A fluid–structure interaction model of the aortic valve with coaptation and compliant aortic root (original) (raw)
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Journal of Biomechanical Engineering, 2013
Native aortic valve cusps are composed of collagen fibers embedded in their layers. Each valve cusp has its own distinctive fiber alignment with varying orientations and sizes of its fiber bundles. However, prior mechanical behavior models have not been able to account for the valve-specific collagen fiber networks (CFN) or for their differences between the cusps. This study investigates the influence of this asymmetry on the hemodynamics by employing two fully coupled fluid-structure interaction (FSI) models, one with asymmetricmapped CFN from measurements of porcine valve and the other with simplified-symmetric CFN. The FSI models are based on coupled structural and fluid dynamic solvers. The partitioned solver has nonconformal meshes and the flow is modeled by employing the Eulerian approach. The collagen in the CFNs, the surrounding elastin matrix, and the aortic sinus tissues have hyperelastic mechanical behavior. The coaptation is modeled with a masterslave contact algorithm. A full cardiac cycle is simulated by imposing the same physiological blood pressure at the upstream and downstream boundaries for both models. The mapped case showed highly asymmetric valve kinematics and hemodynamics even though there were only small differences between the opening areas and cardiac outputs of the two cases. The regions with a less dense fiber network are more prone to damage since they are subjected to higher principal stress in the tissues and a higher level of flow shear stress. This asymmetric flow leeward of the valve might damage not only the valve itself but also the ascending aorta.
Computational Analyses of Mechanically Induced Collagen Fiber Remodeling in the Aortic Heart Valve
Journal of Biomechanical Engineering-transactions of The Asme, 2003
To optimize the mechanical properties and integrity of tissue-engineered aortic heart valves, it is necessary to gain insight into the effects of mechanical stimuli on the mechanical behavior of the tissue using mathematical models. In this study, a finite-element (FE) model is presented to relate changes in collagen fiber content and orientation to the mechanical loading condition within the engineered construct. We hypothesized that collagen fibers aligned with principal strain directions and that collagen content increased with the fiber stretch. The results indicate that the computed preferred fiber directions run from commissure to commissure and show a strong resemblance to experimental data from native aortic heart valves.
Numerical Methods for Fluid–Structure Interaction Models of Aortic Valves
Archives of Computational Methods in Engineering, 2014
In the recent years, fluid structure interaction (FSI) models of the aortic valve and root have become increasingly common for two main reasons. The medical reason is that millions of patients suffer from aortic valve disorders. The second reason is that this challenging problem combines several fields of computational mechanics. The key motive for these modeling attempts is their potential to shed light on phenomena that cannot be captured in experiments or in simplified models of solely hemodynamics or structural mechanics. The aim of this paper is to review the state-of-theart FSI methods in general and their application to the aortic valve in particular. A brief overview of the medical background is provided. The numerical methods and appropriate assumptions are then presented with examples of previous aortic valve models, followed by a discussion of the limitation of current models and recommendations for overcoming them in future research. The methods presented in this paper could help readers to choose the modelling approach and assumptions that are most suitable for their goals.
Medical & Biological Engineering & Computing, 2013
A bicuspid aortic valve (BAV) is a congenital cardiac disorder where the valve consists of only two cusps instead of three, as in a normal tricuspid valve (TAV). Although 97 % of BAVs include asymmetric cusps, little or no prior studies have investigated the blood flow through a three-dimensional BAV and root. The aim of the present study was to characterize the effect of asymmetric BAV on the blood flow using fully coupled fluid-structure interaction (FSI) models with improved boundary conditions and tissue properties. This study presents four FSI models, including a native TAV, asymmetric BAVs with or without a raphe, and an almost symmetric BAV. Cusp tissue is composed of hyperelastic finite elements with collagen fibres embedded in the elastin matrix. A full cardiac cycle is simulated by imposing the same physiological blood pressures for all the TAV and BAV models. The latter have significantly smaller opening areas compared with the TAV. Larger stress values were found in the cusps of BAVs with fused cusps, at both the systolic and diastolic phases. The asymmetric geometry caused asymmetric vortices and much larger flow shear stress on the cusps which could be a potential initiator for early valvular calcification of BAVs.
A three-dimensional computational analysis of fluid–structure interaction in the aortic valve
Journal of Biomechanics, 2003
Numerical analysis of the aortic valve has mainly been focused on the closing behaviour during the diastolic phase rather than the kinematic opening and closing behaviour during the systolic phase of the cardiac cycle. Moreover, the fluid-structure interaction in the aortic valve system is most frequently ignored in numerical modelling. The effect of this interaction on the valve's behaviour during systolic functioning is investigated. The large differences in material properties of fluid and structure and the finite motion of the leaflets complicate blood-valve interaction modelling. This has impeded numerical analyses of valves operating under physiological conditions. A numerical method, known as the Lagrange multiplier based fictitious domain method, is used to describe the large leaflet motion within the computational fluid domain. This method is applied to a three-dimensional finite element model of a stented aortic valve. The model provides both the mechanical behaviour of the valve and the blood flow through it. Results show that during systole the leaflets of the stented valve appear to be moving with the fluid in an essentially kinematical process governed by the fluid motion. r
Medical Engineering & Physics, 2013
Sturla et al., Impact of modeling fluid-structure interaction in the computational analysis of aortic root biomechanics. Med Eng Phys (2013) Sturla et al., Impact of modeling fluid-structure interaction in the computational analysis of aortic root biomechanics. Med Eng Phys (2013) 2 ABSTRACT Numerical modeling can provide detailed and quantitative information on aortic root (AR) biomechanics, improving the understanding of AR complex pathophysiology and supporting the development of more effective clinical treatments.
A two-dimensional fluid–structure interaction model of the aortic value
Journal of Biomechanics, 2000
Failure of synthetic heart valves is usually caused by tearing and calci"cation of the lea#ets. Lea#et "ber-reinforcement increases the durability of these values by unloading the delicate parts of the lea#ets, maintaining their physiological functioning. The interaction of the valve with the surrounding #uid is essential when analyzing its functioning. However, the large di!erences in material properties of #uid and structure and the "nite motion of the lea#ets complicate blood}valve interaction modeling. This has, so far, obstructed numerical analyses of valves operating under physiological conditions. A two-dimensional #uid}structure interaction model is presented, which allows the Reynolds number to be within the physiological range, using a "ctitious domain method based on Lagrange multipliers to couple the two phases. The extension to the three-dimensional case is straightforward. The model has been validated experimentally using laser Doppler anemometry for measuring the #uid #ow and digitized high-speed video recordings to visualize the lea#et motion in corresponding geometries. Results show that both the #uid and lea#et behaviour are well predicted for di!erent lea#et thicknesses.
Journal of Biomechanical Engineering, 2004
Accurate constitutive models are required to gain further insight into the mechanical behavior of cardiovascular tissues. In this study, a structural constitutive framework for cardiovascular tissues is introduced that accounts for the angular distribution of collagen fibers. To demonstrate its capabilities, the model is applied to study the biaxial behavior of the arterial wall and the aortic valve. The pressure–radius relationships of the arterial wall accurately describe experimentally observed sigma-shaped curves. In addition, the nonlinear and anisotropic mechanical properties of the aortic valve can be analyzed with the proposed model. We expect that the current model offers strong possibilities to further investigate the complex mechanical behavior of cardiovascular tissues, including their response to mechanical stimuli.
Improved Prediction of the Collagen Fiber Architecture in the Aortic Heart Valve
Journal of Biomechanical Engineering, 2004
Living tissues show an adaptive response to mechanical loading by changing their internal structure and morphology. Understanding this response is essential for successful tissue engineering of load-bearing structures, such as the aortic valve. In this study, mechanically induced remodeling of the collagen architecture in the aortic valve was investigated. It was hypothesized that, in uniaxially loaded regions, the fibers aligned with the tensile principal stretch direction. For biaxial loading conditions, on the other hand, it was assumed that the collagen fibers aligned with directions situated between the principal stretch directions. This hypothesis has already been applied successfully to study collagen remodeling in arteries. The predicted fiber architecture represented a branching network and resembled the macroscopically visible collagen bundles in the native leaflet. In addition, the complex biaxial mechanical behavior of the native valve could be simulated qualitatively wi...
Journal of Biomechanics, 2011
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.