Charge Injection Capacities of Femtosecond Laser-induced Porous Electrodes measured in vitro and in vivo: Comparison between porous and smooth electrodes

Abstract

Purpose: We have been developing retinal prosthesis based on Suprachoroidal-Transretinal Stimulation (STS). We also reported a Femtosecond Laser-induced Porous Electrodes (FLiP electrodes) as large-surface-area stimulating electrodes for STS [Terasawa et al., ARVO E-abstracts 5538, 2012]. The purpose of this study is to quantify the increase of charge injection capacities (CICs) of FLiP electrodes.

Methods: An electrode array with two stimulating electrodes was developed for this study. The diameter and height of an electrode were 0.5mm and 0.3mm respectively. Two different versions of arrays were developed, ones with FLiP electrodes and the others with smooth-surface electrodes. Charge injection capacities as well as cyclic voltammograms and impedance spectra were obtained in phosphate-buffered saline (PBS) before implantation, in vivo before electrical stimulation, in vivo after one-month stimulation, and after explantation in PBS. The in-vivo experimental details were described elsewhere [Terasawa et al, proceedings of IEEE EMBC, pp.3567-3570, 2013]. In brief, the electrode array was inserted into a scleral pocket of a rabbit eye and sutured onto the sclera. Charge-balanced biphasic pulses were applied to one of two electrodes on the array eight hour per day for one month. All in vivo experiments were conducted in accordance with the ARVO statement for the use of animals and institutional guidelines.

Results: The CICs measured in vivo were an order of magnitude lower than those measured in vitro. This was consistent with previous studies. The gain of CIC by femtosecond laser irradiation, described as the ratio of the CIC of a FLiP electrode divided by that of a smooth-surface electrode, were 6.2 (in PBS before implantation), 8.0 (in vivo before stimulation), 5.2 (in vivo after one-month stimulation), and 7.2 (in PBS after explantation) respectively. No significant differences were detected between activated electrodes and inactivated electrodes.

Conclusions: The gain of CIC decreased after one-month implantation, which suggested that some part of porous surface was covered with biological tissue. Nonetheless, the CIC of FLiP electrodes kept five times higher than those of smooth-surface electrodes. This suggested that electrode surface modification with femtosecond laser was a promising approach to increase CIC both in vitro and in vivo.

Keywords: 688 retina