Collective Summary of in vivo Experiments of Sub-Retinal Implantation of Microfabricated Electrode Arrays in Pigs

Abstract

Purpose: : This work is related to the efforts of the Boston Retinal Implant Project to develop a sub-retinal prosthesis to restore vision to the blind. The specific purpose of this report is to provide a summary of anatomical and electrical behavior outcomes of implantation of electrode arrays designed for a retinal prosthesis.

Methods: : Fourteen Yucatan mini-pigs were used for these experiments. Survival times extended to three months for anatomical studies and up to three months for studies of the electrical behavior of the arrays. An ab externo surgery was used to implant ultra-thin, microfabricated arrays; SU-8 plastic arrays with 3-D pillars were used for biocompatibility studies; arrays with metallized planar electrodes with IrOx coating were used for electrical studies. Serial sections of the SU-8 implants were used for biological studies. Electrical behavior included measurements of the passive and active properties of the electrodes, including open-circuit potentials, impedance and cyclic voltammetry.

Results: : All but one surgery was successful. One of the thirteen survival animals developed an intraocular infection. Retinal histology showed full integration of the total length of the pillars (75µm) into the retina without significant gliosis. Electrical studies revealed higher access voltages than comparable in vitro experiments but excellent charge injection performance over months.

Conclusions: : Penetrating structures incorporated well into retinas of large animals. The electrical performance of the IrOx electrodes provided stable charge injection over months of implantation that substantially exceeds the needs for human perception with a retinal prosthesis.

Keywords: retina • retinitis • age-related macular degeneration