Topical pickering emulsion versus classical excipients: A study of the residual film on the human skin.

The interest in Pickering emulsions is based on the possibility of replacing classical emulsifiers with solid particles. These emulsions are very attractive in the pharmaceutical field for their stability virtues and as a vehicle to deliver active ingredients. The study aimed to analyze the properties of the residual film of the Pickering emulsions on the human skin compared to conventional systems. For this project, three types of solid particles were used: titanium dioxide, zinc oxide and silicon dioxide. All of them are capable of stabilizing the oil/water interface and thus forming totally emulsified systems. To create an emulsion of reference, a classical surfactant was used as an excipient. Complementary systems containing both particles and the emulsifier were also analyzed. Then, a combined approach between physicochemical and biometrological in vivo analysis was employed. The study proved that Pickering emulsions stabilized by the metal oxides were distinct from the reference emulsion in terms of droplet sizes and organization, rheological and textural responses. Consequently, it impacted the properties of the residual film once the product was applied to the skin. The particle-stabilized emulsions formed a hydrophobic film counter to conventional excipients. Also, the Friction parameter (or the roughness of the film) was directly linked to the quantity of the particles used in the formulation and their perception on the skin surface. The use of the particles blurs the glossy effect of the oil phase. Finally, it was observed that the appearance of the residual film was impacted by the type of the particle, namely TiO2 and ZnO particles.

Bio-sourced polymers in cosmetic emulsions: a hidden potential of the alginates as thickeners and gelling agents.

OBJECTIVE: The present work aims to investigate the impact of the alginates on the texture properties of cosmetic emulsions. For this purpose, five systems were selected: a classical emulsion without polymer and four emulsions containing polymers, as texture modifiers, at the level of 1%. Two different grades of alginates were chosen: one rich in mannuronic acid and one rich in guluronic acid. The objective was also to evaluate the potential of in-situ gelation during formulation. The guluronic rich sample was gelled to evaluate the effect on the texture properties. Finally, alginates-based systems were compared to the xanthan gum as a bio-sourced polymer reference. METHODS: The sensory profile of the systems was established through a combination of prediction models and sensory analysis. The emulsion residual films obtained with natural polymers, Alginates and Xanthan Gum used as thickeners, as well as with the gelled version, were similar. However, the structural differences between polymers intervene during the characterisation of the sensory properties "before" and "during" application. A multi-scale physicochemical analysis was used to explain these differences. RESULTS: Due to a controlled formulation process, the use of the polymers did not affect the microstructure of the emulsion which remained similar to the control one. The main impact of the polymers was observed on the macroscopic level: both alginates showed their unique textural signature, different from the classical Xanthan Gum. Due to weak structural differences, mechanical and textural properties were very close between the mannuronic rich and guluronic rich samples, when not gelled, compared to other emulsions. However, the molar mass and the mannuronic/guluronic acids ratio were proved to be crucial for the stretching and consistency properties, showing that this structural difference may have an impact when products are handled in traction and compression. CONCLUSION: Meanwhile, the viscoelastic properties and the dynamic viscosity were greatly increased for the emulsion containing the gelled version of the alginate when compared to the classical polymers. The emulsion was also more consistent as proved by the textural analysis, pointing at better stability and suspension potential of the gelled emulsion versus the classical one containing the usual natural thickening agents.

OBJECTIF: Ce document vise à étudier l'impact des alginates sur les propriétés de texture des émulsions cosmétiques. À cet effet, cinq systèmes ont été sélectionnés: une émulsion classique sans polymère et quatre émulsions contenant des polymères, qui jouent le rôle de modificateurs de texture, à raison d'une teneur de 1%. Deux grades différents d'alginates ont été choisis : un alginate riche en acide mannuronique et un autre riche en acide guluronique. L'objectif était également d'évaluer le potentiel de gélification in situ pendant la formulation. L'échantillon riche en guluronique a été gélifié pour évaluer l'effet sur les propriétés de texture. Enfin, les systèmes à base d'alginates ont été comparés à la gomme xanthane, prise comme polymère d'origine biologique de référence. MÉTHODES: Le profil sensoriel des systèmes a été établi par une combinaison de modèles de prédiction et d'analyse sensorielle. Les films résiduels d'émulsion obtenus avec les polymères naturels, les alginates et la gomme de xanthane utilisés comme épaississants, ainsi qu'avec la version gélifiée, étaient similaires. Cependant, des différences structurelles entre les polymères se manifestent lors de la caractérisation des propriétés sensorielles « avant ¼ et « pendant ¼ l'application. Une analyse physico-chimique à échelles multiples a été utilisée pour expliquer ces différences. RÉSULTATS: En raison d'un procédé de formulation contrôlé, l'utilisation des polymères n'a pas affecté la microstructure de l'émulsion qui est restée la même que celle du témoin. Le principal impact des polymères a été observé au niveau macroscopique: les deux alginates ont montré leur signature texturale propre, laquelle diffère de la gomme de xanthane classique. En raison de faibles différences structurelles, comparées à d'autres émulsions, les propriétés mécaniques et texturales étaient très proches entre les échantillons riches en mannuronique et en guluronique, lorsqu'ils n'étaient pas gélifiés. Cependant, la masse molaire et le rapport acides gluturoniques/acides mannuroniques se sont avérés essentiels pour les propriétés d'étirement et de consistance, ce qui montre que cette différence structurelle peut avoir un impact lorsque les produits sont manipulés en traction et compression. CONCLUSION: Pendant ce temps, les propriétés viscoélastiques et la viscosité dynamique ont été considérablement augmentées pour l'émulsion contenant la version gélifiée de l'alginate par rapport aux polymères classiques. L'émulsion présentait également une plus grande uniformité, comme le prouve l'analyse texturale, indiquant un potentiel de stabilité et de suspension de l'émulsion gélifiée supérieur à celui de l'émulsion classique contenant les agents épaississants naturels habituels.