Shape-Dependent Transport of Microparticles in Blood Flow: From Margination to Adhesion

We explore the shape effect of microparticles (MPs) on their margination behaviors in blood flow through three-dimensional numerical simulations. Six different shapes of MPs were considered with identical volume, such as sphere, rod, cubic, disk, oblate, and prolate with different aspect ratios. These MPs were immersed in the blood plasma, which consisted of a suspension of red blood cells (RBCs). A simple shear flow was applied with moderate shear rate ($200{\mathrm{s}}^{-1}$). The fluid flow and immersed particles (RBCs and MPs) were solved by the lattice Boltzmann method (LBM) and lattice spring model, respectively. The fluid–structure interaction was coupled by the immersed boundary method. Additionally, we adopted a stochastic model to capture the adhesive behavior of MPs near the vessel wall for ligand–receptor binding. Without near-wall adhesion, the spherical particles demonstrated the strongest margination in the blood flow. It can be attributed to the large collision displacement with RBCs and small migration distance in the cross-stream direction under shear flow of spherical particles. Furthermore, under the influence of near-wall adhesion, the margination of differently shaped MPs was examined. Interestingly, the adhesion can either promote or impede the margination behavior depending on the shapes of MPs. When the major axes of MPs are smaller than or comparative to the thickness of the cell-free layer in the flow channel, the adhesion can promote margination of these MPs, while for MPs with large major axes, due to the near-wall adhesion effect, the reduced tumbling frequencies enable them to have enough time to interact with RBCs. In turn, the long interaction with RBCs can drag these MPs to the central stream of blood flow, impeding their margination. However, the prolate particles demonstrated distinct behaviors. Apart from tumbling, the transition to precession of prolate particles near the vessel wall results in the enhancement of margination. Overall, the spherical MPs outperform other nonspherical MPs for their high margination propensity under the influence of near-wall adhesion and moderate shear flow rate. This study might offer theoretical guidance to design MP-based drug carriers in blood flow with high efficacy.