Synthesis and characterization of hydroxyapatite whiskers by hydrothermal homogeneous precipitation using acetamide

Long and uniform HA whiskers with high crystallinity, controlled morphology and high aspect ratio were successfully synthesized by hydrothermal homogeneous precipitation using acetamide. Compared with the additive urea, which is commonly used to raise the pH to drive nucleation and growth of HA crystals, acetamide has a low hydrolysis rate under the required hydrothermal conditions. This allows better and easier control, giving rise to rapid growth of whiskers at a low supersaturation. Whisker length and width were in turn determined by solution conditions, including the concentration of Ca and PO4. Whiskers had a mean length of 60–116 μm and an aspect ratio of 68–103 for starting solutions containing 42–84 mmol L−1 Ca and 25–50 mmol L−1 PO4 with a fixed Ca/P ratio of 1.67. Such whiskers are favourable for their improved bone bonding and bioactivity, as well as their mechanical properties. Whiskers were slightly Ca-deficient with Ca/P = 1.60–1.65, with the preferred direction of growth along the c-axis. Variation of acetamide concentration did not affect the constitution, the crystallinity or the crystal growth habit.