Objective Uniaxial Identification of Transition Points in Non-Linear Materials: Sample Application to Porcine Coronary Arteries and the Dependency of Their Pre- and Post-Transitional Moduli with Position

This study aimed to develop an objective method for the elastic characterisation of pre- and post-transitional moduli of left anterior descending (LAD) porcine coronary arteries. Methods Eight coronary arteries were divided into proximal, middle and distal test specimens. Specimens underwent uniaxial extension up to 3 mm. Force–displacement measurements were used to determine the induced true stress and stretch for each specimen. A local maximum of the stretch-true stress data was used to identify a transition point. Pre- and post-transitional moduli were calculated up to and from this point, respectively. Results The mean pre-transitional moduli for all specimens was 0.76 MPa, as compared to 4.86 MPa for the post-transitional moduli. However, proximal post-transitional moduli were significantly greater than that of middle and distal test specimens (p < 0.05). Conclusion Post-transitional uniaxial properties of the LAD are dependent on location along the artery. Further, it is feasible to objectively identify a transition point between pre- and post-transitional moduli

Dynamic Viscoelasticity and Surface Properties of Porcine Left Anterior Descending Coronary Arteries

The aim of this study was, for the first time, to measure and compare quantitatively the viscoelastic properties and surface roughness of coronary arteries. Porcine left anterior descending coronary arteries were dissected ex vivo. Viscoelastic properties were measured longitudinally using dynamic mechanical analysis, for a range of frequencies from 0.5 to 10 Hz. Surface roughness was calculated following three-dimensional reconstructed of surface images obtained using an optical microscope. Storage modulus ranged from 14.47 to 25.82 MPa, and was found to be frequency-dependent, decreasing as the frequency increased. Storage was greater than the loss modulus, with the latter found to be frequency-independent with a mean value of 2.10 ± 0.33 MPa. The circumferential surface roughness was significantly greater (p < 0.05) than the longitudinal surface roughness, ranging from 0.73 to 2.83 and 0.35 to 0.92 µm, respectively. However, if surface roughness values were corrected for shrinkage during processing, circumferential and longitudinal surface roughness were not significantly different (1.04 ± 0.47, 0.89 ± 0.27 µm, respectively; p > 0.05). No correlation was found between the viscoelastic properties and surface roughness. It is feasible to quantitatively measure the viscoelastic properties of coronary arteries and the roughness of their endothelial surface