SNU Retinal Implant : Progress Toward a Chronic Retinal Stimulation System With Flexible Microelectrode Arrays

Abstract

Purpose: : To develop a long-term implantable retinal stimulation system, 3-D and hybrid microelectrode arrays (MEAs) were developed and tested in vivo, and the revised in vitro reliability tests are proposed.

Methods: : The 3-D polyimide electrodes and the silicone-polyimide hybrid electrodes were fabricated and implanted in the suprachoroidal space of rabbit eyes, and electrically evoked cortical potentials (EECP) were recorded. A novel multi Inter-digitated electrode (MIDE) pattern was designed to detect the leakage electric current through polymer encapsulation. Silicone elastomer (MED6233 Nusil), polyimide (PI2525, HD Microsystems) and parylene-C (Hansong System., LTD, Korea) based MIDE samples were fabricated and the accelerated soak tests was performed at 90°C. During the soak tests, 5 V direct current biased electrical current was regularly applied to each channel of the samples and the leakage currents were measured by picoammeter (Model 6485, Keithley Instruments Inc).

Results: : The 3-D polyimide electrodes and the hybrid electrodes were successfully fabricated and implanted in the suprachoroidal space. Both electrodes showed good stability and biocompatibility in vivo, and the hybrid electrodes showed improved surgical safety. EECP were recorded well in both cases. All MIDE samples were successfully fabricated. The leakage currents of the silicone elastomer and parylene-C based samples were measured about ~100 nA and ~1 nA respectively over all channels within 60 minutes after soaking. However, the leakage currents of the polyimide based samples showed minute leakage current until 1200 minutes of soaking time, and after then, were measured differently between inner (~10 pA) and outer (~1 nA) channels after 1200 minutes of soaking.

Conclusions: : The 3-D polyimide electrodes and the hybrid electrodes have been developed and under long-term biocompatibility and in vivo stability evaluation. Acute and short-term experiment showed moderate results in electrical retinal stimulation. Proposed in vitro tests could be used to characterize the electrical reliability of various polymer based electrodes in biological environment.

Keywords: retina • electrophysiology: non-clinical • retinal adhesion