Regional mechanical properties of spinal cord gray and white matter in transverse section

Understanding spinal cord injury requires a comprehensive knowledge of its mechanical properties, which remains debated due to the variability reported. This study aims to characterize the regional mechanical properties of the spinal cord in transverse sections using micro-indentation. Quasi-static indentations were performed on the entire surface of transverse slices obtained from 10 freshly harvested porcine thoracic spinal cords using a 0.5 mm diameter flat punch. No significant difference in average longitudinal elastic modulus was found between white matter (n = 183, E = 0.51 + 0.21 kPa) and gray matter (n = 51, E = 0.53 + 0.25 kPa). In the gray matter, the elastic modulus in the dorsal horn (0.48 + 0.18 kPa) was significantly smaller than in the ventral horn (0.57 + 0.24 kPa) (GLMM, p < 0.05). The elastic modulus in the dorsal horn was also significantly smaller than in the lateral (0.52 + 0.22 kPa) and ventral funiculi (0.53 + 0.18 kPa) of the white matter (GLMM, p < 0.05). However, there was no significant difference in the elastic modulus among the ventral, lateral and dorsal funiculi of the white matter (GLMM, p > 0.05). The average elastic modulus strongly varies between samples, ranging from 0.23 (+0.06) kPa to 0.79 (+0.18) kPa and the testing time postmortem was significantly associated with a decrease in elastic modulus (t =-5.2, p < 0.001). The spinal cord's white matter demonstrated significantly lower elastic modulus compared to published data on brain tissue tested under similar conditions. These findings enhance our comprehension of the mechanical properties of spinal cord white and gray matter, challenging the homogeneity assumption of current models.