The inner ear is home to hair, wax, lint, and occasionally the padding from earbud headphones. What you may not know is that, inside the cochlea of mammals, is a small chamber divided by a membrane, and the imbalance of sodium and potassium ions on either side of the membrane, in conjunction with the particular arrangement of the cellular ion pumps, creates electrical voltage. A mouthful, it simply means you have an inner ear full of energy — a natural battery — and it goes by the name of Endocochlear Potential.
For a study printed in Nature Biotechnology, a team of researchers from MIT, the Massachusetts Eye and Ear Infirmary (MEEI), and the Harvard-MIT Division of Health Sciences and Technology (HST)performed tests on guinea pigs, implanting electrodes into those ear batteries. To the electrodes they attached tiny low-power devices, developed by MIT’s Microsystems Technology Laboratories (MTL), able to wirelessly transmit data about the ear’s chemical conditions, none of which affected the guinea pigs’ hearing, as test results show. Though the voltage created is the body’s highest, outside of individual cells, it’s still low, and only a fraction of its power can be harvested without disrupting one’s hearing. So what then?
The MTL researchers added a ultralow-power radio transmitter to the chip, but since it still couldn’t run off of the natural battery itself, they added power-conversion circuitry to the chip to build up a charge, which takes somewhere between 40 seconds and four minutes to gain enough to power the radio. Despite efforts to reduce power consumption in every aspect of the chip, making the chip functional still needed more voltage than the ear could offer, though once it would start, it could then run on self-sustaining power. So one short burst of kick-starting radio waves later, and they had their solution.
Of course, further tests have to be done using human ears, but the team hopes that these devices, while initially monitoring imbalances and hearing therapies, might one day be able to provide the therapies themselves. A hearing aid powered by the thing it’s been implanted to help. It isn’t a perpetual motion machine, of course, but it could be the next best thing we have. Now, if anyone can figure out a way to plug my lawn mower into itself and make it cut grass without me, I’m all electrode-free ears.