Rechargeable polyamide-based N-halamine nanofibrous membranes for renewable, high-efficiency, and antibacterial respirators

Reversible bacteria-killing and bacteria-releasing cotton fabric with anti-bacteria adhesion ability for potential sustainable protective clothing applications

Multifunctional antibacterial surfaces are playing an essential role in various areas. Smart antibacterial materials equipped with switchable "bacteria-killing" and "bacteria-releasing" abilities have been created by scientists. However, most of them are either biologically incompatible, or complex fabricating procedures, or cannot prevent themselves from being attached by bacteria. In this work, a double-layer smart antibacterial surface was created easily by simple surface initiate atom transfer radical polymerization: the upper layer PSBMA provides anti-bacteria adhesion capacity, the NCl bond can show bacteria-killing ability and the under layer PNIPAM can exhibit bacteria-releasing property. Remarkably, the NCl bond can interconvert with the NH bond easily, which allows switching between bacteria-killing and bacteria-releasing. As a result, the functional cotton fabrics can resist about 99.66 % of bacteria attaching, kill nearly 100 % of attached bacteria after 5 min contacting and release about 99.02 % of the formerly attached bacteria. Furthermore, the functional cotton fabric kept excellent anti-bacteria adhesion ability (about 99.27 %) and bacteria-releasing capacity (about 98.30 %) after 9 cycles of re-chlorination. In general, a reversible "bacteria-killing" and "bacteria-releasing" cotton fabric was fabricated with well anti-bacteria adhesion capacity in a simple way, and this smart multifunctional cotton fabric shows a great potential application in reusable protective clothing.

Recent nanotechnology-based strategies for interfering with the life cycle of bacterial biofilms

Biofilm formation plays an important role in the resistance development in bacteria to conventional antibiotics. Different properties of the bacterial strains within biofilms compared with their planktonic states and the protective effect of extracellular polymeric substances contribute to the insusceptibility of bacterial cells to conventional antimicrobials. Although great effort has been devoted to developing novel antibiotics or synthetic antibacterial compounds, their efficiency is overshadowed by the growth of drug resistance. Developments in nanotechnology have brought various feasible strategies to combat biofilms by interfering with the biofilm life cycle. In this review, recent nanotechnology-based strategies for interfering with the biofilm life cycle according to the requirements of different stages are summarized. Additionally, the importance of strategies that modulate the bacterial biofilm microenvironment is also illustrated with specific examples. Lastly, we discussed the remaining challenges and future perspectives on nanotechnology-based strategies for the treatment of bacterial infection.

Surface modification of titanium with antibacterial porous N-halamine coating to prevent peri-implant infection

Peri-implant infection remains one of the greatest threats to orthopedics. The construction of bone implants with good antibacterial and osteogenic properties is beneficial for reducing the risk of implant-related infections and healing bone defects. In this study, N-halamine coating (namely N-Cl) was grafted onto alkali-heat treated titanium (Ti) using polydopamine to endow Ti-based orthopedic implants with strong bactericidal activity. Surface characterization revealed that the N-Cl coating has porous structure loaded with active chlorine (Cl⁺). The N-Cl coating also provided micro/nano-structured Ti surfaces with excellent antibacterial ability via transformation between N-H and N-Cl, and approximately 100% disinfection was achieved. Furthermore, the as-prepared N-Cl coating exhibited good biocompatibility and osteogenesis abilityin vitro. These results indicate that applying N-Cl coatings on Ti could prevent and treat peri-implant infections.

A comprehensive review on facemask manufacturing, testing, and its environmental impacts

The coronavirus pandemic (COVID-19) is currently the biggest threat to human lives due to its rapid transmission rate causing severe damage to human health and economy. The transmission of viral diseases can be minimized at its early stages with proper planning and preventive practices. The use of facemask has proved to be most effective measure to curb the spread of virus along with social distancing and good hygiene practices. This necessitates more research on facemask technology to increase its filtration efficiencies and proper disposal, which can be accelerated with knowledge of the current manufacturing process and recent research in this field. This review article provides an overview of the importance of facemask, fundamentals of nonwoven fabrics, and its manufacturing process. It also covers topics related to recent research reported for improved facemask efficiencies and testing methods to evaluate the performance of facemask. The plastic waste associated with the facemask and measures to minimize its effect are also briefly described. A systematic understanding is given in order to trigger future research in this field to ensure that we are well equipped for any future pandemic.

A pandemic-induced environmental dilemma of disposable masks: solutions from the perspective of the life cycle

The coronavirus disease 2019 (COVID-19) has swept the world and still afflicts humans. As an effective means of protection, wearing masks has been widely adopted by the general public. The massive use of disposable masks has raised some emerging environmental and bio-safety concerns: improper handling of used masks may transfer the attached pathogens to environmental media; disposable masks mainly consist of polypropylene (PP) fibers which may aggravate the global plastic pollution; and the risks of long-term wearing of masks are elusive. To maximize the utilization and minimize the risks, efforts have been made to improve the performance of masks (e.g., antivirus properties and filtration efficiency), extend their functions (e.g., respiration monitoring and acting as a sampling device), develop new disinfection methods, and recycle masks. Despite that, from the perspective of the life cycle (from production, usage, and discard to disposal), comprehensive solutions are urgently needed to solve the environmental dilemma of disposable masks in both technologies (e.g., efficient use of raw materials, prolonging the service life, and enabling biodegradation) and policies (e.g., stricter industry criteria and garbage sorting).

Development of PET Fabrics Containing N-halamine Compounds with Durable Antibacterial Property

Antibacterial textile materials are widely used in daily life, but most are disposable products with poor antibacterial durability. N-halamine can rapidly inactivate microorganisms, has good stability, and shows great potential applications in antibacterial fabrics. In this study, an N-halamine monomer precursor was synthesized and treated onto PET fabrics. The treated PET fabrics were rendered antibacterial functionality after chlorination, and exhibited good antibacterial properties with inactivation rate of 100.0 % for both E. coli O157:H7 and S. aureus. After 50 wash cycles, the chlorinated treated PET fabrics could maintain 80.0 % antibacterial efficacy, demonstrating durable antibacterial properties. Storage stability and UV irradiation tests showed that the treated PET fabrics had remarkable regenerable properties. The reduction of the breaking strength was within 12 % after treatment, which is in a satisfying range in antimicrobial finishing.

One stone two birds: a sinter-resistant TiO2 nanofiber-based unbroken mat enables PM capture and in situ elimination

Airborne particulate matter (PM) primarily resulting from fossil fuel burning is an increasingly global issue. In this work, an intrinsically fragile TiO₂ nanofibrous mat was facilely engineered with good structural integrity, flexibility, foldability, and high-temperature resistance (~1300 °C), by suppressing the sintering (i.e., growth) of nanocrystallites in each single nanofiber. Such functionalization enables self-regenerative air filtration for PM capture and in situ catalytic elimination in a "one-stone-two-birds" approach. Finite element analysis simulation revealed the retained nanopores in each anti-sintering nanofiber could facilitate the air flow during filtration. Without any chemical or physical modification, this self-standing and lightweight (7.1 g m^-2) fibrous mat showed 96.05% filtration efficiency for 3-5 μm NaCl particles, with a low pressure drop of only 18 Pa and high quality factor of 0.179 Pa^-1 under an airflow velocity of 32 L min^-1. By utilizing its photocatalytic attribute, the nanofibrous mat in situ eliminated the captured particles from incense burning under one Sun irradiation in 4 h, and thereby spontaneously regenerated in an easy manner. The straightforward grafting of Au nanoparticles onto nanofibers could enable a quick degradation toward cigarette smoke, mainly due to the photothermally elevated local temperature by Au around the reactive sites. The plasmonic fibrous mat kept a high and stable filtration efficiency of PM_0.3, PM_2.5, and PM₁₀ over 98.62%, 99.76%, and 99.99% during an outdoor long-term filtration test for 12 h under sunlight irradiation (Nanjing, China, September, 26^th, 2020, 7:30 to 19:30). This work provides a solution for solving the airborne pollution from its source, prolonging the lifetime of the filter, and avoiding the risk of producing secondary pollution.

Antibacterial N-halamine fibrous materials

Pathogenic microbial contamination poses serious threats to human healthcare and economies worldwide, which instigates the booming development of challenging antibacterial materials. N-halamine fibrous materials (NFMs), as an important part of antibacterial materials, featuring structural continuity, good pore connectivity, rapid sterilization, rechargeable bactericidal activity, and safety to humans and environment, have received significant research attention. This review aims to present a systematic discussion of the recent advances in N-halamine antibacterial fibrous materials. We firstly introduce the chemical structures and properties of N-halamine materials. Subsequently, the developed NFMs can be categorized based on their fabrication strategies, including surface modification and one-step spinning. Then some representative applications of these fibrous materials are highlighted. Finally, challenges and future research directions of the materials are discussed in the hope of giving suggestions for the following studies.

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The chemical structures and properties of N-halamine materials are briefly introduced.

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Design and fabrication strategies of N-halamine fibrous materials are systematically reviewed.

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The functional applications of the N-halamine fibrous materials are discussed.

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Challenges and future research directions of the antibacterial N-halamine fibrous materials are provided.

Face Masks and Respirators in the Fight against the COVID-19 Pandemic: A Review of Current Materials, Advances and Future Perspectives

The outbreak of COVID-19 has spread rapidly across the globe, greatly affecting how humans as a whole interact, work and go about their daily life. One of the key pieces of personal protective equipment (PPE) that is being utilised to return to the norm is the face mask or respirator. In this review we aim to examine face masks and respirators, looking at the current materials in use and possible future innovations that will enhance their protection against SARS-CoV-2. Previous studies concluded that cotton, natural silk and chiffon could provide above 50% efficiency. In addition, it was found that cotton quilt with a highly tangled fibrous nature provides efficient filtration in the small particle size range. Novel designs by employing various filter materials such as nanofibres, silver nanoparticles, and nano-webs on the filter surfaces to induce antimicrobial properties are also discussed in detail. Modification of N95/N99 masks to provide additional filtration of air and to deactivate the pathogens using various technologies such as low- temperature plasma is reviewed. Legislative guidelines for selecting and wearing facial protection are also discussed. The feasibility of reusing these masks will be examined as well as a discussion on the modelling of mask use and the impact wearing them can have. The use of Artificial Intelligence (AI) models and its applications to minimise or prevent the spread of the virus using face masks and respirators is also addressed. It is concluded that a significant amount of research is required for the development of highly efficient, reusable, anti-viral and thermally regulated face masks and respirators.

Electrospun nanofibers of polyelectrolyte-surfactant complexes for antibacterial wound dressing application

The development of polyelectrolyte-surfactant complexes (PESCs) has attracted extensive research interest in different fields of applications. However, the liquid state of PESCs has limited their utility in applications where solid materials are required. In this study, novel antibacterial fibers were fabricated via electrospinning PESCs in the solid state without any additives. The PESCs were prepared in aqueous mixtures of pre-hydrolyzed polyacrylonitrile (HPAN), a polyelectrolyte, and cetyltrimethyl ammonium chloride (CTAC), an antibacterial cationic surfactant, by taking advantage of the self-aggregation behavior of the polyelectrolyte and surfactant, which increased the antibacterial agent loading ability and, thus, the antibacterial activity of polymers. By release-killing and contact-killing mechanisms, the as-spun PESC nanofibrous membranes exhibited strong antibacterial ability against both Gram-positive and Gram-negative bacteria, killing 5 log CFU of E. coli and S. aureus within a contact time as short as 30 min. Furthermore, PESCs were blended with polycaprolactone (PCL) to prepare composite nanofibrous membranes as a novel wound dressing, which showed excellent antibacterial activity and favorable cytocompatibility, with the mechanical strength high enough to satisfy the clinical application requirements. The PESC fibers with durable antibacterial activity presented in the current work would be promising for medical applications.

Novel ZnO/N-halamine-Mediated Multifunctional Dressings as Quick Antibacterial Agent for Biomedical Applications

Cutaneous hemorrhage often occurs in daily life which may cause infection and even amputation. This research aims to develop a novel chitosan dressing impregnated with ZnO/N-halamine hybrid nanoparticles for quick antibacterial performance, outstanding hemostatic potential, high porosity, and favorable swelling property through combining sonication and lyophilization processing. After 30 days of storage, about 90% bacterial cell viability loss could be observed toward both Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli O157:H7 within 30 min of contact by colony counting method. The hybrids assembled much more platelet and red blood cell as compared with pure chitosan control. Moreover, the lower blooding clotting index value gave evidence that these composites could control hemorrhaging and reduce the probability of wound infection. No potential skin irritation and toxicity were detected using in vitro cytocompatibility and a skin stimulation test. Therefore, this work demonstrated a facile and cost-effective approach for the preparation of N-halamine-based hybrid sponges which show promising application for wound dressings.