Dynamics of vesicles in a wall-bounded shear flow
Manouk Abkarian 1* and Annie Viallat 2
1 Harvard University
2 Laboratoire de Spectrométrie Physique
* To whom correspondence should be addressed. E-mail: mabkaria{at}deas.harvard.edu.
Submitted on November 10, 2004
Revised on December 3, 2004
Accepted on 14 April 2005
 |
Abstract |
|---|
We report a detailed study of the behavior (shapes, experienced forces, velocities) of giant lipid vesicles subjected to a shear flow close to a wall. Vesicle buoyancy, size and reduced volume were separately varied. We show that vesicles are deformed by the flow and exhibit a tanktreading motion with steady orientation. Their shapes are characterized by two non dimensional parameters: the reduced volume and the ratio of the shear stress with the hydrostatic pressure. We confirm the existence of a force (1), able to lift away non spherical buoyant vesicles from the substrate. We give the functional variation and the value of this lift force (up to 150 pN in our experimental conditions) as a function of the relevant physical parameters: distance vesicle-substrate, wall shear rate, viscosity of the solution, vesicle size and reduced volume. Circulating deformable cells disclosing a non spherical shape also experience this force of viscous origin, which contributes to take them away from the endothelium and should be taken into account in studies on cell adhesion in flow chambers, where cells membrane and the adhesive substrate are in relative motion. Finally, the kinematics of vesicles along the flow direction can be described in a first approximation with a model of rigid spheres.
Key Words:
deformation, distance to the substrate, kinematics, lift force, shape, side view
