Effect of long-term preservation on the mechanical properties of cortical bone in goats

Background and purpose?Bones used in mechanical studies are frequently harvested from human cadavers that have been embalmed in a buffered formaldehyde solution. It has been reported that formaldehyde fixation or freezing hardly affects the mechanical properties of bone after a storage period of several weeks. However, human cadaver bones are usually stored for longer periods of time before use. We therefore investigated the effects of long-term embalming or freezing on the mechanical properties of cortical bone.

Methods?After 5 different storage periods (ranging from 0 to 12 months), goat femora and humeri were used to evaluate the effect of embalming and freezing on torsion, and on bending stiffness and strength. The effect on hardness and bone mineral density (BMD) was also evaluated.

Results?Even after 1 year, no statistically significant differences could be found in stiffness, strength, and energy absorption when we compared embalmed or frozen bones to a fresh reference group. In addition, although we found no significant change in BMD, there appears to be a tendency to increasing hardness.

Interpretation?We found that there was no effect on the mechanical properties of bone after storage periods of 1 year. We conclude that embalmed or frozen bones can safely be used for mechanical testing, at least for storage periods of up to one year.     

Effect of age on mechanical properties of the collagen phase in different orientations of human cortical bone

The collagen phase plays an important role in mechanical behaviors of cortical bone. However, aging effects on the mechanical behavior of the collagen phase is still poorly understood. In this study, micro-tensile tests were performed on demineralized human cortical bone samples from young, middle-aged, and elderly donors and aging effects on the mechanical properties of the collagen phase in different orientations (i.e. longitudinal and transverse directions of bone) were examined. The results of this study indicated that the elastic modulus and ultimate strength of the demineralized bone specimens decreased with aging in both the longitudinal and transverse orientations. However, the failure strain exhibited no significant changes in both orientations regardless of aging. These results suggest that the stiffness and strength of the collagen phase in bone are deteriorated with aging in both longitudinal and transverse directions. However, the aging effect is not reflected in the failure strain of the collagen phase in both longitudinal and transverse orientations, implying that the maximum sustainable deformation of the collagen phase is independent of aging and orientation.     

Effects of preservation and sterilization on cortical bone grafts

The effects of preservation and sterilization on the structural properties of cortical bone were investigated. Specimens of cortical bone from rat tibiae were frozen (–70°C for 28 days), freeze-dried, irradiated (1, 5, 25 and 50 kGy) or autoclaved (at 134°C for 3 or 5 min), and examined by scanning electron microscopy. Cryopreservation and irradiation had no deleterious effects on the surface structure of the cortical bone. Freeze-drying caused microcracks running parallel to the mineralized fiber bundles. After autoclaving, a time-dependent distension, swelling and amalgamation of the fibrillary matrix was observed. This denaturation of the organic matrix was more pronounced after 5 min than 3 min autoclaving. The alterations of the fibrillary structure described above might be due to a preservation- and sterilization-induced decrease of the biological and biomechanical potential of bone grafts.Supported by DFG grant     

The associations between mineral crystallinity and the mechanical properties of human cortical bone

It is well known that the amount of mineralization renders bone its stiffness. However, besides the mere amount of the mineral phase, size and shape of carbonated apatite crystals are postulated to affect the mechanical properties of bone tissue as predicted by composite mechanics models. Despite this predictive evidence, there is little experimental insight on the relation between the characteristics of mineral crystals and hard tissue mechanics. In this study, Raman spectroscopy was used to provide information on the crystallinity of bone's mineral phase, a parameter which is an overall indicator of mineral crystal size and stoichiometric perfection. Raman scans and mechanical tests (monotonic and fatigue; n=64 each) were performed on the anterior, medial, lateral and posterior quadrant sections of 16 human cadaveric femurs (52 y.o.-85 y.o.). The reported coefficient of determination values (R(2)) were adjusted for the effects of age to bring out the unbiased contribution of crystallinity. Crystallinity was able to explain 6.7% to 48.3% of the variation in monotonic mechanical properties. Results indicated that the tissue-level strength and stiffness increased with increasing crystallinity while the ductility reduced. Crystallinity explained 11.3% to 63.5% of the variation in fatigue properties. Moduli of specimens with greater crystallinity degraded at a slower rate and, also, they had longer fatigue lives. However, not every anatomical quadrant displayed these relationships. In conclusion, these results acknowledge crystal properties as an important bone quality factor and raise the possibility that aberrations in these properties may contribute to senile osteoporotic fractures.     

Effects of ionizing radiation on the mechanical properties of human bone

Allogeneic bone grafts are frequently sterilized by means of ionizing radiation. We investigated the effects of ionizing radiation on both quasistatic and impact mechanical properties of human bone. Specimens from four paired femora of four donors received doses of 29.5 kGy (“Standard” frequently used by tissue bandks), 94.7 kGy (“high”) or 17 kGy (“low”) of ionizing radiation. Young's modulus was unchanged by any level of radiation. Radiation significantly reduced bending strength, work to fracture, and impact energy absorption; in each case, the severity of the effect increased from low to standard to high doses of radiation. Work to fracture was particularly severely degraded; specimens irradiated with the high dose absorbed only 5% of the energy of the controls. Radiation. even at relatively low doses, makes the bone more brittle and thereby reduces its energy-absorbing capacity. We suggest that because the level of radiation required to produce an acceptable level of viral inactivation (90 kGy) produces an unacceptable reduction in the mechanical integrity of the bone. low levels of radiation, sufficient to produce bacterial safety, should be used in conjunction with biological tests to ensure viral safety.     

Effects of intermittent administration of pamidronate on the mechanical properties of canine cortical and trabecular bone

The mechanical properties of cortical and trabecular bones from beagles treated with the bisphosphonate pamidronate (administered intermittently 1 week every month for 3 months, at a dosage of 0.45 μmol/kg/day) were assessed. The mechanical properties of cortical bone were measured by four-point bending tests on femoral quadrants, in order to measure their elastic modulus and ultimate stress. The structural properties of whole tibias were measured in torsion to determine the torsional stiffness and failure torque. The elastic modulus and maximum compressive stress of the trabecular bone samples were measured by compression tests of trabecular cores. Intermittent treatment with pamidronate did not change the pattern of mechanical properties that occurs naturally around the femur or the torsional stiffness and failure torque of the tibias. By contrast, pamidronate did significantly increase the modulus of elasticity (by 19%) and maximum compressive stress (by 33%) of vertically aligned cylindrical trabecular specimens taken from the vertebrae of the beagles.     

Effect of microstructure on the mechanical properties of Haversian cortical bone

The mechanical properties of cortical bone have been extensively studied at the macrostructural scale. However, knowledge of the macroscopic mechanical properties is not sufficient to predict local phenomena, such as damage or bone remodeling, both of which are dependent on local mechanical behavior. The objective of this study is to quantify the mechanical properties of cortical bone at several length scales, with emphasis on the microstructure of Haversian systems. Samples of mature bovine cortical bone, with a Haversian microstructure, were obtained from the posterior area of the mid-femoral diaphysis. A nanoindentation technique was used to measure the local Young's modulus. The distribution of the bone mineral content was obtained by backscattered electron imaging using a scanning electron microscope. A novel compression device employing microextensometry techniques was developed to quantify local strains. Digital image correlation was performed on the microstructure imaged by optical microscopy during compression tests. This study demonstrated that the local Young's modulus and strain were heterogeneous at the scale of an osteon. For both properties, the ratio between the maximum and minimum values was approximately two. The local Young's modulus and bone-mineral content were reasonably correlated (r2 = 0.75; P < 0.0001), but this was not the case for the distribution of local strains versus bone mineral content (r2 = 0.395; P < 0.0001). Hence, local strains cannot be described simply in terms of the bone mineral content, as the Haversian canal and osteonal microstructure have a major influence on these properties. In conclusion, the microstructure must be considered in evaluating the local strain and stress fields of cortical bone.     

γ射线消毒对不同保存方法牛颈静脉管道机械性能的影响

目的探讨γ射线消毒对不同保存方法牛颈静脉管道机械性能的影响,寻求牛颈静脉管道合适的灭菌和保存方法。方法：将采集、制作好的牛颈静脉拉力条按不同保存方法分为6组：新鲜对照组(A组),冷冻干燥组(B组),溶剂干燥组(C组),深冻组(D组),PBS缓冲液保存组(E组),60％乙醇保存组(F组)。各组经25 kGyγ射线消毒(A组不进行γ射线消毒)后分别行单轴拉伸试验、细菌培养及组织形态学观察。结果上述5种方法保存的牛颈静脉管道经γ射线消毒后,其最大负荷与极限抗张强度分别为(25．23±15．95)N、(4．6±2．53)Mpa(B组),(35．28±14．66) N、(7．10±2．08)Mpa(C组),(25．44±7．97)N、(5．20±1．43)Mpa(D组),(31．55±12．32)N、(6．20±2．72)Mpa(E组),(32．02±18．44)N、(6．80±2．03)Mpa(F组)。与对照组[(23．43±11．21)N、(5．12±3．06)Mpa]相比,P＞0．05。断裂延伸率分别为(86．08±31．21)％(B组)、(137．99±38-80)％(C组)、(133．39±42．19)％(D组)、(153．23±55．00)％(E组)和(142．09±54．03)％(F组),与对照组(193.80±37．53)％相比,P＜0．05。细菌培养结果全部为阴性。组织切片显示B组和D组组织呈空腔空泡状改变。结论经25 kGyγ射线消毒后,上述五种保存方法处理牛颈静脉管道其最大负荷与极限抗张强度变化不明显,但其断裂延伸率均下降,尤以冷冻干燥保存组为甚。     

Effects of cold preservation on the lung mechanical properties in rats

In lung transplantation, cold preservation is an important process. However, the mechanical changes in the airway and tissue during cold preservation, especially before reperfusion, are unknown. To test the hypothesis that the mechanical changes in the airway and lung parenchyma start during cold preservation, we investigated the mechanical properties of the rat lung as a whole organ and in excised lung strips. In the 0 h group, the lungs were not preserved. In the 9 and 24 h group, the lungs were preserved for 9 and 24 h at 4 degrees C. After preservation, we evaluated the static compliance (Csta) of the whole lung as obtained from the pressure volume curves (n=5 in each group). Also, we measured the input impedance taken by a computer-controlled small-animal ventilator (n=9 in each group). All data were analyzed using a homogeneous linear model, which includes airway resistance (Raw), tissue elastance (H), and tissue resistance (G). Hysteresivity (eta) was calculated as G/H. Moreover, the tissue elasticity (Eqs) obtained from the quasi-static stress-strain curves was compared. There was no significant difference in Csta among the three groups. Raw was significantly lower in the 24 h group than in the 0 h group (p<0.01). Eqs was significantly higher in the preserved groups than in the 0 h group (p<0.01). These results demonstrated that the changes in the three mechanical properties of the airway and the tissue started within 9 h of preservation.     

Estimation of mechanical properties of cortical bone by computed tomography

It is difficult to assess from conventional x-rays the amount of loading that a bone can tolerate. The question therefore was asked whether the mechanical properties of cortical bone could be estimated by using a computed tomography (CT) system typically employed in the clinical setting. In vitro cross sectional diaphyseal scans of adult human tibiae were made using a GE 9800 scanner and linear attenuation coefficients determined in several regions of the central cross sections. Samples from the mid-diaphyses of these tibiae were harvested, tested in three-point bending to failure, and mechanical properties as well as density and ash fraction determined. The respective relationships between CT measurements, mechanical properties, and physical properties were calculated using regression analysis. In addition, a solid calibration phantom (tricalciumphosphate) was scanned to evaluate the variability of CT measurements. The physical parameters measured in this study were found to be comparable with data from other authors but correlations were moderate to weak. Linear regression revealed the following correlation coefficients with CT data: r = 0.55 (Young's modulus), r = 0.50 (strength), r = 0.65 (apparent density) and r = 0.46 (ash fraction). The correlation coefficients of these regressions for both linear and power fits were not significantly different. A high linear correlation (r = 0.99) was found between the chamber densities and the measured attenuation coefficients, but accuracy varied between 2 and 6%. The small range of specimen mechanical properties as well as the limitations inherent with the methods employed may explain these results. We conclude that clinical equipment as used in this study is not sufficient to accurately estimate the mechanical properties of cortical bone.     

阿仑膦酸钠对骨小梁力学特性的作用

目的　评价阿仑膦酸钠对骨小梁力学特性的作用。方法　选取成年雌性Hound犬 16只 ,随机分成两组 ,实验组 8只 ,口服阿仑膦酸钠 ,剂量为 0 5mg·kg-1·d-1,另选 8只作为对照组。 12周后处死 16只犬并收集其L1和L2 标本 ,进行压缩试验计算腰椎力学参数。结果　实验组在服用阿仑膦酸钠后其杨氏模量在样本头尾 (CC)、前后 (AP)和左右 (LR)方向上分别增加了 18 5 %、2 7 8%和3 3 1%。与对照组相比 ,实验组极限应力、骨折能量和头尾方向上的杨氏模量显著增加。结论　口服阿仑膦酸钠 ,剂量为 0 5mg·kg-1·d-1时 ,进行短期治疗能增强犬科骨小梁的力学特性。故阿仑膦酸钠短期内有增强健康骨小梁力学特性的作用     

The mechanical and biological properties of demineralised cortical bone allografts in animals

We studied the calcium content and mechanical strength of cortical bone from rats and dogs after different periods of demineralisation, showing that the rate of demineralisation differed considerably between the species. Specimens from the rat were further treated by chemical extraction and autolysis and tested for osteoinductive properties. We showed that partially demineralised cortical bone retained adequate mechanical strength, while retaining the biological effects of completely demineralised bone. This shows that it is possible to prepare allografts which have adequate mechanical strength and still retain osteo-inductive properties.     

Age-specific profiles of tissue-level composition and mechanical properties in murine cortical bone

There is growing evidence that bone composition and tissue-level mechanical properties are significant determinants of skeletal integrity. In the current study, Raman spectroscopy and nanoindentation testing were co-localized to analyze tissue-level compositional and mechanical properties in skeletally mature young (4 or 5 months) and old (19 months) murine femora at similar spatial scales. Standard multivariate linear regression analysis revealed age-dependent patterns in the relationships between mechanical and compositional properties at the tissue scale. However, changes in bone material properties with age are often complex and nonlinear, and can be missed with linear regression and correlation-based methods. A retrospective data mining approach was implemented using non-linear multidimensional visualization and classification to identify spectroscopic and nanoindentation metrics that best discriminated bone specimens of different age-classes. The ability to classify the specimens into the correct age group increased by using combinations of Raman and nanoindentation variables (86-96% accuracy) as compared to using individual measures (59-79% accuracy). Metrics that best classified 4 or 5 month and 19 month specimens (2-age classes) were mineral to matrix ratio, crystallinity, modulus and plasticity index. Metrics that best distinguished between 4, 5 and 19 month specimens (3-age classes) were mineral to matrix ratio, crystallinity, modulus, hardness, cross-linking, carbonate to phosphate ratio, creep displacement and creep viscosity. These findings attest to the complexity of mechanisms underlying bone tissue properties and draw attention to the importance of considering non-linear interactions between tissue-level composition and mechanics that may work together to influence material properties with age. The results demonstrate that a few non-linearly combined compositional and mechanical metrics provide better discriminatory information than a single metric or a single technique.     

卵巢切除对大鼠皮质骨结构和力学性能的影响

目的：研究卵巢切除大鼠皮质骨的几何学改变和力学性能改变,探讨雌激素缺乏时皮质骨改变的发生机理。方法：选雌性SD大鼠56只,分为Sham组和OVX组,动物分别在4、12、20和28周时处死7只,取其胫骨备用。左侧于近3/5和远2/5交界部切断,在电镜下摄片,计测截面总面积、皮质骨面积、骨外径周长、骨髓腔面积和骨内径周长。右侧以近3/5与远2/5交界点为加载点进行三点弯曲力学实验。结果：Sham组术后4周至28周胫骨截面总面积和骨外径周长逐渐增加。（P＜0.005),而髓腔面积和内径周长变化不明显。OVX组截面总面积和外径周长也有逐渐增加趋势。但差异无显性。而内径周长和髓腔面积都明显增加,在相同时期显大于Sham组（P＜0.005),而皮质骨面积却与Sham组差异无显性。三点弯曲试验结果表明,从4-28周实验对照两组抗弯强度和刚度均逐渐增加,但两组间差异无显性。在各时期骨组织材料力学性能也无显性差异。结论：卵巢切除对皮质骨的影响主要表现在使骨髓控扩大,对骨外膜的影响较小,在短期内皮质骨的力学性能无明显影响。     

三种抗生素骨水泥抗菌作用和机械强度的研究

目的探讨常用抗生素在国产骨水泥中的抗菌作用及对其机械性能的影响. 方法在不同细菌培养皿内放置含不同比例的硫酸妥布霉素粉剂、硫酸庆大霉素粉剂和西力欣三种抗生素的骨水泥,培养并观察抑菌环的大小和抑菌时间;同时测试含各种浓度抗生素骨水泥的抗拉强度和弹性模量. 结果 0.5～2.0 g抗生素(40 g骨水泥)对细菌有明显抑制作用,0.5～1.5 g组骨水泥抗拉强度和弹性模量较空白对照略有增加,2.0 g组开始下降.加水剂抗生素抗拉强度较粉剂和空白对照明显降低. 结论加入适量和适当剂型抗生素既可以发挥抗菌作用,同时也不降低骨水泥的机械性能.     

Stability of human bone cortex following various preservation and sterilization methods]

In a biomechanical study we evaluated the stability of human femurs. In order to document the inter- and intraindividual differences in bending stability, and the changes in breaking strength after different storing and sterilizing procedures, we tested 200 bony blocks, which were harvested from the femurs of 5 multiorgan donors. The bending tests were performed with a material testing machine (ZWICK) under standardized conditions. The bone blocks we randomized into five different treatment groups (-25 degrees C deep freezing, steam sterilization, lyophilization, lyophilization + gamma irradiation, lyophilization + gamma-irradiation in argon). The statistical analysis was performed by a multivariant analysis. Our results revealed significant differences concerning breaking strength among different femurs of the 5 multiorgan donors, and a significant difference concerning stability in different areas of the same femur. Further on we found a significant difference with regard to the treatment modalities of the five groups. Compared to the control group (-25 degrees C deep freezing), we documented a decrease of 8.7% after steam sterilization, an increase of 18.9% after lyophilization, a decrease of 1.7% after lyophilization + gamma-irradiation, and an increase of 3.4% after lyophilization + gamma-irradiation in argon.     

Estimation of mechanical properties of the distal radius from bone mineral content and cortical width

Bone mineral content (BMC) was determined by photon absorptiometry and cortical width (CW) by radiographic morphometry at two levels in 17 radii obtained postmortem from women ranging in age from 39 to 95 years. One level was the region in which Colles' fracture occurs (lower level) and the other about 6 cm from the styloid tip (upper level). Principal compressive strain at a 600-N load, fracture load, compliance, and work/unit length to fracture were measured in longitudinal compression tests. In general, BMC provides more precise estimates of mechanical properties than CW. The correlation coefficient between fracture load and BMC at the lower level was +0.83 (less than 0.001). Between work/unit length to fracture and BMC the coefficient was +0.81 (p less than 0.001).