Degradation of alumina and zirconia toughened alumina (ZTA) hip prostheses tested under microseparation conditions in a shock device

This paper considers the degradation of alumina and zirconia toughened alumina vs. alumina for hip implants. The materials are as assumed to be load bearing surfaces subjected to shocks in wet conditions. The load is a peak of force; 9 kN was applied over 15 ms at 2 Hz for 800,000 cycles. The volumetric wear and roughness are lower for ZTA than for alumina. The long ZTA ageing did not seem to have a direct influence on the roughness. The ageing increased the wear volumes of ZTA and it was found to have a higher wear resistance compared to alumina.Comment: International Conference on BioTribology (ICoBT 2011), Londres, 18 au 21 septembre 2011, Londres : United Kingdom (2011

Degradation of alumina and zirconia toughened alumina (ZTA) hip prostheses tested under microseparation conditions in a shock device

International audienceThis paper considers the degradation of alumina and zirconia toughened alumina vs. alumina for hip implants. The materials are as assumed to be load bearing surfaces subjected to shocks in wet conditions. The load is a peak of force; 9 kN was applied over 15 ms at 2 Hz for 800,000 cycles. The volumetric wear and roughness are lower for ZTA than for alumina. The long ZTA ageing did not seem to have a direct influence on the roughness. The ageing increased the wear volumes of ZTA and it was found to have a higher wear resistance compared to alumina

Durées de vie de prothèses de hanche en biocéramiques soumises à des dégradations par chocs

National audienceLes prothèses de hanche visent à remplacer l'articulation coxo-fémorale. Les céramiques, notamment l'alumine, sont très utilisées pour la réalisation des têtes fémorales et des cupules cotyloïdiennes. Grâce à une machine unique en Europe, on peut tester dans des conditions sévères, le comportement des prothèses de hanche soumises aux chocs, afin d'estimer leur durée de vie. Le cycle de force appliqué est un pic de force de 9 kN pendant 30 ms à une fréquence de 2 Hz. Les essais ont été menés à sec, articulation non lubrifiée, ou en solution (sérum bovin). L'ensemble tête-cupule est incliné à 45° pour respecter la position anatomique. Les prothèses étudiées sont en alumine. Les essais, doublés ou triplés selon le milieu, sont conduits jusqu'à 800000 cycles ou jusqu'à la rupture de la cupule. A sec, la rupture est intervenue pour 254000 ± 43000 cycles. En solution, aucune rupture n'a été observée après 800000 cycles. Des ruptures intergranulaire et intragranulaire ont été observées au Microscope Electronique à Balayage (MEB). Pour tous les essais, on met en évidence des bandes d'usure sur la tête, analogues à celles observées ex vivo. Cette dégradation est plus rapide pour les essais à sec qu'en solution. La rupture de la cupule se produit lorsque la bande d'usure supérieure est voisine de 4 mm. Les analyses de rugosité par Microscopie à Force Atomique (AFM) ont montré que, pour les zones non usées, Ra-3D (rugosité 3D) = 9,1 ± 5,1 nm et pour les zones usées Ra-3D = 277,9 ± 29,4 nm ; ces valeurs sont comparables avec celles mesurées ex vivo. Ces résultats valident la machine de chocs comme un dispositif qui permet de reproduire et de comprendre les mécanismes d'endommagement des prothèses de hanche en biocéramique. Enfin, ces travaux expérimentaux nous permettront d'obtenir des résultats de référence et de les comparer à ceux qui découleront d'investigations autour de la modélisation multi-échelles

How do the grains slide in fine-grained zirconia polycrystals at high temperature?

Degradation of mechanical properties of zirconia polycrystals is hardly discussed in terms of solution-precipitation grain-boundary sliding due to experimental controversies over imaging of intergranular amorphous phases at high and room temperatures. Here, the authors applied the techniques of mechanical spectroscopy and transmission electron microscopy (TEM) to shed light on the amorphization of grain interfaces at high temperature where the interface-reaction determines the behaviour of fine-grained zirconia polycrystals. They present mechanical spectroscopy results, which yield evidences of an intergranular amorphous phase in silica doped and high-purity zirconia at high temperature. Quenching of zirconia polycrystals reveals an intergranular amorphous phase on TEM images at room temperature.Comment: 12 pages, 3 figure

Structural transformations of bioactive glass 45S5next term with thermal treatments

International audienceWe report on the structural transformations of Bioglass® during thermal treatments. Just after the glassy transition, at 550 °C, a glassy phase separation occurs at 580 °C, with the appearance of one silicate- and one phosphate-rich phase. It is followed by the crystallization of the major phase Na2CaSi2O6, from 610 to 700 °C and of the secondary phase, silico-rhenanite, at 800 °C. The latter evolves from the phosphate-rich glassy phase, which is still present after the first crystallization. In order to control the processing of glass-ceramic products from Bioglass®, crystallization kinetics were studied via differential scanning calorimetry measurements in the range of 620–700 °C and temperature–time–transformation curves were established

Accurate characterization of pure silicon-substituted hydroxyapatite powders synthesized by a new precipitation route

International audienceThis paper presents a new aqueous precipitation method to prepare silicon-substituted hydroxyapatites Ca10(PO4)6-y(SiO4)y(OH)2-y(VOH)2-y (SiHAs) and details the characterization of powders with varying Si content up to y = 1.25 mol molSiHA−1. X-ray diffraction, transmission electron microscopy, solid-state nuclear magnetic resonance and Fourier transform infrared spectroscopy were used to accurately characterize samples calcined at 400°C for 2 h and 1000°C for 15 h. This method allows the synthesis of monophasic SiHAs with controlled stoichiometry. The theoretical maximum limit of incorporation of Si into the hexagonal apatitic structure is y < 1.5. This limit depends on the OH content in the channel, which is a function of the Si content, temperature and atmosphere of calcination. These results, particularly those from infrared spectroscopy, raise serious reservations about the phase purity of previously prepared and biologically evaluated SiHA powders, pellets and scaffolds in the literature