For 60 years, scientists have known that deep within the inner ear lies a natural battery -- a chamber filled with ions that produces an electrical potential to drive neural signals -- which allows the brain to understand what our ears hear. No researchers had attempted using this battery to power implantable devices before because it was seen as too dangerous, but those smarties at MIT have set out to prove it's possible.
MIT News gives a little background on the natural battery, "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."
It's a very low voltage, so all the components had to be very low-power. The researchers developed a device consisting of a low-power chip equipped with an ultralow-power radio transmitter and power-conversion circuitry that builds up charge in a capacitor because the voltage in the natural battery fluctuates.
Using a guinea pig as their test subject, they implanted electrodes attached to the device into the natural battery of each of its ears. The chip remained outside although it was small enough to fit in the cavity of the middle ear. MIT News says, "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 devices could monitor biological activity in the ears of people with hearing or balance impairments. They could also monitor people's responses to therapies and even possibly deliver those therapies.
“The fact that you can generate the power for a low voltage from the cochlea itself raises the possibility of using that as a power source to drive a cochlear implant,” Cliff Megerian, chairman of the otolaryngology department at Case Western Reserve University says. “Imagine if we were able to measure that voltage in various disease states. There would potentially be a diagnostic algorithm for aberrations in that electrical output.”
“I’m not ready to say that the present iteration of this technology is ready,” Megerian continues. “If we could tap into the natural power source of the cochlea, it could potentially be a driver behind the amplification technology of the future.”