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NMR, shows how with increasing phosphate content in the glass, precipitation of calcium fluoride during immersion is superseded by fluorapatite precipitation.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.
In this work the influence of thermal treatment conditions on crystallization of a sol‐gel‐derived 45S5 bioactive glass was evaluated using DSC, XRD, TEM, EDX, and X‐ray nanocomputed tomography ...(nano‐CT). Temperature and time of the thermal treatment strongly influence the composition of the crystalline phases. At the onset of the glass transition temperature (600°C), combeite crystallizes as the main phase along with a calcium silicate‐phosphate phase, which decomposes into rhenanite from 2 hours of thermal treatment at this temperature. At the crystallization temperature (700°C), combeite remains as the main crystalline phase. Additionally, Na2Ca2Si2O7 crystalline phase is formed. Our results provide a basic platform for tailoring the crystalline phases by controlling the nucleation and growth of crystalline phases via thermal treatments. Different morphologies (round particles, stacked layers, toothpick‐like, and long features) were discerned by TEM as a function of temperature and time of treatment. It is the first time that bioactive glass is investigated by nano‐CT at laboratory scale. This novel technique enables the 3D visualization of features in the nanometer range, giving clear information about the volumetric distribution of phases in the sample.
Fluoride‐containing bioactive glasses and glass‐ceramics in the SiO2‐P2O5‐CaO‐CaF2 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 P2O5 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 CaF2 and SiO2 mixtures as reference samples, and the fluorine loss upon glass melting has been determined as a function of P2O5 content. The P2O5‐free glass shows the lowest fluorine loss (13%), with HF volatilization likely being responsible for the loss. By contrast, the glass with the highest P2O5 content (11.33 wt%) exhibits the largest fluorine loss (55%), owing to additional mechanisms involving the volatilization of phosphorus species like POF3.
The antioxidant activity of Mn as additive in a 45S5 type glass system with and without P2O5 was studied by mimicking the activity of catalase (CMA) and superoxide dismutase (SOD) enzymes. Glasses ...were melted either under oxidizing or reducing atmosphere (N2/H2) to compare the processing influence on the Mn oxidation state. Thermal (DTA) and optical (UV–Vis) characterizations of the glass powders were carried out to obtain further insight into the structural role of Mn. A correlation of in vitro apatite formation between Tris buffer solution and Simulated Body Fluid (SBF) was performed to optimise Mn substitution, where a decrease in apatite formation was observed by increasing Mn content. Despite this, glasses with up to 1.0 mol% MnO did not show any delay in apatite formation and maintained their CMA and SOD activity. The antioxidant effect of Mn can be attributed to the interconversion Mn2+ ↔ Mn3+ occurring on the glass surface through a heterogeneous catalysis. P2O5 plays an important role in the antioxidant effect of the glass, possibly by charge balancing Mn ions and forming more stable units compared to those formed with Ca and Na. The amount of Mn2+ is predominant in the glass network with respect to Mn3+ in all synthetized glasses. Moreover, glass melting in a reducing atmosphere further avoided Mn oxidation.
•Crystallization of bulk Bioglass 45S5 has been imaged from nano- to microscale.•Combining ex situ and in situ techniques allows to follow the entire crystallization process.•Combeite crystallizes ...with a sphere-like morphology visualized by nano-CT.•Combeite spheres present a grain-like internal structure.•Crystallinity of powder and bulk samples have been correlated with the images.
One key issue influencing a broader application of Bioglass 45S5 in tissue engineering is its inherent crystallization tendency, severely limiting the mechanical strength of 3D porous scaffolds. Despite numerous studies, Bioglass 45S5 crystallization is not yet fully understood with regard to the mechanisms involved or morphology of the crystal phases forming. Here we show how two cutting-edge imaging techniques, state-of-the-art transmission electron microscopy (TEM) with image correction including energy dispersive X-ray spectroscopy and X-ray nano-computed tomography (nano-CT), allowed us to visualize changes in microstructure from near-nucleation to almost full crystallization in bulk Bioglass 45S5. At early times of heat treatment at 660 °C the formation of phase-separated nano-droplets within the glassy matrix was observed. Later, besides surface crystallization, bulk crystallization of combeite spheres was predominant. The formation of the first combeite spheres, their coarsening with time and finally their merging at near full crystallization were recorded by in situ high-temperature optical microscopy videos. The 3D nature of these spheres was confirmed by nano-CT, while TEM showed that their internal structure was composed of sub-micron grains. X-ray diffraction analysis at early time points showed a much higher crystalline fraction in bulk samples compared to powder samples, highlighting the influence of processing and sample morphology. These results show the importance of using complementary techniques for gaining insight into the crystallization process in the volume. In addition, we show that TEM and nano-CT are suitable characterization techniques to visualize the crystallization even in fast crystallizing systems, such as bioactive glasses.
•13–93 bioactive glass was synthesized via sol–gel method.•Crystallinity of 13–93 BG powder tailored in the range 5–43 wt.% by controlling heat treatment parameters.•TEM revealed the presence of ...different morphologies in the glass-ceramic microstructure as a function of heat treatment.•Nano-CT volumetric images showed the morphology and porosity of heated treated samples.
Multicomponent silicate bioactive glass (BG) (53SiO2‐20CaO‐6Na2O‐4P2O5‐12K2O‐ 5MgO in wt. %) (13–93 composition) was prepared via the sol–gel process. The influence of thermal treatment on the crystallization was evaluated using differential scanning calorimetry (DSC), X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray nano-computed tomography (nano-CT). The temperature and time of the thermal treatment strongly influenced the formation of the crystalline phases. The preliminary outcomes demonstrate the possibility of tailoring the crystallinity of 13–93 BG powder in the range 5–43 wt. % by controlling the temperature and time of the heat treatment. The microstructure of powders sintered at two different temperatures (650 °C and 700 °C from 30 min to 4 h) was evaluated by TEM. X-ray nano-computed tomography (nano-CT) was used to visualize the 3D morphology and distribution of crystallization areas in the samples in powder form. A large range between the glass transformation and the crystallization temperatures is observed, which provides the prospect of a suitable material to manufacture directly 3D structures (e.g. porous scaffolds) without an intermediate processing step.
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 SiO
-CaO-P
O
-CaF
. 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.
Currently available cements and granules for bone repair include devices based on glass ionomer cement (GICs) technology. These cements are based on the setting reaction between an aluminium ...containing fluorosilicate glass, poly (acrylic acid) (PAA) and a setting modifier. The glass powder is acid degradable, which crosslinks with the ionised acid, resulting in a matrix of polyacrylates salts with reacted glass particles. However, bone demineralisation, as well as neurotoxicity in craniofacial applications are drawbacks associated with aluminium. These disadvantages have created a scientific interest on developing aluminium free compositions with the potential to be used as cements and bone grafts. Therefore, new glass compositions have been researched to substitute the alumina (Al2O3) with oxides such as ZnO, GeO, MgO, and TiO. However, no previous detailed study has investigated variations of the classic Hench Bioglass® composition (45SiO2-24.5Na2O-24.5CaO-6P2O5 wt. %) for preparation of cements, with Mirvakily studying this system, but focusing solely on one cement composition (Mirvakily, 2009). In the present work, eight glasses were prepared and characterised by X-ray diffraction (XRD), differential thermal analysis (DTA), scanning electron microscopy (SEM), and Fourier transformed infrared spectroscopy (FTIR-ATR). These glasses were mixed with varying quantities of poly (acrylic acid), and a phosphoric acid solution (H3PO4 (sol)), to evaluate their cement forming properties and setting times. The most suitable glasses were chosen along with the optimised cement combination, this being a powder/liquid (P/L) ratio of two, 10.7 % PAA powder and 25% H3PO4 (sol), to further investigate their mass change, ion release and conductivity when immersed in distilled water, along with their setting chemistry. Results showed that glasses based on a SiO2-Na2O-CaO-SrO-P2O5 system could be used to produce setting pastes that were stable in distilled water, with net setting times varying between 34 min and 115 min. The setting mechanism was found to have similarities to GICs, by release of Ca2+, Sr2+, and Na+ after PAA ionisation and formation of the respective polyacrylate salts. The use of phosphoric acid was found to be essential to prevent the gelation in water of aged cements (set for one day, 37 °C), suggesting that this addition aided glass dissolution and precipitation of phosphate containing salts. Their mass loss in distilled water, reached its maximum after one day for the cements prepared with the 45S5 and 45S5Sr10 glasses (with lower SiO2 content), while this peak was observed after one week for the cements prepared with the 49P9 and 53P4 glasses (with higher SiO2 content). The cement dissolution was further confirmed by the release of Si, Ca, Na, and P; with the direct in vitro short-term test showing that the cement based on the 45S5 glass was not cytotoxic. The study carried out with the commercial cement Serenocem™, showed that its dissolution and ion release was very low, which suggested the limited solubility of the Al containing glass. Therefore, the findings of this research provide an alternative system for the preparation of aluminium free cements for craniofacial applications, showing that no additional ionic substitution was required to produce a setting cement with ion release comparable to that of bioactive glasses.
Currently available cements and granules for bone repair include devices based on glass ionomer cement (GICs) technology. These cements are based on the setting reaction between an aluminium ...containing fluorosilicate glass, poly (acrylic acid) (PAA) and a setting modifier. The glass powder is acid degradable, which crosslinks with the ionised acid, resulting in a matrix of polyacrylates salts with reacted glass particles. However, bone demineralisation, as well as neurotoxicity in craniofacial applications are drawbacks associated with aluminium. These disadvantages have created a scientific interest on developing aluminium free compositions with the potential to be used as cements and bone grafts. Therefore, new glass compositions have been researched to substitute the alumina (Al2O3) with oxides such as ZnO, GeO, MgO, and TiO. However, no previous detailed study has investigated variations of the classic Hench Bioglass® composition (45SiO2-24.5Na2O-24.5CaO-6P2O5 wt. %) for preparation of cements, with Mirvakily studying this system, but focusing solely on one cement composition (Mirvakily, 2009). In the present work, eight glasses were prepared and characterised by X-ray diffraction (XRD), differential thermal analysis (DTA), scanning electron microscopy (SEM), and Fourier transformed infrared spectroscopy (FTIR-ATR). These glasses were mixed with varying quantities of poly (acrylic acid), and a phosphoric acid solution (H3PO4 (sol)), to evaluate their cement forming properties and setting times. The most suitable glasses were chosen along with the optimised cement combination, this being a powder/liquid (P/L) ratio of two, 10.7 % PAA powder and 25% H3PO4 (sol), to further investigate their mass change, ion release and conductivity when immersed in distilled water, along with their setting chemistry. Results showed that glasses based on a SiO2-Na2O-CaO-SrO-P2O5 system could be used to produce setting pastes that were stable in distilled water, with net setting times varying between 34 min and 115 min. The setting mechanism was found to have similarities to GICs, by release of Ca2+, Sr2+, and Na+ after PAA ionisation and formation of the respective polyacrylate salts. The use of phosphoric acid was found to be essential to prevent the gelation in water of aged cements (set for one day, 37 °C), suggesting that this addition aided glass dissolution and precipitation of phosphate containing salts. Their mass loss in distilled water, reached its maximum after one day for the cements prepared with the 45S5 and 45S5Sr10 glasses (with lower SiO2 content), while this peak was observed after one week for the cements prepared with the 49P9 and 53P4 glasses (with higher SiO2 content). The cement dissolution was further confirmed by the release of Si, Ca, Na, and P; with the direct in vitro short-term test showing that the cement based on the 45S5 glass was not cytotoxic. The study carried out with the commercial cement Serenocem™, showed that its dissolution and ion release was very low, which suggested the limited solubility of the Al containing glass. Therefore, the findings of this research provide an alternative system for the preparation of aluminium free cements for craniofacial applications, showing that no additional ionic substitution was required to produce a setting cement with ion release comparable to that of bioactive glasses.
PDF
