The zona pellucida (ZP) is a thick glycoprotein shell surrounding the mammalian egg cell (oocyte) that regulates spermatozoa access during fertilization and protects the zygote during early embryonic development [1]. Hardening of the zona pellucida over the cell fertilization cycle is a well-recognized phenomenon and has been investigated using contact methods to measure shear and bending elasticity from indentation and micropipette aspiration [2, 3]. However, the area elasticity of the ZP, which provides resistance to cell swelling under variable osmotic environments, has not yet been reported. A recently devised theoretical model [4] suggests that the ZP area expansion modulus may be determined through non-contact hypo-osmotic loading of the oocyte. If successful, this method may be suited for implementation by practicing fertility health professionals during routine manipulation.

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