Human sperm cells swimming in micro-channels

TL;DR

This study investigates how human sperm cells navigate micro-channel geometries, revealing their preference for channel corners, the influence of fluid viscosity, and implications for understanding sperm migration in the female reproductive tract.

Contribution

It provides new insights into sperm navigation behaviors in micro-structured environments, highlighting the importance of geometry and viscosity in guiding motile cells.

Findings

Sperm cells prefer swimming along channel corners.

Sharp turns cause sperm to leave the corners at specific angles.

Viscosity influences the departure angles and navigation patterns.

Abstract

The migratory abilities of motile human spermatozoa in vivo are essential for natural fertility, but it remains a mystery what properties distinguish the tens of cells which find an egg from the millions of cells ejaculated. To reach the site of fertilization, sperm must traverse narrow and convoluted channels, filled with viscous fluids. To elucidate individual and group behaviors that may occur in the complex three-dimensional female tract environment, we examine the behavior of migrating sperm in assorted micro-channel geometries. Cells rarely swim in the central part of the channel cross-section, instead traveling along the intersection of the channel walls (`channel corners'). When the channel turns sharply, cells leave the corner, continuing ahead until hitting the opposite wall of the channel, with a distribution of departure angles, the latter being modulated by fluid viscosity. If the channel bend is smooth, cells depart from the inner wall when the curvature radius is less than a threshold value close to 150 micron. Specific wall shapes are able to preferentially direct motile cells. As a consequence of swimming along the corners, the domain occupied by cells becomes essentially 1-dimensional. This leads to frequent collisions and needs to be accounted for when modeling the behavior of populations of migratory cells and considering how sperm populate and navigate the female tract. The combined effect of viscosity and three-dimensional architecture should be accounted for in future in vitro studies of sperm chemoattraction.