Dissolution of Hydroxyapatite Reinforced Grain Boundary by Glassy Phases
Several sintering additives for hydroxyapatite have been tested in order to enhance its sinterability without decomposing the hydroxyapatite(Ca10(PO4)6(OH)2) and without decreasing the bioactivity and/or biocompatibility. In case of sintered pure hydroxyapatites significant dissolution was occurred after immersion in distilled water or in simulated body fluid. At first the dissolution was iniciated at grain boundary creating the nano-size defects such as small pores and grew up to micro scale by increasing the immersion time. This dissolution resulted in grain separation at the surfaces and finally in fracture. And the dissolution was concentrated on those grains adjacent to pores rather than those in the dense region. So glass-reinforced hydroxyapatite(GR-HA) ceramics were prepared to strengthening the grain boundary to prevent dissolution. Several glasses were added at 0 to 10wt.% and sintered at 1200 °C for 2h in air with moisture protection. Glass phase was incorporated into hydroxyapatite to act as the sintering aids followed by crystallization in order to improve the mechanical properties without reducing the biocompatibility. From dissolution test, significant damage was reduced even more than 7days. X-ray diffraction and SEM showed no decomposition of hydroxyapatite to secondary phases and fracture toughness was increased more than pure hydroxyapatite.
Xingdong Zhang, Xudong Li, Hongsong Fan, Xuanyong Liu
S. H. Youn et al., "Dissolution of Hydroxyapatite Reinforced Grain Boundary by Glassy Phases", Key Engineering Materials, Vols. 330-332, pp. 31-34, 2007