Navigation and selection of spermatozoa in a radial flow microfluidic device

The rheotactic behavior of spermatozoa in an outward radial flow was studied using a combination of theoretical and experimental approaches. Simulations suggested that at moderate flow rates, spermatozoa exhibited directed migration towards the flow origin, while at higher flow rates, the spermatozoa were predicted to display rotational rheotaxis, circling the origin while gradually moving inward, delaying their arrival at the center. Leveraging these findings, we developed a microfluidic device combining radial flow with strategically placed contracted pathways for efficient sperm selection, the sperm unidirectional navigation chip (SUN chip). This platform processed raw bovine semen to isolate highly motile (up to 98% motility) and vital spermatozoa suitable for assisted reproductive technologies. The yield of motile sperm retrieval for the SUN chip is ∼30%, and the cells in the processed population were 50% faster on average compared to raw semen. Our results demonstrate the potential of radial flow microfluidics to enhance sperm selection processes and can be used to investigate other microswimmer dynamics.