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This study evaluated the moisturizing effect of serine-loaded solid lipid nanoparticles (serine-SLN) and polysaccharide-rich reed (Phragmites communis) root extract (RRE) incorporated in hydrogel bases. The hydrogels with serine-SLN and/or RRE were carefully applied on the volar forearm of human volunteers. Their moisturizing efficacy was evaluated by monitoring conductance values using a skin surface hygrometer. The values of the area under the normalized conductance-time curve (AUCC) were developed and compared as a parameter for the water holding capacity of the skin. Hydrogels with serine-SLN did not significantly moisturize the skin, while hydrogel containing 0.25% RRE produced a significant increase in the moisture content of the skin. However, adding more than 0.25% of RRE into the hydrogel base decreased the moisturizing effect due to the marked reduction of viscosity. Significantly enhanced moisturizing effect was observed with the hydrogel containing 0.25% RRE and 3% serine-SLN, with AUCC increased 2.21 times compared to than blank hydrogel. The results imply that effective delivery of serine into the skin is possible using lipid-based nanocarriers and RRE, which could be a promising strategy to moisturize the skin effectively.

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. [ABSTRACT FROM AUTHOR]