A laboratory testing and driving system for AIROF microelectrodes


The charge-injection currents of AIROF (activated iridium oxide film) microelectrodes, which are subjected to charge-balanced biphasic pulsing or monophasic current pulsing, have to be limited such that the anodic and cathodic voltage excursions are kept within safe limits of operation. In earlier studies it has been shown that when using anodic bias asymmetry in the magnitude of the balanced biphasic waveform can be used to increase the charge injection capacity of AIROF electrodes. We present the design of a single-channel testing and driving system for laboratory testing and driving of AIROF microelectrodes within safe charge-injection limits.

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    • "To achieve high charge delivery capacity, the electrodes were D.C. coupled and anodically biased [3]. To protect the electrode from irreversible damage, the chip also uses a compliance-limited driving strategy [4] that basically clamps the electrode voltage within ±0.6 V vs. a Ag/AgCl reference electrode. As shown in Fig. 2, there are two current sources for each channel. "
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    ABSTRACT: Capacitive coupling within high-density microelectrode arrays can degrade neural recording signal or disperse neural stimulation current. Material deterioration in a chronically implanted neural stimulation/recording system can cause such an undesired effect. We present a simple method with an iterative algorithm to quantify the cross-coupling capacitance, in-situ.
    Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 02/2006; 1:3365-8. DOI:10.1109/IEMBS.2006.259543
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    • "In this paper, we report cyclic voltammetry (CV) and compliance limited [7] current pulse measurements that were made on the same AIROF microelectrodes that were repeatedly implanted into and explanted out of the brain of an anesthetized zebra finch over a short period of time. The experiment showed that the AIROF microelectrodes could not deliver as much current in the interstitial fluid environment of the bird's brain as in the in vitro electrolyte. "
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    ABSTRACT: Activated Iridium Oxide Film (AIROF) microelectrodes are thought to be well-suited for neural stimulation of the cortex because they can sustain high charge capacity (about ten times higher than Pt microelectrodes) when characterized in phosphate-buffered saline (PBS) or other high ionic strength electrolytes. However, it is known that their capacity diminishes after they are implanted in vivo. It has been suggested that tissue encapsulation is an underlying cause. In this paper, we report electrochemical measurements of AIROF microelectrodes that were performed acutely in the brain of the zebra finch. The experiment showed that the interstitial fluid environment in the bird's brain did not maintain the high charge delivery capacity of the AIROF microelectrodes. A simple compensation for access resistance may create hazards to sustained electrode integrity.
    Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 02/2006; 1:886-9. DOI:10.1109/IEMBS.2006.259869
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    • "shows a CAD drawing for the ASIC. Each of the 16 electrodes electrode is driven by a dedicated compliance supply limited constant current driver [1]. "
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    ABSTRACT: A conservative estimate for the number of electrodes to be used in a first generation intracortical visual prosthesis is approximately 1000 individual electrodes. Our recent surgical experiences with animal models have led us to the conclusion that even if grouping the electrodes in 16-electrode arrays, the 60 cables would have to cross the dura may pose considerable risk of infection or damaging tethering of the electrodes. Therefore we are pursuing a design for a wireless array module that contains power, communication, and elecrode drivers within an application specific integrated circuit (ASIC).
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