Effect of tube diameter and capillary number on platelet margination and near-wall dynamics

TL;DR

This study investigates how tube diameter and capillary number influence platelet movement near vessel walls, revealing that margination depends on flow conditions and confinement, with implications for blood flow dynamics.

Contribution

It demonstrates the role of non-diffusive radial transport and flow regimes in platelet margination, highlighting the effects of tube size and capillary number on platelet dynamics.

Findings

Margination facilitated by non-diffusive radial transport at Ca > 0.2.

Platelet trapping in the cell-free layer is reversible for Ca ≤ 0.2.

Tumbling rate increases with tube diameter D.

Abstract

The effect of tube diameter $D$ and capillary number $Ca$ on platelet margination in blood flow at $\approx 37\%$ tube haematocrit is investigated. The system is modelled as three-dimensional suspension of deformable red blood cells and nearly rigid platelets using a combination of the lattice-Boltzmann, immersed boundary and finite element methods. Results show that margination is facilitated by a non-diffusive radial platelet transport. This effect is important near the edge of the cell-free layer, but it is only observed for $Ca > 0.2$, when red blood cells are tank-treading rather than tumbling. It is also shown that platelet trapping in the cell-free layer is reversible for $Ca \leq 0.2$. Only for the smallest investigated tube ($D = 10 \mu\text{m}$) margination is essentially independent of $Ca$. Once platelets have reached the cell-free layer, they tend to slide rather than tumble. The tumbling rate is essentially independent of $Ca$ but increases with $D$. Tumbling is suppressed by the strong confinement due to the relatively small cell-free layer thickness at $\approx 37\%$ tube haematocrit.