Mechanical characterization of porcine and bovine dura mater: a better understanding in mild traumatic brain injury

Abstract

About 80% of all traumatic brain injuries are mild, making them a substantial societal and economic burden. To improve the understanding of the physical mechanism underlying traumatic brain damage and to design more effective preventative measures, such as protective helmets, accurate biofidelic head models are required. For such models to be effective, precise material descriptions of all structures activated in the head during this mechanism are crucial. Although meninges are necessary for protecting the brain from injury, little is known about their mechanical behaviour and resistance to strain-induced damage. This study investigates and assesses the geometrical, mechanical, and structural characteristics of porcine and bovine meninges. The elastic modulus of both species was evaluated by uniaxial testing and nanoindentation, and the susceptibility of porcine meninges to strain-mediated damage was determined by subfailure damage testing. In addition, the specific mechanical property of the region close to the frontal, parietal, temporal, and occipital lobes of the cerebellum was analysed on bovine meninges. In terms of geometry and modulus of elasticity, porcine dura is superior (thickness 0.73 mm, bulk elastic modulus 16.34 MPa) to bovine dura (thickness 0.46 mm, bulk elastic modulus 0.51 MPa). On the other hand, the elastic modulus of porcine dura was observed to be strongly dependent on characterization technique. Nanoindentation techniques produced a substantially smaller mechanical response (1.24 kPa) compared to tensile loading (16.34 MPa). Geometrically, the dura was found to be isotropic, however the parietal region displayed higher tensile strength (0.14 MPa) and elastic modulus (0.58 MPa) than the other regions. The elastic modulus for the frontal, temporal and occipital regions were found 0.43 MPa, 0.55 MPa and 0.45 MPa respectively. The subfailure damage test revealed that the dura is more susceptible to this type of injury than other tissues, such as tendon and ligament. The viscoelastic nature of dura was confirmed by all characterisation approaches, which may have implications for FE head modelling. The relationship between the meningeal tissue's structural composition and its mechanical performance under tension was determined using scanning electron microscopy-based structural analysis. This research demonstrated that the dura has a layered structure, with each layer possessing a thick, randomly aligned collagen network. In addition, fatigue was observed with a higher value (0.698) in the dura mater after 10 preconditioning cycles, which may have significant consequences for repeated mild traumatic brain injury.