Start of the microfluidic channel demonstrating how human spermatozoa gain entry into the channel. Arrow indicates the direction of the flow. An asterisk indicates the starting well. Sperm progression was recorded under 100X magnification on an inverted microscope (CK40; Olympus, Center Valley, USA). This video (http://movie-usa.glencoesoftware.com/video/10.1530/REP-20-0364/video-1) is available from the online version of the article at https://doi.org/10.1530/REP-20-0364.