Effect of bottlebrush poloxamer architecture on binding to liposomes

Poloxamers – triblock copolymers consisting of poly(ethylene oxide) and poly(propylene oxide) – have demonstrated cell membrane stabilization efficacy against numerous types of stress. However, the mechanism responsible for this effect remains elusive, hindering engineering of effective therapeutics. Bottlebrush polymers have a wide parameter space and known relationships between architectural parameters and properties, enabling their use as a tool for mechanistic investigations of polymer-lipid bilayer interactions. In this work, we utilized a versatile synthetic platform to create novel bottlebrush analogs to poloxamers, and then employed pulsed-field-gradient NMR, and an in vitro osmotic stress assay to explore the effects of bottlebrush architectural parameters on binding to, and protection of, phospholipid bilayers. We found that the binding affinity of a bottlebrush poloxamer (BBP) is about three times higher than a linear poloxamer with a similar composition and number of PPO units. BBP binding is sensitive to overall molecular weight, side chain length, and architecture (statistical versus block). All tested BBPs exhibit a protective effect on cell membranes under stress at sub-μM concentrations. As the factors controlling membrane affinity and protection efficacy of bottlebrush poloxamers are not understood, these results provide important insight into how they adhere to and stabilize a lipid bilayer surface.