The complex folds of the fallopian tube inner surface have been found to alter the behaviour of sperm.
Researchers at Monash University in Melbourne, Australia found that the folded surface of the fallopian tube tissue acts as a guidance cue to sperm. To meet the egg, sperm must swim across the uterus and up the fallopian tube – where more narrow folds, with higher curvature, are found in the surface of the tube closest to the site where the egg is fertilised. This curvature provides sperm with a physical cue that provokes them to swim in what the authors described as an 'attacking' mode.
Dr Reza Nosrati, one of the research group leaders, said 'This is a highly dynamic and perfectly timed response mechanism in sperm, triggered by the natural anatomy of the female fallopian tube, to facilitate natural fertilisation.'
To mimic the fallopian tube surface, the group used a microfluidics technique to encapsulate sperm cells in fluid droplets of different sizes. Suspended in another fluid, the interface of the droplet and surrounding fluid is designed to mimic the mechanical properties of the fallopian tube tissue. The varying droplet size was used to expose the sperm cells to the range of curvature typically found in the tissue surface.
The study found that in response to higher curvatures, sperm were found to swim 33 percent slower and in contact with the curved surface for 1.66 times as long.
Co-study leader Professor Adrian Neild said this behaviour change is 'a remarkable transition from aimless motion to a highly directed movement.'
Published in Nature Communications, the study offers insight into the contribution of the physiology of the fallopian tubes in assisting fertilisation. It was already known that the surfaces of the fallopian tubes provide chemical guidance that impacts sperm survival and timing of fertilisation, the effect of the physical shape of these surfaces is still poorly understood.
Dr Nosrati said the research findings could be used 'for sperm selection applications', as the new understanding of this mechanism 'could be of benefit to couples struggling with infertility across the world.'