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).     

Biophysical characteristics of skin in diabetes: a controlled study

Background  Cutaneous complications are common in diabetes. Previous assays suggest that hyperglycemia and decreased insulin signal are involved in the impairment of skin function. The aim of this study was to evaluate the biophysical characteristics of skin in patients with diabetes mellitus and compares them with healthy non-diabetic controls.
Objective  To measure biophysical characteristic of skin including transepidermal water loss (TEWL), water content, sebum and skin elasticity in patients with diabetes mellitus and compare them with healthy non-diabetic controls.
Methods  This case-control study was conducted on 38 patients with diabetes and 40 age- and sex-matched healthy people. The biophysical properties of skin including stratum corneum (SC) hydration, sebum content, TEWL and skin elasticity were measured and compared between the two groups at three different locations of the body.
Results  The measurement of SC hydration and TEWL showed no significant difference between diabetics and controls. The skin surface lipids on the forehead but not other sites were significantly lower in the diabetics than in the controls. Acoustic wave propagation speed, a measurement related to skin elasticity, was significantly lower in forearm and forehead of diabetics.
Conclusion  Diabetes affects some functional properties of epidermis and dermis that may responsible for many cutaneous manifestations of diabetes. These results suggest that patients with diabetes mellitus tend to show a normal hydration state of the SC together with decreased sebaceous gland activity and impaired skin elasticity, without any impairment of the SC barrier function.

Conflicts of interest

None declared     

Study of skin–fabric interactions of relevance to decubitus: friction and contact-pressure measurements

Background/purpose: Prolonged pressure as well as friction and shear forces at the skin–textile interface are decisive physical parameters in the development of decubitus. The present article describes the contact phenomena at the skin–textile interface and the development of a purpose-built textile friction analyser (TFA) for the tribological assessment of skin–fabric interactions, in connection with decubitus prevention.
Methods: Interface pressure distributions were recorded in the pelvic and femoral regions between supine persons and a foam mattress. Fabrics made of various natural and synthetic yarns were investigated using the TFA. A vertical load of 7.7 kPa was applied to the swatches, simulating high interface pressures at the skin–fabric interface and clinical conditions of bedridden persons. Fabrics were rubbed in reciprocating motions against a validated skin-simulating material to determine static as well as dynamic friction coefficients (COFs).
Results: Maximum contact pressures ranged from 5.2 to 7.7 kPa (39–58 mmHg) and exceeded the capillary closure pressure (32 mmHg) in all investigated bedding positions. For both COFs, a factor of 2.5 was found between the samples with the lowest and highest values. Our results were in a similar range to COFs found in measurements on human skin in vivo . The results showed that our test method can detect differences of 0.01 in friction coefficients.
Conclusion: TFA measurements allow the objective and reliable study of the tribology of the skin–textile biointerface and will be used to develop medical textiles with improved performance and greater efficacy for decubitus prevention.     

老年人皮肤生物物理特性的改变及其意义

随着机体的衰老,各器官(包括皮肤)的生物功能发生变化。在皮肤,这些生物功能的改变通常体现在皮肤生物物理特性的变化。与年轻者相比,老年皮肤的共振传导速度加快、pH升高、弹性降低、皮脂减少、角质层含水量减少以及表皮通透屏障功能降低等。测量老年皮肤生物物理特性的变化不仅有利于了解其皮肤的生物功能,也有助于对某些皮肤治疗和保健品的研发及疗效的评估。     

Contribution of skin biometrology to the diagnosis of the Ehlers–Danlos syndrome in a prospective series of 41 patients

Background/purpose: The diagnosis of the Ehlers–Danlos syndrome (EDS) is primarily clinical. Clinical signs result from modifications of the rheological properties of the skin: thickness, extensibility and hydration. Our main objective was to demonstrate what skin biometry can contribute to the diagnosis and evaluation of the different types of EDS.
Methods: Forty-one patients clinically diagnosed with EDS were paired by age and sex to 41 healthy subjects with no known dermatologic disease, in particular connective tissue diseases. We measured skin thickness, extensibility, hydration and sebum secretion by skin ultrasonography, use of a Cutometer^®, a Corneometer^® and a Sebumeter^®.
Results: The skin is thinner in all three disease types (classical, hypermobility and vascular). It is more extensible only in the classical type, and more hydrated and fatty in the hypermobility type.
Conclusion: Non-invasive measurement of skin thickness and elasticity are quantitative parameters that can be used to better diagnose EDS. Moreover, the sebaceous rate can help to diagnose the hypermobility type whereas the immediate retraction distinguishes the classical form from vascular and hypermobile types.     

Study of skin-fabric interactions of relevance to decubitus: friction and contact-pressure measurements.

BACKGROUND/PURPOSE: Prolonged pressure as well as friction and shear forces at the skin-textile interface are decisive physical parameters in the development of decubitus. The present article describes the contact phenomena at the skin-textile interface and the development of a purpose-built textile friction analyser (TFA) for the tribological assessment of skin-fabric interactions, in connection with decubitus prevention. METHODS: Interface pressure distributions were recorded in the pelvic and femoral regions between supine persons and a foam mattress. Fabrics made of various natural and synthetic yarns were investigated using the TFA. A vertical load of 7.7 kPa was applied to the swatches, simulating high interface pressures at the skin-fabric interface and clinical conditions of bedridden persons. Fabrics were rubbed in reciprocating motions against a validated skin-simulating material to determine static as well as dynamic friction coefficients (COFs). RESULTS: Maximum contact pressures ranged from 5.2 to 7.7 kPa (39-58 mmHg) and exceeded the capillary closure pressure (32 mmHg) in all investigated bedding positions. For both COFs, a factor of 2.5 was found between the samples with the lowest and highest values. Our results were in a similar range to COFs found in measurements on human skin in vivo. The results showed that our test method can detect differences of 0.01 in friction coefficients. CONCLUSION: TFA measurements allow the objective and reliable study of the tribology of the skin-textile biointerface and will be used to develop medical textiles with improved performance and greater efficacy for decubitus prevention.     

我国正常人皮肤表面皮脂和水分含量的研究

目的：了解我国不同年龄、不同性别正常人皮肤角质层含水量、皮肤表面皮脂含量及皮肤皮脂的分泌速度。方法：利用皮肤表面皮脂测量仪和皮肤水分含量测量仪对我国北方325名正常人的前额及前臂屈侧皮肤皮脂量和皮肤含水量进行测量。结果：12岁以前，男女前额皮脂量无差异；13岁以后，男性前额的皮脂量明显高于女性。除36～50岁年龄组外，女性前额的皮脂分泌快于男性。男女前臂的皮脂量无差异。除男性13～35岁组的前额皮肤含水量高于女性外，其他各年龄组各部位男、女皮肤含水量无显著差别。13～35岁组男、女性前额的含水量均高于前臂。其他各年龄组前额和前臂皮肤含水量无明显部位差异。13-35岁组男性前额皮肤含水量最高。结论：正常人皮肤表面含水量和皮脂含量因性别、年龄和部位的不同而有差异。     

Comparative study of skin sebum and elasticity level in patients with sulfur mustard‐induced dermatitis and healthy controls

Background: Sulfur mustard (SM) – a chemical agent – has both acute and chronic effects on skin. Xerosis, which is deemed to be due to the damage of hydrolipidic barrier of the skin, is the most common complaint of veterans exposed to the chemical. This study was designed to evaluate skin sebum and elasticity in veterans with a history of SM contact. Methods: Three hundred and ten subjects were enrolled in this study and were divided into four groups: SM‐exposed patients with current skin lesions (n=87); SM‐exposed patients without skin lesions (n=71); patients with dermatitis (n=78); and normal controls (n=74). The skin sebum and elasticity were measured in four areas (forehead, suprasternal, palm and back of the hands) using a Sebumeter and a Reviscometer. Results: Skin sebum was higher in participants who presented with dermatitis and had history of contact with SM than others; the difference was only statistically significant on the forehead. There was no significant difference in the skin elasticity between the four groups. Conclusion: While SM may increase skin sebum in long term, there is no evidence that it has a substantial effect on skin elasticity.     

Skin critical surface tension

Background/aims: Surface energy phenomena result from molecular interaction between substances. On the skin, they are involved in sweat and sebum dispersion, and in foreign substances, in spreading and absorption. However, they are unknown due to the scarce number of studies. The aim of this work was to find the skin critical surface tension (CST), an index of wettability, through a reliable technique, and to study the influence of skin lipid and of some oil-in-water (O/W) and water-in-oil (W/O) preparations.
Method: The CST was calculated using the Zisman equation, from the contact angle at equilibrium, of droplets of liquids whose surface tension was known. Contact angles were computed from the base and the height of the droplets viewed from their side through an operating microscope provided with a slanted mirror. Both volar forearm and forehead were studied.
Results: On volar forearm, the skin CST was 27.5±2.4 dyne/cm (n=12) and normally distributed. Forehead CST was above 50.7 dyne/cm. On both areas, defatting with ether reduced CST down to 21.6±2.6 dyne/cm, and 29.3±1.7 dyne/cm, respectively ( p <0.001). Washing with soap reduced forearm CST down to 23.7±1.0 dyne/cm ( p <0.01), and occlusion down to 21.6±3.4 dyne/cm ( p <0.001). O/W cream application strongly decreased both forearm and glass slide CST, whereas W/O cream application either raised CST or left it unchanged; in all cases, changes were less marked on skin than on glass.
Conclusion: These data demonstrate that the skin surface is primarily hydrophobic and paradoxically becomes more wettable through its lipidic component, especially the sebum. Emulsions seemed to interact with the skin and change its CST as would do their continuous phase only.     

Biophysical methods of providing objective documentation of the effects of moisturizing creams

Background/aims: Moisturizers are widely used to relieve the clinical and subjective impressions of dry skin, such as roughness, scaling, and an uncomfortable feeling of tightness. Several noninvasive methods are available for objectively evaluating the physical properties of the stratum corneum and the quality of its surface. Increasing demands for scientific documentation of advertising claims have led to the use of these methods for studying skin response to moisturizers. This review provides some insight into how performance of moisturizers can be measured.
Methods: Biophysical methods for examination of skin properties, such as surface contour, scaling, surface lipids, friction, transepi-dermal water loss, hydration and elasticity are briefly described.
Conclusions: Application of moisturizers to the skin induces measurable tactile, visual and functional skin changes, which can be measured with noninvasive instruments. The use of such instruments allows objective examination and follow-up of therapeutic effects without interfering with the studied skin area.     

Skin biophysical properties of a population living in Valais, Switzerland

Background/purpose: Switzerland has one of the highest rates of skin diseases and particularly skin cancer, in Europe. Skin elastosis, roughness and atopy are also frequent. High UV exposure and prevalence of light skin individuals could be the cause. Valais, in Southern Switzerland, is a mountain region with elevated sun irradiation and low air humidity, an ideal location to study the effect of the environment and life style on skin biophysical characteristics. The purpose of the study was to measure skin biophysical parameters non‐invasively on healthy subjects living in Valais, and to correlate the measures with their life style. Methods: One hundred and ten women were examined between October 2001 and February 2002. Measures of skin hydration, sebum content, pH and visco‐elasticity were taken in a closed environment with constant temperature and controlled air humidity, utilizing commercially available non‐invasive devices. Subjects were interviewed using a questionnaire and data on personal traits and life style were collected. Correlations between subject's skin parameters and life style were statistically examined. Results: On average we observed low values of skin capacitance that identify subjects with dry skin. Measures of skin visco‐elasticity ratios were also particularly low, while skin pH and sebum content were in the normal range. Age was correlated with a decrease of skin elasticity and sebum content, but there was no correlation with hydration or pH. Conclusions: We confirm, as reported in other studies, the effect of age on skin elasticity and sebum content and we identify, for the first time, a region with a population characterized by particularly low levels of skin hydration and skin visco‐elasticity. Although people examined were free of skin diseases, we believe that protection from the sun and treatment of skin with hydrating products need to be emphasized as a prevention strategy, in regions such as Valais, with high sun irradiation and low humidity.     

Dynamic indentation on human skin in vivo: ageing effects

Background/purpose: Knowledge of the mechanical properties of the human skin is very important for cosmetic and clinical research. Objective and quantitative measurements are essential to compare studies performed by different experimenters in different centres. The aim of this paper is to present a method to measure the viscoelastic properties of human skin in vivo using dynamic indentation.
Methods: A complete device to assess the stiffness and damping of skin has been developed. The frequency and strain amplitude range from 10 to 60 Hz and from 1 to 10 μm. Tests on pure elastic inert materials have been performed to validate the device. An in vivo study including dynamic indentation, suction test, hydration measurement and topographic analysis has been performed on 46 subjects aged from 18 to 70 years, divided into three groups.
Results: Results on inert materials show the validity of the device developed. The mechanical behaviour of the skin can be described by a Kelvin–Voight model under dynamic indentation. A comparison with a suction test, hydration and topographic measurements shows that the stiffness and the damping measured by dynamic indentation correspond mainly to the natural tense state of the skin on the body due to the dermis. A weak correlation has been found between dynamic indentation and suction parameters. The complex modulus measured by dynamic indentation at 10 Hz frequency stress ranges from 7.2 ± 2.1 kPa for the oldest group to 10.7 ± 2.6 kPa for the youngest group.
Conclusion: The device presented gives convincing results. The measurement of stiffness and damping complements the viscoelastic phenomenological parameters of the suction test.     

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.     

Influence of age and hormone replacement therapy on the functional properties of the lips

Aims: To investigate the influence of age and hormonal status on some functional properties of the lips of women.
Methods: Lips properties were measured and compared through four groups of women (young with normal menses, aged with normal menses, aged and menopaused, aged, menopaused receiving hormonal replacement therapy). The following parameters were recorded: sebum excretion rate on the forehead. On the lower lip: TEWL, mechanical damping, color, tactile acuity. Moreover, capacitance images of each lips were recorded and the mean capacitance measured.
Results: Changes in TEWL, mechanical damping and tactile acuity appear clearly linked to age while the increase in lip darkness could be due to hormones. Sebum excretion rate is also clearly linked to hormonal status. Surprisingly, no changes of lips capacitance were detected vs. age or hormonal status. This study confirms that upper lip is more hydrated than the lower one.
Conclusion: Most of the parameters measured on the lips have similar variations than the same parameters measured on the skin. Only sebum and color appear being dependant on the hormonal status.     

Coefficient of friction: tribological studies in man – an overview

Background/purpose: Compared to other studies of skin, relatively few studies have focused on the friction of skin. This work reviews existing skin friction, emphasizing test apparatuses and parameters that have added to information regarding the friction coefficient. This review also outlines what factors are important to consider in future friction studies.
Methods: Past studies have utilized numerous designs for a test apparatus, including probe geometry and material, as well as various probe motions (rotational vs. linear). Most tests were performed in vivo ; a few were performed in vitro and on porcine skin.
Results: Differences in probe material, geometry and smoothness affect friction coefficient measurements. An increase in skin hydration, either through water or through moisturizer application, increases its friction coefficient; a decrease in skin hydration, either through clinical dermatitis or through alcohol addition, decreases the coefficient. Differences are present between anatomical sites. Conflicting results are found regarding age and no differences are apparent as a result of gender or race.
Conclusion: Skin friction appears to be dependent on several factors – such as age, anatomical site and skin hydration. The choice of the probe and the test apparatus also influence the measurement.     

Effect of skin pH for wrinkle formation on Asian: Korean,Vietnamese and Singaporean

Background Skin pH may be influenced by various factors, such as hydration of stratum corneum, rate of sebum excretion rate, transepidermal water loss (TEWL) and sweating in relation to skin ageing. Objective The aim of this study was to evaluate the correlation between skin pH and wrinkle formation that is directly related to ageing. In addition, we investigated the factors related to skin ageing by comparing the association between skin pH and other skin properties. Methods Three hundred volunteers were selected from three countries: Korea, Vietnam and Singapore. Hydration on the stratum corneum, the rate of sebum excretion rate, melanin index, TEWL and skin temperature on the cheek were measured in a controlled room, and wrinkle length and depth using replicas were compared with skin pH variation. Results The mean and standard deviation of skin surface pH among the three countries were 5.510 ± 0.625. The greatest gap of skin pH that revealed significant differences for skin properties was represented between the Koreans and the Vietnamese. For all three countries, skin hydration, melanin contents, wrinkle length, wrinkle depth and skin temperature were significantly correlated with skin pH. Factors related to skin moisturizing, such as skin hydration, sebum excretion rate and skin temperature, were negatively correlated with skin pH. Wrinkle length and depth decreased as skin pH became more acidic. Conclusions Skin properties displayed various values depending on skin pH. In particular, wrinkle formation significantly decreased as skin pH becomes more acidic. We conclude that skin pH is determined by skin properties, such as skin hydration, sebum excretion rate, melanin concentration, TEWL and skin temperature that affects wrinkle formation.     

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.     

Evaluation of facial skin type by sebum secretion: Discrepancies between subjective descriptions and sebum secretion

Background/aims: Facial skin is usually classified as dry, normal, and oily in the cosmetics field. However, there is no standard objective method for classifying facial skin.
Methods: We measured sebum excretion with Sebumeter^® at four sites on the face. Based on the amount of sebum secretion, we reclassified skin type according to the guidelines provided by the manufacturer. The mean of sebum excretion (mean facial sebum excretion; MFSE) was also calculated.
Results: People secrete varying amounts of sebum at different skin sites. Reclassification of skin type based on sebum secretion revealed that most participants underestimated the amount of facial sebum excretion. When sebum secretion amounts were compared, a statistically significant difference was apparent between the oily and dry skin types. However, there were no statistical differences between oily and normal, and normal and dry skin.
Conclusion: We showed that subjective skin type does not match the amount of sebum secreted. Thus, this simple and subjective classification is of very limited use and it should be re-evaluated by using an objective and standardized measuring tool.     

痤疮患者皮肤生理功能测定

目的 探讨痤疮患者面部皮肤生理功能的特点，以期指导痤疮患者的治疗。方法 选取受试对象120例，试验组为痤疮患者60例，其中男20例，女40例，平均年龄23.4岁；对照组为健康志愿者60例，其中男20例，女40例，平均年龄25.1岁。运用无创性皮肤生理功能测试仪，测量受试者的面颊及T区（油脂分泌旺盛区域）皮肤油脂、面颊皮肤弹性和水分。结果 试验组面部T区油脂量为（199.98 ± 58.21） μg/cm2，健康对照组为（117.55 ± 63.16） μg/cm2，两组差异有统计学意义（t = 7.34，P < 0.05）。试验组面颊油脂量为（154.45 ± 55.06） μg/cm2，健康对照组为（87.50 ± 47.36） μg/cm2，两组差异有统计学意义（t = 7.14，P < 0.05）。试验组皮肤弹性（0.7931 ± 0.0755R）与健康对照组（0.7882 ± 0.0498R）比较，差异无统计学意义（P > 0.05），试验组皮肤水分（30.75% ± 3.87%）与健康对照组（30.94% ± 2.91%）比较，差异也无统计学意义（P > 0.05）。结论 痤疮患者颜面皮肤油脂分泌过多。