Clarification of degradation mechanism on retinal prosthesis using photoelectric dyes coupled to polyethylene film by mass spectrometry

Photoelectric dyes have stimulated retinal neurons by absorbing light and generating an electric potential. Therefore, a photoelectric dye was used to develop a retinal prosthesis to restore vision loss due to retinitis pigmentosa. The retinal prosthesis, referred to as a dye-coupled film, was prepared by chemically coupling the dyes to a polyethylene film surface through amide bonds. However, the coupled dyes decreased during an implantation test in a monkey eye. This study clarifies the degradation mechanism of the dye-coupled film. Since the dyes were selectively coupled to the film surface, it is difficult to detect the eliminated dyes in a solution. Therefore, a model compound that mimicked the chemical structure of the dye-coupled film by converting the carboxylic acid of dye to the amide bond is used. It was found that the elimination of the side chain, including the amide bond, occurred before the degradation of the conjugated structure according to mass spectrometry of the model compound. The degradation mechanism of the dye-coupled film was predicted based on that of the model compound. It was concluded that chemical bonds between the dye and the film surface were preferentially decomposed, leading to the detachment of the dyes from the film surface.