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

Abstract

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.

The Martini Model in Materials Science

“…[ 57,58 ] Moreover, polymers have also been developed within the Dry Martini [ 59 ] version of the force field: examples include PEO, [ 60 ] PAMAM dendrimers, [ 61 ] and charged polysaccharide. [ 62 ] Within the Dry Martini model, water is represented implicitly rather than explicitly by CG particles. This is achieved by re‐parametrizing the nonbonded interactions between the Martini CG building blocks, such that the free energy of transfer between the implicit‐water and organic solvents is kept close to the original explicit‐water values.…”

“…[ 59 ] It has been shown to work well in the context of lipid bilayer simulations, [ 59 ] and it has also been successfully used for simulating polymers. [ 60–62 ] However, problems for example in polymer solvation have also been reported when using the Dry version of the model. [ 64 ] In general, re‐balancing of the interactions and introduction of friction comes at a price.…”

A platform for light-controlled formation of free-stranding lipid membranes

“…Depending on the intended application, the properties of vesicles may be optimized. Electrostatic interactions are key for vesicles' attraction to the underlying support, and, because of the short radius of curvature, small vesicles tend to rupture [23]. Thus, small charged vesicles are perfect for bilayer formation from vesicle dispersion.…”

“…Phosphatidylcholine bilayers (LB) supported by a polyelectrolyte multi-layer (PEM) of polyethyleneimine (PEI) and poly(sodium 4-styrenesulfonate) (PSS) were obtained by the vesicle rupture [23][24][25] and layer-by-layer (LbL) technique [26] on top of TiO 2 . The light-induced activity and resulting proton concentration close to the surface under localized 5 mm irradiation were studied using a scanning vibrating electrode technique (SVET) and a scanning ion-selective electrode technique (SIET).…”

Structural Investigation of a Self-Cross-Linked Chitosan/Alginate Dialdehyde Multilayered Film with in Situ QCM-D and Spectroscopic Ellipsometry

“…26−29 The buildup process and properties of CHI/ALG multilayered films have been widely investigated using different methods, such as quartz crystal microbalance with dissipation monitoring (QCM-D), IR spectroscopy, atomic force microscopy (AFM), transmission electron microscopy, confocal laser scanning microscopy, scanning electron microscopy, and molecular dynamics simulation. 23−25,30−34…”