Swimming by reciprocal motion at low Reynolds number.

Tian Qiu,Peer Fischer,Tung-Chun Lee,Alexander M Leshansky,Stefan Turek,Otto Mierka,Raphael Münster,Konstantin I Morozov,Andrew G Mark

doi:10.1038/ncomms6119

Abstract

Biological microorganisms swim with flagella and cilia that execute nonreciprocal motions for low Reynolds number (Re) propulsion in viscous fluids. This symmetry requirement is a consequence of Purcell’s scallop theorem, which complicates the actuation scheme needed by microswimmers. However, most biomedically important fluids are non-Newtonian where the scallop theorem no longer holds. It should therefore be possible to realize a microswimmer that moves with reciprocal periodic body-shape changes in non-Newtonian fluids. Here we report a symmetric ‘micro-scallop’, a single-hinge microswimmer that can propel in shear thickening and shear thinning (non-Newtonian) fluids by reciprocal motion at low Re. Excellent agreement between our measurements and both numerical and analytical theoretical predictions indicates that the net propulsion is caused by modulation of the fluid viscosity upon varying the shear rate. This reciprocal swimming mechanism opens new possibilities in designing biomedical microdevices that can propel by a simple actuation scheme in non-Newtonian biological fluids.

Highlights

Biological microorganisms swim with flagella and cilia that execute nonreciprocal motions for low Reynolds number (Re) propulsion in viscous fluids
This is known as the low Reynolds number (Re) regime (Reoo1) characterized by instantaneous and time-reversible flows that are described by the time-independent Stokes equation
Our micro-scallops are constructed from polydimethylsiloxane (PDMS), loaded with phosphorescent pigment, cast into a three-dimensional (3D) printed mold, which permits the use of different materials in a parallel fabrication process

Summary

Introduction

Biological microorganisms swim with flagella and cilia that execute nonreciprocal motions for low Reynolds number (Re) propulsion in viscous fluids. This symmetry requirement is a consequence of Purcell’s scallop theorem, which complicates the actuation scheme needed by microswimmers. Excellent agreement between our measurements and both numerical and analytical theoretical predictions indicates that the net propulsion is caused by modulation of the fluid viscosity upon varying the shear rate This reciprocal swimming mechanism opens new possibilities in designing biomedical microdevices that can propel by a simple actuation scheme in non-Newtonian biological fluids. Low Re locomotion of a true reciprocal motion microswimmer propelled by periodic body-shape changes has not been reported previously

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Results

Conclusion