An On-Wall-Rotating Strategy for Effective Upstream Motion of Untethered Millirobot: Principle, Design, and Demonstration

Untethered miniature robots that can access narrow and harsh environments in the body show great potential for fu-ture biomedical applications. Despite the many types of millirobot that have been developed, swimming against the fast blood flow remains a big challenge due to lack of the ability to stay still and the large fluidic resistance from blood. This article proposes an on-wall-rotating strategy and a streamlined millirobot to achieve effective upstream motion in the lumen. First, the principle of on-wall-rotating strategy and the dynamic motion model of the millirobot is established. Then, a critical safety angle theta(s) is theoretically and experimentally analyzed for the safe and stable control of the robot. After that, a series of experiments are conducted to verifythe proposed driving strategy. The results suggest that the robot is able to move at a speed of 5 mm/s against flow velocity of 138 mm/s, which is comparable to the blood flow of 2700 mm(3)/(s) and several times faster than other reported driving strategies. This work offers a new strategy for the untethered magnetic robot construction and control for blood vessels, which would promote the application of millirobot for biomedical engineering.