Wetting-induced formation of controllable monodisperse multiple emulsions in microfluidics

Abstract

Multiple emulsions, which are widely applied in a myriad of fields because of their unique ability to encapsulate and protect active ingredients, are typically produced by sequential drop-formations and drop-encapsulations using shear-induced emulsification. Here we report a qualitatively novel method of creating highly controlled multiple emulsions from lower-order emulsions. By carefully controlling the interfacial energies, we adjust the spreading coefficients between different phases to cause drops of one fluid to completely engulf other drops of immiscible fluids; as a result multiple emulsions are directly formed by simply putting preformed lower-order emulsion drops together. Our approach has highly controllable flexibility. We demonstrate this in preparation of both double and triple emulsions with a controlled number of inner drops and precisely adjusted shell thicknesses including ultra-thin shells. Moreover, this controllable drop-engulfing-drop approach has a high potential in further investigations and applications of microfluidics. Importantly, this innovative approach opens a window to exploit new phenomena occurring in fluids at the microscale level, which is of great significance for developing novel microfluidics.

Structured Biodegradable Polymeric Microparticles for Drug Delivery Produced Using Flow Focusing Glass Microfluidic Devices

“…Emulsification can be carried out using conventional top-down methods based on breaking larger droplets into smaller ones, 21 such as mechanical agitation, high-pressure homogenization, and sonication or bottom-up methods, based on direct drop-by-drop generation, such as membrane emulsification [22][23][24] , microchannel emulsification, 25 and microfluidic techniques. [26][27][28][29] Conventional emulsification methods are energy intensive and often lead to polydispersed microspheres. Microfluidic methods allow production of particles with low polydispersity (CV = Standard Deviation/Mean < 3%) and high encapsulation efficiency that are perfectly tailored to meet the needs of pharmaceutical industry.…”

Microfluidic approach for encapsulation via double emulsions

“…For example, by adding separating agents, phase separation of single drop can be induced; this produces double emulsions evolved from one single drop, with controllable size and efficient encapsulation of components into the desired inner and outer drops (Figure 1i,j) [29 ]. Moreover, manipulation of the interfacial energies of two different drops also allows wetting-induced spreading of one drop over another drop to produce controllable double emulsions from drop pairs in microchannel (Figure 1k) [28 ]. These results demonstrate the diversity of microfluidic techniques for generating double emulsions for controllable encapsulation.…”

“…(i,j) Sequential optical snapshots (i) showing the evolution of single drop into double emulsions via phase-separation, and fluorescence image of resultant double emulsions (j)showing that the encapsulated components, water-soluble (sulforhodamine B) dyes (red) and oil-soluble (fluorescein) dyes (green), can be respectively entrapped into the inner core and the outer shell[29 ]. (k) Wetting-induced formation of double emulsions from two single drops[28 ].…”

Controllable microfluidic strategies for fabricating microparticles using emulsions as templates

“…Alternatively, by manipulating the interfacial energy as well as the spreading coefficients of different dispersed phases and the continuous phase, droplets of one phase can spread onto droplets of another phase via a wetting process, to produce complex multiple emulsions from pairs of simple emulsion droplets in a microchannel ( Fig. 3(e) and (f)) (Deng et al, 2013). Because the size and composition of the primary emulsion droplets used to construct the multiple emulsions can be precisely manipulated, such microfluidic strategies can provide excellent control over the size, structure and composition of the resultant multiple emulsions ( Fig.…”