Dual-Stage Propulsion Strategy for Microalgae-Based Biohybrid Microrobots

Biohybrid microrobots, based on swimming microalgae, offer outstanding self-propulsion and functionalization capabilities, making them promising platforms for cargo loading and delivery. However, current technologies predominantly focus on in vitro nanodrug transport, lacking an integrated strategy for the efficient capture and directional transport of large microscale cargo, particularly for biological targets. Here, we propose a dual-stage propulsion strategy for biohybrid microrobots, enabling the coupled capture and directional transport of large targets. Inspired by the multistage propulsion of rockets, the microrobots first utilize the autonomous motility of microalgae to establish a self-propulsion-driven primary phase. Surface functionalization creates a dynamic 3D biomimetic capture interface, enhancing the target capture efficiency. Subsequently, an external magnetic field activates a secondary propulsion mechanism, enabling precise directional transport. As a proof of concept, <i>Chlamydomonas reinhardtii</i> was employed as the biological carrier and noninvasively integrated with 2 μm magnetic beads to construct dual-actuated biohybrid microrobots. This design preserved the natural motility of the microalgae while providing abundant aptamers and strong magnetic actuation. Using 20 μm polystyrene microspheres and circulating tumor cells as model targets, we successfully demonstrated high-efficiency capture (up to 93%) and directional transport (14 μm/s) of large microscale targets, highlighting the potential of this strategy for biomedical, environmental, and analytical applications.