Experimental and computational validation of Hele-Shaw stagnation flow with varying shear stress
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ORIGINAL PAPER
Experimental and computational validation of Hele-Shaw stagnation flow with varying shear stress Brandon J. Tefft · Adrian M. Kopacz · Wing Kam Liu · Shu Q. Liu
Received: 5 May 2013 / Accepted: 1 June 2013 © Springer-Verlag Berlin Heidelberg 2013
Abstract An in vitro flow model system with continuous variation of fluid shear stress can be used to test cell responses to a range of shear stresses. In this investigation, we validated such a flow system computationally for steady and unsteady flow conditions and experimentally for steady flow conditions. The unsteady flow validation is important for studying cells such as endothelial cells that experience unsteady flow conditions in their native environment. The system is capable of exposing cells in different regions of the chamber to steady or unsteady shear stress conditions with average values ranging linearly from 0 to 30 dyn/cm2 . These tests and analyses demonstrate that the variable-width parallel plate flow system can be used to test the influence of a range of steady and unsteady fluid shear stress levels on cell activities. Keywords Flow chamber · Unsteady flow · Shear stress · Endothelial cells · adhesion
B. J. Tefft · S. Q. Liu Department of Biomedical Engineering, Northwestern University, Evanston, IL, USA A. M. Kopacz · W. K. Liu Department of Mechanical Engineering, Northwestern University, Evanston, IL, USA W. K. Liu King Abdulaziz University (KAU), Jeddah, Saudi Arabia W. K. Liu Sung Kyun Kwan University, Seoul, South Korea B. J. Tefft (B) Mayo Clinic, Stabile Bldg 4-45, 200 1st St. SW, Rochester, MN 55905, USA e-mail: [email protected]
1 Introduction Fluid shear stress is of great importance to many physiological and pathological processes, especially in the cardiovascular system. Vascular endothelial cells are positioned to sense fluid shear stress and will respond by altering function, adhesion, morphology, and gene expression [1]. Elevated shear stress, for example, induces endothelial cells to release vasodilators such as nitric oxide [2] and prostacyclin [3] in order to reduce the shear stress. Conversely, reduced shear stress, such as in regions of turbulent blood flow, results in endothelial cell dysfunction and the initiation and progression of atherosclerosis [4]. Due to the important influence of shear stress on vascular physiology and pathology, in vitro flow models are often used to study the activity of endothelial cells exposed to carefully controlled fluid shear stress levels. Tissue engineers also find such flow models useful for studying the important problem of cell detachment from vascular graft materials [5]. Endothelial cells are exquisitely sensitive to shear stress and it is often desirable to study their activity in a range of shear stress conditions. Usami et al. [6] developed a variablewidth parallel plate flow chamber (PPFC) capable of exposing cells to a range of steady fluid shear stress levels. However, endothelial cells experience unsteady flow conditions in their native environment
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