Conductive fiber-based free-standing grid electrodes for user-friendly facial muscle movement detection

Skin electrodes are increasingly employed not only in biomedical devices but also for continuous monitoring of users’ health and psychological states in daily life. This trend demand drives the need for developing highly user-friendly multi-purpose skin electrodes which require soft, conformable, breathable, and close-to-transparent electrical materials/structures, leading to stable electrophysiological recording and long-term wearing comfort on skin. Herein, we report a grid-structured PEDOT:PSS fiber net for user-friendly free-standing skin electrodes by judiciously self-fusing highly-conductive PEDOT:PSS fibers. Self-fused PEDOT:PSS fiber grids achieve both high optical transparency (>98%) and a low sheet resistance of ~100 Ω sq−1 through optimization of constituent fiber diameter and grid pitch. Simultaneously, the grid architecture remains stable under humid conditions and accommodates ~30% deformation with marginal electrical performance loss, enabling reliable acquisition of bioelectrical signal on skin in conjunction with electrospun PVA–PAA nanofibers soaked with ion gel for improved skin adhesion and guaranteed moisture permeability. The resultant transparent free-standing skin electrodes successfully record various types of bioelectrical signals (e.g., ECG, EMG, and EOG) with baseline noise levels comparable to conventional Ag/AgCl gel electrodes and a signal-to-noise ratio of up to ~30 dB for 3 days. Finally, they are capable of capturing facial muscle activities, highlighting the potential for user-friendly facial EMG recording/analysis and human emotion detection.