Budday Silvia, Nay Richard, de Rooij Rijk, Steinmann Paul, Wyrobek Thomas, Ovaert Timothy C, Kuhl Ellen
Chair of Applied Mechanics, University of Erlangen-Nuremberg, 91058 Erlangen, Germany.
Hysitron, Inc., Eden Prairie, MN 55344, USA.
J Mech Behav Biomed Mater. 2015 Jun;46:318-30. doi: 10.1016/j.jmbbm.2015.02.024. Epub 2015 Mar 2.
The mammalian brain is composed of an outer layer of gray matter, consisting of cell bodies, dendrites, and unmyelinated axons, and an inner core of white matter, consisting primarily of myelinated axons. Recent evidence suggests that microstructural differences between gray and white matter play an important role during neurodevelopment. While brain tissue as a whole is rheologically well characterized, the individual features of gray and white matter remain poorly understood. Here we quantify the mechanical properties of gray and white matter using a robust, reliable, and repeatable method, flat-punch indentation. To systematically characterize gray and white matter moduli for varying indenter diameters, loading rates, holding times, post-mortem times, and locations we performed a series of n=192 indentation tests. We found that indenting thick, intact coronal slices eliminates the common challenges associated with small specimens: it naturally minimizes boundary effects, dehydration, swelling, and structural degradation. When kept intact and hydrated, brain slices maintained their mechanical characteristics with standard deviations as low as 5% throughout the entire testing period of five days post mortem. White matter, with an average modulus of 1.89 5kPa ± 0.592 kPa, was on average 39% stiffer than gray matter, p<0.01, with an average modulus of 1.389 kPa ± 0.289 kPa, and displayed larger regional variations. It was also more viscous than gray matter and responded less rapidly to mechanical loading. Understanding the rheological differences between gray and white matter may have direct implications on diagnosing and understanding the mechanical environment in neurodevelopment and neurological disorders.
哺乳动物的大脑由外层灰质和内层白质组成。灰质由细胞体、树突和无髓鞘轴突构成，白质的核心主要由有髓鞘轴突组成。最近的证据表明，灰质和白质之间的微观结构差异在神经发育过程中起着重要作用。虽然从流变学角度对整个脑组织已有很好的表征，但对灰质和白质的个体特征仍了解不足。在这里，我们使用一种稳健、可靠且可重复的方法——平冲头压痕法来量化灰质和白质的力学性能。为了系统地表征不同压头直径、加载速率、保持时间、死后时间和位置下的灰质和白质模量，我们进行了一系列n = 192次压痕测试。我们发现，对完整的厚冠状切片进行压痕可消除与小样本相关的常见挑战：它自然地将边界效应、脱水、肿胀和结构退化降至最低。当保持完整和水润时，脑切片在死后五天的整个测试期内都保持其力学特性，标准偏差低至5%。白质的平均模量为1.895 kPa±0.592 kPa，平均比灰质硬39%，p<0.01，灰质的平均模量为1.389 kPa±0.289 kPa，且区域差异更大。白质也比灰质更具粘性，对机械加载的反应较慢。了解灰质和白质之间的流变学差异可能对诊断和理解神经发育及神经疾病中的力学环境有直接影响。
