Superhelix flow structures drive sperm locomotion

Sperm and pusher eukaryotic cells achieve locomotion through a complex interaction between their flagellar movement and the surrounding fluid. The flagellar waveform arises from a balance of dynein-driven cytoskeletal forces, passive structural resistance, and hydrodynamic drag. However, the underlying mechanisms of cell-fluid interactions remain poorly understood due to the limitations of current measurement techniques. Here, we employ a dual-imaging microscopy method to simultaneously resolve sperm and the surrounding hydrodynamic field with high spatiotemporal resolution, allowing virtual reconstruction of the three-dimensional (3D) flow field around sperm. The results reveal that sperm flagellar activity generates 3D superhelix flow structures that act as rolling corkscrews to propel the cell forward. The major asymmetric flow structures in the head sagittal plane rotate with the cell, enabling symmetric forward motion. Our imaging and analysis methods can be applied to a wide range of microswimmers to locate the cell and simultaneously reconstruct the surrounding flow field. • Sperm propulsion is driven by rolling superhelix flow structures acting like corkscrews • Dual-imaging microscopy resolves both sperm motion and its surrounding 3D hydrodynamic flow • Asymmetric flow structures rotate with sperm, enabling symmetric forward thrust • Sperm-generated flow follows a stresslet model, decaying as r −3 near surfaces Akbaridoust et al. investigated sperm locomotion by imaging both movement and the surrounding hydrodynamic field. They found that 3D superhelix flow structures act as rolling corkscrews to drive propulsion. Their study provides new insights into sperm motility and a framework for exploring cell-fluid interactions in confined environments.