| As an important load-bearing biological tissue structure,bone is closely related to the quality of life,which provides mechanical support and protection for human body and organs.Osteoporosis(OP),characterized by decreased bone strength and increased risk of fracture,has become an obvious public heathy issue.With the aging of China's population,the impact of orthopedic chronic disease on the social economy,public health issue and family life will be increasingly prominent.Due to the deficiencies of current description framework of micro-/ nano-properties,experimental characterization and clinical diagnostic criteria of bone,we systematically study the mechanical properties of cancellous bone in different health states and their influence factors based on bone mass,microarchitecture and bone tissue property comprehensively with the mode of “combination of medical and engineering”,using medical imaging,mechanical testing and characterization method.The specific work is summarized as follows:(1)Based on the mechanics theory of composite materials,a three-factor framework of "bone mass-microarchitecture-bone tissue property" was proposed to describe the mechanical properties of cancellous bone.Under this framework,the effect of "bone mass","microarchitecture" and "bone tissue property" on the mechanical properties of cancellous bone were systematically studied.We made mice cancellous bone models in different health state(health,mild and severe osteoporosis)and used high resolution CT scan and 3d digital reconstruction to obtain representative volume element of the cancellous bone.Based of Nano-indentation test of bone tissue property on the trabecular scale,the equivalent mechanical properties of each cancellous bone element were established and analyzed by the finite element method simulation.Under the guidance of the ternary framework of "bone mass-microarchitecture-bone tissue property",the influence of single factor of "bone mass","microstructure" and "bone tissue property" on cancellous bone mechanical properties were analyzed by digital modeling technology.The results show that :(1)Corresponding to the longitudinal load bearing function of bone,the bone mechanical property of healthy cancellous bone showed obvious longitudinal advantage,which was an important feature of the topological microstructure of healthy cancellous bone;(2)Compared with healthy bone,cancellous bone in osteoporosis not only significantly reduces the bone mass,but also deteriorates the topological microarchitecture and destroys the longitudinal advantage of mechanical property.(3)The three factors decoupling analysis found that the effects of bone mass on the mechanical properties of cancellous bone with the aspect of "quantity"(such as the level of modulus),the effects of microarchitecture on mechanical properties of cancellous bone with the effect of the "quality"(such as anisotropy,longitudinal advantage),and small change in bone tissue property affects cancellous bone mechanical properties weakly.(2)The concept of bone tissue distribution uniformity was proposed,and the material distribution uniformity parameter and calculation method were defined.Statistical analysis showed that this parameter could effectively correlate to the microarchitecture of cancellous bone and its mechanical properties.Specifically,based on the high-precision CT scan data,the change curve of the bone tissue area ratio of each section along the longitudinal and transverse directions with the position was calculated and analyzed,and as the sum of the absolute values of secant slope of the area ratio curve.The correlation between the UDBT and the mechanical properties was manifested statistically by means of Kendall ?-b correlation analysis,Spearman correlation analysis,and the Canonical correlation methods.(3)The dynamic Nano-indentation test technology was used to measure and draw the high-resolution distribution map of the dynamic modulus of single bone trabeculae in different health states for the first time.The spatial resolution accuracy was as high as 2 microns(that is,the distance between the measuring points was as small as 2 microns).Accurate measurement of mechanical properties of bone trabeculae on micro-/ nano-scale will form the basis of FEM analysis and clinical evaluation of cancellous bone mechanical properties,which directly affects the accuracy or correctness of analysis and evaluation.For this reason,we used the quasi-static and dynamic Nano-indentation testing technology to conduct fine mechanical test of bone trabecula-the basic unit of cancellous bone,and gave high-precision distribution cloud maps of dynamic modulus of single bone trabecula in different health states.For the first time,we provided the map of the dynamic mechanical properties of single bone trabeculae in 2-micron resolution,which is an important reference for subsequent experiments,theories and calculations.The results show that(1)type ? osteoporosis has little effect on the material properties of bone trabeculae.(2)bone trabecula has good viscoelastic properties under low frequency load,which is consistent with its physiological function.(4)Nickel-titanium(NiTi)alloy is one of usually used biomaterials in the orthopedics medicine field.Therefore,we prepared Nitinol alloy with nano-size grain,and found that the refinement of size grain to nano scale can effectively improve the wear resistance of NiTi alloy biomaterial.After several times of cold rolling and heat treatment,we manufactured NiTi alloys with grain sizes of 10 nm,42nm and 80 nm.The nano-wear behavior of NiTi alloys with different grain sizes under different wear forces and wear passes conditions was measured by Nano-wear test and found that the wear resistance of NiTi alloy can be improved by refinement of the grain size to nano scale.The effects of grain size on the hardness and phase transition were also carefully analyzed. |
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