(455g) 3D Dynamics of Red Blood Cells and Vesicles in Confined Passages, Constrictions, and Post Arrays

In the microvasculature, cells must navigate small blood vessels whose diameter is comparable to that of the cell.  Even in larger vessels, the extravasation of leukocytes and cancer cells through the cell wall is important in their mobility throughout the human body.  Understanding the dynamics of cells and vesicles in confined spaces allows us to devise ways to help drug delivery agents navigate these spaces and to hinder the extravasation of cancer cells.  We wish to answer the questions of what stresses affect the cells and how these stresses impact the shape.

In this work we conduct 3D boundary element method simulations to determine the dynamics of red blood cells and vesicles in geometries under tight confinement and in post arrays.  Red blood cells and vesicles are differentiated in modeling in that the vesicles are modeled with a Helfrich bending energy and a constrained surface area, whereas the red blood cells possess an additional shear elasticity due to the spectrin proteins embedded in their surface.  Simulation of the vesicle problem is particularly numerically stiff and we employ Loop subdivision surfaces to resolve the vesicle bending force accurately.  We consider cells in both pressure-driven flows and constant external force conditions resembling optical tweezers.  We focus on the implications of flowing cells through a fully 3D geometry that does not exhibit axisymmetry, e.g., on the distribution of cellular surface stress.  We compare and contrast the results between red blood cells and vesicles of equivalent volumes but different surface areas.  Our results suggest that it is possible to construct artificially created vesicles in a laboratory that more efficiently navigate tight spaces in flow than biological cells.