The biological fuel cell uses glucose, a sugar in blood, with a non-toxic substance used to draw electrons from glucose, said the team led by Matsuhiko Nishizawa, bio-engineering professor at the graduate school of state-run Tohoku University.

"Since the electron mediator is based on Vitamin K3, which exists in human bodies, it excels in safety and could in the future generate power from blood as an implant-type fuel cell," the group said in a statement.

Most other bio-fuel cells under study use a metal complex, spawning concern about harm if used for implants.

The newly developed cell in the size of a tiny coin is able to generate 0,2 milliwatts of electricity, enough to power a device that measures blood sugar level and transmits data elsewhere, the group said.