Microorganisms such as algae and bacteria move in a viscous environment with extremely low Reynolds ($Re$), where the viscous drag dominates the inertial forces. They have adapted to this environment by developing specialized features such as whole-body deformations and flexible structures such as flagella (with various shapes, sizes, and numbers) that break the symmetry during the motion. In this study, we hypothesize that the changes in the flexibility of the flagella during a cycle of movement impact locomotion dynamics of flagellated locomotion. To test our hypothesis, we developed an autonomous, self-propelled robot with four flexible, multi-segmented flagella actuated together by a single DC motor. The stiffness of the flagella during the locomotion is controlled via a cable-driven mechanism attached to the center of the robot. Experimental assessments of the robot's swimming demonstrate that increasing the flexibility of the flagella during recovery stroke and reducing the flexibility during power stroke improves the swimming performance of the robot. Our results give insight into how these microorganisms manipulate their biological features to propel themselves in low viscous media and are of great interest to biomedical and research applications.

翻译：微生物（如藻类和细菌）在高粘性、极低雷诺数（$Re$）环境中运动，此时粘性阻力主导惯性力。它们通过演化出整体形变及鞭毛等柔性结构（具有不同形状、尺寸和数量）以打破运动对称性，从而适应这种环境。本研究假设鞭毛在一个运动周期内柔韧性的变化会影响鞭毛运动的动力学特性。为验证该假设，我们开发了一种自主推进的机器人，其配备由单个直流电机共同驱动的四根柔性多节鞭毛。运动过程中鞭毛的刚度通过连接至机器人中心的缆绳驱动机构进行控制。机器人游泳实验评估表明，在恢复行程增加鞭毛柔韧性、在动力行程降低柔韧性可提升机器人的游泳性能。我们的研究结果揭示了微生物如何操控自身生物特性在低粘性介质中推进，并为生物医学及科研应用提供了重要启示。