Morphology-mechanics coupling in intraluminal thrombus from abdominal aortic aneurysm visualized by synchrotron...

Abdominal aortic aneurysm (AAA) rupture is a life-threatening event, yet current rupture risk assessment based on aneurysm size and growth rate fails to fully predict outcomes. Intraluminal thrombus (ILT), present in most AAAs, may influence wall mechanics and rupture potential, but the relationship between its microstructure and mechanical behavior remains poorly understood. This study first analyzed the human ILT morphology using synchrotron radiation-based phase-contrast micro-computed tomography (SR-PhC-μCT). Then for the first time stress-relaxation compression was applied in-situ to ILT, enabling high-resolution visualization of fibrin fibers and pores under mechanical load. Phase-contrast imaging revealed layer-specific differences observed by histology, and also allowed quantification of the 3D microstructure of ILTs, such as porosity, pore diameters and pore interconnections. As previously observed, ILTs exhibited non-linear viscoelastic behavior with stiffer responses in samples containing both luminal and medial layers. Our results suggest that compression causes pore collapse and fibrin fiber compaction, densifying the microstructure (porosity decreases by up to 40%), and increasing Young's modulus (by up to threefold) and secant modulus. The interlaced fiber network limits structural relaxation. Our findings provide insight into how mechanical loading could alter the microstructure of the ILT and offer a framework for studying the interactions between structure and mechanics in AAA progression. Statement of Significance: Abdominal aortic aneurysms (AAAs) are associated with high risk of rupture, a leading cause of mortality. Understanding how intraluminal thrombus (ILT) structure responds to mechanical loading is important to explore its potential role in aneurysm progression and wall weakening. We combined synchrotron phase-contrast micro-computed tomography (SR-PhC-μCT) with in-situ mechanical compression to investigate how ILT microstructure - including fibrin fibers and pores - reorganizes under strain and how these changes relate to mechanical behavior in a limited number of human samples. This methodology provides a novel framework for studying the interplay between ILT microstructure, mechanical behavior, and AAA pathology, potentially informing improved rupture risk assessment through initial insight into factors that could contribute to hypoxia related weakening, while not intended to establish general mechanisms or represent the full heterogeneity of ILT.