Department of Biomedical Engineering, Worcester Polytechnic Institute, Worcester, MA 01605, USA.
Department of Biomedical Engineering, Worcester Polytechnic Institute, Worcester, MA 01605, USA; Department of Mechanical Engineering, Worcester Polytechnic Institute, Worcester, MA 01609, USA.
J Mech Behav Biomed Mater. 2018 Apr;80:222-234. doi: 10.1016/j.jmbbm.2018.02.005. Epub 2018 Feb 6.
Material properties of the brain have been extensively studied but remain poorly characterized. The vast variations in constitutive models and material constants are well documented. However, no study exists to translate the variations into disparities in impact-induced brain strains most relevant to brain injury. Here, we reviewed a subset of injury-relevant brain material properties either characterized in experiments or adopted in recent head injury models. To highlight how variations in measured brain material properties manifested in simulated brain strains, we selected six experiments that have provided a complete set of brain material model and constants to implement a common head injury model. Responses resulting from two extreme events representing a high-rate cadaveric head impact and a low-rate in vivo head rotation, respectively, varied substantially. We hypothesized, and further confirmed, that the time-varying shear moduli at the appropriate time scales (e.g., ~5 ms and ~40 ms corresponding to the impulse durations of the major acceleration peaks for the two impacts, respectively), rather than the initial or long-term shear moduli, were the most indicative of impact-induced brain strains. These results underscored the need to implement measured brain material properties into an actual head injury model for evaluation. They may also provide guidelines to better characterize brain material properties in future experiments and head injury models. Finally, our finding provided a practical solution to satisfy head injury model validation requirements at both ends of the impact severity spectrum. This would improve the confidence in model simulation performance across a range of time scales relevant to concussion and sub-concussion in the real-world.
大脑的材料特性已经得到了广泛的研究，但仍未得到充分的描述。本构模型和材料常数的巨大变化得到了充分的记录。然而，目前还没有研究将这些变化转化为与脑损伤最相关的冲击引起的脑应变差异。在这里，我们回顾了一组与损伤相关的脑材料特性，这些特性要么是在实验中得到了描述，要么是在最近的头部损伤模型中得到了采用。为了突出测量的脑材料特性在模拟脑应变中的变化，我们选择了六个实验，这些实验提供了完整的脑材料模型和常数来实现一个常见的头部损伤模型。分别代表高速尸体头部冲击和低速体内头部旋转的两个极端事件的响应变化非常大。我们假设，并进一步证实，在适当的时间尺度上的时变剪切模量（例如，分别对应于两个冲击的主要加速度峰值的脉冲持续时间约为 5ms 和 40ms），而不是初始或长期剪切模量，最能指示冲击引起的脑应变。这些结果强调了将测量的脑材料特性实施到实际的头部损伤模型中进行评估的必要性。它们也可能为未来的实验和头部损伤模型提供更好地描述脑材料特性的指南。最后，我们的发现为满足冲击严重程度谱两端的头部损伤模型验证要求提供了一个实际的解决方案。这将提高对与现实世界中的脑震荡和亚脑震荡相关的一系列时间尺度的模型模拟性能的信心。
