Design and fabrication of a microelectrode array dedicated for cortical electrical stimulation

A manufacturing process has been developed for a microelectrode array that can be used for stimulation of the visual cortex to provide an effective sense of sight to the blind. The first prototype merges sixteen 316L stainless steel electrodes on a 4×4 array. Several arrays can then be assembled together in a mosaic configuration to cover a large portion of the visual area. To reduce brain injuries while maximizing the quality of the phosphenes, the electrodes must be sharp, thin (50 μm-diameter), separated 400 μm apart and have stimulation sites located at 1.5 mm under the surface of the cortex. Using electrical discharge machining followed by an electrochemical surface treatment, it has been shown that it was possible to reach such geometrical ratios at this scale. This technique can be combined with electrodeposition of porous platinum to create low impedance stimulation sites. Encapsulation and biocompatibility of the array are also discussed.