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Programmable design and performance of modular magnetic microswimmers
Synthetic microswimmers are promising agents for targeted in-vivo healthcare as well as important frameworks from which to advance the understanding of locomotion strategies at the microscopic scale.[1,2] Nevertheless, constructing these types of devices with flexibility of design and in large numbers remains a challenge, stymieing the realization and scope of their application and the understanding and manipulation of their isolated and collective swimming strategies.[3] We take a step to meeting this challenge by using the programmed shape and arrangement of superparamagnetic modules to generate a tailored kinematic response to an external magnetic field that drives their assembly into bespoke jointed biomimetic microswimmers.
To demonstrate the capacity of this method for design innovation and production at scale, we employ it to assemble populations of four distinct swimmer architectures simultaneously. On actuation of the thus assembled swimmers with a magnetic field, we find that on an individual level their strokes can be characterized by a balance of viscous and magnetic forces, but that the magnitude of their velocities varies considerably. Linking performance to architecture, we find swimmers formed by tip-to-base connections of a series of size-graded triangular modules, locomote faster than more traditional designs comprising of a circular head and a slender tail, an enhancement we attribute to a stroke that better breaks its beating symmetry. By focusing on a flock of triangle-based swimmers we reveal four swimming couplings, thereby opening up avenues for theoretical comparison. In addition to the generation of tailored microswimmers, we envision that our flexible and robust approach to assembly will facilitate the engineering of microrobots of programmed design and functionalities drawing closer a broad range of applications at low Reynolds number.
Fig. 1 : Magnetic assembly of a jointed microswimmer from superparamagnetic modules. Scale bar is 20 microns.
References
[1] K. Bente et al, Small 14, 1-25 (2018)
[2] S. Metri et al., Physiol. Behav. 87, 052425 (2014)
[3] E. Diller, Found. Trends Robot. 2, 143–59 (2011)