Shear-flow-induced negative tension of phospholipid bilayer: Molecular dynamics simulation

Shear flow has been theoretically predicted to suppress the undulation of surfactant bilayers and generate negative tension, which is considered to be a driving force of the transition from the lamellar phase to the multilamellar vesicle phase in surfactant/water suspensions, the so-called onion transition. We performed coarse-grained molecular dynamics simulations of a single phospholipid bilayer under shear flow to clarify the relationship between the shear rate, bilayer undulation, and negative tension, providing molecular-level insight into the undulation suppression. An increasing shear rate suppressed bilayer undulation and increased negative tension; these results are consistent with theoretical predictions. The non-bonded forces between the hydrophobic tails facilitated negative tension, whereas the bonded forces within the tails suppressed it. The force components of the negative tension were anisotropic in the bilayer plane and prominently changed in the flow direction, although the resultant tension was isotropic. Our findings regarding a single bilayer will underlie further simulation studies of multilamellar bilayers, including inter-bilayer interactions and topological changes of bilayers under shear flow, which are essential for the onion transition and are unresolved in the theoretical and experimental studies.