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A poly(acrylic acid)/gelatin interpenetrating network hydrogel was synthesized by aqueous solution polymerization. The influences of preparation conditions including cross-linker, initiator, gelatin content, and neutralization degree on the swelling ratios of the hydrogels are investigated. The swelling, mechanical strength, biodegradability, and drug-release properties of poly(acrylic acid)/gelatin hydrogel are evaluated. The hydrogel has excellent mechanical properties; tensile strength is 1500 kPa, and elongation at break is 887%, respectively. The in vitro biodegradation shows that an interpenetrating network structure exists in the poly(acrylic acid)/gelatin hybrid hydrogel. A release study indicates that the theophylline release from the hydrogel depends on the cross-linking density of the hydrogel and pH of the medium, and the drug diffusion obeys an anomalous transport model.

I. INTRODUCTION

Superabsorbent hydrogels are structurally cross-linked hydrophilic polymers, which have the ability to absorb considerable amounts of water or aqueous fluids.1 Owing to the hydrogel’s unique properties, many biomedical and technological applications such as artificial implants, contact lens, biosensors, metal ions reclamation, and conducting hydrogel have been researched.1–5 Among natural polymers, preferred for their low toxicity and biocompatibility, gelatin is a good raw material candidate because of its excellent physical and chemical properties.6 Hori et al.7 have explored the use of biodegradable gelatin series hydrogels for drug-controlled release8,9 and succeeded in enhancing the in vivo biological activity of growth factor (GF) in angiogenesis,10 osteogenesis,11 and adipogenesis.12 However, gelatin presents the main drawback of rapid solubilization in aqueous environments, thus resulting in fast drug release. Poly(acrylic acid), a typical superabsorbent polymer with a three-dimensional (3D) network structure, has been used to synthesize smart or intelligent hydrogels and functional hydrogels.13–16 To improve the properties of gelatin, acrylic acid monomer and gelatin are synchronously cross-linked to form a novel superabsorbent hydrogel with interpenetrating network structure and multifunctional properties. In this paper, a poly(acrylic acid)/gelatin superabsorbent hydrogel is synthesized by an aqueous polymerization. The influence of preparation conditions on the

II. EXPERIMENTAL A. Materials

Acrylic acid monomer was distilled prior to use. Gelatin, a mixture of water-soluble macromolecular protein made from porcine skin (300 Bloom), was used as received. Ammonium peroxydisulfate (APS) was a radical initiator for the synthesis reaction of poly(acrylic acid)/gelatin hybrid. N,N0 -methylene bisacrylamide (NMBA), as a cross-linker for preparation of the hybrid, was purified by recrystallization from 66 wt% ethanol/water solution. Hydrochloric acid and sodium hydroxide were used to control the pH value of solution. The aforementioned materials were all analysis reagents and purchased from Shanghai Chemical Rea