Individual leaflet phase effect on nanometer-scale surface properties of phospholipid bilayers

Curvature effect on nanometer-scale surface properties of phospholipid layers

Phospholipid bilayers were formed through liposome fusion on surfaces with different curvatures that were defined with silica spheres deposited on silicon water. Prior to the fusion, the surfaces became hydrophobic with octadecyltrimethoxysilane solution. Using atomic force microscope, surface forces were measured on dipalmitoylphosphatidylcholine (DPPC) layers and dioleoylphosphatidylcholine (DOPC) layers upon the curvature at 25°C. The short-range repulsions were higher at 20 and 100 nm curvatures than other curvatures for the DPPC layer, while they were lower for the DOPC layer. Since it was known that the forces are related to its low mechanical stability of the lipid layer, this opposite behavior was analyzed in terms of stability upon the curvature, which appears to be eventually determined by the correlation between the lipid molecule geometry and the surface curvature.

Probe chemistry effect on surface properties of asymmetric-phase lipid bilayers

Phospholipid bilayers were formed on mica using Langmuir-Blodgett technique and liposome fusion, as a model system for biomembranes. Nanometer-scale surface physical properties were quantitatively characterized upon the different phases of the monolayers with the different surface chemistry. The less hydration/steric forces were observed at the liquid-phase of the lipid layer than at the solid-phase for the OH-modified probe, while the forces with the CH(3)-modified probe were independent of the mechanical stability of the layer. The forces appear to be related to the surface chemistry of the probe to the layer as well as the mechanical stability of the lipid layer, which depends on the phase and the asymmetry of the lipid bilayer. After the breakthrough of the lipid bilayer, the CH(3)-modified probe adhered more strongly to the lipid bilayers than do the OH-modified probe. Using results from the JKR theory, it is found that the adhesion can be accounted for in both cases by surface energy consideration, not mechanical effects.