On the Bending Properties of Porcine Mitral, Tricuspid, Aortic, and Pulmonary Valve Leaflets

Brazile, B. L., Wang, B., Wang, G., Bertucci, R., Prabhu, R., Patnaik, S.S, Butler, J. R., Claude, A., Brinkman-Ferguson, E., Williams, L. N., & Liao, J. (2015). On the Bending Properties of Porcine Mitral, Tricuspid, Aortic, and Pulmonary Valve Leaflets. Journal of Long-Term Effects of Medical Implants. 25(1-2), 1-14.

Abstract

The atrioventricular valve leaflets (mitral and tricuspid leaflets) are different from the semi-lunar valve leaflets (aortic and pulmonary leaflets) in layered structure, ultrastructural constitution and organization, and leaflet thickness. These differences warrant a comparative look at bending properties of the four types of valve leaflets. In this study, we found that the moment-curvature relationships in atrioventricular valves were stiffer than in semilunar valves, and the moment-curvature relationships of the left-side valve leaflets were stiffer than their morphological analog of the right side. The above trends were supported by the moment-curvature curves and the flexural rigidity analysis (EI value decreased from mitral, tricuspid, aortic, to pulmonary leaflets). However, after taking away the geometric effect (moment of inertia I), the instantaneous effective bending modulus E showed a reversed trend. The overall trend of flexural rigidity (EI: mitral leaflet > tricuspid leaflet > aortic leaflet > pulmonary leaflet) might correlated with the thickness variations among the four types of leaflets (thickness: mitral leaflet > tricuspid leaflet > aortic leaflet > pulmonary leaflet). The overall trend of the instantaneous effective bending modulus (E: mitral leaflet < tricuspid leaflet < aortic leaflet < pulmonary leaflet) might be correlated to the layered fibrous ultrastructures of the four types of valve leaflets, of which the fibers in mitral and tricuspid leaflets were less aligned, and the fibers in aortic and pulmonary leaflets were highly aligned. We also found that, for all types of leaflets, moment-curvature relationships are stiffer in against curvature (AC) bending than with curvature bending (WC), implicating that leaflets tend to flex towards their natural curvature and comply with blood flow, while having a tendency to resist bending against their natural curvature. Lastly, we observed that the leaflets were stiffer in circumferential bending as compared to radial bending, likely reflecting the physiological motion of the leaflets, i.e., more bending moment and movement were experienced in radial direction than circumferential direction.