Tensile Properties Of Skin Research Articles

Resolving the viscoelasticity and anisotropy dependence of the mechanical properties of skin from a porcine model.

The mechanical response of skin to external loads is influenced by anisotropy and viscoelasticity of the tissue, but the underlying mechanisms remain unclear. Here, we report a study of the main effects of tissue orientation (TO, which is linked to anisotropy) and strain rate (SR, a measure of viscoelasticity), as well as the interaction effects between the two factors, on the tensile properties of skin from a porcine model. Tensile testing to rupture of porcine skin tissue was conducted to evaluate the sensitivity of the tissue modulus of elasticity (E) and fracture-related properties, namely maximum stress (σU) and strain (εU) at σU, to varying SR and TO. Specimens were excised from the abdominal skin in two orientations, namely parallel (P) and right angle (R) to the torso midline. Each TO was investigated at three SR levels, namely 0.007-0.015 s(-1) (low), 0.040 s(-1) (mid) and 0.065 s(-1) (high). Two-factor analysis of variance revealed that the respective parameters responded differently to varying SR and TO. Significant changes in the σU were observed with different TOs but not with SR. The εU decreased significantly with increasing SR, but no significant variation was observed for different TOs. Significant changes in E were observed with different TOs; E increased significantly with increasing SR. More importantly, the respective mechanical parameters were not significantly influenced by interactions between SR and TO. These findings suggest that the trends associated with the changes in the skin mechanical properties may be attributed partly to differences in the anisotropy and viscoelasticity but not through any interaction between viscoelasticity and anisotropy.

Asymmetric facial skin viscoelasticity during climacteric aging.

BackgroundClimacteric skin aging affects certain biophysical characteristics of facial skin. The purpose of the present study was to assess the symmetric involvement of the cheeks in this stage of the aging process.MethodsSkin viscoelasticity was compared on both cheeks in premenopausal and post-menopausal women with indoor occupational activities somewhat limiting the influence of chronic sun exposure. Eighty-four healthy women comprising 36 premenopausal women and 48 early post-menopausal women off hormone replacement therapy were enrolled in two groups. The tensile characteristics of both cheeks were tested and compared in each group. A computerized suction device equipped with a 2 mm diameter hollow probe was used to derive viscoelasticity parameters during a five-cycle procedure of 2 seconds each. Skin unfolding, intrinsic distensibility, biological elasticity, and creep extension were measured.ResultsBoth biological elasticity and creep extension were asymmetric on the cheeks of the post-menopausal women. In contrast, these differences were more discrete in the premenopausal women.ConclusionFacial skin viscoelasticity appeared to be asymmetric following menopause. The possibility of asymmetry should be taken into account in future studies of the effects of hormone replacement therapy and any antiaging procedure on the face in menopausal women.

Connexin43 Carboxyl-Terminal Peptides Reduce Scar Progenitor and Promote Regenerative Healing Following Skin Wounding

Gap-junctional connexin43 (Cx43) has roles in multiple aspects of skin wound healing - including scarring. The aim here was to study the effects of a cell-permeant peptide from the Cx43 carboxyl-terminus (CT) on scarring and regeneration following cutaneous injury. The effects of Cx43 CT peptide were studied in mouse and pig models of cutaneous injury. The parameters assessed included neutrophil density, wound closure, granulation, regeneration and skin tensile properties. Cx43 CT-peptide prompted decreases in area of scar progenitor tissue and promoted restoration of dermal histoarchitecture and mechanical strength following wounding of skin. These changes in healing were preceded by peptide-induced reduction in inflammatory neutrophil infiltration and alterations in the organization of epidermal Cx43, including increased connexon aggregation. Cx43 CT peptide promotes regenerative healing of cutaneous wounds and may have applications in tissues other than skin, including heart, cornea and spinal cord.

128 A New Method to Evaluate the Biomechanical Properties of Skin in a Porcine Model

Aims: A method to test the axial and transverse tensile properties of skin was developed in order to improve our understanding of the mechanical behavior of skin, and how it changes with the scarring response. This experimental technique was used to investigate the bidirectional mechanics of skin in the juvenile Yorkshire pig model. Methods: Skin samples were taken upon sacrifice, and all subcutaneous tissue was carefully removed via dissection. Dumbbell-shaped specimens were obtained from the skin using a custom designed stainless steel punch, to provide consistent geometry, and to avoid stress concentrations that can result from specimen gripping. Samples were taken in the axial (cranial-caudal) and transverse (dorsal-ventral) directions. Specimens were secured in an INSTRON universal test machine with serrated soft tissue grips, elongated to a desired preload, subjected to a 10% elongation and held for a 4-min isometric period. They were then returned to the original length and failed in tension at constant velocity. Results: This method of sample preparation indicated high repeatability in specimen geometry, showing standard deviations of 2% and 3% in gauge length and width, respectively (N = 12). Furthermore, no slippage was observed at the skin/grip interface, and all failures occurred within the specimen gauge length. Conclusions: This technique shows great promise for evaluating the viscoelastic and failure properties of skin, scar tissue, and pathologic scarring. Combining this biomechanical method with our parallel studies in molecular biology and biochemistry can likely produce correlations between constituent material organization and the mechanical properties of the tissue, as well as provide valuable information for the design of bioengineered tissue constructs. Acknowledgments: Alberta Ingenuity Fund, CIHR, and NSERC

Objective Evaluation of the Placebo Effect in Cosmetic Treatments. A Randomized Controlled Study

A product's packaging and claimed efficacy may stimulate pleasant emotions during the use of cosmetics, thus enhancing their perceived benefits. The aim of this study was to evaluate if smart packaging and strongly claimed efficacy attributes can influence the objectively measured efficacy, allowing a true placebo effect to be associated with a given cosmetic treatment. A marketed anti‐aging gluconolactone‐based formulation was selected for the study and packaged both in a fancy sophisticated jar and in an unbranded plain container. Thirty‐six female volunteers (age range: 30‐‐55 years) with facial photoageing were selected for the study and randomly assigned to the fancy or plain packaged product. Pre‐agreed messages aimed at extolling the product's cosmetic effects accompanied delivery of the fancy‐packaged product to panellists. The given product was applied to the face twice a day for 8 weeks. Instrumental measurements of the skin colour (a* and L* parameter), skin capacitance, skin tensile properties (R0, R2, R6), skin thickness and skin microrelief parameters (Ra and Rz) were taken at baseline and after 4 and 8 weeks of use. Clinical and subjective evaluations were also carried out at each control visit. Moreover, the amount of cream consumed during usage was calculated by weighing the given jars at each visit. Statistical analysis of the data obtained showed a significant improvement in all instrumental parameters for both groups (‘fancy’ and ‘plain’ packaging), although no significant differences were detected between the two groups at any time. The improvement was higher in the ‘plain’ group for most instrumental parameters except for micro‐relief parameters where the outcome was better in the ‘fancy’ group. Promotion of facial muscle relaxation deriving from the application of the fancy‐packaged cream could be a possible explanation for this finding. Also the product's efficacy and sensory properties were perceived with a higher positive impact in the fancy group. The better performance of the plain packaging group could be related to daily application of the ‘proper’ amount of cream. In fact, this group consumed a larger amount of cream than the ‘fancy’ group. These results show that a true placebo effect cannot be induced by packaging characteristics, although they can slightly influence the degree of the expected skin benefits in different ways. Moreover, proper daily dosage of the product appears to be a key factor in improving the biophysical skin properties related to anti‐ageing and restoring effects.Paper presented at the IFSCC Conference 2005, Florence, Italy.

Measurements of the Tensile Properties of Skin in vivo and in vitro-A Study of Relationship between Tensile Properties of Skin and Clothing Materials-

The tensile properties of skin in vivo and in vitro were investigated experimentally. The uniaxial and biaxial extension properties of the back of a hand in vivo and chicken skin in vitro are measured in detail by using a fine tensile tester. We found that their initial properties characteristically have extreme nonlinearity and hysteresis. These properties are similar to the properties of fiber assemblies, that is, woven and knitted fabrics used for clothing materials. The stress relaxation of chicken skin in vitro was also investigated. The results show the strain and temperature dependence of these properties. These properties of skin should be considered as basic data related to the materials of products used in close contact with the human skin, for example, clothing materials.

Skin tensile properties revisited during ageing. Where now, where next?

Skin and its subcutaneous layer represent a complex composite of tissues, whose mechanical characteristics depend upon the mutual interdependence of their constituent parts. The molecular and microanatomical structures of skin allow it to meet normal mechanical demands. They also determine the orientation both of Langer's lines and of relaxed skin tension lines. Ageing, photodamage, hormones, drugs, cosmetic products and dermatological interventions may modify the skin's overall tensile properties. In turn, any variation in mechanical stresses and strains imposed upon the skin's connective tissue influences the metabolic activity and phenotypic expression of fibroblasts and dermal dendrocytes. The viscoelastic functions of ageing skin can be tested by altering the orientation and magnitude of imposed stresses and strains over time. Assessment can be made of various biomechanical properties of skin: tensile, torsional, acoustic shear wave, indentation, impact and elevation. Such objective biomechanical assessments may be applied to dermocosmetic interventions, so providing opportunity for progress in cosmetic dermatological science.

Skin Tensile Properties in Patients Treated for Acromegaly

Background: Somatotropic effects are described in the skin. Indeed, acromegaly is in part clinically recognized by cutaneous coarsening. The actual changes in tensile properties associated with the cutaneous manifestations are largely unknown. Objectives: To study the relationships between the skin tensile properties and the severity of acromegaly as assessed by serum levels of growth hormone (GH) and insulin-like growth factor 1 (IGF-1). Patients and Method: Assessments were made in 13 patients with acromegaly treated by somatostatin agonists combined or not with surgery. A total of 39 age- and sex-matched healthy subjects served as controls. Skin tensile properties were measured on the forearm and nape of the neck using a computerized suction device. Results: Significant differences were yielded between the skin tensile properties in patients and normal subjects. The highest IGF-1 values in the patients’ medical records were positively correlated with both skin distensibility and biologic elasticity. The most recent IGF-1 serum levels were negatively correlated with the visco-elastic ratio. No correlations were yielded between any of the biomechanical parameters and GH levels, disease duration and treatment dosages, respectively. Conclusion: The skin in acromegaly appears to be functionally more redundant and elastic than normal skin. The biomechanical changes appear quite different from those observed in other diseases with collagen deposition such as diabetes mellitus and scleroderma.

Comparative effect of hormone replacement therapy on bone mass density and skin tensile properties

Objectives: connective tissues constitutive of skin and bones are affected during the climacteric. Hormone replacement therapy (HRT) can help mitigate their atrophy. The aim of this study was to compare the HRT effect on the skin tensile properties and bone mass density. Methods: a total of 120 postmenopausal women (60 untreated, 60 receiving HRT) were enrolled in the study. Skin tensile properties were assessed on the volar forearm using a computerized suction device. A 500 mbar suction was applied through a 4-mm diameter hollow probe. Two operating modes were applied using a steep and a progressive suction, respectively. BMD was measured on the hip, femoral neck and lumbar spine using dual X-ray absorptiometry. Results: in both groups of women skin elasticity was correlated with BMD. HRT significantly reduced the climacteric-associated decline in skin elasticity. A trend in better preserved BMD was also found in these women without, however, reaching significance. Conclusions: it is concluded that measures of the skin tensile properties can be sensitive enough to disclose HRT efficacy upon connective tissue atrophy. Any decrease in skin elasticity during the climacteric should prompt to perform a BMD assessment.

Tensile properties of relaxed excised skin exhibiting striae distensae

Tensile properties of skin determine some important physical attributes of skin. They may be conveniently assessed using recent technologies. The aim of the study was to compare ex vivo the tensile properties of normal looking skin and striae distensae. The Cutometer was used with 2 and 4 mm diameter probes. Skin distensibility values were dependent on the suction force and area of the skin tested. Conversely, tensile ratios yielding elasticity parameters were not affected by the same variables. Although tensile properties of excised normal skin resembled thosepreviouslyreported in vivo, striaedistensae showed markedly different properties in vivo and ex vivo. The ex vivo and in vivo evaluations of the tensile properties and functions of skin are complementary particularly when the connective tissue is abnormal.

Ageing in the sun parlour

Photoageing of the dermis was often ascribed to chronic sun exposure. By contrast, it was traditionally thought that a tanning bed was not harmful. However, recent evidence suggests that UVA could contribute to the risk of skin cancers. Furthermore, UVA could affect the dermal structures and modify their physical properties. The objective of this study was to evaluate the effect of iterative sunbed irradiations upon the tensile properties of skin. A computerized suction devise was used to derive measures of skin extensibility, elasticity and hysteresis. The skin colour was assessed using the so-called individual typology angle (ITA degrees ). The longitudinal study consisted of quarterly measurements performed over 5 years in two groups of 20 women who frequented or did not use tanning salons. Frequent UVA suberythemal irradiations for indoor tanning induced skin slackness corresponding to an increase in extensibility and hysteresis and to a parallel reduction in elasticity. Variations in the two latter rheological parameters were correlated with ITA degrees values. It is concluded that the unremitting frequentation of a sun parlour fuels a functional decline of the dermis resembling premature ageing.

Gravitational Syndrome and Tensile Properties of Skin in the Elderly

Background: To evaluate the influence of gravitational edema due to chronic venous insufficiency upon the tensile properties of skin. Method: A total of 30 women aged 66–75 years participated in the study. Evaluations were made twice in the same subjects following the use or nonuse of daytime elastic compression. Mechanical properties of the skin were measured in the midportion of the legs using a computerized suction device. Results: The consistency of skin which shows abnormal rheological characteristics at the site of gravitational edema was significantly modified by compression therapy. Both skin extensibility and hysteresis were increased after wearing tight stockings although the biologic elasticity remained unchanged. Conclusion: Noninvasive measurements of the tensile properties of the skin represent an objective assessment of the severity of leg edema and of its correction by compression therapy.

A method for obtaining repeatable measurements of the tensile properties of skin at low strain

Initial attempts at measuring the low strain tensile properties of skin led to results which were not repeatable. It appeared that strains induced in the sample due to the handling needed to mount it in a simple clamp led to the low precision of the test. A new method which minimized the manipulation needed to mount a sample in a testing machine was then developed. Using this method the skin was aligned with a set of grips in a saline bath. When aligned, the saline was removed and the sample clamped in the grips without the need for additional handling. This approach produced a marked improvement in the repeatability of the tensile properties of skin at low strains.