Blood crystal: emergent order of red blood cells under wall-confined shear flow

TL;DR

This study reveals that deformable red blood cells form crystal-like patterns in confined shear flow due to hydrodynamic interactions, with potential applications in diagnosing blood diseases.

Contribution

It demonstrates the emergence of ordered structures of RBCs driven purely by hydrodynamics in confined shear flow, highlighting the role of cell deformability.

Findings

Deformable RBCs form regular patterns in shear flow.

Rigid RBCs remain disordered under the same conditions.

Pattern formation depends on cell concentration and confinement.

Abstract

Driven or active suspensions can display fascinating collective behavior, where coherent motions or structures arise on a scale much larger than that of the constituent particles. Here, we report experiments and numerical simulations revealing that red blood cells (RBCs) assemble into regular patterns in a confined shear flow. The order is of pure hydrodynamic and inertialess origin, and emerges from a subtle interplay between (i) hydrodynamic repulsion by the bounding walls which drives deformable cells towards the channel mid-plane and (ii) intercellular hydrodynamic interactions which can be attractive or repulsive depending on cell-cell separation. Various crystal-like structures arise depending on RBC concentration and confinement. Hardened RBCs in experiments and rigid particles in simulations remain disordered under the same conditions where deformable RBCs form regular patterns, highlighting the intimate link between particle deformability and the emergence of order. The difference in structuring ability of healthy (deformable) and diseased (stiff) RBCs creates a flow signature potentially exploitable for diagnosis of blood pathologies.