Extracting energy from your ear

There's a battery in your ears. And now for the first time, scientists have used this natural battery found in the inner ear to power an implantable medical device.

For the first time, scientists were able to power an implantable medical device using a natural battery found deep in the inner ear.

Okay, so within the inner ear of mammals, there naturally exists a battery-like ‘endocochlear potential’ -- a chamber filled with ions that produces an electrical gradient to drive neural signals, MIT News explains.

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.

Cool. “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 study researcher Konstantina Stankovic from Harvard.

But now, scientists have managed to harvest energy from the cochlea and use it to power a small, implantable wireless transmitter – without impairing hearing.

The device could one day power implantable hearing aids, drug-delivery devices, or other sensors placed near the ear. Or monitor activity in the ears of people with hearing or balance impairments.

Capturing it has been difficult because the voltage and extractable power are very low – so a team led by Stankovic and MIT’s Anantha Chandrakasan had to design a special electronics chip (pictured) with power-conversion circuitry.

Then they placed the chip in an anesthetized guinea pig and connected it to tiny electrodes embedded in the cochlea. From this, they were able to extract enough power to run the wireless radio that was transmitting inner ear data to an external receiver.

The work was published in Nature Biotechnology this week.

[Via MIT News]

Image from P.P. Mercier et al., Nature Biotechnology

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