Embryo vitrification is a fundamental technology utilized in assisted reproduction and fertility preservation. Vitrification involves sequential loading and unloading of cryoprotectants (CPAs) with strict time control, and transferring the embryo in a minimum CPA droplet to the vitrification straw. However, manual operation still cannot effectively avoid embryo loss, and the existing automatic vitrification systems have insufficient system reliability, and operate differently from clinical vitrification protocol. Through collaboration with in vitro fertilization (IVF) clinics, we are in the process realizing a robotic system that can automatically conduct the embryo vitrification process, including the pretreatment with CPAs, transfer of embryo to the vitrification straw, and cryopreservation with liquid nitrogen (LN2).
Technically, in this paper, we focused on the design of a new robotic system for embryo vitrification, which included an open microfluidic chip (OMC) as the interface between the manual operator and the automatic machine system, and commonly used Cryotop safety kit as the embryo carrier during the freezing and thawing processes. To provide a more simplified and standardized vitrification process while remaining high-throughput, the novel open microfluidic chip was proposed, that utilized a capillary gap and micro channel to realize the exchange of CPAs, fixation of embryos/oocytes and the transfer of embryos/oocytes to the standard Cryotop, with assistance of the robotic system.
The solution exchange performance of the OMC was evaluated by both the numerical simulation and fluorescence tracer experiments. The width of the capillary gap, which is a key parameter for our OMC, was optimized at 80 µm to simultaneously ensure the solution exchange efficiency and embryos safety. In a practical experiment using mouse embryos, our robotic system showed a 100% success rate to transfer and vitrify the embryos and achieved comparable embryo survival (90.9% vs. 94.4%) and development rates (90.0% vs. 94.1%) compared with the manual group conducted by the senior embryologist.