Measurements of mechanical anisotropy in brain tissue and implications for transversely isotropic material models of white matter.
Measurements of mechanical anisotropy in brain tissue and implications for transversely isotropic material models of white matter.
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DOI：
10.1016/j.jmbbm.2013.04.007
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发表时间：
2013-07
影响因子：
3.9
通讯作者：
Bayly PV
中科院分区：
文献类型：
--
作者：
Feng Y;Okamoto RJ;Namani R;Genin GM;Bayly PV
大脑中的白质在结构上是各向异性的，主要由排列整齐、髓磷脂鞘的轴突纤维束组成。人们认为白质也具有机械各向异性。具体而言，预期局部具有横向各向同性，各向同性平面垂直于局部平均纤维方向。合适的材料模型涉及应变能密度函数，该函数取决于柯西-格林应变张量的 I4 和 I5 伪不变量，以解释相对刚性纤维的影响。伪不变量I4是纤维方向拉伸比的平方； I5 包含平行于纤维轴的平面中剪切应变的贡献。大多数（如果不是全部）已发表的白质模型依赖于 I4，但不依赖于 I5。在这里，我们在探测这些依赖性的实验测量的背景下探索这些模型的小应变极限。应变能取决于 I4 而不是 I5 的模型可以捕获杨氏（拉伸）模量的差异，但在平行和垂直于轴突平均方向的加载时不会表现出剪切模量的差异。我们通过结合剪切和不对称压痕测试的实验表明，白质确实在拉伸模量和剪切模量上表现出这种差异。压痕试验是通过在小应变极限下有限元模型的反拟合来解释的。结果强调：（1）横向各向同性组织（例如白质）的超弹性模型应包括 I4 和 I5 应变伪不变量的贡献； （2）小应变状态下的行为可以有效地指导更通用的白质材料模型的选择和初始参数化。
White matter in the brain is structurally anisotropic, consisting largely of bundles of aligned, myelin-sheathed axonal fibers. White matter is believed to be mechanically anisotropic as well. Specifically, transverse isotropy is expected locally, with the plane of isotropy normal to the local mean fiber direction. Suitable material models involve strain energy density functions that depend on the I4 and I5 pseudo-invariants of the Cauchy–Green strain tensor to account for the effects of relatively stiff fibers. The pseudo-invariant I4 is the square of the stretch ratio in the fiber direction; I5 contains contributions of shear strain in planes parallel to the fiber axis. Most, if not all, published models of white matter depend on I4 but not on I5. Here, we explore the small strain limits of these models in the context of experimental measurements that probe these dependencies. Models in which strain energy depends on I4 but not I5 can capture differences in Young’s (tensile) moduli, but will not exhibit differences in shear moduli for loading parallel and normal to the mean direction of axons. We show experimentally, using a combination of shear and asymmetric indentation tests, that white matter does exhibit such differences in both tensile and shear moduli. Indentation tests were interpreted through inverse fitting of finite element models in the limit of small strains. Results highlight that: (1) hyperelastic models of transversely isotropic tissues such as white matter should include contributions of both the I4 and I5 strain pseudo-invariants; and (2) behavior in the small strain regime can usefully guide the choice and initial parameterization of more general material models of white matter.
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影响因子：
2.5
作者：
Alexander, GM;Godwin, DW
通讯作者：
Godwin, DW
影响因子：
2.4
作者：
FALLENSTEIN, GT;HULCE, VD;MELVIN, JW
通讯作者：
MELVIN, JW
影响因子：
2.4
作者：
Arbogast, KB;Margulies, SS
通讯作者：
Margulies, SS
DOI：
10.1115/1.1785808
发表时间：
2004-08-01
影响因子：
1.7
作者：
Bischoff, JE
通讯作者：
Bischoff, JE
DOI：
10.1115/1.4004494
发表时间：
2011-07-01
影响因子：
1.7
作者：
Elkin, Benjamin S.;Ilankova, Ashok;Morrison, Barclay, III
通讯作者：
Morrison, Barclay, III