Importance of Polymer Chain Conformation in Lipid--Block Co-polymer Hybrid Membranes

Lipid bilayers are ubiquitous in biological and synthetic applications. Analogous membranes synthesized from amphiphilic block co-polymers display increased mechanical resiliency and expand the design space. Mixing lipid and polymers in a single membrane can exhibit synergistic behaviors, such as improved membrane protein folding, single molecule detection and drug release kinetics. Due to the potential for synergistic properties, the modes and mechanisms by which polymers and lipids mix are of interest. Coarse-grained molecular dynamics simulations utilizing the Martini force field enable the investigation of polymer chains and lipids as the system demixes. We find that hydrophobic block of the polymer chain conformation is uniquely sensitive to the incorporation in lipid membranes and determines the resulting membrane morphology. We identify two modes of micro-phase separation: lateral separation and unzipping of the lipid membrane. The preference for a system to form these morphologies is dictated by the entropic cost of chain confinement in the membrane and chain stretching to match the membrane thickness. Finally, we discuss the chain conformations in comparison to the pure polymer membranes and discuss on the resulting mechanical and physiological properties. This understanding informs the accessible morphologies in experimental systems given the molecular weight of the polymer chain and enables the engineering of hybrid lipid--polymer membranes with targeted morphologies.