Estimating Young's modulus of zona pellucida by micropipette aspiration in combination with theoretical models of ovum

Abstract

The zona pellucida (ZP) is the spherical layer that surrounds the mammalian oocyte. The physical hardness of this layer plays a crucial role in fertilization and is largely unknown because of the lack of appropriate measuring and modelling methods. The aim of this study is to measure the biomechanical properties of the ZP of human/mouse ovum and to test the hypothesis that Young's modulus of the ZP varies with fertilization. Young's moduli of ZP are determined before and after fertilization by using the micropipette aspiration technique, coupled with theoretical models of the oocyte as an elastic incompressible half-space (half-space model), an elastic compressible bilayer (layered model) or an elastic compressible shell (shell model). Comparison of the models shows that incorporation of the layered geometry of the ovum and the compressibility of the ZP in the layered and shell models may provide a means of more accurately characterizing ZP elasticity. Evaluation of results shows that although the results of the models are different, all confirm that the hardening of ZP will increase following fertilization. As can be seen, different choices of models and experimental parameters can affect the interpretation of experimental data and lead to differing mechanical properties.

Estimating zona pellucida hardness under microinjection to assess oocyte/embryo quality: Analytical and experimental studies

“…The present work is in line with our previous researches concerning engineering analysis to study the mechanical properties of an oocyte ZP [26,27] and has been setup to define a novel criterion for predicting the hardness of oocytes and embryos ZP under microinjection.…”

“…Both the experimental setup and equipment used for this experiment have been previously reported [26,27]. Since measurement of the ZP elastic modulus was essential to determine the penetration force of each oocyte ZP, an aspiration test was initially done.…”

“…Numerous studies concerning the mechanical properties of oocytes have been reported [21][22][23][24][25][26][27]. These studies have shown that the variations within the oocytes' hardness are strongly influenced by mechanical characteristics of the biomembranes (i.e.…”

“…Female partners were first superovulated following downregulation, as described elsewhere [26,27,29]. In brief, suppression of pituitary gonadotrophin secretion with the gonadotrophin-releasing hormone agonist (GnRHa) buserelin acetate (Superfact, Hoechst AG, Germany) was commenced during the mid-luteal phase of the preceding ovarian cycle (day 21).…”

Elastic and Viscoelastic Characterization of Mouse Oocytes Using Micropipette Indentation

“…Direct comparison of the results to other studies is not available since most of the previous research on mouse oocytes or embryos has been focused on the mechanical properties of ZP, which is the glycoprotein membrane enveloping the oocyte. The reported elastic modulus of the ZP, which was measured by various experimental techniques and mechanical models, 8,21,30 ranges from 8.26 to 17.9 kPa. Using the micropipette aspiration technique, the Young's modulus of the human oocyte ZP was measured to be 2.41 ± 0.75 kPa.…”