The effect of different gravity fields on mass transfer in the rat bone lacunar-canalicular system

The bone lacunar-canalicular system(LCS)is an important microscopic infrastructure for signaling and solute transport in bone tissue,which guarantees normal physiological processes of the tissue,but the mass transfer laws in the LCS under different gravity fields have not yet been clarified.SD rats were injected intraperitoneally with different concentrations of sodium fluorescein tracer and subjected to mass transfer experiments in the LCS under normal gravity and hypergravity.The fluorescence distribution in the osteon was observed using laser scanning confocal microscopy.The hypergravity environment was provided by a self-designed high-G loading centrifuge.The fluorescence intensity of the Haversian canal in the osteon was the highest.The fluorescence intensity of lacunae farther away from the Haversian canal was lower,and the fitted curve was parabolic.With the increasing distance from the Haversian canal,the curve first rapidly decreased,and then the decreasing trend gradually became slower.Hypergravity promoted mass transfer in the LCS,and the 10 G hypergravity showed varying degrees of fluorescence intensity in each layer of the osteon relative to normal gravity,with intensity enhancements in the range of 132.7–249.0%.The fluorescence intensity was also significantly increased when the tracer concentration was halved and the gravity field magnitude was increased to 10G.In conclusion,hypergravity promoted the transport of solute molecules,nutrients,and signaling molecules within the LCS.The effect of hypergravity on mass transfer in the LCS was greater than that of tracer concentration.This may help to understand bone diseases from a mass transfer perspective.

Biomedical response of femurs in male Wistar rat in chronic hypergravity environments

Bone is sensitive to mechanical stimulation and plays a loading-bearing role in the human body.However,regulation of bone biomechanical properties in chronic hypergravity environments is still unclear.In this study,male Wistar rats exposed to chronic hypergravity environments(4
g,8
g,10
g,and 20
g)for 4 weeks were set as the hypergravity groups,and rats exposed to the normal gravity as the control group.Morphology parameters and bone remodeling factors were obtained by means of micro-CT,Western blot,and q-PCR.Mechanical properties of femurs were measured utilizing three points bending test and creep test and were fitted into a viscoelastic-viscoplastic constitutive equation.The results indicate osteoporosis occurred in femurs of hypergravity groups.Accordingly,the protein and gene expressions of bone remodeling factors(OPG,RANKL,runx2)in hypergravity groups were significantly different from that in the control group,demonstrating that bone formation level increased and bone resorption level decreased.Meanwhile,mechanical properties of femurs in hypergravity groups showed that Young's modulus of femurs in the 20
g group was significantly higher than that in the control group.The viscoelastic-viscoplastic properties of bone tissue were changed in hypergravity environments.Among them,the 8
g group was closest to the control group in morphology and mechanical properties.To sum up,the biomechanical response regulation of rat femur under 4-20
g chronic hypergravity environments was presented.Hypergravity environments could lead to osteoporosis.The balance between bone formation and bone resorption would be disrupted in hypergravity groups due to bone adaptation.20
g environment has a significant effect on elastic modulus on femurs.Due to the difference in biomechanical response of femurs,the viscoelastic-viscoplastic characteristics of femurs have a nonlinear relationship with hypergravity values.Bone tissue was least affected by 8
g hypergravity in morphology and mechanical properties.