Acetic acid derived mesoporous bioactive glasses with an enhanced in vitro bioactivity

In this paper, a novel mesoporous bioactive glass (MBG) with a nanoscale surface feature in the SiO₂–CaO–P₂O₅ system has been synthesized by means of the acetic acid-assisted sol–gel process. As a comparison, the normal sol–gel derived bioactive glass (NBG) with the same composition was also synthesized. The structure and in vitro bioactivity of as-prepared samples were characterized using various methods. The results indicated that using acetic acid as a structure-assisted agent and hydrolysis catalyst is in favor of preparing the bioactive glass with nanoscale surface morphology, larger specific surface area, relatively homogeneous sized mesopore distribution. Depending on this novel structure, MBG presented an enhanced formation of hydroxyl-carbonate apatite layer and high in vitro bioactivity.     

Synthesis and bioactive properties of macroporous nanoscale SiO2–CaO–P2O5 bioactive glass

A macroporous nanoscale bulk bioactive glass (SiO₂–CaO–P₂O₅ system) was prepared by sol–gel co-template method. Porosimeter analysis showed that the as-synthesized bioactive glasses (BGs) had a porosity of 85% and exhibited a multimodal pore size distribution, nanopores (10–40 nm) and macropores (100 nm–10 μm). Morphological and structural characterizations showed the pores were interconnected with pore walls of about 250 nm in width and 1 μm in length. In vitro bioactivity test indicated that the as-synthesized bulk BGs exhibited faster apatite layer formation capability than the conventional sol–gel BGs. Additionally, the deposited layer was identified as hydroxycarbonate apatite, which is similar to the inorganic part of human bone.     

Synthesis and characterization of calcium phosphate based bioactive quaternary P2O5-CaO-Na2O-K2O glasses

Calcium phosphate based bioactive quaternary glass systems P₂O₅-CaO-Na₂O-K₂O were prepared by melt growth technique. Glasses were prepared in five different compositions by fixing P₂O₅ at 47 mol% and CaO at 30.5 mol% and by varying the K₂O and Na₂O concentrations. The structural properties of the glasses are analyzed using X-ray diffraction (XRD) studies and scanning electron microscopy (SEM) studies; and the composition of the glasses are studied using energy dispersive X-ray spectrum (EDS). The microhardness of the glass systems are studied by Vickers hardness measurements and the bioactivity of the glasses are studied using in vitro study. The thermal properties have been examined by means of thermogravimetric analysis (TGA) and differential thermal analysis (DTA). The ultrasonic velocity measurements show that the addition of K₂O contents produces non-bridging oxygen ion and hence weaken of the glass structure. The weakening of the glass structure reduces the ultrasonic velocity and hence an increase in attenuation.     

Preparation,in vitro bioactivity and drug release property of well-ordered mesoporous 58S bioactive glass

Bioactive glasses (BG) have proved to be able to chemically bond to living bone due to the formation of an apatite-like layer on its surface. In this paper, well-ordered mesoporous 58S bioactive glass (M58S) was synthesized in aqueous solution by a two-step acid-catalyzed self-assembly process combined with hydrothermal treatment. The drug release behavior of the M58S was investigated in phosphate buffered saline (PBS) at 37.5 °C for 20 days, and the assessment of in vitro bioactivity of M58S powders was carried out in simulated body fluid (SBF) at 37.5 °C. The results showed that M58S possessed good drug release behavior due to its well-ordered mesoporous structure, and a higher ability to induce hydroxyapatite formation in SBF. Therefore, well-ordered mesoporous bioactive glasses might be used as a bioactive drug release system for preparation of bone implant materials.     

Functionalization and bioactivity in vitro of mesoporous bioactive glasses

Amino and carboxylic groups functionalized mesoporous bioactive glasses (denoted as N-MBGs and C-MBGs, respectively) were successfully synthesized through a post-grafting process and characterized by XRD, N₂ sorption, TEM, FT-IR and TG techniques. Their in vitro bioactivity and degradation behavior were investigated in simulated body fluid and examined by various techniques. The results demonstrate that the bioactivity of all the samples and the morphology of carbonated hydroxyapatite were affected remarkably by the introduction of functional groups. Spherical carbonated hydroxyapatite particles were observed grown on the N-MBGs surfaces after soaking in simulated body fluid for 8 h, which is different from the rod-like carbonated hydroxyapatite grown on conventional mesoporous bioactive glasses. While for C-MBGs, the nucleation and growth rate of carbonated hydroxyapatite was decreased at increased contents of carboxylic groups.     

Preparation of bioactive glass ceramic nanoparticles by combination of sol-gel and coprecipitation method

SiO₂-CaO-P₂O₅ ternary bioactive glass ceramic nanoparticles were prepared via the combination of sol-gel and coprecipitation processes. Precursors of silicon and calcium were hydrolyzed in acidic solution and gelated in alkaline condition together with ammonium dibasic phosphate. Gel particles were separated by centrifugation, followed by freeze drying, and calcination procedure to obtain the bioactive glass ceramic nanoparticles. The investigation of the influence of synthesis temperature on the nanopartilce’s properties showed that the reaction temperature played an important role in the crystallinity of nanoparticle. The glass ceramic particles synthesized at 55 °C included about 15% crystalline phase, while at 25 °C and 40 °C the entire amorphous nanopowder could be obtained. In vitro testing showed that the bioactive glass ceramic nanoparticles can induce the formation of hydroxylaptite from simulated body fluid rapidly. As a result, this bioactive glass ceramic nanoparticle with excellent bioactivity would be a promising filler material for bone tissues engineering.     

Silver release from hydroxyapatite self-assembling calcium–phosphate glasses

The in vitro behavior of xAg₂O (100 ? x)[50P₂O₅ · 30CaO · 20Na₂O] glasses (0.14 ? x ? 20 mol%) is investigated in simulated body fluid (SBF) mainly with respect to bioactivity and silver ions release. In order to estimate the biodegradability and bioactivity, the samples were soaked in SBF, which has almost equal ions concentration to those of human blood plasma, and kept at 37 °C for fixed periods of time up to 18 days. After the fixed periods of time analyses were performed on the SBF solutions. Calcium and silver ions concentration of SBF after different soaking times of the glass samples were primarily examined. Conductivity data support the assumption that the released silver ions are reduced in SBF and their release is obstructed by growth of the bioactive layer on the glass surface. X-ray diffraction and infrared analysis attest the development on glass surface of a hydroxyapatite type layer.     

Influence of morphology on in vitro compatibility of bioactive glasses

In vitro bioactivity and biocompatibility of fiber and bulk bioactive glasses were studied. After synthesis with tetraethoxysilane, individual bulk and fiber samples were soaked in a simulated body fluid solution and removed at intervals of 5 and 30 days, respectively. Fourier transform infrared spectroscopic analysis showed hydroxyapatite characteristic P–O vibrational bands for simulated body fluid soaked fibers and bulk samples. Osteoblast viability and alkaline phosphatase production were evaluated by cell incubation in the presence of samples and compared to controls. Fiber glass-incubated osteoblasts showed lower viability but the same alkaline phosphatase production when compared to bulk sample and controls.     

Structural characterization of phosphate glasses doped with silver

The present paper reports the influence of silver oxide addition on the local structure of 2P₂O₅ · CaO · 0.05ZnO glass matrix. The glass samples were investigated through several methods: X-ray powder diffraction (XRD), scanning electron microscopy (SEM), infrared absorption (FT-IR) and Raman scattering. The X-ray diffraction patterns confirm the vitreous character of these samples over the explored compositional range and the SEM pictures confirm this information. The phosphate structural units of the network former are assessed from FT-IR and Raman spectra as ultra-, meta-, pyro- and orthophosphate units. A slight structural depolymerization process of these phosphate-based glasses was evidenced for higher silver oxide content. In vitro behavior of the bulk glass sample with the highest silver oxide content was tested by immersion in simulated body fluid (SBF). X-ray diffraction and SEM measurements made on the SBF treated sample revealed growth of a crystalline phase on the surface sample.     

The role of MgO on thermal properties,structure and bioactivity of bioactive glass coating for dental implants

The successful application of bioactive glasses as a coating for titanium implants to improve osseointegration is dependent on achieving a thermal expansion coefficient (TEC) match between the two phases. Many studies have indicated that magnesium affects the thermal and structural properties of a glass. However, its effect on bioactivity of bioactive glasses is still under debate. In this study, we characterize the effect of magnesium on the thermal properties, structure and bioactivity of glasses containing MgO. Seven glasses with different MgO concentrations have been synthesized by melt-derived technique. All these glasses contain SiO₂, CaO, MgO, ZnO, Na₂O, K₂O and P₂O₅ and have been characterized by X-ray diffraction (XRD), differential scanning calirometry (DSC) and dilatometry. Additionally, the oxygen density and bulk density have been investigated. The bioactivity of the MgO glass series was evaluated in simulated body fluid (SBF) and Tris-buffer solution. The results indicate that magnesium suppresses crystallization and decreases TEC, glass transition temperature (T_g) and softening (T_s) temperature. Oxygen density increases proportionally with MgO content; whereas glass density decreases. After different time points, XRD and Fourier transform infra-red spectroscopy (FTIR) show that magnesium does not inhibit the apatite forming ability of the glasses, but retards the time of apatite deposition. The glass coatings of this series exhibit clear clinical application for use as a functional barrier: osteoblastic attachment and growth was poor, however, fibroblastic biocompatibility was good.     

Sol-gel synthesis of a new composition of bioactive glass in the quaternary system SiO2-CaO-Na2O-P2O5: Comparison with melting method

New sol-gel experimental conditions were tested to prepare a new SiO₂-based bioactive glass with high Na₂O content. The aim of this work is to investigate the real influence of the synthesis route (sol-gel versus melting) on the glass intrinsic properties and then, later, on the glass behavior and particularly on bioactivity. The obtained glass and its melt derived counterpart were characterized from structural and morphological (porosity, specific surface area) point of view. It could be noticed that the synthesis mode has no significant influence on glass structure. Conversely, the synthesis mode greatly influences the glass texture. The sol-gel derived glass exhibits a greatly higher specific surface area and pore volume than melt derived glass. This parameter may be a key factor of glass bioactivity.     

Effect of strontium substitution on the structure,ionic diffusion and dynamic properties of 45S5 Bioactive glasses

Strontium ions can promote bone growth and enhance bioactivity in bioactive glasses that find critical biomedical applications. In this paper, the effect of SrO/CaO substitution on the structure, ionic diffusion, and dynamic properties of 45S5 bioactive glasses has been studied using constant pressure molecular dynamics simulations with a set of effective partial charge potentials. The simulated structure models were validated by comparing with experimental neutron diffraction results. It was found that the SrO/CaO substitution leads to an increase of glass density and decrease of oxygen density, a measure of compactness of the glass, in excellent agreement with available experimental data. On the other hand, the substitution does not significantly change of the medium range glass structures as characterized by silicon and phosphorous Q_n distributions, network connectivity, and ring size distributions. The diffusion and dynamic behavior of these glasses and their melts were also determined by calculating the mean square displacements and velocity autocorrelation functions. It was found that the diffusion energy barriers of sodium, calcium and strontium ions remain nearly constant with respect to the level of substitution. However, strontium ions do influence the diffusion behaviors of calcium and sodium ions at high temperature, as evidenced from their velocity autocorrelation functions. Like calcium and sodium, strontium ions only contribute to the lower frequency (around 100 cm^? 1) of the vibrational spectra the substitution has little effect on high frequency features and the general shape of the vibrational density of states. These results suggest that the increase of the dissolution rate in strontium containing glasses are mainly due to the increase of free volume and the non-local effect that weakens the silicon-oxygen network due to strontium ions.     

Sol–gel synthesis and characterization of unexpected rod-like crystal fibers based on SiO2–(1-x)CaO–xSrO–P2O5 dried-gel

Sol–gel technique has several benefits for the preparation of glass, and morphology can be better controlled compared to conventional methods. In this research, new sol–gel derived bioactive glasses based on SiO₂–CaO–SrO–P₂O₅ dried-gel were synthesized and characterized. Herein, a series of 58S bioactive glasses with the composition of 60%SiO₂–36%(CaO/SrO)–4%P₂O₅ (mol%) were synthesized, and the effect of adding strontium (Sr) to the glass structure SiO₂–(1-x)CaO–xSrO–P₂O₅ (where x = 0, 0.5, 0.1, 0.25, 0.5 and 1) was investigated by gradually substitution of Sr with calcium (Ca). The obtained results indicated that the Sr free sample totally takes amorphous state indicative of the internal disorder, glassy nature and non-crystalline states of this material. Surprisingly, after further addition of Sr to the glass structure, the X-ray diffraction (XRD) patterns and scanning electron microscopy (SEM) micrographs showed unexpected significant rod-like crystal fibers, and the major diffraction peaks of Sr(NO₃)₂, SrCO₃ and Sr₂Si₂O₄ became sharper and more apparent up to the final addition of Sr. The complicated and contradictory results underscore the need for better knowledge of how impurities act upon by growing rod-like crystals. In addition, totally understanding the effect of Sr on the morphology of samples from the bottom up is a daunting challenge.     

Towards the origin of the memory effect in oxide glasses

Glass samples with same composition and properties but different thermal histories can exhibit different behavior upon a subsequent heat-treatment, a phenomenon known as the memory effect. Generally, it is considered that the memory effect is due to nanoscale density fluctuation, which exists in all glasses and causes non-exponential relaxation with more than one relaxation time. Earlier, we studied the memory effect of various silica glasses and found that some pure silica glasses did not exhibit the memory effect while some silica glasses with higher impurity contents exhibited the memory effect. Based upon this finding, we suggested that the phenomenon originated from concentration fluctuation rather than density fluctuation. In this study, the memory effect in 6 mol% K₂O-94 mol% SiO₂ glass was investigated. The K₂O-SiO₂ glass system has a metastable immiscibility below the glass transition temperature and the chosen glass composition is the critical composition corresponding to the estimated critical temperature of the immiscibility boundary. Thus, it is expected that this glass composition would exhibit large super-critical concentration fluctuation, which increases with decreasing heat-treatment temperature. Density fluctuation, on the other hand, increases with increasing heat-treatment temperature. A much larger memory effect was observed at the lower heat-treatment temperature for the present glass. This result supports our earlier contention that the origin of the memory effect is composition fluctuation rather than density fluctuation.     

Tetracycline and/or hydrocortisone incorporation and release by bioactive glasses compounds

The delivery of the tetracycline and hydrocortisone drugs that have been incorporated into bioactive glasses was studied in this work. The potentiality of these systems in direct pulp capping is also discussed. A bioactive glass with a composition of (SiO₂)_0.80(P₂O₅)_0.04(CaO)_0.16, was prepared by sol-gel. Sols were prepared with the addition of approximately 2 wt% of tetracycline or hydrocortisone separately for the delivery studies. A third set of samples of bioglass sols containing 2 wt% of each drug were prepared with the same purpose. The amounts of drugs delivered were monitored by ultraviolet spectrophotometry in the tetracycline and hydrocortisone wavelengths. The drug release behavior was strongly dependent on the system. The glass-tetracycline samples showed a rapid drug release kinetics, while glass-hydrocortisone samples show much slow release profiles. The different drug release behaviors have been explained by faster gel formation reaction between hydrocortisone and TEOS due to a stronger interaction between these reagents. On the samples with both drugs, the release was simultaneous and for each drug, the amounts delivered followed a profile similar to the samples with only this specific drug.     

Fluoride-containing bioactive glasses: Fluoride loss during melting and ion release in tris buffer solution

Melt-derived bioactive glasses (SiO₂-P₂O₅-CaO-Na₂O-CaF₂; CaF₂ 0 to 17.76 mol%) lost fluoride during melting, but nominal and analysed CaF₂ contents in the glass correlated linearly. Analysed CaO contents were increased, showing that fluoride was lost as hydrofluoric acid after reaction with atmospheric water during melting. Weight loss on ignition reduced linearly with increasing CaF₂, suggesting that CaF₂ impedes absorption of atmospheric water. pH changes in tris buffer solution showed that pH is controlled by the silicate matrix (via ion exchange processes), and fluoride release contributes less to the overall pH. Glasses formed apatite in tris buffer; phosphate concentration of the glass was the limiting factor, resulting in fluorite formation for increasing fluoride content in the glass and calcite formation for the fluoride-free composition. These results allow for tailoring of novel fluoride-containing bioactive glasses to address specific needs, particularly in dentistry and for remineralising toothpastes.     

Influence of the partial substitution of CaO with MgO on the thermal properties and in vitro reactivity of the bioactive glass S53P4

The influence of up to 4 mol% substitution of MgO for CaO on the properties of the bioactive glass S53P4 was studied. Thermal analysis, hot stage microscopy and X-ray diffractometry were utilized to measure the thermal properties and the crystallization characteristics of the glasses. The in-vitro bioactivity was measured by immersing the glasses for 4 h to one week in simulated body fluid. The formation of silica rich and hydroxyapatite layers was assessed from FTIR spectra analysis and SEM images of the glasses surface. Increasing substitution of MgO for CaO decreased the glass transition, the onset and endset of melting and the fusion temperatures. The activation energies for glass transition and crystallization also decreased from (790 ± 30) to (407 ± 30) kJ/mol and from (283 ± 30) to (145 ± 30) kJ/mol, respectively, indicating a decrease in bond length and an increase in bond strength with progressive MgO at the expense of CaO. All glasses dissolved identically in SBF during the first 24 h of immersion with subsequent formation of hydroxyapatite at the grain surfaces. The thickness of the surface layers decreased with increasing MgO content. For longer duration of immersion, the glasses with the highest MgO contents exhibited a slower reaction tendency, with simulated body fluid, than the Mg-free glass. These changes in the glass structure and in-vitro properties may be of interest for products from bioactive glasses with large surface area to volume ratio.     

Crystallization of monoclinic WO3 in tungstate fluorophosphate glasses

Tungstate fluorophosphate glass compositions with high WO₃ concentration were prepared in the ternary system (80−0.8x)NaPO₃-(20−0.2x)BaF₂-xWO₃ with x = 40,50 and 60 mol%. Transparency decreases as WO₃ concentration increases but can be improved by addition of oxidizing systems such as CeO₂ or Sb₂O₃/NaNO₃. Characterizations by thermal analysis (DSC) point out that an increase in the amount of WO₃ results in a higher glass transition temperature. In addition, such compositions are very stable against devitrification since samples containing 40% and 50% of WO₃ donot even exhibit the expected crystallization event. In these samples, the stability against crystallization decreases with the WO₃ content and vitreous sample containing 60% of WO₃ exhibits an endothermic event around 620 °C due to crystallization of monoclinic WO₃ phase. In these glasses, it was shown that the nucleation stage can be induced by thermal-treatment when external nucleating agents such as Ti or Sb are used. Finally, gold-doped samples exhibit a higher crystallization tendency and monoclinic WO₃ phase can be grown in such glasses.     

Sulfur behavior in silicate glasses and melts: Implications for sulfate incorporation in nuclear waste glasses as a function of alkali cation and V2O5 content

The presence of sulfur in radioactive waste to be incorporated in borosilicate glasses entails difficulties mainly due to the relatively low solubility of sulfates in the vitreous phase. In this work a study is presented on the effects of the ratio R = [Na₂O]/[B₂O₃], the type of sulfate added and the addition of V₂O₅ on the incorporation of sulfates in borosilicate glasses. Glass samples were prepared at the laboratory scale (up to 50-100 g) by melting oxide and sulfate powders under air in Pt/Au crucibles. XRF and ICP/AES chemical analysis, SEM/EDS, microprobe WDS and Raman spectroscopy were employed to characterize the fabricated samples. The main experimental results confirm that the incorporation of sulfates in borosilicate glasses is favored by the network depolymerization, which evolves with the ratio R. The addition of V₂O₅ seems to accelerate the kinetics of sulfur incorporation in the glass and, probably, increase the sulfate solubility by modifying the borate network and fostering the formation of voids of shape and size compatible with the sulfur coordination polyhedron in the glassy network. The kinetics of X₂SO₄ incorporation in the glass seems to be slower when X = Cs.     

In vitro changes in the structure of a bioactive calcia–silica sol–gel glass explored using isotopic substitution in neutron diffraction

Bioactive sol–gel derived glass scaffolds bond to bone and their dissolution products stimulate new bone growth in vitro and in vivo; they may therefore be used to regenerate diseased or damaged bone to its original state and function in bone tissue engineering applications. We seek herein to cast light upon these reaction mechanisms by attempting to quantify changes in the atomic-scale structure of the glass scaffold as a result of in vitro reaction with simulated body fluid (SBF). We report the results of a study using neutron diffraction with isotopic substitution (NDIS) to gain new insights into the nature of the atomic scale calcium environment in bioactive sol–gel glasses. This is augmented by high-energy X-ray total diffraction. We have thereby begun to explore the nature of the principal stages to the generation of hydroxyapatite (i.e. the mineral ‘building block’ of bone) on the bioactive glass surface. The data are examined in light of our complementary solid-state NMR and computer modelling studies. The results reveal that the Ca–O environment in an SBF exposed (CaO)_0.3(SiO₂)_0.7 sol–gel glass, which initially comprises three distinct but partially overlapping correlation shells centered at 2.3 Å, 2.5 Å and 2.75 Å, preferentially loses the shortest length correlation. A Ca⋯H correlation appears at 2.95 Å. The surface deposited Ca⋯P environment consists of three partially overlapping, but nonetheless distinct, correlation shells, at 3.15 Å, 3.40 Å and 3.70 Å.