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.

Fragrance in dermocosmetic emulsions: From microstructure to skin application.

Fragrance is added to almost all dermocosmetic emulsions, as it has been found to be a key driver in consumer choice and contributes to the perception of product performance. Fragrance is a complex mixture of odorant chemicals at different concentrations. When incorporated into a formulation, the individual fragrance chemicals partition between the emulsion phases depending on their physicochemical properties, which can impact the structure, stability, texture and odour of the final product. On the other hand, it is well known in the food industry how the composition and structure of food emulsion matrices influence the release of aroma chemicals. Fragranced dermocosmetic emulsions have been studied to a lesser extent but it is interesting to apply findings from the food domain since emulsion structure, composition and aroma compounds share common features. This review aims to give an overview of the literature dealing with the interactions between fragrance and dermocosmetic emulsions. The effects of fragrance on emulsion microstructure, stability and texture are highlighted and discussed. The effects of composition and structure of emulsion on the release of fragrance molecules are also presented. Finally, the interactions between skin and fragranced emulsions are addressed.

Des parfums sont ajoutés dans la plupart des émulsions dermocosmétiques. L'odeur d'un produit est en effet un facteur déterminant lors du choix par les consommateurs, et elle peut même contribuer à la perception de ses performances. Le parfum est un mélange complexe de substances chimiques odorantes à différentes concentrations. Lorsqu'elles sont incorporées dans une formule, les molécules odorantes se répartissent entre les phases de l'émulsion en fonction de leurs propriétés physicochimiques, ce qui peut avoir un impact sur la structure, la stabilité, la texture et l'odeur du produit fini. D'autre part, il est bien connu dans l'industrie alimentaire que la composition et la structure des matrices alimentaires influencent la libération des molécules aromatiques. Les émulsions dermocosmétiques parfumées ont été moins étudiées dans la littérature, mais les résultats obtenus dans le domaine alimentaire peuvent être utiles pour comprendre les phénomènes mis en jeu dans ces systèmes. En effet, la structure et la composition des deux types d'émulsions, et la nature des composés aromatiques et odorants présentent de nombreuses caractéristiques communes. Cette revue vise à donner une analyse de la littérature traitant des interactions entre les parfums et les émulsions dermocosmétiques. Dans un premier temps, les effets des parfums sur la microstructure, la stabilité et la texture des émulsions sont présentés et discutés. Puis, les effets de la composition et de la structure de l'émulsion sur la libération des molécules parfumantes sont abordés. Enfin, les interactions entre la peau et les émulsions parfumées sont renseignées.

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.

Impact of cigarette smoke on physical-chemical and molecular proprieties of human skin in an ex vivo model.

BACKGROUND: This is a study about the skin ageing exposome, focusing on the effect of cigarette smoke. Human living skin explants (HSE) were exposed to cigarette smoke (CS) of two cigarettes for 2 hours using a custom-made exposure chamber, the Pollubox® . Effects on the surface physico-chemistry and molecular properties of the skin were analyzed and reported for the first time. BASIC PROCEDURES: To this end, transcriptomic study followed by immunohistochemistry, MDA (Malondialdehyde Dosage), and surface physio-chemistry data: surface free energy determination, TEWL (Trans Epidermal Water Loss), skin pH and FT-IR (Fourier Transform-Infrared) spectroscopy of the explant were collected from untreated and treated HSE. MAIN FINDINGS: Results showed a decrease of the total surface free energy of the treated HSE. This decrease reflected higher interactions with polar compounds from the environment and consequently a decrease of the surface hydrophobicity. Additionally, an increase of TEWL and skin pH was observed after treatment. The transcriptomic analysis showed downregulation of mitochondrial genes (PON2-NDUFA4L2-ATP1A1-ALDH2-PRODH) combined with an increase of MDA in CS-treated HSE. CONCLUSIONS: CS-induced oxidation of lipids at HSE surface alters the skin barrier: interactions with polar products are enhanced and the lipid chain packing at the surface is modified. Consequently, skin permeability could increase which correlated with repression of CA9 and AQP1 genes. Beside activation of AHR-NRF2 pathway in CS-exposed HSE, our results suggested that mitochondrial functions were strongly impacted and oxidized lipids failed to be eliminated promoting skin barrier alteration. A mitophagy activity was suggested through the confirmation of PINK1 accumulation in the epidermis by immunostaining.

Residual film formation after emulsion application: Understanding the role and fate of excipients on skin surface.

This study focuses on the fate of excipients contained in topical emulsions once applied on the skin. The aim was thus to develop a methodology to characterize the residue left on the skin shortly after emulsion application. To this end, both the role and the impact of the different excipients on the formation and properties of the residue left on the skin surface once a product is applied were investigated. To that purpose, an O/W emulsion composed of an ester as oily phase, an emulsifier (alkylpolyglucoside-based vehicles), a polymer and a humectant (hydrophilic excipient) was first developed. Then, systems with fewer ingredients were prepared to understand their respective role in the residual film. This residual film was studied in vivo by means of biophysical instrumental methods, all being performed on the participants' forearm. Results highlighted the major role of the ester giving a bright and hydrophobic residue. While the surfactant structuration as the presence of glycerin and polymer provided a specific water distribution inside the residue on the skin surface. Finally, this work evidenced the ingredients organization in the residue depending on the systems composition, with a particular stratification on skin surface which could be considered in the formulation strategy for efficient active delivery and skin protection.

Complementary approaches to understand the spreading behavior on skin of O/W emulsions containing different emollientss.

The human skin is a very complex living tissue, in a permanent evolution and self-renewing by constant lipids secretion. The characterization of this biological material is a major concern in dermo-cosmetic and pharmaceutics fields. Understanding the skin interaction with its environment, during application of skincare products, is consequently of genuine interest to better control the different phenomena occurring. In sensory language, the application of products on the skin is defined as the spreading behavior. Five O/W emulsions were formulated with different ratios of two emollients (isohexadecane and stearic acid). Complementary instrumental and sensory analysis of spreading behavior was carried out in vivo on human skin as well as in vitro on non-biological skin surface in order to investigate the impact of two emollients, and their mixtures in the spreadability and penetration of O/W emulsions. A first screening was made to link the physico-chemical properties (polarity, physical state and ratio) of emollients with the spreading behavior on human skin. Then, interesting parameters (the plateau value, its length and the increase of the friction value) from the tribological study on skin were considered to allow deepening the product/skin interactions after application of different emulsions and over time. In the last part of the study, an original method, using non-biological surfaces mimicking the human skin, was successfully tested with very good reproducibility of the spreading behavior. This original tool is of great interest to study the efficacy of new formulas on skin, but also for fundamental research and help performing standardized measurements as well as solving the logistic and safety problems of in vivo studies.

Design of a Lipid-Coated Polymeric Material Mimic Human Skin Surface Properties: a Performing Tool to Evaluate Skin Interaction with Topical Products.

An original nonbiological skin model (NBSM) has been developed to mimSic skin surface properties. This skin model presents several improvements when compared to existing ones: it has a topography identical to that of in vivo skin and a lipid composition close to that of the skin face. This imparts to the model surface a physicochemistry similar to in vivo skin. The concept and design of the skin model are presented, followed by an instrumental characterization performed using 3D microscopy, attenuated total reflectance-Fourier transformed infrared spectroscopy, and contact angle measurements. Surface free energy components are calculated for the NBSM using the Van Oss approach and compared to ex vivo experiments performed on human living skin explants. A comparison was made with the commercial skin model VITRO-SKIN, this latter being a reference in terms of the NBSM. The effect of several emollients on skin physicochemistry was investigated in vivo and on both nonbiological models. The study focused on several emollients and oils, including silicones and esters, and three emulsions (oil-in-water or water-in-oil). The results obtained confirm the high reliability of the developed model as it shows a skin-like surface behavior. This very interesting tool shows promising results concerning the study of the residual film present after product application or to study skin/product interactions.

Pharmacotechnical Development of a Nasal Drug Delivery Composite Nanosystem Intended for Alzheimer's Disease Treatment.

Direct nose-to-brain delivery has been raised as a non-invasive powerful strategy to deliver drugs to the brain bypassing the blood-brain barrier (BBB). This study aimed at preparing and characterizing an innovative composite formulation, associating the liposome and hydrogel approaches, suitable for intranasal administration. Thermosensitive gel formulations were obtained based on a mixture of two hydrophilic polymers (Poloxamer 407, P407 and Poloxamer 188, P188) for a controlled delivery through nasal route via liposomes of an active pharmaceutical ingredient (API) of potential interest for Alzheimer's disease. The osmolarity and the gelation temperature (T° sol-gel) of formulations, defined in a ternary diagram, were investigated by rheometry and visual determination. Regarding the issue of assays, a mixture composed of P407/P188 (15/1%, w/w) was selected for intranasal administration in terms of T° sol-gel and for the compatibility with the olfactory mucosal (280 ± 20 mOsmol, pH 6). Liposomes of API were prepared by the thin film hydration method. Mucoadhesion studies were performed by using mucin disc, and they showed the good natural mucoadhesive characteristics of in situ gel formulations, which increased when liposomes were added. The study demonstrated successful pharmacotechnical development of a promising API-loaded liposomes in a thermosensitive hydrogel intended for nasal Alzheimer's disease treatment.

Brazilian and French sensory perception of complex cosmetic formulations: a cross-cultural study.

OBJECTIVE: Brazil and France are two major beauty markets worldwide. Despite this, there is not much cross-information on sensory analysis of cosmetic products between both population of these countries. The objective of this study was to compare the sensory perception of cosmetic formulations between Brazilian and French assessors and establish cross-culturally preferences. METHODS: For this, a total panel of 100 consumers of cosmetics evaluated four different products. The same protocol for the sensory analysis was followed in both countries. RESULTS: The panellists were able to perceive differences in the products and the method proved to be repeatable in both countries. The presence of UV filters in the formulation was noticed and displeased both populations. Brazilians, although dissatisfied with the sensory aspect of the sunscreen, are willing to use it for its UV protection. CONCLUSION: This work delivers important information on the sensory perception of cosmetics by people from different countries and brings important knowledge to develop products with textural properties that will be appreciated worldwide.

OBJECTIFS: Le Brésil et la France sont deux pays majeurs pour le marché de la beauté. Malgré cela, il y a peu d'étude interculturelle sur la perception sensorielle des produits cosmétiques entre ces deux populations. L'objectif de cette étude était donc de comparer l'analyse de formules cosmétiques par deux jurys, l'un brésilien et l'autre français, et d'établir leur préférence. METHODES: Pour cela, nous avons demandé à 100 consommateurs au total d'évaluer 4 produits cosmétiques différents. Le même protocole d'analyse sensorielle a été scrupuleusement suivi dans les deux pays. RESULTATS: Les évaluateurs ont été capables de percevoir des différences significatives entre les produits, et de façon répétable dans chaque pays. Chaque jury a noté la présence de filtres UV dans les formules et ces dernières ont été peu appréciées. Cependant, le jury brésilien était favorable à leur utilisation pour se protéger des UV, et ce malgré leurs propriétés sensorielles insatisfaisantes. CONCLUSION: Ce travail fournit des informations indispensables sur la perception sensorielle des produits cosmétiques par des populations différentes, ainsi que de nouvelles connaissances pour développer des formules avec des textures qui pourront être appréciées à travers le monde.

Skin characterization and immediate effects of different dermocosmetic treatments in French and Brazilian skin.

BACKGROUND: All over the world, people face the same skin problems. However, their skin characteristics are different. Thus, it is a challenge to prescribe treatments that will be effective on different skin types. Therefore, it is very important to consider the skin biology when indicating a dermocosmetic treatment. OBJECTIVES: To assess skin biophysical parameters in French and Brazilian subjects and to verify the efficacy of four dermocosmetic treatments in these populations. METHODS: Five test areas were defined on each volar forearm of the eighteen Brazilian and eighteen French participants using a randomized design. Biophysical measurements in terms of skin hydration, skin barrier function, skin brightness, and skin viscoelasticity were performed before and after 60 minutes of treatment. RESULTS: Skin biophysical differences between populations were found. French skin has been shown to be more hydrated regarding epidermal mechanic properties and stratum corneum water content and more radiant when compared with Brazilian skin. However, it showed more signs of cutaneous aging and fatigue effects on skin. The Brazilian skin showed better skin barrier function. In addition, the treatments were effective in both populations. CONCLUSIONS: Despite the differences found in French and Brazilian skin, the proposed dermocosmetic treatments showed effective in both populations.

Instrumental and sensory methodologies to characterize the residual film of topical products applied to skin.

BACKGROUND: The work is aimed at the development of a methodology to characterize the tactile properties of topical products during application. Specific attention was paid to the study of the residual properties left at the surface of the skin. This approach was interestingly used to better understand the formulation factors governing the skinfeel of topical preparations. MATERIALS AND METHODS: Cosmetic and pharmaceutical topical products were selected based on their various texture, galenic form (gel or emulsion), and composition (polymer used as texturing agent). Key texture attributes namely Firmness, Stickiness, Spreadability, and Amount of residue were objectively evaluated using sensory analysis. Additionally, texture analysis (compression test), rheology (flow test), and tribology (in vivo friction test) were carried out. RESULTS: Sensory evaluations highlighted a great diversity of tactile properties among products when applied to skin. For example, assessors perceived an important amount of residue left by emulsions whereas gels were not leaving any residue after application to the skin. These results were confirmed by in vivo tactile friction measurements with two distinct evolutions in time of the residual film properties. CONCLUSION: The present investigation shows how the tactile properties of topical gels and emulsions are studied using complementary tests in order to understand and improve the skinfeel of topical preparations.

Squalene Oxidation Induced by Urban Pollutants: Impact on Skin Surface Physico-Chemistry.

The effect of urban pollutants on skin properties has been revealed through several epidemiological studies. However, comprehension of involved mechanisms remains undetermined. In addition, the impact of such stressors on skin surface properties, especially skin physico-chemistry, has not been investigated. Consequently, the present study aims to develop a new aging protocol able to highlight the impact of selected urban pollutants on a model sebaceous lipid: the squalene. Its quality has been followed during aging using LC-MS analysis. Results showed that the quality of the control solution containing only squalene remains stable during 45 days, whereas the quality of the solution containing squalene mixed with pollutants appears greatly altered, especially in the presence of heavy metals: a large amount of oxidation compounds was evidenced due to oxidation and dehydrogenation mechanisms. In addition, a physicochemical study was performed using a validated nonbiological skin model able to mimic skin physico-chemistry. Surface free energy components were calculated using contact angle measurements according to the Van Oss model. The application of degraded squalene significantly increased skin hydrophilic and monopolar behavior compared to the application of control squalene. Those modifications are essentially explained by the nature of squalene oxidation products. It must be noted from this study that squalene oxidation due to pollutants or due to high temperature did not lead to the same physicochemical consequences neither to the same oxidation products, as shown by thermal analysis. This study gives original and precious information to explain alterations induced by pollutants on skin surface properties, especially skin chemistry and physico-chemistry.

Skin surface physico-chemistry: Characteristics, methods of measurement, influencing factors and future developments.

Physico-chemical properties such as surface free energy, polarity or hydrophobicity of solid surfaces have been largely studied in literature because they are involved in many physical phenomena: adhesion, friction, wetting … Nowadays, the study of biointerfaces is of great interest for the medical, the pharmaceutical or the cosmetic field but also for material design researches, especially for the development of biomimetic surfaces. The present paper focuses on a particular biointerface, namely skin, which is the most extended organ of the human body. The different ways for the study of skin physico-chemistry are first reviewed, followed by their practical uses, from pharmaceutical to cosmetic science. Those properties depict the ways skin interacts with topical products, its lipid composition but also its hydration state. In addition, this article aims to present recent approaches using original model materials in order to mimic human skin; indeed, in vivo experiments are often limited by the inter and intra individual variability, the safety regulation and above all the time and the cost of such studies. Finally, further data clearly highlight the importance of skin surface properties for dermatological and pharmaceutical researches.

Prediction of residual film perception of cosmetic products using an instrumental method and non-biological surfaces: The example of stickiness after skin application.

Prediction of sensory texture attributes using instrumental measurements is a very important challenge for cosmetic industry because in vivo sensory studies are expensive, time consuming and limited by the safety issue of applied products. The aim of this work is to investigate how residual sensory properties of cosmetic products can be predicted without using a panel of assessors, focusing on the residual film attribute "Stickiness". 10 cosmetic products with different galenics have been selected and evaluated in vivo using a classical sensory protocol, developed according to the Spectrum™ Descriptive Analysis method. In addition to this study, products were evaluated after their application on non-biological skin models in order to compare perceptions onto in vivo skin and artificial surfaces. Results obtained show that in vivo perceptions can be compared with the ones on artificial surfaces meaning that residual film stickiness is similar between in vivo skin and non-biological skin models. An instrumental protocol using a texture analyzer has been set up to evaluate residual film adhesiveness. This protocol has been tested and validated in vivo (r²adjusted = 0.90; RPD = 3.07) before being optimized on a selected non-biological skin model Bioskin® (Beaulax, Co. Ltd. Tokyo, Japan) owning good correlation with in vivo perceptions. Established model shows excellent predictive ability with a r²adjusted of 0.94 and a RPD of 3.38, as highlighted by the 4 steps cross-validation performed. It proves that physical stimulus responsible for cosmetic film stickiness can be instrumentally measured on both in vivo skin and artificial skin.

Interactions between UV filters and active substances in emulsion: Effect on microstructure, physicochemical and in-vivo properties.

The objective of the present study was to develop, characterize and evaluate the clinical efficacy of topical formulations containing or not active substances and UV-filters, separate and in combination. To this end a stable formulation was developed to which four aqueous active substances and four lipophilic UV-filters were added. The formulations were then submitted to microscopic characterization by light microscopy, to particle size measurement, and to macroscopic characterization by rheology and texture analysis. Finally, a clinical efficacy study was conducted to determine the effect of the formulations on the skin after application for 1 h. The formulation containing UV-filters showed a high polydisperse microstructure and a large amount of liquid crystals. The formulations containing active substances showed higher resistance to deformation, compression and penetration tests. Regarding spreadability, formulations containing UV filters alone or in combination with active substances showed higher resistance to spreading. This behavior was associated with greater clinical efficacy in terms of stratum corneum water content, protection of the skin barrier function and skin surface brightness. It was demonstrated that the efficacy of the formulation is mainly associated with its structure and the way it interacts with the skin surface. Finally, this study showed that the mixture of these ingredients for the development of multifunctional sunscreens improves the performance of the formulations.

Impact of coated TiO2-nanoparticles used in sunscreens on two representative strains of the human microbiota: Effect of the particle surface nature and aging.

The impact of two differently coated TiO2-nanoparticles (NPs) was evaluated on two representative bacteria from the cutaneous microbiota (Staphylococcus aureus and Pseudomonas fluorescens) in conditions of use. Particles were coated in order to exhibit either hydrophilic or hydrophobic behavior. A first exposure scenario within some fresh/aged model emulsions was developed in order to measure both the impact of the NPs presence and their surface nature during the emulsions conservation. Thanks to this protocol, it was demonstrated that, during aging, the hydrophobic NPs modified the physicochemical characteristics of the emulsions, such as the pH or the colloids sizes, and favored the development of potential pathogenic bacteria. A second scenario was then envisaged, aiming to mimic the exposition of the skin, especially of the cutaneous bacteria, to NPs. Tested NPs were extracted from emulsions with different aging, and results highlighted the importance of both the NP coating nature and their history in emulsion. The different NPs impacts on the bacteria growth were discussed and linked to their surface properties modifications during aging, as polarity and charges. Finally, through two exposition scenarios, this work highlights the major impact of the NPs surface properties on bacteria.

Spreading properties of cosmetic emollients: Use of synthetic skin surface to elucidate structural effect.

The study focuses on the impact of structural and physicochemical properties of emollients on their spreadability. Fifty-three emollients, among which esters, silicones, vegetable and mineral oils, have been characterized. Their viscosity, surface tension, density and spreadability have been measured. Vitro-skin®, an artificial skin substitute, was used as an artificial porous substrate to measure spreadability. Two different methods have been selected to characterize spreadability, namely contact angle and spreading value. Dynamic contact angle measurements showed that emollient spreadability is first governed by spontaneous spreading and that, in a second phase, absorption and migration into the porous substrate becomes the driver of the extension of the spreading area. Statistical analysis of physicochemical and spreading value data revealed that viscosity has a major impact on the spreading behavior of emollients whatever their chemical type. A special emphasis was placed on the ester family in which chemical diversity is very wide. The results highlighted a difference between "high viscosity esters" for which viscosity is the main factor impacting spreadability and "low viscosity esters" for which structural variations (mono/diester, saturated/unsaturated chain, linear/branched chain) have to be considered in addition to viscosity. Linear regressions were used to express spreading value as a function of viscosity for each of the four emollient families tested (esters, silicones, vegetable and mineral oils). These regressions allowed the development of reliable predictive models as a powerful tool for formulators to forecast spreadability of emollients.

Development of preservative-free nanoparticles-based emulsions: Effects of NP surface properties and sterilization process.

Model emulsions were developed with or without commercial titanium dioxide nanoparticles (NP) carrying various surface treatments in order to get close physicochemical properties whatever the NP surface polarity (hydrophilic and hydrophobic). Rheology and texturometry highlighted that the macroscopic properties of the three formulated emulsions were similar. However, characterizations by optical microscopy, static light scattering and zetametry showed that their microstructures reflected the diversity of the incorporated NP surface properties. In order to use these model emulsions as tools for biological evaluations of the NP in use, they had to show the lowest initial microbiological charge and, specifically for the NP-free emulsion, the lowest bactericidal effect. Hence, formulae were developed preservative-free and a thermal sterilization step was conducted. Efficiency of the sterilization and its impact on the emulsion integrity were monitored. Results highlighted the effect of the NP surface properties: only the control emulsion and the emulsion containing hydrophilic NP fulfilled both requirements. To ensure the usability of these model emulsions as tools to evaluate the 'NP effect' on representative bacteria of the skin microflora (S. aureus and P. fluorescens), impact on the bacterial growth was measured on voluntary inoculated formulae.

Stretching properties of xanthan and hydroxypropyl guar in aqueous solutions and in cosmetic emulsions.

Filament stretchability of xanthan gum (XG) and hydroxypropyl guar (HPG) was investigated in aqueous solutions (0.125, 0.25, 0.5, 1, 1.2 and 1.5% w/w) and in O/W emulsions using a texture analyzer. Additionally, rheological characterizations were carried out on the systems and shear and oscillation parameters were used to interpret stretching properties. XG solutions exhibited a solid-like behavior with rheological parameters much higher than for HPG one whatever the concentration. Filament stretching values of XG solutions were superior to HPG for concentration below 1% w/w and then became comparable for higher concentrations. No meaningful relationship was found between rheological and stretching values. Synergy was observed for all XG/HPG mixtures at 0.125, 0.25 and 0.5% influencing both the rheological and the filament stretching values. The 25/75 XG/HPG ratio showed the maximum synergistic effect at all concentrations while the filament stretchability was enhanced in a wider range of ratios. XG and HPG did not present the same behavior in emulsions. No clear synergistic effect was observed and XG markedly influenced the emulsion filament stretching.

Effects of aging on structure and stability of TiO2 nanoparticle-containing oil-in-water emulsions.

Formulations incorporating different cosmetic grade TiO2 nanoparticles were developed according to a self-produced protocol on the basis of typical sunscreen cream oil-in-water emulsions. Role of nanoparticles and, more specifically, the impact of two different lipophilic surface treatments on microstructure and stability of the formulations were assessed. Aging of formulations was performed under classical conditions at room temperature or under accelerated conditions at 50 °C, with or without TiO2, and was characterized by several tools such as rheology, microscopy, and particle size measurements. Changes in emulsion stability and aggregation state of nanoparticles were followed over time. Destabilization phenomena were identified: under accelerated aging, the formulation without nanoparticles underwent a coalescence occurrence whereas the formulation incorporating nanoparticles was subjected to aggregation of the colloidal particles. Besides, TiO2 nanoparticles strongly affected the particle-droplets interactions and thus modified the emulsion microstructure with a coating-dependent effect: destabilization mechanisms occur more rapidly with alumina (and) triethoxycaprylylsilane (coating 1) TiO2 nanoparticles as compared to alumina (and) isopropyl titanium triisostearate (and) triethoxycaprylylsilane crosspolymer (coating 2) nanoparticles.