A novel additive manufacturing approach towards fabrication of multi-level three-dimensional microelectrode array for electrophysiological investigations

Traditional planar microelectrode arrays (MEAs) have contributed significantly to broaden our knowledge on neuronal electrophysiological signaling by enabling simultaneous recording and stimulation of intracellular activities. However, planar MEAs are not suitable for investigating the electrophysiological behavior of complex 3D neuronal cultures. To exploit the potential of these 3D cultures, more advanced tools are needed which can assess the network-wide electrophysiological activity of neurons in 3D space. In this work, we propose a novel approach to develop a multi-level 3D microstructured array built on a well-established planer MEA setup. Initially, a planer MEA is realized using standard photolithography and physical vapor deposition (PVD) technique. During fabrication of the planer MEA, circuitry is added to connect the planar microelectrodes separately into individual groups. In addition to it, an electroplating process is utilized to grow gold micro-pillars on the planar electrode pads using a chemically amplified negative photoresist (KMPR 1050) from Kayaku Microchem as the mold. The circuitry allows independent control of the heights of the individual groups of 3D multi-level gold microelectrodes on the array. The mold is then stripped off. The microelectrodes can be insulated with Parylene-C and crowned with spherical gold beads using the ball bonding technique. The spherical gold beads could act as the interface between the device and the neuronal culture. The spherical shape of the bead would allow omnidirectional growth of neuronal networks, better mimicking the in vivo growth patterns. Experiment work to record and stimulate the electrophysiological activities of neuronal networks is ongoing. All fabrication techniques utilized in this approach are well established, allowing the fabricated devices to be reproducible, cost-effective, and scalable.