Addressing a future pandemic: how can non-biological complex drugs prepare us for antimicrobial resistance threats?

Loss of effective antibiotics through antimicrobial resistance (AMR) is one of the greatest threats to human health. By 2050, the annual death rate resulting from AMR infections is predicted to have climbed from 1.27 million per annum in 2019, up to 10 million per annum. It is therefore imperative to preserve the effectiveness of both existing and future antibiotics, such that they continue to save lives. One way to conserve the use of existing antibiotics and build further contingency against resistant strains is to develop alternatives. Non-biological complex drugs (NBCDs) are an emerging class of therapeutics that show multi-mechanistic antimicrobial activity and hold great promise as next generation antimicrobial agents. We critically outline the focal advancements for each key material class, including antimicrobial polymer materials, carbon nanomaterials, and inorganic nanomaterials, and highlight the potential for the development of antimicrobial resistance against each class. Finally, we outline remaining challenges for their clinical translation, including the need for specific regulatory pathways to be established in order to allow for more efficient clinical approval and adoption of these new technologies.

Design of nanoengineered antibacterial polymers for biomedical applications

Pathogenic bacteria have become global threats to public health. Since the advent of antibiotics about 100 years ago, their use has been embraced with great enthusiasm because of their effective treatment of bacterial infections. However, the evolution of pathogenic bacteria with resistance to conventional antibiotics has resulted in an urgent need for the development of a new generation of antibiotics. The use of antimicrobial polymers offers the promise of enhancing the efficacy of antimicrobial agents. Of the various antibacterial polymers that effectively eradicate pathogenic bacteria, those that are nanoengineered have garnered significant research interest in their design and biomedical applications. Because of their high surface area and high reactivity, these polymers show greater antibacterial activity than conventional antibacterial agents, by inhibiting the growth or destroying the cell membrane of pathogenic bacteria. This review summarizes several strategies for designing nanoengineered antibacterial polymers, explores the factors that affect their antibacterial properties, and examines key features of their design. It then comments briefly on the future prospects for nanoengineered antibacterial polymers. This review thus provides a feasible guide to developing nanoengineered antibacterial polymers by presenting both broad and in-depth bench research, and it offers suggestions for their potential in biomedical applications.

Synthesis of novel multi-hydroxyl N-halamine precursors based on barbituric acid and their applications in antibacterial poly(ethylene terephthalate) (PET) materials

Two novel multi-hydroxyl N-halamine precursors were successfully synthesized in a green and facile way via Knoevenagel condensation reaction between barbituric acid and an aldehyde (citral or cinnamaldehyde), followed by a hydroxylation reaction with hydrogen peroxide. 1H-NMR and FT-IR spectral analyses confirmed their formation. Through the melt-blending process, the multi-hydroxyl derivatives of barbituric acid were introduced via transesterification into poly(ethylene terephthalate) (PET) at 265 °C in a rheometer. The crystallization behaviors of the modified PET samples were investigated using X-ray diffraction (XRD), differential scanning calorimetry (DSC), and polarized optical microscopy (POM) analyses. The results showed that the crystallization temperature and crystallization rate of PET were significantly improved upon the introduction of the precursor. Meanwhile, the relative crystallinity of the modified PET samples increased with an increase in the dosage of the N-halamine precursor. After the treatment with sodium hypochlorite solution, the PET surfaces modified with N-halamine derivatives would impart powerful antibacterial properties and achieve 100% killing of Staphylococcus aureus (ATCC 6538) and Escherichia coli (CMCC44103) cells within 30 min. Therefore, the multi-hydroxyl N-halamine precursors exhibit great potential as bifunctional additives (nucleating and antibacterial agents) in the manufacturing of functional PET materials.

Synthesis of cationic acrylate copolyvidone-iodine nanoparticles with double active centers and their antibacterial application

Antibacterial materials are rapidly emerging as a primary component in the mitigation of bacterial pathogens, and functional polymers play a vital role in the preparation of antibacterial coatings. In this study, a novel antibacterial polymer with double active centers was synthesized. Firstly, using one-pot soap-free emulsion polymerization technology, the cationic acrylate copolymeric polyvidone (CACPV) was synthesized by copolymerization of four monomers with different functions, which were methyl methacrylate (MMA), N-vinyl-2-pyrrolidone (NVP), γ-methacryloxypropyltrimethoxysilane (MAPTS) and [3-(methacryloylamino)propyl]trimethylammonium chloride (MAPTAC). Secondly, using iodine complexation, the cationic acrylate copolyvidone-iodine (CACPVI) nanoparticles were prepared. After being characterized by scanning electron microscopy (SEM), dynamic light scattering (DLS), X-ray photoelectron spectroscopy (XPS) and contact angle test, the antibacterial activity of CACPVI was evaluated against the typical human pathogens Escherichia coli (E. coli, Gram-negative) and Staphylococcus aureus (S. aureus, Gram-positive). Additionally, CACPVI was used to improve the antibacterial activities of some materials, such as ink, dye and coatings. It was found that CACPVI presented an excellent antibacterial synergy. When the antibacterial activities were more than 99% at a concentration of 40.00 μg mL-1, CACPVI exhibited long-term antibacterial performance as expected. The antibacterial mechanism of this synergy was also investigated. In summary, a novel antibacterial polymer material with double active centers was successfully synthesized and was widely applied in coating, dye and ink materials for minimizing bacterial infection.

Contact/Release Coordinated Antibacterial Cotton Fabrics Coated with N-Halamine and Cationic Antibacterial Agent for Durable Bacteria-Killing Application

Coating a cationic antibacterial layer on the surface of cotton fabric is an effective strategy to provide it with excellent antibacterial properties and to protect humans from bacterial cross-infection. However, washing with anionic detergent will inactivate the cationic antibacterial coating. Although this problem can be solved by increasing the amount of cationic antibacterial coating, excessive cationic antibacterial coating reduces the drapability of cotton fabric and affects the comfort of wearing it. In this study, a coordinated antibacterial coating strategy based on quaternary ammonium salt and a halogenated amine compound was designed. The results show that the antibacterial effect of the modified cotton fabric was significantly improved. In addition, after mechanically washing the fabric 50 times in the presence of anionic detergent, the antibacterial effect against Staphylococcus aureus and Escherichia coli was still more than 95%. Furthermore, the softness of the obtained cotton fabric showed little change compared with the untreated cotton fabric. This easy-to-implement and cost-effective approach, combined with the cationic contact and the release effect of antibacterial agents, can endow cotton textiles with durable antibacterial properties and excellent wearability.

Antimicrobial Particle-Based Novel Sanitizer for Enhanced Decontamination of Fresh Produce

Microbial food safety of raw or minimally processed fresh produce is a significant challenge. The current sanitation processes are effective for inactivation of bacteria in wash water but have limited efficacy (<2 log/g reduction) for inactivation of microbes on the surfaces of fresh produce. This study demonstrates a novel concept to enhance effectiveness of chlorine using a particle-based sanitizer to improve decontamination of fresh produce. In this concept, enhanced effectiveness is achieved by localized high concentration of chlorine bound to the surfaces of silica particles and improved surface contact of microparticles with the produce surface using mechanical shear during a washing process. The results of this study demonstrate that 500 ppm active chlorine can be bound to the surfaces of modified silica particles. These modified particles maintain over 90% of their initial chlorine content during extended storage in aqueous solution and provide improved inactivation of both Escherichia coli O157:H7, Listeria innocua, and Pseudomonas fluorescens in the presence of organic content in contrast to conventional chlorine sanitizer. The modified particles exhibit effective sanitation of fresh produce (>5-log reduction) in the presence of relatively high organic content (chemical oxygen demand of 500 mg/liter), demonstrating a potential to address a significant unmet need to improve fresh produce sanitation. The particle-based sanitizer had no significant effect on the quality of fresh lettuce.IMPORTANCE The limitation of current sanitation processes for inactivation of microbes on the surfaces of fresh produce is due to nonspecific consumption of sanitizers by reactions with the food matrix and complexity of surface chemistries and structural features of produce surfaces. This study demonstrates a novel approach to enhance sanitation effectiveness of fresh produce using a particle-based sanitizer. The particle-based sanitizer concept provides localized high concentration delivery of chlorine to the surfaces of fresh produce and enables more than 5 logs of inactivation of inoculated bacteria on fresh produce surfaces without significant changes in produce quality. The results of this study illustrate the potential of this approach to address the unmet need for improving sanitation of fresh produce. Further validation of this approach using a scaled-up produce washing system will enable commercialization of this novel concept.

Development of new hydantoin-based biocidal polymers with improved rechargeability and anti-microbial activity

Novel hydantoin based co-polymers containing both amide and imide positions for halogen capture with improved rechargeability and antibacterial activity were developed.

Electrofabrication of functional materials: Chloramine-based antimicrobial film for infectious wound treatment

Electrical signals can be imposed with exquisite spatiotemporal control and provide exciting opportunities to create structure and confer function. Here, we report the use of electrical signals to program the fabrication of a chloramine wound dressing with high antimicrobial activity. This method involves two electrofabrication steps: (i) a cathodic electrodeposition of an aminopolysaccharide chitosan triggered by a localized region of high pH; and (ii) an anodic chlorination of the deposited film in the presence of chloride. This electrofabrication process is completed within several minutes and the chlorinated chitosan can be peeled from the electrode to yield a free-standing film. The presence of active NCl species in this electrofabricated film was confirmed with chlorination occurring first on the amine groups and then on the amide groups when large anodic charges were used. Electrofabrication is quantitatively controllable as the cathodic input controls film growth during deposition and the anodic input controls film chlorination. In vitro studies demonstrate that the chlorinated chitosan film has antimicrobial activities that depend on the chlorination degree. In vivo studies with a MRSA infected wound healing model indicate that the chlorinated chitosan film inhibited bacterial growth, induced less inflammation, developed reorganized epithelial and dermis structures, and thus promoted wound healing compared to a bare wound or wound treated with unmodified chitosan. These results demonstrate the fabrication of advanced functional materials (i.e., antimicrobial wound dressings) using controllable electrical signals to both organize structure through non-covalent interactions (i.e., induce chitosan's reversible self-assembly) and to initiate function-conferring covalent modifications (i.e., generate chloramine bonds). Potentially, electrofabrication may provide a simple, low cost and sustainable alternative for materials fabrication.

STATEMENT OF SIGNIFICANCE

We believe this work is novel because this is the first report (to our knowledge) that electronic signals enable the fabrication of advanced antimicrobial dressings with controlled structure and biological performance. We believe this work is significant because electrofabrication enables rapid, controllable and sustainable materials construction with reduced adverse environmental impacts while generating high performance materials for healthcare applications. More specifically, we report an electrofbrication of antimicrobial film that can promote wound healing.

Synthesis and polymerization of a new hydantoin monomer with three halogen binding sites for developing highly antibacterial surfaces

Novel three halogen capturing hydantoin monomer-based copolymers were synthesized and evaluated for their antibacterial properties.

N-Halamine-Containing Electrospun Fibers Kill Bacteria via a Contact/Release Co-Determined Antibacterial Pathway

N-Halamine-based antibacterial materials play a significant role in controlling microbial contamination, but their practical applications are limited because of their complicated synthetic process and indistinct antibacterial actions. In this study, novel antibacterial N-halamine-containing polymer fibers were synthesized via an one-step electrospinning of N-halamine-containing polymers without any additives. By adjusting the concentration of precursor and the molecular weight of polymers, the morphology and size of the as-spun N-halamine-containing fibers can be regulated. The as-spun fibers showed antibacterial activity against both Gram-positive and Gram-negative bacteria. After an antibacterial assessment using different biochemical techniques, a combined mechanism of contact/release co-determined killing action was evidenced for the as-spun N-halamine-containing fibers. With the aid of contact action and/or release action, this combined mechanism can allow N-halamines to attack bacteria, making the as-spun fibers wide in the application of antibacterial fields, whatever it is in dry or wet environment. Also, a recycle antibacterial test demonstrated that the as-spun fibers can still offer antibacterial property after five recycle experiments.

Cytocompatible antibacterial fibrous membranes based on poly(3-hydroxybutyrate-co-4-hydroxybutyrate) and quaternarized N-halamine polymer

A novel polymeric N-halamine-containing quaternary ammonium salt (PHQS) was synthesized and used to make antibacterial electrospun fibrous membranes by blending with biodegradable poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P(3HB-4HB)).

Unexpected Enhancement in Antibacterial Activity of N-Halamine Polymers from Spheres to Fibers

Preventing bacterial infections is a main focus of medical care. Antibacterial agents with broad and excellent disinfection capability against pathogenic bacteria are in fact urgently required. Herein, a novel strategy for the development of N-halamine polymers from spheres to fibers using a combined copolymerization-electrospinning-chlorination technique was reported, allowing fight against bacterial pathogen. Optimizing the process conditions, e.g., comonomer molar ratio, concentration of electrospinning solution, chlorination order, and chlorination period, resulted in the formation of N-halamine fibers with controllable morphology. N-Halamine polymers were tested against two common bacterial pathogens, Escherichia coli and Staphylococcus aureus, and were found to be extremely potent against both bacteria, suggesting that they possess powerful sterilizing properties. Remarkably, compared with those with sphere morphology, N-halamine fibers show unexpected enhancement toward both pathogens possibly because of their shape (fiber morphology), surface state (rough surfaces), and surface charge (positive zeta potentials). It is believed that this approach has great potential to be utilized in various fields where antifouling and antibacterial properties are highly required.

Decorating CdTe QD-Embedded Mesoporous Silica Nanospheres with Ag NPs to Prevent Bacteria Invasion for Enhanced Anticounterfeit Applications

Quantum dots (QDs) as potent candidates possess advantageous superiority in fluorescence imaging applications, but they are susceptible to the biological circumstances (e.g., bacterial environment), leading to fluorescence quenching or lose of fluorescent properties. In this work, CdTe QDs were embedded into mesoporous silica nanospheres (m-SiO2 NSs) for preventing QD agglomeration, and then CdTe QD-embedded m-SiO2 NSs (m-SiO2/CdTe NSs) were modified with Ag nanoparticles (Ag NPs) to prevent bacteria invasion for enhanced anticounterfeit applications. The m-SiO2 NSs, which serve as intermediate layers to combine CdTe QDs with Ag NPs, help us establish a highly fluorescent and long-term antibacterial system (i.e., m-SiO2/CdTe/Ag NSs). More importantly, CdTe QD-embedded m-SiO2 NSs showed fluorescence quenching when they encounter bacteria, which was avoided by attaching Ag NPs outside. Ag NPs are superior to CdTe QDs for preventing bacteria invasion because of the structure (well-dispersed Ag NPs), size (small diameter), and surface charge (positive zeta potentials) of Ag NPs. The plausible antibacterial mechanisms of m-SiO2/CdTe/Ag NSs toward both Gram-positive and Gram-negative bacteria were established. As for potential applications, m-SiO2/CdTe/Ag NSs were developed as fluorescent anticounterfeiting ink for enhanced imaging applications.

Microstructure and antibacterial performance of functionalized polyurethane based on polysiloxane tethered cationic biocides

The designed polyurethane containing polysiloxanes tethered quaternary ammonium salt groups exhibited special surface migrations, low surface free energy and excellent antibacterial activity towardsEscherichia coli.

Synthesis and bactericidal evaluation of imide N-halamine-loaded PMMA nanoparticles

Antibacterial imide N-halamine-loaded PMMA nanoparticles were fabricated, and their bactericidal activities were systematically evaluated.