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Topic Last Updated on 09-07-2024
Slow Down Time
There are many reasons we might want to freeze a human being — for example, perhaps someone we know is suffering from an untreatable disease, the cure for which will only be invented a couple of decades into the future. Meanwhile, the patient’s body is being ravaged by illness now. If only we could push pause on their life until the day arrives that doctors will be able to save them!
We can think of other situations that are much more common than incurable diseases, like car crashes, severe injuries, strokes, and heart attacks. In all of these cases, you have to save the victim very quickly, and if we were able to suspend all of the processes in their bodies, it would help to buy us more time.
The storage of donor organs presents a big problem. Often, they must be transported from far away, and sometimes the recipient is not ready for surgery upon an organ’s arrival, so the doctors have to wait a few days to start a transplant. Unfortunately, most organs cannot be kept intact for more than a few hours. Only recently, scientists succeeded in keeping a liver “alive” for two days — a transplant, however, was not attempted.
The Challenges of Whole-Body Freezing
Though scientists have long known how to store cells and tissues with the help of liquid nitrogen, freezing an entire body is not an easy task. A cell is a soup made up of lots of different molecules, so it freezes unevenly. At temperatures below freezing, water collects into crystals in the intercellular substance, and the cells shrivel. Returning them to their original state is hard to pull off: ice crystals are very sharp — a large one can burst a blood vessel, while a smaller one can destroy cells. Thus, total freezing works well only for very small objects, like individual cells.
Ice Is Dangerous
If you take 185 gal of room-temperature nitrogen, compress and cool it to –319 °F, you’ll end up with just 0.26 gal of liquid. In liquid nitrogen, you can quickly freeze cell cultures, embryos, or tissue fragments. Frozen specimens are stored inside special “thermoses” — cryogenic storage dewars that maintain low temperatures with thermal insulation. This works out to be much more reliable and affordable than keeping specimens in refrigerators.
What We Can Do
Cryopreservation (from the Greek kryos, meaning “cold”) is used in the preservation of germ cells, thanks to which we know that the process of freezing itself can be quite safe. The record holders in this regard are the spermatozoa of the Australian Merino breed of sheep, specimens of which have lain in liquid nitrogen for 50 years and are still used for breeding purposes today.
We also know how to freeze ova, or egg cells, even though they are much larger. This can be useful, for example, if a young person wants to keep their eggs healthy in order to give birth to a child at a more mature age. They do so by undergoing hormonal stimulation — several eggs are matured and released at once inside their body, which are then cryopreserved so that, in a few years, they can be defrosted and artificially fertilized. In rare cases, even immature eggs can be frozen, such as in the case of a patient with cancer.
If they need radiation therapy, there is a chance their eggs may die, but stimulating them with hormones is often unsafe — it could accelerate the growth of tumors. So, the patient’s immature eggs are collected, which can later be thawed and placed back inside the ovaries after any tumors have disappeared, or they can be grown outside of the patient’s body in a laboratory.
How Are Egg Cells Preserved?
Water is partially removed from the egg or embryo
They are quickly immersed in liquid nitrogen and frozen after approximately ten seconds
In the place of water, cryoprotectants are inserted into the cells
The cells are lowered into a container and stored as long as needed
With embryos, things are more complicated. When eggs are fertilized in vitro, often many back-up cells are collected — not all of the embryos will develop normally or take root in the uterus. Moreover, in case a patient does not get pregnant after the first attempt and decides to try again, they need to have some “spare embryos” on hand. To do so, embryos are also frozen. Previously, a method of slow freezing was used. Embryos were impregnated with cryoprotectants, substances that make a solution more viscous and inhibit the growth of crystals. Usually, a pair of cryoprotectants were employed: one penetrated the cell (glycerol, for example), while the other worked in the intercellular substance (often sucrose). Afterward, the embryo was slowly immersed in liquid nitrogen.
However, this method was not very reliable — crystals still managed to form. The day was saved by a new method called vitrification, the essence of which involves an increased dose of cryoprotectants that are injected into the embryo before quickly immersing them in nitrogen. In this case, the contents of the cells are so viscous that crystals do not form, but they are also so hard that life processes stop. The tissue actually turns into glass.
However, both slow freezing and vitrification are quite safe — there are already children in the world who, as embryos, spent up to 20 years in liquid nitrogen, and it did not affect their subsequent quality of life.
Two Methods of Freezing
