Enhancing piezoelectric effect of PVDF electrospun fiber through NiO nanoparticles for wearable applications

Flexible electrospun fiber-based piezoelectric nanogenerator (PENG) has attracted a lot of interest due to its ability of generating electrical energy from mechanical energy sources. The present work aims to improve the piezoelectric output of PENG devices based on electrospun polyvinylidene fluoride (PVDF) doped with nickel oxide nanoparticles (NiO NPs) in different concentrations (2, 4, 6, 8 and 10 wt.-%). Crystalline phase changes and β-crystalline content in electrospun fibers were evaluated using XRD and FTIR-ATR, respectively. Surface morphology and surface roughness of the electrospun fibers were observed using FE-SEM and AFM, respectively. The hydrophobic nature of the fibers was analyzed using a wettability test. PENG output voltage and short-circuit current performance of neat PVDF and PVDF doped with NiO (PN) composite electrospun fibers were calculated using a customized variable-pressure setup with an optimized force of 1.0 kgf and 1.0 Hz frequency. Neat PVDF-based PENG exhibited only 1.7 V and 0.7 μA, whereas, PVDF doped with 6 wt.-% NiO NP (PN-6) based PENG generated a high output voltage of 5.5 V and 1.83 μA current. The optimized PN-6 PENG device is demonstrated for use in wearable devices towards identifying certain body movements like tapping, wrist movement, walking and running.

Scaffold-Based Poly(Vinylidene Fluoride) and Its Copolymers: Materials, Fabrication Methods, Applications, and Perspectives

Tissue engineering involves implanting grafts into damaged tissue sites to guide and stimulate the formation of new tissue, which is an important strategy in the field of tissue defect treatment. Scaffolds prepared in vitro meet this requirement and are able to provide a biochemical microenvironment for cell growth, adhesion, and tissue formation. Scaffolds made of piezoelectric materials can apply electrical stimulation to the tissue without an external power source, speeding up the tissue repair process. Among piezoelectric polymers, poly(vinylidene fluoride) (PVDF) and its copolymers have the largest piezoelectric coefficients and are widely used in biomedical fields, including implanted sensors, drug delivery, and tissue repair. This paper provides a comprehensive overview of PVDF and its copolymers and fillers for manufacturing scaffolds as well as the roles in improving piezoelectric output, bioactivity, and mechanical properties. Then, common fabrication methods are outlined such as 3D printing, electrospinning, solvent casting, and phase separation. In addition, the applications and mechanisms of scaffold-based PVDF in tissue engineering are introduced, such as bone, nerve, muscle, skin, and blood vessel. Finally, challenges, perspectives, and strategies of scaffold-based PVDF and its copolymers in the future are discussed.

Revealing an important role of piezoelectric polymers in nervous-tissue regeneration: A review

Nerve injuries pose a drastic threat to nerve mobility and sensitivity and lead to permanent dysfunction due to low regenerative capacity of mature neurons. The electrical stimuli that can be provided by electroactive materials are some of the most effective tools for the formation of soft tissues, including nerves. Electric output can provide a distinctly favorable bioelectrical microenvironment, which is especially relevant for the nervous system. Piezoelectric biomaterials have attracted attention in the field of neural tissue engineering owing to their biocompatibility and ability to generate piezoelectric surface charges. In this review, an outlook of the most recent achievements in the field of piezoelectric biomaterials is described with an emphasis on piezoelectric polymers for neural tissue engineering. First, general recommendations for the design of an optimal nerve scaffold are discussed. Then, specific mechanisms determining nerve regeneration via piezoelectric stimulation are considered. Activation of piezoelectric responses via natural body movements, ultrasound, and magnetic fillers is also examined. The use of magnetoelectric materials in combination with alternating magnetic fields is thought to be the most promising due to controllable reproducible cyclic deformations and deep tissue permeation by magnetic fields without tissue heating. In vitro and in vivo applications of nerve guidance scaffolds and conduits made of various piezopolymers are reviewed too. Finally, challenges and prospective research directions regarding piezoelectric biomaterials promoting nerve regeneration are discussed. Thus, the most relevant scientific findings and strategies in neural tissue engineering are described here, and this review may serve as a guideline both for researchers and clinicians.

Nanocelluloses fine-tuned polyvinylidene fluoride (PVDF) membrane for enhanced separation and antifouling

To mitigate membrane fouling and address the trade-off between permeability and selectivity, we fabricated nanocellulose (NC) fine-tuned polyvinylidene fluoride (PVDF) porous membranes (NC-PVDFs) using phase inversion method through blending NCs with varied aspect ratios, surface charges and grafted functional groups. NC-PVDF presented rougher surface (increased by at least 18.3 %), higher porosity and crystallinity compared to PVDF membrane. Moreover, cellulose nanocrystals incorporated PVDF (CNC-PVDF) elevated membrane surface charge and hydrophilicity (from 74.3° to 71.7°), while 2,2,6,6-tetramethylpiperidine-1-oxyl-oxidized cellulose nanofibers modified PVDF (TCNF-PVDF) enhanced the porosity (from 25.0 % to 40.3 %) and tensile strength (63.6 % higher than PVDF). For separation performance, NC improved flux, rejection and fouling resistance due to facilitation of phase transition thermokinetics as pore-forming agent and increased hydrophilicity at both interface and pore wall. For water flux, NC-PVDFs (139-228 L·m-2·h-1) resulted in increased permeability compared to bare PVDF. CNC-PVDF membrane exhibited the highest water flux because of improved porosity, roughness and hydrophilicity. For bovine serum albumin (BSA) rejection, the removal rates of all NC-PVDFs were all above 90 %. Notably, TCNF-PVDF exhibited the most remarkable elevation of BSA rejection (95.1 %) owing to size exclusion and charge repulsion in comparison with PVDF.

Carbon nanoparticles fabricated microfilm: A potent filter for microplastics debased water

Microplastics were found to be the major pollutant across the globe. Plastic microbeads, like 0.5 mm, are very small and mainly used for exfoliation. The marine species cannot distinguish between their usual food and these microbeads. Microbeads have the potential to transfer up the food chain, which may lead to consumption by humans in the end. Activated carbon from inexpensive sources has greatly interested separation systems, especially in water treatment. In that view, carbon nanoparticles were produced, combined with polyvinylidene fluoride (PVDF) polymer, and used as a membrane to trap the microplastic particles. UV-Vis, FTIR, TEM, and powder X-ray diffraction (XRD) analysis confirmed the produced carbon nanoparticles. FT-RAMAN Spectroscopy studies, microbial viable cell count, and turbidity analysis followed the membrane preparation and post-treatment. The carbon nanoparticle fabricated nanofilm effectively eliminates the microbial count and microplastics and reduces the turbidity (0.13 NTU). This study confirms that the membrane effectively filters microplastics and other contaminants. Nowadays, nanofiltration technologies have been considered beneficial for eliminating microplastics to an efficiency of 95%. Further research is needed to determine a feasible low-cost, ecologically suitable, and effective solution to remove the microplastics in water.

Keggin-type polyoxometalate embedded polyvinylidene fluoride for thin film microextraction of organophosphorus pesticides

The present research is the first report on the application of Keggin-type phosphotungstic acid/polyvinylidene fluoride membrane. This compound as a simple, cost-effective and novel sorbent was used for the extraction and pre-concentration of two organophosphorus pesticides in real samples in the thin film solid-phase microextraction (TFME) method. TFME as one of the sub-branches of solid phase microextraction resolves the problems of SPME methods, including their limited absorption capacity. These extraction methods have a high surface-to-volume ratio, which improves their sensitivity compared to other geometries. Under optimal conditions, the limit of detections (LODs), the limit of quantifications (LOQs), and relative standard deviation (RSD) of this method varied in the ranges of 0.29-0.31 μg L-1, 0.96-1.0 μg L-1, and 3.9%-6.2%, respectively. This method showed a linear dynamic range (LDR) of 1.0-500 μg L-1 with a coefficient of determination (r2) above 0.9978. This promising method was used to analyze malathion and diazinon.

Encapsulation of tannic acid in polyvinylidene fluoride mediated electrospun nanofibers and its antibiofilm and antibacterial activities

In the past 15 years or more, interest in polymer-mediated nanofibers (NFs), a significant class of nanomaterials, has grown. Although fibers with a diameter of less than 1 mm are frequently commonly referred to as NFs, and are typically defined as having a diameter of less than several hundreds of nanometers. Due to the increased antibiotic resistance of many diseases nowadays, NFs with antibacterial activity are quite important. A flexible technique for creating NFs with the desired characteristics is called electrospinning. This research article describes how to make electrospun NFs of tannic acid (TA) with polyvinylidene fluoride (PVDF) as the template. As a result, the absorbance of the obtained NFs has been raised without forming any additional peaks in the spectral ranges. The obtained NF has a gradual increase in intensity, and the FT-IR data show that the TA is present in the NFs. FE-SEM images show that the NFs are discovered to be completely bead-free. Since TA reduced the viscosity of the spinning solution while marginally increasing solution conductivity, PVDF NFs have a greater average fiber diameter (AFD) than NFs of TA with PVDF, which is likely a result of the TA solutions in it. The findings showed that TA greatly decreased S. aureus and E. coli's ability to attach. The acquired NFs created in this work may have significant potential for reducing the pathogenicity of S. aureus and E. coli as well as their ability to build biofilms.

Incorporation of graphene oxide/titanium dioxide with different polymer materials and its effects on methylene blue dye rejection and antifouling ability

Exposure of synthetic dye, such as methylene blue (MB), in water bodies led to a serious threat to living things because they are toxic and non-degradable. Amongst the introduced dye removal methods, membrane separation process can be considered a powerful technique for treating dye contamination. However, this method commonly suffered from drawbacks, such as short membrane lifetime, low permeability and selectivity. To overcome these issues, graphene oxide (GO) and titanium dioxide (TiO₂) were used as additives to fabricate polyethersulfone (PES)- and polyvinylidene fluoride (PVDF)-based hybrid membranes via non-solvent-induced phase separation method. Prior to membrane fabrication, GO was synthesised via electrochemical exfoliation method assisted by customised triple-tail surfactant. The potential of PES- and PVDF-based hybrid membranes for wastewater treatment has been discussed widely. However, direct comparison between these two polymeric membranes is not critically discussed for MB dye separation application yet. Therefore, this study is aimed at evaluating the performance of different types of polymers (e.g. PES and PVDF) in terms of membrane morphology, properties, dye rejection and antifouling ability. Results showed that the incorporation of GO and TiO₂ alters the morphology of the fabricated membranes and affects dye rejection further, as well as their antifouling performance. In contrast with pristine membrane, PES-GO/TiO₂ and PVDF-GO/TiO₂ possessed high hydrophilicity, as indicated by their low contact angle (67.38° and 62.12°, respectively). Based on this study, PVDF-GO/TiO₂ showed higher porosity value (94.88%), permeability (87.32 L/m²hMPa) and MB rejection rate (92.63%), as well as flux recovery ratio value of > 100% as compared with others. Overall, the incorporation of GO and TiO₂ with PVDF polymer are proven to be effective hybrid materials of membrane fabrication for dye rejection application in the near future. The polymer material's intrinsic properties can affect the attributes of the fabricated membrane.

On PVDF composite as partially absorbable smart implants

For various orthopedic needs, several studies have been testified on non-absorbable implants, prepared with different metals/alloys, and composites. But yet little has been stated on the partially absorbable smart implants of thermoplastic composites for online health monitoring of veterinary patients. This article highlights the in-house development of affordable, polyvinylidene fluoride (PVDF) composite-based partially absorbable smart implants (with online sensing capability) for orthopedic needs in canines. Hydroxyapatite (HAp) and chitosan (CS) nanoparticles were reinforced in the PVDF matrix by a melt processing route with various weight proportions (wt.%) to fabricate a partially absorbable smart implant for the canine. The study suggests that the 8.0 wt.% HAp and 2.0 wt.% CS in PVDF is the superlative composition/proportion of reinforcement for preparing feedstock stock filaments (for 3D printing of partially absorbable smart implants), based on rheological, mechanical, thermal, dielectric, and voltage-current-resistance (V-I-R) characteristics. For the selected composition/proportion of PVDF composite, acceptable mechanical properties (such as modulus of toughness (MoT) 2.0 MPa, Young's modulus (E) 889 MPa), and dielectric properties (dielectric constant (ε_r) 9.6 at room temperature (30°C) and 20 MHz) for online sensing capabilities (for health monitoring) was observed. The results are braced by attenuated total reflection Fourier transform infrared (ATR-FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) analysis.

Prospective cohort study on mesh shrinkage measured with MRI after robot-assisted minimal invasive retrorectus ventral hernia repair using an iron-oxide-loaded polyvinylidene fluoride mesh

BACKGROUND

Mesh-reinforced ventral hernia repair is considered the gold standard treatment for all but the smallest of hernias. Human data on mesh shrinkage in the retrorectus mesh position is lacking. A prospective observational cohort study was performed to measure mesh shrinkage in robot-assisted minimal invasive retrorectus repair of ventral hernias.

METHODS

A cohort of 20 patients underwent a robot-assisted minimal invasive retrorectus repair of their ventral hernia. Magnetic resonance imaging (MRI) imaging was performed one month and thirteen months after implantation of an iron-oxide-impregnated polyvinylidene fluoride (PVDF) mesh to assess the decrease in mesh surface area. Inter-rater reliability among three radiologists regarding measurement of the mesh dimensions was analyzed. Quality of Life scoring was evaluated.

RESULTS

The inter-rater reliability between the radiologists reported as the intra-class correlations proved to be excellent for mesh width (ICC 0.95), length (ICC 0.98) and surface area (ICC 0.99). Between MRI measurements at one month and thirteen months postoperatively, there was a significant increase in mesh surface area (+ 12.0 cm², p = 0.0013) and mesh width (+ 0.8 cm, p < 0.001), while the length of the mesh remained unchanged (-0.1 cm, p = 0.754). Quality of Life Scoring showed a significant improvement in Quality of Life after one month and a further improvement at thirteen months (p < 0.001).

CONCLUSION

There was an excellent inter-rater reliability between three radiologists when measuring width, length, and surface area of an iron-oxide-impregnated PVDF mesh using MRI visualization. Mesh shrinkage was not observed, instead the effective mesh surface area and width of the mesh increased.

Effect of Polyvinylpyrrolidone on Polyvinylidene Fluoride/Hydroxyapatite- Blended Nanofiltration Membranes: Characterization and Filtration Properties

INTRODUCTION

The application of polyvinylidene fluoride (PVDF) as a filtration membrane is limited due to its hydrophobicity. This paper elaborated on the fabrication process of nanofiltration PVDF membrane incorporating various quantities of hydrophilic polyvinylpyrrolidone (PVP) and hydroxyapatite (HA) using a wet phase inversion method to improve its hydrophilicity.

METHODS

The membrane was fabricated by using the wet phase inversion method. It was then characterized in terms of water permeability, water contact angle, water content, surface energy, and surface porosity. Bacteria and Fe ions filtration was conducted to investigate the membrane filtration performance.

RESULTS

The PVDF/PVP/HA-blended membrane showed the highest water permeability (6,165 LMH/Bar), water content (45.2 %), and surface energy (104.1 mN/m) when 2 wt.% of PVP was introduced into the base polymer PVDF. This fabricated membrane, labeled as PVP 2.0, also showed the lowest contact angle (64°) and the highest surface porosity (42%).

CONCLUSION

Overall, the PVP introduction patents into the polymeric membrane doping solution potentially improves membrane hydrophilicity and permeability.

Polyvinylidene fluoride multi-scale nanofibrous membrane modified using N-halamine with high filtration efficiency and durable antibacterial properties for air filtration

HYPOTHESIS

Particulate matter (PM) pollution and the coronavirus (COVID-19) pandemic have increased demand for protective masks. However, typical protective masks only intercept particles and produce peculiar odors if worn for extended periods owing to bacterial growth. Therefore, new protective materials with good filtration and antibacterial capabilities are required.

EXPERIMENTS

In this study, we prepared multi-scale polyvinylidene fluoride (PVDF) nanofibrous membranes for efficient filtration and durable antibacterial properties via N-halamine modification.

FINDINGS

The N-halamine-modified nanofibrous membrane (PVDF-PAA-TMP-Cl) had sufficient active chlorine content (800 ppm), and the tensile stress and strain were improved compared with the original membrane, from 6.282 to 9.435 MPa and from 51.3 % to 56.4 %, respectively. To further improve the interception efficiency, ultrafine nanofibers (20-35 nm) were spun on PVDF-PAA-TMP-Cl nanofibrous membranes, and multi-scale PVDF-PAA-TMP-Cl nanofibrous membranes were prepared. These membranes exhibited good PM_0.3 interception (99.93 %), low air resistance (79 Pa), promising long-term PM_2.5 purification ability, and high bactericidal efficiency (>98 %). After ten chlorination cycles, the antibacterial efficiency against Escherichia coli and Staphylococcus aureus exceeded 90 %; hence, the material demonstrated highly efficient filtration and repeatable antibacterial properties. The results of this study have implications for the development of air and water filtration systems and multi-functional protective materials.

Electrically assisted solution blow spinning of PVDF/TPU nanofibrous mats for air filtration applications

In this study, pure polyvinylidene fluoride (PVDF), pure thermoplastic polyurethane (TPU), and PVDF/TPU blend nanofibers (1:3, 2:2, 3:1 ratios) were produced via electrically assisted solution blow spinning for air filtration applications. Scanning electron microscopy (SEM) analysis was conducted to investigate the diameters and morphology of nanofibers. The filtration performance of nanofibrous mats was examined by air filtration test with challenging with 0.26 ± 0.07 μm salt particles. Moreover, the flexibility and strength of the samples were determined via tensile tests. Results showed that pure TPU nanofibers had better mechanical properties, while pure PVDF nanofibers showed better filtration performance. However, 3PVDF/1TPU nanofibrous sample had high filtration efficiency (98.86%) close to pure PVDF (99.85%) and better flexibility (32.80% elongation) compared to pure PVDF (11.64% elongation).

Switchable Piezoelectricity of Polyvinylidene Fluoride Films Induced by Crystal Transition in Shape Memory Process

With the rapid development of wearable self-powered devices, the piezoelectric materials having deformable and switchable characteristics are attracting extensive attention. Herein, the cross-linked polyvinylidene fluoride (cPVDF) was fabricated through an alkali-catalyzed defluorination and chemical cross-linking method by introducing trimethylhexamethylenediamine (THDA). The system filled with 1 wt % THDA (CP1) was proved to possess balanced cross-linking density and crystallinity, which would play a crucial role in achieving a switchable piezoelectric effect. In comparison to pristine PVDF, the cross-linked one exhibited repeatable shape memory characterization due to restrained plastic deformation above the melting transition. Both the shape-fixing and shape-recovery ratios were stably maintained above 90%. More significantly, the thermo-mechanical program also triggered the α-β-α crystal transition accompanied by the variation of conformational entropy. The largest amount of β crystals was produced in the temporary shape, whereas the original and recovery shapes were dominated by α crystals. Such structural transition occurred repeatedly in the successive shape memory cycles, which thereby induced the periodic fluctuation of the piezoelectric constant (d₃₃). For the CP1 sample, its d₃₃ was only about 2 pC/N in the original and recovery shapes but reached up to 9.4 pC/N in the temporary shape. When the latter one was fabricated into a piezoelectric device, alternating voltage and current were generated by performing periodic impact force and were demonstrated to be capable of monitoring some pressure-related motions in real time without an external power supply. Finally, the switchable piezoelectric effect of the CP1 at different shape memory stages was further revealed through its electroactive response to the sinusoidal voltage stimulation. This work offers a special perspective in tailoring piezoelectric performance through the structural transition in shape memory progress, which is of great significance for enriching the types and applications of piezoelectric polymers.

O- and F-doped porous carbon bifunctional catalyst derived from polyvinylidene fluoride for sulfamerazine removal in the metal-free electro-Fenton process

Heteroatom-doped carbon materials can effectively activate H₂O₂ into •OH during the metal-free electro-Fenton (EF) process. However, information on bifunctional catalysts for the simultaneous generation and activation of H₂O₂ is scarce. In this study, O- and F-doped porous carbon cathode materials (PPCs) were prepared by the direct carbonization of polyvinylidene fluoride (PVDF) for sulfamerazine (SMR) removal in a metal-free EF process. The porous structure and chemical composition of the PPCs were regulated by the carbonization temperature. PPC-6 (carbonized at 600 °C) exhibited optimal electrocatalytic performance in terms of electrochemical H₂O₂ generation and activation owing to its high specific surface area, mesoporous structure, and optimum fractions of doped O and F. Excellent performance of the 2e^- oxygen reduction reaction was found with an H₂O₂ selectivity of 93.5% and an average electron transfer number of 2.13. An H₂O₂ accumulative concentration of 103.9 mg/L and an SMR removal efficiency of 90.1% were achieved during the metal-free EF process. PPC-6 was able to stably remove SMR over five consecutive cycles, retaining 92.6% of its original performance. Quantitative structure-activity relationship analysis revealed that doped oxygen functional groups contributed substantially to H₂O₂ generation, and semi-ionic C-F bonds with high electronegativity were the cause of the activation of H₂O₂ to •OH. These findings suggest that the PVDF-derived carbonaceous catalysts are feasible and desirable for metal-free EF processes.

Preparation and characterization of micro/nanocellulose reinforced PVDF/wood composites

Polyvinylidene fluoride (PVDF) is commonly used in the chemical, electronic, and petrochemical industries because of its chemical and physical attributes. This study aimed to make novel PVDF-based composite with a high loading of silanized wood powder and micro/nanocellulose fibers, where glycerol acts as both a dispersant and a plasticizer all-in-one composite application for the first time. The purpose was also extended to systematically investigate their mechanical properties and melt flow. Results have demonstrated the efficiency of utilizing the cellulose fibers in bio-composites. With the addition of 30 wt% of filling materials, When the content of silanized cellulose fibers in glycerol dispersion is 25 wt%, the flexural strength and tensile strength reach the maximum value 72.30 MPa and 52.28 MPa. The experimental results indicate that silanized micro/nanocellulose fiber-reinforced PVDF/wood composites are a promising composite formula to help improve performance and reduce costs. It is an excellent example of utilizing biomass resources as a renewable/recyclable, sustainable and low-cost material to reduce the use of petroleum-based polymer, and improve the mechanical properties of composites.

Effect of carbon nitride synthesized by different modification strategies on the performance of carbon nitride/PVDF photocatalytic composite membranes

Carbon nitride (CN)/polyvinylidene fluoride (PVDF) photocatalytic composite membrane (PCM) is considered as a promising candidate to improve the anti-fouling characteristic of conventional PVDF membrane and overcome the difficulty encountered during recovery of powder catalyst simultaneously. However, the effects of differently-modified CN on PCM and its mechanism are still unclear. In this study, bulk-CN (BCN), carbon defects CN (CCN), nitrogen defect CN (DCN), mesoporous CN (MCN), and nitrogen-rich CN (NCN) were incorporated into PVDF by phase inversion method. The influence of changes in the physical and chemical properties of CN, including hydrophilic groups, photocatalytic activity, and particle size, on the permeability, anti-fouling characteristic, and photocatalytic self-cleaning activity of CN/PVDF was systematically analyzed. The mechanism of excellent performance of PCM was revealed by experimental test and theoretical calculation. The flux of PCM was significantly improved by increasing the hydrophilic group on modified CN. However, the differences in particle size and interaction between different types of modified CN and PVDF chains endowed the CN/PVDF with different porosity. DCN/PVDF showed high porosity and hydrophilicity, leading to high water flux and rejection rate of 293.6 L (m² h)^-1 and 90.1%, respectively. Compared to pure PVDF, the flux recovery rate of DCN₃₀/PVDF increased by 27.6%, and the irreversible fouling decreased from 36.9% to 9.2%. The modified CN/PVDF showed excellent photocatalytic activity for the removal of cefotaxime (CFX) and E. coli. Owing to the narrow band gap of DCN, large specific surface area, and low photogenerated carrier recombination rate, the CFX removal rate reached 99% in 2 h, and E. coli inactivation achieved 3.7 log within 4 h via DCN₃₀/PVDF.

Improved anti-organic fouling and antibacterial properties of PVDF ultrafiltration membrane by one-step grafting imidazole-functionalized graphene oxide

At present, membrane fouling is a thorny issue that limits the development of polyvinylidene fluoride (PVDF) composite membrane, which seriously affects its separation performance and service lifespan. Herein, an imidazole-functionalized graphene oxide (Im-GO) with hydrophilicity and antibacterial performance was synthesized, and it was used as a modifier to improve the anti-organic fouling and antibacterial properties of PVDF membrane. The anti-organic fouling test showed that the maximum flux recovery ratios against bovine serum albumin and humic acid were 88.9% and 94.5%, respectively. Conspicuously, the grafted imidazole groups could effectively prevent the bacteria from growing on the membrane surface. It was gratifying that the antibacterial modifier Im-GO was almost not lost from the hybrid membranes even by the ultrasonic treatment, which was different from the conventional release-killing antibacterial agents. Owing to the long-term anti-organic fouling and antibacterial properties, Im-GO/PVDF hybrid membranes exhibit a great application potential in the fields of rough separation and concentration of biomedical products.

Preparation of polyvinylidene fluoride composite ultrafiltration membrane for micro-polluted surface water treatment

Blending modification of graphene oxide (GO) and deposition of silver carbonate (Ag₂CO₃) on the membrane surface by suction filtration was used to prepare polyvinylidene fluoride (PVDF) composite ultrafiltration (UF) membranes (denoted as PGA membranes). The effect of this strategy on the morphology and performance of the pure PVDF membrane was investigated. Owing to an increased hydrophilicity and the formation of a more open pore, the pollution resistance and permeability of the PGA membrane were improved. The pure water flux of the PGA-3 membrane (254 LMH) was increased to more than 2-fold compared to that of the neat PVDF membrane (126 LMH). In addition, the results of antifouling experiments showed that the flux recovery rate, flux decay rate, and antibacterial performance of the PGA-3 membrane was superior to those of the other membranes synthesized in this study. Finally, after conducting multi-cycle filtration experiments with lake water, the flux and recovery rate of the PGA-3 membrane was observed to be the highest, and the water quality of the lake water filtered by the PGA-3 membrane was the best. Thus, the above results indicate that this membrane modification strategy is extraordinarily effective in improving the antifouling properties and permeability of the PVDF UF membranes in practical applications.

High-performance anti-haze window screen based on multiscale structured polyvinylidene fluoride nanofibers

Indoor air quality (IAQ) has assumed new significance given the extensive amount of time spent indoor due to the coronavirus pandemic and particulate matter (PM) pollution. Accordingly, the development of window air filters to effectively intercept PM from outdoor air under natural ventilation conditions is an important research topic. However, most existing filters inevitably suffer from the compromise among filtration capability, transparency, and air permeability. In this study, we fabricate a high-performance transparent air filter to improve IAQ via natural ventilation. polyvinylidene fluoride (PVDF) superfine nanofibers of size 20-35 nm are prepared using extremely dilute solution electrospinning; a multi-scale nanofiber structure is then designed. By adjusting the ratio of PVDF superfine nanofibers (SNs) to PVDF coarse fibers (CNs), we balance the structure-performance relationship. Benefiting from the multiscale structural features that include a small pore size (0.72 μm) and high porosity (92.22%), the resulting filters exhibit excellent performance including high interception efficiency (99.92%) for PM_0.3, low air resistance (69 Pa), high transparency (∼80%) and stable filtration after 100 h of UV irradiation. This work describes a new strategy for the fabrication of nanofibers with true-nanoscale diameters and the design of high-performance air filters.

Continuous in situ portable SERS analysis of pollutants in water and air by a highly sensitive gold nanoparticle-decorated PVDF substrate

The increasingly serious environmental pollution worldwide has posed a great threat to the ecosystem and human health, and yet the development of portable in situ monitoring techniques that are sensitive to gaseous and water pollutants remains incomplete. Herein, we report a highly active surface-enhanced Raman spectroscopy (SERS) substrate fabricated by immobilizing gold nanoparticles (AuNPs) onto a polyvinylidene fluoride (PVDF) membrane for continuous in situ SERS detection of pollutants in water and atmosphere. 4-Mercaptobenzoic acid (4-MBA) was adopted as a probe molecule to evaluate the performance of the substrate, and the results indicate that the polymer-based flexible substrate features high sensitivity, uniformity, and repeatability. The fabricated PVDF/SERS substrate was integrated with a portable Raman spectrometer operating under both passing-by and passing-through modes. The integrated system accomplishes quantitative detection and real-time online monitoring of pH in a liquid environment with a response speed of less than 10 s and the rapid SERS response to gas molecules at a low concentration within 30 s. We also demonstrated the highly sensitive detection for mainstream smoke (MS) and sidestream (SS) of cigarette smoke and verified their differences in the main constituent which contributes to the harmful secondhand smoke in public. The developed portable Raman system has excellent application prospects in online liquid and gas environmental detection.

Degradation resistance of PVDF mesh in vivo in comparison to PP mesh

Mesh implant has been applied in hernia repair and urogynecological reconstruction. Polypropylene (PP) is now the most widely used material for non-resorbable mesh implants. A degradation phenomenon of PP mesh, which is apparent on the mesh surface as cracking, flaking and peeling, was discovered in the 1990's. This phenomenon of mesh implant has drawn attention because of mesh-related litigations. Polyvinylidene fluoride (PVDF), due to its high biocompatible performance, has been used since 2003 as an alternative material for non-resorbable mesh implants. Till now, no such degradation phenomenon of PVDF mesh has been reported, although limited study on PVDF mesh is available. In this paper, we researched the degradation of PVDF meshes taking the degradation of PP mesh as a reference. The meshes analysed in this study were received from a previous animal experiment. To expose the surface of explanted meshes, a tissue removing method with protease was used and the result of this cleaning process was tested by X-ray Photoelectron Spectroscopy (XPS). The morphological condition of the mesh surface was compared using Scanning Electron Microscopy (SEM) and the chemical condition concerning degradation was analysed through Fourier Transform Infrared Spectroscopy (FTIR). The surface condition of PVDF mesh after 3-, 6-, 12- and 24-month implantation was illustrated and compared with two types of PP meshes. XPS revealed an absence of nitrogen, confirming the successful removal of tissue residues using protease. SEM results presented no notable morphological surface change of the PVDF mesh and progressive surface cracking processes over time of both types of PP meshes. FTIR spectra of the implanted PVDF meshes had no considerable difference from the spectrum of the pristine mesh, while FTIR spectra of both types of PP meshes had extra chemical functional groups (carbonyl (CO) and hydroxyl (-OH) groups) increasing with implantation time, indicating progressive degradation. This study highlights the morphological and chemical stability of the PVDF mesh and demonstrates that the PVDF mesh is more resistant to degradation in comparison to the other two types of PP meshes.

Improved hydrophilicity and durability of polarized PVDF coatings on anodized titanium surfaces to enhance mineralization ability

Polyvinylidene fluoride (PVDF) coating with piezoelectric properties was prepared on surface of titanium-based materials to improve the bio inertness of the surface. The surface of titanium-based materials with piezoelectric properties similar to human bone promotes the growth of osteoblasts. However, not only new bone growth but also osseointegration are observed in the process of bone repair. The hydrophobicity of PVDF coating is unfavorable for mineralization. In this study, a PVDF coating was prepared on the titanium surface by using titanium dioxide nanotubes as a transition layer, and PVDF was attached to the wall of the titanium dioxide nanotube. The contact angle of the polarized PVDF coating decreases from 108° to 47°, which indicates that it changes from hydrophobic to hydrophilic due to the reduction in surface energy and the effect of negative surface charge. After the coating is left for a period of time, its contact angle only increases by 20° due to the loss of negative surface charge. After a physiological loading is applied to the polarized PVDF coating, the durability of its surface hydrophilicity is maintained. The mineralization ability of the polarized PVDF coating after being immersed in simulated body fluid (SBF) for 1, 7, and 14 days is significantly higher than that of the unpolarized sample. The increase in mineralization ability is mainly due to the hydrophilicity of the surface and the attraction of negative charges to calcium ions. Notably, after the polarized PVDF coating is subjected to physiological load, the mineralization ability is further improved after being immersed in SBF for 14 days, and its surface is covered with a layer of bone-like apatite. The high mineralization ability of the PVDF coating on the titanium surface after polarization can promote osseointegration and therefore shorten the bone repair cycle. Accordingly, this coating has potential application value in the clinical treatment of bone defect repair in middle-aged and elderly people.

Computer simulation of zwitterionic polymer brush grafted silica nanoparticles to modify polyvinylidene fluoride membrane

Dissipative particle dynamics (DPD) simulations was adopted to investigate the modification of polyvinylidene fluoride (PVDF) membrane by adding zwitterionic polymer brush poly(sulfobetaine methacrylate)- tetraethyl orthosilicate (PSBMA-TEOS) grafted silicon nanoparticles (SNPs) to the casting solution. The effects of polymer concentration and grafting architecture (PSBMA length and SNPs grafting ratio) on membrane morphology are discussed. When the polymer concentration reaches 40%, part of the SNPs is embedded in the membrane; the optimal polymer concentration is around 25-30%. In the SNPs system with the grafting ratio of 1, some SNPs are eluted into solution during phase separation. Compared with different grafting architectures, M_8-5, M_10-5 and M_12-5 system (M_x-y, where x represents the length of the zwitterionic polymer brush and y represents the grafting ratio of the silica nanoparticles) exhibited stable membrane morphologies. This work can provide guidance for the design and modification of organic-inorganic composite membrane and help understand the distribution of modified materials on the membrane surface.

Anti-biofouling microfiltration membranes based on 1-vinyl-3-butylimidazolium chloride grafted PVDF with improved bactericidal properties and vitro biocompatibility

Polyvinylidene fluoride (PVDF) porous membranes have been widely used as the filtration and separation industry. Herein, novel microfiltration membranes based on 1-vinyl-3-butylimidazolium chloride ([VBIm][Cl]) grafted PVDF (PVDF-g-[VBIm][Cl]) were prepared via the non-solvent induced phase separation method. The chemical composition and microstructure of PVDF-g-[VBIm][Cl] membranes were characterized by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, Scanning electron microscopy and Water contact angle measurements. The results showed that an increasing in [VBIm][Cl] grafting content leads to the increasing hydrophilicity and wetting capacity of the PVDF-g-[VBIm][Cl] porous membranes. The anti-biofouling properties of membranes were evaluated by measuring the water flux before and after Bovine serum albumin solution treatment. It was found that the modified membranes presented a good anti-biofouling property. The degree of irreversible flux loss caused by protein adsorption dramatically reduced from 42.1% to 2.9% compared with the pristine hydrophobic PVDF membranes. Meanwhile, these PVDF-g-[VBIm][Cl] membranes also exhibited excellent bactericidal properties against both gram-positive bacteria Staphylococcus saureus and gram-negative bacteria Escherichia coli, while PVDF membranes did not show any antibacterial activity. The vitro biocompatibility of the modified membranes was studied by hemolysis analysis, the platelet adhesion observation, thromboelastography assay and cytotoxicity assay. It was found that the incorporation of [VBIm][Cl] into PVDF membranes has less effect on the hemolysis and cytotoxicity of PVDF membranes. Furthermore, both hydrophilicity and charges of the membrane surface played important role in the adhesion and activation of platelet cells, which consequently affected the clotting process of whole blood. The membrane with appropriate [VBIm][Cl] grafting ratio (2.94 wt.%) exhibited good hemocompatibility with less blood coagulation effect. As an ultrafiltration membrane, PVDF-g-[VBIm][Cl] membranes have potential applications in the biomedical field due to the improved antibacterial property and biocompatibility.

Use of polyvinylidene fluoride (PVDF) meshes for ventral hernia repair in emergency surgery

PURPOSE

The implantation of non-absorbable meshes is the gold standard technique for ventral hernia (VH) repairs. However, emergency surgeries are often related to contaminated/infected fields, where the implantation of prosthetic materials may not be recommendable. Our aim was to evaluate the results of polyvinylidene fluoride (PVDF) meshes used for contaminated and/or complicated VH repairs in the acute setting.

METHODS

We conducted a retrospective analysis of patients with VH who underwent emergency surgery involving PVDF meshes, in a tertiary hospital (from November 2013 to September 2019). We analyzed postoperative complications and 1-year recurrence rates. We evaluated the relationships between contamination grade, mesh placement, infectious complications, and recurrences.

RESULTS

We gathered data on 123 patients; their mean age was 62.3 years, their mean BMI was 31.1 kg/m², and their mean CeDAR index was 51.6. 96.4% of patients had a grade 2-3 ventral hernia according to the Rosen index. The mean defect width was 8 cm (IQR 2-18). 93 cases (75.6%) were described as contaminated or dirty surgeries. A PVDF mesh was placed using an IPOM technique in 56.3% of cases, and via interposition location in 39.9%. The one-month recurrence rate was 5.7% and recurrence after one year was 19.1%. The overall mortality rate was 27.6%. Risk of recurrence was related to patients with a Rosen score over 2 (p < 0.001), as well as with postoperative SSI (p = 0.045). Higher recurrence rates were not related to PVDF mesh placement.

CONCLUSION

The use of PVDF meshes for emergency VH repairs in contaminated surgeries seems safe and useful, with reasonable recurrence rates, and acceptable infectious complication rates, similar to those published in the literature.

Experimental and numerical study on the performance of printed alginate/hyaluronic acid/halloysite nanotube/polyvinylidene fluoride bio-scaffolds

The growing usage of printed bio scaffolds in the field of regenerative medicine has made this field very important in biomedical engineering. In this regard, three-dimensional printing (3D) technique needs bio-materials with higher mechanical and biological performance. The biomaterials with high mechanical performance beside its bio compatibility are limited. A novel bio-material made of Alginate, Hyaluronic acid, Halloysite Nanotube and Polyvinylidene Fluoride was used and characterized for printing cartilage bio scaffolds through numerical studies. CaCl2 was used for crosslinking of biomaterial. Scanning Electron Microscopy, mechanical tests (tensile and compressive test), MTT assay were conducted for evaluating this novel biomaterial. Different structures of bio material were simulated for numerical studies. The numerical study was performed in ANSYS 18 using three parameter Mooney-Rivlin model. According to experimental and numerical results, Halloysite Nanotube increases the tensile and compressive strength of biomaterial up to 47%. Results show that biomaterial have good mechanical performance due to mechanical forces required for cartilage bio scaffolds besides its high biological performance. Polyvinylidene fluoride reduces the mechanical performance while increasing the cell viability. MTT assay results performed on day 0, day 2 and day 6 show increase in cell number to be about twice for biomaterial containing 40 mg/ml alginate, 40 mg/ml halloysite nanotube, 10 mg/ml hyaluronic acid and 1 w/v Polyvinylidene fluoride. Numerical simulation shows high mechanical performance of bio material in different scaffolds structure. The best structure of bio scaffolds was achieved with 0.4 mm nozzle diameter and 0.4 space between rows.

Multifunctional PVDF/CNT/GO mixed matrix membranes for ultrafiltration and fouling detection

Membrane fouling can be effectively addressed by modifying the membrane to realize anti-fouling capability together with real-time fouling detection. Here, we present the synthesis and water treatment testing of a promising candidate for this application, a composite membrane of polyvinylidene fluoride (PVDF) and functionalized carbon nano-materials prepared by a facile phase inversion method. The synergistic effect of oxidized multi-walled carbon nanotubes (OMWCNTs) and graphene oxide (GO) enabled better surface pore structures, higher surface roughness, hydrophilicity, and better antifouling property as compared with that of pristine PVDF membranes. The PVDF/OMWCNT/GO mixed matrix membranes (MMMs) achieved a high water flux of 125.6 L m^-2 h^-1 with high pollutant rejection rate, and their electrical conductivity of 2.11 × 10^-4 S cm^-1 at 100 kHz was sensitive to the amount of pollutant uptake. By using hybrid MMMs, we demonstrate simultaneous pollutant filtering and uptake monitoring, which is an important step in revolutionizing the water treatment industry.

A low-toxicity and high-efficiency deep eutectic solvent for the separation of aluminum foil and cathode materials from spent lithium-ion batteries

The separation of cathode materials from aluminum (Al) foil is a key issue worthy of attention in the process of resource utilization of spent lithium-ion batteries (LIBs). Traditional technologies for the Al foil and cathode materials separation have the disadvantages of the use of corrosive acid/alkali, release of HF hazards, and environment and healthy risks of the toxicity reagent. In this study, a low-toxicity, high-efficiency, and low-cost deep eutectic solvent (DES), choline chloride-glycerol, was synthesized and applied to solving the separation dilemma of Al foil and cathode materials in spent LIBs. The experimental results show that separation of the Al foil and cathode materials can be achieved under optimal conditions designed by the response surface method: heating temperature 190 ℃, choline chloride: glycerol molar ratio 2.3:1, and heating time 15.0 min; the peeling percentage of cathode material can reach 99.86 wt%. Mechanism analysis results confirm that the separation of Al foil and cathode materials was the result of the deactivation of the organic binder polyvinylidene fluoride (PVDF), which can be attributed to an alkali degradation process caused by the attack of the hydroxide of choline chloride on the acidic hydrogen atom in PVDF.

Polyvinylidene fluoride-Hyaluronic acid wound dressing comprised of ionic liquids for controlled drug delivery and dual therapeutic behavior

To improve the efficacy of transdermal drug delivery systems, the physical and chemical properties of drugs need to be optimized to better penetrate into the stratum corneum and to better diffuse into the epidermis and dermis layers. Accordingly, dual-biological function ionic liquids composed of active pharmaceutical ingredients were synthesized, comprising both analgesic and anti-inflammatory properties, by combining a cation derived from lidocaine and anions derived from hydrophobic nonsteroidal anti-inflammatory drugs. Active pharmaceutical ingredient ionic liquids (API-ILs) were characterized through nuclear magnetic resonance, cytotoxicity assay, and water solubility assay. All properties were compared with those of the original drugs. By converting the analgesic and anti-inflammatory drugs into dual-function API-ILs, their water solubility increased up to 470-fold, without affecting their cytotoxic profile. These API-ILs were incorporated into a bilayer wound dressing composed of a hydrophobic polyvinylidene fluoride (PVDF) membrane to act as a drug reservoir and a biocompatible hyaluronic acid (HA) layer. The prepared bilayer wound dressing was characterized in terms of mechanical properties, membrane drug uptake and drug release behavior, and application in transdermal delivery, demonstrating to have desirable mechanical properties and improved release of API-ILs. The assessment of anti-inflammatory activity through the inhibition of LPS-induced production of nitric oxide and prostaglandin E2 by macrophages revealed that the prepared membranes containing API-ILs are as effective as those with the original drugs. Cell adhesion of fibroblasts on membrane surfaces and cell viability assay confirmed improved the viability and adhesion of fibroblasts on PVDF/HA membranes. Finally, wound healing assay performed with fibroblasts showed that the bilayer membranes containing dual-function API-ILs are not detrimental to wound healing, while displaying increased and controlled drug delivery and dual therapeutic behavior. STATEMENT OF SIGNIFICANCE: This work shows the preparation and characterization of bilayer wound dressings comprising dual-biological function active pharmaceutical ingredients based on ionic liquids with improved and controlled drug release and dual therapeutic efficiency. By converting analgesic and anti-inflammatory drugs into ionic liquids, their water solubility increases up to 470-fold. The prepared bilayer wound dressing membranes have desirable mechanical properties and improved release of drugs. The prepared membranes comprising ionic liquids display anti-inflammatory activity as effective as those with the original drugs. Cell adhesion of fibroblasts on membrane surfaces and cell viability assays show improved viability and adhesion of fibroblasts on PVDF/HA membranes, being thus of high relevance as effective transdermal drug delivery systems.

Fabrication of layered membrane electrolytes with spin coating technique as anhydrous proton exchange membranes

Spin coating technique is a simple and effective method to fabricate layered membranes and it has been widely used in the field of energy storage and transformation, biomaterials and electronics. The aim of this work is to develop anhydrous proton exchange membranes (PEMs) based on cheap polymers bearing the simple structure with spin coating technique. Successful fabrication of anhydrous PEMs based on polyvinylidene fluoride (PVDF) polymer, cadmium telluride (CdTe) nanocrystals and phosphoric acid (PA) molecules has been demonstrated by identification of high and stable proton conductivity. Specifically, (PVDF-CdTe-PA)₅/85%PA membranes present the maximum proton conductivity of 7.70 × 10^-2 S/cm at 160 °C and 1.42 × 10^-2 S/cm at 140 °C lasting 620 h. The decreased proton conduction resistance is revealed from the drastic reduction of activation energy (Ea) owing to the layered structure and the adsorption of PA molecules. The introduction of CdTe nanocrystals to form the organic/inorganic composite membranes that is substantially more effective at improving proton conductivity and stiffness, showing great promise in solving the dilemma of proton conductivity and mechanical property. This study provides the support to exploit anhydrous PEMs with more cheap polymers using spin coating technique.

Preparation and characterization of PVDF/CaCO3 composite membranes etched by hydrochloric acid

This study aimed to improve the pore size, porosity, and hydrophobicity of polyvinylidene fluoride (PVDF) membranes for desalination by vacuum membrane distillation (VMD). New membranes were prepared via etching PVDF/calcium carbonate (CaCO₃) composite membranes using hydrochloric acid (HCl), depending on the chemical reaction of CaCO₃ and HCl. Etched membranes were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), differential scanning calorimetry (DSC), contact angle (CA), atomic force microscope (AFM), and scanning electron microscopy (SEM). The results showed that CaCO₃ of composite membranes was completely reacted by 1.5 mol/L HCl after composite membranes had been etched 90 min. The crystallinity of etched membranes was the same as that of PVDF/CaCO₃ composite membranes, and no new functional groups appeared in etched membranes, which indicated that etched membranes had good chemical stability. The surface roughness increased and led to the increase of contact angle, which means the hydrophobicity of etched membranes was enhanced. As a result, the increment of permeation flux had been improved in a VMD process. It was found that the maximum flux of etched membrane was enhanced and up to 1.65 times of composite membrane when the concentration of sodium chloride (NaCl) solution was 5.0 wt%, and the maximum flux reached up to 30.9 kg m^-2 h^-1.

Functionalized BaTiO3 enhances piezoelectric effect towards cell response of bone scaffold

Piezoelectric effect of polyvinylidene fluoride (PVDF) plays a crucial role in restoring the endogenous electrical microenvironment of bone tissue, whereas more β phase in PVDF leads to higher piezoelectric performance. Nanoparticles can induce the nucleation of the β phase. However, they are prone to aggregate in PVDF matrix, resulting in weakened nucleation ability of β phase. In this work, the hydroxylated BaTiO₃ nanoparticles were functionalized with polydopamine to promote their dispersion in PVDF scaffolds fabricated via selective laser sintering. On one hand, the catechol groups of polydopamine could form hydrogen bonding with the hydroxyl groups of the BaTiO₃. On the other hand, the amino groups of polydopamine were able to bond with CF group of PVDF. As a result, the functionalized BaTiO₃ nanoparticles homogeneously distributed in PVDF matrix, which significantly increased the β phase fraction from 46% to 59% with an enhanced output voltage by 356%. Cell testing confirmed the enhanced surface electric cues significantly promoted cell adhesion, proliferation and differentiation. Furthermore, the scaffolds exhibited enhanced tensile strength and modulus, which was ascribed to the rigid particle strengthening effect and the improved interfacial adhesion. This study suggested that the piezoelectric scaffolds shown a potential application in bone repair.

One-step tailoring surface roughness and surface chemistry to prepare superhydrophobic polyvinylidene fluoride (PVDF) membranes for enhanced membrane distillation performances

Superhydrophobic polyvinylidene fluoride (PVDF) membrane is a promising material for membrane distillation. Existing approaches for preparing superhydrophobic PVDF membrane often involve separate manipulation of surface roughness and surface chemistry. Here we report a one-step approach to simultaneously manipulate both the surface roughness and surface chemistry of PVDF nanofibrous membranes for enhanced direct-contact membrane distillation (DCMD) performances. The manipulation was realized in a unique solvent-thermal treatment process, during which a treatment solution containing alcohols was involved. We demonstrate that by using different chain-length alcohols in the treatment solvent, surface roughness can be promoted by creating nanofin structures on the PVDF nanofibers using an alcohol which has moderate affinity with PVDF. Meanwhile, surface chemistry can be tuned by adjusting the fraction distribution of crystal phases (nonpolar α phase and polar β phase) in the membrane using different alcohols. PVDF membranes with different surface wettabilities were used to evaluate the effects of surface roughness and surface energy on the DCMD performances. Combining both low surface energy and multi-scale surface roughness, pentanol-treated PVDF membrane achieved best anti-water property (water contact angle of 164.1° and sliding angle of 8.1°), and exhibited superior water flux and enhanced anti-wetting ability to low-surface-tension feed in the DCMD application.

Fabrication of a novel polyvinylidene fluoride membrane via binding SiO2 nanoparticles and a copper ferrocyanide layer onto a membrane surface for selective removal of cesium

A novel polyvinylidene fluoride (PVDF) membrane was fabricated through chemical binding SiO₂ nanoparticles (NPs) and copper ferrocyanide (CuFC) layers onto a membrane surface simultaneously to improve the removal efficiency of Cs. The results indicated that the SiO₂ NPs were strongly deposited onto the membrane surface, and the CuFC layer was firmly attached on the surface of SiO₂ NPs and the membrane. CuFC/SiO₂/PVDF membrane remained stable after the acidic solution and sonication stress treatments. CuFC/SiO₂/PVDF membrane showed good permeate flux and high selectivity on removal of Cs, and adsorbing capacity reached 1440.4 mg m^-2 for Cs. The membrane remained high rejections of Cs in a wide pH, and could be regenerated well by H₂O₂ and N₂H₄. Selective adsorption and electrostatic interaction govern the rejection of Cs. The coexisting cations decreased the rejection of Cs mainly in accordance to the order of cations' hydration radii as K⁺ > Na⁺ > Ca²⁺ > Mg²⁺. In addition, the rejection of Cs could still reach 99.4% in 8 h in the filtration of humic acid solution and natural surface water. The membrane could removal of Cs from water effectively by directly rapid filtration, suggesting it can be applied as promising technology for radioactive wastewater treatment.

Laparoscopic bilateral cervicosacropexy: introduction to a new tunneling technique

INTRODUCTION AND HYPOTHESIS

To elevate and suspend the apical end of the vagina, the uterosacral ligaments (USL) were replaced by polyvinylidene fluoride (PVDF) structures. These PVDF structures were placed in the peritoneal folds of the USL at the pelvic wall to mimic the lateral and backward tension and to avoid rectal obstruction. A special tunneling device was used, which allowed the semi-circular placement of the structure without destroying the peritoneum.

METHODS

A 59-year-old woman with mixed urinary incontinence and apical prolapse (pelvic organ prolapse quantification system, POP-Q, stage 2) of the uterus underwent laparoscopic bilateral USL replacement. USLs were replaced by PVDF structures by performing the cervicosacropexy (CESA) technique using a semi-circular tunneling device.

RESULTS

Apical support was restored (POP-Q stage 0), and the patient was continent thereafter. The tunneling device was pulled through the peritoneal folds of the USLs toward the cervix. The new USL structures were brought to their physiological position. The new technique did not lead to any complications and did not cause any side effects during 1-year follow-up.

CONCLUSIONS

Restoration of apical prolapse and urinary continence was achieved by bilateral USL replacement using a semi-circular tunneling device that was inserted through the lateral abdominal trocar incision.

Self-Polarization of PVDF Film Triggered by Hydrophilic Treatment for Pyroelectric Sensor with Ultra-Low Piezoelectric Noise

Polyvinylidene fluoride (PVDF) films possess multifunctional ability for piezo/pyro/ferroelectronic applications. One critical challenge of the traditional techniques is the complicated fabrication process for obtaining the poled films. In this work, the PVDF film is facilely prepared by the solution cast on hydrophilically treated substrates. The obtained PVDF films exhibit fairly good pyroelectricity comparable to those fabricated by thermal poling, indicating the film is self-polarized. This result is attributed to the hydrogen-bonding-induced orderly arrangement of the first sub-nanolayer at the bottom, which serves as a "seed layer" and triggered alignment of the rest of the film in a layer-by-layer approach. Additionally, to suppress the piezoelectric noise, a pyroelectric sensor with a novel bilayer structure is developed using the as-prepared PVDF film. Compared with the conventional monolayer sensor, the signal-to-noise ratio of the bilayer one is drastically improved to 38 dB from 18 dB. The above results provide great possibilities for achieving a high-performance wearable pyroelectric sensor with reduced cost and simple procedures.

N, F-Codoped Microporous Carbon Nanofibers as Efficient Metal-Free Electrocatalysts for ORR

Currently, the oxygen reduction reaction (ORR) mainly depends on precious metal platinum (Pt) catalysts. However, Pt-based catalysts have several shortcomings, such as high cost, scarcity, and poor long-term stability. Therefore, development of efficient metal-free electrocatalysts to replace Pt-based electrocatalysts is important. In this study, we successfully prepared nitrogen- and fluorine-codoped microporous carbon nanofibers (N, F-MCFs) via electrospinning polyacrylonitrile/polyvinylidene fluoride/polyvinylpyrrolidone (PAN/PVDF/PVP) tricomponent polymers followed by a hydrothermal process and thermal treatment, which was achieved for the first time in the literature. The results indicated that N, F-MCFs exhibit a high catalytic activity (E_onset: 0.94 V vs. RHE, E_1/2: 0.81 V vs. RHE, and electron transfer number: 4.0) and considerably better stability and methanol tolerance for ORR in alkaline solutions as compared to commercial Pt/carbon (Pt/C, 20 wt%) catalysts. Furthermore, in acidic media, N, F-MCFs showed a four-electron transfer pathway for ORR. This study provides a new strategy for in situ synthesis of N, F-MCFs as highly efficient metal-free electrocatalysts for ORR in fuel cells.

Fabrication of PVDF nanofibrous hydrophobic composite membranes reinforced with fabric substrates via electrospinning for membrane distillation desalination

To improve the mechanical properties of the electrospun nanofibrous membrane, the nonwoven fabrics and spacer fabrics were employed as support substrates to fabricate polyvinylidene fluoride (PVDF) nanofibrous composite membranes. The influences of the substrate on membrane morphology, hydrophobicity, pore size and pore size distribution, porosity, mechanical strength and permeability were comprehensive evaluated. The electrospun composite membranes had a three dimension bead-fiber interconnected open structure and a rough membrane surface. The membrane surface presented a multilevel re-entrant structure and all the water contact angles were above 140°. In contrast with the pure PVDF nanofibrous membrane, the stress at break and the elastic modulus of the composite membranes increased by 4.5-16 times and 17.5-37 times, respectively. Since the spacer fabrics had less resistance to mass transfer, the membranes composited with spacer fabrics exhibited greater permeate fluxes compared with the composite membranes with the nonwoven fabrics as substrates. During the membrane distillation test, the highest permeate flux was up to 49.3kg/m²/hr at the feed temperature of 80°C. The long-time and repeat operation of membrane distillation desalination indicated the fabricated membrane with a good resistance to scaling and wetting. The results suggested the potential of the electrospun composite membrane for membrane distillation application.

Chitin nanowhisker - Inspired electrospun PVDF membrane for enhanced oil-water separation

The requirement of promoting a revolution in filtration technology has led to growing devotion in advanced functional materials such as electrospun membranes for filtering devices as a solution for providing water at lower energy costs. In this study, electrospun polyvinylidene fluoride membranes were fabricated by reinforcing 0.5 and 1 wt. % of chitin nanowhiskers in order to improve their thermal stability, mechanical properties, pure water flux and oil-water filtration performance for the possible application as filtration membranes. Morphological analysis revealed the porous and fibrous structure of membranes which confirmed by BET surface area analysis. Incorporation of chitin nanowhiskers improved the mechanical properties of the membranes such as elongation at break and tensile strength (specifically at 1 wt. % of chitin nanowhisker) while resulted in substantial enhancement of their thermal properties. Furthermore, polyvinylidene fluoride/chitin nanowhisker membranes showed enhanced oil-water separation ability, while reinforcement of chitin nanowhisker led to increase pure water flux rate, which measured as a crucial point in filtration membranes. The oil-water separation results compared with a commercial polyvinylidene fluoride membrane and the results signified the potential of electrospun polyvinylidene fluoride/chitin nanowhisker to be used for filtration application.

Tackling membrane fouling in microalgae filtration using nylon 6,6 nanofiber membrane

Microalgae technology, if managed properly, has promising roles in solving food-water-energy nexus. The Achilles' heel is, however, to lower the costs associated with cultivation and harvesting. As a favorable technique, application of membrane process is strongly limited by membrane fouling. This study evaluates performance of nylon 6,6 nanofiber membrane (NFM) to a conventional polyvinylidene fluoride phase inverted membrane (PVDF PIM) for filtration of Chlorella vulgaris. Results show that nylon 6,6 NFM is superhydrophilic, has higher size of pore opening (0.22 vs 0.18 μm) and higher surface pore density (23 vs 18 pores/μm²) leading to higher permeance (1018 vs 493 L/m²hbar) and better fouling resistant. Such advantages help to outperform the filterability of PVDF PIM by showing much higher steady-state permeance (286 vs 120 L/m²hbar), with comparable biomass retention. In addition, unlike for PVDF PIM, imposing longer relaxation cycles further enhances the performance of the NFM (i.e., 178 L/m²hbar for 0.5 min and 236 L/m²hbar for 5 min). Overall findings confirm the advantages of nylon 6,6 NFM over the PVDF PIM. Such advantages can help to reduce required membrane area and specific aeration demand by enabling higher flux and lowering aeration rate. Nevertheless, developments of nylon 6,6 NFM material with respect to its intrinsic properties, mechanical strength and operational conditions of the panel can still be explored to enhance its competitiveness as a promising fouling resistant membrane material for microalgae filtration.

Polyvinylidene Fluoride Alters Inflammatory Responses by Activation-induced Cell Death in Macrophages

Carbon nanotubes (CNTs) are nanomaterials that have been employed in generating diverse materials. We previously reported that CNTs induce cell death in macrophages, possibly via asbestosis. Therefore, we generated CNT-attached polyvinylidene fluoride (PVDF), which is an established polymer in membrane technology, and then examined whether CNT-attached PVDF is immunologically safe for medical purposes compared to CNT alone. To test this, we treated RAW 264.7 murine macrophages (RAW cells) with CNT-attached PVDF and analyzed the production of nitric oxide (NO), a potent proinflammatory mediator, in these cells. RAW cells treated with CNT-attached PVDF showed reduced NO production in response to lipopolysaccharide. However, the same treatment also decreased the cell number suggesting that this treatment can alter the homeostasis of RAW cells. Although cell cycle of RAW cells was increased by PVDF treatment with or without CNTs, apoptosis was enhanced in these cells. Taken together, these results indicate that PVDF with or without CNTs modulates inflammatory responses possibly due to activation-induced cell death in macrophages.

A Self-Powered Breath Analyzer Based on PANI/PVDF Piezo-Gas-Sensing Arrays for Potential Diagnostics Application

The increasing morbidity of internal diseases poses serious threats to human health and quality of life. Exhaled breath analysis is a noninvasive and convenient diagnostic method to improve the cure rate of patients. In this study, a self-powered breath analyzer based on polyaniline/polyvinylidene fluoride (PANI/PVDF) piezo-gas-sensing arrays has been developed for potential detection of several internal diseases. The device works by converting exhaled breath energy into piezoelectric gas-sensing signals without any external power sources. The five sensing units in the device have different sensitivities to various gas markers with concentrations ranging from 0 to 600 ppm. The working principle can be attributed to the coupling of the in-pipe gas-flow-induced piezoelectric effect of PVDF and gas-sensing properties of PANI electrodes. In addition, the device demonstrates its use as an ethanol analyzer to roughly mimic fatty liver diagnosis. This new approach can be applied to fabricating new exhaled breath analyzers and promoting the development of self-powered systems.

Sandwich-structured composite fibrous membranes with tunable porous structure for waterproof, breathable, and oil-water separation applications

HYPOTHESIS

In general, microporous membranes with waterproofness, breathability, and oil-water separation performance are prepared from hydrophobic raw materials and demonstrated to exhibit an interconnected porous structure. Hence, constructing porous and gradient-structured composite membranes by integrating robust hydrophobic/lipophilic polyvinylidene fluoride (PVDF) and breathable polyurethane (PU) microporous membranes could help realize a selective separation process.

EXPERIMENT

Here, novel polyvinylidene fluoride-carbon nanotube/polyurethane/polyvinylidene fluoride-carbon nanotube (PVDF-CNT/PU/PVDF-CNT) sandwich-structured microporous membranes were fabricated by sequential electrospinning. The influence of the thickness ratios of PVDF/PU/PVDF and carbon nanotube (CNT) content on the fibrous construction, porous structure, and wettability of the composite membranes was systematically studied by scanning electron microscopy (SEM), pore size, porosity and contact angle. Significantly, the effect of the fibrous construction, porous structure, and wettability on the waterproofness, breathability, and oil-water separation ability of the composite membranes was investigated.

FINDINGS

The novel separation system proved the 'complementary effect' between the PVDF and PU membranes. Further, because of the elaborate gradient construction, superior porous structure, and robust hydrophobicity-oleophilicity, the resultant membranes exhibited moderate waterproofness (38 kPa) and excellent breathability (8.63 kg m^-2 d^-1), and oil-water separation, confirming that they could be promising alternatives for numerous practical applications, such as protective clothing, treatment of oil-contaminated water, and membrane distillation.

Improved PVDF membrane performance by doping extracellular polymeric substances of activated sludge

Polyvinylidene fluoride (PVDF) membrane has been widely applied in water and wastewater treatment because of its high mechanical strength, thermal stability and chemical resistance. However, the hydrophobic nature of PVDF membrane makes it readily fouled, substantially reducing water flux and overall membrane rejection ability. In this work, an in-situ blending modifier, i.e., extracellular polymeric substances (EPS) from activated sludge, was used to enhance the anti-fouling ability of PVDF membrane. Results indicate that the pure water flux of the membrane and its anti-fouling performance were substantially improved by blending 8% EPS into the membrane. By introducing EPS, the membrane hydrophilicity was increased and the cross section morphology was changed when it interacted with polyvinl pyrrolidone, resulting in the formation of large cavities below the finger-like pores. In addition, the fraction of pores with a size of 100-500 nm increased, which was also beneficial to improving membrane performance. Surface thermodynamic calculations indicate the EPS-functionalized membrane had a higher cohesion free energy, implying its good pollutant rejection and anti-fouling ability. This work provides a simple, efficient and cost-effective method to improve membrane performance and also extends the applications of EPS.

Polydiacetylene-coated polyvinylidene fluoride strip aptasensor for colorimetric detection of zinc(II)

We report a new polydiacetylene (PDA) sensor strip for simple visual detection of zinc ions in aqueous solution. The specificity of this sensor comes from Zn²⁺ DNA aptamer probes conjugated onto PDA. Effects of aptamer length and structure on the sensitivity of PDA's color transition were first investigated. PDA conjugated with the optimal aptamer sequence was then coated onto a strip of polyvinylidene fluoride membrane and photopolymerized by UV exposure. The newly developed sensor successfully exhibited a blue-to-red chromatic change in a semi-quantitative manner in response to zinc ions. No discernable change was observed in solutions containing other common ions. Advantages of this sensor include its ease of fabrication, high specificity, and equipment-free detection, all of which are desirable for in-field applications and use in resource-limited settings.

Tissue reaction to urogynecologic meshes: effect of steroid soaking in two different mesh models

INTRODUCTION AND HYPOTHESIS

Steroid soaking may decrease mesh-triggered inflammatory reaction in tissue. We aimed to investigate the tissue reaction to a steroid-soaked mesh material and an unsoaked mesh material in the rat model.

METHODS

Neutral and steroid-soaked type I macroporous polypropylene (PP) monofilament and polyvinylidene fluoride (PVF) mesh materials were implanted on the rectus abdominis muscle of 20 mature Wistar albino rats. Animals were divided into four groups: PP mesh with steroid (PP-S), PP mesh without steroid, PVF mesh with steroid (PVF-S), and PVF mesh without steroid. The rats were killed after 12 weeks, and histologic, immunohistochemical and electron microscopic examinations were performed. For immunohistochemical analysis, polyclonal rabbit anti-mouse CD3, rabbit anti-mouse CD68, rabbit anti-mouse CD15, and rabbit anti-mouse CD34 antibodies were used for the detection of lymphocytes, macrophages, polymorphonuclear leukocyte foreign body giant cells, and fibromyocyte stem cells, respectively. Samples were stained with hematoxylin and eosin for the histologic evaluation of inflammation and with Masson's trichrome stain for the evaluation of collagen deposition. Pore size and mesh ultrastructure were evaluated by electron microscopy.

RESULTS

Expression of CD3 was lower in the PVF, PVF-S and PP-S groups, and expression of CD34 was higher in the PVF-S and PP-S groups than in the PP groups (p < 0.05). Collagen deposition was lower in the PVF, PVF-S and PP-S groups (p < 0.05). Histologically, the intensity of inflammation was lower in the PVF-S and PP-S groups than in the PP mesh group (p < 0.05). There were no significant differences among the groups in terms of pore size and mesh ultrastructure on electron microscopic examination (p > 0.05).

CONCLUSIONS

PVF mesh induces less inflammation than PP mesh, and in both mesh types steroid soaking further decreases inflammation without changing the pore size.

Constructing a novel zwitterionic surface of PVDF membrane through the assembled chitosan and sodium alginate

A novel zwitterionic surface of PVDF membrane with significantly improved antifouling properties was prepared though pressure-assisted layer by layer self-assembly method based on the electrostatic interactions of chitosan (CS), sodium alginate (SA) and polyfunctional lysine. For the modified C-S-C-S-L membrane, the contact angle decreased to 35°, the bovine serum albumin (BSA) adsorption mass of static fouling on the membrane surface decreased to 10μg/cm(2), and the secondary water flux recovery rate (FRR) of dynamic fouling of BSA and humic acid (HA) pollutants increased to 98% and 99%, respectively, exhibiting excellent antifouling performance. The results demonstrated that using charged bio-macromolecules and amino acids to build zwitterionic surface was effective and convenient to change the interface properties of the separation membrane through the pressure-assisted self-assembly modification method, and provided a new way for the industrial scale hydrophilic modification of hydrophobic porous membrane materials.

Nanofibrous biomimetic mesh can be used for pelvic reconstructive surgery: A randomized study

BACKGROUND

Implantation of nonabsorbable polypropylene (PP) mesh in the vagina is the main surgical treatment for pelvic organ prolapse (POP); however, clinical outcomes remain controversial and far from satisfactory. In particular, reducing the exposure or erosion of vaginal implants to obtain improved functional reconstruction is challenging. There is an urgent need for the development of new materials and/or products for POP treatment. A nanofibrous biomimetic mesh was recently developed to address this issue.

OBJECTIVE

In this study, the basic properties of the newly developed mesh, including structural characteristics, mechanical properties, biological response of human umbilical cord mesenchymal stem cells in vitro, and tissue regeneration and biocompatibility in vivo, were evaluated and compared with those of Gynemesh™PS.

METHODS

Scanning electron microscopy and uniaxial tensile methods were used to evaluate microstructure and mechanical properties, respectively. Mesenchymal stem cell growth on the meshes was observed by fluorescence microscopy to visualize the expression of enhanced red fluorescent protein. Twenty-four mature female Sprague Dawley rats were randomly assigned to two groups: group 1 (nanofibrous biomimetic mesh, Medprin, Germany, n=12) and group 2 (Gynemesh(TM)PS, Ethicon, USA; n=12). The posterior vaginal wall was incised from the introitus, and the mesh was then implanted. Three implants of each type were tested for 1, 4, 8 and 12 weeks. Connective tissue organization, inflammation, vascularization, and regenerated tissue were histologically assessed.

RESULTS

The nanofibrous biomimetic mesh is a relatively heavy material and exhibited lower porosity than Gynemesh(TM)PS. The new mesh was stiffer than Gynemesh(TM)PS (p<0.001) but supported human umbilical cord mesenchymal stem cell attachment. Erosion of the grafts did not occur in any animal. The nanofibrous biomimetic mesh was encapsulated by a thicker layer of connective tissue and was associated with significantly greater inflammatory scores compared with Gynemesh(TM)PS. At 12 weeks, the vascularization of the new mesh was greater than that of Gynemesh(TM)PS (p<0.05). No significant difference in the thickness of the smooth muscle layer following implantation was observed between the two groups (p>0.05).

CONCLUSIONS

The nanofibrous biomimetic mesh is a candidate for reinforcing pelvic reconstruction. The mesh could be improved by decreasing its weight and stiffness and increasing its porosity. This mesh could serve as a carrier for stem cells in future regenerative medicine and tissue engineering research.

Dye removal by surfactant encapsulated polyoxometalates

A novel surfactant encapsulated polyoxometalate (SEP) has been synthesized by using a simple ion-exchange reaction. The prepared SEP complex was found to self-assemble into nanospherical particles whose morphology and component were characterized by TEM and XPS. The SEP was further incorporated into polyvinylidene fluoride (PVDF) to fabricate SEP incorporated composite membrane (SEP-M). Both the SEP and SEP-M exhibited excellent dye removal activities, which is for the first time reported as an intriguing property of the SEP. A regeneration scheme for SEP-M was successfully proposed without any loss of dye removal efficiency. Detailed mechanism studies were carried out to elucidate the nature of dye decolorization. Ion exchange was revealed to play a dominant role in the dye removal process. The current research not only renders a new example for the simple and direct synthesis of SEP but more importantly provides an efficient dye removal methodology.