Flagellar swimming at low Reynolds numbers: zoospore-inspired robotic swimmers with dual flagella for high-speed locomotion

Traditional locomotion strategies fail in low-Reynolds-number fluid environments, where viscous forces dominate over inertial forces. Microorganisms have developed specialized structures such as cilia and flagella to overcome this challenge, enabling efficient movement through highly resistive environments. Among these organisms,<i>Phytophthora</i>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 planar flagella and oscillatory propulsion mechanisms to emulate the natural swimming behavior of zoospores. Our experiments and theoretical model reveal that both flagellar shape 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, is dominant 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.