Differential Tensile Strength and Collagen Composition in Ascending Aortic Aneurysms by Aortic Valve Phenotype

Abstract

Background Ascending thoracic aortic aneurysm (ATAA) predisposes patients to aortic dissection and has been associated with diminished tensile strength and disruption of collagen. ATAA arising in patients with bicuspid aortic valve (BAV) develop earlier than those with tricuspid aortic valves (TAV) and have a different risk of dissection. The purpose of this study was to compare aortic wall tensile strength between BAV and TAV ATAAs and determine if the collagen content of the ATAA wall is associated with tensile strength and valve phenotype. Methods Longitudinally and circumferentially oriented strips of ATAA tissue obtained during elective surgery were stretched to failure and collagen content was estimated by hydroxyproline assay. Experimental stress-strain data were analyzed for failure strength and elastic mechanical parameters: α, β and maximum tangential stiffness. Results The circumferential and longitudinal tensile strengths were higher for BAV ATAA when compared with TAV ATAA. The α and β were lower for BAV ATAA when compared with TAV ATAA. The maximum tangential stiffness was higher for circumferential when compared with longitudinal orientation in both BAV and TAV ATAA. Amount of hydroxyproline was equivalent in BAV and TAV ATAA specimens. While there was a moderate correlation between the collagen content and tensile strength for TAV, this correlation is not present in BAV. Conclusion The increased tensile strength and decreased values of α and β in BAV ATAAs despite uniform collagen content between groups indicate that micro-structural changes in collagen contribute to BAV-associated aortopathy.

Human dilated ascending aorta: Mechanical characterization via uniaxial tensile tests

“…Pichamuthu et al [43], whereas disagree with the results of Vorp et al [31], which found non-significant difference between the two orientations.…”

“…In particular, some studies move from the presentation of new tools in imaging analysis to evidence possible alterations in the morphology and in the micro-structure of the diseased aortic tissues [26,27]. Other studies focus on the use of mechanical tests (uniaxial and biaxial tensile tests) to evaluate and compare mechanical properties of both healthy and diseased tissues [28][29][30][31][32][33] and, at the same time, to investigate factors which can influence tissue properties like location and orientation [23,[34][35][36][37], patient age [30,38,39], patient sex [39,40], and presence of concomitant pathologies [25,33,36,[41][42][43][44].…”

Is There a Role for Biomechanical Engineering in Helping to Elucidate the Risk Profile of the Thoracic Aorta?

“…The process is dynamic, highly heterogeneous, and may fluctuate as a function of local stress and biologic activity. Changes in the tissue microstructure caused by aging [23], disease progression [13], and underlying pathologies [27,28,29,30] significantly affect tissue structural organization and strength. One of the challenges of aneurysm simulation is the integration of dynamic wall weakening in the biomechanical model so that current estimates of local properties and local strength can be used to predict the risk of rupture.…”

Failure of the Porcine Ascending Aorta: Multidirectional Experiments and a Unifying Microstructural Model

“…Tissue from the ascending aorta has been tested in a variety of configurations (reviewed by Avanzini et al [17]), with uniaxial and equibiaxial stretch tensile tests being the most common. In-plane uniaxial [18][19][20] and biaxial tension tests [21][22][23][24] provide information on tensile failure in the plane of the medial lamella ðr hh ; r zz Þ; and the biaxial tests can provide some additional information on in-plane shear ðr hz Þ. Although the dominant stresses in these tests may be the primary stresses during vessel rupture, they are not those driving dissection.…”