Medical implants are getting smaller and smaller every day, but battery tech to power the devices remains big in comparison. When they are small enough to fit, they have a limited life longitude and need to be replaced by surgery.
One of the latest experiments in this area is tapping into the electrochemical gradient that body naturally maintains in the fluids of the inner ear. The difference in charge between these the inner-ear fluids convert mechanical impulses that hit the eardrum as sound waves into neurotransmitter firings that the auditory nerve can understand.
A report in Nature Biotechnology explains how Boston scientists collected power from the inner ear of a guinea pig using a miniature circuit board and electrodes snaking into its cochlea. (In future tests, they anticipate the board will be implanted.) They extracted power of a little over 1 nano watt for about 5 hours. This was small amount, but it was enough for the device to emit a radio signal that measured the electric potential within the chamber about every minute. The lab of MIT’s Anantha Chandrakasan, one of the lead authors of the study, provided the low-power chip used in the experiment.
It is the first time when a device of this kind has been implanted without harming the existing structures in the ear. Even after a test device was implanted in their ears, guinea pigs responded to hearing tests.