An ultraflexible polyurethane yarn-based wearable strain sensor with a polydimethylsiloxane infiltrated multilayer sheath for smart textiles

Waterproof fiber-based strain sensors with a high gauge factor and outstanding stability are essential for smart textiles, wearable devices and biomedical electronics. In this work, we demonstrate a highly flexible, stretchable, sensitive, and waterproof core-sheath structure strain sensor with a relatively wide strain-sensing range fabricated by a simple approach. Such a core-sheath structure is composed of a superelastic core material polyurethane (PU) yarn; a highly conductive multilayer sheath material, namely, graphene nanosheets/thin gold film/graphene nanosheets (GNSs/Au/GNSs); and a thin polydimethylsiloxane (PDMS) wrapping layer. The combination of the PU yarn, multilayer GNSs/Au/GNSs, and PDMS wrapping layer enables the strain sensor to achieve high flexibility and stretchability, high sensitivity, broad strain-sensing range, and good waterproof property simultaneously due to the infiltration of PDMS into the multilayer during stretching. Particularly, the yarn strain sensor exhibits a high gauge factor (GF: 661.59), outstanding stability with an applied strain of 50% for approximately 10 000 stretch/release cycles, and superior water resistance. Moreover, it can be readily integrated into textiles, including medical textile bandages and textile gloves, for monitoring various human motions ( e.g. , phonation, pulse, finger bending, and walking) and effectively control a hand robot. Therefore, strain sensors show considerable potential in textile, wearable, and biomedical electronics for healthcare-related applications, such as disease diagnosis, preventive healthcare, and rehabilitation care, and robot controlling-related applications ( e.g. , controlling a hand robot to catch some objects). This paper proposes an ultraflexible polyurethane yarn-based strain sensor. It demonstrates superior performance and enormous potential in monitoring full-range human motions and manipulate a hand robot to move, catch, and grasp some objects.