Tunable motile sperm separation based on sperm persistence in migrating through shear barriers

Rheotaxis is one of the major migratory mechanisms used in autonomous swimmers such as sperms and bacteria. Here, we present a microfluidic chip using joint rheotaxis and boundary-following behavior that selects sperms based on the motility and persistence. The proposed device consists of a channel decorated with diamond-shaped pillars that create spots of increased velocity field and shear rate. These spots are supposed as hydrodynamic barriers that impede the passage of less motile sperms through the channels, while highly motile sperms were able to overcome the generated barrier and swim through the structures. The proposed device was able to populate the chamber with sorted sperms that were fully viable and motile. The experimental results validated the separation of highly motile sperms with enhanced motility parameters compared with the initial sample. Our device was able to improve linear straight velocity, curvilinear velocity, and average path velocity of the sorted population surpassing 35%, compared with the raw semen. The processing time was also reduced to 20 min.