Thurner P J, Wyss P, Voide R, Stauber M, Stampanoni M, Sennhauser U, Müller R
Electronics/Metrology Laboratory, Swiss Federal Laboratories for Materials Testing and Research, EMPA, Uberlandstrasse 129, 8600 Dübendorf, Switzerland.
Bone. 2006 Aug;39(2):289-99. doi: 10.1016/j.bone.2006.01.147. Epub 2006 Mar 15.
Synchrotron radiation micro-computed tomography (SRmicroCT) is a very useful technique when it comes to three-dimensional (3D) imaging of complex internal and external geometries. Being a fully non-destructive technique, SRmicroCT can be combined with other experiments in situ for functional imaging. We are especially interested in the combination of SRmicroCT with mechanical testing in order to gain new insights in the failure mechanism of trabecular bone. This interest is motivated by the immense costs in health care due to patients suffering from osteoporosis, a systemic skeletal disease resulting in decreased bone stability and increased fracture risk. To better investigate the different failure mechanisms on the microlevel, we have developed a novel in situ mechanical compression device, capable of exerting both static and dynamic displacements on experimental samples. The device was calibrated for mechanical testing using solid aluminum and bovine trabecular bone samples. To study different failure mechanisms in trabecular bone, we compared a fatigued and a non-fatigued bovine bone sample with respect to failure initiation and propagation. The fatigued sample failed in a burst-like fashion in contrast to the non-fatigued sample, which exhibited a distinct localized failure band. Moreover, microscopic cracks - microcracks and microfractures - were uncovered in a 3D fashion illustrating the failure process in great detail. The majority of these cracks were connected to a bone surface. The data also showed that the classification of microcracks and -fractures from 2D section can sometimes be ambiguous, which is also true for the distinction of diffuse and distinct microdamage. Detailed investigation of the failure mechanism in these samples illustrated that trabecular bone often fails in delamination, providing a mechanism for energy dissipation while conserving trabecular bone architecture. In the future, this will allow an even better understanding of bone mechanics related to its hierarchical structural organization.
同步辐射微计算机断层扫描（SRmicroCT）在对复杂的内部和外部几何结构进行三维（3D）成像时是一项非常有用的技术。作为一种完全无损的技术，SRmicroCT可以与其他原位实验相结合用于功能成像。我们尤其对SRmicroCT与机械测试的结合感兴趣，以便深入了解小梁骨的失效机制。这种兴趣源于骨质疏松症患者给医疗保健带来的巨大成本，骨质疏松症是一种全身性骨骼疾病，会导致骨稳定性下降和骨折风险增加。为了更好地在微观层面研究不同的失效机制，我们开发了一种新型的原位机械压缩装置，该装置能够对实验样品施加静态和动态位移。该装置使用实心铝和牛小梁骨样品进行了机械测试校准。为了研究小梁骨中的不同失效机制，我们比较了疲劳和未疲劳的牛骨样品在失效起始和扩展方面的情况。与未疲劳样品呈现出明显的局部失效带不同，疲劳样品以突发的方式失效。此外，以三维方式发现了微观裂纹——微裂纹和微骨折——详细地展示了失效过程。这些裂纹中的大多数都与骨表面相连。数据还表明，从二维切片对微裂纹和微骨折进行分类有时可能会模棱两可，对于区分弥散性和明显的微观损伤也是如此。对这些样品失效机制的详细研究表明，小梁骨通常以分层方式失效，这为能量耗散提供了一种机制，同时保留了小梁骨结构。未来，这将有助于更好地理解与其层次结构组织相关的骨力学。
