" Cardiac Valve Modeling and Tissue Engineering "
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Abstract: It is becoming appreciated that the aortic valve is an extremely complex, highly specialized structure.  Indeed, one of the major limitations in the advancement of tissue valve design has been the lack of (i) understanding of valve tissue microstructure, and (ii) engineering tools for their analysis and development. A tissue-engineered valve must include the complex microstructure of native valves in order to mimic their unique mechanical properties. The functional components include collagen fiber bundles, mesh networks, branches, and layers of elastin. Likewise, accurate computational models need to mimic the underlying microstructure and thus the micromechanical behavior of these complex tissues.

Existing FEA models have been developed by either copying the 3-D shape of an aortic valve, or by representing an idealized geometry, and then assuming a material model. While these FEA models have been shown to mimic some of the deformation patterns of native valves, there is no way to determine if the computed stresses actually represent the internal mechanics of the real valve.  We have developed Fluid-Solid Interaction (FSI) models in Adina and LS-Dyna, using simple isotropic models, as well as more sophisticated dispersed isotropy fiber models. These models will be reviewed and their utility described.

For tissue engineering of the cardiac valves, our approach has been to develop each structural component of the heart valve separately in vitro and then integrate all the components together into a composite valve structure.  Collagen fiber bundles were fabricated using directed collagen gel shrinkage in various geometries and configurations, and subjected to static and dynamic loading protocols.  Elastin sheets were grown by culturing cells on crosslinked hyaluronan substrates, texturized by UV light irradiation to enhance cells attachment and matrix synthesis. We expect this integrative approach to ultimately yield more structurally, and hence functionally, accurate tissue-engineered materials for cardiac valve replacement.