Bioinspired Millimeter‐Scale Aquatic Interfacial Robot Enabling Microplastic Collection, Bacterial Sampling, and Targeted Release via Multi‐Modal Control

ABSTRACT Millimeter‐scale robots operating at the water–air interface represent an emerging frontier in microsystems, particularly for tasks within confined and topologically complex aquatic environments. However, their development is hindered by scale‐dominated physical effects, the strong influence of surface tension and pressure resistance, which challenge both reliable structural fabrication and controllable multimodal locomotion. Here, we report a bioinspired design strategy that integrates tailored mechanical architectures, additive manufacturing, and stimuli‐responsive materials to create a Chlamydomonas ‐inspired millirobot (CI‐Robot). The CI‐Robot combines Marangoni propulsion with a flagellum‐mimetic capillary network and modular control elements, including photo‐responsive hydrogel valves and magnetic eyes. The gel‐valves gate fuel pathways on demand, enabling programmable switching between straight translation and rotational gaits driven by Marangoni surface‐tension gradients. Coupling valve‐defined outlet states with Marangoni‐enhanced mass transfer and capillary liquid retention further allows microsample capture and retention, including microplastics and bacteria (detection limit: 100 CFU/mL), with >30 min sample retention. In parallel, the magnetic‐eyes provide robust reorientation and guided navigation, enabling complex path planning, obstacle avoidance, and site‐specific payload release in confined, cluttered settings. By unifying programmable locomotion, environmental adaptability, and multifunctional execution within a single materials‐integrable platform, CI‐Robot provides a practical route toward precision sampling, responsive monitoring, and targeted intervention in confined aquatic systems.