Quo Vadis, Implanted Fuel Cell?

The road to safe and effective implantable electrical power devices has been long-and the goal has not been reached yet, although a certain amount of scientific and technological progress has been made. This brief review is focused on highlighting the stages of development of implanted fuel cells capable of providing electrical power for running implanted "personal electronics". The paper starts with early efforts to implant glucose-burning fuel cells in dogs, and ends with realistic attempts at interfacing a more sophisticated enzymatic glucose/oxygen fuel cell in an actual human blood stream. However, before that, the review deals with thermodynamic aspects of fuel cells, emphasizing the general advantages of these devices. Further steps, which are needed to realize the potential of this technology and which somehow differ from generally accepted ideas, are presented. These next steps are evaluated in the context of theoretically achievable abilities of implantable chemical power sources, which are not as great as many researchers might expect.