Effects of hydrolysis on dodecyl alcohol-modified bioactive glasses and PDLLA/modified bioactive glass composite films

In this article, mesoporous 58S and 58S bioactive glasses (BGs) were surface modified by dodecyl alcohol through esterification reaction and PDLLA/modified BGs composite films were prepared. The purpose of this study was to investigate the properties of the modified BGs particles and the PDLLA/modified BGs composite films before and after hydrolytic treatment. The modified BGs powders and composite films were treated in boiling water for 20 min to remove the dodecyl chains. After hydrolytic treatment, the modified BGs powders showed increased hydrophilicity and the FTIR analysis revealed that most dodecyl chains were removed. Furthermore, the hydrophilicity of the PDLLA/modified BGs composite films was also greatly improved. The tensile strength of the composite films after hydrolysis decreased slightly, but was still much higher than that of pure PDLLA film. In addition, bone marrow mesenchymal stem cells from dogs on the composite films after hydrolytic treatment showed the highest proliferation rate. The results suggest that hydrolytic treatment is an effective and practicable method to remove alcohol chains from surface-modified BGs and polymers/modified BG composites, which may be used for preparation of bioactive scaffolds for tissue engineering applications.     

Preparation and Characterization of Eu<Superscript>3+</Superscript>-Doped Transparent Oxyfluoride Glasses

A process has been proposed for the preparation of oxyfluoride glasses based on the SiO₂–B₂O₃–Bi₂O₃–ZnO–CaF₂ system at various ratios of batch components, and transparent glasses have been obtained at a temperature below 1000°C. According to X-ray diffraction data, all of the glasses are X-ray amorphous. The surface morphology of the glasses has been examined and their glass transition temperatures have been determined. Their local structure has been studied by IR spectroscopy and it has been shown that, independent of composition, the glasses contain complex polyborate anions formed by [BO₃] and [BO₄] groups. Bismuth is incorporated into the glass network to form Bi–O–Si bonds and [BiO₆] network-formers.     

Bioactivity of Fe2O3-containing CaO-SiO2 glasses: in vitro evaluation

In order to reveal conditions for obtaining bioactive and ferrimagnetic glass-ceramics useful as thermoseeds for hyperthermia treatment of cancer, the effects of additives on the bioactivity of an Fe₂O₃-CaO-SiO₂ glass were investigated by examining apatite formation on the surfaces of the glasses in a simulated body fluid with ion concentrations nearly equal to those in human blood plasma. A 3Fe₂O₃, 100CaO · SiO₂ (in weight ratio) glass did not form an apatite layer on its surface in the fluid, but glasses of the same compositions with 3Na₂O, B₂O₃ and/or P₂O₅ added (in weight ratio) formed an apatite layer. This indicates that bioactive and ferrimagnetic glass-ceramics could be obtained from Fe₂O₃-containing CaO-SiO₂ glasses with Na₂O, B₂O₃ and/or P₂O₅ added. Apatite formation on the surfaces of the glasses with the additives are interpreted in terms of the dissolution of the calcium and silicate ions from the glasses.     

Bioactivity of CaO·SiO2-based glasses:in vitro evaluation

In order to fundamentally study compositional dependence of bioactivity of glasses, both the surface structural changes of P₂O₅-free CaO · SiO₂ glass due to exposure to a simulated body fluid and the effects of adding a third component, such as Na₂O, MgO, B₂O₃, Fe₂O₃, P₂O₅ and CaF₂, were investigated. An acellular aqueous solution which had almost equal ion concentrations to those of the human blood plasma was used as the simulated body fluid. The surface structure changes were examined by electronprobe X-ray microanalysis, thin-film X-ray diffraction (XRD) and Fourier transform infrared (FTIR) reflection spectroscopy. It was found that even P₂O₅-free CaO · SiO₂ glass forms an apatite layer on its surface in the simulated body fluid, and that the rate of formation of the surface apatite layer is increased with the addition of Na₂O and P₂O₅ while it decreased with the addition of MgO, B₂O₃, CaF₂ and Fe₂O₃. This indicates that even P₂O₅-free CaO · SiO₂ glass can bond to living bone, forming the surface apatite layer in the body and that its bioactivity is increased with the addition of Na₂O and P₂O₅ while it is decreased with MgO, B₂O₃, CaF₂ and Fe₂O₃. It is speculated that a glass of the composition CaO · SiO₂ 100, Fe₂O₃ 3 in weight ratio does not bond to living bone.On leave from: Sumitomo Metal Industries, Ltd, Otemachi, Tokyo 100, Japan.     

Spectroscopic characterization of alkali borosilicate glasses containing iron ions

Structural properties of alkali borosilicate glasses containing iron ions were investigated using infrared, laser Raman and Mössbauer spectroscopy. Two types of glasses were prepared: SRL-type with the composition 18.5 wt% Na₂O, 10.0 wt% B₂O₃, 52.5 wt% SiO₂, 4.0 wt% Li₂O, 10 wt% TiO₂ and 5.0 wt% CaO, and sodium borosilicate glass with the composition 16.7 wt% Na₂O, 18.7 wt% B₂O₃ and 64.6 wt% SiO₂. Raman spectroscopy showed that orthosilicates are the dominant amorphous phase in the SRL-type of glass. Incorporation of iron in the SRL-type of glass induced polymerization of silicate units and -Si-O-Fe- copolymerization. It was concluded that different amorphous phases are simultaneously present in the SRL-type of glass containing iron ions. Interpretation of the Raman spectra is given. Incorporation of iron ions into the sodium borosilicate glass also affected the corresponding IR spectra. The valence state of iron and its coordination were determined by⁵⁷Fe Mössbauer spectroscopy.     

Low temperature sintering and characteristics of K2O–B2O3–SiO2–Al2O3 glass/ceramic composites for LTCC applications

The K₂O–B₂O₃–SiO₂, K₂O–B₂O₃–SiO₂–2 %Al₂O₃, K₂O–B₂O₃–SiO₂–4 %Al₂O₃ glasses with different Al₂O₃ content were prepared. Different proportions (50, 55, 60, 65, 70 %) of the three glasses were respectively mixed with alumina ceramic-filler, then the mechanical and dielectric properties were investigated. The results showed K₂O–B₂O₃–SiO₂–2 %Al₂O₃ glass/alumina filler (glass:alumina = 60:40) had the excellent comprehensive properties, so further study was continued with part of alumina ceramic-filler replaced by the silica ceramic-filler on this composite. Then the X-ray diffraction analysis revealed that the alumina and silica fillers existed as the crystal phase, and the densification was seriously damaged when the silica content reached to three quarters of the fillers. With the increase of the silica-filler, the composites’ density and dielectric constant exhibited uniform decrease, but thermal expansion coefficient (TEC) uniformly increased. When the glass:alumina:silica was equal to 60:30:10, a best composite property was presented as a bulk density of 2.582 (g cm^?1), a dielectric constant of 6.1 and a dielectric loss of 2 × 10^?3 at 1 MHz, a flexural strength of 168 MPa, and a TEC of 8.62 × 10^?6 °C^?1.     

Raman spectroscopic investigation of sodium borosilicate glass structure

Raman spectra of sodium borosilicate glasses with a wide range of Na₂O/B₂O₃ ratios were systematically measured. Variations of the spectra with glass composition were studied to interpret the implied distribution of Na⁺ ions between silicate and borate units. When Na₂O/B₂O₃ is less than 1, all Na⁺ ions are associated with borate units as indicated by the absence of the 1100 cm⁻¹ band of Si-O⁻ non-bridging bond stretching. For the (1−x)Na₂O · SiO₂ ·xB₂O₃ glass withx≦0.4 the peak-height ratio of the 950 cm⁻¹ band to the 1080 cm⁻¹ band was used to analyse semiquantitatively the distribution of the Na⁺ ions between silicate and borate units. Sodium ions are divided between silicate and borate units approximately in proportion to the amount of SiO₂ and B₂O₃ present in these glasses. Some of the high sodium content glasses were crystallized and their spectra were compared with the bulk glass spectra. The distribution of Na⁺ ions in the glass was quite different from their distribution after crystallization. Spectra of high silica glasses that had been heat-treated for phase separation indicated exclusion of borate units from the silica network and the formation of borate groups. For high boron content glasses, no change was observed on heat treatment. Raman bands due to borate groups seem to be little affected by their environments. Also affiliated with the Department of Geosciences.     

Role of MgF2 on properties of glass–ceramics

Formation of machinable glass–ceramic in the system MgO–SiO₂–Al₂O₃–K₂O–B₂O₃–F with and without addition of MgF₂ has been investigated. Crystallization of glass sample was done by controlled thermal heat treatment at nucleation and crystallization temperatures. The results showed that MgF₂ in high concentration had a synergistic effect and enhanced the formation of interlocked mica crystals. Non-isothermal DTA experiments showed that the crystallization activation energies of base glasses were changed in the range of 235–405 kJ/mol, while the crystallization activation energies of samples with addition of MgF₂ were changed in the range of 548–752 kJ/mol.     

Compositional effects in the dissolution of multicomponent silicate glasses in aqueous HF solutions

The dissolution rate of multicomponent silicate glasses in a 2.9m aqueous HF solution is investigated as a function of its composition. The glasses studied are composed of SiO₂, B₂O₃, Al₂O₃, CaO, MgO, ZnO, Na₂O and K₂O, covering the compositions of most of the technologically important glasses. Unlike many physical properties, no linear relations are observed between the composition of the glass and its dissolution rate. The dissolution rate of a multicomponent silicate glass is found to be largely determined by two factors: The degree of linkage or connectivity of the silicate network and the concentration of SiO₂ in the glass. It is proposed that the dissolution of the glasses is preceded by the leaching of alkali and alkaline earth components present in the glass, followed by the subsequent dissolution of the leached layer. Probably fluorine species will diffuse into the leached layer to enhance the dissolution rate. Analysis of the activation energy data indicates that in some corrosive glasses the leaching itself becomes rate determining.     

Characterization and electrochemical properties of P2O5–ZrO2–SiO2 glasses as proton conducting electrolyte

The H₂/O₂ fuel cell based on the proton conducting P₂O₅–ZrO₂–SiO₂ glasses was prepared by sol–gel technique. Structural characterization were carried out using X-ray diffraction spectroscopy (XRD), Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (³¹P MAS NMR), N₂ adsorption–desorption analysis, differential thermal analysis (DTA) and thermal gravimetric analysis (TGA) and impedance measurements. The absorption bonds of Si–O–Si, Si–O–P and Si–O–Zr were observed in the P₂O₅–ZrO₂–SiO₂ glasses which were heat treated at 600 °C. A sample (5P₂O₅–4ZrO₂–91SiO₂, mol%) was selected as the electrolyte for the H₂/O₂ fuel cell test and yielded the maximum power density value of 8.5 mW/cm² using electrochemical measurements at 30 °C under relative humidity atmosphere.     

Do properties of bioactive glasses exhibit mixed alkali behavior?

The effect of substituting K₂O for Na₂O on the physical and chemical properties of 15 glasses in the system Na₂O–K₂O–CaO–P₂O₅–SiO₂ was studied for three series: low (52 mol% SiO₂), medium (60 mol% SiO₂) and high (66 mol% SiO₂) silica. The SiO₂ content expressed as weight-% varied from 46 to 64 wt%, thus suggesting that the compositions were either bioactive or biocompatible. The crystallization tendency and sintering behavior were studied using differential thermal analysis and hot stage microscopy. Formation of silica- and hydroxy-apatite-rich layers were studied for glass plates immersed in static simulated body fluid. The release of inorganic ions into Tris buffer solution was analyzed using inductively coupled plasma optical emission spectrometer in dynamic and static conditions. Substitution of K₂O for Na₂O suggested mixed alkali effect (MAE) for the thermal properties with a minimum value around 25% substitution. With increased share of K₂O in total alkali oxides, the hot working window markedly expanded in each series. Silica and hydroxyapatite layers were seen only on the low silica glasses, while a thin silica-rich layer formed on the other glasses. In each series, greater dissolution of alkali and alkali earth ions was seen from K-rich glasses. Clear MAE and preferential ion dissolution were recorded for medium and high silica series, while for low silica glasses, the initial MAE dissolution trends become rapidly covered by other simultaneous surface reactions. MAE enables designing especially low silica bioactive glasses for improved hot working properties and medium and high silica glasses for controlled dissolution.     

Leachability of zinc ions from ternary phosphate glasses

With a view to using glasses as a source of zinc, which is one of the micronutrients required by plants, a systematic study on leachability of zinc ions from ternary phosphate glasses having molar composition 60ZnO · 5X · 35P₂O₅ (where X = Li₂O, Na₂O, K₂O, CaO, B₂O₃ and SiO₂) was carried out. Leaching of zinc ions has been studied as a function of pH and the results show that leaching increases with increasing pH of the solutions. The concentration of zinc ions in the leachate decreases with increasing bond strength between non-bridging oxygen ions and the cations in glasses. The leaching of zinc ions increases with increase in leaching time and decreases with increase in particle size of glasses. P₂O₅ was also leached along with zinc ions. The leaching characteristics of P₂O₅ from the glasses are also reported.     

Glasses and glass-ceramics in the SrO–TiO2–Al2O3–SiO2–B2O3 system and the effect of P2O5 additions

The glass formation abilities of various compositions in SrO–TiO₂–Al₂O₃–SiO₂, SrO–TiO₂–B₂O₃–SiO₂, SrO–TiO₂–Al₂O₃–B₂O₃, and SrO–TiO₂–Al₂O₃–SiO₂–B₂O₃ systems were studied. Many new compositions were found to be suitable for the casting of crack-free, optically clear glasses of different color and with glass transition temperatures ranging from 595 to 775 °C. The crystallization behavior, structure, and thermal expansion behavior of selected glasses were analyzed by DTA, XRD, dilatometry, and heat treatment. The effect of P₂O₅ on the glass structure and crystallization behavior was also studied. P₂O₅ played a dual role depending on composition. In some glasses it acted as a nucleating agent while in others it suppressed crystallization. Heat treatment of borate and borosilicate glasses transformed them into glass-ceramics while comparable SrO–TiO₂–Al₂O₃–SiO₂ glasses showed a lower tendency to crystallize and form glass-ceramics under the same conditions.     

Effect of surfactant concentration and composition on the structure and properties of sol-gel-derived bioactive glass foam scaffolds for tissue engineering

Bioactive glasses are known to have the ability to regenerate bone, and to release ionic biological stimuli that promote bone cell proliferation by gene activation, but their use has been restricted mainly to the form of powder, granules or small monoliths. Resorbable 3D macroporous bioactive scaffolds have been produced for tissue engineering applications by foaming sol-gel-derived bioactive glasses. The foams exhibit a hierarchical structure, with interconnected macropores (10–500 m), which provide the potential for tissue ingrowth and mesopores (2–50 nm), which enhance bioactivity and release of ionic products. The macroporous matrices were produced by the foaming of sol-gel glasses with the use of a surfactant. Three glass systems SiO₂, SiO₂-CaO and SiO₂-CaO-P₂O₅were foamed using various concentrations of surfactant, in order to investigate the effect of surfactant concentration and composition on the structure and properties of the hierarchical construct.     

Two-liquid phase structure of photoconducting oxide glasses

An electron microscopic study of a series of photoconducting oxide glasses in the systems CdO/B₂O₃/SiO₂, CdO/B₂O₃/GeO₂ and PbO/Al₂O₃/SiO₂, has shown the essential diphasic nature of these materials. The samples were examined by replica techniques, in transmission and by scanning electron microscopy. Two-liquid features have been identified, as has very fine-scale crystallisation, both on the basis of textures of fracture surfaces and of electron diffraction patterns. Physical models proposed to explain the electronic properties of glasses such as these must take account of this obvious two-phase nature of such materials.     

Fabrication of CaO–NaO–SiO2/TiO2 scaffolds for surgical applications

A series of titanium (Ti) based glasses were formulated (0.62 SiO₂?C0.14 Na₂O?C0.24 CaO, with 0.05?mol% TiO₂ substitutions for SiO₂) to develop glass/ceramic scaffolds for bone augmentation. Glasses were initially characterised using X-ray diffraction (XRD) and particle size analysis, where the starting materials were amorphous with 4.5???m particles. Hot stage microscopy and high temperature XRD were used to determine the sintering temperature (~700?°C) and any crystalline phases present in this region (Na₂Ca₃Si₆O₁₆, combeite and quartz). Hardness testing revealed that the Ti-free control (ScC??2.4?GPa) had a significantly lower hardness than the Ti-containing materials (Sc1 and Sc2 ~6.6?GPa). Optical microscopy determined pore sizes ranging from 544 to 955???m. X-ray microtomography calculated porosity from 87 to 93?% and surface area measurements ranging from 2.5 to 3.3?SA/mm³. Cytotoxicity testing (using mesenchymal stem cells) revealed that all materials encouraged cell proliferation, particularly the higher Ti-containing scaffolds over 24?C72?h.     

Microstructure and dielectric properties of glass/Al2O3 composites with various low softening point borosilicate glasses

The effects of various low softening point borosilicate glasses on both the sintering behavior and dielectric properties of glass/Al₂O₃ composites were investigated by FTIR, DSC, XRD, SEM and EDS. Results show that the addition of alkali oxides and PbO can decrease the glass softening temperature. While, the addition of Al₂O₃ and more SiO₂ content in the glass can increase the continuity of glass network and further increase the glass softening temperature of samples. Glass with lower softening temperature has more time to flow to finish the densification of samples, and that can contribute to get better sintered composites. By contrast, CaO–PbO–B₂O₃–SiO₂–Na₂O–K₂O glass/Al₂O₃ composites sintered at 875?°C for 15?min exhibit better properties of a bulk density of 3.06?g/cm³, a porosity of 0.17?%, a λ value of 2.47?W/m?K, a ε _r value of 8.05 and a tan δ value of 8.8?×?10^?4 at 10?MHz.     

Preparation and characterization of Li<Subscript>2</Subscript>O–CaO–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–P<Subscript>2</Subscript>O<Subscript>5</Subscript>–SiO<Subscript>2</Subscript> glasses as bioactive material

The aim of the present investigation was to study the role of Al₂O₃ in the Li₂O–CaO–P₂O₅–SiO₂ bioactive glass for improving the bioactivity and other physico-mechanical properties of glass. A comparative study on structural and physico-mechanical properties and bioactivity of glasses were reported. The structural properties of glasses were investigated by X-ray diffraction, Fourier transform infrared spectrometry, scanning electron microscopy and the bioactivity of the glasses was evaluated by in vitro test in simulated body fluid (SBF). Density, compressive strength, Vickers hardness and ultrasonic wave velocity of glass samples were measured to investigate physical and mechanical properties. Results indicated that partial molar replacement of Li₂O by Al₂O₃ resulted in a significant increase in mechanical properties of glasses. In vitro studies of samples in SBF had shown that the pH of the solution increased after immersion of samples during the initial stage and then after reaching maxima it decreased with the increase in the immersion time. In vitro test in SBF indicated that the addition of Al₂O₃ up to 1.5 mol% resulted in an increase in bioactivity where as further addition of Al₂O₃ caused a decrease in bioactivity of the samples. The biocompatibility of these bioactive glass samples was studied using human osteoblast (MG-63) cell lines. The results obtained suggested that Li₂O–CaO–Al₂O₃–P₂O₅–SiO₂-based bioactive glasses containing alumina would be potential materials for biomedical applications.     

An emulsification–solvent evaporation route to mesoporous bioactive glass microspheres for bisphosphonate drug delivery

Regular spherical mesoporous bioactive glass microspheres (MBG-MSs) with tunable SiO₂–CaO–P₂O₅ composition and adjustable mesoporous structure have been synthesized by a new approach of emulsification and solvent evaporation-induced self-assembly. Less ordered mesostructure and enhanced bioactivity resulting from the addition of CaO are investigated through scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction characterizations. The MBG-MSs have high storage capacities and sustained release patterns of anti-osteoporosis (alendronate sodium, NaAL) drugs which are hardly absorbed via oral administration. Furthermore, to some extent the dosage and release rate could also be controlled by CaO content. Cell viability and proliferation assay with rabbit bone marrow stromal cells indicates a positive effect of the CaO/P₂O₅ components on improving the cell growth cumulatively in about 2 weeks.     

Doping of iron phosphate glasses with Al2O3, SiO2 or B2O3 for improved thermal stability

The effects of doping 60 P₂O₅–40 Fe₂O₃ (mol%) glasses with 5–10 mol% SiO₂, Al₂O₃ or B₂O₃ on their thermal stability, iron environments and redox were investigated. Thermal stability improved markedly with 5% dopant addition in the order Al₂O₃ > SiO₂ > B₂O₃ ≫ base glass. Solubility of pro rata additions when melted at 1150 °C was 5–10% SiO₂, <5% Al₂O₃, and >10% B₂O₃. It was possible to dissolve 5% Al₂O₃ by replacing Fe₂O₃. These additions generally had little effect on dilatometric measurements and iron environments, however the Fe²⁺/ΣFe redox ratio increased in the order base glass < Al₂O₃ < SiO₂ < B₂O₃. This behaviour was broadly consistent with the effects of glass basicity. The increased thermal stability of these glasses may improve their suitability for applications such as waste immobilisation or sealing.