Structure-function characterization of fresh human heart valves

OBJECTIVES The four human heart valves (HVs) exhibit differences in their physiology which are reflected in their structural and mechanical properties. HVs physiological properties still remain poorly characterized and are largely neglected in the design of commercially available prosthetic devices, with data being extracted only from animal or cadaveric tissues. This study aims to fully characterize human HVs structure and mechanics at the organ and tissue scale. METHODS Human valve samples from heart transplant patients were tested within 24 hours from the explant procedure. Thickness was measured across the whole leaflet area for the aortic, mitral, pulmonary, and tricuspid valves (AV, MV, PV, TV). Leaflet cellular and structural constituents were characterized using histological staining a decellularization protocol allowed for fiber network analysis via electron microscopy. Collagen fiber angle distribution and bundle diameter were quantified with digital image processing. Biaxial mechanics was measured on belly region samples utilizing a Lagrangian equi-stress control protocol with 400kPa peak stress. RESULTS Results showed that HVs collagen quantity and thickness correlates with transvalvular pressure, with increased thickness values measured at coaptation and free edge regions. The MV exhibited a higher average thickness. MV and TV showed greater stiffness than the semilunar valves (AV, PV), along the radial direction. CONCLUSIONS This study highlights structural and functional differences in fresh human HVs. Establishing a detailed HV structural-function database remains critical to assist valve engineering, and implement biomimicry in leaflet, supra and sub-valvular apparatus design.