Hydrothermal processing of hydroxyapatite nanoparticles—A Taguchi experimental design approach

Chemical precipitation followed by hydrothermal processing is conventionally employed in the laboratory-scale synthesis of hydroxyapatite (HAp) and extensive information on its processing conditions has therefore been provided in literature. However, the knowledge about the influence of some operating parameters, especially those important for a large-scale production, is yet insufficient. A specific approach based on a Taguchi orthogonal array was therefore used to evaluate these parameters and to optimize them for a more effective synthesis. This approach allowed us to systematically determine the correlation between the operating factors and the powder quality. Analysis of signal-to-noise ratios revealed the great influence of temperature and pH on the characteristic of powder. Additionally, the injection rate of one reagent into another was found to be the most important operating factor affecting the stoichiometric ratio of powders. As-prepared powders were also studied for their in-vitro bioactivity. The SEM images showed the accumulation of a new apatite-like phase on surface of the powder along with an interesting morphological change after a 45-day incubation of powder in SBF, indicating a promising bioactivity. Some results also showed the capability of simple hydrothermal method for the synthesis of a lamellar structure without the help of any templating system.

► CaP powders with novel structures and shapes were synthesized using a simple route.
► Effect of industrially important parameters was evaluated through Taguchi method.
► Fibrous lamellar HAp was synthesized without the help of any templating system.
► Nucleation of HAp at harsh acidic pH is found to be possible.
► Characteristics of powder can be improved with increasing the injection rate.