Microfabrication of Surgically Compatible Retinal Implant for the Blind

Massachusetts Institute Of Technology, Cambridge MA

Investigators

Abstract

0001296 Wyatt This SGER project would develop three processes for integration into a single fabrication sequence needed for a testable prototype of a device for blind patients to allow them to walk down a street unaided. Improved vision at this level depends more on having a sufficiently wide visual field than on the ability to resolve small objects or text with high acuity. Three experiments are to be conducted to establish that the basic steps for fabricating the inflatable retinal prosthesis are feasible. Also needed is verification that the polyimide layer, though not adequate to protect CMOS circuitry against saline, is adequate to insulate gold leads from current shunting in extended soak tests. The first experiment is to determine the dependence of the ultimate achievable length of the microchannels on the height and width of the oxide stripes which give rise to the channels after etching. This will determine whether the 3-5 mm length required will necessitate etching from both ends of the device simultaneously, or whether single-ended etching will be sufficient. The second experiment is to develop a workable process for creating the silicon "nib" structure shown in the proposal (Figure 2). This will involve multiple-step etching in a Bosch process rapid silicon etching system and conventional RIE tools. An appropriate masking material for the process must be developed, and an endpoint indicator determined. The third experiment is to develop a suitable method for attaching the silicone tube carrying the compressed air to the silicon/polyimide implant structure in a blocompatible manner. In parallel with these process development steps, the polyimide electrodes already fabricated would be tested to determine if their saline resistance is adequate for protecting the gold wires. The fabrication experiments are to be conducted at the NSF-funded Cornell Nanofabrication Facility (CNF) in Ithaca, NY by Dr. Douglas Shire, an independent contractor who has been collaborating with the PI on the Retinal Implant Project for the past two years. Immersion testing of existing polyimide arrays will be done at MIT's Draper Laboratory under the supervision of the PI. The CNF and the MIT test system are capable of carrying out the work. Its successful completion will provide the proof-of-concept for a detailed proposal addressing the long-term biocompatibility, encapsulation and power conversion issues for a flexible, inflatable retinal prosthesis. A proof-of-concept resulting from this investigation would be used as the basis of a non-SGER proposal, which would be subject to full merit review.