Encapsulamento do óleo essencial da Lippia alba em nanopartículas de poli-e-caprolactona (PCL) para avaliação da estabilidade e atividade larvicida contra o Aedes aegypti

Abstract

The aim of this work was to develop biodegradable nanoparticles of Poly-ɛ-caprolactone (PCL) to encapsulate the essential oil of Lippia alba species using two types of preservatives (NE and sodium benzoate). The intention is to formulate controlled release systems that can act as efficient larvicides against Aedes aegypti. The chromatographic analysis (GC-MS) of the essential oil in natura revealed a composition mainly monoterpenic constituted by Carvone (54,54%) and Limonene (21,49%). The essential oil presented no antioxidant activity against the DPPH radical, nor was enzymatic for AChE. Larvicidal tests were performed with in natura essential oil revealing CL50 and CL90 about 106 and 130 μg.mL-1, respectively. The nanoprecipitation method was efficient, resulting in a high percentage of encapsulation of the essential oil. Through the AFM and DLS techniques, it was possible to estimate the average diameter of the developed nanoparticles, which was estimated around (136 ± 2) nm for empty nanoparticles and around (266 ± 6) nm for those with encapsulated essential oil. The value of the zeta potential was around -8.02 mV for pH = 4. FTIR measures allowed the identification of the main stretches of the majority molecules, besides the qualitative verification of the encapsulation efficiency. Stability studies were performed by monitoring pH, electrical conductivity and encapsulation efficiency over time. It was observed that the evaluated systems (containing 500 μg.mL-1 of encapsulated essential oil and NE preservative or sodium benzoate) were stable for 50 days. In contrast, the system containing the same concentration of oil andwithout preservatives remained stable for 30 days. The controlled release assays were performed at different pHs (4, 7 and 10), showing that the release was faster at neutral and basic pH because they cause destabilization of the system due to its approximation with the isoelectric point. Larvicidal tests were carried out with the purpose of evaluating the effect of the formulation against larvae of A. aegypti. It was observed that CL90 was maintained in the larvicidal assays. However, the mortality time of the larvae was smaller than that observed in the release curves. These data suggest a possible ingestion of nanoparticles containing encapsulated oil, showing that the proposed formulation is an effective alternative for A. aegypti larvae control.