Injectable self-healing nanocellulose hydrogels crosslinked by aluminum: Cellulose nanocrystals vs. cellulose nanofibrils

Abstract

• Three types of hydrogels were successfully constructed from nanocellulose. • Aluminum ion was applied as crosslinker to reinforce the hydrogels. • The properties of the hydrogels were compared and summarized in a radar chart. • Cellulose nanocrystals hydrogels showed stronger water holding capacity. • Cellulose nanofibrils hydrogels had higher hardness and stronger antidegradation. With excellent biocompatibility and unique physiochemical properties, nanocelluloses including cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs) are promising candidates for preparing biomedical hydrogels. CNCs and CNFs are different in morphology and surface charges. Herein, CNCs and two CNFs (CNFs-C, Carboxylated CNFs; CNFs-P, Phosphorylated CNFs) were synthesized and applied to fabricate hydrogels through metal crosslinking. Aluminum crosslinking was found to be the best choice for enhancing the strength. This study systematically compared the morphologies, storage modulus, loss factor, continuous shear ramp, self-healing, swelling, in vitro degradation and injectable properties of the fabricated hydrogels. Further, a radar chart is summarized as guidelines to direct the rational selection to meet the specific requirements of further biomedical applications. At the same nanocellulose concentration and after Al 3+ crosslinking, CNCs hydrogels had strong water holding capacity twice as much as that of CNFs hydrogels. While CNFs hydrogels showed higher hardness and stronger resistance to degradation than that of CNCs. These results provide detailed insights into nanocellulose hydrogels, making it possible to use these guidelines to select hydrogels for desired performance.