Magnetically induced anisotropic conductive hydrogels for multidimensional strain sensing and magnetothermal physiotherapy

In this study, we present the development of wearable electronic devices with integrated sensing and physiotherapy functionalities, aiming to advance flexible multidimensional strain sensors. The as-developed electronic devices are based on a composite hydrogel with unique anisotropic electromechanical properties and exceptional magnetothermal capabilities. Specifically, two-dimensional nanohybrids possessing both conductive and magnetic properties are induced to align orientationally within the polyvinyl alcohol (PVA) network through a magnetic field pre-induction strategy, resulting in the conductive hydrogels with anisotropic structures. The as-optimized composite hydrogel demonstrates distinct conductivities in the parallel and vertical directions, enabling the creation of a multidimensional strain sensor. This sensor is capable of accurately sensing strains in orthogonal directions, with distinguishable gauge factors (GF_∥ = 3.20, while GF_⊥ = 1.78) within the tensile strain range of 0 ∼ 60%. Additionally, the strain sensor exhibits a relatively fast response time (t_∥ = 74.47 ms, t_⊥ = 157.63 ms). Moreover, the composite hydrogel exhibits excellent magnetothermal physiotherapy capabilities, making it suitable for therapeutic applications. Furthermore, the conductive hydrogel can be assembled into a 3D distribution array, enabling the detection of both the magnitude and spatial distribution of stress. In summary, the anisotropic conductive hydrogel shows promise as a next-generation, multidimensional flexible strain and stress sensors with rehabilitation assistant functions.