Title of dissertation : Dynamics of Erythrocytes and Microcapsules

Title of dissertation: Dynamics of Erythrocytes and Microcapsules Walter R. Dodson III Doctor of Philosophy, 2008 Fischell Department of Bioengineering Dissertation directed by: Panagiotis Dimitrakopoulos, Ph.D. Department of Chemical and Biomolecular Engineering The erythrocytes are the primary carriers of oxygen and carbon dioxide to and from the systemic tissue. The ability of these cells to deform and navigate through the capillary beds is of fundamental importance for proper functioning of the cardiovascular transport system. The erythrocyte is essentially a capsule, and flow-induced erythrocyte deformation involves the interfacial dynamics of a membrane-enclosed fluid volume stressed in a viscous flow. Elastic capsule dynamics is a complicated problem involving the coupling of fluid and membrane forces; it is also found in a variety of scientific and engineering applications. In this work, we investigate the dynamics of elastic capsules and erythrocytes using the Spectral Boundary Element (SBE) method, a high-order / high-accuracy method for capsule and cellular dynamics. For strain-hardening Skalak elastic capsules in an extensional flow, our investigations demonstrate a shape transition in accordance with experimental observations [6] to a cusped conformation at high flow rates, which allows the capsule to withstand the increased hydrodynamic forces. Our computational methodology reveals a region of bifurcation, in which both spindled and cusped steady-state geometries coexist for a single flow rate. The method is also used to investigate the dynamics of strain-softening Neohookean capsules in the same flow pattern. The strain-softening capsules become highly extended at weaker flow rates than strain-hardening capsules, and do not form steady-state cusped shapes. The SBE method has been extended to model the erythrocyte by using a biconcave disc reference geometry and adaptive prestress to enforce area incompressibility. The method accurately reproduces experimental data from erythrocyte ektacytometry, but allows examination of the erythrocyte dynamics beyond the geometric constraints inherent in ektacytometry and other experimental techniques, including observation of the three-dimensional oscillatory behavior over a range of capillary numbers and viscosity ratios. Our results support a prediction by Fischer, Skalak, and coworkers [32] that the erythrocyte shear modulus decreases at small shear deformations. Our work also suggests that cellular deformation is largely independent of the flow pattern, consistent with the findings of experimental investigators [78]. Dynamics of Erythrocytes and Microcapsules by Walter R. Dodson III Dissertation submitted to the Faculty of the Graduate School of the University of Maryland, College Park in partial fulfillment of the requirements for the degree of Doctor of Philosophy 2008 Advisory Committee: Professor Panagiotis Dimitrakopoulos, Chair/Advisor Professor Raymond A. Adomaitis Professor Helim Aranda-Espinoza Professor Marco Colombini Professor Keith E. Herold c © Copyright by Walter R. Dodson III 2008 Dedicated to my beautiful and wonderful wife Pawinee,