Molecular Tagging Velocimetry (MTV) to Measure Wall Shear Stress in Model Cardiovascular Flows*

WSS measurements in cardiovascular flows have been challenging when using traditional non-intrusive and tracer particle-based optical diagnostic techniques. The goal of this study is to perform high-fidelity, experimental wall shear stress (WSS) measurements in straight, rigid, cylindrical tubes representing canonical artery phanta with Newtonian blood analog fluids. Molecular Tagging Velocimetry (MTV) is used to determine near-wall velocity gradients under physiological flow pertinent to the cardiovasculature. The traditional limitations of spatio-temporal resolution of MTV techniques for liquids are overcome by a novel photobleaching approach with Talbot-effect structured illumination using a pair of common neodymium-doped pulsed lasers (355 and 527 nm).  The results are benchmarked using Womersley’s analytical solution for pulsatile flow in a tube, wherein an analytical expression for near-wall, pulsatile drag force was obtained and the dimensionless Womersley number was introduced.  This exploratory study aims to evaluate the utility of MTV techniques for extensive, experimental WSS-data analysis pertinent to in vitro models of cardiovascular flows.