Vision is an extraordinary sense through which we can appreciate the beauty of the world we live in, gain invaluable knowledge and communicate with others using visual expression and arts. On the contrary, blindness is a threatening medical condition disrupting the life of affected people and their families. Therefore, restoring sight is one of the open challenges of our society. Today, the synergistic convergence of science and technology holds the potential to provide blind patients with artificial vision using visual prostheses: a type of implantable medical device able to reactivate visual neurons using electrical stimulation. Although clinical trials showed that vision restoration is still far away, significant technological advances make visual prostheses a valuable solution for blind patients. This review is not only a description of the state-of-the-art. Instead, it provides the reader with an update on recent developments, a critical discussion of the open challenges, and an overview of promising future directions.

Bioelectronic and neuroprosthetic interfaces rely on implanted microelectrode arrays (MEAs) to interact with the human body. Printing techniques, such as inkjet and screen printing, are attractive methods for the manufacturing of MEAs because they allow flexible, room‐temperature, scalable, and cost‐effective fabrication processes. Herein, the fabrication of all‐printed electrocorticography arrays made by inkjet printing of platinum and screen printing of polyimide is shown. Next, mechanical and electrochemical characterizations are performed. As a proof of concept, in vivo visually evoked cortical potentials are recorded in rabbits upon flash stimulation. Lastly, it is shown that the all‐printed electrocorticography arrays are not cytotoxic. Altogether, the results enable the use of printed MEAs for neurological applications.

Objective. Optic nerve’s intraneural stimulation is an emerging neuroprosthetic approach to provide artificial vision to totally blind patients. An open question is the possibility to evoke individual non-overlapping phosphenes via selective intraneural optic nerve stimulation. To begin answering this question, first, we aim at showing in preclinical experiments with animals that each intraneural electrode could evoke a distinguishable activity pattern in the primary visual cortex. Approach. We performed both patterned visual stimulation and patterned electrical stimulation in healthy rabbits while recording evoked cortical activity with an electrocorticogram array in the primary visual cortex. Electrical stimulation was delivered to the optic nerve with the intraneural array OpticSELINE. We used a support vector machine algorithm paired to a linear regression model to classify cortical responses originating from visual stimuli located in different portions of the visual field and electrical stimuli from the different electrodes of the OpticSELINE. Main results. Cortical activity induced by visual and electrical stimulation could be classified with nearly 100% accuracy relative to the specific location in the visual field or electrode in the array from which it originated. For visual stimulation, the accuracy increased with the separation of the stimuli and reached 100% for separation higher than 7°. For electrical stimulation, at low current amplitudes, the accuracy increased with the distance between electrodes, while at higher current amplitudes, the accuracy was nearly 100% already for the shortest separation. Significance. Optic nerve’s intraneural stimulation with the OpticSELINE induced discernible cortical activity patterns. These results represent a necessary condition for an optic nerve prosthesis to deliver vision with non-overlapping phosphene. However, clinical investigations will be required to assess the translation of these results into perceptual phenomena.

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