Cortical bone is the main mechanical bearing structure of bone, and the mechanical properties of materials are not only related to bone mineral density, but also largely depend on its pores microstructure which affected by blood vessels. However, the change of pores structure in cortical bone under microgravity was still unclear. In this study, in order to clear the changes of pore structure with cortical vascular pores and its effect on bone mechanical properties, rat tail-suspension was used to simulate microgravity and the changes of the microstructure in rat tibia cortices were investigated by high-resolution micro-CT (3 μm) while the bone mechanical properties were measured via three point bending test. The results showed the bone mineral density of cortical bone didn't change in tail-suspended rats. However, the pore structure of cortical bone in tail-suspended rats changed significantly, the proportion of pores greater than 15 μm (cortical vascular pores) increased while that less than 15 μm decreased. The mechanical properties of bone (such as maximum load and maximum stress) in tail-suspended rats deteriorated. And the volume ratio of pore vessels (vessel volume/tissue volume) was negatively correlated with the mechanical properties. In conclusion, the increase of cortical vascular pores in rats caused by the simulated microgravity contributes to the decrease of mechanical properties.
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