Microfabricated cylindrical multielectrodes for neural stimulation

The effects of spinal cord injuries are likely to be ameliorated with the help of functional electrical stimulation of the spinal cord, a technique that may benefit from a new style of electrode: the cylindrical multielectrode. This paper describes the specifications for, fabrication techniques for, and in vitro evaluation of cylindrical multielectrodes. Four tip shapes were tested to determine which shape required the lowest peak force and would, therefore, be expected to minimize dimpling during implantation. The impedance of the electrode interface was monitored for changes due to insertion as well as repetitive delivery of current pulses. The charge delivery capacity was determined by testing with safe ([less than or equal to] 0.6 mC/[cm.sup.2]) and damaging levels ([greater than or equal to] 0.8 mC/[cm.sup.2]) of charge density. The results of these tests suggest that this electrode design could be used to stimulate neurons in the ventral horn of the spinal cord. Index Terms--Depth electrodes, impedance testing, microelectromechanical systems (MEMS), microstimulation, neural prosthesis.