Mechanical Properties of Dura Mater from the Rat Brain and Spinal Cord

Abstract

The dura mater is the outermost and most substantial meningial layer of central nervous system (CNS) tissue that acts as a protective membrane for the brain and spinal cord. In animal models of traumatic brain injury and spinal cord injury, mechanical insults are often delivered directly to the dura to injure the underlying tissue. As such, including a description of the mechanical properties of dura mater is critical for biomechanical analyses of these models. We have characterized the mechanical response of dura mater from the rat brain and spinal cord in uniaxial tension. Testing was performed at low (0.0014 sec(-1)) and high (19.42 sec(-1)) strain rates. Both rat cranial dura and spinal dura demonstrated non-linear stress-strain responses characteristic of collagenous soft tissues. The non-linear increase in stress lagged in the spinal dura compared to the cranial dura. The slow rate data was fit to a one-term Ogden hyperelastic constitutive law, and significant differences were observed for the stiffness, G, and the parameter, alpha, which nominally introduces non-linearity. High strain rate stress-relaxation tests were performed to 10% strain, which was held for 10 sec. The relaxation was fit to a four-term Prony series exponential decay. Cranial dura and spinal dura demonstrated similar overall relaxation, but significant differences were identified in the distribution of the relaxation over the Prony series parameters, which demonstrated that cranial dura tended to relax faster. Polarized light microscopy revealed that the structural entities of spinal dura were aligned in the axial direction, whereas cranial dura did not demonstrate a preferential alignment. This was confirmed qualitatively with Masson's Tri-chrome and Verhoeff's Van Gieson staining for collagen and elastin, which also indicated greater elastin content for the spinal dura than for the cranial dura.