Rheotaxis of sperm cells: mechanism and applications in microfluidic separation

Rheotaxis serves as a long-distance guidance mechanism for sperm cells within the female reproductive tract. In this review, we discuss the mechanisms underlying rheotaxis and summarize key experimental, theoretical, and numerical studies that have advanced our understanding of this hydrodynamic phenomenon. Particular emphasis is placed on the role of rheotaxis in sperm selection and separation within microfluidic environments. The review further categorizes rheotaxis-based approaches into distinct design strategies, including trapping geometries for selective sperm capture, combining rheotaxis with boundary-following behavior, and platforms integrating rheotaxis with other guidance cues such as chemotaxis and thermotaxis. Overall, this review provides a comprehensive perspective on sperm rheotaxis as a biomimetic mechanism for passive sperm selection. By mimicking the natural filtration and guidance processes of the female reproductive tract, rheotaxis-driven microfluidic systems offer a promising, non-invasive approach for isolating highly motile and viable sperm, enhancing the efficiency and reliability of assisted reproductive technologies (ART), and informing future research toward more practical, high-throughput, and biologically validated separation strategies.