Lipid Membranes Cushioned by Polymer Brushes: A Coarse-Grained Molecular Dynamics Study

Solid-supported lipid bilayers (SLBs) are commonly used as biomimetic membranes for understanding the physico-chemical properties of biomembranes and membrane-bound proteins. The thin aqueous layer between the bilayer and the substrate, with typical thickness varying between 0.5 and 3 nm, makes SLBs not suitable for studying transmembrane proteins with protruding domains. The closeness of the lipid bilayer to the substrate also hidners out-of-plane deformations of the bilayer, which are necessary for many biological processes. Polymer-cushioned lipid bilayers are attractive alternative systems for biomembranes in cell-mimicking environments. Here, we present a numerical study, based on coarse-grained molecular dynamics simulations of an implicit-solvent model, of lipid membranes that are cushioned by polymer brushes. Our investigation over a wide range of polymer-lipid interactions, polymer chain lengths and polymer grafting densities, shows that the polymer brush has a strong effect on the elastic properties of the lipid membrane. In particular, we found that attractive interactions between the polymer chains and the lipid head groups lead to a decrease of the tension of the membrane and an increase of the membrane's bending modulus. These effects are amplified with increasing the chain length or grafting density.