Antibacterial properties of cationic copolymers as a function of pendant alkyl chain length and degree of quaternization

Bactericidal and Antifouling Coatings with the "Killing-Repelling-Killing" Triple Function Based on Cationic Copolymers with Structure Conversion and Capsaicin Analogue Release

The capsaicin analogue N-(4-hydroxy-3-methoxybenzyl) acrylamide (HMBA) was linked with polylauryl methacrylate-b-poly(2-(N,N-dimethylamino)ethyl methacrylate) (PLMA-b-PDMAEMA) via a quaternization reaction with 4-(acrylamidomethyl)-2-methoxyphenyl 2-chloroacetate (AAMPCA). The amphiphilic copolymers were capable of transforming its structure in response to the solvent change from aprotic to protic, which was verified by the 1H NMR spectrum. The resulting cationic copolymers underwent a hydrolysis process in water, yielding zwitterionic groups on surfaces. Meanwhile, the bactericidal reagent HMBA was released. It was proved that the hydrolysis rate of the copolymers accelerated with higher temperature, higher pH value, and higher hydrophilic block units. And the controllable, sustainable release of HMBA was achieved with copolymer-mediated hydrolysis. Protein-repellent and bactericidal tests on the surface of the coating proved that antifouling and bactericidal performances of the coating correlated to the structure conversion abilities of the corresponding copolymer. The dynamic monitoring of Escherichia coli adhesion in 3 h evidenced the antifouling and bactericidal process of copolymers with different block ratios and concentrations. The coating incorporated with 3% PLMA120-b-(PDMAEMA-AAMPCA)120 in polylactic acid base materials showed an adhesion ratio of E. coli less than 1% within 1 h, and the survival ratio of the adhered bacteria is <1%, suggesting its rapid speed and high efficiency in "bacterial repelling and killing". Also, the PLMA120-b-(PDMAEMA-AAMPCA)120 copolymer demonstrated enhanced bactericidal ability compared with the mixture of cationic poly(laruyl methacrylate)120-b-poly(carboxybetaine methacrylate ester)120 (PLMA120-b-PCBMAE120) and free HMBA. The lowest minimal inhibitory concentration was 0.078 mg/mL against Staphylococcus aureus and 0.312 mg/mL against E. coli, respectively.

Genome editing in Acinetobacter baumannii through enhanced natural transformation

Acinetobacter baumannii, a multidrug-resistant bacterium has become a significant cause of life-threatening infections acquired in hospitals worldwide. The existing drugs used to treat A. baumannii infections are rapidly losing efficacy, and the increasing antimicrobial resistance, which is expected to turn into a global health crisis, underscores the urgency to develop novel prevention and treatment strategies. We reasoned that the discovery of novel virulence targets for vaccine and therapy interventions requires a more enhanced method for the introduction of multiple elements of foreign DNA for genome editing than the current methods of natural transformation techniques. Herein, we employed a novel and a much-improved enhanced technique for the natural transformation of elements of the genome editing system CRISPR-Cas9 to suppress specific genomic regions linked to selectively suppress bacterial virulence. We modified the genome of the laboratory-adapted strain of A. baumannii BAA-747 by targeting the AmpC, as a marker gene, for disruption by three different genomic manipulation strategies, and created mutant strains of A. baumannii that are, at least, fourfold susceptible to ampicillin. This work has established an optimized enhanced natural transformation system that enables efficient genome editing of pathogenic bacteria in a laboratory setting, providing a valuable future tool for exploring the function of unidentified virulence genes in bacterial genomes.

Construction of gelatin/alginate hydrogels doped hemicyanine derivatives for photodynamic antibacterial application

Hydrogel systems based on natural polymer materials have provided alternative opportunities for preparing antimicrobial dressings. A composite antibacterial hydrogel system containing gelatin (Gel), alginate (Alg) and hemicyanine derivatives with different chain lengths (C3, C6 and C10) was constructed. The composite hydrogels have excellent swelling ability and low degradability due to the classical three-dimensional network structure. Because of the photosensitization ability of C3, C6 and C10, hydrogels containing these molecules can also effectively produce reactive oxygen species (ROS) under light. Importantly, the hydrogel containing C3 molecules that have higher spatial extension structure and shorter alkyl chain than C6 and C10 shows better photo-responsive antibacterial effect against drug-resistant Escherichia coli. The bacterial killing activity of the composite hydrogel system could be regulated by changing the alkyl chain length of the photosensitizers. This effective and photo-responsive composite hydrogel system is expected to be used for bacteria-infected wound repair and promoting wound healing.

Construction of Electrostatic Spinning Membranes Based on Conjugated Hemicyanine Derivatives for Photodynamic Antibacterial Application

The preparation of efficient antibacterial membrane materials is one of the important strategies to fight against bacterial infection and alleviate drug resistance. Herein, hemicyanine derivatives with different chain lengths (C3, C6, and C10) that exhibit excellent photodynamic antibacterial activity were doped into spinnable polyvinyl alcohol solution (PVA, 8%) to obtain composite fiber membrane Cn/PVA (C3/PVA, C6/PVA, and C10/PVA) by a simple "one-pot" method using electrospinning technology. The antibacterial nanofiber membrane has a dense fiber structure which has a good interception effect, high thermal stability, and great biocompatibility. Importantly, Cn/PVA nanofibers could efficiently sensitize oxygen to generate reactive oxygen species (ROS), leading to high photokilling efficacy against drug-resistant bacteria. The variation of structure for hemicyanines causes the difference of Cn/PVA nanofibers in the effects of antibacterial performance, and it is found that C3/PVA and C10/PVA with three and ten carbons in the alkyl chain could kill more than 97% of ampicillin-resistant E. coli, which is much better than that of C6/PVA. Moreover, C3/PVA and C10/PVA exhibited killing efficiencies of 98.6 and 90.6% against MRSA, respectively. The construction of Cn/PVA composite fibers provides research ideas for the development of structure-dependent antimicrobial surface materials and is expected to be applied as superficial medical antibacterial protection materials.

Antimicrobial cryogel dressings towards effective wound healing

Cryogels are macroporous hydrogels that have been widely utilized in a variety of biomedical applications including wound dressings. Cryogels reveal superior mechanical and swelling properties as well as large and interconnected porosity. As traditional hydrogel wound dressings generally show undesirable mechanical and swelling characteristics, cryogels, due to their toughness and superfast swelling, offer an outstanding platform to address the growing number of various types of wounds. Moreover, recently, cryogel wound dressings loaded with an antimicrobial agent emerged as a feasible option to reduce infection, and thus improve the wound healing process. However, a comprehensive review of antimicrobial cryogels as a wound dressing is still lacking in the literature. In this review, we summarize the progress of cryogels in the area of wound dressings and provide an overview of the various polymers, namely, natural and synthetic which have been employed in cryogel wound dressing preparation. Furthermore, the most prominent antimicrobial agents incorporated in cryogel wound dressings are provided. Finally, the future directions of cryogel wound dressings for wound healing are also discussed.

Poly(vinyl pyridine) and Its Quaternized Derivatives: Understanding Their Solvation and Solid State Properties

A series of N-methyl quaternized derivatives of poly(4-vinylpyridine) (PVP) were synthesized in high yields with different degrees of quaternization, obtained by varying the methyl iodide molar ratio and affording products with unexplored optical and solvation properties. The impact of quaternization on the physicochemical properties of the copolymers, and notably the solvation properties, was further studied. The structure of the synthesized polymers and the quaternization degrees were determined by infrared and nuclear magnetic spectroscopies, while their thermal characteristics were studied by differential scanning calorimetry and their thermal stability and degradation by thermogravimetric analysis (TG-DTA). Attention was given to their optical properties, where UV-Vis and diffuse reflectance spectroscopy (DRS) measurements were carried out. The optical band gap of the polymers was calculated and correlated with the degree of quaternization. The study was further orientated towards the solvation properties of the polymers in binary solvent mixtures that strongly depend on the degree of quaternization, enabling a better understanding of the key polymer (solute)-solvent interactions. The assessment of the underlying solvation phenomena was performed in a system of different ratios of DMSO/H₂O and the solvatochromic indicator used was Reichardt’s dye. Solvent polarity parameters have a significant effect on the visible spectra of the nitrogen quaternization of PVP studied in this work and a detailed path towards this assessment is presented.

Nanotechnology-Based Antimicrobial and Antiviral Surface Coating Strategies

Biocontamination of medical devices and implants is a growing issue that causes medical complications and increased expenses. In the fight against biocontamination, developing synthetic surfaces, which reduce the adhesion of microbes and provide biocidal activity or combinatory effects, has emerged as a major global strategy. Advances in nanotechnology and biological sciences have made it possible to design smart surfaces for decreasing infections. Nevertheless, the clinical performance of these surfaces is highly depending on the choice of material. This review focuses on the antimicrobial surfaces with functional material coatings, such as cationic polymers, metal coatings and antifouling micro-/nanostructures. One of the highlights of the review is providing insights into the virus-inactivating surface development, which might particularly be useful for controlling the currently confronted pandemic coronavirus disease 2019 (COVID-19). The nanotechnology-based strategies presented here might be beneficial to produce materials that reduce or prevent the transmission of airborne viral droplets, once applied to biomedical devices and protective equipment of medical workers. Overall, this review compiles existing studies in this broad field by focusing on the recent related developments, draws attention to the possible activity mechanisms, discusses the key challenges and provides future recommendations for developing new, efficient antimicrobial and antiviral surface coatings.