(a) Schematic of the vortex-aided inertial microfluidic design. Flow resistances r of the side outlet channel and R the main outlet channel can be modulated to optimize device performance. (b) Illustration of the separation principle. The red dashed line indicates the boundary streamline of separating the main and sheath flow regions. (c) Bright-filed images at various downstream positions illustrating the separation phenomenon at Re = 110. Re was calculated using input flow rate (0.5 ml/min) and focusing channel geometry (50 μm × 100 μm w × h).
Optimization of flow conditions for particle capture. (a) ESI CFD-ACE+ simulation shows the boundary streamline (red line) of the main flow and sheath flow regions. Only one of the two symmetric chambers is shown. Inset figure indicates definitions of db and dp . (b) Boundary streamline position db is modulated by Re. (c) Experimental measurement of particle focusing position dp of various sized particles. (d) Boundary position db changes at different channel height h. Grey hollow circles represent the boundary position, while the blue solid circles represent focusing position of 21 μm particles. dm is defined as a difference between the particle focusing position and location of the separation boundary, given as dm = dp – db . The investigated area is the upper left quadrant of the channel cross-section, shaded blue area in the inset 3D schematic.
(a) Experimental observations demonstrating behavior of 23 μm diameter particles at different Re. Only one of the two symmetric chambers is shown. (b) Concentration of 23 μm diameter particles from side outlet (green) and main outlet (purple) at various Re. Inset figure shows the corresponding separation efficiency η at various Re. Error bars represent stand deviation (n = 3).
Optimization of flow conditions for particle release. (a) Experiments with tracer-beads (TRITC) demonstrating geometric evolution of the vortex as Re increases. Only one of the two symmetric chambers is shown. The white dashed line indicates the vortex area. Diagrams of the larger particle route show particle at different Re. (b) Experimental (red circle) and simulation (blue circle) measurements showing the increasing vortex size at 0 < Re < 400.
Optimization of the outlets. (a) Microfluidic network of the device and the corresponding electrical circuit (EC) model. (b) Schematics illustrating shift of boundary streamline at different r/R. (c) ESI CFD-ACE+ simulation illustrates boundary streamline position db for 1 < r/R < 100. (d) ESI CFD-ACE+ simulation demonstrates geometric progression of the vortex at different r/R, and (e) the corresponding quantitative measurements of vortex dimension from both numerical models (blue circles) and experimental (red circles) at for 1 < r/R < 100. (f) Experimental observations illustrate motion of the 23 μm (FITC) and 15.5 μm (TRITC) diameter particles at different r/R ratios at Re = 110.
Ultra-selective separation of 21 μm from 18.5 μm diameter particles in a device with r/R = 5. (a) The top bright-field image shows separation at the device chamber. The lower three images show particles at the inlet, side outlet and main outlet. The black dots are 21 μm diameter non-fluorescent particles in bright-field view. The white dots are fluorescent 18.5 μm diameter particles. (b) Histograms of inlet, side outlet and main outlet samples indicate the efficient separation. (c) Concentration of 21 μm and 18.5 μm diameter particles in inlet, side and main outlet samples. Normalized count shows a separation efficiency of ∼90% for both particles. Error bars represent stand deviation (n = 3).
Continuous extraction from blood sample. (a) Separation of 21 μm diameter particles from human blood in a device with r/R = 10. The top bright-field image shows separation at the device chamber. The lower three images show the particles at the inlet, side outlet and main outlet. (b) The concentration of 21 μm diameter particles in the side outlet increases 5 × as compared to the inlet. Normalized count of 21 μm diameter particles in side and main outlets shows a capture efficiency of 86%, while 99% RBCs exit through main outlet. Error bars represent the stand deviation of three individual experiments.
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