Integrating functional subunits into a microrobot offers a promising pathway to enhance its operational capabilities. The functional integration of microrobots lies in organizing subunit distribution into a 3-D morphology while balancing the geometry formation affected by subunits and locomotion performance. Here, in this article, discrete microstructured soft-magnetic teeth (MTs) are circularly embedded into an artificial bacterial flagellum (ABF) to function as equivalent subunits, representing a good start to demonstrate the integration of subelements in microrobots through local stress regulation. Based on various substructure patterns, the controllable geometry modulation of ABF-MTs has unveiled the tunable angle-dependent deformation behavior, offering numerous possibilities for geometric morphology and propulsion extension. The outstanding kinematic performance demonstrates the seamless fusion of functionality and propulsion by maintaining locomotion speed, trajectory planning, pursuit, and step-motion-like behavior. Such a physical-forming strategy offers an avenue for incorporating subdevices in microrobot functionalization.

Due to the limited cargo/functional element loading and other capabilities of individual microrobots, assembling them for locomotion and disassembling them as arriving at the target is more effective. An approach called rendezvous and docking is proposed in this paper to control the assembly and disassembly of helical microrobots actuated by a uniform rotating magnetic field. Docking is realized around the intersection of their arc orbits with the assistance of a fluidic field. To adjust the distance between the adjacent helical robots suspending in solution but with a distance beyond the acceptable range of the magnetic interaction, their asynchronized velocities are achieved using the interaction between the robots and fluids. For robots rotating at different speeds around their longitudinal axes at a driving frequency lower than the cut-off frequency, different fluidic flows will be generated. Based on the interaction between the robots and the fluids, the translational trajectory paths may be tuned, causing the adjacent robots to move closer. Docking along the tangential direction of rendezvous arc trajectories avoids the instability of the helical robot rotating around the radial direction and the problem of excessive linear speed at the end during assembly so that the robot can rotate stably around its axis while completing the assembly. Besides these, assembled microrobots can also lower the requirements on the imaging resolution of motion tracking and the forces for driving; hence much lower cost for both imaging and driving equipment.

Sub-structures such as micro-structured magnetic teeth fabricated with an artificial bacteria flagellum (ABF) are designed for achieving more motion modes, higher precision, and better controllability. To achieve these, a more precise model considering the non-circular cross-sectional features is setup without simplifying the structure as a helical filament with a circular cross-section as having been used in previous investigations, making it possible to include the effects of the substructures into the motion equation. Analyses and experiments verified the correctness. Besides of the geometric effects, our experimental observation also shows an anomalous step-out frequency appeared in an ABF. This asynchronous motion is attributed to the lag of magnetization with respect to the external rotating magnetic field due to the geometries and the soft-magnetic materials of the ribbons, which is different from the regular asynchronous motion solely caused by low Reynolds number of fluid to microscopic swimmers. While the lag of magnetization can be further attributed initiatively to the soft magnetic materials adopted, the feasibility to arrange the easy axis will enable many new possibilities, which is of particular interest in generating more modes for swarms such as cascade stepping out of ABFs with the same nominal overall sizes and for more precise positioning using stepping motion.