Preparation and characterization of alginate-based capsules containing lavender essential oil for acne therapy

• Zinc-crosslinked alginate capsules containing lavender oil were prepared. • Capsule morphology was influenced by the alginate and the cations concentrations. • Oil capsules had a smooth surface and highly porous interior. • Oil encapsulation efficiency averaged 98 % for all samples. • Oil capsules showed higher ductility and flexibility compared to empty capsules. In this study, we prepared alginate-based capsules containing lavender essential oil for cosmetic applications and acne treatment. To tune their preparation, several parameters have been changed to obtain empty and oil-containing beads, i.e. the alginate molecular weight and concentration and the cation concentration. Calcium-crosslinked beads were also studied as a reference system. The capsules were characterized by Optical Microscopy (OM), Environmental Scanning Electron Microscopy (ESEM), Thermogravimetric Analysis (TGA) and Dynamic Mechanical Analysis (DMA), while Encapsulation Efficiency was calculated by Gas Chromatography-Mass Spectrometry (GC–MS). Significant differences in the morphology of empty capsules are observed depending on the concentration of cation used and of the alginate solution; differently, capsules containing oil, regardless of the cation used, have a smooth surface and a highly porous interior. Encapsulation efficiency was very good, averaging 98 % for all samples. As for the mechanical properties of the capsules, the Young Modulus and the force at break were determined for oily and empty capsules with both cations. The empty capsules resulted more rigid and resistant than the oil-containing ones, while the latter showed an elastoplastic behaviour.