Fabrication of a MEMS retinal tack and long-term in vivo biocompatibility evaluation for retinal prostheses

A silicon and PMMA (poly-(methyl methacrylate)) retinal tack with barbs is developed for retinal prostheses. The MEMS retinal tack presented in this paper has barbs, which are intended for the fixation of the epiretinal-type retina-stimulating microelectrode array. Although conventional retinal tacks made of titanium are available, they are expensive, invasive, and restricted in shape. The silicon retinal tack is fabricated using silicon micromachining, and the PMMA retinal tack is fabricated by X-ray lithography for accurate micro-patterning, which is very scalable and is suitable for inexpensive and repeatable mass production. In this paper, long-term in vivo biocompatibility evaluation of silicon and PMMA retinal tacks is presented. The MEMS retina tack is implanted with epiretinal microelectrodes onto the retinal surface of the rabbit eye and harvested after 1 year for the silicon retinal tack and 6 months for the PMMA retinal tack. Through histological examination, no inflammatory infiltrates in retina, choroid, nor sclera are revealed. Scanning electron microscope (SEM) images show no chemical reaction trace nor mechanical fracture of the implanted device. The results indicate that both silicon and PMMA retinal tacks are suitable for mechanical fixation of microelectrode arrays. Also, the long-term evaluation of the durability in vivo shows acceptable biocompatibility for further use in retinal prostheses.