Comparative study of Newtonian and non-Newtonian flow inside a compliant aortic bifurcation model

Shear-thinning properties of non-Newtonian fluids such as blood significantly affect the flow in compliant vessels. In particular, under physiologically realistic pulsatile inflow conditions, these shear-thinning properties can alter the flow field and thus the fluid–structure interaction. Yet, non-Newtonian effects are frequently neglected in in vitro experiments due to increased experimental complexity. This study aims to provide a comparative analysis of the combined influence of pulsatile flow conditions and non-Newtonian fluid properties on the flow field and fluid–structure interaction in a compliant abdominal aortic bifurcation model. Therefore, a fully transparent compliant bifurcation phantom was manufactured from two-component PDMS (RTV-615) using a wax-based lost-core technique to ensure dimensional accuracy and smooth internal surfaces. The model was integrated into a pulsatile flow loop, and time-resolved three-dimensional velocity fields were acquired by three-dimensional particle-tracking velocimetry (3D PTV) using the Shake-the-Box algorithm. The flow field, static pressure, wall dilatation, and volume flux were measured for both a Newtonian fluid and a blood-analogue non-Newtonian fluid across three Reynolds numbers and two Womersley numbers, representing physiologically relevant flow regimes. The flow measurements indicate that for both fluids an increase of the Womersley number yields broader and more uniform high-velocity cores and smoother axial transitions. Results for the non-Newtonian fluid consistently exhibit wider velocity distributions and more synchronized fluid–structure interaction dynamics in all cases that were investigated. Overall, the findings suggest that the shear-thinning rheology of the non-Newtonian fluid shifts the temporal response characteristics of the coupled system toward behavior observed at higher Womersley numbers. This indicates an altered phase relationship between the flow field and wall deformation. Thus, the present measurements indicate that non-Newtonian properties significantly influence both the flow field and the fluid–structure interaction in compliant vascular models under pulsatile conditions. Combining compliant, optically transparent phantoms with time-resolved 3D PTV provides a powerful platform for quantifying these coupled effects, advancing the understanding of physiological hemodynamics, and improving the reliability of in vitro studies and simulation validation efforts.