Structure Of Human Skin Research Articles

Dual-mode OCT/fluorescence system for monitoring the morphology and metabolism of laser-printed 3D full-thickness skin equivalents.

The 3D structure of native human skin is fundamental for studying skin health, diseases, wound healing, and for testing the safety of skin care products, as well as personalized treatments for skin conditions. Tissue regeneration, driven by tissue engineering, often involves creating full-thickness skin equivalents (FSE), which are widely used for developing both healthy and diseased skin models. In this study, we utilized human skin cell lines to create FSE. We designed high-resolution 3D scaffolds to support the growth and maturation of these skin models. Additionally, we developed and validated a cost-effective, custom-built system combining fluorescence spectroscopy (FS) and optical coherence tomography (OCT) for non-destructive analysis of the metabolism and morphology of 3D FSEs. This system proved highly sensitive in detecting fluorescence from key metabolic co-enzymes (NADH and FAD) in solutions and cell suspensions, while OCT provided adequate resolution to observe the morphology of FSEs. As a result, both the 3D FSE model and the dual-mode optical system hold significant potential for use in 3D bioprinting of biological tissues, as well as in the development of cosmetics, drugs, and in monitoring their maturation over time.

Lignin-induced rapid polymerization of asymmetrical adhesion Janus gel for strain sensor

Functional hydrogel sensors have shown explosive growth in the health and medical fields. However, the uniform adhesion and the complicated polymerization process of hydrogels seriously hinder their further development. Herein, inspired by the layered structure of human skin, we prepare a Janus gel using in-situ polymerization. Based on the lignin-Fe3+ dual catalytic system, the rapid polymerization of the gel was achieved at room temperature. By tailoring the mass ratio of lignin and Fe3+ in the precursor, the adhesion of the upper and bottom layers can be easily adjusted. In addition, hydrophobic association is introduced into the upper layer to improve the gel's mechanical properties. The obtained asymmetric bilayer gel has a significant difference in adhesion (7 times), and exhibits excellent mechanical properties in the elongation at break (1437 %) and the breaking strength (463.2 kPa). Moreover, the bilayer gel also has good freezing and UV resistance. We use the bilayer gel as a wearable strain sensor, which shows a wide strain detection range of 0–800 % (maximum gauge factor = 5.3). The proposed simple strategy avoids UV irradiation and heating processes, which provides a new idea for the rapid polymerization of multifunctional Janus hydrogels with adjustable performances.

Translational potential of test systems in modelling thermal burn wounds

The article describes the advantages and features of experimental models of thermal burns using in vitro, ex vivo and in vivo test systems. An objective assessment of the application of each approach depending on the type of study is given. For example, cell culture models are simple but do not fully reflect the structure of human skin, which limits their translational value. Ex vivo models, such as skin explants, provide the necessary architectonics to study intercellular interactions, but they also have drawbacks, primarily related to short viability. In general, in vitro and ex vivo models have limitations in reproducing all aspects of burn wound pathogenesis and healing. In this regard, laboratory animals, primarily mice, rats, and pigs, are widely used to study burn wound pathology, its effects on the body, and the efficacy of therapy. The decision to use experimental animal models is made taking into account their translational relevance to humans. In rodents, wound healing occurs mainly by contraction, in contrast to the re-epithelialisation and granulation seen in humans, which contributes to faster wound healing in rodents. The significant similarities between certain properties of pig and human skin make the latter a relevant test system in pharmacodynamic studies of thermal burn wounds.

Biomimetic three-dimensional microchannel non-destructive self-healing flexible strain sensor based on liquid metal-polydimethylsiloxane elastomer

Flexible strain sensors (FSS) have garnered widespread attention due to their immense potential in wearable electronics, motion health monitoring, artificial electronic skin, and soft robotics. However, FSSs are susceptible to mechanical damage such as wear, cracks or breaks during long-term use, which diminish their reliability and service life. Inspired by the self-healing dual-phase structure of human skin and vascular networks, this study proposes a biomimetic three-dimensional microchannel non-destructive self-healing flexible strain sensor (B-TMN-SHFSS) based on the liquid metal-polydimethylsiloxane (LM-PDMS) elastomer. The B-TMN-SHFSS employs a layered design, layer-by-layer fabrication, and interlayer self-healing techniques to construct the microchannel within the self-healing PDMS elastomer (SPE), with the liquid metal (LM) being injected into the microchannel using a negative pressure injection method. Based on the modified protective layer design of the biomimetic three-dimensional microchannel, the high self-healing efficiency of the SPE and the fluidity of the LM, the B-TMN-SHFSS is able to restore the initial sensing performance after self-healing, while maintaining the integrity of the 3D microchannels with an electrical healing efficiency (EHE) of 100 %. Additionally, the B-TMN-SHFSS features high sensitivity (GFmax = 3.464) and a wide measurement range (0 to 216.68 %), making it suitable for human motion detection.

Bionic Artificial Skin Based on Self-Healable Ionogel Composites with Tailored Mechanics and Robust Interfaces.

Bionic artificial skin which imitates the features and functions of human skin, has broad applications in wearable human-machine interfaces. However, equipping artificial materials with skin-like mechanical properties, self-healing ability, and high sensitivity remains challenging. Here, inspired by the structure of human skin, an artificial skin based on ionogel composites with tailored mechanical properties and robust interface is prepared. Combining finite element analysis and direct ink writing (DIW) 3D printing technology, an ionogel composite with a rigid skeleton and an ionogel matrix is precisely designed and fabricated, realizing the mechanical anisotropy and nonlinear mechanical response that accurately mimic human skin. Robust interface is created through co-curing of the skeleton and matrix resins, significantly enhancing the stability of the composite. The realization of self-healing ability and resistance to crack growth further ensure the remarkable durability of the artificial skin for sensing application. In summary, the bionic artificial skin mimics the characteristics of human skin, including mechanical anisotropy, nonlinear mechanical response, self-healing capability, durability and high sensitivity when applied as flexible sensors. These strategies provide strong support for the fabrication of tissue-like materials with adaptive mechanical behaviors.

Tannic acid-modified acellular dermal matrix dressings for promoting full-thickness wound healing

Wound healing is a significant clinical and public health concern, and wound dressings are currently the primary method for addressing it. This study aimed to develop a multifunctional, all-natural wound dressing with antibacterial and anti-inflammatory properties using porcine acellular dermal matrix (PADM), a bioderived material that closely resembles the structure of human skin. The cells were decellularized using hypertonic salt and strong alkaline to remove immunogenicity while retaining the extracellular matrix. Subsequently, the wound dressing was prepared through tannic acid modification. In vitro cytotoxicity, scratch, anti-inflammatory, and antibacterial tests were used to assess the multifunctionality of the biomaterials. A full-thickness skin defect wound was created in rats, and the wound healing was analyzed using gross and histological staining. The results indicated that tannic acid-modified acellular dermal matrix exhibits favorable mechanical properties and biocompatibility. In vitro experiments demonstrated its effective inhibition of the growth of Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus. It can downregulate nitric oxide (NO) production and the expression levels of pro-inflammatory factors in macrophages stimulated by lipopolysaccharide. In vitro experiments demonstrated that the dressing can enhance wound healing. Therefore, tannic acid-modified acellular dermal matrix accelerates wound healing through anti-inflammatory and antibacterial effects. Its excellent properties make it a potential biological material for promoting wound healing.

Biomimetic multilayer flexible sensors for multifunctional underwater sensing

The development of multifunctional flexible sensors capable of monitoring different physiological signals of the body underwater holds great practical significance in safeguarding the well-being of divers during their subaquatic activities. Here, we prepared a multilayer multifunctional sensor that mimics the structure of human skin by sequentially constructing a sensing layer formed by multi-walled carbon nanotubes and a hydrophobic protective layer formed by organosilicon dioxide (o-SiO2) on the elastomer surface. The o-SiO2 layer is superhydrophobic and breathable, also allowing the sensing layer to be only partially wetted. The sensor can monitor human respiration by sensing humidity due to breathability of protective layer. Additionally, the superhydrophobic surface ensures stable strain monitoring even underwater. The partially wetted sensing layer allows the sensor to respond to its immersion and surfacing processes, as well as underwater bubbles. These multifunctional sensors are capable of real-time monitoring of divers' physiological signals, including breathing patterns and motions, throughout underwater activities.

Multifunctional robot skin based on liquid metal composites and electrode arrays

While human skin regulates body temperature and protects the organism, robots also need multifunctional skin that can protect their internal electronics. Currently, most of the research on robotic skin focuses on the limbs with the aim of improving their sensory functions. There is a lack of a robotic skin with protective features that can be applied to the whole body. In some complex working environments, too high or too low temperatures can directly jeopardize the operation of the robot's internal circuitry. In addition, ubiquitous electromagnetic waves can damage the electronic system of robots. Therefore, an e-skin that protects the robot from external factors was desired. In this study, with reference to the structure of human skin, a gallium-based liquid metal and a bismuth-based low-melting-point alloy were combined to prepare a highly thermally conductive e-skin that can withstand both thermal shock and low temperature. This skin not only features thermal management, but also touch positioning and electromagnetic shielding. The development of multifunctional robot skin (MFR skin) will extend the service life of robots, broaden their application areas, and enable future robots to replace humans to accomplish more complex and operationally difficult tasks.

Bioinspired 3D printed elastomer-hydrogel hybrid with robust interfacial bonding for flexible ionotronics

Hydrogels are widely used in flexible ionotronics due to their continuous conductive phase and good biocompatibility. However, their poor mechanical properties affect their stability and lifespan. It is a significant challenge to prepare hydrogels with both high conductivity and mechanical strength, as improving the mechanical properties often results in a tighter network, which reduces electrical conductivity. Human skin is composed of a stiff collagen fibril scaffold for resisting external damage, and a soft matrix that detect various stimuli through ion transport. Herein, inspired by the structure of human skin, a hydrogel composite with remarkable mechanical properties, high ionic conductivity, and self-healing property is prepared. The composite structure with 3D printed elastomeric skeleton and hydrogel matrix, addresses both the contradiction between the ionic conductivity and mechanical properties of hydrogels, as well as the difficulty of realizing complex macrostructures of the skeleton. The issue of weak interface in composites is resolved by creating interfacial covalent bonds. The composite’s self-healing property, combined with a robust interface, ensure the stability and longevity of the composite when used as flexible sensors. This novel approach of creating robust interface is also employed in the encapsulation of hydrogels and the fabrication of flexible microcircuits.

Dehydrated Biomimetic Membranes with Skinlike Structure and Function.

Novel vapor-permeable materials are sought after for applications in protective wear, energy generation, and water treatment. Current impermeable protective materials effectively block harmful agents but trap heat due to poor water vapor transfer. Here we present a new class of materials, vapor permeable dehydrated nanoporous biomimetic membranes (DBMs), based on channel proteins. This application for biomimetic membranes is unexpected as channel proteins and biomimetic membranes were assumed to be unstable under dry conditions. DBMs mimic human skin's structure to offer both high vapor transport and small molecule exclusion under dry conditions. DBMs feature highly organized pores resembling sweat pores in human skin, but at super high densities (>1012 pores/cm2). These DBMs achieved exceptional water vapor transport rates, surpassing commercial breathable fabrics by up to 6.2 times, despite containing >2 orders of magnitude smaller pores (1 nm vs >700 nm). These DBMs effectively excluded model biological agents and harmful chemicals both in liquid and vapor phases, again in contrast with the commercial breathable fabrics. Remarkably, while hydrated biomimetic membranes were highly permeable to liquid water, they exhibited higher water resistances after dehydration at values >38 times that of commercial breathable fabrics. Molecular dynamics simulations support our hypothesis that dehydration induced protein hydrophobicity increases which enhanced DBM performance. DBMs hold promise for various applications, including membrane distillation, dehumidification, and protective barriers for atmospheric water harvesting materials.

A Superhuman Sensing Triboelectric Nanogenerator with Boosted Power Density and Durability via a Bio‐Inspired Janus Structure

AbstractTriboelectric nanogenerators (TENG) not only enable sustainable self‐powered sensing of devices, but also have superhuman noncontact/contact identification capabilities, which are propelling humanity toward the intelligent era. However, the inherently low dielectric constant of triboelectric materials as well as the mechanical mismatch between electrodes and dielectric materials severely limited their efficient and stable output performance. Taking inspiration from the asymmetric structure and function of human skin, a novel single‐electrode TENG is developed, whose electrode and dielectric layer are integrated in a Janus architecture. By tuning the balance between gravity and the internal noncovalent interactions, gradient dispersion of carbon nanotubes in waterborne polyurethane networks can be feasibly achieved, which can boost the device performance by reinforcement in both the charge trapping capacity of the dielectric layer and the charge transfer of the electrode layer. As a proof‐of‐concept, triboelectric sensing and deep learning are integrated to realize the evolution from perception to identification under both noncontact (motion prediction) and contact (material identification) modes. The bionic design strategy of gradient Janus film can offer valuable insights into improving the output performance and durability of TENG. Additionally, the proximal prediction and tactile identification functions are also desirable attempts for future human‐machine interfaces.

Bioinspired Integrated Multidimensional Sensor for Adaptive Grasping by Robotic Hands and Physical Movement Guidance

AbstractThe construction of piezoresistive sensors capable of distinguishing multiple mechanical stimuli is important for sensing higher level applications. However, the mutual interference between sensing signals is a technical bottleneck for sensors to recognize multiple mechanical stimuli. Inspired by the structure of human skin and muscle, a multidimensional sensor is designed by integrating three sub‐sensors. Each sub‐sensor is only sensitive to stimulus components in one of the three orthogonal axes, whereas it remains insensitive to others because of its anisotropic sensing properties. Specifically, an omnidirectional gradient wrinkled polyurethane film with MXene‐embedded ZnO nanowire arrays serves as a strain‐insensitive pressure sub‐sensor, while two aligned segmental polyimide/polyurethane films through orthogonal stacking act as two pressure‐insensitive anisotropic strain sub‐sensors. A unique characteristic of multidimensional sensor is its ability to distinguish and measure the type, magnitude, and direction of strain, pressure, and shear. Moreover, multidimensional sensor exhibits maximal gauge factor of 863.7 for strain and highest sensitivity of 187.71 kPa−1 for pressure. Importantly, multidimensional sensor exhibits an unprecedented ability to quantitatively evaluate shear using a library of electrical responses. The adaptive grasping of robotic hands and free‐throw training of players have been demonstrated to initiate the development of robotic object manipulation and physical movement guidance.

Dermatology: Human Skin, in Reflection of Phaleristics, on Thematic Badges

The article presents materials related to the reflection in phaleristics, on thematic icons of human skin, its structure and function. A significant number of thematic badges are presented - 65 copies, the obverse of which is colorfully decorated with screenshots of drawings dedicated to the structure of human skin.

Top-down architecture of magnetized micro-cilia and conductive micro-domes as fully bionic electronic skin for de-coupled multidimensional tactile perception.

Electronic skin (E-skin) has attracted considerable attention for simulating the human sensory system for use in prosthetics, human-machine interactions, and healthcare monitoring. However, it is still challenging to fully mimic the skin function that can de-couple stimuli such as normal/tangential forces, contact/non-contact behaviors, and react to high-frequency inputs. Herein, we propose fully bionic E-skin (FBE-skin), which consists of a magnetized micro-cilia array (MMCA), a micro-dome array (MDA), and flexible electrodes to completely duplicate the hairy layer, epidermis/dermis interface, and subcutaneous mechanoreceptors of human skin. The optimized MDA and interdigital electrode enable the FBE-skin to perceive static forces with a linear sensitivity of 96.6 kPa-1 up to 100 kPa, while the branch of electromagnetic induction allows the FBE-skin to sensitively capture dynamic stimuli with vibrating signals up to 100 Hz. The top-down integration of MDA and MMCA not only replicates the three-dimensional structure of human skin, but also synergistically provides the FBE-skin with bionic rapidly adapting (RA) and slowly adapting (SA) receptors. Consequently, the FBE-skin is capable of perceiving dynamic/static, normal/tangential, and contact/non-contact stimuli with a broad range of working pressures and frequencies. We expect that the design of FBE-skin will be promising for widespread applications from intelligent sensing to human-machine interactions.

Human-Inspired Tactile Perception System for Real-Time and Multimodal Detection of Tactile Stimuli.

A human can intuitively perceive and comprehend complicated tactile information because the cutaneous receptors distributed in the fingertip skin receive different tactile stimuli simultaneously and the tactile signals are immediately transmitted to the brain. Although many research groups have attempted to mimic the structure and function of human skin, it remains a challenge to implement human-like tactile perception process inside one system. In this study, we developed a real-time and multimodal tactile system that mimics the function of cutaneous receptors and the transduction of tactile stimuli from receptors to the brain, by using multiple sensors, a signal processing and transmission circuit module, and a signal analysis module. The proposed system is capable of simultaneously acquiring four types of decoupled tactile information with a compact system, thereby enabling differentiation between various tactile stimuli, texture characteristics, and consecutive complex motions. This skin-like three-dimensional integrated design provides further opportunities in multimodal tactile sensing systems.

Multifunctional Conductive Double-Network Hydrogel Sensors for Multiscale Motion Detection and Temperature Monitoring.

As typical soft materials, hydrogels have demonstrated great potential for the fabrication of flexible sensors due to their highly compatible elastic modulus with human skin, prominent flexibility, and biocompatible three-dimensional network structure. However, the practical application of wearable hydrogel sensors is significantly constrained because of weak adhesion, limited stretchability, and poor self-healing properties of traditional hydrogels. Herein, a multifunctional sodium hyaluronate (SH)/borax (B)/gelatin (G) double-cross-linked conductive hydrogel (SBG) was designed and constructed through a simple one-pot blending strategy with SH and gelatin as the gel matrix and borax as the dynamic cross-linker. The obtained SBG hydrogels exhibited a moderate tensile strength of 25.3 kPa at a large elongation of 760%, high interfacial toughness (106.5 kJ m-3), strong adhesion (28 kPa to paper), and satisfactory conductivity (224.5 mS/m). In particular, the dynamic cross-linking between SH, gelatin, and borax via borate ester bonds and hydrogen bonds between SH and gelatin chain endowed the SBG hydrogels with good fatigue resistance (>300 cycles), rapid self-healing performance (HE (healing efficiency) ∼97.03%), and excellent repeatable adhesion. The flexible wearable sensor assembled with SBG hydrogels demonstrated desirable strain sensing performance with a competitive gauge factor and exceptional stability, which enabled it to detect and distinguish various multiscale human motions and physiological signals. Furthermore, the flexible sensor is capable of precisely perceiving temperature variation with a high thermal sensitivity (1.685% °C-1). As a result, the wearable sensor displayed dual sensory performance for temperature and strain deformation. It is envisioned that the integration of strain sensors and thermal sensors provide a novel and convenient strategy for the next generation of multisensory wearable electronics and lay a solid foundation for their application in electronic skin and soft actuators.

Biomimetic Electronic Skin through Hierarchical Polymer Structural Design.

Human skin comprises multiple hierarchical layers that perform various functions such as protection, sensing, and structural support. Developing electronic skin (E-skin) with similar properties has broad implications in health monitoring, prosthetics, and soft robotics. While previous efforts have predominantly concentrated on sensory capabilities, this study introduces a hierarchical polymer system that not only structurally resembles the epidermis-dermis bilayer structure of skin but also encompasses sensing functions. The system comprises a polymeric hydrogel, representing the "dermis", and a superimposed nanoporous polymer film, forming the "epidermis". Within the film, interconnected nanoparticles mimic the arrangement of interlocked corneocytes within the epidermis. The fabrication process employs a robust in situ interfacial precipitation polymerization of specific water-soluble monomers that become insoluble during polymerization. This process yields a hybrid layer establishing a durable interface between the film and hydrogel. Beyond the structural mimicry, this hierarchical structure offers functionalities resembling human skin, which includes (1) water loss protection of hydrogel by tailoring the hydrophobicity of the upper polymer film; (2) tactile sensing capability via self-powered triboelectric nanogenerators; (3) built-in gold nanowire-based resistive sensor toward temperature and pressure sensing. This hierarchical polymeric approach represents a potent strategy to replicate both the structure and functions of human skin in synthetic designs.

Biomimetic nanofiber-iongel composites for flexible pressure sensors with broad range and ultra-high sensitivity

To achieve high-performance flexible pressure sensors, it is imperative to develop biomimetic devices that mimic the functional structure and sensing mechanism of human skin. Nevertheless, the creation of skin-like sensors with both ultra-high sensitivity and broad response range poses a formidable challenge. Drawing inspiration from the tactile sensing mechanisms and hierarchical structure of human skin, we engineered a nanofiber-iongel (NFIG) composite with internally graded stiffness characteristics and surface semi-embedded microstructures through the application of electrostatic spinning and droplet injection methods. The gel mimics the layered nanofiber structure of human skin, along with its ion-sensing mechanism, and comprises an ion gel infused with highly elastic PVDF-HFP nanofibers. This study explores the impact of Young's modulus and external pressure on unit capacitance, and it establishes a fiber-gel composite model to assess how the fibers influence sensor performance, encompassing ion fluxes, displacements, and alterations in electric potential. These findings reveal that the utilization of high-modulus materials enhances ion mobility, decreases the double electrical layer thickness, and augments pressure resistance. Based on these discoveries, we engineered the NFIG sensor, which exhibits ultra-high sensitivity (>10,000 kPa−1), a wide pressure range (∼1000 kPa), and exceptional stability (over 5000 cycles). Furthermore, this sensor is versatile, finding utility in a range of human monitoring contexts, array configurations, and even skateboard monitoring, thereby substantiating its promise in the fields of human-computer interaction and sports health.

Strat-M® positioning for skin permeation studies: A comparative study including EpiSkin® RHE, and human skin

In the development and optimization of dermatological products, In Vitro Permeation Testing (IVPT) is pivotal for controlled study of skin penetration. To enhance standardization and replicate human skin properties reconstructed human skin and synthetic membranes are explored as alternatives. Strat-M® is a membrane designed to mimic the multi-layered structure of human skin for IVPT. For instance, in Strat-M®, the steady-state fluxes (JSS) of resorcinol in formulations free of permeation enhancers were found to be 41 ± 5 µg/cm2·h for the aqueous solution, 42 ± 6 µg/cm2·h for the hydrogel, and 40 ± 6 µg/cm2·h for the oil-in-water emulsion. These results were closer to excised human skin (5 ± 3, 9 ± 2, 13 ± 6 µg/cm2·h) and surpassed the performance of EpiSkin® RHE (138 ± 5, 142 ± 6, and 162 ± 11 µg/cm2·h). While mass spectrometry and Raman microscopy demonstrated the qualitative molecular similarity of EpiSkin® RHE to human skin, it was the porous and hydrophobic polymer nature of Strat-M® that more faithfully reproduced the skin's diffusion-limiting barrier. Further validation through similarity factor analysis (∼80–85%) underscored Strat-M®'s significance as a reliable substitute for human skin, offering a promising approach to enhance realism and reproducibility in dermatological product development.

Bioinspired Young's Modulus-Hierarchical E-Skin with Decoupling Multimodality and Neuromorphic Encoding Outputs to Biosystems.

As key interfaces for the disabled, optimal prosthetics should elicit natural sensations of skin touch or proprioception, by unambiguously delivering the multimodal signals acquired by the prosthetics to the nervous system, which still remains challenging. Here, a bioinspired temperature-pressure electronic skin with decoupling capability (TPD e-skin), inspired by the high-low modulus hierarchical structure of human skin, is developed to restore such functionality. Due to the bionic dual-state amplifying microstructure and contact resistance modulation, the MXene TPD e-skin exhibits high sensitivity over a wide pressure range and excellent temperature insensitivity (91.2% reduction). Additionally, the high-low modulus structural configuration enables the pressure insensitivity of the thermistor. Furthermore, a neural model is proposed to neutrally code the temperature-pressure signals into three types of nerve-acceptable frequency signals, corresponding to thermoreceptors, slow-adapting receptors, and fast-adapting receptors. Four operational states in the time domain are also distinguished after the neural coding in the frequency domain. Besides, a brain-like machine learning-based fusion process for frequency signals is also constructed to analyze the frequency pattern and achieve object recognition with a high accuracy of 98.7%. The TPD neural system offers promising potential to enable advanced prosthetic devices with the capability of multimodality-decoupling sensing and deep neural integration.