New Cochlear Implant Requires No Exterior Hardware

Cochlear implants, around for about 30 years, have allowed more than 200,000 deaf people to obtain various degrees of hearing. Although the cochlear implants are among the most successful hearing devices available, the hardware that makes them work can be stigmatizing and downright annoying. Existing versions require that a disk-shaped transmitter about an inch in diameter be affixed to the skull, with a wire that snakes down to a joint microphone and power source that looks like an oversized hearing aid around the patient’s ear. Another drawback is that the device can’t be worn in the shower.

Recently, a team of scientists developed a new, alternative design that eliminates all the external hardware and allows it to be charged wirelessly with a smartphone. As described in a Spectrum Online article, the key to the new design is an implantable low-power signal processing chip developed by Anantha Chandrakasan and his colleagues at MIT in Cambridge, Mass. Here’s how it works: A piezoelectric sensor, mounted at the umbo in the middle ear, picks up sound. That signal, a measure of the sound-induced motion of the umbo, travels to the microchip implanted elsewhere in the ear where it is conditioned, digitized, and processed. The chip then converts the signal to electrical waveforms and pumps them to electrodes implanted in the part of the ear known as the cochlea. The waveforms received by the electrodes stimulate auditory nerve fibers and allows the user to experience representations of sound that might help in developing language ability. (More information is available in an MIT News item.)

In 2012, Darrin Young designed a MEMS-accelerator-based middle ear microphone at the University of Utah that moves all the external components of the cochlear implant inside the body. One drawback is that the sensor pulls a few milliwatts of power–more than MIT’s design, thus establishing the need for an implanted rechargeable battery. Young is working on improving the prototype to bring down the power below 100uW.

MIT researcher, Marcus Yip, PhD., and his colleagues Rui Jin and Nathan Ickes (both in MIT’s Department of Electrical Engineering and Computer Science), recently exhibited a prototype charger that plugs into an ordinary cell phone and can recharge the signal processing chip in roughly two minutes. Lowering the power requirements of the converter chip was the key to eliminating the skull-mounted hardware.

“It’s very cool,” says Lawrence Lustig, director of the Cochlear Implant Center at the Uniiversity of California at San Francisco. “There’s a much greater stigma of having a hearing loss that there is of having a visual loss. So people would be very keen on losing the externals for that reason alone.” He says that there is also the added functional benefit of not having to remove the device when around water.

Because of the complexity of the surgery, the new cochlear implant would require about three to four hours in the operating room. Lustig doubts that this will be much of an obstacle and believes there wouldn’t be any extra risks involved.