Materials Sciences Division, Lawrence Berkeley National Laboratory, United States.
J Mech Behav Biomed Mater. 2011 Oct;4(7):1504-13. doi: 10.1016/j.jmbbm.2011.05.020. Epub 2011 May 17.
The age-related deterioration in the quality (e.g., strength and fracture resistance) and quantity (e.g., bone-mineral density) of human bone, together with increased life expectancy, is responsible for increasing incidence of bone fracture in the elderly. The present study describes ex vivo fracture experiments to quantitatively assess the effect of aging on the fracture toughness properties of human cortical bone specifically in the transverse (breaking) orientation. Because bone exhibits rising crack-growth resistance with crack extension, the aging-related transverse toughness is evaluated in terms of resistance-curve (R-curve) behavior, measured for bone taken from a wide range of age groups (25-74 years). Using this approach, both the ex vivo crack-initiation and crack-growth toughness are determined and are found to deteriorate with age; however, the effect is far smaller than that reported for the longitudinal toughness of cortical bone. Whereas the longitudinal crack-growth toughness has been reported to be reduced by almost an order of magnitude for human cortical bone over this age range, the corresponding age-related decrease in transverse toughness is merely ~14%. Similar to that reported for X-ray irradiated bone, with aging cracks in the transverse direction are subjected to an increasing incidence of crack deflection, principally along the cement lines, but the deflections are smaller and result in a generally less tortuous crack path.
随着人类预期寿命的延长，与年龄相关的人类骨骼质量（例如，强度和断裂阻力）和数量（例如，骨矿物质密度）的恶化，是导致老年人骨折发病率增加的原因。本研究描述了体外骨折实验，以定量评估年龄对人体皮质骨横向（断裂）方向断裂韧性特性的影响。由于骨骼在裂纹扩展过程中表现出不断增加的裂纹扩展阻力，因此，与老化相关的横向韧性是根据阻力曲线（R 曲线）行为来评估的，该行为是针对取自广泛年龄组（25-74 岁）的骨骼进行测量的。通过这种方法，可以确定体外裂纹起始和裂纹扩展韧性，并且发现它们随着年龄的增长而恶化；然而，这种影响远小于皮质骨纵向韧性的报道。虽然据报道，在这个年龄段内，人体皮质骨的纵向裂纹扩展韧性降低了近一个数量级，但横向韧性的相应老化相关性降低仅为~14%。与 X 射线辐照骨骼的报道相似，在横向方向上的裂纹会发生越来越多的裂纹偏斜，主要沿着水泥线，但偏斜较小，导致通常较不曲折的裂纹路径。
