Sperm motility in modulated microchannels

Abstract

Sperm cells swim through the fluid by a periodic wave-like beating of their flagellum. At low Reynolds numbers and in confinement, the directed motion of sperm and other microswimmers is strongly influenced by steric and hydrodynamic wall interactions. We model sperm motility in mesoscale hydrodynamics simulations by imposing a planar traveling bending wave along the flagellum. Sperm are simulated swimming in curved, straight, shallow and zigzag-shaped microchannels. Changes in the sidewall modulations and the imposed beat pattern allow the identification of a strong dependence of the surface attraction on the beat-shape envelope of the sperm cell. For swimming in zigzag microchannels, the deflection-angle distribution at sharp corners is calculated and found to be in good agreement with recent microfluidic experiments. The simulations reveal a strong dependence of the deflection angle on the orientation of the beat plane with respect to the channel sidewall, and thus deepen the understanding of sperm navigation under strong confinement. Detachment of sperm, while swimming along curved walls, is dominated by the change of beat-plane orientation. Therefore, either the emergence of a nonplanar component of the flagellar beat with increasing wavelength or the strong confinement in shallow channels drastically increases wall attraction. Our simulation results reveal a consistent picture of passive sperm guidance that is dominated by the steric interactions of the beat pattern with the nearby surfaces.

Active particles in geometrically confined viscoelastic fluids

“…Furthermore, the presence of confining walls and patterned surfaces, can significantly affect the motion of microswimmers compared to that in the bulk [8]. For instance, steric, phoretic and hydrodynamic interactions can modify the motility of individual sperm cells navigating in microchannels [9], as well as the collective behavior of crowded bacterial colonies under confinement [10]. Investigating such processes is also of major importance for the understanding of intracellular motility, as many organelles have to move through highly confined viscoelastic media within cells [11].…”

Effect of flagellar beating pattern on sperm rheotaxis and boundary-dependent navigation

“…At the near-wall condition (< the sperm body length), the dipole approximation is no longer valid (35) and the sperm-wall interaction can be understood by near-field approximations, as previous theoretical (38, 64) and simulation-based (65) studies suggest. We categorize the sperm interaction with the curved sidewall into four different types: 1) a progressive sperm encounters the wall, rotates, and follows it, as can be seen in Fig.…”

Sperm-hybrid micromotors: on-board assistance for nature’s bustling swimmers

“…The ability to navigate through the female reproductive tract -often a complex, obstructed and even hostile environment -is the key property of mammalian sperm to successfully deliver the haploid nucleus in their head to the egg cell. Whereas the actual fusion of sperm and oocyte is mainly a biochemical process triggered by the so-called acrosome reaction of the sperm head, the preceding DNA transport -that is, the swimming journey of the sperm cell -is a mechanical process that is therefore in the focus of our interest as physicists and engineers, not only to provide theoretical groundwork and practical calculations to understand the motion patterns of sperm like in several insightful works (Lauga and Powers 2009, Saggiorato et al 2017, Kromer et al 2018, Rode et al 2018 or to reconstruct their journey through the reproductive tract, but also to technically support or even exploit their swimming capability as natural micromotors.…”