STRUCTURAL STUDIES OF POLYMER-CUSHIONED LIPID BILAYERS

The structure of softly supported polymer-cushioned lipid bilayers, pr epared in two different ways at the quartz-solution interface, were de termined using neutron reflectometry, The polymer cushion consisted of a thin layer of branched, cationic polyethyleneimine (PEI), and the b ilayers were formed by adsorption of small unilamellar dimyristoylphos phatidylcholine (DMPC) vesicles. When vesicles were first allowed to a dsorb to a bare quartz substrate, an almost perfect bilayer formed. Wh en the polymer was then added to the aqueous solution, it appeared to diffuse beneath this bilayer, effectively lifting it from the substrat e. In contrast, if the polymer layer is adsorbed first to the bare qua rtz substrate followed by addition of vesicles to the solution, there is very little interaction of the vesicles with the polymer layer, and the result is a complex structure most likely consisting of patchy mu ltilayers or adsorbed vesicles.