One research team circumvented the problem through ‘supercooling’, a phenomenon where water remains unfrozen at sub-zero temperatures, using strategies inspired by animals that do the same by synthesizing special chemicals called cryoprotective agents, such as glucose, as the temperature decreases. This strategy is challenging to apply to large human organs, such as livers, and ice formation can’t be prevented entirely. 

To overcome this challenge, the team supercooled human livers with a mix of chemical treatments. They developed a protocol that avoids ice formation by perfusing the livers with cryoprotective agents. The team’s approach extends the storage lifetime of livers to 5 days.

In another study, researchers optimised organ preservation through ‘vitrification’ – where organs loaded with cryoprotective agents are rapidly cooled to extremely low temperatures of -150°C. This method allows no time for ice-crystal formation, and leads to a solid yet stable ice-free state, called a ‘vitrified’ state. However, using typical vitrification methods, organs are often sensitive to ice crystal formation and thermal stresses on rewarming.

To overcome this, the researchers developed a technique named ‘nanowarming’. This method involves perfusing organs with iron oxide nanoparticles along with cryoprotective agents before the cooling step. By applying alternating magnetic fields to the vitrified organs, the nanoparticles impart uniform warming throughout, preventing ice crystals or cracks from forming. Afterwards, the nanoparticles can be easily flushed out. The kidney in this study was stored for 100 days, transplanted successfully into a rat. However, this technology allows organs to be stored indefinitely.

In a final study, a third research group examined how new cryopreservation approaches could enable them to store mature samples of coral – which are especially vulnerable to ice-crystal formation. The group prevented ice formation using ‘isochoric vitrification’. Here, samples are vitrified while being kept in a constant volume chamber, which minimizes the thermodynamic fluctuations that lead to ice nucleation.                   

Combining this technique with advances in coral husbandry, the group preserved fragments of mature coral, rewarmed them, and demonstrated their survival. They are now working to reduce the stress of this process, and hope that these samples could be used in future to revive damaged coral reefs.

In future, the teams’ methods will allow more patients to receive life-saving organ transplants, and will also help to preserve one of Earth’s most vital and vulnerable ecosystems.