Hydroxyapatite Formation on the Alumina coated with Bioactive Glass

초록

Alumina has been used as an orthopedic material because of its high mechanical strength and nontoxicity in human body. However, it doesn’t have a behavior of chemical bonding to living tissue. On the other hand, Bioactive glass shows a bonding behavior to living tissue in human body. However, application of bioactive glass is limited by its poor mechanical strength. Therefore, in this study, bioactive glass was coated on an alumina to make an orthopedic material, which has a high mechanical strength as well as bioactivity. Usually, the thermal expansion coefficient of a bioactive glass is much higher than that of an alumina. This difference causes the cracks in the glass layer when you coat the glass on the alumina. Therefore, we tried to coat another glass layer between bioactive glass and alumina in order to buffer the thermal expansion difference Each glass powder was spray-coated on an alumina disc. The ground coat was fired at 1250℃ for 30min., and the bioactive glass coat (cover coat) was fired at 1100and 1200 ℃ for 30min. The obtained samples were reacted in SBF. When the bioactive glass coated on an alumina was fired at 1100℃, the glass layer was crystallized into a b-wollastonite with small amount of apatite. On the other hand, when the sample was fired at 1200℃, the layer was crystallized into an a-wollastonite as major phase. When the samples were reacted in SBF, the hydroxyapatite crystal precipitation rate was much faster in a a-wollastonite crystal-containing layer than in a b-wollastonite-containing layer. And the hydroxyapatite forming rate was even faster than that in the bulk glass with same composition.