EVALUATION OF THE EFFECT OF SKIN FRICTION ON THE PERFORMANCE OF A PROSTHETIC AORTIC VALVE USING FLUID- STRUCTURE INTERACTION SIMULATIONS K.H. Dellimore 1 , I. H. Kemp 2 , C. Scheffer 3 , H.S. Weich 4 and A.F. Doubell 5 1. ABSTRACT The performance of a 19 mm diameter prosthetic aortic valve at a heart rate of 72bpm was investigated during systole, through fluid-structure interaction simulations using four different leaflet skin friction coefficients (0.0, 9.24x10 -4 , 4.80x10 -2 and 4.80x10 -1 ). The numerical predictions were validated against experimental data for the systolic transvalvular pressure gradient (STVPG) and yielded reasonable qualitative and quantitative agreement (rms error < 13% in all cases). Increasing the leaflet skin friction was found to increase the magnitude of the STVPG, increase the peak velocity and decrease the valve orifice area when the leaflets were fully open, which are consistent with the effects of calcific stenosis. However, the results for the leaflet dynamics during opening and closing were inconsistent with expectation since increasing the leaflet skin friction decreased rapid valve closing time and had a negligible effect on the ejection time and rapid valve opening time. The deficiencies in the numerical predictions may be attributed to the use of a constant leaflet elastic modulus in the simulations. 2. INTRODUCTION Aortic valve stenosis caused by progressive calcification of aortic valve leaflets is among the leading causes of aortic valve disease in the elderly and is the most common reason for prosthetic valve replacement in adults [1]. Over the past fifty years there have been several advances in the development of prosthetic aortic replacement valves; however, many challenges still remain due to their poor long-term durability caused by calcification and mechanical failure [2]. Further research is needed to improve their longevity and to advance our understanding of their operation. Many previous studies have investigated the mechanics and functioning of native and prosthetic aortic valves using numerical simulations. Advances in computational power have allowed the fluid- structure interaction (FSI) between the valve and blood flow to be modeled numerically. In particular work by Carmody et al. [3], De Hart et al. [4], Van Loon et al. [5] and Nobili et al. [6] has underscored the strong coupling between the blood flow and the valve structure. However, these previous studies have not considered leaflet skin friction, which may influence valve function, especially under calcific conditions. Previous work by Clark [7] suggests that the flow surfaces of a calcified valve may be hydraulically rough due to calcium deposition which can lead to increased turbulence levels within the valve. It is therefore useful to account for leaflet skin friction, in addition to FSI, when modeling prosthetic valves since it may provide insight into valve 1 Department of M&M Engineering, Stellenbosch University, Private Bag X1, Matieland, South Africa 2 Department of M&M Engineering, Stellenbosch University, Private Bag X1, Matieland, South Africa 3 Department of M&M Engineering, Stellenbosch University, Private Bag X1, Matieland, South Africa 4 Division of Cardiology, Tygerberg Hospital, Private Bag X1, Tygerberg, South Africa 5 Division of Cardiology, Tygerberg Hospital, Private Bag X1, Tygerberg, South Africa