Materials Science and Engineering Department, University of Tennessee, Knoxville, TN 37996, USA.
Materials Science and Engineering Department, University of Tennessee, Knoxville, TN 37996, USA; Department of Materials Science and Engineering, Texas A&M University, College Station, TX 77843-3003, USA.
Bone. 2021 Jul;148:115949. doi: 10.1016/j.bone.2021.115949. Epub 2021 Apr 14.
The incidence of bone fracture increases with age, due to both declining bone quantity and quality. Toward the goal of an improved understanding of the causes of the age-related decline in the fracture toughness of male cortical bone, nanoindentation experiments were performed on femoral diaphysis specimens from men aged 21-98 years. Because aged bone has less matrix-bound water and dry bone is less viscoelastic, we used a nanoindentation method that is sensitive to changes in viscoelasticity. Given the anisotropy of bone stiffness, longitudinal (n = 26) and transverse (n = 25) specimens relative to the long axis of the femur diaphysis were tested both dry in air and immersed in phosphate buffered saline solution. Indentation stiffness (storage modulus) and hardness increased with age, while viscoelasticity (loss modulus) was independent of donor age. The increases in indentation stiffness and hardness with age were best explained by increased mineralization with age. Indentation stiffness and hardness were negatively correlated with previously acquired fracture toughness parameters, which is consistent with a tradeoff between material strength and toughness. In keeping with the complex structure of bone, a combination of tissue-level storage modulus or hardness, bound water, and osteonal area in regression models best explained the variance in the fracture toughness of male human cortical bone. On the other hand, viscoelasticity was unchanged with age and was not associated with fracture toughness. In conclusion, the age-related increase in stiffness and hardness of male cortical bone may be one of the multiple tissue-level characteristics that contributes to decreased fracture toughness.
随着年龄的增长，骨折的发病率增加，这既与骨量的减少有关，也与骨质量的下降有关。为了更好地了解男性皮质骨骨折韧性随年龄下降的原因，我们对 21-98 岁男性的股骨骨干标本进行了纳米压痕实验。由于老年骨的基质结合水较少，干骨的粘弹性较低，我们使用了一种对粘弹性变化敏感的纳米压痕方法。鉴于骨刚度的各向异性，我们对相对于股骨骨干长轴的纵向（n=26）和横向（n=25）标本进行了干空气和磷酸盐缓冲盐水浸泡两种条件下的测试。压痕硬度（储能模量）和硬度随年龄增长而增加，而粘弹性（损耗模量）与供体年龄无关。随着年龄的增长，压痕硬度和硬度的增加可以最好地用年龄引起的矿化增加来解释。压痕硬度和硬度随年龄的增加与先前获得的骨折韧性参数呈负相关，这与材料强度和韧性之间的权衡一致。考虑到骨的复杂结构，组织水平的储能模量或硬度、结合水和骨单位面积的组合在回归模型中最好地解释了男性皮质骨骨折韧性的变化。另一方面，粘弹性随年龄而不变，与骨折韧性无关。总之，男性皮质骨刚度和硬度随年龄的增加可能是导致骨折韧性降低的多个组织水平特征之一。
