Injectable Photoacoustic Hydrogel for Minimally Invasive Retinal Prostheses

Retinal prostheses aim to restore vision in patients with vision loss due to photoreceptor degeneration by stimulating the remaining retinal cells. Current retinal prosthesis technologies require surgeries to implant electrodes or photovoltaic devices in the retina. Additionally, due to the limited sclerotomy size allowed, rigid solid-state retinal prostheses provide a narrow visual angle, below the minimum 30-degree retinal coverage necessary for normal mobility tasks and navigation-related activities. Alternatively, photoacoustic neural stimulation has been emerging as a high-precision non-genetic method, and hydrogel-based photoacoustic materials have been developed for successful neural stimulation. Here, we introduce an injectable retinal prosthesis design based on a PEG-based double-network hydrogel. We have shown the injectable photoacoustic materials developed can be injected into the epiretinal space and form stable films with high photoacoustic conversion efficiency upon in-situ cross-link. Robust ex vivo retinal stimulation was demonstrated in rodent retina samples with multielectrode array recording. A temperature rise of less than 2°C was found to be associated with the photoacoustic stimulation, suggesting a non-thermal modulation mechanism and minimal thermal irritation. Overall, the injectable photoacoustic film presents a promising approach as a minimally invasive retinal prosthesis, offering the potential to restore vision with a field of view greater than 60 degrees.