Mild-Temperature-Induced Recombination of Crosslinking Structures in Hydrogels Using Phenylboronic-Acid-Functionalized 3D Nanoparticle Crosslinkers

Self-healing properties can be bestowed to hydrogels by recombination of crosslinking points. This study was aimed at controlling these crosslinking points using the dynamic covalent bonds (DCBs) of a boronic ester formed by phenylboronic acid (PBA) and the diols of poly(vinyl alcohol) (PVA) under temperature changes. Interestingly, boronic ester dissociated at a lower temperature than that of other DCBs and completely dissociated above 60 °C. PBA-incorporated nanoparticles underwent three-dimensional (3D) crosslinking with PVA to form a hydrogel and exhibited a reversible gel–sol phase transition at 39.7 °C. The viscoelasticity changed in response to the bonding/dissociation of the boronic-ester-based crosslinking points. The viscoelasticity of the hydrogel decreased rapidly upon heating at 50 °C and recovered to 82% of the original value after 10 min of cooling. Therefore, facile recombination of the crosslinking points in the hydrogel was achieved via mild temperature changes to avoid possible water evaporation in high-temperature treatment. Additionally, hydrogels crosslinked with glutaraldehyde showed self-healing properties upon lowering the temperature from 45 to 25 °C. These boronic-ester-DCB-functionalized nanoparticles can enable the recombination of crosslinking points in hydrogels for biomedical applications.