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Sample records for nonporous cross-linked polymers

  1. Polymeric molecular sieve membranes via in situ cross-linking of non-porous polymer membrane templates

    Science.gov (United States)

    Qiao, Zhen-An; Chai, Song-Hai; Nelson, Kimberly; Bi, Zhonghe; Chen, Jihua; Mahurin, Shannon M.; Zhu, Xiang; Dai, Sheng

    2014-04-01

    High-performance polymeric membranes for gas separation are attractive for molecular-level separations in industrial-scale chemical, energyand environmental processes. Molecular sieving materials are widely regarded as the next-generation membranes to simultaneously achieve high permeability and selectivity. However, most polymeric molecular sieve membranes are based on a few solution-processable polymers such as polymers of intrinsic microporosity. Here we report an in situ cross-linking strategy for the preparation of polymeric molecular sieve membranes with hierarchical and tailorable porosity. These membranes demonstrate exceptional performance as molecular sieves with high gas permeabilities and selectivities for smaller gas molecules, such as carbon dioxide and oxygen, over larger molecules such as nitrogen. Hence, these membranes have potential for large-scale gas separations of commercial and environmental relevance. Moreover, this strategy could provide a possible alternative to ‘classical’ methods for the preparation of porous membranes and, in some cases, the only viable synthetic route towards certain membranes.

  2. Light-harvesting cross-linked polymers for efficient heterogeneous photocatalysis.

    Science.gov (United States)

    Wang, Cheng; Xie, Zhigang; deKrafft, Kathryn E; Lin, Wenbin

    2012-04-01

    Nonporous, phosphorescent cross-linked polymers (Ru-CP and Ir-CP) were synthesized via Pd-catalyzed Sonogashira cross-coupling reactions between tetra(p-ethynylphenyl)methane and dibrominated Ru(bpy)(3)(2+) or Ir(ppy)(2)(bpy)(+), respectively. The resultant particulate cross-linked polymer (CP) materials have very high catalyst loadings (76.3 wt % for Ru-CP and 71.6 wt % for Ir-CP), and are nonporous with negligibly small surface areas (2.9 m(2)/g for Ru-CP and 2.7 m(2)/g for Ir-CP). Despite their nonporous nature, the insoluble CP materials serve as highly active and recyclable heterogeneous photocatalysts for a range of organic transformations such as aza-Henry reaction, aerobic amine coupling, and dehalogenation of benzyl bromoacetate. An efficient light-harvesting mechanism, which involves collection of photons by exciting the (3)MLCT states of the phosphors and migration of the excited states to the particle surface, is proposed to account for the very high catalytic activities of these nonporous CPs. Steady-state and time-resolved emission data, as well as the reduced catalytic activity of Os(bpy)(3)(2+)-doped Ru-CPs supports efficient excited state migration for the CP frameworks. This work uncovers a new strategy in designing highly efficient photocatalysts based on light-harvesting cross-linked polymers.

  3. Gelation threshold of cross-linked polymer brushes.

    Science.gov (United States)

    Hoffmann, Max; Lang, Michael; Sommer, Jens-Uwe

    2011-02-01

    The cross-linking of polymer brushes is studied using the bond-fluctuation model. By mapping the cross-linking process into a two-dimensional (2D) percolation problem within the lattice of grafting points, we investigate the gelation transition in detail. We show that the particular properties of cross-linked polymer brushes can be reduced to the distribution of bonds which are formed between the grafted chains, and we propose scaling arguments to relate the gelation threshold to the chain length and the grafting density. The gelation threshold is lower than the percolation threshold for 2D bond percolation because of the longer range and broad distribution of bonds formed by the cross-linking process. We term this type of percolation problem star percolation. We observe a broad crossover from mean-field to critical percolation behavior by analyzing the cluster size distribution near the gelation threshold.

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

    Science.gov (United States)

    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.

  5. Computer simulation of randomly cross-linked polymer networks

    CERN Document Server

    Williams, T P

    2002-01-01

    In this work, Monte Carlo and Stochastic Dynamics computer simulations of mesoscale model randomly cross-linked networks were undertaken. Task parallel implementations of the lattice Monte Carlo Bond Fluctuation model and Kremer-Grest Stochastic Dynamics bead-spring continuum model were designed and used for this purpose. Lattice and continuum precursor melt systems were prepared and then cross-linked to varying degrees. The resultant networks were used to study structural changes during deformation and relaxation dynamics. The effects of a random network topology featuring a polydisperse distribution of strand lengths and an abundance of pendant chain ends, were qualitatively compared to recent published work. A preliminary investigation into the effects of temperature on the structural and dynamical properties was also undertaken. Structural changes during isotropic swelling and uniaxial deformation, revealed a pronounced non-affine deformation dependant on the degree of cross-linking. Fractal heterogeneiti...

  6. Investigation of anisotropic thermal transport in cross-linked polymers

    Science.gov (United States)

    Simavilla, David Nieto

    Thermal transport in lightly cross-linked polyisoprene and polybutadine subjected to uniaxial elongation is investigated experimentally. We employ two experimental techniques to assess the effect that deformation has on this class of materials. The first technique, which is based on Forced Rayleigh Scattering (FRS), allows us to measure the two independent components of the thermal diffusivity tensor as a function of deformation. These measurements along with independent measurements of the tensile stress and birefringence are used to evaluate the stress-thermal and stress-optic rules. The stress-thermal rule is found to be valid for the entire range of elongations applied. In contrast, the stress-optic rule fails for moderate to large stretch ratios. This suggests that the degree of anisotropy in thermal conductivity depends on both orientation and tension in polymer chain segments. The second technique, which is based on infrared thermography (IRT), allows us to measure anisotropy in thermal conductivity and strain induced changes in heat capacity. We validate this method measurements of anisotropic thermal conductivity by comparing them with those obtained using FRS. We find excellent agreement between the two techniques. Uncertainty in the infrared thermography method measurements is estimated to be about 2-5 %. The accuracy of the method and its potential application to non-transparent materials makes it a good alternative to extend current research on anisotropic thermal transport in polymeric materials. A second IRT application allows us to investigate the dependence of heat capacity on deformation. We find that heat capacity increases with stretch ratio in polyisoprene specimens under uniaxial extension. The deviation from the equilibrium value of heat capacity is consistent with an independent set of experiments comparing anisotropy in thermal diffusivity and conductivity employing FRS and IRT techniques. We identify finite extensibility and strain

  7. Polymer Composition and Substrate Influences on the Adhesive Bonding of a Biomimetic, Cross-Linking Polymer

    OpenAIRE

    Matos-Pérez, Cristina R.; White, James D.; Wilker, Jonathan J.

    2012-01-01

    Hierarchical biological materials such as bone, sea shells, and marine bioadhesives are providing inspiration for the assembly of synthetic molecules into complex structures. The adhesive system of marine mussels has been the focus of much attention in recent years. Several catechol-containing polymers are being developed to mimic the cross-linking of proteins containing 3,4-dihydroxyphenylalanine (DOPA) used by shellfish for sticking to rocks. Many of these biomimetic polymer systems have be...

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

    Energy Technology Data Exchange (ETDEWEB)

    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}.

  9. Molecular Dynamics Simulations of Polymer Networks Undergoing Sequential Cross-Linking and Scission Reactions

    DEFF Research Database (Denmark)

    Rottach, Dana R.; Curro, John G.; Budzien, Joanne;

    2007-01-01

    The effects of sequential cross-linking and scission of polymer networks formed in two states of strain are investigated using molecular dynamics simulations. Two-stage networks are studied in which a network formed in the unstrained state (stage 1) undergoes additional cross-linking in a uniaxia......The effects of sequential cross-linking and scission of polymer networks formed in two states of strain are investigated using molecular dynamics simulations. Two-stage networks are studied in which a network formed in the unstrained state (stage 1) undergoes additional cross...... good agreement with the predictions of Flory and Fricker. It was found that the fractional stress reduction upon removal of the first-stage cross-links could be accurately calculated from the slip tube model of Rubinstein and Panyukov modified to use the theoretical transfer functions of Fricker.  ...

  10. Designing of superporous cross-linked hydrogels containing acrylic-based polymer network

    Directory of Open Access Journals (Sweden)

    Ray Debajyoti

    2008-01-01

    Full Text Available Biodegradable cross-linked polymer, 2-hydroxyethyl methacrylate-co-acrylic acid was synthesized by free radical polymerization technique using N,N"-methylene-bis-acrylamide as cross-linker and benzoyl peroxide as reaction initiator. FT-IR, 1 H-NMR, scanning electron microscopy (SEM, and thermogravimetric analysis (TGA studies of the copolymer along with homopolymers were carried out. FT-IR studies showed no interactions on copolymerization. SEM studies of the copolymer were carried out and mean particle size was found to be 50 µm. TGA analysis indicated an increase in thermal stability by cross-linking the polymer network. Swelling behavior of the copolymer showed more swelling by increasing pH of the medum and the prepared polymer was found to be biodegradable. The prepared cross-linked polymer system holds good for further drug delivery studies in connection to its super swelling and biodegradability.

  11. Click Cross-Linking-Improved Waterborne Polymers for Environment-Friendly Coatings and Adhesives.

    Science.gov (United States)

    Hu, Jianqing; Peng, Kaimei; Guo, Jinshan; Shan, Dingying; Kim, Gloria B; Li, Qiyao; Gerhard, Ethan; Zhu, Liang; Tu, Weiping; Lv, Weizhong; Hickner, Michael A; Yang, Jian

    2016-07-13

    Waterborne polymers, including waterborne polyurethanes (WPU), polyester dispersions (PED), and polyacrylate emulsions (PAE), are employed as environmentally friendly water-based coatings and adhesives. An efficient, fast, stable, and safe cross-linking strategy is always desirable to impart waterborne polymers with improved mechanical properties and water/solvent/thermal and abrasion resistance. For the first time, click chemistry was introduced into waterborne polymer systems as a cross-linking strategy. Click cross-linking rendered waterborne polymer films with significantly improved tensile strength, hardness, adhesion strength, and water/solvent resistance compared to traditional waterborne polymer films. For example, click cross-linked WPU (WPU-click) has dramatically improved the mechanical strength (tensile strength increased from 0.43 to 6.47 MPa, and Young's modulus increased from 3 to 40 MPa), hardness (increased from 59 to 73.1 MPa), and water resistance (water absorption percentage dropped from 200% to less than 20%); click cross-linked PED (PED-click) film also possessed more than 3 times higher tensile strength (∼28 MPa) than that of normal PED (∼8 MPa). The adhesion strength of click cross-linked PAE (PAE-click) to polypropylene (PP) was also improved (from 3 to 5.5 MPa). In addition, extra click groups can be preserved after click cross-linking for further functionalization of the waterborne polymeric coatings/adhesives. In this work, we have demonstrated that click modification could serve as a convenient and powerful approach to significantly improve the performance of a variety of traditional coatings and adhesives.

  12. Photochromic cross-link polymer for color changing and sensing surface

    Science.gov (United States)

    Fu, Richard; Shi, Jianmin; Forsythe, Eric; Srour, Merric

    2016-12-01

    Photochromic cross-link polymers were developed using patented ultraviolet (UV) photoinitiator and commercial photochromic dyes. The photochromic dyes have been characterized by measuring absorbance before and after UV activation using UV-visible (Vis) spectrometry with varying activation intensities and wavelengths. Photochromic cross-link polymers were characterized by a dynamic xenon and UV light activation and fading system. The curing processes on cloth were established and tested to obtain effective photochromic responses. Both PulseForge photonic curing and PulseForge plus heat surface curing processes had much better photochromic responses (18% to 19%, 16% to 25%, respectively) than the xenon lamp treatment (8%). The newly developed photochromic cross-link polymer showed remarkable coloration contrasts and fast and comparable coloration and fading rates. Those intelligent, controlled color changing and sensing capabilities will be used on flexible and "drapeable" surfaces, which will incorporate ultra-low power sensors, sensor indicators, and identifiers.

  13. Effect of Cross Linking Agent on Alkali/Surfactant/Polymer

    Institute of Scientific and Technical Information of China (English)

    ZHANG,Ke; LU,Xiang-Guo

    2008-01-01

    Alkali/surfactant/polymer (ASP) multisystem flooding technique, which has an expansive application prospect,is one of the enhancing oil recovery (EOR) methods. By adding the organic chromium to the ASP, the molecular structure of polymer was made to change, and the capability of controlling mobility coefficient of ASP was improved. The results showed that multisystem could still keep ultra-low interfacial tension between the multisystem and crude oil after addition of Cr3+. The resistance factor and residual resistance factor, the indicator which describes the capability of controlling mobility, upgraded strikingly. However its storage modulus and loss modulus,the indicator which describes viscoelasticity, increased. The results of physical simulation experiment indicated that this type of improved ASP could increase the recovery ratio by 4.3% compared to common ASP multisystem.

  14. ROMP-based thermosetting polymers from modified castor oil with various cross-linking agents

    Science.gov (United States)

    Ding, Rui

    Polymers derived from bio-renewable resources are finding an increase in global demand. In addition, polymers with distinctive functionalities are required in certain advanced fields, such as aerospace and civil engineering. In an attempt to meet both these needs, the goal of this work aims to develop a range of bio-based thermosetting matrix polymers for potential applications in multifunctional composites. Ring-opening metathesis polymerization (ROMP), which recently has been explored as a powerful method in polymer chemistry, was employed as a unique pathway to polymerize agricultural oil-based reactants. Specifically, a novel norbornyl-functionalized castor oil alcohol (NCA) was investigated to polymerize different cross-linking agents using ROMP. The effects of incorporating dicyclopentadiene (DCPD) and a norbornene-based crosslinker (CL) were systematically evaluated with respect to curing behavior and thermal mechanical properties of the polymers. Isothermal differential scanning calorimetry (DSC) was used to investigate the conversion during cure. Dynamic DSC scans at multiple heating rates revealed conversion-dependent activation energy by Ozawa-Flynn-Wall analysis. The glass transition temperature, storage modulus, and loss modulus for NCA/DCPD and NCA/CL copolymers with different cross-linking agent loading were compared using dynamic mechanical analysis. Cross-link density was examined to explain the very different dynamic mechanical behavior. Mechanical stress-strain curves were developed through tensile test, and thermal stability of the cross-linked polymers was evaluated by thermogravimetric analysis to further investigate the structure-property relationships in these systems.

  15. Mechanically Strong, Polymer Cross-linked Aerogels (X-Aerogels)

    Science.gov (United States)

    Leventis, Nicholas

    2006-01-01

    Aerogels comprise a class of low-density, high porous solid objects consisting of dimensionally quasi-stable self-supported three-dimensional assemblies of nanoparticles. Aerogels are pursued because of properties above and beyond those of the individual nanoparticles, including low thermal conductivity, low dielectric constant and high acoustic impedance. Possible applications include thermal and vibration insulation, dielectrics for fast electronics, and hosting of functional guests for a wide variety of optical, chemical and electronic applications. Aerogels, however, are extremely fragile materials, hence they have found only limited application in some very specialized environments, for example as Cerenkov radiation detectors in certain types of nuclear reactors, aboard spacecraft as collectors of hypervelocity particles (refer to NASA's Stardust program) and as thermal insulators on planetary vehicles on Mars (refer to Sojourner Rover in 1997 and Spirit and Opportunity in 2004). Along these lines, the X-Aerogel is a new NASA-developed strong lightweight material that has resolved the fragility problem of traditional (native) aerogels. X-Aerogels are made by applying a conformal polymer coating on the surfaces of the skeletal nanoparticles of native aerogels (see Scanning Electron Micrographs). Since the relative amounts of the polymeric crosslinker and the backbone are comparable, X-Aerogels can be viewed either as aerogels modified by the templated accumulation of polymer on the skeletal nanoparticles, or as nanoporous polymers made by remplated casting of polymer on a nanostructured framework. The most striking feature of X-Aerogels is that for a nominal 3-fold increase in density (still a ultralighweight material), the mechanical strength can be up to 300 times higher than the strength of the underlying native aerogel. Thus, X-Aerogels combine a multiple of the specific compressive strength of steel, with the the thermal conductivity of styrofoam. X

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

    Energy Technology Data Exchange (ETDEWEB)

    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.

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

    Science.gov (United States)

    Lacevic, Naida; Gee, Richard H; Saab, Andrew; Maxwell, Robert

    2008-09-28

    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 octafunctional 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 netlike 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.

  18. Polymers and Cross-Linking: A CORE Experiment to Help Students Think on the Submicroscopic Level

    Science.gov (United States)

    Bruce, Mitchell R. M.; Bruce, Alice E.; Avargil, Shirly; Amar, Francois G.; Wemyss, Thomas M.; Flood, Virginia J.

    2016-01-01

    The Polymers and Cross-Linking experiment is presented via a new three phase learning cycle: CORE (Chemical Observations, Representations, Experimentation), which is designed to model productive chemical inquiry and to promote a deeper understanding about the chemistry operating at the submicroscopic level. The experiment is built on two familiar…

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

    Energy Technology Data Exchange (ETDEWEB)

    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.

  20. Cross-linked aromatic cationic polymer electrolytes with enhanced stability for high temperature fuel cell applications

    DEFF Research Database (Denmark)

    Ma, Wenjia; Zhao, Chengji; Yang, Jingshuai

    2012-01-01

    Diamine-cross-linked membranes were prepared from cross-linkable poly(arylene ether ketone) containing pendant cationic quaternary ammonium group (QPAEK) solution by a facile and general thermal curing method using 4,4′-diaminodiphenylmethane with rigid framework and 1,6-diaminohexane with flexible...... framework as cross-linker, respectively. Self-cross-linked cationic polymer electrolytes membranes were also prepared for comparison. The diamines were advantageously distributed within the polymeric matrix and its amine function groups interacted with the benzyl bromide of QPAEK, resulting in a double...... that the diamine-cross-linked membranes using the rigid cross-linker show much improved properties than that using the flexible cross-linker. More properties relating to the feasibility in high temperature proton exchange membrane fuel cell applications were investigated in detail....

  1. Comparative studies of photochemical cross-linking methods for stabilizing the bulk hetero-junction morphology in polymer solar cells

    DEFF Research Database (Denmark)

    Carlé, Jon Eggert; Andreasen, Birgitta; Tromholt, Thomas;

    2012-01-01

    -light illumination to give solvent resistant films and reduced phase separation and growth of PCBM crystallites in polymer:PCBM films. The stability of solar cells based on the cross-linked polymers was tested under various conditions. This study showed that cross-linking can improve morphological stability...

  2. Preparation and Characterization of a pH-Responsive Core Cross-linked Polymer Micelle

    Energy Technology Data Exchange (ETDEWEB)

    Kousaka, Shouta; Sugahara, Makoto; Endo, Tatsuya; Yusa, Shin-ichi, E-mail: yusa@eng.u-hyogo.ac.jp [Department of Materials Science and Chemistry, Graduate School of Engineering, University of Hyogo, 2167 Shosha, Himeji, Hyogo 671-2280 (Japan)

    2011-01-01

    Poly(ethylene glycol)-b-poly(2-(diethylamino) ethyl methacrylate-co-2-cinnamoyl-oxyethyl acrylate) (PEG-b-P(DEA/CEA)) was prepared by reversible addition-fragmentation chain transfer (RAFT) controlled radical polymerization. pH-responsive association behaviour of PEG-b-P(DEA/CEA) in 0.1 M NaCl was characterized by dynamic light scattering (DLS). As solution pH is increased from an acidic pH, the hydrodynamic radius (R{sub h}) increases, indicative of the polymer micelle formation. The formation of a micelle was also supported by static light scattering (SLS) data. The cinnamoyl groups in the core of the polymer micelle undergo photodimerization, yielding cross-links between polymer chains. The core of the polymer micelle was fixed, which was confirmed by DLS, SLS, and small angle X-ray scattering (SAXS) techniques. When pH is decreased to 3, R{sub h} of the core cross-linked (CCL) polymer micelle slightly increases due to the protonation of the DEA unit in the cross-linked core. The reversible pH-induced swelling and shrinking behaviour can be observed.

  3. Molecular dynamics simulations of highly cross-linked polymer networks: prediction of thermal and mechanical properties

    Science.gov (United States)

    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.

  4. Polymer composition and substrate influences on the adhesive bonding of a biomimetic, cross-linking polymer.

    Science.gov (United States)

    Matos-Pérez, Cristina R; White, James D; Wilker, Jonathan J

    2012-06-06

    Hierarchical biological materials such as bone, sea shells, and marine bioadhesives are providing inspiration for the assembly of synthetic molecules into complex structures. The adhesive system of marine mussels has been the focus of much attention in recent years. Several catechol-containing polymers are being developed to mimic the cross-linking of proteins containing 3,4-dihydroxyphenylalanine (DOPA) used by shellfish for sticking to rocks. Many of these biomimetic polymer systems have been shown to form surface coatings or hydrogels; however, bulk adhesion is demonstrated less often. Developing adhesives requires addressing design issues including finding a good balance between cohesive and adhesive bonding interactions. Despite the growing number of mussel-mimicking polymers, there has been little effort to generate structure-property relations and gain insights on what chemical traits give rise to the best glues. In this report, we examine the simplest of these biomimetic polymers, poly[(3,4-dihydroxystyrene)-co-styrene]. Pendant catechol groups (i.e., 3,4-dihydroxystyrene) are distributed throughout a polystyrene backbone. Several polymer derivatives were prepared, each with a different 3,4-dihyroxystyrene content. Bulk adhesion testing showed where the optimal middle ground of cohesive and adhesive bonding resides. Adhesive performance was benchmarked against commercial glues as well as the genuine material produced by live mussels. In the best case, bonding was similar to that obtained with cyanoacrylate "Krazy Glue". Performance was also examined using low- (e.g., plastics) and high-energy (e.g., metals, wood) surfaces. The adhesive bonding of poly[(3,4-dihydroxystyrene)-co-styrene] may be the strongest of reported mussel protein mimics. These insights should help us to design future biomimetic systems, thereby bringing us closer to development of bone cements, dental composites, and surgical glues.

  5. Core Cross-linked Star Polymers for Temperature/pH Controlled Delivery of 5-Fluorouracil

    Directory of Open Access Journals (Sweden)

    Elizabeth Sánchez-Bustos

    2016-01-01

    Full Text Available RAFT polymerization with cross-linking was used to prepare core cross-linked star polymers bearing temperature sensitive arms. The arms consisted of a diblock copolymer containing N-isopropylacrylamide (NIPAAm and 4-methacryloyloxy benzoic acid (4MBA in the temperature sensitive block and poly(hexyl acrylate forming the second hydrophobic block, while ethyleneglycol dimethacrylate was used to form the core. The acid comonomer provides pH sensitivity to the arms and also increases the transition temperature of polyNIPAAm to values in the range of 40 to 46°C. Light scattering and atomic force microscopy studies suggest that loose core star polymers were obtained. The star polymers were loaded with 5-fluorouracil (5-FU, an anticancer agent, in values of up to 30 w/w%. In vitro release experiments were performed at different temperatures and pH values, as well as with heating and cooling temperature cycles. Faster drug release was obtained at 42°C or pH 6, compared to normal physiological conditions (37°C, pH 7.4. The drug carriers prepared acted as nanopumps changing the release kinetics of 5-FU when temperatures cycles were applied, in contrast with release rates at a constant temperature. The prepared core cross-linked star polymers represent advanced drug delivery vehicles optimized for 5-FU with potential application in cancer treatment.

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

    Science.gov (United States)

    Jiang, Dayue (David)

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

  7. Cross-Linked Liquid Crystalline Systems From Rigid Polymer Networks to Elastomers

    CERN Document Server

    Broer, Dirk

    2011-01-01

    With rapidly expanding interest in liquid crystalline polymers and elastomers among the liquid crystal community, researchers are currently exploring the wide range of possible application areas for these unique materials, including optical elements on displays, tunable lasers, strain gauges, micro-structures, and artificial muscles. Written by respected scientists from academia and industry around the world, who are not only active in the field but also well-known in more traditional areas of research, "Cross-Linked Liquid Crystalline Systems: From Rigid Polymer Networks to Elastomers&qu

  8. Biomolecule-recognition gating membrane using biomolecular cross-linking and polymer phase transition.

    Science.gov (United States)

    Kuroki, Hidenori; Ito, Taichi; Ohashi, Hidenori; Tamaki, Takanori; Yamaguchi, Takeo

    2011-12-15

    We present for the first time a biomolecule-recognition gating system that responds to small signals of biomolecules by the cooperation of biorecognition cross-linking and polymer phase transition in nanosized pores. The biomolecule-recognition gating membrane immobilizes the stimuli-responsive polymer, including the biomolecule-recognition receptor, onto the pore surface of a porous membrane. The pore state (open/closed) of this gating membrane depends on the formation of specific biorecognition cross-linking in the pores: a specific biomolecule having multibinding sites can be recognized by several receptors and acts as the cross-linker of the grafted polymer, whereas a nonspecific molecule cannot. The pore state can be distinguished by a volume phase transition of the grafted polymer. In the present study, the principle of the proposed system is demonstrated using poly(N-isopropylacrylamide) as the stimuli-responsive polymer and avidin-biotin as a multibindable biomolecule-specific receptor. As a result of the selective response to the specific biomolecule, a clear permeability change of an order of magnitude was achieved. The principle is versatile and can be applied to many combinations of multibindable analyte-specific receptors, including antibody-antigen and lectin-sugar analogues. The new gating system can find wide application in the bioanalytical field and aid the design of novel biodevices.

  9. Azide-based cross-linking of polymers of intrinsic microporosity (PIMs) for condensable gas separation

    KAUST Repository

    Du, Naiying

    2011-03-11

    Cross-linked polymers of intrinsic microporosity (PIM)s for gas separation membranes, were prepared by a nitrene reaction from a representative PIM in the presence of two different diazide cross-linkers. The reaction temperature was optimized using TGA. The homogenous membranes were cast from THF solutions of different ratios of PIM to azides. The resulting cross-linked structures of the PIMs membranes were formed at 175 °C after 7.5 h and confirmed by TGA, XPS, FT-IR spectroscopy and gel content analysis. These resulting cross-linked polymeric membranes showed excellent gas separation performance and can be used for O 2/N 2 and CO 2/N 2 gas pairs, as well as for condensable gases, such as CO 2/CH 4, propylene/propane separation. Most importantly, and differently from typical gas separation membranes derived from glassy polymers, the crosslinked PIMs showed no obvious CO 2 plasticization up to 20 atm pressure of pure CO 2 and CO 2/CH 4 mixtures. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  10. Polymeric Nanocapsule from Silica Nanoparticle@Cross-linked Polymer Nanoparticles via One-Pot Approach

    Directory of Open Access Journals (Sweden)

    Shen Ruoping

    2009-01-01

    Full Text Available Abstract A facile strategy was developed here to prepare cross-linked polymeric nanocapsules (CP nanocapsules with silica nanoparticles as templates. The silica nanoparticle@cross-linked polymer nanoparticles were prepared by the encapsulation of the silica nanoparticles by the one-pot approach via surface-initiated atom transfer radical polymerization of hydroxyethyl acrylate in the presence ofN,N′-methylenebisacrylamide as a cross-linker from the initiator-modified silica nanoparticles. After the silica nanoparticle templates were etched with hydrofluoric acid, the CP nanocapsules with particle size of about 100 nm were obtained. The strategy developed was confirmed with Fourier transform infrared, thermogravimetric analysis and transmission electron microscopy.

  11. 21 CFR 888.3353 - Hip joint metal/ceramic/polymer semi-constrained cemented or nonporous uncemented prosthesis.

    Science.gov (United States)

    2010-04-01

    ... cemented or nonporous uncemented prosthesis. 888.3353 Section 888.3353 Food and Drugs FOOD AND DRUG... prosthesis. (a) Identification. A hip joint metal/ceramic/polymer semi-constrained cemented or nonporous uncemented prosthesis is a device intended to be implanted to replace a hip joint. This device...

  12. Polymer-additive extraction via pressurized fluids and organic solvents of variously cross-linked poly(methylmethacrylates).

    Science.gov (United States)

    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.

  13. Cross-linked supramolecular polymer metallogels constructed via a self-sorting strategy and their multiple stimulus-response behaviors.

    Science.gov (United States)

    Wang, Xu-Qing; Wang, Wei; Yin, Guang-Qiang; Wang, Yu-Xuan; Zhang, Chang-Wei; Shi, Jia-Meng; Yu, Yihua; Yang, Hai-Bo

    2015-12-01

    Novel cross-linked supramolecular polymer metallogels were successfully constructed from four components via a self-sorting strategy, and feature interesting multiple stimulus-response behaviors under various external stimuli, including halide, base, and competitive guests.

  14. Shape-memory behavior of cross-linked semi-crystalline polymers and their blends

    Directory of Open Access Journals (Sweden)

    I. Kolesov

    2015-03-01

    Full Text Available The present study deals with thermally induced one-way and invertible two-way shape-memory effect (SME in covalent networks on the basis of crystallizable (copolymers and their blends and is an attempt to generalize the results of own investigation received by the authors in the last ten years. The main focus of work clearly lies on research of covalently crosslinked binary and ternary blends having two and three crystalline phases with different thermal stability, respectively. The existence of two or three crystalline phases possessing different melting and crystallization temperatures in heterogeneous polymer networks can lead to triple-shape or even quadruple-shape behavior of such networks. However, the performed investigations point to crucial effect of phase morphology of crosslinked polymer blends on multiplicity of their shapememory behavior beside the influence of blend content, crystallinity and cross-link density of blend phases as well as of processing conditions. For instance, triple-shape memory behavior in binary blends can be realized only if the continuous phase has a lower melting temperature than the dispersed phase. Cross-linked polymer blends are a facile alternative to expensive and complex synthesis of interpenetrating or block-copolymer networks used for shape memory polymers. In addition to findings of experimental investigation of SME in crystallizable covalent polymer networks, the results of modeling their shape-memory behavior on the basis of self-developed physically reasonable model have been briefly described and discussed. Thereby, good accordance between results of theory and experiment was achieved with physically justified fitting parameters.

  15. Removal of anionic azo dyes from aqueous solution by functional ionic liquid cross-linked polymer

    Energy Technology Data Exchange (ETDEWEB)

    Gao, Hejun [Key Laboratory of Colloid and Interface Chemistry, Shandong University, Ministry of Education, Jinan 250100 (China); Chemical Synthesis and Pollution Control Key Laboratory of Sichuan Province, China West Normal University, Nanchong 637000 (China); Kan, Taotao [CNOOC Energy Technology and Services-oilfield Technology Services Co., Tanggu, Tianjin 300452 (China); Zhao, Siyuan; Qian, Yixia; Cheng, Xiyuan; Wu, Wenli [School of Chemistry and Chemical Engineering, Shandong University, Jinan 250100 (China); Wang, Xiaodong [Shandong Provincial Analysis and Test Center, Jinan 250100 (China); Zheng, Liqiang, E-mail: lqzheng@sdu.edu.cn [Key Laboratory of Colloid and Interface Chemistry, Shandong University, Ministry of Education, Jinan 250100 (China)

    2013-10-15

    Highlights: • Equilibrium, kinetic and thermodynamic of adsorption of dyes onto PDVB-IL was investigated. • PDVB-IL has a high adsorption capacity to treat dyes solution. • Higher adsorption capacity is due to the functional groups of PDVB-IL. • Molecular structure of dyes influences the adsorption capacity. -- Abstract: A novel functional ionic liquid based cross-linked polymer (PDVB-IL) was synthesized from 1-aminoethyl-3-vinylimidazolium chloride and divinylbenzene for use as an adsorbent. The physicochemical properties of PDVB-IL were investigated by Fourier transform infrared spectroscopy, scanning electron microscopy and thermogravimetric analysis. The adsorptive capacity was investigated using anionic azo dyes of orange II, sunset yellow FCF, and amaranth as adsorbates. The maximum adsorption capacity could reach 925.09, 734.62, and 547.17 mg/g for orange II, sunset yellow FCF and amaranth at 25 °C, respectively, which are much better than most of the other adsorbents reported earlier. The effect of pH value was investigated in the range of 1–8. The result shows that a low pH value is found to favor the adsorption of those anionic azo dyes. The adsorption kinetics and isotherms are well fitted by a pseudo second-order model and Langmuir model, respectively. The adsorption process is found to be dominated by physisorption. The introduction of functional ionic liquid moieties into cross-linked poly(divinylbenzene) polymer constitutes a new and efficient kind of adsorbent.

  16. Simulation and theory of self-assembly and network formation in reversibly cross-linked equilibrium polymers

    Science.gov (United States)

    Kindt, James T.

    2005-10-01

    A simulation model of hard spheres capable of reversible assembly into chains, which then may reversibly cross-link into networks, has been studied through grand canonical Monte Carlo simulation. Effects of varying intra- and interchain bond strengths, chain flexibilities, and restrictions on cross-linking angle were investigated. Observations including chain-length distributions and phase separation could be captured in most cases using a simple model theory. The coupling of chain growth to cross-linking was shown to be highly sensitive to the treatment of cross-linking by chain ends. In some systems, ladderlike domains of several cross-links joining two chains were common, resulting from cooperativity in the cross-linking. Extended to account for this phenomenon, the model theory predicts that such cooperativity will suppress phase separation in weakly polymerizing chains and at high cross-link concentration. In the present model, cross-linking stabilizes the isotropic phase with respect to the nematic phase, causing a shift in the isotropic-nematic transition to higher monomer concentration than in simple equilibrium polymers.

  17. Langevin dynamcis simulations of driven polymer translocation into a cross-linked gel.

    Science.gov (United States)

    Sean, David; Slater, Gary W

    2017-03-01

    We investigate the dynamics of driving a polyelectrolyte such as DNA through a nanopore and into a cross-linked gel. Placing the gel on the trans-side of the nanopore can increase the translocation time while not negatively affecting the capture rates. Thus, this setup combines the mechanics of gel electrophoresis with nanopore translocation. However, contrary to typical gel electrophoresis scenarios, the effect of the field is localized in the immediate vicinity of the nanopore and becomes negligible inside the gel matrix. Thus, we investigate the process by which a semiflexible polymer can be pushed into a gel matrix via a localized field and we describe how the dynamics of gel penetration depends upon the field intensity, polymer stiffness, and gel pore size. Our simulation results show that a semiflexible polymer enters the gel region with two distinct mechanisms depending upon the ratio between the bending length scale and the gel pore size. In both regimes, the gel fibers cause a net increase in the mean translocation time. Interestingly, the translocation rate is found to be constant (a potentially useful feature for many applications) during the predominant part of the translocation process when the polymer is stiff over a length scale comparable to the gel pore size.

  18. Fabrication and morphology of spongelike polymer material based on cross-linked sulfonated polystyrene particles.

    Science.gov (United States)

    Ji, Xiang; Wang, Mozhen; Xu, Dezhi; Ge, Xuewu; Liu, Huarong; Tang, Tao

    2012-04-03

    A novel spongelike polymer material has been fabricated by γ-ray induced polymerization of methylmethacrylate (MMA) in an emulsion containing cross-linked sulfonated polystyrene (CSP) particles. Scanning electron microscopy (SEM) images reveal that the spongelike structure is made up of interlinked nanosized PMMA particles with micrometer-sized CSP-PMMA particles embedded inside. The nitrogen adsorption isotherm discloses that the spongelike material has a high specific surface area of 29 m(2)/g and a narrow pore size distribution of 60-120 nm. The formation mechanism is discussed in this paper, which indicates that the key steps to form the spongelike material include a Pickering emulsion stabilized by the CSP particles, followed by the swelling process of MMA into these particles. This approach offers a more convenient alternative to prepare polymeric spongelike material without any etching procedure.

  19. Networking properties of cyclodextrin-based cross-linked polymers probed by inelastic light-scattering experiments.

    Science.gov (United States)

    Rossi, Barbara; Caponi, Silvia; Castiglione, Franca; Corezzi, Silvia; Fontana, Aldo; Giarola, Marco; Mariotto, Gino; Mele, Andrea; Petrillo, Caterina; Trotta, Francesco; Viliani, Gabriele

    2012-05-03

    An integrated experimental approach, based on inelastic light-scattering techniques, has been here employed for a multilength scale characterization of networking properties of cyclodextrin nanosponges, a new class of cross-linked polymeric materials built up from natural oligosaccharides cyclodextrins. By using Raman and Brillouin scattering experiments, we performed a detailed inspection of the vibrational dynamics of these polymers over a wide frequency window ranging from gigahertz to terahertz, with the aim of providing physical descriptors correlated to the cross-linking degree and elastic properties of the material. The results seem to suggest that the stiffness of cross-linked polymers can be successfully tuned by acting on the type and the relative amount of the cross-linker during the synthesis of a polymer matrix, predicting and controlling their swelling and entrapment properties. The proposed experimental approach is a useful tool for investigating the structural and physicochemical properties of polymeric network systems.

  20. Physically Cross-linked Polymer Binder Induced by Reversible Acid-Base Interaction for High-Performance Silicon Composite Anodes.

    Science.gov (United States)

    Lim, Sanghyun; Chu, Hodong; Lee, Kukjoo; Yim, Taeeun; Kim, Young-Jun; Mun, Junyoung; Kim, Tae-Hyun

    2015-10-28

    Silicon is greatly promising for high-capacity anode materials in lithium-ion batteries (LIBs) due to their exceptionally high theoretical capacity. However, it has a big challenge of severe volume changes during charge and discharge, resulting in substantial deterioration of the electrode and restricting its practical application. This conflict requires a novel binder system enabling reliable cyclability to hold silicon particles without severe disintegration of the electrode. Here, a physically cross-linked polymer binder induced by reversible acid-base interaction is reported for high performance silicon-anodes. Chemical cross-linking of polymer binders, mainly based on acidic polymers including poly(acrylic acid) (PAA), have been suggested as effective ways to accommodate the volume expansion of Si-based electrodes. Unlike the common chemical cross-linking, which causes a gradual and nonreversible fracturing of the cross-linked network, a physically cross-linked binder based on PAA-PBI (poly(benzimidazole)) efficiently holds the Si particles even after the large volume changes due to its ability to reversibly reconstruct ionic bonds. The PBI-containing binder, PAA-PBI-2, exhibited large capacity (1376.7 mAh g(-1)), high Coulombic efficiency (99.1%) and excellent cyclability (751.0 mAh g(-1) after 100 cycles). This simple yet efficient method is promising to solve the failures relating with pulverization and isolation from the severe volume changes of the Si electrode, and advance the realization of high-capacity LIBs.

  1. FTIR spectroscopy and thermodynamics of hydrogen adsorbed in a cross-linked polymer.

    Science.gov (United States)

    Spoto, Giuseppe; Vitillo, Jenny G; Cocina, Donato; Damin, Alessandro; Bonino, Francesca; Zecchina, Adriano

    2007-09-28

    The adsorption of H(2) in a cross-linked poly(styrene-co-divinylbenzene) (St-DVB) microporous polymer (BET surface area 920 m(2) g(-1)) is studied by volumetric and gravimetric methods, FTIR spectroscopy at variable temperature (300-14 K) and ab initio calculations. At 77 K the polymer reversibly stores up to 1.3 mass% H(2) at a pressure of 1 bar and 1.8 mass% at 10 bar. The adsorption process involves the specific interaction of H(2) with the structural phenyl rings through weak dispersive forces. The interacting molecules become IR active and give rise to vibrational and rotational-vibrational manifestations which are affected by the temperature, the contact time and the H(2) equilibrium pressure. The spectra of the H(2)/St-DVB system reported here represent the first IR evidence of the adsorption of hydrogen on unsaturated molecules. The adsorption enthalpy is evaluated by the VTIR (variable temperature IR spectroscopy) method (C. Otero Areán et al., Phys. Chem. Chem. Phys., 2007, DOI: 10.1039/b615535a) and compared with the results of ab initio calculations for the H(2)/benzene interaction and with literature data.

  2. Silica-shell cross-linked micelles encapsulating fluorescent conjugated polymers for targeted cellular imaging.

    Science.gov (United States)

    Tan, Happy; Zhang, Yu; Wang, Miao; Zhang, Zhongxing; Zhang, Xinhai; Yong, Anna Marie; Wong, Siew Yee; Chang, Alex Yuang-chi; Chen, Zhi-Kuan; Li, Xu; Choolani, Mahesh; Wang, John

    2012-01-01

    A bioinspired silification approach was successfully used to encapsulate fluorescent conjugated polymers inside silica-shell cross-linked polymeric micelles (CP-SSCL) in the highly benign synthesis environment of room temperature and near-neutral aqueous environment. Four different conjugated polymers were employed to demonstrate the versatility of the bioinspired silification, resulting in the formation of CP-SSCL with different emission wavelengths across the visible spectrum. The CP-SSCL are characterized by a large absorption coefficient and high quantum yield, indicating that they exhibit the required high fluorescence brightness for cellular imaging application. In addition, the CP-SSCL also exhibit a high colloidal stability and low cytotoxicity. The in vitro studies of using MDA-MB-231 breast cancer cells show that the CP-SSCL are successfully uptaken by the cancer cells and located at the cytoplasm of the cells. Furthermore, by conjugating folic acid on their surfaces, the uptake of CP-SSCL by MDA-MB-231 cells was enhanced significantly, suggesting their great potential for targeted imaging and early detection of cancer cells.

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

    Science.gov (United States)

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

    2005-01-01

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

  4. Formation of enzyme polymer engineered structure for laccase and cross-linked laccase aggregates stabilization.

    Science.gov (United States)

    Hassani, Thanina; Ba, Sidy; Cabana, Hubert

    2013-01-01

    Laccase and laccase-based cross-linked enzyme aggregates (CLEAs) were stabilized through the formation of a surrounding polymeric network made of chitosan and 3-aminopropyltriethoxysilane. The thermoresistance of the resulting enzyme polymer engineered structures of laccase (EPES-lac) and CLEAs (EPES-CLEA) were more than 30 times higher than that of free laccase and CLEAs at pH 3 and 40 °C. The EPES showed higher residual activity than the unmodified biocatalysts against chaotropic salts (up to 10 times), EDTA (up to 5 times), methanol (up to 15 times) and acetone (up to 20 times). The Michaelis-Menten kinetic parameters revealed that the affinity for 2,2'-azino-bis-(3-ethylbenzothiazoline-6-sulphonic acid) has doubled for the EPES-lac and EPES CLEA compared to their unmodified forms. The EPES-lac structures acted optimally at pH 4 and their activity was nearly temperature-independent, while the laccase activity of EPES-CLEA was optimal at pH 4 and 60 °C. Globally, the EPES have shown significantly improved properties which make them attractive candidate for the development of laccase-based applications.

  5. Optimization of β-cyclodextrin cross-linked polymer for monitoring of quercetin

    Science.gov (United States)

    Zhu, Xiashi; Ping, Wenhui

    2014-11-01

    A novel method for the separation/analysis of quercetin was described, which was based on the investigation of the inclusion interactions of β-cyclodextrin cross-linked polymer (β-CDCP) with quercetin (Qu) and the adsorption behavior of Qu on β-CDCP. The inclusion interaction of β-CDCP with Qu was studied through FTIR, TGA and 13C NMR. Under the optimum conditions, the preconcentration factor of the proposed method was approximately 8.8, the β-CDCP could be used repeatedly for 30 times and offered better recovery. The linear range, limit of detection (LOD) and the relative standard deviation (RSD) was found to be 0.10-12.0 μg mL-1, 4.6 ng mL-1 and 3.10% (n = 3, c = 2.0 μg mL-1) respectively. This technique had been successfully applied to the determination of Qu in real samples.

  6. Highly Stable and Porous Cross-Linked Polymers for Efficient Photocatalysis

    Energy Technology Data Exchange (ETDEWEB)

    Xie, Zhigang; Wang, Cheng; deKrafft, Kathryn E.; Lin, Wenbin

    2011-02-23

    Porous cross-linked polymers (PCPs) with phosphorescent [Ru(bpy)₃]{sup 2+} and [Ir(ppy)₂(bpy)]{sup +} building blocks were obtained via octacarbonyldicobalt (Co₂(CO)₈)-catalyzed alkyne trimerization reactions. The resultant Ru- and Ir-PCPs exhibited high porosity with specific surface areas of 1348 and 1547 m²/g, respectively. They are thermally stable at up to 350 °C in air and do not dissolve or decompose in all solvents tested, including concentrated hydrochloric acid. The photoactive PCPs were shown to be highly effective, recyclable, and reusable heterogeneous photocatalysts for aza-Henry reactions, α-arylation of bromomalonate, and oxyamination of an aldehyde, with catalytic activities comparable to those of the homogeneous [Ru(bpy)₃]{sup 2+} and [Ir(ppy)₂(bpy)]{sup +} photocatalysts. This work highlights the potential of developing photoactive PCPs as highly stable, molecularly tunable, and recyclable and reusable heterogeneous photocatalysts for a variety of important organic transformations.

  7. Using Selected Chemical and Physical Factors to Cross-link a BioCo Polymer Binder - Mineral Matrix System

    Directory of Open Access Journals (Sweden)

    B. Grabowska

    2013-04-01

    Full Text Available This publication describes research on the course of the process of cross-linking new BioCo polymer binders - in the form of water-based polymer compositions of poly(acrylic acid or poly(sodium acrylate/modified polysaccharide - using selected physical and chemical factors. It has been shown that the type of cross-linking factor used influences the strength parameters of the moulding sand. The crosslinking factors selected during basic research make it possible to obtain sand strengths similar to those of samples of sands bonded with commercial binders. Microwave radiation turned out to be the most effective cross-linking factor in a binder-matrix system. It was proven that adsorption in the microwave radiation field leads to the formation of polymer lattices with hydrogen bonds which play a major role in maintaining the formed cross-linked structures in the binder-matrix system. As a result, the process improves the strength parameters of the sand, whereas the hardening process in a microwave field significantly shortens the setting time.

  8. Exceptionally stable polymer electrolyte for a lithium battery based on cross-linking by a residue-free process

    Science.gov (United States)

    Daigle, Jean-Christophe; Asakawa, Yuichiro; Vijh, Ashok; Hovington, Pierre; Armand, Michel; Zaghib, Karim

    2016-11-01

    In this paper, we report the synthesis of cross-linked copolymers of glycidyl methacrylate (GMA) and poly (ethylene glycol) methyl methacrylate (PEGMA) for use as solid polymer electrolytes (SPE). The cross-linking is performed with volatile ethylene diamine, thus preventing the accumulation of undesirable precursors in the final membrane. The structure of the cross-linked polymer electrolyte was investigated by 13C solid NMR and its physical properties were examined by DSC, TGA and stress-strain tests. The ionic conductivities were determined by AC Impedance, which showed that the SPEs have good conductivities (10-5 Scm-1) at 80 °C. The highest capacity measured with these polymers was 151 mAh g-1 at C/6 and 80 °C for a LFP/SPE/Lithium battery. The retention capacity is high, at 97% after 80 cycles at different rates of cycling. The Young's modulus of the membranes is as high as 1 GPa. The SEM images showed no evidence of lithium dendrites and no degradation after cycling. Therefore, the polymer is a good candidate for battery operation over a long time. Especially important is the ability of this polymer to prevent growth of dendrites on the Li-metal electrode.

  9. Stabilized sulfonated aromatic polymers by in situ solvothermal cross-linking

    Directory of Open Access Journals (Sweden)

    Maria Luisa eDi Vona

    2014-10-01

    Full Text Available The cross-link reaction via sulfone bridges of sulfonated polyetheretherketone (SPEEK by thermal treatment at 180 °C in presence of dimethylsulfoxide (DMSO is discussed. The modifications of properties subsequent to the cross-linking are presented. The mechanical strength as well as the hydrolytic stability increased with the thermal treatment time, i.e., with the degree of cross-linking. The proton conductivity was determined as function of temperature, IEC, degree of cross-linking and hydration number. The memory effect, which is the membrane ability to remember the water uptake reached at high temperature also at lower temperature, is exploited in order to achieve high values of conductivity. Membranes swelled at 110 °C can reach a conductivity of 0.14 S/cm at 80°C with a hydration number ( of 73.

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

    Science.gov (United States)

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

    2014-03-26

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

  11. Emerging synthetic strategies for core cross-linked star (CCS) polymers and applications as interfacial stabilizers: bridging linear polymers and nanoparticles.

    Science.gov (United States)

    Chen, Qijing; Cao, Xueteng; Xu, Yuanyuan; An, Zesheng

    2013-10-01

    Core cross-linked star (CCS) polymers become increasingly important in polymer science and are evaluated in many value-added applications. However, limitations exist to varied degrees for different synthetic methods. It is clear that improvement in synthetic efficiency is fundamental in driving this field moving even further. Here, the most recent advances are highlighted in synthetic strategies, including cross-linking with cross-linkers of low solubility, polymerization-induced self-assembly in aqueous-based heterogeneous media, and cross-linking via dynamic covalent bonds. The understanding of CCS polymers is also further refined to advocate their role as an intermediate between linear polymers and polymeric nanoparticles, and their use as interfacial stabilizers is rationalized within this context.

  12. Clinical safety and wear resistance of the phospholipid polymer-grafted highly cross-linked polyethylene liner.

    Science.gov (United States)

    Moro, Toru; Takatori, Yoshio; Tanaka, Sakae; Ishihara, Kazuhiko; Oda, Hiromi; Kim, Yoon Taek; Umeyama, Takashige; Fukatani, Eisei; Ito, Hideya; Kyomoto, Masayuki; Oshima, Hirofumi; Tanaka, Takeyuki; Kawaguchi, Hiroshi; Nakamura, Kozo

    2016-11-03

    To reduce the production of wear particles and subsequent aseptic loosening, we created a human articular cartilage-mimicked surface for a highly cross-linked polyethylene liner, whose surface grafted layer consisted of a biocompatible phospholipid polymer, poly(2-methacryloyloxyethyl phosphorylcholine). Although our previous in vitro findings showed that poly(2-methacryloyloxyethyl phosphorylcholine)-grafted particles were biologically inert and caused no subsequent bone resorptive responses, and poly(2-methacryloyloxyethyl phosphorylcholine) grafting markedly decreased wear in hip joint simulator tests, the clinical safety, and in vivo wear resistance of poly(2-methacryloyloxyethyl phosphorylcholine)-grafted highly cross-linked polyethylene liners remained open to question. Therefore, in the present study, we evaluated clinical and radiographic outcomes of poly(2-methacryloyloxyethyl phosphorylcholine)-grafted highly cross-linked polyethylene liners 5 years subsequent to total hip replacement in 68 consecutive patients. No reoperation was required for any reason, and no adverse events were associated with the implanted liners. The average Harris Hip Score increased from 38.6 preoperatively to 96.5 5 years postoperatively, and health-related quality of life, as indicated by the Short Form 36 Health Survey, improved. Radiographic analyses showed no periprosthetic osteolysis or implant migration. Between 1 and 5 years postoperatively, the mean steady-state wear rate was 0.002 mm/year, which represented a marked reduction relative to other highly cross-linked polyethylene liners, and appeared to be unaffected by patient-related or surgical factors. Although longer follow up is required, poly(2-methacryloyloxyethyl phosphorylcholine)-grafted highly cross-linked polyethylene liners improved mid-term clinical outcomes. The clinical safety and wear-resistance results are encouraging with respect to the improvement of long-term clinical outcomes with poly(2

  13. Molecular Dynamics Simulation of Cross-Linked Epoxy Polymers: the Effect of Force Field on the Estimation of Properties

    Directory of Open Access Journals (Sweden)

    B. Arab

    2013-03-01

    Full Text Available In this paper, the molecular dynamics method was used to calculate the physical and mechanical properties of the cross-linked epoxy polymer composed of diglycidyl ether of bisphenol-A (DGEBA as resin and diethylenetriamine (DETA as curing agent. Calculation of the properties was performed using the constant-strain (static approach. A series of independent simulations were carried out based on four widely used force fields; COMPASS, PCFF, UFF and Dreiding. Proper comparisons between the results and also with experimental observations were made to find the most suitable force field for molecular dynamics simulation of polymer materials.

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

    Science.gov (United States)

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

    2016-05-01

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

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

    Science.gov (United States)

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

    2016-05-18

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

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

    Science.gov (United States)

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

    2016-01-01

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

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

    Science.gov (United States)

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

    This study reports the development of a new system of porous, chemically cross-linked, gel polymer electrolytes based on poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) copolymer as a polymer matrix, polyethylene glycol (PEG) as a plasticizer, and polyethylene glycol dimethacrylate (PEGDMA) as a chemical cross-linking oligomer. The electrolytes are prepared by a combination of controlled evaporation and thermal polymerization of PEGDMA. PVdF-HFP/PEG/PEGDMA gel polymer electrolytes with a composition of 5/3/2 exhibit both high ambient ionic conductivity, viz., >1 mS cm -1, and a high tensile modulus of 52 MPa, because of their porous and network structures. All the blends of electrolytes are electrochemically stable up to 5 V versus Li/Li + in the presence of 1 M LiPF 6/ethylene carbonate-diethyl carbonate (EC-DEC). With these polymer electrolytes, rechargeable lithium batteries composed of carbon anode and LiCoO 2 cathode have acceptable cycleability and a good rate capability.

  18. Core Cross-Linked Multiarm Star Polymers with Aggregation-Induced Emission and Temperature Responsive Fluorescence Characteristics

    KAUST Repository

    Zhang, Zhen

    2017-05-19

    Aggregation-induced emission (AIE) active core cross-linked multiarm star polymers, carrying polystyrene (PS), polyethylene (PE), or polyethylene-b-polycaprolactone (PE-b-PCL) arms, have been synthesized through an “arm-first” strategy, by atom transfer radical copolymerization (ATRP) of a double styrene-functionalized tetraphenylethene (TPE-2St) used as a cross-linker with linear arm precursors possessing terminal ATRP initiating moieties. Polyethylene macroinitiator (PE–Br) was prepared via the polyhomologation of dimethylsulfoxonium methylide with triethylborane followed by oxidation/hydrolysis and esterification of the produced PE–OH with 2-bromoisobutyryl bromide; polyethylene-block-poly(ε-caprolactone) diblock macroinitiator was derived by combining polyhomologation with ring-opening polymerization (ROP). All synthesized star polymers showed AIE-behavior either in solution or in bulk. At high concentration in good solvents (e.g., THF, or toluene) they exhibited low photoluminescence (PL) intensity due to the inner filter effect. In sharp contrast to the small molecule TPE-2St, the star polymers were highly emissive in dilute THF solutions. This can be attributed to the cross-linked structure of poly(TPE-2St) core which restricts the intramolecular rotation and thus induces emission. In addition, the PL intensity of PE star polymers in THF(solvent)/n-hexane(nonsolvent) mixtures, due to their nearly spherical shape, increased when the temperature decreased from 55 to 5 °C with a linear response in the range 40–5 °C.

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

    Science.gov (United States)

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

    2015-02-25

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

  20. Effect of Cross-Linking on the Structure and Growth of Polymer Films Prepared by Interfacial Polymerization.

    Science.gov (United States)

    Berezkin, Anatoly V; Kudryavtsev, Yaroslav V

    2015-11-10

    Interfacial polymerization of tri- and bifunctional monomers (A3B2 polymerization) is investigated by dissipative particle dynamics to reveal an effect of cross-linking on the reaction kinetics and structure of the growing polymer film. Regardless of the comonomer reactivity and miscibility, the kinetics in an initially bilayer melt passes from the reaction to diffusion control. Within the crossover period, branched macromolecules undergo gelation, which drastically changes the scenario of the polymerization process. Comparison with the previously studied linear interfacial polymerization (Berezkin, A. V.; Kudryavtsev, Y. V. Linear Interfacial Polymerization: Theory and Simulations with Dissipative Particle Dynamics J. Chem. Phys. 2014, 141, 194906) shows similar conversion rates but very different product characteristics. Cross-linked polymer films are markedly heterogeneous in density, their average polymerization degree grows with the comonomer miscibility, and end groups are mostly trapped deeply in the film core. Products of linear interfacial polymerization demonstrate opposite trends as they are spontaneously homogenized by a convective flow of macromolecules expelled from the reactive zone to the film periphery, which we call the reactive extrusion effect and which is hampered in branched polymerization. Influence of the comonomer architecture on the polymer film characteristics could be used in various practical applications of interfacial polymerization, such as fabrication of membranes, micro- and nanocapsules and 3D printing.

  1. Nanosecond laser-induced periodic surface structuring of cross-linked azo-polymer films

    Energy Technology Data Exchange (ETDEWEB)

    Berta, Marco, E-mail: marco.berta@univ-amu.fr [Aix Marseille Université, CNRS, ICR (Institut de Chimie Radicalaire) UMR 7273, 13397 Marseille Cedex 20 (France); Biver, Émeric [Aix Marseille Université, CNRS, LP3 UMR 7341, 13288 Marseille (France); Maria, Sébastien; Phan, Trang N.T. [Aix Marseille Université, CNRS, ICR (Institut de Chimie Radicalaire) UMR 7273, 13397 Marseille Cedex 20 (France); D’Aleo, Anthony; Delaporte, Philippe; Fages, Frederic [Aix Marseille Université, CNRS, CINaM UMR 7325, 13288 Marseille (France); Gigmes, Didier [Aix Marseille Université, CNRS, ICR (Institut de Chimie Radicalaire) UMR 7273, 13397 Marseille Cedex 20 (France)

    2013-10-01

    In this work we discuss the response to laser ablation of a poly(4-vinylbenzyl azide-random-methyl methacrylate) (p((S-N{sub 3})-r-MMA)) random copolymer. This material is cross-linkable thermally and upon exposure to UV light, and on cross-linked films the irradiation with a 248 nm ns KrF laser induces the formation of laser induced periodical surface structure (LIPSS). The LIPSS morphology is dependent on the amount of 4-vinylbenzyl azide (S-N{sub 3}) groups in the pristine copolymer. We propose a crosslinking mechanism based on the scission of azide with formation of azo groups and we discuss the possible relationship between this chemical modifications and the formation of ripples on the bottom of laser ablation cavities.

  2. Nanosecond laser-induced periodic surface structuring of cross-linked azo-polymer films

    Science.gov (United States)

    Berta, Marco; Biver, Émeric; Maria, Sébastien; Phan, Trang N. T.; D'Aleo, Anthony; Delaporte, Philippe; Fages, Frederic; Gigmes, Didier

    2013-10-01

    In this work we discuss the response to laser ablation of a poly(4-vinylbenzyl azide-random-methyl methacrylate) (p((S-N3)-r-MMA)) random copolymer. This material is cross-linkable thermally and upon exposure to UV light, and on cross-linked films the irradiation with a 248 nm ns KrF laser induces the formation of laser induced periodical surface structure (LIPSS). The LIPSS morphology is dependent on the amount of 4-vinylbenzyl azide (S-N3) groups in the pristine copolymer. We propose a crosslinking mechanism based on the scission of azide with formation of azo groups and we discuss the possible relationship between this chemical modifications and the formation of ripples on the bottom of laser ablation cavities.

  3. Removal of Parabens from Aqueous Solution Using β-Cyclodextrin Cross-Linked Polymer

    OpenAIRE

    Mhd Radzi Bin Abas; Sharifah Mohamad; Yuk Ping Chin

    2010-01-01

    The removal of four parabens, methyl-, ethyl-, propyl-, and benzyl-paraben, by β-cyclodextrin (β-CD) polymer from aqueous solution was studied. Different β-CD polymers were prepared by using two cross-linkers, i.e., hexamethylene diisocyanate (HMDI) and toluene-2,6-diisocyanate (TDI), with various molar ratios of cross-linker. β-CD-HMDI polymer with molar ratio of 1:7 and β-CD-TDI polymer with ratio 1:4 gave the highest adsorption of parabens among the β-CD-HMDI and β-CD-TDI series, and were ...

  4. Sorption of 2-Chlorophenol from aqueous solutions by functionalized cross-linked polymers

    Directory of Open Access Journals (Sweden)

    Rodrigo Martins Fráguas

    2013-01-01

    Full Text Available This manuscript describes the synthesis of three polymers based on styrene (STY, divinylbenzene (DVB and two different vinyl monomers: methyl methacrylate (MMA and acrylonitrile (AN. The STY-DVB, STY-DVB-MMA and STY-DVB-AN polymers were synthesized employing the aqueous suspension technique. Reaction yields were 73%, 81% and 75%, respectively. They were morphological and chemically characterized using different techniques. The extraction capacity of the polymers was evaluated using 2-chlorophenol. The polymer extraction capacities were evaluated varying contact time the (1 h, 3 h and 5 h, temperature (30 °C, 35 °C and 40 °C, and pH (3, 5.6 and 8. The STY-DVB-AN polymer was the most efficient; it removed around 95% of the analyte using a contact time 50 h.

  5. Fabrication of Redox-Responsive Degradable Capsule Particles by a Shell-Selective Photoinduced Cross-Linking Approach from Spherical Polymer Particles.

    Science.gov (United States)

    Kitayama, Yukiya; Takeuchi, Toshifumi

    2017-09-18

    In this study, a fabrication route towards functional capsule particles was successfully developed by means of a self-templating shell-selective cross-linking strategy that enables us to prepare shell-cross-linked hollow polymer particles directly from homogeneous spherical polymer particles. To prepare redox-responsive degradable capsule particles, a newly designed monomer bearing a photoinduced post-cross-linking group (cinnamoyl group) and a redox-environment-responsive cleavable group (disulfide group), N-cinnamoyl-N'-methyacryloylcystamine (MCC), was synthesized. Redox-responsive degradable capsule particles were successfully prepared from homogeneous spherical poly(MCC)-based particles by a self-templating shell-selective photoinduced cross-linking approach. Moreover, the cargo loading capability of the shell-cross-linked hollow particles was confirmed through a solvent exchange procedure using dyes, polymer precursors and anticancer reagents. Furthermore, redox-responsive degradability of the capsule polymer particles was also confirmed by adding a reducing agent for cleavage of the disulfide linkage. We hope that the efficient fabrication route of functional capsule particles directly from spherical polymer particles opens efficient routes for the fabrication of a wide range of capsule particles; in particular, this technique is robust, productive, and facile because neither additional sacrificial template particles nor toxic solvents are required. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  6. Removal of Parabens from Aqueous Solution Using β-Cyclodextrin Cross-Linked Polymer

    Science.gov (United States)

    Chin, Yuk Ping; Mohamad, Sharifah; Abas, Mhd Radzi Bin

    2010-01-01

    The removal of four parabens, methyl-, ethyl-, propyl-, and benzyl-paraben, by β-cyclodextrin (β-CD) polymer from aqueous solution was studied. Different β-CD polymers were prepared by using two cross-linkers, i.e., hexamethylene diisocyanate (HMDI) and toluene-2,6-diisocyanate (TDI), with various molar ratios of cross-linker. β-CD-HMDI polymer with molar ratio of 1:7 and β-CD-TDI polymer with ratio 1:4 gave the highest adsorption of parabens among the β-CD-HMDI and β-CD-TDI series, and were subsequently used for further studies. The adsorption capacity of β-CD-HMDI is 0.0305, 0.0376, 0.1854 and 0.3026 mmol/g for methyl-, ethyl-, propyl-, and benzyl-paraben, respectively. β-CD-TDI have higher adsorption capacities compared with β-CD-HMDI, the adsorption capacity are 0.1019, 0.1286, 0.2551, and 0.3699 mmol/g methyl-, ethyl-, propyl-, and benzyl-paraben respectively. The parameters studied were adsorption capacity, water retention, and reusability. Role of both cross-linker in adsorption, hydrophobicity of polymers, and adsorption capacity of different parabens were compared and discussed. All experiments were conducted in batch adsorption technique. These polymers were applied to real samples and showed positive results. PMID:20957106

  7. Removal of Parabens from Aqueous Solution Using β-Cyclodextrin Cross-Linked Polymer

    Directory of Open Access Journals (Sweden)

    Mhd Radzi Bin Abas

    2010-09-01

    Full Text Available The removal of four parabens, methyl-, ethyl-, propyl-, and benzyl-paraben, by β-cyclodextrin (β-CD polymer from aqueous solution was studied. Different β-CD polymers were prepared by using two cross-linkers, i.e., hexamethylene diisocyanate (HMDI and toluene-2,6-diisocyanate (TDI, with various molar ratios of cross-linker. β-CD-HMDI polymer with molar ratio of 1:7 and β-CD-TDI polymer with ratio 1:4 gave the highest adsorption of parabens among the β-CD-HMDI and β-CD-TDI series, and were subsequently used for further studies. The adsorption capacity of β-CD-HMDI is 0.0305, 0.0376, 0.1854 and 0.3026 mmol/g for methyl-, ethyl-, propyl-, and benzyl-paraben, respectively. β-CD-TDI have higher adsorption capacities compared with β-CD-HMDI, the adsorption capacity are 0.1019, 0.1286, 0.2551, and 0.3699 mmol/g methyl-, ethyl-, propyl-, and benzyl-paraben respectively. The parameters studied were adsorption capacity, water retention, and reusability. Role of both cross-linker in adsorption, hydrophobicity of polymers, and adsorption capacity of different parabens were compared and discussed. All experiments were conducted in batch adsorption technique. These polymers were applied to real samples and showed positive results.

  8. Removal of parabens from aqueous solution using β-cyclodextrin cross-linked polymer.

    Science.gov (United States)

    Chin, Yuk Ping; Mohamad, Sharifah; Abas, Mhd Radzi Bin

    2010-09-20

    The removal of four parabens, methyl-, ethyl-, propyl-, and benzyl-paraben, by β-cyclodextrin (β-CD) polymer from aqueous solution was studied. Different β-CD polymers were prepared by using two cross-linkers, i.e., hexamethylene diisocyanate (HMDI) and toluene-2,6-diisocyanate (TDI), with various molar ratios of cross-linker. β-CD-HMDI polymer with molar ratio of 1:7 and β-CD-TDI polymer with ratio 1:4 gave the highest adsorption of parabens among the β-CD-HMDI and β-CD-TDI series, and were subsequently used for further studies. The adsorption capacity of β-CD-HMDI is 0.0305, 0.0376, 0.1854 and 0.3026 mmol/g for methyl-, ethyl-, propyl-, and benzyl-paraben, respectively. β-CD-TDI have higher adsorption capacities compared with β-CD-HMDI, the adsorption capacity are 0.1019, 0.1286, 0.2551, and 0.3699 mmol/g methyl-, ethyl-, propyl-, and benzyl-paraben respectively. The parameters studied were adsorption capacity, water retention, and reusability. Role of both cross-linker in adsorption, hydrophobicity of polymers, and adsorption capacity of different parabens were compared and discussed. All experiments were conducted in batch adsorption technique. These polymers were applied to real samples and showed positive results.

  9. In Vitro and in Vivo Evaluation of Novel Cross-Linked Saccharide Based Polymers as Bile Acid Sequestrants

    Directory of Open Access Journals (Sweden)

    Francisco Javier Lopez-Jaramillo

    2015-02-01

    Full Text Available Bile acid sequestrants (BAS represent a therapeutic approach for the management of hypercholesterolemia that relies on the cationic polymeric nature of BAS to selectively bind negatively charged bile acids. We hypothesized that the cross-linking of β-cyclodextrin (β-CD and saccharides such as starch or dextrin with divinyl sulfone (DVS yields homo- and hetero-polymeric materials with the ability to trap sterols. Our hypothesis was put to test by synthesizing a library of 22 polymers that were screened to evaluate their capability to sequester both cholesterol (CHOL and cholic and deoxycholic acids (CA and DCA. Three polymers synthesized in high yield were identified as promising. Two were neutral hetero-polymers of β-CD and starch or dextrin and the third was a weakly cationic homo-polymer of starch, highlighting the importance of the cavity effect. They were tested in hypercholesterolemic male Wistar rats and their ability to regulate hypercholesterolemia was similar to that for the reference BAS cholestyramine, but with two additional advantages: (i they normalized the TG level and (ii they did not increase the creatinine level. Neither hepatotoxicity nor kidney injury was detected, further supporting them as therapeutical candidates to manage hypercholesterolemia.

  10. A colourimetric method for the determination of the degree of chemical cross-linking in aspartic acid-based polymer gels

    Directory of Open Access Journals (Sweden)

    B. Gyarmati

    2015-02-01

    Full Text Available A 2,4,6-trinitrobenzenesulphonic acid (TNBS-based assay is developed to determine the degree of chemical cross-linking in aspartic acid-based polymer gels. The conventional colourimetric method for the quantitative determination of amine groups is difficult to use in polymer networks; thus, an improved method is developed to analyse polymer gels swollen in dimethyl sulfoxide (DMSO. Reaction products of the derivatizing reaction are examined by NMR. The chemical stability of the reagent is increased in DMSO, and the method shows satisfactory linearity and accuracy. The degree of chemical cross-linking in the investigated gels is close to its theoretical maximum, but the conversion of the pendant amine groups to cross-linking points is strongly dependent on the feed composition of the gels.

  11. Molecular dynamics simulation of cross-linked urea-formaldehyde polymers for self-healing nanocomposites: prediction of mechanical properties and glass transition temperature.

    Science.gov (United States)

    Arab, Behrouz; Shokuhfar, Ali

    2013-11-01

    Urea-formaldehyde polymers, which are utilized in the adhesives industry, have recently been shown to be suitable materials for synthesizing micro/nanocapsules for use in self-healing (nano)composites. In this study, molecular dynamics was employed to simulate the process in which urea and formaldehyde are cross-linked via methylene and ether cross linkers, and to study the structure and mechanical/thermal properties of simulated poly(urea-formaldehyde)s (PUFs). The elastic stiffness constants of the simulated materials were calculated using the constant-strain (static) method. A temperature cycle was applied to the cross-linked PUFs, and the glass transition behavior of each material was investigated through the mean squared displacement (MSD) and temperature evolution of the energy and the specific volume of the polymer. The simulation results confirmed that there was considerable improvement in the properties of the poly(UF) materials upon cross linking. The radial distribution function was also used to study the local structures of the polymers, and this revealed that increasing the temperature and cross linking density results in a significant drop in hydrogen bonding intensity in the cross-linked PUF systems.

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

    Science.gov (United States)

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

    2016-06-22

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

  13. Synthesis, characterisation, and evaluation of a cross-linked disulphide amide-anhydride-containing polymer based on cysteine for colonic drug delivery.

    Science.gov (United States)

    Lim, Vuanghao; Peh, Kok Khiang; Sahudin, Shariza

    2013-12-18

    The use of disulphide polymers, a low redox potential responsive delivery, is one strategy for targeting drugs to the colon so that they are specifically released there. The objective of this study was to synthesise a new cross-linked disulphide-containing polymer based on the amino acid cysteine as a colon drug delivery system and to evaluate the efficiency of the polymers for colon targeted drug delivery under the condition of a low redox potential. The disulphide cross-linked polymers were synthesised via air oxidation of 1,2-ethanedithiol and 3-mercapto-N-2-(3-mercaptopropionamide)-3-mercapto propionic anhydride (trithiol monomers) using different ratio combinations. Four types of polymers were synthesised: P10, P11, P151, and P15. All compounds synthesised were characterised by NMR, IR, LC-MS, CHNS analysis, Raman spectrometry, SEM-EDX, and elemental mapping. The synthesised polymers were evaluated in chemical reduction studies that were performed in zinc/acetic acid solution. The suitability of each polymer for use in colon-targeted drug delivery was investigated in vitro using simulated conditions. Chemical reduction studies showed that all polymers were reduced after 0.5-1.0 h, but different polymers had different thiol concentrations. The bacterial degradation studies showed that the polymers were biodegraded in the anaerobic colonic bacterial medium. Degradation was most pronounced for polymer P15. This result complements the general consensus that biodegradability depends on the swellability of polymers in an aqueous environment. Overall, these results suggest that the cross-linked disulphide-containing polymers described herein could be used as coatings for drugs delivered to the colon.

  14. Synthesis, Characterisation, and Evaluation of a Cross-Linked Disulphide Amide-Anhydride-Containing Polymer Based on Cysteine for Colonic Drug Delivery

    Directory of Open Access Journals (Sweden)

    Vuanghao Lim

    2013-12-01

    Full Text Available The use of disulphide polymers, a low redox potential responsive delivery, is one strategy for targeting drugs to the colon so that they are specifically released there. The objective of this study was to synthesise a new cross-linked disulphide-containing polymer based on the amino acid cysteine as a colon drug delivery system and to evaluate the efficiency of the polymers for colon targeted drug delivery under the condition of a low redox potential. The disulphide cross-linked polymers were synthesised via air oxidation of 1,2-ethanedithiol and 3-mercapto-N-2-(3-mercaptopropionamide-3-mercapto propionic anhydride (trithiol monomers using different ratio combinations. Four types of polymers were synthesised: P10, P11, P151, and P15. All compounds synthesised were characterised by NMR, IR, LC-MS, CHNS analysis, Raman spectrometry, SEM-EDX, and elemental mapping. The synthesised polymers were evaluated in chemical reduction studies that were performed in zinc/acetic acid solution. The suitability of each polymer for use in colon-targeted drug delivery was investigated in vitro using simulated conditions. Chemical reduction studies showed that all polymers were reduced after 0.5–1.0 h, but different polymers had different thiol concentrations. The bacterial degradation studies showed that the polymers were biodegraded in the anaerobic colonic bacterial medium. Degradation was most pronounced for polymer P15. This result complements the general consensus that biodegradability depends on the swellability of polymers in an aqueous environment. Overall, these results suggest that the cross-linked disulphide-containing polymers described herein could be used as coatings for drugs delivered to the colon.

  15. Preparation and characterization of cross-linked β-cyclodextrin polymer/Fe3O4 composite nanoparticles with core-shell structures

    Institute of Scientific and Technical Information of China (English)

    Rui Xue Li; Shu Mei Liu; Jian Qing Zhao; Hideyuki Otsuka; Atsushi Takahara

    2011-01-01

    Cross-linked β-cyclodextrin polymer/Fe3O4 composite nanoparticles with core-shell structures were prepared via cross linking reaction on the surface of carboxymethyl β-cyclodextrin (CM-β-CD) modified Fe3O4 nanoparticles in β-cyclodextrin alkaline solution by using epichlorohydrin as crosslinking agent. The morphology, structure and magnetic properties of the prepared composite nanoparticles were investigated by transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectrometry, X-ray diffraction (XRD) measurement, thermogravimetric analysis (TGA) and Vibrating sample magnetometry (VSM), respectively.

  16. Influences of dehydration and rehydration on the lubrication properties of phospholipid polymer-grafted cross-linked polyethylene.

    Science.gov (United States)

    Yarimitsu, Seido; Moro, Toru; Kyomoto, Masayuki; Watanabe, Kenichi; Tanaka, Sakae; Ishihara, Kazuhiko; Murakami, Teruo

    2015-07-01

    Surface modification by grafting of biocompatible phospholipid polymer onto the surface of artificial joint material has been proposed to reduce the risk of aseptic loosening and improve the durability. Poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC)-grafted cross-linked polyethylene (CLPE) has shown promising results for reducing wear of CLPE. The main lubrication mechanism for the PMPC layer is considered to be the hydration lubrication. In this study, the lubrication properties of PMPC-grafted CLPE were evaluated in reciprocating friction test with rehydration process by unloading in various lubricants. The start-up friction of PMPC-grafted CLPE was reduced, and the damage of PMPC layer was suppressed by rehydration in water or hyaluronic acid solutions. In contrast, the start-up friction of PMPC-grafted CLPE increased in fetal bovine serum solution, and the damage for PMPC layer was quite noticeable. Interestingly, the start-up friction of PMPC-grafted CLPE was reduced in fetal bovine serum solution containing hyaluronic acid, and the damage of the PMPC layer was suppressed. These results indicate that the rehydration by unloading and hyaluronic acid are elemental in maximizing the lubrication effect of hydrated PMPC layer.

  17. Highly stable CO2/N2 and CO2/CH4 selectivity in hyper-cross-linked heterocyclic porous polymers.

    Science.gov (United States)

    Saleh, Muhammad; Lee, Han Myoung; Kemp, K Christian; Kim, Kwang S

    2014-05-28

    The largest obstacles for landfill/flue gas separation using microporous materials are small adsorption values and low selectivity ratios. This study demonstrates that these adsorption and selectivity challenges can be overcome by utilizing a series of hyper-cross-linked heterocyclic polymer networks. These microporous organic polymers (MOPs) were synthesized in a single step by inexpensive Friedel-Crafts-catalyzed reactions using dimethoxymethane as an external linker. The amorphous networks show moderate Brunauer-Emmett-Teller surface areas up to 1022 m(2) g(-1), a narrow pore size distribution in the range from 6 to 8 Å, and high physicochemical stability. Owing to the presence of the heteroatomic pore surfaces in the networks, they exhibit maximum storage capacities for CO2 of 11.4 wt % at 273 K and 1 atm. Additionally, remarkable selectivity ratios for CO2 adsorption over N2 (100) and CH4 (15) at 273 K were obtained. More importantly, as compared with any other porous materials, much higher selectivity for CO2/N2 (80) and CO2/CH4 (15) was observed at 298 K, showing that these selectivity ratios remain high at elevated temperature. The very high CO2/N2 selectivity values are ascribed to the binding affinity of abundantly available electron-rich basic heteroatoms, high CO2 isoteric heats of adsorption (49-38 kJ mol(-1)), and the predominantly microporous nature of the MOPs. Binding energies calculated using the high level of ab initio theory showed that the selectivity is indeed attributed to the heteroatom-CO2 interactions. By employing an easy and economical synthesis procedure these MOPs with high thermochemical stability are believed to be a promising candidate for selective CO2 capture.

  18. The Performance of a Thermally Cross-Linked Polymer of Intrinsic Microporosity (PIM-1) for Gas Separation

    KAUST Repository

    Alghunaimi, Fahad I.

    2013-05-01

    Gas transport properties of PIM-1 (the first ladder polymer with intrinsic microporosity) and TC-PIM-1 (thermally cross-linked PIM-1) at 35°C and different pressures were thoroughly studied. The purpose of this study was to evaluate and compare the performance of the TC-PIM-1 membranes with PIM-1 for natural gas separation. The TC-PIM-1 polymer was prepared by post-modification of PIM-1 at 300°C for a period of two days. Sorption isotherms of seven gases, including N2, O2, CH4, CO2, C2H6, C3H8 and n-C4H10, were determined for PIM-1 and TC-PIM-1 using the dual-volume barometric sorption technique at 35°C at different pressures. The sorption isotherms followed the dual-mode sorption model, which is typical for glassy polymers. Moreover, permeability (P) of eight gases, including He, H2, N2, O2, CH4, CO2, C3H8 and n-C4H10, were determined for PIM-1 and TC-PIM-1 at 35°C and 2.0 atm. Furthermore, average diffusion coefficients (D ̅) were calculated from the permeability and solubility data for all tested gases for both polymers. The sorption (S), permeability (P) and average diffusion coefficients (D ̅) for the TC-PIM-1 membrane exhibited lower values than the PIM-1 membrane. However, the TC-PIM-1 membrane showed exceptional gas separation performance. The TC-PIM-1 membrane had a helium (He) permeability of 1218 barrer with He/CH4 and He/N2 ideal selectivities of 27.1 and 23.9 respectively, and carbon dioxide (CO2) permeability of 1088 barrer with CO2/CH4 and CO2/N2 ideal selectivities of 24.2 and 21.3 respectively. Additionally, the TC-PIM-1 membrane showed a hydrogen (H2) permeability of 2452 barrer with an ideal H2/CH4 selectivity of 54.5.

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

    Science.gov (United States)

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

    2016-09-08

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

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

    Science.gov (United States)

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

    2013-04-10

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

  1. Preparation and characterization of a micro-porous polymer electrolyte with cross-linking network structure for dye-sensitized solar cell

    Energy Technology Data Exchange (ETDEWEB)

    Wei, T.C.; Wan, C.C.; Wang, Y.Y. [Department of Chemical Engineering, National Tsing-Hua University, 101, Section 2, Kuang Fu Road, Hsin-Chu 300 (China)

    2007-12-14

    A PVdF-HFP/PEG/PEGDMA cross-linking film has been prepared as the electrolyte for dye-sensitized solar cell (DSSC). The film can be made porous by controlling the evaporation behavior of solvents. Room temperature ionic conductivity of the micro-porous film exceeds 1 mS/cm. In addition, we also evaluated the significance of cell gap in DSSC by analyzing the impedance spectroscopy of the cell with polymer electrolyte. Finally, by decreasing the film thickness, the DSSC equipped with 11 {mu}m, micro-porous and cross-linked film showed a conversion efficiency over 4% and 5% under 1 and 0.16 Sun, respectively. (author)

  2. Jacket-free stir bar sorptive extraction with bio-inspired polydopamine-functionalized immobilization of cross-linked polymer on stainless steel wire.

    Science.gov (United States)

    Zhang, Zixin; Zhang, Wenpeng; Bao, Tao; Chen, Zilin

    2015-08-14

    Stainless steel wire (SSW) is a good substrate for stir bar sorptive extraction (SBSE). However, it is still a challenge to immobilize commonly used cross-linked polymers onto SSW. In this work, we present a new approach for immobilization of the cross-linked organic polymer onto SSW for jacket-free SBSE. A dopamine derivative was firstly synthesized; by introducing a mussel-inspired polydopamine process, a stable coating layer was finally generated on the surface of SSW. Secondly, the cross-linked polymer was synthesized on the polydopamine-modified SSW by using acetonitrile as the porogen, acrylamide (AA) as the functional monomer, ethylene glycol dimethacrylate (EGDMA) as the cross-linker and 2,2'-azobis (2-methylpropionitrile) as the initiator. A diluted pre-polymerization solution was carefully prepared to generate a thin layer of the polymer. The prepared poly(EGDMA-AA)-modified stir bar showed high stability and good tolerance toward stirring, ultrasonication, organic solvents, and strong acidic and basic conditions. Morphology and structure characterization of coatings were performed by scanning electron microscopy and Fourier transform infrared spectra, respectively. The prepared poly(EGDMA-AA)-modified stir bar showed great extraction efficiency toward protoberberines, with enrichment factors of 19-42. An SBSE-HPLC method was also developed for quantitative analysis of protoberberines. The method showed low limits of detection (0.06-0.15 ng mL(-1)), wide linear range (0.5-400 ng mL(-1)), good linearity (R≥0.9980) and good reproducibility (RSD≤3.60% for intra-day, RSD≤4.73% for inter-day). The developed method has been successfully applied to determine protoberberines in herb and rat plasma samples, with recoveries of 88.53-114.61%. Copyright © 2015 Elsevier B.V. All rights reserved.

  3. One-Step Synthesis of Cross-Linked Ionic Polymer Thin Films in Vapor Phase and Its Application to an Oil/Water Separation Membrane.

    Science.gov (United States)

    Joo, Munkyu; Shin, Jihye; Kim, Jiyeon; You, Jae Bem; Yoo, Youngmin; Kwak, Moo Jin; Oh, Myung Seok; Im, Sung Gap

    2017-02-15

    In spite of the huge research interest, ionic polymers could not have been synthesized in the vapor phase because the monomers of ionic polymers contain nonvolatile ionic salts, preventing the monomers from vaporization. Here, we suggest a new, one-step synthetic pathway to form a series of cross-linked ionic polymers (CIPs) in the vapor phase via initiated chemical vapor deposition (iCVD). 2-(Dimethylamino)ethyl methacrylate (DMAEMA) and 4-vinylbenzyl chloride (VBC) monomers are introduced into the iCVD reactor in the vapor phase to form a copolymer film. Simultaneously in the course of the deposition process, the tertiary amine in DMAEMA and benzylic chloride in VBC undergo a Menshutkin nucleophilic substitution reaction to form an ionic ammonium-chloride complex, forming a highly cross-linked ionic copolymer film of p(DMAEMA-co-VBC). To the best of our knowledge, this is the first report on the synthesis of CIP films in the vapor phase. The newly developed CIP thin film is further applied to the surface modification of the membrane for oil/water separation. With the hydrophilic and underwater oleophobic membrane whose surface is modified with the CIP film, excellent separation efficiency (>99%) and unprecedentedly high permeation flux (average 2.32 × 10(5) L m(-2) h(-1)) are achieved.

  4. Poly-cross-linked PEI through aromatically conjugated imine linkages as a new class of pH-responsive nucleic acids packing cationic polymers

    Directory of Open Access Journals (Sweden)

    Shun eChen

    2016-02-01

    Full Text Available Cationic polyimines polymerized through aromatically conjugated bis-imine linkages and intra-molecular cross-linking were found to be a new class of effective transfection materials for their flexibility in structural optimization, responsiveness to intracellular environment, the ability to facilitate endosome escape and cytosol release of the nucleic acids, as well as self-metabolism. When three phthalaldehydes of different substitution positions were used to polymerize highly branched low molecular weight polyethylenimine (PEI-1.8K, the product through ortho-phthalimines (named PPOP showed significantly higher transfection activity than its two tere- and iso-analogues (named PPTP and PPIP. Physicochemical characterization confirmed the similarity of three polyimines in pH-responded degradability, buffer capacity, as well as the size and Zeta potential of the polyplexes formed from the polymers. A mechanistic speculation may be that the ortho-positioned bis-imine linkage of PPOP may only lead to the straight trans-configuration due to steric hindrance, resulting in larger loops of intra-polymer cross-linking and more flexible backbone.

  5. Self-replenishing ability of cross-linked low surface energy polymer films investigated by a complementary experimental-simulation approach

    Science.gov (United States)

    Esteves, A. C. C.; Lyakhova, K.; van Riel, J. M.; van der Ven, L. G. J.; van Benthem, R. A. T. M.; de With, G.

    2014-03-01

    Nowadays, many self-healing strategies are available for recovering mechanical damage of bulk polymeric materials. The recovery of surface-dependent functionalities on polymer films is, however, equally important and has been less investigated. In this work we study the ability of low surface energy cross-linked poly(ester urethane) networks containing perfluorinated dangling chains to self-replenish their surface, after being submitted to repeated surface damage. For this purpose we used a combined experimental-simulation approach. Experimentally, the cross-linked films were intentionally damaged by cryo-microtoming to remove top layers and create new surfaces which were characterized by water Contact Angle measurements and X-Ray Photoelectron Spectroscopy. The same systems were simultaneously represented by a Dissipative Particles Dynamics simulation method, where the damage was modeled by removing the top film layers in the simulation box and replacing it by new "air" beads. The influence of different experimental parameters, such as the concentration of the low surface energy component and the molecular mobility span of the dangling chains, on the surface recovery is discussed. The combined approach reveals important details of the self-replenishing ability of damaged polymer films such as the occurrence of multiple-healing events, the self-replenishing efficiency, and the minimum "healing agent" concentration for a maximum recovery.

  6. Thiolated and S-protected hydrophobically modified cross-linked poly(acrylic acid)--a new generation of multifunctional polymers.

    Science.gov (United States)

    Bonengel, Sonja; Haupstein, Sabine; Perera, Glen; Bernkop-Schnürch, Andreas

    2014-10-01

    The aim of this study was to create a novel multifunctional polymer by covalent attachment of l-cysteine to the polymeric backbone of hydrophobically modified cross-linked poly(acrylic acid) (AC1030). Secondly, the free thiol groups of the resulting thiomer were activated using 2-mercaptonicotinic acid (2-MNA) to provide full reactivity and stability. Within this study, 1167.36 μmol cysteine and 865.72 μmol 2-MNA could be coupled per gram polymer. Studies evaluating mucoadhesive properties revealed a 4-fold extended adherence time to native small intestinal mucosa for the thiomer (AC1030-cysteine) as well as an 18-fold prolonged adhesion for the preactivated thiomer (AC1030-Cyst-2-MNA) compared to the unmodified polymer. Modification of the polymer led to a higher tablet stability concerning the thiomer and the S-protected thiomer, but a decelerated water uptake could be observed only for the preactivated thiomer. Neither the novel conjugates nor the unmodified polymer showed severe toxicity on Caco-2 cells. Evaluation of emulsification capacity proofed the ability to incorporate lipophilic compounds like medium chain triglycerides and the preservation of the emulsifying properties after the modifications. According to these results thiolated AC1030 as well as the S-protected thiolated polymer might provide a promising tool for solid and semisolid formulations in pharmaceutical development.

  7. Optimum design of amphiphilic polymers bearing hydrophobic groups for both cell surface ligand presentation and intercellular cross-linking.

    Science.gov (United States)

    Takeo, Masafumi; Li, Cuicui; Matsuda, Masayoshi; Nagai, Hiroko; Hatanaka, Wataru; Yamamoto, Tatsuhiro; Kishimura, Akihiro; Mori, Takeshi; Katayama, Yoshiki

    2015-01-01

    Amphiphilic polymers bearing hydrophobic alkyl groups are expected to be applicable for both ligand presentation on the cell surface and intercellular crosslinking. To explore the optimum design for each application, we synthesized eight different acyl-modified dextrans with varying molecular weight, alkyl length, and alkyl modification degree. We found that the behenate-modified polymers retained on the cell surface longer than the palmitate-modified ones. Since the polymers were also modified with biotin, streptavidin can be presented on the cell surface through biotin-streptavidin recognition. The duration of streptavidin on the cell surface is longer in the behenate-modified polymer than the palmitate-modified one. As for the intercellular crosslinking, the palmitate-modified polymers were more efficient than the behenate-modified polymers. The findings in this research will be helpful to design the acyl-modified polymers for the cell surface engineering.

  8. The Role of Inclusion Binding Contributions for β-Cyclodextrin Polymers Cross-Linked with Divinyl Sulfone?--A Comment on Morales-Sanfrutos et al. Entitled "Divinyl Sulfone Cross-Linked Cyclodextrin-Based Polymeric Materials: Synthesis and Applications as Sorbents and Encapsulating Agents", Molecules, 2015, 20, 3565-3581.

    Science.gov (United States)

    Wilson, Lee D; Mohamed, Mohamed H; McMartin, Dena W

    2016-01-14

    This commentary reports on a recent scientific study reported in this journal (cf. Molecules 2015, 20(3), 3565-3581). Some key scientific issues that require further explanation and clarification in the former article are as follows: (i) the relationship between the inclusion site accessibility and the level of cross-linking employed are brought into question for the case of α-CD and β-CD cross-linked adsorbent materials; (ii) the binding affinity of the CD/guest complexes were not related to the isotherm parameters for the CD-polymer/guest systems; (iii) the limited molecular level structural characterization of the cross-linked polymer materials; and (iv) the interpretation of the adsorption isotherm results by the authors.

  9. The Role of Inclusion Binding Contributions for β-Cyclodextrin Polymers Cross-Linked with Divinyl Sulfone?—A Comment on Morales-Sanfrutos et al. Entitled “Divinyl Sulfone Cross-Linked Cyclodextrin-Based Polymeric Materials: Synthesis and Applications as Sorbents and Encapsulating Agents”, Molecules, 2015, 20, 3565–3581.

    Directory of Open Access Journals (Sweden)

    Lee D. Wilson

    2016-01-01

    Full Text Available This commentary reports on a recent scientific study reported in this journal (cf. Molecules 2015, 20(3, 3565–3581. Some key scientific issues that require further explanation and clarification in the former article are as follows: (i the relationship between the inclusion site accessibility and the level of cross-linking employed are brought into question for the case of α-CD and β-CD cross-linked adsorbent materials; (ii the binding affinity of the CD/guest complexes were not related to the isotherm parameters for the CD-polymer/guest systems; (iii the limited molecular level structural characterization of the cross-linked polymer materials; and (iv the interpretation of the adsorption isotherm results by the authors.

  10. Cross-linking and ultrathin grafted gradation of fluorinated polymers synthesized via initiated chemical vapor deposition to prevent surface reconstruction.

    Science.gov (United States)

    Liu, Andong; Goktekin, Esma; Gleason, Karen K

    2014-12-02

    Poly(fluoroalkyl acrylate)s with long perfluorooctyl pendant groups have been found to lead to the release of biopersistent perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS). Those with no more than six perfluorinated carbons in pedant groups do not cause such problems. They, however, give poor dynamic water repellency due to extensive reorganization of surface fluorinated groups when exposed to the water interface. In this work, thin films exhibiting improved dynamic water repellency, as evidenced by water contact angle (WCA) measurements, were synthesized via substrate-independent initiated chemical vapor deposition (iCVD) from 1H,1H,2H,2H-perfluorooctyl acrylate (C6PFA) and divinylbenzene (DVB) using two methods: copolymerization and ultrathin grafted gradation. The copolymerization between C6PFA and the cross-linker, DVB, was confirmed by Fourier transform infrared (FTIR) spectroscopy. The cross-linking is concluded to hinder the reorganization of surface fluorinated groups. The grafted gradation, consisting of an ultrathin pC6PFA top layer and a pDVB base layer, was characterized by angle-resolved X-ray photoelectron spectroscopy (ARXPS) measurements, which indicated that the top layer of pC6PFA is water repellency. The outmost surface of this structure is fully covered by fluorinated groups, giving hydrophobicity. Concurrently, thanks to the interlayer grafting and the ultrathinness of the top layer, the fluorinated groups' tendency to migrate away from water interface is sterically blocked by the highly cross-linked pDVB base layer. The proposed approaches effectively reduced WCA hysteresis of C6PFA-based thin film to as low as 26.9° while maintaining sufficient hydrophobicity (advanced WCA of 119.6°). Due to the conformal and substrate-independent nature of iCVD technique, the films could be used to coat textured surfaces to generate superhydrophobicity.

  11. Balancing the stability and drug release of polymer micelles by the coordination of dual-sensitive cleavable bonds in cross-linked core.

    Science.gov (United States)

    Deng, Hongzhang; Zhang, Yumin; Wang, Xue; Jianhuazhang; Cao, Yan; Liu, Jinjian; Liu, Jianfeng; Deng, Liandong; Dong, Anjie

    2015-01-01

    The optimal structure design of nanocarriers to inhibit premature release of anticancer drugs from nanocarriers during blood circulation and improve drug release inside tumor cells is still a significant issue for polymer micelles applied to antitumor drug delivery. Herein, in order to balance the contradiction between polymer micellar stability and drug release, dual-sensitive cleavable cross-linkages of benzoic imine conjugated disulfide bonds were introduced into the core of the amphiphilic copolymer micelles to form core-cross-linked micelles. First, biodegradable poly(ethylene glycol)-b-(polycaprolactone-g-poly(methacrylic acid-p-hydroxy benzaldehyde-cystamine)), i.e. mPEG-b-(PCL-g-P(MAA-Hy-Cys)) (PECMHC) copolymers were synthesized and assembled into PECMHC micelles (PECMHC Ms). Then, simply by introducing H2O2 to the PECMHC Ms dispersions to oxidate the thiol groups of cystamine moieties in the core, core-cross-linked PECMHC micelles (cc-PECMHC Ms) ∼100 nm in size were readily obtained in water. In vitro studies of doxorubicin (DOX)-loaded cc-PECMHC Ms show that the cross-linked core impeded the drug release in the physical conditions, owing to the high stability of the micelles against both extensive dilution and salt concentration, while it greatly accelerated DOX release in mildly acidic (pH ∼5.0-6.0) medium with glutathione, owing to the coordination of the pH-sensitive cleaving of benzoic imine bonds and the reduction-sensitive cleaving of disulfide bonds. The in vivo tissue distribution and tumor accumulation of the DOX-loaded cc-PECMHC Ms were monitored via fluorescence images of DOX. DOX-loaded cc-PECMHC Ms exhibited enhanced tumor accumulation because of their high stability in blood circulation and less DOX premature release. Therefore, the cc-PECMHC Ms with dual-sensitive cleavable bonds in the cross-linked core were of excellent biocompatibility, high extracellular stability and had intelligent intracellular drug release properties

  12. Wear resistance of the biocompatible phospholipid polymer-grafted highly cross-linked polyethylene liner against larger femoral head.

    Science.gov (United States)

    Moro, Toru; Takatori, Yoshio; Kyomoto, Masayuki; Ishihara, Kazuhiko; Kawaguchi, Hiroshi; Hashimoto, Masami; Tanaka, Takeyuki; Oshima, Hirofumi; Tanaka, Sakae

    2015-07-01

    The use of larger femoral heads to prevent the dislocation of artificial hip joints has recently become more common. However, concerns about the subsequent use of thinner polyethylene liners and their effects on wear rate have arisen. Previously, we prepared and evaluated the biological and mechanical effects of a novel highly cross-linked polyethylene (CLPE) liner with a nanometer-scaled graft layer of poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC). Our findings showed that the PMPC-grafted particles were biologically inert and caused no subsequent bone resorptive responses and that the PMPC-grafting markedly decreased wear in a hip joint simulator. However, the metal or ceramic femoral heads used in this previous study had a diameter of 26 mm. Here, we investigated the wear-resistance of the PMPC-grafted CLPE liner with a 40-mm femoral head during 10 × 10(6) cycles of loading in the hip joint simulator. The results provide preliminary evidence that the grafting markedly decreased gravimetric wear rate and the volume of wear particles, even when coupled with larger femoral heads. Thus, we believe the PMPC-grafting will prolong artificial hip joint longevity both by preventing aseptic loosening and by improving the stability of articular surface.

  13. A hydrated phospholipid polymer-grafted layer prevents lipid-related oxidative degradation of cross-linked polyethylene.

    Science.gov (United States)

    Kyomoto, Masayuki; Moro, Toru; Yamane, Shihori; Takatori, Yoshio; Tanaka, Sakae; Ishihara, Kazuhiko

    2017-01-01

    The surface and substrate of a cross-linked polyethylene (CLPE) liner are designed to achieve resistance against oxidative degradation in the construction of hip joint replacements. In this study, we aimed to evaluate the oxidative degradation caused by lipid absorption of a highly hydrophilic nanometer-scaled thickness layer prepared by grafting a poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) layer and a high-dose gamma-ray irradiated CLPE with vitamin E blending (HD-CLPE[VE]). The HD-CLPE(VE) and PMPC-grafted HD-CLPE(VE) exhibited extremely high oxidation resistance regardless of lipid absorption, even though residual-free radical levels were detectable. The water wettability of the PMPC-grafted CLPE and PMPC-grafted HD-CLPE(VE) surfaces was considerably greater than that of untreated surfaces. The hydrated PMPC-grafted layer also exhibited extremely low solubility for squalene. Lipids such as squalene and cholesterol esters diminished the oxidation resistance of CLPE despite the vitamin E improvement. Notably, the PMPC-grafted surface was resistant to lipid absorption and diffusion as well as subsequent lipid-related oxidative degradation, likely because of the presence of the hydrated PMPC-grafted layer. Together, these results provide preliminary evidence that the resistance against lipid absorption and diffusion of a hydrated PMPC-grafted layer might positively affect the extent of resistance to the in vivo oxidation of orthopedic implants.

  14. Catalytic trimerization of aromatic nitriles and triaryl-s-triazine ring cross-linked high temperature resistant polymers and copolymers made thereby

    Science.gov (United States)

    Hsu, L. C. (Inventor)

    1979-01-01

    Triazine compounds and cross-linked polymer compositions are made by heating aromatic nitriles to a temperature in the range of from about 100 C to about 700 C, and preferably in the range of from about 200 C to about 350 C, in the presence of a catalyst or mixture of catalysts selected from one or more of the following groups: (1) organic sulfonic and sulfinic acids, (2) organic phosphonic and phosphinic acids, and (3)metallic acetylacetonates, at a pressure in the range of from about atmospheric pressure to about 10,000 psi and preferably in the range of from about 200 psi to about 750 psi. Aromatic nitrile-modified (terminated and/or appended) imide, benzimidazole, imidazopyrrolone, quinoxaline, and other condensation type prepolymers or their precopolymers are made which are trimerized with or without a filler by the aforementioned catalytic trimerization process into triaryl-s-triazine ring containing or cross-linked polymeric or copolymeric products useful in applications requiring high thermal-oxidative stability and high performance structural properties at elevated temperatures.

  15. Initiated Chemical Vapor Deposition (iCVD) of Highly Cross-Linked Polymer Films for Advanced Lithium-Ion Battery Separators.

    Science.gov (United States)

    Yoo, Youngmin; Kim, Byung Gon; Pak, Kwanyong; Han, Sung Jae; Song, Heon-Sik; Choi, Jang Wook; Im, Sung Gap

    2015-08-26

    We report an initiated chemical vapor deposition (iCVD) process to coat polyethylene (PE) separators in Li-ion batteries with a highly cross-linked, mechanically strong polymer, namely, polyhexavinyldisiloxane (pHVDS). The highly cross-linked but ultrathin pHVDS films can only be obtained by a vapor-phase process, because the pHVDS is insoluble in most solvents and thus infeasible with conventional solution-based methods. Moreover, even after the pHVDS coating, the initial porous structure of the separator is well preserved owing to the conformal vapor-phase deposition. The coating thickness is delicately controlled by deposition time to the level that the pore size decreases to below 7% compared to the original dimension. The pHVDS-coated PE shows substantially improved thermal stability and electrolyte wettability. After incubation at 140 °C for 30 min, the pHVDS-coated PE causes only a 12% areal shrinkage (versus 90% of the pristine separator). The superior wettability results in increased electrolyte uptake and ionic conductivity, leading to significantly improved rate performance. The current approach is applicable to a wide range of porous polymeric separators that suffer from thermal shrinkage and poor electrolyte wetting.

  16. Chemical modification of wheat protein-based natural polymers: grafting and cross-linking reactions with poly(ethylene oxide) diglycidyl ether and ethyl diamine.

    Science.gov (United States)

    Kurniawan, Lusiana; Qiao, Greg G; Zhang, Xiaoqing

    2007-09-01

    Mobile poly(ethylene oxide) diglycidyl ether (PEODGE) segments were chemically grafted onto a soluble wheat protein (WP), and different network structures were formed via coupling reactions with ethyl diamine (EDA) in different PEODGE/EDA (PE) ratios. When the PE ratio was 1:1, linear PEs were the predominant segments grafted onto WP chains and the whole WP-PEODGE-EDA (WPE) system was still soluble with an increased molecular weight. Reducing the amount of EDA in the systems produced insoluble cross-linked WPE networks. The broad distribution of network structures and chain mobility resulted in a broad glass transition for the WPE materials. However, the glass transition started at lower temperatures, and the materials became flexible at room temperature. The PE segments were present in all rigid, intermediate, and mobile phases in WPE networks, while the proportion of mobile WP chains was increased as a result of the plasticization effect from the mobile PE segments. The mobility of the most mobile component lipid was also restricted to some extent when forming the cross-linked WPE networks. The study demonstrated that the formation of different network structures with PE segments could significantly improve the flexibility of WP materials, vary the solubility, and modify the mechanical performance of WP-based natural polymer materials.

  17. Cross-linked branching nanohybrid polymer electrolyte with monodispersed TiO2 nanoparticles for high performance lithium-ion batteries

    Science.gov (United States)

    Ma, Cheng; Zhang, Jinfang; Xu, Mingquan; Xia, Qingbing; Liu, Jiatu; Zhao, Shuai; Chen, Libao; Pan, Anqiang; Ivey, Douglas G.; Wei, Weifeng

    2016-06-01

    Nanohybrid polymer electrolytes (NHPE) with ceramic particles have attracted significant attention owing to their improvement in electrochemical performance. However, particle aggregation and weak nanoparticle/polymer matrix interaction restrict their further application in lithium-ion batteries (LIBs). We demonstrate a facile in-situ polymerization/crystallization method to synthesize a homogeneous TiO2-grafted NHPE with a cross-linked branching structure, comprised of ion-conducting poly(ethylene glycol) methyl ether methacrylate (PEGMEM) and non-polar stearyl methacrylate (SMA). This technique is different from existing methods of blending functionalized ceramic particles into the polymer matrix. Highly monodispersed TiO2 nanocrystals enhance the effective interfacial interactions between particles and polymer matrix, which suppress the crystallization of ethylene oxide (EO) groups and facilitate forming continuously interconnected ion-conducting channels. Moreover, an increased dissociation degree of Li salt can also be achieved. The TiO2-grafted NHPE exhibits superior electrochemical properties with an ionic conductivity of 1.1 × 10-4 S cm-1 at 30 °C, a high lithium ion transference number and excellent interfacial compatibility with the lithium electrode. In particular, a lithium-ion battery based on TiO2-grafted NHPE demonstrates good C-rate performance, as well as excellent cycling stability with an initial discharge capacity of 153.5 mAh g-1 and a capacity retention of 96% after 300 cycles at 1 C (80 °C).

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

    Science.gov (United States)

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

    2013-07-01

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

  19. β-Cyclodextrin cross-linked polymer as solid-phase extraction material coupled with the spectrophotometric method for the analysis of serum albumin

    Science.gov (United States)

    Wu, Min; Zhu, Xiashi

    2010-12-01

    The β-cyclodextrin cross-linked polymer (β-CDCP) was synthesized and used as solid-phase extraction material to preconcentrate/analysis bovine serum albumin (BSA) coupled with UV-vis spectroscopy. The method based on the complex (BSA-phenylfluorone (PF)) adsorbed on β-CDCP. Adsorption kinetics and various factors of the formation procedure of BSA-PF and its retention on β-CDCP were investigated. The linear range and detection limit (DL) was 20.0-200.0 and 0.03 mg/L, respectively. Moreover, the β-CDCP could be used repeatedly. The proposed method has been applied to analysis serum albumin with satisfactory results.

  20. Investigation of Cross-Linked and Additive Containing Polymer Materials for Membranes with Improved Performance in Pervaporation and Gas Separation

    Directory of Open Access Journals (Sweden)

    Karl Kleinermanns

    2012-10-01

    Full Text Available Pervaporation and gas separation performances of polymer membranes can be improved by crosslinking or addition of metal-organic frameworks (MOFs. Crosslinked copolyimide membranes show higher plasticization resistance and no significant loss in selectivity compared to non-crosslinked membranes when exposed to mixtures of CO2/CH4 or toluene/cyclohexane. Covalently crosslinked membranes reveal better separation performances than ionically crosslinked systems. Covalent interlacing with 3-hydroxypropyldimethylmaleimide as photocrosslinker can be investigated in situ in solution as well as in films, using transient UV/Vis and FTIR spectroscopy. The photocrosslinking yield can be determined from the FTIR-spectra. It is restricted by the stiffness of the copolyimide backbone, which inhibits the photoreaction due to spatial separation of the crosslinker side chains. Mixed-matrix membranes (MMMs with MOFs as additives (fillers have increased permeabilities and often also selectivities compared to the pure polymer. Incorporation of MOFs into polysulfone and Matrimid® polymers for MMMs gives defect-free membranes with performances similar to the best polymer membranes for gas mixtures, such as O2/N2 H2/CH4, CO2/CH4, H2/CO2, CH4/N2 and CO2/N2 (preferentially permeating gas is named first. The MOF porosity, its particle size and content in the MMM are factors to influence the permeability and the separation performance of the membranes.

  1. Removal of some organic pollutants in water employing ceramic membranes impregnated with cross-linked silylated dendritic and cyclodextrin polymers.

    Science.gov (United States)

    Allabashi, Roza; Arkas, Michael; Hörmann, Gerold; Tsiourvas, Dimitris

    2007-01-01

    Triethoxysilylated derivatives of poly(propylene imine) dendrimer, polyethylene imine and polyglycerol hyperbranched polymers and beta-cyclodextrin have been synthesized and characterized. These compounds impregnated ceramic membranes made from Al(2)O(3), SiC and TiO(2) and subsequently sol-gel reaction led to their polymerization and chemical bond formation with the ceramic substrates. The resulting organic-inorganic filters were tested for the removal of a variety of organic pollutants from water. They were found to remove of polycyclic aromatic hydrocarbons (up to 99%), of monocyclic aromatic hydrocarbons (up to 93%), trihalogen methanes (up to 81%), pesticides (up to 43%) and methyl-tert-butyl ether (up to 46%).

  2. Aerogels of 1D Coordination Polymers: From a Non-Porous Metal-Organic Crystal Structure to a Highly Porous Material

    Directory of Open Access Journals (Sweden)

    Adrián Angulo-Ibáñez

    2016-01-01

    Full Text Available The processing of an originally non-porous 1D coordination polymer as monolithic gel, xerogel and aerogel is reported as an alternative method to obtain novel metal-organic porous materials, conceptually different to conventional crystalline porous coordination polymer (PCPs or metal-organic frameworks (MOFs. Although the work herein reported is focused upon a particular kind of coordination polymer ([M(μ-ox(4-apy2]n, M: Co(II, Ni(II, the results are of interest in the field of porous materials and of MOFs, as the employed synthetic approach implies that any coordination polymer could be processable as a mesoporous material. The polymerization conditions were fixed to obtain stiff gels at the synthesis stage. Gels were dried at ambient pressure and at supercritical conditions to render well shaped monolithic xerogels and aerogels, respectively. The monolithic shape of the synthesis product is another remarkable result, as it does not require a post-processing or the use of additives or binders. The aerogels of the 1D coordination polymers are featured by exhibiting high pore volumes and diameters ranging in the mesoporous/macroporous regions which endow to these materials the ability to deal with large-sized molecules. The aerogel monoliths present markedly low densities (0.082–0.311 g·cm−3, an aspect of interest for applications that persecute light materials.

  3. Effect of Cross-linking Density on Creep and Recovery Behavior in Epoxy-Based Shape Memory Polymers (SMEPs) for Structural Applications

    Science.gov (United States)

    Rao, Kavitha V.; Ananthapadmanabha, G. S.; Dayananda, G. N.

    2016-12-01

    Epoxy-based shape memory polymers (SMEPs) are gaining importance in the area of aerospace structures due to their high strength and stiffness which is a primary requirement for an SMEP in structural applications. The understanding of viscoelastic behavior of SMEPs is very essential to assess their shape memory effect. In the present work, three types of SMEPs with varying cross-linking densities were developed by curing an aromatic epoxy resin with aliphatic amines. Glass transition temperature ( T g) was measured for these SMEPs using advanced rheometric expansion system, and from the T g measurements, a range of temperatures from glassy to rubbery regimes were chosen. At selected temperatures, creep-recovery tests were performed in order to evaluate the viscoelastic behavior of SMEPs and also to investigate the effect of temperature on creep-recovery. Further, a three-parameter viscoelastic model (Zener) was used to fit the data obtained from experiments. Model parameters like moduli of the springs and viscosity of the dashpot were evaluated by curve fitting. Results revealed that Zener model was well suited to describe the viscoelastic behavior of SMEPs as a function of test temperatures.

  4. Effective removal of effluent organic matter (EfOM) from bio-treated coking wastewater by a recyclable aminated hyper-cross-linked polymer.

    Science.gov (United States)

    Yang, Wenlan; Li, Xuchun; Pan, Bingcai; Lv, Lu; Zhang, Weiming

    2013-09-01

    Effluent organic matter (EfOM) is a complex matrix of organic substance mainly from bio-treated sewage effluent and is considered as the main constraint to further advanced treatment. Here a recyclable aminated hyper-cross-linked polymeric adsorbent (NDA-802) featured with aminated functional groups, large specific surface area, and sufficient micropore region was synthesized for effective removal of EfOM from the bio-treated coking wastewater (BTCW), and its removal characteristics was investigated. It was found that hydrophobic fraction was the main constituent (64.8% of DOC) in EfOM of BTCW, and the hydrophobic-neutral fraction had the highest SUVA level (7.06 L mg(-1) m(-1)), which were significantly different from that in the domestic wastewater. Column adsorption experiments showed that NDA-802 exhibited much higher removal efficiency of EfOM than other polymeric adsorbents D-301, XAD-4, and XAD-7, and the efficiency could be readily sustained according to continuous 28-cycle batch adsorption-regeneration experiments. Moreover, dissolved organic matter (DOM) fractionation and excitation-emission matrix (EEM) fluorescence spectroscopy study indicated that NDA-802 showed attractive adsorption preference as well as high removal efficiency of hydrophobic and aromatic compounds. Possibly ascribed to the presence of functional aminated groups, relatively large specific surface area and micropore region of the unique polymer, NDA-802 possesses high and sustained efficiency for the removal of EfOM, and provides a potential alternative for the advanced treatment.

  5. Unusual Transformation from a Solvent-Stabilized 1D Coordination Polymer to a Metal-Organic Framework (MOF)-Like Cross-Linked 3D Coordination Polymer.

    Science.gov (United States)

    Lee, Seung-Chul; Choi, Eun-Young; Lee, Sang-Beom; Kim, Sang-Wook; Kwon, O-Pil

    2015-10-26

    An unusual 1D-to-3D transformation of a coordination polymer based on organic linkers containing highly polar push-pull π-conjugated side chains is reported. The coordination polymers are synthesized from zinc nitrate and an organic linker, namely, 2,5-bis{4-[1-(4-nitrophenyl)pyrrolidin-2-yl]butoxy}terephthalic acid, which possesses highly polar (4-nitrophenyl)pyrrolidine groups, with high dipole moments of about 7 D. The coordination polymers exhibit an unusual transformation from a soluble, solvent-stabilized 1D coordination polymer into an insoluble, metal-organic framework (MOF)-like 3D coordination polymer. The coordination polymer exhibits good film-forming ability, and the MOF-like films are insoluble in conventional organic solvents.

  6. Ester Cross-Link Profiling of the Cutin Polymer of Wild-Type and Cutin Synthase Tomato Mutants Highlights Different Mechanisms of Polymerization.

    Science.gov (United States)

    Philippe, Glenn; Gaillard, Cédric; Petit, Johann; Geneix, Nathalie; Dalgalarrondo, Michèle; Bres, Cécile; Mauxion, Jean-Philippe; Franke, Rochus; Rothan, Christophe; Schreiber, Lukas; Marion, Didier; Bakan, Bénédicte

    2016-02-01

    Cuticle function is closely related to the structure of the cutin polymer. However, the structure and formation of this hydrophobic polyester of glycerol and hydroxy/epoxy fatty acids has not been fully resolved. An apoplastic GDSL-lipase known as CUTIN SYNTHASE1 (CUS1) is required for cutin deposition in tomato (Solanum lycopersicum) fruit exocarp. In vitro, CUS1 catalyzes the self-transesterification of 2-monoacylglycerol of 9(10),16-dihydroxyhexadecanoic acid, the major tomato cutin monomer. This reaction releases glycerol and leads to the formation of oligomers with the secondary hydroxyl group remaining nonesterified. To check this mechanism in planta, a benzyl etherification of nonesterified hydroxyl groups of glycerol and hydroxy fatty acids was performed within cutin. Remarkably, in addition to a significant decrease in cutin deposition, mid-chain hydroxyl esterification of the dihydroxyhexadecanoic acid was affected in tomato RNA interference and ethyl methanesulfonate-cus1 mutants. Furthermore, in these mutants, the esterification of both sn-1,3 and sn-2 positions of glycerol was impacted, and their cutin contained a higher molar glycerol-to-dihydroxyhexadecanoic acid ratio. Therefore, in planta, CUS1 can catalyze the esterification of both primary and secondary alcohol groups of cutin monomers, and another enzymatic or nonenzymatic mechanism of polymerization may coexist with CUS1-catalyzed polymerization. This mechanism is poorly efficient with secondary alcohol groups and produces polyesters with lower molecular size. Confocal Raman imaging of benzyl etherified cutins showed that the polymerization is heterogenous at the fruit surface. Finally, by comparing tomato mutants either affected or not in cutin polymerization, we concluded that the level of cutin cross-linking had no significant impact on water permeance. © 2016 American Society of Plant Biologists. All Rights Reserved.

  7. Comparative investigation of thermal and mechanical properties of cross-linked epoxy polymers with different curing agents by molecular dynamics simulation.

    Science.gov (United States)

    Jeyranpour, F; Alahyarizadeh, Gh; Arab, B

    2015-11-01

    Molecular dynamics (MD) simulations were carried out to predict the thermal and mechanical properties of the cross-linked epoxy system composed of DGEBA resin and the curing agent TETA. To investigate the effects of curing agents, a comprehensive and comparative study was also performed on the thermal and mechanical properties of DGEBA/TETA and DGEBA/DETDA epoxy systems such as density, glass transition temperature (Tg), coefficient of thermal expansion (CTE) and elastic properties of different cross-linking densities and different temperatures. The results indicated that the glass transition temperature of DGEBA/TETA system calculated through density-temperature data, ∼ 385-395 °K, for the epoxy system with the cross-linking density of 62.5% has a better agreement with the experimental value (Tg, ∼ 400 °K) in comparison to the value calculated through the variation of cell volume in terms of temperature, 430-440 °K. They also indicated that CTE related parameters and elastic properties including Young, Bulk, and shear's moduli, and Poisson's ratio have a relative agreement with the experimental results. Comparison between the thermal and mechanical properties of epoxy systems of DGEBA/TETA and DGEBA/DETDA showed that the DGEBA/DETDA has a higher Tg in all cross linking densities than that of DGEBA/TETA, while higher mechanical properties was observed in the case of DGEBA/TETA in almost all cross linking densities.

  8. Scientific Opinion on the safety evaluation of the active substance, acrylic acid, sodium salt, co-polymer with acrylic acid, methyl ester, methacrylic acid, 2 hydroxypropylester, and acrylic acid cross-linked for use in active food contact materials

    Directory of Open Access Journals (Sweden)

    EFSA Panel on Food Contact Materials, Enzymes, Flavourings and Processing Aids (CEF

    2013-04-01

    Full Text Available This scientific opinion of the EFSA Panel on Food Contact Materials, Enzymes, Flavourings and Processing Aids deals with the safety evaluation of the acrylic acid, sodium salt, co-polymer with acrylic acid, methyl ester, methacrylic acid, 2 hydroxypropylester, and acrylic acid cross-linked (CAS No. 117675-55-5, FCM Substance No 1022, to be used as liquid absorber in the form of fibres in absorbent pads for the packaging of fresh or frozen meat, poultry, and fish as well as fresh fruits and vegetables. The Panel considered that migration is not expected when the absorption capacity of the pads is not exceeded. Therefore no exposure from the consumption of the packed food is expected. The Panel also considered that none of these starting substances and the cross-linked polymer gives rise to concern for genotoxicity. Therefore the CEF Panel concluded that the use of the substance acrylic acid, sodium salt, co-polymer with acrylic acid, methyl ester, methacrylic acid, 2 hydroxypropylester, and acrylic acid cross-linked does not raise a safety concern when used as fibres in absorber pads for the packaging of fresh or frozen meat, poultry, fish, fruits and vegetables under conditions under which the absorption capacity of the pads is not exceeded and mechanical release of the fibres from the pads is excluded.

  9. Reversible Guest Binding in a Non-Porous FeII Coordination Polymer Host Toggles Spin Crossover

    DEFF Research Database (Denmark)

    Lennartson, Anders; Southon, Peter; Sciortino, Natasha F.

    2015-01-01

    )4 CN)2 ](SbF6 )4 ( 2 ) are low spin at room temperature, as are those in the polymeric adiponitrile-linked acetone solvate polymer {[Fe(bpte)(μ2-NC(CH2)4CN)]-(BPh4)2⋅Me2CO} ( 3⋅ Me2 CO). On heating 3⋅ Me2CO to 80 °C, the acetone is abruptly removed with an accompanying purple to dull lavender colour...

  10. bis-Nitrile and bis-Dialkylcyanamide Platinum(II) Complexes as Efficient Catalysts for Hydrosilylation Cross-Linking of Siloxane Polymers.

    Science.gov (United States)

    Islamova, Regina M; Dobrynin, Mikhail V; Ivanov, Daniil M; Vlasov, Andrey V; Kaganova, Elena V; Grigoryan, Galina V; Kukushkin, Vadim Yu

    2016-03-05

    cis- and trans-Isomers of the platinum(II) nitrile complexes [PtCl2(NCR)2] (R = NMe2, N(C₅H10), Ph, CH2Ph) were examined as catalysts for hydrosilylation cross-linking of vinyl-terminated polydimethylsiloxane and trimethylsilyl-terminated poly(dimethylsiloxane-co-ethylhydrosiloxane) producing high quality silicone rubbers. Among the tested platinum species the cis-complexes are much more active catalysts than their trans-congeners and for all studied platinum complexes cis-[PtCl2(NCCH2Ph)2] exhibits the best catalytic activity (room temperature, c = 1.0 × 10(-4) mol/L, τpot-life 60 min, τcuring 6 h). Although cis-[PtCl₂(NCCH2Ph)2] is less active than the widely used Karstedt's catalyst, its application for the cross-linking can be performed not only at room temperature (c = 1.0 × 10(-4) mol/L), but also, more efficiently, at 80 °C (c = 1.0 × 10(-4)-1.0 × 10(-5) mol/L) and it prevents adherence of the formed silicone rubbers to equipment. The usage of the cis- and trans-[PtCl2(NCR)2] complexes as the hydrosilylation catalysts do not require any inhibitors and, moreover, the complexes and their mixtures with vinyl- and trimethylsilyl terminated polysiloxanes are shelf-stable in air. Tested catalysts do not form colloid platinum particles after the cross-linking.

  11. Inulin crystal initiation via a glucose-fructose cross-link of adjacent polymer chains: atomic force microscopy and static molecular modelling.

    Science.gov (United States)

    Cooper, Peter D; Rajapaksha, K Harinda; Barclay, Thomas G; Ginic-Markovic, Milena; Gerson, Andrea R; Petrovsky, Nikolai

    2015-03-06

    Semi-crystalline microparticles of inulin (MPI) have clinical utility as potent human vaccine adjuvants but their relevant surface structure and crystal assembly remain undefined. We show inulin crystal surfaces to resemble multi-layered, discoid radial spherulites resulting from very rapid formation of complex tertiary structures, implying directed crystal initiation. Physical and in silico molecular modelling of unit cells confirm steric feasibility of initiation by hydrogen-bonded cross-linking of terminal glucose to a fructose of another chain, mimicking bonding in sucrose crystals. A strong, chelate-like dual H-bond is proposed to compel the known antiparallel alignment of inulin chains. Such cross-linking would require one extra fructose per chain in the native inulin crystal, as observed. Completion of five H-bonded internal ring-domains would 'lock in' each new 6-fructose structural unit of each antiparallel helix pair to create a new isoform. All known properties of inulin isoforms follow readily from these concepts.

  12. Amphiphilic Cross-Linked Liquid Crystalline Fluoropolymer-Poly(ethylene glycol) Coatings for Application in Challenging Conditions: Comparative Study between Different Liquid Crystalline Comonomers and Polymer Architectures.

    Science.gov (United States)

    Zigmond, Jennifer S; Letteri, Rachel A; Wooley, Karen L

    2016-12-14

    Linear and hyperbranched poly(ethylene glycol)-cross-linked amphiphilic fluoropolymer networks comprised of different liquid crystalline comonomers were developed and evaluated as functional coatings in extreme weather-challenging conditions. Through variation of the liquid-crystalline comonomer and hydrophilic:hydrophobic component ratios, several series of coatings were synthesized and underwent a variety of analyses including differential scanning calorimetry, water contact angle measurements and solution stability studies in aqueous media. These materials maintained an unprecedented reduction in the free water melting transition (Tm) temperature across the hyperbranched and linear versions. The coatings synthesized from hyperbranched fluoropolymers preserved the liquid crystalline character of the mesogenic components, as seen by polarized optical microscopy, and demonstrated stability in saltwater aqueous environments and in cold weather conditions.

  13. Thermally Cross-Linked Anion Exchange Membranes from Solvent Processable Isoprene Containing Ionomers

    Science.gov (United States)

    2015-01-15

    capacities (IECs). Solution cast membranes were thermally cross- linked to form anion exchange membranes. Cross-linking was achieved by taking advantage...distribution is unlimited. Thermally Cross-Linked Anion Exchange Membranes from Solvent Processable Isoprene Containing Ionomers The views...Box 12211 Research Triangle Park, NC 27709-2211 Anion Exchnage Membrane, Polymer synthesis, Morphology, Anion Conductivity REPORT DOCUMENTATION PAGE

  14. Polymer micelle with pH-triggered hydrophobic-hydrophilic transition and de-cross-linking process in the core and its application for targeted anticancer drug delivery.

    Science.gov (United States)

    Fan, Jianquan; Zeng, Fang; Wu, Shuizhu; Wang, Xiaodan

    2012-12-10

    In this study, an novel amphiphilic block copolymer P[PEGMA-b-(DEMA-co-APMA)]-FA and its cross-linker uracil-(CH2)6-uracil (U-(CH2)6-U) were synthesized and used as the targeted and pH-responsive nanocarriers for anticancer drug delivery. The hydrophobic block of the copolymer contains adenine (A) and tertiary amine moieties and the hydrophilic block is terminated with a targeting ligand folic acid (FA). Under neutral pH, the hydrophobic chain segments of the copolymer are cross-linked by U-(CH2)6-U through the A-U nucleobase pairing based on complementary multiple hydrogen bonding, and the copolymer forms stable micelles with their mean diameter of around 170 nm in water. While under acidic pH, the micelles dissociate as a result of protonation of tertiary amines and disruption of the A-U nucleobase pairing. Flow cytometry and fluorescent microscope observation show that, when loaded with an anticancer drug DOX, the micelles can preferably enter folate receptor (FR)-positive cancer cells and kill the cells via intracellular release of the anticancer drug. Cytotoxicity tests (MTT tests) indicate that the micelles with FA on their surfaces exhibit higher cytotoxicity toward FR-positive cells than those without FA. This study provides useful insights on designing and improving the applicability of copolymer micelles for other targeted drug delivery systems.

  15. Development and characterization of polymer electrolyte membranes based on ionical cross-linked poly(1-vinyl-1,2,4 triazole) and poly(vinylphosphonic acid)

    Energy Technology Data Exchange (ETDEWEB)

    Aslan, Ayse; Bozkurt, Ayhan [Fatih University, Department of Chemistry, 34500 Bueyuekcekmece-Istanbul (Turkey)

    2009-06-15

    The fabrication, thermal and proton conducting properties of complex polymer electrolytes based on poly(vinylphosphonic acid) (VPA) and poly(1-vinyl-1,2,4-triazole) (PVTri) were investigated throughout this work. The membrane materials were produced by complexation of PVPA with PVTri at various concentrations to get PVTriP(VPA){sub x} where x designates the molar ratio of the polymer repeating units and varied from 0.25 to 4. The complexed structure of the polymers was confirmed by FT-IR spectroscopy. The TGA results verified that the presence of PVTri in the complex polymer electrolytes suppressed the formation of phosphonic acid anhydrides up to 150 C. The DSC and SEM results demonstrated the homogeneity of the materials. Proton conductivity, activation energy and water/methanol uptake of these membranes were also measured. PVTriP(VPA){sub 2} showed a proton conductivity of 2.5 x 10{sup -5} S cm{sup -1} at 180 C in the anhydrous state. After humidification (RH = 50%), PVTri-P(VPA){sub 4} and PVTri-P(VPA){sub 2} showed respective proton conductivities of 0.008 and 0.022 S cm{sup -1} at 100 C, where the conductivity of the latter is close to Nafion 117 at the same humidity level. (author)

  16. Investigation of Optimum Polymerization Conditions for Synthesis of Cross-Linked Polyacrylamide-Amphoteric Surfmer Nanocomposites for Polymer Flooding in Sandstone Reservoirs

    Directory of Open Access Journals (Sweden)

    A. N. El-hoshoudy

    2015-01-01

    Full Text Available Currently enhanced oil recovery (EOR technology is getting more attention by many countries since energy crises are getting worse and frightening. Polymer flooding by hydrophobically associated polyacrylamides (HAPAM and its modified silica nanocomposite are a widely implemented technique through enhanced oil recovery (EOR technology. This polymers class can be synthesized by copolymerization of acrylamide (AM, reactive surfmer, functionalized silica nanoparticles, and a hydrophobic cross-linker moiety in the presence of water soluble initiator via heterogeneous emulsion polymerization technique, to form latexes that can be applied during polymer flooding. Chemical structure of the prepared copolymers was proven through different techniques such as Fourier transform infrared spectroscopy (FTIR, and nuclear magnetic spectroscopy (1H&13C-NMR, and molecular weight was measured by gel permeation chromatography. Study of the effects of monomer, surfmer, cross-linker, silica, and initiator concentrations as well as reaction temperature was investigated to determine optimum polymerization conditions through single factor and orthogonal experiments. Evaluation of the prepared copolymers for enhancing recovered oil amount was evaluated by carrying out flooding experiments on one-dimensional sandstone model to determine recovery factor.

  17. Collagen cross linking: Current perspectives

    Directory of Open Access Journals (Sweden)

    Srinivas K Rao

    2013-01-01

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

  18. Mechanism of Action and Pharmacology of Patiromer, a Nonabsorbed Cross-Linked Polymer That Lowers Serum Potassium Concentration in Patients With Hyperkalemia

    Science.gov (United States)

    Harrison, Stephen D.; Cope, M. Jamie; Park, Craig; Lee, Lawrence; Salaymeh, Faleh; Madsen, Deidre; Benton, Wade W.; Berman, Lance; Buysse, Jerry

    2016-01-01

    Hyperkalemia is a potentially life-threatening condition, and patients who have chronic kidney disease, who are diabetic, or who are taking renin–angiotensin–aldosterone system inhibitors are at increased risk. Therapeutic options for hyperkalemia tend to have limited effectiveness and can be associated with serious side effects. Colonic potassium secretion can increase to compensate when urinary potassium excretion decreases in patients with renal impairment, but this adaptation is insufficient and hyperkalemia still results. Patiromer is a novel, spherical, nonabsorbed polymer designed to bind and remove potassium, primarily in the colon, thereby decreasing serum potassium in patients with hyperkalemia. Patiromer has been found to decrease serum potassium in patients with hyperkalemia having chronic kidney disease who were on renin–angiotensin–aldosterone system inhibitors. Results of nonclinical studies and an early phase clinical study are reported here. Two studies with radiolabeled drug, one in rats and the other in dogs, confirmed that patiromer was not absorbed into the systemic circulation. Results of an in vitro study showed that patiromer was able to bind 8.5 to 8.8 mEq of potassium per gram of polymer at a pH similar to that found in the colon and had a much higher potassium-binding capacity compared with other resins, including polystyrene sulfonate. In a study in hyperkalemic rats, a decrease in serum potassium was observed via an increase in fecal potassium excretion. In a clinical study in healthy adult volunteers, a significant increase in fecal potassium excretion and a significant decrease in urinary potassium excretion were observed. Overall, patiromer is a high-capacity potassium binder, and the chemical and physical characteristics of patiromer may lead to good clinical efficacy, tolerability, and patient acceptance. PMID:26856345

  19. Effects of Supercritical CO 2 Conditioning on Cross-Linked Polyimide Membranes

    KAUST Repository

    Kratochvil, Adam M.

    2010-05-25

    The effects of supercritical CO2 (scCO2) conditioning on high-performance cross-linked polyimide membranes is examined through gas permeation and sorption experiments. Under supercritical conditions, the cross-linked polymers do not exhibit a structural reorganization of the polymer matrix that was observed in the non-cross-linkable, free acid polymer. Pure gas permeation isotherms and mixed gas permeabilities and selectivities show the cross-linked polymers to be much more stable to scCO2 conditioning than the free acid polymer. In fact, following scCO2 conditioning, the mixed gas CO2 permeabilities of the cross-linked polymers increased while the CO2/CH4 separation factors remained relatively unchanged. This response highlights the stability and high performance of these cross-linked membranes in aggressive environments. In addition, this response reveals the potential for the preconditioning of cross-linked polymer membranes to enhance productivity without sacrificing efficiency in practical applications which, in effect, provides another tool to \\'tune\\' membrane properties for a given separation. Finally, the dual mode model accurately describes the sorption and dilation characteristics of the cross-linked polymers. The changes in the dual mode sorption model parameters before and after the scCO2 exposure also provide insights into the alterations in the different glassy samples due to the cross-linking and scCO2 exposure. © 2010 American Chemical Society.

  20. Physically cross-linked polymer binder based on poly(acrylic acid) and ion-conducting poly(ethylene glycol-co-benzimidazole) for silicon anodes

    Science.gov (United States)

    Lim, Sanghyun; Lee, Kukjoo; Shin, Inseop; Tron, Artur; Mun, Junyoung; Yim, Taeeun; Kim, Tae-Hyun

    2017-08-01

    The practical applications of Si electrodes in lithium-ion batteries are limited since they undergo large changes in volume during charge and discharge, and consequently become highly deteriorated. A novel binder system holding silicon particles together and preventing disintegration of the electrode during operation hence needs to be developed to enable reliable cycleability. In the current work, such a new polymer binder system, based on poly(acrylic acid) (PAA) and poly(ethylene glycol-co-benzimidazole) (PEGPBI), is developed for silicon anodes. The physical crosslinking using acid-base interactions between PAA and PBI, together with the ion-conducting PEG group, yields physical properties for the resulting PAA-PEGPBI-based anodes that are better than those of electrodes based on the currently available PAA binder, and yields good cell performances. A Si-based electrode with high loading levels of 1.0-1.3 mg cm-2 (0.7-0.91 Si mg cm-2) is reliably manufactured using specifically PAA-PEGPBI-2, which is made with 2 wt% of PEGPBI relative to PAA, and shows a very high capacity value of 1221 mAh g-1 at a rate of 0.5 C after 50 cycles, and a high capacity value of more than 1600 mAh g-1 at a high rate of 2 C.

  1. B, N co-doped carbon from cross-linking induced self-organization of boronate polymer for supercapacitor and oxygen reduction reaction

    Science.gov (United States)

    Chang, Ying; Yuan, Conghui; Liu, Cheng; Mao, Jie; Li, Yuntong; Wu, Haiyang; Wu, Yuzhe; Xu, Yiting; Zeng, Birong; Dai, Lizong

    2017-10-01

    A novel strategy has been developed to generate B, N co-doped carbon materials (CNBs) through the pyrolysis of boronate polymer nanoparticles (BPNs) derived from the condensation reaction between catechol and boronic monomers. The morphology, surface area and heteroatom (viz. B and N) content of the CNBs can be easily adjusted by altering the molar ratio between catechol and boronic monomers. The supercapacitor and oxygen reduction reaction (ORR) performance of the CNBs are optimized. CNBs derived from equal molar ratio of catechol and boronic monomers exhibit favorable performance for supercapacitor, featuring a specific capacitance of up to 299.4 F/g at 0.2 A/g, an improved rate capability and excellent cycle stability. Notably, CNBs prepared using 1/2 molar ratio of catechol to boronic monomers show excellent ORR performance, as they demonstrate good electrocatalytic activity, high tolerance for methanol and long durability. Our findings may be of interest in the design of carbon materials with optimized electrochemical properties through the control over surface area and the content of heteroatom.

  2. Cross-linked fluoroalkyl end-capped co-oligomeric nanoparticle-encapsulated fullerenea new approach to the surface modification of traditional organic polymers with fullerene-containing nanoparticles.

    Science.gov (United States)

    Mugisawa, Masaki; Kasai, Remi; Sawada, Hideo

    2009-01-06

    Cross-linked fluoroalkyl end-capped co-oligomeric nanoparticle-encapsulated fullerenes, prepared by deprotecting a fluoroalkyl end-capped isocyanatoethyl methacrylate 2-butanone oxime adduct-1-hydroxy-5-adamantylacrylate co-oligomer in the presence of fullerene, were of well-defined size in the nanometer range (28-82 nm) and exhibited good dispersibility in a variety of solvents such as methanol, ethanol, isopropyl alcohol, tetrahydrofuran, N,N-dimethylformamide, dimethyl sulfoxide, and 1,2-dichloroethane. Transmission electron microscopy images also showed that these nanocomposites were particles with a mean diameter of 45 nm and that the fullerenes were tightly encapsulated into fluorinated nanoparticle cores. In methanol, these fluorinated nanoparticles emitted fluorescence related to the presence of fullerene and were applied in the surface modification of traditional organic polymers such as poly(methyl methacrylate) (PMMA) to effect good oleophobicity imparted by fluorine on the modified film surfaces. Interestingly, a higher fluorescent intensity of fullerene was observed on the modified PMMA surfaces, although the reverse side of these film surfaces yielded an extremely weak fluorescent intensity. More interestingly, a fluorescence microscopy image of the cross-section of the modified PMMA film showed that encapsulated fullerene was arranged regularly above the modified PMMA film surface.

  3. Electrospinning formaldehyde cross-linked zein solutions

    Science.gov (United States)

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

  4. Rheology of Cross-linked Polymer Networks

    DEFF Research Database (Denmark)

    Jensen, Mette Krog

    Hudklæbere bruges i mange dagligdags sammenhænge, fra simple fingreplastre til mere avancerede produkter som stomiposer eller sårbandager. Set ud fra et økonomisk synspunkt, er dette et område, hvor en lille forbedring kan have stor indflydelse. Rent menneskeligt kan dårligt formulerede klæbere f...

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

    OpenAIRE

    Oral, Ebru; Muratoglu, Orhun K.

    2007-01-01

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

  6. Covalently Cross-Linked Sulfone Polybenzimidazole Membranes with Poly(Vinylbenzyl Chloride) for Fuel Cell Applications

    DEFF Research Database (Denmark)

    Yang, Jingshuai; Aili, David; Li, Qingfeng;

    2013-01-01

    Covalently cross-linked polymer membranes were fabricated from poly(aryl sulfone benzimidazole) (SO(2) PBI) and poly(vinylbenzyl chloride) (PVBCl) as electrolytes for high-temperature proton-exchange-membrane fuel cells. The cross-linking imparted organo insolubility and chemical stability against...

  7. Corneal collagen cross-linking

    Directory of Open Access Journals (Sweden)

    Jankov II Mirko

    2010-01-01

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

  8. Chemical cross-linking of Chlamydia trachomatis

    DEFF Research Database (Denmark)

    Birkelund, Svend; Lundemose, AG; Christiansen, Gunna

    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...

  9. Temperature- and pH-sensitive interpenetrating polymer networks grafted on PP: Cross-linking irradiation dose as a critical variable for the performance as vancomycin-eluting systems

    Science.gov (United States)

    Muñoz-Muñoz, Franklin; Ruiz, Juan-Carlos; Alvarez-Lorenzo, Carmen; Concheiro, Angel; Bucio, Emilio

    2012-05-01

    This work focuses on the effect of gamma-ray radiation conditions on the stimuli-responsiveness and drug-eluting performance of polypropylene (PP) substrates grafted with interpenetrating networks of N-isopropylacrylamide (NIPAAm) and acrylic acid (AAc). PNIPAAm was cross-linked applying 10-100 kGy doses in the presence and absence of the chemical cross-linker N,N'-methylenebisacrylamide (MBAAm). Then, the net-PP-g-PNIPAAm was interpenetrated with PAAc synthesized under a 2.5 kGy dose to obtain net-PP-g-PNIPAAm-inter-net-PAAc films. The amount of grafted PNIPAAm (80%, 125% and 145% levels) and the cross-linking radiation dose (10, 40 and 70 kGy levels) strongly determine the interpenetration of PAAc, the swelling degree, the amount of vancomycin loaded and its release rate. The chemical cross-linker only caused a minor decrease in the degree of swelling. The higher the PNIPAAm grafted on PP and the lower the cross-linking radiation dose, the more the PAAc in the IPN and, consequently, the higher the vancomycin loaded through specific interactions and the more sustained the release (>8 h). The films possessing these features exhibited vancomycin release rate per surface unit suitable to prevent bacterial growth. Thus, adequate tuning of the radiation doses during grafting and cross-linking of the PNIPAAm networks may enable to achieve surface-modified materials for medical devices with an antibiofilm performance.

  10. In vitro cross-linking of elastin peptides and molecular characterization of the resultant biomaterials.

    Science.gov (United States)

    Heinz, Andrea; Ruttkies, Christoph K H; Jahreis, Günther; Schräder, Christoph U; Wichapong, Kanin; Sippl, Wolfgang; Keeley, Fred W; Neubert, Reinhard H H; Schmelzer, Christian E H

    2013-04-01

    Elastin is a vital protein and the major component of elastic fibers which provides resilience to many vertebrate tissues. Elastin's structure and function are influenced by extensive cross-linking, however, the cross-linking pattern is still unknown. Small peptides containing reactive allysine residues based on sequences of cross-linking domains of human elastin were incubated in vitro to form cross-links characteristic of mature elastin. The resultant insoluble polymeric biomaterials were studied by scanning electron microscopy. Both, the supernatants of the samples and the insoluble polymers, after digestion with pancreatic elastase or trypsin, were furthermore comprehensively characterized on the molecular level using MALDI-TOF/TOF mass spectrometry. MS(2) data was used to develop the software PolyLinX, which is able to sequence not only linear and bifunctionally cross-linked peptides, but for the first time also tri- and tetrafunctionally cross-linked species. Thus, it was possible to identify intra- and intermolecular cross-links including allysine aldols, dehydrolysinonorleucines and dehydromerodesmosines. The formation of the tetrafunctional cross-link desmosine or isodesmosine was unexpected, however, could be confirmed by tandem mass spectrometry and molecular dynamics simulations. The study demonstrated that it is possible to produce biopolymers containing polyfunctional cross-links characteristic of mature elastin from small elastin peptides. MALDI-TOF/TOF mass spectrometry and the newly developed software PolyLinX proved suitable for sequencing of native cross-links in proteolytic digests of elastin-like biomaterials. The study provides important insight into the formation of native elastin cross-links and represents a considerable step towards the characterization of the complex cross-linking pattern of mature elastin. Copyright © 2013 Elsevier B.V. All rights reserved.

  11. Bioreducible cross-linked nanoshell enhances gene transfection of polycation/DNA polyplex in vivo.

    Science.gov (United States)

    Piao, Ji-Gang; Ding, Sheng-Gang; Yang, Lu; Hong, Chun-Yan; You, Ye-Zi

    2014-08-11

    In this study, we have prepared a self-cross-linking PEG-based branched polymer, which easily forms a bioreducible nanoshell around polyplexes of cationic polymer and DNA, simply via heating the polyplex dispersions in the presence of this self-cross-linking branched polymer. This nanoshell can prevent the polyplex from dissociation and aggregation in physiological fluids without inhibiting the electrostatic interactions between the polymer and DNA. Furthermore, glutathione (GSH) can act as a stimulus to open the nanoshell after it has entered the cell. The polyplexes coated with the bioreducible nanoshell show an obvious enhancement in gene transfection in vivo compared with bare polyplexes.

  12. The contraction of granules of nanoporous super-cross-linked polystyrene sorbents as a result of the exclusion of large-sized mineral electrolyte ions from the polymer phase

    Science.gov (United States)

    Pastukhov, A. V.; Davankov, V. A.; Tsyurupa, M. P.; Blinnikova, Z. K.; Kavalerskaya, N. E.

    2009-03-01

    The deformation of neutral super-cross-linked polystyrene sorbents and ionites based on styrene-divinylbenzene gel-type copolymers brought in contact with concentrated solutions of HCl, H3PO4, NaOH, NH4Cl, (NH4)2SO4, and LiCl electrolytes was studied by dilatometry for separate spherical granules. Considerable contraction of super-cross-linked polystyrene matrices swollen in water was observed in concentrated solutions containing large-sized lithium, sulfate, and phosphate ions. Volume compressive strain correlated with the size of excluded hydrated ions. The contraction effect was caused by the difference in the osmotic pressure of water in thin pores and water in concentrated solutions filling large pores. The exclusion effect ignored earlier should also influence the degree of ion exchange and volume deformation of standard ion-exchange resins brought in contact with solutions of various electrolytes.

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

    Science.gov (United States)

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

    2014-12-21

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

  14. Grafted, cross-linked carbon black as a double-layer capacitor electrode material

    Energy Technology Data Exchange (ETDEWEB)

    Richner, R.; Mueller, S.; Wokaun, A.

    2001-03-01

    Isocyanate prepolymers readily react with oxidic functional groups on carbon black. On carbon black grafted with diisocyanates, reactive isocyanate groups are available for cross-linking to a polyurethane system. This cross-linked carbon black was considered as a new active material for electrochemical electrodes. Active material for electric double-layer capacitor electrodes was produced which had values of specific capacitance of up to 200 F/g. Cross-linking efficiencies of up to 58 % of the polymers utilised were achieved. (author)

  15. Permanent Set of Cross-Linking Networks: Comparison of Theory with Molecular Dynamics Simulations

    DEFF Research Database (Denmark)

    Rottach, Dana R.; Curro, John G.; Budzien, Joanne

    2006-01-01

    The permanent set of cross-linking networks is studied by molecular dynamics. The uniaxial stress for a bead-spring polymer network is investigated as a function of strain and cross-link density history, where cross-links are introduced in unstrained and strained networks. The permanent set...... is found from the strain of the network after it returns to the state-of-ease where the stress is zero. The permanent set simulations are compared with theory using the independent network hypothesis, together with the various theoretical rubber elasticity theories: affine, phantom, constrained junction...

  16. Permanent Set of Cross-Linking Networks: Comparison of Theory with Molecular Dynamics Simulations

    DEFF Research Database (Denmark)

    Rottach, Dana R.; Curro, John G.; Budzien, Joanne;

    2006-01-01

    is found from the strain of the network after it returns to the state-of-ease where the stress is zero. The permanent set simulations are compared with theory using the independent network hypothesis, together with the various theoretical rubber elasticity theories: affine, phantom, constrained junction......The permanent set of cross-linking networks is studied by molecular dynamics. The uniaxial stress for a bead-spring polymer network is investigated as a function of strain and cross-link density history, where cross-links are introduced in unstrained and strained networks. The permanent set...

  17. Cross-linking chemistry of squid beak.

    Science.gov (United States)

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

    2010-12-03

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

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

    Science.gov (United States)

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

    2011-07-01

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

  19. Cross-linked structure of network evolution

    Science.gov (United States)

    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.

  20. Cross-linked structure of network evolution

    Energy Technology Data Exchange (ETDEWEB)

    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); Porter, Mason A. [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); 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.

  1. Method of preparing cross-linked enzyme particles

    NARCIS (Netherlands)

    Mateo, C.; Van Langen, L.M.; Van Rantwijk, F.

    2004-01-01

    The invention relates to a method of preparing cross-linked enzyme particles using a cross-linking agent. According to the invention, the enzyme particles are formed and subsequently cross-linked using a cross-linking agent having at least n reactive groups where N>=3 and a molecular weight of

  2. Method of preparing cross-linked enzyme particles

    NARCIS (Netherlands)

    Mateo, C.; Van Langen, L.M.; Van Rantwijk, F.

    2004-01-01

    The invention relates to a method of preparing cross-linked enzyme particles using a cross-linking agent. According to the invention, the enzyme particles are formed and subsequently cross-linked using a cross-linking agent having at least n reactive groups where N>=3 and a molecular weight of >2,00

  3. The cross linking of EPDM and NBR rubber

    Directory of Open Access Journals (Sweden)

    Samardžija-Jovanović Suzana

    2005-01-01

    Full Text Available In the process of macromolecule cross linking, the choice of type and quantity of the components and the experimental conditions are important to obtain the new cross linked materials with better mechanical and chemical characteristics. The cross linking method depends on the rubber type and structure. Intermolecular cross linking results in the formation elastomer network. The basis of the cross linking process, between ethylene propylene diene rubber (EPDM and acrylonitrile butadiene rubber (NBR, is a chemical reaction. Fillers and other additives are present in different mass ratios in the material. The exploitation properties of the cross linked materials depend on the quantity of additive in the cross linked systems.

  4. Insights into the swelling process and drug release mechanisms from cross-linked pectin/high amylose starch matrices

    Directory of Open Access Journals (Sweden)

    Fernanda M. Carbinatto

    2014-02-01

    Full Text Available Cross-linked pectin/high amylose mixtures were evaluated as a new excipient for matrix tablets formulations, since the mixing of polymers and cross-linking reaction represent rational tools to reach materials with modulated and specific properties that meet specific therapeutic needs. Objective: In this work the influence of polymer ratio and cross-linking process on the swelling and the mechanism driving the drug release from swellable matrix tablets prepared with this excipient was investigated. Methods: Cross-linked samples were characterized by their micromeritic properties (size and shape, density, angle of repose and flow rate and liquid uptake ability. Matrix tablets were evaluated according their physical properties and the drug release rates and mechanisms were also investigated. Results: Cross-linked samples demonstrated size homogeneity and irregular shape, with liquid uptake ability insensible to pH. Cross-linking process of samples allowed the control of drug release rates and the drug release mechanism was influenced by both polymer ratio and cross-linking process. The drug release of samples with minor proportion of pectin was driven by an anomalous transport and the increase of the pectin proportion contributed to the erosion of the matrix. Conclusion: The cross-linked mixtures of high amylose and pectin showed a suitable excipient for slowing the drug release rates.

  5. Comparative study of PBI Cross Linked Utilizing Agents of Varying Steric Configurations

    DEFF Research Database (Denmark)

    Kirkebcek, Andreas; Aili, David; Li, Qingfeng;

    2016-01-01

    The high thermal and chemical stability of poly[2,2'-(m-phenylene)-5,5' bibenzimidazole] (PBI) accounts for its wise spread use in high temperature polymer electrolyte membrane fuel cells (HT- PEMFC). By doping the membrane with phosphoric acid (PA) ionic conductivity is obtained. Thus conductivity...... ionic or covalent cross linking. When considering such, little attention is devoted to explore the effect of the sterical configuration of the cross linking agent. In this contribution three different cross linking agents are utilized to evaluate how these affects final membrane properties....... is dependent on the amount of PA present within the membrane. However mechanical properties are reduced are significantly reduced due to the plasticizing effect shown by PA [1]. This effect is due to PBI chain displacement. This effect can be lessened by use of cross linking [2-4]. This can be obtained using...

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

    Science.gov (United States)

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

    2010-06-01

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

  7. [Corneal collagen cross-linking for keratoconus].

    Science.gov (United States)

    Zotov, V V; Pashtaev, N P; Pozdeeva, N A

    2015-01-01

    Over the last decade, corneal collagen cross-linking (CXL) has become a conventional treatment method for progressive keratoconus. Laboratory studies have shown that CXL increases the diameter of collagen fibers and also the number of intra- and interfibrillar cross-links, thus, increasing biomechanical strength of the irradiated cornea. As confirmed by a series of clinical and randomized controlled trials, CXL is able to slow down and, perhaps, to stop the progression of keratoconus. In most post-CXL patients visual acuity improves, while keratometric readings, spherical equivalent, and higher order aberrations reduce. Although published results prove CXL effective in the treatment of progressive keratoconus, its late consequences are yet unknown. This article reviews the stages of CXL development and results of published experimental and clinical studies. Prospects for CXL modifications that do not require epithelial debridement are discussed.

  8. Characterization of Cross-Linked Lipase Aggregates

    DEFF Research Database (Denmark)

    Prabhavathi Devi, Bethala Lakshmi Anu; Guo, Zheng; Xu, Xuebing

    2009-01-01

    Commercially available microbial lipases from different sources were immobilized as cross-linked enzyme aggregates (CLEAs) using different precipitants and glutaraldehyde as cross-linkers. These CLEAs were assayed based on esterification between lauric acid and n-propanol in solvent-free systems...... change upon CLEA formation. This work presents a characterization of CLEAs based on an esterification activity assay, which is useful for exploring the synthetic application potential of CLEA technology with favorable perspectives....

  9. Thermal Analyse sof Cross-Linked Polyethylene

    Directory of Open Access Journals (Sweden)

    Radek Polansky

    2007-01-01

    Full Text Available The paper summarizes results obtained during the structural analyses measurements (Differential Scanning Calorimetry DSC, Thermogravimetry TG, Thermomechanical analysis TMA and Fourier transform infrared spectroscopy FT-IR. The samples of cross-linked polyethylene cable insulation were tested via these analyses. The DSC and TG were carried out using simultaneous thermal analyzer TA Instruments SDT Q600 with connection of Fourier transform infrared spectrometer Nicolet 380. Thermomechanical analysis was carried out by TMA Q400EM TA Instruments apparatus.

  10. Collagen cross-linking in thin corneas

    Directory of Open Access Journals (Sweden)

    Prema Padmanabhan

    2013-01-01

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

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

    Science.gov (United States)

    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.

  12. Fiber optic immunosensor for cross-linked fibrin concentration

    Science.gov (United States)

    Moskowitz, Samuel E.

    2000-08-01

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

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

    Science.gov (United States)

    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.

  14. Cross-linking for microbial keratitis

    Directory of Open Access Journals (Sweden)

    Jayesh Vazirani

    2013-01-01

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

  15. Cross-Linking Poly(lactic acid) Film Surface by Neutral Hyperthermal Hydrogen Molecule Bombardment.

    Science.gov (United States)

    Du, Wangli; Shao, Hong; He, Zhoukun; Tang, Changyu; Liu, Yu; Shen, Tao; Zhu, Yan; Lau, Woon-ming; Hui, David

    2015-12-16

    Constructing a dense cross-linking layer on a polymer film surface is a good way to improve the water resistance of poly(lactic acid) (PLA). However, conventional plasma treatments have failed to achieve the aim as a result of the unavoidable surface damage arising from the charged species caused by the uncontrolled high energy coming from colliding ions and electrons. In this work, we report a modified plasma method called hyperthermal hydrogen-induced cross-linking (HHIC) technology to construct a dense cross-linking layer on PLA film surfaces. This method produces energy-controlled neutral hyperthermal hydrogen, which selectively cleaves C-H bonds by molecule collision from the PLA film without breaking other bonds (e.g., C-C bonds in the polymer backbone), and results in subsequent cross-linking of the carbon radicals generated from the organic molecules. The formation of a dense cross-linking layer can serve as a barrier layer to significantly improve both the hydrophobicity and water vapor barrier property of the PLA film. Because of the advantage of selective cleavage of C-H bonds by HHIC treatment, the original physical properties (e.g., mechanical strength and light transmittance) of the PLA films are well-preserved.

  16. Grafted Cross-Linked Polyolefin Substrates for Peptide Synthesis and Assays

    DEFF Research Database (Denmark)

    1999-01-01

    suited for use in solid-phase biosystems, notably bioassays, such as immunoassays, DNA hybridization assays or PCR amplification. The grafted chains may bear substituents which are such that the polymer-grafted cross-linked polyolefin substrate is swellable by water or aqueous media, in other words...

  17. 21 CFR 177.2710 - Styrene-divinylbenzene resins, cross-linked.

    Science.gov (United States)

    2010-04-01

    ... SERVICES (CONTINUED) FOOD FOR HUMAN CONSUMPTION (CONTINUED) INDIRECT FOOD ADDITIVES: POLYMERS Substances..., preparing, treating, packaging, transporting, or holding food, in accordance with the following prescribed... 21 Food and Drugs 3 2010-04-01 2009-04-01 true Styrene-divinylbenzene resins, cross-linked....

  18. Swelling properties of cross-linked DNA gels.

    Science.gov (United States)

    Costa, Diana; Miguel, M Graça; Lindman, Björn

    2010-07-12

    This work represents our contribution to the field of physical chemistry of DNA gels, and concerns the synthesis and study of novel chemically cross-linked DNA gels. The use of covalent DNA gels is a very promising way to study DNA-cosolute interactions, as well as the dynamic behaviour of DNA and cationic compacting agents, like lipids, surfactants and polycations. Manipulating DNA in new ways, like DNA networks, allows a better understanding and characterization of DNA-cosolute complexes at the molecular level, and also allows us to follow the assembly structures of these complexes. The use of responsive polymer gels for targeted delivery of toxic and/or labile drugs has, during the past few years, shown to be a promising concept. The features found in the proposed system would find applications in a broader field of gel/drug interaction, for the development of controlled release and targeted delivery devices.

  19. Reinforced films based on cross-linked water-soluble sulfonated carbon nanotubes with sulfonated polystyrene.

    Science.gov (United States)

    Dai, Ying; Haiping, Hong; Guiver, Michael; Welsh, Jeffry S

    2009-09-01

    Reinforced films based on sulfonated polystyrene cross-linked with water-soluble sulfonated carbon nanotubes were fabricated using a free-standing film-making method. Transmission and scanning electron microscopy (TEM and SEM), and X-ray photoelectron spectroscopy (XPS) were used to verify the cross-linking reaction. The mechanical properties of these films demonstrated that the tensile strength increases with an increase in the sulfonated nanotube concentration. At 5 wt% nanotube loading, the tensile strength increased 84% compared with polymer containing no nanotube loading. The relationships between structure and mechanical properties are discussed and a possible direction for making ultra thin and ultra lightweight film is proposed.

  20. Synthesis and properties of reprocessable sulfonated polyimides cross-linked via acid stimulation for use as proton exchange membranes

    Science.gov (United States)

    Zhang, Boping; Ni, Jiangpeng; Xiang, Xiongzhi; Wang, Lei; Chen, Yongming

    2017-01-01

    Cross-linked sulfonated polyimides are one of the most promising materials for proton exchange membrane (PEM) applications. However, these cross-linked membranes are difficult to reprocess because they are insoluble. In this study, a series of cross-linkable sulfonated polyimides with flexible pendant alkyl side chains containing trimethoxysilyl groups is successfully synthesized. The cross-linkable polymers are highly soluble in common solvents and can be used to prepare tough and smooth films. Before the cross-linking reaction is complete, the membranes can be reprocessed, and the recovery rate of the prepared films falls within an acceptable range. The cross-linked membranes are obtained rapidly when the cross-linkable membranes are immersed in an acid solution, yielding a cross-linking density of the gel fraction of greater than 90%. The cross-linked membranes exhibit high proton conductivities and tensile strengths under hydrous conditions. Compared with those of pristine membranes, the oxidative and hydrolytic stabilities of the cross-linked membranes are significantly higher. The CSPI-70 membrane shows considerable power density in a direct methanol fuel cell (DMFC) test. All of these results suggest that the prepared cross-linked membranes have great potential for applications in proton exchange membrane fuel cells.

  1. The Cross - linking reaction of HEC

    Institute of Scientific and Technical Information of China (English)

    XIONG Jian; YE Jun; XUAN Zhiyong; XIE Guohui

    2001-01-01

    @@ Cellulose ethers are important components for light industries such as food and papermaking industries. Its modification research is a frontline science to widen their uses and realize their industrialization. The target of modification is to make high production value, low input and meet the needs better in industries. O-(2-hydroxyethl) cellulose (HEC) is one of the best-known cellulose ether derivatives. It is mainly used as thickeners, dispersants, adhesives, extenders, and films because of its water solubility and gel-forming properties. The present research,by means of cross-linking, we study the influence on HEC about rheological behavior.This will provide a feasible scheme for cellulose ethers modification.

  2. The Cross - linking reaction of HEC

    Institute of Scientific and Technical Information of China (English)

    XIONG; Jian

    2001-01-01

    Cellulose ethers are important components for light industries such as food and papermaking industries. Its modification research is a frontline science to widen their uses and realize their industrialization. The target of modification is to make high production value, low input and meet the needs better in industries.  O-(2-hydroxyethl) cellulose (HEC) is one of the best-known cellulose ether derivatives. It is mainly used as thickeners, dispersants, adhesives, extenders, and films because of its water solubility and gel-forming properties. The present research,by means of cross-linking, we study the influence on HEC about rheological behavior.This will provide a feasible scheme for cellulose ethers modification.……

  3. Studies on Cross-linking of succinic acid with chitosan/collagen

    Directory of Open Access Journals (Sweden)

    Tapas Mitra

    2013-01-01

    Full Text Available The present study summarizes the cross-linking property of succinic acid with chitosan /collagen. In detail, the chemistry behind the cross-linking and the improvement in mechanical and thermal properties of the cross-linked material were discussed with suitable instruments and bioinformatics tools. The concentration of succinic acid with reference to the chosen polymers was optimized. A 3D scaffold prepared using an optimized concentration of succinic acid (0.2% (w/v with chitosan (1.0% (w/v and similarly with collagen (0.5% (w/v, was subjected to surface morphology, FT-IR analysis, tensile strength assessment, thermal stability and biocompatibility. Results revealed, cross-linking with succinic acid impart appreciable mechanical strength to the scaffold material. In silico analysis suggested the prevalence of non-covalent interactions, which played a crucial role in improving the mechanical and thermal properties of the cross-linked scaffold. The resultant 3D scaffold may find application as wound dressing material, as an implant in clinical applications and as a tissue engineering material.

  4. Cross-linking study on skeletal muscle actin: properties of suberimidate-treated actin.

    Science.gov (United States)

    Ohara, O; Takahashi, S; Ooi, T; Fujiyoshi, Y

    1982-06-01

    Cross-linking experiments were performed on muscle skeletal actin, using imidoesters of various chain lengths. Chemical analyses on all products except one (derived from succinimidate) show evidence of the presence of intramolecular cross-links in the molecule. The detailed properties of suberimidate-treated actin (SA) are as follows: SA contains nearly 1 mol of intramolecular cross-link per mol of actin and less than 15% of intermolecularly cross-linked products. Even at a low salt concentration, SA is polymeric, exchanges slowly its bound nucleotide with free nucleotides in solution, and shows an F-actin-type CD spectrum. Electron micrographs of SA reveal that SA exists actually as fibrous polymers in solutions of low ionic strength, although the fibers seem to be less rigid than those at high salt concentration. The F-form of SA at a high salt concentration is indistinguishable from intact F-actin. SA can bind heavy meromyosin and activate the ATPase of heavy meromyosin as observed for intact F-actin. Tropomyosin binds SA only at a high salt concentration. These results show that SA possesses the properties of F-actin even in media of low salt concentration, which are favorable for depolymerization of F-actin. Thus, we may infer that the conformation of SA is frozen in the F-state of actin by the introduction of intramolecular cross-links in the protein.

  5. Grass Cell Walls: A Story of Cross-Linking

    Science.gov (United States)

    Hatfield, Ronald D.; Rancour, David M.; Marita, Jane M.

    2017-01-01

    Cell wall matrices are complex composites mainly of polysaccharides, phenolics (monomers and polymers), and protein. We are beginning to understand the synthesis of these major wall components individually, but still have a poor understanding of how cell walls are assembled into complex matrices. Valuable insight has been gained by examining intact components to understand the individual elements that make up plant cell walls. Grasses are a prominent group within the plant kingdom, not only for their important roles in global agriculture, but also for the complexity of their cell walls. Ferulate incorporation into grass cell wall matrices (C3 and C4 types) leads to a cross-linked matrix that plays a prominent role in the structure and utilization of grass biomass compared to dicot species. Incorporation of p-coumarates as part of the lignin structure also adds to the complexity of grass cell walls. Feruoylation results in a wall with individual hemicellulosic polysaccharides (arabinoxylans) covalently linked to each other and to lignin. Evidence strongly suggests that ferulates not only cross-link arabinoxylans, but may be important factors in lignification of the cell wall. Therefore, the distribution of ferulates on arabinoxylans could provide a means of structuring regions of the matrix with the incorporation of lignin and have a significant impact upon localized cell wall organization. The role of other phenolics in cell wall formation such as p-coumarates (which can have concentrations higher than ferulates) remains unknown. It is possible that p-coumarates assist in the formation of lignin, especially syringyl rich lignin. The uniqueness of the grass cell wall compared to dicot sepcies may not be so much in the gross composition of the wall, but how the distinctive individual components are organized into a functional wall matrix. These features are discussed and working models are provided to illustrate how changing the organization of feruoylation and p

  6. Cross-link guided molecular modeling with ROSETTA.

    Directory of Open Access Journals (Sweden)

    Abdullah Kahraman

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

  7. Cross Linked Metal Particles for Low Noise Bolometer Materials

    Science.gov (United States)

    2016-12-12

    SECURITY CLASSIFICATION OF: This final report summarizes WSU’s progress from 4/2/2015 to 09/30/2016 on the project, "Cross-linked Metal Particles ...2016 Final Report: Cross-linked Metal Particles for Low-noise Bolometer Materials The views, opinions and/or findings contained in this report are...peer-reviewed journals: Number of Papers published in non peer-reviewed journals: Final Report: Cross-linked Metal Particles for Low-noise Bolometer

  8. Cross-linked PEG via degradable phosphate ester bond: synthesis, water-swelling, and application as drug carrier.

    Science.gov (United States)

    Liu, Zhaoxing; Wang, Lei; Bao, Chunyan; Li, Xinxin; Cao, Lei; Dai, Kerong; Zhu, Linyong

    2011-06-13

    A new series of degradable and water-swellable cross-linked PEG phosphoester polymers (CPPs) based on a facile cross-linked reaction between diphosphoesters of polyethylene glycol (P-PEG-P) and diglycidyl ether of polyethylene glycol (E-PEG-E) has been prepared and characterized. The molecular weights and ratios of the prepolymers played an important role for the properties of CPPs polymers, such as mechanical property, swelling, and degradation rates. In the curing process, the glycidyl ether was consumed by both hydroxyl of the phosphoester (P-OH) and hydroxyl generated from the opened glycidyl ethers (C-OH) with the presence of acid, which generated degradable phosphate esters as cross-linked points and ether bonds as the short branches, respectively. Drug entrapment and release test and biological cytotoxicity studies in vitro suggested that the polymers and generated hydrogels have great potential applications in drug delivery system and biological materials.

  9. Cross-linking and rheological changes of whey proteins treated with microbial transglutaminase.

    Science.gov (United States)

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

    2004-03-10

    Modification of the functionality of whey proteins using microbial transglutaminase (TGase) has been the subject of recent studies. However, changes in rheological properties of whey proteins as affected by extensive cross-linking with TGase are not well studied. The factors affecting cross-linking of whey protein isolate (WPI) using both soluble and immobilized TGase were examined, and the rheological properties of the modified proteins were characterized. The enzyme was immobilized on aminopropyl glass beads (CPG-3000) by selective adsorption of the biotinylated enzyme on avidin that had been previously immobilized. WPI (4 and 8% w/w) in deionized water, pH 7.5, containing 10 mM dithiothreitol was cross-linked using enzyme/substrate ratios of 0.12-10 units of activity/g WPI. The reaction was carried out in a jacketed bioreactor for 8 h at 40 degrees C with continuous circulation. The gel point temperature of WPI solutions treated with 0.12 unit of immobilized TGase/g was slightly decreased, but the gel strength was unaffected. However, increasing the enzyme/substrate ratio resulted in extensive cross-linking of WPI that was manifested by increases in apparent viscosity and changes in the gelation properties. For example, using 10 units of soluble TGase/g resulted in extensive cross-linking of alpha-lactalbumin and beta-lactoglobulin in WPI, as evidenced by SDS-PAGE and Western blotting results. Interestingly, the gelling point of WPI solutions increased from 68 to 94 degrees C after a 4-h reaction, and the gel strength was drastically decreased (lower storage modulus, G'). Thus, extensive intra- and interchain cross-linking probably caused formation of polymers that were too large for effective network development. These results suggest that a process could be developed to produce heat-stable whey proteins for various food applications.

  10. The cross-linking influence of electromagnetic radiation on water-soluble polyacrylan compositions with biopolymers

    Directory of Open Access Journals (Sweden)

    B. Grabowska

    2009-01-01

    Full Text Available The results of examinations of the cross-linking influence of electromagnetic radiation - in a microwave range – on polyacrylancompositions with biopolymers, are presented in the hereby paper. The cross-linking process of the tested compositions was determined on the basis of the FT-IR spectroscopic methods. It was shown that microwave operations can lead to the formation of new cross-linkedstructures with strong covalent bonds. The adsorption process and formation of active centres in polymer molecules as well as in highsilica sand were found due to microwave radiations. In this process hydroxyl groups (-OH - present in a polymer - and silane groups (Si- O-H - present in a matrix - are mainly taking part. Spectroscopic and strength tests performed for the system: biopolymer binding agent – matrix indicate that the microwave radiation can be applied for hardening moulding sands with biopolymer binders.

  11. Sub- T g Cross-Linking of a Polyimide Membrane for Enhanced CO 2 Plasticization Resistance for Natural Gas Separation

    KAUST Repository

    Qiu, Wulin

    2011-08-09

    Decarboxylation-induced thermal cross-linking occurs at elevated temperatures (∼15 °C above glass transition temperature) for 6FDA-DAM:DABA polyimides, which can stabilize membranes against swelling and plasticization in aggressive feed streams. Despite this advantage, such a high temperature might result in collapse of substructure and transition layers in the asymmetric structure of a hollow fibers based on such a material. In this work, the thermal cross-linking of the 6FDA-DAM:DABA at temperatures much below the glass transition temperature (∼387 °C by DSC) was demonstrated. This sub-Tg cross-linking capability enables extension to asymmetric structures useful for large scale membranes. The resulting polymer membranes were characterized by swelling in known solvents for the un-cross-linked materials, TGA analysis, and permeation tests of aggressive gas feed stream at higher pressure. The annealing temperature and time clearly influence the degree of cross-linking of the membranes, and results in a slight difference in selectivity for membranes under various cross-linking conditions. Results indicate that the sub-Tg thermal cross-linking of 6FDA-DAM:DABA dense film membrane can be carried out completely even at a temperature as low as 330 °C. Permeabilities were tested for the polyimide membranes using both pure gases (He, O2, N2, CH4, CO2) and mixed gases (CO2/CH4). The selectivity of the cross-linked membrane can be maintained even under very aggressive CO2 operating conditions that are not possible without cross-linking. Moreover, the plasticization resistance was demonstrated up to 700 psia for pure CO 2 gas or 1000 psia for 50% CO2 mixed gas feeds. © 2011 American Chemical Society.

  12. Radiation cross-linked polyolefin-insulated wire

    Science.gov (United States)

    Sano, K.; Ishitani, H.

    Because radiation cross-linked polyolefin has excellent mechanical heat resistance, its application limit can be expanded extremely by improving the resistance against heat oxidation and flame. This paper is concerning a halogen free radiation cross-linked polyolefin-insulated wire having excellent heat resistance and flameretardant property, which is used for appliances.

  13. Research Progress in Corneal Cross-linking Agents

    Institute of Scientific and Technical Information of China (English)

    Na Li; Xiujun Peng; Zhengjun Fan

    2014-01-01

    Corneal collagen cross-linking with UVA-riboflavin is cur-rently the only method for preventing the progression of kera-toconus from the pathological perspective. Topical application of a direct cross-linking agent is now attracting widespread at-tention in clinical settings..This article reviews the research progress in the application of indirect or direct cross-linking agents (e.g., riboflavin, glucose, ribose, glutaraldehyde, formaldehyde,.glyceraldehyde,.short chain aliphatic β-nitro alcohol, and genipin) in the treatment of corneal diseases and analyzes the cross-linking efficacy,.toxicity,.and merits and disadvantages of each cross-linking agent,.providing clinical information for further studies.

  14. Controlled delivery of valsartan by cross-linked polymeric matrices: Synthesis, in vitro and in vivo evaluation.

    Science.gov (United States)

    Sohail, Muhammad; Ahmad, Mahmood; Minhas, Muhammad Usman; Ali, Liaqat; Khalid, Ikrima; Rashid, Haroon

    2015-06-20

    The purpose of study was to develop chemically cross-linked chitosan-co-poly(AMPS) hydrogel based on low molecular weight chitosan for pH-responsive and controlled drug delivery of a model drug. Cross-linking was achieved chemically, by using free radical polymerization technique. Polymer (low molecular weight chitosan) was chemically cross-linked with monomer (2-acrylamido-2-methylpropane sulfonic acid) in aqueous medium. N, N'-Methylenebisacrylamide (MBA) was used as cross-linking agent. Sodium hydrogen sulfite (SHS) and ammonium peroxodisulphate (APS) were used as initiators in a chemical reaction. Hydrogels were characterized by FT-IR, SEM and DSC. Swelling studies and pH-sensitivity of hydrogels were studies at pH 1.2 and 7.4. Chitosan-co-poly(AMPS) hydrogels were administered to rabbits orally to evaluate its pharmacokinetic behavior. As a result of successful cross-linking of polymer and monomer, novel co-polymer has been developed, having suitable characteristics as desired for controlled release drug delivery system. Maximum swelling, drug loading and release have been observed at pH 7.4. In vivo results exhibited significant drug release and absorption at pH 7.4 in rabbits. It is concluded that highly swelling chitosan-AMPS based hydrogels were developed having pH independent swelling and pH dependent drug release properties. These hydrogels have great potential to be used for loading and controlled release of various therapeutic agents.

  15. Design of phosphated cross-linked microspheres of bael fruit gum as a biodegradable carrier.

    Science.gov (United States)

    Mahammed, Nawaz; Gowda, D V; Deshpande, Rohan D; Thirumaleshwar, Shailesh

    2015-01-01

    Present work was aimed at designing of phosphated cross-linked microspheres of bael fruit gum (BFG) by emulsification method using sodium-tri-meta phosphate as a cross-linking agent for treatment of colon cancer using 5-fluorouracil as model drug. Stirring speed was found to be 1,000 rpm for about 5 h to be optimal to obtain reproducible microspheres. It was found that there is an increase in particle size as polymer concentration is increased whereas a reduction in particle size was observed as there is increase in stirring speed. Cross-linked BFG microspheres were successfully prepared by emulsification method. Optimum surfactant concentration was found to be 2 % w/w. Scanning electron microscopy studies showed that the drug-loaded microspheres were non-aggregated and in spherical shape. Differential scanning calorimetry and Fourier transform infrared-spectroscopy studies showed that drug and excipients are compatible. Release studies showed that drug release was more profound in cecal medium induced with enzymes causing degradation of the cross linked BFG than that of the release showed in simulated intestinal fluid. Stability studies showed that there were no significant changes in the drug content and physical appearance of microspheres.

  16. Elasticity of cross-linked semiflexible biopolymers under tension.

    Science.gov (United States)

    von der Heydt, Alice; Wilkin, Daniel; Benetatos, Panayotis; Zippelius, Annette

    2013-09-01

    Aiming at the mechanical properties of cross-linked biopolymers, we set up and analyze a model of two weakly bending wormlike chains subjected to a tensile force, with regularly spaced inter-chain bonds (cross-links) represented by harmonic springs. Within this model, we compute the force-extension curve and the differential stiffness exactly and discuss several limiting cases. Cross-links effectively stiffen the chain pair by reducing thermal fluctuations transverse to the force and alignment direction. The extra alignment due to cross-links increases both with growing number and with growing strength of the cross-links, and is most prominent for small force f. For large f, the additional, cross-link-induced extension is subdominant except for the case of linking the chains rigidly and continuously along their contour. In this combined limit, we recover asymptotically the elasticity of a weakly bending wormlike chain without constraints, stiffened by a factor of 4. The increase in differential stiffness can be as large as 100% for small f or large numbers of cross-links.

  17. Poly(methyl vinyl ether-co-maleic acid)-polyethylene glycol nanocomposites cross-linked in situ with cellulose nanowhiskers.

    Science.gov (United States)

    Goetz, Lee; Foston, Marcus; Mathew, Aji P; Oksman, Kristiina; Ragauskas, Arthur J

    2010-10-11

    Nanocomposites were developed by cross-linking cellulose nanowhiskers with poly(methyl vinyl ether-co-maleic acid) and polyethylene glycol. Nuclear magnetic resonance (NMR) studies showed cross-linking occurs between the matrix and cellulose nanowhiskers via an esterification reaction. Proton NMR T(2) relaxation experiments provided information on the mobility of the polymer chains within the matrix, which can be related to the structure of the cross-linked nanocomposite. The nanocomposite was found to consist of mobile chain portions between cross-linked junction points and immobilized chain segments near or at those junction points, whose relative fraction increased upon further incorporation of cellulose nanowhiskers. Atomic force microscopy images showed a homogeneous dispersion of nanowhiskers in the matrix even at high nanowhisker content, which can be attributed to cross-linking of the nanowhiskers in the matrix. Relative humidity conditions were found to affect the mechanical properties of the composites negatively while the nanowhiskers content had a positive effect. It is expected that the cross-links between the matrix and the cellulose nanowhiskers trap the nanowhiskers in the cross-linked network, preventing nanowhisker aggregation subsequently producing cellulose nanocomposites with unique mechanical behaviors. The results show that in situ cross-linking of cellulose nanowhiskers with a matrix polymer is a promising route to obtain nanocomposites with well dispersed nanowhiskers, tailored nanostructure, and mechanical performance.

  18. Study of temperature dependence of thermal conductivity in cross-linked epoxies using molecular dynamics simulations with long range interactions

    Science.gov (United States)

    Kumar, A.; Sundararaghavan, V.; Browning, A. R.

    2014-03-01

    In this work, we demonstrate the use of the Green-Kubo integral of the heat flux autocorrelation function, incorporating long-range corrections to model the thermal conductivity versus temperature relationship of cross-linked polymers. The simulations were performed on a cross-linked epoxy made from DGEBA and a curing agent (diamino diphenyl sulfone) using a consistent valence force field (CVFF). A dendrimeric approach was utilized for building equilibrated cross-linked structures that allowed replication of the experimental dilatometric curve for the epoxy system. We demonstrate that the inclusion of a long-range correction within the Ewald/PPPM approach brings the results close to experimentally measured conductivity within an error of 10% while providing a good prediction of the relationship of thermal conductivity versus temperature. This method shows significant promise towards the computation of thermal conductivity from simulations even before synthesis of the polymer for purposes of materials by design.

  19. Molecular Structures of Isolevuglandin-Protein Cross-Links.

    Science.gov (United States)

    Bi, Wenzhao; Jang, Geeng-Fu; Zhang, Lei; Crabb, John W; Laird, James; Linetsky, Mikhail; Salomon, Robert G

    2016-10-17

    Isolevuglandins (isoLGs) are stereo and structurally isomeric γ-ketoaldehydes produced through free radical-induced oxidation of arachidonates. Some isoLG isomers are also generated through enzymatic cyclooxygenation. Post-translational modification of proteins by isoLGs is associated with loss-of-function, cross-linking and aggregation. We now report that a low level of modification by one or two molecules of isoLG has a profound effect on the activity of a multi subunit protease, calpain-1. Modification of one or two key lysyl residues apparently suffices to abolish catalytic activity. Covalent modification of calpain-1 led to intersubunit cross-linking. Hetero- and homo-oligomers of the catalytic and regulatory subunits of calpain-1 were detected by SDS-PAGE with Western blotting. N-Acetyl-glycyl-lysine methyl ester and β-amyloid(11-17) peptide EVHHQKL were used as models for characterizing the cross-linking of protein lysyl residues resulting from adduction of iso[4]LGE2. Aminal, bispyrrole, and trispyrrole cross-links of these two peptides were identified and fully characterized by mass spectrometry. Aminal and bispyrrole dimers were both detected. Furthermore, a complex mixture of derivatives of the bispyrrole cross-link containing one or more additional atoms of oxygen was found. Interesting differences are evident in the predominant cross-link type generated in the reaction of iso[4]LGE2 with these peptides. More aminal cross-links versus bispyrrole are formed during the reaction of the dipeptide with iso[4]LGE2. In contrast, more bispyrrole versus aminal cross-links are formed during the reaction of EVHHQKL with iso[4]LGE2. It is tempting to speculate that the EVHHQKL peptide-pyrrole modification forms noncovalent aggregates that favor the production of covalent bispyrrole cross-links because β-amyloid(11-17) tends to spontaneously oligomerize.

  20. Current status of accelerated corneal cross-linking

    Directory of Open Access Journals (Sweden)

    Michael Mrochen

    2013-01-01

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

  1. Effect of nordihydroguaiaretic acid cross-linking on fibrillar collagen: in vitro evaluation of fibroblast adhesion strength and migration

    Directory of Open Access Journals (Sweden)

    Ana Y. Rioja

    2017-04-01

    Full Text Available Fixation is required to reinforce reconstituted collagen for orthopedic bioprostheses such as tendon or ligament replacements. Previous studies have demonstrated that collagen fibers cross-linked by the biocompatible dicatechol nordihydroguaiaretic acid (NDGA have mechanical strength comparable to native tendons. This work focuses on investigating fibroblast behavior on fibrillar and NDGA cross-linked type I collagen to determine if NDGA modulates cell adhesion, morphology, and migration. A spinning disk device that applies a range of hydrodynamic forces under uniform chemical conditions was employed to sensitively quantify cell adhesion strength, and a radial barrier removal assay was used to measure cell migration on films suitable for these quantitative in vitro assays. The compaction of collagen films, mediated by the drying and cross-linking fabrication process, suggests a less open organization compared to native fibrillar collagen that likely allowed the collagen to form more inter-chain bonds and chemical links with NDGA polymers. Fibroblasts strongly adhered to and migrated on native and NDGA cross-linked fibrillar collagen; however, NDGA modestly reduced cell spreading, adhesion strength and migration rate. Thus, it is hypothesized that NDGA cross-linking masked some adhesion receptor binding sites either physically, chemically, or both, thereby modulating adhesion and migration. This alteration in the cell-material interface is considered a minimal trade-off for the superior mechanical and compatibility properties of NDGA cross-linked collagen compared to other fixation approaches.

  2. Electrospinning of polyvinyl alcohol/gelatin nanofiber composites and cross-linking for bone tissue engineering application.

    Science.gov (United States)

    Linh, Nguyen Thuy Ba; Lee, Byong-Taek

    2012-09-01

    A three-dimensional polymer composite system consisting of polyvinyl alcohol/gelatin (PVA/GE) was fabricated via the electrospinning method and physically cross linked by methanol treatment. The effects of cross-linking between PVA/GE blend on physical, mechanical, and biological properties were investigated. After treating with methanol, PVA/GE mats become dense, hard, and aggregative with increased resistance to water dissolution. Osteoblasts like MG-63 cells were seeded on the surfaces of the cross linked PVA/GE mats and were found to attach firmly by expressing philopodial extensions. In addition, MTT assay and Western Blot analysis confirmed that the cells readily proliferated on the cross linked PVA/GE scaffolds. The osteoblast cell-matrix interaction demonstrated that the active biocompatibility of the mats was facilitated by using GE and cross-linking. In conclusion, our results suggest that cross-linked PVA/GE scaffolds hold promise for tissue engineering applications, especially in the field of artificial bone implant.

  3. The effect of an additional phosphite stabilizer on the properties of radiation cross-linked vitamin E blends of UHMWPE.

    Science.gov (United States)

    Oral, Ebru; Neils, Andrew; Yabannavar, Pooja; Muratoglu, Orhun K

    2014-06-01

    Antioxidant stabilization of radiation cross-linked ultrahigh molecular weight polyethylene (UHMWPE) has been introduced to improve the oxidative stability of total joint implant bearing surfaces. Blending of an antioxidant with UHMWPE resin powder followed by consolidation and radiation cross-linking has been cleared by the FDA for use in both total hips and total knees for designs incorporating two antioxidants, namely vitamin E and Covernox™ (a medical grade version of Irganox™ 1010). The antioxidants in the polymer are expected to protect the polymer during consolidation, during radiation cross-linking, on the shelf before implantation, and in vivo after implantation. To maximize the protection of the polymer afforded by the antioxidant in vivo, a novel approach may be the use of multiple antioxidants, especially to protect the primary antioxidant for a longer period of time. We hypothesized that the addition of a phosphite stabilizer (Irgafos 168™) commonly used in conjunction with hindered phenolic antioxidants in polymer processing could improve the oxidative stability of radiation cross-linked blends of vitamin E. To test our hypothesis, we prepared UHMWPE blends with 0.05 wt% Irgafos and 0.05 wt% vitamin E and compared its cross-link density, wear resistance, tensile properties, and impact strength to control blends containing only vitamin E. Our hypothesis was not supported; the cross-link density of UHMWPE was significantly decreased by the additive without additional benefit to oxidative stability. To our knowledge, this was the first attempt at using multiple stabilizers in medical grade UHMWPE.

  4. Controlled Release of Salicylic Acid from Biodegradable Cross-Linked Polyesters.

    Science.gov (United States)

    Dasgupta, Queeny; Chatterjee, Kaushik; Madras, Giridhar

    2015-09-08

    The purpose of this work was to develop a family of cross-linked poly(xylitol adipate salicylate)s with a wide range of tunable release properties for delivering pharmacologically active salicylic acid. The synthesis parameters and release conditions were varied to modulate polyester properties and to understand the mechanism of release. Varying release rates were obtained upon longer curing (35% in the noncured polymer to 10% in the cured polymer in 7 days). Differential salicylic acid loading led to the synthesis of polymers with variable cross-linking and the release could be tuned (100% release for the lowest loading to 30% in the highest loading). Controlled release was monitored by changing various factors, and the release profiles were dependent on the stoichiometric composition, pH, curing time, and presence of enzyme. The polymer released a combination of salicylic acid and disalicylic acid, and the released products were found to be nontoxic. Minimal hemolysis and platelet activation indicated good blood compatibility. These polymers qualify as "bioactive" and "resorbable" and can, therefore, find applications as immunomodulatory resorbable biomaterials with tunable release properties.

  5. EGDMA-cross-linked polystyrene resin: An efficient support for gel phase peptide synthesis

    Indian Academy of Sciences (India)

    P K Ajikumar; K S Devaky

    2000-08-01

    This article illustrates the application of a 2% ethyleneglycol dimethacrylate-cross-linked polystyrene support (EGDMA-PS) in manual solid phase peptide synthesis. This copolymer has been characterised and optimised for peptide synthesis by performing the synthesis of a few model peptides and two biologically important peptides. EGDMA-cross-linked polystyrene support was prepared by the suspension polymerisation of the monomers EGDMA and styrene. EGDMA-PS resin undergoes facile swelling in a variety of solvents, both polar and nonpolar, used in peptide synthesis. The polymer was functionalised by Friedel-Crafts chloromethylation reaction. Peptides were assembled on a 2% cross-linked chloromethyl polymer support of capacity 1.63 mmol Cl/g. The biological peptides synthesised are an 11-residue peptide ATP binding site of the CDC2 kinase and a difficult sequence-a nineresidue peptide 34-42 corresponding to a portion of the hydrophobic terminus of the-amyloid protein 1-42. After synthesis, the peptides were cleaved from the support by treating with neat TFA. Purity of the peptides obtained in good yield was checked by TLC and HPLC methods and found to be fairly high.

  6. Cross-linked multilayer-dye films deposited onto silica surfaces with high affinity for pepsin

    Science.gov (United States)

    Bucatariu, Florin; Ghiorghita, Claudiu-Augustin; Cocarta, Ana-Irina; Dragan, Ecaterina Stela

    2016-12-01

    Cross-linked thin films based on pH-responsive polymers with a specific ligand inside the organic layer are useful materials in separation processes or in fabrication of controlled delivery systems. Herein, we report the step-by-step deposition of polymer multilayers based on poly(ethyleneimine) (PEI), poly(acrylic acid) (PAA) and poly(sodium methacrylate) (PMAA) followed by the Congo red (CR) immobilization onto composite Daisogel silica microparticles and silicon wafers. The non-crosslinked composites were not stable in extreme basic medium (pH = 13), while thermal and chemical cross-linked samples with CR inside were stable over a wide range of pH. The interaction properties of different proteins [pepsin (PEP), lysozyme, trypsin, bovine serum albumin] with modified solid surfaces were followed by potentiometric titrations, UV and AFM measurements. Only the PEP macromolecules were sorbed onto the Daisogel composite microparticles with CR inside the cross-linked multilayer. The maximum sorbed amount was nearly 200 mg PEP/g Daisogel//(PEI/PAA)4.5 + CR. This high sorbed amount was in accordance with the AFM images, the average high and roughness increased drastically after the sorption of PEP.

  7. Covalently cross-linked polyetheretherketone proton exchange membrane for DMFC

    CSIR Research Space (South Africa)

    Luo, H

    2009-05-01

    Full Text Available -7 cm2/s) and good electrochemical stability. The results suggested that cross-linked polyetheretherketone membrane is particularly promising to be used as proton exchange membrane for the direct methanol fuel cell application....

  8. Non-cross-linked polystyrene-supported 2-imidazolidinone chiral auxiliary: synthesis and application in asymmetric alkylation reactions

    Science.gov (United States)

    Nguyen, Quynh Pham Bao

    2013-01-01

    Summary Asymmetric alkylation reactions using non-cross-linked polystyrene (NCPS)-supported 2-imidazolidinone chiral auxiliaries were successfully investigated with excellent diastereocontrol (>99% de). The recovery and the recycling of this soluble polymer-supported chiral auxiliary were achieved in order to produce highly optical pure carboxylic acids. PMID:24204423

  9. Photochemical Patterning of Ionically Cross-Linked Hydrogels

    Directory of Open Access Journals (Sweden)

    Marion Bruchet

    2013-08-01

    Full Text Available Iron(III cross-linked alginate hydrogel incorporating sodium lactate undergoes photoinduced degradation, thus serving as a biocompatible positive photoresist suitable for photochemical patterning. Alternatively, surface etching of iron(III cross-linked hydrogel contacting lactic acid solution can be used for controlling the thickness of the photochemical pattering. Due to biocompatibility, both of these approaches appear potentially useful for advanced manipulation with cell cultures including growing cells on the surface or entrapping them within the hydrogel.

  10. ROLE OF CORNEAL COLLAGEN CROSS LINKING IN KERATOCONUS

    OpenAIRE

    Atul; Superna; Bhimasankar; Vijayleela

    2015-01-01

    To evaluate the outcome of collagen cross linkage using riboflavin 0.1% and ultraviolet A radiation of a wavelength 370nm . PURPOSE : To determine the effect of collagen cross linking for keratoconus on pachymetry , corneal topography, uncorrected visual acuity, specular count, IOP at 1, 3, 6 months . METHODS : The current study was designed as a prospective interventional trial of corneal collagen cross - linking in subjects w...

  11. Anisotropic nanoparticles with controllable morphologies from non-cross-linked seeded emulsion polymerization.

    Science.gov (United States)

    Niu, Qun; Pan, Mingwang; Yuan, Jinfeng; Liu, Xiao; Wang, Xiaomei; Yu, Haifeng

    2013-09-01

    A simple and elegant approach to fabricate anisotropic P(VC-co-AAEM)/PS nanoparticles with controllable morphologies via emulsifier-free seeded emulsion polymerization is presented. Non-cross-linked P(VC-co-AAEM) seeds with hydrophilic surface are first synthesized through copolymerization of vinyl chloride (VC) and acetoacetoxyethyl methacrylate (AAEM), which are used to prepare P(VC-co-AAEM)/PS NPs with multiple bulges by SEP of styrene. Electron microscopy observation indicates that the content of AAEM in seeds is crucial to control the phase separation and morphology of the composite NPs. Moreover, the thermodynamic immiscibility between PVC and PS is the driving force for the formation of PS bulges onto the P(VC-co-AAEM) seeds. The resultant anisotropic NPs with non-cross-linked feature may promisingly serve as compatibilizers for further polymer processing. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  12. Elasticity of cross-linked semiflexible biopolymers under tension

    CERN Document Server

    von der Heydt, Alice; Benetatos, Panayotis; Zippelius, Annette

    2013-01-01

    Aiming at the mechanical properties of cross-linked biopolymers, we set up and analyze a model of two weakly bending wormlike chains subjected to a tensile force, with regularly spaced inter-chain bonds (cross-links) represented by harmonic springs. Within this model, we compute the force-extension curve and the differential stiffness exactly and discuss several limiting cases. Cross-links effectively stiffen the chain pair by reducing thermal fluctuations transverse to the force and alignment direction. The extra alignment due to cross-links increases both with growing number and with growing strength of the cross-links, and is most prominent for small force f. For large f, the additional, cross-link-induced extension is subdominant except for the case of linking the chains rigidly and continuously along their contour. In this combined limit, we recover asymptotically the elasticity of a weakly bending wormlike chain without constraints, stiffened by a factor four. The increase in differential stiffness can ...

  13. Non-cross-linked and cross-linked poly(alkylmethyldiallylammonium halides) : synthesis and aggregation behavior

    NARCIS (Netherlands)

    Wang, Guang-Jia; Engberts, Jan B.F.N.

    1998-01-01

    Hydrophobically modified polyelectrolytes (polysoaps) are a unique class of water-soluble polymers containing distinct hydrophobic and hydrophilic regions. Above a certain concentration, polysoaps form intramolecular and intermolecular aggregates in aqueous solution. They have attracted much attenti

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

    Science.gov (United States)

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

    2016-03-01

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

  15. Novel cross linked guar gum-g-poly(acrylate) porous superabsorbent hydrogels: Characterization and swelling behaviour in different environments.

    Science.gov (United States)

    Chandrika, Ksv Poorna; Singh, Anupama; Rathore, Abhishek; Kumar, Anil

    2016-09-20

    A new series of eco-friendly cross linked guar gum-g-poly(acrylate) porous superabsorbent hydrogels was prepared by in situ grafting polymerization and cross-linking on to a natural guar gum employing N,N-methylene bis acrylamide as cross linker. Morphological and structural characterization of the prepared hydrogels (SPHs) done by Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and solid state C(13) NMR spectroscopy confirmed formation of porous grafted and crosslinked hydrogel structure. Increase in cross linker concentration in the feed mass exhibited decrease in porosity and increase in density of the hydrogels. Swelling of an optimized hydrogel (SPH) in response to external stimuli namely, salt solutions, fertilizer solutions, temperature, and pH exhibited high swelling ratios in various environments. Swelling rate of the SPH was faster than the corresponding nonporous superabsorbent hydrogel. The prepared hydrogels can serve as excellent carriers of pesticides, fertilizers and agriculturally important microbes. Biocontrol formulations based on a representative SPH exhibited excellent shelf-life characteristics and bioefficacy against phytopathogenic fungus Pythium aphanidermatum.

  16. Cross-linked polystyrene sulfonic acid and polyethylene glycol as a low-fouling material.

    Science.gov (United States)

    Alghunaim, Abdullah; Zhang Newby, Bi-min

    2016-04-01

    A negatively charged hydrophilic low fouling film was prepared by thermally cross-linking a blend consisting of polystyrene sulfonic acid (PSS) and polyethylene glycol (PEG). The film was found to be stable by dip-washing. The fouling resistance of this material toward bacterial (Escherichia coli) and colloidal (polystyrene particles) attachment, non-specific protein (fibronectin) adsorption and cell (3T3 NIH) adhesion was evaluated and was compared with glass slides modified with polyethylene glycol (PEG) brushes, oxidized 3-mercaptopropyltrimethoxysilane (sulfonic acid, SA), and n-octadecyltrichlorosilane (OTS). The extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory and thermodynamic models based on surface energy were used to explain the interaction behaviors of E. coli/polystyrene particles-substrate and protein-substrate interactions, respectively. The cross-linked PSS-PEG film was found to be slightly better than SA and PEG toward resisting non-specific protein adsorption, and showed comparable low attachment results as those of PEG toward particle, bacterial and NIH-3T3 cells adhesion. The low-fouling performance of PSS-PEG, a cross-linked film by a simple thermal curing process, could allow this material to be used for applications in aqueous environments, where most low fouling hydrophilic polymers, such as PSS or PEG, could not be easily retained.

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

    Science.gov (United States)

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

    2015-04-01

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

  18. Electrospinning of Cross-Linked Magnetic Chitosan Nanofibers for Protein Release.

    Science.gov (United States)

    Nicknejad, Ehsan Tayerani; Ghoreishi, Seyyed Mohammad; Habibi, Neda

    2015-12-01

    A poly(vinylalcohol) (PVA) electrospun/magnetic/chitosan nanocomposite fibrous cross-linked network was fabricated using in situ cross-linking electrospinning technique and used for bovine serum albumin (BSA) loading and release applications. Sodium tripolyphosphate (TPP) and glutaraldehyde (GA) were used as cross-linkers which modified magnetic-Fe3O4 chitosan as Fe3O4/CS/TPP and Fe3O4/CS/GA, respectively. BSA was used as a model protein drugs which was encapsulated to form Fe3O4/CS/TPP/BSA and Fe3O4/CS/GA/BSA nanoparticles. The composites were electrospun with PVA to form nanofibers. Nanofibers were characterized by field emission scanning electron microscopy (FESEM) and Fourier transform infrared spectroscopy (FTIR). The characterization results suggest that Fe3O4 nanoparticles with average size of 45 nm were successfully bound on the surface of chitosan. The cross-linked nanofibers were found to contain uniformly dispersed Fe3O4 nanoparticles. The size and morphology of the nanofibers network was controlled by varying the cross-linker type. FTIR data show that these two polymers have intermolecular interactions. The sample with TPP cross-linker showed an enhancement of the controlled release properties of BSA during 30-h experimental investigation. Graphical Abstract ᅟ.

  19. Extreme dryness and DNA-protein cross-links

    Science.gov (United States)

    Bieger-Dose, A.; Dose, K.; Meffert, R.; Mehler, M.; Risi, S.

    Exposure of fungal conidia (Aspergillus ochraceus) or spores of Bacillus subtilis to extreme dryness or vacuum induces DNA lesions, including strand breaks and the formation of DNA-protein cross-links. In wet cells only a small amount of protein is bound to DNA, but exposure to conditions of lowered water activity results in an increasing number of cross-links between DNA and proteins. In fungal conidia these cross-links are detected after selective iodination (125J) of the DNA-bound proteins followed by gel electrophoresis and subsequent autoradiography. Another approach is the labelling of DNA with 32p by means of nick translation and the detection of differences in the electrophoretic mobility of DNA before and after digestion with proteinase K of proteins bound to DNA.

  20. Photo-cross-linked poly(ethylene carbonate) elastomers: synthesis, in vivo degradation, and determination of in vivo degradation mechanism.

    Science.gov (United States)

    Cornacchione, L A; Qi, B; Bianco, J; Zhou, Z; Amsden, B G

    2012-10-01

    Low-molecular-weight poly(ethylene carbonate) diols of varying molecular weight were generated through catalyzed thermal degradation of high-molecular-weight poly(ethylene carbonate). These polymers were then end functionalized with acrylate groups. The resulting α,ω-diacrylates were effectively photo-cross-linked upon exposure to long-wave UV light in the presence of a photoinitiator to yield rubbery networks of low sol content. The degree of cross-linking effectively controlled the in vivo degradation rate of the networks by adherent macrophages; higher cross-link densities yielded slower degradation rates. The cross-link density did not affect the number of adherent macrophages at the elastomer/tissue interface, indicating that cross-linking affected the susceptibility of the elastomer to degradative species released by the macrophages. The reactive species likely responsible for in vivo degradation appears to be superoxide anion, as the in vivo results were in agreement with in vitro degradation via superoxide anion, while cholesterol esterase, known to degrade similar poly(alkylene carbonate)s, had no affect on elastomer degradation.

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

    Energy Technology Data Exchange (ETDEWEB)

    Ng, Hon-Meng [Department of Chemical Engineering, Faculty of Engineering and Science, Universiti Tunku Abdul Rahman, Jalan Genting Kelang, 53300 Setapak, Kuala Lumpur (Malaysia); Bee, Soo-Tueen, E-mail: beest@utar.edu.my [Department of Chemical Engineering, Faculty of Engineering and Science, Universiti Tunku Abdul Rahman, Jalan Genting Kelang, 53300 Setapak, Kuala Lumpur (Malaysia); Ratnam, C.T. [Radiation Processing Technology Division, Malaysian Nuclear Agency, Bangi, 43000 Kajang, Selangor (Malaysia); Sin, Lee Tin; Phang, Yee-Yao; Tee, Tiam-Ting [Department of Chemical Engineering, Faculty of Engineering and Science, Universiti Tunku Abdul Rahman, Jalan Genting Kelang, 53300 Setapak, Kuala Lumpur (Malaysia); Rahmat, A.R. [Department of Polymer Engineering, Faculty of Chemical Engineering, Universiti Teknologi Malaysia, 81310 UTM Skudai, Johor (Malaysia)

    2014-01-15

    Highlights: • Investigation of trimethylopropane trimethacrylate (TMPTMA) on electron beam irradiated PLA. • Irradiated PLA blends were weakened by incorporation of high amount of TMPTMA. • TMPTMA interacts with polymer free radicals to build crosslinking network. -- Abstract: 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.

  2. FTIR Spectroscopic Studies on Cross Linking of SU-8 Photoresist

    Science.gov (United States)

    Kalaiselvi, S. M. P.; Tan, T. L.; Rawat, R. S.; Lee, P.; Heussler, S. P.; Breese, M. B. H.

    2013-11-01

    The usage of chemically-amplified, negative tone SU-8 photoresist is numerous, spanning industrial, scientific and medical fields. Hence, in this study, some preliminary studies were conducted to understand the dosage and heat treatment requirements of the SU-8 photoresist essential for pattern generation using X-ray lithography. In this work, using Synchrotron as the X-ray source, SU-8 photoresist was characterized for X-ray lithography in terms of its process parameters such as X-ray exposure dose, post exposure bake (PEB) time and temperature for various photoresist thicknesses which is considered worthwhile in view of applications of SU-8 for the fabrication of very high aspect ratio micro structures. The process parameters were varied and the resultant cross linking of the molecular chains of the photoresist was accurately monitored using a Fourier Transform Infra-Red (FTIR) spectrometer and the results are discussed. The infrared absorption peak at 914 cm-1 in the spectrum of the SU-8 photoresist was found to be a useful indicator for the completion of cross linking in the SU-8 photoresist. Results show that the cross linking of the SU-8 photoresist is at a higher rate from 0 J/cm3 to 30 J/cm3 after which the peak almost saturates regardless of the PEB time. It is a good evidence for the validation of dosage requirement of SU-8 photoresist for effective completion of cross linking, which in turn is a requirement for efficient fabrication of micro and nano structures. An analogous behavior was also observed between the extent of cross linking and the PEB time and temperature. The rate of cross linking declines after a certain period of PEB time regardless of PEB temperature. The obtained results also show a definite relation between variation of the absorbance area of the peak at 914 cm-1 and the X-ray exposure dose.

  3. Biopolymers from vegetable oils via catalyst- and solvent-free "click" chemistry: effects of cross-linking density.

    Science.gov (United States)

    Hong, Jian; Luo, Qiang; Wan, Xianmei; Petrović, Zoran S; Shah, Bipin K

    2012-01-09

    New monomers were prepared by introducing the azide groups in castor, canola, corn, soybean, and linseed oils. Polymerization of the azidated oils with alkynated soybean oil under thermal "click" chemistry conditions (without using a solvent or a catalyst) yielded fully cross-linked elastomers (1-5) of almost the same density (1.05 × 10(-3) kg/m(3)). The degree of cross-linking gradually increased from the castor-derived polymer (220 mol/m(3)) to the linseed-derived polymer (683 mol/m(3)). A systematic correlation between the degree of cross-linking and the thermal and mechanical properties was observed in these biopolymers. Tensile strength (0.62-3.39 MPa) and glass transition temperature (-5 to 16 °C) increased and the linear thermal expansion coefficient decreased in the series from the canola-derived polymer (2) to the linseed-derived polymer (5). The castor-derived polymer (1) that possesses an additional hydroxyl group per fatty acid chain behaved differently.

  4. Oligo(ethylene glycol)-sidechain microgels prepared in absence of cross-linking agent: Polymerization, characterization and variation of particle deformability.

    Science.gov (United States)

    Welsch, Nicole; Lyon, L Andrew

    2017-01-01

    We present a systematic study of self-cross-linked microgels formed by precipitation polymerization of oligo ethylene glycol methacrylates. The cross-linking density of these microgels and, thus, the network flexibility can be easily tuned through the modulation of the reaction temperature during polymerization. Microgels prepared in absence of any difunctional monomer, i.e. cross-linker, show enhanced deformability and particle spreading on solid surfaces as compared to microgels cross-linked with varying amounts of poly(ethylene glycol diacrylate) (PEG-DA) in addition to self-crosslinking. Particles prepared at low reaction temperatures exhibit the highest degree of spreading due to the lightly cross-linked and flexible polymer network. Moreover, AFM force spectroscopy studies suggest that cross-linker-free microgels constitute of a more homogeneous polymer network than PEG-DA cross-linked particles and have elastic moduli at the particle apex that are ~5 times smaller than the moduli of 5 mol-% PEG-DA cross-linked microgels. Resistive pulse sensing experiments demonstrate that microgels prepared at 75 and 80°C without PEG-DA are able to deform significantly to pass through nanopores that are smaller than the microgel size. Additionally, we found that polymer network flexibility of microgels is a useful tool to control the formation of particle dewetting patterns. This offers a promising new avenue for build-up of 2D self-assembled particle structures with patterned chemical and mechanical properties.

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

    Science.gov (United States)

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

    2014-09-24

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

  6. Evaluation of cross-linked chitosan microparticles containing acyclovir obtained by spray-drying

    Energy Technology Data Exchange (ETDEWEB)

    Stulzer, Hellen Karine [Laboratorio Quitech, Departamento de Quimica, Universidade Federal de Santa Catarina (Brazil); Laboratorio de Controle de Qualidade, Departamento de Ciencias Farmaceuticas, Universidade Federal de Santa Catarina (Brazil); Laboratorio de Controle de Qualidade, Departamento de Ciencias Farmaceuticas, Universidade Estadual de Ponta Grossa (Brazil)], E-mail: hellen.stulzer@gmail.com; Tagliari, Monika Piazzon [Laboratorio de Controle de Qualidade, Departamento de Ciencias Farmaceuticas, Universidade Federal de Santa Catarina (Brazil); Parize, Alexandre Luis [Laboratorio Quitech, Departamento de Quimica, Universidade Federal de Santa Catarina (Brazil); Silva, Marcos Antonio Segatto [Laboratorio de Controle de Qualidade, Departamento de Ciencias Farmaceuticas, Universidade Federal de Santa Catarina (Brazil); Laranjeira, Mauro Cesar Marghetti [Laboratorio Quitech, Departamento de Quimica, Universidade Federal de Santa Catarina (Brazil)

    2009-03-01

    The aim of this study was to obtain microparticles containing acyclovir (ACV) and chitosan cross-linked with tripolyphosphate using the spray-drying technique. The resultant system was evaluated through loading efficiency, differential scanning calorimetry (DSC), thermogravimetric analysis (TG), X-ray powder diffraction (XRPD), scanning electron microscopy (SEM), in vitro release and stability studies. The results obtained indicated that the polymer/ACV ratio influenced the final properties of the microparticles, with higher ratios giving the best encapsulation efficiency, dissolution profiles and stability. The DSC and XRPD analyses indicated that the ACV was transformed into amorphous form during the spray-drying process.

  7. Advanced Corneal Cross-Linking System with Fluorescence Dosimetry

    Directory of Open Access Journals (Sweden)

    Marc D. Friedman

    2012-01-01

    Full Text Available 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.

  8. The Database of Ribosomal Cross-links: an update.

    OpenAIRE

    Baranov, P V; Kubarenko, A V; Gurvich, O L; Shamolina, T A; Brimacombe, R

    1999-01-01

    The Database of Ribosomal Cross-links (DRC) was created in 1997. Here we describe new data incorporated into this database and several new features of the DRC. The DRC is freely available via World Wide Web at http://visitweb.com/database/ or http://www. mpimg-berlin-dahlem.mpg.de/ approximately ag_ribo/ag_brimacombe/drc/

  9. Elasticity of Rigidly Cross-Linked Networks of Athermal Filaments

    NARCIS (Netherlands)

    Zagar, Goran; Onck, Patrick R.; Van der Giessen, Erik

    2011-01-01

    Actin filaments assemble into network-like structures and play an important role in various cellular mechanical processes. It is known that the response of actin networks cross-linked by stiff proteins is characterized by two distinct regimes: (i) a linear stress strain response for small deformatio

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

    Science.gov (United States)

    Mathesan, Santhosh; Rath, Amrita; Ghosh, Pijush

    2016-02-01

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

  11. Porous Cross-Linked Polyimide-Urea Networks

    Science.gov (United States)

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

    2015-01-01

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

  12. Femtosecond laser collagen cross-linking without traditional photosensitizers

    Science.gov (United States)

    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.

  13. Scleral lens tolerance after corneal cross-linking for keratoconus

    NARCIS (Netherlands)

    Visser, Esther Simone; Soeters, Nienke; Tahzib, Nayyirih G.

    2015-01-01

    Purpose. Subjective and objective evaluation of scleral lens tolerance and fitting before and after corneal cross-linking (CXL) for progressive keratoconus. Methods. In this prospective cohort, evaluations were made of 18 unilateral eyes in patients who underwent CXL and had been wearing scleral len

  14. Lactoferrin binding to transglutaminase cross-linked casein micelles

    NARCIS (Netherlands)

    Anema, S.G.; de Kruif, C.G.

    2012-01-01

    Casein micelles in skim milk were either untreated (untreated milk) or were cross-linked using transglutaminase (TGA-milk). Added lactoferrin (LF) bound to the casein micelles and followed Langmuir adsorption isotherms. The adsorption level was the same in both milks and decreased the micellar zeta

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

    Science.gov (United States)

    Meador, Mary Ann B. (Inventor)

    2016-01-01

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

  16. 21 CFR 177.2420 - Polyester resins, cross-linked.

    Science.gov (United States)

    2010-04-01

    .... Pentaerythritol. Polyoxypropylene ethers of 4,4′-isopropylide-nediphenol (containing an average of 2-7.5 moles of...-pentanediol. (3) Cross-linking agents: Butyl acrylate. Butyl methacrylate. Ethyl acrylate. Ethylhexyl acrylate... the production of the resins or added thereto to impart desired technical or physical...

  17. Cross-linked enzyme aggregates (CLEAs): stable and recyclable biocatalysts

    NARCIS (Netherlands)

    Sheldon, R.A.

    2007-01-01

    The key to obtaining an optimum performance of an enzyme is often a question of devising an effective method for its immobilization. In the present review, we describe a novel, versatile and effective methodology for enzyme immobilization as CLEAs (cross-linked enzyme aggregates). The method is

  18. Hyper-cross-linked, hybrid membranes via interfacial polymerization

    NARCIS (Netherlands)

    Raaijmakers, M.J.T.

    2015-01-01

    Hyper-cross-linked, hybrid membranes consist of covalent networks of alternating organic and inorganic, or biological groups. This thesis reports on the preparation of such hybrid networks via interfacial polymerization. The structure-property relationships of the hybrid networks depend strongly on

  19. Effects of Molecular Weight upon Irradiation-Cross-Linked Poly(vinyl alcohol)/Clay Aerogel Properties.

    Science.gov (United States)

    Chen, Hong-Bing; Zhao, Yan; Shen, Peng; Wang, Jun-Sheng; Huang, Wei; Schiraldi, David A

    2015-09-16

    Facile fabrication of mechanically strong poly(vinyl alcohol) (PVOH)/clay aerogel composites through a combination of increasing polymer molecular weights and gamma irradiation-cross-linking is reported herein. The aerogels produced from high polymer molecular weights exhibit significantly increased compressive moduli, similar to the effect of irradiation-induced cross-linking. The required irradiation dose for fabricating strong PVOH composite aerogels with dense microstructure decreased with increasing polymer molecular weight. Neither thermal stability nor flammability was significantly changed by altering the polymer molecular weight or by modest gamma irradiation, but they were highly dependent upon the polymer/clay ratio in the aerogel. Optimization of the mechanical, thermal, and flammability properties of these composite aerogels could therefore be obtained by using relatively low levels of polymer, with very high polymer molecular weight, or lower molecular weight coupled with moderate gamma irradiation. The facile preparation of strong, low flammability aerogels is an alternative to traditional polymer foams in applications where fire safety is important.

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

    Directory of Open Access Journals (Sweden)

    Ikuko Machida-Sano

    2012-01-01

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

  1. Evaluation of the wear performance of a polycarbonate-urethane acetabular component in a hip joint simulator and comparison with UHMWPE and cross-linked UHMWPE.

    Science.gov (United States)

    St John, Kenneth; Gupta, Minakshi

    2012-07-01

    Acetabular hip joint components manufactured from gamma-sterilized ultra high molecular weight polyethylene (UHMWPE), gamma cross-linked UHMWPE, or polycarbonate-urethane (PCU) polymers were evaluated in a hip joint simulator, using cobalt alloy femoral components, for at least 5 million cycles. The volume of material losses due to wear was calculated for each type of sample, based upon mass loss measurements, every 500,000 cycles. The loss of material for the conventional UHMWPE was much higher than for the cross-linked UHMWPE, showing about a 70% reduction in wear due to cross-linking. The material loss for the PCU samples appears to have been at least 24% lower than for the cross-linked UHMWPE. Based upon these results, the PCU material seems to have potential for use as an alternative bearing material to UHMWPE for total hip replacement surgeries.

  2. Antioxidant films based on cross-linked methyl cellulose and native Chilean berry for food packaging applications.

    Science.gov (United States)

    López de Dicastillo, Carol; Rodríguez, Francisco; Guarda, Abel; Galotto, Maria José

    2016-01-20

    Development of antioxidant and antimicrobial active food packaging materials based on biodegradable polymer and natural plant extracts has numerous advantages as reduction of synthetic additives into the food, reduction of plastic waste, and food protection against microorganisms and oxidation reactions. In this way, active films based on methylcellulose (MC) and maqui (Aristotelia chilensis) berry fruit extract, as a source of antioxidants agents, were studied. On the other hand, due to the high water affinity of MC, this polymer was firstly cross-linked with glutaraldehyde (GA) at different concentrations. The results showed that the addition of GA decreased water solubility, swelling, water vapor permeability of MC films, and the release of antioxidant substances from the active materials increased with the concentration of GA. Natural extract and active cross-linked films were characterized in order to obtain the optimal formulation with the highest antioxidant activity and the best physical properties for latter active food packaging application.

  3. Assessment of using laponite cross-linked poly(ethylene oxide) for controlled cell adhesion and mineralization.

    Science.gov (United States)

    Gaharwar, Akhilesh K; Schexnailder, Patrick J; Kline, Benjamin P; Schmidt, Gudrun

    2011-02-01

    The in vitro cytocompatibility of silicate (Laponite clay) cross-linked poly(ethylene oxide) (PEO) nanocomposite films using MC3T3-E1 mouse preosteoblast cells was investigated while cell adhesion, spreading, proliferation and mineralization were assessed as a function of film composition. By combining the advantageous characteristics of PEO polymer (hydrophilic, prevents protein and cell adhesion) with those of a synthetic and layered silicate (charged, degradable and potentially bioactive) some of the physical and chemical properties of the resulting polymer nanocomposites could be controlled. Hydration, dissolution and mechanical properties were examined and related to cell adhesion. Overall, this feasibility study demonstrates the ability of using model Laponite cross-linked PEO nanocomposites to create bioactive scaffolds.

  4. Transient Anisocoria after Corneal Collagen Cross-Linking

    Science.gov (United States)

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

    2014-01-01

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

  5. Transient Anisocoria after Corneal Collagen Cross-Linking

    Directory of Open Access Journals (Sweden)

    George D. Kymionis

    2014-01-01

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

  6. Cytokines and growth factors cross-link heparan sulfate

    Science.gov (United States)

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

    2015-01-01

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

  7. Comparison of hydrazone heterobifunctional cross-linking agents for reversible conjugation of thiol-containing chemistry.

    Science.gov (United States)

    Christie, R James; Anderson, Diana J; Grainger, David W

    2010-10-20

    Reversible covalent conjugation chemistries that allow site- and condition-specific coupling and uncoupling reactions are attractive components in nanotechnologies, bioconjugation methods, imaging, and drug delivery systems. Here, we compare three heterobifunctional cross-linkers, containing both thiol- and amine-reactive chemistries, to form pH-labile hydrazones with hydrazide derivatives of the known and often published water-soluble polymer, poly[N-(2-hydroxypropyl methacrylamide)] (pHPMA), while subsequently coupling thiol-containing molecules to the cross-linker via maleimide addition. Two novel cross-linkers were prepared from the popular heterobifunctional cross-linking agent, succinimidyl-4-(N-maleimidomethyl) cyclohexane-1-carboxylate (SMCC), modified to contain either terminal aldehyde groups (i.e., 1-(N-3-propanal)-4-(N-maleimidomethyl) cyclohexane carboxamide, PMCA) or methylketone groups (i.e., 1-(N-3-butanone)-4-(N-maleimidomethyl) cyclohexane carboxamide, BMCA). A third cross-linking agent was the commercially available N-4-acetylphenyl maleimide (APM). PMCA and BMCA exhibited excellent reactivity toward hydrazide-derivatized pHPMA with essentially complete hydrazone conjugation to polymer reactive sites, while APM coupled only ∼60% of available reactive sites on the polymer despite a 3-fold molar excess relative to polymer hydrazide groups. All polymer hydrazone conjugates bearing these bifunctional agents were then further reacted with thiol-modified tetramethylrhodamine dye, confirming cross-linker maleimide reactivity after initial hydrazone polymer conjugation. Incubation of dye-labeled polymer conjugates in phosphate buffered saline at 37 °C showed that hydrazone coupling resulting from APM exhibited the greatest difference in stability between pH 7.4 and 5.0, with hydrolysis and dye release increased at pH 5.0 over a 24 h incubation period. Polymer conjugates bearing hydrazones formed from cross-linker BMCA exhibited intermediate stability

  8. Electrochemical Characterization of Ultrathin Cross-Linked Metal Nanoparticle Films.

    Science.gov (United States)

    Han, Chu; Percival, Stephen J; Zhang, Bo

    2016-09-06

    Here we report the preparation, characterization, and electrochemical study of conductive, ultrathin films of cross-linked metal nanoparticles (NPs). Nanoporous films ranging from 40 to 200 nm in thickness composed of gold and platinum NPs of ∼5 nm were fabricated via a powerful layer-by-layer spin coating process. This process allows preparation of uniform NP films as large as 2 × 2 cm(2) with precise control over thickness, structure, and electrochemical and electrocatalytic properties. Gold, platinum, and bimetallic NP films were fabricated and characterized using cyclic voltammetry, scanning electron microscopy, and conductance measurements. Their electrocatalytic activity toward the oxygen reduction reaction (ORR) was investigated. Our results show that the electrochemical activity of such NP films is initially hindered by the presence of dense thiolate cross-linking ligands. Both electrochemical cycling and oxygen plasma cleaning are effective means in restoring their electrochemical activity. Gold NP films have higher electric conductivity than platinum possibly due to more uniform film structure and closer particle-particle distance. The electrochemical and electrocatalytic performance of platinum NP films can be greatly enhanced by the incorporation of gold NPs. This work focuses on electrochemical characterization of cross-linked NP films and demonstrates several unique properties. These include quick and easy preparation, ultrathin and uniform film thickness, tunable structure and composition, and transferability to many other substrates.

  9. Preparation of Thermo-Responsive and Cross-Linked Fluorinated Nanoparticles via RAFT-Mediated Aqueous Polymerization in Nanoreactors.

    Science.gov (United States)

    Ma, Jiachen; Zhang, Luqing; Geng, Bing; Azhar, Umair; Xu, Anhou; Zhang, Shuxiang

    2017-01-25

    In this work, a thermo-responsive and cross-linked fluoropolymer poly(2,2,2-Trifluoroethyl) methacrylate (PTFEMA) was successfully prepared by reversible addition-fragmentation chain transfer (RAFT) mediated aqueous polymerization with a thermo-responsive diblock poly(dimethylacrylamide-b-N-isopropylacrylamide) (PDMA-b-PNIPAM) that performed a dual function as both a nanoreactor and macro-RAFT agent. The cross-linked polymer particles proved to be in a spherical-like structure of about 50 nm in diameter and with a relatively narrow particle size distribution. ¹H-NMR and (19)F-NMR spectra showed that thermo-responsive diblock P(DMA-b-NIPAM) and cross-linked PTFEMA particles were successfully synthesized. Influence of the amount of ammonium persulfate (APS), the molar ratio of monomers to RAFT agent, influence of the amount of cross-linker on aqueous polymerization and thermo-responsive characterization of the particles are investigated. Monomer conversion increased from 44% to 94% with increasing the molar ratio of APS and P(DMA-b-NIPAM) from 1:9 to1:3. As the reaction proceeded, the particle size increased from 29 to 49 nm due to the consumption of TFEMA monomer. The size of cross-linked nanoparticles sharply decreased from 50.3 to 40.5 nm over the temperature range 14-44 °C, suggesting good temperature sensitivity for these nanoparticles.

  10. Long-term durability of HT-PEM fuel cells based on thermally cross-linked polybenzimidazole

    Science.gov (United States)

    Søndergaard, Tonny; Cleemann, Lars Nilausen; Becker, Hans; Aili, David; Steenberg, Thomas; Hjuler, Hans Aage; Seerup, Larisa; Li, Qingfeng; Jensen, Jens Oluf

    2017-02-01

    Long-term durability of high temperature polymer electrolyte membrane fuel cells based on thermally cross-linked polybenzimidazole membranes was studied and compared with reference membranes based on linear polybenzimidazole. The test was conducted at 160 °C under constant load currents of 200 mA cm-2 for periods of 1000, 4400, and 13,000 h. Extensive beginning-of-life (BoL) and end-of-test (EoT) characterisation was carried out, and disturbance of the steady state operated cells was minimised by limiting in-line diagnostics to the low-invasive technique of electrochemical impedance spectroscopy (EIS). Up until the operating time of 9200 h, the cell equipped with the cross-linked membrane showed an average degradation rate of 0.5 μV h-1, compared to 2.6 μV h-1 for the reference membrane, though parallel tests for a shorter period of time showed deviations, likely due to malfunctioning contact between layers or cell components. For the full test period of 13,000 h, the average voltage decay rate was about 1.4 and 4.6 μV h-1 for cells equipped with cross-linked and linear polybenzimidazole membranes, respectively. EIS and post-test analysis revealed that the cross-linked membrane showed better stability in terms of area specific resistance due to improved acid retention characteristics.

  11. Keratin/Polyvinyl Alcohol Blend Films Cross-Linked by Dialdehyde Starch and Their Potential Application for Drug Release

    Directory of Open Access Journals (Sweden)

    Yao Dou

    2015-03-01

    Full Text Available Feather keratin (FK extracted from feathers represents a valuable source of biodegradable and biocompatible polymer. The aim of this study was the development and characterization of blended films based on FK and polyvinyl alcohol (PVA cross-linked by dialdehyde starch (DAS for a potential drug release application. The compatibility of FK/PVA was improved when cross-linked by DAS: the relative crystallinity of the PVA/FK film slightly decreased, and the enthalpy value for the melting peak decreased by about 50% for the cross-linked films. The total soluble mass of all blend films in water was below 35% at 37 °C, indicating a good stability of the films in water. The results of the Rhodamine B dye (as a model drug release tests showed that the release rates decreased with increasing DAS content. DAS-induced cross-linking improves several important properties of the FK/PVA films, such as the compactness, the compatibility, and the stability in water. These improvements offer the potential to expand the application of FK films in the biomaterial field.

  12. Characterization of Cross-linked Alkaline Lignin/Poly (Vinyl Alcohol Film with a Formaldehyde Cross-linker

    Directory of Open Access Journals (Sweden)

    Ling Su

    2014-06-01

    Full Text Available On the basis of previous experiments, industrial alkaline lignin/poly (vinyl alcohol (PVOH cross-linked films, industrial alkaline lignin/poly (vinyl alcohol blend films, and neat poly (vinyl alcohol films were prepared by casting. The films were investigated by Fourier transform infra-red spectroscopy (FTIR, X-ray diffraction (XRD, thermogravimetry analysis (TGA, and dynamic mechanical analysis (DMA. The water contact angles for the three kinds of films were studied as well. The crosslinking reaction between alkaline lignin and PVOH was strong, which was attributed to the high hydrolysis degree of PVOH and the high reactivity of formaldehyde. Compared with the neat PVOH film, the crystallinity of the cross-linked film decreased slightly; the thermal stability of the cross-linked film was higher; DMA analysis showed that the Tg and the tanδ magnitude of the alkaline lignin/PVOH reaction film both decreased slightly. Lignin and the cross-linking reaction both improved the water resistance of films. Therefore, this research has provided a detailed analysis of the characterization of the films while exploring the potential of direct usage of industrial alkaline lignin in polymer materials.

  13. Self-cross-linking biopolymers as injectable in situ forming biodegradable scaffolds.

    Science.gov (United States)

    Balakrishnan, Biji; Jayakrishnan, A

    2005-06-01

    The injectable polymer scaffolds which are biocompatible and biodegradable are important biomaterials for tissue engineering and drug delivery. Hydrogels derived from natural proteins and polysaccharides are ideal scaffolds for tissue engineering since they resemble the extracellular matrices of the tissue comprised of various amino acids and sugar-based macromolecules. Here, we report a new class of hydrogels derived from oxidized alginate and gelatin. We show that periodate-oxidized sodium alginate having appropriate molecular weight and degree of oxidation rapidly cross-links proteins such as gelatin in the presence of small concentrations of sodium tetraborate (borax) to give injectable systems for tissue engineering, drug delivery and other medical applications. The rapid gelation in the presence of borax is attributed to the slightly alkaline pH of the medium as well as the ability of borax to complex with hydroxyl groups of polysaccharides. The effect of degree of oxidation and concentration of alginate dialdehyde, gelatin and borax on the speed of gelation was examined. As a general rule, the gelling time decreased with increase in concentration of oxidized alginate, gelatin and borax and increase in the degree of oxidation of alginate. Cross-linking parameters of the gel matrix were studied by swelling measurements and trinitrobenzene sulphonic acid (TNBS) assay. In general, the degree of cross-linking was found to increase with increase in the degree of oxidation of alginate, whereas the swelling ratio and the degree of swelling decreased. The gel was found to be biocompatible and biodegradable. The potential of the system as an injectable drug delivery vehicle and as a tissue-engineering scaffold is demonstrated by using primaquine as a model drug and by encapsulation of hepatocytes inside the gel matrix, respectively.

  14. Reactive polymer fused deposition manufacturing

    Energy Technology Data Exchange (ETDEWEB)

    Kunc, Vlastimil; Rios, Orlando; Love, Lonnie J.; Duty, Chad E.; Johs, Alexander

    2017-05-16

    Methods and compositions for additive manufacturing that include reactive or thermosetting polymers, such as urethanes and epoxies. The polymers are melted, partially cross-linked prior to the depositing, deposited to form a component object, solidified, and fully cross-linked. These polymers form networks of chemical bonds that span the deposited layers. Application of a directional electromagnetic field can be applied to aromatic polymers after deposition to align the polymers for improved bonding between the deposited layers.

  15. Thermally cross-linked superparamagnetic iron oxide nanoparticles: synthesis and application as a dual imaging probe for cancer in vivo.

    Science.gov (United States)

    Lee, Haerim; Yu, Mi Kyung; Park, Sangjin; Moon, Sungmin; Min, Jung Jun; Jeong, Yong Yeon; Kang, Hae-Won; Jon, Sangyong

    2007-10-24

    We report the fabrication and characterization of thermally cross-linked superparamagnetic iron oxide nanoparticles (TCL-SPION) and their application to the dual imaging of cancer in vivo. Unlike dextran-coated cross-linked iron oxide nanoparticles, which are prepared by a chemical cross-linking method, TCL-SPION are prepared by a simple, thermal cross-linking method using a Si-OH-containing copolymer. The copolymer, poly(3-(trimethoxysilyl)propyl methacrylate-r-PEG methyl ether methacrylate-r-N-acryloxysuccinimide), was synthesized by radical polymerization and used as a coating material for as-synthesized magnetite (Fe3O4) SPION. The polymer-coated SPION was further heated at 80 degrees C to induce cross-linking between the -Si(OH)3 groups in the polymer chains, which finally generated TCL-SPION bearing a carboxyl group as a surface functional group. The particle size, surface charge, presence of polymer-coating layers, and the extent of thermal cross-linking were characterized and confirmed by various measurements, including dynamic light scattering, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The carboxyl TCL-SPION was converted to amine-modified TCL-SPION and then finally to Cy5.5 dye-conjugated TCL-SPION for use in dual (magnetic resonance/optical) in vivo cancer imaging. When the Cy5.5 TCL-SPION was administered to Lewis lung carcinoma tumor allograft mice by intravenous injection, the tumor was unambiguously detected in T2-weighted magnetic resonance images as a 68% signal drop as well as in optical fluorescence images within 4 h, indicating a high level of accumulation of the nanomagnets within the tumor site. In addition, ex vivo fluorescence images of the harvested tumor and other major organs further confirmed the highest accumulation of the Cy5.5 TCL-SPION within the tumor. It is noteworthy that, despite the fact that TCL-SPION does not bear any targeting ligands on its surface, it was highly effective for tumor

  16. Polymeric redox-responsive delivery systems bearing ammonium salts cross-linked via disulfides

    Directory of Open Access Journals (Sweden)

    Christian Dollendorf

    2013-08-01

    Full Text Available A redox-responsive polycationic system was synthesized via copolymerization of N,N-diethylacrylamide (DEAAm and 2-(dimethylaminoethyl methacrylate (DMAEMA. N,N’-bis(4-chlorobutanoylcystamine was used as disulfide-containing cross-linker to form networks by the quaternization of tertiary amine groups. The insoluble cationic hydrogels become soluble by reduction of disulfide to mercaptanes by use of dithiothreitol (DTT, tris(2-carboxyethylphosphine (TCEP or cysteamine, respectively. The soluble polymeric system can be cross-linked again by using oxygen or hydrogen peroxide under basic conditions. The redox-responsive polymer networks can be used for molecular inclusion and controlled release. As an example, phenolphthalein, methylene blue and reactive orange 16 were included into the network. After treatment with DTT a release of the dye could be recognized. Physical properties of the cross-linked materials, e.g., glass transition temperature (Tg, swelling behavior and cloud points (Tc were investigated. Redox-responsive behavior was further analyzed by rheological measurements.

  17. Multivalent anchoring and cross-linking of mussel-inspired antifouling surface coatings.

    Science.gov (United States)

    Wei, Qiang; Becherer, Tobias; Mutihac, Radu-Cristian; Noeske, Paul-Ludwig Michael; Paulus, Florian; Haag, Rainer; Grunwald, Ingo

    2014-08-11

    In this work, we combine nature's amazing bioadhesive catechol with the excellent bioinert synthetic macromolecule hyperbranched polyglycerol (hPG) to prepare antifouling surfaces. hPG can be functionalized by different amounts of catechol groups for multivalent anchoring and cross-linking because of its highly branched architecture. The catecholic hPGs can be immobilized on various surfaces including metal oxides, noble metals, ceramics, and polymers via simple incubation procedures. The effect of the catechol amount on the immobilization, surface morphology, stability, and antifouling performance of the coatings was studied. Both anchoring and cross-linking interactions provided by catechols can enhance the stability of the coatings. When the catechol groups on the hPG are underrepresented, the tethering of the coating is not effective; while an overrepresentation of catechol groups leads to protein adsorption and cell adhesion. Thus, only a well-balanced amount of catechols as optimized and described in this work can supply the coatings with both good stability and antifouling ability.

  18. Low-Temperature Cross-Linking of PEDOT:PSS Films Using Divinylsulfone.

    Science.gov (United States)

    Mantione, Daniele; Del Agua, Isabel; Schaafsma, Wandert; ElMahmoudy, Mohammed; Uguz, Ilke; Sanchez-Sanchez, Ana; Sardon, Haritz; Castro, Begoña; Malliaras, George G; Mecerreyes, David

    2017-05-31

    Recent interest in bioelectronics has prompted the exploration of properties of conducting polymer films at the interface with biological milieus. Poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate) (PEDOT:PSS) from a commercially available source has been used as a model system for these studies. Different cross-linking schemes have been used to stabilize films of this material against delamination and redispersion, but the cost is a decrease in the electrical conductivity and/or additional heat treatment. Here we introduce divinylsulfone (DVS) as a new cross-linker for PEDOT:PSS. Thanks to the higher reactiveness of the vinyl groups of DVS, the cross-linking can be performed at room temperature. In addition, DVS does not reduce electronic conductivity of PEDOT:PSS but rather increases it by acting as a secondary dopant. Cell culture studies show that PEDOT:PSS:DVS films are cytocompatible and support neuroregeneration. As an example, we showed that this material improved the transconductance value and stability of an organic electrochemical transistor (OECT) device. These results open the way for the utilization of DVS as an effective cross-linker for PEDOT:PSS in bioelectronics applications.

  19. Nanomechanical characterization and molecular mechanism study of nanoparticle reinforced and cross-linked chitosan biopolymer.

    Science.gov (United States)

    Rath, Amrita; Mathesan, Santhosh; Ghosh, Pijush

    2015-03-01

    Chitosan (CS) is a biomaterial that offers many sophisticated and innovative applications in the biomedical field owing to its excellent characteristics of biodegradability, biocompatibility and non-toxicity. However, very low mechanical properties of chitosan polymer impose restriction on its further development. Cross-linking and nanoparticle reinforcement are the two possible methods to improve the mechanical properties of chitosan films. In this research, these two methods are adopted individually by using tripolyphosphate as cross-linker and nano-hydroxyapatite as particle reinforcement. The nanomechanical characterizations under static loading conditions are performed on these modified chitosan films. It is observed that nanoparticle reinforcement provided necessary mechanical properties such as ductility and modulus. The mechanisms involved in improvement of mechanical properties due to particle reinforcement are studied by molecular dynamics (MD). Further, improvement in mechanical properties due to combination of particle reinforcement and cross-linking agent with chitosan is investigated. The stress relaxation behavior for all these types of films is characterized under dynamic loading conditions using dynamic mechanical analysis (nanoDMA) experiment. A viscoelastic solid like response is observed for all types of film with modulus relaxing by 3-6% of its initial value. A suitable generalized Maxwell model is fitted with the obtained viscoelastic response of these films. The response to nano-scratch behavior is also studied for particle reinforced composite films.

  20. Chemical, Physical, and Mechanical Characterization of Isocyanate Cross-linked Amine-Modified Silica Aerogels

    Science.gov (United States)

    Katti, Atul; Shimpi, Nilesh; Roy, Samit; Lu, Hongbing; Fabrizio, Eve F.; Dass, Amala; Capadona, Lynn A.; Leventis, Nicholas

    2006-01-01

    We describe a new mechanically strong lightweight porous composite material obtained by encapsulating the skeletal framework of amine-modified silica aerogels with polyurea. The conformal polymer coating preserves the mesoporous structure of the underlying silica framework and the thermal conductivity remains low at 0.041 plus or minus 0.001 W m(sup -1 K(sup -1). The potential of the new cross-linked silica aerogels for load-carrying applications was determined through characterization of their mechanical behavior under compression, three-point bending, and dynamic mechanical analysis (DMA). A primary glass transition temperature of 130 C was identified through DMA. At room temperature, results indicate a hyperfoam behavior where in compression cross-linked aerogels are linearly elastic under small strains (less than 4%) and then exhibit yield behavior (until 40% strain), followed by densification and inelastic hardening. At room temperature the compressive Young's modulus and the Poisson's ratio were determined to be 129 plus or minus 8 MPa and 0.18, respectively, while the strain at ultimate failure is 77% and the average specific compressive stress at ultimate failure is 3.89 x 10(exp 5) N m kg(sup -1). The specific flexural strength is 2.16 x 10(exp 4) N m kg(sup -1). Effects on the compressive behavior of strain rate and low temperature were also evaluated.

  1. Kinetics of chromium ion absorption by cross-linked polyacrylate films

    Science.gov (United States)

    May, C. E.

    1984-01-01

    Three cross-linked ion exchange membranes were studied as to their ability to absorb chromium ion from aqueous chromium III nitrate solutions. Attention was given to the mechanism of absorption, composition of the absorbed product, and the chemical bonding. The membranes were: calcium polyacrylate, polyacrylic acid, and a copolymer of acrylic acid and vinyl alcohol. For the calcium polyacrylate and the copolymer, parabolic kinetics were observed, indicating the formation of a chromium polyacrylate phase as a coating on the membrane. The rate of absorption is controlled by the diffusion of the chromium ion through this coating. The product formed in the copolymer involves the formation of a coordination complex of a chromium ion with 6 carboxylic acid groups from the same molecule. The absorption of the chromium ion by the polyacrylic acid membranes appears to be more complicated, involving cross-linking. This is due to the coordination of the chromium ion with carboxylic acid groups from more than one polymer molecule. The absorption rate of the chromium ion by the calcium salt membrane was found to be more rapid than that by the free polyacrylic acid membrane.

  2. The Influence of Chitosan Cross-linking on the Properties of Alginate Microparticles with Metformin Hydrochloride—In Vitro and In Vivo Evaluation

    Directory of Open Access Journals (Sweden)

    Marta Szekalska

    2017-01-01

    Full Text Available Sodium alginate is a polymer with unique ability to gel with different cross-linking agents in result of ionic and electrostatic interactions. Chitosan cross-linked alginate provides improvement of swelling and mucoadhesive properties and might be used to design sustained release dosage forms. Therefore, the aim of this research was to develop and evaluate possibility of preparing chitosan cross-linked alginate microparticles containing metformin hydrochloride by the spray-drying method. In addition, influence of cross-linking agent on the properties of microparticles was evaluated. Formulation of microparticles prepared by the spray drying of 2% alginate solution cross-linked by 0.1% chitosan was characterized by good mucoadhesive properties, high drug loading and prolonged metformin hydrochloride release. It was shown that designed microparticles reduced rat glucose blood level, delayed absorption of metformin hydrochloride and provided stable plasma drug concentration. Additionally, histopathological studies of pancreas, liver and kidneys indicated that all prepared microparticles improved degenerative changes in organs of diabetic rats. Moreover, no toxicity effect and no changes in rats behavior after oral administration of chitosan cross-linked alginate microparticles were noted.

  3. The Influence of Chitosan Cross-linking on the Properties of Alginate Microparticles with Metformin Hydrochloride-In Vitro and In Vivo Evaluation.

    Science.gov (United States)

    Szekalska, Marta; Sosnowska, Katarzyna; Zakrzeska, Agnieszka; Kasacka, Irena; Lewandowska, Alicja; Winnicka, Katarzyna

    2017-01-22

    Sodium alginate is a polymer with unique ability to gel with different cross-linking agents in result of ionic and electrostatic interactions. Chitosan cross-linked alginate provides improvement of swelling and mucoadhesive properties and might be used to design sustained release dosage forms. Therefore, the aim of this research was to develop and evaluate possibility of preparing chitosan cross-linked alginate microparticles containing metformin hydrochloride by the spray-drying method. In addition, influence of cross-linking agent on the properties of microparticles was evaluated. Formulation of microparticles prepared by the spray drying of 2% alginate solution cross-linked by 0.1% chitosan was characterized by good mucoadhesive properties, high drug loading and prolonged metformin hydrochloride release. It was shown that designed microparticles reduced rat glucose blood level, delayed absorption of metformin hydrochloride and provided stable plasma drug concentration. Additionally, histopathological studies of pancreas, liver and kidneys indicated that all prepared microparticles improved degenerative changes in organs of diabetic rats. Moreover, no toxicity effect and no changes in rats behavior after oral administration of chitosan cross-linked alginate microparticles were noted.

  4. Comparative laboratory studies of well treatment techniques based on in situ cross linking and polymerization

    Energy Technology Data Exchange (ETDEWEB)

    Lakatos, I.; Kiss, G.M.; Lakatos, S.J.

    1982-01-01

    In order to improve the water oil ratio in operating oil wells in 1972-1978, a number of methods were developed and tested based on treating the well with polymers. Under laboratory conditions methods were studied that were based on processes occurring in situ of cross linking of polymers by multivalent cations and polymerization of monomer solutions. The polymers used were different types of polyacrylamide, and the monomers were acrylamide and N, N-methylenebis-acrylamide. The effect of the forming gel on permeability was studied on the linear section of the nonconsolidated porous material, and on the change in water-oil ratio in radial geometry on a sandstone core sample. Comparative analysis of the methods indicated that the upper limit of the temperature stability of the gel bonded by multivalent cations does not exceed 80-100/sup 0/C. The effectiveness of the method can be considerably improved by adding aliphatic alcohols or by using polymer-silicate systems. The main advantage of the method of polymerization in situ as compared to the indicated method is higher temperature of gel stability (up to 100/sup 0/C and higher). In this case gel formation does not depend on the process of dispersion, occurs in the complete volume of the injected fluid, and the gel parameters can be regulated in broad limits. Of use of the methods of in situ polymerization should be preceded by an economic evaluation of work under specific conditions.

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

    Science.gov (United States)

    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.

  6. DNA interstrand cross-linking by a mycotoxic diepoxide.

    Science.gov (United States)

    Millard, J T; Katz, J L; Goda, J; Frederick, E D; Pierce, S E; Speed, T J; Thamattoor, D M

    2004-06-01

    The diepoxide mycotoxin (2R, 3R, 8R, 9R)-4,6-decadiyne-2,3:8,9-diepoxy-1,10-diol (repandiol) was both isolated from the mushroom Hydnum repandum and synthesized de novo. Repandiol was found to form interstrand cross-links within a restriction fragment of DNA, linking deoxyguanosines on opposite strands primarily within the 5'-GNC and 5'-GNNC sequences preferred by diepoxyoctane. However, repandiol was a significantly less efficient cross-linker than either of the diepoxyalkanes (diepoxyoctane and diepoxybutane) to which it was compared.

  7. Newer protocols and future in collagen cross-linking

    Directory of Open Access Journals (Sweden)

    Arthur B Cummings

    2013-01-01

    Full Text Available 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

  8. Probing native protein structures by chemical cross-linking, mass spectrometry, and bioinformatics.

    Science.gov (United States)

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

    2010-08-01

    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.

  9. SYNTHESIS AND APPLICATIONS OF CROSS-LINKED POLY(DIALLYLDIMETHYL AMMONIUM CHLORIDE) AND ITS DERIVATIVE COPOLYMERS AS EFFICIENT PHASE TRANSFER CATALYST FOR NUCLEOPHILIC SUBSTITUTION REACTIONS

    Institute of Scientific and Technical Information of China (English)

    Hossein Mahdavi; Mahdi Mahmoudian

    2011-01-01

    Cross-linked poly(diallyldimethylammonium chloride) and its derivative eopolymers were synthesized and used as phase transfer catalyst in the nucleophilic substitution reaction especially halogen exchange reactions. In addition, the effect of hydrophilic-hydrophobic character of the polymers in the nucleophilic reactions was investigated.

  10. Cross-linked comb-shaped anion exchange membranes with high base stability

    Energy Technology Data Exchange (ETDEWEB)

    Li, NW; Wang, LZ; Hickner, M

    2014-01-01

    A unique one-step cross-linking strategy that connects quaternary ammonium centers using Grubbs II-catalyzed olefin metathesis was developed. The cross-linked anion exchange membranes showed swelling ratios of less than 10% and hydroxide conductivities of 18 to 40 mS cm(- 1). Cross-linking improved the membranes' stability to hydroxide degradation compared to their non-cross-linked analogues.

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

    Science.gov (United States)

    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.

  12. In situ thermally cross-linked polyacrylonitrile as binder for high-performance silicon as lithium ion battery anode.

    Science.gov (United States)

    Shen, Lanyao; Shen, Lian; Wang, Zhaoxiang; Chen, Liquan

    2014-07-01

    Electrode integrity and electric contact between particles and between particle and current collector are critical for electrochemical performance, especially for that of electrode materials with large volume change during cycling and with poor electric conductivity. We report on the in situ thermally cross-linked polyacrylonitrile (PAN) as a binder for silicon-based anodes of lithium-ion batteries. The electrode delivers excellent cycle life and rate capability with a reversible capacity of about 1450 mA h g(-1) even after 100 cycles. The improved electrochemical performance of such silicon electrodes is attributed to heat-treatment-induced cross-linking and the formation of conjugated PAN. These findings open new avenues to explore other polymers for both anode and cathode electrodes of rechargeable batteries.

  13. Cross-linking e segmento de anel corneano intraestromal

    Directory of Open Access Journals (Sweden)

    Adimara da Candelaria Renesto

    2011-02-01

    Full Text Available O cross-linking corneano é um procedimento usado para a estabilização mecânica e aumento da rigidez corneana em pacientes com ceratocone (reduzindo a possibilidade de progressão, e também em processos inflamatórios de afinamento corneano. Os segmentos de anéis corneanos intraestromais têm como princípio o aplanamento central da córnea. Inicialmente utilizados para correção de baixa miopia, a principal indicação atual é em pacientes com ceratocone, para melhorar a acuidade visual não corrigida, a acuidade visual corrigida e permitir uma melhor tolerância ao uso de lentes de contato como também retardar a necessidade de um transplante de córnea. O objetivo deste artigo é revisar algumas publicações relacionadas ao cross-linking corneano e à inserção do segmento de anel intraestromal, apresentando suas indicações, resultados e complicações relatadas até o momento.

  14. Phosphate uptake studies of cross-linked chitosan bead materials.

    Science.gov (United States)

    Mahaninia, Mohammad H; Wilson, Lee D

    2017-01-01

    A systematic experimental study is reported that provides a molecular based understanding of cross-linked chitosan beads and their adsorption properties in aqueous solution containing phosphate dianion (HPO4(2-)) species. Synthetically modified chitosan using epichlorohydrin and glutaraldehyde cross-linkers result in surface modified beads with variable hydrophile-lipophile character and tunable HPO4(2-) uptake properties. The kinetic and thermodynamic adsorption properties of cross-linked chitosan beads with HPO4(2-) species were studied in aqueous solution. Complementary structure and physicochemical characterization of chitosan beads via potentiometry, Raman spectroscopy, DSC, and dye adsorption measurements was carried out to establish structure-property relationships. The maximum uptake (Qm) of bead systems with HPO4(2-) at equilibrium was 52.1mgg(-1); whereas, kinetic uptake results for chitosan bead/phosphate systems are relatively rapid (0.111-0.113min(-1)) with an intraparticle diffusion rate-limiting step. The adsorption process follows a multi-step pathway involving inner- and outer-sphere complexes with significant changes in hydration. Phosphate uptake strongly depends on the composition and type of cross-linker used for preparation of chitosan beads. The adsorption isotherms and structural characterization of bead systems illustrate the role of surface charge, hydrophile-lipophile balance, adsorption site accessibility, and hydration properties of the chitosan bead surface. Copyright © 2016 Elsevier Inc. All rights reserved.

  15. Adsorption of methyl orange onto protonated cross-linked chitosan

    Directory of Open Access Journals (Sweden)

    Ruihua Huang

    2017-01-01

    Full Text Available The adsorption of methyl orange (MO from aqueous solutions on protonated cross-linked chitosan was studied in a batch system. The results showed that the adsorption of MO onto protonated cross-linked chitosan was affected significantly by initial MO concentration, adsorbent dosage, adsorption temperature, and contact time. The pH value of solution had a minor impact on the adsorption of MO in a pH range of 1.0–9.1. The equilibrium isotherms at different temperatures (293, 303, and 313 K and pH values (4.5, 6.7, and 9.1 were investigated. Langmuir model was able to describe these Equilibrium data fitted perfectly. The maximum monolayer adsorption capacities obtained from the Langmuir model were 89.29, 130.9, and 180.2 mg/g at 293, 303, and 313 K, respectively. Adsorption kinetics at different concentrations (100, 200 and 300 mg/L and pH values (4.5, 6.7 and 9.1 were also studied. The kinetics was correlated well with the pseudo second-order model.

  16. Microbial Keratitis After Collagen Cross-linking Treatment

    Directory of Open Access Journals (Sweden)

    Banu Torun Acar

    2012-07-01

    Full Text Available A 33-year-old woman presented with pain, redness, and diminution of vision that occurred 2 days after collagen cross-linking had been performed for keratoconus in the right eye. Culture results from the patient's contact lens and corneal scrapings were positive for Staphylococcus epidermidis. According to the results of antibiotic susceptibility testing, the patient was treated with hourly topical fortified vancomycin and exocin. Before collagen cross-linking, the best-corrected visual acuity (BCVA was 4/10, the manifest refraction was -7.00 -1.755 3°. Four months after the procedure, the BCVA was 4/10, the manifest refraction was -5.50 -1.75 10°. Slit-lamp examination revealed a mild residual haze in the upper midperipheral cornea, and stromal opacities had disappeared. Collagen crosslinking is less invasive compared to other methods for treatment of keratoconus, but epithelial debridement and bandage contact lens wearing may lead to the development of bacterial keratitis. (Turk J Oph thal mol 2012; 42: 300-2

  17. Covalently Cross-Linked Arabinoxylans Films for Debaryomyces hansenii Entrapment

    Directory of Open Access Journals (Sweden)

    Ramsés González-Estrada

    2015-06-01

    Full Text Available In the present study, wheat water extractable arabinoxylans (WEAX were isolated and characterized, and their capability to form covalently cross-linked films in presence of Debaryomyces hansenii was evaluated. WEAX presented an arabinose to xylose ratio of 0.60, a ferulic acid and diferulic acid content of 2.1 and 0.04 µg∙mg−1 WEAX, respectively and a Fourier Transform Infra-Red (FT-IR spectrum typical of WEAX. The intrinsic viscosity and viscosimetric molecular weight values for WEAX were 3.6 dL∙g−1 and 440 kDa, respectively. The gelation of WEAX (1% w/v with and without D. hansenii (1 × 107 CFU∙cm−2 was rheologically investigated by small amplitude oscillatory shear. The entrapment of D. hansenii decreased gel elasticity from 1.4 to 0.3 Pa, probably by affecting the physical interactions between WEAX chains. Covalently cross-linked WEAX films containing D. hansenii were prepared by casting. Scanning electron microscopy images show that WEAX films containing D. hansenii were porous and consisted of granular-like and fibre microstructures. Average tensile strength, elongation at break and Young’s modulus values dropped when D. hansenii was present in the film. Covalently cross-lined WEAX containing D. hansenii could be a suitable as a functional entrapping film.

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

    Science.gov (United States)

    Schiffman, Jessica D; Schauer, Caroline L

    2007-09-01

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

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

    Directory of Open Access Journals (Sweden)

    Pantelis Georgiades

    Full Text Available 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.

  20. Small Strain Topological Effects of Biopolymer Networks with Rigid Cross-Links

    NARCIS (Netherlands)

    Zagar, G.; Onck, P. R.; Van der Giessen, E.; Garikipati, K; Arruda, EM

    2010-01-01

    Networks of cross-linked filamentous biopolymers form topological structures characterized by L, T and X cross-link types of connectivity 2, 3 and 4, respectively. The distribution of cross-links over these three types proofs to be very important for the initial elastic shear stiffness of isotropic

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

    NARCIS (Netherlands)

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

    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

  2. Absorbed Pb2+ and Cd2+ Ions in Water by Cross-Linked Starch Xanthate

    Directory of Open Access Journals (Sweden)

    Kai Feng

    2017-01-01

    Full Text Available A cross-linked starch xanthate was prepared by graft copolymerization of acrylamide and sodium acrylate onto starch xanthate using potassium persulfate and sodium hydrogen sulfite initiating system and N,N′-methylenebisacrylamide as a cross-linker. As this kind of cross-linked potato starch xanthate can effectively absorb heavy metal ions, it was dispersed in aqueous solutions of divalent heavy metal ions (Pb2+ and Cd2+ to investigate their absorbency by the polymer. Factors that can influence absorbency were investigated, such as the ratio of matrix to monomers, the amount of initiator and cross-linker, pH, and the concentration of metal ions. Results were reached and conclusion was drawn that the best synthetic conditions for the polymer adsorbing Pb2+ and Cd2+ were as follows: the quality ratio of matrix to monomers was 1 : 12 and 1 : 11, the amount of initiator was 2.4% and 3.2% of matrix, and the amount of cross-linker was 12 mg and 13 mg. When the initial concentration of ions was 10 mg/L, the highest quantities of adsorption of Pb2+ and Cd2+ were 47.11 mg/g and 36.55 mg/g. Adsorption mechanism was discussed by using Fourier transform infrared (FTIR spectroscopy, X-ray diffraction (XRD, scanning electron microscope (SEM, Energy Dispersive X-Ray Spectroscopy (EDS test, and adsorption kinetic simulation.

  3. Use of cross-linked carboxymethyl cellulose for soft-tissue augmentation: preliminary clinical studies

    Directory of Open Access Journals (Sweden)

    Mauro Leonardis

    2010-11-01

    Full Text Available Mauro Leonardis1, Andrea Palange2, Rodrigo FV Dornelles3, Felipe Hund41Department of Plastic Surgery, Salvator Mundi International Hospital, Roma, Italy; 2Department of Aesthetic Medicine, Fisiobios, Roma, Italy; 3Department of Plastic Surgery, Núcleo de Plástica Avançada, São Paulo, SP, Brazil; 4Department of Plastic Surgery, Consultorio de Cirurgia Plastica, Criciuma, SC, BrazilPurpose: The continual search for new products for soft-tissue augmentation has in recent years led to the introduction of long lasting alternatives to hyaluronic acids and collagen that are composed of other polymers able to improve clinical persistence over time. This is the first report in which sodium carboxymethyl cellulose (CMC has been chemically treated by the cross-linking process and thus used as a hydrogel for soft-tissue augmentation through injection with thin needles. The study evaluates, from a clinical point of view, the behavior of cross-linked carboxymethyl cellulose hydrogel used in the aesthetic field and its side effects so as to check the safety and performance of the polymer following intradermal injections.Patients and methods: This work shows the preliminary results of an ongoing clinical study conducted between 2006 and 2009, performed on 84 healthy volunteers (62 females, 22 males aged between 18 and 72 years, for the treatment of 168 nasolabial folds, 45 perioral wrinkles, and 39 lip volume.Results: Study results show an excellent correction of facial defects. Tolerance and aesthetic quality of the correction obtained indicate considerable safety features and absence of side effects. From a clinical point of view, hydrogel is gradually absorbed into the injection site without migration issues.Conclusion: Cross-linked CMC hydrogel proves to be an ideal agent for soft tissue augmentation with regard to safety and ease of application. It did not cause infection, extrusion, migration, or adverse reactions in the patients who have been

  4. Optimization of protein cross-linking in bicomponent electrospun scaffolds for therapeutic use

    Energy Technology Data Exchange (ETDEWEB)

    Papa, Antonio [Institute for Polymers, Composites and Biomaterials, National Research Council of Italy (IPCB-CNR), V.le Kennedy 54, Naples 80125 (Italy); IMAST SCaRL, Piazza Bovio 22, 80133 Naples (Italy); Guarino, Vincenzo, E-mail: vincenzo.guarino@cnr.it; Cirillo, Valentina; Oliviero, Olimpia; Ambrosio, Luigi [Institute for Polymers, Composites and Biomaterials, National Research Council of Italy (IPCB-CNR), V.le Kennedy 54, Naples 80125 (Italy)

    2015-12-17

    Bio-instructive electrospun scaffolds based on the combination of synthetic polymers, such as PCL or PLLA, and natural polymers (e.g., collagen) have been extensively investigated as temporary extracellular matrix (ECM) analogues able to support cell proliferation and stem cell differentiation for the regeneration of several tissues. The growing use of natural polymers as carrier of bioactive molecules is introducing new ideas for the design of polymeric drug delivery systems based on electrospun fibers with improved bioavailability, therapeutic efficacy and programmed drug release. In particular, the release mechanism is driven by the use of water soluble proteins (i.e., collagen, gelatin) which fully degrade in in vitro microenvironment, thus delivering the active principles. However, these protein are generally rapidly digested by enzymes (i.e., collagenase) produced by many different cell types, both in vivo and in vitro with significant drawbacks in tissue engineering and controlled drug delivery. Here, we aim at investigating different chemical strategies to improve the in vitro stability and mechanical strength of scaffolds against enzymatic degradation, by modifying the biodegradation rates of proteins embedded in bicomponent fibers. By comparing scaffolds treated by different cross-linking agents (i.e., GC, EDC, BDDGE), we have provided an extensive morphological/chemical/physical characterization via SEM and TGA to identify the best conditions to control drug release via protein degradation from bicomponent fibers without compromising in vitro cell response.

  5. Optimization of protein cross-linking in bicomponent electrospun scaffolds for therapeutic use

    Science.gov (United States)

    Papa, Antonio; Guarino, Vincenzo; Cirillo, Valentina; Oliviero, Olimpia; Ambrosio, Luigi

    2015-12-01

    Bio-instructive electrospun scaffolds based on the combination of synthetic polymers, such as PCL or PLLA, and natural polymers (e.g., collagen) have been extensively investigated as temporary extracellular matrix (ECM) analogues able to support cell proliferation and stem cell differentiation for the regeneration of several tissues. The growing use of natural polymers as carrier of bioactive molecules is introducing new ideas for the design of polymeric drug delivery systems based on electrospun fibers with improved bioavailability, therapeutic efficacy and programmed drug release. In particular, the release mechanism is driven by the use of water soluble proteins (i.e., collagen, gelatin) which fully degrade in in vitro microenvironment, thus delivering the active principles. However, these protein are generally rapidly digested by enzymes (i.e., collagenase) produced by many different cell types, both in vivo and in vitro with significant drawbacks in tissue engineering and controlled drug delivery. Here, we aim at investigating different chemical strategies to improve the in vitro stability and mechanical strength of scaffolds against enzymatic degradation, by modifying the biodegradation rates of proteins embedded in bicomponent fibers. By comparing scaffolds treated by different cross-linking agents (i.e., GC, EDC, BDDGE), we have provided an extensive morphological/chemical/physical characterization via SEM and TGA to identify the best conditions to control drug release via protein degradation from bicomponent fibers without compromising in vitro cell response.

  6. Cross-linked hyaluronic acid in pressure ulcer prevention.

    Science.gov (United States)

    Beniamino, P; Vadalà, M; Laurino, C

    2016-07-02

    Long-term bedridden patients are at high risk of acquring pressure ulcers (PUs). In this group of patients, prevention is necessary to cut the health costs, improve quality of life and reduce the mortality. Here, we evaluated the effectiveness of a cross-linked hyaluronic acid (HA) as plastic bulking-agent filling and remodelling the deep dermis and subcutaneous space of the skin areas exposed to the risk of necrosis. Our work hypothesis has been to inflate a sub-dermal elastic cushion, filled with a natural ECM component, with the aim to induce a stronger tissue background resistant to the ulcerative process. All the patients had an increased risk of PUs, at the sacral, ileum or heel skin. Patients were being nursed accordingly to the standard orthopaedic ward management with a pressure relieveing air mattress. The standard protocol consisted in body mobilisation every 3 hours, 24 hours a day and accurate cleaning of the skin with liquid soap and water without any towel friction and without adding any cream or lotion for the skin protection. Our filling protocol enclosed: accurate disinfection of the skin to be injected with povidone-iodine solution, followed by a local anaesthesia with 28G 13 mm needle, injecting 1.5 ml of 1% xylocaine. Then slow, deep, subcutaneous injection of cross-linked HA was performed with a 18G long needle, in order to deliver a homogeneous, soft gel layer underneath and around the whitish erythematous skin edges at risk of ulceration. Patients' tolerability of the compound and adverse events were also recorded. There were 15 patients (78-94 years old) who participated in the study. All tolerated the procedure very well and no serious side effects were declared. No skin pressure ulceration was detected in the four weeks follow-up Conclusion: We have demonstrated the safety and tolerability of a cross-linked HA subdermal injection in PUs prevention. The compound stratifies in a soft, elastic, interstitial bulk into the deep dermis, thus

  7. Biocatalytic cross-linking of pectic polysaccharides for designed food functionality

    DEFF Research Database (Denmark)

    Zaidel, Dayang Norulfairuz Abang; Meyer, Anne S.

    2012-01-01

    Recent research has demonstrated how cross-linking of pectic polysaccharides to obtain gel formation can be promoted by enzymatic catalysis reactions, and provide opportunities for functional upgrading of pectic polysaccharides present in agro-industrial sidestreams. This review highlights...... the mechanisms of formation of functional pectic polysaccharide cross-links, including covalent cross-links (notably phenolic esters and uronyl ester linkages) and non-covalent, ionic cross-links (which involve calcium and borate ester links). The treatise examines how such cross-links can be designed via...

  8. Stiffening of semiflexible biopolymers and cross-linked networks

    CERN Document Server

    Van Dillen, T; Van der Giessen, E

    2006-01-01

    We study the mechanical stiffening behavior in two-dimensional (2D) cross-linked networks of semiflexible biopolymer filaments under simple shear. Filamental constituents immersed in a fluid undergo thermally excited bending motions. Pulling out these undulations results in an increase in the axial stiffness. We analyze this stiffening behavior of 2D semiflexible filaments in detail: we first investigate the average, {static} force-extension relation by considering the initially present undulated configuration that is pulled straight under a tensile force, and compare this result with the average response in which undulation dynamics is allowed during pulling, as derived earlier by MacKintosh and coworkers. We will show that the resulting mechanical behavior is rather similar, but with the axial stiffness being a factor 2 to 4 larger in the dynamic model. Furthermore, we study the stretching contribution in case of extensible filaments and show that, for 2D filaments, the mechanical response is dominated by {...

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

    Science.gov (United States)

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

    2015-09-01

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

  10. Studies on N-vinylformamide cross-linked copolymers

    Science.gov (United States)

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

    2015-12-01

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

  11. Peptidoglycan Cross-Linking in Glycopeptide-Resistant Actinomycetales

    Science.gov (United States)

    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

  12. The wear of cross-linked polyethylene against itself.

    Science.gov (United States)

    Joyce, T J; Ash, H E; Unsworth, A

    1996-01-01

    Cross-linked polyethylene (XLPE) may have an application as a material for an all-plastic surface replacement finger joint. It is inexpensive, biocompatible and can be injection-moulded into the complex shapes that are found on the ends of the finger bones. Further, the cross-linking of polyethylene has significantly improved its mechanical properties. Therefore, the opportunity exists for an all-XLPE joint, and so the wear characteristics of XLPE sliding against itself have been investigated. Wear tests were carried out on both reciprocating pin-on-plate machines and a finger function simulator. The reciprocating pin-on-plate machines had pins loaded at 10 N and 40 N. All pin-on-plate tests show wear factors from the plates very much greater than those of the pins. After 349 km of sliding, a mean wear factor of 0.46 x 10(-6) mm3/N m was found for the plates compared with 0.021 x 10(-6) mm3/N m for the pins. A fatigue mechanism may be causing this phenomenon of greater plate wear. Tests using the finger function simulator give an average wear rate of 0.22 x 10(-6) mm3/N m after 368 km. This sliding distance is equivalent to 12.5 years of use in vivo. The wear factors found were comparable with those of ultra-high molecular weight polyethylene (UHMWPE) against a metallic counterface and, therefore, as the loads across the finger joint are much less than those across the knee or the hip, it is probable that an all-XLPE finger joint will be viable from a wear point of view.

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

    Science.gov (United States)

    Venerus, David C.; Kolev, Dimitre

    2008-07-01

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

  14. Yield and Failure Behavior Investigated for Cross-Linked Phenolic Resins Using Molecular Dynamics

    Science.gov (United States)

    Monk, Joshua D.; Lawson, John W.

    2016-01-01

    Molecular dynamics simulations were conducted to fundamentally evaluate the yield and failure behavior of cross-linked phenolic resins at temperatures below the glass transition. Yield stress was investigated at various temperatures, strain rates, and degrees of cross-linking. The onset of non-linear behavior in the cross-linked phenolic structures was caused by localized irreversible molecular rearrangements through the rotation of methylene linkers followed by the formation or annihilation of neighboring hydrogen bonds. The yield stress results, with respect to temperature and strain rate, could be fit by existing models used to describe yield behavior of amorphous glasses. The degree of cross-linking only indirectly influences the maximum yield stress through its influence on glass transition temperature (Tg), however there is a strong relationship between the degree of cross-linking and the failure mechanism. Low cross-linked samples were able to separate through void formation, whereas the highly cross-linked structures exhibited bond scission.

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

    DEFF Research Database (Denmark)

    Steen, H; Petersen, J; Mann, M

    2001-01-01

    Protein-nucleic acid complexes are commonly studied by photochemical cross-linking. UV-induced cross-linking of protein to nucleic acid may be followed by structural analysis of the conjugated protein to localize the cross-linked amino acids and thereby identify the nucleic acid binding site. Mass....... coli single-stranded DNA binding protein (SSB) that was UV-cross-linked to a 5-iodouracil containing DNA oligomer. Two methods were optimized to circumvent the need for standard liquid chromatography and gel electrophoresis, thereby dramatically increasing the overall sensitivity of the analysis....... Enzymatic degradation of protein and oligonucleotide was combined with miniaturized sample preparation methods for enrichment and desalting of cross-linked peptide-nucleic acid heteroconjugates from complex mixtures prior to mass spectrometric analysis. Detailed characterization of the peptidic component...

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

    Energy Technology Data Exchange (ETDEWEB)

    Lai, Jui-Yang, E-mail: jylai@mail.cgu.edu.tw

    2014-12-01

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

  17. Guest-responsive covalent frameworks by the cross-linking of liquid-crystalline salts: tuning of lattice flexibility by the design of polymerizable units.

    Science.gov (United States)

    Ishida, Yasuhiro; Sakata, Hiroaki; Achalkumar, Ammathnadu S; Yamada, Kuniyo; Matsuoka, Yuki; Iwahashi, Nobutaka; Amano, Sayaka; Saigo, Kazuhiko

    2011-12-23

    Cross-linked polymers prepared by the in-situ polymerization of liquid-crystalline salts were found to work as solid-state hosts with a flexible framework. As a component of such hosts, four kinds of polymerizable amphiphilic carboxylic acids bearing alkyl chains with acryloyloxy (A), dienyl (D), and/or nonreactive (N) chain ends (monomeric carboxylic acids; M(AAA), M(ANA), M(DDD), and M(DND)) were used. The carboxylic acids were mixed with an equimolar amount of a template unit, (1R,2S)-norephedrine (guest amine; G(RS)), to form the corresponding salts. Every salt exhibited a rectangular columnar LC phase at room temperature, which was successfully polymerized by (60)Co γ-ray-induced polymerization without serious structural disordering to afford the salt of cross-linked carboxylic acid (polymeric carboxylic acid; P(AAA), P(ANA), P(DDD), and P(DND)) with G(RS) . Owing to the noncovalency of the interactions between the polymer framework P and the template G(RS), the cross-linked polymers could reversibly release and capture a meaningful amount of G(RS). In response to the desorption and adsorption of G(RS), the cross-linked polymers dramatically switched their nanoscale structural order. A systematic comparison of the polymers revealed that the choice of polymerizable groups has a significant influence on the properties of the resultant polymer frameworks as solid-state hosts. Among these polymers, P(DDD) was found to be an excellent solid-state host, in terms of guest-releasing/capturing ability, guest-recognition ability, durability to repetitive usage, and unique structural switching mode.

  18. Physical Characterization Of High Amylose/Pectin Mixtures Cross-Linked With Sodium Trimetaphosphate; Caracterizacao fisica de misturas alta amilose/pectina reticuladas com trimetafosfato de sodio

    Energy Technology Data Exchange (ETDEWEB)

    Carbinatto, F.M.; Cury, B.S.F.; Evangelista, R.C., E-mail: curybsf@fcfar.unesp.b [UNESP, Araraquara, SP (Brazil). Fac. de Ciencias Farmaceuticas

    2010-07-01

    Some researches have reported that pectin and high amylose mixtures presented superior mechanical properties in relation to those of the isolated polymers. In this work, mixtures at different ratios (1:4; 1:1) of pectin and high amylose were crosslinked with sodium trimetaphosphate at different degrees by varying reaction conditions. All samples were characterized by rheological and X-ray diffraction analyses. Samples without cross-linker were prepared as control. The oscillatory dynamic tests showed that all samples exhibited predominant elastic behavior, although cross-linked samples presented higher G' values, suggesting that crosslinking by phosphorylation resulted in more strength structures. The diffractograms showed that cross-linked samples underwent structural modifications that resulted in increase of crystallinity due to cross-linking process. (author)

  19. Preparation and Characterization of Non-porous Superparamagnetic Microspheres with Epoxy Groups by Dispersion Polymerization

    Institute of Scientific and Technical Information of China (English)

    马志亚; 官月平; 刘先桥; 刘会洲

    2005-01-01

    Non-porous superparamagnetic polymer microspheres with epoxy groups were prepared by dispersion polymerization of glycidyl methacrylate (GMA) in the presence of magnetic iron oxide (Fe3O4) nanoparticles coated with oleic acid. The polymerization was carried out in the ethanol/water medium using polyvinylpyrrolidone (PVP) and 2,2’-azobisisobutyronitrile (AIBN) as stabilizer and initiator, respectively. The magnetic microspheres obtained were characterized with scanning electron microscopy (SEM), vibrating sample magnetometry (VSM) and Fourier transform infrared spectroscopy (FTIR). The results showed that the magnetic microspheres had an average size of-1μm with superparamagnetic characteristics. The saturation magnetization was found to be 4.5emu.g-1. There was abundance of epoxy groups with density of 0.028 mmol·g-1 in microspheres. The magnetic PGMA microspheres have extensive potential uses in magnetic bioseparation and biotechnology.

  20. Imade-imide cross-linked PEEK proton exchange membrane.

    CSIR Research Space (South Africa)

    Luo, H

    2009-08-01

    Full Text Available The proton exchange membrane is a key component of polymer electrolyte membrane fuel cell (PEMFC). It plays an important role, conducts protons and separates the fuel from oxidant in PEMFC. DuPont’s Nafion is a perfluorinated sulfonic acid polymer...

  1. In-line formation of chemically cross-linked P84® co-polyimide hollow fibre membranes for H2/CO2 separation

    KAUST Repository

    Choi, Seung Hak

    2010-12-13

    In this study, chemically cross-linked asymmetric P84® co-polyimide hollow fibre membranes with enhanced separation performance were fabricated, using a dry-wet spinning process with an innovative in-line cross-linking step. The chemical modification was conducted by controlled immersion of the coagulated fibre in an aqueous 1,5-diamino-2-methylpentane (DAMP) cross-linker solution before the take-up. The effect of the cross-linker concentration on the thermal, mechanical, chemical and gas transport properties of the membranes was investigated. FT-IR/ATR analysis was used to identify the chemical changes in the polymer, while DSC analysis confirmed the changes in the Tg and the specific heat of the polymer upon cross-linking. Chemical cross-linking with a 10 wt.% aqueous DAMP solution strongly enhanced the H2/CO2 ideal selectivity from 5.3 to 16.1, while the H2 permeance of the membranes decreased from 7.06 × 10−3 to 1.01 × 10−3 m3(STP) m−2 h−1 bar−1 for a feed pressure of 1 bar at 25 °C. The increase of selectivity with decreasing permeance is somewhat higher than the slope in the Robeson upper bound, evidencing the positive effect of the cross-linking on the separation performance of the fibres. Simultaneously, the cross-linking leads to improved mechanical resistance of the membranes, which could be further enhanced by an additional thermal treatment. The produced membranes are therefore more suitable for use under harsh conditions and have a better overall performance than the uncross-linked ones.

  2. Wear resistance of artificial hip joints with poly(2-methacryloyloxyethyl phosphorylcholine) grafted polyethylene: comparisons with the effect of polyethylene cross-linking and ceramic femoral heads.

    Science.gov (United States)

    Moro, Toru; Kawaguchi, Hiroshi; Ishihara, Kazuhiko; Kyomoto, Masayuki; Karita, Tatsuro; Ito, Hideya; Nakamura, Kozo; Takatori, Yoshio

    2009-06-01

    Aseptic loosening of artificial hip joints induced by wear particles from the polyethylene (PE) liner remains the ruinous problem limiting their longevity. We reported here that grafting with a polymer, poly(2-methacryloyloxyethyl phosphorylcholine (MPC)) (PMPC), on the PE liner surface dramatically decreased the wear production under a hip joint simulator condition. We examined that the effect of properties of both PE by cross-linking and femoral head by changing the materials on wearing properties of PE. The PMPC grafting on the liners increased hydrophilicity and decreased friction torque, regardless of the cross-linking of the PE liner or the difference in the femoral head materials. During the hip joint simulator experiments (5 x 10(6) cycles of loading), cross-linking caused a decrease of wear amount and a reduction of the particle size, while the femoral head materials did not affect it. The PMPC grafting abrogated the wear production, confirmed by almost no wear of the liner surface, independently of the liner cross-linking or the femoral head material. We concluded that the PMPC grafting on the PE liner surpasses the liner cross-linking or the change of femoral head materials for extending longevity of artificial hip joints.

  3. Preparation and Characterization of Ionotropic Cross-Linked Chitosan Microparticles for Controlled Release of Aceclofenac

    Directory of Open Access Journals (Sweden)

    N. G. Raghavendra Rao

    2010-04-01

    Full Text Available Aceclofenac, (2-[2-[2-(2, 6-dichlorophenyl aminophenyl] acety] oxyacetic acid a non-steroidal anti-inflammatory drug (NSAID, has been indicated for various conditions like post-traumatic pain, rheumatoid arthritis, ankylosing spondylitis. Multiple-unit systems have been reported to avoid the variations in gastric emptying and different transit rates through gastro-intestinal and spread over a large area preventing exposure of the absorbing site to high drug concentration on chronic dosing. The purpose of this study was therefore to develop aceclofenac loaded chitosan microparticles by ionotropic gelation method. Drug loading efficiency (DLE of microparticles was found between 62.20 to 92.93 % and depended on the formulation variables. Increase in the Tripolyphosphate (TPP concentration, pH of the TPP solution and cross-linking time decreased the drug release. The particle size decreased with increase in cross-linking time and found between the ranges of 1194.1 to 1568.9 µm. Drug release showed slight burst effect in phosphate buffer pH 7.4 in first hour followed by prolonged release for 8 hrs. FTIR and DSC revealed that there was no interaction between drug and polymer. The release data was fitted into first order, zero order and Higuchi model to find release kinetics. The values of regression coefficient r2 were found to be greater (£ 0.9541 for first order than for zero order (£ 0.8740 and the r2 value for Higuchi was £ 0.9805 suggesting diffusion controlled process. The result concluded that TPP-chitosan microparticles developed by ionotropic gelation method might become potential delivery system to prolonging the release of aceclofenac.

  4. Filler reinforcement in cross-linked elastomer nanocomposites: insights from fully atomistic molecular dynamics simulation.

    Science.gov (United States)

    Pavlov, Alexander S; Khalatur, Pavel G

    2016-06-28

    Using a fully atomistic model, we perform large-scale molecular dynamics simulations of sulfur-cured polybutadiene (PB) and nanosilica-filled PB composites. A well-integrated network without sol fraction is built dynamically by cross-linking the coarse-grained precursor chains in the presence of embedded silica nanoparticles. Initial configurations for subsequent atomistic simulations are obtained by reverse mapping of the well-equilibrated coarse-grained systems. Based on the concept of "maximally inflated knot" introduced by Grosberg et al., we show that the networks simulated in this study behave as mechanically isotropic systems. Analysis of the network topology in terms of graph theory reveals that mechanically inactive tree-like structures are the dominant structural components of the weakly cross-linked elastomer, while cycles are mainly responsible for the transmission of mechanical forces through the network. We demonstrate that quantities such as the system density, thermal expansion coefficient, glass transition temperature and initial Young's modulus can be predicted in qualitative and sometimes even in quantitative agreement with experiments. The nano-filled system demonstrates a notable increase in the glass transition temperature and an approximately two-fold increase in the nearly equilibrium value of elastic modulus relative to the unfilled elastomer even at relatively small amounts of filler particles. We also examine the structural rearrangement of the nanocomposite subjected to tensile deformation. Under high strain-rate loading, the formation of structural defects (microcavities) within the polymer bulk is observed. The nucleation and growth of cavities in the post-yielding strain hardening regime mainly take place at the elastomer/nanoparticle interfaces. As a result, the cavities are concentrated just near the embedded nanoparticles. Therefore, while the silica nanofiller increases the elastic modulus of the elastomer, it also creates a more

  5. Preparation and Characterization of Epoxy Resin Cross-Linked with High Wood Pyrolysis Bio-Oil Substitution by Acetone Pretreatment

    Directory of Open Access Journals (Sweden)

    Yi Liu

    2017-03-01

    Full Text Available The use of cost effective solvents may be necessary to store wood pyrolysis bio-oil in order to stabilize and control its viscosity, but this part of the production system has not been explored. Conversely, any rise in viscosity during storage, that would occur without a solvent, will add variance to the production system and render it cost ineffective. The purpose of this study was to modify bio-oil with a common solvent and then react the bio-oil with an epoxy for bonding of wood without any loss in properties. The acetone pretreatment of the bio-oil/epoxy mixture was found to improve the cross-linking potential and substitution rate based on its mechanical, chemical, and thermal properties. Specifically, the bio-oil was blended with epoxy resin at weight ratios ranging from 2:1 to 1:5 and were then cured. A higher bio-oil substitution rate was found to lower the shear bond strength of the bio-oil/epoxy resins. However, when an acetone pretreatment was used, it was possible to replace the bio-oil by as much as 50% while satisfying usage requirements. Extraction of the bio-oil/epoxy mixture with four different solvents demonstrated an improvement in cross-linking after acetone pretreatment. ATR-FTIR analysis confirmed that the polymer achieved a higher cross-linked structure. DSC and TGA curves showed improved thermal stability with the addition of the acetone pretreatment. UV-Vis characterization showed that some functional groups of the bio-oil to epoxy system were unreacted. Finally, when the resin mixture was utilized to bond wood, the acetone pretreatment coupled with precise tuning of the bio-oil:epoxy ratio was an effective method to control cross-linking while ensuring acceptable bond strength.

  6. Characterization of Interstrand DNA-DNA Cross-Links Using the α-Hemolysin Protein Nanopore.

    Science.gov (United States)

    Zhang, Xinyue; Price, Nathan E; Fang, Xi; Yang, Zhiyu; Gu, Li-Qun; Gates, Kent S

    2015-12-22

    Nanopore-based sensors have been studied extensively as potential tools for DNA sequencing, characterization of epigenetic modifications such as 5-methylcytosine, and detection of microRNA biomarkers. In the studies described here, the α-hemolysin protein nanopore embedded in a lipid bilayer was used for the detection and characterization of interstrand cross-links in duplex DNA. Interstrand cross-links are important lesions in medicinal chemistry and toxicology because they prevent the strand separation that is required for read-out of genetic information from DNA in cells. In addition, interstrand cross-links are used for the stabilization of duplex DNA in structural biology and materials science. Cross-linked DNA fragments produced unmistakable current signatures in the nanopore experiment. Some cross-linked substrates gave irreversible current blocks of >10 min, while others produced long current blocks (10-100 s) before the double-stranded DNA cross-link translocated through the α-hemolysin channel in a voltage-driven manner. The duration of the current block for the different cross-linked substrates examined here may be dictated by the stability of the duplex region left in the vestibule of the nanopore following partial unzipping of the cross-linked DNA. Construction of calibration curves measuring the frequency of cross-link blocking events (1/τon) as a function of cross-link concentration enabled quantitative determination of the amounts of cross-linked DNA present in samples. The unique current signatures generated by cross-linked DNA in the α-HL nanopore may enable the detection and characterization of DNA cross-links that are important in toxicology, medicine, and materials science.

  7. Cross-linked polyethylenimine–tripolyphosphate nanoparticles for gene delivery

    Directory of Open Access Journals (Sweden)

    Huang XZ

    2014-10-01

    Full Text Available Xianzhang Huang,1 Sujing Shen,2 Zhanfeng Zhang,1 Junhua Zhuang1 1Department of Laboratory Science, Second Affiliated Hospital of Guangzhou University of Chinese Medicine, 2Department of Laboratory Science, Guangdong Second Provincial Traditional Chinese Medicine Hospital, Guangzhou, People’s Republic of China Abstract: The high transfection efficiency of polyethylenimine (PEI makes it an attractive potential nonviral genetic vector for gene delivery and therapy. However, the highly positive charge of PEI leads to cytotoxicity and limits its application. To reduce the cytotoxicity of PEI, we prepared anion-enriched nanoparticles that combined PEI with tripolyphosphate (TPP. We then characterized the PEI-TPP nanoparticles in terms of size, zeta potential, and Fourier-transform infrared (FTIR spectra, and assessed their transfection efficiency, cytotoxicity, and ability to resist deoxyribonuclease (DNase I digestion. The cellular uptake of PEI-TPP with phosphorylated internal ribosome entry site–enhanced green fluorescent protein C1 or FAM (fluorouracil, Adriamycin [doxorubicin] and mitomycin-labeled small interfering ribonucleic acids (siRNAs was monitored by fluorescence microscopy and confocal laser microscopy. The efficiency of transfected delivery of plasmid deoxyribonucleic acid (DNA and siRNA in vitro was 1.11- to 4.20-fold higher with the PEI-TPP particles (7.6% cross-linked than with the PEI, at all N:P ratios (nitrogen in PEI to phosphorus in DNA tested. The cell viability of different cell lines was more than 90% at the chosen N:P ratios of PEI-TPP/DNA complexes. Moreover, PEI-TPP nanoparticles resisted digestion by DNase I for more than 2 hours. The time-dependent absorption experiment showed that 7.6% of cross-linked PEI-TPP particles were internalized by 293T cells within 1 hour. In summary, PEI-TPP nanoparticles effectively transfected cells while conferring little or no toxicity, and thus have potential application in gene

  8. Riboflavin-ultraviolet a corneal cross-linking for keratoconus

    Directory of Open Access Journals (Sweden)

    El-Raggal Tamer

    2009-01-01

    Full Text Available Purpose: To evaluate the safety, efficacy of riboflavin-ultraviolet A irradiation (UVA corneal cross-linking and present refractive changes induced by the treatment in cases of keratoconus. Materials and Methods: The study includes 15 eyes of 9 patients with keratoconus with an average keratometric (K reading less than 54 D and minimal corneal thickness greater than 420 microns. The corneal epithelium was removed manually within the central 8.5 mm diameter area and the cornea was soaked with riboflavin eye drops (0.1% in 20% dextran t-500 for 30 minutes followed by exposure to UVA radiation (365 nm, 3 mW/cm 2 for 30 minutes. During the follow-up period, uncorrected visual acuity (UCVA, best spectacle-corrected visual acuity (BSCVA, manifest refraction, slit lamp examination and topographic changes were recorded at the first week, first month, 3 and 6 months. Results: There was statistically significant improvement of UCVA from a preoperative mean of 0.11 ± 0.07 (range 0.05-0.3 to a postoperative mean of 0.15 ± 0.06 (range 0.1-0.3 (P < 0.05. None of the eyes lost lines of preoperative UCVA but 1 eye lost 1 line of preoperative BSCVA. The preoperative mean K of 49.97 ± 2.81 D (range 47.20-51.75 changed to 48.34 ± 2.64 D (range 45.75-50.40. This decrease in K readings was statistically significant (P < 0.05. All eyes developed minimal faint stromal haze that cleared in 14 eyes within 1 month. In only 1 eye, this resulted in a very faint corneal scar. Other sight threatening complications were not encountered in this series. Progression of the original disease was not seen in any of the treated eyes within 6 months of follow-up. Conclusion: Riboflavin-UVA corneal cross-linking is a safe and promising method for keratoconus. Larger studies with longer follow up are recommended.

  9. Energy harvesting from vibration with cross-linked polypropylene piezoelectrets

    Directory of Open Access Journals (Sweden)

    Xiaoqing Zhang

    2015-07-01

    Full Text Available Piezoelectret films are prepared by modification of the microstructure of polypropylene foam sheets cross-linked by electronic irradiation (IXPP, followed by proper corona charging. Young’s modulus, relative permittivity, and electromechanical coupling coefficient of the fabricated films, determined by dielectric resonance spectra, are about 0.7 MPa, 1.6, and 0.08, respectively. Dynamic piezoelectric d33 coefficients up to 650 pC/N at 200 Hz are achieved. The figure of merit (FOM, d33 ⋅ g33 for a more typical d33 value of 400 pC/N is about 11.2 GPa−1. Vibration-based energy harvesting with one-layer and two-layer stacks of these films is investigated at various frequencies and load resistances. At an optimum load resistance of 9 MΩ and a resonance frequency of 800 Hz, a maximum output power of 120 μW, referred to the acceleration g due to gravity, is obtained for an energy harvester consisting of a one-layer IXPP film with an area of 3.14 cm2 and a seismic mass of 33.7 g. The output power can be further improved by using two-layer stacks of IXPP films in electric series. IXPP energy harvesters could be used to energize low-power electronic devices, such as wireless sensors and LED lights.

  10. Cross-linking da cornea: protocolo padrão

    Directory of Open Access Journals (Sweden)

    Marcony R. Santhiago

    Full Text Available RESUMO O objetivo desta revisão é de determinar as indicações e eficácia da cirurgia que promove novas ligações covalentes entre as fibras de colágeno da córnea, conhecida como Cross-Linking (CXL, assim como esclarecer seus objetivos. O ceratocone é uma doença ectasica da córnea, bilateral, assimétrica, que, principalmente, cursa com encurvamento e afinamentos progressivo, e se inicia em geral na segunda década de vida. O uso primário do CXL tem sido na interrupção da progressão do Ceratocone. Apesar do conhecido encurvamento no estroma da córnea ocorrer nesses pacientes, a fisiopatologia por trás do ceratocone ainda é desconhecida e parece ser multifatorial. Pela evidencia literária disponível até o momento, o CXL da córnea esta, portanto indicado nos pacientes com doença em progressão. Concluímos que existe evidencia suficiente para afirmar que o CXL da córnea é eficaz na estabilização da doença ectásica da cornea.

  11. Cross-linking of polytetrafluoroethylene during room-temperature irradiation

    Energy Technology Data Exchange (ETDEWEB)

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

    2008-01-01

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

  12. Synthesis and Properties of Cross-Linked Polyamide Aerogels

    Science.gov (United States)

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

    2015-01-01

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

  13. Energy harvesting from vibration with cross-linked polypropylene piezoelectrets

    Science.gov (United States)

    Zhang, Xiaoqing; Wu, Liming; Sessler, Gerhard M.

    2015-07-01

    Piezoelectret films are prepared by modification of the microstructure of polypropylene foam sheets cross-linked by electronic irradiation (IXPP), followed by proper corona charging. Young's modulus, relative permittivity, and electromechanical coupling coefficient of the fabricated films, determined by dielectric resonance spectra, are about 0.7 MPa, 1.6, and 0.08, respectively. Dynamic piezoelectric d33 coefficients up to 650 pC/N at 200 Hz are achieved. The figure of merit (FOM, d33 ṡ g33) for a more typical d33 value of 400 pC/N is about 11.2 GPa-1. Vibration-based energy harvesting with one-layer and two-layer stacks of these films is investigated at various frequencies and load resistances. At an optimum load resistance of 9 MΩ and a resonance frequency of 800 Hz, a maximum output power of 120 μW, referred to the acceleration g due to gravity, is obtained for an energy harvester consisting of a one-layer IXPP film with an area of 3.14 cm2 and a seismic mass of 33.7 g. The output power can be further improved by using two-layer stacks of IXPP films in electric series. IXPP energy harvesters could be used to energize low-power electronic devices, such as wireless sensors and LED lights.

  14. Energy harvesting from vibration with cross-linked polypropylene piezoelectrets

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Xiaoqing [Shanghai Key Laboratory of Special Artificial Microstructure Materials and Technology & School of Physics Science and Engineering, Tongji University, Shanghai 200092 (China); Institute for Telecommunications Technology, Merckstrasse 25, 64283 Darmstadt (Germany); Wu, Liming [Shanghai Key Laboratory of Special Artificial Microstructure Materials and Technology & School of Physics Science and Engineering, Tongji University, Shanghai 200092 (China); Sessler, Gerhard M., E-mail: g.sessler@nt.tu-darmstadt.de [Institute for Telecommunications Technology, Merckstrasse 25, 64283 Darmstadt (Germany)

    2015-07-15

    Piezoelectret films are prepared by modification of the microstructure of polypropylene foam sheets cross-linked by electronic irradiation (IXPP), followed by proper corona charging. Young’s modulus, relative permittivity, and electromechanical coupling coefficient of the fabricated films, determined by dielectric resonance spectra, are about 0.7 MPa, 1.6, and 0.08, respectively. Dynamic piezoelectric d{sub 33} coefficients up to 650 pC/N at 200 Hz are achieved. The figure of merit (FOM, d{sub 33} ⋅ g{sub 33}) for a more typical d{sub 33} value of 400 pC/N is about 11.2 GPa{sup −1}. Vibration-based energy harvesting with one-layer and two-layer stacks of these films is investigated at various frequencies and load resistances. At an optimum load resistance of 9 MΩ and a resonance frequency of 800 Hz, a maximum output power of 120 μW, referred to the acceleration g due to gravity, is obtained for an energy harvester consisting of a one-layer IXPP film with an area of 3.14 cm{sup 2} and a seismic mass of 33.7 g. The output power can be further improved by using two-layer stacks of IXPP films in electric series. IXPP energy harvesters could be used to energize low-power electronic devices, such as wireless sensors and LED lights.

  15. Subclinical inflammatory response after accelerated corneal cross-linking

    Institute of Scientific and Technical Information of China (English)

    Hassan Hashemi; Nahid Ashraf; Ebrahim Jafarzadehpur; Alireza Hedayatfar; Soheila Asgari

    2016-01-01

    Background: To evaluate the inlfammatory response after accelerated collagen cross-linking (CXL) in eyes with keratoconus. Methods: Consecutive eyes with keratoconus undergoing CXL surgery were included in this non-randomized interventional study. Aqueous lfare was measured pre- and post-operatively with a laser lfare photometer at 1 week, 1, 3 and 6 months after CXL. Results: Sixty eyes of 60 patients were entered into the study. Before CXL, the mean lfare value was 4.5 photons per millisecond (ph/ms). The lfare values observed at week 1 (7.1 ph/ms; P=0.008), month 1 (6.5 ph/ms; P=0.04), month 3 (6.7 ph/ms; P=0.004) and month 6 (6.7 ph/ms; P=0.004) were signiifcantly higher compared to baseline. Flare values were not signiifcantly different from week 1 up to 6 months after CXL (P=0.930). No statistically significant correlation was detected between the amount of inlfammation and keratometric indices. Conclusions: Accelerated CXL in patients with keratoconus may cause a subclinical inflammatory response which is evident as slight but rather long-lasting rise of aqueous lfare.

  16. Pyridinium cross-links in heritable disorders of collagen

    Energy Technology Data Exchange (ETDEWEB)

    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.

  17. Analysis of protein-nucleic acid interactions by photochemical cross-linking and mass spectrometry

    DEFF Research Database (Denmark)

    Steen, Hanno; Jensen, Ole Nørregaard

    2002-01-01

    Photochemical cross-linking is a commonly used method for studying the molecular details of protein-nucleic acid interactions. Photochemical cross-linking aids in defining nucleic acid binding sites of proteins via subsequent identification of cross-linked protein domains and amino acid residues....... Mass spectrometry (MS) has emerged as a sensitive and efficient analytical technique for determination of such cross-linking sites in proteins. The present review of the field describes a number of MS-based approaches for the characterization of cross-linked protein-nucleic acid complexes...... and for sequencing of peptide-nucleic acid heteroconjugates. The combination of photochemical cross-linking and MS provides a fast screening method to gain insights into the overall structure and formation of protein-oligonucleotide complexes. Because the analytical methods are continuously refined and protein...

  18. Characterization of the deoxyguanosine-lysine cross-link of methylglyoxal.

    Science.gov (United States)

    Petrova, Katya V; Millsap, Amy D; Stec, Donald F; Rizzo, Carmelo J

    2014-06-16

    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 Nα-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.

  19. Fabrication of patterned calcium cross-linked alginate hydrogel films and coatings through reductive cation exchange.

    Science.gov (United States)

    Bruchet, Marion; Melman, Artem

    2015-10-20

    Calcium cross-linked alginate hydrogels are widely used in targeted drug delivery, tissue engineering, wound treatment, and other biomedical applications. We developed a method for preparing homogeneous alginate hydrogels cross-linked with Ca(2+) cations using reductive cation exchange in homogeneous iron(III) cross-linked alginate hydrogels. Treatment of iron(III) cross-linked alginate hydrogels with calcium salts and sodium ascorbate results in reduction of iron(III) cations to iron(II) that are instantaneously replaced with Ca(2+) cations, producing homogeneous ionically cross-linking hydrogels. Alternatively, the cation exchange can be performed by photochemical reduction in the presence of calcium chloride using a sacrificial photoreductant. This approach allows fabrication of patterned calcium alginate hydrogels through photochemical patterning of iron(III) cross-linked alginate hydrogel followed by the photochemical reductive exchange of iron cations to calcium.

  20. An Open Data Format for Visualization and Analysis of Cross-Linked Mass Spectrometry Results.

    Science.gov (United States)

    Hoopmann, Michael R; Mendoza, Luis; Deutsch, Eric W; Shteynberg, David; Moritz, Robert L

    2016-11-01

    Protein-protein interactions are an important element in the understanding of protein function, and chemical cross-linking shotgun mass spectrometry is rapidly becoming a routine approach to identify these specific interfaces and topographical interactions. Protein cross-link data analysis is aided by dozens of algorithm choices, but hindered by a lack of a common format for representing results. Consequently, interoperability between algorithms and pipelines utilizing chemical cross-linking remains a challenge. pepXML is an open, widely-used format for representing spectral search algorithm results that has facilitated information exchange and pipeline development for typical shotgun mass spectrometry analyses. We describe an extension of this format to incorporate cross-linking spectral search results. We demonstrate application of the extension by representing results of multiple cross-linking search algorithms. In addition, we demonstrate adapting existing pepXML-supporting software pipelines to analyze protein cross-linking results formatted in pepXML. Graphical Abstract ᅟ.

  1. Reduction in aggregation and energy transfer of quantum dots incorporated in polystyrene beads by kinetic entrapment due to cross-linking during polymerization.

    Science.gov (United States)

    Vaidya, Shyam V; Couzis, Alex; Maldarelli, Charles

    2015-03-17

    We report the development of barcoded polystyrene microbeads, approximately 50 μm in diameter, which are encoded by incorporating multicolored semiconductor fluorescent nanocrystals (quantum dots or QDs) within the microbeads and using the emission spectrum of the embedded QDs as a spectral label. The polymer/nanocrystal bead composites are formed by polymerizing emulsified liquid droplets of styrene monomer and QDs suspended in an immiscible continuous phase (suspension polymerization). We focus specifically on the effect of divinylbenzene (DVB) added to cross-link the linearly growing styrene polymer chains and the effect of this cross-linking on the state of aggregation of the nanocrystals in the composite. Aggregated states of multicolor QDs give rise to nonradiative resonance energy transfer (RET) which distorts the emission label from a spectrum recorded in a reference solvent in which the nanocrystals are well dispersed and unaggregated. A simple barcode is chosen of a mixture of QDs emitting at 560 (yellow) and 620 nm (red). We find that for linear chain growth (no DVB), the QDs aggregate as is evident from the emission spectrum and the QD distribution as seen from confocal laser scanning microscopy (CLSM) and transmission electron microscopy (TEM) images. Increasing the extent of cross-linking by the addition of DVB is shown to significantly decrease the aggregation and provide a clear label. We suggest that in the absence of cross-linking, linearly growing polymer chains, through enthalpic and entropic effects, drive the nanocrystals into inclusions, while cross-linking kinetically entraps the particle and prevents their aggregation.

  2. Tailoring the properties of cholecyst-derived extracellular matrix using carbodiimide cross-linking.

    LENUS (Irish Health Repository)

    Burugapalli, Krishna

    2009-01-01

    Modulation of properties of extracellular matrix (ECM) based scaffolds is key for their application in the clinical setting. In the present study, cross-linking was used as a tool for tailoring the properties of cholecyst-derived extracellular matrix (CEM). CEM was cross-linked with varying cross-linking concentrations of N,N-(3-dimethyl aminopropyl)-N\\'-ethyl carbodiimide (EDC) in the presence of N-hydroxysuccinimide (NHS). Shrink temperature measurements and ATR-FT-IR spectra were used to determine the degree of cross-linking. The effect of cross-linking on degradation was tested using the collagenase assay. Uniaxial tensile properties and the ability to support fibroblasts were also evaluated as a function of cross-linking. Shrink temperature increased from 59 degrees C for non-cross-linked CEM to 78 degrees C for the highest EDC cross-linking concentration, while IR peak area ratios for the free -NH(2) group at 3290 cm(-1) to that of the amide I band at 1635 cm(-1) decreased with increasing EDC cross-linking concentration. Collagenase assay demonstrated that degradation rates for CEM can be tailored. EDC concentrations 0 to 0.0033 mmol\\/mg CEM were the cross-linking concentration range in which CEM showed varied susceptibility to collagenase degradation. Furthermore, cross-linking concentrations up to 0.1 mmol EDC\\/mg CEM did not have statistically significant effect on the uniaxial tensile strength, as well as morphology, viability and proliferation of fibroblasts on CEM. In conclusion, the degradation rates of CEM can be tailored using EDC-cross-linking, while maintaining the mechanical properties and the ability of CEM to support cells.

  3. Effect of Cross-Linking and Enzymatic Hydrolysis Composite Modification on the Properties of Rice Starches

    Directory of Open Access Journals (Sweden)

    Gao-Qiang Liu

    2012-07-01

    Full Text Available Native rice starch lacks the versatility necessary to function adequately under rigorous industrial processing, so modified starches are needed to meet the functional properties required in food products. This work investigated the impact of enzymatic hydrolysis and cross-linking composite modification on the properties of rice starches. Rice starch was cross-linked with epichlorohydrin (EPI with different concentrations (0.5%, 0.7%, 0.9% w/w, on a dry starch basis, affording cross-linked rice starches with the three different levels of cross-linking that were named R1, R2, and R3, respectively. The cross-linked rice starches were hydrolyzed by α-amylase and native, hydrolyzed, and hydrolyzed cross-linked rice starches were comparatively studied. It was found that hydrolyzed cross-linked rice starches showed a lower the degree of amylase hydrolysis compared with hydrolyzed rice starch. The higher the degree of cross-linking, the higher the capacity to resist enzyme hydrolysis. Hydrolyzed cross-linked rice starches further increased the adsorptive capacities of starches for liquids and decreased the trend of retrogradation, and it also strengthened the capacity to resist shear compared to native and hydrolyzed rice starches.

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

    Science.gov (United States)

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

    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.

  5. ROLE OF CORNEAL COLLAGEN CROSS LINKING IN KERATOCONUS

    Directory of Open Access Journals (Sweden)

    Atul

    2015-09-01

    Full Text Available To evaluate the outcome of collagen cross linkage using riboflavin 0.1% and ultraviolet A radiation of a wavelength 370nm . PURPOSE : To determine the effect of collagen cross linking for keratoconus on pachymetry , corneal topography, uncorrected visual acuity, specular count, IOP at 1, 3, 6 months . METHODS : The current study was designed as a prospective interventional trial of corneal collagen cross - linking in subjects with progressive keratoconus between a period of J anuary 2013 to J uly 2014 including 50 eyes of 30 patients. This study rece ived approval from Ethics committee. Informed written consent was obtained from all patients prior to treatment. RESULTS: Mean follow up period of 6 months. There was statistically significant decline in effective k readings from mean pre op (51.7D to pos t op value (49.65D . Pachymetry showed initial increase post operatively followed by reduction in corneal thickness in 3 month s follow up , followed by gradual increase in thickness over a period of 6 months though it was not equivalent to pre - operative values. paired t test p value was 0.00 1 in 1 n 3 month and 0. 043 in 6 month, concluding significant reduction in early post op period with im provement over time . Specular count reduced from pre - op (2673.80 levels to post - op (2654.60 levels ,the reduction in specular count was not statistically significant P value (0.014 The uncorrected visual acuity showed decrease in refractive error with in crease in visual acuity gradually over 6 months, log MAR scale visual acuity was used for statistical analysis with P value (0.001 which was statistically significant .visual acuity improved by 1.5 lines in snellens equivalence or from 0.5 to 0.4 in log MA R char y ± 20cells/mm 3 , P value(0. 001 . IOP statically show ed no significant change in pre - operative and post operatively , paired t test p value was 0. 44 showing it was not significant . CONCLUSIONS : 1. Visual acuity improved in

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

    Science.gov (United States)

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

    2015-12-30

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

  7. Integrated Cryogenic Satellite Communications Cross-Link Receiver Experiment

    Science.gov (United States)

    Romanofsky, R. R.; Bhasin, K. B.; Downey, A. N.; Jackson, C. J.; Silver, A. H.; Javadi, H. H. S.

    1995-01-01

    An experiment has been devised which will validate, in space, a miniature, high-performance receiver. The receiver blends three complementary technologies; high temperature superconductivity (HTS), pseudomorphic high electron mobility transistor (PHEMT) monolithic microwave integrated circuits (MMIC), and a miniature pulse tube cryogenic cooler. Specifically, an HTS band pass filter, InP MMIC low noise amplifier, HTS-sapphire resonator stabilized local oscillator (LO), and a miniature pulse tube cooler will be integrated into a complete 20 GHz receiver downconverter. This cooled downconverter will be interfaced with customized signal processing electronics and integrated onto the space shuttle's 'HitchHiker' carrier. A pseudorandom data sequence will be transmitted to the receiver, which is in low Earth orbit (LEO), via the Advanced Communication Technology Satellite (ACTS) on a 20 GHz carrier. The modulation format is QPSK and the data rate is 2.048 Mbps. The bit error rate (BER) will be measured in situ. The receiver is also equipped with a radiometer mode so that experiment success is not totally contingent upon the BER measurement. In this mode, the receiver uses the Earth and deep space as a hot and cold calibration source, respectively. The experiment closely simulates an actual cross-link scenario. Since the receiver performance depends on channel conditions, its true characteristics would be masked in a terrestrial measurement by atmospheric absorption and background radiation. Furthermore, the receiver's performance depends on its physical temperature, which is a sensitive function of platform environment, thermal design, and cryocooler performance. This empirical data is important for building confidence in the technology.

  8. The theory and art of corneal cross-linking

    Directory of Open Access Journals (Sweden)

    Rebecca McQuaid

    2013-01-01

    Full Text Available 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.

  9. Transglutaminases: widespread cross-linking enzymes in plants.

    Science.gov (United States)

    Serafini-Fracassini, Donatella; Del Duca, Stefano

    2008-08-01

    Transglutaminases have been studied in plants since 1987 in investigations aimed at interpreting some of the molecular mechanisms by which polyamines affect growth and differentiation. Transglutaminases are a widely distributed enzyme family catalysing a myriad of biological reactions in animals. In plants, the post-translational modification of proteins by polyamines forming inter- or intra-molecular cross-links has been the main transglutaminase reaction studied. The few plant transglutaminases sequenced so far have little sequence homology with the best-known animal enzymes, except for the catalytic triad; however, they share a possible structural homology. Proofs of their catalytic activity are: (a) their ability to produce glutamyl-polyamine derivatives; (b) their recognition by animal transglutaminase antibodies; and (c) biochemical features such as calcium-dependency, etc. However, many of their fundamental biochemical and physiological properties still remain elusive. It has been detected in algae and in angiosperms in different organs and sub-cellular compartments, chloroplasts being the best-studied organelles. Possible roles concern the structural modification of specific protein substrates. In chloroplasts, transglutaminases appear to stabilize the photosynthetic complexes and Rubisco, being regulated by light and other factors, and possibly exerting a positive effect on photosynthesis and photo-protection. In the cytosol, they modify cytoskeletal proteins. Preliminary reports suggest an involvement in the cell wall construction/organization. Other roles appear to be related to fertilization, abiotic and biotic stresses, senescence and programmed cell death, including the hypersensitive reaction. The widespread occurrence of transglutaminases activity in all organs and cell compartments studied suggests a relevance for their still incompletely defined physiological roles. At present, it is not possible to classify this enzyme family in plants owing to

  10. Long-Term Sustained Release from a Biodegradable Photo-Cross-Linked Network for Intraocular Corticosteroid Delivery.

    Science.gov (United States)

    Amsden, Brian G; Marecak, Dale

    2016-09-06

    Intravitreal sustained delivery of corticosteroids such as dexamethasone is an effective means of treating a number of ocular diseases, including diabetic retinopathy, uveitis, and age-related or diabetic macular edema. There are currently marketed devices for this purpose, yet only one, Ozurdex, is degradable. In vitro release of dexamethasone from the Ozurdex device is limited to approximately 30 days, however. It was the objective of this study to examine the potential for prolonged and sustained release of a corticosteroid in vitro from a degradable polymer prepared from terminally acrylated star co- and ter-prepolymers composed of d,l-lactide, ε-caprolactone, and trimethylene carbonate co-photo-cross-linked with poly(ethylene glycol) diacrylate. Through manipulation of the network polymer glass transition temperature and degradation rate, a sustained release of triamcinolone was achieved, with an estimated release duration greater than twice that of the Ozurdex system. Moreover, a period of nearly constant release was obtained using a network prepared from 5000 Da star-poly(trimethylene carbonate-co-d,l-lactide) triacrylate (3:1 trimethylene carbonate:d,l-lactide) co-cross-linked with 700 Da poly(ethylene glycol diacrylate). These formulations show promise as implantable, intravitreal corticosteroid delivery devices.

  11. Synthesis, characterization and cytocompatibility of a poly(diol-tricarballylate) visible light photo-cross-linked biodegradable elastomer.

    Science.gov (United States)

    Shaker, Mohamed A; Doré, Jules J E; Younes, Husam M

    2010-01-01

    The synthesis, characterization and in vitro cytocompatibility of a new family of photo-cross-linked amorphous poly(diol-tricarballylate) (PDT) biodegradable elastomeric polyesters are reported. The synthesis was based on the polycondensation reaction between tricarballylic acid and alkylene diols, followed by acrylation. The prepared and acrylated poly(diol-tricarballylate) (APDT) was characterized by means of FT-IR, (1)H-NMR, GPC and DSC. Liquid-to-solid photo-curing was carried out by exposing the APDT to visible light in the presence of camphorquinone as a photoinitiator. The thermal properties, mechanical characteristics, sol content, long-term in vitro degradation and cytocompatibility of the prepared PDT elastomers were also reported. The mechanical and degradation properties of this new photocurable elastomer can be precisely controlled by varying the density of acrylate moieties in the matrix of the polymer, and through changes in the pre-polymer chain length. The use of visible light cross-linking, possibility of solventless drug loading, controllable mechanical properties and cytocompatibility of these new elastomers make them excellent candidates for use in controlled implantable drug-delivery systems of protein drugs and other biomedical applications.

  12. Feruloylated arabinoxylans are oxidatively cross-linked by extracellular maize peroxidase but not by horseradish peroxidase.

    Science.gov (United States)

    Burr, Sally J; Fry, Stephen C

    2009-09-01

    Covalent cross-linking of soluble extracellular arabinoxylans in living maize cultures, which models the cross-linking of wall-bound arabinoxylans, is due to oxidation of feruloyl esters to oligoferuloyl esters and ethers. The oxidizing system responsible could be H2O2/peroxidase, O2/laccase, or reactive oxygen species acting non-enzymically. To distinguish these possibilities, we studied arabinoxylan cross-linking in vivo and in vitro. In living cultures, exogenous, soluble, extracellular, feruloylated [pentosyl-3H]arabinoxylans underwent cross-linking, beginning abruptly 8 d after sub-culture. Cross-linking was suppressed by iodide, an H2O2 scavenger, indicating dependence on endogenous H2O2. However, exogenous H2O2 did not cause precocious cross-linking, despite the constant presence of endogenous peroxidases, suggesting that younger cultures contained natural cross-linking inhibitors. Dialysed culture-filtrates cross-linked [3H]arabinoxylans in vitro only if H2O2 was also added, indicating a peroxidase requirement. This cross-linking was highly ionic-strength-dependent. The peroxidases responsible were heat-labile, although relatively heat-stable peroxidases (assayed on o-dianisidine) were also present. Surprisingly, added horseradish peroxidase, even after heat-denaturation, blocked the arabinoxylan-cross-linking action of maize peroxidases, suggesting that the horseradish protein was a competing substrate for [3H]arabinoxylan coupling. In conclusion, we show for the first time that cross-linking of extracellular arabinoxylan in living maize cultures is an action of apoplastic peroxidases, some of whose unusual properties we report.

  13. Analytical characterisation of glutardialdehyde cross-linking products in gelatine-gum arabic complex coacervates

    Energy Technology Data Exchange (ETDEWEB)

    Fuguet, Elisabet [Advanced Measurement and Imaging, Unilever Food and Health Research Institute, Olivier van Noortlaan 120, 3133 AT Vlaardingen (Netherlands)], E-mail: eli.fuguet@gmail.com; Platerink, Chris van [Advanced Measurement and Imaging, Unilever Food and Health Research Institute, Olivier van Noortlaan 120, 3133 AT Vlaardingen (Netherlands); Department of Biomolecular Mass Spectrometry, Bijvoet Center for Biomolecular Research, Utrecht University, Sorbonnelaan 16, 3584 CA Utrecht (Netherlands); Janssen, Hans-Gerd [Advanced Measurement and Imaging, Unilever Food and Health Research Institute, Olivier van Noortlaan 120, 3133 AT Vlaardingen (Netherlands); van' t Hoff Institute for Molecular Sciences, University of Amsterdam, Nieuwe Achtergracht 166, 1018 WV Amsterdam (Netherlands)

    2007-11-26

    Encapsulates having shells of cross-linked mixtures of proteins and polysaccharides are widely used in the food and pharmaceutical industry for controlled release of actives and flavour compounds. In order to be able to predict the behaviour and the release characteristics of the microcapsules, a better understanding of the nature and extent of the cross-linking reaction is needed. Several analytical techniques were applied for the characterisation of glutardialdehyde (GDA) cross-linked encapsulates made of gelatine and gum arabic. To allow the use of sensitive, high-resolution methods such as chromatography and mass spectrometry, the sample first had to be hydrolysed. In this way, a mixture of amino acids, small peptides and the cross-link moieties was obtained. High-resolution liquid chromatography coupled to high-resolution mass spectrometry (HPLC-MS) was applied to detect possible cross-link markers through a comparison of HPLC-MS mass-chromatograms obtained for cross-linked and non-cross-linked coacervates. HPLC-MS/MS was used to identify the species responsible for the differences. Cross-linking occurred between GDA molecules and lysine and hydroxylysine {epsilon}-amino groups, and up to eight cross-link products of different nature could be identified. They included pyridinium ions and Schiff bases, and also unreacted GDA condensation products. Next, based on the insight gained in the possible chemical structures present in the cross-link markers, methods for selective labelling of these functionalities were employed to allow easier detection of related reaction products. Both liquid chromatography (LC) and gas chromatography (GC) were used in these experiments. Unfortunately, these approaches failed to detect new cross-link markers, most likely as a result of the low levels at which these are present.

  14. Feruloylated Arabinoxylans Are Oxidatively Cross-Linked by Extracellular Maize Peroxidase but Not by Horseradish Peroxidase

    Institute of Scientific and Technical Information of China (English)

    Sally J. Burr; Stephen C. Fry

    2009-01-01

    Covalent cross-linking of soluble extraceUular arabinoxylans in living maize cultures, which models the cross-linking of wall-bound arabinoxylans, is due to oxidation of feruloyl esters to oligoferuloyl esters and ethers. The oxidizing system responsible could be H_2O_2/peroxidase, O_2/laccase, or reactive oxygen species acting non-enzymically. To distinguish these possibilities, we studied arabinoxylan cross-linking in vivo and in vitro. In living cultures, exogenous, soluble, extra-cellular, feruloylated [pentosyl-~3H]arabinoxylans underwent cross-linking, beginning abruptly 8 d after sub-culture. Cross-linking was suppressed by iodide, an H_2O_2 scavenger, indicating dependence on endogenous H2O2. However, exogenous H_2O_2 did not cause precocious cross-linking, despite the constant presence of endogenous peroxidases, suggesting that younger cultures contained natural cross-linking inhibitors. Dialysed culture-filtrates cross-linked [~3H]arabinoxylans in vitro only if H_20_2 was also added, indicating a peroxiclase requirement. This cross-linking was highly ionic-strength-dependent. The peroxidases responsible were heat-labile, although relatively heat-stable peroxidases (assayed on o-dianisidine) were also present, Surprisingly, added horseradish peroxidase, even after heat-denaturation, blocked the arabinoxylan-cross-linking action of maize peroxidases, suggesting that the horseradish protein was a competing substrate for [~3H]arabino-xylan coupling. In conclusion, we show for the first time that cross-linking of extracellular arabinoxylan in living maize cultures is an action of apoplastic peroxidases, some of whose unusual properties we report.

  15. SYNTHESIS AND CATALYTIC PROPERTIES OF CROSS-LINKED HYDROPHOBICALLY ASSOCIATING POLY(ALKYLMETHYLDIALLYLAMMONIUM BROMIDES)

    NARCIS (Netherlands)

    WANG, GJ; ENGBERTS, JBFN

    1994-01-01

    Cross-linked, hydrophobically associating homo- and copolymers were synthesized by free-radical cyclo(co)polymerization of alkylmethyldiallylammonium bromide monomers with a small amount of N,N'-methylenebisacrylamide in aqueous solution using ammonium persulfate as the initiator. The cross-linked h

  16. Rheological properties of dispersions of enzymatically cross-linked apo-α-lactalbumin

    NARCIS (Netherlands)

    Saricay, Yunus; Wierenga, Peter A.; Vries, de Renko

    2016-01-01

    The enzymatic cross-linking of apo-α-lactalbumin (α-LA) with horseradish peroxidase (HRP) leads to the formation of hydrophilic protein aggregates with controlled size and architecture. We explore the rheological properties of dispersions of these HRP-cross-linked α-LA aggregates with a hydrodyna

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

    Science.gov (United States)

    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...

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

    Science.gov (United States)

    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...

  19. Self-assembly made durable: water-repellent materials formed by cross-linking fullerene derivatives.

    Science.gov (United States)

    Wang, Jiaobing; Shen, Yanfei; Kessel, Stefanie; Fernandes, Paulo; Yoshida, Kaname; Yagai, Shiki; Kurth, Dirk G; Möhwald, Helmuth; Nakanishi, Takashi

    2009-01-01

    Fullerene flakes: A diacetylene-functionalized fullerene derivative self-organizes into flakelike microparticles (see picture). Both the diacetylene and C(60) moieties can be effectively cross-linked, which leads to supramolecular materials with remarkable resistivity to solvent, heat, and mechanical stress. Moreover, the surface of the cross-linked flakelike objects is highly durable and water-repellent.

  20. Quantification of carboxyl groups in carbodiimide cross-linked collagen sponges

    NARCIS (Netherlands)

    Everaerts, Frank; Torrianni, Mark; Hendriks, Marc; Feijen, Jan

    2007-01-01

    Glutaraldehyde (GA) fixation of bioprosthetic tissue is a well adapted technique, with commercial products on the market for almost 40 years. Amine groups present in tissue react with GA to form different types of cross-links. An estimation of the degree of cross-linking of the tissue can be obtaine

  1. Infrared microspectroscopic determination of collagen cross-links in articular cartilage

    Science.gov (United States)

    Rieppo, Lassi; Kokkonen, Harri T.; Kulmala, Katariina A. M.; Kovanen, Vuokko; Lammi, Mikko J.; Töyräs, Juha; Saarakkala, Simo

    2017-03-01

    Collagen forms an organized network in articular cartilage to give tensile stiffness to the tissue. Due to its long half-life, collagen is susceptible to cross-links caused by advanced glycation end-products. The current standard method for determination of cross-link concentrations in tissues is the destructive high-performance liquid chromatography (HPLC). The aim of this study was to analyze the cross-link concentrations nondestructively from standard unstained histological articular cartilage sections by using Fourier transform infrared (FTIR) microspectroscopy. Half of the bovine articular cartilage samples (n=27) were treated with threose to increase the collagen cross-linking while the other half (n=27) served as a control group. Partial least squares (PLS) regression with variable selection algorithms was used to predict the cross-link concentrations from the measured average FTIR spectra of the samples, and HPLC was used as the reference method for cross-link concentrations. The correlation coefficients between the PLS regression models and the biochemical reference values were r=0.84 (p<0.001), r=0.87 (p<0.001) and r=0.92 (p<0.001) for hydroxylysyl pyridinoline (HP), lysyl pyridinoline (LP), and pentosidine (Pent) cross-links, respectively. The study demonstrated that FTIR microspectroscopy is a feasible method for investigating cross-link concentrations in articular cartilage.

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

    NARCIS (Netherlands)

    Mentink, CJAL; Hendriks, M; Levels, AAG; Wolffenbuttel, BHR

    2002-01-01

    Back-ground: 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

  3. Peroxidase-mediated cross-linking of a tyrosine-containing peptide with ferulic acid

    NARCIS (Netherlands)

    Oudgenoeg, G.; Hilhorst, R.; Piersma, S.R.; Boeriu, C.G.; Gruppen, H.; Hessing, M.; Voragen, A.G.J.; Laane, C.

    2001-01-01

    The tyrosine-containing peptide Gly-Tyr-Gly (GYG) was oxidatively cross-linked by horseradish peroxidase in the presence of hydrogen peroxide. As products, covalently coupled di- to pentamers of the peptide were identified by LC-MS. Oxidative cross-linking of ferulic acid with horseradish peroxidase

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

    NARCIS (Netherlands)

    Rothamel, D.; Schwarz, F.; Sager, M.; Herten, M. van; Sculean, A.; Becker, J.M.

    2005-01-01

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

  5. Biomimetic hydration lubrication with various polyelectrolyte layers on cross-linked polyethylene orthopedic bearing materials.

    Science.gov (United States)

    Kyomoto, Masayuki; Moro, Toru; Saiga, Kenichi; Hashimoto, Masami; Ito, Hideya; Kawaguchi, Hiroshi; Takatori, Yoshio; Ishihara, Kazuhiko

    2012-06-01

    Natural joints rely on fluid thin-film lubrication by the hydrated polyelectrolyte layer of cartilage. However, current artificial joints with polyethylene (PE) surfaces have considerably less efficient lubrication and thus much greater wear, leading to osteolysis and aseptic loosening. This is considered a common factor limiting prosthetic longevity in total hip arthroplasty (THA). However, such wear could be mitigated by surface modification to mimic the role of cartilage. Here we report the development of nanometer-scale hydrophilic layers with varying charge (nonionic, cationic, anionic, or zwitterionic) on cross-linked PE (CLPE) surfaces, which could fully mimic the hydrophilicity and lubricity of the natural joint surface. We present evidence to support two lubrication mechanisms: the primary mechanism is due to the high level of hydration in the grafted layer, where water molecules act as very efficient lubricants; and the secondary mechanism is repulsion of protein molecules and positively charged inorganic ions by the grafted polyelectrolyte layer. Thus, such nanometer-scaled hydrophilic polymers or polyelectrolyte layers on the CLPE surface of acetabular cup bearings could confer high durability to THA prosthetics.

  6. Cross-linked β-cyclodextrin and carboxymethyl cellulose hydrogels for controlled drug delivery of acyclovir

    Science.gov (United States)

    Malik, Nadia Shamshad; Ahmad, Mahmood; Minhas, Muhammad Usman

    2017-01-01

    To explore the potential role of polymers in the development of drug-delivery systems, this study investigated the use of β-cyclodextrin (β-CD), carboxymethyl cellulose (CMC), acrylic acid (AA) and N’ N’-methylenebis-acrylamide (MBA) in the synthesis of hydrogels for controlled drug delivery of acyclovir (ACV). Different proportions of β-CD, CMC, AA and MBA were blended with each other to fabricate hydrogels via free radical polymerization technique. Fourier transform infrared spectroscopy (FTIR) revealed successful grafting of components into the polymeric network. Thermal and morphological characterization confirmed the formation of thermodynamically stable hydrogels having porous structure. The pH-responsive behaviour of hydrogels has been documented by swelling dynamics and drug release behaviour in simulated gastrointestinal fluids. Drug release kinetics revealed controlled release behaviour of the antiviral drug acyclovir in developed polymeric network. Cross-linked β-cyclodextrin and carboxymethyl cellulose hydrogels can be used as promising candidates for the design and development of controlled drug-delivery systems. PMID:28245257

  7. Assessment of protein function following cross-linking by alpha-dicarbonyls.

    Science.gov (United States)

    Miller, Antonia G; Gerrard, Juliet A

    2005-06-01

    Protein cross-linking via the Maillard reaction with alpha-dicarbonyl compounds has been the subject of intense scrutiny in the literature. We report here a study of the impact of this cross-linking on enzyme function. Protein function following glycation was examined by treating ribonuclease A with methylglyoxal, glyoxal, and diacetyl, which cross-linked the enzyme and impaired its activity. The effects of two reported Maillard reaction inhibitors, aminoguanidine and 3,5-dimethylpyrazole-1-carboxamidine, on the cross-linking reaction were assessed, with a parallel measurement of the effect on enzyme activity. The results demonstrate that preventing protein cross-linking does not necessarily preserve enzyme activity. These results cast doubt on the likely efficacy of some purported antiaging compounds in vivo.

  8. Characteristic of hyaluronic acid derivative films cross-linked by polyethylene glycol of low water content

    Institute of Scientific and Technical Information of China (English)

    Chen Jinghua; Chen Jingtao; Xu Zheng; Gu Qisheng

    2008-01-01

    Objective: To test the characteristics of byaluronic acid (HA) derivative cross-linked by polyethylene glycol films of low water content. Methods: The cross-linked HA film with 200 μm thickness was got at atmospheric pressure at 25℃ for 5 d. After dried, cross-linked films of 10 mm×10 mm were weighed and immersed in phosphate buffered saline (PBS pH 7.45) at 37℃ for 24 h. Then the solution fraction and water content were estimated. Meanwhile, cross-linked HA derivative films were immersed in phosphate buffered saline (PBS: pH 7.45) at 37℃ for determined time and then implanted subcutaneously in the back of white rats to test in vitro or in vivo degradation characteristic. Results and Conclusion: HA hydrogel cross-linked by polyethylene glycol with water content is as low as 60% and this kind of HA derivative has a slow degradation rate.

  9. Disuccinimidyl suberate cross-linked hemoglobin as a novel red blood cell substitute

    Institute of Scientific and Technical Information of China (English)

    LU; Xiuling; ZHENG; Chunyang; XU; Yuhong; SU; Zhiguo

    2005-01-01

    Disuccinimidyl suberate (DSS) intramolecularly cross-linked hemoglobin (Hb) was developed as a novel red blood cell substitute. A multi-angle laser light scattering detector coupled with size exclusion HPLC was applied to determine the molecular weight of the modified Hb. SDS-PAGE was also used as a complement. It was proved that 83.8% of the product was intramolecularly cross-linked Hb with weight-average molecular weights (Mw) of 67.5 kD, 12% was dimeric Hb with Mw of 146.6 kD, and 4.2% was trimeric Hb with Mw of 306.4 kD. The tetramer structure of the cross-linked Hb was stable as shown in size-exclusion chromatography using a mobile phase containing 1 mol/L MgCl2. Analysis by LC-MS demonstrated that the reaction of DSS with Hb mainly took place between the twoα subunits within a Hb molecule, resulting in stabilization of the tetramer structure. However, the cross-linking was not site-specific. The P50 of the cross-linked Hb decreased from 21.8 mmHg to 14.3 mmHg, and the Hill coefficient decreased from 2.22 to 1.41. Result of isoelectric focusing showed that the pI of DSS cross-linked Hb was in the range of 4.6-5.2, similar to that of serum albumin. The safety of DSS cross-linked Hb was favored by animal tests on rats and guinea pigs. Exchange transfusion experiment with DSS cross-linked Hb using rats as a model indicated no pressor effect or other significant side effects. The characteristics and properties of DSS cross-linked Hb were also compared with that of diaspirin cross-linked Hb reported in the literature.

  10. Physiologically relevant oxidative degradation of oligo(proline) cross-linked polymeric scaffolds.

    Science.gov (United States)

    Yu, Shann S; Koblin, Rachel L; Zachman, Angela L; Perrien, Daniel S; Hofmeister, Lucas H; Giorgio, Todd D; Sung, Hak-Joon

    2011-12-12

    Chronic inflammation-mediated oxidative stress is a common mechanism of implant rejection and failure. Therefore, polymer scaffolds that can degrade slowly in response to this environment may provide a viable platform for implant site-specific, sustained release of immunomodulatory agents over a long time period. In this work, proline oligomers of varying lengths (P(n)) were synthesized and exposed to oxidative environments, and their accelerated degradation under oxidative conditions was verified via high performance liquid chromatography and gel permeation chromatography. Next, diblock copolymers of poly(ethylene glycol) (PEG) and poly(ε-caprolactone) (PCL) were carboxylated to form 100 kDa terpolymers of 4%PEG-86%PCL-10%cPCL (cPCL = poly(carboxyl-ε-caprolactone); i% indicates molar ratio). The polymers were then cross-linked with biaminated PEG-P(n)-PEG chains, where P(n) indicates the length of the proline oligomer flanked by PEG chains. Salt-leaching of the polymeric matrices created scaffolds of macroporous and microporous architecture, as observed by scanning electron microscopy. The degradation of scaffolds was accelerated under oxidative conditions, as evidenced by mass loss and differential scanning calorimetry measurements. Immortalized murine bone-marrow-derived macrophages were then seeded on the scaffolds and activated through the addition of γ-interferon and lipopolysaccharide throughout the 9-day study period. This treatment promoted the release of H(2)O(2) by the macrophages and the degradation of proline-containing scaffolds compared to the control scaffolds. The accelerated degradation was evidenced by increased scaffold porosity, as visualized through scanning electron microscopy and X-ray microtomography imaging. The current study provides insight into the development of scaffolds that respond to oxidative environments through gradual degradation for the controlled release of therapeutics targeted to diseases that feature chronic

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

    Directory of Open Access Journals (Sweden)

    Prema Padmanabhan

    2014-01-01

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

  12. The Release Behavior and Kinetic Evaluation of Tramadol HCl from Chemically Cross Linked Ter Polymeric Hydrogels

    Directory of Open Access Journals (Sweden)

    Muhammad A Malana

    2013-01-01

    Full Text Available Background and the purpose of the study: Hydrogels, being stimuli responsive are considered to be effective for targeted and sustained drug delivery. The main purpose for this work was to study the release behavior and kinetic evaluation of Tramadol HCl from chemically cross linked ter polymeric hydrogels.MethodsTer-polymers of methacrylate, vinyl acetate and acrylic acid cross linked with ethylene glycol dimethacrylate (EGDMA were prepared by free radical polymerization. The drug release rates, dynamic swelling behavior and pH sensitivity of hydrogels ranging in composition from 1-10 mol % EGDMA were studied. Tramadol HCl was used as model drug substance. The release behavior was investigated at pH 8 where all formulations exhibited non-Fickian diffusion mechanism.Results and major conclusion: Absorbency was found to be more than 99% indicating good drug loading capability of these hydrogels towards the selected drug substance. Formulations designed with increasing amounts of EGDMA had a decreased equilibrium media content as well as media penetrating velocity and thus exhibited a slower drug release rate. Fitting of release data to different kinetic models indicate that the kinetic order shifts from the first to zero order as the concentration of drug was increased in the medium, showing gradual independency of drug release towards its concentration. Formulations with low drug content showed best fitness with Higuchi model whereas those with higher concentration of drug followed Hixson-Crowell model with better correlation values indicating that the drug release from these formulations depends more on change in surface area and diameter of tablets than that on concentration of the drug. Release exponent (n derived from Korse-Meyer Peppas equation implied that the release of Tramadol HCl from these formulations was generally non-Fickian (n>0.5>1 showing swelling controlled mechanism. The mechanical strength and controlled release capability of

  13. The release behavior and kinetic evaluation of tramadol HCl from chemically cross linked Ter polymeric hydrogels

    Directory of Open Access Journals (Sweden)

    Malana Muhammad A

    2013-01-01

    Full Text Available Abstract Background and the purpose of the study Hydrogels, being stimuli responsive are considered to be effective for targeted and sustained drug delivery. The main purpose for this work was to study the release behavior and kinetic evaluation of Tramadol HCl from chemically cross linked ter polymeric hydrogels. Methods Ter-polymers of methacrylate, vinyl acetate and acrylic acid cross linked with ethylene glycol dimethacrylate (EGDMA were prepared by free radical polymerization. The drug release rates, dynamic swelling behavior and pH sensitivity of hydrogels ranging in composition from 1-10 mol% EGDMA were studied. Tramadol HCl was used as model drug substance. The release behavior was investigated at pH 8 where all formulations exhibited non-Fickian diffusion mechanism. Results and major conclusion Absorbency was found to be more than 99% indicating good drug loading capability of these hydrogels towards the selected drug substance. Formulations designed with increasing amounts of EGDMA had a decreased equilibrium media content as well as media penetrating velocity and thus exhibited a slower drug release rate. Fitting of release data to different kinetic models indicate that the kinetic order shifts from the first to zero order as the concentration of drug was increased in the medium, showing gradual independency of drug release towards its concentration. Formulations with low drug content showed best fitness with Higuchi model whereas those with higher concentration of drug followed Hixson-Crowell model with better correlation values indicating that the drug release from these formulations depends more on change in surface area and diameter of tablets than that on concentration of the drug. Release exponent (n derived from Korse-Meyer Peppas equation implied that the release of Tramadol HCl from these formulations was generally non-Fickian (n > 0.5 > 1 showing swelling controlled mechanism. The mechanical strength and controlled

  14. Fluorinated and Thermo-Cross-Linked Polyhedral Oligomeric Silsesquioxanes: New Organic-Inorganic Hybrid Materials for High-Performance Dielectric Application.

    Science.gov (United States)

    Wang, Jiajia; Sun, Jing; Zhou, Junfeng; Jin, Kaikai; Fang, Qiang

    2017-04-12

    A fluorinated and thermo-cross-linked polyhedral oligomeric silsesquioxane (POSS) has been successfully synthesized by thermal polymerization of a fluorinated POSS monomer having an inorganic silsesquioxane core and organic side chains bearing thermo-cross-linkable trifluorovinyl ether groups. This new inorganic-organic hybrid polymer shows high thermostability with a 5 wt % loss temperature of 436 °C, as well as good transparency (a sheet with an average thickness of 1.5 mm shows high transmittance of 92% varying from 400 to 1100 nm). Moreover, the polymer exhibits both low dielectric constant (polymer also shows low water uptake (polymer is very suitable to be utilized as a high-performance dielectric material for fabrication of high-frequency printed circuit boards or encapsulation resins for integrated circuit dies in the microelectronic industry. Furthermore, this work also provides a route for the preparation of fluorinated POSS-based polymers.

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

    Science.gov (United States)

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

    2008-08-27

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Sarika, P.R. [Department of Chemistry, Indian Institute of Space Science and Technology, Valiamala, Thiruvananthapuram, Kerala 695 547 (India); Cinthya, Kuriakose [Tissue Culture Laboratory, Biomedical Technology Wing, Sree Chitra Tirunal Institute for Medical Sciences and Technology, Poojappura, Thiruvananthapuram, Kerala 695 012 (India); Jayakrishnan, A. [Department of Biotechnology, Indian Institute of Technology Madras, Chennai 600 036 (India); Anilkumar, P.R., E-mail: anilkumarpr@sctimst.ac.in [Tissue Culture Laboratory, Biomedical Technology Wing, Sree Chitra Tirunal Institute for Medical Sciences and Technology, Poojappura, Thiruvananthapuram, Kerala 695 012 (India); James, Nirmala Rachel, E-mail: nirmala@iist.ac.in [Department of Chemistry, Indian Institute of Space Science and Technology, Valiamala, Thiruvananthapuram, Kerala 695 547 (India)

    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. - Highlights: • Gum arabic cross-linked gelatin scaffold was developed for tissue engineering. • Cross-linking was achieved by Schiff's base reaction. • The scaffold is non-cytotoxic and non adherent to fibroblast and hepatocytes. • The scaffolds are potential candidates for spheroid cell culture.

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

    Science.gov (United States)

    Chen, Fan; Nielsen, Simone; Zenobi, Renato

    2013-07-01

    Chemical cross-linking, combined with mass spectrometry, has been applied to map three-dimensional protein structures and protein-protein interactions. Proper choice of the cross-linking agent, including its reactive groups and spacer arm length, is of great importance. However, studies to understand the details of reactivity of the chemical cross-linkers with proteins are quite sparse. In this study, we investigated chemical cross-linking from the aspects of the protein structures and the cross-linking reagents involved, by using two structurally well-known proteins, glyceraldehyde 3-phosohate dehydrogenase and ribonuclease S. Chemical cross-linking reactivity was compared using a series of homo- and hetero-bifunctional cross-linkers, including bis(sulfosuccinimidyl) suberate, dissuccinimidyl suberate, bis(succinimidyl) penta (ethylene glycol), bis(succinimidyl) nona (ethylene glycol), m-maleimidobenzoyl-N-hydroxysulfosuccinimide ester, 2-pyridyldithiol-tetraoxaoctatriacontane-N-hydrosuccinimide and succinimidyl-[(N-maleimidopropionamido)-tetracosaethyleneglycol]ester. The protein structure itself, especially the distances between target amino acid residues, was found to be a determining factor for the cross-linking efficiency. Moreover, the reactive groups of the chemical cross-linker also play an important role; a higher cross-linking reaction efficiency was found for maleimides compared to 2-pyrimidyldithiols. The reaction between maleimides and sulfhydryl groups is more favorable than that between N-hydroxysuccinimide esters and amine groups, although cysteine residues are less abundant in proteins compared to lysine residues. Copyright © 2013 John Wiley & Sons, Ltd.

  18. Novel antimicrobial superporous cross-linked chitosan/pyromellitimide benzoyl thiourea hydrogels.

    Science.gov (United States)

    Mohamed, Nadia A; Abd El-Ghany, Nahed A; Fahmy, Mona M

    2016-01-01

    In this work, chitosan (CS) was cross-linked with different amounts of pyromellitimide benzoyl thiourea moieties. The structure of the cross-linked CS was confirmed by elemental analyses, FTIR and (1)H- NMR spectroscopy. The cross-linking process proceeds via reacting of the amino groups of CS with the isothiocyanate groups of the N,N'-bis [4-(isothiocyanate carbonyl)phenyl] pyromellitimide cross-linker. The amount of the cross-linker was varied with respect to CS to produce four new pyromellitimide benzoyl thiourea cross-linked CS (PIBTU-CS) hydrogels designated as PIBTU-CS-1, PIBTU-CS-2, PIBTU-CS-3, and PIBTU-CS-4 of increasing cross-linking degree percent of 11, 22, 44 and 88%, respectively. The scanning electron microscopy observation indicates the extremely porous structure of the hydrogels. XRD results showed that the crystallinity of CS was decreased upon cross-linking. The four hydrogels exhibit a higher antibacterial activity on Bacillus subtilis and Streptococcus pneumoniae as Gram positive bacteria and against Escherichia coli as Gram negative bacteria and higher antifungal activity on Aspergillus fumigatus, Syncephalastrum racemosum and Geotricum candidum than that of the parent CS as shown from their higher inhibition zone diameters and their lower MIC values. The swell ability of the hydrogel as well as their antimicrobial activity increased with increasing cross-linking density.

  19. Biological Effects of Drug-Free Alginate Beads Cross-Linked by Copper Ions Prepared Using External Ionotropic Gelation.

    Science.gov (United States)

    Pavelková, M; Kubová, K; Vysloužil, J; Kejdušová, M; Vetchý, D; Celer, V; Molinková, D; Lobová, D; Pechová, A; Vysloužil, J; Kulich, P

    2016-08-08

    External ionotropic gelation offers a unique possibility to entrap multivalent ions in a polymer structure. The aim of this experimental study was to prepare new drug-free sodium alginate (ALG) particles cross-linked by Cu(2+) ions and to investigate their technological parameters (particle size, sphericity, surface topology, swelling capacity, copper content, release of Cu(2+) ions, mucoadhesivity) and biological activity (cytotoxicity and efficiency against the most common vaginal pathogens-Herpes simplex, Escherichia coli, Candida albicans) with respect to potential vaginal administration. Beads prepared from NaALG dispersions (3 or 4%) were cross-linked by Cu(2+) ions (0.5 or 1.0 M CuCl2) using external ionotropic gelation. Prepared mucoadhesive beads with particle size over 1000 μm exhibited sufficient sphericity (all ˃0.89) and copper content (214.8-249.07 g/kg), which increased with concentration of polymer and hardening solution. Dissolution behaviour was characterized by extended burst effect, followed by 2 h of copper release. The efficiency of all samples against the most common vaginal pathogens was observed at cytotoxic Cu(2+) concentrations. Anti-HSV activity was demonstrated at a Cu(2+) concentration of 546 mg/L. Antibacterial activity of beads (expressed as minimum inhibition concentration, MIC) was influenced mainly by the rate of Cu(2+) release which was controlled by the extent of swelling capacity. Lower MIC values were found for E. coli in comparison with C. albicans. Sample ALG-3_1.0 exhibited the fastest copper release and was proved to be the most effective against both bacteria. This could be a result of its lower polymer concentration in combination with smaller particle size and thus larger surface area.

  20. Characterization of solid UV cross-linked PEGDA for biological applications

    KAUST Repository

    Castro, David

    2013-10-20

    This paper reports on solid UV cross-linked Poly(ethylene)-glycol-diacrylate (PEGDA) as a material for microfluidic devices for biological applications. We have evaluated biocompatibility of PEGDA through two separate means: 1) by examining cell viability and attachment on cross-linked PEGDA surfaces for cell culture applications, and 2) by determining if cross-linked PEGDA inhibits the polymerase chain reaction (PCR) processes for on-chip PCR. Through these studies a correlation has been found between degree of curing and cell viability, attachment, as well as on PCR outcome.

  1. A genetic anomaly of oriented collagen biosynthesis and cross-linking: Keratoconus.

    Science.gov (United States)

    Bourges, J L; Robert, A M; Robert, L

    2015-02-01

    Oriented collagen biosynthesis is one of the major mechanisms involved in tissue and organ formation during development. Corneal biogenesis is one example. Defects in this process lead to anomalies in tissue structure and function. The transparency of cornea and its achievement are a good example as well as its pathological modifications. Keratoconus is one example of this type of pathologies, involving also inappropriate cross-linking of collagen fibers. Among the tentatives to correct this anomaly, the riboflavin-potentiated UV-cross-linking (CXL) of keratoconus corneas appears clinically satisfactory, although none of the experiments and clinical results published prove effective cross-linking. The published results are reviewed in this article.

  2. Hybrid cross-linked polyaniline-WO3 nanocomposite thin film for NO(x) gas sensing.

    Science.gov (United States)

    Kaushik, Ajeet; Khan, Raju; Gupta, Vinay; Malhotra, B D; Ahmad, Sharif; Singh, S P

    2009-03-01

    Nanocomposite thin film of cross-linked polyaniline [CLPANI, derived from polyaniline and aniline formaldehyde condensate (AFC)] and WO3 has been fabricated using vacuum thermal evaporation technique. X-ray diffraction pattern of as-grown film shows broad reflections of polymer along with mixed reflection of nonhydrated and hydrated WO3 nanoparticles. The scanning electron microscopy studies reveal uniform dispersion of WO3 nanoparticles in CLPANI network. The broadening of the absorption band at 320 nm corresponding to PANI and AFC-WO3 nanocomposite is attributed to cross-linking between the polymeric units. The NO(x) gas sensing characteristics of vacuum deposited CLPANI-WO3 thin film have been studied by measuring the change in resistance with respect to time. The sensor can be operated at room temperature, resulting in extended shelf life of the sensor. The response time and recovery time of the sensor operated at room temperature have been experimentally determined as 30 s and 11 minutes respectively.

  3. Cryo-imaging and modeling of the super molecular structure of cross-linked gelatin and its applications

    Science.gov (United States)

    Marmorat, Clement; Arinstein, Arkadi; Koifman, Naama; Talmon, Yeshayahu; Zussman, Eyal; Rafailovich, Miriam

    The need for naturally derived materials to synthetize bio-compatible scaffolds is growing. In its natural state, gelatin derives its properties from a network of structured, intertwined, triple helical chains. The mechanical properties can be further controlled by additional enzymatic cross-linking. But, in contrast to simple polymer systems, the response to an imposed deformation is then determined by two competing factors, the establishment of the cross-linked mesh vs. the self-assembly of the fibrils into larger and therefore stronger hierarchical structures. Properties deduced from the response functions to measurements; such as rheology or swelling, are then a combination of these two very different factors, hence impossible to model unless more precise knowledge is available regarding the internal structure. We applied cryogenic-temperature scanning electron microscopy (cryo-SEM) to image the networks. Based on these images, a theoretical model was developed, for which we obtained excellent agreement for the mesh size of both networks, and their mechanical properties. We then used these controlled scaffolds, embedding them with fluorescent beads, to image live cells traction forces at stake during cell migration.

  4. Highly stable pyridinium-functionalized cross-linked anion exchange membranes for all vanadium redox flow batteries

    Science.gov (United States)

    Zeng, L.; Zhao, T. S.; Wei, L.; Zeng, Y. K.; Zhang, Z. H.

    2016-11-01

    It has recently been demonstrated that the use of anion exchange membranes (AEMs) in vanadium redox flow batteries (VRFBs) can reduce the migration of vanadium ions through the membrane due to the Donnan exclusion effect among the positively charged functional groups and vanadium ions. However, AEMs are plagued by low chemical stability in harsh chemical environments. Here we propose and fabricate a pyridinium-functionalized cross-linked AEM for VRFBs. The pyridinium-functionalized bromomethylated poly (2,6-dimethyl-1,4-phenylene oxide) exhibits a superior chemical stability as a result of the strengthened internal cross-linking networks and the chemical inertness of the polymer backbone. Therefore, the membrane exhibits littler decay in a harsh environment for 20 days during the course of an ex situ immersion test. A cycling test also demonstrates that the VRFB assembled with the membrane enable to retain 80% of the initial discharge capacity over 537 cycles with a capacity decay rate of 0.037% cycle-1. Meanwhile, the membrane also shows a low vanadium permeability and a reasonably high conductivity in supporting electrolytes. Hence, all the measurements and performance tests reported in this work suggest that the membrane is a promising AEM for redox flow batteries to achieve excellent cycling stability and superior cell performance.

  5. 原位交联杂化型聚合物电解质膜的形成机理、结构模型及其电化学性能%Formation Mechanism, Structure Model and Electrochemical Performance of an In situ Cross Linking Hybrid Polymer Electrolyte Membrane

    Institute of Scientific and Technical Information of China (English)

    梁桂杰; 钟志成; 许杰; 徐卫林; 陈美华; 张增常; 李文联

    2012-01-01

    A Nano-TiO2/poly(citric acid titanium complex-polyethylene glycol)/Lil/l2 crosslinked hybrid polymer electrolyte membrane has been prepared via in-situ polymerization and compositing. Specifically, the method used the synthesized crosslinked network of poly(citric acid titanium complex-polyethylene glycol) containing the Ti(VI) hybrid center as a substrate, the hydrolyzed Nano-TiO2 as fillers and Lil/I2 as conductive ionics. The formation mechanism of the crosslinked hybrid polymer matrix is discussed. A structural model was established with a local density approximation (LDA) method. The influence of Ti(iOPr)4 content on the structure and electrochemical performance of the electrolyte membrane were investigated with Raman spectra, Fourier transform infrared spectra (FTIR), transmission electron microscopy (TEM), and an energy dispersive X-ray analysis (EDXA) technique. It was found that when the Ti(iOPr)4 content was higher than 12% (w), the combined action of Nano-TiO2 particles and the Ti(VI) hybrid center improved not only the room-temperature ionic conductivity (σ), but also the interfacial stability. At 48% (w) Ti(iOPr)4 content, the value of a reached a maximum of 9.72×10~5 S · cm-1 and the interface resistance became stable after 6 d.%合成含有Ti(VI)杂化中心的交联(柠檬酸钛络合体-聚乙二醇)聚酯网络作为基体,水解生成的Nano-TiO2粒子为填料,LiI/I2为导电介质,通过原位聚合复合法制备了Nano-TiO2/(柠檬酸钛络合体-聚乙二醇)/LiI/I2交联杂化型聚合物电解质膜.采用局域密度近似(LDA)法、Raman光谱、傅里叶变换红外(FTIR)光谱、透射电子显微镜(TEM)和能量散射X射线分析(EDXA)探讨了交联杂化聚合物基体的形成机理,并建立了其相应的结构模型.在此基础之上,研究了四异丙氧基钛(Ti(iOPr)4)的含量对Nano-TiO2/(柠檬酸钛络合体-聚乙二醇)/LiI/I2电解质膜的结构及电化学性能的影响.研究表明:当Ti(iOPr)4

  6. Properties of Poly(ethylene glycol) Hydrogels Cross-Linked via Strain-Promoted Alkyne-Azide Cycloaddition (SPAAC).

    Science.gov (United States)

    Hodgson, Sabrina M; Bakaic, Emilia; Stewart, S Alison; Hoare, Todd; Adronov, Alex

    2016-03-14

    A series of poly(ethylene glycol) (PEG) hydrogels was synthesized using strain-promoted alkyne-azide cycloaddition (SPAAC) between PEG chains terminated with either aza-dibenzocyclooctynes or azide functionalities. The gelation process was found to occur rapidly upon mixing the two components in aqueous solution without the need for external stimuli or catalysts, making the system a candidate for use as an injectable hydrogel. The mechanical and rheological properties of these hydrogels were found to be tunable by varying the polymer molecular weight and the number of cross-linking groups per chain. The gelation times of these hydrogels ranged from 10 to 60 s at room temperature. The mass-based swelling ratios varied from 45 to 76 at maximum swelling (relative to the dry state), while the weight percent of polymer in these hydrogels ranged from 1.31 to 2.05%, demonstrating the variations in amount of polymer required to maintain the structural integrity of the gel. Each hydrogel degraded at a different rate in PBS at pH = 7.4, with degradation times ranging from 1 to 35 days. By changing the composition of the two starting components, it was found that the Young's modulus of each hydrogel could be varied from 1 to 18 kPa. Hydrogel incubation with bovine serum albumin showed minimal protein adsorption. Finally, a cell cytotoxicity study of the precursor polymers with 3T3 fibroblasts demonstrated that the azide- and strained alkyne-functionalized PEGs are noncytotoxic.

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

    DEFF Research Database (Denmark)

    Steen, H; Petersen, J; Mann, M

    2001-01-01

    of two different peptide-DNA heteroconjugates was accomplished by matrix-assisted laser desorption/ionization mass spectrometry and allowed assignment of tryptophan-54 and tryptophan-88 as candidate cross-linked residues. Sequencing of those peptide-DNA heteroconjugates by nanoelectrospray quadrupole...

  8. Tissue-specific effects of aldose reductase inhibition on fluorescence and cross-linking of extracellular matrix in chronic galactosemia. Relationship to pentosidine cross-links.

    Science.gov (United States)

    Richard, S; Tamas, C; Sell, D R; Monnier, V M

    1991-08-01

    Chronic experimental hyperglycemia mediated by galactose has been shown to induce browning and cross-linking of rat tail tendon collagen that could be duplicated in vitro by nonenzymatic galactosylation. To investigate the nature of these changes, Sprague-Dawley rats were placed on a 33% galactose diet without and with sorbinil for 6 and 12 mo. Collagen-linked fluorescence and pentosidine cross-links increased with age and galactosemia in tail tendons (P less than 0.001) and skin but were essentially unresponsive to aldose reductase inhibition (ARI). In contrast, tendon breaking time in urea, a likely parameter of cross-linking, was markedly improved (P less than 0.001) by ARI. Fluorescence that was inhibited by sorbinil treatment was increased in pepsin and proteinase K digest of aortic tissue from galactosemic rats (P less than 0.001), but impaired enzymatic digestibility was not observed. Systolic blood pressure as potential consequence of aortic stiffening was not increased in galactosemia. These data suggest that fluorescence in skin and tendon might be in part due to advanced glycosylation and pentosidine formation because these were not decreased by ARI. However, they also suggest that nonfluorescent cross-links may also be forming because, in contrast to fluorescence, tail tendon breaking time was partly corrected by ARI. Thus, it appears that extracellular matrix changes in chronic galactosemia are complex, being partly attributable to advanced glycosylation and partly to polyol-pathway activation.

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

    Science.gov (United States)

    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

  10. An Investigation on Rheology of Peroxide Cross-linking of Low Density Polyethylene

    DEFF Research Database (Denmark)

    Ghasemi, Ismaeil; Rasmussen, Henrik K.; Szabo, Peter

    2005-01-01

    One of the most important post-reactor modifications of polyethylene is cross-linking. It improves some properties of polyethylene such as environmental stress cracking resistance, chemical and abrasion resistance, and service temperature. In this study, the effect of peroxide cross-linking on th......One of the most important post-reactor modifications of polyethylene is cross-linking. It improves some properties of polyethylene such as environmental stress cracking resistance, chemical and abrasion resistance, and service temperature. In this study, the effect of peroxide cross......-linking on the rheological behaviour of low density polyethylene was investigated by using a combination of creep test and differential scanning calorimeter (DSC) in isotherm condition. The used peroxide was di-cumyl peroxide and its concentration was 2 wt%. The experiments were carried out at 150,160, and 170 degrees C...

  11. PROSPECTS OF HIGH-CURRENT ELECTRON BEAMS APPLICATION TO RADIATION POLYETHYLENE CROSS-LINKING

    Directory of Open Access Journals (Sweden)

    A.G. Gurin

    2013-09-01

    Full Text Available A possibility of applying a pulse-periodic high-current induction electron accelerators to radiation polyethylene cross-linking is considered in the article. A comparative analysis with other devices used for irradiation is made.

  12. Riboflavin cross-linking of collagen porous scaffolds for periodontal regeneration

    Directory of Open Access Journals (Sweden)

    Seciu A-M.

    2016-05-01

    Full Text Available Periodontitis treatment using occlusive membranes presented variable efficacy due to their rapid degradation in the complex biologic environment of the damaged periodontium. The aim of this study was to prepare novel composites based on collagen, chondroitin sulfate and fibronectin, and to establish the optimal parameters for their photochemical cross-linking using riboflavin and UV exposure. The degree of cross-linking, biodegradability and density of all scaffold variants were investigated. Their cytotoxicity was evaluated in a culture of gingival fibroblasts by MTT assay and light microscopy. The results indicated that the higher the cross-linking degree, the lower was the scaffold biodegradation. Cell culture studies showed that composite scaffolds were favorable for cellular survival. In conclusion, the cross-linking method using riboflavin and UV exposure resulted in stable and biocompatible collagen-based composite scaffolds that could be used for periodontitis treatment.

  13. Hydrogen peroxide and ferulic acid-mediated oxidative cross-linking ...

    African Journals Online (AJOL)

    STORAGESEVER

    2009-12-15

    Dec 15, 2009 ... Oxidative cross-linked casein mediated by hydrogen peroxide and ferulic acid was prepared at ... functional properties of food proteins treated (Motoki and. Seguro, 1998 ..... Team of Northeast Agricultural University (No.

  14. CrossWork: Software-assisted identification of cross-linked peptides

    DEFF Research Database (Denmark)

    Rasmussen, Morten; Refsgaard, Jan; Peng, Li;

    2011-01-01

    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. Cross...

  15. A Review of Collagen Cross-Linking in Cornea and Sclera

    Directory of Open Access Journals (Sweden)

    Xiao Zhang

    2015-01-01

    Full Text Available Riboflavin/UVA cross-linking is a technique introduced in the past decades for the treatment of keratoconus, keratectasia, and infectious keratitis. Its efficacy and safety have been investigated with clinical and laboratory studies since its first clinical application by Wollensak for the treatment of keratoconus. Although its complications are encountered during clinical practice, such as infection inducing risk, minimal invasion merits a further investigation on its future application in clinical practice. Recently, collagen cross-linking in sclera shows a promising prospect. In present study, we summarized the representative studies describing the clinical and laboratory application of collagen cross-linking published in past decades and provided our opinion on the positive and negative results of cross-linking in the treatment of ophthalmic disorders.

  16. New insights into the pros and cons of cross-linking decellularized bioartificial organs.

    Science.gov (United States)

    Hussein, Kamal H; Park, Kyung-Mee; Lee, Yun-Suk; Woo, Jae-Seok; Kang, Byung-Jae; Choi, Ki-Young; Kang, Kyung-Sun; Woo, Heung-Myong

    2017-01-25

    ABSTRACTDecellularization is an attractive method for scaffold designing in regenerative medicine. The resulting extracellular matrix (ECM) consists of structural proteins such as collagen and elastin, growth factors, and glycosaminoglycans, which can direct site-appropriate remodeling after in vivo implantation. Mainly, collagen and elastin of ECM are exposed to the enzymatic biodegradation in the host. To control the biodegradation process, treatment of decellularized tissue by a cross-linking agent is required. Cross-linking also reduces antigenicity and increases the storage properties. Cross-linkers should be nontoxic, with the ability to preserve the ECM components, especially glycosaminoglycans and associated growth factors for retention of scaffold bioactivity. In this review, we describe the different cross-linking agents and methods of evaluation of cross-linking efficiency.

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

    Science.gov (United States)

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

    2013-06-12

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

  18. Design of cross-linked semicrystalline poly(ε-caprolactone)-based networks with one-way and two-way shape-memory properties through Diels-Alder reactions.

    Science.gov (United States)

    Raquez, Jean-Marie; Vanderstappen, Sophie; Meyer, Franck; Verge, Pierre; Alexandre, Michael; Thomassin, Jean-Michel; Jérôme, Christine; Dubois, Philippe

    2011-08-29

    Cross-linked poly(ε-caprolactone) (PCL)-based polyesterurethane (PUR) systems have been synthesized through Diels-Alder reactions by reactive extrusion. The Diels-Alder and retro-Diels-Alder reactions proved to be useful for enhancing the molecular motion of PCL-based systems, and therefore their crystallization ability, in the design of cross-linked semicrystalline polymers with one-way and two-way shape-memory properties. Successive reactions between α,ω-diol PCL (PCL(2) ), furfuryl alcohol, and methylene diphenyl 4,4'-diisocyanate straightforwardly afforded the α,ω-furfuryl PCL-based PUR systems, and subsequent Diels-Alder reactions with N,N-phenylenedimaleimide afforded the thermoreversible cycloadducts. The cross-linking density could be modulated by partially replacing PCL-diol with PCL-tetraol. Interestingly, the resulting PUR systems proved to be semicrystalline cross-linked polymers, the melting temperature of which (close to 45 °C) represented the switching temperature for their shape-memory properties. Qualitative and quantitative measurements demonstrated that these PUR systems exhibited one-way and two-way shape-memory properties depending on their cross-linking density.

  19. The level of cross-linking and the structure of anisotropic magnetorheological elastomers

    Energy Technology Data Exchange (ETDEWEB)

    Borin, Dmitry, E-mail: dmitry.borin@tu-dresden.de [Institute of Fluid Mechanics, Technische Universitaet Dresden, Dresden 01062 (Germany); Guenther, David [Institute of Fluid Mechanics, Technische Universitaet Dresden, Dresden 01062 (Germany); Hintze, Christian; Heinrich, Gert [Leibniz Institute of Polymer Research, Dresden 01069 (Germany); Odenbach, Stefan [Institute of Fluid Mechanics, Technische Universitaet Dresden, Dresden 01062 (Germany)

    2012-10-15

    The influence of the concentration of the magnetic powder on the level of cross-linking of magnetorheological elastomers (MREs) has been studied. Afterwards the structural characterisation of manufactured MREs has been performed by using non-destructive method, specifically the computed tomography. The correlation between internal structures of MREs and the developing of its cross-linking level during the curing was found. It was shown that changes in the concentration of the powder significantly affect morphologies of the sample.

  20. Novel thermoplastic vulcanizates (TPVs based on silicone rubber and polyamide exploring peroxide cross-linking

    Directory of Open Access Journals (Sweden)

    K. Naskar

    2014-04-01

    Full Text Available Novel thermoplastic vulcanizates (TPVs based on silicone rubber (PDMS and polyamide (PA12 have been prepared by dynamic vulcanization process. The effect of dynamic vulcanization and influence of various types of peroxides as cross-linking agents were studied in detail. All the TPVs were prepared at a ratio of 50/50 wt% of silicone rubber and polyamide. Three structurally different peroxides, namely dicumyl peroxide (DCP, 3,3,5,7,7-pentamethyl 1,2,4-trioxepane (PMTO and cumyl hydroperoxide (CHP were taken for investigation. Though DCP was the best option for curing the silicone rubber, at high temperature it suffers from scorch safety. An inhibitor 2,2,6,6-tetramethylpiperidinyloxyl (TEMPO was added with DCP to stabilize the radicals in order to increase the scorch time. Though CHP (hydroperoxide had higher half life time than DCP at higher temperature, it has no significant effect on cross-linking of silicone rubber. PMTO showed prolonged scorch safety and better cross-linking efficiency rather than the other two. TPVs of DCP and PMTO were made up to 11 minutes of mixing. Increased values of tensile strength and elongation at break of PMTO cross-linked TPV indicate the superiority of PMTO. Scanning electron micrographs correlate with mechanical properties of the TPVs. High storage modulus (E' and lower loss tangent value of the PMTO cross-linked TPV indicate the higher degree of cross-linking which is also well supported by the overall cross-link density value. Thus PMTO was found to be the superior peroxide for cross-linking of silicone rubber at high temperature.

  1. Analysis of glycation induced protein cross-linking inhibitory effects of some antidiabetic plants and spices

    OpenAIRE

    Perera, Handunge Kumudu Irani; Handuwalage, Charith Sandaruwan

    2015-01-01

    Background Protein cross-linking which occurs towards the latter part of protein glycation is implicated in the development of chronic diabetic complications. Glycation induced protein cross-linking inhibitory effects of nine antidiabetic plants and three spices were evaluated in this study using a novel, simple, electrophoresis based method. Methods Methanol extracts of thirteen plants including nine antidiabetic plants and three spices were used. Lysozyme and fructose were incubated at 37 °...

  2. Porphyrin-induced photodynamic cross-linking of hepatic heme-binding proteins.

    Science.gov (United States)

    Vincent, S H; Holeman, B; Cully, B C; Muller-Eberhard, U

    1986-01-27

    Three types of hepatic proteins, a heme-binding Z protein, a mixture of the glutathione S-transferases and a cytochrome P450 isozyme, were shown to be susceptible to photodynamic cross-linking and loss in antigenicity by naturally occurring porphyrins. At 50 microM, uroporphyrin caused the most and protoporphyrin the least photodecomposition. Hemopexin, a specific serum heme carrier, was photodecomposed but no cross-linking was detected. Heme and scavengers of singlet oxygen partially prevented protein photodecomposition.

  3. Aliphatic polycarbonates based on carbon dioxide, furfuryl glycidyl ether, and glycidyl methyl ether: reversible functionalization and cross-linking.

    Science.gov (United States)

    Hilf, Jeannette; Scharfenberg, Markus; Poon, Jeffrey; Moers, Christian; Frey, Holger

    2015-01-01

    Well-defined poly((furfuryl glycidyl ether)-co-(glycidyl methyl ether) carbonate) (P((FGE-co-GME)C)) copolymers with varying furfuryl glycidyl ether (FGE) content in the range of 26% to 100% are prepared directly from CO2 and the respective epoxides in a solvent-free synthesis. All materials are characterized by size-exclusion chromatography (SEC), (1)H NMR spectroscopy, and differential scanning calorimetry (DSC). The furfuryl-functional samples exhibit monomodal molecular weight distributions with Mw/Mn in the range of 1.16 to 1.43 and molecular weights (Mn) between 2300 and 4300 g mol(-1). Thermal properties reflect the amorphous structure of the polymers. Both post-functionalization and cross-linking are performed via Diels-Alder chemistry using maleimide derivatives, leading to reversible network formation. This transformation is shown to be thermally reversible at 110 °C.

  4. Preparation and properties of gel membrane containing porous PVDF-HFP matrix and cross-linked PEG for lithium ion conduction

    Institute of Scientific and Technical Information of China (English)

    Mei ZHANG; Aiqing ZHANG; Zhenyu CUI; Baoku ZHU; Gaigc HAN; Youyi XU

    2008-01-01

    Lithium ion conducting membranes are the key materials for lithium batteries. The lithium ion conducting gel polymer electrolyte membrane (Li-GPEM) based on porous poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) matrix and cross-linked PEG network is pre-pared by a typical phase inversion process. By immersing the porous PVDF-HFP membrane in liquid electrolyte con-taining poly(ethylene glycol) diacrylate (PEGDA) and an initiator to absorb the liquid electrolyte at 25℃, and then thermally cross-linking at 60℃, the Li-GPEM is fabricated successfully. The measurements on its weight loss, mech-anical and electrochemical properties reveal that the obtained Li-GPEM has better overall performance than the liquid and blend gel systems used as conductive media in lithium batteries. The ionic conductivity of the fabricated Li-GPEM can reach as high as 2.25 × 10-3S/cm at 25℃.

  5. Characterization of the receptor for endothelial cell growth factor (ECGF) by affinity cross-linking

    Energy Technology Data Exchange (ETDEWEB)

    Friesel, R.; Burgess, W.H.; Mehlman, T.; Maciag, T.

    1986-05-01

    The authors have demonstrated high affinity receptors for ECGF on endothelial cells by covalent cross-linking of (/sup 125/I)-ECGF with disuccinimidyl suberate and observe a single chain cross-linked polypeptide species with an apparent M/sub r/ of 170K. The M/sub r/ 170K species represents (/sup 125/I)-ECGF bound to its receptor since (i) excess unlabeled ECGF inhibits the cross-linking of (/sup 125/I)-ECGF, (ii) labeling of the M/sub r/170K species does not take place in the absence of cross-linker, (iii) cells previously shown to be refractory to ECGF and lack ECGF receptors do not yield a cross-linked species, (iv) the cross-linked species can be immunoprecipitated with anti-ECGF antibodies, and (v) preincubation of cells with ECGF at 37/sup 0/C significantly reduces cross-linking while incubation at 4/sup 0/C does not. These data demonstrate that ECGF induced cell proliferation occurs through the occupancy of a specific cell surface polypeptide receptor with an apparent M/sub r/ of 150K, and suggests that internalization of the receptor-ligand complex may be relevant to ECGF-induced signal transduction.

  6. Directing the oligomer size distribution of peroxidase-mediated cross-linked bovine alpha-lactalbumin.

    Science.gov (United States)

    Heijnis, Walter H; Wierenga, Peter A; van Berkel, Willem J H; Gruppen, Harry

    2010-05-12

    Enzymatic protein cross-linking is a powerful tool to change protein functionality. For optimal functionality in gel formation, the size of the cross-linked proteins needs to be controlled, prior to heating. In the current study, we addressed the optimization of the horseradish peroxidase-mediated cross-linking of calcium-depleted bovine alpha-lactalbumin. To characterize the formed products, the molecular weight distribution of the cross-linked protein was determined by size exclusion chromatography. At low ionic strength, more dimers of alpha-lactalbumin are formed than at high ionic strength, while the same conversion of monomers is observed. Similarly, at pH 5.9 more higher oligomers are formed than at pH 6.8. This is proposed to be caused by local changes in apo alpha-lactalbumin conformation as indicated by circular dichroism spectroscopy. A gradual supply of hydrogen peroxide improves the yield of cross-linked products and increases the proportion of higher oligomers. In conclusion, this study shows that the size distribution of peroxidase-mediated cross-linked alpha-lactalbumin can be directed toward the protein oligomers desired.

  7. Cross-linking proteins by laccase-catalyzed oxidation: importance relative to other modifications.

    Science.gov (United States)

    Steffensen, Charlotte L; Andersen, Mogens L; Degn, Peter E; Nielsen, Jacob H

    2008-12-24

    Laccase-catalyzed oxidation was able to induce intermolecular cross-links in beta-lactoglobulin, and ferulic acid-mediated laccase-catalyzed oxidation was able to induce intermolecular cross-links in alpha-casein, whereas transglutaminase cross-linked only alpha-casein. In addition, different patterns of laccase-induced oxidative modifications were detected, including dityrosine formation, formation of fluorescent tryptophan oxidation products, and carbonyls derived from histidine, tryptophan, and methionine. Laccase-catalyzed oxidation as well as transglutaminase induced only minor changes in surface tension of the proteins, and the changes could not be correlated to protein cross-linking. The presence of ferulic acid was found to influence the effect of laccase, allowing laccase to form irreducible intermolecular cross-links in beta-lactoglobulin and resulting in proteins exercising higher surface tensions due to cross-linking as well as other oxidative modifications. The outcome of using ferulic acid-mediated laccase-catalyzed oxidation to modify the functional properties of proteinaceous food components or other biosystems is expected to be highly dependent on the protein composition, resulting in different changes of the functional properties.

  8. Smooth muscle cell phenotype modulation and contraction on native and cross-linked polyelectrolyte multilayers.

    Science.gov (United States)

    Moussallem, Maroun D; Olenych, Scott G; Scott, Shannon L; Keller, Thomas C S; Schlenoff, Joseph B

    2009-11-09

    Smooth muscle cells convert between a motile, proliferative "synthetic" phenotype and a sessile, "contractile" phenotype. The ability to manipulate the phenotype of aortic smooth muscle cells with thin biocompatible polyelectrolyte multilayers (PEMUs) with common surface chemical characteristics but varying stiffness was investigated. The stiffness of (PAH/PAA) PEMUs was varied by heating to form covalent amide bond cross-links between the layers. Atomic force microscopy (AFM) showed that cross-linked PEMUs were thinner than those that were not cross-linked. AFM nanoindentation demonstrated that the Young's modulus ranged from 6 MPa for hydrated native PEMUs to more than 8 GPa for maximally cross-linked PEMUs. Rat aortic A7r5 smooth muscle cells cultured on native PEMUs exhibited morphology and motility of synthetic cells and expression of the synthetic phenotype markers vimentin, tropomyosin 4, and nonmuscle myosin heavy chain IIB (nmMHCIIB). In comparison, cells cultured on maximally cross-linked PEMUs exhibited the phenotype markers calponin, smooth muscle myosin heavy chain (smMHC), myocardin, transgelin, and smooth muscle alpha-actin (smActin) that are characteristic of the smooth muscle "contractile" phenotype. Consistent with those cells being "contractile", A7r5 cells grown on cross-linked PEMUs produced contractile force when stimulated with a Ca(2+) ionophore.

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

    Science.gov (United States)

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

    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.

  10. Cross-linked survey analysis is an approach for separating cause and effect in survey research.

    Science.gov (United States)

    Redelmeier, Donald A; Thiruchelvam, Deva; Lustig, Andrew J

    2015-01-01

    We developed a new research approach, called cross-linked survey analysis, to explore how an acute exposure might lead to changes in survey responses. The goal was to identify associations between exposures and outcomes while reducing some ambiguities related to interpreting cause and effect in survey responses from a population-based community questionnaire. Cross-linked survey analysis differs from a cross-sectional, longitudinal, and panel survey analysis by individualizing the timeline to the unique history of each respondent. Cross-linked survey analysis, unlike a repeated-measures self-matching design, does not track changes in a repeated survey question given to the same respondent at multiple time points. Pilot data from three analyses (n = 1,177 respondents) illustrate how a cross-linked survey analysis can control for population shifts, temporal trends, and reverse causality. Accompanying graphs provide an intuitive display to readers, summarize results, and show differences in response distributions. Population-based individual-level linkages also reduce selection bias and increase statistical power compared with a single-center cross-sectional survey. Cross-linked survey analysis has limitations related to unmeasured confounding, pragmatics, survivor bias, statistical models, and the underlying artifacts in survey responses. We suggest that a cross-linked survey analysis may help in epidemiology science using survey data. Copyright © 2015 Elsevier Inc. All rights reserved.

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

    Energy Technology Data Exchange (ETDEWEB)

    Jejurikar, Aparna; Lawrie, Gwen; Groendahl, Lisbeth [School of Chemistry and Molecular Biosciences, University of Queensland, Brisbane, Queensland 4072 (Australia); Martin, Darren, E-mail: l.grondahl@uq.edu.au [Australian Institute for Bioengineering and Nanotechnology, University of Queensland, Brisbane, Queensland 4072 (Australia)

    2011-04-15

    The properties of alginate films modified using two cross-linker ions (Ca{sup 2+} and Ba{sup 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{sup 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{sup 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{sup 2+} cross-linked gels. For the Ca{sup 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{sup 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.

  12. Digestibility of β-lactoglobulin following cross-linking by Trametes versicolor laccase and apple polyphenols

    Directory of Open Access Journals (Sweden)

    DRAGANA STANIĆ-VUČINIĆ

    2011-06-01

    Full Text Available β-Lactoglobulin (BLG is an important nutrient of dairy products and an important allergen in cow’s milk allergy. The aim of this study was to investigate the potential of laccase to cross-link BLG in the presence of an apple phenolic extract (APE and to characterize the obtained products for their digestibility by pepsin and pancreatin. The composition of the apple phenolics used for cross-linking was determined by liquid chromatography–electrospray ionization-mass spectrometry (LC–ESI-MS. The apple phenolic extract contained significant amounts of quercetin glycosides, catechins and chlorogenic acid. The laccase cross-linked BLG in the presence of apple phenolics. The polymerization rendered the protein insoluble in the reaction mixture. Sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS-PAGE analysis of the cross-linking reaction mixture revealed a heterogeneous mixture of high molecular masses (cross-linked BLG, with a fraction of the BLG remaining monomeric. Enzymatic processing of BLG by laccase and apple polyphenols as mediators can decrease the biphasal pepsin–pancreatin digestibility of the monomeric and cross-linked protein, thus decreasing its nutritional value. In addition, reduced BLG digestibility can decrease its allergenic potential. Apple polyphenols can find usage in the creation of new, more functional food products, designed to prevent obesity and hypersensitivity-related disorders.

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

    Science.gov (United States)

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

    2012-06-01

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

  14. A Comparative Study of the Characteristics of Cross-Linked, Oxidized and Dual-Modified Rice Starches

    Directory of Open Access Journals (Sweden)

    Feng-Xiang Yu

    2012-09-01

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

  15. Rapid removal of organic micropollutants from water by a porous β-cyclodextrin polymer

    Science.gov (United States)

    Alsbaiee, Alaaeddin; Smith, Brian J.; Xiao, Leilei; Ling, Yuhan; Helbling, Damian E.; Dichtel, William R.

    2016-01-01

    The global occurrence in water resources of organic micropollutants, such as pesticides and pharmaceuticals, has raised concerns about potential negative effects on aquatic ecosystems and human health. Activated carbons are the most widespread adsorbent materials used to remove organic pollutants from water but they have several deficiencies, including slow pollutant uptake (of the order of hours) and poor removal of many relatively hydrophilic micropollutants. Furthermore, regenerating spent activated carbon is energy intensive (requiring heating to 500-900 degrees Celsius) and does not fully restore performance. Insoluble polymers of β-cyclodextrin, an inexpensive, sustainably produced macrocycle of glucose, are likewise of interest for removing micropollutants from water by means of adsorption. β-cyclodextrin is known to encapsulate pollutants to form well-defined host-guest complexes, but until now cross-linked β-cyclodextrin polymers have had low surface areas and poor removal performance compared to conventional activated carbons. Here we crosslink β-cyclodextrin with rigid aromatic groups, providing a high-surface-area, mesoporous polymer of β-cyclodextrin. It rapidly sequesters a variety of organic micropollutants with adsorption rate constants 15 to 200 times greater than those of activated carbons and non-porous β-cyclodextrin adsorbent materials. In addition, the polymer can be regenerated several times using a mild washing procedure with no loss in performance. Finally, the polymer outperformed a leading activated carbon for the rapid removal of a complex mixture of organic micropollutants at environmentally relevant concentrations. These findings demonstrate the promise of porous cyclodextrin-based polymers for rapid, flow-through water treatment.

  16. Rapid removal of organic micropollutants from water by a porous β-cyclodextrin polymer.

    Science.gov (United States)

    Alsbaiee, Alaaeddin; Smith, Brian J; Xiao, Leilei; Ling, Yuhan; Helbling, Damian E; Dichtel, William R

    2016-01-14

    The global occurrence in water resources of organic micropollutants, such as pesticides and pharmaceuticals, has raised concerns about potential negative effects on aquatic ecosystems and human health. Activated carbons are the most widespread adsorbent materials used to remove organic pollutants from water but they have several deficiencies, including slow pollutant uptake (of the order of hours) and poor removal of many relatively hydrophilic micropollutants. Furthermore, regenerating spent activated carbon is energy intensive (requiring heating to 500-900 degrees Celsius) and does not fully restore performance. Insoluble polymers of β-cyclodextrin, an inexpensive, sustainably produced macrocycle of glucose, are likewise of interest for removing micropollutants from water by means of adsorption. β-cyclodextrin is known to encapsulate pollutants to form well-defined host-guest complexes, but until now cross-linked β-cyclodextrin polymers have had low surface areas and poor removal performance compared to conventional activated carbons. Here we crosslink β-cyclodextrin with rigid aromatic groups, providing a high-surface-area, mesoporous polymer of β-cyclodextrin. It rapidly sequesters a variety of organic micropollutants with adsorption rate constants 15 to 200 times greater than those of activated carbons and non-porous β-cyclodextrin adsorbent materials. In addition, the polymer can be regenerated several times using a mild washing procedure with no loss in performance. Finally, the polymer outperformed a leading activated carbon for the rapid removal of a complex mixture of organic micropollutants at environmentally relevant concentrations. These findings demonstrate the promise of porous cyclodextrin-based polymers for rapid, flow-through water treatment.

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

    Science.gov (United States)

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

    2005-06-01

    The aim of the present study was to compare the biodegradation of differently cross-linked collagen membranes in rats. Five commercially available and three experimental membranes (VN) were included: (1) BioGide (BG) (non-cross-linked porcine type I and III collagens), (2) BioMend (BM), (3) BioMendExtend (BME) (glutaraldehyde cross-linked bovine type I collagen), (4) Ossix (OS) (enzymatic-cross-linked bovine type I collagen), (5) TutoDent (TD) (non-cross-linked bovine type I collagen, and (6-8) VN(1-3) (chemical cross-linked porcine type I and III collagens). Specimens were randomly allocated in unconnected subcutaneous pouches separated surgically on the back of 40 wistar rats, which were divided into five groups (2, 4, 8, 16, and 24 weeks), including eight animals each. After 2, 4, 8, 16, and 24 weeks of healing, the rats were sacrificed and explanted specimens were prepared for histologic and histometric analysis. The following parameters were evaluated: biodegradation over time, vascularization, tissue integration, and foreign body reaction. Highest vascularization and tissue integration was noted for BG followed by BM, BME, and VN(1); TD, VN(2), and VN(3) showed prolongated, while OS exhibited no vascularization. Subsequently, biodegradation of BG, BM, BME and VN(1) was faster than TD, VN(2), and VN(3). OS showed only a minute amount of superficial biodegradation 24 weeks following implantation. Biodegradation of TD, BM, BME, VN(2), and VN(3) was associated with the presence of inflammatory cells. Within the limits of the present study, it was concluded that cross-linking of bovine and porcine-derived collagen types I and III was associated with (i) prolonged biodegradation, (ii) decreased tissue integration and vascularization, and (iii) in case of TD, BM, BME, VN(2), and VN(3) foreign body reactions.

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

    Science.gov (United States)

    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, PUHMWPE particles have reduced osteolytic potential in vivo when compared to virgin UHMWPE.

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

    CERN Document Server

    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...

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

    DEFF Research Database (Denmark)

    Bichara, David A; Malchau, Erik; Sillesen, Nanna H

    2014-01-01

    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

  1. Theory of compact nonporous windscreens for infrasonic measurements.

    Science.gov (United States)

    Zuckerwar, Allan J

    2010-06-01

    The principle of the compact nonporous windscreen is based on the great penetrability of infrasound through matter. The windscreen performance is characterized by the ratio of the sound pressure at an interior microphone, located in the center of a windscreen, to the incident sound pressure in the free field. The frequency dependence of this pressure ratio is derived as a function of the windscreen material and geometric properties. Four different windscreen geometries are considered: a subsurface, box-shaped windscreen, a cylindrical windscreen of infinite length, a cylindrical windscreen of finite length, and a spherical windscreen. Results are presented for windscreens made of closed-cell polyurethane foam and for typical dimensions of each of the above geometries. The cylindrical windscreen of finite length, featuring evanescent radial modes, behaves as a unity-gain, low-pass filter, cutting off sharply at the end of the infrasonic range. The remaining geometries reveal a pass band that extends well into the audio range, terminated by a pronounced peak beyond which the response plummets rapidly.

  2. Sticking of molecules on non-porous amorphous water ice

    CERN Document Server

    He, Jiao; Vidali, Gianfranco

    2016-01-01

    Accurate modeling of physical and chemical processes in the interstellar medium requires detailed knowledge of how atoms and molecule adsorb on dust grains. However, the sticking coefficient, a number between 0 and 1 that measures the first step in the interaction of a particle with a surface, is usually assumed in simulations of ISM environments to be either 0.5 or 1. Here we report on the determination of the sticking coefficient of H$_2$, D$_2$, N$_2$, O$_2$, CO, CH$_4$, and CO$_2$ on non-porous amorphous solid water (np-ASW). The sticking coefficient was measured over a wide range of surface temperatures using a highly collimated molecular beam. We showed that the standard way of measuring the sticking coefficient --- the King-Wells method --- leads to the underestimation of trapping events in which there is incomplete energy accommodation of the molecule on the surface. Surface scattering experiments with the use of a pulsed molecular beam are used instead to measure the sticking coefficient. Based on th...

  3. Preparation of cross-linked hen-egg white lysozyme crystals free of cracks

    Science.gov (United States)

    Yan, Er-Kai; Lu, Qin-Qin; Zhang, Chen-Yan; Liu, Ya-Li; He, Jin; Chen, Da; Wang, Bo; Zhou, Ren-Bin; Wu, Ping; Yin, Da-Chuan

    2016-01-01

    Cross-linked protein crystals (CLPCs) are very useful materials in applications such as biosensors, catalysis, and X-ray crystallography. Hence, preparation of CLPCs is an important research direction. During the preparation of CLPCs, an often encountered problem is that cracks may appear in the crystals, which may finally lead to shattering of the crystals into small pieces and cause problem in practical applications. To avoid cross-link induced cracking, it is necessary to study the cracking phenomenon in the preparation process. In this paper, we present an investigation on how to avoid cracking during preparation of CLPCs. An orthogonal experiment was designed to study the phenomenon of cross-link induced cracking of hen-egg white lysozyme (HEWL) crystals against five parameters (temperature, solution pH, crystal growth time, glutaraldehyde concentration, and cross-linking time). The experimental results showed that, the solution pH and crystal growth time can significantly affect cross-link induced cracking. The possible mechanism was studied, and optimized conditions for obtaining crack-free CLPCs were obtained and experimentally verified. PMID:27703210

  4. Supercritical CO2 Foaming of Radiation Cross-Linked Isotactic Polypropylene in the Presence of TAIC

    Directory of Open Access Journals (Sweden)

    Chen-Guang Yang

    2016-12-01

    Full Text Available Since the maximum foaming temperature window is only about 4 °C for supercritical CO2 (scCO2 foaming of pristine polypropylene, it is important to raise the melt strength of polypropylene in order to more easily achieve scCO2 foaming. In this work, radiation cross-linked isotactic polypropylene, assisted by the addition of a polyfunctional monomer (triallylisocyanurate, TAIC, was employed in the scCO2 foaming process in order to understand the benefits of radiation cross-linking. Due to significantly enhanced melt strength and the decreased degree of crystallinity caused by cross-linking, the scCO2 foaming behavior of polypropylene was dramatically changed. The cell size distribution, cell diameter, cell density, volume expansion ratio, and foaming rate of radiation-cross-linked polypropylene under different foaming conditions were analyzed and compared. It was found that radiation cross-linking favors the foamability and formation of well-defined cell structures. The optimal absorbed dose with the addition of 2 wt % TAIC was 30 kGy. Additionally, the foaming temperature window was expanded to about 8 °C, making the handling of scCO2 foaming of isotactic polypropylene much easier.

  5. Incorporation of Decanethiol-Passivated Gold Nanoparticles into Cross-Linked Poly(Dimethylsiloxane Films

    Directory of Open Access Journals (Sweden)

    Motohiro Tagaya

    2011-01-01

    Full Text Available Cross-linking degree of a poly(dimethylsiloxane (PDMS film was controlled, and the incorporation of hydrophobic decanethiol-passivated gold (Au nanoparticles into the film was investigated. FT-IR spectra indicated that the hydrosilylation reaction between a vinyl group and a hydrosilyl group occurred with the cross-linking. The swelling degree of the film in toluene changed with a cross-linker concentration, indicating the control of the cross-linking degree of PDMS film. By EDX analysis, the amount of incorporated Au nanoparticles increased with decreasing a cross-linker concentration, indicating the enlarged free volume of the film. The Au nanoparticle-PDMS composite film containing a cross-linker at 6 wt% showed brown color attributed to plasmon resonance of Au nanoparticles, suggesting the Au nanoparticles in the film at monodispersion state. The UV-visible absorbance of the composite film decreased without spectralshift by swelling with toluene, and the changes were reversible. The aggregation among Au nanoparticles in the composite film after calcination also depended on the cross-linking degree. Thus, the control of cross-linking degree of PDMS film successfully leaded to a simple way of fabricating the Au nanoparticle-PDMS composite film at the mono-dispersion state.

  6. Mapping of the dimer interface of the Escherichia coli mannitol permease by cysteine cross-linking.

    Science.gov (United States)

    van Montfort, Bart A; Schuurman-Wolters, Gea K; Wind, Joyce; Broos, Jaap; Robillard, George T; Poolman, Bert

    2002-04-26

    A cysteine cross-linking approach was used to identify residues at the dimer interface of the Escherichia coli mannitol permease. This transport protein comprises two cytoplasmic domains and one membrane-embedded C domain per monomer, of which the latter provides the dimer contacts. A series of single-cysteine His-tagged C domains present in the native membrane were subjected to Cu(II)-(1,10-phenanthroline)(3)-catalyzed disulfide formation or cysteine cross-linking with dimaleimides of different length. The engineered cysteines were at the borders of the predicted membrane-spanning alpha-helices. Two residues were found to be located in close proximity of each other and capable of forming a disulfide, while four other locations formed cross-links with the longer dimaleimides. Solubilization of the membranes did only influence the cross-linking behavior at one position (Cys(73)). Mannitol binding only effected the cross-linking of a cysteine at the border of the third transmembrane helix (Cys(134)), indicating that substrate binding does not lead to large rearrangements in the helix packing or to dissociation of the dimer. Upon mannitol binding, the Cys(134) becomes more exposed but the residue is no longer capable of forming a stable disulfide in the dimeric IIC domain. In combination with the recently obtained projection structure of the IIC domain in two-dimensional crystals, a first proposal is made for alpha-helix packing in the mannitol permease.

  7. Effects of partial hydrolysis and subsequent cross-linking on wheat gluten physicochemical properties and structure.

    Science.gov (United States)

    Wang, Kaiqiang; Luo, Shuizhong; Cai, Jing; Sun, Qiaoqiao; Zhao, Yanyan; Zhong, Xiyang; Jiang, Shaotong; Zheng, Zhi

    2016-04-15

    The rheological behavior and thermal properties of wheat gluten following partial hydrolysis using Alcalase and subsequent microbial transglutaminase (MTGase) cross-linking were investigated. The wheat gluten storage modulus (G') and thermal denaturation temperature (Tg) were significantly increased from 2.26 kPa and 54.43°C to 7.76 kPa and 57.69°C, respectively, by the combined action of partial hydrolysis (DH 0.187%) and cross-linking. The free SH content, surface hydrophobicity, and secondary structure analysis suggested that an appropriate degree of Alcalase-based hydrolysis allowed the compact wheat gluten structure to unfold, increasing the β-sheet content and surface hydrophobicity. This improved its molecular flexibility and exposed additional glutamine sites for MTGase cross-linking. SEM images showed that a compact 3D network formed, while SDS-PAGE profiles revealed that excessive hydrolysis resulted in high-molecular-weight subunits degrading to smaller peptides, unsuitable for cross-linking. It was also demonstrated that the combination of Alcalase-based partial hydrolysis with MTGase cross-linking might be an effective method for modifying wheat gluten rheological behavior and thermal properties.

  8. Site specificity of psoralen-DNA interstrand cross-linking determined by nuclease Bal31 digestion

    DEFF Research Database (Denmark)

    Zhen, W P; Buchardt, O; Nielsen, Henrik

    1986-01-01

    A novel method for determination of psoralen photo-cross-linking sites in double-stranded DNA is described, which is based on a pronounced inhibition of Bal31 exonuclease activity by psoralen-DNA interstrand cross-links. The results using a 51 base pair fragment of plasmid pUC19 and a 346 base pair...... fragment of pBR322 show that 5'-TA sequences are preferred cross-linking sites compared to 3'-TA sequences. They also indicate that sequences flanking the 5'-TA site influence the cross-linking efficiency at the site. The DNA photo-cross-linking by 4,5',8-trimethylpsoralen and 8-methoxypsoralen...... was analyzed, and these two psoralens showed identical site specificity. The 5'-TA preference is rationalized on the basis of the local DNA structure in terms of the pi-pi electronic interaction between the thymines and the intercalated psoralens, as well as on the base tilt angles of the DNA....

  9. A General Method for Targeted Quantitative Cross-Linking Mass Spectrometry

    Science.gov (United States)

    Chavez, Juan D.; Eng, Jimmy K.; Schweppe, Devin K.; Cilia, Michelle; Rivera, Keith; Zhong, Xuefei; Wu, Xia; Allen, Terrence; Khurgel, Moshe; Kumar, Akhilesh; Lampropoulos, Athanasios; Larsson, Mårten; Maity, Shuvadeep; Morozov, Yaroslav; Pathmasiri, Wimal; Perez-Neut, Mathew; Pineyro-Ruiz, Coriness; Polina, Elizabeth; Post, Stephanie; Rider, Mark; Tokmina-Roszyk, Dorota; Tyson, Katherine; Vieira Parrine Sant'Ana, Debora; Bruce, James E.

    2016-01-01

    Chemical cross-linking mass spectrometry (XL-MS) provides protein structural information by identifying covalently linked proximal amino acid residues on protein surfaces. The information gained by this technique is complementary to other structural biology methods such as x-ray crystallography, NMR and cryo-electron microscopy[1]. The extension of traditional quantitative proteomics methods with chemical cross-linking can provide information on the structural dynamics of protein structures and protein complexes. The identification and quantitation of cross-linked peptides remains challenging for the general community, requiring specialized expertise ultimately limiting more widespread adoption of the technique. We describe a general method for targeted quantitative mass spectrometric analysis of cross-linked peptide pairs. We report the adaptation of the widely used, open source software package Skyline, for the analysis of quantitative XL-MS data as a means for data analysis and sharing of methods. We demonstrate the utility and robustness of the method with a cross-laboratory study and present data that is supported by and validates previously published data on quantified cross-linked peptide pairs. This advance provides an easy to use resource so that any lab with access to a LC-MS system capable of performing targeted quantitative analysis can quickly and accurately measure dynamic changes in protein structure and protein interactions. PMID:27997545

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

    Science.gov (United States)

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

    2014-09-01

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

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

    Directory of Open Access Journals (Sweden)

    Long-Biao Guo

    2013-05-01

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

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

    Science.gov (United States)

    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.

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

    Science.gov (United States)

    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.

  14. Novel Technique of Transepithelial Corneal Cross-Linking Using Iontophoresis in Progressive Keratoconus

    Science.gov (United States)

    Raffa, Paolo; Rosati, Marianna

    2016-01-01

    In this work, the authors presented the techniques and the preliminary results at 6 months of a randomized controlled trial (NCT02117999) comparing a novel transepithelial corneal cross-linking protocol using iontophoresis with the Dresden protocol for the treatment of progressive keratoconus. At 6 months, there was a significant average improvement with an average flattening of the maximum simulated keratometry reading of 0.72 ± 1.20 D (P = 0.01); in addition, corrected distance visual acuity improved significantly (P = 0.08) and spherical equivalent refraction was significantly less myopic (P = 0.02) 6 months after transepithelial corneal cross-linking with iontophoresis. The novel protocol using iontophoresis showed comparable results with standard corneal cross-linking to halt progression of keratoconus during 6-month follow-up. Investigation of the long-term RCT outcomes are ongoing to verify the efficacy of this transepithelial corneal cross-linking protocol and to determine if it may be comparable with standard corneal cross-linking in the management of progressive keratoconus. PMID:27597895

  15. Novel Technique of Transepithelial Corneal Cross-Linking Using Iontophoresis in Progressive Keratoconus

    Directory of Open Access Journals (Sweden)

    Marco Lombardo

    2016-01-01

    Full Text Available In this work, the authors presented the techniques and the preliminary results at 6 months of a randomized controlled trial (NCT02117999 comparing a novel transepithelial corneal cross-linking protocol using iontophoresis with the Dresden protocol for the treatment of progressive keratoconus. At 6 months, there was a significant average improvement with an average flattening of the maximum simulated keratometry reading of 0.72±1.20 D (P=0.01; in addition, corrected distance visual acuity improved significantly (P=0.08 and spherical equivalent refraction was significantly less myopic (P=0.02 6 months after transepithelial corneal cross-linking with iontophoresis. The novel protocol using iontophoresis showed comparable results with standard corneal cross-linking to halt progression of keratoconus during 6-month follow-up. Investigation of the long-term RCT outcomes are ongoing to verify the efficacy of this transepithelial corneal cross-linking protocol and to determine if it may be comparable with standard corneal cross-linking in the management of progressive keratoconus.

  16. DNA interstrand cross-link induced by estrogens as well as their complete and synergic carcinogenesis

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    The estrogens show negative activity in Ames test, but estrodiol and diethylstilbestrol in estrogens both are carcinogens based upon animal experiments and epidemiological investigation. It is concluded from the di-region theory, a mechanism conception put forward by one of the present authors, that the carcinogenesis of estrogens is switched on by the covalent cross-link between complementary DNA bases induced by them. We verified for the first time by the DNA alkaline elution method that both estrodiol and diethylstilbestrol cause covalent cross-link between DNA-protein and DNA interstrands after metabolic activation with dosage correlation, but neither the non-carcinogens cholesterol nor pyrene can lead to these sorts of cross-link in the same condition. It has been known that there is a synergetic effect between estrogen and pollution of polycyclic aromatic hydrocarbons. Although non-carcinogenic pyrene alone cannot induce cross-link, its addition with equal molar quantity to estrodiol culture causes synergically the total and DNA interstrand cross-link ratios to be respectively four and three times more than the ones in the cultivation with estrodiol only. It is shown that not only the estrodiol set off the formation of pyrene bi-radicals, but also the pyrene radicals arouse conversely the production of estrodiol bi-radicals.

  17. Constructing Cross-Linked Polymer Networks Using Monte Carlo Simulated Annealing Technique for Atomistic Molecular Simulations

    Science.gov (United States)

    2014-10-01

    of these networks, the specific volume and the coefficient of volumetric thermal expansion (CVTE), are shown in Fig. 4. Specific volume is...CVTE values are somewhat lower than expected from experimental measurements of the coefficient of linear thermal expansion ,27 which can be...coefficient of volumetric thermal expansion db equilibrium bond length DCPD dicyclopentadiene GAFF general AMBER force field ID identification K

  18. Synthesis and properties of cross-linked polymers from epoxidized rubber seed oil and triethylenetetramine

    NARCIS (Netherlands)

    Abduh, Muhammad Yusuf; Iqbal, Muhammad; Picchioni, Francesco; Manurung, Robert; Heeres, Hero J.

    2015-01-01

    A series of epoxidized oils were prepared from rubber seed, soybean, jatropha, palm, and coconut oils. The epoxy content varied from 0.03 to 7.4 wt %, in accordance with the degree of unsaturation of the oils (lowest for coconut, highest for rubber seed oil). Bulk polymerization/curing of the epoxid

  19. Synthesis and Characterization of Chemically Cross-Linked Acrylic Acid/Gelatin Hydrogels: Effect of pH and Composition on Swelling and Drug Release

    Directory of Open Access Journals (Sweden)

    Syed Majid Hanif Bukhari

    2015-01-01

    Full Text Available This present work was aimed at synthesizing pH-sensitive cross-linked AA/Gelatin hydrogels by free radical polymerization. Ammonium persulfate and ethylene glycol dimethacrylate (EGDMA were used as initiator and as cross-linking agent, respectively. Different feed ratios of acrylic acid, gelatin, and EGDMA were used to investigate the effect of monomer, polymer, and degree of cross-linking on swelling and release pattern of the model drug. The swelling behavior of the hydrogel samples was studied in 0.05 M USP phosphate buffer solutions of various pH values pH 1.2, pH 5.5, pH 6.5, and pH 7.5. The prepared samples were evaluated for porosity and sol-gel fraction analysis. Pheniramine maleate used for allergy treatment was loaded as model drug in selected samples. The release study of the drug was investigated in 0.05 M USP phosphate buffer of varying pH values (1.2, 5.5, and 7.5 for 12 hrs. The release data was fitted to various kinetic models to study the release mechanism. Hydrogels were characterized by Fourier transformed infrared (FTIR spectroscopy which confirmed formation of structure. Surface morphology of unloaded and loaded samples was studied by surface electron microscopy (SEM, which confirmed the distribution of model drug in the gel network.

  20. Synthesis of cross-linked magnetic composite microspheres containing carboxyl groups

    Institute of Scientific and Technical Information of China (English)

    Jili ZHAO; Zhaorang HAN; Qiang SONG; Ying WANG; Dan SUN

    2008-01-01

    Fe3O4 magnetic nano-particles were prepared by a co-precipitation method and were modified using oleic acid. Then, the cross-linked magnetic composite microspheres containing a carboxyl group were prepared by using an improved emulsion polymerization with divinylbenzene (DVB) as the cross-linking agent. The composite microspheres comprised the Fe3O4 magnetic nano-partictes as cores and the copolymer of styrene and acrylic acid as shells. The morphology and structure of the composite microsphere were characterized by FT-IR, transmission electron microscopy (TEM), X-ray diffrac-tion (XRD), X-ray photoelectron spectrum (XPS) and so on. The results show that the composite microspheres were well dispersed in emulsion with uniform sizes and carboxyl groups on their surface. They were cross-linked and stable in 1 mol/L of HCl and DMF.

  1. Genipin Cross-Linked Polymeric Alginate-Chitosan Microcapsules for Oral Delivery: In-Vitro Analysis

    Directory of Open Access Journals (Sweden)

    Hongmei Chen

    2009-01-01

    Full Text Available We have previously reported the preparation of the genipin cross-linked alginate-chitosan (GCAC microcapsules composed of an alginate core with a genipin cross-linked chitosan membrane. This paper is the further investigation on their structural and physical characteristics. Results showed that the GCAC microcapsules had a smooth and dense surface and a networked interior. Cross-linking by genipin substantially reduced swelling and physical disintegration of microcapsules induced by nongelling ions and calcium sequestrants. Strong resistance to mechanical shear forces and enzymatic degradation was observed. Furthermore, the GCAC membranes were permeable to bovine serum albumin and maintained a molecular weight cutoff at 70 KD, analogous to the widely studied alginate-chitosan, and alginate-poly-L-lysine-alginate microcapsules. The release features and the tolerance of the GCAC microcapsules in the stimulated gastrointestinal environment were also investigated. This GCAC microcapsule formulation offers significant potential as a delivery vehicle for many biomedical applications.

  2. Cross-linked PAN-based thin-film composite membranes for non-aqueous nanofiltration

    KAUST Repository

    Pérez-Manríquez, Liliana

    2015-01-01

    A new approach on the development of cross-linked PAN based thin film composite (TFC) membranes for non-aqueous application is presented in this work. Polypropylene backed neat PAN membranes fabricated by phase inversion process were cross-linked with hydrazine to get excellent solvent stability toward dimethylformamide (DMF). By interfacial polymerization a selective polyamide active layer was coated over the cross-linked PAN using N,N′-diamino piperazine (DAP) and trimesoyl chloride (TMC) as monomers. Permeation and molecular weight cut off (MWCO) experiments using various dyes were done to evaluate the performance of the membranes. Membranes developed by such method show excellent solvent stability toward DMF with a permeance of 1.7 L/m2 h bar and a molecular weight cut-off of less than 600 Da.

  3. Light-triggered cross-linking of alginates with caged Ca2+.

    Science.gov (United States)

    Cui, Jiaxi; Wang, Miao; Zheng, Yijun; Rodríguez Muñiz, Gemma Maria; del Campo, Aránzazu

    2013-05-13

    A strategy to light-trigger ionic cross-linking of alginates by incorporating a photosensitive Ca2+ cage (nitr-T) is presented. Upon irradiation, free Ca2+ was released, and this caused gelation of the alginate solution. Addition of Ca2+ "on-demand" allowed us to obtain homogeneous alginate (ALG) gels using concentrated initial ALG solutions (10%), not possible with other ionic gelation approaches. The cross-linking degree and derived mechanical properties of the hydrogel were modulated by the exposure dose. The light-mediated cross-linked alginate hydrogel displayed a significant improvement in the mechanical properties and homogeneity when compared to mixtures of alginate and soluble Ca2+ at comparable concentrations.

  4. Effect of cross-linking degree on selected properties of retrograded starch adipate.

    Science.gov (United States)

    Kapelko, M; Zięba, T; Michalski, A; Gryszkin, A

    2015-01-15

    The aim of this study was to determine the effects of the concentration of paste used to produce retrograded starch, and esterification degree, on selected properties of the resultant distarch adipate. Starch paste was prepared from native potato starch (1, 4, 10, 18 or 30 g/100g), frozen, defrosted and dried. Thus produced preparations of retrograded starch were cross-linked with various doses of a cross-linking agent (0.125, 0.25, 0.5, 1.0 or 2.0 ml per 100g of starch). Properties of the produced adipates depended on both the concentration of paste used to produce retrograded starch and the degree of substitution with adipic acid residues. Solubility in water and swelling power of the cross-linked preparations of retrograded starch, as well as pasting temperature and viscosity of produced pastes, all decreased along with the increasing degree of substitution with adipic acid residues.

  5. Cheese whey protein recovery by ultrafiltration through transglutaminase (TG) catalysis whey protein cross-linking.

    Science.gov (United States)

    Wen-Qiong, Wang; Lan-Wei, Zhang; Xue, Han; Yi, Lu

    2017-01-15

    In whey ultrafiltration (UF) production, two main problems are whey protein recovery and membrane fouling. In this study, membrane coupling protein transglutaminase (TG) catalysis protein cross-linking was investigated under different conditions to find out the best treatment. We found that the optimal conditions for protein recovery involved catalyzing whey protein cross-linking with TG (40U/g whey proteins) at 40°C for 60min at pH 5.0. Under these conditions, the recovery rate was increased 15-20%, lactose rejection rate was decreased by 10%, and relative permeate flux was increase 30-40% compared to the sample without enzyme treatment (control). It was noticeable that the total resistance and cake resistance were decreased after enzyme catalysis. This was mainly due to the increased particle size and decreased zeta potential. Therefore, membrane coupling enzyme catalysis protein cross-linking is a potential means for further use.

  6. Solution processed organic light-emitting diodes using the plasma cross-linking technology

    Science.gov (United States)

    He, Kongduo; Liu, Yang; Gong, Junyi; Zeng, Pan; Kong, Xun; Yang, Xilu; Yang, Cheng; Yu, Yan; Liang, Rongqing; Ou, Qiongrong

    2016-09-01

    Solution processed multilayer organic light-emitting diodes (OLEDs) present challenges, especially regarding dissolution of the first layer during deposition of a second layer. In this work, we first demonstrated a plasma cross-linking technology to produce a solution processed OLED. The surfaces of organic films can be cross-linked after mixed acetylene and Ar plasma treatment for several tens of seconds and resist corrosion of organic solvent. The film thickness and surface morphology of emissive layers (EMLs) with plasma treatment and subsequently spin-rinsed with chlorobenzene are nearly unchanged. The solution processed triple-layer OLED is successfully fabricated and the current efficiency increases 50% than that of the double-layer OLED. Fluorescent characteristics of EMLs are also observed to investigate factors influencing the efficiency of the triple-layer OLED. Plasma cross-linking technology may open up a new pathway towards fabrication of all-solution processed multilayer OLEDs and other soft electronic devices.

  7. Improvement on Physical Properties of Pullulan Films by Novel Cross-Linking Strategy.

    Science.gov (United States)

    Chen, Chieh-Ting; Chen, Kuan-I; Chiang, Hsin-Han; Chen, Yu-Kuo; Cheng, Kuan-Chen

    2017-01-01

    Pullulan based films possess several advantages, including high transparency, low toxicity, good biodegradability, good mechanical properties, and low oxygen permeability, are preferable for food packaging. The application of pullulan films on food packaging, however, has inherent disadvantage of high water solubility. In this study, glutaraldehyde and glycerol were used as the cross-linking reagent and the plasticizer respectively to improve water resistance and physical properties of the pullulan films. Effects of cross-linking degree on physical properties, including water absorptions, swelling behaviors, water vapor permeability and tensile strengths of films were evaluated. FTIR results demonstrated that the pullulan films were successfully cross-linked by glutaraldehyde. The tensile strength of pullulan films could be enhanced significantly (P glycerol as a plasticizer enhanced the extensibility of films as well as the hydrophilicity, resulting in higher water vapor permeability.

  8. Study on Chemical Cross-linking Modification of Hyaluronan and the Biocompatibility of its Derivatives

    Institute of Scientific and Technical Information of China (English)

    HU Guo-ying; LIU Xin; GU Han-qing

    2006-01-01

    Objective: Prepare cross-linked HA gels with higher mechanical stability,lower degradation velocity and desirable biocompatibility,so as to extend the usage of HA.Method: 1.Test molecular weight of HA (MrHA) by viscosimetry;2.Prepare cross-linked HA gels by DVS,GTA,DEC;3.Discuss the cross-linking and degradation procedure;4,evaluate the biocompatibility of the best HA gels.Results: The mechanical stability and durability to degradation of HA-DVS gels are superior to those of other gels,and when HA :DVS = 40:1 (g/g),at 35℃ and in 0.2M NaOH solution,the HA-DVS gel shows the best mechanical stability,and its cytotoxicity reaches class I,hemolysis ratio is lower than 5 %.Conclusion:Our HADVS gel can be used to prepare biologic scaffolds.

  9. Chloroacetamide-Linked Nucleotides and DNA for Cross-Linking with Peptides and Proteins.

    Science.gov (United States)

    Olszewska, Agata; Pohl, Radek; Brázdová, Marie; Fojta, Miroslav; Hocek, Michal

    2016-09-21

    Nucleotides, 2'-deoxyribonucleoside triphosphates (dNTPs), and DNA probes bearing reactive chloroacetamido group linked to nucleobase (cytosine or 7-deazadaenine) through a propargyl tether were prepared and tested in cross-linking with cysteine- or histidine-containing peptides and proteins. The chloroacetamide-modifed dNTPs proved to be good substrates for DNA polymerases in the enzymatic synthesis of modified DNA probes. Modified nucleotides and DNA reacted efficiently with cysteine and cysteine-containing peptides, whereas the reaction with histidine was sluggish and low yielding. The modified DNA efficiently cross-linked with p53 protein through alkylation of cysteine and showed potential for cross-linking with histidine (in C277H mutant of p53).

  10. Comparison of Wear and Oxidation in Retrieved Conventional and Highly Cross-Linked UHMWPE Tibial Inserts.

    Science.gov (United States)

    Currier, Barbara H; Currier, John H; Franklin, Katherine J; Mayor, Michael B; Reinitz, Steven D; Van Citters, Douglas W

    2015-12-01

    Two groups of retrieved tibial inserts from one manufacturer's knee system were analyzed to evaluate the effect of a highly cross-linked bearing surface on wear and in vivo oxidation. The two groups ((1) conventional gamma-inert sterilized and (2) highly cross-linked, coupled with the same rough (Ra=0.25) Ti-6Al-4V tray) were matched with statistically similar in vivo duration and patient variables. The retrieved inserts were analyzed for ketone oxidation and wear in the form of dimensional change. The difference in oxidation rate between highly cross-linked and conventional gamma-inert sterilized inserts did not reach statistical significance. Observations suggest that the majority of wear can be accounted for by the backside interface with the rough Ti-6Al-4V tray; however, wear measured by thickness-change rate was statistically indistinguishable between the two bearing materials.

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

    Energy Technology Data Exchange (ETDEWEB)

    Mathapati, Santosh; Bishi, Dillip Kumar [Stem Cell and Molecular Biology Laboratory, Department of Biotechnology, Indian Institute of Technology Madras, Chennai (India); Frontier Lifeline Pvt Ltd. and Dr. K. M. Cherian Heart Foundation, Mogappair, Chennai (India); Healthcare and Energy Materials Laboratory, NUSNNI, Faculty of Engineering, National University of Singapore (Singapore); Guhathakurta, Soma [Departmet of Engineering Design, Indian Institute of Technology Madras, Chennai (India); Cherian, Kotturathu Mammen [Frontier Lifeline Pvt Ltd. and Dr. K. M. Cherian Heart Foundation, Mogappair, Chennai (India); Venugopal, Jayarama Reddy; Ramakrishna, Seeram [Healthcare and Energy Materials Laboratory, NUSNNI, Faculty of Engineering, National University of Singapore (Singapore); Verma, Rama Shanker, E-mail: vermars@iitm.ac.in [Stem Cell and Molecular Biology Laboratory, Department of Biotechnology, Indian Institute of Technology Madras, Chennai (India)

    2013-04-01

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

  12. Solvent Composition is Critical for Carbodiimide Cross-Linking of Hyaluronic Acid as an Ophthalmic Biomaterial

    Directory of Open Access Journals (Sweden)

    Jui-Yang Lai

    2012-10-01

    Full Text Available Hyaluronic acid (HA is one of the most important ophthalmic biomaterials, while also being used for tissue engineering and drug delivery. Although chemical cross-linking is an effective way to improve the material performance, it may as a consequence be detrimental to the living cells/tissues. Given that the cross-linking efficiency is mediated by the solvent composition during the chemical modification, this study aims to explore the stability and biocompatibility of carbodiimide cross-linked HA in relation to material processing conditions by varying the acetone/water volume ratio (from 70:30 to 95:5 at a constant 1-ethyl-3-(3-dimethyl aminopropyl carbodiimide (EDC concentration of 100 mM. Our results indicated that after the EDC treatment in the presence of an acetone/water mixture (85:15, v/v, the HA hydrogel membranes have the lowest equilibrium water content, the highest stress at break and the greatest resistance to hyaluronidase digestion. Live/Dead assays and pro-inflammatory cytokine expression analyses showed that the cross-linked HA hydrogel membranes, irrespective of the solvent composition, are compatible with human RPE cell lines without causing toxicity and inflammation. However, it should be noted that the test samples prepared by the cross-linking in the presence of acetone/water mixtures containing 70, 75, and 95 vol % of acetone slightly inhibit the metabolic activity of viable ARPE-19 cultures, probably due to the alteration in the ionic interaction between the medium nutrients and polysaccharide biomaterials. In summary, the water content, mechanical strength and RPE cell proliferative capacity strongly depends on the solvent composition for carbodiimide cross-linking of HA materials.

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

    Science.gov (United States)

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

    1991-01-01

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

  14. Enhanced Mechanical Properties in Cellulose Nanocrystal-Poly(oligoethylene glycol methacrylate) Injectable Nanocomposite Hydrogels through Control of Physical and Chemical Cross-Linking.

    Science.gov (United States)

    De France, Kevin J; Chan, Katelyn J W; Cranston, Emily D; Hoare, Todd

    2016-02-08

    While injectable hydrogels have several advantages in the context of biomedical use, their generally weak mechanical properties often limit their applications. Herein, we describe in situ-gelling nanocomposite hydrogels based on poly(oligoethylene glycol methacrylate) (POEGMA) and rigid rod-like cellulose nanocrystals (CNCs) that can overcome this challenge. By physically incorporating CNCs into hydrazone cross-linked POEGMA hydrogels, macroscopic properties including gelation rate, swelling kinetics, mechanical properties, and hydrogel stability can be readily tailored. Strong adsorption of aldehyde- and hydrazide-modified POEGMA precursor polymers onto the surface of CNCs promotes uniform dispersion of CNCs within the hydrogel, imparts physical cross-links throughout the network, and significantly improves mechanical strength overall, as demonstrated by quartz crystal microbalance gravimetry and rheometry. When POEGMA hydrogels containing mixtures of long and short ethylene oxide side chain precursor polymers were prepared, transmission electron microscopy reveals that phase segregation occurs with CNCs hypothesized to preferentially locate within the stronger adsorbing short side chain polymer domains. Incorporating as little as 5 wt % CNCs results in dramatic enhancements in mechanical properties (up to 35-fold increases in storage modulus) coupled with faster gelation rates, decreased swelling ratios, and increased stability versus hydrolysis. Furthermore, cell viability can be maintained within 3D culture using these hydrogels independent of the CNC content. These properties collectively make POEGMA-CNC nanocomposite hydrogels of potential interest for various biomedical applications including tissue engineering scaffolds for stiffer tissues or platforms for cell growth.

  15. 1,3-Diphenylethenylcarbazolyl-Based Monomer for Cross-Linked Hole Transporting Layers

    Directory of Open Access Journals (Sweden)

    Maryte Daskeviciene

    2015-05-01

    Full Text Available A new cross-linkable monomer containing 1,3-diphenylethenylcarbazolyl-based hole-transporting moieties and four reactive epoxy groups, was prepared by a multistep synthesis route from 1,3-bis(2,2-diphenylethenyl-9H-carbazol-2-ol and its application for the in situ formation of cross-linked hole transporting layers was investigated. A high concentration of flexible aliphatic epoxy chains ensures good solubility and makes this compound an attractive cross-linking agent. The synthesized compounds were characterized by various techniques, including differential scanning calorimetry, xerographic time of flight, and electron photoemission in air methods.

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

    Science.gov (United States)

    Chen, Yukun; Yuan, Daosheng; Xu, Chuanhui

    2014-03-26

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

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

    Directory of Open Access Journals (Sweden)

    Evan M. Masutani

    2014-01-01

    Full Text Available 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.

  18. A novel DTPA cross-linking of hyaluronic acid and metal complexation thereof.

    Science.gov (United States)

    Buffa, Radovan; Běťák, Jiří; Kettou, Sofiane; Hermannová, Martina; Pospíšilová, Lucie; Velebný, Vladimír

    2011-09-27

    Macromolecular conjugates of a natural polysaccharide, hyaluronic acid, with diethylenetriaminepentaacetic acid (DTPA)-metal complexes were synthesized and characterized by FTIR, NMR, SEC-MALLS and ICP analysis. Several parameters of the cross-linking reaction as molecular weight of starting HA, temperature, equivalent of DTPA bis-anhydride, concentration of HA, presence of transacylation catalyst DMAP and reaction time were studied. The mechanism for the reaction was suggested and relationship between the molecular weight assigned by SEC-MALLS, reaction parameters and rheological properties of the final cross-linked products were investigated. Copyright © 2011 Elsevier Ltd. All rights reserved.

  19. Preparation and in vitro evaluation of chitosan matrices cross-linked by formaldehyde vapors.

    Science.gov (United States)

    Rao, B S; Murthy, K V

    2000-10-01

    Rifampicin-chitosan matrices were prepared by a chemical cross-linking method to develop a sustained-release form. The effects of cross-linking agent (formaldehyde) on the drug release rate and release kinetics were investigated in this study. Moreover, the kinetics of rifampicin released from chitosan matrices exposed to formaldehyde vapors for predetermined time intervals were analyzed using Ritger and Peppas exponential equation. The in vitro release kinetics exhibited a non-Fickian transport model. Increasing the exposure time to formaldehyde vapors decreased the release rate of rifampicin from chitosan matrices as a result of formation of greater structural strength and tighter texture.

  20. Kinetics of enzyme-catalyzed cross-linking of feruloylated arabinan from sugar beet

    DEFF Research Database (Denmark)

    Abang Zaidel, Dayang Norulfairuz; Arnous, Anis; Holck, Jesper

    2011-01-01

    the kinetics of HRP catalyzed cross-linking of FA esterified to α-(1,5)-linked arabinans are affected by the length of the arabinan chains carrying the feruloyl substitutions. The kinetics of the HRP-catalyzed cross-linking of four sets of arabinan samples from sugar beet pulp, having different molecular...... weights and hence different degrees of polymerization, were monitored by the disappearance of FA absorbance at 316 nm. MALDI-TOF/TOF-MS analysis confirmed that the sugar beet arabinans were feruloyl-substituted, and HPLC analysis verified that the amounts of diFAs increased when FA levels decreased...

  1. In Situ Cross-Linking of Stimuli-Responsive Hemicellulose Microgels during Spray Drying

    OpenAIRE

    Zhao, Weifeng; Nugroho, Robertus Wahyu N.; Odelius, Karin; Edlund, Ulrica; Zhao, Changsheng; Albertsson, Ann-Christine

    2015-01-01

    Chemical cross-linking during spray drying offers the potential for green fabrication of microgels with a rapid stimuli response and good blood compatibility and provides a platform for stimuli-responsive hemicellulose microgels (SRHMGs). The cross-linking reaction occurs rapidly in situ at elevated temperature during spray drying, enabling the production of microgels in a large scale within a few minutes. The SRHMGs with an average size range of ∼1–4 μm contain O-acetyl-galactoglucomannan as...

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

    Science.gov (United States)

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

    2009-01-01

    The capsid of bacteriophage HK97 is stabilized by ∼400 covalent cross-links between subunits which form without any action by external enzymes or cofactors. Cross-linking only occurs in fully assembled particles after large-scale structural changes bring together side chains from three subunits at each cross-linking site. Isopeptide cross-links form between asparagine and lysine side chains on two subunits. The carboxylate of glutamic acid 363 (E363) from a third subunit is found ∼2.4 Å from the isopeptide bond in the partly hydrophobic pocket that contains the cross-link. It was previously reported without supporting data that changing E363 to alanine abolishes cross-linking, suggesting that E363 plays a role in cross-linking. This alanine mutant and six additional substitutions for E363 were fully characterized and the proheads produced by the mutants were tested for their ability to cross-link under a variety of conditions. Aspartic acid and histidine substitutions supported cross-linking to a significant extent, while alanine, asparagine, glutamine, and tyrosine did not, suggesting that residue 363 acts as a proton acceptor during cross-linking. These results support a chemical mechanism, not yet fully tested, that incorporates this suggestion, as well as features of the structure at the cross-link site. The chemically identical isopeptide bonds recently documented in bacterial pili have a strikingly similar chemical geometry at their cross-linking sites, suggesting a common chemical mechanism with the phage protein, but the completely different structures and folds of the two proteins argues that the phage capsid and bacterial pilus proteins have achieved shared cross-linking chemistry by convergent evolution. PMID:19091865

  3. Cross-linked, biodegradable, cytocompatible salicylic acid based polyesters for localized, sustained delivery of salicylic acid: an in vitro study.

    Science.gov (United States)

    Chandorkar, Yashoda; Bhagat, Rajesh K; Madras, Giridhar; Basu, Bikramjit

    2014-03-10

    In order to suppress chronic inflammation while supporting cell proliferation, there has been a continuous surge toward development of polymers with the intention of delivering anti-inflammatory molecules in a sustained manner. In the above backdrop, we report the synthesis of a novel, stable, cross-linked polyester with salicylic acid (SA) incorporated in the polymeric backbone and propose a simple synthesis route by melt condensation. The as-synthesized polymer was hydrophobic with a glass transition temperature of 1 °C, which increases to 17 °C upon curing. The combination of NMR and FT-IR spectral techniques established the ester linkages in the as-synthesized SA-based polyester. The pH-dependent degradation rate and the rate of release of salicylic acid from the as-synthesized SA-based polymer were studied at physiological conditions in vitro. The polyester underwent surface erosion and exhibited linear degradation kinetics in which a change in degradation rate is observed after 4-10 days and 24% mass loss was recorded after 4 months at 37 °C and pH 7.4. The delivery of salicylic acid also showed a similar change in slopes, with a sustained release rate of 3.5% in 4 months. The cytocompatibility studies of these polyesters were carried out with C2C12 murine myoblast cells using techniques like MTT assay and flow cytometry. Our results strongly suggest that SA-based polyester supports cell proliferation for 3 days in culture and do not cause cell death (salicylic acid and have applications in adjuvant cancer therapy, chronic wound healing, and as an alternative to commercially available polymers like poly(lactic acid) and poly(glycolic acid) or their copolymers.

  4. Sustained Release of Diltiazem Hydrochloride from Cross-linked Biodegradable IPN Hydrogel Beads of Pectin and Modified Xanthan Gum.

    Science.gov (United States)

    Giri, T K; Choudhary, C; Alexander, A; Ajazuddin; Badwaik, H; Tripathy, M; Tripathi, D K

    2013-11-01

    Interpenetrating polymer network hydrogel beads of pectin and sodium carboxymethyl xanthan were prepared by ionotropic gelation with Al(+3) ions and covalent cross-linking with glutaraldehyde for sustained delivery of diltiazem hydrochloride. Fourier transform infrared spectroscopy, X-ray diffraction, differential scanning colorimetry and scanning electron microscopy were used to characterise the hydrogel beads. The swelling of the hydrogel and the release of drug were relatively low in pH 1.2 buffer solutions. However, higher swelling and drug release were observed in pH 6.8 buffer solutions. The carboxyl functional groups of hydrogels undergo ionisation and the osmotic pressure inside the beads increases resulting in higher swelling and drug release in higher pH. The release of drug depends on concentration of polymer, amount and exposure time of cross-linker and drug content in the hydrogel matrices. The present study indicated that the hydrogel beads minimised the drug release in pH 1.2 buffer solutions and to prolong the drug release in pH 6.8 buffer solutions.

  5. Sustained release of diltiazem hydrochloride from cross-linked biodegradable IPN hydrogel beads of pectin and modified xanthan gum

    Directory of Open Access Journals (Sweden)

    T K Giri

    2013-01-01

    Full Text Available Interpenetrating polymer network hydrogel beads of pectin and sodium carboxymethyl xanthan were prepared by ionotropic gelation with Al +3 ions and covalent cross-linking with glutaraldehyde for sustained delivery of diltiazem hydrochloride. Fourier transform infrared spectroscopy, X-ray diffraction, differential scanning colorimetry and scanning electron microscopy were used to characterise the hydrogel beads. The swelling of the hydrogel and the release of drug were relatively low in pH 1.2 buffer solutions. However, higher swelling and drug release were observed in pH 6.8 buffer solutions. The carboxyl functional groups of hydrogels undergo ionisation and the osmotic pressure inside the beads increases resulting in higher swelling and drug release in higher pH. The release of drug depends on concentration of polymer, amount and exposure time of cross-linker and drug content in the hydrogel matrices. The present study indicated that the hydrogel beads minimised the drug release in pH 1.2 buffer solutions and to prolong the drug release in pH 6.8 buffer solutions.

  6. Single-sided Nuclear Magnetic Resonance for condition monitoring of cross-linked polyethylene exposed to aggressive media.

    Science.gov (United States)

    Adams, A; Piechatzek, A; Schmitt, G; Siegmund, G

    2015-08-05

    The potential of single-sided Nuclear Magnetic Resonance (NMR) to monitor truly non-invasive changes in polymer materials during aging under aggressive media is for the first time evaluated. For this, the NMR method is used in combination with other condition monitoring methods including mechanical measurements, mass uptake, and differential scanning calorimetry. It is validated by studying for the first time the aging kinetics of silane cross-linked polyethylene (PEX) exposed to media used in oil and gas production and transportation, including aliphatic and aromatic hydrocarbons, sulphur solvents, and corrosion inhibitors in combination with CO2 and H2S. All investigated parameters changed, with the strongest effects detected for the NMR chain mobility and in the presence of hydrocarbons. Furthermore, a universal linear correlation curve could be established between the depression of the tensile strength and the chain mobility. This result represents a fundamental step towards establishing single-sided NMR as a new analytical tool for in situ condition monitoring of polyethylene working under sour conditions. The proposed approach can be easily extended to other polymer materials.

  7. Clinical trade-offs in cross-linked ultrahigh-molecular-weight polyethylene used in total joint arthroplasty.

    Science.gov (United States)

    Pruitt, Lisa A; Ansari, Farzana; Kury, Matt; Mehdizah, Amir; Patten, Elias W; Huddlestein, James; Mickelson, Dayne; Chang, Jennifer; Hubert, Kim; Ries, Michael D

    2013-04-01

    Highly cross-linked formulations of ultrahigh-molecular-weight polyethylene (XLPE) offer exceptional wear resistance for total joint arthroplasty but are offset with a reduction in postyield and fatigue fracture properties in comparison to conventional ultrahigh-molecular-weight polyethylene (UHMWPE). Oxidation resistance is also an important property for the longevity of total joint replacements (TJRs) as formulations of UHMWPE or XLPE utilizing radiation methods are susceptible to free radical generation and subsequent embrittlement. The balance of oxidation, wear, and fracture properties is an enduring concern for orthopedic polymers used as the bearing surface in total joint arthroplasty. Optimization of material properties is further challenged in designs that make use of locking mechanisms, notches, or other stress concentrations that can render the polymer susceptible to fracture due to elevated local stresses. Clinical complications involving impingements, dislocations, or other biomechanical overloads can exacerbate stresses and negate benefits of improved wear resistance provided by XLPE. This work examines trade-offs that factor into the use of XLPE in TJR implants.

  8. Mechanisms of gas permeation through polymer membranes

    Energy Technology Data Exchange (ETDEWEB)

    Stern, S.A.

    1991-01-01

    The objective of the present study is to investigate the mechanisms of gas transport in and through polymer membranes and the dependence of these mechanisms on pressure and temperature. This information is required for the development of new, energy-efficient membrane processes for the separation of industrial gas mixtures. Such processes are based on the selective permeation of the components of gas mixtures through nonporous polymer membranes. Recent work has been focused on the permeation of gases through membranes made from glassy polymers, i.e., at temperatures below the glass transition of the polymers (Tg). Glassy polymers are very useful membrane materials for gas separations because of their high selectivity toward different gases. Gases permeate through nonporous polymer membranes by a solution-diffusion'' process. Consequently, in order to understand the characteristics of this process it is necessary to investigate also the mechanisms of gas solution and diffusion in glassy polymers. 23 refs., 10 figs., 4 tabs.

  9. Use of proteinase K nonspecific digestion for selective and comprehensive identification of interpeptide cross-links: application to prion proteins.

    Science.gov (United States)

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

    2012-07-01

    Chemical cross-linking combined with mass spectrometry is a rapidly developing technique for structural proteomics. Cross-linked proteins are usually digested with trypsin to generate cross-linked peptides, which are then analyzed by mass spectrometry. The most informative cross-links, the interpeptide cross-links, are often large in size, because they consist of two peptides that are connected by a cross-linker. In addition, trypsin targets the same residues as amino-reactive cross-linkers, and cleavage will not occur at these cross-linker-modified residues. This produces high molecular weight cross-linked peptides, which complicates their mass spectrometric analysis and identification. In this paper, we examine a nonspecific protease, proteinase K, as an alternative to trypsin for cross-linking studies. Initial tests on a model peptide that was digested by proteinase K resulted in a "family" of related cross-linked peptides, all of which contained the same cross-linking sites, thus providing additional verification of the cross-linking results, as was previously noted for other post-translational modification studies. The procedure was next applied to the native (PrP(C)) and oligomeric form of prion protein (PrPβ). Using proteinase K, the affinity-purifiable CID-cleavable and isotopically coded cross-linker cyanurbiotindipropionylsuccinimide and MALDI-MS cross-links were found for all of the possible cross-linking sites. After digestion with proteinase K, we obtained a mass distribution of the cross-linked peptides that is very suitable for MALDI-MS analysis. Using this new method, we were able to detect over 60 interpeptide cross-links in the native PrP(C) and PrPβ prion protein. The set of cross-links for the native form was used as distance constraints in developing a model of the native prion protein structure, which includes the 90-124-amino acid N-terminal portion of the protein. Several cross-links were unique to each form of the prion protein, including

  10. The Effect of Glutaraldehyde Cross-Linking on the Enzyme Activity of Immobilized &beta-Galactosidase on Chitosan Bead

    Directory of Open Access Journals (Sweden)

    He Chen

    2013-07-01

    Full Text Available The effect of glutaraldehyde solution concentration, cross-linking time, cross-linking pH and cross-linking temperature on the enzyme activity of the immobilized &beta-galactosidase on Chitosan beads were studied. The enzyme activity was measured after immobilized by detecting the absorbance value at 420 nm.The results were as follows: the immobilized enzyme activity reached the maximum when the concentration of glutaraldehyde solution was 0.3%.The immobilized enzyme had optimal cross-linking time of 3h, optimal cross-linking pH of 6.5, optimal cross-linking temperature of 25°C, under these conditions, the immobilized enzyme activity reached 101, 96, 90 U/g, respectively.

  11. Physicochemical properties and micro-structural characteristics in starch from kudzu root as affected by cross-linking.

    Science.gov (United States)

    Chen, Boru; Dang, Leping; Zhang, Xiao; Fang, Wenzhi; Hou, Mengna; Liu, Tiankuo; Wang, Zhanzhong

    2017-03-15

    Kudzu starch was cross-linked with sodium trimetaphosphate (STMP) at different temperatures, time and of STMP concentrations in this work. The cross-linked starches (CLSs) were fractionated further into cross-linked amylose and amylopectin in order to compare the effect of cross-linking on the microstructure. According to scanning electron microscope (SEM), CLSs displayed the resemble appearance of spherical and polygonal shapes like NS. X-ray diffraction (XRD) revealed that amylose of native starch (A), NS and CLS displayed a combination of A-type and B-type structure, while that was not found in amylose of cross-linked starch (CLA). The deconvoluted fourier transform infrared (FT-IR) indicated that crystal structure of kudzu starch was losing with the proceeding of cross-linking reaction. The CLSs exhibited a higher retrogradation and freeze-thaw stability than NS. This was accompanied by a significant decrease in sedimentation, transparency, swelling power and solubility.

  12. Elevated carboxy terminal cross linked telopeptide of type I collagen in alcoholic cirrhosis

    DEFF Research Database (Denmark)

    Møller, S; Hansen, M; Hillingsø, Jens

    1999-01-01

    BACKGROUND: The carboxy terminal cross linked telopeptide of type I collagen (ICTP) has been put forward as a marker of bone resorption. Patients with alcoholic liver disease may have osteodystrophy. AIMS: To assess circulating and regional concentrations of ICTP in relation to liver dysfunction...

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

    NARCIS (Netherlands)

    Bastiaansen-Jenniskens, Y.M.; Koevoet, W.; Bart, A.C.W. de; Zuurmond, A.-M.; Bank, R.A.; Verhaar, J.A.N.; Groot, J. de; Osch, G.J.V.M. van

    2008-01-01

    Transforming growth factor beta (TGFβ) is often used in cartilage tissue engineering to increase matrix formation by cells with various phenotypes. However, adverse effects of TGFβ, such as extensive cross-linking in cultured fibroblasts, have also been reported. Our goal was to study effects of

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

    Directory of Open Access Journals (Sweden)

    Katherine Vorvolakos

    2010-12-01

    Full Text Available Katherine Vorvolakos1, Irada S Isayeva1, Hoan-My Do Luu1, Dinesh V Patwardhan1, Steven K Pollack21Division of Chemistry and Material Science, 2Office of Science and Engineering Laboratories, Center for Devices and Radiological Health, Food and Drug Administration, Silver Spring, MD, USAAbstract: Hyaluronic acid (HA, in linear or cross-linked form, is a common component of cosmetics, personal care products, combination medical products, and medical devices. In all cases, the ability of the HA solution or gel to wet surfaces and/or disrupt and lubricate interfaces is a limiting feature of its mechanism of action. We synthesized ferric ion–cross-linked networks of HA based on an adhesion barrier, varied the degree of cross-linking, and performed wetting goniometry, viscometry, and dynamic mechanical analysis. As cross-linking increases, so do contact angle, viscosity, storage modulus, and loss modulus; thus, wetting and lubrication are compromised. These findings have implications in medical device materials, such as adhesion barriers and mucosal drug delivery vehicles.Keywords: hyaluron, adhesion barrier, wetting, contact angle, viscosity, lubrication, elasticity, viscoelastic, hydrogel, ferric

  15. Characteristic features and biotechnological applications of cross-linked enzyme aggregates (CLEAs)

    NARCIS (Netherlands)

    Sheldon, R.A.

    2011-01-01

    Cross-linked enzyme aggregates (CLEAs) have many economic and environmental benefits in the context of industrial biocatalysis. They are easily prepared from crude enzyme extracts, and the costs of (often expensive) carriers are circumvented. They generally exhibit improved storage and operational

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

    Energy Technology Data Exchange (ETDEWEB)

    Khabaz, Fardin, E-mail: rajesh.khare@ttu.edu; Khare, Ketan S., E-mail: rajesh.khare@ttu.edu; Khare, Rajesh, E-mail: rajesh.khare@ttu.edu [Department of Chemical Engineering, Texas Tech University, Lubbock, TX 79409 (United States)

    2014-05-15

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

  17. Mocaf cross-linking with gluten to improve the quality of mocaf dough

    Science.gov (United States)

    Raharja, Sapta; Udin, Faqih; Suparno, Ono; Febrianti, Faricha Helfi; Nuraisyah, Ani

    2017-03-01

    Crosslink between mocaf and gluten is conducted to increase the using of mocaf which has very big potential in Indonesia. The effort of cross-linking between mocaf and gluten is to get mocaf flour with better dough quality. This study aims to produce a cross-linked mocaf-gluten flour and to evaluate the influence of heating temperature (X1) and the addition of gluten concentration (X2) using completely randomized design factorial (RAFL). The cross-linking is carried out in alkaline solution with 10%, 20%, and 30% gluten addition and heating temperature at 50, 55, and 60 °C. The result showed that mocaf - gluten flour with the treatment of 30% gluten addition at 55 °C had the largest amount of protein and baking expansion (i.e 19.77% and 2.78 mL/g). Swelling power of the flour was increasing along with the increasing of water absorbing capacity of the mocaf - gluten flour. Birefringence properties of mocaf - gluten flour tended to be reduced as the increasing heating temperature. FTIR analysis of mocaf - gluten flour showed that there was peak strengthening of the infrared spectrum of the C - N bond at 1167-1159 cm-1 which was presumably resulted from the gluten addition and the cross-linking properties.

  18. A minimal model for stabilization of biomolecules by hydrocarbon cross-linking

    Science.gov (United States)

    Hamacher, K.; Hübsch, A.; McCammon, J. A.

    2006-04-01

    Programmed cell death regulating protein motifs play an essential role in the development of an organism, its immune response, and disease-related cellular mechanisms. Among those motifs the BH3 domain of the BCL-2 family is found to be of crucial importance. Recent experiments showed how the isolated, otherwise unstructured BH3 peptide can be modified by a hydrocarbon linkage to regain function. We parametrized a reduced, dynamic model for the stability effects of such covalent cross-linking and confirmed that the model reproduces the reinforcement of the structural stability of the BH3 motif by cross-linking. We show that an analytically solvable model for thermostability around the native state is not capable of reproducing the stabilization effect. This points to the crucial importance of the peptide dynamics and the fluctuations neglected in the analytic model for the cross-linking system to function properly. This conclusion is supported by a thorough analysis of a simulated Gō model. The resulting model is suitable for rational design of generic cross-linking systems in silicio.

  19. Sensitizing potential of enzymatically cross-linked peanut proteins in a mouse model of peanut allergy.

    NARCIS (Netherlands)

    Smit, Joost|info:eu-repo/dai/nl/250600706

    2014-01-01

    SCOPE: The cross-linking of proteins by enzymes to form high-molecular-weight protein, aggregates can be used to tailor the technological or physiological functionality of food products. Aggregation of dietary proteins by food processing may promote allergic sensitization, but the effects of enzymat

  20. Design and Preparation of Cross-Linked Polystyrene Nanoparticles for Elastomer Reinforcement

    Directory of Open Access Journals (Sweden)

    Ming Lu

    2010-01-01

    Full Text Available Cross-linked polystyrene (PS particles in a latex form were synthesized by free radical emulsion polymerization. The nano-PS-filled elastomer composites were prepared by the energy-saving latex compounding method. Results showed that the PS particles took a spherical shape in the size of 40–60 nm with a narrow size distribution, and the glass-transition temperature of the PS nanoparticles increased with the cross-linking density. The outcomes from the mechanical properties demonstrated that when filled into styrene-butadiene rubber (SBR, nitrile-butadiene rubber (NBR, and natural rubber (NR, the cross-linked PS nano-particles exhibited excellent reinforcing capabilities in all the three matrices, and the best in the SBR matrix. In comparison with that of the carbon black filled composites, another distinguished advantage of the cross-linked PS particles filled elastomer composites was found to be light weight in density, which could help to save tremendous amount of energy when put into end products.

  1. Substituent distribution within cross-linked and hydroxypropylated sweet potato starch and potato starch

    NARCIS (Netherlands)

    Zhao, J.; Schols, H.A.; Chen Zenghong,; Jin Zhengyu,; Buwalda, P.L.; Gruppen, H.

    2012-01-01

    Revealing the substituents distribution within starch can help to understand the changes of starch properties after modification. The distribution of substituents over cross-linked and hydroxypropylated sweet potato starch was investigated and compared with modified potato starch. The starches were

  2. EVA交联机理的研究%The Research of EVA Cross-linking Mechanism

    Institute of Scientific and Technical Information of China (English)

    王川艳; 苑会林

    2011-01-01

    研究了过氧化二异丙苯(DCP)对乙烯-醋酸乙烯共聚物(EVA)交联的影响,分析交联过程的反应机理.对交联的EVA样品进行紫外光辐照,分析在该过程中所发生的反应,并研究加入紫外线吸收剂2-羟基-4-正辛氧基-二苯甲酮(UV-531)后,对交联EVA样品在紫外光辐照下交联的影响.%The effect of peroxide (DCP) on Ethylene-Vinyl Acetate (EVA) cross-linking were studied, the reaction mechanism of EVA cross-linking were analyzed. Upon the exposure of cross-linked EVA samples to ultraviolet light, the reaction during this process were analyzed, and also, after adding the ultraviolet absorber (UV-531) , the influences to cross-linked EVA samples during the ultraviolet radiation process were researched.

  3. Dynamic Heterogeneity in Highly Cross-linked Epoxy in the Vicinity of Glass Transition

    Science.gov (United States)

    Lin, Po-Han; Khare, Rajesh

    2010-03-01

    Cross-linked epoxy has been widely used in aerospace and electronics industries. The highly cross-linked nature of these systems leads to different chain dynamics as compared to the linear polymeric systems. In this work, we have used molecular dynamics (MD) simulations to study the dynamic heterogeneity in cross-linked epoxy near the glass transition temperature. Well-relaxed atomistic models of cross-linked epoxy were first created by employing the simulated annealing polymerization approach. The specific epoxy system studied consisted of diglycidyl ether of bisphenol-A (DGEBA) as the epoxy monomer and trimethylene glycol di-p-aminobenzoate (TMAB) as the cross-linker. The glass transition temperature of these model structures was determined from MD simulation by monitoring their volume-temperature behaviour in a stepwise cooling run. The chain dynamics of these systems were characterized by their local translational and orientational mobility. Furthermore, dynamic heterogeneity was studied by analyzing the spatial distribution of the mobile and immobile atoms in the system near the glass transition temperature.

  4. Preparation of Nanocellulose Reinforced Chitosan Films, Cross-Linked by Adipic Acid.

    Science.gov (United States)

    Falamarzpour, Pouria; Behzad, Tayebeh; Zamani, Akram

    2017-02-13

    Adipic acid, an abundant and nontoxic compound, was used to dissolve and cross-link chitosan. After the preparation of chitosan films through casting technique, the in situ amidation reaction was performed at 80-100 °C as verified by Fourier transform infrared (FT-IR). The reaction was accompanied by the release of water which was employed to investigate the reaction kinetics. Accordingly, the reaction rate followed the first-order model and Arrhenius equation, and the activation energy was calculated to be 18 kJ/mol. Furthermore, the mechanical properties of the chitosan films were comprehensively studied. First, optimal curing conditions (84 °C, 93 min) were introduced through a central composite design. In order to evaluate the effects of adipic acid, the mechanical properties of physically cross-linked (uncured), chemically cross-linked (cured), and uncross-linked (prepared by acetic acid) films were compared. The use of adipic acid improved the tensile strength of uncured and chemically cross-linked films more than 60% and 113%, respectively. Finally, the effect of cellulose nanofibrils (CNFs) on the mechanical performance of cured films, in the presence of glycerol as a plasticizer, was investigated. The plasticized chitosan films reinforced by 5 wt % CNFs showed superior properties as a promising material for the development of chitosan-based biomaterials.

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

    Directory of Open Access Journals (Sweden)

    Alexandre Arsenault

    2011-01-01

    Full Text Available 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-dimethylaminopropylcarbodiimide 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.

  6. Standard and hypoosmolar corneal cross-linking in various pachymetry groups

    NARCIS (Netherlands)

    Soeters, Nienke; Tahzib, Nayyirih G

    2015-01-01

    PURPOSE: To investigate the influence of corneal thickness on the outcome of corneal cross-linking (CXL) for progressive keratoconus. METHODS: In this cohort study, 72 unilateral eyes were treated by CXL and divided into three groups according to central corneal thickness (CCT) measured by ultrasoun

  7. The peptidoglycan of Mycobacterium abscessus is predominantly cross-linked by L,D-transpeptidases.

    Science.gov (United States)

    Lavollay, Marie; Fourgeaud, Martine; Herrmann, Jean-Louis; Dubost, Lionel; Marie, Arul; Gutmann, Laurent; Arthur, Michel; Mainardi, Jean-Luc

    2011-02-01

    Few therapeutic alternatives remain for the treatment of infections due to multiresistant Mycobacterium abscessus. Here we show that the peptidoglycans of the "rough" and "smooth" morphotypes contain predominantly 3→3 cross-links generated by l,d-transpeptidases, indicating that these enzymes are attractive targets for the development of efficient drugs.

  8. Cross-linking Electrospun Polydioxanone-Soluble Elastin Blends: Material Characterization

    Directory of Open Access Journals (Sweden)

    Michael J. McClure

    2008-03-01

    Full Text Available The purpose of this study was to establish whether material properties of elastin co-electrospun with polydioxanone (PDO would change over time in both the uncross-linked state and the cross-linked state. First, uncross-linked scaffolds were placed in phosphate buffered saline (PBS for three separate time periods: 15 minutes, 1 hour, and 24 hours, and subsequently tested using uniaxial materials testing. Several cross-linking reagents were then investigated to verify their ability to crosslink elastin: 1-ethyl-3-(dimethylaminopropyl-carbodiimide (EDC, ethylene glycol diglycidyl ether (EGDE, and genipin. Uniaxial tensile testing was performed on scaffolds cross-linked with EDC and genipin, yielding results that warranted further investigation for PDO-elastin blends. Material properties of the cross-linked scaffolds were then found within range of both pig femoral artery and human femoral artery. These results demonstrate PDO-elastin blends could potentially be favorable as vascular grafts, thus warranting future in vitro and in vivo studies.

  9. Is dialdehyde starch a valuable cross-linking agent for collagen/elastin based materials?

    Science.gov (United States)

    Skopinska-Wisniewska, J; Wegrzynowska-Drzymalska, K; Bajek, A; Maj, M; Sionkowska, A

    2016-04-01

    Collagen and elastin are the main structural proteins in mammal bodies. They provide mechanical support, strength, and elasticity to various organs and tissues, e.g. skin, tendons, arteries, and bones. They are readily available, biodegradable, biocompatible and they stimulate cell growth. The physicochemical properties of collagen and elastin-based materials can be modified by cross-linking. Glutaraldehyde is one of the most efficient cross-linking agents. However, the unreacted molecules can be released from the material and cause cytotoxic reactions. Thus, the aim of our work was to investigate the influence of a safer, macromolecular cross-linking agent--dialdehyde starch (DAS). The properties of hydrogels based on collagen/elastin mixtures (95/5, 90/10) containing 5 and 10% of DAS and neutralized via dialysis against deionized water were tested. The homogenous, transparent, stiff hydrogels were obtained. The DAS addition causes the formation of intermolecular cross-linking bonds but does not affect the secondary structure of the proteins. As a result, the thermal stability, mechanical strength, and, surprisingly, swelling ability increased. At the same time, the surface properties test and in vitro study show that the materials are attractive for 3T3 cells. Moreover, the materials containing 10% of DAS are more resistant to enzymatic degradation.

  10. Corneal Cross-Linking for Pediatric Keratoconus : Long-Term Results

    NARCIS (Netherlands)

    Godefrooij, Daniel A; Soeters, Nienke; Imhof, Saskia M; Wisse, Robert P L

    2016-01-01

    PURPOSE: To assess the efficacy and safety of cross-linking in pediatric patients with keratoconus and to provide a systematic literature overview regarding this subject. METHODS: In this prospective cohort, 54 eyes of 36 pediatric patients with keratoconus underwent standard epithelium-off cross-li

  11. Pickering emulsions stabilized by whey protein nanoparticles prepared by thermal cross-linking

    NARCIS (Netherlands)

    Wu, Jiande; Shi, Mengxuan; Li, Wei; Zhao, Luhai; Wang, Ze; Yan, Xinzhong; Norde, Willem; Li, Yuan

    2015-01-01

    A Pickering (o/w) emulsion was formed and stabilized by whey protein isolate nanoparticles (WPI NPs). Those WPI NPs were prepared by thermal cross-linking of denatured WPI proteins within w/o emulsion droplets at 80. °C for 15. min. During heating of w/o emulsions containing 10% (w/v) WPI protein

  12. Preparation of Nanocellulose Reinforced Chitosan Films, Cross-Linked by Adipic Acid

    Directory of Open Access Journals (Sweden)

    Pouria Falamarzpour

    2017-02-01

    Full Text Available Adipic acid, an abundant and nontoxic compound, was used to dissolve and cross-link chitosan. After the preparation of chitosan films through casting technique, the in situ amidation reaction was performed at 80–100 °C as verified by Fourier transform infrared (FT-IR. The reaction was accompanied by the release of water which was employed to investigate the reaction kinetics. Accordingly, the reaction rate followed the first-order model and Arrhenius equation, and the activation energy was calculated to be 18 kJ/mol. Furthermore, the mechanical properties of the chitosan films were comprehensively studied. First, optimal curing conditions (84 °C, 93 min were introduced through a central composite design. In order to evaluate the effects of adipic acid, the mechanical properties of physically cross-linked (uncured, chemically cross-linked (cured, and uncross-linked (prepared by acetic acid films were compared. The use of adipic acid improved the tensile strength of uncured and chemically cross-linked films more than 60% and 113%, respectively. Finally, the effect of cellulose nanofibrils (CNFs on the mechanical performance of cured films, in the presence of glycerol as a plasticizer, was investigated. The plasticized chitosan films reinforced by 5 wt % CNFs showed superior properties as a promising material for the development of chitosan-based biomaterials.

  13. Detection of DNA cross-links in tumor cells with the ethidium bromide fluorescence assay

    NARCIS (Netherlands)

    de Jong, Steven; Zijlstra, J G; Timmer-Bosscha, H; Mulder, N H; de Vries, Liesbeth

    1986-01-01

    Until now the fluorescence assay with ethidium bromide has only been used on pure DNA. This assay depends on the difference in fluorescence between single- and double-stranded DNA (dsDNA). Cross-links in DNA are measured by the return of fluorescence of dsDNA after heat denaturation at pH 12. Under

  14. Horseradish peroxidase-catalyzed cross-linking of feruloylated arabinoxylans with β-casein

    NARCIS (Netherlands)

    Boeriu, C.G.; Oudgenoeg, G.; Spekking, W.T.J.; Berendsen, L.B.J.M.; Vancon, L.; Boumans, H.; Gruppen, H.; Berkel, W.J.H. van; Laane, C.; Voragen, A.G.J.

    2004-01-01

    Heterologous conjugates of wheat arabinoxylan and β-casein were prepared via enzymatic cross-linking, using sequential addition of the arabinoxylan to a mixture of β-casein, peroxidase, and hydrogen peroxide. The maximal formation of adducts between the β-casein and the feruloylated arabinoxylan was

  15. Cross-linking methods of electrospun fibrinogen scaffolds for tissue engineering applications

    Energy Technology Data Exchange (ETDEWEB)

    Sell, Scott A; Garg, Koyal; McClure, Michael J; Bowlin, Gary L [Department of Biomedical Engineering, Virginia Commonwealth University, Richmond, VA 23284-3067 (United States); Francis, Michael P [Department of Pathology, Virginia Commonwealth University, Richmond, VA 23298-0709 (United States); Simpson, David G [Department of Anatomy and Neurobiology, Virginia Commonwealth University, Richmond, VA 23298-0709 (United States)], E-mail: glbowlin@vcu.edu

    2008-12-15

    The purpose of this study was to enhance the mechanical properties and slow the degradation of an electrospun fibrinogen scaffold, while maintaining the scaffold's high level of bioactivity. Three different cross-linkers were used to achieve this goal: glutaraldehyde vapour, 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) in ethanol and genipin in ethanol. Scaffolds with a fibrinogen concentration of 120 mg ml{sup -1} were electrospun and cross-linked with one of the aforementioned cross-linkers. Mechanical properties were determined through uniaxial tensile testing performed on scaffolds incubated under standard culture conditions for 1 day, 7 days and 14 days. Cross-linked scaffolds were seeded with human foreskin fibroblasts (BJ-GFP-hTERT) and cultured for 7, 14 and 21 days, with histology and scanning electron microscopy performed upon completion of the time course. Mechanical testing revealed significantly increased peak stress and modulus values for the EDC and genipin cross-linked scaffolds, with significantly slowed degradation. However, cross-linking with EDC and genipin was shown to have some negative effect on the bioactivity of the scaffolds as cell migration throughout the thickness of the scaffold was slowed.

  16. Mature enzymatic collagen cross-links, hydroxylysylpyridinoline and lysylpyridinoline, in the aging human vitreous

    NARCIS (Netherlands)

    Ponsioen, T.L.; van Deemter, M.; Bank, R.A.; Snabel, J.M.; Zijlstra, G.S.; van der Worp, R.J.; Hooymans, J.M.M.; Los, L.I.

    2009-01-01

    Purpose. The vitreous body of the human eye undergoes progressive morphologic changes with aging. Since the enzymatic collagen cross-links hydroxylysylpyridinoline (HP) and lysylpyridinoline (LP) are known to be important for the integrity of the collagen matrix, the presence in the vitreous on agin

  17. Mature Enzymatic Collagen Cross-Links, Hydroxylysylpyridinoline and Lysylpyridinoline, in the Aging Human Vitreous

    NARCIS (Netherlands)

    Ponsioen, Theodorus L.; van Deemter, Marielle; Bank, Rudolf A.; Snabel, Johanna M.; Zijlstra, Gerrit S.; van der Worp, Roelofje J.; Hooymans, Johanna M. M.; Los, Leonoor I.

    2009-01-01

    PURPOSE. The vitreous body of the human eye undergoes progressive morphologic changes with aging. Since the enzymatic collagen cross-links hydroxylysylpyridinoline (HP) and lysylpyridinoline (LP) are known to be important for the integrity of the collagen matrix, the presence in the vitreous on agin

  18. Formation and Distribution of Space-Charge in Cross-Linked Polyethylene

    Science.gov (United States)

    Zhang, Ye-Wen; Li, Ji-Xiao; Zheng, Fei-Hu; Peng, Zong-Ren; Wu, Chang-Shun; Xia, Zhong-Fu

    2002-08-01

    The formation and distribution of space-charge in a cross-linked polyethylene (XLPE) sample are investigated by means of pressure wave propagation, infrared spectroscopy and electrostatic force microscopy (EFM). The related mechanism of space-charge distribution and the structure of XLPE are discussed. The EFM images show that quite large quantitative space-charges locate at the surface of spherulites.

  19. Crown ether activation of cross-linked subtilisin Carlsberg crystals in organic solvents

    NARCIS (Netherlands)

    Unen, van Dirk-Jan; Sakodinskaya, Inna K.; Engbersen, Johan F.J.; Reinhoudt, David N.

    1998-01-01

    The activity of cross-linked subtilisin Carlsberg crystals in the catalysis of peptide bond formation can be significantly enhanced by pretreatment of the enzyme crystals with crown ethers. Soaking of the enzyme crystals in a solution of crown ether in acetonitrile followed by evaporation of the sol

  20. Phosphoric acid doped polysulfone membranes with aminopyridine pendant groups and imidazole cross-links

    DEFF Research Database (Denmark)

    Hink, Steffen; Elsøe, Katrine; Cleemann, Lars Nilausen;

    2015-01-01

    Udel polysulfone based membranes with 4-aminopyridine pendant groups and cross-linking imidazole units are synthesized in a simple two step reaction. The ratio of 4-aminopyridine and imidazole is varied and the materials are extensively characterized. The average phosphoric acid uptake (in 85 wt...

  1. Effect of dual modification with hydroxypropylation and cross-linking on physicochemical properties of taro starch.

    Science.gov (United States)

    Hazarika, Bidyut Jyoti; Sit, Nandan

    2016-04-20

    Dual modification of taro starch by hydroxypropylation and cross-linking was carried out and the properties of the modified starches were investigated. Two different levels of hydroxypropylation (5 and 10%) and cross-linking (0.05 and 0.10%) were used in different sequences. The amylose contents of the starch decreased due to single and dual modification. For the dual-modified starches, the swelling, solubility and clarity was found to increase with level of hydroxypropylation and decrease with level of cross-linking. The freeze-thaw stability of the dual-modified starches was also affected by the sequence of modification. The viscosities of the cross-linked and dual-modified starches were more than native and hydroxypropylated starches. The firmness of the dual-modified starches was also higher than native and single modified starches. The dual-modified starches have benefits of both type of modifications and could be used for specific purposes e.g. food products requiring high viscosity as well as freeze-thaw stability.

  2. Vitamin E diffused highly cross-linked polyethylene in total hip arthroplasty at five years

    DEFF Research Database (Denmark)

    Nebergall, Audrey K; Greene, M. E.; Laursen, M B

    2017-01-01

    AIMS: The objective of this five-year prospective, blinded, randomised controlled trial (RCT) was to compare femoral head penetration into a vitamin E diffused highly cross-linked polyethylene (HXLPE) liner with penetration into a medium cross-linked polyethylene control liner using radiostereome......AIMS: The objective of this five-year prospective, blinded, randomised controlled trial (RCT) was to compare femoral head penetration into a vitamin E diffused highly cross-linked polyethylene (HXLPE) liner with penetration into a medium cross-linked polyethylene control liner using...... radiostereometric analysis. PATIENTS AND METHODS: Patients scheduled for total hip arthroplasty (THA) were randomised to receive either the study E1 (32 patients) or the control ArComXL polyethylene (35 patients). The median age (range) of the overall cohort was 66 years (40 to 76). RESULTS: The five-year median...... (interquartile range) proximal femoral head penetration into the E1 was -0.05 mm (-0.13 to -0.02) and 0.07 mm (-0.03 to 0.16) for ArComXL. At three and five years, the penetration was significantly greater in the ArComXL group compared with the E1 group (p = 0.029 and p = 0.019, respectively). All patient...

  3. Thermal Degradation and Fire Performance of Cross-linking Polystyrene%交联聚苯乙烯的热分解与燃烧性能研究

    Institute of Scientific and Technical Information of China (English)

    楚广成; 李英飞; 马乐; 刘继纯

    2011-01-01

    采用二乙烯基苯(DVB)为交联剂,与苯乙烯(St)单体进行共聚合成了一系列交联聚苯乙烯(PS).采用热重分析,高温热分解、水平燃烧、氧指数、锥形量热分析等方法研究了交联PS的热分解行为和燃烧性能.结果表明:与线型PS相比,交联PS的热分解温度提高,成炭量增加,热稳定性显著增强;交联PS在燃烧时熔融滴落和发烟量显著减少,热释放速率、质量损失速率和燃烧速率降低,氧指教增加,阻燃性能增强;当St/DVB的质量比为100/3时得到的交联PS的阻燃性能最隹;交联PS在燃烧时生成的大量炭残余物覆盖在聚合物表面形成保护层,对热量传递、氧气和燃料分子的迁移产生屏蔽和阻隔作用,降低了聚合物的热分解速率,提高了其阻燃性能.%A series of cross-Iinking polystyrene (PS) materials were synthesized by taking copolymerizing styrene (St) as monomer and divinyl benzene(OVB) as cross-linking agent. The thermal degradation behavior and fire performance of cross-linking PS were studied by means of thermogravimetry, high-temperature pyrolysis, horizontal burning, oxygen index and cone calorimetry. The results show that both degradation temperature and char residue amoynt of cross-linking PS increase, and the thermal stability of cross-linking PS is enhanced noticeably, compared with linear PS; the cross-linking PS produces much less melt-dripping and smoke during burning; the heat release rate (HRR), mass loss rate (MLR) and burning rate all decrease, while the oxygen index value increases, which indicate that the flame retardancy of cross linking PS Is enhanced compared with its linear counterpart; it is found that the cross-linking PS exhibits optimal flame retardancy when the mass ratio of St/DVB is 100/3; the cross linking PS produces much char residue during combustion, which covers on the surface of the polymer material and forms a protection layer; the shielding and obstructing effects of the

  4. Synthesis, Optimization, Property, Characterization, and Application of Dialdehyde Cross-Linking Guar Gum

    Directory of Open Access Journals (Sweden)

    Tang Hongbo

    2016-01-01

    Full Text Available Dialdehyde cross-linking guar gum (DCLGG, as a novel material, was synthesized using phosphorus oxychloride as a cross-linking reagent, sodium periodate as an oxidant, and ethanol as a solvent through keeping the original particle form of guar gum. The process parameters such as the reaction temperature, reaction time, pH, amount of sodium periodate, and amount of ethanol were optimized by the response surface methodology in order to obtain the regression model of the oxidization. The covalent binding of L-asparagine onto the surfaces of DCLGG was further investigated. The results showed that the best technological conditions for preparing DCLGG were as follows: reaction temperature = 40°C, reaction time = 3.0 h, pH = 4.0, and amount of ethanol = 74.5%. The swelling power of DCLGG was intermediate between cross-linking guar gum and dialdehyde guar gum. The cross-linking and dialdehyde oxidization reduced the viscosity of GG. The cross-liking reduced the melting enthalpy of GG. However, the oxidization increased melting enthalpy of ACLGG. The thermal stability of GG was increased by cross-linking or oxidization. The variation of the onset decomposition temperature and end decomposition temperature of GG was not consistent with thermal stability of GG. L-asparagine could be chemically bound well by DCLGG through forming Schiff base under the weak acidity. The maximum adsorption capacity of L-asparagine on DCLGG with aldehyde content of 56.2% reached 21.9 mg/g.

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

    Science.gov (United States)

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

    2013-04-01

    Glutaraldehyde (GLUT) processing, cellular antigens, calcium ions in circulation, and phospholipids present in the native tissue are predominantly responsible for calcification, degeneration, and lack of natural microenvironment for host progenitor cell migration in tissue implants. The study presents an improved methodology for adhesion and proliferation of endothelial progenitor cells (EPCs) without significant changes in biomechanical and biodegradation properties of the processed acellular bovine pericardium. The anti-calcification potential of the processed tissue was enhanced by detoxification of GLUT-cross-linked bovine pericardium by decellularization, pretreating it with ethanol or removing the free aldehydes by citric acid treatment and lyophilization. The treated tissues were assessed for biomechanical properties, GLUT ligand quantification, adhesion, proliferation of EPCs, and biodegradability. The results indicate that there was no significant change in biomechanical properties and biodegradability when enzymatic hydrolysis (p>0.05) is employed in detoxified acellular GLUT cross-linked tissue (DBP-G-CA-ET), compared with the native detoxified GLUT cross-linked bovine pericardium (NBP-G-CA-ET). DBP-G-CA-ET exhibited a significant (p>0.05) increase in the viability of EPCs and cell adhesion as compared to acellular GLUT cross-linked bovine pericardium (ppericardium, employed in our study as an alternative to conventional GLUT cross-linked bovine pericardium, might provide longer durability and better biocompatibility, and reduce calcification. The developed bovine pericardium patches could be used in cardiac reconstruction and repair, arteriotomy, soft tissue repair, and general surgical procedures with tissue regeneration dimensions. Copyright © 2012 Elsevier B.V. All rights reserved.

  6. Wear measurement of highly cross-linked UHMWPE using a 7Be tracer implantation technique.

    Science.gov (United States)

    Wimmer, Markus A; Laurent, Michel P; Dwiwedi, Yasha; Gallardo, Luis A; Chipps, Kelly A; Blackmon, Jeffery C; Kozub, Raymond L; Bardayan, Daniel W; Gross, Carl J; Stracener, Daniel W; Smith, Michael S; Nesaraja, Caroline D; Erikson, Luke; Patel, Nidhi; Rehm, Karl E; Ahmad, Irshad; Greene, John P; Greife, Uwe

    2013-04-01

    The very low wear rates achieved with the current highly cross-linked ultrahigh molecular weight polyethylenes (UHMWPE) used in joint prostheses have proven to be difficult to measure accurately by gravimetry. Tracer methods are therefore being explored. The purpose of this study was to perform a proof-of-concept experiment on the use of the radioactive tracer beryllium-7 ((7)Be) for the determination of in vitro wear in a highly cross-linked orthopedic UHMWPE. Three cross-linked and four conventional UHMWPE pins made from compression-molded GUR 1050, were activated with 10(9) to 10(10) (7)Be nuclei using a new implantation setup that produced a homogenous distribution of implanted nuclei up to 8.5 μm below the surface. The pins were tested for wear in a six-station pin-on-flat apparatus for up to 7.1 million cycles (178 km). A Germanium gamma detector was employed to determine activity loss of the UHMWPE pins at preset intervals during the wear test. The wear of the cross-linked UHMWPE pins was readily detected and estimated to be 17 ± 3 μg per million cycles. The conventional-to-cross-linked ratio of the wear rates was 13.1 ± 0.8, in the expected range for these materials. Oxidative degradation damage from implantation was negligible; however, a weak dependence of wear on implantation dose was observed limiting the number of radioactive tracer atoms that can be introduced. Future applications of this tracer technology may include the analysis of location-specific wear, such as loss of material in the post or backside of a tibial insert.

  7. The Quest for Converting Biorenewable Bifunctional α-Methylene-γ-butyrolactone into Degradable and Recyclable Polyester: Controlling Vinyl-Addition/Ring-Opening/Cross-Linking Pathways

    KAUST Repository

    Tang, Xiaoyan

    2016-10-04

    α-Methylene-γ-butyrolactone (MBL), a naturally occurring and biomass-sourced bifunctional monomer, contains both a highly reactive exocyclic C═C bond and a highly stable five-membered γ-butyrolactone ring. Thus, all previous work led to exclusive vinyl-addition polymerization (VAP) product P(MBL)VAP. Now, this work reverses this conventional chemoselectivity to enable the first ring-opening polymerization (ROP) of MBL, thereby producing exclusively unsaturated polyester P(MBL)ROP with Mn up to 21.0 kg/mol. This elusive goal was achieved through uncovering the thermodynamic, catalytic, and processing conditions. A third reaction pathway has also been discovered, which is a crossover propagation between VAP and ROP processes, thus affording cross-linked polymer P(MBL)CLP. The formation of the three types of polymers, P(MBL)VAP, P(MBL)CLP, and P(MBL)ROP, can be readily controlled by adjusting the catalyst (La)/initiator (ROH) ratio, which is determined by the unique chemoselectivity of the La–X (X = OR, NR2, R) group. The resulting P(MBL)ROP is degradable and can be readily postfunctionalized into cross-linked or thiolated materials but, more remarkably, can also be fully recycled back to its monomer thermochemically. Computational studies provided the theoretical basis for, and a mechanistic understanding of, the three different polymerization processes and the origin of the chemoselectivity.

  8. Folic acid-targeted disulfide-based cross-linking micelle for enhanced drug encapsulation stability and site-specific drug delivery against tumors

    Directory of Open Access Journals (Sweden)

    Zhang Y

    2016-03-01

    Full Text Available Yumin Zhang,1,* Junhui Zhou,2,* Cuihong Yang,1 Weiwei Wang,3 Liping Chu,1 Fan Huang,1 Qiang Liu,1 Liandong Deng,2 Deling Kong,3 Jianfeng Liu,1 Jinjian Liu1 1Tianjin Key Laboratory of Radiation Medicine and Molecular Nuclear Medicine, Institute of Radiation Medicine, Chinese Academy of Medical Science and Peking Union Medical College, 2Department of Polymer Science and Technology, School of Chemical Engineering and Technology, Tianjin University, 3Tianjin Key Laboratory of Biomaterial Research, Institute of Biomedical Engineering, Chinese Academy of Medical Science and Peking Union Medical College, Tianjin, People’s Republic of China *These authors contributed equally in this work Abstract: Although the shortcomings of small molecular antitumor drugs were efficiently improved by being entrapped into nanosized vehicles, premature drug release and insufficient tumor targeting demand innovative approaches that boost the stability and tumor responsiveness of drug-loaded nanocarriers. Here, we show the use of the core cross-linking method to generate a micelle with enhanced drug encapsulation ability and sensitivity of drug release in tumor. This kind of micelle could increase curcumin (Cur delivery to HeLa cells in vitro and improve tumor accumulation in vivo. We designed and synthesized the core cross-linked micelle (CCM with polyethylene glycol and folic acid-polyethylene glycol as the hydrophilic units, pyridyldisulfide as the cross-linkable and hydrophobic unit, and disulfide bond as the cross-linker. CCM showed spherical shape with a diameter of 91.2 nm by the characterization of dynamic light scattering and transmission electron microscope. Attributed to the core cross-linking, drug-loaded CCM displayed higher Nile Red or Cur-encapsulated stability and better sensitivity to glutathione than noncross-linked micelle (NCM. Cellular uptake and in vitro antitumor studies proved the enhanced endocytosis and better cytotoxicity of CCM-Cur against

  9. Synthesis, characterization, and in vitro degradation of a biodegradable photo-cross-linked film from liquid poly(epsilon-caprolactone-co-lactide-co-glycolide) diacrylate.

    Science.gov (United States)

    Shen, Jin Y; Pan, Xiao Y; Lim, Chin H; Chan-Park, Mary B; Zhu, Xiao; Beuerman, Roger W

    2007-02-01

    There has been little study on the effect of composition or molecular weight on the biodegradation rate of photo-cross-linked biodegradable aliphatic polyesters though such information is important for tissue engineering scaffolds. We have synthesized a new series of photopolymerizable linear poly(epsilon-caprolactone-co-lactide-co-glycolide) diacrylates with different molecular weights (Mn = 1800, 4800, and 9300 Da) and compositions (20%, 40%, and 60% epsilon-CL) and studied their biodegradation rates. The resultant oligomers were amorphous and appeared as viscous liquids at room temperature. Liquid-to-solid polymerization was carried out by UV irradiation in the presence of a photoinitiator. The photocuring yield was high (greater than 95%), and the photo-cross-linked polymers were amorphous and rubbery. Mechanical measurements showed that the polymers can be stretchable or rigid; the high molecular weight/low epsilon-CL network has a strain of 176% and a modulus of 1.66 MPa while the low molecular weight/high epsilon-CL network has a strain of 21% and a modulus of 12.3 MPa. In a 10 week in vitro biodegradation study, the polymers exhibited a two-stage degradation behavior. In the first stage, the polymer weight and strain remained almost constant, but a linear decrease in the Young's modulus (E) and ultimate stress (sigma) were observed. Lower oligomer molecular weight or epsilon-CL content correlated with a faster decrease in Young's modulus. In the second stage, which began when the Young's modulus dropped below 1 MPa, there was rapid weight loss and strain increase. The lower the epsilon-CL content, the earlier the second stage happened. Low molecular weight and high epsilon-CL content correlated with a longer modulus half-life (time for the modulus to degrade to 50% of its initial value). The degradation results suggest principles that may be helpful in predicting the biodegradation behavior of similar polymeric cross-linked networks. Films formed from these

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

    Science.gov (United States)

    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

  11. Wheat gluten films cross-linked with 1-ethyl-3-(3-demethylaminopropyl) carbodiimide and N-hydroxysuccinimide

    NARCIS (Netherlands)

    Tropini, V.; Lens, J.P.; Mulder, W.J.; Silvestre, F.

    2004-01-01

    Wheat gluten films were cast from aqueous dispersions containing 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) and N-hydroxysuccinimide (NHS) as cross-linking reagents and glycerol as a plasticizer. Cross-linking was carried out to improve film properties such as water sensitivity and tensile

  12. Effect of PDMS cross-linking degree on the permeation performance of PAN/PDMS composite nanofiltration membranes

    NARCIS (Netherlands)

    Stafie, N.; Stamatialis, Dimitrios; Wessling, Matthias

    2006-01-01

    This work focuses on the effect of poly(dimethyl siloxane) (PDMS) cross-linking on the permeation performance of the poly(acrylonitrile) (PAN)/PDMS nanofiltration (NF) composite membrane. PDMS membrane of various cross-linking degrees could be obtained by changing the ratio of a vinyl-terminated

  13. Dehydration of an ethanol/water azeotrope through alginate-DNA membranes cross-linked with metal ions by pervaporation.

    Science.gov (United States)

    Uragami, Tadashi; Banno, Masashi; Miyata, Takashi

    2015-12-10

    To obtain high dehydration membranes for an ethanol/water azeotrope, dried blend membranes prepared from mixtures of sodium alginate (Alg-Na) and sodium deoxyribonucleate (DNA-Na) were cross-linked by immersing in a methanol solution of CaCl2 or MaCl2. In the dehydration of an ethanol/water azeotropic mixture by pervaporation, the effects of immersion time in methanol solution of CaCl2 or MaCl2 on the permeation rate and water/ethanol selectivity through Alg-DNA/Ca(2+) and Alg-DNA/Mg(2+) cross-linked membranes were investigated. Alg-DNA/Mg(2+) cross-linked membrane immersed for 12h in methanol solution of MaCl2 exhibited the highest water/ethanol selectivity. This results from depressed swelling of the membranes by formation of a cross-linked structure. However, excess immersion in solution containing cross-linker led to an increase in the hydrophobicity of cross-linked membrane. Therefore, the water/ethanol selectivity of Alg-DNA/Mg(2+) cross-linked membranes with an excess immersion in cross-linking solution was lowered. The relationship between the structure of Alg-DNA/Ca(2+) and Alg-DNA/Mg(2+) cross-linked membranes and their permeation and separation characteristics during pervaporation of an ethanol/water azeotropic mixture is discussed in detail.

  14. Corneal cross-linking in a 10-year-old child with stage III keratoconus.

    Science.gov (United States)

    Abbondanza, Marco; Felice, Valentina De; Abbondanza, Gabriele

    2016-07-01

    Keratoconus is a corneal dystrophy characterized by progressive thinning, conical shape of the cornea and irregular astigmatism. It is particularly insidious when it occurs in very young patients. We report the case of a 10-year-old child with an aggressive stage III keratoconus, who was suggested to undergo a Penetrating Keratoplasty. We performed Corneal Collagen Cross-linking with epithelium removal instead, which was successful in arresting the rapid progression of keratoconus. Eighteen months later, Kmax had decreased by 1.3 D, astigmatism by 0.8 D, thinnest pachimetry had improved by 69 μm and CDVA was 20/32. This case confirms that Corneal Collagen Cross-linking is a safe and effective procedure for the treatment of keratoconus even in its aggressive forms. We encourage ophthalmic surgeons to favor conservative treatments when dealing with very young patients. © NEPjOPH.

  15. Development and Evaluation of Dual Cross-Linked Pulsatile Beads for Chronotherapy of Rheumatoid Arthritis

    Directory of Open Access Journals (Sweden)

    Abanesh kumar Bansal

    2013-01-01

    Full Text Available In the present investigation, pulsatile release beads were prepared by ionic gelation technique. Lornoxicam dual cross-linked beads were prepared by dropping dispersed phase of lornoxicam, pectin, and sodium alginate into the dispersion phase of different concentrations of calcium chloride solution followed by aluminium chloride solution. The formulated beads were further coated by Eudragit L & S 100 in the ratio 1 : 2 w/w in order to achieve desired lag time. In vitro release study showed lag time of 5–8 h before release of lornoxicam from the formulated beads. Thus, formulated dual cross-linked beads when administered at bed time may release lornoxicam when needed most for chronotherapeutics of early morning rheumatoid arthritis attacks in chronic patients.

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

    Science.gov (United States)

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

    2014-01-01

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

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

    Science.gov (United States)

    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.

  18. Thermally Conductive-Silicone Composites with Thermally Reversible Cross-links.

    Science.gov (United States)

    Wertz, J T; Kuczynski, J P; Boday, D J

    2016-06-08

    Thermally conductive-silicone composites that contain thermally reversible cross-links were prepared by blending diene- and dienophile-functionalized polydimethylsiloxane (PDMS) with an aluminum oxide conductive filler. This class of thermally conductive-silicones are useful as thermal interface materials (TIMs) within Information Technology (IT) hardware applications to allow rework of valuable components. The composites were rendered reworkable via retro Diels-Alder cross-links when temperatures were elevated above 130 °C and required little mechanical force to remove, making them advantageous over other TIM materials. Results show high thermal conductivity (0.4 W/m·K) at low filler loadings (45 wt %) compared to other TIM solutions (>45 wt %). Additionally, the adhesion of the material was found to be ∼7 times greater at lower temperatures (25 °C) and ∼2 times greater at higher temperatures (120 °C) than commercially available TIMs.

  19. pH-sensitive genipin-cross-linked chitosan microspheres for heparin removal.

    Science.gov (United States)

    Kamiński, Kamil; Zazakowny, Karolina; Szczubiałka, Krzysztof; Nowakowska, Maria

    2008-11-01

    Chitosan hydrogel microspheres were obtained by cross-linking chitosan in its inverse emulsion using genipin as cross-linker. The genipin-cross-linked chitosan microspheres (ChGp) swell significantly in water at pH values below 6.5 and shrink to a smaller extent at pH values above 6.5. ChGp microspheres bind heparin in water. The kinetics of heparin binding was found to be pH dependent and was faster and more efficient at a lower pH. That can be also controlled by the weight of ChGp microspheres used. Rate and efficiency of heparin adsorption at pH 7.4, which is typical of blood, could be increased by quaternization of ChGp microspheres using glycidyltrimethylammonium chloride (GTMAC). The polymeric material obtained thus can be potentially useful for heparin removal in biomedical applications.

  20. Preparation of bioimprinting cross-linked enzyme aggregates of phenylalanine ammonia lyase and it's partial properties

    Directory of Open Access Journals (Sweden)

    Jiandong CUI

    2015-12-01

    Full Text Available Phenylalanine ammonia lyase (PAL is a key enzyme for production of L-phenylalanine. Currently, PAL is mainly obtained from Rhodotorula PAL However, Rhodotorula PAL exhibits poor stability, which limits its industrial application. In this study, bioimprinting cross-linked enzyme aggregates of PAL (PAL-iCLEAs is developed by combining cross-linked enzyme aggregates technology and imprinted enzyme method. The most optimal imprinting molecule substrate is screened. Moreover, some characteristics of the PAL-iCLEAs are examined. The results show that the most suitable substrates for preparing PAL-iCLEAs is tran-cinnamic acid. The optimal temperature and pH was 50 ℃ and 10.5, respectively. In addition, PAL-iCLEAs shows good reusability, the recovery of PAL activity still remained 32% after reusing 9 times.

  1. Synthesis of Cross-Linked Polymeric Micelle pH Nanosensors

    DEFF Research Database (Denmark)

    Ek, Pramod Kumar; Jølck, Rasmus Irming; Andresen, Thomas Lars

    2015-01-01

    at the micelle shell using CuAAC results in a stabilized micelle pH nanosensor. Compared to the postmicelle modification strategy, the mixed-micellization approach increases the control of the overall composition of the nanosensors.Both approaches provide stable nanosensors with similar pKa profiles and thereby......The design flexibility that polymeric micelles offer in the fabrication of optical nanosensors for ratiometric pH measurements is investigated. pH nanosensors based on polymeric micelles are synthesized either by a mixed-micellization approach or by a postmicelle modification strategy. In the mixed......-micellization approach, self-assembly of functionalized unimers followed by shell cross-linking by copper-catalyzed azide-alkyne cycloaddition (CuAAC) results in stabilized cRGD-functionalized micelle pH nanosensors. In the postmicelle modification strategy, simultaneous cross-linking and fluorophore conjugation...

  2. Mechanical properties and collagen cross-linking of the patellar tendon in old and young men

    DEFF Research Database (Denmark)

    Couppé, C; Hansen, P; Kongsgaard, M

    2009-01-01

    Age-related loss in muscle mass and strength impairs daily life function in the elderly. However, it remains unknown whether tendon properties also deteriorate with age. Cross-linking of collagen molecules provides structural integrity to the tendon fibrils and has been shown to change with age...... in animals but has never been examined in humans in vivo. In this study, we examined the mechanical properties and pyridinoline and pentosidine cross-link and collagen concentrations of the patellar tendon in vivo in old (OM) and young men (YM). Seven OM (67 +/- 3 years, 86 +/- 10 kg) and 10 YM (27 +/- 2...... contractions. Percutaneous tendon biopsies were taken and analyzed for hydroxylysyl pyridinoline (HP), lysyl pyridinoline (LP), pentosidine, and collagen concentrations. We found no significant differences in the dimensions or mechanical properties of the tendon between OM and YM. Collagen concentrations were...

  3. [Use of native and cross-linked collagen membranes for guided tissue and bone regeneration].

    Science.gov (United States)

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

    2006-01-01

    A material which is used as a barrier for GBR/GTR procedures has to satisfy several physicochemical characteristics such as biocompatibility, tissue integration, barrier function, and dimensional stability. Recently, many investigations reported on the use of products derived from type I and type III porcine or bovine collagen. Collagen membranes are predominantly resorbed by enzymatic activity (protease and collagenase). To decrease resorption, various physical and chemical cross-linking techniques have been used. Although nowadays cross-linking of collagen seems to be a commonly used procedure, its impact on physicochemical properties of the membrane is still unknown. The aim of the present literature review is to evaluate the potential use of different collagen membranes for GBR/GTR procedures.

  4. Investigation of cross-linking poly(methyl methacrylate) as a guiding material in block copolymer directed self-assembly

    Science.gov (United States)

    Seidel, Robert; Rincon Delgadillo, Paulina; Ramirez-Hernandez, Abelardo; Wu, Hengpeng; Her, Youngjun; Yin, Jian; Nealey, Paul; de Pablo, Juan; Gronheid, Roel

    2014-03-01

    Directed self-assembly (DDSA) of block copolymers ((BCP) is attracting a growing amount of interest as a techhnique to expand traditional lithography beyond its current limits. It has reecently been demonstrated that chemoepitaxy can be used to successfully ddirect BCP assembly to form large arrays off high-density features. The imec DSA LiNe flow uses lithography and trim-etch to produce a "prepattern" of cross-linked polystyrene (PS) stripes, which in turn guide the formation of assembled BCPP structures. Thhe entire process is predicated on the preferential interaction of the respective BCP domains with particular regionss of the underlying prepattern. The use of polystyrene as the guiding material is not uniquely required, however, and in fact may not even be preferable. This study investigates an alternate chemistry -- crosslinked poly(methyl methacrylate), X-PMMA, -- as the underlying polymer mat, providing a route to higher auto-affinity and therefore a stronger guiding ability. In addition to tthe advantages of the chemistry under investigation, this study explores the broader theme of extending BCP DSA to other materials.

  5. Influence of MeV H+ ion beam flux on cross-linking and blister formation in PMMA resist

    Directory of Open Access Journals (Sweden)

    Somrit Unai

    2012-02-01

    Full Text Available In soft lithography, a pattern is produced in poly(dimethylsiloxane (PDMS elastomer by casting from a master mould. The mould can be made of poly(methylmethacrylate (PMMA resist by utilising either its positive or negative tone induced by an ion beam. Here we have investigated the irradiation conditions for achieving complete cross-linking and absence of blister formation in PMMA so that its negative characteristic can be used in making master moulds. PMMA thin films approximately 9 µm thick on Si were deposited by spin coating. The 2-MeV H+ ion beam was generated using a 1.7-MV tandem Tandetron accelerator. The beam was collimated to a 500×500 µm2 cross section using programmable proximity aperture lithography system with a real-time ion beam monitoring system and a high precision current integrator. The irradiated areas were investigated by a standard scanning electron microscope and a profilometer. It was found that both the ion beam flux and the stopping power of the ions in the polymer have a critical influence on the blister formation.

  6. Covalent cross-linking of cell-wall polysaccharides through esterified diferulates as a maize resistance mechanism against corn borers.

    Science.gov (United States)

    Barros-Rios, Jaime; Santiago, Rogelio; Jung, Hans-Joachim G; Malvar, Rosa A

    2015-03-04

    There is strong evidence to suggest that cross-linking of cell-wall polymers through ester-linked diferulates has a key role in plant resistance to pests; however, direct experimentation to provide conclusive proof is lacking. This study presents an evaluation of the damage caused by two corn borer species on six maize populations particularly selected for divergent diferulate concentrations in pith stem tissues. Maize populations selected for high total diferulate concentration had 31% higher diferulates than those selected for low diferulates. Stem tunneling by corn borer species was 29% greater in the population with the lowest diferulates than in the population with the highest diferulates (31.7 versus 22.6 cm), whereas total diferulate concentration was negatively correlated with stem tunneling by corn borers. Moreover, orthogonal contrasts between groups of populations evaluated showed that larvae fed in laboratory bioassays on pith stem tissues from maize populations with higher diferulates had 30-40% lower weight than larvae fed on the same tissues from maize populations with lower diferulates. This is the first report that shows a direct relationship between diferulate deposition in maize cell walls and corn borer resistance. Current findings will help to develop adapted maize varieties with an acceptable level of resistance against borers and be useful in special kinds of agriculture, such as organic farming.

  7. Controlled gelation kinetics of cucurbit[7]uril-adamantane cross-linked supramolecular hydrogels with competing guest molecules

    Science.gov (United States)

    Chen, Hao; Hou, Shengzhen; Ma, Haili; Li, Xu; Tan, Yebang

    2016-02-01

    Gelation kinetics of hydrogels is closely linked to many applications such as the development of injectable and printable hydrogels. However, the control of gelation kinetics without compromising the structure and other properties of the hydrogels, remains a challenge. Here, we demonstrate a method to control the gelation kinetics of cucurbit[7]uril-adamantane (CB[7]-AD) cross-linked supramolecular hydrogels by using competing guest molecules. The association between CB[7] and AD moieties on the polymer backbone was impeded by pre-occupying the CB[7] cavity with competing guest molecules. By using various guest molecules and concentrations, the gelation of the hydrogels could be varied from seconds to hours. The strong interaction of CB[7]-AD pair endue the hydrogels good mechanical properties and stability. Moreover, the binding of functionalized guest molecules of CB[7] moieties offers a facile approach for tailoring of the hydrogels’ scaffold. Combined with hydrogel injection and printing technology, this method offers an approach for the development of hydrogels with advanced temporal and spatial complexity.

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

    Science.gov (United States)

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

    2015-01-01

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

  9. Multi-ring Aggregate Formation in Styrene Polymers

    Institute of Scientific and Technical Information of China (English)

    何炳林; 王国昌; 叶彦春; 栗凤珍; 高传喜

    1994-01-01

    The photophysical properties of some cross-linked/linear styrene polymers are studied.Ithas been further demonstrated that the phenyl multi-ring aggregate forms not only in excited state instyrene/divinylbenzene cross-linked polymers hut also in ground state.Moreover,the similar multi-ring ag-gregate has also been observed in linear polystyrene with structural heterogeneity.These results are ex-plained in terms of "superdense structure" formed by chemical cross-linking and physical gelation,whichcharacterize the morphological heterogeneity in styrene polymers.

  10. Acute corneal hydrops during pregnancy with spontaneous resolution after corneal cross-linking for keratoconus: a case report.

    Science.gov (United States)

    Stock, Ricardo Alexandre; Thumé, Thaís; Bonamigo, Elcio Luiz

    2017-02-25

    Keratoconus may progress to acute corneal hydrops even after cross-linking. In some cases, keratoconus progresses during pregnancy. In this report, we present a case of a patient with increased anterior stromal resistance after cross-linking that would favor nonprogression of keratoconus during pregnancy. We report that cross-linking is likely to have had a protective effect in a white pregnant patient with acute corneal hydrops who showed rapid improvement, as documented by corneal topography. Improvement occurred within 8 days, whereas up to 250 days are reported in the literature. No keratoconus progression occurred in the 20-month follow-up period. Cross-linking failed to prevent the occurrence of acute corneal hydrops after rupture of Descemet's membrane but most likely helped to accelerate the resolution of the condition. Corneal hardening resulting from cross-linking may have also contributed to stabilizing keratoconus during pregnancy.

  11. The process of EDC-NHS cross-linking of reconstituted collagen fibres increases collagen fibrillar order and alignment

    Directory of Open Access Journals (Sweden)

    D. V. Shepherd

    2015-01-01

    Full Text Available We describe the production of collagen fibre bundles through a multi-strand, semi-continuous extrusion process. Cross-linking using an EDC (1-ethyl-3-(3-dimethylaminopropylcarbodiimide, NHS (N-hydroxysuccinimide combination was considered. Atomic Force Microscopy and Raman spectroscopy focused on how cross-linking affected the collagen fibrillar structure. In the cross-linked fibres, a clear fibrillar structure comparable to native collagen was observed which was not observed in the non-cross-linked fibre. The amide III doublet in the Raman spectra provided additional evidence of alignment in the cross-linked fibres. Raman spectroscopy also indicated no residual polyethylene glycol (from the fibre forming buffer or water in any of the fibres.

  12. The process of EDC-NHS cross-linking of reconstituted collagen fibres increases collagen fibrillar order and alignment

    Science.gov (United States)

    Shepherd, D. V.; Shepherd, J. H.; Ghose, S.; Kew, S. J.; Cameron, R. E.; Best, S. M.

    2015-01-01

    We describe the production of collagen fibre bundles through a multi-strand, semi-continuous extrusion process. Cross-linking using an EDC (1-ethyl-3-(3-dimethylaminopropyl)carbodiimide), NHS (N-hydroxysuccinimide) combination was considered. Atomic Force Microscopy and Raman spectroscopy focused on how cross-linking affected the collagen fibrillar structure. In the cross-linked fibres, a clear fibrillar structure comparable to native collagen was observed which was not observed in the non-cross-linked fibre. The amide III doublet in the Raman spectra provided additional evidence of alignment in the cross-linked fibres. Raman spectroscopy also indicated no residual polyethylene glycol (from the fibre forming buffer) or water in any of the fibres.

  13. Molecular contacts for chlorosome envelope proteins revealed by cross-linking studies with chlorosomes from Chlorobium tepidum

    DEFF Research Database (Denmark)

    Li, Hui; Frigaard, Niels-Ulrik; Bryant, Donald A

    2006-01-01

    type and mutants lacking a single chlorosome protein were cross-linked with the zero-length cross-linker 1-ethyl-3-[3-(dimethylamino)propyl]carbodiimide (EDC) and analyzed by gel electrophoresis. Similar cross-linking products were observed when the time and temperature were varied or when EDC...... was replaced with glutaraldehyde. Specific interactions between chlorosome proteins in cross-linked products were identified by immunoblotting with polyclonal antibodies raised against recombinant chlorosome proteins. We confirmed these interactions by demonstrating that these products were missing...... in appropriate mutants. Confirming the location of CsmA in the paracrystalline baseplate, cross-linking showed that CsmA forms dimers, trimers, and homomultimers as large as dodecamers and that CsmA directly interacts with the Fenna-Matthews-Olson protein. Cross-linking further suggests that the precursor form...

  14. Synthesis and Characterisation of Novel Cross Linked Biopolyesters from Olive Oil as Eco-friendly Biodegradable Materials

    Directory of Open Access Journals (Sweden)

    J. Shakina

    2012-01-01

    Full Text Available Novel cross linked biopolyesters were synthesised from naturally available olive oil, oligomeric polytriglyceride fumarate (o-PTF was prepared by glycerolysis of the olive oil followed by condensation with maleic anhydride. The (o-PTF was characterised by spectral (FTIR, UV, NMR and physicochemical properties (specific gravity, viscosity, saponification value, iodine value. The molecular weight of o-PTF was estimated using gel permeation chromatography (GPC. The cross linked biopolyesters were prepared by treating o-PTF of olive with N-vinyl-2-pyrrolidone and vinyl acetate. The cross linked biopolyesters were evaluated for spectral properties (FT IR, cross linked density, thermal properties, mechanical properties and biodegradation. The potential antifungal and anti bacterial activities of the newly prepared biopolyesters were evaluated. The environment degradation was assessed by soil burial test. The outcome of the studies has revealed that the newly prepared cross linked biopolyesters are potential biodegradable material for various consumer application like package materials and agricultural applications.

  15. Blind testing of cross-linking/mass spectrometry hybrid methods in CASP11.

    Science.gov (United States)

    Schneider, Michael; Belsom, Adam; Rappsilber, Juri; Brock, Oliver

    2016-09-01

    Hybrid approaches combine computational methods with experimental data. The information contained in the experimental data can be leveraged to probe the structure of proteins otherwise elusive to computational methods. Compared with computational methods, the structures produced by hybrid methods exhibit some degree of experimental validation. In spite of these advantages, most hybrid methods have not yet been validated in blind tests, hampering their development. Here, we describe the first blind test of a specific cross-link based hybrid method in CASP. This blind test was coordinated by the CASP organizers and utilized a novel, high-density cross-linking/mass-spectrometry (CLMS) approach that is able to collect high-density CLMS data in a matter of days. This experimental protocol was developed in the Rappsilber laboratory. This approach exploits the chemistry of a highly reactive, photoactivatable cross-linker to produce an order of magnitude more cross-links than homobifunctional cross-linkers. The Rappsilber laboratory generated experimental CLMS data based on this protocol, submitted the data to the CASP organizers which then released this data to the CASP11 prediction groups in a separate, CLMS assisted modeling experiment. We did not observe a clear improvement of assisted models, presumably because the properties of the CLMS data-uncertainty in cross-link identification and residue-residue assignment, and uneven distribution over the protein-were largely unknown to the prediction groups and their approaches were not yet tailored to this kind of data. We also suggest modifications to the CLMS-CASP experiment and discuss the importance of rigorous blind testing in the development of hybrid methods. Proteins 2016; 84(Suppl 1):152-163. © 2016 The Authors Proteins: Structure, Function, and Bioinformatics Published by Wiley Periodicals, Inc.

  16. Fluorescence imaging of tryptophan and collagen cross-links to evaluate wound closure ex vivo

    Science.gov (United States)

    Wang, Ying; Ortega-Martinez, Antonio; Farinelli, Bill; Anderson, R. R.; Franco, Walfre

    2016-02-01

    Wound size is a key parameter in monitoring healing. Current methods to measure wound size are often subjective, time-consuming and marginally invasive. Recently, we developed a non-invasive, non-contact, fast and simple but robust fluorescence imaging (u-FEI) method to monitor the healing of skin wounds. This method exploits the fluorescence of native molecules to tissue as functional and structural markers. The objective of the present study is to demonstrate the feasibility of using variations in the fluorescence intensity of tryptophan and cross-links of collagen to evaluate proliferation of keratinocyte cells and quantitate size of wound during healing, respectively. Circular dermal wounds were created in ex vivo human skin and cultured in different media. Two serial fluorescence images of tryptophan and collagen cross-links were acquired every two days. Histology and immunohistology were used to validate correlation between fluorescence and epithelialization. Images of collagen cross-links show fluorescence of the exposed dermis and, hence, are a measure of wound area. Images of tryptophan show higher fluorescence intensity of proliferating keratinocytes forming new epithelium, as compared to surrounding keratinocytes not involved in epithelialization. These images are complementary since collagen cross-links report on structure while tryptophan reports on function. HE and immunohistology show that tryptophan fluorescence correlates with newly formed epidermis. We have established a fluorescence imaging method for studying epithelialization processes during wound healing in a skin organ culture model, our approach has the potential to provide a non-invasive, non-contact, quick, objective and direct method for quantitative measurements in wound healing in vivo.

  17. Progress of research on corneal collagen cross-linking for corneal melting

    Directory of Open Access Journals (Sweden)

    Ke-Ren Xiao

    2016-06-01

    Full Text Available Corneal collagen cross-linking(CXLcould increase the mechanical strength, biological stability and halt ectasia progression due to covalent bond formed by photochemical reaction between ultraviolet-A and emulsion of riboflavin between collagen fibers in corneal stroma. Corneal melting is an autoimmune related noninfectious corneal ulcer. The mechanism of corneal melting, major treatment, the basic fundamental of ultraviolet-A riboflavin induced CXL and the clinical researches status and experiment in CXL were summarized in the study.

  18. Histological response to injected gluteraldehyde cross-linked bovine collagen based implant in a rat model

    Directory of Open Access Journals (Sweden)

    Cağlar Melda

    2006-02-01

    Full Text Available Abstract Background The aim of present study is to investigate the short and long term histopathological alterations caused by submucosal injection of gluteraldehyde cross-linked bovine collagen based on an experimental rat model. Methods Sixty Sprague-Dawley rats were assigned into two groups as group I and II each containing 30 rats. 0.1 ml of saline solution and 0.1 ml of gluteraldehyde cross-linked bovine collagen were injected into the submucosa of bladder of first (control and second groups, respectively. Both group I and II were further subdivided into 3 other groups as Group IA, IB, IC and Group IIA, IIB, IIC according to the sacrification period. Group IA and IIA, IB and IIB, IC and IIC rats (10 rats for each group were sacrificed 3, 6, and 12 months after surgical procedure, respectively. Two slides prepared from injection site of the bladder were evaluated completely for each rat by being unaware of the groups and at random by two independent senior pathologists to determine the fibroblast invasion, collagen formation, capillary ingrowth and inflammatory reaction. Additionally, randomized brain sections from each rat were also examined to detect migration of the injection material. The measurements were made using an ocular micrometer at ×10 magnification. The results were assessed using t-tests for paired and independent samples, with p Results Migration to the brain was not detected in any group. Significant histopathological changes in the gluteraldehyde cross-linked bovine collagen injected groups were fibroblast invasion in 93.3%, collagen formation in 73.3%, capillary ingrowth in 46.6%, inflamatory reaction in 20%. Conclusion We emphasize that the usage of gluteraldehyde cross-linked bovine collagen in children appears to be safe for endoscopic treatment of vesicoureteral reflux.

  19. Synthesis and Properties of Lactic Acid-based Cross-linked Poly(ester-amide)

    Institute of Scientific and Technical Information of China (English)

    Yue Ying HE; Cong Ming XIAO

    2006-01-01

    A novel lactic acid-based cross-linked poly(ester-amide) (LCPEA) was synthesized. The gel fraction of the LCPEA could be modulated by the reaction conditions and it affected the mechanical and thermal properties of the LCPEA. The tensile strength, elastic modulus and bend strength of the LCPEA of 65% gel fraction were 4.65, 136.55 and 39.63 MPa, respectively. The thermal decomposition temperature (50 wt%) of the LCPEA was around 410 ℃.

  20. Identification of dityrosine cross-linked sites in oxidized human serum albumin.

    Science.gov (United States)

    Annibal, Andrea; Colombo, Graziano; Milzani, Aldo; Dalle-Donne, Isabella; Fedorova, Maria; Hoffmann, Ralf

    2016-04-15

    Reactive oxygen species (ROS) can oxidize virtually all cellular components. In proteins cysteine, methionine, tryptophan, and tyrosine residues are most prone to oxidation and their oxidized forms are thus considered as biomarkers of oxidative protein damages. Ultraviolet radiation and some endogenous ROS can produce tyrosine radicals reacting with other tyrosine residues yielding intra- or intermolecular cross-links in proteins. These 3,3'-dityrosines can be quantified by their characteristic fluorescence, but analytical methods to identify the modification sites in proteins are still missing. Although mass spectrometry (MS) is routinely used to map other post-translational modifications, the analysis of dityrosines is challenged by simultaneous fragmentations of both cross-linked peptide chains producing complex tandem mass spectra. Additionally, the fragmentation patterns differ from linear peptides. Here, we studied the fragmentation behavior of dityrosine cross-linked peptides obtained by incubating three peptides (AAVYHHFISDGVR, TEVSSNHVLIYLDK, and LVAYYTLIGASGQR) with horseradish peroxidase in the presence of hydrogen peroxide. Homo- and hetero-dimerization via dityrosine was monitored by fluorescence spectroscopy and MS. The fragmentation characteristics of dityrosine-linked peptides were studied on an ESI-LTQ-Orbitrap-MS using collision induced dissociation, which allowed localizing the cross-linked positions and provided generic rules to identify this oxidative modification. When human serum albumin oxidized with 50-fold molar excess of HOCl in phosphate buffer saline was analyzed by nanoRPC-ESI-MS/MS, an automatic database search considering all possible (in-silico generated) tyrosine-containing peptides as dynamic modifications revealed four different types of oxidatively modified tyrosine residues including dityrosines linking ten different Tyr residues. The automatic database search was confirmed by manual interpretation of each tandem mass spectrum.