The battery-like electrochemical gradient that naturally exists in the inner ear of a mammal has been harvested for the first time and used to power a small wireless transmitter. As reported in a study published online this week in Nature Biotechnology, with further optimization, this approach may one day serve to power drug-delivery vehicles, molecular sensors or other devices implanted in the vicinity of the human ear, such as hearing aids.
The ‘endocochlear potential’ in the inner ear is the only electrochemical potential in animals that occurs across such a large anatomical structure. A major challenge in capturing the energy of the endocochlear potential is that the voltage and extractable power are very low-at least ten times lower than what can be captured using the most efficient existing circuits.
Anantha Chandrakasan, Konstantina Stankovic and colleagues overcame this challenge using a specially designed electronics chip. With the chip placed on the surface of an anesthetized guinea pig and connected to tiny electrodes embedded in the cochlea, the authors succeeded in extracting ~1 nW of power for as long as 5 hours, which was enough power to run a wireless radio that transmitted measurements of the endocochlear potential.