This article will discuss such a concept as vitrification of embryos. Dr. Masashige Kuwayama invented this method on cryotopes in another two thousandth year. The first child was born thanks to vitrification embryos in 2003. Oocyte survival was increased by 98 percent.
In half of women who are prescribed in vitro fertilization, embryos remain. Cryopreservation is performed for them, which saves patients money. Indeed, defrosting and transferring embryos is much easier than carrying out the in vitro fertilization procedure anew. It is also a kind of insurance in case the woman does not get pregnant. Cryopreservation has an undeniable advantage - the death of viable embryos that remained after the protocol is prevented.
Ontogenesis
The course of the subjective development of the organism, or ontogenesis, originates from the moment of fertilization and ends in its death. This movement is continuous in time and has an irreparable character. And we can’t stop it or slow down its development. But in nature there are exceptions. These are plants, invertebrate animals, and even some elementary vertebrates, which at low temperature do not exhibit properties characteristic of living organisms.
What is suspended animation?
We will consider vitrification of embryos below. An individual period of calm is called suspended animation. For example, many Siberian animals survive temperatures of up to -90 degrees, and almost complete dehydration. When studying this period of ontogenesis in natural conditions, the question arises of the possible use of low temperatures for the partial and reversible interruption of the functioning of higher vertebrate creatures, including humans.
Cryopreservation
Cryopreservation is an effective method of suspending biological processes in cells by exposure to low temperature. At the same time, the vital activity of cells during heating is maintained. In popularity, this method is inferior to vitrification of embryos. 1 cryotope (labeled cryocarrier) contains from 1 to 3 embryos.
For example, when performing a procedure such as IVF, the best action is to move no more than two embryos into the uterine cavity. The remaining quality embryos can be cryopreserved for future use. They can also be used for repeated IVF after some time, if the procedure shows a negative result. For such purposes, vitrification of embryos on individual carriers is carried out.
In some cases, all embryos are frozen. For women who have ovarian hyperstimulation syndrome with the induction of superovulation, this is most common. Who else is recommended freezing? Patients suffering from cancer, in particular before chemotherapy or radiotherapy. Then these embryos are transferred to the uterine cavity. Freezing is indicated for everyone who has a reduced chance of pregnancy after IVF. This can be an endometrial polyp, insufficient thickness of the endometrium by the time the transfer is planned, dysfunctional bleeding.
Stages of freezing
Embryos are frozen at various stages:
- a fertilized egg (zygote);
- embryo crushing stage;
- blastocyst.
There are currently two ways to freeze embryos.
Slow freeze
Vitrification of embryos is carried out with slow freezing. This method was proposed back in the 70s and is one of the first classical methods of embryo freezing. It is based on slow cooling at a constant speed. After the embryos are stored in liquid nitrogen.
But it should be noted that during slow freezing, microscopic ice crystals form in the cryoprotective solution, which negatively affect the cells of the embryo. This can provoke a partial or complete death of the biomaterial during heating. The number of embryos successfully transferred during slow freezing and warming is approximately 70 percent.
Vitrification
After 2010, they began to apply a new and more effective method of cryopreservation - vitrification. Compared to the previous method, this is an ultrafast way to freeze biomaterial. Most often, vitrification of embryos after PGD (genetic diagnosis) is carried out .
Using this procedure, the cryoprotective solution where the embryos are placed does not form ice crystals upon freezing. Thus, the probability of disturbance of the embryo is reduced. The priority of this method is not only the method of freezing, but also the percentage of survival of the embryos after heating. According to statistics, the number of survivors after the process of vitrification of embryos is at least 95 percent.
What happens after warming up?
After warming up, the embryos hardly differ from ordinary embryos. They also take root and develop well. When heated, all embryos are subjected to an auxiliary hatching process. During this action, the surface layer of the embryo is separated by a laser beam at the desired and safe angle. This facilitates the exit of the embryo from the membrane and increases the possibility of successful transplantation into the uterine cavity.
Freezing makes it possible to store embryos for a long time. This process is economically advantageous, since the cost of preserving, warming, and implanting the embryo in the uterine cavity is lower than the repeated process of in vitro fertilization.
Vitrification is considered as a phased transition, where a cold solution when cooled below the glass transition temperature. At the same time, it remains amorphous, receives the structure of glass and a quality similar to crystalline solids. Thus, living cells, and even the whole embryo turn into "glass". The vitreous glassy structure of the liquid is obtained due to its rapid cooling, that is, the entropy of the liquid decreases in a shorter period of time than the entropy of the required crystalline structure.
In simple words, the liquid does not freeze when its entropy approaches the entropy of the crystal. But in order to properly vitrify a living organism, it is necessary to achieve a rate of temperature decline of ≈ 108 ° C / min., And this is practically impossible, because the cryogenic liquid used does not have enough temperature for this, and it is impossible to use a vitrified solution in a smaller volume than the volume oocyte. This is all that implies vitrification of embryos. What is it, now it has become more or less clear.
Scientists were able to prove that an increase in the environment for freezing cryoprotectants makes it possible to quickly reduce the speed of freezing. So, at a density of 10% ethylene glycol and propylene glycol, the speed decreases significantly, at 40 percent density, vitrification is possible at a cooling rate of 10 ° C / min, and at 60% the speed drops to 50 ° C / min. But with an increase in the density of cryoprotectants entering the medium, their negative effect on the freezing of biomaterials increases. Slow freezing provokes an accumulation of chilled water in the biological body and intracellular element. This condition is observed due to severe dehydration of the cell with the appearance of extracellular ice.
Accordingly, upon receipt of a glass-like structure, the chemical and physical processes of dehydration of the body cease. Despite the fact that vitrification of embryos (that it was described in detail above) is a rather difficult physical system, materials of such a structure can be found in our everyday life (glass, silicone, and so on).
Vitrification of embryos: reviews
This method collects only positive reviews. The vitrification procedure is feasible. But it has many features at different stages of development in IVF laboratories. Vitrification is not the latest way to cryopreserve living cells. It is the last stage of slow freezing. Today, many women have the opportunity to have a baby thanks to scientific developments.
conclusions
Due to the work of many scientists, vitrification can be carried out without the use of an expensive programmed freezer, but with the use of simple equipment that the operator controls. Thus, the method is simplified and the final result is improved. Despite the great achievements in cryopreservation, the implementation of the proper preservation of living organisms at low temperatures is currently impossible.