PEO-PPO block polymers interact with phospholipid bilayers and can have a stabilizing effect on cell membranes under stress. The stabilization mechanism remains unknown but previous studies have found that a wide range of cell signaling pathways are upregulated and downregulated. Liposomes are useful membrane models because they can be prepared with custom compositions to probe the effect of different membrane components on polymer-lipid interactions. Previous research has shown that ternary mixtures with saturated lipids, unsaturated lipids, and cholesterol lead to phase coexistence. In this work, we leverage published ternary phase diagrams to explore the impact of lipid phase behavior on the binding of Poloxamer F127 to different membrane compositions of phosphatidylcholine, palmitoylsphingomyelin, and cholesterol. Unimodal liposomes were prepared with a vesicle extrusion diameter of 50 nm. Dynamic light scattering was used to validate the prepared liposomes, and pulse-field-gradient NMR was used to quantify the amount of F127 bound to the liposomes. We observed that the addition of cholesterol significantly reduced polymer binding to the liposomes relative to the POPC control. The addition of PSM also decreased binding non-monotonically. Compositions with Ld/Lo/So coexistence showed maximal binding of polymer, possibly because phase boundaries on the lipid bilayer present attractive binding sites.

Effect of lipid phase behavior on polymer binding to liposomes

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