Down the Line: A New Way to Hear
A ribbon-like implant could greatly improve hearing for deaf people and simplify insertion to help surgeons minimize damage to healthy ear tissue. A team of engineers led by Kensall Wise, director of the National Science Foundation's engineering research center for wireless integrated microsystems at the University of Michigan (Ann Arbor), made the implant using thin-film electrodes that stimulate the auditory nerve.
Approximately 100,000 patients today have received cochlear implants worldwide. However, Wise claims that the current technology is bulky and difficult for surgeons to insert. It also doesn't allow a great range of perceived frequencies.
"The present implants use electrodes formed from a bundle of wires fed into the snail-shaped cochlea of the inner ear," says Wise. "But, difficulties inserting such devices make it tough to achieve the deep insertion needed to [receive stimulation from] lower-frequency sounds. And collisions with the cochlear wall can damage any residual hearing that still exists."
The ribbon film technology lets engineers embed other functions in the implant, such as position sensors that allow surgeons to watch the implant's progress on a monitor as they're feeding it into the cochlea.
"Eventually, the idea is to be able to take the signals from the position sensors and use them to control actuators in an insertion tool, so that the electrode array can achieve deep insertion and navigate around any obstacles in its path," explains Wise. Doctors would use a pneumatic insertion tool that can be inflated or deflated, similar to a spiral party favor, and is prestressed to hug the inner wall of the cochlea.
"The position sensors set the stage for doing that because they give you feedback on what's happening when you insert these devices," says Wise. "The range of frequencies that can be [detected] depends on how far into the cochlea the implant can go, with the lower frequencies located further up toward the apex of the spiral canal."
With current technology, each implant has anywhere from 16 to 22 stimulating sites along its length. By contrast, the thin-film electrode implant will host up to 128 stimulating sites. "More sites mean greater tonal range and better frequency perception," Wise points out. "And the implant's flexibility will minimize damage to existing hearing."
The implants are assembled with the same processes used to make integrated circuits, which means they can be made in batch. Wise hopes the new hearing device will be commercially available in 4 to 5 years. He says it could be used in current cochlear patients, after the old device is removed.