Alteration of mechanical properties of remodeling bone adapted to mechanical stimuli

It is an interesting but complicated problem to understand the relationship between the local mechanical property of bone and its structure. An ultra-microindenter was utilized for the evaluation of the local mechanical properties of rabbit and rat bone tissues. The tangents of the loading curve and the unloading curve, A and D, were adopted as the parameters for the hardness and elasticity of the bone tissue respectively. An anisotropy due to the orientation of collagen fibers between sagital and transverse planes of rabbit tibia was observed under the loading condition of 19.6 mN. When the indentation load was lower, the fragile properties of the hydroxyapatite could be evaluated. This indenter was further used for the rat caudal vertebrae during mechanical adaptation in order to investigate in-plane distribution of the local mechanical property. The decrease of A and the increase of 1/D observed near the periosteum in the cortex indicated that the immature bone was formed and mineralized progressively. Additionally, higher A and lower 1/D in the subchondral bone of the loaded rat suggested that the subchondral bone stiffened to adapt to the mechanical stimulation.