Comparison of vitrification efficiency using thin plastic strip (TPS) and electron microscope (EM) grid on mouse blastocysts

Abstract

OBJECTIVE: As a vitrification tool, the EM grid has a strong point that has the highest cooling rate due to the extremely low volume of vitrification medium and directly plunging into liquid nitrogen(LN2). However, it also has a problem which is an expert embryo handling and an attaching embryo in grid after thawed. Accordingly, we attempted to apply a loading of plasticware which is everywhere made of polypropylene as a new vitrification tool, named thin plastic strip(TPS) for vitrification of mouse blastocysts. DESIGN: The aim of this study is to investigate the usefulness of TPS in vitrification of late stage mouse blastocysts comparing with an EM grid. MATERIALS AND METHODS: Blastocysts obtained from six weeks-old BDF1 mouse. The expanded blastocysts(EdB,n=166) were vitrified respectively using TPS(n=75) and EM grid(n=91) after artificial shrinkage. And hatching blastocysts(HgB,n=243) were vitrified respectively using TPS(n=122) and EM grid(n=121) following artificial shrinkage. Minimum volume of vitrification medium mixed with blastocysts loaded on TPS. Except loading method, other process of vitrification and thawing were prepared according to the previously described method (Son et al.,2003). The blastocysts were thawed a month later and cultured for a day. The viability was then assessed through survival and recovery. RESULTS: The recovery rate of the TPS(EdB,100%,75/75,HgB,100%,122/122) was significantly higher than EM grid(EdB,90.5%,83/91,HgB,75.2%,99/121)(P<0.05). There was no significant difference in the survival rate of the TPS(EdB, 93.3%,67/75,HgB,88.3%,100/122) and EM grid(EdB,85.1%, 74/91,HgB, 68.6%,87/121)(P<0.05). CONCLUSION: This study showed that the vitrification using TPS has a potential usefulness on late stage mouse blastocysts. Comparison of survival rate of TPS is similar to EM grid. But, recovery rate of TPS is higher than EM grid. Therefore, the TPS would be useful as an alternative tool that overcomes the problems of EM grid. And also, it has the potential for clinical applications.