Mechanical and topographical anisotropy for human skin: Ageing effect

The Effects of an Oral Supplementation of a Natural Keratin Hydrolysate on Skin Aging: A Randomized, Double-Blind, Placebo-Controlled Clinical Study in Healthy Women

BACKGROUND

Keratin hydrolysates are active components used in food supplements to alleviate aging signs on skin, hair, and nails.

AIMS

This randomized, double-blind, placebo-controlled study evaluates a novel keratin hydrolysate obtained from poultry feathers. This feather keratin hydrolysate (FKH) results in a characteristic mix of free L-amino acids (≥ 83.5%). FKH was administered as a food supplement to a panel of adult women showing aging physiological signs.

METHODS

Participants were randomly assigned in three groups to receive daily dosages of 500 or 1000 mg of FKH or placebo for 90 days. Parameters of skin roughness, wrinkle features, deep skin moisturization, skin maximum elongation and elasticity, skin thickness, skin anisotropy, skin density, gloss of skin, hair and nails, and nail hardness were evaluated. Subjects also answered a questionnaire related to the treatment efficacy perception.

RESULTS

Both FKH treatments showed a significant improvement of all parameters compared to day 0 and to placebo, with an exception for fiber anisotropy and fiber density which showed a significant improvement compared to day 0 and a tendency to improve compared to placebo. These measurements were bolstered by the results of a self-assessment questionnaire, showing an overall set of positive answers for both treatments compared to placebo.

CONCLUSIONS

Oral supplementation of FKH for 90 days is associated with an improvement in the appearance of facial skin, hair, and nails. This study highlights the benefits of free L-amino acids mix as potential aminobiotics and not just as building blocks of proteins, suggesting a new perspective of nutricosmetic food.

Estimating the viscoelastic anisotropy of human skin through high-frequency ultrasound elastography

BACKGROUND

The skin is the largest organ of the human body and serves distinct functions in protecting the body. The viscoelastic properties of the skin play a key role in supporting the skin-healing process, also it may be changed due to some skin diseases.

PROPOSE

In this study, high-frequency ultrasound (HFUS) elastography based on a Lamb wave model was used to noninvasively assess the viscoelastic anisotropy of human skin.

METHOD

Elastic waves were generated through an external vibrator, and the wave propagation velocity was measured through 40 MHz ultrafast HFUS imaging. Through the use of a thin-layer gelatin phantom, HFUS elastography was verified to produce highly accurate estimates of elasticity and viscosity. In a human study involving five volunteers, viscoelastic anisotropy was assessed by rotating an ultrasound transducer 360°.

RESULTS

An oval-shaped pattern in the elasticity of human forearm skin was identified, indicating the high elastic anisotropy of skin; the average elastic moduli were 24.90 ± 6.63 and 13.64 ± 2.67 kPa along and across the collagen fiber orientation, respectively. The average viscosity of all the recruited volunteers was 3.23 ± 0.93 Pa·s.

CONCLUSIONS

Although the examined skin exhibited elastic anisotropy, no evident viscosity anisotropy was observed.

Noninvasive identification of directionally-dependent elastic properties of soft tissues using full-field optical data

This paper introduces an innovative approach for elastic property characterization of soft tissues, having directional-dependent material behavior, via their vibration response measurement and interpretation. The full-field time-dependent surface displacements as a result of externally excited soft tissues are collected through digital image correlation (DIC). A developed analytical model, capturing the low-amplitude vibration behavior of anisotropic layered human skin with the incorporation of the influence of subcutaneous elasticity and inertia, is employed to accurately predict its resonant frequencies and pertaining displacement field images. An efficient solution approach for the model is implemented into an inverse algorithm to rapidly characterize the anisotropic elastic properties based on importing the vibration characteristics. To show the merit of the approach, a 3-D finite element (FE) simulation model was used to generate full-field data, detected and matched with a set of specific vibration modes via modal assurance criterion (MAC). The validity of the model implemented into the inverse characterization algorithm is demonstrated through a comparison of predicted vibration frequencies and mode-shapes simulated via the 3-D FE model for different cases with anisotropic elastic properties in different layers of the skin. It is shown that modes are influenced differently when anisotropic properties are introduced to the model. Thus, the established inverse characterization algorithm is capable of rapidly predicting the elastic material properties of anisotropic soft sheets with adequate accuracy.

Impact of Indenter Size and Microrelief Anisotropy on the Tribological Behavior of Human Skin

Everyday, we interact with screens, sensors, and many other devices through contact with the skin. Experimental efforts have increased our knowledge of skin tribology but are challenged by the fact that skin has a complex structure, undergoes finite deformations, has nonlinear material response, and has properties that vary with anatomical location, age, sex, and environmental conditions. Computational models are powerful tools to dissect the individual contribution of these variables to the overall frictional response. Here, we present a three-dimensional high-fidelity multilayer skin computational model including a detailed surface topography or skin microrelief. Four variables are explored: local coefficient of friction (COF), indenter size, mechanical properties of the stratum corneum, and displacement direction. The results indicate that the global COF depends nonlinearly on the local COF, implying a role for skin deformation on the friction response. The global COF is also influenced by the ratio of the indenter size to the microrelief features, with larger indenters smoothing out the role of skin topography. Changes in stiffness of the uppermost layer of skin associated with humidity have a substantial effect on both the contact area and the reaction forces, but the overall changes in the COF are small. Finally, for the microrelief tested, the response can be considered isotropic. We anticipate that this model and results will enable the design of materials and devices for a desired interaction against skin.

Chitosan-Collagen Electrospun Nanofibers Loaded with Curcumin as Wound-Healing Patches

Composite chitosan-collagen nanofibrous mats embedded with curcumin were prepared via a single-step electrospinning procedure and explored as wound-healing patches with superior biological activity. A mild crosslinking protocol consisting of a short exposure to ammonia vapor and UV radiation was developed to ensure proper stability in physiological-like conditions without affecting the intrinsic biocompatibility of chitosan and collagen. The fabricated composite patches displayed a highly porous, homogeneous nanostructure consisting of fibers with an average diameter of 200 nm, thermal stability up to 200 °C, mechanical features able to ensure protection and support to the new tissues, and water-related properties in the ideal range to allow exudate removal and gas exchange. The release kinetic studies carried out in a simulated physiological environment demonstrated that curcumin release was sustained for 72 h when the mats are crosslinked hence providing prolonged bioactivity reflected by the displayed antioxidant properties. Remarkably, combining chitosan and collagen not only ensures prolonged stability and optimal physical-chemical properties but also allows for better-promoting cell adhesion and proliferation and enhanced anti-bacteriostatic capabilities with the addition of curcumin, owing to its beneficial anti-inflammatory effect, ameliorating the attachment and survival/proliferation rates of keratinocytes and fibroblasts to the fabricated patches.

Analysis of In Vivo Skin Anisotropy Using Elastic Wave Measurements and Bayesian Modelling

In vivo skin exhibits viscoelastic, hyper-elastic and non-linear characteristics. It is under a constant state of non-equibiaxial tension in its natural configuration and is reinforced with oriented collagen fibers, which gives rise to anisotropic behaviour. Understanding the complex mechanical behaviour of skin has relevance across many sectors including pharmaceuticals, cosmetics and surgery. However, there is a dearth of quality data characterizing the anisotropy of human skin in vivo. The data available in the literature is usually confined to limited population groups and/or limited angular resolution. Here, we used the speed of elastic waves travelling through the skin to obtain measurements from 78 volunteers ranging in age from 3 to 93 years old. Using a Bayesian framework allowed us to analyse the effect that age, gender and level of skin tension have on the skin anisotropy and stiffness. First, we propose a new measurement of anisotropy based on the eccentricity of angular data and conclude that it is a more robust measurement when compared to the classic "anisotropic ratio". Our analysis then concluded that in vivo skin anisotropy increases logarithmically with age, while the skin stiffness increases linearly along the direction of Langer Lines. We also concluded that the gender does not significantly affect the level of skin anisotropy, but it does affect the overall stiffness, with males having stiffer skin on average. Finally, we found that the level of skin tension significantly affects both the anisotropy and stiffness measurements employed here. This indicates that elastic wave measurements may have promising applications in the determination of in vivo skin tension. In contrast to earlier studies, these results represent a comprehensive assessment of the variation of skin anisotropy with age and gender using a sizeable dataset and robust modern statistical analysis. This data has implications for the planning of surgical procedures and questions the adoption of universal cosmetic surgery practices for very young or elderly patients.

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.

Biochemical, structural and physical changes in aging human skin, and their relationship

Skin is the largest organ of the human body, having the purpose of regulating temperature, protecting us from microbes or mechanical shocks, and allowing the sensations from touch. It is generally accepted that aging induces profound changes in the skin's biochemical, structural and physical properties, which can lead to impaired biological functions and/or diverse diseases. So far, the effects of aging on these skin properties have been well documented. However, very few studies have focused exclusively on the relationship among these critical properties in the aging process, which is this review's primary focus. Many in vivo, ex vivo, and in vitro techniques have been previously used to characterize these properties of the skin. This review aims to provide a comprehensive overview on the effects of aging on the changes in biochemical, structural, and physical properties, and explore the potential mechanisms of skin with the relation between these properties. First, we review different or contradictory results of aging-related changes in representative parameters of each property, including the interpretations of the findings. Next, we discuss the need for a standardized method to characterize aging-related changes in these properties, to improve the way of defining age-property relationship. Moreover, potential mechanisms based on the previous results are explored by linking the biochemical, structural, and physical properties. Finally, the need to study changes of various functional properties in the separate skin layers is addressed. This review can help understand the underlying mechanism of aging-related alterations, to improve the evaluation of the aging process and guide effective treatment strategies for aging-related diseases.

Mechanical modeling and characterization of human skin: A review

This paper reviews the advances made in recent years on modeling approaches and experimental techniques to characterize the mechanical properties of human skin. The skin is the largest organ of the human body that has a complex multi-layered structure with different mechanical behaviors. The mechanical properties of human skin play an important role in distinguishing between healthy and unhealthy skin. Furthermore, knowing these mechanical properties enables computer simulation, skin research, clinical studies, as well as diagnosis and treatment monitoring of skin diseases. This paper reviews the recent efforts on modeling skin using linear, nonlinear, viscoelastic, and anisotropic materials. The work also focuses on aging effects, microstructure analysis, and non-invasive methods for skin testing. A detailed explanation of the skin structure and numerical models, such as finite element models, are discussed in this work. This work also compares different experimental methods that measure the mechanical properties of human skin. The work reviews the experimental results in the literature and shows how the mechanical properties of human skin vary with the skin sites, the layers, and the structure of human skin. The paper also discusses how state-of-the-art technology can advance skin research.

Skin anisotropy: Finding the optimal incision line for volar forearm in males and females

PURPOSE

Proper understanding of skin biomechanics, viscoelasticity and investigation of skin tension vectors is necessary to find optimal incision lines. Great tension across a healing wound after any surgical procedure might lead to forming hypertrophic scars. The aim of the study was to investigate tension lines in volar forearm skin in young males and females, in order to ensure best incision line.

METHODS

Five biomechanical and viscoelastic parameters were measured using a hand-held myotonometer: Oscillation Frequency [Hz], Dynamic Stiffness [N/m], Logarithmic Decrement of tissue's natural oscillation, Mechanical Stress Relaxation Time [ms], and Creep. Measurements were taken in four different directions; Along Forearm, Across Forearm, Along Langer's Line and Across Langer's Line.

RESULTS

Significant main effects for direction were found for Oscillation Frequency (p < 0.001, η² = 0.371) [Hz], Dynamic Stiffness (p < 0.001, η² = 0.522) [N/m], Logarithmic Decrement (p < 0.001, η² = 0.083), Mechanical Stress Relaxation Time (p < 0.001, η² = 0.494) [ms] and Creep (p < 0.001, η² = 0.480). For each parameter except for logarithmic decrement results obtained Along Langers Line and Across Forearm were significantly different to Across Langers Line and Along Forearm (p < 0.001, d = -2.76 - 2.66). Significant main effects for sex were found for logarithmic decrement Along Forearm (p < 0.001, d = 1.698) and Across Langer's Line (p = 0.021, d = 1.697).

CONCLUSIONS

Our results suggested that optimal incision line for this age group in males and females could potentially be performed diagonally i.e. Across Langer's Line or parallel i.e. Along Forearm to forearm axis. These directions would provide the lowest tension across a healing wound and possibly minimalize the risk of hypertrophic scarring post incision.

Nanoparticle platforms for dermal antiaging technologies: Insights in cellular and molecular mechanisms

Aging is a continuous process defined by a progressive functional decline in physiological parameters. Skin, being one of the most vulnerable organs, shows early signs of aging which are predominantly affected by intrinsic factors like hormone, gender, mood, enzymes, and genetic predisposition, and extrinsic factors like exposure to radiation, air pollution, and heat. Visible morphological and anatomical changes associated with skin aging occur due to underlying physiological aberrations governed by numerous complex interactions at cellular and subcellular levels. Nanoparticles are perceived as a powerful tool in the cosmeceutical industry both for augmenting the efficacy of existing agents and as a novel standalone therapy. Both organic and inorganic nanoparticles have been extensively investigated in antiaging applications. The use of nanoparticles helps to enhance the activity of antiaging molecules by selectively targeting cellular and molecular pathways. On the other hand, the nanoparticle platforms also gained increasing popularity as the skin protectant against extrinsic factors such as UV radiation and pollutants. This review comprehensively discusses skin aging and its mechanism by highlighting the impact on cellular, subcellular, and epigenetic elements. Importantly, the review elaborates on the examples of organic and inorganic nanoparticle-based formulations developed for antiaging application and provides mechanistic insights on how they modulate the mechanisms of skin aging. The clinical progress of nanoparticle antiaging technologies and factors that impact clinical translation are also explored. This article is categorized under: Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Therapeutic Approaches and Drug Discovery > Emerging Technologies.

Regulating Tissue-Mimetic Mechanical Properties of Bottlebrush Elastomers by Magnetic Field

We report on a new class of magnetoactive elastomers (MAEs) based on bottlebrush polymer networks filled with carbonyl iron microparticles. By synergistically combining solvent-free, yet supersoft polymer matrices, with magnetic microparticles, we enable the design of composites that not only mimic the mechanical behavior of various biological tissues but also permit contactless regulation of this behavior by external magnetic fields. While the bottlebrush architecture allows to finely tune the matrix elastic modulus and strain-stiffening, the magnetically aligned microparticles generate a 3-order increase in shear modulus accompanied by a switch from a viscoelastic to elastic regime as evidenced by a ca. 10-fold drop of the damping factor. The developed method for MAE preparation through solvent-free coinjection of bottlebrush melts and magnetic particles provides additional advantages such as injection molding of various shapes and uniform particle distribution within MAE composites. The synergistic combination of bottlebrush network architecture and magnetically responsive microparticles empowers new opportunities in the design of actuators and active vibration insulation systems.

Changes in the three-dimensional microscale topography of human skin with aging impact its mechanical and tribological behavior

Human skin enables interaction with diverse materials every day and at all times. The ability to grasp objects, feel textures, and perceive the environment depends on the mechanical behavior, complex structure, and microscale topography of human skin. At the same time, abrasive interactions, such as sometimes occur with prostheses or textiles, can damage the skin and impair its function. Previous theoretical and computational efforts have shown that skin's surface topography or microrelief is crucial for its tribological behavior. However, current understanding is limited to adult surface profiles and simplified two-dimensional simulations. Yet, the skin has a rich set of features in three dimensions, and the geometry of skin is known to change with aging. Here we create a numerical model of a dynamic indentation test to elucidate the effect of changes in microscale topography with aging on the skin's response under indentation and sliding contact with a spherical indenter. We create three different microrelief geometries representative of different ages based on experimental reports from the literature. We perform the indentation and sliding steps, and calculate the normal and tangential forces on the indenter as it moves in three distinct directions based on the characteristic skin lines. The model also evaluates the effect of varying the material parameters. Our results show that the microscale topography of the skin in three dimensions, together with the mechanical behavior of the skin layers, lead to distinctive trends on the stress and strain distribution. The major finding is the increasing role of anisotropy which emerges from the geometric changes seen with aging.

Use of Vibrational Optical Coherence Tomography to Analyze the Mechanical Properties of Composite Materials

Energy storage and dissipation by composite materials are important design parameters for sensors and other devices. While polymeric materials can reversibly store energy by decreased chain randomness (entropic loss) they fail to be able to dissipate energy effectively and ultimately fail due to fatigue and molecular chain breakage. In contrast, composite tissues, such as muscle and tendon complexes, store and dissipate energy through entropic changes in collagen (energy storage) and viscous losses (energy dissipation) by muscle fibers or through fluid flow of the interfibrillar matrix. In this paper we review the molecular basis for energy storage and dissipation by natural composite materials in an effort to aid in the development of improved substrates for sensors, implants and other commercial devices. In addition, we introduce vibrational optical coherence tomography, a new technique that can be used to follow energy storage and dissipation by composite materials without physically touching them.

Liraglutide-loaded PLGA/gelatin electrospun nanofibrous mats promote angiogenesis to accelerate diabetic wound healing via the modulation of miR-29b-3p

Diabetic wounds remain a serious clinical challenge whereas current therapies have limited effects on reducing the high disability and morbidity. Impaired vascularization is closely associated with delayed healing of diabetic wounds and liraglutide (Lira), a GLP-1R receptor agonist, has been reported to promote the angiogenic ability of endothelial cells. However, its application is hindered owing to the unsustainable drug concentration. In this study, we prepared a poly (lactic-co-glycolic acid)/gelatin (PLGA/Gel) nanofibrous mat scaffold to sustain the release of Lira for skin tissue engineering through 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide/N-hydroxy sulfosuccinimide (EDC/NHS), a green cross-linking-graft integration method. The incorporation of Lira into PLGA/Gel increased the pore size, hydrophilicity, elasticity and degradation properties of nanofibrous mats, which were advantageous to wound healing. In addition, the effects on diabetic wound healing, vascularization and its underlying mechanism were evaluated. The results revealed that PLGA/Gel/Lira remarkably improved the healing efficiency of diabetic dermal wounds characterized by shortened wound closure time, increased blood vessel density, and elevated collagen deposition and alignment. In vitro, Lira reversed the inhibitory effects on proliferation, migration, tube differentiation, and VEGF secretion of endothelial cells induced by high glucose (HG). As for the underlying mechanism, Lira specifically decreased the level of miR-29b-3p, targeting the AKT/GSK-3β/β-catenin pathway to regulate the biological function of endothelial cells. In conclusion, for the first time this study combined PLGA/Gel with Lira to take advantage of their synergistic effects to promote vascularization, a promising strategy to accelerate diabetic wound repair.