Straining Flow Effects on Sperm Flagellar Energetics in Microfluidic Cross-Slot Traps

Sperm need to effectively navigate the intricate pathways of the female reproductive tract, which are filled with various complex fluid flows. Despite numerous population-based studies, the effects of flow on the flagellar beating pattern of individual sperm remain poorly understood. In this study, a microfluidic cross-slot trap is employed to immobilize individual motile sperm for an extended period without physical tethering, thereby reducing potential cell damage and movement restriction compared to the conventional head-tethering method. The impact of pure straining flow on trapped single sperm is investigated. The experimental results demonstrate that at strain rates of 11.33 s^-1 and higher, the periodic and repetitive beating pattern of the sperm flagellum changes to irregular movement. Furthermore, an increase in strain rate from 1.89 to 11.33 s^-1 leads to a 35.4% reduction in beating amplitude and a 41.2% decrease in hydrodynamic power dissipation. These findings underscore the capability of the microfluidic cross-slot platform to trap sperm with high stability, contributing to a better understanding of sperm behavior in response to fluid flows.