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.
Highlights
The fallopian tube is lined with a highly complex folded epithelium surrounding a lumen that progressively narrows
The fallopian tube is lined with complex labyrinthine epithelium which forms crevice-like lumens which narrow towards the egg[4,5,6] (Fig. 1a) intensifying the role of hydrodynamic interactions in sperm function[1,4,7]
Droplet microfluidics is well suited to the generation of soft curved interfaces of controlled shape and size[41] for studying sperm behavior, providing an environment that closely mimics the architecture and mechanical properties of the female fallopian tube
Summary
The fallopian tube is lined with a highly complex folded epithelium surrounding a lumen that progressively narrows. Droplet microfluidics is well suited to the generation of soft curved interfaces of controlled shape and size[41] for studying sperm behavior, providing an environment that closely mimics the architecture and mechanical properties of the female fallopian tube In these systems, immiscible fluid phases form droplets of one phase within the other[42]. We reveal that hydrodynamic effects lead to an active response mechanism in sperm to decrease their flagellar wave amplitude by up to 66% at larger curvatures (smaller droplets) These findings highlight the role of changes in mammalian fallopian tube geometry[1,4] to either guide the sperm towards the site of fertilization or facilitate sperm–egg interaction. The lower curvature of the epithelial tissue in the isthmus encourages a surface aligned motility mode for sperm navigation, while higher curvatures in the ampulla activates an aggressive-surface attacking motility mode to encourage sperm–epithelial cell contact facilitating sperm capacitation and fertilization potential
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