Numerical simulations of cell sorting through inertial microfluidics

What is it about?

The dynamics of a cell suspended in a Newtonian liquid subjected to a pressure-driven flow at non-negligible inertia in cylindrical and square-cross-section microfluidic channels is studied through three-dimensional numerical simulations. The cell is modeled as an hyper-elastic particle. The cell-to-channel relative dimension is fixed to 0.2, whereas the Reynolds number Re, measuring the relative importance of liquid inertial and viscous forces, and the elastic capillary number Cae, measuring the relative importance of liquid viscous stress and solid elastic stress, are varied by several orders of magnitude. In a cylindrical tube, the cell migrates transversally to the flow direction until reaching a radial equilibrium position depending on Re and Cae. Given Re, the softer the cell (i.e., the larger Cae) the closer its equilibrium position to the tube axis, thus allowing for the separation of healthy and diseased cells which have similar dimensions, but different mechanical properties. In a channel with a square cross section, a much more complex dynamics is found. Depending on Re and Cae, the cell can either migrate to the channel centerline, to the closest median of the channel cross section (thus, four equilibrium positions can be identified due to symmetry), to the closest diagonal (again, four equilibrium positions), or to an intermediate position in between the median and the diagonal (eight equilibrium positions).

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Photo by National Cancer Institute on Unsplash

Photo by National Cancer Institute on Unsplash

Why is it important?

The equilibrium position diagrams can be used to design a microfluidic device to separate cells with similar dimensions, but different mechanical properties, e.g., healthy and diseased cells. Our findings show that cell separation would surely be more straightforward in cylindrical than in square cross-section channels, yet the latter are sometimes preferred in microfluidics due to easier manufacturing.

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