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The hierarchical network relaxation enabled by dynamic cross-linked network facilitates combining 3D shapes and aligned CNTs in polyolefin elastomer, paving new avenues for realizing smart materials with advanced RSME.

Wearable strain sensors have huge potential for applications in healthcare, human-machine interfacing, and augmented reality systems. However, the nonlinear response of the resistance signal to strain has caused considerable difficulty and complexity in data processing and signal transformation, thus impeding their practical applications severely. Herein, we propose a simple way to achieve linear and reproducible resistive signals responding to strain in a relatively wide strain range for flexible strain sensors, which is achieved via the fabrication of Janus and heteromodulus elastomeric fiber mats with micropatterns using microimprinting second processing technology. In detail, both isotropic and anisotropic fiber mats can turn into Janus fiber mats with periodical and heteromodulus micropatterns via controlling the fiber fusion and the diffusion of local macromolecular chains of thermoplastic elastomers. The Janus heterogeneous microstructure allows for stress redistribution upon stretching, thus leading to lower strain hysteresis and improved linearity of resistive signal. Moreover, tunable sensing performance can be achieved by tailoring the size of the micropatterns on the fiber mat surface and the fiber anisotropy. The Janus mat strain sensors with high signal linearity and good reproducibility have a very low strain detection limit, enabling potential applications in human-machine interfacing and intelligent control fields if combined with a wireless communication module.

Soft actuators with integrated mechanical and actuation properties and self-sensing ability are still a challenge. Herein, a stiffness variable polyolefin elastomer (POE) with a reversible shape memory effect is prepared by introducing a typical phase change material, i.e., paraffin wax (PW). It is found that the variable stiffness of POE induced by PW can balance the reversible strain and load-bearing capability of actuators. Especially, carbon nanotubes (CNTs) are concentrated in a thin surface layer by spraying and hot pressing in the soft state of POE/PW blends, providing signal transductions for the strain and temperature perception for actuators. Taking advantage of tunable reversible deformation and mechanical transformation of the POE/PW actuator, different biomimetic robotics, including grippers with high load-bearing capability (weight-lifting ratio146), walking robots that can sense angles of joints, and high-temperature warning robots are demonstrated. A scheme combining the variable stiffness and electrical properties provides a versatile strategy to integrate actuation performance and self-sensing ability, inspiring the development of multifunctional composite designs for soft robotics.

Mechanochemical vitrimerization, as a method to recycle cross-linked thermosets by converting the permanent network into a recyclable and reprocessable vitrimer network, inevitably requires a catalyst to accelerate the bond exchange reactions. Here, we demonstrate a catalyst-free approach to achieve the recycling of a cross-linked biobased epoxy into high-performance nanocomposites with cellulose nanocrystals (CNCs). CNCs provide abundant free hydroxyl groups to promote the transesterification exchange reactions while also acting as reinforcing fillers for the resultant nanocomposites. This technique introduces an effective way to fabricate high-performance thermoset nanocomposites based on recycled polymers in an ecofriendly way, promoting the recycle and reuse of thermosets as sustainable nanocomposites for different applications.

Carbon nanofillers are widely used to blend with polymers for fabricating high-performance polymer nanocomposites (PNCs) toward structural, electronic and sensory material applications. However, it is generally of challenge to achieve significant property improvement by using single carbon nanofiller. Alternatively, using hybrid carbon nanofillers has been proved to be a facile and promising strategy to effectively boost electrical and piezoresistive properties of PNCs. This paper provides a state of the art review on the effects of hybrid carbon fillers on electrical properties of PNCs and corresponding applications in piezoresistive sensing scenarios. The effects of hybrid carbon nanofillers on electrical percolation threshold, electrical conductivities and piezoresistive sensitivity of PNCs are systematically discussed.

The novel vitrimerization concept of converting permanently cross-linked networks of thermoset polymers into dynamic exchangeable networks often relies on transesterification reactions. Transesterification exchange reactions, for example, in epoxy vitrimers, are usually contingent on equivalent ratios of hydroxyl to ester groups and large amounts of catalysts to achieve proper dynamic exchange capability. In general, postconsumer epoxy cured with anhydrides contains very few hydroxyl groups in the network, and it is challenging to convert it into efficient dynamic networks by vitrimerization. Here, we demonstrate that introducing cellulose nanocrystals as feedstock of external hydroxyl groups in the mechanochemical vitrimerization process could improve the exchange reaction rate as well as the thermomechanical properties of the vitrimerized epoxy. This work offers an effective way to recycle and reprocess postconsumer epoxy/anhydride waste with inherent low ratios of hydroxyl to ester groups into higher value-added vitrimer nanocomposites.

Flexible wearable electronics play an important role in the healthcare industry due to their unique skin affinity, portability and breathability. Despite great progress, it still remains a big challenge to facilely fabricate stretchable electrodes with low resistance, excellent stability and a wide tensile range. Here, we propose a handy and time-saving strategy for the fabrication of elastomeric films consisting of wave-like fibers with a robust conductive layer of silver nanoparticles (AgNPs) immobilized using polydopamine (PDA) and silicone rubber (SR). To realize better stretchability, electrospun thermoplastic polyurethane (TPU) mats with oriented nanofibers were treated via ethanol to achieve a wavy structure, which also allowed for the decoration of AgNP precursors on the TPU surface via PDA assisted electroless deposition (ELD). Therefore, the electrodes achieved a stretchability of 120% with high electrical conductivity (486 S cm−1). The films with a reduction time of 30 min showed superior electrical conductivity indicated by a resistance increase of only 100% within 50% strain. The TPU/PDA/AgNP/SR composites with a shorter reduction time of silver precursors could monitor human motions as wearable strain sensors with a wide work strain range (0–98%) and a high sensitivity (with a gauge factor (GF) of up to 81.76) for a strain of 80–98%. Therefore, they are an excellent candidate for potential application in prospective stretchable electronics.

An increasing utilization of flexible healthcare electronics and biomedicine-related therapeutic materials urges the development of multifunctional wearable/flexible smart fabrics for personal therapy and health management. However, it is currently a challenge to fabricate multifunctional and on-body healthcare electronic devices with reliable mechanical flexibility, excellent breathability, and self-controllable joule heating effects. Here, we fabricate a multifunctional MXene-based smart fabric by depositing 2D Ti3C2Tx nanosheets onto cellulose fiber nonwoven fabric via special MXene-cellulose fiber interactions. Such multifunctional fabrics exhibit sensitive and reversible humidity response upon H2O-induced swelling/contraction of channels between the MXene interlayers, enabling wearable respiration monitoring application. Besides, it can also serve as a low-voltage thermotherapy platform due to its fast and stable electro-thermal response. Interestingly, water molecular extraction induces electrical response upon heating, i.e., functioning as a temperature alarm, which allows for real-time temperature monitoring for thermotherapy platform without low-temperature burn risk. Furthermore, metal-like conductivity of MXene renders the fabric an excellent Joule heating effect, which can moderately kill bacteria surrounding the wound in bacteria-infected wound healing therapy. This work introduces a multifunctional smart flexible fabric suitable for next-generation wearable electronic devices for mobile healthcare and personal medical therapy.

Hydrogel bioelectronics as one of the next-generation wearable and implantable electronics ensures excellent biocompatibility and softness to link the human body and electronics. However, volatile, opaque, and fragile features of hydrogels due to the sparse and microscale three-dimensional network seriously limit their practical applications. Here, we report a type of smart and robust nanofibrillar poly(vinyl alcohol) (PVA) organohydrogels fabricated via one-step physical cross-linking. The nanofibrillar network cross-linked by numerous PVA nanocrystallites enables the formation of organohydrogels with high transparency (90%), drying resistance, high toughness (3.2 MJ/m3), and tensile strength (1.4 MPa). For strain sensor application, the PVA ionic organohydrogel after soaking in NaCl solution shows excellent linear sensitivity (GF = 1.56, R2 > 0.998) owing to the homogeneous nanofibrillar PVA network. We demonstrate the potential applications of the nanofibrillar PVA-based organohydrogel in smart contact lens and emotion recognition. Such a strategy paves an effective way to fabricate strong, tough, biocompatible, and ionically conductive organohydrogels, shedding light on multifunctional sensing applications in next-generation flexible bioelectronics.

International audience; Dielectric nanomaterials offer great promise for diverse technological applications such as capacitors, actuators, and sensors. Unfortunately, the exploitation of desirable dielectric properties in polymer nanocomposites is a great challenge due to lack of efficient routes to achieve uniform dispersion of nanoparticles and good compatibility of interfaces at high nanoparticle loadings. A dilemma between the nanofiller loading and dispersion as well as interfacial compatibility makes it impossible to fully exploit the intrinsic polarization of the nanoparticles. Herein, we solve such a dilemma and fabricate highly filled barium titanate/silicone rubber (BT/SR) nanocomposites through chemically bonding BT nanoparticles with SR by “thiol–ene click” and isostatic pressing techniques. BT loading varies from 88 wt% to 97 wt% without compromising the uniform dispersion quality and good interfacial adhesion with the SR matrix. The 90 wt% BT nanocomposite shows an optimum dielectric constant as high as 55, while its loss tangent can be kept as low as 0.019 at 103 Hz. Meanwhile, it displays good stability of dielectric properties from room temperature up to 100 °C. In addition, the breakdown strength just decreases slightly compared to neat SR (97 MV m−1) but is still beyond 75 MV m−1. The present work provides a facile strategy towards superior dielectric polymer nanocomposites.

Solar energy triggered steam generation has emerged as a green and sustainable strategy that can potentially address the long-standing global freshwater scarcity issue. However, given that there is inadequate light illumination early in the morning or late afternoon or cloudy days, it is continuous steam generation in all weather that is a great challenge for the state-of-the-art solar-driven steam generators. Here, we present an all-weather-available steam generation system, which is capable of harvesting solar energy to continuously generate steam based on the alternative photo-thermal and electro-thermal conversion of crosslinked MXene aerogels (CMAs) in the day time and at night. In virtue of the strong light absorption and excellent electrical conductivity of the CMA, the constructed steam generation system can not only convert sunlight into heat for steam generation on sunny days but persistently achieve heat generation by utilization of electricity in low-light or dark circumstances. Furthermore, the ingenious introduction of solar cells-battery components makes full use of the daytime sunlight to further power the steam generation system for heating up the CMA at night, avoiding extra electrical energy input and loss. This work offers new insights into developing continuous steam generation technologies applicable to day–night alternation and complex environments.

Wearable strain sensors are a compelling need for health monitoring while designing facile and flexible strain sensors with both super-high sensitivity and a wide strain range in an environment-friendly and scalable way remains challenging. Besides, the mechanism underlying these sensors is still insufficiently studied. Here, we propose a handy method to fabricate flexible strain sensors based on an electrospun thermoplastic polyurethane (TPU) mat by coupling silver nanowires (AgNWs) and reduced graphene oxide (rGO). The TPU-based strain sensors with AgNWs and rGO alone exhibited high strain sensitivity and a broad working range, respectively, due to the morphological differences between the two types of nanomaterials. In contrast, the rGO/AgNWs/TPU sensor showed a synergistic effect on strain sensitivity and sensing range because of the interaction between the AgNWs and rGO, as well as the coupling effect arising from their assembly. For instance, the sensors with hybrid nanomaterials had ultrahigh sensitivity (gauge factor, GF ≈ 4.4 × 107) and a wider detection range in comparison with the counterpart strain sensors with AgNWs/TPU and rGO/TPU (both GFs in the range of hundreds). Besides, the sensors showed reliable responses to various frequencies and strains, as well as long-term stretching (1000 cycles). These strain sensors were applied to monitor human body motions, such as joint motion and muscle movement, which revealed their potential in healthcare and human-machine interfacing applications.

Flexible and stretchable strain sensors have broad applications in human physiological activities, object deformation, as well as human–machine interface. However, it is still challenging to fabricate stretchable strain sensors with linear and superior piezoresistive signal response. Herein, we report a facile and scalable microstructure design strategy to generate a unique segmental hierarchical fiber-surface structure that mimics an arthropod's body and a lobster's tail structure for achieving linear strain sensing response. The alternate modulus difference of the micro-nanoscale segmental soft (thermoplastic polyurethane, TPU)-hard (polystyrene, PS) configurations enables the initiation of significant strain concentration effect, which is consistent with the finite element analysis, thus allowing to tune the sensing properties, for e.g., the linear degree varies from 0.48 to 0.99 and the gauge factor ranges from 5.25 to 23 800 for the strain within 30%. The bionic structured fiber sensors demonstrate potential applications for the detection of human skin epidermal disturbance, small curvature changes, sound wave vibration, as well as mechanochromic response if a fluorescent agent is added to the TPU core. Besides, they are also capable of detecting various types of organic vapors due to the strain amplification effect heterogeneous structure design, paving a new way for the design of multifunctional flexible sensors for variable human–machine interface applications.

As a renewable and environment-friendly technology for seawater desalination and wastewater purification, solar energy triggered steam generation is attractive to address the long-standing global water scarcity issues. However, practical utilization of solar energy for steam generation is severely restricted by the complex synthesis, low energy conversion efficiency, insufficient solar spectrum absorption and water extraction capability of state-of-the-art technologies. Here, for the first time, we report a facile strategy to realize hydrogen bond induced self-assembly of a polydopamine (PDA)@MXene microsphere photothermal layer for synergistically achieving wide-spectrum and highly efficient solar absorption capability (≈ 96% in a wide solar spectrum range of 250–1,500 nm wavelength). Moreover, such a system renders fast water transport and vapor escaping due to the intrinsically hydrophilic nature of both MXene and PDA, as well as the interspacing between core-shell microspheres. The solar-to-vapor conversion efficiencies under the solar illumination of 1 sun and 4 sun are as high as 85.2% and 93.6%, respectively. Besides, the PDA@MXene photothermal layer renders the system durable mechanical properties, allowing producing clean water from seawater with the salt rejection rate beyond 99%. Furthermore, stable light absorption performance can be achieved and well maintained due to the formation of ternary TiO2/C/MXene complex caused by oxidative degradation of MXene. Therefore, this work proposes an attractive MXene-assisted strategy for fabricating high performance photothermal composites for advanced solar-driven seawater desalination applications.

Piezoelectric materials, a type of “smart” material that generates electricity while deforming and vice versa, have been used extensively for many important implantable medical devices such as sensors, transducers, and actuators. However, commonly utilized piezoelectric materials are either toxic or nondegradable. Thus, implanted devices employing these materials raise a significant concern in terms of safety issues and often require an invasive removal surgery, which can damage directly interfaced tissues/organs. Here, we present a strategy for materials processing, device assembly, and electronic integration to 1) create biodegradable and biocompatible piezoelectric PLLA [poly(l-lactic acid)] nanofibers with a highly controllable, efficient, and stable piezoelectric performance, and 2) demonstrate device applications of this nanomaterial, including a highly sensitive biodegradable pressure sensor for monitoring vital physiological pressures and a biodegradable ultrasonic transducer for blood–brain barrier opening that can be used to facilitate the delivery of drugs into the brain. These significant applications, which have not been achieved so far by conventional piezoelectric materials and bulk piezoelectric PLLA, demonstrate the PLLA nanofibers as a powerful material platform that offers a profound impact on various medical fields including drug delivery, tissue engineering, and implanted medical devices.

Traditional devices, including conventional rigid electronics and machines, as well as emerging wearable electronics and soft robotics, almost all have a single mechanical state for particular service purposes. Nonetheless, dynamic materials with interchangeable mechanical states, which enable more diverse and versatile applications, are urgently necessary for intelligent and adaptive application cases in the future electronic and robot fields. Here, we report a gel-like material composed of a crosslinking polymer network impregnated with a phase changing molten liquid, which undergoes an exceptional stiffness transition in response to a thermal stimulus. Vice versa, the material switches from a soft gel state to a rigid solid state with a dramatic stiffness change of 105 times (601 MPa versus 4.5 kPa) benefiting from the liquid–solid phase change of the crystalline polymer once cooled. Such reversibility of the phase and mechanical transition upon thermal stimuli enables the dynamic gel mechanical transformation, demonstrating potential applications in an adhesive thermal interface gasket (TIG) to facilitate thermal transport, a high-temperature warning sensor and an intelligent gripper. Overall, this dynamic gel with a tunable stiffness change paves a new way to design and fabricate adaptive smart materials toward intelligent control of versatile devices.

Electrically conductive elastomer composites (CECs) with segregated networks of conductive nanofillers show high potential in stretchable strain sensors due to balanced mechanical and electrical properties, yet the sensitivity at low strain is generally insufficient for practical application. Herein, we report an easy and effective way to improve the resistive response to low strain for CECs with segregated network structure via adding stiff alumina into carbon nanostructures (CNS). The CEC containing 0.7 ​wt% CNS and 5 ​wt% Al2O3 almost sustains the same elasticity (elongation at break of ∼900%) and conductivity (0.8 ​S/m) as the control, while the piezoresistive sensitivity is significantly improved. Thermoplastic polyurethane (TPU) composites with a segregated network of hybrid nanofillers (CNS and Al2O3) show much higher strain sensitivity (Gauge factor, GF ​= ​566) at low strain (45% strain) due to a local stress concentration effect, this sensitivity is superior to that of TPU/CNS composites (GF ​= ​11). Such a local stress concentration effect depends on alumina content and its distribution at the TPU particle interface. In addition, CECs with hybrid fillers show better reproducibility in cyclic piezoresistive behavior testing than the control. This work offers an easy method for fabricating CECs with a segregated filler network offering stretchable strain sensors with a high strain sensitivity.

Flexible wearable electronics play an important role in the healthcare industry due to their unique skin affinity, portability and breathability. Despite great progress, it still remains a big challenge to facilely fabricate stretchable electrodes with low resistance, excellent stability and a wide tensile range. Here, we propose a handy and time-saving strategy for the fabrication of elastomeric films consisting of wave-like fibers with a robust conductive layer of silver nanoparticles (AgNPs) immobilized using polydopamine (PDA) and silicone rubber (SR). To realize better stretchability, electrospun thermoplastic polyurethane (TPU) mats with oriented nanofibers were treated

Multiresponsive flexile sensors with strain, temperature, humidity, and other sensing abilities serving as real electronic skin (e-skin) have manifested great application potential in flexible electronics, artificial intelligence (AI), and Internet of Things (IoT). Although numerous flexible sensors with sole sensing function have already been reported since the concept of e-skin, that mimics the sensing features of human skin, was proposed about a decade ago, the ones with more sensing capacities as new emergences are urgently demanded. However, highly integrated and highly sensitive flexible sensors with multiresponsive functions are becoming a big thrust for the detection of human body motions, physiological signals (e.g., skin temperature, blood pressure, electrocardiograms (ECG), electromyograms (EMG), sweat, etc.) and environmental stimuli (e.g., light, magnetic field, volatile organic compounds (VOCs)), which are vital to real-time and all-round human health monitoring and management. Herein, this review summarizes the design, manufacturing, and application of multiresponsive flexible sensors and presents the future challenges of fabricating these sensors for the next-generation e-skin and wearable electronics.

Acute kidney injury (AKI), as a common oxidative stress‐related renal disease, causes high mortality in clinics annually, and many other clinical diseases, including the pandemic COVID‐19, have a high potential to cause AKI, yet only rehydration, renal dialysis, and other supportive therapies are available for AKI in the clinics. Nanotechnology‐mediated antioxidant therapy represents a promising therapeutic strategy for AKI treatment. However, current enzyme‐mimicking nanoantioxidants show poor biocompatibility and biodegradability, as well as non‐specific ROS level regulation, further potentially causing deleterious adverse effects. Herein, the authors report a novel non‐enzymatic antioxidant strategy based on ultrathin Ti3C2‐PVP nanosheets (TPNS) with excellent biocompatibility and great chemical reactivity toward multiple ROS for AKI treatment. These TPNS nanosheets exhibit enzyme/ROS‐triggered biodegradability and broad‐spectrum ROS scavenging ability through the readily occurring redox reaction between Ti3C2 and various ROS, as verified by theoretical calculations. Furthermore, both in vivo and in vitro experiments demonstrate that TPNS can serve as efficient antioxidant platforms to scavenge the overexpressed ROS and subsequently suppress oxidative stress‐induced inflammatory response through inhibition of NF‐κB signal pathway for AKI treatment. This study highlights a new type of therapeutic agent, that is, the redox‐mediated non‐enzymatic antioxidant MXene nanoplatforms in treatment of AKI and other ROS‐associated diseases., A novel non‐enzymatic antioxidant MXene nanoplatform with excellent biocompatibility and great chemical reactivity toward multiple ROS is developed to potentially scavenge the overexpressed ROS and subsequently suppress oxidative stress‐induced inflammatory response through the inhibition of NF‐κB signaling pathway in the prevention and treatment of AKI and other ROS‐related diseases.

Dynamics of exchange within vitrimer networks are influenced by mobility of the chemical species involved in the exchange reaction, then it can be affected by the crystalline phase when boronic ester bond is introduced into the thermoplastic elastomers with crystalline phase as physical cross-links. In this work, the dynamic dioxaborolane cross-links were introduced into commercial poly(ethylene-α-octene) (POE) with crystalline phases as physical cross-links to prepare POE vitrimers. The results of stress relaxation show that relaxation time (τ) follows an Arrhenius law with the temperature at the melting range for not only POE vitrimers and thermally treated POE vitrimers with dynamic cross-links, but also neat POE with purely physical cross-links. The liquid-to-solid transition temperature can raise to 35.3 °C for POE vitrimers from -42.9 °C of the thermally treated one, due to the constrained mobility by residual crystalline phases. The resulted POE vitrimers maintain a stress at break of higher than 27.5 MPa and an elongation at break of higher than 800% at room temperature. With the temperature increasing, the crystal melting induced weakening of the physical cross-linking in POE decreases the strength, but the storage modulus and the stress at 300% and 500% elongation of POE vitrimers are improved. The properties of POE vitrimers can almost keep unchanged after recycling or healing. All these results show that the introduction of reversible boronic ester bonds is a promising strategy to improve the performances and recyclability of physically cross-linked POE materials.