Mechanical stability of phase-segregated multicomponent lipid bilayers enhanced by PS-b-PEO diblock copolymersElectronic supplementary information (ESI) available: AFM height images, line profiles, representative forcedistance curves of DOPC/ESM/Chol with 0.05 mol% PS(3.6)-b-PEO(25), PS(3.6)-b-PEO(16.6), PS(3.8)-b-PEO(6.5), and PS(19)-b-PEO(6.4), and analysis of breakthrough force histograms to obtain the spreading pressures and line tensions. See DOI: 10.1039/c3sm50855b

Polymeric additives affect the mechanics of phospholipid vesicles, but little is known about the effect to supported lipid bilayers that are phase segregated on the submicron length scale. In this study, we use AFM-based force mapping, by means of breakthrough forces, to quantify the spreading pressures and line tensions of raft-forming lipid bilayers consisting of dioleoylphosphatidylcholine (DOPC), egg sphingomyelin (ESM), and cholesterol (Chol) in the presence of diblock copolymers comprised of polystyrene (PS) and poly(ethylene oxide) (PEO), PS- b -PEO. Varying molecular weights of PS- b -PEO were used in the experiments. The presence of the polymer leads to higher breakthrough forces when compared to pure DOPC/ESM/Chol bilayers. The lipidpolymer composite made with a PS block radius of gyration comparable to the bilayer thickness and a PEO block length that is the shortest exhibits the highest breakthrough forces and hence is the most stable mechanically. The breakthrough force distributions are analyzed to extract the spreading pressures and line tensions of the lipidpolymer composites. The spreading pressure is seen to increase with the addition of PS- b -PEO, and on average, increases with decreasing PEO block length. Based on the results, we propose the incorporation of the PS moiety into the bilayer core as the main mechanism of this enhanced resistance to bilayer breakthrough by the AFM tip. AFM-based tip breakthrough force map shows that the mechanical stability and spreading pressures of raft-forming DOPC/ESM/Chol bilayers are enhanced by the addition of PS- b -PEO diblock copolymers.