Metallic Muscles, developed by our team, are monolithic macroscopic bodies of nanoporous metal. By reversibly varying the capillary forces at the interface between the solid and a gas or liquid in the pore space, one can induce reversible elastic strain of the entire macroscopic sample, with amplitudes up to and exceeding 1%. The performance suggests possible applications as stiff, large strain actuators. The strain can be controlled by electric signals or similar to muscle activity in biological systems it can be prompted by direct conversion of chemical energy into mechanical work.
J. Weissmüller, R.N. Viswanath, D. Kramer, P. Zimmer., R. Würschum and H. Gleiter
Charge-Induced Reversible Strain in a Metal
Science 300 (2003), 312.
D. Kramer, R. N. Viswanath and J. Weissmüller
Surface-Stress Induced Macroscopic Bending of Nanoporous Gold Cantilevers
Nano Letters 4 (2004) 793.
J. Biener, A. Wittstock, L. Zepeda‑Ruiz, M. M. Biener, D. Kramer, R. N. Viswanath, J. Weissmüller, M. Bäumer and A. V. Hamza
Surface chemistry driven actuation in nanoporous gold
Nature Mater. 8 (2009) 47.
H.J. Jin, X.L. Wang, S. Parida, K. Wang, M. Seo and J. Weissmüller
Nanoporous Au-Pt Alloys as Large Strain Electrochemical Actuators
Nano Letters 10 (2010) 187.
H.J. Jin and J. Weissmüller
Bulk Nanoporous Metal for Actuation
Adv. Eng. Mater. 12 (2010) 714.
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The bond forces between the atoms in the outermost layer of a metal surface can be manipulated by means of space-charge layers. Such layers are readily induced and controlled as part of the electrochemical double layer at the metal-electrolyte interface. Since nanoporous metals dispose of many surfaces, the modified bond forces induce large stress and strain in the bulk of the porous solid.