1. Biophysical Engineering and Nanobiopolymers Laboratory, School of Engineering and Applied Science, University of Pennsylvania, Philadelphia, PA 19104, USA.
2. Laboratory for Cell and Tissue Engineering, School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA.
3. Stem Cell Bioengineering Laboratory, Institute of Biomaterials and Biomedical Engineering, Centre for Biomedical and Biomolecular Research, University of Toronto, Toronto, ON M5S 3E1, Canada.