Abstract
Diffuse axonal injury (DAI) is a severe form of traumatic brain injury and often induced by blunt trauma. The closed head impact acceleration (IA) model is the most widely used rodent DAI model. However, this model results in large variations of injury severity. Recently, the impact device/system was modified to improve the consistency of the impact energy, but variations of the head kinematics and subsequent brain injuries were still observed. This study was aimed to utilize a Finite Element (FE) model of a rat head/body and simulation to investigate the potential biomechanical factors influencing the impact energy transfer to the head. A detailed FE rat head model containing detailed skull and brain anatomy was developed based on the MRI, microCT and atlas data. The model consists of over 722,000 elements, of which 310,000 are in the brain. The white matter structures consisting of highly aligned axonal fibers were simulated with transversely isotropic material. The rat body was modeled to provide a realistic boundary at the spine-medulla junction. Rodent experiments including dynamic cortical deformation, brain-skull displacement, and IA kinematics were simulated to validate the FE model. The model was then applied to simulate the rat IA experiments. Parametric studies were conducted to investigate the effect of the helmet inclination angles (0°–5°) and skull stiffness (varied 20%) on the resulting head kinematics and maximum principal strain in the brain. The inclination angle of the helmet at 5° could vary head linear acceleration by 8–31%. The change in head rotational velocity was inversely related to the change in linear acceleration. Varying skull stiffness resulted in changes in head linear acceleration by 3% but with no effect on rotational velocity. The brain strain in the corpus callosum was only affected by head rotation while the strain in the brainstem was influenced by the combined head kinematics, local skull deformation, and head-neck position. Validated FE models of rat impact head injury can assist in exploring various biomechanical factors influencing the head impact response and internal brain response. Identification of these variables may help explain the variability of injury severity observed among experiments and across different labs.
Highlights
Traumatic Brain injury (TBI) is caused primarily by mechanical loading to the head
It has been suggested that Diffuse axonal injury (DAI) be renamed to Traumatic Axonal Injury (TAI) due to the extent of the injury being multifocal among white matter structures rather than diffuse (Smith and Meaney, 2000)
The results showed the potential variations in the mechanical system, which may explain various mortality rates reported by different groups using the same model (Suehiro et al, 2001; Rhodes et al, 2002; Geeraerts et al, 2006; Marmarou et al, 2006; Ucar et al, 2006; Fei et al, 2007; Pascual et al, 2007)
Summary
Traumatic Brain injury (TBI) is caused primarily by mechanical loading to the head. Diffuse axonal injury (DAI) is the most frequent type of TBIs in closed head injuries (Wright and Ramesh, 2012). It has been suggested that DAI be renamed to Traumatic Axonal Injury (TAI) due to the extent of the injury being multifocal among white matter structures rather than diffuse (Smith and Meaney, 2000). Researchers used various in vivo or in vitro animal models to introduce TAI in the laboratory settings to mimic human injury, and to investigate the underlying injury mechanisms. The rodent is the most frequently used in vivo animal model in the brain injury research due to its low cost, small size, and standardization (Cernak, 2005; O’Connor et al, 2011; Xiong et al, 2013)
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