Ultrafast Miniature Robotic Swimmers with Upstream Motility

Abstract

With the development of materials science and micro-nano fabrication techniques, miniature soft robots at millimeter or submillimeter size can be manufactured and actuated remotely. The small-scaled robots have the unique capability to access hard-to-reach regions in the human body in a noninvasive manner. To date, it is still challenging for miniature robots to accurately move in the diverse and dynamic environments in the human body (e.g., in blood flow). To effectively locomote in the vascular system, miniature swimmers with upstream swimming capability are required. Herein, we design and fabricate a miniature robotic swimmer capable of performing ultrafast swimming in a fluidic environment. The maximum velocity of the swimmer in water is 30 cm/s, which is 60 body lengths. Moreover, in a tubular environment, the swimmer can still obtain a swimming velocity of 17 cm/s. The swimmer can also perform upstream swimming in a tubular environment with a velocity of 5 cm/s when the flow speed is 10 cm/s. The ultrasound-guided navigation of the swimmer in a phantom mimicking a blood vessel is also realized. This work gives insight into the design of agile undulatory milliswimmers for future biomedical applications.

Fig. 1.

Design and fabrication of the miniature swimmer. (A) Schematics of the fabrication process. (B) Schematics of the actuation strategy. The blue arrow indicates the direction of the oscillating magnetic field, and the red arrow indicates the magnetization direction. (C) The top view and side view of the miniature swimmer. Scale bar: 1 mm.

Fig. 2.

The swimming performance of the swimmer in the water. (A) Swimmer B swims in the water actuated by the oscillating magnetic field with a frequency of 40 Hz and an oscillating angle of 60°. The red point indicates the position of the swimmer, and the black dashed line indicates the trajectory of the swimmer. Scale bar: 5 mm. (B and C) The swimming velocity of swimmer B (B) and swimmer C (C) actuated by the oscillating magnetic field with frequencies f (f = 10 Hz, 20 Hz, 40 Hz, 60 Hz, 80 Hz, and 100 Hz) and oscillating angle (θ = 20°, 40°, 60°, and 80°).

Fig. 3.

The swimmer swims vertically in the water. (A to C) The vertical swimming of the swimmer under the oscillating magnetic field with an oscillating angle of 20°, and oscillating frequencies of 20 Hz (A), 40 Hz (B), and 60 Hz (C). The red dashed line indicates the moving direction of the swimmer, and the white dashed lines indicate the trajectory of the swimmer. Scale bar: 5 mm.

Fig. 4.

The swimming performance of swimmer B in a thin tube. (A) The swimming velocity of swimmer B in a thin tube. (B) The swimming process of the swimmer swimming across a thin tube under oscillating magnetic fields with different oscillating angles. The red dashed rectangle indicates the tube. Scale bar: 5 mm.

Fig. 5.

The upstream swimming performance of swimmer B in a thin tube. (A) The swimming velocity of swimmer B in fluid flow with flow speeds of 5 and 10 cm/s. (B) The swimming process of the swimmer swimming across a thin tube against the fluid flow with flow speeds of 5 and 10 cm/s, respectively. The red dashed rectangle indicates the tube. The red arrow indicates the direction of the flow. Scale bar: 5 mm.

Fig. 6.

The swimming performance of the swimmer in the biofluid. The miniature swimmer swims in porcine whole blood. The white dashed line indicates the position of the swimmer. Scale bar: 5 mm.

Fig. 7.

Ultrasound-guided locomotion of the swimmer. The miniature swimmer swims through a blood vessel phantom. The white dashed line indicates the position of the swimmer. Scale bar: 5 mm.