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.

Tail feather strength in tail-assisted climbing birds is achieved through geometric, not material change

Birds encompass vast ecomorphological diversity and practise numerous distinct locomotor modes. One oft-cited feature seen in climbing birds is an increase in tail 'stiffness', yet it remains unclear to what extent these feathers are altered, and the specific mechanism by which differences in functional performance are attained. We collected a broad taxonomic sample of tail feathers (6525 total, from 774 species representing 21 avian orders and ranging in size from approximately 3 g to greater than 11 kg) and present data on their material properties, cross-sectional geometry and morphometrics. Ordinary and phylogenetic least-squares regressions of each variable versus body mass were conducted to assess scaling relationships and demonstrate that tail-supported climbers exhibit longer tail feathers with a wider rachis base and tip, and a greater second moment of area and maximum bending moment. However, no differences were observed in the material properties of the keratin itself. This suggests that tail-supported arboreal climbing birds of multiple orders have independently adopted similar morphologies. Moreover, these geometric relationships follow the same allometric scaling relationships as seen in the long bones of mammalian limbs, suggesting that the morphology of these developmentally and evolutionarily distinct structures are governed by similar functional constraints of weight support.

Impregnation of healthy nail tissue with optical clearing agents for improved optical coherence tomography imaging

OBJECTIVES

The impact of optical tissue clearing on optical coherence tomography (OCT) for nail tissue imaging has not been investigated. This study seeks to compare the effects of an emollient and water on visualization of micromorphology and morphometric outcomes.

MATERIALS AND METHODS

Thirty-six healthy nail plates were processed with a fractional CO₂ laser, imaged with OCT, and measured with calipers in duplicates. All samples were reassessed after 12-hour long sequential immersion in water and an emollient (Crodamol™ STS). OCT images were evaluated for thickness and scattering signal of the nail.

RESULTS

Emollient-impregnation caused stronger scatter responses (P < .0001) and decreased nail thickness (MD 45 μm, P < .0001) measured on OCT. Caliper-derived measurements were not affected by Crodamol™ (MD 11 μm, P = .5538). Hydration increased nail thickness on OCT (MD 49 μm, P < .0001) but reduced thickness measurements taken with calipers (MD 41 μm, P < .0001). Emollient-impregnation improved visualization of onychocytes compared with dry (P = .0209) and hydrated samples (P < .0001), and reduced occurrence of refractive artifacts (P < .0001).

CONCLUSION

The use of an emollient for OCT imaging can enhance nail tissue visualization without significant effects on caliper measurements. Hydration of nails, in contrast with emollient-impregnation, may lead to disagreement between caliper- and OCT-measured nail thickness and should be practiced cautiously.

Physicochemical investigations of native nails and synthetic models for a better understanding of surface adhesion of nail lacquers

The human nail, like any biological material, is not readily available in large amounts and shows some variability from one individual to another. Replacing it by synthetic models is of great interest to perform reproducible and reliable tests in order to assess drug diffusion or nail lacquer adhesion for example. Keratin films, produced at the lab scale from natural hair, and the commercially available Vitro-nail® sheets have been proposed as models of human nails. In this study, we have investigated in detail these two materials. Surface aspect, composition, surface energy and water permeation were determined by SEM-EDS, ATR-FTIR, XPS, DVS and tensiometry and were compared to those of nails clippings. The development of a probe tack test using a rotational rheometer allowed us to measure the adhesion of three different nail lacquers on each substrate and the results were correlated with the surface state. It is shown that except roughness, keratin films exhibit similar composition, water sorption and surface energy as human nails. Vitro-nail® presents a more hydrophilic and permeable behavior than natural nail due to probable higher proportions of amide functions and absence of disulfide bridges. With the aim to improve nail lacquer residence, the importance of adsorption, electrostatic and mechanical adhesions as well as water sorption behavior is highlighted and allowed to show the importance of roughness, a low surface energy, a moderate hydrophobicity and an ability to form hydrogen and electrostatic bonds in order to optimize adhesion.

Hierarchical structure and compressive deformation mechanisms of bighorn sheep (Ovis canadensis) horn

Bighorn sheep (Ovis canadensis) rams hurl themselves at each other at speeds of ∼9 m/s (20 mph) to fight for dominance and mating rights. This necessitates impact resistance and energy absorption mechanisms, which stem from material-structure components in horns. In this study, the material hierarchical structure as well as correlations between the structure and mechanical properties are investigated. The major microstructural elements of horns are found as tubules and cell lamellae, which are oriented with (∼30⁰) angle with respect to each other. The cell lamellae contain keratin cells, in the shape of pancakes, possessing an average thickness of ∼2 µm and diameter of ∼20-30 µm. The morphology of keratin cells reveals the presence of keratin fibers and intermediate filaments with diameter of ∼200 nm and ∼12 nm, respectively, parallel to the cell surface. Quasi-static and high strain rate impact experiments, in different loading directions and hydration states, revealed a strong strain rate dependency for both dried and hydrated conditions. A strong anisotropy behavior was observed under impact for the dried state. The results show that the radial direction is the most preferable impact orientation because of its superior energy absorption. Detailed failure mechanisms under the aforementioned conditions are examined by bar impact recovery experiments. Shear banding, buckling of cell lamellae, and delamination in longitudinal and transverse direction were identified as the cause for strain softening under high strain rate impact. While collapse of tubules occurs in both quasi-static and impact tests, in radial and transverse directions, the former leads to more energy absorption and impact resistance.

STATEMENT OF SIGNIFICANCE

Bighorn sheep (Ovis canadensis) horns show remarkable impact resistance and energy absorption when undergoing high speed impact during the intraspecific fights. The present work illustrates the hierarchical structure of bighorn sheep horn at different length scales and investigates the energy dissipation mechanisms under different strain rates, loading orientations and hydration states. These results demonstrate how horn dissipates large amounts of energy, thus provide a new path to fabricate energy absorbent and crashworthiness engineering materials.

Protection during production: Problems due to prevention? Nail and skin condition after prolonged wearing of occlusive gloves

Wearing of occlusive gloves during the whole working shift is considered a risk factor for developing hand eczema, similar to wet work. Moreover, the increased hydration due to glove occlusion may lead to brittle nails. Two hundred and seventy clean room workers, wearing occlusive gloves for prolonged periods, and 135 administrative employees not using gloves were investigated. This included a dermatological examination of the nails and the hands, using the Hand Eczema ScoRe for Occupational Screening (HEROS), measurement of transepidermal water loss (TEWL), and a standardized interview. Of the clean room workers, 39%, mainly women, reported nail problems, mostly brittle nails with onychoschisis. Skin score values showed no significant differences between HEROS values of both groups. TEWL values of exposed subjects were similar to TEWL values of controls 40 min after taking off the occlusive gloves. In a multiple linear regression analysis, male gender and duration of employment in the clean room were associated with a significant increase in TEWL values. The effect of occlusion on TEWL seems to be predominantly transient and not be indicative of a damaged skin barrier. This study confirmed the results of a previous investigation showing no serious adverse effect of wearing of occlusive gloves on skin condition without exposure to additional hazardous substances. However, occlusion leads to softened nails prone to mechanical injury. Therefore, specific prevention instructions are required to pay attention to this side effect of occlusion.

Rachis morphology cannot accurately predict the mechanical performance of primary feathers in extant (and therefore fossil) feathered flyers

It was previously suggested that the flight ability of feathered fossils could be hypothesized from the diameter of their feather rachises. Central to the idea is the unvalidated assumption that the strength of a primary flight feather (i.e. its material and structural properties) may be consistently calculated from the external diameter of the feather rachis, which is the only dimension that is likely to relate to structural properties available from fossils. Here, using three-point bending tests, the relationship between feather structural properties (maximum bending moment, M_max and Young's modulus, E_bend) and external morphological parameters (primary feather rachis length, diameter and second moment of area at the calamus) in 180 primary feathers from four species of bird of differing flight style was investigated. Intraspecifically, both E_bend and M_max were strongly correlated with morphology, decreasing and increasing, respectively, with all three morphological measures. Without accounting for species, however, external morphology was a poor predictor of rachis structural properties, meaning that precise determination of aerial performance in extinct, feathered species from external rachis dimensions alone is not possible. Even if it were possible to calculate the second moment of area of the rachis, our data suggest that feather strength could still not be reliably estimated.

Preliminary Assessment of Ergonomic Injury Risk Factors in the Extravehicular Mobility Unit Spacesuit Glove

Injuries to the hands and fingers are commonly reported among astronauts who perform and train for Extravehicular Activities in the Extravehicular Mobility Unit Spacesuit. In an effort to better understand the physical and environmental ergonomic injury risk factors associated with spacesuit glove use, a custom built carrier glove with multiple integrated sensors was developed to be worn within the spacesuit glove with the purpose of measuring the physical and environmental variables acting on the fingers and hand, and the physiological response, within two pressurized glove conditions in a 1G laboratory setting. One male subject performed multiple dynamic and functional tasks in a pressurized EMU. Results indicate that the sensor glove is capable of measuring multiple physical and environmental variables associated the development of finger and hand injuries observed in astronauts.

Pangolin armor: Overlapping, structure, and mechanical properties of the keratinous scales

The pangolin has a flexible dermal armor consisting of overlapping keratinous scales. Although they show potential for bioinspired flexible armor, the design principles of pangolin armor are barely known. Here we report on the overlapping organization, hierarchical structure (from the nano to the mesolevel), and mechanical response of scales from ground (Chinese) and arboreal (African tree) pangolins. Both scales exhibit the same overlapping organization, with each scale at the center of neighboring scales arranged in a hexagonal pattern. The scales have a cuticle of several layers of loosely attached flattened keratinized cells, while the interior structure exhibits three regions distinguished by the geometry and orientations of the keratinized cells, which form densely packed lamellae; each one corresponds to one layer of cells. Unlike most other keratinous materials, the scales show a crossed-lamellar structure (∼5μm) and crossed fibers (∼50μm). A nano-scale suture structure, observed for the first time, outlines cell membranes and leads to an interlocking interface between lamellae, thus enhancing the bonding and shear resistance. The tensile response of the scales shows an elastic limit followed by a short plateau prior to failure, with Young's modulus ∼1 GPa and tensile strength 60-100MPa. The mechanical response is transversely isotropic, a result of the cross lamellar structure. The strain rate sensitivity in the range of 10(-5)-10(-1)s(-1) region is found to be equal to 0.07-0.08, typical of other keratins and polymers. The mechanical response is highly dependent on the degree of hydration, a characteristic of keratins.

STATEMENT OF SIGNIFICANCE

Although many fish and reptiles have protective scales and carapaces, mammals are characteristically fast and light. The pangolin is one of the few mammal possessing a flexible dermal armor for protection from predators, such as lions. Here we study the arrangement of the scales as well as their hierarchical structure from the nano to the mesolevel and correlate it to the mechanical properties. The study reveals a unique structure consisting of crossed lamellae and interlocking sutures that provide exceptional performance and in-plane isotropy.

Development of ciclopirox nail lacquer with enhanced permeation and retention

Onychomycosis is a prevailing disease caused by fungal infection of nails that mostly affects athletes and the elderly. Ciclopirox is approved by the US Food and Drug Administration for the topical treatment of onychomycosis. However, the desired penetration of ciclopirox into the nail bed has not been achieved via topical application for efficient treatment. Therefore, the main aim of this study was to enhance ciclopirox permeation and retention in nail by the development of a new nail lacquer formulation. We screened the effects of different solvents, alkalizing agents, and permeation enhancers on the permeation of bovine hooves by ciclopirox and its retention in human nail clippings. The results suggest that isopropyl alcohol, potassium hydroxide, and urea as the solvent, alkalizing agent, and permeation enhancer, respectively, improved the permeation of the ciclopirox nail lacquer formulation the most with high flux rates. Comparison of the final formulation and marketed product revealed enhanced retention of ciclopirox from our developed formulation in human nail clippings. Therefore, our newly developed nail lacquer may be a potentially effective formulation for the treatment of onychomycosis in humans.

Development of topical therapeutics for management of onychomycosis and other nail disorders: a pharmaceutical perspective

The human nail plate is a formidable barrier to drug permeation. Development of therapeutics for management of nail diseases thus remains a challenge. This article reviews the current knowledge and recent advances in the field of transungual drug delivery and provides guidance on development of topical/ungual therapeutics for management of nail diseases, with special emphasis on management of onychomycosis, the most common nail disease. Selection of drug candidates, drug delivery approaches, and evaluation of formulations are among the topics discussed. A comprehensive mathematical description for transungual permeation is also introduced.

Matrix based system of isotretinoin as nail lacquer to enhance transungal delivery across human nail plate

The project was aimed at development of isotretinoin nail lacquer and assessment of its penetration efficiency across human nail plate. Preliminary studies (hydration enhancement factor and SEM) aided the selection of thioglycolic acid as permeation and eugenol was selected as local anesthetic in the formulation. The nail lacquer was optimized by 3(2) factorial design and a total of nine formulations were prepared and screened. In vitro adhesion and ex vivo permeation (cumulative drug permeation per unit area (CDP/A) = 6.61 ± 0.57 mg/cm(2)) across bovine hoof guided the selection of F3 as optimized formulation that was improvised. Viscosity adjustments to improve handling characteristics were affected by incorporation of ethyl cellulose (6%; F3M1) that scaled the viscosity to 312.681 cp and insignificantly (p > 0.05) affected CDP/A (6.32 ± 0.45 mg/cm(2)). In comparison to marketed preparation (Retino-A cream) F3M1 afforded two fold increase in CDP/A. The permeation characteristics were defined by Higuchi model (r(2) = 0.964) and flux value of 176 μg/cm(2)/h. Confocal laser scanning microscopy, after 72 h of nail lacquer application, revealed extensive distribution of the fluorescent tracer across the human nail plate in comparison to control that was confined to the top layer. Conclusively, an efficacious and stable nail lacquer of isotretinoin was developed for potential clinical topical use to target the drug to nail bed in treatment of nail psoriasis.

The human nail--barrier characterisation and permeation enhancement

The human nail remains one of the most challenging membranes for formulation scientists to target and for clinicians to heal. Its formidable barrier properties are the primary reason that oral therapy remains the primary approach to manage ungual infections. This article considers the major structural properties underlying the excellent barrier function of the nail, with particular emphasis on the role of biophysical methods in advancing our knowledge of this appendage. Formulations currently available for management of ungual disease are discussed and their therapeutic efficacy is assessed. Finally, experimental strategies to enhance ungual permeation are reviewed and prospects for future developments in the field are considered.