Synergistic adhesion enhancement of double-crosslinking chitosan hydrogel via catechol-Fe³⁺ coordination and Schiff base

Ionic crosslinking and Schiff base are employed to construct hydrogel wound dressings. However, the contributions of these crosslinking to the swelling behavior and adhesion performance of hydrogels are still unclear. Here, double-crosslinking chitosan hydrogel (DCH) is designed via catechol-Fe³⁺ coordination and Schiff base between catechol modified chitosan and oxidized chitosan. The swelling ratio decreased by catechol-Fe³⁺ coordination and Schiff base are 79.6 % and 54.4 %, respectively. Catechol-Fe³⁺ coordination mainly contributes to the swelling behavior. Notably, the adhesion strength of DCH is 45.6 kPa which significantly higher than catechol-Fe³⁺ coordination (12.1 kPa) or Schiff base (15.7 kPa). Catechol-Fe³⁺ coordination and Schiff base synergistically enhance tissue adhesion strength by 3-time that of the fibrin glue. Specifically, the adhesion strength enhancement of the Schiff base and catechol-Fe³⁺ coordination is 2.47 and 1.68 times, respectively. Schiff base mainly contributes to the adhesion performance. Schiff base not only improves the crosslinking degree of hydrogel but also enhances the adhesion strength. This research offers insightful guidance for the design and modulation of the swelling and adhesion properties of double-crosslinking hydrogels.