Design, fabrication and modeling of a cuff electrode for peripheral nerve stimulation

Functional electrical stimulation is an important tool towards rehabilitation of lost motor functions on individuals who have had spinal cord injury or stroke. Peripheral nerves are preferential targets for electrical stimulation because of easy surgical access, where electrodes serve as interfaces between neuroprostheses and the peripheral nerve. The selection of an electrode is a trade-off between the nerve invasiveness and the degree of selectivity of the electrode to stimulate neurons innervating different muscles. A flexible multipolar cuff electrode based on polyimide is presented - this type of electrode offers higher degree of axonal selectivity than the `classical´ ring cuff electrode with minimum nerve invasiveness. Electroless nickel-gold plating finish was applied to seal the aluminum interconnect of fabricated devices in order to form a stable interface between the electrode and the biological tissue. The surface morphology of flash gold layer was studied using SEM. A characterization of the electrode in terms of impedance spectra is also shown. Simulations of impedance spectroscopy were done over the frequency range 1 Hz - 1 MHz, using a 10 mVpp sine voltage. Below 10 kHz a capacitive behavior prevails whereas above 10 kHz a resistive one is dominant.