The team of Professor Zhao Gang, chairman of the Yinfeng Cryomedicine Expert Committee, and his collaborators published a report [Cryopreservation method of mouse follicles based on synergistic ice suppression effect]

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In recent years, the incidence of malignant diseases (such as breast cancer and hematological diseases) among young women has increased. Although aggressive chemoradiotherapy or bone marrow transplantation can cure 90% of young women, these treatments can still damage their gonads. It can even lead to premature ovarian failure. In addition, many women who delay childbearing due to work or financial reasons are also affected by infertility. Therefore, the demand for fertility preservation among women is increasing dramatically. Currently, methods for preserving female fertility mainly include cryopreservation of embryos, unfertilized oocytes and ovarian tissue. Among them, embryo cryopreservation requires women to have a male partner or use donated sperm, which may involve religious, moral, ethical and other issues. Oocyte cryopreservation is mainly used for women who have reached puberty and can withstand multiple rounds of ovarian stimulation. For adult women and unmarried female cancer patients, follicle cryopreservation is almost their only option.



In fertility research, mouse preantral follicles (PAFs) are often used as a model to optimize cryopreservation, in vitro culture conditions, and fertility preservation. Common follicle cryopreservation methods include slow freezing and vitrification. The former will inevitably form a large number of ice crystals, which will then cause irreversible damage to the follicles; the latter, in order to achieve the glass transition of the sample and avoid ice crystal damage, needs to introduce a very high concentration of cryoprotectant (usually 6M), which will cause greater Large chemical toxicity damage. In addition, recrystallization and/or devitrification may occur during the rewarming and melting process, which is often fatal to the damage to the sample. In summary, the preservation of follicles poses a great challenge to cryobiologists. How to achieve safe and efficient vitrification preservation of low-concentration, low-toxic or even non-toxic cryoprotectants?



Zhao Gang, chairman of the Yinfeng Cryomedicine Expert Committee, and his team developed a vitrification method for the preservation of mouse follicles with a low-concentration cryoprotectant based on the synergistic ice-suppressing effect. They combined magnetothermal and photothermal space rewarming with hydrogel microencapsulation to achieve synergistic ice suppression, reducing the concentration of the osmotic protective agent by 75% (only 1.5M). Among them, space rewarming technology uses the dual thermal effects of magnetothermal and photothermal to effectively improve the rewarming rate and temperature distribution uniformity, solve the problem of devitrification/recrystallization that may occur during the heating process, and avoid excessive cell damage. Hydrogel microencapsulation can not only provide a protective barrier for cells, reduce extracellular ice damage, and prevent the growth of intracellular ice nuclei; it can also effectively reduce the toxic and side effects during the vitrification process by reducing the growth of ice crystals during cooling and heating. The need for protective agents; it can also provide a three-dimensional microenvironment similar to the extracellular matrix for in vitro PAFs culture, which strongly supports the in vitro development of 3D cultured mouse follicles after rewarming. After cryopreservation, the survival rate of PAFs is as high as 90%; and mature oocytes can be successfully discharged after 13 days of 3D culture in vitro. These mature oocytes develop to the blastocyst stage after in vitro fertilization, and the fertilized eggs are in the 2-cell Early transplantation into surrogate mice can give birth to healthy mouse pups.

In summary, this study successfully established a technical system that integrates microencapsulation, freezing, rewarming and 3D culture, opening up a new path for cryopreservation and full utilization of PAFs, which may help improve post-treatment outcomes. The patient's chance of regaining fertility. Additionally, the method could potentially be used to preserve female germ cells from high-risk animal species, spurring the creation and development of cryobanks in medical centers around the world.

As a forward-looking field of human medical research, cryogenic medicine cannot be separated from the joint efforts of scientific research teams from all parties. The international cryogenic biomedical research system organized and led by the Yinfeng cryogenic medicine team will build an academic exchange and achievement sharing platform for global cryogenic biomedical research teams, integrate international and domestic scientific research academic forces in multiple fields, and build a systematic cryogenic medical research system. Jointly promote the development of cryogenic medicine research and let global cryogenic medicine researchers gather into a powerful force of organic synergy.

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