The effect of the components of microemulsions on both size and crystalline structure of solid lipid nanoparticles (SLN) containing a series of model molecules

Solid lipid nanoparticles (SLN) were prepared by dispersing warm oil- in-water microemulsions in cold water. This study evaluates the influence of the microemulsion components on size and crystalline structure of SLN. Two microemulsion formulations containing stearic acid and water were prepared and using different surfactants and cosurfactants. For one, two nonionic molecules, Tween 20 and butanol, were used, and for the other, two ionic molecules, taurodeoxycholate and monooctylphosphate as cosurfactants and Epikuron 200 as surfactant were used. Model molecules incorporated into SLN were a series of polycyclic aromatic hydrocarbons and some derivatives (naphthalene, 2-methylnaphthalene, phenanthrene 2-methylphenanthrene, 2- hydroxynaphthalene, 9-hydroxyphenanthrene, 1,2-naphthoquinone, 1,4- naphthoquinone). The size of SLN varied with microemulsion composition and the molecules incorporated. The crystalline structure was examined by means of thermal analysis; SLN obtained from the first microemulsion contained only one polymorph of stearic acid (form C); moreover all model molecules were dispersed in SLN in amorphous state. The SLN obtained from the second microemulsion contained the form C of stearic acid and no crystalline features of the model molecules; but in the case of the derivatives containing oxygenated functions, the B form of stearic acid was present alongside the C form, and the incorporated molecules were crystallized to some extent.