The development of electrodeposited iridium oxide films (EIROFs) as low impedance, high-capacity charge-injection coatings for neural recording and stimulation electrodes is proposed. In Phase I, the biocompatibility of EIROF coatings on metal shafts implanted in rabbit cortex was evaluated by quantitative histology and found comparable with activated iridium oxide (AIROF) and iridium metal controls. No adverse neural pathology was observed with any of these materials for a 60 day implantation period. In vitro measurements established the electrochemical properties of EIROF relevant to neural recording and stimulation, and provided charge-injection limits for stimulation electrodes. These data were used to identify neuroprosthetic and electrical-stimulation based therapies for which EIROF could provide advantages over conventional metal electrodes or other types of electroactive coatings. The applications include peripheral nerve electrodes, cochlear and retinal sensory implants, and intracortical stimulation and recording electrodes. Applications in stimulation-based therapies such as deep-brain stimulation and cardiac pacing were also identified. The particular advantages of EIROF over AIROF and other competing electrode coatings are the simplicity of the electrodeposition process, suitability for coating most metals used as conductors in neural prostheses, and a significantly reduced coating cost with minimal investment in capital equipment required to implement high-volume coating operations. Based on these findings, the Phase II objectives are 1) to demonstrate biocompatibility and functional performance of EIROF coatings for long-term chronic recording and stimulation using EIROF-coated Ptlr microelectrodes implanted in cortex for periods up to one year, 2) to broadly characterize the electrochemical and mechanical properties of EIROF coatings relative to the requirements of neural prostheses and stimulation-based therapies, 3) to demonstrate suitability for a wide range of neural prostheses by incorporating EIROF into penetrating, intracortical microelectrodes, flexible electrode arrays, and micromachined silicon-based electrodes, 4) to develop and demonstrate scale-up of the EIROF deposition process and to establish protocols for handling and sterilization of coatings prior to implantation, and 5) to facilitate adoption of EIROF by end-users and device manufacturers by developing and providing protocols for in vivo use, monitoring and maintenance of EIROF coatings and to validate these protocols by testing in cortex.
