Dynamic swelling and <i> in vitro</i> release of insulin from semiinterpenetrating polymer networks of poly(vinyl alcohol) and poly(methacrylic acid)

Abstract

Semi-interpenetrating polymer networks of poly(vinyl alcohol) and poly(methacrylic acid) were prepared by free radical polymerization of methacrylic acid in presence of poly(vinyl alcohol) using N,N-methylenebisacrylamide as cross linking agent. The dynamic swelling behavior of the semi-interpenetrating polymer networks was studied to determine the water transport mechanism. The effect of cross linking agent and methacrylic acid concentration on the swelling and insulin release characteristics were evaluated. Swelling ratio and water diffusion coefficients were used to characterize the water uptake process. Swelling rates correlated well with the polymer composition, the slowest rate of water uptake was observed in hydrogel samples containing large quantities of N,N-methylenebisacrylamide and maximum swelling was observed with hydrogels containing higher methacrylic acid content. The mechanism of water transport in these semi-interpenetrating polymer network hydrogels was significantly affected by the pH of the swelling medium. At pH 2.0 mechanism was Fickian (diffusion controlled) and became case II (relaxation controlled) at pH 7.4. Insulin was incorporated by active loading technique and the insulin incorporated in the semi-interpenetrating polymer network hydrogels was in the range of 28-35%. The formulations showed decreased insulin release in pH 2.0, while complete release was observed in pH 7.4 pH buffer. The diffusion coefficient of insulin through the hydrogels was in the range of 3.84×10 -6 to 5.59×10 -6 cm 2 /min in pH 2.0 buffer and in pH 7.4 buffer it was in the range of 7.55×10 -6 to 21.636×10 -6 cm 2 /min.