Southwest Research Institute, 6220 Culebra Road, San Antonio, TX 78230, USA.
J Mech Behav Biomed Mater. 2011 Apr;4(3):383-91. doi: 10.1016/j.jmbbm.2010.11.007. Epub 2010 Nov 21.
The microcracking and damage accumulation process in human cortical bone was characterized by performing cyclic loading under four-point bending at ambient temperature. A non-destructive nuclear magnetic resonance (NMR) spin-spin (T(2)) relaxation technique was applied to quantify the apparent changes in bone porosity as a function of cyclic loading and prior damage accumulation, first to unloaded cortical bone to quantify the initial porosity and then to fatigued cortical bone that was subjected to cyclic loading to various levels of modulus degradation and microdamage in the form of microcracks. The NMR T(2) relaxation time and amplitude data of the fatigued bone were compared against the undamaged state. The difference in the T(2) relaxation time data was taken as a measure of the increase in pore size, bone porosity or microcrack density due to microdamage induced by cyclic loading. A procedure was developed to deduce the number and size distributions of microcracks formed in cortical bone. Serial sectioning of the fatigued bone showed the formation of microcracks along the cement lines or within the interstitial tissue. The results on the evolution of microdamage derived from NMR measurements were verified by independent experimental measurements of microcrack density using histological characterization techniques. The size distribution and population of the microcracks were then utilized in conjunction with an analytical model to predict the degradation of the elastic modulus of cortical bone as a function of damage accumulation.
在常温下进行四点弯曲循环加载，研究了人皮质骨的微裂纹和损伤累积过程。应用一种无损的核磁共振（NMR）自旋-自旋（T(2)）弛豫技术来定量评估骨孔隙率随循环加载和先前损伤累积的表观变化，首先对未加载的皮质骨进行定量分析以确定初始孔隙率，然后对疲劳皮质骨进行分析，疲劳皮质骨经历了不同程度的模量降低和微裂纹形式的微损伤的循环加载。将疲劳骨的 NMR T(2)弛豫时间和幅度数据与无损状态进行比较。将 T(2)弛豫时间数据的差异作为由于循环加载引起的微损伤导致的孔径、骨孔隙率或微裂纹密度增加的量度。开发了一种程序来推断皮质骨中形成的微裂纹的数量和尺寸分布。对疲劳骨的连续切片显示，微裂纹沿着骨线或间质组织形成。从 NMR 测量得出的微损伤演化的结果通过使用组织学特征技术对微裂纹密度进行独立的实验测量进行了验证。然后，利用微裂纹的尺寸分布和种群与分析模型相结合，预测皮质骨弹性模量随损伤累积的降解。
