The present invention provides a microfluidic device with a confined geometry for isolating a slither-capable subpopulation of sperm which is of higher quality than the raw sperm population. The proposed device isolates slither-capable sperm based on their ability to enter and traverse a confined region where 3D locomotion is restricted. The DNA integrity of the selected sperm was higher than that of the corresponding raw samples by 55% and 122% for donors and patients, respectively. In side-by-side testing this method outperforms current clinical selection methods, density gradient centrifugation and swim-up, as well as sperm selected via general motility. Slithering represents a viable selection mechanism, readily applicable to clinical workflows with the potential to improve outcomes for couples and offspring.