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Technical Briefs

The Relationship Between Sperm Velocity and Pressures Applied to the Zona Pellucida During Early Sperm-Oocyte Penetration

[+] Author and Article Information
Amit Gefen

Department of Biomedical Engineering, Faculty of Engineering, Tel Aviv University, Tel Aviv 69978, Israelgefen@eng.tau.ac.il

1

Corresponding author.

J Biomech Eng 132(12), 124501 (Nov 12, 2010) (4 pages) doi:10.1115/1.4002857 History: Received July 20, 2010; Revised October 12, 2010; Posted October 25, 2010; Published November 12, 2010; Online November 12, 2010

Sperm velocity is long known to be an important indicator of sperm quality but without much biophysical theory explaining it. Contact mechanics based modeling was developed here to determine the effects that sperm velocity (vs) and sperm head density (ρs)—which is an indicator of the stiffness of the head, have on the peak sperm-zona pellucida contact pressure (pm) during the early phase of sperm penetration. The modeling identified vs as being more influential on pm compared with the influence that ρs has, which means that for spermatozoa competing on the same oocyte, greater vs is a more important advantage than higher ρs. Specifically, pm was more sensitive by a power of 2 to changes in vs than to changes in ρs. It was further demonstrated that each 0.1 g/cc increase in ρs (within the physiologically relevant range of 1.3–1.7 g/cc) would be equivalent to just 3% rise in vs, indicating again that faster swimming is a better strategy for spermatozoa compared with head stiffening. The modeling hence provided some useful insights regarding sperm biomechanics, which theoretically elucidate the well-recognized importance of sperm velocity measurements as being indicative of sperm quality.

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Copyright © 2010 by American Society of Mechanical Engineers
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Figures

Grahic Jump Location
Figure 1

The spermatozoon-oocyte contact model. It is assumed that the kinetic energy of the spermatozoon is converted into work of elastic deformation of the ZP coating the oocyte so that the ZP is penetrated by the spermatozoon with a force F to a depth h=2αRs, where Rs is the characteristic radius of the head of the spermatozoon and α is the penetration index, which ranges between 0 and 1.

Grahic Jump Location
Figure 2

Peak contact pressures at the sperm-oocyte contact site pm versus the straight line velocity vs of sperm for oocytes with elastic moduli Eo at the mean (central area), mean plus one standard deviation (top area), and mean minus one standard deviation (bottom area) of reported experimental Eo data (11). Each gray stripe represents the pm pressure range corresponding to a given velocity vs for an apparent density of the head of the spermatozoon (ρs) that spans over the entire physiologically feasible range: 1–1.7 g/cc.

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