Fluid displacement during droplet formation at microfluidic flow-focusing junctions

Abstract

Microdroplets and microcapsules have been widely produced using microfluidic flow-focusing junction for biomedical and chemical applications. However, the multiphase microfluidic flow at the flow-focusing junction has not been well investigated. In this study, the displacement of two (core and shell) aqueous fluids that disperse into droplets altogether in a carrier oil emulsion was investigated both numerically and experimentally. It was found that extensive displacement of the two aqueous fluids within the droplet during its formation could occur as a result of the shear effect of the carrier fluid and the capillary effect of interfacial tension. We further identified that the two mechanisms of fluid displacement can be evaluated by two dimensionless parameters. The quantitative relationship between the degree of fluid displacement and these two dimensionless parameters was determined experimentally. Finally, we demonstrated that the degree of fluid displacement could be controlled to generate hydrogel microparticles of different morphologies using planar or nonplanar flow-focusing junctions. These findings should provide useful guidance to the microfluidic production of microscale droplets or capsules for various biomedical and chemical applications.

One step fabrication of hydrogel microcapsules with hollow core for assembly and cultivation of hepatocyte spheroids

“…In order to generate microcapsules with the desired core-shell morphology, it was critical to control fluid displacement of the miscible polymer solutions during droplet formation and crosslinking. [24] We found that tuning polymer solution viscosity and the timing of DTT presentation enabled minimal core-shell mixing while still allowing droplet capsules to relax toward a spherical shape with a uniform shell thickness. To modulate the rate of core-shell mixing, we added inert 35 kDa PEG at 0–20% w/v to the core channel.…”

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

“…As a result, Ө-shaped distribution of shell fluid and resultant hydrogel microcapsules can be formed post gelation (Fig. 2(D)) 81 . In addition, fluid displacement and associated mixing can alter the core size and constitution of 3D core-shell structured microcapsules (Fig.…”

“…Besides these three basic configurations, other modified devices were proposed for specific applications, such as the microcapillary coaxial glass devices to generate multiple emulsions 76, 77 and FFJ with two dispersed aqueous fluids to produce core-shell structured microcapsules 78, 79 . Some common types of hydrogel microcapsules with different internal fabrics, such as core-shell structured 80 , Ө-shaped 81 , and Janus 82 microcapsules, are illustrated in Fig. 2(G).…”

Microfluidic Encapsulation of Ovarian Follicles for 3D Culture

“…At the flow-focusing junction, the aqueous core and shell solutions were pinched into droplets by the oil emulsion flow due to the Rayleigh-Plateau instability 52–54 . Sodium alginate solution in the shell was crosslinked ( i.e.…”