Characterization of the mechanical properties of a dermal equivalent compared with human skin in vivo by indentation and static friction tests

Background/aims: The study of changes in skin structure with age is becoming all the more important with the increase in life. The atrophy that occurs during aging is accompanied by more profound changes, with a loss of organization within the elastic collagen network and alterations in the basal elements. The aim of this study is to present a method to determine the mechanical properties of total human skin in vivo compared with dermal equivalents (DEs) using indentation and static friction tests.
Methods: A new bio-tribometer working at a low contact pressure for the characterization the mechanical properties of the skin has been developed. This device, based on indentation and static friction tests, also allows to characterize the skin in vivo and reconstructed DEs in a wide range of light contact forces, stress and strain.
Results: This original bio-tribometer shows the ability to assess the skin elasticity and friction force in a wide range of light normal load (0.5–2 g) and low contact pressure (0.5–2 kPa). The results obtained by this approach show identical values of the Young's modulus E ^* and the shear modulus G ^* of six DEs obtained from a 62-year-old subject ( E ^*=8.5±1.74 kPa and G ^*=3.3±0.46 kPa) and in vivo total skin of 20 subjects aged 55 to 70 years ( E ^*=8.3±2.1 kPa, G ^*=2.8±0.8 kpa).     

A numerical-experimental method to characterize the non-linear mechanical behaviour of human skin

Background/aims: Human skin is a complex tissue consisting of several distinct layers. Each layer consists of various components with a specific structure. To gain a better insight into the overall mechanical behaviour of the skin, we wish to study the mechanical properties of the different layers. A numerical-experimental method was developed to characterize the non-linear mechanical behaviour of human dermis.
Methods: Suction measurements at varying pressures were performed on the volar forearm skin of 10 subjects aged 19–24 years old. Deformation of dermis and fat during suction was measured using ultrasound. The experiment was simulated by a finite element model exhibiting extended Mooney material behaviour to account for the non-linear stress–strain relationship. An identification method is used to compare the experimental and numerical results to identify the parameters of the material model.
Results: C _{10, dermis} was found to be 9.4 ± 3.6 kPa and C _{11, dermis} to be 82 ± 60 kPa. A first rough estimate of C _{10, fat} was 0.02 kPa.
Conclusions: The resulting finite element model demonstrated its ability to describe the response of the skin to suction at various pressures. In the future, this method can be used to characterize the mechanical behaviour of different skin layers using various aperture sizes and to characterize the skin behaviour under various loading conditions.     

Ceramide 1 and ceramide 3 act synergistically on skin hydration and the transepidermal water loss of sodium lauryl sulfate-irritated skin

Background  Stratum corneum intercellular lipids, such as ceramides, play an important role in the regulation of skin water barrier homeostasis and water-holding capacity.
Aim  To evaluate the potential water retention capacity of control emulsion and three oil-in-water (o/w) emulsions containing ceramide 1, ceramide 3, or both.
Methods  Fifteen healthy Asian women (age, 20–30 years) with healthy skin, pretreated with sodium lauryl sulfate (SLS), applied the tested emulsions twice daily over a period of 28 days. Skin hydration and transepidermal water loss (TEWL) values were measured on the indicated days with a Corneometer®825 and a TEWAMETER TM210, respectively.
Results  The maximum increase in skin humidity was reached after 4 weeks, with values of 21.9 ± 1.8% and 8.9 ± 0.9% for emulsion C and control emulsion, respectively. The maximum decrease in TEWL was also reached after 4 weeks, with values of 36.7 ± 4.7% and 5.1 ± 0.8% for the same emulsions.
Conclusions  It can be concluded that all the tested ceramide-containing emulsions improved skin barrier function when compared with untreated skin. There was some indication that ceramides 1 and 3 contained in emulsion C might exert a beneficial synergistic effect on skin biochemical properties, such as skin hydration and TEWL, and play a key role in the protection mechanism against SLS irritation.     

Effects of lipid nanocarriers on the performance of topical vehicles in vivo

Background/aims  Nanocarrier systems have been extensively studied for their suitability in personal care formulations. Theoretically, they could enhance skin delivery of active compounds, thereby improving in vivo efficacy of the products. As such the aim of this study was to evaluate the effect of a lipid nanocarrier (LNC) system loaded with tocopheryl acetate (TA) on the hydration, biomechanical properties, and antioxidant capacity of human skin, when used in two different vehicles, and compare it with a non-LNC formulation.
Methods  TA-loaded lipid nanocarriers (TA-LNCs) were produced by the phase inversion method, using physiological lipids and purified by ultra-centrifugation. They were incorporated into a hydrophilic gel and foam, and their performance compared with a saturated TA solution in silicon oil. Skin hydration and biomechanical properties were measured by means of a corneometer and a cutometer, respectively, while a high-resolution spectrophotometer was used to assess skin redness after stimulation by methyl nicotinate in a micro-inflammatory test. Both short-term (3 h) and long-term trials (4 weeks) were performed.
Results  The results confirmed that the LNCs enhanced skin hydration in both studies, while skin viscoelastic parameters remained practically unchanged during the 4-week study. The antioxidant assessment failed to show significant difference between the test sites.
Conclusions  TA-loaded LNCs exhibited the ability to enhance skin hydration, while their effect on skin biomechanical properties and on antioxidant efficacy could not be statistically proved.     

Skin hydration and transepidermal water loss in patients with a history of sulfur mustard contact: a case–control study

Background   Skin lesions are among the most common complications of contact with sulfur mustard.
Objective   This study was aimed to measure skin water content and transepidermal water loss (TEWL) in patients with a history of sulfur mustard contact.
Methods   Three hundred ten male participants were included in this study: 87 (28.1%) sulfur mustard–exposed patients with current skin lesions (group 1), 71 (22.9%) sulfur mustard–exposed patients without skin lesions (group 2), 78 (25.2%) patients with dermatitis (group 3) and 74 (23.8%) normal controls (group 4) The water content and TEWL of skin was measured at four different locations of the body: forehead, suprasternal, palm and dorsum of hand. Nonparametric statistical tests (Kruskal–Wallis) were used to compare the four groups, and P  < 0.05 was considered statistically significant.
Results   The mean age of participants were 44.0 ± 6.7, 41.9 ± 5.9, 43.8 ± 9.3 and 44.8 ± 8.9 years in groups 1 to 4, respectively ( P  = 0.146). Xerosis, post-lesional hyperpigmentation and lichenification were significantly more common in either sulfur mustard–exposed participants or non-exposed participants with dermatitis ( P  < 0.05). Skin hydration was higher in subjects with sulfur mustard contact than in non-injured participants ( P  < 0.05) in the dorsum and palm of hands and forehead. TEWL was significantly higher in participants only in suprasternal area and dorsum of hand.
Conclusion   Contact with sulfur mustard agent can alter biophysical properties of the skin-especially the function of stratum corneum as a barrier to water loss-several years after exposure.

Conflicts of interest

None declared.     

A new device for assessing changes in skin viscoelasticity using indentation and optical measurement

Background/aims: Skin is a viscoelastic material, comprised of fluidic and fibrous components. Changes in viscoelasticity can arise due to a number of conditions including dehydration, swelling (associated with injury or disease), impaired heart function, rehydration therapy, ageing, scarring, sun exposure and genetic conditions affecting connective tissue. Quantification of changes in skin viscoelasticity due to these processes is of great clinical interest in the fields of therapy monitoring, wound healing and disease screening. However, devices currently available to measure aspects of the mechanical properties of skin have limitations in ease‐of‐use, accessibility, and depth of measurement. This paper describes a new technique to follow changes in the viscoelasticity of the skin, using a novel approach to an indentation manoeuvre. The device is portable, low‐cost and easy to use while at the same time providing rich information on the mechanical response of the skin. Methods: The method proposed optically tracks the skin's recovery from an initial strain, made with a novel linear indentor, using diffuse side‐lighting and a CCD video camera. Upon indentation, the skin's elastin fibres are stretched and fluid is displaced from the compressed region. When the indentor is removed, the rate of recovery of the skin from this imprint is therefore principally dependent on its hydration and elasticity. Using the blue colour plane of the image and polarisation filtering, it is possible to examine the surface topography only, and track the decay of the imprint over time. Results: The decrease in size of the imprint over time (decay curve) recorded by the device is shown to agree with the theoretical predictions of an appropriate viscoelastic model of skin mechanical behaviour. The contributors to the response measured using the indentation device are fully characterised and evaluated using separate measurement techniques including high‐frequency ultrasound, polarisation spectroscopy and optical coherence tomography. Conclusion: The device developed is capable of tracking the viscoelastic response of skin to minimal indentation. The high precision achieved using low‐cost materials means that the device could be a viable alternative to current technologies.     

Is it possible to characterize objectively sensitive skin?

Background/purpose: Sensitive skin is a subject of intense research work. However, its contours have not been defined and properly investigated so far. The aim of this work was to characterize objectively the consumers of cosmetic products, which referred skin susceptibility to several agents or conditions.
Methods: Twenty-four healthy female volunteers, mean age 38.9±13 years were recruited. The volunteers were fully informed about the study having previously expressed their consent, and were grouped in to I: individuals without any skin sensitivity complaint and II: individuals with self-reported sensitive skin to regular contact with household cleaning products. Sodium lauryl sulphate was used as a 'provocative' agent and it was applied on the back of the volunteers' hands, as an occlusive patch for 24 h. After the patch removal (30 min, 7 and 14 days), the variables erythema, transepidermal water loss, stratum corneum hydration and blood perfusion were measured.
Results: No evidence of a statistical difference was found between the biomechanical behaviour of the skin of the two groups.
Conclusion: The results of our study did not enable us to establish a clear discrimination between sensitive and non-sensitive skin, which once again underlines the subjective nature of this condition.     

Influence of age and regional differences on skin elasticity as measured by the Cutometer®

Background/aim: Aging of skin is accompanied by decrease of skin elasticity. Using the noninvasive suction device Cutometer^®, we evaluated the age and regional body differences of the viscoelastic properties of human skin. The objectives of this study were to evaluate the correlation between age and the biomechanical parameters and the regional skin variations.
Methods: A total of 96 healthy women aged 20–75 years were included in this study. The biomechanical properties of the skin were measured by using the Cutometer^®. Measurements were made on the face, upper arm and back.
Results: The age of subjects showed significant positive correlation with R4 and R6, and negative correlation with R2, R5 and R7. The face showed bigger changes of elastic properties than the arm and the back. Especially, the R7 of face was most significantly decreased with aging. We could estimate the so-called 'skin age' by using a correlation equation for this parameter.
Conclusion: The viscoelastic properties were significantly influenced by aging. Also, significant regional variations in the viscoelastic properties were observed. Skin elasticity measurement is useful for the quantitative evaluation of age-related changes.     

In vivo model of the mechanical properties of the human skin under suction

Background/aims: A new method for the in vivo characterization of the mechanical properties of skin has been developed. This comprises a suction chamber and an ultrasound device to measure both the vertical displacement of the skin's surface, and the skin's thickness. Methods: A mathematical model of the mechanical behaviour of a taught elastic membrane is used to obtain a set of parameters intrinsic to the skin, such as Young's modulus (E) and the initial stress (σ₀), which reflect the stiffness and the natural tension of the skin, respectively. We also calculated an index of non‐elasticity of the skin (unrestored energy ratio, UER), which takes into account the volume of tissue mobilized. It determines a ratio between the energy input to the skin and the energy it dissipates. These parameters were evaluated from the volar forearm of 10 normal male volunteers. Results: The results were: 129±88 kPa for E, 13.5±5 kPa for σ₀, and 0.42±0.04 for UER; with reproducibilities of 9.5%, 12.4% and 6.4%, respectively. Conclusions: This new suction device was found useful for the study of the behaviour of the skin, and the device may be used for the evaluation of certain skin diseases and their therapy.     

FS03.7Tape stripping procedure: influence of anatomic site, application pressure, duration and removal

Background and Objectives:  Tape stripping is a common method for investigating stratum corneum (SC) physiology as well as bioavailability and bioequivalence of topical drugs. However, little is known concerning the influence of procedures (anatomic site, pressure, pressure duration, tape removal rate) inherent in each stripping protocol.
Methods:  Tape stripping was performed using tapes on the forearm, forehead and back. On the forearm different pressures (165 and 330 g cm⁻²), durations of pressure (2s and 10s), and removal rate (slow and rapid removal) was performed. Changes in skin physiology were evaluated by measurement of transepidermal water loss (TEWL) and hydration.
Results:  A significant influence of all parameters on the TEWL‐increase as a function of tape strip number was observed. The fastest increase was demonstrated on the forehead, followed by the back and, lastly, the forearm. Rapid removal produced a protracted increase in comparison to the slow removal. 10s pressure induced a faster increase of TEWL than 2s pressure. Likewise, the 330 g cm⁻² pressure induced an earlier increase than the 165 g cm⁻². Skin hydration was not influenced by the variables tested.
Conclusion:  Tape stripping results are influenced dramatically by all investigated parameters. A standardized procedure is necessary for a comparable study design. A dynamic SC stress test to more closely investigate SC cohesion is proposed based on the present observations.     

Expression of minichromosome maintenance proteins in Merkel cell carcinoma

Objective  Minichromosome maintenance (MCM) nuclear proteins have barely been employed in the diagnosis of skin malignancies. We aimed to assess whether MCM immunohistochemistry can be utilized to examine tumour proliferation in Merkel cell carcinoma (MCC).
Methods  In this pilot study, we studied skin specimens of eight patients with MCC. As a control, eight patients with cutaneous malignant melanoma (MM) were included. Immunohistochemistry was performed for MCM4, MCM6, MCM7, Ki-67, p53, and p21.
Results  Protein expression of MCM4 (66.0 ± 26.5% vs. 33.9 ± 22.4%; P  = 0.017), MCM6 (70.9 ± 11.9 vs. 31.7 ± 22.7; P  = 0.0031), and MCM7 (76.5 ± 16.4% vs. 34.9 ± 25.5%; P  = 0.0013) was significantly increased in tumour cells of MCC when compared to tumour cells of MM. Ki-67 immunoreactivity was also significantly higher in MCC than in MM (28.7 ± 7.9 vs. 11.0 ± 9.2; P  = 0.0012). Immunolabelling of p53 (68.6 ± 26.2 vs. 58.4 ± 28.8; P  = 0.46) and p21 (40.1 ± 38.8 vs. 25.8 ± 16.1; P  = 0.35) was relatively high but not significantly increased in MCC when compared to MM.
Conclusion  Our preliminary data indicate that MCM immunohistochemistry may be a useful tool for the determination of tumour cell proliferation in MCC.     

Elevated frequency of p53 genetic mutations and AgNOR values in squamous cell carcinoma

Background:  Epidermal squamous cell carcinoma (SCC) is a common malignancy in Pakistan. We hypothesize that it is characterized by higher frequency of p53 genetic mutations and increased AgNOR values compared with squamous cell papilloma (SCP) and basal cell carcinoma (BCC).
Experimental design: To test our hypothesis, 140 skin biopsies (including 20 normal skin, 20 SCP, 20 BCC and 80 SCC samples of various grades) were examined for p53 mutations using immunohistochemistry (IHC) and polymerase chain reaction (PCR). AgNOR staining was used for histological determination of AgNOR index.
Results:  Both markers were undetectable in normal skin and were low in SCP. They were upregulated in BCC and SCC. PCR experiments revealed p53 mutations in 70% and 96.25% of BCC and SCC, respectively. Higher AgNOR values were seen in SCC than in BCC (mean AgNOR count = 5.81 ± 31 and 8.36 ± 19; percentage of AgNOR was 43.5% and 53% in BCC and SCC, respectively). Finally, p53 IHC score was found to be related to the AgNOR index in the histological grading of BCC and SCC (r = +0.983, p < 0.0001).
Conclusion:  Our results suggest that a higher frequency of p53 genetic mutations and increased AgNOR values exist in SCC compared with BCC and SCP. 'Consequently, SCC patients may have poorer prognosis'.     

Skin–textile friction and skin elasticity in young and aged persons

Background/purpose: The mechanical properties of human skin are known to change with ageing, rendering skin less resistant to friction and shear forces, as well as more vulnerable to wounds. Until now, only few and contradictory results on the age-dependent friction properties of skin have been reported. This study has investigated in detail the influence of age on the friction of human skin against textiles.
Methods: In vivo skin-friction measurements on a force plate were combined with skin analyses concerning elasticity, hydration, pH value and sebum content. Thirty-two young and 28 aged persons rubbed their volar forearm in a reciprocating motion against various textiles on the force plate, using defined normal loads and sliding velocities, representing clinically relevant contact conditions.
Results: Mean friction coefficients ranged from 0.30 ± 0.04 (polytetrafluoroethylene) to 0.43 ± 0.04 (cotton/polyester). No significant differences in the friction properties of skin were found between the age groups despite skin elasticity being significantly lower in the aged persons. Skin hydration was significantly higher in the elderly, whereas no significant differences were observed in either skin pH value or sebum content.
Conclusion: Adhesion is usually assumed to be the dominant factor in skin friction, but our observations imply that deformation is also an important factor in the friction of aged skin. In the elderly, lower skin elasticity and skin turgor are associated with more pronounced skin tissue displacements and greater shear forces during frictional contact, emphasizing the importance of friction reduction in wound-prevention programmes.     

Relationship of immunohistochemistry scores of altered p53 protein expression in relation to patient's habits and histological grades and stages of squamous cell carcinoma

Background:  p53 mutations are etiologically associated with the development of squamous cell carcinomas (SCCs) or with exposure to specific carcinogens. The study was conducted to examine the relationship of immunohistochemistry (IHC) scores between altered p53 protein expression in relation to patient's habits and histological grades and stages of SCC.
Materials and Methods:  IHC scores of p53 protein expression were determined and correlated on 100 biopsies from patients with matched habits, age, sex and site including 20 normal skin and 80 SCC samples of various grades and stages.
Results:  A good association of p53 expression was seen among smokers and betel quid (BQ) users. As compared with normal skin (2.45 ± 1.26), the SCC sample showed a significant rise in IHC scores for p53 protein expression, with transitions from SCC in situ to well-differentiated SCC to moderately differentiated SCC to poorly differentiated SCC (27.5 ± 2.7, 41.2 ± 5.8, 42.83 ± 5.26 and 71.05 ± 13.3, respectively). Finally, IHC scores for p53 expression were found to be related to histological grading and staging of SCC (r = 0.9322, r = 0.863, p < 0.0001 and p < 0.5) .
Conclusion:  IHC scores of altered p53 protein expression are closely related to the habits of the patients and histological grades and stages of SCC. 'This relationship may be accounted for by the facts that smoking and use of BQ may induce an alteration to p53 that, in turn, may lead to the development and progression of SCC'.     

Local tissue water assessed by measuring forearm skin dielectric constant: dependence on measurement depth, age and body mass index

Background: Tissue dielectric constant (TDC) measured at 300 MHz via the coaxial line reflection method is useful to evaluate local tissue water (LTW) and its change. Because excitation field penetration depth depends on size and geometry of the coaxial probe in contact with the skin, TDC values reflect skin and subcutaneous fat to varying depths depending on the probe used. Because tissue changes that occur with age or body mass index (BMI) may affect tissue water content and its depth distribution, our goal was to use TDC measurements to characterize depth patterns of LTW in normal tissue and to investigate the possible impact of age and BMI.
Methods: TDC was measured to depths of 0.5, 1.5, 2.5 and 5.0 mm on both forearms of 69 healthy women (age: 22–82 years, BMI: 18.7–46.1 kg/m²).
Results: Independent of age or BMI, TDC values decreased significantly with increasing measurement depth (33.7±5.8 at 0.5 mm to 21.8±3.7 at 5.0 mm) but at all depths dominant and non-dominant TDC values were similar to each other with ratios ranging from 1.025±0.081 at 0.5 mm to 1.017±0.097 at 5.0 mm. TDC values only at 2.5 and 5.0 mm decreased significantly with increasing BMI whereas TDC values only at 0.5 and 1.5 mm increased significantly with age.
Conclusion: The findings indicate that normal TDC values are affected differentially by BMI and age in a depth-dependent manner. Possible explanations are discussed.     

Skin biomechanical properties: in vivo evaluation of influence of age and body site by a non-invasive method

Background/aims: Biomechanical properties of the skin are evaluated in vivo by torsion or extension methods. We assessed their modifications as function of age, probe diameter and regional body site.
Methods: For measuring skin extensibility (or traction), we used a non-invasive suction device on a total of 37 volunteers, consisting of (A) 14 younger women (30.1±7.6 years) and (B) 23 older women (60.2±6.5 years). Measurements were performed on three different areas with 4 different probe diameters. The parameters used were ( U _E) extensibility; ( U _V) plasticity; ( U _R) tonicity; ( U _R U _E) elasticity; the difference between the lowest point of the last curve (5th) and that of the 1st is the fatiguability. Concurrently, we measured on each volunteer the microdepressionary network (mDN) length.
Results: Generally, tonicity, extensibility and elasticity decreased; fatiguability increased and plasticity stayed the same; all of these factors apply regardless of age. Results are more homogenous on the volar face of the forearm and with 2, 4 and 6 mm probe diameters. As a general trend, mDN length decreases with age.
Conclusions: The knowledge of this variation is important in interpreting the results obtained after product application. Standardisation of measures with the 2-mm probe will allow product efficacy determination and the comparison of different products.     

Cosmetic effectiveness of topically applied hydrolysed keratin peptides and lipids derived from wool

Background/purpose: Skin moisturisation, elasticity, feel and appearance can all be improved through the topical application of protein hydrolysates. Recent studies suggest that supplementing intercellular lipids of the stratum corneum can enhance the functioning of the skin.
Methods: In this study, a hydrolysed keratin peptide (molecular weight <1000 Da) was prepared from wool and tested on skin in two different formulations: an aqueous solution and an internal wool lipids (IWL) liposome suspension. In vivo long-term studies were performed to evaluate the water barrier function of the skin after topical application of different formulations. During the treatment period, hydration and elasticity were determined. A sorption–desorption test was also performed to assess the hygroscopic properties and water-holding capacity of the different treated skin sites.
Results: Significant differences were found between the control and treated sites, with the treated areas showing an increase in hydration and elasticity as a result of keratin peptide application. Measurements also indicated that the keratin formulations reinforce the skin barrier integrity, improving its water-holding capacity.
Conclusion: A combination of the keratin peptide with the IWL showed beneficial effects, indicating that this combination is suitable for designing new cosmetics products.     

A rapid, accurate, and facile method to quantify the antioxidative capacity of topical formulations

Background/aims: Various methodologies have been developed to quantify antioxidant activity. A simple, rapid and accurate method is demanded. This study examined the antioxidative status of a pH balanced vitamin E containing formulation versus its vehicle control utilizing a photochemiluminescence device.
Methods/results: A pH balanced 5% Vitamin E containing formulation and its vehicle control were tested. The quantity of antioxidant capacity for the pH balanced vitamin E formulation and its vehicle control were 2.28 ± 0.05 and 0.16 ± 0.03, respectively. The pH balanced vitamin E formulation showed a significant ( P  < 0.001) higher antioxidant capacity compared to its vehicle control.
Conclusions: This method not only provides quantitative data, but also is rapid, accurate, and facile in performance. The in vitro data obtained in this study require validation by in vivo studies to properly place them in context to alternate methods.     

Development of a novel method for quantitative evaluation of sensory skin irritation inhibitors

Background/aims: Sensory skin irritation is regarded as one of the most serious side effects of cosmetic use. Thus, it is desirable to develop good inhibitors of sensory skin irritation. However, it is difficult to quantify the effect of sensory skin irritation inhibitors.
Methods: We investigated the possibility of using an electrical current perception threshold (CPT) measurement for the quantitative evaluation of these inhibitors. We divided study populations into stinger and non-stinger groups based on their response to 5% lactic acid and assessed CPT values at 2000, 250, and 5 Hz on the cheek. Stingers showed significantly lower CPT values than non-stingers did at 250 and 5 Hz. We also measured CPT values before and after the application of nine materials with inhibitory effects on sensory skin irritation. To investigate the relationship between the change in CPT values and the effect of each material in the clinical stinging test, we conducted the stinging test with the test materials in a 5% lactic acid solution and with a 5% lactic acid solution (positive control).
Results: There was a positive correlation between the change in CPT values and the inhibitory effect that each material had on the stinging test.
Conclusion: The change in CPT values can be used for the quantitative evaluation of sensory skin irritation inhibitors .