The effect of friction and impact angle on the spermatozoa–oocyte local contact dynamics

• Sperm–oocyte local contact dynamics are studied trough biomechanical FEM analysis.
• Sperm–oocyte contact was defined as non-linear frictional contact.
• Deformations of ZP relative to different sperm impact angles (SIA) are discussed.
• An effect which resembles the “slip-stick” effect was identified.
• Favorable ZP-stress state for sperm penetration for different SIA are discussed.

Although a large proportion of biomolecules involved in spermatozoa–oocyte interaction has been discovered so far, many details of fertilization mechanism remain unknown. Both biochemical and biomechanical components exist in the fertilization process. Mammalian sperm evolved a ZP (zona pelucida) thrust reduction penetration strategy probably in response to the ZP resilient elasticity.Using a biomechanical approach and FEM analysis, local contact stress, ZP deformations during impact and attempt of sperm head penetration relative to different sperm impact angles (SIA) were studied. The sperm–oocyte contact was defined as non-linear frictional contact. A transient structural analysis at 37 °C revealed that, from the mechanical standpoint there are SIA that are more favorable for possible ZP penetration due to larger equivalent stress of ZP. An “slip-stick” resembling effect was identified for almost all examined SIA. The sperm head–ZP contact area increases as SIA decreases. Favorable ZP-stress state for sperm penetration regarding SIA are discussed.

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