Neural prostheses are devices integrated with the neural tissue for diagnostic or therapeutic purposes. Despite a large variety of devices exists, a shared future is the presence of cables connecting the electrode-tissue interface to implantable electronic circuits for signal management. The presence of wires and connectors is a significant disadvantage for neural prostheses often leading to failure; they exert mechanical forces and tractions on the implant and the tissue, and they are often transcranial or transcutaneous connections that might lead to post-surgical complications, such as infection. Also, the use of implantable electronic units is another disadvantage. Several aspects limit their operation, such as power consumption, excessive heat generation, and high risk of failure in a wet environment due to leakage.

In neural prostheses, wireless electrodes are desirable. Retinal prostheses are a particular category of neural prostheses, in which wireless neuronal stimulation was achieved thanks to photovoltaic technology, that also avoids the need for active implantable electronic units. In the case of retinal stimulation, photovoltaic technology is intuitive since the retina is made to absorb light entering from the pupil naturally. Although photovoltaic retinal prostheses do not work with ambient and natural light, electrical stimulation is triggered by artificial light projected into the pupil and absorbed by semiconductor elements embedded into the stimulating pixels. This solution allows retinal prostheses to avoid a transscleral flat cable which limits the maximum number of stimulating pixels on the device and induce post-operative complications such as eye inflammation or leakage through the incision.

In the first part of this talk, a wide-field, photovoltaic, and injectable retinal prosthesis will be reported. POLYRETINA is a wide-field epiretinal prosthesis which contains more than 10k photovoltaic electrodes distributed over a large area with high pixel density. The results obtained both in-vitro with retinal explants and in-vivo with large animal models will be reported.

In the second part of the talk, a novel visual prosthesis based on intra-neural stimulation of the optic nerve will be described. OpticSELINE is an intraneural 3D electrode array capable of selectively activating the optic nerve fibres to induce artificial vision. This technology is essential to overcome the exclusion criteria of retinal implants. The results from our in-vivo preclinical trial in large animals will be presented.

In conclusion, the use of photovoltaic technology to design novel neuroprostheses will be highlighted.