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1.  Neural Electrode Degradation from Continuous Electrical Stimulation: Comparison of Sputtered and Activated Iridium Oxide 
The performance of neural electrodes in physiological fluid, especially in chronic use, is critical for the success of functional electrical stimulation devices. Tips of the Utah Electrode Arrays (UEA) were coated with sputtered iridium oxide film (SIROF) and activated iridium oxide film (AIROF) to study the degradation during charge injection consistent with functional electrical stimulation (FES). The arrays were subjected to continuous biphasic, cathodal first, charge balanced (with equal cathodal and anodal pulse widths) current pulses for 7 hours (> 1 million pulses) at a frequency of 50 Hz. The amplitude and width of the current pulses were varied to determine the damage threshold of the coatings. Degradation was characterized by scanning electron microscopy, inductively coupled plasma mass spectrometry, electrochemical impedance spectroscopy and cyclic voltammetry. The injected charge and charge density per phase were found to play synergistic role in damaging the electrodes. The damage threshold for SIROF coated electrode tips of the UEA was between 60 nC with a charge density of 1.9 mC/cm2 per phase and 80 nC with a charge density of 1.0 mC/cm2 per phase. While for AIROF coated electrode tips, the threshold was between 40 nC with a charge density of 0.9 mC/cm2 per phase, and 50 nC with a charge density of 0.5 mC/cm2 per phase. Compared to AIROF, SIROF showed higher damage threshold and therefore is highly recommended to be used as a stimulation material.
doi:10.1016/j.jneumeth.2009.10.016
PMCID: PMC2814928  PMID: 19878693
Functional electrical stimulation; neuronal damage; iridium oxide; pulse DC reactive sputtering; Inductively Coupled Plasma Mass spectrometry (ICP-MS)
2.  Integrated device for optical stimulation and spatiotemporal electrical recording of neural activity in light-sensitized brain tissue 
Journal of neural engineering  2009;6(5):055007.
Neural stimulation with high spatial and temporal precision is desirable both for studying the real-time dynamics of neural networks and for prospective clinical treatment of neurological diseases. Optical stimulation of genetically targeted neurons expressing the light sensitive channel protein Channelrhodopsin (ChR2) has recently been reported as a means for millisecond temporal control of neuronal spiking activities with cell-type selectivity. This offers the prospect of enabling local delivery of optical stimulation and the simultaneous monitoring of the neural activity by electrophysiological means, both in the vicinity of and distant to the stimulation site. We report here a novel dual-modality hybrid device, which consists of a tapered coaxial optical waveguide (‘optrode’) integrated into a 100 element intra-cortical multi-electrode recording array. We first demonstrate the dual optical delivery and electrical recording capability of the single optrode in in vitro preparations of mouse retina, photo-stimulating the native retinal photoreceptors while recording light-responsive activities from ganglion cells. The dual-modality array device was then used in ChR2 transfected mouse brain slices. Specifically, epileptiform events were reliably optically triggered by the optrode and their spatiotemporal patterns were simultaneously recorded by the multi-electrode array.
doi:10.1088/1741-2560/6/5/055007
PMCID: PMC2921864  PMID: 19721185

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