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IR spectroscopy of probe molecules (pyridine, 2,6-dimethylpyridine, and CO) as well as high-resolution solid state NMR and especially double-resonance experiments give a new insight into the acidic sites of amorphous silica alumina (ASA). ASA samples are heterogeneous compounds that contain a silica alumina mixed phase as well as aluminum clusters and pure silica zones. The distribution of various forms depends both on the preparation method and on the Si/Al ratio. Formation of mixed phase leads to the creation of acidic hydroxyl groups of various strength, up to that present in dealuminated HY zeolite. Detailed spectroscopic analyses show that these acidic OH groups correspond to the silanol groups located in close vicinity to an Al atom in tetrahedral environment. The strength of the acidity of the OH species of ASA could be modified both by the location of the vicinal Al atom on the surface or in the bulk and by the number of aluminum atoms in the vicinity of silanol group. Cogelification of high silica-containing ASA appears as the best mean to prepare homogeneous amorphous aluminosilicate, which exhibits the strongest Brønsted acidity. [ABSTRACT FROM AUTHOR]

A novel organic-inorganic hybrid, based on SiO 2 -CaO-ZnO bioactive glass (BG) and polycaprolactone (PCL), associating the highly bioactive and versatile bioactive glass with clinically established PCL was examined. The BG-PCL hybrid is obtained by acid-catalyzed silica sol-gel process inside PCL solution either by direct or indirect printing. Apatite-formation tests in simulated body fluid (SBF) confirm the ion release along with the hybrid's bone-like apatite forming. Kinetics differ significantly between directly and indirectly printed scaffolds, the former requiring longer periods to degrade, while the latter demonstrates faster calcium phosphate (CaP) formation. Remarkably, Zn diffusion and accumulation are observed at the surface within the newly formed active CaP layer. Zn release is found to be dependent on printing method and immersion medium. Investigation of BG at the atomic scale reveals the ambivalent role of Zn, capable of acting both as a network modifier and as a network former linking the BG silicate network. In addition, hMSCs viability assay proves no cytotoxicity of the Zn hybrid. LIVE/DEAD staining demonstrated excellent cell viability and proliferation for over seven weeks. Overall, this hybrid material either non-doped or doped with a metal trace element is a promising candidate to be translated to clinical applications for bone regeneration.

Water in calcium silicate hydrate (C-S-H) is one of the key parameters driving the macroscopic behavior of cement materials for which water vapor partial pressure has an impact on Young's modulus and the volumic properties. Several samples of C-S-H with a bulk Ca/Si ratio ranging between 0.6 and 1.6 were characterized to study their dehydration/hydration behavior under water-controlled conditions using 29 Si NMR, water adsorption volumetry, X-ray diffraction, and Fourier-transform near-infrared diffuse reflectance under various water pressures. Coherent with several previous studies, it was observed that an increase in the Ca/Si ratio is due to the progressive omission of Si bridging tetrahedra, with the resulting charge being compensated for by interlayer Ca, and that water conditioning influences the layer-to-layer distance and the achieved NMR spectral resolution. Water desorption experiments exhibit one step toward low relative pressure, accompanied by a decrease in the layer-to-layer distance. When sufficient energy is provided to the system ( T ≥ 40 °C under vacuum) to remove the interlayer water, the shrinkage/swelling is partially reversible in our experimental conditions. A change in layer-to-layer distance of less than 3 Å is measured in the C-S-H between the wet and dried states. When the bridging SiO 2 tetrahedra are omitted, interlayer Ca interacts with layer O and water interacts with the cations and potentially with the surfaces. This structural organization is interpreted as a mid-plane monolayer of water in the interlayer space, this latter accounting for about 30% of the volume of C-S-H particles.

Calcium is an essential component of osteogenesis and is often required for imparting significant bioactivity to synthetic bone substitutes and, in particular, silicate-based materials. However, the mechanism of calcium incorporation inside sol-gel silicates is poorly understood. In this work, we shed light on the determinant parameters for incorporation of calcium into acid-base-catalyzed sol-gel silicates at ambient temperature: increasing the pH above the isoelectric point of silicic acid and the nature of the calcium counterion in the calcium precursor are found to be the key. Based on our proposed reaction sequence, we were able to compare calcium precursors and select an ideal candidate compound for the synthesis of bioactive glasses (BG) and organic-inorganic hybrids at ambient temperature. Reproducible syntheses and gel times of SiO 2 -CaO BG were obtained using calcium hydroxide (CH), and we demonstrate its usability in the synthesis of promising BG-polycaprolactone hybrid scaffolds. BG and hybrids prepared with CH were able to form nanocrystalline nonstoichiometric apatite in simulated body fluid. The increased reliability of low-temperature syntheses associated with the use of a stable and inexpensive alkaline-earth precursor are major steps toward the translation of calcium silicate hybrids or other alkaline-earth silicates from bench to clinic.

An injectable purely apatitic calcium phosphate cement (CPC) was successfully combined to a water-soluble radiopaque agent (i.e., Xenetix ® ), to result in an optimized composition that was found to be as satisfactory as poly(methyl methacrylate) (PMMA) formulations used for vertebroplasty, in terms of radiopacity, texture and injectability. For that purpose, the Xenetix dosage in the cement paste was optimized by injection of the radiopaque CPC in human cadaveric vertebrae under classical PMMA vertebroplasty conditions, performed by interventional radiologists familiar with this surgical procedure. When present in the cement paste up to 70 mg I mL -1 , Xenetix did not influence the injectability, cohesion, and setting time of the resulting composite. After hardening of the material, the same observation was made regarding the microstructure, mechanical strength and alpha-tricalcium phosphate to calcium deficient apatite transformation rate. Upon implantation in bone in a small animal model (rat), the biocompatibility of the Xenetix-containing CPC was evidenced. Moreover, an almost quantitative release of the contrast agent was found to occur rapidly, on the basis of in vitro static and dynamic quantitative studies simulating in vivo implantation. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 2786-2795, 2018., (© 2017 Wiley Periodicals, Inc.)

Mesoporous bioactive glasses (MBGs) in the system SiO 2 -CaO-P 2 O 5 -Ga 2 O 3 have been synthesized by the evaporation induced self-assembly method and subsequent impregnation with Ga cations. Two different compositions have been prepared and the local environment of Ga(III) has been characterized using 29 Si, 71 Ga and 31 P NMR analysis, demonstrating that Ga(III) is efficiently incorporated as both, network former (GaO 4 units) and network modifier (GaO 6 units). In vitro bioactivity tests evidenced that Ga-containing MBGs retain their capability for nucleation and growth of an apatite-like layer in contact with a simulated body fluid with ion concentrations nearly equal to those of human blood plasma. Finally, in vitro cell culture tests evidenced that Ga incorporation results in a selective effect on osteoblasts and osteoclasts. Indeed, the presence of this element enhances the early differentiation towards osteoblast phenotype while disturbing osteoclastogenesis. Considering these results, Ga-doped MBGs might be proposed as bone substitutes, especially in osteoporosis scenarios., Statement of Signifcance: Osteoporosis is the most prevalent bone disease affecting millions of patients every year. However, there is a lack of bone grafts specifically designed for the treatment of bone defects occurred because of osteoporotic fractures. The consequence is that osteoporotic bone defects are commonly treated with the same biomaterials intended for high quality bone tissue. In this work we have prepared mesoporous bioactive glasses doped with gallium, demonstrating osteoinductive capability by promoting the differentiation of pre-osteoblast toward osteoblasts and partial inhibition of osteoclastogenesis. Through a deep study of the local environment of gallium within the mesoporous matrix, this work shows that gallium release is not required to produce this effect on osteoblasts and osteoclasts. In this sense, the presence of this element at the surface of the mesoporous bioactive glasses would be enough to locally promote bone formation while reducing bone resorption., (Copyright © 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.)

Two commercial formulations of apatitic calcium phosphate cements (CPCs), Graftys® Quickset (QS) and Graftys® HBS (HBS), similar in composition but with different initial setting time (7 and 15min, respectively), were combined to ovine whole blood. Surprisingly, although a very cohesive paste was obtained after a few minutes, the setting time of the HBS/blood composite dramatically delayed when compared to its QS analogue and the two blood-free references. Using solid state NMR, scanning electron microscopy and high frequency impedance measurements, it was shown that, in the particular case of the HBS/blood composite, formation of a reticulated and porous organic network occurred in the intergranular space, prior to the precipitation of apatite crystals driven by the cement setting process. The resulting microstructure conferred unique biological properties to this material upon implantation in bone defects, since its degradation rate after 4 and 12weeks was more than twice that for the three other CPCs, with a significant replacement by newly formed bone., Statement of Significance: A major challenge in the design of bone graft substitutes is the development of injectable, cohesive, resorbable and self-setting calcium phosphate cement (CPC) that enables rapid cell invasion with initial mechanical properties as close as bone ones. Thus, we describe specific conditions in CPC-blood composites where the formation of a 3D clot-like network can interact with the precipitated apatite crystals formed during the cement setting process. The resulting microstructure appears more ductile at short-term and more sensitive to biological degradation which finally promotes new bone formation. This important and original paper reports the design and in-depth chemical and physical characterization of this groundbreaking technology., (Copyright © 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.)

Understanding calcium silicate hydrates (CSHs) is of paramount importance for understanding the behavior of cement materials because they control most of the properties of these man-made materials. The atomic scale water content and structure have a major influence on their properties, as is analogous with clay minerals, and we should assess these. Here, we used a multiple analytical approach to quantify water distribution in CSH samples and to determine the relative proportions of water sorbed on external and internal (interlayer) surfaces. Water vapor isotherms were used to explain the water distribution in the CSH microstructure. As with many layered compounds, CSHs have external and internal (interlayer) surfaces displaying multilayer adsorption of water molecules on external surfaces owing to the hydrophilic surfaces. Interlayer water was also quantified from water vapor isotherm, X-ray diffraction (XRD), and thermal gravimetric analyses (TGA) data, displaying nonreversible swelling/shrinkage behavior in response to drying/rewetting cycles. From this quantification and balance of water distribution, we were able to explain most of the widely dispersed data already published according to the various relative humidity (RH) conditions and measurement techniques. Stoichiometric formulas were proposed for the different CSH samples analyzed (0.6 < Ca/Si < 1.6), considering the interlayer water contribution.

Thanks to their active promotion of bone formation, bioactive glasses (BG) offer unique properties for bone regeneration, but their brittleness prevents them from being used in a wide range of applications. Combining BG with polymers into a true hybrid system is therefore an ideal solution to associate toughness from the polymer and stimulation of bone mineralization from the glass. In this work, we report the synthesis and characterization of hybrid scaffolds based on SiO 2 -CaO bioactive glass and gelatin, a hydrolyzed form of bone type-I collagen. Incorporation of calcium ions, known to trigger bone formation and cellular activity, into the hybrid structure was achieved at ambient temperature through careful control of chemistry of the sol-gel process. Thorough characterization of the materials highlights the effect of grafting an organoalkoxysilane coupling molecule to covalently link networks of BG and gelatin, and proves it a successful means to take control over the degradation and bioactive properties of hybrids. Importantly, BG-gelatin hybrids are synthesized in a process fully conducted at ambient temperature that allows obtaining open-porous scaffolding structures, with well-controlled and tuneable porosity with regards to both pore and interconnection sizes. Mechanical properties of the scaffolds under compression are similar to that of trabecular bone and their apatite-forming ability is even higher than that of pure BG scaffold foams.

Bioactive glass hybrids are among the most promising materials for bone regeneration, but the incorporation of calcium, a key element for mineralization properties of the implant, into the inorganic part of the hybrid network is challenging. We present here a synthesis route towards both class I and II gelatin-bioactive glass hybrids allowing the efficient incorporation of calcium ions at low temperature.

Unlike the long-range order of ideal crystalline structures, local order is an intrinsic characteristic of real materials and often serves as the key to the tuning of their properties and their final applications. Although researchers can easily assess local ordering using two-dimensional imaging techniques with resolution that approaches the atomic level, the diagnosis, description, and qualification of local order in three dimensions is much more challenging. Solid-state nuclear magnetic resonance (NMR) and its panel of continually developing instruments and methods enable the local, atom-selective characterization of structures and assemblies ranging from the atomic to the nanometer length scales. By making use of the indirect J-coupling that distinguishes chemical bonds, researchers can use solid-state NMR to characterize a variety of materials, ranging from crystalline compounds to amorphous or glassy materials. In crystalline compounds showing some disorder, we describe and distinguish the contributions of topology, geometry, and local chemistry in ways that are consistent with X-ray diffraction and computational approaches. We give examples of materials featuring either chemical disorder in a topological order or topological disorder with local chemical order. For glasses, we show that we can separate geometric and chemical contributions to the local order by identifying structural motifs with a viewpoint that extends from the atomic scale up to the nanoscale. As identified by solid state NMR, the local structure of amorphous materials or glasses consists of well-identified structural entities up to at least the nanometer scale. Instead of speaking of disorder, we propose a new description for these structures as a continuous assembly of locally defined structures, an idea that draws on the concept of locally favored structures (LFS) introduced by Tanaka and coworkers. This idea provides a comprehensive picture of amorphous structures based on fluctuations of chemical composition and structure over different length scales. We hope that these local or molecular insights will allow researchers to consider key questions related to nucleation and crystallization, as well as chemically (spinodal decomposition) or density-driven (polyamorphism) phase separation, which could lead to future applications in a variety of materials.

This article reports on the identification, synthesis, and in-situ structure determination of a new crystalline calcium borosilicate compound of composition CaSi(1/3)B(2/3)O(8/3). Synthesis was carried out by complete crystallization on annealing from a corresponding glassy composition in the widely studied CaO-SiO2-B2O3 ternary system. The crystallographic structure was determined ab initio using electron diffraction information and the charge flipping algorithm performed on synchrotron and neutron powder diffraction data collected in situ at high temperature. CaSi(1/3)B(2/3)O(8/3) is found to crystallize in the Pna2(1) (no. 33) orthorhombic space group, with a = 12.1025(4) Å, b = 5.2676(1) Å, c = 3.7132(1) Å, and V = 236.71(1) Å(3) at 650 °C. Solid-state (29)Si and (11)B NMR experiments have confirmed the existence of finite chains along the c axis, formed by corner-sharing SiO4 tetrahedra and BO3 units. Silicon and boron species share a crystallographic site, and the Si/B distribution induces different possible arrangements of the chains which are discussed in light of DFT calculations. At room temperature, the existence of a superstructure, resulting from the ordering within nanoscale domains, was explored by transmission electron microscopy.

The synthesis and structure resolution of RbLaF(4) are described. RbLaF(4) is synthesized by solid-state reaction between RbF and LaF(3) at 425 °C under a nonoxidizing atmosphere. Its crystal structure has been resolved by combining neutron and synchrotron powder diffraction data refinements (Pnma,a = 6.46281(2) Å, b = 3.86498(1) Å, c = 16.17629(4) Å, Z = 4). One-dimensional (87)Rb, (139)La, and (19)F MAS NMR spectra have been recorded and are in agreement with the proposed structural model. Assignment of the (19)F resonances is performed on the basis of both (19)F-(139)La J-coupling multiplet patterns observed in a heteronuclear DQ-filtered J-resolved spectrum and (19)F-(87)Rb HMQC MAS experiments. DFT calculations of both the (19)F isotropic chemical shieldings and the (87)Rb, (139)La electric field gradient tensors using the GIPAW and PAW methods implemented in the CASTEP code are in good agreement with the experimental values and support the proposed structural model. Finally, the conductivity of RbLaF(4) and luminescence properties of Eu-doped LaRbF(4) are investigated.

Ordering of disordered materials occurs during the activated process of nucleation that requires the formation of critical clusters that have to surmount a thermodynamic barrier. The characterization of these clusters is experimentally challenging but mandatory to improve nucleation theory. In this paper, the nucleation of a magnesium alumino-silicate glass containing the nucleating oxide TiO(2) is investigated using neutron scattering with Ti isotopic substitution and (27)Al NMR. We identified the structural changes induced by the formation of crystals around Ti atoms and show important structural reorganization of the glassy matrix.

From one- to two- and three-dimensional MAS NMR solid-state experiments involving (31)P and (27)Al, we show that the structure of microporous alumino-phosphate AlPO(4)-40 contains at least four times more sites than expected, and we attribute two types of Al(IV) sites. The newly described (27)Al-(31)P MQ-HMQC opens new possibilities of describing details of three-dimensional bounded networks., (2009 John Wiley & Sons, Ltd.)

The structure of the glass 2MgO-2Al(2)O(3)-5SiO(2)-TiO(2) was investigated using neutron diffraction with isotopic substitution. Reverse Monte Carlo (RMC) modeling was used to reproduce experimental structure factors derived from diffraction experiments. The local environment of titanium atoms was determined and it corresponds to an average of 5.4 ± 0.2 oxygen atoms at a mean distance of 1.86 ± 0.02 Å. This coordination number agrees with the predominance of fivefold coordination, with the coexistence of four- and sixfold coordination in similar amounts. (27)Al nuclear magnetic resonance (NMR) results revealed that the proportion of highly coordinated aluminum atoms in this titanium-bearing glass was higher than in the titanium-free sample. RMC modeling was used to interpret the structural role of these ([5])Al species and we show a trend for preferential bonding between ([5])Al and Ti atoms. This favored linkage is important to understand the role of titanium dioxide as a nucleating agent in inorganic glass-ceramics fabrication.

MgAl2O4 and ZnAl2O4 spinels have been irradiated by swift heavy ions (86Kr and 36S) simulating the irradiation by fission products for applications in the transmutation targets. The structures of unirradiated and irradiated spinel samples have been studied by NMR spectroscopy, with 27Al magic angle spinning and multiple-quantum magic angle spinning experiments. The parameters of fluence and electronic stopping power have been compared. For 86Kr ions, the obtained spectra are modified by irradiation: we observe a rise of the amount of aluminum in tetrahedral sites and a widening of the lines associated with the different aluminum environments compared with those of the pristine samples. Site exchange in the cationic sublattice is then observed and can be quantified from NMR spectra, determining the inversion parameter. An inversion parameter of 0.77 is estimated for the MgAl2O4 spinel irradiated with 1013 Kr ions/cm2, for a value of 0.275 in the pristine samples. Moreover, a line attributed to aluminum in 5-fold coordination with oxygen is observed in irradiated spinel samples at the maximum fluence for krypton. These new aluminum environments can characterize a transition layer which could change toward an amorphous layer, increasing the electronic stopping power and/or the fluence.

We show that weak 2J(71Ga-O-31P), typically approximately 12 Hz in GaPO4, can be used to efficiently establish heteronuclear 31P-71Ga correlation using a MAS HMQC experiment in gallo-phosphate materials. The experiment demonstrated for cristobalite GaPO4 is then applied to Ga(PO3)3, where it allows the differentiation of the signature of three different Ga sites overlapping in the 1D spectrum., (Copyright 2006 John Wiley & Sons, Ltd.)

Through-bond homonuclear correlation experiments can be realised in solids between spins of type X, separated by four chemical bonds, in X-O-Y-O-X motifs, provided a J coupling between X and Y exists: central transitions of quadrupolar 27Al spins can be correlated via the J2 scalar coupling between 27Al (X) and 31P (Y) in materials featuring Al-O-P-O-Al motifs.

27Al decoupling has been used to remove residual J-coupling interactions between 31P and 27Al in microporous aluminophosphates AlPO4-14 and AlPO4-40. In combination with 1H high-power decoupling, 27Al adapted decoupling yields 31P spectra with optimal sensitivity and resolution. The importance of double-resonance decoupling is further demonstrated by incorporating this technique in the MQHETCOR sequence. Unambiguous assignment of all the AlPO4-14 nuclear magnetic resonances is achieved by combining multiple-quantum evolution in the 27Al dimension and double-resonance decoupling in the 31P acquisition domain.

Phosphonate esters react with gamma-alumina under microwave (MW) irradiation; this reaction is a simple preparative method to graft organic pendant groups onto the surface of alumina; the efficiency of the grafting was readily checked by solid-state NMR techniques (31P and 27Al).

We report new measurements of NMR parameters for 71Ga in gallium bearing oxide reference compounds, ranging from perfectly ordered systems to disordered crystalline structures and their aluminate counterparts. Static, MAS, and QPASS spectra are obtained at magnetic fields ranging from 7.0 to 18.8 T. With these results we enhance the previously established correlation between isotropic chemical shifts of 71Ga and 27Al and propose a correlation between gallium and aluminum electric field gradients (EFG). This correlation shows that the EFG at 71Ga sites are generally three times greater than those at equivalent 27Al sites.