Bioactive properties for borate and borosilicate glass: An in vitro study

We have investigated the local structure of alkali atoms in mixed alkali silicate, borate, and borosilicate glasses, which contain Cs+ and Na+, using strong magnetic field magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy of 133Cs and 23Na. The spectral peaks of 133Cs in borosilicate (Si:B = 1:1) and Si-rich borosilicate (Si:B = 2:1) glasses shifted to upfield with increasing Cs+/(Na+ + Cs+) ratio, which implies that the coordination number of Cs+ decreased as in the case of silicate and borate glasses. However, this trend was not observed in the 23Na spectra of either borosilicate glass. This might be because the chemical shift of 23Na in borosilicate glass is strongly affected by nearby species such as Si or B, and not by the coordination number of Na+.

Compositional modification of bioactive 45S5 glass was performed by replacing the SiO 2 content partially or fully with B 2 O 3 to form borosilicate and borate glasses. Its effect on the conversion of the glass to hydroxyapatite (HA) in dilute phosphate solution was investigated using kinetic, chemical, and structural techniques. A higher B 2 O 3 content of the glass produced an increase in the conversion rate and a decrease in the pH of the solution. Particles of the borate glass (150-300 μm) were fully converted within 4 days, yielding pseudomorphic HA particles with a nanoscale structure. Silicate and borosilicate glass particles were only partially converted even after 70 days, forming a composite structure consisting of a SiO 2 -rich core surrounded by a HA layer. Regardless of the composition, all the Na and B present in the glass particles dissolved into solution, but the Ca either reacted to from HA or remained in the unconverted SiO 2 -rich core. The results are applicable to the development of bioaetive glasses with controllable conversion rates to HA, which may provide a novel class of scaffold materials for bone tissue engineering.

Dissolution of borate and borosilicate bioactive glasses and the influence of ion (Zn, Cu) doping in different solutions

In borosilicate glasses, not only the question of the fraction of four- and three-fold coordinated boron deserves special consideration, but also the connectivity of the tetrahedral and trigonal borate groups with each other and with the silicate network. Older structural studies and models of borate and borosilicate glasses often invoke an avoidance rule in the context that negatively charged borate tetrahedra will not be directly linked in glasses. This statement is analogous to the Loewenstein rule which was postulated for aluminate tetrahedra in zeolites. However, contrary to aluminium, directly linked [BØ 4 ] – tetrahedra are known to exist in natural minerals such as danburite, and not surprisingly, they also occur in glasses (Ø denotes bridging oxygen atoms). Raman spectroscopy confirms, for example, the presence of borate rings consisting of one neutral [BO 3 ] 0 trigonal and two charged [BØ 4 ] – tetrahedral units. Four membered danburite-like rings consisting of two linked silicate and two linked borate tetrahedra were also identified by their Raman band at 630 cm –1 in glasses with higher Na 2 O fractions. Additionally, borate rings consisting of three tetrahedral orthoborate units, [BØ 2 O 2 ] 3– , were identified by vibrational spectroscopy in borate glasses containing high levels of MnO or Eu 2 O 3 . The presence of such rings strengthens the glass network and results in a second boron oxide anomaly as evidenced by an increase in the glass transition temperature at very high metal oxide contents. Two dimensional NMR experiments in alkali poor borosilicate glasses reveal a preference of [BØ 4 ] – tetrahedra to bond to borate rather than silicate entities of the glass network. For these low alkaline glasses, R<0·5 (R is the fraction Na 2 O:B 2 O 3 ), B 4 –O–Si links are formed in quenched glasses but tend to disappear after annealing, whereas the remaining connections between the borate and silicate sub-networks involve predominantly B 3 –O–Si linkages.

Bioactive glasses with controllable conversion rates to hydroxyapatite (HA) may provide a novel class of scaffold materials for bone tissue engineering. The objective of the present work was to comprehensively characterize the conversion of a silicate bioactive glass (45S5), a borate glass, and two intermediate borosilicate glass compositions to HA in a dilute phosphate solution at 37 degrees Celsius. The borate glass and the borosilicate glasses were derived from the 45S5 glass by fully or partially replacing the SiO(2) with B(2)O(3). Higher B(2)O(3) content produced a more rapid conversion of the glass to HA and a lower pH value of the phosphate solution. Whereas the borate glass was fully converted to HA in less than 4 days, the silicate (45S5) and borosilicate compositions were only partially converted even after 70 days, and contained residual SiO(2) in a Na-depleted core. The concentration of Na(+) in the phosphate solution increased with reaction time whereas the PO(4) (3-) concentration decreased, both reaching final limiting values at a rate that increased with the B(2)O(3) content of the glass. However, the Ca(2+) concentration in the solution remained low, below the detection limit of atomic absorption, throughout the reaction. Immersion of the glasses in a mixed solution of K(2)HPO(4) and K(2)CO(3) produced a carbonate-substituted HA but the presence of the K(2)CO(3) had little effect on the kinetics of conversion to HA. The kinetics and mechanisms of the conversion process of the four glasses to HA are compared and used to develop a model for the process.

This study is aimed at the comparative analysis of structure sensitive properties of alkali borate and borosilicate glasses and crystals. Among the properties under consideration are density and refractive index. The comparison of physical properties between crystals and glasses considers the dependence on alkali content and the size of the alkali cation. New experimental data on density and refractive index of potassium and rubidium borate and borosilicate glasses are presented. The mass density measurements were performed by employing the method of hydrostatic weighing. The refractive index measurements were carried out on a polarization microscope with a series of immersion liquids, using the Becke line method. The compared crystal density data were calculated from the crystal structures.

Tuning the structural and optical properties in cobalt oxide-doped borosilicate glasses

Topographic surface studies of optical glasses after they come in contact with a moist atmosphere are carried out by white-light interference microscopy. It is shown that the roughness changes are minimal in silicate glasses and maximal in borosilicate glasses, while borate glasses occupy an intermediate position. The increase of the roughness in silicate glasses is caused by the growth of peaks on the surface and in borosilicate and borate glasses by the growth of both peaks and valleys.

To assess in vitro the effect of two novel phase separated borosilicate glasses (PSBS) in the system SiO2 -B2 O3 -K2 O-CaO-Al2 O3 on dental pulp cells; and to compare their bioactivity and mechanical properties to a conventional fluoroaluminosilicate glass ionomer cement namely FUJI IX. The cytocompatibility assessment of the two novel borosilicate glasses, one without alumina (PSBS8) and one containing alumina (PSBS16), was performed on cultured primary human pulp cells. Alamar blue assay was used to assess cell metabolic activity and cell morphology was evaluated by confocal imaging. The bioactivity in Stimulated Body Fluid was also evaluated after 1 and 3 weeks of immersion using SEM-EDX analysis. Vickers microhardness and flexural strength were assessed after incorporating the glass particles into a commercial glass ionomer cement (GIC) liquid containing both polyacrylic and polybasic carboxylic acid. The data revealed that the two borosilicate glasses enhanced cell viability ratios at all-time points in both direct and indirect contact assays. After 3 days of contact, PSBS8 without alumina showed higher viability rate (152%) compared to the PSBS16 containing alumina (145%) and the conventional glass ionomer particles (117%). EDX analysis confirmed an initial Ca/P ratio of 2.1 for 45S5K and 2.08 for PSBS8 without alumina after 3 weeks of immersion. The cement prepared using PSBS8 showed significantly higher Vickers hardness values (p=.001) than that prepared using PSBS16 (46.6 vs. 36.7 MPa). After 24 h of maturation, PSBS8 (without alumina) exhibited a flexural strength of 12.9 MPa compared to a value of 16.4 MPa for the commercial control. PSBS8 without alumina had a higher strength than PSBS16 with alumina, after 1 and 7 days of maturation (p=.001). The present in vitro results demonstrated that the borosilicate bioactive glass without alumina enhanced pulp cell viability, spreading and acellular bioactivity better than the conventional GIC and the experimental borosilicate glass containing alumina.

Non-bridging oxygens in borate glasses: characterization by 11B and 17O MAS and 3QMAS NMR

Understanding the role of post-indentation recovery on the hardness of glasses: Case of silica, borate, and borosilicate glasses

Various borate and borosilicate glasses doped with Tb 3+ in a broad concentration range of 1 × 10 18 to 1 × 10 21 Tb 3+ per cm 3 (~0.01 to 10 wt% Tb 2 O 3 ) were prepared and characterized by different methods. Static fluorescence excitation and emission spectra of Tb 3+ in the ultraviolet‐visible range were recorded. The fluorescence decay rates of the green emission were measured and fitted. Different lifetimes dependent on different local sites of Tb 3+ ions were detected. To identify these different local sites crystalline terbium borate, TbBO 3 , was prepared and investigated. X‐ray diffraction (XRD) and electron microscopy measurements were used. Very strong clustering effects of Tb 3+ ions were detected as preliminary stage of phase separation by formation of a very short decay rate in optically clear borate containing glasses with low optical basicity. In glass samples with phase separation, the Tb 3+ ions were accumulated in the phase with higher optical basicity. The local sites of the Tb 3+ ions in the clusters induce a short lifetime which is similar to the lifetime of crystalline TbBO 3 . Only mono‐exponential decay curves for Tb 3+ fluorescence were detected in sodium borosilicate glass with high optical basicity, and in zinc borate glass, without tendency to phase separation.

Lithium-ion conducting borate glasses are suitable for solid-state batteries as an interfacial material between a crystalline electrolyte and an electrode, thanks to their superior formability. Chlorine has been known to improve the electron conductivity of borate glasses as a secondary anion. To examine the impact of chlorine on lithium dynamics, molecular dynamics (MD) simulations were performed with a machine-learning interatomic potential (MLIP). The accuracy of the MLIP in modeling chlorine-doped lithium borate (LBCl) and borosilicate (LBSCl) glasses was verified by comparing with available experimental data on density, neutron diffraction S(q), and glass transition temperatures (Tg). While the MLIP-MD simulations underestimated the density when an isobaric-isothermal (NPT) ensemble was used, the glass models relaxed using the NPT ensemble after a melt-quench simulation employing a canonical (NVT) ensemble possessed reasonable density. The LBCl and LBSCl glass models exhibited increased lithium ion diffusion, and the ions were found to travel longer distances with an increase in the chlorine content. According to the structural analyses, it was observed that chlorine ions primarily interacted with lithium ions rather than the network formers. Consequently, lithium ions that interacted with a higher amount of chlorine showed a moderate increase in mobility. In summary, the MLIP demonstrated reasonable accuracy in modeling chlorine-containing borate glasses and enabled the investigation of the effect of chlorine on electron conductivity. In contrast, the first sharp diffraction peaks in S(q) deviated from the experimental diffractions, suggesting that additional efforts are required to accurately model the middle-range structure of the glasses.

Spectral hole burning in Sm 2+-doped alkaliborate glasses and Tb 3+-doped silicate and borate glasses

Predicting boron coordination in multicomponent borate and borosilicate glasses using analytical models and machine learning