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K. Wang, D. Loftus, T. Leng, J.S. Harris, H. Fishman; Carbon Nanotubes as Microelectrodes for a Retinal Prosthesis . Invest. Ophthalmol. Vis. Sci. 2003;44(13):5054.
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Purpose: Current retinal prostheses use metals and other non-biologic materials as planar electrodes. We are seeking to develop a more biocompatible electrical based retinal prosthesis using carbon nanotubes (CNT). The purpose of this work was to determine whether carbon nanotubes can be (1) fabricated into an array of penetrating electrodes, and (2) capable of penetrating into retinal tissue without breakage or incompatibility. Methods: Fabrication of a CNT microelectrode array was readily integrated into the conventional silicon-based micro-fabrication process at low cost. We grew vertically self-assembled, conductive, multi-wall CNT towers on pre-patterned catalyst pads by chemical vapor deposition. Catalyst pads were connected to embedded metal contacts so that the CNT bundles were individually addressable. Full retina explants and retinal ganglion cell cultures were used to test the biocompatibility and strength of CNT microelectrodes. Results: We found that CNTs have intriguing mechanical and electrical properties for use in retinal prostheses. The heights of vertically grown conductive CNT towers could be adjusted (20-100 µm), and thus formed a penetrating microelectrode array with controllable stimulation depth. CNTs were grown successfully at pre-defined and electrically addressable regions. Moreover, the diameter and spacing of the CNT towers could be controlled within 2µm precision. Electrical testing showed good electrical contact between CNTs and the underlying metal pads, as well as good conductive behavior of the CNT electrodes. CNT arrays were found to be flexible, yet showed durability in retina penetration studies: towers of 50 µm diameter and 100 µm height penetrate easily into retina without breaking. Finally, CNT were found to support the growth of retinal ganglion cell cultures, potentially indicating good biocompatibility. Conclusions: CNT towers are robust, flexible, conductive and biocompatible. Conductive multi-wall CNT tower arrays may hold significant potential as stimulating microelectrodes for retina prostheses applications.
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