Novel Zinc Containing Phosphate Glasses for Glass–Ionomer Cements for Bone Cement Applications

PhDGlass‐ionomer cements (GICs) are acid base reaction cements used in dentistry for restorative applications. In conventional GICs aluminosilicate glass is used to react with a polyalkenoic acid such as poly acrylic acid. Glass–ionomer cements have the potential to be used for bone cement applications, however there is a concern over the neurotoxicity of aluminium in the glass component of these cements. In this work zinc containing phosphate glass based glass–ionomer cement has been developed for the bone cement application. In this relation structure of zinc containing phosphate glasses in the system Na2O:CaO:ZnO:P2O5 ranging from metaphosphate compositions to invert phosphate compositions has been examined. Various advanced techniques in solid state nuclear magnetic resonance (NMR) such as dipolar recoupling and solid state NMR of low quadrupolar nuclei (67Zn and 43Ca) and neutron diffraction have been employed. Special emphasis has been focused on structural role of zinc in glasses of different composition and the effect of different cations on coordination of zinc along with the effect on phosphate tetrahedra. 67Zn and 43Ca solid state NMR spectra of selected glass samples have been successfully acquired at ultrahigh field 900 MHz using Solid Echo pulse sequence. In addition solid state NMR spectra of two polymorphs of crystalline Zn(PO3)2 have also been acquired at 850 MHz using DFS– WURST–QCPMG pulse sequence in order to distinguish between the magnitude and orientation of electric field gradient (EFG) of zinc in octahedral and tetrahedral coordination. Structure determined through various techniques has been related to the dissolution behaviour of glass compositions from metaphosphate to invert phosphate. A decrease in pH of surrounding medium has been observed due to the presence of zinc. Insertion of ZnO4 tetrahedra between PO4 tetrahedra has been observed in invert phosphate glasses with high zinc oxide content which renders them suitable for glass– ionomer cements. Glass–ionomer cement from glass composition 10Na2O:50ZnO:10CaO:30P2O5 and hydroxyapatite and, acrylic acid and vinyl phosphonic acid co‐polymer has been produced successfully.Queen Mary Post Graduate Research Fund (PGRF

Sensitivity improvement in 5QMAS NMR Experiments Using FAM-N Pulses

We would like to thank the ERC (EU FP7 Consolidator Grant 614290 “EXONMR”) and EPSRC (award of a studentship to HC through EP/K503162/1). SEA would also like to thank the Royal Society and Wolfson Foundation for a merit award. The UK 850 MHz solid-state NMR Facility used in this research was funded by EPSRC and BBSRC (contract reference PR140003), as well as the University of Warwick including via part funding through Birmingham Science City Advanced Materials Projects 1 and 2 supported by Advantage West Midlands (AWM) and the European Regional Development Fund (ERDF). Collaborative assistance from the 850 MHz Facility Manager (Dinu Iuga, University of Warwick) is acknowledged. The research data supporting this publication can be accessed at DOI: 10.17630/04b0c37f-b803-4dd7-b13a-2004b0b5c482.[49]The multiple-quantum magic-angle spinning (MQMAS) experiment is a popular choice for obtaining high-resolution solid-state NMR spectra of quadrupolar nuclei with half-integer spin quantum number. However, its inherently poor sensitivity limits its application in more challenging systems. In particular, the use of higher-order multiple-quantum coherences, which have the potential to provide higher resolution in the isotropic spectrum, results in a further decrease in sensitivity. Here we extend our recent work, which introduced an automated, high-throughput approach to generate amplitude-modulated composite pulses (termed FAM-N) to improve the efficiency of the conversion of three-quantum coherences, and explore the use of similar pulses in five-quantum MAS experiments. We consider three different approaches, and are able to demonstrate that all three provide good enhancements over single pulse conversion in all but the most extreme cases, and work well at a range of spinning rates. We show that FAM-N pulses are robust to variation in the quadrupolar coupling and rf nutation rate, demonstrating their applicability in multisite systems and systems where direct experimental optimisation of complex composite pulses is not feasible. This work will ease the implementation of higher-order MQMAS experiments and enable their application to materials and systems that were previously deemed to difficult to study.Publisher PDFPeer reviewe

Rationalization of solid-state NMR multi-pulse decoupling strategies : coupling of spin I = ½ and half-integer quadrupolar nuclei

This work benefited from a grant from Agence Nationale de la Recherche (ANR MOSAIC 13-BS08-0018-01).In this paper we undertake a study of the decoupling efficiency of the Multiple-Pulse (MP) scheme, and a rationalization of its parameterization and of the choice of instrumental set up. This decoupling scheme is known to remove the broadening of spin-1/2 spectra I, produced by the heteronuclear scalar interaction with a half-integer quadrupolar nucleus S, without reintroducing heteronuclear dipolar interaction. The resulting resolution enhancement depends on the set-up of the length of the series of pulses and delays of the MP, and some intrinsic material and instrumental parameters. Firstly through a numerical approach, this study investigates the influence of the main intrinsic material parameters (heteronuclear dipolar and J coupling, quadrupolar interaction, spin nature) and instrumental parameters (spinning rate, pulse field strength) on efficiency and resolution enhancement of the scalar decoupling scheme. A guideline is then proposed to obtain quickly and easily the best resolution enhancement via the rationalization of the instrumental and parameter set up. It is then illustrated and tested through experimental data, probing the efficiency of MP-decoupling set up using this guideline. Various spin systems were tested (31P-51V in VOPO4, 31P-93Nb in NbOPO4, 119Sn-17O in Y2Sn2O7), combined with simulations results.PostprintPostprintPeer reviewe

Highly porous phosphate-based glasses for controlled delivery of antibacterial Cu ions prepared via sol–gel chemistry

Mesoporous glasses are a promising class of bioresorbable biomaterials characterized by high surface area and extended porosity in the range of 2 to 50 nm. These peculiar properties make them ideal materials for the controlled release of therapeutic ions and molecules. Whilst mesoporous silicate-based glasses (MSG) have been widely investigated, much less work has been done on mesoporous phosphate-based glasses (MPG). In the present study, MPG in the P2O5–CaO–Na2O system, undoped and doped with 1, 3, and 5 mol% of Cu ions were synthesized via a combination of the sol–gel method and supramolecular templating. The non-ionic triblock copolymer Pluronic P123 was used as a templating agent. The porous structure was studied via a combination of Scanning Electron Microscopy (SEM), Small-Angle X-ray Scattering (SAXS), and N2 adsorption–desorption analysis at 77 K. The structure of the phosphate network was investigated via solid state 31P Magic Angle Spinning Nuclear Magnetic Resonance (31P MAS-NMR) and Fourier Transform Infrared (FTIR) spectroscopy. Degradation studies, performed in water via Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES), showed that phosphates, Ca2+, Na+ and Cu ions are released in a controlled manner over a 7 days period. The controlled release of Cu, proportional to the copper loading, imbues antibacterial properties to MPG. A significant statistical reduction of Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) bacterial viability was observed over a 3 days period. E. coli appeared to be more resistant than S. aureus to the antibacterial effect of copper. This study shows that copper doped MPG have great potential as bioresorbable materials for controlled delivery of antibacterial ions

The effect of the incorporation of fluoride into strontium containing bioactive glasses

Recently, the porous bioactive glasses have attracted a lot of attention for use as scaffolds for tissue engineering bone; such glasses include the high phosphate, strontium containing glass (Stronbone P). However, the previous studies suggest that strontium can have a detrimental effect on the ability of apatite-like phase formation of the glass. The previously studied high phosphate all Sr glass showed an unidentified phase rather than an apatite-like phase upon immersion. Octa-calcium phosphate (OCP) is believed to be a precursor phase to apatite, however octa-strontium phosphate does not exist. Fluoride is known to knock out the OCP formation and promotes fluorapatite formation. This work presents the incorporation of a small amount of fluoride into calcium/strontium bioactive glasses. Differential scanning calorimetry was used to estimate the glass thermal properties. All of the studied glass compositions were subjected to bioactivity studies in Tris buffer (pH = 7.4) for up to 21 days. The initial glasses and the resultant precipitates were analysed using Fourier transform infrared spectroscopy, X-ray diffraction and magic angle spinning-nuclear magnetic resonance. The findings showed that all the fluoride containing glasses were amorphous and there was a marked increase in the rate of apatite formation in vitro compared to the equivalent fluoride free glasses, particularly for the all strontium containing glass. This indicates that the presence of fluoride affects the pathway of apatite formation, forming fluorapatite directly instead of via the transformation from OCP to hydroxyapatite. Therefore, fluoride may have potential future clinical applications as an additive to increase apatite formation

Strontium substituted bioactive glasses for tissue engineered scaffolds: the importance of octacalcium phosphate

Porous bioactive glasses are attractive for use as bone scaffolds. There is increasing interest in strontium containing bone grafts, since strontium ions are known to up-regulate osteoblasts and down regulate osteoclasts. This paper investigates the influence of partial to full substitution of strontium for calcium on the dissolution and phase formation of a multicomponent high phosphate content bioactive glass. The glasses were synthesised by a high temperature melt quench route and ground to a powder of <38 microns. The dissolution of this powder and its ability to form apatite like phases after immersion in Tris buffer (pH 7.4) and simulated body fluid (SBF) was followed by inductively coupled plasma optical emission spectroscopy (ICP), Fourier transform infra red spectroscopy (FTIR), X-ray powder diffraction (XRD) and (31)P solid state nuclear magnetic resonance spectroscopy up to 42 days of immersion. ICP indicated that all three glasses dissolved at approximately the same rate. The all calcium (SP-0Sr-35Ca) glass showed evidence of apatite like phase formation in both Tris buffer and SBF, as demonstrated after 3 days by FTIR and XRD analysis of the precipitate that formed during the acellular dissolution bioactivity studies. The strontium substituted SP-17Sr-17Ca glass showed no clear evidence of apatite like phase formation in Tris, but evidence of an apatite like phase was observed after 7 days incubation in SBF. The SP-35Sr-0Ca glass formed a new crystalline phase termed “X Phase” in Tris buffer which FTIR indicated was a form of crystalline orthophosphate. The SP-35Sr-0Ca glass appeared to support apatite like phase formation in SBF by 28 days incubation. The results indicate that strontium substitution for calcium in high phosphate content bioactive glasses can retard apatite like phase formation. It is proposed that apatite formation with high phosphate bioactive glasses occurs via an octacalcium phosphate (OCP) precursor phase that subsequently transforms to apatite. The equivalent octa-strontium phosphate does not exist and consequently in the absence of calcium, apatite formation does not occur. The amount of strontium that can be substituted for calcium in OCP probably determines the amount of strontium in the final apatite phase and the speed with which it forms

Sensitivity improvement in 5QMAS NMR Experiments Using FAM-N Pulses

The multiple-quantum magic-angle spinning (MQMAS) experiment is a popular choice for obtaining high-resolution solid-state NMR spectra of quadrupolar nuclei with half-integer spin quantum number. However, its inherently poor sensitivity limits its application in more challenging systems. In particular, the use of higher-order multiple-quantum coherences, which have the potential to provide higher resolution in the isotropic spectrum, results in a further decrease in sensitivity. Here we extend our recent work, which introduced an automated, high-throughput approach to generate amplitude-modulated composite pulses (termed FAM-N) to improve the efficiency of the conversion of three-quantum coherences, and explore the use of similar pulses in five-quantum MAS experiments. We consider three different approaches, and are able to demonstrate that all three provide good enhancements over single pulse conversion in all but the most extreme cases, and work well at a range of spinning rates. We show that FAM-N pulses are robust to variation in the quadrupolar coupling and rf nutation rate, demonstrating their applicability in multisite systems and systems where direct experimental optimisation of complex composite pulses is not feasible. This work will ease the implementation of higher-order MQMAS experiments and enable their application to materials and systems that were previously deemed to difficult to study

The effect of the incorporation of fluoride into strontium containing bioactive glasses

Recently, the porous bioactive glasses have attracted a lot of attention for use as scaffolds for tissue engineering bone; such glasses include the high phosphate, strontium containing glass (Stronbone P). However, the previous studies suggest that strontium can have a detrimental effect on the ability of apatite-like phase formation of the glass. The previously studied high phosphate all Sr glass showed an unidentified phase rather than an apatite-like phase upon immersion. Octa-calcium phosphate (OCP) is believed to be a precursor phase to apatite, however octa-strontium phosphate does not exist. Fluoride is known to knock out the OCP formation and promotes fluorapatite formation. This work presents the incorporation of a small amount of fluoride into calcium/strontium bioactive glasses. Differential scanning calorimetry was used to estimate the glass thermal properties. All of the studied glass compositions were subjected to bioactivity studies in Tris buffer (pH = 7.4) for up to 21 days. The initial glasses and the resultant precipitates were analysed using Fourier transform infrared spectroscopy, X-ray diffraction and magic angle spinning-nuclear magnetic resonance. The findings showed that all the fluoride containing glasses were amorphous and there was a marked increase in the rate of apatite formation in vitro compared to the equivalent fluoride free glasses, particularly for the all strontium containing glass. This indicates that the presence of fluoride affects the pathway of apatite formation, forming fluorapatite directly instead of via the transformation from OCP to hydroxyapatite. Therefore, fluoride may have potential future clinical applications as an additive to increase apatite formation

Sensitivity Improvement in 5QMAS NMR Experiments Using FAM-N Pulses (dataset)

The data will be available soon. In the meantime, if you would like to access the dataset, please email [email protected]