Royal jelly-loaded sodium alginate nanoparticles fabricated by Ca2+ crosslinking: Preparation, characterization and bioactivity evaluation.

To improve the stability of the natural bioactive substance royal jelly (RJ), this study prepared RJ-loaded sodium alginate nanoparticles (RJ-SANPs) via Ca2+-mediated ion-gelation method. SEM and TEM showed predominantly spherical nanoparticles. FTIR spectroscopy confirmed the formation of hydrogen bonds between RJ and SA, while XRD analysis revealed the coexistence of crystalline RJ domains with the amorphous SA matrix, together confirming its successful encapsulation. Moreover, the RJ-SANPs showed hydrodynamic diameter of 532.63 ± 64.22 nm to 662.73 ± 63.65 nm and its encapsulation efficiency (EE) ranges from 42.33% to 58.62%. The in vitro release of 10-HDA from RJ-SANPs followed a Fickian diffusion mechanism, as described by the Korsmeyer-Peppas model. DSC results indicated that SA's "egg-box" structure enhanced the thermal stability of RJ by altering its thermal behavior. The 1:1 RJ-SANPs exhibited good biocompatibility toward HaCaT and HFF-1 cells. It increased type I collagen content in HFF-1 cells in a concentration-dependent manner, reaching 593.64 ng/mL at 0.025% (v/v) (p < 0.05), and also showed antioxidant activity with a maximum ABTS radical scavenging rate of 62.10%, as well as antibacterial activity against E. coli, P. fluorescens, B. cereus, and S. aureus. However, the low concentrations tested did not significantly upregulate AQP3 expression, which might be attributed to the dose-dependent bioactivity of RJ-SANPs. They retained stability at 4 °C, pH 3.0-7.0, and 0-300 mmol/L NaCl. The work confirmed that SA encapsulation enhances RJ stability while preserving key bioactivities, suggesting the potential of RJ-SANPs as antioxidant and collagen-promoting functional ingredients for skin-care applications.