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

Abstract

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. INDEX TERMS magnetic microrobot; microswimmer; multi-segment structure.

Enhancing magnetically driven microswimmer velocity via low Reynolds number hydrodynamic interactions

“…Additionally, multi-link structures with various rigid segments linked by joints, are an imitation of the discrete flagellum and have similar propulsion effectiveness to wave motion [32,33]. Theoretical and experimental research by Xing et al [34] on a multi-segmented microswimmer propelled by an external oscillating magnetic field revealed the ideal segment number for better efficacy and substantiated that a microswimmer with four segments exhibits superior performance. As we can see, the multi-link models are relatively simple to derive their equation of motion compared to the continuous model of flagellated microswimmer where coupled partial differential equations are involved [35].…”

A review on microrobots driven by optical and magnetic fields

“…11(b). 151 Its body was fabricated using two-photon photolithography and its head segment was deposited with a thin layer of Ni. This work used many theoretical analyses and experiments to demonstrate that the microrobot required a minimum of three segments to move forward smoothly and required more segments (four, five is the maximum) to achieve good moving performance.…”

“…135,137 Alternating magnetic fields combine the features of a rotating magnetic field and magnetic gradient field, which can actuate soft microrobots or microrobots with flexible components based on asymmetric reciprocating motions or undulatory motions. 150,151 Optical actuation has a limited manipulation area which the light must reach, and the light pathway should not be blocked. Magnetic actuation has a relatively large operation area and can control objects to move in 2D or 3D space.…”

Buoyant magnetic milliswimmers reveal design rules for optimizing microswimmer performance

“…11 For example, Xing et al constructed a multilink swimmer (3-5 links) with revolute joints using two-photon polymerization, and demonstrated net translation through a fluid using a sinusoidally oscillating magnetic field as a control input. 12 Dreyfus et al, as well as recent work from our lab by Harmatz et al, demonstrated that microspheres could be chained together with various DNA nanostructures, 8,13 and both Maier et al and Pauer et al used microspheres coated in DNA nanostructures to achieve net translation by leveraging the DNA's flexibility to serve as a "flagella", reminiscent of the motion of eukaryotic cells. 14,15 However, the relative polydispersity of common microscale building materialssuch as magnets and polymer microspheres 13 increases as we move to smaller scales.…”

“…4,22,23 There are many instances of microrobots constructed with TPP, including examples of helices, rollers and tumblers, flexible flagella, 4 and even multi-link swimmers. 12 However, none of these swimmers provide buoyancy control, which is important to prevent the possibility of the swimmers crawling on the surfacenanoswimmers are small enough to be buoyant in their fluid environments, and any representative model must replicate this behavior. To address this gap in our ability to build and model microscale and nanoscale two-link systems, we built a buoyant experimental platform on the milliscale that we can use to experiment with the design and control of various two-link systems to find parameters that can be applied to smaller scale systems to increase their net velocities.…”