Using the surfaces of droplets formed using droplet-based microfluidic technologies to study biomolecular interactions




McDonald, Alex R.

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This thesis explores droplet-based microfluidic technologies to fabricate bespoke emulsions, focusing on lipid- and protein-based interactions on the surface of the droplets. I introduce microfluidic technologies for droplet formation and factors that influence droplet shape and size. Different approaches to forming single and double emulsions using droplet-based microfluidic technologies are discussed along with considerations such as surface chemistry, droplet stability, and applications. First, I use double emulsions to produce biomimetic vesicles (liposomes) and explain why dewetting is a key step in liposome fabrication. I fabricated a lipid-based surface on aqueous droplets as a bottom-up cell membrane model using a novel combination of naturally-derived lipids in the aqueous phase and a simple plug-and-play microcapillary platform. These asymmetric liposomes remain stable in an asymmetric conformation for over 24 h and are within the size range of actual eukaryotic cells. I show that this cell membrane model is more biomimetic than other current models based on the lipid composition and conditions it is fabricated in. Second, I create a protein-based surface on oil droplets to explore the roles of proteins on droplet stability in beer. This was the first time a hop-oil-in-beer emulsion was made on a microfluidic device to explore the role that proteins have in long-term emulsion stability, which serves as the first step in understanding the unknown stabilization mechanism that keeps beer shelf-stable. By digesting gluten, a protein commonly found in beer during fermentation, with a gluten-specific enzyme, I show that hop-oil emulsion stability is influenced by the concentration of gluten present in solution. This thesis highlights the potential of droplet-based microfluidic technologies to create custom surfaces on emulsions and characterize their properties in two distinct applications: academic and industry.



microfluidics, biomolecular, droplets, surfaces, proteins, brewing, lipids, liposomes