Pig kidneys glass-frozen for a year and brought back to working order

What was done

A University of Minnesota-led team loaded whole pig kidneys with chemical cryoprotectants that act like antifreeze, then infused iron oxide nanoparticles. The organs were cooled with cold nitrogen vapor to a glass-like (vitrified) state at about -120°C before settling at around -150°C. The approach avoids damaging ice crystals.

Why rewarming is hard

Heating the organ evenly without damage is the tough part. An electromagnetic field makes the nanoparticles release heat throughout the organ, and adjusting the field's power controls how fast it warms. Pig kidneys are roughly 100 times heavier than the rat kidneys the team vitrified in 2023, so the cryoprotectant mix had to be reworked, a process that took three years.

What the tests showed

Rewarmed kidneys were tested on perfusion machines and transplanted into pigs for two hours. In both cases they "pink right up" and made urine within about a minute, though only about two-thirds of the normal amount. The year-old kidney, tested on a perfusion machine, produced urine immediately and looked better than many of the others.

Why it matters

Human organs can currently be preserved for only 24 to 36 hours, turning matching and transport into a race. Long-term organ banking could give doctors time to match donors to recipients and prepare patients' immune systems, potentially reducing the need for lifelong anti-rejection drugs.

Hurdles ahead

The kidneys aren't perfect: they produced less urine than expected and showed injury attributed to the cryoprotectants. Outside experts note the experiments can't show whether the kidneys could have supported life. Next steps include longer tests in pigs, less toxic cryoprotectants and experiments with human kidneys.