Morphological control and in vitro bioactivity of nanoscale bioactive glasses

In this study, nanoscale bioactive glasses with different morphologies were prepared through sol-gel process using lactic acid as hydrolysis promoter. The effect of lactic acid concentration on the morphology of bioactive glass was characterized. The influence of the morphology on the in vitro bioactivity of samples was investigated in simulated body fluid and examined by various methods. The results showed that nanoscale surface morphologies with high roughness, created by addition of lactic acid, greatly enhanced the in vitro bioactivity of as-prepared samples. It was found that the morphology with nanoscale surface feature and pore size distribution, in addition to specific surface area and pore volume, plays an important role in accelerating the formation of carbonated hydroxyapatite. According to our results, bioactive glasses possessing surface morphology with significant numbers of nanoscale bioactive glass particles and a narrow unimodal or bimodal mesopore structure, exhibit the best 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.     

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.     

Mesoporous bioactive glasses. I. Synthesis and structural characterization

Highly ordered mesoporous bioactive glasses (MBGs) with different compositions have been synthesized by a combination of surfactant templating, sol–gel method and evaporation-induced self-assembly (EISA) processes. The texture properties and compositional homogeneity of MBGs have been characterized and compared with conventional bioactive glasses (BGs) synthesized in the absence of surfactants by evaporation method. The formation mechanism (pore – composition dependence) and compositional homogeneity in the case of MBG materials are different from those in conventional BGs. Unlike conventional sol–gel-derived BGs that shows a direct correlation between their composition and pore architecture, MBGs with different compositions may possess similar pore volume and uniformly distributed pore size when the same structure-directing agent is utilized. The framework of MBG is homogeneously distributed in composition at the nanoscale and the inorganic species generally exists in the form of amorphous phase. MBGs calcined at temperatures ⩽1073 K exhibit ordered mesopores; at higher temperature such as 1173 K, the inorganic wall becomes crystalline and the mesostructure is collapsed. The leaching test of MBG in water indicates that MBGs may have excellent degradability in body fluid, which is important for prospective bio-applications.     

A structural study of sol–gel and melt-quenched phosphate-based glasses

Phosphate-based glasses have recently attracted much interest as a new generation of biomaterials because of their ability to react and dissolve in the physiological environment and eventually to be replaced by regenerated hard or soft tissue. A series of phosphate-based glasses containing 45 mol% P₂O₅ and various amounts of CaO and Na₂O were synthesized by sol–gel and melt-quenching techniques. A comparison between the structure of the sol–gel glass and the structure of the analogous melt-quenched glasses has been undertaken. A broad-based characterization approach combining different techniques has been used to investigate the short-range structure of the glasses and the effect of adding modifier oxides to the network structure (conventional and high energy X-ray diffraction, infra-red spectroscopy, ³¹P solid state magic angle spinning NMR spectroscopy). Sol–gel and melt-quenched glasses appear to have a similar structure, showing similar Qⁿ distributions and atomic correlations.     

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.     

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.     

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.     

Synthesis and structural characterization of P2O5–CaO–Na2O sol–gel materials

Ternary phosphate-based glasses in the system P₂O₅–CaO–Na₂O were synthesized using the sol–gel approach. Glasses in this system have the potential for use as bioactive materials. A mixture of mono- and dialkyl phosphate PO(OH)_3−x(OC₂H₅)_x (x = 1, 2) and alkoxides of sodium and calcium in an ethylene glycol solution were used as precursors. One of the compositions has also been synthesized by sonocatalysis (application of ultrasonic vibration to the sol). The systems synthesized, which remain fully amorphous even after calcination at 400 °C given the appropriate composition, have been characterized using X-ray diffraction (XRD). Thermal properties have been examined by means of thermogravimetric analysis (TGA) and differential thermal analysis (DTA). The structure of the phosphate network has been studied as a function of composition using Fourier transform infrared spectroscopy (FT-IR) and ³¹P MAS NMR.     

Preparation of TiO2–Na2O glass by sol–gel method and structural characterization

The applicability of sol–gel process in glass formation of binary system, (100 − x)TiO₂–xNa₂O (x = 10, 20, 30), was investigated and the glasses were prepared successfully by the sol–gel process for the first time. The process of glass formation was checked by using X-ray diffraction measurement and DTA–TG analysis. In the baking step, a DTA peak related to the crystallization of gel was found. The short-range structure of glassified samples was studied by neutron scattering measurement. It is found from the results of neutron scattering measurement that the coordination number of O atom around Ti atom is about 4, and the O atoms around Ti atom form a planer square rather than a regular tetrahedron.     

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.     

Acid catalyst concentration effect on structure and ion relaxation studies of Li2O–P2O5–B2O3–SiO2 glasses synthesized by sol–gel process

Lithium phosphoborosilicate (LPBS) glasses were synthesized through the sol–gel process by varying nitric acid concentrations as a catalyst. The sol–gel process was monitored through XRD and DSC to optimize the LPBS glass forming treatment. Characterization of LPBS glasses was conducted using XRD, FTIR and DSC techniques. Impedance measurements were carried out at different temperatures on LPBS samples synthesized by sol–gel process with various nitric acid concentrations and impedance data were analyzed using Boukamp equivalent circuit software. The conductivity of LPBS samples was calculated from analyzed impedance data and it was found that sample synthesized with 2.5 N nitric acid concentration showed the high conductivity σ = 2.28(±0.02) × 10⁻⁷ S cm⁻¹ at 443 K. Activation energy (E_a) is obtained from Arrhenius plots of dc conductivity and it is found to be 0.39 (±0.02) eV for the high conductance sample. Ac conductivity data were analyzed using Jonscher’s power law (JPL) and the power law exponent (s) exhibits a low s value for high conducting LPBS sample and a non-linear behavior with temperature. The electric modulus data were fitted with Kohlraush–William–Watts (KWW) stretched exponential function and modulus formalism is used to study the ionic relaxation behavior at different temperatures in LPBS glasses synthesized with varying nitric acid concentrations.     

Low‐temperature preparation of bismuth ferrite microcrystals by a sol‐gel‐hydrothermal method

Well‐crystallized pure perovskite bismuth ferrite (BiFeO₃) powders with various morphologies have been synthesized by a novel sol‐gel‐hydrothermal route for the first time, which combined the conventional sol‐gel process and the hydrothermal method. The as‐prepared samples were characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM), differential thermal analysis (DTA) and ferroelectric test system. The results revealed that the compositions, morphological and dimensional changes in bismuth ferrite samples synthesized by sol–gel–hydrothermal method strongly depend on the concentrations of mineralizer. Ferroelectric hysteresis loops are displayed in the BiFeO₃ samples. The bismuth ferrites were hydrothermally synthesized at as low a temperature as 180 °C, which is comparatively lower than that synthesized by the normal sol–gel route. The formation mechanism of the bismuth ferrite crystalline was also discussed. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

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.     

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.     

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.     

Tetracycline and propolis incorporation and release by bioactive glassy compounds

This study compares the release of tetracycline and propolis incorporated into four silica-based bioactive glassy systems. The bioactive glasses, with composition (SiO₂)x(P₂O₅)y(CaO)z, were prepared using a sol–gel process at room temperature. Tetraethoxysilane (TEOS), triethylphosphate, and calcium chloride were used as Si, P, and Ca precursors, respectively. The quantities of tetracycline and propolis incorporated were 2% in weight. For delivery assays, the samples were individually immersed in deionized water and buffered with tris-hydroxymethyl amino methane, pH 7.4, and kept in water bath (37 °C) for thirty days. Aliquots were withdrawn and analyzed by ultraviolet spectrophotometry in the tetracycline (270 nm) and propolis (420 nm) wavelengths. For the glass–tetracycline compounds, it was observed that four days after release had started all samples had released about 90% of the total tetracycline concentration. In contrast, 90% of the propolis was released in about 30 days’ time. Sample characterization was made using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopic (FTIR), and thermogravimetry (TG).     

Periodic alignment of sol–gel derived,monodisperse phenylsilsesquioxane particles on a pregrooved substrate

Preparation and alignment of monodisperse inorganic–organic hybrid particles have become one of the most attractive research topics in recent years. In this study, phenylsilsesquioxane (PhSiO_3/2) particles were synthesized from phenyltriethoxysilane (PhSi(OEt)₃), ethanol (EtOH), hydrochloric acid for hydrolysis and ammonia water for polycondensation via sol–gel process. Spherical PhSiO_3/2 particles of 0.1–5.0 μm in diameter were obtained by varying the composition of the sols. The particle size distribution decreased with increasing the amounts of catalyst-containing H₂O and EtOH, and increasing the concentrations of catalysts. Monodisperse particles obtained were aligned on a pregrooved glass substrate using an ascending liquid flow and an attractive capillary force between the particles.     

Improvement of the chemical resistance of zirconium fluoride glasses coated with a Tiron® modified tin oxide layer prepared by the sol–gel process

In order to improve the chemical resistance of zirconium fluoride glass a protective transparent SnO₂ layer was deposited by the sol–gel dip-coating process in the presence of Tiron^® as particle surface modifier agent. After water immersion for different periods of time, both coated and non-coated fluoride glasses were analyzed by scanning electron microscopy, mass loss evaluation, infrared spectroscopy and X-ray photoelectron spectroscopy. In contrast to the effects occurring for non-coated glass, where the surface undergoes a rapid selective dissolution of the most soluble species, the results for the SnO₂-coated glass showed that the filling of the film nanopores by dissolved glass material results in a hermetic barrier protecting the glass surface. The selective glass dissolution was confirmed by liquid chromatography measurements of the etching solution after each exposure time.     

Development of novel surfactant-templated nanostructured thin SiO2, and SiO2–TiO2 films

Nanostructured oxidic thin films are of interest due to their applicability in many different fields like filtration technology, catalysis, biomaterials and self purification. In this paper, we present sol–gel derived SiO₂ and SiO₂–TiO₂ thin films with a new fingerprint-like nanostructure. The films were produced by dip-coating glass slides into the sol and a temperature treatment at 500 and 600 °C. The characterization methods were FEGSEM and AFM. The dimensions of the nanostructured surface pattern were calculated from the AFM data with the power spectral density method.