Sculpting Mesoscopic Helical Chirality into Covalent Organic Framework Nanotubes from Entirely Achiral Building Blocks.

The diversification of chirality in covalent organic frameworks (COFs) holds immense promise for expanding their properties and functionality. Herein, we introduce an innovative approach for imparting helical chirality to COFs and fabricating a family of chiral COF nanotubes with mesoscopic helicity from entirely achiral building blocks for the first time. We present an effective 2,3-diaminopyridine-mediated supramolecular templating method, which facilitates the prefabrication of helical imine-linked polymer nanotubes using unprecedented achiral symmetric monomers. Through meticulous optimization of crystallization conditions, these helical polymer nanotubes are adeptly converted into imine-linked COF nanotubes boasting impressive surface areas, while well preserving their helical morphology and chiroptical properties. Furthermore, these helical imine-linked polymers or COFs could be subtly transformed into corresponding more stable and functional helical ß-ketoenamine-linked and hydrazone-linked COF nanotubes with transferred circular dichroism via monomer exchange. Notably, despite the involvement of covalent bonding breakage and reorganization, these exchange processes overcome thermodynamic disadvantages, allowing mesoscopic helical chirality to be perfectly preserved. This research highlights the potential of mesoscopic helicity in conferring COFs with favourable chiral properties, providing novel insights into the development of multifunctional COFs in the field of chiral materials chemistry.

Fiber organic electrochemical transistors based on multi-walled carbon nanotube and polypyrrole composites for noninvasive lactate sensing.

Multi-walled carbon nanotubes (MWCNT) play a synergistic role with conducting polymer in practical applications such as biological sensing. In this paper, multi-walled carbon nanotube and polypyrrole (PPy) composites were prepared on a fiber surface for the first time, and their morphology and electrical properties were characterized. Compared with PPy-coated fiber, the presence of carbon nanotubes induced the growth of large areas of PPy nanowires. In addition, fiber organic electrochemical transistors (FECTs) based on PPy and MWCNT were assembled, showing a higher on/off ratio, better stability, and greater flexibility. The lactate biosensor based on FECTs exhibits high sensitivity, with a correlation coefficient of R = 0.9889, quick response time of 0.6-0.8 s, a wide linear response range of 1 nM-1 mM, and excellent selectivity for lactate. Furthermore, the lactate concentration in human sweat was successfully detected by a FECT-based sensor. The hybrid fibers can be easily woven and placed on fabric simply by stitching. This favorable performance of the FECT-based sensor makes it suitable for noninvasive sensing of lactate. Therefore, it provides a promising platform for future use in healthcare and detection applications. Graphical abstract.

Hierarchically Three-Dimensional Nanofiber Based Textile with High Conductivity and Biocompatibility As a Microbial Fuel Cell Anode.

Microbial fuel cells (MFCs) encompass complex bioelectrocatalytic reactions that converting chemical energy of organic compounds to electrical energy. Improving the anode configuration is thought to be a critical step for enhancing MFCs performance. In present study, a hierarchically structured textile polypyrrole/poly(vinyl alcohol-co-polyethylene) nanofibers/poly(ethylene terephthalate) (referred to PPy/NFs/PET) is shown to be excellent anode for MFCs. This hierarchical PPy/NFs/PET anode affords an open porous and three-dimensional interconnecting conductive scaffold with larger surface roughness, facilitating microbial colonization and electron transfer from exoelectrogens to the anode. The mediator-less MFC equipped with PPy/NFs/PET anode achieves a remarkable maximum power density of 2420 mW m(-2) with Escherichia coli as the microbial catalyst at the current density of 5500 mA m(-2), which is approximately 17 times higher compared to a reference anode PPy/PET (144 mW m(-2)). Considering the low cost, low weight, facile fabrication, and good winding, this PPy/NFs/PET textile anode promises a great potential for high-performance and cost-effective MFCs in a large scale.

Ion sensors based on novel fiber organic electrochemical transistors for lead ion detection.

Fiber organic electrochemical transistors (FECTs) based on polypyrrole and nanofibers have been prepared for the first time. FECTs exhibited excellent electrical performances, on/off ratios up to 10(4) and low applied voltages below 2 V. The ion sensitivity behavior of the fiber organic electrochemical transistors was investigated. It exhibited that the transfer curve of FECTs shifted to lower gate voltage with increasing cations concentration, the sensitivity reached to 446 µA/dec in the 10(-5)-10(-2) M Pb(2+) concentration range. The ion selective properties of the FECTs have also been systematically studied for the detection of potassium, calcium, aluminum, and lead ions. The devices with different cations showed great difference in response curves. It was suitable for selectively monitoring Pb(2+) with respect to other cations. The results indicated FECTs were very effective for electrochemical sensing of lead ion, which opened a promising perspective for wearable electronics in healthcare and biological application. Graphical Abstract The schematic diagram of fiber organic electrochemical transistors based on polypyrrole and nanofibers for ion sensing.

Photopolymerized multifunctional sodium alginate-based hydrogel for antibacterial and coagulation dressings.

Trauma caused by tissue damage in clinical applications has posed a serious threat to public safety. Dressings with a single function cannot meet the needs of wound healing, but multifunctional dressings are difficult to achieve and obtain. To address this issue, this research designed a facile one-pot photo-crosslinking method to prepare multifunctional sodium alginate-based hydrogel dressings for effective wound healing. According to irregular wounds, sodium alginate-based hydrogel dressings can be quickly prepared anytime and anywhere. The structure and physicochemical properties of hydrogels are regulated by modulating the proportion of main components sodium alginate and acrylamide. The results showed the sodium alginate-based composite hydrogel as a candidate multifunctional dressing that exhibits excellent stretchability and compressibility, viscoelasticity, and suitable tissue-like adhesion. In vitro drug release and antibacterial experiments indicated that the hydrogel has effective antibacterial properties against S. aureus and P. aeruginosa. Furthermore, the haemostatic behaviour of the hydrogel was demonstrated using the coagulation activation test, whole blood-clotting test, and blood cell and platelet adhesion experiments. All these results demonstrated that the sodium alginate-based hydrogel had high application potential as a multifunctional medical dressing for wound healing.

Large-Scale, Stretchable, Self-Protective, and Multifunctional Perovskite Luminescent Filament with Ultra-High Stability.

Lead halide perovskites possess great application potential in flexible displays and wearable optoelectronics owing to their prominent optoelectronic properties. However, the intrinsic instability upon moisture, heat, and ultraviolet (UV) light irradiation hinders their development and application. In this work, an ultra-stable CsPbX3 (X = Cl, Br, I) perovskite luminescent filament (PLF) with high stretchability (≈2400%) and luminescence performance (photoluminescence quantum yield (PLQY) of 24.5%, tunable emission spectrum, and high color purity) is introduced by a facile environmental-friendly wet-spinning technology via solvent extraction. Benefiting from the in situ encapsulation of the hydrophobic thermoplastic polyurethane (TPU) and the chelation of Lewis base CO in TPU with Lewis acid Pb2+, the CsPbBr3 PLF demonstrates ultra-high photoluminescence (PL) stability when stored in ambient air and high humidity circumstance, annealed at 50 °C, and dipped in water for 30 days, illuminated under ultraviolet light for 300 min, and immersed in organic solvents and solutions with pH of 1-13 for 5 min, respectively. Impressively, it retains 80% of its initial PL after being recycled five times. Overall, the CsPbX3 PLF demonstrates promising prospects in multifunctional applications, including organic dyes and tensile strain sensing, flexible pattern displays, secondary anti-counterfeiting, and hazard warning systems.

Multi-Layer Polyurethane-Fiber-Prepared Entangled Strain Sensor with Tunable Sensitivity and Working Range for Human Motion Detection.

The entanglement of fibers can form physical and topological structures, with the resulting bending and stretching strains causing localized changes in pressure. In this study, a multi-layer polyurethane-fiber-prepared (MPF) sensor was developed by coating the CNT/PU sensing layer on the outside of an elastic electrode through a wet-film method. The entangled topology of two MPFs was utilized to convert the stretching strain into localized pressure at the contact area, enabling the perception of stretching strain. The influence of coating mechanical properties and surface structure on strain sensing performance was investigated. A force regulator was introduced to regulate the mechanical properties of the entangled topology of MPF. By modifying the thickness and length proportion of the force regulator, the sensitivity factor and sensitivity range of the sensor could be controlled, achieving a high sensitivity factor of up to 127.74 and a sensitivity range of up to 58%. Eight sensors were integrated into a sensor array and integrated into a dance costume, successfully monitoring the multi-axis motion of the dancer's lumbar spine. This provides a new approach for wearable biomechanical sensors.

N-Halamine-Based Polypropylene Melt-Blown Nonwoven Fabric with Superhydrophilicity and Antibacterial Properties for Face Masks.

Polypropylene melt-blown nonwoven fabric (PP MNF) masks can effectively block pathogens in the environment from entering the human body. However, the adhesion of surviving pathogens to masks poses a risk of human infection. Thus, embedding safe and efficient antibacterial materials is the key to solving pathogen infection. In this study, stable chlorinated poly(methacrylamide-N,N'-methylenebisacrylamide) polypropylene melt-blown nonwoven fabrics (PP-P(MAA-MBAA)-Cl MNFs) have been fabricated by a simple UV cross-link and chlorination process, and the active chlorine content can reach 3500 ppm. The PP-P(MAA-MBAA)-Cl MNFs show excellent hydrophilic and antibacterial properties. The PP-P(MAA-MBAA)-Cl MNFs could kill all bacteria (both Escherichia coli and Staphylococcus aureus) with only 5 min of contact. Therefore, incorporating PP-P(MAA-MBAA)-Cl MNF as a hydrophilic antimicrobial layer into a four-layer PP-based mask holds great potential for enhancing protection and comfort.

Highly Conductive, Ultrastrong, and Flexible Wet-Spun PEDOT:PSS/Ionic Liquid Fibers for Wearable Electronics.

Conductive poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) fibers with high electrical conductivity, flexibility, and robustness are urgently needed for constructing wearable fiber-based electronics. In this study, the highly conductive (4288 S/cm), ultrastrong (a high tensile strength of 956 MPa), and flexible (a low Young's modulus of 3.8 GPa) PEDOT:PSS/1-ethyl-3-methylimidazolium dicyanamide (EMIM:DCA) (P/ED) fiber was prepared by wet-spinning and a subsequent H2SO4-immersion-drawing process. As far as we know, this is the best performance of the PEDOT:PSS fiber reported so far. The structure and conformation of the P/ED fiber were characterized by FESEM, XPS, Raman spectroscopy, UV-vis-NIR spectroscopy, and WAXS. The results show that the high performances of the P/ED fiber are mainly attributed to the massive removal of PSS and high degree of crystallinity (87.9%) and orientation (0.71) of PEDOT caused by the synergistic effect of the ionic liquid, concentrated sulfuric acid, and high stretching. Besides, the P/ED fiber shows a small bending radius of 0.1 mm, and the conductivity of the P/ED fiber is nearly unchanged after 1000 repeated cycles of bending and humidity changes within 50-90%. Based on this, various P/ED fiber-based devices including the circuit connection wire, thermoelectric power generator, and temperature sensor were constructed, demonstrating its wide applications for constructing flexible and wearable electronics.

Construction Strategy for Flexible and Breathable SiO2/Al/NFs/PET Composite Fabrics with Dual Shielding against Microwave and Infrared-Thermal Radiations for Wearable Protective Clothing.

Microwave and infrared-thermal radiation-compatible shielding fabrics represent an important direction in the development of wearable protective fabrics. Nevertheless, effectively and conveniently integrating compatible shielding functions into fabrics while maintaining breathability and moisture permeability remains a significant challenge. Here, we take hydrophilic PVA-co-PE nanofibrous film-coated PET fabric (NFs/PET) as a flexible substrate and deposit a dielectric/conductive (SiO2/Al) bilayer film via magnetron sputtering. This strategy endows the fabric surface with high electrical conductivity, nanoscale roughness comparable to visible and infrared waves, and a dielectric-metal contact interface possessing localized plasmon resonance and Mie scattering effects. The results demonstrate that the optimized SiO2/Al/NFs/PET composite conductive fabric (referred to as S4-1) possesses favorable X-band electromagnetic interference (EMI) shielding effectiveness (50 dB) as well as excellent long-wave infrared (LWIR) shielding or IR stealth performance (IR emissivity of 0.60). Notably, the S4-1 fabric has a cooling effect of about 12.4 °C for a heat source (80 °C) and an insulating effect of about 17.2 °C for a cold source (-20 °C), showing excellent shielding capability for heat conduction and heat radiations. Moreover, the moisture permeability of the S4-1 fabric is about 300 g/(m2·h), which is better than the requirement concerning moisture permeability for wearable fabrics (≥2500-5000 g/(m2·24 h)), indicating excellent heat and moisture comfort. In short, our fabrics have lightweight, thin, moisture-permeable and excellent shielding performance, which provides novel ideas for the development of wearable multi-band shielding fabrics applied to complex electromagnetic environments.

Silicon Distribution-Induced Actuation Film with Bidirectional Bending Deformation and Versatile Bionic Applications.

As an important branch of intelligent materials, the research and development of stimulus-responsive flexible intelligent actuation materials is of great significance to promote the industrialization of intelligent materials. In this study, the asymmetric PVA-co-PE/silicon nanoparticle (PPSN) composite films and PVA-co-PE/silicon sol (PPSS) composite film with different silicon distributions were prepared by a simple spraying method. The silicon nanoparticle layer in the PPSN composite film was similar to the sand-like water-absorbing layer, which can quickly absorb water and permeate it into the interior region, leading to the hygroscopic expansion behavior on one side of the nanofiber film. Then, the PPSN composite film would quickly bend and deform to the silicon nanoparticle side. However, in the PPSS composite film, due to the excellent hygroscopicity and swelling characteristics of the silica sol layer, the composite film can be rapidly deformed to the PVA-co-PE nanofiber film side under moisture stimulation. The above results subvert the traditional asymmetric actuation film, which mainly depends on the hydrophilicity difference to determine the hygroscopic responsiveness and deformation direction, and ignore that the swelling degree is the main factor determining the bending direction of actuator. In addition, both the composite films can quickly respond to moisture stimulation (<1 s) and produce large-scale bending deformation (180°). Furthermore, due to the excellent interface adhesion formed by the continuity structure in the PPSS composite film, it has better actuation stability than the PPSN composite film. The excellent actuation characteristics and different bending directions of the PPSN and PPSS composite films make it a great application prospect in the field of bionics in the future.

Fiber based organic electrochemical transistor integrated with molecularly imprinted membrane for uric acid detection.

In this study, poly(3, 4-ethylenedioxythiophene) (PEDOT) nanocluster structure was synthesized on the reduced graphene oxide (rGO) modified cotton fibers. The organic electrochemical transistors based on the modified fiber have been assembled and their performance of different gate electrode transistors has been investigated. The transistor exhibits an excellent transconductance of up to 15.5 mS and a high on-off ratio close to 2*102. The bending angle and bending times have little effect on the device performance. The uric acid (UA) sensor based transistor has been fabricated for the first time. Flexible sensors based on molecularly imprinted polymer (MIP) membrane with different fiber gate electrodes have been investigated. The UA sensor with MIP/PEDOT/carbon fiber as the gate electrode has a sensitivity of 100 µA per decade from 1 nM to 500 µM, a linear coefficient of 0.97143, excellent selectivity, and good reproducibility. In addition, fiber based organic electrochemical transistors (FECTs) can be sewn into the fabric for monitoring and have successfully evaluated the detection of UA in artificial urine sample, with data consistent well with the UA concentration obtained from single fiber. Therefore, the sensor based FECTs can be used for low cost, accurate, non-enzymatic detection of UA in clinical diagnostics and bioanalytical applications.

Graphene Oxide/Nanofiber-Based Actuation Films with Moisture and Photothermal Stimulation Response for Remote Intelligent Control Applications.

The rapid development of intelligent technology and industry has induced higher requirements for multifunctional materials, especially intelligent materials with stimulus-responsive self-actuation behavior. In this study, a Cu@PVA-co-PE/GO composite actuation film, with an asymmetric sandwich structure, was prepared by attaching graphene oxide (GO) to the surface of a polyvinyl alcohol ethylene copolymer (PVA-co-PE) nanofiber composite film containing copper nanoparticles (Cu) through layer-on-layer adsorption. This unique structural design endowed the composite film with not only excellent structural stability but also different bending directions (in response to moisture and infrared light). The actuation performance shows that when the adsorption time was 4 h, the maximum bending angle of the Cu@PVA-co-PE/GO composite film was up to 90° within 5.99 s. Furthermore, the actuation behavior was stable after 100 cycles of reversible moisture stimulation. Additionally, the maximum actuation strain of the composite film was up to 1.35 MPa during the illumination time of 6.8 s and maintained an excellent stability for 400 s under continuous infrared stimulation of 0.53 W/cm2. The rapid and sensitive stimulus response of the Cu@PVA-co-PE/GO composite film exhibited self-actuation behavior under the remote control of moisture and infrared light. This, in turn, suggests prospects for wide applications in emerging technologies, such as intelligent switches, artificial muscles, intelligent medical treatment, and flexible robots.

Humidity-Driven Switch in the Transparency of a Nanofiber Film for a Smart Window.

Traditional smart windows use electrical signals to transform transparency. However, this electric transmission mode greatly limits their uses. Here, we have prepared a transparent PVA-co-PE/CA composite film, which can realize the reversible transformation of transparency under the stimulation of humidity. The preparation method of the composite film included simple immersion and a thermal curing process, showing high optical transparency (96.61%) and an excellent tensile strain at break of 536.34%. Once exposed to moisture stimulation, the rapid hygroscopic swelling of the composite film led to the increase in the difference in the refractive index between the citric acid filling phase and the nanofibers, which directly led to the sharp decrease in the composite film's transparency. Moreover, the composite film can be arbitrarily attached to the surface of the transparent substrate and designed as some special visualization devices or smart windows, which have a promising future in information encryption and intelligent homes.

Full-Textile Human Motion Detection Systems Integrated by Facile Weaving with Hierarchical Core-Shell Piezoresistive Yarns.

The tremendous progress of the wearable intelligent system has brought an urgent demand for flexible pressure sensors, especially for those possessing high sensing performances, simple manufacture technology, and efficient integration. In this work, hierarchical core-shell piezoresistive yarns (HCPYs), which contain internal silver-plated nylon electrodes and surface microporous structured carbon nanotubes (CNTs)/thermoplastic polyurethane (TPU) sensing layer, are designed and manufactured via facile wet-spinning accompanied by a water vapor coagulating bath. The obtained HCPY can either be inserted into traditional textiles to assemble a single-pressure sensor, or be woven into a textile-based flexible pressure sensors array with expected size and resolution, without compromising their comfort, breathability, and three-dimensional (3D) conformability. Simultaneously, to further enhance the sensing performance, the surface microporous structures of HCPYs are optimized by altering the treatment humidity and exposure time during the process of water vapor-induced phase separation. The wearable pressure sensors assembled by the optimal HCPY achieved a high sensitivity up to 84.5 N-1, a good durability over 5000-cycle tests, a fast response time of 2.1 ms, and a recovery time of 2.4 ms. Moreover, the wearable pressure sensors have been successfully used to monitor physical signals and human motions. The textile-based flexible pressure sensors array has also been seamlessly integrated with sportswear to detect movements of the elbow joint and map spatial pressure distribution, which makes HCPY a promising candidate for constructing next-generation wearable electronics.

Synergistically Improving Flexibility and Thermoelectric Performance of Composite Yarn by Continuous Ultrathin PEDOT:PSS/DMSO/Ionic Liquid Coating.

Combining fabrics with a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) coating is the most promising method to fabricate wearable thermoelectric (TE) devices. However, the high modulus, low strain, and low TE performance of PEDOT:PSS coating lead to poor flexibility and low power generation efficiency. In this study, dimethyl sulfoxide (DMSO) and ionic liquids (ILs) were selected as a modifier to enhance the flexibility and TE performance of PEDOT:PSS. Different from the penetrating structure and coil conformation of pristine PEDOT:PSS coating, a flexible continuous ultrathin layer of PEDOT:PSS/DMSO/1-ethyl-3-methylimidazolium dicyanamide (P/D/ED) with a linear conformation forms on the surface of cotton yarn. The morphology and structure of PEDOT:PSS and P/D/ED coating were characterized by FESEM, XPS, and Raman spectroscopy. Compared with the pristine PEDOT:PSS film, the P/D/ED film shows significantly reduced modules and enhanced strain and bending stability. Moreover, the TE performance of P/D/ED-coated yarn is significantly enhanced with nearly half mass loading. Based on this, a large-area wearable TE fabric with enhanced flexibility and TE performance was prepared. The output power density is 136.1 mW/m2 at ΔT = 40.8 K, which is a typically high value compared with the former reported composite TE fabrics. This study provides a new way to synergistically enhance the flexibility and TE performance of composite yarn, and the prepared TE fabric has great potential as a wearable power source.

Supported growth of inorganic-organic nanoflowers on 3D hierarchically porous nanofibrous membrane for enhanced enzymatic water treatment.

Organic-inorganic nanoflower is a new type of functional material that can effectively immobilize a wide range of enzymes to form flower-like structures for various enzymatic applications with enhanced catalytic performance and stability. In order to avoid the processing inconvenience and flower structure damage caused by the particular form of these hybrid nanoflowers during material fabrication and catalytic application, different substrates have been used to carry out supported growth of hybrid nanoflowers. However, all previously used substrates have only 2-dimensional feature and only incorporate hybrid nanoflowers on surface with limited nanoflower loading. In this study, three-dimensional (3D) hierarchically porous nanofibrous PVA-co-PE membranes (HPNM) are prepared by a simple template method for effectively immobilizing laccase-Cu2(PO4)3•3H2O hybrid nanoflowers. Compared with dense nanofibre membrane with only small sized pores (<1 micron), the coexistence of both small and large sized (30-80 microns) pores of HPNM could significantly increase the nanoflower density and allow the penetrated growth of hybrid nanoflowers into the inner structure of the membrane. The hybrid nanoflower containing hierarchically porous nanofibrous membranes (HNF-HPNM) show excellent catalytic performance in degrading different types of textile dyes (reactive blue 2, acid blue 25, acid yellow 76 and indigo carmine), with a degradation efficiency of ˜99.5% for indigo carmine. In addition, the HNF-HPNM could be reused at least 14 times for indigo carmine degradation, with a negligible degradation efficiency drop from 99.48% to 98.52%. These results indicate that hierarchically porous nanofibrous membrane can be a promising type of materials for supported hybrid nanoflower growth for practical applications such as waste water treatment, dye degradation and biosensing.

Flexible and Super-Sensitive Moisture-Responsive Actuators by Dispersing Graphene Oxide into Three-Dimensional Structures of Nanofibers and Silver Nanowires.

Smart actuators with excellent flexibility, sensitive responsiveness, large-scale bending-deformation, and rapid deformation-recovery performance have been sought after by researchers. Two-dimensional graphene oxide (GO) is considered as an ideal candidate for humidity-responsive actuators because of its excellent moisture sensitivity. Herein, a flexible membrane-based actuator was prepared by evenly dispersing GO sheets into a three-dimensional network formed by one-dimensional PVA-co-PE nanofibers (NFs) and silver nanowires (AgNWs). The three-dimensional interlaced pore structure of the AgNWs/NFs/GO composite membrane ensured its larger contact area (19.33 m2/g), faster moisture exchange rate, and large bending deformation under moisture stimulation. In addition, a new explanation for the spatial distribution of adsorbed water molecules and their actuating effect on the bending behaviors of composite membranes is proposed. The adsorbed water lies between the interlayer and surface layer of the composite membrane. The interlayer water molecules make the film volume expand, resulting in a large bending angle of the membrane. On the other hand, the water on the surface layers of the membrane only leads to the change in film weight, having little effect on the bending behavior. Moreover, to make the soft actuator more practical and multifunctional, a conductive AgNWs-NFs/GO bilayer membrane-based actuator was prepared by layered spraying of a AgNW on the NFs/GO membrane, which can be directly used in switching control circuits. The novel flexible membrane-based actuators are of great significance for the soft robot and intelligent control systems in the future.

Breathable and Large Curved Area Perceptible Flexible Piezoresistive Sensors Fabricated with Conductive Nanofiber Assemblies.

The rapid development of wearable electronics, humanoid robots, and artificial intelligence requires sensors to sensitively and stably detect external stress variations in large areas or on three-dimensional (3D) irregularly shaped surfaces while possessing the comfort. Most importantly, the flexibility and 3D compliance of sensors, and the fitting state of the interface between the sensor and the object are of great significance to the sensing accuracy and reliability. The ordered or random stacking and entangling of flexible and electrically conductive fiber materials can form a highly porous and mechanically stable fiber assembly. The changes in external stress can lead to the air trapped in the fiber assembly to flow in and out rapidly and repeatedly, as well as the reversible mechanical deformation of fiber materials. Correspondingly, the contact areas between electrically conductive fibers in the fiber assembly are reversibly changed, which makes the conductive and flexible fiber assembly be an ideal candidate for piezoresistive sensing material. It can be further expected that the statistical stability of contact points between conductive fibers under the stress may significantly increase with the decrease in fiber diameters. Herein, a new method to make a flexible piezoresistive sensor with conductive and porous fiber assembly was proposed. An ultrasensitive piezoresistive material was facilely prepared by fabricating conductive poly(vinyl alcohol-co-ethylene) (EVOH) nanofiber assemblies. The sensing performance of the piezoresistive sensor was optimized by regulating the nanofiber morphology, electrical conductivity, and mechanical properties. The flexible piezoresistive sensor exhibited a sensitivity of 2.79 kPa-1, a response time of 3 ms, and a recovery time of 10 ms. The sensing performance at different working frequencies was stable and durable within 4500 cycling tests. The flexible sensor showed good pressure-sensing accuracy and reliability when used on irregular surfaces and therefore was further applied in the static monitoring of large-area spatial pressure distribution and the wearable intelligent interactive device, demonstrating great application potential.

Highly Accurate Wearable Piezoresistive Sensors without Tension Disturbance Based on Weaved Conductive Yarn.

Wearable piezoresistive sensors have attracted wide attention for application in human activities monitoring, smart robots, medical detection, etc. However, most of the sensing signals collected from the piezoresistive sensor are triggered by coupling forces, such as the combination of tension and pressure. Thus, the piezoresistive sensor would be incapable of accurately monitoring and evaluating specific human motion due to the mutual interference from tension and pressure, as the tension is difficult to be decoupled or eliminated from the coupling forces. Herein a prestretchable conductive yarn (PCY) sensor with pressure sensitivity but tension insensitivity was introduced to remove the disturbance from tension. The PCY-based piezoresistive sensor is tension insensitive (gauge factor of 0.11) but pressure sensitive (sensitivity of 187.33 MPa-1). The fabric-based pressure sensor assembled with cross-arranged PCY weft and warp revealed magnified pressure sensitivity compared with the single PCY yarn sensor, as well as tension insensitivity to strain and tensile angle. Moreover, it possessed benign cyclicity during 5000 cycles of pressing/releasing. Therefore, the fabric piezoresistive sensor based on weaved conductive yarns is suitable for highly accurate and large area pressure detection, such as monitoring massage intensity of acupuncture points.