New Hearing Implant Uses Less Power, No External Hardware
February 10, 2014

New Hearing Implant Uses Less Power, No External Hardware

[ Watch the Video: The Sound Of Innovation For Deafness ]

Lawrence LeBlond for - Your Universe Online

Hundreds of thousands of deaf, or near-deaf, people around the world have benefited from cochlear implants. While these devices are undoubtedly a good thing, the hardware to make them work has been somewhat of a pain.

Cochlear implants typically require a small transmitter affixed to the skull with a wire dangling down to a microphone, as well as a battery pack that must be worn around the patient’s ear. While the pros may seemingly outweigh the cons, some people may opt to not use the devices at all.

Now, researchers from MIT’s Microsystems Technology Laboratory (MTL), working with physicians from Harvard Medical School and the Massachusetts Eye and Ear Infirmary (MEEI), may have a solution to this problem.

The team has developed a new, low-power signal-processing chip that works with a cochlear implant and requires no external hardware. The researchers say the implant could work for eight hours between charges, which would be done wirelessly without the need for an unsightly battery pack on the outer ear.

Presenting the developments in a paper at this week’s International Solid-State Circuits Conference, lead author Marcus Yip, PhD, and coauthors Rui Jin and Nathan Ickes, both of MIT’s Department of Electrical Engineering and Computer Science, will exhibit a prototype charger at the conference that plugs into a smartphone and can recharge the chip in two minutes.

“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,” Anantha Chandrakasan, the Joseph F. and Nancy P. Keithley Professor of Electrical Engineering and corresponding author on the new paper, said in a statement. “Or you could imagine a smart pillow, so you charge overnight, and the next day, it just functions.”

Along with losing the bulky battery pack, the team show that the external microphone is no longer needed. Instead, the chip will implement the natural microphone of the middle ear, which is almost always intact in cochlear-implant patients.

The newly designed chip uses technology from another common device known as the middle-ear implant. The ossicles – three delicate bones (malleus, incus, and the stapes) located in the middle ear – convey vibrations of the eardrum to the small chamber (cochlea) within the inner ear and converts acoustic sounds to electrical signals. The cochlea remains functional in patients with middle-ear implants; however, the stapes doesn’t vibrate with enough force to stimulate the auditory nerve. The middle-ear implant uses a tiny sensor that detects vibrations from the ossicles and an actuator that helps the stapes work accordingly.

A key component of the new device was lower power consumption. Chandrakasan and his team at MTL specialize in low-power chips and the new device employs several tricks developed in his lab over the years. But the team have also developed a new signal-generating circuit that reduces power consumption of the chip by an additional 20 to 30 percent.

With a developed prototype in their hands, the next thing to do was to test it.

MEEI researchers Konstantina Stankovic, MD, PhD, an ear surgeon who co-led the study with Chandrakasan, and Don Eddington, PhD, tested the new device on four patients who were already using cochlear implants, finding that the new device had no effect on their ability to hear. Then, along with Heidi Nakajima, MD, PhD, another MEEI collaborator, the team tested the chip and sensor on a human cadaver. They showed that both the chip and sensor are able to pick up and process speech played into the ear of the cadaver.

“It’s very cool,” said Lawrence Lustig, MD, director of the Cochlear Implant Center at the University of California at San Francisco. “There’s a much greater stigma of having a hearing loss than there is of having a visual loss. So people would be very keen on losing the externals for that reason alone. But then there’s also the added functional benefit of not having to take it off when you’re near water or worrying about components getting lost or broken or stolen. So there are some important practical considerations as well.”

While the cons of the existing technology insist on the patient wearing somewhat unsightly external hardware, Lustig noted that the new technology isn’t necessarily less-invasive. The new cochlear implant requires a more complex surgery than what the existing implants do.

“A current cochlear-implant operation takes an hour, hour and a half,” he said. “My guess is that the first surgeries will take three to four hours.”

“As we get better and better and better, that time will shorten,” Lustig noted. “And three to four hours is still a relatively straightforward operation. I don’t anticipate putting a lot of extra risk into the procedure.”