Retinal dystrophies such as Retinitis pigmentosa are among the most prevalent causes of inherited legal blindness, for which treatments are in demand. Retinal prostheses have been developed to stimulate the inner retinal network that, initially spared by degeneration, deteriorates in the late stages of the disease. We recently reported that conjugated polymer nanoparticles persistently rescue visual activities after a single subretinal injection in the Royal College of Surgeons rat model of Retinitis pigmentosa. Here we demonstrate that conjugated polymer nanoparticles can reinstate physiological signals at the cortical level and visually driven activities when microinjected in 10-months-old Royal College of Surgeons rats bearing fully light-insensitive retinas. The extent of visual restoration positively correlates with the nanoparticle density and hybrid contacts with second-order retinal neurons. The results establish the functional role of organic photovoltaic nanoparticles in restoring visual activities in fully degenerate retinas with intense inner retina rewiring, a stage of the disease in which patients are subjected to prosthetic interventions.
Although the efficiency
of organic polymer-based retinal devices
has been proved, the interpretation of the working mechanisms that
grant photostimulation at the polymer/neuron interface is still a
matter of debate. To contribute solving this issue, we focus here
on the characterization of the interface between poly(3-hexyltiophene)
films and water by the combined use of electrochemistry and mathematical
modeling. Simulations well reproduce the buildup of photovoltage (zero
current condition) upon illumination of the working electrode made
by a polymer film deposited onto an indium tin oxide (ITO) substrate.
Due to the essential unipolar transport in the photoexcited film,
diffusion leads to a space charge separation that is responsible for
the initial photovoltage. Later, electron transfer reactions toward
oxygen in the electrolyte extract negative charge from the polymer.
In spite of the simple model studied, all of these considerations
shed light on the possible coupling mechanisms between the polymeric
device and the living cell, supporting the hypothesis of pseudocapacitive
coupling.
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