Understanding bioactivity and polarizability of hydroxyapatite doped with tungsten

This study investigates the use of hydroxyapatite (HAp) doped with hexavalent tungsten to improve its interaction with bone cells and to influence the polarizing capacity of HAp. Increases in dopant concentration increased the β-TCP phases and decreased the HAp phases in sintered samples. Results of thermally stimulated depolarization current measurements suggested that doped HAp had stored fewer charge compared with pure HAp. However, the decrease in stored charge was related to fraction of HAp or β-TCP phases present in sintered samples. Activation energy of dipole relaxation and stored charge was used to examine the mechanism of polarization. The charge stored in doped samples due to polarization was attributed to the migration of H(+) ions in HAp phases and O(2-) or Ca(2+) ions in β-TCP phases. Hindrance of ion migration due to the presence of different phases appeared to lower charge storage ability in doped samples. In vitro study revealed an increase in bioactivity of doped HAp when compared with pure HAp. Polarization further improved the bioactivity of doped HAp. Results of our study provide evidence for the use of higher valent cations to improve biological performance of HAp ceramics.