23.7

Conclusions and Future Perspectives

This chapter presents findings on stoichiometric HA and HA substituted with ions

like potassium, zinc, magnesium, strontium, europium, fluorine, and silicon as

single, dual or multi-substituted and synthesized by sol-gel process, followed by

suitable heat treatment. Ionic substitution and heat treatment have a significant

influence on the crystallite size, crystallinity, lattice parameters “a” and “c,” as

well as morphology. In addition, the phase constitution indicating conversion of

hydroxyapatite phase to β-TCP and α-TCP phases is affected by both the substitution

and the heat treatment. The ionic substitution of HA with elements like F, K, and Zn

enhances the structural stability, while Eu, Si, Sr, and Mg substitution results in

lowering the structural stability. Furthermore, the substitution of HA with elements

like Eu, F, and Si improves the thermal stability of HA, but ionic substitution with Zn

and Mg is responsible in lowering the thermal stability. The degradation of ionic

substituted powders in SBF during in vitro immersion study clearly indicates the

bioactive behavior of the as-synthesized as well as heat-treated nanopowders. The

mineralization of nanopowders, during immersion in SBF, resulted in the formation

of apatite like phase on the surface of nanopowders. This indicates that the

nanopowders are likely to help in promoting bone growth under in vivo conditions

as well.

Literature reports that secondary phases form in hydroxyapatite on ionic substi-

tution, due to which there is a significant change in Ca/P molar ratio. Moreover, a

Fig. 23.11 ZnFHA coated 316L SS

448

S. Kapoor et al.