Characterization of rheotaxis of bull sperm using microfluidics

We report detailed characterization of rheotaxis of bull sperm inside microchannels. Positive rheotaxis (PR) is the ability of sperm to swim against the flow. Our results show that PR is prevalent in bull sperm, which confirms rheotaxis as a strong mechanism for guiding sperm to the oocyte. Sperm can swim against secretions flowing downstream the female genital tract after coitus to reach the oocyte. We found that increasing flow velocity increases the percentage of sperm cells exhibiting PR and sperm swimming speed. PR sperm cells were found more likely to swim near channel walls, where local flow velocity is low, and cells were able to advance faster there compared with sperm at channel center.