BPS2026 – Sperm circling-and-wandering

During migration through the female reproductive tract, sperm undergo physiological changes known as capacitation, which include a motility transition called hyperactivation. Hyperactivation is essential for fertilization, particularly for effective migration within the tract, yet how it facilitates this migration remains unclear. In this work, we profiled bull sperm hyperactivation in Newtonian and complex fluids near microfluidic surfaces, mimicking generic swimming conditions in the tract. We identified three swim gaits: wandering (persistent random walks), circling, and a circling-and-wandering mode characterized by stochastic switching between the two. Over long timescales, all gaits display diffusive behavior, with wandering showing 10-fold higher diffusivity than circling, and circling-and-wandering falling in between. We found that wandering sperm scatter from both convex and concave surfaces, whereas circling sperm become trapped around pillars, underscoring the distinct nature of each gait. Moreover, stochastic simulations in porous media revealed that as geometrical complexity increases, circling-and-wandering outperforms either strategy alone in spreading through the environment. Together, our findings suggest that while wandering promotes exploration and circling supports local exploitation, the circling-and-wandering mode integrates both strategies, balancing exploration and exploitation to adapt motility, enhance migration, and potentially improve target search.