Non-contact dilatometry of hard and soft porcelain compositions

Two different porcelain compositions were studied: a soft and a hard one. DTA, optical non-contact dilatometry and DSC were used to evaluate the thermal behaviour of the porcelain compositions with the aim to master the suitable thermal cycle for each. Results were interpreted on the basis of mineralogy and microstructure: the amorphous phase, abundant in soft porcelain, plays an important role on thermal expansion (8·10^–6 K^–1 for soft and 6·10^–6 K^–1 for hard at 1000°C). Thermal expansion behaviour as function of firing time was also studied. Non-contact dilatometry characterisation of porcelain bodies enable to master the suitable thermal cycle for the sintering.     

Nanostructured carbon nanotube/TiO2 composite coatings using electrophoretic deposition (EPD)

Electrophoretic deposition (EPD) has been used to combine multi-walled carbon nanotubes of diameter in the range 20–30 nm and commercially available TiO₂ nanoparticles (23 nm particle size) in composite films. Laminate coatings with up to four layers were produced by sequential EPD, while composite coatings were obtained by electrophoretic co-deposition of carbon nanotubes and TiO₂ nanoparticles, respectively. Scanning electron microscopy was used to characterize the resultant microstructures. The mechanism of EPD of carbon nanotube/TiO₂ nanoparticle composites is discussed.     

Characterization of TiO<Subscript>2</Subscript> nanoparticle suspensions for electrophoretic deposition

The rheology of suspensions is critically important for the successful achievement of defect-free TiO₂ deposits by electrophoretic deposition (EPD). The rheological behaviour of TiO₂ nanoparticle suspensions in acetylacetone with and without iodine was investigated over a broad solid-concentration range (0.3–2.5 wt.%) and at different shear rates ( = 10–250 s⁻¹). The influence of these parameters on the quality of TiO₂ films obtained by EPD on stainless steel substrates was assessed. The pure solvent and the 1 wt.% TiO₂ nanoparticles suspension without iodine exhibited shear-thickening flow behaviour. For other concentrations, the suspensions showed shear-thinning behaviour followed by an apparent shear-thickening effect at a critical shear rate (100 s⁻¹). For the suspension with 1 wt.% TiO₂ containing iodine, a shear-thickening flow behaviour was observed over the whole shear rate range investigated. The maximum solids fraction (ϕ_m) was experimentally determined from a linear relationship between solid concentration and viscosity. The estimated value was ϕ_m = 7.94 wt.% for this system. Using a suspension with 1 wt.% concentration, good-quality TiO₂ deposits on stainless steel planar substrates were obtained by EPD at constant voltage condition. The influence of pH on suspension stability was determined in the range pH = 1–9, being pH ≈ 5 the optimal value for this system in terms of EPD results.     

Pulse electrodeposition and characterization of non-continuous,multi-element-doped hydroxyapatite bioceramic coatings

Journal of Solid State Electrochemistry - Multi-element-modified bioactive hydroxyapatite (mHAp) coatings were developed onto commercial titanium alloy material (Ti6Al4V) in clusters. The coatings...     

Bioactive glass (type 45S5) nanoparticles: in vitro reactivity on nanoscale and biocompatibility

Bioactive glasses represent important biomaterials being investigated for the repair and reconstruction of diseased bone tissues, as they exhibit outstanding bonding properties to human bone. In this study, bioactive glass (type 45S5) nanoparticles (nBG) with a mean particle size in the range of 20?C60?nm, synthesised by flame spray synthesis, are investigated in relation to in vitro bioreactivity in simulated body fluid (SBF) and response to osteoblast cells. The structure and kinetics of hydroxyapatite formation in SBF were investigated using transmission electron microscopy (TEM), X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FT-IR) revealing a very rapid transformation (after 1?day) of nBG to nanocrystalline bone-like carbonated HAp. Additionally, calcite is formed after 1?day of SBF immersion because of the high surface reactivity of the nBG particles. In the initial state, nBG particles were found to exhibit chain-like porous agglomerates of amorphous nature which are transformed on immersion in SBF into compact agglomerates covered by hydroxyapatite with a reduced size of the primary nanoparticles. In vitro studies revealed high cytocompatibility of nBG with human osteoblast cells, indicated through high lactatedehydrogenase (LDH) and mitochondrial activity as well as alkaline phosphatase activity. Hence, this study contributes to the understanding of the structure and bioactivity of bioactive glass (type 45S5) nanoparticles, providing insights to the phenomena occurring at the nanoscale after immersion in SBF. The results are relevant in relation to the understanding of the nanoparticles?? bioreactivity required for applications in bone tissue engineering.     

Alternating current electrophoretic deposition (EPD) of TiO2 nanoparticles in aqueous suspensions

TiO(2)-nanostructured coatings from aqueous suspensions have been successfully prepared by the application of alternating current (AC) instead of direct current (DC) during electrophoretic deposition (EPD). No organic additives in suspension were required for successful EPD. The quality of the AC-EPD TiO(2) coatings in terms of homogeneity and extent of microcracking, upon drying, observed by SEM, was superior to that of DC-EPD coatings made from the same type of suspensions. The main difference between AC- and DC-EPD was the suppression of bubble formation. The absence of water electrolysis at the electrodes can be explained by the particular distribution of the electric field during AC mode, which prevents the nucleation of bubbles. The preparation of TiO(2) coatings from aqueous suspension and without the aid of organic stabilizers opens the possibility for co-deposition of sensitive materials such as biomolecules and even cells for biomedical applications, given the high biocompatibility of TiO(2). The deposition of TiO(2) coatings from aqueous suspensions is also attractive from environmental and economical points of view.     

Unique microstructure of glass-metal composites obtained by microwave assisted heat-treatments

The present study deals with the computer-aided simulation of the microwave heating of metal/glass composites in single mode applicator and the rapid densification of borosilicate glass matrix composites containing molybdenum particle inclusions. The selective and penetrating microwave heating led to a layered porous structure of the samples. They consisted of a highly porous core containing spherical pores and a relatively dense outer shell. Pores in the central region were formed in the molten glass phase due to gas evolution and entrapment. The outer region of the sample remained at lower temperature and it sintered by viscous flow with minimal distortion. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of buffer in simulated body fluid on morphology and crystallinity of hydroxyapatite precipitated on 45S5 bioactive glass-derived glass–ceramic scaffolds: comparison of Good’s buffer systems and TRIS

In vitro tests that verify the ability of a material to form bone-like apatite precipitated (HAp) use a solution that imitates the inorganic part of blood plasma, simulated body fluid (SBF). During such tests, it is necessary to maintain a neutral pH, for which purpose the International Standards Organization recommends the TRIS (tris(hydroxymethyl)aminomethane) buffer (ISO 23,317:2014). To do this, TRIS buffer must remain inert, but, as we have previously reported, TRIS interacts with highly bioreactive materials (such as 45S5 Bioglass-derived scaffolds), thereby accelerating scaffold dissolution. In the search for an alternative to TRIS, we have also recently published results for the 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) and 3-(N-morpholino) propanesulfonic acid (MOPS) buffers, which were also unable to maintain a neutral pH in SBF. Thus, we here continue our search for a more suitable Good’s buffer by comparing BES (N,N-bis(2-hydroxyethyl)-2-aminoethanesulfonic acid) and TES (2-[(2-hydroxy-1,1-bis(hydroxymethyl) ethyl) amino] ethanesulfonic acid) with TRIS. 45S5-derived glass–ceramic scaffolds were tested under static–dynamic conditions for bone-like apatite formation using SBF + BES and SBF + TES solutions. The pH measurements, leachate analysis [atomic absorption spectrophotometry (AAS) (Ca²⁺, Si^IV), UltraViolet-Visible (UV-VIS) spectrophotometry (PO₄)^3?], and scaffold analysis [X-Ray powder diffraction analysis (XRD), X-ray fluorescent analysis (XRF), scanning electron microscopy (SEM)/energy dispersive spectroscopy (EDS), Brunauer.Emmett.Teller specific surface area analysis (BET)] all showed that both BES and TES quickly interacted with the tested material. Moreover, the kinetics of the glass–ceramic dissolution affected the crystallinity and morphology of the precipitated HAp. Based on our previous results and the present data, it appears that Good’s buffers are not suitable for the in vitro testing of bioactivity of highly bioreactive materials.     

Crack growth in glass matrix composite reinforced by long SiC fibres

Theoretical and experimental work are made for bridged cracks in chevron-notched three point bend specimens made of glass matrix composite reinforced by long SiC fibres. The fracture toughness (K_IC) values are determined using the chevron-notch technique and compared with the theoretical predictions based on micromechanical analysis exploiting weight functions. The weight functions for orthotropic material are obtained numerically by means of detailed FEM analysis using the ANSYS package and they are further used together with appropriate bridging models for the theoretical prediction of the R-curve behaviours typical of the investigated composites.     

Incorporation of Boron in Mesoporous Bioactive Glass Nanoparticles Reduces Inflammatory Response and Delays Osteogenic Differentiation

Mesoporous bioactive glass nanoparticles (MBG) are multifunctional building blocks for tissue regeneration and nanomedicine applications. Incorporation of biologically active ions can endow MBG with additional functionalities toward promoted therapeutic effects. Here, boron is incorporated into MBG by using a sol–gel approach. The concentration of boron incorporated is controllable by tuning the amount of boron precursor. Two types of boron-doped MBG, namely 10B- and 15B-MBG (5.8 and 6.5 mol% of B₂O₃, respectively) are synthesized. Boron incorporation does not significantly influence the particle morphology. All synthesized particles exhibit a sphere-like shape with a size ranging from 100 to 300 nm. 10B- and 15B-MBG show large specific surface area (346 and 320 m² g⁻¹, respectively) and pore volume. Both boron-doped MBG exhibit remarkable in vitro bioactivity and noncytotoxicity. Boron incorporation is shown to reduce the inflammatory response linked to macrophages as indicated by downregulated expression of pro-inflammatory genes. However, boron incorporation delays the osteogenic differentiation in osteoblasts as indicated by the downregulated expression of pro-osteogenic genes. The results demonstrate the promising potential of using boron-doped MBG to modulate inflammatory response for bone regeneration under inflammatory conditions, as shown in this study for the first time.