Compartmentalizing a lipid bilayer by tuning lateral stress in a physisorbed polymer-tethered membrane

Abstract

The current study reports the compartmentalization of a physisorbed polymer-tethered phospholipid bilayer built using subsequent Langmuir–Blodgett (LB) and Langmuir–Schaefer (LS) transfers, where compartmentalization is due to buckling in the bottom (LB) monolayer and polymer-specific stress relaxation processes. Buckling arises from lateral stress within the membrane induced by a high (15–30 mol%) concentration of poly(2-ethyl-2-oxazoline) lipopolymers in the LB monolayer. Epifluorescence microscopy (EPI) and fluorescence recovery after photobleaching (FRAP) experiments confirm the formation of a homogeneous bilayer at low lipopolymer molar concentrations (low lateral stress), but demonstrate the compartmentalization of the bilayer into µm size compartments at elevated lipopolymer concentrations (high lateral stress). Quantitative EPI of the LB monolayer as well as additional atomic force microscopy (AFM) experiments show that bilayer compartmentalization, buckling and partial delamination of the LB monolayer occur without causing notable phospholipid–lipopolymer phase separations, but do preclude bilayer formation above buckled/delaminated regions after LS transfer. As long-time tracking experiments of photostable quantum dot-conjugated lipids in the compartmentalized bilayer system confirm, our membrane system enables the facile adjustment of the permeability of diffusion boundaries between bilayer compartments, thus providing an excellent experimental tool to mimic length-scale dependent diffusion processes observed in cellular membranes. We expect that the fundamental concept of lateral stress regulation and buckling-associated membrane compartmentalization can also be applied to other polymer–lipid composite materials than the one studied in this work.