System for gas treatment of cellular implants. The system enhances the viability and function of cellular implants, particularly those with high cellular density, for use in human or veterinary medicine. The system utilizes a miniaturized electrochemical gas generator subsystem that continuously supplies oxygen and/or hydrogen to cells within an implantable and immunoisolated cell containment subsystem to facilitate cell viability and function at high cellular density while minimizing overall implant size. The cell containment subsystem is equipped with features to allow gas delivery through porous tubing or gas-only permeable internal gas compartments within the implantable cell containment subsystem. Furthermore, the gas generator subsystem includes components that allow access to water for electrolysis while implanted, thereby promoting long-term implantability of the gas generator subsystem. An application of the system is a pancreatic islet (or pancreatic islet analogue) implant for treatment of Type 1 diabetes (T1D) that would be considered a bio-artificial pancreas.