It is commonly known that cortical bone exhibits viscoelastic-viscoplastic behavior which affects the biomechanical response when an implant is subjected to an external load. In addition, long term effects such as cre...It is commonly known that cortical bone exhibits viscoelastic-viscoplastic behavior which affects the biomechanical response when an implant is subjected to an external load. In addition, long term effects such as creep, relaxation and remodeling affect the success of the implant over time. Constitutive material models are commonly derived from data obtained in in vitro experiments. However during function, remodeling of bone greatly affects the bone material over time. Hence it is essential to include long term in vivo effects in a constitutive model of bone. This paper proposes a constitutive material model for cortical bone incorporating viscoelasticity, viscoplasticity, creep and remodeling to predict stress-strain at various strain rates as well as the behavior of bone over time in vivo. The rheological model and its parameters explain the behavior of bone subjected to longitudinal loading. By a proper set of model parameters, for a specific cortical bone, the present model can be used for prediction of the behavior of this bone under specific loading conditions. In addition simulation with the proposed model demonstrates excellent agreement to in vitro and in vivo experimental results in the literature.展开更多
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,ma...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(4g,8g,10g,and 20g)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 20g 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 8g group was closest to the control group in morphology and mechanical properties.To sum up,the biomechanical response regulation of rat femur under 4-20g 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.20g 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 8g hypergravity in morphology and mechanical properties.展开更多
文摘It is commonly known that cortical bone exhibits viscoelastic-viscoplastic behavior which affects the biomechanical response when an implant is subjected to an external load. In addition, long term effects such as creep, relaxation and remodeling affect the success of the implant over time. Constitutive material models are commonly derived from data obtained in in vitro experiments. However during function, remodeling of bone greatly affects the bone material over time. Hence it is essential to include long term in vivo effects in a constitutive model of bone. This paper proposes a constitutive material model for cortical bone incorporating viscoelasticity, viscoplasticity, creep and remodeling to predict stress-strain at various strain rates as well as the behavior of bone over time in vivo. The rheological model and its parameters explain the behavior of bone subjected to longitudinal loading. By a proper set of model parameters, for a specific cortical bone, the present model can be used for prediction of the behavior of this bone under specific loading conditions. In addition simulation with the proposed model demonstrates excellent agreement to in vitro and in vivo experimental results in the literature.
基金the Chinese National Natural Science Foundation(No.12072235,No.12002388,No.11432016)the Science Foundation of PAPF Logistics University(WHB202004).
文摘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(4g,8g,10g,and 20g)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 20g 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 8g group was closest to the control group in morphology and mechanical properties.To sum up,the biomechanical response regulation of rat femur under 4-20g 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.20g 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 8g hypergravity in morphology and mechanical properties.
