What effects does being cryogenically frozen have on a person's body?

Question

I'm wondering what effects are *known* to happen to a person's cells when a person is cryogenically frozen, especially those that need to be overcome in order to "bring them back to life."From a cellular and maybe even molecular level, is the person exactly the same as before?

Answer 1

Hi there,

By and large, most biomolecules will be relatively stable if flash frozen (though not slow frozen), and all biochemical processes inside an organism will subsequently slow down tremendously. As a result, the freezing process itself won't affect the biochemistry of a body too much. The single biggest problem that we face in cryonics is actually from the physical formation of crystals. Have you ever frozen a plastic water bottle? It swells up like a balloon because ice is less dense than water and so takes up a greater volume for the same mass. The expansion this causes is just fine in a water bottle because the plastic is deformable (and also non-living). The formation of ice inside a cell, however, could rupture the cell membrane as the ice expands and kill the cell when it thaws. Flash freezing helps mitigate this somewhat, by preventing large ice crystals from forming, but even then the problem persists. Freezing a human body with the technology we have today would certainly cause catastrophic damage to tissues from the physical force of ice crystals forming.

Nature has some ingenious solutions to this problem in the form of various natural "antifreeze" molecules in many species that undergo repetitive freeze-thaw cycles, which have the same effect in tissues that automobile antifreezes have in engines. Wood frogs, for example, have a whole suite of proteins that hinder the growth of ice crystals and alter intracellular salt concentrations to allow them to survive freezing solid in the winter and thawing again come spring.

A secondary problem is one of the thawing process as a whole. Let's assume that you've properly flash frozen a human body with some sort of natural antifreeze so that there is minimal physical damage to tissues from ice crystals and minimal chemical damage from the process of freezing itself. Thawing the body quickly in high heat will damage tissues and cause chemical damage, but thawing slowly could result in some tissues thawing before others. If the organs thaw but the circulatory system is frozen for too much longer, tissues could suffer from lack of gas exchange, and if the heart starts beating before the circulatory system thaws fully, any remaining ice crystals could cause significant damage to the delicate structures of the circulatory system.

Outside of the physical damage that could result from the thawing process, the temperature change that would result in the thawing process could potentially also cause either genetic (to DNA) or epigenetic (to DNA modifications) changes from harmful agents like free radicals that can then alter cell viability. These changes could be minimal, but if any changes to the genome/epigenome or proteome occur in the central nervous system, there is a risk of changing something more fundamental to a person's identity or being. As a result, it's also essential to learn more about how to better facilitate successful thawing and effective recovery from any freeze/thaw damage before cryonics can be applied to whole bodies.

To my knowledge, organs such as livers or kidneys have been frozen and thawed for transplant in the past, so cryo-freezing a whole body can in theory be done. It just gets a little complicated with you're dealing with a whole body over a single tissue.