Constructing highly selective multidirectional hydrogel strain sensors with a pre-stretching strategy

Abstract

Multidirectional hydrogel strain sensors play a crucial role in detecting complex human motions. Despite extensive research efforts to enhance anisotropic sensing capabilities, current hydrogel strain sensors suffer from low selectivity (<1) due to incomplete segregation of conductive and insulating components. Herein, we present a highly selective hydrogel strain sensor in which a bilayer sensing structure is coated on the surface of a fatigue-resistant and environmentally adaptable hydrogel substrate for isolating the conductive network from the non-conductive matrix. The bilayer structure is formed through biaxial pre-stretching, followed by pre-stretching along the x-axis to create a wrinkled MXene layer at the bottom and a crack-wrinkled silver nanowire (AgNW) layer on top. The wrinkles in the MXene layer effectively bridge expanding cracks in the AgNW sensing layer when stretched along the y-axis to provide high sensitivity with a gauge factor (GF) of 575.51, while the wrinkles aligning perpendicularly along the x-axis direction contribute to an outstanding anisotropic selectivity of 7.93. To demonstrate its application, a multidirectional sensor fabricated using two hydrogel sensors is used to monitor multiaxial human joint movements and recognize sign language signs. This approach holds significant promise for next-generation flexible electronics, personalized healthcare monitoring, and advanced human–machine interfaces.