Increasing the Antimicrobial Activity of Amphiphilic Cationic Copolymers by the Facile Synthesis of High Molecular Weight Stars by Supplemental Activator and Reducing Agent Atom Transfer Radical Polymerization

Effect of Star Topology Versus Linear Polymers on Antifungal Activity and Mammalian Cell Toxicity

The global increase in invasive fungal infections and the emergence of drug-resistant strains demand the urgent development of novel antifungal drugs. In this context, synthetic polymers with diverse compositions, mimicking natural antimicrobial peptides, have shown promising potential for combating fungal infections. This study investigates how altering polymer end-groups and topology from linear to branched star-like structures affects their efficacy against Candida spp., including clinical isolates. Additionally, the polymers' biocompatibility is accessed with murine embryonic fibroblasts and red blood cells in vitro. Notably, a low-molecular weight star polymer outperforms both its linear polymeric counterparts and amphotericin B (AmpB) in terms of an improved therapeutic index and reduced haemolytic activity, despite a higher minimum inhibitory concentration against Candida albicans (C. albicans) SC5314 (16-32 µg mL-1 vs 1 µg mL-1 for AmpB). These findings demonstrate the potential of synthetic polymers with diverse topologies as promising candidates for antifungal applications.

Size-Controlled Ammonium-Based Homopolymers as Broad-Spectrum Antibacterials

Ammonium group containing polymers possess inherent antimicrobial properties, effectively eliminating or preventing infections caused by harmful microorganisms. Here, homopolymers based on monomers containing ammonium groups were synthesized via Reversible Addition Fragmentation Chain Transfer Polymerization (RAFT) and evaluated as potential antibacterial agents. The antimicrobial activity was evaluated against Gram-positive (M. luteus and B. subtilis) and Gram-negative bacteria (E. coli and S. typhimurium). Three polymers, poly(diallyl dimethyl ammonium chloride), poly([2-(methacryloyloxy)ethyl]trimethylammonium chloride), and poly(vinyl benzyl trimethylammonium chloride), were examined to explore the effect of molecular weight (10 kDa, 20 kDa, and 40 kDa) on their antimicrobial activity and toxicity to mammalian cells. The mechanisms of action of the polymers were investigated with dye-based assays, while Scanning Electron Microscopy (SEM) showed collapsed and fused bacterial morphologies due to the interactions between the polymers and components of the bacterial cell envelope, with some polymers proving to be bactericidal and others bacteriostatic, while being non-hemolytic. Among all the homopolymers, the most active, non-Gram-specific polymer was poly([2-(methacryloyloxy)ethyl]trimethylammonium chloride), with a molecular weight of 40 kDa, with minimum inhibitory concentrations between 16 and 64 µg/mL, showing a bactericidal mode of action mediated by disruption of the cytoplasmic membrane. This homopolymer could be useful in biomedical applications such as surface dressings and in areas such as eye infections.

Antibacterial, anti-inflammatory and wet-adhesive poly(ionic liquid)-based oral patch for the treatment of oral ulcers with bacterial infection

Oral aphthous ulcers are a common inflammatory efflorescence of oral mucosa, presenting as inflammation and oral mucosal damage and manifesting as pain. The moist and highly dynamic environment of the oral cavity makes the local treatment of oral aphthous ulcers challenging. Herein, a poly(ionic liquid)-based diclofenac sodium (DS)-loaded (PIL-DS) buccal tissue adhesive patch fabricated with intrinsically antimicrobial, highly wet environment adhesive properties and anti-inflammatory activities to treat oral aphthous ulcers was developed. The PIL-DS patch was prepared via polymerization of a catechol-containing ionic liquid, acrylic acid, and butyl acrylate, followed by anion exchange with DS-. The PIL-DS can adhere to wet tissues, including mucosa muscles and organs, and efficiently deliver the carried DS- at wound sites, exerting remarkable synergistic antimicrobial (bacteria and fungi) properties. Accordingly, the PIL-DS elicited dual therapeutic effects on oral aphthous ulcers with Staphylococcus aureus infection through antibacterial and anti-inflammatory activities, significantly accelerating oral aphthous ulcer healing as an oral mucosa patch. The results indicated that the PIL-DS patch, with inherently antimicrobial and wet adhesion properties, is promising for treating oral aphthous ulcers in clinical practice. STATEMENT OF SIGNIFICANCE: Oral aphthous ulcers are a common oral mucosal disease, which could lead to bacterial infection and inflammation in severe cases, especially for people with large ulcers or low immunity. However, moist oral mucosa and highly dynamic oral environment make it challenging to maintain therapeutic agents and physical barriers at the wound surface. Therefore, an innovative drug carrier with wet adhesion is urgently needed. Herein, a poly(ionic liquid)-based diclofenac sodium (DS)-loaded (PIL-DS) buccal tissue adhesive patch was developed to treat oral aphthous ulcers showing intrinsically antimicrobial and highly wet environment adhesive properties due to the presence of catechol-containing ionic liquid monomer. Additionally, the PIL-DS showed significantly therapeutic effects on oral aphthous ulcers with S. aureus infection through antibacterial and anti-inflammatory activities. We expect that our work can provide inspiration for the development of treatment for microbially infected oral ulcers.

Structural Engineering of Star Block Biodegradable Polymer Unimolecular Micelles for Drug Delivery in Cancer Cells

The present investigation reports the structural engineering of biodegradable star block polycaprolactone (PCL) to tailor-make aggregated micelles and unimolecular micelles to study their effect on drug delivery aspects in cancer cell lines. Fully PCL-based star block copolymers were designed by varying the arm numbers from two to eight while keeping the arm length constant throughout. Multifunctional initiators were exploited for stepwise solvent-free melt ring-opening polymerization of ε-caprolactone and γ-substituted caprolactone to construct star block copolymers having a PCL hydrophobic core and a carboxylic PCL hydrophilic shell, respectively. A higher arm number and a higher degree of branching in star polymers facilitated the formation of unimolecular micelles as opposed to the formation of conventional multimicellar aggregates in lower arm analogues. The dense core of the unimolecular micelles enabled them to load high amounts of the anticancer drug doxorubicin (DOX, ∼12-15%) compared to the aggregated micelles (∼3-4%). The star unimolecular micelle completely degraded leading to 90% release of the loaded drug upon treatment with the lysosomal esterase enzyme in vitro. The anticancer efficacies of these DOX-loaded unimolecular micelles were tested in a breast cancer cell line (MCF-7), and their IC₅₀ values were found to be much lower compared to those of aggregated micelles. Time-dependent cellular uptake studies by confocal microscopy revealed that unimolecular micelles were readily taken up by the cells, and enhancement of the drug concentration was observed at the intracellular level up to 36 h. The present work opens new synthetic strategies for building a next-generation biodegradable unimolecular micellar nanoplatform for drug delivery in cancer research.

Polymers showing intrinsic antimicrobial activity

Pathogenic microorganisms are considered to a major threat to human health, impinging on multiple sectors including hospitals, dentistry, food storage and packaging, and water contamination. Due to the increasing levels of antimicrobial resistance shown by pathogens, often caused by long-term abuse or overuse of traditional antimicrobial drugs, new approaches and solutions are necessary. In this area, antimicrobial polymers are a viable solution to combat a variety of pathogens in a number of contexts. Indeed, polymers with intrinsic antimicrobial activities have long been an intriguing research area, in part, due to their widespread natural abundance in materials such as chitin, chitosan, carrageen, pectin, and the fact that they can be tethered to surfaces without losing their antimicrobial activities. In addition, since the discovery of the strong antimicrobial activity of some synthetic polymers, much work has focused on revealing the most effective structural elements that give rise to optimal antimicrobial properties. This has often been synthesis targeted, with the generation of either new polymers or the modification of natural antimicrobial polymers with the addition of antimicrobial enhancing modalities such as quaternary ammonium or guanidinium groups. In this review, the growing number of polymers showing intrinsic antimicrobial properties from the past decade are highlighted in terms of synthesis; often based on post-synthesis modification and their utilization. This includes as surface coatings, for example on medical devices, such as intravascular catheters, orthopaedic implants and contact lenses, or directly as antibacterial agents (specifically as eye drops). Surface functionalisation with inherently antimicrobial polymers is highlighted and has been achieved via various techniques, including surface-bound initiators allowing RAFT or ATRP surface-based polymerization, or via physical immobilization such as by layer-by-layer techniques. This article also covers the mechanistic modes of action of intrinsic antimicrobial polymers against bacteria, viruses, or fungi.

Self-Assembled Cationic Nanoparticles Combined with Curcumin against Multidrug-Resistant Bacteria

The overuse of antibiotics exacerbates the development of antibiotic-resistant bacteria, threatening global public health, while most traditional antibiotics act on specific targets and sterilize through chemical modes. Therefore, it is a desperate need to design novel therapeutics or extraordinary strategies to overcome resistant bacteria. Herein, we report a positively charged nanocomposite PNs-Cur with a hydrodynamic diameter of 289.6 nm, which was fabricated by ring-opening polymerization of ε-caprolactone and Z-Lys-N-carboxyanhydrides (NCAs), and then natural curcumin was loaded onto the PCL core of PNs with a nanostructure through self-assembly, identified through UV-vis, and characterized by scanning electron microscopy (SEM) and dynamic light scattering (DLS). Especially, the self-assembly dynamics of PNs was simulated through molecular modeling to confirm the formation of a core-shell nanostructure. Biological assays revealed that PNs-Cur possessed broad-spectrum and efficient antibacterial activities against both Gram-positive and Gram-negative bacteria, including drug-resistant clinical bacteria and fungus, with MIC values in the range of 8-32 μg/mL. Also, in vivo evaluation showed that PNs-Cur exhibited strong antibacterial activities in infected mice. Importantly, the nanocomposite did not indeed induce the emergence of drug-resistant bacterial strains even after 21 passages, especially showing low toxicity regardless of in vivo or in vitro. The study of the antibacterial mechanism indicated that PNs-Cur could indeed destruct membrane potential, change the membrane potential, and cause the leakage of the cytoplasm. Concurrently, the released curcumin further plays a bactericidal role, eventually leading to bacterial irreversible apoptosis. This unique bacterial mode that PNs-Cur possesses may be the reason why it is not easy to make the bacteria susceptible to easily produce drug resistance. Overall, the constructed PNs-Cur is a promising antibacterial material, which provides a novel strategy to develop efficient antibacterial materials and combat increasingly prevalent bacterial infections.

Preparation of antibacterial polypeptides with different topologies and their antibacterial properties

Antimicrobial peptides (AMPs) are attractive antimicrobial agents used to combat bacterial infections, and have been advanced to be one of the most promising alternatives to conventional antibiotics. They stand out for their attractive broad-spectrum activity, unmatched antibacterial mechanism that is not prone to develop drug resistance and diversified topologies, which can be fabricated with manifold amino acid blocks. In this study, using n-hexylamine and amine-terminated polyamidoamine dendrimers (Gx-PAMAM, x = 1-2) as initiators, a series of AMPs with linear and star-shaped topological structures were constructed via the controllable ring-opening polymerization (ROP) of N-carboxyanhydrides (NCAs). The antibacterial performances of the tailored linear and star-shaped AMPs were comprehensively evaluated in both solution states and surface-bonded states. The results indicated that the star-shaped AMPs exhibited enhanced bactericidal activity against Gram-negative E. coli and similar bactericidal activity against Gram-positive S. aureus when compared with the linear AMPs. It is worth mentioning that star-shaped AMPs demonstrated a significantly faster bactericidal efficiency (completely killed bacteria within 5 min at a concentration of 2 × MIC for S. aureus) than their linear analogues (took 15 min to achieve the same effect). However, when the AMPs were immobilized to the surface, they similarly exhibited superior antibacterial activity and fast bactericidal efficiency towards S. aureus and E. coli in the case of the same surface grafting amount. In addition, both the surfaces grafted with AMPs of different topologies demonstrated favorable biocompatibility in vitro.

Antibacterial and cytotoxic properties of star-shaped quaternary ammonium-functionalized polymers with different pendant groups

The correlation between the structure and biological activity of polymers is critically important for rationally designing effective antibacterial polymers. Here, the antibacterial activity, cytotoxicity, and selectivity of structurally well-defined, star-shaped...

Bioactive Synthetic Polymers

Synthetic polymers are omnipresent in society as textiles and packaging materials, in construction and medicine, among many other important applications. Alternatively, natural polymers play a crucial role in sustaining life and allowing organisms to adapt to their environments by performing key biological functions such as molecular recognition and transmission of genetic information. In general, the synthetic and natural polymer worlds are completely separated due to the inability for synthetic polymers to perform specific biological functions; in some cases, synthetic polymers cause uncontrolled and unwanted biological responses. However, owing to the advancement of synthetic polymerization techniques in recent years, new synthetic polymers have emerged that provide specific biological functions such as targeted molecular recognition of peptides, or present antiviral, anticancer, and antimicrobial activities. In this review, the emergence of this generation of bioactive synthetic polymers and their bioapplications are summarized. Finally, the future opportunities in this area are discussed.

Quaternary ammonium substituted pullulan accelerates wound healing and disinfects Staphylococcus aureus infected wounds in mouse through an atypical 'non-pore forming' pathway of bacterial membrane disruption

The emergence of multi-drug resistant pathogens has fueled the search for alternatives to the existing line of antibiotics that can eradicate pathogens without inducing resistance development. Here, we report the accelerated wound healing and disinfection potential of a non-amphiphilic quaternized fungal exopolysaccharide, pullulan, without resistance generation in pathogens. The quaternary ammonium substituted pullulan (CP) derivatives showed excellent bactericidal activity against both Gram negative (MBC₉₀ = 1.5 μg mL^-1) and Gram positive (MBC₉₀ = 0.25 μg mL^-1) bacteria at very low concentrations without showing any toxicity towards mammalian cells. A combined approach of atomistic molecular dynamics simulation and experimental assays revealed that CP exerts a membrane directed bactericidal action through an atypical "non-pore forming" pathway which is not yet established for any known antibacterial polysaccharides. This involves an increase in membrane roughness, disorder among anionic lipid tails, formation of localized anionic lipid clusters and membrane depolarization, finally leading to physical disruption of the membrane integrity. Moreover, CP also displayed biofilm eradication abilities and emerged as an excellent therapeutic material for disinfection and healing of infected wounds. The present work shows the potential of exploiting polysaccharides as next-generation broad-spectrum antimicrobials and provides a platform for further development of rationally designed pullulan-based functional materials for biomedical applications.

The Two Weapons against Bacterial Biofilms: Detection and Treatment

Bacterial biofilms are defined as complex aggregates of bacteria that grow attached to surfaces or are associated with interfaces. Bacteria within biofilms are embedded in a self-produced extracellular matrix made of polysaccharides, nucleic acids, and proteins. It is recognized that bacterial biofilms are responsible for the majority of microbial infections that occur in the human body, and that biofilm-related infections are extremely difficult to treat. This is related with the fact that microbial cells in biofilms exhibit increased resistance levels to antibiotics in comparison with planktonic (free-floating) cells. In the last years, the introduction into the market of novel compounds that can overcome the resistance to antimicrobial agents associated with biofilm infection has slowed down. If this situation is not altered, millions of lives are at risk, and this will also strongly affect the world economy. As such, research into the identification and eradication of biofilms is important for the future of human health. In this sense, this article provides an overview of techniques developed to detect and imaging biofilms as well as recent strategies that can be applied to treat biofilms during the several biofilm formation steps.

Host-Pathogen Adhesion as the Basis of Innovative Diagnostics for Emerging Pathogens

Infectious diseases are an existential health threat, potentiated by emerging and re-emerging viruses and increasing bacterial antibiotic resistance. Targeted treatment of infectious diseases requires precision diagnostics, especially in cases where broad-range therapeutics such as antibiotics fail. There is thus an increasing need for new approaches to develop sensitive and specific in vitro diagnostic (IVD) tests. Basic science and translational research are needed to identify key microbial molecules as diagnostic targets, to identify relevant host counterparts, and to use this knowledge in developing or improving IVD. In this regard, an overlooked feature is the capacity of pathogens to adhere specifically to host cells and tissues. The molecular entities relevant for pathogen–surface interaction are the so-called adhesins. Adhesins vary from protein compounds to (poly-)saccharides or lipid structures that interact with eukaryotic host cell matrix molecules and receptors. Such interactions co-define the specificity and sensitivity of a diagnostic test. Currently, adhesin-receptor binding is typically used in the pre-analytical phase of IVD tests, focusing on pathogen enrichment. Further exploration of adhesin–ligand interaction, supported by present high-throughput “omics” technologies, might stimulate a new generation of broadly applicable pathogen detection and characterization tools. This review describes recent results of novel structure-defining technologies allowing for detailed molecular analysis of adhesins, their receptors and complexes. Since the host ligands evolve slowly, the corresponding adhesin interaction is under selective pressure to maintain a constant receptor binding domain. IVD should exploit such conserved binding sites and, in particular, use the human ligand to enrich the pathogen. We provide an inventory of methods based on adhesion factors and pathogen attachment mechanisms, which can also be of relevance to currently emerging pathogens, including SARS-CoV-2, the causative agent of COVID-19.

Antimicrobial materials produced by incorporating copper acetate into ethylene-vinyl alcohol copolymer for its use in personal care and cosmetic packaging

Currently, there is a great demand for functional materials with effective pathogen-killing properties. In this research, we describe the use of green technology “reactive extrusion” for the synthesis of potent antimicrobial materials based on Ethylene-vinyl alcohol copolymer (EVOH). Herein, the antimicrobial agent, copper (II) acetate was used without pretreatment and introduced into the EVOH matrices at high temperatures. The thermal reaction of copper (II) acetate within the EVOH matrices and their effect on the thermal and thermomechanical properties of the polymer were investigated in regards to their concentration. The physicochemical, thermal, and rheological features, as well as, metal salt release kinetics were reported. The antimicrobial agent had significant effects on the properties of the matrix. Results showed a reduction in the glass transition temperatures and storage modulus of the materials in response to the incorporation of copper (II) acetate. Finally, the antimicrobial activity of the products was studied and demonstrated a possibility to create antimicrobial materials in a one-step, solvent-free extrusion process.

Structure-dependent antimicrobial mechanism of quaternary ammonium resins and a novel synthesis of highly efficient antimicrobial resin

The demand for powerful and multifunctional water-treatment materials and reagents is increasing, because we are facing worse raw water quality, various tolerant bacteria, and risky disinfection by-products (DBPs) in drinking water. Quaternary ammonium resins (QARs) are promising candidates for water disinfection and purification, but their limited bactericidal capacities are difficult to improve because of the lack of guidelines for enhancing antibacterial efficiency. Therefore, we first systematically studied the structure-dependent antimicrobial mechanism of QARs and found that the best resin skeleton is acrylic-type, the optimal bactericidal alkyl is hexyl or octyl, the most applicable sizes are 80-100 meshes, the best counter anion is iodide ion, and the optimum quaternization reagent is iodoalkane. Moreover, the antibacterial capacity was demonstrated to depend on surficial N⁺ groups, correlating with surficial N⁺ charge density (R² of 0.98) but not with exchange capacity (R² of 0.26), physical adsorption of resin skeleton, or electrostatic adsorption of N⁺ groups. Based on these principles, we synthesized a new resin, Ac-81, with a surficial antibacterial design, which simultaneously exhibited better antimicrobial efficiency (two orders of magnitude) as well as higher contaminant removal potential (61.92%) compared to the traditional Ac-8C antibacterial resin. Furthermore, the new resin showed remarkable broad-spectrum antibacterial effects against Gram-negative E. coli and P. aeruginosa and Gram-positive B. subtilis and S. aureus in simulated water and actual water. Simultaneously, water quality was significantly improved, with HCO₃^-, SO₄^2-, TN, TP, and TOC reduced by 79-90%, >99%, 66-85%, >99%, and 22-26%, respectively. Ac-81 is characterized by facile reusability, high treatment capacity of 1500 bed volume, and good adaptability for treating actual water, providing a promising alternative for drinking-water disinfection and purification.

Broad-Spectrum Bactericidal Activity of a Synthetic Random Copolymer Based on 2-Methoxy-6-(4-Vinylbenzyloxy)-Benzylammonium Hydrochloride

Low-molecular-weight organic ammonium salts exert excellent antimicrobial effects by interacting lethally with bacterial membranes. Unfortunately, short-term functionality and high toxicity limit their clinical application. On the contrary, the equivalent macromolecular ammonium salts, derived from the polymerization of monomeric ammonium salts, have demonstrated improved antibacterial potency, a lower tendency to develop resistance, higher stability, long-term activity, and reduced toxicity. A water-soluble non-quaternary copolymeric ammonium salt (P7) was herein synthetized by copolymerizing 2-methoxy-6-(4-vinylbenzyloxy)-benzylammonium hydrochloride monomer with N, N-di-methyl-acrylamide. The antibacterial activity of P7 was assessed against several multidrug-resistant (MDR) clinical isolates of both Gram-positive and Gram-negative species. Except for colistin-resistant Pseudomonas aeruginosa, most isolates were susceptible to P7, also including some Gram-negative bacteria with a modified charge in the external membrane. P7 showed remarkable antibacterial activity against isolates of Enterococcus, Staphylococcus, Acinetobacter, and Pseudomonas, and on different strains of Escherichia coli and Stenotrophomonas maltophylia, regardless of their antibiotic resistance. The lowest minimal inhibitory concentrations (MICs) observed were 0.6-1.2 µM and the minimal bactericidal concentrations (MBC) were frequently overlapping with the MICs. In 24-h time-kill and turbidimetric studies, P7 displayed a rapid non-lytic bactericidal activity. P7 could therefore represent a novel and potent tool capable of counteracting infections sustained by several bacteria that are resistant to the presently available antibiotics.

Facile Synthesis of Imidazolium-Based Block Copolypeptides with Excellent Antimicrobial Activity

Antimicrobial polypeptides are promising mimics of antimicrobial peptides (AMPs) with low risks of antimicrobial resistance (AMR). Polypeptides with facile and efficient production, high antimicrobial activity, and low toxicity toward mammalian cells are highly desirable for practical applications. Herein, triblock copolypeptides with chloro groups (PPG_n-PCPBLG_m) and different main-chain lengths were synthesized via an ultrafast ring-opening polymerization (ROP) using a macroinitiator, namely poly(propylene glycol) bis(2-aminopropyl ether), and purified or nonpurified monomer (i.e., CPBLG-NCA). PPG_n-PCPBLG_m with 90 amino acid residues can be readily prepared within 300 s. Imidazolium-based block copolypeptides (PPG_n-PIL_m) were facilely prepared via nucleophilic substitution of PPG_n-PCPBLG_m with NaN₃ and subsequent "click" chemistry. α-Helical PPG_n-PIL_m can self-assemble into nanostructured and cationic micelles which displayed highly potent antimicrobial activity and low hemolysis. The top-performing material, namely PPG₃₄-PIL₇₀, showed low minimum inhibitory concentration (MIC) against both Gram-positive S. aureus and Gram-negative E. coli (25 μg mL^-1). It also displayed low toxicity against mouse embryonic fibroblast (NIH 3T3) and human embryonic kidney (293T) cells at 2× MIC.

Synthesis, Characterization, and Bactericidal Activity of a 4-Ammoniumbuthylstyrene-Based Random Copolymer

The growing resistance of bacteria to current chemotherapy is a global concern that urgently requires new and effective antimicrobial agents, aimed at curing untreatable infection, reducing unacceptable healthcare costs and human mortality. Cationic polymers, that mimic antimicrobial cationic peptides, represent promising broad-spectrum agents, being less susceptible to develop resistance than low molecular weight antibiotics. We, thus, designed, and herein report, the synthesis and physicochemical characterization of a water-soluble cationic copolymer (P5), obtained by copolymerizing the laboratory-made monomer 4-ammoniumbuthylstyrene hydrochloride with di-methyl-acrylamide as uncharged diluent. The antibacterial activity of P5 was assessed against several multi-drug-resistant clinical isolates of both Gram-positive and Gram-negative species. Except for strains characterized by modifications of the membrane charge, most of the tested isolates were sensible to the new molecule. P5 showed remarkable antibacterial activity against several isolates of genera Enterococcus, Staphylococcus, Pseudomonas, Klebsiella, and against Escherichia coli, Acinetobacter baumannii and Stenotrophomonas maltophilia, displaying a minimum MIC value of 3.15 µM. In time-killing and turbidimetric studies, P5 displayed a rapid non-lytic bactericidal activity. Due to its water-solubility and wide bactericidal spectrum, P5 could represent a promising novel agent capable of overcoming severe infections sustained by bacteria resistant the presently available antibiotics.

Light-Activated Antimicrobial Surfaces Using Industrial Varnish Formulations to Mitigate the Incidence of Nosocomial Infections

Evidence has shown that hospital surfaces are one of the major vehicles of nosocomial infections caused by drug-resistant pathogens. Smart surface coatings presenting multiple antimicrobial activity mechanisms have emerged as an advanced approach to safely prevent this type of infection. In this work, industrial waterborne polyurethane varnish formulations containing for the first time cationic polymeric biocides (SPBs) combined with photosensitizer curcumin were developed to afford contact-active and light-responsive antimicrobial surfaces. SPBs were prepared by atom transfer radical polymerization, which allows control over the polymer features that influence antimicrobial efficiency (e.g., molecular weight), while natural curcumin was employed to impart photodynamic activity to the surface. Antibacterial testing against Gram-negative Escherichia coli revealed that glass surfaces coated with the new formulations displayed photokilling effect under white-light (42 mW/cm²) irradiation within only 15 min of exposure. In addition, it was observed a combined antimicrobial effect between the two biocides (cationic SPB and curcumin), with a higher reduction in the number of viable bacteria observed for the surfaces containing cationic SPB/curcumin mixtures in comparison with the one obtained for surfaces only with polymer or without biocides. The waterborne industrial varnish formulations allowed the formation of homogeneous films without the need for addition of a coalescing agent, which can be potentially applied in diverse surface substrates to reduce bacterial transmission infections in healthcare environments.

Antibacterial Layer-by-Layer Coatings for Medical Implants

The widespread occurrence of nosocomial infections and the emergence of new bacterial strands calls for the development of antibacterial coatings with localized antibacterial action that are capable of facing the challenges posed by increasing bacterial resistance to antibiotics. The Layer-by-Layer (LbL) technique, based on the alternating assembly of oppositely charged polyelectrolytes, can be applied for the non-covalent modification of multiple substrates, including medical implants. Polyelectrolyte multilayers fabricated by the LbL technique have been extensively researched for the development of antibacterial coatings as they can be loaded with antibiotics, antibacterial peptides, nanoparticles with bactericide action, in addition to being capable of restricting adhesion of bacteria to surfaces. In this review, the different approaches that apply LbL for antibacterial coatings, emphasizing those that can be applied for implant modification are presented.

Supramolecular self-assemblies of engineered polyethylenimines as multifunctional nanostructures for DNA transportation with excellent antimicrobial activity

In this study, indole-3-butanoic acid (IBA), a biologically and environmentally safe entity, has been grafted onto low and high molecular weight (1.8 and 25 kDa) polyethylenimines (PEI) mainly through primary amines to obtain amphiphilic indole-3-butanoyl-polyethylenimines (IBPs). Two series of IBPs (IBP_1.8 and IBP₂₅) were prepared which, on self-assembly in aqueous medium, yielded multifunctional nanomicellar structures (IBP_1.8 and IBP₂₅) capable of transporting genetic material in vitro and exhibiting other biological activities. Physicochemical characterization showed the size of IBP_1.8 and IBP₂₅ nanostructures in the range of ~332-234 nm and ~283-166 nm, respectively, with zeta potential varying from ~+29-17 mV and ~+37-25 mV. DNA release assay demonstrated higher release of plasmid DNA from IBP nanostructures as compared to native PEIs. Cytotoxicity showed a decreasing pattern with increasing degree of grafting of IBA onto PEIs making these nanostructures non-toxic. pDNA complexes of these nanostructures (both IBPs_1.8 and IBPs₂₅) displayed considerably higher transfection efficiency, however, IBP_1.8/pDNA complexes performed much better (~7-9 folds) as compared to native PEI/pDNA and Lipofectamine/pDNA complexes on mammalian cells. CLSM analysis revealed that these complexes entered nucleus in sufficient amounts suggesting higher uptake and efficient internalization of the complexes. Besides, these supramolecular nanostructures not only exhibited excellent antimicrobial potential (MIC ~49-100 µg/ml) against clinical as well as resistant pathogenic strains but also found to possess antioxidant property. Overall, the projected low molecular weight PEI-based vectors could serve as more effective multifunctional nanomaterials having promising potential for future gene therapy applications with capability to provide protection against other bacterial infections.

Positively Charged Polymers as Promising Devices against Multidrug Resistant Gram-Negative Bacteria: A Review

Antibiotic resistance has increased markedly in Gram-negative bacteria, causing severe infections intractable with traditional drugs and amplifying mortality and healthcare costs. Consequently, to find novel antimicrobial compounds, active on multidrug resistant bacteria, is mandatory. In this regard, cationic antimicrobial peptides (CAMPs)—able to kill pathogens on contact—could represent an appealing solution. However, low selectivity, hemolytic toxicity and cost of manufacturing, hamper their massive clinical application. In the recent years—starting from CAMPs as template molecules—less toxic and lower-cost synthetic mimics of CAMPs, including cationic peptides, polymers and dendrimers, have been developed. Although the pending issue of hemolytic toxicity and biodegradability is still left not completely solved, cationic antimicrobial polymers (CAPs), compared to small drug molecules, thanks to their high molecular weight, own appreciable selectivity, reduced toxicity toward eukaryotic cells, more long-term activity, stability and non-volatility. With this background, an updated overview concerning the main manufactured types of CAPs, active on Gram-negative bacteria, is herein reported, including synthetic procedure and action’s mechanism. Information about their structures, antibacterial activity, advantages and drawbacks, was reported in the form of tables, which allow faster consultation and quicker learning concerning current CAPs state of the art, in order not to retrace reviews already available.

Facile and scalable synthesis of topologically nanoengineered polypeptides with excellent antimicrobial activities

A facile and scalable strategy for the quick library synthesis of linear-, hinged-, star-, and cyclic-polypeptides with broad-spectrum antimicrobial activity has been reported.

The 40 kDa Linear Polyethylenimine Inhibits Porcine Reproductive and Respiratory Syndrome Virus Infection by Blocking Its Attachment to Permissive Cells

Porcine reproductive and respiratory syndrome (PRRS) is one of the most economically devastating infectious diseases in pigs worldwide. The causative agent is the PRRS virus (PRRSV). In this study, we explored polyethylenimine (PEI), a cationic polymer with different forms (linear or branched), to inhibit the replication of PRRSV. Our results demonstrate that the linear but not the 40 kDa branched PEI, or the 25 kDa linear PEI, were well tolerated in cultured cells and exhibited a broad-spectrum inhibition of heterogeneous PRRSV-2 isolates in both MARC-145 cells and primary porcine pulmonary alveolar macrophages (PAMs). Further analysis suggests that PEI could prevent the attachment of PRRSV virions to the susceptible cells. Notably, PEI had a minimal effect on PRRSV internalization in MARC-145 cells, whereas PEI promoted the internalization of PRRSV virions in PAMs, which suggests that these two types of cells might have different internalization processes of PRRSV virions. In conclusion, our data demonstrate that PEI could be used as a novel inhibitor against PRRSV.