Wall Shear Stress Measurements in an Arterial Flow Bioreactor

In vitro arterial flow bioreactor systems are widely used in tissue engineering to investigate response of endothelial cells to shear. However, the assumption that such models reproduce physiological flow has not been experimentally tested. Furthermore, shear stresses experienced by the endothelium are generally calculated using a Poiseuille flow assumption. Understanding the performance of flow bioreactor systems is of great importance, since interpretation of biological responses hinges on the fidelity of such systems and the validity of underlying assumptions. Here we test the physiologic reliability of arterial flow bioreactors and the validity of the Poiseuille assumption for a typical system used in tissue engineering. A particle image velocimetry system was employed to experimentally measure the flow within the vessel with high spatial and temporal resolution. Two types of vessels were considered: first, fluorinated ethylene propylene (FEP) tubing representative of a human artery without cells; and second, FEP tubing with a confluent layer of endothelial cells on the vessel lumen. Instantaneous wall shear stress (WSS), time-averaged WSS, and oscillatory shear index were computed from velocity field measurements and compared between cases. The flow patterns and resulting wall shear were quantitatively determined to not accurately reproduce physiological flow, and that the Poiseuille flow assumption was found to be invalid. This work concludes that analysis of cell response to hemodynamic parameters using such bioreactors should be accompanied by corresponding flow measurements for accurate quantification of fluid stresses.