Bone consists of a mineral phase (carbonate apatite) and an organic phase (principally collagen). Cancellous bone is characterized by interconnecting porosity necessary for tissue ingrowth and nourishment of bone cells. The purpose of the present study was to fabricate macroporous carbonate apatite (CAP) blocks with interconnecting porosity as potential bone substitute biomaterials by hydrothermal conversion of alpha-TCP foam in carbonate solution. The fabrication of the macroporous CAP was accomplished in two steps: (1) preparation of alpha-TCP foams using polyurethane foams as templates, and (2) hydrothermal conversion at 200 degrees C of alpha-TCP foam in the presence of ammonium carbonate solutions of different concentrations. The maximum carbonate content of the resultant CAP foam was approximately 7.4 wt %. The mean porosity of the CAP foam was as high as 93 vol %. The macroporous CAP blocks or granules prepared in this manner has properties similar to that of bone in mineral composition and in having interconnecting macroporosity necessary for osteoconductivity and tissue ingrowth. On the basis of composition and interconnecting macroporosity, the CAP foam materials could be ideal biomaterials for bone repair and as scaffolds for tissue engineering.

The effect of temperature on crystallinity of carbonate apatite (CAp) foam prepared from α-tricalcium phosphate (α-TCP) foam by hydrothermal treatment was investigated in the present study. The α-TCP foams were prepared through a conventional sintering method using polyurethane foam as template. Then, the resultant α-TCP foams were hydrothermally treated with Na 2 CO 3 aqueous solution at 100 • C, 150 • C and 200 • C for 72 h. After hydrothermal treatment, the cancellous bone-like macroporous structure of the α-TCP foams was maintained. However, microscopic morphology of the foams' frame significantly changed after the 72 h treatment period. The smooth surface of α-TCP foam disappeared and the whole surface was covered with plate-like deposits. The plate-like deposits treated at 150 • C and 200 • C had smooth surface while those treated at 100 • C were constructed from spherical particles of approximately 200 nm in diameter. The results of X-ray diffraction and Fourier transform infrared analysis showed that α-TCP was completely converted to CAp and the crystallinity of CAp prepared at 100 • C was significantly lower than those prepared at 150 • C and 200 • C. Hydrothermal treatment of α-TCP foam at 100 • C allowed the formation of low-crystalline CAp foam but complete conversion needs a longer treatment period.

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