1 School of Materials Science and Engineering, Nanyang Technological University, Singapore, Singapore. njcho@ntu.edu.sg.
2 Department of Medicine, Division of Gastroenterology and Hepatology, Stanford University School of Medicine, Stanford, CA, USA. jsglenn@stanford.edu.
3 Department of Microbiology and Immunology, Stanford University School of Medicine, Stanford, CA, USA. jsglenn@stanford.edu.