"This is the first demonstration that you can use few-layer graphene and molybdenum disulfide to successfully fabricate an artificial retina," Nanshu Lu, Ph.D., says. "Although this research is still in its infancy, it is a very exciting starting point for the use of these materials to restore vision," she says, adding that this device could also be implanted elsewhere in the body to monitor heart and brain activities.
The retina, located at the back of the eye, contains specialized photoreceptor cells called rods and cones that convert incoming light into nerve signals. These impulses travel into the brain via the optic nerve where they are decoded into visual images. Various diseases can damage or destroy the retinal tissue, leading to vision loss or complete blindness. There is no cure for many of these diseases, but silicon-based retinal implants have partly restored vision in some cases. However, Lu says these devices are rigid, flat and fragile, making it hard for them to replicate the natural curvature of the retina. As a result, silicon-based retinal implants often produce blurry or distorted images and can cause long-term strain or damage to surrounding eye tissue, including the optic nerve. Lu, who is at the University of Texas at Austin, and her collaborator Dae-Hyeong Kim, Ph.D., who is at Seoul National University, sought to develop a thinner, more flexible alternative that would better mimic the shape and function of a natural retina.
The researchers used 2D materials, including graphene and molybdenum disulfide, as well as thin layers of gold, alumina and silicon nitrate to create a flexible, high-density and curved sensor array. The device, which resembles the surface of a flattened soccer ball, conforms to the size and shape of a natural retina without mechanically disturbing it.
In laboratory and animal studies, photodetectors on the device readily absorbed light and passed it through a soft external circuit board. The circuit board housed all of the electronics needed to digitally process light, stimulate the retina and acquire signals from the visual cortex. Based on these studies, the researchers determined that this prototype artificial retina is biocompatible and successfully mimics the structural features of the human eye. They say it could be an important step in the quest to develop the next generation of soft bio-electronic retinal prostheses.