Cationic Lipid Absorption on Titanium:  A Counterion-Mediated Bilayer-to-Lipid-Tubule-Network Transition

Abstract

By carefully tuning the screening effects of monovalent salt in solution, it is possible to control the formation of different lipid morphologies on a titanium dioxide substrate. A transition from an absorbed vesicle layer to fluid lipid bilayers is observed as a function of monovalent salt concentration in solution, and, above a threshold salt concentration, a network of lipid tubules with a fascinating distorted-hexagonal structure is formed in two dimensions on the substrate. We present fluorescence microscopy data for these different morphologies, confirming the connectivity and fluidity of the bilayers and tubules.

The Electrochemistry of Liposomes

“…The surface force apparatus (SFA) has also been proved to be useful to study the adhesion of liposomes on surfaces 149 . Fluorescence microscopy can be used to determine the rate of spreading of a bilayer on a surface 150 and to follow the morphology changes of the attached membranes 151 . The formation and properties of intermembrane junctions (liposomes adhering on previously formed supported membranes) has been followed analyzing the fluorescence resonance energy transfer (FRET) response on the intermembrane space 152 .…”

“…149 Fluorescence microscopy can be used to determine the rate of spreading of a bilayer on a surface 150 and to follow the morphology changes of the attached membranes. 151 The formation and properties of intermembrane junctions (liposomes adhering on previously formed supported membranes) has been followed analyzing the fluorescence resonance energy transfer (FRET) response on the intermembrane space. 152 The kinetics of spreading of vesicles at the air-water interface followed, e.g., by measuring the changes of the film pressure as a function of time, has also been an interesting object of study.…”

Contribution of the Hydration Force to Vesicle Adhesion on Titanium Oxide

“…Depending on material substrate properties along with vesicle characteristics and experimental conditions, adsorbed vesicles may either remain intact (e.g., titanium oxide) or rupture to form a planar lipid bilayer (e.g., silicon oxide) (see refs and and references therein). The deformation of adsorbed vesicles strongly influences the rate of rupture, and the extent of vesicle deformation is commonly studied by using adsorbed vesicles on titanium oxide as a model system. , In order to form a planar bilayer on titanium oxide, experimental methods have also been devised, including peptide-induced vesicle rupture and enhancement of the vesicle–substrate interaction. − …”

“…Hence, it appears that divalent cations may generally modulate the lipid–substrate interaction. The rupture of zwitterionic lipid vesicles has also been achieved by changing the solution pH in order to promote electrostatic attraction. , Besides changing the solution pH, vesicles containing a high fraction of positively charged lipids (50 mol % or greater) may rupture on titanium oxide due to electrostatic attraction as well. , Additional interfacial forces have also been identified to promote bilayer formation, including the van der Waals force on rutile titanium oxide surfaces. , …”

Calcium-ion-controlled nanoparticle-induced tubulation in supported flat phospholipid vesicles

“…It is well established that tubes can be generated from giant unilamellar vesicles and cells by mechanical methods such as micropipette pulling, 13 exposure to hydrodynamic flows, [14][15][16] optical tweezers, 17,18 and by action of motor proteins 19 or motor protein-bead complexes. 20 Nanotubes can also be generated by chemical means as exemplified by counter ion mediation, 21 curvature-inducing proteins, 22 gangliosides, 23 and even cholesterol. 24 Detailed understanding of properties, formation conditions and formation-, and retraction-dynamics of tubes is of great importance, and we report here on a model system displaying transient tubulation in nanoparticle-containing, surface-supported flat giant unilamellar vesicles (FGUVs).…”