*4.1. Screening of Drug and Excipients*

The selected lipids were compatible and miscible at the concentrations tested and a ratio of 70:30 (%, *w*/*w*) was shown to be the best proportions of Precirol® ATO5 and vitamin E for the preparation of the NLC formulation, as previously developed in our group [52]. Several studies have shown that a high concentration of liquid lipids increases drug retention, as drug solubility in liquid lipids is usually higher than in solid lipids, which decreases the particle size due to the decreased viscosity and surface tension of the NLC [46,79,88].

The higher solubility of the drug in the lipid mixture was observed over individual lipids, due to the absence of oil droplets on the filter paper (Supplementary Data, Section 3.1, Figure S6). This can be explained by the imperfect lipid matrix formed in the mixture that allowed for higher amounts of drug molecules [46,79,88]. Accordingly, the selected drug concentration was 0.12%.
