The lateral channel of the microfluidic device showing how human spermatozoa progress through it. Sperm progression was recorded under 200X magnification on an inverted microscope (CK40; Olympus, Center Valley, USA). This video (http://movie-usa.glencoesoftware.com/video/10.1530/REP-20-0364/video-3) is available from the online version of the article at https://doi.org/10.1530/REP-20-0364.