Short-term electrostimulation enhancing neural repair in vitro using large charge capacity nanostructured electrodes

Abstract

Electrostimulation of the neural system in functional or repair therapies requires new materials that protect the living system from electric field (EF) effects at the interface. Intercalation materials offer an alternative to radical formation during stimulation. Furthermore, nanostructuring of the electroactive material used as electrode offers an enlargement of the charge capacity which in turn involves changes in the EF effect. In this work, electric field stimulation of cortical neuron cultures has been applied in an in vitro model of lesion, namely, a physical scratch in the cell culture creates a cell-free area reminiscent of a lesion where new neurites grow. Regeneration of the “wound” zone upon EF stimulation is observed for various types of electrode materials, and compared to the spontaneous process and to platinum electrodes. Significantly, electric field effects are highly dependent on the electrode material used, even for the same charge delivered and similar impedance values. Electrode coatings with large charge storage capacity yield significantly better results than that of bare Pt electrodes. Neurite outgrowth at the scratched “wound” zone is lowest, below spontaneous regeneration, when using Pt electrodes. On the other hand, electroactive materials, such as bilayers of PEDOT and polypyrrole with lysine counterions or iridium oxide-pristine graphene hybrids, promote further regeneration. Beyond impedance considerations, the optimal material is the nanostructured one with the largest charge capacity, even at low charge deliveries. It is remarkable that IrOx-graphene hybrids reach regenerations above spontaneous case in very short stimulation times, for equal charge deliveries and potential protocols. The implications from the results suggest that EF application using these new coatings, may have an immediate use in safer electrostimulation procedures, and open routes for much needed neural repair.