Invisible Cochlear Implants

A cochlear implant with no exterior hardware would use the natural “microphone” of the middle ear, which is almost always intact in cochlear-implant patients,to create at least limited hearing for people who otherwise would be totally deaf. The device, developed at the Massachusetts Institute of Technology with colleagues from Harvard Medical School and the Massachusetts Eye and Ear Infirmary, can be wirelessly recharged and would run for about eight hours on each charge..

A release from MIT note that existing versions of cochlear implants use an external microphone to gather sound and require that a disk-shaped transmitter about an inch in diameter be affixed to the skull, with a wire snaking down to a joint microphone and power source that looks like an oversized hearing aid around the patient's ear.

The researchers describe their chip in a paper they're presenting this week at the International Solid-State Circuits Conference. The paper's lead author, Marcus Yip PhD, and colleagues will also exhibit a prototype charger that plugs into an ordinary cell phone and can recharge the signal-processing chip in roughly two minutes.

The release quotes corresponding author Anantha Chandrakasan as saying, "The idea with this design is that you could use a phone, with an adaptor, to charge the cochlear implant, so you don't have to be plugged in. Or you could imagine a smart pillow, so you charge overnight, and the next day, it just functions."

The researchers' design exploits the mechanism of a different type of medical device, known as a middle-ear implant. Delicate bones in the middle ear, known as ossicles, convey the vibrations of the eardrum to the cochlea, the small, spiral chamber in the inner ear that converts acoustic signals to electrical. In patients with middle-ear implants, the cochlea is functional, but one of the ossicles — the stapes — doesn't vibrate with enough force to stimulate the auditory nerve. A middle-ear implant consists of a tiny sensor that detects the ossicles' vibrations and an actuator that helps drive the stapes accordingly.

The new device would use the same type of sensor, but the signal it generates would travel 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. Lowering the power requirements of the converter chip was the key to dispensing with the skull-mounted hardware.

Chandrakasan's lab at MTL specializes in low-power chips, and the new converter deploys several of the tricks that the lab has developed over the years, such as tailoring the arrangement of low-power filters and amplifiers to the precise acoustic properties of the incoming signal.