Swimming Performance Enhancement of the Magnetic Helical Microrobots Based on Surface Microstructure Modification

Magnetic helical microrobots have attracted considerable attraction in microscale targeted delivery due to their high propulsion efficiency and movement flexibility. However, for biomedical applications in unstructured and multibranched liquid environments, the capabilities of high swimming performance and precise selective control over a robot group of are essential. Here, we introduce a method for achieving high-performance propulsion and selective control of individual magnetic microrobots within a group by modulating surface wettability through localized surface microstructure modifications. We treated the surface of the helical microrobots with dimples and pimples of varying diameters and spacings to effectively distinguish the wettability. Our findings demonstrate that helical microrobots after surface modification exhibit higher step-out frequencies (ω<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">step-out</sub>) and maximum velocities (v<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r-max</sub>), where the modified microrobots become more hydrophobic compared to the microrobots before modification. The variation of microrobots' step-out frequencies (ω<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">step-out</sub>) and the maximum velocities (v<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r-max</sub>) correlate positively with the surface hydrophobicity. The swimming performance on the surface-modified microrobots is performed which demonstrates a maximum increase of 67% in forward velocity and 76% in step-out frequency. Furthermore, our method was effectively employed to actuate a helical microrobots group to achieve selective navigation in a multi-branched microchannel. We anticipate that this approach can be applied to achieve highefficiency and precise targeted delivery in biomedical applications.