Effects of lithium fluoride and maleic acid on the bioactivity of calcium aluminate cement: Formation of hydroxyapatite in simulated body fluid.

To improve the bioactivity of calcium aluminate cement (CAC), which has the potential of restoring defective bone and the joints between artificial prostheses and natural bone, lithium fluoride and maleic acid were added to CAC. Then the bioactivity of the CAC, together with the lithium fluoride and maleic acid, was estimated by examining the hydroxyapatite (HAp) formation on its surface in simulated body fluid (SBF). When 0.5 g of lithium fluoride and 8.75 g of maleic acid were added to 100 g of CAC, LiAl(2)(OH)(7).2H(2)O was formed on the surface of CAC after 1 day of soaking, and HAp was formed after 2 days. The depth of the LiAl(2)(OH)(7). 2H(2)O and HAp-mixed layers after 60 days of immersion was approximately 20 microm. However, after CAC, which contains only 8.75 g of maleic acid per 100 g of CaO.Al(2)O(3), had been soaking for just 30 days, 3CaO.Al(2)O(3).6H(2)O and HAp were detected. These results indicate that lithium fluoride accelerates HAp formation on the surface of CAC in SBF while maleic acid has little influence on HAp formation. The promotion of HAp formation on the surface of CAC in SBF can be explained in terms of the help of an intermediate layer, LiAl(2)(OH)(7).2H(2)O, which contains hydroxyl groups that act as the nuclei of HAp formation and a tremendous dissolution of calcium ions from CAC into the SBF solution within a short induction time.