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Massoud L. Khraiche, Deli Wang, Yuhwa Lo, Gert Cauwenberghs, Igor Kozak, William R. Freeman, Gabriel Silva; Ultrahigh Photosensitivity Silicon Nanophotonics For Retinal Prosthesis. Invest. Ophthalmol. Vis. Sci. 2012;53(14):302.
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© ARVO (1962-2015); The Authors (2016-present)
Age related macular degeneration (AMD) and retinitis pigmentosa (RP), lead to the loss of the photoreceptor cells rendering the retina incapable of detecting light. There have been several engineering approaches aimed at replacing the function of the photorecptors (PRs) by detecting light via an external camera or photodiodes and electrically stimulating the remaining retinal tissue to restore vision. These efforts face several challenges including low resolution, high power consumption and poor tissue integration. In this work, we will introduce a nanophotonic technology that has the potential to be at the heart of nanoengineered retinal prosthesis.
Large arrays of 1cm X 1cm Nanowires were fabricated via nanoimprint lithography. The Nanowire array was used to stimulate retinal explants from the subretinal stimulation site while ganglion cells activity was measured via a Microelectrode array placed at the epiretina.
Our results showed the Nanawires possess characteristics that make them ideal replacements for the photoreceptors; Topography and spatial control: The nanowires can be fabricated to match the functional organization of the photoreceptors in the retina. Light adaptation and amplification: The rods and cones can operate on an extremely large range of illumination. The nanowires can be made to mimic this control via feedback control of bias voltage. Neural stimulation: The PRs stimulate neural tissue via the release of neurotransmitters. Driving a current through neural tissue can also excite neurons. Our data shows the NW platform capable of producing current levels and waveforms sufficient for neural stimulation in response to light. The Nanowires were stimulated with a laser at 635nm, a wavelength we confirmed is not able to produce an electrophysiological response on its own the rat retina.
The presented body of work shows our Nanowires technology has a lot of promise for application in a prosthetic platform to replace the function of the PRs. The long term aims of our group is to produce a nanoengineered retinal prosthesis capable of tissue integration on a scale comparable to those of proteins and lipids, with light sensing and stimulation elements near rod and cons light sensitivity and spatial distribution.
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