Study on the mechanical properties of hard tissues using nanoindentation tests

皮质骨的力学特性是矿物质和胶原蛋白组分相互作用的结果。一块骨头中矿物质含量的微小变化会对其力学性能产生很大影响。研究表明，维氏显微硬度与矿物含量，维氏显微硬度和弹性模量之间的相关性采用三点和四点弯曲试验。然而，统计关系的确切性质尚未确定。纳米压痕是由维氏显微硬度测试演变而来的，它允许在纳米尺度上测量皮质骨的力学性能。纳米压痕技术已被用于在微观尺度上估计骨的力学性能，克服了传统的小样本力学测试的局限性。本研究采用纳米压痕法测定了牛和猪股骨皮质骨的力学性能。牛丛状骨和哈弗氏骨的纵向弹性模量平均值分别为17.3±5.7 GPa和10.6±5.1 GPa。猪丛状骨的平均弹性模量为13.7±4.5 GPa，猪哈弗氏骨的平均弹性模量为8.2±3.3 GPa。骨组织硬度与弹性模量的变化趋势相似。接下来，研究了不同年龄大鼠股骨皮质骨纳米压痕测量的力学性能与外围定量计算机断层扫描（pQCT）测量的体积骨矿物质密度（vBMD）之间的关系。本研究所用大鼠皮质骨标本为哈弗森骨。实验测量的弹性模量与vBMD相关（r=0.62 ~ 0.76）。骨组织硬度与vBMD也有很好的相关性（r=0.85 ~ 0.90）。

The mechanical properties of cortical bone are a consequence of the interaction between the mineral and collagen components. Small variations in the amount of mineral present in a section of bone can have a large influence on its mechanical properties. Studies have shown the correlations between Vickers microhardness and mineral content, and Vickers microhardness and elastic modulus using three-point and four-point bending tests. However, the precise nature of statistical relationship has yet to be established. Nanoindentation, which evolved from Vickers microhardness test, allows for measurement of mechanical properties of cortical bone at the nanometer scale. The nanoindentation technique has been applied to estimate mechanical properties of bone at a microscopic length scale, overcoming the limitations of traditional mechanical tests for small specimens. In this study, mechanical properties of bovine and porcine femoral cortical bone were measured by nanoindentation. For bovine plexiform and Haversian bone specimens, the averages for the longitudinal elastic moduli were 17.3±5.7 GPa and 10.6±5.1 GPa, respectively. The average elastic modulus measured for porcine plexiform bone was 13.7±4.5 GPa, and the average for porcine Haversian bone was 8.2±3.3 GPa. The hardness showed a tendency similar to the elastic modulus among all types of bone tissues. Next, the relationships between mechanical properties measured by nanoindentation and volumetric Bone Mineral Density(vBMD) measured by peripheral Quantitative Computed Tomography(pQCT) in femoral cortical bone from a variety of ages of rats were investigated. The specimen of rat cortical bone used here was Haversian bone. Experimentally measured elastic modulus correlated with vBMD(r=0.62〜0.76). It was found that a good correlation also existed between hardness and vBMD(r=0.85〜0.90) of bone tissues.