Mechanical Properties Of Skin Research Articles

Acetyl hexapeptide-3 in a cosmetic formulation acts on skin mechanical properties - clinical study

abstract Acetyl hexapeptide-3 has been used in anti-aging topical formulations aimed at improving skin appearance. However, few basic studies address its effects on epidermis and dermis, when vehiculated in topical formulations. Thus, the objective of this study was to determine the clinical efficacy of acetyl hexapeptide-3 using biophysical techniques. For this purpose, formulations with and without acetyl hexapeptide-3 were applied to the ventral forearm and the face area of forty female volunteers. Skin conditions were evaluated after 2 and 4-week long daily applications, by analyzing the stratum corneum water content and the skin mechanical properties, using three instruments, the Corneometer(r) CM 825, CutometerSEM 575 and ReviscometerRV600. All formulations tested increased the stratum corneum water content in the face region, which remained constant until the end of the study. In contrast, only formulations containing acetyl hexapeptide-3 exhibit a significant effect on mechanical properties, by decreasing the anisotropy of the face skin. No significant effects were observed in viscoelasticity parameters. In conclusion, the effects of acetyl hexapeptide-3 on the anisotropy of face skin characterize the compound as an effective ingredient for improving conditions of the cutaneous tissue, when used in anti-aging cosmetic formulations.

Body mass index and dermal remodelling.

It is now well established that not only is raised body mass index (BMI) a risk factor for pressure ulcers and impaired wound healing but that hypertrophy of subcutaneous adipocytes is associated with remodelling of dermal collagen architecture and abundance 1. However, whilst fibrillar collagens are the most abundant proteins in the dermis, other extracellular matrix (ECM) assemblies such as those that comprise the elastic fibre system, also play key roles in mediating skin mechanical properties. Components of this elastic fibre system, whilst more sparsely distributed than dermal fibrillar collagens, confer resilience (elasticity) and crucially act as sensitive histological markers of ECM remodelling in both mild 2 and severe photo-ageing 3 and in the skin of smokers 4. Additionally, restoration of the elastic fibre architecture in the papillary dermis, which may be induced by both topical retinoids and commercial anti-ageing formulations, is also associated with a clinically measureable reduction in skin wrinkles 5. Few studies, however, have attempted to characterise the effects of raised BMI and adipocyte hypertrophy on the elastic fibre system although Orpheu and colleagues have previously reported on the differential loss of collagen but not elastin after bariatric surgery-induced weight loss 6. Previously, Ezure and Amano have shown that subcutaneous adipose tissue volume is negatively correlated with elasticity in human photo-exposed facial skin 7. Now the same investigators, in their recent study published in Experimental Dermatology, present evidence for a link between raised BMI, adipocyte hypertrophy and the loss of elastic fibres in human abdominal skin 8. Elastic fibres are complex macro-molecular assemblies 9 which adopt a well-characterised architecture in young photoprotected human skin (Fig. 1). In the reticular dermis, large diameter elastic fibres, which are rich in highly cross-linked elastin, are associated with fibrillin microfibrils. In the papillary dermis however, the ratio of elastin to fibrillin is progressively reduced until bundles of fibrillin microfibrils, known as oxytalan fibres, intercalate into the DEJ. With their recent publication in this journal, Ezure and Amano present data which suggests that, in addition to the well-characterised effects of extrinsic (photo-) and intrinsic (chronological) ageing on dermal elastic fibres, increased subcutaneous fat may also be a mediator of elastic fibre degradation. In contrast with intra-cellular proteins, structural extracellular proteins and assemblies, including elastic fibres, are thought to persist in tissues for many decades 10. As a consequence, the reduced abundance of elastic fibres in the skin of high BMI individuals is likely to be due to increased degradative activity rather than to decreased deposition. In their skin biopsies, Ezure and Amano identify increased MMP9 expression as a potential mediator of elastic fibre degradation. Whilst it is clear that this enzyme can degrade both elastin and fibrillin, it is also the case that increased MMP9 activity would be expected to impact on other dermal components such as collagen IV and collagen VII which are integral to the structure of the DEJ 11. An alternative mechanism for the loss of elastic fibres may be the increased local oxidative stress which is positively correlated with increased adipocyte hypertrophy 1. We have recently demonstrated that solar-simulated radiation (operating directly or via photodynamically produced reactive oxygen species intermediates) can selectively degrade key elastic fibre components 12. Given the potential roles played by disrupted fibrillin microfibrils in mediating downstream matrix remodelling (via the release of sequestered TGF-β or the promotion of MMP expression), it may be that selective oxidation of elastic fibre-associated components (such as fibrillin-1 and fibulin-5) could, in turn, trigger further dermal remodelling 13-15. Ezure and Amano have made an important contribution by highlighting BMI as a mediator of elastic fibre architecture in human subjects. However, as should be the case with important scientific studies, their work also raises many additional questions. First, which mechanisms drive this remodelling? Potential candidates include not only perturbations in the normal homeostasis of ECM protease expression, activation and inhibition but also the selective oxidation of cysteine, tryptophan and tyrosine-rich elastic fibre components. Second, does adipocyte hypertrophy exacerbate the effects of UV exposure? Third and most intriguingly, how rapidly are elastic fibres lost as a consequence of subcutaneous adipocyte hypertrophy and, as appears to be the case for dermal collagen, is this loss irreversible 1? The author would like to acknowledge the financial support of Walgreens Boots Alliance Inc. The authors have declared no conflicting interests.

From the rhombic transposition flap toward Z-plasty: An optimized design using the finite element method

In this paper, an optimized design for rhombic transposition flaps is created using a reliable finite element model that assures convergence for stress and deformation results. Defining a general configuration for rhombic flaps, the surgical process of wound closure is simulated for a wide variety of patterns. To address the intrinsic uncertainties associated with modelling skin's mechanical properties, four different sets of material parameters are considered, to investigate statistical measures. The results suggest that implementing the rhombic flap technique in a way similar to Z-plasty leads to an optimized surgical technique. The proposed flap, which can be employed for 60° to 90° rhombic defects, can reduce the maximum von Mises stress by 53% (on average) with respect to the Dufourmentel flap, and, in the case of a 60° defect, 43% with respect to the Limberg flap. To avoid any depressed area such as dog-ear formation, the maximum compressive principal stress is examined to assure that it remains within the limits of the stresses in the existing surgical techniques. The deformed configuration is also taken into consideration. Ease of implementation, in terms of both construction and orientation with respect to the relaxed skin tension lines, is another design feature offered by the proposed flap.

Influence of different berry thermal treatment conditions, grape anthocyanin profile, and skin hardness on the extraction of anthocyanin compounds in the colored grape juice production

To reduce the production surplus of grapes in the wine industry and, at the same time, to meet the growing demand of nutritious foods by health-conscious consumers, alternative processes with better sustainability are needed. In the production of colored grape juices for direct consumption, the application of heat on crushed grapes is a possible technology to increase extraction of anthocyanins and other phenolic compounds. To achieve this aim, three different thermal treatments were performed on crushed grapes of two different red varieties with peonidin or malvidin prevalence in the anthocyanin profile. Qualitative and quantitative differences in the chemical composition and color characteristics of the juices were evaluated to pinpoint the time–temperature combination that allowed the highest extraction of anthocyanins. Furthermore, the modification of skin mechanical properties during thermal treatment and impact of the peonidin/malvidin ratio on juice color were investigated. The use of high temperatures for short times was the most profitable time–temperature combination based on the extraction efficacy, color stability and energetic requirements.

Thresholds of cutaneous afferents related to perceptual threshold across the human foot sole.

Perceptual thresholds are known to vary across the foot sole, despite a reported even distribution in cutaneous afferents. Skin mechanical properties have been proposed to account for these differences; however, a direct relationship between foot sole afferent firing, perceptual threshold, and skin mechanical properties has not been previously investigated. Using the technique of microneurography, we recorded the monofilament firing thresholds of cutaneous afferents and associated perceptual thresholds across the foot sole. In addition, receptive field hardness measurements were taken to investigate the influence of skin hardness on these threshold measures. Afferents were identified as fast adapting [FAI (n = 48) or FAII (n = 13)] or slowly adapting [SAI (n = 21) or SAII (n = 20)], and were grouped based on receptive field location (heel, arch, metatarsals, toes). Overall, perceptual thresholds were found to most closely align with firing thresholds of FA afferents. In contrast, SAI and SAII afferent firing thresholds were found to be significantly higher than perceptual thresholds and are not thought to mediate monofilament perceptual threshold across the foot sole. Perceptual thresholds and FAI afferent firing thresholds were significantly lower in the arch compared with other regions, and skin hardness was found to positively correlate with both FAI and FAII afferent firing and perceptual thresholds. These data support a perceptual influence of skin hardness, which is likely the result of elevated FA afferent firing threshold at harder foot sole sites. The close coupling between FA afferent firing and perceptual threshold across foot sole indicates that small changes in FA afferent firing can influence perceptual thresholds.

Surface deformation tracking and modeling of soft materials.

Characterizing the mechanical properties of skin may lead to improvements in surgical scarring, burns treatments, artificial skin science, and disease detection. We present a method of validating a phase-based crosscorrelation method of material point tracking, used to measure surface deformations in soft tissues, using a silicone gel phantom. Tracking of a high spatial-resolution speckle pattern was validated using independent fluorescent microsphere markers. A finite element mesh was deformed according to the tracked speckle pattern, and used to predict the location of the markers. Predictions of microsphere location were compared to stereo-reconstructions. Under a 2900 μm indentation, markers under rms displacements of 125 μm produced a discrepancy between prediction and reconstruction of 23 μm. The same deformation conditions were used to illustrate the use of surface tracking for identifying mechanical properties. A force-driven finite element mesh, using a Neo-Hookean constitutive model, reproduced the surface deformation with an rms error of 172 μm.

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.

Effect of orally administered collagen hydrolysate on gene expression profiles in mouse skin: a DNA microarray analysis.

Dietary collagen hydrolysate has been hypothesized to improve skin barrier function. To investigate the effect of long-term collagen hydrolysate administration on the skin, we evaluated stratum corneum water content and skin elasticity in intrinsically aged mice. Female hairless mice were fed a control diet or a collagen hydrolysate-containing diet for 12 wk. Stratum corneum water content and skin elasticity were gradually decreased in chronologically aged control mice. Intake of collagen hydrolysate significantly suppressed such changes. Moreover, we used DNA microarrays to analyze gene expression in the skin of mice that had been administered collagen hydrolysate. Twelve weeks after the start of collagen intake, no significant differences appeared in the gene expression profile compared with the control group. However, 1 wk after administration, 135 genes were upregulated and 448 genes were downregulated in the collagen group. This suggests that gene changes preceded changes of barrier function and elasticity. We focused on several genes correlated with functional changes in the skin. Gene Ontology terms related to epidermal cell development were significantly enriched in upregulated genes. These skin function-related genes had properties that facilitate epidermal production and differentiation while suppressing dermal degradation. In conclusion, our results suggest that altered gene expression at the early stages after collagen administration affects skin barrier function and mechanical properties. Long-term oral intake of collagen hydrolysate improves skin dysfunction by regulating genes related to production and maintenance of skin tissue.

Thresholds of skin sensitivity are partially influenced by mechanical properties of the skin on the foot sole.

Across the foot sole, there are vibration and monofilament sensory differences despite an alleged even distribution of cutaneous afferents. Mechanical property differences across foot sole sites have been proposed to account for these differences. Vibration (VPT; 3 Hz, 40 Hz, 250 Hz), and monofilament (MF) perception threshold measurements were compared with skin hardness, epidermal thickness, and stretch response across five foot sole locations in young healthy adults (n = 22). Perceptual thresholds were expected to correlate with all mechanical property measurements to help address sensitivity differences between sites. Following this hypothesis, the MedArch was consistently found to be the thinnest and softest site and demonstrated the greatest sensitivity. Conversely, the Heel was found to be the thickest and hardest site, and was relatively insensitive across perceptual tests. Site differences were not observed for epidermal stretch response measures. Despite an apparent trend of elevated sensory threshold at harder and thicker sites, significant correlations between sensitivity measures and skin mechanical properties were not observed. Skin hardness and epidermal thickness appeared to have a negligible influence on VPT and minor influence on MF within this young healthy population. When normalized (% greater or smaller than subject mean) to the subject mean for each variable, significant positive correlations were observed between MF and skin hardness (R2 = 0.422, P < 0.0001) and epidermal thickness (R2 = 0.433, P < 0.0001) providing evidence that skin mechanics can influence MF threshold. In young healthy adults, differences in sensitivity are present across the foot sole, but cannot solely be accounted for by differences in the mechanical properties of the skin.

Conformal piezoelectric systems for clinical and experimental characterization of soft tissue biomechanics

Mechanical assessment of soft biological tissues and organs has broad relevance in clinical diagnosis and treatment of disease. Existing characterization methods are invasive, lack microscale spatial resolution, and are tailored only for specific regions of the body under quasi-static conditions. Here, we develop conformal and piezoelectric devices that enable in vivo measurements of soft tissue viscoelasticity in the near-surface regions of the epidermis. These systems achieve conformal contact with the underlying complex topography and texture of the targeted skin, as well as other organ surfaces, under both quasi-static and dynamic conditions. Experimental and theoretical characterization of the responses of piezoelectric actuator-sensor pairs laminated on a variety of soft biological tissues and organ systems in animal models provide information on the operation of the devices. Studies on human subjects establish the clinical significance of these devices for rapid and non-invasive characterization of skin mechanical properties.

Aging effect on tactile perception: Experimental and modelling studies

We investigated the effects of aging on tactile perception. Ageing reduces the elasticity and extensibility of the skin throughout the epidermis, dermis and subcutaneous tissues, which greatly affects their mechanical properties as well as the layer thickness. These changes lead to a decrease in the overall Young modulus of the skin and the skin ability to detect different textures. The effects of ageing on touch perception are studied by means of experimental work and finite element simulations. Ageing behaviors are studied through the investigation of the skin geometrical and mechanical properties. As an experimental approach, we have developed two different systems: the air flow system to identify the rheological properties of the skin and the tribo-haptic system which allows the quantification of the vibrations transmitted to the finger in a tactile perception test. To better understand the mechanics of touch and the effect of ageing, new 2D finite element models of a viscoelastic multilayer finger are developed under ABAQUS environment. These models simulate the friction (finger/surface) of two groups of healthy young and old men in order to understand the effect of ageing on tactile perception and calculate the vibrations transmitted through the human finger tissue during a touch test under the same experimental conditions. The decline in tactile sensory capacity in older subjects has been highlighted. Results proved that the sense of touch decreases with age.

Estrogen mediates the mechanical properties of skin and prevents elastic fibre degeneration

Estrogen mediates the mechanical properties of skin and prevents elastic fibre degeneration

Compressive viscoelasticity of freshly excised mouse skin is dependent on specimen thickness, strain level and rate.

Although the skin’s mechanical properties are well characterized in tension, little work has been done in compression. Here, the viscoelastic properties of a population of mouse skin specimens (139 samples from 36 mice, aged 5 to 34 weeks) were characterized upon varying specimen thickness, as well as strain level and rate. Over the population, we observed the skin’s viscoelasticity to be quite variable, yet found systematic correlation of residual stress ratio with skin thickness and strain, and of relaxation time constants with strain rates. In particular, as specimen thickness ranged from 211 to 671 μm, we observed significant variation in both quasi-linear viscoelasticity (QLV) parameters, the relaxation time constant (τ1 = 0.19 ± 0.10 s) and steady-state residual stress ratio (G∞ = 0.28 ± 0.13). Moreover, when τ1 was decoupled and fixed, we observed that G∞ positively correlated with skin thickness. Second, as steady-state stretch was increased (λ∞ from 0.22 to 0.81), we observed significant variation in both QLV parameters (τ1 = 0.26 ± 0.14 s, G∞ = 0.47 ± 0.17), and when τ1 was fixed, G∞ positively correlated with stretch level. Third, as strain rate was increased from 0.06 to 22.88 s−1, the median time constant τ1 varied from 1.90 to 0.31 s, and thereby negatively correlated with strain rate. These findings indicate that the natural range of specimen thickness, as well as experimental controls of compression level and rate, significantly influence measurements of skin viscoelasticity.

A new water absorbable mechanical Epidermal skin equivalent: The combination of hydrophobic PDMS and hydrophilic PVA hydrogel

Research on human skin interactions with healthcare and lifestyle products is a topic continuously attracting scientific studies over the past years. It is possible to evaluate skin mechanical properties based on human or animal experimentation, yet in addition to possible ethical issues, these samples are hard to obtain, expensive and give rise to highly variable results. Therefore, the design of a skin equivalent is essential. This paper describes the design and characterization of a new Epidermal Skin Equivalent (ESE). The material resembles the properties of epidermis and is a first approach to mimic the mechanical properties of the human skin structure, variable with the length scale.The ESE is based on a mixture of Polydimethyl Siloxane (PDMS) and Polyvinyl Alcohol (PVA) hydrogel cross-linked with Glutaraldehyde (GA). It was chemically characterized by XPS and FTIR measurements and its cross section was observed by macroscopy and cryoSEM.Confocal Microscope analysis on the surface of the ESE showed an arithmetic roughness (Ra) between 14–16μm and contact angle (CA) values between 50–60°, both of which are close to the values of in vivo human skins reported in the literature. The Equilibrium Water Content (ECW) was around 33.8% and Thermo Gravimetric Analysis (TGA) confirmed the composition of the ESE samples. Moreover, the mechanical performance was determined by indentation tests and Dynamo Thermo Mechanical Analysis (DTMA) shear measurements. The indentation results were in good agreement with that of the target epidermis reported in the literature with an elastic modulus between 0.1–1.5MPa and it showed dependency on the water content. According to the DTMA measurements, the ESE exhibits a viscoelastic behavior, with a shear modulus between 1–2.5MPa variable with temperature, frequency and the hydration of the samples.

The contributions of skin structural properties to the friction of human finger-pads

This paper describes three series of tests that were designed to investigate how skin mechanical and structural properties, measured using a ‘Cutometer’ and optical coherence tomography, affect the frictional behaviour of human finger-pads. First, the skin mechanical properties across all fingers and the palm in participants’ dominant hands were assessed. Results showed that the distensibility of skin (total deformation in a suction test) is associated with stratum corneum thickness and that this in turn affects friction (thicker stratum corneum leads to higher friction), giving a link between distensibility and friction. Tape stripping to remove the superficial layer of the skin led to increased moisture (and/or electric charge on the skin surface) that led to higher friction. No accompanying changes were seen in structural properties, so it was concluded that moisture was the main cause of the adhesion increase. More work is required to isolate moisture and possible changes in electric charge using alternative measurement techniques. When rubbing with sand-paper, the stratum corneum thinned considerably and friction reduced. Moisture was ruled out as a cause of friction changes in this instance. Skin normal stiffness also did not change, but lateral stiffness changes have been seen in previous work when the stratum corneum thickness has been reduced, so this is likely to be the cause of the reduced friction. This will be investigated further in future work using dynamic optical coherence tomography measurements.

Relationship of subcutaneous tissue and mechanical properties of skin

Relationship of subcutaneous tissue and mechanical properties of skin

J1610105 ウェアラブル皮膚振動センサの応用に関する基礎検討 : 接触力がセンサ出力に及ぼす影響

We have developed a wearable tactile sensor using a PVDF film, which detects skin-propagated vibration based on the mechanical interaction between the fingertip and the object. The sensor allows users to touch the object with bare fingertips. The output from this sensor involves in each user's skin mechanical properties as well as touch object and behavior such as contact force and scanning velocity. The sensor has a potential of the evaluation of individual tactile sensations and tactile communications. In this paper, influence of the contact force on the sensor output is investigated. The result shows that the contact force affects the intensity and frequency response of the sensor output.

Natural and sun-induced aging of human skin.

With worldwide expansion of the aging population, research on age-related pathologies is receiving growing interest. In this review, we discuss current knowledge regarding the decline of skin structure and function induced by the passage of time (chronological aging) and chronic exposure to solar UV irradiation (photoaging). Nearly every aspect of skin biology is affected by aging. The self-renewing capability of the epidermis, which provides vital barrier function, is diminished with age. Vital thermoregulation function of eccrine sweat glands is also altered with age. The dermal collagenous extracellular matrix, which comprises the bulk of skin and confers strength and resiliency, undergoes gradual fragmentation, which deleteriously impacts skin mechanical properties and dermal cell functions. Aging also affects wound repair, pigmentation, innervation, immunity, vasculature, and subcutaneous fat homeostasis. Altogether, age-related alterations of skin lead to age-related skin fragility and diseases.

Preparation and characterisation of antibacterial silver-containing nanofibres for wound healing in diabetic mice

Impaired wound healing is a common complication of diabetes mellitus. Nanofibre can be served as powerful tools in advanced wound care management. The aim of this work is to evaluate the role of antibacterial nanofibres by incorporating silver nanoparticles into celluose acetate nanofibres as wound dressing on excisional wound healing in diabetic mice. Celluose acetate nanofibres were prepared by electrospinning technique. The prepared nanofibres were characterised using scanning electron microscope (SEM), and Fourier-transform infrared (FTIR) spectrophotometer. The antimicrobial activity was tested against Gram-positive and Gram-negative bacteria. A full thickness of the excision wound of circular area 95 mm2 and 2 mm depth was created. Wound dressed by silver containing nanofibres, the wound closure rate were assessed, skin wounds were processed for histopathological examination and comparing the mechanical properties of healed skin. It was found that, wounds dressed with silver containing nanofibres showed marked increase in collagen production which improve the skin mechanical properties.

Depth Evaluation of Soft Tissue Mimicking Phantoms Using Surface Acoustic Waves

Surface acoustic wave (SAW) shows advantages in revealing skin mechanical properties. In this paper, we evaluates the elasticity of tissue mimicking phantoms by inversion of SAWs phase velocity to Young's Modulus, the estimated SAWs evaluating depth is determined based on the assumption of that SAWs penetration approximately equals one wavelength. The tissue mimicking phantoms are made of agar with concentration of 1%, 2% and 3%. Their elasticity tested from our system is 13.3kPa, 53.4kPa and 257.9kPa respectively, with expected gradient. The evaluation depth is then estimated as 0.542mm to 3.403mm underneath the phantom surface, which indicates that this method is suitable to measure elasticity in dermis layer of skin.