Biological microorganisms swim with flagella and cilia that execute non reciprocal 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 micro-swimmers. However, most biomedically important fluids are non-Newtonian where the scallop theorem no longer holds. It should therefore be possible to realize a micro-swimmer that moves with reciprocal periodic body-shape changes in non-Newtonian fluids. Here, we report a symmetric “micro-scallop”, a single-hinge micro-swimmer 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 micro-devices that can propel by a simple actuation scheme in non-Newtonian biological fluids. (Nat. Commun. 5: 5119 (2014). doi: 10.1038/ncomms6119.)
Tian Qiu, Tung-Chun Lee, Andrew G. Mark, Konstantin I. Morozov, Raphael
Munster, Otto Mierka, Stefan Turek, Alexander M. Leshansky, and Peer
Fischer. Swimming by Reciprocal Motion at Low Reynolds Number. Nat. Commun.
5: 5119 doi: 10.1038/ncomms6119 (2014).