1,720,982 research outputs found
Protection of biomedical stainless steel and titanium by ALD single and multi-layered thin films made of Al2O3 and HfO2
No full textStainless steel- and Ti-based alloys are one of the most commonly used materials for production of biomedical implants. Although these materials have good anti-corrosive properties, due to their specific application, different strategies have been employed to protect them and improve their functionality in vivo. Atomic layer deposition (ALD) is a novel method for deposition of ultrathin protective barrier films. In this work we focused on the deposition of Al2O3 and HfO2 films of different thicknesses on stainless steel 316L (SS316L) and commercially pure titanium (CP-Ti). Furthermore, multi-layered ALD films were also deposited and compared with the protective properties of the single films. ALD thin films was obtained using trimethylaluminium as a precursor for Al2O3, and tetrakis(ethylmethylamido) hafnium(IV) as a precursor for HfO2. Single-layer films of two thicknesses were prepared: 20 nm and 60 nm. The thickness of multi-layered films was 60 nm: 20 nm Al2O3 + 20 nm HfO2 + 20 nm Al2O3. In each group, several specimens were prepared as a cross section by using inert adhesive tape at one half of the surface to form a step. Prior to deposition, all specimens were properly ground, polished to high smoothness and ultra-sonicated in ethanol for 15 minutes. Prepared specimens were investigated by FE-SEM/EDS analysis. For 20 nm thin Al2O3 and HfO2 films, uncovered parts of the metal surface or pinholes may occur, which was later reflected on electrochemical measurements. Thicker films achieved a complete coverage of the metal surface, but with defects present, such as agglomerates of deposited materials. Specimens prepared with the step were subjected to AFM-SKPFM measurements, which confirmed the expected thickness of both ALD thin films. The differences in the Volta potential between bare metal surface and ALD film were almost the same in the case of 20 and 60 nm thick films. In general, due to the very high passivation ability of these metallic materials, especially CP-Ti, the increase in Volta potential of ALD film is not so high, but it is noticeable. Also, it was observed that HfO2 provides a higher Volta potential, i.e. it has shown better insulating properties than Al2O3. Potentiodynamic measurements were carried out in Hanks’ physiological solution at 37°C simulating a human body conditions. The best anti-corrosive properties were shown by multilayer ALD films, followed by HfO2 and finally Al2O3 films. Thinner, 20 nm thick films initially showed weaker barrier properties than thicker films, which was also confirmed by SEM investigations
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 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
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
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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