Abstract
Since the initial report that inert biocompatible polymers such as ethylene-vinyl acetate copolymer could be used for the controlled release of macromolecules (M.W.> 1000) (1), these systems have been used by different investigators in many areas of research (2–21). Macromolecules such as enzymes (22), antigens (23) and insulin (24) have been released in biologically active form for up to six months invivo. Extensive studies invitro have demonstrated that the release rates of drugs from these devices can be adjusted over a 2000-fold range by simple alterations in the fabrication procedures of those macromolecule-polymer matrices (25). Constant release rates have been achieved using appropriate geometric design of these matrices (26) and a method of externally regulating the release rates of these systems using magnetism has been developed (27).