Phase evolution, mechanical properties and MRI contrast behavior of GdPO4 doped hydroxyapatite for dental applications.

Ca10(PO4)6(OH)2 doped with GdPO4 (HA-GP) was synthesized by a sol-gel technique, and its phase composition depended on the GdPO4 content. At low doping levels, the phase structure was composed of hydroxyapatite and some Ca3(PO4)2, and the content of the latter decreased with the doping content; when the doping content reached to 15 mol%, however, the Ca3(PO4)2 amount revealed a significant increase, and GdPO4 turned to be precipitated. With the addition of GdPO4, the microstructure of HA-GP pellets became dense, and the grain size decreased. GdPO4 doping enhanced the hardness of HA-GP due to a grain size effect. With increasing the doping content, the toughness increased initially followed by a decrease, and 7.5 mol% doping (HA-GP7.5) led to the highest toughness. Magnetization tests revealed that GdPO4 had paramagnetic behavior, which made it suitable for magnetic resonance imaging (MRI) contrast agent. The MRI contrast behavior of HA-GP7.5 was investigated. With the increase of the concentration, the T1 weighted MR image revealed enhanced brightness, while the brightness of T2 weighted MR images reduced gradually. Considering the phase structure, mechanical properties, and MRI contrast behavior, HA-GP7.5 might have a potential to be used in clinical medicine.