Effect of serum proteins on solution-induced surface transformations of bioactive ceramics

The kinetics of immersion-induced surface transformation reactions of synthetic bone bioactive ceramics were studied in vitro in either protein-free or protein-containing simulated physiological solutions. Both solutions had an ion content similar to that of plasma. Synthetic ceramics used for the study included Ca-deficient hydroxyapatite (CDHA), stoichiometric HA either not well crystallized or well crystallized (s-HA nwc or s-HA wc), oxyhydroxyapatite (OHA), beta-tricalcium phosphate (beta-TCP), and porous coralline HA (I-HA) and calcium carbonate (CC). Only CDHA and nwc s-HA led to immediate precipitation in both protein-free and protein-containing solutions. In contrast, reactions of wc HA and I-HA showed lag times to onset of precipitation in the protein-free solution and a further delay in the presence of proteins. The reactions of nonapatitic ceramics whose lag times in the protein-free solution were longer than those of apatitic, were completely blocked in the presence of proteins within the duration of the experiment (up to 3 days). CDHA and nwc s-HA were the only ceramics that, in the presence of serum proteins, led to the formation of B-type carbonated apatite, typical for calcified tissue apatite.