Double Emulsion Templated Monodisperse Phospholipid Vesicles
Original entry: Warren Lloyd Ung, APPHY 225, Fall 2009
"Double Emulsion Templated Monodisperse Phospholipid Vesicles"
Ho Cheung Shum, Daeyeon Lee, Insun Yoon, Tom Kodger, and David A. Weitz
Soft Matter Keywords
phospholipid vesicle, double emulsion, self-assembly
Shum et al. have developed a method for fabricating phospholipid vesicles from double emulsion templates using glass capillary microfluidic devices (see Figure 2). The double emulsions can be produced using previously published apparatus, which carefully controls the flow rates of the three different phases (two aqueous and one oil) to produce a single drop of aqueous solution within a single drop of oil in a continuous aqueous phase.
The vesicle is formed from the water/oil/water (W/O/W) double emulsion by utilizing a volatile organic solvent with dissolved phospholipids as the oil phase. When placed into contact with the aqueous solutions, the phospholipids adsorb to the water/oil and oil/water interfaces. The volatile oil phase is then allowed to evaporate slowly, leaving a phospholipid bi-layer or a phospholipid vesicle behind.
Vesicles provide a robust delivery mechanism and are in fact used in cells to transport various materials. Note that the two aqueous phases need not be identical, as a result, the inner aqueous phase can contain a desirable aqueous solution, for instance a drug, designed for release at a later time. This method of creating vesicles yields uniform vesicle size as well since they are made from a monodisperse double emulsion (ie. all the double emulsions are approximately the same).
Soft Matter Discussion
The device used here takes advantage of the fact that phospholipids act as surfactants which self-assemble into a layer at each interface between oil and water. This creates a reverse micelle within a larger micelle. As the solvent is evaporated, the micelle and reverse micelle are brought into contact, forming a phospholipid bi-layer. The device exploits the ability to create double emulsions with well-controlled drop sizes to control the final size of the vesicle. By utilizing the double emulsion device and carefully selecting the oil phase to be volatile, the technique results in a relatively high encapsulation efficiency producing vesicles containing the desired inner aqueous phase.