Polymer-tethered bimolecular lipid membranes

This contribution describes the assembly and structural and functional characterization of various types of polymer-supported lipid bilayer membranes.We start with the description of the polymer-cushioned membrane that can be prepared by first attaching (covalently) polymer coils (as tethers or cushions) from solution to a reactive solid support, followed by the covalent coupling of a lipid monolayer containing reactive anchor lipids. Alternatively, a lipopolymer monolayer (if needed mixed with "normal" lipids) is pre-organized at the water-air interface in a Langmuir trough and then transferred to a solid substrate which is again pre-functionalized by a reactive coating. A special case discussed is the use of glycolipopolymers for the assembly of the proximal tethered monolayer. From all these interfacial architectures the final structure, the supported bilayer, is obtained by the fusion of vesicles forming the distal monolayer of the membrane. For some of these polymer-tethered lipid bilayers a few key performance indicators are discussed. In particular, we describe structural parameters obtained from surface plasmon resonance spectroscopy and compare those to important functional features, i.e., the electrical capacitance and resistance of the membrane. Furthermore, the ability of the polymer tethers to swell in water and evidence for the resulting lateral mobility of the lipid molecules in the membrane as an indicator for the fluid nature of the tethered bilayers are presented. Next, the use of polyelectrolyte multilayers, prepared in by the layer-by-layer deposition protocol, as well as the use of polymer cushions prepared by plasmapolymerization is introduced. Evidence for the proper structural and functional characteristics of the corresponding tethered bilayers is derived from neutron reflectivity and from IR data, and by the observation of the functional incorporation of proteins. And finally, the very promising application of hydrogels as cushions but also as protective coatings for the tethered membrane architectures, eventually allowing even for operations in air, is presented and discussed.