Impact of superhydrophobic slip surface on modulating the hemodynamics of a bileaflet mechanical heart valve under functional and dysfunctional states

Valvular heart diseases are on the rise globally, often causing damage or complete destruction of our native heart valves, necessitating their replacement with artificial mechanical heart valves (MHVs). Among various types, the bileaflet mechanical heart valves (BMHVs) are the most advanced and widely used ones due to their superior durability and flow characteristics. However, they are not without limitations, particularly the lifelong requirement for anticoagulation therapy to prevent or minimize the formation of thrombi due to damage to red blood cells and platelet activation. Therefore, extensive research efforts have been devoted to improving the performance of BMHVs, with a particular focus on surface modifications via coatings or micro- and nano-texturing. These modifications render the valve leaflet surfaces superhydrophobic, increasing blood-repelling properties and reducing the risk of blood cell damage by diminishing their interaction with the valve wall. However, the mechanisms by which these surface modifications lead to slip conditions on valve surfaces and influence the corresponding hemodynamics of BMHVs remain poorly understood. This is a vital gap in the literature, as hemodynamic performance directly influences several parameters of clinical importance, including pressure gradients, wall shear stress (WSS), and the blood damage index (BDI), all of which ultimately determine the functional efficiency of an MHV. To address this gap, this study performs extensive numerical simulations for both functional and dysfunctional conditions of a bileaflet MHV and provides a direct means to compare whether the (partial and/or free) slip conditions induced by valve surface superhydrophobicity improve hemodynamics relative to a surface with no slip conditions. Our numerical computations replicate those cases where both heart valve leaflets are fixed at a leaflet angle of 5° (excluding fluid–structure interaction), representing the fully open position of the standard St. Jude Medical valve during the systolic stage of the cardiac cycle. Overall, the present analysis demonstrates that the influence of slip or no-slip conditions on hemodynamics is strongly dependent on the specific time instants of the cardiac cycle and the functional conditions of the valve. A detailed comparison is presented and discussed in terms of surface contours of velocity magnitude and von Mises stress, vortex dynamics, pressure distribution, a kymograph of the axial velocity component, and surface- or volume-averaged parameters, including WSS, BDI, etc. Therefore, the findings of this study will provide valuable guidance for designing and developing next-generation MHVs with superhydrophobic surfaces to enhance biocompatibility and long-term performance.