Polymer Cushions in Supported Phospholipid Bilayers Reduce Significantly the Frictional Drag between Bilayer and Solid Surface

The reduction of fluid lecithin bilayer−substrate coupling by the presence of a hydrophilic polymer cushion in spherical supported bilayers of dipalmitoylphosphatidylcholine (DPPC) has been studied by measuring the lecithin molecular order and lateral diffusion using a deuterium NMR relaxation method. We obtained for both monolayers of the supported bilayer a lateral diffusion coefficient ( D = 13.5 × 10 -12 m 2 /s at 55 °C) similar to that measured previously in the outer monolayer of a supported bilayer on a bare silica surface, indicating that the presence of the polymer cushion can indeed largely eliminate the slow down effect of the solid surface on the bilayer dynamics. Moreover, we found that the polymer cushion rendered the molecular order of the lipids identical to that measured for multilamellar bilayer vesicles (MLV). A comparison of the measured D values with those obtained for oriented planar multilayer stacks of DPPC strongly suggests that lateral diffusion in these systems is still a factor of 2 faster than that of single bilayers on a support.