Effect of long-term cyclic compression loading on the structural evolution of trabecular bone

Dynamic remodeling of bone tissue is mediated by the synergistic effects of osteoblast-driven bone formation and Osteoclast-dominated bone resorption.However,how bone cells perceive the mechanical stimuli and regulate bone remodeling have not been fully understood.This study aims to evaluate the effect of cyclic compression loading on trabecular microstructure for 42 days and identify the relationship between the evolution of trabecular microstructure and cell distribution.The eighth caudal vertebrae of rats were subjected to long-term cyclic compression loading with different frequencies.The compression displacement is 1 mm.In vivo micro-computed tomography was performed at 0,14,28 and 42 days to determine the structural parameters.The bone volume fraction(BV/TV)in the 1 Hz cyclic compression loading group was significantly higher than that in the control and 10 Hz groups,whereas the trabecular separation(Tb.Sp)was significantly lower.The 10 Hz cyclic compression group had the lowest BV/TV and highest Tb.Sp.After 14 days of loading,the BV/TV values of 1 Hz group were 29.62%and 41.6%higher than those of the control and 10 Hz groups,respectively.Conversely,the Tb.Sp of 1 Hz group was approximately 12.33%and 16.52%lower than that of the control and 10 Hz group,respectively.More bone formation and less bone resorption were observed in the 1 Hz group than the control group.In addition,more osteoblasts were attached to the area of bone formation,while more osteoclasts were located in the area of bone resorption.These findings may provide a basis for further understanding mechanical stimulation-regulated bone remodeling.

Changes of cortical bone pores structure and their effects on mechanical properties in tail-suspended rats

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(3μm)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 15μm(cortical vascular pores)increased while that less than 15μm 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.