1. Department of Metallic BiomaterialsInstitute of Biomaterials and Bioengineering, Tokyo Medical and Dental UniversityTokyo101‐0062Japan
2. Aisin Seiki Co., Ltd. Kariya Aichi 448‐8650 Japan
3. Department of Materials EngineeringGraduate School of Engineering, The University of Tokyo Tokyo 113–8656 Japan