Greiner Alexander, Reiter Nina, Hinrichsen Jan, Kainz Manuel P, Sommer Gerhard, Holzapfel Gerhard A, Steinmann Paul, Comellas Ester, Budday Silvia
Department of Mechanical Engineering, Institute of Continuum Mechanics and Biomechanics, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany.
Institute of Biomechanics, Graz University of Technology, Graz, Austria.
Interface Focus. 2024 Dec 6;14(6):20240026. doi: 10.1098/rsfs.2024.0026.
The brain is arguably the most complex human organ and modelling its mechanical behaviour has challenged researchers for decades. There is still a lack of understanding on how this multiphase tissue responds to mechanical loading and how material parameters can be reliably calibrated. While previous viscoelastic models with two relaxation times have successfully captured the response of brain tissue, the Theory of Porous Media provides a continuum mechanical framework to explore the underlying physical mechanisms, including interactions between solid matrix and free-flowing interstitial fluid. Following our previously published experimental testing protocol, here we perform finite element simulations of cyclic compression-tension loading and compression-relaxation experiments on human brain white and gray matter specimens. The solid volumetric stress proves to be a crucial factor for the overall biphasic tissue behaviour as it strongly interferes with porous effects controlled by the permeability. An inverse parameter identification reveals that poroelasticity alone is insufficient to capture the time-dependent material behaviour, but a poro-viscoelastic formulation captures the response of brain tissue well. We provide valuable insights into the individual contributions of viscous and porous effects. However, due to the strong coupling between porous, viscous, and volumetric effects, additional experiments are required to reliably determine all material parameters.
大脑可以说是人类最复杂的器官，几十年来，对其力学行为进行建模一直是研究人员面临的挑战。对于这种多相组织如何响应机械载荷以及如何可靠地校准材料参数，人们仍然缺乏了解。虽然之前具有两个松弛时间的粘弹性模型成功地捕捉到了脑组织的响应，但多孔介质理论提供了一个连续介质力学框架来探索潜在的物理机制，包括固体基质与自由流动的间质液之间的相互作用。按照我们之前发表的实验测试方案，我们在此对人脑白质和灰质标本进行了循环压缩 - 拉伸加载以及压缩 - 松弛实验的有限元模拟。固体体积应力被证明是整体双相组织行为的关键因素，因为它强烈干扰了由渗透率控制的多孔效应。反向参数识别表明，仅多孔弹性不足以捕捉随时间变化的材料行为，但多孔粘弹性公式能很好地捕捉脑组织的响应。我们对粘性和多孔效应的各自贡献提供了有价值的见解。然而，由于多孔、粘性和体积效应之间的强耦合，需要进行额外的实验来可靠地确定所有材料参数。
