We successfully controlled the morphology of hydroxyapatite (HAp) grown in a solution system based on simulated body fluid (SBF). Nanometric low-dimensional forms, such as sheets and needles elongated in the c axis, were produced with phosphate-surplus (or calcium-deficient) HAp in the solution at human body temperature. The nanoneedles were obtained on the seed crystals under gentle growth conditions at pH 6.5; the nanosheets were grown through coalescence of tiny grains or needles at a relatively high growth rate above pH 7.0. On the other hand, micrometric bulky hexagonal shapes and faceted plates of semi-stoichiometric HAp were grown under hydrothermal conditions at pH 7.0 and 7.4, respectively. The variation of the morphology is discussed on the basis of the change of the growth mode of HAp crystals depending on the supersaturated conditions.

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