Silica-based Glasses Research Articles

Bioactive Glasses with Low Ca/P Ratio and Enhanced Bioactivity.

Three new silica-based glass formulations with low molar Ca/P ratio (2–3) have been synthesized. The thermal properties, the crystalline phases induced by thermal treatments and the sintering ability of each glass formulation have been investigated by simultaneous differential scanning calorimetry-thermogravimetric analysis (DSC-TG), X-ray diffraction (XRD) and hot stage microscopy (HSM). The glasses exhibited a good sintering behavior, with two samples achieving shrinkage of 85%–95% prior to crystallization. The bioactivity of the glasses in simulated body fluid (SBF) has been investigated by performing XRD and Fourier transform infrared spectroscopy (FTIR) on the samples prior and after immersion. The glasses with lower MgO contents were able to form a fully crystallized apatite layer after three days of immersion in simulated body fluid (SBF), while for the glass exhibiting a higher MgO content in its composition, the crystallization of the Ca–P layer was achieved after seven days. The conjugation of these properties opens new insights on the synthesis of highly bioactive and mechanically strong prosthetic materials.

Influence of the composition and viscosity of volcanic ashes on their adhesion within gas turbine aeroengines

This paper presents experimental investigations into adhesion characteristics of four types of (Icelandic) volcanic ash (VA). Firstly, powder (∼5–50 μm) was injected into a modified vacuum plasma spray set-up and the fractional mass of particles that adhered to a substrate was measured. Secondly, large (∼6 mm), dense pellets of each ash were heated and projected at a substrate, with their impact response monitored via high speed photography. The four ashes fall into two groups of two, one with high Si content (>20%) and the other containing less Si, but higher levels of lower valence cations (such as Ca, Mg & Fe). The glass transition temperatures were all relatively low (∼650–750 °C), favouring particle adhesion on surfaces in gas turbines. All of the ashes tended to adhere, especially with higher gas temperatures and impingement velocities. However, this tendency was much greater for the two ashes with high levels of the lower valence cations. The high speed photography confirmed that this was due to these two ashes having much lower viscosities (at high strain rates). This behaviour could not have been predicted solely on the basis of Tg or glass content values. However, these cations act as “network-modifiers” in silica-based glasses, effecting sharp reductions in melt viscosity, so inferences about the danger of specific VA may be possible from simple compositional analysis. In any event, it's clearly important for VA being generated during any particular eruption to be sampled (presumably by drones) and analysed, rather than relying solely on remote measurement of atmospheric ash levels.

Excitation and relaxation dynamics in ultrafast laser irradiated optical glasses

We discuss the dynamics of ultrashort pulsed laser excitation in bulk optical silica-based glasses (fused silica and borosilicate BK7) well-above the permanent modification threshold. We indicate subsequent structural and thermomechanical energy relaxation paths that translate into positive and negative refractive index changes, compression and rarefaction zones. If fast electronic decay occurs at low excitation levels in fused silica via self-trapping of excitons, for carrier densities in the vicinity of the critical value at the incident wavelength, persistent long-living absorptive states indicate the achievement of low viscosity matter states manifesting pressure relaxation, rarefaction, void opening and compaction in the neighboring domains. An intermediate ps-long excited carrier dynamics is observed for BK7 in the range corresponding to structural expansion and rarefaction. The amount of excitation and the strength of the subsequent hydrodynamic evolution is critically dependent on the pulse time envelope, indicative of potential optimization schemes.

Characterization of silica-based and borate-based, titanium-containing bioactive glasses for coating metallic implants

Bioactive glasses have found applications in diverse fields, including orthopedics and dentistry, where they have been utilized for the fixation of bone and teeth and as scaffolds for drug delivery. The present work outlines the characterization of two novel titanium-containing glass series, one silica-based and one borate-based. For the silica-based series, titanium is added at the expense of silicon dioxide whereas for the borate-based series, it is added at the expense of boron oxide as confirmed by Energy Dispersive Spectroscopy. Amorphous structures are obtained for silica-based glass at 15mol% TiO2 and for borate-based glasses at 0mol% and 5mol%, with low crystal peak intensities exhibited within the remaining glasses. MAS-NMR proves the role of P2O5 as a network modifier for both glass series by evidencing only Q0 structures (and Q1 structures for the silica-based glasses with crystal structures), whereas FTIR proves that Ti acted as a network modifier in the glass as there was an absence of peaks assignable to titanium bonding. This implies that the two glass series will degrade in-situ and release ions at the site of implantation. Additionally, thermal data sourced from these glasses indicate processing windows which make them suitable for enameling onto implants, with the borate-based series exhibiting greater processing windows over the silica-based series, hence making the borate glasses more suitable for coating metallic implants compared to their silica-based counterparts.

The dependence of Raman defect bands in silica glasses on densification revisited

This paper focuses on the densification signature measured by Raman spectroscopy in silica-based glasses. We have studied a pure silica glass and a 25GeO2–75SiO2 binary glass fabricated by plasma chemical vapor deposition (PCVD), using the fictive temperature T f as a variable parameter ranging from 950 to 1400 °C. Macroscopic density measurements highlighted two opposite behaviors: the higher the fictive temperature, the lower the density of the GeO2–SiO2 glass, in contrast to what is observed in the pure silica glass. Yet, Raman spectra of both these glasses showed similar trends: the intensities of the two defect bands, D1 and D2, increase with increasing fictive temperature. Therefore, the D1 and D2 bands cannot be used as a reliable signature of densification in binary glasses.

Antibacterial and bioactive composite bone cements containing surface silver-doped glass particles

A bioactive silica-based glass powder (SBA2) was doped with silver (Ag+) ions by means of an ion-exchange process. Scanning electron microscopy (SEM), energy dispersion spectrometry (EDS) and x-ray diffraction (XRD) evidenced that the glass powder was enriched with Ag+ ions. However, a small amount of Ag2CO3 precipitated with increased Ag concentrations in the exchange solution. The minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) of Ag-SBA2 towards Staphylococcus aureus were also evaluated and were respectively 0.05 mg ml−1 and 0.2 mg ml−1. Subsequently, Ag-SBA2 glass was used as filler (30%wt) in a commercial formulation of bone cement (Simplex™ P) in order to impart both antibacterial and bioactive properties. The composite bone cement was investigated in terms of morphology (using SEM) and composition (using EDS); the glass powder was well dispersed and exposed on the cement surface. Bioactivity tests in simulated body fluid (SBF) evidenced the precipitation of hydroxyapatite on sample surfaces. Composite cement demonstrated antibacterial properties and a compressive strength comparable to the commercial formulation.

Sol Gel Synthesis and In Vitro Evaluation of Apatite Forming Ability of Silica-Based Composite Glass in SBF

In this study, xerogel glass based on SiO-CaO-PO4 was synthesized by a low temperature acid catalysed sol-gel route. The in vitro evaluation of apatite forming ability for the glass was conducted in simulated body fluid (SBF) solution as the glasses were immersed for duration of 1, 7, 24 hours and 7 days. The XRD analysis showed that the glass formed semi-crystalline structure when sintered at 1000oC and consisted of Ca2O7P2 and Ca2O4Si phases. Image captured using FESEM showed the apatite-like structures were eventually formed on the glass top surface in small numbers after the glass immersed in SBF for only an hour. The numbers of the apatite structures were continuously grown with the increase period of immersion time. The apatite structure mostly covered on top of the glass surface after 24 hours of immersion and continuously growth into bone-like apatite structure when immersed for 7 days in the SBF. The apatite layer formed on the surface of the glass was confirmed as crystalline structure of hydroxyl-carbonate-apatite (HCA) as revealed by the complimentary results of EDS, XRD and FTIR analysis.

A Novel Technique for the Connection of Ceramic and Titanium Implant Components Using Glass Solder Bonding.

Both titanium and ceramic materials provide specific advantages in dental implant technology. However, some problems, like hypersensitivity reactions, corrosion and mechanical failure, have been reported. Therefore, the combining of both materials to take advantage of their pros, while eliminating their respective cons, would be desirable. Hence, we introduced a new technique to bond titanium and ceramic materials by means of a silica-based glass ceramic solder. Cylindrical compound samples (Ø10 mm × 56 mm) made of alumina toughened zirconia (ATZ), as well as titanium grade 5, were bonded by glass solder on their end faces. As a control, a two-component adhesive glue was utilized. The samples were investigated without further treatment, after 30 and 90 days of storage in distilled water at room temperature, and after aging. All samples were subjected to quasi-static four-point-bending tests. We found that the glass solder bonding provided significantly higher bending strength than adhesive glue bonding. In contrast to the glued samples, the bending strength of the soldered samples remained unaltered by the storage and aging treatments. Scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) analyses confirmed the presence of a stable solder-ceramic interface. Therefore, the glass solder technique represents a promising method for optimizing dental and orthopedic implant bondings.

Segmented cladding fiber fabricated in silica-based glass

We report fabrication of a segmented cladding fiber (SCF) in silica-based glass. An SCF with a uniform core of pure silica and cladding of periodically arranged pure silica and fluorine-doped silica in an angular direction has been fabricated by using the stack-and-draw technique. The fabricated fiber has been characterized by capturing its near-field intensity pattern at 633 nm wavelength. The number of modes has been estimated from the captured near-field intensity pattern by using neural network analysis. A four-segment SCF of 30- μ m core diameter and 0.43% relative index differences between the high- and low-index segments shows few-mode operation by filtering out higher-order modes of an otherwise highly multimode fiber.

Silica‐based mesoporous nanobiomaterials as promoter of bone regeneration process

Silica-based mesostructured nanomaterials have emerged as a full family of biomaterials with tremendous potential to address the requirements for the bone regeneration process. This review focuses on more recent advances in bone regeneration process based on silica-based mesoporous biomaterials during 2012 to January 2015. In this review, we describe application of silica-based mesoporous mesostructured nanomaterials (possessing pore sizes in the range 2-50 nm) for the bone regeneration process. We summarize the preparation methods, the effect of mesopore templates and composition on the mesopore-structure characteristics, and different forms of these materials, including particles, fibers, spheres, scaffolds, and composites. The effect of structural and textural properties of mesoporous materials on the development of new biomaterials for treatment of different bone pathologies such as infection, osteoporosis, cancer, and so forth is discussed. In addition, silica-based mesoporous bioactive glass, as a potential drug/growth factor carrier, is reviewed, which includes the composition-structure-drug delivery relationship and the functional effect on the antibacteria and tissue-stimulation properties. Also, application of different mesoporous materials on construction of 3D macroporous scaffolds for bone tissue engineering was disused. Finally, this review discusses the possibility of covalently grafting different osteoinductive agents to the silica-based mesoporous scaffold surface that act as attracting signals for bone cells to promote the bone regeneration process.

Optimization of the CaO and P2O5 contents on PDMS–SiO2–CaO–P2O5 hybrids intended for bone regeneration

Osteoproductive materials that induce quick bone regeneration are needed for the developing area of scaffold-based bone engineering. Bioactive silica-based glasses, ceramics, and hybrids are called to play an important role in this field. Organic–inorganic hybrid materials based on SiO2-modified PDMS–P2O5–CaO are studied in this work. These materials are synthesized by the sol–gel method, and the influence of the composition on the reaction kinetic, obtained porosities, degradation and bioactive behavior, and cytotoxicity is studied. Materials with greater contents in CaO yield faster reaction kinetics and produce porous materials that favor a quicker degradation, whereas with greater P2O5 contents produce denser and more stable materials. The incorporation of CaO and P2O5 up to 5 and 25 % in weight into the SiO2 network, respectively, resulted in an increase of the apatite-forming ability in PBS. None of the studied compositions are cytotoxic, showing cellular viability over 70 % at all times.

Calcium environment in silicate and aluminosilicate glasses probed by 43Ca MQMAS NMR experiments and MD-GIPAW calculations

43Ca MQMAS NMR spectra of three silica-based glasses in which Ca2+ ions play different structural roles have been collected and processed in order to extract the underlying NMR parameter distributions. The NMR parameters have been interpreted with the help of molecular dynamics simulations and DFT-GIPAW calculations. This synergetic experimental–computational approach has allowed us to investigate the Ca environment, to estimate Ca coordination numbers from MD-derived models, and to push further the discussion about 43Ca NMR sensitivity to the first and second coordination spheres: 43Ca δiso and Ca–O distance can be successfully correlated as a function of Ca coordination number.

Enhanced apatite precipitation on a biopolymer-coated bioactive glass

AbstractIn this work, sintered pellets of a silica-based bioactive glass were dip-coated with a biocompatible natural-derived polymer in order to investigate the influence of the organic coating on the glass bioactivity. After the sintering process optimization, uncoated and coated pellets have been characterized by means of scanning electron microscopy with energy dispersive spectroscopy (SEM, EDS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and pH measurements, after the immersion in a simulated body fluid (SBF). An increased apatite forming ability and a better control of the pH during soaking of the samples in SBF were observed in the presence of the biopolymer. This result opens a new insight on the simple fabrication of highly bioactive hybrid inorganic-organic materials for medical applications.

Effect of ytterbium co-doping on erbium clustering in silica-doped glass

The effect of ytterbium co-doping on erbium ion clustering in silica-based glass was studied. It was experimentally shown that the pump-to-signal conversion efficiency could be significantly increased if the number of Yb3+ ions in the fiber core was 20 times higher than the number of Er3+ ions. Estimations of the number of Er3+ ions in clusters confirmed a decrease in their clustering at high Yb concentrations.

Angular Dependence of the Second Harmonic Generation Induced by Femtosecond Laser Irradiation in Silica-Based Glasses: Variation with Writing Speed and Pulse Energy

To control second harmonic generation (SHG) in silica-based glasses is crucial for fabricating photonic devices, such as frequency doubling waveguides. Here, we investigated SHG of laser induced nonlinear optical crystals in silica-based glasses, according to writing speed and pulse energy. We observed two regions with different probing laser polarization angular dependence: a) a well-defined cosine-like curve with period of 180° at low pulse energy (0.8 μJ) whatever the writing speed or at high pulse energy (1.4 μJ) with high writing speed (25 μm/s). This is accounted for by a well-defined texture for the nano crystals with their polar axis oriented perpendicular to the writing laser polarization; and b) a double cosine-like curve revealing a second texture of the crystals at high pulse energy (1.4 μJ) with low writing speed (5 μm/s) and with the polar axis oriented closer parallel to the writing laser polarization. Therefore, a SHG dependence on probing laser polarization angle may show high contrast by a correct choice of the writing speed and pulse energy. These results pave the way for elaboration of nonlinear optical devices.

Encapsulation of graphene oxide/metal hybrids in nanostructured sol–gel silica ORMOSIL matrices and its applications in optical limiting

Abstract Optically transparent organically modified silica (ORMOSIL) gel glasses doped with graphene oxide (GO)/metal nanoparticle (NP) hybrids were synthesized using a simple sol–gel technique. The two-dimensional GO/metal NP hybrids dramatically changed the surface characteristics of silica-based gel glasses whilst maintaining their structural integrity during the sol–gel procedure. The optical limiting (OL) properties of GO/metal NP-doped ORMOSIL gel glasses were investigated using a nanosecond open-aperture Z-scan technique at 532 nm. The metal NP hybrids exhibited significantly enhanced OL performance compared with their individual counterparts in ORMOSIL gel glasses. The improvement in GO/Au NP-doped gel glasses is attributed to surface plasmon resonance, while interband transition is responsible for the enhancement in GO/Pd NP-doped gel glasses. The OL behavior of GO/metal NP-doped gel glasses were mostly attributed to the combined mechanisms of excited state absorption and nonlinear scattering.

One-step photoinscription of asymmetrically oriented fresnoite-type crystals in glass by ultrafast laser.

Oriented fresnoite-type crystals (Sr(2)TiSi(2)O(8)) were photoinduced directly in bulk silica-based glass by femtosecond laser irradiation at high repetition rate (typ. 300 kHz). Unlike related results obtained from other researchers, asymmetrical polar-axis orientation of those nonlinear crystals in transverse direction of the cross section has been demonstrated by electron backscattered diffraction and micro-second-harmonic generation (SHG). The nonlinear optical property of laser lines has been further characterized by SHG measurement. We found that the preferential directions of the polar axis were in the laser motion direction with a small dispersion in part of the heated volume. The other part of the crystallized volume shows an axis perpendicular to the writing direction. The mechanism of asymmetric orientation of femtosecond-laser-induced crystallization also is discussed.

Brillouin scattering properties of lanthano-aluminosilicate optical fiber.

Utilizing measurements on a lanthano-aluminosilicate core optical fiber, the specific effects of lanthana (La2O3) on the Brillouin characteristics of silica-based oxide glass optical fibers are described. Lanthana is an interesting species to investigate since it possesses a wide transparency window covering the common fiber laser and telecom system wavelengths. As might be expected, it is found that the properties of lanthana are very similar to those of ytterbia (Yb2O3), namely, low acoustic velocity, wide Brillouin spectral width, and a negative photoelastic constant, with the latter two properties affording significant reductions to the Brillouin gain coefficient. However, lanthana possesses thermo-acoustic and strain-acoustic coefficients (acoustic velocity versus temperature or strain, TAC and SAC, respectively) with signs that are opposed to those of ytterbia. The lanthano-aluminosilicate (SAL) fiber utilized in this study is Brillouin-athermal (no dependence of the Brillouin frequency on temperature), but not atensic (is dependent upon the strain), which is believed to be, to the best of our knowledge, the first demonstration of such a glass fiber utilizing a compositional engineering approach.

Evaluation of gentamicin encapsulated hierarchically meso-macroporous silica-based calcium phosphates glass powders

In this study, 80SiO2–15CaO–5P2O5 powders prepared using either a polyurethane foam sponge-F127 co-template (SCP-CoT) or only a polyurethane foam sponge macrotemplate (SCP-T) were used to evaluate the gentamicin encapsulation of hierarchically meso-macroporous silica-based calcium phosphate glass powders. The SCP-CoT powders exhibited an approximately three times larger specific surface area compared to the SCP-T powders. The formation of a hysteresis loop also signified the presence of mesoporous structures in the SCP-CoT powders samples; a hysteresis loop was not observed for the SCP-T samples, which had approximately 1/5 of the pore volume of the SCP-CoT powder samples. The encapsulation capacities of gentamicin for the SCP-CoT and SCP-T powders were 29.4% and 5.4%, respectively, indicating that significantly more gentamicin drug can be loaded into the SCP-CoT powders due to their higher surface area and pore volume. Notably, when the initial gentamicin concentration was 1mg/ml, the SCP-CoT powder provided a sufficient surface area and pore volume to achieve nearly 100% encapsulation efficiency. Although increasing the initial concentration of gentamicin decreased the encapsulation efficiency, the total amount of encapsulated gentamicin increased. The maximum value of encapsulated gentamicin (39.9mg/g) was observed at an initial concentration of 50mg/ml.

Short and medium range order in two-component silica glasses by positron annihilation spectroscopy

The dependence of chemical composition on the average sizes of subnanometer-scale intrinsic structural open spaces surrounded by glass random networks in two-component silica-based glasses was investigated systematically using positronium (Ps) confined in the open spaces. The average sizes of the open spaces for SiO2-B2O3 and SiO2-GeO2 glasses are only slightly dependent on the chemical compositions because the B2O3 and GeO2 are glass network formers that are incorporated into the glass network of the base SiO2. However, the open space sizes for all SiO2-R2O (R = Li, Na, K) glasses, where R2O is a glass network modifier that occupies the open spaces, decrease rapidly with an increase in the R2O concentration. Despite the large difference in the ionic radii of the alkali metal (R) atoms, the open space sizes decrease similarly for all the alkali metal atoms studied. This dependence of the chemical composition on the open space sizes in SiO2-R2O observed by Ps shows that the alkali metal atoms do not randomly occupy the structural open spaces, but filling of the open spaces by R2O proceeds selectively from the larger to the smaller open spaces as the R2O concentrations are increased.