1. Wyss Institute for Biologically Inspired Engineering, Harvard University, 3 Blackfan Circle, Boston, MA 02115, USA.
2. Department of Physical Therapy and Athletic Training, Boston University, 635 Commonwealth Avenue, Boston, MA 02215, USA.
3. Harvard John A. Paulson School of Engineering and Applied Sciences, Harvard University, 60 Oxford Street, Suite 403, Cambridge, MA 02138, USA.