In recent years, considerable research efforts have been devoted to new types of microscopic biomedical devices. A prominent example is nanoparticles which are injected into the blood stream for targeted drug delivery. It was shown experimentaly that such particles move towards the walls of a straight blood vessel while the red blood cells are predominantly encountered in the center. Velocity fluctuations are the root root cause of particle migration. My question is, is there any difference between migration and margination and why do these particle are expelled toward the wall?
Do you have a reference showing that nanoparticles are expelled to the wall? This would be an interesting case that would allow for greater marginalization and targeting of inflamed endothelium. However, as far as I am aware, nanoparticles tend to move in the center of blood vessels with the RBCs, whereas micron-scale particles phase separate. For example, see Namdee et al., 2013 Langmuir 29(8):2530 - doi:10.1021/la304746p.
Your question piqued my interest and I came across a good answer. The main factor determining the margination is the Stokes number, which describes the relative significance of partial inertia (St = rho*a^2*S/mu, where rho is particle density, a is particle diameter, S is wall shear rate, and mu is fluid viscosity). If St >> 0.1, the particle inertia will be significant and there will be a net flux of the particle away from the fluid streamlines and towards the wall. This occurs under physiological conditions for micrometer-scale particles. If St
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