Next-generation wearable sensors: toward multi-directional strain sensing in sensory integration platforms

Wearable technologies and flexible electronics have developed rapidly owing to the emergence of cutting-edge cross-disciplines. The flexibility and tunable properties of organic materials enable wearable sensory systems to adapt to complex surface deformations and detect physiological signals sensitively. The demand for high-performance strain sensors, to accurately detect complex movements and environmental changes, in wearable technology has increased notably. However, current sensors primarily detect strain in a single direction, which restricts their effectiveness in detecting multi-directional strains, such as in natural human movements or robotic joints. In this review, we examine the advances and future challenges that may arise in the development of strain sensors that can measure both the magnitude and direction of external tensile strain. Additionally, we examine the sensor materials (platform and sensing materials) required to develop a strain sensor to detect the direction of tension, structural research on strain sensors, and various application fields such as human motion detection and human–machine interaction via system integration. Finally, we discuss the prospects and current challenges involved in the development of direction-selective strain sensors for wearable smart electronic systems or electronic skin. This review should provide a comprehensive reference for future technologies.