Synthesis process of a compliant fluidmechanical actuator for use as an adaptive electrode carrier for cochlear implants

The cochlear implant, consisting of an electrode carrier and embedded electrodes, is an auditory neuroprosthesis surgically inserted into the cochlea in order to create an auditory impression in deaf or profoundly hearing-impaired patients. This contribution presents a fluidically actuated electrode carrier with a changeable curvature to simplify insertion. Targeted deformation of the carrier is accomplished by applying pressure internally as well as using a non-stretchable thin fibre embedded in its wall. An analytical examination of the scaled model shows that enlarged geometrically similar systems can be studied in place of actual systems, reducing the effort required for measurements. The geometry of the electrode carrier was determined using model-based synthesis combining the finite element method with an analytical model. The material parameters for the finite element model were found experimentally and fitted by using a third-order Ogden material model. The result of the synthesis yielded a conical shape for the carrier. Synthesis of other forms is also possible and one form is shown which was calculated using a polynomial approach. Demonstrators (3:1-scale) were manufactured and measured. The difference between the measured and calculated pressures was less than 0.6 bar for the cylindrical form and less than 0.78 bar for the conical form.