A group of scientists has revealed that an ear chamber filled with ions and which produces an electrical potential to drive neural signals can be used to power medical devices.
A team of researchers from MIT, the Massachusetts Eye and Ear Infirmary (MEEI) and the Harvard-MIT Division of Health Sciences and Technology (HST) demonstrated for the first time that this natural battery could power implantable electronic devices without impairing hearing.
The devices could monitor biological activity in the ears of people with hearing or balance impairments, or responses to therapies.
In experiments, Konstantina Stankovic, an otologic surgeon at MEEI, and HST graduate student Andrew Lysaght implanted electrodes in the biological batteries in guinea pigs' ears.
Attached to the electrodes were low-power electronic devices developed by MIT's Microsystems Technology Laboratories (MTL).
After the implantation, the guinea pigs responded normally to hearing tests, and the devices were able to wirelessly transmit data about the chemical conditions of the ear to an external receiver.
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.
The MTL researchers - Anantha Chandrakasan, who heads MIT's Department of Electrical Engineering and Computer Science; his former graduate student Patrick Mercier, and Saurav Bandyopadhyay, a graduate student in Chandrakasan's group - equipped their chip with an ultralow-power radio transmitter.
But while the radio is much more efficient than those found in cellphones, it still couldn't run directly on the biological battery.
So the MTL chip also includes power-conversion circuitry - like that in the boxy converters at the ends of many electronic devices' power cables - that gradually builds up charge in a capacitor.
The research is published in journal Nature Biotechnology.