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Soft layers give a push to flowing objects

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In contrast to a speeding plane ready for take-off, a spherical particle moving slowly past a flat surface is not supposed to lift away from it… unless the particle or the surface are soft enough to be deformed by the pressure in the fluid into which they are immersed.

This coupling between flow and deformation is known as elastohydrodynamics and it is essential in the mechanical behaviour of suspensions or pastes, or in biolubrication processes taking place in human joints. Here, we demontrate experimentally that the presence of a very thin layer of polymer decorating a rigid surface is enough to make flowing microbeads lift away, and that such lift is directly controlled by the softness of the layer. We mimick a typical blood flow situation : micron-sized circulating cells interacting with vessel walls lined by a thin and compliant layer of biopolymers named « glycocalyx ». This study thus emphasizes the importance of elastohydrodynamics in blood circulation and unveils a new mechanism by which the glycocalyx may be involved in regulating the interactions between circulating cells and vascular walls.

See online on the website of INP CNRS

View online : Elastohydrodynamic lift at a soft wall, Heather S. Davies, Delphine Débarre, Nouha El Amri, Claude Verdier, Ralf P. Richter and Lionel Bureau, Phys. Rev. Lett. 120, 198001