The use of nanotechnology in enhancing the efficacy of cosmetic actives of natural origin

The trend towards natural cosmetics has had a strong and lasting impact on the cosmetics development. However, producing efficient and acceptable natural products presents a major technical challenge. The aim of this study was to investigate how adaptation of a new technology (nanotechnology) could influence the efficacy of natural actives in cosmetic products.

The introductory part of this thesis presents a review of natural cosmetics in terms of their legal status and market share, including various attempts to define natural and/or organic cosmetics and comparisons of relevant certifications, as well as the merits of skin delivery systems in topical delivery. In this study, an ester form of Vitamin E, d-a-tocopheryl acetate (TA) , was chosen as a model natural active. Obtained from natural sources, vitamin E alcohol (tocopherol) has undergone esterification process in order to gain increased stability. This places it into the group of naturally derived actives, a subcategory of natural actives. A suitable, 'fit for purpose' analytical method for the assessment of TA was then developed and validated, employing high performance liquid chromatography (HPLC).

The production of TA-Ioaded lipid nanocarriers (TA-LNC), with well-tolerated and in vivo biodegradable ingredients, has been achieved using the phase inversion method. High-speed centrifuging was established to be the most efficient purification method for LNC suspension. The size of lipid nanocarriers have been characterised by photon correlation spectroscopy (PCS) and by nanoparticle tracking analysis method (NTA). The TA-LNC have proven to be monodisperse, with the particle size of less than 60 nm and stable for at least 28 days in different temperatures (0 °C, 4°C and 28°C). The nanocarriers showed 57.7 ± 4.9% encapsulation efficiency of the original 110 mg of TA added. The recovery of TA from the purification method was found to be 90.4% ± 2.2. In the next stage, a suitable semi-solid dosage form was developed by adding sodium hyaluronate (HA) to a dispersion of purified TA-LNC. Rheological study of obtained HA hydrogels showed an increase in both elastic (G') and viscous (Gil) moduli and a decrease in the crossover frequencies, which indicated that the addition of TA-LNC had enhanced the stability of the HA gel network.

The release of TA from nanoparticle formulations and its in vitro permeation through both porous (nylon) and non-porous (silicon) synthetic membranes was assessed using a novel lipid receiver fluid. In vitro adsorption tests, employing tape striping method, using pig and human skin have shown 1.65% ± 0.90% adsorption of TA from nanoparticles formulation into pig skin, but no absorption into human skin, under given experimental conditions. This indicated a marked difference in barrier properties of these two membranes.

In vivo investigation was performed using both short (3 hours) and long term (4 weeks) trials on human volunteers. The TA-LNC formulations enhanced skin hydration significantly compared to negative control in both trials, with both standard topical vehicle (HA hydrogel) and in an innovative vehicle (foam). While skin viscoelastic parameters remained practically unchanged during the 4-week study. The micro-inflammatory method used for assessing the antioxidant potential of TA was not able to detect significant differences between the employed formulations.

In conclusion, lipid nanocarriers produced and assessed in this study have shown potential as effective carriers for cosmetic actives of natural origin. The results of this study indicate that active materials with lower lipophilicity than vitamin E would be more suitable for the incorporation into the type of lipid nanocarriers assessed here. Nevertheless, research findings obtained in this study, as well as a number of test procedures established for the purpose of this study, provide a solid ground for future development.

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