Segmental variations in trabecular bone density and microstructure of the spine in senescence-accelerated mouse (SAMP6): a murine model for senile osteoporosis

The senescence-accelerated mouse strain P6 (SAMP6) is a model of senile osteoporosis, which possesses many features of senile osteoporosis in humans. So far, little is known about the systemic bone microstructural changes that occur at the cervical, thoracic, and lumbar vertebrae. In this study, we therefore investigated segmental variations of vertebral trabecular bone mineral density (BMD) and three-dimensional microstructure in SAMP6 and the normal control mouse (SAMR1) at 12 months of age using quantitative micro computed tomography (micro-CT) and image analysis software. The vertebral height and vertebral cross-sectional area (CSA) increased, while vertebral trabecular BMD and trabecular bone volume fraction (BV/TV) decreased from the cervical to lumbar spine both in SAMR1 and SAMP6. As compared with SAMR1, the thoracic vertebral CSA had a tendency to be low and the lumbar vertebral CSA was significantly declined in SAMP6. The vertebral trabecular BMD, BV/TV, trabecular thickness (Tb.Th), and trabecular number (Tb.N) significantly decreased in cervical, thoracic and lumbar spine of SAMP6. Trabecular bone pattern factor (TBPf) was higher at the lumbar spine and the structure model index (SMI) of the lower thoracic and lumbar spine was higher in SAMP6. These results indicate that vertebral trabecular bone microstructures are remarkably heterogeneous throughout the spine in both SAMR1 and SAMP6. The decrease of vertebral trabecular bone density in SAMP6 advanced faster caudally than cranially within the spine, similar phenomena were observed in humans. These findings highlight the relevance of SAMP6 for studies of vertebral fragility associated with senile osteoporosis.     

雄性ApoE基因敲除小鼠不同时期骨密度和骨微结构的改变

目的 观察ApoE基因敲除(ApoE-/-)小鼠的骨微结构、骨密度、骨矿含量(BMC)的变化,探讨ApoE在骨重建中的作用.方法 15、28和40周龄雄性ApoE-/-纯合子小鼠以及同性别、同周龄的野生型小鼠共48只,应用显微CT测定小鼠右侧股骨远端松质骨和皮质骨的骨微结构参数,双能X线骨密度仪(DXA)测定左侧股骨骨密度.并分析骨微结构、骨密度、BMC相关性.结果 与野生鼠相比,不同时期ApoE-/-鼠的股骨松质骨体积骨密度(vBMD)、组织骨密度、BMC、骨体积分数(BV/TV)、骨小梁数量(Tb.N)、骨小梁厚度(Tb.Th)明显增加(P<0.05),骨面积分数(BS/BV)、骨小梁间隔(Tb.SP)和结构模型指数明显减低(P<0.05).股骨皮质骨内径周长、皮质骨外径周长、皮质骨面积、骨髓腔面积、截面总面积和截面惯性矩增加,而皮质骨骨密度、皮质骨BMC和皮质骨厚度变化不明显.DXA测定显示28周龄ApoE-/-鼠的总体骨密度明显高于野生型鼠(P<0.05),15和40周龄ApoE-/-鼠总体骨密度与对照组相比,无统计学差异.28周龄ApoE-/-鼠vBMD与BMC、BV/TV、Tb.Th、BS/BV和皮质骨BMC明显相关,相关系数分别为0.955、0.944、0.834、0.923和0.903,而与其他参数不相关.结论 ApoE-/-鼠表现出骨量增加,提示ApoE在骨重建中起重要作用.     

去卵巢大鼠椎体松质骨骨小梁微结构改变及其对生物力学的影响

目的观察骨质疏松和正常状态下椎体松质骨的微观结构改变,分析其对骨生物力学的影响。方法将12只4月龄雌性Lewis大鼠随机分为去卵巢组(OVX)组和假手术组(Sham),每组各6只。OVX组行双侧卵巢切除术,假手术组仅显露双侧卵巢。术后6个月处死动物,取尾椎(L_(4-7))行Micro-CT分析及生物力学测试。结果去卵巢6个月后,OVX组大鼠体积骨密度(vBMD)和组织骨密度(tBMD)较Sham组显著降低,松质骨骨小梁的骨体积分数(BV/TV)和数目(TB.N)都明显低于Sham组,骨小粱表面积密度(BS/BV)、结构模拟指数(SMI)和间距(Tb.Sp)显著高于Sham组,差异有统计学意义。但2组间骨小梁厚度(Tb.Th)差异无统计学意义。生物力学测试结果表明,去势6个月后,OVX组大鼠骨质生物力学性能显著下降。骨小梁力学性能与骨小梁体积分数(Adjusted R~2=0.750和数目(Adjusted R~2=0.861)呈正线性相关,而与结构模拟指数(Adjusted R~2=0.716)和骨小梁间距(Adjusted R~2=0.830)呈负线性相关。结论松质骨骨小梁微观结构的改变可影响骨质的生物力学性能,二者之间具有一定的线性关系。     

大鼠去卵巢后不同时期骨微结构和力学性能的变化特征

目的揭示大鼠在去卵巢后不同时期腰椎松质骨微结构退变的变化特征,探讨骨整体力学性能下降的同时可能存在的各种适应性代偿性变化。方法50只7月龄SD大鼠随机分为基线、去卵巢组（OVX组）和假手术组（SHAM）。基线组10只,其余每组均20只。实验开始时先将基线组10只处死,OVX组和SHAM组分别在手术后3周、15周各处死10只,留取动脉血清及腰椎标本,骨微结构、力学和生化指标的测定。结果去卵巢后3周时OVX组表观骨密度、骨体积分数、骨小梁厚度和骨小梁数量均较SHAM和基线降低（P〈0．05）,各向异性度较基线下降（P〈0．05）而与SHAM组无统计学差异。骨小梁面积密度、骨小梁间隔和结构模型指数均较SHAM和基线组增加（P〈0．05）。去卵巢后3周时OVX组最大应力、弹性模量、血清TRAP-5b和骨细胞密度均低于基线（P〈0．05）而与SHAM组无统计学差异。去卵巢后15周时OVX组表观骨密度、骨体积分数、骨小梁数量和联接密度、最大应力、TRAP-Sb和骨细胞密度均较SHAM和基线组降低（P〈0.05）,骨小梁结构模型指数、骨小梁间隔和各向异性度均较SHAM和基线组增加（P〈0．05）,骨小梁面积密度和厚度均与SHAM和基线组无统计学差异。结论大鼠去卵巢后腰椎骨量快速丢失,骨微结构逐渐退变,而血清TRAP-5b水平下降及骨细胞密度、骨小梁各向异性度和厚度的适应性增加,可能在一定程度上代偿骨力学性能的下降,有利于维持骨结构的完整性。     

Site-specific bone loss in senescence-accelerated mouse (SAMP6): A murine model for senile osteoporosis

The senescence-accelerated mouse strain P6 (SAMP6) is a model of senile osteoporosis, which possesses many features of senile osteoporosis in humans. So far, little is known about the systemic bone microstructural changes that occur at multiple skeletal sites. In this study, we therefore, investigated site (vertebra, femur and tibia) dependence of bone microstructure and bone mineral density (BMD) in SAMP6 and the normal control mouse (SAMR1) at 5 and 12 months of age using quantitative micro computed tomography (micro-CT) and image analysis software. As compared with SAMR1, the most prominent change in SAMP6 was the reduction of vertebral trabecular bone volume fraction (BV/TV) and trabecular BMD. Moderate decrease of trabecular bone mass was observed in the proximal tibia and distal femur. Increased marrow area and periosteal perimeter were investigated, though the cortical area and cortical thickness had no marked changes in the mid-tibial and mid-femoral cortical bones. These results indicate that bone microstructural properties in SAMP6 are remarkably heterogeneous throughout the skeleton, which is analogous to changes that occur in human bones. These findings further validate the relevance of SAMP6 as a model of senile osteoporosis.     

Bone histomorphometry in 50 normal tunisian subjects

Summary Quantitative bone histomorphometry was done on undecalcified sections of iliac crest bone specimens obtained at autopsy from 50 normal subjects (24 males and 26 females). The following parameters were measured: cortical thickness (Ct.Th), trabecular bone volume (BV/TV), trabecular number (Tb.N), trabecular thickness (Tb.Th), osteoid volume (OV/BV), osteoid surfaces (OS/BS), osteoid thickness (O.Th) and eroded surfaces (ES/BS). There was a significant age-related decrease in BV/TV in both sexes which followed a x³ polynomial regression. A significant decrease of Tb.Th was noted in males after the fifth decade. In males, bone loss was 1.5% per decade, but in females it was 0.36% before menopausal period and 2% after. Other parameters were unrelated to age and sex.     

旋转中心偏移对显微CT松质骨定量分析的影响

目的观察旋转中心微小偏移对显微CT测量参数的影响。方法20只7月龄sD大鼠随机分为去卵巢组（OVX）和假手术组（SHAM）。手术后3周处死,应用显微cT扫描胫骨近干骺端。手动校正以获取每次扫描的最佳旋转中心,分析各旋转中心在偏移±0．5、±1．0、±1．5和±2．0像素条件下的密度及微结构参数。结果一般线性模型分析结果显示OVX组与SHAM组比较,表观骨密度、组织骨密度、骨体积分数、骨小梁数量和联接密度明显下降,骨小梁间隔明显增宽（P〈0．05）。组织骨密度、各向异性度、骨小梁面积密度和联接密度随旋转中心的偏移下降,骨体积分数和骨小梁厚度随偏移幅度的加大逐渐升高。旋转中心偏移±1．5像素内,对组织骨密度、骨体积分数、各向异性度和联接密度的测量无影响。而骨小梁厚度和骨小梁面积密度在旋转中心偏移±1．0像素内影响较小。OVX组与SHAM组各参数随旋转中心偏移的变化趋势基本一致。各参数随旋转中心偏移服从二次回归方程趋势。通过二次回归方程拟合,可以获得实际旋转中心。以该中心获取的图像质量高,并能确保定量分析数据的准确。实际旋转中心与人为校正的最佳旋转中心之间存在微小差异。结论旋转中心的微小偏移对表观骨密度、结构模型指数、骨小梁间隔和数量的测量无明显影响。组织骨密度、骨小梁厚度、骨小梁面积密度、骨体积分数、各向异性度和联接密度受旋转中心偏移影响较大。通过二次曲线方程拟合能找到正确的旋转中心,该中心与人为校正获取的最佳旋转中心存在一定误差。     

骨细胞GLP-1受体表达对2型糖尿病大鼠骨微结构的影响

目的观察2型糖尿病大鼠股骨颈骨细胞表达胰高血糖素样肽-1受体(GLP-1R)阳性细胞百分数的变化,探讨骨组织GLP-1R变化对骨微结构的影响。方法雄性Wistar大鼠60只,随机分为实验组(30只)和对照组(30只),实验组采用高糖高脂饲料喂养至12周时加小剂量链脲佐菌素腹腔注射诱导糖尿病模型,对照组采用普通饲料喂养。分别于造模成功时和成模后第12周,处死10只大鼠作为糖尿病0周组(DM0w组,n=10)和糖尿病12周组(DM12w组,n=10),对照组分别于同期各处死10只大鼠作为正常对照(NGT0w组,n=10;NGT12w组,n=10)。经腹主动脉采血测定空腹血糖(FBG)、胆固醇(TC)、三酰甘油(TG)。取近端股骨颈,制备脱钙和不脱钙骨切片,备免疫组化检测GLP-1R阳性的骨细胞,采用Simple软件分析骨小梁形态计量学指标:骨小梁占骨髓腔体积百分比(BV/TV)、骨小梁厚度(Tb.Th)、骨小梁数目(Tb.N)。采用单因素方差分析比较各组大鼠股骨颈表达GLP-1R阳性的骨细胞百分数,BV/TV、Tb.Th、Tb.N的变化,采用Pearson行相关分析。结果与同期对照组相比,DM0w组、DM12w组大鼠FBG、TC、TG升高(均P0.05);与同期对照组相比,DM0w组、DM12w组大鼠股骨颈表达GLP-1R阳性骨细胞百分数和BV/TV、Tb.Th均减少(均P0.05);与DM0组相比,DM12组大鼠股骨颈表达GLP-1R阳性的骨细胞百分数、BV/TV、Tb.Th、Tb.N均减少(均P0.05);Pearson相关分析显示大鼠股骨颈GLP-1R阳性骨细胞百分数与股骨颈BV/TV、Tb.Th、Tb.N均呈正相关,相关系数分别为r=0.803,P0.05;r=0.545,P0.05;r=0.771,P0.05。结论糖尿病大鼠股骨颈骨细胞GLP-1R的表达减少,同时BV/TV、Tb.N减少,Tb.Th变薄,骨细胞GLP-1R的表达可能是影响2型糖尿病骨微结构的因素之一。     

The effects of binge alcohol exposure on bone resorption and biomechanical and structural properties are offset by concurrent bisphosphonate treatment

BACKGROUND: Chronic alcohol consumption reduces bone mass and strength, increasing fracture risk for alcohol abusers. Mechanisms underlying this vulnerability involve modulation of bone remodeling. Direct effects of alcohol on bone formation have been documented; those on bone resorption are less well studied. Skeletal effects of exposure to high blood alcohol concentrations (BAC's) attained during binge drinking have not been studied. We examined the effects of repeated binge-like alcohol treatment on bone resorption, bone mineral density and vertebral compressive strength in adult male rats treated with the aminobisphosphonate, risedronate. METHODS: A binge alcohol exposure model was developed using intraperitoneal (IP) injection to administer a 20% (vol/vol) alcohol/saline solution (3 g/kg, 1X/day) on four consecutive days for 1, 2 or 3 weeks in 400 g rats, with and without weekly risedronate treatment (0.5 mg/kg, 1X/week). Total serum deoxypyridinoline (Dpd) a crosslink of bone type collagen released during resorption was measured by ELISA. Bone mineral density (BMD) was measured using peripheral quantitative computed tomography (pQCT). Vertebral compressive strength was determined using an Instron materials testing machine. Trabecular integrity was analyzed by computer-aided trabecular analysis system (TAS). RESULTS: Peak BAC's averaged 308.5 +/- 12 mg/dL; average BAC was 258.6 +/- 28.7 mg/dL at time of euthanasia. No significant effects of treatment were observed after 1 or 2 weeks of binge alcohol exposure. At 3 weeks of alcohol treatment serum Dpd was significantly increased (205%, p < 0.05) over controls. Bone mineral density (BMD) in cancellous bone of distal femur and lumbar spine were significantly decreased (34% and 21% respectively, p < 0.01) after 3 weeks of binge treatment. Vertebral (L4) compressive strength (maximum load sustained before failure) also decreased (27%, p < 0.05) after 3 binge alcohol cycles. Risedronate maintained the Dpd level (p < 0.01), BMD (p < 0.001) and vertebral structural biomechanical properties (p < 0.01) of binge-treated rats at control levels (E vs ER). Indices of trabecular architectural integrity [Trabecular bone volume/tissue volume (BV/TV), bone area (BAR) and trabecular separation (Tb.Sp)] analyzed at week 3 showed (BV/TV) and (BAR) were significantly reduced in alcohol-binged rats (p < 0.01), while (Tb.Sp) was significantly increased (p < 0.01). Risedronate also maintained the trabecular architectural indices of binge-treated rats at control levels (E versus ER, p < 0.01). CONCLUSIONS: In adult male rats, BAC's reflective of those attained during alcoholic binge drinking may affect the skeleton in part by stimulating bone resorption, an effect mitigated by risedronate.     

Decreased bone strength in HLA-B27 transgenic rat model of spondyloarthropathy

OBJECTIVE: To investigate the nature of osteopenia/osteoporosis in spondyloarthropathy, an inflammatory disorder, using the HLA-B27 transgenic rat model. METHODS: HLA-B27 transgenic rats were housed individually and sacrificed at the peak of their disease (8-month-old). The spine and femurs were removed and stored in saline at -20 degrees C until analysis. The bone structure and strength were determined using a micro-computed tomography (micro-CT) device (Scanco Medical) and mechanical testing (Instron 5543). Vertebral bodies and femurs were scanned to determine trabecular structural properties in terms of bone volume (BV/TV), trabecular thickness, and spacing. After scanning, the mid-shaft femurs were subjected to a 3-point bending test (along anterior-posterior direction), the femoral necks were tested in bending, and the vertebral bodies (L4) were tested in compression. Structural (ultimate/yield load, stiffness) and apparent material (ultimate/yield stress, modulus) strength parameters were then determined. RESULTS: The majority of the bone structural and strength parameters were significantly lower (P < 0.05) in the HLA-B27 transgenic rats as compared with control littermates. Micro-CT data suggested that the transgenic animals had lower BV/TV and trabecular thickness in their vertebral bodies. The poor trabecular structure observed in HLA-B27 rats is also indicative of the poor biomechanical strength properties in the vertebral bodies as well. CONCLUSION: The HLA-B27 transgenic rats develop bone fragility similar to that seen in spondyloarthropathy and may be an important model for the study of osteoporosis in spondyloarthropathy.     

Bone Density Micro-CT Assessment during Embedding of the Innovative Multi-Spiked Connecting Scaffold in Periarticular Bone to Elaborate a Validated Numerical Model for Designing Biomimetic Fixation of Resurfacing Endoprostheses

Our team has been working for some time on designing a new kind of biomimetic fixation of resurfacing endoprostheses, in which the innovative multi-spiked connecting scaffold (MSC-Scaffold) that mimics the natural interface between articular cartilage and periarticular trabecular bone in human joints is the crucial element. This work aimed to develop a numerical model enabling the design of the considered joint replacement implant that would reflect the mechanics of interacting biomaterials. Thus, quantitative micro-CT analysis of density distribution in bone material during the embedding of MSC-Scaffold in periarticular bone was applied. The performed numerical studies and corresponding mechanical tests revealed, under the embedded MSC-Scaffold, the bone material densification affecting its mechanical properties. On the basis of these findings, the built numerical model was modified by applying a simulated insert of densified bone material. This modification led to a strong correlation between the re-simulation and experimental results (FVU = 0.02). The biomimetism of the MSC-Scaffold prototype that provided physiological load transfer from implant to bone was confirmed based on the Huber–von Mises–Hencky (HMH) stress maps obtained with the validated finite element (FE) model of the problem. The micro-CT bone density assessment performed during the embedding of the MSC-Scaffold prototype in periarticular bone provides insight into the mechanical behaviour of the investigated implant-bone system and validates the numerical model that can be used for the design of material and geometric features of a new kind of resurfacing endoprostheses fixation.     

Risedronate prevents the loss of microarchitecture in glucocorticoid-induced osteoporosis in rats

Osteoporosis is a severe complication of glucocorticoid treatment. Bisphosphonates are a powerful therapeutic option to prevent osteoporotic fractures. The aims of this study were: a) to determine bone alterations induced by therapy with glucocorticoids (GC); b) to establish the efficacy of risedronate (Ris) in the prevention of these effects. We studied 40 female Sprague-Dawley rats randomly divided into 4 groups of treatment, administered 3 times a week sc: 1. Control: vehicle of methylprednisolone (GC) + vehicle of Ris; 2. Ris: Ris 5 mug/kg body weight vehicle of GC; 3. GC: GC 7 mg/kg + vehicle of Ris; 4. GC+Ris: GC 7 mg/kg, Ris 5 microg/kg. Animals were treated for 30 days and then were sacrificed. Densitometry was performed at baseline and at the end of the treatment. Right tibiae were removed for histomorphometric analyses. The GC group showed a 7% decrease in bone density vs controls (p<0.05), while the GC+Ris group was associated with a 3.5% increase in bone density vs controls (p<0.05). In the GC group, histomorphometric evaluations showed reduced bone volume (BV/TV) and thinning of trabeculae (Tb.Th) vs controls (BV/TV: 31+/-1 vs 35+/-1%, p<0.05; Tb.Th: 43+/-2 vs 50+/-3 microm, p<0.01; Ac.f: 1.8+/-0.2 vs 1.6+/-0.3 N/yr). The GC+Ris group had increased BV/TV and Tb.Th, and reduced Ac.f vs the GC group. Ris also maintained trabecular microarchitecture. At the histological level, glucocorticoid-induced osteoporosis was characterized by decreased bone volume, reduced osteoblastic activity, and deterioration of microarchitecture. Ris counteracted these effects both by prolonging osteoblast activity, and by maintaining bone microarchitecture.     

The histomorphometry of bone in primary hyperparathyroidism: preservation of cancellous bone structure

To evaluate the effects of primary hyperparathyroidism (PHPT) on bone mass and structure, we have studied the iliac crest biopsies of 27 patients, 10 males (28-68 yr old) and 17 females (26-72 yr old) with mild PHPT after in vivo tetracycline labeling. All patients had mild hypercalcemia in the absence of any other cause and elevated levels of PTH without radiological evidence of bone disease. Static parameters of bone turnover (osteoid surface, osteoid volume, and eroded surface) were elevated in both men and women compared to normal values; the midmolecule RIA for PTH (PTHMM) was positively correlated with osteoid surface (r = 0.44; P less than 0.025) and eroded surface (r = 0.58; P less than 0.005). Dynamic parameters of bone turnover (mineralizing surface, expressed as double plus half single labeled surface, and bone formation rate at tissue level) were elevated compared to normal values; PTHMM was positively correlated with double plus half single labeled surfaces (r = 0.33; P less than 0.05) and with bone formation rate at the tissue level (r = 0.37; P less than 0.05). The mineral apposition rate was within the limits of normal values and positively correlated with PTHMM (r = 0.34; P less than 0.05). Histomorphometric parameters of bone structure [cancellous bone volume (BV/TV), trabecular thickness (Tb. Th), trabecular number (Tb.N), trabecular separation (Tb.Sp), cortical thickness (Ct.Th), and total bone density (TBD)] were compared to those in 20 autopsy control subjects, 12 men (33-60 yr old) and 8 women (27-75 yr old). BV/TV and Tb.N were significantly higher in PHPT patients than controls (P less than 0.02 and P less than 0.001, respectively). Tb.Sp was significantly lower in PHPT patients than controls (P less than 0.001), whereas Tb.Th was not significantly different between PHPT patients and controls. Ct.Th was significantly lower in PHPT patients than in controls (P less than 0.001), whereas TBD was not significantly different between the two groups. BV/TV was negatively correlated with age in both controls and PHPT patients. Tb.N showed a negative correlation and Tb.Sp a positive correlation with age in controls (r = -0.47; P less than 0.05 and r = 0.52; P less than 0.02, respectively), but they were not significantly dependent on age in PHPT patients. Tb.Th, while showing no significant age-related change in controls, was negatively correlated with age in PHPT patients (r = -0.42; P less than 0.05).(ABSTRACT TRUNCATED AT 400 WORDS)     

Leydig cell hyperplasia and the maintenance of bone volume: bone histomorphometry and testicular histopathology in 29 male leprosy autopsy cases

This study was conducted to determine if osteoporosis in male leprosy patients is caused by testicular atrophy. Bone volume (BV/TV), trabecular number (TbN), trabecular thickness (TbTh), and trabecular separation (TbSp) were measured in two areas in decalcified paraffin sections of lumbar bones from 29 male leprosy and 6 male nonleprosy autopsy cases. We found significant differences in the average BV/TV measurements among the 7 patients with nodular Leydig cell hyperplasia (BV/TV 12.24%) and the 22 patients without hyperplasia (BV/TV 7.35%) and 6 patients without leprosy (BV/TV 12.98%). Bone volume was maintained in patients with nodular Leydig cell hyperplasia, and we determined no clinical factor other than the Leydig cell hyperplasia that reflected the bone volume. The osteoporosis of male leprosy patients was attributed to secondary gonadal dysfunction due to testicular atrophy, and Leydig cell hyperplasia appears to preserve bone volume.     

Impact of the Dopant Species on the Thermomechanical Material Properties of Thermoelectric Mg2Si0.3Sn0.7

Thermoelectric generators are an excellent option for waste heat reuse. Materials for such devices have seen their thermoelectric properties improving constantly. The functioning of a generator, however, does not only depend on thermoelectric properties. Thermal and mechanical properties play a decisive role in the feasibility of any thermoelectric generator. To shed light on the properties exhibited by thermoelectric materials, we present the temperature dependent characterization of Young’s modulus and coefficient of thermal expansion for Mg₂Si_0.3Sn_0.7. Comparing undoped to Bi-doped n-type and Li-doped p-type material, we investigated the influence of doping in the relevant temperature regime and found the influences to be minor, proving similar properties for n- and p-type. We found a Young’s modulus of 84 GPa for the p-type and 83 GPa for the n-type, similar to that of the undoped compound with 85 GPa. The thermal expansion coefficients of undoped, as well as n- and p-type were equally similar with values ranging from 16.5 to 17.5 × 10⁻⁶ 1/K. A phase analysis was performed to further compare the two materials, finding a similar phase distribution and microstructure. Finally, using the gathered data, estimations on the possible thermally induced stresses under a temperature difference are provided to evaluate the relevance of knowing temperature dependent thermal and mechanical properties.     

Once-monthly oral ibandronate improves biomechanical determinants of bone strength in women with postmenopausal osteoporosis

CONTEXT: Bone strength and fracture resistance are determined by bone mineral density (BMD) and structural, mechanical, and geometric properties of bone. DESIGN, SETTING, AND OBJECTIVES: This randomized, double-blind, placebo-controlled outpatient study evaluated effects of once-monthly oral ibandronate on hip and lumbar spine BMD and calculated strength using quantitative computed tomography (QCT) with finite element analysis (FEA) and dual-energy x-ray absorptiometry (DXA) with hip structural analysis (HSA). PARTICIPANTS: Participants were women aged 55-80 yr with BMD T-scores -2.0 or less to -5.0 or greater (n = 93). INTERVENTION: Oral ibandronate 150 mg/month (n = 47) or placebo (n = 46) was administered for 12 months. OUTCOME MEASURES: The primary end point was total hip QCT BMD change from baseline; secondary end points included other QCT BMD sites, FEA, DXA, areal BMD, and HSA. All analyses were exploratory, with post hoc P values. Results: Ibandronate increased integral total hip QCT BMD and DXA areal BMD more than placebo at 12 months (treatment differences: 2.2%, P = 0.005; 2.0%, P = 0.003). FEA-derived hip strength to density ratio and femoral, peripheral, and trabecular strength increased with ibandronate vs. placebo (treatment differences: 4.1%, P < 0.001; 5.9%, P < 0.001; 2.5%, P = 0.011; 3.5%, P = 0.003, respectively). Ibandronate improved vertebral, peripheral, and trabecular strength and anteroposterior bending stiffness vs. placebo [7.1% (P < 0.001), 7.8% (P < 0.001), 5.6% (P = 0.023), and 6.3% (P < 0.001), respectively]. HSA-estimated femoral narrow neck cross-sectional area and moment of inertia and outer diameter increased with ibandronate vs. placebo (respectively 3.6%, P = 0.003; 4.0%, P = 0.052; 2.2%, P = 0.049). CONCLUSIONS: Once-monthly oral Ibandronate for 12 months improved hip and spine BMD measured by QCT and DXA and strength estimated by FEA of QCT scans.     

Heat Treatments of Metastable β Titanium Alloy Ti-24Nb-4Zr-8Sn Processed by Laser Powder Bed Fusion

Titanium alloys, especially β alloys, are favorable as implant materials due to their promising combination of low Young’s modulus, high strength, corrosion resistance, and biocompatibility. In particular, the low Young’s moduli reduce the risk of stress shielding and implant loosening. The processing of Ti-24Nb-4Zr-8Sn through laser powder bed fusion is presented. The specimens were heat-treated, and the microstructure was investigated using X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The mechanical properties were determined by hardness and tensile tests. The microstructures reveal a mainly β microstructure with α″ formation for high cooling rates and α precipitates after moderate cooling rates or aging. The as-built and α″ phase containing conditions exhibit a hardness around 225 HV5, yield strengths (YS) from 340 to 490 MPa, ultimate tensile strengths (UTS) around 706 MPa, fracture elongations around 20%, and Young’s moduli about 50 GPa. The α precipitates containing conditions reveal a hardness around 297 HV5, YS around 812 MPa, UTS from 871 to 931 MPa, fracture elongations around 12%, and Young’s moduli about 75 GPa. Ti-24Nb-4Zr-8Sn exhibits, depending on the heat treatment, promising properties regarding the material behavior and the opportunity to tailor the mechanical performance as a low modulus, high strength implant material.     

Effect of Strain Rate and Temperature on Tensile and Fracture Performance of AA2050-T84 Alloy

AA2050-T84 alloy is widely used in primary structures of modern transport aircraft. AA2050-T84 is established as a low-density aluminum alloy with improved Young’s modulus, less anisotropy, and temperature-dependent mechanical properties. During flights, loading rate and temperature variation in aircraft engine subsequent parts are commonly observed. The present work focuses on the effect of loading rate and temperature on tensile and fracture properties of the 50 mm thick (2-inch) AA2050-T84 alloy plate. Quasi-static strain rates of 0.01, 0.1, and 1 s⁻¹ at −20 °C, 24 °C and 200 °C are considered. Tensile test results revealed the sensitivity of mechanical properties towards strain rate variations for considered temperatures. The key tensile properties, yield, and ultimate tensile stresses were positive strain rate dependent. However, Young’s modulus and elongation showed negative strain rate dependency. Experimental fracture toughness tests exhibited the lower Plane Strain Fracture Toughness (K_IC) at −20 °C compared to 24 °C. Elastic numerical fracture analysis revealed that the crack driving and constraint parameters are positive strain rate dependent and maximum at −20 °C, if plotted and analyzed over the stress ratio. The current results concerning strain rates and temperatures will help in understanding the performance-related issues of AA2050-T84 alloy reported in aircraft applications.     

Influence of Size on the Microstructure and Mechanical Properties of an AISI 304L Stainless Steel—A Comparison between Bulk and Fibers

In this work, the mechanical properties and microstructural features of an AISI 304L stainless steel in two presentations, bulk and fibers, were systematically studied in order to establish the relationship among microstructure, mechanical properties, manufacturing process and effect on sample size. The microstructure was analyzed by XRD, SEM and TEM techniques. The strength, Young’s modulus and elongation of the samples were determined by tensile tests, while the hardness was measured by Vickers microhardness and nanoindentation tests. The materials have been observed to possess different mechanical and microstructural properties, which are compared and discussed.     

The Potential of Stereolithography for 3D Printing of Synthetic Trabecular Bone Structures

Synthetic bone models are used to train surgeons as well as to test new medical devices. However, currently available models do not accurately mimic the complex structure of trabecular bone, which can provide erroneous results. This study aimed to investigate the suitability of stereolithography (SLA) to produce synthetic trabecular bone. Samples were printed based on synchrotron micro-computed tomography (micro-CT) images of human bone, with scaling factors from 1 to 4.3. Structure replicability was assessed with micro-CT, and mechanical properties were evaluated by compression and screw pull-out tests. The overall geometry was well-replicated at scale 1.8, with a volume difference to the original model of <10%. However, scaling factors below 1.8 gave major print artefacts, and a low accuracy in trabecular thickness distribution. A comparison of the model–print overlap showed printing inaccuracies of ~20% for the 1.8 scale, visible as a loss of smaller details. SLA-printed parts exhibited a higher pull-out strength compared to existing synthetic models (Sawbones ™), and a lower strength compared to cadaveric specimens and fused deposition modelling (FDM)-printed parts in poly (lactic acid). In conclusion, for the same 3D model, SLA enabled higher resolution and printing of smaller scales compared to results reported by FDM.