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Review
. 2018 Jun 1;18(6):1762.
doi: 10.3390/s18061762.

Progress of Inertial Microfluidics in Principle and Application

Yixing Gou  1 , Yixuan Jia  2 , Peng Wang  3 , Changku Sun  4
Affiliations
Review

Progress of Inertial Microfluidics in Principle and Application

Yixing Gou et al. Sensors (Basel). .

Abstract

Inertial microfluidics has become a popular topic in microfluidics research for its good performance in particle manipulation and its advantages of simple structure, high throughput, and freedom from an external field. Compared with traditional microfluidic devices, the flow field in inertial microfluidics is between Stokes state and turbulence, whereas the flow is still regarded as laminar. However, many mechanical effects induced by the inertial effect are difficult to observe in traditional microfluidics, making particle motion analysis in inertial microfluidics more complicated. In recent years, the inertial migration effect in straight and curved channels has been explored theoretically and experimentally to realize on-chip manipulation with extensive applications from the ordinary manipulation of particles to biochemical analysis. In this review, the latest theoretical achievements and force analyses of inertial microfluidics and its development process are introduced, and its applications in circulating tumor cells, exosomes, DNA, and other biological particles are summarized. Finally, the future development of inertial microfluidics is discussed. Owing to its special advantages in particle manipulation, inertial microfluidics will play a more important role in integrated biochips and biomolecule analysis.

Keywords: Dean vortex; inertial microfluidics; lab-on-a-chip; particle manipulation.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Schematic of the focusing position of particles migrating through channels with different cross-section shapes: (a) circular channel; (b) square channel; (c) high-aspect-ratio rectangular channel; and (d) low-aspect-ratio rectangular channel.
Figure 2
Figure 2
Secondary flow in cross-section. Ref. [40]. Copyright (2009), with permission from the Royal Society of Chemistry.
Figure 3
Figure 3
Distribution of equilibrium positions with an increase in velocity in different cross-sections: (a) square channel and (b) rectangular channel.
Figure 4
Figure 4
(a) Flow field of FLS; (b) Flow field of FLW; (c) Flow field distribution in channel and inertial-lift-force schematic diagram.
Figure 5
Figure 5
Superposition of effects of inertial migration and secondary flow on particles in curved channel cross-section. Ref. [40]. Copyright (2009), with permission from Royal Society of Chemistry.
Figure 6
Figure 6
Applications of straight-rectangular-channel inertial microfluidics. (a) Counting and differentiation of red blood cells and leukocytes in blood. Ref. [23]. Copyright (2009), with permission from Royal Society of Chemistry; (b) Separating pathogenic bacteria cells from diluted blood. Ref. [57]. Copyright (2010), with permission from Wiley Periodicals, Inc.; (c) Inertial focusing and ordering of Euglena gracilis. Ref. [58]. Copyright (2017), with permission from Springer Nature; (d) Inertial manipulation of bubbles in rectangular microfluidics channels. Ref. [60]. Copyright (2018), with permission from Royal Society of Chemistry.
Figure 7
Figure 7
Applications of contraction-expansion-array-channel inertial microfluidics. (a) Enriching malaria parasites from blood to facilitate a more reliable and specific PCR-based malaria detection. Ref. [7]. Copyright (2014), with permission from Royal Society of Chemistry; (b) High-throughput vortex chip that integrates a crowd of CEA channels to enrich rare circulating tumor cells (CTC). Ref. [66]; (c) Multi-stage flow fractionation (MS-MOFF) device designed for separating breast cancer cells from blood. Ref. [67]. Rights managed by AIP Publishing; (d) CEA channel simulated by continuous microcolumns to enrich CTCs. Ref. [68]. Copyright (2013), with permission from Royal Society of Chemistry; (e) Asymmetric CEA channel used to separate various kinds of cancer cells with high recovery and high throughput. Ref. [69]. Copyright (2013), with permission from American Chemical Society; (f) Particle capture and separation along unique particle trajectory made by CEA channel. Ref. [9]. Copyright (2017), with permission from Royal Society of Chemistry.
Figure 8
Figure 8
Applications of arcuate channel inertial microfluidics. (a) Three-dimensional hydrodynamic focusing device which can serve as a basis for microfluidic flow cytometry. Ref. [73]. Copyright (2013), with permission from Royal Society of Chemistry; (b) Continuous airborne microorganism collector for applications in real-time bioaerosol detection. Ref. [74]. Copyright (2017), with permission from American Chemical Society; (c) Labyrinth formed by high number of arcuate channels to separate satellite cells and fibroblasts. Ref. [75].
Figure 9
Figure 9
Applications of sinusoidal-channel inertial microfluidics. (a) System put forward to separate cells with high throughput of 1 g/h. Ref. [78]; (b) Microfluidic concentration for harvesting cyanobacterium Synechocystis sp. PCC 6803. Ref. [80]. Copyright (2017), with permission from Elsevier B.V. All rights reserved; (c) Square-wave channel to realize focusing of particles without effects of sheath flow or external force field. Ref. [82]. Copyright (2013), with permission from Springer-Verlag Berlin Heidelberg.
Figure 10
Figure 10
Applications of spiral-channel inertial microfluidics. (a) Sheathless flow cytometry system based on principle of Dean-coupled inertial microfluidics. Ref. [88]. Copyright (2009), with permission from Springer Nature; (b) Spiral system to realize enrichment of CTCs with recovery of 85% and 99.99% depletion of white blood cells in whole blood. Ref. [90]. Copyright (2015), with permission from Springer Nature; (c) Spiral microfluidic device with trapezoidal cross-section. Ref. [94]. Copyright (2017), with permission from Springer Nature; (d) Redesign of outlet channel as a series of side-branching channels perpendicular to main channel to separate 7-μm, 10-μm, and 15-μm fluorescent beads. Ref. [97]; (e) Three-dimensional spiral inertial focusing device using glass capillary tubes to realize separation of particles with 100% efficiency. Ref. [99]. Rights managed by AIP Publishing; (f) Method to isolate bacteria from whole blood rapidly based on principle of Dean flow. Ref. [102].
Figure 11
Figure 11
Applications of integration of inertial microfluidics and other active microfluidics. (a) Schematic diagram of CTC-iChip, which contains deterministic lateral displacement, inertial focusing in sinusoidal channel, and magnetophoresis sorting. Ref. [113]. Copyright (2014), with permission from Springer Nature; (b) Micromixer unit integrated cancer cells and microbeads with high efficiency (97.1%) and inertial flow unit for detection and separation on centrifugal platform. Ref. [116]. Copyright (2014), with permission from Springer Nature; (c) An innovative hybrid DEP-inertial microfluidic platform for particle tunable separation. Ref. [111]. Copyright (2018), with permission from American Chemical Society; (d) An automated microfluidic instrument with a fully integrated microfluidic device. Ref. [115]. Copyright (2018), with permission from Elsevier B.V.
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