| 1. |
- Filho, Luimar, et al.
(författare)
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The effect of N, C, Cr, and Nb content on silicon nitride coatings for joint applications
- 2020
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Ingår i: Materials. - : MDPI AG. - 1996-1944. ; 13:8
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Tidskriftsartikel (refereegranskat)abstract
- Ceramic coatings are an alternative to achieve or maintain a high wear resistance of metallic surfaces, and simultaneously allow for a reduction in metal ion release. Silicon nitride based (SiNx) coatings deposited by high power impulse magnetron sputtering (HiPIMS) have shown potential for use in joint implants seen from an improved chemical stability in combination with a good adhesion. The aim of this study was to investigate the effect of N, C, Cr and Nb content on the tribocorrosive performance of 3.7 to 8.8 µm thick SiNx coatings deposited by HiPIMS onto CoCrMo discs to improve the mechanical properties and/or chemical stability of SiNx .Coating composition was evaluated by X-ray photoelectron spectroscopy (XPS) and the surface roughness by Vertical Scanning Interferometry (VSI). Hardness and Young’s modulus were investigated by nanoindentation and coating adhesion was measured by scratch tests. Multidirectional wear tests against UHMWPE pins were performed for 2 million cycles in bovine serum solution (25%) at 37°C, at an estimated contact pressure of 2.1 MPa.Coatings with a relatively low hardness tended to fail earlier in the wear test, due to chemical reactions and eventually dissolution, accelerated by the tribological contact. In fact, while no definite correlation could be observed between coating composition (N: 42.6-55.5 at%, C: 0-25.7 at%, Cr: 0 or 12.8 at%, and Nb: 0-24.5 at%) and wear performance, it was apparent that high-purity and/or -density coatings (i.e. low oxygen content and high nitrogen content) were desirable to prevent coating and/or counter surface wear. Coatings deposited with a higher energy fulfilled the target profile in terms of low surface roughness (Ra<20nm), adequate adhesion (Lc2>30N), chemical stability over time in the tribocorrosive environment, as well as low polymer wear, presenting potential for a future application in joint bearings.
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| 2. |
- Gonzales-Siles, Lucia, et al.
(författare)
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A Pangenome Approach for Discerning Species-Unique Gene Markers for Identifications of Streptococcus pneumoniae and Streptococcus pseudopneumoniae
- 2020
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Ingår i: Frontiers in Cellular and Infection Microbiology. - : Frontiers Media SA. - 2235-2988. ; 10
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Tidskriftsartikel (refereegranskat)abstract
- Correct identifications of isolates and strains of the Mitis-Group of the genus Streptococcus are particularly difficult, due to high genetic similarity, resulting from horizontal gene transfer and homologous recombination, and unreliable phenotypic and genotypic biomarkers for differentiating the species. Streptococcus pneumoniae and Streptococcus pseudopneumoniae are the most closely related species of the clade. In this study, publicly-available genome sequences for Streptococcus pneumoniae and S. pseudopneumoniae were analyzed, using a pangenomic approach, to find candidates for species-unique gene markers; ten species-unique genes for S. pneumoniae and nine for S. pseudopneumoniae were identified. These species-unique gene marker candidates were verified by PCR assays for identifying S. pneumoniae and S. pseudopneumoniae strains isolated from clinical samples. All determined species-level unique gene markers for S. pneumoniae were detected in all S. pneumoniae clinical isolates, whereas fewer of the unique S. pseudopneumoniae gene markers were present in more than 95% of the clinical isolates. In parallel, taxonomic identifications of the clinical isolates were confirmed, using conventional optochin sensitivity testing, targeted PCR-detection for the "Xisco" gene, as well as genomic ANIb similarity analyses for the genome sequences of selected strains. Using mass spectrometry-proteomics, species-specific peptide matches were observed for four of the S. pneumoniae gene markers and for three of the S. pseudopneumoniae gene markers. Application of multiple species-level unique biomarkers of S. pneumoniae and S. pseudopneumoniae, is proposed as a protocol for the routine clinical laboratory for improved, reliable differentiation, and identification of these pathogenic and commensal species.
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| 3. |
- Högberg, Hans, et al.
(författare)
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Reactive sputtering of CSx thin solid films using CS2 as precursor
- 2020
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Ingår i: Vacuum. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0042-207X .- 1879-2715. ; 182
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Tidskriftsartikel (refereegranskat)abstract
- We deposit CSx thin solid films by reactive direct current magnetron sputtering of a C target in an argon plasma, using carbon disulfide (CS2) as a precursor to film growth. We investigate the influence of the partial pressure of the CS2 vapor introduced into the plasma on the composition, the chemical bonding structure, the structural, and the mechanical properties as determined by x-ray photoelectron spectroscopy (XPS), Raman spectroscopy, scanning electron microscopy (SEM), and nanoindentation for films deposited at 150 and 300 degrees C. The Raman and the XPS results indicate that S atoms are incorporated in mostly sp(2) bonded C network. These results agree with previous ab-initio theoretical findings obtained by modeling of the CSx compound by the Synthetic Growth Concept. The microstructure of the films as well as the results of their Raman characterization and the nano mechanical testing results all point out that with the increasing S content some spa bonding is admixed in the predominantly sp(2) bonded CSx network, leading to typical amorphous structure with short and interlocked graphene-like planes for S contents between 2% and 8%. We conclude that CSx thin solid films deposited by using CS2 as a precursor would be CSx films deposited at low temperature of similar to 150 degrees C and with an S content in the region of 6 at.% may be interesting candidates for applications as hard/elastic protective coatings.
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