1,721,017 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
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
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
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
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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