Silicon microfluidic flow focusing

K. Keohane, D. Brennan, P. Galvin, B.T. Griffin. Silicon microfluidic flow focusing devices for the production of size controlled PLGA based drug loaded microparticles. Int J Pharm 467, 60-69, 2014. 

The very first flow focusing device was developed by Stone and coworkers [11] and was used for the emulsification of water in silicone oil. The geometry of this device is depicted in Figure 18.7 and was obtained after replication of a positive relief of the microchannels patterned in SU-8 photoresist. The authors named this FFD a microfluidic flow focusing device (MFFD). A few years after the development of this microsystem, Kumacheva and coworkers [12] used an MFFD (Figure 18.7, top left) made out of PDMS or polyurethane (PU) for the emulsification and polymerization of several multifunctional acrylates ethylene glycol dimethacrylate (EGDMA),... 

Organic core-shell droplets in an aqueous phase, which can be described as an O1/O2/W emulsion, can be produced in hydrophilic microfluidic channels [90-93]. In this case, localized surface modification is not needed when the organic phase to be encased (Oi) is more hydrophobic than the middle organic phase (O2). For example, Kumacheva and coworkers [90] produced photopolymerizable droplets that encapsulate smaller droplets of silicone oil through the flow focusing of a coaxial stream of the two organic phases. Encapsulation of fluorinated oil droplets in other organic phases has also been reported [91-93]. 

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