Design of a phytosphingosine-containing, positively-charged nanoemulsion as a colloidal carrier system for dermal application of ceramides

Positively charged oil/water (o/w) nanoemulsions (PN) are effective vehicles to change the permeability of the skin. This study focused on the preparation and characterisation of phytosphingosine (PS) containing PN (PPN) which serve as colloidal carriers for the dermal application of ceramide IIIB (CIIIB) and the stratum corneum (SC) lipids (PPNSC) such as ceramide III (CIII), cholesterol, and palmitic acid. The investigations were conducted using appropriate emulsification and homogenisation processing conditions to optimise PPNSC with regard to droplet size, physical stability, and solubility of PS, CIII and CIIIB. A decrease in droplet size was observed through eight homogenisation cycles at a pressure of 500 bar and a temperature of 50 °C. Above these optimal values, an increase in droplet size was observed. PS and ceramides have low solubilities in oil and water. When Lipoid E-80® (LE80) was added to the oil phase, the solubility of PS and ceramides increased, indicating some interactions shown by DSC measurements. SC lipids and CIIIB could be successfully incorporated in PPN without producing any physical instability. The high stability of PPNSC is probably due to the presence of a hydrophilic (Tween 80) and a lipophilic surfactant (LE80), supported by the lipophilic cosurfactant PS, at the o/w interface. It was shown that PS was responsible for the positive charge and thus supported the high physical stability of PPNSC. This optimised emulsion was selected for further skin absorption evaluation.