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Edited by John A. Rogers, Northwestern University, Evanston, IL, and approved January 5, 2021 (received for review July 8, 2020)
Significance
Soft structures and materials are easily susceptible to mechanical instabilities, which can be harnessed for function, such as controlled locomotion. Here, we show how a reversible conical buckling instability of a pneumatically actuated sheet leads to an amphibious morph-bot that can crawl on land or swim in water. Our approach enables the design of novel shape-changing robots and other bioinspired machines at multiple scales using simple constituent materials and power sources.
Abstract
Locomotion of an organism interacting with an environment is the consequence of a symmetry-breaking action in space-time. Here we show a minimal instantiation of this principle using a thin circular sheet, actuated symmetrically by a pneumatic source, using pressure to change shape nonlinearly via a spontaneous buckling instability. This leads to a polarized, bilaterally symmetric cone that can walk on land and swim in water. In either mode of locomotion, the emergence of shape asymmetry in the sheet leads to an asymmetric interaction with the environment that generates movement––via anisotropic friction on land, and via directed inertial forces in water. Scaling laws for the speed of the sheet of the actuator as a function of its size, shape, and the frequency of actuation are consistent with our observations. The presence of easily controllable reversible modes of buckling deformation further allows for a change in the direction of locomotion in open arenas and the ability to squeeze through confined environments––both of which we demonstrate using simple experiments. Our simple approach of harnessing elastic instabilities in soft structures to drive locomotion enables the design of novel shape-changing robots and other bioinspired machines at multiple scales.
Footnotes
↵1A.N. and W.-K.L. contributed equally to this work.
- ↵2To whom correspondence may be addressed. Email: gwhitesides{at}gmwgroup.harvard.edu or lmahadev{at}g.harvard.edu.
Author contributions: A.N., W.-K.L., G.M.W., and L.M. designed research; A.N., W.-K.L., D.J.P., M.P.N., N.-N.D., and L.M. performed research; A.N., W.-K.L., and L.M. contributed new reagents/analytic tools; A.N., W.-K.L., G.M.W., and L.M. analyzed data; and A.N., W.-K.L., G.M.W., and L.M. wrote the paper.
Competing interest statement: G.M.W. acknowledges an equity interest in and board position with Soft Robotics, Inc.; the work described here has no current impact on practical soft robots and actuators.
This article is a PNAS Direct Submission.
This article contains supporting information online at https://www.pnas.org/lookup/suppl/doi:10.1073/pnas.2013801118/-/DCSupplemental.
Data Availability
All study data are included in the article and/or supporting information.
Published under the PNAS license.
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Elastic-instability–enabled locomotion
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- Engineering
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