Organic semiconductor reverses blindness in rats

The researchers were able to insert the prosthetic siconductor implant into the retina of rats with degenerative blindness, without damaging the eyes, where it then stimulated retinal neurons. These neurons transmitted signals to the brain and eventually led to restored vision.Previous attpts at similar implants have been hampered as most have required a power supply, and wiring into the eyeball is incredibly complex and risky. One solution has been a photovoltaic cell that generates voltage from incoming light, however, there is generally not enough ambient light to stimulate the neurons, and the silicon material the cell is made out of is much stiffer than nervous tissue.Materials scientist Guglielmo Lanzani, from the Centre for Nano Science and Technology in Genoa, navigated this probl by designing a more flexible organic implant derived from a polymer solar cell. A thin layer of conductive polymer was deposited on a silk-based substrate covered with a siconducting polymer.As the siconductor absorbs a photon it generates an electron-hole pair called an exciton. The positive holes are then absorbed in the conducting polymer, while electrons stay in the siconductor to create a negative charge.{{image2-a:r-w:400}}A team of ophthalmologists surgically implanted the device under the retina of rats at the Royal College of Surgeons (RCS). These rats belonged to a strain of mouse that developed RP as a result of a genetic mutation similar to reported cases of the disease in some humans.The siconductor devices were implanted in a way that ensured there was contact with the retinal neurons, in order for a negative charge to be applied to the cells as it absorbed light. After 30 days, the team conducted vision tests with the test rats, untreated RCS rats, and healthy rats.The results of the tests showed that light sensitivity and visual acuity were significantly better compared to untreated RCS rats. Results of a positron ission tomography also showed that metabolism of the primary visual cortices of treated rats were higher. Additionally, light tests showed the treated rats – which were naturally drawn to darker environments – avoided light more effectively than untreated ones.Later tests also showed almost the same level to light sensitivity and visual acuity after 180 and 300 days, despite the declining quality of the implants over time.However, several experts, were skeptical about the findings given the instense light the scientists used to test the implant. They also pointed out that the untreated RCS rats responded to every visual test, indicating they still had photoreceptors.Nonetheless, according to one of the lead researchers, neuroscientist Mr Fabio Benfenati, they are now testing an adapted implant in pig eyes: “We believe, based on these data, we could probably attpt the first [human] implant…within the next two years.”