Biomechanical Properties of Fiber Bundle and Membrane Mesostructures of the Porcine Aortic Valve

BACKGROUND AND AIM OF THE STUDY: Aortic valve leaflets have a complex, anisotropic structure that likely plays an important role in their biomechanical function. The larger scale (bulk) biomechanical properties of the valve have been well documented. However, limited data are available regarding the biomechanical properties of individual fiber bundles and membranes that connect the bundles. The study aim was to characterize these intermediate-scale ‘mesostructures’ and explore biomechanical variability across the three leaflets of the aortic valve. Methods: A custom uniaxial micro-testing system was developed to test mesostructures of the aortic valve leaflet. This system uses elliptically polarized light to enhance collagen features, providing ‘texture’ for image correlation-based strain measurements. Porcine aortic valve membrane and fiber bundle specimens were subjected to controlled stretch-and-hold tests. Synchronized video and load data were used to measure strain, elastic modulus, relaxation time, and degree of relaxation (among other parameters). These metrics were then compared between specimen types and across the three leaflets. METHODS: A custom uniaxial micro-testing system was developed to test mesostructures of the aortic valve leaflet. This system uses elliptically polarized light to enhance collagen features, providing ‘texture’ for image correlation-based strain measurements. Porcine aortic valve membrane and fiber bundle specimens were subjected to controlled stretch-and-hold tests. Synchronized video and load data were used to measure strain, elastic modulus, relaxation time, and degree of relaxation (among other parameters). These metrics were then compared between specimen types and across the three leaflets. RESULTS: Fiber bundles were found to have a significantly higher elastic modulus (13.87 ± 2.81 MPa) than the membranes (2.27± 0.36 MPa). Both specimen types had similar relaxation time constants (6.75 ± 0.73 s) and degrees of relaxation (0.223 ± 0.016). The elastic modulus of the fiber bundles from the left coronary and non-coronary leaflets was significantly higher than that of the right coronary leaflet. The fiber bundle elastic modulus also negatively correlated with the fiber bundle width. CONCLUSION: The resulting differences in biomechanical properties of mesostructures are likely related to their biomechanical and hemodynamic requirements. The study findings highlight the importance of considering aortic valve leaflets as inhomogeneous. Further studies are required to characterize the morphologies, nonaffine deformations, and biomechanical properties of the valve’s complex fiber-membrane mesostructures, potentially enabling the development of improved models and designs for durable replacement/repair strategies.