First Totally Implantable Hearing Device

Hearing loss can occur as a result of aging, genetic predisposition, an illness or injury, or over the course of years of exposure to loud sounds, which cause intense vibrations that damage the hair cells inside the cochlea. It is estimated that 10 percent of the world’s population has hearing problems. Without treatment, people with hearing loss experience social isolation, and are more prone to psychological illness, depression, anxiety, and paranoia. Loss of hearing means loss of information, networking, and economic power for an individual and the economy.

To address this problem, Envoy Medical Corp., St. Paul, MN, developed the Esteem® prosthetic hearing restoration device, the only fully implantable hearing device for moderate to severe sensorineural hearing loss. It uses the natural ear as a microphone and is surgically implanted to help improve hearing and enhance quality of life.

Initial concept for the device and the implanted sensor began in 1985. Early animal and temporal bone studies were performed in 1997 after initial prototypes were developed. The first acute human implant was performed in 1998. Basic science research culminated in a phase 1 trial conducted in the United States and Germany from 2000 to 2002. Phase 2 trials were conducted from 2004 to 2009. European CE Mark clearance was granted in 2006. A subsequent clinical trial conducted in the U.S. in 2008 and 2009 resulted in a pre-market approval from the U.S. Food & Drug Administration in March 2010 for commercial distribution of the device.

Sensorineural hearing loss (sensory loss) is caused by damage to the hair cells or other parts of the cochlea. The damage makes it more difficult for the cochlea to convert these sound waves into electrical signals.

Benefits Over Alternatives

Alternate options to address hearing loss include cochlear implants and hearing aids. Cochlear implants are specifically designed for patients with profound hearing loss. Cochlear implants also use an external microphone/processor.

Hearing aids are limited by acoustic feedback, maintenance (cleaning and changing batteries), occlusion affect, and lifestyle impact (can’t shower, swim, or sleep with hearing aids). The Esteem is specifically designed for those patients with moderate to severe hearing loss. It uses the body’s natural method of hearing, including using the outer ear (the pinna). It maintains frequency discrimination and is a totally invisible maintenance-free alternative to hearing aids.

Various other middle ear implants have been developed throughout the ’90s and 2000s. None of these products have been commercially viable and all of them have used external components. The device was specifically designed to be totally implantable, and therefore uses very minimal power to prolong battery life. It is fully implanted in the middle ear and is not a hearing aid. Unlike hearing aids, it does not use a microphone or a speaker. Instead, it uses the natural ear drum as a microphone to detect sound and send a clear message to the brain, via the auditory nerve, by stimulating the cochlea with its prosthetic simulator. In this way, the ear helps to minimize background noise, distortion, and acoustic feedback that people experience with conventional hearing aids. Many surgeons have called the Esteem an electronic prosthetic hearing device.

Titanium and Bioplastics

Deliver Performance The technology consists of the Sound Pro cessor, implanted behind the outer ear, and two transducers (called the Sensor and Driver) that are implanted in the middle ear. The materials used to make the Esteem hearing device have been pro ven safe and reliable in millions of pace makers and other implanted medical de vices. The Sensor and Driver are customde signed components with titanium construction. The Sound Processor has a very similar design to a pacemaker, and is also constructed primarily of titanium.

The Sensor is attached to the ossicular chain. It picks up vibrations from the eardrum, malleus, and incus bones and converts the vibrations into electrical signals. These signals are sent to the Sound Processor. The Sound Processor filters and increases the electrical signals and sends them to the Driver. The Sound Processor is programmed by a health care professional to customize settings for the patient’s particular hearing needs. The Sound Processor case also holds the battery.

The Driver is attached to the stapes in the middle ear. The Driver converts the electrical signals that it has received from the Sound Processor back into mechanical vibrations and transmits these signals to the stapes and the cochlea. The Personal Programmer is the personal “remote control” that can be used to turn the device on or off (standby), select the volume, and select one of three unique program settings.

The innovative design incorporates two terminal connectors (0.1" x 0.5" or 2.54 mm by 12.7 mm) for the transducers which are injection molded of Zeniva® polyetheretherketone (PEEK) resin from Solvay Specialty Polymers USA, LLC, Alpharetta, GA. Zeniva PEEK — part of Solvay’s family of Solviva® Biomaterials — provides biocompatibility, strong insulative properties, and excellent mechanical performance. The biomaterial offers better insulative properties and higher mechanical strength than previously used materials like silicone. Benefits include biocompatibility and chemical inertness. Based on biocompatibility testing, this material demonstrates no evidence of cytotoxicity, sensitization, irritation, or acute systemic toxicity. It also boasts high strength and stiffness and has radiolucent properties, which permit X-ray procedures.

Clinical results show an improvement in Speech Reception Threshold and Word Recognition Score compared to the patients’ pre-implanted hearing aid re sults. There are also the lifestyle benefits that a fully implantable system provides, including no maintenance, and the ability to shower, swim, exercise, and even scuba dive.

The unit’s maintenance-free battery lasts 4.5 to 9 years, depending on use. Once it is depleted, the battery is replaced in a minor outpatient surgical operation.

Envoy Medical Corp., St. Paul, MN, sells the implantable hearing device directly to patients. The company matches patients with Envoy-approved surgical centers throughout the US along with its own independently owned surgical center in The Woodlands, TX. About 1,000 Esteem devices have been implanted in patients so far.

This article was written by Shawn Shorrock, global healthcare market manager for Solvay Specialty Polymers USA, LLC, Alpharetta, GA. For more information about Solvay Specialty Polymers, visit http://info.hotims.com/40440-  164, and for more information about Envoy Medical Corp., visit http://info.hotims.com/40440-165 .

---