Skin homeostasis: Mechanism and influencing factors

BACKGROUND

The skin is the largest organ in the human body, not only resisting the invasion of harmful substances, but also preventing the loss of moisture and nutrients. Maintaining skin homeostasis is a prerequisite for the proper functioning of the body. Any damage to the skin can lead to a decrease in local homeostasis, such as ultraviolet radiation, seasonal changes, and air pollution, which can damage the skin tissue and affect the function of the skin barrier.

OBJECTIVE

This article reviews the maintenance mechanism and influencing factors of skin homeostasis and the symptoms of homeostasis imbalance.

METHODS

We searched for articles published between 1990 and 2022 in English and Chinese using PubMed, Web of Science, CNKI, and other databases in the subject area of dermatology, using the following search terms in various combinations: "skin homeostasis," "skin barrier," and "unstable skin." Based on our results, we further refined our search criteria to include a series of common skin problems caused by the destruction of skin homeostasis and its treatments. Limitations include the lack of research on dermatological and cosmetic problems triggered by the disruption of skin homeostasis.

RESULTS

This study describes the neuroendocrine-immune system, skin barrier structure, and skin metabolic system that maintain skin homeostasis. In addition, we discuss several common symptoms that occur when skin homeostasis is out of balance, such as dryness, redness, acne, sensitivity, and aging, and explain the mechanism of these symptoms.

CONCLUSION

This article provides an update and review for students and practitioners, and provides a theoretical basis for the development of skin care products for the maintenance and repair of skin homeostasis.

From consistent subjective assessment of skin sensitivity severity to its accurate objective scoring

BACKGROUND

Sensitive skin (SenS) is a syndrome leading to unpleasant sensations with little visible signs. Grading its severity generally relies on questionnaires or subjective ratings.

MATERIALS AND METHODS

The SenS status of 183 subjects was determined by trained assessors. Answers from a four-item questionnaire were converted into numerical scores, leading to a 0-15 SenS index that was asked twice or thrice. Parameters from hyperspectral images were used as input for a multi-layer perceptron (MLP) neural network to predict the four-item questionnaire score of subjects. The resulting model was used to evaluate the soothing effect of a cosmetic cream applied to one hemiface, comparing it to that of a placebo applied to the other hemiface.

RESULTS

The four-item questionnaire score accurately predicts SenS assessors' classification (92.7%) while providing insight into SenS severity. Most subjects providing repeatable replies are non-SenS, but accepting some variability in answers enables identifying subjects with consistent replies encompassing a majority of SenS subjects. The MLP neural network model predicts the SenS score of subjects with consistent replies from full-face hyperspectral images (R2 Validation set  = 0.969). A similar quality is obtained with hemiface images. Comparing the effect of applying a soothing cosmetic to that of a placebo revealed that subjects with the highest instrumental index (> 5) show significant SenS improvement.

CONCLUSION

A four-item questionnaire enables calculating a SenS index grading its severity. Objective evaluation using hyperspectral images with an MLP neural network accurately predicts SenS severity and its favourable evolution upon the application of a soothing cream.

Investigating the impact of sebum secretion on liquid makeup foundation darkening and its solution

OBJECTIVES

Darkening has been an issue of concern for foundation products. The secretion of sebum plays a significant role in the process of foundation darkening, but the underlying mechanisms and solutions have been rarely reported. The aim of this study was to explore the relationship between sebum secretion and liquid foundation darkening and to provide possible solutions for reducing sebum-induced darkening in liquid foundation.

METHODS

Artificial sebum in different concentrations was added to a basic liquid foundation to simulate different stages of sebum secretion. The colour of the mixture was then measured by a spectrophotometer on the standard opacity chart. Potential technical solutions for anti-darkening were applied to a basic liquid foundation, and its ability to anti-darkening was further verified in vivo.

RESULTS

(1) The influences of sebum addition on liquid foundation darkening had a significant positive correlation with the increase in transmissivities (R2  = 0.852, p < 0.01). (2) A certain range of sebum addition can reduce the darkening of volatile foundations. (3) The liquid foundations using pigments with high dispersibility in sebum were less influenced by sebum. (4) The replacement of pigments with oil-fixing ability could effectively reduce the darkening of liquid foundations induced by sebum (p < 0.01).

CONCLUSION

The effect of sebum on the darkening of liquid foundation was accompanied by a greater transmissivity as its pigment concentration decreased. Balanced volatility, the addition of powders with higher sebum dispersibility and the replacement of oil-fixing powders could reduce the darkening of the liquid foundation caused by sebum secretion.

Autonomic responses to pressure sensitivity of head, face and neck: Heart rate and skin conductance

Subjective scales are frequently used in the design process of head-related products to assess pressure discomfort. Nevertheless, some users lack fundamental cognitive and motor abilities (e.g., paralyzed patients). Therefore, it is vital to find non-verbal measurements of pressure discomfort and pressure pain. This study gathered the autonomic response data (heart rate and skin conductance) of 30 landmarks in head, neck and face from 31 participants experiencing pressure discomfort and pressure pain. The results indicate that pressure stimulation can change heart rate (HR) and skin conductance (SC). SC can be more useful in assessing pressure discomfort than HR for specific landmarks, and SC also possesses a faster arousal rate than HR. Moreover, HR decreased in response to pressure stimulation, while SC decreased followed by an increase. In comparisons between genders, the subjective pressure discomfort threshold (PDT) and pressure pain threshold (PPT) of women were lower than those of men, but men's autonomic responses (HR and SC) were more intense. Furthermore, there was no linear correlation between subjective pressure thresholds (PDT and PPT) and autonomic response intensity. This study has significant implications for resolving ergonomic issues (pressure discomfort and pain) associated with head-related products.

Evaluation of the effects of 10% and 30% gluconolactone chemical peel on sebum, pH, and TEWL

BACKGROUND

Gluconolactone (GLA) exhibits antioxidant and moisturizing effects. It also presents soothing effects, protects elastin fibers from UV-induced degradation, and improves the function of the skin barrier.

AIMS

Evaluation of skin parameters such as pH, transepidermal water loss (TEWL), sebum levels before, during, and after a series of applications of 10% and 30% GLA chemical peel in a split-face model.

MATERIALS AND METHODS

The study involved 16 female subjects. Three split-face procedures were performed using two concentrations of GLA solution applied on two sides of the face. The skin parameters were measured before treatments and 7 days after the last procedure at four measurement sites on either side of the face, that is, on the forehead, around the eye, on the cheek, and on the nose wing.

RESULTS

Measurement of sebum demonstrated some statistically significant changes between sebum levels in the cheeks after a series of treatments. The pH measurement showed that the pH value was reduced after each treatment at all measurement points. The level of TEWL after treatments was significantly lower around the eyes, on the left forehead, and on the right cheek. There were no significant differences between the use of different concentrations of the GLA solution.

CONCLUSIONS

The results of the study show that GLA has a significant influence on lowering skin pH and TEWL. GLA also has seboregulatory properties.

Molecular insights of human skin epidermal and dermal aging

Human skin is the most widespread and abundant type of tissue in the human body. With the passage of time, most of our organs, including a substantial part of the skin, tend to undergo a gradual thinning or decrease in size. As we age, there is a gradual and progressive reduction in the thickness of both the epidermis and dermis layers of our skin. This is primarily attributed to the decline of epidermal stem cells and the loss of dermal collagen, which is the most abundant protein in the human body. Age-related alterations of the epidermis and dermis impair skin structure/function and create a tissue microenvironment that promotes age-related skin diseases, such as impaired skin barrier, delayed wound healing, and skin cancer development. This review will examine the current body of literature pertaining to our knowledge of skin epidermal and dermal aging.

Investigating causal relationships between obesity and skin barrier function in a multi-ethnic Asian general population cohort

BACKGROUND

Skin diseases impact significantly on the quality of life and psychology of patients. Obesity has been observed as a risk factor for skin diseases. Skin epidermal barrier dysfunctions are typical manifestations across several dermatological disturbances.

OBJECTIVES

We aim to establish the association between obesity and skin physiology measurements and investigate whether obesity may play a possible causal role on skin barrier dysfunction.

METHODS

We investigated the relationship of obesity with skin physiology measurements, namely transepidermal water loss (TEWL), skin surface moisture and skin pH in an Asian population cohort (n = 9990). To assess for a possible causal association between body mass index (BMI) and skin physiology measurements, we performed Mendelian Randomization (MR), along with subsequent additional analyses to assess the potential causal impact of known socioeconomic and comorbidities of obesity on TEWL.

RESULTS

Every 1 kg/m2 increase in BMI was associated with a 0.221% (95%CI: 0.144-0.298) increase in TEWL (P = 2.82E-08), a 0.336% (95%CI: 0.148-0.524) decrease in skin moisture (P = 4.66E-04) and a 0.184% (95%CI: 0.144-0.224) decrease in pH (P = 1.36E-19), adjusting for age, gender, and ethnicity. Relationships for both TEWL and pH with BMI remained strong (Beta 0.354; 95%CI: 0.189-0.520 and Beta -0.170; 95%CI: -0.253 to -0.087, respectively) even after adjusting for known confounders, with MR experiments further supporting BMI's possible causal relationship with TEWL. Based on additional MR performed, none of the socioeconomic and comorbidities of obesity investigated are likely to have possible causal relationships with TEWL.

CONCLUSION

We establish strong association of BMI with TEWL and skin pH, with MR results suggestive of a possible causal relationship of obesity with TEWL. It emphasizes the potential impact of obesity on skin barrier function and therefore opportunity for primary prevention.

Relationship Between Degree of Neonatal Physiologic Desquamation and Skin Barrier Function

BACKGROUND/OBJECTIVES

This study examined the relationship between degree of neonatal physiologic desquamation and skin barrier functionality. In addition, we identified factors associated with neonatal desquamation.

METHODS

This cross-sectional study assessed 4-day-old newborns. The desquamation level was evaluated and placed in one of the following categories based on the severity of the desquamation: no desquamation, a small amount, and severe (including cracked or bleeding). Skin barrier function was assessed by evaluating transepidermal water loss, stratum corneum hydration, skin pH, and sebum secretion.

RESULTS

Among study participants, 67 (39.9%) showed no desquamation, 82 (48.8%) displayed a small amount, and 19 (11.3%) had severe desquamation. The group with severe desquamation had significantly elevated facial transepidermal water loss levels and reduced levels of stratum corneum hydration throughout the body, indicating skin barrier dysfunction, than other groups. In addition, the group with severe desquamation had a significantly longer gestational age, lower temperature and humidity level, smaller vernix caseosa, and tended to be born during winter.

CONCLUSIONS

To our knowledge, this is the first report indicating that infants with severe desquamation had worsened skin barrier function versus those with moderate and no desquamation. Future research should consider what kind of care should be provided to newborns with severe desquamation.

The Five Basic Human Senses Evoke Electrodermal Activity

Electrodermal activity (EDA) usually relates to variations in the electrical properties of palmar or plantar skin sites. EDA responses, namely skin conductance responses (SCRs), skin potential responses (SPRs) and skin susceptance responses (SSRs) are shown to be sensitive indexes of sympathetic nervous system activation and are studied in many research projects. However, the association between EDA responses and the five basic human senses has not been investigated yet. Our study aimed to explore the relationship between the three EDA responses (SCRs, SSRs and SPRs) and the five basic human senses. These three EDA responses were measured simultaneously at the same skin site on each of the 38 volunteers. The tested five senses were sight, hearing, touch, taste and smell. The results showed that the different tested senses led to different degrees of EDA responses due to activation of the sympathetic nervous system and corresponding secretion of sweat. Although a controlled study on the degree of EDA as a function of the strength of each stimulus was not performed, we noted that the largest EDA responses were typically associated with the smell sense test. We conclude that EDA responses could be utilized as measures for examining the sensitivity of the human senses. Hence, EDA devices may have important roles in sensory systems for future clinical applications.

Bio-potential noise of dry printed electrodes: physiology versus the skin-electrode impedance

Objective. To explore noise characteristics and the effect physiological activity has on the link between impedance and noise.Approach. Dry-printed electrodes are emerging as a new and exciting technology for skin electro-physiology. Such electrode arrays offer many advantages including user convenience, quick placement, and high resolution. Here we analyze extensive electro-physiological data recorded from the arm and the face to study and quantify the noise of dry electrodes, and to characterize the link between noise and impedance. In particular, we studied the effect of the physiological state of the subject (e.g. rapid eye movement sleep) on noise.Main results. We show that baseline noise values extracted from dry electrodes in the arm are in agreement with the Nyquist equation. In the face, on the other hand, the measured noise values were higher than the values predicted by the Nyquist equation. In addition, we studied how different electrode properties affect performances, including electrode size, shape, and material properties.Significance. Altogether, the results presented here provide a basis for understanding dry electrode performances and substantiate their great potential in electro-physiological investigations.

Emergence of New Concepts in Skin Physiopathology through the Use of in vitro Human Skin Explants Models

BACKGROUND

This review summarizes uses and new applications for dermatological research of in vitro culture models of human skin explants (HSEs). In the last decade, many innovations have appeared in the literature and an exponential number of studies have been recorded in various fields of application such as process culture engineering, stem cell extractions methodology, or cell-to-cell interaction studies under physiological and pathological conditions, wound-healing, and inflammation. Most studies also concerned pharmacology, cosmetology, and photobiology. However, these topics will not be considered in our review.

SUMMARY

A better understanding of the mechanisms driving intercellular relationships, at work in the maintenance of 3D tissue architectures has led to the improvement of cell culture techniques. Many papers have focused on the physiological ways that govern in vitro tissue maintenance of HSEs. The analysis of the necessary mechanical stress, intercellular and cell-matrix interactions, allows the maintenance and prolonged use of HSEs in culture for up to 15 days, regardless of the great variability of study protocols from one laboratory to another and in accordance with the objectives set. Because of their close similarities to fresh skin, HSEs are increasingly used to study skin barrier repair and wound healing physiology. Easy to use in co-culture, this model allows a better understanding of the connections and interactions between the peripheral nervous system, the skin and the immune system. The development of the concept of an integrated neuro-immuno-cutaneous system at work in skin physiology and pathology highlighted by this article represents one of the new technical challenges in the field of in vitro culture of HSE. This review of the literature also reveals the importance of using such models in pathology. As sources of stem cells, HSEs are the basis for the development of new tissue engineering models such as organoids or optical clearing tissues technology. This study identifies the main advances and cross-cutting issues in the use of HSE.

Skin maturation from birth to 10 years of age: Structure, function, composition and microbiome

Infant and adult skin physiology differ in many ways; however, limited data exist for older children. To further investigate the maturation processes of healthy skin during childhood. Skin parameters were recorded in 80 participants of four age groups: babies (0-2 years), young children (3-6 years), older children (7-<10 years) and adults (25-40 years). Overall, skin barrier function continues to mature, reaching adult levels of transepidermal water loss (TEWL), lipid compactness, stratum corneum (SC) thickness and corneocyte size by the age of about 6 years. Higher levels of lactic acid and lower levels of total amino acids in the SC of babies and young children further indicate higher cell turnover rates. In all age groups, TEWL and skin surface hydration values remain higher on the face compared with the arm. Skin becomes darker and contains higher levels of melanin with increasing age. The composition of skin microbiome of the dorsal forearm in all children groups is distinct from that in adults, with Firmicutes predominating in the former and Proteobacteria in the latter. Skin physiology, along with the skin microbiome, continues to mature during early childhood in a site-specific manner.

Intradermal Microdialysis: An Approach to Investigating Novel Mechanisms of Microvascular Dysfunction in Humans

The cutaneous vasculature is an accessible tissue that can be used to assess microvascular function in humans. Intradermal microdialysis is a minimally invasive technique used to investigate mechanisms of vascular smooth muscle and endothelial function in the cutaneous circulation. This technique allows for the pharmacological dissection of the pathophysiology of microvascular endothelial dysfunction as indexed by decreased nitric oxide-mediated vasodilation, an indicator of cardiovascular disease development risk. In this technique, a microdialysis probe is placed in the dermal layer of the skin, and a local heating unit with a laser Doppler flowmetry probe is placed over the probe to measure the red blood cell flux. The local skin temperature is clamped or stimulated with direct heat application, and pharmacological agents are perfused through the probe to stimulate or inhibit intracellular signaling pathways in order to induce vasodilation or vasoconstriction or to interrogate mechanisms of interest (co-factors, antioxidants, etc.). The cutaneous vascular conductance is quantified, and mechanisms of endothelial dysfunction in disease states can be delineated.

The role of the dorsolateral prefrontal cortex in control of skin sympathetic nerve activity in humans

The dorsolateral prefrontal cortex (dlPFC) is primarily involved in higher order executive functions, with there being evidence of lateralization. Brain imaging studies have revealed its link to the generation of skin sympathetic nerve activity (SSNA), which is elevated in states of emotional arousal or anxiety. However, no studies have directly explored dlPFC influences on SSNA. Transcranial alternating current stimulation (-2 to 2 mA, 0.08 Hz, 100 cycles) was applied between the left or right dlPFC and nasion via surface electrodes. Spontaneous bursts of SSNA were recorded from the common peroneal nerve via a tungsten microelectrode in 21 healthy participants. The modulation index was calculated for each stimulation paradigm by constructing cross-correlation histograms between SSNA and the sinusoidal stimulus. Stimulation of the dlPFC caused significant modulation of SSNA, but there was no significant difference in the median modulation index across sides. Stimulation also caused cyclic modulation of skin blood flow and sweat release. We have shown for the first time that stimulation of the dlPFC causes modulation of SSNA, also reflected in the effector-organ responses. This supports a role for the dlPFC in the control of SSNA, which likely contributes to the ability of emotions to bring about cutaneous vasoconstriction and sweat release.

Transepidermal water loss and stratum corneum hydration in forearm versus hand palm

BACKGROUND

Skin measurements of transepidermal water loss (TEWL) and stratum corneum hydration (SCH) reflect different aspects of skin physiology. Since epidermal water loss depends on epidermal-to-air water vapor gradients, a possible quantitative relationship between TEWL and SCH may exist. This investigation's purpose was to test the possible TEWL-SCH relationship.

MATERIALS AND METHODS

SCH and TEWL were measured noninvasively on forearm and palmer thenar eminence (hand) in 40 young adults (20 males) along with total body fat percentage (FAT) via bioimpedance.

RESULTS

A significant positive nonlinear correlation (p < 0.001) was detected between SCH and TEWL in hands of the male cohort that occurred when SCH exceeded a threshold level. This threshold level was not exceeded in male or female forearms and forearms did not display a SCH-TEWL correlation. There was a weak inverse dependence of TEWL on FAT on both forearm and hand (p < 0.05), but no SCH-FAT relationship was observed. TEWL values on the forearm and hand were moderately correlated with each other (p = 0.002) but SCH values were not.

CONCLUSION

The findings clarify the relationship between forearm and palmer hydration and TEWL values, and their relationship to total body fat percentages in young healthy adults. The significant correlation between palmer stratum corneum hydration and palmer TEWL that was discovered in the male but not the female cohort suggests a threshold hydration level for which TEWL depends both on skin barrier function and stratum corneum hydration. This implies that conditions with increased SCH may in part account for elevated TEWL values.

The Skin Microbiome: Current Landscape and Future Opportunities

Our skin is the largest organ of the body, serving as an important barrier against the harsh extrinsic environment. Alongside preventing desiccation, chemical damage and hypothermia, this barrier protects the body from invading pathogens through a sophisticated innate immune response and co-adapted consortium of commensal microorganisms, collectively termed the microbiota. These microorganisms inhabit distinct biogeographical regions dictated by skin physiology. Thus, it follows that perturbations to normal skin homeostasis, as occurs with ageing, diabetes and skin disease, can cause microbial dysbiosis and increase infection risk. In this review, we discuss emerging concepts in skin microbiome research, highlighting pertinent links between skin ageing, the microbiome and cutaneous repair. Moreover, we address gaps in current knowledge and highlight key areas requiring further exploration. Future advances in this field could revolutionise the way we treat microbial dysbiosis associated with skin ageing and other pathologies.

An evaluation of mechanical and biophysical skin parameters at different body locations

BACKGROUND

Skin is the largest organ in the body, representing an important interface to monitor health and disease. However, there is significant variation in skin properties for different ages, genders and body regions due to the differences in the structure and morphology of the skin tissues. This study aimed to evaluate the use of non-invasive tools to discriminate a range of mechanical and functional skin parameters from different skin sites.

MATERIALS AND METHODS

A cohort of 15 healthy volunteers was recruited following appropriate informed consent. Four well-established CE-marked non-invasive techniques were used to measure four anatomical regions: palm, forearm, sole and lower lumbar L3, using a repeated measures design. Skin parameters included trans-epidermal water loss (TEWL), pH (acidity), erythema, stratum corneum hydration and stiffness and elasticity using Myoton Pro (skin and muscle probe). Differences between body locations for each parameter and the intra-rater reliability between days were evaluated by the same operator.

RESULTS

The results indicate that parameters differed significantly between skin sites. For the Myoton skin probe, the sole recorded the highest stiffness value of 1006 N/m (SD ± 179), while the lower lumbar recorded the least value of 484 N/m (SD ± 160). The muscle indenter Myoton probe revealed the palm's highest value of 754 N/m (± 108), and the lower lumbar recorded the least value of 208 N/m (SD ± 44). TEWL values were lowest on the forearm, averaging 11 g/m2/h, and highest on the palm, averaging 41 g/m2/h. Similar skin hydration levels were recorded in three of the four sites, with the main difference being observed in the sole averaging 13 arbitrary units. Erythema values were characterised by a high degree of inter-subject variation, and no significant differences between sites or sides were observed. The Myoton Pro Skin showed excellent reliability (intra-class correlation coefficients > 0.70) for all sites with exception of one site right lower back; the Myoton pro muscle probes showed good to poor reliability (0.90-017), the corneometer showed excellent reliability (>0.75) among all the sites tested, and the TEWL showed Good to poor reliability (0.74-0.4) among sites.

CONCLUSION

The study revealed that using non-invasive methods, the biophysical properties of skin can be mapped, and significant differences in the mechanical and functional properties of skin were observed. These parameters were reliably recorded between days, providing a basis for their use in assessing and monitoring changes in the skin during health and disease.

Multiple Effects of Echinochrome A on Selected Ion Channels Implicated in Skin Physiology

Echinochrome A (Ech A), a naphthoquinoid pigment from sea urchins, is known to have anti-inflammatory and analgesic effects that have been suggested to be mediated by antioxidant activity and intracellular signaling modulation. In addition to these mechanisms, the ion channels in keratinocytes, immune cells, and nociceptive neurons may be the target for the pharmacological effects. Here, using the patch clamp technique, we investigated the effects of Ech A on the Ca²⁺-permeable TRPV3, TRPV1 and Orai1 channels and the two-pore domain K⁺ (K2P) channels (TREK/TRAAK, TASK-1, and TRESK) overexpressed in HEK 293 cells. Ech A inhibited both the TRPV3 and Orai1 currents, with IC₅₀ levels of 2.1 and 2.4 μM, respectively. The capsaicin-activated TRPV1 current was slightly augmented by Ech A. Ech A alone did not change the amplitude of the TREK-2 current (I_TREK2), but pretreatments with Ech A markedly facilitated I_TREK2 activation by 2-APB, arachidonic acid (AA), and acidic extracellular pH (pH_e). Similar facilitation effects of Ech A on TREK-1 and TRAAK were observed when they were stimulated with 2-APB and AA, respectively. On the contrary, Ech A did not affect the TRESK and TASK-1 currents. Interestingly, the I_TREK2 maximally activated by the combined application of 2-APB and Ech A was not inhibited by norfluoxetine but was still completely inhibited by ruthenium red. The selective loss of sensitivity to norfluoxetine suggested an altered molecular conformation of TREK-2 by Ech A. We conclude that the Ech A-induced inhibition of the Ca²⁺-permeable cation channels and the facilitation of the TREK/TRAAK K2P channels may underlie the analgesic and anti-inflammatory effects of Ech A.

How Skin Color Depends on Tissue Oxygenation

BACKGROUND

Skin color is essential to skin and wound assessment as it brings valuable information about skin physiology and pathology. An approach, which can help deconvolute and isolate various mechanisms affecting skin color, could be helpful to drive the remote photoplethysmography (rPPG) utility beyond its current applications.

AIM

The present work aims to create a simple analytical framework that links skin color with blood oxygenation and perfusion.

MATERIAL AND METHODS

The model consists of two parts. First, the model's core connects changes in tissue chromophore concentrations with changes in tissue reflectance. In the second step, the tissue reflectance is convoluted with the response curves of a sensor (tristimulus response in the case of the human eye) and the light source's spectrum.

RESULTS

The model allows linking changes in blood oxygenation and perfusion with changes in skin color.

CONCLUSION

The model can be helpful for the interpretation of the amplitudes of various components of the rPPG signal.

Acidic skin care promotes cutaneous microbiome recovery and skin physiology in an acute stratum corneum stress model

INTRODUCTION

Skin microbiome and skin physiology are important indicators of the epidermal homeostasis status. Stress models can reveal pathological conditions and modulating effects. Here we investigated the cutaneous microbiome in relation to skin physiology after mild tape stripping (TS) without treatment compared to two cosmetic leave-on lotions (pH 5.5 vs. pH 9.3) in 25 healthy volunteers.

METHODS

The microbiome was analyzed by 16S-rRNA-gene amplicon sequencing and put in relation to the following skin physiology parameter: epidermal barrier function (TEWA-Meter TM300), stratum corneum hydration (Corneometer CM 825), surface pH (pH-Meter) and skin erythema (Mexameter).

RESULTS

TS reduced the alpha diversity with a recovery over 7 days without treatment. Both lotions significantly accelerated the recovery of the alpha-diversity already after 2 days with a slightly higher rate for the acidic lotion. After TS, the relative abundance of Proteobacteria was increased, whereas Actinobacteria were reduced. The relative abundances of typical skin-associated genera were reduced after TS. Taxa compositions returned to normal levels after 7 days in all treatment groups. An accelerated normalization could be observed with both lotions already after two days. A significant difference in skin pH was observed on day2 and day7 with an increased pH for the alkaline lotion. Both lotions induced an increase in stratum corneum hydration.

CONCLUSION

The study proved the suitability of an experimental stress model in the assessment of skin surface microbiome in relation to skin physiology. Stratum corneum hydration increased significantly with both lotions already at day2. Microbiome parameters (alpha-diversity, mean relative taxa, abundance of selected genera) normalized over 2-7 days. The following mechanisms could be responsible for the accelerated normalization of the microbiome: a) optimized hydration during the recovery phase, b) the composition of the lotion c) the induced repair mechanism. Thus, the formulation has a positive effect on the stratum corneum hydration and subsequently on cutaneous microbiome and skin physiology. Furthermore, this has eventually implications in the modulation of exogenous stress-induced epidermal alterations.

Physiological characterization of electrodermal activity enables scalable near real-time autonomic nervous system activation inference

Electrodermal activities (EDA) are any electrical phxenomena observed on the skin. Skin conductance (SC), a measure of EDA, shows fluctuations due to autonomic nervous system (ANS) activation induced sweat secretion. Since it can capture psychophysiological information, there is a significant rise in the research work for tracking mental and physiological health with EDA. However, the current state-of-the-art lacks a physiologically motivated approach for real-time inference of ANS activation from EDA. Therefore, firstly, we propose a comprehensive model for the SC dynamics. The proposed model is a 3D state-space representation of the direct secretion of sweat via pore opening and diffusion followed by corresponding evaporation and reabsorption. As the input to the model, we consider a sparse signal representing the ANS activation that causes the sweat glands to produce sweat. Secondly, we derive a scalable fixed-interval smoother-based sparse recovery approach utilizing the proposed comprehensive model to infer the ANS activation enabling edge computation. We incorporate a generalized-cross-validation to tune the sparsity level. Finally, we propose an Expectation-Maximization based deconvolution approach for learning the model parameters during the ANS activation inference. For evaluation, we utilize a dataset with 26 participants, and the results show that our comprehensive state-space model can successfully describe the SC variations with high scalability, showing the feasibility of real-time applications. Results validate that our physiology-motivated state-space model can comprehensively explain the EDA and outperforms all previous approaches. Our findings introduce a whole new perspective and have a broader impact on the standard practices of EDA analysis.

The current state-of-the-art lacks physiology-motivated models for electrodermal activities (EDA) that have the power to comprehensively describe the variations in skin conductance (SC)–a measure of EDA. In this study, we propose a physiology-motivated state-space model to address previous challenges. On the other hand, there is also an absence of a scalable autonomic nervous system (ANS) activation inference method that simultaneously solve for the physiological system parameters. Furthermore, we develop a scalable ANS activation inference approach based on the proposed model with a goal for real-time edge computation. We utilize a dataset with 26 participants to validate the new model and the scalable method. Results demonstrate that our physiology-motivated state-space model can comprehensively explain the EDA. Our findings introduce a whole new perspective and have a broader impact on standard practices of EDA analysis.

Modeling subjective fear using skin conductance: a preliminary study in virtual reality

Reliably measuring fear perception could help evaluate the effectiveness of treatments for pathological conditions such as specific phobias or post-traumatic stress syndrome (e.g., exposure therapy). In this study, we developed a novel vir-tual reality (VR) scenario to induce fear and evaluate the related physiological response by the analysis of skin conductance (SC) signal. Eighteen subjects voluntarily experienced the fear VR scenario while their SC was recorded. After the experiment, each participant was asked to score the perceived subjective fear using a Likert scale from 1 to 10. We used the cvxEDA algorithm to process the collected SC signals and extract several features able to estimate the autonomic response to the fearful stimuli. Finally, the extracted features were linearly combined to model the subjective fear perception scores by means of LASSO linear regression. The sparsification imposed by the LASSO procedure to mitigate the overfitting risk identified an optimal linear model including only the standard deviation of the tonic SC component as a regressor (p = 0.007; R2 = 0.3337). The significant contribution of this feature to the model suggests that subjects experiencing more intense subjective fear have a more variable and unstable sympathetic tone.

Skin Minerals: Key Roles of Inorganic Elements in Skin Physiological Functions

As odd as it may seem at first glance, minerals, it is what we are all about…or nearly. Although life on Earth is carbon-based, several other elements present in the planet’s crust are involved in and often indispensable for functioning of living organisms. Many ions are essential, and others show supportive and accessory qualities. They are operative in the skin, supporting specific processes related to the particular situation of this organ at the interface with the environment. Skin bioenergetics, redox balance, epidermal barrier function, and dermal remodeling are amongst crucial activities guided by or taking advantage of mineral elements. Skin regenerative processes and skin ageing can be positively impacted by adequate accessibility, distribution, and balance of inorganic ions.

Multiscale Computational Model Predicts Mouse Skin Kinematics Under Tensile Loading

Skin is a complex tissue whose biomechanical properties are generally understood in terms of an incompressible material whose microstructure undergoes affine deformations. A growing number of experiments, however, have demonstrated that skin has a high Poisson's ratio, substantially decreases in volume during uniaxial tensile loading, and demonstrates collagen fiber kinematics that are not affine with local deformation. In order to better understand the mechanical basis for these properties, we constructed multiscale mechanical models (MSM) of mouse skin based on microstructural multiphoton microscopy imaging of the dermal microstructure acquired during mechanical testing. Three models that spanned the cases of highly aligned, moderately aligned, and nearly random fiber networks were examined and compared to the data acquired from uniaxially stretched skin. Our results demonstrate that MSMs consisting of networks of matched fiber organization can predict the biomechanical behavior of mouse skin, including the large decrease in tissue volume and nonaffine fiber kinematics observed under uniaxial tension.

Fructus Xanthii-Inspired Low Dynamic Noise Dry Bioelectrodes for Surface Monitoring of ECG

The microstructured surfaces of bioelectrical dry electrodes are important aspects of dry electrode design. However, traditional surfaces for microstructured bioelectrical dry electrodes are costly to produce and require complex fabrication methods. In this study, a novel stacked-template method is proposed for the first time, rapidly producing microstructured dry electrodes at a low cost and with a large surface area. Three types of microstructured Ag/AgCl thermoplastic polyurethane (TPU) electrodes with a Fructus xanthii-inspired barb structure (FXbs) are prepared using this method; then, the dynamic friction, hair interference resistance, electrochemical, and electrocardiogram (ECG) signal acquisition performance of the electrodes are tested, and the dynamic noise characteristics of the electrodes are comprehensively evaluated with simulated instruments. Compared to the plate structure, the dynamic friction coefficient of the FXbs electrode improved by about 38.8%, exhibiting strong hair interference resistance. In addition, the FXbs electrode exhibits low dynamic noise and comparable performance to the wet electrode, in terms of signal acquisition, when it is tested using simulated instruments. Therefore, the prepared FXbs electrode increases the friction coefficient between the electrode and the skin, which effectively resolves issues related to dynamic noise in bioelectrical signals, making it suitable for dynamic measurements.

The off-line effect of affective touch on multisensory integration and tactile perceptual accuracy during the somatic signal detection task

Affective touch refers to the emotional and motivational facets of tactile sensation and has been linked to the activation of a specialised system of mechanosensory afferents (the CT system), that respond optimally to slow caress-like touch. Affective touch has been shown to play an important role in the building of the bodily self: the multisensory integrated global awareness of one’s own body. Here we investigated the effects of affective touch on subsequent tactile awareness and multisensory integration using the Somatic Signal Detection Task (SSDT). During the SSDT, participants were required to detect near-threshold tactile stimulation on their cheek, in the presence/absence of a concomitant light. Participants repeated the SSDT twice, before and after receiving a touch manipulation. Participants were divided into two groups: one received affective touch (CT optimal; n = 32), and the second received non-affective touch (non-CT optimal; n = 34). Levels of arousal (skin conductance levels, SCLs) and mood changes after the touch manipulation were also measured. Affective touch led to an increase in tactile accuracy, as indicated by less false reports of touch and a trend towards higher tactile sensitivity during the subsequent SSDT. Conversely, non-affective touch was found to induce a partial decrease in the correct detection of touch possibly due to a desensitization of skin mechanoreceptors. Both affective and non-affective touch induced a more positive mood and higher SCLs in participants. The increase in SCLs was greater after affective touch. We conclude that receiving affective touch enhances the sense of bodily self therefore increasing perceptual accuracy and awareness. Higher SCLs are suggested to be a possible mediator linking affective touch to a greater tactile accuracy. Clinical implications are discussed.

Current Insights Into the Role of Neuropeptide Y in Skin Physiology and Pathology

Neuropeptide Y is widely distributed within the body and has long been implicated as a contributor to skin disease based on the correlative clinical data. However, until recently, there have been few empirical investigations to determine whether NPY has a pathophysiological role in the skin. Due to appearance-altering phenotypes of atopic dermatitis, psoriasis, and vitiligo, those suffering from these diseases often face multiple forms of negative social attention. This often results in psychological stress, which has been shown to exacerbate inflammatory skin diseases - creating a vicious cycle that perpetuates disease. This has been shown to drive severe depression, which has resulted in suicidal ideation being a comorbidity of these diseases. Herein, we review what is currently known about the associations of NPY with skin diseases and stress. We also review and provide educated guessing what the effects NPY can have in the skin. Inflammatory skin diseases can affect physical appearance to have significant, negative impacts on quality of life. No cure exists for these conditions, highlighting the need for identification of novel proteins/neuropetides, like NPY, that can be targeted therapeutically. This review sets the stage for future investigations into the role of NPY in skin biology and pathology to stimulate research on therapeutic targeting NPY signaling in order to combat inflammatory skin diseases.

A Visualisation Driven Training for Vibrotactile Skin Reading

Vibrotactile skin-reading effectively conveys rich information via vibrotactile patterns, which has gained attention due to recent advancements. However, training to recognize and associate vibrotactile patterns with their meaning is time-consuming and tedious. The conventional training methods use repetitive exposure of the vibrotactile stimuli along with visual and auditory cues of the corresponding symbol. This work proposes a novel visual-based training method to teach users the associations between semantic information and vibrotactile patterns. Our proposed visual explanation training is compared with the conventional training method in a study with 18 participants. Results show that participants achieve a better performance using the new visual explanation training when identifying single English alphabet characters. Moreover, the proposed training also incurred a significantly lower workload (NASA TLX) and was preferred by study participants. The proposed method is thus effective and offers a less stressful form of training users for skin reading.

Microbiome and Human Aging: Probiotic and Prebiotic Potentials in Longevity, Skin Health and Cellular Senescence

The role of the microbiome in human aging is important: the microbiome directly impacts aging through the gastrointestinal system. However, the microbial impact on skin has yet to be fully understood. For example, cellular senescence is an intrinsic aging process that has been recently associated with microbial imbalance. With age, cells become senescent in response to stress wherein they undergo irreversible growth arrest while maintaining high metabolic activity. An accumulation of senescent cells has been linked to various aging and chronic pathologies due to an overexpression of the senescence-associated secretory phenotype (SASP) comprised of proinflammatory cytokines, chemokines, growth factors, proteases, lipids and extracellular matrix components. In particular, dermatological disorders may be promoted by senescence as the skin is a common site of accumulation. The gut microbiota influences cellular senescence and skin disruption through the gut-skin axis and secretion of microbial metabolites. Metabolomics can be used to identify and quantify metabolites involved in senescence. Moreover, novel anti-senescent therapeutics are warranted given the poor safety profiles of current pharmaceutical drugs. Probiotics and prebiotics may be effective alternatives, considering the relationship between the microbiome and healthy aging. However, further research on gut composition under a senescent status is needed to develop immunomodulatory therapies.

Detachable dissolvable microneedles: intra-epidermal and intradermal diffusion, effect on skin surface, and application in hyperpigmentation treatment

Delivering bioactive compounds into skin tissue has long been a challenge. Using ex vivo porcine and rat skins, here we demonstrate that a detachable dissolvable microneedle (DDMN) array, a special dissolvable microneedle that allows needle detachment from the base within 2 min post administration, can effectively embed a model compound into epidermis and dermis. Diffusion of the compound from the needle embedding sites to the nearby skin tissue is demonstrated at various post administration periods. The relationship between the time that a conventional dissolvable microneedle array is left on skin without needle detachment from the base and the degree of skin surface abrasion at each microneedle penetration spot is also demonstrated on skin of human volunteers. Co-loading glutathione with vitamin C (vitC) can stabilize vitC in the DDMN. DDMN loaded with vitC and glutathione can help erasing post-acne-hyperpigmentation spots.

Advanced glycation end products via skin autofluorescence as potential marker of carotid atherosclerosis in patients with type 2 diabetes

BACKGROUND AND AIMS

Advanced glycation end products (AGEs) are reported to be correlated with diabetic vascular complications. This study aimed to investigate the association between AGEs and carotid atherosclerosis (CAS) as a surrogate marker of cardiovascular disease (CVD).

METHODS AND RESULTS

A total of 1006 patients with type 2 diabetes were included. CAS was defined as the presence of carotid arterial atherosclerotic plaque in any of bilateral carotid artery segments measured by ultrasonography. AGEs were measured by the noninvasive skin autofluorescence method. AGE_age index was calculated as AGEs × age/100. Patients with CAS showed a significantly higher AGE_age (P < 0.01), and the prevalence of CAS increased with ascending AGE_age levels (P for trend < 0.001). Logistic regression analysis revealed that AGE_age was significantly positively associated with odds of CAS, and the odds ratios of the presence of CAS across quartiles of AGE_age were 1.00, 3.00 [95% confidence interval (CI) 1.90-4.74], 4.04 (95%CI 2.50-6.53) and 4.99 (95%CI 2.97-8.40) for the multivariable-adjusted model (P for trend <0.001), respectively. In the fully adjusted model, each 5.0 increase in AGE_age was associated with a 0.019 mm increment in carotid intima-media thickness. Furthermore, AGE_age presented an acceptable predictive value for CAS, with an optimal cutoff point of 43.2, and the sensitivity, specificity and area under the curve (AUC) were 74.5% (95%CI 70.7-78.1%), 61.9% (95%CI 57.2-66.4%) and 0.735 (0.706-0.762), respectively.

CONCLUSION

AGE_age, the noninvasive measurement of AGEs combined with age is a promising approach for triaging patients at high risk of CVDs.

Differential Cutaneous Thermal Sensitivity in Humans: Method of Limit vs. Method of Sensation Magnitude

INTRODUCTION

The method of limits (MLI) and method of level (MLE) are commonly employed for the quantitative assessment of cutaneous thermal sensitivity. Thermal sensation and thermal comfort are closely related and thermal sensations evoked from the peripheral thermoreceptors play an important role in thermoregulatory response to maintain normal body temperature. The purpose of this study was to compare the regional distribution of cutaneous warm and cold sensitivity between MLI and the method of sensation magnitude (MSM).

METHOD

Twenty healthy men completed MLI and MSM to compare the regional distribution of cutaneous warm and cold sensitivity in the thermal neutral condition. The subjects rested on a bed in a supine position for 20 min. Next, the cutaneous thermal sensitivity of ten body sites was assessed by the means of MLI and MSM for both warmth and cold stimuli.

RESULTS

The absolute mean heat flux in MLI and thermal sensation magnitude in MSM showed significantly greater sensitivity to cold than to warm stimulation (p < 0.01), together with a similar pattern of regional differences across ten body sites. Both sensory modalities indicated acceptable reliability (SRD%: 6.29-8.66) and excellent reproducibility (ICC: 0.826-0.906; p < 0.01). However, the Z-sore distribution in MSM was much narrower than in MLI, which may limit the test sensitivity for the detection of sensory disorders and/or comparison between individuals.

CONCLUSION

The present results showed that both MLI and MSM are effective means for evaluating regional cutaneous thermal sensitivity to innocuous warm and cold stimulations to a strong degree of reliability and reproducibility.

Essential Role of STAT3 Signaling in Hair Follicle Homeostasis

Dominant-negative mutations associated with signal transducer and activator of transcription 3 (STAT3) signaling, which controls epithelial proliferation in various tissues, lead to atopic dermatitis in hyper IgE syndrome. This dermatitis is thought to be attributed to defects in STAT3 signaling in type 17 helper T cell　specification. However, the role of STAT3 signaling in skin epithelial cells remains unclear. We found that STAT3 signaling in keratinocytes is required to maintain skin homeostasis by negatively controlling the expression of hair follicle-specific keratin genes. These expression patterns correlated with the onset of dermatitis, which was observed in specific pathogen-free conditions but not in germ-free conditions, suggesting the involvement of Toll-like receptor-mediated inflammatory responses. Thus, our study suggests that STAT3-dependent gene expression in keratinocytes plays a critical role in maintaining the homeostasis of skin, which is constantly exposed to microorganisms.

Skin Barrier Dysregulation in Psoriasis

The skin barrier is broadly composed of two elements-a physical barrier mostly localised in the epidermis, and an immune barrier localised in both the dermis and epidermis. These two systems interact cooperatively to maintain skin homeostasis and overall human health. However, if dysregulated, several skin diseases may arise. Psoriasis is one of the most prevalent skin diseases associated with disrupted barrier function. It is characterised by the formation of psoriatic lesions, the aberrant differentiation and proliferation of keratinocytes, and excessive inflammation. In this review, we summarize recent discoveries in disease pathogenesis, including the contribution of keratinocytes, immune cells, genetic and environmental factors, and how they advance current and future treatments.

The Keratinocyte as a Crucial Cell in the Predisposition, Onset, Progression, Therapy and Study of the Atopic Dermatitis

The keratinocyte (KC) is the main functional and structural component of the epidermis, the most external layer of the skin that is highly specialized in defense against external agents, prevention of leakage of body fluids and retention of internal water within the cells. Altered epidermal barrier and aberrant KC differentiation are involved in the pathophysiology of several skin diseases, such as atopic dermatitis (AD). AD is a chronic inflammatory disease characterized by cutaneous and systemic immune dysregulation and skin microbiota dysbiosis. Nevertheless, the pathological mechanisms of this complex disease remain largely unknown. In this review, we summarize current knowledge about the participation of the KC in different aspects of the AD. We provide an overview of the genetic predisposing and environmental factors, inflammatory molecules and signaling pathways of the KC that participate in the physiopathology of the AD. We also analyze the link among the KC, the microbiota and the inflammatory response underlying acute and chronic skin AD lesions.

Effect of the skincare product on facial skin microbial structure and biophysical parameters: A pilot study

Daily use of cosmetics is known to affect the skin microbiome. This study aimed to determine the bacterial community structure and skin biophysical parameters following the daily application of a skincare product on the face. Twenty-five Korean women, who used the same skincare product for four weeks participated in the study. During this period, skin hydration, texture, sebum content, and pH were measured, and skin swab samples were collected on the cheeks. The microbiota was analyzed using the MiSeq system. Through these experiments, bacterial diversity in facial skin increased and the microbial community changed after four weeks of skincare product application. The relative abundance of Cutibacterium and Staphylococcus increased, significant changes in specific bacterial modules of the skin microbial network were observed, and skin hydration and texture improved. It was suggested that daily use of skincare products could affect the microbial structure of facial skin as well as the biophysical properties of the facial skin. These findings expand our understanding of the role of skincare products on the skin environment.

Gelatin Loaded Titanium Dioxide and Silver Oxide Nanoparticles: Implication for Skin Tissue Regeneration

Treatment of burn wounds has many requirements to ensure wound closure with healthy tissue, increased vascularization, guarantee edema resolution, and control bacterial infection. We propose that titanium oxide (TiO₂) nanoparticles (NPs) will be more efficient than silver dioxide (Ag₂O) in the treatment of burn wounds. Herein, gelatin loaded NPs (GLT-NPs) were evaluated for their efficacy to regenerate second-degree burn wound in rabbit skin. TEM results revealed that the average particle sizes were ⁓ 7.5 and 17 nm for Ag₂O and TiO₂ NPs, respectively. The results of the in vivo application of GLT-NPs on burn wound in the rabbit revealed that both Ag₂O and TiO₂ NPs were efficient than the control none treated (CTRL) and GLT group. In terms of the healing rate, the GLT-TiO₂ did not show any significant difference than GLT-Ag₂O (99.57% vs. 99.85%, p = 0.2). Meanwhile, the healing rate was significantly higher in both NPs' treated groups than CTRL (94.16%, p < 0.01) and GLT group (95.07%, p < 0.05). Also, the histological analysis using H&E staining showed re-epithelization, less edema, and enhanced vascularization in both GLT-NPs than CTRL and GLT groups. Furthermore, immunohistochemical analysis of TGF-β1 and α-SMA revealed significantly a higher expression in both GLT-NPs groups than CTRL and GLT groups at weeks 1 and 2 (p < 0.05). Interestingly, TGF-β1 and α-SMA were substantially higher in GLT- TiO₂ than GLT-Ag₂O at weeks 1 and 2 (p < 0.05), but the expression was not significant at week 3. In conclusion, GLT-NPs showed higher regenerative capacity and enhanced the healing quality after burn wound compared to CTRL and GLT. Graphical abstract.

Identification, Mechanism, and Treatment of Skin Lesions in COVID-19: A Review

Coronavirus disease 2019 (COVID-19) is a multisystem disease caused by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), that primarily causes respiratory symptoms. However, an increasing number of cutaneous manifestations associated with this disease have been reported. The aim of this study is to analyze the scientific literature on cutaneous manifestations associated with SARS-CoV-2 by means of a narrative literature review until June 2021. The search was conducted in the following electronic databases: Medline (PubMed), SciELO, and Cochrane Library Plus. The most common cutaneous manifestations in patients with COVID-19 are vesicular eruptions, petechial/purpuric rashes, acral lesions, liveoid lesions, urticarial rash, and maculopapular-erythematous rash. These manifestations may be the first presenting symptoms of SARS-CoV-2 infection, as is the case with acral lesions, vesicular eruptions, and urticaria. In relation to severity, the presence of liveoid lesions may be associated with a more severe course of the disease. Treatment used for dermatological lesions includes therapy with anticoagulants, corticosteroids, and antihistamines. Knowledge of the dermatologic manifestations associated with SARS-CoV-2 contributes to the diagnosis of COVID-19 in patients with skin lesions associated with respiratory symptoms or in asymptomatic patients. In addition, understanding the dermatologic lesions associated with COVID-19 could be useful to establish a personalized care plan.

Children's vicarious ratings of social touch are tuned to the velocity but not the location of a caress

Affective sharing is a bottom-up process involving automatic processing of sensory inputs that facilitate vicarious experience of another's emotional state. It is grounded directly in the prior experiences of the perceiver. In adults, vicarious ratings of affective touch match the known velocity tuning and hypothesised anatomical distribution of C-tactile afferents (CT), a subclass of C-fibre which respond preferentially to low force/velocity stroking touch, typically perceived as pleasant. Given the centrality of touch to early nurturing interactions, here we examined whether primary school aged children's vicarious ratings of affective touch show the same anatomical and velocity specific patterns reported in adults. Forty-four children aged between 8 and 11 (mean age 9, 24 male) rated a sequence of video clips depicting one individual being touched by another on 5 different upper-body sites (palm, dorsal forearm, ventral forearm, upper-arm and back) at 3 different velocities (static, CT optimal, slow stroking and non-CT optimal, fast stroking). Immediately after viewing each clip, participants were asked to rate how pleasant they perceived the touch to be. While children rated the CT optimal velocity significantly higher than static or non-CT optimal touch, unlike adults their ratings did not vary across skin sites. This difference may reflect the fact children's ratings are grounded in bottom-up affective resonance while adults also draw on top-down cognitive evaluation of the broader social context when rating the stimuli.

Fabrication and characterization of scaffolds containing different amounts of allantoin for skin tissue engineering

Using the skin tissue engineering approach is a way to help the body to recover its lost skin in cases that the spontaneous healing process is either impossible or inadequate, such as severe wounds or burns. In the present study, chitosan/gelatin-based scaffolds containing 0.25, 0.5, 0.75, and 1% allantoin were created to improve the wounds' healing process. EDC and NHS were used to cross-link the samples, which were further freeze-dried. Different in-vitro methods were utilized to characterize the specimens, including SEM imaging, PBS absorption and degradation tests, mechanical experiments, allantoin release profile assessment, antibacterial assay, and cell viability and adhesion tests. The results indicated that the scaffolds' average pore sizes were approximately in the range of 390-440 µm, and their PBS uptake amounts were about 1000% to 1250% after being soaked in PBS for 24 h. Around 70% of the specimens were degraded in 6 days, but they were not fully degraded after 21 days. Besides, the samples showed antibacterial activity against S. aureus and E. coli bacteria. In general, the MTT cell viability test indicated that the cells' density increased slightly or remained the same during the experiment. SEM images of cells seeded on the scaffolds indicated appropriate properties of the scaffolds for cell adhesion.

Glutamic acid promotes hair growth in mice

Glutamic acid is the main excitatory neurotransmitter acting both in the brain and in peripheral tissues. Abnormal distribution of glutamic acid receptors occurs in skin hyperproliferative conditions such as psoriasis and skin regeneration; however, the biological function of glutamic acid in the skin remains unclear. Using ex vivo, in vivo and in silico approaches, we showed that exogenous glutamic acid promotes hair growth and keratinocyte proliferation. Topical application of glutamic acid decreased the expression of genes related to apoptosis in the skin, whereas glutamic acid increased cell viability and proliferation in human keratinocyte cultures. In addition, we identified the keratinocyte glutamic acid excitotoxic concentration, providing evidence for the existence of a novel skin signalling pathway mediated by a neurotransmitter that controls keratinocyte and hair follicle proliferation. Thus, glutamic acid emerges as a component of the peripheral nervous system that acts to control cell growth in the skin. These results raise the perspective of the pharmacological and nutritional use of glutamic acid to treat skin diseases.

Molecular Basis for Mechanical Properties of ECMs: Proposed Role of Fibrillar Collagen and Proteoglycans in Tissue Biomechanics

Collagen and proteoglycans work in unison in the ECM to bear loads, store elastic energy and then dissipate excess energy to avoid tissue fatigue and premature mechanical failure. While collagen fibers store elastic energy by stretching the flexible regions in the triple helix, they do so by lowering their free energy through a reduction in the entropy and a decrease in charge-charge repulsion. Entropic increases occur when the load is released that drive the reversibility of the process and transmission of excess energy. Energy is dissipated by sliding of collagen fibrils by each other with the aid of decorin molecules that reside on the d and e bands of the native D repeat pattern. Fluid flow from the hydration layer associated with the decorin and collagen fibrils hydraulically dissipates energy during sliding. The deformation is reversed by osmotic forces that cause fluid to reform a hydration shell around the collagen fibrils when the loads are removed. In this paper a model is presented describing the organization of collagen fibers in the skin and cell-collagen mechanical relationships that exist based on non-invasive measurements made using vibrational optical coherence tomography. It is proposed that under external stress, collagen fibers form a tensional network in the plane of the skin. Collagen fiber tension along with forces generated by fibroblasts exerted on collagen fibers lead to an elastic modulus that is almost uniform throughout the plane of the skin. Tensile forces acting on cells and tissues may provide a baseline for stimulation of normal mechanotransduction. We hypothesize that during aging, changes in cellular metabolism, cell-collagen interactions and light and UV light exposure cause down regulation of mechanotransduction and tissue metabolism leading to tissue atrophy.

Elementary integrate-and-fire process underlies pulse amplitudes in Electrodermal activity

Electrodermal activity (EDA) is a direct read-out of sweat-induced changes in the skin’s electrical conductance. Sympathetically-mediated pulsatile changes in skin sweat measured as EDA resemble an integrate-and-fire process, which yields an inverse Gaussian model as the inter-pulse interval distribution. We have previously showed that the inter-pulse intervals in EDA follow an inverse Gaussian distribution. However, the statistical structure of EDA pulse amplitudes has not yet been characterized based on the physiology. Expanding upon the integrate-and-fire nature of sweat glands, we hypothesized that the amplitude of an EDA pulse is proportional to the excess volume of sweat produced compared to what is required to just reach the surface of the skin. We modeled this as the difference of two inverse Gaussian models for each pulse, one which represents the time required to produce just enough sweat to rise to the surface of the skin and one which represents the time requires to produce the actual volume of sweat. We proposed and tested a series of four simplifications of our hypothesis, ranging from a single difference of inverse Gaussians to a single simple inverse Gaussian. We also tested four additional models for comparison, including the lognormal and gamma distributions. All models were tested on EDA data from two subject cohorts, 11 healthy volunteers during 1 hour of quiet wakefulness and a different set of 11 healthy volunteers during approximately 3 hours of controlled propofol sedation. All four models which represent simplifications of our hypothesis outperformed other models across all 22 subjects, as measured by Akaike’s Information Criterion (AIC), as well as mean and maximum distance from the diagonal on a quantile-quantile plot. Our broader model set of four simplifications offered a useful framework to enhance further statistical descriptions of EDA pulse amplitudes. Some of the simplifications prioritize fit near the mode of the distribution, while others prioritize fit near the tail. With this new insight, we can summarize the physiologically-relevant amplitude information in EDA with at most four parameters. Our findings establish that physiologically based probability models provide parsimonious and accurate description of temporal and amplitude characteristics in EDA.

Electrodermal activity (EDA) is an indirect read-out of the body’s sympathetic nervous system, or fight-or-flight response, measured as sweat-induced changes in the electrical conductance properties of the skin. Interest is growing in using EDA to track physiological conditions such as stress levels, sleep quality, and emotional states. Our previous worked showed that the times in between EDA pulses obeyed a specific statistical distribution, the inverse Gaussian, that arises from the physiology of EDA production. In this work, we build on that insight to analyze the amplitudes of EDA pulses. In an analysis of EDA data recorded in 11 healthy volunteers during quiet wakefulness and 11 different healthy volunteers during controlled propofol sedation, we establish that the amplitudes of EDA pulses also have specific statistical structure, as the differences of inverse Gaussians, that arises from the physiology of sweat production. We capture that structure using a series of progressively simpler models that each prioritize different parts of the pulse amplitude distribution. Our findings show that a physiologically-based statistical model provides a parsimonious and accurate description of EDA. This enables increased reliability and robustness in analyzing EDA data collected under any circumstance.

The Role of Skin Mast Cells in Acupuncture Induced Analgesia in Animals: A Preclinical Systematic Review and Meta-analysis

While mast cells (MCs) are previously well-known as a pathological indicator of pain, their role in alleviating pain is recently emerged in acupuncture research. Thus, this study systematically reviews the role of MC in acupuncture analgesia. Animal studies on MC changes associated with the acupuncture analgesia were searched in PubMed and EMBASE. The MC number, degranulation ratio and pain threshold changes were collected as outcome measures for meta-analyses. Twenty studies were included with 13 suitable for meta-analysis, most with a moderate risk of bias. A significant MC degranulation after acupuncture was indicated in the normal and was significantly higher in the pain model. In the subgroup analysis by acupuncture type, manual (MA) and electrical (EA, each P < .00001) but not sham acupuncture had significant MC degranulation. Meta-regression revealed the linear proportionality between MC degranulation and acupuncture-induced analgesia (P < .001), which was found essential in MA (P < .00001), but not in EA (P = .45). MC mediators, such as adenosine and histamine, are involved in its mechanism. Taken together, skin MC is an essential factor for acupuncture-induced analgesia, which reveals a new aspect of MC as a pain alleviator. However, its molecular mechanism requires further study. PERSPECTIVE: This systematic review synthesizes data from studies that examined the contribution of skin MC in acupuncture analgesia. Current reports suggest a new role for skin MC and its mediators in pain alleviation and explain a peripheral mechanism of acupuncture analgesia, with suggesting the need of further studies to confirm these findings.

The significance of CYP11A1 expression in skin physiology and pathology

CYP11A1, a member of the cytochrome P450 family, plays several key roles in the human body. It catalyzes the first and rate-limiting step in steroidogenesis, converting cholesterol to pregnenolone. Aside from the classical steroidogenic tissues such as the adrenals, gonads and placenta, CYP11A1 has also been found in the brain, gastrointestinal tract, immune systems, and finally the skin. CYP11A1 activity in the skin is regulated predominately by StAR protein and hence cholesterol levels in the mitochondria. However, UVB, UVC, CRH, ACTH, cAMP, and cytokines IL-1, IL-6 and TNFα can also regulate its expression and activity. Indeed, CYP11A1 plays several critical roles in the skin through its initiation of local steroidogenesis and specific metabolism of vitamin D, lumisterol, and 7-dehydrocholesterol. Products of these pathways regulate the protective barrier and skin immune functions in a context-dependent fashion through interactions with a number of receptors. Disturbances in CYP11A1 activity can lead to skin pathology.

Detection of Burmese pythons in the near-infrared versus visible band

Human task performance studies are commonly used for detecting and identifying potential military threats. In this work, these principles are applied to detection of an environmental threat: the invasive Burmese python. A qualitative detection of Burmese pythons with a visible light camera and an 850 nm near-infrared (NIR) camera was performed in natural Florida backgrounds. The results showed that the difference in reflectivity between the pythons and native foliage was much greater in NIR, effectively circumventing the python's natural camouflage in the visible band. In this work, a comparison of detection performance in the selected near-infrared band versus the visible band was conducted. Images of foliage backgrounds with and without a python were taken in each band in daylight and at night with illumination. Intensities of these images were then calibrated and prepared for a human perception test. Participants were tasked with detecting pythons, and the human perception data was used to compare performance between the bands. The results show that the enhanced contrast in the NIR enabled participants to detect pythons at 20% longer ranges than the use of visible imagery.

Colorimetric Ionic Organohydrogels Mimicking Human Skin for Mechanical Stimuli Sensing and Injury Visualization

Artificial skins with sensing ability have great potential in applications of wearable devices and soft robotics. Inspired by the functions of human skins including sensing stimuli via electrical signal and bruising for injury indication, an ionic conductive and mechanochromic organohydrogel is synthesized and demonstrated as ionic skin (I-skin). The gel consisting of mechanochromophore cross-linked micelles is mechanically robust, stretchable, and deformation durable with minor hysteresis, and it also displays good solvent retention. The change of relative resistance during elongation and compression suggests a high sensitivity. An optical change from pale yellow to bruise-like blue-purple color is observed under a large deformation. The ionic conductive organohydrogel as I-skin is attached to different parts of the human body with movements mimicking various body-bruising scenarios, demonstrating successful perception and visualization of mechanical stimuli. The work vividly presents a strain sensor with the functions of injury visualization and damage warning for mechanical impacts. The I-skin can be potentially used in the applications including prosthetic devices, wearable electronics, and intelligent robots.