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 (∼1100% elongation), and improved mechanical robustness (tensile and compressive strength of ∼180 kPa and ∼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 (∼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.