Chemically and physically crosslinked lignin hydrogels with antifouling and antimicrobial properties

As the second most abundant polymer on earth, lignin has been largely underestimated as biomaterial in the biomedical field. In this work, we proposed a strategy to transform lignin into noncytotoxic functional hydrogel with antifouling and antimicrobial properties. A spectrum of lignin hydrogels was prepared by free radical polymerization of sulfobetaine methacrylate (SBMA) and partially methacrylated lignin (lignin-MA), where lignin-MA served as hydrogel skeleton and antibacterial agent. The formation of a double network structure consisting of chemical and physical crosslinking between SBMA and lignin-MA was confirmed. Moreover, the lignin/SBMA hydrogels demonstrated high hydrophilicity due to the hydration of the zwitterionic SBMA, which can effectively reduce protein adsorption as well as prevent bacteria attachment, resulting in much better antifouling property relative to the commonly employed biomedical material poly(2-hydroxyethyl methacrylate) (PHEMA) hydrogels. Antimicrobial property of the hydrogel was significantly enhanced with the addition of lignin, showing the best reduction rate of 94.8 % against E. coli and 95.7 % against S. aureus with 40 % lignin-MA, notably higher than the respective 80.6 % and 81.5 % reduction rates for the PSBMA hydrogel without lignin. More importantly, the biocompatibility of lignin hydrogels was retained. This study presented a facile and versatile route for incorporating lignin derivative into biomaterials to achieve excellent antifouling and antimicrobial properties, which may lead to potential applications in medical devices and biological material fields.