How do sperm interact with non-uniform viscosity fluids?

Lead Research Organisation: University of Birmingham
Department Name: School of Mathematics

Abstract

In natural conception, sperm must penetrate the interface between semen and cervical mucus, which involves a contrast in viscosity. The challenge presented to sperm by a step-change in viscosity is not understood and a number of questions arise. For example, (1) is it important to have many cells working together to mix the fluid interface, or (2) does the viscosity contrast present a challenge enabling entry by only the strongest cells? Better physical characterisation of a viscosity-contrast system may help in the development of drug treatments to improve natural conception rates. The project will involve developing numerical methods to quantify forces during interface penetration and mixing effects due to motility of multiple cells. These predictions will be verified against experimental data.

This project is in the area of Mathematical Sciences (Continuum Mechanics, Numerical Analysis, Mathematical Biology) and aligns with the theme of Healthcare Technologies.

Publications

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Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/N509590/1 01/10/2016 30/09/2021
1955742 Studentship EP/N509590/1 25/09/2017 31/03/2021 Cara Neal
 
Description Through elastohydrodynamic modelling we have shown that the inclusion of a mechanically inactive distal region of sperm flagellar confers a significant propulsive advantage to cells. This was achieved by measuring how factors such as the swimming speed and efficiency of cells change with varying active tail length. In particular, we found that the optimal inactive length (typically around 2-5% but possibly much higher) depends on both the wavenumber and viscous-elastic ratio used in modelling. These results are often consistent with experimental data for human sperm, but more research needs to be done into why exactly the inactive region enhances swimming of cells. These findings have a range of potential applications. For example, they motivate the development of new methodology for improving the analysis of flagellar imaging data; by model fitting the experimentally visible region it may be possible to resolve the difficult to image distal segment. Further work involves investigating whether the presence of the inactive end piece of the cell could confer an advantage to cells when penetrating highly viscous cervical mucus. Research into this question is already underway, through the implementation of the finite element method for solving the non-linear equations present when modelling cervical mucus, which is non-Newtonian.
Exploitation Route A better understanding of how sperm swim and what might affect this process could help in the development of drug treatments to improve natural conception rates. It could also help in differentiating between sperm fertility problems for better targeted treatment. The results produced through this project will help better our understanding of these processes. The models and code produced could also be useful to build upon in the future.
Sectors Healthcare