We investigate Paramecium, which exhibits a negative galvanotactic response, as a biological actuator for bio-hybrid micromachines. Object transportation is difficult owing to low behavioral control accuracy, and tool attachment has a low success rate. In this study, control precision was significantly improved to increase collision probability without using mechanical tools. A 10 mm pool with electrode separation and continuous solution exchange was used to suppress pH variation, and the control algorithm was refined to determine the electric field angle from path deviation and swimming velocity. An automatic transportation system driven by a single Paramecium was constructed, in which repeated collisions enabled payload movement. A 330 µm gel particle was autonomously transported for 1.7 cycles along a star-shaped path (with a 3.24 mm side length) over 72 min in a horizontal pool. These results show that reducing control deviation to less than half the body length is critical for autonomous object transportation. This study demonstrates that reducing the behavioral control deviation of Paramecium to less than approximately half its body length is a critical prerequisite for autonomous object transportation.

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