a coaxial implant has been developed using entirely biodegradable polymeric materials . as referred to herein , a coaxial implant is a device having a core containing drug , surrounded by a semi - permeable membrane that controls the rate of release of material from the core . the device is formed by extrusion , using a pre - milling and extruding step to maximize uniformity of drug dispersion within the polymeric material . in one embodiment , the polymer is processed to yield a semi - crystalline polymer , rather than an amorphous polymer . the core containing the drug and the polymer membrane can be the same or different polymer . the polymer can be the same or different composition of different monomer ratios , or polycaprolactone outside of a core of poly ), of the same or different molecular weights , and of the same or different chemical structure . the core acts as a reservoir of drug , which partitions from the core polymer to form a saturated solution of at least 10 % drug at the polymer membrane .