Nanomechanical Stability of Phase-Segregated Multicomponent Lipid Bilayers Enhanced by Pluronics

Abstract

Lipid-polymer/peptide systems have been used as platforms to understand various cellular components, functions, and processes such as the cell glycocalyx, the hydrophobic mismatch, and interaction of specific peptides with lipid bilayers. In this study, we used AFM-based force mapping to quantify by means of breakthrough forces the nanomechanical stability of raft-forming lipid bilayers consisting of dioleoylphosphatidylcholine, sphingomyelin, and cholesterol (DEC) in the presence of diblock copolymers comprised of polystyrene(PS) and polyethylene oxide(PEO). Varying molecular weights of PS-b-PEO (Pluronics-mimics): PS(3.6)-b-PEO(25), PS(3.6)-b-PEO(16.6), PS(3.8)-b-PEO(6.5), PS(19)-b-PEO(6.4) were used in the experiments. The presence of the polymer led to a significant increase in the breakthrough forces when compared to a pure DEC bilayer. Bilayers with greater proportion of PS exhibited the highest breakthrough force hence is the most mechanically stable. Based on the results, we proposed the incorporation of the PS moiety into the bilayer core as the main mechanism of the enhanced stability. Our force mapping results provide a direct measurement of the effect of Pluronics on the stability of phase-separated multicomponent lipid bilayers that mimic biological membrane. In addition, the lipid bilayer-Pluronic-mimics systems presented in this study pose as an attractive platform for obtaining fundamental understanding on the role of Pluronics in drug delivery application as well as being a biological response modifier.