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Philip R. Troyk, Sungjae Suh, Zhe Hu, Kevin Kayvani, Glenn DeMichele, Douglas Kerns; Assessment Of Technology For An Intracortical Visual Prosthesis. Invest. Ophthalmol. Vis. Sci. 2012;53(14):5552.
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The intracortical visual prosthesis project (ICVP) at IIT has reached a point of planning for testing in a human volunteer. To accomplish this, a comprehensive assessment of the status of technology suitable for the implantation of up to 1000 electrodes on the dorso-lateral surface of the occipital lobe has been made. A critical element in the technology is a self-contained implantable stimulator module. The operation and stability of the implantable stimulator module have been examined within the context of suitability for implantation in a human.
The ICVP system uses a collection of 16-electrode stimulator modules. Each module measures 5mm diameter and consists of a ceramic substrate that maintains eighteen metal electrodes at a 450-micron spacing (16 channels, 1 counter, 1 reference). Electronic circuitry in the form of a custom application-specific-integrated-circuit (ASIC) contains sixteen dedicated electrode drivers, wireless inductive link power and communication modules, and sophisticated functionality specific to activated iridium oxide film (AIROF) electrodes. The stimulator ASIC is powered and commanded over a transcutaneous inductive link. Constant current electrode drivers use a unique method of protecting the AIROF electrodes from damage. Not found in any other stimulator design is the ability to grow the AIROF as a final part of the assembly step, over the inductive link. This is essential since the AIROF would be destroyed by elevated temperatures necessary for the polymer packaging of the stimulator module. Prototype stimulator modules have been tested environmentally in 2-week autoclave exposure (125 degree C, 1.5 bar). Wireless growth of AIROF was tested using discrete electrodes subjected to cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and pulsed injectable charge measurements.
Stimulator modules subjected to the autoclave exposure showed no signs of physical deterioration. Electrical characteristics of the inductive link remained virtually unchanged. Electrodes activated over the wireless link showed typical increases in charge capacity as measured by CV and pulsed charge injection. Reverse telemetry from the modules shows electrode voltage waveforms and activation conditions
A novel stimulator design has been tested and confirmed for functional use in an implanted ICVP. Activation of Ir electrodes, over an inductive link and facilitated by the ASIC, is necessary to preserve the integrity of the AIROF during module fabrication, and has been confirmed in this design. Lifetime tests support the use of the polymer-protected electronics. Our assessment is that this stimulator design is suitable for an ICVP human trial.
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