Effect of bioactive ceramic composition and structure on in vitro behavior. III. Porous versus dense ceramics.

In vitro reaction kinetics of surface transformations of porous and dense bioactive ceramics were studied after immersion in simulated physiologic solution (SPS). Porous ceramics with identical macroporosity were commercially obtained: calcium carbonate marine coral (I-CC), coralline HA (I-HA), and a product, labeled as beta-tricalcium phosphate, which was partially transformed into beta-calcium pyrophosphate (I-beta-CP). Previously studied dense ceramics were used for comparison: Ca-deficient HA (CDHA), stoichiometric HA, both well and not well crystallized (wc and nwc s-HA), beta- and alpha-tricalcium phosphate (beta- and alpha-TCP). The induction time to precipitation increased as follows: CDHA, nwc HA < wc HA, I-HA < beta-TCP, I-CC << I-beta-CP. The reaction kinetics of ceramics with identical macroporosity varied substantially depending on composition, crystal structure, and ultrastructure. One of the porous ceramics, I-beta-CP, showed an inhibiting effect on precipitation reactions.