Na2O CaO P2O5 Research Articles

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

Bioactive glasses are able to bond to bone through formation of carbonated hydroxyapatite in body fluids, and fluoride-releasing bioactive glasses are of interest for both orthopaedic and, in particular, dental applications for caries inhibition. Melt-derived glasses in the system SiO2–P2O5–CaO–Na2O with increasing amounts of CaF2 were prepared by keeping network connectivity and the ratio of all other components constant. pH change, ion release and apatite formation during immersion of glass powder in simulated body fluid at 37°C over up to 2weeks were investigated. Crystal phases formed in SBF were characterized using infrared spectroscopy, X-ray diffraction with Rietveld analysis and solid-state nuclear magnetic resonance spectroscopy (19F and 31P MAS–NMR). Results show that incorporation of fluoride resulted in a reduced pH rise in aqueous solutions compared to fluoride-free glasses and in formation of fluorapatite (FAp), which is more chemically stable than hydroxyapatite or carbonated hydroxyapatite and therefore is of interest for dental applications. However, for increasing fluoride content in the glass, fluorite (CaF2) was formed at the expense of FAp. Apatite formation could be favoured by increasing the phosphate content in the glass, as the release of additional phosphate into the SBF would affect supersaturation in the solution and possibly favour formation of apatite.

Intense 1.54 μm fluorescence of Er3+/Yb3+ codoped phosphate glass and the three-photon phenomenon of near infrared upconversion luminescence

Transparent P2O5–CaO–Na2O glasses codoped with Er3+ and Yb3+ ions were fabricated by high-temperature melting technique. Strong near infrared and visible upconversion luminescence were observed under 975 nm laser diode excitation, and the luminescence processes were explained in details. For 1.54 μm band, the calculated peak emission cross sections is 1.04×10−20 cm2, and it is better than that in germinate, tellurite, silicate, and other phosphate glasses. The near infrared upconversion emission around 828 nm contains two-photon and three-photon processes, and it is attributed to the transition S43/2→I413/2, which enhances the population of the upper level for 1.54 μm laser emission and reduces the energy loss due to upconversion. Efficient near infrared fluorescence indicates Er3+/Yb3+ codoped phosphate glass is a promising laser and amplifier material.

Influence of addition of Al2O3 on physical, structural, acoustical and in‐vitro bioactive properties of phosphate glasses

AbstractFour different formulations of phosphate glasses in the system P2O5–CaO–Na2O–Al2O3 were developed. The elastic moduli have been obtained using the known method at room temperature. Their physicochemical and structural evolution was analyzed during in‐vitro degradation in SBF (simulating body fluid) at 37 °C after 30 days. The results showed that the weight loss of the glass is greatly reduced with the incorporation of only 3 mol% of Al2O3 in P2O5–CaO–Na2O glass composition. Fourier transform infrared (FTIR) spectroscopy performed on glasses before and after dipping in SBF showed calcium phosphate glasses in the system P2O5–CaO–Na2O reinforced with Al2O3 offer an interesting option for slowly resorbable materials as compared to other calcium phosphate glasses with high degradation velocity. The chemical formulation of these glasses allows the synthesis of materials with a controlled solubility. However, the substitution of Al2O3 ≥ 5 mol% negatively affects the bioactivity of the P2O5–CaO–Na2O glasses. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Structural characterization by x-ray methods of novel antimicrobial gallium-doped phosphate-based glasses

Antimicrobial gallium-doped phosphate-based glasses of general composition (P(2)O(5))(0.45)(CaO)(0.16)(Na(2)O)(0.39-x)(Ga(2)O(3))(x) (where x=0, 0.01, 0.03, and 0.05) have been studied using the advanced synchrotron-based techniques of Ga K-edge x-ray absorption spectroscopy and high-energy x-ray diffraction to provide a structural insight into their unique properties. The results show that the Ga(3+) ions are octahedrally coordinated. Furthermore, substitution of Na(2)O by Ga(2)O(3) strengthens the phosphate network structure because the presence of GaO(6) octahedra inhibits the migration of the remaining Na(+) ions. The results are discussed in terms of the use of Na(2)O-CaO-P(2)O(5) glasses as controlled-delivery devices for antimicrobial Ga(3+) ions in biomedical applications. We are thereby able to relate the atomic-scale environment of the Ga(3+) ions beneficially to the glass dissolution, and thus to their ability to disrupt bacterial cell activity by usurping the role of iron.

Structure of fluoride-containing bioactive glasses

Fluoride prevents dental cavities, stimulates bone mineralisation and decreases the melting temperature of glasses and is therefore an interesting component of bioactive glasses for use as dental or orthopaedic biomaterials. However, when designing new glass compositions, the structural role of fluoride in the glass needs to be better understood. We have characterised a glass series in the system SiO2–P2O5–CaO–Na2O with increasing concentrations of CaF2. Network connectivity was fixed at 2.13 by adding CaF2 while the ratio of all other components was kept constant. 19F and 29Si MAS NMR spectra showed that addition of CaF2 does not cause disruption of the glass network by formation of Si–F bonds but forms mixed calcium sodium fluoride species. 31P MAS NMR showed phosphate being present as orthophosphate. Hence it does not form part of the actual glass network backbone and no Si–O–P bonds are present. 23Na MAS NMR showed the presence of multiple sodium sites with an increase in the mean coordination number of sodium with increasing CaF2 content. The glass transition temperature decreased with increasing amounts of CaF2. As no Si–F bonds were formed, this can be explained by formation of hypothetical CaF+ species. The results can be used for designing new fluoride-containing bioactive glass compositions for specific applications.

Synthesis and structural characterization of P2O5–CaO–Na2O sol–gel materials

Ternary phosphate-based glasses in the system P2O5–CaO–Na2O were synthesized using the sol–gel approach. Glasses in this system have the potential for use as bioactive materials. A mixture of mono- and dialkyl phosphate PO(OH)3−x(OC2H5)x (x=1,2) and alkoxides of sodium and calcium in an ethylene glycol solution were used as precursors. One of the compositions has also been synthesized by sonocatalysis (application of ultrasonic vibration to the sol). The systems synthesized, which remain fully amorphous even after calcination at 400°C given the appropriate composition, have been characterized using X-ray diffraction (XRD). Thermal properties have been examined by means of thermogravimetric analysis (TGA) and differential thermal analysis (DTA). The structure of the phosphate network has been studied as a function of composition using Fourier transform infrared spectroscopy (FT-IR) and 31P MAS NMR.

ESR dosimeter based on P2O5–CaO–Na2O glass system

This paper presents the results of a study of thermal properties, solubility and response to 60Co γ-rays by electron spin resonance of the P2O5–CaO–Na2O glass system. The sample compositions were selected by fixing the P2O5mol% content at 50mol%, and varying the CaO mol% at 30 and 40mol%. The spectrum is characterized by hyperfine doublet from 31P isotope (nuclear spin=1/2), and its stability and response to the γ-ray dose were studied to establish the suitability of this glass as a γ-ray dosimeter.

Influence of particle size on the crystallization process and the bioactive behavior of a bioactive glass system

Bioactive glasses have attracted considerable interest in recent years, due to their technological application, especially in biomaterials research. Differential scanning calorimetry (DSC) has been used in the study of the crystallization mechanism in the SiO2–Na2O–CaO–P2O5 glass system, as a function of particle size. The curve of the bulk glass presents a slightly asymmetric crystallization peak that could be deconvoluted into two separate peaks, their separation being followed in the form of powder glasses. Also, a shift of the crystallization peaks to lower temperatures was observed with the decrease of the particle size. FTIR studies – that are confirmed by XRD measurements – proved that the different peaks could be attributed to different crystallization mechanisms. Moreover, it is presented the bioactive behavior of the specific glass as a function of particle size. The study of bioactivity is performed through the process of its immersion in simulated human blood plasma (simulated body fluid, SBF) and the subsequent examination of the development of carbonate-containing hydroxyapatite layer on the surface of the particles. The bioactive response is improved with the increase of the particle size of powders up to 80 μm and remains almost unchanged for further increase, following the specific surface to volume ratio decrease.

X-ray absorption spectroscopy and high-energy XRD study of the local environment of copper in antibacterial copper-releasing degradable phosphate glasses

Phosphate-based glasses of the general formula Na2O–CaO–P2O5 are degradable in an aqueous environment, and therefore can act as antibacterial materials through the inclusion of ions such as copper. In this study, CuO and Cu2O were added to Na2O–CaO–P2O5 glasses (1–20mol% Cu) and X-ray absorption spectroscopy (XAS) and high-energy X-ray diffraction (HEXRD) used to probe the local environment of the copper ions. Copper K-edge X-ray absorption near-edge structure (XANES) spectra confirm the oxidation state of copper to be predominantly 2+ in all samples regardless of which copper oxide was used in the preparation. The XANES results suggest the structural environment of copper to be octahedral with respect to oxygen in all samples. The HEXRD results yield a Cu–O nearest-neighbour distance of 1.98Å and associated coordination number of approximately six, both consistent with octahedral coordination. Analysis of the extended X-ray absorption fine structure (EXAFS) data also yields structural parameters consistent with copper in an octahedral environment. The HEXRD and EXAFS results reveal a Cu–P distance of 3.13Å, which confirms that the copper ions are coordinated within the phosphate glass network and not phase-separated in domains of copper oxide.

Sol–gel synthesis of the P2O5–CaO–Na2O–SiO2 system as a novel bioresorbable glass

A series of phosphate-based sol–gel glasses in the system P2O5–CaO–Na2O–SiO2 were synthesised using PO(OH)3−x(OC2H5)x (x = 1, 2) as a phosphorus precursor and alkoxides of sodium, calcium and silicon in an ethylene glycol solution. It has been found that the upper limit for gel formation is about 22 mol% phosphorus and that the gelation time increases with increasing phosphorus content of the sol. X-ray diffraction (XRD) along with X-ray fluorescence chemical analysis (XRF) have been performed on samples containing 45 mol% of P2O5 and 0, 10, 15 and 25 mol% of SiO2 with varying amount of modifier oxides (CaO, Na2O). All the samples are predominantly amorphous up to 400 °C and some of them, depending on the composition, retain their amorphous structure up to 600 and 800 °C. To the knowledge of the authors, this is the first time that phosphate-based glasses having these compositions have successfully been synthesised via the sol–gel method.

Characterisation of antibacterial copper releasing degradable phosphate glass fibres

Phosphate-based glass fibres (PGF) of the general formula Na2O–CaO–P2O5 are degradable in an aqueous environment, and therefore can function as antibacterial delivery systems through the inclusion of ions such as copper. In this study, PGF with varying amounts of copper oxide (CuO) were developed for potential uses in wound healing applications. PGF with 0, 1, 5 and 10mol% CuO were produced with different diameters and characterised in terms of structural and antibacterial properties. The effect of CuO and fibre pulling speed on the glass properties were investigated using rapid differential scanning calorimetry, differential thermal analysis and X-ray diffraction. The effect of two fibre diameters on short-term (3h) attachment and killing against Staphylococcus epidermidis were investigated and were related to their rate of degradation in deionised water, as well as copper ion release measured using ion chromatography.Thermal analysis showed that there was a significant increase in the PGF glass transition temperature as the CuO content increased. There was a significant decrease in the rate of degradation with increasing CuO content and an increase in fibre diameter. Over 6h, both the amount and rate of copper ions released increased with CuO content, as well as a reduction in fibre diameter thus increasing the surface area to volume ratio. There was a decrease in the number of viable staphylococci both attached to the CuO-containing fibres and in the surrounding environment.

X‐ray microanalysis in STEM of short‐term physicochemical reactions at bioactive glass particle/biological fluid interface. Determination of O/Si atomic ratios

AbstractShort‐term physicochemical reactions at the interface between bioactive glass particles and biological fluids are studied and we focus our attention on the measurements of O/Si atomic ratio. The studied bioactive glass is in the SiO2Na2OCaOP2O5K2OAl2O3MgO system. The elemental analysis is performed at the submicrometre scale by scanning transmission electron microscopy associated with energy‐dispersive x‐ray spectroscopy (EDXS) and electron energy‐loss spectroscopy (EELS). We previously developed an EDXS quantification method based on the ratio method and taking into account local absorption corrections. In this way, we use EELS data to determine, by an iterative process, the local mass thickness, which is an essential parameter for correcting absorption in EDXS spectra. After different immersion times of bioactive glass particles in a simulated biological solution, results show the formation of different surface layers at the bioactive glass periphery. Before 1 day of immersion, we observe the presence of an already shown (Si,O,Al)‐rich layer at the periphery. In this paper, we demonstrate that a thin ‘electron dense’ (Si,O)‐layer is formed on top of the (Si,O,Al)‐layer. In this (Si,O)‐layer, depleted in aluminium, we point out an increase of oxygen weight concentration that can be interpreted by the presence of Si(OH)4 groups, which permit the formation of a (Ca,P)‐layer. Aluminium plays a role in the glass solubility and may inhibit apatite nucleation. After the beginning of the (Ca,P)‐layer formation, the size of the ‘electron dense’ (Si,O)‐layer decreases and tends to disappear. After 2 days of immersion, the (Ca,P)‐layer grows in thickness and leads to apatite precipitation. Copyright © 2004 John Wiley & Sons, Ltd.

Physicochemical Degradation of Titania‐Stabilized Soluble Phosphate Glasses for Medical Applications

Four different formulations of phosphate glasses in the system P2O5–CaO–Na2O–TiO2 were developed. Their physicochemical, morphologic, and structural evolution was analyzed during in vitrodegradation in SBF (simulated body fluid) at 37°C up to 16 weeks. The results showed that the addition of TiO2 into the glass system enhanced both the elastic modulus and the chemical durability of the glasses. Indeed, the elastic modulus increased from 66.6 to 75.95 GPa and the weight loss percentage diminished from 1.6% to 0.3% with the addition of 8 mol% TiO2. A uniform and superficial degradation mechanism could be observed throughout the dissolution time by means of environmental scanning electron microscopy (ESEM), inductively coupled plasma mass spectroscopy (ICP‐MS), and Raman spectroscopy. The degradation process undergone by these glasses allows them to maintain their mechanical properties during the degradation process. Therefore, these materials offer an interesting choice for slowly resorbable materials in biomedical applications.

Dissolution Kinetics, Selective Leaching, and Interfacial Reactions of a Bioglass Coating Enriched in Alumina

Bioglass coatings are interesting for developing a direct bond between prostheses and bone. But the high solubility of these materials limits their application. The addition of alumina can be used to control their solubility, but may inhibit the bonding mechanisms. In this paper, we study a bioglass in the SiO2–Na2O–CaO–P2O5–K2O–Al2O3–MgO system. After delays of implantation from 2 to 12 months, the bioglass/bone interface is characterized by energy-dispersive X-ray spectroscopy coupled with scanning transmission electron microscopy. Bioglass dissolution can be decomposed into three steps with selective leaching. Results show that, at 2 months after implantation, the bioglass is composed of Al, Si, Ca, and P. Alumina addition increases the coating stability without inhibiting the bonding process. Complex physicochemical reactions take place at the bioglass periphery. The coating bonds to bone through a Ca–P layer on top of a pure Si-rich layer. These phenomena are associated with bioactivity properties, which occur for up to 6 months. After 12 months, the bioglass is composed of silicon.