Fabrication of Bioactive, 3D-Printed, Porous, Yttria-Stabilized Zirconia via Mg/Zn-Incorporated Modified Simulated Body Fluid Pretreatment

Yttria-stabilized zirconia (YSZ) has attracted attention as a ceramic implant material owing to its excellent mechanical strength, biocompatibility, and aesthetic properties. However, YSZ is bioinert and lacks the ability to directly bond with bone. This study aims to enhance the bioactivity of 3D-printed porous YSZ through modified simulated body fluid (m-SBF) pretreatments. The porous YSZ substrates fabricated by fused deposition modeling were first etched with hydrofluoric acid (HF) to increase the surface roughness, followed by immersion in CO₃^2-, Mg²⁺, and/or Zn²⁺ ion-incorporated m-SBFs. Among the tested solutions, the apatite coating formed in Mg²⁺- and Zn²⁺-containing m-SBF within one day, exhibiting uniform precipitation and a reduced tetragonal-to-monoclinic (t→m) transition. The incorporated Mg²⁺ and Zn²⁺ ions were successfully detected on the apatite coating, with Mg/Ca and Zn/Ca ratios of approximately 4.82% and 3.33%, respectively. Mg²⁺ is known to stimulate osteogenesis, while Zn²⁺ exhibits antibacterial activity. Furthermore, compared with standard SBF under high-temperature and high-pH conditions, the m-SBF induced markedly less t→m phase transition on YSZ substrates, suggesting that m-SBF, as a biomimetic medium for imparting bioactivity, provides a more suitable environment for YSZ substrates. This study demonstrates that HF surface treatment combined with Mg²⁺- and Zn²⁺-containing m-SBF pretreatment effectively imparts bioactivity to 3D-printed YSZ, offering a promising approach for next-generation osteoconductive ceramic implants.