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The structural information on the influence of ionic additions in biphasic (hydroxyapatite (HAP) and b-tricalciumphosphate (b-TCP)) mixtures ranging from single ionic substitutions to combined ionic substitutions of most of the essential ions embedded in biological apatite was analyzed through the Rietveld refinement technique. The results have proved that the determined quantitative phase composition of HAP and b-TCP in biphasic mixtures was dependent on the initial calcium (Ca) deficiency of the precursor powders precipitated from the different molar concentrations used in the synthesis. The substitution of cations (Na 1 , Mg 21 , and K 1 ) improved the stabilization of the b-TCP structure whereas anions (F À and Cl À ) were found incorporated at the OH À site of the HAP phase. Rietveld analysis of X-ray powder diffraction data from the present study proved to be a powerful technique to describe the position and occupancy of certain ions like Mg 21 and Cl À in the biphasic mixtures. However, it has also shown limitations in tracking back other ions like Na 1 , K 1 , and F À , which require the use of other complementary characterization methods. Feature D. J. Green-contributing editor Financially supported by the Portuguese Foundation for Science and Technology from the project POCTI/CTM/60207/2004.

Scaffolds of AB-type carbonated hydroxyapatite (HA) were successfully produced via hydrothermal transformation (HT) of aragonitic cuttlefish bones at 200 degrees C. The transformation was seemingly complete after 9 h of HT and no intermediate products were registered. Beyond low production cost, worldwide availability, and natural-biological origin of raw materials, the produced scaffolds preserved the initial structure of cuttlefish bone, featuring good biocompatibility in osteoblasts tests and ideal pore size ( approximately 80 microm in width and approximately 100 microm in height) and interconnectivity for supporting biological activities, such as bone tissue growth and vascularization. The highly channeled structure and the use of fresh cuttlefish bones favored the diffusion of the reaction solution towards the aragonite resulting in fast kinetics (after 1 h, hydroxyapatite was the dominant crystalline phase).