Morphologically Controlled Fibrous Spherulites of an Apatite Precursor Biocrystal

Unique and characteristically formed spherulitic crystals of octacalcium phosphate (OCP, Ca 8 H 2 (PO 4 ) 6 ·5H 2 O) were grown for the first time by the gel method, using the system Ca(NO 3 ) 2 −(NH 4 ) 2 HPO 4 −agar. The shape of test tubes crucially affected the morphological development of the OCP crystals. The feature of OCP spherulites grown in U-type test tubes was an aggregation of a relatively ordered, large number of ultralong and flexible whiskers radiating from the center region of the spheres, resulting in high porosity. On the other hand, OCP crystals grown in straight test tubes were a spherulite consisting of a large number of short plate-like, well-faceted crystallites radiating from a common origin. In both cases, OCP crystals grew with spherulitic morphologies even under varied conditions of different growth parameters, including gel concentration, reactant concentration, and growth period.