Low-Temperature-Tolerant Strain-Sensing Flexible Composite for Soft Body Armor.

Developing soft body armor with sensing characteristics in various application scenarios is a challenge but important for creating a peaceful world and personal safety, whereas existing materials suffer from indefinite protective effects and stimulus response at subzero temperatures in the long term. Herein, an anti-freezing and flexible puncture-resistance composite with strain-sensing ability is developed by compounding a NaCl-soaked poly(vinyl alcohol) (PVA)/sodium alginate (SA)/glycerol (Gly) hydrogel (PSGN hydrogel) with Kevlar fabric. After freezing-thawing treatment once and NaCl immersion for 10 h, the Kevlar/PSGN-10 composite has excellent puncture-resistance properties and linear, rapid response, wide band, and stable strain-sensing behaviors at 25 and -30 °C. The composite's maximum puncturing force and energy dissipation at -30 °C are 53.92 N and 370 mJ, respectively, increased by 285 and 302% compared with neat Kevlar fabric. The flexibility reduction and the mass addition of the Kevlar/PSGN-10 composite are merely 19 and 40%, respectively, showing superior wearable comfortability and protection efficiency. The composites also reveal remarkable strain-sensing abilities at -30 °C (linear strain sensitivity with GF = 0.27 and R2 = 0.981, a wide working frequency range of 0.16-1.3 Hz, and sensing stability for 1500 cycles). Moreover, the composite could respond to multipart body motion directly, including fingers, elbows, wrists, and knees. Consequently, the Kevlar/PSGN composite developed in this paper is promising for intelligent soft body armor at various temperatures.

Flexible Self-Powered Friction Piezoelectric Sensor Based on Structured PVDF-Based Composite Nanofiber Membranes.

With the rapid development of the economy and technology, intelligent wearable devices have gradually entered public life. Flexible sensors, as the main component of wearable devices, have been widely concerned. However, traditional flexible sensors need an external power supply, lacking flexibility and sustainable power supply. In this study, structured poly(vinylidene fluoride) (PVDF)-based composite nanofiber membranes doped with different mass fractions of MXene and zinc oxide (ZnO) were prepared by electrospinning and were then assembled to flexible self-powered friction piezoelectric sensors. The addition of MXene and ZnO endowed PVDF nanofiber membranes with better piezoelectric properties. The structured PVDF/MXene-PVDF/ZnO (PM/PZ) nanofiber membranes with a double-layer structure, interpenetrating structure, or core-shell structure could further enhance the piezoelectric properties of PVDF-based nanofiber membranes through the synergistic effects of filler doping and structural design. In particular, the output voltage of the self-powered friction piezoelectric sensor made of a core-shell PM/PZ nanofiber membrane showed a good linear relationship with the applied pressure and could produce a good piezoelectric response to the bending deformation caused by human motion.

Green-Solvent-Processable Composite Micro/Nanofiber Membrane with Gradient Asymmetric Structure for Efficient Microfiltration.

Electrospinning technology has attracted extensive attention in recent decades and is widely used to prepare nanofiber membranes from hundreds of polymers. Polyvinyl formal acetal (PVFA), as a polymer with excellent properties such as high strength and heat resistance, is not reported on the electrospun water treatment membrane. In this paper, the preparation process of electrospun PVFA nanofiber membrane is optimized, and the effect of sodium chloride (NaCl) addition on the physical and mechanical properties and microfiltration performance of nanofiber membrane is also explored. And the hydrophobic PVFA nanofiber filter layer is then combined with a hydrophilic nonwoven support layer to construct a composite micro/nanofiber membrane with a pore-size gradient structure and a hydrophilic/hydrophobic asymmetric structure. Finally, unidirectional water transport and water treatment performance are further investigated. The results show that the tensile breaking strength of the composite membrane can reach up to 37.8 MPa, the retention rate for particles with the size of 0.1-0.3 µm is 99.7%, and the water flux is 513.4 L m-2 h-1 under the hydrostatic pressure. Moreover, it still has a retention of more than 98% after three repeated uses. Therefore, the electrospun PVFA composite membrane has a great potential in microfiltration.

Synthesis and properties of SiO2/SiO2@Ag two-phase STFs.

Soft body armor with a strain-sensing function using conductive shear thickening fluids (STFs) has gradually gained research interest. In this study, conductive SiO2@Ag core-shell microspheres were synthesized and the influence of process parameters on their properties was evaluated. Subsequently, SiO2 and SiO2@Ag were used as dispersed phases to prepare two-phase STFs, the effect of the core-shell microspheres' proportion on the rheological properties of the STFs was investigated, and its mechanism was discussed. The results indicated that SiO2@Ag core-shell microspheres were coated with elemental silver and when the concentration of sodium hydroxide and glucose were 0.07 and 0.09 mol L-1, respectively, the coating surface was the most uniform and compact, and the conductivity reached the minimum value of 0.56 Ω cm. The two-phase STFs exhibited good and reversible shear thickening behaviors and the critical shear rate decreased with increasing core-shell microsphere concentration. Additionally, when the mass fraction of SiO2 and SiO2@Ag core-shell microspheres was 45% and 20%, respectively, the thickening rate was 325%, and the resistance of two-phase STFs decreased simultaneously with the emergence of shear thickening that reached the lowest value of 795.16 kΩ. This study provides a novel strategy for synthesizing conductive STFs for strain-sensing flexible stab-resistant composites.

Three-Dimensional Modeling of Spun-Bonded Nonwoven Meso-Structures.

As a type of fiber system, nonwoven fabric is ideal for solid-liquid separation and air filtration. With the wide application of nonwoven filter materials, it is crucial to explore the complex relationship between its meso structure and filtration performance. In this paper, we proposed a novel method for constructing the real meso-structure of spun-bonded nonwoven fabric using computer image processing technology based on the idea of a "point-line-body". Furthermore, the finite element method was adopted to predict filtration efficiencies based on the built 3D model. To verify the effectiveness of the constructed meso-structure and simulation model, filtration experiments were carried out on the fabric samples under different pollution particle sizes and inlet velocities. The experimental results show that the trends observed in the simulation results are consistent with those of the experimental results, with a relative error smaller than 10% for any individual datum.

Research Progress of Water Treatment Technology Based on Nanofiber Membranes.

In the field of water purification, membrane separation technology plays a significant role. Electrospinning has emerged as a primary method to produce nanofiber membranes due to its straightforward, low cost, functional diversity, and process controllability. It is possible to flexibly control the structural characteristics of electrospun nanofiber membranes as well as carry out various membrane material combinations to make full use of their various properties, including high porosity, high selectivity, and microporous permeability to obtain high-performance water treatment membranes. These water separation membranes can satisfy the fast and efficient purification requirements in different water purification applications due to their high filtration efficiency. The current research on water treatment membranes is still focused on creating high-permeability membranes with outstanding selectivity, remarkable antifouling performance, superior physical and chemical performance, and long-term stability. This paper reviewed the preparation methods and properties of electrospun nanofiber membranes for water treatment in various fields, including microfiltration, ultrafiltration, nanofiltration, reverse osmosis, forward osmosis, and other special applications. Lastly, various antifouling technologies and research progress of water treatment membranes were discussed, and the future development direction of electrospun nanofiber membranes for water treatment was also presented.

Electrospun PVDF-based piezoelectric nanofibers: materials, structures, and applications.

Polyvinylidene fluoride (PVDF) has been considered as a promising piezoelectric material for advanced sensing and energy storage systems because of its high dielectric constant and good electroactive response. Electrospinning is a straightforward, low cost, and scalable technology that can be used to create PVDF-based nanofibers with outstanding piezoelectric characteristics. Herein, we summarize the state-of-the-art progress on the use of filler doping and structural design to enhance the output performance of electrospun PVDF-based piezoelectric fiber films. We divide the fillers into single filler and double fillers and make comments on the effects of various dopant materials on the performance and the underlying mechanism of the PVDF-based piezoelectric fiber film. The effects of highly oriented structures, core-shell structures, and multilayer composite structures on the output properties of PVDF-based piezoelectric nanofibers are discussed in detail. Furthermore, the perspectives and opportunities for PVDF piezoelectric nanofibers in the fields of health care, environmental monitoring, and energy collection are also discussed.

Recent Advances in Wearable Biosensors for Non-Invasive Detection of Human Lactate.

Lactate, a crucial product of the anaerobic metabolism of carbohydrates in the human body, is of enormous significance in the diagnosis and treatment of diseases and scientific exercise management. The level of lactate in the bio-fluid is a crucial health indicator because it is related to diseases, such as hypoxia, metabolic disorders, renal failure, heart failure, and respiratory failure. For critically ill patients and those who need to regularly control lactate levels, it is vital to develop a non-invasive wearable sensor to detect lactate levels in matrices other than blood. Due to its high sensitivity, high selectivity, low detection limit, simplicity of use, and ability to identify target molecules in the presence of interfering chemicals, biosensing is a potential analytical approach for lactate detection that has received increasing attention. Various types of wearable lactate biosensors are reviewed in this paper, along with their preparation, key properties, and commonly used flexible substrate materials including polydimethylsiloxane (PDMS), polyethylene terephthalate (PET), paper, and textiles. Key performance indicators, including sensitivity, linear detection range, and detection limit, are also compared. The challenges for future development are also summarized, along with some recommendations for the future development of lactate biosensors.

Preparation and performance study of a reactive polyurethane hot-melt adhesive/CS-Fe3O4 magnetic nanocomposite film/fabric.

Magnetic nanoparticles are attracting significant attention for their wide application as biomaterials and magnetic storage materials. As an environmentally friendly adhesive, reactive polyurethane hot-melt adhesive (PUR) is a biocompatible polymer with a wide range of applications. In this paper, chitosan (CS)-surface-modified magnetic Fe3O4 nanoparticles were synthesized by the sol-gel method. Surface modification of the Fe3O4 nanoparticles with CS enhanced their mechanical properties in PUR. The nanoparticles were characterized by Fourier transform infrared (FTIR) and X-ray diffraction (XRD) analyses, while their surface morphology was elucidated using scanning electron microscopy (SEM) and projection electron microscopy (TEM) techniques. Subsequently, PUR/CS-Fe3O4 magnetic nanocomposite films were prepared using an in situ method, wherein different amounts of CS-surface-modified magnetic Fe3O4 nanoparticles were doped into the PUR and coated on the films. The thermal, UV resistance and mechanical properties of the PUR/CS-Fe3O4 magnetic nanocomposite films were investigated by TGA, UV spectrometer and tensile testing. CS-Fe3O4 nanoparticles were successfully prepared using the sol-gel method and CS to modify the surface of the Fe3O4 nanoparticles. The results show that the mechanical properties and UV resistance of PUR/CS-Fe3O4 magnetic nanocomposites are improved by almost 50%, so the constructed PUR/CS-Fe3O4 magnetic nanocomposites have good UV-resistant properties and mechanical properties. The as-synthesized CS-Fe3O4 magnetic nanocomposites show great potential for application to mechanical and textile development.

Mechanical and Dielectric Properties of a Flexible Anisotropic Rubber-Based Composite.

Rubber-based conductive composites are widely used in sensors, wearable electronic devices and electromagnetic fields. In this work, by using the two-roll milling and hot-pressing process, chopped glass fiber (CGF) and graphene (Gr) as additives, and acrtlinitrile-brtadiene rubber (NBR) as the matrix, a series of anisotropic flexible rubber-based composites were prepared. Using this preparation method, both CGF and Gr additives were directly arranged in the material. When the content of CGF was 1 wt.%, the tensile strength in both the T and W directions of the material reached 27 MPa and 28 MPa, respectively. When the content of CGF was fixed at 1 wt.% and Gr was 1.5 wt.% and the elongation at break in both directions reached 328% and 347%. By focusing on the comparison of the dielectric differences in the T and W directions in the X band, it was found that the directional arrangement of the additives led to differences in the dielectric properties.

Self-Supported Reduced Graphene Oxide Membrane and Its Cu2+ Adsorption Capability.

Graphene stratiform membrane materials have been recently applied to heavy metal removal in aqueous systems via adsorption due to their high mechanical strength, chemical stability, and other properties. We applied reduced graphene oxide (rGO) alone as an adsorbent to remove heavy metal ions from wastewater. Self-supported rGO membrane was prepared using a green reduction method with sodium hydrosulfite. We used the Raman spectra to observe the structure of the rGO membrane. The morphology of the self-supported membrane was measured by a scanning electron microscope. The Cu2+ adsorption performance was measured in terms of pH, reaction time, metal ion concentration, and temperature. The maximum Cu2+ adsorption capacity of the rGO membrane was found to be 149.25 mg/g. The adsorption process followed a pseudo-second-order kinetic model, and adsorption isotherms were simulated by the Freundlich model.

Multiple-Jet Needleless Electrospinning Approach via a Linear Flume Spinneret.

There is a great limitation to improving the quality and productivity of nanofibers through the conventional single-needle method. Using needleless electrospinning technology to generate multiple jets and enhance the productivity of nanofibers has attracted lots of interest for many years. This study develops a novel linear flume spinneret to fabricate nanofibers. Multiple jets with two rows can be formed simultaneously on the surface of the spinneret. The solution concentration has a significant impact on the average nanofiber diameter compared with applied voltage and collection distance. The effects of different spinning process parameters on the productivity of nanofibers are investigated. High-quality nanofibers with small nanofiber diameter and error can be fabricated successfully. The average nanofiber diameter is 108 ± 26 nm. The average error is 24%. The productivity of nanofibers can reach 4.85 ± 0.36 g/h, which is about 24 times more than that of the single-needle method. This novel linear flume spinneret needleless electrospinning technology exhibits huge potential for mass production of nanofibers in the field of industrialization.

3D printing of silk fibroin-based hybrid scaffold treated with platelet rich plasma for bone tissue engineering.

3D printing/bioprinting are promising techniques to fabricate scaffolds with well controlled and patient-specific structures and architectures for bone tissue engineering. In this study, we developed a composite bioink consisting of silk fibroin (SF), gelatin (GEL), hyaluronic acid (HA), and tricalcium phosphate (TCP) and 3D bioprinted the silk fibroin-based hybrid scaffolds. The 3D bioprinted scaffolds with dual crosslinking were further treated with human platelet-rich plasma (PRP) to generate PRP coated scaffolds. Live/Dead and MTT assays demonstrated that PRP treatment could obviously promote the cell growth and proliferation of human adipose derived mesenchymal stem cells (HADMSC). In addition, the treatment of PRP did not significantly affect alkaline phosphatase (ALP) activity and expression, but significantly upregulated the gene expression levels of late osteogenic markers. This study demonstrated that the 3D printing of silk fibroin-based hybrid scaffolds, in combination with PRP post-treatment, might be a more efficient strategy to promote osteogenic differentiation of adult stem cells and has significant potential to be used for bone tissue engineering.

Large-Scale and Rapid Preparation of Nanofibrous Meshes and Their Application for Drug-Loaded Multilayer Mucoadhesive Patch Fabrication for Mouth Ulcer Treatment.

Electrospinning provides a simple and convenient method to fabricate nanofibrous meshes. However, the nanofiber productivity is often limited to the laboratory scale, which cannot satisfy the requirements of practical application. In this study, we developed a novel needleless electrospinning spinneret based on a double-ring slit to fabricate drug-loaded nanofibrous meshes. In contrast to the conventional single-needle electrospinning spinneret, our needless spinneret can significantly improve nanofiber productivity due to the simultaneous formation of multiple jets during electrospinning. Curcumin-loaded poly(l-lactic acid) (PLLA) nanofiber meshes with various concentrations and on the large scale were manufactured by employing our developed needleless spinneret-based electrospinning device. We systematically investigated the drug release behaviors, antioxidant properties, anti-inflammatory attributes, and cytotoxicity of the curcumin-loaded PLLA nanofibrous meshes. Furthermore, a bilayer nanofibrous composite mesh was successfully generated by electrospinning curcumin-loaded PLLA solution and diclofenac sodium loaded poly(ethylene oxide) solution in a predetermined time sequence, which revealed potent antibacterial properties. Subsequently, novel mucoadhesive patches were assembled by combining the bilayer composite nanofibrous meshes with (hydroxypropyl)methyl cellulose based mucoadhesive film. The multilayered mucoadhesive patch has excellent adhesion properties on the porcine buccal mucosa. Overall, our double-ring slit spinneret can provide a novel method to rapidly produce large-scale drug-loaded nanofibrous meshes to fabricate mucoadhesive patches. The multiple-layered mucoadhesive patches enable the incorporation of multiple drugs with different targets of action, such as analgesic, anti-inflammatory, and antimicrobial compounds, for mouth ulcer or other oral disease treatments.

Distribution of butyltins at dredged material dumping sites around the coast of China and the potential ecological risk.

Previous research has found butyltin pollution at dumping sites, which are the final fate of dredged material mostly originating from harbors and navigation systems. The distribution and impacts of butyltins were assessed in sediments at 12 dumping sites of China. Total butyltins (monobutyltin, dibutyltin, and tributyltin) concentrations ranged from 1.76 to 486.62 ng Sn g-1 dw. This study also presents evidence of considerable historic inputs of tributyltin (TBT) to Dumping sites 01, 05, 06, 08, 09 and 11, with evidence of heavier recent TBT input at Dumping site 04 and 10. The butyltin contamination at dumping sites was comparatively light and historic compared to research in other countries, but was more serious than other sea regions. TBT levels at Dumping site 09 probably have negative effects on biological systems. Overall, more attention should be paid to the level and impacts of butyltins in the sediment at dumping sites in China.

Enhanced photocatalytic activity of wool fibers having titanium dioxide nanoparticles formed inside their cortex.

A wool-TiO2 nanoparticle composite material having TiO2 nanoparticles both infiltrated in the matrix between macrofibrils inside cortical cells of wool fibers and grafted on the fiber surface is obtained in this study, and the wool-nanoparticle composite material is found to have highly photocatalytic activities with an extremely narrow band gap of 2.8 eV. The wool fibers are obtained using three successive technical steps: wool fibers are swollen by using lithium bromide, then saturated with tetrabutyl titanate ethanol solution and subsequently treated in boiling water. It was demonstrated that the chemical bonds formed between the as-synthesized TiO2 nanoparticles and the wool fibers swollen by lithium bromide include C-Ti4+(Ti3+), N-Ti4+(Ti3+), O-Ti3+, and S-Ti4+(Ti3+) bonds. The modified wool fibers have shown markedly improved photocatalytic efficiency due to their enhanced visible light absorption capability, which is much better than the (N-doped) TiO2 coated wool fibers. In contrast, TiO2 modified wool fibers swollen by using formic acid have poorer photoactivity, this might be due to the elimination of trivalent titanium between TiO2 nanoparticles and the wool fibers.

Preparation of electrospun core-sheath yarn with enhanced bioproperties for biomedical materials.

OBJECTIVES: To create a multifunctional medical material that combines the advantages of both nanofibers and macroyarns. RESULTS: A novel electrospinning-based approach was developed for creating polycaprolactone (PCL) nanofiber covered yarns (PCL-NCYs) in which polyglycolic acid multi-strand filaments (PGA-MFs) were used as the core. BALB/3T3 (mouse embryonic fibroblast cell line) cells were cultured on the PCL-NCYs substrate and cell morphology and proliferation were determined by methylthiazol tetrazolium (MTT) assay. Compared with PGA-MFs, PCL-NCYs had a higher porosity and tensile strength of 88 ± 8% and 348 ± 16 MPa and in particular, the porosity was four times higher. BALB/3T3 cells attached more easily onto the nanofiber structure and proliferated along the direction of nanofibers, indicating that PCL-NCYs can achieve better cell differentiation and proliferation. CONCLUSIONS: PCL-NCYs can be created by combining electrospinning covering and textile twisting, and have better mechanical property and higher porosity, and can be used as a novel scaffold in tissue engineering.