1. Research Department, Japan Medical Materials Corporation, 3-3-31 Miyahara, Yodogawa-ku, Osaka 532-0003, Japan, and Department of Materials Engineering, School of Engineering, Division of Science for Joint Reconstruction, School of Medicine, and Center for NanoBio Integration, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan