Nyman Jeffry S, Roy Anuradha, Reyes Michael J, Wang Xiaodu
Vanderbilt Center for Bone Biology and Department of Orthopaedics and Rehabilitation, Vanderbilt University Medical Center, Nashville, Tennessee 37215, USA.
J Biomed Mater Res A. 2009 May;89(2):521-9. doi: 10.1002/jbm.a.31974.
The capacity of bone for post-yield energy dissipation decreases with age. To gain information on the causes of such a change, we examined age-related changes in the mechanical behavior of human cadaveric bone as a function of progressive deformation. In this study, tensile specimens from tibiae of nine middle aged and eight elderly donors were loaded till failure in an incremental and cyclic (load-dwell-unload-dwell-reload) scheme. The elastic modulus, maximum stress, permanent strain, stress relaxation, permanent strain energy, elastic release strain energy, and hysteresis energy were determined in each loading cycle at incremental strains. Similar with previous work, the results of the present study also indicated that elderly bone failed at much lower strains compared to middle aged bone. However, no significant differences in the mechanical behavior of bone were observed between the two age groups except for the premature failure of elderly bone. After yielding, the energy dissipation and permanent strain of bone appeared to linearly increase with increasing strain applied, while nonlinear changes occurred in the modulus loss and stress relaxation with increasing strain. Moreover, stress relaxation tended to peak at 1% strain beyond which few elderly bone specimens survived. This study suggests that damaging mechanisms in bone vary with deformation, and aging affects the post-yield mechanisms, thus giving rise to the age-related differences in the mechanical properties of bone, especially the capacity of the tissue for energy dissipation.
骨骼屈服后能量耗散的能力会随着年龄的增长而下降。为了了解这种变化的原因，我们研究了人类尸体骨骼力学行为随年龄的变化，以及其与渐进性变形的关系。在本研究中，对来自9名中年捐赠者和8名老年捐赠者胫骨的拉伸试样进行加载，直至其失效，加载方式为增量循环（加载-保持-卸载-保持-再加载）。在每个加载循环中，测定增量应变下的弹性模量、最大应力、永久应变、应力松弛、永久应变能、弹性释放应变能和滞后能。与之前的研究类似，本研究结果也表明，与中年骨骼相比，老年骨骼在低得多的应变下就会失效。然而，除了老年骨骼的过早失效外，两个年龄组之间的骨骼力学行为没有观察到显著差异。屈服后，骨骼的能量耗散和永久应变似乎随着施加应变的增加而线性增加，而模量损失和应力松弛则随着应变增加而发生非线性变化。此外，应力松弛在1%应变时趋于峰值，超过该应变后，很少有老年骨骼试样能够承受。本研究表明，骨骼中的损伤机制随变形而变化，衰老会影响屈服后机制，从而导致骨骼力学性能出现与年龄相关的差异，尤其是组织的能量耗散能力。
