This article will discuss such a concept as vitrification of embryos. Dr. Masashige Kuwayama invented this method on cryotopes back in the year 2000. The first child was born thanks to vitrification embryos in 2003. Oocyte survival was increased by 98 percent.
Half of women who undergo in vitro fertilization still have embryos. Cryopreservation is carried out for them, which saves money for patients. After all, it is much easier to defrost and transfer the embryos than to carry out the in vitro fertilization procedure again. It is also a kind of insurance in case a woman does not become pregnant. Cryopreservation has an undeniable advantage - the death of viable embryos that remain after the protocol is prevented.
Ontogeny
The course of the subjective development of an organism, or ontogenesis, originates from the moment of fertilization and ends with its death. This movementcontinuous in time and has an irreparable character. And there is no way we can stop it or slow down its development. But in nature there are exceptions. These are plants, invertebrates and even some elementary vertebrates, which at low temperatures do not exhibit the properties characteristic of living organisms.
What is suspended animation?
Vitrification of embryos will be discussed below. An individual period of calm is called suspended animation. So, for example, many Siberian animals survive temperatures reaching -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 partial and reversible interruption of the functioning of higher vertebrate creatures, including humans.
Cryoconservation
Cryoconservation is an effective method of suspending biological processes in cells by exposure to low temperatures. At the same time, the vital activity of the cells is preserved during heating. In popularity, this method is inferior to the 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 later use. They can also be used to repeat IVF after a while, if the procedure shows a negative result. With suchpurposes, vitrification of embryos on individual carriers is carried out.
In some cases, all embryos are frozen. For women who have ovarian hyperstimulation syndrome on superovulation induction, this is done most frequently. Who else is recommended to freeze? Patients suffering from oncological diseases, in particular before the procedure of 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 for some reason. It could be an endometrial polyp, insufficient thickness of the endometrium by the time the transfer is planned, dysfunctional bleeding.
Freezing steps
Embryos are frozen at various stages:
- fertilized egg (zygote);
- stage of embryo crushing;
- 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 for freezing embryos. It is based on slow cooling at a constant rate. After the embryos are stored in liquid nitrogen.
But it should be noted that during slow freezing in the cryoprotective solution, microscopic ice crystals are formed, which negatively affect the cells of the embryo. It mayprovoke partial or complete death of the biomaterial during heating. The success rate of embryos transferred during the slow freeze and thaw process is approximately 70 percent.
Vitrification
After 2010, a new and more effective method of cryopreservation began to be used - vitrification. Compared to the previous method, this is an ultra-fast method of freezing biomaterial. Most often, vitrification of embryos is performed after PGD (genetic diagnosis).
When using this procedure, the cryoprotective solution where the embryos are placed does not form ice crystals when frozen. Thus, the probability of embryo disturbance is reduced. The priority of this method is not only the method of freezing, but also the percentage of survival of embryos after thawing. 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, the embryos almost do not differ from ordinary embryos. They also take root and develop well. Upon rewarming, all embryos undergo an assisted hatching process. When carrying out this action, the surface layer of the embryo is divided by a laser beam at the desired and safe angle. This facilitates the exit of the embryo from the shell and increases the possibility of a successful transfer into the uterine cavity.
Freezing makes it possible to store embryos for a long time. This process is economically beneficial, since the cost of preserving, warming andimplantation of the embryo into the uterine cavity is less than the repeated process of in vitro fertilization.
Vitrification is considered as a phased transition, where the cold solution when cooled below the glass transition temperature. At the same time, it remains amorphous, acquires a glass structure and a quality similar to crystalline solids. Thus, both living cells and even the whole embryo turn into "glass". The glassy structure of the liquid during vitrification 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 crystal structure.
In simple words, a liquid does not freeze when its entropy approaches the entropy of a crystal. But in order to properly vitrify a living organism, it is necessary to achieve a temperature drop rate of ≈ 108 °C/min, and this is impossible in practice, because the temperature of the cryogenic liquid used is insufficient for this, and it is impossible to use the vitrified solution in a smaller volume than the volume oocyte. This is all about the vitrification of embryos. What it is, now it has become more or less clear.
Scientists were able to prove that the addition of cryoprotectants to the freezing medium makes it possible to quickly reduce the freezing rate. This means that at 10% density of ethylene glycol and propylene glycol, the rate decreases significantly, at 40% density vitrification is possible with a cooling rate of 10 °C/min, and at 60% the rate drops to 50 °C/min. But with increasing densitycryoprotectants entering the environment, their negative effect on the freezing of biomaterials increases. Slow freezing provokes the accumulation of chilled water in the biological organism and the intracellular element. This condition is observed due to severe dehydration of the cell when extracellular ice appears.
Accordingly, when a glass-like structure is obtained, the chemical and physical processes of dehydration of the body stop. Despite the fact that embryonic vitrification (what it is, was described in detail above) is a rather difficult physical system, materials of this structure can be found in our daily life (glass, silicone, and so on).
Vitrification of embryos: reviews
This method collects only positive feedback. The vitrification procedure is feasible. But it has many features at different stages of development in IVF laboratories. Vitrification is not the newest method of cryopreservation of 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 simple equipment controlled by an operator. Thus, the method is simplified and the end result is improved. Despite the great achievements in cryopreservation, the implementation of the correct preservation of living organisms at low temperatures todayimpossible.
