Numerical and analytical approaches to an advection-diffusion problem at small Reynolds number and large Péclet number

Abstract

Obtaining a detailed understanding of the physical interactions between a cell and its environment often requires information about the flow of fluid surrounding the cell. Cells must be able to effectively absorb and discard material in order to survive. Strategies for nutrient acquisition and toxin disposal, which have been evolutionarily selected for their efficacy, should reflect knowledge of the physics underlying this mass transport problem. Motivated by these considerations, in this paper we discuss the results from an undergraduate research project on the advection-diffusion equation at small Reynolds number and large Péclet number. In particular, we consider the problem of mass transport for a Stokesian spherical swimmer. We approach the problem numerically and analytically through a rescaling of the concentration boundary layer. A biophysically motivated first-passage problem for the absorption of material by the swimming cell demonstrates quantitative agreement between the numerical and analytical approaches. We conclude by discussing the connections between our results and the design of smart toxin disposal systems.

Separation and enrichment of sodium-motile bacteria using cost-effective microfluidics

“…For example, bacteria may get separated due to advection of fluid flow rather than diffusion. Estimations of Peclet number for motile bacteria at our flow rates (P e = 26310) (20) showed that the bacterial sample flown through the channel length of our device (i.e., 20 mm) would only separate due to advection of fluid flow after the bacteria travels 26,310 times the channel width (1 mm) i.e., approximately 26 meter long. This agreed with our observation that we were not able to collect cells at outlet 2 when we ran both inlets in sodium-free solution (SI Fig.…”