The mechanical characteristics of a porcine spinal cord under static loading in vitro

Abstract

Background – In spite of a number of researchers, it is well known that mechanical behaviour of a spinal cord under loading has not yet been studied extensively enough. Methods - Specimens were loaded at various strain rates: 0.02/s and 0.002/s to 5% and 10% strain. After reaching defined strain value, samples were left at a constant strain for stress relaxation. Findings – The demonstrated tensile testing stress-strain response is a highly non-linear curve corresponding to low stiffness. In the toe region stress increases exponentially with the applied strain. The highest calculated stress value for 10% strain was 0,014 MPa (strain rate 0,02/s) and 0,008 MPa (strain rate 0,002/s). Linear approximation of the stress by the least square method allowed to derive Young modulus of the value: 39,68 kPa at strain rate 0,02/s and 31,07 kPa at strain rate 0,002/s. R squared value for both regressions was above 0,99 and confirmed a good quality of approximation. A and β coefficients were 1,5MPa and 31,3 at 0,02/s strain rates and 1,3MPa and 25,3 at 0,002/s strain rates correspondingly. Relative stress relaxation increased from 20% to 37% after 60 s. Absolute stress relaxation was from 0,4kPa to 2,4kPa, at 0,002/s strain rate by 5% maximum strain and 0,02/s strain rate by 10% respectively. Interpretation - Mechanical characteristics demonstrated a visible strain-rate dependence as stiffness was significantly increasing with an increase of strain rate. Mechanical characteristics demonstrated a visible strain-rate dependence as stiffness was significantly increasing with an increase of strain rate.