an improved implantable pharmaceutical depot for the prolonged release of at least one biologically active substance , the depot comprising a polymeric carrier and the biologically active substance , the improvement wherein the depot is coated or surface modified with a biologically active and biocompatible glass , glass - ceramic or ceramic material , the coating or modified surface being capable of forming a bond to soft tissue upon implantation . methods for forming the biologically active and biocompatible glass , glass - ceramic or ceramic coating or modified surface on the silicone based depot are also disclosed .