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D.M. Schneeweis, L. Saggere; Feasibility Analysis of a Light–Actuated Microdispenser for Chemically Stimulating Retinal Neurons . Invest. Ophthalmol. Vis. Sci. 2005;46(13):1504.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Most current retinal prosthesis concepts rely exclusively on electrical stimulation of neurons to communicate visual information to the retina. Electrical stimulation is conceptually straightforward, but alternative modes of stimulation may offer certain advantages. Chemical stimulation is particularly appealing due to its biomimetic nature. In this preliminary study we explore the feasibility of using a novel technology as the basis of such a biomimetic retinal prosthesis. The element central to the long–range concept is a light modulated, micron–scale fluid dispenser that could be powered by light naturally reaching the retina. This approach is distinct from chemical–based strategies recently proposed by other groups. Methods: Modeling and optimization was done with Matlab and Simulink (The Mathworks, Inc.), MAPLE (symbolic solver), and ANSYS (finite element analysis software) by applying the fundamental constitutive relationships and mechanics of the materials involved. Results: In this feasibility analysis we propose a design for a microfluidic dispenser that is actuated by light. The key element of this microdispenser is a light–driven actuator comprised of a silicon membrane attached to a relatively stiffer wall around the edge with a thin–film of a piezo material at the center. A microphotodiode (MPD) is integrated with the silicon substrate and connects to the piezo element. Other features of the microdispenser include a reservoir for the chemical agent (neurotransmitter), and microports for delivering the agent to target neurons. Voltage generated by the MPD as a result of absorption of light actuates the piezo element, causing an increase in pressure in the reservoir and ejection of the chemical through the microports. Design thus far has focused on optimizing a benchtop prototype having dimensions on the order of 100 µm and capable of delivering flow rates of 0.1–1 pL/s. A consideration of energy availability and utilization suggests that such a light–actuated microdispenser could be modulated by light levels at the retina under bright photopic conditions. Conclusions: In this design study we propose to combine enabling technologies from micro–engineering, piezoelectric materials science, and microfluidics to create a microdispenser capable of delivering minute quantities of chemical under photic modulation. An array of such units could constitute the core of a prosthetic device capable of transducing visual stimuli into a 2–D chemical signal delivered to retinal neurons.
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