Heterogeneity of Ex Vivo and In Vivo Properties along the Length of the Abdominal Aortic Aneurysm

Abstract

The current clinical guidelines for the management of aortic abdominal aneurysms (AAAs) overlook the structural and mechanical heterogeneity of the aortic tissue and its role in the regional weakening that drives disease progression. This study is a comprehensive investigation of the structural and biomechanical heterogeneity of AAA tissue along the length and circumference of the aorta, by means of regional ex vivo and in vivo properties. Biaxial testing and histological analysis were performed on ex vivo human aortic specimens systematically collected during open repair surgery. Wall-shear stress and three-dimensional principal strain analysis were performed to allow for in vivo regional characterization of individual aortas. A marked effect of position along the aortic length was observed in both ex vivo and in vivo properties, with the central regions corresponding to the aneurysmal sac being significantly different from the adjacent regions. The heterogeneity along the circumference of the aorta was reflected in the ex vivo biaxial response at low strains and histological properties. Present findings uniquely show the importance of regional characterization for aortic assessment and the need to correlate heterogeneity at the tissue level with non-invasive measurements aimed at improving clinical outcomes.

Tissue Mechanics and Tissue Engineering

“…One paper [3] deals with cell encapsulation in biomaterials for protection against immune reactions. Two papers underline that tissue mechanics play a key role in understanding tissue functions, the former focusing on the role of biomechanics related to the prediction of aortic aneurysm rupture [4], whereas the latter on the role of biomechanics for early diagnosis of glaucoma [5].…”

“…Forneris et al [4] extensively investigated the structural and biomechanical heterogeneity of human abdominal aortic aneurysm tissue along the length and circumference of the aorta by means of regional ex vivo and in vivo properties. Results uniquely show the importance of regional characterization for aortic assessment and the need to correlate heterogeneity at the tissue level with non-invasive measurements aimed at improving clinical outcomes.…”

“…In other words, obtaining the normal living tissue mechanical properties is one of the goals of researchers for tissue regeneration. Diseases often change tissue mechanical properties, and therefore, their measurement may help detect and follow the evolution of pathologies, thus improving the clinical outcome of the patients [4,5].…”

Medial Collagen Type and Quantity Influence Mechanical Properties of Aneurysm Wall in Bicuspid Aortic Valve Patients

“…A combination of biaxial tensile and uniaxial tensile tests were performed on specimens to characterize the tissue response under varied mechanical conditions. For all tests, loading was induced in one or both of the defined principal directions: circumferential (Tsamis et al, 2013), referring to the direction along the circumference of the aorta; and axial (Forneris et al, 2021), referring to the direction along the length of the aorta. From each specimen, one circumferential and one axial test strip was removed for uniaxial testing, with the remainder designated for biaxial tensile testing (Figure 2B).…”

“…Multiple studies have sought to understand the process and effects of collagen remodeling and changes in the ECM observed using histology (Smoljkić et al, 2017;Deveja et al, 2018), microscopy (Pasta et al, 2016), and biochemical assays (Pichamuthu et al, 2013;Chim et al, 2020). Though it is likely that the microstructural changes observed in the ECM histopathologically would have biomechanical implications, there are relatively few studies that have investigated the relationship between biomechanical properties and collagen changes in the ECM of aortic aneurysm (Rizzo et al, 1989;Tanios et al, 2015;Forneris et al, 2021), and even fewer that are specific to the ascending aorta and BAV (Pichamuthu et al, 2013;Pasta et al, 2016). Further investigation into the relationship between microstructural and mechanical characteristics of AsAA may provide insight into the complex, multifactorial mechanisms of AsAA development and progression.…”