Laurus nobilis Essential Oil Nanoemulsion as a Natural-Product Phase for Gel-Based Delivery: Antimicrobial, Antibiofilm, Cytotoxic and Wound-Closure Activities In Vitro

Laurus nobilis L. essential oil displays a broad range of biological activities, yet its poor aqueous dispersibility, high volatility and susceptibility to oxidative degradation restrict its use in aqueous biological systems. In this study, an ultrasound-assisted L. nobilis oil nanoemulsion (LNNO) was formulated, characterized and, within a single experimental framework, compared directly with the unformulated oil for its antimicrobial, antibiofilm, cytotoxic and wound-closure responses. GC-MS profiling identified eucalyptol (1,8-cineole; 35.12%) as the predominant constituent. LNNO showed an intensity-weighted Z-average hydrodynamic diameter of 77.10 nm (number-weighted mean 72.30 ± 0.5 nm; TEM 65.4 nm), a PDI of 0.231, and an apparent zeta potential of −31.10 mV, and it remained nanoscale without visible phase separation over 60 days of storage. LNNO inhibited all six tested microorganisms (MIC 7.8–31.25 µg/mL), with MIC values four- to eightfold lower than those of pure oil, and reduced biofilm biomass by up to 96.80% (Bacillus subtilis) and 96.63% (Candida albicans) at 75% of the MBC/MFC; at this level concentrations equal or exceed the MIC, and the least confounded antibiofilm comparison (25% MBC/MFC, below MIC) still showed 45.28––72.45% inhibition versus 18.45–32.61% for pure oil. In Caco-2 colorectal adenocarcinoma cells, the MTT IC50 of LNNO was approximately half that of pure oil (107.4 versus 215 µg/mL), whereas the IC50 in normal HFB4 fibroblasts was 368.81 µg/mL (selectivity index 3.43). At a non-cytotoxic concentration, LNNO increased scratch closure in HFB4 monolayers from 28.4 ± 2.1% (untreated) and 30.1 ± 2.4% (oil-free vehicle) to 58.7 ± 3.2% at 48 h (p < 0.001; n = 3 independent experiments). The oil-free vehicle was inactive in all assays. In a single preliminary compatibility experiment, LNNO retained nanoscale dispersion and antimicrobial activity after incorporation into a carbomer gel, while the blank gel was inactive. Together, these data show that nanoemulsification improves the measured in vitro responses to L. nobilis oil and provides a characterized platform for mechanistic studies and subsequent in vivo evaluation.