1. Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139-4307, USA.
2. John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA.
3. Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
4. Department of Biological Sciences, University of South Carolina, Columbia, SC 29208, USA.
5. Experimental Facilities Division, Advanced Photon Source, Argonne National Laboratory, Argonne, IL 60439, USA.
6. Wyss Institute for Biologically Inspired Engineering, Harvard University, Cambridge, MA 02138, USA.
7. Kavli Institute for Bionano Science and Technology, Harvard University, Cambridge, MA 02138, USA.