Boron substitution in silicate bioactive glass scaffolds to enhance bone differentiation and regeneration

Commercially available bioactive glasses (BAGs) are exclusively used in powder form, due to their tendency to crystallize. Silicate BAG 1393 was developed to allow fiber drawing and scaffold sintering, but its slow degradation limits its potential. To enable scaffold manufacturing while maintaining glass dissolution rate close to that of commercially available BAGs, the borosilicate glass 1393B20 was developed. This study investigates the potential of 1393B20 scaffolds to support bone regeneration and mineralization in vitro and in vivo, in comparison to silicate 1393. Both scaffolds supported human adipose stem cells proliferation, either in direct contact for the 1393, or mainly around for the 1393B20. Similarly, both BAGs induced osteogenesis and angiogenesis in vitro, with a better pro-angiogenic influence of the 1393B20. In addition, these scaffolds supported bone regeneration and osteoclast/osteoblast activity in vivo in critical-sized rat calvarial defect. Nevertheless, mineralization and collagen formation were significantly enhanced for the 1393B20, at 3-months post-implantation, assigned to faster and more complete dissolution of the scaffolds. Thus, 1393B20 demonstrates greater promise for bone tissue engineering certainly due to its time-controlled release of boron and silicon. STATEMENT OF SIGNIFICANCE: Bioactive glasses (BAGs) show great promise in bone tissue engineering as they effectively bond with bone tissue, fostering integration and regeneration. Silicate BAG 1393 was developed to allow fiber drawing and scaffold sintering, but its slow degradation limits its potential. To enable scaffold manufacturing while maintaining glass dissolution rate close to that of commercially available BAGs, the borosilicate glass 1393B20 was developed. Both BAGs induced osteogenesis and angiogenesis in vitro, with a better pro-angiogenic influence of the 1393B20. The presence of boron in the 1393B20 enhanced mineralization and collagen formation in vivo compared to 1393, probably due to its faster dissolution rate. Here, 1393B20 demonstrated greater promise for bone tissue engineering compared to the well-known 1393 BAG.

A novel injectable boron doped-mesoporous nano bioactive glass loaded-alginate composite hydrogel as a pulpotomy filling biomaterial for dentin regeneration

BACKGROUND

Different materials have been used as wound dressings after vital pulp therapies. Some of them have limitations such as delayed setting, difficult administration, slight degree of cytotoxicity, crown discoloration and high cost. Therefore, to overcome these disadvantages, composite scaffolds have been used in regenerative dentistry. This study aims to construct and characterize the physicochemical behavior of a novel injectable alginate hydrogel loaded with different bioactive glass nanoparticles in various concentrations as a regenerative pulpotomy filling material.

METHODS

Alginate hydrogels were prepared by dissolving alginate powder in alcoholic distilled water containing mesoporous bioactive glass nanoparticles (MBG NPs) or boron-doped MBG NPs (BMBG NPs) at 10 and 20 wt% concentrations. The mixture was stirred and incubated overnight in a water bath at 50 0 C to ensure complete solubility. A sterile dual-syringe system was used to mix the alginate solution with 20 wt% calcium chloride solution, forming the hydrogel upon extrusion. Then, constructed hydrogel specimens from all groups were characterized by FTIR, SEM, water uptake percentage (WA%), bioactivity and ion release, and cytotoxicity. Statistical analysis was done using One-Way ANOVA test for comparisons between groups, followed by multiple pairwise comparisons using Bonferroni adjusted significance level (p < 0.05).

RESULTS

Alginate/BMBG loaded groups exhibited remarkable increase in porosity and pore size diameter [IIB1 (168), IIB2 (183) (µm)]. Similarly, WA% increased (~ 800%) which was statistically significant (p < 0.05). Alginate/BMBG loaded groups exhibited the strongest bioactive capability displaying prominent clusters of hydroxyapatite precipitates on hydrogel surfaces. Ca/P ratio of precipitates in IIA2 and IIB1 (1.6) were like Ca/P ratio for stoichiometric pure hydroxyapatite (1.67). MTT assay data revealed that the cell viability % of human gingival fibroblast cells have declined with increasing the concentration of both powders and hydrogel extracts in all groups after 24 and 48 h but still higher than the accepted cell viability % of (˃70%).

CONCLUSIONS

The outstanding laboratory performance of the injectable alginate/BMBGNPs (20 wt%) composite hydrogel suggested it as promising candidate for pulpotomy filling material potentially enhancing dentin regeneration in clinical applications.

In vitro biomineralization potential in simulated wound fluid and antibacterial efficacy of biologically-active glass nanoparticles containing B2O3/ZnO

In the present study, SiO₂-CaO-B₂O₃-ZnO (SCBZ), SiO₂-CaO-B₂O₃ (SCB), SiO₂-CaO-ZnO (SCZ) and SiO₂-CaO (SC) silicate-based glasses were synthesized by the sol-gel method to elucidate the influence of B₂O₃ and ZnO substitution on glass characteristics aiming to further use in wound healing applications. The amorphous nature, spherical-shaped morphology and nano-sized primary particles of glasses were revealed by XRD and SEM analysis. Moreover, investigating the antibacterial activity of glasses against E.coli and S.aureus bacteria indicated the improved antibacterial properties of SCBZ glass against both bacterial strains compared with SCB and SCZ glasses. Assessment of ion release revealed that the incorporation of zinc induces a more stable glass network with a lower tendency to dissolution contrary to the incorporation of boron, which facilitated the dissolution of glass by the formation of more reactive SiOB and BO bonds. Glasses were immersed in Simulated Wound Fluid (SWF) to predict their mineralization susceptibility. Morphological studies and FTIR analysis showed the formation of cauliflower-like hydroxy-carbonated apatite on the surface of SCB and SC glasses after 14 days. In contrast, the presence of Zn in SCBZ and SCZ glasses inhibited the formation of crystalline apatite and induced the deposition of spherical-shaped amorphous apatite. Our study suggests that the co-incorporation of B and Zn in SCBZ glass make this material a potential multifunctional candidate for accelerating the healing of skin wounds.

Vanadium Oxidation States and Structural Role in Aluminoborosilicate Glasses: An Integrated Experimental and Molecular Dynamics Simulation Study

Vanadium-containing glasses have aroused interest in several fields such as electrodes for energy storage, semiconducting glasses, and nuclear waste disposal. The addition of V₂O₅, even in small amounts, can greatly alter the physical properties and chemical durability of glasses; however, the structural role of vanadium in these multicomponent glasses and the structural origins of these property changes are still poorly understood. We present a comprehensive study that integrates advanced characterizations and atomistic simulations to understand the composition-structure-property relationships of a series of vanadium-containing aluminoborosilicate glasses. UV-vis spectroscopy, X-ray photoelectron spectroscopy, and X-ray absorption near-edge structure (XANES) have been used to investigate the complex distribution of vanadium oxidation states as a function of composition in a series of six-component aluminoborosilicate glasses. High-energy X-ray diffraction and molecular dynamics simulations were performed to extract the detailed short- and medium-range atomistic structural information such as bond distance, coordination number, bond angle, and network connectivity, based on recently developed vanadium potential parameters. It was found that vanadium mainly exists in two oxidation states: V⁵⁺ and V⁴⁺, with the former being dominant (∼80% from XANES) in most compositions. V⁵⁺ ions were found to exist in 4-, 5-, and 6-fold coordination, while V⁴⁺ ions were mainly in 4-fold coordination. The percentage of 4-fold-coordinated boron and network connectivity initially increased with increasing V₂O₅ up to around 5 mol % but then decreased with higher V₂O₅ contents. The structural role of vanadium and the effect on glass structure and properties are discussed, providing insights into future studies of sophisticated structural descriptors to predict glass properties from composition and/or structure and aiding the formulation of borosilicate glasses for nuclear waste disposal and other applications.

A modified random network model for P2O5-Na2O-Al2O3-SiO2 glass studied by molecular dynamics simulations

We investigated the short- and medium-range structural features of sodium aluminosilicate glasses with various P₂O₅ (0–7 mol%) content and Al/Na ratios ranging from 0.667 to 2.000 by using molecular dynamics simulations. The local environment evolution of network former cations (Si, Al, P) and the extent of clustering behavior of modifiers (Na⁺) is determined through pair distribution function (PDF), total correlation function (TDF), coordination number (CN), Q_xⁿ distribution and oxygen speciation analysis. We show that Al–O–P and Si–O–Al linkage is preferred over other connections as compared to a random model and that Si–O–Si linkage is promoted by the P₂O₅ addition, which is related to structural heterogeneity and generates well-separated silicon-rich and aluminum–phosphorus-rich regions. Meanwhile, due to the relatively high propensity of Al to both Si and P, heterogeneity can be partly overcome with high Al content. A small amount of Si–O–P linkages have been detected at the interface of separated regions. Clustering of Na⁺ is also observed and intensified with the addition of P₂O₅. Based on the simulated structural information, a modified random network model for P₂O₅-bearing sodium aluminosilicate glass has been proposed, which could be useful to optimize the mobility of sodium ions and design novel functional glass compositions.

(A) A modified structural model proposed for P₂O₅-bearing sodium aluminosilicate glasses. (B) Degree of preferred connection (DPC) of different T–O–T network linkage for LAP, MAP and HAP glass compositions with various P₂O₅ content.

Estimation of TiO2-FeO-Na2O slag viscosity through molecular dynamics simulations for an energy efficient ilmenite smelting process

Along with the increasing demand for the TiO2 pigment, the ilmenite smelting process has also become significant because it can utilize both rock- and sand-type ilmenite. However, due to the high liquidus temperature of the TiO2 slag system, the smelting process is highly energy consuming. In the present study, the viscosity of molten ilmenite slag was estimated using molecular dynamic simulations at a high temperature to achieve an appropriate and efficient slag design. To verify the validity of the simulation technique, experimental measurements were performed in parallel and their results were compared. The effects of FeO and Na2O addition on viscosity of TiO2 slag were also investigated. The addition of Na2O as a flux enhanced the ilmenite smelting process by not only lowering the liquidus temperature but also slowing the drastic viscosity increase. Statistical information obtained from the molecular dynamic simulations revealed a three-dimensional TiO6 octahedral network structure. The relationship between viscosity and structural change with varying FeO and Na2O concentrations was explored considering the coordination number of Ti and various bonding types.

Structure and Stability of High CaO- and P2O5-Containing Silicate and Borosilicate Bioactive Glasses

The present work elucidates about the structure of bioactive glasses having chemical compositions expressed as (mol %) (50.0 - x)SiO₂-xB₂O₃-9.3Na₂O-37CaO-3.7P₂O₅, where x = 0.0, 12.5, 25, and 37.5, and establishes a correlation between the structure and thermal stability. The structural modifications in the parent boron-free glass (B0) with the gradual substitutions of B₂O₃ for SiO₂ are assessed by Raman and ²⁹Si, ³¹P, ¹¹B, and ²³Na magic angle spinning (MAS)-nuclear magnetic resonance (NMR) spectroscopies. The structural studies reveal the presence of Q_Si² and Q_Si³ structural units in both silicate and borosilicate glasses. However, Q_Si⁴(3B) units additionally form upon incorporating B₂O₃ in B0 glass. B-containing silicate glasses exhibit both three-coordinated boron (B^III) and four-coordinated boron (B^IV) units. The ³¹P MAS-NMR studies reveal that the majority of phosphate species exist as isolated orthophosphate (Q_P⁰) units. The incorporation of B₂O₃ in B0 glass increases the cross-linking between the SiO₄ and BO₄ structural units. However, incorporation of B₂O₃ lowers the glass thermal stability (ΔT), as shown by differential scanning calorimetry. Although both silicate and borosilicate glasses exhibit good in vitro apatite-forming ability and cell compatibility, the bactericidal action against Escherichia coli bacteria is more evident in borosilicate glass in comparison to silicate base glass. The controlled release of (BO₃)^3- ions from boron-modified bioactive glasses improves both the cell proliferation and the antibacterial properties, making them promising for hard tissue engineering applications.