Biological performance evaluation of graphene nanoplatelets for intracranial direct current stimulation

Graphene nanoplatelets (GNPs) offer promising properties for neural interface applications, particularly in intracranial direct current (DC) stimulation, due to their high charge injection capacity, flexibility, and biocompatibility. In this study, we comprehensively evaluate the biological and functional performance of GNP-based electrodes for acute and chronic cortical stimulation and recording. GNP electrodes were fabricated via screen-printing on flexible polyimide substrates. They were assessed for cytotoxicity using RAW 264.7 macrophage cell lines and primary hippocampal cultures, showing no evidence of cell death or toxicity. Long-term implantation in non-human primates (50 days) revealed no signs of infection, inflammation, or cortical damage, supporting the biostability of the material. Magnetic resonance imaging confirmed that GNPs produce no imaging artifacts, affirming their compatibility with standard neuroimaging protocols. Functionally, epidural DC stimulation using GNP electrodes modulated neuronal firing rates in the auditory cortex in a polarity-dependent manner, consistent with classical effects of DC stimulation. Furthermore, the same electrodes reliably recorded auditory-evoked potentials, demonstrating dual functionality for stimulation and recording. These findings position screen-printed GNP electrodes as safe, versatile, and effective tools for neurophysiological applications, and highlight their potential for future use in translational neuroscience and neurotherapeutic settings.