Margination of 2D Platelet Microparticles in Blood.

Margination describes the movement of particles toward the endothelial wall within blood vessels. While there have been several studies tracking the margination of spherical particles in blood, the behavior of anisotropic particle shapes is not well described. In this study 2D platelet particles which possess many attractive qualities for use as a drug delivery system, with their high surface area allowing for increased surface binding activity, were directly monitored and margination quantified. The margination propensity of 1 and 2 μm 2D platelet particles was contrasted to that of 2 μm spherical particles at apparent wall shear rates (WSRs) of 50, 100, and 200 s -1 by both directly tracking labeled particles using fluorescent microscopy as well as using small-angle X-ray scattering (SAXS). For fluorescence studies, margination was quantified using the margination parameter M , which describes the number of particles found closest to the walls of a microfluidic device, with an M -value of 0.2 indicating no margination. Increased margination was seen in 2D platelet particles when compared to spherical particles tested at all flow rates, with M -values of 0.39 and 0.31 seen for 1 and 2 μm 2D platelet particles, respectively, while 2 μm spherical particles had an M -value of 0.21. Similarly, margination was observed qualitatively using SAXS, with increased scattering seen for platelet particles near the microfluidic channel wall. For all particles, increased margination was seen at increasing shear rates.