Injectable, rapid self-healing, antioxidant and antibacterial nanocellulose-tannin hydrogels formed via metal-ligand coordination for drug delivery and wound dressing

Nanocellulose-based hydrogels have attracted increasingly attention due to their biocompatibility, biodegradability, and hydrophilic properties. In this work, we proposed a simple route to fabricate composite hydrogels using TEMPO oxidized cellulose nanofibrils (TOCNF) and tannin through metal-ligand coordination. Calcium ions were utilized to rapidly cross-link the carboxyl groups on TOCNF and the tannins' catechol moieties via metal-ligand bonding, resulting in the formation of TOCNF-Ca2+-T composite hydrogels. The incorporation of tannins endowed the hydrogel with high antioxidant and antibacterial properties. The rheological analysis revealed that the addition of tannin led to an improved gel strength of the composite hydrogel. The hydrogel was injectable and could autonomously self-healed in 1 min without any trigger. Tetracycline hydrochloride (TH) was successfully loaded into the composite hydrogels, achieving a maximum encapsulation rate of 97.32%. TOCNF-Ca2+-40%T demonstrated a cumulative drug release of 36% at pH 1.3 and 86% at pH 7.4, indicating its pH-responsive nature. These hydrogels, derived from plant sources, exhibited high antibacterial and antioxidant properties, as well as biocompatibility, rapid self-healing, and injectability, which open up new possibilities for applications in wound dressing and drug delivery.