Do blast induced skull flexures result in axonal deformation?

Abstract

Subject-specific computer models (male and female) of the human head were used to investigate the possible axonal deformation resulting from the primary phase blast-induced skull flexures. The corresponding axonal tractography was explicitly incorporated into these finite element models using a recently developed technique based on the embedded finite element method. These models were subjected to extensive verification against experimental studies which examined their pressure and displacement response under a wide range of loading conditions. Once verified, a parametric study was developed to investigate the axonal deformation for a wide range of loading overpressures and directions as well as varying cerebrospinal fluid (CSF) material models. This study focuses on early times during a blast event, just as the shock transverses the skull (< 5 milliseconds). Corresponding boundary conditions were applied to eliminate the rotation effects and the resulting axonal deformation. A total of 138 simulations were developed– 128 simulations for studying the different loading scenarios and 10 simulations for studying the effects of CSF material model variance–leading to a total of 10,702 simulation core hours. Extreme strains and strain rates along each of the fiber tracts in each of these scenarios were documented and presented here. The results suggest that the blast-induced skull flexures result in strain rates as high as 150–378 s-1. These high-strain rates of the axonal fiber tracts, caused by flexural displacement of the skull, could lead to a rate dependent micro-structural axonal damage, as pointed by other researchers.

Cerebral Vasculature Influences Blast-Induced Biomechanical Responses of Human Brain Tissue

“…The larger peak-pressure discrepancy between our study and Garimella et al could be due to the differences in the algorithm implemented to apply the blast load to the head. Similar to Sharma (2011) and Garimella et al (2018), we observed oscillations in the simulated pressuretime profiles compared to the experimental values. These oscillations in the frontal lobe could be possibly attributed to the blast wave continuously deforming the skull as it propagates through the head (Garimella et al, 2018;Moss et al, 2009) as well as reflections from the skin-skull, skull-subarachnoid space, and subarachnoid space-brain interfaces (Ganpule et al, 2013).…”

“…The three key attributes of our 3-D high-fidelity human-head FE model are 1) the detailed network of cerebral veins and arteries (Figure 1), 2) the representation of the brain-tissue gyri and sulci, and 3) the hyper-viscoelastic material properties to model blastinduced brain-tissue deformations (Table 1). In contrast, Sharma (2011), Singh et al (2014), and Panzer et al (2012, who developed coupled FE models similar to our study, and Garimella et al (2018), who applied a blast load to a humanhead FE model using the Conventional Weapons Program (Hyde, 1991), did not model the cerebral vasculature or the brain-tissue gyri and sulci. Moreover, Sharma (2011), Singh et al (2014), andPanzer et al (2012) employed linear viscoelastic brain-tissue properties, whereas Garimella et al (2018) used hyperviscoelastic material properties to model blast-induced braintissue deformations.…”

“…In contrast, Sharma (2011), Singh et al (2014), and Panzer et al (2012, who developed coupled FE models similar to our study, and Garimella et al (2018), who applied a blast load to a humanhead FE model using the Conventional Weapons Program (Hyde, 1991), did not model the cerebral vasculature or the brain-tissue gyri and sulci. Moreover, Sharma (2011), Singh et al (2014), andPanzer et al (2012) employed linear viscoelastic brain-tissue properties, whereas Garimella et al (2018) used hyperviscoelastic material properties to model blast-induced braintissue deformations. In turn, while the coupled FE models developed by Ganpule et al (2013), Wang et al (2014), Taylor andFord (2009), andNyein et al (2010) included the gyri and sulci, they did not model the cerebral vasculature.…”

Sex as a Biological Variable in Preclinical Modeling of Blast-Related Traumatic Brain Injury

“…Factors associated with biomechanical differences related to scaling, sex, and age are also of relevance. For example, blast effect sex differences for human males and females have received little attention, but—while there is significant overlap—there are reported average differences in size and skull thickness that can have different consequences on skull flexure during shock wave loading ( 211 – 213 ). Likewise, the skull shape differences are significantly dissimilar for different species used in preclinical study ( 214 ), for the determination of sex differences in primates, but mouse differences appear to be trivial ( 215 ).…”

In silico investigation of biomechanical response of a human subjected to primary blast

“…(Tanielian, 2008;Warden, 2006) Understanding how the blast wave interacts with the head-brain parenchyma is crucial for devising blast mitigation strategies, clinical interventions, therapeutics, and recreating injury in a laboratory. Several mechanisms of blast induced traumatic brain injury have been proposed, including direct intracranial transmission, (Nyein et al, 2010;Sundaramurthy et al, 2012;Taylor and Ford, 2009) skull flexure, (Bolander et al, 2011;Garimella et al, 2018;Moss et al, 2009) a thoracic mechanism, (Cernak et al, 2001;Simard et al, 2014) cavitation, (Panzer et al, 2012;Salzar et al, 2017) and head acceleration. (Goldstein et al, 2012;Gullotti et al, 2014) Yet, the current understanding of the contribution of each mechanism in generating mechanical fields within the brain is limited (Fievisohn et al, 2018;Meaney et al, 2014) and findings in the literature are contradictory.…”