Droplet Manipulations in Two Phase Flow Microfluidics

Abstract

Even though droplet microfluidics has been developed since the early 1980s, the number of applications that have resulted in commercial products is still relatively small. This is partly due to an ongoing maturation and integration of existing methods, but possibly also because of the emergence of new techniques, whose potential has not been fully realized. This review summarizes the currently existing techniques for manipulating droplets in two-phase flow microfluidics. Specifically, very recent developments like the use of acoustic waves, magnetic fields, surface energy wells, and electrostatic traps and rails are discussed. The physical principles are explained, and (potential) advantages and drawbacks of different methods in the sense of versatility, flexibility, tunability and durability are discussed, where possible, per technique and per droplet operation: generation, transport, sorting, coalescence and splitting.

Generation and manipulation of hydrogel microcapsules by droplet-based microfluidics for mammalian cell culture

“…Sorting techniques are classified as either “active” or “passive”. Active sorting relies on external power, such as electric fields, magnetic fields, acoustic waves, and optical forces, for the detection and deflection of microcapsules of interests 52 . Passive sorting, on the other hand, is performed without any extra power source, usually by exploiting the dynamic interactions between the fluid flow field and suspended microcapsules under specific experimental conditions 128 .…”

“…The size, components, structure, and properties of the cell-laden microcapsules can be tuned via multiphase microfluidic dynamics 48–51 . In addition, various on-chip manipulation strategies, such as fission, fusion, and separation, could be streamlined together on miniaturized devices to improve the qualities of microcapsules 48, 52 .…”

Electrode-assisted trapping and release of droplets on hydrophilic patches in a hydrophobic microchannel

“…Compared to only using electrowetting for all droplet manipulations (Malic et al 2009), the addition of two-phase flow microfluidics helps in the release of a droplet from a patch. Furthermore, microfluidics enables the high-speed generation of picoliter-sized droplets (Pit et al 2015b), which, for instance, can contain single cells (Chabert and Viovy 2008). These small volumes are required to quickly reach sufficient concentrations of cell-excreted molecules inside the droplets to enable SPR detection.…”

“…One thing must be noted: by using protocols involving individual droplets that have to perform complicated tasks, a manipulation method is required. Many methods have been developed (Chen and Jiang 2012;Cho et al 2003;Pit et al 2015b). For combination with SPR, pneumatic membrane valves (Luo et al 2008) and electrowetting-on-dielectric (EWOD) (Malic et al 2009(Malic et al , 2011 have been used.…”

Study of flow behaviors of droplet merging and splitting in microchannels using Micro-PIV measurement

“…Different strategies have been developed for microdroplet manipulations (Day et al 2012; Fatoyinbo and Labeed 2015), such as microdroplet generation (Wu et al 2009; Wang et al 2010; Chong et al 2016), merging (Gu et al 2011; Wu et al 2014; Pit et al 2015), splitting (Christopher et al 2009; Pit et al 2015), injecting (Abate et al 2010), mixing (Song et al 2003) and sorting (Schmid et al 2014; Salánki et al 2014). However, the microdroplet flow behaviors during these manipulations are complex due to the deformable interface of the microdroplets and the variations of interfacial tension (Liu et al 2007; Christopher et al 2009; Baroud et al 2010; Huerre et al 2015; Wang et al 2015a, b).…”