Polyurethane elastomer with PEO-PTMO-PEO soft segment for sustained release of drugs

Blood-compatible segmented polyurethanes and polyurethaneureas were evaluated as drug delivery matrices using crystal violet and benzethonium chloride as model drugs. These polymers were synthesized from ABA-type triblock copolyether as a prepolymer, where A stands for poly(ethylene oxide) and B for poly(tetramethylene oxide). Microphase separation was observed in segmented polyurethaneureas, including drug-doped films. Crystal violet dissolved more in the hard segment domain than in the soft segment matrix, whereas benzethonium chloride was easily dissolved in the soft segment matrix. The drug release behaviours from these films were analysed by the exponent relation Mt/M infinity = ktn, where k and n are constants and Mt/M infinity is the fraction of drug released until time, t. The constant k grew with increasing poly(ethylene oxide) content in the prepolymer, i.e. increased swelling. The constant n was found to be close to 0.5 in many samples, which suggests the release of drug from these polymers is explained by the Fickian diffusion model. However, the mechanism became non-Fickian with increased swelling of the devices.