title: Phase transition-controlled flip-flop in asymmetric lipid membranes.
abstract: Lipid membrane asymmetry is of fundamental importance for biological systems and also provides an attractive means for molecular control over biomaterial surface properties (including drug carriers). In particular, temperature-dependent changes of surface properties can be achieved by taking advantage of distinct phase transitions in lipid membrane coatings where lipids exchange (flip-flop) between leaflets. In this study, temperature is used to control flip-flop of lipids in asymmetric lipid membranes on planar solid supports, where the two leaflets of the lipid membrane are in different phase states. More specifically, the lower leaflet is prepared from a supported lipid membrane composed of a high Tm lipid mixture of phosphocholine (PC), phosphatidylserine (PS), and a bioactive lipid on TiO2, followed by selective removal of the top leaflet by detergent. Next, at a lower temperature, where the remaining leaflet is in the gel state, a top leaflet of a different lipid composition and in the fluid phase is formed. Phase transition-induced changes in membrane surface properties following upon temperature-activation of the prepared asymmetric membrane are demonstrated by the detection of biotinylated lipids, which were initially located (thus "hidden") in the lower-gel phase leaflet, at the surface of the top leaflet. These processes were monitored in real-time by the quartz crystal microbalance with dissipation (QCM-D) and the dual polarization interferometry (DPI) techniques, allowing modeling of the mass and the anisotropic property of the lipid structures in different phase states.
authors.affiliation: Department of Applied Physics, Chalmers University of Technology , SE-412 96 Göteborg, Sweden.
authors.forename: Yujia
authors.initials: Y
authors.lastname: Jing
authors.forename: Angelika
authors.initials: A
authors.lastname: Kunze
authors.forename: Sofia
authors.initials: S
authors.lastname: Svedhem
mesh_terms: D007368:Interferometry; D008081:Liposomes / Q000737:chemistry; D008563:Membrane Lipids / Q000737:chemistry*; D044367:Phase Transition; D010713:Phosphatidylcholines / Q000737:chemistry; D010718:Phosphatidylserines / Q000737:chemistry; D058525:Quartz Crystal Microbalance Techniques; D013696:Temperature; D014025:Titanium / Q000737:chemistry
chemical_list: D008081:Liposomes; D008563:Membrane Lipids; D010713:Phosphatidylcholines; D010718:Phosphatidylserines; C009495:titanium dioxide; D014025:Titanium