The power of your ear

For the first time, scientists have managed to connect a medical implant and feed it with the energy of a natural battery that we all carry in our inner ear. Yes, all mammals have in their inner ear an "endocochlear potential" similar to a battery. It is located in a chamber filled with ions that, with the aid of sound waves, produce electricity gradients which become auditory nerve signals processed by the brain. In words of the discovers at MIT: 

"The ear converts a mechanical force — the vibration of the eardrum — into an electrochemical signal that can be processed by the brain; the biological battery is the source of that signal’s current. Located in the part of the ear called the cochlea, the battery chamber is divided by a membrane, some of whose cells are specialized to pump ions. An imbalance of potassium and sodium ions on opposite sides of the membrane, together with the particular arrangement of the pumps, creates an electrical voltage." 

"We have known for 60 years that this battery exists and that it’s really important for normal hearing, but nobody has attempted to use this battery to power useful electronics." says Konstantina Stankovic, a researcher at Harvard-MIT Division of Health Sciencies and Technology. 

So far, they have managed to use this source of electricity to power a tiny device without affect hearing.

Image: Patrick P. Mercier - MIT website

This technique could be used to power small ear implants which assist people with hearing loss, to deliver drugs to the body or to feed other sensors. At present, the voltage and power are so weak that scientists had to design a mini converter circuit so the electricity could be exploited by a small electronic device (see the image for a close view into the device size).

http://web.mit.edu/newsoffice/2012/biological-battery-1107.html