CAMBRIDGE, MA—As long as people have been using hearing aids, replacing the batteries has been part of the drill. However, someday—though no time soon—people may power their own hearing devices, at least implantable ones.
How can that be? Well, people and other mammals have a natural battery located inside the cochlea. It’s a chamber filled with ions that produce electricity to drive neural signals.
Scientists have known for 60 years or so that this battery exists, and that it is a crucial part of the auditory system. When sound causes the eardrum to vibrate, the ear converts that mechanical force into an electrical signal that the brain can recognize. It’s the biological battery that powers that electrical signal.
Until recently, no one had figured out any way to use the battery in ways beyond its natural function. Now, however, researchers from the Massachusetts Institute of Technology (MIT), the Massachusetts Eye and Ear Infirmary (MEEI), and the Harvard-MIT Division of Health Sciences and Technology (HST) have demonstrated that this battery could potentially be used to power implantable electronic devices.
As reported by the MIT News Office, Konstantina Stankovic, an otologic surgeon at MEEI, and Andrew Lysaght, a graduate student at HST, implanted electrodes in the biological batteries in ears of guinea pigs. They attached to the electrodes low-power electronic devices developed by MIT’s Microsystems Technology Laboratories.
Low-power devices were required because the voltage created by the biological battery is so low. To avoid disrupting hearing in the guinea pigs, the researchers had to make sure to divert only a small fraction of the power generated by the battery.
Their effort proved successful. 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.
How might the researchers’ discoveries be applied in the future? Cliff Megerian, chairman of otolaryngology at Case Western Reserve University and University Hospitals Case Medical Center, told MIT News that he sees three potential applications: for cochlear implants, diagnostics, and implantable hearing aids.
Megerian noted, “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.”