Alginate/GelMA microparticles viaoil-free interface shearing for untethered magnetic microbotsElectronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d4bm00875h

Microrobots hold broad application prospects in the field of precision medicine, such as intravenous drug injection, tumor resection, opening blood vessels and imaging during abdominal surgery. However, the rapid and controllable preparation of biocompatible hydrogel microparticles still poses challenges. This study proposes the one-step direct acquisition of biocompatible sodium alginate and gelatin methacrylate (GelMA) hydrogel microparticles using an oil-free aqueous solution, ensuring production with a controllable generation frequency. An adaptive interface shearing platform is established to fabricate alginate/GelMA microparticles using a mixture of the hydrogel, photoinitiator, and Fe3O4nanoparticles (NPs). By adjusting the static magnetic field intensity (Bs), vibration frequency, and flow rate (Q) of the dispersed phase, the size and morphology of the hydrogel microparticles can be controlled. These hydrogel microparticle robots exhibit magnetic responsiveness, demonstrating precise rotating and rolling movements under the influence of an externally rotating magnetic field (RMF). Moreover, hydrogel microparticle robots with a specific critical frequency (Cf) can be customized by adjusting the Bsand the concentration of Fe3O4NPs. The directional in situuntethered motion of the hydrogel microparticle robots can be successfully realized and accurately controlled in the climbing over obstacles and in vitroexperiments of animals, respectively. This versatile and fully biodegradable microrobot has the potential to precisely control movement to bone tissue and the natural cavity of the human body, as well as drug delivery.