Highly adhesive conductive hydrogels fabricated by catechol lignin/liquid metal-initiated polymerization of acrylic acid for strain sensors

Conductive hydrogels have emerged as promising candidates for next-generation flexible electronics owing to their unique combination of electrical conductivity and mechanical compliance. However, the development of an eco-friendly and efficient polymerization strategy to simultaneously achieve robust adhesion and superior functionality remains a challenge. In the work, catechol lignin (DAL)/liquid metal (LM) were utilized as initiators for the polymerization of acrylic monomers (PAA), resulting in the preparation of conductive hydrogels (PAA-DAL-LM). The engineered DAL component serves dual functions of establishing an interfacial stabilization layer for LM nanoparticles while participating in radical generation for polymerization initiation, and this synthesis protocol eliminates conventional toxic initiators through LM-mediated radical generation mechanisms. The resultant PAA-DAL-1.6 %LM hydrogel demonstrated remarkable performance characteristics, including exceptional compressive strength (688.5 KPa), good self-healing properties, and high electrical conductivity (0.24 S/m). Structural modification of alkali lignin through catechol incorporation significantly improved both the water solubility and interfacial adhesion strength (16.23 KPa). Systematic characterization revealed stable strain-responsive electrical behavior with high strain sensing accuracy as well as stable electrical output. These multifunctional hydrogels not only hold significant potential for advancing flexible sensor technologies but also pave the way for sustainable valorization of lignin biopolymers in advanced material applications.