Comparison of the stratum corneum thickness measuredin vivowith confocal Raman spectroscopy and confocal reflectance microscopy

Microneedle-Enabled Breakthroughs in Nucleic Acid Therapeutics

Nucleic acid therapy demonstrates great potential in cancer treatment, infectious disease prevention, and vaccine development due to its advantages, such as rapid production, long-lasting effects, and high target specificity. Although nucleic acid therapy is considered ideal for the development of novel therapeutic strategies, its clinical application still faces numerous challenges, including the lack of efficient delivery systems, insufficient drug formulation stability, and the limitations imposed by the skin barrier on drug dosage delivery. Microneedles, as an innovative transdermal drug delivery technology, can penetrate the stratum corneum and directly access the skin's microcirculation, enabling the efficient delivery of genes and drugs. This technology offers several advantages, such as ease of operation, minimally invasive and painless application, and high safety. Combining microneedle technology with nucleic acid therapy fully leverages the strengths of both approaches, significantly enhancing therapeutic efficacy and bioavailability while maximizing treatment potential. This review explores the application prospects and advantages of combining microneedle delivery systems with nucleic acid therapy.

Synergy of dissolving microneedles and ultrasound to enhance transdermal delivery for rheumatoid arthritis

Dissolving microneedles (DMNs) are an emerging transdermal drug delivery system that has gained increasing attention as an alternative to traditional oral and injectable methods for treating rheumatoid arthritis (RA). However, these DMNs encounter challenges related to insufficient drug diffusion through passive mechanisms. To address this issue, we developed biocompatible DMNs fabricated from hyaluronic acid (HA) loaded with ultrasound-responsive nanoparticles, aiming at enhancing drug permeation and diffusion through ultrasound (US) assistance. Methotrexate (MTX), a first-line treatment for RA, was encapsulated in poly (lactic-co-glycolic acid) (PLGA)-based nanoparticles containing perfluoro-n-pentane (PFP), referred to as MTX-PFP-NPs. These nanoparticles were then incorporated into DMNs, designated as MTX-PFP-NPs@DMNs. Under the cavitation effect of ultrasound, PFP undergoes a phase transition that facilitates drug release and diffusion. The synergistic effect of the DMNs system and US were demonstrated in both an ex-vivo rat skin model and a collagen-induced arthritis (CIA) mouse model. The MTX-PFP-NPs@DMNs exhibited sufficient mechanical strength to penetrate the stratum corneum and dissolve completely within 20 min, enabling effective drug delivery. The synergistic effect of the DMNs system and US was evidenced by enhanced FITC penetration and diffusion in the ex-vivo rat skin model. Additionally, in vivo studied showed improved therapeutic efficacy in reducing joint swelling, bone erosion, cartilage damage, and pro-inflammatory cytokines level compared to only MTX-PFP-NPs@DMNs. This research underscores the promising integration of DMNs technology and US, offering a high-compliance approach to transdermal drug delivery that could significantly improve treatment outcomes for chronic conditions like RA.

Composition and structure analysis of different depths in the stratum corneum using confocal Raman microscopy combined with two-dimensional correlation spectroscopy

The chemical composition and structure of the stratum corneum (SC) play a crucial role in the skin barrier function. Therefore, accurately determining the SC thickness and studying the changes in lipid and keratin structure and distribution within it are key aspects of skin barrier research. Currently, there are limited analytical tools and data analysis methods available for real-time and online studies of SC composition and structural changes. In this study, we focus on depth as a perturbation and employ confocal Raman microscopy combined with moving-window two-dimensional correlation spectroscopy (MW2D) technique to investigate the SC thickness. Additionally, we employ confocal Raman microscopy combined with perturbation-correlation moving-window two-dimensional correlation spectroscopy (PCMW2D) to precisely characterize the stratification of the SC. Furthermore, the two-dimensional correlation spectroscopy (2DCOS) method is utilized to examine the content of various conformations in the keratin secondary structure within the SC, as well as the subtle interrelationships between lipid and keratin structures.

Advancements in transdermal drug delivery: A comprehensive review of physical penetration enhancement techniques

Transdermal drug administration has grown in popularity in the pharmaceutical research community due to its potential to improve drug bioavailability, compliance among patients, and therapeutic effectiveness. To overcome the substantial barrier posed by the stratum corneum (SC) and promote drug absorption within the skin, various physical penetration augmentation approaches have been devised. This review article delves into popular physical penetration augmentation techniques, which include sonophoresis, iontophoresis, magnetophoresis, thermophoresis, needle-free injection, and microneedles (MNs) Sonophoresis is a technique that uses low-frequency ultrasonic waves to break the skin's barrier characteristics, therefore improving drug transport and distribution. In contrast, iontophoresis uses an applied electric current to push charged molecules of drugs inside the skin, effectively enhancing medication absorption. Magnetophoresis uses magnetic fields to drive drug carriers into the dermis, a technology that has shown promise in aiding targeted medication delivery. Thermophoresis is the regulated heating of the skin in order to improve drug absorption, particularly with thermally sensitive drug carriers. Needle-free injection technologies, such as jet injectors (JIs) and microprojection arrays, offer another option by producing temporary small pore sizes in the skin, facilitating painless and effective drug delivery. MNs are a painless, minimally invasive method, easy to self-administration, as well as high drug bioavailability. This study focuses on the underlying processes, current breakthroughs, and limitations connected with all of these approaches, with an emphasis on their applicability in diverse therapeutic areas. Finally, a thorough knowledge of these physical enhancement approaches and their incorporation into pharmaceutical research has the potential to revolutionize drug delivery, providing more efficient and secure treatment choices for a wide range of health-related diseases.

Effect of Penetration Enhancer on the Structure of Stratum Corneum: On-Site Study by Confocal Polarized Raman Imaging

Keratin and lipid structures in the stratum corneum (SC) are closely related to the SC barrier function. The application of penetration enhancers (PEs) disrupts the structure of SC, thereby promoting infiltration. To quantify these PE-induced structural changes in SC, we used confocal Raman imaging (CRI) and polarized Raman imaging (PRI) to explore the integrity and continuity of keratin and lipid structures in SC. The results showed that water is the safest PE and that oleic acid (OA), sodium dodecyl sulfate (SDS), and low molecular weight protamine (LMWP) disrupted the ordered structure of keratin, while azone and liposomes had less of an effect on keratin. Azone, OA, and SDS also led to significant changes in lipid structure, while LMWP and liposomes had less of an effect. Establishing this non-invasive and efficient strategy will provide new insights into transdermal drug delivery and skin health management.

Advancements in Skin-Mediated Drug Delivery: Mechanisms, Techniques, and Applications

Skin-mediated drug delivery methods currently are receiving significant attention as a promising approach for the enhanced delivery of drugs through the skin. Skin-mediated drug delivery offers the potential to overcome the limitations of traditional drug delivery methods, including oral administration and intravenous injection. The challenges associated with drug permeation through layers of skin, which act as a major barrier, are explored, and strategies to overcome these limitations are discussed in detail. This review categorizes skin-mediated drug delivery methods based on the means of increasing drug permeation, and it provides a comprehensive overview of the mechanisms and techniques associated with these methods. In addition, recent advancements in the application of skin-mediated drug delivery are presented. The review also outlines the limitations of ongoing research and suggests future perspectives of studies regarding the skin-mediated delivery of drugs.

Line-field confocal optical coherence tomography coupled with artificial intelligence algorithms to identify quantitative biomarkers of facial skin ageing

Quantitative biomarkers of facial skin ageing were studied from one hundred healthy Caucasian female volunteers, aged 20-70 years, using in vivo 3D Line-field Confocal Optical Coherence Tomography (LC-OCT) imaging coupled with Artificial Intelligence (AI)-based quantification algorithms. Layer metrics, i.e. stratum corneum thickness (SC), viable epidermal thickness and Dermal-Epidermal Junction (DEJ) undulation, as well as cellular metrics were measured for the temple, cheekbone and mandible. For all three investigated facial areas, minimal age-related variations were observed in the thickness of the SC and viable epidermis layers. A flatter and more homogeneous epidermis (decrease in the standard deviation of the number of layers means), a less dense cellular network with fewer cells per layer (decrease in cell surface density), and larger and more heterogeneous nuclei within each layer (increase in nuclei volume and their standard deviation) were found with significant variations with age. The higher atypia scores further reflected the heterogeneity of nuclei throughout the viable epidermis. The 3D visualisation of fine structures in the skin at the micrometric resolution and the 1200 µm × 500 µm field of view achieved with LC-OCT imaging enabled to compute relevant quantitative biomarkers for a better understanding of skin biology and the ageing process in vivo.

Topical Microemulsions: Skin Irritation Potential and Anti-Inflammatory Effects of Herbal Substances

Microemulsions (MEs) have gained prominence as effective drug delivery systems owing to their optical transparency, low viscosity, and thermodynamic stability. MEs, when stabilized with surfactants and/or co-surfactants, exhibit enhanced drug solubilization, prolonged shelf life, and simple preparation methods. This review examines the various types of MEs, explores different preparation techniques, and investigates characterization approaches. Plant extracts and bioactive compounds are well established for their utilization as active ingredients in the pharmaceutical and cosmetic industries. Being derived from natural sources, they serve as preferable alternatives to synthetic chemicals. Furthermore, they have demonstrated a wide range of therapeutic effects, including anti-inflammatory, antimicrobial, and antioxidant activities. However, the topical application of plant extracts and bioactive compounds has certain limitations, such as low skin absorption and stability. To overcome these challenges, the utilization of MEs enables enhanced skin absorption, thereby making them a valuable mode of administration. However, considering the significant surfactant content in MEs, this review evaluates the potential skin irritation caused by MEs containing herbal substances. Additionally, the review explores the topical application of MEs specifically for herbal substances, with an emphasis on their anti-inflammatory properties.

Color-variable dual-dyed photodynamic antimicrobial polyethylene terephthalate (PET)/cotton blended fabrics

The urgent demand for scalable, potent, color variable, and comfortable antimicrobial textiles as personal protection equipment (PPE) to help reduce infection transmission in hospitals and healthcare facilities has significantly increased since the start of the COVID-19 pandemic. Here, we explored photodynamic antimicrobial polyethylene terephthalate/cotton (TC) blended fabrics comprised of photosensitizer-conjugated cotton fibers and polyethylene terephthalate (PET) fibers dyed with disperse dyes. A small library of TC blended fabrics was constructed wherein the PET fibers were embedded with traditional disperse dyes dominating the fabric color, thereby enabling variable color expression, while the cotton fibers were covalently coupled with the photosensitizer thionine acetate as the microbicidal agent. Physical (SEM, CLSM, TGA, XPS and mechanical strength) and colorimetric (K/S and CIELab values) characterization methods were employed to investigate the resultant fabrics, and photooxidation studies with DPBF demonstrated the ability of these materials to generate reactive oxygen species (i.e., singlet oxygen) upon visible light illumination. The best results demonstrated a photodynamic inactivation of 99.985% (~ 3.82 log unit reduction, P = 0.0021) against Gram-positive S. aureus, and detection limit inactivation (99.99%, 4 log unit reduction, P ≤ 0.0001) against Gram-negative E. coli upon illumination with visible light (60 min; ~ 300 mW/cm²; λ ≥ 420 nm). Enveloped human coronavirus 229E showed a photodynamic susceptibility of ~ 99.99% inactivation after 60 min illumination (400-700 nm, 65 ± 5 mW/cm²). The presence of the disperse dyes on the fabrics showed no significant effects on the aPDI results, and furthermore, appeared to provide the photosensitizer with some measure of protection from photobleaching, thus improving the photostability of the dual-dyed fabrics. Taken together, these results suggest the feasibility of low cost, scalable and color variable thionine-conjugated TC blended fabrics as potent self-disinfecting textiles.

The CSIESA: A Novel Score for the Assessment of Intrinsic and Extrinsic Skin Aging Based on Reflectance Confocal Microscopy Imaging

Skin aging is an intricate physiological process governed by intrinsic and extrinsic factors. Increasing life expectancy has turned skin aging into a growing concern for the general population. Clinical examination of the skin does not fully describe the skin aging process. This study aims to evaluate the healthy skin of five different age groups in order to develop an easy-to-use confocal score for quantifying signs of skin aging and test the correlation between this new score and the already described clinical score, SCINEXA (score of intrinsic and extrinsic skin aging). Thirty-five subjects split into five age groups: <35; 36−45; 46−55; 56−65, and >65 years old were enrolled. Clinical signs were quantified using the SCINEXA score, and known confocal variables of skin aging were evaluated. Three different semi-quantitative scores were calculated: epidermal disarrangement score (EDS), epidermal hyperplasia score (EHS), and dermal score (DS). The EDS showed a stable trend up to the age of 65 and a dramatic increase in older subjects. EHS was characterized by an ascending trend from younger subjects to middle-aged ones. The DS was progressive with age, with a different proportion of distinct collagen types. The confocal CSIESA (confocal score for the assessment of intrinsic and extrinsic skin aging) score correlated well with the SCINEXA score. Reflectance confocal microscopy is a powerful, non-invasive technique for microscopically quantifying aging signs.

Dermal Delivery of Diclofenac Sodium-In Vitro and In Vivo Studies

Previously, we reported the use of confocal Raman spectroscopy (CRS) as a novel non-invasive approach to determine drug disposition in the skin in vivo. Results obtained by CRS were found to correlate with data from the well-established in vitro permeation test (IVPT) model using human epidermis. However, these studies used simple vehicles comprising single solvents and binary or ternary solvent mixtures; to date, the utility of CRS for monitoring dermal absorption following application of complex marketed formulations has not been examined. In the present work, skin delivery of diclofenac sodium (DFNa) from two topical dermatological drug products, namely Diclac® Lipogel 10 mg/g and Primofenac® Emulsion gel 1%, was determined by IVPT and in vivo by both CRS and tape stripping (TS) methodologies under similar experimental conditions. The in vivo data were evaluated against the in vitro findings, and a direct comparison between CRS and TS was performed. Results from all methodologies showed that Diclac promoted significantly greater DFNa delivery to the skin (p < 0.05). The cumulative amounts of DFNa which permeated at 24 h in vitro for Diclac (86.5 ± 9.4 µg/cm2) were 3.6-fold greater than the corresponding amounts found for Primofenac (24.4 ± 2.7 µg/cm2). Additionally, total skin uptake of DFNa in vivo, estimated by the area under the depth profiles curves (AUC), or the signal intensity of the drug detected in the upper stratum corneum (SC) (4 µm) ranged from 3.5 to 3.6-fold greater for Diclac than for Primofenac. The shape of the distribution profiles and the depth of DFNa penetration to the SC estimated by CRS and TS were similar for the two methods. However, TS data indicated a 4.7-fold greater efficacy of Diclac relative to Primofenac, with corresponding total amounts of drug penetrated, 94.1 ± 22.6 µg and 20.2 ± 7.0 µg. The findings demonstrate that CRS is a methodology that is capable of distinguishing skin delivery of DFNa from different formulations. The results support the use of this approach for non-invasive evaluation of topical products in vivo. Future studies will examine additional formulations with more complex compositions and will use a wider range of drugs with different physicochemical properties. The non-invasive nature of CRS coupled with the ability to monitor drug permeation in real time offer significant advantages for testing and development of topical dermatological products.

Chitosan-based microneedle arrays for dermal delivery of Centella Asiatica

Centella asiatica, a medicinal herb used for wound healing, has a limited effect when delivered as an ointment. Centella asiatica's active component asiatic acid (AA) increases extracellular matrix development and reduces inflammation but cannot penetrate the stratum corneum to access deeper skin layers. To bypass the stratum corneum, we formulated two types of AA-loaded microneedle arrays. We fabricated, characterised and optimised a dissolving array made from chitosan and PVA and a hydrogel array made from chitosan and PVP. Both needles were strong and long enough to pierce the epidermis without breaking. Both were biocompatible with keratinocytes and fibroblasts (>75% viability at 100% concentration) and showed a sustained drug release over 48 hours. The hydrogel microneedle released more AA (52.2%) than the dissolving formulation (26.4%); thus, we evaluated them in an excisional rat model. The hydrogel microneedle arrays significantly increased the rate of wound closure compared to the control. This research has shown that the chitosan-PVA hydrogel microneedles could penetrate the epidermis, effectively release AA, and increase the wound closure rate. This AA-loaded delivery system shows promise as a natural treatment for wound healing and may be applied to other bioactive compounds with similar physiochemical properties in the future.

In vivo multiphoton multiparametric 3D quantification of human skin aging on forearm and face

Quantifying skin aging changes and characterizing its 3D structure and function in a non-invasive way is still a challenging area of research, constantly evolving with the development of imaging methods and image analysis tools. In vivo multiphoton imaging offers means to assess skin constituents in 3D, however prior skin aging studies mostly focused on 2D analyses of dermal fibers through their signals’ intensities or densities. In this work, we designed and implemented multiphoton multiparametric 3D quantification tools for in vivo human skin pigmentation and aging characterization. We first demonstrated that despite the limited field of view of the technic, investigation of 2 regions of interest (ROIs) per zone per volunteer is a good compromise in assessing 3D skin constituents in both epidermis and superficial dermis. We then characterized skin aging on different UV exposed areas—ventral and dorsal forearms, face. The three major facts of aging that are epidermal atrophy, the dermal–epidermal junction (DEJ) flattening and dermal elastosis can be non-invasively quantified and compared. Epidermal morphological changes occur late and were only objectified between extreme age groups. Melanin accumulation in suprabasal layers with age and chronic exposure on ventral and dorsal forearms is less known and appears earlier. Superficial dermal aging changes are mainly elastin density increase, with no obvious change in collagen density, reflected by SHGto2PEF ratio and SAAID index decrease and ImbrN index increase on all skin areas. Analysis of the z-dermal distribution of these parameters highlighted the 2nd 20 µm thickness normalized dermal sub-layer, that follows the DEJ shape, as exhibiting the highest aging differences. Moreover, the 3D ImbrN index allows refining the share of photoaging in global aging on face and the 3D SAAID index on forearm, which elastin or fibrillar collagens densities alone do not allow. Photoaging of the temple area evolves as a function of chronic exposure with a more pronounced increase in elastin density, also structurally modified from thin and straight elastic fibers in young volunteers to dense and compact pattern in older ones. More generally, multiphoton multiparametric 3D skin quantification offers rich spatial information of interest in assessing normal human skin condition and its pathological, external environment or product induced changes.

Automating reflectance confocal microscopy image analysis for dermatological research: a review

SIGNIFICANCE

Reflectance confocal microscopy (RCM) is a noninvasive, in vivo technology that offers near histopathological resolution at the cellular level. It is useful in the study of phenomena for which obtaining a biopsy is impractical or would cause unnecessary tissue damage and trauma to the patient.

AIM

This review covers the use of RCM in the study of skin and the use of machine learning to automate information extraction. It has two goals: (1) an overview of information provided by RCM on skin structure and how it changes over time in response to stimuli and in disease and (2) an overview of machine learning approaches developed to automate the extraction of key morphological features from RCM images.

APPROACH

A PubMed search was conducted with additional literature obtained from references lists.

RESULTS

The application of RCM as an in vivo tool in dermatological research and the biologically relevant information derived from it are presented. Algorithms for image classification to epidermal layers, delineation of the dermal-epidermal junction, classification of skin lesions, and demarcation of individual cells within an image, all important factors in the makeup of the skin barrier, were reviewed. Application of image analysis methods in RCM is hindered by low image quality due to noise and/or poor contrast. Use of supervised machine learning is limited by time-consuming manual labeling of RCM images.

CONCLUSIONS

RCM has great potential in the study of skin structures. The use of artificial intelligence could enable an easier, more reproducible, precise, and rigorous study of RCM images for the understanding of skin structures, skin barrier, and skin inflammation and lesions. Although several attempts have been made, further work is still needed to provide a definite gold standard and overcome issues related to image quality, limited labeled datasets, and lack of phenotype variability in available databases.

Depth-dependent hydration dynamics in human skin: Vehicle-controlled efficacy assessment of a functional 10% urea plus NMF moisturizer by near-infrared confocal spectroscopic imaging (KOSIM IR) and capacitance method complemented by volunteer perception

BACKGROUND

Stratum corneum (SC) hydration is vital for the optimal maintenance and appearance of healthy skin. In this context, we evaluated the efficacy of an NMF-enriched moisturizer containing 10% urea on different aspects of SC hydration of dry skin.

MATERIAL AND METHODS

In two clinical studies, the hydration efficacy of the moisturizer in comparison to its vehicle was investigated. In the first study, 42 subjects applied the moisturizer and the vehicle to one lower leg each. Thirty minutes and 24 h after this single treatment, SC hydration was measured by corneometry. Volunteers also rated skin moisturization and evaluated product properties. In the second study, 27 subjects each treated one forearm twice daily for 2 weeks with the moisturizer and the vehicle. Then, depth-resolved water-absorption spectra were measured by near-infrared confocal spectroscopic imaging (KOSIM IR).

RESULTS

The moisturizer exerted a superior hydrating effect compared to the vehicle. KOSIM IR measurements show that, compared to the vehicle, the moisturizer significantly improved the water gradient in the SC from the surface to a depth of 15 μm. Moreover, the moisturizer received high acceptance ratings from the volunteers and was preferred to the vehicle.

CONCLUSION

The humectants applied in the investigated moisturizer improved SC water content in total and as a function of depth. The combination of depth-resolved data (KOSIM IR) with classical corneometry provides an integrated concept in the measurement of skin hydration, rendering both methods complementary. These findings were in line with the volunteers` self-assessments of the moisturizer properties that are relevant to treatment adherence.

Topical drug delivery: History, percutaneous absorption, and product development

Topical products, widely used to manage skin conditions, have evolved from simple potions to sophisticated delivery systems. Their development has been facilitated by advances in percutaneous absorption and product design based on an increasingly mechanistic understanding of drug-product-skin interactions, associated experiments, and a quality-by-design framework. Topical drug delivery involves drug transport from a product on the skin to a local target site and then clearance by diffusion, metabolism, and the dermal circulation to the rest of the body and deeper tissues. Insights have been provided by Quantitative Structure Permeability Relationships (QSPR), molecular dynamics simulations, and dermal Physiologically Based PharmacoKinetics (PBPK). Currently, generic product equivalents of reference-listed products dominate the topical delivery market. There is an increasing regulatory interest in understanding topical product delivery behavior under 'in use' conditions and predicting in vivo response for population variations in skin barrier function and response using in silico and in vitro findings.

In vivo examination of healthy human skin after short-time treatment with moisturizers using confocal Raman spectroscopy and optical coherence tomography: Preliminary observations

Skin is our barrier against environmental damage. Moisturizers are widely used to increase hydration and barrier integrity of the skin; however, there are contrasting observations on their in vivo effects in real-life settings. In cosmetic studies, corneometers and tewameters are traditionally used to assess skin hydration. In this study, two novel noninvasive diagnostic techniques, optical coherence tomography (OCT) and confocal Raman spectroscopy, were used to analyze stratum corneum and epidermal thickness (ET), water content, blood flow in function of depth, skin roughness, attenuation coefficient, natural moisturizing factor, ceramides and free fatty acids, cholesterol, urea, and lactates in 20 female subjects aged between 30 and 45 before and after 2 weeks application of a commercially available moisturizing lotion on one forearm. The untreated forearm served as control. A third measurement was conducted 1 week after cessation of moisturizing to verify whether the changes in the analyzed parameters persisted. We noticed a reduction in skin roughness, an increase in ceramides and free fatty acids and a not statistically significant increase in ET. As a conclusion, short time moisturizing appears insufficient to provide significant changes in skin morphology and composition, as assessed by OCT and RS. Novel noninvasive imaging methods are suitable for the evaluation of skin response to topical moisturizers. Further studies on larger sample size and longer treatment schedules are needed to analyze changes under treatment with moisturizers and to standardize the use of novel noninvasive diagnostic techniques.

Small nerve fiber selectivity of laser and intraepidermal electrical stimulation: A comparative study between glabrous and hairy skin

OBJECTIVES

In clinical neurophysiology practice, various methods of stimulation can be used to activate small-diameter nociceptive cutaneous afferents located in the epidermis. These methods include different types of laser and intraepidermal electrical stimulation techniques. The diffusion of the stimulation in the skin, inside or under the epidermis, depends on laser wavelength and electrode design, in particular. The aim of this study was to compare several of these techniques in their ability to selectively stimulate small nerve fibers.

METHODS

In 8 healthy subjects, laser stimulation (using a CO₂ or Nd:YAP laser) and intraepidermal electrical stimulation (using a micropatterned, concentric planar, or concentric needle electrode), were applied at increasing energy or intensity on the dorsal or volar aspect of the right hand or foot. The subjects were asked to define the perceived sensation (warm, pinprick, or electric shock sensation, corresponding to the activation of C fibers, Aδ fibers, or Aβ fibers, respectively) after each stimulation. Depending on the difference in the sensations perceived between dorsal (hairy skin with thin stratum corneum) and volar (glabrous skin with thick stratum corneum) stimulations, the diffusion of the stimulation inside or under the epidermis and the nature of the activated afferents were determined.

RESULTS

Regarding laser stimulation, the perceived sensations turned from warm to pinprick with increasing energies of stimulation, in particular with the Nd:YAP laser, of which pulse could penetrate deep in the skin according to its short wavelength. In contrast, CO₂ laser stimulation produced only warm sensations and no pricking sensation when applied to the glabrous skin, perhaps due to a thicker stratum corneum and the shallow penetration of the CO₂ laser pulse. Regarding intraepidermal electrical stimulation using concentric electrodes, the perceived sensations turned from pinprick to a combination of pinprick and electrical shocks with increasing intensities. Using the concentric planar electrode, the sensations perceived at high stimulation intensity even consisted of electric shocks without concomitant pinprick. In contrast, using the micropatterned electrode, only pinprick sensations were produced by the stimulation of the hairy skin, while the stimulation of the glabrous skin produced no sensation at all within the limits of stimulation intensities used in this study.

CONCLUSIONS

Using the CO₂ laser or the micropatterned electrode, pinprick sensations were selectively produced by the stimulation of hairy skin, while only warm sensation or no sensation at all were produced by the stimulation of glabrous skin. These two techniques appear to be more selective with a limited diffusion of the stimulation into the skin, restricting the activation of sensory afferents to the most superficial and smallest intraepidermal nerve fibers.

Relating transdermal delivery plasma pharmacokinetics with in vitro permeation test (IVPT) findings using diffusion and compartment-in-series models

Increasing emphasis is being placed on using in vitro permeation test (IVPT) results for topical products as a surrogate for their in vivo behaviour. This study sought to relate in vivo plasma concentration - time pharmacokinetic (PK) profiles after topical application of drug products to IVPT findings with mechanistic diffusion and compartment models that are now widely used to describe permeation of solutes across the main skin transport barrier, the stratum corneum. Novel in vivo forms of the diffusion and compartment-in-series models were developed by combining their IVPT model forms with appropriate in vivo disposition functions. Available in vivo and IVPT data were then used with the models in data analyses, including the estimation of prediction intervals for in vivo plasma concentrations derived from IVPT data. The resulting predicted in vivo plasma concentration - time profiles for the full models corresponded closely with the observed results for both nitroglycerin and rivastigmine at all times. In contrast, reduced forms of these in vivo models led to discrepancies between model predictions and observed results at early times. A two-stage deconvolution procedure was also used to estimate the in vivo cumulative amount absorbed and shown to be linearly related to that from IVPT, with an acceptable prediction error. External predictability was also shown using a separate set of in vitro and in vivo data for different nitroglycerin patches. This work suggests that mechanistic and physiologically based pharmacokinetic models can be used to predict in vivo behaviour from IVPT data for topical products.

Presence of intralesional melanocytes as a histopathological feature of actinic keratosis based on in vivo harmonic generation microscopy in Asians

BACKGROUND

Most patients with actinic keratosis (AK) present with more than one lesion. Although histopathological examination is the gold standard for diagnosing this condition, performing an invasive skin biopsy for each AK is impractical. Thus, this study aimed to identify AK's morphological characteristics based on harmonic generation microscopy (HGM). Moreover, the correlation between features observed using HGM and histopathological grading of AK was examined.

METHODS

Lesions of seven patients were examined using HGM (n = 1, ex vivo and n = 6, in vivo), and histopathological examinations of the biopsy specimens were also performed. The features of each AK, based on HGM, were assessed and compared with corresponding standard histopathological findings.

RESULTS

Using the histopathological findings as a standard reference, HGM's accuracy in detecting features of AK lesions, such as hyperkeratosis, epidermal thinning, abnormal architecture, and atypical honeycomb pattern, was 100%. Approximately five (72%) patients had similar histopathological grades. Moreover, based on HGM, except for one patient with grade 1 AK, six (85.71%) patients had lesions with intraepidermal dendritic cell-like cells, representing melanocytes.

CONCLUSION

Harmonic generation microscopy can be used in vivo to provide critical diagnostic information with a resolution comparable to histopathological examination. In addition, intralesional melanocytes in AK, which may be correlated with disease severity, can be specifically enhanced using HGM.

Enhancement strategies for transdermal drug delivery systems: current trends and applications

Transdermal drug delivery systems have become an intriguing research topic in pharmaceutical technology area and one of the most frequently developed pharmaceutical products in global market. The use of these systems can overcome associated drawbacks of other delivery routes, such as oral and parenteral. The authors will review current trends, and future applications of transdermal technologies, with specific focus on providing a comprehensive understanding of transdermal drug delivery systems and enhancement strategies. This article will initially discuss each transdermal enhancement method used in the development of first-generation transdermal products. These methods include drug/vehicle interactions, vesicles and particles, stratum corneum modification, energy-driven methods and stratum corneum bypassing techniques. Through suitable design and implementation of active stratum corneum bypassing methods, notably microneedle technology, transdermal delivery systems have been shown to deliver both low and high molecular weight drugs. Microneedle technology platforms have proven themselves to be more versatile than other transdermal systems with opportunities for intradermal delivery of drugs/biotherapeutics and therapeutic drug monitoring. These have shown that microneedles have been a prospective strategy for improving transdermal delivery systems.

Increased preferential activation of small cutaneous nerve fibers by optimization of electrode design parameters

OBJECTIVE

Electrical preferential activation of small nociceptive fibers may be achieved with the use of specialized small area electrodes, however, the existing electrodes are limited to low stimulation intensities. As existing electrodes have been developed empirically, the present study aimed to use computational modeling and optimization techniques to investigate if changes in electrode design parameters could improve the preferential activation of small fibers.

APPROACH

Two finite element models; one of a planar concentric and one of an intra-epidermal electrode were combined with two multi-compartmental nerve fiber models of an Aδ-fiber and an Aβ-fiber. These two-step hybrid models were used for the optimization of four electrode parameters; anode area, anode-cathode distance, cathode area, and cathode protrusion. Optimization was performed using a gradient-free bounded Nelder-Mead algorithm, to maximize the current activation threshold ratio between the Aβ-fiber model and the Aδ-fiber model.

MAIN RESULTS

All electrode parameters were optimal at their lower bound, except the cathode protrusion, which was optimal a few micrometers above the location of the Aδ-fiber model. A small cathode area is essential for producing a high current density in the epidermal skin layer enabling activation of small fibers, while a small anode area and anode-cathode distance are important for the minimization of the current spread to deeper tissues, making it less likely to activate large fibers. Combining each of the optimized electrode parameters improved the preferential activation of small fibers in comparison to existing electrodes, by increasing the activation threshold ratio between the two nerve fiber types. The maximum increase in the activation threshold ratio was 289% and 595% for the intra-epidermal and planar concentric design, respectively.

SIGNIFICANCE

The present study showed that electrical preferential small fiber activation can be improved by electrode design. Additionally, the results may be used for the production of an electrode that could potentially be used for clinical assessment of small fiber neuropathy.

Ex vivo penetration analysis and anti-inflammatory efficacy of the association of ferulic acid and UV filters

BACKGROUND

Unprotected chronic exposure to ultraviolet (UV) radiation generates many harmful effects to human skin and sunscreens are essential to health, however, traditional products do not provide enough protection against cutaneous oxidative stress, a process amplified by UV radiation. Therefore, the development of multifunctional photoprotective formulations seems to be a more efficacious approach, since these enable the absorption/reflection of UV radiation and maintain the cutaneous homeostasis.

OBJECTIVES

In the present study, ferulic acid (FA), a well-known antioxidant, has been combined with two UV filters, bemotrizinol and ethylhexyl triazone, and the safety and efficacy of this formulation has been assessed combining ex vivo and in vivo methods.

METHODS

Skin permeation assays were performed by applying the formulation in the volar forearm of participants, after which consecutive samples of the stratum corneum were collected by tape stripping, and the quantification of FA, bemotrizinol and ethylhexyl triazone was performed by high-performance liquid chromatography (HPLC). Also, the FA anti-inflammatory action in combination with the UV filters was probed through a method employing Laser Doppler flowmetry to measure the vasodilatory response to methyl nicotinate topical application.

RESULTS

Skin permeation assay was able to characterize the penetration depth of each substance. It should also be noted that a specific HPLC analytical method was developed in this study to enable the rapid simultaneous quantification of the three substances. Results from Laser Doppler flowmetry showed that the FA was able to mitigate the vasodilatory response.

CONCLUSIONS

FA proved to be a valuable resource in a multifunction sunscreen, not only providing an increase in the SPF of sunscreens, previously published, but also decreasing the extent of inflammation.

In Vivo Assessment of Water Content, Trans-Epidermial Water Loss and Thickness in Human Facial Skin

Mapping facial skin in terms of its biophysical properties plays a fundamental role in many practical applications, including, among others, forensics, medical and beauty treatments, and cosmetic and restorative surgery. In this paper we present an in vivo evaluation of the water content, trans-epidermial water loss and skin thickness in six areas of the human face: cheeks, chin, forehead, lips, neck and nose. The experiments were performed on a population of healthy subjects through innovative sensing devices which enable fast yet accurate evaluations of the above parameters. A statistical analysis was carried out to determine significant differences between the facial areas investigated and clusters of statistically-indistinguishable areas. We found that water content was higher in the cheeks and neck and lower in the lips, whereas trans-epidermal water loss had higher values for the lips and lower ones for the neck. In terms of thickness the dermis exhibited three clusters, which, from thickest to thinnest were: chin and nose, cheek and forehead and lips and neck. The epidermis showed the same three clusters too, but with a different ordering in term of thickness. Finally, the stratum corneum presented two clusters: the thickest, formed by lips and neck, and the thinnest, formed by all the remaining areas. The results of this investigation can provide valuable guidelines for the evaluation of skin moisturisers and other cosmetic products, and can help guide choices in re-constructive/cosmetic surgery.

Structural skin changes in elderly people investigated by reflectance confocal microscopy

BACKGROUND

Reflectance confocal microscopy (RCM) is particularly suitable for the study of skin ageing because it provides nearly histological information in vivo and non-invasively. However, there are no studies that evaluated RCM skin features of a large population older than 70 years.

OBJECTIVES

The aim of our investigation was to study age-related skin changes in an elderly population by RCM and to evaluate their topographical and gender differences.

METHODS

We obtained RCM images of photoprotected (volar arm) and chronic (face) and intermittently photoexposed (dorsal forearm) body sites of 209 volunteers (105 women and 104 men, mean age: 77.5, range 74-81 years). 15 previously reported and new RCM parameters related to skin ageing were assessed.

RESULTS

Photoexposed sites had thicker suprapapillary epidermis, more linear, distant and thin furrows, higher presence of mottled pigmentation, polycyclic papillae and coarse and huddled collagen and lower presence of dermal papillae than the photoprotected site. Irregular honeycomb pattern was not higher in photoexposed sites, indicating that it is probably more dependent on intrinsic ageing. Two ageing scores defined for facial skin ageing (epidermal disarray score and epidermal hyperplasia score) were found useful for the identification of photoageing. Gender differences only concerned some RCM parameters (i.e. thickness of different layers of the epidermis, furrows and collagen score) and some body sites, in line with the fact that women and men of our cohort had no major differences in clinically visible skin ageing.

CONCLUSIONS

Our study confirmed that RCM is a powerful non-invasive technique to microscopically quantify ageing signs and our observations contribute to highlight the differences between intrinsic and extrinsic ageing.

Investigation of TEMPO partitioning in different skin models as measured by EPR spectroscopy - Insight into the stratum corneum

Electron paramagnetic resonance (EPR) spectroscopy represents an established tool to study properties of microenvironments, e.g. to investigate the structure and dynamics of biological and artificial membranes. In this study, the partitioning of the spin probe 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) in ex vivo human abdominal and breast skin, ex vivo porcine abdominal and ear skin as well as normal and inflammatory in vitro skin equivalents was investigated by EPR spectroscopy. Furthermore, the stratum corneum (SC) lipid composition (as determined by high-performance thin-layer chromatography), SC lipid chain order (probed by infrared spectroscopy) and the SC thickness (investigated by histology) were determined in the skin models. X-band EPR measurements have shown that TEMPO partitions in the lipophilic and hydrophilic microenvironment in varying ratios in different ex vivo and in vitro skin models. Ex vivo human abdominal skin exhibited the highest amount of TEMPO in the lipophilic microenvironment. In contrast, the lowest amount of TEMPO in the lipophilic microenvironment was determined in ex vivo human breast skin and the inflammatory in vitro skin equivalents. Individual EPR spectra of epidermis including SC and dermis indicated that the lipophilic microenvironment of TEMPO mainly corresponds to the most lipophilic part of the epidermis, the SC. The amount of TEMPO in the lipophilic microenvironment was independent of the SC lipid composition and the SC lipid chain order but correlated with the SC thickness. In conclusion, EPR spectroscopy could be a novel technique to determine differences in the SC thickness, thus suitably complementing existing methods.

Characterization and validation of an in vivo confocal Raman spectroscopy led tri-method approach in the evaluation of the lip barrier

Background/Aim

It was the aim to establish and validate in vivo confocal Raman spectroscopy for characterization of the lip barrier in conjunction with transepidermal water loss (TEWL) and skin capacitance assessments. For the first time in vivo, barrier‐relevant components of the lip (derived, natural moisturizing factors (NMFs) and ceramides are described.

Methods

In 32 healthy volunteers, a dental tongue fixation device was inserted to prevent both voluntary and involuntary lip moisturization during measurements. Seventeen individual parameters relating to water, ceramide, and NMF content were assessed via Raman spectroscopy. Additionally, corneometry and TEWL were measured. To give a guidance for the required volunteer group size of future lip barrier studies for all test parameters, coefficients of variation (CV) were calculated and plots showing the required sample size for a given percentage treatment effect.

Results

Raman spectroscopy assessed parameters on the lower lip comprehensively characterized the state of the lip barrier. Parameter variability was sufficiently low to corroborate changes in most parameters using relatively small study populations.

Conclusions

Lip skin is comparatively well hydrated. Biophysical measurement of the lip barrier function is a challenge, as unconscious licking of the lower lip has to be prevented. In vivo confocal Raman spectroscopy provides insightful parameters for the characterization of the lip barrier and sufficiently low inter‐individual variability to assess relatively small parameter changes employing relatively few study subjects. Differences at the molecular level and at a high spatial resolution are detectable, and these insights might provide a breakthrough in the evaluation of lip barrier function and developing solutions for lip care.

Modelling the intradermal delivery of microneedle array patches for long-acting antiretrovirals using PBPK

INTRODUCTION

Existing HIV therapy using oral antiretrovirals (ARVs) can result in pill fatigue and sub-optimal adherence. Microneedle array patches (MAPs) offer non-invasive, blood-free and painless drug delivery, and may improve patient adherence. The objective of this study was to develop a novel physiologically-based pharmacokinetic (PBPK) model to simulate the systemic pharmacokinetics of cabotegravir and rilpivirine MAPs using the intradermal route.

METHODS

The developed PBPK models were qualified against observed pharmacokinetic data after intramuscular (IM) and intradermal administration of long-acting nanoformulated rilpivirine to rats, and for IM administration of both drugs to healthy adults. Qualified models were then utilised to estimate suitable MAP characteristics (e.g. nanoformulation dose and release rates) and inform dosing strategies to maintain plasma concentrations above target trough concentrations for the designated dosing interval.

RESULTS

PBPK models simulated q4-weekly loading and maintenance doses of 360 mg and 180 mg for long-acting formulated cabotegravir between the release rates of 1 × 10^-3-3 × 10^-3h^-1 and 1 × 10^-3-1.5 × 10^-3h^-1 respectively, for a 70 kg adult. Estimated patch size was 60 cm² for a 360 mg dose of cabotegravir. For q4-weekly dosing, rilpivirine required a 1080 mg loading dose and a 540 mg maintenance dose with release rates of 1.5 × 10^-3-2.5 × 10^-3h^-1 and 5 × 10^-4-1 × 10^-3h^-1, respectively. Weekly dosing was also evaluated to assess the potential application from a smaller patch size. The ability to self-administer via a patch that is only left in place for a short duration makes longer durations less important than for some other long-acting approaches. Weekly cabotegravir required 60 mg between release rates 7 × 10^-3-9 × 10^-3h^-1 and rilpivirine required 270 mg and 180 mg respectively between release rates of 7 × 10^-3-9 × 10^-3h^-1.

DISCUSSION

This model estimated optimal dose and release rates for cabotegravir and rilpivirine MAPs. Our approach provides a computational platform to support rational development of intradermal administration strategies to tackle problems associated with chronic oral ARV administration.

Wool/Acrylic Blended Fabrics as Next-Generation Photodynamic Antimicrobial Materials

The adoption of self-sterilizing materials to reduce infection transmission in hospitals and related healthcare facilities has been hampered by the availability of scalable, cost-effective, and potent antimicrobial textiles. Here, we investigated whether photodynamic materials comprising photosensitizer-embedded wool/acrylic blends were able to mediate the photodynamic inactivation of Gram-positive and Gram-negative bacteria. A small library of wool/acrylic (W/A) blended fabrics was constructed wherein the wool fibers were embedded with rose Bengal (RB) as a photosensitizer and the acrylic fibers were dyed with a traditional cationic yellow X-8GL dye, thereby enabling a broader color palette than was achievable with a single photosensitizer. The resultant photodynamic materials were characterized by physical (SEM, DSC, TGA, tensile strength), spectroscopic (fluorescence), colorimetric (K/S and CIELab values), and color fastness (against rubbing, washing) studies, and their photooxidation of the model substrate potassium iodide demonstrated the ability of these materials to generate microbicidal reactive oxygen species (i.e., singlet oxygen) upon illumination. Our best results yielded the photodynamic inactivation of Gram-positive S. aureus (99.98%) and B. subtilis (99.993%) by ∼4 log units upon illumination with visible light (60 min; 65 ± 5 mW/cm²; λ ≥ 420 nm), although more modest activity was observed against Gram-negative P. aeruginosa and E. coli (1-2 log units pathogen reduction). While there were no statistically significant differences for dual-dyed materials that were produced through either sequential or simultaneous dyeing steps, it was noted that high loadings of the cationic yellow X-8GL dye did inhibit the antimicrobial activity of the RB photosensitizer, with the dual-dyed materials able to mediate a 2.9 log unit reduction against S. aureus at a 1% o.w.f X-8GL loading. These findings indicate that the antimicrobial photodynamic inactivation of dual-dyed materials is independent of the dyeing process itself, yet exhibits limitations on the loading of the traditional dye with regards to the activity of the photosensitizer. Taken together, the results suggest the feasibility of photosensitizer-embedded blended fabrics produced through a one-step dyeing process as a low-cost and scalable method for creating effective self-disinfecting textiles for infection prevention, and whose inclusion of a second traditional dye for color variation will further benefit their adoption from a commercial standpoint.

In vivo Change of Keratin-Bound Molecules in the Human Stratum Corneum following Exposure to Ultraviolet Radiation

BACKGROUND/OBJECTIVES

Ultraviolet (UV) radiation damages the stratum corneum (SC) and disrupts the skin barrier. The damaged skin changes in the molecular composition of the SC, including its water content. However, it is difficult to examine the in vivo SC changes with existing methods, so those have not been well characterized. Therefore, we investigated in vivo changes of UV-induced SC damage using confocal Raman spectroscopy.

METHOD

We irradiated the volar forearm of 10 subjects with 0.5, 1, and 1.5 minimal erythemal doses of UV radiation. Then, we examined erythema, the transepidermal water loss (TEWL), the water content, the natural moisturizing factor (NMF), and the lipids of the skin.

RESULTS

After UV irradiation, erythema and TEWL of the skin were both increased. The bound water content of the SC was also increased following UV irradiation. The NMF of the SC revealed different tendencies. All free amino acids (FAAs) of the NMF were increased after UV irradiation, except proline. trans-urocanic acid, pyrrolidone carboxylic acid, lactate, and urea, which are NMF components produced by the subsequent catabolism of FAAs and sweat, were decreased after UV irradiation. The amount of ceramide in the SC was also decreased after UV exposure, while cholesterol was increased.

CONCLUSIONS

The bound water content of the SC was increased by UV exposure along with increasing TEWL, several NMF components, and cholesterol. These in vivo results for UV-damaged SC obtained via Raman spectroscopy could be applied to research with regard to protecting the SC from UV radiation and treating UV-damaged SC.

Evaluation of acute corneal damage induced by 222-nm and 254-nm ultraviolet light in Sprague-Dawley rats

Two hundred twenty-two nanometres ultraviolet (UV) light produced by a krypton-chlorine excimer lamp is harmful to bacterial cells but not skin. However, the effects of 222-nm UV light exposure to the eye are not fully known. We evaluated acute corneal damage induced by 222- and 254-nm UV light in albino rats. Under deep anaesthesia, 6-week-old Sprague-Dawley albino rats were exposed to UV light. The exposure levels of corneal radiation were 30, 150, and 600 mJ/cm². Epithelial defects were detected by staining with fluorescein. Superficial punctate keratitis developed in corneas exposed to more than 150 mJ/cm² of UV light, and erosion was observed in corneas exposed to 600 mJ/cm² of UV light. Haematoxylin and eosin staining also showed corneal epithelial defects in eyes exposed to 254-nm UV light. However, no damage developed in corneas exposed to 222-nm UV light. Cyclobutane pyrimidine dimer-positive cells were observed only in normal corneas and those exposed to 254-nm UV light. Although some epithelial cells were stained weakly in normal corneas, squamous epithelial cells were stained moderately, and the epithelial layer that was detached from the cornea exposed to 600 mJ/cm² of light was stained intensely in corneas exposed to 254-nm UV light. In the current study, no corneal damage was induced by 222-nm UV light, which suggested that 222-nm UV light may not harm rat eyes within the energy range and may be useful for sterilising or preventing infection in the future.

Molecular Dynamics Simulations of Membrane Permeability

This Review illustrates the evaluation of permeability of lipid membranes from molecular dynamics (MD) simulation primarily using water and oxygen as examples. Membrane entrance, translocation, and exit of these simple permeants (one hydrophilic and one hydrophobic) can be simulated by conventional MD, and permeabilities can be evaluated directly by Fick's First Law, transition rates, and a global Bayesian analysis of the inhomogeneous solubility-diffusion model. The assorted results, many of which are applicable to simulations of nonbiological membranes, highlight the limitations of the homogeneous solubility diffusion model; support the utility of inhomogeneous solubility diffusion and compartmental models; underscore the need for comparison with experiment for both simple solvent systems (such as water/hexadecane) and well-characterized membranes; and demonstrate the need for microsecond simulations for even simple permeants like water and oxygen. Undulations, subdiffusion, fractional viscosity dependence, periodic boundary conditions, and recent developments in the field are also discussed. Last, while enhanced sampling methods and increasingly sophisticated treatments of diffusion add substantially to the repertoire of simulation-based approaches, they do not address directly the critical need for force fields with polarizability and multipoles, and constant pH methods.

Evaluation of topical econazole nitrate formulations with potential for treating Raynaud's phenomenon

The purpose of this work was to design and characterize a topical formulation of econazole nitrate (EN) with potential for treating Raynaud's phenomenon (RP). Four topical dosage forms (F1_topical solution, F2_HPMC or hydroxypropyl methylcellulose dispersion, F3_VersaBase^® cream, and F4_{_}Lipoderm^® Activemax™ Cream) containing 3% w/w EN were prepared and characterized for drug content, pH, viscosity, spreadability, drug crystallinity, stability, and in vitro permeation using Franz cells across pig ear skin, and results were compared to the 1% marketed EN cream. All four formulations had acceptable physical and visual characteristics required for topical application, with 3% w/w EN. The order of amount of drug permeated from highest to lowest was F2 (10.27%) > F4 (2.47%) > F1 (2.28%) > F3 (1.47%) > marketed formulation (0.22%). Formulation F2 showed better penetration of the drug into the stratum corneum, epidermis, and dermis layers. The drug concentration in the stratum corneum and epidermis was approximately 10-20 times higher with F2 compared to the marketed formulation. All formulations were found to be stable for up to 6 months. All four EN formulations were found to be better than the 1% marketed cream. Formulation F2_{_}HPMC dispersion could be further explored as a treatment option for RP.

Confocal Raman Spectroscopy as a tool to measure the prevention of skin penetration by a specifically designed topical medical device

BACKGROUND/AIM

The scope of this study was to utilize confocal Raman spectroscopy in the evaluation of the degree of non-penetration into the viable skin layers of a paraffin and petrolatum-based product for use in the intimate areas of the skin. The formulation was purposely designed with properties to prevent undesirable skin penetration.

METHODS

Product-The test product was a proprietary topical medical device comprising paraffinum liquidum, petrolatum, paraffin, and tocopheryl acetate. Volunteers-A total of 20 healthy volunteers were recruited onto the study-17 females and three males. Product Testing-Raman spectra were obtained at Baseline and 90 minutes after product application. Product Penetration-Skin penetration was calculated from Raman spectra taken at skin depths of -5, 0, 5, 10, 15, and 20 μm.

RESULTS

Raman spectra of the investigated product could be clearly differentiated from the skin spectrum. The minimum measurable concentration of the test product was determined at a detection level of 0.5%. In this study, the test product did not penetrate down to skin depths of 10 to 20 μm.

CONCLUSIONS

Within the precision range of the test method, the investigated product did not penetrate into the compact part of the stratum corneum. The study revealed Raman spectroscopy to be suitable to detect not only penetration but also non-penetration of substances into human skin.

In Vivo Determination of Moisturizers Efficacy on Human Skin Hydration by Confocal Raman Spectroscopy

This research work deals with in vivo testing of the efficacy of commercial moisturizer products on the hydration of human skin, as there are various in vitro and ex vivo studies questioning their activity. Confocal Raman spectroscopy was used for this purpose of assessing the efficacy of moisturizers on skin hydration mainly owing to its simple, non-invasive, non-destructive, timesaving, and cost-effective nature. Water content and natural moisturizing factor (NMF) of stratum corneum were analyzed and compared using this method at high wavenumber (2500-4000 cm^-1) and fingerprint (400-1800 cm^-1) spectral regions, respectively, as these two parameters are correlated to skin hydration. Four commercial moisturizer products of different brands were tested on volar forearm region of healthy human female volunteers. This study was conducted for a period of 30 days with 0, 7, and 30 days as time points of analysis. The results of this study clearly indicate that not all the moisturizer products hydrate the skin to the expected levels, and this extent of skin hydration varies with duration of application of these products.

In Vivo Human Skin Penetration Study of Sunscreens by Confocal Raman Spectroscopy

This research work mainly deals with the application of confocal Raman spectroscopic technique to study in vivo human skin penetration of sunscreen products, as there are a lot of controversies associated with their skin penetration. Healthy human volunteers were tested for penetration of two commercial sunscreen products into their volar forearm skin for a period of 2 h. Measurements were taken before and after application of these sunscreen products. All the confocal Raman spectra were pre-processed and then subjected to multivariate two-dimensional principal component analysis and classical least squares analysis to determine the skin penetration of these sunscreens in comparison to the "sunscreen product spectrum" which was considered as the control. Score plots of principal component analysis of confocal Raman spectra indicated clear separation between the spectra before and after application of sunscreen products. Loading plots showed the maximum differences in the spectral region from 1590 to 1626 cm^-1 where the characteristic peak of the pure sunscreen products was observed. Classical least squares analysis has shown a significant penetration to a depth of 10 μm in the volar forearm skin of healthy human volunteers for both these sunscreen products. The results confirm that the penetration of these tested sunscreen products was restricted to stratum corneum and also prove that confocal Raman spectroscopy is a simple, fast, nondestructive, and noninvasive semi-quantitative analytical technique for these studies.

ATR-IR study of skin components: Lipids, proteins and water. Part I: Temperature effect

In this work we report the studies of the effect of temperature on skin components, such as lipids, proteins and water. Modifications of lipids structure induced by increasing temperature (from 20 to 90°C) have been studied using ATR-IR (Attenuated Total Reflectance Infrared) spectroscopy, which is a powerful tool for characterization of the molecular structure and properties of tissues, such as skin. Due to the small depth of penetration (0.6-5.6μm), ATR-IR spectroscopy probes only the outermost layer of the skin, i.e. the stratum corneum (SC). The assignment of main spectral features of skin components allows for the determination of phase transitions from the temperature dependencies of band intensities [e.g. ν_as(CH₂) and ν_s(CH₂)]. The phase transitions were determined by using two methods: the first one was based on the first derivative of the Boltzmann function and the second one employed tangent lines of sigmoidal, aforementioned dependencies. The phase transitions in lipids were correlated with modifications of the structure of water and proteins.

The relationship between skin function, barrier properties, and body-dependent factors

BACKGROUND

Skin is a multilayer interface between the body and the environment, responsible for many important functions, such as temperature regulation, water transport, sensation, and protection from external triggers.

OBJECTIVES

This paper provides an overview of principal factors that influence human skin and describes the diversity of skin characteristics, its causes and possible consequences. It also discusses limitations in the barrier function of the skin, describing mechanisms of absorption.

METHODS

There are a number of in vivo investigations focusing on the diversity of human skin characteristics with reference to barrier properties and body-dependent factors.

RESULTS

Skin properties vary among individuals of different age, gender, ethnicity, and skin types. In addition, skin characteristics differ depending on the body site and can be influenced by the body-mass index and lifestyle. Although one of the main functions of the skin is to act as a barrier, absorption of some substances remains possible.

CONCLUSIONS

Various factors can alter human skin properties, which can be reflected in skin function and the quality of everyday life. Skin properties and function are strongly interlinked.

Deformable Nanovesicles Synthesized through an Adaptable Microfluidic Platform for Enhanced Localized Transdermal Drug Delivery

Phospholipid-based deformable nanovesicles (DNVs) that have flexibility in shape offer an adaptable and facile method to encapsulate diverse classes of therapeutics and facilitate localized transdermal delivery while minimizing systemic exposure. Here we report the use of a microfluidic reactor for the synthesis of DNVs and show that alteration of input parameters such as flow speeds as well as molar and flow rate ratios increases entrapment efficiency of drugs and allows fine-tuning of DNV size, elasticity, and surface charge. To determine the ability of DNV-encapsulated drug to be delivered transdermally to a local site, we synthesized, characterized, and tested DNVs carrying the fluorescently labeled hydrophilic bisphosphonate drug AF-647 zoledronate (AF647-Zol). AF647-Zol DNVs were lyophilized, resuspended, and applied topically as a paste to the calvarial skin of mice. High-resolution fluorescent imaging and confocal microscopy revealed significant increase of encapsulated payload delivery to the target tissue-cranial bone-by DNVs as compared to nondeformable nanovesicles (NVs) or aqueous drug solutions. Interestingly, NV delivery was not superior to aqueous drug solution. Our studies show that microfluidic reactor-synthesized DNVs can be produced in good yield, with high encapsulation efficiency, reproducibility, and stability after storage, and represent a useful vehicle for localized transdermal drug delivery.

Sensitive Skin: Assessment of the Skin Barrier Using Confocal Raman Microspectroscopy

BACKGROUND/AIMS

Sensitive skin (SS), a frequently reported condition in the Western world, has been suggested to be underlined by an impaired skin barrier. The aim of this study was to investigate the skin barrier molecular composition in SS subjects using confocal Raman microspectroscopy (CRS), and to compare it with that of non-SS (NSS) individuals as well as atopic dermatitis (AD) and allergic rhinoconjunctivitis (AR) subjects, who frequently report SS.

METHODS

Subjects with SS (n = 29), NSS (n = 30), AD (n = 11), and AR (n = 27) were included. Stratum corneum (SC) thickness, water, ceramides/fatty acids, and natural moisturizing factor (NMF) were measured by CRS along with transepidermal water loss and capacitance on the ventral forearm, thenar, and cheek. Sebum levels were additionally measured on the forearm and cheek.

RESULTS

No differences between SS and NSS subjects were found regarding SC thickness, water, and NMF content, yet a trend towards lower ceramides/fatty acids was observed in the cheek. Compared to AD subjects, the SS group showed higher ceramides/fatty acid content in the forearm, whereas no differences emerged with AR. The correlation of macroscopic biophysical techniques and CRS was weak, yet CRS confirmed the well-known lower content of NMF and water, and thinner SC in subjects with filaggrin mutations.

CONCLUSION

The skin barrier in SS is not impaired in terms of SC thickness, water, NMF, and ceramides/fatty acid content. The failure of biophysical techniques to follow alterations in the molecular composition of the skin barrier revealed by CRS emphasizes a strong need in sensitive and specific tools for in vivo skin barrier analysis.

Dermal uptake directly from air under transient conditions: advances in modeling and comparisons with experimental results for human subjects

To better understand the dermal exposure pathway, we enhance an existing mechanistic model of transdermal uptake by including skin surface lipids (SSL) and consider the impact of clothing. Addition of SSL increases the overall resistance to uptake of SVOCs from air but also allows for rapid transfer of SVOCs to sinks like clothing or clean air. We test the model by simulating di-ethyl phthalate (DEP) and di-n-butyl phthalate (DnBP) exposures of six bare-skinned (Weschler et al. 2015, Environ. Health Perspect., 123, 928) and one clothed participant (Morrison et al. 2016, J. Expo. Sci. Environ. Epidemiol., 26, 113). The model predicts total uptake values that are consistent with the measured values. For bare-skinned participants, the model predicts a normalized mass uptake of DEP of 3.1 (μg/m² )/(μg/m³ ), whereas the experimental results range from 1.0 to 4.3 (μg/m² )/(μg/m³ ); uptake of DnBP is somewhat overpredicted: 4.6 (μg/m² )/(μg/m³ ) vs. the experimental range of 0.5-3.2 (μg/m² )/(μg/m³ ). For the clothed participant, the model predicts higher than observed uptake for both species. Uncertainty in model inputs, including convective mass transfer coefficients, partition coefficients, and diffusion coefficients, could account for overpredictions. Simulations that include transfer of skin oil to clothing improve model predictions. A dynamic model that includes SSL is more sensitive to changes that impact external mass transfer such as putting on and removing clothes and bathing.

Depth profiles of hydrogen bound water molecule types and their relation to lipid and protein interaction in the human stratum corneum in vivo

Confocal Raman microscopy has been used to measure depth-dependent profiles of human SC in vivo in the high wavenumber (HWN) region. In order to keep the linearity of HWN region boundaries and to not remove an informative signal from Raman spectra, a new baseline subtraction procedure has been introduced. After baseline subtraction, the HWN spectrum was deconvoluted using 10 Gaussian functions with individual chemical meanings. The results show that the hydrogen bound water molecule types contributed differently to the water diffusion process in the SC. The most concentrated double donor-double acceptor (DDAA) and single donor-single acceptor (DA) water molecule types in the SC represent more than 90% of the SC's water and mostly contribute to the water flux in the skin. Single donor-double acceptor (DAA) and weakly-bound water molecule types represent less than 10% of the SC's water content. The most tightly hydrogen bound water molecule type, DAA, reaches its maximum concentration near the skin surface and does not take part in the water diffusion process via the SC. The results show that the hydrogen bonding state of water (DA/DDAA water molecule type ratio) reaches its maximum at the depth of approx. 30% of the SC thickness, which correlates well with the maximum lateral packing order of intercellular lipids (ICL) and the natural moisturizing factor (NMF), and does not coincide with the folding/unfolding state of keratin. The NMF's contribution to the bonding of water in the SC is supposed to dominate over that of ICL.

A new topical panthenol-containing emollient: skin-moisturizing effect following single and prolonged usage in healthy adults, and tolerability in healthy infants

PURPOSE

Two studies were conducted with a new topical panthenol-containing emollient (NTP-CE) to investigate the skin-moisturizing effect in healthy adults and tolerability in healthy infants.

METHODS

In Study 1 (N = 44), a single skin application of NTP-CE was performed followed by a 4-week twice-daily application. Skin hydration and stratum corneum (SC) water content change (using Raman spectroscopy) were measured. In the 4-week Study 2 (N = 65, aged 3-25 months), NTP-CE tolerability was assessed using a 5-point scoring system; skin hydration was determined in a subset (N = 21).

RESULTS

In Study 1, mean AUC_{0 - 24 h} for skin capacitance change from baseline was 302.03 i.u. with NTP-CE and -15.90 i.u. in control areas (p < .001). With NTP-CE (at 4 h), the water content within the upper SC part was reduced (-45.10 vs. -13.39 g/cm², p = .013) and the water gradient increased (0.51 vs. 0.11 g/cm⁴, p = .036), indicating relocation of water into deeper layers. In Study 2, there was no statistically significant change from baseline in mean cutaneous tolerability scores. At days 7, 14, and 28, skin hydration had increased by 42%, 54%, and 49%, respectively (all p < .001).

CONCLUSIONS

Single and prolonged NTP-CE usage is associated with sustained and deep skin moisturization. NTP-CE is well tolerated by healthy infants.

Unsupervised delineation of stratum corneum using reflectance confocal microscopy and spectral clustering

BACKGROUND

Measuring the thickness of the stratum corneum (SC) in vivo is often required in pharmacological, dermatological, and cosmetological studies. Reflectance confocal microscopy (RCM) offers a non-invasive imaging-based approach. However, RCM-based measurements currently rely on purely visual analysis of images, which is time-consuming and suffers from inter-user subjectivity.

METHODS

We developed an unsupervised segmentation algorithm that can automatically delineate the SC layer in stacks of RCM images of human skin. We represent the unique textural appearance of SC layer using complex wavelet transform and distinguish it from deeper granular layers of skin using spectral clustering. Moreover, through localized processing in a matrix of small areas (called 'tiles'), we obtain lateral variation of SC thickness over the entire field of view.

RESULTS

On a set of 15 RCM stacks of normal human skin, our method estimated SC thickness with a mean error of 5.4 ± 5.1 μm compared to the 'ground truth' segmentation obtained from a clinical expert.

CONCLUSION

Our algorithm provides a non-invasive RCM imaging-based solution which is automated, rapid, objective, and repeatable.