A Miniaturized, Eye-conformable, and Long-term Reliable Retinal Prosthesis using Monolithic Fabrication of Liquid Crystal Polymer (LCP)

Abstract

A novel retinal prosthetic device was developed using liquid crystal polymer (LCP) to address the problems associated with conventional metal- and polymer-based devices: the hermetic metal package is bulky, heavy and labor-intensive, whereas a thin, flexible and MEMS-compatible polymer-based system is not durable enough for chronic implantation. Exploiting the advantageous properties of LCP such as a low moisture absorption rate, thermo-bonding and thermo-forming, a small, light-weight, long-term reliable retinal prosthesis was fabricated that can be conformally attached on the eye-surface. A LCP fabrication process using monolithic integration and conformal deformation was established enabling miniaturization and a batch manufacturing process as well as eliminating the need for feed-through technology. The fabricated 16-channels LCP-based retinal implant had 14 mm-diameter with the maximum thickness of 1.4 mm and weight of 0.4 g and could be operated wirelessly up to 16 mm of distance in the air. The long-term reliability of the all-LCP retinal device was evaluated in vitro as well as in vivo. Because an all-polymer implant introduces intrinsic gas permeation for which the traditional helium leak test for metallic packages was not designed to quantify, a new set of reliability tests were designed and carried out specifically for all-polymer implants. Moisture ingress through various pathways were classified into polymer surface, polymer-polymer and polymer-metal adhesions each of which were quantitatively investigated by analytic calculation, in vitro aging test of electrode part and package part, respectively. The functionality and long-term implantation stability of the device was verified through in vivo animal experiments by measuring the cortical potential and monitoring implanted dummy devices for more than a year, respectively. Samples of the LCP electrodes array failed after 114 days in 87°C salin as a result of water penetration through the LCP-metal interface. An eye-confirmable LCP package survived more than 35 days in an accelerated condition at 87°C. The in vivo results confirmed that no adverse effects around the retina were observed after implantation of the device for more than a year.