Fig 4. Frequency response of robotic sperm in silicone oil with viscosity of 1 Pa.s indicates the influence of the propulsion mode on the swimming speed.

(a) Helical flagellar propulsion enables the robot to swim at higher speed than planar flagellar propulsion below actuation frequency of 6 Hz (S2 Video). (b) At actuation frequency ω = 1 Hz, a 358-μm-long robotic sperm swims at average speed of 18.9 ± 0.5 μm/s (n = 5) and 38.1±0.6 μm/s (n = 5) using planar and helical flagellar propulsion, respectively (S2 Dataset).