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 vitroassessment of the bioactivity of artificial materials and for the formation of bonelike apatite on various substrates. Ion concentrations of conventional SBF cSBF are, however, not exactly equal to those of blood plasma, and hence the apatite formed in cSBF is not the same as bone apatite in its composition and structure. Recently, the present authors prepared new kinds of SBFs rSBF, iSBF, and mSBF with ion concentrations nearer to those of blood plasma. The rSBF and iSBF have ion concentrations equal to those of blood plasma in total and dissociated amounts, respectively. The mSBF has ion concentrations equal to those of blood plasma in total amount except for the HCO−3concentration, which was set to the saturated level with respect to calcite. In the present study, the stabilities of cSBF, rSBF, iSBF and mSBF were examined in terms of cluster formation in the fluids by means of dynamic light scattering photometry. The cSBF and mSBF were found to form only calcium phosphate clusters, whose initial hydrodynamic diameter was ∼1 nm, and this did not change with storage time at 36.5°C. Besides the calcium phosphate clusters, rSBF and iSBF 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 rSBF and iSBF can be attributed to their supersaturation with respect to calcite. These indicate that rSBF and iSBF lack longterm stability. The mSBF 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. © 2002 Wiley Periodicals, Inc. J Biomed Mater Res 64A: 339–348, 2003