Self-adaptive and efficient propulsion of Ray sperms at different viscosities enabled by heterogeneous dual helixes

Significance For decades, the propulsion of sperms has been traditionally attributed to the beating or rotating of the soft tails. However, this work disclosed an unusual swimming model of Ray sperms whose propulsion is from not only the helical tail but also the unique spiral head (i.e., the head can contribute ∼31% of the force in propulsion). Such a propulsion mechanism provides Ray sperms with high adaptability to large environmental viscosities along with advantages in linearity, straightness, and efficiency. This study expands our knowledge on the microorganisms’ motion and provides inspirations for engineering design.