1. Institute of Materials Research and Engineering, Agency for Science, Technology and Research, 3 Research Link, Singapore 117602
2. Centre d'Elaboration de Matériaux et d'Etudes Structurales, CNRS-Université de Toulouse, 29 Rue Jeanne Marvig, 31055 Toulouse, France
3. Division of Bioengineering, National University of Singapore, 9 Engineering Drive 1, Singapore 117576