title: An inverse modeling approach for stress estimation in mitral valve anterior leaflet valvuloplasty for in-vivo valvular biomaterial assessment.
abstract: Estimation of regional tissue stresses in the functioning heart valve remains an important goal in our understanding of normal valve function and in developing novel engineered tissue strategies for valvular repair and replacement. Methods to accurately estimate regional tissue stresses are thus needed for this purpose, and in particular to develop accurate, statistically informed means to validate computational models of valve function. Moreover, there exists no currently accepted method to evaluate engineered heart valve tissues and replacement heart valve biomaterials undergoing valvular stresses in blood contact. While we have utilized mitral valve anterior leaflet valvuloplasty as an experimental approach to address this limitation, robust computational techniques to estimate implant stresses are required. In the present study, we developed a novel numerical analysis approach for estimation of the in-vivo stresses of the central region of the mitral valve anterior leaflet (MVAL) delimited by a sonocrystal transducer array. The in-vivo material properties of the MVAL were simulated using an inverse FE modeling approach based on three pseudo-hyperelastic constitutive models: the neo-Hookean, exponential-type isotropic, and full collagen-fiber mapped transversely isotropic models. A series of numerical replications with varying structural configurations were developed by incorporating measured statistical variations in MVAL local preferred fiber directions and fiber splay. These model replications were then used to investigate how known variations in the valve tissue microstructure influence the estimated ROI stresses and its variation at each time point during a cardiac cycle. Simulations were also able to include estimates of the variation in tissue stresses for an individual specimen dataset over the cardiac cycle. Of the three material models, the transversely anisotropic model produced the most accurate results, with ROI averaged stresses at the fully-loaded state of 432.6±46.5 kPa and 241.4±40.5 kPa in the radial and circumferential directions, respectively. We conclude that the present approach can provide robust instantaneous mean and variation estimates of tissue stresses of the central regions of the MVAL.
authors.affiliation: Center for Cardiovascular Simulation, Institute for Computational Engineering and Sciences (ICES), Department of Biomedical Engineering, The University of Texas at Austin, 201 East 24th Street, ACES 5.236, 1 University Station C0200, Austin, TX 78712, USA.
authors.forename: Chung-Hao
authors.initials: CH
authors.lastname: Lee
authors.affiliation: Department of Biomedical Engineering, The University of Akron, Auburn Science and Engineering Center 275, West Tower, Akron, OH 44325, USA.
authors.forename: Rouzbeh
authors.initials: R
authors.lastname: Amini
authors.affiliation: Gorman Cardiovascular Research Group, University of Pennsylvania, 3400 Civic Center Blvd, Philadelphia, PA 19104, USA.
authors.forename: Robert C
authors.initials: RC
authors.lastname: Gorman
authors.affiliation: Gorman Cardiovascular Research Group, University of Pennsylvania, 3400 Civic Center Blvd, Philadelphia, PA 19104, USA.
authors.forename: Joseph H
authors.initials: JH
authors.lastname: Gorman
authors.affiliation: Center for Cardiovascular Simulation, Institute for Computational Engineering and Sciences (ICES), Department of Biomedical Engineering, The University of Texas at Austin, 201 East 24th Street, ACES 5.236, 1 University Station C0200, Austin, TX 78712, USA. Electronic address: msacks35@gmail.com.
authors.forename: Michael S
authors.initials: MS
authors.lastname: Sacks
mesh_terms: D000818:Animals; D016880:Anisotropy; D063126:Balloon Valvuloplasty; D001672:Biocompatible Materials; D001696:Biomechanical Phenomena; D003198:Computer Simulation; D006350:Heart Valve Prosthesis; D008297:Male; D008943:Mitral Valve / Q000502:physiology*; D008955:Models, Cardiovascular; D012756:Sheep; D013314:Stress, Mechanical; D023822:Tissue Engineering
chemical_list: D001672:Biocompatible Materials
keywords: Finite element (FE) inverse modeling; Genetic algorithm; In-vivo stress estimation; Mapped collagen fiber architecture