Cochlear implants have been transformative for millions of people with hearing loss, but current models are only partially implanted and rely on cumbersome external devices. These external components limit users' activities, such as swimming and sleeping, and can deter some individuals from using the technology altogether. To address these limitations, researchers from the Massachusetts Institute of Technology, Massachusetts Eye and Ear, Harvard Medical School, and Columbia University have developed a groundbreaking implantable microphone designed to work seamlessly with a fully internal cochlear implant system.
This tiny microphone, named the UmboMic, represents a major leap forward in hearing technology. Constructed from biocompatible piezoelectric materials, the microphone detects minuscule vibrations on the ear drum's underside. Piezoelectric materials, like the polyvinylidene fluoride used in the UmboMic, generate an electric charge in response to mechanical stress. The research team, led by Jeffrey Lang from MIT and Hideko Heidi Nakajima from Harvard Medical School, has also developed a low-noise amplifier to enhance the microphone's performance while minimizing electronic noise.
One of the significant challenges in creating a fully internal cochlear implant is developing a microphone that can accurately capture sound in the body's humid and dynamic environment. Traditional cochlear implants rely on external microphones that use the outer ear's structure to filter and localize sound. However, the new microphone targets the umbo, a part of the middle ear that moves in response to sound vibrations. The team designed the UmboMic to be a triangular sensor, approximately 3 millimeters on each side and 200 micrometers thick, which fits snugly against the umbo to capture these vibrations.
The research team faced several hurdles, including the challenge of fabricating the PVDF material without degrading its piezoelectric properties. High temperatures required for coating the sensor with titanium were managed by carefully controlling the temperature and using a heat sink. Additionally, the team designed the UmboMic with a "PVDF sandwich" structure, which reduces noise by canceling out electrical interference through differential charging of the PVDF layers.
Testing of the UmboMic on cadaver ear bones demonstrated its ability to detect sounds within the human speech frequency range and perform with a low noise floor. The microphone's design effectively captures the tiny vibrations of the umbo, and the integrated low-noise amplifier ensures clear signal amplification. Researchers are now preparing to test the UmboMic in live animals to further evaluate its performance and biocompatibility.
The development of the UmboMic is a crucial step toward achieving a fully internal cochlear implant. The research team is also exploring methods to encapsulate the sensor to ensure its longevity and flexibility once implanted. This includes investigating alternative materials and mounting techniques that will preserve the sensor's functionality while integrating seamlessly into the ear's anatomy.
This pioneering work, funded by the National Institutes of Health, the National Science Foundation, and international organizations such as the Cloetta Foundation and the University of Basel Research Fund, promises to advance the field of auditory technology. With continued refinement and testing, the UmboMic could soon offer a new level of convenience and performance for individuals relying on cochlear implants, moving towards a future where the technology is fully internalized and unobtrusive.
