Scientists Supercooled Pig Kidneys to Minus 4 Degrees and Kept Them Viable for Days

Supercooled to Minus Four: Pig Kidneys Survived 72 Hours and a Transplant

In some years, roughly one in three donated kidneys in the United States gets discarded. Not because the organ is diseased or damaged. Because no surgeon could get it into a matching recipient before the 24-hour storage window closed. 1

That window has barely moved in three decades. Once removed from a donor, a kidney goes on ice at about 4°C (39°F), and surgeons have roughly a day to find a match, transport the organ, and operate. Over 104,000 people in the US are waiting for a kidney transplant. An estimated 17 die each day before one becomes available. 1

Matthew Powell Palm, a thermodynamicist at Texas A&M University, and his team built a device that cools organs to -4°C (25°F) without forming ice, and in new research, they supercooled pig kidneys for up to 72 hours and then transplanted them back into the donor animals. The organs recovered. 1

The device is a hermetically sealed chamber with a transparent lid. The organ sits submerged in the same preservation solution surgeons already use. Sensors at the base monitor temperature and watch for ice formation. The technique is called isochoric supercooling, and it requires no cryoprotectant chemicals, which removes a major regulatory hurdle. 1

Ice is what has defeated every previous attempt at sub-zero organ storage. When water freezes inside tissue, crystals puncture cells and shred the structures that keep an organ functional. Lower temperatures preserve tissue longer in principle, but only if ice never forms. That is the barrier this approach clears. 1

In the study, Powell Palm's team removed kidneys from pigs, flushed them with preservation solution, and divided them into groups. Some went on ice for two or 24 hours to match current clinical practice. Others went into the supercooling chamber for 24, 48, or 72 hours. Each kidney was then transplanted back into the pig it came from, with the animal's second kidney removed so the preserved organ had to carry the full workload alone. 1

The 24-hour supercooled kidneys produced urine immediately after transplantation. Markers of kidney function returned to normal within about 10 days. The organs preserved for 48 and 72 hours performed similarly to each other, and all the supercooled kidneys recovered faster than those kept on ice for the standard 24 hours. Heidi Yeh, a transplant surgeon at Mass General Brigham for Children who researches organ preservation, noted that kidneys stored for 48 hours in other studies typically take a week or two to resume functioning. 1

Over 30 days, the pigs grew by about 30 percent and the transplanted kidneys nearly doubled in size to compensate. One animal was monitored for 200 days, and its kidney still looked healthy when researchers examined it. The team presented the findings at the American Transplant Congress in Boston. 1

A Canadian team earlier this year also cooled pig kidneys below freezing and transplanted them, but that protocol relied on cryoprotectant chemicals and the organs survived for a week after 48 hours of storage. Powell Palm's study extends storage to 72 hours, drops the chemicals entirely, and tracks organ health over months instead of days. 1

Three days of shelf life would reorganize the entire transplant supply chain. Kevin Myer, president and CEO of LifeGift, an organ procurement organization based in Texas, frames the constraint in operational terms: the assumed 18-to-24-hour window dictates how kidneys are matched, how far they can travel, and how fast a surgical team must mobilize. Stretch that to 72 hours and the geography inverts. A kidney harvested in one city could reach a recipient on another continent. An organ discarded for lack of a nearby match could wait for the best possible recipient instead. "If we can get up to 72 hours," Myer said, "that would change everything." 1

The ceiling may be higher. In preliminary work, organs stored for up to 120 hours appeared healthy under examination, though those have not yet been transplanted. And because the method introduces no new chemicals into the preservation process, Powell Palm's team hopes for an accelerated path through FDA review. 1

The organs being thrown away today are not defective. They are viable tissue trapped inside a logistics system built around a 24-hour expiration date. The constraint was never the organ. It was the ice.