Gamete and tissue cryopreservation is a powerful tool against infertility, but how does it really work and what ways are there to do it? Today there are two techniques used by reproductive medicine: slow freezing and a novel technique called vitrification.
The first of these, slow freezing, as its name suggests, refers to the cooling of biological material, either eggs, sperm, or embryos at a low and constant speed. This cooling rate is crucial because it prevents the formation of ice crystals inside the cell that perforate the membrane and compromise its integrity. However, if the speed is too slow, compounds accumulate in the cell that, at high concentrations, are harmful to life. In slow freezing, a cooling rate must be found that is both fast and slow enough.
On the other hand, vitrification is an ultra-fast cooling technique. While in slow freezing the drop in temperature can occur over minutes to hours on a scale of 10º to 30º, in vitrification it is immediate.
This technique consists of immersing the cells in cryoprotective liquid of very high viscosity. Then all the mixture is added directly into liquid nitrogen which is at an average temperature of -195.8º. The drop in temperature is such that all the water inside, as well as all its components, is “paralyzed” in time. Let us look at it this way. In liquid water, the molecules that form it are free, but when they freeze, they settle with each other in a more stable structure and with less movement. This is reflected in the stable structure of the ice. In slow freezing the water molecules regroup into crystals, the tips of which burst the cell like a balloon, but in vitrification this does not happen. The cooling is so sudden that the water molecules do not have enough time to sort themselves out and are stuck in time, detained inside the viscous cryoprotective liquid like millions of tiny mosquitoes trapped in amber.
Both slow freezing and vitrification have their pros and cons, and how do you know which is better? Although theoretically vitrification is better, there is still research around the world to optimize cryopreservation processes. However, it is very important to know what we are interested in preserving.
For example, slow freezing is more used to preserve cells such as sperm or eggs, but recent studies have shown that vitrification has a higher success rate when it comes to embryos. What is really important is that thanks to these techniques it is possible to preserve people’s fertility, no matter what their condition is. We can put a stop to any evil that affects us and safeguard what matters most.
If you have any doubts, come to our experts. Remember that here at Citmer we want to be part of your history.
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Colombian Journal of Obstetrics and Gynecology. 57(4): 291 – 300.