Muscle-inspired anisotropic hydrogel strain sensors with ultra-strong mechanical properties and improved sensing capabilities for human motion detection and Morse code transmission

Combining superior mechanical and electrochemical capabilities into conductive hydrogel sensors has attracted considerable attention in the field of flexible electronics. However, traditional hydrogels with randomly oriented polymer networks often exhibit isotropic mechanical and electrical properties, whereas the magic of anisotropy is universal in nature. Inspired by the anisotropic structure-dependent properties of muscles, this study develops a general and simple method for fabricating anisotropic ultra-high strength conducting hydrogels via tensile remodeling followed by ion coordination crosslinking. Highly oriented polymer networks of anisotropic hydrogels greatly improve their mechanical and sensing capabilities. The tensile stress and conductivity of the PVA-PAA/Fe3+ hydrogels along the parallel direction are significantly increased to 47.26 MPa and 292.64 mS/m, which are considerably greater than that of the vertical-oriented hydrogels (12.42 MPa and 169.09 mS/m). Moreover, the gauge factors (GF) of the parallel-oriented hydrogels are higher than that of the vertical-oriented hydrogels, demonstrating enhanced strain sensing performance. Anisotropic hydrogel sensors can monitor various human movements in real-time and integrate with Morse code for information decoding and transmission. This research work is expected to accelerate the burgeoning pace of conductive hydrogel sensors in soft electronics.