Currently, surgically implanted cochlear implant microphones and related electronics must be worn outside the head, raising reliability issues, and social and cosmetic considerations, and preventing patients from swimming. Now, a University of Utah engineer and colleagues in Ohio have developed a tiny prototype microphone that can be implanted in the middle ear.
The proof-of-concept device (pictured) has been successfully tested in the ear canals of four cadavers, the researchers report in a study just published online in the Institute of Electrical and Electronics Engineers journal Transactions on Biomedical Engineering.
While the prototype is about the size of an eraser on a pencil, the device isn’t ready for human tests yet. The developers still want to reduce the size and improve its ability to detect quieter, low-pitched sounds, so human trials are about 3 years away, says the study’s senior author, Darrin J. Young, an associate professor of electrical and computer engineering at the University of Utah and USTAR, the Utah Science Technology and Research initiative.
The study showed incoming sound is transmitted most efficiently to the microphone if surgeons first remove the incus or anvil. Of course, US Food and Drug Administration approval would be needed for an implant requiring such surgery.
The current prototype of the packaged, middle-ear microphone measures 2.5-by-6.2 millimeters (roughly one-tenth by one-quarter inch) and weighs 25 milligrams, or less than a thousandth of an ounce. Young wants to reduce the package to 2-by-2 millimeters.
In traditional cochlear implants, the microphone, signal processor and transmitter coil are worn outside the head and send signals to the internal receiver-stimulator, which is implanted in bone under the skin and sends the signals to the electrodes implanted in the cochlea to stimulate auditory nerves. The ear canal, eardrum, and hearing bones are bypassed.
The system developed by Young implants all the external components. Sound moves through the ear canal to the eardrum, which vibrates as it does normally. But at the umbo, a sensor known as an accelerometer is attached to detect the vibration. The sensor also is attached to a chip, and together they serve as a microphone that picks up the sound vibrations and converts them into electrical signals sent to the electrodes in the cochlea.
The device still would require patients to wear a charger behind the ear while sleeping at night to recharge an implanted battery. Young says he expects the battery would last one to several days between charging.
Young says the microphone also might be part of an implanted hearing aid that could replace conventional hearing aids for a certain class of patients who have degraded hearing bones unable to adequately convey sounds from conventional hearing aids.
Young conducted the study with Mark Zurcher and Wen Ko, and with ENT physicians Maroun Semaan and Cliff Megerian of University Hospitals Case Medical Center.
To hear a recording of the start of Beethoven’s Ninth Symphony through the new microphone implanted in a cadaver’s middle ear, click here.
SOURCE: University of Utah
Photo credit: Case Western Reserve University and University of Utah