a
Center for Biomedical Engineering, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Cambridge, U. S. A
E-mail: alik@rics.bwh.harvard.edu
b
Harvard-MIT Division of Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge, U. S. A.
c
Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, U. S. A.
d
World Premier International-Advanced Institute for Materials Research (WPI-AIMR), Tohoku University, Sendai 980-8577, Japan