Skin-inspired high-strength, adhesive, healable and smart thermoregulation hydrogel sensors for multi-sensing via one-pot PET-RAFT

Currently, smart hydrogel sensors with excellent physicochemical properties and exceptional sensitivity to multiple external stimuli demonstrate considerable potential in various simulations of human skin's functions. In this study, a poly(N-isopropylacrylamide) (PNIPAM)/polypyrrole (PPy) and para-aramid nanofiber (ANF) composite hydrogel (NPAH) was synthesized under ultraviolet irradiation using photoinduced electron transfer reversible addition-fragmentation chain transfer (PET-RAFT) technology. The incorporation of PPy and ANFs resulted in a substantial enhancement of hydrogel mechanical strength, from 0.1069 MPa for the PNIPAM hydrogel (NH) to 0.9190 MPa for the NP₅₈A₄H composite. Furthermore, NP₅₈A₄H exhibited remarkable self-healing (91% tensile strength recovery after 6 h healing) and potent adhesive properties (enhanced contact with a material interface) when adhering to various substrates. The NP₅₈A₄H sensor demonstrated an effective response to temperature (relative resistance change is 1.2% °C^-1) and strain (GF = 1.37) variations, as well as the capacity to detect tension and monitor human movement. Moreover, the photothermal conversion capability of PPy accelerated the lower critical solution temperature (LCST) phase transition of PNIPAM to 31.9 °C and it possessed selectivity in transmitting light in the visible band of solar radiation and could facilitate the "transparent-opaque" transition to realize the thermoregulation up to a 9.6 °C temperature difference. The proposed NP₅₈A₄H with excellent integrated properties, especially the high mechanical strength, self-healing, self-adhesiveness and sensitive dual-sensing of temperature and strain, shows great potential for simulation of the human skin to perception of touch, pressure and ambient temperature simultaneously, indicating promising applications in the fields of wearable healthcare, human-machine interfaces, and intelligent thermal management.