Strain-rate stiffening of cortical bone: observations and implications from nanoindentation experiments
Strain-rate stiffening of cortical bone: observations and implications from nanoindentation experiments
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DOI：
10.1039/c4nr03180f
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发表时间：
2014-01-01
期刊：
影响因子：
6.7
通讯作者：
Miyazaki, Takashi
中科院分区：
文献类型：
--
作者：
Maruyama, Noriko;Shibata, Yo;Miyazaki, Takashi
虽然骨矿化被认为是其刚度的原因，但与基质蛋白的时间依赖性粘弹性部分相关的骨耐久性仍不清楚。在这里，我们展示了一种几乎独立于固有粘弹性行为的高度矿化骨耐久性的新机制，以及用于测量矿化组织机械性能的协议。应变率纳米压痕测试显示高度矿化的颅骨显着变硬，而在恒定负载或位移测试中分别观察到大的蠕变或应力松弛。基于高度矿化结构的较低粘弹性，如此大的时间依赖性响应似乎与纳米级尺寸恢复相关，而不是粘弹性行为，这意味着相反的即应变率相关的膨胀行为。这种膨胀膨胀增加了压头进入表面的穿透阻力，从而增强了瞬时刚度。相关的硬化和较高的有效弹性模量高度依赖于应变率，并且在矿化程度较高的组织（例如颅骨）中更容易观察到。这种应变率硬化和随之而来的尺寸恢复可能是骨组织对抗过度变形以维持组织完整性的重要反应。
While bone mineralization is considered to be responsible for its stiffness, bone durability partially associated with the time-dependent viscoelasticity of matrix proteins is still poorly elucidated. Here we demonstrate a novel mechanism of highly mineralized bone durability almost independent of inherent viscoelastic behaviour along with a protocol for measuring the mechanical properties of mineralized tissues. Strain-rate nanoindentation tests showed substantial stiffening of the highly mineralized calvarial bone, whereas large creep or stress relaxation was observed during constant load or displacement tests, respectively. Based on the lower viscoelasticity of the highly mineralized structure, such large time-dependent response appears to be associated with nanoscale dimensional recovery, rather than viscoelastic behaviour, implying the inverse namely strain-rate dependent dilatant behaviour. This dilatant expansion increased the indenter penetration resistance into the surface, enhancing instantaneous stiffness. The associated stiffening and higher effective elastic modulus were highly strain-rate dependent and more readily observed in more highly mineralized tissues such as the calvarial bone. Such strain-rate stiffening and consequent dimensional recovery may be vital responses of bone tissues against excessive deformation to maintain tissue integrity.