How do Sperm Swim?

The tail (flagellum) of the sperm does not simply push the body, but uses a rhythmical beating with pushing and fraying over a 4-beat pattern, as demonstrated in the video.

The new dynamical model for a swimming sperm was developed by Kenta Ishimoto at Kyoto University using high-frame-rate microscopic images to obtain detailed information of the moving tail. The hope is that by understanding the swimming mechanism used by sperm, we may be able to better treat infertility issues in the future.

Research by Kenta Ishimoto at the University of Kyoto. Interview with University of Oxford Mathematician Dr Tom Crawford.

This video is part of a collaboration between FYFD and the Journal of Fluid Mechanics featuring a series of interviews with researchers from the APS DFD 2017 conference.

Sponsored by FYFD, the Journal of Fluid Mechanics, and the UK Fluids Network. Produced by Tom Crawford and Nicole Sharp with assistance from A.J. Fillo.

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Featuring: K. Ishimoto et al. "Regularized Stokeslet representations for the flow around a human sperm"
http://meetings.aps.org/link/BAPS.2017.DFD.E8.5

The sperm flagellum does not simply push the sperm. We have established a new theoretical scheme for the dimensional reduction of swimming sperm dynamics, via high-frame-rate digital microscopy of a swimming human sperm cell. This has allowed the reconstruction of the flagellar waveform as a limit cycle in a phase space of PCA modes. With this waveform, boundary element numerical simulation has successfully captured fine-scale sperm swimming trajectories. Further analyses on the flow field around the cell has also demonstrated a pusher-type time-averaged flow, though the instantaneous flow field can temporarily vary in a more complicated manner - even pulling the sperm. Applying PCA to the flow field, we have further found that a small number of PCA modes explain the temporal patterns of the flow, whose core features are well approximated by a few regularized Stokeslets. Such representations provide a methodology for coarse-graining the time-dependent flow around a human sperm and other flagellar microorganisms for use in developing population level models that retain individual cell dynamics.

Publication:
Coarse-Graining the Fluid Flow around a Human Sperm
Kenta Ishimoto, Hermes Gadêlha, Eamonn A. Gaffney, David J. Smith, and Jackson Kirkman-Brown
Phys. Rev. Lett. 118, 124501
DOI: https://doi.org/10.1103/PhysRevLett.118.124501

Special thanks to:
Nicole Sharp
A. J. Fillo
Kenta Ishimoto
The Lucky Urchin
A. S. Suffian