• cochlear implants;
  • coextrusion;
  • hydrogel actuation;
  • overmolding

A self-bending electrode shaft for application in cochlear implants (CI) is presented. It is desired to reduce the distance between the electrode contacts and nerve cells in the modiolus of the inner ear. Therefore a coextrusion and overmolding device to fabricate a novel electrode shaft consisting of an eccentrically positioned hydrogel swelling actuator was established. Finite-element-analysis (FEA) was performed to analyse the self-bending effect in relationship to the applied hydrostatic pressure. The mechanical actuation of a fabricated electrode shaft was tested in vitro by injection of water into the hydrogel. Curving of the electrode shaft was observed. Osmotic pressure in relation to the mass fraction of the swelling polymer inside the hydrogel was calculated.