Tough, Freeze-Resistant, Pressure-Response Gel Polymer Electrolytes with Redox Pairs for Flexible Supercapacitors.

Gel polymer electrolytes are an indispensable part of flexible supercapacitors, since their various characteristics determine the device performance. Here, a composite gel electrolyte (FLPS) mainly consisting of polyvinyl alcohol (PVA), sodium alginate (SA), K3Fe(CN)6/K4Fe(CN)6, and LiCl is rationally designed, in which PVA and SA form a robust three-dimensional network, the redox pair of K3Fe(CN)6/K4Fe(CN)6 serves as a cross-linking agent with SA and even donates the oxidation-reduction reaction from the Fe3+/Fe2+ couple with additional capacitance for the device, and LiCl functions as an ion carrier and a water-retaining salt to improve the long-term stability of FLPS. Thus, the FLPS-based supercapacitor exhibits superior electrochemical characteristics, displaying impressive pseudocapacitance across all current densities and excellent cycling stability (∼99.07% of capacitance retention after 10,000 cycles). Moreover, the FLPS-based supercapacitor demonstrates great low-temperature working ability and pressure responsiveness, suggesting its freeze-resistance, flexibility, and pressure sensing potential. This work provides a promising strategy for preparing tough gel polymer electrolytes with both ion transfer and charge storage ability.

Evolution of the Electronic Properties of Tellurium Crystals with Plasma Irradiation Treatment.

Tellurium exhibits exceptional intrinsic electronic properties. However, investigations into the modulation of tellurium's electronic properties through physical modification are notably scarce. Here, we present a comprehensive study focused on the evolution of the electronic properties of tellurium crystal flakes under plasma irradiation treatment by employing conductive atomic force microscopy and Raman spectroscopy. The plasma-treated tellurium experienced a process of defect generation through lattice breaking. Prior to the degradation of electronic transport performance due to plasma irradiation treatment, we made a remarkable observation: in the low-energy region of hydrogen plasma-treated tellurium, a notable enhancement in conductivity was unexpectedly detected. The mechanism underlying this enhancement in electronic transport performance was thoroughly elucidated by comparing it with the electronic structure induced by argon plasma irradiation. This study not only fundamentally uncovers the effects of plasma irradiation on tellurium crystal flakes but also unearths an unprecedented trend of enhanced electronic transport performance at low irradiation energies when utilizing hydrogen plasma. This abnormal trend bears significant implications for guiding the prospective application of tellurium-based 2D materials in the realm of electronic devices.

Flexible Self-Powered Low-Decibel Voice Recognition Mask.

In environments where silent communication is essential, such as libraries and conference rooms, the need for a discreet means of interaction is paramount. Here, we present a single-electrode, contact-separated triboelectric nanogenerator (CS-TENG) characterized by robust high-frequency sensing capabilities and long-term stability. Integrating this TENG onto the inner surface of a mask allows for the capture of conversational speech signals through airflow vibrations, generating a comprehensive dataset. Employing advanced signal processing techniques, including short-time Fourier transform (STFT), Mel-frequency cepstral coefficients (MFCC), and deep learning neural networks, facilitates the accurate identification of speaker content and verification of their identity. The accuracy rates for each category of vocabulary and identity recognition exceed 92% and 90%, respectively. This system represents a pivotal advancement in facilitating secure and efficient unobtrusive communication in quiet settings, with promising implications for smart home applications, virtual assistant technology, and potential deployment in security and confidentiality-sensitive contexts.

A Highly Sensitive and Stretchable Core-Shell Fiber Sensor for Gesture Recognition and Surface Pressure Distribution Monitoring.

This work reports a highly-strain flexible fiber sensor with a core-shell structure utilizes a unique swelling diffusion technique to infiltrate carbon nanotubes (CNTs) into the surface layer of Ecoflex fibers. Compared with traditional blended Ecoflex/CNTs fibers, this manufacturing process ensures that the sensor maintains the mechanical properties (923% strain) of the Ecoflex fiber while also improving sensitivity (gauge factor is up to 3716). By adjusting the penetration time during fabrication, the sensor can be customized for different uses. As an application demonstration, the fiber sensor is integrated into the glove to develop a wearable gesture language recognition system with high sensitivity and precision. Additionally, the authors successfully monitor the pressure distribution on the curved surface of a soccer ball by winding the fiber sensor along the ball's surface.

Tough Hydro-Aerogels with Cation Specificity Enabled Ultra-High Stability for Multifunctional Sensing and Quasi-Solid-State Electrolyte Applications.

The anion-specific effects of the salting-in and salting-out phenomena are extensively observed in hydrogels, whereas the cation specificity of hydrogels is rarely reported. Herein, a multi-step strategy including borax pre-gelation, saline soaking, freeze-drying, and rehydrating is developed to fabricate polyvinyl alcohol gels with cation specificity, exhibiting the specific ordering of effects on the mechanical properties of gels as Ca2+ > Li+ > Mg2+ >> Fe3+ > Cu2+ >> Co2+ ≈ Ni2+ ≈ Zn2+. The multiple effects of the fabrication strategy, including the electrostatic repulsion among cations, skeleton support function of graphene oxide nanosheets, and water absorption and retention of ions, endow the gels with the dual characteristics of hydrogels and aerogels (i.e., hydro-aerogels). The hydro-aerogels prepared with the cationic salting-out effect display attractive pressure sensing performance with excellent stability over 90 days and enable continuous monitoring of ambient humidity in real-time and effective work in seawater to detect various parameters (e.g., depth, salinity, and temperature). The hydro-aerogels prepared without borax pretreatment or using the cationic salting-in effect can serve as quasi-solid-state electrolytes in supercapacitors, with 99.59% capacitance retention after 10 000 cycles. This study realizes cation specificity in hydrogels and designs multifunctional hydro-aerogels for promising applications in various fields.

An All-Protein Multisensory Highly Bionic Skin.

To achieve a highly realistic robot, closely mimicking human skin in terms of materials and functionality is essential. This paper presents an all-protein silk fibroin bionic skin (SFBS) that emulates both fast-adapting (FA) and slow-adapting (SA) receptors. The mechanically different silk film and hydrogel, which exhibited skin-like properties, such as stretchability (>140%), elasticity, low modulus (<10 kPa), biocompatibility, and degradability, were prepared through mesoscopic reconstruction engineering to mimic the epidermis and dermis. Our SFBS, incorporating SA and FA sensors, demonstrated a highly sensitive (1.083 kPa-1) static pressure sensing performance (in vitro and in vivo), showed the ability to sense high-frequency vibrations (50-400 Hz), could discriminate materials and sliding, and could even identify the fine morphological differences between objects. As proof of concept, an SFBS-integrated rehabilitation glove was synthesized, which could help stroke patients regain sensory feedback. In conclusion, this work provides a practical approach for developing skin equivalents, prostheses, and smart robots.

Array Integration and Far-Field Detection of Biocompatible Wireless LC Pressure Sensors.

In this paper, three configurations of LC (inductor-capacitor) pressure sensors are developed, namely series LC pressure sensors, compact LC pressure sensors, and far-field LC pressure sensor tags. The modified silk protein films have been chosen as substrates due to their good biocompatibility and air/water permeability, which is suitable for continuously pasting such substrates on skin. For series LC pressure sensors, conducting wire is used to connect the flexible capacitor and spiral inductor. It exhibits good cycling stability and high sensitivities, suitable for electronic skin. For compact LC pressure sensors, the spiral coil functions as inductor, antenna, and capacitor electrode simultaneously, minimizing the space cost and is suitable for array integration, while the sensitivities remain the same. By tailoring the turn of the spiral coil, the resonate frequency can be regulated continuously. An annular array of compact LC sensors with ten distinct resonate frequencies ranged from 400 to 1000 MHz is developed to remotely monitor the press of number 0-9. Finally, far-field LC pressure sensor tags with elongated detection distances are developed in which each compact LC sensor acts as a filter. A wireless in-shoe plantar to detect the sole pressure distribution using the far-field LC sensor configuration is developed.

Free-Standing, Flexible Carbon@MXene Films with Cross-Linked Mesoporous Structures toward Supercapacitors and Pressure Sensors.

The preparation of multifunctional materials with low cost and simple synthesis processes is still challenging. Herein, by employing various sizes (50-500 nm) of polystyrene (PS) spheres as templates, different free-standing carbon@MXene films with three-dimensional (3D) mesoporous structures were fabricated through a simple multistep route. The microstructure, composition, mechanical property, conductivity, electrochemical activity, and sensing characteristics of these carbon@MXene films were investigated in detail. The intercalation of the PS spheres can effectively reduce the self-accumulation of MXene nanosheets and construct 3D cross-linked mesoporous structures, therefore broadening the ion transport channels and exposing more active sites of carbon@MXene films. When applied in a symmetrical supercapacitor, the optimized carbon@MXene electrode has a satisfactory specific capacitance of 447.67 F g-1 at a current density of 1 A g-1. Moreover, the 3D mesoporous structures of carbon@MXene films can significantly improve the sensitivity of the resultant pressure sensors with excellent stability (10,000 cycles). Thus, such mesoporous carbon@MXene films prepared by a facile yet robust route will be a versatile material for many applications.

Stretchable, Stable, and Degradable Silk Fibroin Enabled by Mesoscopic Doping for Finger Motion Triggered Color/Transmittance Adjustment.

As a kind of biocompatible material with long history, silk fibroin is one of the ideal platforms for on-skin and implantable electronic devices, especially for self-powered systems. In this work, to solve the intrinsic brittleness as well as poor chemical stability of pure silk fibroin film, mesoscopic doping of regenerated silk fibroin is introduced to promote the secondary structure transformation, resulting in huge improvement in mechanical flexibility (∼250% stretchable and 1000 bending cycles) and chemical stability (endure 100 °C and 3-11 pH). Based on such doped silk film (SF), a flexible, stretchable and fully bioabsorbable triboelectric nanogenerator (TENG) is developed to harvest biomechanical energy in vitro or in vivo for intelligent wireless communication, for example, such TENG can be attached on the fingers to intelligently control the electrochromic function of rearview mirrors, in which the transmittance can be easily adjusted by changing contact force or area. This robust TENG shows great potential application in intelligent vehicle, smart home and health care systems.

Highly Stretchable, Adhesive, and Self-Healing Silk Fibroin-Dopted Hydrogels for Wearable Sensors.

In recent years, the preparations of flexible electronic devices have attracted great attention. Here, a simple one-pot method of thermal polymerization is introduced to fabricate silk fibroin-dopted hydrogels (SFHs), which are both chemically and physically cross-linked by acrylamide (AM), acrylic acid (AA), and silk fibroin (SF). The addition of SF can effectively enhance the mechanical property of the SFH12% by 59% compared with SFH0% . Taking the advantage of its wide working range of stress (about 0.455-568.9 kPa), the SFH can work as a resistance-type pressure sensor to monitor different human motions. What is more, the excellent adhesion, about 75.17 N m-1 of SFH46% enables it to fit tightly to other objects during the testing, which significantly reduces the loss of small signals due to poor fit. In addition, the SFH demonstrates excellent self-healing property without requiring external excitation and a sensitive temperature response in the range of -10 to 60 °C. The SFH is expected to be applied in the field of electronic skin, soft robots, and other flexible electronic products as well as speech recognition.

Subcutaneous Energy/Signal Transmission Based on Silk Fibroin Up-Conversion Photonic Amplification.

Transmission of energy and signals through human skin is critically important for implantable devices. Because near-infrared (NIR) light can easily penetrate through human skin/tissue, in this study we report on silk fibroin (SF) up-conversion photonic amplifiers (SFUCPAs) integrated into optoelectronic devices, which provide a practical approach for subcutaneous charging and communication via NIR lasers. SFUCPAs achieve a 4 times higher fluorescence than the control, which gives rise to a 47.3 time increase in subcutaneous NIR energy conversion efficiency of a single fibrous dye-sensitized solar cell compared with the control. Moreover, the hybrid printed electrodes exhibited reversible switching to NIR exposure with a response time of ∼1.06/1.63 s for a 3 s ON/OFF switch. Owing to the flexible, biocompatible, and cost-efficient design NIR-driven optoelectronic performance, the SFUCPAs are promising for use in applications of subcutaneous medical electronics for charging, storing information, and controlling implanted devices.

Transparent, stretchable and degradable protein electronic skin for biomechanical energy scavenging and wireless sensing.

Self-powered flexible sensors play an increasingly important role in wearable and even implantable electronic devices. Silk protein is an ideal material for flexible sensors because of its terrific biocompatibility and controllable degradation rate. Here, we overcome the problem of mechanical flexibility and poor electrical conductivity of proteins, and develop a highly transparent, biocompatible, full-degradable and flexible triboelectric nanogenerator (Bio-TENG) for energy harvesting and wireless sensing. First, the mechanical flexibility of the silk protein film is greatly enhanced by the mesoscopic functionalization of regenerated silk fibroin (RSF) via adding glycerol and polyurethane (PU). Second, hollow silver nanofibers are constructed on the silk film to form an air-permeable, stretchable, biocompatible and degradable thin layer and utilized as friction electrode. The obtained Bio-TENG demonstrates high transparency (83% by one Ag gird layer), stretchability (Ɛ = 520%) and an instantaneous peak power density of 0.8 W m-2 that can drive wearable electronics. Besides, the Bio-TENG can work as artificial electronic skin for touch/pressure perception, and also for wirelessly controlling Internet of Things as a switch.

A Machine-Fabricated 3D Honeycomb-Structured Flame-Retardant Triboelectric Fabric for Fire Escape and Rescue.

Fire disaster is one of the most common hazards that threaten public safety and social development: how to improve the fire escape and rescue capacity remains a huge challenge. Here, a 3D honeycomb-structured woven fabric triboelectric nanogenerator (F-TENG) based on a flame-retardant wrapping yarn is developed. The wrapping yarn is fabricated through a continuous hollow spindle fancy twister technology, which is compatible with traditional textile production processes. The resulting 3D F-TENG can be used in smart carpets as a self-powered escape and rescue system that can precisely locate the survivor position and point out the escape route to timely assist victim search and rescuing. As interior decoration, the unique design of the honeycomb weaving structure endows the F-TENG fabric with an excellent noise-reduction ability. In addition, combining with its good machine washability, air permeability, flame-retardency, durability, and repeatability features, the 3D F-TENG may have great potential applications in fire rescue and wearable sensors as well as smart home decoration.

Carbon dots-based dual-emission ratiometric fluorescence sensor for dopamine detection.

The detection of Dopamine (DA) is significant for disease surveillance and prevention. However, the development of the precise and simple detection techniques is still at a preliminary stage due to their high tester requirements, time-consuming process, and low accuracy. In this work, we present a novel dual-emission ratiometric fluorescence sensing system based on a hybrid of carbon dots (CDs) and 7-amino-4-methylcoumarin (AMC) to quickly monitor the DA concentration. Linked via amide bonds, the CDs and AMC offered dual-emissions with peaks located at 455 and 505 nm, respectively, under a single excitation wavelength of 300 nm. Attributed to the fluorescence of the CDs and AMC in the nanohybrid system can be quenched by DA, the concentration of DA could be quantitatively detected by monitoring the ratiometric ratio change in fluorescent intensity. More importantly, the CDs-AMC-based dual-emission ratiometric fluorescence sensing system demonstrated a remarkable linear relationship in the range of 0-33.6 µM to detection of DA, and a low detection limit of 5.67 nM. Additionally, this sensor successfully applied to the detection of DA in real samples. Therefore, the ratiometric fluorescence sensing system may become promising to find potential applications in biomedical dopamine detection.

Continuous and Scalable Manufacture of Hybridized Nano-Micro Triboelectric Yarns for Energy Harvesting and Signal Sensing.

Textile-based triboelectric nanogenerators (TENG) that can effectively harvest biomechanical energy and sense multifunctional posture and movement have a wide range of applications in next-generation wearable and portable electronic devices. Hence, bulk production of fine yarns with high triboelectric output through a continuous manufacturing process is an urgent task. Here, an ultralight single-electrode triboelectric yarn (SETY) with helical hybridized nano-micro core-shell fiber bundles is fabricated by a facile and continuous electrospinning technology. The obtained SETY device exhibits ultralightness (0.33 mg cm-1), extra softness, and smaller size (350.66 µm in diameter) compared to those fabricated by conventional fabrication techniques. Based on such a textile-based TENG, high energy-harvesting performance (40.8 V, 0.705 µA cm-2, and 9.513 nC cm-2) was achieved by applying a 2.5 Hz mechanical drive of 5 N. Importantly, the triboelectric yarns can identify textile materials according to their different electron affinity energies. In addition, the triboelectric yarns are compatible with traditional textile technology and can be woven into a high-density plain fabric for harvesting biomechanical energy and are also competent for monitoring tiny signals from humans or insects.

Stretchable, Biocompatible, and Multifunctional Silk Fibroin-Based Hydrogels toward Wearable Strain/Pressure Sensors and Triboelectric Nanogenerators.

Nowadays, great effort has been devoted to establishing wearable electronics with excellent stretchability, high sensitivity, good mechanical strength, and multifunctional characteristics. Herein, a soft conductive hydrogel is rationally designed by proportionally mixing silk fibroin, polyacrylamide, graphene oxide, and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate). The resultant hydrogel has considerable stretchability and compressibility, which enables it to be assembled into a strain/pressure sensor with a wide sensing range (strain, 2%-600%; pressure, 0.5-119.4 kPa) and reliable stability. Then, the corresponding sensor is capable of monitoring a series of physical signals of the human body (e.g., joint movement, facial gesture, pulse, breathing, etc.). In particular, the hydrogel-based sensor is biocompatible, with no anaphylactic reaction on human skin. More interestingly, this conductive hydrogel exhibits a positive response when it works in a triboelectric nanogenerator; consequently, it lights up 20 commericial green light-emitting diodes. Thus, this silk fibroin-based hydrogel is a kind of multifunctional material toward wearable electronics with versatile applications in health and exercise monitors, soft robots, and power sources.

A leaf vein-like hierarchical silver grids transparent electrode towards high-performance flexible electrochromic smart windows.

As essential components of numerous flexible and wearable optoelectronic devices, the flexible transparent conducting electrodes (TCEs) with sufficient optical transmittance and electric conductivity become more and more important. In this work, we fabricated a large-area flexible TCE based on leaf vein-like hierarchical metal grids (HMG) comprising of mesoscale "trunk" and microscale "branches". The self-formed branched grids made the conducting paths distributing uniformly while the laser-etching trunk grids enabled to transport the collected electrons across long-distance. The Ag HMG exhibited high optical transmittance (~81%) with low sheet resistance (1.36 Ω sq-1), which could be simply optimized through adjusting the grids' widths, spaces, and the sizes of the TiO2 colloidal crackle patterns. In addition, on the basis of such advanced HMG electrode, flexible electrochromic devices (ECDs) with remarkable cyclic performance were fabricated. The HMG with high transparency, conductivity, and flexibility provides a promising TCE for the next-generation flexible and wearable optoelectronic devices.

All-Textile Electronic Skin Enabled by Highly Elastic Spacer Fabric and Conductive Fibers.

Electronic fabrics that combine traditional fabric with intelligent functionalities have attracted increasing attention. Here an all-fabric pressure sensor with a wireless battery-free monitoring system was successfully fabricated, where a 3D penetrated fabric sandwiched between two highly conductive fabric electrodes acts as a dielectric layer. Thanks to the good elastic recovery of the spacer fabric, the capacitance pressure sensor exhibits a high sensitivity of 0.283 KPa-1 with a fast response time and good cycling stability (≥20 000). Water-soluble poly(vinyl alcohol) template-assisted silver nanofibers were constructed on the high-roughness fabric surface to achieve high conductivity (0.33 Ω/sq), remarkable mechanical robustness, and good biocompatibility with human skin. In addition, the coplanar fabric sensor arrays were successfully designed and fabricated to spatially map resolved pressure information. More importantly, the gas-permeable fabrics can be stuck on the skin for wireless real-time pressure detection through a fiber inductor coil with a resonant frequency shift sensitivity of 6.8 MHz/kPa. Our all-fabric sensor is more suitable for textile technology compared with traditional pressure sensors and exhibited wide potential applications in the field of intelligent fabric for electronic skin.

Silk Composite Electronic Textile Sensor for High Space Precision 2D Combo Temperature-Pressure Sensing.

Wearable electronic textiles based on natural biocompatible/biodegradable materials have attracted great attention due to applications in health care and smart clothes. Silkworm fibers are durable, good heat conductors, insulating, and biocompatible, and are therefore regarded as excellent mediating materials for flexible electronics. In this paper, a strategy on the design and fabrication of highly flexible multimode electronic textiles (E-textile) based on functionalized silkworm fiber coiled yarns and weaving technology is presented. To achieve enhanced temperature sensing performance, a mixture of carbon nanotubes and an ionic liquid ([EMIM]Tf2 N) is embedded, which displays top sensitivity of 1.23% °C-1 and stability compared with others. Furthermore, fibrous pressure sensing based on the capacitance change of each cross-point of two yarns gives rise to highly position dependent and sensitivity sensing of 0.136 kPa-1 . Based on weaving technologies, a unique combo textile sensor, which can sense temperature and pressure independently with a position precision of 1 mm2 , is obtained. The application to intelligent gloves endows the position dependent sensing of the weight, and temperature distribution sensing of the temperature.