1. Advanced Fibro Science, Kyoto Institute of Technology, Matsugasaki, Sakyo-Ku, Kyoto 606-8585, Japan, Institute of Materials Research and Engineering, ASTAR (Agency for Science, Technology and Research), 3 Research Link, Singapore 117602, Singapore, and Division of Bioengineering, Faculty of Engineering, National University of Singapore, 9 Engineering Drive 1, Singapore 117576, Singapore