SAN FRANCISCO—What cochlear implant wearers have long yearned for—an entirely implantable system without the external transmitter, wire, microphone, and battery that are now standard—appears to have moved a step closer to reality this week.
In a paper to be presented February 11 at the IEEE International Solid State Circuits Conference in San Francisco, researchers describe a newly developed low-power signal-processing chip that could make it possible to design a cochlear implant that needs no external hardware to function. The chip was developed by researchers at MIT’s Microsystems Technology Laboratory (MTL), along with physicians from Harvard Medical School and the Massachusetts Eye and Ear Infirmary (MEEI).
Unlike today’s cochlear implants which include an external microphone to gather sound, it is envisioned that the new system would use the natural microphone of the middle ear, which is usually intact in cochlear implant users. Borrowing technology from middle ear implants, this system would include a tiny sensor that detects the vibrations of the ossicles (the three tiny bones in the middle ear). The sensor would then send the signal to a microchip implanted in the ear, which would convert it to an electrical signal and pass it on to an electrode in the cochlea.
Key to eliminating the need for skull-mounted hardware is that the signal-processing microchip developed by the Boston-area research team uses only a small fraction of the power that is consumed by existing cochlear implants. As a result, instead of cochlear implant patients having to wear a bulky battery behind their ear, the system as conceived would be wirelessly recharged. A prototype charger (which is being exhibited at the conference in San Francisco) has been developed that plugs into an ordinary cell phone. In about two minutes it can fully recharge the signal-processing chip to run for about eight hours before re-charging.
The lead author of the paper presented at the IEEE conference is Marcus Yip, PhD, of the MIT Department of Electrical Engineering and Computer Science. His co-authors are Rui Jin and Nathan Ickes, graduate students in the same department.
The research team that developed the microchip was led by Konstantina Stankovic, MD, PhD, an ear surgeon at MEEI; Anantha Chandrakasan, a professor of electrical engineering at MIT, and Don Eddington, PhD, director of the Cochlear Implant Research Laboratory at MEEI.
In an interview with the MEEI public affairs office, Stankovic noted that the benefits of an entirely implantable system go far beyond its invisibility. She said, “In addition to the cosmetic aspect of an invisible cochlear implant, a potential major functional benefit is that it can facilitate sound localization. Our system relies on a sound sensor located in the middle ear so that the user can benefit from directional cues provided by the auricle and ear canal. Conventional cochlear implants detect sound by a microphone located outside of the ear so important directional cues are lost.”