[1] Stanford Univ, Dept Appl Phys, Stanford, CA 94305 USA
[2] Stanford Univ, Dept Mech Engn, Stanford, CA 94305 USA
[3] Tech Univ Munich, Inst Prod Dev, D-85748 Garching, Germany
[4] Univ Calif Berkeley, Ctr Interdisciplinary Bioinspirat Educ & Res, Berkeley, CA 94720 USA