Bactericidal Specificity and Resistance Profile of Poly(Quaternary Ammonium) Polymers and Protein–Poly(Quaternary Ammonium) Conjugates

Sensing, Imaging, and Therapeutic Strategies Endowing by Conjugate Polymers for Precision Medicine

Conjugated polymers (CPs) have promising applications in biomedical fields, such as disease monitoring, real-time imaging diagnosis, and disease treatment. As a promising luminescent material with tunable emission, high brightness and excellent stability, CPs are widely used as fluorescent probes in biological detection and imaging. Rational molecular design and structural optimization have broadened absorption/emission range of CPs, which are more conductive for disease diagnosis and precision therapy. This review provides a comprehensive overview of recent advances in the application of CPs, aiming to elucidate their structural and functional relationships. The fluorescence properties of CPs and the mechanism of detection signal amplification are first discussed, followed by an elucidation of their emerging applications in biological detection. Subsequently, CPs-based imaging systems and therapeutic strategies are illustrated systematically. Finally, recent advancements in utilizing CPs as electroactive materials for bioelectronic devices are also investigated. Moreover, the challenges and outlooks of CPs for precision medicine are discussed. Through this systematic review, it is hoped to highlight the frontier progress of CPs and promote new breakthroughs in fundamental research and clinical transformation.

Porous Microspheres as Pathogen Traps for Sepsis Therapy: Capturing Active Pathogens and Alleviating Inflammatory Reactions

Sepsis is a systemic inflammatory response syndrome caused by pathogen infection, while the current antibiotics mainly utilized in clinical practice to combat infection result in the release of pathogen-associated molecular patterns (PAMPs) in the body. Herein, we provide an innovative strategy for controlling sepsis, namely, capturing active pathogens by means of extracorporeal blood purification. Carbon nanotubes (CNTs) were modified with dimethyldiallylammonium chloride (DDA) through γ-ray irradiation-induced graft polymerization to confer a positive charge. Then, CNT-DDAs are blended with polyurethane (PU) to prepare porous microspheres using the electro-spraying method. The obtained microspheres with a pore diameter of 2 μm served as pathogen traps and are termed as PU-CNT-DDA microspheres. Even at a high flow rate of 50 mL·min-1, the capture efficiencies of the PU-CNT-DDAs for Escherichia coli and Staphylococcus aureus remained 94.7% and 98.8%, respectively. This approach circumvents pathogen lysis and mortality, significantly curtails the release of PAMPs, and hampers the production of pro-inflammatory cytokines. Therefore, hemoperfusion using porous PU-CNT-DDAs as pathogen traps to capture active pathogens and alleviate inflammation opens a new route for sepsis therapy.

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.

Design of Thermoplastic Polyurethanes with Conferred Antibacterial, Mechanical, and Cytotoxic Properties for Catheter Application

Thermoplastic polyurethanes (TPUs) are proposed as suitable solution for the fabrication of biocompatible catheters with appropriate mechanical parameters and confirmed antibacterial and cytocompatible properties. For this purpose, a series of quaternary ammonium salts (QASs) and quaternary phosphonium salts (QPSs) based monomers were prepared followed by the determination of their minimal inhibitory concentrations (MICs) against Gram-positive Staphylococcus aureus (S. aureus) and Gram-negative Pseudomonas aeruginosa (P. aeruginosa). A combination of the most active ammonium (QAS-C₁₄) and phosphonium (QPS-TOP) salts led to a MIC down to 2.4 μg/mL against S. aureus and 9 μg/mL against P. aeruginosa, corroborating the existence of a synergistic effect. These quaternary onium salt (QOS) units were successfully incorporated along the polymer chain, as part of a two-step synthesis approach. The resulting TPU-QOS materials were subsequently characterized through thermal, mechanical, and surface analyses. TPU-Mix (combining the most active QAS-C₁₄ and QPS-TOP units) showed the highest antibacterial efficiency, confirming the synergistic effect between both QOS groups. Finally, an MTT assay on the SiHa cell line revealed the low cytotoxicity level of these polymeric films, making these materials suitable for biomedical application. To go one step further in the preindustrialization approach, proof of concept regarding the catheter prototype fabrication based on TPU-QAS/QPS was validated by extrusion.

Polydimethyldiallylammonium chloride induces oxidative stress in anaerobic digestion of waste activated sludge

The effects and key mechanisms of polydimethyldiallylammonium chloride on anaerobic digestion of waste activated sludge were investigated. Polydimethyldiallylammonium chloride at 38.1 g/kg total solids substantially reduced cumulative methane production from 138.2 ± 5.5 to 49.4 ± 5.0 L CH₄/kg volatile solids added, a reduction of 64.3 ± 0.2%. The quaternary ammonium groups on polydimethyldiallylammonium chloride agglomerated sludge flocs by neutralizing negatively charged amino groups in in extracellular polymeric substances, which hindered the release of organic matter. Quaternary ammonium groups induce oxidative stress by inducing the production of reactive oxygen species, thereby inhibiting the activity of anaerobic digestive enzymes. In addition, quaternary amine groups reduced the abundance of hydrolyzing bacteria, acidifying bacteria, and acetylotrophic methanogens. Oxidative stress could be an underappreciated mechanism that quaternary ammonium groups deteriorate anaerobic digestion, which could be transformative for understanding the potential risks of quaternary ammonium cationic flocculants in biological sludge treatment.

Secondary Ammonium-Based Hyperbranched Poly(amidoamine) with Excellent Membrane-Active Property for Multidrug-Resistant Bacterial Infection

With the rapid emergence of microbial infections induced by "superbugs", public health and the global economy are threatened by the lack of effective and biocompatible antibacterial agents. Herein, we systematically design a series of secondary ammonium-based hyperbranched poly(amidoamine) (SAHBP) with different alkyl chain lengths for probing high-efficacy antibacterial agents. SAHBP modified with alkyl tails at the hyperbranched core could efficiently kill Escherichia coli and Staphylococcus aureus, two types of clinically important bacteria worldwide. The best SAHBP with 12-carbon-long alkyl tails (SAHBP-12) also showed high activity against problematic multidrug-resistant bacteria, including Pseudomonas aeruginosa and methicillin-resistant S. aureus (MRSA). Based on ζ potential, isothermal titration microcalorimetry (ITC), and membrane integrity assays, it is found that SAHBP-12 could attach to the cell membrane via electrostatic adsorption and hydrophobic interactions, following which the integrity of the bacterial cell wall and the cell membrane is disrupted, resulting in severe cell membrane damage and the leakage of cytoplasmic contents, finally causing bacterial cell death. Impressively, benefiting from excellent membrane-active property, SAHBP-12 exhibited robust therapeutic efficacy in MRSA-infected mice wounds. Moreover, SAHBP-12 also showed excellent biosafety in vitro and in vivo, which undoubtedly distinguished it as a potent weapon in combating the growing threat of problematic multidrug-resistant bacterial infections.

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...

Regiospecific vs. non regiospecific click azide-alkyne polymerization: In vitro study of water-soluble antibacterial poly(amide aminotriazole)s

Novel linear cationic poly(amide aminotriazole)s (PATnD) with secondary amine groups in the backbone were obtained by using azide-alkyne 1,3-dipolar cycloaddition reactions: metal- and solvent-free (thermal conditions, PATTnD) or copper(I)-catalyzed (Sharpless conditions, PATCnD). PATnD were investigated in vitro against strains of E. coli, P. aeruginosa, S. aureus, and S. epidermidis. Hemolytic activity was tested using human red blood cells (hRBC), and very low or no hemolytic activity was observed. The cytotoxicity of PATnD polymers against Human Gingival Fibroblasts (HGnF) cells was concentration-dependent, and significant differences between PATT1D and PATC1D were observed. The ability of these polymers to induce resistance against both Gram-positive and Gram-negative bacteria was also assessed. Studied bacterial strains acquired resistance to catalytic polymers (PATCnD) in initial passages meanwhile resistance to thermal polymers (PATTnD) appears in later passages, being the increase of the minimum inhibitory concentration lower than in catalytic polymers. This result, together with the higher biocidal capacity of thermal polymers compared to catalytic ones, seems to suggest an influence of the regiospecificity of the polymers on their antibacterial characteristics. This study also demonstrates that PAT1D polymers, which do not appear to have strong hydrophobic residues, can exert significant antimicrobial activity against Gram-positive bacteria such as S. epidermidis. This pair of polymers, PATC1D and PATT1D, displays the greatest antimicrobial activity while not causing significant hemolysis along with the lowest susceptibility for resistance development of the polymers evaluated.

Synthesis of Ag@chitosan/copolymer with dual-active centers for high antibacterial activity

The prevention and treatment of microorganism contamination on substrate surfaces have recently generated significant concern of scientists. In this paper, a novel diblock copolymer containing antibacterial quaternary ammonium groups as pendant groups, poly(3-(methacryloylamino) propyltrimethyl ammonium chloride)-b-poly(styrene) (PMS), was synthesized by interfacial polymerization. Also, PMS anisotropic particles (APs) could be successfully obtained based on different assembly behaviors by adjusting the ratios of monomers and the toluene/styrene (Tol/St). Moreover, silver loaded chitosan (Ag@CS) and PMS APs were combined to prepare natural/synthetic polymer antibacterial materials with dual-active centers (Ag@CS/PMS-4 APs), aiming to expand the application of carbohydrate polymers and improve the antibacterial activity of composite materials. Remarkably, the resulting series of PMS particles, especially worm-like PMS-4 APs, and Ag@CS/PMS-4 APs composite film ((Ag@CS/PMS-4 APs)-F) exhibited excellent antibacterial properties, which can be employed as interface materials to prevent the transmission of infectious diseases caused by microorganism contamination.

Polymer Modification of Lipases, Substrate Interactions, and Potential Inhibition

An industrially important enzyme, Candida antarctica lipase B (CalB), was modified with a range of functional polymers including hydrophilic, hydrophobic, anionic, and cationic character using a "grafting to" approach. We determined the impact of polymer chain length on CalB activity by synthesizing biohybrids of CalB with each polymer at three different chain lengths, using reversible addition-fragmentation chain transfer (RAFT) polymerization. The activity of CalB in both aqueous and aqueous-organic media mixtures was significantly enhanced for acrylamide (Am) and N,N-dimethyl acrylamide (DMAm) conjugates, with activity remaining approximately constant in 25 and 50% ethanol solvent systems. Interestingly, the activity of N,N-dimethylaminopropyl-acrylamide (DMAPA) conjugates increased gradually with increasing organic solvent content in the system. Contrary to other literature reports, our study showed significantly diminished activity for hydrophobic polymer-protein conjugates. Functional thermal stability assays also displayed a considerable enhancement of retained activity of Am, DMAm, and DMAPA conjugates compared to the native CalB enzyme. Thus, this study provides an insight into possible advances in lipase production, which can lead to new improved lipase bioconjugates with increased activity and stability.

Atom Transfer Radical Polymerization for Biorelated Hybrid Materials

Proteins, nucleic acids, lipid vesicles, and carbohydrates are the major classes of biomacromolecules that function to sustain life. Biology also uses post-translation modification to increase the diversity and functionality of these materials, which has inspired attaching various other types of polymers to biomacromolecules. These polymers can be naturally (carbohydrates and biomimetic polymers) or synthetically derived and have unique properties with tunable architectures. Polymers are either grafted-to or grown-from the biomacromolecule's surface, and characteristics including polymer molar mass, grafting density, and degree of branching can be controlled by changing reaction stoichiometries. The resultant conjugated products display a chimerism of properties such as polymer-induced enhancement in stability with maintained bioactivity, and while polymers are most often conjugated to proteins, they are starting to be attached to nucleic acids and lipid membranes (cells) as well. The fundamental studies with protein-polymer conjugates have improved our synthetic approaches, characterization techniques, and understanding of structure-function relationships that will lay the groundwork for creating new conjugated biomacromolecular products which could lead to breakthroughs in genetic and tissue engineering.

Self-disinfecting surfaces and infection control

According to World Health Organization, every year in the European Union, 4 million patients acquire a healthcare associated infection. Even though some microorganisms represent no threat to healthy people, hospitals harbor different levels of immunocompetent individuals, namely patients receiving immunosuppressors, with previous infections, or those with extremes of age (young children and elderly), requiring the implementation of effective control measures. Public spaces have also been found an important source of infectious disease outbreaks due to poor or none infection control measures applied. In both places, surfaces play a major role on microorganisms' propagation, yet they are very often neglected, with very few guidelines about efficient cleaning measures and microbiological assessment available. To overcome surface contamination problems, new strategies are being designed to limit the microorganisms' ability to survive over surfaces and materials. Surface modification and/or functionalization to prevent contamination is a hot-topic of research and several different approaches have been developed lately. Surfaces with anti-adhesive properties, with incorporated antimicrobial substances or modified with biological active metals are some of the strategies recently proposed. This review intends to summarize the problems associated with contaminated surfaces and their importance on infection spreading, and to present some of the strategies developed to prevent this public health problem, namely some already being commercialized.

Red Fluorescence Conjugated Polymer with Broad Spectrum Antimicrobial Activity for Treatment of Bacterial Infections In Vivo

To address the problem of bacterial resistance, a practical strategy for broad spectrum antimicrobial based on conjugated polymers was proposed in the work. Three red fluorescence conjugated polymers (P1, P2, and P3) bearing quaternary ammonium groups with different length of side chains were designed and synthesized. By virtue of inserting capacity of the longer side chain, conjugated polymer (P3) displayed well broad spectrum antimicrobial activity toward Gram-negative and Gram-positive bacteria and fungi under a white light density of 25 mW cm^-2 and short time (15 min) by aid of dark toxicity and light toxicity, derived from the quaternary ammonium groups and reactive oxygen species produced by the backbone, respectively. Notably, for ampicillin-resistant Escherichia coli TOP10, P3 could kill the bacteria 100% at a very low concentration of 5 μM upon light irradiation. Furthermore, wound healing tests indicated that the polymer could be expediently employed for wound disinfection in vivo without any tissue damaging. The contribution of the work not only provides an efficient and broad spectrum antimicrobial material but also offers a multimodal antimicrobial strategy to fight against bacterial infections in vivo.

Advanced Materials by Atom Transfer Radical Polymerization

Atom transfer radical polymerization (ATRP) has been successfully employed for the preparation of various advanced materials with controlled architecture. New catalysts with strongly enhanced activity permit more environmentally benign ATRP procedures using ppm levels of catalyst. Precise control over polymer composition, topology, and incorporation of site specific functionality enables synthesis of well-defined gradient, block, comb copolymers, polymers with (hyper)branched structures including stars, densely grafted molecular brushes or networks, as well as inorganic-organic hybrid materials and bioconjugates. Examples of specific applications of functional materials include thermoplastic elastomers, nanostructured carbons, surfactants, dispersants, functionalized surfaces, and biorelated materials.

Recent Progress in Polymer Research to Tackle Infections and Antimicrobial Resistance

Global health is increasingly being threatened by the rapid emergence of drug-resistant microbes. The ability of these microbes to form biofilms has further exacerbated the scenario leading to notorious infections that are almost impossible to treat. For addressing this clinical threat, various antimicrobial polymers, polymer-based antimicrobial hydrogels and polymer-coated antimicrobial surfaces have been developed in the recent past. This review aims to discuss such polymer-based antimicrobial strategies with a focus on their current advancement in the field. Antimicrobial polymers, whose designs are inspired from antimicrobial peptides (AMPs), are described with an emphasis on structure-activity analysis. Additionally, antibiofilm activity and in vivo efficacy are delineated to elucidate the real potential of these antimicrobial polymers as possible therapeutics. Antimicrobial hydrogels, prepared from either inherently antimicrobial polymers or biocide-loaded into polymer-derived hydrogel matrix, are elaborated followed by various strategies to engineer polymer-coated antimicrobial surfaces. In the end, the current challenges are accentuated along with future directions for further expansion of the field toward tackling infections and antimicrobial resistance.