Development of a w/o emulsion using ionic liquid strategy for transdermal delivery of anti – aging component α – lipoic acid: Mechanism of different ionic liquids on skin retention and efficacy evaluation

Skin aging affects personal image and health. α - lipoic acid (ALA), with excellent free radical scavenging capacity, was used in this research to prepare W/O emulsion. Considering the instability of ALA, ionic liquid strategy was adopted to heighten the solubility of ALA for dissolving in water phase. The mechanism of different ionic liquids (ILs) on skin retention of ALA was investigated by in vitro skin permeation experiment, emulsion quality characterization, rheological test, ATR - FTIR and molecular simulation. The results showed that ionic liquid strategy had a positive influence on the solubilization of ALA. Different ILs were different in skin retention and regulated by skin layers rather than drug release, in which ALA - triethanolamine (ALA - TEOA) presented the best affinity with both stratum corneum (SC) and viable epidermis and dermis (VED), while ALA - N - (2 - Hydroxyethyl) piperidine (ALA - HEPP) as well as ALA - N - (2 - hydroxyethyl) pyrrolidine (ALA - HEPR) showed affinity with either SC or VED respectively. Finally, the emulsion presented brilliant anti - aging efficacy. This study provided a new method of emulsion research and had great significance for the development of topical formulations.