Large-displacement 3D structural analysis of an aortic valve model with nonlinear material properties

Abstract

Grafts used in aortic valve-sparing procedures should ideally not only reproduce the geometry of the natural aortic root but also its material properties. Indeed, a number of studies using the finite element method have shown the importance of the natural sinus shape of the root in the functioning of the normal aortic valve, and the relative increase in stresses due to the replacement of the valve by a stiffer synthetic graft. Because of the wide range in experimentally measured values of aortic wall and leaflet material properties, studies by different research groups have incorporated very different material properties in their models. The aim of the present study was to investigate the influence of material properties on aortic wall displacements, and to determine which material properties would most closely match reported experimental data. Two geometrically accurate 3D models corresponding to the closed and open valve configurations were created in Pro/Engineer CAD software. Loads corresponding to systolic and diastolic pressures were specified and large-displacement structural analyses were carried out using the ANSYS package. Results have indicated that the closest match to experiments using isotropic material properties occurred for a Young's modulus of about 2000 KPa. Nonlinear models based on experimental stress-strain curves have shown similar displacements, but altered strain distribution patterns and significantly lower stresses. These results suggest that an accurate comparison of potential new graft models would have to be made with natural aortic valve models incorporating nonlinear material behavior.

Fluid–structure interaction of deformable aortic prostheses with a bileaflet mechanical valve

“…A linear elastic material with Young's modulus equal to 2 MPa was used for the two coronaries. In terms of displacement and strain results, this value gives a good match with respect to more sophisticated models adopted in literature to model the natural aortic root, that use non-linear material properties (Ranga et al, 2004). The leaflets are considered to be rigid and made by pyrolytic carbon.…”

Patient-specific simulations of transcatheter aortic valve stent implantation

“…Aortic wall and native valve leaflets were assumed to be, respectively, 2 and 0.5 mm thick [8,28] with a density equal to 1,120 kg/m 3 for all models. To describe the mechanical behaviour of the aortic root in the FE model, a Mooney-Rivlin hyperelastic constitutive law was adopted incorporating experimental stress-strain data from the ascending aorta [24].…”

Bayesian sensitivity analysis of a model of the aortic valve

“…Thubrikar quotes the ranges of l* and C5L, which are known to vary from person to person (Thubrikar, 1990). C1S, being the neo-Hookean coefficient, is varied according the range specified in (Ranga et al, 2004) (after conversion). Note that C1S and C5L are hyperelastic parameters and are not equivalent to elastic moduli.…”

“…To ignore the uncertainty in these parameters can only place the validity of the model in doubt. Some work has been performed (Ranga et al, 2004) to investigate uncertainty in the material properties of the aortic root, although this was not a formal statistical analysis. This paper aims to perform a detailed Uncertainty Analysis (UA) specifically on an AV model, and on a broader scale to highlight the importance (and feasibility) of UA in modelling biological systems in general.…”