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Hydroxyapatite (Ca5(PO4)3(OH)) forms on pseudowollastonite (psW) (α-CaSiO3) in vitro in simulated body fluid, human parotid saliva and cell-culture medium, and in vivo in implanted rat tibias. We used crystallographic constraints with ab initio molecular orbital calculations to identify the active site and reaction mechanism for heterogeneous nucleation of the earliest calcium phosphate oligomer/phase. The active site is the planar, cyclic, silicate trimer (Si3O9) on the (0 0 1) face of psW. The trimer has three silanol groups (>SiOH) arranged at 60° from each other, providing a stereochemical match for O atoms bonded to Ca2+ on the (0 0 1) face of hydroxyapatite. Calcium phosphate nucleation is modeled in steps as hydrolysis of surface Ca–O bonds with leaching of Ca2+ into solution, protonation of the surface Si–O groups to form silanols, calcium sorption as an inner-sphere surface complex and, attachment of HPO42−. Our model explains the experimental solution and high resolution transmission electron microscopy data for epitaxial hydroxyapatite growth on psW in vitro and in vivo. We propose that the cyclic silicate trimer is the universal active site for heterogeneous, stereochemically promoted nucleation on silicate-based bioactive ceramics. A critical active site-density and a point of zero charge of the bioceramic less than physiological pH are required for bioactivity.

Pseudowollastonite ceramic (psW) is a bioactive ceramic that binds to bone when implanted in vivo and may be useful for the treatment of skeletal defects. However, there have been no studies that examined the interaction between psW and osteoblastic cells in vitro. This study investigated the suitability of psW as a substratum for cell attachment and the ability of the material to effect osteoblasts at a distance from the material surface. Fetal rat calvarial cells were plated onto the ceramic and examined by scanning electron microscopy. The findings reported show that cells attached and proliferated on the surface to the ceramic. Attachment by cells to the material can be enhanced by preincubation of psW in serum or media containing fibronectin. The adhesion of cells can be inhibited by addition of GRGDS peptides suggesting that adhesion to psW is mediated by integrin binding to adsorbed proteins. To study the effects of psW at a distance, cells were cultured in the presence but not in direct contact with the material. Subsequent changes in proliferation, alkaline phosphatase expression, and bone nodule formation were assessed. Cells grown in wells containing psW demonstrated an increase in both the rate and total numbers of bone nodules formed, although there were no differences in proliferation or alkaline phosphatase expression. Overall, these results suggest that psW is biocompatible and osteoconductive.

This study aimed to evaluate the cytotoxicity of substances leached by pseudowollastonite (CaSiO(3)). It has been previously shown that calcium (Ca(2+)) and silicate (SiO(3)(-)) ions are released from pseudowollastonite into biological solutions. Both of these ions are known to influence the biological metabolism of osteoblastic cells essential in the mineralization process and bone-bonding mechanism. The indirect toxicity evaluation was performed by extraction method, according to International Standard Organization (ISO). Pseudowollastonite pellets obtained by solid-state reaction were incubated, in culture medium, during 24, 48, 72 or 168 h at different concentrations (5, 10, 15, 50, 100, 200 mg/ml). The cytotoxicity of each extract in presence of human osteoblastic cell line (SaOS-2) was quantitatively assessed by measuring the viability (succinate dehydrogenase activity, MTT), the membrane integrity (the uptake of the neutral red by viable cells, NR) as well as the cell necrosis by measuring the lactate dehydrogenase (LDH) released in the culture medium. No significant alteration of membrane integrity or cell suffering was detectable. However, increased cell metabolism was observed for cells exposed to pseudowollastonite extract with longest extraction time (168 h). In conclusion, mineral elements leached by pseudowollastonite do not significantly affect the metabolism of osteoblastic cells.

This paper reports on the structural morphology of the interface in vivo between implants composed of bioactive synthetic pseudowollastonite ceramic and bone in rat tibias. Thin sections of the interfaces were examined after 6 and 8 weeks of implantation period in a high resolution transmission electron microscope up to the lattice plane resolution level. The interfaces developed normal biological and chemical activities and remained reactive over the 8-week period. The regions showing direct bone tissue bonding to the implant contained nanocrystals of hydroxyapatite-like phase growing epitaxially across the interface in the [002] direction. The nanocrystals were also identified in the bone tissue formed in the interfacial area. The reactivity of the implant caused in the first instance formation of an amorphous woven type of bone, which transformed into a crystalline lamellar type containing collagen fibres. The Ca/P ratio of the interfacial region was found to be between 1.67 in the mature bone tissue formed about 5 microm from the interface, and 2.06 in the regions right at the interface.

The synthesis of a number of halogenated aromatic methacrylate monomers was achieved by (1) the esterification of hydroxyl-containing methacrylate esters with 2,3,5-tri-iodobenzoic acid and (2) by the nucleophilic addition of 2,3,5-tri-iodobenzoic acid, or polyhalogenated phenols, to 2,3-epoxypropyl methacrylate, yielding white crystalline products which were fully characterized. These monomers could be homopolymerized in the melt to produce clear, intensely X-ray opaque glasses possessing high refractive indices. The monomers themselves were soluble in a variety of methacrylate monomers with which they could be copolymerized to produce clear radiopaque materials. The stability of the homopolymers in an aqueous environment was excellent as was thermal stability, exhibiting little decomposition below 300°C.

Diopside ceramic pellets with a nominal composition of 55.5 wt % SiO2-25.9 wt % CaO-18.0 wt % MgO were soaked in human parotid saliva (HPS) over different time intervals, to investigate the behavior of the material in a natural medium of high protein content. The results showed the formation of a hydroxyapatite (HA)-like layer on the surface of the ceramic, and suggested that the mechanism of HA-like layer formation in saliva was similar to that showed in vitro test by other silica-based materials. The HA-like layer formed at the interface was found to be compact, continuous, and composed of many small crystallites with ultrastructure similar to that of natural cortical bone and dentine. The study concluded that the high pH conditions (9.8) existing right at the ceramic/human parotid saliva interface promoted HA-like phase precipitation. At this stage of the study, it is possible to suggest that the diopside ceramic could be of interest in specific periodontal applications for bone restorative purposes. Morphology, structure, and composition of the interfacial reaction product were examined by Scanning and Transmission Electron Microscopy techniques (SEM and TEM), combined with Energy Dispersive X-say Spectroscopy (EDS). Changes in ionic concentrations were measured using Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES), while the pH right at the interface of diopside/PHS were determined with an Ion Sensitive Field Effect Transistor (ISFET-Meter) instruments. © 2005 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 73B: 54–60, 2005

In a previous study, a new ceramic material (Bioeutectic), prepared by slow solidification through the eutectic temperature region of the wollastonite-tricalcium phosphate system, was found to be reactive in a simulated body fluid. In the present study, the reactivity of the Bioeutectic was assessed in human parotid saliva. Samples of the material were soaked for one month in human parotid saliva at 37 degrees C. The experiments showed the formation of two separate zones of carbonate-hydroxyapatite-like phase on the periphery of the samples. The first zone was formed by reaction of the bioeutectic with the saliva and progressed inside the material. The other zone developed on the surface of the bioeutectic by precipitation from the media. The mechanism of carbonate-hydroxyapatite-like phase formation in human parotid saliva appeared to be similar to that of apatite-like phase found in a simulated body fluid.

Objectives: Pseudowollastonite (CaO·SiO2) was found to be bioactive in a simulated body fluid environment. In the present study, `in vitro' bioactivity of pseudowollastonite was further assessed in human parotid saliva. The main objective was to compare behaviour of the material in a natural medium of high protein content (human parotid saliva) with its behaviour in an acellular protein-free solution (simulated body fluid). Methods: Samples of polycrystalline pseudowollastonite were immersed for one month in human parotid saliva at 37°C. Changes in ionic concentrations in the human parotid saliva and the pH right at the interface of pseudowollastonite/human parotid saliva were determined. The products of the interfacial reactions were studied by thin-film X-ray diffraction, scanning and transmission electron microscopy. Results: The results confirmed formation of a hydroxyapatite-like layer on the surface of the material, and also suggested that the mechanism of hydroxyapatite-like layer formation in saliva was similar to that showed in simulated body fluid. Conclusions: The hydroxyapatite-like layer formed at the interface was found to be compact, continuous and composed of many small crystallites with ultrastructure similar to that of natural cortical bone and dentine. The study also concluded that the high pH conditions (10.32) existing right at the pseudowollastonite/human parotid saliva interface promoted hydroxyapatite-like precipitation. At this stage of the study, similarities of the material behaviour in saliva and acellular simulated body fluid suggest that the pseudowollastonite could be of interest in specific periodontal applications for bone restorative purposes.

Strength and fracture toughness of reaction-sintered mullite/zirconia composites (RSMZ) and reaction-sintered mullite/alumina/zirconia composites have been investigated as a function of temperature. Thermal shock resistance has also been determined. It was found that dispersion of zirconia particles and the particular microstructure of mullite obtained by means of anin situ reaction process leads to improved properties, with a room temperature fracture toughness of about 5.25 MPa m1/2. Up to 1000° C fracture strength and toughness values are quite high, which make these materials potential candidates for high temperature applications.

By studying simultaneous densification kinetics and reaction kinetics during the sintering and hot pressing of alumina-zircon mixtures, it has been possible to distinguish between the particle rearrangement and particle reshaping (diffusive) stages of the densification process. Particle rearrangement is found to be more significant during hot pressing (20 MN m−2) and is the dominant mechanism at relative densities up to 72%. In pressureless sintering, diffusive processes become dominant above relative densities of about 62%.

Solid state reactions between ZrO2· SiO2 and αAl2O3 in mixed powders were studied by quantitative X-ray diffraction, density measurements and qualitative EDAX. Data were obtained at temperatures ranging from 1400 to 1600° C for 5 h; the initial molar ratios of the reactants (Al2O3/ZrO2 · SiO2) varying from 0 to 5. The results indicate that: (1) ZrO2· SiO2 and αAl2O3 react and form ZrO2, crystalline 3Al2O3 · 2SiO2 and a noncrystalline mullite phase; (2) the non-crystalline mullite phase is an important transitional phase towards equilibrium under subsolidus conditions. In the experimental conditions used the amount of the non-crystalline phase varies by as much as about 15%. This phase is of great importance in the mechanisms of reaction sintering between ZrO2 · SiO2 and αAl2O3.

For years now Materials Science has been recognized as a specific scientific speciality. Does the Science which consists in preparing materials and in studying their properties possess its own basic foundations or, on the contrary, is its fundamental part only constituted by concepts from other scientific fields such as solid state physics, mechanics, electricity, crystallography, etc. It is the author's opinion that some particular key concepts such as “processing”, “non-equilibrium and evolution”, for instance, are specific to the Materials Science field and that a better definition of their content and of their mutual action may lead to a “global view” of Materials Science. An attempt is made here to look at and define such concepts and to initiate discussion and, above all, controversies.

On presente une methode de calcul du facteur d'intensite de contrainte pour un composite mullite-ZrO 2 apres frittage reactif

The crystallization of foils of Te100−xTlx prepared by rapid cooling from the liquid state has been studied. In most cases the early stages of the amorphous‐crystalline transformation lead to a metastable cubic phase with a metallic character.