Laser Technology Can Improve Hearing

Photo: Chochlea implant in the inner ear

Approximately 95 per cent of all those who are highly hearing impaired have an adequately intact auditory nerve, enough to provide at least partial hearing. An important device for this process is a cochlea implant (CI), and electronical acoustic aid or prosthesis, which takes over the function of damaged sensory cells in the inner ear. This aid consists of an implant, which is placed in the bone, under the skin behind the ear, an electrode which is placed directly in the cochlea, and a microphone and speech processor, which is also placed behind the ear. The aid functions in this way: When sound waves are registered by the microphone, they are “translated” into a series of electrical impulses, which are then lead to the electrode on the auditory nerve in the inner ear.

The basilar membrane, which is covered by tiny sensory cells or hairs, can only provide optimal hearing if it is not damaged. If this membrane is damaged, this can lead to complete loss of residual hearing. This means that the cochlea electrode must be inserted extremely carefully, to avoid damage to the membrane.

The group “Surface Technology” at the LZH is currently working on a process to simplify the operation and improve the insertion technique of the electrode into the complicated form of the cochlea. In order to accomplish this, the scientists use the special properties of nickel-titanium shape memory alloys (NiTi-SMA) in manufacturing the CI electrodes. By heating the electrode, or via electrical impulses, this material “remembers” the form or shape it was manufactured in, thus allowing specific movement and fitting of the electrode. On the one hand, laser melting is used to form the NiTi-SMA into a highly individual implant. On the other hand, the special characteristics of the material can be 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.

At the LZH a second approach is also being used to optimise the characteristics of implants. The group Laser Micromachining has set a goal of improving the surface of implants by using laser structuring. “The surface of conventional cochlea implants is not subject to special treatment, and a great potential is lost. We have learned from mother nature that biological surfaces, for example of lotus leaves or shark skin, have defined structures for special functions” explains Elena Fadeeva. By using a femtosecond laser, the platinum electrodes can be structured in a special way. Special nanostructures, looking very rough when magnified, can be manufactured, which reduce attachment of connective tissue and improve interaction with the nerve cells. Simultaneously, nanostructuring decreases frequency-dependent electrical resistance, meaning less energy is needed. The special challenge of this innovative development is that the structures must be made on an implant which is only 300 µm in diameter, and which has a curved surface.; Source: Laser Zentrum Hannover (LZH)