Flexible dry electrodes for electrocardiographic monitoring: Working principles, design strategies, and recent advances

The electrocardiogram (ECG) signal relies heavily on electrode performance, where flexible electronic materials play a crucial role. Flexible dry electrodes (FDEs), characterized by their skin-like Young's modulus and adhesion to biological interfaces, have emerged as an ideal solution for long-term, dynamic ECG monitoring. To fully explore their potentialities, an in-depth understanding of their working principles of both single-lead and multi-lead ECG monitoring systems is deeply examined, together with various ECG leads and electrode suitability. The design strategies for FDEs are analyzed, focusing on material selection and structural optimization and their impact on electrode performance. Furthermore, cutting-edge advances, such as e-skin/tattoo electrodes, textile-based electrodes, and microarray electrodes, are highlighted, emphasizing their clinical and practical significance. Finally, challenges in signal stability, environmental adaptability, and long-term usability are discussed, and the future directions for next-gen ECG monitoring solutions are proposed. This review aims to outline a roadmap for developing high-performance, user-centered ECG electrodes.