The leaflets of the atrioventricular heart valves (AHVs) regulate the one-directional flow of blood through a subtle coordination of the extracellular matrix components of the tissue, including collagen fibers, elastin fibers, and glycosaminoglycans. Dysfunction of the AHVs, such as those caused by unfavorable microstructural remodeling, lead to valvular heart diseases and improper blood flow, which can ultimately cause heart failure. In order to better understand mechanics and remodeling of the AHV leaflets and how therapeutics can inadvertently cause adverse microstructural changes, a systematic characterization of the role of each constituent in the biomechanical properties is appropriate. Previous studies have quantified the contributions of the microstructural components to the tissue-level behavior for semilunar valve cusps, but not for AHV leaflets. In this study, for the first time, we quantify the relationships between microstructure and mechanics of the AHV leaflet using a three-step experimental procedure: (i) biaxial tension and stress relaxation testing of control (untreated) porcine AHV anterior leaflet specimens; (ii) enzyme treatment to remove a portion of either the collagen or elastin constituent; and (iii) biaxial tensile and stress relaxation testing of the constituent-removed (treated) specimens. We have observed that the removal of ∼100% elastin resulted in a ∼10% decrease in the tissue extensibility with biaxial tension and a ∼75% increase in the overall stress reduction with stress relaxation. In contrast, removal of 46% collagen content from the leaflets contributed to a ∼3% increase in tissue extensibility with biaxial tension and a ∼0% increase in overall stress decay with stress relaxation. These findings provide an insight into the microstructure-mechanics relationship of the AHVs and will be beneficial for future developments and refinements of microstructurally informed constitutive models for the simulation of diseased and surgically intervened AHV functions.
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