Flexible Skin Research Articles

Few-mode optical fiber-based flexible pressure feedback tentacle doped with fluorescence temperature pointer

Abstract In this paper, a flexible fiber pressure feedback whisker is proposed, which consists of a water droplet shaped polydimethylsiloxane (PDMS) elastomer with an embedded balloon shaped few mode fiber. The mechanical sensing performance of the device was analyzed and optimized using a combination of finite element method and beam propagation method (BPM). The built-in cladding corroded few-mode fiber increases pressure sensitivity by more than four times. The collection efficiency of fluorescence signal is improved by cladding corrosion. The PDMS elastomer was doped with upconversion nanoparticles NaYF4:Yb, Er@NaYF4 in order to achieve temperature measurement by fluorescence intensity ratio technology. The combination of fluorescence signal and interference spectrum can not only achieve real-time and accurate pressure detection at different temperatures, but also incorporate fluorescent materials into flexible bionic skin for temperature self-compensation, which has potential application value for the development of bionic fiber micro-nano sensing and control devices.

Dynamic multicolor electrochromic skin in high-brightness flexible WO3/Au asymmetric Fabry–Perot nanocavity fabricated on Nylon 66 porous substrate

Recently, the Fabry–Perot (F–P) cavity electrochromic devices, which are constructed by combining nano-size inorganic electrochromic material WO3 and reflective metal layers, have attracted considerable attention due to their potentials in the fields of dynamic multicolor displays and active camouflage. However, in the few studies that have been reported, the peak reflectance of flexible F–P cavity multicolor electrochromic devices in the visible wavelength band is generally lower than 30 %, which limits their reflective display and camouflage effects in high-brightness environments. Thus, we have combined multicolor reflective electrochromic electrodes in WO3/Au asymmetric F–P nanocavity constructed by magnetron sputtering on a Nylon 66 porous substrate with a highly transparent UV-cured gel electrolyte and a PET plastic sealing procedure. As a result, a flexible and dynamic multicolor electrochromic skin with high reflectance (Rmax＞50 %) and excellent flexibility (bending radius of 4 mm) has been fabricated. The WO3 electrochromic layer at the top works as the dynamic dielectric layer in the broadband absorption Fabry–Perot cavity, and the inert metal Au layer at the bottom works as the reflective layer. The WO3/Au asymmetric F–P cavity can acutely capture the variation in optical constants of WO3 due to the thickness change and electric-driven effects. This cavity facilitates the selective reflection and absorption of the energy distribution of the spectrum after the induced interferometric resonance. As a result, the cavity exhibits a rich array of structural colors, including ocher, taupe, yellow, orange, green, and violet. The electrochromic skin exhibits a fast switching time and maintains 99.43 % of the optical modulation amplitude (ΔR) after 110 coloring/bleaching cycles. It provides a potential option in the field of flexible high-brightness reflective displays and dynamic camouflage in the future.

Expanded Properties and Applications of Porous Flame-Retardant Polymers Containing Graphene and Its Derivatives.

With the integration and miniaturization of modern equipment and devices, porous polymers, containing graphene and its derivatives, with flame-retardancy have become a research hotspot. In this paper, the expanded properties and high-end applications of flame-retardant porous materials containing graphene and its derivatives were discussed. The research progress regarding graphene-based porous materials with multiple energy conversion, thermal insulation, an electromagnetic shielding property, and a high adsorption capacity were elucidated in detail. The potential applications of materials with the above-mentioned properties in firefighter clothing, fire alarm sensors, flexible electronic skin, solar energy storage, energy-saving buildings, stealth materials, and separation were summarized. The construction strategies, preparation methods, comprehensive properties, and functionalization mechanisms of these materials were analyzed. The main challenges and prospects of flame-retardant porous materials containing graphene and its derivatives with expanded properties were also proposed.

Integrated Electromechanical Structure for Iontronic Pressure Sensors with Linear High‐Sensitivity Response and Robust Sensing Stability

AbstractA linear high‐sensitivity response is crucial for flexible electronic skin, particularly in precision detection for applications like intelligent robotics and human‐machine interactions. Prevailing strategies typically adopt a layered, multifaceted material design to cultivate this response, yet this approach often culminates in a diminished capacity to augment sensing stability. The root causes of these limitations are predominantly material mechanical mismatches and interface incompatibilities inherent in these designs. To address these challenges, an electromechanical integration strategy is introduced that simultaneously enhances linear highsensitivity and stability. This strategy is centered on constructing a robust, integrated mechanical and electrical interface within a polyurethane material system through an in situ growth and adhesion process. The iontronic pressure sensor exhibits a linear high‐sensitivity response (16.24 kPa−1, R2 = 0.999) within a wide range (0–300 kPa). Moreover, the sensor's integrated structure, self‐encapsulated through the adhesion between the electrode and dielectric layers, exhibits robust stability, even under complex mechanical stresses. The applications of the sensors in precision weighing and haptic feedback within intelligent gripping systems demonstrate their advantages of both linearity and stable sensing. This work delineates a strategic pathway for the fabrication of high‐performance flexible pressure sensors, contributing significantly to the field of advanced sensing technologies.

Free Fibular Osteocutaneous Flap Combined With Simultaneous Tendon Reconstruction for Midfoot Restoration After Myoepithelial Carcinoma Resection.

Myoepithelial carcinomas of soft tissue are rare, and most are malignant. The optimal treatment is surgical excision. The arches of the foot are a composite structure responsible for weight bearing and pressure distribution, so it is a vast challenge in reconstruction. We report a case of reconstruction of the midfoot with a free fibular bone flap and tendon graft. We review the literature to compare various options in foot reconstructions and sort out the outcomes of different bone flaps. The free fibula osteocutaneous flap is the superior choice for midfoot reconstruction owing to its sufficient length, strength, flexible skin paddles, easy-to-withstand osteotomy, and simultaneous tendon graft harvesting.

Engineering robust and transparent dual-crosslinked hydrogels for multimodal sensing without conductive additives

Conductive hydrogels are pivotal for the advancement of flexible sensors, electronic skin, and healthcare monitoring systems, facilitating transformative innovations. However, issues such as inadequate intrinsic compatibility, mismatched mechanical properties, and limited stability curtail their potential, resulting in compromised device efficacy and performance degradation. In this research, we engineered functional hydrogels featuring a dual-crosslinked network composed of (PA/PVA)-P(AM-AA) to address these challenges. This design eliminates the need for conductive additives, thereby enhancing intrinsic compatibility. Notably, the hydrogels exhibit exceptional mechanical properties, with high tensile strength (∼700 %), Young's modulus (∼5.33 MPa), increased strength (∼2.46 MPa) and toughness (∼6.59 MJ m−3). They also achieve a compressive strength of ∼7.33 MPa at 80 % maximal compressive strain and maintain about 89 % transparency. Moreover, flexible sensors derived from these hydrogels demonstrate enhanced multimodal sensing capabilities, including temperature, strain, and pressure detection, enabling precise monitoring of human movements. The integration of multiple hydrogels into a three-dimensional sensor array facilitates detailed spatial pressure distribution mapping. By strategically applying dual-crosslinked network engineering and eliminating conductive additives, we have streamlined the design and manufacturing of hydrogels to meet the rising demand for high-performance wearable sensors.

Research on FBG Tactile Sensing Shape Recognition Based on Convolutional Neural Network.

Shape recognition plays a significant role in the field of robot perception. In view of the low efficiency and few types of shape recognition of the fiber tactile sensor applied to flexible skin, a convolutional-neural-network-based FBG tactile sensing array shape recognition method was proposed. Firstly, a sensing array was fabricated using flexible resin and 3D printing technology. Secondly, a shape recognition system based on the tactile sensing array was constructed to collect shape data. Finally, shape classification recognition was performed using convolutional neural network, random forest, support vector machine, and k-nearest neighbor. The results indicate that the tactile sensing array exhibits good sensitivity and perception capability. The shape recognition accuracy of convolutional neural network is 96.58%, which is 6.11%, 9.44%, and 12.01% higher than that of random forest, k-nearest neighbor, and support vector machine. Its F1 is 96.95%, which is 6.3%, 8.73%, and 11.94% higher than random forest, k-nearest neighbor, and support vector machine. The research of FBG shape sensing array based on convolutional neural network provides an experimental basis for shape perception of flexible tactile sensing.

Wealth in Water: A Blueprint for Sustainable Global Ocean Research

Pushing forward with leveraging water resources, promoting international cooperation, and ensuring transparency in deep-sea mining operations. There is also a concern about where to discharge the toxins of unpurified water. Artificial Intelligence has created a dominance in the applications field with a totally automated system. Out of a thorough analysis completed with indicators, satellite radar, and A Journals, there are 30 years of research and 8 years of monitored testing to achieve accuracy and relevance. The patents in place are, Oceanic Mining System (4446636), Flexible Solar Skin in Combination with an Airplane (4768738), Cargo Torpedo (4421050), Oceanic seaplow system (4398362), and previous articles like “Is Extracting Lithium and deep-sea mining more sustainable?”, “AI as a Means of Water Purification Protection”, “Global Water Distribution”, and “Can Deep Sea Water be Processed into Potable Water and Distributed into the Middle East’? To report some ballpark numbers on the proposal and how we would navigate these projects, there will be an exact location of where the plant will be built as well as a water/salinity report of the water being treated. There are still issues with analyzing the cost of desalination compared to other alternatives. Deep Sea Water proves to be a higher quality water and the investment is well worth it. The surveys lean toward clients preferring the International Standards Operating Procedure. All recipients agree there should be a sense of urgency on water shortages. Currently, AI has proven to be a vital asset in eliminating biases and expenses.

Nonlinear fluid-solid coupling responses of flexible skin-based morphing camber wings

Two original finger-like morphing camber wings (MCWs) based on flexible woven and corrugated composite skins are elaborately designed and skillfully manufactured, and experimentally validated. It is manifested that both original finger-like MCWs could flexibly and continuously morph without buckling and wrinkling, illustrating the ideal morphing camber function. In accordance with the MCWs geometries and constitutive relationships of flexible composite skins, novel analytical model is then devised for predicting the material and geometric nonlinear mechanical behaviours of the MCWs. Good agreement has been achieved between the experiments and the predictions, demonstrating the effective usage of new analytical model of finger-like MCWs. Finally, new fluid-solid coupling FE model is generated for evaluating fluid-solid interaction on mechanical responses of the MCWs under aerodynamic pressure. It is born out that fluid-solid coupling has a significant adverse impact on mechanical behaviours of finger-like MCW, and flexible woven composite skin holds superiority over flexible corrugated composite skin in terms of out-of-plane deformation resistance and bearing-load capacity under aerodynamic pressure. New model opens an avenue to numerically evaluate fluid-solid interaction on mechanical responses of the MCWs under aerodynamic pressure.

NdFeB-based magnetic triboelectric nanogenerator for enhanced bioenergy harvesting and tactile perception

High performance and versatility may be the key for the development of flexible electronic skins that are based on triboelectric nanogenerators (TENGs), and multifunctional components at the triboelectric interface is essential for empowering these devices to mimic or even surpass the sensing properties of human skin, and enabling their response to both environmental and intrinsic conditions. In this context, we present an efficient, low-cost strategy for constructing magnetically responsive TENGs by introducing NdFeB powders into a polydimethylsiloxane film. Besides superior stability, resiliency, and flexibility, the as-designed TENG presents an enhanced output of open circuit voltage of 150 V, short circuit current of 16.7 mA/m2, and Qsc of 35 nC, which is almost 3.5 times of the pristine one. Interestingly, the output performance of MR-TENG shows dependence on both the concentration of NdFeB and the direction and intensity of magnetization. Such a correlation in turn provides the linear relationship of the output with the magnetic field (∼80 V/T) and the applied dynamic force (∼0.64 V/N), which helps seamlessly integrating energy harvesting with tactile sensing for self-powered human activity monitoring and other intelligent sensing applications.

Fluid-Solid Interfacial Properties and Drag-Reducing Characterization of the Flexible Conical Microstructured Film Inspired by the Streamlined Body Surface of the Pufferfish.

Given the challenges in accurately replicating the surface of the pufferfish, this study employed three-dimensional (3D) printing to create a model based on inverse modeling. The morphology of the pufferfish exhibits a streamlined configuration, characterized by a gradual widening from the anterior oral region to the central ocular area, followed by a progressive narrowing from the midabdominal region toward the caudal extremity. The RNG k-ε turbulence simulation results demonstrate that the streamlined body surface of the pufferfish diminishes differential pressure resistance. This enhancement promotes laminar flow formation, delays fluid separation, minimizes turbulence-induced vortices, and reduces frictional resistance. Moreover, the pufferfish's supple and uneven outer epidermis was simplified into a flexible, nonsmooth planar film to conduct fluid-solid coupling simulations. These revealed that the pufferfish's unique skin can absorb turbulent energy and minimize momentum transfer between the fluid and the solid film, lowering the fluid resistance during swimming. In summary, The high-efficiency swimming capacity of pufferfish stems not only from their streamlined body surface but also significantly from the unique structural characteristics and mechanical properties of their flexible skin. This research provides critical theoretical underpinnings for the design of functional bionic surfaces aimed at drag reduction.

Bioinspired electronic-skin for proximity and pressure detection in robot active sensing

Active sensing technology plays an essential role in environment–robot interactions. Inspired by the proximity sensing approach of weakly electric fish, which relies on distributed electroreceptors capable of detecting electric fields, we propose a flexible electronic skin (e-skin) for proximity and pressure detection. Conductive thermoplastic polyurethane and dielectric polyurethane are employed for fabricating flexible electrodes and substrates, respectively. An Ecoflex-based elastic layer enables proximity and pressure information to be decoupled from the electric field. The proposed e-skin can detect objects up to 160 mm away while performing real-time proximity and pressure sensing. Finally, we demonstrate that robots equipped with the e-skin can easily explore their surroundings and perform specific tasks such as recognition, avoidance, and grasping. Because of its proximity and pressure sensing capabilities and low-cost fabrication process, the e-skin has broad application potential for robot active sensing.

Multifunctional and high‐stability RGO/PANI wrapped polyurethane foam for flexible piezoresistive sensor applications

AbstractDue to its excellent durability and steady mechanical qualities, three‐dimensional porous polyurethane foam (PUF) presents a wide range of possibilities for flexible piezoresistive sensors. Its extreme flammability, poor electrical conductivity, and susceptibility to outside factors present serious difficulties, though. In this study, a waterborne polyurethane‐coated flexible PUF sensor that incorporates reduced graphene oxide (RGO) and polyaniline (PANI) through a methodical, step‐by‐step dip‐coating methodology is successfully developed. The final product has a water contact angle of 133°, which improves its ability to adapt to a variety of environmental circumstances. Flexible graphene sheets are incorporated to improve heat resistance and flame retardancy, and PANI and RGO provide strong bonding to the PUF framework, ensuring outstanding structural stability even after 1500 cycles. The flexible foam sensor shows promise for use in flexible piezoresistive sensors and electronic skin due to its remarkable strain monitoring range of up to 70%, quick response time of 0.39 s in sensitivity experiments, and adaptability to different physical activities like walking and gesturing.

Carbon nanotube/nonwoven fabric-based electronic skins for smart clothing and electronic glove

In recent years, flexible, easy-to-fabricate, and low-cost electronic skins (E-skins) have attracted considerable attention, due to their enormous demand in wearable device applications. Based on a carbon nanotube (CNT)/nonwoven fabric, three types of E-skins were fabricated using a low-cost and scalable approach, and detected various signals, like pressure, stretch, flexion, temperature, and humidity. Due to the wrinkled and porous microstructure of CNT/nonwoven fabric, the pressure-sensitive E-skin demonstrates a high gauge factor (GF) value of 19.12 kPa-1 and 5.38 kPa-1 with a pressure range of 15–6125 Pa and 6125–12005 Pa, respectively. Unlike traditional paper-based E-skins, the stretch/flexion/temperature-sensitive E-skin could detect the stretch strain, and its GF values were 3.81, 0.51 rad-1, and 1.4×10-3 ℃-1 for the detection of stretch, flexion and temperature. For the humidity-sensitive E-skin, its GF value was calculated to be 2.8×10-2 and 0.20 with the relative humidity range of 55–75% and 75–95%. The favorable performance of the E-skins allows their integration into smart clothing, where they successfully monitored human motion, physiological and external environmental signals in real time. Furthermore, the prepared E-skins have also been integrated into an electronic glove, where they simultaneously detected the bending and pressure signals of human fingers, demonstrating application potential in the field of telediagnosis.

Silver nanowires/waterborne polyurethane composite film based piezoresistive pressure sensor for ultrasensitive human motion monitoring

Flexible piezoresistive pressure sensors are gaining significant attention, particularly in the realm of flexible wearable electronic skin. Here, a flexible piezoresistive pressure sensor was developed with a broad sensing range and high sensitivity. We achieved this by curing polydimethylsiloxane (PDMS) on sandpaper, creating a PDMS film as the template with a micro-protrusion structure. The core sensing layer was formed using a composite of silver nanowires (AgNWs) and waterborne polyurethane (WPU) with a similar micro-protrusion structure. The sensor stands out with its exceptional sensitivity, showing a value of 1.04 × 106 kPa−1 with a wide linear range from 0 to 27 kPa. It also boasts a swift response and recovery time of 160 ms, coupled with a low detection threshold of 17 Pa. Even after undergoing more than 1000 cycles, the sensor continues to deliver stable performance. The flexible piezoresistive pressure sensor based on AgNWs/WPU composite film (AWCF) can detect small pressure changes such as pulse, swallowing, etc, which indicates that the sensor has great application potential in monitoring human movement and flexible wearable electronic skin.

Design and Validation of the Trailing Edge of a Variable Camber Wing Based on a Two-Dimensional Airfoil.

Variable camber wing technology stands out as the most promising morphing technology currently available in green aviation. Despite the ongoing advancements in smart materials and compliant structures, they still fall short in terms of driving force, power, and speed, rendering mechanical structures based on kinematics the preferred choice for large long-range civilian aircraft. In line with this principle, this paper introduces a linkage-based variable camber trailing edge design approach. Covering coordinated design, internal skeleton design, flexible skin design, and drive structure design, the method leverages a two-dimensional supercritical airfoil to craft a seamless, continuous two-dimensional wing full-size variable camber trailing edge structure, boasting a 2.7 m span and 4.3 m chord. Given the significant changes in aerodynamic load direction, ground tests under cruise load utilize a tracking-loading system based on tape and lever. Results indicate that the designed single-degree-of-freedom Watt I mechanism and Stephenson III drive mechanism adeptly accommodate the slender trailing edge of the supercritical airfoil. Under a maximum cruise vertical aerodynamic load of 17,072 N, the structure meets strength requirements when deflected to 5°. The research in this paper can provide some insights into the engineering design of variable camber wings.

Creating sustainable and flexible architectural skin with microbial cellulose-based material: synthesis and mechanical characterization

AbstractAttaining sustainability by developing efficient architectural materials will be a suitable remedy for various environmental problems. Incorporating clean biotechnology, particularly Bacterial Cellulose (BC), into the field of Architecture Design offers a novel strategy with the objective of creating environmentally-friendly architectural materials. The key goal of this research is to investigate the synthesis of BC by cultivating kombucha SCOBY in a culture medium that has been supplemented with sugar and tea extract. The linear density, tensile strength and strain of the BC bio-film and BC composites were assessed in order to determine the material’s degree of fitness in potential applications. The tensile test showed that BC bio-film and its jute composite had tensile strengths of 5 MPa and 10 MPa respectively, indicating notable resilience and durability as a feasible substitute for conventional construction materials. The study delves deeper into the sustainability, biodegradability, and economic feasibility of BC, emphasising its potential as an independent foundational material. The incorporation of jute fibres into BC enhances its capabilities, resulting in the development of a novel composite material known as BC + jute. This composite exhibits superior mechanical and psychochemical characteristics, making it suitable for the creation of sophisticated architectural prototypes. The results of this research establish a strong foundation for the advancement of ecologically conscious architectural solutions, demonstrating the feasibility and capacity of BC in promoting sustainability within the construction sector.Keywords: Microbial Cellulose, Scopy, Architecture, Environmental-friendly, sustainability, interior design, jute fiber, biomaterials.

High-performance and frost-resistance MXene co-ionic liquid conductive hydrogel printed by electrohydrodynamic for flexible strain sensor

Conductive hydrogels with high performance and frost resistance are essential for flexible electronics, electronic skin, and soft robots. Nonetheless, the preparation of hydrogel-based flexible strain sensors with rapid response, wide strain detection range, and high sensitivity remains a considerable challenge. Furthermore, the inevitable freezing and evaporation of water in sub-zero temperatures and dry environments lead to the loss of flexibility and conductivity in hydrogels, which seriously limits their practical application. In this work, ionic liquids (ILs) and MXene are introduced into gelatin/polyacrylamide (PAM) precursor solution, and a PAM/gelatin/ILs/MXene/glycerol (PGIMG) hydrogel-based flexible strain sensor with MXene co-ILs ion–electron composite conductive network is prepared by combining the electrohydrodynamic (EHD) printing method and in-situ photopolymerization. The introduction of ILs provides an ionic conductive channel for the hydrogel. The introduction of MXene nanosheets forms an interpenetrating network with gelatin and PAM, which not only provides a conductive channel, but also improves the mechanical and sensing properties of the hydrogel-based flexible strain sensor. The prepared PGIMG hydrogel with the MXene co-ILs ion–electron composite conductive network demonstrates a tensile strength of 0.21 MPa at 602.82 % strain, the conductivity of 1.636 × 10−3 S/cm, high sensitivity (Gauge Factor, GF = 4.17), a wide strain detection range (1–600 %), and the response/recovery times (73 ms and 74 ms). In addition, glycerol endows the hydrogel with excellent freezing (−60 °C) and water retention properties. The application of the hydrogel-based flexible strain sensor in the field of human motion detection and information transmission shows the great potential of wearable devices, electronic skin, and information encryption transmission.

Polyacrylamide/sodium alginate/sodium chloride photochromic hydrogel with high conductivity, anti-freezing property and fast response for information storage and electronic skin

Photochromic hydrogels have promising prospects in areas such as wearable device, information encryption technology, optoelectronic display technology, and electronic skin. However, there are strict requirements for the properties of photochromic hydrogels in practical engineering applications, especially in some extreme application environments. The preparation of photochromic hydrogels with high transparency, high toughness, fast response, colour reversibility, excellent electrical conductivity, and anti-freezing property remains a challenge. In this study, a novel photochromic hydrogel (PAAm/SA/NaCl-Mo7) was prepared by loading ammonium molybdate (Mo7) and sodium chloride (NaCl) into a dual-network hydrogel of polyacrylamide (PAAm) and sodium alginate (SA) using a simple one-pot method. PAAm/SA/NaCl-Mo7 hydrogel has excellent conductivity (175.9 S/cm), water retention capacity and anti-freezing properties, which can work normally at a low temperature of −28.4 °C. In addition, the prepared PAAm/SA/NaCl-Mo7 hydrogel exhibits fast response (<15 s), high transparency (>70 %), good toughness (maximum elongation up to 1500 %), good cyclic compression properties at high compressive strains (60 %), good biocompatibility (78.5 %), stable reversible discolouration and excellent sensing properties, which can be used for photoelectric display, information storage and motion monitoring. This work provides a new inspiration for the development of flexible electronic skin devices.

Mechanical Behaviors of Hybrid Composites with Orthogonal Spiral Wire Mesh and Polyurethane Elastomer

This work aims to significantly improve the mechanical properties of conventional rigid lattice structures under repeatable large deformations. A novel hybrid material is proposed based on the concept of interpenetrating composite materials. The material utilizes a woven TC4 orthogonal spiral wire mesh as the skeleton and PU elastomer (OSWM‐PU) as the matrix. The uniaxial tensile tests demonstrate that OSWM‐PU possesses the excellent load‐bearing capacity, allowing for large deformations (≥60%) while maintaining partial integrity even after matrix fracture. Optical measurements and simulation analysis reveal that Poisson's ratio can be adjusted within a certain range by manipulating the microscopic parameters (p, d) of the longitudinal helical filaments. Cyclic tensile experiments further demonstrate that OSWM‐PU exhibits exceptional energy absorption performance, multiple energy dissipation modes, and a more pronounced Mullins effect. The stress relaxation experiment reveals the significant influence of the volume fraction of the skeleton on long‐term loading conditions. The orthogonal spiral wire skeleton exhibits a superior hooking effect without dividing the matrix, enabling OSWM‐PU to possess enhanced collaborative deformation capability and inherent designability in the orthogonal direction. These characteristics make it highly promising for applications in various robot joints and as flexible aircraft skin, offering excellent prospects for utilization.