Effect of silane coupling agent on swelling behaviors and mechanical properties of thermosensitive hybrid gels

A series of organic–inorganic hybrid thermosensitive gels with three different structures were prepared from N‐isopropylacrylamide (NIPAAm), and N, N′‐methylenebisacrylamide (NMBA) and tetraethoxysilane (TEOS) [N‐IPN]; NIPAAm, 3‐(trimethoxysilyl) propyl methacrylate (TMSPMA) as coupling agent and TEOS [NT‐IPN]; and NIPAAm, TMSPMA, and TEOS [NT‐semi‐IPN] by emulsion polymerization and sol–gel reaction in this study. The effect of different gel structures and coupling agent on the swelling behavior, mechanical properties, and morphologies of the present gels was investigated. Results showed that the properties of the gels would be affected by the gel networks such as IPN or semi‐IPN and with or without existence of TMSPMA as the bridge chain between networks. The NT‐semi‐IPN gel had higher swelling ratio and faster diffusion rate because poly(NIPAAm) moiety in the semi‐IPN gels was not restricted by NMBA network. However, the IPN gels such as N‐IPN and NT‐IPN had good mechanical properties and lower swelling ratio, but had a poor thermosensitivity due to the addition of coupling agent, TMSPMA, into the gel system that resulted in denser link between organic and inorganic components. The morphology showed that IPN gels had partial aggregation (siloxane domain) and showed some denser phases. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effects of TEOS contents on swelling behaviors and mechanical properties of thermosensitive hybrid gels

A series of organic‐inorganic hybrid thermosensitive gels with three different structures and different contents of tetraethoxysilane (TEOS) were prepared from N‐isopropylacrylamide (NIPAAm), and N,N′‐methylene‐bis‐acrylamide (NMBA) and TEOS [N‐IPN]; NIPAAm, 3‐(trimethoxysilyl) propyl methacrylate (TMSPMA) as coupling agent and TEOS [NT‐IPN]; and NIPAAm, TMSPMA and TEOS [NT‐semi‐IPN] by emulsion polymerization and sol‐gel reaction in this study. The effect of TEOS content on the swelling behavior, mechanical properties, and morphologies of the present gels was investigated. Results showed that the properties of the gels would be affected by the gel networks such as IPN or semi‐IPN, existence of TMSPMA as the bridge chain between networks, and content of TEOS. The NT‐semi‐IPN gel had higher swelling ratio because poly (NIPAAm) moiety in the semi‐IPN gels was not restricted by NMBA network. However, the IPN gels such as N‐IPN and NT‐IPN had good mechanical properties and lower swelling ratio, but had bad thermosensitivity due to the addition of coupling agent, TMSPMA, into the gel system that resulted in denser link between organic and inorganic components. Increasing TEOS content would also reduce the thermosensitivity of the hybrid gels. The morphology showed that IPN gels had partial aggregation (siloxane domain) and showed some denser phases. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

An interpenetrating network biohydrogel of gelatin and gellan gum by using a combination of enzymatic and ionic crosslinking approaches

Gelatin is a popular substrate for cell culture applications due to its biocompatibility and biodegradability. However, the mechanical property of gelatin is not satisfactory in certain tissue engineering areas where tunable and higher mechanical strengths are required. To achieve this purpose without exposure of materials to cytotoxic chemicals or procedures, a new biohydrogel of gelatin and gellan gum with an interpenetrating network (IPN) structure was prepared using a combination of enzymatic and ionic crosslinking approaches. The gelation procedure and thermal stability of the IPN structure were demonstrated in detail by a rheological study. The resulting IPN biohydrogel exhibited significantly increased and tunable mechanical strength, decreased swelling ratios and lower degradation rate compared with pure gelatin gel. The composite biohydrogels supported the attachment and proliferation of L929 fibroblasts as shown in vitro. These results indicate that this mechanically robust biohydrogel has the promising potential for serving as a cell support in the field of tissue engineering. © 2013 Society of Chemical Industry     

Electrical behavior of chitosan and poly(hydroxyethyl methacrylate) hydrogel in the contact system

Semi‐interpenetrating polymer networks (semi‐IPNs), as polymer hydrogels composed of chitosan and poly(hydroxyethyl methacrylate) (PHEMA), exhibiting electrical‐sensitive behavior, were prepared. The swelling behavior of the chitosan/PHEMA hydrogels was studied by immersing the gels in various concentrations of aqueous NaCl solution. The electrical responses of the semi‐IPN hydrogel, in applied electric fields, were also investigated. When the semi‐IPN hydrogels were swollen, where one electrode was placed in contact with the gel and the other fixed 30 mm apart from one, they exhibited bending behavior on the application of an electric field on a contact system. The electroresponsive behavior of the present semi‐IPN was also affected by the electrolyte concentration of the external solution. The semi‐IPN also showed various degrees of increased bending behavior depending on the electric stimulus. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 915–919, 2004     

Imaging bacterial polysaccharides by AFM

Summary Atomic force microscopy has been used to image the bacterial polysaccharides xanthan, acetan and gellan. Images were obtained under constant force conditions in a liquid cell. Drops of dilute solutions of the polysaccharides were deposited onto freshly cleaved surfaces of mica and allowed to dry in air. The deposits were then imaged under butanol. Xanthan and acetan form entangled networks upon deposition. Individual molecules can be identified. Under suitable circumstances it has been possible to image the helical structure of acetan. Gellan forms gels upon concentration during drying and images have been obtained of the gel network.     

Characterization of hydrogels based on chitosan and copolymer of poly(dimethylsiloxane) and poly(vinyl alcohol)

Copolymers composed of poly(vinyl alcohol) (PVA) and poly(dimethylsiloxane) (PDMS) were crosslinked with chitosan to prepare semi‐interpenetrating polymer network (IPN) hydrogels by an ultraviolet (UV) irradiation method for application as potential biomedical materials. PVA/PDMS copolymer and chitosan was cast to prepare hydrogel films, followed by a subsequent crosslinking with 2,2‐dimethoxy‐2‐phenylacetophenone as a nontoxic photoinitiator by UV irradiation. Various semi‐interpenetrating polymer networks (semi‐IPNs) were prepared from different weight ratios of chitosan and the copolymer of PVA/PDMS. Photocrosslinked hydrogels exhibited an equilibrium water content (EWC) in the range of 65–95%. Swelling behaviors of these hydrogels were studied by immersion of the gels in various buffer solutions. Particularly, the PCN13 as the highest chitosan weight ratio in semi‐IPN hydrogels showed the highest EWC in time‐dependent and pH‐dependent swelling. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2591–2596, 2002     

Synthesis and Characterization of Poly(acrylic acid)/Poly(vinyl alcohol)-xanthan Gum Interpenetrating Network (IPN) Superabsorbent Polymeric Composites

Initially interpenetrating network (IPN) hydrogel was prepared by dispersing xanthan gum (XG) into poly(vinyl alcohol) (PVA) backbone in an aqueous medium. Polyacrylic acid (PAA)/Poly (vinyl alcohol)-Xanthan gum IPN superabsorbent composite were fabricated well by dispersing the prepared IPN hydrogel in acrylic acid and polymerized in a complete aqueous environment through chemical cross-linking method. These superabsorbent polymeric composites were analytically evaluated by scanning electron microscopy (SEM), Fourier Transform Infrared Spectra (FTIR), Thermal analysis (DSC) and X-ray diffraction (XRD) analysis. Simultaneously water absorbency, swelling kinetics and water retention abilities of this prepared superabsorbent polymeric composites were also investigated systematically.     

Preparation and characteristic of a sodium alginate/carboxymethylated bacterial cellulose composite with a crosslinking semi‐interpenetrating network

A novel ionic crosslinking sodium alginate (SA)/carboxymethylated bacterial cellulose (CM‐BC) composite with a semi‐interpenetrating polymer network (semi‐IPN) structure was developed in this study. The composite was prepared through the blending of an SA gel with CM‐BC then crosslinking by Ca²⁺ followed by a freeze‐drying process. Scanning electron microscopy showed the composite matrix organized in a three‐dimensional network of CM‐BC interpenetrated against SA molecular chains with a quantity of calcium alginate microspheres upon the surface. The swelling ratios of the composite were enhanced by 183, 198, and 212% with the supplementation of CM‐BC weight fractions of 25, 50, and 75%, respectively; the swelling ratios changed with changing pH. The tensile modulus, tensile strength, and elongation at break of SA were enhanced by 165, 152, and 188%, respectively, with the addition of 50 wt % CM‐BC. This study demonstrated that the semi‐IPN structure dramatically changed the swelling and mechanical properties of the composite, and the semi‐IPN will be a promising candidate for biomedical applications such as wound dressings and skin tissue engineering. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39848.     

Fabrication of poly(3,4‐ethylenedioxythiophene)‐polysaccharide composites

Poly(3,4‐ethylenedioxythiophene) (PEDOT) doped with a series of anionic polysaccharides such as carboxymethyl cellulose, sodium hyaluronate, xanthan gum, pectin, gellan gum were prepared by electropolymerization in aqueous solutions. Some other dopants of potassium nitrate, potassium sulfate, sodium poly(styrenesulfonate), and sodium polyacrylate were used in comparison with the anionic polysaccharides. The electrochemical properties and stability of the obtained PEDOT films were also investigated. It was found that indium tin oxide (ITO) conductive glass could be used as the working electrode of the electropolymerization of EDOT and that the dopant had a great influence on polymerization potential and overoxidation potential. These charged biomolecules of anionic polysaccharides were found to facilitate electropolymerization of EDOT instead of common doping anions as counterion. The electroactive PEDOT films doped with anionic polysaccharides showed stable electrochemical properties, good texture, and adhesion properties to the ITO conductive glass. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Degradation behavior of ionic‐covalent entanglement hydrogels

Ionic‐covalent entanglement (ICE) hydrogels are a recently introduced new type of robust materials for potential future application in the fields of tissue engineering and soft robotics. Here the degradation behavior of gellan gum/polyacrylamide ICE hydrogels immersed in PBS or enzyme solutions is presented. It is demonstrated that ICE gels immersed in enzymes became stiffer, whereas under cyclic testing their mechanical responses stabilize after 10 loading/unloading cycles whether immersed in PBS or enzyme solutions. The leachates of the ICE hydrogels were found to be non‐cytotoxic for the growth of L929 and PC12 cells. These findings will be of benefit to the future development of tissue engineering applications based on these gel materials. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41216.     

In vitro degradation and protein release of semi‐IPN hydrogels consisted of poly(acrylic acid‐acrylamide‐methacrylate) and amylose

The enzymatic degradation mechanism of semi‐interpenetrating network (semi‐IPN) hydrogel of poly (acrylic acid‐acrylamide‐methacrylate) crosslinked by azocompound and amylose in vitro was investigated in the presence of Fungamyl 800L (α‐amylase) and rat cecum content (cecum bacteria). The degradation mechanism involves degradable competition, i.e., reduction of azo crosslinkage is dominant in the earlier period of degradation. Subsequently, the degradation of gels is continued by combination of reduction of azo crosslinkage and hydrolysis of amylose. The cumulative release ratios of Bovine serum albumin (BSA, as a model drug) loaded semi‐IPN gels are 25% in pH 2.2 buffer solutions and 74% in pH 7.4 buffer solutions within 48 h. Moreover, the release behavior of BSA from the semi‐IPN gels indicates that it follows Fickian diffusion mechanism in pH 2.2 media and non‐Fickian diffusion and polymer chains relaxation mechanism in pH 7.4 media. The results indicate that the release of BSA from the semi‐IPN gels was controlled via a combined mechanism of pH dependent swelling and specificity to enzymatic degradation. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Gellan gum capped silver nanoparticle dispersions and hydrogels: cytotoxicity and in vitro diffusion studies

The preparation of highly stable water dispersions of silver nanoparticles using the naturally available gellan gum as a reducing and capping agent is reported. Further, exploiting the gel formation characteristic of gellan gum silver nanoparticle incorporated gels have also been prepared. The optical properties, morphology, zeta potential and long-term stability of the synthesized silver nanoparticles were investigated. The superior stability of the gellan gum-silver nanoparticle dispersions against pH variation and electrolyte addition is revealed. Finally, we studied the cytotoxicity of AgNP dispersions in mouse embryonic fibroblast cells (NIH3T3) and also evaluated the in vitro diffusion of AgNP dispersions/gels across rat skin.     

Novel semi‐interpenetrating network structural phase change composites with high phase change enthalpy

High phase change enthalpy, controllable temperature, and stable shape can expand the application of phase change materials (PCMs) in energy storage. In this study, a series of novel form‐stable PCMs with high phase change enthalpy (169–195 J/g) and controllable temperature (45.3–61.4°C) were prepared. The PCMs exhibited a semi‐interpenetrating polymer network (semi‐IPN) structure resulting from the combination of polyethylene glycol (PEG) and a three‐dimensional (3‐D) network gel. The gel itself featured an inherent phase change characteristic and a 3‐D network structure. Thus, it improved the phase transition enthalpy of the materials and facilitated the formation of a semi‐IPN that endowed the materials with excellent form‐stable properties. In addition, the latent heat of the composites (169–195 J/g) is much higher than most of the previously reported composites using PEG as phase change component (68–132 J/g). © 2017 American Institute of Chemical Engineers AIChE J, 64: 688–696, 2018     

Mechanical and dynamic mechanical studies of epoxy/VAc‐EHA/HMMM IPN–jute composite systems

Epoxy [50:50 mixture of Di‐Glycidyl Ether of Bis‐Phenol A (DGEBA) and Epoxidized Novolac (EPN)] was solution blended with Vinyl Acetate‐2‐ Ethylhexylacrylate (VAc‐EHA) resin in aqueous medium, in varying weight fractions, with Hexamethoxymethylmelamine (HMMM) as a crosslinker and data was compared with a control. The present work was aimed to optimize the tensile strength, dynamic mechanical strength, impact strength, and toughness by preparing a blend followed by jute composites of a semi‐ and full interpenetrating network (IPN). In control experiments epoxy alone was crosslinked (semi‐IPN), whereas the DGEBA‐EPN and VAc‐EHA/HMMM were crosslinked separately (full‐IPN), using jute as the substrate for making composites. Composites of full‐IPN systems of epoxy/VAc‐EHA system had higher moduli and UTS than the semi‐IPN systems. Dynamic mechanical study showed that full‐IPN systems have higher T_g values than semi‐IPN systems. The impact strength increases with increasing proportions of VAc‐EHA copolymer. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 958–963, 2004     

Polysaccharides derived from tragacanth as biocompatible polymers and Gels

Tragacanth gum (TG) is a natural gum whose biomedical applications are limited because of the low water solubility and the possibility to form only weak water‐insoluble gels. An innovative method to produce water‐soluble tragacanth (WST) is assessed in this work. WST structural characterization indicates a high‐molecular weight polyuronic acid, which can undergo gelling by ionotropic complexation. Biological characterization shows no cytotoxicity on Hela, HepG2, and L929 cell lines. Furthermore, TG‐based and WST‐based gel beads prepared by ionic crosslinking with ferric and zinc ions are studied. Ferric WST gels exerted better cell adhesion with L929 cells than ferric alginate gels. These characteristics make WST a promising candidate for tissue engineering and drug delivery applications. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Synthesis,characterization, and application of semi‐interpenetrating liquid crystalline polymer networks LCP/PS

Attempts to extend the IPN technology to liquid crystalline polymer (LCP) systems have been made in search for a new approach for enhancing the compatibility of liquid crystalline polymer with engineering thermoplastics. A new type of interpenetrating polymer network based on liquid crystalline polymer : semi‐interpenetrating liquid crystalline polymer network comprising liquid crystalline polymer PET/60PHB (LCP) and crosslinked polystyrene (PS) (for short: semi‐ILCPN LCP/PS) has been successfully prepared. The compatibility and thermal properties of the semi‐ILCPN LCP/PS with different amount of crosslinking agent were investigated by FTIR, SEM, DSC, and TGA, respectively. Furthermore, the possible application of the semi‐ILCPN LCP/PS as a new kind of compatibilizer in PPO/LCP blends was also studied and discussed. Well‐compatibilized PPO/LCP composites with considerably improved mechanical properties were obtained. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1141–1150, 2000     

Preparation and Characterization of Semi‐IPN Fluorine Containing Polybenzimidazole/Nafion Composite Membrane for Fuel Cells

A facile way to prepare semi‐interpenetrating polymer network (semi‐IPN) membrane which adopted 1,3‐benzenedisulfonyl azide (1,3‐BDSA) to crosslink with fluorine containing polybenzimidazole (Aliphatic‐16F‐PBI) in the Aliphatic‐16F‐PBI/Nafion composite membranes was proposed. By means of Fourier transformed infrared (FTIR) spectra analysis, the possible crosslinking reaction mechanism was investigated. Results suggested that 1,3‐BDSA molecule loses a nitrogen and forms nitrene upon heating. Then this nitrene reacts with C–H bond of Aliphatic‐16F‐PBI. Scanning electron microscope (SEM) images showed that the compatibility of PBI and Nafion improved while hexadecafluoro‐octyl groups were implanted into Aliphatic‐16F‐PBI molecule. The properties of Aliphatic‐16F‐PBI/Nafion composite membranes for fuel cell applications were determined through tests of gel fraction, thermogravimetry (TG), dimensional stability, mechanical property and proton conductivity. The gel fraction could reach 27.9% when 7.4% 1,3‐BDSA was added into the composite membranes. The proton conductivity of the semi‐IPN Aliphatic‐16F‐PBI/Nafion composite membranes could reach 0.69 × 10^–2 S cm^–1 at 120 °C at 100% relative humidity. Such high crosslink degree resulted in the improvement of the tensile strength, dimensional stability and chemical oxidative stability of semi‐IPN Aliphatic‐16F‐PBI/Nafion composite membranes. Nonetheless, it had little effect on the thermal stability.     

Preparation and characterization of a semi‐interpenetrating network gel polymer electrolyte

Poly(PEG200 maleate) was synthesized as a new type crosslinkable prepolymer and the semi‐interpenetrating polymer network (semi‐IPN) gel electrolytes were prepared by means of thermal polymerization. Their intrinsic properties were characterized by FTIR spectroscopy, differential scanning calorimetry (DSC), X‐ray diffractions (XRD), scanning electron microscopy, alternating current impedance (AC impedance), and linear sweep voltammetry. The prepared polymer hosts are transparent and have good mechanical properties. The results of DSC and XRD confirm that the prepared hosts are in amorphous state and they can hold enough liquid electrolytes, which is favorable for Li⁺ ions to transport via both the absorbed liquid electrolyte and the gel of the entire systems. The semi‐IPN gel electrolytes exhibit high ionic conductivity on the order of 10^?3 S cm^?1. Their electrochemical stability up to +4.6 V against Li⁺/Li also makes them potential candidates for application as polymer electrolytes in devices. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Preparation of alginate/poly(N‐isopropylacrylamide) semi‐interpenetrating and fully interpenetrating polymer network hydrogels with γ‐ray irradiation and their swelling behaviors

Semi‐interpenetrating polymer network (semi‐IPN) and fully interpenetrating polymer network (full‐IPN) hydrogels composed of alginate and poly(N‐isopropylacrylamide) were prepared with γ‐ray irradiation. The semi‐IPN hydrogels were prepared through the irradiation of a mixed solution composed of alginate and N‐isopropylacrylamide (NIPAAm) monomer to simultaneously achieve the polymerization and self‐crosslinking of NIPAAm. The full‐IPN hydrogels were formed through the immersion of the semi‐IPN film in a calcium‐ion solution. The results for the swelling and deswelling behaviors showed that the swelling ratio of semi‐IPN hydrogels was higher than that of full‐IPN hydrogels. A semi‐IPN hydrogel containing more alginate exhibited relatively rapid swelling and deswelling rates, whereas a full‐IPN hydrogel showed an adverse tendency. All the hydrogels with NIPAAm exhibited a change in the swelling ratio around 30–40°C, and full‐IPN hydrogels showed more sensitive and reversible behavior than semi‐IPN hydrogels under a stepwise stimulus. In addition, the swelling ratio of the hydrogels continuously increased with the pH values, and the swelling processes were proven to be repeatable with pH changes. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4439–4446, 2006     

Cure kinetics and physical properties of dicyanate/polyetherimide semi‐IPNs

The curing behavior and physical properties of dicyanate/polyetherimide (PEI) semi‐interpenetrating polymer network (IPN) systems were investigated. Differential scanning calorimetry (DSC) was used to study the curing behavior of the dicyanate/PEI semi‐IPN systems. The curing rate of the semi‐IPN system decreased as the PEI content increased. An autocatalytic reaction mechanism can describe well the curing kinetics of the semi‐IPN systems. The reaction kinetic parameters were determined by fitting DSC conversion data to the kinetic equation. The glass transition temperature of the semi‐IPNs decreased with increasing PEI content. Two glass transitions due to phase‐separated morphology were observed for the semi‐IPN containing over 15 phr (parts per hundred parts of dicyanate resin) PEI. The thermal stability and dynamic mechanical properties of the semi‐IPNs were measured by thermal analysis.