Formation and growth of clusters in conventional and new kinds of simulated body fluids

Simulated body fluid (SBF) with ion concentrations approximately equal to those of human blood plasma has been widely used for the in vitro assessment of the bioactivity of artificial materials and for the formation of bone-like apatite on various substrates. Ion concentrations of conventional SBF (c-SBF) are, however, not exactly equal to those of blood plasma, and hence the apatite formed in c-SBF is not the same as bone apatite in its composition and structure. Recently, the present authors prepared new kinds of SBFs (r-SBF, i-SBF, and m-SBF) with ion concentrations nearer to those of blood plasma. The r-SBF and i-SBF have ion concentrations equal to those of blood plasma in total and dissociated amounts, respectively. The m-SBF has ion concentrations equal to those of blood plasma in total amount except for the HCO3- concentration, which was set to the saturated level with respect to calcite. In the present study, the stabilities of c-SBF, r-SBF, i-SBF and m-SBF were examined in terms of cluster formation in the fluids by means of dynamic light scattering photometry. The c-SBF and m-SBF were found to form only calcium phosphate clusters, whose initial hydrodynamic diameter was similar to1 nm, and this did not change with storage time at 36.5degreesC. Besides the calcium phosphate clusters, r-SBF and i-SBF formed calcium carbonate clusters, whose initial hydrodynamic diameters were 10-30 nm, and these increased significantly with storage time. The formation and growth of calcium carbonate clusters in r-SBF and i-SBF can be attributed to their supersaturation with respect to calcite. These indicate that r-SBF and i-SBF lack long-term stability. The m-SBF is recommended for the assessment of bioactivity of artificial materials as well as the formation of bonelike apatite on various substrates from the viewpoint of stability as well as similarity to blood plasma. (C) 2002 Wiley Periodicals, Inc.