Exploring the mechanical behavior of the spinal dura mater: experimental insights and measurement dilemmas

Spinal dura mater provides essential structural protection for the spinal cord and helps maintain cerebrospinal fluid pressure, yet its mechanical characterization remains challenging because of its thinness and anisotropy. This study investigated the uniaxial tensile behavior of spinal dura mater and examined how speckle-paint application, the strain-measurement method (Digital Image Correlation (DIC)-derived strain vs. crosshead displacement), preconditioning, and donor demographics affect measured mechanical parameters. Samples were harvested postmortem from seven donors and assigned to three groups: painted & not preconditioned, unpainted & preconditioned, and unpainted & not preconditioned. A 3D-printed adapter was used to standardize sample geometry. Tests were conducted at a crosshead displacement rate of 5 mm·min⁻¹ (strain rate of 0.0042 s⁻¹), with some specimens undergoing cyclic preloading. Speckle paint increased stiffness but did not affect failure stress or stretch. DIC-derived elastic moduli were higher than those from crosshead displacement. After correcting for paint- and method-induced effects, the mean elastic moduli in the longitudinal and circumferential directions were ~ 283 MPa and ~ 16 MPa, respectively. Both orientations exhibited a failure stretch of ~ 1.10–1.12. The apparent Poisson function (Hencky form) ranged from 1.57 to 4.84 (longitudinal) and 2.91 to 6.29 (circumferential), indicating volumetric changes that challenge near-incompressibility assumptions. These findings emphasize the importance of standardized protocols and data normalization when investigating soft tissue mechanics. The higher DIC-based moduli arise primarily from local, gauge-region strain measurement and stiffening induced by the acrylic speckle coating, while the elevated apparent Poisson’s ratios likely reflect fluid redistribution and collagen-fiber reorientation under tensile loading in this highly anisotropic tissue.