Conductive Gels for Wearable and Attachable Healthcare Devices: Materials, Sensing Mechanisms, Interfaces and Applications

Wearable and attachable healthcare devices provide valuable insights across a broad range of applications, from health monitoring and disease diagnosis to the assessment of daily human activities. For these devices, both the formation of high-performance electrodes and mechanical, electrical, and physiological stability at human-device interfaces are critically important. Conductive gels, which combine deformable polymer networks with electrical conductivity, show considerable potential as functional materials for such applications. However, existing reviews have often considered material properties, interfacial behavior, and device reliability separately. This review examines hydrogels, ionogels, and organogels by linking material design, stimulus- and analyte-responsive sensing, biological and device interfaces, and healthcare applications. This integrated perspective emphasizes evaluating conductive gels within complete healthcare devices, where material properties, biological interfaces, and device integration jointly determine practical performance. Such evaluation needs to address signal quality and the stability of the assembled system during deformation, environmental exposure, and prolonged use. Future progress will require reproducible device fabrication and standardized validation tailored to the intended application, with systematic assessment of long-term biosafety and alignment with relevant regulatory requirements. Integration with flexible electronics, intelligent data processing, and feedback control may further enable reliable and responsive healthcare platforms.