The physiological inflammation response depends upon the multibody interactions of blood cells in the microcirculation that bring leukocytes (white blood cells) to the vessel walls. We investigate the fluid mechanics of this using numerical simulations of 29 red blood cells and one leukocyte flowing in a two-dimensional microvessel, with the cells modeled as linearly elastic shell membranes. Despite its obvious simplifications, this model successfully reproduces the increasingly blunted velocity profiles and increased leukocyte margination observed at lower shear rates in actual microvessels. Red cell aggregation is shown to be unnecessary for margination. The relative stiffness of the red cells in our simulations is varied by over a factor of 10, but the margination is found to be much less correlated with this than it is to changes associated with the blunting of the mean velocity profile at lower shear rates. While velocity around the leukocyte when it is near the wall depends upon the red cell properties, it changes little for strongly versus weakly marginating cases. In the more strongly marginating cases, however, a red cell is frequently observed to be leaning on the upstream side of the leukocyte and appears to stabilize it, preventing other red cells from coming between it and the wall. A well-known feature of the microcirculation is a near-wall cell-free layer. In our simulations, it is observed that the leukocyte’s most probable position is at the edge of this layer. This wall stand-off distance increases with velocity following a scaling that would be expected for a lubrication mechanism, assuming that there were a nearly constant force pushing the cells toward the wall. The leukocyte’s near-wall position is observed to be less stable with increasing mean stand-off distance, but this distance would have potentially greater effect on adhesion since the range of the molecular binding is so short.
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February 2007
Research Article|
February 20 2007
Leukocyte margination in a model microvessel
Jonathan B. Freund
Jonathan B. Freund
Mechanical Science and Engineering and Aerospace Engineering,
University of Illinois at Urbana-Champaign
, Urbana, Illinois 61801
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Physics of Fluids 19, 023301 (2007)
Article history
Received:
March 11 2006
Accepted:
January 09 2007
Citation
Jonathan B. Freund; Leukocyte margination in a model microvessel. Physics of Fluids 1 February 2007; 19 (2): 023301. https://doi.org/10.1063/1.2472479
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