Presence Of Crosslinker Research Articles

Fabrication of dual-sensitive keratin-based polymer hydrogels and their controllable release behaviors

Using feather keratin (FK) as a biocompatible and inexpensive biopolymer, a kind of dual-sensitive keratin-based polymer hydrogel (FK/PNiPA/PIAc-Gel) with interpenetrating network structure was prepared by two-step polymerization of N-isopropyl acrylamide (NiPA) and itaconic acid (IAc) in presence of crosslinker. After being characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis and scanning electron microscopy, its swelling behaviors and environmental sensitivity were investigated. The obtained biopolymer based hydrogel has good swelling and deswelling performance, and it is sensitive to pH value, temperature and salts of environment. Using anticancer drug, doxorubicin hydrochloride (Dox·HCl), and Bovine serum albumin (BSA) as different drug molecules, its release behaviors in different environment were investigated. It was found that the release behaviors of FK/PNiPA/PIAc-Gel were controllable via adjusting pH value or temperature of environment. The cumulative release of the anticancer drug (Dox·HCl) reached 93.3% within 16 h, and the cumulative release rate of macromolecular drug (BSA) got to 75.9% in 24 h. In summary, the keratin-based biopolymer hydrogel with interpenetrating network structure, pH-sensitivity and temperature sensitivity are potentially applied to sustain drug carrier and humid medicinal material in the biomedical field or clinical nursing field.

In-situ photocrosslinkable nanohybrid elastomer based on polybutadiene/polyhedral oligomeric silsesquioxane

Hydroxyl functionalized nano-sized POSS or ethyleneglycol as diol monomers was incorporated to hydroxyl-terminated polybutadiene (HTPBD) chain in the presence of fumaryl chloride as extender. Blue light photocrosslinking system based on camphorquinone (photoinitiator) and dimethylaminoethyl methacrylate (accelerator) was applied to cure these two synthesized fumarate based macromers. Self-crosslinkability of unsaturated macromers and also crosslinking in presence of a reactive diluent were investigated in absence and presence of 1,4-butanediol dimethacrylate, respectively. Finally, photocured samples were characterized by XRD, SEM, equilibrium swelling study, TGA, DMTA, AFM and cell culture. The results showed that incorporation of POSS nanoparticle into the polymer matrix with a perfect distribution and dispersion can enhance thermal stability, mechanical and biocompatibility properties which can prove a good potential of this in-situ photocrosslinkable nanohybrid in medical applications.

Memory phenomenon in a lanthanum based bulk metallic glass

In this paper, we experimentally investigate two memory phenomena in a lanthanum based bulk metallic glass (BMG). While the temperature memory effect (TME) is not found by differential scanning calorimeter (DSC) test, shape recovery is observed in samples indented at both low and high temperatures. In terms of shape memory related characteristics, this BMG shares some features of shape memory alloys (SMAs) due to its metal nature, and some other features of shape memory polymers (SMPs) owing to its glassy–rubbery transition. The formation of protrusion in the polished sample after heating to super-cooled liquid region (SCLR) indicates that surface tension is not a necessarily positive contributor for shape recovery. Release of internal elastic stress is concluded as the major player. Although the amorphous nature of BMGs enables for storing appreciable amount of internal elastic stress upon deformation, without the presence of cross-linker as in typical SMPs, the shape recovery in BMGs is rather limited.

Fumaric acid cross-linked carboxymethylcellulose/poly(vinyl alcohol) hydrogels

Carboxymethylcellulose (CMC)/poly(vinyl alcohol) (PVA) hydrogels were synthesized by crosslinking in presence of fumaric acid (FA) and characterized with different methods (FTIR, TGA/DTG, XRD and SEM) of analysis. The water absorbencies of these hydrogels in different pH solutions were investigated. The equilibrium swelling capacity of the gels reduced due to increasing crosslinking between CMC and PVA. pH sensitivity and reversibility of hydrogels were also investigated. The results indicated that the hydrogels had pH reversibility behavior which swelled at pH = 8 and shrinked at pH = 2.6. The FTIR results pointed toward the cross-linking reaction between carboxyl group of FA with hydroxyl groups of PVA and NaCMC through ester formation. The crosslinking improved the thermal stability of the hydrogels. SEM analysis showed highly porous structure for 10FA and 15FA hydrogels.

Ultraviolet-induced polymerization of superabsorbent composites based on sodium humate and its urea release behavior

This study was carried out to develop a superabsorbent composite for agriculture application, which is based on acrylic acid and sodium humate and prepared by ultraviolet-induced polymerization in the presence of crosslinker and composite initiator.

Thermo-responsive hydrogels containing mesoporous silica toward controlled and sustainable releases

Here we prepare thermo-responsive hydrogel containing mesoporous silica (KIT-6) with high surface area. Our hybrid hydrogel is prepared by gelation of NIPAM monomer with mesoporous silica particles in presence of cross linker. Owing to the doped mesoporous silica, a large amount of guest molecules are adsorbed easily. With increase of temperature, the hybrid hydrogel shrinks to retard the release of guest molecules.

Exploring Cardiac Calcium ATPase Dimerization

Previous studies have suggested that the cardiac calcium ATPase (SERCA) can form homo-dimers. To investigate this in heterologous cells, we fused Cerulean (Cer) or yellow fluorescent protein (YFP) to the N-terminus of canine SERCA2a. We measured 18% maximum fluorescence resonance energy transfer (FRET) from Cer-SERCA to YFP-SERCA, indicating an interaction between SERCA protomers. To determine whether the measured FRET was specific, we co-transfected cells with unlabeled SERCA to compete for binding with Cer-SERCA and YFP-SERCA. FRET progressively decreased with increasing molar ratios of unlabeled competitor SERCA to a minimum of 5%. Competition with increasing molar ratios of unlabeled phospholamban (PLB) did not reduce the measured FRET or the apparent affinity of the SERCA dimer. In order to determine whether PLB phosphorylation status altered SERCA dimerization, we enhanced phosphorylation of PLB at serine 16 by foskolin or using a phosphomimetic PLB (S16E). This did not alter the maximum FRET or the apparent affinity of the SERCA protomers for each other. Additionally, the apparent affinity was unchanged with various concentrations of cytosolic calcium or ATP, or in the presence of the SERCA inhibitor, thapsigargin. SERCA dimerization was also suggested by co-immunoprecipitation experiments in cells co-transfected with YFP-SERCA and myc-tagged SERCA. Immunoprecipitation with an anti-mycTag antibody co-immunoprecipitated YFP-SERCA, as detected by western blot. To analyze SERCA dimerization in cardiac myocytes, we used benzophenone-4-maleimide crosslinking. Rabbit left ventricular myocytes were isolated and permeabilized in the presence of crosslinker. Western blot analysis revealed two bands: the first at approximately 110 kD, consistent with monomeric SERCA, and the second at approximately 200 kD, a value compatible with the predicted molecular weight of a homo-dimer. Our data suggest that SERCA2a forms obligate homo-dimers in live cells, including cardiac myocytes. We have not determined a regulatory component for this interaction.

Crosslinking-induced morphology change of latex nanoparticles: A study of RAFT-mediated polymerization in aqueous dispersed media using amphiphilic double-brush copolymers as reactive surfactants

Amphiphilic double-brush copolymers (DBCs) with each graft site quantitatively carrying both a hydrophilic poly(ethylene oxide) (PEO) graft and a hydrophobic polystyrene (PSt) graft are synthesized by sequential reversible addition-fragmentation chain transfer (RAFT) polymerization and ring-opening metathesis polymerization (ROMP). These DBCs are used as both surfactants and polyfunctional RAFT agents in the radical polymerization of St in aqueous dispersed media. Miniemulsions with narrowly dispersed St-based nanodroplets are readily obtained after ultrasonication of the reaction mixtures. Without the presence of crosslinker, chain-extension polymerization of St from the DBCs yields well-defined polymeric latexes with narrow size distributions. However, with the presence of divinylbenzene (DVB) as the crosslinker, vesicular polymeric nanoparticles are formed as the major product. Such crosslinking-induced change in morphology of the resulting latex nanomaterials may be ascribed to the increase of interfacial curvature in the heterophase systems during crosslinking polymerization. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 3250–3259

Can green solvents be alternatives for thermal stabilization of collagen?

“Go Green” campaign is gaining light for various industrial applications where water consumption needs to be reduced. To resolve this, industries have adopted usage of green, organic solvents, as an alternative to water. For leather making, tanning industry consumes gallons of water. Therefore, for adopting green solvents in leather making, it is necessary to evaluate its influence on type I collagen, the major protein present in the skin matrix. The thermal stability of collagen from rat tail tendon fiber (RTT) treated with seven green solvents namely, ethanol, ethyl lactate, ethyl acetate, propylene carbonate, propylene glycol, polyethylene glycol-200 and heptane was determined using differential scanning calorimetry (DSC). Crosslinking efficiency of basic chromium sulfate and wattle on RTT in green solvents was determined. DSC thermograms show increase in thermal stability of RTT collagen against heat with green solvents (>78°C) compared to water (63°C). In the presence of crosslinkers, RTT demonstrated thermal stability >100°C in some green solvents, resulting in increased intermolecular forces between collagen, solvent and crosslinkers. The significant improvement in thermal stability of collagen potentiates the capability of green solvents as an alternative for water.

Preparation of Antimicrobial PHEMA-<i>g</i>-PCBMAE Hydrogels with Improved Mechanical Properties

A series of poly (hydroxyethyl methacrylate)-g-polycarboxybetaine methacrylate ester (PHEMA-g-PCBMAE) hydrogels were synthesized using reversible addition-fragmentation chain transfer (RAFT) polymerization in the presence of crosslinker. Then differential scanning calorimetry (DSC) was used to characterize PHEMA-g-PCBMAE hydrogels. The compression stresses of these hydrogels were investigated to evaluate the mechanical properties. The mechanical study suggested that PHEMA-g-PCBMAE hydrogels presented improved mechanical strengths comparing with polycarboxybetaine methacrylate ester (PCBMAE) hydrogel. Besides, the antimicrobial properties of PHEMA-g-PCBMAE hydrogels also estimated by usingStaphylococcus aureusas a model bacterial.

Dextrin crosslinked with poly(lactic acid): A novel hydrogel for controlled drug release application

AbstractA new class of biodegradable crosslinked hydrogel, consisting of hydrophobic polylactic acid (PLA) and hydrophilic dextrin in presence of crosslinker N,N‐methylene bisacrylamide (MBA) has been synthesized by free‐radical polymerization technique using potassium persulfate (KPS) as initiator. By variation of crosslinker concentration, a series of hydrogels have been prepared and the optimized grade has been selected on the basis of higher crosslinking efficiency as well as lower equilibrium swelling characteristics, XRD analysis. The hydrogels have been characterized by FTIR spectra, 13C‐NMR spectra, CHN analysis, SEM analysis, swelling characteristics, and toxicity study. In vitro release study of model drugs (ciprofloxacin and ornidazole) from hydrogel matrix has been performed in various buffer solutions at 37°C. The drug release kinetics and mechanism have been studied using zero order, first‐order kinetic models, Korsemeyar–Peppas model, Higuchi model, Hixson–Crowell model, and nonlinear Kopcha model. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40039.

Modeling and Comparison of Different Simulations for Release of Amoxicillin from Chitosan Hydrogels

In this research work, different devices made of glutaraldehyde cross-linked chitosan hydrogels loaded by amoxicillin, have been prepared using freeze-drying method. Effects of system parameters such as cross-linker concentration, pH, and gel structure on the morphology and release behavior of devices have been investigated using standard methods. Morphological studies were performed using SEM instrument and controlled releases are followed via spectrophotometeric method. Reaction of glutaraldehyde with chitosan has been studied using FTIR instrument. SEM micrographs have shown that with increasing cross-linker percentage in hydrogel, pore sizes increased where pore size distribution decreased. Considering that biocompatibility and drug release rate of the device can be affected by presence of cross-linker, effects of cross-linker concentration on drug release rate and biocompatibility of the device have been investigated and its appropriate concentration have been determined. Experimental release data were analyzed using Higuchi model originally developed for porous devices and swellable polymer model presented for porous swellable systems. Comparison of experimental results and model predictions shows that the Higuchi's model would be valid for systems with molar ratio (cross-linker-chitosan amine groups) less than 0.18, whereas the swellable polymer model could better predict behavior of systems with molar ratio more than 0.18.

Kinetics of Free-Radical Cross-Linking Polymerization: Comparative Experimental and Numerical Study

Modeling free radical polymerization processes in the presence of cross-linkers is a challenging problem that has been addressed using numerous techniques for over more than half a century. However, a model providing a comprehensive description of the phenomenon has not been proposed yet. In this work, we implement a simple free-radical polymerization scheme of a monovinyl (difunctional) monomer and a divinyl (tetrafunctional) cross-linker in a Monte Carlo (MC) scheme, which describes polymer dynamics using a bond-fluctuation model. MC simulations allow us to follow the entire polymerization kinetics and the formation of a percolating network (gel phase) by realistically taking into account diffusion limitations, to extract scaling information at the percolation threshold and to recover the distribution of number of monomer units between two successive fully cross-linked units, from which the extent of swelling can be computed. The predictions of MC simulations are also successfully compared to a kinetic model based on numerical fractionation, with kinetic constants used as fitting parameters. MC data and kinetic simulations are compared to some experimental data on the swelling behavior of polyacrylamide hydrogels and of poly(methyl methacrylate) (PMMA) gels, exhibiting good agreement. We conclude that the proposed MC simulation scheme represents a powerful tool from which precious and experimentally inaccessible information on polymerization processes in the presence of cross-linkers can be extracted.

Cross-linked Aromatic Polymers for High Durability PEM Membranes: Materials and Methods

Sulfonated aromatic polymers (SAP) are promising ionomer materials, however for applications as fuel cell membranes these polymers must be improved in terms of durability. The goal is to achieve a locally high density of functional groups such as sulfonic acid groups, but to keep the swelling low by appropriate cross-linking. Thermal cross-linking in presence of residual solvent dimethylsulfoxide without any addition of cross-linker molecules increases spectacularly the mechanical and hydrolytic stability of SAP, making them suitable for use up to 130 {degree sign}C. The developed method is also inexpensive, being incorporated in the normal membrane casting procedure.

Novel Fluorescent Membrane for Metronidazole Sensing Prepared by Covalent Immobilization of a Pyrenebutyric Acid Derivative

In the present paper, we report the fabrication of a new sensing membrane for fluorescence detection of metronidazole (MNZ). Briefly, a pyrenebutyric acid derivative, 2-(methacryloyloxy) ethyl-4-(1-pyrenyl) butanoate (MPB) with a double bond, was synthesized and copolymerized with 2-hydroxyethylmethacrylate (HEMA) on the activated glass surface by thermal initiation in the presence of cross-linker. The sensor responds linearly to metronidazole in the concentration range of 1.23~35.48 mg.L(-1) in aqueous solution with a detection limit of 0.36 mg.L(-1). The lifetime is enhanced by covalently immobilizing the pyrenebutyric acid derivative on glass slide, which hinders leaching of the dye from the membrane. The sensor could be regenerated after use by washing in methanol (RSD = 2.42 %), and it shows sufficient stability, and selectivity. Interference of other pharmaceuticals on membrane performance is discussed. The developed membrane has been successfully applied for the direct determination of metronidazole in human serum sample without pretreatment.

Initiator Concentration Effect on Rheological Properties of a pH-Sensitive Semi-IPN Hydrogel Based on Konjac Glucomannan and Methacrylic Acid

A pH-sensitive semi-interpenetrating polymer network (semi-IPN) hydrogel based on Konjac glucomannan(KGM) and methylacrylic acid(MAA) was prepared by free radical polymerization at different concentrations of initiator potassium persulfate (KPS) in presence of crosslinker N,N-methylene-bis-acrylamide (MBA). The chemical structure and rheological properties of hydrogels were characterized by FT-IR and rheometry, respectively. In addition, the swelling behavior of the hydrogels were studied in buffer solution at different pHs.

High performance sulfonated aromatic ionomers by solvothermal macromolecular synthesis

Thermal cross-linking in presence of residual solvent dimethylsulfoxide without any addition of cross-linker molecules is described. This elegant method increases spectacularly the mechanical and hydrolytic stability of sulfonated aromatic polymers (SAP), making them suitable for use in liquid water also at 145 °C. Data on water uptake, mechanical properties and proton conductivity are presented and discussed from a bond energy point of view. The developed method is also inexpensive, being incorporated in the normal membrane casting procedure. This opens new horizons and hitherto conventionally disregarded SAP membranes should be reconsidered as fuel cell membranes.

Stimuli-Responsive Hydrogel Hollow Capsules by Material Efficient and Robust Cross-Linking-Precipitation Synthesis Revisited

Monodisperse stimuli-responsive hydrogel capsules were synthesized in the 100-nm-diameter to 10-μm-diameter range from poly(4-vinylpyridine) (P4VP) and poly(ethyleneimine) (PEI) through a simple, efficient two-step cross-linking-precipitation template method under conditions of a good solvent. In this method, the core-shell particles were obtained by the deposition (heterocoagulation mechanism) of the cross-linked P4VP, PEI, or their mixtures on the surfaces of the template colloidal silica particles in nitromethane (for PEI) or a nitromethane-acetone mixture (for P4VP and P4VP-PEI mixtures) in the presence of cross-linker 1,4-diiodobutane. The cross-linked polymeric shell swollen in a good solvent stabilized the core-shell colloids. This mechanism provided the conditions for the synthesis of core-shell colloids in a submicrometer range of dimensions with an easily adjusted shell thickness (wall of the capsules) ranging from a few to hundreds of nanometers. The chemical composition of the shell was tuned by varying the ratio of co-cross-linked shell-forming polymers (P4VP and PEI). In the second step, the hollow capsules were obtained by etching the silica core in HF solutions. In this step, the colloidal stability of the hollow capsules was provided by ionized P4VP and PEI cross-linked shells. The hollow capsules demonstrate that the pH- and ionic-strength-triggered swelling and shrinking result in size-selective uptake and release properties. Cross-linked via quaternized functional groups, P4VP capsules undergo swelling and shrinking transitions at a physiologically relevant pH of around 6. The 200-nm-diameter hollow capsule with 25-nm-thick walls demonstrated a factor of 2 greater capacity to accommodate cargo molecules than the core-shell particles of the same dimensions because of an internal compartment and a combination of radial and a circumferential swelling modes in the capsules.

The use of N,N′-diallylaldardiamides as cross-linkers in xylan derivatives-based hydrogels

N,N′ -Diallylaldardiamides (DA) were synthesized from galactaric, xylaric, and arabinaric acids, and used as cross-linkers together with xylan (X) derivatives to create new bio-based hydrogels. Birch pulp extracted xylan was derivatized to different degrees of substitution of 1-allyloxy-2-hydroxy-propyl (A) groups combined with 1-butyloxy-2-hydroxy-propyl (B) and/or hydroxypropyl (HP) groups. The hydrogels were prepared in water solution by UV induced free-radical cross-linking polymerization of derivatized xylan polymers without DA cross-linker (xylan derivative hydrogel) or in the presence of 1 or 5 wt % of DA cross-linker (DA hydrogel). Commercially available cross-linker (+)- N,N′-diallyltartardiamide (DAT) was also used. The degree of substitution (DS) of A, B, and HP groups in xylan derivatives was analyzed according to 1H NMR spectra. The DS values for the cross-linkable A groups of the derivatized xylans were 0.4 (HPX-A), 0.2 (HPX-BA), and 0.4 (X-BA). The hydrogels were examined with FT-IR and elemental analysis which proved the cross-linking successful. Water absorption of the hydrogels was examined in deionized water. Swelling degrees up to 350% were observed. The swollen morphology of the hydrogels was assessed by scanning electron microscopy (SEM). The presence of cross-linkers in DA hydrogels had only a small impact on the water absorbency when compared to xylan derivative hydrogels but a more uniform pore structure was achieved.

Structural Dynamics of an Actin Spring

Actin-based motility in cells is usually associated with either polymerization/depolymerization in the presence of cross-linkers or contractility in the presence of myosin motors. Here, we focus on a third distinct mechanism involving actin in motility, seen in the dynamics of an active actin spring that powers the acrosomal reaction of the horseshoe crab ( Limulus polyphemus) sperm. During this process, a 60- μm bent and twisted bundle of cross-linked actin uncoils and becomes straight in a few seconds in the presence of Ca 2+. This straightening, which occurs at a constant velocity, allows the acrosome to forcefully penetrate the egg. Synthesizing ultrastructural information with the kinetics, energetics, and imaging of calcium binding allows us to construct a dynamical theory for this mechanochemical engine consistent with our experimental observations. It also illuminates the general mechanism by which energy may be stored in conformational changes and released cooperatively in ordered macromolecular assemblies.