A PDMS-based Elastic Multi-Electrode Array for Spinal Cord Surface Stimulation and its Electrode Modification to Enhance
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1009-U05-03
A PDMS-based Elastic Multi-Electrode Array for Spinal Cord Surface Stimulation and Its Electrode Modification to Enhance Performance Liang Guo, Kathleen K. Williams, Richard J. Giuly, Stephen P. DeWeerth Dept. of Biomedical Engineering, Georgia Inst. of Technology/Emory Univ., Atlanta, GA
For our ongoing research involving electrical stimulation of rat spinal cord axonal tracts, it is desirable to use a microelectrode array which highly conforms to the surface of the spinal cord. The elastic polymer, polymethylsiloxane (PDMS, known commercially as Sylgard), possesses properties which make it suitable to meet this demand by serving as the electrode substrate. In addition to elasticity, cured PDMS is also gas permeable and biocompatible, and the surface multi-electrode array (MEA) fabricated on such a substrate would cause minimal damage to the cord in that the electrodes do not penetrate spinal tissue. Using standard microfabrication technology, we have previously implemented such an elastic MEA on the PDMS substrate(Fig. 1a). Our fabrication process involves patterning gold traces onto a PDMS substrate cured on a glass slide, covering the traces with another thinner PDMS layer for insulation, and then exposing the sites of electrodes and contact pads. The advantages of fabrication of this type of MEA include achievement of high electrode spatial density, high geometrical precision, and ability to be fabricated easily in batches with little geometrical and electrical difference between each other. These advantages in turn enable high spatiotemporal stimulation selectivity and parallel stimulation capabilities, as well as reliable data reproducibility. To enhance the performance of this PDMS-based Multi-Electrode array, we have recently implemented volcano-like conical PDMS electrode shells around each electrode on the MEA(Fig. 1b) with the help of microfabrication techniques. We then electroplate platinum-black in the central vent of the conical shell(Fig. 1c), at the bottom of which the electrode sits. The volcano-like conical PDMS shell potentially provides improved contact between the electroplated electrode and the spinal cord surface as well as a more isolated micro-environment for current exchange between the electrode and spinal cord. This technique also serves to protect the electroplated platinum-black from being rubbed off. The electroplated platinum-black in the central vent of the conical PDMS shell also lowers the electrode impedance, thus providing better electrical performance. We present in vitro performance evaluation of this new MEA design architecture using the isolated young rat spinal cord preparation. Both the physical and electrical performances are excellent. Therefore, our MEA provides a powerful tool for researchers to study spinal cord systems via multi-site surface stimulation.
(a) (b) (c) Fig.1 PDMS-based elastic Multi-Electrode Array with conical electrodes. (a) The MEA; (b) SEM picture of conical electrodes; (c) SEM picture of platinum-black electroplated in the electrode
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