  Deterministic lateral displacement (DLD) microfluidic devices promise
versatile and precise processing of biological samples. However, this prospect
has been realized so far only for rigid spherical particles and remains limited
for biological cells due to the complexity of cell dynamics and deformation in
microfluidic flow. We employ mesoscopic hydrodynamics simulations of red blood
cells (RBC) in DLD devices with circular posts to better understand the
interplay between cell behavior in complex microfluidic flow and sorting
capabilities of such devices. We construct a mode diagram of RBC behavior (e.g.
displacement, zig-zagging, and intermediate modes) and identify several regimes
of RBC dynamics (e.g. tumbling, tank-treading, and trilobe motion).
Furthermore, we link the complex interaction dynamics of RBCs with the post to
their effective cell size and discuss relevant physical mechanisms governing
the dynamic cell states. In conclusion, sorting of RBCs in DLD devices based on
their shear elasticity is in general possible, but requires fine-tuning of flow
conditions to targeted mechanical properties of the RBCs.
