The antibacterial activity and mechanism of polyurethane coating with quaternary ammonium salt

Cetyltrimethylammonium-chloride assisted in situ metabolic incorporation of nano-sized ROS-generating cascade-reaction containers in Gram-positive and Gram-negative peptidoglycan layers for the control of bacterially-induced sepsis

Cascade-reaction containers generating reactive oxygen species (ROS) as an alternative for antibiotic-based strategies for bacterial infection control, require endogenous oxygen-sources and ROS-generation close to or preferably inside target bacteria. Here, this is achieved by cetyltrimethylammonium-chloride (CTAC) assisted in situ metabolic labeling and incorporation of mesoporous SiO2-nanoparticles, dual-loaded with glucose-oxidase and Fe3O4-nanoparticles as cascade-reaction containers, inside bacterial cell walls. First, azide-functionalized d-alanine (D-Ala-N3) was inserted in cell wall peptidoglycan layers of growing Gram-positive pathogens. In Gram-negatives, this could only be achieved after outer lipid-membrane permeabilization, using a low concentration of CTAC. Low concentrations of CTAC had no adverse effect on in vitro blood clotting or hemolysis nor on the health of mice when blood-injected. Next, dibenzocyclooctyne-polyethylene-glycol modified, SiO2-nanoparticles were in situ click-reacted with d-Ala-N3 in bacterial cell wall peptidoglycan layers. Herewith, a two-step cascade-reaction is facilitated inside bacteria, in which glucose-oxidase generates H2O2 at endogenously-available glucose concentrations, while subsequently Fe3O4-nanoparticles catalyze generation of •OH from the H2O2 generated. Generation of •OH inside bacterial cell walls by dual-loaded mesoporous SiO2-nanoparticles yielded more effective in vitro killing of both planktonic Gram-positive and Gram-negative bacteria suspended in 10 % plasma than SiO2-nanoparticles solely loaded with glucose-oxidase. Gram-positive or Gram-negative bacterially induced sepsis in mice could be effectively treated by in situ pre-treatment with tail-vein injected CTAC and d-Ala-N3, followed by injection of dual-loaded cascade-reaction containers without using antibiotics. This makes in situ metabolic incorporation of cascade-reaction containers as described attractive for further investigation with respect to the control of other types of infections comprising planktonic bacteria. STATEMENT OF SIGNIFICANCE: In situ metabolic-incorporation of cascade-reaction-containers loaded with glucose-oxidase and Fe3O4 nanoparticles into bacterial cell-wall peptidoglycan is described, yielding ROS-generation from endogenous glucose, non-antibiotically killing bacteria before ROS inactivates. Hitherto, only Gram-positives could be metabolically-labeled, because Gram-negatives possess two lipid-membranes. The outer membrane impedes direct access to the peptidoglycan. This problem was solved by outer-membrane permeabilization using a quaternary-ammonium compound. Several studies on metabolic-labeling perform crucial labeling steps during bacterial-culturing that in real-life should be part of a treatment. In situ metabolic-incorporation as described, can be applied in well-plates during in vitro experiments or in the body as during in vivo animal experiments. Surprisingly, metabolic-incorporation proceeded unhampered in blood and a murine, bacterially-induced sepsis could be well treated.

Exploiting the advantages of cationic copolymers and AgBr nanoparticles to optimize the antibacterial activity of chitosan

Recently, the chitosan (CS)-based composites have attracted increasing attention for controlling and preventing the spread of pathogenic microorganisms. Herein, an amphiphilic copolymer containing epoxy and quaternary ammonium groups (PBGDBr) was synthesized via three common acrylate monomers. The epoxy groups of this copolymer were then crosslinked with the amino groups of CS to synthesize a natural/synthetic (PBGDBr-C) composite to increase the water solubility of CS under alkaline conditions and enhance its antibacterial activity based on chemical contact-type modes. Moreover, silver bromide nanoparticles (AgBr NPs)-decorated PBGDBr-C (AgBr@PBGDBr-C) composite was prepared, which aimed to endow the final AgBr@PBGDBr-C composite with a photodynamic antibacterial mode relying on the formation of Ag/AgBr nanostructures catalyzed by visible light on AgBr NPs. The results showed that the final composite possessed satisfactory bactericidal effects at concentrations higher than 64 and 128 μg/mL against Escherichia coli and Staphylococcus aureus, respectively. Additionally, The L929 cells treated with the final composite retained high cell viability (>80 %) at a concentration of 128 μg/mL, indicating its low toxicity to L929 cells. Overall, our synthetic strategy exploits a multi-modal system that enables chemical-photodynamic synergies to treat infections caused by pathogenic bacteria while delaying the development of bacterial resistance.

An intumescent flame-retardant system based on carboxymethyl cellulose for flexible polyurethane foams with outstanding flame retardancy, antibacterial properties, and mechanical properties

A novel and eco-friendly intumescent flame-retardant system based on sodium carboxymethyl cellulose (CMC) was established for wide-used flexible polyurethane foams (FPUFs). FPUF-(APP₆CMC₁)GN₁ with extremely uniform coatings extinguished and reached the UL-94 V-0 rating, and presented an improvement of thermal insulation properties. Moreover, there was a 58 % reduction in peak heat release rate for FPUF-(APP₆CMC₁)GN₁ compared with that of FPUF, and the microstructure analysis of char residues indicated that a perfect intumescent char layer had formed on the surface of FPUFs. Especially, CMC and GN enhanced the compactness and stability of char layers. Therefore, little volatile production was generated under the protection of physical layers in the high temperature as evaluated during the thermal degradation processes. Meanwhile, the flame-retardant FPUFs remained the ideal mechanical properties and obtained excellent antibacterial properties, and the antibacterial rates of E.coli and S.aureus were 99.9 % (FPUF-(APP₆CMC₁)GN₁). This work provides an eco-friendlier strategy for the design of multi-function FPUFs.

Flourishing Antibacterial Strategies for Osteomyelitis Therapy

Osteomyelitis is a destructive disease of bone tissue caused by infection with pathogenic microorganisms. Because of the complex and long-term abnormal conditions, osteomyelitis is one of the refractory diseases in orthopedics. Currently, anti-infective therapy is the primary modality for osteomyelitis therapy in addition to thorough surgical debridement. However, bacterial resistance has gradually reduced the benefits of traditional antibiotics, and the development of advanced antibacterial agents has received growing attention. This review introduces the main targets of antibacterial agents for treating osteomyelitis, including bacterial cell wall, cell membrane, intracellular macromolecules, and bacterial energy metabolism, focuses on their mechanisms, and predicts prospects for clinical applications.