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Massoud Khraiche, William R Freeman, Gabriel Silva; High Density Flexible Optoelectronic Platform For Retinal Prosthesis. Invest. Ophthalmol. Vis. Sci. 2014;55(13):1839.
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© ARVO (1962-2015); The Authors (2016-present)
Both photovoltaic and optoelectronic devices have been used to restore light sensitivity in retinas blind due to degenerative diseases. These approaches have utilized mostly flat silicon photodetectors, which lack the efficiency to convert light under normal retinal irradiance to generate enough current to stimulate ganglion cells while supporting reasonably size stimulation sites. We have developed Nanowire photodetectors that pack silicon structures in a high surface to volume ratio allowing for smaller size stimulation sites. In addition, we have integrated this into a flexible platform that can cover the macular while conforming to the curvature of the retina.
Lithography is used to pattern Nickel dots on silicon surface were used as mask for reactive ion etching of silicon. Polydimethylsiloxane (PDMS) was spun coated on the surface and used to mechanically release the nanowires. Indium Tin Oxide the top contact. Conductive epoxy used to establish a bottom lead, which connects to bias source for control of pulse shape and polarity. Light responses were measured via a Microelectrode array.
We have successfully fabricated and tested a photodetector/neurostimulator platform with 2 orders of magnitude larger surface area from conventional thin film photodetectors. Light pulse stimulation of the Nanowires results in charge balanced waveforms and bias control alters the direction and magnitude of the resulting photocurrent. Microelectrode array recording for unpowered arrays show .1 μA current pulses in response to light stimulation at .1μW/mm2 (normal retinal irradiance) which is only one order of magnitude lower than the amount of current needed for neural stimulation. Also, we successfully transferred these photodetector with high yield into a functional flexible platform. Our group is carrying extensive in vitro experiments to fully characterize rat retina responses to stimulation via our flexible platform.
We have fabricated and tested a high-density flexible optoelectronic retinal stimulator based on a high surface to volume photodetectors. The device can cover large areas of the retina with fine control over individual sites. The final device increases the surface area of single stimulation site by 2 orders of magnitude, which have a significant affect on size of stimulation site for any retinal prosthesis utilizing optoelectronic or photovoltaic approaches to stimulate the retina.
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