Effect of bioactivation treatment using phosphoric acid on mechanical properties and osteogenesis for 3Y-TZP

Yttria stabilized tetragonal zirconia polycrystals (Y-TZP) are attractive bone grafting materials for dental and orthopedic applications because of their high strength, high fracture toughness, and excellent biocompatibility. The bioinertness of zirconia makes it suitable for tribological applications such as bone heads. On the other hand, using zirconia as a bone grafting material requires direct bonding ability to living bone. Therefore, attention has been focused on developing surface treatment techniques to directly provide bioactivity to the zirconia surface. Chemical treatment using phosphoric acid has been reported to show excellent apatite-forming ability using simulated body fluid in an in vitro model. Also, it is known that zirconia reacts with water or water vapor and undergoes low-temperature degradation (LTD) accompanied by a phase transformation from tetragonal to monoclinic. However, there is still insufficient research on the degradation behavior of zirconia during phosphoric acid treatment and its effect on bioactivity. This study investigated the osteogenic evaluation employing MC3T3-E1 cells and the LTD behavior of 3Y-TZP after treatment with a phosphoric acid solution. The results revealed the conditions that improve osteogenesis after phosphoric acid treatment. The conditions were, first, excellent cell proliferation and second, a medium contact angle of 40-60 degrees. Also, the decrease in strength with phosphoric acid treatment was limited. Therefore, the possibility of improving osteogenesis was shown by optimizing the phosphoric acid treatment conditions.