Effect of bioactivation through acid/alkali process on the flexure strength of zirconia-based ceramics and composites

Zirconia-based ceramics such as tetragonal zirconia polycrystals (TZP) and alumina toughened zirconia (ATZ) are attractive as biomaterials because of their high strength, high fracture toughness, and excellent biocompatibility. However, their application has been limited by their bio-inertness, which prevents them from directly bonding to the living bone. Therefore, the bioactivation of zirconia materials through the acid/alkali process has been studied. Currently, there is little information on the low-temperature degradation (LTD) behavior associated with this treatment. In this study, we investigated the degradation behavior of TZP or ATZ by examining the monoclinic fraction and biaxial flexure strength after immersion in sodium hydroxide or phosphoric acid aqueous solutions. The results showed that the monoclinic fraction increased significantly, indicating LTD at the surface, whereas the strength was not affected. In addition, more apatite formation was observed on TZP than on ATZ after immersion in SBF for 7 days. In particular, under the phosphoric acid treatment condition, almost the entire surface was covered with apatite. The contact angle measurement showed the possibility of predicting the apatite formation ability during immersion in SBF.