Computer Simulations Of Phase Separation Behaviors In Two-component Lipid Bilayers

Lipid Bilayer is the basic skeleton of the biomembrane. There are a large number of lipids in the membrane, but their lateral distributions are uneven. It is found in experiments that, even for a simple two-component lipid bilayer, phase separation occurs and lipids domains appear in the membrane. The heterogeneity of the biomembrane is tightly associated with many biological function of the membrane, such as endocytosis and cellular signaling. Therefore, the studies on the phase separation will be helpful to understand the biological significance of the biomembrane.Here, we study the phase separation behaviors of two-component lipid bilayers by using dissipative particle dynamics(DPD). DPD is a coarse-grained simulation technique, which has been extensively applied in the studies of biomembrane. The influence of the surface tension of the membrane, line tension between different lipid phase, and the bond angle potential of lipid tail(which could affect the rigidity of lipid molecule and area per lipid, etc.) on the phase separation of the bilayers are investigated by us. Furthermore, the number of the domains formed in the bilayer, the length of domain interface and the area of domains are examined by Hoshen-Kopelman algorithm and search-first depth algorithm in undirected graphs, which could quantitatively provide the information of dynamics of phase separation of the lipid bilayer. We find that, with the increase of line tension, the phase separation accelerates; on the other hand, the increase of the bond angle potential of lipid tail could impede the proceeding of phase separation. Additionally, the zero membrane tension also benefits the appearance of domains in the bilayer. It is also found that these factors influence each other. For example, for our simulations, the degree of phase separation of the lipid bilayer is the highest for the larger line tension, low bond angle potential of lipid tail and zero membrane tension. Our studies are helpful to understand the complicated phase behaviors of lipid bilayers and the related mechanism.