Alginate-based Self-healing and pH-responsive Hydrogels Formed by Dynamic Covalent Bonding

A self-healable hydrogel was prepared by self-crosslinking two biocompatible materials oxidized alginate containing dialdehyde groups and PEG with acylhydrazine groups. Oxidation reactions on -OH groups at C-2 and C-3 positions of the uronic units of sodium alginate were performed with sodium periodate. PEG with acylhydrazine terminals was synthesized by PEG and hydrazine hydrate. The generation of the self-crosslinked hydrogel relies on the dynamic covalent linkage through acylhydrazone bonds. Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), universal testing machine and rheometer were used to characterize the structure and properties of the hydrogel. The results demonstrate that the hydrogel has good flexibility and mechanical strength. The gelation time and mechanical properties can be adjusted by the polymer concentration. The hydrogel can repair itself under mild physiological condition without adding any agent. In both of compression and tensile tests, about 90% recovery of stresses was achieved after healing for 24 h. In addition, the pH responsive hydrogel may undergo gel-sol transition by adjusting pH value of the environment and the transition can be repeated several times. The combination of self-healing, pH sensitive, biocompatibility, along with an easy method of synthesis, made this material ideal candidate for further biomedical applications.