Development of sucrose stearate-based nanoemulsions and optimisation through γ-cyclodextrin

Nanoemulsions aimed at dermal drug delivery are usually stabilised by natural lecithins. However, lecithin has a high tendency towards self-aggregation and is prone to chemical degradation. Therefore, the aim of this study was to develop nanoemulsions with improved structure and long-term stability by employing a natural sucrose ester mixture as sole surfactant. A thorough comparison between the novel sucrose stearate-based nanoemulsions and corresponding lecithin-based nanoemulsions revealed that the sucrose ester is superior in terms of emulsifying efficiency, droplet formation as well as physical and chemical stability. The novel formulations exhibited a remarkably homogeneous structure in cryo TEM investigations, as opposed to the variable structure observed for lecithin-based systems. The in vitro skin permeation rates of lipophilic drugs from sucrose stearate nanoemulsions were comparable to those obtained with their lecithin-based counterparts. Furthermore, it was observed that addition of γ-cyclodextrin led to enhanced skin permeation of the steroidal drug fludrocortisone acetate from 9.99 ± 0.46 to 55.10 ± 3.67 μg cm−2 after 24 h in the case of sucrose stearate-based systems and from 9.98 ± 0.64 to 98.62 ± 24.89 μg cm−2 after 24 h in the case of lecithin-based systems. This enhancement effect was significantly stronger in formulations based on lecithin (P < 0.05), which indicates that synergistic mechanisms between the surfactant and the cyclodextrin are involved. Cryo TEM images suggest that the cyclodextrin is incorporated into the interfacial film, which might alter drug release rates and improve the droplet microstructure.

The graphical abstract depicts the change in nanoemulsion microstructure after addition of γ-CD as observed with TEM. The left-hand pictures show nanoemulsions with sucrose stearate or lecithin. The right-hand side pictures show the corresponding formulations with additional CD.Figure optionsDownload as PowerPoint slide