The controlled release behavior and pH‐ and thermo‐sensitivity of alginate/poly(vinyl alcohol) blended hydrogels

Poly(vinyl alcohol) (PVA) was blended with sodium alginate (Alg) in various ratios and crosslinked with calcium chloride and made into hydrogel membranes. The dependence of the swelling behavior of these Alg‐Ca/PVA hydrogels on pH was investigated. The temperature‐dependent swelling behavior of the semi‐interpenetrating network (semi‐IPN) hydrogels was examined at temperatures from 2 to 45°C and the enthalpy of mixing (ΔH_mix) was determined at various temperatures. The molecular structure of the hydrogels was studied by infrared spectroscopy and their water structure in the semi‐IPN hydrogels was measured by differential scanning calorimetry (DSC). The influence of Ca²⁺ content on the network structure of Alg‐Ca/PVA hydrogels was investigated in terms of the compressive elastic modulus, effective crosslinking density, and the polymer–solvent interaction parameter based on the Flory theory. The loading of alizarin red S (ARS) followed the Langmuir isotherm mechanism and the release kinetics of ARS from the Alg‐Ca/PVA hydrogels followed the Fickian diffusion mechanism. Copyright © 2008 John Wiley & Sons, Ltd.     

Physical Hydrogels of Poly(vinyl alcohol) with Different Syndiotacticity Prepared in the Presence of Lactosilated Chitosan Derivatives

Poly(vinyl alcohol) (PVA) physical hydrogels were prepared by repeated freeze–thawing cycles using aqueous solutions of two PVA samples having different degrees of syndiotacticity, a‐PVA and s‐PVA with 55% and 61% of syndiotactic diads, respectively. The hydrogels were prepared in the presence of different amounts of lactosilated chitosan derivatives (LC) of different molecular weight. The PVA stereoregularity was found to have a dramatic effect on the amount of PVA incorporated into the hydrogels, leading to remarkable differences in the swelling degree and porosity of a‐PVA and s‐PVA hydrogels. A significant amount of LC was retained in the hydrogels after equilibrium swelling. The swelling of the a‐PVA hydrogels was found to increase significantly by increasing the amount of LC while it was only slightly increased in the case of s‐PVA hydrogels. The amount of LC released after equilibrium swelling was lower when chitosan derivatives with higher molecular weights were used. Increased initial concentrations of LC resulted in much higher porosity of the hydrogels. TGA and DSC studies showed that LC is stabilized by the incorporation in the PVA hydrogels. The melting temperature of the crystalline regions of PVA was not significantly influenced by LC. Conversely, the extension of the crystalline domains increased in the presence of LC. The retention of a chitosan derivative bearing β‐D ‐galactose side chain residues makes these hydrogels potentially useful as scaffolds for hepatocytes culture.

Scanning electron micrographs of PVA‐LC hydrogels: (a) a‐PVA; (b) a‐PVA/LC₁₅₀ 80:20; (c) a‐PVA/LC₁₅₀ 50:50.     

Swelling behavior of chitosan hydrogels in ionic liquid-water binary systems

The swelling behavior of chitosan hydrogels in ionic liquid-water binary systems was studied using hydrophilic room-temperature ionic liquids (RTILs) to elucidate the swelling mechanism of chitosan hydrogels. No penetration of RTIL into a dry chitosan material was observed. Swelling was achieved by soaking in water-RTIL binary mixtures, with larger swelling observed at higher water contents. In one instance, the binary mixture was acidic and produced larger than expected swelling due to the dissociation of the amine groups in the chitosan. The equilibrium binary system content behavior of the chitosan hydrogels depended upon the amount of free water, which is a measure of the number of water molecules that do not interact with the ionic liquid. After evaporation of water, remnant RTIL remained in the chitosan network and hardness testing indicated a plasticization effect, suggesting that the RTIL molecularly mixed with the chitosan. Chitosan hydrogels containing only RTIL were prepared by dropping pure RTIL onto a fully preswollen hydrogel followed by water evaporation. This method may be a useful means for preparing air-stable swollen chitosan gels.     

Manufacturing of pH sensitive PVA/PVP/MWCNT and PVA/PEG/MWCNT nanocomposites: an approach for significant drug release

The purpose of this paper is studying the effect of incorporation of Multiwall Carbon Nanotubes (MWCNT) into two different nanocomposites in poly vinyl alcohol (PVA)/polyvinylpyrrolidone (PVP), and PVA/Polyethylene glycol (PEG). MWCNT were synthesized by chemical vapor deposition (CVD) method using acetylene and Fe/Co/Al₂O₃ as carbon precursor and catalyst, respectively. Nitric acid and sulfuric acid were used for purification and functionalization of MWCNT. Afterward, highly pure and functionalized MWCNT (0, 0.02, and 0.05% w/w) were incorporated in PVA/PVP and PVA/PEG to synthesize PVA/PVP/MWCNT and PVA/PEG/MWCNT nanocomposites hydrogel membranes that cross-linked by freezing–thawing. PEG and PVP were selected in these nanocomposites as dispersion matrix for MWCNT as well as for increasing the elasticity of the nanocomposites membranes. The morphology of the hydrogels was characterized by SEM, FTIR, XRD, TGA, and the mechanical properties of the hydrogel membranes were investigated. The swelling behavior in different pH-buffer solutions was studied as well as studying weight loss percentage and swelling kinetic. The drug releasing process of the hydrogel membranes was investigated using salicylic acid as a model drug. It was found that MWCNT are dispersed well into the polymers and crystallinity, mechanical properties and thermal stability of the hydrogels contain MWCNT are better than that without MWCNT. Maximum degree of swelling was observed at pH 7 and swelling degree increases with increasing the ratio of MWCNT in the hydrogels from 0.02 to 0.05%. All hydrogel membranes followed non-Fickian mechanism and drug releasing were controlled by varying the pH and amount of MWCNT.     

PVA改性PAMPS-PAM超高力学性能双网络水凝胶的制备

采用紫外光引发聚合制备了聚乙烯醇(PVA)改性的聚(2-丙烯酰胺基-2-甲基丙磺酸)-聚丙烯酰胺(PAMPS-PAM)双网络(DN)水凝胶.测定并比较了PVA改性前后PAMPS-PAM双网络水凝胶的溶胀动力学;通过扫描电子显微镜(SEM)观察了单网络水凝胶的结构;测定PVA改性前后PAMPS-PAM双网络水凝胶的压缩及拉伸性能.结果表明,经PVA改性后的PAMPS-PAM双网络水凝胶有较高的溶胀比;0.82%PVA用量的PAMPS-PAM双网络水凝胶在90%压缩形变率下仍保持完整、最大拉伸应力达到0.5 MPa,大幅提高PAMPS-PAM双网络水凝胶的力学性能.     

大孔PAMPS/PVA半互穿网络型水凝胶的制备及其性能研究

以PEG6000为成孔剂, 合成了大孔聚(2-丙烯酰胺-2-甲基丙磺酸)/聚乙烯醇半互穿网络型(s-IPN)水凝胶. 红外分析表明, PVA与PAMPS之间形成了较强的氢键, 使得PVA分子上的C—O伸缩振动吸收峰移向了低波数处. X射线衍射分析发现, 当PVA用量较高时, 由于部分的PVA结晶, 使得凝胶的半互穿网络结构不均匀. 电镜分析结果表明, 没有使用成孔剂的凝胶表面成褶皱形, 不存在任何孔洞结构; 而以PEG6000为成孔剂的凝胶表面存在相互贯穿的大孔结构. 研究了该水凝胶的溶胀性能, 结果表明, 该水凝胶的平衡溶胀度在116至320之间; 而成孔剂PEG6000的加入能较大幅度提高凝胶的溶胀速率, 凝胶在240 min之内就能达到溶胀平衡. 对凝胶抗压缩性能的研究表明, 当PVA用量为9.1% (w)时, 凝胶的抗压缩强度最大, 可达12.0 MPa; 而成孔剂的加入会在一定程度削弱凝胶的抗压缩强度. 该凝胶具有较好的电场敏感性, 研究发现, 将吸去离子水达到溶胀平衡的凝胶放入施加有电场的0.2 mol•L－1 NaCl溶液中时, 凝胶迅速偏向阳极. 而PVA和成孔剂PGE6000的用量均对凝胶的偏转速度以及最大偏转角存在较大的影响.     

先辐射后冻融法制备聚乙烯醇/水溶性壳聚糖/甘油水凝胶的云南白药药物释放性能研究

采用先辐射后冻融的方法制备了一系列聚乙烯醇(PVA)/水溶性壳聚糖/甘油水凝胶,通过浸泡法在水凝胶中载入云南白药,并且研究了溶液pH值、离子强度、冻融次数和PVA浓度对水凝胶溶胀性能和云南白药释放性能的影响.研究发现水凝胶的溶胀度随溶液离子强度的增大而下降,且酸性溶液大于中性溶液.水溶性壳聚糖的加入有利于云南白药载入凝胶,同时使云南白药的释放具有pH和离子强度敏感性.云南白药的释放量在模拟体液中最大,在中性溶液中次之,在水和酸性溶液中最小,与溶胀度变化关系相反.而水凝胶的溶胀度和云南白药释放量均随冻融次数和PVA浓度的增大而下降.分析表明,云南白药在不同介质中的释放量主要取决于药物和溶液中离子的交换能力;在相同介质中,不同凝胶的药物释放量受溶胀度影响明显.凝胶溶胀速率远大于药物释放速率说明后者主要由扩散过程控制.药物释放的pH敏感性表明该水凝胶具备用作云南白药的口服载体的潜力.     

pH‐Sensitive Mechanical Properties of Elastin‐Based Hydrogels

Ionizable amino acids in protein‐based hydrogels can confer pH‐responsive behavior. Because elastin‐like polypeptides (ELPs) have an established sequence and can crosslink to form hydrogels, they are an ideal system for creating pH‐sensitive materials. This study examines different parameters that might affect pH‐sensitive behavior and characterizes the mechanical and physical properties between pH 3 and 11 of three ELP‐based crosslinked hydrogels. The first finding is that varying the amount of crosslinker affects the overall stiffness and resilience of the hydrogels but does not strongly affect water content, swelling ratio, or pH sensitivity. Second, the choice of two popular tag sequences, which vary in histidine and aspartic acid content, does not have a strong effect on pH‐sensitive properties. Last, selectively blocking lysine and tyrosine residues through acetylation significantly decreases the pH‐sensitive zeta potential. Acetylated hydrogels also demonstrate different behavior at low pH values with reduced swelling, reduced water content, and higher stiffness. Overall, this work demonstrates that ELP hydrogels with ionizable groups are promising materials for environmentally‐responsive applications such as drug delivery, tissue engineering, and microfluidics.     

Preparation of hydrogel from green polymer

A new method was used for the production of hydrogels from green polymer with a higher swelling ratio. These hydrogels were synthesized first by graft copolymerization between acrylamide (AM) and poly(vinyl alcohol) (PVA) with alkaline or kraft lignin (AM‐PVA‐g‐lignin) and then by mixing with acrylamide monomer. The kraft and alkaline lignins were isolated from pulping liquor and characterized using UV and FT‐IR spectroscopy, and the formed hydrogels were characterized using FT‐IR spectroscopy and scanning electron microscopy (SEM). Compared with kraft lignin hydrogel, the alkaline lignin hydrogel had very high swelling ratios and slower water uptake and deswelling rates attributed to its compatible network structure. The hydrogels formed were used also to study the influence of sodium chloride on the absorption capacity at room temperature and swelling ratios at different temperatures. Copyright © 2004 John Wiley & Sons, Ltd.     

Properties of low temperature swelling hydrogels prepared with partially saponified PVA and drug release using the hydrogels

The hydrogels prepared by the crosslinking of partially saponified poly(vinyl alcohol) (PVA) which has low critical solution temperature (LCST) in water showed characteristics of swelling at low temperature and shrinkage at high temperature. The hydrogels showed repeatable swelling–shrinking behavior. The hydrogels containing release substances such as cyanocobalamin, p‐acetamidophenol, insulin and ovalbumin were prepared by dipping these aqueous solutions and the release substances were studied. Insulin and ovalbumin were not absorbed by the hydrogels when the use of partially PVA with the degrees of polymerization (DPs) of 540 were prepared, but absorbed by the hydrogels with DPs of 1860. The size of the polymer network prepared with a higher DP was suitable for the absorption of insulin and ovalbumin. In accordance with release substances, the release patterns were different. In this way, the polymer network sizes and their swelling behaviors of partially saponified PVAs were estimated. Copyright © 2003 John Wiley & Sons, Ltd.     

Preparation and Characterization of Poly(N‐Vinylpyrrolidone‐co‐Methacrylic Acid) Hydrogels

In this study, N‐vinylpyrrolidone (VP)/methacrylic acid (MAA) copolymers have been prepared at three different mole percents, the methacrylic acid composition being around 5, 10, 15%. MAA and VP monomer mixtures have been irradiated in ⁶⁰Co‐γ source at different irradiation doses and percent conversions have been determined gravimetrically. ～80% conversion of monomers into hydrogels were performed at 3.4 kGy irradiation dose. These hydrogels were swollen in distilled water at pH 4.0, 7.0, and 9.0. P(VP/MAA) hydrogel which contains 5% methacrylic acid showed the maximum % swelling at pH 9.0 in water. Diffusion of water was found to be of non‐Fickian character. Diffusion coefficients of water in P(VP/MAA) hydrogels were calculated. Initial swelling rates of P(VP/MAA) hydrogels increased with increasing pH and MAA content in hydrogels. Swelling kinetics of P(VP/MAA) hydrogels was found to be of second order. Thermal behavior of PMAA, PVP and P(VP/MAA) hydrogel were investigated by thermal analysis. P(VP/MAA) hydrogel gained new thermal properties and the temperature for maximum weight loss and temperature for half‐life of P(VP/MAA) hydrogel were determined.     

Water uptake and dye sorption studies of chemically crosslinked highly swollen novel ternary acrylamide‐based hydrogels including citraconic acid and sodium acrylate

Highly swollen hydrogels made by the polymerization of acrylamide (AAm) with some anionic monomers such as citraconic acid (CITA) and sodium acrylate (SA) were investigated as a function of composition to find materials with swelling and dye sorption properties. Highly swollen AAm/CITA/SA or AAm/SA/CITA hydrogels were prepared by free radical solution polymerization in aqueous solutions of AAm with CITA and SA as co‐monomers and two multifunctional crosslinkers such as ethylene glycol dimethacrylate (EGDMA) and 1,4‐butanediol dimethacrylate (BDMA). Swelling experiments were performed in water at 25°C, gravimetrically. Chemically crosslinked AAm/CITA/SA or AAm/SA/CITA hydrogels were used in experiments on sorption of water‐soluble monovalent cationic dye such as “Nil blue” (Basic Blue 12; BB 12). Equilibrium percentage swelling values of AAm/CITA/SA or AAm/SA/CITA hydrogels were calculated in the range of 1797–22,098%. Some swelling kinetic parameters were found. Diffusion behavior of water was investigated. Water diffusion into the hydrogels was found to be non‐Fickian in character. For sorption of cationic dye, BB 12 into the hydrogels was studied by batch sorption technique at 25°C. AAm/CITA/SA or AAm/SA/CITA hydrogels in the dye solutions showed coloration, whereas AAm hydrogel did not show sorption of any dye from the solution. The sorption capacity of AAm/CITA/SA or AAm/SA/CITA hydrogels was investigated. At the end of the experiments, 21.70–78.91% BB 12 adsorptions were determined. Copyright © 2007 John Wiley & Sons, Ltd.     

Synthesis and Properties of Poly(AAm‐KMA‐MA) Hydrogels

In this investigation, poly(acrylamide‐co‐potassium methacrylate‐co‐maleic acid) hydrogels, poly(AAm‐KMA‐MA) were synthesized by redox copolymerization in aqueous solution. The effect of reaction parameters, such as concentration of maleic acid, crosslinking agent, initiator and activator, on the swelling behavior was investigated in detail. The swelling/diffusion characteristics were also evaluated for 1,4‐butanediol diacrylate (BDDA) and 1,2‐ethyleneglycol dimethacrylate (EGDMA) crosslinked hydrogels having different amounts of maleic acid. The results indicate that the water diffusion of hydrogels was of a non‐Fickian type. The hydrogels were characterized by IR spectroscopy and thermogravimetric analysis (TGA). Their surface characteristics were observed by using scanning electron microscopy (SEM). Furthermore, their swelling phenomena in different pH and salt solutions and simulated biological fluids was also studied.     

Swelling studies of copolymeric acrylamide/crotonic acid hydrogels as carriers for agricultural uses

In this study, highly swollen acrylamide/crotonic acid hydrogels (in a rod form) containing some inorganic salts such as ammonium nitrate, potassium nitrate and ammonium sulphate used as fertilizer, an agricultural drug such as Dalapon (sodium 2,2‐dichloropropionate) and two crosslinkers such as ethylene glycol dimethacrylate and 1,4‐butandiol dimethacrylate were prepared by copolymerization of acrylamide and crotonic acid with γ‐radiation. As a result of swelling tests, the influence of γ‐ray dose and relative content of crotonic acid on the swelling properties, the diffusional behavior of water, diffusion coefficients and network properties of the hydrogel systems were examined. Acrylamide/crotonic acid hydrogels containing these salts and agricultural drug were swollen in the range 2045–400% in water, while polyacrylamide hydrogels swelled in the range 660–700%. Water intake of hydrogels followed a nonFickian‐type diffusion. Copyright © 2000 John Wiley & Sons, Ltd.     

Cryogenic Designing of Biocompatible Blends of Polyvinyl alcohol and Starch with Macroporous Architecture

The present paper discusses synthesis, characterization, and blood compatibility studies of macroporous cryogels of PVA and starch. Biocompatible spongy porous hydrogels of polyvinyl alcohol–starch have been synthesized by repeated freezing–thawing methods and characterized by Infra red (FTIR) and environmental scanning electron microscopy (ESEM) techniques, respectively, to gain insights for structural and morphological features. The FTIR analysis of prepared cryogels indicated that starch was introduced into the network of cryogel possibly via formation of hydrogen bonds between the PVA and starch clusters. The “cryogels” were evaluated for their water uptake potentials and influence of various factors such as chemical architecture of the spongy hydrogels, pH and temperature of the swelling bath were investigated on the degree of water sorption by the cryogels. The hydrogels were also swollen in salt solutions and various simulated biological fluids. The biocompatibility of the prepared cryogels was judged by in vitro methods of blood–clot formation viz. percent haemolysis and protein (BSA) adsorption. The cryogels were also studied for their pores morphology and percent porosity and the effect of chemical composition on the extent of porosity was also investigated.     

A study on the swelling behavior of poly(acrylic acid) hydrogels obtained by electron beam crosslinking

Poly(acrylic acid) (PAA) hydrogels were prepared by using electron beam (EB) crosslinking of PAA homopolymer from its aqueous solutions. The swelling behavior of the hydrogels was studied as a function of the concentration of PAA solution, radiation dose, pH of the swelling medium and swelling time. Also the environmental pH effect on the water diffusion mode into hydrogels was investigated. These hydrogels clearly showed pH-sensitive swelling behavior with Fickian type of diffusion in the stomach-like pH medium (pH 1.3) and non-Fickian type in the intestine-like pH medium (pH 6.8).     

Effect of the water state on the electrical bending behavior of chitosan/poly(diallyldimethylammonium chloride) hydrogels in NaCl solutions

Semi‐interpenetrating polymer network (SIPN) hydrogels, composed of chitosan (CS) and poly(diallyldimethylammonium chloride) (PDADMAC), were prepared, and they exhibited electrically sensitive behavior. The swelling behavior of the CS/PDADMAC SIPN hydrogels was studied through the immersion of the gels in various concentrations of aqueous NaCl solutions, and their responses to stimuli in electric fields were also investigated. When the swollen SIPN hydrogels were placed between a pair of electrodes, they exhibited bending behavior upon the application of an electric field, which was stepwise and dependent on the magnitude of the field. To clarify the relationship between the equilibrium‐swelling ratio and the bending behavior of the SIPN hydrogels, the state of water in the SIPN hydrogels was also investigated with differential scanning calorimetry. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 914–921, 2004     

Development of Antibacterial,Degradable and pH-Responsive Chitosan/Guar Gum/Polyvinyl Alcohol Blended Hydrogels for Wound Dressing

The present research is based on the fabrication preparation of CS/PVA/GG blended hydrogel with nontoxic tetra orthosilicate (TEOS) for sustained paracetamol release. Different TEOS percentages were used because of their nontoxic behavior to study newly designed hydrogels’ crosslinking and physicochemical properties. These hydrogels were characterized using Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and wetting to determine the functional, surface morphology, hydrophilic, or hydrophobic properties. The swelling analysis in different media, degradation in PBS, and drug release kinetics were conducted to observe their response against corresponding media. The FTIR analysis confirmed the components added and crosslinking between them, and surface morphology confirmed different surface and wetting behavior due to different crosslinking. In various solvents, including water, buffer, and electrolyte solutions, the swelling behaviour of hydrogel was investigated and observed that TEOS amount caused less hydrogel swelling. In acidic pH, hydrogels swell the most, while they swell the least at pH 7 or higher. These hydrogels are pH-sensitive and appropriate for controlled drug release. These hydrogels demonstrated that, as the ionic concentration was increased, swelling decreased due to decreased osmotic pressure in various electrolyte solutions. The antimicrobial analysis revealed that these hydrogels are highly antibacterial against Gram-positive (Staphylococcus aureus and Bacillus cereus) and Gram negative (Pseudomonas aeruginosa and Escherichia coli) bacterial strains. The drug release mechanism was 98% in phosphate buffer saline (PBS) media at pH 7.4 in 140 min. To analyze drug release behaviour, the drug release kinetics was assessed against different mathematical models (such as zero and first order, Higuchi, Baker–Lonsdale, Hixson, and Peppas). It was found that hydrogel (CPG2) follows the Peppas model with the highest value of regression (R² = 0.98509). Hence, from the results, these hydrogels could be a potential biomaterial for wound dressing in biomedical applications.     

Phase Transition of Acrylamide‐Based Polyampholyte Gels in Water

The swelling behavior of acrylamide (AAm)–based polyampholyte hydrogels in water and in aqueous salt (NaCl) solutions was investigated. [(Methacrylamido)propyl]trimethyl‐ammonium chloride (MAPTAC) and acrylic acid (AAc) were used as the ionic comonomer in the hydrogel preparation. Three sets of hydrogels containing 70 mol% AAm and 30 mol% ionic comonomers of varying mole ratios were prepared. The variations of the hydrogel volume in response to changes in pH, and salt concentration were measured. As pH increases from 1, the hydrogel volume V _eq in water first increases and reaches a maximum value at a certain pH. Then, it decreases again with a further increase in pH and attains a minimum value around the isoelectric point (IEP). After passing the collapsed plateau region, the gel reswells again up to pH=7.1. The reswelling of the collapsed gels containing 10 and 4% MAPTAC occurs as a first‐order phase transition at pH=5.85 and 4.35, respectively, while the hydrogel with 1% MAPTAC reswells continuously beyond its IEP. Depending on pH of the solution, the hydrogels immersed in salt solutions exhibit typical polyelectrolyte or antipolyelectrolye behavior. The experimental swelling data were compared with the predictions of the Flory‐Rehner theory of swelling equilibrium including the ideal Donnan equilibria. It was shown that the equilibrium swelling theory qualitatively predicts the experimental behavior of polyampholyte hydrogels.     

Modified carrageenan. 5. Preparation,swelling behavior,salt‐ and pH‐sensitivity of partially hydrolyzed crosslinked carrageenan‐graft‐polymethacrylamide superabsorbent hydrogel

The polysaccharide, kappa‐carrageenan (κC) was chemically modified to achieve a novel superabsorbent hydrogel via graft copolymerization of methacrylamide (MAM) onto the substrate followed by alkaline hydrolysis. Ammonium persulfate (APS) and N,N′‐methylene bisacrylamide (MBA) were used as a free‐radical initiator and a crosslinker, respectively. The saponification reaction was carried out using sodium hydroxide aqueous solution. Either κC‐g‐PMAM or hydrolyzed κC‐g‐PMAM (PMAM: polymethacrylamide) was characterized by FT‐IR spectroscopy. The effect of grafting variables (i.e. concentration of MBA, MAM, and APS) and alkaline hydrolysis conditions (i.e. NaOH concentration, hydrolysis time and temperature) were systematically optimized to achieve a hydrogel with swelling capacity as high as possible. The swelling capacity of these hydrogels was also measured in various salt solutions. Results indicated that the swelling ratios decreased with an increase in the ionic strength of the salt solutions. This behavior can be attributed to charge screening effect for monovalent cations, as well as ionic crosslinking for multivalent cations. Absorbency of superabsorbing hydrogels was examined in buffer solutions with pH range 1–13. Also, the pH reversibility and on–off switching behavior, at pH values 3.0 and 8.0, makes the synthesized hydrogels good candidates for controlled delivery of bioactive agents. Finally, swelling kinetics in distilled water and various salt solutions was preliminary investigated. Results showed that the swelling in water was faster than in saline solutions. Copyright © 2004 John Wiley & Sons, Ltd.