Abstract: A device that includes a living cell or tissue and an agent that inhibits the ability of a host molecule to damage the cell or tissue. The device can be constructed in various forms including an implantable device, a composite microreactor and a double composite microreactor. The composite microreactor includes an internal particle that includes a living cell or tissue, an internal particle matrix that includes the living cell or tissue and an internal semipermeable coating enclosing the internal particle matrix, a gel super matrix in which the internal particle is embedded, and an agent that inhibits the ability of a host molecule to damage the cell or tissue. The double composite microreactor includes an internal particle, a particle that includes a particle matrix in which the internal particle is embedded, a super matrix in which the particle is embedded, and an agent that inhibits the ability of a host molecule to damage the living cell or tissue.