Stimuli‐Responsive, Self‐Healing, and Injectable Hydrogels with Dual‐Crosslinked Design from Phenolphthalein‐Grafted N‐Carboxyethyl Chitosan

Abstract A new biomaterial, a hydrogel, with dual‐crosslinked design, has been created with enhanced mechanical performance. The hydrogels are fabricated based on water‐soluble chitosan, with dual‐crosslinking of imine linkages and host–guest interactions. Phenolphthalein‐grafted N ‐carboxyethyl chitosan (CECS‐g‐PHP), as a guest polymer, is synthesized and structurally characterized and complexed with hexamethylenediamine modified β‐cyclodextrin (β‐CD‐HDA), as a host molecule. Oxidized sodium alginate (OSA) is added to form crosslinking networks via imine linkages with the existing amino groups. The hydrogels show significantly shorter gelation times and higher compressive stresses, compared with single‐crosslinked hydrogels. The phenolphthalein units in the hydrogel change color with pH and other added chemicals. Moreover, the hydrogels can be injected and are self‐healing with >80% recovery within 4 h. Thus, these dual‐crosslinked hydrogels, which respond to pH and other stimuli, are promising designs for new multifunctional biomaterials.