Constitutive Modeling and Numerical Implementation of Brain Tissue Including Damage

Introduction:

Brain injury is one of the main causes of mortality and morbidity. Different types of Traumatic Brain Injury (TBI) are known where Ischemia is a common pathway. Elevated intracranial pressure (ICP) is associated with ischemia and poor outcome after TBI. The brain is consisted of different constituents such as cerebrospinal fluid (CSF), the porous solid tissue and the blood. The values of normal and raised ICP are given in medical textbooks however, it is based on experimental observations and is not clear why the normal and raised ICP values are higher in adults than infants, children or elderlies. Besides that, the role of CSF or blood in most of mechanical models is neglected however, we are not sure if this is a correct simplification. Not only this, but also ICP monitoring is an invasive process where the surgeon has to insert a probe into the brain tissue and if one can govern a relationship between CSF velocity and the ICP, it would be beneficial for surgeons to monitor ICP non-invasively.
 

Research Plans

The research which is still in progress is to obtain an analytical solution for a damaged media using theory of porous media (TPM). It is demanded to investigate the role of CSF and to obtain the total pore pressure inside the damaged media. Based on that, the critical ICP can be computed which will be used in the numerical simulation.

It is planned to simulate the impact test on a real geometry using a FE software for Adults, infants, children and elderlies considering different Dirichlet and Neumann boundary conditions. For each simulation, if the total pore pressure inside a RVE (representative volume element) reaches the critical value, which was obtained before from analytical solution, that RVE is considered as damaged media. Based on that, the initiated damage by an external force, e.g. an impact, is numerically computed and the size of computed damage is compared to the experimental results.

In the FE simulations, the solid only simulation and the simulations based on the TPM will be compared and the role of CSF will be analyzed.