* Corresponding authors

^a Department of Materials Science and Engineering, University of Pennsylvania, 3231 Walnut Street, Philadelphia, PA, USA
E-mail: shuyang@seas.upenn.edu
Fax: +1 (215) 573-2128
Tel: +1 (215) 898-9645

^b Department of Mechanical Engineering, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei, Taiwan

^c Department of Chemical Engineering, Lehigh University, 111 Research Drive, Bethlehem, PA, USA
E-mail: anj6@lehigh.edu
Fax: +1 (610) 758-5057
Tel: +1 (610) 758-4396

^d Department of Theoretical and Applied Mechanics, Cornell University, 322 Thurston Hall, Ithaca, New York, USA