Figure 1.

Equilibrium conditions of a lipid droplet connected to a PL bilayer. (A) Schematic view of a lipid droplet embedded in a bilayer. The two PL monolayers covering the oil droplet are in continuity with the leaflets of the bilayer allowing PL exchanges. (B) The mechanical equilibrium, resulting from the balance of the surface tension forces acting on the contact line, imposes the shape of the droplet reported by the two contact angles ${\theta }_e$ and ${\theta }_i$. The bilayer tension, the external monolayer tension, and the internal monolayer tension are respectively ${\gamma }_b$, ${\gamma }_{me}$, and ${\gamma }_{mi}$. (C) Chemical equilibrium between PLs in the bilayer leaflet and in the monolayer. The equilibrium distribution between PLs in contiguous bilayer leaflet and LD monolayer is determined by the balance of their chemical potentials ${\mu }_b$ and ${\mu }_m$. PLs of a given membrane leaflet are free to exchange by lateral diffusion between the contiguous LD monolayer and the bilayer leaflet but PL flip-flop is considered irrelevant. ${\rho }_{me}$ and ${\rho }_{mi}$ are the PL density in the external and internal monolayer, ${\rho }_{be}$ and ${\rho }_{bi}$ are the density in the external and internal leaflet of the bilayer.