Cochlear implants, small electronic devices designed to aid those who are deaf or hard-of-hearing by providing a sense of sound, have significantly improved the lives of over a million individuals worldwide, as suggested by the National Institutes of Health. However, current cochlear implants are partially externally installed, dependent on hardware that is usually fixed to the side of the head. This arrangement restricts users in activities like swimming, exercising or sleeping while wearing the unit, deterring many from opting for the implant.
In a bid to develop a fully internalized cochlear implant, a diverse research team from the Massachusetts Institute of Technology (MIT), Massachusetts Eye and Ear, Harvard Medical School, and Columbia University, has developed an implantable microphone that matches the performance of commercial external hearing aid microphones. The microphone, one of the significant obstacles to adopting a fully internalized cochlear implant, is a sensor made from a biocompatible piezoelectric material that measures tiny movements on the inner side of the eardrum. Piezoelectric materials generate an electric charge when compressed or stretched. To optimize the device’s performance, the team also created a low-noise amplifier that boosts the signal while minimizing electronic noise.
Although numerous challenges remain before such a microphone can be used with a cochlear implant, the collaborative team is eager to further refine and test this prototype, which builds off work begun at MIT and Mass Eye and Ear over ten years ago.
The researchers are focusing on the part of the middle ear known as the umbo, which vibrates in a single direction, making these movements easier to sense. The umbo has the largest range of movements among middle-ear bones but moves only by a few nanometers, making the development of a device that can measure such tiny vibrations a challenge.
The team has overcome these hurdles by creating the UmboMic, a tiny, triangular sensor made from two layers of a biocompatible piezoelectric material called polyvinylidene difluoride (PVDF). The sensor is as small as a grain of rice and 200 micrometers thick. The narrow tip of the UmboMic would be placed against the umbo, and as the umbo vibrates, it pushes against the piezoelectric material, causing the PVDF layers to bend and generate electric charges.
The team used a unique “PVDF sandwich” design to reduce noise, and the sensor’s performance was tested with human ear bones from cadavers, demonstrating strong performance within the intensity and frequency range of human speech.
The researchers are now preparing to conduct live animal studies to further explore this finding and are studying ways to encapsulate the sensor so it can safely remain in the body for up to 10 years while still being flexible enough to capture vibrations. They also plan to explore methods for mounting the UmboMic that won’t introduce vibrations.
This research, published in the Journal of Micromechanics and Microengineering, was funded in part by the National Institutes of Health, the National Science Foundation, the Cloetta Foundation in Zurich, Switzerland, and the Research Fund of the University of Basel, Switzerland.
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