Catechol-based all-wood hydrogels with anisotropic, tough, and flexible properties for highly sensitive pressure sensing

In recent years, research on multifunctional conductive hydrogels has focused on improving their mechanical properties. However, challenges remain in achieving all these properties by natural polymers and inorganic molecules. Here, we assembled all-wood tough hydrogels with anisotropic mechanical properties through the formation of dynamic bonding between cellulose fibers, natural wood lignin, Polyacrylamide (PAM) chains, and iron ions. Inspired by the catechol-based chemistry, the Fe3+ ions and catechol groups of lignin can trigger the rapid self-gelation of the hydrogels under the effect of Ammonium peroxydisulfate (APS), and serve as the reversible hydrogen bonds and metal-coordination bonds to endow the hydrogel with the flexible property. The highly aligned delignified wood acts as a frame structure endows the hydrogel with strong mechanical strength. Meanwhile, the PAM chains flooding the cellulose fibers further enhance the mechanical properties of hydrogels by hydrogen bonds. The all-wood hydrogel displays much higher stretchability (up to 0-50% strain) than natural wood (0-5% strain). The all-wood hydrogels hold great potential for compressive sensing due to their wide range of strain, high sensitivity, and good flexibility.