Traumatic Brain Injury at Multiple Length Scales: Relating Diffuse Axonal Injury to Discrete Axonal Impairment

The length scales involved in the development of diffuse axonal injury, typically range from the head level (i.e., mechanical loading) to the cellular level, where discrete axonal injuries are located near inclusions. The aim is to investigate the local axonal strains near an inclusion in relation to the tissue level strains of the brain stem during mechanical loading of the head and the resulting orientation dependence of tissue level injury criteria. For this, a multi-scale FE approach is adopted. The results show that the axonal strains cannot be trivially correlated to the tissue strain without taking into account the axonal orientations, which indicates that the heterogeneities at the cellular level play an important role in brain injury and reliable predictions of it.