Development of Microelectrode Arrays for Artificial Retinal Implants using Liquid Crystal Polymers

Abstract

Purpose: To develop a liquid crystal polymer (LCP) based, long-term implantable, retinal stimulation microelectrode array using a novel fabrication method. Methods: The fabrication process used laser micromachining and customized thermal press bonding to produce LCP based microelectrode arrays. To evaluate the fabrication process and the resulting electrode arrays, in vitro reliability tests and in vivo animal experiments were performed. The in vitro tests consisted of electrode site impedance recording and electrode inter-layer adhesion monitoring during accelerated soak tests. For in vivo testing, the fabricated electrode arrays were implanted in the suprachoroidal space of rabbit eyes. Optical coherence tomography (OCT) and electrically evoked cortical potentials (EECPs) were used to determine long-term biocompatibility and functionality of the implant.Results: The fabricated structure had a smooth, rounded edge profile and exhibited moderate flexibility, which are advantageous features for safe implantation without guide tools. Following accelerated soak tests at 75°C in phosphate buffered saline, the electrode sites showed no degradation and the inter-layer adhesion of the structure showed acceptable stability for more than 2 months. The electrode arrays were safely implanted in the suprachoroidal space of rabbit eyes, and 1 EECP waveforms were recorded. Over a 3-month postoperative period, no choroioretinal inflammation or structural deformities were observed by OCT and histological examination. Conclusions: LCP based flexible microelectrode arrays can be successfully applied as retinal prostheses. The results demonstrate that such electrode arrays are safe, biocompatible, mechanically stable, and can be effective as part of a chronic retinal implant system.