Papers by Author: Mikko Tukiainen

Abstract: Melts in the composition range of bioactive glasses have their liquidus temperatures within or close to the working range. Additionally, bioactive glasses show a strong tendency to crystallization due to their composition. Thus, many bioactive glass compositions are unsuitable for demanding working procedures such as fiber drawing. In this work we discuss the suitability of different methods for measuring liquidus temperature of bioactive glasses. Thermal analysis was used, and complemented by sintering curves as given by hot stage microscopy. Hot stage microscopy could be used to measure liquidus also when the thermal effect associated with liquidus was low and consequently the DTA was not suitable. Liquidus of some glasses was measured with optical microcopy for samples heat treated in a gradient furnace. The values indicating the crystallization of the samples during viscosity measurement with rotational viscosimeter were compared with the other measurements. The crystalline phases formed at liquidus were identified with XRD and SEM-EDXA. The measured liquidus temperatures were also tested by drawing fibers directly from molten glass and from preforms heated to typical fiber drawing viscosity values. For all compositions the fiber drawing viscosity values were below liquidus. Continuous fibers could be manufactured of compositions only with low rates of crystal nucleation and growth.

Abstract: Implants with long lasting bioactivity and mechanical sustainability would be of interest in several novel clinical applications. By processing bioactive glass fibers and biodegradable polymers into 3D structures, bone formation ability of glasses and flexibility of polymers can be combined. In order to achieve desired physiological response, reactivity of bioactive glass fibers must be specified. Bundles of fibers within the range of bioactivity were soaked in the simulated body fluid at stationary conditions for several time intervals after which the cross-sectional surfaces of the fibers were studied with SEM-EDXA. The reaction layers and precipitations formed on the fiber surfaces suggest that the fibers react according to three mechanisms depending on the glass composition. Fibers with a high in vitro bioactivity showed the formation of distinct and thick silica –rich and calcium phosphate –rich layers already at one day’s immersion. Fibers of medium bioactivity did not show any clear silica –rich layer but a formation of calcium phosphate precipitations or layers at one day’s immersion. Slow glasses showed sporadic calcium phosphate precipitation only after the longest immersion times. The results indicate that the medium and slow glasses are interesting alternatives for applications where a long term mechanical durability suggested by their slow reactivity in combination with their osteoconductive tendency is desired.