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[bgwowk]

There are three issues relevant to cryopreservation of tissue as opposed to cell suspensions. They are

1) Mechanical damage from ice.

2) Cryoprotectant penetration

3) Heat transfer

1) If tissue is frozen instead of vitrified, disruption of required cell-to-cell connections is an issue even if individual cells survive. Some tissues are more tolerant of this injury than other tissues. Whole dog intenstines have been successfully frozen to liquid nitrogen temperature and successfully transplanted. Kidneys, on the other hand, will not survive much ice formation. Both freezing and vitrification have been successfully used on reproductive tissue (including whole mouse ovaries), so such tissue is apparently tolerant of some freezing injury (meaning that the individual cells preserved are more important than the detailed tissue structure).

2) Tissue pieces of up to a hundred microliters volume, or so, can be equilibrated with cryoprotectant by passive difusion (soaking in cryprotectant). Larger tissues and organs require introduction and removal of cryoprotectant by vascular perfusion. Although I did not look up the studies cited by prometheus, they were almost certainly done by soaking, not perfusion.

3) Larger tissues and organs cool and rewarm slower. This requires higher cryoprotectant concentrations for vitrification, and longer exposure time to toxic cryoprotectants during cooling and rewarming (an issue for both freezing and vitrification). This is the biggest obstacle to reversible cryopreservation of large tissue masses.

---BrianW