Preformation Characterization of a Torque-Driven Magnetic Microswimmer with Multi-Segment Structure

Magnetically powered microswimmers exhibit various advantages in practical applications, including simplified propulsion mechanism of nonreciprocal motion in a low Reynolds (Re) number environment, high flexibility, and high efficiency. Inspired by the morphological and dynamic analyses of microscale nonreciprocal locomotion, this study characterizes the properties of torque-driven segmented microswimmers that actuated by an external oscillating magnetic field. The proposed microswimmer includes a magnetized head and several non-magnetized rigid body segments fabricated by two-photon lithography. The components of the microswimmer are linked together by rigid mechanical joints with an angle limiting mechanism, thereby forming simplified and discrete wave locomotion in a low Reynolds number environment. The motion of this multi-segment structure with different segment number is analyzed, and swimming locomotion involving segment interaction of the microswimmers and ambient liquid is characterized. Theoretical and experimental studies indicate that a minimum of three segments are needed to enable the microswimmers to move forward, whereas having four segments exhibits the best comprehensive performance. Based on this analysis, the geometric parameters of the four-segment microswimmers are further optimized, and experiments verify the enhancement of its motion capacity in a low Re number regime.