Researchers use inner ear 'battery' to power medical implants

The team from MIT believes this new type of biological battery could one day power implantable electronics devices without impairing hearing, and even be used to deliver medicines and therapies. In experiments, the researchers implanted electrodes in the biological batteries in guinea pigs' ears. After the implantation, the guinea pigs were said to respond 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 chip was equipped with an ultra low power radio transmitter and power conversion circuitry. To reduce its power consumption, the control circuit had to be drastically simplified. Like the radio, however, it still required a higher voltage than the biological battery could provide. Once the control circuit was up and running, it could drive itself; the problem was getting it up and running. The researchers solved this problem with a one off burst of radio waves. The team implanted electrodes attached to the chip on both sides of the membrane in the biological battery of each guinea pig's ear. "In the very beginning, we need to kick start it," said Anantha Chandrakasan's, from MIT's Microsystems Technology Laboratories. "Once we do that, we can be self sustaining. The control runs off the output." The researchers see three possible applications for their work: in cochlear implants, diagnostics and implantable hearing aids. "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," said Chandrakasan. "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." Chandrakasan concluded: "I'm not ready to say that the present iteration of this technology is ready. But 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." The work was carried out in collaboration with the Massachusetts Eye and Ear Infirmary and the Harvard-MIT division of Health Sciences and Technology.