Inkjet-Printing of Nanoparticle-Based Flexible Electrode Arrays

Abstract

Introduction Electrode systems are well-established tools to interface electronics with either cell cultures, tissue, or the human body. Applications include electrophysiological characterization of cells and tissues in vitro, measurement of electromyograms (EMGs) on the skin, active neural implants, and many more. However, conventional microelectrode arrays (MEAs) are primarily rigid, leading to tissue damage and immunological reactions. Furthermore, they are mainly reliant on time-consuming and costly cleanroom-based processes. Therefore, we seek to address these challenges by implementing additively manufactured inkjet-printed electrodes on flexible substrates. Methods The inks used in this work were rheologically characterized and printed with a commercial inkjet printer equipped with Dimatix Samba cartridges with a drop volume of 2.4 pl. We determined various printing parameters, i.e., printing speed and drop spacing, for conductive and dielectric ink printing parameters on flexible substrates, i.e., polyimide. We assessed the properties of our fine-printed lines by electrical analysis with impedance spectroscopy and four-point measurements, dimensional measurements of height and width, and optical analysis using bright-field microscopy. Results We were able to print conductive lines, which also define the minimal electrode dimension of about 60 μm. Printing of insulators, i.e. SU-8, was achieved at the same dimension. We obtained specific resistivities in the range of published values for certain conductive inks, i.e., silver nanoparticle ink. Conclusion We show that inkjet-printed electrode arrays are feasible on flexible substrates. In future experiments, we will use them for electrophysiological recordings and stimulation.