1. Department of Ceramic Engineering, School of Advanced Materials Engineering, Yonsei University, 134 Shinchon‐dong, Seodaemun‐gu, Seoul 120‐749, Korea
2. Department of Material Chemistry, Graduate School of Engineering, Kyoto University, Yoshida, Sakyo‐ku, Kyoto 606‐8501, Japan
3. Department of Orthopaedic Surgery, Graduate School of Medicine, Kyoto University, Shogoin, Sakyo‐ku, Kyoto 606‐8507, Japan