Tribological Behavior of Thermal Spray Coatings, Deposited by HVOF and APS Techniques, and Composite Electrodeposits Ni/SiC at Both Room Temperature and 300 °C

The Both the thermal spray and the electroplating coatings are widely used because of their high wear resistance combined with good corrosion resistance. In particular the addition of both micro particles or nano‐particles to the electro deposited coatings could lead to an increase of the mechanical properties, caused by the change of the coating microstructure. The thermal spray coatings were deposited following industrial standards procedures, while the Ni/SiC composite coatings were produced at laboratory scale using both micro‐and nano‐sized ceramic particles. All the produced coatings were characterized regarding their microstructure,mechanical properties and the wear resistance. The tribological properties were analyzed using a tribometer under ball on disk configuration at both room temperature and 300oC. The results showed that the cermet thermal spray coatings have a high wear resistance, while the Ni nano‐composite showed good anti wear properties compared to the harder ceramic/cermet coatings deposited by thermal spray technique

On growth and morphology of tio2 nanotubes on ti6al4v by anodic oxidation in ethylene glycol electrolyte: Influence of microstructure and anodization parameters

Different studies demonstrated the possibility to produce TiO2 nanotubes (TNTs) on Ti6Al4V alloy by electrochemical anodization. However, the anodizing behavior of \u3b1 and \u3b2-phases in organic electrolytes is not yet clarified. This study reports on the anodizing behavior of the two phases in an ethylene glycol electrolyte using different applied potentials and anodizing times. Atomic force and scanning electron microscopies were used to highlight the anodic oxides differences in morphology. It was demonstrated that the initial compact oxide grew faster over the \u3b2-phase as the higher Al content of the \u3b1-phase caused its re-passivation, and the higher solubility of the V-rich oxide led to earlier pores formation over the \u3b2-phase. The trend was inverted once the pores formed over the compact oxide of the \u3b1-phase. The growth rate of the \u3b1-phase TNTs was higher than that of the \u3b2-phase ones, leading to the formation of long and well defined nanotubes with thin walls and a honeycomb tubular structure, while the ones grown over the \u3b2-phase were individual, shorter, and with thicker walls

The effect of surface preparation on the protective properties of Al2O3 and HfO2 thin films deposited on cp-titanium by atomic layer deposition

Atomic layer deposition (ALD), a method that allows the formation of thin and conformal films on substrates of interest, was employed to prepare thin films of alumina (Al2O3) and hafnia (HfO2), with the aim of protecting the surface of the commercially pure titanium (cp-Ti) used in biomedical applications. Prior to deposition, cp-Ti specimens have been prepared in two ways \u2013 grinding and grinding followed by polishing. Such surfaces have been denoted as rough and smooth, respectively. The thickness, composition, morphology and topography of alumina and hafnia films have been determined using ellipsometry, focused ion beam microscopy with energy dispersive X-ray spectroscopy, time-of-flight secondary ion mass spectrometry and 3D profilometry. A homogeneous stoichiometric composition of alumina and hafnia was obtained with a layer thickness of ca. 150 nm. The anti-corrosive properties of ALD thin films were measured in simulated body fluid solution, using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization curves. The roughness of the cp-Ti surface plays an important role in the protective properties of these films, especially those of hafnia. In general, when deposited on a smooth surface, ALD films with better anti-corrosive properties were obtained, as evidenced by EIS long-term, 40-day tests. ALD films showed very low porosity, calculated from electrochemical parameters, and significantly lower corrosion current densities, compared with those from bare cp-Ti specimens. Lower porosity and slightly better protective properties were provided by films of hafnia. On the other hand, according to EIS long-term tests, alumina retained slightly greater impedance values than hafnia. Since both alumina and hafnia are biocompatible materials, this study confirms the possibility of their use to reduce the risk of failure of medical implants made of cp-Ti, in the human body environment

Implementation of NSOM to biological samples

Near-field scanning optical microscopy is a technique providing images of structures with spatial resolution better than $\lambda/2$, which is undetectable in far-field where the Abbe law of limiting resolution is critical. In parallel to the optical imaging, topography maps are also acquired. Near-field scanning optical microscopy measurements can be performed both in air and liquid environments. The later makes the technique very useful for biomaterials analysis offering information that could not be obtained with other methods. Our work presents the results of recent studies on application of near-field scanning optical microscopy to imaging of cells in air as well as in physiological buffers. Differences in cell's topography and morphology have been noticed between two cell lines from human bladder non-malignant (HCV29) and malignant (T24) cancers. Presented results are part of the research that characterizes physiological changes of cells depending on stage of cancer

Follistatin, a Novel Biomarker for Malignant Gliomas

Molecular biomarkers are commonly used for the management of several types of malignant tumours in routine clinical practice. However, this is not the case for malignant gliomas. Cytokines and Angiogenesis factors are potential candidates due to their intrinsic role in tumourigenesis. Pre- and post-operative serum from 36 malignant glioma patients and 36 controls was analysed using the Bio-Plex Pro Angiogenesis and Cytokines Assay (Bio-Rad, USA). Amongst the molecules tested, the serum concentration of follistatin was significantly higher in patients than in controls. Moreover, the serum concentration of follistatin of the patients postoperatively was significantly reduced compared to that preoperatively. Factors such as age and gender did not affect the concentrations of follistatin measured in the serum of patients pre- and post-operatively as well as healthy controls. This is the first report of follistatin as potential biomarker for the detection of malignant gliomas

In Vitro Evaluation of the Antibacterial Activity of the Peptide Fractions Extracted from the Hemolymph of Hermetia illucens (Diptera: Stratiomyidae)

Antimicrobial peptides (AMPs) are a chemically and structurally heterogeneous family of molecules produced by a large variety of living organisms, whose expression is predominant in the sites most exposed to microbial invasion. One of the richest natural sources of AMPs is insects which, over the course of their very long evolutionary history, have adapted to numerous and different habitats by developing a powerful innate immune system that has allowed them to survive but also to assert themselves in the new environment. Recently, due to the increase in antibiotic-resistant bacterial strains, interest in AMPs has risen. In this work, we detected AMPs in the hemolymph of Hermetia illucens (Diptera, Stratiomyidae) larvae, following infection with Escherichia coli (Gram negative) or Micrococcus flavus (Gram positive) and from uninfected larvae. Peptide component, isolated via organic solvent precipitation, was analyzed by microbiological techniques. Subsequent mass spectrometry analysis allowed us to specifically identify peptides expressed in basal condition and peptides differentially expressed after bacterial challenge. We identified 33 AMPs in all the analyzed samples, of which 13 are specifically stimulated by Gram negative and/or Gram positive bacterial challenge. AMPs mostly expressed after bacterial challenge could be responsible for a more specific activity

Structures in multicomponent polymer films : their formation, observation, applications in electronics and biotechnology

Several strategies to form multicomponent films of functional polymers, with micron, submicron and nanometer structures, intended for plastic electronics and biotechnology are presented. These approaches are based on film deposition from polymer solution onto a rotating substrate (spin-casting), a method implemented already on manufacturing lines. Film structures are determined with compositional (nanometer) depth profiling and (submicron) imaging modes of dynamic secondary ion mass spectrometry, near-field scanning optical microscopy (with submicron resolution) and scanning probe microscopy (revealing nanometer features). Self-organization of spin-cast polymer mixtures is discussed in detail, since it offers a one-step process to deposit and align simultaneously domains, rich in different polymers, forming various device elements: (i) Surface segregation drives self-stratification of nanometer lamellae for solar cells and anisotropic conductors. (ii) Cohesion energy density controls morphological transition from lamellar (optimal for encapsulated transistors) to lateral structures (suggested for light emitting diodes with variable color). (iii) Selective adhesion to substrate microtemplates, patterned chemically, orders lateral structures for plastic circuitries. (iv) Submicron imprints of water droplets (breath figures) decorate selectively micron-sized domains, and can be used in devices with hierarchic structure. In addition, selective protein adsorption to regular polymer micropatterns, formed with soft lithography after spin-casting, suggests applications in protein chip technology. An approach to reduce lateral blend film structures to submicron scale is also presented, based on (annealed) films of multicomponent nanoparticles

Monolayered versus multilayered electroless NiP coatings: Impact of the plating approach on the microstructure, mechanical and corrosion properties of the coatings

Electroless nickel-phosphorous (NiP) coatings were produced on low carbon steel substrates for a total plating time of 3\u202fh. Different preparation modalities were pursued. Multilayered coatings were produced by stacking three layers of the same composition by successive electroless plating with rinsing steps in between. On the other hand, coatings termed \u2018monolayered\u2019 for the sake of comparison were deposited by one step electroless process, with and without undergoing bath replenishment of the electrolyte during plating. All the samples were subjected to thermal annealing at 400\u202f\ub0C for 1\u202fh under argon atmosphere. The results show that the multilayer approach prevents crack propagation in the as-deposited coatings because the interfaces between layers block the advance of defects. Bath replenishment during monolayered coatings production creates pseudo-interfaces similar to those of the multilayered case but they are ineffective in terms of corrosion protection. Un-replenishment of the electrolyte promotes a change in the coating's microstructure from lamellar to columnar which severely worsens their performance. Upon annealing, the presence of interfaces, along with the recrystallization of the metallic matrix, promotes an upgrading of the corrosion performance of the multi-layered coatings. The corrosion products spread laterally at the interface where they stockpile. At a certain point, the accumulation of these by-products provokes the exfoliation of the outermost layer exposing the layer underneath to the corrosive media, thereby delaying the advancement of the corrosion attack. The results of this study highlight the importance of the plating approach selection, as well as the need for proper electrolyte maintenance during the production of high-performance electroless coatings

Effect of hydrogen peroxide on bovine serum albumin adsorption on Ti6Al4V alloy: A scanning Kelvin probe force microscopy study

Abstract Protein adsorption on the surface of implant materials greatly affects the performance of the implants, such as their stability as well as the release of metal ions from and the adhesion of cells to their surface. In addition, the production of extracellular H2O2 from the activation of inflammatory cells could interfere with protein–metal interactions and/or modify the conformation of adsorbed proteins. In this study, we utilised scanning Kelvin probe force microscopy (SKPFM) to visualise the impact of H2O2 on bovine serum albumin (BSA) adsorption on the positively polarised Ti6Al4V alloy in a phosphate-buffered saline (PBS) solution. We show that the negatively charged BSA adsorbs onto the surface of polished and anodically polarised Ti6Al4V in a dense layer with a continuous network-like morphology or cluster shape and reduces the variation in the total surface potential compared to that of blank Ti6Al4V. However, addition of H2O2 to the PBS solution interferes with the formation of the dense protein network, and only a thin and discontinuous protein layer adsorbs onto the surface of the Ti6Al4V alloy, lowering the total surface potential difference. The information presented in this work provides new insights into the adsorption distribution of proteins on metallic substrates in biomaterials field

Caratterizzazione microstrutturale ed elettrochimica di rivestimenti per applicazioni in campo energetico

Il miglioramento delle prestazioni dei rivestimenti spessi nel campo energetico è di notevole importanzain quanto le tecnologie attualmente a disposizione sono molto costose e presentano problemi di diversanatura, principalmente nel campo della resistenza alla corrosione. Il materiale di substrato sceltoè un acciaio ASTM 387 grado 22, su cui saranno depositati rivestimenti in Nichel chimico, riporti metallicio cermet depositati con tecnologia HVOF (High Velocity Oxygen Fuel) e rivestimenti ceramici depositaticon tecnica APS (Arc Plasma Spray). I sistemi rivestiti sono composti da: substrato + rivestimento, substrato +interlayer + rivestimento. Alcuni di questi sistemi sono stati sigillati con resina epossidica.Le varie combinazioni di rivestimenti sono state caratterizzate tramite microscopia ottica, misuredi microdurezza e analisi SEM con sonda EDXS, per studiare microstruttura e composizione chimica.Per testare il comportamento a corrosione dei rivestimenti sono state eseguite misure di polarizzazionepotenziodinamica in soluzione simulante un ambiente simile a quello delle centrali geotermiche. I risultatihanno messo in evidenza un effetto barriera, fornito dai rivestimenti studiati in questo lavoro