Incredible Fully Internal Cochlear Implants on the Way as Massachusetts Engineers Overcame All Obstacles

An infant wearing a cochlear implant – credit Bjorn Knetsch, CC 2.0.

Biotech engineers have developed the first entirely internal cochlear implant that will allow users to move, exercise, swim, and enjoy a full range of human activities without worrying about external hardware.

This external hardware typically sits on top of the ear or around the head and prohibits all manner of vigorous activities—including sleep, since the device presses against the soft bones of the temple.

Despite these hindrances, cochlear implants are one of the most widely-used pieces of biotech on Earth, and have allowed over one million people to hear the world around them.

This doesn’t just include older people whose hearing has gone, but infants born deaf or hard of hearing who desperately need noise, particularly human voices, for normal social and educational development.

But because infants don’t realize the importance of the implant for their development, they’re liable to try and fiddle, or remove entirely, the external hardware, and with no other option, parents and physicians have to apply medical tape or childproof headgear that prevents them from removing it.

To try and remove this burden from all cochlear users, researchers at MIT, Massachusetts Eye and Ear, Harvard Medical School, and Columbia University have pioneered the first cochlear implant that’s entirely surgically inserted.

Its novel design relies on the single-direction vibrations of a bone in the middle part of hearing canal called the umbo.

The team had to address many challenges to produce their prototype. The umbo vibrations are measured in nanometers—requiring an extremely sensitive microphone. A microphone so sensitive would also need to have gating properties to block the equally loud sound of the electronics working within it. It would also have to measure in the low millimeters.

Any implantable sensors would also have to cope with the dynamic fluid and hot environment of the human body. However, a fully implantable cochlear device would have major advantages as well. Because they are mounted on the sides of the head, the audio amplification device can’t avail the user of the noise filtering and sound localization cues provided by the structure of the outer ear.

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The team overcame all these obstacles to create the UmboMic, a triangular, 3-millimeter by 3-millimeter motion sensor. It’s composed of a ‘piezoelectric’ material called polyvinylidene difluoride (PVDF). Piezoelectric materials generate electrical charge when compressed or stretched, and when placed just barely against the umbo, the hearing bone’s vibrations generate the charge that powers the device.

The PVDF sandwiches a flexible printed circuit board, and to maximize the device’s performance, a low-noise amplifier enhances the signal while minimizing noise from the electronics. No amplifier that fit the teams’ specifications existed, so they had to build their own.

Karl Grosh, a professor of mechanical engineering at the University of Michigan who didn’t participate in the research or development, told MIT Press that the capabilities of this totally new invention are both surprising and impressive.

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“The results in this paper show the necessary broad-band response and low noise needed to act as an acoustic sensor,” said Grosh.

“This result is surprising, because the bandwidth and noise floor are so competitive with the commercial hearing aid microphone. This performance shows the promise of the approach, which should inspire others to adopt this concept.”

The team is now moving into animal trials.

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