The next generation of electrodes for neural protheses will require arrays of microelectrodes for highly selective stimulation and monitoring of the stimulated environment. The goal of this program is to develop ultramicroelectrode structures that are simple to produce, have good long term stability in biological environments, and are compatible with a new generation of electrochemically reversible, high charge capacity electrode materials such as activated iridium oxide. The Phase I study investigated band ultramicroelectrodes with geometric areas from 2 X 10-5 to 2 X 10-8 cm2 formed from the edge of a thin film of sputter deposited Ir. AFter activation of the iridium, the electrodes charge injection density limits with constant current pulses in buffered saline equalled or exceeded the values obtained on other iridium oxide electrodes. Their electrochemical characteristics were unchanged after several hours of pulsing or soaking in saline overnight. The proposed Phase II program will deal with 1) optimization of the fabrication and activation of multielectrode arrays, 2) long term stability testing of the structures, 3) evaluating the electrodes as microsensors of the local chemical environment and 4) fabrication of implantable microelectrode arrays for in vivo testing.
