Key Engineering Materials Vols. 330-332

Abstract: Cadmium uptake by hydroxyapatite from aqueous solution was studied in time intervals between 2 minutes and 96 hours, using different Cd2+ concentrations (21 to 768 mg L-1). The solution pH after Cd2+ uptake was assessed. Dissolution experiments at fixed pH were performed in order to evaluate the ion exchange process. Cd2+sorption by hydroxyapatite is fast and it happens simultaneously by different mechanisms. Ion exchange is the main mechanism, where mechanism Cd2+ present in aqueous solution replaces Ca2+ from hydroxyapatite structure.

Abstract: Serum immersion, a new method of pre-treated HA ceramics, has been compared with SBF immersion and untreated HA particles in cell culture condition. MTT assay indicates that serum-immersion lessens particles cytotoxity of HA particles in cultured L929 mouse fibroblast cell (p<0.05). Neither immersion nor traditional physical factors such as particle size, shape should be responsible for these because SBF immersion with the similar factors results in no significant improvement. The reason might be serum proteins adsorption and biommetic microstructure formation on the ceramics surface, which affect cellular membrane behaviors, phagosome metabolization and cellular protein secretion. Otherwise, cells with particles degraded early apparently, which indicated that particles influence the cell cycle. The whole processes must be correlated intensively with cytokine, protease and intracellular ion concentration, which would be discussed in our follow-up studies.

Abstract: Titania layer was fabricated on the titanium substrates with chemical treatment with 20ml or 40ml of hydrogen peroxide solution and subsequent heat treatment at 400°C, coded as CHT20 and CHT40, respectively. CHT20 spontaneously deposited apatite on the surface in a simulated body fluid (SBF), while CHT40 did not. TF-XRD patterns showed that the diffraction intensity of anatase of CHT20 was higher than that of CHT40. It was suggested that the thicker titania layer indicated in vitro apatite forming ability. The cell proliferation of CHT20 and CHT40 were lower than NT and HT. Since the surface of titania layers became hydrophobic after autoclaving, we can suppose that the cell proliferation on CHT20 and CHT40 were lower than NT and HT due to their surface hydrophobicity.

Abstract: Bioceramic fibres, scaffolds and mats are important structures in biomedical applications. Electrohydrodynamic routes are relatively new for processing advanced materials and in this paper we use electrospinning to prepare zirconia fibres diameter down to 200nm and hydroxyapatite (HA) fibres down to 1$m. Zirconia-polymer and nHA-polymer composite scaffolds structures (mats) with 400-1000 $m windows were also prepared.

Abstract: Beta tricalcium phosphate (β - TCP) has been synthesized at relatively low temperature. The reaction product has been characterized by XRD, FT-IR and TEM. It is found that the polarity of synthesis media plays an important role in the formation of β - TCP crystal phase. In light of XRD, FT-IR and TEM results, the difference of reaction product between high and low polarity synthesis media might be attributed to carbonate groups, which might suppress the phase transformation process.

Abstract: The effect of hydrothermal reaction temperature and pH on crystallite size, phase stability, and sintered density of hydroxyapatite (HAp) has been investigated. The crystallite size increased with the increase in temperature but was not significantly affected by pH. The decomposition of HAp into tricalcium phosphate was observed at 1250°C and the extent of decomposition decreased with increase in pH. The influence of temperature and pH on the crystallite size and the decomposition was related to the decrease in solubility of Ca2+. The phase stability of HAp, prepared hydrothermally, in HAp/zirconia composites was higher than that of commercial HAp due to its high sintered density.

Abstract: In this study, 2.5-10 weight % natural zeolite (clinoptilolite) was added into phosphate bonded- investment in consideration of its molecular sieve property. Before casting, thicknesses of specimens were measured in 50 x magnifying stereo microscope. Average surface roughness (Ra) was measured. The first group was assigned as control and no zeolite addition was performed. In the second group, 2.5%, in the third group 5%, in the fourth group 7.5% and in the fifth group 10% zeolite by weight was added to investment powder. According to our study, volumetric increase was determined in each group. The highest increase was observed in the second group with 1.87%. The lowest one was observed in the fifth group with 1.03%. The lowest surface roughness was determined in the second group with 4.41.m. Although surface roughness and volumetric change values demonstrated differences, the change between groups could not reach statistical significance. It can be concluded that zeolite can be added to phosphate-bonded investment in order to decrease surface roughness and dimensional change of casting.

Abstract: A new type of glass-ceramic for novel dental fillers, which require excellent chemical durability, was investigated. A 40CaO-5CaF2-25TiO2-30P2O5 (in mol%) glass-ceramic was newly suggested. The glass-ceramic was prepared by a conventional two-step heating method. The resulting glass-ceramic included Nasicontype-CaTi4(PO4)6, titanium phosphates, such as (TiO)2P2O7 and Ti(PO3)3, and TiO2 (anatase) with apatite crystal, which was induced by incorporation of fluorine. In the glass-ceramic, dissolution by acid-treatment was strictly controlled. The excellent chemical durability of the glass-ceramic was suggested to originate from increase in the amount of the crystalline phases and a high content of titanium constituent in the residual glassy phase.

Abstract: This study investigated the mixed alkali effect in a series of phosphate based glasses. These glasses were of the composition 0.5P2O5-0.2CaO-0.3-xNa2O-xK2O where x=0 to 0.3 in steps of 0.05. This study considered density measurements using Archimedes’s principle, thermal characterisation using differential scanning calorimetry, phase analysis following crystallisation using X-ray powder diffraction (XRD), and degradation studies combined with ion release. The results showed that these mixed alkali glasses showed a linear decrease in density, with the ternary single alkali glass with 0.3mol K2O showing a 3% reduction in density as compared to that with 0.3mol Na2O which correlated well with the difference in ionic diameter and atomic weight of both cations. These glasses also showed intermediate glass transition temperature (Tg) values, compared to those of the ternary single alkali glasses having the same alkali oxide content, and the minimum Tg value was recorded for equimolar amounts of both alkali oxides. However, they did not show any significant change in the degradation rate compared to the glass with 0.3mol Na2O with the exception of the 0.25mol K2O glass. The single alkali glass with 0.3mol K2O showed a significant increase in the degradation rate by an approximate one order of magnitude. For the mixed alkali glasses with low molar concentration of K2O, only sodium phosphate-rich phases [NaCa(PO3)3 and Na4Ca(PO3)6] were detected from XRD; at high molar concentrations however, potassium phosphate-rich phases [KCa(PO3)3 and KPO3] were detected. At equimolar concentration of both alkali cations, KCa(PO3)3 and Na4Ca(PO3)6 were identified. K+, Ca2+, and P3O9 3- release followed the degradation behaviour where the highly degrading glasses with 0.25 and 0.3mol K2O released the highest amount of these ions; however, there was no definite trend in the remaining glass compositions.