Development of a mathematical model for microindentation of aortic valve leaflets to aid in the determination of local micromechanical properties

A problem presented at the US Bio PSW Ohio MBI 2012.

Presented by:
Dr Matthew Doyle (Department of Mechanical and Industrial Engineering, University of Toronto)
Prof Craig Simmons (Department of Mechanical and Industrial Engineering, University of Toronto)
C Breward, H Byrne, M Doyle, P Fok, H Huang, G Lewis, D Moulton, S O'Keeffe, D Schwendeman, J Siggers, CA Simmons, S Sivaloganathan, T Stepien, Y Tseng, B Vandiver

Problem Description

Calcific aortic valve disease (CAVD) is the most common heart valve disease, affecting over 25% of the population in developed countries. The hallmark of early CAVD is focal changes in the mechanical properties of the extracellular matrix (ECM) in the valve leaflets. In particular, proteoglycan-rich lesions begin to form on the surface of the fibrosa layer of these leaflets. Maladaptive remodeling of the ECM is hypothesized to negatively influence valve cell function, ultimately resulting in stiffened leaflets that do not function properly. To date, the local micromechanical properties of healthy and diseased valve leaflets have not been characterized.

Microindentation will be used to obtain force-displacement data for porcine aortic valve leaflets, which may or may not contain lesions indicative of the early stages of CAVD. At each measurement location, we will also have measurements of the thicknesses of the lesion (if present) and the three leaflet layers. From this information, the objective of our proposed problem is to develop a method to determine the mechanical properties of the lesion and the leaflet layers at each measurement location and to do so in such a way as to ensure the uniqueness of the solution. This proposed method could be one that gives an analytical solution to this problem, or more likely, provides an approximate solution that could be used as an initial condition for inverse finite element simulations. In addition, because both the fibrosa and the ventricular layers have been shown to be anisotropic, a secondary objective of our study would be to develop a method of obtaining additional experimental data that would enable us to account for this anisotropy in material models of these layers.

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