Starch Pickering Emulsion: A Safe Vehicle for Topical Drug Delivery

Pickering emulsions differ from classical emulsions, because the first are stabilized by solid particles instead of surfactants. This type of emulsions has been widely investigated in pharmaceutical and cosmetic fields since they present less adverse effects than the classical emulsions that are stabilized by surfactants. The present study was conducted in order to characterize physically and chemically a preservative free and surfactant-free w/o emulsion for topical application and to evaluate its safety profile. Oscillatory and steady state shear measurements were performed for angular frequencies (ω) between 1 and 100 rad s-1 and shear rates ( ) between 1 and 1000 s-1 at 25 ºC, and the emulsions were examined by brightfield light microscopy. The antimicrobial activity was performed according to a modification of membrane filtration method described in the Ph.Eur.. In order to predict the cutaneous irritation to the emulsion the cell viability was evaluated using Df and HaCaT cell lines in a MTT assay. A HRIPT was used to study the irritancy and sensitizing potential of emulsion in 53 volunteers. Rheological measurements indicated that the system is well structured. The microstructure is related to the rheological behaviour in relation to particle size, shape and distribution. The antimicrobial study demonstrates that this particular w/o emulsions present self-preservation properties. Cytotoxicity results showed that the emulsion can be considered non-irritant. And in vivo studies confirmed that both emulsions did not induce any irritative or allergic reactions, showing that this product show very good skin compatibility. This study confirms that starch Pickering emulsions present a well structure system with a safe profile and the use of appropriate excipients allows preparing w/o emulsions with the obvious benefits of avoiding the drawbacks often associated with antimicrobial preservatives and surfactants agents.