Elkin Benjamin S, Ilankovan Ashok, Morrison Barclay
Department of Biomedical Engineering, Columbia University, New York, NY 10027, USA.
J Biomech Eng. 2010 Jan;132(1):011010. doi: 10.1115/1.4000164.
Age-dependent outcomes following traumatic brain injury motivate the study of brain injury biomechanics in experimental animal models at different stages of development. Finite element models of the rat brain are used to better understand the mechanical mechanisms behind these age-dependent outcomes; however, age- and region-specific rat brain tissue mechanical properties are required for biofidelity in modeling. Here, we have used the atomic force microscope (AFM) to measure region-dependent mechanical properties for subregions of the cortex and hippocampus in P10, P17, and adult rats. Apparent elastic modulus increased nonlinearly with indentation strain, and a nonlinear Ogden hyperelastic model was used to fit the force-deflection data. Subregional heterogeneous distributions of mechanical properties changed significantly with age. Apparent elastic modulus was also found to increase overall with age, increasing by >100% between P10 and adult rats. Unconfined compression tests (epsilon=-0.3) were performed on whole slices of the hippocampus and cortex of P10, P17, and adult rats to verify the mechanical properties measured with the AFM. Mean apparent elastic modulus at an indentation strain of 30% from AFM measurements for each region and age correlated well with the long-term elastic modulus measured from 30% unconfined compression tests (slope not significantly different from 1, p>0.05). Protein, lipid, and sulfated glycosaminoglycan content of the brain increased with age and were positively correlated with tissue stiffness, whereas water content decreased with age and was negatively correlated with tissue stiffness. These correlations can be used to hypothesize mechanistic models for describing the mechanical behavior of brain tissue as well as to predict relative differences between brain tissue mechanical properties of other species, at different ages, and for different regions based on differences in tissue composition.
创伤性脑损伤后的年龄依赖性结果促使人们在不同发育阶段的实验动物模型中研究脑损伤生物力学。大鼠脑的有限元模型用于更好地理解这些年龄依赖性结果背后的力学机制；然而，为了使模型具有生物逼真度，需要年龄和区域特异性的大鼠脑组织力学特性。在这里，我们使用原子力显微镜（AFM）测量了P10、P17和成年大鼠皮质和海马亚区域的区域依赖性力学特性。表观弹性模量随压痕应变呈非线性增加，并使用非线性奥格登超弹性模型拟合力-挠度数据。力学特性的亚区域异质性分布随年龄显著变化。还发现表观弹性模量总体上随年龄增加，在P10和成年大鼠之间增加超过100%。对P10、P17和成年大鼠的海马和皮质全切片进行无侧限压缩试验（ε=-0.3），以验证用AFM测量的力学特性。每个区域和年龄在压痕应变为30%时，AFM测量的平均表观弹性模量与30%无侧限压缩试验测量的长期弹性模量相关性良好（斜率与1无显著差异，p>0.05）。脑内蛋白质、脂质和硫酸化糖胺聚糖含量随年龄增加，与组织硬度呈正相关，而含水量随年龄降低，与组织硬度呈负相关。这些相关性可用于假设描述脑组织力学行为的机制模型，以及基于组织组成差异预测其他物种、不同年龄和不同区域的脑组织力学特性之间的相对差异。
