Hydrodynamic resistance and mobility of deformable objects in microfluidic channels

This work reports experimental and theoretical studies of hydrodynamic behaviour of deformable objects such as droplets and cells in a microchannel. Effects of mechanical properties including size and viscosity of these objects on their deformability, mobility, and induced hydrodynamic resistance are investigated. The experimental results revealed that the deformability of droplets, which is quantified in terms of deformability index (D.I.), depends on the droplet-to-channel size ratio rho and droplet-to-medium viscosity ratio lambda. Using a large set of experimental data, for the first time, we provide a mathematical formula that correlates induced hydrodynamic resistance of a single droplet Delta R-d with the droplet size rho and viscosity lambda. A simple theoretical model is developed to obtain closed form expressions for droplet mobility phi and Delta R-d. The predictions of the theoretical model successfully confront the experimental results in terms of the droplet mobility phi and induced hydrodynamic resistance Delta R-d . Numerical simulations are carried out using volume-of-fluid model to predict droplet generation and deformation of droplets of different size ratio rho and viscosity ratio lambda, which compare well with that obtained from the experiments. In a novel effort, we performed experiments to measure the bulk induced hydrodynamic resistance Delta R of different biological cells (yeast, L6, and HEK 293). The results reveal that the bulk induced hydrodynamic resistance Delta R is related to the cell concentration and apparent viscosity of the cells. (C) 2014 AIP Publishing LLC.