Multi-scale Modeling of Sperm Cell Activation in a Micromixer

Zebrafish sperm cells lead an extraordinary, albeit short-lived, life. They are introduced into an isotonic environment, and only become active when they encounter a trans-membrane osmotic gradient. Once active, motor proteins move down the flagella which forces microtubules bundled together to bend. This bending creates a propagating wave down the flagella, which is responsible for thrust. Although it varies between species, zebrafish sperm cells swim for roughly 30 seconds before dying. The short lifespan and the size of sperm cells make high-throughput microdevices a logical environment for the study of their activation and motility.

In this work, we use numerical methods along with the laws of physics to investigate the life of a sperm cell in a microfluidic mixer. Micromixers have recently been used to rapidly and consistently dilute the sperm’s isotonic environment and study activation and motility. As in real life, in the model the cells are subjected to forces that carry them throughout the device; they encounter a spatially varying concentration profile and there is solute/solvent exchange across their cell membranes; and finally, the sperm begin swimming once active. Our results are validated by experimental data from literature and our collaborators. Outcomes of this work could help design microfluidic devices for activation and analysis of sperm, and facilitate studies of sperm physiology.