Development of Implantable Electrode for Functional Electrical Stimulation.

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The functional electrical stimulation (FES) system is very effective in order to restore motor functions of the paralyzed extremities in spinal cord injury and carebral disease patients. The applicants have been developed as stimulator with percutaneous intramuscular electrodes and have been utilizing clinically the system. However, this system has unavoidable problems such as infection and breakage at the position where electrodes go through skin, careful daily maintenance, and cosmetically unfavorable upon patients. Therefore, development of a totally implanted FES system is necessary. In this study more reliable electrodes have been developed than the present percutaneous electrodes. The obtained results are as follows :1. Chromium-cobalt alloy was refined by electro-slag remelting and 25 mum diameter wire was drawn as well as SUS316L stainless steel. The mechanical properties were well satisfied.2. Pitting corrosion was observed on the SUS316L wire in saline solution with accelerated corrosion test by applying electric current, on the contrary, no pitting corrosion on the 604PH wire.3. In order to easily and stably connect electrodes with the stimulator during operation, design of connectors and electrode tip were developed.4. Prototype systems of totally implanted FES with the electrodes of two kinds of materials (SUS316L and 604PH) were implanted in sheep and operating check of the system has been carried out. Useful information has been expected for development of the final system.