Properties and behavior of carbon nanomaterials when interfacing neuronal cells: How far have we come?

In the last two decades, an increasing amount of studies have investigated the use of components based on carbon-(nano)materials in the engineering of neural interfaces, to improve the performance of current state of the art devices. Carbon is an extremely versatile element, characterized by a variety of allotropes and structures with different properties due to their sp, sp² or sp³ hybridization. Among the diverse carbon nanomaterials, carbon nanotubes and graphene are naturally excellent electrical conductors, thus representing ideal candidates for interfacing electrical-excitable tissues. In addition, their dimensional range holds the potential to enhance the material interactions with bio-systems. Successful interfacing of the nervous system with devices that record or modulate neuronal electrical activity requires their stable electrical coupling with neurons. The efficiency of this coupling can be improved significantly by the use of conductive, ad hoc designed, nanomaterials. Here we review different carbon-based nanomaterials currently under investigation in basic and applied neuroscience, and the recent developments in this research field, with a special focus on in vitro studies.