Multifunctional silane polymers for persistent surface derivatization and their antimicrobial properties

The antibacterial potency and antibacterial mechanism of a commercially available surface-anchoring quaternary ammonium salt (SAQAS)-based biocide in vitro

AIMS

To determine the antimicrobial potency of a surface-anchored quaternary ammonium salt (SAQAS)-based biocide during in vitro wet and dry fomite assays and to determine the mechanism of killing bacteria on the surface.

METHODS AND RESULTS

Wet and dry fomite assays were established in vitro for a commercially available biocide (SAQAS-A) applied to glass and low-density polyethylene (LDPE) surfaces. Both wet and dry fomite tests showed the active killing of Gram-positive and Gram-negative bacteria but not endospores. Assays measuring membrane permeability (ATP and DNA release), bacterial membrane potential and bacterial ROS production were correlated with the time-to-kill profiles to show SAQAS-A activity in suspension and applied to a surface.

CONCLUSIONS

SAQAS-A is an effective biocide against model strains of vegetative bacteria. The killing mechanism for SAQAS-A observed minimal membrane depolarization, a surge in ROS production and assessment of membrane permeability supported the puncture of cells in both suspension and surface attachment, leading to cell death.

SIGNIFICANCE AND IMPACT OF THE STUDY

SAQAS represents effective surface biocides against single challenges with bacteria through a mechanical killing ability that supports real-world application if their durability can be demonstrated to maintain residual activity.

Detection of bacteria using antimicrobial polymer derived via ring-opening metathesis (romp) pathway

There is growing interest in the detection of bacteria in consumables, for example, in the food and water sectors. In this study, the aim was to produce a polymer-based bacteria biosensor via ROMP (ring opening metathesis polymerization). In the first part of the study, block and random copolymers were synthesized, and their biocidal activities were tested on the glass surface. Interdigitated electrode arrays coated with the polymers possessing the highest activity were used to screen the affinity towards different bacterial strains by monitoring impedance variations in real-time. The polymer-coated electrode could detect gram-positive and gram-negative bacteria strains at a concentration of 107 cfu/mL. The results show that ROMP-based polymer offers bacterial detection and can be used in developing biosensor devices for efficiently detecting pathogenic bacteria.

Degradation Behavior of Polymers Used as Coating Materials for Drug Delivery-A Basic Review

The purpose of the work was to emphasize the main differences and similarities in the degradation mechanisms in the case of polymeric coatings compared with the bulk ones. Combined with the current background, this work reviews the properties of commonly utilized degradable polymers in drug delivery, the factors affecting degradation mechanism, testing methods while offering a retrospective on the evolution of the controlled release of biodegradable polymeric coatings. A literature survey on stability and degradation of different polymeric coatings, which were thoroughly evaluated by different techniques, e.g., polymer mass loss measurements, surface, structural and chemical analysis, was completed. Moreover, we analyzed some shortcomings of the degradation behavior of biopolymers in form of coatings and briefly proposed some solving directions to the main existing problems (e.g., improving measuring techniques resolution, elucidation of complete mathematical analysis of the different degradation mechanisms). Deep studies are still necessary on the dynamic changes which occur to biodegradable polymeric coatings which can help to envisage the future performance of synthesized films designed to be used as medical devices with application in drug delivery.

Covalent layer-by-layer films: chemistry, design, and multidisciplinary applications

Covalent layer-by-layer (LbL) assembly is a powerful method used to construct functional ultrathin films that enables nanoscopic structural precision, componential diversity, and flexible design. Compared with conventional LbL films built using multiple noncovalent interactions, LbL films prepared using covalent crosslinking offer the following distinctive characteristics: (i) enhanced film endurance or rigidity; (ii) improved componential diversity when uncharged species or small molecules are stably built into the films by forming covalent bonds; and (iii) increased structural diversity when covalent crosslinking is employed in componential, spacial, or temporal (labile bonds) selective manners. In this review, we document the chemical methods used to build covalent LbL films as well as the film properties and applications achievable using various film design strategies. We expect to translate the achievement in the discipline of chemistry (film-building methods) into readily available techniques for materials engineers and thus provide diverse functional material design protocols to address the energy, biomedical, and environmental challenges faced by the entire scientific community.

Designing of membrane-active nano-antimicrobials based on cationic copolymer functionalized nanodiamond: Influence of hydrophilic segment on antimicrobial activity and selectivity

Designing cationic nano-antimicrobial is a promising solution for combating drug resistant microbes. In this work, hydrophilic cationic copolymer was applied for the surface functionalization of nanodiamonds (NDs) aiming at developing a highly membrane-active nano-antibacterial agent with satisfactory selectivity. As a result, after functionalization, the increased repulsive forces within NDs and interaction with solvent molecular network made the heavily aggregated pristine NDs break down into tiny nanoparticles with particle size ranging from 10 to 100 nm. The improved hydrophilicity and enlarged surface area endowed QND-H₅ and QND-H₁₀ a powerful bactericidal capability toward both of Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus aureus (S. aureus). In the further bactericidal assessment, it was also demonstrated that the formation of hydrogen bonding between the 2-hydroxyethyl methacrylate (HEMA) side chains and lipid head groups of bacterial membrane also contributed to the enhanced bactericidal ability. Field emission scanning electron microscopy analysis confirmed that as-prepared nano-hybrid acted bactericidal ability via physical nature of outer membrane and cytoplasmic membrane-separating destruction mechanism toward E. coli, which may derive from the hydrogen bonding ability, making them more effective toward bacterial. More importantly, it was found that with just 10% of HEMA, QND-H₁₀ displayed good selectivity toward bacteria over mammalian cells as shown by the high HC₅₀ values with relatively low MIC values, suggesting the great potential application in medical fields. These results indicate that hydrogen bonding is an important element to achieve the desired high antibacterial activity and selectivity, particularly when cationic nano-antibacterial agents are required for medical application.

Reaction Product Variability and Biological Activity of the Lactoperoxidase System Depending on Medium Ionic Strength and pH, and on Substrate Relative Concentration

The potential of ions produced in water by the lactoperoxidase system against plant pests has shown promising results. We tested the bioactivity of ions produced by the lactoperoxidase oxidation of I^- and SCN^- in several buffers or in tap water and characterized the ions produced. In vitro biological activity was tested against Penicillium expansum, the causal agent of mold in fruits, and the major cause of patulin contamination of fruit juices and compotes. In buffers, the ionic concentration was increased 3-fold, and pathogen inhibition was obtained down to the 1:15 dilution. In tap water, the ionic concentration was weaker, and pathogen inhibition was obtained only down to the 1:3 dilution. Acidic buffer increased ion concentrations as compared to less acidic (pH 5.6 or 6.2) or neutral buffers, as do increased ionic strength. ¹³ C-labelled SCN^- and MS showed that different ions were produced in water and in buffers. In specific conditions the ion solution turned yellow and a product was formed, probably diiodothiocyanate (I₂ SCN^- ), giving an intense signal at 49.7 ppm in ¹³ C-NMR. The formation of the signal was unambiguously favored in acidic media and disadvantaged or inhibited in neutral or basic conditions. It was enhanced at a specific SCN^- : I^- ratio of 1:4.5, but decreased when the ratio was 1:2, and was inhibited at ratio SCN^- >I^- . We demonstrated that the formation of the signal required the interaction between I₂ and SCN^- , and MS showed the presence of I₂ SCN^- .

Advances in the synthesis of silyl-modified polymers (SMPs)

Silyl-modified polymers (SMPs) are being synthesized from chemical modification and olefin metathesis strategies.

Tuning the properties of α,ω-bis(trialkoxysilyl) telechelic copolyolefins from ruthenium-catalyzed chain-transfer ring-opening metathesis polymerization (ROMP)

Low viscosity liquid α,ω-bis(trialkoxysilyl) telechelic copolyolefins are reported.

Layer-by-layer assemblies for antibacterial applications

This review describes the latest update on research in the area of layer-by-layer assemblies for antibacterial applications.

Antimicrobial oligo(p-phenylene-ethynylene) film deposited by resonant infrared matrix-assisted pulsed laser evaporation

The antimicrobial oligomer, oligo(p-phenylene-ethynylene) (OPE), was deposited as thin films by resonant infrared matrix-assisted pulsed laser evaporation (RIR-MAPLE) on solid substrates and exhibited light-induced biocidal activity. The biocidal activity of OPE thin films deposited by spin-coating and drop-casting was also investigated for comparison. Enhanced bacterial attachment and biocidal efficiency of the film deposited by RIR-MAPLE were observed and attributed to nanoscale surface topography of the thin film.

Construction of degradable multilayer films for enhanced antibacterial properties

Infections associated with medical devices have become a major concern. The adhesion of bacteria to the devices' surfaces during the initial 24 h is believed to be a "decisive period" for implant-associated infections, which pose key challenges to optimal antiadhesion of microbes in this period. Herein, we have designed and constructed a (heparin/chitosan)10-(polyvinylpyrrolidone/poly(acrylic acid))10 [(HEP/CHI)10-(PVP/PAA)10] multilayer film by layer-by-layer self-assembly. Assembly of the underlying (HEP/CHI)10 multilayer film is based on electrostatic interactions, showing the properties of contact killing of bacteria. Deposition of the top (PVP/PAA)10 multilayer film is based on hydrogen bond interactions. The PAA molecules are then cross-linked to form anhydride groups by thermal treatment at 110 °C for 16 h. Therefore, it shows a top-down degradable capability in the determined period, leading to almost no adhesion of bacteria in 24 h. Our system combining the adhesion resistance and the contact killing properties shows an enhanced antibacterial capability through targeting the "decisive period" of implantation may have great potential for applications in medical implants, tissue engineering, etc.

Dual-functional ROMP-based betaines: effect of hydrophilicity and backbone structure on nonfouling properties

Foundational materials for nonfouling coatings were designed and synthesized from a series of novel dual-functional zwitterionic polymers, Poly[NRZI], which were easily obtained via ring-opening metathesis polymerization (ROMP) followed by a single step transformation of the cationic precursor, Poly[NR(+)], to the zwitterion, Poly[NRZI]. The resulting unique dual-functional structure contained the anion and the cation within the same repeat unit but on separate side chains, enabling the hydrophilicity of the system to be tuned at the repeat unit level. These dual-functional zwitterionic polymers were specifically designed to investigate the impact of structural changes, including the backbone, hydrophilicity, and charge, on the overall nonfouling properties. To evaluate the importance of backbone structure, and as a direct comparison to previously studied methacrylate-based betaines, norbornene-based carbo- and sulfobetaines (Poly[NCarboZI] and Poly[NSulfoZI]) as well as a methacrylate-based sulfobetaine (Poly[MASulfoZI]) were synthesized. These structures contain the anion-cation pairs on the same side chain. Nonfouling coatings were prepared from copolymers, composed of the zwitterionic/cationic precursor monomer and an ethoxysilane-containing monomer. The coatings were evaluated by using protein adsorption studies, which clearly indicated that the overall hydrophilicity has a major influence on the nonfouling character of the materials. The most hydrophilic coating, from the oligoethylene glycol (OEG)-containing dual-functional betaine, Poly[NOEGZI-co-NSi], showed the best resistance to nonspecific protein adsorption (Γ(FIB) = 0.039 ng/mm(2)). Both norbornene-based polymers systems, Poly[NSulfoZI] and Poly[NCarboZI], were more hydrophilic and thus more resistant to protein adsorption than the methacrylate-based Poly[MASulfoZI]. Comparing the protein resistance of the dual-functional zwitterionic coatings, Poly[NRZI-co-NSi], to that of their cationic counterparts, Poly[NR(+)-co-NSi], revealed the importance of screening electrostatic interactions. The adsorption of negatively charged proteins on zwitterionic coatings was significantly less, despite the fact that both coatings had similar wetting properties. These results demonstrate that the unique, tunable dual-functional zwitterionic polymers reported here can be used to make coatings that are highly efficient at resisting protein adsorption.

Self-assembled antimicrobial and biocompatible copolymer films on titanium

Copolymers of 4-vinyl-N-hexylpyridinium bromide and dimethyl(2-methacryloyloxyethyl) phosphonate self-assemble to form ultrathin layers on titanium surfaces that show antimicrobial activity, and biocompatibility. The copolymer layers are characterized by contact angle measurements, ellipsometry and XPS. Antibacterial activity is assessed by investigation of adherence of S. mutans. Biocompatibility is rated based on human gingival fibroblast adhesion and proliferation. By balancing the opposing effects of the chemical composition on biocompatibility and antimicrobial activity, copolymer coatings are fabricated that are able to inhibit the growth of S. mutans on the surface but still show attachment of gingival fibroblasts, and therefore might prevent biofilm formation on implants.

Novel acridone-modified MCM-41 type silica: Synthesis, characterization and fluorescence tuning

A Mobil Composition of Matter (MCM)-41 type mesoporous silica material containing N-propylacridone groups has been successfully prepared by co-condensation of an appropriate organic precursor with tetraethyl orthosilicate (TEOS) under alkaline sol-gel conditions. The resulting material was fully characterized by means of X-ray diffraction (XRD), N(2)-adsorption-desorption, transmission electron microscopy (TEM), IR and UV-vis spectroscopy, as well as (29)Si and (13)C CP-MAS NMR techniques. The material features a high inner surface area and a highly ordered two-dimensional hexagonal pore structure. The fluorescence properties of the organic chromophore can be tuned via complexation of its carbonyl group with scandium triflate, which makes the material a good candidate for solid state sensors and optics. The successful synthesis of highly ordered MCM materials through co-condensation was found to be dependent on the chemical interaction of the different precursors.

Antibacterial surfaces by adsorptive binding of polyvinyl-sulphonate-stabilized silver nanoparticles

This paper presents a novel and facile method for the generation of efficient antibacterial coatings which can be applied to practically any type of substrate. Silver nanoparticles were stabilized with an adsorbed surface layer of polyvinyl sulphonate (PVS). This steric layer provided excellent colloidal stability, preventing aggregation over periods of months. PVS-coated silver nanoparticles were bound onto amine-containing surfaces, here produced by deposition of an allylamine plasma polymer thin film onto various substrates. SEM imaging showed no aggregation upon surface binding of the nanoparticles; they were well dispersed on amine surfaces. Such nanoparticle-coated surfaces were found to be effective in preventing attachment of Staphylococcus epidermidis bacteria and also in preventing biofilm formation. Combined with the ability of plasma polymerization to apply the thin polymeric binding layer onto a wide range of materials, this method appears promising for the fabrication of a wide range of infection-resistant biomedical devices.

Antibacterial inorganic-organic hybrid coatings on stainless steel via consecutive surface-initiated atom transfer radical polymerization for biocorrosion prevention

To enhance the corrosion resistance of stainless steel (SS) and to impart its surface with antibacterial functionality for inhibiting biofilm formation and biocorrosion, well-defined inorganic-organic hybrid coatings, consisting of a polysilsesquioxane inner layer and quaternized poly(2-(dimethyamino)ethyl methacrylate) (P(DMAEMA)) outer blocks, were prepared via successive surface-initiated atom transfer radical polymerization (ATRP) of 3-(trimethoxysilyl)propyl methacrylate (TMSPMA) and 2-(dimethylamino)ethyl methacrylate (DMAEMA). The cross-linked P(TMASPMA), or polysilsesquioxane, inner layer provided a durable and resistant coating to electrolytes. The pendant tertiary amino groups of the P(DMAEMA) outer block were quaternized with alkyl halide to produce a high concentration of quaternary ammonium groups with biocidal functionality. The so-synthesized inorganic-organic hybrid coatings on the SS substrates exhibited good anticorrosion and antibacterial effects and inhibited biocorrosion induced by sulfate-reducing bacteria (SRB) in seawater media, as revealed by antibacterial assay and electrochemical analyses, and they are potentially useful to steel-based equipment under harsh industrial and marine environments.

A substrate-independent approach for bactericidal surfaces

Existing methods for imparting antibacterial performance to solid surfaces tend to either be substrate-specific or rely upon leaching modes of action that cause ecological damage. An alternative approach is outlined comprising plasmachemical functionalization of solid surfaces with poly(4-vinyl pyridine) moieties and their subsequent activation (quaternization) with bromobutane to yield bactericidal activity. These bioactive surfaces can be applied to a host of different substrate materials and are easily regenerated by rinsing in water.

Inorganic-organic hybrid coatings on stainless steel by layer-by-layer deposition and surface-initiated atom-transfer-radical polymerization for combating biocorrosion

To improve the biocorrosion resistance of stainless steel (SS) and to confer the bactericidal function on its surface for inhibiting bacterial adhesion and biofilm formation, well-defined inorganic-organic hybrid coatings, consisting of the inner compact titanium oxide multilayers and outer dense poly(vinyl-N-hexylpyridinium) brushes, were successfully developed. Nanostructured titanium oxide multilayer coatings were first built up on the SS substrates via the layer-by-layer sol-gel deposition process. The trichlorosilane coupling agent, containing the alkyl halide atom-transfer-radical polymerization (ATRP) initiator, was subsequently immobilized on the titanium oxide coatings for surface-initiated ATRP of 4-vinylpyridine (4VP). The pyridium nitrogen moieties of the covalently immobilized 4VP polymer, or P(4VP), brushes were quaternized with hexyl bromide to produce a high concentration of quaternary ammonium salt on the SS surfaces. The excellent antibacterial efficiency of the grafted polycations, poly(vinyl-N-pyridinium bromide), was revealed by viable cell counts and atomic force microscopy images of the surface. The effectiveness of the hybrid coatings in corrosion protection was verified by the Tafel plot and electrochemical impedance spectroscopy measurements.