Current materials for 3D-printed flexible medical electrodes

Electrodes serve as essential tools for both acquiring and stimulating electrical signals, pivotal in monitoring human health through electrophysiological signals and playing a significant role in disease management and treatment. Notably, Young's modulus of flexible electrodes is similar to that of tissues and organs, thereby avoiding tissue or organ damage arising from mechanical mismatch. Thus, flexible electrodes become the fundamental devices for ensuring the stable, long-term acquisition of electrical signals and delivering reversed electrical stimulation to guide disease treatment. Reducing the size of flexible electrodes and increasing the number of electrode channels are significant for improving the sensitivity and accuracy of signal acquisition. In comparison to traditional manufacturing methods, 3D printing technology is able to fabricate products with higher resolution at a much faster speed. It is customizable and provides a novel approach for preparing flexible electrodes. Many conductive materials have been developed and applied to prepare flexible electrodes, and some have been integrated into 3D printing techniques, driving forward the development of 3D-printed flexible electrodes in medical fields. This article reviews recent research advances concerning the combination of these materials with 3D printing technology to prepare flexible electrodes and categorizes the materials into four main groups, namely metallic materials, carbon-based materials, conductive polymers, and other materials. In addition, we outline the future directions regarding the application of 3D-printed flexible electrodes in clinical research and medical translation.