Biphasic theory can provide a mechanistic description of deformation and transport phenomena in soft tissues, and has been used to model surgery and drug delivery in the brain for decades. Knowledge of corresponding mechanical properties of the brain is needed to accurately predict tissue deformation and flow transport in these applications. Previously in our group, creep indentation tests were conducted for multiple anatomical regions in acute rat brain tissue slices. In the current study, a biphasic finite element model of creep indentation was developed with which to compare these data. Considering the soft tissue structure of brain, the solid matrix was assumed to be composed of a neo-Hookean ground matrix reinforced by continuously distributed fibers that exhibits tension-compression nonlinearity during deformation. By fixing Poisson's ratio of the ground matrix, Young's modulus, fiber modulus and hydraulic permeability were estimated. Hydraulic permeability was found to be nearly independent of the properties of the solid matrix. Estimated modulus (40 Pa to 1.1 kPa for the ground matrix, 3.2–18.2 kPa for fibers) and hydraulic permeability ($\text{1.2}-\text{5.5×}{10}^{\text{-13}}{\mathrm{m}}^4\text{/N s}$) fell within an acceptable range compared with those in previous studies. Instantaneous indentation depth was dominated by tension provided by fibers, while the tissue response at equilibrium was sensitive to Poisson's ratio. Results of sensitivity analysis also point to the necessity of considering tension-compression nonlinearity in the solid phase when the biphasic material undergoes large creep deformation.

双相理论可以提供对软组织中变形和运输现象的机械描述，并且已被用于模拟外科手术和大脑中的药物输送数十年。在这些应用中，需要准确了解大脑的相应机械特性，才能准确预测组织变形和血流传输。先前在我们组中，对急性大鼠脑组织切片中的多个解剖区域进行了蠕变压痕测试。在当前的研究中，开发了蠕变压痕的双相有限元模型，用于与这些数据进行比较。考虑到大脑的软组织结构，假设固体基质由新霍克纤维基质组成，该基质由连续分布的纤维增强，在变形过程中表现出拉张-压缩非线性。通过修复泊松' 估算了基体的比值，杨氏模量，纤维模量和水力渗透率。发现水渗透性几乎与固体基质的性质无关。估计模量（地面基质为40 Pa至1.1 kPa，纤维为3.2-18.2 kPa）和水力渗透率（$\text{1.2}-\text{5.5×}{10}^{\text{-13}}{\mathrm{米}}^4\text{/秒}$）与以前的研究相比处于可接受的范围内。瞬时压痕深度受纤维提供的张力支配，而平衡状态下的组织反应对泊松比敏感。敏感性分析的结果还指出，当双相材料经历大的蠕变变形时，必须考虑固相中的拉伸-压缩非线性。