1. School of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Drive, 637553 Singapore
2. Division of Gastroenterology and Hepatology, Department of Medicine, Stanford University School of Medicine, Stanford, California 94305, United States
3. Advanced Institute of Convergence Technology, Seoul National University, Suwon 443-270, South Korea
4. Veterans Administration Medical Center, Palo Alto, California 94304, United States
5. School of Chemical and Biomedical Engineering, Nanyang Technological University, 62 Nanyang Drive, 637459 Singapore