Collective dynamics of human sperm swimming in a viscoelastic medium*

We have numerically investigated collective dynamics of sperm swimming, modelling cells as superposition of regularized flow singularities, based on experimentally obtained human sperm images in watery low viscous medium and highly viscous-weakly elastic, methylcellulose medium. In both media, the time-averaged flow around the cell is that of a typical pusher-type swimmer, and the cells tend to form dynamical clustering. However, considering the temporal fluctuating contributions, it is found that the cell yaw and cell pulling dynamics inhibit clustering in low viscous media. This study therefore emphasizes that the finer-scale temporal dynamics of sperm flagellar movement can impact large-scale collective behaviors, and also motivates the need for the characterization of sperm waveform and their dynamics.