Implantable medical devices are fabricated from polymer blends with star-block copolymers. The polymer blends include a biodegradable matrix polymer blended with a biodegradable star-block copolymer. The copolymer has at least three arms and the arms include inner segments and outer segments. The inner segments form a discrete phase within a continuous phase, the continuous phase including the matrix polymer and the outer segments. The segments can include units having acidic degradation products that enhance the degradation rate of the blend.
