Hydroxyapatite-coated ZrO2 scaffolds with a fluorapatite intermediate layer produced by direct ink writing

Zirconia scaffolds with total porosity ranging between 61.1 and 75.3 vol% were fabricated by direct ink writing. The rheology of the ink, as well as the density, morphology and mechanical properties of the produced ZrO2 scaffolds were characterized. The compressive strength was dependent upon the porosity level, and ranged from 20.8 to 62.9 MPa. ZrO2 scaffolds having porosity of 75.3 vol% were then coated with hydroxyapatite (HA) by slurry infiltration. To suppress the reaction upon sintering between HA and ZrO2, fluorapatite (FA) as an intermediate layer was introduced. The ZrO2/FA/HA scaffolds were immersed in simulated body fluid (SBF) and physiological saline solution (0.9% NaCl) for up to 28 days to evaluate their bioactivity and dissolution behavior, respectively. ZrO2/HA/HA scaffolds were also tested, for comparison. The results show that the specimens with FA/HA layers possessed better bioactivity and exhibited slower dissolution rate than the samples with the HA/HA coating.