Recent advances in materials and structural designs for flexible surface electromyography electrodes

Flexible electrodes play an essential role in collecting surface electromyography (sEMG) signals and are becoming a promising alternative and supplement to needle electrodes and rigid sEMG electrodes, featuring flexibility, wearability, and non-invasiveness. However, flexible electrodes face the challenges of high electrode–skin interfacial impedance and a tendency to detach under large and continuous deformation. This review outlines the latest advancements aimed at minimizing contact impedance and improving electrode contact stability, primarily achieved through two fundamental aspects: the optimization of materials and the design of structures. Materials are categorized into metals, carbon, and conductive polymers, along with recent practical applications in flexible sEMG electrodes. Several advanced structural designs are summarized considering two key challenges in improving interfacial contact stability: electrode stretchability and interfacial contact quality. Finally, this review discusses the future directions for developing flexible sEMG electrodes and the subsequent challenges expected to arise in this field.