Engineering Model Bio-Membranes: Enhanced Stability of Freestanding Lipid Bilayer and its Stability Criteria
Cell membranes are involved in a lot of biological processes such as motility, cell division, and signal process. Despite of their importance, complexity of cell membranes hampers the study of membranes on their physical properties. Accordingly, many model systems have been developed including vesicles, supported lipid bilayers, black lipid membranes, but they all have some disadvantages. We are interested in creating free-standing lipid bilayer as model biomembranes. Once stable free-standing lipid bilayers are formed, they provide a superb model system to interrogate intriguing behaviors and properties of biomembranes in a variety of approaches.
We present a new strategy to dramatically enhance the stability of freestanding lipid bilayers. We found that an addition of a water in oil emulsion stabilizer, SPAN 80 to a solvent phase guarantees nearly millimeter-scale stable freestanding lipid bilayers. The water permeability, 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 we studied the effect of solvent on freestanding 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 < ΦSPAN 80 < 15/1, and we suggest general stability criteria for bilayer formation. This technique and the suggested stability criteria can be potentially helpful to many model membrane-based researches in life sciences, physical sciences and biomedical engineering fields.
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