At high pH, the neutral MC3 or KC2 does not form any topology resembling an inverse hexagonal phase. In the presence of DSPC small inverse micelle pockets are formed, with the same being observed for the cholesterol-containing systems, though there, the neutral IL mixes with cholesterol and separates from the water phase completely, see Figure and. This aligns well with experimental SAXS data , suggesting that the parameters can indeed reproduce the known pH-dependent phase behaviour of these ILs. A large library of IL models can enable various studies, including the screening and characterization of different LNP lipid formulations, in terms of their packing, phase behaviour, and fusiogenic behaviour against different membrane models. To illustrate the potential of this IL model library and to propose an approach for assessing LNP efficiency, we focus here on quantifying the fusiogenic properties of different formulations. For this purpose, we used the protocol by Hub et al. to perform Potential of Mean Force (PMF) fusion assays of stalk formation between different LNP formulations and a plasma membrane model . The LNP interacting leaflet of this membrane is composed of (in mol%) 24 % POPC, 12 % PAPC, 2 % POPE, 6 % DIPE, 24 % DPSM and 31 % CHOL while the non-interacting leaflet contains 14 % POPC, 8 % PAPC, 5 % POPE, 16 % DIPE, 11 % DPSM, 28 % CHOL, 25 % PAPS, 2 % PAP6. Additionally, we also studied the stalk formation between the LNP formulations and a membrane model enriched with 10 mol % PAPS lipids in the LNP-interacting leaflet to better mimic the compositional differences observed in the endosome. PAPS was also included in this leaflet based on the hypothesis that anionic lipids, such as PS, could play an important role in the transfection mechanism, and to better represent the increase in negatively charged lipid found in late endosomes .