Poly(ε-caprolactone) nanocapsules coated with Chitosan optimize the antimicrobial activity of Tea Tree Oil and Azithromycin against oral pathogens

Abstract

This study aimed to develop poly(ε-caprolactone) nanocapsules coated with chitosan, loaded with Tea Tree Oil (TTO) and Azithromycin (AZI), to optimize the antimicrobial activity and bioavailability of these actives. The nanocapsules suspension (NP-TTO-AZI-CH) was prepared using the preformed polymer interfacial precipitation method and coated with a 2 % chitosan solution. Physicochemical characterization included evaluating the pH, mean hydrodynamic diameter (Z-Average), Zeta potential (ZP), polydispersity index (PdI), encapsulation efficiency (EE) of the essential oil, and morphological assessment by Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). Biological tests conducted encompassed Minimum Inhibitory Concentration (MIC), Minimum Microbicidal Concentration (MMC), and cell viability assessments. NP-TTO-AZI-CH showed a Z-Average of 238.5 ± 1.7 nm and a PdI of 0.245 ± 0.010, indicating homogeneity in particle size and distribution. The positive ZP (+28.06 ± 1.10 mV) suggested the presence of chitosan on the nanocapsule surfaces, making the suspension more acidic (pH 4.38). EE was high at 89.89 ± 1.29 %. SEM images revealed the spherical/oval shape of the nanocapsules, and AFM confirmed their nanometric size and distribution within the system. Encapsulated TTO and AZI demonstrated lower MIC values compared to their free forms for all tested strains within 24 h, indicating enhanced antimicrobial efficacy. NP-TTO-AZI-CH exhibited bactericidal activity and maintained 70 % cell viability within the first 24 h at concentrations ranging from 0.5 mg/mL + 20 μg/mL to 0.06 mg/mL + 2.5 μg/mL (TTO + AZI). This formulation proved to be a promising tool for enhancing the antimicrobial activity of bioactives and combating various oral microbial strains.

Keywords: Anti-infective agents; Essential oil; Nanotechnology; Polymeric nanoparticles.