Polymer-cushioned bilayers. I. A structural study of various preparation methods using neutron reflectometry

This neutron reflectometry study evaluates the structures resulting from di fferent methods of preparing polymer-cushioned lipid bilayers. Four differe nt techniques to deposit a dimyristoylphosphatidylcholine (DMPC) bilayer on to a polyethylenimine (PEI)-coated quartz substrate were examined: 1) vesic le adsorption onto a previously dried polymer layer; 2) vesicle adsorption onto a bare substrate, followed by polymer adsorption; and 3, 4) Langmuir-B lodgett vertical deposition of a lipid monolayer spread over a polymer-cont aining subphase to form a polymer-supported lipid monolayer, followed by fo rmation of the outer lipid monolayer by either 3) horizontal deposition of the lipid monolayer or 4) vesicle adsorption. We show that the initial cond itions of the polymer layer are a critical factor for the successful format ion of our desired structure, i.e., a continuous bilayer atop a hydrated PE I layer. Our desired structure was found for all methods investigated excep t the horizontal deposition. The interaction forces between these polymer-s upported bilayers are investigated in a separate paper (Wong, J. Y., C. K. Park, M. Seitz, and J. Israelachvili. 1999. Biophys. J. 77:1458-1463), whic h indicate that the presence of the polymer cushion significantly alters th e interaction potential. These polymer-supported bilayers could serve as mo del systems for the study of transmembrane proteins under conditions more c losely mimicking real cellular membrane environments.