Mechanically toughened conductive hydrogels with shape memory behavior toward self-healable, multi-environmental tolerant and bidirectional sensors

Abstract

• A toughened, self-healing, anti-freezing, anti-drying, and anti-swelling hydrogel is prepared. • Hydrogel sensors exhibit excellent self-healing capability and multi-environmental stability. • Hydrogel sensors display an attracting feature on distinguishing the direction of human motion. • Hydrogels possess significant shape memory and information storage functions even at −40 °C. Conductive hydrogels have considered as promising materials to revolutionize flexible electronics, biomedical devices and soft robotics. Despite significant progress has been made in the design of hydrogels, simultaneous realization of outstanding mechanical properties, self-healing capability, multi-environmental tolerance (e.g., freezing, drying, water, and oil), and multiple stimuli-responsiveness in a single hydrogel still remains a tremendous challenge. Herein, an extraordinary stretchable (1769%), toughened (0.46 MPa), self-healing, water-retaining (78% after 8 days), anti-freezing (below −40 °C), and anti-swelling (in water/organic solvents) conductive hydrogel is designed and prepared by simultaneously introducing zwitterionic proline, metal ions, and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) into vinyl hybrid silica nanoparticles cross-linked polyacrylic acid networks. Based on this hydrogel, the fabricated strain sensor exhibits excellent strain sensitivity (GF = 3.07), wide sensing range (from 5 to 700%), reliable stability (800 cycles at 200% strain), and accurate human motion detection along two opposite directions (bend down or bend up). In particular, it can not only withstand outstanding mechanical damages but also maintain stable sensing performances in water/organic solvent environments and freezing condition of −40 °C. More interestingly, under FeCl 3 -EG (ethylene glycol) and ascorbic acid-EG solution external stimuli, the resultant hydrogels also display the significant shape memory behaviors and repeated information recording/erasing capabilities even at an extremely cold temperature (−40 °C). These remarkable performances greatly expand the application fields of hydrogels in harsh environments.