The Laser Zentrum Hannover e.V. (LZH) is developing innovative
technologies for improved insertion techniques and exact fitting of
cochlea implants in the inner ear, as well as better quality for
Approximately 95% 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 Laser Zentrum Hannover, a second approach is also being used to
optimize the characteristics of cochlea 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 scientist 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. At the moment, the LZH is working on a unit,
which can provide these complex structures on a very small scale.
Cochlea implants are especially interesting for people who, even with
the best hearing aids, cannot understand spoken language well enough.
Over 200,000 people worldwide could profit from these “artificial
inner ears”. About half of the adults using CIs could even use
the telephone again after sufficient training takes place. For those
having shortly lost hearing, or for children, the success rate should
be even higher.
Current activities at the LZH concerning cochlea implants are being
financially supported within the framework of the German Federal
Ministry of Education and Research (BMBF) project Gentle CI, and by the
interdisciplinary special research program 599 of the German Research
Foundation (DFG). Among the project partners is the Hannover Medical
School (MHH), which has the world’s largest cochlea implant
program for the extremely hearing impaired.
More information at http://www.lzh.de/