Ultrafast Fabrication of Lignin-Encapsulated Silica Nanoparticles Reinforced Conductive Hydrogels with High Elasticity and Self-Adhesion for Strain Sensors

Conductive hydrogels are receiving considerable attention because of their important applications, such as flexible wearable electronic, human-machine interfaces, and smart/soft robotics. However, the insufficient mechanical performance and inferior adhesive capability severely hinder the potential applications in such an emerging field. Herein, a highly elastic conductive hydrogel that integrated mechanical robustness, self-adhesiveness, UV-filtering, and stable electrical performance was achieved by the synergistic effect of sulfonated lignin-coated silica nanoparticles (LSNs), polyacrylamide (PAM) chains, and ferric ions (Fe3+). In detail, the dynamic redox reaction was constructed between the catechol groups of LSNs and Fe3+, which could promote the rapid gelation of the acrylamide (AM) monomers in 60 s. The optimized conductive hydrogels containing 1.5 wt % LSNs as the dynamic junction points exhibited the excellent elasticity (<15% hysteresis ratio), high stretchability (similar to 1100% elongation), and improved mechanical robustness (tensile and compressive strength of similar to 180 kPa and similar to 480 kPa). Notably, the abundant catechol groups of LSNs endowed the conductive hydrogels with the long-lasting and robust self-adhesion, enabling seamless adhesion to the human skin. Meanwhile, the catechol groups also provided an exceptional UV-blocking capability (similar to 95.1%) for the conductive hydrogels. The combined advantages of the conductive hydrogels were manifested in flexible sensors for the high-fidelity detection of various mechanical deformations over a wide range of strain (10-200%) with good repeatability and stability. We believed that the designed conductive hydrogels may become a promising candidate material in future flexible wearable electronics for long-term and stable human movements monitoring.