Papers by Keyword: Apatite Layer

Abstract: Mineralization experiments on glasses of the Si-Ca-P-Mg system were carried out for 7 days in carbonated simulated inorganic plasma (CSIP) buffered with CO2/HCO3 -. This method enables physiological buffering of the solution within the 7.3–7.4 pH interval by maintaining a HCO3 - concentration between 24 and 27 mmol.L-1, which is the normal concentration range in blood plasma. XRD, SEM/EDS and FTIR were used to characterise the glass surfaces. All glasses exhibited an apatite-like deposit whose Ca/P ratio was dependent on glass composition.

Abstract: Two different techniques were used to promote a bioactive surface on a cobalt base alloy: i) the cobalt alloy melt was cast into wollastonite-coated cavities of an investment mold, or ii) wollasonite-encapsulated as-cast samples were heat treated at 1220°C for 1 h, this is the typical treatment performed to this alloy for improving its mechanical behavior. In vitro bioactivity was assessed by immersing samples in a simulated body fluid for 21 days. Potentially bioactive layers were obtained in both of the cases. A thicker apatite layer was formed on the samples obtained by investment casting. However, since the heat treatment needs to be performed, the heat treatment method is also a promising technique for promoting the bone-bonding ability of this Co alloy.

Abstract: In the aim to decrease the degradation rate of magnesium in simulated body fluid, pure magnesium was treated by two different routes, i) by soaking specimens in an HF aqueous solution at 30oC for 30 min and ii) by heating specimens at 345oC for 15 min. The treated samples were immersed in simulated body fluid (SBF) at 37oC for different periods of time. Samples with no treatment were also immersed in SBF. The magnesium released into the SBF, the weight loss of the specimens and the pH of SBF increased with time of immersion in all the cases. The heat treated samples showed a lower degradation rate and lower pH values. A substantial decrease of magnesium concentration in the SBF corresponding to the heat treated samples was also observed. However, the degradation rate of the heat treated samples remains being extremely high. On the other hand, a bonelike apatite layer was observed after only 3 days of immersion in SBF in all the cases. The thickness of this layer increased with time of immersion. Further research needs to be performed to decrease the degradation rate. However, these results indicate that magnesium is a highly potential bioactive material for biomedical applications.

Abstract: Bioactive Mg-PSZ composites were developed by using wollastonite ceramics either as a constituent of the composite formulation or as a bioactive bed during the biomimetic treatment in simulated body fluids. The zirconia composites were prepared by uniaxial pressing of powder mixtures and sintered at 1550oC in air. Wollastonite containing zirconia/alumina composites were also sintered at 1350oC. The composites were immersed in SBF for 7 days on a bed of wollastonite powder and then re-immersed in 1.5SBF for 7 days. Tests were also performed with no wollastonite bed. A highly bioactive surface was observed on the Mg-PSZ/CaSiO3 and Mg-PSZ/Al2O3 composites. A homogeneous apatite layer was detected on the Mg-PSZ/CaSiO3 composites immersed for only 7 days in SBF. No apatite was formed on the Mg-PSZ/Al2O3/CaSiO3 composite. During the sintering mechanism at either 1550 or 1350oC small amounts of aluminosilicate phases are formed. These phases inhibited the apatite formation.

Abstract: In silicate glasses the kinetics of apatite layer formation is usually rapid but the adhesion to the base glass is poor. Glass ceramics promote a stronger bonding between layer and substrate but decrease the rate of the apatite layer formation. In this work a glass of composition (wt%) 54,89%C3P-24,81%SiO2-20,30%MgO has been studied. This glass was heat treated at four temperatures (840 °C, 870 °C, 890 °C and 910 °C) to obtain glass ceramics with different contents of the same crystalline phase. A calcium magnesium phosphate phase was formed in all glass ceramics in a volume percent increasing with temperature. The apatite layer precipitated after immersion in simulated body fluid (SBF) formed faster on the glass than on the glass ceramics and a decrease in the amount of apatite formed was observed with the increase in crystallinity. It was generally concluded that heat treatment can turn a reactive glass into glass ceramics of different surface behaviors, from bioactive to quasi bio inert materials.

Abstract: Wollastonite ceramics was used in a biomimetic method to promote apatite formation on a Co-Cr-Mo alloy (ASTM F-75). The metallic samples were initially chemically treated in a 5M NaOH aqueous solution. The treated samples were immersed for 7 days in SBF on a bed of wollastonite and then immersed 7 or 14 days in 1.5SBF. For comparative purposes no wollastonite was used during the first 7 days in some tests. A homogeneous bonelike apatite layer was formed on the samples immersed in SBF on the wollastonite bed. The morphology and the Ca/P ratio of the layer were closely similar to those observed on the existing bioactive systems. A thinner homogeneous bonelike apatite layer was formed on the samples immersed in SBF and 1.5SBF without using wollastonite. However, the morphology and the Ca/P ratio of this layer differs slightly to that observed on the existing bioactive systems. The immersion of the samples during the first days in SBF on a wollastonite bed improves significantly the quality and thickness of the bonelike apatite layer.