Preparation of pH-Responsive Polyvinyl Alcohol Hydrogels and Their Drug-Releasing Behavior

For the purpose of drug-carrying in oral administration, pH-responsive polyvinyl alcohol (PVA) hydrogels were prepared by the gelation of PVA with tetracarboxylic acid dianhydride as crosslinking part and pH-sensitive part. The resulting hydrogels were estimated on the swelling behavior and the releasing behavior of loaded drug in pH 1.6 buffer solution as imitation of gastric condition and pH 7.4 buffer solution as imitation of intestinal condition at 37°C. The swelling degree was drastically decreased in pH 1.6 buffer solution, but high swelling degree was observed in pH 7.4 buffer solution at 37°C. The equilibrium swelling degree in pH 7.4 buffer solution at 37°C was dependent on the amount of carboxylic acid groups introduced in hydrogels. The releasing behavior of diclofenac sodium (DFNa) as acidic model drug was analogous to the swelling behavior of hydrogels. The releasing rate of DFNa was also dependent on the amount of carboxylic acid groups introduced in hydrogels. However, the release of imipramine hydrochloride as basic model drug was not controlled with pH.