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Mechanical damage to the meninges, which protect the spinal cord from blunt external forces, can cause idiopathic cerebrospinal fluid (CSF) leakage. This is probably because even a small meningeal failure leads to the leakage of CSF out of the subarachnoid space. However, the dura mater, the outermost layer of the meninges, is especially resilient and structurally tough. Moreover, CSF leakage can be caused by daily activities, including coughing, sneezing, and falling. Because of these contradicting facts, the essential mechanism of CSF leakage is difficult to understand. Recently, extensive efforts have been made to elucidate the mechanism of traumatic and impact-related injuries through computational simulations. It is crucial to comprehend the actual failure mode of biological materials under in vivo-like injurious loading conditions to enhance the accuracy of injury prediction. Therefore, in this study, we focused on the relationship between the intrinsic shape of wrinkles formed on the dural surface and the mechanical failure mode of the spinal dura mater. We found that a generated crack runs along the microscopic wrinkles in the longitudinal direction even when the spinal dura mater is statically pressurized.

In this study, we developed an equi-load biaxial tensile tester and applied it to a series of mechanical tests using specimens obtained from the porcine spinal dura mater. The dural sample exhibited a nonlinear and anisotropic behavior as it was more deformable in the longitudinal direction rather than in the circumferential direction at lower strains; i.e., mechanical response of the longitudinal direction was significantly compliant in the Toe region compared to that of the circumferential direction under 1:1 biaxial stretching. However, we have not observed a significant difference with respect to the resultant strain and Young’s modulus between the longitudinal and circumferential directions at higher strains or in the Linear region. Our results also indicated that the upper thoracic region (T1) was relatively compliant compared to the lumbar region (L), where the failure load was almost equal between them because the dural thickness of T1 was five-fold greater than that of L; i.e., spinal dura mater became stiffer and stronger at further distances from the brain. This shows structural effectiveness and may be preferable to mechanically protect the vulnerable spinal cord from externally applied impact loads.

This study conducted a series of biaxial stretching tests on the spinal dura mater. To investigate the specific effects of different loading patterns on mechanical responses of the dura mater, load-controlled asymmetric (longitudinal vs. circumferential loading at 1:0.5 and 0.5:1 ratios) and equi-load (longitudinal vs. circumferential at a 1:1 ratio) biaxial stretching tests were performed. The dural meninge was found to be most compliant when a circumferentially dominant loading pattern (longitudinal vs. circumferential at a 0.5:1 ratio or physiological biaxial stretch) was used. Additionally, physiological biaxial stretch resulted in the lowest strain energy density in the toe region of stress–strain curves, i.e., physiological deformation ranges, whereas mechanical loading caused abruptly stiffening of the linear region of stress–strain curves even under circumferentially dominant loading. On the other hand, stress relaxation and elastin content of the dural tissue had no effect on stored strain energy density within the range of biaxial stretch tested in this study. These results indicate that physiological biaxial stretching contributes to structural protection of the spinal cord and the spinal dura, which may be attributable to changes in the arrangement of embedded collagen fibers and concomitant mechanical interactions with surrounding tissues.