Mechanical properties of binary DPPC/DPPS bilayers

In this work, we studied how the lipid composition and ionic strength of an aqueous solution affect the mechanical properties of the lipid bilayer. The interfacial tension, the bending modulus, the Gaussian curvature modulus and the bilayer curvature energy of the lipid bilayer were studied by molecular dynamics simulation. For this purpose, the lipid bilayer was modelled as a binary symmetric lipid bilayer of DPPC (DiPalmitoylPhosphatidylCholine) and DPPS (DiPalmitoylPhosphatidylSerine) at different molar ratios of these two lipids in the absence of salt and in presence of 0.5 N NaCl in aqueous solution. The results of the simulations in absence of salt showed how an increase in the DPPS concentration of the lipid bilayer strongly affects most of its mechanical properties, including the lateral pressure across the membrane, interfacial tension, or the bending modulus of the lipid bilayer. However, in the presence of 0.5 N NaCl, the interfacial tension of the lipid bilayer becomes independent of the lipid composition (in the range of 15-70% DPPS), behavior that may have notable implications from a biological point of view, due to the contribution that this property may provide to the stability of biological membranes.