Flexible Microfabricated Parylene Multielectrode Arrays for Retinal Stimulation and Spinal Cord Field Modulation

The first flexible parylene-based multielectrode arrays (MEAs) designed for functional electrical stimulation (FES) in retinal prostheses, and the extension of this technology toward enabling reflex-arc neuromodulation in cases of spinal cord damage or transection, are presented. A single metal layer 16 ×16 retinal electrode array of 125 μm-diameter thin-film Ti/Pt electrodes and lines of 12 μm-pitch has been fabricated as a demonstration of this technology. To allow for even higher density arrays, a novel dual-layer process has also been implemented that enables leads to pass under overlying electrodes without making electrical contact to them. A biomimetic parylene-based electrode array consisting of 1024 electrodes of highly variable spacing, 60 of which have been connected in this manner, has been fabricated according to this paradigm. A parylene-parylene annealing process has also been developed to increase device longevity under accelerated-lifetime saline soak conditions. Surgical tests of novel anatomically-conformal geometries that enable such parylene-based electrode systems to interact with their neuronal targets of interest while causing minimal mechanical damage to tissues or to the implants are also presented. The use of these flexible electrode arrays in spinal cord stimulation experiments in animal models has proven their efficacy in stimulating neurons.