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Failure of vascular tissue with applications to the aneurysm wall, carotid plaque and myocardial tissue
KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Biomechanics.
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: urn:nbn:se:kth:diva-122840ISBN: 978-91-7501-798-3 (print)OAI: oai:DiVA.org:kth-122840DiVA: diva2:623563
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
List of papers
1. Numerical simulation of the failure of ventricular tissue due to deep penetration: The impact of constitutive properties
Open this publication in new window or tab >>Numerical simulation of the failure of ventricular tissue due to deep penetration: The impact of constitutive properties
2011 (English)In: Journal of Biomechanics, ISSN 0021-9290, E-ISSN 1873-2380, Vol. 44, no 1, 45-51 p.Article in journal (Refereed) Published
Abstract [en]

Lead perforation is a rare but serious clinical complication of pacemaker implantation, and towards understanding this malfunction, the present study investigated myocardial failure due to deep penetration by an advancing rigid punch. To this end, a non-linear Finite Element model was developed that integrates constitutive data published in the literature with information from in vitro tensile testing in cross-fibre direction of porcine myocardial tissue. The Finite Element model considered non-linear, isotropic and visco-elastic properties of the myocardium, and tissue failure was phenomenologically described by a Traction Separation Law. In vitro penetration testing of porcine myocardium was used to validate the Finite Element model, and a particular objective of the study was to investigate the impact of different constitutive parameters on the simulated results. Specifically, results demonstrated that visco-elastic properties of the tissue strongly determine the failure process, whereas dissipative effects directly related to failure had a minor impact on the simulation results. In addition, non-linearity of the bulk material did not change the predicted peak penetration force and the simulations did not reveal elastic crack-tip blunting. The performed study provided novel insights into ventricular failure due to deep penetration, and provided useful information with which to develop numerical failure models.

Keyword
Myocardium, Fracture, Penetration failure, Soft biological tissue, Pacemaker lead perforation, Constitutive properties, FEM, Cohesive zone, Fracture process zone, Visco-elastic, Non-linear
National Category
Other Engineering and Technologies not elsewhere specified
Identifiers
urn:nbn:se:kth:diva-30529 (URN)10.1016/j.jbiomech.2010.08.022 (DOI)000286550500008 ()2-s2.0-78650014072 (Scopus ID)
Funder
Swedish Research Council, 2007-4514
Note
QC 20110304Available from: 2011-03-04 Created: 2011-02-28 Last updated: 2017-12-11Bibliographically approved
2. The numerical implementation of invariant-based viscoelastic formulations at finite strains. An anisotropic model for the passive myocardium
Open this publication in new window or tab >>The numerical implementation of invariant-based viscoelastic formulations at finite strains. An anisotropic model for the passive myocardium
2011 (English)In: Computer Methods in Applied Mechanics and Engineering, ISSN 0045-7825, E-ISSN 1879-2138, Vol. 200, no 49-52, 3637-3645 p.Article in journal (Refereed) Published
Abstract [en]

The present study developed a conceptual framework for finite strain viscoelasticity thought to be suitable to capture the salient features of a class of passive soft biological tissues like the myocardium. A superposition of a Maxwell Body and an Elastic Body defines the viscoelastic continuum, and its deformation is related to two independent reference configurations. The reference configuration of the Maxwell Body moves in space as it is described (apart from rigid body rotation) by a rate equation in strain space, and stores the history of the deformation. At thermodynamic equilibrium the reference configuration of the Maxwell Body coincides with the current configuration of the continuum. The Helmholtz free energy is expressed as a function of two independent strain variables and entirely renders the constitution of the viscoelastic body. Although this view is to some extent different from reported viscoelastic concepts for finite strains, its linearization around the thermodynamic equilibrium coincides with earlier suggested viscoelastic models. The linearized viscoelastic model has been implemented for a particular anisotropic constitutive model for the passive myocardium. Non-negative dissipation of the model is guaranteed. Material parameters were estimated from in vitro testing of porcine myocardium and the response due to pushing a rigid punch into the myocardium was studied. Results between anisotropic and isotropic descriptions of the myocardium differed significantly, which justified the implementation of an anisotropic model for the myocardium.

Keyword
finite strains, anisotropy, viscoelastic, myocardium, soft biological tissue, pacemaker lead perforation, constitutive properties, FEM, nonlinear
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-31037 (URN)10.1016/j.cma.2011.08.022 (DOI)000297494700011 ()2-s2.0-80053501618 (Scopus ID)
Funder
Swedish Research Council, 2007-4514
Note
QC 20110307Available from: 2011-03-07 Created: 2011-03-07 Last updated: 2017-12-11Bibliographically approved
3. Spatial orientation of collagen fibers in the abdominal aortic aneurysm's wall and its relation to wall mechanics
Open this publication in new window or tab >>Spatial orientation of collagen fibers in the abdominal aortic aneurysm's wall and its relation to wall mechanics
Show others...
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.

Keyword
Collagen formation, Constitutive modeling, AAA wall, Polarized light microscopy, Microhistology
National Category
Medical Engineering
Identifiers
urn:nbn:se:kth:diva-101118 (URN)10.1016/j.actbio.2012.04.044 (DOI)000306631100022 ()2-s2.0-84863201228 (Scopus ID)
Note

QC 20120827

Available from: 2012-08-27 Created: 2012-08-23 Last updated: 2017-06-19Bibliographically approved
4. The Quasi-Static Failure Properties of the Abdominal Aortic Aneurysm Wall Estimated by a Mixed Experimental-Numerical Approach
Open this publication in new window or tab >>The Quasi-Static Failure Properties of the Abdominal Aortic Aneurysm Wall Estimated by a Mixed Experimental-Numerical Approach
2012 (English)In: Annals of Biomedical Engineering, ISSN 0090-6964, E-ISSN 1573-9686, Vol. 41, no 7, 1554-1566 p.Article in journal (Refereed) Published
Abstract [en]

Assessing the risk for abdominal aortic aneurysm (AAA) rupture is critical in the management of aneurysm patients and an individual assessment is possible with the biomechanical rupture risk assessment. Such an assessment could potentially be improved by a constitutive AAA wall model that accounts for irreversible damage-related deformations. Because of that the present study estimated the elastic and inelastic properties of the AAA wall through a mixed experimental-numerical approach. Specifically, finite element (FE) models of bone-shaped tensile specimens were used to merge data from failure testing of the AAA wall with their measured collagen orientation distribution. A histo-mechanical constitutive model for collagen fibers was employed, where plastic fibril sliding determined not only remaining deformations but also weakening of the fiber. The developed FE models were able to replicate the experimentally recorded load-displacement property of all 16 AAA wall specimens that were investigated in the study. Tensile testing in longitudinal direction of the AAA defined a Cauchy strength of 569(SD 411) kPa that was reached at a stretch of 1.436(SD 0.118). The stiffness and strength of specimens decreased with the wall thickness and were elevated (p = 0.018; p = 0.030) in patients with chronic obstructive pulmonary disease (COPD). Smoking affected the tissue parameters that were related to the irreversible deformation response, and no correlation with gender and age was found. The observed effects on the biomechanical properties of the AAA wall could have long-term consequences for the management of aneurysm patients, i.e., specifically they might influence future AAA rupture risk assessments. However, in order to design appropriate clinical validation studies our findings should firstly be verified in a larger patient cohort.

Place, publisher, year, edition, pages
Springer-Verlag New York, 2012
Keyword
Aneurysm rupture, Collagen, Constitutive modeling, Damage, Plasticity
National Category
Medical Biotechnology
Identifiers
urn:nbn:se:kth:diva-122848 (URN)10.1007/s10439-012-0711-4 (DOI)000320329200018 ()2-s2.0-84879422869 (Scopus ID)
Funder
Swedish Research Council, 2007-4514EU, FP7, Seventh Framework Programme, FAD-200647
Note

QC 20130719

Available from: 2013-05-28 Created: 2013-05-28 Last updated: 2017-12-06Bibliographically approved
5. Identification of carotid plaque tissue properties using an experimental-numerical approach
Open this publication in new window or tab >>Identification of carotid plaque tissue properties using an experimental-numerical approach
Show others...
2013 (English)In: Journal of The Mechanical Behavior of Biomedical Materials, ISSN 1751-6161, E-ISSN 1878-0180, Vol. 27, 226-238 p.Article in journal (Refereed) Published
Abstract [en]

A biomechanical stress analysis could help to identify carotid plaques that are vulnerable to rupture, and hence reduce the risk of thrombotic strokes. Mechanical stress predictions critically depend on the plaque's constitutive properties, and the present study introduces a concept to derive viscoelastic parameters through an experimental-numerical approach. Carotid plaques were harvested from two patients during carotid endarterectomy (CEA), and, in total, nine test specimens were investigated. A novel in-vitro mechanical testing protocol, which allows for dynamic testing, keeping the carotid plaque components together, was introduced. Macroscopic pictures overlaid by histological stains allowed for the segmentation of plaque tissues, in order to develop high-fidelity and low-fidelity Finite Element Method (FEM) models of the test specimens. The FEM models together with load-displacement data from the mechanical testing were used to extract constitutive parameters through inverse parameter estimation. The applied inverse parameter estimation runs in stages, first addressing the hyperelastic parameters then the viscoelastic ones. Load-displacement curves from the mechanical testing showed strain stiffening and viscoelasticity, as is expected for both normal and diseased carotid tissue. The estimated constitutive properties of plaque tissue were comparable to previously reported studies, Due to the highly non-linear elasticity of vascular tissue, the applied parameter estimation approach is, as with many similar approaches, sensitive to the initial guess of the parameters.

Keyword
Carotid plaque, Nonlinear, Constitutive description, Viscoelasticity, Vascular tissue
National Category
Medical Biotechnology
Identifiers
urn:nbn:se:kth:diva-122850 (URN)10.1016/j.jmbbm.2013.05.001 (DOI)000325304700021 ()2-s2.0-84884281688 (Scopus ID)
Funder
Swedish Research Council, 2010-4446
Note

QC 20131107. Updated from accepted to published.

Available from: 2013-05-28 Created: 2013-05-28 Last updated: 2017-12-06Bibliographically approved
6. Failure properties for the thoracic aneurysm wall: Differences between BicuspidAortic Valve (BAV) and Tricuspid Aortic Valve (TAV) patients
Open this publication in new window or tab >>Failure properties for the thoracic aneurysm wall: Differences between BicuspidAortic Valve (BAV) and Tricuspid Aortic Valve (TAV) patients
(English)Manuscript (preprint) (Other academic)
National Category
Medical Biotechnology
Identifiers
urn:nbn:se:kth:diva-122862 (URN)
Note

QS 2013

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

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Citation style
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  • Other locale
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