Vibrational spectroscopy coupled to classical least square analysis, a new approach for determination of skin moisturizing agents' mechanisms

Effects of solar radiations on stratum corneum hydration: Part I, protective role of skin surface lipids

This study used Raman spectroscopy to develop a new approach to evaluate the effects of solar radiation on the stratum corneum (SC). The method measures the SC's hydration and dehydration kinetics by calculating the vOH/vCH ratio to monitor the relative water content during the drying process. The study also investigated the role of skin surface lipids (SSLs) in protecting the SC from solar radiation. The SSLs film is a complex mixture of free fatty acids, triglycerides, wax esters, squalene, free and esterified cholesterols, that play a crucial role in the skin's barrier function. The results showed that solar radiation alters the water content and balance within the SC, and SSLs provide protection by acting as an optical filter by absorbing some of the energy of the solar light. This is confirmed by high temperature gas chromatography coupled to mass spectrometry analyses by revealing a decrease in specific lipids after irradiating the SSLs .

Glycerol and natural sugar-derived complex modulate differentially stratum corneum water-binding properties and structural parameters in an in vitro Raman-desorption model

The epidermal protective functions are closely associated with skin hydration homeostasis. The understanding of different states of water binding is a rising concept in assessing topically applied formulations and their interaction within the stratum corneum (SC). In addition to global water content, primary bound water, partially bound water, and unbound water and barrier-related lipid lateral packing and protein secondary structure can be measured by Raman spectroscopy. This study aimed to establish an in vitro SC model to evaluate differences in the efficacy of a natural sugar-derived complex in combination with glycerol and a botanical extract in modulating SC water binding and structural proteins and barrier lipids. These compounds were selected due to their water-binding and soothing properties. The SC water profiles were assessed at the surface and in 8 μm SC depth. After a 12-hour hyperhydration and subsequent product incubation the measurements were performed during a 6 hours desiccation phase. The maximal water caption and the time until reaching a steady state are measured as well as water retention and resistance against water loss. Global water content, partially bound, and unbound water, as well as lipid and protein structures were assessed with confocal Raman microspectroscopy. Both the natural sugar-derived mixture and more pronounced, the same mixture with additional glycerol increased all three water-binding parameters at the surface and in 8 μm SC depth at the beginning and during the desiccation phase. Further addition of botanical extract did not result in an additional increase of the water-binding. All three formulations showed an increase in the lipid lateral packing values prevented the protein alteration as measured by β-sheets signal compared to blank. The present model is suited for screening studies comparing the specific effects of different compounds on hydration states. The natural sugar-derived mixture Aquaxyl showed evidence for an improvement of all SC hydration states, lipid and protein structure which was further enhanced by the addition of glycerol 5%. This improvement was evidenced at the surface and within the SC for all hydration-related parameters, and the lipid as well the protein structures. The addition of botanical extract phytoessence blue daisy did not show further improvement.

Raman confocal microscopy and biophysics multiparametric characterization of the skin barrier evolution with age

Skin aging is a multifactorial phenomenon that involves alterations at the molecular, cellular and tissue levels. Our aim was to carry out a multiparametric biophysical and Raman characterization of skin barrier between individuals of different age groups (<24 and >70 years old). Our results showed a significant decrease of lipids to proteins ratio overall the thickness of the stratum corneum and higher lateral packing in the outer part of the SC for elderly. This can explain the decrease in trans epidermal water loss measured values rather than only SC thickening. Both age groups showed similar water content at SC surface while elderly presented higher water content in deep SC and viable epidermis. Mechanical measurements showed a decrease in the elasticity and an increase in the fatigability with age and were correlated with partially bound water. Highest correlation and anti-correlation values were observed for the deepest part of the SC and the viable epidermis.

Raman spectroscopic analysis of skin penetration and moisturizing effects of Bionics vernix caseosa cream compared with Vaseline

BACKGROUND:

The stratum corneum (SC) is the outermost layer of human skin and deemed as barrier against chemical exposure and water loss. Moisturizers have beneficial effects in treating dry skin, especially the SC. Confocal Raman spectroscopy (CRS) was used to evaluate the efficacy of moisturizers on skin hydration and penetration, with such agents posing inherent characteristics of being noninvasive, nondestructive, timesaving, and cost effective. Bionics vernix caseosa (BVC) cream mimics the composition of vernix caseosa (VC), which could protect the newborn skin.

METHODS:

This research applied CRS to evaluate the penetration depth and water content variation during the intervention with two moisturizers, BVC cream and Vaseline. Volunteers received the 2 h application of BVC cream and Vaseline on the forearms. The evaluations on 0 h, 2 h, 4 h and 6 h were performed clinical assessment. Experimental data was processed by least square method and analysis of variance (ANOVA).

RESULTS:

The penetration depth of Vaseline was deeper than that of Bionics vernix caseosa cream. Specifically, BVC cream penetrated 18 μm into human skin, while Vaseline penetrated at least 20 μm. Compared with Vaseline, only BVC cream increased skin hydration, with a moisturizing effect lasting for 4 h. At 6 h, the Vaseline moisturizing effect decreased significantly.

In vivo Raman spectroscopy study on the stimulation mechanism of surfactant

BACKGROUND

Surfactant is widely used in skin care products and cleansers, while it may cause physical discomfort. In this study, in vivo Raman spectroscopy was used to explore surfactant irritation mechanism on skin, which was not found in literature.

METHODS

Sodium dodecyl sulfate (SDS) was chosen to represent surfactant. Research on the negative effect of SDS was undertaken by scanning the two states of the skin (without and with the contact of SDS), respectively, on six volunteers, by means of Raman technique and skin magnifier.

RESULTS

The damage to the surface of normal skin by SDS was visible from the photographs taken by skin magnifier, and the apparent damage matched the damage that was happening underneath the skin elucidated by Raman spectra. Compared to the normal skin, the inter-cellular lipids (ICL) lateral packing order of the damaged skin was significantly reduced in 2-12 μm of skin depth (P < 0.05), deeper than 12 μm was not detected. The skin depth of 0-2 μm could not be determined due to strong interference of SDS. Significant change in the secondary and tertiary structures of keratin was not found.

Effect of propylene glycol on the skin penetration of drugs

Propylene glycol (PG) has been used in formulations as a co-solvent and/or to enhance drug permeation through the skin from topical preparations. Two skin in vitro permeation approaches are used to determine the effect of PG on drug penetration. The in vitro Skin-PAMPA was performed using 24 actives applied in aqueous buffer or PG. PG modulates permeability by increasing or diminishing it in the compounds with poor or high permeability, respectively. Percutaneous absorption using pigskin on Franz diffusion cells was performed on seven actives and their commercial formulations. The commercial formulations evaluated tend to have a lower permeability than their corresponding PG solutions but maintain the compound distribution in the different strata: stratum corneum, epidermis and dermis. The results indicate the enhancer properties of PG for all compounds, especially for the hydrophilic ones. Additionally, the Synchrotron-Based Fourier Transform Infrared microspectroscopy technique is applied to study the penetration of PG and the molecular changes that the vehicle may promote in the different skin layers. Results showed an increase of the areas under the curve indicating the higher amount of lipids in the deeper layers and altering the lipidic order of the bilayer structure to a more disordered lipid structure.

Review of Modern Techniques for the Assessment of Skin Hydration

Skin hydration is a complex process that influences the physical and mechanical properties of skin. Various technologies have emerged over the years to assess this parameter, with the current standard being electrical probe-based instruments. Nevertheless, their inability to provide detailed information has prompted the use of sophisticated spectroscopic and imaging methodologies, which are capable of in-depth skin analysis that includes structural and composition details. Modern imaging and spectroscopic techniques have transformed skin research in the dermatological and cosmetics disciplines, and are now commonly employed in conjunction with traditional methods for comprehensive assessment of both healthy and pathological skin. This article reviews current techniques employed in measuring skin hydration, and gives an account on their principle of operation and applications in skin-related research.

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.

Skin care in nursing: A critical discussion of nursing practice and research

Skin (self-)care is part of human life from birth until death. Today many different skin care practices, preferences, traditions and routines exist in parallel. In addition, preventive and therapeutic skin care is delivered in nursing and healthcare by formal and informal caregivers. The aim of this contribution is a critical discussion about skin care in the context of professional nursing practice. An explicit skin assessment using accurate diagnostic statements is needed for clinical decision making. Special attention should be paid on high risk skin areas, which may be either too dry or too moist. From a safety perspective the protection and maintenance of skin integrity should have the highest priority. Skin cleansing is the removal of unwanted substances from the skin surface. Despite cleansing efficacy soap, other surfactants and water will inevitably always result in the destruction of the skin barrier. Thousands of products are available to hydrate, moisturize, protect and restore skin properties dependent upon their formulation and the concentration of ingredients. These products intended to left in contact with skin exhibit several actions on and in the skin interfering with skin biology. Unwanted side effects include hyper-hydration and disorganization of lipid bilayers in the stratum corneum, a dysfunctional barrier, increased susceptibility to irritants and allergies, and increases of skin surface pH. Where the skin barrier is impaired appropriate interventions, e.g. apply lipophilic products in sufficient quantity to treat dry skin or protect the skin from exposure to irritants should be provided. A key statement of this contribution is: every skin care activity matters. Every time something is placed on the skin, a functional and structural response is provoked. This response can be either desired or undesired, beneficial or harmful. The choice of all skin care interventions in nursing and healthcare practice must be based on an accurate assessment of the skin and concomitant health conditions and on a clearly defined outcome. A standardized skin care and skin care product language is needed for researchers planning and conducting clinical trials, for reviewers doing systematic reviews and evidence-base summaries, for nurses and other healthcare workers to deliver evidence-based and safe skin care.