A biocompatible polymeric controlled release matrix barrier structure comprising: a body structure formed of a compliant material comprising one or more compliant biocompatible polymers and one or more bioactive agents, the body structure comprising a pre-formed tube structure; and the body structure defining a central aperture through which a subcutaneous element of an implantable medical device passes; wherein the body structure further comprises a blend of a first poly(D,L-lactide-co-glycolide-co-ε-caprolactone) terpolymer having a molecular weight (Mw) of from 75,000 to 250,000 Daltons and a polydispersity index of less than 2.0 and a second poly(D,L-lactide-co-glycolide-co-ε-caprolactone) terpolymer having a molecular weight (Mw) of 130,000 Daltons or less and a polydispersity index of less than 2.0, the second poly(D,L-lactide-co-glycolide-co-ε-caprolactone) having a molecular weight (Mw) that is less than the first poly(D,L-lactide-co-glycolide-co-ε-caprolactone); wherein the controlled release matrix barrier structure further comprises a central projection that is disposed about the central aperture at a top portion of the body structure and a flange disposed around the central projection, the flange having an outer surface with one or more suture loops disposed thereon; wherein the weight ratio of the first poly(D,L-lactide-co-glycolide-co-ε-caprolactone) to the second poly(D,L-lactide-co-glycolide-co-ε-caprolactone) is from about 90:10 to about 60:40; and wherein the central projection is configured to pass through a patient's skin to the outside such that the skin of the patient can fit against the flange. a body structure formed of a compliant material comprising one or more compliant biocompatible polymers and one or more bioactive agents, the body structure comprising a pre-formed tube structure; and the body structure defining a central aperture through which a subcutaneous element of an implantable medical device passes; wherein the body structure further comprises a blend of a first poly(D,L-lactide-co-glycolide-co-ε-caprolactone) terpolymer having a molecular weight (Mw) of from 75,000 to 250,000 Daltons and a polydispersity index of less than 2.0 and a second poly(D,L-lactide-co-glycolide-co-ε-caprolactone) terpolymer having a molecular weight (Mw) of 130,000 Daltons or less and a polydispersity index of less than 2.0, the second poly(D,L-lactide-co-glycolide-co-ε-caprolactone) having a molecular weight (Mw) that is less than the first poly(D,L-lactide-co-glycolide-co-ε-caprolactone); wherein the controlled release matrix barrier structure further comprises a central projection that is disposed about the central aperture at a top portion of the body structure and a flange disposed around the central projection, the flange having an outer surface with one or more suture loops disposed thereon; wherein the weight ratio of the first poly(D,L-lactide-co-glycolide-co-ε-caprolactone) to the second poly(D,L-lactide-co-glycolide-co-ε-caprolactone) is from about 90:10 to about 60:40; and wherein the central projection is configured to pass through a patient's skin to the outside such that the skin of the patient can fit against the flange.