Diffusion of drug in acrylic-type pressure-sensitive adhesive matrices. I. Influence of physical property of the matrices on the drug diffusion

Abstract

Pressure-sensitive adhesive (PSA) matrices of varying ratio of 2-ethylhexylacrylate/acrylic acid co-polymers were prepared. The diffusion coefficients of prostaglandin El (PGE1) from the PSA matrices at 37 °C were calculated from release profiles. The apparent viscosity of the PSA matrices, as measured by a shear creep method, increased with increasing acrylic acid content, average molecular weight of copolymer and crosslinking agent in the PSA matrices. Generally, the PGE1 diffusion coefficient was inversely proportional to the viscosity of the PSA matrices with varying acrylic acid content. In contrast, the diffusion coefficient was virtually independent of the apparent viscosity with varying copolymer MW and crosslinking density. To further understand the relationship between the diffusion coefficient and viscosity, the microscopic viscosity of the migration routes of PGE1 in the PSA matrix was evaluated from the glass transition temperatures (Tg) to determine whether the microscopic and macroscopic (apparent) viscosities are similar. The results suggest that PGE1 diffusion coefficients from the PSA matrices can be predicted from the Tg's and microscopic viscosities.