The present invention is directed to medial articles having bioerodible polymeric regions that contain biodegradable block copolymers. The biodegradable block copolymers include at least one first biodegradable polymer block and least one second biodegradable polymer block that differs from the first biodegradable polymer block. The bioerodible polymeric regions comprise a first phase domain formed from the at least one first biodegradable polymer block and a second phase domain formed from the at least one second biodegradable polymer block. At least one of the first and second phase domains is a discontinuous phase domain in the form of dispersed phase elements, substantially all of which have a longest cross-sectional dimension that is less than 1 micron.