Design of Experiments Study of Hydroxyapatite Synthesis for Orthopaedic Application Using Fractional Factorial Design

Hydroxyapatite, (HAp), Ca-10(PO4)(6)(OH)(2), is a naturally occurring mineral found in the inorganic component of enamel and human bone, consequently the present research focus is its ability to promote bone growth onto femoral implants when the HAp powder is sprayed using plasma thermal spraying. As the sprayed deposit requires certain mechanical and biological performances, the characteristics of the starting HAp powder will provide these properties. Hap powders were synthesized via a wet chemical precipitation technique using a Fractional Factorial, Resolution IV, two-level experimental design to evaluate the critical process parameters (reagent addition rate, reaction temperature, stirring speed, ripening time, initial calcium concentration, and the presence of an inert atmosphere) and their effect (main and interaction) on the final HAp powder characteristics, such as, phase composition, purity, crystallinity, crystallite size, lattice parameters, particle size, and particle size distribution. All six selected variables investigated, showed an influence (either as a minor or major significance) on one or more of the responses investigated, either as a main or interaction effect. However, both the ripening time and the stirring speed were found to significantly affect the majority of the five responses, with the reaction temperature also having a significant effect on the final phase composition, lattice parameters, and particle size.