POLYMER MATRIX CONTROLLED RELEASE SYSTEMS - INFLUENCE OF POLYMER CARRIER AND TEMPERATURE ON WATER-UPTAKE AND PROTEIN RELEASE

The release of bovine serum albumin (BSA) from two types of ethylene-co-vinyl acetate (EVAc) polymer matrices was studied over the temperature range 4-50-degrees-C. Protein release and weight change of the matrices were evaluated in vitro. The copolymers were characterized using differential scanning calorimetry (DSC) and thermomechanical analysis (TMA). During release, the devices initially exhibit a rapid increase in weight to a maximum, followed by a more gradual decrease for the duration of the release. The time to the maximum weight and the magnitude of the maximum weight gain are temperature dependent. These effects are related to the temperature-dependent diffusivity of the BSA and elastic modulus of the EVAc. The DSC and TMA reveal melting of the crystalline phase of the polymer. The corresponding loss of mechanical integrity of the polymer leads to anomalous weight gains at these temperatures. The observed swelling and release is explained by a model in which the osmotic pressure of the protein within the pore network causes elastic deformation of the polymer matrix.