Self‐Healing Hydrogels and Cryogels from Biodegradable Polyurethane Nanoparticle Crosslinked Chitosan

Hydrogels are widely used in tissue engineering owing to their high water retention and soft characteristics. It remains a challenge to develop hydrogels with tunable degradation rates, proper environmental responsiveness, and injectability. In this study, biodegradable difunctional polyurethane (DFPU) nanoparticle dispersions are synthesized from an eco‐friendly waterborne process involving the use of glyoxal. Such DFPU is used to crosslink chitosan (CS). Schiff base linkages between DFPU and CS successfully produce self‐healing hydrogels at room temperature. Moreover, cryogels are generated after being frozen at −20 °C. These gels are found to be sensitive to low pH and amine‐containing molecules owing to the property of Schiff bases. Furthermore, the degradation rates can be adjusted by the type of the component oligodiols in DFPU. Rheological evaluation verifies the excellent self‐healing properties (≈100% recovery after damage). Both the self‐healing gels and cryogels are injectable (through 26‐gauge and 18‐gauge needles, respectively) and biocompatible. Rat implantation at 14 d shows the low immune responses of cryogels. The functionalized biodegradable polyurethane nanoparticles represent a new platform of crosslinkers for biomacromolecules such as chitosan through the dynamic Schiff reaction that may give rise to a wide variety of self‐healing gels and cryogels for biomedical applications.