Microfluidic labyrinth device separates particles and cells

In cancer research, isolating and characterizing circulating tumor cells from blood can aid with assessment of disease stage and monitor the efficacy of treatment strategies. This requires a robust method to separate cancer cells from blood cells.

Gangadhar and Vanapalli investigated inertial, size-based separation of cells and particles of controlled size in a microfluidic labyrinth device, which combines a spiral geometry with a multitude of tight-curvature U-turns.

“The microfluidic labyrinth device was previously reported in the literature, but we were interested in how the sharp U-turns can impact focusing for different particle and cell sizes and flow conditions,” said author Anirudh Gangadhar. “Additionally, we wanted to evaluate the influence of the complex flow field at the turn on focusing dynamics and separation.”

In the curved microfluidic channel, the fluid is pushed radially outwards by centrifugal forces. This creates an empty pocket at the center, which is immediately filled with liquid from the top and bottom of the channel. The ensuing Dean vortex drives lateral migration of cells and particles, which is necessary to achieve good size-based separation.

Sudden changes in channel curvature significantly changed the structure of the Dean vortices. The focusing increased or decreased depending on Reynolds number and particle and cell size. These effects were most pronounced for smaller particles and at higher Reynolds numbers. By using a smoother, sinusoidal U-turn of constant curvature, the team minimized fluctuations in the cross-sectional flow field, which is expected to improve the separation.

The labyrinth separated cells much better than rigid spherical particles of a similar size. In the future, the researchers aim to explore the effect of cell deformability on focusing hydrodynamics to examine why this may be the case.

Source: “Inertial focusing of particles and cells in the microfluidic labyrinth device: Role of sharp turns,” by Anirudh Gangadhar and Siva A Vanapalli, Biomicrofluidics (2022). The article can be accessed at https://doi.org/10.1063/5.0101582 .