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Turnover of fibrillar collagen in soft biological tissue with application to the expansion of abdominal aortic aneurysms
KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Biomechanics. (vascuMECH)
KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Biomechanics.
2012 (English)In: Journal of the Royal Society Interface, ISSN 1742-5662, E-ISSN 1742-5689, Vol. 9, no 77, 3366-3377 p.Article in journal (Refereed) Published
Abstract [en]

A better understanding of the inherent properties of vascular tissue to adapt to its mechanical environment is crucial to improve the predictability of biomechanical simulations. Fibrillar collagen in the vascular wall plays a central role in tissue adaptation owing to its relatively short lifetime. Pathological alterations of collagen turnover may fail to result in homeostasis and could be responsible for abdominal aortic aneurysm (AAA) growth at later stages of the disease. For this reason our previously reported multiscale constitutive framework (Martufi, G. & Gasser, T. C. 2011 J. Biomech. 44, 2544-2550 (doi:10.1016/j.jbiomech.2011.07.015)) has been enriched by a collagen turnover model. Specifically, the framework's collagen fibril level allowed a sound integration of vascular wall biology, and the impact of collagen turnover on the macroscopic properties of AAAs was studied. To this end, model parameters were taken from the literature and/or estimated from clinical follow-up data of AAAs (on average 50.7 mm-large). Likewise, the in vivo stretch of the AAA wall was set, such that 10 per cent of collagen fibres were engaged. Results showed that the stretch spectrum, at which collagen fibrils are deposed, is the most influential parameter, i.e. it determines whether the vascular geometry grows, shrinks or remains stable over time. Most importantly, collagen turnover also had a remarkable impact on the macroscopic stress field. It avoided high stress gradients across the vessel wall, thus predicted a physiologically reasonable stress field. Although the constitutive model could be successfully calibrated to match the growth of small AAAs, a rigorous validation against experimental data is crucial to further explore the model's descriptive and predictive capabilities.

Place, publisher, year, edition, pages
2012. Vol. 9, no 77, 3366-3377 p.
Keyword [en]
remodelling, aneurysm, growth, rupture, constitutive modelling, vascular tissue
National Category
Medical Engineering
URN: urn:nbn:se:kth:diva-101983DOI: 10.1098/rsif.2012.0416ISI: 000310573100020ScopusID: 2-s2.0-84868575742OAI: diva2:550173
Swedish Research Council, 2006-7568VinnovaSwedish Foundation for Strategic Research EU, FP7, Seventh Framework Programme, FAD-200647

QC 20121207

Available from: 2012-09-06 Created: 2012-09-06 Last updated: 2012-12-07Bibliographically 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.
Trita-HFL. Report / Royal Institute of Technology, Solid mechanics, ISSN 1654-1472 ; 0530
National Category
Mechanical Engineering Medical Engineering Materials Engineering Applied Mechanics
urn:nbn:se:kth:diva-101990 (URN)
Public defence
2012-09-20, Sal L1, Drottning Kristinas väg 30, KTH, Stockholm, 10:00 (English)

QC 20120907

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

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