A Flexible Inkjet-Printed Three-Dimensional Microelectrode Array Enables Neural Recordings in a Locust Ganglion

Microelectrode arrays (MEAs) are widely used for electrophysiological studies, but conventional planar MEAs lack capabilities for penetration into 3D biological systems. In this work, we fabricated an inkjet-printed 3D MEA on a flexible thin film. The bottom structure of the MEA, including pads and traces, was fabricated by standard lithography in a clean room. Subsequently, silver shanks were inkjet-printed on top of the planar structure, followed by the deposition of parylene-C for insulation. Tips were opened using laser or focus ion beam (FIB) technology for accurately defining the electrode positions. Gold galvanization on the electrodes was employed to avoid tissue exposure to silver ions. We achieved a high aspect ratio (> 30), and the laser-ablated shanks showed an impedance of around 100 kΩ at 1 kHz after gold galvanization. FIB-generated microelectrodes on the tips show better insulation properties of parylene on exposed silver electrodes compared to laser-ablated tips due to the highly defined ablation process. As a proof of principle, we implanted the device in a locust ganglion, which controls the movements of the legs. Our 3D MEA allowed the recording and stimulation of neuronal activity, demonstrating that this platform facilitates studies in small animal models.