Strong and Multifunctional Lignin/Liquid Metal Hydrogel Composite as Flexible Strain Sensors

Conductive hydrogel is a promising material for flexible sensors due to its good electrical conductivity, adhesion, and high sensitivity. However, the challenge of integrating conductive fillers like liquid metals lies in their poor interface compatibility, which adversely affects their mechanical strength and lifespan. Addressing the challenge of achieving both mechanical strength and conductivity, this study harnessed 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO)-oxidized lignin to form a stable interface between the liquid metal (LM) and the hydrogel system. Furthermore, this innovation (lignin-LM) facilitates the free radical polymerization of acrylic acid (PAA) at room temperature, resulting in conductive hydrogels. These hydrogels demonstrated excellent self-healing, adhesive, tensile, and antibacterial properties, alongside high strain sensing accuracy and stable electrical output in flexible sensor applications. In conclusion, the PAA-Lignin-LM hydrogel holds excellent promise for wearable, flexible electronic products, introducing a novel approach for the high-value utilization of lignin.