About 6,400 liver transplants took place in 2013 in the U.S., but demand far outpaces supply: more than 15,000 patients are on the current waiting list. Compounding the lack of availability, livers have only a small window of time to reach their destinations. The organs stay fresh for just 12 hours, during which they are kept on ice with a cold preservation solution. That is because freezing them is not an option—the process creates ice crystals that slice through the cells on thawing.

At Harvard Medical School, researchers are ditching the conventional storage technique in favor of a method that could extend the shelf life of livers and other organs. In results published in July in Nature Medicine, they report preserving viable rat livers for three whole days.

To preserve the organs for that long, the team used a specialized machine to erect a chemical buffer zone around the organ's cells. That buffer protected the cells' membranes against the threat of ice. The team then slowly cooled the livers to −6 degrees Celsius without actually freezing them—“supercooling” them.

In the experiment, six rats received livers supercooled for three days, and each one survived for three months (at which point the experiment ended, and they were euthanized). As expected, rats that received three-day-old livers preserved on ice all died. The supercooling method, however, cannot work indefinitely: only about 60 percent of rats receiving livers stored for four days managed to survive for the study's duration. Next, the team plans on testing the method with pigs and humans.

The success with this approach, the authors say, could extend the reach of organ transplants and so provide greater access to patients. In the U.S., the national map for liver distribution is currently far from equal. For instance, patients living near trouble spots, such as big highways prone to traffic accidents, have a higher chance of receiving a viable liver.

In the future, supercooling may also support research with organs on a chip, according to Korkut Uygun, who was part of the liver experiment and is an assistant professor of surgery at Harvard Medical School. Organs on a chip are collections of laboratory-grown human cells designed to mimic the organs in the body. They are a highly anticipated way to study how our organs work and how they respond to various drugs. Supercooling would make shipping them from manufacturing labs to researchers more practical. For now the promise of getting transplant organs to patients remains the primary focus. The waiting list for all organs has climbed above 122,000.