Formation Mechanism and Properties of Polyelectrolyte Multilayer-Supported Lipid Bilayers: A Coarse-Grained Molecular Dynamics Study

Polyelectrolyte multilayer (PEM)-supported lipid bilayers (SLBs) that connect with functional proteins are popular models for cell membranes and are usually obtained via vesicle adsorption and spreading. However, the exact mechanism by which SLBs are formed is not fully understood. In this study, we employ coarse-grained molecular dynamics simulations to investigate the pathways by which vesicles undergo spreading upon the deposition on PEM-cushioned substrates. The substrates consist of positive chitosan (CHI)/negative alginate (ALG) multilayers. We find that an isolated vesicle tends to completely disintegrate upon deposition, forming a well-ordered lipid bilayer at appropriate polymer ionic strengths by a mechanism described as "parachute" model. Lipids from the vesicle's outer leaflet are predominantly oriented toward the bulk after the formation of the SLB. The PEM cushion provides adsorption energy of 26.9 kJ mol(-1) per lipid for the SLBs. The process by which SLBs are formed is almost independent of the number of layers of CHI/ALG in the PEM cushion. Additional simulations on vesicle clusters also demonstrate that the formation of SLBs can be catalyzed by either neighboring vesicles or preexisting bilayer edges on the support. Moreover, our simulations show that SLBs created on PEM supports preserve the lateral mobility and the symmetric density profile of the phospholipids, as in a freestanding bilayer.