Novel Interface to Biological Systems for Retinal Prosthetics
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Novel interface to biological systems for retinal prosthetics Mark C. Peterman1, Christina Lee2, Theodore Leng3, Philip Huie3, Harvey A. Fishman3 1
Department of Applied Physics, Stanford University, Stanford, CA 94305-4090 Department of Chemical Engineering, Stanford University, Stanford, CA 94305 3 Department of Ophthalmology, Stanford University, Stanford, CA 94305-5308 2
ABSTRACT The development of retinal prostheses requires a method for interconnecting an imaging system to the retina. Such a system must be able to individually address and stimulate retinal neurons, a significant advance from current technology. As a step toward this goal, we present a novel electronic-to-biologic interface using microfabricated apertures in a silicon substrate. Apertures are created in a thin silicon nitride membrane, after which the surface is appropriately modified to support cell growth. Excitable cells are seeded on the device and imaged using Ca2+-sensitive fluorescent dyes in either an inverted or confocal microscope. Using rat pheochromocytoma (PC12) cells, we show the ability to stimulate locally through the apertures. The device allows for the stimulation of cells at precise locations, a necessary requirement for future highresolution retinal prostheses. INTRODUCTION Finding the appropriate interface between electronic devices and the nervous system is a critical step in developing successful neural prosthetics. With this work, we present a first step towards a chemical-based neural prosthetic. We set out to build a biomimetic, microfabricated device that mimics the localized chemical release of a synapse. While our interest is in building an artificial prosthetic retina, this device has applications for all neural systems. When devising a system to stimulate the nervous system with an external device, electrical stimulation is the most commonly used. Electrical stimulation provides a strong advantage of simplicity; the signals generated by an external source, such as a photodiode array, are electrical. Furthermore, the microelectronics industry provides a great deal of experience in handling electrical signals with precision at the submicron scale. And there has already been a great deal of work towards electrical retinal prostheses [1, 2]. Nevertheless, electrical stimulation has serious neurobiological challenges that chemical stimulation can resolve. The retina consists of as many as 55 cell types [3], including 10 to 15 retinal ganglion cell types, all in very close proximity. Specificity in the retina is provided by different neurotransmitter/receptor systems, including both inhibitory and excitory transmitters. It is difficult for electrical stimulation to provide specificity for the variety of retinal cell types. Whereas neurons release specific neurotransmitters necessary to excite specific cells, electrical stimulation nonspecifically activates all cells. Additionally, some neurotransmitters inhibit cell activation; inhibition by electrically hyperpolarizing a cell using extracellular electrodes difficult.
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