Bio-inspired progressive motile sperm separation using joint rheotaxis and boundary-following behavior

Area of Science:

• Biomedical Engineering
• Reproductive Biology
• Microfluidics

Background:

• Male factor infertility accounts for approximately 50% of all infertility cases.
• Current sperm processing methods like density gradient centrifugation can induce sperm DNA fragmentation.
• Sperm migration mechanisms, including rheotaxis and boundary-following, are crucial for natural fertilization.

Purpose of the Study:

• To develop a bio-inspired microfluidic device for high-quality sperm selection.
• To leverage natural sperm migratory behaviors for improved sperm sorting.
• To reduce DNA fragmentation in processed sperm samples.

Main Methods:

• A microfluidic device was designed to mimic the geometry of the uterotubal junction (UTJ).
• The device utilizes sperm rheotaxis and boundary-following behavior within a series of parallel channels and UTJ-like constrictions.
• Sperm were sorted sequentially based on propulsive velocity and linearity of motion.

Main Results:

• Sorted sperm populations exhibited significantly increased straight-line velocity (63.4–74 μm s⁻¹) compared to raw semen (35.2 μm s⁻¹).
• The device achieved over a 30% reduction in the sperm DNA fragmentation index.
• Two distinct subpopulations of motile sperm were successfully fractionated.

Conclusions:

• The bio-inspired microfluidic device effectively separates progressive motile sperm with high quality.
• This method offers a clinically applicable and straightforward approach to sperm retrieval with reduced DNA damage.
• The device presents a promising alternative to conventional sperm processing techniques for assisted reproduction.