Microstructural and tribological comparison of HVOF-sprayed and post-treated M-Mo-Cr-Si (M = Co, Ni) alloy coatings

High velocity oxygen-fuel (HVOF)-sprayed wear resistant Co-28%Mo-17%Cr-3%Si and Ni-32%Mo-15%Cr-3%Si coatings, both as-sprayed and after heat treatments at 600 degrees C for 1 h, have been studied. Particularly, their dry sliding wear behaviour has been compared by ball-on-disk tests against different counterbodies (100Cr6 steel and sintered alumina), and differences were discussed based on microstructural characteristics and micromechanical properties (Vickers microindentation and scratch test responses). As-sprayed coatings contain oxide stringers, are mostly amorphous and display rather low Vickers microhardness (about 7.4 GPa for the Co-based and 6.2 GPa for the Ni-based), toughness and elastic modulus. Heat-treated ones display sub-micrometric crystalline intermetallics, improving hardness (9.6 GPa and 7.4 GPa, respectively) and elastic modulus. Scratch tests indicate greater brittleness of the Ni-based alloy (higher tendency to cracking). Due to low hardness and toughness, both as-sprayed coatings undergo wear loss against steel and alumina counterparts. The more plastic Co-based alloy undergoes higher adhesive wear against steel and lower abrasive wear against alumina; the situation is reversed for the Ni-based alloy. After heat treatment, the wear loss against steel is very low for both coatings; abrasive wear still occurs against alumina. (c) 2007 Elsevier B.V. All rights reserved

Short range investigation of sub-micron zirconia particles

The Perturbed Angular Correlations technique was used to determine the configurations around Zirconium ions and their thermal behavior in non-aggregated sub-micron zirconia spherical particles. Three residues containing- Zr surroundings were determined for the non-crystalline starting particles, which were identified under the assumption of a certain chemical reactions sequence during synthesis. While the one made up mainly by hydroxyl groups was common to both samples, the two involving mainly organic residues were particle size dependent. Upon crystallization, both samples stabilized in the t'- and t- tetragonal forms and the Xc-cubic form but their amounts and temperatures of appearance were different. On heating, the structure of the smaller particles became gradually monoclinic achieving total degradation upon the subsequent cooling to RT.Instituto de Física La Plat

Fabrication and Characterization of Quinary High Entropy-Ultra-High Temperature Diborides” Ceramics

Due to their inherently chemical complexity and their refractory nature, the obtainment of highly dense and single-phase High Entropy (HE) diborides represents a very hard target to achieve. In this framework, homogeneous (Hf0.2Nb0.2Ta0.2Mo0.2Ti0.2)B2, (Hf0.2Zr0.2Ta0.2Mo0.2Ti0.2)B2, and (Hf0.2Zr0.2Nb0.2Mo0.2Ti0.2)B2 ceramics with high relative densities (97.4, 96.5 and 98.2 %, respectively) are successfully produced by Spark Plasma Sintering (SPS) using powders prepared by Self-propagating High-temperature Synthesis (SHS). Although the latter technique does not lead to the complete conversion of initial precursors into the prescribed HE phases, such goal is fully reached after SPS (1950°C/20min/20 MPa). The three HE products show similar, even better in some cases, mechanical properties compared to ceramics with the same nominal composition attained using alternative processing methods. Superior Vickers hardness and elastic modulus values are found for the (Hf0.2Nb0.2Ta0.2Mo0.2Ti0.2)B2 and (Hf0.2Zr0.2Ta0.2Mo0.2Ti0.2)B2 systems, i.e. 28.1 GPa/538.5 GPa and 28.08 GPa/498.1 GPa, respectively, in spite of the correspondingly higher residual po-rosities (1.2 and 2.2 vol.%, respectively). In contrast, the third ceramic, not containing Tantalum, displays lower values of these two properties (25.1 GPa/404.5 GPa). However, the corresponding fracture toughness (8.84 MPa m1/2) is relatively higher. This fact can be likely ascribed to the smaller residual porosity (0.3 vol.%) of the sintered material

In-vivo evaluations of bone regenerative potential of two novel bioactive glasses

: Due to the aging of population, materials able to repair damaged tissues are needed. Among others, bioactive glasses (BGs) have attracted a lot of interest due to their outstanding properties both for hard and soft tissues. Here, for the first time, two new BGs, which gave very promising results in preliminary in vitro-tests, were implanted in animals in order to evaluate their regenerative potential. The new BGs, named BGMS10 and Bio_MS and containing specific therapeutic ions, were produced in granules and implanted in rabbits' femurs for up to 60 days, to test their biocompatibility and osteoconduction. Additionally, granules of 45S5 Bioglass® were employed and used as a standard reference for comparison. The results showed that, after 30 days, the two novel BGs and 45S5 displayed a similar behavior, in terms of bone amount, thickness of new bone trabeculae and affinity index. On the contrary, after 60 days, 45S5 granules were mainly surrounded by wide and scattered bone trabeculae, separated by large amounts of soft tissue, while in BGMS10 and Bio_MS the trabeculae were thin and uniformly distributed around the BG granules. This latter scenario could be considered as more advantageous, since the features of the two novel BG granules allowed for the neo-formation of a uniformly distributed bony trabeculae, predictive of more favorable mechanical behavior, compared to the less uniform coarse trabeculae, separated by large areas of soft tissue in 45S5 granules. Thus, BGMS10 and Bio_MS could be considered suitable products for tissue regeneration in the orthopedic and dental fields.Due to the aging of population, materials able to repair damaged tissues are needed. Among others, bioactive glasses (BGs) have attracted a lot of interest due to their outstanding properties both for hard and soft tissues. Here, for the first time, two new BGs, which gave very promising results in preliminary in vitro-tests, were implanted in animals in order to evaluate their regenerative potential. The new BGs, named BGMS10 and Bio_MS and containing specific therapeutic ions, were produced in granules and implanted in rabbits' femurs for up to 60 days, to test their biocompatibility and osteoconduction. Additionally, granules of 45S5 Bioglass® were employed and used as a standard reference for comparison. The results showed that, after 30 days, the two novel BGs and 45S5 displayed a similar behavior, in terms of bone amount, thickness of new bone trabeculae and affinity index. On the contrary, after 60 days, 45S5 granules were mainly surrounded by wide and scattered bone trabeculae, separated by large amounts of soft tissue, while in BGMS10 and Bio_MS the trabeculae were thin and uniformly distributed around the BG granules. This latter scenario could be considered as more advantageous, since the features of the two novel BG granules allowed for the neo-formation of a uniformly distributed bony trabeculae, predictive of more favorable mechanical behavior, compared to the less uniform coarse trabeculae, separated by large areas of soft tissue in 45S5 granules. Thus, BGMS10 and Bio_MS could be considered suitable products for tissue regeneration in the orthopedic and dental fields

Short range investigation of sub-micron zirconia particles

The Perturbed Angular Correlations technique was used to determine the configurations around Zirconium ions and their thermal behavior in non-aggregated sub-micron zirconia spherical particles. Three residues containing- Zr surroundings were determined for the non-crystalline starting particles, which were identified under the assumption of a certain chemical reactions sequence during synthesis. While the one made up mainly by hydroxyl groups was common to both samples, the two involving mainly organic residues were particle size dependent. Upon crystallization, both samples stabilized in the t'- and t- tetragonal forms and the Xc-cubic form but their amounts and temperatures of appearance were different. On heating, the structure of the smaller particles became gradually monoclinic achieving total degradation upon the subsequent cooling to RT.Instituto de Física La Plat

Human mesenchymal stem cell combined with a new strontium-enriched bioactive glass: An ex-vivo model for Bone Regeneration

A 3D cellular model that mimics the potential clinical application of a biomaterial is here applied for the first time to a bioactive glass, in order to assess its biological potential. A recently developed bioactive glass (BGMS10), whose composition contained strontium and magnesium, was produced in the form of granules and fully investigated in terms of biocompatibility in vitro. Apart from standard biological characterization (Simulated Body Fluid (SBF) testing and biocompatibility as per ISO10993), human bone marrow mesenchymal stromal/stem cells (BM-MSCs) were used to investigate the performance of the bioactive glass granules in an innovative 3D cellular model. The results showed that BGMS10 supported human BM-MSCs adhesion, colonization, and bone differentiation. Thus, bioactive glass granules seem to drive osteogenic differentiation and thus look particularly promising for orthopedic applications, bone tissue engineering and regenerative medicine

Short range investigation of sub-micron zirconia particles

The Perturbed Angular Correlations technique was used to determine the nanoconfigurations and their thermal behavior in two non-aggregated zirconia nanospheres of unlike sizes obtained by adding different water amounts during preparation. Three residues containing- Zr surroundings were determined for the non-crystalline starting zirconias, the two organics containing- ones being particle size dependent. Upon crystallization, the nanospheres showed the stabilization of both tetragonal (t´- and t- forms) and cubic (Xc- form) phases. Nevertheless, their amounts, temperature of appearance and thermal evolution depended on the residues containing- precursors. It was observed, in addition, that the structure of the smaller nanospheres became gradually monoclinic. The bigger spheres remained stabilized up to the highest temperatures certainly due to their lower specific surface area that favors the permanence of the oxygen defective t´- form

Short range investigation of sub-micron zirconia particles

The Perturbed Angular Correlations technique was used to determine the configurations around Zirconium ions and their thermal behavior in non-aggregated sub-micron zirconia spherical particles. Three residues containing- Zr surroundings were determined for the non-crystalline starting particles, which were identified under the assumption of a certain chemical reactions sequence during synthesis. While the one made up mainly by hydroxyl groups was common to both samples, the two involving mainly organic residues were particle size dependent. Upon crystallization, both samples stabilized in the t'- and t- tetragonal forms and the Xc-cubic form but their amounts and temperatures of appearance were different. On heating, the structure of the smaller particles became gradually monoclinic achieving total degradation upon the subsequent cooling to RT.Instituto de Física La Plat

Peripapillary Microvascular and Neural Changes in Diabetes Mellitus: An OCT-Angiography Study

Purpose: To evaluate peripapillary vessel density and morphology in patients with diabetes mellitus (DM) without clinical signs of diabetic retinopathy (DR) and with mild, nonproliferative DR and to correlate with peripapillary nerve fiber layer (NFL) thickness.Methods: One hundred seventeen eyes (34 healthy controls, 54 patients with DM without DR [noDR group] and 24 patients with mild DR [DR group]) were prospectively evaluated. All subjects underwent peripapillary and macular optical coherence tomography angiography (OCT-A). Peripapillary NFL thickness was also recorded. OCT-A slab of radial peripapillary plexus (RPC) and macular superficial capillary plexus (SCP) were analysed in order to calculate perfusion density (PD) and vessel density (VD). Further an image analysis of RPC slab was performed to identify number of branches (NoB) and total branches length (tBL).Results: In peripapillary area there was a significant decrease in VD (P = 0.003), NoB (P < 0.001), and tBL (P < 0.001) in noDR group versus controls; PD values were not different among groups (P = 0.126); there was a significant decrease in average NFL thickness in DR versus controls (P = 0.008) and in the inferior quadrant in noDR group versus controls (P = 0.03); there was a significant correlation between OCT-A and NFL thickness values (\u3c1 ranging from 0.19-0.57). In macular region PD and VD were decreased only in DR group (P < 0.05).Conclusions: There are early changes in the peripapillary vessel morphology and VD of the RPC in patients with DM without DR that correlate to NFL thinning. Earlier changes in superficial vessel density are documented in the peripapillary than in the macular region. These data may confirm a coexistence of an early neuronal and microvascular damage in patients with DM without clinical signs of DR

FDG-PET/CT imaging for staging and target volume delineation in conformal radiotherapy of anal carcinoma

Background: FDG-PET/CT imaging has an emerging role in staging and treatment planning of various tumor locations and a number of literature studies show that also the carcinoma of the anal canal may benefit from this diagnostic approach. We analyzed the potential impact of FDG-PET/CT in stage definition and target volume delineation of patients affected by carcinoma of the anal canal and candidates for curative radiotherapy. Methods: Twenty seven patients with biopsy proven anal carcinoma were enrolled. Pathology was squamous cell carcinoma in 20 cases, cloacogenic carcinoma in 3, adenocarcinoma in 2, and basal cell carcinoma in 2. Simulation was performed by PET/CT imaging with patient in treatment position. Gross Tumor Volume (GTV) and Clinical Target Volume (CTV) were drawn on CT and on PET/CT fused images. PET-GTV and PET-CTV were respectively compared to CT-GTV and CT-CTV by Wilcoxon rank test for paired data. Results: PET/CT fused images led to change the stage in 5/27 cases (18.5%): 3 cases from N0 to N2 and 2 from M0 to M1 leading to change the treatment intent from curative to palliative in a case. Based on PET/CT imaging, GTV and CTV contours changed in 15/27 (55.6%) and in 10/27 cases (37.0%) respectively. PET-GTV and PET-CTV resulted significantly smaller than CT-GTV (p = 1.2 7 10-4) and CT-CTV (p = 2.9 7 10-4). PET/CT-GTV and PET/CT-CTV, that were used for clinical purposes, were significantly greater than CT-GTV (p = 6 7 10-5) and CT-CTV (p = 6 7 10-5). Conclusions: FDG-PET/CT has a potential relevant impact in staging and target volume delineation of the carcinoma of the anal canal. Clinical stage variation occurred in 18.5% of cases with change of treatment intent in 3.7%. The GTV and the CTV changed in shape and in size based on PET/CT imaging