Listening to the chemical
conversation around the egg.

Not a race. A conversation.

Fertilisation has long been pictured as a race won by the fastest swimmer. Research over the last decade tells a more active story: the egg itself takes part, releasing chemical signals that help guide sperm toward it¹. As sperm travel through the female reproductive tract, rheotaxis and thermotaxis already help steer their path²; along the way they undergo capacitation, a sequence of biochemical changes that prepares them for fertilisation³.

Capacitation brings a shift in how the tail beats, from a symmetrical stroke to an asymmetrical one known as hyperactivation, letting a sperm cell force its way through the cumulus-oocyte complex surrounding the egg⁴. The fluid around the egg is rich in signalling molecules (progesterone, EGF, BDNF, GDF9, fibronectin, and others) thought to shape this final approach⁵. But exactly how the flagellum adapts, beat by beat, to that chemical landscape is still poorly understood: existing methods typically test only a narrow set of these signals, and rarely under conditions that resemble the real tract.

MicroBeaCh is the first study to comprehensively assess sperm flagellar beating across a dynamic chemical landscape, rather than a single fixed stimulus. Three things make that possible:

• A customised microfluidic platform capable of generating complex, controlled chemical gradients, not just a single concentration step.
• AI-based computer vision integrated directly with the platform, analysing flagellar motion as it happens rather than from post-hoc video review.
• A biomimetic focus throughout: every condition tested is chosen to resemble what sperm actually encounter in vivo, not an artificial lab simplification.