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 dipalmi toylphosphatidylcholine (DPPC) has been studied by measuring the lecithin m olecular order and lateral diffusion using a deuterium NMR relaxation metho d. me obtained for both monolayers of the supported bilayer a lateral diffu sion coefficient (D = 13.5 x 10(-12) m(2)/s at 55 degreesC) similar to that measured previously in the outer monolayer of a supported bilayer on a bar e silica surface, indicating that the presence of the polymer cushion can i ndeed largely eliminate the slow down effect of the solid surface on the bi layer dynamics. Moreover, we found that the polymer cushion rendered the mo lecular order of the Lipids identical to that measured for multilamellar bi layer vesicles (MLV). A comparison of the measured D values with those obta ined for oriented planar multilayer stacks of DPPC strongly suggests that l ateral diffusion in these systems is still a factor of 2 faster than that o f single bilayers on a support.