(224a) On the Surface Adsorption of Colloidal Particles in Microfluidic Flows

Shaqfeh, E. S. G., Stanford University
Fitzgibbon, S., Stanford University

Recently, there have been a host of microfluidic flow experiments focused on assessing the efficacy of creating surface adsorption of colloidal particles in flow. Most of these experiments are designed to test a variety of formulations of drug delivery and cancer nanotherapy particles. The relationship between the adsorption rates in these in vitro experiments and the associated therapeutic application is therefore of crucial importance in assessing the particle designs. However, this relationship is far from straightforward owing in part to the fact that the nonequilibrium adsorption rates of functionalized particles, even on fluidic channel surfaces that are uniformly coated with the appropriate receptors, can vary greatly because of the variation in shear rate at the channel walls. We therefore examine the theoretical problem of small particle adsorption in a microfluidic channel of arbitrary cross section including the Taylor-Dispersion and average adsorption rates under conditions where i) an appropriate Dahmkohler number, Da, is small but the adsorption rate is an arbitrary smooth function of position along the cross section, and ii) The value of Da is arbitrary. In the former case, we develop a Taylor-Dispersion type theory using the method of averaged equations which demonstrates that the average adsorption rates are very sensitive to the cross sectional geometry. In case ii) we develop Brownian dynamics simulations. In both cases, we demonstrate that certainly care must be taken in assessing the efficacy of adsorption via in vitro (i.e. rectangular channel) experiments versus the in vivo microcirculation application. We finish by discussing applications of our theory where the diffusive process is created by shear induced diffusion in a flowing suspension.