Archivio istituzionale della ricerca dell'Università degli Studi di Palermo

Descrizione: Mitral valve disease is considered one of the most prevalent cardiac valve disorders, particularly among the ageing population. At the beginning of the 21st century, it was estimated that between 2 and 2.5 million individuals in the United States were affected by mitral valve disease. Over the past decades, the mitral valve has been the focus of numerous research studies to improve the understanding of its biomechanics, advance diagnostic methods, and develop new treatment strategies. Mitral regurgitation is the primary condition affecting the mitral valve. Current treatments for mitral regurgitation focus on using repair or replacement approach. Although valve repair is the most used technique, mitral valve replacement is necessary in some cases. Currently available prosthetic valves include both mechanical and bioprosthetic options, which are implanted based on clinical criteria specific to the patient's condition. While both types have many advantages, they also exhibit differences compared to the native mitral valve. The first difference is observed in morphology. The native mitral valve consists of two asymmetric leaflets, while bioprosthetic valves feature three leaflets, and mechanical bileaflet valves have two leaflets but with a different design compared to native mitral valves. Another important difference is observed in the materials used. Although bioprosthetic valves have leaflets made from bovine or porcine pericardium, they are supported by metallic stents. Conversely, mechanical valves are made from pyrolytic carbon, which makes commercial devices stiffer than native valves. Lastly, the third difference concerns the sub-valvular apparatus. The native mitral valve presents a complex system of chordae tendineae and papillary muscles, which determines continuity between the valve leaflets and the left ventricle. However, this system is completely absent in commercial valves. The BIOMITRAL project (ERC grant ID: 101002561) aims to evaluate whether a biomimetic approach at both the macroscopic and microscopic levels can influence valve functionality. The project aims to develop an engineered, stentless polymeric valve with a chordal apparatus. This thesis focuses on the in-silico studies of the BIOMITRAL project, which involves numerical simulations through the finite element method. The goal of this study is to evaluate the performance of the BIOMITRAL valve, including the chordal apparatus. The developed numerical model analyzes various parameters, including the number of chordae tendineae (2, 4, 6, and 8), the anchoring position of the chordae along the free edge of the valve, and he effects of different chordal lengths (80%, 100%, and 120% of the distance between the marginal edge of the leaflets and the papillary muscles). The numerical model also includes the physiological pressure gradient, the position of the papillary muscles, and leaflet contact during the coaptation phase. Additionally, the valve leaflets are modelled using an anisotropic material to better describe the material of the native valve. This thesis also contributed to the development of a saddle-shaped annulus for the BIOMITRAL valve. By employing a parametric approach using hyperbolic paraboloids and bean functions, they ensure the definition of the saddle-shaped annulus and the characteristic "D" shape of the mitral valve when viewed from the atrium. This work also developed numerical simulations to compare the saddle-shaped and flat-shaped annulus, evaluating the coaptation length and stress distribution on the valve leaflets.

Tipologia: Tesi di dottorato