Dewetting-Induced Membrane Formation by Adhesion of Amphiphile-Laden Interface

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Entry by Max Darnell, AP 225, Fall 2011


Title: Dewetting-Induced Membrane Formation by Adhesion of Amphiphile-Laden Interface

Authors: Shum HC, Santanach-Carreras E, Kim JW, Ehrlicher A, Bibette J, Weitz DA

Journal: J Am Chem Soc. 2011 Mar 30;133(12):4420-6. Epub 2011 Mar 7


In biology, the cell utilizes a number of structures to encapsulate aqueous solutions. For example, liposomes and vesicles can encapsulate proteins and other cargo, as well isolate the surrounding environment from deleterious internal conditions such as low pH. Such methods are effective in biology in allowing enzymes to function at varied conditions without impacting the rest of the cell, as well as providing a means to transport cargoes within and outside the cell.

The artificial leveraging of such structures for bioengineering uses holds great promise in a number of areas. For instance, polymersomes could be used for drug delivery, intra-cell bioreactors for enzymatic reactions, and could be used in artificial cells. one of the main issues, however, with developing artificial vesicles is that there is very little control over vesicle formation, as the process is mainly mediated by self-assembly, which is poorly understood. One alternative method has involved a stream of polymer containing suspension directed at the cargo of choice, but such a method has showed poor efficacy due to poor control over all of the polymer in the stream.

In the past, water-in-oil emulsions have been used to aggregate emulsions, but an approach involving water-in-oil emulsions formed via capillary microfluidics is a promising technique to create polymersomes with a high degree of control.


Poly(ethylene glycol)-b-poly(lactic acid) [PEG(5000)-b-PLA(5000)] was chosen as the copolymer that would ultimately form the polymersome membrane. It was dissolved into a mixture of chloroform and hexane, and a double-emulsion was created via a previous method in a glass capillary microfluidic device. In this setup, the PEG is in the middle-phase while the PLA is in the solvent-phase. A relation yielding a negative spreading coefficient is given as follows:

Darnell2 1.jpg

A negative spreading coefficient implies that there is an attractive force between the outer-middle and middle-inner phases, thus yielding the micelle. Due to the difference in solubility involving hexane and chloroform and the negative spreading coefficient, it becomes energetically favorable for dewetting to take place as shown in Figure 1:

Figure 1: Attraction-induced dewetting in polymersome


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