Bioinspired Untethered Rolling Millirobot for Delivery and Biopsy in Blood Vessels 


Student thesis: Doctoral Thesis

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Award date23 Aug 2022


Untethered miniature robots that can access narrow and complex regions inside human bodies provide promising solutions for diagnosis and treatment. These small-scale robots can serve as (drug) carriers, sensors, or surgical tools in the gastrointestinal (GI) tract, the circulatory system, the urinary system, and other tissues/organs that have natural lumens for future clinical applications. Unlike conventional robots that have batteries for energy storage, robots at millimeter scale and smaller are usually driven by wireless power transmission (e.g., magnetic field, ultrasonic waves, and light) or harvest energy from the environment via chemical reactions. Magnetic actuation among them is a preferred option and widely applied in recent years considering its good controllability, rapid responsiveness, as well as safety.

Despite the above achievements, driving and controlling medical robots inside the body remains significant challenges because of the complex in vivo environment, particularly inside blood vessels with blood flow resistance. Some proofs of concepts have been proposed to propel against the flow by locomotion on or close to the channel wall. However, realizing the controllable locomotion of these robots inside blood vessels is still challenging, let along conducting in vivo medical tasks. Here, we present two rolling strategies for the locomotion of millirobots in pipes and propose an untethered streamlined millirobot that can move against a fast flow via spiral rolling for delivery and biopsy in blood vessels.

Firstly, the advantage of rolling locomotion in blood vessels is introduced. An on-wall-rotating strategy is proposed to achieve upstream locomotion in the lumen. Based on the strategy, the untethered magnetic millirobot can be controlled to achieve stable locomotion against flow. The best upstream performance is demonstrated against flow velocity up to 138 mm/s, which is several times faster than the reported works.

Secondly, the rotating gradient magnetic field and the streamlined millirobot are designed to enhance the upstream swimming ability of rolling locomotion. The dynamics analysis of the spiral-rolling locomotion is presented to elucidate how the millirobot moves against blood flow. Compared with the direct dragging, which can hardly drive the robot, the millirobot can reach a forward speed of 14 mm/s against a blood phantom flow as high as 138 mm/s through on-wall spiral rolling.

Thirdly, the design and fabrication of the bioinspired spiral-rolling millirobot for endovascular interventions is presented. Inspired by the mosquito and fly in nature, we design the pressure-based delivery module and the EAT (easy-to-open and auto-closed tail) biopsy module for the robot. The characterization and in vitro demonstrations suggest that the functionalized millirobot is feasible and effective for in vivo endovascular applications.

Finally, the untethered spiral-rolling millirobots are tested in blood vessels. The ex vivo experiments in swine and sheep aortas and in vivo tests in rabbits verify the effectiveness of the actuation and control strategy. Integration of self-sealing orifice and elastic cavity provides a controllable wireless delivery method in blood vessels, which has been verified by drug delivery, liquid biopsy, and cell transportation tests in vivo in rabbit abdominal aortas. The biopsy function is based on a pre-cut tail and a fine needle, which has been verified via the biopsy of blood clots and endothelium in vivo in rabbits.

In conclusion, the proposed functionalized millirobot can swim against fast flow via spiral rolling, and realize controllable transportation, delivery, and endovascular biopsy in blood vessels. This work would benefit the development of wireless millirobot for controllable, minimally invasive, highly integrated, and multi-functional endovascular interventions, and inspire new designs of miniature robots for biomedical applications.

    Research areas

  • untethered millirobots, on-wall rotating, spiral rolling, magnetic control, upstream swimming, drug delivery, endovascular biopsy, biomedical applications