Improved Biphasic Pulsing Power Efficiency with Pt-Ir Coated Microelectrodes
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Improved Biphasic Pulsing Power Efficiency with Pt-Ir Coated Microelectrodes Artin Petrossians1, 2, Navya Davuluri3, John J. Whalen III2, Florian Mansfeld1, James D. Weiland2, 3 1 Mork Family Department of Chemical Engineering and Materials Science, 2 Department of Ophthalmology, 3 Department of Biomedical Engineering, University of Southern California, Los Angeles, California, USA
ABSTRACT Neuromodulation devices such as deep brain stimulators (DBS), spinal cord stimulators (SCS) and cochlear implants (CIs) use electrodes in contact with tissue to deliver electrical pulses to targeted cells. In general, the neuromodulation industry has been evolving towards smaller, less invasive devices. Improving power efficiency of these devices can reduce battery storage requirements. Neuromodulation devices can realize significant power savings if the impedance to charge transfer at the electrode-tissue interface can be reduced. High electrochemical impedance at the surface of stimulation microelectrodes results in larger polarization voltages. Decreasing this polarization voltage response can reduce power required to deliver the current pulse. One approach to doing this is to reduce the electrochemical impedance at the electrode surface. Previously we have reported on a novel electrochemically deposited 60:40% platinum-iridium (Pt-Ir) electrode material that lowered the electrode impedance by two orders of magnitude or more. This study compares power consumption of an electrochemically deposited Pt-Ir stimulating microelectrode to that of standard Pt-Ir probe microelectrode produced using conventional techniques. Both electrodes were tested using in-vitro in phosphate buffered saline (PBS) solution and in-vivo (live rat) models. INTRODUCTION Neuromodulating implants are used to treat a variety of neurological disorders, including deafness, movement disorders (Parkinson’s), and chronic back pain [1-4]. Recently, implantable stimulators have been approved for use for blindness in the US [5]. Obsessive Compulsive Disorder [6], treatmentresistant depression [7], Alzheimer’s disease [8], and migraine [9, 10] are emerging targets for implants. Electrodes are the critical interface between implants and the surrounding neural tissue. An implantable neurostimulator’s efficacy, efficiency, longevity, precision, and the fabrication cost are impacted by the choice of electrode technology used. The evolution of these devices continues to move towards smaller sized and greater quantity of electrodes per device. This evolution is driven by the need for more precise and complex stimulus patterns, to avoid side effects seen in brain stimulation and to enable complex sensory input as in visual prostheses. Electrode size reduction increases the electrochemical impedance of the electrode-tissue interface, reducing power efficiency. For chronic stimulation/pacing devices, where the same amount of charge must be delivered across a smaller interface, the impedance increase results in increased power consumption [11]. It is therefore desirable to m
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