Fig. 1

Structure of device forming chemotactic gradient. a Illustration of the anatomy of the female reproductive system through which sperm are naturally selected during fertilization. b Photograph of device; left, base of device; right, device cap. c Schematic diagram of the structure of the base of the device. Chamber A, sample chamber; R, the radius, 10 mm; Chamber F, control chamber; Chamber G, chemotactic chamber; r, the radius, 5 mm; Position C, the middle of the channel between Chamber F and Chamber G, similar to the uterus; Position B, the middle of the channel between Chamber A and Position C, similar to the cervix. The gap width between both walls of the channel is 2 mm, the height is 15 mm. D1, D2, and D3, grooves between Position C and Chamber F; E1, E2, and E3, the grooves between Position C and Chamber G; the dimensions of all grooves is 5 mm (length) × 2 mm (width) × 2 mm (height), the distance between neighboring grooves is 10 mm, except the interval between D1 and E1 which is 15 mm; the grooves held the agar mixed with the chemoattractant that formed the gradient