Fracture tolerance induced by dynamic bonds in hydrogels

Among soft materials, hydrogels with dynamic bonds that can be activated by a range of stimuli including temperature, pH, and infrared or ultraviolet light, constitute a special class of materials with unusual properties such as self-healing, actuation, and controlled degradation. Here, we take a hydrogel with reconfigurable disulfide crosslinks as an example and investigate its mechanical behavior. We demonstrate that this material has excellent fracture and fatigue resistance when the disulfide crosslinks are activated by ultraviolet illumination. We propose a simple constitutive model that describes the mechanical behavior of the material under a broad range of conditions.