Application of a finite element model of the brain to study traumatic brain injury mechanisms in the rat.

Complete validation of any finite element (FE) model of the human brain is very difficult due to the lack of adequate experimental data. However, more animal brain injury data, especially rat data, obtained under well-defined mechanical loading conditions, are available to advance the understanding of the mechanisms of traumatic brain injury. Unfortunately, internal response of the brain in these experimental studies could not be measured. The aim of this study was to develop a detailed FE model of the rat brain for the prediction of intracranial responses due to different impact scenarios. Model results were used to elucidate possible brain injury mechanisms. A FE model, consisting of more than 250,000 hexahedral elements with a typical element size of 100 to 300 microns, was developed to represent the brain of a rat. The model was first validated locally against peak brain deformation data obtained from nine unique dynamic cortical deformation (vacuum) tests. The model was then used to predict biomechanical responses within the brain due to controlled cortical impacts (CCI). A total of six different series of CCI studies, four with unilateral craniotomy and two with bilateral craniotomy, were simulated and the results were systematically analyzed, including strain, strain rate and pressure within the rat brain. In the four unilateral CCI studies, approximately 150 rats were subjected to velocities ranging from 2.25 to 4 m/s, and cortical deformations of 1, 2 or 3 mm, with impactor diameters of 2.5 or 5 mm. Moreover, the impact direction varied from lateral 23 degrees to vertical. For the bilateral craniotomy CCI studies, about 70 rats were injured at 4.7 or 6 m/s, with deformations of 1.5 or 2.5 mm and impactor diameters of 3 or 5 mm, and at an impact direction of about 23-30 degrees laterally. Simulation results indicate that intracranial strains best correlate with experimentally obtained injuries.