Date of Award

1-1-2010

Document Type

Campus Access Thesis

Department

Mechanical Engineering

First Advisor

Arash Kheradvar

Abstract

Heart valves play an important role in directing blood flow and preventing back flow in the heart. Design and development of bioprosthetic heart valves has been a major focus of research in the field of cardiovascular engineering as they are a better replacement for natural diseased valves than mechanical heart valves. Their lower risks of thrombogenicity and superior hemodynamics have given these valves remarkable advantages. However, one of the major problems facing bioprosthetic heart valves involves excessive stress around the tip of the leaflet which can lead to calcification. Reducing this stress can potentially increase the valve's longevity and will result in a lower risk of fatigue and leaflet tearing, and ultimately minimize the chance of valve degeneration and failure.

This work is focused on the assessment of mechanical behavior and optimization of a bi-leaflet bioprosthetic mitral valve by using Finite Element Analysis. The valve system consists of a flexible, saddle shaped annulus that is made of superelastic Nitinol. The saddle shape of this valve's annulus dynamically deflects during a cardiac cycle according to the shape of the cardiac base, making it unique in imitating the characteristics of a natural mitral valve. The latest constitutive law for the tissue has been employed, which takes into account the tissue's dependency on fiber direction. The stress distribution over the valve leaflets has been studied and shows that the dynamics of the saddle annulus minimizes the stress at the tip of the leaflet. It is the saddle annulus that dampens the pressure load over the valve during cardiac cycle and adapts to a configuration whose geometry has the minimum energy. The framework of this study can be easily used to design, analyze, and optimize all types of bioprosthetic heart valves.

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