Design of a Neurotransmitter–Based Retinal Prosthetic Chip Powered by the Ambient Light.

Abstract

Abstract: : Purpose: To determine the feasibility of a self–contained, ambient light–powered retinal prosthesis chip. Methods: Calculations were based on microfluidic data obtained with model chips made in our laboratory and from the literature. Power considerations were derived from hydrodynamic calculations of electro–osmotic flow. Results: We have designed microfluidic chips that convert an image on the retina into pulsatile flow of neurotransmitter through an array of microapertures. The pulsatile flow is activated by an electro–osmotic mechanism, and the device is capable of delivering femtoliters of fluid per microchannel. Calculations and experimental data show that these neurotransmitter quantities are sufficient to stimulate single nerve cell bodies and single axonal processes if they are in close proximity to the site of release. We have already shown that such proximity can be achieved through several tissue engineering techniques (directed neurite growth using microcontact printing, retinal cell migration, and carbon nanotube scaffolds). With electro–osmotic flow control, a very low amount of power (1 nW/ microaperture) is needed for transmitter release. At these power requirements, bright ambient light in the eye can activate thousands of photosensitive pixels on the scale of a prosthetic chip. Given the small amount of transmitter needed for neural stimulation (thousands of molecules), we estimate that 10 or more years of transmitter supply could be held within a peripheral subretinal reservoir chip connected to the stimulation unit. Conclusions: Using microfabricated neurotransmitter chips that transduce images into a pattern of electro–osmotic flow channels, in conjunction with directed neuronal growth or migration to bring neurons into proximity, it is technically feasible to build an ambient light–powered chip for neuronal stimulation in the retina. It should be emphasized that these prototype specifications show the feasibility of a self–contained implant, but refinements will be needed to reach small photocell pixel sizes and better resolution with lower light levels.

Keywords: neurotransmitters/neurotransmitter systems • age–related macular degeneration • retinal connections, networks, circuitry