Mechanical behaviour of porous hydroxyapatite

The aim of the study was to investigate the role of microstructure and porosity on the mechanical behaviour of sintered hydroxyapatite. Hydroxyapatite disks with four different porosities were used in this investigation. With a nanoindentation system, elastic modulus, hardness, contact stress–strain relationship, energy absorption and indentation creep behaviour were investigated. The elastic modulus and hardness of hydroxyapatite exhibited an exponential relationship (e^−bP) with the porosity P, which is similar to Rice’s finding with the minimum solid area model. High porosity samples showed more substantial inelastic behaviour, including higher energy absorption, no linear elastic region in the contact stress–strain curve and some indentation creep behaviour. We conclude that porous microstructure endows hydroxyapatite with inelastic deformation properties, which are important in a material for bone substitution usage.     

图像相关法测试股骨近端骨小梁压缩特性

目的改善传统方法做压缩测试的不足,更准确地反映骨小梁的压缩弹性模量,探究股骨近端骨小梁的压缩生物力学特性,为临床诊疗提供实验室依据。方法运用微材料力学测试系统,对正常国人(45～60岁)尸体股骨近端骨小梁沿主压力方向及与其垂直方向的压缩性能进行实验研究。结果测得了股骨近端骨小梁在主压力方向压缩弹性模量为(335.26±183.85)MPa,与其垂直方向的压缩弹性模量为(59.27±23.88)MPa,骨小梁在主压力方向上的生物力学性能要明显高于主张力方向;记录了载荷下的骨小梁的位移及应变分布图,负载时骨小梁的位移及应变分布是不均匀的。结论应用微材料力学测试系统测试股骨近端骨小梁压缩弹性模量以更准确地反映其力学性能的方法是可行的,股骨近端骨小梁的压缩性能具有各向异性和不均匀性。     

Similar damage initiation but different failure behavior in trabecular and cortical bone tissue

The mechanical properties of bone tissue are reflected in its micro- and nanostructure as well as in its composition. Numerous studies have compared the elastic mechanical properties of cortical and trabecular bone tissue and concluded that cortical bone tissue is stiffer than trabecular bone tissue. This study compared the progression of microdamage leading to fracture and the related local strains during this process in trabecular and cortical bone tissue. Unmachined single bovine trabeculae and similarly-sized cortical bovine bone samples were mechanically tested in three-point bending and concomitantly imaged to assess local strains using a digital image correlation technique. The bone whitening effect was used to detect microdamage formation and propagation. This study found that cortical bone tissue exhibits significantly lower maximum strains (trabecular 36.6%±14% vs. cortical 22.9%±7.4%) and less accumulated damage (trabecular 16100±8800 pix/mm2 vs. cortical 8000±3400 pix/mm2) at failure. However, no difference was detected for the maximum local strain at whitening onset (trabecular 5.8%±2.6% vs. cortical 7.2%±3.1%). The differences in elastic modulus and mineral distribution in the two tissues were investigated, using nanoindentation and micro-Raman imaging, to explain the different mechanical properties found. While cortical bone was found to be overall stiffer and more highly mineralized, no apparent differences were noted in the distribution of modulus values or mineral density along the specimen diameter. Therefore, differences in the mechanical behavior of trabecular and cortical bone tissue are likely to be in large part due to microstructural (i.e. orientation and distribution of cement lines) and collagen related compositional differences.     

超重环境对骨组织生物力学性能和形态结构的影响

目的 探讨超重环境对骨组织生物力学性能及骨组织形态结构的影响,为航天员和飞行员安全飞行训练及 最大耐受高重力值的确定提供理论支撑。 方法 采用本课题组自主设计的超重加载平台构建超重动物模型,加载 方式为腹背方向承受向心加速度,加速度分别为 5、10、20 g,离心 45 s,1 次/ d,5 d / 周,连续 4 周。 使用 Instron 5865 材料力学试验机对离体骨组织进行三点弯曲试验,通过测量力学参数的变化,分析超重环境对骨组织生物力学性 能的影响;通过双能 X 线骨密度仪扫描、Micro-CT 扫描、骨组织染色等技术,检测骨矿物质含量、骨密度及骨小梁等 形态学参数的变化,观察超重环境对骨组织形态结构的影响。 结果 超重加载可显著降低小鼠胫骨的断裂应力及 弹性模量。 超重环境导致骨组织中骨体积分数下降,骨小梁厚度以及骨小梁数量显著降低,骨小梁排列紊乱。 结 论 超重环境对骨组织生物力学性能及骨组织形态结构的影响与超重载荷的强度密切相关。 低(5 g)强度超重载 荷能够降低骨小梁厚度,但对其力学性能的影响很小。 中(10 g)、高(20 g)强度超重载荷能够显著触发骨流失以 及骨力学性能的下降。 随着超重载荷的增加,机体的生理调节无法阻止骨量和力学性能下降的趋势     

不同角度载荷下股骨头骨小梁的生物力学特性

目的 探讨不同角度载荷对股骨头骨小梁形态学与力学性能的影响,为研究股骨头坏死、塌陷的生物力学机制提供理论依据。方法 利用12月龄羊股骨头和人尸体股骨头分别制作羊股骨头骨小梁试件94个和人股骨头骨小梁试件43个。按照受力方向与骨小梁主压力方向之间的不同夹角,将骨小梁以10°间隔分为内翻10°、0°和外翻10°、20°、30°共计5组,模拟股骨颈骨折内固定术后不同戈登（Garden）对线指数下的复位情况。通过分别对羊股骨头骨小梁进行micro-CT扫描、计算与压缩破坏试验以及对人尸体股骨头骨小梁进行循环压缩试验,分析不同受力方向下股骨头骨小梁的骨体积分数（BV/TV）、骨表面积/骨体积（BS/BV）、骨小梁平均厚度（Tb.Th）、骨小梁数量（Tb.N）、骨小梁间距（Tb.Sp）等形态学指标以及弹性模量、极限强度、屈服强度、初始弹性模量、循环次数等力学指标。结果 加载方向与骨小梁的主压力方向之间夹角为0°时,BV/TV、Tb.Th以及弹性模量、极限强度、屈服强度、初始弹性模量、循环次数均为最大,而BS/BV与Tb.N为最小,并随着夹角增大前者呈递减而后者呈递增趋势。结论 12月龄羊股骨头骨小梁BV/TV与极限强度随受力方向与骨小梁主压力方向之间夹角变化的趋势与人股骨头骨小梁一致;加载方向与主压力骨小梁之间夹角增大时,股骨头骨小梁形态学与力学性能均下降;Garden指数偏离160°越大时,股骨头内骨小梁越易发生损伤。     

Mechanical properties of hydroxyapatite whisker reinforced polyetherketoneketone composite scaffolds

The apparent mechanical properties of hydroxyapatite (HA) whisker reinforced polyetherketoneketone (PEKK) scaffolds were evaluated in unconfined, uniaxial compression to investigate the effects of the porosity (75%, 82.5% and 90%), HA content (0, 20 and 40 vol%) and mold temperature (350, 365 and 375 C). Increased porosity resulted in a non-linear decrease in the elastic modulus and yield strength for both reinforced and unreinforced PEKK scaffolds, as expected. The increase in elastic modulus and yield strength with increased relative density followed a power-law, similar to trabecular bone and other open-cell foams. HA whisker reinforcement generally resulted in an increased elastic modulus from 0 to 20 vol% HA and a subsequent decrease from 20 to 40 vol% HA, while the yield strength and strain were decreased in scaffolds with 40 vol% HA compared to those with 0 or 20 vol% HA. Increased mold temperature resulted in an increased elastic modulus, yield strength and yield strain. These effects enabled the mechanical properties to be tailored to mimic human trabecular bone. The elastic modulus was greater than 50 MPa, and the yield strength was greater than 0.5 MPa, for scaffolds with 75% porosity at all combinations of reinforcement level and mold temperature. Scaffolds with 75% porosity and 20 vol% HA molded at 375 C exhibited a mean elastic modulus and yield strength of 149 MPa and 2.2 MPa, respectively, which was the highest of the conditions investigated in this study and similar to human vertebral trabecular bone. Therefore, HA whisker reinforced PEKK scaffolds may be advantageous for permanent implant fixation, including interbody spinal fusion.     

不同角度载荷下股骨头骨小梁的生物力学特性

目的探讨不同角度载荷对股骨头骨小梁形态学与力学性能的影响,为研究股骨头坏死、塌陷的生物力学机制提供理论依据。方法利用12月龄羊股骨头和人尸体股骨头分别制作羊股骨头骨小梁试件94个和人股骨头骨小梁试件43个。按照受力方向与骨小梁主压力方向之间的不同夹角,将骨小梁以10°间隔分为内翻10°、0°和外翻10°、20°、30°共计5组,模拟股骨颈骨折内固定术后不同戈登(Garden)对线指数下的复位情况。通过分别对羊股骨头骨小梁进行micro-CT扫描、计算与压缩破坏试验以及对人尸体股骨头骨小梁进行循环压缩试验,分析不同受力方向下股骨头骨小梁的骨体积分数(BV/TV)、骨表面积/骨体积(BS/BV)、骨小梁平均厚度(Tb.Th)、骨小梁数量(Tb.N)、骨小梁间距(Tb.Sp)等形态学指标以及弹性模量、极限强度、屈服强度、初始弹性模量、循环次数等力学指标。结果加载方向与骨小梁的主压力方向之间夹角为0°时,BV/TV、Tb.Th以及弹性模量、极限强度、屈服强度、初始弹性模量、循环次数均为最大,而BS/BV与Tb.N为最小,并随着夹角增大前者呈递减而后者呈递增趋势。结论 12月龄羊股骨头骨小梁BV/TV与极限强度随受力方向与骨小梁主压力方向之间夹角变化的趋势与人股骨头骨小梁一致;加载方向与主压力骨小梁之间夹角增大时,股骨头骨小梁形态学与力学性能均下降;Garden指数偏离160°越大时,股骨头内骨小梁越易发生损伤。     

不同角度载荷下股骨头骨小梁的生物力学特性

目的 探讨不同角度载荷对股骨头骨小梁形态学与力学性能的影响,为研究股骨头坏死、塌陷的生物力学机制提供理论依据。方法 利用12月龄羊股骨头和人尸体股骨头分别制作羊股骨头骨小梁试件94个和人股骨头骨小梁试件43个。按照受力方向与骨小梁主压力方向之间的不同夹角,将骨小梁以10°间隔分为内翻10°、0°和外翻10°、20°、30°共计5组,模拟股骨颈骨折内固定术后不同戈登（Garden）对线指数下的复位情况。通过分别对羊股骨头骨小梁进行micro-CT扫描、计算与压缩破坏试验以及对人尸体股骨头骨小梁进行循环压缩试验,分析不同受力方向下股骨头骨小梁的骨体积分数（BV/TV）、骨表面积/骨体积（BS/BV）、骨小梁平均厚度（Tb.Th）、骨小梁数量（Tb.N）、骨小梁间距（Tb.Sp）等形态学指标以及弹性模量、极限强度、屈服强度、初始弹性模量、循环次数等力学指标。结果 加载方向与骨小梁的主压力方向之间夹角为0°时,BV/TV、Tb.Th以及弹性模量、极限强度、屈服强度、初始弹性模量、循环次数均为最大,而BS/BV与Tb.N为最小,并随着夹角增大前者呈递减而后者呈递增趋势。结论 12月龄羊股骨头骨小梁BV/TV与极限强度随受力方向与骨小梁主压力方向之间夹角变化的趋势与人股骨头骨小梁一致;加载方向与主压力骨小梁之间夹角增大时,股骨头骨小梁形态学与力学性能均下降;Garden指数偏离160°越大时,股骨头内骨小梁越易发生损伤。     

2-Cys peroxiredoxin PfTrx-Px1 is involved in the antioxidant defence of Plasmodium falciparum

Peroxiredoxins (Trx-Px) are ubiquitous antioxidant enzymes that catalyse the thioredoxin-dependent reduction of hydroperoxides. The number of characteristic active site (VCP/T) motifs defines these proteins as 1-Cys and 2-Cys Trx-Px. Steady-state kinetic parameters of Plasmodium falciparum 2-Cys Trx-Px (PfTrx-Px1) were determined using stopped flow rapid kinetics. The bi-substrate reaction displays ping-pong kinetics and the K_m values for H₂O₂ and thioredoxin were determined to be 0.78±0.14 μM and 18.94±3.01 μM, respectively. The V_max^app and k_cat^app for H₂O₂ were found to be 4±0.6 U mg⁻¹ and 1.67±0.25 s⁻¹, respectively and those for thioredoxin are 23.0±0.2 U mg⁻¹ and 9.65±0.1 s⁻¹, emphasising the specificity of the enzyme for the substrate H₂O₂. After subjection to exogenous and endogenous oxidative stress, P. falciparum blood stage forms showed a marked elevation of PfTrx-Px1 mRNA and protein levels consistent with the hypothesis that it is an important component of the parasite’s antioxidant machinery. Gel filtration, cross-linking and electron microscopy (EM) revealed that the protein forms decamers consisting of pentamers of homodimers that have a doughnut-like shape consistent with the structures of related proteins. No dimeric forms of the protein were detectable after gel filtration suggesting that PfTrx-Px1 predominantly exists as an oligomer.     

Stiffness index identifies patients with osteoporotic fractures better than ultrasound velocity or attenuation alone

Objectives: To compare a composite ultrasonometry variable, the stiffness index (SI), with its two component variables of speed of sound (SOS) and broadband ultrasound attenuation (BUA), in identifying post-menopausal women with low bone mineral density (BMD) and/or osteoporotic fracture. Methods: A cross sectional sample of 1217 women (mean (S.D.) age 53.9 (9.7) years) was studied. Risk factors for osteoporosis were assessed by detailed questionnaire and women with diseases, or those taking treatments known to affect bone metabolism were excluded. Women were allocated to one of four groups: pre-menopausal women (n=476), healthy post-menopausal women (n=583), post-menopausal women with low BMD (n=101), and post-menopausal women with osteoporotic fracture (n=57). An Achilles ultrasonometer was used to perform quantitative ultrasonometry (QUS) at the os calcis. The SI, calculated mathematically from SOS and BUA, was computed. Results: Analysis of receiver operating curves (ROC) between healthy post-menopausal women and post-menopausal women with low BMD but no fracture, showed that the area under the curve (AUC) for SI was significantly greater than that for BUA (P<0.001) or SOS (P<0.05). For healthy post-menopausal women compared to women with fracture, the area AUC for SI was significantly greater than that for BUA (P<0.05) or SOS (P<0.001). No significant difference was found for AUC between BUA and SOS. Conclusion: QUS variables discriminated women with low density or fracture from healthy postmenopausal controls. The SI was a significantly better indicator than BUA or SOS in this retrospective study.     

Acoustic emission and mechanical properties of trabecular bone

The mechanical properties of trabecular bone and a simple plug prosthetic system have been determined over a range of displacement from 0.1 to 5 mm/min. Acoustic emission, a technique which is capable of detecting dynamic processes within a material, was used to monitor the compression tests on the prosthetic system. It was found that the stiffness and strength of trabecular bone and the prosthetic system increased with increasing strain rate of testing. The acoustic emission results demonstrated that the improvement in mechanical behaviour at the fast strain rates was accompanied by a decrease in the extent of the failure of the trabeculae. The technique of activation analysis has been applied to the results in order to identify the rate controlling fracture mechanism. Finally, the strength of the prosthetic system was correlated with the shear and compressive strengths of trabecular bone.     

Mechanical behavior of human cortical bone in cycles of advancing tensile strain for two age groups

The capacity of bone for post-yield energy dissipation decreases with age. To gain information on the causes of such a change, we examined age-related changes in the mechanical behavior of human cadaveric bone as a function of progressive deformation. In this study, tensile specimens from tibiae of nine middle aged and eight elderly donors were loaded till failure in an incremental and cyclic (load-dwell-unload-dwell-reload) scheme. The elastic modulus, maximum stress, permanent strain, stress relaxation, permanent strain energy, elastic release strain energy, and hysteresis energy were determined in each loading cycle at incremental strains. Similar with previous work, the results of the present study also indicated that elderly bone failed at much lower strains compared to middle aged bone. However, no significant differences in the mechanical behavior of bone were observed between the two age groups except for the premature failure of elderly bone. After yielding, the energy dissipation and permanent strain of bone appeared to linearly increase with increasing strain applied, while nonlinear changes occurred in the modulus loss and stress relaxation with increasing strain. Moreover, stress relaxation tended to peak at 1% strain beyond which few elderly bone specimens survived. This study suggests that damaging mechanisms in bone vary with deformation, and aging affects the post-yield mechanisms, thus giving rise to the age-related differences in the mechanical properties of bone, especially the capacity of the tissue for energy dissipation.     

The influence of physical activity on the response of bone mineral density to 5 years tibolone

Objectives: Menopausal hormone replacement therapy (HRT) maintains bone mineral density (BMD) and reduces risk of fracture in postmenopausal women. It has been suggested that sex steroids and loading may have synergistic effects on bone. We therefore investigated whether habitual physical activity influences the response of BMD to tibolone in postmenopausal women. Methods: The subjects were 42 postmenopausal women aged mean (SE) 65.8±6.2 year who had taken tibolone for prevention/ treatment of osteoporosis over 5 years. Bone mineral density was measured annually by dual X-ray absorptiometry and physical activity was assessed using accelerometers after 5 years therapy. Results: Twenty-six women were classified as having low physical activity (LPA; <15 min day⁻¹) and sixteen as high physical activity (HPA; >15 min day⁻¹). Spine BMD did not differ significantly between groups at baseline and increased significantly by 2 years of treatment with further increase to 5 years. The magnitude of increase did not differ between groups. Hip BMD at baseline was 7.3% higher in HPA women (P=0.07). Hip BMD increased over 2 years tibolone treatment in LPA women (+5.6%, P<0.01) whilst no significant change occurred in the HPA group (−0.5%). This difference in response between groups was statistically significant (P=0.002) and persisted after adjustment for age and body mass (P=0.002). Hip BMD was maintained in both groups over the subsequent 3 years of treatment. Conclusions: Spine BMD increased significantly in response to tibolone irrespective of physical activity participation. The more physically active women had higher hip BMD at baseline but the response to tibolone was greater in the less physically active women. The difference in response between groups may be due to physically active women having lower resorption at the hip and hence reduced response to anti-resorptive effects of HRT.     

Structural and material mechanical properties of human vertebral cancellous bone

The structural Young's modulus (i.e. that of the cancellous framework) was determined by non-destructive compressive mechanical testing in the three orthogonal axes of 48 vertebral bone cubes. In addition, the material Young's modulus (i.e. of the trabeculae themselves) was estimated using an ultrasonic technique. Apparent and true density were determined by direct physical measurements. Significant mechanical anisotropy was observed: mean structural Young's modulus varied from 165 MPa in the supero-inferior direction to 43 MPa in the lateral direction. Structural Young's modulus correlated with apparent density, with power-law regression models giving the best correlations (r² = 0.52-0.88). Mechanical anisotropy increased as a function of decreasing apparent density (p < 0.001). Material Young's modulus was 10.0 ± 1.3 GPa, and was negatively correlated with apparent density (p < 0.001). In multiple regression models, material Young's modulus was a significant independent predictor of structural Young's modulus only in the supero-inferior direction. The data suggest the presence of two effects in vertebral bone associated with decreasing apparent density and, by implication, bone loss in general: (a) increased mechanical anisotropy, such that there is relative conservation of stiffness in the axial direction compared with the transverse directions; and (b) increased stiffness of the trabeculae themselves.     

Comparison of the influences of structural characteristics on bulk mechanical behaviour: experimental study using a bone surrogate

An experimental study was conducted to classify the influence of trabecular architecture and cortical shell thickness on the mechanical properties using a bone surrogate. Thirty-six rectangular prisms and 18 vertebral-shaped specimens were fabricated with fused deposition modelling (FDM) as a bone surrogate with controlled structural characteristics (cortical wall thickness, strut spacing, strut angle and strut orientation). The apparent density of the FDM specimens was evaluated using quantitative computed tomography (QCT) imaging and related to the apparent elastic modulus measured with compression testing. The effects of the structural parameters on the apparent elastic modulus were analysed using analysis of variance (ANOVA). The results obtained corroborate that the structural parameters have a significant effect on the apparent mechanical properties of the bulk material. The cortical shell thickness was found to have more influence than trabecular architecture. Therefore, accurate modelling of the cortical shell thickness should be considered more important than trabecular architecture in development of bone finite element models and bone surrogates.     

Biomechanics of the saphenous artery and vein in spontaneous hypertension in rats

Incremental compliance and distensibility of certain muscular arteries were recently reported to be normal or slightly increased in hypertension at the same pressure levels. In this work biomechanical properties of isolated perfused and superfused veins and large muscular arteries from saphenous bed from male spontaneously hypertensive (SHR) and Wistar–Kyoto (WKY) rats were compared in vitro. Outer diameter of cylindrical vessel segments was measured and intraluminal pressure (IP) was changed cyclically. We found larger contractile response to methoxamine (1.06×10⁻⁵ mol/l) in SHR arteries compared to WKY (active strain e.g. at 100 mmHg IP: 7.12±4.1 vs 0.35±0.46%). Resting incremental distensibility was higher (e.g. 100 mmHg IP: 3.4±0.4×10⁻⁶ vs 1.2±0.3×10⁻⁷ m²/N), elastic modulus lower (e.g. 100 mmHg IP: 3.7±0.6×10⁵ vs 27±7.6×10⁵ N/m²) in the arteries from SHR in pressure range of 60–110 mmHg. After papaverine administration (2.8×10⁻⁴ mol/l) the artery became more rigid, thus the increased incremental elasticity of SHR artery might be due to the enhanced smooth muscle tone. However, compared at in vivo pressure levels the differences were negligible suggesting a shift in the elastic parameters toward the higher operation pressures. Saphenous vein of SHR had larger diameter, than that of WKY, while in the wall thicknesses no difference were found (therefore external radius-wall thickness ratio was larger, e.g. at 6 mmHg IP: 15.9±3.0 vs 8.1±0.7). Consequently, lumen capacity of the vein was also higher in SHR, however, elastic parameters did not exhibit significant differences. We conclude that pressure-distensibility curve of muscular type arteries like SHR saphenous artery is shifted to higher pressure levels compared with that of normotensive controls. This shift is due to the enhanced smooth muscle contractility. The unchanged elasticity of veins suggests that the arterial deformations in SHR are not primary but secondary alterations.     

Effect of estrogen replacement therapy on speed of sound at multiple skeletal sites

Objectives: To evaluate the effect of estrogen replacement therapy (ERT) on postmenopausal bone loss by multi-site ultrasound measurement. Methods: A cross-sectional comparison of postmenopausal women, ERT users and non-users. The two study groups were enrolled for the reference database collection for the Sunlight Omnisense™ (Omnisense) and were matched by years since menopause. Speed of sound (SOS) was measured at the distal radius (RAD), mid-shaft tibia (TIB), fifth metatarsus (MTR) and proximal phalanx (PLX). Results: 143 ERT users for 5.2±3.6 years were compared with 139 ERT non-users (age: 57.0±5.3 and 57.5±5.5, respectively). Both groups were 7.1±5.0 years since menopause. SOS, expressed in T-score units, was higher at the RAD in ERT users as compared to ERT non-users (−0.55±1.30 and −1.36±1.60, respectively, P<0.0001), and at the TIB (−0.73±1.34 and −1.28±1.45, respectively, P=0.003). Same trend was observed at the MTR and PLX, but not statistically significant because of fewer observations. In early post menopause period, the ERT-non users RAD data shows an annual SOS decrease of 0.17 versus annual increase of 0.12 T-score units (P=0.037). Similar effect is observed at the TIB, though not statistically significant (non-users decrease of 0.20 vs. users increase of 0.08 T-score units/year, P=0.086). Conclusions: SOS measurements by Omnisense at multiple skeletal sites support the ERT protective effect on bone.     

股骨近端主压力骨小梁生物力学特性

目的股骨头坏死是一种常见病,导致其发病的原因有很多,其中股骨颈骨折后股骨头坏死的原因尚不清楚,机制不明,由于其局部解剖结构特殊,根据其内部结构特点,对骨小梁结构进行研究,为解释股骨颈骨折后股骨头坏死的发生原因提供实验依据。方法对正常中国人(45～60岁)尸体股骨近端主压力骨小梁系统从上到下分成3个区,分别在Endura TEC ELF3200生物力学材料动态力学性能测试系统上,从主压力骨小梁方向及与其垂直方向上进行拉伸、压缩性能实验研究。结果得出了股骨近端主压力骨小梁系统3个区在主压力骨小梁系统方向及与其垂直方向的压缩、拉伸屈服强度、极限强度、弹性模量等测试指标的实验结果。从上到下3个区的弹性模量等生物力学性能依次递增,主压力方向的压缩生物力学性能要明显高于拉伸生物力学性能,并且生物力学性能在主压力系统方向及与其垂直方向有明显差异。结论股骨近端主压力骨小梁的主要力学性能是承受压应力,并且具有明显的各向异性。     

Elastic strains in antler trabecular bone determined by synchrotron X-ray diffraction

The microstructure and associated mechanical properties of antler trabecular bone have been studied using a variety of techniques. The local trabeculae properties, as well as the three-dimensional architecture were characterized using nanoindentation and X-ray microtomography, respectively. An elastic modulus of 10.9+/-1.1 GPa is reported for dry bone, compared with 5.4+/-0.9 GPa for fully hydrated bone. Trabeculae thickness and separation were found to be comparable to those of bovine trabecular bone. Uniaxial compression conducted in situ during X-ray microtomography showed that antler can undergo significant architectural rearrangement, dominated by trabeculae bending and buckling, due to its low mineral content. High-energy synchrotron X-ray diffraction was used to measure elastic strains in the apatite crystals of the trabeculae, also under in situ uniaxial compression. During elastic loading, strain was found to be accommodated largely by trabeculae aligned parallel to the loading direction. Prior to the macroscopic yield point, internal strains increased as trabeculae deformed by bending, and load was also found to be redistributed to trabeculae aligned non-parallel to the loading direction. Significant bending of trabecular walls resulted in tensile strains developing in trabeculae aligned along the loading direction.     

各向异性松质骨弹性性能有限元分析

骨质疏松会导致松质骨细化从而降低松质骨力学性能。为了评估椎体松质骨的力学特性,文中采用有限元参数化建模,利用十四面体模型模拟棒状小梁骨的微结构,对各向异性松质骨的弹性性能进行了计算分析。通过控制输入参数Tb.Th、Tb.Sp、E0模拟不同骨质疏松程度的松质骨。计算结果表明,松质骨模量与骨体积分数呈平方律关系;随着各向异性比的增加,松质骨纵、横向模量间的比值呈线性增加,而横向两个模量保持基本一致。结果说明该微结构模型较好地反映了松质骨的横观各向同性性质,并能较好地反映受载松质骨的应力分布。