Effect of thermal treatment on elastic properties of SiO2–Na2O–CaO–P2O5 glasses for biomedical applications

Glasses of the system SiO₂–Na₂O–CaO–P₂O₅ have been prepared for different compositions of SiO₂ employing the normal melting and annealing technique. The glasses of different compositions have been subjected to different thermal treatments to explore the change in structure, mechanical and other related properties. The ultrasonic velocities and attenuation measurements have been made on different compositions of the pure and thermal-treated glasses at a fundamental frequency of 5 MHz at 303 K. The observed linear increase in density, velocities and elastic moduli with increase in thermal treatment temperature is same in all composition studied. The above results reveal an increase in hardness and the predominant nature of network bonds per unit volume rather than the coordination/cross-link changes, with the influence of thermal treatment.     

Effects of CaO/P2O5 ratio on the structure and elastic properties of SiO2–CaO–Na2O–P2O5 bioglasses

The evolution of elastic properties and structure upon the change of CaO/P₂O₅ ratio in SiO₂–CaO–Na₂O–P₂O₅ glasses (45S5-derived and 55S4-derived) at ambient conditions has been studied by using both Brillouin and Raman spectroscopy coupled with X-ray diffraction. Under the same SiO₂/Na₂O ratio, it is found that a decrease in CaO/P₂O₅ molar ratio has caused a more-polymerized silicate network via a net consumption of Q⁰, Q¹, and Q² species yet enriching in Q³ and Q⁴ species. Brillouin experiments revealed that all the bulk, shear and Young’s moduli of the glasses studied increases with the increase of CaO/P₂O₅ molar ratio. The unexpected variation trend in shear modulus can be correlated to the contribution from cohesion, the less-polymerized phosphate Q species, and density. Compared to the 45S5-derived, the more-polymerized 55S4-deived glass has a lower bulk but slightly higher shear modulus at the given CaO/P₂O₅ ratio.     

Textural and structural studies of sol–gel derived SiO2–CaO–P2O5–MgO glasses by substitution of MgO for CaO

The partial substitution of MgO for CaO in the ternary SiO₂–CaO–P₂O₅ glass system was conducted by the sol–gel method and a comparison of the textural and structural properties was reported. The textural properties (specific surface area and pore size distribution) were obtained by N₂-adsorption measurement and the glasses structure was elucidated by Fourier transform infrared spectroscopy. It is observed that, in general, all synthesized glasses show high specific surface area and present porous nature in mesopore region. The presence of MgO in glass composition has little influence on its textural properties, however, with increasing MgO concentration the frequency of Si–O(s,asym) group shifts towards lower energy and the absorbance intensity ratio of Si–O–NBO(Q³)/Si–O–Si(s,sym)(Q⁴) declines, indicating the structure modification of MgO in glass composition.     

Effect of MgO contents on the mechanical properties and biological performances of bioceramics in the MgO–CaO–SiO2 system

The aim of this research was to investigate the effect of the chemical composition on the mechanical properties, bioactivity, and cytocompatibility in vitro of bioceramics in the MgO–CaO–SiO₂ system. Three single-phase ceramics (merwinite, akermanite and monticellite ceramics) with different MgO contents were fabricated. The mechanical properties were tested by an electronic universal machine, while the bioactivity in vitro of the ceramics was detected by investigating the bone-like apatite-formation ability in simulated body fluid (SBF), and the cytocompatibility was evaluated through osteoblast proliferation and adhesion assay. The results showed that their mechanical properties were improved from merwinite to akermanite and monticellite ceramics with the increase of MgO contents, whereas the apatite-formation ability in SBF and cell proliferation decreased. Furthermore, osteoblasts could adhere, spread and proliferate on these ceramic wafers. Finally, the elongated appearance and minor filopodia of cells on merwinite ceramic were more obvious than the other two ceramics.     

Characterisation of Ga2O3–Na2O–CaO–ZnO–SiO2 bioactive glasses

The structural role of Gallium (Ga) is investigated when substituted for Zinc (Zn) in a 0.42SiO₂–0.40–xZnO–0.10Na₂O–0.08CaO glass series, (where x = 0.08). Each starting material was amorphous, and the network connectivity (NC) was calculated assuming Ga acts as both a network modifier (1.23), and also as a network former. Assuming a network forming role for Ga the NC increased with increasing Ga concentration throughout the glass series (Control 1.23, TGa-1 2.32 and TGa-2 3.00). X-ray photoelectron spectroscopy confirmed both composition and correlated NC predictions. Raman spectroscopy was employed to investigate Q-structure and found that a shift in wavenumbers occurred as the Ga concentration increased through the glass series, from 933, 951 to 960 cm^?1. Magic angle spinning nuclear magnetic resonance determined a chemical shift from ?73, ?75 to ?77 ppm as the Ga concentration increased, supporting Raman data. These results suggest that Ga acts predominantly as a network former in this particular Zn-silicate system.     

Effect of borosilicate glasses on the microwave dielectric properties of ZnO–Nb2O5–Ta2O5 system

(1 ? y)[0.5ZnNb₂O₆–0.5Zn₃Nb₂O₈]–yZnTa₂O₆ with y = 0.91 (ZNT) ceramic have been prepared by conventional solid state ceramic route. The effect of glass additives on the microstructure, densification, and microwave dielectric properties of the ZNT ceramic for low temperature co-fired ceramic applications was investigated. Different weight percentages of quenched glass such as ZnO–B₂O₃–SiO₂, BaO–B₂O₃–SiO₂, LiO–B₂O₃–SiO₂ and MgO–B₂O₃–SiO₂ were added to ZNT powder. The crystal structure of the ceramic–glass composites was studied by X-ray diffraction and microstructure by scanning electron microscopy. The microwave dielectric properties such as relative permittivity (ε_r), quality factor (Q_uxf) and co-efficient of temperature variation of resonant frequency (τ_f) of the ceramics have been measured in the frequency range 4–6 GHz. The 5 wt% ZnO–B₂O₃–SiO₂ added ZNT ceramic sintered at 900 °C showed: ε_r = 28.1, Q_uxf = 32820 GHz (at 4.92 GHz), and τ_f = ?7.7 ppm/^oC respectively.     

Fabrication and characterization of ZrO2–CaO–P2O5–Na2O–SiO2 bioactive glass ceramics

SiO₂–CaO–Na₂O–P₂O₅–ZrO₂ based bioactive glasses with different compositions of SiO₂ and yttrium stabilized ZrO₂ were prepared by the conventional melt quenching technique. The effects on the chemical–mechanical properties of bioactive glasses due to the addition of ZrO₂ by replacing SiO₂ were investigated. Microstructure and phase behavior were studied by scanning electron microscopy, energy-dispersive spectroscopy, and X-ray diffraction analysis. Compressive strength, porosity, Vickers hardness, and Young’s modulus were measured as mechanical properties. Bioactivity and cell viability were investigated by immersion in simulated body fluid and MTT assay analysis. Osteosarcoma cell proliferation on the specimen surfaces was examined by confocal laser scanning microscopy. The results showed that replacing SiO₂ with ZrO₂ helps the bioactive glass to be completely vitrified at comparatively lower sintering temperature than conventional Bioglass^®. The mechanical properties were also improved without compromising biocompatibility. Bioactive glass containing 10 wt% ZrO₂ and 35 wt% SiO₂ showed compressive strength of 399.71 MPa, Young's modulus of 22.3 GPa, Vicker’s hardness of 502.54 HV, and porosity of 26 vol%.     

Effect of Ca/Si ratio on the microstructures and properties of CaO–B2O3–SiO2 glass-ceramics

CaO–B₂O₃–SiO₂ glass-ceramics were synthesized by sol–gel method, and the effect of Ca/Si ratio on the microstructures, electrical properties and mechanical characteristics of this ternary system was investigated. The results showed that the increase of CaO content is favorable for the crystallization of CaO–B₂O₃–SiO₂ system and formation of the desired glass-ceramics. The bending strength of the sintered glass-ceramics increases with CaO content by increasing of crystalline phases. When the Ca/Si ratio increases, the dielectric constant (ε _r) decreases and loss (tanδ) increases gradually. The thermal expansion coefficient (TEC) enhances by increasing CaO contents due to the formation of other crystal phases with large TEC value. The glass-ceramics exhibit low dielectric constant and loss (ε _r < 4.7, tanδ < 5 × 10^-4 at 1 MHz), high resistivity (ρ > 10¹² Ω · cm), as well as excellent mechanical properties (σ ≈ 160 MPa, α ≈ 3.6 × 10⁻⁶/°C).     

Development and bioactivity evaluation of bioglasses with low Na2O content based on the system Na2O–CaO–MgO–P2O5–SiO2

Osteoconductive bioglasses, free of K(2)O and Al(2)O(3) and with content of Na(2)O lower than 10?mol%, were designed based on the ratio (SiO(2)?+?MgO)/(P(2)O(5)?+?CaO?+?Na(2)O) in the system Na(2)O-CaO-MgO-P(2)O(5)-SiO(2). The developed glasses have shown a strong potential for the formation of hydroxycarbonated apatite (HCA) in vitro. The particles of HCA aggregates tend to be of finer size with increasing the ratio of (SiO(2)?+?MgO)/(CaO?+?P(2)O(5)?+?Na(2)O) in the glass chemical composition indicating significant bioactivity. Critical size bone defects created in the femurs of albino adult female rats, and grafted with the glass particles for 12?weeks post implantation, were completely healed by filling with mineralized bone matrix without infection showing a strong potential for new bone formation in vivo. Osteoblasts and osteocytes were observed close to the surface of the granular implants with active areas of bone deposition, resorption and remodelling. The bioglass with lowest (SiO(2)?+?MgO)/(CaO?+?P(2)O(5)?+?Na(2)O) ratio has shown the highest bioactivity while the bioglass with the highest (SiO(2)?+?MgO)/(CaO?+?P(2)O(5)?+?Na(2)O) has shown the lowest bioactivity. The newly formed bone in vivo has shown a similar structure to that of the original bone as indicated by the histology and microstructural results. In addition, Ca/P molar ratio of the newly formed bone was found to be (~1.67), which is similar to that of the original bone.     

Bioactivity and cytotoxicity of glass and glass–ceramics based on the 3CaO·P2O5–SiO2–MgO system

The mechanical strength of bioactive glasses can be improved by controlled crystallization, turning its use as bulk bone implants viable. However, crystallization may affect the bioactivity of the material. The aim of this study was to develop glass–ceramics of the nominal composition (wt%) 52.75(3CaO·P₂O₅)–30SiO₂–17.25MgO, with different crystallized fractions and to evaluate their in vitro cytotoxicity and bioactivity. Specimens were heat-treated at 700, 775 and 975 °C, for 4 h. The major crystalline phase identified was whitlockite, an Mg-substituted tricalcium phosphate. The evaluation of the cytotoxicity was carried out by the neutral red uptake methodology. Ionic exchanges with the simulated body fluid SBF-K9 acellular solution during the in vitro bioactivity tests highlight the differences in terms of chemical reactivity between the glass and the glass–ceramics. The effect of crystallinity on the rates of hydroxycarbonate apatite (HCA) formation was followed by Fourier transformed infrared spectroscopy. Although all glass–ceramics can be considered bioactive, the glass–ceramic heat-treated at 775 °C (V775-4) presented the most interesting result, because the onset for HCA formation is at about 24 h and after 7 days the HCA layer dominates completely the spectrum. This occurs probably due to the presence of the whitlockite phase (3(Ca,Mg)O·P₂O₅). All samples were considered not cytotoxic.     

The influence of phosphorus precursors on the synthesis and bioactivity of SiO2–CaO–P2O5 sol–gel glasses and glass–ceramics

Bioactive glasses and glass–ceramics of the SiO₂–CaO–P₂O₅ system were synthesised by means of a sol–gel method using different phosphorus precursors according to their respective rates of hydrolysis—triethylphosphate (OP(OC₂H₅)₃), phosphoric acid (H₃PO₄) and a solution prepared by dissolving phosphorus oxide (P₂O₅) in ethanol. The resulting materials were characterised by differential scanning calorimetry and thermogravimetry, X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy coupled with energy dispersive X-ray spectroscopy and by in vitro bioactivity tests in acellular simulated body fluid. The different precursors significantly affected the main steps of the synthesis, beginning with the time required for gel formation. The most striking influence of these precursors was observed during the thermal treatments at 700–1,200 °C that were used to convert the gels into glasses and glass–ceramics. The samples exhibited very different mineralisation behaviours; especially those prepared using the phosphoric acid, which had a reduced onset temperature of crystallisation and an increased resistance to devitrification. However, all resulting materials were bioactive. The in vitro bioactivity of these materials was strongly affected by the heat treatment temperature. In general, their bioactivity decreased with increasing treatment temperature. For crystallised samples obtained above 900 °C, the bioactivity was favoured by the presence of two crystalline phases: wollastonite (CaSiO₃) and tricalcium phosphate (α-Ca₃(PO₄)₂).     

Facile route to obtain a highly bioactive SiO2–CaO–Na2O–P2O5 crystalline powder

This work describes a facile method to obtain highly bioactive crystalline powders of the SiO₂–CaO–Na₂O–P₂O₅ system using a simple route: solid state reaction. Success in obtaining the highly bioactive crystal phase of interest (sodium calcium silicate Na₂Ca₂Si₃O₉ containing phosphorus) involves heating the starting reactant powder mixture under an oxidizing atmosphere for 480 min in the temperature range 950–1000 °C. Despite a significant loss of phosphorus at heat treatment temperatures above 950 °C, the resulting Na₂Ca₂Si₃O₉ crystal phase is thermally stable up to 1100 °C. Longer treatment times favor the formation of a secondary phase (sodium calcium phosphate NaCaPO₄), which, according to recent studies, further increases the bioactivity of a similar material. Finally, in vitro bioactivity tests in acellular simulated body fluid (SBF) of a powder containing only the Na₂Ca₂Si₃O₉ phase has shown behavior similar to that of Biosilicate® — an ~ 99.5% crystalline glass–ceramic whose outstanding characteristics of interaction with living tissue have already been reported in the literature.     

Gel-derived SiO2–CaO–Na2O–P2O5 bioactive powders: Synthesis and in vitro bioactivity

In the present work, bioactive powders of the quaternary SiO₂–CaO–Na₂O–P₂O₅ system were synthesized by means of a sol–gel route. In their synthesis, tetraethoxysilane (Si(OC₂H₅)₄), calcium nitrate tetrahydrate (Ca(NO₃)₂? 4H₂O) and sodium nitrate (NaNO₃) were chosen as precursors of SiO₂, CaO and Na₂O, respectively. For P₂O₅, two different precursors were tested: triethylphosphate (OP(OC₂H₅)₃) and phosphoric acid (H₃PO₄). The gels were then converted into ceramic powders by heat treatments in the temperature range 700–1000 °C. The resulting materials were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy coupled with energy dispersive spectroscopy (SEM/EDS) and in vitro bioactivity in acellular simulated body fluid (SBF). During the conversion of the gels into ceramics the mineralization behavior of the two sets of samples was different, but all the resulting materials were bioactive. The samples prepared using phosphoric acid exhibited the best in vitro bioactivity. This result was attributed to the preferential formation of bioactive sodium calcium silicate Na₂Ca₂Si₃O₉ crystals, especially in the samples submitted to heat treatments at 700 and 800 °C, which could not be observed in the samples prepared using triethylphosphate.     

Effect of processing parameters on textural and bioactive properties of sol–gel-derived borate glasses

A compositional range of recently developed bioactive sol–gel-derived borate glasses (SGBGs) have demonstrated remarkably rapid rates of conversion to hydroxy-carbonated apatite (HCA) in simulated body fluid (SBF). Although the composition of SGBGs did not greatly impact HCA conversion rates, it is still unknown how the sol–gel processing parameters affect the textural properties and thus bioactivity of the glass. In this study, a borate-substituted Bioglass^® “45S5” formulation [(46.1)B₂O₃-(26.9)CaO-(24.4)Na₂O-(2.6)P₂O₅; mol%] was fabricated using different sol–gel processing parameters including precursor materials, ageing time and temperature, along with calcination rate and temperature. It was found that a higher calcination temperature led to a partially crystallized glass with almost a magnitude decrease in specific surface area relative to the other glasses. All processing routes resulted in highly bioactive glasses according to Fourier transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy, which confirmed HCA formation in SBF in as little as 2 h. The majority of ion-exchange occurred within 30 min, facilitating this rapid conversion to bone-like HCA. Interestingly, the partially crystallized glasses (i.e., glass–ceramics) also underwent full conversion to HCA in SBF. Furthermore, ageing time and temperature did not affect the bioactive properties of these glasses, which allow for significantly reduced processing times. In summary, this study demonstrates that SGBGs can be tailored for targeted tissue engineering applications by varying the sol–gel processing parameters.     

Synthesis,characterization and in vitro bioactivity of sol-gel-derived SiO2–CaO–P2O5–MgO bioglass

In this study, the synthesis of SiO₂–CaO–P₂O₅–MgO bioactive glass was performed by the sol-gel method. Sol-gel-derived bioglass material was produced both in powder and in discs form by uniaxial pressing, followed by sintering at 700 °C. The obtained material was evaluated by X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), thermal gravimetric analysis (TGA) and differential scanning caloremetry (DSC) analyses. The biocompatibility evaluation of the formed glass was assessed through in vitro cell culture [alkaline phosphatase (AP) activity of osteoblasts] experiments and immersion studies in simulated body fluid (SBF) for different time intervals while monitoring the pH changes and the concentration of calcium, phosphorus and magnesium in the SBF medium. The SEM, XRD and FTIR studies were conducted before and after soaking of the material in SBF. At first, an amorphous calcium phosphate was formed; after 7 days this surface consisted of deposited crystalline apatite. The present investigation also revealed that the sol-gel derived quaternary bioglass system has the ability to support the growth of human fetal osteoblastic cells (hFOB 1.19). Finally, this material proved to be non-toxic and compatible for the proposed work in segmental defects in the goat model in vivo.     

Effect of heat treatment on the tribological properties of Al–Cu–Mg/nanoSiC composites

In this study, the effect of heat treatment on the tribological properties of Al–Cu–Mg alloy reinforced with 4 wt.% SiC particles with 650 nm average particle size has been investigated. The age hardening process consists of solution treatment at 540 °C for 6 h, followed by water quenching and ageing at different temperatures of 175, 200 and 225 °C with soaking times of 3, 6 and 9 h. Hardness measurements were applied to monitor the precipitation effect and the aged samples were then subjected to wear tests under dry sliding conditions against steel and alumina counterfaces. The results showed that the reinforced material exhibits an enhanced ageing response compared to the unreinforced material in the same heat treatment conditions. The rate of ageing increases with increasing temperature; however, ageing at 200 and 225 °C for more than 6 h resulted in over-ageing. The best combinations for the enhanced tribological properties for the composite material were selected as 6 h ageing at 225 °C. The precipitation effect for this alloy can be enhanced by the small addition of SiC nanoparticles. Having a small amount of nanoSiC particles with fine precipitates inside the matrix further increases the hardness and wear properties.     

The effect of Sr concentration on bioactivity and biocompatibility of sol–gel derived glasses based on CaO–SrO–SiO2–P2O5 quaternary system

In the present study, sol–gel derived glasses based on CaO–SrO–SiO₂–P₂O₅ system were prepared and the effect of Sr concentration on in vitro bioactivity and cellular properties of the glasses were investigated. SrO was substituted for CaO in the glass formula up to 10 mol% and in vitro bioactivity of the samples was evaluated by soaking them in simulated body fluid followed by structural characterization using XRD, FTIR and SEM techniques. The effects of various glass compositions on proliferation and differentiation of osteoblastic cells were also evaluated. The results showed that the substitution of Sr for Ca in the glass composition retarded formation of apatite layer onto the glass surfaces. Morphologies of the apatite layers were also different in which abundance of the crystals decreased with increasing Sr concentration. The bioactive glasses did not exert cytotoxic effect on the cells, however the proliferation and alkaline phosphatase activity of the cells on the samples containing low doses of Sr were higher than those of control and the samples with high dose of Sr. Glass specimen with 5 mol% of Sr exhibited appropriate bioactivity with optimal cell proliferation and ALP activity.     

Effects of Li2O3–B2O3–SiO2 addition on dielectric properties and microstructure of MgO–TiO2–ZnO–CaO ceramics

The effect of Li₂O₃–B₂O₃–SiO₂ (LBS) liquid-phase additives on the sintering, microstructures, and dielectric properties of MgO–TiO₂–ZnO–CaO (MTZC) ceramics was investigated. It was found that the sintering temperature could be lowered easily, and the dielectric properties of MTZC ceramics could be greatly improved by adding a small amount of LBS solution additives. With the addition of 10 wt% LBS, the ceramics sintered at 900 °C showed favorable dielectric properties with ε_r = 21.7, Qf = 5.0 × 10⁴ GHz, and TCF = ?21.6 ppm/ °C. The distructive physical analysis showed an excellent co-firing interfacial behavior between the MTZC ceramic and the Ag electrode. It indicated that MTZC ceramics with LBS solution additives have a number of potential applications on passive integrated devices based on the low-temperature co-fired ceramics technology.     

Effect of iron on the electrical properties of lead–bismuth glasses

Semiconducting oxide glasses of the system (80 − x)Bi₂O₃–20PbO–xFe₂O₃, where x = 5, 10 and 15 mol.%, were prepared and investigated for dielectric properties in the frequency range 120–100 KHz and temperature range 300–550 K. Analysis of the electrical properties has been made in the light of small polaron hopping model. The parameters obtained from the fits of the experimental data to this model are reasonable and consistent with glass composition. The conduction is attributed to non-adiabatic hopping of small polaron. The ac conductivity results suggest that the correlated barrier hopping (CBH) is dominant in ac conductivity.