Papers by Author: Heimo O. Ylänen

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Authors: Hanna Arstila, Di Zhang, Erik Vedel, Leena Hupa, Heimo O. Ylänen, Mikko Hupa
Abstract: The crystallization tendency for 30 experimental glasses in the system Na2O-K2O-MgOCaO-B2O3-P2O5-SiO2 was studied with thermal methods, DTA, HSM and XRD. The glasses were also immersed into simulated body fluid for 8 and 72 hours. The formation of the silica-rich gel and calcium phosphate layer on the glasses were analyzed with SEM. The in vitro behavior and crystallization tendency for heat-treated glasses were then related. This information is essential for choosing glass compositions that can be manufactured to desired products with controlled bioactivity for different applications. In general, glasses with low alkali content can tolerate heattreatment without crystallization but have less initial Si-gel formation ability and show less in vitro bioactivity than glasses with high alkali content.
Authors: Di Zhang, Eveliina Munukka, Outi Leppäranta, Leena Hupa, Heimo O. Ylänen, Jukka I. Salonen, Erkki Eerola, Matti K. Viljanen, Mikko Hupa
Abstract: Antibacterial effects of three powdered bioactive glasses were compared by measuring the pH of the simulated body fluid in immediate contact with the glass powder particles and by cultivating four microorganisms in the powder-solution mixtures. After individual cultivation with the microorganisms the bioactive glasses showed ability to kill bacteria, but the effects were very dependent on glass composition and on the microorganism as well as on cultivation time. The results indicated that antimicrobial property of bioactive glasses correlates with their ability to change the pH of the body fluid in immediate contact with the glass. However, the increase in pH is not the only factor influencing the antimicrobial properties.
Authors: Heimo O. Ylänen, Clifford Ekholm, Nikita Beliaev, Kaj H. Karlsson, Hannu T. Aro
Authors: N. Moritz, Erik Vedel, Heimo O. Ylänen, Mika Jokinen, Mikko Hupa, Antti Yli-Urpo
Authors: Erik Vedel, N. Moritz, Heimo O. Ylänen, Mika Jokinen, Antti Yli-Urpo, Mikko Hupa
Authors: Minna Vaahtio, Eveliina Munukka, Outi Leppäranta, Di Zhang, Erkki Eerola, Heimo O. Ylänen, Timo Peltola
Abstract: Four different bioreactive ceramics were prepared using a sol-gel method and a standard melting process. The aim was to study antibacterial effect of these materials on the growth of Staphylococcus epidermidis. The dissolution (Si and Ca ions) of fine (≤ 45 !m) ceramic powders in a tryptone soya broth (TSB) was investigated. Also the pH changes in TSB solution were measured. In addition the adherence of Enterococcus faecalis (Ef) to materials was investigated. The bacterial adhesion was studied using scanning electron microscopy (SEM). In the bacterial and the adhesion test, CaPSiO2 and S53P4 had the strongest antimicrobial effect against studied bacteria. It was shown that bioreactive sol-gel derived ceramic with sufficient high Ca ion release (> 270 ppm) can reach strong antibacterial effect also at lower pH values (< 9.6).
Authors: Di Zhang, Heimo O. Ylänen, Mikko Hupa, Leena Hupa
Abstract: In this work we summarize the most important findings of the influence of glass composition, sample shape and fluid circulation on in vitro behavior of bioactive glasses in the system Na2O-K2O-MgO-CaO-B2O3-P2O5-SiO2. The sample shapes included plates, particulates, powdered glasses, glass fibers and sintered cones with interconnected porosity. The in vitro bioactivity was measured as the changes observed in the immersion solution, SBF, and the formation of reaction layers on the samples at 4 to 168 h immersion. A lower surface area to volume ratio gave smaller changes on the ion concentrations and pH of the immersion solution but thicker reaction layers on the glass surfaces. In particulate systems with circulating fluid the pH gradients in SBF were lower but surface layers more even than in static systems. The influence of glass composition on reaction layer formation as suggested by glass plates correlated with the in vitro behavior of glass particulates larger than 250 µm, porous cones and fibers when using similar SA/V ratio.
Authors: Di Zhang, Eveliina Munukka, Leena Hupa, Heimo O. Ylänen, Matti K. Viljanen, Mikko Hupa
Abstract: Factors controlling the antibacterial ability of three bioactive glasses were studied by comparing the changes in the SBF during immersion of the glasses with their response to four microorganisms. After immersion of 100 mg/ml fine powder (<45μm) of the glasses in the SBF for 1, 2, 4, 8, 16, 27 and 48 hours, the immersion solutions were filtered and the pH in the bulk solution was measured. Ionic concentrations of Na, K, Ca, Mg, P and Si ions in the immersion solutions were determined by ICP-OES. The antibacterial activity of the glasses showed good correlation with the changes of the pH values in the SBF solutions. No correlation was found between the ionic concentration and the antibacterial ability of the three glasses against the four tested microorganisms. The results suggest that, the antimicrobial effect of the glass powder against the microorganisms tested is mostly dependent on the increase of the pH in the solution to values detrimental for the bacteria growth.
Authors: Di Zhang, Hanna Arstila, Erik Vedel, Heimo O. Ylänen, Leena Hupa, Mikko Hupa
Abstract: In vitro reactions of bundles of fibers with diameters 20-500 μm and crushed glasses of fractions 500-800 μm were compared with the reactions of plates of the same bioactive glasses. The samples were immersed in simulated body fluid (SBF) for 2-7 days. After immersion the changes on the surfaces of the samples were observed by SEM/EDXA. Layer formation on the glass surface was found to vary with glass composition, sample shape and local condition of single particle/fiber. However, only some fibers or particles formed similar in vitro reaction layers as the plates. The product form did not change the in vitro bioactivity of particles or fibers exposed to the bulk immersion solution. When the glasses were used as fiber bundles or particle beds, the packing degree and the flow of body fluids within the system interfered with the reactivity. Also a clear correlation between in vivo layer formation in bone and in vitro of the glass plates could be found.
Authors: D. Cacaina, Reeta Viitala, Mika Jokinen, Heimo O. Ylänen, Mikko Hupa, S. Simon
Abstract: Biodegradable silica microspheres containing neutron activable yttrium cations were investigated as a potential material for in situ radiotherapy of cancers. The sol-gel method used for preparing the microspheres allows obtaining at relative low temperatures materials of high purity and homogeneity, with controlled rate of biodegradability. The influence of yttrium on the biodegradability of the silica microspheres was studied in a simulated body fluid (SBF). The chemical durability of the microspheres was investigated under in vitro conditions and the concentration of yttrium released from the microspheres was determined.
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