Schedule Aug 17, 2003
From steady to unsteady dynamics of biological vesicles in a flow within an advected field approach
Chaouqi Misbah (Grenoble)

Various dynamical behaviours of a vesicle in a flow are discussed (tank-treading, tumbling, lift force...). We discuss a new approach, namely the advected field approach (akin to phase field), which is flexible and, unlike boudary integral formulation, allows to incorporate non newtonian constitutive laws for the enclosed fluid as well as the ambient one. We present a description of a bifurcation from steady tank-treading of vesicles, to their tumbling, a bifurcation which is known for red blood cells. Surprisingly, the bifurcation occurs for a given viscosity contrast which is not far from that known for red cells (in other words red cells seem to operate close to the critical point). The tumbling bifurcation is of saddle-node type. We discuss other effects studied by the advected field approach such as the existence of an optimal lift force occuring for a special substrate deformability, a onptimum which is attributed to the elasticity of the endothelial glycocalyx.

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