Microemulsion containing Kaffir lime oil using photo-crosslinkable bio-based copolymer

The research aimed to prepare a microemulsion of Kaffir lime oil (KLO) using photocrosslinkable bio-based copolymers as polymer shells. First, cinnamyl alcohol was used as a biomonomer, which was functionalized with methacrylic anhydride via an esterification reaction to contain a double bond named cinnamyl methacrylate. Then, it was copolymerized with methacrylic acid by solution iodine transfer polymerization, resulting in polymethacrylic acid-block-polycinnamyl methacrylate-block-poly methacrylic acid (PMAA-b-PCMA-b-PMAA) with a molecular weight of 2700 g/mol and a chain length of PMAA-b-PCMA-b-PMAA equals 7: 6: 7 units. After that, PMAA-b-PCMA-b-PMAA (BioSurf) was used as the polymer shell to encapsulate KLO in a microemulsion system cooperative with Tween 80 (surfactant; Surf) and ethanol (co-surfactant; CoSurf). The ratio of kaffir lime oil: Surf-CoSurf was varied from 1: 9 to 9: 1 (wt) where Surf_mix was BioSurf: Surf: Co-Surf ratio of 1: 1: 1 (wt) dispersed in water at 400 rpm for 5 min. The optimal contents of oil, Surf_mix, and water were 6 %, 24 %, and 70 %, respectively, with the nanocapsule size at about 68 nm. After UV curing at 254 nm for 120 min, the dimerization of cinnamyl groups in PCMA was confirmed by UV spectroscopy, where the absorbance peaks of cinnamyl groups at 283 and 294 nm significantly decreased. The encapsulated KLO was slowly permeating skin which was only 10 % after 1 h, with the anti-inflammatory percentage of inhibited nitric oxide production in macrophage cells at 19.24 ± 1.63. Moreover, nanocapsules did not show toxicity to human skin cells at concentrations less than or equal to 1 v/v%. Moreover, the microemulsion is thermodynamically stable at 4 °C, 30 °C, and 45 °C. The encapsulation of KLO in microemulsion might be an alternative candidate for cosmetic products and related applications.