"Dual-Bottle, Dual-Mode" Intelligent Delivery System for Scenario-Specific Delivery of Astaxanthin and Skin Photoaging Protection.

Astaxanthin (AX) faces several challenges in topical skin applications, including poor water solubility, low photostability, undesirable staining, and uncontrolled release. To address these, this study developed a "dual-bottle, dual-mode" intelligent delivery system. First, sulfobutylether-β-cyclodextrin (SBE-β-CD) inclusion technology was used to prepare an AX@SBE-β-CD inclusion complex, greatly improving AX water solubility and increasing its retention rate from 14.4 (free AX) to 61.3% after 4 h of UVA irradiation. The AX@SBE-β-CD complex was next loaded into a UVA-responsive chitosan (CS)-based precursor (CS/4-PA/DCA), forming a drug-loaded precursor solution (bottle A) and further enhancing AX photostability, with a retention rate of 78.4%. Bottle A was kept separate from bottle B, an activating solution containing the photoinitiator LAP; together, they created the "dual-bottle" system. During daily low-UVA exposure, the use of bottle A alone enabled basic protection mode and sustained AX release (about 22.5% over 24 h). In high-UVA scenarios such as outdoor activities, mixing bottles A and B switched the system to "photo-triggered enhanced mode" the mixture rapidly gelled within 10 s of UVA irradiation, triggering a UVA dose-dependent burst of AX release. As UVA doses ranged from 5 to 20 J/cm2, the 10 min burst release increased from 8.3 to 20.6%, enabling on-demand release. Furthermore, the system alleviated AX-related skin staining, reducing residual color difference by about 78.2% after cleaning compared to conventional cream. In vitro and in vivo experiments confirmed that the system scavenged reactive oxygen species (ROS), protected skin cells, and regulated the TGFβ/Smad pathway to inhibit MMP1 expression, promote COL1A1 synthesis, and improve wrinkles, skin elasticity, and collagen damaged by photoaging. Thus, this study offers an integrated solution for topical AX that addresses enhanced stability, controlled release, and improved user experience. The dual-mode design, basic protection, and phototriggered enhancement also sets a direction for environmentally responsive and personalized skincare platforms.