Curvature in the reproductive tract alters sperm–surface interactions

Abstract

The fallopian tube is lined with a highly complex folded epithelium surrounding a lumen that progressively narrows. To study the influence of this labyrinthine complexity on sperm behavior, we use droplet microfluidics to create soft curved interfaces over a range of curvatures corresponding to the in vivo environment. We reveal a dynamic response mechanism in sperm, switching from a progressive surface-aligned motility mode at low curvatures (larger droplets), to an aggressive surface-attacking mode at high curvatures (smaller droplets of <50 µm-radius). We show that sperm in the attacking mode swim ~33% slower, spend 1.66-fold longer at the interface and have a 66% lower beating amplitude than in the progressive mode. These findings demonstrate that surface curvature within the fallopian tube alters sperm motion from a faster surface aligned locomotion in distal regions to a prolonged physical contact with the epithelium near the site of fertilization, the latter being known to promote capacitation and fertilization competence.

Sperm Inspection for In Vitro Fertilization via Self-Assembled Microdroplet Formation and Quantitative Phase Microscopy

“…Inside the droplets, the sperm cells swam in a different way than their usual progressive movement in free medium. Inside the droplets, the cell heads tended to be in contact with the edges of the droplets [ 28 ]. For this reason, the velocities of the sperm cells inside the droplets were lower than the velocities in free medium.…”

CRISPs Function to Boost Sperm Power Output and Motility

“…Herein we have utilized the planar motion of head-tethered sperm to investigate the role of CRISPs in establishing optimal flagellar beating as it is relevant to the situation in mammals wherein sperm are known to accumulate and swim close to epithelial surfaces and display largely planar motility ( Nosrati et al, 2015 ; Raveshi et al, 2021 ). Such an analysis would not be appropriate for species where sperm swim freely through aqueous fluids e.g., species where spawning occurs.…”

“…Recently, we have solved this challenge through the development of an imaging and analysis pipeline capable of mathematically quantifying the flagellar waveform with sufficient resolution to enable the measurement of kinematic characteristics such as the beat frequency and flagellar velocities and the spatiotemporal distribution of the hydrodynamic power dissipated along the tail ( Nandagiri et al, 2021 ). Our approach takes advantage of the fact that many mammalian sperm are known to swim close to walls with their flagella beating in a plane that is parallel to the surfaces ( Nosrati et al, 2015 ; Raveshi et al, 2021 ). We obtain high-resolution videos of sperm tethered at their heads to a glass slide.…”

Unraveling the Kinematics of Sperm Motion by Reconstructing the Flagellar Wave Motion in 3D

“…These results indicate that the 3D waveform is highly constrained for a head-tethered moused sperm to beat in a 2D plane potentially caused by the increased hydrodynamic drag near surfaces, steric interactions, and/or the inherent nature of the flagellar wave to beat in a 2D plane. [15,38] The 3D data were used to quantify local helicity (h), indicating the flagellar winding along the flagellum in either clockwise or counterclockwise directions as viewed from the front. Figure 5a shows a representative kymograph of local helicity during ≈5 beat cycles.…”