Abstract
The cerebral meninges, made up of the dura, arachnoid, and pia mater, is a tri-layer membrane that surrounds the brain and the spinal cord and has an important function in protecting the brain from injury. Understanding its mechanical behavior is important to ensure the accuracy of finite element (FE) head model simulations which are commonly used in the study of traumatic brain injury (TBI). Mechanical characterization of freshly excised porcine dura-arachnoid mater (DAM) was achieved using uniaxial tensile testing and bulge inflation testing, highlighting the dependency of the identified parameters on the testing method. Experimental data was fit to the Ogden hyperelastic material model with best fit material parameters of μ = 450 ± 190 kPa and α = 16.55 ± 3.16 for uniaxial testing, and μ = 234 ± 193 kPa and α = 8.19 ± 3.29 for bulge inflation testing. The average ultimate tensile strength of the DAM was 6.91 ± 2.00 MPa (uniaxial), and the rupture stress at burst was 2.08 ± 0.41 MPa (inflation). A structural analysis using small angle light scattering (SALS) revealed that while local regions of highly aligned fibers exist, globally, there is no preferred orientation of fibers and the cerebral DAM can be considered to be structurally isotropic. This confirms the results of the uniaxial mechanical testing which found that there was no statistical difference between samples tested in the longitudinal and transversal direction (p = 0.13 for μ, p = 0.87 for α). A finite element simulation of a craniotomy procedure following brain swelling revealed that the mechanical properties of the meninges are important for predicting accurate stress and strain fields in the brain and meninges. Indeed, a simulation using a common linear elastic representation of the meninges was compared to the present material properties (Ogden model) and the intracranial pressure was found to differ by a factor of 3. The current study has provided researchers with primary experimental data on the mechanical behavior of the meninges which will further improve the accuracy of FE head models used in TBI.
Highlights
Traumatic brain injury (TBI), caused by a fierce acceleration or impact to the head, is a critical public health problem throughout the world (Peeters et al, 2015; MacManus et al, 2017a)
As concluded by Budday et al (2019) in their review paper of brain tissue, we have considered that, provided the tissue is kept sufficiently hydrated, the degeneration process of post-mortem tissues is negligible
It was confirmed that the global behavior of the porcine DAM can be considered isotropic
Summary
Traumatic brain injury (TBI), caused by a fierce acceleration or impact to the head, is a critical public health problem throughout the world (Peeters et al, 2015; MacManus et al, 2017a). Since the 2000s, both multibody dynamics models and finite element (FE) head models have been developed by researchers to better understand the response of the human head to dynamic loads (Gilchrist et al, 2001; Horgan and Gilchrist, 2003; King et al, 2006; Kleiven, 2006; Chafi et al, 2009; Li et al, 2011) These models have since provided insights into the fundamental mechanisms of TBI in road traffic accidents (Kleiven, 2007), accidental falls (Doorly and Gilchrist, 2006; Raul et al, 2006; Pascoletti et al, 2019), impact sports (Post et al, 2013), and ballistics impacts (Li et al, 2016). Van Noort et al (1981b), using polarized light and Hamann et al (1998), using small angle light scattering (SALS) to analyse the collagen fiber architecture of human cerebral DM concluded that while there are regions of highly aligned collagen fibers, this alignment is only seen over short distances and the global structure of the cerebral DM can be considered as isotropic
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