Preparation and properties of antibacterial PVDF composite thin films

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.

Natural Clay-Modified Piezocatalytic Membrane for Efficient Removal of Coliform Bacteria from Wastewater

In the modern era, water pollution, especially from industries, agricultural farms, and residential areas, is caused by the release of a large scale of heavy metals, organic pollutants, chemicals, etc., into the environment, posing a serious threat to aquatic ecosystems and nature. Moreover, untreated sewage waste discharged directly into nearby water bodies can cause various diseases to mankind due to the high load of fecal coliform bacteria. This work demonstrates the development of a biocompatible, cost-effective, highly robust, efficient, flexible, freestanding, and reusable membrane using naturally formed biocompatible kaolinite clay-doped poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) for effective piezodynamic destruction of coliform bacteria. In this study, Escherichia coli (E. coli) and Enterococcus faecalis (E. faecalis) have been used to evaluate the mechanical stimulus-responsive antibacterial efficacy of the nanocomposite membrane. The membrane can effectively eradicate nearly 99% viable E. coli and 97% E. faecalis within a span of 40 min under mechanical stimulation (soft ultrasound ∼15 kHz). To further understand the mechanism, an evaluation of reactive oxygen species and bacterial FESEM was performed. These studies revealed that bacterial cells suffered severe visible cell damage after 40 min of piezocatalysis, elucidating the fact that the synthesized membrane is capable of producing a superior piezodynamic antibacterial effect.

Smart and Multifunctional Materials Based on Electroactive Poly(vinylidene fluoride): Recent Advances and Opportunities in Sensors, Actuators, Energy, Environmental, and Biomedical Applications

From scientific and technological points of view, poly(vinylidene fluoride), PVDF, is one of the most exciting polymers due to its overall physicochemical characteristics. This polymer can crystalize into five crystalline phases and can be processed in the form of films, fibers, membranes, and specific microstructures, being the physical properties controllable over a wide range through appropriate chemical modifications. Moreover, PVDF-based materials are characterized by excellent chemical, mechanical, thermal, and radiation resistance, and for their outstanding electroactive properties, including high dielectric, piezoelectric, pyroelectric, and ferroelectric response, being the best among polymer systems and thus noteworthy for an increasing number of technologies. This review summarizes and critically discusses the latest advances in PVDF and its copolymers, composites, and blends, including their main characteristics and processability, together with their tailorability and implementation in areas including sensors, actuators, energy harvesting and storage devices, environmental membranes, microfluidic, tissue engineering, and antimicrobial applications. The main conclusions, challenges and future trends concerning materials and application areas are also presented.

An Intelligent Wearable Filtration System for Health Management

To develop intelligent wearable protection systems is of great significance to human health engineering. An ideal intelligent air filtration system should possess reliable filtration efficiency, low pressure drop, healthcare monitoring function, and man-machine interactive capability. However, no existing intelligent protection system covers all these essential aspects. Herein, we developed an intelligent wearable filtration system (IWFS) via advanced nanotechnology and machine learning. Based on the triboelectric mechanism, the fabricated IWFS exhibits a long-lasting high particle filtration efficiency and bacteria protection efficiency of 99% and 100%, respectively, with a low-pressure drop of 5.8 mmH₂O. Correspondingly, the charge accumulation of the optimized IWFS (87 nC) increased to 3.5 times that of the pristine nanomesh, providing a significant enhancement of the particle filtration efficiency. Theoretical principles, including the enhancement of the β-phase and the lower surface potential of the modified nanomesh, were quantitatively investigated by molecular dynamics simulation, band theory, and Kelvin probe force microscopy. Furthermore, we endowed the IWFS with a healthcare monitoring function and man-machine interactive capability through machine learning and wireless transmission technology. Crucial physiological signals of people, including breath, cough, and speaking signals, were detected and classified, with a high recognition rate of 92%; the fabricated IWFS can collect healthcare data and transmit voice commands in real time without hindrance by portable electronic devices. The achieved IWFS not only has practical significance for human health management but also has great theoretical value for advanced wearable systems.

2D Ag Ion-Loaded Anionic Nanosheets for Polymer-Based Film with Durable Antibacterial Activities

Silver (Ag) has been demonstrated to have excellent performance to kill bacteria, fungi, and some viruses because it can release positively charged Ag ions with highly antibacterial and antifungal activities. However, effectively controlling the slow release of Ag ions is the key to preparing high-performance Ag-based antibacterial agents, which remains a challenge. In this work, we have developed a new Ag-based antibacterial agent composed of Ag ions loaded on 2D anionic 2D Sb₃P₂O₁₄ ^3- nanosheets (denoted as Ag-Sb₃P₂O₁₄). 2D anionic nanosheets not only adsorb a large amount of Ag ions but also control their slow release through electrostatic interaction between nanosheets and Ag ions. 2D Ag-Sb₃P₂O₁₄ nanofillers enable excellent high antibacterial activities for the poly(vinylidene fluoride) (PVDF) film composites against microorganisms including Escherichia coli and Staphylococcus aureus. Moreover, the PVDF membrane with 5 wt % 2D Ag-Sb₃P₂O₁₄ nanofillers can kill almost all bacterial after 50 times washing, demonstrating its excellent durable antibacterial activities. This work opens up a new and promising route to durable Ag-based antibacterial agents for polymer-based composites.

Electro-Assisted 3D Printing Multi-Layer PVDF/CaCl2 Composite Films and Sensors

Polyvinylidene fluoride (PVDF) films are widely used in sensors for their wide response frequency, good flexibility, low acoustic impedance, and chemical stability. In this work, PVDF/CaCl2 piezoelectric films were prepared by an electro-assisted 3D printing method and used to form a multi-layer composite film sensor. The study found that the addition of CaCl2 can effectively increase the β-phase content in the PVDF film and improve the piezoelectric and dielectric properties of the PVDF composite film sensors. When the content of CaCl2 is 0.15 wt.%, the β-phase content of the PVDF/CaCl2 composite film can reach the highest value of up to 48.47%, and the output voltage response of the sensor is 0.62 V at an input frequency of 10 Hz, 10 V voltage. The output voltage of PVDF composite film sensor with two and three layers is 1.306 and 1.693 times that of a single layer, respectively. The sensitivity of the multi-layer sensors has also been greatly improved.

Preparation and Luminescence Properties of PVDF/ZnS:Mn Flexible Thin-Film Sensors

Flexible luminescent thin-film sensors have attracted widespread attention for their potential applications in biomedical detection, structural health detection, and smart wear. In this work, PVDF/ZnS:Mn flexible luminescent thin-film sensors were fabricated using electro-assisted 3D-printing techniques. The interaction and influence of PVDF thin film and ZnS:Mn were studied. The mechanism through which the PVDF matrix and ZnS:Mn particles affects the luminescence of the flexible thin-film sensor were investigated. The results demonstrate that the ZnS:Mn luminescent particles in PVDF thin films can promote the formation of the β-phase in the PVDF thin films. The mechano-luminesce spectra of the PVDF/ZnS:Mn composite thin film is consistent with the photoluminescence spectra, both of which exhibit yellow light with a wavelength of 580 nm. Mn entering the ZnS lattice increases the number of effective luminescent centres. Because of the double piezoelectric field, when the Mn content of ZnS:Mn is 4 at.% and PVDF films contain 3 wt.% ZnS:Mn particles, the PVDF/ZnS:Mn flexible thin-film sensors demonstrate excellent mechano-luminescence performance.

Preparation of Polyvinylidene Fluoride-Gold Nanoparticles Electrospinning Nanofiber Membranes

In this work, gold nanoparticles (AuNPs) and curcumin drug were incorporated in polyvinylidene fluoride (PVDF) nanofibers by electrospinning as a novel tissue engineering scaffold in nerve regeneration. The influence of AuNPs on the morphology, crystallinity, and drug release behavior of nanofiber membranes was characterized. A successful composite nanofiber membrane sample was observed by scanning electron microscopy (SEM). The addition of AuNPs showed the improved as well as prolonged cumulative release of the drug. The results indicated that PVDF-AuNPs nanofiber membrane could potentially be applied for nerve regeneration.