Multi-Conductive Layer Flexible Bioelectronic Implants for Neural Recording and Stimulation

Advancements in flexible bioelectronic implants are enhancing minimally invasive neural activity recording and stimulation. Increasing electrode density by superimposing conductive leads, is one of the major approaches for fabrication of high-resolution implants. The superimposition can enhance the number of electrodes without increasing device width, but this introduces crosstalk issues due to capacitive coupling (CC). We present an investigation into CC in devices containing multi-gold layer thin-film arrays, based on PEDOT:PSS electrodes, and with parylene C (PaC) insulation layer between leads. These results show that capacitance due to CC decreases non-linearly and then linearly with increased insulation thickness. We identify an optimal PaC thickness that reduces CC without significantly increasing device thickness. We developed multilayer electrocorticography implants with the optimal insulation. They exhibit an <i>in vivo</i> performance comparable to single-layer devices, confirming their suitability for high-quality recordings. Additionally, we demonstrate that depth implants with the same architecture offer alternatives to conventional rigid devices for chronic brain stimulation, thanks to high charge injection capacity and better tissue compliance. We developed intracortical depth implants targeting the rat hippocampus for safe and extended micro-stimulation and recording. Acute <i>in vivo</i> experiments identified parameters for maximal LFP generation in CA1 in response to electrical stimulation of Schaffer collaterals. A 16-day study in freely moving rats demonstrated consistent LFP generation in CA1 in response to axonal stimulation in Stratum Radiatum. Together, our results demonstrate an excellent performance of flexible bioelectronic implants for acute and chronic stimulation and recording, as well as their high potential in neuroscience research.