Structure Of Human Skin Research Articles

Characterization of the structure of human skin substitutes by infrared microspectroscopy

The skin acts mainly as a protective barrier from the external environment, thanks to the stratum corneum which is the outermost layer of the skin. As in vitro tests on skin are essential to elaborate new drugs, the development of skin models closer to reality becomes essential. It is now possible to produce in vitro human skin substitutes through tissue engineering by using the self-assembly method developed by the Laboratoire d'Organogénèse Expérimentale. In the present work, infrared microspectroscopy imaging analyses were performed to get in-depth morpho-spectral characterization of the three characteristic layers of human skin substitutes and normal human skin, namely the stratum corneum, living epidermis, and dermis. An infrared spectral analysis of the skin is a powerful tool to gain information on the order and conformation of the lipid chains and the secondary structure of proteins. On one hand, the symmetric stretching mode of the lipid methylene groups (2,850cm(-1)) is sensitive to the acyl chain conformational order. The evolution profile of the frequency of this vibrational mode throughout the epidermis suggests that lipids in the stratum corneum are more ordered than those in the living epidermis. On the other hand, the frequencies of the infrared components underneath the envelop of the amide I band provide information about the overall protein conformation. The analysis of this mode establishes that the proteins essentially adopt an α-helix conformation in the epidermis, probably associated with the presence of keratin, while modifications of the protein content are observed in the dermis (extracellular matrix made of collagen). Finally, the lipid organization, as well as the protein composition in the different layers, is similar for human skin substitutes and normal human skin, confirming that the substitutes reproduce essential features of real skin and are appropriate biomimetics.

Piezoelectric Vibratory-Cantilever Force Sensors and Axial Sensitivity Analysis for Individual Triaxial Tactile Sensing

Vibratory force sensors are fabricated using piezoelectric capacitors on microcantilever structures for triaxial sensitivity by the individual sensor element. The cantilevers have been formed into a 3-D curved shape by controlling residual stress combination of the multilayered structure. Triaxial tactile sensitivity of the cantilever sensor is analyzed under a tactile load application onto the surface of an elastomer in which the cantilever is embedded, mimicking human skin structure. The cantilever is converse-piezoelectrically excited by an external ac voltage and three resonant modes are developed to detect the applied load vector components by the single sensor element. Resonant frequency shifts of each mode are investigated upon load applications. The results show that the frequencies vary to the three axial tactile loads independently and they can be superposed with corresponding to the superposition of the load components. The applied load vectors are estimated by resonant frequencies of the single cantilever sensor with compensating nonlinearities of the sensor response. The estimated error is less than 1.1% to the full scale of the load ±4 kPa.

Bioengineered Skin: The Self-Assembly Approach

Tissue-engineered skin substitutes represent an innovative therapeutic option for the treatment of burns and skin ulcers as well as a powerful tool for fundamental research. To be efficient, in vitro skin substitutes must closely mimic human skin structures and exogenous material has to be reduced as much as possible. The self-assembly approach is based on the capacity of fibroblasts to create their own extracellular matrix in vitro, which allows the production of cell sheets that are easy to handle. Therefore, a skin substitute devoid of exogenous extracellular matrix proteins and synthetic material is produced, which demonstrates many histological, physico-chemical and mechanical characteristics found in normal human skin in vivo. A particularity of this approach is the possibility to add various other cell types (keratinocytes, melanocytes, adipocytes, endothelial and immunological cells, etc.) according to needs. Furthermore, pathological cells (hypertrophic scar, sclerodermic, tumoral and psoriatic cells) can be used for the production of pathological skin substitutes. The development of these models represents a key component in the fight against such diseases because they can lead to a better understanding of the pathology and to the development of new pharmaceutical therapies.This review will present the need for tissue-engineered skin substitutes, the implication of tissue engineering in the cutaneous field (basic and applied research), the selfassembly approach and its characteristics as well as the actual state of research on healthy and pathological selfassembled skin models.

Feasibility of using optical coherence tomography to study the influence of skin structure on finger friction

This paper presents work using an in vivo technique, optical coherence tomography (OCT), to investigate the structure of human finger pad skin and the influences of some related parameters on skin friction, such as contact area, deformation and hydration. The experimental results show that there was no significant relationship between the thickness of the stratum corneum (SC) and the friction coefficient as well as the number of sweat ducts (SD). The real contact length was found to increase with increasing the applied normal force following the power law of A∝Wa. The study of hydration found an increasing linear relationship between the SC moisture and the friction coefficient (up to 72au).

Adaptation of the dermal collagen structure of human skin and scar tissue in response to stretch: An experimental study

Surgeons are often faced with large defects that are difficult to close. Stretching adjacent skin can facilitate wound closure. In clinical practice, intraoperative stretching is performed in a cyclical or continuous fashion. However, exact mechanisms of tissue adaptation to stretch remain unclear. Therefore, we investigated collagen and elastin orientation and morphology of stretched and nonstretched healthy skin and scars. Tissue samples were stretched, fixed in stretched-out position, and processed for histology. Objective methods were used to quantify the collagen orientation index (COI), bundle thickness, and bundle spacing. Also sections were analyzed for elastin orientation and quantity. Significantly more parallel aligned collagen bundles were found after cyclical (COI = 0.57) and continuous stretch (COI = 0.57) compared with nonstretched skin (COI = 0.40). Similarly, more parallel aligned elastin was found after stretch. Also, significantly thicker collagen bundles and more bundle spacing were found after stretch. For stretched scars, significantly more parallel aligned collagen was found (COI = 0.61) compared with nonstretched scars (COI = 0.49). In conclusion, both elastin and collagen realign in a parallel fashion in response to stretch. For healthy skin, thicker bundles and more space between the bundles were found. Rapid changes in extension, alignment, and collagen morphology appear to be the underlying mechanisms of adaptation to stretching.

FINITE ELEMENT ANALYSIS OF THE ANGIOGENESIS PROCESS IN WOUND HEALING

The occurrence of wounds is a main health concern in Western society due to their high frequency and treatment cost. During wound healing, the formation of a functional blood vessel network through angiogenesis is an essential process. Angiogenesis allows the reestablishment of the normal blood flow, the sufficient exchange of oxygen and nutrients and the removal of metabolic waste, necessary for cell proliferation and viability. Mathematical and computational models provide new tools to improve the healing process. In fact, over the last thirty years, in silico models have been continuously formulated to describe the effect of several biological and mechanical factors in angiogenesis during wound healing. Additionally, with different levels of complexity, these models allow coupling the human skin structure, to distinct cell types and growth factors, to study extracellular matrix composition and to understand its deformation. This paper discusses how in silico models, which are more economical and less time-consuming comparatively to laboratory methodologies, can help test new strategies to promote/optimize angiogenesis. The continuum, cell-based and hybrid mathematical models of wound healing angiogenesis are reviewed in the present paper, in order to identify possible improvements. Accordingly, the development of higher dimension models incorporating multiscale analysis at molecular, cellular and tissue level remains a challenge that future models should consider.

Approach to quantify human dermal skin aging using multiphoton laser scanning microscopy

Extracellular skin structures in human skin are impaired during intrinsic and extrinsic aging. Assessment of these dermal changes is conducted by subjective clinical evaluation and histological and molecular analysis. We aimed to develop a new parameter for the noninvasive quantitative determination of dermal skin alterations utilizing the high-resolution three-dimensional multiphoton laser scanning microscopy (MPLSM) technique. To quantify structural differences between chronically sun-exposed and sun-protected human skin, the respective collagen-specific second harmonic generation and the elastin-specific autofluorescence signals were recorded in young and elderly volunteers using the MPLSM technique. After image processing, the elastin-to-collagen ratio (ELCOR) was calculated. Results show that the ELCOR parameter of volar forearm skin significantly increases with age. For elderly volunteers, the ELCOR value calculated for the chronically sun-exposed temple area is significantly augmented compared to the sun-protected upper arm area. Based on the MPLSM technology, we introduce the ELCOR parameter as a new means to quantify accurately age-associated alterations in the extracellular matrix.

Low-gradient single-sided NMR sensor for one-shot profiling of human skin

This paper describes a shimming approach useful to reduce the gradient strength of the magnetic field generated by single-sided sensors simultaneously maximizing its uniformity along the lateral directions of the magnet. In this way, the thickness of the excited sensitive volume can be increased without compromising the depth resolution of the sensor. By implementing this method on a standard U-shaped magnet, the gradient strength was reduced one order of magnitude. In the presence of a gradient of about 2T/m, slices of 2mm could be profiled with a resolution that ranges from 25μm at the center of the slice to 50μm at the borders. This sensor is of particular advantage for applications, where the scanning range is of the order of the excited slice. In those cases, the full profile is measured in a single excitation experiment, eliminating the need for repositioning the excited slice across the depth range to complete the profile as occurs with standard high gradient sensors. Besides simplifying the experimental setup, the possibility to move from a point-by-point measurement to the simultaneous acquisition of the full profile led to the shortening of the experimental time. A further advantage of performing the experiment under a smaller static gradient is a reduction of the diffusion attenuation affecting the signal decay measured with a CPMG sequence, making it possible to measure the T2 of samples with high diffusivity (comparable to the water diffusivity). The performance of the sensor in terms of resolution and sensitivity is first evaluated and compared with conventional singled-sided sensors of higher gradient strength using phantoms of known geometry and relaxation times. Then, the device is used to profile the structure of human skin in vivo. To understand the contrast between the different skin layers, the distribution of relaxation times T2 and diffusion coefficients is spatially resolved along the depth direction.

Epithelial and Stromal Developmental Patterns in a Novel Substitute of the Human Skin Generated with Fibrin-Agarose Biomaterials

Development of human skin substitutes by tissue engineering may offer new therapeutic alternatives to the use of autologous tissue grafts. For that reason, it is necessary to investigate and develop new biocompatible biomaterials that support the generation of a proper human skin construct. In this study, we generated a novel model of bioengineered human skin substitute using human cells obtained from skin biopsies and fibrin-agarose biomaterials and we evaluated this model both at the ex vivo and the in vivo levels. Once the dermal fibroblasts and the epithelial keratinocytes were isolated and expanded in culture, we used fibrin-agarose scaffolds for the development of a full-thickness human skin construct, which was evaluated after 1, 2, 3 and 4 weeks of development ex vivo. The skin substitutes were then grafted onto immune-deficient nude mice and analyzed at days 10, 20, 30 and 40 postimplantation using transmission electron microscopy, histochemistry and immunofluorescence. The results demonstrated that the fibrin-agarose artificial skin had adequate biocompatibility and proper biomechanical properties. A proper development of both the bioengineered dermis and epidermis was found after 30 days in vivo, although the tissues kept ex vivo and those implanted in the animal model for 10 or 20 days showed lower levels of differentiation. In summary, our model of fibrin-agarose skin equivalent was able to reproduce the structure and histological architecture of the native human skin, especially after long-term in vivo implantation, suggesting that these tissues could reproduce the native skin.

Retrieving skin properties from in vivo spectral reflectance measurements

A previously developed inverse method was applied to in vivo normal-hemispherical spectral reflectance measurements taken on the inner and outer forearm as well as the forehead of healthy white Caucasian and black African subjects. The inverse method was used to determine the thickness and melanin concentration in the epidermis, dermal blood volume fraction and oxygen saturation, and skin's spectral scattering coefficient. It was established that changes in melanin concentration due to racial difference and tanning, and differences in epidermal thickness and blood volume with anatomical location were detectable. The retrieved values were also consistent with independent measurements reported in the literature. The same method could be used for optical diagnosis of pathologies affecting the structure and pigmentation of human skin.

Emulation of Fast and Slow Pains Using Multi-Layer Sensor Modeled the Layered Structure of Human Skin

In human and robot coexistence, human sensory and emotional feelings are aroused in the case of interaction. This causes such an unpleasant feeling called pain. It’s an important feeling in avoiding danger. For more safe interaction between human and robot, it becomes important for robots to sense pain. To emulate fast and slow pain, we use a pain emulation system consisting of a pain model and a multilayer sensor. After an overview of the superficial pain model, we discuss a multilayer sensor we developed to model the laminated human skin structure. We measure sensor response and emulate fast and slow pain using our proposed system in experiments. Results confirmed that, the proposed system responds similarly to both fast and slow pain in the subjects tested.

Expression of keratins in cutaneous epithelial tumors and related disorders - distribution and clinical significance

Keratins are a highly diverse family of cytoskeletal proteins and important markers of epithelial cell differentiation. In this review, applying the new keratin nomenclature recently introduced, we summarize and discuss the distribution and significance of keratin patterns in cutaneous epithelial tumors in relation to the epithelial structures of normal human skin. The available literature data show that the analysis of keratin profiles broadens our understanding of the differentiation, nature and histogenetic origin of the various, highly singular epithelial tumors arising in the skin. Moreover, keratins may aid in histological diagnosis and, in certain instances, may be helpful for the recognition of tumor malignancy and aggressiveness. Furthermore, we briefly address the topic of keratin-related skin disorders.

Simulation of optical coherence tomography images by Monte Carlo modeling based on polarization vector approach

Monte Carlo method is applied for simulation of 2D optical coherence tomography (OCT) images of skin-like model. Layer boundaries in skin model feature curved shape which agrees with physiological structure of human skin. The effect of coherence properties of probing radiation on OCT image formation and speckles in the detected OCT signal is considered. The developed model is employed for image simulation both for conventional and polarization dependent time-domain OCT modalities. Simulation of polarized OCT signal is performed using vector approach developed previously for modeling of electromagnetic field transfer in turbid media.

Studies on the Structure and Function of Human Skin

Studies on the Structure and Function of Human Skin

Skin age testing criteria: characterization of human skin structures by 500 MHz MRI multiple contrast and image processing

Ex vivo magnetic resonance microimaging (MRM) image characteristics are reported in human skin samples in different age groups. Human excised skin samples were imaged using a custom coil placed inside a 500 MHz NMR imager for high-resolution microimaging. Skin MRI images were processed for characterization of different skin structures. Contiguous cross-sectional T1-weighted 3D spin echo MRI, T2-weighted 3D spin echo MRI and proton density images were compared with skin histopathology and NMR peaks. In all skin specimens, epidermis and dermis thickening and hair follicle size were measured using MRM. Optimized parameters TE and TR and multicontrast enhancement generated better MRI visibility of different skin components. Within high MR signal regions near to the custom coil, MRI images with short echo time were comparable with digitized histological sections for skin structures of the epidermis, dermis and hair follicles in 6 (67%) of the nine specimens. Skin % tissue composition, measurement of the epidermis, dermis, sebaceous gland and hair follicle size, and skin NMR peaks were signatures of skin type. The image processing determined the dimensionality of skin tissue components and skin typing. The ex vivo MRI images and histopathology of the skin may be used to measure the skin structure and skin NMR peaks with image processing may be a tool for determining skin typing and skin composition.

Characterization of vascular structures and skin bruises using hyperspectral imaging, image analysis and diffusion theory

Hyperspectral imaging, image analysis and diffusion theory were used to visualize skin vasculature and to monitor the development of fresh skin bruises. Bruises were inflicted in a porcine model, and the development of the hemorrhage was monitored using white light hyperspectral imaging (400-1000 nm). Hyperspectral images from human volunteers were also included in the study. Statistical image analysis was used to classify bruised regions and to visualize the skin vasculature. Biopsies were collected from the animals to reveal the true depth of the bruising. A three-layer diffusion model and an analytic hemoglobin transport model were used to model the reflectance spectra from the images. The results show that hyperspectral images contain depth information, and that the approximate depth and extent of bruises can be retrieved using a combination of statistical image analysis and diffusion theory. This technique also shows potential to visualize vascular structures in human skin.

0043: Visualization of Microstructure of the Skin by 3D Ultrasound Microscope

Non-invasive imaging technique capable of visualizing microstructure of the skin is strongly desired for dermatological and cosmetic purposes. In the present study, three-dimensional (3D) ultrasound microscope with the central frequency of 100 MHz was developed and applied for imaging of 3D structure of human skin.

Pig as an experimental model for the study of snake venom induced local tissue necrosis

Local tissue necrosis due to snake envenoming has resulted in considerable chronic disability. Specific antivenom, though highly useful in systemic poisoning, is not very effective in preventing the local tissue damages which occur within minutes of envenomation. Most of the studies on local tissue necrosis have been done in rodents whose skin structures are significantly different from human skin structure. In this study, pig, which is similar to human in this respect, was used as an experimental model for the study of local tissue damage caused by snake venom. An intradermal (i.d.) injection of Calloselasma rhodostoma (CR) venom induced induration and hemorrhage at the same injection site, the areas of which could be estimated at 30–45 min and at 4 h after injection, respectively. Both the hemorrhage and induration were dose-dependent and a total of 24 data points of each assay per pig could be obtained. Catheterization of the jugular vein for gentle serial blood collection could be performed without any hematologic sequelae. Venom injected subcutaneously induced myonecrosis as demonstrated by the increment of serum creatine kinase (CK) level which peaked at 23 h. Furthermore, biopsies at varying distances and depths around the venom injection sites could be made within seconds of injection to study the pathological changes caused by snake venom. These results demonstrated that pig should be a useful animal model for the quantitation, pathogenesis and wound healing studies of snake venom induced local tissue necrosis, and for the search for effective treatment modality.

Tactile impression and friction of water on human skin

Water has a unique touch as well as characteristic physical properties. However, nobody knows the real identity of its touch. Here, we show that water creates a stick-slip feel when a small amount is rubbed using fingertip on an artificial skin that mimics the structure of human skin. The results of frictional analyses predict that this stick-slip feel is caused by a drastic change in frictional resistance. The present result is valuable for biologists and robot engineers as well as cognitive scientists and tribologists, because it is a new example of stick-slip phenomena on biological surfaces. The tactile texture of this most familiar material could also be applied to consumer products or virtual reality systems.

Stellenwert der Zellkulturmodelle in kutaner Tumorbiologie

There are several limitations to the use of the classical monolayer cell culture and the results obtained by means of it. The two-dimensional architecture and the analysis of pure cell populations of individual cell lines are the most several deviations from the situation prevailing in tissues in vivo, with inevitable consequences for the phenotypic traits displayed on the one hand, and for the genome structure and expression on the other hand. Newer developments in cell culture methodology seek approaches to mimic the in vivo situation in the cell culture as closely as possible. Remarkable variety of such approaches can be noticed, ranging from relative simple three-dimensional conditions of culturing pure cell lines on collagen gels or in form of multicell tumor spheroids. More complex forms try to combine multiple cell types in a single co-culture, e.g. of tumour cells and stromal fibroblasts. The most complex and most revealing among the three-dimensional culture arrangements is unquestionably the organotypic skin culture, in which all the relevant skin cell types are combined in a tissue-resembling construct, with resulting marked similarity to the anatomical structure of normal human skin. Several crucial results were obtained thereby, among others an intrinsic difference in the development of invasive squamous cell carcinoma and melanoma could be demonstrated. Just another experimental direction aims at direct tumourigenic transformation of normal human keratinocytes and melanocytes using highly efficient retroviral vectors. Immediately after establishing of the organotypic skin culture are such directly transformed primary cells transplanted on a nude mouse and the whole tumourigenic process is then essentially followed in vivo. This example illustrates finally the various possibilities of combination of in vitro and in vivo experimental approaches.