Scientists have revived pig kidneys frozen to -150 °C and stored for over a year, marking a potential advance in organ preservation. The kidneys, similar in size to human organs, were cooled into a glass-like state and later rewarmed, regaining function and producing urine—key indicators of viability. The research, posted on bioRxiv, has not yet undergone peer review but has already drawn praise from experts.
The work builds on earlier experiments where the same researchers successfully vitrified and rewarmed rat kidneys stored for up to 100 days. Pig kidneys presented greater difficulties due to their larger size and structural complexity. To adapt the process, the team spent three years redesigning the mixture of cryoprotectants, chemicals that prevent ice crystal damage, needed for larger organs.
Current organ preservation methods limit storage to 24 to 36 hours, creating urgent timelines for donor-recipient matching. Extended storage could eliminate this pressure, allowing organs to be preserved like blood and matched to patients over time. It might also reduce the need for immunosuppressive drugs, which carry risks of infection and cancer.
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Nanoparticles enable precise organ rewarming
Erik Finger, a transplant surgeon at the University of Minnesota who co-led the study, said after the last transplant, “This is a big deal.” The team’s method uses iron oxide nanoparticles infused into the organ. When exposed to an electromagnetic field, these particles generate heat, enabling precise control over rewarming rates. This avoids the damage caused by uneven thawing, a longstanding issue in cryopreservation.
In tests, the rewarmed kidneys regained their pink color, a visual sign of restored blood flow, and began producing urine within minutes. One kidney, stored for over a year, performed comparably to those preserved for shorter periods, though all showed some injury from the cryoprotectants. The researchers now plan to test the organs in live pigs for extended durations and refine the chemical formula to reduce damage.
For decades, scientists have struggled to vitrify whole organs, despite success with smaller biological materials like eggs and sperm. If successfully scaled, it could transform transplantation by making organs available on demand rather than as perishable goods.
How the vitrification process works step-by-step
The process begins by flushing a donor kidney of blood and loading it with cryoprotectants over two hours. Iron oxide nanoparticles are then introduced for seven to eight minutes before the organ is cooled with nitrogen vapor. At -120 °C, it reaches a glass-like state, stable for months or longer. Rewarming requires careful monitoring to prevent cracking, with the team adjusting the electromagnetic field to control heating speed.
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Greg Fahy noted that while blood flow recovery is promising, long-term function remains untested. The team’s next steps include transplanting vitrified pig kidneys into live animals for extended periods and exploring less harmful cryoprotectants. Finger remains confident, saying the results represent a milestone achievement.
The team’s success with pig kidneys now opens the possibility of testing human organs, though major challenges remain before clinical use. Human kidneys, like those of pigs, are structurally complex, and ensuring uniform vitrification across their entire volume is far more difficult than with smaller organs. The current cryoprotectant mixture, effective in pigs, may require adjustments to reduce toxicity in humans, where kidney function and blood flow patterns differ slightly. Finger and his colleague emphasize that the chemical balance must protect against ice damage while maintaining cellular compatibility, a challenge that could take additional years to resolve.
Remaining hurdles for human kidney viability
Beyond chemical adjustments, the researchers must address the long-term durability of vitrified organs. While the rewarmed pig kidneys regained color and produced urine, key signs of restored function, they did not operate at full capacity. Perfusion tests showed urine output at roughly two-thirds of normal levels, and microscopic analysis revealed cellular damage, particularly in the kidneys’ outer layers. This suggests that while the organs are viable in the short term, their ability to sustain life over months or years remains unproven.