Alginate microcapsules for topical delivery of lavender essential oil: Impact of divalent crosslinkers on release, antibacterial efficacy and biocompatibility

Lavender essential oil has shown antibacterial activity against acne-associated bacteria; however, its volatility, oxidative instability, and potential skin irritation limit direct topical application. Moreover, the incorporation of essential oils into hydrogel-based delivery systems presents formulation challenges related to nanoemulsion stability, encapsulation efficiency, and controlled release. The objective of this study was to develop and characterise alginate-based capsules containing lavender oil, crosslinked with either zinc or calcium ions, as a potential topical delivery system for acne therapy. Capsules crosslinked with zinc or calcium ions were prepared using a scalable combination of ionic gelation and nanoemulsion techniques, yielding high encapsulation efficiency (around 98 ± 0.2%). Capsules prepared with 2% alginate and 2% crosslinker exhibited spherical morphology and reproducible size. Oil-loaded capsules showed a porous internal structure and reduced mechanical stiffness compared to empty systems. Isothermal thermogravimetric analysis demonstrated improved oil retention in calcium-crosslinked formulations. Biological evaluation revealed antibacterial and anti-inflammatory activity, with distinct ion-dependent effects and formulation-specific cytocompatibility profiles. This study demonstrates that alginate-based microcapsules can serve as effective delivery systems for essential oils, enabling stabilisation, controlled release, and enhanced biological activity. The results underline the importance of crosslinker selection in balancing efficacy and safety, providing formulation-level design guidelines for the development of essential oil-based topical drug delivery systems.