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D.B. Shire, M. Gingerich, J.F. Rizzo, J.L. Wyatt; Recent Developments in Inflatable Prostheses for Epiretinal Stimulation and/or Recording . Invest. Ophthalmol. Vis. Sci. 2005;46(13):1534.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To provide a means of introducing a polymer–based retinal prosthesis or recording electrode array having a large area (and thus subtending a significant visual angle) safely into the intraocular space while limiting the size of the pars plana incision required. Methods: This 12 micron thick microfabricated device contains a micromachined silicon nib for connecting a silicone tube carrying compressed air to inflate the device. The nib is integrated with inflatable polyimide wings which extend radially outward from the central silicon pod. The inflatable cavity within the microstructure arises from the dissolution of a sacrificial Al film in the inter–layer space by wet chemical etching. This is filled using a syringe for manual control of the internal pressure. Input/output pads located on the host silicon substrate are routed to iridium oxide electrodes located on the front or epiretinal side of the device by means of a novel multilayer metallization scheme which allows the completed devices to flex freely. Results: The initial microfabricated silicon nibs did not etch uniformly using a Bosch process etcher, and this was remedied using SOI starting material. The first microchannels were formed by thermal decomposition of a spin–coated polynorbornene polymer, and were only 50 microns wide. Improved performance and shape memory after inserting the completed devices through narrow openings and subsequently inflating them was achieved using broader, 250 – 3000 micron wide wedge–shaped channels, however. The erosion rate of the sacrificial Al material was also enhanced by increasing the diameter of the central nib microstructure. The Al was completely encapsulated in polyimide until just prior to the etching step in which the cavity was formed. Conclusions: A viable means of introducing a 9 mm diameter prosthesis or recording array safely to the epiretinal surface through a narrow incision has been developed, and this device is easily restored to its original shape and orientation after insertion by applying compressed air. This technology is readily extended to the fabrication of other, microfluidic MEMS–based implantable devices.
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