Freeze-cast composite scaffolds prepared from sol-gel derived 58S bioactive glass and polycaprolactone

This work deals with the preparation of freeze-cast scaffolds using sol-gel derived 58S bioactive glass and a hypoeutectic naphthalene-camphor mixture as the starting powder and freezing vehicle, respectively. After the freeze-casting step, samples were air sintered at 1250?°C for 2?h, which led to the crystallization of 58S. The obtained scaffolds were subsequently infiltrated with poly(ε-caprolactone) (PCL), a biodegradable polymer with potential application for bone tissue repair. The prepared materials were examined by helium pycnometry, laser granulometry, scanning electron microscopy (SEM), Archimedes tests, X-ray microtomography (micro-CT), Fourier transform infrared spectroscopy (FTIR), N₂ adsorption, X-ray diffraction (XRD), and uniaxial compression tests. Samples cytotoxicity was evaluated by (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) tetrazolium reduction (MTT) and LIVE/DEAD assays. Their biocompatibility was also examined after soaking in a simulated body fluid (SBF) solution at 37?°C for up to 14 days. It was observed that the infiltration of PCL into the 58S scaffolds greatly increased their mechanical stability. Moreover, it was shown that these composites displayed a high cell viability (above 70%), which reveals that they did not interfere in the production of osteoblast cells. A hydroxyapatite coating was observed on the samples surface upon soaking in SBF, reinforcing that they are biocompatible materials. As far as we know, this is the first time that freeze-cast scaffolds were obtained using sol-gel derived 58S particles and a naphthalene-camphor mixture. Besides, as the infiltration of PCL into freeze-cast bioactive glass scaffolds improved their mechanical stability without impairing their bioactivity, this is a promising approach to prepare samples for load-bearing applications in bone tissue engineering.     

Effect of sintering temperature on compressive strength of porous yttria-stabilized zirconia ceramics

Porous yttria-stabilized zirconia (YSZ) ceramics were fabricated by tert-butyl alcohol (TBA)-based gel-casting method for potential applications in heat-insulation materials. The effect of sintering temperature on compressive strength of porous YSZ ceramics was investigated on the basis of measurements linear shrinkage, porosity and pore size. As the sintering temperature increased from 1350 to 1550 °C, a decrease of porosity from 77 to 65%, a decrease of average pore size from and an increase of linear shrinkage from 15.4 to 31.8% were observed. The compressive strength increased remarkably from 3 to 27 MPa with increasing sintering temperature from 1350 to 1550 °C, which was related to the corresponding change of linear shrinkage, porosity, pore size and microstructure. A remarkable decrease of compressive strength with increasing porosity was observed. The compressive strength decreased also with increasing pore size.     

Characterization,in vitro bioactivity and biological studies of sol-gel synthesized SrO substituted 58S bioactive glass

Bioactive glasses (BGs) are considered as a high potential candidate in bone repair and replacement. In the present study, sol–gel derived BGs based on 60% SiO₂-(36%-x) CaO-4%P₂O₅-x SrO (where x = 0, 5 and 10 mol%) quaternary system were synthesized and characterized. The effect of Sr substitutions on bioactivity, proliferation, alkaline phosphatase activity of osteoblast cell line MC3T3-E1 and antibacterial activity were investigated. Dried gels were stabilized at 700 °C to eliminate the nitrates and prevent the crystallization of bioactive glasses. X-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy results confirmed the formation of hydroxycarbonate apatite on the BG surfaces. The 3-(4,5dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide and alkaline phosphate activity results showed that 5% SrO increased both differentiation and proliferation of MC3T3-E1 cells, while 10% SrO resulted in a decrease in bioactivity. Live/Dead and DAPI/Actin staining exhibited viable cell and the morphology of actin fibers and nuclei of MC3T3 cells treated with BG-0 and BG-5. The result of antibacterial test showed that strontium substituted 58S BG exhibited antibacterial effect against methicillin-resistant Staphylococcus aureus bacteria. Taken together, results suggest that 58S BG with 5 mol% SrO is a good candidate for bone tissue engineering with maximum cell proliferation and ALP activity, good bioactivity and high antibacterial efficiency.     

Innovative hydroxyapatite/bioactive glass composites processed by spark plasma sintering for bone tissue repair

Hydroxyapatite-based composites (HA-C) with bioglass as second phase are usually produced by hot-pressing or pressureless sintering. However, such methods require thermal levels which exceed the crystallization temperature of the glass, with possible negative effects on the bioactivity of the final system. Spark plasma sintering (SPS) is a powerful consolidation technique in terms of both processing time and temperature. In this work SPS has been employed, for the first time, to obtain HA-C with an innovative bioglass as second phase. Such glass was designed to be used whenever a thermal treatment is required, thanks to its low tendency to crystallize. A systematic study is conducted to identify the optimal sintering conditions for preparing highly dense composites and, at the same time, to minimize the crystallization of the glassy phase. The obtained samples are highly bioactive and display higher compactness and hardness with respect to the counterparts produced by conventional sintering methods.     

Spark plasma sintering,mechanical and in-vitro behavior of a novel Sr- and Mg-containing bioactive glass for biomedical applications

The so-called BGMS10, a bioactive glass containing 10 mol.% SrO and 10 mol.% MgO, displays a low inclination to crystallize, as confirmed by its high activation energy (538.9 kJ/mol). Such peculiar aspect and the beneficial use of SPS allow for the obtainment of 99.7 % dense and fully amorphous products at 750 °C. The incipient crystallization in the glass is observed when temperature is increased to 850 °C, while 95 wt. % crystallized ceramics are produced at 950 °C. Main crystalline phases are α- and β-CaSiO₃, with grain size of 89 and 97 nm, respectively. Glass crystallization is accompanied by Young’s modulus increase from 90.92 to 98.38 GPa. On the other hand, partially crystallized samples (850 °C) exhibit higher Vickers hardness (718.8) compared to fully crystallized ones (619.8), which show lower density (98.6 %). In-vitro tests in SBF indicate that the silica-gel film preceding apatite nucleation is mostly formed on the amorphous substrate region.     

Effect of composition and sintering process on mechanical properties of glass ceramics from solid waste

Sintered diopside glass ceramics were successfully prepared from mixtures of blast furnace slag, fly ash and mining tailing. Results showed that sample C2 with relatively low iron oxides and mass ratio of CaO/SiO₂ possessed the highest bending strength value among samples. A low content of iron oxide enhanced densification degree because pores were developed by reduction of ferric oxide into ferrous oxide. Moreover, a low CaO/SiO₂ mass ratio also greatly promoted the densification process by prolonging the sintering time and delaying the crystallisation. In addition, sample C1 developed by one-stage sintering had a worse mechanical performance than that obtained by two-stage sintering although they had the same crystals. For all samples, despite of different compositions and sintering processes, the main crystal phases are augite and diopside ferrian.     

Fluoride promoted crystallization and mechanical properties of Sr-fluorphlogopite glass

Crystallization, microstructure and mechanical behavior of strontium fluorphlogopite glass-ceramics, SrO·4MgO·Al₂O₃·6SiO₂·2MgF₂, was studied by varying the fluorine content. A number of glass-ceramics of each glass batch with excess MgF₂ [SR0 (0% MgF₂), SR5 (5% MgF₂) and SR10 (10% MgF₂)] were prepared by heating at its respective nucleation temperature followed by at different crystallization temperatures (780–1150 °C). Differential Thermal Analysis (DTA), X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Micro Hardness Indenter were used to study the crystallization, microstructure and mechanical behavior of resulting three glass batches. DTA analysis revealed that the peak crystallization (T_p) and glass transition (T_g) temperatures decreased with increasing fluorine content that also lowers down the activation energy (E) as evident from crystallization kinetics. Hardness and fracture toughness values are higher for less fluorine containing glass-ceramics when they are treated isothermally. However, more fluorine based glass-ceramics is found to be more machinable than the less fluorine one.     

Bioactivity and biodegradability of high temperature sintered 58S ceramics

Bioactive glasses are often considered in bone tissue engineering applications where mechanical strength is essential. As such, bioactive glass scaffolds are often sintered to improve mechanical strength. However, sintering can lead to crystallization, which reduces bioactivity and biodegradability. It has generally been considered that amorphous biomaterials exhibit better bioactivity. However, the in-vitro bioactivity and biodegradability of the sintered 58S made from initial amorphous powder and partially crystalline powder with the same chemical compositions (60SiO₂-36CaO-4P₂O₅ (mol%)) have not been compared before.In this study, 58S bioactive glass (fully amorphous) and glass-ceramic (partially crystallized) powders were synthesized using the sol-gel process, followed by heat-treating at 600 °C for 3 h (calcination). The powders were mixed with carboxymethyl cellulose solution as a binder, shaped in a cylindrical mold, dried, and then sintered at 1100 °C for 5 h. The in-vitro bioactivity and biodegradability of the sintered samples were assessed in simulated body fluid (SBF) for times up to 28 days. The specimens were investigated before and after immersion in SBF using X-ray powder diffraction (XRD), Scanning Electron Microscopy (SEM), and Fourier transform infrared spectroscopy (FT-IR). The In-vitro bioactivity and biodegradability rate of the sintered 58S produced from the glass ceramic powder were higher than that from fully amorphous powder. This study shows that the initial structure after calcination is important and affects the subsequent crystallization during sintering. Therefore, crystallinity and formation of hydroxyapatite after calcination are important controlling mechanisms that can increase the bioactivity and biodegradability rate of sintered 58S.     

Low temperature pressureless sintering of dense silicon nitride using BaO-Al2O3-SiO2 glass as sintering aid

Dense Si₃N₄ ceramic with BaO-Al₂O₃-SiO₂ low temperature glass powders as sintering aids were prepared by pressureless sintering techniques at a relatively low temperature (1550 °C). Four kinds of glass powders of compositions melting at 1120 °C, 1300 °C, 1400 °C and 1500 °C, respectively, have been introduced as sintering aids. XRD results demonstrate that the BaO-Al₂O₃-SiO₂ glass powders reacted with BaAl₂O₄ and converted into hexagonal celsian, which is a high-temperature phase with melting point of 1760 °C, so being beneficial to the high temperature properties of the materials. In addition, a portion of α-Si₃N₄ transformed to rod like β-Si₃N₄ with high aspect ratio as shown by XRD and SEM analysis. The bulk density increased with the rise of the melting temperature of the BaO-Al₂O₃-SiO₂ glass powders, the sample obtained with the BaO-Al₂O₃-SiO₂ glass powder melting at 1500 °C reaching a maximum density of 98.8%, an high flexural strength (373 MPa) and a fracture toughness (4.8 MPa m^1/2).     

Variations in structure and properties of vitrified bonds and vitrified diamond composites prepared by sol-gel and melting methods at different sintering temperature

Differences in structure and properties of Na₂O–Al₂O₃–B₂O₃–SiO₂ vitrified bonds and vitrified diamond composites prepared by sol-gel and melting methods were methodically discussed. Results showed that the vitrified bond prepared by sol-gel method contained more [AlO₄] tetrahedron and owned higher bending strength, with the maximum value reaching 137 MPa, 31.73% higher than that prepared by melting method (104 MPa). As the sintered temperature rose, coefficient of thermal expansion of the vitrified bond prepared by sol-gel method increased first and then decreased, acquiring a maximum value of 5.75 × 10⁻⁶ °C ⁻¹ at 720 °C, which was still much lower than the minimum value of vitrified bond prepared by melting method (7.02 × 10⁻⁶ °C ⁻¹). The vitrified diamond composite prepared by sol-gel method possessed lower sintering shrinkage than that prepared by melting method, and could be applicable to the production of grinding tools with high dimensional accuracy. What's more, the maximum bending strength of vitrified diamond composites obtained by sol-gel method was 106 MPa, 24.7% higher than that of vitrified diamond composites prepared by melting method (85 MPa).     

Effect of sintering temperature on microstructure and mechanical properties of zirconia-toughened alumina machinable dental ceramics

This study investigated the effect of sintering temperature on the microstructure and mechanical properties of dental zirconia-toughened alumina (ZTA) machinable ceramics. Six groups of gelcast ZTA ceramic samples sintered at temperatures between 1100 °C and 1450 °C were prepared. The microstructure was investigated by mercury intrusion porosimetry (MIP), X-ray diffraction (XRD), and scanning electron microscopy (SEM) techniques. The mechanical properties were characterized by flexural strength, fracture toughness, Vickers hardness, and machinability. Overall, with increasing temperature, the relative density, flexural strength, fracture toughness, and Vickers hardness values increased and more tetragonal ZrO₂ transformed into monoclinic ZrO₂; on the other hand, the porosity and pore size decreased. Significantly lower brittleness indexes were observed in groups sintered below 1300 °C, and the lowest values were observed at 1200 °C. The highest flexural strength and fracture toughness of ceramics reached 348.27 MPa and 5.23 MPa m^1/2 when sintered at 1450 °C, respectively. By considering the various properties of gelcast ZTA that varied with the sintering temperature, the optimal temperature for excellent machinability was determined to be approximately 1200–1250 °C, and in this range, a low brittleness index and moderate strength of 0.74–1.19 µm^−1/2 and 46.89–120.15 MPa, respectively, were realized.     

Effect of sintering temperature on mechanical properties of magnesia partially stabilized zirconia refractory

The optimized sintering conditions for a 3.5 wt% magnesia partially stabilized zirconia (Mg-PSZ) refractory were proposed in our recent research. The influence of the sintering temperature on the development of phase composition, microstructure, densification, thermal expansion and mechanical strength was studied in detail by X-ray diffraction (XRD), scanning electron microscope (SEM), He-pycnometer, high temperature dilatometry and three-point bending test. The samples sintered at 1670 °C had the highest bend strength, the maximum densification, the lowest thermal expansion coefficient (CTE), a homogeneous microstructure and a linear change in thermal expansion.     

Influence of sintering temperature on the crystallization and mechanical properties of BN-MAS composites

A type of boron nitride–magnesium aluminum silicate (BN-MAS) composite ceramics was fabricated by hot-press sintering at different sintering temperatures. The relationship between the sintering temperature and microstructure was investigated by analyzing the interaction between hexagonal boron nitride (h-BN) and the MAS phase. The main MAS phase in the composite ceramics is the α-cordierite phase at a sintering temperature of 1300°C. At temperatures above 1400°C, the inhibitory effect of h-BN on the crystallization of the MAS system is significant, and MAS mainly exists in the form of an amorphous phase. The composite sintered at 1700°C exhibited the highest bending strength of 218MPa. h-BN and MAS were co-enhanced. MAS can be used as an effective liquid-phase sintering aid to assist in the sintering of h-BN, whereas h-BN can absorb the fracture energy of the composite ceramics through the pull-out and bridging effect of the particles.     

Effect of tetragonal zirconia nanoparticle content on enamel strength

The fracture failure of enamel is caused by hole-type flaws and cracks generally present in enamel. In this study, the effect of tetragonal zirconia nanoparticles (nano-t-ZrO₂) on enamel strength was investigated. The addition of nano-t-ZrO₂ improved the surface morphology and reduced the porosity of the enamel as determined by morphological and porosity distribution analyses. The strain on the enamel surface was recorded using a strain gauge attached to the enamel surface. The crack initiation force and strain were measured using the strain gauge, and the crack propagation diagrams at various stages of the tensile process were recorded. The relationship between the crack initiation energy and nano-t-ZrO₂ content was found to be non-linear. Nano-t-ZrO₂ affected the strength of the enamel. Moreover, the tensile force required for the appearance of cracks first increased and then decreased with an increase in the nano-t-ZrO₂ content. The addition of nano-t-ZrO₂ to the enamel matrix suppressed the formation of stress concentration regions and decreased the brittleness of the enamel. At a nano-t-ZrO₂ content of more than 5 wt%, the ZrO₂ particles agglomerated.     

Effect of Bi-substitution on the microstructure and electromagnetic properties of YCaZrVIG with low sintering temperature

Bi substituted YCaZrVIG ferrites, Y_2.3−xBi_xCa_0.7Zr_0.3V_0.2Fe_4.42O₁₂ (x=0.1, 0.25, 0.4, 0.5, 0.75) ferrites were prepared by conventional oxide method. The addition of Bi₂O₃ promoted the sintering performance and lowered the sintering temperature from 1420–1230 °C. However, it also resulted in the formation of minor second phases and the decrease of grain size. With the increase of Bi concentration, the dielectric constant increases linearly and then remains unchanged. The dielectric loss decreased firstly and then increased. The saturation magnetization (4πM_s) almost retained unchanged as the Bi concentration increased except for the sample with 0.75. The coercivity (H_c) decreased firstly and reached the minimum of 1.32 Oe at 0.25, and then rose when x>0.25, which was related to the facility of magnetic domain wall motion and magnetic moment reverse. Moderate addition of Bi also can increase the remanence (B_r) by improving sintering process. Additionally, we got the optimum electromagnetic properties in the samples with x=0.25 at 1230 °C: RD>97%, ε_r=15.7, tan δ_e=2.48×10⁻⁴, H_c=1.32Oe, 4πM_S=1663 Gs, B_r=583.91 Gs.     

利用粉煤灰低温熔制基础玻璃的研究

以粉煤灰为主要原材料,添加适当的工业级硼酸、石灰石、氧化锌、氧化镁、二氧化硅、碳酸钠作为辅助材料,选择铝硅酸盐系统作为配方,制备基础玻璃。通过DTA和TEM研究不同配比的基础玻璃配方表明,最合理基础玻璃在1 200℃熔制是可行的,粉煤灰的利用率达到了30%以上,最适宜的玻璃组成是(%):S iO245~60,A l2O39~15,CaO 12~20,MgO 2~5,Na2O 3~11,ZnO 2~5,S 0~1,B2O30.5~1.5,F 0~2.5。     

Effect of glass fiber‐reinforced polymer and epoxy injection on compressive strength of elevated temperature damaged concrete

Glass fiber‐reinforced polymer (GFRP) materials have received a great deal of interest among civil engineers during the past decade. This paper presents an overview of experimental studies carried out on GFRP‐wrapped and epoxy‐injected concrete samples exposed to elevated temperatures. For this purpose, 0.30, 0.35 and 0.40 water to binder (w/b) ratios were used. For each w/b ratio, normal aggregates were replaced by lightweight aggregates with a size fraction of 0–2 mm at three different volume fractions such as 10%, 20% and 30% of total aggregate volume. At the same time, a group of air‐entrained samples was also cast for each w/b ratios. Prepared samples were exposed to 600 °C for 3 h. The damaged samples were separately repaired by GFRP and epoxy injection. Before and after elevated temperature exposure, water absorption and compressive strength were tested. After repairing with GFRP and epoxy injection, only the compressive strength test was carried out. GFRP improved the compressive strength between 1–22% and 348–1403% for samples before and after being exposed to elevated temperatures, respectively. Epoxy injection increased the compressive strength of the samples, exposed to elevated temperature, between 1% and 123%. However, the epoxy injection process failed to recover the compressive strength of the samples before elevated temperature exposure. Copyright © 2012 John Wiley & Sons, Ltd.     

Synthesis,characterization, bioactivity and cytotoxicity assessment of nano ZrO2 reinforced bioactive glass ceramics

Bioactive glass and glass ceramics have travelled a long way as biomaterials. Several research works have been devoted to improving mechanical properties, especially using various additives. Out of these, ZrO₂-containing glass and glass ceramics have shown promising outcomes. In this present work, a set of 3 Nano-ZrO₂ containing novel bioactive glass and glass ceramics of composition 37.5 nano-SiO₂–(17-X)Al₂O₃–26.5CaO–11.5CaF₂–7.5P₂O₅–X nano-ZrO₂ (where, X= 0.75, 1.7, 2.7, all in mol %) were synthesized by melt-quenching technique. Standard characterization procedures were performed to assess the physical and chemical properties, structure and surface morphologies. In vitro bioactivity and cytotoxicity assessments were also done. Fluorapatite (Ca₅(PO4)₃F) and Anorthite (Ca(Al₂Si₂O₈)) along with tetragonal Zirconia (t-ZrO₂) at higher nano-ZrO₂ content of 2.7 mol% were discovered as the primary crystalline phases. Adding nano-zirconia enhanced the glasses' thermal stability and the glass ceramics' micro-hardness. The formation of nanometer-size hydroxyapatite (HAp) on the glass-ceramics samples confirmed the good bioactive nature. The non-toxic nature of the samples towards living cells was demonstrated by cytotoxicity assessment.     

Effect of sintering temperature on the morphology,crystallinity and mechanical properties of carbonated hydroxyapatite (CHA)

Effect of sintering temperature on the physical and mechanical properties of synthesized B-type carbonated hydroxyapatite (CHA) over a range of temperature in CO₂ atmosphere has been investigated. The B-type CHA in nano size was synthesized at room temperature by using a direct pouring wet chemical precipitation method. The synthesized CHA powders were subsequently consolidated by sintering treatment from 800 to 1100 °C. The sintered CHA samples were evaluated using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectrometry, X-ray fluorescence (XRF), carbon-hydrogen-nitrogen-sulfur-oxygen (CHNS/O) elemental analyzer, Field emission scanning electron microscopy (FESEM), and Vicker's indentation technique. The results obtained from XRD and FESEM indicated that the synthesized B-type CHA powders were nanometer in size. The crystallinity and crystallite size of the sintered CHA samples were increased due to increasing sintering temperature. The heat treatment between 800 °C and 1000 °C has resulted in coarsening and increased hardness of the sintered CHA samples. However, these properties began to deteriorate when sintering beyond 1100 °C due the formation of calcium oxide.     

Studies on the synthesis and sintering of nanocrystalline yttria

Nanocrystalline yttria powders were synthesized from yttrium nitrate by the citrate gel-combustion technique. The auto-ignition of five different gels with fuel to oxidant (citric acid/nitrate) ratios 0.25, 0.5, 0.75, 1.0 and 1.1 was studied. All these mixtures yielded precursors which upon calcination in air at 1073 K yielded yttria. The bulk densities, specific surface area, X-ray crystallite size, size distribution of particles as well as the residual carbon present in these powders were determined. The influence of the fuel to oxidant ratio on the powder properties was analyzed. Scanning electron microscopy (SEM) showed that these powders were porous while the high resolution transmission electron microscopy (HRTEM) revealed that they consist of randomly oriented cuboidal nanocrystallites with an average crystallite size of 25±7 nm. These powders were compacted at 120 MPa without any lubricant or binder and their sinterability was studied. Pellets with a sintered density as high as 98–99% T.D. (theoretical density) could be obtained at a relatively low sintering temperature of 1673 K. Studies on the dependence of the properties of nanocrystalline yttria powders on the composition of the initial mixture used in the citrate gel-combustion as well as the sintering characteristics of these powders are being reported for the first time. Our investigations revealed that an initial mixture comprising equimolar quantities of the nitrate and citric acid yielded a powder with characteristics most suitable for fabricating yttria crucibles.