A Numerical Investigation of Blood Damage in the Hinge Area of Aortic Bileaflet Mechanical Heart Valves During the Leakage Phase B. MIN YUN, 1 JINGSHU WU, 1 HELENE A. SIMON, 2 SHIVA ARJUNON, 4 FOTIS SOTIROPOULOS, 3 CYRUS K. AIDUN, 1 and AJIT P. YOGANATHAN 2,4 1 G. W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA, USA; 2 School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, GA, USA; 3 Department of Civil Engineering, University of Minnesota, Minneapolis, MN, USA; and 4 The Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology, 313 Ferst Drive, BME Building, Room 2119, Atlanta, GA 30332-0535, USA (Received 21 June 2011; accepted 23 December 2011; published online 4 January 2012) Associate Editor Peter E. McHugh oversaw the review of this article. Abstract—Previous experimental and numerical blood stud- ies have shown that high shear stress levels, long exposure times to these shear stresses, and flow recirculation promote thromboembolism. Artificial heart valves, in particular bileaflet mechanical heart valves (BMHVs), are prone to developing thromboembolic complications. These complica- tions often form at the hinge regions of BMHVs and the associated geometry has been shown to affect the local flow dynamics and the associated thrombus formation. However, to date no study has focused on simulating the motion of realistically modeled blood elements within the hinge region to numerically estimate the hinge-related blood damage. Consequently, this study aims at (a) simulating the motion of realistically modeled platelets during the leakage (mid- diastole) phase in different BMHV hinge designs placed in the aortic position and (b) quantitatively comparing the blood damage associated with different designs. Three designs are investigated to assess the effects of hinge geometry and dimensions: a 23 mm St. Jude Medical Regent TM valve hinge with two different gap distances between the leaflet ear and hinge recess; and a 23 mm CarboMedics (CM) aortic valve hinge. The recently devel- oped lattice-Boltzmann method with external boundary force method is used to simulate the hinge flow and capture the dynamics and surface shear stresses of individual platelets. A blood damage index (BDI) value is then estimated based on a linear shear stress-exposure time BDI model. The velocity boundary conditions are obtained from previous 3D large- scale simulations of the hinge flow fields. The trajectories of the blood elements in the hinge region are found to be qualitatively similar for all three hinges, but the shear stresses experienced by individual platelets are higher for the CM hinge design, leading to a higher BDI. The results of this study are also shown to be in good agreement with previous studies, thus validating the numerical method for future research in BMHV flows. This study provides a general numerical tool to optimize the hinge design based on both hemodynamic and thromboembolic performance. Keywords—Blood damage modeling, Computational fluid dynamics (CFD), Platelet activation, Hinge flow, Particulate numerical simulations, Thromboembolism, Bileaflet mechan- ical heart valve. INTRODUCTION Native heart valves may become defective due to congenital birth defects or disease. Defective valves are often replaced by prosthetic heart valves, for which demand has grown 10–12% every year. 7 Among prosthetic heart valves, mechanical heart valves are currently the most popular choice, with 55% of defective native heart valves replaced by mechanical heart valves. Among mechanical heart valve designs, the bileaflet mechanical heart valve (BMHV) is cur- rently the most popular and accounts for 80% 36 of implanted mechanical heart valves. Its popularity over other prosthetic heart valves such as caged-ball and tilting disc valves is mainly due to its superior dura- bility, function, and bulk flow hemodynamics. Despite numerous geometrical improvements, BMHVs can still cause serious complications such as hemolysis, platelet activation, and thromboembolic events. 10,14 These major complications are thought to be due to the non-physiologic shear stress levels im- posed on blood elements by the complex flows through BMHVs, in particular through the hinge region. Address correspondence to Ajit P. Yoganathan, The Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology, 313 Ferst Drive, BME Building, Room 2119, Atlanta, GA 30332-0535, USA. Electronic mail: ajit.yoganathan@bme. gatech.edu Annals of Biomedical Engineering, Vol. 40, No. 7, July 2012 (Ó 2012) pp. 1468–1485 DOI: 10.1007/s10439-011-0502-3 0090-6964/12/0700-1468/0 Ó 2012 Biomedical Engineering Society 1468