Weakly Coupled Lipid Bilayer Membranes on Multistimuli-Responsive Poly(N-isopropylacrylamide) Copolymer Cushions

Polymer-cushioned lipid bilayers are frequently used to mimic the native environment of cellular membranes in respect to the extracellular matrix and intracellular structures. With the aim to actively tune lipid membrane characteristics, we pursue the approach to use temperature and pH responsive polymer thin films of poly(N-isopropylacrylamide-co-carboxyacrylamide) (PNIPAAm-co-carboxyAAM) as cushions for supported lipid bilayers. A cationic lipid bilayer composed of dioleoylphosphatidylcholine (DOPC) and dioleoyltrimethylammoniumpropane (DOTAP) (9:1) was formed on top of the polymer thin film in a drying/rehydration process. Fluorescence recovery after photobleaching (FRAP) yielded higher lipid diffusion coefficients (6.3-9.6 mu m(2)s(-1)) on polymer cushions in comparison to solid glass supports (3.0-5.9 mu m(2) s(-1)). No correlation of the lipid mobility was found with the swelling state of (PNIPAAm-co-carboxyAAM), which is ascribed to restrained interfacial electrostatic interactions and dispersion forces. The results revealed a minimal coupling of the lipid bilayer with the polymer cushions, and thus, bilayers supported by (PNIPAAm-co-carboxyAAM) provide interesting opportunities for unperturbed lipid diffusion combined with control of transmembrane protein mobility due to the impact of a tunable frictional drag.