Abstract
The use of lipid nanoparticles as drug delivery systems has been growing over recent decades. Their biodegradable and biocompatible profile, capacity to prevent chemical degradation of loaded drugs/actives and controlled release for several administration routes are some of their advantages. Lipid nanoparticles are of particular interest for the loading of lipophilic compounds, as happens with essential oils. Several interesting properties, e.g., anti-microbial, antitumoral and antioxidant activities, are attributed to carvacrol, a monoterpenoid phenol present in the composition of essential oils of several species, including Origanum vulgare, Thymus vulgaris, Nigellasativa and Origanum majorana. As these essential oils have been proposed as the liquid lipid in the composition of nanostructured lipid carriers (NLCs), we aimed at evaluating the influence of carvacrol on the crystallinity profile of solid lipids commonly in use in the production of NLCs. Different ratios of solid lipid (stearic acid, beeswax or carnauba wax) and carvacrol were prepared, which were then subjected to thermal treatment to mimic the production of NLCs. The obtained binary mixtures were then characterized by thermogravimetry (TG), differential scanning calorimetry (DSC), small angle X-ray scattering (SAXS) and polarized light microscopy (PLM). The increased concentration of monoterpenoid in the mixtures resulted in an increase in the mass loss recorded by TG, together with a shift of the melting point recorded by DSC to lower temperatures, and the decrease in the enthalpy in comparison to the bulk solid lipids. The miscibility of carvacrol with the melted solid lipids was also confirmed by DSC in the tested concentration range. The increase in carvacrol content in the mixtures resulted in a decrease in the crystallinity of the solid bulks, as shown by SAXS and PLM. The decrease in the crystallinity of lipid matrices is postulated as an advantage to increase the loading capacity of these carriers. Carvacrol may thus be further exploited as liquid lipid in the composition of green NLCs for a range of pharmaceutical applications.
Highlights
Carvacrol is chemically known as 5-isopropyl-2-methylphenol and is obtained from a range of aromatic plants such as oregano (Origanum vulgare L.), marjoram (Origanum majoranaL.), black cumin (Nigella sativa L.) or thyme (Thymus vulgaris L.) [1,2]
Due to the biological properties of carvacrol, this monoterpene has potential to be used as an active ingredient in pharmaceutical formulations; its oily liquid character makes this compound a suitable ingredient in formulating nanostructured lipid carriers (NLCs)
Carvacrol was found to be well mixed with melted stearic acid, beeswax and carnauba wax, while the binary mixtures resulted in less ordered structures, which can be further exploited as drug delivery carriers
Summary
Carvacrol (or cymophenol) is chemically known as 5-isopropyl-2-methylphenol and is obtained from a range of aromatic plants such as oregano (Origanum vulgare L.), marjoram (Origanum majoranaL.), black cumin (Nigella sativa L.) or thyme (Thymus vulgaris L.) [1,2]. Biocompatible and of low toxicity, the major advantages of NLCs include their green nature, capacity for protecting loaded drugs/actives from chemical degradation and the provision of a controlled release of the payload [19,24,25,26,27,28,29]. Due to their nanostructured matrix, obtained by disrupting the crystal packing of the solid lipid by mixing it with a liquid lipid, NLCs may offer a triggered release [30]. The use of lipid mixtures that crystallize in a less organized matrix is linked to higher loading capacity of the nanocarriers
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