Influence of preparation path on the formation of discs and threadlike micelles in DSPE-PEG(2000)/lipid systems

In a recent study we showed that the surfactant 1,2-distearoyl-sn-glycero-3-phosphatidylethanolamine-N-[methoxy(polyethylene glycol)-2000 (DSPE-PEG(2000)) induce mixed micelles of either threadlike or discoidal shape when mixed with different types of lipids. In certain lipid systems the discoidal micelles adapt sizes large enough to be characterized as bilayer discs. The discs hold great potential for use in various biotechnical applications and may e.g. be used as model membranes in drug/membrane partition studies. Depending on the application, discs with certain characteristics, such as a particular size or size homogeneity, may be required. These factors can in our experience be influenced by the preparation method. In this study we systematically investigated three different PEG-lipid/lipid mixtures prepared by four commonly used preparation techniques. The techniques used were simple hydration, freeze-thawing, sonication and detergent depletion, and the aggregate size and structure was analyzed by cryo transmission electron microscopy (cryo-TEM) and dynamic light scattering (DLS). Our results show that the type and size of the micellar structure found, as well as the structure homogeneity of the preparation, can be modified by the choice of preparation path.