Numerical simulation of deformability cytometry: Transport of a biological cell through a microfluidic channel

Abstract

Deformability cytometry is an important technique for label-free morphology-based characterization of large biological cell populations by physical properties. Numerical simulations are needed to extract mechanical properties of the measured cells that deform due to the hydrodynamic stress. Here, we look at real-time deformability cytometry (RT-DC) and extend the existing numerical models to take into account the correct three-dimensional geometry of the microfluidic chip as well as the time-dependent viscoelastic behavior. To this extent, the correct inflow and outflow of the narrow channel are considered and we solve the full bidirectional interaction between the non-Newtonian fluid of the extracellular medium and the viscoelastic cell. The findings are compared to the results of the previous works that assume axisymmetric flow and the limits of this approximation are discussed. We then analyze the stresses acting on the cell surface as well as the resulting deformations of the cell and explore the effect of higher cell viscosities on the deformation at the outflow. Finally, we propose an improved methodology to extract cytoplasmic viscosity based on experimentally observable shape relaxation inside the channel. Our results explain discrepancies in the current viscosity extraction from experimental measurements. With this most complete numerical description of RT-DC, to date, we pave the way for the full viscoelastic characterization of biological cells in high-throughput experiments.