Enhancing the Stability of Hydrogels by Doubling the Schiff Base Linkages

Schiff base bonds formed by primary amines and aldehydes are attractive for the construction of self-healing and injectable hydrogels. However, biomedical applications of the Schiff base-based (SB) hydrogels are usually limited by their inherent low stability due to the rapid exchange dynamic of the Schiff base bond under physiological condition. Herein, a general method to improve the stability of SB hydrogels by simply doubling the Schiff base linkages at the cross-linking points is proposed. The hydrogels formed by single Schiff base linkage (hydrogel I) disorganize into nano-aggregates due to the rapid exchange dynamic of Schiff base bond, while the hydrogels formed by double Schiff base linkage (hydrogel II) maintain the gel network for longer times due to the improved stability of the double Schiff base linkage at cross-linking points. Moreover, the hydrogel II displays excellent self-healing and injectable properties due to the rapid dynamic nature of Schiff base bonds.