The invention relates to a valve that comprises a housing and a thermostatic member having a mobile piston that carries a plug for controlling the fluid flow between two accesses to the housing. The fuel cell system includes a first conduit in fluid communication with the first catalytic electrode for delivering fuel to the first catalytic electrode at ambient temperature and a second conduit in fluid communication with the second catalytic electrode for delivering oxidant thereto. The release region regulates the rate of release of the therapeutic agent from the medical device upon implantation or insertion of the device into a patient.