Development and chemical properties of retinal prostheses using photoelectric dyes coupled to polyethylene films with various anions to achieve high durability

Photoelectric dyes, which absorb light and generate electric potential, have been shown to stimulate retinal neurons. Therefore, in the present work, a photoelectric dye was used to develop a retinal prosthesis to restore vision loss due to diseases, such as retinitis pigmentosa. The retinal prosthesis, referred to as a dye-coupled film, was prepared by chemically coupling the dyes to a polyethylene film surface. However, the amount of coupled dye decreased during an implantation test in a monkey’s eye. The dye consisted of a cation with photoresponsivity and Br⁻. Because thermal stability can be improved by anion exchange, we expected anion exchange to lead to stabilization of the chemical structure, resulting in improvement of the long-term durability of a retinal prosthesis. Therefore, the effects of exchanging Br⁻ anions for PF₆⁻, BF₄⁻, and bis(trifluoromethanesulfonyl)imide (TFSI⁻) anions on the durability were investigated. The long-term durability of the dye-coupled films was found to be strongly related to the thermal stability of the photoelectric dye. The long-term durability of the dye-coupled film–PF₆⁻ and dye-coupled film–TFSI⁻ improved by 637 and 215%, respectively, compared with that of the dye-coupled film–Br⁻.