Hierarchical Structure and Properties of the Bone at Nano Level

Bone is a highly hierarchical complex structure that consists of organic and mineral components represented by collagen molecules (CM) and hydroxyapatite crystals (HAC), respectively. The nanostructure of bone can significantly affect its mechanical properties. There is a lack of understanding how collagen fibrils (CF) in different orientations may affect the mechanical properties of the bone. The objective of this study is to investigate the effect of interaction, orientation, and hydration on atomic models of the bone composed of collagen helix (CH) and HAC, using molecular dynamics simulations and therefrom bone-related disease origins. The results demonstrate that the mechanical properties of the bone are affected significantly by the orientation of the CF attributed to contact areas at 0 degrees and 90 degrees models. The molecular dynamics simulation illustrated that there is significant difference (p < 0.005) in the ultimate tensile strength and toughness with respect to the orientation of the hydrated and un-hydrated CF. Additionally, the results indicated that having the force in a longitudinal direction (0 degrees) provides more strength compared with the CF in the perpendicular direction (90 degrees). Furthermore, the results show that substituting glycine (GLY) with any other amino acid affects the mechanical properties and strength of the CH, collagen-hydroxyapatite interface, and eventually affects the HAC. Generally, hydration dramatically influences bone tissue elastic properties, and any change in the orientation or any abnormality in the atomic structure of either the CM or the HAC would be the main reason of the fragility in the bone, affecting bone pathology.

Automated summary

This study investigates the influence of collagen fibril orientation, hydration, and interaction on the mechanical properties of bone. The results show that the orientation of collagen fibrils significantly affects the mechanical properties of bone, with longitudinal force providing greater strength compared to perpendicular force. Additionally, the orientation of hydrated and un-hydrated collagen fibrils leads to significant differences in ultimate tensile strength and toughness. Substituting glycine with other amino acids also impacts the mechanical properties and strength of the collagen-hydroxyapatite interface and, consequently, the hydroxyapatite.