1. Department of Materials Science and Engineering, Seoul National University, Seoul 151-744, Republic of Korea
2. Center for Biomaterials, Korea Institute of Science & Technology, 5, 14 Hwarang-ro, Seongbuk-gu, Seoul 02792, Republic of Korea
3. Graduate School of Nanoscience and Technology, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 305-701, Republic of Korea
4. Department of New Biology, DGIST, Dalseong, Daegu 711-873, Republic of Korea