Magnetic alginate microrobots with dual-motion patterns through centrifugally driven flow control

Mobile microrobots have gained increasing attention in biomedical applications because they can be precisely actuated to targeted positions in a tiny space. However, their use in biomedical applications is hindered by the costly and complicated fabrication method. Herein, a facile fabrication method is proposed to produce magnetic alginate microrobots with adjustable dimensions, including teardrop and tadpole shapes, via tunable centrifugally-driven flows. The formation of these microrobots is interpreted by finite element analysis, revealing that the transition between the dripping and jetting regimes of the flow alters the microrobot's shape. The dimensions of the microrobots are quantitatively analyzed based on the flow's extrusion velocity, controlled by nozzle diameters and revolution speeds. Incorporating magnetic nanoparticles into the alginate-based hydrogel enables the microrobots to exhibit distinct motion patterns under a magnetic field. The teardrop-like microrobot can reach a maximum rolling velocity of approximately 2.7 body length s⁻¹ at 2 Hz, while the maximum stick-slip velocity of the tadpole-like microrobot reaches about 0.42 body length s⁻¹ at 5 Hz, comparable to the existing bioinspired magnetic microrobots. These two motion patterns allow the microrobot to overcome obstacles and navigate in vertically constrained environments, respectively. Last, an ultrasound imaging system is deployed to monitor the locomotion and degradation of the microrobots, showing their potential for targeted drug delivery applications.