Influence of lipid nanocapsules composition on their aptness to freeze-drying

Purpose. To link the aptness to freeze-drying and the stability under storage to the topology of lipid nanocapsules. Methods. The aptness to freeze-drying and the stability under storage of lipid nanocapsules prepared from different compositions with a lecithin content in the 2-20% range were estimated from the preservation of the physical structure, preventing the leakage of the oily phase. The influence of the outer shell composition and of the physical characteristics (investigated by photon correlation spectroscopy and differential scanning calorimetry) on the physical stability was correlated to the topology of the nanoparticulate carrier. Results. Confirming the assumption that lecithin confers hardness to the outer shell of lipid nanocapsules, this study shows that the aptness to freeze-drying and the stability under storage depend on the Solutol (R)/lecithin (S/L) ratio in the formulation. The DSC study points out a complexation between lecithin and trehalose, the cryoprotectant, reinforcing the stabilising properties of lecithin. Conclusions. This paper is a contribution to methodological development of the formulation of lipid nanocapsules, with a special emphasis on the aptness to freeze-drying and the stability under storage.