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PubMed2001

Early dissolution of a morsellised impacted silicate-free bioactive glass in metaphyseal defects.

The purpose of this study was to evaluate the biological properties of idealized, morsellised impacted Corglaes, a soluble silicate-free glass. Twenty-two sheep underwent implantation of pellets in six metaphyseal defects in both rear limbs. Particle size distribution of all aggregates (except the autograft) approached the ideal logarithmic grading line and all implants were impacted to a standard compactive effort. Treatment groups consisted of (1) empty defect (negative control), (2) autograft (positive control), (3) allograft (clinical control), (4) allograft idealized with Corglaes, (5) 50/50 allograft/Corglaes and (6) Corglaes. Defects were sealed with polymethylmethacrylate. Healing of the defects was evaluated at 7 weeks (n=6) and 14 weeks (n=16) with computed tomography, histology, and histomorphometry. Remnants of Corglaes were found within one of the defects 7 weeks after implantation. Defects filled with mixtures containing 50% or 100% Corglaes were less dense, contained less bone and more fibrous tissue than defects with allograft, autograft, or allograft idealized with Corglaes. Allograft idealized with Corglaes may be considered for impaction grafting in revision hip arthroplasty, as well as local delivery of antibiotics. However, further studies and potential revision of the agent are required before mixtures containing concentrations of Corglaes equal to or higher than 50% can be recommended.

Animals↗
PubMed2003

Siliceous spicules and skeleton frameworks in sponges: origin, diversity, ultrastructural patterns, and biological functions.

Silica deposition is a fundamental process in sponges. Most sponges in the Classes Demospongiae and Hexactinellida secrete siliceous elements, which can subsequently fuse, interlock with each other, or form three-dimensional structures connected by spongin. The resulting skeletal frameworks allow sponges to grow upwards and facilitate water exchange with minimal metabolic cost. Several studies on sponge skeletogenesis have been published. We are beginning to understand the mechanisms of spicule secretion and the role of spicules and skeletal frameworks in the biology, ecology, and evolution of sponges. Molecular techniques and ecological experiments have demonstrated the genetic control of the process and the contribution of environmental factors to the expression of a sponge spicule, respectively. However, other classic topics such as the role of membranes in silicon transport or whether spicules are formed in situ or secreted anywhere in the sponge mesohyl and then transported to the skeletal framework require further investigation. We review the process of silica deposition in sponges at the molecular and cellular levels, as well as the biological and ecological functions of spicules and skeletons. The genetic control of spicule shapes makes them useful in the reconstruction of sponge phylogeny, although recent experiments have demonstrated the influence of environmental factors in modulating spicule size, shape, and the presence or absence of one or more spicule types. The implications of such variations in sponge taxonomy may be important. Besides supporting sponge cells, spicules can help larvae stay buoyant while in the plankton or reach the bottom at settlement, enhance reproduction success, or catch prey. Conversely, the role of spicules and skeletons in deterring predation has not been demonstrated. Knowledge of several aspects is still based on a single or a few species and extrapolations should be made only with caution. With the advent of new molecular techniques, new lines of research are presently open and active in this field.

Animals↗
PubMed1989

First stages of crystallization in a silicate glass: study by high-resolution electron microscopy.

The first stages of crystallization have been investigated for a glass in the system SiO2-Al2O3-Li2O with small amounts of titanium and zirconium as nucleating elements. The studies were performed by electron diffraction and electron microscopy in high-resolution mode. It has been found that the two phases forming the final glass ceramic crystallize successively. The first one gives small crystallites (less than 5 nm) randomly dispersed. The lattice plane images in several orientations are in good agreement with TiZrO4 crystal lattice. At 780 degrees C the average crystal size increases with increasing time of the heat treatments from 2.5 nm at 0.5 h to 4.5 nm at 2 h and then remains nearly constant. The crystallization of the second phase, a silicate solid solution with beta-quartz structure, occurs after complete crystallization of TiZrO4.

Ceramics↗
PubMed1996

A Stray Field Magnetic Resonance Imaging Study of the Drying of Sodium Silicate Films.

Stray field magnetic resonance imaging (STRAFI) is shown to be highly suited to the study of drying processes in thin films. Sodium silicate films have been chosen as a model system exhibiting many of the properties of film drying in general. Films have been dried, as a function of temperature in the range 22 to 62 degrees C, down to water contents of order 28% by weight, at which stage the film is glassy. The experimental results have been quantitatively analyzed by treating the drying film as a colloidal solution. The results suggest that the localized hydrogen spin-spin relaxation time, and hence the mobility of the water in the films is independent of the drying regime and depends primarily on the local water concentration.

Journal Article↗
PubMed2002

Silver-palladium nanodispersions in silicate matrices: highly uniform, stable, bimetallic structures.

Ag-Pd nanobimetallic colloidal particles are prepared in a single step by a chemical reduction method. Organically modified aminosilicate is used as a supporting matrix as well as a stabilizing agent, to obtain very uniform, well-distributed bimetallic particles. These nanoparticles are found to be stable for several months in both the solid and the liquid phases. The structure of the bimetallic particles has been followed by X-ray photoelectron spectroscopy and ultraviolet-visible spectroscopy. The distribution and the particle size are determined by transmission electron microscope and X-ray diffraction studies. Polymerization and condensation of the support silicate material have been confirmed by Fourier transform infrared spectroscopy.

Journal Article↗
PubMed1996

Selection of internal standards for analysis of silicate rocks and limestones by laser ablation inductively coupled plasma atomic emission spectrometry (LA-ICP-AES).

Included (Si, Ca) and added (Li, B) internal standards (IS) have been used comparatively in LA-ICP-AES of silicates and limestones to improve both precision and accuracy. A Q-switched Nd:YAG laser (355 nm, 10 Hz, 10 mJ per shot) has been applied for ablation. Samples have been prepared by fusion with Li(2)B(4)O(7) and measured using a Perkin-Elmer Optima 3000 ICP system. Both types of IS have given a relative standard deviation (RSD) less than 2-1%, which improved the repeatability by a factor of 2-10 and calibration graphs have been linear over the whole concentration range.

Journal Article↗
PubMed1996

Total digestion of silicate containing matrices (plants, soil, sludges) using a pressure ashing device with PFA-vessels.

A digestion procedure for silicate containing matrices like soil, sludge, etc. by using a commercially available pressure ashing device (Seif-Aufschlubetatechnik, Germany) with PFA (perfluoroalkoxy) sample vessels is described at the results for different matrix- and trace elements in different suitable certified standard reference materials. The advantages of this technique compared with the use of Teflon(R)-(PTFE, polytetrafluoroethylene) vessels and the open treatment in Pt-crucibles will be discussed.

Journal Article↗
PubMed2006

Novel method for aroma recovery from the bioconversion of lutein to beta-ionone by Trichosporon asahii using a mesoporous silicate material.

In this work, we report on the synthesis and ability of the mesoporous material MCM-41 to adsorb the norisoprenoid beta-ionone. This compound, with a violet aroma note, can be produced from lutein by the yeast Trichosporon asahii through a bioconversion process. We found that beta-ionone inhibited the yeast growth and constrained aroma formation. Growth inhibition was overcome using silicate MCM-41 as sorbent device in a fermentation system that allowed product removal from the culture medium by headspace manipulation. Compared to a commercial silica gel, the mesoporous material exhibited a 4.5-fold higher beta-ionone adsorption. Contrasting to cultures without the sorbent device, the presence of MCM-41 allowed a marked increase (14-fold) in beta-ionone production. Our results suggested that confinement of the norisoprenoid into the sorbent material bypassed its toxicity which allowed a better beta-ionone production. This study represents the first report on the use of MCM-41 to recover an aroma produced by fermentation and therefore, a novel application for a mesoporous material.

Adsorption↗
PubMed2002

Diversity of mineral cell coverings and their formation processes: a review focused on the siliceous cell coverings.

Mineral cell coverings are found in various protists. Some macroalgae accumulate calcium carbonate in the intercellular space, and some unicellular organisms use calcium carbonate or silica for the construction of loricas, scales, and frustules. Diatoms are representatives of those utilizing silica for the material of the cell covering called a frustule. The development of the frustule is initiated in a silica-deposition vesicle (SDV), which occurs just beneath the plasma membrane and, subsequently, the silicified cell covering expands its area, following the expansion of the SDV from valve face to valve mantle. Sequential valve development with whole valves is reviewed in several diatoms placed in different phylogenetic positions. Every diatom commences its valve formation from its pattern center and then develops by means of individual procedures. The results indicate that the valve development reflects the phylogeny of diatoms. In addition, recent progress in silica biomineralization is briefly reviewed, and the phylogeny of ability concerning siliceous cell covering formation is inferred.

Journal Article↗
PubMed1988

Synthesis of a phosphono analogue of cardiolipin and study of its silicic acid column chromatographic behaviour.

The synthesis is reported of the phosphono analogue of cardiolipin namely of 1,2-dipalmitoyloxypropyl-3-(2'-hydroxy propyl-3'-(1",2"-dipalmitoyl glycerol]biphosphonate. This was prepared by the condensation of 1,2-dipalmitoyl glycerol with 1,2-dipalmitoyl-oxypropyl-3-(2'-hydroxy propyl-3')-biphosphonate catalyzed by tri-isopropylbenzene sulfonyl chloride in pyridine. The final product was characterized by elemental analyses, phosphono phosphorus determinations, thin-layer chromatography and IR spectroscopy. The silicic acid column chromatographic behaviour of the phosphono analogue of cardiolipin was also studied.

Cardiolipins↗
PubMed1976

The determination of silicates in urinary calculi.

The determination of silica and silicates in urinary calculi is rendered difficult by the common occurrence in such material of high concentrations of calcium, magnesium and orthophosphate. The problem has been studied, and manual and semi-automated procedures for the determination are described. 145 stones from the urinary tracts of patients with spinal cord injury were analysed, but in all of them the silicon content was below the limit of detection of 0.7 gSiO2 per 100 g calculus.

Autoanalysis↗
PubMed1989

Siliceous pneumoconiosis in two dogs.

A siliceous pneumoconiosis was detected in two dogs by light microscopical, transmission electron microscopical and elemental analysis methods. Aluminium and silicon were the predominant elements and were present in macrophages associated with airways and vessels. The significance and origin of the deposits are discussed.

Aluminum↗
PubMed1995

1H solid-state nuclear magnetic resonance study of the mobility of the tetrapropylammonium template in a purely siliceous MFI-type zeolite.

Dynamics of tetrapropylammonium (TPA) cation occluded during the synthesis in a siliceous MFI zeolite is investigated by 1H broad-line nuclear magnetic resonance (NMR) methods. Second moments M2, spin-lattice relaxation times T1 and T1 rho are measured in a large temperature domain. To al comparison, similar measurements are also reported in bulk tetrapropylammonium bromide (TPABr). Whereas methyl reorientation at low temperature and tumbling of the cation in the plastic phase are observed in crystalline TPABr in accordance with published studies, a new slower motion which could not be identified is observed below the phase transition. Such a motion is much more clearly shown by the existence of a minimum of T1 rho in a quenched sample. Our measurements in the zeolite demonstrate that the TPA template exhibits a larger and more complex mobility below 378 K. Beyond the fast methyl reorientation, the results disclose a motion which probably involves the entire propyl arms inside the channels. So the zeolite framework seems to make such a kind of motion easier. On the contrary, even at 450 K, the highest temperature investigated, the tumbling which would necessitate exchange of the propyl arms between the channels is not observed. A slow motion, responsible for a decrease of T1 rho above 350 K, could not be identified. While a simple correlation time is sufficient to describe the relaxation time dependences in TPABr, a distribution (such as Williams-Watts) is required to account for those in the zeolite.

Magnetic Resonance Spectroscopy↗
PubMed1995

Deconvolution of 29Si magic-angle spinning nuclear magnetic resonance spectra of silicate glasses revisited--some critical comments.

It is common practice to quantify 29Si magic-angle spinning nuclear magnetic resonance (MAS NMR) spectra of silicate glasses by using lineshape fitting routines based on Gaussian distribution functions. This procedure depends on several -implicit -assumptions. In this contribution we have addressed and questioned these underlying assumptions. Also "goodness-of-fit" criteria and experimental considerations ("goodness-of-data") have been discussed. Some illustrative practical examples (silica glass, binary Na2O-SiO2 glasses with different Na:Si ratio) are given.

Algorithms↗
PubMed2003

Size distribution of colloidal silica in sodium silicate solutions investigated by dynamic light scattering and viscosity measurements.

Three types of aqueous sodium silicate solutions characterized by molar SiO(2):Na(2)O ratios of 2.2, 3.3, and 3.9 were investigated by dynamic light scattering and viscosity measurements. The solutions were prepared by diluting concentrated commercial products to SiO(2) content between 0.5 and 15 wt%. Dynamic light scattering (DLS) was used for the investigation of size distributions of colloids immediately after dilution. At least three size classes of colloidal particles were detected, which exist in parallel in the solutions. The respective radii are 0.4 to 0.6 nm, 2.5 to 13 nm, and 75 to 85 nm. The larger colloids dominate the mass distribution, whereas the smaller colloids control the surface area of the colloidal fraction. Material properties such as pH, viscosity, refractive index, and density were measured as a function of dilution. The evaluation of the viscosity data indicated that the colloids have a lower density than dense amorphous silica. Aging effects could be suppressed by measuring within 1 h after dilution.

Journal Article↗
PubMed2005

Polysaccharides as a template for silicate generated by sol-gel processes.

The polysaccharides, as established previously (Yu.A. Shchipunov, J. Colloid Interface Sci. 268 (2003) 68; Yu.A. Shchipunov, T.Yu. Karpenko, Langmuir 20 (2004) 3882), can manipulate the formation of hybrid silica nanocomposites by sol-gel processes. Here atomic force microscopy was applied to show whether carbohydrate macromolecules serve as a template for silicate. Mica was used as a substrate to adsorb polysaccharide. It was found that its surface is not neutral to the sol-gel processes, providing the silica precipitation. To hinder it, the mica was protected by a monomolecular film of arachidic acid with the help of a Langmuir-Blodgett technique. Hydrophobically modified cationic hydrohyethylcellulose was adsorbed from a diluted aqueous solution. It was demonstrated that the carbohydrate macromolecules located on the hydrophobic surface did promote silica precipitation, serving as a template.

Journal Article↗
PubMed2005

Application of mean-field model of polymer melt intercalation in organo-silicates for nanocomposites.

The mean-field, lattice-based model of polymer melt intercalation in organically-modified layered silicates (OLS) originally developed by Vaia and Giannelis was applied for different polymers such as poly(methyl methacrylate) (PMMA), polypropylene (PP), and poly(ethylene oxide) (PEO). The nature of each polymer controls significantly the intercalation of the system. The internal energy change caused by the interaction of polymer, surfactant and clay is the strongest factor in determining the equilibrium structure of the nanocomposite system.

Journal Article↗
PubMed2005

Bimetallic nanoparticles: a single step synthesis, stabilization, and characterization of Au-Ag, Au-Pd, and Au-Pt in sol-gel derived silicates.

Nanobimetallic particles consisting of Au-Pd, Au-Ag, and Au-Pt have been synthesized in a single step by a sol-gel process and stabilized in liquid and solid matrices. Organically modified silicates (Ormosils) that play a dual role of a matrix and of a stabilizer have been used to obtain very stable dispersions in the form of sols, gels, and monoliths. The simultaneous reduction of metal ions leads to either a surface enriched with one component or an alloy type of structure depending on the bimetal combination. The nanometallic dispersions are characterized by absorbance, TEM, XRD, IR, XPS, and CO adsorption studies. The stabilized nanoparticles are found to be good electrocatalysts and the preliminary results on the electrochemical reduction of oxygen are reported.

Journal Article↗