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.     

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.     

A nonlinear elastic behavior to identify the mechanical parameters of human skin in vivo

Background/purpose: Various analyses have been performed to identify the mechanical properties of the human skin tissue in vivo . They generally use different approaches and hypotheses (behavior laws as well as mechanical tests) and the obtained results are consequently difficult to analyze and compare. In this paper, an inverse method that can be adapted to any kind of mechanical tests and behavior laws is presented.
Method: A suction deformation performed on the volar aspect of the forearm of a subject is considered. This test is modeled with the finite element method to compare the experimental and simulated curves using an inverse method that allows the skin mechanical parameters identification. This process is based on two optimization algorithms, Kalman's filter and Gauss–Newton's methods. To account for the nonlinear behavior of the skin, a specific nonlinear elastic law, which is then compared with standard linear elastic and neo-Hookean's mechanical behaviors, was developed.
Results: The obtained results first prove that neither linear elasticity nor neo-Hookean's laws can be used to model the skin. On the contrary, the nonlinear elastic model presents a relevant fit of the experimental curves. The skin thickness is also proved to be another key point to be taken into consideration.
Conclusions: The obtained results are successfully compared with literature and the reliability of the proposed method is underlined with the identification of 300 additional experimental curves. The different works we are currently focusing on are finally introduced.     

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.     

Model of the viscoelastic behaviour of skin in vivo and study of anisotropy

BACKGROUND: The single-axis extension test is relatively little used to study the mechanical properties of human skin in vivo. A campaign of tests was carried out with an original, modern machine developed in our laboratory. It can perform extension or compression tests using servo-controlled position or force in different directions. The load can either be of the extension or monotonous compression type, creep or relaxation. The results obtained were used to develop a viscoelastic model. The elastic modulus calculated helps us to determine the main directions of anisotropy on the forearm. METHODS: We use a new in vivo single-axis extension machine (patent no. FR03/09220 application in progress). With it, we can carry out monotonous, creep and relaxation tests on the forearm. An associated finite elements model enables conversion to the intrinsic parameters of the skin under stress and strain from external stress applied in force and displacement. From the tests, we can propose a viscoelastic model and the identification of his parameters. We carried out tests in four directions with respect to the axis of the forearm of 63 people of different ages. The present report is limited to a brief presentation of the experimental set-up used, and a more complete presentation of the viscoelastic model and how it is defined and also the work on the anisotropy in the elastic domain. RESULTS: The viscoelastic model proposed has only four intrinsic parameters: elasticity parameters E(e) and E(ve) and viscosity parameters epsilon(ve) and A. Skin being considered as orthotropic, we were able to determine the average main direction of 63 people, which is of 5.33+/-5.78 around the longitudinal axis of the arm. An average modulus E(1) (ave)=6.57E(5) (Pa) can be found in the direction close to the axis of the arm and E(2) (ave)=1.30E(5) (Pa) in the perpendicular direction and a G(12)=1.32E(5) (Pa) shear modulus. CONCLUSIONS: The parameters obtained with the viscoelastic model are independent of the type of load, the same coefficients enable a correct representation in creep and relaxation tests. The main directions vary from one person to another, Young's modulus in these directions could be an indicator for dermatologists and cosmeticians.     

Heel skin stiffness effect on the hind foot biomechanics during heel strike

Background: The human heel pad is a complex biological structure consisting of the fat pad and the skin. The mechanical properties of the skin layer are of significant importance to the load‐bearing function of the heel pad and human locomotion. The condition of the heel skin is also directly associated with some medical conditions such as heel ulcers that may become a site for the skin breakdown, which is the most common precursor to lower extremity amputation among persons with diabetes. It is essential to develop a detailed understanding of the properties of the heel skin layer and its effect on hind foot biomechanics during heel strike. Objectives: This work aims to gain a better insight into the biomechanical behaviour of the heel skin layer through a combined experimental and numerical study. The main objective is to characterise the biomechanical responses of the hind foot system during heel strike with potential variation of the skin stiffness based on a subject‐specific finite element (FE) model and biomechanical testing. Methods: A three‐dimensional (3D) FE model of the human hind foot incorporating a separate heel skin layer was developed based on subject‐specific medical images. An inverse FE analysis of the in vivo indentation test was carried out to study the nonlinear material property of the heel skin. The FE model was then used to study the deformation of the hind foot during heel strike in comparison with the plantar pressure measurement results and to establish the effects of stiffness of the heel skin on the stress and pressure distributions. Results: The FE foot model with subject‐specific heel skin properties was successfully used to predict the deformation of the hind foot during heel strike, and the results showed good agreements with biomechanical pressure measurements. The results showed that the high pressure and stress in the heel skin appeared in the centre region during a heel strike. Heel skin stiffness sensitivity studies showed that an increase in the skin stiffness had a limited effect on the stress and contact pressure of the hind foot bones, but caused a slight increase in the skin stresses, while skin softening caused a decrease in the peak plantar pressure and its distribution pattern changed. In addition, the results also suggest that skin softening may cause a higher stress level in the bones and ligaments. Conclusion: The nonlinear parameter of the heel skin has been successfully predicted from in vivo indentation tests based on a subject‐specific FE model. Skin properties' sensitivity tests clearly showed that the stiffness of the heel skin could have a direct effect on the biomechanics of the hind foot. The results suggest that individuals with a pathologically stiffened heel skin could exert an increase in the heel pressure, which may potentially lead to skin breakdown or ulcer.     

Influence of hydration and experimental length scale on the mechanical response of human skin in vivo, using optical coherence tomography

BACKGROUNDS/AIMS: Human skin is a complex tissue consisting of different layers. To gain better insight into the mechanical behaviour of different skin layers, the mechanical response was studied with experiments of various length scales. Also, the influence of (superficial) hydration on the mechanical response is studied. The work is based on the hypothesis that experiments with different length scales represent the mechanical behaviour of different skin layers. For suction, this means that a large aperture diameter reflects the behaviour of mainly dermis, whereas a very small diameter reflects the behaviour of only the top layer of the skin. METHODS: Suction measurements at varying pressures and aperture sizes were performed on the volar forearm of 13 subjects aged 29-47 years. The deformation of the skin was visualized using ultrasound (US) (dermis) and optical coherence tomography (OCT) (epidermis and dermis). US measurements were performed on hydrated skin, OCT measurements on dry and hydrated skin. The experiment was simulated by a finite element model (FEM) exhibiting extended Mooney material behaviour. An identification method was used to compare the experimental and numerical results to identify the parameters of the material. RESULTS: The material parameters C(10) and C(11) were calculated for four subjects: C(10)=29.6+/-21.1 kPa and C(11)=493+/-613 kPa for 6 mm aperture diameter, C(10)=11.5+/-8.7 kPa and C(11)=18.3+/-12.6 kPa for 2 mm aperture diameter and C(10)=10.8+/-9.5 kPa and C(11)=9.3+/-7.7 kPa for 1 mm aperture diameter. Skin hydration caused ambiguous effects on the mechanical response. CONCLUSIONS: US and OCT, combined with suction, using varying apertures sizes, proved to be a valuable tool to study the mechanical behaviour of different skin layers. With increasing experimental length scale, increasing values for the parameters of the material model were found. This indicates the need of a multi-layered material layer FEM, which can be used to identify mechanical behaviour of epidermis and dermis.     

Experimental and numerical study on the mechanical behavior of the superficial layers of the face

Background/purpose: This paper reports a study on the quasi‐static mechanical response of the superficial soft tissue of the face, in particular the skin and the superficial muscoloaponeurotic system (SMAS) plus the superficial fat. The mechanical characterization of soft tissues represents one of the main uncertainties of previously developed numerical models for face simulation. Methods: Two instruments based on the suction method were used for collecting experimental data: the Cutometer^® (2 mm probe aperture diameter) and the Aspiration device (8 mm). Tests were performed in five different regions of the face (jaw, nasolabial, parotideomasseteric, zygomatic and forehead) on the same subject whose magnetic resonance imaging (MRI) scans were used to generate a full 3D finite element model of the face and for whom a series of experimental results for different loading cases are already available. The mechanical parameters of the tissue layers were determined through an inverse finite element analysis. Anatomical data (tissue layers' thickness) were determined through the analysis of a set of high‐resolution MRI scans and ultrasound measurements performed in the regions tested. Results: The results of Cutometer^® measurements show a relatively homogeneous mechanical response in different face regions, while the results of aspiration device measurements, which involve deeper tissues, show a larger variability. Mechanical model parameters of the skin and SMAS were determined for two constitutive model equations: a hyperelastic model based on the Rubin–Bodner formulation and a reduced polynomial model of second order. Conclusion: The results reported in this work suggest that for simulations of the global behavior of facial soft tissue, such as craniofacial and maxillofacial surgery planning, the skin could be considered as a layer of uniform thickness and of uniform mechanical response through the different regions. Additionally, mechanical models were determined for skin and SMAS that could be used for simulations of surgical procedures requiring a distinction between these tissue layers.     

Nonlinear model of skin mechanical behaviour analysis with finite element method

Background/aims: A problem commonly encountered in plastic and reconstructive surgery is the prediction of the stress put on the skin when various types of skin flaps are used.
Methods/results: We developed a mathematical model based on the finite element method, in order to determine the stress field, by simulating the mechanical behaviour of human skin during wound closure. We chose to take into account the low compressive strength by modifying the mechanical parameters of the model at each step of the calculation. The model has been developed and tested on a diamond-shaped incision and applied on a Limberg incision.
Conclusion: The results presented are the Von Mises stress in the area of skin around the scar and, when possible, the resultant closure force. They show the relevance of the method.     

Evaluation of modifications of the traditional patch test in assessing the chemical irritation potential of feminine hygiene products

Background/aims: The first main objective of the work presented in this paper was to investigate ways of optimizing the current arm patch test protocol by (1) increasing the sensitivity of the test in order to evaluate more effectively the products that are inherently non‐irritating, and/or (2) reducing the costs of these types of studies by shortening the protocol. The second main objective was to use the results of these studies and the results of the parallel studies conducted using the behind‐the‐knee method to better understand the contribution of mechanical irritation to the skin effects produced by these types of products. In addition, we were interested in continuing the evaluation of sensory effects and their relationship to objective measures of irritation. Methods: Test materials were prepared from three, currently marketed feminine protection pads. Wet and dry samples were applied to the upper arm using the standard 24‐h patch test. Applications were repeated daily for 4 consecutive days. The test sites were scored for irritation prior to the first patch application, and 30–60 min after removal of each patch. Some test sites were treated by tape stripping the skin prior to the initial patch application. In addition, in one experiment, panelists were asked to keep a daily diary describing any sensory skin effects they noticed at each test site. Results: All protocol variations ([intact skin/dry samples], [compromised skin/dry samples], [intact skin/wet samples], and [compromised skin/wet samples]) gave similar results for the products tested. When compared to the behind‐the‐knee test method, the standard upper arm patch test gave consistently lower levels of irritation when the test sites were scored shortly after patch removal, even though the sample application was longer (24 vs. 6 h) in the standard patch test. The higher level of irritation in the behind‐the‐knee method was likely due to mechanical irritation. The sensory skin effects did not appear to be related to a particular test product or a particular protocol variation. However, the mean irritation scores at those sites where a sensory effect was reported were higher than the mean irritation scores at those sites were no sensory effects were reported. Conclusions:

• ? All four protocol variations of the standard upper arm patch test can be used to assess the inherent chemical irritant properties of feminine protection products.
• ? For these products, which are inherently non‐irritating, tape stripping and/or applying wet samples does not increase the sensitivity of the patch test method.
• ? Differences in irritation potential were apparent after one to three 24‐h applications. Therefore, the standard patch test protocol can be shortened to three applications without compromising our ability to detect differences in the chemical irritation produced by the test materials.
• ? The patch test can be used to evaluate effectively the inherent chemical irritation potential of these types of products. However, this method is not suitable for testing the mechanical irritation due to friction that occurs during product use.
• ? There is no relationship between specific test conditions, i.e., compromised skin and/or testing wet samples and reports of perceived sensory reactions.
• ? However, there seems to be a clear relationship between sensory reactions and objective irritation scores.

     

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).     

不同取皮法对白癜风自体移植表皮角质形成细胞的影响

目的 探讨负压吸疱和切削取皮对移植表皮角质形成细胞生理状态的影响。方法 免疫组化法检测32例稳定期白癜风患者两种取皮法获得的自体表皮PCNA和Caspase-3的表达情况。 结果 32例白癜风患者两种方法所取正常表皮组织皆有不同程度的PCNA表达,发疱所获表皮阳性细胞多灶状分布于基底层,切削所取表皮少数阳性细胞还见于棘层中下部,切削取皮与发疱取皮总的阳性表达率比较差异有统计学意义（χ2 = 10.99,P ＜ 0.05）,切削取皮与正常人对照比较差异无统计学意义（χ2 = 1.31,P ＞ 0.05）,而发疱取皮与正常人对照的表达差异有统计学意义（χ2 = 14.08,P ＜ 0.05）。32例白癜风患者两种方法所取皮肤组织切片皆见Caspase-3表达,主要见于基底层及棘层中下部的角质形成细胞的胞质,两两比较发现患者切削取皮、发疱取皮与正常人对照组总的阳性表达率差异无统计学意义（χ2 = 1.41、2.89、1.91,P ＞ 0.05）。结论 表皮细胞增殖功能对移植表皮的成活可能有重要的作用,切削取皮较吸疱取皮对角质形成细胞的增殖功能影响小。     

Liminal perception threshold of cutaneous distension

BACKGROUND: Cutaneous sensorial perception is complex and proves to be difficult to quantify. Skin sensitivity to mechanical distension is largely unexplored. We have developed an original method aimed at quantifiying these physiological parameters.VOLUNTEERS AND METHODS: The study was performed on 24 adult volunteers aged 20 to 50 years. A Cutometer SEM 474 equipped with 2 and 4 mm diameter probes was used to exert a progressive or a steep suction on the cheeks. The intensities of both the suction and the skin deformation observed at the earliest moment the traction was perceived by the volunteers were recorded.RESULTS: The liminar sensorial detection under progressive suction force was 1.5 times lower when using the 4 mm probe than the 2 mm probe. Suction necessary for liminar sensation was 7 times lower under steep suction than in response to the progressive mode. The skin deformation corresponding to the liminar sensorial perception was almost constant (C=0.5 p. 100) for each subject. By contrast, a large inter individual heterogeneity unrelated to age was present.COMMENTS: Sensitivity of facial skin to stretching can be explored using a precise suction method. Perception is more related to the rate of traction than to the surface area submitted to suction. Cutaneous deformation, nearly constant for each individual, appears to be the main parameter. Steep and progressive suctions appear to stimulate distinct types of mechanoreceptors. The presently described method can be applied in cosmetology and in functional investigation of various diseases such as diabetes, acromegaly and atopic dermatitis among others.     

Suction purpura.

BACKGROUND--Purpuric eruptions due to local mechanical causes are commonly seen, particularly in children. These eruptions are not always recognized as isolated purpura, and the patient may be submitted to an unnecessary extensive hematologic workup. We present various causes of suction purpura and outline a logical investigational approach. OBSERVATIONS--Suction purpura result from an external force exerting negative pressure on a circumscribed area of the skin, producing small grouped petechiae. We present a number of such suction purpura-causing mechanisms: Pressure during the delivery of a neonate, children's habits or play activities, and iatrogenic causes produce similar cutaneous lesions. We also describe the gas mask suction purpura for the first time. CONCLUSIONS--Once the causative factor is established, there is no need for further investigation or treatment of suction purpura. The lesions will fade completely within a few days.     

In vivo study of skin mechanical properties in patients with systemic sclerosis

BACKGROUND: Measurements of skin elasticity are more sensitive than the skin severity score and appropriate for evaluation of sclerodermatous skin. OBJECTIVE: Our purpose was to investigate the mechanical properties of the skin in patients with systemic sclerosis depending on the stage of the disease. METHODS: Seventeen patients, 8 with edematous phase and 9 with indurative phase of skin involvement, and 16 healthy subjects were studied. Clinical scoring of skin thickness and measurements of skin elasticity with a noninvasive suction device (Cutometer) were performed over 11 anatomic regions. RESULTS: Edematous phase was characterized by significantly lower immediate distention (Ue) and final distention (Uf), and higher viscoelastic to elastic ratio (Uv/Ue) of the skin compared with indurative phase, except for the forehead (8 mm probe). The changes in skin mechanical parameters for fingers were identical in both phases. Low values of skin distensibility correlated with severe skin thickness or hidebound skin. Results were influenced by body site and by the diameter of measuring probe used. CONCLUSION: The noninvasive method applied is suitable for objective and quantitative monitoring of skin involvement in patients with systemic sclerosis.     

Mechanics of wrinkle formation: micromechanical analysis of skin deformation during wrinkle formation in ultraviolet‐irradiated mice

Background/purpose: The mechanical aspects of wrinkle formation were studied in the dorsal skin of hairless mice. Methods: Wrinkles were induced by irradiating with ultraviolet (UV) B for 10 weeks, while observing skin deformation during wrinkle formation. Changes in skin dimensions were also observed during the specimen excision process. Wrinkle depth and interval were measured before and after removal of the cutaneous muscle layer. Local deformation of wrinkled skin during uniaxial stretch was also measured. Changes in curvature of skin specimens upon muscle layer removal were then observed to determine the force balance in skin layers. Results: The skin showed spontaneous contraction in response to UV irradiation. Wrinkled skin showed a marked decrease in the wrinkle depth and a slight increase in wrinkle interval following muscle layer removal, a peculiar mechanical response that cannot be explained by homogeneous deformation of the skin. This response was due to compressive deformations of dermal tissue caused by the muscle layer and concentrated at valleys of the wrinkles. Curvature measurements indicated that the muscle layer compressed the dermal tissue predominantly in the craniocaudal direction. Morphological observations showed that the wrinkles coincided with rows of pores and sulci cutis, where the structural stiffness of the horny layer was relatively low. The horny layer showed significant thickening. Conclusion: Taken together, we propose the following hypothetical mechanisms of wrinkle formation during UV irradiation: spontaneous contraction of the dermis while maintaining or increasing the epidermal area induces buckling of the epidermis into the dermis at mechanically weak lines, namely, the rows of pores and sulci cutis, and buckling may be amplified by the axial compression of the dermis by the muscle layer.     

Application of Cutometer area parameters for the study of human skin fatigue

BACKGROUND/AIM: The age-related decrease of skin elasticity results in larger fatigue of adult skin than young skin after applying multiple stress at one and the same anatomic region. The aim of this study was to compare the informativeness of Cutometer standard R-parameters with new area parameters regarding the age-related changes in human skin fatigue. MATERIALS/METHODS: A total of 40 healthy volunteers aged 12-82 years were studied. Mechanical parameters of the skin were determined using a non-invasive suction skin elasticity meter (Cutometer). Measurements were made on the temporal region and volar forearm. Skin mechanical parameters analyzed by Win-Cutometer MPA software were R3, R4 and R9 (R-parameters), and F2 and F3 (area parameters). RESULTS: The adult skin was characterized by significantly higher values of R4, R9 and F2, and lower F3 compared with young skin. R3 was not significantly altered. There were not any sex-related differences. F2 correlated positively with parameters R3, R4 and R9, while F3 correlated negatively with R4. A positive correlation within the parameters R3, R4 and R9 was established at both anatomic regions. CONCLUSION: The non-invasive method applied can be useful for objective and quantitative investigation of age-related changes in skin fatigue and evaluation of the effects of cosmetic and anti-aging topical products. The mechanical parameters R4 and F3 are most indicative of human skin fatigue.     

Characterisation of gravity-induced facial skin oedema using biophysical measurement techniques

Background/aims: In humans, the microgravity environment can be expected to induce swelling of facial tissues and shrinking of the tissues in the lower limbs, together with a loss in body weight. To evaluate fluid shifts in skin, the head‐down bed‐rest model was used. The aim of the present study was to evaluate the appearance of facial oedema in subjects undergoing anti‐orthostatic bed‐rest at an angle of ?10°. Methods: The forehead of each of four subjects was measured before and after 1, 10 and 24 h in this head‐down tilt position. At these time points, interstitial fluid migration and facial oedema were assessed using a high resolution B‐scan ultrasound and a device for measuring the skin's mechanical properties. Results: The results obtained showed a progressive increase in dermal thickness and initial stress, and a reduction in stiffness and elasticity of the skin during the study period. Conclusions: This preliminary study has demonstrated the feasability of the method in measuring fluid displacement and retention in the skin. Furthermore, it highlights the influence of fluids on the mechanical behaviour of the skin. These techniques could be used for studying the redistribution of liquid masses during periods spent in space.