Anti-margination of microparticles and platelets in the vicinity of branching vessels

TL;DR

This study combines 3D simulations and in vivo microscopy to show that microparticles and platelets tend to be displaced from vessel walls to the center after vessel confluences, affecting their distribution in blood flow.

Contribution

It reveals the anti-margination effect of confluences on microparticles and platelets, a phenomenon not observed at bifurcations, supported by both simulations and experimental validation.

Findings

Cell-free layer forms after vessel confluence and contains microparticles.

Anti-margination persists up to 100 μm downstream of confluence.

Bifurcations do not produce similar margination effects.

Abstract

We investigate the margination of microparticles/platelets in blood flow through complex geometries typical for in vivo vessel networks: a vessel confluence and a bifurcation. Using 3D Lattice-Boltzmann simulations, we confirm that behind the confluence of two vessels a cell-free layer devoid of red blood cells develops in the channel center. Despite its small size of roughly one micrometer, this central cell-free layer persists for up to 100 $\mu$m after the confluence. Most importantly, we show from simulations that this layer also contains a significant amount of microparticles/platelets and validate this result by in vivo microscopy in mouce venules. At bifurcations, however, a similar effect does not appear and margination is largely unaffected by the geometry. This anti-margination towards the vessel center after a confluence may explain in vivo observations by Woldhuis et al. [Am. J. Physiol. 262, H1217 (1992)] where platelet concentrations near the vessel wall are seen to be much higher on the arteriolar side (containing bifurcations) than on the venular side (containing confluences) of the vascular system.