A New Milestone in Cryopreservation Research

A kidney preserved at −150°C for an entire year sounds like something that belongs in science fiction. But researchers at the University of Minnesota are bringing that possibility closer to reality, demonstrating that pig kidneys can survive extended cryogenic storage and recover important biological functions after being carefully rewarmed.

The findings, reported in an October 2026 preprint, mark an encouraging step in organ preservation research. While the ability to freeze and store individual cells has existed for decades, preserving an entire organ presents a much greater challenge. The researchers are now exploring whether those limitations can be overcome, potentially giving transplant teams more time to store, transport, and match donor organs.

Freezing biological material isn't as simple as lowering the temperature. As water inside cells freezes, ice crystals can form and damage delicate structures. The larger and more complex the biological material, the harder it becomes to prevent that damage throughout the entire sample.

A kidney presents a particularly difficult challenge. Its network of blood vessels, specialized tissues, and millions of cells must all remain intact for the organ to function properly after rewarming.

To address this, the University of Minnesota team used a technique called vitrification. Instead of allowing water to form ice crystals, researchers introduced cryoprotective agents that help the tissue transition into a glass-like state at extremely low temperatures.

The kidneys were cooled to approximately −150°C, allowing researchers to investigate whether whole organs could remain preserved for months or even years without losing their ability to function.

Keeping the kidneys preserved was only half the challenge. Bringing them back to a functional state required a carefully controlled warming process.

When frozen tissue warms unevenly, temperature differences can cause physical damage, while ice formation during warming can threaten cell survival. These risks become particularly difficult to manage in larger organs.

The researchers addressed this problem using nanowarming, a technique involving specially coated iron oxide nanoparticles. Introduced into the kidneys before cooling, these particles respond to radiofrequency energy and generate heat throughout the organ, allowing for more uniform warming.

After rewarming, the researchers evaluated the kidneys using machine perfusion, a process that circulates fluid through the organ to assess its condition and function.

The results were encouraging. Kidneys preserved for extended periods showed restored blood flow and urine production, including one stored for approximately a year. In separate short-term transplantation experiments, rewarmed kidneys also produced urine after being transplanted into pigs.

These findings demonstrate meaningful progress, although urine production alone does not establish that the kidneys had recovered normal, long-term function.

Figure 2. Cooling and nanowarming of pig kidneys, including temperature measurements and imaging used to assess vitrification. Source: Han et al., Functional recovery of vitrified and nanowarmed human-scale pig kidneys (2026).

Organ transplantation is a race against time. Once an organ is recovered from a donor, medical teams have a limited window to transport it, identify a suitable recipient, and complete the procedure.

Kidneys can generally be preserved longer than hearts or lungs, but even their storage window is typically measured in hours rather than days or weeks.

If long-term cryogenic preservation becomes viable for human organs, that timeline could change considerably. Transplant centers might have more time to coordinate surgeries, conduct compatibility testing, and transport organs over greater distances. It could also create opportunities to preserve donated organs until a suitable recipient is available.

However, the University of Minnesota findings are still experimental. Although the researchers demonstrated encouraging signs of kidney function after rewarming, important questions remain about tissue damage, cryoprotectant toxicity, and whether preserved organs can sustain normal function over longer periods following transplantation.

The study was released as a preprint and has not yet undergone peer review. Further testing will be needed before researchers can determine whether this approach could eventually be used in human transplantation.

These images compare pig kidneys from different experimental groups following normothermic machine perfusion, including kidneys that underwent vitrification and nanowarming. The visual differences offer a closer look at how the organs responded to the preservation process, although their appearance alone cannot establish how well they functioned.

While organ transplantation is the ultimate goal of this research, the findings also offer an interesting perspective on the broader science of biological preservation.

Laboratories have long relied on low-temperature and cryogenic storage to preserve cells, tissues, and other biological materials for future research. Maintaining the integrity of these samples depends on more than temperature alone. Storage conditions, material compatibility, handling procedures, and the processes used to freeze and thaw samples can all influence their quality.

Preserving an entire kidney is considerably more complex than storing individual biological samples. Still, both applications share a fundamental challenge: protecting biological material through storage and recovery so it remains useful when needed.

The University of Minnesota research shows how much progress is being made toward overcoming some of these challenges. Although practical applications in human transplantation remain years of research away, the ability to preserve and recover function in increasingly complex biological systems is an encouraging development for the field.

For researchers working with valuable biological materials, it's another reminder of how important preservation science is—and how much there is still to discover.