Multi-scale modeling of phase separation in mixed lipid bilayers

Area of Science:

• Biophysics
• Computational Chemistry
• Materials Science

Background:

• Understanding phase separation in lipid bilayers is crucial for membrane biophysics.
• Bridging different simulation scales (molecular to mesoscopic) remains a challenge.
• Phenomenological field theories offer a mesoscopic description, while molecular dynamics provides atomistic detail.

Purpose of the Study:

• To develop an approach connecting phenomenological field theory with coarse-grained molecular dynamics (CG MD) simulations.
• To characterize liquid-gel phase separation in binary lipid mixtures.
• To validate a mesoscopic model using CG MD simulation data.

Main Methods:

• Coarse-grained molecular dynamics (CG MD) simulations of a 1:1 dipalmitoylphosphatidylcholine/dipalmitoylphosphatidylethanolamine lipid mixture.
• Definition of a local order parameter based on lipid tail orientation.
• Bridging CG MD data to a mesoscopic Landau-Ginzberg free-energy functional model.

Main Results:

• The mesoscopic model accurately reproduces equilibrium properties, including collective fluctuations, order parameter correlations, and line tension.
• Parameters for the mesoscopic model were derived from phase boundary structure and order parameter distributions.
• The study explored the potential of time-dependent Landau-Ginzberg models for simulating phase separation dynamics.

Conclusions:

• The developed approach successfully bridges CG MD simulations and phenomenological field theory for lipid bilayer phase separation.
• The mesoscopic model provides a robust framework for understanding the equilibrium properties of lipid mixtures.
• This work lays the foundation for simulating phase separation dynamics in complex lipid systems.