Swimming Back and Forth Using Planar Flagellar Propulsion at Low Reynolds Numbers

Area of Science:

• Biomimetic robotics
• Soft robotics
• Microfluidics

Background:

• Peritrichously flagellated bacteria like Escherichia coli exhibit complex swimming behaviors.
• Monotrichous bacteria struggle to reverse direction efficiently with a single flagellum.
• Understanding bacterial locomotion is key to developing advanced micro-robotics.

Purpose of the Study:

• To design and develop a magnetically driven soft microrobot.
• To enable directional reversal without U-turns or altering wave propagation.
• To mimic and quantify bacterial flagellar swimming dynamics.

Main Methods:

• A soft microrobot with two collinear, unequal, and opposite ultrathin tails was fabricated.
• Magnetic microparticles were embedded in the polymer head for magnetic manipulation.
• A uniform magnetic field with a sinusoidally varying orthogonal component was used for propulsion and steering.

Main Results:

• The microrobot demonstrated directional reversal by selectively exciting its two tails.
• Distinct reversal frequencies were identified based on tail length ratios.
• Flagellated motion in opposite directions was achieved by operating below or above specific reversal frequencies.

Conclusions:

• The developed microrobot successfully replicates bacterial flagellar swimming and directional reversal.
• This technology offers a novel platform for studying microbial locomotion and designing micro-scale devices.
• The findings have implications for micro-robotics, drug delivery, and micro-manipulation systems.