Quaternary ammonium-based biomedical materials: State-of-the-art, toxicological aspects and antimicrobial resistance

Microbial infections affect humans worldwide. Many quaternary ammonium compounds have been synthesized that are not only antibacterial, but also possess antifungal, antiviral and anti-matrix metalloproteinase capabilities. Incorporation of quaternary ammonium moieties into polymers represents one of the most promising strategies for preparation of antimicrobial biomaterials. Various polymerization techniques have been employed to prepare antimicrobial surfaces with quaternary ammonium functionalities; in particular, syntheses involving controlled radical polymerization techniques enable precise control over macromolecular structure, order and functionality. Although recent publications report exciting advances in the biomedical field, some of these technological developments have also been accompanied by potential toxicological and antimicrobial resistance challenges. Recent evidenced-based data on the biomedical applications of antimicrobial quaternary ammonium-containing biomaterials that are based on randomized human clinical trials, the golden standard in contemporary medicinal science, are included in the present review. This should help increase visibility, stimulate debates and spur conversations within a wider scientific community on the implications and plausibility for future developments of quaternary ammonium-based antimicrobial biomaterials.

Nanomaterials for Functional Textiles and Fibers

Nanoparticles are very interesting because of their surface properties, different from bulk materials. Such properties make possible to endow ordinary products with new functionalities. Their relatively low cost with respect to other nano-additives make them a promising choice for industrial mass-production systems. Nanoparticles of different kind of materials such as silver, titania, and zinc oxide have been used in the functionalization of fibers and fabrics achieving significantly improved products with new macroscopic properties. This article reviews the most relevant approaches for incorporating such nanoparticles into synthetic fibers used traditionally in the textile industry allowing to give a solution to traditional problems for textiles such as the microorganism growth onto fibers, flammability, robustness against ultraviolet radiation, and many others. In addition, the incorporation of such nanoparticles into special ultrathin fibers is also analyzed. In this field, electrospinning is a very promising technique that allows the fabrication of ultrathin fiber mats with an extraordinary control of their structure and properties, being an ideal alternative for applications such as wound healing or even functional membranes.

Antimicrobial polymer nanostructures: synthetic route, mechanism of action and perspective

Protection against bacterial infections is an important research field in modern society. Antimicrobial polymers have received considerable attention as next-generation biocides because they represent an ecologically friendly approach that does not promote resistance. In the last decade, many authors have reported the development of nano-sized antimicrobial polymers with enhanced bactericidal performance by increasing the active-area of biocides. This review presents several suitable methods of synthesis of antimicrobial polymer nanomaterials with various shapes, including a nanosphere and fibrous and tubular structures. We also discuss the antimicrobial mechanisms of these polymers. In addition, antimicrobial polymer thin films, which can inhibit bacterial adhesion, are introduced briefly with examples. Our aim is to present synthetic routes and formation mechanisms of various antimicrobial polymer nanostructures.

Antimicrobial fibers: therapeutic possibilities and recent advances

The emergence of multi-drug-resistant bacteria such as methicillin-resistant strains of Staphylococcus aureus (MRSA), vancomycin-resistant enterococci, Pseudomonas aeruginosa, Acinetobacter baumannii and extended-spectrum β-lactamase (carbapenemase)-producing Enterobacteriaceae is becoming a serious threat. New-generation antimicrobial agents need to be developed. This includes the design of novel antimicrobial compounds and drug-delivery systems. This review provides an introduction into different classes of antimicrobial materials. The main focus is on strategies for the introduction of antimicrobial properties in polymer materials. These can be roughly divided into surface modification, inclusion of antimicrobial compounds that can leach from the polymer, and the introduction of polymer-bound moieties that provide the polymer with antimicrobial properties. One of the main challenges in the development of antimicrobial polymers for the use in contact with human tissue is the concomitant demand of non-cytotoxicity. Current research is strongly focused on the latter aspect.

Polylactide stereocomplex-based electrospun materials possessing surface with antibacterial and hemostatic properties

Novel fibrous materials of stereocomplex between high-molecular-weight poly(d- or l-)lactide (HMPDLA or HMPLLA) and diblock copolymers consisting of poly(l- or d-)lactide and poly(N,N-dimethylamino-2-ethyl methacrylate) blocks, respectively (PLLA-block-PDMAEMA or PDLA-block-PDMAEMA), were prepared by solution electrospinning. Fibers with mean diameters ranging from 1400 to 1700 nm were obtained. The stereocomplex formation was evidenced by differential scanning calorimetry (DSC) and X-ray diffraction (XRD) analyses. Annealing at 100 degrees C for 8 h resulted in the appearance of crystalline peaks at 2theta values of 12, 21, and 24 degrees for PLA stereocomplex. X-ray photoelectron spectroscopy (XPS) analyses revealed the gradient composition of the fibers with a surface enriched in tertiary amino groups from PDMAEMA blocks. The availability of tertiary amino groups imparts hemostatic and antibacterial properties to the stereocomplex fibrous materials, as indicated by the performed tests on blood cells and on pathogenic microorganisms.

Fabrication of Nanostructured Self-Detoxifying Nanofiber Membranes that Contain Active Polymeric Functional Groups

Military soldiers, medicinal doctors, and ordinary people require protection against chemical and biological warfare (C&B) agents. Activated charcoal impregnated with metal ions is currently used in protective clothing applications, which has some disadvantages. Electrospinning is emerging as one of the cheapest technologies to produce continuous nanofibers with a high surface area-to-volume ratio. In the present study, electrospinning of a poly(ethylene imine) (PEI)/nylon blend has been carried out in which PEI acts as a support material as well as a catalytic media. The membrane is combined with non-selective metal oxide nanoparticles to degrade C&B agents into non-toxic products. In addition, these membranes possess hydrophilic properties, hence they are suitable candidates for protective clothing applications.

Antibacterial Nanofibers of Self-quaternized Block Copolymers of 4-Vinyl Pyridine and Pentachlorophenyl Acrylate

Well-defined antibacterial block copolymers of 4-vinyl pyridine (4VP) and pentachlorophenyl acrylate (PCPA) (P(4VP- b-PCPA)) were prepared via reversible addition—fragmentation chain transfer (RAFT) polymerization. Electrospinning of the P(4VP- b-PCPA) from a solution in mixed tetrahydrofuran and dimethylformamide gave rise to fibers with diameters in the range of 0.5—4.0 µm. The quaternary ammonium salts (QASs) were generated by N-alkylation of pyridine groups of P4VP block and chloro-aromatic compounds of PPCPA block (or self-quaternization of P(4VP- b-PCPA)). The self-quaternization of P(4VP- b-PCPA) nanofibers was studied by X-ray photoelectron spectroscopy. Attributable to the hydrophobicity of the PPCPA blocks and the electrostatic interaction of QASs generated from the self-quaternization of P(4VP- b-PCPA), the resulting nanofibers exhibit a high antibacterial efficiency. The antibacterial effect of the P(4VP- b-PCPA) nanofibers was assayed using Escherichia coli and Staphylococcus aureus cultures. It was found that 99.6% of E. coli and 99.1% S. aureus were killed after being in contact with 50 mg nanofibers in 10 min. The permanence of antibacterial activity of the self-quaternized P(4VP- b-PCPA) nanofibers was also demonstrated in repeat application.

Smart nanofibers from combined living radical polymerization, "click chemistry", and electrospinning

A simple method for preparing solvent-resistant nanofibers with a thermal-sensitive surface has been developed by the combined technology of reversible addition-fragmentation chain-transfer (RAFT) polymerization, atom transfer radical polymerization (ATRP), electrospinning, and "click chemistry". Initially, well-defined block copolymers of 4-vinylbenzyl chloride (VBC) and glycidyl methacrylate (GMA) (PVBC-b-PGMA) were prepared via RAFT polymerization. Electrospinning of PVBC-b-PGMA from a solution in tetrahydrofuran gave rise to fibers with diameters in the range of 0.4-1.5 microm. Exposure to a solution of sodium azide (NaN(3)) not only affords nanofibers with azido groups on the surface but also leads to a cross-linking structure in the nanofibers. One more step of "click chemistry" between the PVBC-b-PGMA nanofibers with azido groups on the surface (PVBC-b-PGMA(-N3)) and alkyne-terminated polymers of N-isopropylacrylamide (NIPAM) (PNIPAM(AT)), which were prepared by ATRP, allows the preparation of a PVBC-b-PGMA nanofiber with thermal-sensitive PNIPAM brushes on the surface (PVBC-b-PGMA-g-PNIPAM). PVBC-b-PGMA-g-PNIPAM nanofibers exhibit a good resistance to solvents and thermal-responsive character to the environment, having a hydrophobic surface at 45 degrees C (water contact angle approximately 140 degrees) and having a hydrophilic surface at 20 degrees C (water contact angle approximately 30 degrees).