A Comparative Study of the Sintering and Cell Behavior of Pure and Cobalt Substituted Hydroxyapatite

Abstract

Hydroxyapatite (HA) is a widely studied biomaterial for bone grafting and tissue engineering applications. The crystal structure of HA lends itself to a wide variety of substitutions, which allows for tailoring of material properties. Cobalt is of interest in ion substitution in HA due to its magnetic properties. The synthesis and characterization of cobalt-substituted Hydroxyapatite (CoHA) has not been widely studied, and there is a complete lack of studies on the sintering behaviors of CoHA materials compared to pure HA. Studying the sintering behavior of a substituted apatite provides insight into which applications are appropriate for the substituted material by supplying information regarding how the substitution affects material characteristics such as stability and bulk mechanical properties. In this study both pure HA and CoHA were synthesized, pressed into pellets, and then sintered at temperatures ranging from 900- 1300°C and 700-1200°C, respectively. The study thoroughly examined the comparative sintering behaviors of the two materials. It was found that CoHA is less thermally stable than pure HA, with decomposition to TCP beginning around 1200°C for pure HA samples, while at 800°C for the CoHA. The CoHA also had a lower mechanical strength than that of the pure HA. Although the CoHA would be unsuitable for bulk applications, it is a promising material for a variety of biomedical applications including drug delivery, cancer hyperthermia, and as a MRI contrast agent.