Hydration of human nails investigated by NIR-FT-Raman spectroscopy

Exposome Impact on Nail Health

Background

The nail unit is a complex system with various components, each serving distinct functions. The exposome, encompassing external and internal factors such as UV radiation, air pollution, dietary habits, and cosmetic product usage, substantially influences nail health and can lead to premature nail aging.

Summary

Internal and external exposomal factors can impact differently on nail health, inducing a variety of different clinical conditions. Effective therapeutic strategies exist, but a comprehensive understanding of how the exposome affects nails is lacking. This article aims to bridge this knowledge gap by exploring the relationship between the exposome and nail health, emphasizing it as a central focus of our analysis.

Key Messages

(1) The exposome, comprising various external and internal factors, may significantly influence nail health negatively, leading to premature nail aging. (2) Different nail conditions may arise due to the exposomal influence on nails. (3) Understanding the exposome's impact on nail health is crucial for developing solutions to mitigate negative effects and improve overall nail well-being.

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.

Iontophoresis to Overcome the Challenge of Nail Permeation: Considerations and Optimizations for Successful Ungual Drug Delivery

Iontophoresis is a widely used drug delivery technique that has been used clinically to improve permeation through the skin for drugs and other actives in topical formulations. It is however not commonly used for the treatment of nail diseases despite its potential to improve transungual nail delivery. Instead, treatments for nail diseases are limited to relatively ineffective topical passive permeation techniques, which often result in relapses of nail diseases due to the thickness and hardness of the nail barrier resulting in lower permeation of the actives. Oral systemic antifungal agents that are also used are often associated with various undesirable side effects resulting in low patient compliance. This review article discusses what is currently known about the field of transungual iontophoresis, providing evidence of its efficacy and practicality in delivering drug to the entire surface of the nail for extended treatment periods. It also includes relevant details about the nail structure, the mechanisms of iontophoresis, and the associated in vitro and in vivo studies which have been used to investigate the optimal characteristics for a transungual iontophoretic drug delivery system. Iontophoresis is undoubtedly a promising option to treat nail diseases, and the use of this technique for clinical use will likely improve patient outcomes.Graphical abstract.

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.

Effect of Penetration Enhancers on Drug Nail Permeability from Cyclodextrin/Poloxamer-Soluble Polypseudorotaxane-Based Nail Lacquers

Nail delivery has interest for local treatment of nail diseases. Nevertheless, the low permeability of drugs in the nail plaque precludes the efficacy of local treatments. The use of penetration enhancers can increase drug permeability and improve the efficacy of the treatment of nail pathologies. In this work, different chemical substances have been evaluated as potential penetration enhancers. With this aim, the effect of different substances such as sodium lauryl sulfate (SLS), polyethylene glycol 300 (PEG 300), carbocysteine, N-acetylcysteine, lactic acid, potassium phosphate, Labrasol® and Labrafil® in the microstructure, nail surface and drug permeability has been evaluated. The models obtained by mercury intrusion porosimetry and PoreXpert™ software show a more porous structure in nails treated with different enhancers. Permeation studies with bovine hooves and nails revealed that all the hydroalcoholic lacquers developed, and particularly those prepared with SLS, provide better nail penetration of the drugs ciclopirox olamine and clobetasol propionate. Results have shown that the increase of the drug penetration in the nail is caused by the formation of a porous random microstructure and by the decrease of the contact angle between lacquers and the surface or the nail plaque. The presence of SLS produces an improvement in the spreading of the solution on the nail surface and promotes the penetration of the solution into the nail pores. The hydroalcoholic lacquer, elaborated with cyclodextrin/poloxamer soluble polypseudorotaxane and sodium lauryl sulfate as an enhancer, allowed the rate of diffusion and penetration of the active ingredient within the nail to be significantly higher than obtained with the reference lacquers when using either ciclopirox olamine or clobetasol propionate as the active ingredient.

Effect on Nail Structure and Transungual Permeability of the Ethanol and Poloxamer Ratio from Cyclodextrin-Soluble Polypseudorotaxanes Based Nail Lacquer

Aqueous-based nail lacquers have shown potential in promoting the diffusion of drugs into the nail. In our laboratory, we have recently developed a transungual delivery system based on an aqueous dispersion of cyclodextrin-poloxamer soluble polypseudorotaxanes, supramolecular host−guest assemblies that improves the drug permeation into the nail. However, the high-water content and the rheological and adhesive properties of this lacquer negatively affect properties that play a fundamental role in the patients’ acceptance such as stickiness, nail film formation or drying rate, properties. In this work, we have optimized the composition of these lacquers to improve these properties whilst maintaining good drug permeation profiles. Incorporating ethanol into the vehicle and reducing the proportion of Poloxamer 407 (PL), provided a good strategy. The use of hydro-ethanolic mixtures (>50% ethanol) and the reduction of the poloxamer concentration significantly improved the lacquer drying speed by reducing the stickiness and promoting film formation on the nail surface. Additionally, in a surprising way, the use of hydro-ethanolic vehicles further enhanced the permeation of ciclopirox olamine and clobetasol propionate, used for the treatment of onychomycosis and nail psoriasis respectively, into the nail and hooves.

Shortwave-infrared Raman spectroscopic classification of water fractions in articular cartilage ex vivo

Water loss is an early onset indicator of osteoarthritis. Although Raman spectroscopy (RS) holds the potential for measurement of cartilage hydration, the knowledge of Raman OH-stretch bands of biological tissue is very limited. We assesed here the sensitivity of RS to identify and classify water types in the cartilage. Raman spectrum measurements over the high wavenumber range were employed to identify different water fractions in articular cartilage. Raman spectra were collected from wet and sequentially dehydrated cartilage along with pure collagen type II and chondroitin sulfate standards. OH-stretch band of cartilage is dominated by mobile water, up to 95% of total intensities. We identified six peaks in cartilage spectrum using second-derivative analysis: peaks at 3200 and 3650  cm-1 are associated with organic matrix (both collagen and proteglycan) and matrix-bound water molecules. Peaks at 3250, 3453, and 3630  cm-1 are associated with collagen and collagen-related water molecules, whereas the peak at 3520  cm-1 is associated with proteoglycan (PG) and PG-related water molecules. The current work is the first thorough analysis of the Raman OH-stretch band of the cartilage and with the knowledge generated by this study, it may now be possible to study on cartilage hydration by RS.

Voriconazole-loaded nanostructured lipid carriers (NLC) for drug delivery in deeper regions of the nail plate

Voriconazole-loaded nanostructured lipid carriers (VOR-NLC) were developed and drug penetration evaluated in porcine hooves in vitro. Synergistic effect of urea (Ur), selected among other known chemical enhancers according to hoof hydration potential, was also evaluated. VOR-NLC presented a high encapsulation efficiency (74.52±2.13%), approximate mean diameter of 230nm and were positively charged (+27.32±2.74mV). Stability studies indicated they were stable under refrigeration (4±2°C) for up to 150days. SEM images revealed hooves treated with VOR-NLC and VOR-NLC-Ur suffered a disturbance on the surface depicting high roughness and porosity. Permeation data showed a substantial VOR amount retained in superficial hooves sections independent of the formulation used (2.42±0.26; 2.52±0.36 and 2.41±0.60μg/cm² for unloaded VOR, VOR-NLC and VOR-NLC-Ur, respectively, p>0.05). Still, successive extractions, revealed the amount of VOR retained in deeper regions was significantly higher when VOR-NLC or VOR-NLC-Ur was used (0.17±0.04, 0.47±0.14 and 0.36±0.07μg/cm² for unloaded VOR, VOR-NLC and VOR-NLC-Ur, respectively, p<0.05). Such results indicate NLC are promising formulations for the management of onychomycosis. Further studies in diseased nail plates are necessary.

Structural and component mining of nails using bioengineering techniques

The human nail is one of the challenging membranes for the scientists to target and to improve the clinical efficacy of ungual formulations. The understanding of nail physiology, impact of hydration on its properties and presence of trace elements in nails as biomarkers has been explored by various researchers in clinical studies. Despite the importance of biophysical techniques for the assessment of structure and physiology of nail, minimum literature analyses biophysical, biochemical and bioanalytical approaches. However, nowadays scientists in bioengineering field are keen in developing non-invasive, reliable and reproducible techniques for the assessment of different anatomical and functional parameters of nails for testing of ungual products.

Application of Hansen Solubility Parameters to predict drug-nail interactions, which can assist the design of nail medicines

We hypothesised that Hansen Solubility Parameters (HSPs) can be used to predict drug-nail affinities. Our aims were to: (i) determine the HSPs (δD, δP, δH) of the nail plate, the hoof membrane (a model for the nail plate), and of the drugs terbinafine HCl, amorolfine HCl, ciclopirox olamine and efinaconazole, by measuring their swelling/solubility in organic liquids, (ii) predict nail-drug interactions by comparing drug and nail HSPs, and (iii) evaluate the accuracy of these predictions using literature reports of experimentally-determined affinities of these drugs for keratin, the main constituent of the nail plate and hoof. Many solvents caused no change in the mass of nail plates, a few solvents deswelled the nail, while others swelled the nail to varying extents. Fingernail and toenail HSPs were almost the same, while hoof HSPs were similar, except for a slightly lower δP. High nail-terbinafine HCl, nail-amorolfine HCl and nail-ciclopirox olamine affinities, and low nail-efinaconazole affinities were then predicted, and found to accurately match experimental reports of these drugs' affinities to keratin. We therefore propose that drug and nail Hansen Solubility Parameters may be used to predict drug-nail interactions, and that these results can assist in the design of drugs for the treatment of nail diseases, such as onychomycosis and psoriasis. To our knowledge, this is the first report of the application of HSPs in ungual research.

Transungual permeation: current insights

Nail disorders are beyond cosmetic concern; besides discomfort in the performance of daily chores, they disturb patients psychologically and affect their quality of life. Fungal nail infection (onychomycosis) is the most prevalent nail-related disorder affecting a major population worldwide. Overcoming the impenetrable nail barrier is the toughest challenge for the development of efficacious topical ungual formulation. Sophisticated techniques such as iontophoresis and photodynamic therapy have been proven to improve transungual permeation. This article provides an updated and concise discussion regarding the conventional approach and upcoming novel approaches focused to alter the nail barrier. A comprehensive description regarding preformulation screening techniques for the identification of potential ungual enhancers is also described in this review while highlighting the current pitfalls for the development of ungual delivery.

Molecular diffusion in the human nail measured by stimulated Raman scattering microscopy

The effective treatment of diseases of the nail remains an important unmet medical need, primarily because of poor drug delivery. To address this challenge, the diffusion, in real time, of topically applied chemicals into the human nail has been visualized and characterized using stimulated Raman scattering (SRS) microscopy. Deuterated water (D2O), propylene glycol (PG-d8), and dimethyl sulphoxide (DMSO-d6) were separately applied to the dorsal surface of human nail samples. SRS microscopy was used to image D2O, PG-d8/DMSO-d6, and the nail through the O-D, -CD2, and -CH2 bond stretching Raman signals, respectively. Signal intensities obtained were measured as functions of time and of depth into the nail. It was observed that the diffusion of D2O was more than an order of magnitude faster than that of PG-d8 and DMSO-d6. Normalization of the Raman signals, to correct in part for scattering and absorption, permitted semiquantitative analysis of the permeation profiles and strongly suggested that solvent diffusion diverged from classical behavior and that derived diffusivities may be concentration dependent. It appeared that the uptake of solvent progressively undermined the integrity of the nail. This previously unreported application of SRS has permitted, therefore, direct visualization and semiquantitation of solvent penetration into the human nail. The kinetics of uptake of the three chemicals studied demonstrated that each altered its own diffusion in the nail in an apparently concentration-dependent fashion. The scale of the unexpected behavior observed may prove beneficial in the design and optimization of drug formulations to treat recalcitrant nail disease.

Two sensory channels mediate perception of fingertip force

In two experiments we examined the ability of humans to exert forces accurately with the fingertips, and to perceive those forces. In experiment 1 participants used visual feedback to apply a range of fingertip forces with the distal pad of the thumb. Participants made magnitude discriminations regarding these forces, and their just noticeable differences were calculated at a series of standards by means of a two-interval, forced-choice tracking paradigm. As the standard increased, participants demonstrated a relative improvement in force discrimination; and the presence of a possible inflection point, at approximately 400 g, suggested that two sensory channels may contribute to performance. If this is the case, the operative channel at low forces is almost certainly the slowly adapting type I (SA-I) channel, while another mechanoreceptor class, the SA-II nail unit, is a plausible mediator of the more accurate performance seen at high force levels. To test this two-channel hypothesis in experiment 2, we hydrated participants' thumbnails in order to reduce nail rigidity and thus prevent stimulation of underlying SA-II mechanoreceptors. This technique was found to reduce sensory accuracy in a force-matching task at high forces (1000 g) while leaving low force matching (100 g) unimpaired. Taken together, these results suggest that two sensory channels mediate the perception of fingertip forces in humans: one channel predominating at low forces (below approximately 400 g) and another responsible for perceiving high forces which is likely mediated by the SA-II nail unit.

Molecular spectroscopic identification of the water compartments in bone

Matrix bound water is a correlate of bone's fracture resistance and assessment of bound water is emerging as a novel measure of bone's mechanical integrity. Raman spectroscopy is one of the few nondestructive modalities to assess the hydration status in bone; however, it has not been used to study the OH-band in bone. A sequential dehydration protocol was developed to replace unbound (heat drying) and bound (ethanol or deuterium) water in bone. Raman spectra were collected serially to track the OH-band during dehydration. Spectra of synthetic hydroxyapatite, demineralized bone and bulk water were collected to identify mineral and collagen contributions to the OH-band. Band assignments were supported by computational simulations of the molecular vibrations of Gly-Pro-Hyp amino acid sequence. Experimentally and theoretically obtained spectra were interpreted for band-assignments. Water loss was measured gravimetrically and correlated to Raman intensities. Four peaks were identified to be sensitive to dehydration: 3220cm(-1) (water), 3325cm(-1) (NH and water), 3453cm(-1) (hydroxyproline and water), and 3584cm(-1) (mineral and water). These peaks were differentially sensitive to deuterium treatment such that some water peaks were replaced with deuterium oxide faster than the rest. Specifically, the peaks at 3325 and 3584cm(-1) were more tightly bound to the matrix than the remaining bands. Comparison of dehydration in mineralized and demineralized bone revealed a volume of water that may be locked in the matrix by mineral crystals. The OH-range of bone was dominated by collagen and the water since the spectral profile of dehydrated demineralized bone was similar to that of the mineralized bone. Furthermore, water associates to bone mainly by collagen as findings of experimentally and theoretically spectra. The current work is among the first thorough analysis of the Raman OH stretch band in bone and such spectral information may be used to understand the involvement of water in the fragility of aging and in diseased bone.

An alternative method using microwave power saturate in fingernail/electron paramagnetic resonance dosimetry

An alternative method for fingernail/electron paramagnetic resonance (EPR) dosimetry valid at low doses (0-3 Gy) is suggested in this paper. The method consisted of two steps. The first step involved dehydrating fingernail clippings to remove their water content by heating them at 70 °C for 72 h. As the water content in the fingernails decreased, the variability of the EPR signals improved. The second step involved measuring and fitting the EPR signals at successive microwave power levels. A newly derived value known as 'curvature', which was based on the conventional peak-to-peak amplitudes of the EPR signals, was applied for the dosimetry. This method could be used as an alternative method in cases of low-radiation exposure doses (<3 Gy) or where use of the conventional dosimetry method is not proper for a fingernail sample.

Microstructure and mechanical properties of horns derived from three domestic bovines

The microstructure and mechanical properties of horns derived from three domestic bovines (buffalo, cattle and sheep) were examined. The effects of water content, sampling position and orientation of three bovid horns on mechanical properties were systematically investigated by uniaxial tension and micron indentation tests. Meanwhile, the material composition and metal element contents were determined by Raman spectroscopy and elemental analysis respectively, and the microstructures of the horns were measured by scanning electron microscopy (SEM). Results show that the mechanical properties of horns have negative correlation with water contents and depend on sampling position and orientation. The spatial variations of the mechanical properties in horns are attributed to the different keratinization degrees in the proximal, middle and distal parts. And the mechanical properties of horns in the longitudinal direction are better than those in transverse. Among the three kinds of horns, the mechanical properties of buffalo horn are the best, followed by cattle horn, and those in sheep horn are the worst. This is due to the differences in material composition, metal element, and the microstructures of the horns. But the mechanical properties of buffalo horns are not dependent on the source of the buffalo. Therefore, regular engineered buffalo keratinous materials with standard mechanical properties can be obtained from different buffalo horns by using proper preparation methods.

Novel topical formulations of Terbinafine-HCl for treatment of onychomycosis

Terbinafine hydrochloride (TBF-HCl) is an active substance that is using for treatment of onychomycosis. Onychomycosis is a fungal infection which is the most common disease of nail plate. The nail plate is a barrier which prevents effective topical treatment of ungual disorders. In this study, TBF-HCl loaded liposome and ethosome formulations and also gel form of these formulations were prepared. The formulations were characterized and in vitro and ex vivo release studies were performed. Nail characterization studies were also performed to examine the effect of formulations and experimental conditions on nail surface. As a result, all formulations can serve as efficient formulations for ungual application of TBF-HCl. By the way, the results of the accumulation studies suggested that liposome poloxamer gel formulation could be promising system for ungual drug delivery due to the better accumulation and easier application of the formulation.

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.

Raman spectroscopy: a noninvasive analysis tool for the discrimination of human skin cells

Noninvasive monitoring of tissue-engineered (TE) constructs during their in vitro maturation or postimplantation in vivo is highly relevant for graft evaluation. However, traditional methods for studying cell and matrix components in engineered tissues such as histology, immunohistochemistry, or biochemistry require invasive tissue processing, resulting in the need to sacrifice of TE constructs. Raman spectroscopy offers the unique possibility to analyze living cells label-free in situ and in vivo solely based on their phenotype-specific biochemical fingerprint. In this study, we aimed to determine the applicability of Raman spectroscopy for the noninvasive identification and spectral separation of primary human skin fibroblasts, keratinocytes, and melanocytes, as well as immortalized keratinocytes (HaCaT cells). Multivariate analysis of cell-type-specific Raman spectra enabled the discrimination between living primary and immortalized keratinocytes. We further noninvasively distinguished between fibroblasts, keratinocytes, and melanocytes. Our findings are especially relevant for the engineering of in vitro skin models and for the production of artificial skin, where both the biopsy and the transplant consist of several cell types. To realize a reproducible quality of TE skin, the determination of the purity of the cell populations as well as the detection of potential molecular changes are important. We conclude therefore that Raman spectroscopy is a suitable tool for the noninvasive in situ quality control of cells used in skin tissue engineering applications.

Effect of a novel penetration enhancer on the ungual permeation of two antifungal agents

OBJECTIVES

The aim of this study was to demonstrate the effect of a novel permeation enhancer system using two existing marketed nail lacquers and the delivery of terbinafine through human nail samples in vitro.

METHODS

Initially a modified Franz cell was used, where sections of human nail serve as the barrier through which drug penetrates into an agar-filled chamber infected with dermatophytes. A second study was performed using a novel infected nail model where dermatophytes are incubated with and grow into human nail and ATP levels are used as biological marker for antimicrobial activity.

KEY FINDINGS

The novel permeation enhancing system increased the permeation of both existing drugs formulated in nail lacquers and terbinafine through human nail sections mounted in a modified Franz cell. Furthermore the ATP assay confirmed that the system also enhanced the permeation of terbinafine through infected cadaver nail resulting in a decrease in ATP levels equivalent to those of uninfected negative control samples.

CONCLUSIONS

This study has clearly demonstrated that the use of a novel permeation enhancing system, which fundamentally alters the chemical structure of the nail, not only enhances the efficacy of the existing topical formulations but also enables the delivery and efficacy of terbinafine when applied ungually. Such a topically applied system has the possibility of overcoming the systemic side effects when terbinafine is delivered orally.

Permeation studies of novel terbinafine formulations containing hydrophobins through human nails in vitro

Existing treatments of onychomycosis are not satisfactory. Oral therapies have many side effects and topical formulations are not able to penetrate into the human nail plate and deliver therapeutical concentrations of active agent in situ. The purpose of the present study was to determine the amount of terbinafine, which permeates through the human nail plate, from liquid formulations containing enhancers, namely hydrophobins A-C in the concentration of 0.1% (w/v). The used reference solution contained 10% (w/v) of terbinafine in 60% (v/v) ethanol/water without enhancer. Permeability studies have been performed on cadaver nails using Franz diffusion cells modified to mount nail plates and filled with 60% (v/v) ethanol/water in the acceptor chamber. Terbinafine was quantitatively determined by HPLC. The amount of terbinafine remaining in the nail was extracted by 96% ethanol from pulverized nail material after permeation experiment and presented as percentage of the dry nail weight before the milling test. Permeability coefficient (PC) of terbinafine from reference solution was determined to be 1.52E-10 cm/s. Addition of hydrophobins improved PC in the range of 3E-10 to 2E-9 cm/s. Remaining terbinafine reservoir in the nail from reference solution was 0.83% (n=2). An increase of remaining terbinafine reservoir in the nail was observed in two out of three tested formulations containing hydrophobins compared to the reference. In all cases, known minimum inhibitory concentration of terbinafine for dermatophytes (0.003 microg/ml) has been exceeded in the acceptor chamber of the diffusion cells. All tested proteins (hydrophobins) facilitated terbinafine permeation after 10 days of permeation experiment, however one of them achieved an outstanding enhancement factor of 13.05 compared to the reference. Therefore, hydrophobins can be included in the list of potential enhancers for treatment of onychomycosis.

Nail biology and nail science

The nail plate is the permanent product of the nail matrix. Its normal appearance and growth depend on the integrity of several components: the surrounding tissues or perionychium and the bony phalanx that are contributing to the nail apparatus or nail unit. The nail is inserted proximally in an invagination practically parallel to the upper surface of the skin and laterally in the lateral nail grooves. This pocket-like invagination has a roof, the proximal nail fold and a floor, the matrix from which the nail is derived. The germinal matrix forms the bulk of the nail plate. The proximal element forms the superficial third of the nail whereas the distal element provides its inferior two-thirds. The ventral surface of the proximal nail fold adheres closely to the nail for a short distance and forms a gradually desquamating tissue, the cuticle, made of the stratum corneum of both the dorsal and the ventral side of the proximal nail fold. The cuticle seals and therefore protects the ungual cul-de-sac. The nail plate is bordered by the proximal nail fold which is continuous with the similarly structured lateral nail fold on each side. The nail bed extends from the lunula to the hyponychium. It presents with parallel longitudinal rete ridges. This area, by contrast to the matrix has a firm attachment to the nail plate and nail avulsion produces a denudation of the nail bed. Colourless, but translucent, the highly vascular connective tissue containing glomus organs transmits a pink colour through the nail. Among its multiple functions, the nail provides counterpressure to the pulp that is essential to the tactile sensation involving the fingers and to the prevention of the hypertrophy of the distal wall tissue, produced after nail loss of the great toe nail.

Investigation of the content and of the distribution of chemical elements in human nails by SRXRF

The purpose of this investigation is to analyze 20 nails in individuals (and several persons) for the definition of how chemical elements distribute from nail to nail. The aim was to determine whether it will be rightful to take only one nail for the elemental analysis for the diagnostic of human state in future or not? Another purpose of the research is to analyze the elemental content of nails in temporal dynamic (in several persons). Analytical determinations of 20 nails of nine donors (healthy persons), nails of both hands and both feet were carried out. The analysis was performed by SRXRF. Symmetry of the elemental distribution in nails of right and left hands and right and left feet was found. The analysis of the distribution of chemical elements on the total area of a nail (55 points) was performed. The nail cutaway reflects adequately the distribution of several chemical elements over the nail plate area. In this study the elemental concentrations in nails of three donors in a 6-month period was determined. This study found the content of the chemical elements in donors' nails changes with time, individually.

Exposure to toxic agents alters organic elemental composition in human fingernails

BACKGROUND AND OBJECTIVE

The human fingernail plate is highly keratinized. The keratin structure is held together by disulfide bonds. The organic elements sulfur and nitrogen occur almost exclusively in amino acids of the nail plate. This study analyzed whether occupational exposure to harmful chemical agents alters the organic elemental composition in fingernails.

SUBJECTS AND METHODS

Participants were 71 occupationally exposed workers (49 hairdressers, 22 painters) and 49 unexposed controls. Aspects of exposure were assessed by questionnaire. Nail clippings of index and little fingers were analyzed for sulfur (S), nitrogen (N), carbon (C), and hydrogen (H) contents, using an automatic elemental analyzer (Vario EL III, Elementar Analysensysteme, Hanau, Germany). C/N, N/S, and C/S ratios were calculated. Reliability of elemental measurements was tested in a subset.

RESULTS

Reliability analysis of elemental measurements showed a very good agreement. Both painters and hairdressers displayed in their fingernails significantly lower percentages of sulfur, but higher percentages of carbon than unexposed controls. A trend was observed in that sulfur content was lowest in those hairdressers who reported structural changes in their fingernails. As a consequence, the C/S and N/S ratios were significantly increased in both exposed groups.

CONCLUSION

The occupational use of harmful substances leads to decreased sulfur levels in the exposed persons, probably due to diminution of sulfur-rich proteins in the nails, resulting from destruction of disulfide-bonds by alkaline and acid groups. Thus, the C/S ratio seems to be a useful indicator for the amount of damage of nail protein by harmful agents.

Transungual iontophoretic transport of polar neutral and positively charged model permeants: effects of electrophoresis and electroosmosis

Transungual iontophoretic transport of model neutral permeants mannitol (MA), urea (UR), and positively charged permeant tetraethylammonium ion (TEA) across fully hydrated human nail plates at pH 7.4 were investigated in vitro. Four protocols were involved in the transport experiments with each protocol divided into stages including passive and iontophoresis transport of 0.1 and 0.3 mA. Water and permeant uptake experiments of nail clippings were also conducted to characterize the hydration and binding effects of the permeants to the nails. Iontophoresis enhanced the transport of MA and UR from anode to cathode, but this effect (electroosmosis) was marginal. The transport of TEA was significantly enhanced by anodal iontophoresis and the experimental enhancement factors were consistent with the Nernst-Planck theory predictions. Hindered transport was also observed and believed to be critical in transungual delivery. The barrier of the nail plates was stable over the time course of the study, and no significant electric field-induced alteration of the barrier was observed. The present results with hydrated nail plates are consistent with electrophoresis-dominant (the direct field effect) transungual iontophoretic transport of small ionic permeants with small contribution from electroosmosis.

A novel method for human gender classification using Raman spectroscopy of fingernail clippings

This paper illustrates a novel method for human gender classification by measuring the Raman spectrum of fingernail clippings. As Raman spectroscopy reveals the characteristics of vibrational frequencies of the fingernails, it provides unique chemical fingerprints that can be used to describe the molecular structure differences of fingernail between males and females. As the differences of Raman spectra of human fingernails are very subtle, they are enhanced by using a pattern recognition method. In the present study, a combination algorithm of principal component analysis (PCA) and support vector machines (SVM) was implemented to perform the data classification. This combined algorithm provides a classification accuracy of up to 90%. The success of this present method may be used as an alternative rapid tool to identify human gender in forensic applications.

Preliminary work on the development of a novel detection method for osteoporosis

Osteoporosis affects both the organic and mineral phases of bone resulting in a decrease in resistance to fracture. Dual x-ray absorptiometry (DEXA) scans are used for diagnosing osteoporosis, which is conventionally characterised by a decrease in mineral density. Unfortunately, some patients who suffer osteoporotic fractures have normal bone density, because both the organic and the mineral phase are affected. However, there are currently no methods of evaluating the health of the organic phase. Patients undergoing treatment for osteoporosis have reported hardening of their fingernails. As the properties of nail and bone may be linked in a comparable, measurable way, this work used both mechanical (nano-indentation) and chemical (Raman spectroscopy) methods to evaluate differences between fingernails sourced from osteoporotic and non-osteoporotic patients. The difference in mean modulus between the nails sourced from the groups was 1.1 GPa. The disulphide bond content of fingernail samples from each group was measured by Raman spectroscopy and disulphide bond content of fingernail was found to be significantly lower in the osteoporotic group. It can be concluded that a relationship between the mechanical and chemical properties of nail and bone may exist in a measurable way. This work has suggested that changes in the organic phase of bone are reflected in similar proteins, such as keratin, from which fingernails are composed. Collagen and keratin are two distinct structural proteins, but they share the need for protein sulphation and disulphide bond formation, via cysteine, for their structural integrity. A disorder of either process should lead to disordered collagen and keratin synthesis.

Brittle nail syndrome: a pathogenesis-based approach with a proposed grading system

Brittle nail syndrome is a heterogeneous abnormality, characterized by increased fragility of the nail plate. Brittle nails affect about 20% of the population and women are affected twice as frequently as men. The vast majority of patients experience brittle nails as a significant cosmetic problem and a substantial number indicate that these nail abnormalities are painful, impair daily activities, and may have a negative impact on occupational abilities. Pathogenic factors leading to brittle nails are factors that impair intercellular adhesion of the corneocytes of the nail plate or factors that cause a pathologic nail formation by involving the matrix. Clinical features of brittle nail syndrome are onychoschizia and onychorrhexis: the impairment of intercellular adhesive factors of the nail plate is expressed as onychoschizia, whereas the involvement of the nail matrix is expressed as onychorrhexis. Although impairment of life quality has not been evaluated for patients with brittle nail syndrome, the reduction of life quality in other nail problems has been studied and is evident. A proposed scoring system of key features of brittle nails is presented, and therapeutic approaches focussed on the pathogenic factors are discussed.

In vivo measurement of water content of the fingernail and its seasonal change

BACKGROUND/AIMS

Recently, there has been increasing awareness regardless keeping nails in good condition. Maintenance of an optimum water level in the nail plate is very important since water content affects the nail condition. However, a simple method for in vivo measurement of water in the nail plate quantitatively has not been reported. In this study, we applied Near infrared spectroscopy (NIR)-based prediction of water content of the cut nail plate to in vivo measurement to obtain information about the seasonal change of water in the fingernail.

METHODS

Diffused reflectance spectra of the nail plate of the fingernail were collected in the NIR region with an NIR spectrometer in vivo both in summer and winter from the same 15 Japanese female subjects. The water content of the nail plate in vivo was calculated from the NIR spectrum using partial least square regression analysis.

RESULTS

It was possible to apply NIR-based prediction of water content of the cut nail plate to in vivo measurement. We also found that the water content of the nail plate varied from person to person but not with the finger of the individual. The average water content of the nail plate was significantly lower in winter than in summer (P<0.05). In summer, the water content in the double-layered nail tended to be higher than a nail in good condition (P<0.1) and significantly lower in the split nail (P<0.05). There was no significant difference between the groups in winter. On the contrary, the amount of water absorption tended to vary depending on the nail condition. A large amount of water was absorbed in the double-layered nail and a small amount in the split nail both in summer and winter.

CONCLUSION

The water content of the nail plate of fingernail was predicted by in vivo measurement using NIR spectrometry. Physiological information of the nail in vivo, such as aging and other disorders could be obtained by this method.

Conformational differences in protein disulfide linkages between normal hair and hair from subjects with trichothiodystrophy: A quantitative analysis by Raman microspectroscopy

Raman spectra of normal hair shafts and hair shafts from patients exhibiting trichothiodystrophy (TTD) were obtained using line focus laser illumination. Because hair from TTD patients has a significant decrease in the content of the sulfur-containing amino acids in comparison to normal hair, the 550-500 cm(-1) disulfide stretching mode region of the Raman spectrum was examined in detail. A quantitative spectral analysis demonstrates significant increases in the two energetically less favored gauche-gauche-trans (g-g-t) and trans-gauche-trans (t-g-t) forms. These observations suggest that the increased amounts of these less stable disulfide conformers are contributing factors to or associated with the hair brittleness observed for this congenital disorder. Structure-spectra correlations for the three dominant disulfide conformers are confirmed by quantum chemical calculations using modern density functional theory (DFT).

Fiber optic near-infrared Raman spectroscopy for clinical noninvasive determination of water content in diseased skin and assessment of cutaneous edema

Currently, measuring Raman spectra of tissues of living patients online and in real time, collecting the spectra in a very short measurement time, and allowing diagnosis immediately after the spectrum is recorded from any body region, are specific advantages that fiber optic near-infrared Raman spectroscopy (NIR RS) might represent for in vivo clinical applications in dermatology. We discuss various methodological aspects and state of the art of fiber optic NIR RS in clinical and experimental dermatology to outline its present advantages and disadvantages for measuring skin in vivo, particularly its water content. Fiber optic NIR Fourier transform (FT) RS has been introduced to dermatological diagnostics to obtain information regarding the molecular composition of the skin up to several hundred micrometers below the skin surface in a relatively fast nondestructive manner. This has been especially important for probing for in vivo assessment of cutaneous (intradermal) edema in patients patch test reactions. Fiber optic NIR FT Raman spectrometers still require further technological developments and optimization, extremely accurate water concentration determination and its intensity calculation in skin tissue, and for clinical applications, a reduction of measurement time and their size. Another promising option could be the possibility of applying mobile and compact fiber optic charge-coupled device (CCD)-based equipment in clinical dermatology.

Determining water content in human nails with a portable near-infrared spectrometer

The water content of human nail plates was determined using a portable near-infrared (NIR) spectrometer with an InGaAs photodiode array detector. NIR diffuse reflectance (DR) spectra were collected from 108 cut nail plates with different relative humidity and in vivo from fingernails. Partial least-squares (PLS) regression was applied to the NIR spectra in the 1115-1645 nm region to develop calibration models that determine the water content in the cut nail plates and fingernails. A good correlation was obtained between the NIR spectra and the water content measured by nuclear magnetic resonance (NMR) for the NIR measurement of both cut nail plates and fingernails. The results indicate that the water content in the nails can be determined very rapidly (1 s) by means of the portable NIR spectrometer and PLS regression.

Hydration dynamics of human fingernails: an ellipsometric study

We use spectroscopic ellipsometry to obtain the complex refractive index, ñ=n+ik, of human fingernails. By studying the change of ñ upon hydration and dehydration, we reveal three different time domains with typical time constants of 4, 150, and 3200 min. A simple model that takes into account the presence of one fast and one slow process is fully consistent with the observed hydration and dehydration dynamics. We attribute these processes to "free" water incorporated between the keratin filaments and water more tightly "bound" in keratin complexes, respectively. From our model we determine the hydration profiles of "free" and "bound" water during, both, hydration and dehydration.

Medical applications of Raman spectroscopy: from proof of principle to clinical implementation

Raman spectroscopy has recently been applied ex vivo and in vivo to address various biomedical issues such as the early detection of cancers, monitoring of the effect of various agents on the skin, determination of atherosclerotic plaque composition, and rapid identification of pathogenic microorganisms. This leap in the number of applications and the number of groups active in this field has been facilitated by several technological advancements in lasers, CCD detectors, and fiber-optic probes. However, most of the studies are still at the proof of concept stage. We present a discussion on the status of the field today, as well as the problems and issues that still need to be resolved to bring this technology to hospital settings (i.e., the medical laboratory, surgical suites, or clinics). Taken from the viewpoint of clinicians and medical analysts, the potential of Raman spectroscopic techniques as new tools for biomedical applications is discussed and a path is proposed for the clinical implementation of these techniques.

The physical basis of cosmetic defects of the nail plate

Cosmetic defects of the nail cover a range of changes. Some are variants of normal which are considered unattractive, others are part of the normal ageing process and some changes are manifestations of local or systemic disease. Interpretation of these changes relies on recognition of the specific characteristics in question and an understanding of the anatomy and biology of nails. In many instances, therapies are limited and explanation of the changes represents one of the most useful contributions the professional can make to the affected individual. This article covers some of the most common cosmetic defects of nail involving colour, surface, brittleness and behaviour of surrounding tissues. Understanding of the physical basis of these defects is limited in many cases, but current thinking is recorded.