Chiral hierarchical structure of bone minerals

Chirality is an indispensable integral of biological system. As an important part of organisms, chiral organic structure of bone has been extensively investigated. However, the chirality of bone minerals is unclear and not fully determined. Here, we report nine levels of fractal-like chirality of bone minerals by combining electron microscopic and spectrometric characterizations. The primary helically twisted acicular apatite crystals inside collagen fibrils and between fibrils merge laterally to form secondary helical subplatelets. The chiral arrangement of several subplatelets forms tertiary spiral mineral platelets. Further coherent stepwise stacking of mineral platelets with collagen fibrils leads to quaternary to ninth levels, which reconciled the previous conflicting models. The optical activities in the UV-visible, infrared and terahertz regions demonstrated chirality from atomic to macroscopic scales based on circularly selective absorption and Bragg resonance at different levels of chirality. Our findings provide new insight into the structural integrity of bone, osteology, forensic medicine and archaeology and inspire the design of novel biomaterials.