The role of fluoride in the nano-heterogeneity of bioactive glasses

Fluoride-containing bioactive phospho‐silicate glasses have recently attracted interest for dental applications, particularly as remineralising additives in dentifrices, and are potentially attractive for bone regeneration, particularly in patients suffering from osteoporosis. The incorporation of fluoride into phospho­‐silicate glasses is also attractive from a structural viewpoint: Fluoride complexes modifier ions rather than binding to the silicate network, and it thereby adds a significant ionic contribution to the average character of chemical bonds in the system. Molecular dynamics simulations have suggested that this also results in the formation of nano-­eterogeneities. In this paper, we review the current knowledge on the structural role of fluoride in bioactive glasses, with a particular focus on inhomogeneities on a nano-­‐scale

Glass as a biomaterial: strategies for optimising bioactive glasses for clinical applications

Bioactive glasses were the first synthetic materials to bond to human body tissue, making them ideal for replacing and regenerating bone. Since their first development over half a century ago, many new bioactive glass compositions have been developed for medicine and dentistry. This paper looks at different design strategies employed over the years as well as aspects of glass structure relevant to optimising bioactive glass performance. Statistical compositional series allowed for getting an overview of various compositions and their properties. Since the improvement of structural analysis techniques, particularly solid-state NMR, we can directly relate several bioactive glass properties to the atomic structure, i.e. the spatial arrangement of atoms. Such detailed understanding of the impact of composition and structure on bioactive glass properties enables us to minimise the number of compositions in preclinical and clinical tests needed to confirm positive tissue responses

Glass as a biomaterial: strategies for optimising bioactive glasses for clinical applications

Bioactive glasses were the first synthetic materials to bond to human body tissue, making them ideal for replacing and regenerating bone. Since their first development over half a century ago, many new bioactive glass compositions have been developed for medicine and dentistry. This paper looks at different design strategies employed over the years as well as aspects of glass structure relevant to optimising bioactive glass performance. Statistical compositional series allowed for getting an overview of various compositions and their properties. Since the improvement of structural analysis techniques, particularly solid-state NMR, we can directly relate several bioactive glass properties to the atomic structure, i.e. the spatial arrangement of atoms. Such detailed understanding of the impact of composition and structure on bioactive glass properties enables us to minimise the number of compositions in preclinical and clinical tests needed to confirm positive tissue responses

Effect of TiO2 addition on structure, solubility and crystallisation of phosphate invert glasses for biomedical applications

NOTICE: this is the author’s version of a work that was accepted for publication in JOURNAL OF NON-CRYSTALLINE SOLIDS. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in JOURNAL OF NON-CRYSTALLINE SOLIDS, [VOL 356, ISSUE 44-49, (2001)] DOI: 10.1016/j.jnoncrysol.2010.03.02

Fluorine loss determination in bioactive glasses by laser‐induced breakdown spectroscopy (LIBS)

Fluoride‐containing bioactive glasses and glass‐ceramics in the SiO 2 ‐P 2 O 5 ‐CaO‐CaF 2 system are of great interest for dental applications, where the precipitation of fluorapatite supports tooth remineralization. Fluorine quantification in those glasses is key to estimate thermal properties and crystallization tendency. This work presents a study on fluorine determination by laser induced breakdown spectroscopy (LIBS) in four melt‐derived glass powders with varying P 2 O 5 concentrations. LIBS enables fluorine quantification with a reduced analysis time, minimal to no sample preparation, and high spatial resolution. The fluorine calibration curve was obtained from CaF 2 and SiO 2 mixtures as reference samples, and the fluorine loss upon glass melting has been determined as a function of P 2 O 5 content. The P 2 O 5 ‐free glass shows the lowest fluorine loss (13%), with HF volatilization likely being responsible for the loss. By contrast, the glass with the highest P 2 O 5 content (11.33 wt%) exhibits the largest fluorine loss (55%), owing to additional mechanisms involving the volatilization of phosphorus species like POF 3

Fluoride-containing bioactive glasses: Effect of glass design and structure on degradation, pH and apatite formation in simulated body fluid

NOTICE: this is the author’s version of a work that was accepted for publication in Acta Biomaterialia. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Acta Biomaterialia, [VOL 6, ISSUE 8, (2010)] DOI: 10.1016/j.actbio.2010.01.04

Bioactive glass–ceramics containing fluorapatite, xonotlite, cuspidine and wollastonite form apatite faster than their corresponding glasses

Crystallisation of bioactive glasses has been claimed to negatively affect the ion release from bioactive glasses. Here, we compare ion release and mineralisation in Tris–HCl buffer solution for a series of glass–ceramics and their parent glasses in the system SiO2–CaO–P2O5–CaF2. Time-resolved X-ray diffraction analysis of glass–ceramic degradation, including quantification of crystal fractions by full pattern refinement, show that the glass–ceramics precipitated apatite faster than the corresponding glasses, in agreement with faster ion release from the glass–ceramics. Imaging by transmission electron microscopy and X-ray nano-computed tomography suggest that this accelerated degradation may be caused by the presence of nano-sized channels along the internal crystal/glassy matrix interfaces. In addition, the presence of crystalline fluorapatite in the glass–ceramics facilitated apatite nucleation and crystallisation during immersion. These results suggest that the popular view of bioactive glass crystallisation being a disadvantage for degradation, apatite formation and, subsequently, bioactivity may depend on the actual system study and, thus, has to be reconsidered

Nano-imaging confirms improved apatite precipitation for high phosphate/silicate ratio bioactive glasses

Bioactive glasses convert to a biomimetic apatite when in contact with physiological solutions; however, the number and type of phases precipitating depends on glass composition and reactivity. This process is typically followed by X-ray diffraction and infrared spectroscopy. Here, we visualise surface mineralisation in a series of sodium-free bioactive glasses, using transmission electron microscopy (TEM) with energy-dispersive X-ray spectroscopy (EDXS) and X-ray nano-computed tomography (nano-CT). In the glasses, the phosphate content was increased while adding stoichiometric amounts of calcium to maintain phosphate in an orthophosphate environment in the glass. Calcium fluoride was added to keep the melting temperature low. TEM brought to light the presence of phosphate clustering and nearly crystalline calcium fluoride environments in the glasses. A combination of analytical methods, including solid-state NMR, shows how with increasing phosphate content in the glass, precipitation of calcium fluoride during immersion is superseded by fluorapatite precipitation. Nano-CT gives insight into bioactive glass particle morphology after immersion, while TEM illustrates how compositional changes in the glass affect microstructure at a sub-micron to nanometre-level

Impact of borosilicate bioactive glass scaffold processing and reactivity on in-vitro dissolution properties

In this study, bulk borosilicate glasses and 3D scaffolds (processed by the burn-off technique and by robocasting) were synthesized to investigate the impact of the manufacturing method, glass composition and preincubation time on in vitro dissolution and cell response. The studied compositions are based on commercial bioactive glass S53P4 (BonAlive) where 12.5% SiO2 has been replaced by B2O (labelled B12.5), and part of the CaO is replaced with MgO and SrO (labelled B12.5-Mg-Sr). First, the impact of the processing and glass composition, on the dissolution rate, was assessed. As expected, scaffolds were found to exhibit faster dissolution, due to the increased surface area, when compared to the bulk glass. Furthermore, the 3D printed scaffolds were found to dissolve faster than the burn-off scaffolds. Moreover, scaffolds made from B12.5-Mg-Sr glass composition exhibited slower ion release and precipitation of calcium phosphate (CaP) layer, when compared to B12.5, due to the stabilizing effect of Mg and Sr. Finally, dynamic condition produces lower ion releases that static condition and could be more optimal for in vitro cell growth. Secondly, in culture with murine MC3T3-E1 cells, it was shown that 3 days preincubation would be optimal to decrease the burst of ions that is known to lead to cell death. However, it was found that MC3T3-E1 survived and proliferated only in presence of B12.5-Mg-Sr scaffolds. Finally, it was shown that despite scaffolds having different porosities, they had no significant difference on human adipose-derived stem cells (hADSCs) survival. This manuscript brings new information on 1) the impact of material design (porosity) and composition on dissolution kinetic sand reactivity, 2) the impact of static vs dynamic testing on in-vitro dissolution and 3) the impact of materials’ pre-incubation on cell behavior.publishedVersionPeer reviewe