Lasers Can Improve Hearing

New technologies to improve the insertion techniques and exact fitting of cochlear implants in the inner ear could soon provide better-quality residual hearing for more than 200,000 hard-of-hearing people worldwide.

Approximately 95 percent of those who are highly hearing impaired have an adequately intact auditory nerve, enough to provide at least partial hearing. To aid hearing, a cochlear implant — an electrical acoustic aid or prosthesis — takes over the function of damaged sensory cells in the inner ear. This device consists of an implant placed in the bone under the skin behind the ear, an electrode that is placed directly in the cochlea, and a microphone and speech processor placed behind the ear.

When sound waves are registered by the microphone, the device translates the waves into a series of electrical impulses, which are directed to the electrode on the auditory nerve in the inner ear.

Optimal hearing can take place only if the basilar membrane, which is covered by tiny sensory cells or hairs, is not damaged. If this membrane is damaged, complete loss of residual hearing occurs. It is essential to use extreme caution when inserting the cochlear implant so as not to damage these membranes.

To address the need for meticulously precise implantation, scientists in the Laser Zentrum Hannover eV (LZH) Surface Technology group are working to simplify the operation and improve the insertion technique of electrodes into the complex shape of the cochlea. The researchers used nickel-titanium shape memory alloys (NiTi-SMA) in the manufacturing process for the implant electrodes. Heating the electrode enables the material to remember the form or shape it was manufactured in, allowing specific movement and fitting of the electrode.

The group used a laser to melt the NiTi-SMA into a highly individual implant. The special characteristics of the material are used to insert the implant into the cochlea without damaging the basilar membrane.

Basically, the deeper the material is inserted into the cochlea and the better the fit, the better hearing can be, the scientists said.

To optimize the characteristics of cochlear implants, the Laser Micromachining group at LZH has set out to improve the surface of implants by using laser structuring.

“The surface of conventional cochlear implants is not subject to special treatment, and a great potential is lost!” said scientist Elena Fadeeva. “We have learned from Mother Nature that biological surfaces, for example of lotus leaves or shark skin, have defined structures for special functions.”

The researchers used a femtosecond laser to structure platinum electrodes in a special way. Special nanostructures look rough when magnified, but when manufactured they can reduce attachment of connective tissue and improve interaction with the nerve cells. Nanostructuring also decreases frequency-dependent electrical resistance, meaning that less energy is needed.

The challenge of this development, however, is that the structure must be made on an implant with a curved surface and only 300 µm in diameter. The LZH team is currently working to develop such a complex structure on a very small scale.

These newly developed “artificial inner ears” could help the hearing impaired to use the telephone again after sufficient training. For those who have recently lost hearing, or for children, the success rate should be even higher.

The results will be presented April 23-27 at the LZH Stand at Hannover Messe 2012.

For more information, visit: www.lzh.de/en