Thrombosis and thromboembolization remain large obstacles in the design of cardiovascular devices. In this study, the temporal behavior of thrombus size within a backward-facing step (BFS) model is investigated, as this geometry can mimic the flow separation which has been found to contribute to thrombosis in cardiac devices. Magnetic resonance imaging (MRI) is used to quantify thrombus size and collect topographic data of thrombi formed by circulating bovine blood through a BFS model for times ranging between 10 and 90 min at a constant upstream Reynolds number of 490. Thrombus height, length, exposed surface area, and volume are measured, and asymptotic behavior is observed for each as the blood circulation time is increased. Velocity patterns near, and wall shear stress (WSS) distributions on, the exposed thrombus surfaces are calculated using computational fluid dynamics (CFD). Both the mean and maximum WSS on the exposed thrombus surfaces are much more dependent on thrombus topography than thrombus size, and the best predictors for asymptotic thrombus length and volume are the reattachment length and volume of reversed flow, respectively, from the region of separated flow downstream of the BFS.

Heart disease is one of the leading causes of death in the United States. This condition affects roughly 5.7 million Americans, with approximately 670,000 new cases and 300,000 deaths each year [1]. Heart failure, resulting from heart disease, is primarily treated with the implantation of a ventricular assist device (VAD) [2]. Along with VADs, arterial stents (primarily for treatment of atherosclerosis) and prosthetic heart valves (for defects in or other failures of the native heart valves) are other devices that are regularly used by clinicians to treat conditions within the circulatory system. While complications relating to cardiovascular devices have seen a decrease over the years, thrombosis and thromboembolization still remain obstacles. These phenomena are dependent upon the blood/material interface, surface topography, and fluid mechanics within the device [3].