Flagellar Swimming at Low Reynolds Numbers: Zoospore-Inspired Robotic Swimmers with Dual Flagella for High-Speed Locomotion

TL;DR

This paper introduces a zoospore-inspired robotic swimmer with dual flagella, demonstrating how flagellar length and oscillation frequency affect propulsion, and highlighting the anterior flagellum's dominant role in efficiency, advancing microscale robotic design and biological understanding.

Contribution

It presents a novel robotic design inspired by zoospore locomotion, combining dual flexible flagella and oscillatory propulsion, with experimental and theoretical analysis of factors influencing speed and efficiency.

Findings

Longer flagella and higher oscillation frequencies improve speed.

The anterior flagellum significantly enhances propulsion efficiency.

Experimental results reveal the dominant role of the anterior flagellum.

Abstract

Traditional locomotion strategies become ineffective at low Reynolds numbers, where viscous forces predominate over inertial forces. To adapt, microorganisms have evolved specialized structures like cilia and flagella for efficient maneuvering in viscous environments. Among these organisms, Phytophthora zoospores demonstrate unique locomotion mechanisms that allow them to rapidly spread and attack new hosts while expending minimal energy. In this study, we present the design, fabrication, and testing of a zoospore-inspired robot, which leverages dual flexible flagella and oscillatory propulsion mechanisms to emulate the natural swimming behavior of zoospores. Our experiments and theoretical model reveal that both flagellar length and oscillation frequency strongly influence the robot's propulsion speed, with longer flagella and higher frequencies yielding enhanced performance. Additionally, the anterior flagellum, which generates a pulling force on the body, plays a dominant role in enhancing propulsion efficiency compared to the posterior flagellum's pushing force. This is a significant experimental finding, as it would be challenging to observe directly in biological zoospores, which spontaneously release the posterior flagellum when the anterior flagellum detaches. This work contributes to the development of advanced microscale robotic systems with potential applications in medical, environmental, and industrial fields. It also provides a valuable platform for studying biological zoospores and their unique locomotion strategies.