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A constitutive model for vascular tissue that integrates fibril, fiber and continuum levels with application to the isotropic and passive properties of the infrarenal aorta
KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Biomechanics.
KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Biomechanics.
2011 (English)In: Journal of Biomechanics, ISSN 0021-9290, E-ISSN 1873-2380, Vol. 44, no 14, 2544-2550 p.Article in journal (Refereed) Published
Abstract [en]

A fundamental understanding of the mechanical properties of the extracellular matrix (ECM) is critically important to quantify the amount of macroscopic stress and/or strain transmitted to the cellular level of vascular tissue. Structural constitutive models integrate histological and mechanical information, and hence, allocate stress and strain to the different microstructural components of the vascular wall. The present work proposes a novel multi-scale structural constitutive model of passive vascular tissue, where collagen fibers are assembled by proteoglycan (PG) cross-linked collagen fibrils and reinforce an otherwise isotropic matrix material. Multiplicative kinematics account for the straightening and stretching of collagen fibrils, and an orientation density function captures the spatial organization of collagen fibers in the tissue. Mechanical and structural assumptions at the collagen fibril level define a piece-wise analytical stress-stretch response of collagen fibers, which in turn is integrated over the unit sphere to constitute the tissue's macroscopic mechanical properties. The proposed model displays the salient macroscopic features of vascular tissue, and employs the material and structural parameters of clear physical meaning. Likewise, the constitutive concept renders a highly efficient multi-scale structural approach that allows for the numerical analysis at the organ level. Model parameters were estimated from isotropic mean-population data of the normal and aneurysmatic aortic wall and used to predict in-vivo stress states of patient-specific vascular geometries, thought to demonstrate the robustness of the particular Finite Element (FE) implementation. The collagen fibril level of the multi-scale constitutive formulation provided an interface to integrate vascular wall biology and to account for collagen turnover.

Place, publisher, year, edition, pages
2011. Vol. 44, no 14, 2544-2550 p.
Keyword [en]
Collagen, Microfiber, Aneurysm, Aorta, Finite Element, Multiscale
National Category
Biological Sciences
Identifiers
URN: urn:nbn:se:kth:diva-47994DOI: 10.1016/j.jbiomech.2011.07.015ISI: 000295754800004Scopus ID: 2-s2.0-80052408016OAI: oai:DiVA.org:kth-47994DiVA: diva2:456853
Funder
Swedish Research Council, 2006-7568
Note

QC 20111116

Available from: 2011-11-16 Created: 2011-11-15 Last updated: 2017-12-08Bibliographically approved
In thesis
1. Biomechanics of abdominal aortic aneurysm:Experimental evidence and multiscale constitutive modeling
Open this publication in new window or tab >>Biomechanics of abdominal aortic aneurysm:Experimental evidence and multiscale constitutive modeling
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The reliable assessment of Abdominal Aortic Aneurysm (AAA) rupture risk is critically important in reducing related mortality without unnecessarily increasing the rate of elective repair. A multi-disciplinary approach including vascular biomechanics and constitutive modeling is needed to better understand and more effectively treat these diseases. AAAs are formed through irreversible pathological remodeling of the vascular wall and integrating this biological process in the constitutive description could improve the current understanding of this disease as well as the predictability of biomechanical simulations.

First in this thesis, multiple centerline-based diameter measurements between renal arteries and aortic bifurcation have been used to monitor aneurysm growth of in total 51 patients from Computer Tomography-Angiography (CT-A) data. Secondly, the thesis proposes a novel multi-scale constitutive model for the vascular wall, where collagen fibers are assembled by proteoglycan cross-linked collagen fibrils and reinforce an otherwise isotropic matrix (elastin). Collagen fibrils are dynamically formed by a continuous stretch-mediated process, deposited in the current configuration and removed by a constant degradation rate. The micro-plane concept is then used for the Finite Element (FE) implementation of the constitutive model. Finally, histological slices from intra-luminal thrombus (ILT) tissue were analyzed using a sequence of automatic image processing steps. Derived microstructural data were used to define Representative Volume Elements (RVEs), which in turn allowed the estimation of microscopic material properties using the non-linear FE.

The thesis showed that localized spots of fast diameter growth can be detected through multiple centerline-based diameter measurements all over the AAA sac. Consequently, this information might further reinforce the quality of aneurysm surveillance programs. The novel constitutive model proposed in the thesis has a strong biological motivation and provides an interface with biochemistry. Apart from modeling the tissue’s passive response, the presented model is helpful to predict saline feature of aneurysm growth and remodeling. Finally, the thesis provided novel microstructural and micromechanical data of ILT tissue, which is critically important to further explore the role of the ILT in aneurysm rupture.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. 48 p.
Series
Trita-HFL. Report / Royal Institute of Technology, Solid mechanics, ISSN 1654-1472 ; 0530
National Category
Mechanical Engineering Medical Engineering Materials Engineering Applied Mechanics
Identifiers
urn:nbn:se:kth:diva-101990 (URN)
Public defence
2012-09-20, Sal L1, Drottning Kristinas väg 30, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20120907

Available from: 2012-09-07 Created: 2012-09-06 Last updated: 2013-01-14Bibliographically approved

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