Biomimetic Strain-Stiffening in Chitosan Self-Healing Hydrogels.

The strain-stiffening and self-healing capabilities of biological tissues enable them to preserve the structures and functions from deformation and damage. However, biodegradable hydrogel materials with both of these biomimetic characteristics have not been explored. Here, a series of strain-stiffened, self-healing hydrogels are developed through dynamic imine crosslinking of semiflexible -carboxymethyl chitosan (main chain) and flexible dibenzaldehyde-terminated telechelic poly(ethylene glycol) (crosslinker). The biomimetic hydrogels can be reversibly stiffened to resist the deformation and can even recover to their original state after repeated damages. The mechanical properties and stiffening responses of the hydrogels are tailored by varying the component contents (1-3%) and the crosslinker length (4 or 8 kDa). A combinatorial system of in situ coherent small-angle X-ray scattering with rheological testing is developed to investigate the network structures (in sizes 1.5-160 nm) of hydrogels under shear strains and reveals that the strain-stiffening originates from the fibrous chitosan network with poly(ethylene glycol) crosslinking fixation. The biomimetic hydrogels with biocompatibility and biodegradability promote wound healing. The study provides an insight into the nanoscale design of biomimetic strain-stiffening self-healing hydrogels for biomedical applications.