutantsThe Torque of Rotary F-ATPase Can Unfold Subunit Gamma If Rotor and Stator Are Cross-Linked Florian

  3. Reduced ferulate cross link concentration is associated with improved fiber digestibility of corn stover at silage maturity

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Ferulate cross linking of lignin to arabinoxylan is correlated with fiber digestibility in perennial cool-season grasses; however, similar data have not been reported for warm-season grasses. Our objective was to determine if ferulate cross links are associated with fiber digestibility in corn stove...

  4. Polymer-additive extraction via pressurized fluids and organic solvents of variously cross-linked poly(methylmethacrylates).

    PubMed

    Nazem, N; Taylor, L T

    2002-04-01

    Variously cross-linked poly(methylmethacrylates) (PMMAs) are synthesized with three additives incorporated at theoretically 1000 microg of the additive per gram of prepared polymer. The additives are Irganox 1010, Irganox 1076, and Irgafos 168. The in-house" synthesized polyacrylates are then subjected to supercritical fluid extraction (SFE) to determine if additive recovery is a function of percent cross-linking. Although considerable work in this regard has been performed with non-cross-linked polyolefins, the literature is lacking regarding polyacrylates. Some additive degradation apparently occurs during the synthesis, as judged by the increased complexity of the extract high-performance liquid chromatographic trace and the low percent recoveries observed especially for the Irganoxes. For low polymer cross-linking (1%), it appears that both PMMA synthetic reproducibility and readily observed polymer swelling during SFE are serious issues that adversely affect additive percent recovery and precision of results. Higher percent cross-linking yields more consistent analytical data than low percent cross-linking, even though the amount of additive extracted in all PMMA samples (regardless of cross-linking percentage) is essentially the same whether the extraction is via SFE or liquid-solid extraction with methylene chloride. Results for comparably cross-linked poly(ethylmethacrylate) and poly(butylmethacrylate) are similar to PMMA. PMID:12004935

  5. Removal rate of ( sup 3 H)hyaluronan injected subcutaneously in rabbits

    SciTech Connect

    Reed, R.K.; Laurent, U.B.; Fraser, J.R.; Laurent, T.C. (Univ. of Bergen (Norway))

    1990-08-01

    Hyaluronan is an important constituent of the extracellular matrix in skin, and recent studies suggest that there is a pool of easily removable (free) hyaluronan drained by lymph. The removal rate of free hyaluronan in skin was measured from the elimination of ({sup 3}H)hyaluronan, injected subcutaneously in 13 rabbits. The removal of radioactivity was determined from appearance of {sup 3}H in plasma. During the first 24 h after injection, 10-87% of the tracer entered blood, less in injectates with high concentrations of hyaluronan. The removal was monoexponential with a half-life of 0.5-1 day when concentration of hyaluronan was 5 mg/ml or less. When hyaluronan concentration was 10 mg/ml or higher, the removal was slow for about 24 h and then became similar to that in experiments with low hyaluronan concentration. Free hyaluronan at physiological concentrations is thus turned over with the same rate as serum albumin, supporting the concept that hyaluronan is removed essentially by lymph flow to be degraded in lymph nodes and liver.

  6. Effects of chebulic acid on advanced glycation endproducts-induced collagen cross-links.

    PubMed

    Lee, Ji-Young; Oh, Jun-Gu; Kim, Jin Sook; Lee, Kwang-Won

    2014-01-01

    Advanced glycation end-products (AGEs) have been implicated in the development of diabetic complications. We report the antiglycating activity of chebulic acid (CA), isolated from Terminalia chebula on breaking the cross-links of proteins induced by AGEs and inhibiting the formation of AGEs. Aminoguanidine (AG) reduced 50% of glycated bovine serum albumin (BSA) with glycolaldehyde (glycol-BSA)-induced cross-links of collagen at a concentration of 67.8 ± 2.5 mM, the level of CA required for exerting a similar antiglycating activity was 38.8 ± 0.5 µM. Also, the breaking activity on collagen cross-links induced by glycol-BSA was potent with CA (IC50=1.46 ± 0.05 mM), exhibiting 50-fold stronger breaking activity than with ALT-711, a well-known cross-link breaker (IC50=72.2 ± 2.4 mM). IC50 values of DPPH· scavenging activity for CA and ascorbic acid (AA) were 39.2 ± 4.9 and 19.0 ± 1.2 µg dry matter (DM) mL(-1), respectively, and ferric reducing and antioxidant power (FRAP) activities for CA and AA were 4.70 ± 0.06 and 11.4 ± 0.1 mmol/FeSO4·7H2O/g DM, respectively. The chelating activities of CA, AG and ALT711 on copper-catalyzed oxidation of AA were compared, and in increasing order, ALT-711 (IC50 of 1.92 ± 0.20 mM)cross-linking, the activity of which may be explained in large part by its chelating and antioxidant activities, suggesting that CA may constitute a promising antiglycating candidate in intervening AGE-mediated diabetic complications. PMID:24759763

  7. The combination of hydrogen/deuterium exchange or chemical cross-linking techniques with mass spectrometry: mapping of human 14-3-3? homodimer interface.

    PubMed

    Haladová, Kate?ina; Mrázek, Hynek; Je?men, Tomáš; Halada, Petr; Man, Petr; Novák, Petr; Chmelík, Josef; Obšil, Tomáš; Šulc, Miroslav

    2012-07-01

    Hydrogen/deuterium (H/D) exchange or chemical cross-linking by soluble carbodiimide (EDC) was employed in combination with high-resolution mass spectrometry (MS) to extend our knowledge about contact surface regions involved in the well-characterized model of interaction between two molecules of human 14-3-3? regulatory protein. The H/D exchange experiment provided low resolution mapping of interaction in the homodimeric 14-3-3? complex. A lower level of deuteration, suggesting structural protection, of two sequential segments has been demonstrated for dimeric 14-3-3? wild type relative to the monomeric mutant 14-3-3? S58D. The N-terminal sequence (the first 27 residues) from one subunit interacts with region ?C'and ?D'-helices (residues 45-98) of the other molecule across the dimer interface. To identify interacting amino acid residues within the studied complex, a chemical cross-linking reaction was carried out to produce the covalent homodimer, which was detected by SDS-PAGE. The MS analysis (following tryptic in-gel digestion) employing both high resolution and tandem mass spectrometry revealed cross-linked amino acid residues. Two alternative salt bridges between Glu81 and either Lys9 or the N-terminal amino group have been found to participate in transient interactions of the 14-3-3? isotype homodimerization. The data obtained, which have never previously been reported, were used to modify the published 14-3-3 crystal structure using molecular modeling. Based on our findings, utilization of this combination of experimental approaches, which preserve protein native structures, is suitable for mapping the contact between two proteins and also allows for the description of transient interactions or of regions with flexible structure in the studied protein complexes. PMID:22580067

  8. Increase in local protein concentration by field-inversion gel electrophoresis

    Microsoft Academic Search

    Henghang Tsai; Teck Yew Low; Steve Freeby; Aran Paulus; Kalpana Ramnarayanan; Chung-pui Paul Cheng; Hon-chiu Eastwood Leung

    2007-01-01

    BACKGROUND: Proteins that migrate through cross-linked polyacrylamide gels (PAGs) under the influence of a constant electric field experience negative factors, such as diffusion and non-specific trapping in the gel matrix. These negative factors reduce protein concentrations within a defined gel volume with increasing migration distance and, therefore, decrease protein separation efficiency. Enhancement of protein separation efficiency was investigated by implementing

  9. Hyaluronan accumulates in demyelinated lesions and inhibits oligodendrocyte progenitor maturation

    Microsoft Academic Search

    Stephen A Back; Therese M F Tuohy; Hanqin Chen; Nicholas Wallingford; Andrew Craig; Jaime Struve; Ning Ling Luo; Fatima Banine; Ying Liu; Ansi Chang; Bruce D Trapp; Mahendra S Rao; Larry S Sherman

    2005-01-01

    Demyelination is the hallmark of numerous neurodegenerative conditions, including multiple sclerosis. Oligodendrocyte progenitors (OPCs), which normally mature into myelin-forming oligodendrocytes, are typically present around demyelinated lesions but do not remyelinate affected axons. Here, we find that the glycosaminoglycan hyaluronan accumulates in demyelinated lesions from individuals with multiple sclerosis and in mice with experimental autoimmune encephalomyelitis. A high molecular weight (HMW)

  10. Molecular characteristics of some commercial high-molecular-weight hyaluronans.

    PubMed

    Soltés, L; Mendichi, R; Lath, D; Mach, M; Bakos, D

    2002-10-01

    Commercially available hyaluronan (HA) samples were investigated by the method of size exclusion chromatography (SEC). The fractions eluted from the SEC column were on-line molecularly characterized by using a multi-angle laser light scattering (MALLS) photometer. Along with the SEC-MALLS technique, the high-molecular-weight HA biopolymers were (off-line) analyzed by capillary viscometry. PMID:12378558

  11. Microelectromechanics of ionic polymeric gels as synthetic robotic muscles

    Microsoft Academic Search

    Mohsen Shahinpoor

    1994-01-01

    An ionic polymeric gel is defined as a 3-D charged network of a cross-linked macromolecular polyelectrolyte capable of collapsing or swelling in an acidic or alkaline environment, respectively, purely due to pH changes. Fixed electrical charges reside at all cross-links in such macromolecular networks in the presence of wandering mobile charges that tend to change their spatial distribution within the

  12. Intra-articular hyaluronan injections in the treatment of osteoarthritis of the knee: a randomised, double blind, placebo controlled multicentre trial. Hyaluronan Multicentre Trial Group

    Microsoft Academic Search

    L S Lohmander; N Dalén; G Englund; M Hämäläinen; E M Jensen; K Karlsson; M Odensten; L Ryd; I Sernbo; O Suomalainen; A Tegnander

    1996-01-01

    OBJECTIVE: To assess the effects of intra-articular injections of hyaluronan on symptoms of knee osteoarthritis (OA). METHODS: Two hundred and forty patients with symptomatic, radiological knee OA were randomly assigned to treatment with weekly injections for five weeks with either 25 mg of high molecular weight hyaluronan or vehicle. Results were evaluated at weeks 1, 2, 3, 4, 5, 13,

  13. “Zero-length” Cross-linking in Solid State as an Approach for Analysis of Protein -Protein Interactions

    SciTech Connect

    Elshafey, Ahmed; Tolic, Nikola; Young, Malin M.; Sale, Kenneth L.; Smith, Richard D.; Kery, Vladimir

    2006-03-01

    Analyzing the architecture of protein complexes is a difficult task. Chemical cross-linking is often used in combination with mass spectrometric analysis to elucidate the interaction interfaces between proteins. We have developed a new approach for the analysis of interacting interfaces in protein complexes based on cross-linking in the solid state. Protein complexes are freeze-dried under vacuum and cross-links are introduced in the solid phase by dehydrating the protein in a non-water solvent, thus, creating peptide bonds between amino and carboxyl groups of the interacting peptides. Cross-linked proteins are digested into peptides with trypsin in both H216O and H218O and then readily distinguished in mass spectra by characteristic 8 atomic mass unit (amu) shifts reflecting incorporation of two 18O atoms into each C-terminus of proteolytic peptides. Computer analysis of mass spectrometry (MS) and MS/MS data is used to identify the cross-linked peptides.We demonstrated our method by cross-linking homooligomeric protein complexes alone or in a mixture of many other proteins. Cross-linking in the solid state was shown to be specific and reproducible. Glutathione-S-transferase (GST) from Schistosoma japonicum was studied in more detail. Twenty-seven unique intra-molecular and two inter-molecular cross-linked peptides were identified using tryptic mapping followed by LTQ-MS analysis. Identified cross-links were predominantly of amide origin, but six esters and thioesters were also found. Identified cross-linked peptides were validated by computational (visualization of cross-links in the three-dimensional [3D] structure of GST) and experimental (MS/MS) analyses. Most of the identified cross-links matched interacting peptides in the native 3D structure of GST indicating that the structure of GST and its oligomeric complex remained primarily intact after freeze drying. The pattern of oligomeric GST obtained in solid state was the same as that obtained in solution by Ru(II)Bpy32+ catalyzed, oxidative ?zero-length? cross-linking, confirming that it is feasible to use our strategy for analyzing the molecular interfaces of interacting proteins or peptides.

  14. Investigation of different cell types and gel carriers for cell-based intervertebral disc therapy, in vitro and in vivo studies.

    PubMed

    Henriksson, H B; Hagman, M; Horn, M; Lindahl, A; Brisby, H

    2012-10-01

    Biological treatment options for the repair of intervertebral disc damage have been suggested for patients with chronic low back pain. The aim of this study was to investigate possible cell types and gel carriers for use in the regenerative treatment of degenerative intervertebral discs (IVD). In vitro: human mesenchymal cells (hMSCs), IVD cells (hDCs), and chondrocytes (hCs) were cultivated in three gel types: hyaluronan gel (Durolane®), hydrogel (Puramatrix®), and tissue-glue gel (TISSEEL®) in chondrogenic differentiation media for 9?days. Cell proliferation and proteoglycan accumulation were evaluated with microscopy and histology. In vivo: hMSCs or hCs and hyaluronan gel were co-injected into injured IVDs of six minipigs. Animals were sacrificed at 3 or 6?months. Transplanted cells were traced with anti-human antibodies. IVD appearance was visualized by MRI, immunohistochemistry, and histology. Hyaluronan gel induced the highest cell proliferation in vitro for all cell types. Xenotransplanted hMSCs and hCs survived in porcine IVDs for 6?months and produced collagen II in all six animals. Six months after transplantation of cell/gel, pronounced endplate changes indicating severe IVD degeneration were observed at MRI in 1/3 hC/gel, 1/3 hMSCs/gel and 1/3 gel only injected IVDs at MRI and 1/3?hMSC/gel, 3/3?hC/gel, 2/3 gel and 1/3 injured IVDs showed positive staining for bone mineralization. In 1 of 3 discs receiving hC/gel, in 1 of 3 receiving hMSCs/gel, and in 1 of 3 discs receiving gel alone. Injected IVDs on MRI results in 1 of 3 hMSC/gel, in 3 of 3 hC/gel, in 2 of 3 gel, and in 1 of 3 injured IVDs animals showed positive staining for bone mineralization. The investigated hyaluronan gel carrier is not suitable for use in cell therapy of injured/degenerated IVDs. The high cell proliferation observed in vitro in the hyaluronan could have been a negative factor in vivo, since most cell/gel transplanted IVDs showed degenerative changes at MRI and positive bone mineralization staining. However, this xenotransplantation model is valuable for evaluating possible cell therapy strategies for human degenerated IVDs. Copyright © 2011 John Wiley & Sons, Ltd. PMID:22072598

  15. Extracellular processing of the cartilage proteoglycan aggregate and its effect on CD44-mediated internalization of hyaluronan.

    PubMed

    Danielson, Ben T; Knudson, Cheryl B; Knudson, Warren

    2015-04-10

    In many cells hyaluronan receptor CD44 mediates the endocytosis of hyaluronan and its delivery to endosomes/lysosomes. The regulation of this process remains largely unknown. In most extracellular matrices hyaluronan is not present as a free polysaccharide but often is found in complex with other small proteins and macromolecules such as proteoglycans. This is especially true in cartilage, where hyaluronan assembles into an aggregate structure with the large proteoglycan termed aggrecan. In this study when purified aggrecan was added to FITC-conjugated hyaluronan, no internalization of hyaluronan was detected. This suggested that the overall size of the aggregate prevented hyaluronan endocytosis and furthermore that proteolysis of the aggrecan was a required prerequisite for local, cell-based turnover of hyaluronan. To test this hypothesis, limited C-terminal digestion of aggrecan was performed to determine whether a size range of aggrecan exists that permits hyaluronan endocytosis. Our data demonstrate that only limited degradation of the aggrecan monomer was required to allow for hyaluronan internalization. When hyaluronan was combined with partially degraded, dansyl chloride-labeled aggrecan, blue fluorescent aggrecan was also visualized within intracellular vesicles. It was also determined that sonicated hyaluronan of smaller molecular size was internalized more readily than high molecular mass hyaluronan. However, the addition of intact aggrecan to hyaluronan chains sonicated for 5 and 10 s reblocked their endocytosis, whereas aggregates containing 15-s sonicated hyaluronan were internalized. These data suggest that hyaluronan endocytosis is regulated in large part by the extracellular proteolytic processing of hyaluronan-bound proteoglycan. PMID:25733665

  16. Formation and genotoxicity of a guanine–cytosine intrastrand cross-link lesion in vivo

    PubMed Central

    Hong, Haizheng; Cao, Huachuan; Wang, Yinsheng

    2007-01-01

    Reactive oxygen species (ROS) can be induced by both endogenous and exogenous processes, and they can damage biological molecules including nucleic acids. Exposure of isolated DNA to X/?-rays and Fenton reagents was shown to lead to the formation of intrastrand cross-link lesions where the neighboring nucleobases in the same DNA strand are covalently bonded. By employing HPLC coupled with tandem mass spectrometry (LC-MS/MS) with the isotope dilution method, we assessed quantitatively the formation of a guanine–cytosine (G[8-5]C) intrastrand cross-link lesion in HeLa-S3 cells upon exposure to ?-rays. The yield of the G[8-5]C cross-link was 0.037 lesions per 109 nucleosides per Gy, which was ?300 times lower than that of 5-formyl-2?-deoxyuridine (0.011 lesions per 106 nucleosides per Gy) under identical exposure conditions. We further constructed a single-stranded M13 genome harboring a site-specifically incorporated G[8-5]C lesion and developed a novel mass spectrometry-based method for interrogating the products emanating from the replication of the genome in Escherichia coli cells. The results demonstrated that G[8-5]C blocked considerably DNA replication as represented by a 20% bypass efficiency, and the lesion was significantly mutagenic in vivo, which included a 8.7% G?T and a 1.2% G?C transversion mutations. DNA replication in E. coli hosts deficient in SOS-induced polymerases revealed that polymerase V was responsible for the error-prone translesion synthesis in vivo. PMID:17942427

  17. Block Copolymer Cross-linked Nanoassemblies Improve Particle Stability and Biocompatibility of Superparamagnetic Iron Oxide Nanoparticles

    PubMed Central

    Dan, Mo; Scott, Daniel F.; Hardy, Peter A.; Wydra, Robert J.; Hilt, J. Zach; Yokel, Robert A.; Bae, Younsoo

    2014-01-01

    Purpose To develop cross-linked nanoassemblies (CNAs) as carriers for superparamagnetic iron oxide nanoparticles (IONPs). Methods Ferric and ferrous ions were co-precipitated inside core-shell type nanoparticles prepared by cross-linking poly(ethylene glycol)-poly(aspartate) block copolymers to prepare CNAs entrapping Fe3O4 IONPs (CNA-IONPs). Particle stability and biocompatibility of CNA-IONPs were characterized in comparison to citrate-coated Fe3O4 IONPs (Citrate-IONPs). Results CNA-IONPs, approximately 30 nm in diameter, showed no precipitation in water, PBS, or a cell culture medium after 3 or 30 h, at 22, 37, and 43 °C, and 1, 2.5, and 5 mg/mL, whereas Citrate-IONPs agglomerated rapidly (> 400 nm) in all aqueous media tested. No cytotoxicity was observed in a mouse brain endothelial-derived cell line (bEnd.3) exposed to CNA-IONPs up to 10 mg/mL for 30 h. Citrate-IONPs (> 0.05 mg/mL) reduced cell viability after 3 h. CNA-IONPs retained the superparamagnetic properties of entrapped IONPs, enhancing T2-weighted magnetic resonance images (MRI) at 0.02 mg/mL, and generating heat at a mild hyperthermic level (40 ~ 42 °C) with an alternating magnetic field (AMF). Conclusion Compared to citric acid coating, CNAs with a cross-linked anionic core improved particle stability and biocompatibility of IONPs, which would be beneficial for future MRI and AMF-induced remote hyperthermia applications. PMID:23080062

  18. Stabilization of dentin matrix after cross-linking treatments, in vitro

    PubMed Central

    Scheffel, Débora L.S.; Hebling, Josimeri; Scheffel, Régis H.; Agee, Kelli A.; Cadenaro, Milena; Turco, Gianluca; Breschi, Lorenzo; Mazzoni, Annalisa; de Souza Costa, Carlos A.; Pashley, David H.

    2014-01-01

    Objectives To evaluate the effect of EDC on elastic modulus (E), MMPs activity, hydroxyproline (HYP) release and thermal denaturation temperature of demineralized dentin collagen. Methods Dentin beams were obtained from human molars and completely demineralized in 10 wt% H3PO4 for 18 h. The initial E and MMP activity were determined with three-point bending and microcolorimetric assay, respectively. Extra demineralized beams were dehydrated and the initial dry mass (DM) was determined. All the beams were distributed into groups (n = 10) and treated for 30 s or 60 s with: water, 0.5 M, 1 M or 2 M EDC or 10% glutaraldehyde (GA). After treatment, the new E and MMP activity were redetermined. The beams submitted to DM measurements were storage for 1 week in artificial saliva, after that the mass loss and HYP release were evaluated. The collagen thermal denaturation temperature (TDT) was determined by DSC analysis. Data for E, MMP activity and HYP release were submitted to Wilcoxon and Kruskal–Wallis or Mann–Whitney tests. Mass loss and TDT data were submitted to ANOVA and Tukey tests at the 5% of significance. Results EDC was able to significantly increase collagen stiffness in 60 s. 10% GA groups obtained the highest E values after both 30 and 60 s. All cross-linking agents decreased MMP activity and HYP release and increased TDT temperature. Significant differences were identified among EDC groups after 30 or 60 s of cross-linking, 1 M or 2 M EDC showed the lowest MMP activity. Significance Cross-linking agents are capable of preventing dentin collagen degradation. EDC treatment may be clinically useful to increase resin-dentin stability. PMID:24332989

  19. Epoxy Cross-Linked Collagen and Collagen-Laminin Peptide Hydrogels as Corneal Substitutes

    PubMed Central

    Koh, Li Buay; Islam, Mohammad Mirazul; Mitra, Debbie; Noel, Christopher W.; Merrett, Kimberley; Odorcic, Silvia; Fagerholm, Per; Jackson, William. Bruce; Liedberg, Bo; Phopase, Jaywant; Griffith, May

    2013-01-01

    A bi-functional epoxy-based cross-linker, 1,4-Butanediol diglycidyl ether (BDDGE), was investigated in the fabrication of collagen based corneal substitutes. Two synthetic strategies were explored in the preparation of the cross-linked collagen scaffolds. The lysine residues of Type 1 porcine collagen were directly cross-linked using l,4-Butanediol diglycidyl ether (BDDGE) under basic conditions at pH 11. Alternatively, under conventional methodology, using both BDDGE and 1-Ethyl-3-(3-dimethyl aminopropyl) carbodiimide (EDC)/N-hydroxysuccinimide (NHS) as cross-linkers, hydrogels were fabricated under acidic conditions. In this latter strategy, Cu(BF4)2·XH2O was used to catalyze the formation of secondary amine bonds. To date, we have demonstrated that both methods of chemical cross-linking improved the elasticity and tensile strength of the collagen implants. Differential scanning calorimetry and biocompatibility studies indicate comparable, and in some cases, enhanced properties compared to that of the EDC/NHS controls. In vitro studies showed that human corneal epithelial cells and neuronal progenitor cell lines proliferated on these hydrogels. In addition, improvement of cell proliferation on the surfaces of the materials was observed when neurite promoting laminin epitope, IKVAV, and adhesion peptide, YIGSR, were incorporated. However, the elasticity decreased with peptide incorporation and will require further optimization. Nevertheless, we have shown that epoxy cross-linkers should be further explored in the fabrication of collagen-based hydrogels, as alternatives to or in conjunction with carbodiimide cross-linkers. PMID:24956085

  20. Cross-linking in the silks of bees, ants and hornets.

    PubMed

    Campbell, Peter M; Trueman, Holly E; Zhang, Qiang; Kojima, Katsura; Kameda, Tsunenori; Sutherland, Tara D

    2014-05-01

    Silk production is integral to the construction of nests or cocoons for many Aculeata, stinging Hymenopterans such as ants, bees and wasps. Here we report the sequences of new aculeate silk proteins and compare cross-linking among nine native silks from three bee species (Apis mellifera, Bombus terrestris and Megachile rotundata), three ant species (Myrmecia forficata, Oecophylla smaragdina and Harpegnathos saltator) and three hornets (Vespa analis, Vespa simillima and Vespa mandarinia). The well studied silks of spiders and silkworms are comprised of large proteins that are cross-linked and stabilized predominantly by intra and intermolecular beta sheet structure. In contrast, the aculeate silks are comprised of relatively small proteins that contain central coiled coil domains and comparatively reduced amounts of beta sheet structure. The hornet silks, which have the most beta sheet structure and the greatest amount of amino acid sequence outside the coiled-coil domains, dissolve in concentrated LiBr solution and appear to be stabilized predominantly by beta sheet structure like the classic silks. In contrast, the ant and bee silks, which have less beta sheet and less sequence outside the coiled-coil domains, could not be dissolved in LiBr and appear to be predominantly stabilized by covalent cross-linking. The iso-peptide cross-linker, ?-(?-glutamyl)-lysine that is produced by transglutaminase enzymes, was demonstrated to be present in all silks by mass spectrometry, but at greater levels in silks of ants and bees. The bee silks and ant cocoons, but not the Oecophylla nest silks, appeared to be further stabilized by tanning reactions. PMID:24607851

  1. Multinuclear NMR and Kinetic Analysis of DNA Interstrand Cross-link Formation

    PubMed Central

    Ding, Hui; Majumdar, Ananya; Tolman, Joel R.; Greenberg, Marc M.

    2009-01-01

    Recently, a phenyl selenyl modified thymidine (2) was shown to produce DNA interstrand cross-links (ICLs) via two mechanisms. Photolysis of 2 generates 5-(2?-deoxyuridinyl)methyl radical (1), the reactive intermediate that results from formal hydrogen atom abstraction from the thymine methyl group. This reactive intermediate reacts with the opposing dA, and is the first example of a DNA radical to produce ICLs. Kinetic competition studies described below support the proposal that the rate limiting step in ICL formation from 1 involves rotation about the glycosidic bond, and that the rate constant for this process is influenced by flanking sequence. Cross-links also form with the opposing dA when 2 is treated with mild oxidants that result in the formation of an intermediate methide-like species (4). Kinetic experiments described below reveal that 4 reacts with azide, a model nucleophile, via a SN2? pathway. Previous experiments suggested that the same product is produced via 1 or 4, but that the initially formed cross-link rearranges during the enzyme digestion and isolation procedures. In situ product analysis by NMR using synthetic, doubly labeled duplex DNA containing 13C-2 and 15N1-dA provides definitive evidence that the kinetic ICL product formed via the radical and oxidative pathways is the same and corresponds to that arising from formal alkylation of N1-dA. Furthermore, analysis of the thermodynamic product formed upon rearrangement indicates that the primary product isomerizes via an associative mechanism in DNA. PMID:19053196

  2. Disruption of heme-peptide covalent cross-linking in mammalian peroxidases by hypochlorous acid.

    PubMed

    Abu-Soud, Husam M; Maitra, Dhiman; Shaeib, Faten; Khan, Sana N; Byun, Jaeman; Abdulhamid, Ibrahim; Yang, Zhe; Saed, Ghassan M; Diamond, Michael P; Andreana, Peter R; Pennathur, Subramaniam

    2014-11-01

    Myeloperoxidase (MPO), lactoperoxidase (LPO) and eosinophil peroxidase (EPO) play a central role in oxidative damage in inflammatory disorders by utilizing hydrogen peroxide and halides/pseudo halides to generate the corresponding hypohalous acid. The catalytic sites of these enzymes contain a covalently modified heme group, which is tethered to the polypeptide chain at two ester linkages via the methyl group (MPO, EPO and LPO) and one sulfonium bond via the vinyl group (MPO only). Covalent cross-linking of the catalytic site heme to the polypeptide chain in peroxidases is thought to play a protective role, since it renders the heme moiety less susceptible to the oxidants generated by these enzymes. Mass-spectrometric analysis revealed the following possible pathways by which hypochlorous acid (HOCl) disrupts the heme-protein cross-linking: (1) the methyl-ester bond is cleaved to form an alcohol; (2) the alcohol group undergoes an oxygen elimination reaction via the formation of an aldehyde intermediate or undergoes a demethylation reaction to lose the terminal CH2 group; and (3) the oxidative cleavage of the vinyl-sulfonium linkage. Once the heme moiety is released it undergoes cleavage at the carbon-methyne bridge either along the ?-? or a ?-? axis to form different pyrrole derivatives. These results indicate that covalent cross-linking is not enough to protect the enzymes from HOCl mediated heme destruction and free iron release. Thus, the interactions of mammalian peroxidases with HOCl modulates their activity and sets a stage for initiation of the Fenton reaction, further perpetuating oxidative damage at sites of inflammation. PMID:25193127

  3. Biocompatible hydrogels based on hyaluronic acid cross-linked with a polyaspartamide derivative as delivery systems for epithelial limbal cells.

    PubMed

    Fiorica, Calogero; Senior, Richard A; Pitarresi, Giovanna; Palumbo, Fabio Salvatore; Giammona, Gaetano; Deshpande, Pallavi; MacNeil, Sheila

    2011-07-29

    The aim of this work was to evaluate the potential use of hydrogels based on hyaluronic acid (HA) chemically cross-linked with ?,?-poly(N-2-hydroxyethyl) (2-aminoethylcarbamate)-D,L-aspartamide (PHEA-EDA) as substitutes for the amniotic membrane able to release limbal cells for corneal regeneration. Hydrogels, shaped as films, with three different molar ratios (X) between PHEA-EDA and HA (X = 0.5, 1.0 and 1.5) have been investigated. First, it has been evaluated their swelling ability, hydrolytic resistance in simulated physiological fluid and cell compatibility by using human dermal fibroblasts chosen as a model cell line. Then adhesion studies in comparison with collagen gel, have been performed by using immortalized cells, such as human corneal epithelial cells (HCEC) or primary cells, such as rabbit limbal epithelial cells (RLEC) and/or rabbit limbal fibroblasts (RLF). HA/PHEA-EDA hydrogels allow a moderate/poor adhesion of all investigated cells thus suggesting their potential ability to act as cell delivery systems. Finally, commercial contact lenses have been coated, in their inner surface, with each HA/PHEA-EDA film and it has been found that in these conditions, a greater cell adhesion occurs, particularly when RLEC are in co-culture with RLF. However, this adhesion is only transitory, in fact after three days, viable cells are released in the culture medium thus suggesting a potential application of HA/PHEA-EDA hydrogels, for delivering limbal cells in the treatment of corneal damage. PMID:21596121

  4. Cytocompatible cross-linking of electrospun zein fibers for the development of water-stable tissue engineering scaffolds.

    PubMed

    Jiang, Qiuran; Reddy, Narendra; Yang, Yiqi

    2010-10-01

    This paper reports a new method of cross-linking electrospun zein fibers using citric acid as a non-toxic cross-linker to enhance the water stability and cytocompatibility of zein fibers for tissue engineering and other medical applications. The electrospun structure has many advantages over other types of structures and protein-based biomaterials possess unique properties preferred for tissue engineering and other medical applications. However, ultrafine fiber matrices developed from proteins have poor mechanical properties and morphological stability in the aqueous environments required for medical applications. Efforts have been made to improve the water stability of electrospun protein scaffolds using cross-linking and other approaches, but the current methods have major limitations, such as cytotoxicity and low efficiency. In this research electrospun zein fibers were cross-linked with citric acid without using any toxic catalysts. The stability of the cross-linked fibers in phosphate-buffered saline and their ability to support the attachment, spreading and proliferation of mouse fibroblast cells were studied. The cross-linked electrospun fibers retained their ultrafine fibrous structure even after immersion in PBS at 37 degrees C for up to 15 days. Citric acid cross-linked electrospun zein scaffolds showed better attachment, spreading and proliferation of fibroblast cells than uncross-linked electrospun zein fibers, cross-linked zein films and electrospun polylactide fibers. PMID:20438870

  5. The measurement of rheological characteristics of cross-linked fracturing fluids using a pipe viscometer 

    E-print Network

    Tiainen, Ari Lauri

    1986-01-01

    of Rheologics1 Characteristics of Cross-Linked ~ing Fluids Using s pipe Visccmetm. (Deoanber 1986) Ari Lsuri ~, B. S. , Pari. 's Technical University Chairman of Advisory Committee: Dr, S. A. Eolditch In low perme~ty re~s the usual need for long hydraulic... fractures necessitates the use of hi. gh viscosity fluids to create wide fractures and sdectuately transport high strength proppants long distances i. nto the fracture. Smaller tuhing in deeper wells sub)sets the fluid to high mixing shear rates when...

  6. Rapid generation of dityrosine cross-linked A? oligomers via Cu-redox cycling.

    PubMed

    Gunn, Adam P; Roberts, Blaine R; Bush, Ashley I

    2012-01-01

    There is a great interest in the role of free radicals and oxidative stress in Alzheimer's disease and for the role of transition metals in the generation of oligomers of A? peptides. In the literature, there are a multitude of varying methods that can be used to create soluble oligomers of A?, however, the processes that create these oligomers are often stochastic by nature and thus reproducibility is an issue. Here we report a simple and reproducible method for the production of radically derived dityrosine cross-linked oligomers of A?, through reaction with copper and ascorbic acid. PMID:22528079

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

    PubMed Central

    Jensen, Erik A.; Allen, Benjamin D.; Kishi, Yoshito

    2008-01-01

    Low temperature NMR experiments and molecular modeling have been used to characterize the conformational behavior of a covalently cross-linked DNA base pair model. The data suggest that Watson-Crick or reverse Watson-Crick hydrogen bonding geometries have similar energies and can interconvert at low temperatures. This low-temperature process involves rotation about the crosslink CH2–C(5?) (?) carbon-carbon bond, which is energetically preferred over the alternate CH2–N(3) (?) carbon-nitrogen bond rotation. PMID:18706810

  8. Equilibrium and kinetic modeling of adsorption of reactive dye on cross-linked chitosan beads

    Microsoft Academic Search

    Ming-Shen Chiou; Hsing-Ya Li

    2002-01-01

    The adsorption of reactive dye (Reactive Red 189) from aqueous solutions on cross-linked chitosan beads was studied in a batch system. The equilibrium isotherms at different particle sizes (2.3–2.5, 2.5–2.7 and 3.5–3.8mm) and the kinetics of adsorption with respect to the initial dye concentration (4320, 5760 and 7286g\\/m3), temperature (30, 40 and 50°C), pH (1.0, 3.0, 6.0 and 9.0), and

  9. Block ionomer complex micelles with cross-linked cores for drug delivery

    Microsoft Academic Search

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

    2009-01-01

    Soft polymeric nanomaterials were synthesized by template-assisted method involving condensation of the poly(ethylene oxide)-b-polycarboxylate\\u000a anions by metal ions into core-shell block ionomer complex micelles followed by chemical cross-linking of the polyion chains\\u000a in the micelle cores. The resulting materials represent nanogels and are capable of swelling in a pH-dependent manner. The\\u000a structural determinants that guide the self-assembly of the initial

  10. Electrospray low energy CID and MALDI PSD fragmentations of protonated sulfinamide cross-linked peptides

    Microsoft Academic Search

    Mark J. Raftery; Carolyn L. Geczy

    2002-01-01

    Murine S100A8 (A8) is a major cytoplasmic neutrophil protein and is converted to novel oxidation products containing Cys-?\\u000a amino-Lys sulfinamide cross-links and Met-sulfoxide by the neutrophil oxidant HOCl. Seven products were separated using RP-HPLC,\\u000a with electros-pray ionization mass spectrometry (ESI-MS) masses after deconvolution of 10,354, 10,388, ±1, and 20,707, ±3\\u000a Da, and all were resistant to reduction by dithiothreitol. The

  11. In vitro degradation of dermal sheep collagen cross-linked using a water-soluble carbodiimide

    Microsoft Academic Search

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

    1996-01-01

    Bacterial collagenase was used to study the susceptibility of dermal sheep collagen (DSC) crosslinked with a mixture of the water-soluble carbodiimide 1-ethyl-3-(3-dimethyl aminopropyl)-carbodiimide hydrochloride and N-hydroxysuccinimide (E\\/N-DSC) towards enzymatic degradation. Contrary to non-cross-linked DSC (N-DSC), which had a rate of weight-loss of 18.1% per hour upon degradation, no weight loss was observed for E\\/N-DSC during a 24 h degradation period.

  12. Successive epoxy and carbodiimide cross-linking of dermal sheep collagen

    Microsoft Academic Search

    Raymond Zeeman; Pieter J. Dijkstra; Pauline B. van Wachem; Marja J. A. van Luyn; Marc Hendriks; Patrick T. Cahalan; Jan Feijen

    1999-01-01

    Cross-linking of dermal sheep collagen (N-DSC, Ts=46°C, numberofaminegroups=31(n\\/1000)) with 1,4-butanediol diglycidyl ether (BDDGE) at pH 9.0 resulted in a material (BD90) with a high Ts(69°C), a decreased number of amine groups of 15 (n\\/1000) and a high resistance towards collagenase and pronase degradation. Reaction of DSC with BDDGE at pH 4.5 yielded a material (BD45) with a Ts of 64°C,

  13. Single-molecule analysis of DNA cross-links using nanopore technology

    NASA Astrophysics Data System (ADS)

    Wolna, Anna H.

    The alpha-hemolysin (alpha-HL) protein ion channel is a potential next-generation sequencing platform that has been extensively used to study nucleic acids at a single-molecule level. After applying a potential across a lipid bilayer, the imbedded alpha-HL allows monitoring of the duration and current levels of DNA translocation and immobilization. Because this method does not require DNA amplification prior to sequencing, all the DNA damage present in the cell at any given time will be present during the sequencing experiment. The goal of this research is to determine if these damage sites give distinguishable current levels beyond those observed for the canonical nucleobases. Because DNA cross-links are one of the most prevalent types of DNA damage occurring in vivo, the blockage current levels were determined for thymine-dimers, guanine(C8)-thymine(N3) cross-links and platinum adducts. All of these cross-links give a different blockage current level compared to the undamaged strands when immobilized in the ion channel, and they all can easily translocate across the alpha-HL channel. Additionally, the alpha-HL nanopore technique presents a unique opportunity to study the effects of DNA cross-links, such as thymine-dimers, on the secondary structure of DNA G-quadruplexes folded from the human telomere sequence. Using this single-molecule nanopore technique we can detect subtle structural differences that cannot be easily addressed using conventional methods. The human telomere plays crucial roles in maintaining genome stability. In the presence of suitable cations, the repetitive 5'-TTAGGG human telomere sequence can fold into G-quadruplexes that adopt the hybrid fold in vivo. The telomere sequence is hypersensitive to UV-induced thymine-dimer (T=T) formation, and yet the presence of thymine dimers does not cause telomere shortening. The potential structural disruption and thermodynamic stability of the T=T-containing natural telomere sequences were studied to understand how this damage is tolerated in telomeric DNA. The alpha-HL experiments determined that T=Ts disrupt double-chain reversal loop formation but are well tolerated in edgewise and diagonal loops of the hybrid G-quadruplexes. These studies demonstrated the power of the alpha-HL ion channel to analyze DNA modifications and secondary structures at a single-molecule level.

  14. Stability of cross-linked acetic acid lignin-containing polyurethane

    Microsoft Academic Search

    Haihua WangYonghao; Yonghao Ni; M. Sarwar Jahan; Zehua Liu; Thioni Schafer

    2011-01-01

    The thermo-oxidative stability of acetic acid lignin-containing polyurethane (LPU) that contains cross-linking agents, such\\u000a as 1-aminopropyltriethoxy-silane (APTS) and\\/or trimethylolpropane (TMP) was investigated based on the thermogravimetric analysis\\u000a (TGA) method, their kinetic parameters in the thermo-oxidative process was determined. FT-IR certified the occurrence of interaction\\u000a between lignin and polyurethane (PU). It was found that continuous membrane can be formed when lignin

  15. Novel Genipin-Cross-Linked Chitosan\\/Silk Fibroin Sponges for Cartilage Engineering Strategies

    Microsoft Academic Search

    Simone S. Silva; Antonella Motta; Ma?rcia T. Rodrigues; Ana F. M. Pinheiro; Manuela E. Gomes; Joa?o F. Mano; Rui L. Reis; Claudio Migliaresi

    2008-01-01

    The positive interaction of materials with tissues is an important step\\u000d\\u000a in regenerative medicine strategies. Hydrogels that are obtained from\\u000d\\u000a polysaccharides and proteins are expected to mimic the natural cartilage\\u000d\\u000a environment and thus provide an optimum milleu for tissue growth and\\u000d\\u000a regeneration. In this work, novel hydrogels composed of blends of\\u000d\\u000a chitosan and Bombyx mori silk fibroin were cross-linked with

  16. Spatial characterization of corneal biomechanical properties with optical coherence elastography after UV cross-linking

    PubMed Central

    Twa, Michael D.; Li, Jiasong; Vantipalli, Srilatha; Singh, Manmohan; Aglyamov, Salavat; Emelianov, Stanislav; Larin, Kirill V.

    2014-01-01

    Corneal collagen cross-linking (CXL) is a clinical treatment for keratoconus that structurally reinforces degenerating ocular tissue, thereby limiting disease progression. Clinical outcomes would benefit from noninvasive methods to assess tissue material properties in affected individuals. Regional variations in tissue properties were quantified before and after CXL in rabbit eyes using optical coherence elastography (OCE) imaging. Low-amplitude (<1µm) elastic waves were generated using micro air-pulse stimulation and the resulting wave amplitude and speed were measured using phase-stabilized swept-source OCE. OCE imaging following CXL treatment demonstrates increased corneal stiffness through faster elastic wave propagation speeds and lower wave amplitudes. PMID:24877005

  17. Influence of cross-link structure, density and mechanical properties in the mesoscale deformation mechanisms of collagen fibrils.

    PubMed

    Depalle, Baptiste; Qin, Zhao; Shefelbine, Sandra J; Buehler, Markus J

    2014-07-29

    Collagen is a ubiquitous protein with remarkable mechanical properties. It is highly elastic, shows large fracture strength and enables substantial energy dissipation during deformation. Most of the connective tissue in humans consists of collagen fibrils composed of a staggered array of tropocollagen molecules, which are connected by intermolecular cross-links. In this study, we report a three-dimensional coarse-grained model of collagen and analyze the influence of enzymatic cross-links on the mechanics of collagen fibrils. Two representatives immature and mature cross-links are implemented in the mesoscale model using a bottom-up approach. By varying the number, type and mechanical properties of cross-links in the fibrils and performing tensile test on the models, we systematically investigate the deformation mechanisms of cross-linked collagen fibrils. We find that cross-linked fibrils exhibit a three phase behavior, which agrees closer with experimental results than what was obtained using previous models. The fibril mechanical response is characterized by: (i) an initial elastic deformation corresponding to the collagen molecule uncoiling, (ii) a linear regime dominated by molecule sliding and (iii) the second stiffer elastic regime related to the stretching of the backbone of the tropocollagen molecules until the fibril ruptures. Our results suggest that both cross-link density and type dictate the stiffness of large deformation regime by increasing the number of interconnected molecules while cross-links mechanical properties determine the failure strain and strength of the fibril. These findings reveal that cross-links play an essential role in creating an interconnected fibrillar material of tunable toughness and strength. PMID:25153614

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

    Microsoft Academic Search

    I. Chakarska; S. Todinova; K. Idakieva

    2010-01-01

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

  19. A RHAMM Mimetic Peptide Blocks Hyaluronan Signaling and Reduces Inflammation and Fibrogenesis in Excisional Skin Wounds

    PubMed Central

    Tolg, Cornelia; Hamilton, Sara R.; Zalinska, Ewa; McCulloch, Lori; Amin, Ripal; Akentieva, Natalia; Winnik, Francoise; Savani, Rashmin; Bagli, Darius J.; Luyt, Len G.; Cowman, Mary K.; McCarthy, Jim B.; Turley, Eva A.

    2013-01-01

    Hyaluronan is activated by fragmentation and controls inflammation and fibroplasia during wound repair and diseases (eg, cancer). Hyaluronan-binding peptides were identified that modify fibrogenesis during skin wound repair. Peptides were selected from 7- to 15mer phage display libraries by panning with hyaluronan-Sepharose beads and assayed for their ability to block fibroblast migration in response to hyaluronan oligosaccharides (10 kDa). A 15mer peptide (P15-1), with homology to receptor for hyaluronan mediated motility (RHAMM) hyaluronan binding sequences, was the most effective inhibitor. P15-1 bound to 10-kDa hyaluronan with an affinity of Kd = 10?7 and appeared to specifically mimic RHAMM since it significantly reduced binding of hyaluronan oligosaccharides to recombinant RHAMM but not to recombinant CD44 or TLR2,4, and altered wound repair in wild-type but not RHAMM?/? mice. One topical application of P15-1 to full-thickness excisional rat wounds significantly reduced wound macrophage number, fibroblast number, and blood vessel density compared to scrambled, negative control peptides. Wound collagen 1, transforming growth factor ?-1, and ?-smooth muscle actin were reduced, whereas tenascin C was increased, suggesting that P15-1 promoted a form of scarless healing. Signaling/microarray analyses showed that P15-1 blocks RHAMM-regulated focal adhesion kinase pathways in fibroblasts. These results identify a new class of reagents that attenuate proinflammatory, fibrotic repair by blocking hyaluronan oligosaccharide signaling. PMID:22889846

  20. Effect of intra-articular hyaluronan on pressure-flow relation across synovium in anaesthetized rabbits.

    PubMed Central

    McDonald, J N; Levick, J R

    1995-01-01

    1. Hyaluronan is the major polysaccharide of synovial fluid, responsible for its high viscosity. The effect of hyaluronan on fluid transport across the synovial lining of the joint was investigated. Rate of fluid absorption from the joint cavity (Qs) was measured at intra-articular pressures (Pj) of up to 24 cmH2O in knees of anaesthetized rabbits, in the presence or absence of hyaluronan in intra-articular infusates. 2. Viscometry studies in vitro showed that the commercial hyaluronan used had a molecular weight of 549,000-774,000, a radius of gyration of 48-99 nm and a critical concentration for molecular overlap of 1.3 g l-1. 3. With intra-articular Krebs solution (control) or subnormal, subcritical concentrations of hyaluronan (0.5 g l-1), flow increased with pressure. Hyaluronan reduced the fluid escape rate by reducing slope dQs/dPj by 32-64% relative to Krebs solution. 4. At normal to high hyaluronan concentrations (3-6 g l-1) and low pressures, hyaluronan again reduced slope dQs/dPj, by 39-64%. The reduction in slope was slight, however, when compared with the reduction in bulk fluidity (1/relative viscosity). Fluidity at high shear rates was reduced to 6% of control values by 6 g l-1 hyaluronan. The effect on slope did not correlate significantly with the effect on fluidity. 5. At pressures above approximately 12 cmH2O, 3-6 g l-1 hyaluronan altered the shape of the pressure-flow relation: a flow plateau developed. In some joints raising pressure even reduced trans-synovial flow slightly. The pressure required to drive unit trans-synovial flow (an index of outflow resistance) increased 2.5-fold between 5 and 25 cmH2O in the presence of hyaluronan. By contrast, in the absence of hyaluronan the outflow resistance fell as pressure was raised. 6. It is suggested that the increasing resistance to flow in the presence of hyaluronan may be caused by partial molecular sieving of hyaluronan by the small porosities of the synovial interstitial matrix, leading to accumulation of a resistive filter cake of hyaluronan chains at the tissue-cavity interface. Since hyaluronan impedes fluid escape when pressure is raised, it may serve to preserve synovial fluid volume in vivo, e.g. during sustained joint flexion. PMID:7658372

  1. Dynamic non-linear response of cross-linked actin networks: an energy dissipation approach

    NASA Astrophysics Data System (ADS)

    Majumdar, Sayantan; Gardel, Margaret L.

    2014-03-01

    Cross-linked bio-polymer networks that primarily maintain the shape and rigidity in eukaryotic cells show striking non-linear mechanical properties. Here, we study the steady-state energy dissipation (Ediss) over a complete sinusoidal shear strain cycle for a macroscopic assembly of reconstituted network of actin filaments cross-linked with Filamin A, over wide range of strain amplitude and frequency values. For small values of the applied strain amplitudes (linear regime) Ediss increases monotonously with the increasing frequency over the entire frequency range studied but in the non-linear regime (larger applied strain amplitudes), a clear saturation in Ediss is observed at higher frequencies. Also, the normalized dissipated energy distribution binned over the fixed strain intervals along the shear cycle show frequency dependence in the nonlinear regime but remains frequency independent in the linear regime. Remarkably, the monotonously increasing behavior of Ediss with frequency is also observed in the non-linear regime when a more rigid cross-linker A-Actinin is used, suggesting the importance of flexibility of cross-linkers in controlling the non-linear mechanical response in this class of materials. MRSEC Kadanoff-Rice Post Doctoral Fellowship.

  2. [Healing of osseous defects by guided bone regeneration using ribose cross linked collagen membranes].

    PubMed

    Tal, H

    2004-07-01

    The ultimate goal of periodontal therapy has long been the complete regeneration of the periodontal attachment apparatus. Guided Tissue Regeneration (GTR) and Guided Bone Regeneration (GBR) are two regenerative procedures which converted this goal from a dream to reality. In search of a biocompatible resorbable tissue barrier, collagen, being a natural protein and a weak antigen, has attracted much interest and became the focus of much intention during the 80's and the 90's. The understanding that cross linking of collagen with aldehyde sugars, especially ribose, produces collagen which is highly resistant to resorption in vivo led to the development of a "natural" Crossed-Linked Collagen Barrier (CB-SX). Animal and Human studies have shown that the newly developed membrane is biocompatible, remains intact in the tissues 6 months and more, and results in impressive guided tissue/bone regeneration. Spontaneous early exposure of the membrane is common but the healing potential of the resulted tissue dehiscence is favorable with no tendency for bacterial infection. The commercial version of the CB-SX is especially suitable for GBR procedures; it is highly recommended that the gingival flaps involved will properly be released, will lack tension, and be thoroughly sutured. PMID:15503980

  3. A comparison of UV cross-linking and vacuum baking for nucleic acid immobilization and retention

    SciTech Connect

    Nierzwicki-Bauer, S.A.; Gebhardt, J.S.; Linkkila, L.; Walsh, K. (Rensselaer Polytechnic Institute (USA))

    1990-10-01

    The effectiveness of UV cross-linking and in vacuo baking for the immobilization and retention of DNA to various solid supports was investigated. Optimal immobilization treatments for supported and unsupported nitrocellulose and nylon membranes were: UV cross-linking at 254 nm with an exposure of 120 milliJoules/cm{sup 2}, or baking in vacuo for two hours at 80{degrees}C. UV-immobilized nitrocellulose-based membranes showed no increase in sensitivity when compared to baked membranes. An increase in sensitivity was observed for UV-immobilized nylon membranes as compared with baked nylon membranes in some instances, although this varied within lots of the membranes tested. Repeated strippings and heterologous reprobings resulted in loss of target DNA from UV-immobilized nylon membranes as compared to baked nylon membranes. Loss of target DNA from UV-immobilized nitrocellulose-based membranes due to repeated strippings and reprobings was even more pronounced. In vacuo baking of supported and unsupported nitrocellulose and nylon membranes was more effective for immobilization, and more importantly, for retention of target DNA through many reprobings of the same blot.

  4. Core-cross-linked micelles synthesized by clicking bifunctional Pt(IV) anticancer drugs to isocyanates.

    PubMed

    Duong, Hien T T; Huynh, Vien T; de Souza, Paul; Stenzel, Martina H

    2010-09-13

    Most low molecular weight platinum-based anticancer drugs have a short circulation time in the bloodstream. One of the potential strategies to improve the targeted delivery of cisplatin and prolong its circulation is via the use of nanocarriers. An improved drug delivery system was developed via reversible addition-fragmentation chain transfer (RAFT) polymerization. In a one-pot reaction, the incorporation of anticancer drug and core cross-linking was simultaneously carried out by using the highly effective reaction of isocyanate groups in the core of the polymeric micelles poly(oligo(ethylene glycol) methyl ether methacrylate)-block-poly(styrene-co-3-isopropenyl-?,?-dimethylbenzyl isocyanate) (POEGMA-block-P(STY-co-TMI)) with amine groups in the prepared platinum(IV) drug. The micelles with platinum(IV) incorporated with a size of 36 nm were very stable in water. In a reductive environment, in this study simulated using ascorbate, the drug was released at a slow rate of 82% in 22 days and at the same time the cross-linked micelle broke down into free block copolymers as evidenced using inductively coupled plasma-mass spectrometer (ICP-MS), size exclusion chromatography (SEC), and dynamic light scattering (DLS). The in vitro study also revealed the promising antitumor activity of prepared platinum(IV) drugs encapsulated into the micelle structure. PMID:20831272

  5. Modification of sodium and gating currents by amino group specific cross-linking and monofunctional reagents.

    PubMed Central

    Drews, G; Rack, M

    1988-01-01

    To test the possible role of lysine residues in Na channel function the effects of several imidoesters on Na and gating currents were studied in voltage-clamped single frog nerve fibers. Mono- and bisimidoesters were used. These reagents modify amino groups exclusively and do not change the net charge. The three bisimidoesters used easily introduce cross-links between neighboring amino groups. Their structure is almost identical; only the length of the spacers between the two amino-reactive groups is different. An irreversible reduction of Na currents and gating currents was observed with the longest (dimethyl suberimidate [DMS]) and the shortest (dimethyl adipimidate [DMA]) of the cross-linkers used. Of the three cross-linking reagents only the shortest made Na current inactivation slow and incomplete. The steady-state inactivation curve, h infinity (E), was shifted by greater than 25 mV in the hyperpolarizing direction by each of the reagents. The voltage dependence of activation, however, remained unchanged. Furthermore, the effects of two different monoimidoesters (ethyl acetimidate [EAI] and isethionyl acetimidate [IAI]) on gating currents were tested. EAI can penetrate a membrane, whereas IAI is membrane impermeant. IAI was almost without effect, whereas EAI caused a considerable reduction of the gating currents. EAI and DMS reduced the Qoff/Qon ratio without affecting the decay of the Na currents. The results show that lysine residues are critically involved in Na channel gating. PMID:2850028

  6. HPLC analysis of carotenoids from tomatoes using cross-linked C18 column and MS detection.

    PubMed

    Daood, Hussein G; Bencze, Gyula; Palotás, Gábor; Pék, Zoltán; Sidikov, Akmal; Helyes, Lajos

    2014-10-01

    This study was conducted to analyze carotenoids from tomatoes by high-performance liquid chromatography using reversed-phase C18 silica having cross-linked end-capping with diode array and mass spectrometric detection. An efficient gradient elution system was developed to achieve good and reliable separation of both major and minor carotenoids as well as their isomers. Resolution of lycopene, ?-carotene and their isomers was 0.91-3.97 and 1.02-2.86 with cross-linked and conventional C18 column, respectively. The % recovery for zeaxanthin, lycopene and ?-carotene was found to be in the range of 89-97%. Limits of detection and quantification of 19.44 and 64.79 ng/mL for zeaxanthin, 15.6 and 52.4 ng/mL for lycopene and 8.28 and 27.61 ng/mL for ?-carotene were determined. More carotenoid compounds could be separated and detected with the new method as compared with conventional C18 column. Hyphenation of HPLC with photodiode array and mass spectrometry detectors assisted in detection of tetra-dehydrocarotenoid and fatty acid diesters of xanthophylls in tomato products. Content of all-trans-lycopene, ?-carotene and total carotenoid in different industrial tomatoes tested was found to range between 41.87 and 84.65, 0.89 and 1.50 and 53.22 and 112.60 µg/g fresh weight, respectively. PMID:24046161

  7. Specific disulfide cross-linking to constrict the mobile carrier domain of nonribosomal peptide synthetases.

    PubMed

    Tarry, Michael J; Schmeing, T Martin

    2015-06-01

    Nonribosomal peptide synthetases are large, multi-domain enzymes that produce peptide molecules with important biological activity such as antibiotic, antiviral, anti-tumor, siderophore and immunosuppressant action. The adenylation (A) domain catalyzes two reactions in the biosynthetic pathway. In the first reaction, it activates the substrate amino acid by adenylation and in the second reaction it transfers the amino acid onto the phosphopantetheine arm of the adjacent peptide carrier protein (PCP) domain. The conformation of the A domain differs significantly depending on which of these two reactions it is catalyzing. Recently, several structures of A-PCP di-domains have been solved using mechanism-based inhibitors to trap the PCP domain in the A domain active site. Here, we present an alternative strategy to stall the A-PCP di-domain, by engineering a disulfide bond between the native amino acid substrate and the A domain. Size exclusion studies showed a significant shift in apparent size when the mutant A-PCP was provided with cross-linking reagents, and this shift was reversible in the presence of high concentrations of reducing agent. The cross-linked protein crystallized readily in several of the conditions screened and the best crystals diffracted to ?8 Å. PMID:25713404

  8. Solubility study of phytochemical cross-linking agents on dentin stiffness

    PubMed Central

    Castellan, Carina Strano; Pereira, Patricia N. R.; Viana, Grace; Chen, Shao-Nong; Pauli, Guido F.; Bedran-Russo, Ana Karina

    2010-01-01

    Objectives The effects of interactions between cross-linking proanthocyanidins (PA) in polar solvents and type-I collagen of demineralized dentin was investigated. Methods Three PA-rich extracts, two from grape seed (GSEP and GSES) and one from cocoa (COE), were dissolved (water, ethanol:water and acetone:water) and analyzed for their ability to increase the modulus of elasticity of demineralized dentin. Sound dentin beams (0.5 X 1.7 X 7 mm) were fully demineralized and divided into 12 groups according to the type of cross-linking agent and solvents used. Specimens were immersed in the respective solutions and tested at baseline, 10, 30, 60, 120 and 240 min. Results The elastic modulus (EM) of dentin was significantly increased by the PA treatment regardless of time (p<0.05 for all times). The extracts showed different solubility in different solvents. GSEP showed the highest increase in EM when diluted in distilled water and acetone at all exposure times. Both GSEs showed superior results when diluted in distilled water and after 4 hours of treatment, while COE produced strongest enhancement when dissolved in ethanol:water. Conclusions The results indicates that herbal extraction process and other pharmacognostic parameters have an important influence on extract solubility as well as constitution and, consequently, on the PA-dentin matrix interaction. PMID:20171257

  9. Cross-linked polymersomes as nanoreactors for controlled and stabilized single and cascade enzymatic reactions.

    PubMed

    Gräfe, David; Gaitzsch, Jens; Appelhans, Dietmar; Voit, Brigitte

    2014-09-21

    Polymeric vesicles or polymersomes are one of the supramolecular entities at the leading edge of synthetic biology. These small compartments have shown to be feasible candidates as nanoreactors, especially for enzymatic reactions. Once cross-linked and equipped with a pH sensitive material, the reaction can be switched off (pH 8) and on (pH 6) in accordance with the increased permeability of the polymersome membranes under acidic conditions. Thus cross-linked and pH sensitive polymersomes provide a basis for pH controlled enzymatic reactions where no integrated transmembrane protein is needed for regulating the uptake and release of educts and products in the polymersome lumen. This pH-tunable working tool was further used to investigate their use in sequential enzymatic reactions (glucose oxidase and myoglobin) where enzymes are loaded in one common polymersome or in two different polymersomes. Crossing membranes and overcoming the space distance between polymersomes were shown successfully, meaning that educts and products can be exchanged between enzyme compartments for successful enzymatic cascade reactions. Moreover the stabilizing effect of polymersomes is also observable by single enzymatic reactions as well as a sequence. This study is directed to establish robust and controllable polymersome nanoreactors for enzymatic reactions, describing a switch between an off (pH 8) and on (pH 6) state of polymersome membrane permeability with no transmembrane protein needed for transmembrane exchange. PMID:25099948

  10. Site-specific inter-strand cross-links of DNA duplexes

    PubMed Central

    Ye, Miao; Guillaume, Johan; Liu, Yu; Sha, Ruojie; Wang, Risheng

    2013-01-01

    We report the development of technology that allows inter-strand coupling across various positions within one turn of DNA. Four 2?-modified nucleotides were synthesized as protected phosphoramidites and incorporated into DNA oligonucleotides. The modified nucleotides contain either 5-atom or 16-atom linker components, with either amine or carboxylic acid functional groups at their termini, forming 10 or 32 atom (11 or 33 bond) linkages. Chemical coupling of the amine and carboxylate groups in designed strands resulted in the formation of an amide bond. Coupling efficiency as a function of trajectory distance between the individual linker components was examined. For those nucleotides capable of forming inter-strand cross-links (ICLs), coupling yields were found to depend on temperature, distance, and linker length, enabling several approaches that can control regioselective linkage. In the most favorable cases, the coupling yields are quantitative. Spectroscopic measurements of strands that were chemically cross-linked indicate that the global structure of the DNA duplex does not appear to be distorted from the B form after coupling. Thermal denaturing profiles of those strands were shifted to somewhat higher temperatures than those of their respective control duplexes. Thus, the robust amide ICLs formed by this approach are site-specific, do not destabilize the rest of the duplex, and only minimally perturb the secondary structure. PMID:23894693

  11. Angiotensin I-Converting Enzyme Inhibitor Derived from Cross-Linked Oyster Protein

    PubMed Central

    Xie, Cheng-Liang; Kim, Jin-Soo; Ha, Jong-Myung; Choung, Se-Young

    2014-01-01

    Following cross-linking by microbial transglutaminase, modified oyster proteins were hydrolyzed to improve inhibitory activity against angiotensin-converting enzyme (ACE) inhibitory activity with the use of a single protease, or a combination of six proteases. The oyster hydrolysate with the lowest 50% ACE inhibitory concentration (IC50) of 0.40?mg/mL was obtained by two-step hydrolysis of the cross-linked oyster protein using Protamex and Neutrase. Five ACE inhibitory peptides were purified from the oyster hydrolysate using a multistep chromatographic procedure comprised of ion-exchange, size exclusion, and reversed-phase liquid chromatography. Their sequences were identified as TAY, VK, KY, FYN, and YA, using automated Edman degradation and mass spectrometry. These peptides were synthesized, and their IC50 values were measured to be 16.7, 29.0, 51.5, 68.2, and 93.9??M, respectively. Toxicity of the peptides on the HepG2 cell line was not detected. The oyster hydrolysate also significantly decreased the systolic blood pressure of spontaneously hypertensive rats (SHR). The antihypertensive effect of the oyster hydrolysate on SHR was rapid and long-lasting, compared to commercially obtained sardine hydrolysate. These results suggest that the oyster hydrolysate could be a source of effective nutraceuticals against hypertension. PMID:25140307

  12. Robust Self-Healing Hydrogels Assisted by Cross-Linked Nanofiber Networks

    PubMed Central

    Fang, Yuan; Wang, Cai-Feng; Zhang, Zhi-Hong; Shao, Huan; Chen, Su

    2013-01-01

    Given increasing environmental and energy issues, mimicking nature to confer synthetic materials with self-healing property to expand their lifespan is highly desirable. Just like human skin recovers itself upon damage with the aid of nutrient-laden blood vascularization, designing smart materials with microvascular network to accelerate self-healing is workable but continues to be a challenge. Here we report a new strategy to prepare robust self-healing hydrogels assisted by a healing layer composed of electrospun cross-linked nanofiber networks containing redox agents. The hydrogels process high healing rate ranging from seconds to days and great mechanical strengths with storage modulus up to 0.1?MPa. More interestingly, when the healing layer is embedded into the crack of the hydrogel, accelerated self-healing is observed and the healing efficiency is about 80%. The healing layer encourages molecular diffusion as well as further cross-linking in the crack region of the hydrogel, responsible for enhanced healing efficiency. PMID:24091865

  13. Formaldehyde cross-linking of gliadin films: effects on mechanical and water barrier properties.

    PubMed

    Hernández-Muñoz, Pilar; López-Rubio, Amparo; Lagarón, José M; Gavara, Rafael

    2004-01-01

    In this study, pioneering results on specific chemical modifications of wheat gluten gliadins and the corresponding impact on mechanical and water barrier properties of derived films are presented. Films were prepared from gliadins chemically treated with formaldehyde and subsequently mixed with different concentrations of glycerol as a plasticizing agent. Water vapor barrier and mechanical properties of the films were evaluated as a function of relative humidity and glycerol concentration. Formaldehyde treatment led to enhanced mechanical properties and, to a lesser extent, improved water barrier of the films, effects which point to the formation of new intermolecular bonds between monomeric gliadins. The occurrence of cross-linking was supported by SDS-PAGE analysis. Cross-linked films maintained their integrity after immersion in water and had similar optical properties to control films. The effect of glycerol and humidity on water vapor permeability and the mechanical properties of films was less acute when proteins were treated with formaldehyde. Thus, chemical treatment of proteins is shown to be a very effective route for optimizing the use of these films in packaging applications. PMID:15003001

  14. Injectable doubly cross-linked microgels for improving the mechanical properties of degenerated intervertebral discs.

    PubMed

    Milani, Amir H; Freemont, Anthony J; Hoyland, Judith A; Adlam, Daman J; Saunders, Brian R

    2012-09-10

    The use of injectable pH-responsive doubly cross-linked microgels (DX microgels) to improve the mechanical properties of degenerated intervertebral discs is demonstrated for the first time. The microgel comprised methyl methacrylate (MMA), methacrylic acid (MAA), ethyleneglycol dimethacrylate (EGD) and glycidyl methacrylate (GM) and was poly(MMA/MAA/EGD)-GM. The GM facilitated covalent interparticle cross-linking. The DX microgels are shown to have tunable mechanical properties. Degeneration of model bovine intervertebral discs (IVDs) was induced using collagenase. When injected into degenerated IVDs the DX microgels were shown to improve the strain, modulus, toughness and resilience. The extent of mechanical property improvement was an increasing function of DX microgel concentration, suggesting tunability. Cytotoxicity studies showed that the DX microgel was biocompatible under the conditions investigated. The results of this study imply that injectable DX microgels have good potential as a future regenerative medicine strategy for restoring the mechanical properties of degenerated load-bearing soft tissue, such as IVDs. PMID:22877136

  15. A novel material of cross-linked styrylpyridinium salt intercalated montmorillonite for drug delivery

    NASA Astrophysics Data System (ADS)

    Cui, Jing; Wang, Qingqing; Chen, Xiaodong; Wei, Qufu

    2014-08-01

    A facile synthesis of a styrylpyridinium salt (SbQ)/montmorillonite (MMT) via cationic exchange interactions between styrylpyridinium species (specifically SbQ) and MMT platelets is reported in this work. The SbQ-MMT solutions were irradiated under ultraviolet (UV) light for a specific time to obtain the cross-linked SbQ-MMT materials. Scanning electron microscopy and atomic force microscopy analyses revealed the structures and morphologies of MMT and modified MMT. X-ray diffraction and transmission electron microscope analyses indicated that the basal spacing increased from 1.24 to 1.53 nm compared with the pristine MMT, which proved that SbQ had interacted with MMT. Thermal gravimetric analysis curves showed that the amount of SbQ in the MMT interlayers was 35.71 meq/100 g. Fourier transform infrared spectroscopy also confirmed the intercalation of SbQ species into MMT interlayers, and UV spectroscopy was used to follow up the cross-linking of SbQ-MMT. This novel material has potential applications in drug delivery, and it can also be used as an additive to improve the mechanical properties of polymers.

  16. Viability, Apoptosis, Proliferation, Activation, and Cytokine Secretion of Human Keratoconus Keratocytes after Cross-Linking

    PubMed Central

    Stachon, Tanja; Wang, Jiong; Seitz, Berthold; Szentmáry, Nóra

    2015-01-01

    Purpose. The purpose of this study was to determine the impact of cross-linking (CXL) on viability, apoptosis, proliferation, activation, and cytokine secretion of human keratoconus (KC) keratocytes, in vitro. Methods. Primary KC keratocytes were cultured in DMEM/Ham's F12 medium supplemented with 10% FCS and underwent UVA illumination (370?nm, 2?J/cm2) during exposure to 0.1% riboflavin and 20% Dextran in PBS. Twenty-four hours after CXL, viability was assessed using Alamar blue assay; apoptosis using APO-DIRECT Kit; proliferation using ELISA-BrdU kit; and CD34 and alpha-smooth muscle actin (?-SMA) expression using flow cytometry. Five and 24 hours after CXL, FGFb, HGF, TGF?1, VEGF, KGF, IL-1?, IL-6, and IL-8 secretion was measured using enzyme-linked-immunoabsorbent assay (ELISA). Results. Following CXL, cell viability and proliferation decreased (P < 0.05; P = 0.009), the percentage of apoptotic keratocytes increased (P < 0.05) significantly, and CD34 and ?-SMA expression remained unchanged (P > 0.06). Five hours after CXL, FGFb secretion increased significantly (P = 0.037); however no other cytokine secretion differed significantly from controls after 5 or 24 hours (P > 0.12). Conclusions. Cross-linking decreases viability, triggers apoptosis, and inhibits proliferation, without an impact on multipotent hematopoietic stem cell transformation and myofibroblastic transformation of KC keratocytes. CXL triggers FGFb secretion of KC keratocytes transiently (5 hours), normalizing after 24 hours. PMID:25699261

  17. Mechanics and multiple-particle tracking microheterogeneity of alpha-actinin-cross-linked actin filament networks.

    PubMed Central

    Tseng, Y; Wirtz, D

    2001-01-01

    Cell morphology is controlled by the actin cytoskeleton organization and mechanical properties, which are regulated by the available contents in actin and actin regulatory proteins. Using rheometry and the recently developed multiple-particle tracking method, we compare the mechanical properties and microheterogeneity of actin filament networks containing the F-actin cross-linking protein alpha-actinin. The elasticity of F-actin/alpha-actinin networks increases with actin concentration more rapidly for a fixed molar ratio of actin to alpha-actinin than in the absence of alpha-actinin, for networks of fixed alpha-actinin concentration and of fixed actin concentration, but more slowly than theoretically predicted for a homogeneous cross-linked semiflexible polymer network. These rheological measurements are complemented by multiple-particle tracking of fluorescent microspheres imbedded in the networks. The distribution of the mean squared displacements of these microspheres becomes progressively more asymmetric and wider for increasing concentration in alpha-actinin and, to a lesser extent, for increasing actin concentration, which suggests that F-actin networks become progressively heterogeneous for increasing protein content. This may explain the slower-than-predicted rise in elasticity of F-actin/alpha-actinin networks. Together these in vitro results suggest that actin and alpha-actinin provides the cell with an unsuspected range of regulatory pathways to modulate its cytoskeleton's micromechanics and local organization in vivo. PMID:11509377

  18. Kinetics of copper ion absorption by cross-linked calcium polyacrylate membranes

    NASA Technical Reports Server (NTRS)

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

    1983-01-01

    The absorption of copper ions from aqueous copper acetate solutions by cross-linked calcium acrylate membranes was found to obey parabolic kinetics similar to that found for oxidation of metals that form protective oxide layers. For pure calcium polyacrylate membranes the rate constant was essentially independent of copper acetate concentration and film thickness. For a cross-linked copolymer film of polyvinyl alcohol and calcium polyacrylate, the rate constant was much greater and dependent on the concentration of copper acetate. The proposed mechanism in each case involves the formation of a copper polyacrylate phase on the surface of the membrane. The diffusion of the copper ion through this phase appears to be the rate controlling step for the copolymer film. The diffusion of the calcium ion is apparently the rate controlling step for the calcium polyacrylate. At low pH, the copper polyacrylate phase consists of the normal copper salt; at higher pH, the phase appears to be the basic copper salt.

  19. Hydrogel containing silica shell cross-linked micelles for ocular drug delivery.

    PubMed

    Lu, Changhai; Yoganathan, Roshan B; Kociolek, Michael; Allen, Christine

    2013-02-01

    Poly(2-hydroxyethyl methacrylate-methacrylic acid-ethylene glycol dimethacrylate) hydrogels loaded with silica shell cross-linked methoxy(polyethylene glycol)-block-polycaprolactone (MePEG-b-PCL) micelles with rod-like morphology were prepared as a potential soft contact lens material for the sustained release of ocular drugs. The silica shell cross-linked methoxy micelles (SSCMs) comprising a polycaprolactone core surrounded by a silica shell were synthesized and their size, morphology, stability, and drug release kinetics were evaluated. The relationships between the composition of the SSCM-loaded poly(2-hydroxyethyl methacrylate) (pHEMA)-based hydrogels and their transparency, surface wettability, and equilibrium water content were determined. Scanning electron microscopy (SEM) images of SSCM-hydrogel systems showed the presence of intact SSCMs within the hydrogel matrix. Dexamethasone acetate (DMSA), a hydrophobic ophthalmic drug, was loaded into the SSCMs prior to their incorporation into the hydrogels. In vitro release of DMSA from the SSCM-hydrogels, with varying drug loading levels, was observed for up to 30 days. Overall, the incorporation of rod-like SSCMs within pHEMA-based hydrogels provided sustained release over prolonged periods while maintaining optical transparency. This delivery system may be suitable for use as a therapeutic soft contact lens material. PMID:23203974

  20. Cross-Linking Transglutaminases with G Protein-Coupled Receptor Signaling

    NSDL National Science Digital Library

    Siiri E. Iismaa (New South Wales; Victor Chang Cardiac Research Institute, Darlinghurst REV)

    2006-09-19

    Transglutaminases are a family of calcium- and thiol-dependent acyl transferases that catalyze the formation of an amide bond between the ?-carboxamide groups of peptide-bound glutamine residues and the primary amino groups in various compounds, including the ϵ-amino group of lysines in certain proteins. As a result, these enzymes effect posttranslational modification of proteins by amine incorporation, or stabilization of protein assemblies by their cross-linking; such actions profoundly influence critical biological processes such as blood clotting and protection from infection and dehydration by establishing the barrier function of skin. In addition, transglutaminases have other more diverse actions, including involvement in signaling by the superfamily of heterotrimeric guanine nucleotide–binding protein (G protein)–coupled receptors (GPCRs) in one of three ways: (i) through actions as guanosine triphosphate–binding proteins that activate intracellular effectors, such as phospholipase C; (ii) by cross-linking GPCR monomers to enhance signaling as a result of covalent dimer formation; or (iii) by interacting with an apparent growth inhibitory orphan GPCR, GPR56, to limit metastatic spread of melanoma cells. The implications of these receptor-coupled actions of transglutaminases are discussed.

  1. Reduction-responsive cross-linked stearyl peptide for effective delivery of plasmid DNA

    PubMed Central

    Yao, Chong; Tai, Zongguang; Wang, Xiaoyu; Liu, Jiyong; Zhu, Quangang; Wu, Xin; Zhang, Lijuan; Zhang, Wei; Tian, Jing; Gao, Yuan; Gao, Shen

    2015-01-01

    Low efficiency and significant toxicity are the main obstacles to successful gene delivery. We have developed a cationic reduction-responsive vector based on a disulfide cross-linked stearylated polyarginine peptide modified with histidine (C-SHR) for DNA delivery. The structure of the C-SHR was characterized, and the in vitro and in vivo transfection efficiency and cytotoxicity of C-SHR/plasmid DNA complexes were examined. Compared with non-cross-linked stearylated polyarginine peptide (SHR), C-SHR increased the intracellular uptake and dissociation behavior of the complexes. In addition, the gene transfection efficiency of C-SHR/plasmid DNA complexes in HEK293 and HeLa cells was improved and was comparable with that of bPEI-25K/plasmid DNA complexes, and the cytotoxicity of C-SHR was significantly less than that of bPEI-25K. Importantly, the in vivo gene transfection efficiency of C-SHR/plasmid DNA complexes was five fold higher than that of SHR/plasmid DNA complexes, suggesting that C-SHR is an efficient non-viral vector for DNA delivery. PMID:26056440

  2. Probing Akt-inhibitor interaction by chemical cross-linking and mass spectrometry

    PubMed Central

    Huang, Bill X.; Kim, Hee-Yong

    2009-01-01

    The serine/threonine kinase Akt is a critical enzyme that regulates cell survival. As high Akt activity has been shown to contribute to the pathogenesis of various human malignancies, inhibition of Akt activation is a promising therapeutic strategy for cancers. We have previously demonstrated that changes in Akt interdomain arrangements from a closed to open conformation occur upon Akt-membrane interaction, which in turn allows Akt phosphorylation/activation. In the present study, we demonstrate a novel strategy to discern mechanisms for Akt inhibition based on Akt conformational changes using chemical cross-linking and 18O labeling mass spectrometry. By quantitative comparison of two interdomain cross-linked peptides which represent the proximity of the domains involved, we found that the binding of Akt to an inhibitor (PI analog) caused the open interdomain conformation where the PH and regulatory domains moved away from the kinase domain, even before interacting with membranes, subsequently preventing translocation of Akt to the plasma membrane. In contrast, the interdomain conformation remained unchanged after incubating with another type of inhibitor (peptide TLC1). Subsequent interaction with unilamellar vesicles suggested that TCL1 impaired particularly the opening of the PH domain for exposing T308 for phosphorylation at the plasma membrane. This novel approach based on the conformation-based molecular interaction mechanism should be potentially useful for drug discovery efforts for specific Akt inhibitors or anti-tumor agents. PMID:19446470

  3. Genipin-cross-linked fucose-chitosan/heparin nanoparticles for the eradication of Helicobacter pylori.

    PubMed

    Lin, Yu-Hsin; Tsai, Shih-Chang; Lai, Chih-Ho; Lee, Che-Hsin; He, Zih Sian; Tseng, Guan-Chin

    2013-06-01

    Helicobacter pylori is a significant human pathogen that recognizes specific carbohydrate receptors, such as the fucose receptor, and produces the vacuolating cytotoxin, which induces inflammatory responses and modulates the cell-cell junction integrity of the gastric epithelium. The clinical applicability of topical antimicrobial agents was needed to complete the eradication of H. pylori in the infected fundal area. In the present study, we combined fucose-conjugated chitosan and genipin-cross-linking technologies in preparing multifunctional genipin-cross-linked fucose-chitosan/heparin nanoparticles to encapsulate amoxicillin of targeting and directly make contact with the region of microorganism on the gastric epithelium. The results show that the nanoparticles effectively reduced drug release at gastric acids and then released amoxicillin in an H. pylori survival situation to inhibit H. pylori growth and reduce disruption of the cell-cell junction protein in areas of H. pylori infection. Furthermore, with amoxicillin-loaded nanoparticles, a more complete H. pylori clearance effect was observed, and H. pylori-associated gastric inflammation in an infected animal model was effectively reduced. PMID:23499480

  4. The monopolin complex cross-links kinetochore components to regulate chromosome-microtubule attachments

    PubMed Central

    Corbett, Kevin D.; Yip, Calvin K.; Ee, Ly-Sha; Walz, Thomas; Amon, Angelika; Harrison, Stephen C.

    2010-01-01

    Summary The monopolin complex regulates different types of kinetochore-microtubule attachments in fungi, ensuring sister chromatid co-orientation in S. cerevisiae meiosis I and inhibiting merotelic attachment in S. pombe mitosis. In addition, the monopolin complex maintains the integrity and silencing of ribosomal DNA (rDNA) repeats in the nucleolus. We show here that the S. cerevisiae Csm1/Lrs4 monopolin subcomplex has a distinctive V-shaped structure, with two pairs of protein-protein interaction domains positioned ?10 nm apart. Csm1 presents a conserved hydrophobic surface patch that binds two kinetochore proteins: Dsn1, a subunit of the outer-kinetochore MIND/Mis12 complex, and Mif2/CENP-C. Csm1 point-mutations that disrupt kinetochore-subunit binding also disrupt sister chromatid co-orientation in S. cerevisiae meiosis I. We further show that the same Csm1 point-mutations affect rDNA silencing, probably by disrupting binding to the rDNA-associated protein Tof2. We propose that Csm1/Lrs4 functions as a molecular clamp, cross-linking kinetochore components to enforce sister chromatid co-orientation in S. cerevisiae meiosis I and to suppress merotelic attachment in S. pombe mitosis, and cross-linking rDNA repeats to aid rDNA silencing. PMID:20723757

  5. Controlled release of plasmid DNA from photo-cross-linked pluronic hydrogels.

    PubMed

    Chun, Ki Woo; Lee, Jun Bae; Kim, Sun Hwa; Park, Tae Gwan

    2005-06-01

    Chemically cross-linked hydrogels composed of Pluronic, water-soluble tri-block copolymers of poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide), were synthesized by a photo-polymerization method to achieve controlled DNA release. Pluronic F127 was di-acrylated to form a macromer and cross-linked to form a hydrogel structure in the presence and absence of vinyl group-modified hyaluronic acid (HA). UV irradiation time and the presence of the vinyl group-modified HA affected the mechanical property of Pluronic hydrogels to a great extent. Swelling ratio, degradation, and rheological behaviors of Pluronic hydrogels were investigated. When plasmid DNA was loaded in the hydrogels for sustained delivery, various release profiles were attained by varying UV irradiation time and modified HA amounts. Entrapped DNA was gradually damaged with increasing the UV exposure time as evidenced by decreasing the transfection efficiency. The DNA fractions released from the HA/Pluronic hydrogels, however, exhibited considerable transfection efficiencies commensurate with the UV exposure time, suggesting that they were not chemically degraded during the release period and substantially maintained functional gene expression activities despite the UV irradiation. PMID:15603827

  6. Effect of Polymer Concentration and Cross-linking Density on Microgel Size and Shrinking Capacity

    NASA Astrophysics Data System (ADS)

    Streletzky, Kiril; Benmerzouga, Imaan; McKenna, John

    2008-10-01

    Hydroxypropylcellulose (HPC) is a polysaccharide with temperature dependent water solubility. HPC chains can be chemically cross linked into stable nanoparticles called microgels. The structure and dynamics of microgels depend on polymer and salt concentration, crosslinking density, and solution temperature. HPC has easily accessible lower critical solution temperature. At Tc=41^oC, HPC in solution undergoes a reversible transition at which chains form metastable clusters that fall apart when temperature is lowered below Tc. HPC microgels undergo a similar transition in which, however, microgel clusters stay intact below and above Tc. In this transition microgels shrink/swell on average by a factor of eight, a property with a potential for application in targeted drug delivery. Dynamic Light Scattering was used to study microgels in thermal equilibrium. Due to a complexity of microgel spectra the line shape analysis algorithm was employed. Comparison of differently synthesized HPC microgels revealed that higher polymer concentration results in smaller microgels with lower shrinking capacity. The effective cross-linking density that yields relatively monodisperse microgels was determined. The angular dependence of scattering demonstrated that microgels are largely spherical particles. Finally, studying microgels at different temperatures allowed to monitor the shrinking/swelling behavior.

  7. Truncation of a cross-linked GCN4-p1 coiled coil leads to ultrafast folding.

    PubMed

    Bunagan, Michelle R; Cristian, Lidia; DeGrado, William F; Gai, Feng

    2006-09-12

    Structural perturbation has been extensively used in protein folding studies because it yields valuable conformational information regarding the folding process. Here we have used N-terminal truncation on a cross-linked variant of the GCN4-p1 leucine zipper, aiming to develop a better understanding of the folding mechanism of the coiled-coil motif. Our results indicate that removing the first heptad repeat in this cross-linked GCN4-p1 coiled coil significantly decreases the folding free energy barrier and results in a maximum folding rate of (2.0 +/- 0.3 micros)(-1), which is approximately 50 times faster than that of the full-length protein. Therefore, these results suggest that a set of native or nativelike tertiary interactions, distributed throughout the entire sequence, collectively stabilize the folding transition state of the GCN4-p1 coiled coil. While stable subdomains or triggering sequences have been shown to be critical to the stability of GCN4 coiled coils, our results suggest that the folding of such a subdomain does not seem to dictate the overall folding kinetics. PMID:16953584

  8. Oral Delivery of Exenatide via Microspheres Prepared by Cross-Linking of Alginate and Hyaluronate

    PubMed Central

    Zhang, Baojie; He, Dongyang; Fan, Yu; Liu, Nan; Chen, Yijun

    2014-01-01

    Exenatide is an FDA-approved glucose-lowering peptide drug for the treatment of type 2 diabetes by subcutaneous injection. To address the issues on the inconvenience for patient use and the difficulty of oral administration of peptide drugs, chemical cross-linking of two pH-responsive biomaterials, alginate and hyaluronate, was carried out to prepare a new material for the encapsulation of exenatide as a form of microspheres. The exenatide-loaded microspheres exhibited spherical structures with excellent loading and release behaviors in the simulated gastrointestinal tract environments. After oral administration of the microspheres in db/db mice, maximum plasma concentration of exenatide appeared at 4 hours, and blood glucose was effectively reduced to a normal level within 2 hours and maintained for another 4 hours. The bioavailability of the exenatide-loaded microspheres, relative to subcutaneous injection of exenatide, reached 10.2%. Collectively, the present study demonstrated the feasibility of orally delivering exenatide with the new cross-linked biomaterial and formulation, and showed therapeutic potential for clinical applications. PMID:24465870

  9. Analysis of ligand-receptor cross-linked fragments by mass spectrometry

    SciTech Connect

    Son, C.D. [University of Tennessee, Knoxville (UTK); Sargsyan, H. [City University of New York (CUNY); Hurst, Gregory {Greg} B [ORNL; Naider, F. [City University of New York (CUNY); Becker, J.M. [University of Tennessee, Knoxville (UTK)

    2005-01-01

    G-protein coupled receptors (GPCRs) are a class of integral membrane receptor proteins that are characterized by a signature seven-transmembrane (7-TM) configuration. The a-factor receptor (Ste2p) from Saccharomyces cerevisiae is a GPCR that, upon binding of a peptide ligand, transduces a signal to initiate a cascade of events leading to the mating of haploid yeast cells. This study summarizes the application of affinity purification and of matrix-assisted laser-desorption ionization time-of-flight (MALDI-TOF) experiments using biotinylated photoactivatable a-factor analogs. Affinity purification and enrichment of biotinylated peptides by monomeric avidin beads resulted in mass spectrometric detection of specific signals corresponding to crosslinked fragments of Ste2p. Data obtained from cyanogen bromide (CNBr) fragments of receptor cross-linked to an a-factor analog with the photoaffinity group p-benzoyl-L-phenylalanine on position 1 were in agreement with the previous results reported by our laboratory suggesting the cross-linking between position 1 of a-factor and a region of Ste2p covering residues 251 294.

  10. DNA-Protein Cross-Links: Formation, Structural Identities, and Biological Outcomes.

    PubMed

    Tretyakova, Natalia Y; Groehler, Arnold; Ji, Shaofei

    2015-06-16

    Noncovalent DNA-protein interactions are at the heart of normal cell function. In eukaryotic cells, genomic DNA is wrapped around histone octamers to allow for chromosomal packaging in the nucleus. Binding of regulatory protein factors to DNA directs replication, controls transcription, and mediates cellular responses to DNA damage. Because of their fundamental significance in all cellular processes involving DNA, dynamic DNA-protein interactions are required for cell survival, and their disruption is likely to have serious biological consequences. DNA-protein cross-links (DPCs) form when cellular proteins become covalently trapped on DNA strands upon exposure to various endogenous, environmental and chemotherapeutic agents. DPCs progressively accumulate in the brain and heart tissues as a result of endogenous exposure to reactive oxygen species and lipid peroxidation products, as well as normal cellular metabolism. A range of structurally diverse DPCs are found following treatment with chemotherapeutic drugs, transition metal ions, and metabolically activated carcinogens. Because of their considerable size and their helix-distorting nature, DPCs interfere with the progression of replication and transcription machineries and hence hamper the faithful expression of genetic information, potentially contributing to mutagenesis and carcinogenesis. Mass spectrometry-based studies have identified hundreds of proteins that can become cross-linked to nuclear DNA in the presence of reactive oxygen species, carcinogen metabolites, and antitumor drugs. While many of these proteins including histones, transcription factors, and repair proteins are known DNA binding partners, other gene products with no documented affinity for DNA also participate in DPC formation. Furthermore, multiple sites within DNA can be targeted for cross-linking including the N7 of guanine, the C-5 methyl group of thymine, and the exocyclic amino groups of guanine, cytosine, and adenine. This structural complexity complicates structural and biological studies of DPC lesions. Two general strategies have been developed for creating DNA strands containing structurally defined, site-specific DPCs. Enzymatic methodologies that trap DNA modifying proteins on their DNA substrate are site specific and efficient, but do not allow for systematic studies of DPC lesion structure on their biological outcomes. Synthetic methodologies for DPC formation are based on solid phase synthesis of oligonucleotide strands containing protein-reactive unnatural DNA bases. The latter approach allows for a wider range of protein substrates to be conjugated to DNA and affords a greater flexibility for the attachment sites within DNA. In this Account, we outline the chemistry of DPC formation in cells, describe our recent efforts to identify the cross-linked proteins by mass spectrometry, and discuss various methodologies for preparing DNA strands containing structurally defined, site specific DPC lesions. Polymerase bypass experiments conducted with model DPCs indicate that the biological outcomes of these bulky lesions are strongly dependent on the peptide/protein size and the exact cross-linking site within DNA. Future studies are needed to elucidate the mechanisms of DPC repair and their biological outcomes in living cells. PMID:26032357

  11. Methods of controlling cross-linking in negative-tone resists

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

    Negative tone resists based on cross-linking via epoxide/cationic polymerization have a variety of potential advantages over more traditional positive tone resists based on photoacid catalyzed deprotection including low outgassing, intrinsic diffusion control, and improved pattern collapse performance through the higher modulus provided by a cross-linked network. Based on the promising baseline performance achieved previously in simple negative tone systems composed only of an epoxide functionalized molecular glass and a photoacid generator, a series of different methods and additives that can be used to control the extent and rate of cross-linking in such systems have been developed and are reported here which allow for even further improvement in resist performance. Simple addition of base quencher, as is used in conventional chemically amplified resists, is ineffective in these systems because the patterning reaction mechanism is different. Any control method must work by modifying the extent and rate of cationic polymerization of epoxides. By adding molecules containing phenolic OH groups to such an epoxide resist, one can slow the extent of cross-linking due to introduction of an additional reaction pathway and often a concomitant increase in the resist resin glass transition temperature. Generalized additives similar to base quencher were also developed based on the addition of strong nucleophiles such as triphenylphosphine which act essentially as chain termination agents. This approach allows for improved resolution and LER in negative tone epoxide resist systems. A more superior additive was developed that can be described as a photodecomposable nucleophile (PDN). The unexposed PDN acts similarly to the strong nucleophile additives in that it terminates chain propagation. Upon exposure, the PDN can act like a chain transfer agent or an additional initiator, but no longer has the effect of completely terminating chain propagation. This approach allows for high levels of control in the nominally unexposed regions of the resist, but maintains high efficiency of cross-linking in the most highly exposed regions. One particular implementation of a PDN used in this study is the blending of a PAG (i.e. triphenylsulfonium triflate, TPS-Tf) with a more nucleophilic anion that plays the role of a PDN, with the common and highly effective, non-nucleophilic PAG that is conventionally used in epoxide photopolymerizations (i.e. triphenylsulfonium hexafluoroantimonate, TPS-SbF6). Addition of only a few percent of TPS-Tf to a baseline epoxide resist formulation shows a 5-10 nm improvement in ultimate resolution and a reduction in LER to around 65% as compared to the baseline resist without the PDN additive while only incurring a moderate increase in imaging dose. By modulating the amount of the different polymerization control additives, the performance of a particular epoxide resist was improved from a resolution of greater than 30 nm half pitch and an LER of around 9 nm to a resolution of ~20 nm half pitch, with an LER of around 4 nm, and a sensitivity of 18 mJ/cm2. By increasing the additive loading even further, the resolution was improved to ~18 nm half pitch, although with an increase in imaging dose to 39 mJ/cm2.

  12. The decreased secretion of hyaluronan by older human fibroblasts under physiological conditions is mainly associated with the down-regulated expression of hyaluronan synthases but not with the expression levels of hyaluronidases.

    PubMed

    Terazawa, Shuko; Nakajima, Hiroaki; Tobita, Keisuke; Imokawa, Genji

    2015-08-01

    Although it has been reported that levels of hyaluronan are decreased in the dermis of aged skin, little is known about the cellular mechanism(s) underlying that hyaluronan deficiency. Since hyaluronan is produced by dermal fibroblasts and is secreted into the surrounding dermal tissues, we examined the secretion of hyaluronan by dermal fibroblasts and characterized its cellular mechanism using real-time RT-PCR and western blotting for its synthesizing and degrading enzymes, hyaluronan synthase and hyaluronidase, respectively. The secretion of hyaluronan by dermal fibroblasts derived from differently aged human donors, was higher in the younger human fibroblasts tested (0 and 19 years old) compared to the older human fibroblasts tested (39, 56 and 77 years old). The relative secretion levels of hyaluronan by the different human fibroblasts tested were attributable to the relative expression of hyaluronan synthases 1, 2, 3 but not hyaluronidases 1, 2 enzymes at the gene and protein levels among those fibroblasts. These findings indicate that the deficiency of hyaluronan in the aged dermis might result from the down-regulation in the potential of older human fibroblasts to secrete hyaluronan and that decrease in secretory potential is mainly associated with the down-regulated expression of hyaluronan synthases, especially hyaluronan synthase 2, but not with the expression levels of hyaluronidases. PMID:24590928

  13. XLPM: efficient algorithm for the analysis of protein-protein contacts using chemical cross-linking mass spectrometry

    PubMed Central

    2014-01-01

    Background Chemical cross-linking is used for protein-protein contacts mapping and for structural analysis. One of the difficulties in cross-linking studies is the analysis of mass-spectrometry data and the assignment of the site of cross-link incorporation. The difficulties are due to higher charges of fragment ions, and to the overall low-abundance of cross-link species in the background of linear peptides. Cross-linkers non-specific at one end, such as photo-inducible diazirines, may complicate the analysis further. In this report, we design and validate a novel cross-linked peptide mapping algorithm (XLPM) and compare it to StavroX, which is currently one of the best algorithms in this class. Results We have designed a novel cross-link search algorithm -XLPM - and implemented it both as an online tool and as a downloadable archive of scripts. We designed a filter based on an observation that observation of a b-ion implies observation of a complimentary y-ion with high probability (b-y filter). We validated the b-y filter on the set of linear peptides from NIST library, and demonstrate that it is an effective way to find high-quality mass spectra. Next, we generated cross-linked data from an ssDNA binding protein, Rim1with a specific cross-linker disuccinimidyl suberate, and a semi-specific cross-linker NHS-Diazirine, followed by analysis of the cross-linked products by nanoLC-LTQ-Orbitrap mass spectrometry. The cross-linked data were searched by XLPM and StavroX and the performance of the two algorithms was compared. The cross-links were mapped to the X-ray structure of Rim1 tetramer. Analysis of the mixture of NHS-Diazirine cross-linked 15N and 14N-labeled Rim1 tetramers yielded 15N-labeled to 14N-labeled cross-linked peptide pairs, corresponding to C-terminus-to-N-terminus cross-linking, demonstrating interaction between different two Rim1 tetramers. Both XLPM and StavroX were successful in identification of this interaction, with XLPM leading to a better annotation of higher-charged fragments. We also put forward a new method of estimating specificity and sensitivity of identification of a cross-linked residue in the case of a non-specific cross-linker. Conclusions The novel cross-link mapping algorithm, XLPM, considerably improves the speed and accuracy of the analysis compared to other methods. The quality selection filter based on b-to-y ions ratio proved to be an effective way to select high quality cross-linked spectra. PMID:25350700

  14. Entangled Cross-Linked Fibres for an Application as Core Material for Sandwich Structures - Part I: Experimental Investigation

    NASA Astrophysics Data System (ADS)

    Mezeix, L.; Poquillon, D.; Bouvet, C.

    2015-06-01

    Entangled cross-linked fibres were studied for an application as core material for sandwich structures. Specimens were produced from carbon, aramid and glass fibres, and cross-links were achieved using epoxy spraying. It was observed that this type of entangled cross-linked fibres could be fabricated without any major technical difficulties. The scope of this paper is to study the effect of some different parameters on the mechanical properties of these materials. Different effects were investigated: effect of fibres length, of fibres nature, of mixing fibres, of carbon skins and of the resin. The first part of this paper deals with the production of these entangled cross-linked fibres. The compression, tension and three point bending tests are detailed in the second part and the results are compared with usual core material currently used in industries.

  15. Modulation by propranolol of the lysyl cross-links in aortic elastin and collagen of the aneurysm-prone turkey.

    PubMed

    Boucek, R J; Gunja-Smith, Z; Noble, N L; Simpson, C F

    1983-01-15

    dl-Propranolol (propranolol) fed to immature and mature aneurysm-prone turkeys (Broad-Breasted White, BBW) for 6 weeks significantly raised the tensile strength of tissue rings from the abdominal aorta. The drug-mediated increase in tensile strength values was dose-related and independent of its heart rate- and arterial pressure-lowering effects. Propranolol acts, in part, by (a) stimulating lysyl oxidase to produce greater amounts of reactive aldehydes for intermolecular cross-links, (b) enhancing the progression of chemically unstable to stable forms of intermolecular elastin cross-links (lysinonorleucine and the desmosines), and (c) reducing the density of the age-related intermolecular cross-linking of collagen (pyridinoline). These propranolol effects on the lysyl cross-links were demonstrated in both the immature and mature animals and suggest a heretofore unrecognized potential for this widely used cardiovascular drug. PMID:6409122

  16. Arabidopsis CROLIN1, a Novel Plant Actin-binding Protein, Functions in Cross-linking and Stabilizing Actin Filaments*

    PubMed Central

    Jia, Honglei; Li, Jisheng; Zhu, Jingen; Fan, Tingting; Qian, Dong; Zhou, Yuelong; Wang, Jiaojiao; Ren, Haiyun; Xiang, Yun; An, Lizhe

    2013-01-01

    Higher order actin filament structures are necessary for cytoplasmic streaming, organelle movement, and other physiological processes. However, the mechanism by which the higher order cytoskeleton is formed in plants remains unknown. In this study, we identified a novel actin-cross-linking protein family (named CROLIN) that is well conserved only in the plant kingdom. There are six isovariants of CROLIN in the Arabidopsis genome, with CROLIN1 specifically expressed in pollen. In vitro biochemical analyses showed that CROLIN1 is a novel actin-cross-linking protein with binding and stabilizing activities. Remarkably, CROLIN1 can cross-link actin bundles into actin networks. CROLIN1 loss of function induces pollen germination and pollen tube growth hypersensitive to latrunculin B. All of these results demonstrate that CROLIN1 may play an important role in stabilizing and remodeling actin filaments by binding to and cross-linking actin filaments. PMID:24072702

  17. Molecular structure, mechanical behavior and failure mechanism of the C-terminal cross-link domain in type I collagen

    E-print Network

    Uzel, Sebastien Guy Marcel

    Collagen is a key constituent in structural materials found in biology, including bone, tendon, skin and blood vessels. Here we report a first molecular level model of an entire overlap region of a C-terminal cross-linked ...

  18. Cross-linked membranes based on sulfonated poly (ether ether ketone) (SPEEK)\\/Nafion for direct methanol fuel cells (DMFCs)

    Microsoft Academic Search

    Na Zhang; Gang Zhang; Dan Xu; Chengji Zhao; Wenjia Ma; Hongtao Li; Yang Zhang; Shuai Xu; Hao Jiang; Hongcheng Sun; Hui Na

    2011-01-01

    A series of cross-linked membranes based on SPEEK\\/Nafion have been prepared to improve methanol resistance and dimension stability of SPEEK membrane for the usage in the direct methanol fuel cells (DMFCs). Sulfonated diamine monomer is synthesized and used as cross-linker to improve the dispersion of Nafion in the composite membranes and decrease the negative effect of cross-linking on proton conductivity

  19. Removal of copper(II) ions from aqueous solution onto chitosan and cross-linked chitosan beads

    Microsoft Academic Search

    W. S Wan Ngah; C. S Endud; R Mayanar

    2002-01-01

    The adsorption of Cu(II) ions onto chitosan and cross-linked chitosan beads has been investigated. Chitosan beads were cross-linked with glutaraldehyde (GLA), epichlorohydrin (ECH) and ethylene glycol diglycidyl ether (EGDE) in order to obtain sorbents that are insoluble in aqueous acidic and basic solution. Batch adsorption experiments were carried out as a function of pH, agitation period, agitation rate and concentration

  20. Catalytic effects of transition metals in the form of the salts of organic acids in the cross linking of alkyds

    Microsoft Academic Search

    V. Š?áva; D. Veselý; P. Kalenda

    2008-01-01

    Purpose – To study the drying effects of cobalt, manganous and mixed salts for their catalytic action in cross linking reactions occurring during the creation of an alkyd resin film. Design\\/methodology\\/approach – The driers of Co-octoate, Mn-octoate, Mn-octoate with an active organic ligand, and mixed drier containing the salts of Mn, Ca, and Zn were employed in the cross linking