Organ and tissue cryopreservation

In plain language

Freezing living tissue is hard because water turns into ice crystals, and ice can tear cells and tissue apart. One way around this is vitrification, where the tissue is soaked in very high concentrations of protective chemicals called cryoprotectants and cooled so that the liquid sets into a glass-like solid rather than forming crystals.

The harder step is warming it back up. If warming is too slow, ice can form as the glass turns back into liquid, and uneven warming can crack the tissue because the outside and inside expand at different rates. Freezing eggs and embryos this way is now routine in fertility clinics, but whole organs are far harder. In 2023 a team in Minnesota vitrified rat kidneys, stored them for up to 100 days and warmed them with magnetic nanoparticles heated by a radio field. The rats survived the 30-day study, but their kidneys worked less well than fresh ones at first.

Technical explanation

Vitrification means cooling a concentrated solution so that it forms an amorphous glass instead of ordered ice. It needs cryoprotectant concentrations high enough to suppress crystallisation, and cooling fast enough, or uniform enough, to avoid ice in the middle of the sample. Rall and Fahy (1985) reported ice-free cryopreservation of mouse embryos at -196 °C by vitrification. A 2017 narrative review by authors from a fertility centre reports blastocyst survival that routinely exceeds 95% and oocyte survival above 85%, although the same review also gives a 75 to 95% oocyte range. It describes vitrification of whole ovaries and organs as still promising rather than established.

Scaling to organs has needed nanowarming. Manuchehrabadi and colleagues (2017) heated mesoporous silica-coated iron oxide nanoparticles with a radiofrequency field. In 50 mL porcine carotid arteries, viability after nanowarming was 86 ± 3%, against 20 ± 6% after convective warming, and the authors describe convective warming of larger volumes as failing through crystallisation or cracking. The authors note that nanoparticles reach only the vascular space during perfusion, roughly 10% of most tissues, which is a key constraint for whole organs. Han and colleagues (2023) vitrified rat kidneys with VMP at 8.4 M, stored them at -150 °C for 1 to 100 days and nanowarmed them at a mean of 72.0 °C per minute (±8.0). All five nanowarmed recipients survived 30 days, and day-30 creatinine was 0.62 mg/dL against 0.44 mg/dL in fresh controls (P = 0.3). Earlier work by Fahy and colleagues (2009) had vitrified a 12.7 g rabbit kidney, which was transplanted back into its donor, but the authors describe that single surviving case as anecdotal.

Note on whole-body cryonics: whole-body cryonics proposes the same vitrification principles, but no mammal has been shown to be revived after sub-zero storage and thawing. A 2022 review in Frontiers in Veterinary Science reports that no studies have attempted to cryopreserve and revive whole animals, and it describes revival as the most problematic challenge for cryonics. Neuroscientist Clive Coen (2016) argues that cryoprotectants may not reach all brain tissue in time, and that there is no evidence for the sub-zero storage, thawing and revival of any mammal. These are scientific critiques of the cryonics claim, so the revival of preserved people is speculative and disputed.

What the evidence says

Each statement is typed by the strength of its evidence and linked to the source that supports it.

Limitations and open problems

• Whole-organ nanowarming has been tested physically in samples up to 80 mL, but biological viability tests stopped at 50 mL and covered only cells, arteries and heart valve leaflets (Manuchehrabadi and colleagues, 2017).
• Ice formation during warming (devitrification) and cracking remain risks. In the 2009 rabbit work, perfusion at -22 °C left about 7% of the inner medulla crystallised during rewarming (Fahy and colleagues, 2009).
• The rat kidney study used VMP at 8.4 M, a very high cryoprotectant concentration, and toxicity rises with exposure time. The authors report that the earlier VS55 solution caused more kidney damage than VMP on histology (Han and colleagues, 2023).
• Rat kidney evidence comes from small groups (five recipients per transplant arm, and 3 to 8 per group in ex vivo experiments) with a 30-day follow-up. The nanowarmed kidneys had 2 to 3 weeks of initial graft dysfunction and focal tubular necrosis on histology (Han and colleagues, 2023).
• Nanoparticles reach only the vascular space during perfusion, roughly 10% of most tissues. Whole pig or human-sized organs have not been tested in these studies (Manuchehrabadi and colleagues, 2017; Han and colleagues, 2023).
• Two authors of the rat kidney study are named on pending U.S. patent applications, and two authors of the 2017 nanowarming study are named on patents or patent filings, so independent replication matters (Han and colleagues, 2023; Manuchehrabadi and colleagues, 2017).

Possible future uses

Timeline

1. 1 Feb 1985Rall and Fahy report ice-free cryopreservation of mouse embryos at -196 °C by vitrification in Nature. Sources: [1]
2. Jul 2009Fahy and colleagues vitrify, rewarm and transplant a rabbit kidney back into its donor, reporting one surviving animal. Sources: [3]
3. 1 Mar 2017Manuchehrabadi and colleagues report nanowarming of 1 to 80 mL samples and viable 50 mL porcine arteries in Science Translational Medicine. Sources: [4]
4. 9 Jun 2023Han and colleagues report vitrified rat kidneys stored for up to 100 days, nanowarmed and transplanted, with recipients surviving 30 days, in Nature Communications. Sources: [5]

Futures this could help bring about

How far away?

Lab-grown and animal organs for transplant

Pilots · 3 of 8 steps done

How far away?

Reviving people frozen after death

Science unproven · 4 of 9 steps done

Related breakthroughs

• Vitrified rat kidneys rewarmed by nanowarming survive 30 days after transplant (9 Jun 2023)

Glossary

Vitrification

Cooling a concentrated solution so that it sets as a glass-like solid instead of forming ice crystals.

Cryoprotectant

A chemical that protects cells and tissue from ice damage during freezing, often at high concentrations that can also be toxic.

Devitrification

Ice forming in a vitrified sample during warming, usually because warming is too slow or uneven.

Nanowarming

Heating a sample evenly by applying a radio field to magnetic nanoparticles inside it.

Sources

1. peer reviewed paper
   Ice-free cryopreservation of mouse embryos at -196 °C by vitrification
   W. F. Rall, G. M. Fahy. Nature, Feb 1985. DOI: 10.1038/313573a0. Accessed 21 Oct 2026.
2. review article
   Vitrification: the pioneering past to current trends and perspectives of cryopreserving human embryos, gametes and reproductive tissue
   Mitchel C. Schiewe, Robert E. Anderson. Journal of Biorepository Science for Applied Medicine, 6 Sept 2017. DOI: 10.2147/BSAM.S139376. Accessed 21 Oct 2026.
3. peer reviewed paper
   Physical and biological aspects of renal vitrification
   Gregory M. Fahy, Brian Wowk, Roberto Pagotan et al.. Organogenesis, Jul 2009. DOI: 10.4161/org.5.3.9974. Accessed 21 Oct 2026.
4. peer reviewed paper
   Improved Tissue Cryopreservation using Inductive Heating of Magnetic Nanoparticles
   Navid Manuchehrabadi, Zhe Gao, Jinjin Zhang et al.. Science Translational Medicine, 1 Mar 2017. DOI: 10.1126/scitranslmed.aah4586. Accessed 21 Oct 2026.
5. peer reviewed paper
   Vitrification and nanowarming enable long-term organ cryopreservation and life-sustaining kidney transplantation in a rat model
   Zonghu Han, Joseph Sushil Rao, Lakshya Gangwar et al.. Nature Communications, 9 Jun 2023. DOI: 10.1038/s41467-023-38824-8. Accessed 21 Oct 2026.
6. review article
   Cryopreservation of Animals and Cryonics: Current Technical Progress, Difficulties and Possible Research Directions
   Marlene Davis Ekpo, George Frimpong Boafo, Suleiman Shafiu Gambo et al.. Frontiers in Veterinary Science, 9 Jun 2022. DOI: 10.3389/fvets.2022.877163. Accessed 21 Oct 2026.
7. news
   Cryonics and the brain: Professor Clive Coen outlines the risks
   Clive Coen. King's College London (news summary of a New Humanist article), Nov 2016. Accessed 21 Oct 2026.

Revision history

3 changes since this profile was created.