Soft hydrogel-embedded ceramic skeleton mimicking bone structure via sacrificial bond concept

Bone, consisting of calcium phosphate minerals, rigid collagen fibrils, and acidic proteins, exhibits stiff and tough mechanical properties. On a molecular scale, covalent cross-linking in proteins and ionic interactions within proteins and at the protein-mineral boundary contribute to bone's toughness. In addition, hierarchical structures, like the sponge-like arrangement, are also crucial for the energy dissipation system in bone. Inspired by the multiple sacrificial bonds found in bone, we developed a soft/hard composite made up of two components with contrasting mechanical properties: a porous calcium phosphate skeleton and an acidic polymer hydrogel matrix. The porous ceramic skeleton alone is extremely rigid but brittle. However, the presence of the hydrogel matrix transforms the brittle nature of the porous ceramic skeleton into a soft/hard composite with stretchable and tough characteristics. The composite exhibits significant energy dissipation due to the fracture of the ceramic skeleton under small deformation, while catastrophic failure of the composite is prevented because the hybridized matrix disperses the damage throughout the entire sample. The Ca