Soft inertial microfluidics for high throughput separation of bacteria from human blood cells

Abstract

We developed a new approach to separate bacteria from human blood cells based on soft inertial force induced migration with flow defined curved and focused sample flow inside a microfluidic device. This approach relies on a combination of an asymmetrical sheath flow and proper channel geometry to generate a soft inertial force on the sample fluid in the curved and focused sample flow segment to deflect larger particles away while the smaller ones are kept on or near the original flow streamline. The curved and focused sample flow and inertial effect were visualized and verified using a fluorescent dye primed in the device. First the particle behaviour was studied in detail using 9.9 and 1.0 µ m particles with a polymer-based prototype. The prototype device is compact with an active size of 3 mm 2 . The soft inertial effect and deflection distance were proportional to the fluid Reynolds number (Re) and particle Reynolds number (Re p ), respectively. We successfully demonstrated separation of bacteria (Escherichia coli) from human red blood cells at high cell concentrations (above 10 8 /mL), using a sample flow rate of up to 18 µL/min. This resulted in at least a 300-fold enrichment of bacteria at a wide range of flow rates with a controlled flow spreading. The separated cells were proven to be viable.Proteins from fractions before and after cell separation were analyzed by gel electrophoresis and staining to verify the removal of red blood cell proteins from the bacterial cell fraction. This novel microfluidic process is robust, reproducible, simple to perform, and has a high throughput compared to other cell sorting systems. Microfluidic systems based on these principles could easily be manufactured for clinical laboratory and biomedical applications.3

Hydrodynamic mechanisms of cell and particle trapping in microfluidics

“…These applications including but not limited to cell and particle focusing, [61][62][63] sorting, 64 separation, [65][66][67] self-assembly, 68 filtration, [69][70][71] and enrichment and trapping 72 are poised to be high-throughput due to their operation under high flow rates. Recent progress and potential future directions in the area of inertial microfluidics are discussed in a recent review article by Di Carlo.…”

Continuous separation of blood cells in spiral microfluidic devices

“…Inertial microfluidics takes advantage of hydrodynamic forces that act on cells to focus them within the flow. 5,6,[15][16][17][18][19][20]38 These forces cause cells to migrate across streamlines and order in equilibrium positions based on their size, leading to label-free cell separation, purification, and enrichment in a microfluidic device. Inertial migration was first observed by Segre and Silberberg 39 in 1960s who experimented with neutrally buoyant particles in capillaries and observed a narrow annulus formation at $0.2D from walls of a capillary of diameter D. This migration behavior is believed to be caused by the balance of lift forces arising from the curvature of the parabolic velocity profile (the shear-induced inertial lift) and the interaction between particles and the channel wall (the wall-induced lift).…”

Efficient manipulation of microparticles in bubble streaming flows

“…Many applications require control over position and concentration of the objects in order to induce mixing, 3 chemical reactions, 4 biomolecular tagging, 5 or a host of other processes. The necessary manipulations of the objects often rely on actively applying various external force fields, including hydrodynamic (inertial), [6][7][8] electrokinetic, 9-12 dielectrophoretic, [13][14][15][16] magnetic, 17,18 optical 19,20 or acoustic [21][22][23] (ultrasound standing waves, surface acoustic waves) forces. Such forces will usually act differently on particles depending on their size, geometry, and mechanical or electromagnetic properties; as a result, particle separation and sorting become possible.…”