Radical polymerization was used to prepare 2-hydroxyethyl methacrylate (HEMA) and N-vinyl-2-pyrrolidone (NVP) copolymers differing in component proportions, which were crosslinked with butylene glycol dimethacrylate (DMBD) used in various amounts, containing ethanol-soluble estradiol or water-soluble salicylic acid as a model biocide. Ethanol and water were used as respectively a gel-swelling agent and a medium into which the model biocide was released. The kinetics of release of estradiol into ethanol was examined and described by an exponential equation. At the start, a zero-order kinetic equation was found to describe the release (Table 1). The kinetics of release of salicylic acid into water is summarized in Table 2. The release rate, k, was found to be related to the chemical structure of the gel and to the equilibrium content of ethanol or water (swellability) in the copolymer as expressed by the solvent retention value, WR(E) or WR(W). During the first 6 hours, the rate of release was constant and related to the contents of HEMA and DMBD in the copolymer (Figs. 1 and 2). The higher the WR-value, the faster was the rate of release. The rate could be described by a universal function (Fig. 3) for each system under examination. The mechanism of the slow release of estradiol and salicylic acid appears to be related to the rate of solvent diffusion into the gel.
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