Microfluidic Control of Coexisting Chemical Microenvironments within Multiphase Water-in-Fluorocarbon Droplets

Abstract

The use of aqueous polymer-based phase separation within water-in-oil emulsion droplets provides a powerful platform for exploring the impact of compartmentalization and preferential partitioning on biologically relevant solutes. By forming an emulsion, a bulk solution is converted into a large number of chemically isolated microscale droplets. Microfluidic techniques provide an additional level of control over the formation of such systems. This enables the selective production of multiphase droplets with desired solution compositions and specific characteristics, such as solute partitioning. Here, we demonstrate control over the chemical microenvironment by adjusting the composition to increase tie line length for poly­(ethylene glycol) (PEG)-dextran aqueous two-phase systems (ATPS) encapsulated within multiphase water-in-fluorocarbon oil emulsion droplets. Through rational adjustment of microfluidic parameters alone, ATPS droplets containing differing compositions could be produced during the course of a single experiment, with the produced droplets demonstrating a controllable range of tie line lengths. This provided control over partitioning behavior for biologically relevant macromolecules such that the difference in local protein concentration between adjacent phases could be rationally tuned. This work illustrates a broadly applicable technique to rationally create emulsified multiphase aqueous systems of desired compositions through the adjustment of microfluidic parameters alone, allowing for easy and rapid screening of various chemical microenvironments.

Aqueous Two-Phase Systems within Selectively Permeable Vesicles

“…Alternatively, because vesicle membranes, much like cell membranes, are permeable to water, osmosis provides another route to influence phase separations and solute partitioning across different phases. − Unfortunately, conventional methods to vesicle fabrication result in an uncontrolled encapsulation of macromolecules within the vesicles, which limits the utility of current vesicle models for quantitative studies on the phase behavior of ATPSs. The control encapsulation enabled by droplet-based microfluidic technologies overcomes the encapsulation limitations of conventional methods, enabling the formation of multiphase water-in-oil (W/O) droplets with specific phase compositions and thus solute partitioning. − However, a multiphase W/O drop poorly mimics the rich dynamics and phase behavior that arise in the cell as a result of having a membrane separating the internal and external aqueous phases. It is therefore essential to achieve control over the encapsulation of ATPSs in vesicles to dynamically control phase separations.…”

“…The control encapsulation enabled by droplet-based microfluidic technologies overcomes the encapsulation limitations of conventional methods, enabling the formation of multiphase water-in-oil (W/O) droplets with specific phase compositions and thus solute partitioning. 17 − 21 However, a multiphase W/O drop poorly mimics the rich dynamics and phase behavior that arise in the cell as a result of having a membrane separating the internal and external aqueous phases. It is therefore essential to achieve control over the encapsulation of ATPSs in vesicles to dynamically control phase separations.…”