Interaction of micron and nano-sized particles with cells of the dura mater.

Intervertebral total disc replacements (TDR) are used in the treatment of degenerative spinal disc disease. There are, however, concerns that they may be subject to long-term failure due to wear. The adverse effects of TDR wear have the potential to manifest in the dura mater and surrounding tissues. The aim of this study was to investigate the physiological structure of the dura mater, isolate the resident dural epithelial and stromal cells and analyse the capacity of these cells to internalise model polymer particles. The porcine dura mater was a collagen-rich structure encompassing regularly arranged fibroblastic cells within an outermost epithelial cell layer. The isolated dural epithelial cells had endothelial cell characteristics (positive for von Willebrand factor, CD31, E-cadherin and desmoplakin) and barrier functionality whereas the fibroblastic cells were positive for collagen I and III, tenascin and actin. The capacity of the dural cells to take up model particles was dependent on particle size. Nanometer sized particles readily penetrated both types of cells. However, dural fibroblasts engulfed micron-sized particles at a much higher rate than dural epithelial cells. The study suggested that dural epithelial cells may offer some barrier to the penetration of micron-sized particles but not nanometer sized particles.

Poisson's ratio and strain rate dependency of the constitutive behavior of spinal dura mater.

Knowledge of the mechanical behavior of spinal dura mater is important for a number of applications including the experimental and computational modeling of physiological phenomena and spinal cord trauma. However, mechanical characterization of dura mater is relatively sparse and is further compounded by the use of the tangent modulus as the sole measure of stiffness. This study aims to provide a more complete description of the mechanical properties of spinal dura mater, including the effect of strain rate. Bovine dura mater was tested under uniaxial tension in both the longitudinal and the circumferential directions at three different strain rates; 0.01, 0.1, and 1.0 s(-1). An Ogden model was fitted to the resulting stress-stretch data. The morphology of the dura mater was assessed using Sirius red and H&E staining. No significant effect of the strain rate was found for the Ogden model parameters. Longitudinal specimens were significantly stronger and more deformable than circumferential samples, probably due to the structural arrangement of the collagen fibers. At low strains, however, the circumferential specimens were stiffer than the longitudinal ones. The findings of this study will allow more complete representations of the spinal dura mater to be developed.