THE PROCEDURE:
Cryopreservation techniques involve procedures which are critical
to survival of the embryo. One of the most important principles
of this technique is to remove water from the cells before they
freeze. If the water is not removed, large intracellular ice crystals
are formed during freezing which may damage the embryo. In order
to remove water from the embryos, special solutions called cryoprotectants
are used. The embryos are briefly exposed to increasing concentrations
of cryoprotectants. They are then placed inside plastic straws (filled
with one of the cryoprotectants) and transferred to a controlled-rate
freezer where the embryos are cooled slowly. Once the temperature
of the embryos has reached a predetermined point below 0°C, the
straws are plunged into liquid nitrogen (-196°C) and stored there
until thawing.
To thaw the
embryos, the straws are pulled out of the storage tank and warmed
first at room temperature and then in a water bath at 37°C. The
embryos are released from the straws and rinsed in decreasing concentration
of cryoprotectants to replace cellular water. They are then placed
in culture medium and are incubated from 1-2 hours to determine
if they have survived the freeze/thaw process. |
