Recent advances in acoustic microfluidics and its exemplary applications

Abstract

Acoustic-based microfluidics has been widely used in recent years for fundamental research due to its simple device design, biocompatibility, and contactless operation. In this article, the basic theory, typical devices, and technical applications of acoustic microfluidics technology are summarized. First, the theory of acoustic microfluidics is introduced from the classification of acoustic waves, acoustic radiation force, and streaming flow. Then, various applications of acoustic microfluidics including sorting, mixing, atomization, trapping, patterning, and acoustothermal heating are reviewed. Finally, the development trends of acoustic microfluidics in the future were summarized and looked forward to.

FIG. 1.

Development, structures, and applications of acoustofluidics.

FIG. 2.

Schematic diagram of different types of acoustic waves propagating in a microchannel. (a) Traveling surface acoustic waves (TSAWs). (b) Standing surface acoustic waves (SSAWs). (c) Bulk acoustic waves (BAWs).

FIG. 3.

The configuration diagram of IDT with different structures. (a) A slanted IDT; (b) a focused IDT; (c) a chirped IDT.

FIG. 4.

(a) Schematic diagram of a BAW-based microfluidic device for droplet manipulation. (b) Photograph of the device front side. From Leibacher et al., Lab Chip 15(13), 2896–2905 (2015). Copyright 2015 Author(s), licensed under a Creative Commons Attribution (CC BY) License.

FIG. 5.

(a) A design using inclined grooves to enhance surface acoustic wave sorting and a schematic diagram of its sorting process. From Ung et al., Lab Chip 17(23), 4059–4069 (2017). Copyright 2017 Author(s), licensed under a Creative Commons Attribution (CC BY) License. (b) Numerical simulation of cell trajectories: (i) Acoustic radiation force is absent, (ii) ΔV = 1 V, (iii) ΔV = 3 V, and (iv) ΔV = 5 V. The color legend shows the diameter of the particles in μm. Reproduced with permission from Shamloo and Boodaghi, Ultrasonics 84, 234–243 (2018). Copyright 2018 Elsevier B.V. (c) Schematic illustration of the multi-stage device and tumor cell isolation. Reproduced with permission from Wang et al., Sens. Actuators B 258, 1174–1183 (2018). Copyright 2018 Elsevier B.V. (d) Schematic diagram of the hybrid acoustic sorting device for cell separation. From Zhou et al., RSC Adv. 9(53), 31186–31195 (2019). Copyright 2019 Author(s), licensed under a Creative Commons Attribution (CC BY) License.

FIG. 6.

Schematic presentation of 2D focusing of microparticles and the mechanisms of focusing two-dimensional particles in glass capillaries under different ultrasonic excitations. Reproduced with permission from Lei et al. Appl. Phys. Lett. 116(3), 033104 (2020). Copyright 2020 AIP Publishing LLC.

FIG. 7.

(a) Schematic of the CL-FSAW-based mixing device. The two fluids are mixed in the microchannel by applying an RF signal to the CL of the FIDT. In the A-A′ cross section view, leaky SAWs influenced the sample in the microchannel. Reproduced with permission from Nam et al., Sens. Actuators B 258, 991–997 (2018). Copyright 2018 Elsevier B.V. (b) Schematic diagram of the device and the working mechanism of 3D-dSAW microfluidics. Reproduced with permission from Nam and Lim, Sens. Actuators B 255, 3434–3440 (2018). Copyright 2018 Elsevier B.V.

FIG. 8.

(a) Schematic diagram of an array of PDMS micropillars and the process of droplet atomization around micropillars. Reproduced with permission from Cheung et al., Appl. Phys. Lett. 105(14), 144103 (2014). Copyright 2018 AIP Publishing LLC. (b) Schematic of the HYDRA device. Reproduced with permission from Marqus et al., Eur. J. Pharm. Biopharm. 151, 181–188 (2020). Copyright 2020 Elsevier B.V. (c) Schematic of the acoustomicrofluidic nebulization device and an image of new crystalline morphology produced by the device. Reproduced with permission from Ahmed et al., Adv. Mater. 30(3), 1602040 (2018). Copyright 2018 John Wiley & Sons.

FIG. 9.

(a) Illustration of droplet capture and release using acoustic microfluidics. Reproduced with permission from Jung et al., Anal. Chem. 89(4), 2211–2215 (2017). Copyright 2017 American Chemical Society. (b) SAW-based droplet trapping and release multi-height device. Reproduced with permission from Ahmed et al., Anal. Chem. 90(14), 8546–8552 (2018). Copyright 2018 American Chemical Society.

FIG. 10.

(a) Picture of the process of patterning particles into 2D patterns, and the direction of the blue arrow coincides with the direction of SAW propagation. Reproduced with permission from Zheng et al., Sens. Actuators A 284, 168–171 (2018). Copyright 2018 Elsevier B.V. (b) Schematic of acoustic levitation. The suspension containing embryonic stem cells is introduced into the suspension chamber and thrombin is added for the gelation process. The transducer is activated to generate acoustic waves that drive the cells to form a 3D multilayer structure. Reproduced with permission from Bouyer et al., Adv. Mater. 28(1), 161–167 (2016). Copyright 2018 John Wiley & Sons. (c) Schematic diagram of the experimental setup for 3D lines formed by microparticles with a diameter of 10 μm, and the illustration of a 3D structure similar to a crystal lattice. Reproduced with permission from Nguyen et al., Appl. Phys. Lett. 112(21), 213507 (2018). Copyright 2018 AIP Publishing LLC. (d) Particle patterns at different SAW frequencies [(i) 12.2, (ii) 24.0, and (iii) 42.2 MHz] and the change in position of two different size particles after changing the phase angle. Reproduced with permission from Tao et al., Sens. Actuators B 299, 126991 (2019). Copyright 2019 Elsevier B.V.

FIG. 11.

(a) Schematic diagram of the CFPCR chip and the infrared images of penetration depth [(ii) the focused IDT of 128.5 MHz,;(iii) the slanted IDT of 36, 32, 28, 24, and 20 MHz; (iv) the straight IDT of 16.1 MHz; and (v) the straight IDT of 9.8 MHz). From Ha et al., Sci. Rep. 5(1), 11851 (2015). Copyright 2015 Author(s), licensed under a Creative Commons Attribution (CC BY) License. (b) Schematic of the MHIFU device and TSL release. From Meng et al., Theranostics 5(11), 1203–1213 (2015). Copyright 2015 Author(s), licensed under a Creative Commons Attribution (CC BY) License. (c) Diagram of temperature comparison of three different thin-film SAW devices. Reproduced with permission from Wang et al., Sens. Actuators A 318, 112508 (2021). Copyright 2021 Elsevier B.V.