Wearable Strain Sensor With a Graphene Localized Warping Structure for Ultra-Wide Range Strain Detection and Bending Direction Recognition

The practical need for the accurate detection of human activities requires wearable flexible strain sensors that can detect subtle and large strains and recognize the bending direction of joints. However, it remains challenging to integrate these detection capabilities into a single strain sensor. Herein, we prepared flexible strain sensors with firmly attached locally warped graphene on the surface of anhydride-grafted styrene-butadiene-styrene triblock copolymer films using a swelling-self-assembly method. The unique localized warpage structure of graphene sheets gives the sensor excellent strain response performance and the ability to recognize the bending direction. The detection limit of the sensor to strain is independent of the sensitivity to strain, which allows it to detect ultralow (0.01%) and large strains (500%). Moreover, the sensor has a large linear response range (0%–94%) and good test stability (3000 cycles of strain). The sensor can be used to recognize the bending direction by generating opposite response signals to different bending directions. The excellent response behavior allows the sensor to accurately monitor the joint bending angle, the direction of the human body, and subtle tremors of the human skin, which makes it a potential application for wearable devices and smart prosthetics.