1,720,962 research outputs found
Effect of anodizing parameters on the formation of TiO2 nanotubes produced on titanium grade 2 and titanium grade 5
Full text linkTi-based implants are the most widely used solution for bone repair and joint replacement, due to the favorable properties of titanium and its alloys when compared to other commonly used metals, namely, stainless steel and cobalt-chromium alloys. In short, titanium grade 2 and titanium grade 5 present good mechanical properties and biocompatibility without showing toxicity or immune rejection. However, although the inertness of titanium has been considered a favorable characteristic for years, its lack of bioactivity also presents some challenges, regarding inability to actively regulate osteoblast behavior or battle colonization by pathogenic microorganisms. Titanium anodization is a simple and effective surface treatment for the improvement of osteointegration and antimicrobial activity. Extensive work has been performed on the study of the production titania nanotubes on the surface of commercially pure titanium (grade 2) but little work exists on the production of TI nanotubes on the surface of Ti6Al4V (grade 5) alloy the most widely used alloy in orthopedic implants. The aim of this work is to produce and characterize titania nanotubes on the surface of Ti gr.2 and gr. 5 using different anodizing parameters. An ethylene glycol electrolyte containing 0.5wt.% NH4F and 2.5% V H2O was used for the anodization at room temperature. The applied voltage varied from 20 to 120V and the anodization time from 30 to 180 min. The obtained films have been characterized by SEM and XRD regarding the microstructure with particular attention to the structure of TiO2 nanotubes on the α and β phase grains of Ti6Al4V
Effect of anodizing conditions on the formation of TiO2 nanotubes on pure Ti and Ti6Al4V alloy
No full textCommercially pure Ti and Ti6Al4V are the most widely used metallic biomaterials for orthopaedic applications due to their overall good osteointegration capacity, inertness and non-toxicity. Nevertheless, the introduction of an implant in the body is always associated with the risk of microbial infection in particular for the fixation of open-fractured bones and joint-revision surgeries. Considering that the bacteria adhesion mechanisms are very similar to those of the host’s osteogenic cells, once an implant is inserted, the occurrence of infection is dependent on the relative speed by which osteogenic cells and bacterial cells adhere to the implant surface. Moreover, cell and tissue responses are affected not only by the chemical properties of the implant surface, but also by the surface topography and roughness. To this aim specific surface treatments which favor osteointegration and simultaneously discourage bacterial adhesion are required. The anodization of Ti with the formation of TiO2 nanotubes is a cheap method which can lead to an increase of the surface roughness at a nanoscale and enhance osteointegration. Moreover, combined with post anodization annealing or drug loading, the nanotubes porosity could also hinder the bacterial adhesion. The present work focuses on the effect of the anodizing parameters such as applied voltage and time to the microstructure and corrosion resistance of the obtained films. Commercially pure Ti and Ti6Al4V plates have been anodized using an ethylene glycol electrolyte containing 0.5wt.% NH4F and 2.5% V H2O. The applied voltage varied from 20 to 120V and the anodization time from 30 to 180 min. The obtained films have been characterized by SEM and XRD regarding the microstructure with particular attention to the structure of TiO2 nanotubes on the α and β phase grains of Ti6Al4V
Effect of anodization parameters and post-anodizing heat treatments on the corrosion resistance of Ti6Al4V and Cp-Ti
No full textCorrosion of metallic biomaterials in the human body is a commonly overlooked phenomenon, even though it constitutes a serious risk for
implant failure. Nevertheless, a fundamental understanding of the electrochemical reactions occurring at the interface biomaterial/human
body fluid is necessary in order to successfully engineer surfaces on titanium biomedical alloys, the most widely used solution for bone
repair and joint replacement. Cp-Ti (ASTM grade 2) and Ti6Al4V (ASTM grade 5) present good mechanical properties, corrosion
resistance and biocompatibility without showing toxicity or immune rejection. However, although the inertness of titanium has been
considered a favorable characteristic for years, its lack of bioactivity also presents some challenges, namely the inability to actively
regulate osteoblast behavior or battle colonization by pathogenic microorganisms. In this regard, the anodization of titanium is a simple
and effective surface treatment that has the potential to improve both osteointegration and antimicrobial activity.
The aim of this work is to investigate the effect of the anodizing parameters and post anodizing heat treatment of medical grade Cp-Ti and
Ti6Al4V, on their corrosion resistance through potentiodynamic polarization measurements in a simulated body fluid solution. Titania
nanotubes, obtained by anodization in an ethylene glycol electrolyte containing 0.5wt.% NH4F and 2.5% V H2O at different applied
potentials and different anodization times, have been characterized regarding their morphology and structure. The distinct geometry of the
nanotubes and their increased surface area are believed to lead to an improvement in osseointegration. Their particular tubular shape
makes them, in addition, excellent reservoir for antimicrobial agents. Post anodizing heat-treatments can develop a crystalline
microstructure that closely resembles that of the native hydroxyapatite on the human bone. Nevertheless, the anodization and the post
anodization heat treatment can influence the corrosion resistance of the Ti alloys in the human body. The aim of this work is to
understand how the process parameters can influence the microstructure and thus the corrosion resistance, in order to avoid a decrease
of the corrosion properties
Evaluation of electronic property and Volta potential distribution of CoCrMo alloy in presence of protein molecule by SKPFM and electrochemical measurements
Full text linkIn this research, the adsorption evaluation of bovine serum Albumin (BSA) proteins in the phosphate buffered solution on semiconductor character of the passive film on CoCrMo alloy was studied by means of scanning electron microscopy (SEM/EDS), atomic force microscopy (AFM), scanning Kelvin probe force microscopy (SKPFM), and electrochemical measurements. In the entire concentrations of BSA from 0 to 2 g.L-1, the lower corrosion potential and more passivity regions were detected. The potentiodynamic polarization and electrochemical impedance spectroscopy analyses results indicate that the lower concentration of BSA than 0.5 g.L-1 provide the higher corrosion current density and lower the charge transfer resistance. Likewise, the higher concentration of BSA than 0.5 g.L-1 have considerably effect on increasing the corrosion resistance on passive film. It is because that the BSA molecules strongly adsorbs passive film by electrostatic or hydrophobicity (chemisorption through carboxylate/amino group) interactions and then inhibits the electrochemical reactions. Mott-Schottky analysis demonstrated that the BSA protein in the high concentrations has a positive effect on reducing the density of defects including n-type or p-type semiconductor characters and space charge regions on passive film. AFM and SKPFM mappings visualized the presence of BSA protein adsorption on passive film with different topography and Volta potential distribution respect to the matrix
A comprehensive insight on the degradation of NiCo and NiCo/Au coated micro-robots during immersion in simulated body fluids
No full textMicrorobots or motors can be used for different applications such as drug delivery, sensing, environmental remediation, and manipulation of small objects. Among them magnetic micropillars, driven by external magnetic fields, can be used for drug delivery in the human body. Although the fabrication, the magnetic properties and the motion of these microdevices have been extensively studied, their degradation in corrosive environments of the human body has been scarcely investigated. In this work, we report on a combined microscopic, analytical and electrochemical characterization of NiCo and NiCo/Au coated micropillars (with diameter and length dimensions of 1μm and 10 μm respectively) produced by template-assisted electrodeposition. The NiCo micropillars were coated by Au in order to reduce the Ni and Co ions release (toxic elements for the human body) and enhance the biocompatibility. The long-term degradation mechanisms of the micro- structures were investigated in phosphate-buffered solution (PBS) containing bovine serum albumin (BSA) protein to simulate inflammatory conditions close to the human body environment. To this end, scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDXS), atomic force microscopy (AFM), scanning Kelvin probe force microscopy (SKPFM), and electrochemical measurements (potentiodynamic polarization, electrochemical impedance spectroscopy, and Mott–Schottky analysis) were used to reveal the chemical composition, the electronic properties, the electrochemical behaviour and the metal ion releasing process on both NiCo and NiCo/Au coated micro-pillars. SEM/EDXS chemical maps showed a homogeneous chemical composition of both NiCo and NiCo/Au coated micro-pillars. According to electrochemical results, NiCo/Au pillar showed the lower corrosion current density and higher corrosion potential (10 nA.cm-2 and -160 mV vs. Ag/AgCl3M KCl) respect to NiCo pillars with values of 40 nA.cm-2 and -300 mV vs. Ag/AgCl3M KCl. MS analysis showed that the NiCo pillars have a lower space charge region and a higher number of defects density (Nd= 5.8×1022 cm-3, n-type semiconductor character) in comparison with the NiCo/Au coated pillars (Nd= 5.1×1022 cm-3). Likewise, NiCo/Au coated micro-pillars have the higher value of flat band potential (EFB, an important parameter for electronic conductivity) than the NiCo micro-pillars. AFM and SKPFM analyses revealed the presence of some micro and nanoporosity on the Au coating covering the NiCo pillars. The difference in the Volta potential between the Au coating and the NiCo substrate can drive a preferential dissolution of the substrate though the pores (galvanic coupling)
Electrochemical monitoring of the corrosion behavior of functional oxide nanoparticles under biological environments
No full textOwing to their chemical tunability and extraordinary electronic, magnetic, and optical properties, functional oxide nanoparticles have been widely proposed for biomedical applications, such as drug deliveries, brain stimulation and magnetic hyperthermia therapy. Besides their functionalities, however, understanding the behavior of the oxide nanoparticles after injected into body is utmost important as it is directly associated with health issues. Especially, as the particles degrade over time, the interactions between the degradation products and cells and proteins need to be clarified. It has been proven that the iron and cobalt containing nanoparticles, such as iron oxide or cobalt ferrite, can be degraded and captured intracellularly by the endogenous protein, i.e. ferritin. Hitherto, only the local technique, Transmission Electron Microscopy (TEM) analysis, has been employed for the direct observation of Fe, Co ion uptake by ferritin [1,2]. Here, we have performed Electrochemical Impedance Spectroscopy (EIS) measurements on iron and cobalt containing nanoparticles (CoFe2O4 and BiFeO3-CoFe2O4 core-shell nanoparticles) under different biological environments to observe the degradation behavior of the nanoparticles. The impedance measurement showed that the resistance of the nanoparticles gradually reduces as the ferritin captures iron and cobalt ions
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
- …
