Synergistic antimicrobial activities of tea tree oil loaded on mesoporous silica encapsulated by polyethyleneimine

Abstract

In an effort to improve the continuous bacteriostatic properties of tea tree oil (TTO), mesoporous silica (M41S) was prepared by sol-gel method using cetyltrimethylammonium bromide (CTAB) as template and tetraethyl orthosilicate (TEOS) as silica precursor, which was employed as a carrier for TTO. M41S loaded with TTO was then coated with polyethylenimine (PEI) via electrostatic interactions to prepare essential oil/M41S@polyethyleneimine composites (TTO/M41S@PEI). The corresponding structures and morphologies of the as-synthesized materials were systematically studied by N2 adsorption/desorption measurements, X-ray powder diffraction (XRD) and thermogravimetry (TGA). The results confirmed that TTO could be loaded into channels and PEI was found to coated on the outer surface of M41S. Importantly, the modification of PEI did not change the mesostructure of the two-dimensional hexagonal phases of M41S. In addition, the anti-bacterial abilities of TTO/M41S@PEI could be studied by using inhibition zones method. Such study showed that PEI and TTO exhibited synergistic anti-bacterial effects. The bacteriostasis slope of TTO was 2.265, and the slope of TTO/M41S@PEI was 3.275. These findings indicated that the inhibition rate of TTO/M41S@PEI was higher than that of TTO using the same number of colonies. Additionally, the sustained release behavior of TTO/M41S@PEI could be described by the logistic kinetic model. Even after 240 h of natural release, TTO/M41S@PEI still exhibited a stable and sustained bacteriostatic effect compared with TTO.