Zona pellucida shear modulus, a possible novel non-invasive method to assist in embryo selection during in-vitro fertilization treatment

Abstract

eliahu Levitas 3 & iris Har-Vardi 3* the present study investigated the association between oocyte zona pellucida shear modulus (ZpSM) and implantation rate (IR). Ninety-three oocytes collected from 38 in-vitro fertilization patients who underwent intracytoplasmic sperm injection were included in this case-control study. the Zp was modeled as an isotropic compressible hyperelastic material with parameter C 10 , which represents the ZpSM. computational methodology was used to calculate the mechanical parameters that govern Zp deformation. fifty-one developed embryos were transferred and divided into two groups-implanted and not implanted. Multivariate logistic regression analysis was performed to identify the association between ZpSM and iR while controlling for confounders. Maternal age and number of embryos per transfer were significantly associated with implantation. The IR of embryos characterized by C 10 values in the range of 0.20-0.40 kPa was 66.75%, while outside this range it was 6.70%. This range was significantly associated with implantation (p < 0.001). Geometric properties were not associated with implantation. Multivariate logistic regression analysis that controlled for relevant confounders indicated that this range was independently associated with implantation (adjusted OR 38.03, 95% confidence interval 4.67-309.36, p = 0.001). The present study suggests that ZPSM may improve the classic embryo selection process with the aim of increasing iR. The zona pellucida (ZP) is a non-cellular layer of glycoproteins surrounding the oocyte 1. Over the years, numerous studies have described an association between the physical state of a cell and its function or fate 2-5. One of the most studied physical properties of oocytes is zona hardening, resulting from cortical granule release during fertilization 6. This physical property, aimed to prevent polyspermy 6,7 , also occurs spontaneously in response to post-ovulatory aging, and results in poor fertilization rates 8-10. Furthermore, spontaneous zona hardening is associated with exposure to in-vitro culture conditions 11,12 that may consequently hinder the blastocyst's potential to hatch the ZP. Although many studies have investigated animal oocytes or embryos, their observations link physical parameters to fertilization and developmental potential and not to implantation potential. Several approaches have been described in the literature to measure the mechanic properties of the ZP 13 by oocyte indentation 14,15 , compression 16 , or aspiration 17,18. Based on these capabilities, two studies have used the physical inputs as selection criteria for embryos. Murayama et al. measured mouse ZP elasticity using a micro tactile sensor (MTS) system. They demonstrated specific changes in this elasticity during oocyte maturation, fertilization, and embryo development, and concluded that the MTS system can be applied to assisted reproductive technology (ART) to evaluate embryo quality 19. Yanez et al. studied the mechanistic properties of human and

Mechanobiology of the female reproductive system

“… 47 Outside of these ranges, the average implantation rate was 6.70%. 46 , 47 After fertilization, optimal stiffness in the zygote is required for successful human embryonic development. 45 , 46 , 47 A study demonstrated that the viscoelastic properties of the zygote within hours after fertilization can predict blastocyst formation in humans and mice.…”

“…172 In that study, uterine con- outcomes. [45][46][47]152,153 However, before use of these biomarkers can become routine in clinical practice, there are many technical challenges that we must overcome. 152,153 First, we need to validate whether the biomechanical properties of bulk embryos are appropriate biomarkers.…”

“…Other studies additionally demonstrated that human oocytes become softer during maturation, and an optimal stiffness range of the zona pellucida before fertilization is required for successful embryo implantation. 45 , 46 , 47 Using indentation measurements via atomic force spectroscopy, Andolfi et al 46 investigated the mechanical properties of whole human oocytes approximately 3–4 h after retrieval under physiological conditions. Measurements were performed on immature (MI) and mature (MII) oocytes, and MII oocytes were further classified as ‘‘suitable’’ or ‘‘rejected’’ according to their morphological characteristics.…”

“… 46 Another study measured the zona pellucida shear modulus of fresh human oocytes using computational methodology to calculate the mechanical parameters that govern zona pellucida deformation during a routine intracytoplasmic sperm injection (ICSI) procedure. 47 Then, those authors investigated the association between parameter C10, which represents the zona pellucida shear modulus, and implantation rate and showed that oocytes with C10 values of 0.20–0.30 and 0.30–0.40 kPa had the highest implantation rates (50% [6/12] and 88.8% [8/9], respectively). 47 Outside of these ranges, the average implantation rate was 6.70%.…”

“… 47 Then, those authors investigated the association between parameter C10, which represents the zona pellucida shear modulus, and implantation rate and showed that oocytes with C10 values of 0.20–0.30 and 0.30–0.40 kPa had the highest implantation rates (50% [6/12] and 88.8% [8/9], respectively). 47 Outside of these ranges, the average implantation rate was 6.70%. 46 , 47 After fertilization, optimal stiffness in the zygote is required for successful human embryonic development.…”