This paper presents a three-dimensional micromechanical model of brain white matter tissue as a transversely isotropic soft composite described by the generalized Ogden hyperelastic model. The embedded element technique, with corrected stiffness redundancy in large deformations, was used for the embedment of a histology-informed probabilistic distribution of the axonal fibers in the extracellular matrix. The model was linked to a multi-objective, multi-parametric optimization algorithm, using the response surface methodology, for characterization of material properties of the axonal fibers and extracellular matrix in an inverse finite element analysis. The optimum hyperelastic characteristics of the tissue constituents, obtained based on the axonal and transverse direction test results of the corona radiata tissue samples, indicated that the axonal fibers were almost thirteen times stiffer than the extracellular matrix under large deformations. Simulation of the same tissue under a different loading condition, as well as that of another white matter tissue, i.e., the corpus callosum, in the axonal and transverse directions, using the optimized hyperelastic characteristics revealed tissue responses very close to those of the experiments. The results of the model at the sub-tissue level indicated that the stress concentrations were considerably large around the small axons, which might contribute into the brain injury.

本文提出了由广义Ogden超弹性模型描述的作为横向各向同性软复合材料的脑白质组织的三维微观力学模型。具有较大变形的刚度冗余的嵌入式元素技术被用于在细胞外基质中嵌入组织学信息的轴突纤维概率分布。使用响应面方法，将模型与多目标，多参数优化算法链接，以在逆向有限元分析中表征轴突纤维和细胞外基质的材料特性。根据电晕放射线组织样本的轴突和横向测试结果获得的组织成分的最佳超弹性特征，表明在大变形下，轴突纤维的硬度几乎比细胞外基质高13倍。使用优化的超弹性特性，在轴突和横向方向上对不同负荷条件下的相同组织以及另一白质组织（即call体）进行了模拟，结果显示出与实验非常接近的组织响应。在亚组织水平的模型结果表明，在小轴突周围的应力集中相当大，这可能会导致脑损伤。在轴突和横向方向上，使用优化的超弹性特征显示组织响应非常接近实验响应。在亚组织水平的模型结果表明，在小轴突周围的应力集中相当大，这可能会导致脑损伤。在轴突和横向方向上，使用优化的超弹性特征显示组织响应非常接近实验响应。在亚组织水平的模型结果表明，在小轴突周围的应力集中相当大，这可能会导致脑损伤。