3D-Microelectrode Arrays (MEAs) for In Vitro Applications

<u><b>Abstract:</b></u><br/>In the realm of 3D cell cultures and organoids, capturing electrical activity across multiple planes is essential for a comprehensive understanding of their behavior. Conventional microelectrode arrays (MEAs) with surface recordings fall short in addressing this requirement. The limitations of clean-room methods restrict electrode design possibilities and can impede effective cell-electrode coupling. To tackle this challenge, we present a novel approach that leverages rapid prototyping processes to enhance electrode fabrication. Our laser-patterned MEA incorporates printed 3D-electrode structures, enabling precise recording and stimulation within cell tissues. This advancement improves signal quality through enhanced cell-electrode coupling and provides greater flexibility in electrode placement. We believe this innovative approach will significantly contribute to improvements in 3D cell cultures and organoids, opening new avenues for understanding complex biological systems and developing targeted therapeutic interventions.<br/><b><u>Introduction:</u></b><br/>Standard planar MEAs can only record electrophysiological signals in 2D, making them unsuitable for capturing the complexity of emerging 3D cell cultures or organoids [1]. To overcome this limitation, we design and fabricate 3D MEAs using additive manufacturing techniques [2]. These 3D MEAs hold promise for studying neuronal functions and diseases using neuronally differentiated human-induced pluripotent stem cells (hiPSC) in vitro.<br/><u><b>Results and Discussion:</b></u><br/>Here, we present the microfabrication of our 3D MEAs. In the first step, silver ink pillars are printed on suitable substrates, followed by sputtering with gold to create a biocompatible electrode interface. Individual electrodes and feedlines are then generated through laser ablation, with feedline structures patterned within minutes, representing a significant improvement over conventional lift-off techniques. The chips are fully passivated with a parylene C layer deposited via vapor deposition. Laser ablation at different angles is used to open the tips of the pillars precisely, and partial etching is employed to create tubular structures. In the final step, individual pillars undergo stepwise electroplating with gold and PEDOT:PSS to prevent silver contamination during long-term cell culture. Our fabrication method offers a fast and easily adjustable approach compared to traditional clean-room techniques. Using the inkjet printing process with laser ablation and electroplating, the height of each pillar can be accurately determined. This enables the realization of multiple pillars with various heights on a single chip. Moreover, the design of the MEA aligns the electrodes in a manner that simplifies their insertion into organoids or 3D cell models. With this highly flexible approach, we aim to record cellular signals from various planes within the targeted tissue.<br/><u><b>Conclusion:</b></u><br/>This work demonstrates a process for fabricating MEAs with integrated 3D electrodes, providing a platform that facilitates recording and stimulation within 3D cell aggregates or organoid models.<br/><b><u>References:</u></b><br/>[1] D. A. Soscia, D. Lam, A. C. Tooker, H. A. Enright, M. Triplett, P. Karande, S. K. G. Peters, A. P. Sales, E. K. Wheeler, N. O. Fischer, Lab. Chip. 2020, 20, 901 - 911.<br/>[2] L. Grob, P. Rinklin, S. Zips, D. Mayer, S. Weidlich, T. Korkut, L. J. K. Weiß, N. Adly, A. Offenhäusser, B. Wolfrum, Sensors. 2021, 21, 3981.<br/><u><b>Acknowledgments:</b></u><br/>We acknowledge funding from the BMBF (within the project PRISTINE).