Doctor of Philosophy
Mechanical and Materials Engineering
Professor Eric Savory
It is well known that regions inside the human arterial network susceptible to atherosclerosis experience a complex flow environment. Endothelial Cells (ECs) lining the inner wall of arteries are sensors to spatially and temporally varying shear stress (i.e. wall shear stress gradients). This complex force-loading can disrupt local cell-to-cell attachment regions triggering a cascade of biological events leading to the formation of atherosclerotic lesions. Consequently, researchers predominantly use a Parallel Plate Flow Chamber (PPFC) to study the hemodynamic-cell cycle relationship due to its simplicity and ability to achieve a two-dimensional fully-developed steady laminar flow across the cell monolayer. Researchers also resort to a PPFC with a vertical step to disrupt the incoming steady and/or pulsatile flow and, thus, generate a complex force-loading on the live ECs.
The present study is focused on the development and validation (by means of quantifying all elements of the design, performance and experimental uncertainty) of a hemodynamic flow facility allowing two-component ( ) Laser Doppler Velocimetry (LDV) measurements as close as 40 µm from the cell monolayer inside the PPFC. The study uses a backward-facing step (BFS) with 50% area reduction to model an idealized stenosis and, hence, disturb the incoming steady and pulsatile laminar flow. To provide insight not only into the fluid dynamic comparison but also on how the BFS models wall shear stress (WSS) and its spatial and temporal gradient (along with the oscillatory shear index, OSI) in a stenosed tube representing an artery, a detailed quantitative comparison with more realistic models of stenosis is provided (i.e. carotid artery phantom). To the best of the author’s knowledge such a quantitative comparison is not available in the literature. In addition, the present study provides mean flow and turbulence statistics downstream of the BFS, thereby adding knowledge to stenosed cases (away from the wall in the developing shear layer) allowing Computational Fluid Dynamics (CFD) modelers to reference experimental data when simulating intermittent turbulent flows.
The results indicate that despite the simplicity of the chosen geometry, the measured flow downstream of the BFS under steady and pulsatile flow exhibits a number of features that are documented in previous work with more realistic configurations of stenoses (i.e. asymmetric tube stenosis). The author believes this simple geometry will set the stage for more advanced studies in the PPFC with more realistic geometrical configurations of stenoses. Lastly, additional work with live ECs cultured inside the PPFC can be undertaken under disturbed flow conditions reported in the present investigation.
Vratonjic, Marin, "Flow Characterization Under Idealized Stenosis Geometry and Performance Assessment of the Hemodynamic Flow Facility" (2017). Electronic Thesis and Dissertation Repository. 4885.