A bioartificial device, such as a bioartificial pancreas, for implantation in a patient's vascular system. The bioartificial pancreas includes a scaffold adapted to engage an interior wall of a blood vessel, a cellular complex support by the scaffold and extending longitudinally within the interior cavity of the scaffold so as to be exposed to the blood flow when the scaffold is engaged with the blood vessel, the cellular complex support comprising one or more pockets bordered by thin film; and cellular complex comprising pancreatic islets disposed in the one or more pockets, the thin film being adapted to permit oxygen and glucose to diffuse from flowing blood into the one or more pockets at a rate sufficient to support the viability of the islets. The invention also includes methods of making and using a bioartificial pancreas.