Development of an automated device for the optimization of oocyte and embryo vitrification

Oocyte/embryo vitrification is one of the basic techniques employed in assisted reproduction and fertility preservation. However, the current process typically requires manual operation by experienced embryologists, which is both time-consuming and exhibits inconsistent outcomes. To resolve this issue, we herein developed an automated vitrification device for oocytes/embryos. The device consists of a microfluidic mixing unit, a microgrid capillary, and a mechanical sliding unit. The microfluidic mixing unit was adopted to determine continuous changes in cryoprotective agent (CPA) concentration, reducing osmotic damage during CPA loading/removal; and the microgrid capillary was used to load/remove the CPA and vitrify the oocytes/embryos in the same carrier so as to reduce cellular loss due to cell transfer. The medical absorbent dressing was placed under the carrier, and the excess liquid was absorbed to minimize the remaining CPA solution after CPA loading. Eight different loading/removal curves were developed for CPA loading and removal protocols, and we conducted oocyte vitrification with automated vitrification equipment. Our results revealed that a quadratic function-based, loading-removal curve achieved the highest oocyte survival rate within an 8-min loading and removal duration. In addition, there was no significant difference in oocyte survival rates between the automated vitrification device and the Cryotop multi-step equilibration method (90.33 % and 94.33 %, respectively); nor did the two methods differ in terms of survival or hatching rates of 8-cell embryos. The current system automates and standardizes the oocyte/embryo vitrification process while achieving survival and developmental potential.