PHOSPHATE GLASSES AND GLASS-CERAMICS FOR BIOMEDICAL APPLICATIONS

抄録

Calcium phosphate glasses and glass-ceramics with some limited compositions show bioactivity. The glasses could be prepared by including a small amount of TiO₂ and/or Na₂O: the typical compositions were 60CaO-30P₂O₅-xTiO₂-(10−x)Na₂O in mol%. The glasses include orthophosphate and pyrophosphate groups. Hydroxyapatite (HA) forming ability in a simulated body fluid (SBF) is often examined to know the chemical properties of materials for biomedical applications. On the 60CaO-30P₂O₅-xTiO₂-(10−x)Na₂O glasses, HA formed within 7-10 days. In the case of the glasses, the HA-forming ability is suggested to be influenced by various factors such as the basicity of a gel layer formed on them in SBF and the amount of the functional groups for HA nucleation in the layer. Modification of the glass composition, which MgO was substituted to CaO, improved the glassification tendency of the glasses due to the high field strength of Mg²⁺. The MgO-containing glass included a larger amount of orthophosphate group than the original glass, and showed higher ion-releasing ability. Bivalent ions in the phosphate invert glasses play an important role in their glassification and ion-releasing. The glasses were crystallized and subsequently sintered by heating their powder-compacts. The resulting glass-ceramics consist of β-Ca₃(PO₄)₂ and β-Ca₂P₂O₇ with residual glassy phase. Their HA-forming ability in SBF was enhanced after autoclaving in distilled water. By the autoclaving, sodium, calcium, phosphate ions in the glassy phase around the surface dissolved and anatase crystals formed. The glass-ceramics could be coated strongly on a new β-type titanium alloy using a conventional glazing technique. The glass-ceramic-coated materials were implanted into the femurs of Japanese rabbits. After 1 month, bone tissue contacted directly with the coating. After 5 years of implantation, the coating was clarified to be work as a bioactive material on the titanium alloy.