Preparation of bioactive sodium titanate ceramics

The in vitro bioactivity of sol–gel derived sodium titanates with different sodium contents was investigated. Calcined sodium titanates show bioactive behaviour when exposed to simulated body fluid (SBF). A higher sodium content entails higher bioactivity since a higher amount of sodium ions is available for the exchange with H3O+ ions from SBF, which results in the formation of Ti–OH groups and subsequently in the formation of an intermediate calcium titanate. The local pH increase triggers the formation of a biomimetic calcium phosphate layer on the surface. Sintering the samples leads to more crystalline sodium tri- and hexatitanate structures and a decrease of the sodium content. The amount of Na+ ions that can be released from the sodium titanate surface decreases due to a decreasing surface area and the reduced sodium content. As a result bioactivity is lost. Bioactive behaviour can be re-achieved by a subsequent chemical treatment of sintered sodium titanate ceramics in an aqueous NaOH solution.