From microstructure to mechanics: A multi-constituent micro-scale computational model of arterial tissue

Arterial tissues exhibit complex growth and remodeling processes, where cells continuously regulate extracellular matrix (ECM) components in response to mechanical and biochemical stimuli. Understanding the interplay between the arterial microstructure and mechanical behavior is crucial for characterizing cardiovascular diseases, such as hypertension and atherosclerosis. In this study, we developed a microstructure-based representative volume element (RVE) model of the porcine aortic medial layer, incorporating elastic lamellae, elastin fibers, collagen fibers, and smooth muscle cells. The RVE geometry was constructed using multiple imaging modalities, including contrast-enhanced X-ray microfocus computed tomography (CECT), multiphoton microscopy, classical 2D histology, and scanning electron microscopy (SEM). The mechanical properties of the RVE components were assigned based on literature data, and the model was validated against experimental tensile test data. A size convergence study determined that an RVE containing eleven medial lamellar units is necessary to obtain a representative macroscopic mechanical response. Furthermore, we analyzed mesh convergence and performed a parameter sensitivity analysis to assess the influence of mechanical and microstructural properties on the macroscopic behavior. Our results indicate that the material stiffness and volume percentages of elastin and collagen play a dominant role in the stress response. Using a homogenization approach, we quantified the contribution of each microstructural component within the representative volume element (RVE). The analysis showed that elastic lamellae dominate the initial linear region of the stress-strain curve, while the non-linear behavior is primarily governed by collagen fibers. Additionally, we analyzed the stretch distribution within the collagen network and the smooth muscle cells, and demonstrated that the average stretch remained well below the macroscopic stretch of the RVE. This information is highly valuable for advancing our understanding of the interactions between extracellular matrix components and how these interactions contribute to tissue remodeling in disease conditions.