Nanosystems such as microemulsions (ME) and nanoemulsions (NE) offer considerable opportunities for targeted drug delivery to and via the skin. ME and NE are stable colloidal systems composed of oil and water, stabilised by a mixture of surfactants and cosurfactants, that have received particular interest as topical skin delivery systems. There is considerable scope to manipulate the formulation components and characteristics to achieve optimal bioavailability and minimal skin irritancy. This includes the incorporation of established chemical penetration enhancers to fluidize the stratum corneum lipid bilayers, thus reducing the primary skin barrier and increasing permeation. This review discusses nanosystems with utility in skin delivery and focuses on the composition and characterization of ME and NE for topical and transdermal delivery. The mechanism of skin delivery across the stratum corneum and via hair follicles is reviewed with particular focus on the influence of formulation.

Resveratrol (RSV) is a potent lipophilic antioxidant with a low aqueous solubility. Novel nanoformulations have been successfully developed and evaluated to increase the potential of resveratrol as a skin targeting antioxidant. Nanoformulations were prepared using a spontaneous emulsification method, and characterized and evaluated for their capabilities to penetrate/permeate the skin. In nanoformulations, the thermodynamic activity of the RSV penetration into/permeation through the skin was correlated with the thermodynamic activity of the RSV in the formulations. When terpenes were incorporated into the nanoformulations, the permeation of RSV through the skin increased and correlated with an increasing lipophilicity of the terpene. The nanoemulsion containing eugenol showed the highest RSV penetration into the stratum corneum (SC) and the epidermis-dermis-follicle region, whereas the limonene containing nanoemulsion had the highest RSV permeation through the skin (the enhancement ratios, compared to a saturated solution of RSV, were (i) 9.55 and (ii) 12.61, respectively, based on the average RSV amount (i) in each skin region and (ii) permeation through skin).

Astaxanthin (ASX) is a potent lipophilic antioxidant derived from the natural pigment that gives marine animals their distinctive red-orange colour and confers protection from ultraviolet radiation. Self nano-emulsifying drug delivery systems (SNEDDS) have been successfully developed and evaluated to increase the skin penetration of ASX and target its antioxidant and anti-inflammatory potential to the epidermis and dermis. SNEDDS were prepared using a low-temperature spontaneous emulsification method, and their physical characteristics, stability, antioxidant activity, and skin penetration were characterized. Terpenes (D-limonene, geraniol, and farnesol) were included in the SNEDDS formulations to evaluate their potential skin penetration enhancement. An HPLC assay was developed that allowed ASX recovery from skin tissues and quantification. All SNEDDS formulations had droplets in the 20 nm range, with low polydispersity. ASX stability over 28 days storage in light and dark conditions was improved and antioxidant activity was high. SNEDDS-L1 (no terpene) gave significantly increased ASX penetration to the stratum corneum (SC) and the epidermis-dermis-follicle region (E + D + F) compared to an ASX in oil solution and a commercial ASX facial serum product. The SNEDDS-containing D-limonene gave the highest ASX permeation enhancement, with 3.34- and 3.79-fold the amount in the SC and E + D + F, respectively, compared to a similar applied dose of ASX in oil. We concluded that SNEDDS provide an effective formulation strategy for enhanced skin penetration of a highly lipophilic molecule, and when applied to ASX, have the potential to provide topical formulations for UV protection, anti-aging, and inflammatory conditions of the skin.

This article discusses on the natural compounds from the ant plant (Myrmecodia species, family: Rubiaceae

No abstract