Untethered small robots with multiple functions show considerable potential as next-generation catheter-free systems for biomedical applications. However, owing to dynamic blood flow, even effective upstream swimming in blood vessels remains a challenge for the robot, let alone performing medical tasks. This paper presents an untethered millirobot with a streamlined shape that integrates the engine, delivery, and biopsy modules. Based on the proposed spiral-rolling strategy, this robot can move upstream at a record-breaking speed of ≈14 mm s-1 against a blood phantom flow of 136 mm s-1 . Moreover, benefiting from the bioinspired self-sealing orifice and easy-open auto-closed biopsy needle sheath, this robot facilitates several biomedical tasks in blood vessels, such as in vivo drug delivery, tissue and liquid biopsy, and cell transportation in rabbit arteries. This study will benefit the development of wireless millirobots for controllable, minimally invasive, highly integrated, and multifunctional endovascular interventions and will inspire new designs of miniature devices for biomedical applications.
Keywords: magnetic control; spiral-rolling; untethered millirobots; upstream swimming.
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