Silver nanoparticle-doped zirconia capillaries for enhanced bacterial filtration

Fabrication of a Zircon Microfiltration Membrane for Culture Medium Sterilization

Multilayer ceramic membranes to be used for bacteria removal by filtration were prepared from ceramic materials. They consist of a macro-porous carrier, an intermediate layer and a thin separation layer at the top. Tubular and flat disc supports were prepared from silica sand and calcite (natural raw materials), using extrusion and uniaxial pressing methods, respectively. Making use of the slip casting technique, the silica sand intermediate layer and the zircon top-layer were deposited on the supports, in this order. The particle size and the sintering temperature for each layer were optimized to achieve a suitable pore size for the deposition of the next layer. Morphology, microstructures, pore characteristics, strength and permeability were also studied. Filtration tests were conducted to optimize the permeation performance of the membrane. Experimental results show that the total porosity and average pore size of the porous ceramic supports sintered at different temperatures within the range (1150-1300 °C), and lie in the ranges of 44-52% and 5-30 μm, respectively. For the ZrSiO₄ top-layer, after firing at 1190 °C, a typical average pore size of about 0.3 μm and a thickness of about 70 μm were measured, while water permeability is estimated to a value of 440 lh^-1m^-2bar^-1. Finally, the optimized membranes were tested in the sterilization of a culture medium. Filtration results show the efficiency of the zircon-deposited membranes for bacteria removal; indeed, the growth medium was found to be free of all microorganisms.

Complexes of Cu-Polysaccharide of a Marine Red Microalga Produce Spikes with Antimicrobial Activity

Metal-polysaccharides have recently raised significant interest due to their multifunctional bioactivities. The antimicrobial activity of a complex of Cu₂O with the sulfated polysaccharide (PS) of the marine red microalga Porphyridium sp. was previously attributed to spikes formed on the complex surface (roughness). This hypothesis was further examined here using other Cu-PS complexes (i.e., monovalent-Cu₂O, CuCl and divalent-CuO, CuCl₂). The nanostructure parameters of the monovalent complexes, namely, longer spikes (1000 nm) and greater density (2000-5000 spikes/µm²) were found to be related to the superior inhibition of microbial growth and viability and biofilm formation. When Escherichia coli TV1061, used as a bioluminescent test organism, was exposed to the monovalent Cu-PS complexes, enhanced bioluminescence accumulation was observed, probably due to membrane perforation by the spikes on the surface of the complexes and consequent cytoplasmic leakage. In addition, differences were found in the surface chemistry of the monovalent and divalent Cu-PS complexes, with the monovalent Cu-PS complexes exhibiting greater stability (ζ-potential, FTIR spectra, and leaching out), which could be related to spike formation. This study thus supports our hypothesis that the spikes protruding from the monovalent Cu-PS surfaces, as characterized by their aspect ratio, are responsible for the antimicrobial and antibiofilm activities of the complexes.

Environmentally Friendly Cross-Linked Antifouling Coatings Based on Dual Antimicrobial Action

The synthesis of environmentally friendly antimicrobial polymeric coatings, especially in the case of aquaculture, that inhibit the growth of bio-deposits is a very important issue that will contribute to the cost reduction of nets’ cleaning process as well as the protection of the submarine wealth from the biostatic substances used so far. In the present work, the antimicrobial polymers P(SSAmC₁₆-co-VBCHAMx) and the terpolymer P(SSAmC₁₆w-co-VBCHAMx-co-GMAy) were synthesized, bearing quaternary ammonium compounds, electrostatically bound and covalently attached at the same polymer chain. The combination of the two types is of particular importance, as it can provide effective antimicrobial polymeric materials with self-polishing capabilities as a result of the released nature of the antimicrobial, in combination with the permanent local action of the immobilized species. The cross-linking reaction of the terpolymer P(SSAmC₁₆w-co-VBCHAMx-co-GMAy) with the homopolymer polyacrylic acid (PAA) was tested at 120 °C in terms of the equivalent ratio between epoxy and carboxyl groups. The synthesized polymers were further used for the coating of aquaculture nets and tested in terms of antifouling efficiency in lab and scale-up conditions. Uncoated nets were also used in all applications for comparison reasons. The coated nets performed efficiently for 35 days in lab-scale and 66 days in scale-up conditions, showing a high antifouling activity in both fields compared to the uncoated nets.

An introduction of biological performance of zirconia with different surface characteristics: A review

Zirconia (ZrO₂) ceramic is widely used in dentistry as a clinical dental biomaterial. In this review, we are focusing on and summarizing the biological performance of zirconia under different surface characteristics. We have included an initial tissue cell attachment study on zirconia and bacterial adhesion on zirconia. Our results suggest that surface modifications applied on zirconia may change the interfacial surface characteristics e.g. surface roughness, surface free energy, and chemistry of zirconia. The modifications also result in advanced biological performance of zirconia, including enhanced tissue cell attachment and reduction of bacterial adhesion. The recent laboratory research has provided many interesting modification methods and showed clinically interesting and promising outcomes. A few of the outcomes are validated and have been applied in clinical dentistry.

Potential impacts of silver nanoparticles on bacteria in the aquatic environment

It is inevitable that nano-silver will be released into the environment. Therefore, there is an urgent need to better understand the effects of silver nanoparticles (Ag-NPs) on microbes in natural and engineered environments. The most remarkable gap in our knowledge on this lies on the low Ag-NPs dose side. This review summarized studies on the effects of Ag-NPs on bacteria from simple to complicated aquatic systems. A hormetic model with a narrow stimulatory zone has been proposed based on both experimental phenomenon and the potential mechanisms of the observed effects. Spectrum of the stimulating zone depends on Ag-NP properties, bacterial types and environmental conditions tested. This may become a concern in terms of Ag-NP disposal, and further research is required to build a sophisticated toxicity model for Ag-NPs.

Highly efficient inactivation of bacteria found in drinking water using chitosan-bentonite composites: Modelling and breakthrough curve analysis

Disinfection of bacterially-contaminated drinking water requires a robust and effective technique and can be achieved by using an appropriate disinfectant material. The advanced use of nanomaterials is observed as an alternative and effective way for the disinfection process and water treatment as a whole. Hence, the inactivation of Escherichia coli (E. coli) using chitosan-Bentonite (Cts-Bent) composites was studied in a fixed bed column. Cts-Bent composites were synthesized using in situ cross-linking method using Bent-supported silver and zinc oxide nanoparticles. These composites were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy. The effect of the composite bed mass, initial concentration of bacteria, and flow rate on the bacterial inactivation was investigated. The characterization results revealed that the composites were successfully prepared and confirmed the presence of both silver and zinc oxide nanoparticles in the chitosan matrix. The growth curves of E. coli were expressed as breakthrough curves, based on the logistic, Gompertz, and Boltzmann models. The breakthrough time and processed volume of treated water at breakthrough were used as performance indicators, which revealed that the composites performed best at low bacterial concentration and flow rate and with substantial bed mass. The chitosan composites were found to be highly effective, which was demonstrated when no bacteria were observed in the effluent sample within the first 27 h of analysing river water. All the models were suitable for adequately describing and reproducing the experimental data with a sigmoidal pattern. Therefore, the prepared composite is showing potential to work as a disinfectant and provide an alternative solution for water disinfection; hence this study should propel further research of the same or similar materials.

Copper-based water repellent and antibacterial coatings by aerosol assisted chemical vapour deposition

The adhesion and proliferation of bacteria on solid surfaces presents a major challenge in both healthcare and industrial applications. In response to this problem, an effective and simple method is reported to fabricate superhydrophobic antibacterial copper coated polymer films via aerosol assisted chemical vapor deposition (AACVD). The material is characterized using a range of techniques including electron microscopy, water contact angle measurement and elemental mapping. The antibacterial activity of the modified film is tested against the Gram-negative bacterium, Escherichia coli, and the Gram-positive bacterium, Staphylococcus aureus and the film shows highly significant antibacterial activity against both bacteria (>4 log reduction in bacterial numbers) in 15 min and 60 min, respectively. In addition, all the CVD modified samples results in a significant reduction in bacterial cell adhesion compared to the control materials. Thus, we report a new film type that has dual mode of action-the superhydrophobicity helps limit cell adhesion combined with a cytotoxic copper induced bacteria kill.

Antibiofouling Polyvinylidene Fluoride Membrane Modified by Quaternary Ammonium Compound: Direct Contact-Killing versus Induced Indirect Contact-Killing

Widespread applications of membrane technology call for the development of antibiofouling membranes. For the traditional contact-killing strategy, the antibacterial action is restricted to the surface: the membrane loses its antibiofouling efficacy once its surface is completely covered with a fouling layer. However, in this study, polyvinylidene fluoride (PVDF) microfiltration membranes blended with quaternary ammonium compound (QAC) exhibited a surprisingly lasting antimicrobial activity in the vicinity of the membrane surface. The results indicated that QAC was capable of driving surface segregation with a high structural stability, and the QAC modified membrane shows clear antibacterial effects against both Gram-positive and Gram-negative bacteria. Covering the modified membrane surface by an abiotic alginate layer resulted in a loss of antibacterial efficiency by 86.2%. In contrast, the antibacterial efficiency was maintained after developing a biofilm of Staphylococcus aureus of 30 μm in thickness. The current study may suggest that bacteria affected by contact-killing might interact with other bacteria in the vicinity, resulting in retarded biofilm growth. The antibiofouling effect and associated mechanism of the QAC modified membrane were further validated in a membrane bioreactor during long-term operation.

Ag@Ag8W4O16 nanoroasted rice beads with photocatalytic, antibacterial and anticancer activity

Increasing resistance of pathogens and cancer cell line towards antibiotics and anticancer agents has caused serious health problems in the past decades. Due to these problems in recent years, researchers have tried to combine nanotechnology with material science to have intrinsic antimicrobial and anticancer activity. The metals and metal oxides were investigated with respect to their antimicrobial and anticancer effects towards bacteria and cancer cell line. In the present work metal@metal tungstate (Ag@Ag8W4O16 nanoroasted rice beads) is investigated for antibacterial activity against Escherichia coli and Staphylococcus aureus using Mueller-Hinton broth and the anticancer activity against B16F10 cell line was studied. Silver decorated silver tungstate (Ag@Ag8W4O16) was synthesized by the microwave irradiation method using Cetyl Trimethyl Ammonium Bromide (CTAB). Ag@Ag8W4O16 was characterized by using various spectroscopic techniques. The phase and crystalline nature were analyzed by using XRD. The morphological analysis was carried out using Field Emission Scanning Electron Microscopy (FE-SEM), and High Resolution Transmission Electron Microscopy (HR-TEM). Further, Fourier Transform Infrared Spectroscopy (FT-IR) and Raman spectral analysis were carried out in order to ascertain the presence of functional groups in Ag@Ag8W4O16. The optical property was investigated using Diffuse Reflectance Ultraviolet-Visible Spectroscopy (DRS-UV-Vis) and the band gap was found to be 3.08eV. Surface area of the synthesized Ag@Ag8W4O16 wasanalyzed by BET analysis and Ag@Ag8W4O16 was utilized for the degradation of organic dyes methylene blue and rhodamine B. The morphology of the Ag@Ag8W4O16 resembles roasted rice beads with breath and length in nm range. The oxidation state of tungsten (W) and silver (Ag) was investigated using X-ray photoelectron spectroscopy (XPS).