Microbial fuel cells is the big hot topic in research. These cells even work with wastewater or urine. The problem is that they all fail if you try to do upscale these buggers. Once the cells get bigger then the efficiency goes down the drain to the point that they are way too costly and large.
So beeing able to produce a mini cell that produces electricity with blood is easy - to transfer this into a successful application is the really hard part.
