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Abstract

To better understand the link between spinal cord impact and the resulting tissue damage, computational models are often used. These models typically simulate the spinal cord as a homogeneous and isotropic material. Recent research suggests that grey and white matter tissue differences and directional differences, i.e. anisotropy, are important to predict spinal cord damage. The objective of this research was to characterize the mechanical properties of spinal cord grey and white matter tissue in confined compression. Spinal cords (n=11) from the thoracic and cervical regions of pigs (Yorkshire and Yucatan) were harvested immediately following euthanasia. The spinal cords were flash frozen (60 secs at -80 oC) and prepared into four types of test samples: grey matter axial, grey matter transverse, white matter axial, white matter transverse. For each sample type, 2 mm diameter biopsy samples were collected, thawed, and subsequently tested with a custom confined compression apparatus. This was performed within 6 hours of euthanasia, minimizing time post-mortem effects. All samples were compressed to 10% strain at a quasi-static strain rate (0.001/sec) and allowed to relax for 120 secs. A quasi-linear viscoelastic model combining a first-order exponential with a 1-term Prony series was used to characterize the loading and relaxation responses respectively. The effect of tissue type (grey matter vs. white matter), direction (axial vs. transverse), and their interaction were evaluated with a two-way ANOVA (p