Straw thermal stabilizer for embryo cryopreservation.

Embryo cryopreservation procedures have been highly developed to support in vitro fertilization techniques, but the clinical results have not met initial expectations. Many variables influence the outcome of the embryo cryopreservation procedure. Exposure to classical freezing media does not affect further embryo development. Therefore, the first crucial step seems to be embryo thermal behavior during the freezing/thawing procedure. With the aim of avoiding thermal oscillations to the embryos due to liquid nitrogen injection into the freezing chamber, we have developed a straw thermal stabilizer (STS) cryopreservation accessory that when adapted to a programmable biological freezer offers a more exact control of the straws temperature and also a greater reproducibility of the freezing process. The STS incorporates a seeding mechanism controlled by specially designed software. For the biological assays, 2-cell mouse embryos were cooled until seeding at -7 degrees C or frozen to -120 degrees C using 1.5 M 1,2-propanediol and 0.1 M sucrose. As control groups, embryos were either untreated or were exposed to cryoprotectants, developing to blastocyst at rates of 90.8 and 88.4%, respectively. The embryos cooled until seedling or subjected to the complete freezing procedure developed into blastocysts at rates of 95.7 and 82.8%, respectively, disregarding the effect of the cryoprotectant exposure. These results show a substantial improvement in cryopreservation with no loss in embryo development due to the seeding procedure.