People with hearing loss typically regain some of their hearing through hearing aids, cochlear implants, and other devices. However, conventional cochlear implants still rely on external hardware, limiting the users’ auditory experience. Now, a team of American scientists is developing a new type of implantable microphone that could potentially address these limitations.
Cochlear implants are tiny electronic devices that directly stimulate the auditory nerve bypassing the damaged part of the ear, providing sound perception for the deaf or hard of hearing. According to the National Institutes of Health in the United States, cochlear implants have improved hearing for over 1 million people worldwide.
The current cochlear implants are not fully implanted inside the ear. They still require external hardware to pick up sound, which means users cannot utilize the outer ear structure for noise filtering and sound localization. Additionally, wearing cochlear implants restricts some outdoor activities, especially swimming, and may even affect sleeping.
Existing fully implantable assistive devices mainly rely on detecting sounds under the skin or movements from the middle ear bones to perceive external sounds, which may struggle to capture softer sounds and a wide frequency range. Therefore, there has been a continuous desire for a fully implantable cochlear implant or microphone to overcome these drawbacks and enhance the auditory experience for the hearing impaired.
A research team comprising Massachusetts Institute of Technology (MIT), Massachusetts Eye and Ear, Harvard Medical School, and Columbia University has jointly developed a fully implantable microphone named “UmboMic,” aimed at addressing the mentioned limitations. The research manuscript was submitted to the Journal of Micromechanics and Microengineering by the end of June.
The “UmboMic” prototype is shaped like an umbrella, resembling SpaceX rockets, with a 3-millimeter equilateral triangle top containing a dual piezoelectric chip. UmboMic is printed on a flexible printed circuit board (PCB) and coated externally with waterproof and biocompatible piezoelectric material polyvinylidene fluoride (PVDF), with an overall thickness of approximately 200 micrometers (twice the thickness of a human hair).
MIT and Massachusetts Eye and Ear had conducted extensive research for over a decade, with the performance of this invention being comparable to commercially available external hearing aids.
The human ear’s physiological structure consists of the outer ear, middle ear, and inner ear. The outer ear includes the auricle, earlobe, and ear canal. The middle ear, located within the ear cavity, comprises the eardrum connected to three auditory ossicles to identify vibrations and sound waves. The inner ear consists of the cochlea, semicircular canals, auditory nerve, and vestibule responsible for balance and auditory nerve functions, transmitting nerve signals to the brain for hearing.
The nickname “Umbo,” derived from the central depression point of the eardrum, where the research team aimed to target the “eardrum umbrella,” possessing unidirectional vibration (inward and outward) capabilities for easier perception of simple movements.
However, during experiments, they found that the eardrum umbrella’s motion amplitude was very minimal, measuring only a few nanometers, making it difficult for the device to operate with such small signals. Consequently, they developed a low-noise amplifier to enhance the signals and minimize electronic equipment noise as much as possible.
After refinement, they conducted further tests on the device. Results showed that the “UmboMic” exhibited a good response, achieving an effective output of approximately 32.3 decibels within the frequency range of 100 Hertz to 7,000 Hertz, effectively distinguishing very quiet sounds from overall noise.
The successful experimental outcomes have energized the research team. They are preparing for the next step to conduct tests on live animals to determine their response and any existing issues. Moreover, they are exploring packaging methods for the “UmboMic” to enable it to remain inside the ear for about 10 years.
Emma Wawrzynek, a joint lead author of the paper and a graduate student in Electrical Engineering and Computer Science (EECS) at MIT, stated, “Our goal is for the surgeons to implant this device simultaneously while implanting the cochlear implant and internal processor, optimizing the entire surgical procedure.”
Partial funding for this research was provided by the National Institutes of Health (NIH), National Science Foundation (NSF) in the United States, Cloetta Foundation in Switzerland, and the University of Basel in Switzerland.