Reducing stiffness and electrical losses of high channel hybrid nerve cuff electrodes

For restoration of grasp in disabled people by means of functional electrical stimulation of peripheral nerves, 18 polar Hybrid Cuff Electrodes were developed. These electrodes consisted of a micromachined polyimide-based thin-film structure with integrated electrode contacts and interconnection lines which was glued to a silicone cuff. Interconnection lines were made of only 300 nm of sputtered gold, which led to high line drops. Cold electroplating was used to thicken the lines to 3 μm, which reduced the mean track resistance from 480 Ω to 10 Ω. Furthermore, the electrode material was changed from sputtered platinum to electroplated platinum black in order to decrease the phase border impedance of stimulation sites. Applying these techniques, the overall electrode impedance could be reduced from 7.78 kΩ to 624 Ω (at 1 kHz). Additional to the electrical optimization of the cuff electrodes, mechanical properties were enhanced by changing the method of joining silicone and polyimide from using one part silicone adhesive to plasma activation of surfaces: Plasma-treated surfaces were simply pressed face to face. The result was a bondage without any additional layer of glue, which led to a very high mechanical flexibility and higher yield of the overall Hybrid Cuff Electrode.