Stepwise Synthesis of Giant Unilamellar Vesicles on a Microfluidic Assembly Line
Among the molecular milieu of the cell, the membrane bilayer stands out as a complex and elusive synthetic target. We report a microfluidic assembly line that produces uniform cellular compartments from droplet, lipid, and oil/water interface starting materials. Droplets form in a lipid-containing oil flow and travel to a junction where the confluence of oil and extracellular aqueous media establishes a flow-patterned interface that is both stable and reproducible. A triangular post mediates phase transfer bilayer assembly by deflecting droplets from oil, through the interface, and into the extracellular aqueous phase to yield a continuous stream of unilamellar phospholipid vesicles with uniform and tunable size. The size of the droplet precursor dictates vesicle size, encapsulation of small-molecule cargo is highly efficient, and the single bilayer promotes functional insertion of a bacterial transmembrane pore.
How It Works
"The assembly-line process is simple and, from a chemistry standpoint, mechanistically clear," said Sandro Matosevic, research associate and co-author of the study.
A microfluidic circuit generates water droplets in lipid-containing oil. The lipid-coated droplets travel down one branch of a Y-shaped circuit and merge with a second water stream at the Y-junction. The combined flows of droplets in oil and water travel in parallel streams toward a triangular guidepost.
Then, the triangular guide diverts the lipid-coated droplets into the parallel water stream as a wing dam might divert a line of small boats into another part of a river. As the droplets cross the oil-water interface, a second layer of lipids deposits on the droplet, forming a bilayer.
The end result is a continuous stream of uniformly shaped cell-like compartments.
The newly created vesicles range from 20 to 70 micrometers in diameter—from about the size of a skin cell to that of a human hair. The entire circuit fits on a glass chip roughly the size of a poker chip.
The researchers also tested the synthetic bilayers for their ability to house a prototypical membrane protein. The proteins correctly inserted into the synthetic membrane, proving that they resemble membranes found in biological cells.
"Membranes and compartmentalization are ubiquitous themes in biology," noted Paegel. "We are constructing these synthetic systems to understand why compartmentalized chemistry is a hallmark of life, and how it might be leveraged in therapeutic delivery."
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