1 Faculty of Pharmaceutical Sciences, Hokkaido University, Kita 12 Nishi 6, Sapporo, Hokkaido 060-0812, Japan. Electronic address: tnakam@pharm.hokudai.ac.jp.
2 Georgie W. Woodruff School of Mechanical Engineering, Parker H. Petit Institute for Bioengineering and Bioscience, Georgia Institute of Technology, 315 Ferst Drive NW, Atlanta, GA 30332, United States. Electronic address: susan.thomas@gatech.edu.