Naslov
Implementation of Abdominal Aortic Aneurysm Growth and Remodeling Model into Finite Element Code

Autori
Virag, Lana ; Karšaj, Igor ; Sorić, Jurica ; Jay D., Humphrey

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
Multiscale Methods and Validation in Medicine and Biology III / Klug, B. ; Levine, A. - Los Angeles (CA), 2016, 35-35

Skup
Multiscale Methods and Validation in Medicine and Biology

Mjesto i datum
Los Angeles (CA), Sjedinjene Američke Države, 25.02.2016. - 26.02.2016

Vrsta sudjelovanja
Predavanje

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
Abdomina aortic aneurysm; finite element method; growth and remodeling

Sažetak
Abdominal aortic aneurysm (AAA) is local dilatation of infrarenal abdominal aorta, characterized by loss of functional elastin and smooth muscle. AAA is typically asymptotic disease ; however, complications such as dissection, rupture, and embolization can lead to death. In the last decade significant progress was made in numerical modeling of AAAs. Nevertheless, our ability to predict whether a specific lesion will arrest, continue to enlarge either slowly or rapidly, or ultimately rupture remains wanting. The goal of this research is to improve and extend recent 1D growth and remodeling (G&R) models limited to cylindrical geometry (e.g., [1]) to axisymmetric, and ultimately to a general 3D geometry. This requires an implementation of AAA G&R models into a nonlinear finite element analysis program (FEAP). Aortic wall is composite structure organized into layers. These layers entail different structural components. Healthy aorta is composed of three layers: intima, media, and adventitia. Each of these layers contains different amount of constituents (elastin, collagen fibers, and smooth muscle cells). The model is based on constrained mixture model and theory of evolving configurations, as proposed in [2]. Nonlinear material behavior, described by strain energy functions, is implemented in FEAP by modifying user material (umat) subroutine that calculates Cauchy stress and tangent modulus. Special attention is given to enforcement of incompressibility by augmented Lagrange method. Contrary to some implementations in the finite element code, employment of a deviatoric split of the stresses proved to be unstable and the obtained results that are in conflict with theoretical framework. We, therefore, used mixed formulation, as had been verified in several studies (e.g., [3]). Finite element growth and remodeling model of aorta was tested on cases of changed hemodynamics, and aging of healthy aorta. The results strongly agreed with semi- analytical results from Matlab. The simulated development of an AAA was initiated by prescribing a loss of elastin in an initially healthy, but aged aorta, thus avoiding assumptions on pre-stretches and orientations of constituents in already existing aneurysm. Future models should consider degradation of elastin to be dependent on concentration of elastase, and not only on time.

Izvorni jezik
Engleski

Znanstvena područja
Strojarstvo

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