Deformation and Orientation of HAp Crystals at Osteon-Scale Structure in Bovine Cortical Bone

Abstract

AbstractThe strain of hydroxyapatite (HAp) crystals in bone tissue was almost proportional to the tissue strain in the bone axial and circumferential directions. The mechanical properties of the tissue depend on the osteon-scale structures. However, the effects of these structures on the deformation and orientation of the HAp crystals are not well-known. The purpose of this study is to be clear the relationship between the deformation and orientation of HAp crystals and the osteon-scale structures for the bone axial direction. In the experiments, five strip specimens (40×2×1 mm) were cut from the cortical bone in the middle diaphysis of a bovine femur. The longitudinal direction of the specimens was aligned with the bone axial direction. A strain gauge was glued on the surface of each specimen to measure the bone tissue strain ε. The degree of c-axis orientation of HAp crystals for the bone axial direction was calculated using (002) lattice planes of HAp crystals. The lattice strain of the (002) planes of the HAp crystals εH(002) was measured under uniaxial tensile loadings with X-ray irradiation. Furthermore, the osteon-scale structures in the cross sections of each strip specimen were observed at the X-ray irradiation positions by an optical microscope. The value of εH(002)/ε did not show the relation for the area ratio of the osteon region (R2 = 0.09). On the other hand, the degree of c-axis orientation of HAp crystals showed the relation for the area ratio of the osteon region (R2 = 0.81).KeywordsCortical boneHydroxyapatiteLattice StrainOsteonBovine Femur