Exploring multielement nanogranular coatings to forestall implant-related infections.

Introduction: As we approach the post-antibiotic era, the development of innovative antimicrobial strategies that carry out their activities through non-specific mechanisms could limit the onset and spread of drug resistance. In this context, the use of nanogranular coatings of multielement nanoparticles (NPs) conjugated to the surface of implantable biomaterials might represent a strategy to reduce the systemic drawbacks by locally confining the NPs effects against either prokaryotic or eukaryotic cells. Methods: In the present study, two new multielement nanogranular coatings combining Ag and Cu with either Ti or Mg were synthesized by a gas phase physical method and tested against pathogens isolated from periprosthetic joint infections to address their potential antimicrobial value and toxicity in an in vitro experimental setting. Results: Overall, Staphylococcus aureus, Staphylococcus epidermidis and Escherichia coli displayed a significantly decreased adhesion when cultured on Ti-Ag-Cu and Mg-Ag-Cu coatings compared to uncoated controls, regardless of their antibiotic resistance traits. A dissimilar behavior was observed when Pseudomonas aeruginosa was cultured for 30 and 120 minutes upon the surface of Ti-Ag-Cu and Mg-Ag-Cu-coated discs. Biofilm formation was mainly reduced by the active effect of Mg-Ag-Cu compared to Ti-Ag-Cu and, again, coatings had a milder effect on P. aeruginosa, probably due to its exceptional capability of attachment and matrix production. These data were further confirmed by the evaluation of bacterial colonization on nanoparticle-coated discs through confocal microscopy. Finally, to exclude any cytotoxic effects on eukaryotic cells, the biocompatibility of NPs-coated discs was studied. Results demonstrated a viability of 95.8% and 89.4% of cells cultured in the presence of Ti-Ag-Cu and Mg-Ag-Cu discs, respectively, when compared to negative controls. Conclusion: In conclusion, the present study demonstrated the promising anti-adhesive features of both Ti-Ag-Cu and Mg-Ag-Cu coatings, as well as their action in hampering the biofilm formation, highlighting the safe use of the tested multi-element families of nanoparticles as new strategies against bacterial attachment to the surface of biomedical implants.

Insights into the Photoelectrocatalytic Behavior of gCN-Based Anode Materials Supported on Ni Foams.

Graphitic carbon nitride (gCN) is a promising n-type semiconductor widely investigated for photo-assisted water splitting, but less studied for the (photo)electrochemical degradation of aqueous organic pollutants. In these fields, attractive perspectives for advancements are offered by a proper engineering of the material properties, e.g., by depositing gCN onto conductive and porous scaffolds, tailoring its nanoscale morphology, and functionalizing it with suitable cocatalysts. The present study reports on a simple and easily controllable synthesis of gCN flakes on Ni foam substrates by electrophoretic deposition (EPD), and on their eventual decoration with Co-based cocatalysts [CoO, CoFe2O4, cobalt phosphate (CoPi)] via radio frequency (RF)-sputtering or electrodeposition. After examining the influence of processing conditions on the material characteristics, the developed systems are comparatively investigated as (photo)anodes for water splitting and photoelectrocatalysts for the degradation of a recalcitrant water pollutant [potassium hydrogen phthalate (KHP)]. The obtained results highlight that while gCN decoration with Co-based cocatalysts boosts water splitting performances, bare gCN as such is more efficient in KHP abatement, due to the occurrence of a different reaction mechanism. The related insights, provided by a multi-technique characterization, may provide valuable guidelines for the implementation of active nanomaterials in environmental remediation and sustainable solar-to-chemical energy conversion.

Synergistic Effect of Sn and Fe in Fe-Nx Site Formation and Activity in Fe-N-C Catalyst for ORR.

Iron-nitrogen-carbon (Fe-N-C) materials emerged as one of the best non-platinum group material (non-PGM) alternatives to Pt/C catalysts for the electrochemical reduction of O2 in fuel cells. Co-doping with a secondary metal center is a possible choice to further enhance the activity toward oxygen reduction reaction (ORR). Here, classical Fe-N-C materials were co-doped with Sn as a secondary metal center. Sn-N-C according to the literature shows excellent activity, in particular in the fuel cell setup; here, the same catalyst shows a non-negligible activity in 0.5 M H2SO4 electrolyte but not as high as expected, meaning the different and uncertain nature of active sites. On the other hand, in mixed Fe, Sn-N-C catalysts, the presence of Sn improves the catalytic activity that is linked to a higher Fe-N4 site density, whereas the possible synergistic interaction of Fe-N4 and Sn-Nx found no confirmation. The presence of Fe-N4 and Sn-Nx was thoroughly determined by extended X-ray absorption fine structure and NO stripping technique; furthermore, besides the typical voltammetric technique, the catalytic activity of Fe-N-C catalyst was determined and also compared with that of the gas diffusion electrode (GDE), which allows a fast and reliable screening for possible implementation in a full cell. This paper therefore explores the effect of Sn on the formation, activity, and selectivity of Fe-N-C catalysts in both acid and alkaline media by tuning the Sn/Fe ratio in the synthetic procedure, with the ratio 1/2 showing the best activity, even higher than that of the iron-only containing sample (jk = 2.11 vs 1.83 A g-1). Pt-free materials are also tested for ORR in GDE setup in both performance and durability tests.

The Role of Substrate on Thermal Evolution of Ag/TiO2 Nanogranular Thin Films.

In multicomponent thin films, properties and functionalities related to post-deposition annealing treatments, such as thermal stability, optical absorption and surface morphology are typically rationalized, neglecting the role of the substrate. Here, we show the role of the substrate in determining the temperature dependent behaviour of a paradigmatic two-component nanogranular thin film (Ag/TiO2) deposited by gas phase supersonic cluster beam deposition (SCBD) on silica and sapphire. Up to 600 °C, no TiO2 grain growth nor crystallization is observed, likely inhibited by the Zener pinning pressure exerted by the Ag nanoparticles on the TiO2 grain boundaries. Above 600 °C, grain coalescence, formation of However, the two substrates steer the evolution of the film morphology and optical properties in two different directions. anatase and rutile phases and drastic modification of the optical absorption are observed. On silica, Ag is still present as NPs distributed into the TiO2 matrix, while on sapphire, hundreds of nm wide Ag aggregates appear on the film surface. Moreover, the silica-deposited film shows a broad absorption band in the visible range while the sapphire-deposited film becomes almost transparent for wavelengths above 380 nm. We discuss this result in terms of substrate differences in thermal conductivity, thermal expansion coefficient and Ag diffusivity. The study of the substrate role during annealing is possible since SCBD allows the synthesis of the same film independently of the substrate, and suggests new perspectives on the thermodynamics and physical exchanges between thin films and their substrates during heat treatments.