1. Department of Mechanical Engineering, Sogang University, 04107 Seoul, South Korea
2. Departments of Bioengineering, Electrical Engineering and Computer Science, and Biophysics Program, University of California, Berkeley, California 94270, USA
3. Department of Architecture, University of California, Berkeley, California 94270, USA
4. Department of Chemical and Biomolecular Engineering, Sogang University, 04107 Seoul, South Korea