Adhesion induced non-planar and asynchronous flow of a giant vesicle membrane in an external shear flow.

We show the existence of a flow at the surface of strongly adhering giant lipid vesicles submitted to an external shear flow. The surface flow is divided into two symmetric quadrants and presents two stagnation points (SP) on each side of the vesicle meridian plane. The position of these stagnation points depends strongly on the adhesion strength, characterized by the ratio of the contact zone diameter to the vesicle diameter. Contrary to the case of non-adhesive vesicles, streamlines do not lie in the shear plane. By avoiding the motionless contact zone, streamlines result in three-dimensional paths, strongly asymmetric away from the SP. Additional shearing dissipation may occur on the membrane surface as we observed that the mean rotational velocity of the membrane increases towards the vesicle SP, and is mainly determined by the adhesion induced vesicle shape.