After 30 minutes at −6 °C, 24 of 30 newborn mice survived

After 30 minutes at −6 °C, 24 of 30 newborn mice survived

On July 20, Scientific Reports published a study of supercooling, a state in which water in the body remains liquid below its freezing point. After 30 minutes at −6 °C, 24 of 30 mice survived. After the same amount of time at 0–4 °C, none of the 28 mice survived.

The authors of the study worked with mice between one and five days old. Each mouse weighed about one gram and lost heat rapidly. The researchers compared 30 minutes of conventional cooling at 0–4 °C with 30 minutes of supercooling at −6 °C. All 28 mice died after conventional cooling, while 24 of 30 survived the first 24 hours after supercooling.

During supercooling, water remains liquid below its freezing point. Ice damages cells as its crystals grow. To reduce the number of sites where crystals could begin to form, the researchers kept the mice dry in open plastic bags and cooled them with air. They then warmed the animals gradually in an incubator, supplied oxygen, and manually stimulated breathing.

The authors hypothesize that the greater suppression of metabolism at −6 °C helps cells survive storage. In 2019, the same method was used to preserve human livers at −4 °C. After machine perfusion, the livers remained viable outside the body for 27 hours longer. Two days earlier, pig kidneys stored for three days at −4 °C began functioning again after transplantation. A liver or kidney can be stored separately from the body. In this study, the researchers tested a brief period below freezing in an intact mammal.

The surviving mice were monitored for up to three months. Until the age of one month, they gained weight at the same rate as the control animals. The authors then tested coordination, running endurance, sensitivity, gait, and fear conditioning. The study and its abstract report that these tests found no differences from the control group.

In an experiment involving an intact organism, the researchers tested whether a body could be kept below freezing without ice formation, rewarmed, and monitored for the return of breathing, movement, and development. For biostasis, this is the next step after preserving isolated organs.