Surface reaction of stoichiometric and calcium-deficient hydroxyapatite insimulated body fluid

In the present study, the immersion behavior of two kinds of sintered HA wi th different Ca/P ratios in two different extracellular simulated solutions (Tris buffer and Hank's solutions) was investigated and compared. Results indicated that an as-received Ca-deficient HA (FHA) had a lower Ca/P ratio, larger linear shrinkage and higher density than a stoichiometric HA (MHA). When FHA powder was calcined at 900 degreesC, its Ca-deficient apatite str ucture was unstable and a significant amount of beta -TCP phase was formed. When heated to 1250 degreesC in air, the highly crystalline apatite struct ure of MHA was still stable without any noticeable decomposition. The FTIR spectra indicated that both immersed MHA and FHA in Hank's solution were gr adually covered with a layer of precipitated apatite during immersion. When immersed in Tris buffer solution, neither HA showed significant changes in their FTIR spectra. SEM observation indicated that the precipitation rate on immersed FHA surface was much higher than that on MHA surface when immer sed in Hank's solution. The weight loss and pH data confirmed the higher di ssolution rate of FHA than MHA in Hank's solution. (C) 2001 Kluwer Academic Publishers.