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Introduction: Strength and structural stability of the aorta primarily comes from collagen that is mostly found in the media layer of the aorta along with elastin. The risk of life-threatening aortic rupture increases in cases of aortic aneurysm diseases due to local deformation and weakening of the aortic wall. How does local structure affect how the aorta responds to stress? We hypothesize that material and geometric heterogeneity affect the local biomechanics of the aortic wall and that the local responses to stress are not necessarily the same as the global response. Our goal is to develop a novel finite element model (FEM) of collagen and elastin behavior in murine aorta derived from high-resolution micro-computed tomography (microCT). This model will allow us to study how the aorta deforms to blood pressure at the local level. Approach: The collagen and elastin from 100 vertical slices of microCT scans of a murine aorta were segmented, smoothed and meshed to create 3D models for FEM and the aortic ring was divided into 8 sections of varying geometry and composition. Local stress-strain relationships were extracted from uniaxial loading conditions. Simulations were conducted where the stiffness of collagen was set equal to (1X) or made stiffer than elastin by a factor of 10 (10X) or 100 (100X). The average Young’s modulus, E, for each section was calculated and used as parameters for FEM of the aortic ring to investigate the global mechanical behavior of the aortic wall. Results/Conclusions: The strains generated in the radial direction are greater than the strains in the hoop direction in each of the 8 heterogeneous sections of the aortic ring. There was significant variability in the E values in the 10X and 100X systems. FEM of a materially uniform aortic ring yielded smaller maximum principal logarithmic strains compared to a ring that was materially heterogeneous. This study provides evidence that local structure and material distribution are important in aortic biomechanics. Pathogenesis of aneurysmal disease is dependent on collagen and elastin turnover. Aneurysm rupture results from mechanical failure: peak wall stress exceeds local tissue strength. This novel method will allow for development of a complex aortic fracture model to study aortic pathologies.
Cao et al. (Wed,) studied this question.