Abstract
Mini-emulsion polymerization was applied for the synthesis of cross-linked polymeric nanoparticles comprised of methyl methacrylate (MMA) and Triethylene Glycol Dimethacrylate (TEGDMA) copolymers, used as matrix-carriers for hosting D-limonene. D-limonene was selected as a model essential oil, well known for its pleasant odor and its enhanced antimicrobial properties. The synthesized particles were assessed for their morphology and geometric characteristics by Dynamic Light Scattering (DLS) and Scanning Electron Microscopy (SEM), which revealed the formation of particles with mean diameters at the nanoscale (D[3,2] = 0.135 μm), with a spherical shape, while the dried particles formed larger clusters of several microns (D[3,2] = 80.69 μm). The percentage of the loaded D-limonene was quantified by Thermogravimetric Analysis (TGA), complemented by Gas Chromatography-Mass Spectrometry analysis coupled with a pyrolysis unit (Py/GC-MS). The results showed that the volatiles emitted by the nanoparticles were composed mainly of D-limonene (10% w/w of dry particles). Particles subjected to higher temperatures tended to decompose. The mechanism that governs the release of D-limonene from the as-synthesized particles was studied by fitting mathematical models to the release data obtained by isothermal TGA analysis of the dry particles subjected to accelerated conditions. The analysis revealed a two-stage release of the volatiles, one governed by D-limonene release and the other governed by TEGDMA release. Finally, the antimicrobial potency of the D-limonene-loaded particles was demonstrated, indicating the successful synthesis of polymeric nanoparticles loaded with D-limonene, owing to enhanced antimicrobial properties. The overall performance of these nanoparticles renders them a promising candidate material for the formation of self-sterilized surfaces with enhanced antimicrobial activity and potential application in food packaging.
Highlights
All bacterial strains (Escherichia coli (XL1 (Stratagene)), Staphylococcus aureus (NCIM 2079), Bacillus subtilis (ATCC 6633), and Bacillus cereus (ATCC 11778)), used in this study were stored at −80 ◦ C before use
When a fractional factorial design with a low number of experiments is conducted, the results only show a trend and there is no safe conclusion about the statistical significance of the factors and their interaction [29,30]
Cross-linked polymeric nanoparticles comprised of methyl methacrylate (MMA) and Triethylene Glycol Dimethacrylate (TEGDMA), were successfully synthesized via mini-emulsion polymerization, as matrix-carriers of the model essential oil D-limonene
Summary
Essential oils (EOs) are volatile, natural liquids with an oily texture that can be extracted from several plants [1,2]. They are synthesized through complex metabolic pathways and play a protective role for the plant organism against pathogenic microorganisms [3]. Due to the aroma character of EOs, they have been widely used in the cosmetic industry [1,4]. In addition to their pleasant odor, the large bioactivity of EOs has been confirmed by several studies and includes antibacterial, antiviral, anti-inflammatory, antifungal, antimutagenic, antineoplasmatic, and antioxidant activities, along with other miscellaneous activities [3].
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