A strong motivation for studying the flow of soft particles come from the study of hemorheology -- the flow properties of blood. Since the late 19th century, when Poiseuille studied blood flow in capillaries, the non-Newtonian behavior of blood has been of great interest to physicians and physicists alike. It is known that the effective viscosity of blood decreases as the flow rate increases.
The dynamics of deformable particles such as vesicles and cells in flow are investigated in our group using a hybrid Brownian Dynamics-Lattice Boltzmann method. The interplay between particle dynamics and fluid dynamics is complicated by the deformable particle surface. The complex interplay between particle deformation, fluid hydrodynamics and particle dynamics lead to interesting interactions such as wall depletion and aligned structures in flow. In mixtures, flow may be used to separate particles of different elasticity, shapes, and sizes.
An example of what may occur in blood flow is what happens to the cell motion when two cells collide. The collision of two deformable particles is irreversible in flow. As the particles come in close contact, the particles are displaced from each other due to hydrodynamic interactions. The translational momentum of the particles is converted to rotational momentum and particle deformation as the particles collide. This corresponds to a cancellation of fluid momentum as the particles collide.
 C. Hsu and Y.-L. Chen, J. Chem. Phys, 133, 034906