Permeation of drug and swelling agent through polymeric membranes

The permeation of drug (benzocaine) and swelling agent (ethanol) through the polymeric [poly(ethylene-co-vinylacetate) and polyurethane] membranes was investigated theoretically and experimentally. Based on the Flory-Huggins and Yasuda theories, the swelling effect on permeant diffusivity was described by expressing the permeant diffusivity in powers of the activity of the swelling agent. The experimental results suggest that the leading-order term (first order of activity) is accurate enough to describe the diffusivities of benzocaine and ethanol in the poly(ethylene-co-vinylacetate) and polyurethane membranes. The linear dependence of permeant diffusivity on swelling-agent activity was further used to analyze the drug diffusion in a membrane subject to a swelling gradient. With the knowledge of the dependence of benzocaine and ethanol diffusivities on ethanol activity, the activity profile of ethanol across the membrane can be calculated, and the effective diffusivity of benzocaine can then be predicted. Experiments carried out to determine the variation in the effective benzocaine diffusivity corresponding to different swelling gradients agreed well with the calculated results.