pH and temperature responsive UV curable lignin-based hydrogels with controllable and outstanding compressive properties

Functional hydrogels have been widely researched in various fields. However, preparing bio-hydrogels with several functionalities, such as desirable mechanical properties, high swelling ability, and stimuli-responsive properties, still presents a challenge. In this study, a UV-curable lignin-based bio-hydrogel was produced via methacrylation using glycidyl methacrylate, followed by cross-linking with acrylamide. The synthesized lignin hydrogel showed outstanding compressive performance, durability properties, and rheological behaviors, which could be engineered by changing the lignin content. With the increase in lignin concentration, the crosslinking density and storage/loss modulus were increased, whereas tan δ was decreased. Additionally, the hydrogels exhibited excellent swelling ratios (up to several thousand %), meanwhile their swelling behavior and dimensional changes varied with the lignin concentration, and strongly depended on temperature and pH. Finally, a smart strip-shaped hydrogel was designed to explore an actuator behavior, showing a fast and reversible swelling-deswelling response between pH 3 and 9. This can indicate that the lignin-based hydrogel could be a promising material for biomedical applications and 4D printing materials.