the present invention involves porous polymer membranes , suitable for use in medical implants , having controlled pore sizes , pore densities and mechanical properties . methods of manufacturing such porous membranes are described in which a continuous fiber of polymer is extruded through a reciprocating extrusion head and deposited onto a substrate in a predetermined pattern . when cured , the polymeric material forms a stable , porous membrane suitable for a variety of applications , including reducing emboli release during and after stent delivery , and providing a source for release of bioactive substances to a vessel or organ and surrounding tissue .