“Bugsicle” is a biologist's pet name for an insect that spends the winter in a cryogenic (frozen solid) state and wakes up in the spring to reproduce. Being able to freeze people for extended space journeys is a favorite topic for science fiction writers, but we humans suffer severe tissue damage if we become frozen: ice crystals form, puncture cell membranes and destroy them, often resulting in death of and a need to remove the body parts that freeze. Nature, as usual, developed a method to solve this problem long before we humans could. Many animals and plants are able to withstand the rigors of winter by literally freezing in their tracks when temperatures plummet. The seeds of some arctic lupines that were frozen in a lemming burrow under a glacier for over 10,000 years germinated within 48 hours after being thawed and produced mature plants.
Hibernation Differs From Cryogenesis
Bears and chipmunks hibernate to survive the winter. Hibernation is not the same as cryogenic storage, though. While hibernating, the animal retains some warmth, maintains a low level of metabolism, and does not freeze solid. Cryogenesis occurs when animals freeze solid with no heartbeat and all metabolic functions are reduced to zero. These animals revive when the warm weather returns and continue where they left off as winter settled in.
Numerous animals freeze in ice, inside plant stems, and under leaves. Spring peepers and other frogs burrow beneath leaves and grasses at the edges of ponds in the fall and freeze solid when the ponds ice over. This strategy allows them to be ready to breed early in the spring before their usual predators are able to move around.
Goldenrod gall flies and other insects live in galls and feed on the stem tissues. These larvae remain inside the galls, cannot escape winter’s wrath, and must tolerate being frozen. Biologists often store them in a -20oC (-5oF) freezer for several months before working with them.
The female praying mantis, Mantis religiosa, produces a frothy egg case that looks like foam insulation. Inside of this case are up to one hundred eggs that freeze solid in the winter and remain so for several weeks or months with no damage.
How do animals withstand being frozen?
Frozen animals have large body cavities that are the first to freeze. As water freezes in the body cavity, water is extracted from the cells and freezes outside the cells where it can’t damage them. Glucose, the all-important storehouse of energy for our cells, also serves as an important antifreeze in these animals. Organic alcohols are another type of antifreeze molecule that cryogenic animals produce.
The removal of water from the cells during freezing concentrates the glucose and other antifreeze chemicals inside the cells. These chemicals turn the cell contents to slush before gradually freezing solid. The slush protects the cells by preventing the formation of ice crystals that would normally shred the cells’ membranes. When the animals thaw, the process is reversed, the cells rehydrate, and the animal resumes activity once the temperature is warm enough to allow movement.
Is This Applicable To Humans?
Several decades ago, researchers developed methods that allow us to freeze human blood cells, sperm, and even embryos and have them function after thawing. Researchers are currently working to find a process similar to the one used by these animals that will allow storage of donated organs for days or weeks instead of the few hours available to us today. Others hope that we will be able to freeze entire humans when they die, store them until medicine finds a cure for the ailment that killed them, revive them, perform the cure, and the person will resume living as if he or she had never died.
Freezing entire humans is presently not feasible. Our organs are complex and there is not enough space between the cells into which water can be extracted. If we can develop a reversible mode of storage, then people who die from diseases may be frozen until medicine finds a cure for the disease, be thawed out, repaired, and resume active lives.
