Elastic properties of human skin: relation to age, sex, and anatomical region

In the face and neck, keloid scar distribution is related to skin thickness and stiffness changes associated with movement

Keloid scars tend to occur in high-tension sites due to mechanical stimuli that are involved in their development. To date, a detailed analysis of keloid distribution focused specifically on facial and neck areas has not been reported, and limited literature exists as to the related mechanical factors. To rectify this deficiency of knowledge, we first quantified the facial and neck keloid distribution observed clinically in 113 patients. Subsequently, we performed a rigorous investigation into the mechanical factors and their associated changes at these anatomic sites in healthy volunteers without a history of pathologic scarring. The association between keloid-predilection sites and sebaceous gland-dense and acne-prone sites was also examined. To assess skin stretch, thickness and stiffness, VECTRA, ultrasound and indentometer were utilised. Baseline skin stiffness and thickness were measured, as well as the magnitude of change in these values associated with facial expression and postural changes. Within the face and neck, keloids were most common near the mandibular angle (41.3%) and lateral submental (20.0%) regions. These areas of increased keloid incidence were not associated with areas more dense in sebaceous glands, nor linked consistently with acne-susceptible regions. Binomial logistic regression revealed that changes in skin stiffness and thickness related to postural changes significantly predicted keloid distribution. Skin stiffness and thickness changes related to prolonged mechanical forces (postural changes) are most pronounced at sites of high keloid predilection. This finding further elucidates the means by which skin stretch and tension are related to keloid development. As a more detailed analysis of mechanical forces on facial and neck skin, this study evaluates the nuances of multiple skin-mechanical properties, and their changes in a three-dimensional framework. Such factors may be critical to better understanding keloid progression and development in the face and neck.

Discovery of matrix metalloproteinase inhibitors as anti-skin photoaging agents

Photodamage is the result of prolonged exposure of the skin to sunlight. This exposure causes an overexpression of matrix metalloproteinases (MMPs), leading to the abnormal degradation of collagen in the skin tissue and resulting in skin aging and damage. This review presents a detailed overview of MMPs as a potential target for addressing skin aging. Specifically, we elucidated the precise mechanisms by which MMP inhibitors exert their anti-photoaging effects. Furthermore, we comprehensively analyzed the current research progress on MMP inhibitors that demonstrate significant inhibitory activity against MMPs and anti-skin photoaging effects. The review also provides insights into the structure-activity relationships of these inhibitors. Our objective in conducting this review is to provide valuable practical information to researchers engaged in investigations on anti-skin photoaging.

A Scoping Review of Hyaluronidase Use in Managing the Complications of Aesthetic Interventions

BACKGROUND

Hyaluronidase is used as an adjunct or main treatment to manage complications associated with cosmetic hyaluronic acid (HA) filler injections such as necrosis, blindness, hypersensitivity, delayed nodules, and poor aesthetic outcomes.

OBJECTIVE

To systematically map the available evidence and identify the gaps in knowledge on the effectiveness of hyaluronidase use in managing the aesthetic complications associated with HA injections (vascular occlusion, blindness, nodules, delayed hypersensivity, granuloma, poor aesthetic outcome).

METHODS

PubMed, Medline, Embase and Cochrane databases were used up to May 2022, to look for randomized clinical trials (RCTs), clinical trials, and retrospective case-control studies reporting on the use of hyaluronidase for managing the HA filler injection complications.

RESULTS

The database search yielded 395 studies; of those 5 RCTs (all carried out in the USA) were selected (53 subjects), indicating the effectiveness of hyaluronidase for removal of un-complicated injected HA nodules (forearm, upper arm, or back skin). The follow-ups ranged from 14 days to 4 years. The amount of HA filler injected into each site varied from 0.2 to 0.4 mL. A dose dependent response was observed for most HA fillers. No major adverse reactions were reported. Overall, for removal of every 0.1 mL of HA filler they injected 1.25-37.5 units of hyaluronidase (single injections). When 3 consecutive weekly hyaluronidase injection was used much lower doses of 0.375-2.25 unit was utilised. There was no evidence in a form of RCTs, clinical trials, and retrospective case-control studies on the removal/reversal of HA injections in the facial skin, or management of over-corrections, inflammatory nodules, or tissue ischemia/necrosis associated with HA filler injection.

CONCLUSION

Based on studies on the forearm, upper arm and back skin, hyaluronidase can be used for the reversal of uncomplicated HA filler injection nodule. However, further adequately powered studies are warranted to establish the ideal treatment protocol/dose of hyaluronidase for reversal of HA filler injections in the facial region or management of complications associated with aesthetic HA injection.

LEVEL OF EVIDENCE III

This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

In vivo measurement of the biomechanical properties of human skin with motion-corrected Brillouin microscopy

Biomechanical testing of human skin in vivo is important to study the aging process and pathological conditions such as skin cancer. Brillouin microscopy allows the all-optical, non-contact visualization of the mechanical properties of cells and tissues over space. Here, we use the combination of Brillouin microscopy and optical coherence tomography for motion-corrected, depth-resolved biomechanical testing of human skin in vivo. We obtained two peaks in the Brillouin spectra for the epidermis, the first at 7 GHz and the second near 9-10 GHz. The experimentally measured Brillouin frequency shift of the dermis is lower compared to the epidermis and is 6.8 GHz, indicating the lower stiffness of the dermis.

Strategies in surface engineering for the regulation of microclimates in skin-medical product interactions

There is a growing number of personal healthcare devices that are in prolonged contact with the skin. The functionality of these products is linked to the interface formed by the contact between the medical apparatus and the skin. The interface can be characterised by its topology, compliance, and moisture and thermal regulating capabilities. Many devices are, however, described to have suboptimal and occlusive contacts, resulting in physiological unfavourable microclimates at the interface. The resulting poor management of moisture and temperature can impact the functionality and utility of the device and, in severe cases, lead to physical harm to the user. Being able to control the microclimate is therefore expected to limit medical-device related injuries and prevent associated skin complications. Surface engineering can modify and potentially enhance the regulation of the microclimate factors surrounding the interface between a product's surface and the skin. This review provides an overview of potential engineering solutions considering the needs for, and influences on, regulation of temperature and moisture by considering the skin-medical device interface as a system. These findings serve as a platform for the anticipated progress in the role of surface engineering for skin-device microclimate regulation.

Exploring uncertainty in hyper-viscoelastic properties of scalp skin through patient-specific finite element models for reconstructive surgery

Understanding skin responses to external forces is crucial for post-cutaneous flap wound healing. However, the in vivo viscoelastic behavior of scalp skin remains poorly understood. Personalized virtual surgery simulations offer a way to study tissue responses in relevant 3D geometries. Yet, anticipating wound risk remains challenging due to limited data on skin viscoelasticity, which hinders our ability to determine the interplay between wound size and stress levels. To bridge this gap, we reexamine three clinical cases involving scalp reconstruction using patient-specific geometric models and employ uncertainty quantification through a Monte Carlo simulation approach to study the effect of skin viscoelasticity on the final stress levels from reconstructive surgery. Utilizing the generalized Maxwell model via the Prony series, we can parameterize and efficiently sample a realistic range of viscoelastic response and thus shed light on the influence of viscoelastic material uncertainty in surgical scenarios. Our analysis identifies regions at risk of wound complications based on reported threshold stress values from the literature and highlights the significance of focusing on long-term responses rather than short-term ones.

Sex- and age-dependent skin mechanics-A detailed look in mice

Skin aging is of immense societal and, thus, scientific interest. Because mechanics play a critical role in skin's function, a plethora of studies have investigated age-induced changes in skin mechanics. Nonetheless, much remains to be learned about the mechanics of aging skin. This is especially true when considering sex as a biological variable. In our work, we set out to answer some of these questions using mice as a model system. Specifically, we combined mechanical testing, histology, collagen assays, and two-photon microscopy to identify age- and sex-dependent changes in skin mechanics and to relate them to structural, microstructural, and compositional factors. Our work revealed that skin stiffness, thickness, and collagen content all decreased with age and were sex dependent. Interestingly, sex differences in stiffness were age induced. We hope our findings not only further our fundamental understanding of skin aging but also highlight both age and sex as important variables when conducting studies on skin mechanics. STATEMENT OF SIGNIFICANCE: Our work addresses the question, "How do sex and age affect the mechanics of skin?" Answering this question is of both scientific and societal importance. We do so in mice as a model system. Thereby, we hope to add clarity to a body of literature that appears divided on the effect of both factors. Our findings have important implications for those studying age and sex differences, especially in mice as a model system.

Correlating facial skin parameters with age and gender in population of Shaanxi Province, China

OBJECTIVE

This study was designed to comprehensively evaluate the changes in facial skin biophysical parameters with age, as well the influence of gender differences in populations of Shaanxi Province, China.

METHODS

Fourteen skin parameters, including stratum corneum hydration (SCH), transdermal water loss (TEWL), erythema, melanin, R0, R2, R5, R7, F4, gloss, skin surface pH, skin erythema index (a*), wrinkle length, and sebum, were measured by noninvasive instruments in 481 volunteers from Shaanxi Province. Spearman correlation analysis was performed to analyze the relationship between skin parameters and age. Additionally, skin parameters were analyzed for different age groups and different genders.

RESULTS

The results of the study showed a linear decrease in skin surface pH and sebum content with age, and the skin elasticity parameters R0, R2, R5, and R7 decreased significantly at the age of 54-65 years. Wrinkle length showed a linear and increase with age. R5 showed a weak negative correlation with age, R2, R7, and sebum content showed a moderate negative correlation, while wrinkle length showed a strong positive correlation. Considering the effect of gender on skin parameters, the results showed that SCH and gloss were lower in men than in women, while TEWL, erythema, melanin, wrinkle length, and sebum were higher than in women. However, there was no difference in skin elasticity between them.

CONCLUSION

The facial skin parameters, especially for the wrinkle length, exhibited the strong correlation relationship with ages in Shaanxi Province. Meanwhile, most skin parameters show significant differences with gender, which can provide a reference for future research and development in the field of cosmetics.

Hyaluronan Hybrid Cooperative Complexes Injection as a Biostimulation for Postobese Skin Laxity in the Arm: A Histopathologic Study

Background

The Hybrid Cooperative Complexes of high and low molecular weight hyaluronic acids (HHCC) improve skin structure and bioactivity. Massive weight loss damages cellular composition and morphological structure of skin. An injective treatment of postobese skin consisting of HHCC may have a role in counteracting these histopathological alterations.

Objectives

To analyze the histological effects of HHCC injection in the cutaneous tissues of massive weight loss patients suffering from arm laxity.

Methods

Nine ex-obese patients with postweight-loss-related arm laxity and ptosis requiring brachioplasty were prospectively recruited at the first author's department. HHCC injection was performed on only 1 arm, which included 2 injective sessions separated by 30 days. One month posttreatment, patients underwent a bilateral brachioplasty, and the surgical specimens were histologically examined, searching for any variation in the cutaneous connective tissue following injections. Histology on treated specimens showed a statistically significant increased density of elastic fibers along with a lower fragmentation of the same fibers compared to the untreated tissue. Fibroblasts demonstrated a swollen appearance as if involved in a bioactivation process.

Results

Treatment with HHCC increases the number of elastin fibers and determines a more regular elastin deposition and architecture, as well as the bioactivation of fibroblasts. The contralateral untreated area showed an irregular structure with elastosis and elastolysis.

Conclusions

More studies are necessary, but histologically proven benefits are demonstrated in the HHCC-treated skins when compared with basal controlateral skin. These data support the use of HHCC formulations for the treatment of postobese skin laxity.

Level of Evidence 5

Thoughts and perspectives on biomechanical numerical models under impacts: Are women forgotten from research?

The present paper explores a series of articles in the literature which deal with impact biomechanics of the head and thorax/abdomen segments, investigating the "sex specific properties/data" used in the studies. Statements in these studies are analyzed and point out, the use of male or female subjects for the developments of finite element models and their validation against experimental data. The present analysis raises the question about "androcentrism," and how biomechanical engineering findings and the design of the derived protecting devices are focused on male subjects.

Sex- and Age-dependent Skin Mechanics - A Detailed Look in Mice

Skin aging is of immense societal and, thus, scientific interest. Because mechanics play a critical role in skin's function, a plethora of studies have investigated age-induced changes in skin mechanics. Nonetheless, much remains to be learned about the mechanics of aging skin. This is especially true when considering sex as a biological variable. In our work, we set out to answer some of these questions using mice as a model system. Specifically, we combined mechanical testing, histology, collagen assays, and two-photon microscopy to identify age- and sex-dependent changes in skin mechanics and to relate them to structural, microstructural, and compositional factors. Our work revealed that skin stiffness, thickness, and collagen content all decreased with age and were sex dependent. Interestingly, sex differences in stiffness were age induced. We hope our findings not only further our fundamental understanding of skin aging but also highlight both age and sex as important variables when conducting studies on skin mechanics.

Transgenic skin biomechanical properties following first lifesaving epidermal regeneration using combined gene and cell therapy

BACKGROUND

In 2017, we reported the first life-saving regeneration of virtually an entire epidermis by combined gene and stem cell therapy. Recently, we demonstrated excellent long-term stability of this transgenic epidermis. Skin quality in this experimental approach and its potential application in other conditions were elucidated here regarding long-term outcomes of biomechanical properties.

PATIENTS AND METHODS

Analysis of biomechanical properties including skin elasticity, anisotropy and friction was performed on multiple body sites 24, 36 and 60 months following transplantation. Firstly, the sites were matched against and compared to remaining stable non-transgenic areas as well as to a control group of 13 healthy subjects. Parameters for skin elasticity, deformation and friction were assessed non-invasively.

RESULTS

Biomechanical properties of the transgenic epidermis showed encouraging results in comparison to both the remaining stable non-transgenic skin as well as healthy controls. Skin elasticity was comparable to the controls. Skin friction showed some decrease in both transgenic and non-transgenic areas as compared to the controls.

CONCLUSIONS

The excellent functional outcomes of the transgenic epidermis demonstrate stable long-term results of this novel combined gene and stem cell therapy for epidermal regeneration. Thus, other applications for this technology, such as treatment of specific burns, should be explored.

Viscoelastic Properties of Human Facial Skin and Comparisons with Facial Prosthetic Elastomers

Prosthesis discomfort and a lack of skin-like quality is a source of patient dissatisfaction with facial prostheses. To engineer skin-like replacements, knowledge of the differences between facial skin properties and those for prosthetic materials is essential. This project measured six viscoelastic properties (percent laxity, stiffness, elastic deformation, creep, absorbed energy, and percent elasticity) at six facial locations with a suction device in a human adult population equally stratified for age, sex, and race. The same properties were measured for eight facial prosthetic elastomers currently available for clinical usage. The results showed that the prosthetic materials were 1.8 to 6.4 times higher in stiffness, 2 to 4 times lower in absorbed energy, and 2.75 to 9 times lower in viscous creep than facial skin (p < 0.001). Clustering analyses determined that facial skin properties fell into three groups-those associated with body of ear, cheek, and remaining locations. This provides baseline information for designing future replacements for missing facial tissues.

Current understanding of frictional dermatoses: A review

Human skin is continually exposed to internal and external forces, dynamic as well as static. The skin is normally flexible and can resist mechanical trauma due to friction, pressure, vibration, suction and laceration to a considerable degree. However, an excess of these forces can abnormally affect the structure and function of the skin, setting the stage for the development of a skin disorder. Repetitive trauma can cause lichenification, hyperpigmentation, erythema, scaling, fissuring, blisters, ulceration and chronic alterations. Frictional dermatoses is an under-recognised entity with no clear-cut definition and encompasses a variety of terms such as frictional dermatitis, frictional melanosis, frictional pigmentary dermatoses and certain other named entities, many of which are confusing. The authors propose to define frictional dermatoses as 'a group of disorders caused by repetitive trauma to the skin as a result of friction of varied aetiology which can have a wide range of cutaneous manifestations depending on the type of insult.' The exact prevalence of frictional dermatoses as a separate entity is unknown. Authors who conducted this review include a group of dermatologists and post graduate students from various institutions. Literature was reviewed through PubMed, Medscape, Medline, ResearchGate and Google Scholar using the terms 'frictional dermatitis,' 'friction and skin,' 'dermatoses and culture,' 'clothing dermatitis,' 'friction melanosis,' 'PPE induced dermatoses in COVID-19 era,' etc. A total of 122 articles were reviewed and 100 articles among them were shortlisted and included in the study, after removing duplications. The review was followed up with further deliberation which resulted in the formulation of a new definition and classification of frictional dermatoses taking into account the morphology, histopathological characteristics, anatomical region affected and the major predisposing factors. The rising incidence of mechanical dermatoses in the COVID-19 era was also emphasised.

Melanoma Detection by AFM Indentation of Histological Specimens

Melanoma is visible unlike other types of cancer, but it is still challenging to diagnose correctly because of the difficulty in distinguishing between benign nevus and melanoma. We conducted a robust investigation of melanoma, identifying considerable differences in local elastic properties between nevus and melanoma tissues by using atomic force microscopy (AFM) indentation of histological specimens. Specifically, the histograms of the elastic modulus of melanoma displayed multimodal Gaussian distributions, exhibiting heterogeneous mechanical properties, in contrast with the unimodal distributions of elastic modulus in the benign nevus. We identified this notable signature was consistent regardless of blotch incidence by sex, age, anatomical site (e.g., thigh, calf, arm, eyelid, and cheek), or cancer stage (I, IV, and V). In addition, we found that the non-linearity of the force-distance curves for melanoma is increased compared to benign nevus. We believe that AFM indentation of histological specimens may technically complement conventional histopathological analysis for earlier and more precise melanoma detection.

OLDER PATIENTS AND PATIENTS WITH SEVERE ARTERIOSCLEROSIS ARE LESS LIKELY TO DEVELOP KELOIDS AND HYPERTROPHIC SCARS AFTER THORACIC MIDLINE INCISION: A SURVEY-BASED ANALYSIS OF 328 CASES

BACKGROUND

Surgery is a well-known trigger of keloid and hypertrophic scarring. Sternotomy scars are subject to high skin tension, which is also known to promote pathological scarring. This suggests that sternotomies in adults associate with high pathological-scarring rates, which is also our anecdotal experience. However, this notion has never been formally examined. Therefore, we conducted a survey-based cohort study of patients who had undergone a sternotomy.

STUDY DESIGN

All consecutive Japanese adults (≥18 years) who underwent cardiovascular surgery with sternotomy in 2014-2017 were identified in 2019 by chart review and sent a questionnaire. Respondents formed the study cohort. The questionnaire presented randomly-ordered photos of representative mature, keloid, and hypertrophic scars and asked the patients to choose the image that best resembled their midline scar when it was particularly noticeable. The incidence of self-reported pathological scarring (keloids and hypertrophic scars were grouped together) and the patient demographic (age and sex) and clinical characteristics (e.g. intima media thickness of the left and right common and internal carotid arteries) that associated with pathological scarring were determined.

RESULTS

Of the 548 sternotomy patients, 328 (mean age, 67 years; 68.0% male) responded (60% response rate). Of these, 195 (59.5%) reported they had a pathological scar. Compared to mature-scar patients, pathological-scar patients had lower mean age (65 vs. 69 years, p=0.0002) and intima-media thickness (0.92 vs. 1.05 mm, p=0.028).

CONCLUSION

Sternotomy was associated with a high rate of pathological scarring. An older age and arteriosclerosis were associated with less pathological scarring.

Protective roles of mesenchymal stem cells on skin photoaging: A narrative review

Skin is a natural barrier of human body and a visual indicator of aging process. Exposure to ultraviolet (UV) radiation in the sunlight may injure the skin tissues and cause local damage. Besides, it is reported that repetitive or long-term exposure to UV radiation may reduce the collagen production, change the normal skin structure and cause premature skin aging. This is termed "photoaging". The classical symptoms of photoaging include increased roughness, wrinkle formation, mottled pigmentation or even precancerous changes. Mesenchymal stem cells (MSCs) are a kind of cells with the ability of self-renewal and multidirectional differentiation into many types of cells, like adipocytes, osteoblasts and chondrocytes. Researchers have explored diverse pharmacological actions of MSCs because of their migratory activity, paracrine actions and immunoregulation effects. In recent years, the huge potential of MSCs in preventing skin from photoaging has gained wide attention. MSCs exert their beneficial effects on skin photoaging via antioxidant effect, anti-apoptotic/anti-inflammatory effect, reduction of matrix metalloproteinases (MMPs) and activation of dermal fibroblasts proliferation. MSCs and MSC related products have demonstrated huge potential in the treatment of skin photoaging. This narrative review concisely sums up the recent research developments on the roles of MSCs in protection against photoaging and highlights the enormous potential of MSCs in skin photoaging treatment.

Needleless administration of advanced therapies into the skin via the appendages using a hypobaric patch

Needleless delivery into the skin would overcome a major barrier to efficient clinical utilization of advanced therapies such as nanomaterials and macromolecules. This study demonstrates that controlled skin stretching (in porcine, rat, and mouse models) using a patch comprising a hypobaric chamber, to open the skin appendages, can increase the permeability of the tissue and provide a means to enable direct delivery of advanced therapies directly into the skin without the use of a needle or injection system. This technology can facilitate the self-administration of therapeutics including vaccines, RNA, and antigens, thus improving the translation of these products into effective clinical use.

Advanced therapies are commonly administered via injection even when they act within the skin tissue, and this increases the chances of off-target effects. Here we report the use of a skin patch containing a hypobaric chamber that induces skin dome formation to enable needleless delivery of advanced therapies directly into porcine, rat, and mouse skin. Finite element method modeling showed that the hypobaric chamber in the patch opened the skin appendages by 32%, thinned the skin, and compressed the appendage wall epithelia. These changes allowed direct delivery of an H1N1 vaccine antigen and a diclofenac nanotherapeutic into the skin. Fluorescence imaging and infrared mapping of the skin showed needleless delivery via the appendages. The in vivo utility of the patch was demonstrated by a superior immunoglobulin G response to the vaccine antigen in mice compared to intramuscular injection and a 70% reduction in rat paw swelling in vivo over 5 h with diclofenac without skin histology changes.

Palmar skin elasticity measured by the Cutometer MPA 580 is decreased in mild Dupuytren's disease compared to healthy controls

Introduction

Involvement of the palmar skin is often seen in patients with Dupuytren's disease (DD) with severe finger contractures. However, skin elasticity may be already decreased earlier in the disease. The Cutometer MPA 580 could provide an objective skin measurement tool to assess this decrease in elasticity. Linking objective skin measurements to functional outcome measures could lead to better prediction of disease progression. We set up a study to investigate if the Cutometer was able to detect differences in skin elasticity between patients with mild Dupuytren's disease and healthy controls.

Methods

A cross-sectional analytical study was performed. Three assessors measured skin elasticity (palmar hand) on two sites using the Cutometer on 30 patients with mild DD and 30 healthy controls. Student's t-test was used to evaluate differences in skin elasticity and a linear model to evaluate interactions between the groups and sites.

Results

Significant differences in skin elasticity were found between DD patients and controls, as well as differences based on the location examined.

Discussion

Similar to other skin conditions, the Cutometer MPA 580 was able to demonstrate a significant lower elasticity in the palmar skin in DD patients compared to healthy controls. A decrease in skin elasticity in different locations of the hand correlated with areas that often pose problems in the treatment of more severe DD. The Cutometer could potentially be a tool to identify these areas earlier in the disease.

Effect of collagen fibre orientation on the Poisson's ratio and stress relaxation of skin: an ex vivo and in vivo study

During surgical treatment skin undergoes extensive deformation, hence it must be able to withstand large mechanical stresses without damage. Therefore, understanding the mechanical properties of skin becomes important. A detailed investigation on the relationship between the three-dimensional deformation response of skin and its microstructure is conducted in the current study. This study also discloses the underlying science of skin viscoelasticity. Deformation response of skin is captured using digital image correlation, whereas micro-CT, scanning electron microscopy and atomic force microscopy are used for microstructure analysis. Skin shows a large lateral contraction and expansion (auxeticity) when stretched parallel and perpendicular to the skin tension lines, respectively. Large lateral contraction is a result of fluid exudation from the tissue, while large rotation of the stiff collagen fibres in the loading direction explains the skin auxeticity. During stress relaxation, lateral contraction and fluid effluxion from skin reveal that tissue volume loss is the intrinsic science of skin viscoelasticity. Furthermore, the results obtained from in vivo study on human skin show the relevance of the ex vivo study to physiological conditions and stretching of the skin during its treatments.

The role of friction on skin wetness perception during dynamic interactions between the human index fingerpad and materials of varying moisture content

Mechanosensory inputs arising from dynamic interactions between the skin and moisture, such as when sliding a finger over a wet substrate, contribute to the perception of skin wetness. Yet, the exact relationship between the mechanical properties of a wet substrate, such as friction, and the resulting wetness perception remains to be established under naturalistic haptic interactions. We modeled the relationship between mechanical and thermal properties of substrates varying in moisture levels (0.49 × 10⁻⁴; 1.10 × 10⁻⁴; and 2.67 × 10⁻⁴ mL·mm⁻²), coefficient of friction (0.783, 0.848, 1.033, 0.839, 0.876, and 0.763), and maximum thermal transfer rate (Q_max, ranging from 511 to 1,260 W·m⁻²·K⁻¹), and wetness perception arising from the index finger pad’s contact with such substrates. Forty young participants (20M/20F) performed dynamic interactions with 21 different stimuli using their index finger pad at a controlled angle, pressure, and speed. Participants rated their wetness perception using a 100-mm visual analog scale (very dry to very wet). Partial least squares regression analysis indicated that coefficient of friction explained only ∼11% of the variance in wetness perception, whereas Q_max and moisture content accounted for ∼22% and 18% of the variance, respectively. These parameters shared positive relationships with wetness perception, such that the greater the Q_max, moisture content, and coefficient of friction, the wetter the perception. We found no differences in wetness perception between males and females. Our findings indicate that although the friction of a wet substrate modulates wetness perception, it is still secondary to thermal parameters such as Q_max.

NEW & NOTEWORTHY Our skin often interacts with wet materials, yet how their physical properties influence our experience of wetness remains poorly understood. We evaluated wetness perception following naturalistic haptic interactions with materials varying in moisture content, friction, optical profiles, and heat transfer rates. We show that although mechanical parameters can influence wetness perception, their role is secondary to that of thermal factors. These findings expand our understanding of multisensory integration and could guide innovation in healthcare product design.

A mechanistic view on the aging human skin through ex vivo layer-by-layer analysis of mechanics and microstructure of facial and mammary dermis

Age-related changes in skin mechanics have a major impact on the aesthetic perception of skin. The link between skin microstructure and mechanics is crucial for therapeutic and cosmetic applications as it bridges the micro- and the macro-scale. While our perception is governed by visual and tactile changes at the macroscopic scale, it is the microscopic scale (molecular assemblies, cells) that is targeted by topical treatments including active compounds and energies. We report here a large dataset on freshly excised human skin, and in particular facial skin highly relevant for cosmetics and aesthetic procedures. Detailed layer-by-layer mechanical analysis revealed significant age-dependent decrease in stiffness and elastic recoil of full-thickness skin from two different anatomical areas. In mammary skin, we found that the onset of mechanical degradation was earlier in the superficial papillary layer than in the deeper, reticular dermis. These mechanical data are linked with microstructural alterations observed in the collagen and elastic networks using staining and advanced imaging approaches. Our data suggest that with ageing, the earliest microstructural and mechanical changes occur in the top-most layers of dermis/skin and then propagate deeper, providing an opportunity for preventive topical treatments acting at the level of papillary dermis.

Technological scouting of bi-material face masks: experimental analysis on real faces

The need for personal protective equipment rapidly grew during the COVID-19. Companies had to face problems related to their products' sustainability, adherence, and comfortability. Designing a face mask with proper adherence and comfortability in wearing and breathing became a matter of great importance. In this work, the adherence of an innovative face mask and its comfortability were experimentally tested with real faces, considering the deformation of the mask and the soft facial tissues. A stereophotogrammetric acquisition was made of the face with the face mask during these tests. A comparison between the geometries of the face and the mask, undeformed and deformed, gave the respective deformations. The force applied by the mask to the face was calculated, measuring the elastic strain of the mask bands during wearing and the deformation.

A hyperelastic model to capture the mechanical behaviour and histological aspects of the soft tissues

It is well established that the soft connective tissues show a nonlinear elastic response that comes from their microstructural arrangement. Tissues' microstructure alters with various physiological conditions and may affect their mechanical responses. Therefore, the accurate prediction of tissue's mechanical response is crucial for clinical diagnosis and treatments. Thus, a physically motivated and mathematically simplified model is required for the accurate prediction of tissues' mechanical and structural responses. This study explored the 'Exp-Ln' hyperelastic model (Khajehsaeid et al., 2013) to capture soft tissues' mechanical and histological behaviour. In this work, uniaxial tensile test data for the belly and back pig skin were extracted from the experiments performed in our laboratory, whereas uniaxial test data for other soft tissues (human skin, tendon, ligament, and aorta) were extracted from the literature. The 'Exp-Ln; and other hyperelastic models (e.g. Money Rivlin, Ogden, Yeoh, and Gent models) were fitted with these experimental data, and obtained results were compared between the models. These results show that the 'Exp-Ln' model could capture the mechanical behaviour of soft tissues more accurately than other hyperelastic models. This model was also found numerically stable for all modes and ranges of deformation. This study also investigated the link between 'Exp-Ln' material parameters and tissue's histological parameters. The histological parameters such as collagen content, fibre free length, crosslink density, and collagen arrangement were measured using staining and ATR-FTIR techniques. The material parameters were found statistically correlated with the histological parameters. Further, 'Exp-Ln' model was implemented in ABAQUS through the VUMAT subroutine, where the mechanical behaviour of various soft tissues was simulated for different modes of deformation. The finite element analysis results obtained using the 'Exp-Ln' model agreed with the experiments and were more accurate than other hyperelastic models. Overall, these results demonstrate the capability of 'Exp-Ln' model to predict the mechanical and structural responses of the soft tissues.

The Influence of Headform/Helmet Friction on Head Impact Biomechanics in Oblique Impacts at Different Tangential Velocities

Oblique impacts of the helmet against the ground are the most frequent scenarios in real-world motorcycle crashes. The combination of two factors that largely affect the results of oblique impact tests are discussed in this work. This study aims to quantify the effect of the friction at the interface between the headform and the interior of a motorcycle helmet at different magnitudes of tangential velocity. The helmeted headform, with low friction and high friction surface of the headform, was dropped against three oblique anvils at different impact velocities resulting in three different magnitudes of the tangential velocity (3.27 m/s, 5.66 m/s, 8.08 m/s) with the same normal component of the impact velocity (5.66 m/s). Three impact directions (front, left-side and right-side) and three repetitions per impact condition were tested resulting in 54 impacts. Tangential velocity variation showed little effect on the linear acceleration results. On the contrary, the rotational results showed that the effect of the headform’s surface depends on the magnitude of the tangential velocity and on the impact direction. These results indicate that a combination of low friction with low tangential velocities may result into underprediction of the rotational headform variables that would not be representative of real-world conditions.

Efficacy of Dendrobium candidum polysaccharide extract as a moisturizer

INTRODUCTION

This study investigated the role of natural polymers as moisturizers with low toxicity and biodegradability in the cosmetic and pharmaceutical industries. We isolated a polysaccharide extract from Dendrobium candidum (D. candidum) and determined its efficacy in skin hydration when used as an active cosmetic ingredient.

METHODS

The molecular weight distribution of D. candidum polysaccharides was analyzed via gel permeation chromatography (GPC). We performed real-time reverse transcription PCR (RT-PCR) and western blotting assays to investigate the physiological mechanism of the polysaccharides extracted from D. candidum (PDC). Based on in vitro data, the efficacy of PDC in improving skin condition was tested on the face of 21 volunteers.

RESULTS

The expression of filaggrin (FLG), caspase-14, and bleomycin hydrolase, which are the major components contributing to skin hydration, was significantly increased in the PDC-treated group. Further, the PDC upregulated the mRNA expression of occludin and claudin-1, which play a key role in epidermal barrier function. In addition, a topical application of PDC markedly increased skin hydration and improved trans-epidermal water loss (TEWL) and skin elasticity after 2 weeks.

CONCLUSIONS

It is the first study reporting the efficacy of PDC-mediated FLG mechanism associated with positive skin hydration. PDC can be used as an active ingredient in moisturizers. Long-term application of PDC-based moisturizers may result in significant improvement in elasticity and barrier function.

Influence of quarantine mask use on skin characteristics: One of the changes in our life caused by the COVID-19 pandemic

BACKGROUND

The influence of various environmental factors on skin properties is well known. However, there is a lack of research into the effect of quarantine masks on skin properties, even though the use of masks has significantly increased after the COVID-19 outbreak. Therefore, this study aimed to investigate the influence of mask use on skin properties.

MATERIALS AND METHODS

Twenty subjects were enrolled in this study. The subjects used approved quarantine masks for 6 hours a day for 2 weeks. We measured eight skin biophysical parameters: temperature, redness, pore volume, texture, elasticity, trans-epidermal water loss (TEWL), sebum content, and pH, and evaluated acne lesions before and after using quarantine masks. The evaluation was performed on the mask-wearing area of the face.

RESULTS

Skin temperature, redness, and TEWL increased significantly after a 6-hour mask use, while the sebum content increased marginally. Skin elasticity was reduced by the use of masks over 1 and 2 weeks, whereas the pore volume and the number of acne lesions increased after a 2-week mask use. The skin changes caused by mask use showed sex-based differences in the skin elasticity (after 6 hours), redness, and roughness (after 2 weeks).

CONCLUSIONS

The use of quarantine masks causes a change in the skin temperature, redness, and TEWL in the short term and in skin elasticity, pores, and acne in the long term. This study revealed that prolonged mask use could have negative effects on the skin.

Adipose-Derived Mesenchymal Stem Cells (AD-MSCs) against Ultraviolet (UV) Radiation Effects and the Skin Photoaging

The skin is a natural barrier against the ultraviolet (UV) radiation of sunlight. The long-term and/or repetitive exposure to the sunlight and related UV radiation may change the skin structure, decreasing collagen production, promoting premature skin aging, which is termed "photoaging". The signs of photoaging include wrinkle formation, mottled pigmentation, and/or cancerous changes. For many years, adipose-derived mesenchymal stem cells (AD-MSCs) and fat grafting (F-GRF) have been used to combat photoaging signs, wrinkles, loss of elasticity, and face soft tissue defects. Several studies have analyzed in vitro actions of AD-MSCs against photoaging's effects, thanks to their migratory activity, paracrine actions, and related in vivo-ex vivo outcomes. In fact, AD-MSCs act against skin photoaging in vitro via activation of dermal fibroblast proliferation, antioxidant effect, and matrix metalloproteinases (MMPs) reduction. In vivo and ex vivo outcomes regard the local injection of AD-MSCs, F-GRF, and/or enriched-F-GRF with AD-MSCs directly in the wrinkles and the face's soft tissue defects. This concise review summarizes the most recent in vitro, in vivo and ex vivo outcomes and developments on the effects of AD-MSCs and F-GRF against photoaging.

The Effects of Ageing on Tactile Function in Humans

Ageing is accompanied by a steady decline in touch sensitivity and acuity. Conversely, pleasant touch, such as experienced during a caress, is even more pleasant in old age. There are many physiological changes that might explain these perceptual changes, but researchers have not yet identified any specific mechanisms. Here, we review both the perceptual and structural changes to the touch system that are associated with ageing. The structural changes include reduced elasticity of the skin in older people, as well as reduced numbers and altered morphology of skin tactile receptors. Effects of ageing on the peripheral and central nervous systems include demyelination, which affects the timing of neural signals, as well as reduced numbers of peripheral nerve fibres. The ageing brain also undergoes complex changes in blood flow, metabolism, plasticity, neurotransmitter function, and, for touch, the body map in primary somatosensory cortex. Although several studies have attempted to find a direct link between perceptual and structural changes, this has proved surprisingly elusive. We also highlight the need for more evidence regarding age-related changes in peripheral nerve function in the hairy skin, as well as the social and emotional aspects of touch.

High-resolution two-photon polymerization: the most versatile technique for the fabrication of microneedle arrays

Microneedle patches have received much interest in the last two decades as drug/vaccine delivery or fluid sampling systems for diagnostic and monitoring purposes. Microneedles are manufactured using a variety of additive and subtractive micromanufacturing techniques. In the last decade, much attention has been paid to using additive manufacturing techniques in both research and industry, such as 3D printing, fused deposition modeling, inkjet printing, and two-photon polymerization (2PP), with 2PP being the most flexible method for the fabrication of microneedle arrays. 2PP is one of the most versatile and precise additive manufacturing processes, which enables the fabrication of arbitrary three-dimensional (3D) prototypes directly from computer-aided-design (CAD) models with a resolution down to 100 nm. Due to its unprecedented flexibility and high spatial resolution, the use of this technology has been widespread for the fabrication of bio-microdevices and bio-nanodevices such as microneedles and microfluidic devices. This is a pioneering transformative technology that facilitates the fabrication of complex miniaturized structures that cannot be fabricated with established multistep manufacturing methods such as injection molding, photolithography, and etching. Thus, microstructures are designed according to structural and fluid dynamics considerations rather than the manufacturing constraints imposed by methods such as machining or etching processes. This article presents the fundamentals of 2PP and the recent development of microneedle array fabrication through 2PP as a precise and unique method for the manufacture of microstructures, which may overcome the shortcomings of conventional manufacturing processes.

A Weighted Average Phase Velocity Inversion Model for Depth-Resolved Elasticity Evaluation in Human Skin In-Vivo

OBJECTIVE

In current surface acoustic wave (SAW) elastography field, wavelength-depth inversion model is a straightforward and widely used inversion model for depth-resolved elasticity profile reconstruction. However, the elasticity directly evaluated from the wavelength-depth relationship is biased. Thus, a new inversion model, termed weighted average phase velocity (WAPV) inversion model, is proposed to provide depth-resolved Young's modulus estimate with better accuracy.

METHODS

The forward model for SAW phase velocity dispersion curve generation was derived from the numerical simulations of SAWs in layered materials, and inversion was implemented by matching the measured phase velocity dispersion curve to the one generated from the forward model using the least squares fitting. Three two-layer agar phantoms with different top-layer thicknesses and one three-layer agar phantom were tested to validate the proposed inversion model. Then the model was demonstrated on human skin at various sites (palm, forearm and back of hand) in-vivo.

RESULTS

In multi-layered agar phantoms, depth-resolved elasticity estimates provided by the model have a maximal total inversion error of 15.2% per sample after inversion error compensation. In in-vivo human skin, the quantified bulk Young's moduli (palm: 212 ± 78 kPa; forearm: 32 ± 11 kPa and back of hand: 29 ± 8 kPa) are comparable to the reference values in the literature.

CONCLUSION

The WAPV inversion model can provide accurate depth-resolved Young's modulus estimates in layered biological soft tissues.

SIGNIFICANCE

The proposed model can predict depth-resolved elasticity in layered biological soft tissues with a reasonable accuracy which traditional wavelength-depth inversion model cannot provide.

Seasonal variations in the skin parameters of Caucasian women from Central Europe

BACKGROUND

The human skin is greatly affected by external factors such as UV radiation (UVR), ambient temperature (T), and air humidity. These factors oscillate during the year giving rise to the seasonal variations in the skin properties. The aim of this study was to evaluate the effect of seasons, environmental T, relative and absolute humidity on the skin parameters of Caucasian women, perform a literature review and discuss the possible factors lying behind the found changes.

MATERIALS AND METHODS

We measured stratum corneum (SC) hydration, transepidermal water loss (TEWL), sebum level, erythema index, and elasticity parameters R2 and R7 on the forehead and the cheek of Caucasian women from the Czech Republic throughout the year. We also performed a non-systematic literature review focused on the seasonal variations in these skin parameters.

RESULTS

We confirmed a well-documented low SC hydration and sebum production in winter. In spring, we found the lowest TEWL (on the forehead) and the highest SC hydration but also the highest erythema index and the lowest elasticity presumably indicating skin photodamage. For most of the skin parameters, the seasonal variations probably arise due to a complex action of different factors as we extensively discussed.

CONCLUSION

The data about the seasonal variations in the skin parameters are still highly inconsistent and further studies are needed for better understanding of the normal skin changes throughout the year.

The Effect of Strain Rate on the Stress Relaxation of the Pig Dermis: A Hyper-Viscoelastic Approach

The understanding of strain rate-dependent mechanical properties of the skin is important for accurate prediction of its biomechanics under different loading conditions. This study investigated the effect of strain rate, i.e., 0.025/s (low), 0.5/s (medium), and 1.25/s (high), ranging in the physiological loading rate of connective tissue, on the stress-relaxation response of the porcine dermis. Results show that in the initial phase of the relaxation, the value of stress relaxation (extent of relaxation) was found higher for high strain rate. However, the equilibrium stress was found strain rate independent. A Mooney-Rivlin-based five-term quasi-linear viscoelastic (QLV) model was proposed to determine the effect of strain rate on the stress-relaxation behavior of the porcine dermis. The value of relaxation modulus G1 and G2 were found higher for the high strain rate, whereas the reverse trend was observed for G3, G4, and G5. Moreover, the value of time constants τ1,τ2,τ3τ4, and τ5 were found higher for low strain rate. Statistical analysis shows no significant difference in the values of G5, τ4, and τ5 among the three strain rates. The proposed model was found capable to fit the stress-relaxation response of skin with great accuracy, e.g., root-mean-squared-error (RMSE) value equal to 0.015 ± 0.00012 MPa. Moreover, this hyper-viscoelastic model can be utilized: to quantify the effects of age and diseases on the skin; to simulate the stresses on sutures during large wound closure and impact loading.

Frequency dependent inelastic response of collagen architecture of pig dermis under cyclic tensile loading: An experimental study

The evaluation of collagen architecture of the dermis in response to mechanical stimulation is important as it affects the macroscopic mechanical properties of the dermis. A detailed understanding of the processes involved in the alteration of the collagen structure is required to correlate the mechanical stimulation with tissue remodeling. This study investigated the effect of cyclic frequencies i.e. low (0.1 Hz), medium (2.0 Hz), and high (5.0 Hz) (physiological range) in the alteration of pig dermis collagen structure and its correlation with the macroscopic mechanical response of the dermis. The assessment of the collagen structure of virgin and mechanical tested specimens at tropocollagen, collagen fibril, and fiber level was performed using Fourier-transform infrared-attenuated total reflection (FTIR-ATR), atomic force microscopy (AFM), and scanning electron microscopy (SEM) respectively. After 10³ cycles, a significantly higher alteration in collagen structure with discrete plastic-type damage was found for low frequency. This frequency dependent alteration of the collagen structure was found in correlation with the dermis macroscopic response. The value of inelastic strain, stress softening, damage parameter (reduction in elastic modulus), and reduction in energy dissipation were observed significantly large for slow frequency. A power-law based empirical relations, as a function of frequency and number of cycles, were proposed to predict the value of inelastic strain and damage parameter. This study also suggests that hierarchical structural response against the mechanical stimulation is time-dependent rather than cycle-dependent, may affect the tissue remodeling.

Impact of physiologically relevant temperatures on dermal absorption of active substances - an ex-vivo study in human skin

Skin temperature plays a certain role in the dermal absorption of substances, but the extent and mechanisms of skin temperatures-induced modulation in ranges caused by physiological thermoregulation or environmental conditions are largely unknown. The influence of dermal temperature on the absorption of the model lipophilic compound (anisole) and the model hydrophilic compounds (1,4-dioxane, ethanol) through human skin was investigated at three dermal temperatures (25, 32 and 39 °C) in an ex-vivo diffusion cell model. The substances were applied to the skin and transdermal penetration was monitored. All substances showed temperature dependent variations in their penetration behavior (3 h: 25-39 °C: 202-275% increase in cumulative, transdermally penetrated amounts). The relative differences in absorption in relation to temperature were greatest within 45 min after exposure (25-39 °C: 347-653% rise in cumulated penetration), although absolute amounts absorbed were small (45 min vs. 3 h: 4.5-14.5%). Regardless of blood circulation, skin temperature significantly influences the amount and kinetics of dermal absorption. Substance-dependent, temperature-related changes of the lipid layer order or the porous pathway may facilitate penetration. The early-stage modulation of transdermal penetration indicates transappendageal absorption, which may be relevant for short-term exposures. For both, toxicological evaluation and perfusion cell studies, it is important to consider the thermal influence on absorption or to perform the latter at a standardized temperature (32±1 °C).

Single-cell transcriptomes of the human skin reveal age-related loss of fibroblast priming

Fibroblasts are an essential cell population for human skin architecture and function. While fibroblast heterogeneity is well established, this phenomenon has not been analyzed systematically yet. We have used single-cell RNA sequencing to analyze the transcriptomes of more than 5,000 fibroblasts from a sun-protected area in healthy human donors. Our results define four main subpopulations that can be spatially localized and show differential secretory, mesenchymal and pro-inflammatory functional annotations. Importantly, we found that this fibroblast 'priming' becomes reduced with age. We also show that aging causes a substantial reduction in the predicted interactions between dermal fibroblasts and other skin cells, including undifferentiated keratinocytes at the dermal-epidermal junction. Our work thus provides evidence for a functional specialization of human dermal fibroblasts and identifies the partial loss of cellular identity as an important age-related change in the human dermis. These findings have important implications for understanding human skin aging and its associated phenotypes.

Interpersonal differences in the friction response of skin relate to FTIR measures for skin lipids and hydration

Understanding the mechanical response of skin to contact is of importance when developing products that interact with the skin. The shear forces that arise due to friction in the interface are a key aspect of skin interactions, because shear is known to contribute to discomfort and tissue injury. However, the frictional response of skin shows large variations between people. It has been hypothesised that these variations relate to differences between people in the physiological properties of their skin, but the underlying mechanisms are not well understood. In order to gain new insights into these interpersonal differences in friction behaviour, in vivo FTIR measurements and in vivo friction measurements were performed on the same patch of skin. Quantitative analysis of the various peaks in the FTIR spectra provided information on the moisture content of the stratum corneum and the amount and mechanical properties of the lipids on the skin. The lipid viscosity, as characterised by the width of the 2920 cm^-1 peak, correlates with the friction, whilst, interestingly, no relationship was found between the quantity of lipids on the skin surface and the coefficient of friction. Additionally, and as expected, a fairly strong correlation was obtained between the moisture content, as characterised by the height of the Amide I peak and the coefficient of friction. The presented results show that spectroscopy techniques can be used in as a non-invasive method to identify people who may show elevated levels of friction and thus are at increased risk of developing shear induced tissue injury.

The regional-dependent biaxial behavior of young and aged mouse skin: A detailed histomechanical characterization, residual strain analysis, and constitutive model

Skin fulfills several vital functions, many of which are dependent on its mechanical properties. Therefore, as mice have become an invaluable model for skin research, determining murine skin's mechanical properties is important. Specifically, skin's mechanical properties are important for functional tests as well as for prognostic and diagnostic purposes. Additionally, computational simulations of skin behavior are becoming commonplace, rendering accurate models of murine skin's constitutive behavior necessary. To date, our knowledge of mouse skin mechanics shows significant gaps. For example, there are no comprehensive reports correlating skin's mechanical properties with region, age, and direction. Moreover, mouse skin's residual strain behavior has not been reported on. In our current work, we set out to fill these gaps. Based on histology, 2-photon microscopy, and planar biaxial testing, while accurately tracking various reference configurations, we report on differences in gross structure, microstructural organization, and constitutive response of skin, and cast those properties into a versatile Fung-type hyperelastic constitutive law for three reference configurations. Our data is the most comprehensive report contrasting the mechanical properties of young (12 weeks) and aged (52 weeks) mouse skin and will, thus, be valuable to basic science as control data, and provide accurate constitutive laws for mouse skin modeling. STATEMENT OF SIGNIFICANCE: Our findings are significant as they fill several gaps in our understanding of mouse skin mechanics. This is particularly important as mouse skin is becoming a frequent and critical model of human skin for cosmetic and medical science. Specifically, we quantified how mechanical properties of mice skin vary with age, with location, and with direction. Additionally, we cast our findings into constitutive models that can be used by others for predictive computer simulations of skin behavior.

The influence of autogenic training on the physical properties of skin and cardiac autonomic activity in postmenopausal women: an exploratory study

BACKGROUND

Autogenic training (AT) is a major relaxation training technique whose clinical efficacy has been verified in dermatology. Many reports demonstrate ameliorated skin conditions in AT-treated subjects with reduced psychological stress. However, no studies have examined the effects of AT on the skin of postmenopausal women.

OBJECTIVES

We examine the influences of AT on the physical properties of skin and cardiac autonomic activity in postmenopausal women.

METHODS

Postmenopausal women were classed into an AT group and a control one. The women in the AT group were mentored by a professional to practice AT twice a day for 7 weeks. The women in the control group were instructed to close their eyes for 3 minutes instead of AT. Hydration of the stratum corneum (SC), transepidermal water loss (TEWL), skin elasticity and heart-rate variability (HRV) were measured before and after the study period to examine how they changed.

RESULTS

SC hydration and skin elasticity of the cheek, increased in both groups, and the increase was significantly higher in the AT group (n = 14) than in the control group (n = 12) (P < 0.05, Cohen's d = 1.03; P < 0.05, Cohen's d = 0.99; respectively). TEWL did not change in either group. LF/HF was lower in the AT group than in the control group (P < 0.05, Cohen's d = 0.91).

CONCLUSION

AT increased SC hydration and skin elasticity with changes in the balance of autonomic nervous system activity in postmenopausal women, implying that AT may have improvement effects on aged skin by menopause.

Mechanical and topographical anisotropy for human skin: Ageing effect

Skin ageing is a complex process which strongly impacts the three skin layers (epidermis, dermis, hypodermis) both functionally and structurally. Of particular interest are the effects of ageing on the dermis biomechanics and how this evolution can impact the reorganization of the cutaneous lines which compose the skin relief. It has been argued that the skin relief could reflect the underlying mechanical condition of the skin. Nevertheless, there is not yet conclusive evidence of the existence of such a link. This work aims at experimentally studying, in vivo, the correlation between the anisotropy of human skin biomechanics and skin topography as a function of ageing. The study was conducted on a panel of 20 men divided into 4 groups according to age (from 23 to 64 years old). The measurements were performed on the right volar forearm of each volunteer. For the biomechanical measurements, an innovative contactless bio-rheometer was developed. It allows access to the mechanical behaviour of the skin in several directions. This device generates an air blast without any contact with the skin area and measures its dynamic response (evaluation of speed of wave propagation) with a linear laser. Moreover, a turntable enables measurements to be made in different angular directions. To analyse the topography of skin relief, we proposed a new method, based on watershed and linear radon transformations. First, an optical analysis of a replica of the skin relief is performed. Then, from the skin image obtained, the density of the cutaneous lines is calculated in different directions using watersheld transformation. The orientation of the detected lines is then estimated with an algorithm based on linear radon transformation. The results observed show a good correlation between the skin relief and the mechanical properties of the skin all along the ageing process. For both topography and mechanical properties, there is a transition from an almost isotropic mechanical behaviour to an anisotropic one as a function of ageing process. Thus, we might conclude that the skin relief reflects the underlying mechanical conditions of the skin.

DermaTOP Blue and Antera 3D as methods to assess cosmetic solutions targeting eyelid sagging

BACKGROUND

As the eye contour ages, the skin on the lid becomes lax often causing a voluminous protrusion where the superior palpebral sulcus begins to sag onto the upper eyelid. This sagging feature may present a novel anti-ageing target for cosmetic products when treating the eye area. A quantitative method to evaluate the volume of this sagging feature has not been previously established. We investigate the use of the DermaTOP fringe projector and Antera 3D Camera to this end.

METHODS

Eyelid topographic measurements were collected on 20 female volunteers aged 50-75 years with the DermaTOP and Antera 3D. The DermaTOP and Antera 3D measurements were assessed for reproducibility and product effect detection capabilities.

RESULTS

The DermaTOP and Antera 3D successfully measured sagging feature volume, demonstrated reproducibility of measurement and furthermore were suitably sensitive to allow for detection of sagging feature volume reduction after a single application of aqueous tightening serum. DermaTOP parameters were found to moderately correlated with the Antera 3D parameters.

CONCLUSION

Both the DermaTOP and Antera 3D allow for quantitative measurement of eyelid sagging feature volume and in-turn permit evaluation of anti-ageing cosmetic preparations targeting the eyelid.

Aging-related changes in the mid-face skin elasticity in East Asian women

BACKGROUND

Age-related changes in facial skin is a major concern in women. This study aimed to objectively evaluate normal skin elasticity and age-related differences in the faces of East Asian women. There are no standard values for data related to normal skin on East Asian women.

METHODS

We studied 129 healthy East Asian women without a history of cosmetic procedures or surgeries. Skin elasticity was assessed at the cheek and lower eyelid points, which were assessed on both the right and left sides of the face.

RESULTS

The age of the subjects showed significant negative correlations with the R2 and R7 parameters, which represent skin elasticity after deformation.

CONCLUSION

We therefore concluded that the primary decrease in skin elasticity in East Asian women occurs in the midface region.

Resonant Frequency Skin Stretch for Wearable Haptics

Resonant frequency skin stretch uses cyclic lateral skin stretches matching the skin's resonant frequency to create highly noticeable stimuli, signifying a new approach for wearable haptic stimulation. Four experiments were performed to explore biomechanical and perceptual aspects of resonant frequency skin stretch. In the first experiment, effective skin resonant frequencies were quantified at the forearm, shank, and foot. In the second experiment, perceived haptic stimuli were characterized for skin stretch actuations across a spectrum of frequencies. In the third experiment, perceived haptic stimuli were characterized by different actuator masses. In the fourth experiment, haptic classification ability was determined as subjects differentiated haptic stimulation cues while sitting, walking, and jogging. Results showed that subjects perceived stimulations at, above, and below the skin's resonant frequency differently: stimulations lower than the skin resonant frequency felt like distinct impacts, stimulations at the skin resonant frequency felt like cyclic skin stretches, and stimulations higher than the skin resonant frequency felt like standard vibrations. Subjects successfully classified stimulations while sitting, walking, and jogging, perceived haptic stimuli was affected by actuator mass, and classification accuracy decreased with increasing speed, especially for stimulations at the shank. This paper could facilitate more widespread use of wearable skin stretch. Potential applications include gaming, medical simulation, and surgical augmentation, and for training to reduce injury risk or improve sports performance.

Relationship between age, BMI, head posture and superficial neck muscle stiffness and elasticity in adult women

This study determined relationships between age, BMI and cranio-vertebral angle (CVA) (independent variables) and stiffness and elasticity of sternocleidomasteoid [SCM] and upper trapezius [UT] (dependent variables) muscles in sitting posture in 95 women across adult life. Moreover, a stepwise regression was performed to determine to what extent the dependent variables are explained by age, BMI and CVA. Age was moderately correlated with BMI (r = 0.41), and both age and BMI were moderately negatively correlated with CVA (r = −0.54 and −0.55, respectively). High (r = 0.73) and moderate (r = 0.53) linear relationships were present between age and logarithmic decrement (inversely related to elasticity) and stiffness of SCM muscle, respectively. Low (r = 0.36) and moderate (r = 0.47) relationships were present between age and logarithmic decrement and stiffness of UT muscle, respectively. Age accounted for 53% variance in elasticity and 28.5% variance in stiffness of SCM, and for 13% variance in elasticity and 22% variance in stiffness of UT muscle. Introduction of BMI but not CVA to the model explained the variance of these parameters by additional 0–8%. Among the studied factors age is the major correlate of stiffness and elasticity of neck muscles across the adult life.