A biointerface membrane for an implantable device including a nonresorbable solid portion with a plurality of interconnected cavities therein adapted to support tissue ingrowth in vivo, and a bioactive agent incorporated into the biointerface membrane and adapted to modify the tissue response is provided. The bioactive agents can be chosen to induce vascularization and/or prevent barrier cell layer formation in vivo, and are advantageous when used with implantable devices wherein solutes are transported across the device-tissue interface.