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Auricchio F.,University of Pavia | Auricchio F.,CNR Institute for Applied Mathematics and Information Technologies | Auricchio F.,Centro Of Simulazione Numerica Avanzata Cesna | Conti M.,University of Pavia | Morganti S.,University of Pavia
Medical Engineering and Physics | Year: 2011

In some cases of aortic valve leaflet disease, the implant of a stentless biological prosthesis represents an excellent option for aortic valve replacement (AVR). In particular, if compared to more classical surgical approaches, it provides a more physiological hemodynamic performance and a minor trombogeneticity avoiding the use of anticoagulants. The clinical outcomes of AVR are strongly dependent on an appropriate choice of both prosthesis size and replacement technique, which are, at present, strictly related to surgeon's experience and skill. Therefore, also this treatment, like most reconstructive procedures in cardiac surgery, remains "more art than science" [1]. Nowadays computational methodologies represent a useful tool both to investigate the aortic valve behavior, in physiologic and pathologic conditions and to reproduce virtual post-operative scenarios. The present study aims at supporting the AVR procedure planning through a patient-specific Finite Element Analysis (FEA) of stentless valve implantation. Firstly, we perform FEA to simulate the prosthesis placement inside the patient-specific aortic root; then, we reproduce, again by means of FEA, the diastolic closure of the valve to evaluate both the coaptation and the stress/strain state. The simulation results prove that both the valve size and the anatomical asymmetry of the Valsalva sinuses affect the prosthesis placement procedure. © 2011 IPEM.


Auricchio F.,University of Pavia | Auricchio F.,European Center for Training and Research in Earthquake Engineering | Auricchio F.,CNR Institute for Applied Mathematics and Information Technologies | Auricchio F.,Centro Of Simulazione Numerica Avanzata Cesna | And 6 more authors.
CMES - Computer Modeling in Engineering and Sciences | Year: 2010

The use of shape memory alloys (SMA) in an increasing number of applications in many fields of engineering, and in particular in biomedical engineering, is leading to a growing interest toward an exhaustive modeling of their macroscopic behavior in order to construct reliable simulation tools for SMA-based devices. In this paper, we review the properties of a robust three-dimensional model able to reproduce both pseudo-elastic and shape-memory effect; then we calibrate the model parameters on experimental data and, finally, we exploit the model to perform the finite element analysis of pseudo-elastic Nitinol stent deployment in a simplified atherosclerotic artery model. Copyright © 2010 Tech Science Press.


Mazzia A.,University of Padua | Manzini G.,CNR Institute for Applied Mathematics and Information Technologies | Manzini G.,Centro Of Simulazione Numerica Avanzata Cesna | Putti M.,University of Padua
Journal of Computational Physics | Year: 2011

We study the performance of Godunov mixed methods, which combine a mixed-hybrid finite element solver and a Godunov-like shock-capturing solver, for the numerical treatment of the advection-dispersion equation with strong anisotropic tensor coefficients. It turns out that a mesh locking phenomenon may cause ill-conditioning and reduce the accuracy of the numerical approximation especially on coarse meshes. This problem may be partially alleviated by substituting the mixed-hybrid finite element solver used in the discretization of the dispersive (diffusive) term with a linear Galerkin finite element solver, which does not display such a strong ill conditioning. To illustrate the different mechanisms that come into play, we investigate the spectral properties of such numerical discretizations when applied to a strongly anisotropic diffusive term on a small regular mesh. A thorough comparison of the stiffness matrix eigenvalues reveals that the accuracy loss of the Godunov mixed method is a structural feature of the mixed-hybrid method. In fact, the varied response of the two methods is due to the different way the smallest and largest eigenvalues of the dispersion (diffusion) tensor influence the diagonal and off-diagonal terms of the final stiffness matrix. One and two dimensional test cases support our findings. © 2011 Elsevier Inc.


Auricchio F.,University of Pavia | Auricchio F.,Centro Of Simulazione Numerica Avanzata Cesna | Conti M.,CNR Institute for Applied Mathematics and Information Technologies | Morganti S.,University of Pavia | And 4 more authors.
IUTAM Bookseries | Year: 2011

The use of shape memory alloys (SMA) in an increasing number of applications in many fields of engineering, and in particular in biomedical engineering, is leading to a growing interest toward an exhaustive modeling of their macroscopic behavior in order to construct reliable simulation tools for SMA devices. In this paper we review the properties of a robust three-dimensional model able to reproduce both pseudo-elastic and shape-memory effect; we then employ such as a model to perform the Finite Element Analysis of SMA-based devices such as self-expanding stents and spring actuators. © Springer Science+Business Media B.V. 2011.


Auricchio F.,University of Pavia | Auricchio F.,CNR Institute for Applied Mathematics and Information Technologies | Auricchio F.,Centro Of Simulazione Numerica Avanzata Cesna | Conti M.,University of Pavia | Ferrara A.,University of Pavia
Archives of Computational Methods in Engineering | Year: 2014

To perform realistic finite element simulations of cardiovascular surgical procedures (such as balloon angioplasty, stenting or bypass), it is necessary to use appropriate constitutive models able to describe the mechanical behavior of the human arterial wall (in healthy and diseased conditions) as well as to properly calibrate the material parameters involved in such constitutive models. Moving from these considerations, the goal of the present study is to compare the reliability of two isotropic phenomenological models and of four structural invariant-based constitutive models, commonly used to describe the passive mechanical behavior of arteries. The arterial wall is modeled as a thick-wall tube with one- and two- layer structure. Residual stresses inclusion is also considered, to evaluate informations on the stress distribution through the wall thickness. The predictive capability of the investigated models is tested using extension/inflation data on human carotid arteries related by two different experimental works available in the literature. The material parameters involved in the investigated models are computed in the least-square sense thought a best fitting procedure, relying on a multi-start optimization algorithm. The good quality of the optimal solution is validated quantitatively computing proper error measures and comparing the model prediction curves. The final outcome of the paper is a critical review of the six considered constitutive models, comparing their formulation and evidencing the more or less capability of such models to fit the considered experimental data. © 2014 CIMNE, Barcelona, Spain.


Auricchio F.,University of Pavia | Auricchio F.,CNR Institute for Applied Mathematics and Information Technologies | Auricchio F.,Centro Of Simulazione Numerica Avanzata Cesna | Ferrara A.,University of Pavia | Morganti S.,University of Pavia
Annals of Solid and Structural Mechanics | Year: 2012

With the increase of life expectancy and population average age, heart valve diseases have become more frequent, representing an always increasing percentage among cardiovascular diseases, which are the predominant cause of death in the western country. For this reason, research activities within such a context and, in particular, computer-based predictions of valve behavior are strongly motivated. Consequently, the study of the tissue mechanical response and the constitutive relationships for modeling material behavior represent crucial a aspect to be investigated in order to perform realistic simulations. The mechanical response of the aortic valve tissue depends on the contribution, composition, and interaction of different constituents, such as collagen fibers and elastin network. Accordingly, constitutive laws including non-linearity and anisotropy are necessary. Clearly, the complexity of a constitutive model increases more as it takes into account the histological structure of the tissue. Numerous constitutive models have been developed to describe arterial tissue, but relatively few models have been calibrated specifically for the aortic valve. This study focuses on the investigation of constitutive models so far proposed in the literature which could be suitable to capture the mechanical behavior of the aortic valvular tissue. To make the right choice, the comparison between these constitutive models is done in terms of the fitting quality achieved with respect to human aortic valve data proposed in the literature. For this purpose, an optimization technique based on the nonlinear least square method is used. The obtained material parameters could be later used in finite element analysis adopted, in this last decade, as an innovative approach to support the operation planning procedure and the design of artificial grafts. © 2012 Springer-Verlag.


Auricchio F.,University of Pavia | Auricchio F.,European Center for Training and Research in Earthquake Engineering | Auricchio F.,CNR Institute for Applied Mathematics and Information Technologies | Auricchio F.,Centro Of Simulazione Numerica Avanzata Cesna | And 4 more authors.
International Journal of Solids and Structures | Year: 2013

This paper illustrates an application of the so-called dimensional reduction modelling approach to obtain a mixed, 3D, linear, elastic beam-model. We start from the 3D linear elastic problem, formulated through the Hellinger-Reissner functional, then we introduce a cross-section piecewise-polynomial approximation, and finally we integrate within the cross section, obtaining a beam model that satisfies the cross-section equilibrium and could be applied to inhomogeneous bodies with also a non trivial geometries (such as L-shape cross section). Moreover the beam model can predict the local effects of both boundary displacement constraints and non homogeneous or concentrated boundary load distributions, usually not accurately captured by most of the popular beam models. We modify the beam-model formulation in order to satisfy the axial compatibility (and without violating equilibrium within the cross section), then we introduce axis piecewise-polynomial approximation, and finally we integrate along the beam axis, obtaining a beam finite element. Also the beam finite elements have the capability to describe local effects of constraints and loads. Moreover, the proposed beam finite element describes the stress distribution inside the cross section with high accuracy. In addition to the simplicity of the derivation procedure and the very satisfying numerical performances, both the beam model and the beam finite element can be refined arbitrarily, allowing to adapt the model accuracy to specific needs of practitioners. © 2013 Elsevier Ltd. All rights reserved.

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