New formulation technology to boost sun protection.

OBJECTIVE: As every skin type worldwide is concerned by photoprotection, with consumers preferring cosmetic elegant and efficient sunscreen products, we aim at developing the most performant and desirable sun care products. METHODS: We selected an interesting polymer, abbreviated AAHCP and designed scanning electron cryomicroscopy (cryoSEM), small angle and wide angle X-ray scattering and confocal laser scanning microscopy studies to understand its behaviour in solution and in simplex sun care formulations. This allowed us to develop innovative sunscreen formulation technology that was demonstrated by in vitro and in vivo photoprotection methods. Comprehensive photoprotection evaluations were made on the fully developed sun protection product. RESULTS: We observed the polymer oil structuring properties as well as its ability to form small and stable droplets in simplex emulsions. In vitro and in vivo sun protection factor (SPF) measurements demonstrated the sun protection boosting efficacy of AAHCP polymer in several emulsions or as a stand-alone emulsifier. This formulation technology also allowed to filtering system concentration optimization. Use-test performed on a fully developed AAHCP-based sunscreen validated its optimal performances as well as its ideal cosmetic features, with non-sticky, non-greasy perception and invisible skin result. CONCLUSION: For the first time, thanks to a new specific polymer creating a new type of emulsion, we succeed in reconciliate in a single sun care product maximal SPF efficacy, resistance to numerous stresses and optimal sensoriality.

OBJECTIF: Tous les types de peau du monde étant concernés par la photoprotection, avec des consommateurs qui préfèrent des produits solaires élégants et efficaces, nous nous sommes donné pour mission de développer les produits de protection solaire les plus performants et les plus agréables. MÉTHODES: Nous avons sélectionné un polymère intéressant, l'« AAHCP ¼ dans sa forme abrégée, et avons conçu les études de cryomicroscopie électronique à balayage (CryoSEM), de diffusion des rayons X et de microscopie confocale à balayage laser (Confocal Laser Scanning Microscopy) pour comprendre son comportement en solution et dans des formulations de protection solaire simples. Cela nous a permis de développer une technologie innovante de formulation de protection solaire, qui a été démontrée par des méthodes de photoprotection in vitro et in vivo. Le produit de protection solaire a fait l'objet d'évaluations exhaustives de la photoprotection à la fin de sa phase de développement. RÉSULTATS: Nous avons observé les propriétés de structuration de l'huile polymère, ainsi que sa capacité à former de petites gouttelettes stables dans les émulsions de simplex. Les mesures du facteur de protection solaire (sun protection factor, SPF) in vitro et in vivo ont montré que la présence du polymère AAHCP dans plusieurs émulsions ou comme émulsifiant autonome optimise le niveau de protection solaire obtenu. Cette technologie de formulation a également permis d'ajuster la concentration du système de filtration. Le test en conditions réelles d'utilisation effectué sur une protection solaire à base d'AAHCP à la fin de la phase de développement a permis de valider ses performances optimales, ainsi que ses caractéristiques cosmétiques idéales, avec une sensation non collante et non grasse, et un résultat invisible sur la peau. CONCLUSION: Pour la première fois, grâce à un nouveau polymère spécifique créant un nouveau type d'émulsion, nous avons réussi à développer un produit de protection solaire simple à l'efficacité SPF maximale, qui résiste à de nombreuses contraintes et possède une sensibilité optimale.

Spontaneous migration of cellular aggregates from giant keratocytes to running spheroids.

Despite extensive knowledge on the mechanisms that drive single-cell migration, those governing the migration of cell clusters, as occurring during embryonic development and cancer metastasis, remain poorly understood. Here, we investigate the collective migration of cell on adhesive gels with variable rigidity, using 3D cellular aggregates as a model system. After initial adhesion to the substrate, aggregates spread by expanding outward a cell monolayer, whose dynamics is optimal in a narrow range of rigidities. Fast expansion gives rise to the accumulation of mechanical tension that leads to the rupture of cell-cell contacts and the nucleation of holes within the monolayer, which becomes unstable and undergoes dewetting like a liquid film. This leads to a symmetry breaking and causes the entire aggregate to move as a single entity. Varying the substrate rigidity modulates the extent of dewetting and induces different modes of aggregate motion: "giant keratocytes," where the lamellipodium is a cell monolayer that expands at the front and retracts at the back; "penguins," characterized by bipedal locomotion; and "running spheroids," for nonspreading aggregates. We characterize these diverse modes of collective migration by quantifying the flows and forces that drive them, and we unveil the fundamental physical principles that govern these behaviors, which underscore the biological predisposition of living material to migrate, independent of length scale.

Soft matter models of developing tissues and tumors.

Analogies with inert soft condensed matter--such as viscoelastic liquids, pastes, foams, emulsions, colloids, and polymers--can be used to investigate the mechanical response of soft biological tissues to forces. A variety of experimental techniques and biophysical models have exploited these analogies allowing the quantitative characterization of the mechanical properties of model tissues, such as surface tension, elasticity, and viscosity. The framework of soft matter has been successful in explaining a number of dynamical tissue behaviors observed in physiology and development, such as cell sorting, tissue spreading, or the escape of individual cells from a tumor. However, living tissues also exhibit active responses, such as rigidity sensing or cell pulsation, that are absent in inert soft materials. The soft matter models reviewed here have provided valuable insight in understanding morphogenesis and cancer invasion and have set bases for using tissue engineering within medicine.

Spreading dynamics of cellular aggregates confined to adhesive bands.

We examine the spreading of cellular aggregates deposited on adhesive striated glass surfaces consisting of 100 µm large bands alternatively coated with fibronectin and with PolyEthyleneGlycol-Poly-L-lysine (PEG-PLL). The aggregates spread confined to the adhesive fibronectin bands. A front of cells expands from the aggregate at constant velocity. In comparison, the radial spreading of an aggregate on the uniform fibronectin coated glass surface obeys a diffusive law. We develop a common theoretical model in agreement with our experimental observations to describe the apparently disparate spreading kinetics of cellular aggregates. These results demonstrate the dominant role of the permeation in the expansion of the precursor film of cells around the aggregate.

Decorating a liquid interface promotes splashing.

We report on the role of a surfactant monolayer in the impact of small spheres on an air-water interface. We observe that an air cavity (splashing) is induced above a threshold impact velocity. We explore the dependence of this threshold velocity on the bath surface tension and on the bath viscosity using water-ethanol and water-glycerol mixtures, respectively. Interestingly, the threshold velocity for air entrainment is reduced by the presence of a stearic acid monolayer because the hydrophobic tails favor the forced entry of air during the sphere's impact. More generally, we show that this threshold velocity is determined by the wettability of the sphere by the bath, which can equivalently be controlled by tuning the bath properties (presence of a monolayer) or the sphere surface properties (via a surface treatment). These results provide insight into recently developed vesicle production techniques based on the impact of drops or jets on a lipid layer.

Spreading dynamics and wetting transition of cellular aggregates.

We study the spreading of spheroidal aggregates of cells, expressing a tunable level of E-cadherin molecules, on glass substrates decorated with mixed fibronectin and polyethylene glycol. We observe the contact area by optical interferometry and the profile by side-view microscopy. We find a universal law of aggregate spreading at short times, which we interpret through an analogy with the spreading of viscoelastic droplets. At long times, we observe either partial wetting or complete wetting, with a precursor film of cells spreading around the aggregate with two possible states. In strongly cohesive aggregates this film is a cellular monolayer in the liquid state, whereas in weakly cohesive aggregates, cells escape from the aggregate, forming a 2D gas. The escape of isolated cells is a physical mechanism that appears also to be present in the progression of a noninvasive tumor into a metastatic malignant carcinoma, known as the epithelial-mesenchymal transition.