Molecular Dynamics Simulations of Liposomes
Summary¶
Molecular dynamics (MD) simulation — both all-atom and coarse-grained (CG) — is used to study liposome bilayer properties (packing, thickness, fluidity, curvature response) that experimental techniques such as cryo-EM, SAXS, and fluorescence microscopy struggle to resolve at the relevant microsecond timescales. This review surveys how cholesterol content and membrane curvature govern liposome behavior, and how CG force fields capture these effects. The findings are directly relevant to rational design of liposomal drug-delivery systems.[1]
Force Fields¶
| Modality | Force field examples | What it captures |
|---|---|---|
| All-atom (AA) | CHARMM, AMBER | High-resolution lipid-tail ordering, specific solute partitioning |
| Coarse-grained (CG) | MARTINI (2/3), SPICA, SIRAH, ELBA | Mesoscopic bilayer curvature, domain formation, large-scale vesicle stability, microsecond-to-millisecond dynamics |
MARTINI is the most widely used CG force field, using a 4:1 atom-to-bead mapping; MARTINI 2 reproduces bilayer thickness, area-per-lipid, lateral diffusion and phase behavior well, while MARTINI 3 improves chemical specificity and electrostatics. SPICA, SIRAH, and ELBA extend CG modeling to proteins, charged systems, and polarizable interactions respectively. Machine-learning-based CG potentials are noted as an emerging, more flexible alternative.[1]
Cholesterol¶
Cholesterol inserts between phospholipid tails via its amphipathic, rigid tetracyclic ring structure, and:
- increases bilayer thickness by ordering lipid tails (X-ray diffraction shows DPPC bilayer thickness rising from ~36 Å to ~44 Å with increasing cholesterol; CHARMM and MARTINI simulations reproduce thickening of 5–10 Å over comparable ranges);[1]
- lowers bilayer permeability by reducing membrane defects, improving encapsulation efficiency and drug retention;[1]
- lowers the phase-transition temperature, increasing physiological-temperature fluidity while preserving structural integrity;[1]
- promotes non-lamellar (inverted hexagonal) phases under curvature stress, relevant to endosomal escape and membrane fusion.[1]
Curvature¶
Liposome curvature generates lateral pressure gradients between bilayer leaflets that drive lipid flip-flop, interleaflet coupling, and lateral redistribution — phenomena that shape cellular uptake, endocytosis, and membrane fusion. Curvature also modulates bending rigidity and membrane tension; smaller, higher-curvature vesicles show increased bending energy and altered diffusion, affecting fusion behavior and in vivo stability. Curvature-induced asymmetry between leaflets can additionally drive lipid microdomain (raft-like) formation and lateral sorting of membrane components, affecting surface presentation of ligands and encapsulated-drug distribution.[1]
See Also¶
- Lipid Metabolic Flux Analysis (Lipid-MFA) — a complementary, flux-based rather than structural-dynamics view of lipid biology.
- LIPID MAPS — lipidomics infrastructure relevant to characterizing the lipid species used in these simulations.
Citations¶
[1] Khodadadi, Khodadadi, Chaturvedi, Moradi (2025), "Molecular Dynamics Simulations of Liposomes: Structure, Dynamics, and Applications", Membranes, 15(9), 259. Supports: force-field comparison, cholesterol and curvature findings above. Location: Sections 2 (Biophysical Role of Cholesterol), 3 (Foundations of Liposome Simulation).