Towards Better Cell Membrane Mimics: Cholesterol-Containing Supported Lipid Bilayers on TiO2

Abstract

Membranes of cells are based on fluid bilayers containing complex mixtures of various lipids and cholesterol. Charged and biologically active species such as phosphatidyl serine (PS), phosphatidyl ethanolamine (PE) and phosphatidyl inositol (PI) are facing the inside of the cell while the zwitterionic, “inert” lipids and glycolipids facing the outside. 1 Cell membranes are also organized laterally. This lateral organization is thought to be captured in model systems containing high-melting and low-melting lipids and cholesterol. 2 Model systems capturing lipid asymmetry in cell membranes are scarce, however, due to the difficulties associated with controlling lipid self-assembly process. 3 In this context, we 4,5 have recently shown that PS is distributed asymmetrically in supported phospholipid bilayers (SLBs) prepared on titanium dioxide (titania, TiO2) from liposomes containing low-melting PC and PS. In this study, we introduce cholesterol and high-melting lipids into the system to prepare better cell membrane mimics. Their formation and properties are studied by atomic force microscopy, scanning laser confocal fluorescence microscopy, and fluorescence recovery after photobleaching (FRAP). Additional impetus for our studies stems from the desire to understand the interactions between the material commonly used in medical applications (TiO2) and lipid membranes.