Calcification-neighboring regions of atherosclerotic aortic tissue exhibit elevated stiffness without elevated radiodensity

Atherosclerosis, characterized by plaque accumulation and arterial remodeling, poses significant mechanical risks to the aorta such as wall stiffening, aneurysm formation, dissection, and plaque rupture. In this study, we investigated the mechanical and imaging properties of atherosclerotic lesions and their surrounding aortic media in 19 samples dissected from the thoracic aortas of human cadavers. Local stiffness was determined via inverse mechanical analysis of planar biaxial tensile tests, and radiodensity was assessed using micro-CT imaging. Our results show that calcifications are both more radiodense and stiffer than surrounding tissue, consistent with prior studies. However, radiodensity did not reliably predict stiffness in non-calcified regions, highlighting the limitations of micro-CT in capturing mechanical heterogeneity in softer tissues. Notably, we observed a significant stiffness gradient in tissue surrounding calcifications, with stiffness decreasing exponentially with distance. The calcification's biomechanical influence extended an estimated 5.40 ± 0.43 mm into the surrounding aortic media, despite the absence of significant radiodensity gradients in these regions. These findings suggest that calcifications serve as localized mechanical stress concentrators, influencing nearby tissue stiffness beyond their immediate boundary.