The formation of sharp ice crystals fatally lyses cells through mechanical piercing:

"The failure of complex mammalian organs, such as the kidney, to function following freezing to low temperatures is thought to be due largely to mechanical disruption of the intercellular architecture by the formation of extracellular ice." Rall and Fahy, "Ice-free cryopreservation of mouse embryos at -196 degrees C by vitrification" Nature 313 6003 pp573-5 (1985).

This outcome was identified as early as the 1960s by electron microscopy of thawed cells, which revealed many puncture holes in the membrane.

Both freezing and rethawing are opportunities for damage, as recrystallization can occur during the latter regardless of how carefully the former was performed.

Freezing into the crystalline phase of ice (and many other materials) produces sharp dendrites because some crystal orientations exhibit very fast growth kinetics. This issue doesn't arise with amorphous freezing.

As an early discussion, see, for example, Mazur's "Cryobiology: the freezing of biological systems" Science 168 3934 pp. 939-949 (1970) and the references within.

The formation of sharp ice crystals fatally lyses cells through mechanical piercing:

"The failure of complex mammalian organs, such as the kidney, to function following freezing to low temperatures is thought to be due largely to mechanical disruption of the intercellular architecture by the formation of extracellular ice." Rall and Fahy, "Ice-free cryopreservation of mouse embryos at -196 degrees C by vitrification" Nature 313 6003 pp573-5 (1985).

This outcome was identified as early as the 1960s by electron microscopy of thawed cells, which revealed many puncture holes in the membrane.

Both freezing and rethawing are opportunities for damage, as recrystallization can occur during the latter regardless of how carefully the former was performed.

Freezing into the crystalline phase of ice (and many other materials) produces sharp dendrites because some crystal orientations exhibit very fast growth kinetics. This issue doesn't arise with amorphous freezing.

For an early discussion, see, for example, Mazur's "Cryobiology: the freezing of biological systems" Science 168 3934 pp939-49 (1970) and the references within.