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Aim: The cryopreservation of embryos is essential for assisted reproductive technology field. The aim of the present study is to examine the efficacy and ease of use of a new vitrification device, Kitasato Vitrification System (KVS), in cryopreservation of human embryos., Methods: Human embryos at the cleavage or blastocyst stage were vitrified and warmed by KVS or Cryotop (control device). The survival of cleavage- and blastocyst-stage embryos and the developmental competence of cleavage-stage embryos were evaluated. Four individuals inexperienced in vitrification and warming embryos tested both KVS and Cryotop. The vitrification time and the detachment time of the embryos were evaluated., Results: At the cleavage stage, there were no significant differences in the survival rate and the development rate to the blastocyst stage between KVS and Cryotop (100 vs 96.8% and 63.3 vs 61.3%, respectively). At the blastocyst stage, there was no significant difference in the re-expansion rate between KVS and Cryotop (100 vs 88.9%). The vitrification time was shorter for KVS than Cryotop. There was no significant difference in the detachment time between KVS and Cryotop., Conclusion: Kitasato Vitrification System is easy to operate, even for inexperienced users, and the viability of human embryos vitrified by KVS is comparable to that of Cryotop, a widely used vitrification device., (© 2020 Japan Society of Obstetrics and Gynecology.)

Several closed vitrification devices that avoid contact with liquid nitrogen have been reported. Recently, based on the Kitasato Vitrification System (KVS), we developed the Closed-KVS, which is a closed vitrification device. The KVS is an open vitrification device that can absorb excess vitrification solution. In this study, we performed two experiments to evaluate the efficacy of the Closed-KVS as a vitrification device for the cryopreservation of mouse embryos at the blastocyst and two-cell stage. In the first experiment, the blastocysts were vitrified using either the Closed-KVS or the KVS (control device). The survival, re-expansion, and hatching rates were not significantly different between embryos vitrified using the Closed-KVS and those vitrified using the KVS. In the second experiment, we evaluated the embryonic development of the two-cell stage embryos vitrified using the Closed-KVS. There were no significant differences in the survival, blastocyst formation, or hatching rates between vitrified or non-vitrified embryos. Additionally, we evaluated the cooling and warming rates of these devices using a numerical simulation method. The cooling rates of the Closed-KVS were similar regardless of whether the outer cap was pre-cooled and were lower than those of the KVS. However, the warming rates of the Closed-KVS (irrespective of cap pre-cooling) were the same as those of the KVS (612,000 °C/min). In summary, the Closed-KVS is a novel closed vitrification device for the cryopreservation of mouse embryos at the blastocyst and two-cell stage., (Copyright © 2019. Published by Elsevier Inc.)

Background: Currently, the cryopreservation of embryos and oocytes is essential for assisted reproductive technology (ART) laboratories worldwide. This study aimed to evaluate the efficacy of the Kitasato Vitrification System (KVS) as a vitrification device for the cryopreservation of mouse embryos to determine whether this novel device can be adapted to the field of ART., Methods: In Experiment 1, blastocysts were vitrified using the KVS. Vitrified blastocysts were warmed and subsequently cultured for 72 h. In Experiment 2, 2-cell-stage embryos were vitrified using the KVS, and vitrified embryos were warmed and subsequently cultured for 96 h. In Experiment 3, we evaluated the in vivo developmental potential of vitrified 2-cell-stage embryos using the KVS, and in Experiment 4, we evaluated the cooling and warming rates for these devices using a numerical simulation., Results: In Experiment 1, there were no significant differences between the survival rates of the KVS and a control device. However, re-expanded (100%) and hatching (91.8%) rates were significantly higher for blastocysts vitrified using the KVS. In Experiment 2, there were no significant differences between the survival rates, or rates of development to the blastocyst stage, of vitrified and fresh embryos. In Experiment 3, after embryo transfer, 41% of the embryos developed into live offspring. In Experiment 4, the cooling and warming rates of the KVS were 683,000 and 612,000 °C/min, respectively, exceeding those of the control device., Conclusions: Our study clearly demonstrates that the KVS is a novel vitrification device for the cryopreservation of mouse embryos at the blastocyst and 2-cell stage.