Synthesis and characterization of biphasic calcium phosphate substituted cerium as a potential osteoporotic bone filler

Biphasic calcium phosphate substituted cerium (BCP/Ce) is a potential material for osteoporotic bone filler. Synthesis of BCP/Ce was
conducted by the sol-gel method. This work aimed to study the influence of cerium as a precursor on the crystal structures, surface
properties, and agglomeration of BCP/Ce. A series of samples were prepared by various Ce percentages (0.5–16%) and a constant
molar ratio of (Ca + Ce)/P = 1.2. A structural study by Rietveld refinement calculation confirmed that synthesis without Ce produced
BCP that contained hydroxyapatite (HA) and β-tricalcium phosphate (β-TCP) at a ratio of 93:7. The presence of Ce increased β-TCP
content to 73% for the use of Ce 8%. None of Ca in the HA structure was replaced by Ce. Otherwise, Ce replaced Ca in β-TCP structure
by isomorphic substitution at the Wyckoff site of 6a (0,0,-0.085) or Ca (4) position. As the maximum occupancy of Ca (4) = 43%, about
17% of that was substituted by Ce for the use of 14% Ce. Ce was found in two states as Ce3+ and Ce4+ ions with Ce3+/Ce4+ ratio > 1.
The presence of Ce on the particle surface caused a change in the particle shape, from plate-like to spherical. The particle size decreased
to <100 nm with the increase of Ce content. The rise of Ce content in BCP decreased the luminescent property due to the increase of
oxygen vacancies. The negative value of Zeta potential confirms that BCP/Ce surface can accommodate bone cell proliferation.