On the mechanical and biological properties of bredigite-magnetite (Ca7MgSi4O16-Fe3O4) nanocomposite scaffolds

The aim of the present study was to study the mechanical and biologocal properties of the bredigite-magnetite (Ca₇MgSi₄O₁₆-Fe₃O₄) nanocomposite with various amounts of magnetite (0, 10, 20 and 30 wt%). According to the obtained results, the properties of the constructed scaffolds have an extreme dependence on the magnetite content. In this research, the bredigite-30 wt% magnetite as the optimum sample showed a fracture toughness of 2.69 MPa m^1/2 and a Young's modulus of 29 GPa. Increasing bredigite content led to the increase of pH values in the SBF solution. This was originated from the interchange/interaction of Ca²⁺ ion on the scaffold surface. The sample containing 10 wt% magnetite presented a rocky and irregular surface while that of 30 wt% illustrated a smooth and flat outer layer with coarse projections. The results confirmed that the biodegradation rate of the pure bredigite is more than that of 20 wt% sample. The event is originated from the dissolution of the Si ions of the bridigite particles in the absence of magnetite.     

Porous β-Ca2SiO4 ceramic scaffolds for bone tissue engineering: In vitro and in vivo characterization

The biodegradable ceramic scaffolds with desirable pore size, porosity and mechanical properties play a crucial role in bone tissue engineering and bone transplantation. A novel porous β-dicalcium silicate (β-Ca₂SiO₄) ceramic scaffold was prepared by sintering the green body consisting of CaCO₃ and SiO₂ at 1300 °C, which generated interconnected pore network with proper pore size of about 300 μm and high compressive strength (28.13±5.37–10.36±0.83 MPa) following the porosity from 53.54±5.37% to 71.44±0.83%. Porous β-Ca₂SiO₄ ceramic scaffolds displayed a good biocompatibility, since human osteoblast-like MG-63 cells and goat bone mesenchymal stem cells (BMSCs) proliferated continuously on the scaffolds after 7 d culture. The porous β-Ca₂SiO₄ ceramic scaffolds revealed well apatite-forming ability when incubated in the simulated body fluid (SBF). According to the histological test, the degradation of porous β-Ca₂SiO₄ ceramic scaffolds and the new bone tissue generation in vivo were observed following 9 weeks implantation in nude mice. These results suggested that the porous β-Ca₂SiO₄ ceramic scaffolds could be potentially applied in bone tissue engineering.     

Fabrication and characterization of porous β-tricalcium phosphate scaffolds coated with alginate

All porous materials have a common limitation which is lack of strength due to the porosity. In this study, two different methods have been used to produce porous β-tricalcium phosphate (β-TCP) scaffolds: liquid-nitrogen freeze casting and a combination of the direct-foaming and sacrificial-template methods. Among these two methods, porous β-TCP scaffolds with acceptable pore size and compressive strength and defined pore-channel interconnectivity were successfully fabricated by the combined direct-foaming and sacrificial-template method. The average pore size of the scaffolds was in the range of 100–150 µm and the porosity was around 70%. Coating with 4 wt% alginate on porous β-TCP scaffolds led to higher compressive strength and low porosity. In order to make a chemical link between the β-TCP scaffolds and the alginate coating, silane coupling agent was used. Treated β-TCP scaffold showed improvements in compressive strength of up to 38% compared to the pure β-TCP scaffold and 11% compared to coated β-TCP scaffold.     

New 3D stratified Si-Ca-P porous scaffolds obtained by sol-gel and polymer replica method: Microstructural,mineralogical and chemical characterization

The aim of this research was to develop and characterize a novel stratified porous scaffold for future uses in bone tissue engineering. In this study, a calcium silicophosphate porous scaffold, with nominal composition 29.32 wt% SiO₂ – 67.8 wt% CaO – 2.88 wt% P₂O₅, was produced using the sol-gel and polymer replication methods. Polyurethane sponges were used as templates which were impregnated with a homogeneous sol solution and sintered at 950 °C and 1400 °C during 8 h. The characteristics of the 3D stratified porous scaffolds were investigated by Scanning Electron Microscopy, X-Ray Diffraction, Fourier Transform Infrared Spectrometry, Diametric Compression of Discs Test and Hg porosimetry techniques. The result showed highly porous stratified calcium silicophosphate scaffolds with micro and macropores interconnected. Also, the material has a diametrical strength dependent on the number of layers of the stratified scaffolds and the sintering temperature.     

Coagulated concentrated anatase slurry leads to improved strength of ceramic TiO2 bone scaffolds

Slurry behaviour has an important influence on the properties of ceramic scaffolds produced by the polymer sponge method. By adding chloride salts to the TiO₂ slurry, the viscosity was increased depending on the chloride concentration at low pH and high particle concentration. Slurries with higher viscosity led to closed and dense scaffold struts combined with high porosity, resulting in a compressive strength over 1.6 MPa. Furthermore, scaffold prepared with 0.1 M CaCl₂ and SrCl₂ showed the formation of Ca- and Sr-rich phases at the grain boundaries. These ions were also shown to reduce the activation energy for grain growth in the TiO₂ scaffold as indicated by the significantly larger grain size. Ca²⁺-doped scaffolds had the highest compressive strength, while the strength of Sr²⁺-doped scaffolds was reduced by the formation of a solid solution phase below the sintering temperature.     

The control of abnormal grain growth in low-voltage SnO2 varistors by microseed addition

In this research, the addition effects of three different quantities of micron-sized seeds (microseeds) to a SnO₂ varistor prepared from nanomaterials on the microstructure and electrical properties were studied. Moreover, surge-withstanding capability of low-voltage SnO₂ varistors was investigated. The X-ray diffraction pattern disclosed a single phase SnO₂ for microseed grains. The morphological features of samples were characterized using scanning electron microscopy. The abnormal distribution of grain size with elongated grains of SnO₂ in fine grains matrix was observed in sintered samples without microseeds. The low content of microseed addition (0.3 wt%) had not controlled abnormal grain growth, however, it increased mean grain size to 37 µm. Although the high content of microseeds (7.5 wt%) stopped abnormal grain growth, it had a negative effect on relative density and mean grain size. The normal grain size distribution with maximum mean grain size (45 µm) was obtained in samples containing 1.5 wt% microseeds. These samples showed the lowest breakdown field (240 V/cm) and the highest surge-withstanding capability (1.5 kA/cm²). Furthermore, the standard deviation of the electrical parameters of these samples was improved due to normal grain-size distribution.     

Sintering behaviour of a ZnO waste powder obtained as by-product from brass smelting

The effect of two sintering methods (conventional sintering and two-step sintering) and of alumina addition on the sintering behaviour of a ZnO-rich waste powder (ZnO > 95 wt%), a by-product from brass smelting industry, was studied aiming to improve the sintered density and grain size. Both conventional sintering and two-step sintering methods did not lead to fully dense powder compacts, as densification was conditioned by abnormal grain growth and the particle size of the ZnO-rich residue. When two-step sintering was used the grain growth was reduced comparatively to conventional sintering method. The highest relative sintered density (about 90%) was achieved when samples of ZnO waste and samples of ZnO waste with 2 wt% added Al₂O₃ were processed by two-step sintering and corresponded to a mean grain size of around 18 µm and 7 µm, respectively. XRD and SEM results indicated that alumina addition helped to inhibit grain growth due to the formation of gahnite spinel (ZnAl₂O₄) precipitates in the grain boundaries of zincite (ZnO) grains.     

Direct ink writing of highly bioactive glasses

Direct ink writing (DIW), or Robocasting, is an additive manufacturing technique that offers the opportunity to create patient specific bioactive glass scaffolds and high strength scaffolds for bone repair. The original 45S5 Bioglass^® composition crystallises during sintering and until now, robocast glass scaffolds contained at least 51.9 mol% SiO₂ or B₂O₃ to maintain their amorphous structure. Here, ICIE16 and PSrBG compositions, containing <50 mol% SiO₂, giving silicate network connectivity close to that of 45S5, were robocast and compared to 13–93 composition. Results showed Pluronic F-127 can be used as a universal binder regardless of glass reactivity and that particle size distribution affected the ink “printability”. Scaffolds with interconnects of 150 μm (41–43% porosity) had compressive strengths of 32–48 MPa, depending on the glass composition. Robocast scaffolds from these highly reactive bioactive glasses promise greatly improved bone regeneration rates compared with existing bioactive glass scaffolds.     

Fabrication and properties of porous β-tricalcium phosphate ceramics prepared using a double slip-casting method using slips with different viscosities

A new method to enhance the flexural strength of porous β-tricalcium phosphate (β-TCP) scaffolds was developed. This new method provides better control over the microstructures of the scaffolds and enhances the scaffolds’ mechanical properties. Using this technique, we were able to produce scaffolds with mechanical and structural properties that cannot be attained by either the polymer sponge or slip-casting methods alone or by simply combining the polymer sponge and slip-casting methods. The prepared scaffolds had an open, uniform, interconnected porous structure with a bimodal pore size of 100.0–300.0 μm. The flexural strength of the bimodal porous β-TCP scaffold sintered at 1200 °C was 56.2 MPa and had porosity of 61.4 vol%. The scaffolds obtained provide good mechanical support while maintaining bioactivity, and hence, these bioscaffolds hold promise for applications in hard-tissue engineering.     

Wetting of AgCu-Ti filler on porous Si3N4 ceramic and brazing of the ceramic to TiAl alloy

The effect of Ti content on the wettability of AgCu-Ti filler on porous Si₃N₄ ceramic was studied by the sessile drop method. AgCu-2 wt% Ti filler alloy showed a minimum contact angle of 14.6° on porous Si₃N₄ ceramic during the isothermal wetting process. The mechanism of AgCu-Ti filler wetting on porous Si₃N₄ ceramic is clarified in this paper. Porous Si₃N₄ ceramic was brazed to TiAl alloy using AgCu-xTi (x = 0, 2 wt%, 4 wt%, 6 wt%, 8 wt%) filler alloy at 880 °C for 10 min. The effect of Ti content on the interfacial microstructure and mechanical properties of porous-Si₃N₄/AgCu-xTi/TiAl joints are studied. The typical interfacial microstructure of p-Si₃N₄/AgCu-Ti/TiAl joint is p-Si₃N₄/penetration layer (Ag(s,s)+Si₃N₄+TiN+Ti₅Si₃)/Ag(s,s)+Cu(s,s)+TiCu/AlCu₂Ti/TiAl. The maximum shearing strength of the brazed joint was 14.17 MPa and fracture that occurred during the shearing test propagated in the porous Si₃N₄ ceramic substrate for the formation of the penetration layer.     

Calcium phosphate substrates with emulsion-derived roughness: Processing,characterisation and interaction with human mesenchymal stem cells

Calcium phosphates (CaP) have been the subject of several studies that often lack a systematic approach to understanding how their properties affect biological response. CaP particles functionalised with a pH-responsive polymer (BCS) were used to prepare microporous substrates (porosity between 70 and 75% and pore sizes of 5–20 μm) through the aggregation of oil-in-water emulsions by controlling solid loading, emulsification energy, pH, drying and sintering conditions. The combined effect of surface roughness (roughness amplitude, R_a between 0.9–1.7 μm) and chemistry (varying Hydroxyapatite/β-Tricalcium phosphate ratio) on human mesenchymal stem cells was evaluated. HA substrates stimulated higher cell adhesion and proliferation (especially with lower R_a), but cell area increased with β-TCP content. The effect of surface roughness depended of chemistry: HA promoted higher mineralising activity when R_a ～ 1.5 μm, whereas β-TCP substrates stimulated a more osteogenic profile when R_a ～ 1.7 μm. A novel templating method to fabricate microporous CaP substrates was developed, opening possibilities for bone substitutes with controlled features.     

Mechanical properties of porous ceramic scaffolds: Influence of internal dimensions

Highly porous ceramic scaffolds have been fabricated from a 70% SiO₂–30% CaO glass powder using stereolithography and the lost-mould process combined with gel-casting. After sintering at 1200 °C the glass crystallised to a structure of wollastonite and pseudowollastonite grains in a glassy matrix with a bulk porosity of 1.3%. All scaffolds had a simple cubic strut structure with an internal porosity of approximately 42% and internal pore dimensions in the range 300–600 μm. The mean crushing strength of the scaffolds is in the range 10–25 MPa with the largest pore sizes showing the weakest strengths. The variability of scaffold strengths has been characterised using Weibull statistics and each set of scaffolds showed a Weibull modulus of m≈3 independent of pore size. The equivalent strength of the struts within the porous ceramics was estimated to be in the range 40–80 MPa using the models of the Gibson and Ashby. These strengths were found to scale with specimen size consistent with the Weibull modulus obtained from compression tests. Using a Weibull analysis, these strengths are shown to be in accordance with the strength of 3-point bend specimens of the bulk glass material fabricated using identical methods. The strength and Weibull modulus of these scaffolds are comparable to those reported for other porous ceramic scaffold materials of similar porosity made by different fabrication routes.     

Polyurethane-SAPO-34 mixed matrix membrane for CO2/CH4 and CO2/N2 separation

SAPO-34 nanocrystals (inorganic filler) were incorporated in polyurethane membranes and the permeation properties of CO₂, CH_4, and N₂ gases were explored. In this regard, the synthesized PU-SAPO-34 mixed matrix membranes (MMMs) were characterized via SEM, AFM, TGA, XRD and FTIR analyses. Gas permeation properties of PU-SAPO-34 MMMs with SAPO-34 contents of 5 wt%, 10 wt% and 20 wt% were investigated. The permeation results revealed that the presence of 20 wt% SAPO-34 resulted in 4.45%, 18.24% and 40.2% reductions in permeability of CO_2, CH_4, and N₂, respectively, as compared to the permeability of neat polyurethane membrane. Also, the findings showed that at the pressure of 1.2 MPa, the incorporation of 20 wt% SAPO-34 into the polyurethane membranes enhanced the selectivity of CO₂/CH₄ and CO₂/N₂, 14.43 and 37.46%, respectively. In this research, PU containing 20 wt% SAPO-34 showed the best separation performance. For the first time, polynomial regression (PR) as a simple yet accurate tool yielded a mathematical equation for the prediction of permeabilities with high accuracy (R² > 99%).     

Incorporating Zr to achieve self-protecting and enhancement of silica sol bonded SiC castables at active oxidation condition

SiC castables exhibit degraded properties in static air at 1700 °C, due to the formation of gaseous products. The efficiency of different contents of Zr in SiC castables was evaluated by considering sintered properties, mechanical performance, isothermal oxidation behavior, and microstructural analysis of the SiC castables. Specimens with more Zr exhibited enhanced mechanical behavior and anti-oxidation capability. The addition of Zr decreased the evaporation of SiO₂ by reducing its equilibrium partial pressure (g), and formed a dense ZrO₂-SiO₂ protective layer (e.g., the sample with 0.9 wt% Zr) to prevent further degradation of the SiC castable. The Zr that was preferentially oxidized to ZrO₂ reduced the partial pressure of the oxidizing gases (O₂ and CO₂) in the matrix, and increased SiO (g) content, which facilitates formation of SiC fibers, which, in turn, improves the anti-oxidation capability and mechanical behavior of SiC castables, preventing their degradation in static air at 1700 °C. The addition of Zr created a ZrO₂-SiO₂ protective layer on the surface and prevented the decrease in SiC content, by forming SiC fibers. This made the silica sol bonded SiC castable a self-protecting refractory.     

Fabrication of porous fibrous alumina ceramics by direct coagulation casting combined with 3D printing

A novel forming method for preparing porous alumina ceramics using alumina fibers as raw materials by direct coagulation casting (DCC) combined with 3D printing was proposed. Porous fibrous alumina ceramics were fabricated through temperature induced coagulation of aqueous-based DCC process using sodium tripolyphosphate (STPP) as dispersant and adding K₂SO₄ as removable sintering additives. The sacrificial coated sand molds was fabricated by 3D printing technology, followed by the infiltration of silica sol solution for the subsequent suspension casting. Stable alumina suspension of 40 vol% solid loading was obtained by adding 2.0 wt% STPP and 40 wt% K₂SO₄. The controlled coagulation of the suspension could be realized after heating at 90 °C for about 35 min. The ceramic sample sintered at 1450 °C for 2 h showed the highest compressive strength of 24.33 MPa with porosity of 57.38%. All samples sintered at 1300–1450 °C had uniform pore size distributions with average pore size of 7.2 µm, which indicated the good structure stability when sintered at high temperature.     

Preparation and characterization of multilayer anti-reflective coatings via sol-gel process

Single layer and multilayer films consisting of SnO₂, Ta₂O₅, SiO₂, TiO₂, indium tin oxide (ITO) and antimony tin oxide (ATO) have been prepared by sol-gel dip coating technique. All of the multilayer films contained a SiO₂ top layer, which was composed of SiO₂ nanoparticles. The other films had polymeric character. Obtained films were characterized by ellipsometry, XRD, AFM and SEM. Light transmittance values of the films were compared. Films other than SiO₂ and Ta₂O₅ were found to have crystalline structure. Thickness values of the films were in the range of 30–115 nm and roughness values were in 1.2–23 nm range. Single layer porous silica provided 95% light transmittance, whereas ITO-TiO₂-SiO₂ multilayer film provided a light transmittance of 97.2%.     

Robust SiO2 gate dielectric thin films prepared through plasma-enhanced atomic layer deposition involving di-sopropylamino silane (DIPAS) and oxygen plasma: Application to amorphous oxide thin film transistors

DIPAS (di-isopropylamino silane, H₃Si[N(C₃H₇)₂]) and O₂ plasma were employed, using plasma-enhanced atomic layer deposition (PEALD), to deposit silicon oxide to function as the gate dielectric at low temperature, i.e., below 200 °C. The superior amorphous SiO₂ thin films were deposited through the self-limiting reactions of atomic layer deposition with a deposition rate of 0.135 nm/cycle between 125 and 200 °C. PEALD-based SiO₂ thin layer films were applied to amorphous oxide thin film transistors constructed from amorphous In-Ga-Zn-O (IGZO) oxide layers, which functioned as channel layers in the bottom-gated thin film transistor (TFT) structure, with the aim of fabricating transparent electronics. The SiO₂ gate dielectric exhibited the highest TFT performance through the fabrication of heavily doped n-type Si substrates, with a saturation mobility of 16.42 cm²/V·s, threshold voltage of 2.95 V and large on/off current ratio of 3.69 × 10⁸. Ultimately, the highly doped Si was combined with the ALD-based SiO₂ gate dielectric layers, leading to a saturation mobility of 16.42 cm²/V·s, threshold voltage of 2.95 V, S-slope of 0.1944, and on/off current ratio of 3.69 × 10⁸. Semi-transparent and transparent TFTs were fabricated and provided saturation mobilities of 22.18 and 24.29 cm²/V·s, threshold voltages of 4.18 and 2.17 V, S-slopes of 0.1944 and 0.1945, and on/off current ratios of 9.63 × 10⁸ and 1.03 × 10⁷, respectively.     

Influence of glass compositions on the microstructure and dielectric properties of low temperature fired BaTi4O9 microwave material with copper electrodes in reducing atmosphere

BaTi₄O₉ (BT4) dielectric ceramics, containing 10 wt% BaO–ZnO–B₂O₃–SiO₂ (BZBS) glass frit as sintering aid were co-fired with copper paste under reducing atmosphere at 950 °C and investigated on microstructures and dielectric properties. Experimental results show the microstructures and microwave dielectric properties of BT4–BZBS glass composite materials are strongly dependent on the Ba–Zn–B–Si ratio, especially for the content of SiO₂ addition, in BZBS glass. XRD and EDS results indicate that Cu reacts with BZBS glass-added BT4 ceramics seriously to form complicated reaction products such as BaCuO₂ phase, when the BZBS glass composition with lower content of SiO₂ (less than 20 wt%), and transformation of some BaTi₄O₉ into barium titanate with various ratios of Ba/Ti, which, fortunately, does not seriously degrade the dielectric properties.     

The influence of silica nanoparticles addition on the physical,mechanical, thermo-mechanical as well as microstructure of Mag-Dol refractory composites

The high hydration potential of CaO and MgO phases restricted the application of Mag-Dol refractory composites. In this study, the impact of nano-silica (SiO₂) addition on the physical, mechanical, thermo-mechanical as well as microstructure of Mag-Dol refractory composites is investigated. Mag-Dol compositions were prepared by using calcined dolomite and magnesite particles (micron, 0–1, 1–3, 3–5, and 5–8 mm), liquid resin, and 0, 0.5, 1, 1.5, 2, and 2.5 wt% nano SiO₂ as additives. Specimens were heated up to 1650 °C for the 3 h soaking period. Fired specimens were characterized by physical (apparent porosity, bulk density, and hydration resistance), mechanical (cold crushing strength), and thermo-mechanical (flexural strength at 1200 °C) measurements. XRD and SEM/EDS analysis were done to study phases and microstructure analysis of the fired samples, respectively. Results showed that by adding up to 2.5 wt% nano-SiO₂, due to the formation of CaO·MgO·2SiO₂ (Diopside), 2CaO·MgO·2SiO₂ (Akermanite), and CaO·MgO·SiO₂ (Monticellite) phases, physical and mechanical properties were enhanced. But the highest flexural strength value is achieved for 1 wt% nano-SiO₂ containing sample.     

Synthesis and characterization of β-TCP/CNT nanocomposite: Morphology,microstructure and in vitro bioactivity

In this study, β-TCP/CNT nanocomposite has been synthesized by solution precipitation method. Then, the effects of the different percentage of CNT (CNT1β-TCP, CNT3β-TCP, CNT5β-TCP) and surfactant (CNT1β-TCP1SDBS, CNT1β-TCP2SDBS, CNT1β-TCP3SDBS) on β-TCP/CNT nanocomposite powder were studied. The X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and Transmission electron microscopy (TEM) analyses were used to characterize the samples. The observations revealed that the microstructure of 1 wt% CNT could provide dispersion without agglomeration in nanocomposite powder; however, a higher concentration of CNT powder in the nanocomposite resulted in the formation of Ca₂PO₇ phase. Implementing 2 wt% of SDBS as a surfactant modified the shape, size, and distribution of CNT particles on nanocomposites. Finally, the nanocomposite sample was immersed in simulated body fluid (SBF) to evaluate the in vitro bioactivity. It obviously showed an apatite layer on the surface after 7 days of immersion in SBF. Taken together, this nanocomposite might be potentially to be used as bone repair biomaterial.