Intravenous injection of nanoparticles as drug delivery vehicles is a common practice used in in-vivo and clinical trials of therapeutic agents to target specific cancerous or pathogenic sites. The vascular flow dynamics of nanocarriers in human capillaries play an important role in the ultimate efficacy of this drug delivery method. This article reports an experimental study of the effect of nanoparticle size on their margination and adhesion propensity in micro fabricated microfluidic channels of a half elliptical cross-section. Spherical polystyrene particles ranging in diameter from 60 to 970 nm were flown in the microchannels and individual particles adhered to either the channel’s top or bottom wall were imaged using fluorescence microscopy. The results show a significant increase in adhesion for particles with diameter below 200 nm as well as the emergence of a critical nanoparticle diameter of about 970 nm, where no nanoparticle adherence was observed on the top wall. For the same particle number concentration, the total volume of the nanoparticles adhered to the top and bottom walls was found to increase with decreasing diameter for diameters less than 200 nm. The results are explained by the competition between Brownian motion, gravity and hemodynamic forces on the nanoparticles. These findings on the flow behavior of spherical nanoparticles in artificial micro-capillaries provide further insight for the rational design of nanocarriers for targeted cancer therapeutics.

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