Expanding the Frontiers of nail product evaluation: Novel application of differential scanning calorimetry (DSC) for assessing crosslinking density and predicting nail brittleness and flexibility.

OBJECTIVE: While modern industry advancements have expanded nail beautification options, scientific literature primarily focuses on nail biology and medicine, with limited attention on cosmetic treatments. This study aimed to investigate human nail denaturation properties, including gender impact, blending nails to enlarge the sample pool, nail sensitization through bleaching, and active effectiveness testing. The objective was to understand the DSC and bending fatigue relationship, and define the consumer relevance of the DSC test. METHODS: Nail clippings were collected from adult female and male volunteers. The wet DSC was employed to validate sample preparation, explore the effects of gender, and assess the potential of using blended nails for claims substantiation testing. Nails were sensitized through bleaching using hydrogen peroxide. The effects were confirmed through DSC and nail flexure tests. Furthermore, the ability of actives to address concerns related to nail softness and brittleness was assessed using these techniques. RESULTS: The results confirmed the viability of equilibrating nails in water for up to 14 h as a standardized testing method. The denaturation temperature results were independent of gender and suitable for claims substantiation testing. Blending nails from different sources did not yield significant variations in denaturation properties. A preliminary study suggested that cadaver nails should be used with caution because they exhibited differences in denaturation temperature, influenced by the sampling location. Bending fatigue tests highlighted the significance of humidity, with higher humidity conditions (80%) enhancing nail flexibility and providing better resolution for claims substantiation. Sensitizing the nails with hydrogen peroxide induced alterations in both DSC and bending fatigue results. Proof-of-principle studies demonstrated an elevation in denaturation temperature and a decrease in the number of cycles to break, indicating a nail-hardening effect when formaldehyde was applied. The use of a nail softener led to an enhancement in nail fatigue resistance due to a notable reduction in nail crosslinking density. CONCLUSIONS: The measurement of crosslinking density proved to be a sensitive tool for assessing the effects of cosmetic treatments on nails, particularly in predicting outcomes related to nail brittleness and flexibility.

OBJECTIF: Si les progrès de l'industrie moderne ont multiplié les options d'embellissement des ongles, la littérature scientifique se concentre principalement sur la biologie et la médecine des ongles, en portant une attention limitée sur les traitements cosmétiques. Cette étude visait à étudier les propriétés de dénaturation des ongles humains, y compris l'impact en termes de genre, l'uniformisation des ongles pour élargir le pool d'échantillons, la sensibilisation des ongles par le biais d'un blanchiment et les analyses d'efficacité active. L'objectif était de comprendre la relation entre la DSC et la fatigue par flexion, définissant la pertinence du test par DSC pour le consommateur. MÉTHODES: Des coupes d'ongles ont été recueillies auprès de volontaires adultes de sexe féminin et masculin. L'analyse par DSC humide a été utilisée pour valider la préparation des échantillons, étudier les effets en lien avec le genre, et un potentiel d'utilisation d'ongles uniformisés pour les analyses de justification des allégations. Les ongles ont été sensibilisés à l'aide d'un blanchissement au peroxyde d'hydrogène. Les effets ont été confirmés par des analyses par DSC et des tests de flexion des ongles. En outre, la capacité des principes actifs à répondre aux préoccupations liées à la souplesse et à la fragilité des ongles a été évaluée à l'aide de ces techniques. RÉSULTATS: Les résultats ont confirmé la viabilité de l'équilibrage des ongles immergés dans de l'eau pendant une durée maximale de 14 heures comme méthode d'analyse standardisée. Les résultats de la température de dénaturation étaient indépendants du genre et adaptés aux analyses de justification des allégations. L'uniformisation des ongles provenant de différentes sources n'a pas entraîné de variations significatives des propriétés de dénaturation. Une étude préliminaire a suggéré que les ongles prélevés sur des cadavres doivent être utilisés avec prudence, car ils présentaient des différences de température de dénaturation, influencées par le site d'échantillonnage. Les tests de fatigue par flexion ont mis en évidence l'importance de l'humidité, notamment des conditions d'humidité plus élevées (80 %) améliorant la flexibilité de l'ongle et offrant une meilleure résolution pour la justification des allégations. La sensibilisation des ongles avec du peroxyde d'hydrogène a induit des modifications des deux résultats aux analyses par DSC et de fatigue par flexion. Des études de preuve de principe ont démontré une élévation de la température de dénaturation et une diminution du nombre de cycles à rompre, indiquant un effet durcissant de l'ongle lors de l'application de formaldéhyde. L'utilisation d'un émollient unguéal a permis d'améliorer la résistance à la fatigue des ongles en raison d'une réduction notable de la densité de réticulation des ongles. CONCLUSIONS: La mesure de la densité de réticulation s'est avérée être un outil sensible pour évaluer les effets des traitements cosmétiques sur les ongles, en particulier pour prédire les résultats liés à la fragilité et à la flexibilité des ongles.

Effect of equilibrium pH on the structure and properties of bleach-damaged human hair fibers.

Hair proteins are significantly affected by environmental pH. This impact tends to increase with prior hair damage. To understand how pH affects bleached hair properties, we utilized a number of techniques allowing for the determination of hair thermal properties, swelling and water sorption, and dry and wet tensile properties. At pH 5, hair proteins had the best structural integrity, as determined by differential scanning calorimetry and the highest tensile modulus. At pH 10, protein cross-linking density decreased, water content and hair cross-sectional diameter increased. Alkaline treatment, when compared with pH 5, did not reduce intermediate filament conditions (evaluated via enthalpy measurement) nor mechanical property performance in the wet state. In contrast to alkaline-treated hair, bleached hair equilibrated at pH 3 behaved very differently: it contained two different crosslink density zones, was the least stiff in dry and stiffest in wet conditions. Additionally, it absorbed less water and had the lowest diameter because of reduced water binding by protonated carboxyl groups. The pH 3 to 10 did not affect the mechanical strength of bleached hair in dry or wet conditions.

Impact of Interfacial Composition on Emulsion Digestion Using In Vitro and In Vivo Models.

This study explored the influence of different emulsification layers as mono- and bilayers on lipid digestion by using in vitro and in vivo digestion methods. The monolayer emulsion of rapeseed oil contained whey proteins and the bilayer emulsion, whey proteins and carboxymethyl cellulose. The in vitro digestion using human gastrointestinal enzymes showed that the lipid digestion as free fatty acids was slowed down in the bilayer emulsion compared with the monolayer. Droplet size was still low in the gastric phase and pseudoplasticity was well preserved (even though viscosity decreased) during in vitro gastrointestinal digestion. The in vivo studies confirmed a lower fat bioavailability from bilayer emulsions by a reduction in the triglyceride level in the blood of rats, fed by the bilayer emulsion. The results clearly showed that lipid digestion was slower in the bilayer emulsion than in the monolayer. These results provide bio-relevant information about the behavior of emulsions upon digestion. PRACTICAL APPLICATION: The layer-by-layer production approach that was presented here allows the preparation of emulsions with slower fat bioavailability. Such behavior of the bilayer emulsion made it interesting for the formulation of food products with low fat bioavailability.

Effect of human and simulated gastric juices on the digestion of whey proteins and carboxymethylcellulose-stabilised O/W emulsions.

In this study, we analysed the impact of carboxymethylcellulose (CMC) on lipid digestion and physicochemical properties of whey proteins (WP)-stabilised emulsions during in vitro digestion with either artificial or human gastrointestinal juices. The emulsions were made by adsorbing WP on the fat droplets and subsequently adding CMC, which does not interact with the adsorbed proteins. The limited hydrolysis of lipids and their higher physical stability was recorded for WP-stabilised emulsions in the presence of CMC under simulated gastrointestinal conditions. The possible mechanism by which CMC lowers the digestion of WP-stabilised emulsions is related to the limited interaction of fat droplets with gastrointestinal fluids due to the extended thickening network formed by CMC in the continuous phase. The digestion of WP- and CMC-stabilised emulsions in the in vitro model with human gastric fluids led to greater lipid hydrolysis, although the enzymatic activity in both in vitro models was observed at the same level.