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Spatial orientation of collagen fibers in the abdominal aortic aneurysm's wall and its relation to wall mechanics
KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Biomechanics.
KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Biomechanics.
KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Biomechanics.
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2012 (English)In: Acta Biomaterialia, ISSN 1742-7061, E-ISSN 1878-7568, Vol. 8, no 8, 3091-3103 p.Article in journal (Refereed) Published
Abstract [en]

Collagen is the most abundant protein in mammals and provides the abdominal aortic aneurysm (AAA) wall with mechanical strength, stiffness and toughness. Specifically, the spatial orientation of collagen fibers in the wall has a major impact on its mechanical properties. Apart from valuable microhistological information, this data can be integrated by histomechanical constitutive models thought to improve biomechanical simulations, i.e. to improve the biomechanical rupture risk assessment of AAAs. Tissue samples (n = 24) from the AAA wall were harvested during elective AAA repair, fixated, embedded, sectioned and investigated by polarized light microscopy. The birefringent properties of collagen were reinforced by picrosirius red staining and the three-dimensional collagen fiber orientations were identified with a universal rotary stage. Two constitutive models for collagen fibers were used to integrate the identified structural information in a macroscopic AAA wall model. The collagen fiber orientation in the AM wall was widely dispersed and could be captured by a Bingham distribution function (kappa(1) = 11.6, kappa(2) = 9.7). The dispersion was much larger in the tangential plane than in the cross-sectional plane, and no significant difference between the medial and adventitial layers could be identified. The layered directional organization of collagen in normal aortas was not evident in the AAA. The collagen organization identified, combined with constitutive descriptions of collagen fibers that depend on its orientation, explain the anisotropic (orthotropic) mechanical properties of the AAA wall. The mechanical properties of collagen fibers depend largely on their undulation, which is an important structural parameter that requires further experimental investigation.

Place, publisher, year, edition, pages
2012. Vol. 8, no 8, 3091-3103 p.
Keyword [en]
Collagen formation, Constitutive modeling, AAA wall, Polarized light microscopy, Microhistology
National Category
Medical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-101118DOI: 10.1016/j.actbio.2012.04.044ISI: 000306631100022Scopus ID: 2-s2.0-84863201228OAI: oai:DiVA.org:kth-101118DiVA: diva2:547028
Note

QC 20120827

Available from: 2012-08-27 Created: 2012-08-23 Last updated: 2017-06-19Bibliographically approved
In thesis
1. Failure of vascular tissue with applications to the aneurysm wall, carotid plaque and myocardial tissue
Open this publication in new window or tab >>Failure of vascular tissue with applications to the aneurysm wall, carotid plaque and myocardial tissue
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Cardiovascular disease is the leading cause of death in the modern world. Examples are thoracic aortic aneurysm (TAA), abdominal aortic aneurysm (AAA) and stroke due to plaque rupture. Failure in soft tissues caused by medical devices is also a medical challenge. In all these cardiovascular events a better prediction of failure of the tissue and a better understanding about the tissue properties will help in predicament and treatment. For example the diameter-based indication for surgical repair of AAA and TAAs is not sufficient and refined methods are needed. In this thesis failures of some soft vascular tissues, was studied. Experiments have been combined with numerical modeling to understand the elastic and failure properties of AAA, TAA and plaque tissue as well as the ventricular wall. Vascular tissue is anisotropic, time-dependent, nonlinear and shows large deformations. Among others this thesis showed the importance of viscoelasticity which motivates to develop a new continuum mechanical framework. In addition a large part of this thesis dealt with anisotropy of vascular tissue. For the first time the collagen orientation distribution in the AAA wall has been identified. Collagen and its distribution orientation is also an important feature of this tissue. There was a correlation between the strength and stiffness of the AAA samples with the decreasing wall thickness. Increased stiffness was found in the aortic wall of patients with chronic obstructive pulmonary disease (COPD) compared to patients that did not have COPD. As well as difference in stiffness of TAA tissue, in patients with non-pathologic and pathologic aortic valves. Some of the findings in this thesis could have a long-term consequence for management of risk of rupture in AAA, TAA and plaque.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. x, 30 p.
Series
Trita-HFL, ISSN 1104-6813 ; 0545
National Category
Other Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-122840 (URN)978-91-7501-798-3 (ISBN)
Public defence
2013-06-07, Sal D2, Lindstedtsvägen 5, KTH, Stockholm, 09:00 (English)
Opponent
Supervisors
Note

QC 20130528

Available from: 2013-05-28 Created: 2013-05-28 Last updated: 2013-05-29Bibliographically approved

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