Effects of two types of surface treatments on the structural elasticity of human fingernails.

BACKGROUND: The human nail has a three-layered structure. Although it would be useful to quantitatively evaluate the changes in deformability of the nail due to various surface treatments, few studies have been conducted. METHODS: The effects of two types of surface treatment-a chemically acting nail softener and a physically acting nail strengthener-on the deformability of human fingernails were investigated. The Young's modulus of each plate of the nail samples before and after softening treatment was determined by nanoindentation. The Young's modulus of the strengthener was determined by conducting a three-point bending test on a polyethylene sheet coated with the strengthener. RESULTS: Young's modulus decreased in order from the top plate against the softening treatment time, and the structural elasticity for bending deformation (SEB) of the nail sample, which expresses the deformability against bending deformation independent of its external dimensions, decreased to 60% after 6 h of treatment. The Young's modulus of the nail strengthener was 244.5 MPa, which is less than 10% of the SEB of the nail. When the nail strengthener was applied to the nail surface, the SEB decreased to 73%, whereas the flexural rigidity increased to 117%. CONCLUSION: Changes in nail deformability caused by various surface treatments for softening and hardening were quantitatively evaluated successfully.

Nanoindentation study of human fingernail for determining its structural elasticity.

BACKGROUND: Human nails play an important role in transmitting force to the fingertips, and their mechanical properties are important indices. The nail has a three-layered structure consisting of top dorsal, middle intermediate, and under ventral plates, and its internal structure is believed to affect its mechanical properties. However, this has not been investigated in previous studies. METHODS: The Young's moduli of the top, middle, and under plates were measured using nanoindentation, and a theoretical model was developed to estimate the structural elasticity for the bending deformation of human nails, which is an index describing the deformability of the nail without depending on its external dimensions. The structural elasticity of human nails was compared with that of human hair collected from the same person. The effect of the softening treatment on the nails was also evaluated. RESULTS: The Young's moduli of the top, middle, and under plates measured using nanoindentation were 2.9, 3.1, and 2.8 GPa, respectively. The structural elasticity of the nail was estimated to be 2.9 GPa, approximately 75% that of hair. Moreover, softening treatment with a urea cream reduced the structural elasticity of the nail to 70%. CONCLUSION: This paper proposed a method for estimating the structural elasticity of a human nail with a three-layered structure. This index is a mechanical property with "Pa" as a unit, and is useful for comparing deformability with the Young's modulus of other homogeneous materials or for investigating the effect of various treatments quantitatively.

Human Nails Permeation of an Antifungal Candidate Hydroalcoholic Extract from the Plant Sapindus saponaria L. Rich in Saponins.

We evaluated a hydroalcoholic extract of Sapindus saponaria L. pericarps (ETHOSS), as a candidate to a topical antifungal medicine for onychomycosis. ETHOSS was produced by extracting the crushed fruits in ethanol. The saponin contents were identified and characterized by electrospray ionization mass spectrometry. We measured the in vitro antifungal activity against three dermatophyte fungi, isolated from onychomycosis: Trichophyton rubrum, T. mentagrophytes, and T. interdigitale, using broth microdilution tests. The minimum fungicide concentration of ETHOSS ranged from 195.31 to 781.25 µg/mL. The cytotoxicity of the crude extract was tested on the HeLa cell line, and its ability to permeate into healthy human nails by photoacoustic spectroscopy and Fourier transformation infrared spectrometer (FTIR) spectroscopy by attenuated total reflection. Besides its strong antifungal activity, ETHOSS showed low cytotoxicity in human cells. It was able to permeate and reach the full thickness of the nail in one hour, without the aid of facilitating vehicles, and remained there for at least 24 h. These results suggest that ETHOSS has great potential for treating onychomycosis.

Ciclopirox delivery into the human nail plate using novel lipid diffusion enhancers.

CONTEXT: Onychomycosis is a common fungal infection of the nail plate and bed that affects up to 14% of the population and can have a substantial impact on the quality of life of those affected. OBJECTIVE: This study compared the onychopharmacokinetics, nail absorption, nail distribution, and nail penetration of [(14)C]-ciclopirox dissolved in novel lipid diffusion enhancers with that of a commercial ciclopirox nail lacquer using the in vitro finite dose model. MATERIALS AND METHODS: The penetration rate of ciclopirox was determined by applying doses of topical formulation twice daily to human nail plates for 11 d. Drug absorption was then measured by monitoring its rate of appearance in each nail layer and in the cotton pad/nail supporting bed. RESULTS: After a multiple day treatment, cumulative concentrations of ciclopirox formulated with lipid enhancers in the deep nail layer and the nail bed were significantly greater than cumulative concentrations of the commercial ciclopirox lacquer (p < 0.001) as well as several orders of magnitude greater than the minimal inhibitory concentration (MIC) deemed necessary to inhibit the growth of the causative dermatophyte species. CONCLUSION: When formulated with lipid enhancers, the amount of ciclopirox in the ventral/intermediate layer and supporting bed dramatically exceed the inhibitory concentration of ciclopirox for the most common onychomycosis organisms. These results suggest that topical ciclopirox with lipid enhancers has the potential to be an effective topical treatment for onychomycosis, and the lipidic pathway of the nail can be utilized as a means of effective transungual delivery.

Trace Element Levels in Nails of Residents of Addis Ababa Are Shaped by Social Factors and Geography.

The Akaki catchment in Ethiopia is home to Addis Ababa and about five million people. Its watercourses receive a variety of wastes released by the residents and industries. River water is being used for irrigation, livestock watering, and other domestic purposes. This study tested the hypothesis that the river pollution would be reflected in higher levels of trace elements in the nails of residents living in Akaki-Kality Sub-City in the downstream, as compared to those living in Gullele Sub-City in the upstream of the Akaki catchment. Samples were taken and subsequently analysed for metals using inductively coupled plasma optical emission spectrometry (ICP-OES). The mean concentrations of Fe, Zn, Cu, Mn, Ni, Cr, Pb, and As in nails from Akaki-Kality were 488 ± 49, 106 ± 10, 5.2 ± 0.3, 13 ± 1.5, 11 ± 8, 2.2 ± 0.3, 0.09 ± 0.01, and 0.16 ± 0.01 µg/g, respectively. Likewise, the concentrations of Fe, Zn, Cu, Mn, Ni, Cr, Pb, and As in nails from Gullele were 1035 ± 135, 251 ± 10, 6.6 ± 0.4, 31 ± 3.7, 7.4 ± 1.7, 2.0 ± 0.3, 0.63 ± 0.01, and 0.25 ± 0.01 µg/g, respectively. Co and Cd were not detected. Contrary to the initial hypothesis, higher metal levels were found in nails of residents living in the upstream rather than the downstream area of the catchment. In particular, the concentrations of Fe (p = 0.000), Zn (p = 0.01), and Mn (p = 0.000) were significantly elevated in nails from Gullele and also high in comparison with internationally reported values. Besides, geography and social factors, especially education level, correlated to trace metals in nails. Most of the elements were significantly lower in the nails of individuals with a university degree compared to those who were illiterate or only completed primary school.

Comparative Ungual Drug Uptake Studies: Equine Hoof Membrane vs. Human Nail Plate.

Human nail diseases, mostly caused by fungal infections, are common and difficult to treat. The development and testing of new drugs and drug delivery systems for the treatment of nail diseases is often limited by the lack of human nail material for permeation studies. Animal material is frequently used, but there are only few comparative data on the human nail plate, and there is neither a standardized test design nor a nail bed analogue to study drug uptake into the nail. In this study, a new permeation device was developed for permeation studies, and the permeation behavior of three model substances on the human nail plate and a model membrane from the horse hoof was investigated. A linear correlation was found between drug uptake by the human nail plate and the uptake by the equine hoof. The developed and established permeation device is suitable for investigations of ungual drug transport and enables the use of different membrane diameters and the use of a gel-based nail bed analog. The hydrogel-based acceptor medium used ensures adequate stabilization and hydration of the nail membrane.

Mechanism of human nail poration by high-repetition-rate, femtosecond laser ablation.

Optical poration, or drilling, of the human nail has the potential to drastically improve transungual drug delivery. However, this approach is accompanied by thermal damage to the nail tissue surrounding the laser radiation-created pore. In this paper, fluorescence microscopy has been employed to quantitatively evaluate thermal damage to the nail induced by laser ablation with 80 MHz, nanojoule, femtosecond pulses delivered via a hollow-core fibre. An empirical relation has been established between the intensity of the resulting fluorescence signal and temperature to which the nail was exposed. Using this relationship, detailed temperature maps have been created of the areas surrounding the pores, enabling the mechanism of poration to be better understood. It was deduced that plasma-mediated ablation is primarily responsible for nail tissue ablation at the centre of the pore, while cumulative photothermal processes dominate at the pore edges. It is concluded, furthermore, that temperature mapping represents a useful new tool with which to optimise the process of nail poration. The method is potentially generic and may be applicable to other biological materials.

Human nail bed-derived decellularized scaffold regulates mesenchymal stem cells for nail plate regeneration.

Among hand trauma, nail bed is the most involved tissue in hospital emergency departments, resulting in the loss of nail plate, which leads to a disturbance of hand grasp function, long-lasting digit tip pain, hyperpathia, and disesthesia. Treatment of nail bed defects is a significant clinical challenge due to the lack of uniform nail bed thickness and distinct regenerative ability. In this study, it is shown that the extracellular matrix of decellularized nail bed scaffolds can play an important role in inducing bone mesenchymal stem cells to differentiate into nail epithelial cells. Using decellularized nail bed scaffolds combined with bone mesenchymal stem cells, it is revealed that the engineered nail bed can promote nude mouse nail plate regeneration ectopically. The natural extracellular matrix of decellularized nail bed scaffolds can serve as a 3D structural template for bone mesenchymal stem cell differentiation into nail-associated cells, initiating the nail plate regeneration. These results not only provide a proof-of-principle for the generation of transplantable nail grafts based on decellularized nail bed scaffolds derived from clinically wasted amputated fingers but also provide important considerations for clinical treatment for digit tip trauma.

Human nail stem cells are retained but hypofunctional during aging.

The nail is a continuous skin appendage. Cells located around the nails, which display coordinated homeostatic dynamics and release a flow of stem cells in response to regeneration, have been identified in mice. However, very few studies regarding human nail stem cells exist in the literature. Using specimens isolated from humans, we detected an unreported population of cells within the basal layer of postnatal human nail proximal folds (NPFs) and the nail matrix around the nail root. These cells were multi-expressing and expressed stem cell markers, such as keratin 15 (K15), keratin 14 (K14), keratin 19 (K19), CD29, CD34, and leucine-rich repeat-containing G protein-coupled receptor 6 (Lgr6). These cells were very similar to mouse nail stem cells in terms of cell marker expression and their location within the nail. We also found that the putative nail stem cells maintained their abundance with advancing age, but cell proliferation and nail growth rate were decreased on comparison of young and aged specimens. To summarize, we found a putative population of stem cells in postnatal human nails located at NPFs and the nail matrix. These cells may have potential for cell differentiation and be capable of responding to injury, and were retained, but may be hypofunctional during aging.

Estimating uptake of phthalate ester metabolites into the human nail plate using pharmacokinetic modelling.

There is a lack of knowledge regarding uptake of phthalate esters (PEs) and other chemicals into the human nail plate and thus, clarity concerning the suitability of human nails as a valid alternative matrix for monitoring long-term exposure. In particular, the relative importance of internal uptake of phthalate metabolites (from e.g. blood) compared to external uptake pathways is unknown. This study provides first insights into the partitioning of phthalate-metabolites between blood and nail using pharmacokinetic (PK) modelling and biomonitoring data from a Norwegian cohort. A previously published PK model (Lorber PK model) was used in combination with measured urine data to predict serum concentrations of DEHP and DnBP/DiBP metabolites at steady state. Then, partitioning between blood and nail was assessed assuming equilibrium conditions and treating the nail plate as a tissue, assuming a fixed lipid and water content. Although calculated as a worst-case scenario at equilibrium, the predicted nail concentrations of metabolites were lower than the biomonitoring data by factors of 44 to 1300 depending on the metabolite. It is therefore concluded that internal uptake of phthalate metabolites from blood into nail is a negligible pathway and does not explain the observed nail concentrations. Instead, external uptake pathways are more likely to dominate, possibly through deposition of phthalates onto the skin/nail and subsequent metabolism. Modelling gaseous diffusive uptake of PEs from air to nail revealed that this pathway is unlikely to be important. Experimental quantification of internal and external uptake pathways of phthalates and their metabolites into the human nail plate is needed to verify these modelling results. However, based on this model, human nails are not a good indicator of internal human exposure for the phthalate esters studied.

Precise laser poration to control drug delivery into and through human nail.

Drug treatment of diseases of the human nail remains a difficult challenge; topical therapy, in particular, is limited by very poor transport of active agents across the nail itself. The objective of this research was to examine the potential of controlled, and fibre-optic delivered, femtosecond laser light pulses to provide new pathways and opportunities for drug access to targets within and beneath the nail plate. Optical, confocal fluorescence and scanning electron microscopies demonstrated partial and complete laser poration of human nail samples, with the energy per pore and the exposure duration being the key modulating parameters that determined the extent of ablation achieved. Parallel measurements of the penetration of a model drug across laser-treated nails showed that complete poration resulted in essentially complete circumvention of the diffusion barrier, an array of 100 pores in 0.2cm2 area of nail permitting a 103-fold increase in initial drug uptake. Partial ablation of the nail created pores that extended to a range of depths; the nail material adjacent to the ablated area was rendered porous in appearance presumably due to local thermal perturbation of the nail structure. These openings offer, as a result, potential sites in which topical drug formulations might be sequestered post-poration and from which slow, sustained delivery of the active agent into and through the nail may be envisaged.

Use of human nail for reconstruction of the orbital floor: an experimental study in rabbits.

The orbital floor is the thinnest part of the orbital wall, and in 20% of all maxillofacial injuries it is fractured. Autografts, allografts, and alloplastic materials are used in reconstruction, but there is no consensus about which material is the most appropriate. Nail is a semirigid material that is easy to reshape and is not antigenic. Alloplastic materials, which are used in reconstructions of the orbital floor, have various complications and are expensive. Autografts have donor-site problems, high rates of resorption, and take a long time to do. We created bilateral 10mm defects in the orbital floors in 18 New Zealand rabbits. We reconstructed the left orbital floors with double-ground human nail while the right orbital floors were left open as controls. The orbital floors were examined macroscopically and microscopically at 4, 8, and 12 weeks postoperatively, and there were no macroscopic signs of infection, inflammation, or extrusion. Forced duction tests showed that it was possible to induce movement of the eyeball for all 18 of the reconstructed sides throughout the observation period, and in 14 of the 18 rabbits on the control sides. Positive forced duction test shows us that orbital muscles are trapped in orbital floor defect and due to this movement of eyeball is restricted. Acute and chronic inflammation, fibrosis, vascularisation, and the presence of foreign body giant cells were evaluated microscopically. Acute inflammation and the presence of foreign body giant cells were recorded as mild, whereas fibrosis, chronic inflammation, and vascularisation were severe, as were epithelialisation on the maxillary sinus side of the nails, calcification, and progression of collagen. We found no signs of resorption of the nails.

Development of an innovative 9 GHz EPR surface detection method and its application to non-invasive human fingers and nails investigation.

We developed an innovative surface-type cavity for 9 GHz electron paramagnetic resonance (EPR) and used it to non-invasively measure human fingers and nails. This surface-type cavity measures a sample on the top of the cavity instead of a sample inserted into the cavity. To verify the performance of this method, 5-10 µL of 0.1 mM 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPOL) aqueous solution in a 1.0-mm (i.d.) glass capillary was used. Although the detectable radical concentration of the surface-type cavity is lower than that of a commercial cavity, the surface-type cavity can measure biomedical samples. In addition, the cavity is capable of measuring human fingers and nails. The dynamics of a topically applied 1.0-mM TEMPOL solution with a commercial lotion (5:1 by weight) on a human finger and nail were investigated. The present EPR results suggest that TEMPOL in solution may not easily permeate into the finger and nail during the measurements. Therefore, 9 GHz surface-type detection exhibits the good potential to study paramagnetic species in bulky biomedical samples.

Controlled nail delivery of a novel lipophilic antifungal agent using various modern drug carrier systems as well as in vitro and ex vivo model systems.

The penetration behavior into human nails and animal hoof membranes of a novel antifungal agent (EV-086K) for the treatment of onychomycosis was investigated in this study. The new drug provides a high lipophilicity which is adverse for penetration into nails. Therefore, four different formulations were developed, with particular focus on a colloidal carrier system (CCS) due to its penetration enhancing properties. On the one hand, ex vivo penetration experiments on human nails were performed. Afterwards the human nail plates were cut by cryomicrotome in order to quantify the drug concentration in the dorsal, intermediate and ventral nail layer using high-performance liquid chromatography (HPLC) with UV detection. On the other hand, equine and bovine hoof membranes were used to determine the in vitro penetration of the drug into the acceptor compartment of an online diffusion cell coupled with Fourier transform infrared attenuated total reflectance (FTIR-ATR) spectroscopy. In combination, both results should exhibit a correlation between the EV-086K penetration behavior in human nail plates and animal hoof membranes. The investigations showed that the developed CCS could increase drug delivery through the human nail most compared to other formulations (nail lacquer, solution and hydrogel). Using animal hooves in the online diffusion cell, we were able to calculate pharmacokinetic data of the penetration process, especially diffusion and permeability coefficients. Finally, a qualitative correlation between the penetration results of human nails and equine hooves was established.

Transungual delivery of ketoconazole using novel lacquer formulation.

Onychomycosis, a common fungal infection of the nail, can have a substantial impact on quality of life. The success of topical therapy for onychomycosis depends on effective penetration, which can be enhanced using an appropriate delivery method. This study evaluated the effectiveness of a novel topical lacquer on enhancing [(14)C]-ketoconazole penetration by comparing nail absorption, nail distribution, and nail penetration of [(14)C]-ketoconazole dissolved in the novel lacquer versus a commercial ketoconazole cream. Using the in vitro finite dose model, the formulations were applied daily to human nail plates for 7 days. Drug absorption was measured by monitoring rate of appearance in each nail layer and the supporting bed. After the multiple day treatment, cumulative concentrations of ketoconazole formulated in novel lacquer in the deep nail layer and the nail bed were significantly greater than cumulative concentrations of commercial ketoconazole (p<0.05), as well as several orders of magnitude greater than the minimal inhibitory concentration (MIC) deemed necessary to inhibit the growth of causative dermatophytic and yeast species. These results suggest that this novel ketoconazole lacquer has the potential to be an effective topical treatment for onychomycosis.

Effects of organic solvents on the barrier properties of human nail.

The effects of organic solvent systems on nail hydration and permeability have not been well studied. The objectives of the present study were to investigate the effects of binary aqueous organic solvent systems of ethanol (EtOH), propylene glycol (PPG), and polyethylene glycol 400 (PEG) on the barrier properties of nail plates. (3) H-water, (14) C-urea, and (14) C-tetraethylammonium ions were the probes in the nail uptake and transport experiments to study the effect(s) of organic solvents on nail hydration and permeability. Gravimetric studies were also performed as a secondary method to study nail hydration and the reversibility of the nail after organic solvent treatments. Both ungual uptake and transport were directly related to the concentration of the organic solvent in the binary systems. Partitioning of the probes into and transport across the nail decreased with an increase in the organic solvent concentration. These changes corresponded to the changes in solution viscosity and the barrier properties of the nail. In general, the effects for PPG and PEG were more pronounced than those for EtOH. Practically, these results suggest that organic solvents in formulations can increase nail barrier resistivity.