Open-boundary molecular dynamics of red blood cell suspensions.

Blood is a complex suspension of deformable red blood cells (RBCs), and its rheology plays a central role in physiology and pathology. While many computational studies have examined hemorheology under periodic or wall-confined flows, these approaches cannot capture the exchange of mass, momentum, and energy with the surroundings, a feature essential for the realistic simulation of non-equilibrium processes. Open-boundary methods provide this capability but remain largely underexplored. We present the first application of open-boundary molecular dynamics (OBMD) to RBC suspensions, with explicit control of flux exchange across the open boundary. The framework combines dissipative particle dynamics for the solvent and a coarse-grained RBC membrane model and introduces a novel, efficient membrane insertion algorithm capable of handling high hematocrits. It reproduces experimental bulk hemorheological properties, including shear-thinning and hematocrit-dependent viscosity. Our results validate OBMD for modeling blood rheology and establish a computational foundation for future studies of ultrasound-blood interactions and other phenomena where periodic boundaries constrain natural dynamics, such as pressure-driven flows, transient inflows, and cell-free layer formation.