Properties of electroresponsive poly(vinyl alcohol)/poly(acrylic acid) IPN hydrogels under an electric stimulus

Interpenetrating polymer networks (IPNs) composed of poly(vinyl alcohol) (PVA) and poly(acrylic acid) (PAAc) exhibited electrical-sensitive behavior. PAAc as an initial network was prepared inside a PVA solution using UV irradiation; then, PVA networks as a secondary network were formed by a repetitive freeze–thawing process. Their mechanical properties were influenced by the swelling ratio, crosslinking by UV radiation and a freeze–thawing process, and intermolecular force by hydrogen bonding. When a swollen PVA/PAAc IPN was placed between a pair of electrodes, the IPN exhibited bending behavior upon the applied electric field. The equilibrium bending angle (EBA) and the bending speed of the PVA/PAAc IPN increased with the applied voltage and the content of the PAAc network having negatively charged ionic groups within the IPN. The electroresponsive behavior of the present IPN was also affected by the electrolyte concentration of the external solution. Particularly, IPN37 showed a maximum EBA when the critical ionic strength was 0.1. Anisotropic deswelling of the IPN was observed in a direct contact with a pair of electrodes under aerobic conditions. The PVA/PAAc IPN also showed stepwise bending behavior depending on the electric stimulus. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1675–1683, 1999     

Permeation of solutes through interpenetrating polymer network hydrogels composed of poly(vinyl alcohol) and poly(acrylic acid)

The swelling behaviors of poly(vinyl alcohol)–poly(acrylic acid) (PVA–PAAc) interpenetrating networks (IPN) hydrogels in the presence of electrolytes were studied. The ionized carboxylic group within IPN hydrogels at pH 7 strongly interacted with electrolytes in the medium and caused anomalous swelling pattern. The permeabilities of 5 representative solutes were regulated as a function of temperature, pH, ionic strength, solute size, and ionic properties of solutes. The permeation of nonionic solutes followed the swelling behaviors dependent on external stimuli, including the above factors. However, the ionic solutes showed different trends in their permeation through IPN hydrogels. © 1998 John Wiley & Sons, Inc. J Appl Polm Sci 69: 479–486, 1998     

Swelling of thermosensitive interpenetrating polymer networks composed of poly(vinyl alcohol) and poly(acrylic acid)

The swelling behavior of interpenetrating polymer networks (IPNs) composed of poly(vinyl alcohol) (PVA) and poly(acrylic acid) (PAA) in water was studied. The PVA/PAA IPN gels were prepared by four synthetic methods. The swelling behaviors of these IPNs made by different methods were compared. The differences in swelling behaviors of samples are discussed on the basis of their structural and physical differences. © 1996 John Wiley & Sons, Inc.     

Synthesis and characteristics of interpenetrating polymer network hydrogel composed of chitosan and poly(acrylic acid)

Interpenetrating polymer network (IPN) hydrogels composed of chitosan and poly(acrylic acid) (PAAc) were synthesized by UV irradiation method, and their structure, crystallinity, swelling behavior, thermal property, and mechanical property were investigated. Chitosan/PAAc IPNs exhibited relatively high equilibrium water content and also showed reasonable sensitivity to pH. From the swelling behaviors at various pH's, Fourier transform infrared spectra at high temperature and thermal analysis confirmed the formation of polyelectrolyte complex due to the reaction between amino groups in chitosan and carboxyl groups in PAAc. For this reason, even at a swollen state, the present chitosan/PAAc IPNs possess good mechanical properties. Particularly, the CA‐2 sample (with a weight ratio of chitosan/PAAc = 50/50, molar ratio [NH₂]/[COOH] = 25/75) showed the lowest equilibrium water content and free water content, attributed to the more compact structure of the polyelectrolyte than CA‐1 or CA‐3 due to the high amount of interchain bond within the IPN. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 113–120, 1999     

Drug release behavior of electrical responsive poly(vinyl alcohol)/poly(acrylic acid) IPN hydrogels under an electric stimulus

The electrically modulated properties of interpenetrating polymer networks (IPN) composed of poly(vinyl alcohol) (PVA) and poly(acrylic acid) (PAAc) under electric field were investigated for drug delivery systems. PVA/PAAc IPNs with various compositions were synthesized by a sequential method, that is, ultraviolet polymerization of AAc in the mixture of PVA and aqueous AAc monomer solution, followed by a freeze‐thawing process to prepare elastic hydrogels. The amount of loaded drug significantly increased with the content of PAAc containing ionizable groups in IPN. The amount of introduced ionic drug (cefazoline) was greater than that of the nonionic drug (theophylline). Release behaviors of drug molecules from negatively charged PVA/PAAc IPN were switched on and off in a pulsatile pattern depending on the applied electric stimulus. The released amount and the release rate of drug were influenced significantly by the applied voltage, ionic group contents in IPN, ionic properties of drug solute, and the ionic strength of release medium. In addition, the ionic properties of drug molecules dramatically affected release behaviors, thus the release of ionic drug was much more enhanced than that of the nonionic drug. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1752–1761, 1999     

Thermal characteristics of IPNs composed of poly(propylene glycol) and poly(acrylic acid)

Interpenetrating polymer networks (IPNs) based on poly(propylene glycol) (PPG) and poly(acrylic acid) (PAAc) were prepared by UV irradiation and characterized using fourier transform infrared (FTIR), differential scanning calorimetry (DSC), dielectric analysis (DEA), and thermogaravimetry (TGA). The glass transition temperatures (T_gs) of these IPNs exhibited a relatively higher temperature with an increased PAAc content. The decomposition temperature of PAAc is lower than that of PPG. PAAc affects the thermal stability of IPN more than PPG. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2570–2574, 2003     

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     

Indomethacin release behaviors from pH and thermoresponsive poly(vinyl alcohol) and poly(acrylic acid) IPN hydrogels for site-specific drug delivery

A temperature- and pH-responsive drug delivery system was studied by using interpenetrating polymer network (IPN) hydrogels constructed with poly(acrylic acid) (PAAc) and poly(vinyl alcohol) (PVA). The release of indomethacin incorporated into these hydrogels showed pulsatile patterns in response to both pH and temperature. Indomethacin diffused from the polymer matrices through the swelling and deswelling mechanism. The release amount increased at higher temperature because of the swelling caused by the dissociation of hydrogen bonding. The drastic change of drug release was achieved by alternating pH of the buffer solution and was attributed to the change of states of ionic groups within IPN hydrogels. The free water contents were calculated by using differential scanning calorimetry (DSC), and were proved to be the main factor in the swelling. These results demonstrated that the drug release could be controlled by the swelling/deswelling degree of IPN hydrogels as functions of pH and/or temperature. © 1997 John Wiley & Sons, Inc. J Appl Polm Sci 65: 685–693     

Synthesis and characterization of an interpenetrating polymer network composed of poly(methacrylic acid) and poly(vinyl alcohol)

Temperature and pH‐responsive interpenetrating polymer network (IPN) hydrogels, constructed with poly(methacrylic acid) (PMAA) and poly(vinyl alcohol) (PVA), by a sequential IPN method, were studied. The characterization of IPN hydrogels was investigated by Fourier‐transform infrared spectroscopy, differential scanning calorimetry (DSC) and swelling under various conditions. The IPN hydrogels exhibited relatively high swelling ratios, in the range 230–380 %, at 25 °C. The swelling ratios of the PMAA/PVA IPN hydrogels were pH and temperature dependent. DSC was used for the quantitative determination of the amounts of freezing and non‐freezing water. The amount of free water increased with increasing PMAA content in the IPN hydrogels. Copyright © 2004 Society of Chemical Industry     

Swelling behavior of semi‐interpenetrating polymer network hydrogels composed of poly(vinyl alcohol) and poly(acrylamide‐co‐sodium methacrylate)

Interpenetrating polymer network (IPN) hydrogels based on poly(vinyl alcohol) (PVA) and poly(acrylamide‐co‐sodium methacrylate) poly(AAm‐co‐SMA) were prepared by the semi IPN method. These IPN hydrogels were prepared by polymerizing aqueous solution of acrylamide and sodium methacrylate, using ammonium persulphate/N,N,N¹,N¹‐tetramethylethylenediamine (APS/TMEDA) initiating system and N,N¹‐methylene‐bisacrylamide (MBA) as a crosslinker in the presence of a host polymer, poly(vinyl alcohol). The influence of reaction conditions, such as the concentration of PVA, sodium methacrylate, crosslinker, initiator, and reaction temperature, on the swelling behavior of these IPNs was investigated in detail. The results showed that the IPN hydrogels exhibited different swelling behavior as the reaction conditions varied. To verify the structural difference in the IPN hydrogels, scanning electron microscopy (SEM) was used to identify the morphological changes in the IPN as the concentration of crosslinker varied. In addition to MBA, two other crosslinkers were also employed in the preparation of IPNs to illustrate the difference in their swelling phenomena. The swelling kinetics, equilibrium water content, and water transport mechanism of all the IPN hydrogels were investigated. IPN hydrogels being ionic in nature, the swelling behavior was significantly affected by environmental conditions, such as temperature, ionic strength, and pH of the swelling medium. Further, their swelling behavior was also examined in different physiological bio‐fluids. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 302–314, 2005     

Thermal properties of poly(vinyl alcohol)/poly(diallyldi‐methylammonium chloride) interpenetrating polymer networks

Interpenetrating polymer networks (IPNs) constructed with poly(vinyl alcohol) (PVA) and poly(diallyldimethyl ammonium chloride) (PDADMAC) using a sequential IPN method were prepared. The thermal characterization of the IPNs was investigated by differential scanning calorimetry (DSC), dielectric analysis (DEA), and thermogravimtric analysis (TGA). Decreases in the melting temperature of PVA segments in IPNs were observed with increasing PDADMAC content using DSC. DEA was employed to ascertain glass transition temperature of IPNs. The thermal decomposition of IPNs was investigated using TGA, and thermal decomposition of IPNs could be decelerated by changing PVA content. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1346–1349, 2003     

Bending behavior of hydrogels composed of poly(methacrylic acid) and alginate by electrical stimulus

Interpenetrating polymer networks (IPNs) prepared from poly(methacrylic acid) (PMAAc) and sodium alginate (SA) exhibited electrical sensitive behavior. The swelling behavior of the PMAAc/SA IPN hydrogel was studied by immersion of the gel into aqueous HCl solutions at various concentrations and into various pH buffer solutions, and their responses to electric fields were also investigated. When swollen IPN hydrogel was placed between a pair of electrodes it exhibited bending behavior on application of an electric field, and showed stepwise bending behavior depending on the magnitude of the electrical stimulus. Copyright © 2004 Society of Chemical Industry     

Thermal characteristics of interpenetrating polymer networks composed of poly(vinyl alcohol) and poly(N‐isopropylacrylamide)

Interpenetrating polymer networks (IPNs) composed of poly(vinyl alcohol) (PVA) and poly(N‐isopropylacrylamide) (PNIPAAm) were prepared by the sequential‐IPN method. The thermal characterization of the IPNs was investigated using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and dielectric analysis (DEA). Depression of the melting temperature (T_m) of the PVA segment in IPNs was observed with increasing PNIPAAm content using DSC. DEA was employed to ascertain the glass‐transition temperature (T_g) of IPNs. From the result of DEA, IPNs exhibited two T_g values, indicating the presence of phase separation in the IPNs. The thermal decomposition of IPNs was investigated using TGA and appeared at near 200°C. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 881–885, 2003     

pH-/temperature-sensitive carboxymethyl chitosan/poly(N-isopropylacrylamide-co-methacrylic acid) IPN: preparation,characterization and sustained release of riboflavin

Dual crosslinked pH-/temperature-sensitive interpenetrating polymer networks (IPN) were prepared by free-radical copolymerization of N-isopropylacrylamide and methylacrylic acid (MAA) using N,N′-methylenebisacrylamide as a crosslinker in carboxymethyl chitosan (which was crosslinked by Ca²⁺) aqueous solution. Scanning electron microscopy was used to observe the morphologies of the IPN at different pH values and temperatures. The effects of MAA content and environmental pH on the “pH-/temperature-induced” phase transition behavior of the IPN hydrogels were investigated. The phase transition temperature was adjusted to 37 °C by changing the MAA content. The effects of drug-loaded content, crosslinking density, environmental pH, and temperature on the drug release behavior of the drug-loaded IPN hydrogel were also explored. Based on results, the hydrogel possessed pH/temperature sensitivity. The swelling ratio and phase translation temperature of the hydrogel were lower at lower pH. These values were lowest at pH 3.0. The release behavior of riboflavin was dependent on preparation condition, environmental pH, and temperature. Drug cumulative release was only 6 % at pH 1.8 for 2 h. The drug cumulative release was 13 % before the drug-loaded hydrogel reached the position with pH 6.8. The drug release rate was higher at lower temperature. Therefore, dual-crosslinked hydrogel holds much potential as a drug site-specific carrier.     

Drug releasing characteristics of thermo- and pH-sensitive interpenetrating polymer networks based on poly (N-isopropylacrylamide)

Interpenetrating polymer networks (IPNs) of poly(N-isopropylacrylamide)/polyurethane (PNIPAAm/PU) and poly(N-isopropylacrylamide)/poly(acrylic acid) (PNIPAAm/PAA) were synthesized to investigate the swelling and drug releasing behavior. The presence of urethane network in PNIPAAm/PU IPNs improved the mechanical strength, but reduced the swelling and drug releasing rates because of its hydrophobic characteristics. The swelling transition temperatures of PNIPAAm gels were little affected by the incorporation of PU networks in IPN structures. The drug releasing process was analyzed with a simple exponential expression of time dependent fractional drug release. The swelling and drug releasing behavior of PNIPAAm/PAa IPNs was significantly affected by the variation of PAA compositions. The drug release process changed from anomalous to dual type via zero-order mode with increasing PAA concentration due to the competitive swelling rates between PNIPAAm and PAA during release process. The releasing rate decreased in the buffer solution of pH 7.4, but increased in that of pH 5.0 with increasing PAA concentration at both 28 and 37°C because the swelling power of PAA in pH 5.0 was much less than that in pH 7.4. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 2647–2655, 1997     

Synthesis and characterization of pH‐ and temperature‐sensitive silk sericin/poly(N‐isopropylacrylamide) interpenetrating polymer networks

Interpenetrating polymer networks (IPNs) composed of silk sericin (SS) and poly(N‐isopropylacrylamide) (PNIPAAm) were prepared simultaneously. The properties of the resultant IPN hydrogels were characterized by differential scanning calorimetry and SEM as well as their swelling behavior at various temperatures and pH values. The single glass transition temperature (T_g) presented in the IPN thermograms indicated that SS and PNIPAAm form a miscible pair. The swollen morphology of the IPNs observed by SEM demonstrated that water channels (pores present in SEM micrographs) were distributed homogeneously through out the network membranes. The swelling ratio of the IPNs depended significantly on the composition, temperature and pH of the buffer solutions. The dynamic transport of water into the IPN membrane was analyzed based on the Fickian equation. Copyright © 2006 Society of Chemical Industry     

Electroactive characteristics of interpenetrating polymer network hydrogels composed of poly(vinyl alcohol) and poly(N‐isopropylacrylamide)

An interpenetrating polymer network (IPN) composed of poly(vinyl alcohol) (PVA) and poly(N‐isopropylacrylamide) (PNIPAAm) was prepared by the sequential IPN method. The equilibrium swelling ratio and bending behavior under electric fields of the IPN hydrogel were measured in an aqueous NaCl solution. The IPN exhibited a high equilibrium swelling ratio, in the range 280–380%. When the IPN in aqueous NaCl solution was subjected to an electric field, the IPN showed significant and quick bending toward the cathode. The IPN hydrogel also showed stepwise bending behavior, depending on the electric stimulus. In addition, the ionic conductivity of the IPN hydrogel was measured using dielectric analysis, and its conductive behavior followed the Arrhenius equation. The conductivity of the IPN hydrogel and the activation energy for the form of the IPN were 1.68 × 10^?5 S/cm at 36°C and 61.0 kJ/mol, respectively. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 890–894, 2003     

Salt-, pH- and temperature-responsive semi-interpenetrating polymer network hydrogel based on poly(aspartic acid) and poly(acrylic acid)

In this study, a novel salt-, pH- and temperature-responsive semi-interpenetrating network (semi-IPN) hydrogel, composed of poly(aspartic acid) (PAsp) and poly(acrylic acid) (PAAc), was prepared. PAsp/PAAc semi-IPN hydrogel being ionic in nature, the swelling behavior was significantly influenced by various swelling medium. The structure of the triply responsive hydrogel was studied by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM), and the salt-, temperature- and pH-sensitivities were investigated through measuring equilibrium swelling ratios in various environmental solutions. The results indicate that there is a structure of polyelectrolyte complex in the hydrogel, and that the responsive behaviors of this hydrogel to alternating changes in inorganic salt (different physiological bio-fluids), pH and temperature are improved because of the incorporation of PAsp. In addition, during the repeatable swelling and shrinkage period, the semi-IPN hydrogel shows suitable mechanical strength. The salt-, pH- and temperature-responsive hydrogel will have wider applications in biomedical areas.     

Thermal characteristics of poly(vinyl alcohol) and poly(vinylpyrrolidone) IPNs

Interpenetrating polymer network (IPN) hydrogels based on poly(vinyl alcohol) (PVA) and 1‐vinyl‐2‐pyrrolidone (VP) were prepared by radical polymerization using 2,2‐dimethyl‐2‐phenylacetophenone (DMPAP) and methylene bisacrylicamide (MBAAm) as initiator and crosslinker, respectively. The thermal characterization of the IPNs was investigated by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and dielectric analysis (DEA). Depressions of the melting temperatures of PVA segments in IPNs were observed with increasing VP content via the DSC. The DEA was employed to ascertain the glass transition temperature (T_g) of IPNs. From the result of DEA, IPNs exhibited two T_gs indicating the presence of phase separation in the IPN. The thermal decomposition of IPNs was investigated using TGA and appeared at near 270°C. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1844–1847, 2002     

Preparation and characterization of hydroxyl ion-conducting interpenetrating polymer network based on PVA and PEI

Novel interpenetrating polymer networks (IPNs) and semi-interpenetrating polymeric networks (sIPNs) based on polyethyleneimine (PEI) and poly(vinyl alcohol) (PVA) have been prepared via crosslinking reactions with respective crosslinking agent, 1,4-dibromobutane and glutaraldehyde (GA). IPNs, sIPNs and PEI/PVA blend membranes are characterized in detail by Fourier transform Infrared attenuated total reflection (FTIR-ATR) spectroscopy, mechanical properties, water uptake, swelling ratio, field emission scanning electron microscope (FE-SEM), hydroxide ion (OH^?) conductivity. Moderate water uptake and swelling ratio are obtained by the IPN derived from PEI:PVA (1:1), achieving 78.4 and 36.8 %, respectively. And the IPN also shows an acceptable OH^? conductivity of 4.87 mS/cm at 80 °C.