Effect of Bottlebrush Poloxamer Architecture on Binding to Liposomes

Poloxamers─triblock copolymers consisting of poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO)─have demonstrated cell membrane stabilization efficacy against numerous types of stress. However, the mechanism responsible for this stabilizing effect remains elusive, hindering engineering of more effective therapeutics. Bottlebrush polymers have a wide parameter space and known relationships between architectural parameters and polymer 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 analogues to poloxamers and then employed pulsed-field-gradient NMR and an in vitro osmotic stress assay to explore the effect of bottlebrush architectural parameters on binding to, and protection of, model phospholipid bilayers. We found that the binding affinity of a bottlebrush poloxamer (BBP) (B-E₁₀⁴³P₅¹⁵, M_n ≈ 26 kDa) is about 3 times higher than a linear poloxamer with a similar composition and number of PPO units (L-E₉₃P₅₄E₉₃, M_n ≈ 11 kDa). Furthermore, BBP binding is sensitive to overall molecular weight, side-chain length, and architecture (statistical versus block). Finally, 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.