The Mitral Valve (MV) serves to ensure unidirectional blood flow from the pulmonary to systemic circulation. When the MV fails to function correctly, backflow from the left ventricle to left atrium occurs during heart contraction. This condition is called Mitral Valve Regurgitation (MVR) and is estimated to affect 2 to 2.5 million people in the United States alone [1]. Surgical techniques exist to repair MVR, and each affects the structure of the valve in a different way [2]. As the main load-bearing structure in the leaflets, collagen fibers have a tremendous impact on how the leaflets are able to support pressure loads, and their orientation has great functional implications. The goal of this study is therefore to investigate the microstructure of mitral valve tissue. Since collagen makes up approximately 60% of the dry weight of the leaflet [3], we focused our study on this macromolecule. In a complementary in-vivo study, we computed mitral leaflet strains in radial and circumferential direction using a continuum mechanical approach based on the 4D coordinates of 23 radiopaque markers sewn onto the anterior MV leaflet [4]. Results shown in Figure 1. As clearly seen from the figure, strains exhibit pronounced anisotropy. We expect that comparison of the collagen orientation in the leaflet with the these strain profiles will enhance our knowledge of the role of collagen in MV mechanics and the effect that potential surgical interventions may have on MV functionality. While collagen orientation has been determined using Small Angle Light Scattering [5], Polarized Light Microscopy [5], and X-ray Diffraction [6], histological methods to characterize the collagen orientation over the entire leaflet have not been reported. Therefore, we will study the orientation of collagen throughout the anterior ovine MV leaflet using tissue histology.

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