In vitro and in vivo long-term electrochemical properties of electrodes with femtosecond-laser-induced porosity for visual prostheses based on suprachoroidal transretinal stimulation

We developed a visual prosthesis based on suprachoroidal transretinal stimulation (STS) using electrodes with femtosecond-laser-induced porosity (FLiP electrodes). A current of 1.5 mA (1.25 times higher than that of a device under development) was applied by STS in six rabbits for 6 months to evaluate the long-term changes in the electrochemical properties of FLiP electrodes in vivo. The long-term stability of the FLiP electrodes was determined by in vitro and in vivo evaluations. The performance of the electrodes did not deteriorate after the long-term application of electrical stimulation in vivo. As no difference was observed between the in vivo electrochemical performance of the electrodes to which the stimulation current was and was not applied during the experiment, it is confirmed that the FLiP electrodes exhibit sufficient safety performance under long-term stimulation both in vivo and in clinical use. However, variations in the characteristics of the electrodes owing to the manufacturing method of the FLiP electrodes were observed. This variation should be reduced during the manufacturing process to avoid side effects owing to unexpected electrochemical behavior in clinical use. This result is useful in understanding the long-term safety testing results of STS-based retinal prostheses with FLiP electrodes.