Heart valves are complex arrangements of collagen fibers and membranes that oppose retrograde blood flow during contraction of the cardiac chambers. Through its amazing lifetime, the normal healthy valve cycles over 3 billion times. However, disease (such as stenosis/calcification or mechanical wear) can cause the valve to malfunction, permitting backflow or failing to properly open. When a valve cannot be salvaged, treatment can require replacement of the valve to improve hydrodynamic behavior. Replacements are either a mechanical valve or, more commonly, a bioprosthetic valve made of either porcine valves or bovine pericardium. Although bioprosthetic implants are highly successful short-term, their long term durability is still limited. Alternatively, the patient can use a synthetic mechanical valve which will likely necessitate blood thinners for the remainder of his/her life. Thus, there is need for replacement valves that possess both superior durability and hemodynamic function. Current bioprosthetic and mechanical designs do not fully consider the underlying native fiber structure of the aortic valve, nor their fiber-scale biomechanical properties. In the past, the challenge of testing at the fiber bundle length scale precluded experimentation. Thus, there was little previously known regarding how the fiber bundles and membrane structures are arranged as well as their exact role in aortic valve function.

The overall objective of this work was to perform experimental and analytical analyses of the individual collagen fiber and membrane “mesostructures” of the aortic valve. We developed a novel experimental/analytical system to investigate these structures in detail. Using this system, we were able to perform a detailed characterization of the substructures’ morphology and the first quantification of their biomechanical properties. This work offers new insights in structure-function adaptations of the native aortic valve at the tissue level. In addition to the application of a more effective replacement valve design, the results of this thesis can be used in the generation of more precise mathematical models of aortic valve loading behavior.