Comparative studies on the bioactivity of some borate glasses and glass–ceramics from the two systems: Na2O–CaO–B2O3 and NaF–CaF2–B2O3

Combined FTIR spectroscopy and X-ray diffraction analysis have been employed to investigate the bone-bonding ability or bioactivity of some prepared borate glasses and their glass–ceramic derivatives from the two systems (Na₂O–CaO–B₂O₃) and (NaF–CaF₂–B₂O₃). The present study includes the mentioned FTIR spectral and X-ray analytical techniques before and after immersion of the glasses and glass–ceramics for 2 weeks in 0.025 M sodium phosphate (Na₂HPO₄) solution. Also, the work extends to evaluate the corrosion behavior for specified grains of the studied samples (0.3–0.6 mm) after immersion in phosphate solution for 2 weeks at 37 °C. The FTIR spectra of the two glass systems after immersion show some changes in the vibrational bands than before immersion. The generation of the characteristic peaks at about 580 and 680 cm⁻¹ after immersion confirms the bone bonding ability by the formation of hydroxyapatite phase. The X-ray diffraction studies show the separation of (CaF₂) which is known to be an efficient nucleator. Weight loss data show a difference in solubility in the sodium phosphate solution between fluoride and oxide glass systems due to the strong action of the leaching solution and ease of solubility of fluoride glasses than corresponding oxide glasses in this solution. SEM data indicate the formation of small rounded or nodular shape crystals which are characteristics for the formation of hydroxyapatite layer and complete agreement with X-ray data.     

Fabrication and in vitro studies on bioactive borate glasses containing dopant chromium sulfate

This research aims to assess the bioactive properties of the modified borate glasses containing extremely low concentrations (≤5 mol.%) from chromium sulfate (Cr₂(SO₄)₃). The glasses in the system xCr₂(SO₄)₃.(60–x)B₂O₃.15CaO.15Na₂O.10P₂O₅, where x = 0, 1, 2, and 5 mol.% were prepared by the melt quenching technique. All glass samples have been treated thermally at 600 °C for 6 h. Fourier Transform Infrared (FTIR) spectroscopy, Scanning Electron Microscopy (SEM), and X-ray Diffraction (XRD) measurements were carried out to differentiate between the structural changes before and after soaking in the simulated body fluid (SBF) at about 37 °C for 1, 2, and 3 weeks. Glass-ceramic samples have showed sharper peaks that are identified using X-ray diffraction data. These crystalline phases are indexed to crystalline calcium borate (Ca₂B₂O₃) and calcium phosphate (Ca₃(PO₄)₂). In vitro tests, FTIR spectra revealed two small bands in the 560-610 cm⁻¹ range which might be assigned to the formation of a hydroxyapatite layer (HA). The formation of HA was also confirmed by XRD results, particularly after immersion in SBF for 21 days. The study suggests that the presently studied glasses containing Cr₂(SO₄)₃ can possess good bioactivity which might be considered to be suitable for some bio and medical applications.     

Synthesis,Characterization, and In Vitro Bioactivity of Sol‐Gel‐Derived Zn,Mg, and Zn‐Mg Co‐Doped Bioactive Glasses

Bioactive glasses in the systems CaO‐SiO₂‐P₂O₅‐ZnO, CaO‐SiO₂‐P₂O₅‐MgO, and CaO‐SiO₂‐P₂O₅‐MgO‐ZnO were prepared and characterized. Bioactive glass powders were produced by the sol‐gel method. The prepared bioactive glass powders were immersed in a simulated body fluid (SBF) for periods of up to 28 days at 310 K to investigate the bioactivity of the produced samples. Inductively coupled plasma (ICP) and ultraviolet (UV) spectroscopic techniques were used to detect changes in the SBF composition. X‐Ray diffraction (XRD) was utilized to recognize and confirm the formation of a hydroxyapatite (HA) layer on the bioactive glass powders. Microstructural characterizations of the bioactive glass samples were investigated by scanning electron microscopy (SEM) techniques. Density, porosity, and surface area values of bioactive glass powders were also determined in order to characterize the textural properties of the samples. The results revealed the growth of an HA layer on the surface of the bioactive glass samples. MgO in the glass sample increases the rate of formation of an HA layer while ZnO in the glass slows it down.     

Phosphate content affects structure and bioactivity of sol-gel silicate bioactive glasses

Bioactive glasses can heal bone defects and bond with bone through formation of hydroxyl carbonate apatite (HCA) surface layer. Sol-gel derived bioactive glasses are thought to have potential for improving bone regeneration rates over melt-derived compositions. The 58S sol-gel composition (60 mol% SiO₂, 36 mol% CaO, and 4 mol% P₂O₅) has appeared in commercial products. Here, hydroxyapatite (HA) was found to form within the 58S glass during sol-gel synthesis after thermal stabilization. The preformed HA may lead to rapid release of calcium orthophosphate, or nanocrystals of HA, on exposure to body fluid, rather than the release of separate the calcium and phosphate species. Increasing the P₂O₅ to CaO ratio in the glass composition reduced preformed HA formation, as observed by XRD and solid-state NMR. Instead, above 12 mol% phosphate, a phosphate glass network (polyphosphate) formed, creating co-networks of phosphate and silica. Nanopore diameter of the glass and rate of HCA layer formation in simulated body fluid (SBF) decreased when the phosphate content increased.     

Structural and biophysical peculiarities of Nd2O3 doped borate bioglass

Different glasses with a variable composition of x Nd₂O₃.(46-x) B₂O₃.24.5 Na₂O.26.5 CaO.2.6 P ₂O₅ (where X = 0–2.0 mol% of Nd₂O₃) were prepared and studied from the viewpoint of enhancing their bioactivities. All of the as-prepared glasses showed amorphous structures evidenced by the X-ray diffraction (XRD) patterns. On the other hand, XRD patterns of glasses soaked in sodium phosphate buffer solution revealed the formation of a variety of crystalline structures relevant to the formation of carbonated hydroxyapatite derivatives. According to the NMR data, the concentration of BO₃ units increases at the expense of BO₄ with increasing Nd₂O₃ content. Increasing of (BO₃/BO₄) molar ratio with increasing Nd₂O₃ plays the main role of enhancing the bioactivity of borate glasses. The percentage of BO₃, BO_4, and consequently N₄ fraction (N4 =BO₄/BO₃+BO₄) can simply be determined from the deconvolution process of FTIR and NMR spectra. A scanning electron microscope (SEM) and energy-dispersive x-ray (EDX) evaluation of the microstructures support the existence of crystalline HA after immersion. Both EDX and mapping of the sample after prolonged time intervals point to the homogeneity in the HA distribution of the studied sample.     

Effects of boron oxide composition,structure, and morphology on B4C formation via the SHS process in the B2O3–Mg – C ternary system

This study investigates the formation of B₄C in the B₂O₃–Mg–C ternary system via a magnesiothermic reduction process using two kinds of boron oxide (B₂O₃) ‒ the commercial B₂O₃ and that synthesized from boric acid via the coupled chemical-thermal process. In addition to the raw materials, the products were subjected to XRD, FTIR, SEM, and FESEM analyses to determine the effects of microstructural and morphological properties of boron oxide as an important raw material, on B₄C formation in the combustion synthesis process. For this purpose, powder mixtures of B₂O₃:Mg:C were prepared at a stoichiometric molar ratio of 2:6:1 and compacted into pellets using a uniaxial hydraulic press, which were subsequently subjected to the combustion synthesis process based on the self-propagating high-temperature synthesis (SHS). Finally, the samples thus obtained were leached in an aqueous hydrochloric acid solution. Analysis of the commercial B₂O₃ revealed the presence of large amounts of such by-products as magnesium borate (Mg₃B₂O₆) and magnesium oxide (MgO) along with relatively small amounts of boron carbide after the leaching process, while those obtained for the chemically-thermally synthesized B₂O₃ showed a relatively large amount of B₄C (from micron-sized particles to nanoparticles) together with a remaining carbon phase and very small amounts of magnesium borate as by-products. It can be, therefore, concluded that the changes in chemical composition and introduction of a hydrous HBO₂ phase in the boron oxide in the B₂O₃–Mg–C mixture as well as its varied microstructure, morphology, and particle size have significant effects on the efficiency of B₄C production through the SHS process.     

Optimized structural and mechanical properties of borophosphate glass

A series of phosphate glasses composed of (65-x)P₂O₅–15BaO–5Al₂O₃–5ZnO–10Na₂O-xB₂O₃ (x = 0, 2, 4, 6, and 8 mol%) were successfully prepared using the melt-quenching method. The effects of the addition of boron trioxide (B₂O₃) on the physical, structural, and mechanical properties of the glasses were investigated. As the added content of B₂O₃ increased from 0 to 6 mol%, the glass exhibited increased density and transition temperature, and decreased molar volume, indicating optimization of the glass stability. Raman spectroscopy revealed that the introduction of B₂O₃ transformed the glass from a chain structure to a three-dimensional network structure, which enhanced the chemical stability of the glass by the cross-linking of long phosphate chains with boron ions. Regarding the mechanical properties, when the boron content was 6 mol%, the flexural strength of the glass was 41% higher than that of the undoped boron, while the Vickers hardness and Knoop hardness values increased by 20.58% and 7.05%, respectively, and the fracture toughness was slightly decreased. In general, improving the mechanical properties of phosphate glass is of great significance for increasing the applications of this glass.     

New calcium‐free Na2O–Al2O3–P2O5 bioactive glasses with potential applications in bone tissue engineering

Sodium aluminophosphate glasses were evaluated for their bone repair ability. The glasses belonging to the system 45Na₂O–xAl₂O₃‐(55‐x)P₂O₅, with x = (3, 5, 7, 10 mol%) were prepared by a melt‐quenching method. We assessed the effect of Al₂O₃ content on the properties of Na₂O–Al₂O₃–P₂O₅ (NAP) glasses, which were characterized by density measurements, DSC analyses, solubility, bioactivity in simulated body fluid and cytocompatibility with MG‐63 cells. To the best of our knowledge, this is the first investigation of calcium‐free Na₂O–Al₂O₃–P₂O₅ system glasses as bioactive materials for bone tissue engineering.     

High Fraction of Penta‐Coordinated Aluminum and Gallium in Lanthanum–Aluminum–Gallium Borates

This study is focused on structural changes induced by increasing treatment temperature of sol‐gel–derived La₂O₃?Al₂O₃?Ga₂O₃?5B₂O₃ system. The structure of samples heated for 30 min up to 900°C was investigated by X‐ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and magic‐angle spinning nuclear magnetic resonance (MAS‐NMR) analysis of ²⁷Al, ¹¹B, and ⁷¹Ga nuclei. The vitreous structure is preserved inclusively after 800°C treatment, and starting with 850°C the only crystalline phase evidenced in XRD patterns is of LaAl_2.03B₄O_10.54 type, of La(Al,Ga)_2.03B₄O_10.54 composition. The FTIR results point out the presence of BO₃, AlO₄, and AlO₆, and starting with 800°C treatment also of BO₄ and AlO₅ structural units, but more detailed information related to boron, aluminum, and gallium environments is obtained from the analysis of MAS‐NMR data. These data evidenced in both amorphous xerogels and in crystallized samples a high fraction of penta‐coordinated aluminum and gallium.     

Gel-derived SiO2–CaO–P2O5 bioactive glasses and glass-ceramics modified by SrO addition

The effect of SrO substitution for CaO in two sol–gel glasses with different chemical compositions (mol%) A2Sr: (54−x)CaO–xSrO–6P₂O₅–40SiO₂ and S2Sr: (16−x)CaO–xSrO–4P₂O₅–80SiO₂ (x=0, 1, 3 and 5) stabilized at 700 °C on their structure (XRD, FTIR) and bioactive properties (SBF test) was investigated. Preliminary in vitro tests using human articular chondrocytes of selected A2Sr glass were also conducted. Moreover, the subject of this study was to detect the changes on material properties after heat treatment at 1300 °C. The results show that the effect of strontium substitution on structure, bioactivity and crystallization after treatment at both the above temperatures strongly depends on CaO/SiO₂ molar ratio. The presence of 3–5 mol% of strontium ions creates more expanded glass structure but does not markedly affect crystallization ability after low temperature treatment. Sintering at 1300 °C of A2 type glasses results in crystallization of pseudowollastonite, hydroxyapatite and also Sr-substituted hydroxyapatite for 3–5 mol% of SrO substitution. The increase of strontium concentration in silica-rich materials after sintering leads to appearance of calcium strontium phosphate instead of calcium phosphate. Bioactivity evaluation indicates that substitution of Sr for Ca delays calcium phosphate formation on the materials surface only in the case of silica-rich glasses treated at 700 °C. Calcium-rich glasses, after both temperature treatments, reveals high bioactivity, while crystal size of hydroxyapatite decreases with increasing Sr content. High temperature treatment of high-silica glasses inhibits their bioactivity. Preliminary in vitro tests shows Sr addition to have a positive effects on human articular chondrocytes proliferation and to inhibit cell matrix biomineralization.     

Structure and crystallization of ZnO-B<Subscript>2</Subscript>O<Subscript>3</Subscript>-P<Subscript>2</Subscript>O<Subscript>5</Subscript> glasses

Structure and crystalline behavior of the ternary system ZnO-B₂O₃-P₂O₅ glasses were investigated by means of X-ray diffraction (XRD) and infrared Raman spectra. The research showed that number of the planar [BO₃] units increases with the increase of B₂O₃ content. When the B₂O₃ content is above ≥10 mol %, the relative content of planar [BO₃] units increases rapidly and causes weakening of the glass structure and decrease in the chemical stability. In the crystallized glasses the predominant crystal phase Zn₂P₂O₇ decreases with the increase of B₂O₃ content, while the crystal phase BPO₄ increases with it, which cause the declining of chemical stability and the decrease of thermal coefficients of expansion.     

High niobium oxide content in germanate glasses: Thermal,structural, and optical properties

Niobium alkali germanate glasses were synthesized by the melt‐quenching technique. The ternary system (90‐x)GeO₂–xNb₂O₅–10K₂O forms homogeneous glasses with x ranging from 0 to 20 mol%. Samples were investigated by DSC and XRD analysis, FTIR and Raman spectroscopy, and optical absorption. Structural and physical features are discussed in terms of Nb₂O₅ content. The niobium content increase in the glass network strongly modifies the thermal, structural and optical properties of alkali germanate glasses. DSC, Raman and FTIR analysis suggest niobium addition promotes NbO₆ groups insertion close to GeO₄ units of the glass network. XRD analysis also pointed out that samples containing high niobium oxide contents exhibit preferential niobium oxide‐rich phase after crystallization after heat treatment, which is similar to orthorhombic Nb₂O₅. Absorption spectra revealed high transmission range between 400 nm to 6.2 μm, added to a considerably decreased hydroxyl group content as the addition of niobium in the alkali germanate network. The niobium oxide‐rich phase crystallization process was studied and activation energy was determined, as well as nucleation and crystal growth temperatures and time for obtaining transparent glass‐ceramics.     

Hydroxyapatite forming ability,ion release and antibacterial activity of the melt-derived SiO2–P2O5–Na2O–CaO–F glasses modified by replacing CaO with SrO and ZnO

Since the discovery of 1970s, bioactive glass has been a hot topic of research because of its excellent biological activity, which makes it a material that can repair and replace human bone tissue organs. In this work, the bioactive glasses in the system SiO₂–P₂O₅–Na₂O–CaO–F with different amounts of strontium oxide (SrO) and zinc oxide (ZnO) were prepared by the conventional melt quenching technology. The hydroxyapatite (HA) forming ability, ion release and antibacterial activity of these prepared glasses were investigated and the obtained results illustrated that SrO-doped samples had a better ability to form HA in modified simulated body fluid (MSBF) than ZnO-doped samples. As the immersion time of the sample in MSBF increased, the content of HA phase gradually increased. In the same immersion time, the formation ability of HA and the variation of SrO substitution amount showed a non-linear trend, which is mainly related to the influence of SrO content on the glass network structure. The results of ion concentration showed that the formation of HA was the result of the comprehensive action of various ions in the solution, especially the release rate of Si⁴⁺ ions, which had a direct impact on the formation ability of HA. The antibacterial test illustrated that the difference in antibacterial activity of bacteria solution at different sample concentrations may be related to the high pH environment and the osmotic effects caused by the non-physiological concentration of ions in the solution. The glass sample contained 4 wt% SrO showed the minimum bactericidal concentration at 64 mg/mL. The glass samples prepared in this experiment had good biological activity and antibacterial effect, making them suitable for using in dentistry and orthopedic applications, as well as providing a valuable composition reference for the preparation of bioactive glass with excellent comprehensive properties.     

Studies on novel bioactive glasses and bioactive glass-nano-HAp composites suitable for coating on metallic implants

A series of novel zinc oxide (ZnO) containing bioactive glass compositions in SiO₂-Na₂O-CaO-P₂O₅ system and composite with hydroxyapatite (HAp) nano-particles were developed and applied as coating on Ti-6Al-4V substrates. The bioactive glasses and their composites were also processed to yield dense scaffolds, porous scaffolds and porous bone filler materials. The coating materials and the coatings were characterized and evaluated by different in vitro techniques to establish their superior mechanical properties. The cytotoxicity test of the coating material, porous and dense scaffolds and coated specimens showed non-cytotoxicity, biocompatibility and promising in vitro bioactivity for all tested samples. The dissolution behaviour studies of the bioactive glasses and the composites in simulated body fluid showed promising in vitro release pattern and bioactivity for all tested samples. Addition of nanosized HAp improves mechanical properties of the bioactive glass coating without affecting the in vitro bioactivity.     

Synthesis,Characterization and <Emphasis Type="Italic">In Vitro</Emphasis> Biological Evaluation of Sol-gel Derived Sr-containing Nano Bioactive Glass

In this study, bioactive glass of the type SiO₂–CaO–SrO–P₂O₅ was obtained by the sol-gel processing method and the effects of SrO/CaO substitution on the in vitro biological properties of the synthesized glasses were evaluated. The obtained bioactive glasses were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermal gravimetric analysis (TGA), differentioal scanning caloremetry (DSC) and Brunauer, Emmett and Teller (BET) analyses. The effects of various glass compositions on proliferation and differentiation of osteoblastic cells were also evaluated. The results showed that incorporation of Sr in the obtained glass network did not result in any structural alteration due to the similar role of SrO compared with that of CaO. In vitro experiments with human osteosarcoma cell lines (MG-63) indicated that bioactive glass incorporating 5 mol % in the composition revealed optimal cell proliferation and alkaline phosphatase (ALP) activity. Our results ascertained this material to be non-toxic and compatible for the proposed work in segmental defects in the rabbit model in vivo.     

In vitro evaluation and mechanical studies of MgO added borophosphate glasses for biomedical applications

The objective of current research is to evaluate the bioactive and tribological properties of the MgO doped borophosphate glass system. The glass system constituted of 40% B₂O₃ - (20-x) % CaO – 25% Li₂O – 15% P₂O₅ – x % MgO (mol%), x = 0, 0.5, 01, 02, 03 and synthesized using the melt quench technique. In-vitro bioactivity was determined using simulated body fluid (SBF) at 37 °C with time intervals of 7, 14 and 21 days. Hydroxyapatite (HA) layer formation was assessed using characterization techniques like XRD, FTIR and FESEM-EDS for structural, functional and morphological analysis respectively. The effect of MgO content on microhardness and tribological properties was studied by making cylindrical shaped glass samples. MTT assay was performed for various doses (62.5–1000 μg/ml) of glass dilutions using MG-63 cell line. In-vitro bioactivity showed higher Ca/P ratio with increase in MgO content after 21 days of immersion. MgO content seemed to promote degradation of glass due to formation of open structure in glass network. Borophosphate glass having 3% MgO exhibited the highest hardness value of 5.79(±0.08) GPa with minimum specific wear rate of 1.86 × 10^?11 and 1.38 × 10^?11 m³/Nm at a load of 15 N and 20 N respectively. MTT assay demonstrated the non-toxic behaviour of glass samples even at a higher dose level of 1000 μg/ml which confirmed its biocompatible behaviour. The study suggests that produced MgO doped borophosphate glass exhibits essential characteristics of bioactive materials and hence could be effective in bone filling and wound healing applications.     

Structure and crystallization behaviour of some MgSiO3-based glasses

We report on the structure and crystallization behaviour of four enstatite based glasses. Two glasses with nominal compositions of Y_0.125Mg_0.875Si_0.875B_0.125O₃ and Y_0.125Mg_0.725Ba_0.15Si_0.875B_0.125O₃ were prepared as parent glasses while the other two glasses were derived by the addition of 8 wt.% Al₂O₃ to the parent glass compositions, respectively. Structural features of the glasses were accessed by Fourier transform infrared spectroscopy (FTIR). Non-isothermal crystallization kinetics and thermal stability of Al₂O₃-free glasses were studied using differential scanning calorimetry (DSC). It has been shown that these glasses exhibit higher activation energy of viscous flow and are prone to surface crystallization. Activation energy of crystallization decreases with the addition of BaO in the glasses. Crystallization behaviour of all the experimental glasses in the temperature range of 800–1000 °C was followed by X-ray diffraction (XRD) and FTIR. Clinoenstatite and orthoenstatite were the major crystalline phases in the BaO-free glass-ceramics while BaO-containing compositions featured the early formation and stabilization of protoenstatite.     

Effect of Gamma Irradiation on Structural and Optical Investigations of Borosilicate Glass Doped Yttrium Oxide

The structural, physical, and optical properties of prepared glass samples of the composition formula 30SiO₂-(40-x)B₂O₃-20Na₂O-10Al₂O₃-xY₂O₃, where x = 0, 1, 5, 7 (wt%) were studied before and after gamma irradiation using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and UV-visible spectroscopy. The optical absorption spectra of study glasses were recorded in the UV/visible range of 200–900 nm. The optical band gap energies were calculated from absorption data. These results show that E_opt decreases with increasing concentration of Y₂O₃. The changes occurring in the optical parameters obtained from absorption spectra before and after irradiation have been referred to irradiation induced structural defects and compositional changes.     

Thermal properties and formation mechanism of h‐BN nanoneedles synthesized via carbothermic reduction reaction

Hexagonal boron nitride (BN) was synthesized through the carbothermic reduction reaction (CRR) of boric acid using lactose as a carbon source under the nitrogen atmosphere at 1500^°C for 3 hours. The boron/carbon (B/C) molar ratio was controlled during the CRR, and the produced samples were investigated by XRD diffraction pattern, FTIR analysis, and Raman spectra. Boron carbide (B₄C) was formed in samples that have a higher carbon content, in addition to boron nitride. While boron nitride pure sample was produced from lower carbon content samples. Formation of B₄C was found to depend on the B/C molar ratio. The morphology of the produced powder was also investigated by SEM and TEM, which revealed that the samples consist of nanoneedles of BN and hexagonal particles of B₄C. The vapor‐solid (VS) reaction mechanism was processed greatly with increasing boron amount, producing boron nitride nanoneedles, which compete with the liquid‐solid (LS) reaction mechanism. The physicochemical properties of the produced samples were studied by DTA, UV, PL, and AC impedance measurements, and revealed that the samples are promising to many proper applications.     

Bismuth and lead oxides codoped boron phosphate glasses for Faraday rotators

New magneto-optical vitreous materials were obtained by melting-quenching technique comprising wet route raw materials preparation. The glass has the following composition in oxide mol. %: 10 Li₂O, 9 Al₂O₃, 5 ZnO, (35; 20; 50) B₂O₃, (35; 50; 20) P₂O₅, 3 Bi₂O₃, 3 PbO, phosphorus and boron oxide being the vitreous network formers. It was also prepared a similar reference glass composition but without Bi₂O₃ and PbO. Optical and structural characterization by ultraviolet-visible (UV–Vis), Fourier Transform Infrared (FTIR) and Raman Spectroscopy of the bulk glasses showed a transmission over 90%, metaphosphate structure of glass together with Q² boron oxide units and P–O?B bonds. The mechanical parameters, hardness (H), Young's modulus (E) and fracture toughness (K_IC) of boron phosphate glasses, evaluated by micro- and nanoindentation techniques, demonstrated mostly higher values in comparison with those for alumino-phosphate glasses due to mixed boro-phosphate network. Thermal behavior was investigated by Differential Scanning Calorimetry (DSC) putting in evidence the vitreous transition temperature which decreases with about 45 °C when Bi and Pb oxides were added and two crystallization effects. The diamagnetic character of a highly transparent Bi and Pb oxide co-doped boron phosphate glass was confirmed by ellipsometry, and the glass presented high magneto-optical properties at the top of the commercial bulk products.