Tough Hydroxyapatite Hydrogels Based on Bone-like Self-Regulatory Sacrificial Bond Formation

Learning from nature is a promising approach to achieving specific functions of synthetic materials. The high material functions, in turn, shed light on the fundamental mechanisms underlying the high performance of biological tissues. For instance, bone is an attractive metabolic tissue with fascinating capabilities from the perspective of both biochemical and biomechanical functionalities. Bone tissue exhibits exceptional mechanical performance as a skeleton, enabling to sustain the locomotion of mammals. In this study, we design coupled reactions for self-regulatory sacrificial bond formation in poly(acrylic acid) hydrogels by introducing biomineral hydroxyapatite (HAp) found in bones. We demonstrate that through five coupled reactions, HAp regulates the Ca²⁺ bridging to the acidic polymer and toughens the hydrogels in water by the sacrificial bonds effect. This work is expected not only to greatly contribute to the design of tough soft materials but also to give deep insights into the self-regulated bone-toughening mechanisms.