The present invention provides an implantable devices for providing a biologically active agent to a subject in need thereof, the device comprising a microvessel construct in contact with a biocompatible, semi-permeable pouch, the pouch encapsulating a cell or cells capable of producing the biologically active agent. The present invention also provides methods for treating or preventing a disorder in a subject using the implantable device. The present invention also provides specific methods for treating or preventing diabetes in a subject comprising implanting in the subject an immunoisolation device comprising a microvessel construct in contact with a biocompatible, semi-permeable pouch, the pouch encapsulating a cell or cells capable of producing a therapeutically effective amount of insulin. Methods for vascularizing and revascularizing tissue, including engineered tissue, are also provided.
