Determination of Correlations between Mechanical and Microstructural Properties of Aorta by Nanoindentation Technique
Ali Hemmasizadeh (Temple University), Soroush Assari (Temple University), Michael Autieri (Temple University), Kurosh Darvish (Temple University)
Experimental Nanobiomechanics
Mon 9:00 - 10:30
Barus-Holley 163
Aorta is composed of distinct anatomical layers and components with different mechanical characteristics which vary along its wall thickness. Understanding and characterization of the interactions between aorta building blocks and their mechanical properties enable us to quantify changes that may occur in the material behavior of aorta as a result of cardiovascular diseases and also to predict tissue failure caused by aneurysms or traumatic injuries. In this study, using a custom-made nanoindentation technique, heterogeneity of viscoelastic mechanical properties across the aortic wall was characterized and was correlated to the density of elastic lamellae. Cylindrical samples were extracted from 7 fresh porcine aortas and successive nanoindentation tests were performed across the wall thickness at 100 µm intervals. Indentation tests included a ramp-and-hold profile (10 ms and 30 s durations respectively with 40 m amplitude) and the instantaneous Young’s modulus (E) and the steady-state relaxation ratio Ginf were characterized based on experimental data. The density of elastic lamellae per unit length was determined from 6 um transverse sections stained with Verhoeff-van Gieson staining protocol. Mechanical and histological results were categorized and divided into 10 equal regions in the radial direction. A total of 300 indentation data points were collected. Independent hierarchical cluster analysis of mechanical and histological studies showed that the results could be divided into two statistically significant groups (paired t-test p < 0.001) of inner and outer halves for E (60.32±1.65 and 70.27±2.47 kPa respectively), Ginf (0.33±0.01 and 0.35±0.01), and density of elastic lamellae (51.06±1.11 and 65.62±1.17 mm-1). The overall results revealed that the density of elastic lamellae was strongly correlated with E and somewhat related to Ginf.