Engineering model cell membrane

Abstract

In this study, I present new platforms for research on cell membrane by engineering both lipid mono-layer and freestanding bilayer. First, I present a novel technique to study mixing property of lipid monolayers. I merge a lipid coated droplet to a fluorescently-labeled planar monolayer. During the merging process, a monolayer on a droplet displaces the existing planar monolayer, leaving a dark area when viewed under a fluorescence microscope. I measure fractional intensities as the dyes recover, which allows diffusion coeffi-cients to be computed. Using proposed technique, I observed the mixing process between two different mono-layers on the air/water interface, and by this, mixing between two monolayers can be investigated. Second, I present the first stable freestanding lipid bilayers with large area, planar geometry, solvent-free, and exempla-ry lipids as well, which can be a useful in vitro platform for a number of studies related to cell membranes. The new approach is the hybridization of a droplet monolayer and planar monolayer, and a W/O emulsion stabilizer SPAN 80, which gives rise to a nearly millimeter-scale stable freestanding bilayer. The water perme-ability, bilayer area, contact angle, and interfacial tension were measured as a function of time and SPAN 80-to-lipid weight ratio (ΦSPAN 80) with several different solvents. Surprisingly, the SPAN 80, instead of remaining in the bilayer, was moved out of the bilayer during the bilayer formation. Also I studied the effect of solvent on bilayer formation, and found that squalene was the only solvent that was not incorporated into the bilayer. The regime of stable bilayer formation was experimentally determined to be 3/1 < $\phi$SPAN 80 < 15/1, and I sug-gest general stability criteria for bilayer formation. This method and the suggested stability criteria can be potentially helpful to many model membrane-based researches in life sciences, physical sciences and bio-medical engineering fields.