Utilizing the Biologic Battery of the Inner Ear

In the most recent issue of Nature Biotechnology, a team of researchers from Massachusetts Institute of Technology and Massachusetts Eye and Ear Infirmary have published, for the first time, a method to tap into a limitless source of energy from a biological battery located in the most unsuspecting of locations - the inner ear.

Patrick Mercier and colleagues developed a microchip that can be inserted into the inner ear to harvest energy generated by the endocochlear potential within the cochlea. The endocochlear potential is essential for cochlear mechanotransduction, that is, converting auditory sound from waves in the cochlea into nerve impulses that travel up to the brain. The endocochlear potential is generated by the ionic concentration difference between two fluid compartments within the inner ear. This ionic imbalance is, in essence, a biologic battery, resulting in 70 -  100 mV electrochemical potential. By inserting electrodes into each of the fluid compartments of the guinea pig cochlea and connecting these electrodes to a specialized microchip, this study was able to utilize the biologic battery of the inner ear to fuel a 2.4 GHz radio for more than 5 hours.

As the global market for implantable devices, such as cochlear implants and the myriad of deep brain stimulation apparati, grows so does the need to improve methods for providing sustainable power to maintain their operation. Anatomical restrictions often limit the size of usable batteries, resulting in risky surgery for battery replacement or use of awkward out-of-body power sources. Harvesting energy from sources within the human body, as reported in this study, could revolutionize the accessibility and the practicality of implantable electronic devices by resolving the issue of sustainable power.

While transmitting a radio signal for 5 hours may seem like small cheese, this study illustrates the feasibility of utilizing within-human biological batteries to create sustainable power for implantable devices. With further optimization of electrode design, enhancements in microchip processing, and the continually advancement of wireless transmission capabilities, we may see biologic battery-operated cochlear implants in the not-so-distant future.