Rapid polymerization of conductive hydrogels with multifunctionality initiated by lignin-tin organometallic compounds

Recently, conductive hydrogels with multifunctionality have attracted much attention for various applications such as soft robotics and stretchable bioelectronics. Nonetheless, it remains a grand challenge to prepare conductive hydrogels with high strength and toughness at room temperatures without any external energy input. Here, the free radical polymerization of a lignin-based conductive hydrogel simultaneously featuring strong, tough, transparent, and self-healing properties is efficiently induced by a catalytic system comprised of tin metal ions and lignin molecules at room temperature without any external energy input. The tin ions and catechol groups contained in lignin can generate large amounts of hydroxyl radicals under the effect of ammonium peroxydisulfate. These free radicals can trigger the rapid self-gelation of the hydrogels at mild conditions within a few seconds (∼10 s). The dynamic cross-linking between the tin ions and catechol groups of lignin molecules in the hydrogel network endows the material with a tensile strain up to ∼1800%, which is far superior to the hydrogels triggered by other metals such Fe3+, Co2+, Ni2+, and so on. Moreover, the obtained hydrogels exhibit high transparency (∼93.8%), excellent conductivity, and self-healing properties. The multifunctional hydrogels triggered by a simple yet effective self-catalysis strategy could find important applications in soft machines, sensing, and the inscription of information.