Sperm penetration to the zona pellucida of an oocyte: a computational model incorporating acrosome reaction

Manipulation of metabolism to improve liquid preservation of mammalian spermatozoa

Reproductive success in mammals hinges on the ability of sperm to generate sufficient energy through cellular metabolism to perform the energy-intensive processes required for fertilisation, including motility, maturation, and oocyte interactions. It is now widely accepted that sperm exhibit metabolic flexibility, utilising a combination of glycolysis and oxidative phosphorylation (supported by the Krebs cycle and other complementary pathways) to meet their energy demands. However, the preferred pathway for energy production varies significantly among species, making it challenging to map species-specific metabolic strategies, particularly in species with high metabolic flexibility, like the ram. Additionally, differences in methodologies used to measure metabolism have led to biased interpretations of species' metabolic strategies, complicating the development of liquid storage methods aimed at preserving spermatozoa by manipulating energy generation based on species-specific requirements. This review examines sperm energy requirements, current methods for assessing metabolic capacity, and the current research on species-specific metabolism. Future research should focus on establishing a standardised approach for determining metabolic preferences to accurately map species-specific strategies, a critical step before developing effective liquid preservation methods. By identifying species-specific regulatory points, strategies can be designed to temporarily inhibit metabolic pathways, conserving resources and reducing the accumulation of metabolic by-products. Alternatively, supplementation with depleted metabolites can be guided by understanding areas of excessive consumption during prolonged metabolism. Applying this knowledge to develop tailored preservation techniques will help minimise sperm damage and improve survival during in vitro processing and liquid storage, ultimately enhancing the success of artificial breeding programs.

Biomechanics of Early Life in the Female Reproductive Tract

Early human life that starts at the onset of fertilization and ends with implantation of the embryo in the uterine wall is the foundation for a successful pregnancy. The different stages during this period require biomechanical mechanisms, which are mostly unknown due to difficulties to conduct in vivo studies in humans.

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

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.

Influence of sperm impact angle on successful fertilization through mZP oscillatory spherical net model

According to the available literature, penetrating sperm creates an oblique path trough Zona pellucida (ZP)--the most outer surface of oocytes. Considering fertilization process as an oscillatory phenomenon, the influence of sperm impact angle relative to the oscillatory behavior of mouse ZP is described by using the discrete continuum mechanical model in the form of a spherical net model. A parametric frequency analysis of oscillatory behavior of knot material particles in the mouse ZP (mZP) spherical net model is conducted by using generalized Lussajous curves. The influence of impact angles of sperm cells on the corresponding knot mass particles' resultant trajectory is discussed. Favorable sperm impact angles for successful fertilization are identified.

A hybrid characterization framework to determine the visco-hyperelastic properties of a porcine zona pellucida

The zona pellucida (ZP) is a specialized extracellular matrix surrounding the developing oocyte. This thick matrix consists of various types of glycoprotein that play different roles in the fertilization process. Nowadays, several techniques are available for assessing ZP's mechanical response. The basic assumption behind these methods is that the ZP behaves like an elastic body: hence, dissipative forces are neglected and Young's modulus remains unaffected by probe dynamics. However, dissipative forces are strongly regulated by the slippage of ZP chains past one another while reaction forces related to elastic deformations (driven by the ability of each chain to stretch) depend on the ZP structure (i.e. number of cross-links and distances between knots). Although viscous reaction forces generated by the ZP are one of the main factors regulating sperm transit, their peculiar behaviour along the ZP structure remains poorly understood and rarely investigated. In order to overcome this limitation, a novel visco-hyperelastic model describing the porcine ZP reaction forces generated by nanoindentations at different probe rates is developed and verified in this study. Visco-hyperelastic parameters of porcine ZP membranes are determined by means of a hybrid characterization framework combining atomic force microscopy nanoindentation measurements, nonlinear finite-element analysis and nonlinear optimization. Remarkably, it is possible to separate the contributions of hyperelastic and viscous terms to ZP mechanical response and evaluate the error made in the determination of ZP mechanical properties if viscous effects were not considered.