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Hydrogels combining good biocompatibility and super flexibility have attracted tremendous interest in flexible sensors.

The properties and applications of the PDA-rGO/PEDOT:PSS/PAM composite organohydrogel.

The purpose of this paper is to investigate the problem of H∞ controller design for synchronization of the chaotic drive and response systems accompanied with bounded time delays limited by delay r...

Recently, hydrogel-based flexible sensors have attracted tremendous attention for use in wearable soft electronics. However, under sub-zero temperatures, common hydrogel-based flexible devices are always out of work due to their poor stability in freezing environments. To endow hydrogel-based sensors with long-term stability and anti-freezing ability as well as multi-functional abilities, we developed a polydopamine-reduced graphene oxide (PDA-rGO)/sodium alginate (SA)/polyacrylamide (PAM) composite organohydrogel with dual crosslinking networks. The excellent conductivity of the organohydrogel is due to the well-dispersed rGO endowed by mussel-inspired chemistry and ions such as Ca2+, which give the organohydrogel strain, pressure, and temperature sensing capabilities with a high gauge factor (2.09) within a broad strain range (0–250%), short response time (200 ms), and a wide temperature detection range (−20 °C to 60 °C), respectively. Moreover, the assembled sensors can also detect multiple human motions such as finger bending, facial micro-expression, and hand gesture recognition. Especially, owing to the synergistic effects of ion transportation, water–glycerol binary solvent, and the reduced graphene oxide in the composite hydrogel, the organohydrogel achieved an unprecedented thermal sensitivity of 97.60% °C−1 at sub-zero temperatures, which is the most sensitive stretchable thermistor so far reported. Therefore, this as-prepared functional organohydrogel paves the way for potential applications in human–machine interactions and personalized multi-signal monitoring in a broad temperature range.

Using a one-dimensional photonic crystal (1DPhC) film is a promising photoprotection technique for transparent polymer products, since it can be designed to selectively reflect UV light and allow the transmittance of visible light. Cracking and low adhesion caused by mechanical mismatching of 1DPhCs with polymer substrates remain a grand challenge. Herein, a facile and cost-effective approach is developed by combining sol–gel derived organic/inorganic (O/I) nanocomposites with layer-by-layer (LBL) spin-coating to produce 1DPhC films with well-controlled alternating layered structures. With modification using an organosilane, the dispersibility of SiO2 and TiO2 nanoparticles and the interfacial interaction between neighboring layers were improved, which resulted in a defect-free and robust 1DPhC multilayer film tightly bonded onto a polycarbonate (PC) surface. The developed 1DPhC film exhibits enhanced compatibility with the PC substrate and possesses preeminent anti-failure performance in harsh environments. The optical properties of the O/I nanocomposite 1DPhC film were tuned by changing the spin-coating speed. An intense UV reflectance of 70% at 340 nm was achieved by the 1DPhC film, while it still maintained high transmittance of over 86% to visible light. Theoretical and experimental studies verified that the high reflectance of UV light contributed to the efficient decaying of normal incident UV light across the developed 1DPhC film, leading to enhanced photoprotection for the polycarbonate. Therefore, this study provides insights into the design and fabrication of highly compatible and mechanically robust 1DPhC films with defined reflection properties suitable for polymer and flexible substrates.

This article considers finite-time bounded controller design for one-sided Lipschitz nonlinear differential inclusions. Sufficient conditions of finite-time bounded criterion are given employing convex hull Lyapunov function approach. An algorithm is designed to calculate the finite-time bounded controller. Moreover, a system initial state selection method is presented to find the domain of system initial state aid for transforming quasi-linear matrix inequality–based conditions to linear matrix inequality-based conditions. Finally, a numerical example and a comparison experiment example are given to illustrate the effectiveness of this proposed design method.

Triboelectric nanogenerators (TENGs) with high-energy output and high flexibility and transparency are desirable for a number of applications including flexible and transparent wearable devices. Th...

The development of superabsorbent materials with high absorption capacity, selectivity, and stable performance is needed for oil recovery. Remote-controlled oil absorption is highly favorable for oil absorption in harsh environment. In this study, a novel ultralight superhydrophobic nanocomposite aerogel composed of organic cellulose nanofibrils (CNFs), inorganic silica fiber, and magnetic Fe3O4 nanoparticles was developed through a simple freeze drying and surface modification method as a magnetically driven superabsorbent material. The aerogel has a highly porous and fibrous structure that contains hierarchical micro-nano surface topography. Low surface energy carbon–fluorine chains were grafted on aerogel surface which rendered the aerogel superhydrophobic. The addition of Fe3O4 nanoparticles significantly improved the surface area, compressive property, water contact angle, and the separation efficiency of the aerogel, but reduced the absorption capacity due to the increase of bulk density. The developed nanocomposite aerogel has a high absorption capacity (weight gain of 3420–5837%), separation efficiency ~ 100%, and a water contact angle of 150°. It also demonstrated high elasticity and performance stability in repetitive use. Given its magnetic property, the CNF/silica/Fe3O4 nanocomposite aerogel is a promising candidate for selective oil removal from open water, especially for remotely controlled applications.

Proliferation in telecommunications and integrated/intelligent devices entails an intense concern for electromagnetic interference (EMI) shielding and versatility. It remains an activated passion to launch infusive EMI shielding materials integrated with self-powered peculiarities. Herein, a double-layered MXene/polylactic acid (PLA) fabric resonance cavity (D-MPF-RC) comprised of two MXene/PLA fabrics (MPFs) with alternating MXene and PLA structures that are separated by a poly(tetrafluoroethylene) (PTFE) frame is developed. The D-MPF-RC achieved 48.5 and 74.8% improvement in SE

The utilization of solar energy for steam generation is a highly efficient and sustainable technology for seawater desalination to solve the long-standing water crisis. Carbon-based materials have shown promising thermal-heat conversion efficiency due to their broadband solar absorption. Herein, carbon black (CB) was combined with polydopamine (PDA) to develop a high-performance, low-cost, and scalable PDA/CB@PP composite non-woven fabric was fabricated by dip-coating of CB and in situ polymerization of PDA. The hierarchical structure constructed on the fiber surface and the synergetic effects of CB and PDA contributed to the high light absorbance (>95%), superhydrophilicity, and high energy conversion efficiency. The one-way fluidic PDA/CB@PP photothermal based solar steam evaporator demonstrated a high evaporation rate of 1.68 kg m-2h−1 with a solar steam efficiency of 91.5%. Moreover, the PDA/CB@PP fabric shows remarkable salt resistance when purifying seawater because of the water channel preserved by the hydrophilic porous structure of the fabric which could provide sustained water supply. Besides, the PDA/CB@PP fabric possesses excellent purification capability to wastewaters contaminated by heavy-metal and chemical dyes. This study provides insights into the design and development of low-cost, scalable, highly stable, and efficient solar steam generators for seawater desalination and wastewater purification.

An exoskeleton system can be an effective ergonomic intervention for mitigating the risks of developing work-related musculoskeletal disorders, yet little attention is given to the effects of its application on physical risk factors and subjective responses. Therefore, the objective of this study was to examine the effects of a passive exoskeleton system on spinal biomechanics and subjective responses during manual repetitive handling tasks among construction workers. Muscle activity of the Thoracic Erector Spinae (TES), Lumbar Erector Spinae (LES) at L3 vertebrae level, Rectus Abdominis (RA), and External Oblique (EO) during the repetitive handling tasks were measured by surface electromyography (sEMG). Additionally, the Borg categorical rating scale (Borg CR 10), local perceived pressure (LPP), and system usability scale (SUS) were used to measure the ratings of perceived discomfort, perceived musculoskeletal pressure, and system usability, respectively. Our results found that: (1) the use of the passive exoskeleton system significantly reduced LES muscle activity (11–33% MVC), with a greater reduction in LES muscle activity (32.71% MVC) for the heaviest lifting load; (2) the use of the passive exoskeleton system significantly reduced perceived discomfort scores (42.40%) of the lower back for the heaviest lifting load; (3) increased lifting load significantly increased LPP scores of the shoulder, lower back, and leg body parts; and (4) majority of the participants rated the passive exoskeleton system as having acceptable usability. The findings of these results indicate that the developed passive exoskeleton system could reduce the internal muscle force, extensor moments, and spinal forces in the lumbar region.

Triboelectric Nanogenerators (TENGs), as a novel tool that is capable of harnessing ubiquitous mechanical energy, have gained tremendous attention in recent years. Developing flexible and transparent TENGs with high triboelectric output performance is a major challenge towards adaptable and invisible energy harvesters. Previously developed transparent TENGs are normally used in a single electrode working mode or have relatively low output. Herein, a flexible semitransparent dual-electrode hydrogel-based TENG (DH-TENG) with high output was developed. The DH-TENG contains a thermoplastic polyurethane (TPU) tribopositive layer and a polydimethylsiloxane (PDMS) tribonegative layer. Both materials are highly transparent. NaCl containing polyacrylamide (PAM) hydrogels were used as electrodes, and polyethylene terephthalate (PET) sheets were used to provide mechanical stiffness. A benzophenone (BP) grafting method was used to enhance the interfacial bonding between hydrophobic triboelectric materials and hydrophilic hydrogels, which realized a significant improvement in tear strength of over 12 times. The DH-TENG demonstrated a high instant voltage and current of 311.5 V and 32.4 μA respectively. A maximum power density of 2.7 W m−2 was achieved on a 4.7 MΩ resistor. Furthermore, the DH-TENG showed a highly stable output under continuous running and demonstrated the capability to charge capacitors and power small electronics such as a timer, pedometer, and digital watch.

The two-mode-dependent controller design problem for networked Markov system with time-delay in both S/C link and C/A link is investigated in this paper. Two independent Markov chains are used to describe the time-delay in S/C link and C/A link. A two-mode-dependent state feedback controller is proposed that depends on both the S/C time-delay and the mode of the Markov controlled plant. The sufficient conditions on the stochastic stability of the closed-loop system are established. The design method of the controller is also proposed on condition that the transition probability matrices of S/C time-delay and mode of the controlled plant are completely known and partly unknown respectively. A numerical example is exploited to illustrate the effectiveness and superiority of the proposed method.

This paper focuses on how to see through the melting behavior of solid iron tailings in molten blast furnace slag and take a new non-contact visual analytical method to predict its melting law. The optimized convolution neural network (CNN) is used to track the moving target in charge coupled device (CCD) camera system efficiently and accurately, and the melting behavior of SiO2 is described by coordinate translation transformation theory. Hierarchical agglomerative clustering (HAC) and delaunay triangulation were used to extract the characteristic parameters of the melting process of SiO2. The prediction model of the melting rate of SiO2 at high temperature was established by least square fitting (LSF) and dimensional analysis, and compared with the actual melting rate of SiO2 obtained by experiments. The results show that the melting characteristics of SiO2 at high temperature are in accordance with certain function rule. The performance of optimized CNN in terms of processing time and the accuracy are significantly improved, and the fusion rate prediction model of SiO2 is verified by 100% accuracy. It provides theoretical support and model basis for the improvement of slag cotton preparation technology.

The H ∞ control problem for networked control system with data packet dropout in both S-C link and C-A link via observer-based controller is researched in this paper. Firstly, the networked control system with data packet dropout in both S-C link and C-A link is modeled as a discrete Markov jump linear system. Secondly, the sufficient and necessary conditions on the stochastic stability of the closed-loop system is established, the solution method of the controller and observer gain matrix are also given on condition that the transition probability matrix is completely known and partly unknown, respectively. The minimal disturbance suppression performance index is also obtained. Finally, two simulation examples illustrate the validity of the proposed method.

Wearable sensors have emerged as favored novel devices for human healthcare. Current sensors, however, suffer from low sensitivity, non-transparency, and lack of self-healing ability. In this study, we synthesized a polyvinyl alcohol/cellulose nanofibril (PVA/CNF) hydrogel with dual-crosslinked networks for highly transparent, stretchable, and self-healing pressure and strain sensors. The hydrogel contains dynamic borate bonds, metal–carboxylate coordination bonds, and hydrogen bonds, all of which contribute to the hydrogel’s superior dimensional stability, mechanical strength and flexibility, and spontaneous self-healing ability as compared to traditional PVA hydrogels. The developed hydrogel has a moderate modulus of 11.2 kPa, and a high elongation rate of 1900%. It spontaneously self-heals within 15 s upon contact without any external stimuli, has a high transmittance of over 90%, and has excellent compatibility with human fibroblasts. The capacitive sensor developed based on the PVA/CNF hydrogel has high sensitivity to very subtle pressure changes, such as small water droplets. When used as a strain sensor, it was capable of detecting and monitoring various human motions such as finger, knee, elbow, and head movements, breathing, and gentle tapping. The developed hydrogel and sensors not only show great potential in electronic skin, personal healthcare, and wearable devices, but may also inspire the development of transparent, intelligent skin-like sensors.

Electrospun nanofibrous scaffolds are highly recognized in tissue engineering since they can mimic the structure of extracellular matrix (ECM). However, the nanofibers fail to resemble the three dimensional geometry of organs, and the surface nanotopography of collagen fibrils in ECM. In order to mimic the structure of ECM in both macroscale (3D geometry) and microscale (surface nanotopography), an ingenious approach was developed in this study. Electrospun nanofibers collected in ethanol bath was soaked in CO2 saturated ethanol and subsequently foamed in a water bath, due to the escaping of CO2 gas. This simple green method takes the advantage of solubility difference of carbon dioxide (CO2) in ethanol and water, and is applicable to different materials. The foamed fluffy polycaprolactone (PCL) nanofibrous scaffolds achieved a low bulk density of 0.041 g/cm3 and a high porosity of 95.3%. To resemble the surface nanotopography of ECM, shish-kebab structure was introduced onto the fluffy PCL nanofibers by controlled crystallization. The shish-kebab structures greatly enhanced the surface area of scaffolds from 6.9 m2/g for 2D PCL to 10.9 m2/g for 3D SK-PCL. In addition, 3T3 fibroblast cell culture results confirmed that the cells interacted strongly with the 3D fluffy nanofibers and migrated into the inner area of the scaffolds rapidly. Moreover, human fibroblast cell culture results confirmed further enhancement in cell attachment and proliferation on the fluffy shish-kebab structured nanofibrous scaffolds, which indicates the developed biomimetic 3D scaffolds have high potential to be used for 3D tissue regeneration.

Electrospinning is a widely used technique to fabricate a nanofibrous scaffold to resemble the extracellular matrix (ECM) in tissue engineering. However, the intrinsic property (dense structure and...

A stretchable gelatin/silver nanowires (GE-AgNWs) composite hydrogel with enhanced mechanical properties and electrical conductivity has been prepared through chemical grafting and physical crosslinking. By introducing thiol groups on the gelatin molecular chain, better interactions between the reinforcing AgNWs and the gelatin molecules in the hydrogel networks was established. The introduced AgNWs not only reinforced the hydrogels but also formed effective electrical pathways to endow the hydrogel with good conductivity. By using the “salting out” effect, additional physical crosslinks were introduced to the hydrogel network so that the composite hydrogel became stretchable. The resulting composite hydrogel was not only biocompatible, but could also be used as a strain sensor to detect multiple human motions. Hence, these hydrogels have the potential to be used in biosensors, electric skins, and health monitoring applications.

Solar steam generation is an efficient way of harvesting solar energy for water purification. Developing a versatile solar absorber with salt resistance and the capability to purify an oil-in-water emulsion is a grand challenge. Herein, a polypropylene (PP) nonwoven fabric-based photothermal absorber is fabricated by the combination of carbon nanotubes (CNTs), polypyrrole (PPy), and a fluorinated hydrophobic coating in a layer-by-layer approach. The specially designed architecture displays a hierarchical microstructure and Janus wetting properties, facilitating solar absorption and heat generation on the evaporation surface, and can effectively prevent salt crystallization. The water layer formed on the superhydrophilic/underwater superoleophobic bottom surface could repel oil droplets and form a channel to advect concentrated salt back into bulk water, which enabled high purity separation of an oil-in-water emulsion and continuous desalinization of seawater without the reduction of the evaporation rate. As a result, the solar absorber can achieve a remarkable evaporation rate of 1.61 kg m-2 h-1 and an energy efficiency of 91.2% under 1 sun irradiation and shows extraordinary performance in the purification of contaminated wastewater (over 99.8% purity). The strategy proposed provides a pathway for developing versatile high-performance solar absorbers for the sustainable treatment of saline water, wastewater, and oil-containing water.

Fabric-based triboelectric nanogenerators (TENGs) are promising candidates as wearable energy-harvesting devices and self-powered sensors. Booting the power generation performance is an eternal pursuit for TENGs. Herein, an efficient approach was proposed to enhance the triboelectric performance of commercial velvet fabric by enriching the fiber surface with hierarchical structures and amide bonds through chemical grafting of carbon nanotube (CNT) and poly(ethylenimine) (PEI) via a polyamidation reaction. With an optimized modifier concentration, the fabric-based TENG easily achieved over 10 times improvement in output voltage and current at a low modifier content of less than 1 wt %. The modified-fabric-based TENG was fully washable and exhibited excellent robustness and long-term stability. With a maximum power density of 3.2 W/m2 achieved on a 5 × 106 Ω external resistor, the TENG was able to serve as a power source for various small electronics such as pedometer, digital watch, calculator, and digital timer. In addition, the TENG demonstrated capability in self-powered tactile and pressure sensing and promising potential in human-computer interface applications. The approach proposed provides a feasible path for boosting the triboelectric performance of fabric-based TENGs and gives insights into the design of fabric-based nanogenerators and smart textiles.

This paper focuses on consensus of the nonholonomic wheeled mobile robotic systems whose geometric center and centroid do not coincide. A consensus control algorithm for mobile robots based on the nonstandard chain systems is proposed. Firstly, coordinate transformation is used to transform the nonholonomic robotic systems into the nonstandard chain model. Then, a distributed cooperative control algorithm is designed, and the Lyapunov stability theorem and LaSalle invariance principle are used to prove that each state of the mobile robot is consensus. Finally, the effectiveness of the algorithm is proved through numerical simulation.

High-performance low-cost superhydrophobic sponges are desired for selective recycling of leaking oils from open water. Herein, an ingenious method is proposed to fabricate an ultrathin superhydrophobic coating layer on a commercial sponge. The coating layer is composed of a shish-kebab-structured porous ultrahigh molecular weight polyethylene (UHMWPE) film that is fabricated from a UHMWPE/xylene solution by shear flow-induced crystallization. A strong relationship between the shish-kebab crystallite morphology and the superwetting performance is confirmed. The UHMWPE coating layer fabricated at a 900 rpm rotation rate possesses a lamellae size of 95.1 nm and a lamellae distance of 27.4 nm, which lead to a high water contact angle of 157° and a low contact angle hysteresis of 4.5°. The UHMWPE layer prepared in 4 min of treatment is thick enough to prevent the intrusion of water even under vacuum and remain superoleophilic. The developed UHMWPE-coated sponge (UCS) exhibited a high absorption capability of 70-191 g/g toward various oils and solvents, which is comparable with the neat melamine sponge. Its excellent compressibility and durability enabled fast recovery of absorbed oil with a high recovery rate (over 85%) by mechanical squeezing. The UCS could be assembled into small devices to selectively collect oil from open water and a water/oil mixture using a pump, which manifests its promising practical applicability. Apart from these extraordinary properties, the approach developed has the lowest material cost and the shortest processing time hitherto.

Triboelectric nanogenerators (TENGs) with high transparency and stretchability are desired for invisible and adaptable energy harvesting and sensing. Hydrogel-based TENGs (H-TENG) have shown promising attributes toward flexible and transparent devices. However, the effect of hydrogel property on the triboelectric performance of H-TENG is rarely investigated. Herein, dual-network hydrogels composed of dual-cross-linked poly(vinyl alcohol) (PVA) and sodium alginate (SA) were synthesized and used as ionic electrodes in H-TENGs. The elasticity of the hydrogel was controlled by varying the concentration of SA, and the distinct influence of hydrogel viscoelastic property on H-TENG performance was verified for the first time. By tuning the conductivity and viscoelasticity of PVA/SA hydrogel, the optimum H-TENG exhibited high transparency (over 90%) and stretchability (over 250%) and peak output voltage and current of 203.4 V and 17.6 μA, respectively. A specially designed polydimethylsiloxane (PDMS) bag effectively prevents hydrogel dehydration and maintains a stable output in continuous operation. The H-TENG achieved a power density of 0.98 W/m

The severe water contamination caused by oil leakage is calling for low-cost and high-performance absorbent materials for selective oil removal. In this study, a scalable green method was proposed to produce polypropylene (PP)/poly(tetrafluoroethylene) (PTFE) composite foams via conventional processing techniques including twin-screw extrusion and supercritical carbon dioxide foaming. To produce the superhydrophobic foam, micro- and nanosized PTFE particles were melt blended with PP and subsequently foamed. Ascribed to the nanofibrillation of microsized PTFE during processing, the fabricated foam exhibited a special highly porous structure with PTFE nanofibrils and nanoparticles uniformly distributed on the pore surfaces within the PP matrix, which resulted in a remarkably high water contact angle of 156.8° and a low contact angle hysteresis of 1.9°. Unlike traditional surface-modified superhydrophobic absorbers, the foams prepared are entirely superhydrophobic, which means that they remain superhydrophobic when being fractured or cut. Moreover, they are highly durable and maintained the superhydrophobicity when subjected to ultrasonication and mechanical sanding. When used in selective oil absorption, the durable foams exhibited excellent absorption efficiency and high stability in repetitive and long-term use. These advantages make the PP/PTFE foam a promising superabsorbent material for water remediation.

Delamination of coating layer from polymer substrate limits the lifetime and functionality of the protective films. Silicone coating is especially vulnerable to photo irradiation, hydrothermal degradation, and mechanical deformation due to the low interfacial adhesion and mechanical robustness. Herein, an ingenious approach is developed to fabricate ultrastable and durable silicone coating on polycarbonate (PC) substrate through well-controlled nanoscale interfacial engineering. A nanopillar array is fabricated on the PC surface by vacuum-assisted hot embossing using anodic aluminum oxide (AAO) templates. Significant improvement in interfacial shear strength (ISS) is achieved for the silicone coating on the nanostructured PC surface. The delamination mechanism can be controlled by tuning the nanopillar size, and the maximum ISS of 9.9 MPa was reached on a surface with a nanopillar diameter of 320 nm. Attributed to the increased interfacial area and mechanical interlocking structure, the nanostructured interface can effectively dissipate interfacial stress and prevent cracking; therefore, maintaining excellent transparency and performance in the harsh environment. The coating exhibits extraordinary stability and durability when subjected to UV irradiation for 168 h, hydrothermal aging for 120 h, mechanical bending for 1000 cycles, and even surface damage. Thus, the tough silicone coating on polymer substrate realized by nanoscale interfacial engineering is a promising technique for highly stable and durable transparent surface protection.

In recent years, with the appearance of the triboelectric nanogenerator (TENG), there has been a wave of research on small energy harvesting devices and self-powered wearable electronics. Hydrogels—as conductive materials with excellent tensile properties—have been widely focused on by researchers, which encouraged the development of the hydrogel-based TENGs (H-TENGs) that use the hydrogel as an electrode. Due to the great feasibility of adjusting the conductivity and mechanical property as well as the microstructure of the hydrogels, many H-TENGs with excellent performance have emerged, some of which are capable of excellent outputting ability with an output voltage of 992 V, and self-healing performance which can spontaneously heal within 1 min without any external stimuli. Although there are numerous studies on H-TENGs with excellent performance, a comprehensive review paper that systematically correlates hydrogels’ properties to TENGs is still absent. Therefore, in this review, we aim to provide a panoramic overview of the working principle as well as the preparation strategies that significantly affect the properties of H-TENGs. We review hydrogel classification categories such as their network composition and their potential applications on sensing and energy harvesting, and in biomedical fields. Moreover, the challenges faced by the H-TENGs are also discussed, and relative future development of the H-TENGs are also provided to address them. The booming growth of H-TENGs not only broadens the applications of hydrogels into new areas, but also provides a novel alternative for the sustainable power sources.