Toward Flexible Parylene–Based Intraocular Retinal Prostheses

Abstract

Purpose: : To characterize the surgical feasibility, structural integrity, electrical properties, and water–resilience of prototype parylene–based intraocular retinal prostheses.

Methods: : All animal experiments conformed to the ARVO guidelines for animal use. Parylene C–based surgical test structures designed for porcine and canine eye implantation, comprising a flexible radio–frequency (RF) coil region, a flexible cable with embedded thin–film platinum wires, and a stimulation electrode array with platinum electrodes, were microfabricated. Post–process annealing was performed to optimize parylene–parylene adhesion. The line impedances for coil–electrode–coil circuits were determined and the prosthesis structure was then introduced through a corneal incision such that the RF coil region was implanted in the sulcus or lens capsule with a flexible cable connection to the epiretinal electrode array region. Post–surgical line impedances were analyzed after removal to determine if there had been any damage to the embedded lines or electrodes during implantation. Accelerated–lifetime 77°C saline soak tests on test structures and pulse tests of the electrodes were performed to analyze the effects of the annealing process on parylene–parylene adhesion.

Results: : Pre–surgical coil–electrode–coil circuit impedances fell into two groups based on the physical lengths of these circuits, the shorter having a mean impedance of 135 Ω and the longer having a mean impedance of 152 Ω. Surgical implantation in each animal model was successful, demonstrating the surgical feasibility of a parylene–based complete intraocular system. Post–surgical testing of the electrical characteristics of the circuits revealed mean impedances of 136 Ω and 154 Ω for the short and long circuits, respectively, with no lines having been broken during the surgical procedures. The annealing process was shown to optimize the parylene–parylene adhesion for 1 year under the soak conditions in contrast to the unannealed samples. Pulse–tests demonstrated ideal electrochemical characteristics of the thin–film electrodes.

Conclusions: : Progress has been made toward demonstrating the feasibility of parylene–based intraocular retinal prostheses. Test structures held up admirably to physical stresses imposed upon them during surgical implantation, and annealed test structures demonstrate no interfacial delamination under accelerated–lifetime conditions.

Keywords: retina • retinal degenerations: hereditary • vitreoretinal surgery