Disuse impairs the mechanical competence of bone by regulating the characterizations of mineralized collagen fibrils in cortical bone

Bones are made of complex material comprising organic components and mineral hydroxyapatite, both of which formulate the unique hierarchical structure of bone and its mechanical properties. In this study, atomic force microscopy-based imaging and indentation approaches were adopted to investigate the influence of disuse on the morphology and in situ mechanical behavior of the collagen fibrils, under both non-loaded and load-bearing conditions, in the cortical tibia of mice. Results indicate that the orientation and D-periodic spacing of the collagen fibril remained unchanged during bone loss. By contrast, disuse significantly reduced the elastic modulus of the fibrils. Under axial mechanical loading, the collagen fibrils in the disused tibia were significantly misaligned. The elastic modulus of the fibrils returned to the same level across different groups during load-bearing condition. These findings show the unique adaptation regimes of the collagen fibrils in the cortical bone to disuse.