Abstract
As cortical bone has a hierarchical structure, the macroscopic bone strength may be affected by the alterations of mineral crystal and collagen, which are main components of cortical bone. Limited studies focused on the time related alterations of these two components in osteoporosis, and their contributions to bone mechanics at tissue level and whole-bone level. Therefore, the purpose of this study was to elucidate the time related changes of mineral and collagen in cortical bone of ovariectomized (OVX) rabbits, and to relate these changes to cortical bone nanomechanics and macromechanics. 40 Rabbits (7-month-old) were randomly allocated into two groups (OVX and sham). OVX group received bilateral ovariectomy operation. Sham group received sham-OVX operation. Cortical bone quality of five rabbits in each group were assessed by DXA, μCT, nanoindentation, Fourier transform infrared (FTIR) spectroscopy and biomechanical tests (3-point bending of femoral midshaft) at pre-OVX, 4, 6, and 8 weeks after OVX. As time increased from pre-OVX to 8 weeks, the mineral to matrix ratio decreased with time, while both collagen crosslink ratio and crystallinity increased with time in OVX group. Elastic modulus and hardness measured by nanoindentation, whole-bone strength measured by biomechanical tests all decreased in OVX group with time. Bone material properties measured by FTIR correlated well with nano or whole-bone level mechanics. However, bone mineral density (BMD), structure, tissue-level and whole-bone mechanical properties did not change with age in sham group. Our study demonstrated that OVX could affect the tissue-level mechanics and bone strength of cortical bone. And this influence was attributed to the time related alterations of mineral and collagen properties, which may help us to design earlier interventions and more effective treatment strategies on osteoporosis.
Highlights
Osteoporosis is defined by progressive loss of bone mass and impairment of bone quality lead to a reduction in bone strength[1]
Our study demonstrated that OVX could affect the tissue-level mechanics and bone strength of cortical bone
No temporal changes of bone mineral density (BMD) in femoral midshaft were detected in sham group or OVX group
Summary
Osteoporosis is defined by progressive loss of bone mass and impairment of bone quality lead to a reduction in bone strength[1]. Vertebrae and femoral neck are the main sites where osteoporotic fractures happen[2]. As trabecular bone is a main contributor to bone strength in vertebrae and femoral neck, many studies have focused on trabecular bone quality. The main components of cortical bone are mineral and collagen. Mineral accounts for nearly 2/3 of the dry weight of bone matrix, and collagen accounts for 1/3 of the dry weight of bone[5]. The macroscopic mechanical properties are closely related with the hierarchical tissue properties of cortical bone, and the whole bone strength may be affected by the alterations at mineral and collagen levels[4, 6]
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