Green solid lipid nanoparticles by coacervation of fatty acids: An innovative cosmetic ingredient for the delivery of anti-age compounds through the skin

The constant exposure of the skin to internal and external stimuli drives towards skin aging and lost in skin hydration and elasticity. Chronic low-grade inflammation, called inflammaging, and oxidative stress are the leading causes of this phenomenon. Fatty acid coacervation is a preparation method for Solid Lipid Nanoparticles (SLNs), which does not employ solvents, and is associated to low energy consumption. Of note, Green SLNs by coacervation may be obtained from natural soaps. Within this concern, in this experimental work, Mango and Shea SLNs, prepared by coacervation from the corresponding vegetal soaps, were loaded with an UV-filter, 2-ethylhexyl 4-(dimethylamino)benzoate, and two anti-age ingredients, α-Tocopherol and Tocopheryl nicotinate, and characterized by a physico-chemical standpoint. Such Green cosmetic SLNs were monitored for stability after storage at 4, 25, 40 °C for 28 days. Moreover, an anti-age serum and hydrogel were prepared, based upon Green cosmetic SLNs. Stability studies were performed on sera and hydrogels, including physico-chemical stability studies (rheology, pH, centrifugation) and evaluation of organoleptic characteristics (appearance, odour, colour) after storage at 4, 25, 40 °C up to 1 year, with the best results obtained for Mango SLNs-based serum. Therefore, Franz cells studies with pig-ear skin were carried out on Mango SLNs and Mango SLNs-based serum, showing that loading in SLNs enhances the permeation of compounds. A challenge test and a patch test assessed the safety of such serum for human usage, and an efficacy study on human volunteers demonstrated its capability to increase skin hydration and elasticity.