Focused surface acoustic waves induced microdroplets generation and its application for microgels

Abstract

We demonstrate a novel microdroplets generation method by using focused surface acoustic waves (FSAW). The method differs from previous work in the mechanism and the geometry structure of the chip, which is depend on FSAW rather than flow shearing. The acoustic radiation force arising from FSAW acts on the oil-water interface, breaking up the water into microdroplets whose size can be controlled by tuning the driving voltage and frequency of FSAW. This approach overcomes the limitation of microchannel structure and capillary number of the traditional microfluidic droplets formation methods, which enables a fully electrical control of microdroplets size, with a good uniformity. Further, the FSAWinduced microdroplets are used as templates to prepare microgels with uniform size, offering a new platform for the design and synthesis of monodispersed functional microspheres.

Single-cell droplet microfluidics for biomedical applications

“…Depending on whether an external force is needed, droplet generation typically includes two types, that is, passive and active generation of microdroplets, as shown in Table 1. 58,[63][64][65][66][67][68][69][70][71][72][73][74][75][76] Passive methods require no external force, and have simple structure of the microfluidic chip. The formation of droplets is controlled mainly by modifying the microchannel structure and two-phase velocity ratio.…”

“…3E). 69 They observed that size of the droplets was mainly determined by the frequency of the focusing surface acoustic waves, driving voltage, and velocity of the dispersed phase. Their method overcomes the limitations imposed by microchannel structure and capillary number in the general microfluidic droplet technology and has a high degree of uniformity along with a reduced system response time.…”

Regulating the Gas–Liquid Slug Flow in Microchannels through High-Frequency Pulsatile Perturbations

“…In the prevalent oil−water systems, active control on the droplet generation has been vastly investigated. 35,36 Relevant methods include using mechanical valves, 37,38 acoustic perturbations, 39,40 and electric or magnetic actuations. 41−43 In our previous work, synchronized generation of microdroplets of largely different sizes and viscosities was achieved 44,45 using a negative resistance microfluidic oscillator.…”

“…In the prevalent oil–water systems, active control on the droplet generation has been vastly investigated. , Relevant methods include using mechanical valves, , acoustic perturbations, , and electric or magnetic actuations. − In our previous work, synchronized generation of microdroplets of largely different sizes and viscosities was achieved , using a negative resistance microfluidic oscillator. − In another study, we demonstrated that using a PZT actuator, the droplet size and spacing, the generation frequency, and the morphology of double emulsions can be independently controlled . However, in contrast to the oil–water system, the active generation of droplets and bubbles in a gas–liquid flow has been rarely reported.…”

Trapping of Aqueous Droplets under Surface Acoustic Wave-Driven Streaming in Oil-Filled Microwells

“…SAWs have been combined into discrete microwells or microwell arrays to demonstrate the concentration of micro/nanoparticles and cells via microcentrifugation driven by the attenuation of waves in the liquid and have also been used for sensing, tissue culture, and cell culture applications. − Despite growing prominence, the SAW-driven manipulation of droplets in microwells has not received much attention to date. While several SAW-induced droplet-manipulation techniques including generation, − coalescence, − splitting, , and steering − of droplets have been demonstrated in microchannels, the manipulation of droplets in microwells using SAWs has been limited only to the ejection and coalescence of floating droplets.…”