Surface Eroding Methacrylic Anhydride Copolymers and Model Drug Release

Methacrylic anhydride (MAA)-based copolymers are synthesized to probe how comonomer composition and type affect the erosion profiles. Anhydrides readily undergo hydrolysis, which when combined with high crosslink density and hydrophobicity tend to exhibit an ideal surface erosion mechanism for drug delivery, tissue adhesives, and biocement applications. The cylindrical (10 mm diameter x 5 mm height) polyanhydrides are degraded under pseudo-physiological conditions and surface erosion is qualitatively observed via photographs. The non-anhydride comonomer can be utilized to tune erosion profiles while retaining degradability and product solubility. The comonomer can accelerate or slow the degradation process to a greater extent at low MAA concentrations. Drug release is conducted using purpurin to model hydrophobic drugs. Purpurin concentration is quantified using UV-visible spectral analysis. Purpurin extends the degradation profile due to a combination of local pH changes, hydrophobicity, and molecular diffusion. Linear purpurin release is observed as a function of polymer erosion (0.9897 R-2) thus confirming a surface erosion-mediated drug release mechanism.