Preparation, Characterization, and Antibiofilm Activity of Free and Nanoencapsulated Tetradenia riparia (Hochst.) Codd Leaf Essential Oil

Background: Staphylococcus aureus is a clinically relevant pathogen with a strong ability to form biofilms on a wide range of surfaces, which markedly reduces the effectiveness of antimicrobial treatments and contributes to therapeutic failure. Although essential oils (EOs) represent effective and economical antimicrobial alternatives, their clinical application is limited by rapid oxidation, volatility, and potential cytotoxicity. In this context, nanoencapsulation emerges as a promising strategy to improve EO stability, control release, and reduce toxicity. In this study, Tetradenia riparia essential oil was encapsulated into poly(lactide) (PLA) nanoparticles (NP) using the nanoprecipitation method. Methods: The physicochemical properties of the nanoparticles were characterized, and their antibacterial, antibiofilm, and cytotoxic activities were evaluated. Antibiofilm and antibacterial effects against S. aureus were assessed by the broth microdilution method, while cytotoxicity was determined using a VERO cell line. Results: The nanoparticles exhibited nanometric size, spherical morphology, and homogeneous structure. Both free EO and EO-loaded nanoparticles demonstrated antibacterial and antibiofilm activity against S. aureus. Importantly, EO-loaded nanoparticles were significantly less cytotoxic than free EO. Nanoencapsulation effectively prevented rapid EO evaporation and degradation, thereby enhancing stability. The nanoparticles exhibited a zeta potential of approximately −23.1 mV, indicating adequate colloidal stability. Differential scanning calorimetry revealed a reduction in melting enthalpy from 429.63 J/g (blank nanoparticles) to 115.83 J/g for EO-loaded nanoparticles, indicating decreased polymer crystallinity and a system favorable for controlled EO release. Conclusions: Overall, these findings demonstrate that nanoencapsulation of T. riparia essential oil into PLA nanoparticles preserves antimicrobial efficacy, reduces cytotoxicity, and improves physicochemical stability, supporting the potential of this nanostructured system as a promising strategy for the treatment of S. aureus biofilm-associated infections.