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January 2005 Tech News
Committee on Medical and Surgical Materials Creates Subcommittee on Implantable Hearing Devices

ASTM International’s Committee F04 on Medical and Surgical Materials and Devices has established a new subcommittee, F04.37 on Implantable Hearing Devices. The subcommittee is currently in the early stages of developing its first proposed standard on implantable middle-ear hearing devices.

“Millions of people living with sensorineural hearing loss may be appropriate candidates for implantable hearing devices and the new ASTM subcommittee will be a critical part of the process of ensuring that these people receive the greatest benefits of this technology,” says Daniel Schultz, M.D., director, office of science and engineering laboratories, center for devices and radiological health, U.S. Food and Drug Administration.

According to Kenneth Dormer, chair of the new subcommittee, F04.37 will focus on newly emerging technology that addresses the needs of a specific group of hearing-impaired people. “These patients cannot get adequate help from hearing aids and are not candidates for the cochlear implant,” says Dormer. “Implantable, direct-drive hearing devices can provide greater amplification, higher fidelity and higher frequency performance than either hearing aids or cochlear implants.”

Currently, two types of implantable middle ear hearing devices exist: semi-implantable and totally implantable. Semi-implantables use an electromagnetic transducer, while totally implantables use a piezoelectric transducer. Totally implantable devices operate by passing an electric current into a piezoceramic crystal, which causes a change in its volume, thereby producing a vibratory signal. Semi-implantable devices function by passing an electric current into a coil, which creates a magnetic flux that drives an adjacent magnet attached to one of the vibratory structures of the middle ear.

The advantage of these devices, with respect to conventional hearing aids, is that they work by vibrating the bones of the middle ear directly, so they are not dependent on simply increasing sound intensity to the auditory system, as are conventional hearing aids. Other potential benefits driving the development of implantable middle-ear hearing devices include the following:

• Improved fidelity through direct simulation of the ossicles.
• Improved comfort by allowing the ear canal to remain open.
• Elimination of feedback.
• Improved cosmesis through miniaturization/concealment of components.
• Available amplification while swimming/bathing (with totally implantable devices).

The subcommittee hopes to develop a standard for implantable middle ear hearing devices that will help the U.S. Food and Drug Administration in assessing new means of direct-drive technology as they are developed by companies and research teams. “The standard also will help the FDA determine if a device warrants clinical trials. It will help companies and groups to conduct appropriate experiments for submission of their concepts to regulatory agencies, saving them time and money,” says Dormer. //

Technical information:
Kenneth Dormer, professor of physiology, University of Oklahoma College of Medicine
Phone: 405/271-2226 ext. 1221
ASTM staff:
Dan Schultz
Phone: 610/832-9716
Upcoming Meeting:
May 17-20
May Committee Week, Reno, Nev.

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