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OBJECTIVE: Increasing consumer demand for natural and environmentally friendly products is driving the cosmetic industry to seek greener and safer processes. High-frequency ultrasound technology (HFUT) stabilizes emulsions without adding emulsifying surfactants (ES). In this work, the formulation characteristics of an HFUT-treated emulsion and a Reference emulsion were compared for both caffeine and α-tocopherol. METHODS: A comparison was made between ES-free emulsions and the Reference emulsions based on droplet size, viscosity, pH and rheology behaviour for both active cosmetic ingredients. The permeation of caffeine and the skin retention of α -tocopherol were studied in vitro using Franz diffusion cells on human skin biopsies, considered the gold standard for permeation assays. RESULTS: The formulations developed were stable and showed suitable droplet size distribution. In the case of ES-free emulsions, the average droplet size was inferior to 1.5 µm regardless of the polarity of the active. All formulations presented a shear-thinning pseudoplastic behaviour, an attribute usually desired for cosmetic products. The skin permeation studies showed that in the case of caffeine (model hydrophilic molecule), the ES-free emulsion presented a delivery capacity similar to that of the Reference emulsion. However, for α-tocopherol (highly lipophilic model molecule), differences were observed in the distribution of the active in the stratum corneum with an advantage for the Reference emulsion, probably due to the impact of surfactants on the SC lipids. CONCLUSION: This work demonstrates that HFUT is a reliable tool that is able to prepare stable ES-free emulsions loaded with hydrophilic or lipophilic active ingredients. Skin permeation studies confirm that the emulsions produced by HFUT promote the delivery of the actives to the human skin. In the case of α-tocopherol, the delivery efficiency was lower than with the Reference emulsion, especially in the SC layers, due to the absence of surfactants. Nevertheless, the ES-free emulsion still represents a good compromise between efficacy and the need for green cosmetics in the market.

OBJECTIF: La demande croissante des consommateurs pour des produits naturels et respectueux de l'environnement encourage l'industrie cosmétique à développer des procédés plus écologiques et plus sûrs. La technologie des ultrasons à haute fréquence (HFUT) permet de stabilizer les émulsions sans ajouter de tensioactifs émulsionnants (ES). Dans ce travail, les caractéristiques d'une émulsion traitée par HFUT et d'une émulsion de référence ont été comparées. La caféine et l'α-tocophérol ont été utilisés comme actifs modèles. MÉTHODES: Les émulsions sans ES et les émulsions de référence on été comparées en termes de taille des gouttelettes, de viscosité, de pH et de comportement rhéologique pour les deux actifs. La perméation de la caféine et la rétention cutanée de l'α-tocophérol ont été étudiées in vitro sur des biopsies de peau humaine, en utilisant des cellules de diffusion de Franz, le 'gold standard' des tests de perméation. RÉSULTATS: Les formulations développées sont stables et présentent une distribution appropriée de la taille des gouttelettes. La taille moyenne des gouttelettes des émulsions sans ES est inférieure à 1.5 µm, quelle que soit la polarité de l'actif. Toutes les formulations présentent un comportement rhéofluidifiant adapté à un usage cosmétique. Les études de perméation cutanée montrent que l'émulsion sans ES contenant de la caféine (molécule modèle hydrophile) présente une capacité de délivrance similaire à celle de l'émulsion de référence. Dans le cas de l'α-tocophérol (molécule modèle lipophile), des différences ont été observées dans la distribution de l'actif dans le stratum corneum (SC) avec un avantage pour l'émulsion de référence, probablement lié à l'interaction entre les tensioactifs et les lipides du SC. CONCLUSION: Ce travail démontre que le traitement par HFUT permet de préparer des émulsions stables sans ES, quelle que soit la polarité des actifs cosmétiques à véhiculer. Les études de perméation cutanée confirment que les émulsions produites par HFUT permettent la diffusion cutanée des actifs dans la peau humaine. Même si dans le cas de l'α-tocophérol la quantité accumulée était plus faible, l'émulsion traitée par HFUT propose un bon compromis entre efficacité et éco-responsabilité.

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Emulsions are multiphasic systems composed of at least two immiscible phases. Emulsion formulation can be made by numerous processes such as low-frequency ultrasounds, high-pressure homogenization, microfluidization, as well as membrane emulsification. These processes often need emulsifiers' presence to help formulate emulsions and to stabilize them over time. However, certain emulsifiers, especially chemical stabilizers, are less and less desired in products because of their negative environment and health impacts. Thus, to avoid them, promising processes using high-frequency ultrasounds were developed to formulate and stabilize emulsifier-free emulsions. High-frequency ultrasounds are ultrasounds having frequency greater than 100 kHz. Until now, emulsifier-free emulsions' stability is not fully understood. Some authors suppose that stability is obtained through hydroxide ions' organization at the hydrophobic/water interfaces, which have been mainly demonstrated by macroscopic studies. Whereas other authors, using microscopic studies, or simulation studies, suppose that the hydrophobic/water interfaces would be rather stabilized thanks to hydronium ions. These theories are discussed in this review.

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OBJECTIVE: The cosmetic industry endeavours to strengthen the greener and safer claims of processes to respond to the high demand from customers for natural and environmentally friendly products. High-frequency ultrasonication technology (HFUT) is a physical process enabling the stabilization of emulsions without requiring additional ingredients, such as emulsifying surfactants (ES) to be introduced into the formulations. In this study, key formulation characteristics of an emulsion synthesized by HFUT and a reference emulsion (RE) were compared, as well as the permeation kinetics of caffeine, used as a model active cosmetic ingredient, from both types of emulsions. METHODS: The pH, droplet size and viscosity of emulsions prepared by the HFUT and the RE were determined and compared. The permeation of caffeine from the HFUT emulsion and the RE applied to the surface of reconstructed human epidermis (RHE) models was compared. RESULTS: The ES-free formulations prepared by HFUT displayed a nearly 2-fold lower average droplet size and over 3-fold greater viscosity, compared to the RE. Despite these differences, the absence of ES in the HFUT emulsion did not significantly alter the permeation kinetics of caffeine through RHE. The caffeine steady-state flux, lag time and permeability coefficients differed by 20%-30% only. CONCLUSION: This study demonstrates the potential of the HFUT to yield topical cosmetic products with lower requirements ingredients-wise, without losing efficacy, supporting the possible implementation of the technology in the cosmetic industry.

OBJECTIF: l'industrie cosmétique œuvre à renforcer les revendications plus écologiques et plus sûres des processus pour répondre à la forte demande des clients de produits naturels et plus respectueux de l'environnement. La technologie d'ultrasons à haute fréquence (High-Frequency Ultrasonication Technology, HFUT) est un processus physique permettant de stabiliser les émulsions sans qu'il soit nécessaire d'ajouter des ingrédients supplémentaires, tels que des surfactants émulsifiants, aux formulations. Dans cette étude, les principales caractéristiques de formulation d'une émulsion synthétisée par HFUT et d'une émulsion de référence ont été comparées, ainsi que la cinétique de perméation de la caféine, utilisée comme ingrédient cosmétique actif modèle, dans les deux types d'émulsion. MÉTHODES: le pH, la taille des gouttelettes, et la viscosité de l'émulsion préparée par HFUT et de l'émulsion de référence ont été déterminés et comparés. La perméation de la caféine de l'émulsion HFUT et de l'émulsion de référence appliquées à la surface de modèles d'épiderme humain reconstruit a été comparée. RÉSULTATS: la formulation sans surfactants émulsifiants préparée par HFUT présentait une taille moyenne de gouttelettes presque 2 fois plus faible et une viscosité plus de 3 fois supérieure comparée à l'émulsion de référence. Malgré ces différences, l'absence de surfactants émulsifiants dans l'émulsion HFUT n'a pas significativement modifié la cinétique de perméation de la caféine dans l'épiderme humain reconstruit. Le flux à l'état d'équilibre de la caféine, le temps de latence et les coefficients de perméabilité différaient de 20 à 30 % uniquement. CONCLUSION: cette étude démontre le potentiel de la technologie HFUT à générer des produits cosmétiques topiques possédant des exigences plus faibles en termes d'ingrédients, sans perte d'efficacité, soutenant la mise en œuvre éventuelle de la technologie dans l'industrie cosmétique.

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Although the preparation of nano-objects by emulsifier-free controlled/living radical emulsion polymerization has drawn much attention, the morphologies of these formed objects are difficult to predict and to reproduce because of the much more complex nucleation mechanisms of emulsion polymerization compared to only one self-assembling nucleation mechanism of controlled radical dispersion polymerization. The present study compares dispersion polymerization with emulsifier-free emulsion polymerization in terms of nucleation mechanism, polymerization kinetics, and disappearance behavior of the macrochain transfer agent, gel permeation chromatograms curves of the obtained block copolymer as well as the structural and morphological differences between the produced nano-objects on the basis of published data. Moreover, the effects of the inherently heterogeneous nature of emulsion polymerization on the mechanism of reversible addition-fragmentation transfer polymerization and the nano-object morphology are examined, and efficient agitation and adequate solubility of the core-forming monomer in water are identified as the most crucial factors for the fabrication of nonspherical nano-objects.

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Polyisoprene-silica (PIP-co-RAFT-SiO2) nanoparticles were prepared via reversible addition⁻fragmentation chain-transfer (RAFT) emulsifier-free emulsion polymerization using water-soluble initiators, 4,4'-Azobis (4-cyanopentanoic acid) (ACP) and 2,2'-Azobis (2-methylpropionamidine) dihydrochloride (V50). The particle size of emulsion prepared using ACP initiator was smaller than that using V50 initiator because the V50 initiator was more active toward decomposition than the ACP initiator. A high monomer conversion (84%), grafting efficiency (83%) and small particle size (38 nm) with narrow size distribution were achieved at optimum condition. The PIP-co-RAFT-SiO2 nanoparticles exhibited core⁻shell morphology with silica encapsulated with polyisoprene (PIP). The new PIP-SiO2 nanoparticles could be applied as effective filler in rubber composites that possess good mechanical and thermal properties.

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Glycopolymers bearing carbohydrates have an advantage in protein recognition that is attributable to the multivalent effect (cluster effect) of side-chain carbohydrates. A variety of surface-modified polymer particles have been prepared concurrently with the development of new synthetic technology. Here we describe a synthetic method of glycopolymer-grafted polymer particles by surface-initiated living radical polymerization, i.e., atom-transfer radical polymerization (ATRP) and photoiniferter polymerization, for specific lectin recognition.

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Kiton red 620 (KR620) doped polystyrene latex microspheres (PSLs) were synthesized via soap-free emulsion polymerization to be utilized as a relatively nontoxic, fluorescent seed material for airflow characterization experiments. Poly(styrene-co-styrenesulfonate) was used as the PSL matrix to promote KR620 incorporation. Additionally, a bicarbonate buffer and poly(diallyldimethylammonium chloride), polyD, cationic polymer were added to the reaction solution to stabilize the pH and potentially influence the electrostatic interactions between the PSLs and dye molecules. A design of experiments (DOE) approach was used to efficiently investigate the variation of these materials. Using a 4-factor, 2-level response surface design with a center point, a series of experiments were performed to determine the dependence of these factors on particle diameter, diameter size distribution, fluorescent emission intensity, and KR620 retention. Using statistical analysis, the factors and factor interactions that most significantly affect the outputs were identified. These particles enabled velocity measurements to be made much closer to walls and surfaces than previously. Based on these results, KR620-doped PSLs may be utilized to simultaneously measure the velocity and mixing concentration, among other airflow parameters, in complex flows.

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Emulsifier free emulsion was developed with a new patented technique for food and cosmetic applications. This emulsification process dispersed oil droplets in water without any emulsifier. Emulsions were prepared with different vegetable oil ratios 5%, 10% and 15% (v/v) using high frequency ultrasounds generated by piezoelectric ceramic transducer vibrating at 1.7 MHz. The emulsion was prepared with various emulsification times between 0 and 10h. Oil droplets size was measured by laser granulometry. The pH variation was monitored; electrophoretic mobility and conductivity variation were measured using Zêtasizer equipment during emulsification process. The results revealed that oil droplets average size decreased significantly (p<0.05) during the first 6h of emulsification process and that from 160 to 1 µm for emulsions with 5%, 10% and from 400 to 29 µm for emulsion with 15% of initial oil ratio. For all tested oil ratios, pH measurement showed significant decrease and negative electrophoretic mobility showed the accumulation of OH(-) at oil/water interface leading to droplets stability in the emulsion. The conductivity of emulsions showed a decrease of the ions quantity in solution, which indicated formation of positive charge layer around OH(-) structure. They constitute a double ionic layer around oil particles providing emulsion stability. This study showed a strong correlation between turbidity measurement and proportion of emulsified oil.

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