Non-Dynamic Chemical Crosslinking Enables Self-Healing Hydrogels

Self-healing hydrogels possess the intrinsic ability to automatically heal and recover from damage. The healing mechanisms of self-healing hydrogels are mainly classified into two types: dynamic covalent bonds and non-covalent bonds. This study reports a series of self-healing hydrogels based on non-dynamic covalent bonds, through the aminolysis reaction between N-hydroxysuccinimide esters (NHS-ester) and amino (─NH₂) groups. Their autonomous self-healing processes are demonstrated to be rapid and spontaneous. Experiments demonstrate that the self-healing behavior results from the residual unreacted NHS-esters and ─NH₂ groups. Notably, the amino groups/protonated amino groups (─NH₂/─NH₃⁺) equilibrium in the system is shown to enable the storage and release of ─NH₂ groups, a process that plays a central role in the hydrogel's self-healing ability that is absent in conventional non-dynamic covalent hydrogels. This strategy enables the development of self-healing hydrogels that not only exhibit enhanced mechanical strength and strong adhesive properties, but also support the construction of stable complex architectures, such as multilayered and hollow structures. Overall, this study presents a new self-healing mechanism that may offer valuable insights for future design and application of advanced self-healing materials.