Artificial Skin Research Articles

Advanced In-Situ functionalized conductive hydrogels with high mechanical strength for hypersensitive soft strain sensing applications

Conductive hydrogels are used in wearable electronics, soft robotics and artificial skin due to their flexibility, biocompatibility and multifunctionality. However, combining high mechanical strength, conductivity and sensitivity in these hydrogels remains a challenge. This paper proposes a novel in-situ conductive functionalization technology for hydrogels with high mechanical strength, achieving high conductivity (3223.727 S·m−1) and low resistance (0.92 Ω) without sacrificing mechanical properties. Comprehensive experiments reveal the mechanisms and optimal parameters for conductive functionalization. AgNO3 and ascorbic acid (VC) concentrations influence the distribution, reaction rate and aggregation of Ag particles on hydrogel surfaces. Sodium carboxymethylcellulose (CMC) enhances mechanical strength and Ag+ adsorption capacity. Optimal parameters are 1.00 M AgNO3 and 0.08 M VC. An in-situ reduction reaction of silver particles establishes strong interfacial bonding between the silver layer and hydrogel matrix, forming the basis for strain sensing. The hypersensitized sensing mechanism, involving the appearance and recovery of microcracks on the silver layer via the tunneling effect, enables high sensitivity (gauge factor = 36.65). The conductive hydrogels can monitor human physiological signals, tiny strain signals from water droplets (0.01 g) and airflow, with an average response time of 12.7 ms. The developed conductive hydrogels meet the technical requirements for combining high mechanical strength and sensitivity, offering an efficient new approach for conductive hydrogel-based soft strain sensors.

Artificial vascularized scaffolds for 3D-tissue regeneration — a report of the ArtiVasc 3D Project

The aim of this paper is to raise awareness of the ArtiVasc 3D project and its findings. Vascularization is one of the most important and highly challenging issues in the development of soft tissue. It is necessary to supply cells with nutrition within a multilayer tissue, for example in artificial skin. Research on artificial skin is driven by an increasing demand for two main applications. Firstly, for the field of regenerative medicine, the aim is to provide patients with implants or grafts to replace damaged soft tissue after traumatic injuries or ablation surgery. Secondly, another aim is to substitute expensive and ethically disputed pharmaceutical tests on animals by providing artificial vascularized test beds to simulate the effect of pharmaceuticals into the blood through the skin. This paper provides a perspective on ArtiVasc 3D, a major European Commission funded project that explored the development of a full thickness, vascularized artificial skin. The paper provides an overview of the aims and objectives of the project and describes the work packages and partners involved. The most significant results of the project are summarized and a discussion of the overall success and remaining work is given. We also provide the journal papers resulting from the project.

Ultra-Tough Graphene Oxide/DNA 2D Hydrogel with Intrinsic Sensing and Actuation Functions.

Hydrogel devices with mechanical toughness and tunable functionalities are highly desirable for practical long-term applications such as sensing and actuation elements for soft robotics. However, existing hydrogels have poor mechanical properties, slow rates of response, and low functionality. In this work, two-dimensional hydrogel actuators are proposed and formed on the self-assembly of graphene oxide (GO) and deoxynucleic acid (DNA). The self-assembly process is driven by the GO-induced transition of double stranded DNA (dsDNA) into single stranded DNA (ssDNA). Thus, the hydrogel's structural unit consists of two layers of GO covered by ssDNA and a layer of dsDNA in between. Such heterogeneous architectures stabilized by multiple hydrogen bondings have Young's modulus of up to 10GPa and rapid swelling rates of 4.0×10-3 to 1.1×10-2 s-1, which surpasses most types of conventional hydrogels. It is demonstrated that the GO/DNA hydrogel actuators leverage the unique properties of these two materials, making them excellent candidates for various applications requiring sensing and actuation functions, such as artificial skin, wearable electronics, bioelectronics, and drug delivery systems.

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.

Bioinspired waterproof and self-healing Photonic-Ionic skin for underwater interactive sensing

Bioinspired photonic-ionic skins (PI-skins) possessing multiple signals considerably promote the development of soft ionoelectronics owing to the fascinating interactive sensing capabilities. Unfortunately, swelling and leakage in aqueous environments are significantly detrimental to the stability and durability of underwater sensing. Herein, a novel PI-skin with waterproof, self-healing, and highly resilient properties is ingeniously fabricated via integrating the photonic array and dynamically covalently crosslinking fluorine-rich ionogel. Benefiting from the strain-modulated nanostructure and ionic conduction, the PI-skin achieves unique dual-signal sensing capability with sensitive mechanochromic performance and synchronous electrical response. Furthermore, the synergistic water repellency of the trifluoromethyl on the skeleton and the long alkyl chain modified hydrophobic ionic liquid (IL) inhibit swelling and leakage, significantly enhancing underwater stability. Notably, the exchangeable hindered urea bonds (HUBs) were judiciously introduced to construct a stable dynamically covalently crosslinking network, achieving efficient self-healing and high resilience simultaneously. The PI-skin with excellent adhesion and durability demonstrates the application potential in dual-signal underwater sensing and wireless information transmission. This work offers innovative design inspirations for the advancement of multifunctional artificial skins, intelligent interactive devices, and high-performance wearable iontronics.

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.

Thermoregulatory integration in hand prostheses and humanoid robots through blood vessel simulation

In this paper, we introduce an innovative approach for generating robotic faces with a thermal signature similar to that of humans and equipping prosthetic or robotic hands with a lifelike temperature distribution. This approach enhances their detection via infrared cameras and promotes more natural interactions between humans and robots. This method integrates a temperature regulation system into artificial skin, drawing inspiration from the human body’s natural temperature control via blood flow. Central to this technique is a fiber network simulating blood vessels within the artificial skin. Water flows through these fibers under specific temperature and flow conditions, forming a controlled heat release system. The heat emission can be adjusted by changing the dilation of these fibers, primarily by modulating the frequency of circulation. Our findings indicate that this approach can replicate the varied thermal characteristics of different human faces and hand areas. Consequently, the robotic faces appear more human-like in infrared images, aiding their identification by infrared cameras. At the same time, the prosthetic hands achieve a more natural temperature, reducing the discomfort typically felt in direct contact with synthetic limbs. The aim of this study was to address the challenges faced by the users of prosthetic hands. The results from this study show a promising direction in humanoid robotics, fostering improved tactile interactions and redefining human–robot relationships. This innovative technique facilitates further advancements, blurring the lines between artificial aids and natural biological systems.

Jellyfish-Inspired Visual and Sensory Bubbling Robots with Automatic 3D Morphable Films for Underwater Environmental Interactions.

Coelenterates, such as Atolla jellyfish, are capable of integrating color, communication, and motion in a sophisticated manner, thereby enabling them to function as intelligent biological systems that can adapt to the challenges of the underwater environment. Extensive efforts have been dedicated to exploiting underwater visual, sensory, actuating, or combined systems. However, current biomimetic soft systems are still limited by the lack of comprehensive, integrated functional skins that can automatically deform, dynamically sense, and further send color signals when diving into underwater conditions. Here, we propose the synthetic soft skins composed of assembled entangled carbon nanotube networks and fluorescent unit-embedded elastomers which can be applied in a suspended form to allow autonomic 3D deformation, real-time perception, and dynamic fluorescence color transformation. The capabilities of the sensory and color display thresholds were controlled through the entanglement density of carbon nanotubes and the suspended area. As a demonstration, the soft thin skin was integrated into an artificial jellyfish robot, enabling the realization of a closed-loop feedback system for dynamic sensory processing, signal processing, and further 3D morphing-induced fluorescent color change, demonstrating significant potentials in underwater visual display, danger warning, and environmental exploration.

Robust and resilient piezoresistive sensor made of MWCNT-embedded aerogel prepared with elongated amyloid fibrils of α-synuclein

Pressure sensors are widely employed in various fields from biomedical to aerospace engineering. Each field requires pressure sensors with specific sensitivity, response time, recovery time, durability, and detection limit. However, developing pressure sensors that meet the increasing demands of high mechanical strength and sensitive electrical responsiveness influencing reliability and accuracy still remains challenging. Herein, a highly robust and resilient piezoresistive sensor was developed by combining elongated amyloid fibrils (eAFs) aerogel made of a self-assembly protein of α-synuclein, which provided stable porous 3D interconnected network and thus increased surface area, and multi-walled carbon nanotube (MWCNT) as a reinforcement material for improved mechanical and electrical properties. Owing to the integration between eAFs aerogel and MWCNT, the MWCNT-embedded eAFs aerogel exhibited augmentation in mechanical strength and resiliency depending on the amount of MWCNT introduced. Additionally, the MWCNT-embedded eAFs aerogel showed piezoresistive properties with stable pressure sensing capability toward human motions, airflow, and underwater pressure. It is, therefore, suggested that the pressure sensor fabricated with the eAFs aerogel containing MWCNT could be utilized in diverse areas including wearable device and artificial skin development.

Health risks from exposure to chemicals in clothing - Non-regulated halogenated aromatic compounds

The objective of the present study was to investigate some commonly detected halogenated textile pollutants for their bioavailability and hazardous properties. Release into artificial sweat and skin absorption in vitro were examined as well as mutagenic effects by Ames test, and skin-sensitizing properties from a peptide reactivity assay combined with a cell test.All investigated compounds were shown to migrate from the textile into sweat and be absorbed by the skin, although to a different extent. The experimental values for migration were found to be up to 390 times higher compared to literature values. Two of the studied compounds, 2,5-dinitrochlorobenzene and 3,5-dinitrobromobenzene, both exhibited mutagenic effects in the Ames test, while both 2,5-dinitrochlorobenzene and 2,6-dichlorobenzene-1,4-diamine were classified as skin sensitizers. The allergenic reactivity of the latter was found to be due to an oxidized transformation product.Risks for the induction of skin allergy and other non-carcinogenic effects from dermal exposure to the individual compounds were found low, even when considering clothing with the highest reported levels. However, the complex mixtures of chemicals often present in garments may still constitute a health risk, especially when considering the many hours of daily exposure. It is important to further study the toxicity of other frequently occurring chemicals as well as the synergistic effects of chemicals that co-occur in clothing.

Syringaresinol Attenuates α-Melanocyte-Stimulating Hormone-Induced Reactive Oxygen Species Generation and Melanogenesis.

Ginseng has been utilized for centuries in both the medicinal and cosmetic realms. Recent studies have actively investigated the biological activity of ginseng berry and its constituents. (+)-Syringaresinol [(+)-SYR], an active component of ginseng berry, has been demonstrated to have beneficial effects on the skin, but its potential impact on skin pigmentation has not been fully explored. Here, the antioxidant and anti-pigmentary activity of (+)-SYR were evaluated in B16F10 murine melanoma cells and in an artificial human pigmented skin model, Melanoderm™. A real-time PCR, Western blotting, immunofluorescence staining, and histochemistry staining were conducted to confirm the effects of (+)-SYR on pigmentation. (+)-SYR reduced melanogenesis and dendrite elongation in α-melanocyte-stimulating hormone (α-MSH)-primed B16F10 cells with low cytotoxicity. (+)-SYR suppressed the expression of melanogenic genes, namely tyrosinase (TYR), tyrosinase-related protein 1 (TRP-1), and tyrosinase-related protein 2 (TRP-2). Notably, (+)-SYR attenuated α-MSH-induced cytosolic and mitochondrial reactive oxygen species (ROS) generation, which was attributable at least in part to the suppression of NADPH oxidase-4 (NOX 4) expression. Finally, the brightening activities of (+)-SYR were verified using Melanoderm™, underscoring the potential of ginseng berry and (+)-SYR as functional ingredients in skin-brightening cosmetics.

Core-Shell Gel Nanofiber Scaffolds Constructed by Microfluidic Spinning toward Wound Repair and Tissue Regeneration.

Growing demand for wound care resulting from the increasing chronic diseases and trauma brings intense pressure to global medical health service system. Artificial skin provides mechanical and microenvironmental support for wound, which is crucial in wound healing and tissue regeneration. However, challenges still remain in the clinical application of artificial skin since the lack of the synergy effect of necessary performance. In this study, a multi-functional artificial skin is fabricated through microfluidic spinning technology by using core-shell gel nanofiber scaffolds (NFSs). This strategy can precisely manipulate the microstructure of artificial skin under microscale. The as-prepared artificial skin demonstrates superior characteristics including surface wettability, breathability, high mechanical strength, strain sensitivity, biocompatibility and biodegradability. Notably, this artificial skin has the capability to deliver medications in a controlled and sustained manner, thereby accelerating the wound healing process. This innovative approach paves the way for the development of a new generation of artificial skin and introduces a novel concept for the structural design of the unique core-shell gel NFSs.

Isolation and culture of feline keratinocytes and fibroblasts for the generation of artificial skin equivalent

Isolation and culture of feline keratinocytes and fibroblasts for the generation of artificial skin equivalent

Microfluidic bubble-templating 3D printing of ordered macroporous hydrogels

Macroporous hydrogels have broad applications in tissue engineering, drug delivery and flexible biosensors, etc. However, it is still difficult to simultaneously control both the shape and the internal macroporosity. Here, we introduce a microfluidic bubble-templating 3D printing method based on thermosensitive composite hydrogel inks consisting of alginate and Pluronic F127. Two-phase laminar shear in coaxial microfluidics generates exceptionally monodispersed microbubbles as templates, while 3D printing technique provides spatial distribution of these microbubbles. Microbubble generation and 3D printing are coordinated and rheology of the inks are optimized to improve the systematic printability. Macroporous hydrogels with both monodispersed and gradient macropore structures are prepared and characterized. The internal anisotropic macroporosity distribution leads to inhomogeneous mechanical property in the products, making them competent as ergonomic artificial knuckle skins. The microfluidic-assisted 3D printing methodology provides a new insight for bottom-up design of porous soft materials.

Ultra‐Rapidly Responsive Electret‐Based Flexible Pressure Sensor via Functional Polymeric Nanoparticle Synthesis

AbstractFlexible electrets can be used to construct eco‐friendly devices that utilize dielectric materials to measure physical parameters without requiring any power supply. By achieving detection capabilities that surpass human tactile abilities, such devices can be employed to create super‐sensing technologies, such as electronic artificial skin, based on solution processes. In this study, electret‐type particles with self‐power‐generating properties are synthesized and applied to flexible pressure sensors. Notably, an ultrafast response is achieved despite the device being flexible and fabricated using a solution process. Moreover, this technology is successfully implemented in both human and robot applications, detecting tactile signals in real‐time and serving as electronic artificial skin—a key super‐sensing aspect. These results showcase the possibilities offered by high‐performance flexible sensing technology and illuminate potential directions for future applications.

Data-driven inverse design of flexible pressure sensors

Artificial skins or flexible pressure sensors that mimic human cutaneous mechanoreceptors transduce tactile stimuli to quantitative electrical signals. Conventional trial-and-error designs for such devices follow a forward structure-to-property routine, which is usually time-consuming and determines one possible solution in one run. Data-driven inverse design can precisely target desired functions while showing far higher productivity, however, it is still absent for flexible pressure sensors because of the difficulties in acquiring a large amount of data. Here, we report a property-to-structure inverse design of flexible pressure sensors, exhibiting a significantly greater efficiency than the conventional routine. We use a reduced-order model that analytically constrains the design scope and an iterative "jumping-selection" method together with a surrogate model that enhances data screening. As an exemplary scenario, hundreds of solutions that overcome the intrinsic signal saturation have been predicted by the inverse method, validating for a variety of material systems. The success in property design on multiple indicators demonstrates that the proposed inverse design is an efficient and powerful tool to target multifarious applications of flexible pressure sensors, which can potentially advance the fields of intelligent robots, advanced healthcare, and human-machine interfaces.

A Flexural Ultrasonic Transducer for Inducing Acoustic Cavitation on Material Surfaces

Abstract Purpose This paper proposes a flexural ultrasonic transducer specifically designed for surface treatment of materials with delicate surfaces such as skin by acoustic cavitation at low frequencies. The goal of this preliminary study is to assess the resonance frequencies and the output sound pressure of the proposed transducer and confirm generation of acoustic cavitation on the surface of an artificial skin phantom. Methods A transducer prototype was designed based on structural-acoustic simulation and fabricated. The proposed design employs a concave-shaped acoustic resonator with a spherical cavity, which is driven by flexural vibration of a piezoelectric ceramic disk actuator. The transducer prototype has compact dimensions of 15 mm in diameter and 8 mm in axial length, working at frequencies around flexural vibration modes of the piezoelectric disk with a thickness of 1 mm. Results The maximum sound pressure amplitude reached 125 kPa with an input voltage amplitude of 10 V at the second resonance frequency of 167 kHz, where the third axisymmetric eigenmode was excited. Despite enhancing the maximum pressure, the sound pressure outside the resonator attenuates because the near-field distance of the irradiated sound wave is smaller than the height of the resonator. This implies that the proposed method provides the cavitation effect on material surfaces, possibly minimizing the side effect of ultrasound irradiation on the underlying structure. Cavitation generation on a urethane gel surface was directly observed by using a high-speed video camera. Conclusion We confirmed that acoustic cavitation was generated and propelled to the target surface. It concludes that ultrasound irradiation using the proposed ultrasonic transducer could be a promising alternative for effective and safe ultrasound treatment of material surfaces.

Multifunctional Porous Bilayer Artificial Skin for Enhanced Wound Healing.

Meeting the exacting demands of wound healing encompasses rapid coagulation, superior exudate absorption, high antibacterial efficacy, and imperative support for cell growth. In this study, by emulating the intricate structure of natural skin, we prepare a multifunctional porous bilayer artificial skin to address these critical requirements. The bottom layer, mimicking the dermis, is crafted through freeze-drying a gel network comprising carboxymethyl chitosan (CMCs) and gelatin (GL), while the top layer, emulating the epidermis, is prepared via electrospinning poly(l-lactic acid) (PLLA) nanofibers. With protocatechuic aldehyde and gallium ion complexation (PA@Ga) as cross-linking agents, the bottom PA@Ga-CMCs/GL layer featured an adjustable pore size (78-138 μm), high hemostatic performance (67s), and excellent bacterial inhibition rate (99.9%), complemented by an impressive liquid-absorbing capacity (2000% swelling rate). The top PLLA layer, with dense micronanostructure and hydrophobic properties, worked as a shield to effectively thwarted liquid or bacterial penetration. Furthermore, accelerated wound closure, reduced inflammatory responses, and enhanced formation of hair follicles and blood vessels are achieved by the porous artificial skin covered on the surface of wound. Bilayer artificial skin integrates the advantages of nanofibers and freeze-drying porous materials to effectively replicate the protective properties of the epidermal layer of the skin, as well as the cell migration and tissue regeneration of the dermis. This bioabsorbable artificial skin demonstrates structural and functional comparability to real skin, which would advance the field of wound care through its multifaceted capabilities.

Outcomes of Biodegradable Temporizing Matrix for Soft Tissue Reconstruction of the Hand and Extremities.

NovoSorb biodegradable temporizing matrix (BTM) is a novel, bilayer, synthetic skin substitute made of biodegradable polyurethane foam covered with a sealing membrane. BTM has demonstrated excellent outcomes in burn literature; however, few studies have been published for hand and extremity soft tissue reconstruction. All patients who underwent extremity reconstruction with BTM from 2018 to 2023 were reviewed. Demographics, presentations, and clinical outcomes were recorded. A total of 86 cases from 54 patients (53.7% pediatric; age range: 0-81 years) were included. Common indications included trauma (36%), infection (18.6%), and malignancy (11.6%). BTM was placed over exposed tendon (38.4%), bone (19%), joints (12.8%), nerves (8.1%), and/or blood vessels (7%). BTM served as temporary wound coverage in 26 cases. Complications included hematoma (8.1%), infection (4.7%), and spontaneous delamination (4.7%). Wound closure was successfully obtained without flap use in 93.3%. Poor BTM take was associated with peripheral vascular disease, hypertension, immunosuppression, and BTM hematoma and infection (<0.05). This study contributes to the growing body of evidence favoring BTM use in challenging reconstructive cases. Although prospective comparative studies are forthcoming, BTM likely has broad applications in reconstructive surgery.

3D Bioprinting of Artificial Skin Substitute with Improved Mechanical Property and Regulated Cell Behavior through Integrating Patterned Nanofibrous Films.

Three-dimensional (3D) bioprinting has advantages for constructing artificial skin tissues in replicating the structures and functions of native skin. Although many studies have presented improved effect of printing skin substitutes in wound healing, using hydrogel inks to fabricate 3D bioprinting architectures with complicated structures, mimicking mechanical properties, and appropriate cellular environments is still challenging. Inspired by collagen nanofibers withstanding stress and regulating cell behavior, a patterned nanofibrous film was introduced to the printed hydrogel scaffold to fabricate a composite artificial skin substitute (CASS). The artificial dermis was printed using gelatin-hyaluronan hybrid hydrogels containing human dermal fibroblasts with gradient porosity and integrated with patterned nanofibrous films simultaneously, while the artificial epidermis was formed by seeding human keratinocytes upon the dermis. The collagen-mimicking nanofibrous film effectively improved the tensile strength and fracture resistance of the CASS, making it sewable for firm implantation into skin defects. Meanwhile, the patterned nanofibrous film also provided the biological cues to guide cell behavior. Consequently, CASS could effectively accelerate the regeneration of large-area skin defects in mouse and pig models by promoting re-epithelialization and collagen deposition. This research developed an effective strategy to prepare composite bioprinting architectures for enhancing mechanical property and regulating cell behavior, and CASS could be a promising skin substitute for treating large-area skin defects.