Equilibrium structure and lateral stress distribution of amphiphilic bilayers from dissipative particle dynamics simulations

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Abstract
The equilibrium structure and lateral stress profile of fluid bilayer membrane patches are investigated using the Dissipative Particle Dynamics simulation technique. Although there are no attractive forces between the model amphiphiles, they spontaneously aggregate into planar bilayers under suitable conditions of concentration and amphiphile architecture. Pure bilayers of single-chain and double-chain amphiphiles are simulated, and the amphiphile architecture and interaction parameters varied. We find that a strong chain stiffness potential is essential to create the lamellar order typical in natural lipid membranes. Single-chain amphiphiles form bilayers whose lamellar phase is destabilized by reductions in the tail stiffness. Double-chain amphiphiles form bilayers whose rigidity is sensitive to their architecture, and that remain well-ordered for smaller values of their tail stiffness than bilayers of single-chain linear amphiphiles with the same hydrophobic tail length. The lateral stress profile across the bilayers contains a detailed structure reflecting contributions from all the interaction potentials, as well as the amphiphile architecture. We measure the surface tension of the bilayers, and extract estimates of the membrane area stretch modulus and bending rigidity that are comparable to experimental values for typical lipid bilayers. The stress profile is similar to that found in coarse-grained Molecular Dynamics simulations, but requires a fraction of the computational cost. Dissipative Particle Dynamics therefore allows the study of the equilibrium behavior of fluid amphiphilic membranes hundreds of times larger than can be achieved using Molecular Dynamics simulations, and opens the way to the investigation of complex mesoscopic cellular phenomena.