Preparation of chemically crosslinked gels with maleate‐denatured poly(vinyl alcohol) and its application to drug release

Maleate‐denatured poly(vinyl alcohol) (M‐PVA) was crosslinked with heating. The mechanism of crosslinking was studied with several procedures: titration, Fourier transform infrared, and solubility. The carboxyl groups of M‐PVA consisted of carboxylates and a few free carboxyl groups. The crosslink was the ester linkage between hydroxyl and carboxyl groups. Several kinds of M‐PVA tablets were prepared under different conditions: pressures of 200–600 kgf/cm² and grain sizes of 75 (pass) to 250 μm (on). The swelling behavior of these chemically crosslinked tablets was studied in a buffer solution of pH 7.4, mainly at 37°C. Moreover, the effect of temperature from 5 to 50°C and the effect of repeated swell–dry cycles on the behavior of the tablets in a buffer solution [106 μm (on), 200 kgf/cm²] were studied. The release of p‐acetamidophenol from those tablets in the pH 7.4 buffer solution was studied. The different release patterns were due to the differences in the swelling behavior. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1178–1184, 2002; DOI 10.1002/app.10411     

Electric stimuli responses to poly(vinyl alcohol)/chitosan interpenetrating polymer network hydrogel in NaCl solutions

An interpenetrating polymer network (IPN) hydrogel composed of poly(vinyl alcohol) (PVA) and chitosan exhibited electric‐sensitive behavior. The PVA/chitosan IPN hydrogel was synthesized by an ultraviolet (UV) irradiation method that is used in several biomedical and industrial fields. The swelling behavior of the PVA/chitosan IPN hydrogel was studied by immersion of the gel in NaCl aqueous solutions at various concentrations. The swelling ratio decreased with increasing concentration of NaCl solution. The stimuli response of the IPN hydrogel in electric fields was also investigated. When a swollen PVA/chitosan IPN was placed between a pair of electrodes, the IPN exhibited bending behavior in response to the applied electric field. The bending angle and the bending speed of the PVA/chitosan IPN increased with increasing applied voltage and concentration of NaCl aqueous solution. The PVA/chitosan IPN also showed stepwise bending behavior depending on the electric stimulus. In addition, thermal properties of PVA/chitosan IPN were investigated by differential scanning calorimetry (DSC) and dielectric analysis (DEA). © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2285–2289, 2002     

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     

Mechanical properties and drug release rate of poly(vinyl alcohol)/poly(ethylene glycol)/clay nanocomposite hydrogels: Correlation with structure and physical properties

Poly(vinyl alcohol)/poly(ethylene glycol) hydrogels containing curcumin as a drug and the various amounts of a montmorillonite nanoclay are prepared using the freezing–thawing method. Nanoclay quantity influence on the physicomechanical properties and the drug release rate of the hydrogel as well as relationship between them is investigated. X-Ray diffraction and Atomic force microscopy analysis reveal the nanoclays have an intercalation structure in the hydrogel, and the hydrogel crystallization decreases with increasing the nanoclay inclusion. From the SEM micrographs observation, it was revealed that due to the presence of the nanoclay in the hydrogel, its porosity decreased. The naonoclay has an amount-depended dual effect on the hydrogel swelling. The swelling mechanism is a normal Fickian diffusion for all the hydrogel samples. Strong physical interactions between the nanoclays and the polymer chains in the nanocomposite hydrogels are evidenced by the rheological studies. These interactions lead to significant reinforcement of the hydrogel tensile strength, intensified by the nanoclay amount. Interestingly, the nanoclays show the capability of accelerating and, also, decelerating the drug release of the hydrogel. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47843.     

Swelling and drug‐release behavior of the poly(AA‐co‐N‐vinyl pyrrolidone)/chitosan interpenetrating polymer network hydrogels

A series of novel hydrogels were prepared from acrylic acid (AA), N‐vinyl pyrrolidone (NVP), and chitosan by photopolymerization. The swelling behavior, gel strength, and drug release behavior of the poly(AA/NVP) copolymeric hydrogels and corresponding interpenetrating polymer network hydrogels were investigated. Results showed that the swelling ratios for the present hydrogels decreased with an increase of NVP content in the gel, but the gel strength increased with an increase of NVP content in the gel. Results also showed that the drug‐release behavior for the gels is related to the ionicity of drug and the swelling ratio of the gel. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2135–2142, 2004     

Influence of isomery in drug release from poly(butyl monoitaconate‐co‐acrylamide) hydrogels

In this work, we report the synthesis and characterization of poly(butyl monoitaconate‐co‐acrylamide) hydrogels to be used as drug release agents. Four isomers of butanol were used to synthesize the hydrogels. The influence of butyl monoitaconate isomery on swelling behavior, Young's and compression moduli, cross‐linking density and molar mass between cross‐links are reported. It was found that by increasing butyl ramification, equilibrium degree of swelling, and the time for reaching swelling equilibrium decreases. Cross‐linking density, Young's and compression moduli increases as butyl ramification increases. The release of theophylline and aminophylline drugs used in therapy for respiratory diseases were studied and it was found that theophylline was released faster than aminophylline © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Preparation of atactic poly(vinyl alcohol)/silver composite nanofibers by electrospinning and their characterization

Poly(vinyl alcohol) (PVA)/silver composite nanofibers were successfully prepared by the electrospinning method. Water‐based colloidal silver in a PVA solution was directly mixed without any chemical or structural modifications into PVA polymer fibers to form organic–inorganic composite nanofibers. The ratio of silver colloidal solution to PVA played an important role in the formation of the PVA/silver composite nanofibers. We prepared two different atactic PVA/silver nanocomposites with number‐average degrees of polymerization of 1700 and 4000 through electrospinning with various processing parameters, such as initial polymer concentration, amount of silver colloidal solution, applied voltage, and tip‐to‐collector distance. The PVA/silver composite nanofibers were characterized by field emission scanning electron microscopy and transmission electron microscopy (TEM). TEM images showed that silver nanoparticles with an average diameter of 30–50 nm were obtained and were well distributed in the PVA nanofibers. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Miscibility of poly(acrylic acid)/poly(methyl vinyl ketone) blend and in vitro application as drug carrier system

A series of poly(acrylic acid)/poly(methyl vinyl ketone) (PAA/PMVK) blends with different compositions were prepared by the solvent casting method. The miscibility of this pair of polymers was investigated by differential scanning calorimetry(DSC), Fourier transform infra-red (FTIR) and X-Ray diffraction (XRD) techniques. An in-vitro cytotoxicity test of the drug-carrier system via MTT (3-(4,5-demethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay revealed no significant cytotoxic effects at concentrations up to 100 µg· ml^?1. The STX/PAA-50 drug carrier systems were also prepared by solvent casting of solutions containing the sulfamethoxazole (STX) used as drug model and PAA/PMVK blend in N.N-dimethylformamide then crosslinked with acidified ethylene glycol. The release dynamic of STX from the prepared hydrogels was investigated in which the diffusion through the polymer matrix, the enhancement of the water solubility of STX, the influence of the initial drug concentration, the pH of the medium, and the effect of the degree of swelling of the polymer matrix on the release dynamic was evaluated. According to the total gastrointestinal transit time estimated by Belzer, the estimate distribution of STX released in the different organs indicated that the performance is obtained with the drug – carrier-system containing equal ratios of polymer and 10 wt% of STX (STX-10/PAA-50).     

Equilibrium adsorption isotherm and controlled release of antibiotic drug chloroamphenicol from poly(2‐vinyl pyridine/acrylic acid) hydrogels prepared by gamma radiation

High water sorption of 2‐vinyl pyridine (2‐VP)/acrylic acid (AAc) hydrogel were prepared by free‐radical polymerization in aqueous solution of 2‐VP with AAc as comonomer. The amount of ionic monomer (AAc), the irradiation dose of prepared hydrogel, the pH, and the concentration of drug play an important factor on loading, adsorption, and releasing of water‐soluble chloroamphenicol drug. As a result of dynamic swilling tests, the effect of relative content of AAc on the swelling showed that it allowed a non‐Fickian type of water diffusion. The adsorption of the drug onto (2‐VP/AAc) hydrogels was studied by Freundlish adsorption isotherm. The drug concentrations showed an influence on the adsorption of drug which increased with increasing AAc content. From Freundlish adsorption isotherm, the empirical constants, k and n, can be evaluated and showed the ability of hydrogel to be loaded by the drug and the affinity of the drug to be uptake onto the hydrogel respectively. FTIR, TGA, and SEM techniques were used to study the characterization of hydrogel (2‐VP/AAc). Additionally, the release of the drug loaded from hydrogel discs was studied microbiologically to show that hydrophilic structure of the hydrogel has an antimicrobial effect as a dehydration of cytoplasm and unbalance of the cell wall functions. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Poly(N-isopropylacrylamide)/mesoporous silica thermosensitive composite hydrogels for drug loading and release

Temperature-sensitive hydrogels are attracting increasing attention for controlled drug delivery. However, achieving high drug loadings and sustained drug release remains challenging. Herein, we describe the successful synthesis of a series of novel temperature-sensitive poly(N-isopropylacrylamide) (PNIPA)/mesoporous silica nanoparticles (MSN) hydrogels by physical crosslinking of NIPA with MSN. The external and internal structures, temperature sensitivity, drug-loading capacity, and blood compatibility of the PNIPA/MSN composite hydrogels are studied. Results show that MSN addition improved the network structure and adjusted the size of the hole, MSN could also act as drug carrier, thereby enhancing the drug loading capacity. The composite hydrogels underwent a phase transition at 33.7 °C (at the lower critical solution temperature). The hemolysis rate of the composite hydrogels was less than 1%, thus they can be classified as a nonhemolytic materials with good biocompatibility. The composite hydrogels reported here thus have great potential in drug transport and temperature-activated drug release. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48391.     

Sustained release behavior of pH‐responsive poly(vinyl alcohol)/poly(acrylic acid) hydrogels containing activated carbon fibers

The composites of pH‐responsive poly(vinyl alcohol)/poly(acrylic acid) hydrogel and activated carbon fibers (ACFs) were prepared as sustained drug release system with excellent mechanical properties. The mechanical properties of hydrogels were improved greatly by addition of ACFs. The thinner ACFs were more effective in increasing the mechanical properties of composite hydrogels. The cumulative amount of release and the release period were dependent on the surface area and the pore volume of ACFs. The drug release was maximized at basic condition due to the pH‐sensitive hydrogel matrices and the initial bust phenomenon was alleviated by incorporating ACFs in the hydrogels. The drug release was sustained about four times longer and the mechanical property was increased about 2.6 times higher because ACFs worked as drug reservoir and reinforcement. Cytotoxicity evaluation confirmed the biocompatible characteristics of the ACFs‐containing hydrogels. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

On physical and antibacterial properties and drug release behavior of poly(vinyl alcohol) hydrogels: effect of drug loaded chitosan nanoparticles

This paper deals with influence of chitosan nanoparticles (CNPs) loaded by tetracycline, as a drug, on the physico-mechanical and antibacterial properties as well as drug release behavior of poly(vinyl alcohol), PVA, hydrogels prepared by electron beam irradiation. The formation of spherical chitosan particles in nanoscale size prepared by an ionic gelation method was confirmed by FTIR and UV spectroscopy, and scanning electron microscopy analyses. The drug release kinetic studies from drug loaded chitosan nanoparticles (DLCNPs) at pH = 7.4 revealed a linear and steady release behavior over long period of time. The theoretical analysis of the swelling kinetic data, using Peppas’s model showed that the swelling kinetic is governed by Fickian diffusion for all the prepared hydrogels, however, the water diffusion coefficient, and therefore, the swelling content were lower for the hydrogels loaded with DLCNPs as compared to the ones with the neat drug. In agreement with these results, the hydrogels containing DLCNPs exhibited a more controlled drug release behavior with significantly stronger antibacterial activity. The tensile mechanical properties of the hydrogels not affected by the DLCNPs were found to be suitable for wound dressing applications.     

Gelation of a new hydrogel system of atactic‐poly(vinyl alcohol)/NaCl/H2O

a‐PVA/NaCl/H₂O hydrogels have been prepared by gelation of aqueous atactic‐poly(vinyl alcohol) (a‐PVA) solutions in the presence of NaCl. The gelling temperature, melting temperature and the preservation of water of the hydrogels have been measured. The effect of the addition of NaCl to the hydrogels on gelling temperature and melting temperature is marked when the NaCl concentration is over a certain value. High NaCl concentration favours high‐melting‐point hydrogels. When the NaCl concentration is high enough (such as 11%), high‐melting‐point and white turbid opaque a‐PVA/NaCl/H₂O hydrogels can be prepared, regardless of the PVA concentration. Similarly, the low gelling temperature of a‐PVA/NaCl/H₂O solutions comes from low NaCl concentration, while high gelling temperature ranges from 50 to 70 °C when the NaCl concentration is 11%. In appearance, the types of syneresis of a‐PVA/NaCl/H₂O are χ‐type or a mixture of χ‐ and n‐types; water release of the hydrogels is slowed down by the addition of NaCl. © 2002 Society of Chemical Industry     

Crosslinked poly(vinyl alcohol)/carboxymethyl chitosan hydrogels for removal of metal ions and dyestuff from aqueous solutions

Hydrogels composed of poly(vinyl alcohol) (PVA) and carboxymethyl chitosan (CMCh) were synthesized via ultraviolet (UV) irradiation that can be used in several industrial fields. Several analysis tools were used to characterize the physical and thermal properties of CMCh/PVA hydrogels namely FT‐IR, scanning electron microscope (SEM), XRD, thermogravimetric analysis (TGA), and differential scanning calorimetery (DSC). TGA results showed that CMCh/PVA hydrogels are thermally more stable than CMCh and their thermal stability increases as PVA content increases in the hydrogel. Also, DSC results showed that CMCh/PVA hydrogels are at least partial miscible blends. Moreover, the swelling behavior of the CMCh/PVA hydrogels was studied in different buffered solutions and in different salt solutions at various concentrations. CMCh/PVA hydrogels swell much more than CMCh especially at alkaline pH. Both metal and dye uptake were studied for CMCh/PVA hydrogels. The hydrogels adsorb much more dyestuff and metal ions like Cu²⁺, Cd²⁺, and Co²⁺ than CMCh itself. Much dyestuff and metal ions are adsorbed by the hydrogels as PVA content increases in the hydrogel. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Preparation and characterization by radiation of poly(vinyl alcohol) and poly(N‐vinylpyrrolidone) hydrogels containing aloe vera

In these studies, hydrogels for wound dressings were made from a mixture of aloe vera and poly(vinyl alcohol) (PVA)/poly(N‐vinylpyrrolidone) (PVP) by freezing and thawing, γ‐Ray irradiation, or a two‐step process of freezing and thawing and γ‐ray irradiation. We examined the physical properties, including gelation, water absorptivity, gel strength, and degree of water evaporation, to evaluate the applicability of these hydrogels for wound dressings. The PVA:PVP ratio was 6:4, the dry weight of aloe vera was in the range 0.4–1.2 wt %, and the solid concentration of the PVA/PVP/aloe vera solution was 15 wt %. We used γ radiation doses of 25, 35, and 50 kGy to expose mixtures of PVA/PVP/aloe vera to evaluate the effect of radiation dose on the physical properties of the hydrogels. Gel content and gel strength increased as the concentration of aloe vera in the PVA/PVP/aloe vera gels decreased and as radiation dose increased and the number of freeze–thaw cycles was increased. The swelling degree was inversely proportional to the gel content and gel strength. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1477–1485, 2003     

Thermally crosslinked anionic hydrogels composed of poly(vinyl alcohol) and poly(γ‐glutamic acid): Preparation,characterization, and drug permeation behavior

pH‐sensitive anionic hydrogels composed of poly(vinyl alcohol) (PVA) and poly(γ‐glutamic acid) (γ‐PGA) were prepared by the freeze drying method and thermally crosslinked to suppress hydrogel deformation in water. The physical properties, swelling, and drug‐diffusion behaviors were characterized for the hydrogels. In the equilibrium swelling study, PVA/γ‐PGA hydrogels shrunk in pH regions below the pK_a (2.27) of γ‐PGA, whereas they swelled above the pK_a. In the drug‐diffusion study, the drug permeation rates of the PVA/γ‐PGA hydrogels were directly proportional to their swelling behaviors. The cytocompatibility test showed no cytotoxicity of the PVA/γ‐PGA hydrogels for the 3T3 fibroblast cell lines. The results of these studies suggest that hydrogels prepared from PVA and γ‐PGA could be used as orally administrable drug‐delivery systems. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

In vitro silver ion release kinetics from nanosilver/poly(vinyl alcohol) hydrogels synthesized by gamma irradiation

A nanosilver (nano‐Ag)/poly(vinyl alcohol) (PVA) hydrogel device was synthesized with γ irradiation because it is a highly suitable tool for enhanced nano‐Ag technologies and biocompatible controlled release formulations. The amount of the Ag⁺ ions released in vitro by the nano‐Ag/PVA hydrogel device was in the antimicrobial parts per million concentration range. The modeling of the Ag⁺ ion release kinetics with the elements of the drug‐delivery paradigm revealed the best fit solution (R² > 0.99) for the Kopcha and Makoid–Banakar's pharmacokinetic dissolution models. The term A/B, derived from the Kopcha model, indicated that the nano‐Ag/PVA hydrogel was mainly an Ag⁺‐ion diffusion‐controlled device. Makoid–Banakar's parameter and the short time approximated Ag⁺‐ion diffusion constant reflected the importance of the size of the Ag nanoparticles. However, it appeared that the cell oxidation potential of the Ag nanoparticles depended on the diffusion characteristics of the fluid penetrating into the Ag/PVA nanosystem. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40321.     

Preparation and characterization of polyacrylic acid‐poly(vinyl alcohol)‐based interpenetrating hydrogels

Some structural features of hydrogels from poly(acrylic acid) (PAAc) of various crosslinking degrees have been investigated through mechanical and swelling measurements. Interpenetrating polymer hydrogels (IPHs) of poly(vinyl alcohol) (PVA) and PAAc have been prepared by a sequential method: crosslinked PAAc chains were formed in aqueous solution by crosslinking copolymerization of acrylic acid and N,N‐methylenebisacrylamide in the presence of PVA. The application of freeze–thaw (F–T) cycles leads to the formation of a PVA hydrogel within the synthesized PAAc hydrogel. The swelling and viscoelastic properties of the IPHs were evaluated as a function of the content of crosslinker and the application of one F–T cycle. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5789–5794, 2006     

Investigation of the relationships between the chain organization and rheological properties of atactic poly(vinyl alcohol) hydrogels

The structure and rheological behavior of atactic poly(vinyl alcohol) (a-PVA) hydrogels prepared by freeze/thaw cycles were investigated as a function of polymer concentration and number of freeze/thaw cycles. The presence of phases with different mobilities was observed using ¹³C CP/MAS and DP/MAS NMR experiments. The degree of crystallinity of the a-PVA-rich phase was determined by ¹H NMR free decay experiments. Measurements of the shear storage and loss modulus were performed at a fixed frequency of 1 Hz and a strain value of 0.1%, i.e. under conditions where the deformation imposed on the gel structure is entirely reversible. Results thus obtained showed that an increase in the number of freeze/thaw cycles induces an increase in the degree of crystallinity in the polymer-rich phase together with an increase in the storage modulus. The a-PVA hydrogels became more fragile as the number of freeze/thaw cycles was increased. Moreover, both the percentage of protons in a rigid environment measured by ¹H NMR and the storage modulus values tended to a limiting value after six freeze/thaw cycles. These results show that the first five or six freeze/thaw cycles play a very important role in determining the hydrogel structure and rheological properties. A more detailed comparison of NMR and rheological data led to the conclusion that the storage modulus is mainly controlled by the a-PVA crystallinity while the hydrogen bond interactions have a much smaller contribution.     

Thermosensitive soy protein/poly(n‐isopropylacrylamide) interpenetrating polymer network hydrogels for drug controlled release

A series of the thermosensitive interpenetrating polymer network hydrogels composed of soy protein and poly(N‐isopropylacrylamide) were successfully prepared. The structure and properties were systematically characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, and differential scanning calorimetry. It was found that the hydrogels had good miscibility and high porosity, and the volume phase transition temperatures of the hydrogels were around 32°C. The release behavior and the release mechanism of a model protein, bovine serum albumin (BSA), were also investigated in detail. The results indicated that the release behavior of BSA had strong temperature dependence and the release percentage of BSA could be controlled by modulating the amount of soy protein or crosslinking agent. The analysis of the release mechanism revealed that the Fickian diffusion controlled release was dominant under the experimental conditions. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.