Solid Lipid Nanoparticles of Serine Designed by Evaluating Affinity of Solid Lipids to Stratum Corneum for Enhanced Skin Hydration in Combination with Reed Root Extract

The study aimed to assess the skin hydrating effect of hydrogels containing serine-loaded solid lipid nanoparticles (SLN) prepared with lipids having high affinity to the stratum corneum (SC) and polysaccharide-rich reed (Phragmites communis) root extract (RRE). To select a lipid with high affinity to the SC, the interaction between the SC obtained by a tape stripping technique and three different lipids such as glycerol mono-oleate (GMO), lauric acid (LA), and capric acid (CA) was examined by ATR-FTIR. After choosing GMO as the lipid with the highest affinity to the SC, hydrogel formulations containing serine-loaded GMO SLN and/or RRE were prepared, and their skin hydrating effect was evaluated after applying the hydrogels to the surface of human skin. The hydrogel containing serine-loaded GMO SLN and RRE exhibited the greatest skin moisturizing effect, followed by the hydrogels with serine-loaded GMO SLN, RRE, and blank hydrogel. The results implied that SLN prepared with GMO having high affinity to the SC could be used as an efficacious carrier of serine for the purpose of skin hydration, and synergistic skin hydrating effect could be achieved by different skin moisturizing mechanisms of the serine-loaded SLN and RRE.