Abstract: Implantable devices that include a source of a therapeutic substance and a capture agent are disclosed.

Abstract: Microcapsules and composite microreactors are prepared that immunoisolate living cells such as islet cells or genetically engineered cells. A reduced volume microcapsule is formed by coating a gel matrix particle with a polyamino acid of 15,000 daltons or less molecular weight to reduce volume of the particle by at least 30% as compared to volume prior to coating. A composite microreactor includes the microcapsule containing cell embedded in a gel matrix and provides a molecular weight cutoff that prevents molecules larger than about 400,000 daltons from containing the living cell. A double composite microreactor includes an internal particle that includes an internal particle gel matrix containing a living cell and having a coating, a particle that includes the internal particle embedded in a particle gel matrix and a coating, and a gel super matrix in which the particle is embedded. At least one of the coatings is a volume reducing coating of polyamino acid of 15,000 daltons or less molecular weight.