Loading equine oocytes with cryoprotective agents captured with a finite element method model

Sercan Içli,Peter Wriggers,Harald Sieme,Willem F Wolkers,Meisam Soleimani,Harriëtte Oldenhof

doi:10.1038/s41598-021-99287-9

Abstract

Cryopreservation can be used to store equine oocytes for extended periods so that they can be used in artificial reproduction technologies at a desired time point. It requires use of cryoprotective agents (CPAs) to protect the oocytes against freezing injury. The intracellular introduction of CPAs, however, may cause irreversible osmotic damage. The response of cells exposed to CPA solutions is governed by the permeability of the cellular membrane towards water and the CPAs. In this study, a mathematical mass transport model describing the permeation of water and CPAs across an oocyte membrane was used to simulate oocyte volume responses and concomitant intracellular CPA concentrations during the exposure of oocytes to CPA solutions. The results of the analytical simulations were subsequently used to develop a phenomenological finite element method (FEM) continuum model to capture the response of oocytes exposed to CPA solutions with spatial information. FEM simulations were used to depict spatial differences in CPA concentration during CPA permeation, namely at locations near the membrane surface and towards the middle of the cell, and to capture corresponding changes in deformation and hydrostatic pressure. FEM simulations of the multiple processes occurring during CPA loading of oocytes are a valuable tool to increase our understanding of the mechanisms underlying cryopreservation outcome.

Highlights

Cryopreservation can be used to store equine oocytes for extended periods so that they can be used in artificial reproduction technologies at a desired time point
Cell volume response data were fitted using Eqs. (1) and (2) and the parameters listed in Table 1 to derive Lp and Ps values as previously described[18]
Oocytes exhibit a biphasic cell volume behavior when exposed to solutions containing molar concentrations of ethylene glycol (EG)

Summary

Introduction

Cryopreservation can be used to store equine oocytes for extended periods so that they can be used in artificial reproduction technologies at a desired time point. Cryopreservation can be used to store oocytes for extended periods at ultra-low temperatures in liquid nitrogen tanks or mechanical freezers until they are needed Both the water-to-ice phase transition as well as the drastic temperature changes during cooling and re-warming associated with cryopreservation of cells can be very damaging[1]. Vitrification (ice-free cryopreservation) can be used for cryostorage, which requires a combination of high cooling rates and high CPA concentrations to completely avoid ice formation[3] For both cryopreservation approaches, the introduction of CPAs into cells needs to be done with care, because exposing cells to CPA solutions may be toxic and cause osmotic damage. Water can pass the cellular membrane much faster compared to CPAs causing water to initially move out of the cells and a concomitant reduction in cell volume Thereafter, both CPAs and water move into the cell until equilibrium is reached between the extra- and intracellular osmolality. Once cell-specific Lp and Ps values are known, they can be used to predict volume responses during CPA loading and unloading at different CPA concentrations and, if the activation energies of water and CPA permeability are known, at different temperatures[11]

Objectives

Methods

Results

Discussion

Conclusion