Swelling and Release Characteristics of Poly(Sulfopropyl Methacrylate Potassium-Co-Hydroxyethyl Methacrylate) Gels

Abstract

A new polyelectrolyte gel consisting of sulfopropyl methacrylate potassium and 2-hydroxyethyl methacrylate has been synthesized and characterized in terms of swelling and drug release. The swelling of the drug-free gel is influenced by the salt concentration, ranging from a swelling ratio of 44.0 in the absence of NaCl to 3.6 in 2 M NaCl. The degree of swelling does not fluctuate significantly in a variation of swelling ratios from 23.4 to 26.4 with the pH of the swelling medium ranging from 3.0 to 9.8 in 0.01 M NaCl. Even at pH 1.2 the swelling ratio is 10.7 in 0.01 M NaCl. The release of oxprenolol HC1 and diphenhydramine HCl, highly water-soluble drugs, are independent of both buffer concentration (0.01 to 0.1 M) and the pH (1.4 to 7.4) of the dissolution medium. However, the release of less water-soluble drugs, such as propranolol HCl and labetalol HCl, slows down as the pH decreases.