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The fallopian tube is lined with a highly complex folded epithelium surrounding a lumen that progressively narrows. To study the influence of this labyrinthine complexity on sperm behavior, we use droplet microfluidics to create soft curved interfaces over a range of curvatures corresponding to the in vivo environment. We reveal a dynamic response mechanism in sperm, switching from a progressive surface-aligned motility mode at low curvatures (larger droplets), to an aggressive surface-attacking mode at high curvatures (smaller droplets of <50 µm-radius). We show that sperm in the attacking mode swim ~33% slower, spend 1.66-fold longer at the interface and have a 66% lower beating amplitude than in the progressive mode. These findings demonstrate that surface curvature within the fallopian tube alters sperm motion from a faster surface aligned locomotion in distal regions to a prolonged physical contact with the epithelium near the site of fertilization, the latter being known to promote capacitation and fertilization competence.

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Droplet microfluidics, with its small scale isolated samples, offers huge potential in the further miniaturisation of high throughput screening. The challenge is to deliver multiple samples in a manner such that reactions can be performed in numerous permutations. The present study investigates the use of single layer valves to subdivide individual droplets selectively. This partitioning of large droplets, allows the main sample volume to navigate around the chip, with smaller daughter droplets being removed at desired locations. As such, the mother droplet is no longer an isolated sample akin to an onchip test tube, but rather a mobile sample delivery system akin to an on-chip pipette. The partitioning takes place at the entrance to a bypass loop of the main channel. Under normal operating conditions the droplet passes the entrance intact, however, when a valve located at the entrance to the bypass loop is actuated the geometry changes causes the droplet to split. We analyse this transition in behaviour for a range of oil and water inlet, and valve actuation pressures, showing that the valve can be actuated such that the next droplet to pass the bypass loop will be split, but subsequent droplets will not be.