a
Department of Mechanical Engineering, University of California, Santa Barbara, USA
E-mail: yixiao@physics.ucsb.edu
;
Fax: +1 805 8938651
;
Tel: +1 805 8937985
b
Materials Department, University of California, Santa Barbara, USA
c
Biomedical Sciences Department, Institute of Tropical Medicine, 2000 Antwerpen, Belgium
d
Rega Institute, KU Leuven, 3000 Leuven, Belgium