Figure 10.

Various hydrodynamic forces acting on suspended cells in a flow. (A) Drag forces are exerted on a particle in the direction of the flow or in the opposite direction of the flow, depending on the direction of the relative velocity. Drag forces are present in both the creeping and the inertial flow regime. (B) Magnus forces on a rotating particle as a result of a rotation-induced pressure imbalance. Magnus forces are always directed toward the side having the higher relative velocity. (C and D) Wall forces for a particle or a cell moving parallel or perpendicular to a wall. The fluid between the particle and the wall has a lower velocity and higher pressure, forcing the particle away from the wall. (E) Saffman forces for a particle in a simple shear flow. The Saffman force is always directed toward the side having the higher relative velocity and as a result will have a different direction depending on the relative velocity of the particle. (F) Shear-induced lift force as a result of the parabolic velocity profile and the varying relative velocity on either side of the particle. This force is directed toward the side having the higher relative velocity. In a microchannel with a parabolic velocity distribution, a particle will be pushed toward the channel walls.