A Step Toward Fully Implantable Cochlear Implants

Professor Ioannis (John) Kymissis works with a multi-institutional team of researchers to develop a tiny implantable microphone, paving the way for fully internal cochlear implants.

By
Charles Choi
February 03, 2025

For decades, cochlear implants have bestowed a degree of hearing to people who are deaf or severely hard of hearing. However, these devices rely on microphones and other electronics worn on the side of the head, a cumbersome restraint on their use. Now researchers at Columbia Engineering and their colleagues have developed a tiny microphone totally implantable within the head, an advance recently chosen as one of the Journal of Micromechanics and Engineering's highlights of 2024. The work is in collaboration with MIT and Harvard Medical. 

Around the world, more than a million people have received cochlear implants, according to the National Institutes of Health. Cochlear implants depend on a microphone, battery and sound processor that sits behind the ear, which transmits data to an electrode array implanted within the head. This in turn stimulates the auditory nerve leading to the brain.

"The cochlear implant is an amazing example of how engineering can help advance medical innovation," says Elizabeth Olson, professor of biomedical engineering at Columbia Engineering and of auditory biophysics at Columbia’s Vagelos College of Physicians and Surgeons. "It's an extraordinary prosthetic that can be just absolutely transformative in a person's life. Other prosthetics aspire to have a similar impact."

The microphone— a key challenge in achieving a fully implantable cochlear implant

However, a cochlear implant's external hardware imposes many limits on users — they usually cannot swim, bathe, sleep, or play a variety of sports with this machinery on. In addition, its placement on the side of the head means that it cannot take advantage of how the structure of the ear can help direct, filter, amplify and localize sounds.

Ideally, researchers would like to develop a totally implantable cochlear implant. The microphone is one of the greatest obstacles to this goal — miniaturizing every other part of a cochlear implant is technically possible.

Now, by making use of the bones inside the head that allow people to hear, researchers at Columbia Engineering, MIT, Harvard Medical School and Massachusetts Eye and Ear have developed the UmboMic, a prototype microphone that they say is a promising step toward a completely implantable cochlear implant.

"We're taking advantage of millions of years of evolution," says Ioannis (John) Kymissis, the Kenneth Brayer Professor of Electrical Engineering and vice dean of Infrastructure and Innovation at Columbia Engineering. "The ear is exquisitely evolved to pick up sound, and our design gets to make use of all of its adaptations for free."

Normally, the outer part of the human ear funnels sound waves at the eardrum, making this membrane vibrate. This shakes tiny bones in the middle ear, and the inner ear's sensory apparatus converts these vibrations into nerve signals.

A new approach to sound detection

The UmboMic focuses on the motion of the umbo, the tip of the hammer-shaped bone connected to the eardrum. The umbo mostly vibrates only up and down, making it much easier to analyze than the more complex motions of other ear bones.

The key sensor in the UmboMic is an ironing-board-shaped sliver roughly 3 millimeters long, about twice the average length of a flea, and 200 microns thick, about twice the average width of a human hair. This sensor is made of a highly flexible plastic called polyvinylidene difluoride (PVDF), which is piezoelectric — it can convert mechanical energy into electricity.

"We started talking about how PVDF could be incorporated into a totally implantable cochlear implant back in 2009," Kymissis says.

The sensor's triangular tip rests against the umbo, detecting motions only a few nanometers large. In tests of the UmboMic with human temporal bones, which house the internal parts of the ear, the sensor could convert sounds into electrical signals, performing as well as a conventional hearing aid's microphone.

The development of the UmboMic was ultimately only possible through cross-disciplinary research, uniting Olson's knowledge in the mechanics of hearing, Kymissis's experience in thin-film electronics, Hideko Heidi Nakajima at Harvard Medical School and Massachusetts Eye and Ear's expertise on the mechanics of the human ear, and Jeffrey Lang at MIT's skill in sensor development and fabrication. "This work's been extremely collaborative, which makes it interesting, makes it fun," Kymissis says.

The researchers now would like to reengineer this proof-of-concept device with materials that are fully suited for use in the body for at least a decade. "We're also preparing to test the UmboMic in a large animal study in sheep," Olson says. "We're already in discussions with cochlear implant companies, and our dream is that in five years, UmboMic will start seeing use in devices."

The scientists detailed their findings on July 18 in the Journal of Micromechanics and Engineering.

Read the original story: https://www.ee.columbia.edu/news/step-toward-fully-implantable-cochlear-implants