Surface chemical and biological characterization of flax fabrics modified with silver nanoparticles for biomedical applications.

Silver nanophases are increasingly used as effective antibacterial agent for biomedical applications and wound healing. This work aims to investigate the surface chemical composition and biological properties of silver nanoparticle-modified flax substrates. Silver coatings were deposited on textiles through the in situ photo-reduction of a silver solution, by means of a large-scale apparatus. The silver-coated materials were characterized through X-ray Photoelectron Spectroscopy (XPS), to assess the surface elemental composition of the coatings, and the chemical speciation of both the substrate and the antibacterial nanophases. A detailed investigation of XPS high resolution regions outlined that silver is mainly present on nanophases' surface as Ag2O. Scanning electron microscopy and energy dispersive X-ray spectroscopy were also carried out, in order to visualize the distribution of silver particles on the fibers. The materials were also characterized from a biological point of view in terms of antibacterial capability and cytotoxicity. Agar diffusion tests and bacterial enumeration tests were performed on Gram positive and Gram negative bacteria, namely Staphylococcus aureus and Escherichia coli. In vitro cytotoxicity tests were performed through the extract method on murine fibroblasts in order to verify if the presence of the silver coating affected the cellular viability and proliferation. Durability of the coating was also assessed, thus confirming the successful scaling up of the process, which will be therefore available for large-scale production.

Development of silver nano-coatings on silk sutures as a novel approach against surgical infections.

The infections give rise to a range of clinical problems and prolong hospitalization with increased healthcare costs. Moreover, persistent infections exasperate the problem of antibiotic resistance. The aim of this study was the development of effective and low-cost antibacterial silver coatings on surgical sutures by adopting an innovative photochemical deposition process to prevent early contamination of surgical wounds. The silver deposition technology adopted in this work is an innovative process based on the in situ photoreduction of a silver solution. The samples were dipped in the silver solution and then exposed to UV radiation in order to induce the synthesis of silver clusters on the surface of the suture. The homogeneous distribution of silver particles on the surface and on the cross-section of the treated sutures was demonstrated. All the antibacterial studies clearly demonstrated that the use of novel silver treated sutures could represent clinical advantages in terms of the prevention of surgical infections against bacterial colonization. The silver coating deposited on the sutures demonstrated no cytotoxic effect on a selected cell population. The results obtained suggested that the antibacterial silver-coated sutures developed in this work could represent an interesting alternative to conventional sutures, with evident advantages in terms of prevention of the surgical infections and on the health costs. In addiction, very low concentrations of silver significantly inhibited the microbial load, without affecting the cell viability.

In vivo testing of silver treated fibers for the evaluation of skin irritation effect and hypoallergenicity.

Textiles are a fertile breeding ground for a multitude of micro-organisms under appropriate conditions of moisture and temperature. The broad-spectrum biocide properties of silver are well known and many technologies have been developed so far to treat textiles with silver. The efficacy of the silver deposition technology presented in this article has been already demonstrated in previous works, where the strong adhesion of silver nanoparticles to the substrate and their antibacterial capability have been assessed. This work focuses on the evaluation of any possible interaction of silver treated cotton with human skin, in terms of skin irritation and hypoallergenicity. Moreover, the presence of silver and the antibacterial capability against Gram positive and Gram negative bacteria, namely Staphylococcus aureus and Escherichia coli, were verified even after several washing cycles in order to develop a product with long-term antibacterial capability and no adverse effects in terms of skin irritation and hypoallergenicity.

Development of antibacterial and antifungal silver-coated polyurethane foams as air filtration units for the prevention of respiratory diseases.

AIM: The development of silver-coated polyurethane filters as filtration units for the prevention of the respiratory diseases. METHODS AND RESULTS: An innovative silver deposition technology based on the photo-reduction in a silver salt was adopted. The efficacy of the technology in providing a homogeneous distribution of the silver particles was verified by scanning electron microscopy and energy dispersive X-ray spectroscopy. The materials were tested through microbiological procedures used in industry to verify the efficacy of the silver-coated filters on the viability and growth of selected micro-organisms. Direct inoculation test, filtration experiment and shaking tests were performed on microbial human pathogens associated with air filtration units and respiratory disease, namely Legionella pneumophila, Pseudomonas aeruginosa, Aspergillus niger and Aspergillus flavus, by adopting Escherichia coli and Staphylococcus aureus as control organisms. CONCLUSIONS: The results provided evidence of the effectiveness of the silver coating in reducing the bioaerosolization of viable human pathogens into environments using recirculated air. SIGNIFICANCE AND IMPACT OF THE STUDY: Micro-organisms can affect the air quality in indoor environments and can be responsible for infectious, allergic or toxic disturbances on human airways. The development of an adequate bioaerosol control might ameliorate a positive health effect in humans.

Effect of silver nanocoatings on catheters for haemodialysis in terms of cell viability, proliferation, morphology and antibacterial activity.

The onset of infections associated to bacterial proliferation and biofilm formation on indwelling medical devices represents the major risk of morbidity and mortality among patients. In order to contain the risk of infections in clinical practice, there is a growing interest nowadays in silver-based products due to the strong antimicrobial efficacy of silver against a broad spectrum of microorganisms. In this work, temporary catheters for haemodialysis were coated with silver nano-particles through the in situ photo-reduction of a silver salt in alcoholic solution. A homogeneous distribution of silver particles firmly bonded to the substrate was obtained through the adopted technique. An optimisation study was required to define the amount of silver, in order to obtain good efficacy against Gram-positive and Gram-negative bacteria and no cytotoxic effect. At this purpose, three concentrations of silver, 0.1, 0.25 and 0.5 wt%, have been deposited and tested with respect to bacterial reduction percentage and cellular response. Particularly, bacterial enumeration on Escherichia coli and Staphylococcus aureus, and BrdU incorporation, TUNEL assay and Actin staining on a selected primary cell population were performed on catheters treated with the different silver solutions. The silver percentages tested demonstrated strong antibacterial properties together with a good cellular response, thus indicating that the developed product could be proposed in clinical practice and that the lower percentage tested can be preferred with evident advantages in terms of costs.

Efficacy of silver treated catheters for haemodialysis in preventing bacterial adhesion.

The growing resistance of many strains of bacteria to antibiotics and antiseptics is becoming a serious problem in medicine. Nano-silver is one of the most prominent products in medicine because it exhibits unusual physicochemical properties and a strong biological activity. In this work an innovative silver deposition technology was applied to temporary polyurethane catheters for haemodialysis. The working conditions of catheters were reproduced through laboratory equipment that ensured the flow of deionized water and simulated body fluid inside the lumina at corporeal temperature. The growth and the adhesion of Staphylococcus aureus on the surface of the device were studied through fluorescence microscopy. ICP-AES was adopted to calculate the amount of silver released from the substrate. The stability of the coating during the whole working life of the device was demonstrated through thermo-gravimetric analysis.

Antibacterial coatings on haemodialysis catheters by photochemical deposition of silver nanoparticles.

Antibacterial coatings on catheters for acute dialysis were obtained by an innovative and patented silver deposition technique based on the photo-reduction of the silver solution on the surface of catheter, with consequent formation of antibacterial silver nanoparticles. Aim of this work is the structural and morphological characterization of these medical devices in order to analyze the distribution and the size of clusters on the polymeric surface, and to verify the antibacterial capability of the devices treated by this technique against bacterial proliferation. The structure and morphology of the silver nanoparticles were investigated by using scanning and transmission electron microscopy. The antimicrobial capability of the catheters after silver deposition was confirmed by antibacterial tests with Escherichia coli. Both scanning electron microscopy analysis and antibacterial tests were performed also after washing catheters for 30 days in deionized water at 37°C, relating these data to thermogravimetric analysis and to energy dispersive spectroscopy, in order to check the resistance of coating and its antimicrobial capability after the maximum time of life of these devices.

Characterization of antibacterial silver coated yarns.

Surface treatments of textile fibers and fabrics significantly increase their performances for specific biomedical applications. Nowadays, silver is the most used antibacterial agent with a number of advantages. Among them, it is worth to note the high degree of biocompatibility, an excellent resistance to sterilization conditions, antibacterial properties with respect to different bacteria associated with a long-term of antibacterial efficiency. However, there are only a few antibacterial fibres available, mainly synthetic with high production cost and limited effectiveness. Cotton yarns with antimicrobial properties are most suitable for wound healing applications and other medical treatments thanks to their excellent moisture absorbance while synthetic based fibres are most suitable for industrial applications such as automotive tapestry and air filters. The silver-coated fibers were developed applying an innovative and low cost silver deposition technique for natural and synthetic fibers or yarns. The structure and morphology of the silver nanoclusters on the fibers was observed by scanning electron microscopy (SEM), atomic force microscopy analysis (AFM) and XRD analysis, and quantitatively confirmed by thermogravimetric analysis (TGA) measurements. Good silver coating stability has been confirmed performing several industrial washing. Antimicrobial tests with Escherichia coli were performed.