Synthesis of nanosized calcium hydroxyapatite particles by the catalytic decomposition of urea with urease

Nanosized calcium hydroxyapatite particles were synthesized by the catalytic decomposition of urea with urease. The influence of the synthesis parameters, i.e., temperature and ratio of the reagents/urease concentrations, on the size and morphology of the hydroxyapatite particles were investigated. As reagents for the synthesis of hydroxyapatite, various amounts of CaCl₂, NaH₂PO₄, urea, and urease were used. The urease-catalyzed decomposition of urea leads to the homogeneous precipitation of hydroxyapatite because of the release of OH⁻ions during the hydrolysis of urea. In the same process, CO₃²⁻ions are also released and incorporated into the crystal structure of the hydroxyapatite. In the temperature range from 30–40 °C, it was found that low crystalline carbonate hydroxyapatite was formed in all cases. It was found that decreasing the ratio of the concentrations of the reagents to the urease concentration leads to decrease in the particle size to below 100 nm and the morphology changes from leafy-like to spherical.