Highly stretchable, robust, sensitive and wearable strain sensors based on mesh-structured conductive hydrogels

With the rapid development of wearable electronic devices, flexible sensors, as the core components of wearable devices, have received extensive attention. Manufacturing of the strain sensors with excellent mechanical properties, wide working range, and high sensitivity is crucial for the development of wearable devices. Herein, for the first time we proposed a strategy based on mesh-structured conductive hydrogel to sensitively detect the body movement in a large workable strain ranges, and demonstrated the facile fabrication procedure of the sensors by using a direct ink writing 3D printing technique. Low cost conductive hydrogels were prepared by a simple one-pot method of combining dispersant-free carbon nanocolloids with easily synthesized PVA/TA/PAM. The printing of complex mesh-structured hydrogels was optimized with high fidelity. The strain sensor based on the mesh-structured hydrogel exhibited excellent mechanical properties, of which the maximum failure stress of the honeycomb was 1.28 MPa and the maximum failure tensile strain was 704 %, amazing sensitivity (GF = 32.95 for the tensile strain range of 3.5 %-5%, GF = 21.5 for the tensile strain range of 100 %-120 %), wide detection range, good stability and durability (for 500 tensile cycles, the ΔR/R0 value remained unchanged). In addition, the working mechanism during the stretching process of mesh-structured hydrogels was revealed by combining finite element simulation with microscopic morphology observation. At last, the applications of the mesh-structured hydrogel-based sensors to accurately and reliably detect both subtle physiological signals and large joint movements were soundly demonstrated, endowing the ability of achieving all-round detection of human motion. Our work could provide a universe strategy for fabricating highly ventilated, stretchable, robust, sensitive and wearable strain sensors, which would greatly expand the applications of strain sensors in wearable devices.