Comparitive study of the formation of hydroxyapatite in simulated body fluid under static and flowing systems.

alpha-CaSiO3 ceramics of nominal composition CaO 46.0, SiO2 54.0, and Na2O 0.4 mass% were soaked in simulated body fluid (SBF). The soaking systems were maintained under both static and flowing conditions to study their effect on the formation of hydroxyapatite (HAp). Two different flowing systems were designed for soaking, namely, a closed system using a fast flow rate of about 2.8 mL/s (circulating system) and an open system using a slow flow rate of about 40 mL/day (slow flowing system). The HAp layer in all samples initially formed as a rough layer of ball-like particles. Under a fast flow of SBF solution, silica gel particles peeled from silica-rich interlayer during the first soaking period. The silica gel particles then reattached to the product HAp layer and induced the formation of new HAp particles of smaller size. In the slow flowing system, the rough HAp layer initially formed on the ceramic surfaces became gradually smoother after prolonged soaking. The formation rate and thickness of the HAp layer decreased with increasing flow rate of the SBF solution. These results indicate that flowing SBF solution gives rise to differences in the formation rates, formation behavior, and microstructure of the HAp layer. Copyright 2002 John Wiley & Sons, Inc. J Biomed Mater Res 60: 175–185, 2002