The characterization of Pluronic P123 micelles in the presence of sunscreen agents.

OBJECTIVES: The triblock copolymer Pluronic® is widely used in the personal care industry, including sun protection, for its film-forming and solubilization capabilities. In this study, the effect of three commonly used organic UV filters (ethylhexyl methoxycinnamate [EMC], ethylhexyl triazone [EHT], and avobenzone [AVB]) on the structure of Pluronic P123 micelles was investigated. METHODS: The Pluronic P123 micelle structure has been investigated using dynamic surface tension, nuclear magnetic resonance (NMR) and small-angle neutron scattering (SANS). RESULTS: Dynamic surface tension results show strong interactions between the UV filters and Pluronic® evident by sharp changes in the surface activity of the latter. The NMR results have revealed the creation of a hydrophobic microenvironment special to the Pluronic PPO core group in the presence of UV filters. Some interaction with the hydrophilic EO was also recorded, albeit weaker. This is further confirmed by SANS, where the Pluronic P123 micelles interacted with varying strengths with the UV filters, resulting in sharp changes in their size and shape. CONCLUSIONS: We have demonstrated the sensitivity of the Pluronic P123 micelles to the presence of various UVA/B filters. The micelles shape varied from spherical to cylindrical as the concentration and type of the UV filters were varied. These variations in the shape are expected to have a significant effect on the sun protection factor (SPF), as it affects the solubilization of the UV filters within a formulation in addition to the formulations' rheological profile and film-forming behaviour.

OBJECTIFS: le copolymère tribloc Pluronic® est largement utilisé dans le domaine des soins personnels, notamment la protection solaire, pour ses capacités de formation de film et de solubilisation. Cette étude a permis d'étudier l'effet de trois filtres UV organiques couramment utilisés (éthylhexyl méthoxycinnamate [EMC], éthylhexyl triazone [EHT] et avobenzone [AVB]) sur la structure des micelles P123 Pluronic. MÉTHODES: la structure de la micelle P123 Pluronic a été étudiée à l'aide d'une tension superficielle dynamique, d'une résonance magnétique nucléaire (RMN) et d'une diffusion de neutrons aux petits angles (DNPA). RÉSULTATS: les résultats de la tension superficielle dynamique montrent de fortes interactions entre les filtres UV et Pluronic®, ce qui se traduit par de fortes variations de l'activité superficielle de ce dernier. Les résultats de la RMN ont montré la création d'un micro-environnement hydrophobe spécifique au groupe principal de l'OPP pluronique en présence de filtres UV. Une certaine interaction avec l'OE hydrophile a également été enregistrée, quoique plus faible. Ceci est confirmé par la DNPA, où les micelles P123 Pluronic ont interagi avec des forces variables avec les filtres UV, entraînant des changements importants dans leur taille et leur forme. CONCLUSIONS: nous avons démontré la sensibilité des micelles P123 Pluronic à la présence de différents filtres UVA/B. La forme des micelles variait de sphérique à cylindrique en fonction de la concentration et du type de filtres UV. Ces variations de forme devraient avoir un effet significatif sur le facteur de protection solaire (SPF), car elles affectent la solubilisation des filtres UV dans une formulation, en plus du profil rhéologique et du comportement de formation de film des formulations.

Assembly of small molecule surfactants at highly dynamic air-water interfaces.

Small-angle neutron scattering has been used to probe the interfacial structure of foams stabilised by small molecule surfactants at concentrations well below their critical micelle concentration. The data for wet foams showed a pronounced Q-4 dependence at low Q and noticeable inflexions over the mid Q range. These features were found to be dependent on the surfactant structure (mainly the alkyl chain length) with various inflexions across the measured Q range as a function of the chain length but independent of factors such as concentration and foam age/height. By contrast, foam stability (for C < CMC) was significantly different at this experimental range. Drained foams showed different yet equally characteristic features, including additional peaks attributed to the formation of classical micellar structures. Together, these features suggest the dynamic air-water interface is not as simple as often depicted, indeed the data have been successfully described by a model consisting paracrystalline stacks (multilayer) of adsorbed surfactant layers; a structure that we believe is induced by the dynamic nature of the air-water interface in a foam.

Insights into the structure of sunscreen lotions: a small-angle neutron scattering study.

Sunscreen lotions and creams are arguably the most popular products used to protect the skin against harmful UV radiation. Several studies have been conducted to untangle the internal microstructure of creams and lotions. However, the effect of UV filters and other materials such as preservatives, on the internal microstructure and the aesthetics of these products is not yet fully understood. Using small-angle neutron scattering (SANS), we were able to investigate the effect of adding the commonly used organic UV filters (avobenzone (AVB), ethylhexyl methoxycinnamate (EMC), ethylhexyl triazone (EHT) and bemotrizinol (BMT)) and the water soluble preservatives (1,5-pentanediol (1,5-PD) and 1,2-hexanediol (1,2-HD)), on the internal architecture and microstructure of an oil-in-water (o/w) based sunscreen lotion. Our findings highlight the complexities of these formulations, and how the introduction of different additives could influence their structure and possibly their performance.

Segregation versus Interdigitation in Highly Dynamic Polymer/Surfactant Layers.

Many polymer/surfactant formulations involve a trapped kinetic state that provides some beneficial character to the formulation. However, the vast majority of studies on formulations focus on equilibrium states. Here, nanoscale structures present at dynamic interfaces in the form of air-in-water foams are explored, stabilised by mixtures of commonly used non-ionic, surface active block copolymers (Pluronic®) and small molecule ionic surfactants (sodium dodecylsulfate, SDS, and dodecyltrimethylammonium bromide, C12TAB). Transient foams formed from binary mixtures of these surfactants shows considerable changes in stability which correlate with the strength of the solution interaction which delineate the interfacial structures. Weak solution interactions reflective of distinct coexisting micellar structures in solution lead to segregated layers at the foam interface, whereas strong solution interactions lead to mixed structures both in bulk solution, forming interdigitated layers at the interface.

The antimicrobial effects of the alginate oligomer OligoG CF-5/20 are independent of direct bacterial cell membrane disruption.

Concerns about acquisition of antibiotic resistance have led to increasing demand for new antimicrobial therapies. OligoG CF-5/20 is an alginate oligosaccharide previously shown to have antimicrobial and antibiotic potentiating activity. We investigated the structural modification of the bacterial cell wall by OligoG CF-5/20 and its effect on membrane permeability. Binding of OligoG CF-5/20 to the bacterial cell surface was demonstrated in Gram-negative bacteria. Permeability assays revealed that OligoG CF-5/20 had virtually no membrane-perturbing effects. Lipopolysaccharide (LPS) surface charge and aggregation were unaltered in the presence of OligoG CF-5/20. Small angle neutron scattering and circular dichroism spectroscopy showed no substantial change to the structure of LPS in the presence of OligoG CF-5/20, however, isothermal titration calorimetry demonstrated a weak calcium-mediated interaction. Metabolomic analysis confirmed no change in cellular metabolic response to a range of osmolytes when treated with OligoG CF-5/20. This data shows that, although weak interactions occur between LPS and OligoG CF-5/20 in the presence of calcium, the antimicrobial effects of OligoG CF-5/20 are not related to the induction of structural alterations in the LPS or cell permeability. These results suggest a novel mechanism of action that may avoid the common route in acquisition of resistance via LPS structural modification.

Probing competitive interactions in quaternary formulations.

HYPOTHESIS: The interaction of amphiphilic block copolymers of the poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) group with small molecule surfactants may be "tuned" by the presence of selected alcohols, with strong interactions leading to substantial changes in (mixed) micelle morphology, whilst weaker interactions lead to coexisting micelle types. EXPERIMENTS: The nature and the strength of the interactions between Pluronic P123 (EO20PO70EO20) and small molecule surfactants (anionic sodium dodecylsulfate, SDS, C12SO4Na), (cationic dodecyltrimethylammonium bromide, C12TAB) and (non-ionic polyoxyethylene(23)lauryl ether, Brij 35, C12EO23OH) is expected to depend on the partitioning of the short, medium and long chain alcohols (ethanol, hexanol and decanol respectively) and was probed using tensiometry, pulsed-gradient spin-echo nuclear magnetic resonance (PGSE-NMR) and small-angle neutron scattering (SANS). FINDINGS: The SANS data for aqueous P123 solutions with added alcohols were well described by a charged spherical core/shell model for the micelle morphology. The addition of the surfactants led to significantly smaller, oblate elliptical mixed micelles in the absence of alcohols. Addition of ethanol to these systems led to a decrease in the micelle size, whereas larger micelles were observed upon addition of the longer chain alcohols. NMR studies provided complementary estimates of the micelle composition, and the partitioning of the various components into the micelle.